solvent replacement for green processing

Solvent Replacement for Green ProcessingJulie Sherman,1 Bain Chin,2 Paul D.T. Huibers," RicardGarcia-Valls," and T. Alan Hatton"1Department of Chemical Engineering, 2Department of Chemistry,Massachusetts Institute of Technology, Cambridge, Massachusetts

The implementation of the Montreal Protocol, the Clean Air Act, and the Pollution Prevention Actof 1990 has resulted in increased awareness of organic solvent use in chemical processing. Theadvances made in the search to find "green" replacements for traditional solvents are reviewed,with reference to solvent alternatives for cleaning, coatings, and chemical reaction and separationprocesses. The development of solvent databases and computational methods that aid in theselection and/or design of feasible or optimal environmentally benign solvent alternatives forspecific applications is also discussed. - Environ Health Perspect 106(Suppl 1):253-271 (1998).http.//ehpnetl.niehs.nih.gov/docs/1998/Suppl-1/253-271sherman/abstract.html

Key words: solvent substitutes, green chemistry, pollution prevention, solvent cleaning,coatings, property prediction

IntroductionSolvents, defined as substances able todissolve or solvate other substances, arecommonly used in manufacturing and labo-ratory processes and are often indispensablefor many applications such as cleaning, firefighting, pesticide delivery, coatings, syn-thetic chemistry, and separations (1).Billions of pounds of solvent waste are emit-ted to the environment annually, either asvolatile emissions or with aqueous dischargestreams (2). Many of these solvents areknown to upset our ecosystems by depletingthe ozone layer and participating in thereactions that form tropospheric smog. Inaddition, some solvents may cause cancer,are neurotoxins, or may cause sterility inthose individuals frequently exposed tothem. While contained use of these solventswould be acceptable from both an environ-mental and a health perspective, such opera-tions are difficult to achieve, and alternative

solvents are currently being sought to mini-mize the problems inherent in solventrelease to the environment.

As our awareness and understanding ofhow solvents affect the environment andhuman health grow, so do the regulationsthat govern use of these chemicals (Figure1). Government agencies such as theOccupational Safety and Health Admini-stration (OSHA) have been installed toprotect workers from solvent exposure.Indeed, OSH-A has implemented strict reg-ulations, called permissible exposure limits(PEL), for chemical concentrations towhich one may be exposed without detri-mental health effects. Examples of the PELvalues, as well as health effects for a varietyof solvents, are listed in Table 1.

Other regulations aim at protecting theenvironment, which in turn has a positiveimpact on human and animal health. One

Manuscript received at EHP25 July 1997; accepted 15 October 1997.As part of this review, a Web site has been created that includes all links referred to in this paper. The Web

site can be found at http://web.mit.edu/huibers/www/greenchem.htmlWe are grateful to the Idaho National Energy Laboratories for their support. We are also thankful of the

Catalan research fellowship (CIRIT) for the support of R. Garcia-Valls.Address correspondence to Dr. T.A. Hatton, Department of Chemical Engineering, Massachusetts Institute

of Technology, 25 Ames St., 66-309, Cambridge, MA 02139. Telephone: (617) 253-6600. Fax: (617) 253-8723.E-mail: [email protected]

Abbreviations used: CM, Clean Air Act; CAAA, Clean Air Act Amendments; CFC, chlorofluorocarbons; CFC-113, 1,1,2-trichloro-1,2,2-trifluoroethane; CMT, critical micelle temperature; HCFC, hydrochlorofluorocarbon;HFC, hydrofluorocarbon; MTBE, methy tert-butyl ether; OSHA, Occupational Safety and Health Administration;PAH, polyaromatic hydrocarbon; Pc, critical pressure; PCBTF, parachlorobenzotrifluoride; PEG, polyethylene gly-col; PERC, perchloroethylene; PEL, permissible exposure limits; PPA, Pollution Prevention Act of 1990; SAGE,Solvents Alternative Guide; SARA, Superfund Amendments and Reauthorization Act of 1986; SCC02, supercriti-cal carbon dioxide; SCWO, supercritical water oxidation; SFE, supercritical fluid extraction; SHDS, SolventsHandbook Database System; SOLV-DB, Solvents Database; Tc, critical temperature; TCA, 1,1,1-trichloroethane;TCE, trichloroethylene; THF, tetrahydrofuran; U.S. EPA, U.S. Environmental Protection Agency; UV, ultraviolet;VMS, volatile methyl siloxane; VOC, volatile organic compound; WRRC, Waste Reduction Resource Center.

of the most stringent laws in this regard isthe Montreal Protocol, which has bannedthe manufacture and use of stratosphericozone-depleting solvents. Solvents restrictedunder this law are categorized as Class I orClass II compounds, many of which arelisted in Table 2. Class I compounds havealready undergone a major phase-out,whereas Class II compounds will becompletely phased out of use by 2030.

Hazardous air pollutants such as hexaneand methanol are regulated under the CleanAir Act (CAA) (3). Volatile organics,defined by the the U.S. EnvironmentalProtection Agency (U.S. EPA) as com-pounds that evaporate at the temperature ofuse and react with oxygen to form tropos-pheric ozone, are also restricted under theCAA. Further, the Toxic Release InventoryBill requires solvent users to record theirreleases and waste carefully. A summary ofmany of the regulations at the federal, state,and local levels is found in a review byBreen and Dellarco (4).

The Pollution Prevention Act of 1990propelled these regulatory issues to theforefront of process design by suggesting

... the use of materials processes or prac-tices that reduce or eliminate the cre-ation of pollutants or waste at thesource. It includes practices that reducethe use of hazardous materials, energy,water or other resources and practicesthat protect natural resources throughconservation or more efficient use. (5)

The U.S. EPA followed this Act by com-piling a list of 17 priority pollutants, indudingsome solvents and heavy metal compounds,

70en

: 60

) c 50h- az

E 40 -

c E 30--D

X C 20

Elo-

CAAA PPA

SARA

OSHA

1900 1920 1940 1960Year

1980 2000

Figure 1. Cumulative federal regulations. Adaptedfrom Gendron (200). Abbreviations: CAA, Clean Air Act;OSHA, Occupational Safety and Health Adminstration;SARA, Superfund Amendments and ReauthorizationAct of 1986; CAAA, Clean Air Act Amendments; PPA,Pollution Prevention Act of 1990.

Environmental Health Perspectives * Vol 106, Supplement l* February 1998

o

253

SHERMAN ET AL.

Table 1. Compounds on the U.S. EPA 33/50 list.a

OSHA PEL LD50, orallyCompound Solvent use Toxicity (8-hr TWA), ppm in rats

Benzene Synthesis, feedstock, waxes, oils, resins Carcinogen 10 3.8 mI/kg

CChloroformCHCI3

Carbon tetrachlorideCQl4MEK (Methyl ethyl ketone)

0

H3C

MIBK (Methyl isobutyl ketone)

0

H3C

Methylene chloridedichloromethane

CH2CI2

PERC (Perchloroethylene)

Degreasers, rubbers, resins, waxes

Degreasers, rubbers, resins, waxes,feedstock

Coatings, resins

Similar to MEK

Polymers, synthesis, cleaning,and degreasing

Dry cleaning, degreasing

Anticipated carcinogen

Poison, anticipated carcinogen

Headaches, dizziness, nausea

Similar to MEK

Narcotic in high concentrations


Cl Cl

Cl Cl

TolueneCH3

TCA (1,1,1-Trichloroethanemethyl chloroform)

H3C-CC13

TCE (Trichloroethylene)

Cl Cl

H Cl

XylenesMe

0Me

*Toxicity information from Budavari et al. (107).

Feedstock, paints, resins, extractants,gasoline additive

Adhesives, coatings, inks,degreasers, waxes, alkaloids

Cleaning, degreasers, waxes, resins,rubbers, paints, extractants,feedstock

General solvent, feedstock



Inebriation at moderate exposure.Heavy exposure can causeventricular fibrillation, death

Narcotic in high 100 concentrations

whose use was to be voluntarily reduced by50% by 1995. This list, known as the U.S.EPA 33/50 list, was based on the criteriathat the chemicals are used in large vol-ume, they are detrimental either to theenvironment or human health, and there

are available methods to reduce their use

(Table 1) (6). The 33/50 list in con-

junction with the previously mentionedglobal and federal regulations has provideda solid starting point for scientists andengineers to reevaluate traditional methods

and to discover ways to limit or eliminatethe use of hazardous solvents.

As a result, many methods for solventpollution prevention have been developed(7,8). New synthetic pathways that do not

demand the use of deleterious solvents or are

Environmental Health Perspectives * Vol 106, Supplement 1 * February 1998

50 0.9 ml/kg

9528 ppm

200 6.86 ml/kg

100 Similar to MEK

25

100

1.6 mI/kg

8.85 g/kg

200 7.53 g/kg

350

100

0.58 mI/kg

4.92 mI/kg

7.71 mI/kg

254

SOLVENT REPLACEMENT FOR GREEN PROCESSING

Table 2. Ozone-depleting solvents restricted under theMontreal protocol.

Class Ozone-depleting substances

Class CFCs (chlorofluorocarbons)Halon 1211 (bromochlorodifluoromethane)Halon 1301 (bromotrifluoromethane)Halon 2402 (dibromotetrafluoroethane)CC14 (carbon tetrachloride)Methyl chloroform (1,1,1-trichloroethane)CH3Br (methyl bromide)CiHjBrkF, (hydrobromofluorocarbons)

Class II HCFCs (hydrochlorofluorocarbons)

inherently more selective for the compoundof interest have been investigated (9,10).Adjustments can be made to process equip-ment to protect against fugitive emissions(11). Process integration techniques havebeen effective in minimizing waste genera-tion and optimizing solvent recovery andrecycling (10,12-15). Solvent replacementtechniques have also come to the forefront asmany solvents are banned or discouragedfrom industrial use. In this case the onlyoption is to find an alternative solvent.

The impact these regulations andmethods have had on solvent use is seenclearly in Figures 2 and 3. Over the past 10years the use of both hydrocarbon andchlorinated solvents has declined with onlya minor increase in consumption of oxy-genated solvents. In addition, while processsolvents, consumer products, and variousmiscellaneous applications have exhibitedfairly constant solvent consumption, thecleaning and coatings industries havemarkedly decreased solvent use over thelast decade. A more detailed breakdown ofU.S. solvent consumption can be found inan editorial by D'Amico (16).

The purpose of this review is to bringtogether research efforts in the quest tofind "green" replacements for traditionalsolvents used in chemical processing. Thefirst section discusses advances in solventalternatives for cleaning, coatings, and syn-thetic processes such as reaction and extrac-tion. The second section details advancesin the development of solvent databasesand computational methods that aid in theselection and/or design of feasible or opti-mal environmentally benign solvent alter-natives for specific applications. Thoughimportant, halon substitutes for fire fight-ing do not fall into the category of chemi-cal processing and will not be discussedhere; readers are directed to a monographby Mizolek and Tsang (17) for a compre-hensive review of the challenges andprogress in finding halon replacements.

SZro - m' - b,Ohlirproductec m.: Mieoelleneoue-

CL

0 M -

Year

Figure 2. Solvent use by application. Adapted fromKirschner (201).

U)

to

0CL0*_

c0(E

CO

I')

CD0

0

a,

9000 -

5000

3000

2W.,8ao_

= Hyidrocarbon solventsO0xygenatedsolvents

_ Chlorinated solventsF.1;:fiC.41

:^IJA

199 192

Year

.11

-.:

1

1997

Figure 3. Solvent use sorted by solvent type. Adaptedfrom Kirschner (201).

Table 3. Main industrial sectors that use solvent cleaning.

Industrial sector Type of cleaning Type of soil cleaned

Electronic cleaning Defluxing of printed circuit boards Soldering rosinPrecision cleaning Cleaning of sensitive parts such as Organic residues, particulates

optical devices and gyroscopes that haveultrahigh cleanliness standards

Metal cleaning Surface preparation for machining or Oil, grease, particulates,coatings inorganic salts

Dry cleaning Cleaning of textiles that are not stable Oil, organic residuesin aqueous solutions

Green Alternatives for HighSolvents Use Applications

Cleaning solvents are used in four mainindustrial sectors: electronics cleaning, preci-sion cleaning, metal cleaning, and textile ordry cleaning, as indicated in Table 3.Within each of these industrial sectors,operations may be categorized as vapordegreasing, cold cleaning, or spot cleaning.Spot cleaning is a simple operation where anitem is hand wiped with a solvent-soakedcloth to remove contaminants. Cold clean-ing is usually performed by submerging theitem to be cleaned in an ambient tempera-ture solvent bath. As the item soaks, thecontaminants dissolve in the solvent. Thesesolvent baths have a limited lifetime becauseof contaminant accumulation. Vapordegreasing, on the other hand, is performedat high temperatures. The solvent is heatedand the vapor contacts the article to becleaned, condensing on it, and solvating thecontaminants. The high temperature affordsincreased contaminant solubility. The sol-vent vapor remains contaminant free, butcontaminants build up in the condensed

liquid. The choice of solvent and cleaningmethod depends heavily on the material ofwhich the part to be cleaned is composed,chemical nature of the contaminant (often agrease or oil), geometry constraints of theitem (i.e., small holes or bends and twists),and cleanliness criteria (18).

Historically, chlorinated solvents werepreferred for cleaning applications becausethey are nonflammable, an important con-sideration if the cleaning process requireshigh temperatures such as in vapor degreas-ing. Of these, 1,1,1-trichloroethane (TCA)was the most widely used, but it has beenfound that 1,1,2-trichloro-1,2,2-trifluo-roethane (CFC-1 13), trichloroethylene(TCE), perchloroethylene (PERC), andmethylene chloride work well for suchapplications. However, under the MontrealProtocol and the CAA most of these solventsare restricted, forcing many processes toemploy more environmentally friendly alter-natives. Because there are so many considera-tions in choosing a cleaning solution, auniversal "drop-in" replacement usually doesnot exist (16,19). As a result, a vast numberof specialized alternatives are available inthe form of hydrochlorofluorocarbons

Environmental Health Perspectives * Vol 106, Supplement 1 February 1998

^---

255

SHERMAN ETAL.

(HCFCs), hydrofluorocarbons (HFCs),hydrocarbon solvents, oxygenated sol-vents, aqueous solvents, and supercriticalfluid solvents. Stone and Springer (20)have reviewed these alternatives for clean-ing applications in the aerospace industry.Many of these alternatives are available inindustrial quantities from well-knownmanufacturers. Although there are com-putational methods (see "ComputerSimulations") available that can be usedin the selection of the most effective andeconomical cleaning solvent for a givenapplication, much of the work reported todate in the solvent-cleaning literatureinvolves solvent screening and not rationalsolvent selection.

Fluorocarbons. HCFCs and HFCs arealternative solvents that have been imple-mented in all industrial sectors except drycleaning (21). These solvents exhibit manyof the desirable solvent properties of chloro-fluorocarbon (CFC) compounds such ashigh density, high dielectric strength, ther-mal stability, chemical stability, and non-flammability. Thus, they are as close aspossible to a drop-in replacement for CFCsbecause their use requires minimal retro-fitting. Because these compounds are notfully halogenated, they have lower ozonedepletion potentials than CFCs (22). Theyhave been shown to be as effective as CFC-113 in removing solder flux from electronicassemblies when used in an azeotropic mix-ture with methanol (23). These com-pounds have also been investigated in their"neat" form for the same purpose (24).Although they are effective cleaning sol-vents, HCFC and HFC compounds areconsiderably more expensive than CFCcompounds, ranging from 2 to 5 times thecost because they require up to five syn-thetic steps to make versus one for manyCFC compounds (25). Furthermore,HCFCs will be phased out by 2030, requir-ing those who use them to turn to otheralternatives (26).

Perfluorocarbons are nonozone depletingbut have long atmospheric lifetimes. Theyare suitable for some precision cleaningprocesses, as they effectively remove parti-cles and aid in drying (27). Newly intro-duced fluoroiodocarbons, which arenonflammable, noncorrosive, and appearto be nonozone depleting, are also emerg-ing as possible replacements for CFCs(28). Some advocate using methylenechloride, PERC, and trichloroethylene asreplacements for TCA and CFC com-pounds (29). Although methylene chlo-ride and PERC are nonozone-depleting

substances, they are on the U.S. EPA33/50 list and are suspected carcinogens.

Hydrocarbon and OxygenatedSolvents. Volatile organic compounds(VOCs) such as xylene and methyl ethylketone have also been used as cleaning sol-vents, but now their use is being discour-aged by inclusion in the U.S. EPA 33/50list. Some users have returned to usingaliphatic hydrocarbons (petroleum distil-lates) as alternative solvents (a commoncleaning solvent before implementation ofchlorinated compounds) because they arenow available in high purity. They workbest for solvating heavy grease and oilbecause of their chemical similarity but arenot applicable to vapor degreasing becauseof their flammability. In addition, althoughthey are not ozone-depleting substances,many hydrocarbons are regulated as VOCs(22). Reynolds (30) recommends theExxon line of high-purity hydrocarbon sol-vent as a replacement in chlorinated sol-vents for cleaning plastic substrates. In thiscase, the alternative solvent is able to sol-vate contaminants and the low surfacetension results in desirable wettability.

For applications that require an oxy-genated organic solvent to solvate contami-nants such as grease, oil, wax, resins, andpolymers, there are many available alter-natives. A range of fluorinated organics isbecoming available and these presentattractive solvent substitutes. For example,pentafluoropropanol is a nonflammable,nonozone-depleting alcohol that can beused in situations in which alcohol is neces-sary for removing the contaminants (31).Similarly, hydrofluoroethers provide a safealternative for processes in which ethers areneeded (32). Dow Corning's line of volatilemethyl siloxane (VMS) compounds may beused to remove simple oils, grease, and sili-cone elastomers in the same way as hydro-carbon solvents. VMS compounds have theadvantage that they are neither hazardousair pollutants nor ozone depleters (32).N-Methyl pyrolidone is a high-boiling sol-vent suggested for use in degreasing opera-tions (33). It has an advantage over othersolvents in that it is biodegradable, butbecause it is nonvolatile, a rinsing cycle isrequired to eliminate residue. VOC-exemptparachlorobenzotrifluoride (PCBTF) isanother attractive solvent replacementoption. PCBTF is being marketed forcleaning metal, plastics, electronic compo-nents, and glass while reducing volatileemissions (34).

Sometimes a two-step process is neces-sary to match the performance of chlorinated

solvents. Marino (35) suggests that usingan ester-based proprietary solvent in com-bination with a perfluorohexane rinse in aretrofitted vapor degreaser to replace TCAis a cost-competitive option.

Aqueous Solvents. Another approach tosolvent replacement is to switch from neatsolvent to aqueous blends. These semi-aqueous solutions contain organic additivessuch as terpenes, alcohols, and aliphatichydrocarbons. Terpenes are very effective indilute aqueous solutions for removinggrease, resin, and adhesives. They are natu-rally derived from plants and can be dis-posed of fairly easily (32). Although thesecompounds are not ozone depleters, cautionmust be used as the toxicity of terpene com-pounds has not been well characterized(36). Brown et al. (37) demonstrated thatdilute aqueous terpene solutions couldeffectively replace TCA and methanol incleaning metal parts for hip and kneereplacements. Through a series of tensiletests, they demonstrated that the alternativecleaner worked up to 10% more effectivelythan the original solvents. In addition, theyfound that it was more economical toimplement semi-aqueous cleaning than touse the conventional methods. Others havereported similar results but often note thatuse of semi-aqueous solutions requires someinitial process modifications such as agita-tion and extra wash cycles (36,38-44).Another alternative solvent formulation usesaliphatic hydrocarbons diluted by water inthe form of highly dispersed droplets stabi-lized by surfactants. These microemulsions,such as INVERT supplied by The DowChemical Company, (Midland, MI) havebeen found to be effective solvents for coldcleaning (19).

Aqueous solvents have also found aniche in replacing chlorinated cleaning sol-vents in applications such as printed circuitboards, turbine blades, advanced compos-ites, and automotive motor housings (45).Table 4 compares the physical properties ofassorted aqueous cleaning formulationswith those of common chlorinated solvents.These solvents contain additives such asrust inhibitors, surfactants, or chelatingagents and work best if they are slightlyalkaline (46). They clean with similar effec-tiveness and have the advantage of beingeasier to recycle and reuse than conven-tional solvents. In an aqueous environmentthe "soil" will float to the top and may beskimmed off, as opposed to conventionalsolvents where the soil and solvent remainhomogeneous and requireg energy for sepa-ration (47). Augias, Inc. has gone a step



ble 4. Comparison of aqueous and chlorinated cleaning solvents.a

ysical property CH2C2 TCA Aqueous A Aqueous C

iling point, 'C 39.8 74.1 100 100)ecific gravity 1.316 1.322 1.02 1.073sh point, C None None None 23.8ipor pressure, mmHg 340 90)C, lb/gal 10.98 10.92 <0.35 0.92irface tension, Dynes 28 28 29 33

Data from Quitmeyer (45).

irther by adding special nutrients to theirlueous replacement solvent, Oil RemoverS2), which aid microbial growth so the)ntaminants are actually decomposed. Asith the semi-aqueous solution mentionedove, aqueous replacement solvents oftenquire process adjustments such as additionagitation or ultrasonics (48). Further, thegh latent heat of evaporation for waterakes drying more difficult, and often.tra equipment for proper and efficientying is required (22).Supercritical Carbon Dioxide. Above

critical temperature (Tc) and pressure)c), fluids exist as one phase having densi-Cs and viscosities between those of a liq-Ld and a gas and can have significantlyfferent solvating capabilities than the liq-Ld compounds below the critical point.arbon dioxide (C02)is the most com-ionly used compound at supercritical)nditions due to its accessible criticalDint (Tc= 304.2K, Pc= 78 atm). Super-itical CO2 (SCCO2) is a nonpolar sol-mt and thus is capable of effectivelylvating nonpolar oils. Supercriticaleaning requires the parts to be placed inhigh-pressure chamber that is heatedntil the CO2 is beyond its critical point.he supercritical solvent is swept over theirts to be cleaned and sent to a recoverynit. When the chamber is decompressed,iy residual solvent evaporates because02 is a gas at atmospheric pressure. This

method has been shown to work more effi-ciently for contaminated plastic thancleaning with CFC-1 13 (49). The primaryapplication of SCCO2 cleaning is in thecleaning of precision instruments wherethe highest cleanliness standards arerequired (50-56). SCCO2 is also beinginvestigated as a dry-cleaning solvent toreplace PERC (57,58).

Solvent-Free Cleaning. Clearly, themost effective way to avoid problems withsolvent contamination of the environmentis to eliminate the use of the solvententirely. Even though this clearly is notpossible for most applications, there aresome innovative solvent-free cleaningprocesses that deserve mention. Lu andAoyagi (59) demonstrated that a pulsedKrF laser used to clean metal, magneticmaterial, plastic, and glass surfaces worksvery efficiently. It is a high-speed, area-selective, low-noise process. However,because of its area selectivity, it is suitableonly for cleaning small areas, making itbest for printed circuit board cleaning.Blasting with CO2 snow or pellets isanother way that coatings and contamina-tion can be removed. Finally, steps can alsobe taken to eliminate the contaminantfrom ever entering the process. For exam-ple, the development of low solids "noclean" rosin fluxes for soldering printed cir-cuit boards completely eliminates the needfor a cleaning process (60).

CoatingsThe function of a coating is to protect asurface from damaging environments suchas extreme weather or corrosive chemicals.Coating technology spans a wide range ofapplications such as architectural, indus-trial, and antifouling coatings, and printinginks (61). Coatings are typically classifiedaccording to the binder or resin that acts asthe film-forming agent and not accordingto the applications in which they are used.Table 5 lists typical binders and their pri-mary applications. Additives (pigments,catalysts, antifoam agents, and hardeners)play a large role in determining the effec-tiveness and properties of the coating. Thefinal component of a coating formulationis the solvent necessary to give the formula-tion a manageable viscosity for application.Table 5 also lists traditional formulationsolvents used for each resin type. Many ofthe common formulation solvents such asxylene, toluene, MEK, MIBK, and metha-nol are classified as VOCs or appear on theU.S. EPA 33/50 list (62).

Not only are VOCs typically used inthe coating industry, but they are used inlarge quantities, and the nature of theindustry is such that solvent containment ismuch more difficult than in other areas ofsolvent usage. Consequently, solventreleases into the environment can be sub-stantial. Figure 2 indicates that the coatingsindustry is the largest solvent consumer,using 7.5 billion pounds of solvent in 1992alone. The large quantity of and long-termexposure to solvents that many paintersface may cause chronic central nervous sys-tems effects, cancer, and hematologic dis-orders (63). Fortunately, many advanceshave been made in coatings technologythat allow the industry to substantiallydecrease the amount of solvent needed inthe formulation of effective coatings-insome cases, to less than 3.5 lb VOCs/gal.

ible 5. Summary of resin types and applications.

,sin Cure type Formulation solvent Applicationtgetable oil C Hydrocarbons, toluene, xylene Clear varnish, industrial enamels, printing inks, paint primerkyd C Paint)Iyester C Esters, diacetone Heat-sensitive plastics, vehicles, home appliances, woodnino C Paint, lacquerenolic C Metal primer, marine enamels, tank and drum liningoxy C Ketone, ethers, esters, toluene, xylene Marine coatings, enamels, containerslicone C Xylene, hydrocarbons, chlorinated hydrocarbons, ketones Electrical insulating resins, paint additive, brick sealant-rylic C/NC Paintfllulose NC Ketones, esters Wood finishingnyl lacquers NC Ketones Metal substrateslorinated rubber NC Aromatic hydrocarbons, chlorinated hydrocarbons, esters, ketones Alkaline substrates, marine coatingethane C Automotive coatings, wood sealer and finish, concrete sealer

)breviations: C, convertible coating (reacts during cure); NC, nonconvertible coating.

Environmental Health Perspectives * Vol 106, Supplement 1 * February 1998 257

SHERMAN ETAL.

High Solids Formulations. A coating isconsidered to be a high solids formulationwhen the binder and additive content isover 80% (wlw), although formulationshaving solids content between 60 and 80%are often included in this category (64). Inhigh solids formulations, the approach isnot to replace the conventional solvent witha less benign one such as is done in cleaningoperations or to develop tailored solvents asis done in synthetic applications but merelyto use less solvent. The advantages anddisadvantages of high solids coatings aresummarized in Table 6.

One of the main challenges in reducingthe amount of solvent in a formulation ismaintaining a manageable viscosity. Paintformulations with solids compositions upto 70% may still be thin enough to spray orroll, especially if application is done at ahigh temperature. Coatings that use naturaloils such as linseed, tung, and soybean oilare often classified as high solids coatingsand are prevalent in the history of coatings(65). In this case an oil is dispersed in asmall amount of hydrocarbon solvent andas the solvent evaporates, the oil polymer-izes on exposure to oxygen. However,purely oil-based paints such as these oftendiscolor and are not durable; this hasprompted the development of syntheticresins for high solids applications.

Many of the classes of resins listed inTable 5 may be used in high solids coatingformulations. However, to attain coatingsthat contain less than 30% solvent, modifi-cations must be made to the binders usedin conventional formulations. This isaccomplished by using lower-molecular-weight resins that undergo cross-linkingreactions as the paint cures or by usingresin polymers that have narrow molecularweight distributions. Some difficulties suchas slow physical drying and film shrinkageare encountered when adjusting the poly-mer in this manner. However, these diffi-culties can be minimized by optimizing theformulation and cure conditions. Forexample, Bittner and Epple (66) demon-strated that polyurethane paint prepared in

a high solids formulation using resin of lowmolecular weight and narrow-size distribu-tion dries with similar hardness and homo-geneity if dried at 80°C rather than atambient temperatures.

Modifying the molecular structure ofthe resin, e.g., by using branched resins(65), results in polymers with lower intrin-sic viscosities. In turn, the coating formula-tion requires less solvent to reach a certainviscosity. In addition, it can be advanta-geous to pay close attention to the differentmonomer types used in a copolymer resin.For example, Sullivan (67) outlines using2-methyl-1,3-propanediol to improve theflexibility of high solids polyester coatings,while reducing solvent usage. Anotherexample of viscosity reduction is the use ofsilicon-based monomers in place of car-bon-based monomers for the synthesis ofpolyester resins (68).A related approach to high solids

coatings is to incorporate a reactive chemi-cal as the solvent. This allows control ofthe coating viscosity during application butminimizes the VOCs released because thesolvent is cross-linked into the coating(69-74). Reactive diluents take manyforms, sometimes even as a natural oil as inthe case discussed by Dirlikov et al. (75)and Banov (76).

Of course, benign solvent use isencouraged in addition to quantity reduc-tion. For example, VMSs similar to thosedescribed for cleaning have been used inthree different high solids silicone paints,resulting in a VOC reduction withoutcompromising film quality (77). Finally,the need for polymers with specifically tai-lored low molecular weights and distribu-tions for effective high solids coatings hasresulted in a variety of new polymerizationinitiators, synthetic techniques, and cross-linking additives (78-81).

Aqueous FormulationsWaterborne coatings offer another set ofoptions as they provide a safe, nontoxic,and environmentally benign method todramatically reduce or eliminate volatile

Table 6. Advantages and disadvantages to high solids coating formulations.a

Advantages

Applicable to many resin typesEquipment can be retrofitCost effectiveExcellent performance for protective maintenanceand automotive coatings

Disadvantages

Pigment flocculationRheology difficult to control during applicationMay have inferior surface appearance

&Data from Varerkar (199).

organic solvents. In addition, they are usu-ally inexpensive and come in liquid form.Waterborne coatings, primarily in the formof latex paints, have been prevalent since the1950s but were deficient in many areas suchas flow behavior (because of their non-Newtonian nature), drying properties, glossi-ness, corrosion, and foaming (82). However,strict environmental regulations and con-cern for worker exposure have focusedattention on these types of coatings andresearch is targeted at improving the dura-bility and application of water-based coat-ings (83,84). Waterborne paints are appliedby spraying, rolling, etc., but as with clean-ing operations, the process usually requiressome extra time and equipment to allowthe coating to dry properly because of thehigh latent heat of water vaporization. Theadvantages and drawbacks of aqueousformulations are summarized in Table 7.

Waterborne paints fall into two generalclasses: water-reducible coatings and emul-sions. Water-reducible coatings consist ofbinders that can be dissolved in water. Thehigh polarity of water limits the range ofresins compared to that for resins that can beused for high solids applications because ofsolubility difficulties. Resin dasses that havebeen used successfully include epoxies,acrylics, polyesters, and polyurethanes. Theseresins differ from their solvent-borne coun-terparts used in high solids coatings throughthe addition of extra hydrophiic groups suchas carboxylic acids and amines. General over-views of water-reducible polymers have beenoutlined (85,86).

If desired paint properties cannot beobtained using water-soluble resins, formu-lations using a surfactant to emulsify appro-priate resins may be effective. These areoften referred to as latex paints. The poly-mer is most commonly based on acrylateesters, vinyl acetate, or copolymers withstyrene. The polymeric resin is prepared insitu in an emulsion polymerization resultingin a latex-type paint. The emulsions maycontain up to 15% organic solvent as a sta-bilizer resulting in a low VOC coating. It isalso worth mentioning that many water-reducible coatings contain small amounts ofa co-solvent such as a glycol ether or alcoholto aid in coating handling (86).

Specific examples of tailored resins forwaterborne coatings abound. Two-packpolyurethane paints have been developedthat exhibit film properties comparable tothose of solvent-borne polyurethane coat-ings (66,87). Waterborne polyurethanesthat have the performance of solvent-basedsystems can also be made via tailored



Table 7. Advantages and drawbacks to waterborne coatings.

Advantages Disadvantages

Inexpensive High freezing pointEnvironmentally benign High latent heat of vaporizationNontoxic Often need new equipmentLiquid form Extra precautions with electrostatic paint application systems

Limited material compatibility for delivery systemsCan exhibit high water permeabilityPigment flocculation

emulsion polymerization (88). Aromaticpolycarbodiimides act as very efficient cross-linkers in waterborne emulsion systems andhave the added advantage that they are muchless toxic than traditional polyaziridines(89). Eslinger (90) discusses the use ofaliphatic epoxy cross-linkers to cross-linkacid functionalities that promote resin solu-bility. Cross-linking of the epoxy filmsresults in a coating that is more resistant tohumidity and mechanical impact. Water-borne fluoroelastomeric coatings for aggres-sive conditions have been developed (91).These coatings provide high-barrier proper-ties and traditionally large amounts of sol-vent have been used to control viscosityduring application. These new coatings areprepared in a latex form, are easily dispersed,and exhibit good resistance to heat andchemicals. The automotive industry, a largepaint consumer, has recently implementedmetallic water-based coatings (92). Finally,some waterborne coatings incorporate reac-tive diluents, as in high solids coatings. Forexample, Blank (93) describes using a ure-thane diol as a reactive diluent to replaceglycol ether cosolvents in emulsion coatings.

Case studies illustrate that waterbornepaints are indeed feasible for many applica-tions. Waterborne paints can reduce theamount of solvent used in vehicle paintingfrom 42.4 to 7.3 kg (94). RepublicContainer Co. (Nitro, WV), a companythat supplies steel drums, switched from asolvent-based paint to a water-based paint,reducing their VOC emissions to 2.8 lb/galand saving over $10,000 in costs. Cornwell(96) illustrates many successful cases ofwaterborne paint use for steel coating, asubstrate not traditionally coated withwater-based paints because of difficultieswith rusting.

Novel coating additives are also beingstudied as a way to ameliorate the disadvan-tages that have become synonymous withwaterborne paints. Bieleman (82) discussesadvances made in eliminating foaming,undesirable rheology, and poor glossinessdue to agglomeration of the pigment.

Kobayashi (97) has also addressed the issueof pigment dispersion from the funda-mental aspects of molecular interactionsbetween water and the pigment. Klein (98)discusses latex paint formulations that areformulated without the glycols that areusually added as stabilizers but that may betoxic and contribute to the VOC contentof paint.

Supereritical Carbon DioxideFormulations. SCCO2 is used in spraypaint formulation and application becauseit is nontoxic, inexpensive, and has theadded advantage that it has high solvationpower for many polymers. Since CO2 is sovolatile, it is mixed with the coating resinimmediately prior to application and theresulting mixture sprayed onto the sub-strate. It has been demonstrated that up to80% of the organic solvent used to formu-late an acrylic spray paint can be replacedby SCCO2 without compromising thecoating homogeneity (99). In addition,CO2 is such a fast-evaporating solvent thatthe paint dries quickly. Furthermore, itdoes not generate additional CO2 like sol-vent-containing paints that can oxidize toform 2.3 to 3 kg C02/kg solvent. White(100) reached conclusions similar to thoseof Donohue for a variety of resin-pigmentcombinations. Other researchers havepatented their work with supercritical dilu-ents for spray painting applications anddemonstrated reductions in the amount ofsolvent required for adequate coatingapplication (101,102).

Solvent-Free Formulations. As withcleaning, many researchers are lookingtoward solvent-free coatings as the answerto solvent replacement. Powder coatingsrely on thermosetting plastics to be sprayedon a surface at high temperature. Thismethod produces high-gloss, even coatingsbut requires specialized equipment and islimited to metal surfaces that can withstandthe high-melt temperatures (65).Ultraviolet (UV) curable coatings areanother solvent-free alternative. In this casereactive monomers such as ethers and

styrene are used to coat the surface of inter-est and UV light is used to initiate an insitu polymerization. Because the cure ratedepends directly on the distance of the itemto be coated from the UV source, this coat-ing technique is best suited to flat sheets(103). A limitation is that is is difficult toincorporate pigment in UV cure coatings,as the pigments usually tend to absorb UVlight. Finally, many novel coatings tech-nologies are discussed in the review byMcGinniss (104) who discusses advancesmade in environmentally benign coatingsthat include silicon oxides, silica fillers, andhybrid waterborne/UV-curable systems.Another researcher is exploring linearoligoester diols for solvendess coatings (105).

Altenative Solvents for SynthesisSolvents are used widely in the chemicalprocessing industry as they are necessaryfor the solvation of the reactants and prod-ucts in reaction processes. Selection of thesolvent is important in determining thechemical reactivity, selectivity, and yield ofindustrial synthesis operations. Most syn-thesis solvents except carbon tetrachlorideare not Class I or Class II ozone-depletingsubstances, so in contrast to solvents usedin cleaning and coating operations, theirsupply is not threatened. Many of them,however, are on the 33/50 list, and ways toreduce their use are being sought actively.One route is to find or develop replace-ment solvents, which are attractive for rea-sons of safety, toxicity, emissions, andother aspects covered increasingly by themany government regulations. Ideally, newtechniques would allow reactions to occurin the absence of solvents; to this end,some progress has been made using micro-waves (106). Most synthetic reactions aresolvent based, however, and will continueto be so for the foreseeable future. There isclearly a need, then, to search for alterna-tive solvents for synthesis operations moreenvironmentally friendly than the existingsolvents. This search is more complicatedthan in the case of cleaning and coatingoperations as not only should the solvatingcharacteristics of the replacements matchthose of the original solvent as closely aspossible, but the new synthesis solventsmust also be inert to the reactants andproducts, and the yield of the reactionshould not be compromised.

Drop-in Replacements. As with otherapplications, the approach requiring thefewest modifications to already existingsynthetic processes is to find a drop-inreplacement for the conventional solvent.


SHERMAN ET AL.

For example, it is common to replaceextremely flammable diethyl ether withmethyl tert-butyl ether (107) or carcino-genic benzene with toluene (108). Suchfacile substitutions are not always available,however, and experimentation is oftenrequired to find a suitable replacement.Some examples of effective solvent substitu-tions are given in Table 8. In the synthesisof phosphonitrilic hydroquinone prepoly-mers, the carcinogenic and ozone-depletingsolvent carbon tetrachloride was replacedwith cyclohexane with a slight increase inyield (108). Chloroform was considered anexplosive hazard in solvating Schmidt reac-tions involving azides, and it was replacedwith dimethoxyethane (109). Dichloro-methane, or methylene chloride, is one ofthe most popular synthesis solvents, but it isa suspected carcinogen and is highly volatile(bp=40°C). Ogawa and Curran (110)demonstrated that benzotrifluoride (lowtoxicity, bp = 102°C) can be an effectivereplacement for dichloromethane in manyreactions, with similar yields; some examplesare shown in Figure 4.

Tetrahydrofuran (THF) is anotherimportant process solvent often used tosolvate reactions involving strong bases.The workup of strong base reactions oftenincludes an aqueous extraction, creatingthe problem of contaminated aqueouswaste because THF is completely water-miscible. Typically, elaborate steps such assolvent exchange by distillation are takento avoid THF contact with water. This isan energy-intensive process, and a moreeconomical solution is desirable. Hatton'sgroup (111) has examined the use ofTHFderivatives that have similar solvating char-acteristics but are essentially nonvolatileand water insoluble as reaction solvents. Aparticularly effective solvent is n-octyltetrahydrofurfuryl ether, which has beenshown to be a satisfactory replacement forTHF in a series of reactions in the synthe-sis of the human immunodeficiency virus(HIV) protease inhibitor Crixivan. A num-ber of solvent switches and off-line recov-ery operations can potentially be avoidedusing this approach. These solvents there-fore satisfy the criteria for green processing

Reactions

0H DMSO(COCI)2

Et3N -25oC

(0Ac)3MeC \

MeO CH20H O

MeO rt., 1 hr

0

Ph--' s ~ 30% H202 >SePh Pyridine, 25°C

0 v10C14~+.~~SiMe3 250C, 5 min

0

MeO

MeO / CHO

MeO

0

Ph)L

0

0

0) \IC110410-100C, 1.5 hr

Yield inCH2CI2 BTF

71% 76%

96% 92%

96% -100%

72% 64%

54% 73%

Figure 4. Benzotrifluoride as a replacement for dichloromethane.

in that they are less prone to enter the envi-ronment and that a number of energy-intensive separations and solvent exchangescan be avoided. Experiments have alsoshown that ifTHF is attached via an etherlinkage onto a polystyrene-type polymerbackbone, the solvent can be recoveredefficiently through ultrafiltration (111).

Ionic Liquids. Seddon (112) showedthat 1-ethyl-3-methyl imidazolium chloride-aluminum(III) chlorides are ionic liquids attemperatures as low as -90°C. These non-volatile ionic liquids can solvate a wide rangeof organic reactions including oligomeri-sations, polymerizations, alkylations, andacylations (113).

Water. Water is an ideal candidate as areplacement solvent. It is nontoxic, nonflam-mable, readily available, inexpensive, andeasy to handle. Unfortunately, switchingfrom organic to aqueous solvents is not asimple task. As with coating applications, thehigh polarity ofwater offers many difficulties

Table 8. Drop-in solvents for synthesis.

Solvent Problem Replacement Reference

Diethyl ether Flammable, flash point =-40°C Methyl tert-butyl ether (107)Benzene Carcinogenic Toluene (108)Carbon tetrachloride Carcinogenic, ozone depleting Cyclohexane (108)Chloroform Explosive hazard with azides Dimethoxy ethane (109)Dichloromethane Suspected carcinogen, volatile Benzotrifluoride (110)

in its implementation as a reaction mediumbecause many organic compounds do notexhibit good aqueous solubility. None-theless, significant progress has been made indeveloping reaction chemistries that takeplace in substantially aqueous environments.An overview ofsome of the advances in theseareas is given here.

Phase transfer catalysis takes advantageof the solvating properties of biphasic sys-tems. Reagents are solvated in the organicand aqueous phases and a phase transfercatalyst is used to bring them to react inthe organic phase, as illustrated in Figure 5(114). Aqueous alkali hydroxides can beused to replace flammable bases of sodiummetal, sodium hydride, sodamide, andother alkoxides, whereas expensive anhy-drous or aprotic organic solvents such asdimethylsulfoxide, dimethylformamide,and hexamethylphosphoramide can bereplaced with dichloromethane, chloro-form, hexane, and benzene. The reactiontemperature is lowered while the reactionrate improves because the increased reactiv-ity of anions in the nonpolar solvent.Reactions performed with phase transfercatalysts have been reviewed in severalbooks (114-116), as have asymmetricphase transfer reactions (117).

Another approach is to perform thereaction at the organic-aqueous interface.

Environmental Health Perspectives * Vol 106, Supplement l * February 1998260


A-X > A-Y

+ +

Organic A-X [CAT Y-1 [CAT X-]phase Phase

Aqueous y_ Transferphase catalyst Y-

CATY- > CATX-

Figure 5. Phase transfer catalysis uses water to solvate some of the reagents.

Reagents are moved from the organic to theaqueous phase but remain localized near theinterface, and thus the reagents need not besignificantly water soluble. Catalysts areeither solvated homogeneously in a sup-ported thin aqueous film or at the interfaceby surface active ligands (118-120).

The use of the bulk organic solvent canbe avoided completely by exploiting theproperties of aqueous surfactant solutionsin which the surfactants aggregate to formmicelles consisting of apolar cores com-prised of the hydrophobic tail groups stabi-lized by coronae formed by the hydrophilicsurfactant heads (121,122). The apolarcore plays the role of the organic solvent,whereas the palisade layer can provide amedium of intermediate polarity. The lit-erature in this area is vast, but only a few ofthese studies specifically address the use ofthese aqueous micellar solutions as replace-ments for traditional organic solvents. Forexample, Monflier showed that solvent-freetelomeriztion of butadiene with water toform octadienols could be carried outeffectively in the presence of a nonionicsurfactant; the conventional process is per-formed in the solvent sulfolane (123).Replacement of the organic phase with sur-factants to exploit micellar phase transfercatalysis principles was reported recently byRathman et al. (124) for the alkylation ofphenol and aniline. This group had previ-ously demonstrated the synthesis of a sur-factant by micellar autocatalysis, wherebythe surfactant product itself catalyzes thereaction (125).

In some cases even the use of micellarsolvent phases can be avoided and thereactions can be carried out in an entirelyaqueous medium. For water-solublereagents, catalytic reactions such as hydro-genations and hydroformylations may becarried out homogeneously in the aqueousphase with water-soluble ligands such astriphenylphosphinotrisulfonate (120).Barbier-Grignard-type reactions in water(126) between allyl halides and carbonylcompounds can be mediated by metals oftin, zinc, or indium. Usually the generation

of the organometallic reagent takes place inanhydrous organic solvents, but using softermetals allows this reaction to take place inwater. Shu et al. (127) demonstrated epoxi-dation of cyclooctene using oxone in waterwhere the products were easily recovered byphase separation. The Shaw group has alsoshown that brominations are performedreadily in water instead of in carbon tetra-chloride (128). These examples indicate thepotential minimization of solvent usage bythe development of new water-basedchemistries for green processing.

Supercritical Fluids. Water and carbondioxide are the two most commonly usedsupercritical fluids for mediating reactions.These fluids are nontoxic, nonflammable,and inexpensive. However, the technologyis expensive to implement, particularly forwater because of the specialized equipmentnecessary to conduct reactions at hightemperatures and pressures.

Supercritical water (6470 K and 217atm) is considerably less polar than water atambient conditions and has the ability tosolvate most organic molecules. In the pres-ence of oxygen, organic compounds arequite reactive in supercritical water, withcomplete oxidation realized at short reac-tion times. Supercritical water oxidation(SCWO) processes are being developed forwaste management as aqueous wastes con-taining 1 to 20% organics can be oxidizedeconomically to CO2 and water (129). Forwater with less than 1% organics, activatedcarbon is more economical for waste treat-ment and for water with greater than 20%organics, incineration is ideal. For in-depthdiscussions on SCWO, see Tester et al.(129) and Savage et al. (130). Morerecently, research has been conducted toimprove catalysts (131) and reactors (132)that must withstand the corrosive condi-tions faced in SCWO operations.

SCCO2, a nonpolar fluid, has beeninvestigated as a solvent for many reactionsin the areas of fuels processing, biomassconversion, biocatalysis, homogeneous andheterogeneous catalysis, environmental con-trol, polymerization, materials synthesis,

and chemical synthesis), as reviewed by anumber of authors (130,133,134). Mostrecently, Desimone's group has investi-gated this medium for precipitation poly-merization of acrylic acid (135), synthesisof poly(2,6-dimethylphenylene oxide)(136), free radical telomerization of tetra-fluoroethylene (137), cationic polymeriza-tion of vinyl and cyclic ethers (138), anddispersion polymerization of styrene (139).It has been found that fluorination and theformation of micelles with fluorinated sur-factants enhance polymer solubility inSCCO2 (139,140). SCCO2 has been usedas a solvent for homogeneous catalytichydrogenations (141,142), and Burk et al.(143) have shown it to be a good mediumfor asymmetric hydrogenations.

Altemative Solvents forSeparation ProcessesThe application of organic solvents andorganic solutions with carrier compoundsfor the separation of organic substances andmetal ions from different sources is wellknown. These separations are usually per-formed by extracting the target compoundinto the organic phase for purification,enrichment, and pollution remediation. Aswith cleaning, coating, and synthetic appli-cations, it is advantageous to replace theorganic solvents used in liquid extractionswith solvents that are environmentallyfriendly. In some cases it is beneficial toimplement new separation techniques thatreduce the need for large volumes oforganic solvents. Among these, liquidextraction techniques employing supercriti-cal fluids and aqueous formulations con-taining surfactants or soluble polymers aremost frequently considered because of theirenvironmentally friendly characteristicsand because they often afford increasedextracting strength.

Supercritical Fluid Extraction.Thecharacteristics of supercritical fluids makethem ideal for the recovery of natural prod-ucts (144). As a result, the food industrywas among the first to implement supercrit-ical fluid extraction (SFE) widely usingCO2. Not only is this process environmen-tally benign, it is also nontoxic, a primaryconcern when manufacturing edible prod-ucts. Applications in the food industryinclude coffee decaffeination, and processesinvolving hops, vanilla, paprika, celery seed,and chili peppers (145). In one example,the extraction of grape seed oil using SFEyielded a final product of better qualitythan that obtained using conventionalextraction (144).


SHERMAN ET AL.

SFE has also replaced many regulatedsolvents in analytical chemistry applica-tions in recent years, primarily because itprovides a more reliable measure of theconcentrations of environmental contami-nants and can play an important role inpollution assessment, abatement, and con-trol. Dolezal et al. (146) have shown theadvantages of using SFE compared to theconventional Soxhlet extraction withtoluene for determining the presence ofpolychlorinated dibenzo-p-dioxins andpolychlorinated dibenzofurans in ashesfrom a municipal incinerator. SFE allowsthe complete extraction of the analytesfrom the sample, whereas conventionalextraction results in an incomplete, andhence, inferior extraction. Analysis of agro-chemical samples from soils after extractionby Soxhlet methods are now replaced byanalysis following supercritical extractions(147). Alzaga et al. (148) extracted Pirimi-carb (a pesticide present in sediments ofrivers) using supercritical CO2 modifiedwith triethylamine and compared theresults to those obtained with the conven-tional Soxhlet method. The supercriticalfluid method offered increased precision,shorter analysis time, and a 10-fold reduc-tion in solvent usage. Other efforts yieldedsimilar results; for example, Reighard et al.(149) used CO2 enhanced by the additionof methanol (co-solvent) to extractnitroaromatic and phenolics, environ-mental pollutants. This improved the pro-cedure by reducing the solvent volume andthe time necessary for the extraction. Inaddition, it allowed the extraction of polarspecies from complex pollutant matrices.The use of co-solvents can cause sometechnical problems, however, as high pres-sures and high temperatures may be neces-sary in these cases. In addition, someco-solvents may be regulated. An attractiveinterim option from an environmentalstandpoint is the use of HFCs or HCFCs.At supercritical conditions these solventseffectively extract relatively polar com-pounds such as polychlorinated biphenyls,dibenzo-p-dioxins, and dibenzofuranswithout the use of a co-solvent. (150).

Aqueous Surfactant and Macro-molecular Solutions. Removal of organicor heavy metal ion contaminants fromaqueous streams can be achieved using avariety of different separation strategies,one of which is solvent extraction.Potential countercontamination of thestreams being treated with the extractingsolvent can be avoided by eliminating theorganic solvent altogether in favor of

aqueous-based solvent systems that rely fortheir effectiveness on the presence of dis-solved surfactant micelles or polymers.These aggregates or polymers can solubilizeorganic solutes within the aqueous phase orform complexes with the metal ions to beremoved. The question to be addressed is"how are the aqueous-based solvent sys-tems to be separated from the treated feedstream?" Christian and Scamehorn (151)successfully investigated the use of ultrafil-tration for the retention of the surfactantmicelles, whereas Hurter and Hatton (152)argued that efficient separations could beobtained by exploiting the countercurrentprinciples entrenched in chemical engi-neering unit operations. They suggestedthat the micellar solutions be introduced tothe lumens of a hollow fiber ultrafiltrationunit and that the feed solution be intro-duced to the shell side of the unit at theopposite end of the module. The twostreams then flow countercurrently, andthe solute diffuses across the membranefrom the shell side to the micellar solution,where it is taken up by the apolar micellarcores. The purpose of the membrane is toprevent the micelles from mixing with theaqueous feed stream.A particularly important class of

surfactants for the solubilization of organiccompounds in aqueous solutions is thepolyethylene oxide-polypropylene oxide-polyethylene oxide family of block copoly-mers (152,153). These polymers formpolymeric micelles that have a high capacityfor the solubilization of organic com-pounds. Recovery of polyaromatic hydro-carbons (PAHs) by using block copolymermicelles in hollow-fiber membrane extrac-tion was successfully demonstrated byHurter et al. (154). The high capacity ofblock copolymer micelles for trace contam-inants offers the possibility of tailoreddesign of block copolymers for future sepa-rations. An advantage of these polymericmicellar systems is that the micelles formonly above a certain temperature, called thecritical micelle temperature (CMT). Whenthe loaded micellar solution is cooledbelow the CMT, the micelles dissolve andthe PAH precipitates out of solution, thusenabling the simple and efficient regen-eration of the micellar solution. Theseresults and concepts have been confirmedby the more recent work of Lebens andKeurentjes (155).

Water-based solvent systems originallydeveloped for the separation and purifica-tion of proteins and other biomaterials(156) have been suggested for the treatment

of contaminated aqueous waste streams.Certain pairs of water-soluble polymers areincompatible in solution together, and thiscan lead to phase separation in which twophases are formed. Both phases are pre-dominantly water, and each contains onlyone of the two polymers. Similar phasebehavior results with some polymers andhigh concentrations of organic salts. Theproperties of the two phases ensure that theenvironment-afforded targeted species isdifferent in the two phases. This providesthe driving force for separation of differentspecies. A commonly used phase-formingpolymer is polyethylene glycol (PEG),which may or may not be derivatized toimpart added selectivity to the separation.Rogers' group has investigated the poten-tial for using such systems for the separa-tion and recovery of environmentally toxicheavy metals (157) and of pertechnetatefrom simulated Hanford tank wastes(158). The removal of color from textilewastes has also been addressed using suchsystems (158), which have the advantagethat they are are not organic-solvent based,are primarily water, and the PEG polymersused for phase separation are virtually non-toxic and nonflammable, are inexpensiveand available in bulk, and have reasonablephase separation characteristics. As solventreplacements, then, PEG-based aqueousbiphasic polymer systems are an environ-mentally favorable alternative to traditionalorganic solvent phases.

Another class of solvents that appears tohave significant appeal for green processingof metal waste solutions relies on solvent-coated magnetic particles dispersed withinthe feed phase to be treated (159,160). Oncethe desired solutes have been removed byextraction, these particles can be recoveredconveniently using magnetic filtration.

Computer SimulationsAs computers become more pervasive andincreasingly powerful, specialized programsand databases are being developed to assistin a wide variety of research efforts. This istrue in the search for solvent alternatives,and in this section we review the applicationof computers to solvent substitution studies,and cover computer-aided molecular designof new solvents, methods developed for theprediction of physical properties, methodsfor predicting less precise chemical charac-teristics such as toxicity and carcinogenicity,and computer-aided design of alternativesynthetic pathways. These tools may assistthe scientist in two ways. First, the designprocess can be optimized with the use of



more complex constraints than could other-wise be handled. Second, in some cases theneed for time-consuming and costly physi-cal or chemical property measurements canbe eliminated with the use of estimationtechniques for properties of interest.

Computer-Aided Selectionof Replacement SolventsSeveral methods have been proposed toguide the solvent replacement process forthe many applications described above.These efforts attempt to build an organizedframework for this process and provide asubstantial improvement over previously adhoc or trial-and-error approaches to solventreplacement. An excellent example is theapproach of Joback (161), who outlines amethodology for the selection of replace-ment solvents for various processes such asextraction or cleaning. There are basicallyfour steps to this process: identify con-straints on important solvent properties,compile data for all properties, rank solventssatisfying the target constraints, and evaluatetop solvent candidates using simulation.

Constraints on the selection of asolvent are diverse. Environmental, safety,health, reactivity, stability, and regulatoryconsiderations must be considered. Tooptimize solvent selection, these con-straints must be quantified in terms ofphysical or chemical properties or mole-cular structure. Given that a number ofproperties can be determined to govern theconstraints on the solvent application,accurate property values must be found inthe literature, measured, or estimated. Forcompounds with unknown properties,measurement is often too costly to con-sider, so various property estimation tech-niques must be employed. For the thirdstep, given the previously defined con-straints imposed by the application, allcandidate solvents are screened after whichthe remaining candidates can be putthrough a more rigorous trade-off analysis.If no solvents survive the screening, it mustbe determined which constraints can beeased until likely candidates appear. Withavailable process simulation tools (Table9), different solvent candidates can then beevaluated through the whole solvent lifecycle. Additional costs and constraints,such as solvent storage, transportation, reg-ulation and disposal costs, to name a few,must be considered outside those normallyconsidered in a process simulation.

To perform a procedure such as thatdescribed by Joback (161), a significantamount of information must be obtained

on the solvents considered and theirimpact. There are many sources of solventinformation available now on computerthrough the World Wide Web, several ofwhich are summarized in the Appendix.Information on physical and chemicalproperties, government regulations coveringthe use of many solvents, and examples ofsuccessful solvent substitution efforts cannow be readily accessed on the Web. Thesoftware used to evaluate candidatesthrough simulation is generally a commer-cially available process simulator softwarepackage such as Aspen Plus, Pro II, andothers (Table 9). These programs allow thesimulation of engineering and operatingproblems, from the unit scale to full plantsimulations. The impact on the entire plantof a proposed solvent substitution can beestimated using such a program.

Computer-Aided Molecular DesignofNew SolventsMuch current research on solvent substi-tution takes the process a step further thana simple screening of existing solvents byusing an approach consisting of buildingnew molecules from substituent molecularsubgroups and using methods for predict-ing molecular properties from structure.This is done in the framework of a systemin which the rules for the constraints to thesolvent selection are defined and an opti-mization is performed. Several differentapproaches are used, with the most workpublished on algorithms using UNIFACsubgroups as a basis.

Development of the UNIFAC method-ology by Fredenslund et al. (162) for theprediction of properties based on a groupcontribution approach stimulated muchwork in the area of computer-aided solventdesign. The basis of the UNIFACapproach is the definition of submoleculargroups (e.g., CH2, CH3, CH30, CH2C1,OH) and the fitting of a given molecularproperty or activity coefficient to a sum ofcontributions based on the subgroup mole-cular volume and interaction termsbetween the groups.

Separation processes (both liquid-liquidand gas-liquid) are a key element in manyindustrial processes. For this application, sol-vent molecules are built from UNIFACsubmolecular groups, and the relevant prop-erties of the new molecules such as distribu-tion coefficients and selectivities areestimated. Strategies for the design of sol-vents for separation processes were initiallyformulated by Gani and Brignole and laterextended to better model the processes ofsolvent synthesis, solvent evaluation, andsolvent screening (163,164). Gani andFredenslund (165,166) later expanded theircomputer-aided molecular design approach,and provided additional examples of theapplication of this approach to the selectionof refrigerant alternatives, liquid-liquidextraction, azeotropic and extractive distilla-tion, and gas absorption. Naser and Fournier(167) also employed UNIFAC groupcontributions, and developed a continuousoptimization approach, as opposed to thecombinatorial optimization approaches of

Table 9. Programs developed for property prediction, solvent replacement studies, and reaction design.

Program name Application Reference

CAMEO Organic react.product pred. wwwchem./eeds.ac.uk/UK.LHASA Organic synthetic route design wwwchem.Ieeds.ac.ukILUKSYNGEN Organic synthetic route design syngen2.chembrandeis.edu/syngen.html

LEMDS Liquid-liquid extraction Naser and Founier (167)Aspen Plus Steady-state process simulation www.aspentec.comChemCAO Ill Steady-state process simulation wwwphoenix.net/chemstatHYSIM Steady-state process simulation wwwhyprotech.comPRO 11 Steady-state process simulation wwwsimsci.comSPEEDUP Dynamics and plant optimization www aspentec.com

UNIFAC VLE prediction wwwcchem.berkeley.edu/ljmpgrpADAPT General property prediction zeus.chem.psueduCODESSA General property prediction wwwsemichemcom/CODESSA.htmiMOLCONN Topological descriptor calculation www.esIc.vabiotech.comrfmolconnHenry, BIODEG, Property prediction esc_seover.syrres.com/-ESC/estsoft.htmLogKow, etc. (several codes) Syracuse Research Corporation (nonprofit)

ACD/BP, etc. Property prediction. wwwtacdlabs.comDEREK Toxicity prediction wwwchemIeeds.ac.uk/LUKTOPKAT Toxicity prediction wwwoxmolcom/prods/topkatlsw/All links in this table, as well as those in the "Appendix" can be found in web.mit edu/huibers/www/greenchem.html


SHERMAN ET AL.

others, to design optimum solvents forliquid-liquid extraction. Liquid-liquidextraction and multicomponent gas absorp-tion solvent selection has been studied byMacchietto et al. (168) and solvent mixtureselection by Odele and Macchietto (169).More recently, Pretel et al. (170) used aUNIFAC-based molecular design approachto evaluate solvents for liquid extraction andextractive distillation, and provide specificcomparisons to experimental data.

Several researchers describe otheraspects of the problem of designing newsolvents. Klein et al. (170) investigated thedesign of solvent mixtures to achievedesired properties. Duvedi and Achenie(172) demonstrated a computer-aidedmolecular strategy to design environmen-tally safe refrigerants. Venkatasubramanianet al. (173) used a genetic algorithm todesign molecules for given property con-straints; this allowed a search over morediverse properties than possible with tradi-tional algorithms. A design of an optimalpolymer is given as an example. Meniai andNewsham (174,175) applied Monte Carlosimulations to develop relationships betweenthe solute binding energy and both thesolvent selectivity and the partition coeffi-cient. This method is useful in designingliquid-liquid extraction processes.

Prediction ofPhysical Propertiesfrom Molecular StructureAt the core of many of these algorithms forsolvent substitution is a method for pre-dicting the properties of proposed mole-cules, given only the molecular structure.Much work has been done in this areaalone, and several programs have beendeveloped to guide this process. Some ofthese programs are listed in Table 9.Additionally, process simulation softwaresuch as Aspen Plus contain several differentapproaches for the prediction of propertiesfrom molecular structure.

Two different approaches for propertyprediction are apparent, one based ongroup contributions and one based on con-tributions influenced by more than just theimmediate sum of group contributions,such as that captured by the topologicaldescriptors (176). The first approach is thebasis for programs such as the SRC andACD programs, while the latter is used inMOLCONN, ADAPT, and CODESSA(Table 9) (177).

As an example, consider the predictionof aqueous solubility from molecular struc-ture. The group contribution approach hasbeen broadly applied, as reviewed by

Yalkowsky and Banerjee (178). Morerecently, efforts by Kan and Tomson (179)demonstrate the use of the UNIFACapproach to predict aqueous and nonaque-ous solubilities for a variety of compounds.The topological approach is an extensionof simpler group contribution efforts, as itcan include contributions of higher order,where group contributions are essentiallymodified by contributions from nearestneighbors and beyond. Kier and Hall(180,181) developed a series of moleculardescriptors termed the molecular connec-tivity indices and demonstrated their valuein the prediction of many properties.Several other types of topological descrip-tors have been developed and applied toproperty prediction (176,182). Severalresearch groups have taken the topologicaldescriptors along with other types of mole-cular descriptors (geometrical, electrostatic,quantumchemical) and arrived at multiplelinear regressions that allow the predictionof properties. With regard to aqueous solu-bility, several examples of this approach arethe work of Nirmalakhandan and Speece(183), Bodor and Huang (184), and theNelson and Jurs group (185,186).

Prdiction ofToxicology andRelated ParametersProcess simulation is a key tool incomputer-assisted solvent substitution.Often the key to a successful simulation isselection of adequate models for the pre-dict physical properties used in the simula-tion, as reviewed by Carlson (187). Morecomplicated than the prediction of physicaland chemical properties is the prediction ofmore loosely defined molecular characteris-tics such as toxicity. These properties arenot traditionally included in process simu-lation software, so special attention mustbe paid to their prediction.

Traditionally, synthetic chemists focusedon ease of synthesis and commercial use inchemical design. With ever increasingattention being paid to environmentalimpact and toxicity, additional constraintsare being placed on the chemical design pro-cess. DeVito (188) outlines some of theapproaches that chemists may consider forthe design of safer substances; these includereducing absorption, understanding toxicmechanisms, using structure-property rela-tionships, retrometabolism, isosterism, elim-inating the need for associated toxicsubstances, and identifying equally usefulbut less toxic chemicals of another chemicaldass. The basis of chemical carcinogenesis isdiscussed by Lai et al. (189), who proposed

a molecular design method to reduce thecarcinogenicity of compounds.

Prediction of chemical toxicity using acomputer can save time and money (becauseof the high cost of toxicology studies) eitherby eliminating toxicological testing or byreducing the use of laboratory animals byimproving the order of priorities for testing.Several approaches have been used to esti-mate toxicity of a given compound. Someapproaches derive parameters from the mol-ecular structure, and correlate those parame-ters with different common measures oftoxicity. Others correlate toxicity withknown physical properties of the compoundof interest such as its octanol-water parti-tion coefficient. Milne et al. (190) summa-rize various computer methods used topredict toxicity from molecular structure. Ithas been known for some time by medicinalchemists that toxicity, bioavailability, andother important parameters that gauge theinteraction of chemical compounds withhumans and animals correlate well with theoctanol-water partition coefficient.

An attractive aspect of this approach isthat an actual purified sample of the com-pound of interest is not necessary for prop-erty estimation, and no other measuredproperties are necessary, as the toxicity is cor-related with molecular descriptors derivedsolely from molecular structure. Pioneeringwork in this area was done by Kier and Hall(180,181), who developed a series of topo-logical descriptors called molecular-connec-tivity indices, and correlated toxicity andcarcinogenicity with these indices. The fun-damental concepts of the use of topologicaldescriptors to predict chemical behavior hasbeen summarized by Rouvray (176).

An example of another approach isDEREK (191,192), a publicly availableexpert system designed to assist chemistsand toxicologists in predicting toxicologicalhazards based on analysis of chemicalstructure (Table 9). DEREK differs fromother computer methods for toxicity pre-diction in that it makes qualitative ratherthan quantitative predictions and does notrely on algebraic or statistical relationships.A variety of different approaches to the

prediction of toxicity have been developedunder the sponsorship of the Predictive-Toxicology Evaluation project of theNational Institute of Environmental HealthSciences (193).

Computer-Aided Design ofAlterative Synthetic PathwaysA more complicated problem than solventreplacement for applications such as deaning



is that of solvent substitution for organicreaction optimization. The solvent isimportant in organic synthesis, and severalsolvent polarity scales have been developedto attempt to quantify this, specificallywork by Reichardt (194).

Several programs have been developedto assist in this process. The CAMEOprogram (Table 9) uses a mechanisticapproach to make predictions and does notrely on data tables of specific reactions.Consequently, it is capable of predictingnovel chemistry. Given the reactant mole-cules and reaction conditions, CAMEOevaluates the reactions and suggests prod-ucts. Another program, LHASA (Table 9),uses a chemical knowledge base that con-sists of an extensive library of reactiondescriptors (transforms) based on reviewsof the chemical literature. These transformsdefine the scope and limitations of eachreaction type. The knowledge base is notjust a restricted reaction database butenables LHASA to suggest new and innov-ative synthetic routes to chemists. Anotherprogram, SYNGEN (Table 9), auto-matically generates the shortest, most eco-nomic organic synthesis routes for a giventarget compound. Based on Hendrickson'shalf-reaction theory, it does not require areaction database.

Several other approaches for automateddesign of synthetic pathways are discussed inthe literature. Crabtree and El-Halwagi(195) develop the concept of environmen-tally acceptable reactions in which an opti-mization is done considering reactants andbyproducts in an economic model towardthe production of a certain product. Anastas(2) defines computer-assisted organic syn-thesis and describes software developed toidentify alternative and potentially morebenign reaction pathways for the synthesisof commercial chemicals. Optimization ofboth solvent design and reaction path designwithin the context of their previouslydefined methodology for environmentalimpact minimization is addressed byStefanis et al. (196).

Modi et al. (197) have developed asoftware system, SMART (Solvent Measure-ment, Assessment and Revamping Tool)that allows assessment of solvents used forbatch processing based on both empiricaldata and property estimation methods.This system includes a new conjugation-based method for the estimation of reac-tion rates in solution, which is based onthe concept that the absolute reaction ratecoefficient can be obtained from a functiondependent on the change in molecular

charge distribution between reactants andactivated complex (198).

ConclusionsSolvent replacement technology is a diversefield that affects many industries. It is afield driven by regulations implemented toprotect our environment and health ratherthan for purely economic or scientific rea-sons. However, these regulations oftentranslate to economic incentives and havegiven rise to many exciting and innovativetechnologies that otherwise might neverhave been developed.

In the cleaning and coatings industries,heavy government regulation has promptedthe development of greener products,although the selection process for thesenew commercial products seems to be oneof trial and error until a cost-effective solu-tion is found. For synthetic applications,regulations are not as stringent, although itis recognized that significant processingadvantages may be gained by using alterna-tive solvents for existing processes or bydeveloping new chemical routes to desiredproducts that can exploit more benignsolvent systems. Rational design and imple-mentation of these solvents can lead tosignificant decreases in the environmentalburden associated with solvent lossesthrough vapor emissions and aqueousdischarge streams and in energy usagethrough the simplification of process flow-sheets. Water-based systems are gainingattention, particularly in separations opera-tions where in some instances aqueous sur-factant and polymer solutions showconsiderable promise in emulating conven-tional organic solvents. These technologies,although many still in their infancy, seempromising as greener alternatives in theirniche applications.

Finally, it is clear that many experimentalefforts do not take advantage of the wealthof available computer databases and simu-lation techniques that may aid in selectingan appropriate replacement with minimaltesting. The problem of finding suitablesolvent substitutions has led to the develop-ment of several computer programs anddatabases to assist in the process. Of thesecomputer-assisted techniques, several pro-grams are publicly available, and for others,the algorithms have been described. The lit-erature contains several examples of howthese tools have been used to aid researchersin the selection of solvent alternatives for anumber of applications. Specific tools havebeen developed to assist in the moleculardesign of solvent replacement molecules, to

predict physical properties from molecularstructure, to predict activities such as toxic-ity and carcinogenicity, and to assist in thedesign of alternative synthetic pathways.

Appendix: List of SolventSubstitution Resources onthe World Wide WebEnviro$en$ehttp.//es.epa.govSponsor: U.S. Environmental ProtectionAgency, Department of Defense StrategicEnvironmental Research and DevelopmentProgram (DoD SERDP), Arlington,Virginia.

Enviro$en$e attempts to provide a singlerepository for pollution prevention, compli-ance assurance, and enforcement infor-mation databases. Included are pollutionprevention case studies, technologies, pointsof contact, environmental statutes, executiveorders, regulations, and compliance andenforcement policies and guidelines. A majorcomponent of Enviro$en$e is the databaseumbrella architecture for solvent alternatives.Enviro$en$e information may be used toimplement pollution prevention and solventsubstitution programs, ensure compliancewith environmental laws and regulations,solve enforcement cases, and developresearch projects. The search engine is capa-ble of searching multiple web servers andoffers assistance in preparing a search.

The Enviro$en$e project has a numberof links to various solvent substitution datasystems (http://es. epa.gov/ssds/ssds. html),including the Integrated Solvent Substi-tution Data System (ISSDS) (http://es.epa.gov/issds), which facilitates access tosolvent alternative information from multi-ple data systems through a single, easy-to-use command structure, the "SolventAlternatives Guide" (SAGE), the HazardousSolvent Substitution Data System (http.//es.epa.gov/ssds/hssdstel.html, an on-line, com-prehensive system of product information,material safety data sheets, and other relatedinformation on alternatives to hazardoussolvents and related subjects; the JointService Pollution Prevention (P2)Technical Library; the DoD OzoneDepleting Chemical (ODC)/SubstanceInformation Exchange; and the SolventHandbook Database System (SHDS)(http://wastenot. inel.gov/shds), a databaseproviding access to environmental andsafety information on solvents used inmaintenance facilities and paint strippers.SHDS contains empirical data fromlaboratory testing. The Solvents Database


SHERMAN ET AL.

(SOLV-DB) (http://solvdb.ncms.org), willhelp a searcher find a wide variety of data onsolvents quickly and easily. SOLV-DB willassist process engineers to make intelligentchoices about which solvent to use for aparticular application without incuring alegacy of problems. For hands-on users ofsolvents, a better understanding of solventproperties and ofhow to handle the materialwisely can be gained using the SOLV-DB.SOLV-DB will also help erivironmentalengineers delineate their responsibilitiesudder routine conditions and in case of acci-dents. SOLV-DB can help members of thegeneral public locate basic facts aboutmaterials of concern and help them appre-ciate the trade-offs involved in solventselection. The Materials CompatibilityDatabase provides laboratory test data toassist in implementation of ODC-freealternative solvents that are compatiblewith materials used in electronic assemblies.

Solvent Alternatives Guidehttp.//clean. rti.orgSponsor: Research Triangle Institute,Research Triangle Park, North Carolina.

SAGE is a comprehensive guide designedto provide pollution prevention informationon solvent and process alternatives for partscleaning and degreasing. SAGE does notrecommend any ozone-depleting chemicals.It is an interactive computer programdesigned to provide alternatives to solventcleaning after obtaining information fromthe user about current cleaning processes andmaterials. Options are ranked numericallyaccording to their potential for successfullyfulfilling specific cleaning needs. Detaileddescriptions of the cleaning technologiesare provided by SAGE in addition tovendor information.

Coating Alternatives Guidehttp://cage. rti. orgSponsor: Research Triangle Institute,Research Triangle Park, North Carolina.

The Coating Alternatives Guide(CAGE) is a pollution prevention tool forsmall- and medium-size businesses andstate technical assistance program repre-sentatives. CAGE is an expert system andinformation base designed to recommendlow-emitting alternative coating technolo-gies to coatings users. In addition, CAGEprovides summarized information on rec-ommended alternatives. The expert sys-tem asks the user several questions abouttheir current coating process and tries tomatch alternatives that fit the user'soperating conditions.

Joint Service PollutionPrevention TechnicalLibraryhttp.//enviro. nfesc. navy. millp21ibrarySponsor: Naval Facilities EngineeringService Center, Port Hueneme, California.

The Joint Service P2 Technical Librarycomprises three main elements:* The Joint Service P2 Opportunity

Handbook was designed to identifyavailable off-the-shelf pollution preven-tion technologies, management prac-tices, and process changes that willreduce the amount of hazardous wasteand solid waste being generated at jointservice industrial facilities.

* The P2 Equipment Book is valuable foridentifying commercially available P2technologies already being purchased orevaluated by the Navy. The bookincludes equipment summaries con-taining detailed information on equip-ment characteristics, implementationrequirements, benefits, associated costs,and contacts for further assistance.

* Defense Logistics Agency's "Environ-mental Products Catalog" is a user-friendly publication that clearly suggestsalternatives to previously used productsor processes. These alternatives may benonozone depleting, less toxic, or pro-mote recycling and waste minimization.The catalog also has an extensive con-tacts section to help customers requestadditional information.

Pacific Northwest PollutionPrevention Resource Centerhttp:llpprc.pnl.gov/pprcSponsor: Pacific Northwest PollutionPrevention Resource Center, Seattle,Washington

The Pacific Northwest PollutionPrevention Resource Center works to protectpublic health, safety, and the environmentby supporting projects that result in pollu-tion prevention and toxics use eliminationand reduction. The Center sponsors the"Pollution Prevention Technology Reviews"which covers alternative pollution preven-tion technologies that have been proven suc-cessful through actual research anddemonstration projects (http://pprc.pnlgovlpprc/p2tech/p2tech.html). The 1996 series ofreviews focused on cleaning as a part ofmanufacturing. Additional reviews areplanned in the future. The technologyreviews offer links to projects listed in theResearch Projects Database, links to otherrelevant Internet sites, and extensive bibli-ographies. The review series is intended for

manufacturers, researchers, and others inter-ested in the details of new cleaning tech-nologies. These reviews are divided intoseveral sections to make it easier for users tolocate information of interest. Each reviewincludes an overview of the technology andits technical and economic performance,identification of research that has been done,and discussion of gaps in existing research.The topics covered are aqueous cleaning,supercritical carbon dioxide cleaning,"no-clean" technology, cleanliness measure-ment methods, cleaning-related projects inthe Pollution Prevention Research ProjectsDatabase, and other cleaning-relatedInternet sites.

Waste ReductionResource Centerhttp.llwww.p2pays. org/wrrcSponsor: Waste Reduction ResourceCenter, Raleigh, North Carolina.

The Waste Reduction Resource Center(WRRC's) clearinghouse staff providesaccess to and supports the collection ofwaste reduction information. The clearing-house collection contains more than 8000journal articles, case studies, technicalreports, books, and video tapes. You mayread or download the bibliography. Thetopics cover all general industry categories,manufacturing processes, hazardous wastestreams, and water and air discharges.Specific information includes economicaland technical data, process descriptions,waste reduction techniques, and implemen-tation strategies. The collection also con-tains information on municipal recycling,solid waste reduction, environmentalaudits, and perspectives in pollution pre-vention. In addition, the WRRC has list-ings of numerous electronic bulletin boardsproviding information on environmentalissues and technologies. An example is theonline guide Solvents-The Alternativesthat summarizes existing cleaning technolo-gies, equipment, and cleaning procedures.Included are tables representing a cross sec-tion of products available and where addi-tional information can be obtained.

Environmental SoftwareResource Guidehtmp./llwww. envirosw. com/software.htmlSponsor: Environmental SoftwareCooperative, Ventura, California

The "Environmental Software ResourceGuide" is a database application containinginformation on approximately 2200 soft-ware products for the environmental man-agement field and over 600 environmental



software vendors. This resource is currentlybeing used by a wide range of public agen-cies, private companies, and environmentalconsultants around the globe. The databaseis drawn from a variety of sources; productavailability and other information is verifiedannually through direct vendor surveys.

A Brief Survey of PollutionPrevention Softwarehttp.://www.seattle. battelle. org/services/eo%26s/Folder/P2/survey.htmSponsor: Battelle Seattle Research Centers.Report prepared for Idaho NationalEngineering Laboratory, Idaho Falls, Idaho,September 1993.A number of available software packages

are useful for implementing pollution pre-vention in manufacturing processes. Thesepackages apply to different organizationallevels of decision making (policy, manage-ment, or operations) and reflect differentdegrees of pollution prevention orientation.For example, although some packages areexplicitly designed for pollution prevention,others do not explicitly include pollutionprevention components but could still beuseful if applied to pollution prevention.The purpose of the survey is to identify gapsin the available packages that representopportunities for software development andto identify particular software packages thatrepresent opportunities for value-addedextension or enhancement. To this end, thissurvey has located software packages thatrepresent opportunities for development or

that illustrate the current state of the mar-ket. It describes these packages in terms ofthe following two characteristics: theexplicit inclusion of pollution preventionfunctions; and the ability to support struc-tured learning, so users can learn abouttheir production processes and how toincorporate pollution prevention measuresinto those processes.

This survey identified 31 softwarepackages that merited consideration. Ofthese, 20 were identified as having at leastone of the above characteristics. Elevenother packages are also included in thefinal list because they represent potentialopportunities for further developmentefforts or because they are representative ofthe software found.

Clean ProcessAdvisory Systemhttp://cpas. mtu. eduSponsor: This system was codevelopedby the National Center For CleanIndustrial And Treatment Technologies,Houghton, Michigan, the AIChE/Centerfor Waste Reduction Technologies, NewYork, New York and the National Centerfor Manufacturing Sciences Ann Arbor,Michigan.

The Clean Process Advisory System is asystem of software for efficiently deliveringinformation on clean technologies and pol-lution prevention methodologies to theconceptual process and product designeron an as-needed basis. The system is meant

to address the challenge of incorporatingenvironmental considerations into concep-tual process and product design wheremost of the waste can be reduced in acost-effective manner.

Environmental Professional'sHomepagehttp.//www. clay. netSponsor: GZA GeoEnvironmental Tech-nologies, Inc. Newton, Massachusetts.

This site is designed specifically forenvironmental consultants and remedia-tion professionals. It contains links to thefollowing information: federal governmentagencies; state government agencies; federalregulations references; health and safetyissues; professional associations; conferencebulletins, announcements; The EP VirtualDesktop; federal legislation; search engines;and EPA-Environmental ResponseTraining Program training courses.

RiskWorldhttp.//www. riskworld.comSponsor: Tec-Com, Inc., Knoxville,Tennessee.

RiskWorld is an international WorldWide Web publication covering newsand views on risk assessment and riskmanagement. It contains risk-focusednews articles, government reports, paperabstracts, Web-site profiles, and more. Thissite also contains Internet links to sources ofsoftware for risk analysis, toxicology, andsite remediation.

REFERENCES

1. Grayson M, ed. Industrial Solvents. New York:Wiley and Sons,1983.

2. Anastas PT. Benign by design chemistry. In: Benign by Design:Alternative Synthetic Design for Pollution Prevention, ACSSymposium Series 577 (Anastas PT, Farris CA, eds).Washington:American Chemical Society, 1994;1-21.

3. U.S. EPA. Clean Air Act-Code of Federal Regulations, Title40, Part 60. Washington:U.S. Environmental ProtectionAgency, 1990.

4. Breen JJ, Dellarco MJ. Pollution prevention: the new environ-mental ethic. In: Pollution Prevention in Industrial Processes(Breen JJ, Dellarco MJ, eds). Washington:American ChemicalSociety, 1992;2-32.

5. U.S. EPA. EPA Pollution Prevention Directory. Washington:U.S. Environmental Protection Agency, 1990.

6. U.S. EPA. 33/50 Program EPA-741-K-92-001. Washington:U.S. Environmental Protection Agency, 1992.

7. Englehardt JD. Pollution prevention technologies: a review andclassification. J Hazard Mater 35:119-150 (1993).

8. Venkataramani ES, Vaiyda F, Olsen W, Wittmer S. Createdrugs, not waste. CHEMTECH 674-679 (1992).

9. Haggin J. Innovations in catalysis create environmentallyfriendly THF processes. Chem Eng News 73:20-23 (1995).

10. Sheldon RA. Consider the environmental quotient.CHEMTECH 38-47 (1994).

11. Lipton S. Reduce fugitive emissions through improving processequipment. Chem Eng Prog 88:61-67 (1992).

12. Ahmad B. Synthesis of Batch Processes with Integrated SolventRecovery [Ph.D dissertation]. Cambridge, MA:MassachusettsInstitute of Technology, 1997.

13. Dienemann EA, Bacher S. Pollution prevention case studies.In: Environmental Strategies Handbook (Kolluru RV, ed).New York:McGraw Hill, 1994.

14. Manousiouthakis V, Allen D. Process synthesis for waste mini-mization. AICHE Symposium Series 91:72-86 (1995).

15. El-Halwagi MM. Synthesis of reverse-osmosis networks forwaste reduction. AICHEJ 38:1185-1198 (1992).

16. D'Amico E. Alternatives finding way in a stormy market.Chem Week 157:54-55(1995).

17. Miziolek AW, Tsang W, eds. Halon Replacements:Technology and Science. Washington:American ChemicalSociety, 1995.

18. Million JF, Mcllroy K, Zawierucha R. A selection and evalua-tion protocol for alternatives to halogenated hydrocarbon sol-vents for oxygen-cleaning purposes. In: Alternatives toChlorofluorocarbon Fluids in the Cleaning of Oxygen and


SHERMAN ETAL.

Aerospace Systems and Components, Vol 1181 (Bryan CJ,Thompson G, eds). Philadelphia:American Society for Testingand Materials, 1993;141-152.

19. Hairston D. Industrial solvents step up to the mound. ChemEng 102:57-60 (1995).

20. Stone KR Jr, Springer J Jr. Review of solvent cleaning in aero-space operations and pollution prevention alternatives. EnvironProg 14:261-265 (1995).

21. Basu RS, Zyhowski GJ. Environmentally safer hydro-chlorofluorocarbon solvents as CFC alternatives for cleaning.Proc Inst Environ Sci 37:247-251 (1991).

22. Koelsch JR. Breathe easy. Manuf Eng 111:49-54 (1993).23. Bonner JK. New solvent alternatives to CFC cleaning. Int

Society for the Advancement of Material and ProcessEngineering Electron Conf 3:797-803 (1989).

24. Hey D. Cleaning chemicals for electronics. Alternatives toozone-depleting solvents. Spec Chem 10:449-450 (1990).

25. Manzer LE. Chemistry and catalysis. In: Designing SaferChemicals: Green Chemistry for Pollution Prevention, Vol 640(DeVito SC, Garrett RL, eds). Washington:AmericanChemical Society, 1996;144-154.

26. Anderson SO. 1994 Report of the Solvents Coatings andAdhesives Technical Options Committee for the 1195Assessment of the UNEP Montreal Protocol on Substances thatDeplete the Ozone Layer. Nairobi:United Nations EnvironmentProgram Solvents, Coatings, and Adhesives Technical OptionsCommittee, 1995.

27. Kanegsberg B. Precision cleaning without ozone-depletingchemicals. Chem Ind (London) 20:787-791 (1996).

28. Higgins T, Thorn J. Solvents: know your options. Chem Eng101:92-100 (1994).

29. Rupp VL, Hickman JC. Replacing 1,1,1-trichloroethane withother chlorinated solvents. Plat Surf Finish 82:34-38 (1995).

30. Reynolds JM. Cost effective replacements for chlorinated sol-vents and glycol ethers. Spray Technol Market 1:32-36 (1991).

31. Lea C. Solvent alternatives for the 1990's. Electron CommunEngJ 3:53-62 (1991).

32. Hairston DH. Degreasers: lift up and split out. Chem Eng103:69-72 (1996).

33. McGill KM. Pollution prevention in army maintenance. IntSAMPE Symp 39:692-702 (1994).

34. Oxsol 100. Dallas:Oxychem, 1992.35. Marino FA. A New process alternative for replacing ozone-

depleting solvent cleaners. Plat Surf Finish 80:41-45 (1993).36. Wolf K. The truths and myths about water-based cleaning: a

systems approach to choosing the best alternatives. Pollut PrevRev 4:141-153 (1994).

37. Brown LM, Springer J, Bower M. Chemical substitution for1,1,1-trichloroethane and methanol in industrial cleaning oper-ation. J Hazard Mater 29:179-188 (1992).

38. Kennedy ML. Getting to the bottom line: how TCA shows thereal cost of solvent substitution. Pollut Prev Rev 4:155-164(1994).

39. Goeders DC, Bridge DW, Boyaner MR. Investigation of thecleaning effectiveness of the alternative solvents and solventcleaning. Int SAMPE Symp 39:1156-1170 (1994).

40. Copeland AE. Biodegradable solvent substitution. In: SolventSubstitution, Annual International Workshop. 4-7 December1990, Phoenix, Arizona. Washington:Department of Energy,1990;1 15-117.

41. Snyder JT. Aqueous degreasing: a viable alternative to vapordegreasing. In: Solvent Substitution, Annual InternationalWorkshop. 4-7 December 1990, Phoenix, Arizona.Washington:Department of Energy, 1990; 177-179.

42. Thompson LM, Sinamdle RF, Richards HL. Chlorinated sol-vent substitution program at the Oak Ridge Y-12 plant. In:Solvent Substitution, Annual International Workshop 4-7December 1990, Phoenix, Arizona. Washington:Departmentof Energy, 1990;135-142.

43. Karrs S, McMonagle M. An examination of the payback for anaqueous cleaner recovery unit. Plat Surf Finish 80:45-50(1993).

44. Hayes M. Semi-aqueous cleaning: an alternative to halogenatedsolvents. Proc Electron Compon Technol Conf 40:247-252(1990).

45. Quitmeyer J. Aqueous cleaners challenge chlorinated solvents.Pollut Eng 23:88-92 (1991).

46. Quitmeyer J. The evolution of aqueous cleaner technology.Met Finish 93:34-49 (1995).

47. Nicholls LC. Creating a better environment. Finishing14:51-52 (1990).

48. Lowell CR, Sterritt JR. Improving aqueous cleaning power.Surf Mount Technol 4:26-28 (1990).

49. Salerno RF. High pressure supercritical carbon dioxide efficiencyin removing hydrocarbon machine coolants from metal couponsand component parts. In: Solvent Substitution, AnnuualInternational Workshop. 4-7 December 1990, Phoenix,Arizona. Washington:Department of Energy, 1990;79-86.

50. Weber DC. Precision surface cleaning with supercritical carbondioxide. Met Finish 93:22-23 (1995).

51. McGovern WE, Moses JM, Weber DC. The use of supercriti-cal carbon dioxide as an alternative for chlorofluorocarbon(CFC) solvents in precision parts cleaning applications.Proceedings Air Pollution Control Association Annual Meeting11:94-RP137.03 (1994).

52. Supercritical fluids for cleaning metal parts. Hazard WasteConsult 13:1-25 (1995).

53. Hjeresen D, Silva L, Spall D, Stephenson R. National Programfor Supercritical Fluids Cleaning. Int SAMPE Symp Exhibit39:1109-1115 (1994).

54. Mchardy J, Stanford TB, Benjamin LR, Whiting TE, Chao SC.Progress in supercritical CO2 cleaning. SAMPE J 29:20-27(1993).

55. Gallagher PM, Krukonis VJ. Precision parts cleaning withsupercritical carbon dioxide. In: Solvent Substitution, AnnualInternational Workshop. 4-7 December 1990, Phoenix,Arizona. Washington:Department of Energy, 1990;70.

56. Purtell R, Rothman L, Eldridge B, Chess C. Precision partscleaning using supercritical fluids. J Vac Sci Technol11:1696-1701 (1993).

57. Prototype CO2 dry-cleaning process replaces toxic solvent.Environ Sci Technol 29:497A(1995).

58. Iliff RJ, Mitchell JD, Carty DT, Latham JR, Kong SB.Liquid/Supercritical Carbon Dioxide/Dry Cleaning System.Oakland, CA:The Clorox Company, 1995.

59. Lu Y, Aoyagi Y. Laser-induced dry cleaning in air: a new sur-face cleaning technology in lieu of CFC solvents. Jpn J ApplPhys 33:L430-L433 (1994).

60. Sapre A. Electronic assembly solvent substitutes. In: SolventSubstitution, Annual International Workshop. 4-7 December1990, Phoenix, AZ. Washington:Department of Energy1990;131.

61. Oil and Colour Chemists' Association, Australia. SurfaceCoatings: Paints and Application, Vol 2. New York:Chapmanand Hall, 1984.

62. Morgan RE. Put the lid on VOC emissions from maintenancecoatings. Chem Eng Prog 92:54-59 (1996).

63. Burgess WA. Recognition of Health Hazards in Industry: AReview of Materials and Processes, Vol 538. New York:JohnWiley and Sons, 1995.

64. Holmberg K. High Solids Alkyd Resins. New York:MarcelDekker, 1987.

65. Elvers B, Hawkins S, Schuly G, eds. Ulmann's Encyclopedia ofIndustrial Chemistry. New York:VCH Publishers, 1985.

66. Bittner A, Epple U. Aqueous and high solids two-pack industrialfinishes complying Wit the regulations governing the emissionof volatile organic compounds. SurfCoat Int 4:177-183 (1996).

67. Sullivan CJ. High solids performance polyesters with MPD:performance bydesign. Am Paint Coat J H79:80-89 (1994).

68. Thames SF, Panjnani KG. Organosilanes in low volatileorganic component coatings. Prog Org Coat 26:63-71 (1995).

69. Johnson TL. Ultra-low viscosity oxazolidine and aldimaine-based reactive diluents for high-solids polyurethane coatings. JCoat Technol 67:41-47 (1995).

268 Environmental Health Perspectives * Vol 106, Supplement 1 * February 1998


70. Robinson GN, Johnson TL, Hoffman MD. High performancepolyurethane coating systems utilizing oxazolidine-based reac-tive diluents. J Coat Technol 66:69-74 (1994).

71. Adams RC. Use of isophthalic resins in high solids coatings.Polym Paint Colour J 186:17-20 (1996).

72. Rupa Vani JN, Lakeshmi VV, Sitaraman BS, Krishnamurti N.Synthesis of allyl phenyl acrylates and their evaluation as reac-tive diluents in UV-curable coatings. Prog Org Coat21:339-352 (1993).

73. Kuo C, Zhao C, Nirali L, Sirlikov S. Low VOC alkyd coatingsusing (meth)acrylate reactive diluents. Am Paint Coat J79:41-51 (1994).

74. Hoffman. A reactive diluent for flexible, high solids poly-urethane coatings. Am Paint Coat J 80:46-51 (1995).

75. Dirlikov S, Islam MS, Frischinger I, Lepkowski T, Murturi P.Increasing high-solids with a weed. Ind Finish 68:17-20(1992).

76. Banov A. Answers to VOC, HAP headaches: a linseed oil-basedreactive diluent, solvent reformulation options. Am Paint CoatJ 79:45-46 (1994).

77. Finzel W. Volatile methyl siloxanes as exempt solvents in pro-tective coatings. J Coat Technol 68:69-72 (1996).

78. Kamath VR, Sargent JDJ. Production of high solids acryliccoating resins with t-amyl peroxides: a new way to meet VOCrequirements. Chem Eng World 31:57-62 (1996).

79. Nakano S, Morimoto T. High-solids coatings using benzy-lanilinium sulfonates-II, a, a-dimethlbenzylpyridiniump-toluenesulfonate, an effective blocked sulfonic acid. J CoatTechnol 68:83-90 (1996).

80. Gould ML, Dettloff ML, Whiteside RC Jr. Linear pendantanhydrides: novel building blocks for high solids, high perfor-mance coatings. Prog Org Coat 29:117-126 (1996).

81. Wicks DA, Yeske PE. Imine-isocyanate chemistry: new tech-nology for environmentally friendly, high solids coatings. In:Developing Safer Chemicals: Green Chemistry for PollutionPrevention, Vol 640 (Devito SC, Garrett RL, eds).Washington:American Chemical Society, 1996.

82. Bieleman JH. New additives improve performance of water-borne paints. Am Paint Coat J 80:30-34 (1996).

83. Karsa DR, Davies WD, eds. Waterborne Coatings andAdditives. Cambridge:The Royal Society of Chemistry, 1995.

84. Provder T, Winnik MA, Urban MW, eds. Film Formation inWaterborne Coatings. Washington:American ChemicalSociety, 1996.

85. Padget JC. Polymers for water-based coatings: a systematicoverview. J Coat Technol 66:89-105 (1994).

86. Water-reducible resins. In: Surface Coatings: Raw Materialsand Their Usage, Vol 1. New York:Chapman and Hall,1993;263-292.

87. Mirgel V. New resin systems for high performance waterbornecoatings. Prog Org Coat 22:273-277 (1993).

88. Hergernrother R, Ruttmann G. Polyurethane coatings meetVOC challenge. J Prot Coat Linings 7:40-46 (1990).

89. Brown W. Aromatic polycarbodiimides: a new class of crosslink-ers for water-borne coatings. Surf Coat Int 78:238-242 (1995).

90. Eslinger DR. Aliphatic epoxy emulsion crosslinker for water-borne coatings. J Coat Technol 67:45-50 (1995).

91. Poggio T, Lenti D, Masini L. Water-borne fluoroelastomericcoatings with high barrier properties. J Am Oil Colour ChemAssoc 78:289-293 (1995).

92. Neimann J. Waterborne coatings for the automotive industry.Prog Org Coat 21:189-203 (1992).

93. Blank WJ. Novel polyurethane polyols for waterborne and highsolids coatings. Prog Org Coat 20:235-259 (1992).

94. Clancy S. The paint revolution. Transp Eng 10:13-19 (1994).95. Water-borne coating improves air quality. Prod Finish

60:59-61 (1996).96. Cornwell DW. Developments on water-based and low VOC

coatings for the protection of structural steel. Surf Coat Int77:455-459 (1994).

97. Kobayashi T. Pigment dispersion in water-reducible paints.Prog Org Coat 28:79-87 (1996).

98. Klein RJ. Formulating low odor, low VOC interior paints.Mod Paint Coat 83:37-39 (1993).

99. Donohue MD, Geiger JL, Kaimos AA, Nielsen KA. Reductionof volatile organic compound emissions during spray painting.In: Green Chemistry: Designing Chemistry for theEnvironment, Vol 626 (Anastas PT, Williamson TC, eds).Washington:American Chemical Society, 1996;1 52-167.

100. White TF. An economic solution to meeting VOC regulations.Met Finish 89:55-58 (1991).

101. Nielsen KA, Glancy CW. Precursor Coating CompositionSuitable for Spraying with Supercritical Fluids as Diluents.Danbury, CT:Union Carbide Chemicals and Plastics TechnologyCorporation, 1996.

102. Lee C, Hoy KL, Donohue MD. Supercritical Fluids asDiluents in Liquid Spray Application of Coatings. Danbury,CT:Union Carbide Chemicals and Plastics Company, 1990.

103. Marrion AR, ed. The Chemistry and Physics of Coatings.Cambridge:The Royal Society of Chemistry, 1994.

104. McGinniss VD. Advances in environmental benign coatingsand adhesives. Prog Org Coat 27:153-161 (1996).

105. Jones FH. Toward solventless liquid coatings. J Coat Technol68:25-36 (1996).

106. Caddick S. Microwave-assisted organic reactions. Tetrahedron51:10403-10432 (1995).

107. Budavari S, O'Neil M, Smith A, Heckelman PE, eds. TheMerck Index. Rahway:Merck and Co., 1989.

108. Femec DA, Mccaffrey RR. Solvent replacement in the synthesisof persubstituted phosphonitrilic hydroquinone prepolymermaterials. J Appl Polym Sci 52:501-505 (1994).

109. Galvez N, Moreno-Manas M, Sebastian RM, Vallribera A.Dimethoxyethane as an alternative solvent for Schmidt reac-tions. Preparation of homochiral N-(5-Oxazolyl)oxazoli-donones from N-acetoacetyl derivatives of oxazolidinones.Tetradhedron 52:1609-1616 (1996).

110. Ogawa A, Curran DP. Benzotrifluoride: a useful alternative sol-vent for organic reactions currently conducted indichloromethane and related solvents. J Org Chem62:450-451 (1997).

.111. Molnar LK. Polymer Based Solvents for Minimizing PollutionDuring the Synthesis of Fine Chemicals [PhD. dissertation].Cambridge, MA:Massachusetts Institute of Technology 1996.Also summarized in: Molnar LK, Buchwald SL, Hatton TA.Polymer based replacement solvents forminimizing pollutionduring the synthesis of fine chemicals. Polym Mater Sci Eng75:113-114 (1996).

112. Seddon KR. Room-temperature ionic liquids: neoteric solventsfor clean catalysis. Kinet Catal 37:693 (1996).

113. Seddon KR. Ionic liquids for clean technology. J ChemTechnol Biotechnol 68:351-356 (1997).

114. Goldberg Y. Phase Transfer Catalysis: Selected Problems andApplications. Yverdon, Switzerland:Gordon and BreachScience Publishers, 1989.

115. Dehmlow EV, Dehmlow SS. Phase Transfer Catalysis.Weinheim:VCH, 1993.

116. Starks CM, Liota CL, Halpern M. Phase-Transfer Catalysis:Fundamentals, Applications, and Industrial Perspectives. NewYork:Chapman and Hall, 1994.

117. O'Donnell MJ. Asymmetric phase transfer reactions. In:Catalytic Asymmetric Synt esis (Ojima I, ed). NewYork:VCH, 1993;389-412.

118. Dartt CB, Davis ME. Catalysis for environmentally benignprocessing. Ind Eng Chem Res 33:2887-2899 (1994).

119. Lim PK, Zhong Y. Chemically benign synthesis at organic-water interface. In: Green Chemistry: Designing Chemistry forthe Environment (Anastas PT, Williamson TC, eds).Washington:American Chemical Society, 1996;168-177.

120. Papadogianakis G, Sheldon RA. Catalytic conversions in water:environmentally attractive processes employing water solubletransition metal complexes. N J Chem 20:175-185 (1996).

121. Fendler JH, Fendler EJ. Catalysis in Micellar andMacromolecular Systems. New York:Academic Press, 1975.

122. Bunton CA. Kinetics and catalysis. In: Microheterogeneous


SHERMAN ETAL.

Systems, Vol 38 (Gratzel M, Kalyanasundaram K, eds). NewYork:Marcel Dekker, 1991;13-28.

123. Monflier E, Bourdauducq P, Couturier JL, Kervennal J, SuisseI, Mortreux A. Solvent-free telomeriztion of butadiene withwater into octadienols in the presence of nonionic surfactant:efficient micellar catalysis. Catal Lett 34:201-212 (1995).

124. Rathman JF, Siswanto C, Battal T. Alkylation of phenol andanilin in aqueous surfactant solutions by micellar phase-transfercatalysis. Abstr Amer Chem Soc 211: 120-COLL (1996).

125. Kust PR, Rathman JF. Synthesis of surfactants by micellarautocatalysis: N,N-dimethyldodecylamine N-oxide. Langmuir11:3Q07-3012 (1995).

126. Li CJ. Aqueous Barbier-Grignard type reaction: scope, mecha-nism, and synthetic applications. Tetrahedron 52:5643-5668

. (1996).127. Shu HY, Perlmutter HD, Shaw H. Application of a droplet

column type two-phase reactor for the epoxidation ofcyclooctene in water as an alternative solvent. Ind Eng ChemRes 34:3761-3765 (1995).

128. Shaw H, Perlmutter HD, Chen G, Arco SD, Quibuyen TO.Free-radical bromination of selected organic compounds inwater. J Org Chem 62:236-237 (1997).

129. Tester JW, Holgate HR, Armellini FJ, Webley PA, Killilea WR,Hong GT, Barner HE. Supercritical water oxidation technol-ogy. In: ACS Symposium Series, Vol 518. Washington:American Chemical Society, 1993;35-75.

130. Savage PE, Gopalan S, Mizan TI, Martino CJ. Reactions atsupercritical conditions: applications and fundamentals.AICHEJ 41:1723-1778 (1995).

131. Aki SNVK, Ding ZY, Abraham MA. Catalytic supercriticalwater oxidation: stability of Cr203 catalyst. AICHE J42:1995-2004 (1996).

132. Clercq ML. Ceramic reactor for use with corrosive supercriticalfluids. AICHE J 42:1798-1799 (1996).

133. Black H. Supercritical carbon dioxide: the "greener" solvent.Environ Sci Technol 30:124A-128A (1996).

134. Eckert CA, Knutson BL, Debenedetti PG. Supercritical fluidsas solvents for chemical and materials processing. Nature383:313-318 (1996).

135. Romack TJ, Maury EE, Desimone JM. Precipitation polymer-ization of acrylic-acid in supercritical carbon-dioxide.Macromolecules 28:912-915 (1995).

136. Kapellen KK, Mistele CD, Desimone JM. Synthesis ofpoly(2,6-dimethylphenylene oxide) in carbon-dioxide.Macromolecules 29:495-496 (1996).

137. Romack TJ, Kipp BE, Desimone JM. Polymerization of tetra-fluoroethylene in a hybrid carbon dioxide aqueous-medium.Macromolecules 28:8432-8434 (1995).

138. Clark MR, Desimone JM. Cationic polymerization of vinyland cyclic ethers in supercritical and liquid carbon-dioxide.Macromolecules 28:3002-3004 (1995).

139. Canelas DA, Betts DE, DeSimone JM. Dispersion polymer-ization of styrene in supercritical carbon-dioxide-importanceof effective surfactants. Macromolecules 29:2818-2821(1996).

140. Mcclain JB, Betts DE, Canelas DA, Samulski ET, DesimoneJM, Londono JD, Cochran HD, Wignall GD, ChilluramartinoD, Triolo R. Design of nonionic surfactants for supercriticalcarbon-dioxide. Science 274:2049-2052 (1996).

141. Xiao JL, Nefkens SCA, Jessop PG, Ikariya T, Noyori R.Asymmetric hydrogenation of ox,p-unsaturated carboxylic-acidsin supercritical carbon-dioxide. Tetrahedron Lett37:2813-2816 (1996).

142. Jessop PG, Hsiao Y, Ikariya T, Noyori R. Homogeneous catal-ysis in supercritical fluids: hydrogenation of supercritical car-bon-dioxide to formic acid, alkyl formates, and formamides. JAm Chem Soc 118:344-355 (1996).

143. Burk MJ, Feng SG, Gross MF, Tumas W. Asymmetric cat-alytic-hydrogenation reactions in supercritical carbon-dioxide. JAm Chem Soc 117:8277-8278 (1995).

144. Molero Gomez A, Pereyra Lopez E, Martinez de la Ossa E.Recovery of grape seed oil by liquid supercritical carbon

dioxide extraction: a comparison with convention solventextraction. Chem Eng J 61:227-231 (1996).

145. Krukonis V, Brunner G, Perrut M. Industrial operations withsupercritical fluids: current processes and perspectives on thefuture. In: 3rd International Symposium of SupercriticalFluids, 17-19 October 1994, Strasbourg, France. Vandoeuvre-les-Nancy (Meurthe-et-Moselle): INPL, 1994.

146. Dolezal IS, Segebarth KP, Zennegg M, Wunderli S.Comparison between supercritical fluid extraction (SFE)using carbon dioxide/acetone and conventional Soxhletextraction with toluene for the subsequent determination ofPCDD/PCDF in a single electrofilter ash sample. Chemosphere31:4013-4024 (1995).

147. Clement RE, Koester CJ, Eiceman GA. Environmental analy-sis. Anal Chem 65:85R-1 16R (1993).

148. Alzaga R, Bayona JM, Barcelo D. Use of supercritical fluidextraction for pirimicarb determination in soil. J Agric FoodChem 43:398-399 (1995).

149. Reighard TS, Olesik SV. Comparison of the extraction of phe-nolic and nitroaromatic pollutants using supercritical andenhanced-fluidity liquid methanol-CO2 mixtures. JChromatogr A 737:233-242 (1996).

150. Roth M. Thermodynamic prospects of alternative refrigerantsas solvents for supercritical fluid extraction. Anal Chem68:4474-4480 (1996).

151. Christian SD, Scamehorn JF. Use of micellar-enhanced ultrafil-tration to remove dissolved organics from aqueous streams. In:Surfactant-based Separation Processes, Vol 33 (Scamehorn JF,Jeffrey HH, eds). New York:Marcel Dekker, 1989;3-28.

152. Hurter PN, Hatton TA. Solubilization and extraction of poly-cyclic aromatic hydrocarbons in polyethylene oxide-polypropy-lene oxide block copolymer micelles. Langmuir 8:1291-1299(1992).

153. Nagarajan R, Barry M, Ruckenstein E. Unusual selectivity insolubilization by block copolymer micelles. Langmuir2:210-215 (1986).

154. Hurter PN, Anger LA, Vojvodich LJ, Keuey CA, Cohen RE,Hatton TA. Amphiphilic polymer solutions as novel extractantsfor environmental applications. In: Solvent Extraction in theProcess Industries-Proceedings of International SolventExtraction Conference '93, Vol 3 (Logsdail DH, Slater MJ,eds). London:Elsevier, 1993; 1663-1670.

155. Lebens PJM, Keurentjes JTF. Temperature-induced solubiliza-tion of hydrocarbons in aqueous block copolymer cosolution.Ind Chem Res 35:3415-3421 (1996).

156. Walter H, Brooks DE, Fisher D. Partitioning in Aqueous Two-Phase Systems. Theory, Methods, Uses and Applications toBiotechnology. Orlando, FL:Academic Press, 1985.

157. Rogers RD, Zhang J. New technologies for metal ion separa-tions: polyethylene glycol based-aqueous biphasic systems andaqueous biphasic extraction chromatography. In: Ion Exchangeand Solvent Extraction, Vol 13 (Marcus Y, Marinsky JA, eds).New York:Marcel Dekker, 1997.

158. Rogers RD, Bond AH, Bauer CB, Griffin ST, Zhang J.Polyethylene glycol-based aqueous biphasic systems for extrac-tion and recovery of dyes and metal/dye complexes. In: ValueAdding through Solvent Extraction-Proceedings of theInternational Solvent Extraction Conference '96, Vol 2(Shallcross DC, Paiman R, Pavcic LM, eds). Victoria,Australia:The University of Melbourne, 1996;1537-1 542.

159. Kaminski M, Landsberger S, Nunez L, G.F. Vandegrift.Sorption capacity of ferromagnetic microparticles coates withCMPO. Sep Sci Technol 32:115-126 (1997).

160. Nunez L, Buchholz BA, Kminski M, Aase SB, Brown NR,Vandegrift GF. Actinide separation of high-level waste usingsolvent extractants on magnetic microparticles. Sep Sci Technol31:1393-1407 (1996).

161. Joback KG. Solvent substitution for pollution prevention. In:Pollution Prevention via Process and Product Modifications,Vol 90 (El-Hawagi MM, Petrides DP, eds). NewYork:American Institute of Chemical Engineers, 1994;98-104.

162. Fredenslund A, Jones RL, Prausnitz JM. Group contribution

270 Environmental Health Perspectives * Vol 06, Supplement 1 * February 1998


estimation of activity coefficients in nonideal liquid mixtures.AICHE J 21:1086-1099 (1975).

163. Gani R, Brignole EA. Molecular design of solvents for liquidextraction based on UNIFAC. Fluid Phase Equilib 13:331-340(1983).

164. Brignole EA, Bottini S, Gani R. A strategy for the design andselection of solvents for separation processes. Fluid PhaseEquilib 29:125-139 (1986).

165. Gani R, Nielsen B, Fredenslund A. A group contributionapproach to computer-aided molecular design. AICHE J 37(1991).

166. Gani R, Fredenslund A. Computer-aided molecular and mix-ture design with specified property constraints. Fluid PhaseEqulib 82:39-46 (1993).

167. Naser SF, Founier RL. A system for the design of an optimumliquid-liquid extractant molecule. Comput Chem Eng15:397-414 (1991).

168. Macchietto S, Odele 0, Omatsone 0. Design of optimal sol-vents for liquid-liquid extraction and gas absorption processes.Trans I Chem E 68:429-433 (1990).

169. Odele 0, Macchietto S. Computer-aided design: a novelmethod for optimal solvent setection. Fluid Phase Equilib82:47-54 (1993).

170. Pretel EJ, Lopez PA, Bottini SB, Brignole EA. Computer-aidedmolecular design of solvents for separation processes. AICHE J40:1349-1360 (1994).

171. Klein JA, Wu DT, Gani R. Computer-aided mixture designwith specified property constraints. Comput Chem Eng16:s229-s236 (1992).

172. Duvedi AP, Achenie LEK. Designing environmentally saferefrigerants using mathematical programming. Chem Eng Sci51:3727-3739 (1996).

173. Venkatasubramanian V, Chan K, Caruthers JM. Evolutionarydesign of molecules with desired properties using the geneticalgorithm. J Chem InfComput Sci 35:188-195 (1995).

174. Meniai AH, Newsham DMT. A computer-aided moleculardesign of solvents for liquid-liquid extraction. Trans I ChemE74:695-702( 1996).

175. Meniai AH, Newsham DMT. The selection of solvents forliquid-liquid extraction. Trans I ChemE 74:78-87 (1996).

176. Rouvray DH. Predicting chemistry from topology. Sci Am255:40-47 (1986).

177. Ivanciuc 0. CODESSA version 2.13 for Windows. J Chem InfComput Sci 37:405-406 (1997).

178. Yalkowsky SH, Banerjee S. Aqueous Solubility. Methods ofEstimation for Organic Compounds. New York:MarcelDekker, 1992.

179. Kan AT, Tomson MB. UNIFAC prediction of aqueous andnonaqueous solubilities of chemicals with environmental inter-est. Environ Sci Technol 30:1369-1376( 1996).

180. Kier LB, Hall LH. Molecular Connectivity in Chemistry andDrug Research. New York:Academic Press, 1976.

181. Kier LB, Hall LH. Molecular Connectivity in Structure-Activity Analysis. New York:Wiley, 1986.

182. Katritzky AR, Lobanov VS, Karelson M. QSPR: the correlationand quantitative prediction of chemical and physical propertiesfrom structure. Chem Soc Rev 24:279-287 (1995).

183. Nirmalakhandan NN, Speece RE. Prediction of aqueous solu-bility of organic chemicals based on molecular structure.Environ Sci Technol 22:328-338 (1988).

184. Bodor N, Huang MJ. A new method for the estimation of theaqueous solubility of organic compounds. J Pharm Sci81:954-960 (1992).

185. Nelson TM, Jurs PC. Prediction of aqueous solubility of organiccompounds. J Chem InfComput Sci 34:601-609 (1994).

186. Sutter JM, Jurs PC. Prediction of aqueous solubility for adiverse set of heteroatom-containing organic compounds usinga quantitative structure-property relationship. J Chem InfComput Sci 36:100-107 (1996).

187. Carlson EC. Don't gamble with physical properties for simula-tions. Chem Eng Prog 92:35-46 (1996).

188. DeVito SC. General principles for the design of safer chemi-cals: toxicological considerations for chemists. In: DesigningSafer Chemicals: Green Chemistry for Pollution Prevention,Vol 640 (DeVito SC, Garrett RL, eds). Washington:AmericanChemical Society, 1996; 1 6-59.

189. Lai DY, Woo Y, Argus MF, Arcos JC. Cancer risk reductionthrough mechanism based molecular design of chemicals. In:Designing Safer Chemicals: Green Chemistry for PollutionPrevention, Vol 640 (DeVito SC, Garrett RL, eds).Washington:American Chemical Society, 1996;62-73.

190. Milne GWA, Wang S, Fung V. Use of computers in toxicologyand chemical design. In: Designing Safer Chemicals: GreenChemistry for Pollution Prevention, Vol 640 (DeVito SC,Garrett RL, eds). Washington:American Chemical Society,1996;138-155.

191. Sanderson DM, Earnshaw CG. Computer prediction of possi-ble toxic reaction from chemical structure: the DEREK system.Hum Exp Toxicol 10:261-273 (1991).

192. Ridings JE, Barratt MD, Cary R, Earnshaw CG, EggingtonCE, Ellis MK, Judson PN, Langowski JJ, Marchant CA, PayneMP, Watson WP, Yih TD. Computer prediction of possibletoxic action from chemical structure: an update on the DEREKsystem. Toxicology 106:267-279 (1996).

193. Bristol DW, Wachsman JT, Greenwell A. The NIEHSPredictive-Toxicology Evaluation Project. Environ HealthPerspect 104(Suppl 5):1001-1010 (1996).

194. Reichardt C. Solvents and Solvent Effects in OrganicChemistry. New York:VCH, 1990.

195. Crabtree EW, El-Halwagi MM. Synthesis of environmentallyacceptable reactions. In: Pollution Prevention via Process andProduct Modifications, Vol 90 (El-Hawagi MM, Petrides DP,eds). New York:American Institute of Chemical Engineers,1994;1 17-127.

196. Stefanis SK, Buxton A, Livingston AG, Pistikopoulos EN. Amethodology for environmental impact minimization: solventdesign and reaction path issues. Comput Chem Eng20:S1419-S1424 (1996).

197. Modi A, Aumond JP, Mavrovouniotis M, Stephanopoulos G.Rapid plant wide screening of solvents for batch processes.Computers Chem Eng 20(Suppl):S375-S380 (1996).

198. Aumond JP. Personal communication.199. Varerkar MP. Formulating high solids coatings: the solution to

the VOC problem. Paint India 45:19-30 (1996).200. Gendron GR. Information exchange: techniques and their

effects on pollution prevention innovation in the United StatesAir Force [Master's thesis]. Fort Collins CO:NationalTechnology University, 1994.

201. Kirschner EM. Environment, health concerns force shift in useof organic solvents. Chem Eng Prog 72:13-20 (1994).


solvent replacement for green processing

Documents