properties and phase equilibria of fluid mixtures as the basis for developing green chemical...

Fluid Phase Equilibria 302 (2011) 6573

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Fluid Phase Equilibria

journa l homepage: www.e lsev ier .co

Proper esgreen c

Richard La Graduate Sch Univb Department o i 980-c Chinese Acade , Kunm

a r t i c l

Article history:Received 27 MReceived in re26 SeptemberAccepted 26 September 2010Available online 12 October 2010

Keywords:High temperatSupercritical Ionic liquidsDeep eutectic

f uidthis wperat

on real-time images made with diamond anvil cells or visual cells. In the formation of ferrosilite fromquartz (SiO2) and fayalite (Fe2SiO4), the diffusion of SiO2 to the solid fayalite substrate requires less thanseconds to occur in water at high temperatures due to the enhanced solubility of SiO2, which has greattechnological signicance for developing processes for industrially important luminescent materials. It

1. Introdu

Social exproducts wvide us witand methodnew procesples of greefoundationsof safe metatom econolife cycle anneering andeasy to rem

Corresponsity, Aramaki ATel.: +81 22 79

E-mail add

0378-3812/$ doi:10.1016/j.ure wateruids

solvents

is proposed that luminescent materials based on the zinc silicate (Zn2SiO4) family can be made with lowenvironmental burden. The enhanced solubility of natural products in water at high temperatures allowsfor the fractionation of biomass to produce fermentable feedstocks and chemical products as well as forthe efcient separation of natural products. The volumetric properties of n-alkylphenolics with CO2 canallow for efcient separation from their solid matrix due to viscosity reduction and foaming induced bychanges in pressure. The lack of solubility of ionic liquids in supercritical CO2 allows for biphasic sys-tems that can be used to efciently separate phenolic compounds. Equations of state can provide suitablecorrelation. The viscosity reduction provided by solvents such as water, supercritical carbon dioxide, ororganic liquids on ionic liquids allows ionic liquids to be put into a metastable state so that chemicalconversions can occur in ionic liquids below their melting point at room temperature. The physical prop-erties and phase behavior of water and carbon dioxide and mixtures with target compounds are veryimportant for developing new green chemical processes.

2010 Elsevier B.V. All rights reserved.

ction

pectations for chemical processes that manufactureith a minimum of waste and hazardous substances pro-h the opportunity to re-examine the uids, solvents,s being used in industry for the purpose of developingses that are clean, safe, and efcient [1]. The princi-n chemistry [2] and green engineering [3] provide thefor meeting social expectations and embrace the use

hods, nonhazardous chemicals, renewable feedstocks,my, E-factor [4], and concepts that evaluate productd perceived sustainability. The principles of green engi-green chemistry are conveniently summarizedwith anember mnemonic, IMPROVEMENTS PRODUCTIVELY, in

ding author at: Department of Chemical Engineering, Tohoku Univer-za Aoba 6-6-11, Aoba-ku, Sendai 980-8579, Japan.5 5863/5864; fax: +81 22 795 5863/5864.ress: [email protected] (R.L. Smith Jr.).

which the rst Inherently safe and nonhazardous and Minimizematerial diversity are important concepts and provide the basicphilosophy for the solvents and processes discussed in this work[5,6].

Fluids such as air, carbon dioxide, and water can be consideredas some of the most inherently non-hazardous and safe substancesamong those that are used in our daily lives and these will mostlikely be the working uids of choice for the next generation ofgreen products and processes due to their compatibility with theenvironment. The properties of these uids and conditions for theirapplication are very important as illustrated in the next few exam-ples.

In automotive transportation, 30MPa compressed air containedin carbon-ber reinforced tanks has been proposed as the methodof propulsion for automobiles. Although the carbon footprint ofcompressed air vehicles is unfavorable comparedwithbattery elec-tric vehicles, there are clear advantages of compressed air vehiclesin the product life-cycle along with the technological potentialto develop air-engine or pneumatic-combustion hybrid vehicles[7].

see front matter 2010 Elsevier B.V. All rights reserved.uid.2010.09.030ties and phase equilibria of uid mixturhemical processes

. Smith Jr. a,b,, Zhen Fangc

ool of Environmental Studies, Research Center of Supercritical Fluid Technology, Tohokuf Chemical Engineering, Tohoku University, Aramaki Aza Aoba 6-6-11, Aoba-ku, Sendamy of Sciences, Biomass Group, Xishuangbanna Tropical Botanical Garden, 88 Xuefulu

e i n f o

ay 2010vised form2010

a b s t r a c t

The properties and phase equilibria omation and process development. Inseparation characteristics of high temm/locate / f lu id

as the basis for developing

ersity, Aramaki Aza Aoba 6-6-11, Aoba-ku, Sendai 980-8579, Japan8579, Japaning, Yunnan Province 650223, China

mixtures can have great inuence on chemical product for-ork, examples are presented that illustrate the reaction and

urewater, supercritical carbondioxide, and ionic liquids based

66 R.L. Smith Jr., Z. Fang / Fluid Phase Equilibria 302 (2011) 6573

Fig. 1. Carbonheated from awater heater bof the highlysingle-pass sh

In commin a transcrof performaenergy is usand then heexchanger (tled into thand then aCO2. In thewithout phcal) givingoccurring ining usual mtemperaturproperties acoming devuid is highcations in te

In nuclereactor (SCWtype reactolight waterthroughcoohas excellesingle phaseThe very-hifor implemuses helium

chemical water-splitting cycle [11]. Proposals exist for using hightemperature steam hydrolysis with supercritical CO2 cooling and asupercritical CO2 power conversion cycle as a method to simplifythe design and improve its energy efciency. Thus, the properties

r ancho

his wixtu. Theporturocesentcondproc

d tos. Ioned injectit havage o

ter

oper

ingrpert

key py thety, diric pof watein both

In tuidmcessesthe opuous pare prebatchcientlymethoprocesincludThe obics thaadvant

2. Wa

2.1. Pr

Wethe proof thegiven bviscosidielectdioxide as a working uid for producing hot water. Water is beingpproximately 20 C to 90 C: (a) temperature-entropy diagram for aased on using carbon dioxide as the working uid; and (b) schematicnonlinear heat ux along the axial direction for the tube side of aell-and-tube heat exchanger.

ercial hot water systems, carbon dioxide is being useditical cycle to heat water with a very high coefcientnce (COP) as shown conceptually in Fig. 1. Electricaled to compress the CO2 (Fig. 1, ) to around 10MPaat is transferred from the CO2 to the water via a heatFig. 1, ). In the solvent regeneration, CO2 is throt-e two-phase region (Fig. 1, ) to around 2MPa

mbient temperature air is used to vaporize the liquidcycle, heat transfer to the water (Fig. 1, ) occursase change over the critical point of CO2 (transcriti-the device its high practical efciency. The heat uxsuch heat exchanges is highly nonlinear (Fig. 1b) mak-ethods for heat exchanger design based on log meane differences inapplicable. Therefore, accurate physicalnd methods of analysis are imperative for these forth-ices. The cycle shown in Fig. 1 with CO2 as the workingly favorable for simultaneousheating and cooling appli-rms of its total equivalent warming impact [8].ar power applications, the supercritical-water cooledR)was considered as one of the possibleGeneration IV

rs, since they are almost 40%more efcient than presentreactors (44% versus 3335%) and they have a once-lantpathwhichallowsa reduction in size [9]. TheSCWRnt control characteristics since heat is transferred to auid and is being developed in Canada and Russia [10].

gh temperature reactor (VHTR) system chosen by DOEentation of the Next-Generation Nuclear Plant (NGNP)

cooling and produces hydrogen through a thermo-

hydrogen band pressupromote de

For exam20 C and aThe solubilof temperaPotter [13]at constantcan be obse

At a conbility increais increasedincreases toto 0.0081wobserved fothe weakenical region [in water hain materialoperation o

At a consincreasesmple, at 2,0009.07wt% athydrated siin Section 2

2.2. Experim

Batch, seto initially spressures. Fbehavior ofd carbon dioxide will continue to play an important roleosing and implementing the technologies.ork, the properties and phase equilibria of uids and

res are discussed as they relate to developing green pro-solubility of quartz in high temperature water providesnity to develop low-temperature (400600 C) contin-

sses high-volume industrial luminescent materials thatly produced at high temperatures (>1000 C) and underitions. Opportunities also exist for using water to ef-ess biomass. Supercritical water oxidation for use as a

generate energy from biomass is seen as a future greenic liquids, which represent highly versatile solvents arethediscussiondue to their relevance ingreenchemistry.ve of this work is to provide an overview of several top-e been developed and are under development that takef the properties of water and carbon dioxide.

ties and phase equilibria

tner and Franck provide a comprehensive review onies of water including its supercritical state [12]. Someroperties of water include (i) its dissociation equilibriaion product,Kw = aH+aOH, (ii) its transport properties,

ffusivity, heat capacity and thermal conductivity, (iii) itsroperties given by the relative permittivity, and (iv) itsonding network and solution structure. Temperaturere can be used to vary these properties to selectivelysired phenomena for a technological application.ple, the solubility of quartz, SiO2, in neutral water at

tmospheric pressure is approximately 0.0006wt% [13].ity of SiO2 in water can be calculated over a wide rangetures and pressures with the equation of Fournier andas shown in Fig. 2. As the temperature of water is variedpressure, two different trends in the solubility behaviorrved.stant pressure that is lower than 100MPa, the solu-ses and then drastically decreases as the temperature. At a constant pressure of 23MPa, the SiO2 solubilitya value of 0.087wt% at 350 C and drastically decreasest% at 450 C. This retrograde behavior is commonlyr many inorganics in water and can be attributed toing of the hydrogen-bonding network in the supercrit-14]. The retrograde solubility phenomena of inorganicss been shown to have great technological importances formation processes [1518] as well as in practicalf geothermal energy systems [19].tant pressure that is higher than 100MPa, the solubilityonotonically as the temperature is increased. For exam-MPa, the solubility reaches a remarkably high value ofa temperature of 800 C. Dissolution and transport oflicate species can be extremely rapid as demonstrated.3.

ental methods

mi-batch and autoclave reactors are the usual methodtudy many aqueous systems at high temperatures andlow apparatus are used once the reactivities and phasethe compoundsarebetter understood.Our favorite type

R.L. Smith Jr., Z. Fang / Fluid Phase Equilibria 302 (2011) 6573 67

Fig. 2. Solubility of quartz (SiO2) inwater calculated by the relationship given in Ref.[13]. Properties of water used in the calculation were from the IAPWS formulation.

of batch reactor is the diamond anvil cell (DAC) because it allowscomplete visual observation of the entire cell contents and canusedto study a very wide range of temperatures (200 to 1200 C) andpressure (0.13000MPa) easily and safely.

The DAC has been applied to many chemical systems and thereader is referred to a review written for chemical specialists [20].The DAC is based on the force (F)area (A) relationship (P= F/A) andconnes a s

in a sheet of metal that is held by two opposing diamonds that aretemperature-controlled. Heating of the chamber causes the pres-sure to increasealongan isochoreandpressure to increase. Pressurein the chamber is most conveniently determined by calculationwith an equation of state among the many methods proposed inthe literature. The task of pressure calculation has become muchmore convenient with the availability of the ECHO program fromthe University of Tbingen [21] that is based on the equations ofWagner and Pruss [22]. Various types of spectroscopies can be usedwith DAC to enhance visual observations.

2.3. Materials

2.3.1. FayaliteFayalite (Fe2SiO4) is an important mineral in the Earths mag-

matic processes [23] and is contained in many metallurgicalintermediates [24]. Under hydrothermal environments, fayalitewill react with quartz to yield ferrosilite (FeSiO3) as:

Fe2SiO4 + SiO2 2FeSiO3 (1)In water under moderate and neutral conditions, the reaction

might require years or decades to proceed due to the low solubilityof quartz in water, however, at conditions of high temperature andhigh pressure, the reaction proceeds on the time scale of seconds.Fig. 3 shows images of a diamond anvil cell that contains fayalite,quartz, and water at high temperature (ca. 750 C) and high pres-sure (ca. 1400MPa) provided by colleagues at Cornell university[25]. As the temperature of the solution increases from 752 C to758 C over a period of 4 s, it can be seen that ferrosilite begins tocrystallize from the solution on the right face of the fayalite crystal.With a further increase in temperature, the solubility of the quartzin the water greatly increases as judged by the size of the quartzcrystal and crystallization proceeds rapidly over a period of sec-onds. The speciation of ferrosilite has been studied in the literature

r tem

Fig. 3. Dissoluhaving a nomiBassett and K.mall volume of material (ca. 50nL) within a chamber at lowetion of SiO2 in water at high temperatures and pressures and subsequent reaction withnal chamber diameter of 0.5mm. Conditions: (a) 0 s, 752.4 C; (b) 2 s, 754.8 C; (c) 4 s, 757Mibe, Cornell University.peratures [26], but the phase formation mechanism of

fayalite (Fe2SiO4) to form ferrosilite (FeSiO3) in a diamond anvil cell.8 C; (d) 15 s, 767.6 C. Images provided as unpublished data of W.B.


Fig. 4. Dissolu d anvil cell having a nominal chamber diameter of 0.5mm. Conditions: (a)initial conditio ed SiO2 after cooling showing ne dispersed particles.Adapted from

this examplwith quartz

The exachemical scconditions

(i) rapid di(ii) crystall

tures

These twpractical mtions.

2.3.2. WilleWillemi

zinc silicatepractical grtemperatursolid-stateat atmosphtemperaturreaction isamount ofform in natconditionscate materilower tempits favorablsolubilitiesdiffusion cothe productand pressur

Takesueformation o

als, they considered zinc oxalate, zinc oxide, manganese (II), and amorphous spherical silica (d = 500nm). Solubilitiesrawere mwithto dtion of amorphous SiO2 in water at high temperatures and pressures in a diamonns; (b) initial dissolution; (c) homogeneous conditions; (d) precipitation of dissolvRef. [98].

e is not understood even though the reaction of fayaliteis well-known in geology.

mple of fayalite reacting with quartz is of interest toientists and technologists, because under hydrothermalit demonstrates that:

ssolution and diffusion of inorganics occurs andine silicate materials form at relatively low tempera-

materioxalateof thetests wheatedbegano points are developed in discussing the formation ofaterials under hydrothermal and supercritical condi-

mitete is the geological and historical name for the mineral,, Zn2SiO4. Mn-doped zinc silicate (Zn2SiO4:Mn2+) is aeen phosphor that is produced in large volumes by highe (9001500 C) solid-state reaction paths [27]. In thereaction between ZnO, SiO2 and MnCO3, that occurseric pressure in the presence of various gases at highe, ZnO must diffuse into the SiO2 lattice. The solid-statea slow process that requires hours and a considerableenergy to produce material that tends to be nonuni-ure [27]. Water, under hydrothermal or supercriticalon the other hand, has the potential to allow zinc sili-als to be produced rapidly and efciently and at mucheratures than the solid-state reaction process due toe physical properties. The important properties are theof the raw materials in the aqueous environment, theefcients of the reacting species, and the solubility ofmaterial, all of which can be controlled by temperaturee.et al. [28] used a DAC apparatus to examine the phasef Mn-doped zinc silicate in supercritical water. For raw

Fig. 5. Dissoludiamond anviinitial conditioobservance of

Adapted frommaterials in water were not available and so blankade in which small amounts of each raw material waswater. For the amorphous silica (Fig. 4), the compound

issolve in water at around 351 C and dissolved com-tion of zinc oxalate in water at high temperatures and pressures in al cell having a nominal chamber diameter of 0.5mm. Conditions: (a)ns; (b) initial dissolution; (c) formation of polyhedron just after theneedles; (d) cooled sample and conrmation of ZnO by EDX.

Ref. [98].


pletely in water at 417 C and 770MPa. For the case of zinc oxalate(Fig. 5), dissolution began at 132 C. Subsequently needle-shapedparticles appeared at 277 C that were probably ZnCO3 and thesegrew until 359 C and then transformed into polyhedrons (Fig. 5c).The cubic-like particles were conrmed to be zinc oxide. For zincoxide, heating the compound in water showed no visible changeup to 405 C. Thus, the DAC was very useful in evaluating the phasebehavior of the possible raw materials with water before makingdetailed experiments.

Takesue et al. [28] used precursor and achieved homogeneousnucleation conditions through using the phase conditions studiedin the DAC apparatus and followed the phase transformation within situ synchrotron X-ray diffraction [29]. They could conclude that-zinc silicate could be formed under hydrothermal conditions ona very short time scale (ca. min). A review on production meth-ods of zinc silicate with critical comparisons of all known methodshas been wto access thenvironmenable that a cbe developsilicate fam

2.4. Biomas

2.4.1. WateWillow i

source of bifast growin[31]. Convethe presencand energyHot water, odoes not rerial. A comhydrotherm

Hashaikwillow withused to detwhere it wneeded togcondensatioat temperathigher heatphase.

The useliquefactionimentswithto completewere loadedit was fountle or no reand very lowNa2CO3 in

Fig. 6. Proposcrops.

Adapted from

0.8wt% is probably still below the solubility limit [37]. The pro-cess for this method appears in Fig. 6, which does not address therecycle of water. The thermodynamic data required for modelingof the process is considerable although an excellent example doesappear in tbiomass (Hand the challow a homslurries andconversion

2.4.2. HydrBiomass

hemicelluloInstead of ction, it is po

ses. Tt hyds n m

O5)n

O6 6n

O5)n

n moh thees ofcase

rogenO5).e mt of h

0O3)

12O

fect

+ 10

0O3)

nmoing,of hybothactiog et atNilpfuecamgas we catphasas ceneow eximpcataopossidetalytlpfuleact

re imritten and the interested reader is highly encouragedat source [30]. The properties of water, the reactiont that it provides, and its phase behavior make it prob-ontinuous, low-temperature, and efcient process can

ed for making industrial phosphors based on the zincily.

s resource conversion

r soluble compoundss awoodycrop thathas thepotential tobeusedasa localomass for heat, electricity, and chemicals because it isg in cooler regions such as the Tohoku region of Japanrsion of willow by enzymatic hydrolysis is inhibited bye of lignocellulose, whereas acid hydrolysis is processintensive and severely degrades the glucose produced.n the other hand, provides an alternative method thatquire acids or harsh additives to hydrolyze the mate-prehensive overview of the hydrolysis of biomass viaal methods is given by Yu et al. [32].

eh et al. [33] studied the hydrothermal dissolution ofbatch, DAC, and ow type experiments. The DAC was

ermine the qualitative phase behavior of the systemas found that heat rates of greater than 5 C/s wereivedissolutionof thematerial inwaterbut invariably re-n of oligomers occurred that prevented ow operationures higher than 300 C. Thus, short reaction timeswithing rates would seem to be needed for a homogeneous

of alkali salts has been studied for some years in theof biomass [34,35]. FangandFang [36]usedDACexper-willowand considered the use of dilute alkali solutionsly solubilize the material. Willow, Na2CO3 and waterinto theDAC chamber. Then, studiesweremadewhere

d that willow could be completely dissolved with lit-sidue at 330 C by using heating rates of at least 8 C/s

concentrations of Na2CO3 of 0.8wt%. The solubility ofwater decreases with increasing temperature, but still

ed process for production of water soluble compounds from woody

Ref. [34].

procesperfeccontain

(C6H10

nC6H12

6nCO +(C6H10

Forthroug12molFor theof hyd(C5H10mediatamoun

(C10H1

nC10H

per

10nCO

(C10H1

Forreformmoles(9). Inshift re

Fanwithouwas hetures bwherewith thon thetures whomogthe oing the[42]. Awas pr

Conand caeral heof the rlysts ahe literature for the Shell hydrothermal upgrading ofTU) process [38]. Nevertheless, the properties of wateremical effects of a small amount of an inorganic saltogeneous solution to be formed with woody biomasstherefore the development of green processes for the

of biomass are feasible.

ogencan be considered as a mixture of cellulose (C6 sugars),se (C5 sugars) and lignin (polyphenolics) compounds.onverting biomass to chemicals as in the previous sec-ssible toproducehydrogenandmethane foruse inotherhe amount of hydrogen that can be produced from therolysis of cellulose (Eq. (2)) based on a compound thatoles of glucose is:

+nH2O nC6H12O6 perfect cellulose hydrolysis (2)6nH2 +6nCO perfect glucose gasication (3)

H2O 6nH2 +6nCO2 water-gas shift reaction (4)+7nH2O 12nH2 +6nCO2 (5)les of glucose and its perfect gasication (Eq. (3)), andwater-gas shift reaction (Eq. (4)), it is possible to obtainhydrogen for everymole of glucose according to Eq. (5).of hemicellulose represented by (C5H8O4)n, 10 molesare possible to be produced for every mole of xylose

For the case of lignin that can be represented as an inter-onomeric alkylphenolic species, (C10H10O3)n [39], theydrogen that can be produced from n moles

n+nH2OnC10H12O4 perfect ligninhydrolysis (6)

4 +6nH2O 12nH2 +10nCOsteamreforming (7)

nH2O 10nH2 +10nCO2 water-gas shift reaction (8)

n +17nH2O 22nH2 +10nCO2 (9)les of an alkylphenolic, for perfect hydrolysis and steamEqs. (6) and (7), it is theoretically possible to produce 22drogen for every mole of alkylphenolic according to Eq.the gasication of cellulose and lignin, the water-gasn is an important source of hydrogen [40].l. [41] studied cellulose and Na2CO3 additive with and

catalystwithDAC, batch andowexperiments. TheDACl for not only observing the conditions where the mix-e homogeneous, but also for knowing the conditionsas formed and the physical interaction of the solutionalyst. In another work, the effect of catalysts (Ni, Ru, Pt)e behavior of cellulose +water and glucose +watermix-onsidered [42]. The Pt catalyst was found to promote aus and light colored phase in the trialswith glucose andperiment gave a 40mol% H2 gas stream, thus conrm-ortance of the phase observations in the DAC apparatuslytic reactor instead of the bio-reactor shown in Fig. 6ed in that work to produce hydrogen.rable effort has been devoted to the noncatalytic [39,43]ic methods [44,45] to gasify biomass in water and sev-reviews are available [4649]. Both the phase behaviorants and products with water and the selection of cata-portant in developing future green processes.


Fig. 7. Tempe rmalcan be seen (le ottom

2.4.3. EnergAn integ

ried coal wsyngas (COa gas turbinbustedandto supplemgrated gasiof coal andThey are nofacilities su

In prevical water oxbiomass intemperaturstoichiomeabove aboucan be sustabased on sefor the casedized withmight be exis clear andauto-thermabout 17mconvert bioplete oxidastream mixoccurs. Estias the oxida

3. Carbon

Supercritions associ[55], polym

58],ilabls ofen puction

ass s

ds foranerature prole of a biomass boiler for which spent tea leaves are heated in a hydrotheft) and the efuent changes greatly for the case of with air (top) and without air (b

yrated gasication combined cycle (IGCC) combusts slur-ith air or oxygen at high temperatures and produces+H2). Excess heat from combustion is combined withe to produce electricity. The syngas can also be com-

used togenerate electricity. IGCC facilities arebeginningent their feeds with up to 30% biomass. Biomass inte-cation combined cycles (BIGCC) use biomass insteadoften use uidized beds and operate at low pressures.t realized yet, but they are being considered as add-on

raphy [are avaubilitiehas bethis se

3.1. M

Lipimembch as those for sugarcane [50], paper or ethanol [51].ous research, Arai et al. [52] proposed that supercriti-idation technology could be used to efciently convert

to energy. In that proposal [52], the adiabatic amee was calculated for cellulose and water mixtures withtric oxygen at pressures up to 30MPa. At pressurest 20MPa, the combustion becomes spontaneous andined. A ow sheet and apparatus have been developedmi-batch operation. Fig. 7 shows some initial resultsof a biomass feedstock of spent tea leaves that are oxi-air. For the case of no air, water is brown and turbid aspected. However, for the case of with air, the efuentchanges color to become completely transparent. Theal effect can be clearly seen in the gure beginning atin run time. The process, when realized, will be able tomass into energywithhigh efciency. In achieving com-tion in the biomass boiler, the phase behavior and theing are very important along with the heat transfer thatmation methods for the properties and phase behaviortion proceeds are needed to realize the process.

dioxide

tical carbon dioxide (scCO2) is widely used in applica-ated with extractions [53], separations [54], materialser syntheses [56], polymer processing [57], chromatog-

containingto decreasevia volumeThe use ofby disruptinThe techniqherbs [75,7with good[73], the tepromote thbubbles wh3 phases. ACO2, CNSLing a mechaa method inot only forhealth [80]

3.2. Biphas

Carbonwhich makOn the othamounts ofof a third cthe ionic liqenvironment. After air is added to the mixture, an auto-thermal effect).

ionic liquids [59] and reactions [60]. Specialized reviewse [6171] and a comprehensive compilation of the sol-more than 780 solutes in supercritical carbon dioxideblished [72]. Several applications will be discussed into highlight the properties of scCO2.

eparating agent

und in natural products are usually conned withins or within a solid matrix. In the processing of oil-

materials, scCO2 can be used as a non-reactive solutethe time required to separate an oil from a solid matrixexpansion, viscosity reduction or both of these effects.pressure swing enhances the efciency of separationg membranes and promoting oil-scCO2 phase contact.ue has been applied to cashew nut shell liquid [73,74],6], palm kernel oil [77], canola [78], and sh oil [79]results. For the case of cashew nut shell liquid (CNSL)mperature can be used in addition to the pressure toe separation as shown in Fig. 8. As shown in Fig. 8, CNSLen reducing the pressure at 20 C under conditions oft temperatures higher than the critical temperature ofalso bubbles when reducing the pressure thus provid-nism for separating the oil from the solid matrix. Such

s greatly needed in the general processing of cashew,industrial efciency but more importantly, for human

.

ic system

dioxide generally forms two phases with ionic liquids,es it convenient for both separations and reactions.er hand, scCO2 can be made to dissolve considerablean ionic liquid into the supercritical phase by additionomponent [81], or to cause a solute to crystallize fromuid phase [82] or even to be made homogeneous in a


Fig. 8. Phasebfrom Ref. [71].and for CNSL cculated with t

ternary sysbiphasic ion

3.2.1. PartitThepart

and a scCOtion proces[8488]. Apdata use m(LSER) thatmodels suctive correlabased modtions withthis work, twidely appl

In the pa(scCO2 phasseparation

= KwA

KwB

where KwAare the wesolute B, rescorrelated,separation

Fig. 9 shofrom the Sain the [bmimseparationwith increaexamine th

In the Sis considere

60

5

10

15

20

25

benzene-benzyl alcohol

eparam][PF

s thebicperaple frevquid

0 1

0 ismpent ths, 1/n ofehavior of carbondioxidewith cashewnut shell liquid (CNSL) adaptedVisual appearance of oil during pressure changes for CNSL-CO2 onlyontained in the solid matrix (top). Phase behavior of CNSL-CO2 cal-he PengRobinson equation of state.

tem under the proper conditions [83]. In this section,ic liquidscCO2 systems are discussed.

ion coefcientitioningof organic solutesbetweenan ionic liquidphase2 phase is of interest for many separation and reac-ses. Basic data are being measured by several groupsplication of theory to either predict or correlate theethods such as linear solvation energy relationships

sepa

ratio

n fa

ctor

[-]

Fig. 9. Sfor [bmi

ture. ACoulomon teming simpressuionic li

(T) =

wherehigh teconstastancefunctioprovide qualitative information [85], semi-empiricalh as equations of state [89,90] that provide quantita-tion and limited prediction, and quantum chemistryels COSMO-RS [91] that provide quantitative predic-detailed information on the molecular interactions. Inhe SanchezLacombe equation is discussed since it isicable to both polymer and ionic liquid systems.rtitioning of a solute between a supercritical CO2 phasee) and an ionic liquid phase (IL phase), a weight ratiofactor can be dened as:

(10)

(= wscCO2 phaseA /wIL phaseA ) and K

wB (= wscCO2 phaseB /w

IL phaseB )

ight ratio based partition coefcients of solute A andpectively. Once sufcient data have beenmeasured andit is possible to use an equation of state to predict thefactors.ws calculations of the separation factors as determinednchezLacombe equation of state for aromatic solutes][PF6]scCO2 biphasic system [92]. As shown in Fig. 9,

factors have values as high as 20 and these decreasesing pressure. The equation of state can also be used toe variation of the separation factors with temperature.anchezLacombe equation, the interaction energy, *,d to be a constant and does not depend on tempera-

applicationshould provfactors. Theuid systemscan be expe

4. New pro

Many neing and grethe processbehavior ofbuilt with wtinued devethese and o

Low-temmaterials htobeadopteof the zinc sthat provid

Efcientand it is likefeedstocksstrated foron the localstocks such2018161412108

benzene-naphthalene benzene-chlorobenzene benzene-toluene

P [MPa]tion factors calculated with the SanchezLacombe equation of state6]CO2 at 60 C.

temperature of a system changes, it is clear that bothinteractions andhydrogen-bond interactionsdodependture. Machida et al. [93] recently proposed the follow-unction that greatly improves the representation of theolumetemperature behavior of pure uids includings:

T

+ T (11)

the asymptotic value of the interaction energy at therature limit given by the original equation and a is aat depends on the interaction energies. For many sub-

can be considered to be a constant or as a linearthe magnitude of the interaction energies (Fig. 10). Theof Eq. (11) to mixtures is presently being examined andide some insight into the trends of available separationdevelopment of equations of state for scCO2ionic liq-is an ongoing research topic and many developmentscted in the future.cesses on the horizon

w processes that use the principles of green engineer-en chemistry are on the horizon. The foundations ofes depend on the reliability of the properties and phasechemical systems. Many new energy systems will beater or carbon dioxide as the working uids and con-lopment of thermophysical property formulations forther working uids is needed.perature processes for practical industrial luminescent

ave clearedmany of the technical hurdles andwill begindby industry.Demonstrationof continuousproductionilicate family of industrial phosphors is being publishedes appropriate sources of silica [94].ways to either liquefy or gasify biomass are availablely thatmany new chemical processes based on selectedwill be developed. The biomass boiler has been demon-conversion of waste biomass to energy with emphasisscale. Detailed trials will be published on various feed-as spent tea or spent coffee grinds.


5000

1/

[K

]

0

50

100

150

200

250

300

350

400

450

500

550

600

650

700

Fig. 10. CorreSanchezLacoenergies.

Adapted from

Hydrothpresence omethod fortechnologiethermal spapplicationalso as a for

Water ispetroleumrtopic andwthe upgradihighly comptaining the

Many poposed andand separanew opportstate. For exis about 70point, it canof scCO2 oralytic convehighefcienreduction p

5. Conclus

Physicalmixtures cachemical prtheworkingtinue to expit is inevitanew practic

Many physical properties and phase equilibria studies are stillneeded to understand the simplest of examples outlined in thiswork. Through sharing of methods and technologies between

h elds, progress developing green processes can be greatlyated

wled

authucatry ofnaport

nces

nasta. Anassity Pr. Anas101a. SheldY. Tan. Tang269reutzis 4 (20yrne,ionaleE, A T-00, 2harta

E, Nex8.Weing05) 26. Fou919kushi98) 58dschiimabogy 190 [kJ/mol]

1200011000100009000800070006000

1/ = 0.10070 423.9

lation of the temperature dependence of interaction energies in thembe equation of state as a function of themagnitude of the interaction

Ref. [91].

ermal ames, in which an organic is oxidized in thef water, have been studied in the past as an efcientwaste treatment. In the development of new drillings, hydrothermal ames are being evaluated as a newallation drilling technology [95]. Such technology hasnot only as a clean and efcient method for drilling but

researcacceler

Ackno

Thethe EdMinistpartialfor sup

Refere

[1] P. A[2] P.T

ver[3] P.T

94a[4] R.A[5] S.L.[6] S.Y

268[7] F. C

ter[8] P. B

nat[9] DO

002[10] H. K[11] DO

200[12] H.

(20[13] R.O

196[14] Y. I

(19[15] T. A[16] A. A

nol

m of in situ petroleum upgrading.seen as a method for upgrading and extending presenteserves [96]. Bitumenupgradingwithwater is an activeater acts as a solvent for reducing coke formationduringng process. Key to the process is the phase behavior oflex andundenedpolyaromatic compounds andmain-homogeneity of the system as the reaction progresses.ssible separation and reaction processes are being pro-coming online for carbon dioxide. Biphasic reactionstions with supercritical CO2 are attractive. There areunities for using ionic liquids in their metastable liquidample, the melting point of the ionic liquid [bmim][Cl]C. However, if liqueed by heating above its meltingbe made to dissolve solids such as fructose. Addition

organic solvents to reduce the viscosity allows the cat-rsionof fructose to5-hydroxymethylfurfural tooccur atcyat close toambient temperaturesdue to theviscosityrovided by the added solvent or scCO2 [97].

ions

properties and phase behavior of uids and uidn be used to develop many environmentally friendlyocesses. Air, water and carbon dioxide will be used asuids inmany futuredevices andprocesses. Aswecon-lore the properties of these uids and uid mixtures,

ble that there will be some discoveries that will lead toal processes.

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2nd ed., C[28] M. Takes

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gements

ors wish to acknowledge partial nancial support ofion Global Center of Excellence (Global COE) and theEducation, Science, Sports and Culture (RLS) and the

ncial support of the Chinese Academy of Sciences (ZF)of this research.

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Properties and phase equilibria of fluid mixtures as the basis for developing green chemical processesIntroductionWaterProperties and phase equilibriaExperimental methodsMaterialsFayaliteWillemite

Biomass resource conversionWater soluble compoundsHydrogenEnergy

Carbon dioxideMass separating agentBiphasic systemPartition coefficient

New processes on the horizonConclusionsAcknowledgementsReferences

properties and phase equilibria of fluid mixtures as the basis for developing green chemical...

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