cleaner and greener is smarter; conversion of liabilities ... · catalytic hydrogenation has now...
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Cleaner and Greener is Smarter;Conversion Of Liabilities Into Assets
IGCW, 6th Dec. 2013
Professor M. M. Sharma, FRS
Emeritus Professor of EminenceInstitute of Chemical Technology
(Deemed University), Mumbai
1Private Circulation Only
Soda ash by Lablanc Process(1773) replaced by Solvay Process (standard
process; dual process); ultimate success with carbonation of sodium hydroxide
Lead chamber process for sulphuric acid of late 1808 replaced by contact
process; recent development with dual process reduces SO2 emissions to less
than 500 ppm
Electrolytic caustic soda: diaphragm cell; mercury cell; membrane cell with
catalysed electrodes; possibilities of on-site generation of chlorine /
hypochlorite on a small-scale
Classical Processes which have been Converted into New “Friendly” Processes
M M Sharma 2ICT
Tanning of leather with new chromium complexes which allow 98% Cr
retention compared to 65% in the past
Use of fluorosulphonic acid for etching glass is superior to the use of a
mixture of sulphuric and hydrofluoric acid
High solids paints and water based paints are far superior to conventional
organic solvents based paints having lower solids content
Replacement of processes based on acetylene with those based on ethylene
;1,4-Butanediol / THF from Maleic Anhydride 3
M M Sharma 3ICT
Extraction of aromatics with oleum / SO3 / liquid SO2 replaced by solvent
extraction of aromatics
Reduction of nitrobenzene with iron and acid replaced by direct vapour phase
reduction with hydrogen; reduction of aromatic nitro compounds with aqueous
Na2Sx replaced by catalytic liquid phase reduction with H2
Nitric acid from ammonia; strategy of high pressure for absorbers allows NOx
emissions below 300 ppm; CNA via SABAR vs. Extractive Distillation with
sulphuric acid
Old Claus process with a new one with active catalyst at lower temperature
permitting very low emissions of SO2
4M M Sharma 4ICT
The recovery of sulphur from sour natural gas and H2Sin the hydrodesulphurization of heavier petroleumfractions is an outstanding example and practically allsulphur that is sold today is recovered.
Even SO2 can be recovered from flue gases by selectiveabsorption and valorised to sulphuric acid or convertedto sulphur
Sulphur from H2S
5M M Sharma 5ICT
CaC2 + 2H2O Ca + C2H22OH)(
In the manufacture of NP fertilizers via acidulation ofphosphate rock with nitric acid, the Solvay type process isinvolved in the reaction of Ca(NO3)2 with NH3 and CO2, and theprecipitated CaCO3 so obtained can be valorized as a filler andalso for the cement industry.
Acetylene continues to be manufactured from CaC2 viahydration:
CaC2 + 2H2O Ca + C2H22OH)(
This Ca(OH)2 can be valorized as quality precipitated CaCO3.
Valorisation of precipitated CaCO3
6M M Sharma 6ICT
NOX emissions from nitric acid plants and nitricacid based oxidation of organic substanceshave been brought down and valorized,including the selective absorption in aqueoussodium hydroxide to produce value addedsodium nitrite.
Absorption of NOX
7M M Sharma 7ICT
8M M Sharma 8ICT
Friedel-Crafts alkylations (F-C)
This was a notable development in the history of the chemicalindustry where aluminium chloride is used, often instoichiometric amounts, and this creates environmentalproblems. Now many large scale alkylations, like that of benzenewith ethylene and propylene, are carried out with solid zeolitecatalyst. However, there are still innumerable processes in fineorganic chemicals where the F-C process is employed. Herewaste aluminium chloride has been valorized as the so calledpolyaluminium chloride which is very useful as a coagulant intreatment of water. This is very successful and now independentstand-alone plants have been established.
9M M Sharma 9ICT
m -Phenoxybenzaldehyde, required for very efficient and safe
insecticides in the pyrethroids series, can be made via a safer
and cleaner process based on m -phenoxytoluene, in turn
obtained by a pollution-free process involving vapour phase
dehydration of m–cresol and phenol, rather than that based on
bromination of benzaldehyde followed by Ullmann reaction with
m -cresol in the presence of copper catalyst.
Cleaner and Safer Processes
10M M Sharma 10ICT
Byproduct sodium sulphite, along withthe by-product sodium formate, hasbeen valorised to value-added sodiumhydrosulphite
Sodium Sulphite
11M M Sharma 11ICT
Valorisation of HCl and polychlorinated products obtained in organic chemical industry
The most outstanding example is the manufacture ofvinyl chloride via ethylene dichloride (EDC) cracking.Here an oxidative chlorination process has beendeveloped which allows the direct conversion ofethylene via reaction with HCl and O2 to EDC. It may berecalled that when phenol was manufactured frombenzene via chlorobenzene, a process foroxychlorination of benzene was developed.
H2C=CH 2+ 2HCl + 1/2 O2 ClCH 2CH2Cl H2O+
12M M Sharma 12ICT
Unwanted polychlorinated compounds like tri- and polychlorinatedethane have been valorized through chlorinolysis at high temperatureto CCl4 and C2Cl4.
On the subject of polychlorinated organic substance a recent novelsolution may be pointed out in the large-scale manufacture ofepichlorohydrin. Here allyl chloride is reacted with Cl2 in an aqueousmedium where hypochlorous acid reacts with allyl chloride. However,the equilibrium quantity of Cl2 gives unwanted trichloropropane. Anovel approach is to separately make pure aqueous HOCl in aningenious way of absorbing Cl2 in hot aq. caustic soda solutions andsimultaneously stripping HOCl, in a centrifugal absorber reactor, andabsorbtion in water.
Cl2 + aq. NaOH HClO NaCl+
13M M Sharma 13ICT
Desorption of HClO Gas from Rich Hydroxide Solutions
Bulk Liquid
14M M Sharma, ICTM M Sharma 14ICT
Ethylene oxide by chlorohydrin process replaced by direct oxidation of
ethylene with oxygen
Propylene oxide via chlorohydrin process replaced by epoxidation with H2O2
or hydroperoxides (tert-Butyl hydroperoxide ; Ethylbenzene hydroperoxide ;
Cumene hydroperoxide)
Phenols via sulphonation and alkali fusion or via chlorination and alkaline
hydrolysis replaced by cumene type processes; catechol and hydroquinone via
hydroxylation of phenol with H2O2
Safer and More Efficient Organic Processes
15M M Sharma 15ICT
Substitution bromination of aromatic substances
A variety of aromatic substances, such as phenoliccompounds, benzaldehyde, etc are brominated withbromine and HBr is obtained as a byproduct. We canvalorize expensive bromine through two strategies.Firstly we can use BrCl made from 1+1 mole ofbromine and chlorine and then HCl, instead of HBr, willcome out. Secondly we can carry out two-phasebromination with the aqueous phase containing H2O2
so that HBr is converted in situ to bromine which, dueto high distribution coefficient, goes to the organicphase.
M M Sharma 16ICT
Benzaldehyde from toluene via side chain chlorination and
hydrolysis replaced by direct oxidation of toluene in liquid
phase.
Anthraquinone from phthalic anhydride (pan) and benzene
with stoichiometric amount of AlCl3 replaced by direct
oxidation of anthracene or reaction of naphthaquinone and
butadiene (New possibilities of zeolites based reaction
between pan and benzene ).
17M M Sharma 17ICT
Phenyl ethyl alcohol via reaction of benzene with ethylene oxide, in the
presence of stoichiometric amount of AlCl3,replaced by hydrogenation of
styrene oxide in turn obtained by newer epoxidation processes.
Diphenyl oxide and related compounds via Ullmann reaction, using Cu
based catalyst , replaced by vapour phase dehydration of phenols
p-aminophenol from p-nitrochlorobenzene replaced by direct reduction
and rearrangement of nitrobenzene or via acetylation of phenol followed
by oximation and beckmann rearrangement (to get paracetamol directly)
18M M Sharma 18ICT
Process based on Phosgene / MIC : Isoproturon from p-Cumidine and Urea +
Dimethylamine
Processes based on HCN : Acrylonitrile based on acetylene and HCN replaced by
ammoxidation of propylene; Adiponitrile from butadiene and HCN replaced by
dimerization of acrylonitrile or reaction of ammonia with adipic acid
Replacement of the conventional method of making chloromethyl ether which
contains carcinogenic dichloro derivative by a route based on HCl and Methylal
Replacement of reduction based on the use of sodium metal in liquid ammonia
by electrochemical processes
Replacement of Hazardous/ Toxic Chemicalswith “SAFER” Chemicals
19M M Sharma 19ICT
Replacement of chlorinated diphenyls by phenyl xylylethane as dielectrics.
Replacement of mercury salts as catalysts e.g. , sulphonation of anthraquinone
(AQ) (For making 1-Aminoanthraquinone via Ammonolysis replaced by nitration
of AQ followed by replacement of NO2 by NH2 with Ammonia).
Replacement of chromium compounds in water treatment by safer chemicals
based on triazoles etc.
Absorption of CO2 (in ammonia plants) in potash solutions, catalysed by
arsenite replaced by potash solutions activated With diethanolamine.
Replacement of methyl methacrylate, based on acetone and HCN, by the
process based on direct oxidation of isobutylene.
20M M Sharma 20ICT
Very high pressure (>1000 atm) for L.D.P.E. replaced by low
pressure (<40 atm) processes.
High pressure (~200 atm) Oxo -Process replaced by low pressure
(40-50 atm) process.
Very high pressure (~1000 atm) Carbonylation Process for acetic
acid replaced by low pressure (~40 atm) process.
High pressure (~100 atm) Hydrogenations replaced by low
pressure (<10 atm) processes.
High pressure storage of ammonia/ ethylene etc. replaced by
atmospheric pressure refrigerated storage system
Change Over from High Pressure to Low Pressure Processes/ Operations
21M M Sharma 21ICT
Valorization of toluene and C9- aromatics
In the manufacture of xylenes by catalytic reforming we inevitably getC9 aromatics. The technology of transalkylation, with zeolite basedcatalysts, has done an extraordinary job of converting low- value C9-aromatic to high- value xylenes:
+CH3
CH3
CH3 CH3 CH3
CH3
When surplus toluene comes in the product-mix for making benzeneand toluene we have yet another option of carrying outdisproportionation:
+
CH3
2 CH3
CH3
22M M Sharma 22ICT
Reduction of aromatic nitro compounds with stoichiometric reducing reagents
In most bulk processes, like aniline, toluenediamines, etc,catalytic hydrogenation has now been adopted and thisavoids the use of stoichiometric amounts of reducing agents.However, many industrial processes still use stoichiometricamount of reducing agents like Fe/acid, Na2SX, etc. In thecase of Fe/acid, it is possible to convert the co-productliquor to value –added iron oxide pigments. In the case ofNa2SX, valuable sodium thiosulphate can be recovered.
23M M Sharma 23ICT
Selective production of para substituted aromatic compounds
Chlorination and nitration e.g. of toluene is carried out and thedesire is to obtain high yields of the para substituted isomerand this poses problems as the unwanted ortho isomer isinevitably obtained in larger quantity. In recent years abreakthrough, to some extent, has been realized viachlorination in the presence of a zeolite when a very significantincrease in the content of the para isomer has beencommercially realised.
24M M Sharma 24ICT
Valorisation of by-product streams- manufacture of phenol
In the manufacture of phenol, a mixture of alphamethyl styrene(AMS) and cumene is encountered and this used to beearmarked as Fuel. A significant recovery of AMS can result infinancial gain both through the sale of AMS and recoveredcumene being recycled.
Further valorisation can come through the use of AMS-cumenemixture to be converted to the desired unsaturated dimerthrough an ingenious application of cationic ion exchange resingiving 93 to 95% desired dimer, which is sold at a very decentprice.
25M M Sharma 25ICT
The above crude mixture could also be used to make highpurity p-cumyl phenol as a chain terminator in makingpolycarbonates and for phenolic resins. Here also cationicion exchange resin was used as a catalyst. Even 2,4 dicumylphenol is a value - addition product.
CH2CH3
IER
Catalyst
+
OH
CH3
CH3
H3C CH3
C
OH
C
C
CH3H3C
OH
C
26M M Sharma 26ICT
Valorization of by-products from the manufacture of ethyl benzene
m + p Diethylbenzene mixture, obtained as a by-product in themanufacture of ethyl benzene, has been used to make value-added divinylbenzenes which are so essential in makingcationic and anionic ion exchange resins.
3+CH CH2
32CH CH
2H2
2
2
CH CH
CH CH
27M M Sharma 27ICT
Phosgenations: efficient utilisation of expensive phosgene and reduction in the consumption of alkali
A variety of industrially important reactions are carried out withphosgene where neutralisation of the HCl formed is done with analkali. The use of Na2CO3 was prevalent. The undesired alkalinehydrolysis of phosgene is a very fast reaction with the second-orderrate constant much higher than 105 litre / g mole sec. By ensuringexcellent mixing and using powdered NaHCO3 this menace wascontained and highly efficient utilisation of phosgene was ensuredwith advantageous reduction in the consumption of NaHCO3.
COCl2 ++H2O CO2 2HCl
2HCl + 2NaHCO 3 2NaCl + 2H 2O + 2CO2
28M M Sharma 28ICT
Recovery of Raney nickel catalyst with an excess of zeolites
A number of hydrogenations are carried out with Raney Nicatalyst and sometimes for process requirement a large amount ofzeolites is used which are also expensive. It is not economicallyattractive to use this mixture to recover Ni and zeolites. It ispossible to deploy high gradient magnetic separation to removeRaney Ni and this valorizes both Raney Ni and the zeolite.
29M M Sharma 29ICT
Recycle of polymeric substances
This has become an urgent problem. We do have theoutstanding example of recycle of waste polymethylmethacrylate via depolymerisation. Likewisepolyethylene terephthate resins can be recycled via alkalinehydrolysis to give polymersation grade terephthalic acid andmonoethylene glycol. We need cost effective strategies forpolystyrene, ABS, polyamides and polycarbonate.
30M M Sharma 30ICT
Importance of Continuous Processes
Stirred Reactors and Small Tubular Reactors, Micro Rectors
Provide high heat transfer coefficients
Have low inventory
Withstand high pressures
Can be easily stopped
May be operated adiabatically without problems of runway
Conditions by introduction of precooled reactant streams
Advantages
31M M Sharma 31ICT
Waste bottom products from isophorone plant
Unwanted by-products were consigned as fuel by a worldrenowned company. This stream containing a number of othercondensation products was valorised to provide a fragranceproduct which is used by the josssticks industry in India.
3CH3COCH3
O
32M M Sharma 32ICT
Traditional Synthesis of an Aromatic Amine, 4-Amino Diphenylamine
New Synthesis of 4-Aminodiphenylamine avoiding the use of halogenated intermediates
33M M Sharma 33ICT
The Strecker Process for Synthesis DSIDA (Hazardous)
Alternative Synthesis of DSIDA using a Copper Catalyst
34M M Sharma 34ICT
Intrinsic continuous process safety is based on thestability of the reaction system and reactionconditions and minimizes the possibility of dangerousoccurrences resulting from human error or equipmentfailure
A hazard analysis is carried out to determineconditions for chemical/ physical stability of a system
Intrinsic Continuous Process Safeguarding
35M M Sharma 35ICT
Use of Titanium and Ti lined vessels
Use of Tantalum for aggressive chemicals
Adoption of Teflon and PVDF lined valves/ fittings and vessels
Use of structural high performance adhesives for joints
Safety Through the Use of Superior Materials of Construction
36M M Sharma 36ICT
How Raschig and Ammoximation Routes to Caprolactam Compare
37M M Sharma, ICTM M Sharma 37ICT
More from less
Acetone to diacetonealcohol
Homogeneous catalyst sodium ethoxide was used
Na removal was done with phosphoric acid, to crystallise Na2HPO4 and thiswould cause separation problem and clogging resulting in a lot ofdowntime, a loss in yield and substantial reduction in capacity utilisation.
Na removal was then done with cationic ion exchange resin and a neatprocess was swung into action.
Debottlenecking of the separation train along with the above criticalchange allowed the plant capacity to go up by a factor of 4 (even 5)!
OH
2CH3COCH 3 H3C
CH3
CH2COCH 3C
38M M Sharma 38ICT
Recovery of sparingly soluble refractory and toxic organic
substances from aqueous waste streams
The organic chemical industry is replete with examples of large
quantities of aqueous waste streams containing such
substances. A simple, effective and clean process is based on
steam stripping. Thus hydrocarbons (from olefin crackers), EDC,
aromatics, nitro aromatics, etc. are now routinely recovered.
There is potential in some cases to adopt pervaporation and
adsorptive separation.
39M M Sharma 39ICT
Short path distillation
In some fine chemicals processes the desired relatively non-
volatile substance, in the presence of sparingly soluble solvent
in water, is recovered via steam distillation. The aqueous layer
can be treated in the above steam stripping mode. However, in
such cases from overall efficiency point of view it would be
useful to consider the Short Path Distillation method to recover
the solvent and the desired substance.
40M M Sharma 40ICT
Nanofiltration Membranes
Many acutely toxic substances, like in the manufacture of
agrochemicals, pharmaceuticals, dyestuffs etc, are non volatile
and alternative processes have to be considered. In some cases,
nanofiltration membranes will clean the effluent as well as
allow the recovery of the valuable substances. We now have
many commercially proven examples.
41M M Sharma 41ICT
Solvent Extraction
In some cases continuous solvent extraction may prove to be
advantageous, particularly when it can be integrated with the
main process. Consider the case of the large volume of aqueous
effluent containing 2, 4 dichlorophenol and 2,4 dichloro
phenoxy acetic acid (2,4 D), solvent extraction with ,say,
trichlorobenzen or Ca aromatics, allows nearly quantitative
recovery and the extract is stripped with aqueous NaOH and
recycled in the main process.
42M M Sharma 42ICT
Recovery of organic substances in vent streams
The Chemical industry is replete with such example like air oxidationof hydrocarbons, vent stream carrying low boiling substances likemethylene chloride, painting shops using volatile solvents, etc. Thesepose environment problems but are good candidates for recovery viacondensation, absorption, adsorption, etc. Many examples ofcommercially proven cases can be cited.
The exhaust gas from phthalic anhydride plants, based on vapourphase air oxidation of ortho-xylene, contains 3 to 5 % of phthalicanhydride as maleic anhydride and this used to be incinerated. Wenow convert this into an asset via absorption in aqueous solution ofmaleic acid and a corresponding slipstream is subjected toisomerization to sparingly soluble fumaric acid which is recoveredand sold at a decent price.
43M M Sharma 43ICT
Valorisation of agro wastes
The example of bagasse in cane sugar industry can be citedwhere the predominant use is as a fuel in the boiler. However,this fibrous substance is a potential candidate for valorisationto give high alpha cellulose material. The potential of steamexplosion to give 95% alpha cellulose, and separately hemi-cellulose and lignin needs to be exploited as hemi-cellulosecan be acid hydrolysed to fermentable sugars and lignin hasmany uses as lignosulphonates. A variety of agrowaste can betreated in the above manner.
44M M Sharma 44ICT
A novel application of phase transfer catalysis has been
made in recovering phenolic impurities from alkaline waste
liquors. Here, a reactant like benzoyl chloride, p- toluene
sulphonyl chloride, etc is dissolved in toluene and reacted
with the waste stream. The phenolic substance is
converted, almost quantitatively with more than 95 %
selectivity to the corresponding ester which is saleable and
thus a liability is converted into an asset( Krishnakumar and
Sharma, 1984)
45M M Sharma 45ICT
Recovery of metals from lean ores and aqueous waste streams
The valorization of lean copper and nickel ores viahydrometallurgical processes is an outstanding examplewhere reactive solvent extraction is used to recover Cu/Nisulphates. This was sequel to winning real lean orescontaining uranium. The lean aqueous effluents fromelectroplating industry can be valorised to recover heavymetals via fluidized bed electrodes, solvent extraction,precipitation, etc.
46M M Sharma 46ICT
Production of ester montan wax by oxidation with chromic acid followed
by esterification
Earlier batch process carried out in lead-lined stirred vessels polluted
the waste water and was expensive in raw materials and energy.
Alternative continuous process using cascaded bubble column reactors
offers the following advantages:
Reaction exothermicity is exploited to generate steam
Uniform product quality and savings in raw materials
Continuous post purification step possible
Zirconium plate separator used for separation of chromic acid
residmus and this avoids breakdowns
Safer, Cleaner Process DevelopmentBatch to Continuous Mode
47M M Sharma, ICTM M Sharma 47ICT
Simulation Absorption of Olefin and Chloride in Water in the Presence of Microphase
Basic Idea:Preferencial partitioning of the species (Chlorine, Olefin) into themicrophase can lead to enhanced rates of absorption of both the gases
Presence of microphase can give rise to a higher yield of byproductdichloroalkane
Reaction Scheme: In Continuous Phase In Microphase
Cl2 H2O HOCl H+(E) Cl-(E)+ + +
Cl2 RCH CHR+ RCH CHR
Cl
Cl-+
RCH CHR
ClH2O HORCHCHRCl+ H++
RCH CHR
ClCl-+ ClRCHCHRCl (P2)
Kii
K2
K3
K4
K1
Cl2 RCH CHR+ RCH CHR
Cl
Cl-+
RCH CHR
ClCl-+ ClRCHCHRCl
K2
K4
org
org
48M M Sharma 48ICT
Comparison of the Environmental Balance of the Chemical and Biocatalytic Processes
49M M Sharma 49ICT
Examples:
In the Hofmann reaction of an amide with sodium hypochlorite ,
The intermediate isocyanate can be obtained in high yields ( even
though it undergoes a fast reaction) , by using a proper second
liquid phase for which it shows a higher affinity. thus it may be
possible to make some isocyanates ( mono as well as
difunctional) without using phosgene
Extractive Reactions
RCONH2 RNCO RNH2
50M M Sharma 50ICT
Expensive reductions e.g. Birch reduction can be carried out atlower cost and under safe conditions
Oxidation of para-methylanisole to para-anisaldehyde
Conversion of nitrobenzene to para-amino-phenol
Reduction of pyridine to piperidine
Electrohydrodimerization of acrylonitrile to adiponitrile : Use of quaternary ammonium salts
Anodic cyanation of naphthalene using phase transfer catalysts and of dimethoxy benzenes using micellar solutions
Electrochemical Processes
Applications
51M M Sharma 51ICT
Advantages
High specificity
adoption of milder conditions
Ease of scale up
Avoidance of effluents
Use of second liquid phase, micelles, hydrotropes, etc. can bestow
additional benefits
New Developments
Dimensionally stable anode
Membranes based on perfluoro compounds
solid polyelectrolytes
engineering plastics e.g. polyphenylene sulfide as material of construction
compsite membranes
Electrochemical Processes
52M M Sharma, ICTM M Sharma 52ICT
Nanofiltration (NF) for Removal of Pesticides
Fenobucarb, Propyzamide, Chlorothalonil, Isoxathion, Tricyclazole, Carbaryl,
Mefenacet, methyldymron, chloroneb, esprocarb and propiconazole (11 in all)
have been tested. The highest desalting membrane rejected all pesticides at
more than 92.4%, except tricyclazole.
The removal of pesticides, nitrates and hardness from ground water has been
considered. Nitrate concentration has to be below 50 mg per litre and removal of
hardness is desirable for reasons of comfort. NF removes pesticides and nitrate
and hardness simultaneously and thus one step process can be adopted. Atrazine,
simazine, diuron and isoproturon were pesticidal impurities and NF70, NF45, UTC-
20, UTC-60 membrane were used and all of them removed pesticides
satisfactorily and hardness is also efficiently removed. However, nitrate removal is
not satisfactory except in NF70 where it is 76%. NF is an economically attractive
proposition.
53M M Sharma 53ICT
Nanofiltration (NF)Recovery of Amino Acids from Aqueous Solutions
Recovery of L-phenylalanine (LPA) and L- aspartic acid (LAA) from aqueous
solutions with commercial NF membranes, ENSA 2 and ES20 ( from
Hydranautics Corporation and Nitto Denko Corporation) has been reported.
The rejections of LPA and LAA by ESNA 2 were about 0 and 90% respectively,
at the value ranging from 4 to 9. By contrast ES 20 provided rejections of both
compounds at almost 100% irrespective of the pH value. Thus not only LPA
and LAA can be recovered but also separated by choosing proper membrane
and operating conditions. The feed concentration of amino acids were below
at 200 kg. per m3
54M M Sharma 54ICT
Nanofiltration Based Diafiltration Process for Solvent Exchange in Pharmaceutical Manufacturing
Athermal solvent exchange from one organic synthesis step to next step is
highly desirable in bulk pharmaceutical manufacturing due to the
thermally labile nature of the active intermediates. Diafiltration (DF) has
been employed using methanol as the solvent needed in the next
synthesis step to drastically reduce the concentration of ethyl acetate
used as the solvent in the previous synthesis step. Ethyl acetate was
reduced to the level of a low concentration impurity in methanol by both
batch ad continuous DF using solvent resistant nanofiltration membranes
MPF-50 and MPF-60; the latter has a high rejection of around 96% for the
solute, erythromycin, representing an active intermediate.
55M M Sharma 55ICT