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