WO2011055381A1

WO2011055381A1 - Electrodialysis-distillation hybrid process for the recovery of dimethylsulfoxide (dmso) solvent from industrial effluent

Info

Publication number: WO2011055381A1
Application number: PCT/IN2010/000708
Authority: WO
Inventors: Sridhal Sundergopal; Potulapally Ramalu Cheekapally; Venkata Lakshmi Ravikumar Yerrapragada; Sreedhara Menon Raghunandanan Kunduvelil; Giridhara Chalapathi Rao Mannava; Sunitha Kammara; Vishwanadham Boinee
Original assignee: Council Of Scientific & Industrial Research
Priority date: 2009-11-04
Filing date: 2010-10-29
Publication date: 2011-05-12
Also published as: JP5909190B2; WO2011055381A8; GB2487515A; GB2487515B; CA2779656C; GB201208394D0; JP2013510082A; CA2779656A1

Abstract

The invention relates to the removal of the impact-sensitive and hazardous sodium azide (NaN₃) salt along with ammonium chloride (NH₄Cl) for the recovery of dimethyl sulfoxide (DMSO) solvent present in a pharmaceutical industrial effluent generated during the manufacture of antiretroviral drugs. The wastewater cannot be directly distilled for DMSO recovery in the presence of NaN₃, which could cause explosions. Moreover, disposal of the DMSO increases the chemical oxygen demand (COD) load on the effluent treatment plant (ETP). The developed process includes pretreatment of the effluent for the removal of colloidal impurities and suspended solids followed by electrodialysis using cation and anion-exchange membranes stacked alternately for reduction of the salts concentration to ppm levels. The desalted liquor is then subjected to two vacuum distillation steps for recovering pure DMSO solvent.

Description

ELECTRODIALYSIS-DISTELLATION HYBRID PROCESS FOR THE RECOVERY * DIMETHYLSULFOXIDE (DMSO) SOLVENT FROM INDUSTRIAL EFFLUENT

FIELD OF INVENTION

The present invention relates to the development of a suitable integrated process for the recovery of dimethyl sulfoxide (DMSO) from industrial effluents using membrane based electrodialysis and distillation process.

The present invention further relates to the separation of DM$0 from industrial process solution containing undesirable components such as salts (sodium azide and ammonium chloride) and small amount of color imparting substances.

BACKGROUND OF THE INVENTION

Reference may be made to patent US5746920, Mani, issued on 25th. September, 2001, which describes an apparatus and the process producing salts by an electrodialysis operation.

Reference may be, made to patent US 5324403, Baltazar, Varujan Jamaluddin Abul K.M, Kennedy, Mark W, Nazarko, Taras W, issued on 28^th June 1994, which describes a method for the selective removal of alkali metal salts of sulphate (SO₄ ^2'), and thiosulphate (S₂O3^2') from hydrogen sulphide (¾S) scrubber solutions of the liquid redox type using an electrodialysis system. In the process of this invention the H₂S scrubber solution is directed to the diluting compartments within an electrodialysis stack, while collecting a solution with a minimal initial salt content. With the application of a direct current, a portion of the alkali metal salts of sulphate and thiosulphate present in the scrubber solution are transported through ion selective membranes into the collecting solution. Reference may be made to patent US 3755134, Francis, Leo H., Treleven, Gerald J, issued on 28^th August 1973, which relates to an electrodialysis apparatus for reducing the mineral salt content of liquid materials having dispersed organic constituents (e.g., whey).

Reference may_. be made to patent US 5145569, Schneider, Michael, Miess, Georg E, issued on 8^th September 1992, which relates to a process for desalting mixtures of water and water-soluble highly active organic solvents which contain metal salts. This process comprises subjecting the mixtures to electrodialysis employing commercially available ion exchanger membranes.

Reference may be made to U.S. Pat. No 4802965, Puetter, Hermann, Roske, Eckhard, issued on 7^th February 1989, which relates to concentrating the aqueous solutions of organic compounds that contain salts, with simultaneous reduction of the salt content. Aqueous solutions of organic compounds which contain salts are concentrated by electrodialysis with simultaneous reduction of the salt content of these solutions.

Reference may be made to U.S. Pat. No 7351311, Windecker, Gunther, Week, Alexander, Fischer, - Rolf-Hartmuth, Rosch, Markus, Bottke, Nils, Hesse, Michael, Schlitter, Stephan, Borchert, Holger, issued on 1^st April, 2008, which relates to a continuous process for distillative purification of tetrahydrofuran (THF).

. Reference may be made to U.S. Pat. No 4613416, Kau. Heinz Russow. Jurgen. issued on 23rd September. 1986. which relates to application of the process of electrodialysis for concentrating the sulfuric acid containing an alkali metal sulfate, sulfuric acid and alkaline earth metal ions.

Reference may be made to patent US 6627061, Mani, K. N. issued on 30th September. 2003. which describes an apparatus and process produces salts by an electrodialysis operation. The divalent metals are removed by nanofiltration and further sent to electrodialysis to remove multivalent cations.

Reference may be made to patent US 6294066, Mani. K. N. issued on 25th September. 2001, that relates to a process that produces salts by electrodialysis operation by nanofiltering the incoming feed to remove divalent metals.

Reference may be made to patent US 4770748, Cellini. John V. Ronghi. Mario F.Geren. James G, issued on 13th September. 1988. which discloses the application of an improved vacuum distillation system for purifying contaminated liquids, such as seawater, brackish water and chemical effluents.

Reference may be made to patent US 4390396, Koblenzer. Heinz, issued on 28th June. 1983, that relates to an apparatus for the distillation of vaporizable liquids, more particularly, to an energy- conserving distillation system of compact construction for the distillation of vaporizable liquids of all types.

Reference may be made to patent US 4233120, Finlay-Max ell. David, issued on 11^th November 1980, which relates to solvent-recovery processes and provides a method and apparatus whereby substantial heat economy may be achieved in the recovery of a solvent which is soiled by its use in, for example, a dry-cleaning operation, or which in use has become mixed with another solvent.

Reference may be made to patent US 5312524, Barcomb, Lyle.B, issued on 17^th May, 1994, that refers to a distillation system for recovery of volatile components of contaminated liquids used in an industrial process. The literature available from patents describe only the removal of organic or inorganic salts from the industrial process solutions. A proper process is absent for the recovery of valuable solvents present in the pharmaceutical effluents.

Therefore with increasingly strict environmental regulations, industrial effluents require extensive treatment prior to their safe disposal. Moreover, some of these effluents, especially from

)

pharmaceutical industries may contain valuable solvents, which need to be recovered.

Hence there still remains, a need for an improved, cost effective and practical method for the removal of inorganic salts, azide and also color imparting organic compounds present if any, particularly from these types of effluents which contain valuable solvents.

OBJECTIVE OF THE INVENTION

The main objective of the present invention is to provide a process for the recovery of DMSO solvent from a pharmaceutical effluent, useful in bulk drug manufacture.

An object of the invention is to provide a multi-stage process to facilitate maximum possible recovery of the DMSO.

Another objective of the present invention is to remove the ammonium chloride and sodium azide salts present in the pharmaceutical effluent. ->

Yet another objective of the present invention to provide a vacuum distillation apparatus and a method capable of effectively separating liquid mixture components.

Yet another objective of the present invention to provide a process which is able to isolate pure DMSO, as simply as possible and with a high yield, from the desalted liquor obtained from electrodialysis.

Yet another objective of the present invention is to identify the process required to achieve the maximum recovery of the DMSO with minimum losses.

Yet another objective of the present invention is to achieve around 99.8 % of DMSO.

Yet another objective of the present invention is to produce not only as much pure DMSO as possible but at the same time to produce a correspondingly small amount of residue requiring landfill or incineration. ¹ BRIEF DESCRIPTION OF THE DRAWINGS:

FIG.l: Represents the schematic process flow diagram for recovering DMSO from industrial effluent. FIG.2: Represents electrodialysis (ED) stack arrangement.

FIG.3: Represents migration of ions to its respective electrodes.

FIG.4: Schematic showing the description of the whole process.

FIG.5: Graph representing variation of current with time

FIG.6: Graph representing variation of concentration with time

FIG.7: Graph representing variation of concentration with time of all three solutions.

FIG.8: Overall material Balance for a four ED runs and subsequent distillations to recover pure DMSO.

SUMMARY OF THE INVENTION:

Accordingly, present invention provides an electrodialysis-distillation hybrid process for the recovery of pure dimethyl sulfoxide (DMSO) from industrial effluents and the said process comprising the steps of:

i. prefiltering the effluent by passing through the micron filter cartridge to remove the suspended solids followed by an activated carbon column to reduce color and to obtain diluate of conductivity ranging between 15 to 25 mScm^"1;

ii. circulating rinse solution of conductivity ranging between 20-35 mScm^'1 across the electrodes of the electrodialysis stack system followed by diluate as obtained in step (i) and concentrate solutions of conductivity ranging between 1 to 2 mScm^"1 to the electrodialysis stack system until the conductivity of the diluate solution dropped to 0.06 mScm^"1 to obtain desalted diluate;

iii. charging desalted diluate as obtained in step (ii) into two distillation column to obtain water as distillate and impure DMSO as bottoms in the first stage and followed by second distillation to recover colorless pure DMSO as distillate and heavy impurities as bottoms.

In an embodiment of the present invention, industrial effluents contain NaN₃, NH₄CI salts, water, non-volatile heavy organic compounds and small amount of color imparting substances.

In an another embodiment of the present invention, concentration of DMSO in effluent is ranging between 12 to 20 wt%.

In yet another embodiment of the present invention, concentration of NaN₃ and NH4CI in pharmaceutical effluents is ranging between 0.5 to 2 wt%.

In yet another embodiment of the present invention, diluate containing DMSO, NaNj, NH4CI and water. In yet another embodiment of the present invention, concentrating solution contains tap water that contains total dissolved solids (TDS) between 0.03 and 0.19%.

In yet another embodiment of the present invention, rinse solution contain 2.0 to 3.0 % by weight of aqueous solution of sodium bisulphate.

In yet another embodiment of the present invention, electrolyte used in the concentrate is an aqueous solution of a common salt such as sodium chloride which will allow electrical conduction.

In yet another embodiment of the present invention, the flow rate of diluate, concentrate and rinse solution across the membrane stack is ranging between 0.9 and 0.1 liters per second.

A process as claimed in claim 1, wherein said process is carried out in a continuous mode with the solution recycled back.

In yet another embodiment of the present invention, recovery percentage of DMSO is ranging between 88 to 90% and purity percentage is ranging between 99.5 to 99.8%.

In yet another embodiment of the present invention, the re-boiler temperature in the first distillation column varied between 30 and 75 °C, the reflux ratio was varied from 1:5 to 1:15 and the overhead temperature was maintained between 30 and 32 °C using chilled water available at 5°C.

In yet another embodiment of the present invention, the re boiler temperature in the second distillation column varied between 45 and 120°C, the reflux ratio was varied between 1:5 and 1:15 and the overhead temperature varied between 30 and 95°C.

In yet another embodiment of the present invention, the composition of the low boilers leaving the first and second distillation column is determined by a gas chromatograph using a Tenax column, thermal conductivity detector and hydrogen carrier gas with the oven temperature initially maintained at 70°C for 5 minutes and programmed to reach 230°C at the rate of 10°C per minute. In yet another embodiment of the present invention, stages of distillation set up consists of electrically heated 20 L still over which mounted a 3" glass column packed with 25mm ceramic rasching rings and the height of the packing is about 5' ,wherein the DMSO can be separated efficiently with high degree of purity from water. DETAILED DESCRIPTION OF THE INVENTION

The process of the present invention is particularly directed towards the recovery of solvents generally seen as waste byproducts to be incinerated without energy recovery or deposited in protected dumps. The idea that led to the solution of the above problem was that of initially removing the dissolved salts by electrodialysis and further treating the obtained desalted aqueous DMSO solution by distillation for recovering pure DMSO.

Present invention provides a hybrid process including electrodialysis and a simple distillation process to achieve this object.

The present invention generally relates to a process of reducing the salts present in aqueous DMSO effluent, and to use the products obtained by such process. More specifically, the present invention relates to subjecting the effluent containing 2% salts (sodium azide and ammonium chloride) to an electrodialytic treatment to produce an aqueous DMSO solution having a reduced content of salts. The present invention accordingly provides a two stage process of distillation for recovering pure DMSO from the desalted diluate of electrodialysis process.

The process of this invention is further illustrated by making reference to an example of aqueous DMSO distillation carried out in a conventional distillation column operated under vacuum. The process of this invention could, however, be carried out under different conditions, and by using distillation columns designed for varying pressure operation and adjusting the experimental parameters in ways well known to the persons skilled in the art.

Present invention relates to a process for the recovery of DMSO from industrial process solution containing undesirable components such as ammonium salts, sodium azide and small amounts of inorganic color imparting substances. These salts can be removed by membrane based electrodialysis technique to obtain desalted liquor wherein the said process comprising the steps of pre filtration of feed before it is fed into ED system to remove the suspended solids. The pre filtered solution as a feed solution through the electrodialysis system (ED system) containing alternate cation, anion membranes stack with simultaneous application of direct current to enhance separation of ions towards the respective electrodes, wherein the solution is substantially devoid of the salts and undesirable components to obtain desalted liquor.

FIG.l shows the schematic process flow diagram for recovering DMSO from industrial effluent. In brief, effluent from the storage tank is charged for pre filtration process to remove the suspended solids. Pre-filtration followed by the electrodialysis system for separation of salts, for example ammonium chloride and sodium azide from the aqueous solution.

Electrodialysis stack system contain at least 10 alternate anion and cation exchange membranes in a parallel arrangement between anode and cathode electrode plates, electrodialysis stack system also consist of diluating compartment, a concentrating compartment and a rinse compartment where all the three ED compartment solutions are operated under re-circulation mode. Diluating compartments and concentrating compartments arranged in alternate fashion to provide an effective area of 0.525 m 2 area each of cation and aniori-exchange membranes. DC potential between 50 and 70 V is applied across the stack to generate an average current of 3-4 A. Electrodialysis operation results in separation feed as diluate and concentrate. The process depicted in FIG.1 also represents the 2- stage distillation operation, where in water and (DMSO+ Impurities) is obtained in the first stage and followed by second distillation results in recovering colorless DMSO as distillate and heavy impurities as bottoms. However, in the industrial processes of use in the practice of the invention, the entire process may be conducted in a continuous mode with the solution recycled back to the respective tanks. Accordingly, in consequence, the feed composition will vary with time as will the diluate and concentrate tanks.

FIG. 2 represents electrodialysis stack arrangement for desalting the effluent. The desalting electrodialysis cell stack (1) is comprised of at least ten pairs of anion (2) and cation (3) exchange membranes creating diluate and concentrate compartments between the two electrodes anode (A) and cathode (C) electrodes. DC power supply (4) provides the driving force for separation through the arrangement of cell pairs, four of which are indicated as (5) in the Figure. Each cell pair comprises of one cation and one anion exchange membrane. The stack is arranged in a systematic manner, in the form of chambers, such that each chamber consists of respective number and arrangement of gaskets, distributors with alternate membranes. The cation exchange membranes may be of weak acidity (carboxylic acid exchange groups), moderate acidity (e. g. phosphonic acid type), or strongly acidity (e. g. sulfonic acid cation exchange groups). The cation and anion exchange membranes must be stable under the physical and chemical conditions applied in electrodialysis cell; the membranes should have a low resistance in the solution to be dialyzed, high flux and low fouling by colloidal and suspended materials. These may include perfluorinated membranes such as Dupont Nafion. RTM. or any non-perfluorinated cation exchange membrane such as Neosepta, CMX. The anion exchange membranes may be strongly, mildly, or weakly basic and comprised of quaternary or tertiary ammonium groups. This type of membrane will improve the current efficiency of the process by preventing back-migration of protons from the concentrate compartment to the feed compartment. FIG.3 represents migration of ions to the respective electrodes. This Figure diagrams the desalting ED process and the membrane configuration in the ED membrane cell stack used for separating dissolved inorganic salts from pharmaceutical effluent containing DMSO and the dissolved salts such as sodium azide and ammonium chloride. The components of the electrodialysis cell stack (10) include an anode (A) and cathode (C) electrodes rinsed with an electrolyte, having four diluate compartments (Di,D_2, D₃p₄) and three concentrate compartment (Ci,C₂,C3) disposed between the 0 000708

anode and cathode wherein the feed and concentrate compartments are separated by alternating cation and anion exchange membranes, (13) and (14), respectively. ED stack arrangement is shown in FIG. 2 and the movement of positive and negative ions through four membrane cell pairs of the stack is described in FIG. 3 which is an enlarged view of the separation process occurring in indicated part (5) of FIG. 2.

FIG. 4 shows the process utilizing an electrodialysis system and two distillation columns connected in series. Typically, the feed solution derived from the pharmaceutical industry comprises DMSO, water and inorganic salts. A pretreatment step for the feed solution comprises the following: (i) -filtration to remove particulates; (ii) carbon treatment to adsorb color bodies and other organic impurities. The process according to the invention is advantageously carried out initially by prefiltering the pharmaceutical effluent containing suspended solids by passing through the activated carbon and micron filter and then sending to the electrodialysis stack containing alternate anion and cation exchange membranes between two anode and cathode electrode plates made of stainless steel SS 316 L containing 3% molybdenum in a parallel arrangement, sealing the compartments formed by inserted spacer frames off against each other, passing the filtered effluent with salts (diluate) whose initial conductivity is between 15 to 25 mScm^'1 through the feed compartments which are limited in the direction of the anode via an anion exchange membrane, and passing tap water (concentrate) whose initial conductivity is from 1 to 2 mScm^"1 through those compartments limited in the direction of the anode by a cation exchange membrane to receive the salt. The electrolyte used in the concentrate is in general an aqueous solution of a common salt such as sodium chloride which will allow electrical conduction. During the electrodialysis process, an electrolyte-containing solution is preferably guided past the electrodes in order to remove gases which form from the electrode compartments. The electrode rinse used is advantageously an aqueous solution which contains about 2.5 wt% of sodium bisulfate. The preferably obtained desalted diluate from the electrodialysis is charged to the distillative process carried out in two columns connected in series as shown by the Figure 4 for the purification of water- containing DMSO.

Introduction of the feed into the first column is effected at the side through the inlet (4). The inlet (4) is conveniently disposed into the re-boiler of the column. Then the re-boiler is heated to a temperature in accordance to the boiling point of the lighter component present. The lighter component being water vaporizes through the packing material and is condensed and collected as the distillate of the first distillation column. The left out heavier components being DMSO remains as bottoms of the first distillation column. These bottoms of first distillation column are sent to the second distillation column (3) via line (l_s) as feed. The feed of the second distillation column is heated in its re-boiler to a temperature above its boiling point and is vaporized through the packed column and condensed in the condenser and collected as colorless DMSO and the leftover bottoms are collected as heavier compounds via line (lio).

FIG. 4 show the flow of solution across the equipment involved in the inventive process for the recovery of DMSO from pharmaceutical industrial effluent. The Figure shows the step wise procedure of obtaining pure DMSO. In the process, dissolved salts in the effluent are desalted by the electrodialysis process. Then it is further sent to the distillation column for recovering DMSO.

The pharmaceutical industrial effluent containing 2 % sodium azide and ammonium chloride salts and 15 % DMSO with a conductivity ranging between 15-25 mScm. is stored in the storage tank (4) and is pumped to the micron filter (5) through the line (lj) to filter the suspended solids present in the effluent and then sent to the activated carbon column (6) to absorb the contaminants present in the effluent and is sent to the diluate tank (7). The concentrate tank (9) is filled with 10 liters of tap water having conductivity of about 1-2 mScm^'1 Prepared 10 liters of 2.5 % sodium bisulphate solution in distilled water is charged to the rinse tank (8) having a conductivity in the range 20-35 mScm^"1. Initially the rinse solution is circulated across the electrodes of the electrodialysis stack (1) with a known flow rate through pump via line (I3), and then the diluate and concentrate solutions are pumped to the electrodialysis stack (1) through lines (1₂) and (I4) respectively at same flow rates ensuring almost equal pressure drops. After stabilizing the flow an electrical potential was applied through DC (14) across the stack to attain a specific current density for a desired period. All the solutions were circulated through the ED stack until the conductivity of the diluate solution dropped to 0.06 mScm.^'1, to ensure that salt-free diluate solution is sent to the first distillation column (2). The desalted diluate solution containing water and DMSO of tank (7) is charged to the re-boiler of the first distillation column (2) through line (1₅) and heated to a temperature of low boiling component water and is evaporated through the column and collected as distillate in (10) via line (1₇). The bottoms of the first distillation column (2) that is left out with colored DMSO is stored in storage tank (11) through line (1₆) and this is sent to the bottoms of the second distillation column (3) via line (l_g) and heated at high temperature corresponding to the vacuum applied and is distilled through the column (3) and the colorless DMSO is collected as distillate product with a purity of 99.8% in the tank (12) via line (1₉). And the left oyer bottoms of the second distillation column (3) are heavier components.

Re boiler temperature in the first distillation column varied between 30 and 75 °C, the reflux ratio was fixed at 1: 15 and the overhead temperature was maintained between 30 and 32 °C using chilled water available at 5°C. Re boiler temperature in the second distillation column varied between 45 and 120°C, the reflux ratio was fixed at 1:15 and the overhead temperature varied between 30 and 95°C.

In the present invention the feed solution is tested at applying different voltages like 30V, 40 V, 50V, 60V and 70V to find the optimum voltage and current density to be known for the separation of salts in the ED process. The conductivity of the solutions is determined after a definite interval of time, say, 20 or 30 minutes using a digital conductivity meter since the extent of loss of salts from the feed is estimated in accordance to the conductivity of the solutions.

We assume that all the salts have been removed from test solution when the conductivity reaches 0.08 or 0.09 mScm.^'1.

In described process, five batches of 16 kg each of the desalted liquor from electrodialysis unit are fed into the first distillation column of height 100 cm and diameter 7.5 cm packed with glass raschig rings to remove water as the distillate under a vacuum between 30 and 40 mmHg to obtain 16 kg of DMSO-rich residue in the re-boiler of 20 L capacity. 1 L of the concentrated residue from the first distillation column is fed into a second distillation column of design similar to that indicated in claim 1 , but operated under a vacuum between 20 and 30 mmHg to initially remove water as the first fraction followed by recovery of 11.28 kg of colorless DMSO of purity > 99.5 % as the second fraction to yield a final residue of 0.72 Kg in the re-boiler that is enriched in nonvolatile color imparting organic compounds and is sent for incineration.

The process of the invention involves membrane cleaning and maintenance to prevent its fouling and keep the system at good efficiency and long working life.

Gleaning procedure:

• It is recommended to wash the stack with solution comprising of 1 % TSP, 0.5 % EDTA and 0.5 % w/v sodium lauryl sulphate (SLS) in distilled water for 15 minutes.

• The former is followed with tap water wash for 15minutes.

• Successively an acid wash is given for 30 minutes, this is achieved by making a solution of 2 % v/v HC1 in tap water, which helps in removal metal salts and mineral scales and subsequently better electrical conductivity of the system.

• Finally a water wash is given for 15 minutes.

Routine repetition of the above mentioned last 3 steps after each run of electrodialysis will ensure better performance of the system in terms of batch time reduction. An example was taken for instance to note the trend followed by current w.r.t varying time. From the graph it can be depicted that as the time passes the current decreases as the ions migrate from the diluate tank.

Similarly, variation of pH and conductivity with change in time was also noticed for all the three tanks. It has been observed that, the time passes, the conductivit and pH of the diluate tank decreases which can be because of loss of salts from the tank and that of concentrate tank increase linearly for some time and then remain constant. In the case of rinse tank both conductivity and pH remain almost constant through out the experiment. A digital conductivity meter is used to analyze the concentration of total inorganic salts present in the diluate, concentrate and rinse solutions and a digital pH meter is used to assess the pH of the three solutions at regular intervals of time between 0 and 4 hours.

Data was collected using an experimental ultrex ion exchange membranes of area for batch or continuous operation. All runs were conducted at potential difference between 30V - 70V.

The following examples are given by way of illustration of the working of the invention in actual practice and therefore should not be construed to limit the scope of present invention in any way.

EXAMPLE 1

An electrodialysis device of the type as essentially outlined was used for the electrodialysis treatment of the pharmaceutical effluent stream. The resin solution had a salt content of 2 % by weight, a conductivity of 15-25 mScm^and the treatment was started at a temperature of 30 degree C.

10 liters of filtered feed solution (effluent) containing 2% salts (sodium azide + ammonium chloride) in 15% aqueous dimethylsulfoxide (DMSO) was taken in the diluate tank. 10 liters of tap water was taken in the concentrate tank to facilitate conductivity and ion transfer. 7 liters of 2.5% sodium bisulphate (w/v) was taken in the rinse tank to rinse both the electrodes.

After filling tanks with its respective solutions, control valves were adjusted to maintain equal flow rates in diluate and concentrate tanks ensuring almost equal pressure drop. All the solutions were pumped continuously through the electrodialysis stack at controlled flow rates. After stabilizing the flow an electrical potential was applied across the stack to attain a specific current density for a desired period. Initially a voltage of 30 V was applied through direct current and achieved current in the range of 0-4 amps due to high conductivity (24.9 mScm^'1) of the diluate solution. About 30 ml of samples of outlet streams of the three solutions were collected every 1 hr to determine the conductivity of salts by digital conductivity meter and back transferred into their respective tanks to maintain the constant volume through out the experiment. This process continued until the diluate T IN2010/000708

conductivity of 0.07 mScm was reached. Since the amount of salt depleted in the diluate tank is measured through electrical conductivity of the solution. The flow rates of diluate solution concentrate solution and rinse solution are 252.72 L hr^"1, 258.48 L h ¹ and 568.8 L hr^"1 respectively. Voltage Applied: 30V.

The first trial lasted for approximately 18 hours. The results are as reported in Table 1.

Table 1: Experimental data

tank. During the test, the conductivity levels in the diluate decreased, while these levels increased in the concentrate, this is due to the transport of salts from the diluate tank to the concentrate tank.

As the initial conductivity of the feed was very large and the applied voltage was only 30 V this experiment has taken a long time (more than 18 hrs) to reach a final conductivity of 0.07 mScm^"1. In this example, it was observed that the reduction in diluate conductivity was rapid until the solution reached a conductivity of 0.1 mScm^"1 beyond which the process of ion transfer was taking a long time to reach a conductivity of 0.07 mScm^*1.

This was due to decrease in the current as a result of depletion in ion concentration. Further, the organic solvent DMSO that remains in the diluate is substantially prevented from being transported through the membrane. ^' . ^"

EXAMPLE 2 ,

s

The Example 2 was repeated as said in the first test with the same filtered effluent and the same ED stack and the same membranes. Ten liters of, the filtered effluent having a conductivity of 23 mScm^"1 was processed through the E stack for the transfer of salts present in the diluate solution at an applied voltage of 40 V. The flow rates of diluate solution concentrate solution and rinse solution are 293.724 L.h ', 309.456 L.h 'and: 498.96 L.hr ¹ respectively.

Voltage Applied: 40V

Table 2: Experimental data

This trial lasted for 750 minutes. As the initial conductivity of the diluate solution was very large in this case also and the applied voltage was only 40 V this experiment has taken a long time (more than 12 hrs) to reach a final conductivity of 0.06 mScm^"1. EXAMPLE 3

This test also follows the same procedure as said in the example 2. In this example, the initial conductivity of the diluate solution was 18.8 mScm^*1 and the applied voltage was 60 V. The electrodialysis process was continued until the diluate conductivity reached 0.07 mScm ^"'.

The flow rates of diluate solution concentrate solution and rinse solution are 252.72 L-hr^"1, 256.608 L.hr^"1 and 571.32 L.hr ^_1 respectively. Voltage Applied: 60V

Table 3: Experimental data

As the initial conductivity of the diluate solution was 18.8 mS/cm in this case and though the applied voltage was 60 V this experiment has taken 11 hr to reach a final conductivity of 0.07 mScm^'1. In comparison of this experiment with example 1, the observation was that the flow rates of all the tanks being almost same and the applied voltage being doubled to 60 V, there is drastic decrease in time to reach a conductivity of 0.07 mScm^'1. So it can be concluded that at a higher voltage the transfer of ions is faster.

EXAMPLE 4 This test also follows the same procedure as said in the example 2. In this example, the initial conductivity of the diluate solution was 1 .9 mScm-l and the applied voltage was 40 V. The electrodialysis process was continued until the diluate conductivity reached 0.054 mScm-l

The flow rates of diluate solution concentrate solution and rinse solution are 252.72 L.hr^"1, 256.608 L-hr^'1 and 571.32 L.hr^"1 respectively.

Voltage Applied: 40V

Table 4: Experimental data

In this example, though the flow rates are same as mentioned in example 3 and a little less conductivity of 16.9 mScm^"1 and the applied voltage was 40 V, it took more than 13 hrs to reach a conductivity of 0.058 mScm^'1. So at low voltage the transfer rate of ions is slow.

EXAMPLE 5 This test also follows the same procedure as said in the example 2. In this example, the initial conductivity of the diluate solution was 23 mScm^"1 and the applied voltage was 40 V. The electrodialysis process waScontinued until the diluate conductivity reached 0.054 mScm^"1

The flow rates of diluate solution concentrate solution and rinse solution are 252.72 L.hr \ 256.608 r

L.hr^"1 and 571.32 L.hr^_1 respectively.

Voltage Applied: 40V

Table 5: Experimental data

In this example, though the flow rates and applied voltage of 40V are same as mentioned in example 4, as the initial conductivity of the diluate solution is 23 mScm ^"1, this experiment has take a very long time of more than 19 hrs to reach a conductivity of 0.05 mScm^"1. One reason for this long time may be due to high initial conductivity of 23 mScm^"1 but after reaching a conductivity of 0.54 mScm^"1 the current came down to 0.4 A and to reach a conductivity of 0.05 mScm^"1 form 0.19 mScm^"1 it almost took 3 hrs.

These observations of this example demonstrate the progressive decrease in the current throughput arising from presence of the salts in the feed stream and their transport.

This example involved unscheduled downtime and reduced process throughput with the potential for mechanical damage to cell hardware due to heating, meltdown etc. There is also potential long term damage to the membranes as a result of heavy surface precipitation, blistering, etc.

The cell was opened and inspected after the above experiments conducted on the electrodialysis stack. Except the end cation and anion exchange membranes that were adjacent to anode and cathode electrodes remaining membranes were in excellent condition without any physical evidence of fouling. The end cation and anion membrane was cloudy/ opaque and appeared to be fouled because they were badly affected by the gases formed at the electrodes during the experiment. The internal parts of the cell were clean, because the high retention of the ions. The precipitation problems will undoubtedly occur with higher levels of the salt concentration present in the feed stream, or higher process conversions.

All the membranes were well washed wmYa solution containing 1 % TSP (Tri Sodium Phosphate), 0.5 % EDTA and 0.5 % SLS (Sodium Lauryl Sulphate) in distilled water for a long time. The membranes were neatly wiped out and restacked without replacing any membranes.

EXAMPLE 6

This example was also performed with the same procedure as said in the above examples. In this example the initial conductivity of the diluate solution was 23 mScm^"1 and the applied voltage was 50 V. The electrodialysis process was continued until the diluate conductivity reached 0.054 mScm^"1. The flow rates of diluate solution concentrate solution and rinse solution are 324 L.hr ¹, 328 L.h ¹ and 324 L.hr.-1 'pectively.

Voltage Applied: 50V

The resultsters are as follows in Table 6.

Table 6: Experimental data

Time Diluate Concentrate ' Rinse Voltage Current

(min) Conductivity pH Conductivity pH Conductivity PH (V) (A)

Pumps ON 19.7 8.9 0.58 6.3 25.6 3.05

DC Power ON ^■ -. - - - - - 50 7.5

0 19.2 8,85 2.0 3.83 25.2 3.02 50 7.8 30 13.8 8.83 11.6 5.83 22.2 3.08 50 8.1

60 7.1 8.81 19.9 6.02 19.4 3.14 50 5.0

90 3.6 8.87 23.2 6.14 18.8 3.1 50 2.4

120 1.92 8.57 25.4 6.28 19.9 3.07 50 1.3

150 0.88 6.82 25.8 6.4 19.3 3.07 50 0.9

180 0.36 5.46 26.6 6.51 19.4 3.09 50 0.8

195 0.21 4.98 26.2 6.52 18.9 3.05 50 0.4

210 ^' 0.15 4.58 27.0 6.55 19.4 3.09 50 0.3

240 0.12 4.41 27.0 6.55 19.1 3.10 50 0.25

260 0.11 4.40 26.5 6.54 19.1 3.09 50 0.20

270 0.11 - - - - - - DC OFF

09/05 0.74 - - • - - - - -

Before ED was ON

DC ON . 0.36 5.19 26.0 6.32 18.54 3.14 50 0.75

290 0.21 4.98 26.0 6.25 18.7 3.14 50 0.50

310 0.09 4.6 26.1 6.22 18.3 3.06 50 0.4

340 0.07 5.54 26, 1 6.2 18.26 3.13 50 0.3

In this example, as initial conductivity of the diluate solution was 19.7 mScm^'1 and the applied voltage was 50 V, this experiment has taken 5 hr 40 min to reach a final conductivity of 0.07 mScm^"1 by operating the three solutions at same flow rates. In comparison of this experiment with the previous examples, the observation was that there is drastic decrease in time to reach a conductivity of 0.07 mScm^'1 and also the initial current was very high at 50V voliters, which was not observed in the previous examples. So it can be concluded that the experiment is fetched by the acid wash given to the membranes.

After this experiment was over the ED stack was given tap water wash followed by 1% HCl wash for about 30 min each. This is because, 1% HCl wash for about 30 min after every run with effluent is fetching the experiment time and also the life of the membranes is maintained high.

EXAMPLE 7

This example was also performed with the same procedure as said in the above example 6. In this example the initial conductivity of the diluate solution was 16.55 mScm^'1 and the applied voltage was 50 V. The electrodialysis process was continued until the diluate conductivity reached 0.08 ,mScm^"' The flow rates of diluate solution concentrate solution and rinse solution are 324 L.hr^'1, 328 L.hr^'1 and 324 L.hr^"1 respectively.

Voltage Applied: 50V

The results are as follows in Table 7. Table 7: Experimental data

This experiment has take less time, 4 hr 15 min to reach final conductivity of 0.08 mScm^'1 when compared to the previous experiment of example 6, this is because in this case the initial conductivity of the diluate solution was less (i.e.) 16.55 mScm^"1.

After this experiment was over the ED stack was given acid wash followed by 1% HCI^' wash for about 30 min each so as to make the ED stack ready for the next experiment.

EXAMPJLE 8

This example was also performed with the same procedure as said in the above examples. In this example the initial conductivity of the diluate solution was 16.68 mScm^'1 and the applied voltage was 50 V. The electrodialysis process was continued until the diluate conductivity reached 0.07 mScm^*1 The flow rates of diluate solution concentrate solution and rinse solution are 324 L.hr^'1, 328 L-hr^'1 and 324 L.hr^"1 respectively.

Voltage Applied: 50V

The results are as follows in Table 8.

Table 8: Experimental data

Time Diluate Concentrate Rinse Voltage Current (min) Conductivity pH Conductivity pH Conductivity pH (V) (A)

Pumps 16.68 8.76 0.57 5.90 29.0 1.67 - - ON

DC Power - - - - - - 50 8.0 ON 0 16.-72 8.81 1.56 2.50 29.0 1.69 50 7.5 _.

35 10.40 8.64 49.8 5.08 24.5 1.77 50 5.5 .

65 6.28 8.66 27.5 5.37 23.8 1.72 50 3.5

80 4.36 8.64 31.0 5.55 23.1 1.70 50 2.6

110 2.33 8.42 33.0 5.74 23.0 1.71 , 50 1.6

140 1.18 6.87 36.1 5.95 22.5 1.69 50 1.0

165 0.54 4.86 36.9 6.16 22.3 1.69 50 0.8

195 0.18 3.96 36.8 6.44 22.1 1.72 50 ^' 0.5

210 0.10 . 3.73 36.3 6.41 22.1 1.74 50 0.5

265 0.07 3.52 37.1 6.38 21.6 1.69 50 0.5

This experimental result is almost similar to that of the experiment performed in the previous example 7, since the diluate initial conductivity, flow rates and applied voltage are same almost and also the time taken to reach the desired conductivity is 4 hr 25 min. So we can say that the results are reproduced in this example which was possible due to the maintenance of the membrane in the ED stack.

EXAMPLE 9

This example was also performed with the same procedure as said in the above examples. In this example the initial conductivity of the diluate solution was 18.68 mScm^"1 and the applied voltage was 50V. The electrodialysis process was continued until the. diluate conductivity reached 0.09 mScm^'1.

The flow rates of diluate solution concentrate solution and rinse solution are 349 L.hr \ 398 L.hr ¹ and 596 L.hr^'1.

Voltage Applied: 50V

The results are as follows in Table 9.

Table 9: Experimental data

Time Diluate Concentrate Rinse Voltage Current (min) Conductivity PH Conductivity PH Conductivity pH (V) (A) .

Pumps 18.68 8.85 2.10 7.45 26.9 2.98

ON

DC - - - - - -, 50V 9.2 ON

0 18.4 8.83 4.20 3.41 26.80 2.98 50 8.7

20 14.7 8.80 8.30 5.43 24.30 2.98 50 8.1

40 10.50 8.82 14.30 5.68 21.90 3.05 50 7.0

60 6.90 8.79 18.0 5.74 20.20 3.08 50 5.0

80 4,81 8.73 20.90 5.84 18.90 3.13 50 3.5 100 2.90 8.59 22.80 5.89 18.30 3.14 50 2.7

120 1.80 8.26 23.30 5.93 18.00 3.16 50 1.5

145 1.03 6.27 23.70 6.03 17.70 3.20 50 1.0

180 0.27 4.69 24.60 6.07 17.32 3.03 50 0.5

200 0.13 4.10 24.70 6.07 17.40 3.00 50 0.45

230 0.11 3.80 24.20 6.00 17.20 2.58 50 0.4

240 0.09 3.80 24.40 6.00 17.08 2.58 50 0.35

In this experimental the diluate initial conductivity was 18.68 mScm^'1, and the flow rates are varied and applied voltage is same 50 V. The time taken to reach the desired conductivity of 0.09 mScm^"1 is 4 hr. Though the initial conductivity was a bit high in this experiment the time taken to reach final conductivity of 0.09 mScm^{" 1} is 4 hr only. So when the flow rates are varied the time also varies.

EXAMPLE 10

This example was also performed with the same procedure as said in the above examples. In this example the initial conductivity of the diluate solution was 18.35 mScm^*1 and the applied voltage was 50 V. The electrodialysis process was continued until the diluate conductivity reached 0.07 mScm^"1. The flow rates of diluate solution concentrate solution and rinse solution are 349 L.hr^"1, 398 L.h ¹ and 596 L.h ¹.

Voltage Applied: 50V

The results are as follows in Table 10.

Table 10: Experimental data

215 0.07 4.00 22.0 5.77 18.8 2.57 50. 0.4 1

This experimental result is almost similar to that of the experiment performed in the previous example 7, since the diluate initial conductivity, flowrates and applied voltage are same and also the time taken to reach the desired conductivity is 3 hr 35 min. So we can say that the results of the previous example 9 are reproduced in this example.

EXAMPLE 11

This example was also performed with the same procedure as said in the above examples. In this example the initial conductivity of the diluate solution was 17.14 mScm^"1 and the applied voltage was 70 V. The electrodialysis process was continued until the diluate conductivity reached 0.08 mScm^"1. The flow rates of diluate solution concentrate solution and rinse solution are 324X.hr^"1,

328 L-hr ¹ and 324 L.hr^"1.

Voltage Applied: 70V

The results are as follows in Table 11.

Table 11: Experimental data

This experiment lasted for 3 hr 5 min to reach a final conductivity of 0.08 mScm^'1 having an initial conductivity of 17.14 mScm^"1. So at higher applied voltage the experiment takes less time to reach the desired conductivity.

However, there is always the potential for cohcentraiion polarization in the electrodialysis cell. It should be pointed out that the membranes should be cleaned regularly and the cell performance should be improved, as had been done on occasion in the laboratory which is described in the above discussion. Distillation columns are employed in many processes to obtain desired separations. The separations _; may range from single component to the more complex multiple separations like those performed by crude distillation towers. Typically, a feed stream containing at least first and second components is supplied to the fractional distillation column. A substantial portion of the first component contained in the feed stream is removed from the distillation column as an overhead product and a substantial portion of the second component in the feed stream is removed from the distillation process as a bottoms product. However, heat is generally supplied to the fractional distillation column in order to effect the desired separation or the feed may be preheated.

The invention is further illustrated by the following examples which, however, are not intended to limit the scope of the invention. The solutions used in the examples are aqueous solutions.

The batch distillation set-up consists of an electrically heated 20 L still over which mounted a 3" glass column packed with 25 mm ceramic raschig rings. Height of the packing is about 5". A vertical glass condenser with tube side cooling is attached on the top. Vacuum pump is attached to the column to maintain required vacuum. Unit is well instrumented to maintain and control the required reflux ratio and reboiler and condenser temperatures.

Due to difference in capacities of the ED unit and distillation column demonstration runs are conducted in the following way. Each batch of ED outlet produces about 10 kg of the diluent which consists of about 12-15 % DMSO and remaining water along with traces of some non-volatile heavy organics. As the capacity of the still is 20 liters, two batches of ED diluent is charged into the still of the column at a time. About 90 percent of the water is removed as a distillate and the residue, which is enriched DMSO that is discharged from the still and collected. Subsequently, another batch of 20 liters of the diluent is charged into the still and treated in the same way and the residue is collected. Residues thus collected from the above two steps are charged into the still and further distilled to obtain pure DMSO. In this step first water is removed as the first cut and pure DMSO with allowable of moisture content is collected as the subsequent cut. Residue left over in the reboiler is discarded. In short two ED runs produces the required feed for the first step of distillation and the residue collected from two runs of the first step of distillation produces the required feed for the second step of distillation.

The following examples are given by way of illustration to portray the efficacy of the separation characteristics of the distillation operation in separating/purifying DMSO from DMSO-water mixture as described in Figure 4.

EXAMPLE 12 10 000708

A batch of diluate solution of volume 20 liters weighing 20.04 kg is fed to a packed distillation column (2). The distillation operation is carried out under a vacuum of 30 mmHg for about 7 hrs 55 min. A vacuum pump is used to create vacuum which is supplied to the column through the condenser. A vacuum seal was also used which ensures that the column is vacuum tight. Ice is used with vacuum seal. This is because if any of the vapors penetrates the flask, they will be condensed, also ensuring the material balance. The feed charged to the distillation column contained 15.1 wt% DMSO and the rest water. During the course of the run, the reboiler and overhead temperatures are noted for every 10 min duration. The reflux ratio of 1:15 is maintained. An additional 9.1 kg of feed containing 14.75 wt% DMSO is added to the column after which the heating is resumed. After incurring a loss of 2 kg of water into vacuum seal, 17.5 kg of distillate and 9.64 kg of bottoms is obtained. The distillate obtained is pure water whereas the bottoms collected contain 80.15 wt¼ DMSO and 19.85 wt% water. The conductivity and pH of bottoms is 0.04 mScm^'1 and 6.6 respectively.

Table 12: Experimental data sheet : DMSO-water distillation.

16:30 52 31.6 1:15 30

16:45 53 31.6 1:15 30

17:00 55 31.6 1:15 30

17:15 57 32.1 1:15 30

17:30 59 32 1:15 30

17:45 63 31.6 1:15 30

17:55 60 31 1:15 30

18:00 57 30.8 1:15 30

EXAMPLE 13

A batch of diluate solution of volume 20 liters weighing 19.3 kg is fed to a packed distillation column (2). The distillation operation is carried out for a period of 5hrs 36 min under a vacuum of 25 rnmHg. A vacuum pump and a vacuum seal are used to apply vacuum to the column. The composition of the feed charged is 13.32 wt% DMSO and 86.68 wt% water. Applying a reflux ratio of 1:15, the distillation is carried out by making note of the reboiler and overhead temperatures and pressure in the column at every 10 min duration. 14.3 kg of distillate of pure water is obtained whose conductivity and pH are 0.01 mS per cm and 5.49 respectively. The bottoms whose conductivity and pH are 0.06 mS/cm and 5.51 respectively, weighing 4.8 kg consisting of 77.52 wt% DMSO and 22.48 wt% water is obtained. The loss incurred in this run is 0.2 kg water.

Table 13: Experimental data sheet: DMSO-water distillation.

Temperature (°C) Refux Pressure

Time Reboiler Overhead ratio (rnmHg)

13:15 35 31.6 1:15 25

13:30 41 20.1 1:15 25

13:45 44 31.4 1:15 25

14:00 45 29 1:15 25

14:20 45 30.2 1:15 25

14:30 45 29.8 1:15 25

14:45 45 28.7 1:15 22

15:02 45 29 1:15 23

15:16 46 31.5 1:15 25

15:32 46 , 30.4 1:15 26

15:45 46 30.1 1:15 23

16:00 46 29.9 ^• 1:15 24

16:15 46 29.4 1:15 25

16:30 47. 30.7 1:15 25

16:45 46 28.8 1:15 23

17:00 47 29.3 1:15 23

17:15 48 29.4 1:15 23

17:30 49 29 1: 15 23 17:45 50 28.1 1:15 23

18:00 51 27.8 1:15 23

18:15 ^• 55 27.7 1:15 24

18:30 59 27.9 1:15 22

18:40 54 26.7 1:15 22

18:51 62 29.7 1:15 22

EXAMPLE 14

In this example, distillation was carried on a batch of diluate solution weighing 19.54 kg as fed containing 14.38 wt% DSMO and the rest being water for a period of 5 hrs 38 min. With the help of vacuum pump, a vacuum of about 35 mmHg is applied. By carrying out the distillation operation and noting the temperatures at the top and bottom of the column and pressure in the column, 1 .54 kg of distillate of 100% water is obtained. The left over bottoms of 4.5 kg with 90.6 wt% DMSO and 9.4 wt % water is obtained. The conductivity of distillate and bottoms is 0.09 mScm^"1 and 0.39 mScm^"1" respectively. The pH of the distillate and bottoms is 6.05 and 8.79 respectively. The loss incurred in this run is 0.5 kg of water.

16:15 71 32.9 1:15 35

16:30 72 25.6 1:15 35

EXAMPLE 15

In this example, similar to the ones above, 18.94 kg of feed consisting of 82.89 wt% DMSO and 17.11 wt% water is charged to a distillation column of 20 liters capacity wherein a vacuum of 30 mmHg is applied for about 150 min. Similar to the above examples, the reboiler and overhead temperatures and pressure in the column are noted at every 10 min. After 100 min of operation the reflux ratio was changed from 1:1,5 to 1:5. This experiment yielded in distillate of 3.84 kg and bottoms of 14.94 kg. The distillate recorded the conductivity of 0.14 mScm^"1 and bottoms recorded 8.7 mScm^'1 whereas the pH of distillate and bottoms is 6.6 and 0.17 respectively. There has been a loss of 0.16 kg of water. The distillate consists of 97.13 wt% DMSO and 2.087 wt% water.

Table 15: Experimental data sheet: DMSO-water distillation.

(

The reflux ratio is varied from 1:15 to 1 :5 to achieve high purity of both distillate and residue depending upon composition in the re-boiler.

EXAMPLE 16 In this example, 14.94 kg of composite bottoms obtained from above examples of 1 stage distillation operation is charged into a rotavapor which has the capacity to hold 10 liters of solution. The conductivity and pH of the feed is 0.01 mScm^'1 and 8.0 respectively. The feed consisting of 97 % DMSO is fed to the re-boiler and distillation is carried out for 2 hrs 48 min during which the pressure and temperatures in the column are noted using digital meter. The intermediate cut obtained which weighed 1.14 kg consisted of 78.69% DMSO and 21.309%water. The distillate and bottoms obtained were pure water and pure DMSO which weighed 9.9 kg and 3.3 kg respectively. There had been a loss of 0.6 kg of water into the vacuum seal.

The conductivity of distillate (water) 0.003 mScm^'1 and pH of 7.12 and that of bottomSconductivity and pH is 0.58 mScm^'1 and 9.63 respectively.

Table 16: Experimental data sheet: DMSO-water distillation.

The reflux ratio is varied depending upon composition in the reboiler.

EXAMPLE 17 The feed solution of 20 liters volume weighing 18.04 kg is fed to a packed distillation column to which a vacuum of 30 mmHg is applied for about 5 hrs 55 min. The feed charged consists of 11.52 wt% DMSO and 88.48 wt% water which had a conductivity of 0.08 mS/cm and pH of 5.38. The reflux ratio of 1:15 is applied and temperatures at the top and bottom of the column are noted . This distillation experiment resulted in 13.24 kg of distillate which had 1.06 wt% DMSO and 98.94 wt% water and 4.4 kg of bottoms which consisted of 81.15 wt%DMSO and the rest being water. The conductivity of distillate and bottoms is 0.06 mScm^"1 and 6.38 mScm^"1 respectively. The pH of the distillate and bottoms is 8.14 and 0.04 respectively. This run had a loss of 0.4 kg of water.

Table 17: Experimental data sheet : DMSO-water distillation.

EXAMPLE 18

A batch of diluate solution of volume of about 20 liters weighing 21.04 kg is fed to a packed distillation column. The distillation operation is carried out for a period of 5hrs 28 min under a vacuum of 25 mmHg. A vacuum pump and a vacuum seal are used to apply vacuum to the column. The composition of the feed charged is 16.32 wt% DMSO and 83.68 wt% water. Applying a reflux ratio of 1:15, the distillation is carried out by making note of the reboiler and overhead temperatures and pressure in the column at every 10 niin duration. 15.14 kg of distillate of pure water is obtained whose conductivity and pH are 0.01 mScm^*1 and 5.52 respectively. The bottoms whose conducitivity and pH are 0.03 mScm^"1 and 6.92 mScm^"1 respectively, weighing 5.7 kg consisting of 70.14 wt% DMSO and 29.86 wt% water is obtained. The loss incurred in this run is the loss of 0.2 kg water.

Table 18: Experimental data sheet : DMSO-water distillation.

Temperature (°C) Reflux Pressure

Time Reboiler Overhead Ratio (mmHg)

10:10 33 30.5 1:15 30

10:20 39 30.1 1:15 30

10:30 ~ 43 31.1 1:15 30

10:45 45 . 31.7 1:15 30

11:00 46 30 1 :15 25

11:15 46 29.7 1:15 2_.5

11:30 46 29.5 1:15 25

11:45 46 30.2 1:15 25

11:50 44 30 1:15 25

12:10 46 30.2 1:15 25

12:30 47 29.7 1:15 25

12:45 47 29.7 1:15 25

13:00 49 . 32.4 1:15 25

13:20 48 30 1:15 25

13:30 48 30_:2 1 :15 25

13:45 48 29.9 1:15 25

14:00 49 29.7 1:15 25

14:15 50 29,3 1:15 23

14:30 50 28.9 1:15 22

14:45 52 29.7 1:15 23

15:00 53 29 1:15 27

15:15 55 28.6 1:15 23 15:30 60 29 1:15 23

EXAMPLE 19

In this example, similar to the ones above, 18.74 kg of feed consisting of 13.13 wt% DMSO and 86.86 wt% water is charged to a distillation column of 20 liters capacity wherein a vacuum of 25 mmHg is applied for about 7 hrs. Similar to the above examples, the reboiler and overhead temperatures and pressure in the column are noted at every 10 min. This experiment yielded in a distillate of 14.14 kg and bottoms of 4.14 kg. The distillate recorded the conductivity of 0.11 mScm ^"1 and bottoms recorded 0.6 mScm^"1 whereas the pH of distillate and bottoms is 6.94 and 8.75 respectively. There has been a loss of 0.46 kg of water. The distillate consists of 0.92 wt% DMSO and 99.08 wt% water.

Table 19: Experimental data sheet : DMSO-water distillation.

31

0

EXAMPLE 20

The feed solution of about 20 liters of volume weighing 19.34 kg is fed to a packed distillation column to which a vacuum of 25 mmHg is applied for about 6 hrs 45 min. The feed charged consists of 13.05 wt% DMSO and 86.25 %water. The reflux ratio of 1:15 is applied and temperatures at the . top and bottom of the column are noted. This distillation experiment resulted in 14.14 kg of distillate which had pure water and 4.84 kg of bottoms which consisted of 75.15%DMSO and the rest being water. The conductivity of distillate and bottoms is 0.16 mScm ^"1 and 0.54 mScm ^"1 respectively. The pH of the distillate and bottoms is 6.43 and 7.96 respectively. This run had a loss of 0.36 kg of water.

Table 20: Experimental data sheet: DMSO-water distillation.

14:15 49 ^> 29 1:15- 23

14:30 49 28.9 1:15 23

14:45 49 29.4 1:15 25

15:00 50 29.8 1:15 25

15:15 51 29 1:15 24

16:00 50 28.6 1:15 24

16:15 51 28 1:15 25

16:30 55 28.5 1:15 25

16:45 61 29.2 1:15 25

16:50 62 29.3. 1 :15 25 -

17:00 60 27.8 1:15 25

EXAMPLE 21

This example consists of feeding 9.84 kg of desalted solution to rotavapor wherein a vacuum of 25 mmHg is applied. The feed consists of 78.46 wt% DMSO and 21.54 wt% water. The total operation took 75 min to complete during which the temperature across the colunm and pressure in ihe column is noted. The reflux ratio maintained was 1:5. This run yielded 2.24 kg of pure water as distillate. The weight of bottoms obtained is 7.44 kg which consisted of 96.94 wt% DMSO and 3.06 wt% water. The weight of material lost is 0.16 kg. The conductivities of distillate and bottoms is 0.01 mScm^"1 and 8.45 mScm^"1 respectively. The pH of distillate and bottoms is 6.14 and 0.07 respectively.

Table 21: Experimental data sheet: DMSO-water distillation.

The refiux ratio is maintained constant at 1:5. EXAMPLE 22 In this example, similar to the ones above, 8.84 kg of feed consisting of 84.13 wt% DMSO and 15.87 wt% water is charged to a distillation column of 10 liters capacity wherein a vacuum of 25 mmHg is applied for about 150 min. Similar to the above examples, the reboiler and overhead temperatures and pressure in the column are noted at every 10 min. This experiment yielded in a distillate of 1.14 kg of pure water and bottoms of 7.6 kg. The distillate recorded the conductivity of 0.12 mS/cm and bottoms recorded 0.67 mS/cm whereas the pH of distillate and bottoms is 5.76 and 9.56 respectively. There has been a loss of 0.1 kg of water. The bottoms consist of 98.66 wt% DMSO and 1.34 wt% water.

Table 22: Experimental data sheet: DMSO-water distillation.

The reflux ratio is varied from 1:15 to 1:5 depending on reboiler composition.

EXAMPLE 23

In this example, the feed of weight 7.44 kg is charged into a rota vapor of 10 liters capacity wherein a vacuum of 25 mmHg is applied for about 3 hrs. The feed contains about 96.94% DMSO and the rest being water. Similar to the above examples, the reboiler and overhead temperatures and pressure in the column are noted at every 10 min. The reflux ratio was maintained constant at 5:1. During distillation, traces of water is removed as the first cut of the distillate. Most of the DMSO with permissible moisture content, which is colorless, is recovered as second cut of the distillation. Residue left over in the reboiler is discarded. The composition of DMSO in the first and second cuts is 90.67% and 99.43% respectively. The distillate of 4.63 kg and bottoms of 2.34 kg reported the DMSO levels of 99.17% and 98.41% respectively. The distillate recorded the conductivity of 0.007 mScm^"1 and bottoms recorded 0.98 mScm^"1 whereas the pH of distillate and bottoms is 9.46 and 9.56 respectively. There has been a loss of 0.47 kg of water.

Since the feed is rich in DMSO, there arose a need for withdrawing various cuts at different stages of distillation operation before pure components are obtained.

Table 23: Experimental data sheet: DMSO distillation.

The reflux ratio is maintained constant at 5:1 for desirable purity of distillate, which is the final DMSO product. EXAMPLE 24

The feed solution of about 10 liters of volume weighing 7.6 kg of composition 98.66 wt% DMSO and 1.34 wt% water is fed to a rotating type distillation column to which a vacuum of 30 mmHg is applied for about 85 min. The reflux ratio of 1 :5 is applied and temperatures at the top and bottom of the column are noted. This distillation experiment resulted in 4.25 kg of pure water as distillate after withdrawmg first cut which consisted of 64.78 wt% DMSO. About 3.33 kg of pure DMSO is obtained as the bottom product. This run had a loss of 0.02 kg of water.

Table 24: Experimental data sheet: DMSO-water distillation.

14:45 46 44.1 25

15:05 97 32.6 1:05 22

15:15 113 37.9 1:05 25

15:20 126 88 1:05 32

15:25 128 90.6 1:05 32

15:27 130 88.3 1:05 30

15:30 132 85.5 1:05 29

15:32 129 . 103.4 1:05 27

15:34 124 93.9 1:05 27

15:36 116 90.2 1:05 27

15:45 116 90.3 1:05 27

15:50 119 90.9 1:05 27

15:52 119 94.4 1:05 30

15:55 119 96 1:05 31

16:00 119 94.9 1:05 30

.16:05 120 91.4 1:05 25

16:10 120 91.4 1:05 25

EXAMPLE 25

The feed solution weighing 8.97 kg of composition 99.25 wt% DMSO and 0.75% water is fed to a rotating type distillation column to which a vacuum of 30 mmHg is applied for about 95 min. The reflux ratio of 1:15 is applied and temperatures at the top and bottom of the column are noted. This distillation experiment resulted in 6 kg of pure water as distillate after withdrawing first cut which consisted of 95.72%DMSO. About 2.84 kg of pure DMSO is obtained as the bottom product. This run had a loss of 0.13 kg of water. The conductivity, pH of distillate and bottom are 0.031 mScm ^"1, 7.15 and 9.61 mScm^'1, 1.58 respectively.

Table 25: Experimental data sheet: DMSO-water distillation.

11:45 122 87.9 1 :15 23

12:00 119 95.7 1:15 30

12:15 124 94.8 1: 15 28

12:30 121 94.8 1 : 15 30

12:45 120 95.8 1: 15 30

The overall material balance for a four ED runs and subsequent distillations carried out is presented in the Figure 8. DMSO RECOVERY

The water recovered during distillation has shown traces of volatiles and its utility has to be explored by the client. Inter-cut (DMSO rich) from second distillation can be recovered and added to the next batch of second distillation. All the remaining residues from the trials were mixed and taken for further DMSO recovery to study the overall recovery of DMSO. During the demonstration, approximately 25 kg of pure DMSO from a total diluate of 180 kg was recovered which indicates 0.14 kg (89.33%) DMSO recovery was estimated. The final residue comprising mostly of unknown color imparting organics is to be discarded after DMSO recovery.

Chosen cation-exchange membrane (CMT-7000) and anion-exchange membrane (AMI-7001) has excellent chemical resistance to DMSO.

The technical specifications of the CMI-7000 cation exchange membrane are given in Table 26

Table 26: Technical Specifications of the CMI-7000 cation exchange membrane.

Thermal Stability (degree. C) 90

Chemical Stability Range (pH) 1-10

The technical specifications of the AMI-7001 anion exchange membrane are given in Table 27.

Table 27: Technical Specifications of the AMI-7001 anion exchange membrane.

ADVANTAGES OF THE INVENTION:

The developed process facilitates the recovery of DMSO solvent from a pharmaceutical effluent through separation of hazardous compounds such as sodium azide. The process also reduces the load on the effluent treatment plant (ETP which would otherwise have to undergo extensive procedures for neutralization of sodium azide and reduction in chemical oxygen demand (COD). High recovery of DMSO with high purity is possible through the developed process.

Claims

We claim:

1. An electrodialysis-distillatiori hybrid process for the recovery of pure dimethyl sulfoxide (DMSO) from industrial effluents and the said process comprising the steps of:

i. prefiltering the effluent by passing through the micron filter cartridge to remove the suspended solids followed by an activated carbo column to reduce color to obtain diluate of conductivity ranging between 15 to 25 mScm^"1;

ii. circulating rinse solution of conductivit ranging between 20-35 mScm^"1 across the electrodes of the electrodialysis stack system followed by diluate as obtained in step (i) and concentrate solutions of conductivity ranging between 1 to 2 mScm^"1 to the electrodialysis stack system until the conductivity of the diluate solution dropped to 0.06 mScm to obtain desalted diluate;

2. A process as claimed in claim 1, wherein industrial effluents contain aN₃, H₄CI salts, water, non-volatile heavy organic compounds and color imparting substances.

3. A process as claimed in claim 1, wherein concentration of DMSO industrial effluent is ranging between 12 to 20 wt%.

4. A process as claimed in claim 1, wherein concentration of NaN3 and NH CI in industrial effluents is ranging between 0.5 to 2 wt%.

5. A process as claimed in step (i) of claim 1, wherein diluate containing DMSO, NaN₃, NH CI and water.

6. A process as claimed in step (ii) of claim 1, wherein concentrating solution contains tap water that contains total dissolved solids (TDS) between 0.03 and 0.19%.

7. A process as claimed in claim 1, wherein rinse solution contain 2.0 to 3.0% by weight of aqueous solution of sodium bisulphate.

8. A process as claimed in step (ii) of claim 1, wherein electrolyte used in the concentrate is an aqueous solution of a common salt such as sodium chloride which will allow electrical conduction.

9. A process as claimed in step (ii) of claim 1, wherein the flow rate of diluate, concentrate and rinse solution across the membrane stack is ranging between 0.9 and 0.1 liters per second.

10. A process as claimed in claim 1, wherein said process is carried out in a continuous mode with the solution recycled back.

11. A process as claimed in claim 1, wherein recovery percentage of DMSO is ranging between 88 to 90% and purity percentage is ranging between 99.5 to 99.8%.

12. A process as claimed in claim 1, wherein the temperature in the first distillation column varied between 30 and 75 °C, the reflux ratio was varied from 1:5 to 1:15, vacuum was maintained between 20 to 30 mm of Hg and the overhead temperature was maintained between 30 and 32 °C using chilled water available at 5°C.

13. A process as claimed in claim 1, wherein the re-boiler temperature in the second distillation column varied between 45 and 120°C, the reflux ratio was varied between 1:5 and 1:15, vacuum was maintained between 25 to 35 mm of Hg and the overhead temperature varied between 30 and 95°C.