G.S. Trivedi

Studies on the electrochemical and permeation characteristics of asymmetric charged porous membranes

Asymmetric charged porous membranes were prepared by imbedding 10% (W/W) ion-exchange resin in cellulose acetate binder. Membrane potential and conductance measurements have been carried out in sodium chloride solutions at different concentrations to investigate the relationship between concentration of fixed charges and electrochemical properties of developed nonselective cation- and anion-exchange membranes. Counterion transport number and permselectivity of these membranes were found to vary due to the presence of ion-exchange resin. The hydrodynamic and electroosmotic permeability of sodium chloride solutions has been studied in order to compute equivalent pore radius. For cation- and anion-exchange membranes good agreement was observed between pore radius values estimated from hydrodynamic and electroosmotic permeability coefficient separately, while for nonselective membranes no correlation was found. Membrane conductance data, along with values of concentration of fixed charges, were used for the estimation of the tortuosity factor, salt permeability coefficient, and frictional coefficient between solute and membrane matrix employing an interpretation by nonequilibrium thermodynamic principles based on frictional forces. Moreover, surface morphological studies of these membranes also have been carried out and the membranes were found to be reasonably homogeneous.

Characterization of heterogeneous anion-exchange membrane

Abstract This paper reports the studies on the properties of heterogeneous anion-exchange membranes prepared from polyvinyl chloride (PVC) as binder and anion-exchange resin powder. The effect of variation of ion-exchange resin particle size as well as the resin–binder ratio on different mechanical, electrochemical and morphological properties of the membranes have also been studied. It has been found that by using resins of suitable particle size and loading, it is possible to achieve heterogeneous membranes which are comparable with interpolymer membranes in performance. Moreover, heterogeneous membranes are found to have more dimensional stability than interpolymer membranes.

Studies on bipolar membranes. Part II - Conversion of sodium acetate to acetic acid and sodium hydroxide

The electrodialytic water-splitting technology using bipolar membrane is an attractive cost-effective process for the production of acids and alkalies from the corresponding salts occurring in waste waters. Earlier report by us described the preparation of bipolar membranes and its application in converting sodium sulfate into sulfuric acid and sodium hydroxide. In this paper, as an extension of our earlier published work [G.S. Trivedi, B.G. Shah, S.K. Adhikary, V.K. Indusekhar and R. Rangarajan, React. funct. Polym. 28 (1996) 243], the experimental results on the conversion of sodium acetate to acetic acid and sodium hydroxide under different experimental conditions are discussed.

Studies on heterogeneous cation-exchange membranes

Abstract As the preparation of interpolymer type ion-exchange membranes involves the use of hazardous chemicals like chlorosulfonic acid and chloromethyl ether, it was envisaged to prepare heterogeneous membranes through a simple technique involving casting of a solution containing a binder and a polyelectrolyte. This paper reports the studies conducted in the preparation of heterogeneous cation-exchange membranes using polyvinyl chloride (PVC) as binder and cation-exchange resin powder as polyelectrolyte by the solution casting method. The effect of the particle size and loading of resin on the properties of the membranes such as dimensional stability, bursting strength, ion-exchange capacity, electrical resistance, transport number etc. have been studied. It has been found that with respect to dimensional stability the properties of the heterogeneous cation-exchange membranes prepared by using resin of suitable particle size and loading, are almost equally good or even better than interpolymer cation-exchange membranes and hence heterogeneous cation-exchange membranes may replace the interpolymer membranes in some of the electrodialysis (E.D.) applications.

Removal of nitrate by electrodialysis

Abstract A nitrate-specific anion-exchange membrane was prepared from chloromethylated polysulphone by partially aminating it with a secondary amine followed by a tertary amine for completion. The presence of amine groups are required for anion transport. When the nitrate-chloride ratio was equal, nitrate flux was larger than chloride flux by a factor of 1.6 in alkaline medium and 2 in acidic medium. In alkaline medium, the nitrate transport is more than one in all ratios. Selectivity in the transport of anions through ion-exchange membranes under applied electric field, though a desirable area, is not yet achieved satisfactorily. The ions which are all charged take part in migrating across the membrane equally according to the functional group of the membrane. It appears some mechanism is needed to retard one particular ion and accelerate other ion during transport process to bring out selectivity. Perhaps the introduction of polyfunctional groups in the membrane may help in the selectivity. An attempt has been made by Eyal and Kedam to introduce tertiary amino and quarternary ammonium groups. A similar procedure was adopted in this investigation. The transport ratios of nitrate to chloride in different proportions of the mixture in an electrodialysis cell is described in this investigation at three different pH values.

Studies on bipolar membranes

Abstract Bipolar membranes are composed of two distinct layers which are selective to ions of opposite charges. Because of this unique characteristics, bipolar membranes are able to electrically separate water into hydrogen and hydroxyl ions. These membranes in conjunction with conventional cation- and anion-exchange membranes in a cell stack, have been used for the production of acids and bases from their salts. Studies have been conducted to synthesize suitable bipolar membranes from polyvinylchloride (PVC) and ion-exchange resins with or without using plasticisers. Six types of bipolar membranes have been selected for studies in a laboratory stack containing 5 cell units of bipolar, cation- and anion-exchange membranes. Data have been collected for obtaining H2SO4 and NaOH from 0.5 N, 1 N and 1.5 N Na2SO4 solutions under different experimental conditions.

Separation of inorganic and organic acids from glyoxal by electrodialysis

Abstract The electrodialysis (ED) processemploying ion-exchange membranes has been used mainly for the desalination of brackish water and concentration of seawater. Of late ED has become a unique process for the separation of ionic and non-ionic substances from chemical mixtures. In such manufacturing processes, glyoxal is produced by the oxidation of acetaldehyde with nitric acid. After the reaction, the product contains nitric acid, acetic acid, glycolic acid, etc., which are to be separated from the mixture. Attempts were made to make use of ED to separate electrolytes from non-electrolytes and to separate nitric acid and weak organic acids from glyoxal. The experimental results obtained from the separation of nitric acid, organic acids and glyoxal under different experimental conditions are presented and discussed.

Studies on bipolar membranes: Part III: conversion of sodium phosphate to phosphoric acid and sodium hydroxide

The electrodialytic water dissociation process employing bipolar membranes has been used successfully for obtaining acids and alkalies from salts. Earlier reports by us described the preparation of bipolar membranes and their applications in converting sodium sulphate into sulphuric acid and sodium hydroxide; sodium acetate into acetic acid and sodium hydroxide [G.S. Trivedi et al., React. Funct. Polym. 28 (1996) 243; Ibid: 32 (1997) 209]. In this paper as an extension of our earlier published works the experimental results on the conversion of sodium phosphate to phosphoric acid and sodium hydroxide under different experimental conditions are described.

Separation of Sodium Formate and Pentaerythritol by Electrodialysis

The electrodialysis (ED) process using ion-exchange membranes is mainly used for the desalination of brackish water and wheys and for the concentration of seawater. ED has of late become a unique operation for the separation of chemicals from a mixture of ionic and nonionic substances. During the manufacture of pentaerythritol, sodium formate is also formed, which is to be separated from the mixture. Since ED is used to separate electrolytes from nonelectrolytes, attempts were made to make use of this process for the separation of sodium formate and pentaerythritol from their mixture. In this paper we have discussed the experimental results obtained their separation under different experimental conditions.

Preparation and characterization of maleic anhydride based resins in bead and granular form

An anhydride moiety, which leads to carboxylic groups on processing is an interesting starting material as metalchelating agent. Maleic anhydride is found to pose certain problems in preparing a copolymer. Heat of polymerization poses certain problems during copolymerization of styrene-divinylbenzene-maleic anhydride, and also divinylbenzene and maleic anhydride. Two-step addition of solvent is adopted to control the heat of polymerization during the preparation of above copolymers in bulk form. In case of bead polymerization water cannot be used as suspension medium. In the preparation of copolymer beads, even the presence of small amount of water converts anhydride to carboxylic group, which prevents effective polymerization. Attempts have been made to prepare above copolymers both in bulk and bead form to get carboxylic resin. The resin is characterised.