S.K. Thampy

Kappaphycus alvarezii as a source of bioethanol.

The present study describes production of bio-ethanol from fresh red alga, Kappaphycus alvarezii. It was crushed to expel sap--a biofertilizer--while residual biomass was saccharified at 100 °C in 0.9 N H2SO4. The hydrolysate was repeatedly treated with additional granules to achieve desired reducing sugar concentration. The best yields for saccharification, inclusive of sugar loss in residue, were 26.2% and 30.6% (w/w) at laboratory (250 g) and bench (16 kg) scales, respectively. The hydrolysate was neutralized with lime and the filtrate was desalted by electrodialysis. Saccharomyces cerevisiae (NCIM 3523) was used for ethanol production from this non-traditional bio-resource. Fermentation at laboratory and bench scales converted ca. 80% of reducing sugar into ethanol in near quantitative selectivity. A petrol vehicle was successfully run with E10 gasoline made from the seaweed-based ethanol. Co-production of ethanol and bio-fertilizer from this seaweed may emerge as a promising alternative to land-based bio-ethanol.

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.

The effect of conducting spacers on transport properties of ion-exchange membranes in electrodriven separation

Abstract A conventional non-conducting spacer (interpolymer of polyethylene styrene-divinylbenzene copolymer) was transformed into an ion-conducting spacer by chemical modifications. Electrochemical characterization of cation-and anion-exchange membranes when it was alone or kept in between the non-, cation- or anion-conducting spacers was carried out by recording membrane potential and current-voltage curves in contact with NaCl solution of 220 ppm concentration at different flow rate of the solution. Transport parameters such as the counter-ion transport number, ionic permeability, membrane resistance and permselectivity were estimated for different experimental systems. Introduction of cation-conducting spacer near cation-exchange membrane and anion-conducting spacer near anion-exchange membrane led to a dramatic increase in counter-ion transport number and limiting current density along with the reduction in membrane resistance and thickness of diffusion boundary layer. On the basis of these studies, the position of conducting spacers (CS) in electrodialysis (ED) stack were optimized and packed. The performance of this ED stack has been tested with non-conducting and cation-conducting spacers in electrolytic solution of NaCl, NiCl2 and CuCl2 having concentration 500–1000ppm. The presence of conducting spacers not only suppress the concentration polarization but out put of the unit and its current efficiency also increases by about two times.

Preparation and electrochemical characterization of sulfonated interpolymer of polyethylene and styrene–divinylbenzene copolymer membranes

Abstract Preformed interpolymer films of polyethylene and styrene–divinylbenzene copolymer subjected to chemical treatment for various time intervals, in the presence of chlorosulfonic acid and ethylene dichloride mixture of different composition, have been used as membranes in these investigations. Membrane potential and conductance measurements have been carried out in sodium chloride solutions of different concentrations, to investigate the relationship between the concentration of the fixed ionic site and the electrochemical characteristics of these sulfonated membranes. Counter-ion transport numbers and thus permselectivity of these treated membranes were found to be proportional to the concentration of the fixed sulfonic acid groups. Membrane conductance data, along with values of concentration of fixed ionic site in the membrane, were used for the estimation of the tortuosity factor, salt permeability coefficient and frictional coefficient between solute and membrane matrix employing non-equilibrium thermodynamic principles. Furthermore, the transport properties are discussed in relation to the hydrophilic nature and thus the extent of sulfonation of these membranes.

Chronopotentiometric studies on dialytic properties of glycine across ion-exchange membranes

Abstract Chronopotentiometric responses of cation exchange membranes (CEMs) and anion exchange membranes (AEMs) were investigated in dilute solutions of NaCl, HCl and NaOH and its 1:10, 10:1 or 10:10 mixture with glycine. The behavior of both of these membranes was nearly ideal in strong electrolyte solutions. From experimental data, the values of permselectivity, counter-ion transport number and membrane resistance corresponding to each type of membrane at different concentrations of strong electrolyte have been studied. Glycine solution alone at iso-electric pH (5.90) did not exhibit any good inflection for ion-exchange membrane due to the absence of ionic transportation. The presence of glycine along with NaCl (pH=5.80) reduces ionic migration due to masking of ionic sites on the membrane matrix. The extent of masking was found to be proportional to the glycine concentration in the bulk of solution. Furthermore, the electro-transport of gly+ and gly− is possible across the CEM and AEM, respectively. Data are useful in order to ensure efficient desalting of amino acids or for its electro-driven separation.

Desalination of brackish water of higher salinity by electrodialysis

Abstract A laboratory model electrodialysis(ED) stack containing 35 cell pairs of cation and anion exchange membranes of 80 cm 2 effective cross-sectional area is used to study the desalination of brackish water having total dissolved solids (TDS) of 6000 – 10250 ppm. For brackish water containing TDS of 12000 – 27170 ppm, two ED stacks and for TDS of 27100 – 36000 ppm, three ED stacks containing different cell pairs of membranes having same effective cross-sectional area are used. Parallel-cum-series flow system is employed in all the stacks. The reduction in anions like Cl − , NO 3 − along with total hardness and TDS have been reported. The energy requirements and current efficiencies are also given based on the experimental data. Optimum flow rates and energy consumptions are reported for obtaining potable water having TDS of ⋍ 800 ppm from different brackish water. The results will be useful for design and operation of different capacity of electrodialysis plants for desalting brackish water of different salinity.

Seawater desalination by electrodialysis. Part II: a novel approach to combat scaling in seawater desalination by electrodialysis

Abstract Elelctrodialysis is a well accepted process for brackish water desalination but has been considered prohibitively expensive for desalination of seawater due to high energy consumption. With the development of newer and more efficient membranes and improvements in stack design, we felt a need for a fresh look at electrodialysis for desalination of seawater. We thus developed an electrodialysis process using novel methods of stack design and employing dilute sulphuric acid and reject water from concentrate stream as electrode wash feed. The acidity built up in the concentrate compartment, probably due to conversion of MgCl2 into HCl and transport of H+ ions from anode compartment to concentrate stream, prevents any scale formation in the concentrate compartments, thus avoiding reversal of polarity or the need for chemical dosing. The recovery of water is more than 50% at an energy requirement for desalination alone in the range of 14–16 kWh/m3 of product water.

A novel electrodialyzer for the production of demineralized water by electrodialysis

Abstract A twin electrodialyzer with a common anode, in which first an ED stack was packed with non-conductingspacers and second an ED stack was packed with ion-conducting spacers, was developed and tested under various experimental conditions. Experiments were conducted on a laboratory scale at different voltage and flow rates. Each membrane had an effective area of 65 cm2. Two configurations of the twin electrodialyzer [configuration (1), ED stack 1:7 cell pairs and ED stack 2: 7 cell pairs; configuration (2), ED stack 1:10 cell pairs and ED stack 2: 7 cell pairs] were optimized for the production of demineralized water. The results show that from inlet NaCl solutions of 500 and 800 ppm concentrations with conductivity 0.75 and 1.26 mS cm−1, respectively, with a linear velocity 2.52×10−3 m s−1 and at applied voltage 1.5 to 2.0 V/cell pair, an outlet conductivity ranging between 15.0 to 20.0 μS cm−1 was obtained using a twin electrodialyzer. It was concluded that with the twin electrodialyzer, both the stacks perform in an efficient manner, and it is possible to achieve a high degree of demineralization at a lower flow rate and low electrolyte concentration.

SEPARATION OF SODIUM SULFATE AND p-TOLUENE SULFONIC ACID BY ELECTRODIALYSIS

An electrodialysis process is proposed to achieve efficient separation of sodium sulfate from its mixture with p-toluene sulfonic acid. In this process, interpolymer type ion-exchange membranes were used due to their higher chemical stability and durability. Experiments were conducted in laboratory scale electrodialysis unit with an effective area of 65 cm2 and 10 cell pairs, at different compositions of sodium sulfate and p-toluene sulfonic acid in its mixture, to see the effect of their concentration on the process efficiency. Batchwise electrodialysis experiment in four stages was also conducted to separate 12% (w/v) sodium sulfate from 2% (w/v) p-toluene sulfonic acid. Observations indicate that at higher sodium sulfate concentration, energy consumption increases while current efficiency decreases due to enhanced back diffusion from concentrate to treated compartments. Dialytic rate of sodium sulfate is also estimated under different experimental conditions. It is concluded that p-toluene sulfonic acid adsorbed or masked the surface of anion-exchange membrane, which is responsible for the increased reduction in the ionic transportation with the increase in concentration of p-toluene sulfonic acid. Adsorption/masking is completed up to its critical micelle concentration and beyond this concentration; further increase in p-toluene sulfonic acid has no more effect on ionic transportation.

Performance of the first sea water electrodialysis desalination plant in India

Abstract The problem of potable Water shortage in some of the islands and coastal areas of India has led to consider sea water desalination for potable purposes. One of the membrane processes, namely, the electrodialysis(ED) has been designed and fabricated to meet the demand of a section of the population of Kavaratti island (Lakshad weep, Union Territory). The plant having a capacity of 5.5 m 3 /day is based on two stage reduction of salt wherein the first stage reduction upto 85% is achieved by recirculation of sea water. The plant commissioned in February, 1989 is running satisfactorily to its rated capacity. Useful information obtained during the period of first one year is reported here. A novel method of preventing scale formation and other salient features are brought about. An awareness is being created to go in for such plants in near future based on the performance of the above first experimental unit.