Vishwas G. Pangarkar

Photocatalytic degradation of nitrobenzene using titanium dioxide and concentrated solar radiation: chemical effects and scaleup

Photocatalytic degradation of nitrobenzene (NB) using titanium dioxide (Degussa P-25) as photocatalyst and concentrated solar radiation has been studied. The effects of various factors, such as the presence of anions common in the industrial wastewater, the initial pH and the addition of FeSO(4), were investigated. The intermediates detected were o, p,m-nitrophenols and dihhydroxy derivatives indicating that degradation proceeds via z.rad;OH radicals. Degradation of NB was studied in three reactors of different diameters to ascertain the effect of photon penetration depth on the degradation.

Reactive extraction of lactic acid using alamine 336 in MIBK: equilibria and kinetics.

Lactic acid is an important commercial product and extracting it out of aqueous solution is a growing requirement in fermentation based industries and recovery from waste streams. The design of an amine extraction process requires (i) equilibrium and (ii) kinetic data for the acid-amine (solvent) system used. Equilibria for lactic acid extraction by alamine 336 in methyl-iso-butyl-ketone (MIBK) as a diluent have been determined. The extent to which the organic phase (amine +MIBK) may be loaded with lactic acid is expressed as a loading ratio, z=[HL](o)/[B](i,o). Calculations based on the stoichiometry of the reactive extraction and the equilibria involved indicated that more lactic acid is transferred to the organic phase than would be expected from the (1:1) stoichiometry of the reaction. The extraction equilibrium was interpreted as a result of consecutive formation of two acid-amine species with stoichiometries of 1:1 and 2:1. Equilibrium complexation constant for (1:1) and (2:1) has been estimated. Kinetics of extraction of lactic acid by alamine 336 in MIBK has also been determined. In a first study of its kind, the theory of extraction accompanied by a chemical reaction has been used to obtain the kinetics of extraction of lactic acid by alamine 336 in MIBK. The reaction between lactic acid and alamine 336 in MIBK in a stirred cell falls in Regime 3, extraction accompanied by a fast chemical reaction occurring in the diffusion film. The reaction has been found to be zero order in alamine 336 and first order in lactic acid with a rate constant of 1.38 s(-1). These data will be useful in the design of extraction processes.

Sorption and permeation of binary water-alcohol systems through PVA membranes crosslinked with multifunctional crosslinking agents

Sorption and permeation of aqueous alcohol (C1–C4) through PVA membrane cross-linked with a multifunctional cross-linker is reported. The effect of temperature, feed concentration, cross-linker loading and the shape and size of the permeating species on pervaporation characteristics is investigated. Sorption isotherms of cross-linked PVA are obtained for the aqueous alcohol systems namely water+methanol, +ethanol, +n-propanol, +isopropanol, +n-butanol and +isobutanol. Values of activation energy for permeation (ΔEp), diffusion (ΔEd) and heat of sorption (ΔHs) for water through cross-linked PVA are estimated. The value of ΔEd for water was found to vary for all the water-alcohol systems (20–50 kJ mole-1) covered in this work.

Dehydration of acetic acid by pervaporation

Pervaporative dehydration of acetic acid over the entire concentration range of 0-100% is studied using four copolymer membranes of acrylonitrile and high performance Nafion and polyimide membranes. From each copolymer of acrylonitrile, three different membranes were produced with three different copolymer compositions. Polyimide showed high water selectivity but very low flux, while Nafion showed highest flux but lowest selectivity. Copolymers of acrylonitriles showed reasonable flux and selectivity behavior. Among the acrylonitrile copolymers, copolymers with hydroxyethyl methylacrylate yielded water selectivity comparable to that of polyimide with much higher flux.

Intensification of enzymatic conversion of glucose to lactic acid by reactive extraction

Lactic acid is an important commercial product and extracting this out of aqueous solution is a growing requirement in fermentation-based industries and recovery from waste streams. The design of an amine extraction process requires (i) equilibrium and (ii) kinetic data for the acid–amine (solvent) system used. Equilibria and kinetics for lactic acid extraction by Alamine 336 in octanol as a diluent have been determined and compared with other diluents studied earlier. An approach for extracting the lactic acid by a long-chain tertiary amine, which is in the dispersed phase as a liquid ion exchanger (LIX), is presented. A mathematical model for slurry phase reactor with glucose in the continuous aqueous phase, the amine with a diluent in the dispersed phase and the immobilized enzyme as the solid catalyst, has been developed using equilibrium and kinetic data for reactive extraction. Effects of various parameters affecting the conversion of glucose have been discussed. The model has been solved for batch and semi-batch modes. It has been shown that the semi-batch mode yields approximately five times higher productivity than batch mode.

Pervaporative Dehydration of Organic Solvents

Pervaporative separation of acetone/water and isopropanol (IPA)/water systems has been studied in the water-lean range of composition of the feed mixtures. Poly(vinyl alcohol) (PVA) membranes crosslinked with citric acid, adipic acid, maleic acid, glutaraldehyde, and glyoxal were used for this purpose. The sorption characteristics of all the membranes indicate that these membranes have a good sorption selectivity for water in view of the hydrophilic nature of PVA. The type of crosslinker used for crosslinking has been shown to have an important bearing on the permeation characteristics of the membranes. Thus, the trifunctional citric acid yields the highest selectivity but lowest flux. A comparison of the productive capacities of the various membranes indicates that the glutaraldehyde crosslinked membrane has the maximum productive capacity for IPA dehydration whereas maleic acid crosslinked membrane yields the highest productive capacity for acetone dehydration.

The application of fine TiO2 particles for enhanced gas absorption

The physical absorption of pure CO2 in various liquids (water, hexadecane, and sunflower oil) containing micron sized TiO 2 particles has been investigated. Absorption studies were carried out in a batch stirred cell reactor at 298 K and initial pressures of 0.08 MPa. Solid loading and stirring intensities were varied systematically between 0–15 kg/m 3 and 3.3–12.5 s −1 , respectively. Gas absorption rates are enhanced significantly in the presence of TiO 2 particles. Enhancement factors are a function of the solids loading and stirring intensity. Maximum enhancement factors of about 2 were observed for all solvents at low stirring intensities. The rate of gas absorption was theoretically analyzed using a heterogeneous unsteady state mass transfer model based on the Danckwerts surface renewal theory and a Langmuir-type of particle to interface adhesion isotherm. This model not only predicts the trends in the observed enhancement factors very well but also gives an accurate quantitative picture.

Methanol-selective membranes for the pervaporative separation of methanol–toluene mixtures

Abstract Pervaporative separation of methanol–toluene mixtures over the entire range of 0–100% is studied at 30°C using cellulose acetate, cellulose diacetate, cellulose triacetate, three blends of cellulose acetate and cellulose acetate butyrate (CBA), co-polymer of acrylonitrile and hydroxy ethyl methacrylate with three different compositions and polyimide membrane. All the membranes studied showed methanol selectivity. Cellulose acetate showed high selectivity with reasonable flux. Cellulose diacetate showed low selectivity and low flux. Cellulose triacetate showed high flux but low selectivity. Of the three blends considered, the blend with 20% (w/w) CAB showed good results with high flux and high selectivity. Co-polymers of acrylonitrile showed the highest methanol selectivity that was comparable to that of the polyimide membrane but with much better flux.

CHARACTERISATION OF COLLOIDAL GAS APHRONS

Abstract Colloidal Gas Aphrons (CGA) are finding increasing application in wastewater processing, bioseparations, etc. This article describes effect of various operating conditions such as pH, power input, impeller location, surfactant type and its concentration and viscosity of liquid on half life of CGA generated. Further, effects of various additives like, polymer, enzyme, solvents, salt, etc. are also investigated. A procedure for predicting the drainage rate of CGA has been proposed.

Pervaporative stripping of acetone, butanol and ethanol to improve ABE fermentation

Acetone-butanol-ethanol fermentation by anaerobic bacterium C. acetobutylicum is a potential source for feedstock chemicals. The problem of product induced inhibition makes this fermentation economically infeasible. Pervaporation is studied as an effective separation technique to remove the toxic inhibitory products. Various membranes like Styrene Butadiene Rubber (SBR), Ethylene Propylene Diene Rubber (EPDM), plain Poly Dimethyl Siloxane (PDMS) and silicalite filled PDMS were studied for the removal of acetone, butanol and ethanol, from binary aqueous mixtures and from a quaternary mixture. It was found that the overall performance of PDMS filled with 15% w/w of silicalite was the best for removal of butanol in binary mixture study. SBR performance was best for the quaternary mixture studied.