Rajashekhar S. Khinnavar

Pervaporation Separation of Organic-Aqueous and Organic-Organic Binary Mixtures

Abstract In recent years membranes and membrane-related processes have gained much importance in several areas of science and technology. Intensive research activity has been pursued in this area all over the world in the past three decades. Among several membrane-related processes, the pervaporation (PV) technique is well known and has been used to separate mixtures of low molecular weight close-boiling organic liquids, aqueous-alcohol mixtures, and so on. Contrary to other membrane processes such as hyperfiltration and ultrafiltration, a phase transition occurs during the PV process. Consequently, the energy input of the process is at least equal to the heat of vaporization of the permeating liquids. This technique was first developed in the Research Center of the American Oil Company in Texas in the 1950s [1, 2], although the term was coined in 1917 by Kober of the New York State Department of Health at Albany. The technique has regained much attention since the early 1980s owing to membrane and proces...

Diffusion and sorption of organic liquids through polymer membranes: 10. Polyurethane, nitrile-butadiene rubber and epichlorohydrin versus aliphatic alcohols (C1-C5)

Abstract Diffusion and sorption of eight aliphatic alcohols — namely methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-methyl-1-propanol, 1-pentanol and 3-methyl-1-butanol — into three engineering polymer membranes has been studied in the temperature range 25–60°C to investigate the kinetics of the transport mechanism. The results have been analysed in terms of the Fickian diffusion equation. The anomalous transport behaviour of rubber-alcohol systems is attributed to a leaching out of the polymer systems during solvent immersion. The dependence of transport coefficients and activation parameters, as obtained from a temperature dependence of these coefficients, have been discussed in terms of the polymer-solvent interactions and their effect on the size, shape and type of penetrant molecules. Furthermore, the transport results have been interpreted in terms of enthalpy and entropy contributions. Dependence of the transport parameter on penetrant concentration has also been investigated.

RUBBER-SOLVENT INTERACTIONS

Abstract A thorough understanding of the structure physical/mechanical properties of the polymers has made possible the molecular design of macromolecules for specific application needs. Several methods exist for polymer synthesis and processing. When it concerns homopolymers, each polymer structure is identified with a particular method for its realization. Depending upon the situation, one or more of the methods (polycondensation, cationic, anionic, or free radical technique) is sometimes resorted to. Each process has its own merits and demerits. The condensation method is applicable to only a few cases of condensation monomers. A variety of vinyl and cyclic monomers are polymerized by anionic and cationic processes. These processes have obvious disadvantages in the sense that they warrant rigorous polymerization conditions like the need for ultrapure monomers, absolute moisture/oxygen free atmosphere, and cryogenic temperatures which are often difficult to realize on an industrial scale. A recent trend...

Diffusion and Sorption of Organic Liquids Through Polymer Membranes. III. Polyurethane, Neoprene, SBR, EPDM, NBR, and Natural Rubber Versus Cyclic Compounds, Esters, and Hydrocarbons

Abstract Diffusion and sorption of a variety of organic liquids into six engineering polymers have been investigated over the interval of 25°–60°C by the use of a conventional weight-gain experiment. While the method is laborious and time consuming, it yields reliable diffusion data. The transport mechanism depends, to a great extent, on the type of the solvent molecule and the barrier material. In all the polymer-solvent systems, the activated diffusion mechanism is operative and that the Arrhenius parameters of diffusion prove the conventional wisdom that smaller diffusion coefficients and higher activation energies are observed for the bigger solvent molecules. The diffusion mechanism has been classified to be anomalous. Sorption equilibrium data have been used to estimate the polymer-solvent interaction parameter in addition to molar mass between crosslinks and other thermodynamic quantities such as enthalpy and entropy of sorption. A first-order kinetic model appears to explain satisfactorily the tra...

Diffusion and Sorption of Organic Liquids Through Polymer Membranes. IV. Neoprene, SBR, EPDM, NBR, and Natural Rubber Versus Chlorocompounds

Abstract Diffusion coefficients of 1,2-dichloroethane, 1,1,2-trichloroethylene, 1,1,2,2-tetrachloroethane, and carbon tetrachloride into neoprene, SBR, EPDM, NBR, and natural rubber have been obtained from sorption experiments in the temperature interval of 25° to 60°C. Diffusion was found to be dependent on the type and nature of the barrier material in addition to the diffusant size. The mechanism of diffusion appears to follow the anomalous diffusion. Activation energies for diffusion have been estimated and used in the discussion of transport data. Equilibrium sorption data were used to calculate the enthalpy and entropy of sorption for polymer-solvent pairs.

Molecular transport of methyl- and methoxy-substituted benzenes into bromobutyl rubber, chlorosulfonated polyethylene and epichlorohydrin membranes

Abstract The diffusion and sorption of monocyclic aromatics such as benzene, toluene, p-xylene, 1,3,5-trimethylbenzene and methoxybenzene into bromobutyl rubber, chlorosulfonated polyethylene and epichlorohydrin membranes was investigated over the temperature range 25–60°C using a sorption gravimetric technique. The anomalous behaviour of some polymer-solvent systems was attributed to the greater relaxation of polymer chain segments than the movement of solvent molecules within the polymer matrices. Transport results were analysed using the Fickian model. A decrease in transport coefficients with an increase in diffusant size was observed. Arrhenius activation parameters were calculated from the temperature dependence of transport coefficients. Experimental and computed results were used to study polymer-solvent interactions in terms of polymer structures and the nature of solvent molecules.

Diffusion and sorption of organic liquids through polymer membranes. IX : Bromobutyl rubber, chlorosulfonated polyethylene, and epichlorohydrin versus substituted monocyclic aromatic liquids

Abstract Sorption and diffusion of four monocyclic aromatic liquids—namely, chlorobenzene, o-dichlorobenzene, bromobenzene, and nitrobenzene into bromobutyl rubber, chlorosulfonated polyethylene, and epichlorohydrin—have been investigated in the temperature interval of 25–60°C by using a gravimetric technique. The transport results have been analyzed by using the Fickian model of diffusion. The dependence of transport coefficients on the size and shape of the penetrant molecules has been discussed. Transport coefficients have not shown any systematic variation with the penetrant size, but the results are greatly influenced by the polymer-solvent interactions. The Arrhenius activation parameters have been estimated from a temperature dependence of sorption, diffusion, and permeation coefficients. The first-order kinetic rate constants have been obtained from the time-dependent sorption data. Enthalpy and entropy of sorption for the polymer-solvent systems have been studied. The molar mass between network c...

Diffusion and Sorption of Organic Liquids Through Polymer Membranes. VII. Elastomers Versus Acetic Acid and Dichloroacetic Acid

Abstract Diffusion coefficients of five elastomer membranes, viz., nitrile butadiene rubber, styrene–butadiene rubber, ethylene–propylene–diene terpolymer, neoprene, and natural rubber with acetic acid and dichloroacetic acids have been obtained from gravimetric sorption experiments. For acetic acid, the diffusion seems to follow the expected Fickian mechanism whereas for dichloroacetic acid, the diffusion appears to follow the non-Fickian mechanism for natural rubber and nitrile butadiene rubber membranes. While most membranes remain intact during immersion experiments, only natural rubber has shown degradative reactions. The concentration dependence of diffusivity has also been studied.