Ravindra Datta

Membrane-supported nonvolatile acidic electrolytes allow higher temperature operation of proton-exchange membrane fuel cells

The feasibility of using nonvolatile molten and solid acidic electrolyte impregnated ion-exchange membranes in higher temperature proton-exchange membrane fuel cells (PEMFCs) to alleviate their water dependence is investigated. Higher temperature PEMFC operation reduces CO poisoning as well as passivation of the Pt electrocatalyst by other condensable species. Further, higher temperature operation could eventually allow direct use of low-temperature reformable fuels such as methanol in the PEMFC. The methodology proposed here involves supporting an appropriate acidic solid, melt, or solution of low volatility within the pores of Nafion{reg_sign} so as to enhance its protonic conductivity at higher temperatures and lower humidity levels. Preliminary experimental results reported here for a PEM fuel cell operating at temperatures of 110 to 120 C based on Nafion supported solutions of heteropolyacid indicate the feasibility of the technique.

Development of a supported molten-salt Wacker catalyst for the oxidation of ethylene to acetaldehyde

Abstract A modified supported molten-salt Wacker catalyst involving palladium chloride/copper chloride is developed by replacing the conventional aqueous reaction medium (H 2 O + HCl) with a eutectic melt of cuprous chloride and potassium chloride and supporting it on a porous support. Experimental studies for the oxidation of ethylene to acetaldehyde over the supported molten-salt catalyst (SMSC) show the kinetics to be similar to the aqueous-phase Wacker process and the SMSC diffusion-reaction characteristics to be well predicted by the theoretical model of R. Datta and R. G. Rinker ( J. Catal. 95 , 181 (1985)). The SMS catalyst was found to be extremely stable owing to the essentially nonvolatile nature of the molten salt whereas the aqueous-phase supported liquid-phase catalyst deactivated rapidly due to the evaporation of the solvent. The developed supported molten-salt catalyst appears to have substantial advantages over the commen⌝cal liquid-phase Wacker process. Further, the SMSC technique utilized here should prove to be useful in developing efficient catalysts for many other processes.

Supported liquid-phase catalysis: I. A theoretical model for transport and reaction

Abstract A simplified theoretical model is proposed for the transport and chemical reaction of gaseous species in supported liquid-phase catalysts (SLPC) in which catalytic liquids with contact angles less than 90 ° are dispersed within inert porous supports. It is based on the use of the dusty-gas model for the flux in the residual gas pore space. The variation of the structural dusty-gas parameters with liquid loading is correlated by using results borrowed from the parallel-pore model and the random-pore model along with an interconnected near-spherical cell description of the porous medium. The proposed model is free of adjustable parameters and is therefore predictive. It corroborates the existence of a maximum in the reaction rate predicted previously for some systems and also exhibits other trends observed experimentally. In addition, other interesting charac teristics of SLPC are predicted.

DISTILLATION OF BINARY MIXTURES WITH CAPILLARY POROUS PLATES

ABSTRACT Distillation of liquid mixtures using capillary porous plates is a new process which depends upon the use of the intermolecular interactions between solids and liquids to alter the normal vapor-liquid equilibrium of a given mixture. Distillation of different binary mixtures, namely ethanol-water, ethanol-benzene, and acetone-ethanol systems, of different compositions was experimentally studied in a continuous distillation column equipped with four, five, or six porous sintered stainless steel fractionating plates of 13.5 μm pore diameter as well as six normal sieve plates. The results showed that the main factors affecting the separation efficiency in a given porous plate are the polarization of the pure liquids and the polarization difference between the mixture components. For the ethanol-water system, the results showed that while no separation was achieved in a distillation column with conventional stages, the azeotropic point of this system was broken in the distillation column with porous p...

Theoretical study of vapor pressure of pure liquids in porous media

Abstract There are reports in the literature describing vapor pressure reduction in capillaries or porous materials that is substantially in excess of that predicted by the classical Kelvin equation, which relates the vapor pressure over the curved vapor–liquid interface inside a pore to its radius of curvature. However, this effect is negligible except for pores of radii less than 0.1 μ m. In fact, substantial vapor pressure reduction has been observed in larger pores. This is explained here on the basis of the effect of long-range surface forces exerted by the solid on the liquid, while the application of the Kelvin equation to capillary-held liquids tacitly assumes the solid to exert no influence. A generalized Clausius–Clapeyron equation in the presence of external force fields is first obtained. The resulting excess enthalpy of vaporization is next semi-quantitatively related to the molar polarization of the liquid and the porous solid based on a molecular approach.

Performance Analysis of a Continuous Rotating Annular Electrophoresis Column

Abstract A new continuous electrophoresis column is proposed which will allow for the continuous separation of industrial scale multicomponent mixtures. Computer simulated calculations predict steady-state bed temperature, separation distance, and power requirements. The proposed design compares favorably to previous designs in terms of minimizing peak bed temperature and power consumed.

Separation of 2-Propanol–Water Mixture with Capillary Porous Plates

ABSTRACT Distillation of the 2-propanol–water mixture of different compositions was experimentally studied in a continuous distillation column equipped with polar and nonpolar porous plates as well as normal sieve plates. The results showed that while no separation was achieved in a distillation column with porous carbon plates or with conventional stages, the azeotropic. point of this system was broken in a distillation column with polar sintered stainless steel porous plates. A distillate of about 80.0 mol% 2-propanol was obtained for a feed of azeotropic composition, i.e., 68.0 mol% 2-propanol. These results showed that the main factors affecting the separation efficiency in a given porous plate are the polarization of the pure liquids and porous plates as well as the polarization difference between the mixture components.

Theoretical study of vapor–liquid equilibrium inside capillary porous plates

Abstract A generalized thermodynamic framework is provided for vapor–liquid equilibrium (VLE) in the presence of external fields and is utilized to develop a semi-empirical model for VLE within porous materials that accounts for the effect of the long-range surface forces. The alteration of VLE of binary mixtures in capillary porous plates is explained on the basis of the effect of long-range surface forces exerted by the solid on the liquid, which alter the intermolecular interactions amongst the mixture components as well as their vapor pressure. The excess Gibbs energy, activity coefficients, and relative volatility are studied in the presence of external fields in relation to those in their absence. The VLE of cyclohexane–ethanol (components of different polarity) system at 25°C, and acetone–ethanol (similar polarity) system at 32°C are predicted using an approximate approach developed in this study and compared with experimental results. It is found that the results obtained by the approximate approach are in agreement with the experimental ones.

Supported liquid-phase catalysis: III. Experimental evaluation of the diffusion-reaction model

Abstract The theoretical model for transport and reaction in supported liquid-phase catalysis (SLPC) proposed in Part I (R. Datta and R. G. Rinker, J. Catal. 95 , 181, 1985) was tested experimentally using two different homogeneously catalyzed model reactions. The hydrogenation of ethylene catalyzed by a RhCl(CO)(PPh 3 ) 2 solution and the isomerization of quadricyclene catalyzed by a Co(III)TPPCl solution were used to study the behavior of SLPC at low and high solubility, respectively. The experimental results were found to be in good quantitative agreement with the theoretical model for both cases.

Supported liquid-phase catalysis: II. Experimental evaluation of the flux model for liquid-loaded porous media

Abstract An experimental investigation was undertaken to test the model for transport of gases in liquid-impregnated porous media proposed in Part I (R. Datta and R. G. Rinker, J. Catal. 95, 181, 1985) of this series. It was found that the original dusty-gas model needs to be modified by incorporating an additional slip-flow correction factor, σ, in order to reconcile differences in the values of the Knudsen diffusion constant, C1O, obtained separately from isobaric diffusion and flow experiments. Based on the results of the permeability experiments with pure gases and binary mixtures and earlier isobaric diffusion experiments, it is concluded that the correlations proposed to account for the variation of the dusty-gas parameters C0G, C1G, and C2G with degree of liquid loading are entirely adequate. It is also indicated that the dispersion pattern of liquids with a contact angle less than 90 ° is substantially the same in a given porous medium.