Year of Publication

2001

Document Type

Dissertation

College

Engineering

Department

Chemical Engineering

First Advisor

D. Bhattacharyya

Abstract

The separation characteristics of binary alcohol-water mixtures were studied overa wide range of feed concentration and temperature using polymeric and zeoliticpervaporation membranes. For the hydrophilic PVA membrane, the total flux (at 55 0C)for the ethanol-water system decreased from 0.45 to 0.05 kg/m2/hr as the feed ethanolconcentration was increased from 30 to 95 wt. %. The separation factor (water/ethanol)was found to increase by about 100 times for the same range of concentration. TheUNIQUAC theory was used to predict the activity of binary alcohol-water mixtures in thePVA membrane. The UNIQUAC theory successfully takes into account the nonidealitiespresent in the alcohol/water-PVA membrane system. The transport of waterand alcohol species through the PVA membrane was modeled using the UNIQUACtheory in conjunction with the conventional activity driving force model. Using themodel and the experimental pervaporation data, the diffusivity correlations andconcentration profiles for various species through the membrane were developed. Basedon the developed diffusivity correlations, the water and alcohol fluxes through the PVAmembrane were predicted at 80 ??C.Experiments were also conducted on the water selective zeolite (type NaA)membrane using various alcohol-water mixtures and with dimethylformamide-watermixture over a wide range of temperatures (25 to 70 ??C) and solvent concentrations (0 -100 wt. %). The total flux for the ethanol-water mixture was found to decrease from 2 to0.05 kg/m2/hr at 60 ??C as the feed ethanol concentration was increased from 0 to 100 wt.%. Both, the water to ethanol and water to isopropanol separation factors were observedto lie between 1000 and 5000 over a wide range of solvent concentrations. The Maxwell-Stefan theory was used to model the permeation of water through zeolite NaAmembranes. The precise micropore structure of the zeolite cage helps in a partialmolecular sieving of the large solvent molecules leading to high separation factors. Thezeolite membrane active layer may contain certain non-zeolitic interstitial pores withpreferential water sorption. A high degree of hydrophilicity of the zeolite membrane issuggested from a pure water sorption value of 0.6 gm/gm zeolite. The detailedinterpretation of this result, however, requires consideration of both true zeoliticmicrocavity uptake as well as interstitially held water between crystallites. The use ofpervaporation for volume reduction and solvent recovery applications in thepharmaceutical industry has been demonstrated.

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