Aluminum-rich zeolite beta incorporated sodium alginate mixed matrix membranes for pervaporation dehydration and esterification of ethanol and acetic acid

Abstract

Mixed matrix membranes of sodium alginate (NaAlg) were prepared by solution casting by incorporating 2.5, 5, 7.5 and 10 wt.% of zeolite beta particles. The membranes thus prepared were crosslinked with glutaraldehyde and tested for the pervaporation (PV) dehydration of ethanol and acetic acid at 30–60 °C. The aluminum-rich zeolite beta, with its hydrophilic nature as well as molecular sieving effect and its favorable interaction with hydrophilic NaAlg, was responsible to enhance the PV dehydration of acetic acid and ethanol in terms of separation factor, flux, pervaporation separation index (PSI) and enrichment factor ( β). Thermodynamic model for sorption process was investigated typically for water + ethanol mixtures based on Flory–Huggins theory to explain the PV performance. Based on these results, permeance and driving force mechanisms were also elucidated. Extraction or dissolution of zeolite beta from mixed matrix membranes is confirmed by equilibrium sorption. Additionally, the changes in the dimension of pristine and mixed matrix membranes are compared to provide the influence of swelling on the stabilities of mixed matrix membranes. Arrhenius parameters for the process of permeation were calculated using these data at different temperatures to investigate their effects on the nature of the mixed matrix membrane. The plots of ln J p vs. 1/ T were constructed and found to follow the linear trends in the studied range of 30–60 °C for both the feed mixtures, indicating that flux followed the Arrhenius trend. PV experiments were also carried out for 5 and 10 wt.% incorporated NaAlg mixed matrix membranes at 70 °C to verify the suitability of the membranes at the esterification temperature. PV-aided catalytic esterification of acetic acid with ethanol was studied at 70 °C, which led to a considerable increase in ethyl acetate conversion with a reduction in reaction time as compared to the blank reaction due to continuous removal of water permeating through the barrier membrane.