Preparation of ZIF-8 loaded PVA and PES mixed matrix membranes for dehydration of ethanol solutions

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2015
Şenyurt, Elif İrem
Solvent recovery is an important issue in chemical industry when low product cost is desired and also environmental concerns are considered. The conventional methods for solvent recovery are extractive distillation, adsorption, extraction and absorption. However, these methods require excessive amount of energy, cause product contamination due to additional components and need harsh conditions. Pervaporation separation is independent of the vapor-liquid equilibrium; therefore, it is a suitable technique especially for separation of azeotropic mixtures. Ethanol forms azeotrope with water and ethanol dehydration is one of the most popular usage area of pervaporation since high purity ethanol is required for use as biofuel and in pharmaceutical industry. For pervaporation applications, better performing membranes are desired in order to achieve high purity with faster separation. In this study, asymmetric pure PES and PES/ZIF-8 membranes were prepared by non-solvent induced phase separation (NIPS) technique. Also dense pure PVA membranes were prepared with solvent evaporation technique. They were cross-linked both thermally and chemically with glutaraldehyde solution. PVA/ZIF-8 MMMs were prepared with 5 wt. % ZIF-8 loading and cross-linked chemically. In order to examine the effect of particle size of ZIF-8 crystals on the pervaporation performances, MMMs were prepared with ZIF-8 crystals whose particle sizes were 17, 81, 190 and 340 nm. The pervaporation performance of all membranes were tested with ethanol-water (10/90 wt. %) mixture at 25°C Asymmetric pure PES membranes prepared by wet-phase inversion technique and were annealed at three different temperature (40°C, 50°C and 70°C). The most selective membranes were the ones annealed at 50°C and had an average selectivity of 15.6 with an average flux of 71.5 g/m2h. Besides, the flux of 5 wt. % ZIF-8 incorporated membranes was as twice as the flux through the pure PES membrane; however, a selectivity decrease of 75 % was observed. Pure PVA membranes were prepared from 87-89 % degree of hydrolysis PVA and cross-linked by thermal treatment at different temperatures (90°C-160°C) for different times (1 hour and 48 hours). 1 hour thermal treatment caused an excessive decrease in normalized flux and a 20 % approximate increase in selectivity when compared to non-treated membranes. These membranes were also cross-linked chemically with GA solution having GA concentration of 0.5-3.0 wt. %. Membranes cross-linked with solution containing 0.5 wt. % GA had the highest selectivity (18.4, water/ethanol) with normalized flux value of 5800 µm g/m2h, in average. Pure PVA membranes also prepared from 98 % degree of hydrolysis PVA and were cross-linked chemically with GA solution having GA concentration of 0.5-1.5 wt. %. Membranes cross-linked with solution containing 0.5 wt. % GA had the highest selectivity and normalized flux with the average values of 77.2 and 1200 µm g/m2h, respectively. In order to observe the effect of particle size of ZIF-8 crystals on the performance of PVA membranes, the 5 % (w/w) ZIF-8 loaded PVA/ZIF-8 MMMs prepared using ZIF-8 with particle size of 17 nm, 81 nm, 190 nm and 340 nm. It was observed that, both normalized flux and selectivity of MMMs did not have a regular trend as a function of particle size of ZIF-8 particles. The best performing MMMs were the ones filled with 190 nm ZIF-8 with an average normalize flux of 1300 µm g/m2h and selectivity of 66, which was % 64 greater than the selectivity of pure PVA membranes.
Citation Formats
E. İ. Şenyurt, “Preparation of ZIF-8 loaded PVA and PES mixed matrix membranes for dehydration of ethanol solutions,” M.S. - Master of Science, 2015.