Among
various H2 purification technologies, the use
of membrane technology has been considered an ecofriendly approach
for addressing the increasing hydrogen demand. Although many H2-selective membrane materials have been reported, processing
them into hollow fibers or thin-film composites (TFCs) via traditional
methods either affects the performance of the materials or renders
their further processing into applicable membrane forms infeasible.
Herein, we propose a water-casting method for fabricating TFC membranes
for hydrogen purification with high permselectivity. The film integrity
and thickness were manipulated by controlling the spreadability of
the casting solution, and the resultant water-cast TFC membrane that
comprised an ∼30 nm selective layer demonstrated high H2 permeance and H2/CH4 selectivity of
approximately 190 GPU and 100, respectively, under optimized conditions.
We performed a mixed-gas permeation test using a simulated off-gas
of steam–methane reforming from natural gas in a single-stage
system and obtained hydrogen gas of >99 mol % purity. This indicates
not only the suitability of the water-cast membranes for satisfying
the demand for pure hydrogen as a fuel and chemical reagent but also
the great potential of the water-casting method for high-performance
membranes in various industrial and environmental applications.
− Pervaporation is known to be a low energy consumption process since it needs only an electric power to maintain the permeate side in vacuum. Also, the pervaporation is an environmentally clean technology because it does not use the third material such as an entrainer for either an azeotropic distillation or an extractive distillation. In this study, Silicalite-1 particles are hydrothermally synthesized and polydimethylsiloxane(PDMS)-zeolite composite membranes are prepared with a mixture of synthesized Silicalite-1 particles and PDMS-polymer. They are used to separate n-butanol from its aqueous solution. Pervaporation characteristics such as a permeation flux and a separation factor are investigated as a function of the feed concentration and the weight % of Silicalite-1 particles in the membrane. A 1,000 cm 3 aqueous solution containing butanol of low mole fraction such as order of 0.001 was used as a feed to the membrane cell while the pressure of the permeation side was kept about 0.2~0.3 torr. When the butanol concentration in the feed solution was 0.015 mole fraction, the flux of n-butanol significantly increased from 14.5 g/ m 2 /hr to 186.3 g/m 2 /hr as the Silicalite-1 content increased from 0 wt% to 10 wt%, indicating that the Silicalite-1 molecular sieve improved the membrane permselectivity from 4.8 to 11.8 due to its unique crystalline microporous structure and its strong hydrophobicity. Consequently, the concentration of n-butanol in the permeate substantially increased from 0.07 to 0.15 mole fraction. This composite membrane could be potentially appliable for separation of n-butanol from insitu fermentation broth where n-butanol is produced at a fairly low concentration of 0.015 mole fraction.
Generation of water as a byproduct in chemical reactions is often detrimental because it lowers the yield of the target product. Although several water removal methods, using absorbents, inorganic membranes, and additional dehydration reactions, have been proposed, there is an increasing demand for a stable and simple system that can selectively remove water over a wide range of reaction temperatures. Herein we report a thermally rearranged polybenzoxazole hollow fiber membrane with good water permselectivity and stability at reaction temperatures of up to 400 °C. Common reaction engineering challenges, such as those due to equilibrium limits, catalyst deactivation, and water-based side reactions, have been addressed using this membrane in a reactor.
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