(330m) Preparation of Multi-Layer Pdms/pvdf Composite Membranes for Ethanol Recovery from Water by Pervaporation
AIChE Annual Meeting
Tuesday, November 6, 2007 - 4:30pm to 6:30pm
The production of renewable biofuels has been received great attention due to the energy crisis and environment crisis nowadays. And ethanol biofuel is one of the most important biofuels widely used in the world. Ethanol recovery from biomass fermentation processes is inevitably due to that microorganisms used in the fermentation process usually experienced strong ethanol inhibition. Pervaporation, advantageous for the separation of azeotropic mixtures such as ethanol/water mixtures with low energy consumption, has become an efficient, cost-effective manner.
Many membrane materials have been developed for ethanol recovery from water by pervaporation. Poly(dimethylsiloxane) (PDMS) is a typical ethanol perm-selective material due to its hydrophobic properties and large free volume. However, pure PDMS has low selectivity for ethanol recovery from water, with separation factor ranged from 4.4 to 10.8.
To surpass the limit of pure PDMS' selectivity for ethanol recovery, a multi-layer PDMS/PVDF composite membrane with an alternative PDMS/PVDF/non-wovon-fiber/PVDF/PDMS configuration was developed by curing PDMS cast on porous PVDF substrate. The porous PVDF substrate was obtained by coating PVDF solution on the double surface of non-woven fiber. The thickness of the active layer PDMS and the porous PVDF layer was 15µm and 45µm respectively. The multi-layer composite membrane was used for ethanol recovery by pervaporation, and exhibited enhanced separation performance compared with the common silicone/PVDF composite membranes, especially in the low ethanol concentration range. A novel phenomenon appeared that both the separation factor and permeation rate increased as the temperature increased until 60℃, and the separation factor decreased thereafter with the permeation rate increasing all along. And this was thought to be interrelated with the differences in permeation characteristics of the multi-layer composite membrane. The results showed that the membrane gave a best performance with a separation factor of 14.9, permeation rate of 208.6g/m2h at a 4.5wt% ethanol concentration with the temperature of 60℃. Besides, the separation factor increased as the ethanol feed concentration decreased, and the permeation rate followed a reversed order. The separation factor increased from 3.2 to 14.9 with the permeation rate decreasing from 407.3 to 208.6 g/m2h as the ethanol feed concentration decreasing from 30wt% to 4.5wt% at 60℃.
Although the total flux of the multi-layer composite membrane was depressed a little due to the increase of mass transport resistance, the membrane surpassed the utmost of pure PDMS' selectivity remarkably for ethanol recovery. And PDMS may also be expected to be commercially applied as ethanol perm-selective materials.
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