Preparation Of Ethanol-permselective Membranes And Study On The Separation Of Ethanol/water By Pervaporation

It is very important to recover ethanol from fermentation broths to ensure the continuous fuel ethanol production. Distillation is the most prevalent methods that separate ethanol from water, but it surfers from high engrgy consumption, great installation cost and poor economic performance. Pervaporation (PV) is a new membrane separation technique to separate liquid mixtures, which based on the membrane's different selectivity towards the various components in the mixture, especially in the use of the separation of homogeneous mixtures such as azeotropic, closing-boiling and isomeric mixtures, which are difficult to separate by conventional methods.In this paper, firstly, the optimizing conditions of PV performance of polydimethysiloxane (PDMS) membrane were studied. The diameter of the prepared silicalite-1 particles is 0.973μm, then they were incorporated into polydimethysiloxane (PDMS) and polyether block amide (PEBA) to form plat membranes, with polyacrylonitrile ultrofiltration membrane as a supporting layer. All the PDMS/silicalite-1 membranes showed preferential selectivity towards ethanol, stable permeate flux and separation factor.The pervaporation experiments of the separation of ethanol from dilute ethanol aqueous solution with PDMS/silicalite-1 membranes were carried out. It is found that the pervaporation performance of PDMS/silicalite-1 membranes is much better than that of pure PDMS membrane. The flux and selectivity do not take a persistent climbing tendency with the content of silicalite-1 in PDMS from 0 to 3wt%. Both total flux and the concentration of ethanol in the permeate reach the maximal values (total flux: 1645g/m2h, ethanol in the permeate: 30.3wt%) with approximately 2.0 wt% silicalite-1 in PDMS/silicalite-1 membranes.The total flux and separation factor increased with the increasing of temperature and the feed concentration.These results can be ascribed to the swelling behavior of PDMS/silicalite-1 membrane, ie, the maxium degree of swelling is only 4.8 %, so the permeation takes an important role in the membrane.The experiment of the separation of ethanol from dilute ethanol aqueous solution with PEBA/silicalite-1membranes was carried out. The pervaporation performance of PEBA/silicalite-1 membranes is similar to PDMS/silicalite-1 membranes. But both the permeation flux and the separation factor of PDMS/silicalite-1 membranes are better than that of PEBA/silicalite-1 membranes.