The term 'pervaporation' was firstly used by Kober in 1917 to name phenomena observed during laboratory experiment [1].He noted,,,In the course of some experiments on dialyzation,my assistant,Mr.C.W.Eberlein,called my attention to the fact that a liquid in a collodion bag,which was suspended in the air,evaporated,although the bag was tightly closed.At first we were inclined to ascribe it to evaporation through a small aperture at the top of the bag,but further experiments and especially the speed of evaporation soon forced us to the conclusion that the aqueous vapour is given off through the membrane,as though the water were suspended as a solid without any membrane present.This phenomenon we have named pervaporation".Usually,we think about membrane like about strainer,which holds bigger participle,and passes the smaller one.But in pervaporation process,we use smooth,non-porous membranes without ,,holes".The clue of pervaporation phenomena is that this technique is based on a solution-diffusion mechanism combined with a phase change from liquid phase on feed membrane side to gas phase on permeate membrane side.Therefore it can be used to solve separation problems encountered with traditional,equilibrium-based,separation techniques.The driving force in pervaporation is a difference in chemical potential between feed and permeate side.The separation is achieved by different mass transfer rates of the components through the membrane.Generally,the mass transfer of the permeants in pervaporation process can be distinguished by the three different steps [2,3,4,5]:1.selective absorption on membrane surface at the feed side,2.selective diffusion through the membrane (in some cases this effect is con nected with molecular solvatation of the permeants in membrane volume),3.desorption into the vapour permeate on the permeate side.Nowadays,among the various membrane processes,pervaporation is considered as one of the most promising processes for many industrial applications from dehydration of alcohols to recover organic compounds from wastewater [6].Other applications of the pervaporation technology such as separation of organics mixtures and breaking azeotropes have also made progress.
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