Study On Pervaporation For Removal Of Alcohol From Water With PDMS Composite Membrane And Its Mass Transfer

In the process of bio-fermentation, alcohol usually needs to be separatedinstantly from fermentation broths. Pervaporation technique is suitable for thisprocess for its low operating temperature. Because polydimethylsiloxane(PDMS) membrane is hydrophobic and has high permeable selectivity fororganics, it is widely used to separate volatile organics by pervaporation.In this study, the composite membranes have been prepared by coatingPDMS on supports of polysulfone (PS) membrane made in laboratory andcommercial polyvinylidene fluoride (PVDF) membrane, respectively. It isshown that these composite membranes are durable for pervaporation andhave high selectivity.The effects of operating conditions such as operating temperature, feedconcentration and flow rate on the permeating performance were investigatedby pervaporation of ethanol/water with PDMS/PS composite membrane. It isfound that the ethanol permeating flux increases with the increasing ofoperating temperature, feed concentration and flow rate. The selectivityincreases with the increasing of operating temperature, feed concentration andhas independence on flow velocity. By means of the Wilson plot method, the membrane resistance was determined, furthermore, the mass transfercoefficient of liquid phase and mass transfer correlation were obtained. Basedon the study above, the mass transfer semi-experience model for pervaporationwas deduced. The results calculated from the model are in good agreement tomeasuring data, with relative error less than 10%.The composite membranes with two different microporous supportinglayers including PS and PVDF, and different pore sizes PVDF were used inthe pervaporation of ethanol/water system. The results indicated that,PDMS/PVDF composite membrane has larger flux and higher selectivity thanPDMS/PS composite membrane, and PDMS/PVDF composite membrane withlarge pores has higher flux. It is also found that the PDMS/PVDF compositemembrane with different pore sizes produces insignificant effect on selectivity;the selectivity of PDMS/PS membrane increases with the increasing oftemperature and feed concentration, but the PDMS/PVDF membrane isreverse.The comparison of pervaporations performance for ethanol, 1-propanoland n-butanol was carried out using PDMS/PVDF composite membrane with0.45μm supporting layer. It is shown that the permeating flux, selectivity andoverall mass transfer coefficient increase in the following order: n-butanol,1-propanol, ethanol. The results are in accordance with the principles ofsolubility parameter and inter-dissolution with similar polarity.