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

In this dissertation, the composite polydimethylsiloxane (PDMS) membranes supported by cellulose acetate (CA) microfiltration membrane were successfully prepared by adding nano-fumed silica particles modified with silane coupling reagent, NH2-C3H6-Si(OC2H5)3(KH-550). The effects of silica content, feed concentration, and feed temperature on the pervaporation performances of the nano-composite PDMS membranes were investigated for recovering ethanol from aqueous solution by pervaporation.The experimental results showed that all of the prepared membranes possessed the ethanol-permselective ability. Adding the modified silica particles significantly improved the pervaporation performances of the composite membranes. With the increase of the silica content in the membranes, the flux increased significantly and then maintained almost constant, while the selectivity to ethanol firstly increased and then decreased. The flux decreased with the increase of the silica content, while the selectivity to ethanol firstly increased and then decreased. The flux and swelling degree of the membrane increased as the ethanol concentration in the feed increased, but the separation factor followed the reverse order. The mechanical properties of composite membranes were good. The pervaporation performances of the composite membranes kept stable in a period time.Response surface methodology was also used to optimize the preparation conditions. The silica loading, PDMS concentration and KH-550/silica weight ratio were considered as factors. Main effects, quadratic effects and interactions of the three variables on the selectivity of composite membranes were investigated. The results revealed that the three factors had important effects on the the selectivity. The order was as follows:PDMS concentration> (KH-550/silica weight ratio)2> KH-550/silica weight ratio> (silica loading)2> (PDMS concentration)2> silica loading> PDMS concentration x KH-550/silica weight ratio. The regression equations, which described the effects of the three factors on the selectivity of the membranes, were derived from the results of twenty experiments by using a statistical software Design-Expert 7.1.4. The obtained regression equations were confirmed with four groups of experiments. According to the equations, in an ethanol aqueous solution with the concentration of 10 wt%, the maximum selectivity of 11.49 could be obtained at the feed temperature of 40℃, and the corresponding permeation flux was 197.3 g·m-2·h-1. The preparation conditions for the composite membrane with the above separation performances were:5.21 wt%silica loading,13.36 wt%PDMS concentration and 0.59 KH-550/silica weight ratio.