Preparation And Performance Of PDMS /Silane Modified ZSM-5 Composite Membranes

In this dissertation, the composite polydimethylsiloxane (PDMS) membranes supported by cellulose acetate (CA) micro-filtration membrane were successfully prepared by adding zeolite particles modified with a silane coupling agent, NH3-C3H6-Si(OC2H5)3. The sorption and diffusion behaviors of ethanol and water in the PDMS active layers were analyzed. The effects of modified zeolite content, coupling agent amount and feed temperature on the pervaporation performance of the composite membranes in 10 wt.% ethanol/water mixture were investigated.The experimental results showed that with the increase of the modified zeolite content in the PDMS active layers, trends as follows could be observed. The equilibrium ethanol and water uptakes both increased. But compared with ethanol, the equilibrium water uptakes changed very slowly. Both ethanol and water diffusion coefficients firstly increased and then decreased. The solubility selectivity increased remarkably and then maintained almost constant, while the diffusion selectivity firstly increased and then decreased. All these data revealed that adding certain amount of modified zeolite in the membranes was beneficial to the sorption and diffusion of ethanol.The pervaporation experiment results showed that all the prepared membranes possessed the ethanol-permselective ability. With the increase of the modified zeolite content, the flux and separation factor both firstly increased and then decreased, but they peaked at different positions. The permeate separate index followed the same trend as the flux. The flux decreased as the coupling agent amount increased, but the separation factor increased slightly. Oppositely, increase of the feed temperature caused the increase of the flux and the decrease of the separation factor. The mechanical properties of the composite membrane were good. The separation performance of the composite membranes could maintain stable during a period of time in 10 wt% ethanol/water mixture at 40℃.In addition, the effects of three impermeable components (NaCl, MgCl2 and glucose) on the pervaporation performance of the composite membrane were also studied. It was found that the addition of salts and glucose increase both the flux and separation factor in the order MgCl2 > NaCl> glucose.