Preparation Of Modified ZSM-5/PDMS/PES Composite Membrane And Its Performance In Butanol Pervaporation

In this work,the homogenous polydimethylsiloxane(PDMS)membrane was first made.The diffusion of water,ethanol,butanol and acetone which were main substances in fermentation was investigated via experimental method.The diffusion coefficients were tested and verified by Molecular Dynamic simulation(MD).The factors which obstructed molecular diffusion were evaluated by Hansen parameters,solubility,deformation and so on.In the process of butanol separation,the affinity between butanol and ZSM-5 was investigated by physical imbibition.Then the ZSM-5 zeolite was modified by KH-570,and PDMS composite membranes filled with four silica-alumina ratios(25,50,150,300)were prepared.In the process of pervaporation(PV),the influences of Si/Al ratio and loading content ZSM-5 and downstream pressure on composite membrane performance were researched.The experiment finally acquired diffusion coefficients of these four molecules(water,ethanol,acetone,butanol):2.257×10-5,2.484×10-6,3.640×10-6,5.770×10-7 respectively.By comparing Hansen dissolution parameters with experimental dissolution parameters,it was found that the higher the affinity between the molecule and PDMS,the higher the solubility of the membrane to the molecule.The main factors prevent molecular diffusion in the membrane were obtained:(1)For ethanol was the lower solubility;(2)For butanol was the large molecular diameter(3)The solubility of acetone in the membrane is higher and acetone have better separation effect.Adsorption experiments of ZSM-5 zeolites and butanol showed that the affinity of zeolites for butanol was higher with the increase of Si/Al ratio.When the modified ZSM-5 zeolites were filled into the PDMS composite membrane,it was found that the Si/Al ratio increased,the hydrophobicity of the composite membrane was stronger.In the PV process,composite membranes showed that as the ratio of Si/Al increased from 25 to 150,the separation factor increased from 16.5 to 24.1 and the flux decreased from 134.1 g/(m2h)to 107.6 g/(m2h).When the Si/Al ratio exceeds 150,the hydrophobicity of zeolites is no longer enhanced,and the PV performance of the composite membrane also tends to be gentle.In the downstream pressure test,it was found that the downstream pressure has a significant effect on the penetration of small molecules.As the downstream pressure increases,the selectivity of the composite membrane rapidly decreased.When the zeolites loading increased from 0 wt.%to 50 wt.%,hydrophobicity of composite membrane increased.In the PV process,the separation factor increased from 15.6 to 24.0,and the total flux increased from 101.7 g/(m2h)to 146.3 g/(m2h).