Study On The Structure And Separation Performance Of PDMS/PTFE Pervaporation Membrane

With the continuous development of new energy and renewable energy,fuel ethanol receives increasing attention for its clean and environmentally friendly,renewable and other advantages.The traditional ethanol production often use batch fermentation,which with large equipment,low efficiency and product instability.When ethanol concentration reaches 6%-10%,the yeast stops growing,so it is necessary to separate the ethanol in time to achieve continuous production,conventional ethanol separation method often use distillation,extraction and other methods,these methods are energy-intensive and costly.Pervaporation separation technology is a new separation method,which takes advantage of the different components in the mixture have different dissolution,diffusion properties in the pervaporation membrane.The technology has the advantages of low energy consumption,simple equipment,high separation efficiency and convenient operation.Polytetrafluoroethylene(PTFE)microfiltration membrane is a kind of good supporting layer material with stable property,corrosion resistance,high temperature resistance,high porosity and mechanical strength.In this paper,PTFE flat microfiltration membrane was used as a supporting layer,Polydimethylsiloxane(PDMS)was used as the separation layer,the PDMS/ PTFE composite membrane was prepared by coating method and then composite membrane was filled with hybrid particles,The membrane was used to study the separation performance of ethanol/water solution.The specific research contents and conclusions are as follows:(1)PTFE microfiltration membrane with different structure was used as support layer,and PDMS/PTFE composite membrane was prepared by coating method.The effects of support layer structure on the separation performance and mass transfer resistance of PDMS/PTFE composite membranes were studied.The results showed that with the increase of the average pore size of the PTFE,the flux of the composite membrane decreased,the separation factor remained unchanged and then decreased when the thickness of active layer was too thin;With the increase of the pore size of support layer,the infiltration amount of the PDMS polymer into support layer increased,which resulted in a thicker transition layer and the thickness of the dense layerincreased,made the mass transfer resistance of the membrane increased,the flux decreased.(2)PTFE support layer with the same pore structure was used to prepare PDMS/PTFE composite membrane,the preparation conditions of membranes and the effects on the separation performance of ethanol/water solutions were studied.The results showed that the optimum conditions were as follows: the crosslinker content was 4%,the crosslinking temperature was80? and the crosslinking time was 5h.With the increase of the crosslinker content,the flux first decreased and then increased,the separation factor increased first,then decreased slightly and finally stabilized.With the increase of crosslinking temperature,the flux decreased and the separation factor increased first and then remained stable.With the increase of crosslinking time,the flux decreased and the separation factor increased first and then remained unchanged.(3)(ONS)-PDMS/PTFE filled membrane was prepared by using nonporous organophilic nano-silica(ONS)as a filler,then this membrane was used to separate ethanol/water solutions.The results showed that the degree of swelling increased first and then decreased with the increase of the amount of ONS,and the swelling degree was the largest when the amount of ONS was 5wt%.With the increase of the ONS loading,the flux first increased and then decreased,and ethanol concentration in permeate first increased and then decreased.When the amount of ONS was 5 wt%,the flux and separation factor reached the maximum;With the increase of feed temperature,the separation factor and flux increased,and the relationship between flux and temperature was combined with Arrhenius equation.With the increase of feed concentration,the separation factor and flux increased.(4)(ZIF-8)-PDMS/PTFE filled membranes were prepared with ZIF-8 particles as filler.The porous ZIF-8 matrix was prepared by liquid-phase diffusion method.This membrane was used to separate low concentration ethanol/water solutions.With the increase of ZIF-8 particle loading,the flux increased and separation factor first increased and then decreased.When the particle loading was 2wt%,the separation factor reached a maximum value of 9.23,and the permeation flux was 586.3g/(m2h).With the increase of feed temperature,the separation factor and the flux increased.With the increase of feed concentration,the permeation flux of the filled membrane increased and the separation factor decreased gradually.