Preparation Of High-flux Ethanol Perm-selective Pervaporation Membrane

Pervaporation and vapor permeation processes can be coupled with fermentation to achieve the in situ separation of ethanol,which ensures the continuous process of fermentation.The key element of this integrated process is the pervaporation membrane with high flux and separation factor.This study analyzed the influence factors of membrane property from three aspects of macro,micro and meso scales,and then developed the membrane materials according to the film thickness,organic groups and chain flexibility.Firstly,Dimethyldiethoxysilane(DMDES),the silane monomer with hydrophobic Si-O-Si backbone polymerized to PDMS,was employed to prepare a high-flux PDMS membrane.Experimental results showed that DMDES can be used to prepare PDMS thin membrane.When it separated 9wt.%ethanol/water solution at 35?,the total flux was up to 5627 g/(m2·h)and the separation factor was 6.3.Compared to the pristine PDMS membrane,the flux is about one order of magnitude higher,while with a little decline in separation factor.Then four organic silicon monomers with different functional groups were used to investigate the effect of organic groups from the micro scale.They were 3,3,3,(trifluoropropyl)triethoxysilane(TFPTES),Phenyltriethoxysilane(PhTES),Vinyltriethoxysilane(VTES)and Ethyltriethoxysilane(ETES).The total fluxes showed the order of PETES>PTFPTES>PVTES>PPhTES,while the separation factor of PTFPTES>PVTES?PPhTES>PETES.From the characterization results and solubility parameters,for the preparation of membrane polymerized from monomers,the key influence factors of membrane structure are the dehydration condensation reaction rate and the evaporation rate except solubility parameters.The most excellent membrane among these was PTFPTES membrane,with total flux up to 10000 g/(m2 h)and the separation factor of 5.5.But the main problem of the membranes prepared from monomers is the rigidity which would lead to poor stability in the long-term experiment.So we introduced flexible segments to the rigid backbones to improve the membrane performance from the meso scale.When HSO was applied to be copolymerizd with PTFPTES,with the casting solution of TFPTES:HSO:Heptane:DBTL=5:1:10:0.2,film-forming temperature of 120?,the total flux reached 8647.8 g/(m2·h)and the separation factor was 7.02 with a selectivity of 1.72.Finally,in order to test the practical application of the membrane material in the ethanol fermentation system,the PTFPTES-HSO composite membrane was used to be coupled with vapor permeation process to avoid the membrane fouling.And the fermentation performance was compared with PDMS membrane.Experimental results demonstrated that PTFPTES-HSO and PDMS membranes can both be applied to alleviate the product inhibition effect.The ethanol productivity of PTFPTES-HSO membrane reached 3.01 g/(L h),much higher than 2.29 g/(L h)in batch fermentation and 2.94 g/(L h)for PDMS membrane.And benefited from the higher flux of PTFPTES-HSO membrane,when it was used as the separation membrane and then coupled with distillation process,the high ethanol yield and low energy consumption can be achieved,and it showed great potential for the practical application.