Preparation And Pervaporation Performance Of High Flux Pdmdes Ethanol/Water Separation Membrane

Biomass fermentation coupled with pervaporation can achieve an in situ separation of ethanol, which can reduce the product inhibition on microbes and ensure the continuity of fermentation process. In this process, pervaporation membrane plays a vital role. Polydimethylsiloxane (PDMS) is a typically membrane material for separation ethanol with high selectivity, but low flux because it is difficult to prepare thin, defect-free membrane with larger molecular weight. The lower permeation flux limits the practical application of PDMS membrane greatly.To solve this problem, dimethyldiethoxysilane (DMDES) which has a structure similar to PDMS, is used as a film-forming monomer to prepare ultra-thin PDMDES membrane. In this paper, the pervaporation performance of PDMDES membrane which can be affected by operating conditions and membrane-forming conditions are systematically investigated using dilute ethanol aqueous solution. At the same time, pervaporation performance of PDMDES membrane and PDMS membrane are compared, and the differences between PDMDES membrane and PDMS membrane from the perspective of surface structure and internal structure are revealed by some characterization methods, such as AFM, SEM, CA, FTIR, XRD,29Si NMR and TGA to explore the relationship between membrane structure and pervaporation performance preliminarily. Furthermore, PDMDES hollow fiber membrane is also studied and the effects of pre-polymerization time and coating times of casting solution on pervaporation performances of PDMDES hollow fiber membrane are investigated systematically.Experimental results show that DMDES can realize the preparation of ultrathin membrane, and the pervaporation performance of PDMDES membrane is the best when the amount of solvent is10g, the amount of cross-linking agent is3g, the amount of catalyst is0.2g and film-forming temperature is120℃. The total flux and separation factor of PDMDES membrane is up to5627.0g/(m2·h) and6.3respectively at35℃when9wt%ethanol is used as the feed solution. As the feed temperature increase, the separation factor of PDMDES membrane is relatively stable, remaining at about6.3, while the permeation flux shows a sharp upward trend. And as the feed concentration increase, the separation factor of PDMDES membrane decline slowly and permeation flux increases gradually. The PDMDES membrane exhibited a better performance with a sharp increase of one order of magnitude in flux and a little decline in selectivity compared with PDMS membrane, so the target of enhancing permeation flux greatly is achieved. This is because the thickness of PDMDES membrane is nanoscale and the mass transfer resistance is smaller. On the other hands, the three-dimensional network structure of PDMDES polymer is more obvious than PDMS polymer, which make PDMDES membrane has a larger free volume. Furthermore, the preparation of PDMDES hollow fiber membrane can be successfully implemented and the pervaporation performance of PDMDES hollow fiber membrane exhibites good while pre-polymerization time is15min and coating times of casting solution is1. The total flux and separation factor of PDMDES hollow fiber membrane is up to2273.7g/(m2·h) and5.1respectively at35℃when9wt%ethanol is used as the feed solution.