Membrane Formation Mechanism And Application Performance Of Heterogeneous Ppolypropylene Blending Membrane

Membrane distillation(MD)is a separation technology that helps to solve the global water energy crisis.Among them,hydrophobic microporous membrane is a physical barrier between hot material liquid and condensing side,and is one of the core of MD process.In this paper,polypropylene was used as the raw material and thermally induced phase separation(TIPS)was used to study the membrane forming mechanism and application performance of polypropylene isomerized blend membrane.The main contents include:First,a study on the role of the configuration of the main membrane material polypropylene in the membrane-forming process was carried out.According to the phase diagram of the blend system,the compatibility between the polymer and the diluent in the iPP/aPP/soybean oil/DBP system was better.With the increase of the concentration of aPP in the casting solution,the gap between the lumpy spherical crystals in the section of the blend membrane gradually narrowed,and the porosity,pore diameter and mechanical properties first increased and then decreased.The permeability flux also showed a trend of rising first and then decreasing.When the concentration of aPP was 15 wt%,the flux was the highest at 20.29 kg/(m2·h),and the retention rate was 99.9%.Thirdly,the influence of diluent(soybean oil,soybean oil+DBP(1:1)or soybean oil+TBP(1:1))on the hydrophobic microporous membrane configuration and membrane forming process was studied.Compared with the diluent of pure soybean oil,the microporous membrane microstructure of the blend diluent was significantly changed,and its porosity,pore diameter and mechanical properties were improved to a certain extent.Meanwhile,the membrane permeability flux was significantly increased,with the interception rate reaching 99.9%.Among them,the membrane performance of the diluent of soybean oil+DBP(1:1)was the best,with the penetration flux reaching 15.48 kg/(m2·h).Finally,the preparation process optimization of heterogeneous polypropylene blend membrane under iPP/aPP/soybean oil/TBP system was studied.The influence of the proportion of blending diluent and solid content on the membrane forming process was studied.The results showed that the proportion of blending diluent affected the pore structure and pore size distribution of the membrane,while the solid content affected the porosity,pore size,air permeability and liquid penetration pressure.The blend membrane prepared under the optimal conditions has a full cellular membrane pore structure,the flux is up to 21.50 kg/(m2·h),the interception rate is more than 99.9%,and there is no infiltration or leakage after the vacuum membrane distillation of the blend membrane runs for nearly 50 h.To sum up,this paper made an in-depth study on the membrane forming mechanism of the heterogeneous polypropylene blend membrane,and obtained the heterogeneous polypropylene blend membrane under the iPP/aPP/soybean oil/TBP system,which can run stably in the vacuum membrane distillation and maintain a good separation effect,and was verified in the simulated seawater concentration system.