Vacuum Membrane Distillation Concentration For Polyatomic Alcohol Aqueous Solution

Membrane distillation (MD) is an innovative membrane separation technique in recent years,because it possesses some excellences, for example, high efficiency, low energy, working at room temperrture and so on. Accordingly, it is hopeful that MD becomes a low-cost and efficient separation technique. So the application research of membrane distillation is very important. In this paper, vacuum membrane distillation was used to concentrate the polyatomic alcohol aqueous solution which is produced by corn. The polypropylene hollow fiber membrane used in this experiment was produced by our laboratory.Flux and rejection ratio between different type membranes was contrasted under similar operation conditions, and direct contact membrane distillation was compared with vacuum membrane distillation under similar operatation conditions also. We choosed PP1# module in which membrane external diameter is 1000μm, membrane inner diameter is 800μm, membrane pore radius is 0.095μm, membrane porosity is 45.4%. Vacuum membrane distillation was used to concentrate 1,2-dihydroxypropane aqueous solution continuously.The results indicated that the flux increased with the increases of feed temperature and feed flow rate, while flux decreases with the increase of feed concentration and cold side pressure. It was found that the flux is higher when the feed flows inside the hollow fibers while the outlet position of vapor in vacuum membrane distillation almost has no effect on the flux. Rejection ratio decreased with the decreased of cold side pressure,increased of feed concentration and temperature. Increase of feed flow rate had no strong effect on rejection ratio. The influence of these three factors on rejection ratio was the embodiment of changing of membrane wetting. When the temperature of feed was 65℃, the cold side pressure was 0.0123Mpa, the flux could reach 6kg/(m2·h). Vacuum membrane distillation was used to concentrate 1,2-dihydroxypropane aqueous solution continuously. The concentration of solution was 20%, which could be concentrated to 90%. The concentrated multiple was 4.5. Finally the mass transfer principle in the membrane micro-pores was analyzed and the mass transfer models for vacuum membrane distillation were considered.