Affect Of Metal Salt On Poly (Vinyl Alcohol) Membrane And Its Pervaporation Performance

Pervaporation is a high efficiency, energy saving and a new type of membrane separation technology for the separation of liquid compounds, particularly suiting for separation of azeotrope and high concentration systems. Its principle is based on the osmotic pressure difference of two sides of membrane. The solution-diffusion speeds of components in pervaporation membrane were different. So the components could be separated. Ethyl acetate, ethanol, isopropanol and n-butanol were important chemical raw materials. But conventional separation techniques were difficult or costly to produce high purity products because of physical and chemical properties.In this paper, a various of polyvinyl alcohol (PVA) membranes modified by metal salts were prepared. Affect of the type and content of salts on pervaporation performances, degree of swelling, mechanical properties and hydrophilic properties of membrane were studied. It showed that, the contact angles of membranes were decreased after adding metal salts (except aluminum salts). And the flux of membranes was increased after adding metal in separating the solution of ethyl acetate. The flux of membrane modified by LiCl (each 100gPVA 0.3molLiCl added in each 100g PVA) was up to 530gm-2h-1 in separation of 95% ethyl acetate solution at 70℃,200Pa.The membrane with best overall performances was modified by LiCl, witch was added 0.1 mol in each 100g PVA. And its pervaporation performances of ethanol, isopropanol and n-butanol were studied in different temperature and pressure conditions. The results showed that:pervaporation flux of membrane was increased in high temperature and vacuum. And the separation factor of membranes modified by metal salts was effectively increased. In the conditions of operating temperature 50℃, pressure 200Pa and 95wt% ethanol system, pervaporation flux and separation factor of membrane modified by LiCl were:Jethanol/water= 1.0 g/m2/h,αethanol/water=1700; Jisopropanol/water=1.64 g/m2/h,αisopropanol/water=23000; Jn-butanol/water=5.27 g/m2/h,αn-butanol/water=1800.