Preparation Of Chitosan Pervaporation Membranes And Their Application In Separating Isopropanol/water Mixtures

Pervaporation, as one of high efficient and economic membrane separation methods, is capable of separating azeotropic and near-boiling point mixtures. The best developed application is for the dehydration of water-alcohol mixtures. Dehydration of isopropanol has received great attentions from industries due to its uses in various industries. As a hydrophilic material for pervaporation membranes, chitosan has drawn a great attention in past decade. In addition to its rich source and a low cost, high hydrophilic, the good film forming property, high mechanical strength, and chemical resistance make chitosan very promising material.The pervaporation performance of homogeneous chitosan membranes was investigated by altering the molecular weight, the degree of deacetylation of CS, operating temperature, feed composition and feed kinds. It was found that the chitosan membrane with the molecular weight of 3.0×10⁵ and the deacetylation of 90% has best pervaporation performance. For example, when this membrane was used to separation IP/H₂O mixture with 10 wt% water at 50°C, the separation factor reached 2,100, and the flux was 680g/m²h. The experimental results also showed that the membrane has emerged in the anti-trade-off phenomenon. The anti-trade-off phenomenon depends chitosan molecular structures (the molecular weight and degree of deacetylation), chitosan membrane preparation conditions (treated with and without alkali) and feed kinds (Ip/H₂O, EtOH/H₂O and MeOH/H₂O). The extent of anti-trade-off phenomenon was weakened when the chitosan membrane was treated by alkali greatly or with the order of IP/H₂O, EtOH/H₂O and MeOH/H₂O. The anti-trade-off phenomenon is mainly attributed to denser chitosan membrane formation due to the positive charges on the chitosan chains.Polyacrlaminde (PAM) was synthesized by using Ce4⁺ and then hydrolyzed under alkali aqueous solution to partly polyacrlaminde( HP AM). A novel composite membranes with two opposite charge polyelectrolytes, chitosan(CS) and HPAM, were prepared through coating method for isopropanol dehydration. The pervaporation performance of CS/HPAM composite membranes was investigated by altering thecomposition ratio of CS and HPAM polymers, operating temperature and feed composition. It was founded that the CS/HPAM composite membrane with the weight ratio of 75CS/25HPAM (or mole ratio of cation and anion isl:l) has the best pervaporation performance. When this membrane was used to separation IP/H₂O with 10 wt% H₂O at 50°C, the separation factor reached 16,000, the flux was 400g/m2h. It was also founded that the separation factor increased and the flux dropped with increasing water content in the feed. The anti-trade-off phenomenon occurs typically in the CS/HPAM composite membrane with the weight ratio of 75CS/25HPAM. Compared with other composite membranes in literatures the CS/HPAM composite membrane is promising to be developed for industrial use of the isopropanol dehydration...