Pervaporation Separation Of Fatty Acid Methyl Esters And Methanol

The pervaporation separation technology is energy-saving and environmentally friendly,which is one of the new ways to separate fatty acid methyl esters from methanol.Polyvinyl alcohol（PVA）has excellent performance,but the mechanical strength,swelling resistance and separation performance of pure polyvinyl alcohol membrane are insufficient.In order to improve the performance of polyvinyl alcohol membrane,chemical cross-linking modification,doping modification,blending modification,and synergistic modification are adopted.The modified polyvinyl alcohol membranes were prepared by a series of reactions using polyacrylic acid（PAA）,nano-silica（Si O₂）,chitosan（CS）and other substances.The modified membranes were prepared,and the pervaporation separation effect of the modified membranes was explored.The PVA/PAA composite membrane was prepared with polyvinyl alcohol and polyacrylic acid by chemical cross-linking modification method.Through ATR-FTIR,SEM,AFM,contact angle,mechanical property test and other characterization methods,it was proved that after chemical cross-linking modification of the composite membrane,a three-dimensional membrane structure was formed,the surface was dense and the swelling resistance was enhanced.The PVA/PAA composite membrane was applied to the pervaporation separation of fatty acid methyl ester and methanol,and the effects of PVA content,PAA content,temperature and methanol mass fraction on the separation performance were explored.The experimental results showed that under the conditions of PVA content of 5%,PAA content of 5%of PVA,temperature of 40°C,and methanol mass fraction of 20 wt.%,the separation effect of PVA/PAA composite membrane was the best.The permeation flux was 185.3 g·m^-2·h^-1 and the separation factor was 80.1.On the basis of the PVA/PAA composite membrane,the CS-PVA/PAA composite membrane was prepared with polyvinyl alcohol,polyacrylic acid and chitosan by the method of synergistic modification.It was proved that the CS-PVA/PAA composite film had a three-dimensional structure,and chitosan changed the arrangement of polyvinyl alcohol molecules.At the same time,the effects of temperature and methanol mass fraction on the separation effect of composite membranes with different CS contents were explored.Compared with the above membranes,the CS-PVA/PAA composite membrane had greatly improved the permeation flux,the maximum can reach 756.3 g·m^-2·h^-1.Under the conditions CS content of 20%of PVA,temperature of 50°C,and methanol mass fraction of 20 wt.%,the pervaporation separation effect was the best.At this time,the permeation flux was 383.2 g·m^-2·h^-1 and the separation coefficient was 73.2.On the basis of the PVA/PAA composite membrane,the Si O₂-PVA/PAA composite membrane was prepared with polyvinyl alcohol,polyacrylic acid and silica by the method of synergistic modification,and analyzed by various characterization methods,which proved that the composite membrane reacted with polyacrylic acid to form a three-dimensional structure after synergistic modification,and formed a new chemical bond with silica.The effects of Si O₂content,temperature and methanol mass fraction on the pervaporation separation effect were investigated.The results showed that the permeation flux and separation coefficient of the Si O₂-PVA/PAA composite membrane have been greatly improved compared with the PVA/PAA composite membrane.Under the condition Si O₂ content of 20%of PVA,temperature of 50°C,and methanol mass fraction of 10 wt.%,the separation effect was the best.The permeate flux was 413.9 g·m^-2·h^-1 and the separation coefficient was 91.2.