Pervaporation Dehydration Of Ethyl Acetate-Ethanol-Water Azeotrope

Ethyl acetate is an important industrial solvent and can be produced via direct etherification. The resultant crude product containing ethanol and water will form ternary azeotropes. Azeotropic distillation and extractive distillation have been used for the purification of ethyl acetate; however, both of the two processes are suffering from high capital and operating costs because entrainers are required. Pervaporation is an energy efficient process for the separation of organic mixtures, and it is especially attractive for the separation of azeotropic and close-boiling point mixtures. In this thesis, hydrophilic membrane materials were used for the dehydration of ethyl acetate/ethanol/water azeotrope by pervaporation. Chitosan (CS), a kind of cationic polymer, and polyvinyl alcohol (PVA), a kind of nonionic polymer, were selected as the main membrane materials. Both of them were modified to prepare pervaporation membranes. The membranes were characterized by FT-IR, XRD, ESEM, TG-DTA, and contact angle and density measurements. Sorption-desorption, diffusion and pervaporation were also carried out to characterize their performance.Polyvinyl pyrrolidone (PVP), an idea hydrophilic membrane material, was used to enhance the hydrophilicity of the membranes. ESEM tests showed that PVP had good compatibility with both CS and PVA. Experimental results indicated that the hydrophilicity of the membranes was enhanced, the swelling degree and permeation flux increased. The CS/PVP25/GA0.33 membrane has a good permeation flux of 1033 g·m^-2·h^-1 and separation factor of 289 at 25℃; the PVA2.5/PVP1.5/GA1 membrane has a good permeation flux of 713 g·m^-2·h^-1 and separation factor of 372 at 25℃.In order to improve the stability of the membranes, glutaraldehyde (GA) was used as a cross-linking agent, and the membranes were annealed after preparation. Experimental observation showed that the cross-linking can effectively restrain the excess swelling, and as a result, the separation factors increased. The CS/PVP10/GA0.47 membrane exhibits a good separation factor of 1220 and permeation flux of 521 g·m^-2·h^-1; and the PVA3/PVP1/GA1.2 membrane exhibits a good separation factor of 812 and permeation flux of 493 g·m^-2·h^-1. The influence of feed temperature was also studied. Experimental observations indicated that with increasing temperature, the swelling of the membranes and the permeation flux increased, whereas the separation factor decreased at the same time. The CS/PVP15/GA0.33 membrane exhibits a good permeation flux of 1297 g·m^-2·h^-1 and a separation factor of 481, respectively. And the PVA3/PVP1/GA1 membrane exhibits a good permeation flux of 801 g·m^-2·h^-1 and a separation factor of 292, respectively. After immersing in the azeotrope for a long time at an elevated temperature, the CS membranes may be solvated. The PVA membranes exhibit a better stability than the CS membranes. In a word, the modified CS and PVA membranes exhibited good separation performance with low cost...