Preparation Of Bifunctional Asymmetric Catalytic-Pervaporation Polyvinyl Alcohol Membrane And Its Application In Esterification

Esterification is widely used in production in our life.The conventional process in produced esterification usually used homogeneous catalyst such as sulfuric acid.In this case,the reversible reaction is limited by the reaction equilibrium so the conversion rate is limited and the post-treatment process is complicated.Then the cost of operation and equipment investment is high.Therefore,in order to break the chemical balance and increase the conversion rate of the reactants and simplify the process,the catalytic-pervaporation coupling process can be used to achieve the reaction and separation at the same time.The core technology of catalytic-pervaporation coupling is the catalytic-pervaporation membrane.In this paper,polyvinyl alcohol(PVA)that is a hydrophilic material was selected as the membrane material.We prepared a series of asymmetric PVA pervaporation membrane by NIPS method.In this work,we investigated the effect of NIPS operating conditions on the pervaporation performance of single functional membrane and also studied the effect of the concentration of PVA(8%-10wt.%)on the membrane structure.It can be found that when the PVA concentration was 8 wt.%,the membrane could exert excellent performance and the water flux was 423.4 g/m~2h when the temperature was 40°C.Compared with other literatures we could find that the asymmetric PVA membrane has a higher flux than other dense PVA membranes.The reason why we selected 5-sulfosalicylic acid(SA)used as catalyst on the membrane was that the molecular structure of SA has a group namely carboxyl group which could react with PVA.And the SA could retain its own catalytic group which was sulfonic acid group.The bifunctional catalytic-pervaporation asymmetric PVA-SA membrane was prepared by immersing the asymmetric membrane in ethanol and SA solution.The catalytic membrane firmly immobilized the active component in the network structure of polymer by chemical bonds.The catalytic membrane has good catalytic properties and stability.In pervaporation,we tested the separation performance of asymmetric PVA-SA membrane for separating ethyl acetate aqueous solution and found that the water flux could reach a maximum of 1400 g/m~2h.The result was showed that the catalytic membrane has good separation performance.The bifunctional membrane was used as a catalyst for the esterification intermittently reaction.The effect of the catalytic conditions on the catalytic performance was examined and the membrane showed good catalytic performance because it was 2.5 times than without adding the catalyst.The optimal catalytic membrane was used catalytic-pervaporation coupling of acetic acid and ethanol to synthesize ethyl acetate.The conversion rate of acetic acid reached 91.1%,which has good repeatability and the conversion of acetic acid was higher 10%than batch reaction.In summary,the asymmetric PVA single functional membrane has good separation performance.The bifunctional asymmetric PVA catalyst-pervaporation membrane has particularly good coupling performance,which could save investment and operating costs in the process.So this membrane has the potential of application.