Study On Preparation Of PVA/Inorganic Material Mixed Matrix Membrane And Pervaporation Dehydration Performance Of Esterification System

In the esterification process of ethyl acetate,timely removal of water can effectively avoid hydrolysis of the product.In the esterification system,water and ethyl acetate will form azeotrope;acetic acid and water have low relative volatility and strong association,it is difficult to separate them by traditional distillation technology.Pervaporation(PV)technology has the characteristics of green energy saving,low cost and high selectivity,and has more advantages than traditional separation technology in dehydration of ethyl acetate and acetic acid.Polyvinyl alcohol(PVA)is a typical substrate of hydrophilic membrane materials,the preparation of mixed matrix membrane materials by modifying PVA membrane with inorganic materials is expected to improve membrane separation performance,it is the focus of this research.In this paper,calcium phosphate oligomer(CPO)materials were prepared and filled with sodium alginate(SA)solution and PVA solution to prepare a series of PVA/SA/CPO mixed matrix membranes(MMMs)with different CPO filling amounts.The UIO-66 material was prepared by hydrothermal synthesis method and it was filled into PVA solution to obtain a series of PVA/UIO-66 MMMs with different UIO-66 filling amounts.Silicotungstic acid(STA)material was filled into PVA solution to prepare a series of PVA/ STA MMMs with different STA filling amounts.The physical and chemical properties of the prepared membranes,such as specific surface area and average pore diameter,surface morphology and cross section,chemical structure,crystal structure,mechanical properties and swelling properties were analyzed by automated surface area and porosity analyzer(BET),scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FTIR),X-ray diffraction(XRD),water contact angle(WCA),and tensile testing machine.The prepared three types membrane were used for the PV dehydration of ethyl acetate/water and acetic acid/water systems,and the effects of materials filling amount,feed composition and feed temperature on the dehydration effect of these two systems were investigated respectively.The results showed that the CPO material had a mesoporous structure and a high specific surface area;the separation layer was closely combined with the PAN support layer,when the CPO filling amount was 2 wt.%,CPO was uniformly dispersed in the membrane material.With the increase of CPO filling amount,the agglomeration phenomenon on the membrane surface was more obvious,and at the same time,the crystallinity of the PVA/SA/CPO MMMs increased;there were hydrogen bonds and ionic cross-linking effects between PVA,SA and CPO,and generally the CPO particles have no chemical interaction with PVA;with the increase of CPO filling amount,the WCA of the modified membrane material increased;the tensile strength of the membrane material first increases and then decreases with the amount of CPO filling,and the elongation at break first decreases and then increases.In the PV dehydration experiment of ethyl acetate/water system,with the increase of CPO filling amount,the permeation flux decreased first and then increased,and the separation factor increased first and then decreased,when the CPO filling amount was 2 wt.%,the pervaporation separation index(PSI)value reached the maximum value.In the acetic acid/water system,with the increase of CPO filling amount,the permeation flux increased,the separation factor first increased and then decreased.The highest PSI value was obtained when the CPO filling amount was 6 wt.%.The results showed that when the filling amount of UIO-66 was 1 wt.%～5wt.%,UIO-66 was uniformly dispersed in the membrane material,and the membrane surface was dense without obvious defects.There was no chemical reaction between UIO-66 and PVA,but there was hydrogen bond interaction.With the increase of the filling amount of UIO-66,the crystallinity of the membrane first decreases and then increases,the tensile strength of the membrane material increased and the elongation at break decreased.With the increase of the filling amount of UIO-66,the WCA on the surface of the filled membrane material increased,and the WCA was the smallest when the filling amount of UIO-66 was 1 wt.% and the hydrophilicity of the membrane material was the highest.In the ethyl acetate/water system,with the increase of UIO-66 filling amount,the permeation flux increased first and then decreased,and the separation factor decreased,when the UIO-66 filling amount was 1 wt.%,the PSI value reached the maximum value.In the acetic acid/water system,with the increase of UIO-66 filling amount,the permeation flux first decreased and then increased,the separation factor first increased and then decreased.The highest PSI value was obtained when the UIO-66 filling amount was 5 wt.%.The results showed that when the filling amount of STA was 1 wt.%～3wt.%,STA was uniformly dispersed in the membrane material,and the membrane surface was dense without obvious defects.There was no chemical reaction between STA and PVA.With the increase of STA filling amount,the WCA of the membrane material first increased and then decreased,indicated that the hydrophilicity first decreased and then increased.When the STA filling amount was 4 wt.%,the hydrophilicity was the best.With the increase of the filling amount of STA,the tensile strength of the membrane material increased and the elongation at break decreased.In the ethyl acetate/water system,with the increase of STA filling amount,the permeation flux decreased first and then increased,and the separation factor increased first and then decreased,when the STA filling amount was 3 wt.%,the PSI value reached the maximum value.In the acetic acid/water system,with the increase of STA filling amount,the permeation flux first increased and then decreased,the separation factor first decreased and then increased.The highest PSI value was obtained when the STA filling amount was 1 wt.%.Among the above three types of modified mixed matrix membrane materials,the permeation flux and separation factor of PVA/SA/CPO membrane in ethyl acetate/water system and acetic acid/water system were the highest,and the comparison with literature data also showed that the separation effect of the CPO material modified membrane was better,indicated that the PVA/SA/CPO mixed matrix membrane material had the potential for industrial application.