Preparation Of Hydrogen Bonded Complex Membrane And Its Pervaporization Properties Under Acidic Conditions

Pervaporation（PV）,as a novel separation technology,has been widely applied in the field of dehydration of organic solvents at neutral conditions,because of its high-efficiency,low-energy-consumption,and environment-friendly characters.However,the PV process should be conducted under acidic conditions for some practical application,e.g.,in the industrial,ethanol dehydration in biological fermentation,alcohol dehydration in pharmaceutical process,esterification reaction coupling dehydration,and acetic acid dehydration.Resultantly,acidic conditions greatly affect the performance and stability of membrane separation,hampering the practical application of PV technique.The performance of a membrane is mainly determined by the membrane materials.Thus,development of novel membrane materials that can work stably under acidic conditions is of great significance for expanding the application of PV and realizing low-energy-consumption separation process.To tackle the issue,in this study,we proposed to employ p H-responsive polymer as hydrogen-bonding donors and another hydrogen-bonding-acceptor polymer to construct the hydrogen-bonding complexed materials.According to the principle that carboxylic acid dissociation is limited by low p H condition,hydrogen-bonding complexed polymer nanoparticles（HCPN）and composite membrane was prepared via tuning the complexed p H.The such-prepared membrane was used for dehydration of organic solvents by PV under acidic conditions and dehydration of esterification reaction system.Firstly,dispersed HCPN aqueous solution was prepared via controlling the complex p H between PAA and PVP.The HCPN was utilized for membrane fabrication by vacuum-assisted filtration the HCPN on PAN membrane.The surface morphologies and microstructures of the HCPN membrane were investigated by scanning electron microscopy（SEM）,atomic force microscopy（AFM）,low field nuclear magnetism（LFNMR）,Fourier infrared spectroscopy（FT-IR）,etc.,which confirmed that the HCPN was formed due to the hydrogen-bonding between PAA and PVP.The microstructure and performance of the HCPN membrane was optimized by varying the complexed p H and deposition volume of casting solutions.The optimized composite membrane was utilized for pervaporation dehydration under acidic conditions.The effect of feed solution p H on the separation performance was detailed explored,which demonstrated that the separation selectivity increases with the feed solution p H reduction.The HCPN showed a permeation flux and a water in permeate of 1.65 kg/m~2h and 99.79 wt%respectively,when dehydration of 10 wt%water/isopropanol under p H=1 at 50℃.Moreover,the membrane can continuously and stably run for more than 100 hours without obvious performance degradation.Furthermore,the HCPN membrane was pretreated with acid to increase the degree of protonation and the degree of crosslinking,and then used in the esterification reaction of the four-element mixed system dehydration research,due to its distinguished separation performance under acidic condition.The HCPN membrane was immersed in strong acidic solution before use to enhance the hydrogen-bonding crosslinking degree of the membrane.The structure change of HCPN membrane before and after acidic solution treatment was characterized by IR,water contact angle（WCA）,differential scanning calorimetry（DSC）,etc.The result supports that the protonation of PAA after acid treatment,which provided more active hydrogen for further crosslinking.The separation performance of HCPN before and after acid treatment was compared in dehydration of acetic acid contained feed solution.The optimized membrane was used in the dehydration of the esterification reaction system,i.e.,ethyl acetate,isopropyl acetate,and n-butyl acetate synthetic system.The separation performance and long-term operation stability of the membrane was investigated with different acid/alcohol ratios.The results showed that the HCPN membrane treated with acid exhibited good separation performance in dehydration of esterification reaction system.For isopropyl acetate and n-butyl acetate systems with larger molecular dynamics diameters,the permeate water content was 99.44wt%and 99.82wt%,respectively.promising for coupled pervaporation dehydration in the process of esterification reaction.In summary,taking advantages of p H-responsive feature of HCPN,the crosslinking degree of HCPN membrane was enhanced with the acids.As a result,the crosslinking degree enhanced HCPN membrane could work stably under acidic condition,which shows outstanding dehydration ability in acidic PV process.