New Hydrophilic Polymer - Ceramic Infiltration Study Of The Vaporization Of The Composite Membrane

Pervaporation has gained increasing attention in many chemical processes as an effective and energy-saving membrane technique for separating of azeotropes, close-boiling mixtures,isomers and thermally sensitive compounds.However,lower permeation flow of the polymer membranes and the high fabrication cost of the inorganic membranes limit their industrial applications.In recent years,the inorganic/organic composite membranes have attracted more attentions.They are composed of porous ceramic membranes such as SiO₂,Al₂O₃ as supports and covalently anchored hydrophobilic polymer as separation layer for the separation of organic mixtures or the removal of organic compounds from waste water.The experiment results showed that this kind of membranes combined the advantages of the inorganic membrane and polymeric membrane:the good mechanical,thermal or chemical stability as the inorganic membrane and the high selectivity as the polymeric membrane but the permeation flux is higher than it.So this kind of organic-inorganic membranes has a potential application in pervaporation in future.In this article,a novel hydrophilic polymeric-ceramic pervaporation membrane for the dehydration of organic solutions was prepared by the free-radical graft polymerization reaction onto the microporous ceramic membrane which was pre-coated with a SiO₂ layer by in-situ hydrolysis and deposition method and then silylated with a coupling agent.The synthesis condition,the membrane structure and its separation performance at different operation conditions have been systematically studied.Porous ceramic supports should be coated with a SiO₂ active layer in order to regulate the pore size and to introduce the -OH groups as active sites.We developed a new method to hydrolyse in-situ TEOS and then form SiO₂ onto the ceramic surface. The hydrolysis-deposit conditions such as TEOS content and reaction time on the ceramic property were studied.It was found that the pore sizes of the ceramic support can be controlled by changing the TEOS concentration in ethanol and reaction time. For instance,the water permeation flux at 30℃and 150 Pa was about 100 kg·m^-2·h^-1 if a ceramic membrane of pore size about 3μm was treated with TEOS/EtOH of 1:15 (in weight) for 32 h.The obtained membrane with such water permeation flux seems suitable for preparing a high performing membrane after silylation and graft polymerization.Due to its facility in operation and pore size control comparing with conventional technology such as sol-gel or CVD,this method is applicable for inorganic-organic composite membrane preparation.In this work,three hydrophilic compounds:PAA,PVI and P(VI⁺·Cl^-) were used as grafting polymer to preparing organic-inorganic membrane.The composite membranes were characterized by FTIR,SEM and contact angle measurement.Their performance for dehydration of organic solvent by pervaporation was measured.The results showed that all three membranes exhibited high selectivity and high permeation flux for dehydration of alcohol:the water content in permeate was over than 99%and the permeation flux was more than 400 g·m^-2·h^-1.Among them,theâ…¥was applied as grafting monomer and separation barrier material for the first time.It is noticeable that theâ…¥graining-ceramic membrane protonated in ionic form was very selective and stable for the separation of corrosive acetic acid/water mixture in which the most polymeric membranes were no more resistable.The effect of operation conditions on the membrane performances was also studied.It was found that the permeation flux decreased with operation temperature.A similar phenomenon was observed with an AA-filled ceramic membrane which was prepared with a same schedule but without silalyzation by coupling agent,which means no grafting was occupied.According to the fact that the AA-filled membrane was no selective for alcohol dehydration,we may suggest that the active layer of organic -inorganic membrane prepared in this work was composed of the polymer chains grafted on the surface or in the pore wall,and filled inside the pore.That's why we can not observe a dense and homogeneous grafting layer on the ceramic composite membrane by SEM.The thermal swelling of the polymer chains inside the pores and the limit space of ceramic pores made it more difficult for the diffusion of the solvent at higher temperature.That's why the permeation flux decreasing with temperature is observed in our case.According to the separation mechanism of the pervaporation,the membrane performance is determined by the property of the solution and diffusion of the solvents in the membrane which relates with the interaction between the solvents and membrane material.So it is important to study the diffusion behavior of the solvents in membranes.We measured the diffusion coefficients by FTIR-ATR method.The effect of the solvent property and the interaction among the solvents on the diffusion process was systematically studied.The experiment results showed that the bigger were the diffusion coefficients,the closer the property of the solvents with the polymer membrane material.It was found that there was a co-diffusion effect for multicomponents diffused in membranes.The plastication coefficients and the solvent concentration had a function relation to some degree.Besides,we also measured the diffusion coefficients of the water in SPEK-C membrane with different sulfonation degree.The hydrophile of the membranes increased with the increase of the sulfonation degree,and the water diffusion rate in membranes also increased gradually,correspondingly.In this article,a hydrophilic positively charged nanofiltration membrane prepared by UV irradiation graft polymerization of dimethyldiallyammonium chloride (DADMAC) onto the surface of ultrafiltration membranes made of cardo polyetherketone(PEK-C) was also studied.Several analytic methods such as FTIR-ATR,AFM and contact angles were employed to characterize the chemical and physical property of modified membranes.The grafting degree of the membrane and their hydrophilicity increased with the irradiation time and the monomer concentration in grafting solution.The modified PEK-C membrane showed a good retention to most divalent cationic ions salt solutions.For example,the retentions of the membrane modified with 65%of DADMAC for 10 min under 8.7 mW·cm^-2 to high valent cations such as Ca²⁺,Cd²⁺,Ni²⁺ were beyond 95%at 0.5 MPa,which was better than negatively charged nanofiltration membranes.So the modified positively charged nanofiltration membranes will have a potential application in the softening of hard water or the treatment of heavy metal ions wastewater.But the separation performance of modified membranes decreased remarkably at the presence of high valent negative counter-ions such as SO₄^2-.The results showed that the high counter-ions existed in salt solutions produced shielding effect for centered ions. Similarly,the retentions decreased with the salt concentration increase in solutions. This study proved that the electrostatic effect played a major role in nanofiltration by charged membrane.