Study On Preparation,Characterization And Separation Application Of PVA/ZIF-8-NH₂ Mixed Matrix Membranes

As a new type of energy fuel,n-butanol has attracted the attention of a large number of researchers because of its advantage that it can be mixed with gasoline in any ratio.n-Butanol can be produced by biological fermentation,and the fermentation product usually contains n-butanol,acetone and ethanol,etc.Therefore,it is still necessary to further purify and separate n-butanol from the fermentation product to obtain high-concentration n-butanol.In recent decades,pervaporation membrane separation technology has attracted much attention because of its advantages of simple equipment,easy operation,low energy consumption,etc.,which provides an efficient separation path for purification and separation of n-butanol fermentation liquor.Polyvinyl alcohol（PVA）,as a water-soluble polymer with easy degradation,simple preparation,good film-forming property and good resistance to organic solvents,is one of the representative hydrophilic membrane materials for the dehydration of organic solvents by pervaporation.MOF membranes based on metal-organic frameworks（MOFs）typically have good chemical stability.However,the water resistance of PVA membrane is poor,MOF is difficult to form,and the manufacturing cost is high.Therefore,it can combine the advantages of the mixed matrix membrane by adding MOFs to PVA,and there is a good application prospect in the pervaporation separation of alcohol/water.In this paper,PVA/ZIF-8-NH₂mixed matrix membranes were prepared by using amino-modified ZIF-8-NH₂as filler and PVA as matrix,and the properties of synthesized ZIF-8 and ZIF-8-NH₂as well as the properties of the mixed matrix membranes were analyzed by means of characterization.Then,the swelling and adsorption separation performance,pervaporation ethanol dehydration and n-butanol dehydration performance of PVA/ZIF-8-NH₂mixed matrix membrane in alcohol/water mixed solution were investigated,which provided a research reference for the practical application of alcohol/water separation.The main research contents and conclusions of this paper are summarized as follows:（1）Characterization of ZIF-8-NH₂:The XRD pattern shows that ZIF-8-NH₂powder with complete crystal structure is successfully synthesized.The FTIR pattern confirm that the amino group exists in ZIF-8-NH₂.The SEM images show that ZIF-8-NH₂particles are uniform in size and regular in shape.The BET analysis shows that the specific surface area of ZIF-8-NH₂is 1358 m~2/g.（2）Characterization of basic physical properties of PVA/ZIF-8-NH₂mixed matrix membranes:The XRD result shows that with the increase of ZIF-8-NH₂content in the mixed matrix membrane,the intensity of PVA characteristic peak gradually decreased while the intensity of ZIF-8-NH₂characteristic peak gradually increased.The FTIR pattern shows that fumaric acid successfully crosslinked PVA,but there are still a large number of hydroxyl groups in the mixed matrix membrane.SEM images show that with the increase of ZIF-8-NH₂content,the compatibility between filler and matrix becomes worse,and agglomeration phenomenon is more likely to occur.Tensile test results show that fumaric acid cross-linking can enhance the mechanical strength of pure PVA membranes,but the mechanical properties of the membranes gradually decrease with the increase of ZIF-8-NH₂content.The test results of optical performance show that with the increase of ZIF-8-NH₂content,the transmittance of the mixed matrix membranes decreased gradually,and the haze index increased gradually.The contact angle test results indicate that the contact angle between the two polar liquids（water and glycerin）and the mixed matrix membrane is smaller than that of the biododemethhane non-polar liquid,indicating that the surface of the mixed matrix membranes is highly polar,reflecting hydrophilic.（3）Swelling and adsorption separation performance test of PVA/ZIF-8-NH₂mixed matrix membrane:The crosslinked PVA membrane and ZIF-8-NH₂mixed matrix membranes with the content of 10,20 and 30%were selected for determination.The swelling test results of four membranes in three different liquids of water,ethanol and n-butanol at 30℃show that the degree of swelling of the membranes in water is the largest,reflecting the preferential permeability of the membranes.When the ZIF-8-NH₂content is10%,the water swelling degree of the mixed matrix membrane is the largest,which is92.97%.The water swelling degree of the four membranes at different temperatures show that the swelling degree of the membranes with lower ZIF-8-NH₂content increases with the increase of temperature,while the swelling degree of the membranes with higher ZIF-8-NH₂content reach the highest and then decrease when the temperature rose to 40℃.Solubility parameter calculation analysis show that amino modification can increase the hydrophilicity of ZIF-8 particles.The adsorption and separation performance results of the four membranes in the concentration of 85%ethanol/water solution or n-butanol/water solution show that the equilibrium adsorption capacity and adsorption separation factor of the membranes in n-butanol/water solution were higher than that of ethanol/water solution,indicating that the adsorption and separation capacity of the membranes for n-butanol/water solution was stronger.（4）Pervaporation separation performance tests of ethanol/water and n-butanol/water:The experiments show that when ZIF-8-NH₂is 10%,the pervaporation separation effect of mixed matrix membrane is better,the total fluxes of ethanol/water and n-butanol/water are391.1 and 81.5 g/m~2h,and the separation factors are 3.3 and 166.8,respectively.With the increase of ethanol concentration of feed solution,the total flux of membrane decreases and the separation factor increases slightly.However,the increase of n-butanol concentration of feed solution is not conducive to the separation of n-butanol/water solution by pervaporation.The total fluxes of pervaporation separation of ethanol/water and n-butanol/water increased with the increase of temperature.