Study On Preparation Of Chitosan/Sodium Alginate Multilayer Membrane And Separate Performance Of Ethyl Acetate Multi-component System

Ethyl acetate is an important organic solvent,often produced by the direct esterification method.High-purity ethyl acetate usually requires integration with separation processes such as distillation and extraction.Compared with conventional separation technologies,pervaporation（PV）provides many superiorities like low energy consumption,universality,environmental friendliness,and breaking through the limitations of vapor-liquid equilibrium.Thus,developing a suitable pervaporation membrane with high permeability and high selectivity for the esterification system is beneficial for decreasing energy consumption and cost.Polyelectrolyte polymer materials have stable structures and strong hydrophilicity.The polyelectrolyte membranes prepared through the layer-by-layer（Lb L）self-assembly method have stronger interfacial interaction,controllable and nanoscale structure.As a type of pervaporation membrane,it can achieve good separation performance.In this work,the cationic polyelectrolyte material chitosan（CS）and anionic polyelectrolyte material sodium alginate（SA）were selected as the separation layer materials.Based on the concentration of CS in the casting solution and the number of CS/SA layers,CS/SA/PAN polyelectrolyte multilayers were prepared by depositing CS and SA on the surface of polyacrylonitrile（PAN）by Lb L self-assembly.The crystallinity,morphology,and hydrophilicity of CS/SA/PAN polyelectrolyte multilayers were characterized by X-ray diffraction（XRD）,scanning electron microscopy（SEM）,atomic force microscope（AFM）,and contact angle（CA）.The swelling behavior and pervaporation of the membrane material were also investigated.The characterization results indicated that the crystallinity of CS/SA membranes was lower than that of CS and SA membranes.CS/SA/PAN membranes had a multi-layer structure and were defect-free.With the increase of the CS/SA layers in membranes,the thickness and surface roughness increased,respectively.For the increase of the CS concentration in the casting solution,the thickness of the CS/SA separation layer increased,and the surface roughness decreased.The hydrophilicity of CS/SA membrane materials was greater than that of CS and SA membrane materials.With the increase of CS concentration in the casting solution,the hydrophilicity of the membrane decreased.The swelling value of the membranes increased with the increase in solution temperature or water content.Ethanol inhibited the swelling of CS/SA materials in the solution.In addition,the calculation results of the solubility parameter method were consistent with the results of the swelling experiment,and the value of the solubility parameter proved that the affinity order of the CS/SA membrane for four solvents was:water>ethanol>acetic acid>ethyl acetate.The pervaporation dehydration performance of CS/SA/PAN polyelectrolyte multilayers in ethyl acetate/water binary system,ethanol/water binary system,ethyl acetate/ethanol/water ternary system and ethyl acetate/ethanol/water quaternary system were investigated by pervaporation experiments.Experimental results showed that the membrane with CS concentration of 0.5 wt.%in casting solution and the coating layer number of 6exhibited an optimal pervaporation separation index(3.3×10⁷ g?m^-2?h^-1).For binary,ternary,and quaternary systems,the influence trend of water content and temperature on separation efficiency was the same,as the water content increased in the feed,the total flux increased and the separation factor decreased,respectively,with the increase of temperature in the feed,the total flux and separation factor increased simultaneously.Within the test range,water permeance>ethanol permeance>ethyl acetate permeance>acetic acid permeance,and the acetic acid permeability was 0.CS/SA/PAN multilayer membranes had high flux and high separation factor,the maximum total flux and separation factor of CS/SA/PAN multilayer membranes in the binary systems of ethyl acetate/water and ethanol/water were 3208 g?m^-2?h^-1 and35042,and 1880 g?m^-2?h^-1 and 8544,respectively.In the ternary system of ethyl acetate/ethanol/water and the quaternary system of ethyl acetate/ethanol/acetic acid/water,the maximum total flux and separation factor of CS/SA/PAN multilayer membranes were 4048 g?m^-2?h^-1and 1317,and 1675 g?m^-2?h^-1 and3118,respectively.The research results showed that CS/SA/PAN polyelectrolyte multilayers were a kind of pervaporation membrane material with high flux and high separation factor.