Manipulation Of Homogeneous Membranes With Nano-sized Spherical Polyelectrolyte Complexes For Enhanced Pervaporation Performances

Organic polymer membranes,due to their low cost,good film-forming property and excellent separation performance,are potential and promising in the application of organic solvent dehydration.Among them,polyelectrolyte complex membranes（HPECMs）consisted of spherical polyelectrolyte complexes（PECs）are of great interests owing to their high hydrophilicity as well as stable ionic crosslinked structure.At present,how to optimize the structure of the HPECMs and improve their pervaporation performances in the application of alcohol/water separation is one of the urgent problems to be solved.Under this background,this thesis was devoted to fabricating the pervaporation membranes with excellent separation performances which would be applied to the pervaporation of alcohol/water solution.Based on the solution–diffusion mechanism,the pervaporation performances of the HPECMs were further increased by controlling the surface properties and thickness of the HPECMs.Centering on the manipulation and pervaporation performances of the HPECMs,this thesis mainly carried out the following three parts:1.Nano-sized spherical PECs and PEC dispersions of different ionic complexation degree（ICD）values were prepared using the"acid protection–alkali deprotection"method,and the four different thicknesses of the HPECMs were synthesized on the polyacrylonitrile ultrafiltration membranes by regulating the concentrations of the PEC dispersions.The zeta potential,transmission electron microscopy,nanoparticle size analysis,static water contact angle and scanning electron microscopy characterizations indicated that the controllable charge density and nano-sized spherical morphology of the PECs,and the high hydrophilicity and homogeneous nature of the HPECMs of different thicknesses,which were of great significances for the subsequent development of pervaporation applications.2.The synthesized HPECMs were subjected to isopropanol dehydration,the effects of ICD,membrane thickness,operating temperature and water content in feed on the pervaporation performances of the HPECMs were investigated,and the durability and stability of the HPECMs during long-term pervaporation were evaluated.The results showed that the HPECM 0.80-3 with the thickness of ca.1.1μm displayed a pretty high permeation flux(6.12 kg m^–2 h^–1)with an ideal water concentration in permeate（99.85wt%）for 90 wt%isopropanol/water solution at 70°C.A severe loss in separation selectivity was observed when the HPECM thickness was below 1.1μm.In addition,the synthesized HPECMs had satisfactory durability and stability in long-term separation applications.3.Based on the above results,HPECMs with a thickness of ca.1.1μm were used in ethanol dehydration,achieving an efficient pervaporation performance for separation of 90 wt%ethanol aqueous solution.The permeation flux and the water concentration in permeate of the HPECM 0.80-3 were 6.24 kg m^–2 h^–1 and 98.43 wt%at 70°C,respectively,illustrating that the synthesized HPECMs possessed potential in the application of other organic solvent dehydration.