Modification Of Polyacrylonitrile Membrane And Assembly Of Polyion Composite Membrane By A Dynamic Layer-By-Layer Technique

In this paper, the pervaporation complex membranes were assembled by a dynamic layer-by-layer absorption of PEI/PAA polyelectrolyte on hydrolyzed PAN ultrafiltration support membranes. The appropriate hydrolysis conditions of support membranes and effects of assembly process conditions on pervaporation performance of complex membranes were investigated. The characteristics of complex membrane were determined by modern analytical method. Subsequently, the complex membranes were applied to separate different alcohol/water systems.By measuring pure water flux, retention ratio and ionic exchange equivalent weight of PAN and hydrolyzed PAN under different hydrolysis conditions, the suitable hydrolysis conditions were determined as follows: NaOH concentration 2N, hydrolysis temperature 60℃and hydrolysis time 1h. The effects of different inorganic alkaline on the hydrolysis of support membranes were investigated. The results show that alkaline solution with high intensity is beneficial to increase amount of COO- of support membrane and in turn to improve hydrolyzed degree. In addition, it was noted that the MWCO of hydrolyzed PAN support membrane decreased to approximately 6000.The experimental results of contact angle and IR proved that the hydrophilicity and charge property of the hydrolyzed membrane were improved. This would benefit the subsequent assembly of polyelectrolyte composite membranes. The results of SEM and AFM show that hydrolyzed membrane surface became smoother and the average roughness of hydrolyzed membrane surface decreased from 43.655nm to 27.279nm. The effects of hydrolysis conditions of support membranes on pervaporation performances of complex membranes were also investigated. It was found that high hydrolysis degree could facilitate to assemble the pervaporation complex membranes with high performance. Meanwhile, the assembly process of polyelectrolyte membranes was optimized. The unprotoned hydrolysis membranes and ethanol was selected as the support membrane and the solution of PEI, respectively. Then, the effects of operation conditions on the pervaporation separation of different alcohol/water mixtures were subsequently studied. It was found that the higher feed temperature and the larger molecular weight of alcohol could facilitate the separation process. In the case of pervaporation of 95wt% ethanol/water mixtures, under the temperature of 70℃, the separation factor and the permeate flux of the polyelectrolyte complex membranes were about 604 and 314 g/(m2 h), respectively.