Preparation Of Polvelectrolyte Complex Membranes Based On NaCS And PDMDAAC And Its Pervaporation Characteristics

Membrane techniques are one of the 21st century most important new technologies. Exploit new type of membrane material can largely promote membrane technology. In the last ten years, Polyelectrolyte complex membranes have been more and more investigated in the membrane research field because of its advantage in the separation process:one - dimensional control on the molecular level, the simple preparation methods and materials, stabile characters and so on.In this paper, a new types of NaCS/PDMDAAC polyelectrolyte complex (PELC) membranes, supported by PVDF membrane, prepared by interfacial reaction of sodium cellulose sulfate (NaCS) as polyanions and poly (dimethyldiallylammonium chloride) (PDMDAAC) as polycations, was proposed. The preparation conditions, membrane construction, permeability properties and application in pervaporation process were investigated. The main conclusions were as follows:The characters of both NaCS and PDMDAAC, such as viscosity, conductivity and Zeta potential in water and salt solution were investigated. To clarify the complex reaction of NaCS and PDMDAAC in water and salt solution, the turbidity, the conductivity, Zeta potential and Z-average diameter of polyelectrolyte complex were also studied.The preparation conditions of NaCS/PDMDAAC PELC membrane were optimized. The range of preparation conditions was:NaCS 20g/L-40g/L, PDMDAAC 30g/L-200g/L, reaction time 20-30mino The membrane with these conditions possessed compact framework structure, uniform surface and thickness, also steady chemical property.The swelling behavior of the membranes in different concentration of ethanol were measured; the effect of concentration of polyelectrolyte, molecular weights(Mw), time of infusion and temperature of infusion on swelling ratio was investigated, it was found that the PELC membrane had preferential adsorption of water. The swelling ration equilibrium was achieved after 3 hours, and it increased with the increasing temperature, decreased with the increasing concentrations of ethanol, NaCS and PDMDAAC. The static contact angle of PELC membrane surface was measured to characterize membrane wettability. The static contact was among 40°-55°. The effects of concentration of polyelectrolyte, Mw, and reaction time on contact angle were investigated. It was found that NaCS/PDMDAAC PELC membrane was hydrophilic. Its contact angle decreased with the increasing concentration of NaCS and Mw of PDMDAAC, increased with the increasing concentration of PDMDAAC and reaction time.The permeability properties of NaCS/PDMDAAC PELC membrane were investigated by changing preparation conditions and operation conditions. It showed that, Mw of PDMDAAC and reaction times were two important factors, which affected the membrane formation procedure and permeability. The No.1 membranes with the preparation conditions as NaCS 35g/L, PDMDAAC (Mw=250,000-350,000) 70g/L, and reaction time 30min, hold a favorable performance, and steady state in water flux experiment. When the operation pressure was 0.20MPa, the water flux was 213.6 L/m2 · h. Also, the membrane No.1 had an excellent steady state in the repeating experiments.The complicated interaction between the salt and PELC layer should be taken into account when the flux and salt rejection were discussed. The membrane dissolution and cationic adsorption were two major factors which changed the membrane performances and selectivity. The obtained results showed that PELC membrane afforded higher rejections of divalent ions (SO42-) to that of monovalent ions (C1), which indicated the potential capability of this PELC membrane system in the salt rejection process.In the pervaporation experiments, the NaCS/PDMDAAC PELC membrane showed great performances and selectivity in the dehydration of ethanol/water, acetone/water and isopropanol/water systems. The flux of these three system were all above 1500g/m2 · h, and the selectivity factor were all more than 1000. Especially, in the ethanol/water systerm, the selectivity factor was more than 1400, which was more than that of NaCS/PDMDAAC PELC membranes studied in the reported literature. It also displayed steady structure and excellent performance in both repeating and long-term pervaporation experiments.