Preparation And Application Of Ethanol Permselective PDMS/PPESK Pervaporation Membrane

Pervaporation is a new technology of membrane separation for the separation of liquid mixtures, which based on the membrane's different selectivity towards the various components in the mixture. It has special advantage in the use of the separation of homogeneous mixtures such as azeotropic, closing-boiling and isomeric mixtures, which are difficult or impossible to separate by conventional methods, and will also be widely used in the separation of dilute alcohol aqueous solution. Using PPESK flat UF membrane as basement membrane, PDMS(polydimethylsiloxane) as coating material, a novel pervaporation composite membrane was prepared via surface-coated method and used in the separation of ethanol-water mixtures.First, appropriate solvent and nonsolvent additive were chosen to study the phase separation behavior of polymer/solution/nonsolvent additive and the ternary phase diagram was drawed. Structure and performance of the PPESK flat UF membranes prepared based on the phase separation behavior has been systemically researched. The effect of thermodynamics and dynamic factors to the performance of membranes were studied, such as the concentration of polymer, the concentration of additive and evaporation time. The structure research and character analysis were made with pure water flux, retention rate and SEM. A better pervaporation basement membrane was obtained and its pure water flux was 142.0L·m^-2·h^-1 and retention of PEG6000 was 93.7%. The components of casting solution were as following: concentration of PPESK was 17wt.%, concentration of DMAc was 76.9wt.% and concentration of EGME was 6.10wt.%.Second, with the surface-coated method, the pervaporation composite membrane has been prepared using PDMS as the coating material. Composite membrane was detected by IR(infrared spectrum), and the surface-coated method was proved effective by spectrogram. The effect of curing time, curing temperature and the concentration of PDMS were studied. The character analysis was made with permeation flux and separation factor. Appropriate conditions were as following: concentration of PDMS was 12wt. %, curing time was 4 hours, and curing temperature was 80℃. The separation factor was 4.70 and the permeation flux was 1380 g·m^-2·h^-1 in the separation of 5wt.% ethanol-water mixtures. Finally, the effects of temperature, concentration and flow rate of feed solution on the performance of pervaporation composite were studied. The results showed that permeation flux increased and separation factor decreased when the temperature of feed solution increased, permeation flux increased and separation factor decreased when the concentration of feed solution increased, permeation flux and separation factor increased when the flow rate of feed solution increased. A comparative study of the swelling characteristics of PDMS membrane was also carried out. The results showed that swelling behavior increased when the concentration and temperature increased.