Preparation Of New PVA/PA Composite Membrane And Performances Of Separating Isopropanol/Water Mixtures By Pervaporation

It is considered that the membrane technology is playing thestrategic role in industrial innovation in 21th century. The membranematerial is always the core of the whole membrane separation processesand the improvement of its performances is an essential research indeveloping membrane science and technology, which would directlyinfluence the separation effect of mixtures and the investment inmembrane equipment. In recent years, it has been made the significantprogress that the polyamide (PA) membrane for reverse osmosis (RO)desalinization, which has been industrially manufactured, has beendeveloped into the new pervaporation (PV) membrane for separatingorganic mixtures with the appropriate modification technique.In this paper, the highly water-permeable PA RO membrane used asthe support and the hydrophilic polyvinyl alcohol (PVA) membrane withhigh separation factor were compounded. The prepared PVA/PA composite membrane was used in separating isopropanol (IPA)/watermixtures by PV. Moreover, through the optimizationes of PVA castingformularization, the membrane-forming process and the PV operationconditions, the PVA/PA composite membrane with superior separationperformances was prepared. The PA membrane used in this work was onepurchased from the market, and the PVA casting solution was coated onits surface. So, its process and equipment of PVA/PA compositemembrane preparation are simple. It would be easy to realize theindustrial production of the PVA/PA membrane.In the experiments, the membrane surface structures were observedand analyzed through AFM and SEM. Then, the PV performances of PAmembrane, PVA homogeneous membrane and PVA/PA compositemembrane were compared. The results showed that the preparation ofPVA/PA composite membrane on the PA membrane surface through thecomposite process was feasible. Moreover, the morphology and theperformance of the PVA/PA membrane in separating IPA/water mixturesby PV were satisfying. From the SEM pictures, the surface of PA ROmembrane was very rough, but the surface of PVA/PA compositemembrane was much smoother as a result of PVA being coated on the PAsurface. The AFM three-dimensional pictures demonstrated that thesurface of PA membrane was uneven, and the highest protrudent spotreached to about 200nm. However, roughness of the surface of PVA/PAcomposite membrane was improved obviously, and the highest protrudentspot decreased to about 4nm because of PVA being coated on its surfaceto revise the surface of PA membrane.The effects of the membrane-forming conditions, such as the typeand the concentration of the crosslinking agent, the temperature and thetime of the heat treatment, the concentration of PVA in the castingsolution, and the operation conditions on the separation performances of PVA/PA composite membrane were emphatically investigated. Thestability of the membrane performances in the operating process was alsodiscussed. The following conclusions can be drawn from the aboveexperimental results.(1) The concentration of PVA in the casting solution intenselyaffected the PV performances. The separation performances of compositemembrane crosslinked by maleic acid (MA) was better than that byglutaraldehyde.The optimum concentration of PVA and MA in castingsolution were 7wt% and 5wt%, respectively.(2) The effect of the temperature of heat treatment on PVperformances of PVA/PA composite membrane was more remarkablethan the time of heat treatment. The best temperature and time of heattreatment were 150℃and 1h, respectively.(3) The flux (J) and separation factor (α) of PVA/PA compositemembrane were closely related to the concentration of IPA in the feed(C_F-IPA) and the opreration temperature (T). With the increasing of bothC_F-IPA and T, the concentration of IPA in the permeation was always lessthan 1.0wt%. Through the regression of experimental results, the forecastequations of the fluxes for water and isopropanol permeating the PVA/PAcomposite membrane were established.For water:J_w=-1.58C_F-IPA+179.38For IPA:J_IPA=-0.013C_F-IPA+1.35Total:J=1669.03exp(-1105.5/T)(4) PV performances of PVA/PA composite membrane were stablewhen separating IPA/water mixtures. (5) When in the separation of azeotropic IPA/water mixtures on80.4℃, it gave permeate flux 73.10g/m²h and concentration of water inthe permeation more than 99.0wt%.In the design of integration process ofdistillation and PV, PVA/PA composite membrane could be applied to theseparation of IPA/water mixtures in food, biological and pharmaceuticalengineerings. So it can save the expenses.PVA/PA composite membrane with high separation performanceswill reveal its important application values in the actual separationprojects.