Preparation And Performance Of Polyurethane/Polyurea Pervaporation Membranes For Ethanol Dehydration

With the increasing energy consumption and environmental problems,fuel ethanol has attracted tremendous attention with the characteristics of renewable,non-polluting and wide source.In the production of fuel ethanol,pervaporation has been widely researched recently because of its many advantages including energy saving,eco-friendliness,safe operation and it's free limited by gas-liquid equilibrium.As the key of pervaporation technology,pervaporation membranes play a very important role in the whole process.In this paper,polyurethane and polyurea pervaporation membranes were researched by changing preparation processes and membrane materials to improve the membrane performance.Polyvinyl-alcohol?PVA?was crosslinked with 2,4-tolylene diisocyanate?TDI?to prepare polyurethane pervaporation membranes via layer-by-layer process,and the membranes were tested by 95 wt%ethanol/water mixture.It was found that when the PVA concentration exceeded 1 wt%,the surface of the membrane was not uniform due to the increasing viscosity.The crosslinking degree increased with the increasing concentration of TDI,however,the decrease of the hydrophilicity and the introduction of the rigid benzene ring reduced the membrane performance.With the bilayers increasing from 1 to 5,the thickness of the active layer and the separation factor gradually increased,and the surface roughness and permeation flux gradually decreased.The separation factor and permeation flux of the pervaporation membrane with the best performance were 45.15 and 716.33 g·m^-2·h^-1 respectively.In order to further improve the performance of pervaporation membranes,polyethylenimine?PEI?,which could react with TDI more easily during interfacial polymerization,was chose to prepare polyurea pervaporation membranes with multilayers by the spin-coating process.At the spinning rate of 5000 rpm,the membrane with 3 bilayers fabricated by the crosslinking of 0.5 w/v%PEI with 0.1 w/v%TDI for 2 minutes,performed best in the separation of 95 wt%ethanol/water mixture at 80°C.The separation factor and flux were 90.77 and 1445.11 g·m^-2·h^-1 respectively.In addition,the pervaporation membranes with gradient crosslinking degrees were prepared by changing the TDI concentration of each bilayer,and the performance was improved significantly.The separation factor of M_4-2-0 reached to214.58 with a flux of 1098.38 g·m^-2·h^-1.And M_4-2-0 performed excellent stability during the test.