Pervaporation and vapor permeation dehydration of Fischer-Tropsch mixed-alcohols by LTA zeolite membranes

Aiming at the applications in Fischer-Tropsch synthesis of mixed-alcohols, microwave synthesized LTA zeolite membranes were applied to pervaporation and vapor permeation dehydration of unitary and mixed alcohols. The water to methanol separation factor was found to lie between 150 and 1000. Both water to ethanol and water to propanol separation factors were observed to be above 10,000 over a wide range of solvent concentration. It was found that the water flux was only depended on its own driving force, i.e. the pressure difference of water across the membrane. High separation factors were also obtained by vapor permeation for ethanol and isopropanol systems. At the liquid-vapor equilibrium state, the water fluxes of pervaporation and vapor permeation showed no obvious difference. Two different types of F-T mixed-alcohols were dehydrated by pervaporation and vapor permeation, respectively. One is simulated mixed-alcohols based on IFP technique, and the other is actual F-T liquid produced on Rh-based catalysts. The separation factor of the former was similar to that of methanol system, and the water flux was between that of methanol and ethanol. This is coincided with the fact that the mixed-alcohols are mainly composed of methanol and ethanol. As for the latter, good separation performance was obtained at the initial stage. However, the long chain hydrocarbon impurities in the feed fouled the membrane during the operation, which resulted in an obvious decrement of the permeate flux after 3 h of operation. (c) 2007 Elsevier B.V. All rights reserved.