VACUUM-ASSISTED PROCESS FOR PREPARING AN ION-EXCHANGED ZEOLITE MEMBRANE

摘要

Effect ion-exchange of an alpha-alumina supported zeolite (e.g. a MFI zeolite, an LTA zeolite or a FAU zeolite)membrane, which process comprises: a) placing the membrane, which has a first surface and a spaced apart second surface, the first and second surfaces defining therebetween the membrane, in an ion exchange apparatus such that the first surface is in contact with an ion exchange solution and the second surface is in contact with a vapor space that is connected to a source of reduced pressure; b) actuating the source of reduced pressure to create a pressure differential between the first and second membrane surfaces of at least 0.4 atmosphere (0.405 x 105 pascals); and c) maintaining the pressure differential under ion exchange conditions for a period of time sufficient to effect exchange of an ion contained in the ion exchange solution with an ion in the zeolite membrane in an amount that is greater than an amount of ion exchange attained using an apparatus that places the second surface in contact with a liquid solvent that is at a pressure of at least one atmosphere (1.013 x 105 pascals) and the first surface in contact with the ion exchange solution at a pressure of at least two atmospheres (2.026 x 105 pascals) so as to establish a pressure differential between the two surfaces of at least one atmosphere (1.013 x 105 pascals), maintaining the pressure differential for the same period of time, and using the same ion exchange membrane, ion exchange solution and ion exchange temperature, the greater amount of ion exchange yielding an improved ion exchange membrane that a ratio of the ion that entered the membrane from the solution to the ion that left the membrane that is greater than that of the ion exchanged membrane prepared with the second surface in contact with the liquid solvent.