Defect-Patching of Zeolite Membranes by Surface Modification Using Siloxane Polymers for CO2 Separation

Grain boundary defects are normally formed in zeolite membranes during membrane preparation and calcination processes. In thiS work, a siloxane polymer coating with an imidazole group as grafted on the surface of defective SSZ-13 membranes by chemical liquid deposition to seal the defects. The parameters, such as silanization time, polymerization time, monomer type, and concentration, were optimized. Characterizations including Fourier transform infrared spectroscopy, field-emission scanning electron Microscopy, and energy-dispersive X-ray spectroscopy showed that siloxane polymers were coated on the surfaces of SSZ-13 crystals and membrane. Six modified membranes showed decreased CO2 permeance by only 21 +/- 5% [average CO2 permeance of 1.9 X 10(-7) mol/(m(2) s Pa)] and increased CO2/CH4 selectivity by a factor of 9 3 (average CO2/ CH4 selectivity of 108) for an equimolar CCYCH4 mixture at 298 K. CO2/CH4 and CO2/N-2 selectivities of the modified membrane -decreased with pressure and temperature. Membrane stability Was inveStigated by a long-time test and exposures to watet-vapor at temperatures up to 378 K and to sOme organic solutions. This modification method is also effective in sealing the defects of other Zeolite membranes, such as AlPO-18 membranes.