Zeolite NaA membranes supported on α-alumina cylindrical tubes

Zeolite NaA membranes were prepared on the surfaces of alpha-alumina cylindrical supports using the hydrothermal synthesis. Regardless of the porosity size of the alpha-alumina support, the zeolite membranes consisted of three layers. Compared with the previous membrane, which was prepared on mullite support, the zeolite crystals layer was thicker and the intermediate layer was thinner. Grain boundary clearance (non-zeolite pore) size of the membrane was evaluated by permporometry. Average Kelvin diameters, which were defined as the diameters at nitrogen permeance of 50%, were at ca. 1.8 nm Kelvin diameters regardless of the porosity size of the support. The maximum value of the pore size distribution of the zeolite membranes was at ca. 1.6 nm Kelvin diameters regardless of the porosity size of the support, and only its value increased with the increase in the porosity size of the support. The membrane performance in pervaporation (PV) increased with the increase in the porosity size of the support. For industrial application of the membranes, the support of 37.6% porosity was adopted from economic standpoint. The membrane was ca. 1.2 times as high performance as the previous membrane. A high separation mechanism of PV and vapor permeation (VP) based on the capillary condensation (or pore-filling) of water in the non-zeolite pores and the blocking of other molecules from entering the pores was proposed.