The Preparation and Characterization of Silicalite/alumina Composite Membrane

• Main Authors: Cherng-Shyan Tsay, 蔡澄賢
• Other Authors: A.S.T Chiang
• Format: Others
• Language: en_US
• Published: 1998
• Online Access: http://ndltd.ncl.edu.tw/handle/79913415991717033728

博士 === 國立中央大學 === 化學工程研究所 === 87 === Abstract The purpose of this study was devoted to prepare an asymmetric silicalite/alumina composite membrane, and to characterize this membrane by measuring the permeance of single gases at room temperature. The composite membrane was composed of five layers including an alumina support, two intermedium layers of 4 and 1mm a-alumina particles, a ultrafilitration layer of g-alumina, and a separation layer of silicalite-1. For this study, the alumina layers were practiced as the substrate of silicalite-1 layer. Compared to the literature, there are two important procedures of this study. First, we coating a silica layer on alumina substrates before silicalite-1 layer prepared. Then, a novel method of deposition follows by 100oC steaming hydrothermal treatments, an ultra thin silicalite film less than 0.5mm thick can be formed on porous alumina composite support. The deposition process employed 80nm silicalite suspension for these thin silicalite-1 films preparations. The silica layer was employed to improve the surface roughness of alumina substrate and to prevent the invasion of aluminum to sililcaite-1 layer. The thickness of this layer was only 0.2mm and exhibited a inter-pore smaller than 10nm. This layer was prepared by the spin coating of silicate alcohosol, which was composed of 0.05/1/2.11/2.22/0.256 mole ratio of MTES/TEOS/EtOH/H2O/HCl system. After 460oC calcination, a thick and defect-free silica layer was combined on the surface of alumina composite membranes following. This layer exhibited a good selectivity of 12.5 of He/N2 permeability ratio. The utilization of steaming method can be better for controlling the layer thickness of silicalite-1 films if depositing a proper content of silicalite-1 previously. After 100oC steaming treatments and 500oC calcination, it was visible that these silicalite particles of thin film were close packed. Otherwise, the aligned of silicalite-1 only happened possibly on the top layer of deposition, or while depositing a monolayer silicalite-1 crystalline. Compared to literature, we propose here that if the permeability of hydrogen larger than 80x10-13 (mol-m/Pa-s-m2) or of helium larger than 35x10-13 (mol-m/Pa-s-m2), the zeolite membrane prepared should not be defect-free for use. The ultra thin silicalite-1 films in this study gave a 32x10-13 mol-m/Pa-s-m2 permeability of helium at room temperature, and exhibited best He/N2 and CO2/N2 permeability ratio of 1.88 and 1.18, respectively. Give the provide that the behaviors of N2 and CO2 in this silicalite layer were not Knudsen diffusion. The helium permeabilities in this study of a-alumina supports and g-alumina/a-alumina membranes were 1x10-4mol/m2-sec-Pa and 4x10-5mol/m2-sec-Pa from 130 to 300kPa, respectively. This permeability was only smaller than Alcoa (US filiters) and larger than other reported alumina membranes in literature. Otherwise, this composite membrane exhibited a best permeability ratio of CO2/N2 of 1.3, indicating a surface flow cause by the adsorption behavior of CO2 was performed in these membranes. The g-alumina layer of g-alumina/a-alumina membranes was prepared by the spin-coating and a novel peptization process of stable aluminum hydrosol. The use of aluminum hydrosol was composed of 0.25/11.2/0.025 mole ratio of pseudoboehmite/H2O/ HNO3, and the peptizer used was 2.58MHNO3(q). After 560oC calcination, a 1.0 mm thick layer of g-alumina was consolidate on the surface of three-layer a-alumina support. We report here several processes and an ideal approach for silicalite/alumina composite membrane preparation. We suggest a successful method of steaming treatment cooperates with nanometer crystalline deposition give a simple way for ultra thin silicalite-1 film preparation.