Catalytic membrane reactor-separator for environmental applications.

Abstract

Flow-through catalytic membrane reactors offer the potential for improved conversions at reduced operating temperature due to product separation and catalyst activity. An experimental work dealing with a forced flow-through membrane reactor is the subject of this thesis. The focus is on the performance and transport characteristics of selective thin-supported silica membranes and flow-through catalytic membrane systems. The improvement of VOC-selective, H2-selective and CO2-selective membrane properties by the use of systematic dip-coating techniques and the application of the technique in a bi-layer membrane repair concept for gas separation membranes has been studied. In addition, several methods were used to characterize the membranes, including scanning electron microscopy, energy diffraction X-ray, nitrogen adsorption and gas permeation. In the first part of this work, CO2 permeance (3.39 x 10-8 mol m-2 s-1 Pa-1 at 25 0C for γ-Al2O3 membrane after exposing boehmite to the support) was mainly attributed to the Knudsen diffusion mechanism. CO2/CH4 selectivity of 24.07 was obtained from the silica membrane at 25 0C and 0.7 bar. Such a selectivity value could be useful in small-scale carbon dioxide removal units for natural gas treatment processes. In addition, H2/N2 selectivity of 1.36 and 2.72 at 1 bar were obtained from macro and meso porous membranes at 25 0C. The selectivity of propylene (C3H6) over N2 was also obtained. Higher selectivity of 1.79 at 0.05 bar was obtained. This selectivity increased by a factor of 2 compared to the ideal Knudsen selectivity (0.82). Remarkable propane conversion of 95.47% was achieved at a temperature of 378 0C on a 3.52 wt% platinum (Pt) catalyst at different total flow rates, ranging from 166 to 270ml/min. The temperature at which the catalytic combustion takes place for the VOC corroborates with (or is lower than) the one obtained from the literature for the same VOC on 5 wt% Pt/γ-Al2O3 catalysts.