| Summary: | 碩士 === 國立清華大學 === 生醫工程與環境科學系 === 98 === POM is an exothermic reaction that be initiated and reach stable quickly without extra heat supply and suitable to be processed in the compact micro-channel reactor. The micro-channel reactor generally has advantages of low pressure drop, low probability of explosion, and fast in thermal and mass transfer. The heart of micro-channel reactors is active plates which were fabricated by fill-and-dry coating powders of active catalyst onto silicon-based micro-reactor and prepared catalysts by sol-gel method. Furthermore, based on the previous research on the laboratory, we developed the Cu/ZnO-based catalysts modified by manganese which had great performance under POM reaction.
The catalysts were prepared by three different procedures. First, we try to prepared catalysts by citrate-complex method. The catalytic activity of Cu/Mn/ZnO catalysts reduced with increasing ratio of citric acid in the POM reaction. In micro-reactor test, we selected the citric acid/all of metal ion ratio of 1 catalyst to load into micro-reactor by fill-and-dry method. At the 225 oC, the best activity of the catalyst had 17% conversion of methanol and 1.4*10-7 mol/min hydrogen yield. However, the catalytic layer had a serious problem that the catalyst was deposited on side of channel.
To solve this problem, we increased the viscosity of catalyst solution to enhance the adhesion to silicon substrate by citrate-gel method. SEM image showed that catalyst did not aggregate to side of channel because the viscosity of catalyst solution increased by esterification of ethylene glycol and citric acid. However, the catalytic layer still had many cracks. The result would lead to reduce performance of micro-reactor.
In fact, good adhesion was maybe attained by a formation of chemical bond with substrate. The previous study was based on the hydroxide group (-OH) of citric acid bonding with hydroxide group (-OH) of substrate. However, the catalytic layer was stripped adhesion due to the citric acid decomposed during calcination process. Thus, we use the inorganic binder of alumina sol (bentonite/boehmite) as binder. However, the catalytic activity was reduced with increasing binder/catalyst ratio. It was proposed that most of the catalyst particles are covered with the alumina sol and, therefore, the surface areas exposed to reactants is reduced. It would lead to reduce catalytic activity. Besides, the solid content, viscosity, pH, particle size and ratio of Binder/catalyst were important factors at coating catalyst. The optimum condition for preparation the slurry is the solid content (5wt.%), bentonite/boehmite (20wt.%), boehmite/catalyst (15wt.%), pH value (7) and stir time (5 hour) with ball mill technique. The weight loss was 13 wt.% when the density was 0.47 mg/cm2 on silicon substrate. At the 225 oC, the best activity of the catalyst had 53% conversion of methanol and 7.9*10-6 mol/min hydrogen yield.
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