Development of a Microreactor for Catalyzed Gas-Liquid Reaction
Masami KAMIBAYASHI, Yutaka TAKAHASHI and Toshihiko OHTA
Abstract:A microreactor for the catalysis of gas-liquid reactions was designed and fabricated. The microreactor consists of a concentric inner column and an outer cylinder. The interstitial space between these components is a channel for the liquid. The column is made of a porous material, so that gas can be fed to the channel by passing it through the column to the column surface, where micro-bubbles are emitted that can efficiently contact and react with the liquid. The column is made of commercially available graphite, machined by lathe to 18 mm in diameter and 67 mm long. The cylinder is made of SUS304 stainless steel, bored to 18.1 mm in diameter, resulting in an effective channel gap of approximately 50 ƒÊm when the components are fitted together. After machining of the graphite column, a catalyst was fixed to the column. The ratio of the specific surface area of the catalyst to the volume of the mixture becomes very large, due to the gas-liquid mixture flow in the 50 ƒÊm channel. As a model reaction, the hydrogenation of nitrobenzene to aniline was carried out using a nickel catalyst, and catalysis performance was tested for deposition using sputtering, electroplating and electroless plating methods. The following results were obtained: (1) In a conventional autoclave system, which serves as the benchmark for batch methods, the aniline produced is further converted to undesired organic products, due to successive hydrogenation. However, compared with the performance of the conventional reactor, such side reactions can be significantly suppressed using the proposed microreactor, because the product is readily discharged and the residence time is steadily and adequately controlled. (2) Deactivation of the catalyst was observed for continuous operation. The most likely cause is that polymers formed during the reaction are adsorbed on the catalyst surface, thus reducing activity. All catalysts exhibited the same initial conversion; however, the lifespan of the catalyst was dependent on the method of deposition, and followed the order: sputtering>electroplating>electroless plating. This is similar to the deactivation behavior observed for a palladium catalyst with the hydrogenation reaction using a falling film microreactor. Therefore, it is necessary to develop a catalyst deposition method suitable for the microreactor in order to achieve long-term operation. Key Words:Gas-liquid reaction, Microreactor, Micro-bubble, Graphite, Catalyst, Film deposition, Aniline, Batch system, Side reaction, Deactivation