Microreactor for the Catalytic Partial Oxidation of Methane

摘要

Fixed-bed reactors for the partial oxidation of methane to produce synthetic gas still pose hot-spot problems. An alternative reactor, which is known as the shell-and-tube-typed microreactor, has been developed to resolve these problems. The microreactor consists of a 1 cm outside-diameter, 0.8 cm inside-diameter and 11 cm length tube, and a 1.8 cm inside-diameter shell. The tube is made of dense alumina and the shell is made of quartz. Two different methods dip and spray coating were performed to line the tube side with the LaNi_xO_y catalyst. Combustion and reforming reactions take place simultaneously in this reactor. Methane is oxidized in the tube side to produce flue gases (CO_2 and H_2O) which flow counter-currently and react with the remaining methane in the shell side to yield synthesis gas. The methane conversion using the higher-loading catalyst spray-coated tube reaches 97% at 700℃, whereas that using the lower-loading catalyst dip-coated tube reaches only 7.78% because of poor adhesion between the catalyst film and the alumina support. The turnover frequencies (TOFs) using the catalyst spray-and dip-coated tubes are 5.75 x 10~(-5) and 2.24 x 10~(-5) mol/g_(cat) · s, respectively. The catalyst spray-coated at 900℃ provides better performance than that at 1250℃ because sintering reduces the surface-area. The hydrogen to carbon monoxide ratio produced by the spray-coated catalyst is greater than the stoichiometric ratio, which is caused by carbon deposition through methane cracking or the Boudouard reaction.