井上 光浩、中島 裕典、阿部 孝之
Mitsuhiro Inoue, Hironori Nakajima, Takayuki Abe
Thermally self-sustaining CO2 methanation reaction was investigated using highly active TiO2-supported Ru (Ru/TiO2) catalysts prepared by the polygonal barrel-sputtering method. The experiments were conducted using a lab-scale reactor covered with an inner heater for the direct heating + a thermal insulator
and an outer heater for the simulation of outside temperature + a thermal insulator. When the CO2 methanation was carried out by setting the inner and outer heater temperatures at 180 and 90 °C, respectively, the reaction temperature was increased from 183.6 °C to 191.1 and 195.6 °C by increasing the flow rate of a feeding CO2 + H2 gas (CO2/H2 ratio = 1/4 vol./vol.) from 6.7 ml/min to 35.0 and 54.7 ml/min.
According to this result, the thermally self-sustaining reaction was evaluated by supplying the CO2 + H2 gas at 50 ml/min. At the outer heater temperature of 180 °C, the reaction temperature was stable at 230 °C for over 6 h after the inner heater of 180 °C was switched off at 40 min. Similar result was obtained at the outer heater temperature of 170 °C, and the reaction temperature was kept at 210 °C. However, under the outer heater temperature conditions of ≤160 °C, the reaction temperature after switching off the inner heater was rapidly decreased and the stable temperature trend was not observed. It is noted that the thermal transfer simulation based on the lab-scale experimental conditions presented possibility of the thermally self-sustaining reaction without the external heating using a thermal insulator having the thermal conductivity of 8.12 × 10-3 W/(m K). However, this conductivity was ＜ 1/10 time of conventional thermal insulators. In contrast, the simulation for a large-scale reactor indicated that a cooling needs to keep a constant reaction temperature of 250 °C under the flow rate conditions of CO2: 250 ml/in and H2: 1000ml/min. This result implies that for our catalysts, the thermally self-sustaining reaction without both the external heating and the insulators can be achieved by increasing the heat of reaction due to the high flow rates of the reactant gases