Kwang-Deog Jung1, Sung-Hoon Chung1, Palgunadi Jelliako1, Oh-Shim Joo1, and Young-Kwon Park2. (1) Environment and Process Technology Division, Korea Institute of Science and Technology, Hawolgokdong 39-1, Seongbukgu, Seoul 139-791, South Korea, (2) Faculty of Environmental Engineering, University of Seoul, University of Seoul, Dongdaemoon-Gu Cheon-Nong-Deong 90, Seoul, 130-743, South Korea
DME has been attentioned as a clean fuel. DME is commercially produced by methanol dehydration. However, the direct DME synthesis from synthesis gas has been suggested to be economically attractive as compared with the conventional two step processes of methanol synthesis and methanol dehydration. The optimized ratio of hydrogen to carbon monoxide is about 1.0. The conventional steam reforming produces syntheis gas with H2/CO above 3.0. Therefore, many refoming processes such as autothermal and CO2 reforming of methane have been issues for the direct DME synthesis. On the other hand, 1 mol of CO2 is simultaneous produced with 1 mol of DME from the direct DME synthesis, indicating that DME process can be malign in the point of CO2 mitigation, as compared with the two step DME process. In this study, we tried to use the reverse shift reaction to mitigate CO2 and to ajust H2/CO. The key concept is to convert CO2 to CO using excess hydrogen from a reformer and CO2 from a DME reactor. Membrane process is chosen for separating hydrogen from the reformer stream, where H2/CO ratio can be ajusted to be 1.0~2.0 for DME synthesis. The separated hydrogen is combined with CO2 from the DME synthesis reactor, which is introduced into a reverse shift reactor to convert CO2 into CO. The simulation result of this concept showed DME yield of above 97 % based on feed carbon and could mitigate CO2. The reverse water shift reaction temperature should be above 600 oC to achive 60 % conversion of CO2. The commercial shift reaction catalysts such as Cu/Zn/Al or Fe/Cr catalysts at the temperature above 600 o were rapidly deactivated at the high temperature in CO2-H2 stream. However ZnO based catalyst showed the high activity and stability. The ZnO based catalyst was optimized for the reverse shift reaction and pelletized with the size of 4-5 mm and tested in 3.5 L of reator. CO2 flow rate was 3 Nm3/h and the ratio of H2/CO2 was about 3.0. The CO2 conversion of 60 % was achived at 610 oC with the pilot scale reactor, indicating that the reverse shift reaction was ready to be commercilized. The DME bench plant (5 kg DME/day) with the reverse shift reactor was installed to prove the simulation result. The operation results of the bench plant will be discussed.