Development of a MEMS channel device for hydrogen gas separation based on the Soret effect
Journal of Thermal Science and Technology
Introduction Energy sources that are independent of fossil fuels or atomic power are important for the achievement of a sustainable society from the view point of environmental conservation and ecological benefits (Yamaji, 2008) . Hydrogen is regarded as one of the important candidates for new sources, because it imposes a minimum environmental load and exhibits high energy efficiency. To achieve a sustainable society, hydrogen production using renewable energy sources, such as sunlight or wind
... as sunlight or wind power, is necessary. However, as the renewal energy sources are not capable of producing a sufficient amount of hydrogen to meet its demand in various fields, the traditional steam reforming method continues its dominance in the hydrogen production. This process is endothermic reaction and operates with a heat exchanger at 700-800 °C. It produces not only hydrogen gas (H 2 ), but also by products such as CO, CO 2 , and CH 4 , which cannot be used for low-temperature fuel cells due to a large presence of impurities. Therefore, the pressure swing adsorption (PSA) method is used for purifying the hydrogen gas after the steam reforming process. This method can produce high-purity hydrogen gas by using absorbents in repeated cycles of adsorption, desorption, and reproduction under pressurization. Although this method can obtain purity higher than 99%, a large quantity of adsorbents is required to continuously sustain the process. Moreover, as the volume of the processing equipment increases, the energy consumption increases dramatically. To solve these problems, we proposed a new separation technique based on the Soret effect for the purification of hydrogen gas. The Soret effect is a Abstract Energy sources independent of fossil fuels or atomic power are of great importance to achieve a sustainable society from the viewpoint of environmental conservation and benefits. Hydrogen is considered as one of the main candidates for new sources. The steam reforming method is a major contemporary process for manufacturing hydrogen, during which carbon dioxide is simultaneously generated. Therefore, an additional process that can separate hydrogen from carbon dioxide is necessary. For this reason, we proposed the use of a new method based on the Soret effect for the separation of hydrogen and carbon dioxide. The Soret effect is capable of producing a concentration difference only by imposing a temperature difference. However, in previous studies, our group found that a single-step separation process could increase the concentration by only a few percent. Thus, a multi-step separation process is necessary for obtaining high gas concentration. In this study, we adopted micro-electromechanical system (MEMS) fabrication technology to develop a separation device and performed single-step hydrogen-separation experiments. The MEMS technology applied in this study has shown potential for the miniaturization of the device and enhancement of separation cycle number for future experiments.