Direct MCH® ~ one-step chemical hydride production using renewable energy~
Direct MCH® process for importing renewable hydrogen in an industrial scale
Renewable energy (RE) is unevenly distributed around the globe and has not been fully exploited. To achieve green transition, technologies are required which allows transportation of vast amount of RE in an efficient manner with economic feasibility. One of the most challenging issue is to transport RE over large distances. As renewable electricity is less compatible with such a transportation, energy conversion from electricity to chemicals is required. One of the major converted chemicals are hydrogen and is called renewable hydrogen or green hydrogen, produced by water electrolysis. One of the means to transport renewable hydrogen efficiently is hydrogen carriers. Among those, methylcyclohexane (MCH) is promising because of its liquid phase, capable of storing hydrogen more than 500 times densely in volume, and its compatibility with existing oil infrastructure for transportation. The conversion efficiency of RE into MCH is the key factor for reducing the total cost and widespread usage of RE.
MCH is conventionally produced through two steps, i.e. water electrolysis using RE and toluene hydrogenation. To improve the conversion efficiency, we innovated Direct MCH®. This process allows direct reaction of toluene with water (instead of hydrogen) using renewable energy, that eliminates the need for hydrogen gas storage facilities which are necessary in the conventional two step processes. The reaction principles of Direct MCH® and our current challenges are presented in the following paragraphs.
Reaction principles of Direct MCH® and our R&D
The structure of the reaction device (electrolyzer) is schematically illustrated in the figure. Analogous to PEM (polymer electrolyte membrane) -type water electrolysis, water splits into oxygen, protons (H+) and electrons on the anodic catalyst. Protons then propagate from the anode to the cathode through proton exchange membrane and electrons flow to the cathode via external circuit driven by renewable electricity. Finally, protons, electrons and toluene react on the cathodic catalyst to generate MCH. The performance indicators of this reaction are current density (relevant to the reaction rate) and current efficiency (reaction selectivity). Improvement of these indicators leads to total cost reduction by minimizing capital investment.
One of our representative R&D activities to improve the indicators is quick water evacuation from the cathodic catalyst layer. During the electrolysis, water accompanies with protons from the anode to the cathode through the ion exchange membrane. Remaining of the excessive water in the cathodic catalyst layer prevents toluene to diffuse, which end up with preventing MCH production and water electrolysis (H2 production) occur as a side reaction, thus decrease current efficiency of MCH. To address this issue, we modify the micro and macro structure of the components in the cathode as well as those chemical nature toward quick water evacuation.
Development of the commercial scale electrolyzer
For the implementation of Direct MCH®, scaling up of the electrolyzer is necessary. Through our current efforts to expand the electrode area and stacking cells, MW class electrolyzers are planned to be developed in the near future.
We will contribute to GHG reduction through the upcoming renewable hydrogen supply chain where the cost is minimized by implementation of Direct MCH®.