CO2 hydrogenation is the reaction upgrading CO2 with the energy contained in hydrogen to produce useful chemicals. In the light of technologically established electrocatalytic water splitting and increasing efficiency of hydrogen production by means of photocatalysis, utilization of H2 for CO2 valorization will play major roles in the future carbon management and reducing environmental impact of fossil fuels. This article highlights the characteristics of three major CO2 hydrogenation reactions, namely syntheses of methane, methanol and formic acid. All these chemicals can serve as chemical energy carriers as well as C1 feedstock and their application scope is large. The current activities and future challenges of these technologies are described in technical as well as global contexts. Importance of hydrogen production technologies for commercialization of CO2 hydrogenation processes is emphasized.
Methanation technology was proposed by Professor Hashimoto in 1993, and he demonstrated for the first time in the world that it was technically feasible with bench scale methanation system (0.1 Nm3-CH4/h) composed of solar power, electrolyzers, methanation reactor and oxy-combustion burner in 1995. Since then, Hitachi Zosen has been collaborating with Professor Hashimoto.
Recently, methanation technology has attracted attention as one of the measures to suppress greenhouse gases.
At the World Economic Forum General Assembly held in January 2019, Prime Minister Abe stated that “a new limelight for methanation”, and interest in CCU (Carbon dioxide Capture and Utilization) and methanation is increasing not only in Japan but also in other countries around the world. Research is accelerating. Consequently, we introduce our history of development on methanation system in this article.
Jet fuel is not easy to synthesize by the biomass-to-liquid (BTL) process owing to the limitation of the Anderson–Schulz–Flory (ASF) hydrocarbon distribution law in Fischer–Tropsch synthesis (FTS) with biomass-derived syngas (CO + H2). Here, we realized an anti-ASF distribution to selectively produce jet fuel from biomass on a large scale by addition of small amounts of 1-olefin, a FTS product, into syngas, enhancing jet fuel selectivity in hydrocarbons up to 64% and that in liquid oil product to as high as 91%. Furthermore, we first realize direct synthesis of jet fuel from syngas (CO/H2), without subsequent hydrorefining post-treatments, reaching outstanding selectivity for jet fuel as high as 72% using Co-La-mesoY catalyst. Direct conversion of CO2 and H2 to jet fuel is in progress.
CO2 hydrogenation to methanol is one of the important reactions in the future. According to this reaction, CO2 is captured from the atmosphere and from industrial exhaust streams, and can be used as a sustainable C1 building block, leading to the mitigation of CO2 emissions. For the achievement of a sustainable society, H2 will be produced via water electrolysis using renewable energy. In this time, the past and current state of the CO2 hydrogenation plants was summarized.
Enabling CO2 hydrogenation to methanol at lower temperatures is one of the key towards carbon recycling and realization of methanol economy. This is due to the favourable thermodynamics of the reaction at lower temperature (<200 ℃) and possibility to fully convert CO2 to methanol in one pass through a catalytic reactor. We have recently reported two types of catalysts, TiO2-supported Re (Re/TiO2; 1 wt% Re) and MoOx/TiO2-supported Pt (Pt/MoOx/TiO2; 3 wt% Pt, 30 wt% MoO3) which show high activity in the reaction under a mild condition (150 ℃; pCO2 = 1 MPa; pH2 = 5 MPa) in batch operation. In particular, Pt/MoOx/TiO2 reached the equilibrium yield of methanol under the condition tested in our study. Here, we describe our recent efforts on the CO2 hydrogenation to methanol at low temperatures.
While Japan has been leading the development of hydrogen technology, China is likely to chase Japan to be a winner in the hydrogen industry repeating in the renewables and the EV industry under the socialism with Chinese characteristics. To win the market, the government initiative and leadership are key enablers by taking risks on behalf of private sectors in the area of uncertainties and disruptions. Japanese government is expected to look back at lessons learned in the renewables development to review the strategy of hydrogen, energy-mix and carbon recycle to be combined for the realization of decarbonation and new industry creations.