Economic and environmental potential of green hydrogen carriers (GHCs) produced via reduction of amine-captured CO2

Abstract

Hydrogen is deemed as a crucial component in the transition to a carbon-free energy system, and researchers are actively working to realize the hydrogen economy. While hydrogen derived from renewable energy sources is a promising means of providing clean energy to households and industries, its practical usage is currently hindered by difficulties in transportation and storage. Due to the extreme operating conditions required for liquefying hydrogen, various hydrogen carriers are being considered, which can be transported and stored at mild operating conditions and provide hydrogen at the site of usage. Among various candidates, green hydrogen carriers obtained via carbon dioxide utilization have been proposed as an economically and environmentally feasible option. Herein, the potential of using methanol and formic acid as green hydrogen carriers are evaluated regarding various production and dehydrogenation pathways, within a hydrogen distribution system including the recycle of carbon dioxide. Recent progress in carbon dioxide utilization processes, especially conversion of carbon dioxide captured in amine solutions, have demonstrated promising results for methanol and formic acid production. This study analyzes seven scenarios that consider carbon dioxide utilization-based thermocatalytic and electrochemical methanol and formic acid production, as well as different dehydrogenation pathways, and compares them to the scenario of delivering liquefied hydrogen. The scenarios are thoroughly analyzed via techno-economic analysis and life cycle assessment methods. The results of the study indicate that methanol based options are economically viable, reducing the cost up to 43% compared to liquefied hydrogen delivery. As for formic acid, only the electrochemical production method is profitable, retaining 10% less cost compared to liquefied hydrogen delivery. In terms of environmental impact, all of the scenarios show higher global warming impact values than liquefied hydrogen distribution. However, results show that in an optimistic case where wind electricity is widely used, electrochemical formic acid production is competitive with liquefied hydrogen distribution, retaining 39% less global warming impact values. This is because high conversion can be achieved at mild operating conditions for the production and dehydrogenation reactions of formic acid, reducing the input of utilities other than electricity. This study suggests that while methanol can be a shortterm solution for hydrogen distribution, electrochemical formic acid production may be a viable long-term option.