(90e) Integrated Process Development for Reactive CO2 Conversion to Produce Formic Acid

With the steeply-rising amount of anthropogenic CO₂ in the atmosphere, governments and institutions around the world are seeking to find viable solutions for mitigating CO_2. Reactive CO₂ capture and conversion (RCC) has been deemed as an economic and environmentally-benign option for CO₂ utilization, as large amounts of heat usage included in the original CO₂ capture process can be excluded. Despite its promising characteristics, previous studies have not been able to provide feasible RCC solutions that could contribute to CO₂ mitigation, owing to the small conversion rates of CO₂ and extremely high costs of separation processes required for purifying the product. As commercial-scale operation of RCC is essential for practical utilization of CO_2, it is important to develop an integrated process for efficient CO₂ conversion as well as product separation.

In this study, a new process integrating the electrolyzer and energy-efficient separation processes to produce formic acid is presented. Using triethylamine (TREA) as the capture amine, CO₂ is directly converted to formate within the electrolyzer forming an adduct with the TREA. The faradaic efficiency (FE) is enhanced by combining the two metal catalysts, Sn and Cu, at an optimal ratio. With an maximum FE of 67%, rest of the current is devoted to syngas production, which also serve as valuable chemicals providing profit. Downstream of the electrolyzer a separation process for purifying formic acid with high purity of >90 wt.%. Since the catholyte only consists of the amine-formic acid adduct, the amine-exchange separation system presented in the recent study by Kim et al.(Joule 8, 693-713, 2024) can be integrated to produce high-purity formic acid. To evaluate the performance of the system, techno-economic analysis and life cycle assessment are conducted based on a simulation model validated on the experimental results of the electrolyzer and the separation process. Results show that the integrated process shows a levelized cost of formic acid production of < 700$/tFA, which is the lowest of all electrochemical formic acid production systems presented in the literature. While the Global Warming Impact (GWI) index of LCA is relatively high due to large steam usage in the distillation systems, a scenario analysis incorporating widespread use of renewable energy usage shows that the overall system reduces the GWI by >20% compared to conventional formic acid production. These results indicate that the proposed process has potential for large-scale applications, practically contributing to CO₂ mitigation.