CO<sub>2</sub> and Renewable Electricity into Chemicals: Formic Acid Production from Coal Flue Gas

Abstract

Formic acid (FA) is an industrial chemical. It is used as a preservative for silage, as a digestive aid for animals, as a fluid for fracking, as a pharmaceutical intermediate and in leather tanning. The global formic acid market is expected to reach 851.8 million USD by the end of 2026. A new major formic acid application is the use of formic acid as a key feedstock for the bioprocessing industry. It has the potential to grow tremendously if we can lower the cost of formic acid production compared with the current fossil-fuel one. Recently, Dioxide Materials (DM) has developed a technology that can directly convert CO2 to pure formic acid with a three-compartment CO2 electrolyzer. However, the electrolyzer performance needs further improvement for the technology to be commercially viable. The major objective of this project is to develop the electrolyzer technology to enable formic acid as a feedstock for the bioprocessing industry to be economically manufactured from flue gas from a coal fired pilot plant. In particular, the project is to understand how to run the electrolyzer for the conversion of CO2 into formic acid using flue gas from a coal fired power plant as a source of CO2. The work includes characterizing how the performance of the electrolyzer changes with low CO2 concentration and impurities, developing new cell designs that can still operate with feedstocks with low CO2 concentrations, testing simulated flue gas in the electrolyzer system and developing filters to remove any impurities that arise. In this project, DM first conducted experiments to investigate the effect of operation conditions such as flow rate, temperature, pressure, et al. on the electrolyzer performance. The obtained experimental results enabled DM to establish the testing conditions to evaluate the electrolyzer performance in this project. DM has experimentally demonstrated that anion exchange membranes (AEMs) are critical to obtain good electrolyzer performance and developed a new type of Sustainion® membrane which specifically designed for CO2 to formic acid electrolyzer. DM also conducted electrolyzer tests at different CO2 concentrations to evaluate the effect on electrolyzer performance and the testing results showed that the electrolyzer could operate at 14 vol% CO2 concentration, which is the typical CO2 concentration in the flue gas from a coal fired power plant. DM also investigated how the impurities such as O2, NOx and SOx in the flue gas affect the electrolyzer performance. The experimental results indicated that NO and SO2 did not show negative effect on the electrolyzer performance with the concentrations as in the typical flue gas, while O2 in the flue gas showed a deteriorated effect on the electrolyzer performance. The presence of O2 in CO2 feeding gas not only affects the formic acid FE but drastically causes the decrease of electrolyzer stability. Therefore, it is critical to remove O2 from the flue gas for the electrolyzer operation. DM has demonstrated that the O2 concentration in the flue gas could be reduced to less than 0.5 vol% using the strategy DM developed. CO2 electrolyzer operated with this strategy showed stable performance. DM also developed a method to maintain long-term stability of the electrolyzer and demonstrated that the electrolyzer could run for over 1000 hours with different CO2 concentrations using this method. DM then developed a demo electrolyzer system to run on-site test at a coal-fired power plant. The result showed that the developed electrolyzer technology holds promising potential to convert CO2 to formic acid directly using flue gas as a CO2 source. To evaluate economic feasibility and the global warming potential of the technology, technoeconomic analysis and life cycle analysis were conducted. The obtained results suggested that the developed electrolyzer technology provides a cost competitive way to produce formic acid and using renewable or nuclear electricity and flue gas from coal fired power plant as CO2 source will significantly reduce the global warming potential. The detailed project activities and accomplishments were then presented in this report. The technology developed in the project has demonstrated industry relevant current density and stability and sees the potential to become commercially viable. The laboratory scale electrolyzer, along with the experiences and skillsets developed in the project provides a solid start-point for the scale-up transition of the technology in the near future.