Can thermocatalytic transformations of captured CO2 reduce CO2 emissions?

Abstract

Thermocatalytic transformations of captured CO2 into CO, CH3OH, or CH4 via hydrogenation reactions are attractive because they are desired to mitigate the anthropogenic CO2 emission and reduce the atmospheric CO2 concentration. However, CO2 hydrogenation technologies inevitably require a source of H2 and significant energy input, both of which are predominately generated by CO2-emitting fossil fuels, currently. It is unclear whether the overall process is net CO2 negative and which technology pathway has the most potential to achieve net CO2 reduction with various energy sources. In this work, we summarize the energy and material balances of various proposed industrial-scale CO2 hydrogenation processes coupled with credible thermodynamic and kinetic models. The performance of the CO2 conversion to CO, CH3OH, and CH4 processes is evaluated in terms of overall energy consumption, net CO2 emission, and levelized cost of CO2 conversion under various conditions. Simulation results show that the overall energy consumption and net CO2 emission of all the five proposed CO2 hydrogenation processes are relying heavily on the sources of energy and hydrogen. The CO2-CH4 process would show the best CO2 reduction capacity when the energy consumption of H2 production is lower than 61.1 MJ⋅kgH2−1 with more renewable energy added. Thermocatalytic transformations of captured CO2 are at present economically unattractive and emit more CO2 than they convert as the required energy and hydrogen mainly come from fossil fuels. However, these processes can be driven to economically attractive when the cost of renewable energy is decreased (by an order of magnitude), and a potential CO2 tax (0.29 US$⋅kgCO2−1) is implemented, leading to a significant reduction of atmospheric CO2. This work presents a comprehensive analysis of different CO2 hydrogenation processes with thermodynamics and kinetic models based on various energy and hydrogen sources, providing a rational guideline for the industrial application of these hydrogenation processes.