Can thermocatalytic transformations of captured CO2 reduce CO2 emissions?

Highlights: • CO₂-to-CO consumes the minimum energy of 20.8 MJ⋅kgCO₂⁻¹ when coal-based H₂ is used. • H₂ production accounts for over 70% of energy consumption of coal-based CO₂-to-CH₃OH. • CO₂-to-CH₃OH emits 4.5 kg CO₂ per kg CO₂ converted when coal-based energy is used. • CO₂-to-CH₄ achieves a net CO₂ emission of −0.97 kgCO₂⋅kgCO₂⁻¹ with carbon-free energy. • CO₂-to-CO could become economically attractive with a carbon tax of 0.73 US$⋅kgCO₂⁻¹. Thermocatalytic transformations of captured CO₂ into CO, CH₃OH, or CH₄ via hydrogenation reactions are attractive because they are desired to mitigate the anthropogenic CO₂ emission and reduce the atmospheric CO₂ concentration. However, CO₂ hydrogenation technologies inevitably require a source of H₂ and significant energy input, both of which are predominately generated by CO₂-emitting fossil fuels, currently. It is unclear whether the overall process is net CO₂ negative and which technology pathway has the most potential to achieve net CO₂ reduction with various energy sources. In this work, we summarize the energy and material balances of various proposed industrial-scale CO₂ hydrogenation processes coupled with credible thermodynamic and kinetic models. The performance of the CO₂ conversion to CO, CH₃OH, and CH₄ processes is evaluated in terms of overall energy consumption, net CO₂ emission, and levelized cost of CO₂ conversion under various conditions. Simulation results show that the overall energy consumption and net CO₂ emission of all the five proposed CO₂ hydrogenation processes are relying heavily on the sources of energy and hydrogen. The CO₂-CH₄ process would show the best CO₂ reduction capacity when the energy consumption of H₂ production is lower than 61.1 MJ⋅kgH₂⁻¹ with more renewable energy added. Thermocatalytic transformations of captured CO₂ are at present economically unattractive and emit more CO₂ than they convert as the required energy and hydrogen mainly come from fossil fuels. However, these processes can be driven to economically attractive when the cost of renewable energy is decreased (by an order of magnitude), and a potential CO₂ tax (0.29 US$⋅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.