CO₂ Capture and Conversion to Syngas: Rigorous Modeling, Optimization and Superstructure-based Process Synthesis

CO2 emissions from electricity generation have increased by 50% between 2000 and 2013. Large-scale carbon capture and storage is still not deployed for reasons including high cost, technological barriers and uncertainty in geological storage. A promising alternative is to convert CO2 to value-added chemicals via syngas (a mixture of H2 and CO) which is an intermediate for many hydrocarbon-based fuels and chemicals. In this work, we first perform thermodynamic analysis to benchmark different CO2 utilization systems based on energy requirement and syngas selectivity for a range of H2 to CO ratios. Our study reveals that significant energy is required to achieve reasonable levels of CO2 utilization via thermochemical routes. Furthermore, not a single reforming technology is optimal for the entire range of syngas ratios of practical interest. We then perform extensive simulation of various CO2-to-syngas alternatives using equilibrium, pseudo-homogenous and heterogeneous reactor models to characterize the gaps between the best-possible and realistically achievable process performances in terms of energy consumption and CO2 utilization. Lastly, using a superstructure of process flowsheets with all plausible alternatives, we systematically design optimal process networks for CO2 utilization considering various raw materials, such as CO2 from flue gas, methane from stranded sources, oxygen from air and water and hydrogen. Based on our process synthesis results, we conclude that even the best possible configurations would have 15-52% gaps between realistic CO2 utilization and theoretically maximum possible utilization, depending on the target syngas ratio