Superstructure optimization model for design and analysis of CO₂-to-fuels strategies

CO₂ utilization to fuel production, wherein captured CO₂ is used as raw materials and partially replaces the use of fossil fuels, is an effective solution for energy security and global warming. In this study, an optimization-based framework was developed for CO₂-to-fuel superstructure to determine the optimal strategies for desired fuels (i.e., methanol (MeOH), Fischer–Tropsch synthesis (FT) fuels, dimethyl ether (DME), and gasoline). The aim of the framework is to address specific problems of minimizing energy consumption, unit production cost, and net CO₂ equivalent emission. Thus, we first generated a superstructure of alternative CO₂-to-fuel pathways, and each pathway contains a set of carbon conversion and separation technologies toward the final fuel from CO₂ feedstock. Subsequently, a process simulation and energy–economic–environmental parameters of possible pathways were generated and further embedded into the optimization model. The optimization results indicate that, among CO₂ utilization technologies, direct catalytic hydrogenation is recognized as the most economical and environmentally friendly pathway for MeOH at 3.6 $/GGE (reduced 1.01 kg CO₂/GGE), gasoline at 3.71 $/GGE (reduced 1.86 kg CO₂/GGE), and DME at 4.46 $/GGE and near-zero-emission. However, FT fuels are not suggested since they consume more energy for a higher production cost and emit 3.22 kg CO₂/GGE. Using various process system engineering-centric techniques, this study also determined that H₂ feedstock cost, associated with CO₂ utilization strategies, is the major economic–environmental factor and investigated the CO₂-to-fuel application potential in various market conditions based on regions or time.