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

Abstract

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.