Synthesis of green light olefins from direct hydrogenation of CO₂. Part I: Techno-economic, decarbonization, and sustainability analyses based on rigorous simulation

Backgrounds: Converting CO₂ into light olefins through direct hydrogenation is a promising pathway to achieve net-zero emissions. This part aims to present a detailed layout and the analysis results of the process through rigorous simulation. Methodology: The process encompasses three sections (reaction, CO₂ removal, and olefin recovery). Two alternatives for handling the off-gas were proposed, including sending it for additional hydrogen recovery (Scheme 1) or direct combustion (Scheme 2). The minimum required selling price (MRSP), the indirect CO₂ emissions per kg of olefins produced (CO₂-e), and the carbon efficiency are demonstrated for process evaluation. Significant Findings: Scheme 1 demonstrates better economic performance but less decarbonization ability compared to Scheme 2 (i.e. Scheme 1: MRSP = 2327 USD/kg and CO₂-e = -2.036 kg/kg; Scheme 2: MRSP = 2366 USD/kg and CO₂-e = -2.247 kg/kg). To achieve carbon neutrality, the carbon footprint for the hydrogen feedstock should not exceed 6.92 and 7.08 kg-CO₂/kg-H₂ for Schemes 1 and 2, respectively. Considering the trade-offs between MRSP and CO₂-e, using biomass-based hydrogen is currently the most viable option. Finally, the entire process has a 99.7 % carbon efficiency. In summary, the proposed process is effective in CO₂ fixation, with minimal impact on the process economics and sustainability.