Synthesis of green light olefins from direct hydrogenation of CO₂. Part II: detailed process design and optimization

Background: In Part II, our objective is to investigate the optimal configuration and operating conditions for each process section of the CO₂-based light olefin production process described in Part I. Method: The main sections (reaction, CO₂ capture, and olefin recovery) in the entire process are rigorously designed and optimized. Six alternative reactor configurations were proposed, and optimized by maximizing the productivity. The Trade-offs between cost, indirect CO₂ emission, and CO₂ capture ratio were analyzed for the CO₂ capture section through multi-objective optimization. Three scenarios for olefin recovery were proposed and optimized by minimizing costs. Significant findings: For the reaction section, the configuration employing two fixed-bed reactors with co-current heat exchange (Scheme R6) results in the highest conversion (75.45 %) and selectivity towards light olefins (82.49 %). Both are significantly higher than the available data in the literature. For the CO₂ capture section, the optimal configuration has a 90 % CO₂ capture ratio and requires a specific energy of 3.63 GJ/Ton-CO₂. For the olefin recovery section, over 50 % of the costs can be reduced if hydrogen is removed before entering the cryogenic distillation process (Scheme O1). These findings support that the entire process presented in Part I of this study is in economical and environmentally-friendly conditions.