Energy-efficient shipboard CO2 capture via an aqueous ammonia/[C4mim][PF6] blend absorbent: Modeling and system integration

In response to increasingly stringent emission reduction requirements in international shipping, this study proposes an improved onboard carbon capture system (OCCS) using an aqueous ammonia/ionic liquid (IL) blend absorbent to address the large equipment size and high regeneration energy of conventional ammonia-based processes. Property and thermodynamic models for the hybrid system were developed in Aspen Plus based on literature data, and the capture process was rigorously simulated and experimentally validated using a rate-based non-equilibrium stage model. The results show that adding 20% 1-butyl-3-methylimidazolium hexafluorophosphate ([C4mim][PF6]) reduces absorber packing height by 29%-42% through enhanced physical solubility and mass-transfer performance, while decreasing regeneration energy by 4.5% to 2.87 MJ/kg CO2. Parametric optimization identified optimal operating conditions, including a lean solution temperature of 10 °C, a CO2 loading of 0.31 mol/mol, an NH3 concentration of 6%, and a regeneration pressure of 10 bar, enabling a 90% CO2 capture rate with low energy demand. Energy integration analysis indicates that flue gas waste heat alone supports a 75% capture rate but causes power shortages, whereas supplemental gas turbine integration increases the capture rate to 90%, while reducing overall system energy efficiency from 50.3% to 40.14%. A preliminary economic evaluation reveals that the CO2 storage tank dominates the total annual cost (51.5%) under high-pressure ambient-temperature storage, with a cost of CO2 capture (CCC) of 212 USD/tCO2.