Comparative Screening of MDEA, TSA and PSA/VPSA for CO2 Capture Upstream of Artificial Photosynthesis

Capturing CO2 upstream of artificial photosynthesis is worthwhile only if the utility emissions of the capture step do not offset the captured mass. This study compares 30 wt% methyldiethanolamine (MDEA) absorption, temperature swing adsorption (TSA) and pressure/vacuum pressure swing adsorption (PSA/VPSA) on zeolite 13X for a pretreated dry feed containing 35 mol% CO2, combining process simulation, energy analysis, gate-to-gate life-cycle assessment (LCA) and an operating-expenditure (OPEX) screen per kilogram of captured CO2. MDEA achieved 95% recovery and approximately 95% wet-product purity with 3.96 MJ kg−1 of regeneration heat and a climate impact of 0.712 kg CO2-eq kg−1. Raising the TSA regeneration temperature from 383 to 450 K increased recovery from 80.5% to 94.5% and purity from 91.0% to 95.5%, but also heat demand (from 6.78 to 7.75 MJ kg−1) and climate impact (from 0.964 to 1.100 kg CO2-eq kg−1). PSA/VPSA at 3 bar feed and 0.11 bar evacuation gave the lowest climate impact (0.294 kg CO2-eq kg−1) and OPEX (approximately €0.100 kg−1), with 88.9% recovery and 92.8% purity. The ranking applies to the dry, CO2-enriched feed and the European utility mix considered; untreated flue gas, other solvents and full-chain conversion require separate assessment.