Enzyme-assisted CO2 absorption in aqueous amino acid ionic liquid amine blends

The influence of carbonic anhydrase (CA) on the CO₂ absorption rate and CO₂ load in aqueous blends of the amino acid ionic liquid pentaethylenehexamine prolinate (PEHAp) and methyl diethanolamine (MDEA) was investigated and compared to aqueous monoethanolamine (MEA) solutions. The aim was to identify blends with good enzyme compatibility, several fold higher absorption rates than MDEA and superior desorption potential compared to MEA. The blend of 5% PEHAp and 20% MDEA gave a solvent with approximately 5-fold higher initial absorption rate than MDEA and a 2-fold higher regeneration compared to MEA. Experiments in a small pilot absorption rig resulted in a mass transfer coefficient (KGa) of 0.48, 4.6 and 15 mol (m3 s mol fraction)-1 for 25% MDEA, 5% PEHAp 20% MDEA and 25% MEA, respectively. CA could maintain approximately 70% of its initial activity after 2 h incubation in PEHAp MDEA blends. Integration of CA with amine-based absorption resulted in a 31.7% increase in mass of absorbed CO₂ compared to the respective non-enzymatic reaction at the optimal solvent: CA ratio and CA load. Combining novel blends and CA can offer a good compromise between capital and operating costs for conventional amine scrubbers, which could outperform MEA-based systems.