Enhancing Multi-Enzymatic CO2 Conversion via Reactor Engineering: Effects of Mass Transfer on Sustainable and Green Metrics

Abstract

The global energy transition toward decarbonization requires highly efficient Carbon Capture and Utilization (CCU) technologies that combine economic feasibility with operational stability. A key factor for successful CCU is efficient CO₂ gas-liquid transfer, which can be optimized through tailored reactor designs to maximize yields and CO₂ utilization. Technological advances such as CO₂-specific sensors have enabled accurate monitoring of CO₂ mass balance enhancing the efficiency of its conversion. This work addresses an in-depth analysis of CO₂ mass transfer in a stirred-tank reactor, focusing on the impact of volumetric gas flow rate on gas-liquid transfer during the multi-enzymatic conversion of CO₂ into high-value compounds using a co-immobilized biocatalyst of formate dehydrogenase and glycerol dehydrogenase enzymes. The volumetric mass transfer coefficient (kLa) was determined at different gas flow rates (1, 0.5 and 0.1 vvm) from a 24% CO₂ gas mixture, with the reaction carried out at 0.1 vvm achieving an outstanding formate production of 66.1 ± 1.4 mM (3 gL1^-1), due to near-neutral pH conditions that improved the reaction conditions and enhanced biocatalyst stability by at least 1.8-fold compared with high gas flow rate (1.0 vvm). Furthermore, a remarkable CO₂ capture efficiency of 93.3 ± 2.1% was achieved at 0.1 vvm, along with a high selectivity toward formate and glycerol carbonate, reflecting a complete CO₂ conversion into target products. Finally, the environmental impact of the reaction at 0.1 vvm showed a lower contribution to climate change, reaching 13.2 kg CO₂ eq kg products ⁻1 . These results underscore enzymatic CO₂ reduction as an effective and sustainable approach for the development of bio-based industrial processes with a markedly reduced environmental footprint.