A Novel CO2 Capture and Utilization Strategy by Enzyme Catalysis: Preliminary Assessment of Process Layout

Abstract

Catalytic conversion of CO₂ into fuels and valuable chemicals has gained large attention in the scientific and industrial research aimed at developing novel Carbon Capture and Utilization (CCU) processes. Among current uses of CO₂, the Kolbe-Smith process allows the production of salicylic acid through carboxylation of phenol using CO₂ at high pressure and temperatures. A biocatalytic route has been proposed and it is based on the enzymatic carboxylation of phenolic substrates (e.g. catechol and resorcinol) into ortho-hydroxybenzoic acids catalyzed by non-oxidative carboxylases. The main advantages of such biocatalytic carboxylation are related to good selectivity of the biocatalyst, absence of co-substrates, and the mild conditions of temperature and pressure typically applied in enzymatic bioconversions. Experimental studies on enzymatic carboxylation of phenols (Pesci et al., 2015; Meyer et al., 2018) provided data on thermodynamics and kinetics of the process in 1.8 – 2 M K₂CO₃ solutions. The present contribution addresses some process design issues related to the development of an enzymatic carboxylation process as a possible CO₂ utilization route. The following points have been considered in the study: the use of phenolic substrates from pyrolytic bio-oils as renewable carbon source; the capture of CO₂ in the form of bicarbonate in aq. solvents to provide the necessary bicarbonate source to carboxylation; the effect of phenolic substrates solubility on the maximum equilibrium conversion into carboxylic acids. These points have been analyzed by simulations with the ASPEN PLUS® software. In the simulations, a CO₂ absorption column operated with K₂CO₃ solution and immobilized carbonic anhydrase as a promoter. The composition of the solvent from the absorption column has been used for equilibrium calculations of enzymatic carboxylation to assess the potential use of this bicarbonate enriched solvent as carbon vector in the enzymatic CCU process.