Effect of carbonic anhydrase on CO2 absorption promoted by choline hydroxide using supported liquid membranes

Abstract

The development of efficient CO2 capture routes to tackle the unprecedently high concentrations of this gas in the atmosphere is one of the world’s top-priority technological targets. Here, we describe, for the first time, the combined use of the enzyme carbonic anhydrase (CA) and an aqueous solution of choline hydroxide, to effectively absorb CO2. Variables such as choline hydroxide and enzyme concentrations and temperature were investigated. Overall sorption coefficients of up to 105 gCO2 kg−1solution were found (up to 3.8 M absorbent), whereas reaction rate improvements were demonstrated within a low enzyme concentration range (0.1–0.5 mg g−1). FT-IR and in situ1H and 13C NMR experiments supported the elucidation of reaction mechanisms. It was found that in the absence of CA, the choline carbonate species is rapidly shifted to the bicarbonate form, whereas in the presence of the enzyme, the carbonate form is stable, conferring a buffered-like environment. Finally, the solvents containing the enzyme were used for the preparation of supported liquid membranes, which showed CO2 selectivity to N2 and CH4 of up to 90.5 and 28.9 times, respectively. The results here discussed add relevant knowledge towards the implementation of efficient CO2 capture.