Evaluation of a Carbonic Anhydrase Mimic for Industrial Carbon Capture

Abstract

Zinc(II) cyclen, a small molecule mimic of the enzyme carbonic anhydrase, was evaluated under rigorous conditions resembling those in an industrial carbon capture process: high pH (>12), nearly saturated salt concentrations (45% K2CO3) and elevated temperatures (100-130 °C). We found that the catalytic activity of zinc cyclen increased with increasing temperature and pH and was retained after exposure to a 45% w/w K2CO3 solution at 130 °C for 6 days. However, high bicarbonate concentrations markedly reduced the activity of the catalyst. Our results establish a benchmark level of stability and provide qualitative insights for the design of improved small-molecule carbon capture catalysts.

Kinetic performance of CO2 absorption into a potassium carbonate solution promoted with the enzyme carbonic anhydrase: Comparison with a monoethanolamine solution

“…As reported in the literature, the bicarbonate as a product of CO 2 hydration might exert an adverse effect on the CO 2 hydration activity of some CA enzyme isoforms or mimics [29][30][31]. The extent of inhibition depends on the isoforms of the CA enzyme [31].…”

Enzyme-catalyzed Solvents for CO2 Separation

“…Parallel to work on thermostable CAs have been investigations on chemical mimics 171,172 of the Zn-hydroxide CA active site with the rationale that these molecules could catalyze CO 2 (de)hydration and be more robust to industrial conditions than CA. The chemical compounds reported are capable of catalyzing the hydration and dehydration reactions and tolerating high temperatures, but with slower kinetics compared to CA 173,174 or catalyzing unintended oxidation reactions.…”

The use of carbonic anhydrase to accelerate carbon dioxide capture processes

“…If most native CA strains were to be exposed to the operating temperatures within a solvent absorptions process, especially in the stripper stage, they would undergo denaturation extremely readily. Indeed, it is known that most CA strains lose their activity between 55 and 65 °C . However, thermostable CA strains have been found in thermophilic microorganisms and have also been produced in engineered recombinant microorganism strains .…”

“…The most active small molecule CA mimic identified thus far is the 1,4,7,10‐tetraazacyclododecane chelate of zinc(II) perchlorate, referred to as ‘zinc cyclen’ (Fig. ) . This molecule has a five‐fold lower activity than the native enzyme on a mass basis, but is commercially available on a large scale .…”

“…This molecule has a five‐fold lower activity than the native enzyme on a mass basis, but is commercially available on a large scale . Furthermore, it has been shown that zinc cyclen can retain its activity at temperatures of up to 75 °C and to retain its structure up to 100 °C, suggesting that it will survive passage through a standard CO 2 stripping cycle . The catalyst is inhibited by significant bicarbonate concentrations, which drive the reverse reaction in Equation .…”