Assessment of enhanced carbon dioxide absorption in water - The impact of carbonic anhydrase and pH regulation

Abstract

The world is faced with an enormous challenge in the form of climate change. As a part of mitigation strategies, the industrial scale feasibility of a carbon capture process is determined, where CO2 is absorbed in water and reacted to HCO – 3 that could possibly be stored in oceans or in solid form. The focus is on the absorption and reaction stages, and the effects on capture rate of the enzyme catalyst carbonic anhydrase, and addition of base for pH regulation are evaluated. The main methodology consists of simulations performed with the software Aspen Plus. Sensitivity analyses and case studies on plants where the process could be implemented are carried out. Material and energy balances are given attention, as well as operating conditions. Three possible reaction paths are compared based on required liquid phase residence time and column height to reach equilibrium. Two process alternatives are considered with differing strategies for pH control. The results indicate that the carbon capture process is technically feasible to use, with regard to residence time and equipment size. However, pH regulation is critical for adequate performance, and the material flows required, especially the large quantities of base, are limiting due to high production costs. Moreover, the storage of HCO – 3 needs further research before a suitable option can be decided on; the impact on marine life of oceanic storage is unknown, and the energy consumption of salt precipitation is grand. The use of carbonic anhydrase is not a necessity although it can reduce equipment size; a base with OH– anions will yield fast enough reaction rates for realistic column heights without a catalyst.