Integrated Bench-Scale Parametric Study on CO 2 Capture Using a Carbonic Anhydrase Promoted K 2 CO 3 Solvent with Low Temperature Vacuum Stripping Guojie Qi, † Kun Liu, † Reynolds A. Frimpong, † Alan House, § Sonja Salmon, § and Kunlei Liu* ,†,‡ † Center for Applied Energy Research, University of Kentucky, 2540 Research Park Drive, Lexington, Kentucky 40511, United States ‡ Department of Mechanical Engineering, University of Kentucky, Lexington, Kentucky 40506, United States § Novozymes North America Inc., 77 Perry Chapel Church Road, Franklinton, North Carolina 27525, United States * S Supporting Information ABSTRACT: A bench-scale unit was fabricated and used to investigate use of carbonic anhydrase (CA) promoted K 2 CO 3 solvent as an option for CO 2 capture from coal-fired power plants. Bench-scale parametric tests were performed at various CA concentrations, solvent flow rates, and reboiler duties. The CO 2 capture efficiency significantly increases, and regeneration energy requirement decreases, with increasing CA concentrations up to 2.5 g/L, with capture performance leveling off at higher enzyme doses (up to 4 g/L). Thus, at higher enzyme doses, the capture efficiency is equilibrium rather than kinetically controlled at the top of absorber, when using solvent regenerated via vacuum stripping at high (>35%) lean carbonate to bicarbonate (CTB) conversion levels, which limits the driving force for CO 2 absorption. The CO 2 capture efficiency also increases when reboiler duty was increased from 0.85 to 1.1 kW, although this also increases the regeneration energy penalty. In contrast, the effect of solvent flow rate on CO 2 capture efficiency is less pronounced. Further improvements to the CO 2 capture process using CA promoted K 2 CO 3 solvent with low temperature vacuum stripping could be potentially advanced by lowering vacuum pressure, improving strategies for increasing rich CTB conversion (e.g., advanced packing column and optimized L/G ratio), and decreasing absorption temperature. 1. INTRODUCTION Solvent based postcombustion CO 2 capture is one of the preferred options for CO 2 removal from coal-fired combustion power plants. 1,2 A variety of aqueous alkanolamine solutions have been identified as capture solvents. 3 Alkali salts based solvents are an attractive alternative being actively inves- tigated. 4-7 Such solvents are less toxic with minimal degradation, nonvolatile with no aerosol emissions, and have heat of absorptions of CO 2 (for example, 24 kJ/mol CO 2 for carbonate to bicarbonate) much lower than those of amine based solvents. 8 One of the examples of commonly used alkali salt based solvents for CO 2 capture is a 20-30 wt % potassium carbonate-bicarbonate (K 2 CO 3 -KHCO 3 ) aqueous solution, which converts between carbonate and bicarbonate during CO 2 absorption and desorption. 9 However, the major challenge of using a K 2 CO 3 -KHCO 3 solvent is the low absorption rate due to the slow CO 2 hydration step resulting in poor absorption performance. Piperazine (PZ), amino acids, and boric acid, as mass transfer promoters, have been well studied and applied to accelerate the absorption rate. 5,8,10-13 However, drawbacks of these pro- moters, such as toxicity, instability, and corrosiveness, inhibit their extensive use. 9 The enzyme carbonic anhydrase (CA), as an efficient and eco-friendly biocatalyst, has been shown to improve the CO 2 absorption rate in the K 2 CO 3 -KHCO 3 solvent. 14 CA is a zinc Received: September 3, 2016 Revised: November 9, 2016 Accepted: November 9, 2016 Published: November 9, 2016 Article pubs.acs.org/IECR © 2016 American Chemical Society 12452 DOI: 10.1021/acs.iecr.6b03395 Ind. Eng. Chem. Res. 2016, 55, 12452-12459