Development of solvent for CO2 capture for utilization in concrete and storage in geological formations

Abstract

This study focused on developing an environmentally benign solvent for CO2 capture for utilization in concrete and the potential permanent storage in geological formations. Initial solvent screening and the selection included 2M aqueous solvents of KOH, NaOH, K2CO3, Na2CO3, sodium and potassium salts of glycine and lysine at 40oC and 20% CO2 balance nitrogen. The performance of the solvents was evaluated in terms of initial absorption rate, solvent precipitation and CO2 equilibrium loading. To present the best performing solvents as commercial products, the selected solvents were further optimized concerning solvent concentration, precipitation, CO2 partial pressure and absorption temperature. The absorption performance parameter values were 10.99, 11.95 and 13.47 (mol CO2 absorbed)2/(L soln.)2.min) x10-2 for potassium lysinate salt, KOH, and potassium glycinate salts respectively. Moreover, the optimum absorption condition for the best-performing solvents were experimentally determined to be 3M and 40oC, 5M and 60oC, and 6M and 60oC for aqueous potassium lysinate salt, KOH and potassium glycinate salt respectively. In the utilization section, best performing solvents from the optimization studies were loaded with CO2 and used for carbonation reactions. The presence of CaCO3, the main product formed when CO2 reacts with concrete, was confirmed by XRD phase identification analysis. Also, by the TGA thermogram, the calcium carbonates in the precipitate of the K2CO3-Ca(OH)2 reaction was 44.1wt.%, whiles that from CO2-loaded potassium glycinate-Ca(OH)2 was 55.4wt.%, demonstrating the ease with which potassium glycinate easily releases CO2 to concrete compared to carbonates and hydroxide systems. Moreover, these findings proved the concept of utilizing the CO2-loaded solvents in concrete. Finally, kinetic studies were conducted for the best performing solvent concerning both CO2 capture and utilization in concrete, potassium glycinate salt. The kinetic performance was measured in terms of the initial absorption rate. To fit the kinetic data, the power law model was used. With the aid of NL-Reg software, the activation energy obtained was Ea = -5.5x103 J/mol. This was expected because, the rate of absorption decreased with increasing temperature. For reversible reaction such as this, the backward reaction might have been favoured at high temperatures leading to this observation. Also, CO2 and potassium glycinate had reaction orders of 1 and 0.11, respectively. The AAD% obtained was 5.15%, demonstrating how well the model predicts the experimentally observed rates.