Three-component 1,1,3,3-tetramethylguanidine based CO2-binding organic liquids: Statistical solvent design and thermodynamic modeling of CO2 solubility by LJ-Global TPT2 EoS

Abstract

In this study, three-component CO2-binding organic liquids (CO2BOLs) are introduced for high pressure CO2 absorption. The non-aqueous, green solvents consist of a superbase (1,1,3,3-tetramethylguanidine (TMG)), a tertiary alkanolamine (Dimethylethanolamine (DMEA), Diethylethanolamine (DEEA) and N-methyldiethanolamine (MDEA)) and an alcohol (MeOH, n-BuOH, sec‑BuOH, tert‑BuOH and 1-HexOH). The best combination of solvent components was determined to be the TMG/DMEA/n-BuOH BOL (molar ration:1/1/1) based on both CO2 loading (αeq= 0.431 mol CO2/mol solvent) and absorption rate (αR= 0.225 mol CO2/mol solvent within 20 min) by implementing screening experiments. The mixture design approach was applied for the design of experiments, modeling and investigating the effect of components’ proportion on αeq and αR at the constant temperature of 35.0 °C and initial CO2 pressure of 25.0 bar. The highest αeq (0.573 mol CO2/mol BOL) and αR (0.362 mol CO2/mol solvent) were obtained using TMG/n-butanol (1/1) and DMEA BOLs, respectively. The CO2 solubility data in the two-component BOLs: TMG/n-BuOH, TMG/DMEA and DMEA/n-BuOH as well as the three-component TMG/DMEA/n-BuOH BOL were gathered at 25.0, 35.0 and 45.0 °C and the pressures up to 35.0 bar using equimolar solvent mixtures. The LJ-Global TPT2 EoS was used in the simultaneous VLE and chemical equilibrium calculation algorithm for the thermodynamic modeling of CO2 solubility in the BOLs. The AAD% in the modeling of TMG/n-BuOH, TMG/DMEA, DMEA/n-BuOH and TMG/DMEA/n-BuOH BOLs were calculated to be 11.5%, 12.4%, 10.5 and 12.9%, respectively. The enthalpies of CO2 absorption in BOLs and the speciation of the system components were predicted from reaction equilibrium constants and using LJ-Global TPT2 EoS.