Measurement of the Absorption Rates of Carbon Dioxide in Aqueous Solutions of Piperazine and Sulfolane Using the Stopped-flow Technique

Abstract

With the accelaration of the exploitation of natural gas reservoirs, the efficient removal of contaminants such as CO2, H2S, RSH, and COS is becoming of critical importance. In recent years, there is a growing interest in using amine blends or mixed solvents instead of a single amine for gas sweetening processes. Mixed solvents composed of a chemical solvent and a physical solvent take advantage of the benefits of both physical and chemical absorptions. The study of the absorption kinetics of the mixed solvent are necessary for designing and optimizing the process for removal of CO2 from natural gas, synthesis gas, or reformer gas. As a physical solvent, Sulfolane has excellent stability and low corrosiveness, in addition to a high capability for CO2 absorption. Sulfinol is a comercially successful process used in more than 200 plants and based on the use of Sulfolane as a physical solvent and either Diisopropanolamine (DIPA) or Methyldiethanolamine (MDEA) as chemical solvents. Mixed Sulfolane-based solvents have recently been proposed for post-combustion CO2 capture. In this study, the reaction kinetics of carbon dioxide (CO2) in aqueous solutions of aqueous piperazine (PZ) and an aqueous mixed solvent of (PZ + Sulfolane) were measured using the stopped flow technique resulting in the meaurement of observed pseudo-first-order rate constants (k0) allowing for the calculation of the second-order reaction rate constants (k2). The experiments were carried out over) concentration ranges of (10 to 60) for PZ, and (10 to 40, 10 to 200) (mol/m3) for PZ and Sulfolane, respectively and temperatures ranging from (298.15 to 313.15) K. Results show that the kinetic rates of the mixed solvent (PZ + Sulfolane + Water) were higher than those in aqueous PZ at all temperatures. The reaction kinetics in aqueous mixed solents of (PZ + Sulfolane) in reaction with CO2 increase with increasing temperature and concentration. The Termolecular mechanisms correlated the aqueous mixed systems of (PZ + Sulfolane) successfully. The reaction kinetics increased with the increase in temperature and concentration. The addition of Sulfolane to aqueous PZ resulted in increased absorption rates. Thus, the mixed solvent of PZ, Sulfolane and water can be considered an attractive alternative to aqueous amines for the enhancement of CO2 capture.