Kinetics study of carbon dioxide absorption in aqueous solutions of 1,6-hexamethyldiamine (HMDA) and 1,6-hexamethyldiamine, N,N′ di-methyl (HMDA, N,N′)

A study towards the kinetics of CO 2 in aqueous solutions of 1,6-hexamethyl diamine (HMDA) and 1,6-hexamethyl diamine, N,N′ di-methyl (HMDA, N,N′) was performed at concentrations ranging from 0.5 to 2.5 mol/L and temperatures from 283 up to 303 K. The kinetics data were determined by CO 2 absorption experiments using a stirred cell reactor with a flat interface between gas and liquid. These new CO 2 solvents were identified in earlier work for their high CO 2 capacity and limited corrosiveness. The experimental technique was validated using kinetic experiments for a 2.5 mol/L monoethanolamine solution. In view of double amine functionality and the six carbon chain between the amine groups, attention was paid to whether the amine groups acted independently and whether or not internal cyclisation would affect the carbamate forming mechanism. The reaction order with respect to HMDA was found to vary from 1.4 to 1.8 with increasing temperature. Absorption experiments in an equimolar solution of HMDA with HCl showed that the two amine groups react independently from each other towards CO 2. The reactivity of both diamines was more than five times larger than for monoethanolamine. The secondary diamine HMDA, N,N′ was found to be even more reactive towards CO 2. Additionally, the effect of CO 2 loading on the kinetics was studied for 0.5 mol/L aqueous solutions of HMDA and HMDA, N,N′ at 293 K. Both solvents are from absorption kinetics point of view good candidates for further evaluation as solvent (-component) for CO 2 capture. ► CO 2 absorption kinetics for 1,6-Hexamethylenediamine (HMDA) and 1,6-Hexamethylenediamine, N,N′ di-methyl (HMDA, N,N′) was found to be significantly higher. ► Equimolar concentration of HMDA and hydrochloric acid (HCl) showed similar kinetics of CO 2 absorption. ► Effect of CO 2 loading on the reactivity of HMDA and HMDA, N,N′ showed that HMDA, N,N′ has higher kinetics towards CO 2.