Experimental and Thermodynamic Modeling of CO2 Absorption into Aqueous DEA and DEA+Pz Blended Solutions

The important environmental concern of the carbon dioxide (CO2) capture by the absorption process with amine solutions is studied in the current study. The experiments are performed at operating conditions of a temperature range of 25 ̶65 ˚C, a pressure range of 1.5 ̶6.5 bar, diethanolamine (DEA) concentration of 0 ̶1.5 M, PZ concentration of 0 ̶0.5 M, and stirrer speed of 0 ̶300 rpm. The effects of operating conditions on CO2 loading, absorption rate, and mass transfer flux are investigated into two solutions of DEA and DEA+piperazine (Pz) blend in a stirred reactor. In the DEA+CO2+H2O system, by increasing stirrer speed from 0 to 300 rpm, the maximum values of CO2 loading and mass transfer flux at the same DEA concentration are increased 65% and 137%, respectively. The CO2 loading and mass transfer flux have higher values at higher initial pressures. The predicted values for species concentrations into the DEA+CO2+H2O system are also evaluated based on the Pitzer model, mass, and charge balance equations. The results showed that by increasing stirrer speed, the concentration of DEA molecule is decreased 40% but the concentrations of other ions and molecules are increased. In the DEA+Pz+CO2+H2O system, the results indicated that adding Pz to the absorbent solution was more efficient in CO2 capture relative to only the DEA solution. The equilibrium CO2 loading is increased by 20% and 16% for blend solutions with 4:6 and 6:4 molar ratios of DEA and Pz, respectively, but using only Pz solution is increased it up to 29%.