Aqueous piperazine derivatives for CO₂ capture: Accurate screening by a wetted wall column.

Xi Chen; Rochelle, Gary T.

Concentrated aqueous piperazine (PZ) has been identified as a better solvent for CO2 capture than monoethanolamine (MEA), because it has a greater rate of CO2 absorption and greater CO2 capacity. This work evaluates the effect of substitute groups on PZ performance. Many previous screening studies measured absorption/desorption with CO2/N2 sparging, which lacks accuracy and cannot be used to estimate actual absorber performance. In this work a wetted wall column was used to accurately measure absorption/desorption rate at typical rich and lean CO2 loading (α) and simulate performance of real packing. The method also provides accurate measurement of CO2 solubility at 40-100 °C. This study provided rate and solubility data at 40-100 °C and practical ranges of CO2 loading for 8 m 1-methylpiperazine (1-MPZ), 8 m 2-methylpiperazine (2-MPZ), 4 m 2-MPZ/4 m PZ, 7.7 m N-(2-hydroxyethyl)piperazine (HEP), 6 m 1-(2-aminoethyl)piperazine (AEP), 8 m 2-piperidine ethanol (2-PE), and 2 m trans-2,5-dimethylpiperazine (2,5-DMPZ). With the measurements of CO2 flux (NCO2) and equilibrium driving force, liquid film mass transfer coefficients (kg') are calculated. The rate decreases as of 1-MPZ = PZ> 2-MPZ/PZ> 2-MPZ> HEP> MEA> AEP = 2-PE. This method also allows bracketing and determination of equilibrium CO2 partial pressure (PCO2*) at each condition. Semi-empirical solubility models of CO2 for each amine were regressed from experimental solubility data to find the lean and rich CO2 loading corresponding to 0.500 kPa and 5kPa CO2 partial pressure respectively. Based on the solubility model, the actual operating capacity of the solvents without overstripping decreases in the sequence of 2-PE > 2-MPZ > 2-MPZ/PZ > 1-MPZ > PZ > HEP > AEP > MEA. The enthalpy of CO2 absorption (ΔHabs) of all the piperazine derivatives is around 70kJ/mol CO2.

CARBON sequestration; CARBON dioxide; PIPERAZINE; SOLVENTS; SOLUBILITY; ENTHALPY; ABSORPTION; DESORPTION

Chemical Engineering Research & Design: Transactions of the Institution of Chemical Engineers Part A, 2011, Vol 89, Issue 9, p1693

0263-8762

Academic Journal

10.1016/j.cherd.2011.04.002