• Luo, Weiliang
• Melian-Cabrera, Ignacio
• Bruggink, Stefan
• Beyad, Yaser
• Conway, Will

Abstract

Presently monoethanolamine (MEA) remains the industrial standard solvent for CO2 capture processes. Operating issues relating to corrosion and degradation at high temperatures and in the presence of oxygen have introduced the requisite for higher quality and costly stainless steels in the construction of capture equipment. In view of the drawbacks of concentrated MEA solutions alternative solvents systems including aqueous amine blends are gaining momentum as new generation solvents for CO2 capture processes. Given the exhaustive array of amines available to date endless opportunities exist to tune and tailor a solvent to deliver specific performance and physical properties in line with a desired capture process. The current work is focussed on the rationalisation of CO2 absorption behaviour in a series of aqueous amine blends incorporating monoethanolamine, N,N-dimethylethanolamine (DMEA), N,N-diethylethanolamine (DEEA) and 2-amino-2-methyl-1-propanol (AMP) as solvent components. Mass transfer/kinetic measurements have been performed using a wetted wall column (WWC) contactor at 40oC for a series of blends in which the blend properties including amine concentration, blend ratio, and CO2 loadings from 0.0 – 0.4 (moles CO2/ total moles amine) were syetematically varied and assessed. Equilibrium CO2 solubility in each of the blends has been estimated using a software tool developed in Matlab for the prediction of vapour liquid equilibrium using a combination of the known chemical equilibrium reactions and constants for the individual amine components which have been combined into a blend. From the mass transfer data the largest absorption rates were observed in blends containing 3M MEA/3M Am2 while the selection of the Am2 component had only a marginal impact on mass transfer rates. Overall, CO2 mass transfer in the fastest blends containing 3M MEA/3M Am2 was found to be slightly lower than a 5M MEA solution at similar temperatures and CO2 loadings. In terms of equilibrium behaviour a slight decrease in the absorption capacity with increasing Am2 concentration in the blends with MEA was observed while cyclic capacity followed the opposite trend. Significant increases in cyclic capacity (26-111%) were observed in all blends when compared to MEA solutions at similar temperatures and total amine concentrations. In view of the reasonable compromise between CO2 absorption rate and capacity a blend containing 3M MEA and 3M AMP as blend components wouldrepresent a reasonable alternative in replacement of 5M MEA as a standalone solvent.

Topics

• impedance spectroscopy
• stainless steel
• corrosion
• Oxygen
• combustion
• amine