Selected blended amines for postcombustion CO2 capture
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Carbon capture and storage is an important climate measure for a low carbon future. The CO2 capture technology closest to implementation for post-combustion CO2 capture systems is chemical absorption with amine solvents. The technology is technically feasible, but research is still needed to reduce capital and operating costs, and the energy penalty for solvent regeneration. Thus, the primary objective of this thesis is to identify and characterise blended amine solvents that can reduce the energy requirement for solvent regeneration. The literature study showed that most of the amine solvents obtained an absorption capacity and cyclic capacity higher than the benchmark solvent monoethanolamine (MEA). Then, the work identified three tertiary amines which can be used as an alternative to 2-(diethylamino)ethanol (DEEA) in the blend with MAPA. The three tertiary amines were 3-dimethylamino-1-propanol (3DMA1P), 3-diethylamino-1-propanol (3DEA1P) and 1-(2-hydroxyethyl)pyrrolidine (1-(2HE)PRLD). In aqueous solution, the tertiary amines were less volatile than DEEA and when blended with MAPA, they obtained similar absorption rate as the blend DEEA/MAPA and a reboiler heat duty in the range of 2.3 – 2.6 J/tCO2. This heat duty was comparable to other blended amines studied in the literature and to novel solvents tested in pilot plants under realistic process conditions. Due to the large contribution of the heat of desorption to the reboiler heat duty, a further reduction in reboiler heat duty seems only possible with solvent specific optimisation and changes in process configuration. At last, the effect of liquid viscosity on the CO2 absorption rate in MEA- and NaOH-based solutions was studied using an apparatus mimicking an absorption column and a membrane contactor. The observed decrease in the overall mass transfer coefficient was due to decreasing CO2 solubility and diffusivity, and in the membrane contactor case, it seemed also to be due to an additional viscosity-related resistance established at the membrane/liquid interface.