Stability Studies of a Novel Amine Blend for the Capture of CO2 Generated from Indirect Co-Combustion of Natural Gas and Biomass
The use of chemical solvents for post-combustion capture (PCC) of CO2 has proven to be a significant technology for reducing CO2 emissions. Among the various chemical solvents developed for this purpose, amine solvents have seen the most advancement in research, with monoethanolamine (MEA) being the most prominent. MEA is widely recognized and recommended for its rapid initial absorption rate and low solvent cost. However, it is also noted for its high instability, leading to rapid degradation.
Amine degradation in CO2 capture refers to the decreased efficiency of amines in absorbing CO2 from flue gas. Research indicates that this decline in efficiency, due to the reduction in amine molecular concentration, is caused by side reactions with impurities such as O2, SOx, NOx, and metal oxides present in the flue gas. This side reaction is noted to be an endothermic reaction thus, degradation is favoured at higher temperatures. Of all the contaminants mentioned in the flue gas, oxygen is the sole component lacking a feasible pretreatment method. This suggests that the chemical solvents used in PCC are likely to undergo degradation, primarily due to the presence of oxygen.
This work evaluated the stability of a novel amine blend, 4M AMP:1-(2-HE) PRLD, synthesized by Avor et al., 2022 in the presence of pretreated flue gas (CO2, O2 and N2). The research was conducted in a semi-batch reactor, exploring temperatures of 40, 50, and 60° C (± 0.2), along with oxygen partial pressures of 6,12 and 18% (±0.3) with nitrogen balance and the amine blend being preloaded with CO2 (0.25 ± 0.02 mol CO2/ mol amine). Each experimental run was carried out for 21 days.
A widely recognized amine mixture, 5M MEA:DMAE, consisting of a primary amine and a tertiary amine just like the novel blend and also with comparable cyclic capacities, was tested against the novel blend. The novel blend, 4M AMP:1-(2-HE) PRLD, demonstrated superior inherent stability. Furthermore, experimental data derived for 4M AMP:1-(2-HE) PRLD allowed for the development of a correlation between ammonia emission rates and degradation rates, with a coefficient of determination calculated to be 0.923. Additionally, by employing the power law rate reaction equation through nonlinear regression, a kinetic model for degradation was developed, achieving an absolute average deviation (AAD) of 17.9%. The reaction was found to have an overall order of 1.3, with an activation energy of 50.3 kJ/mol.