Experimental evaluation of effect of oxidative degradation of aqueous monoethanolamine on heat of CO₂ absorption, vapor liquid equilibrium and CO₂ absorption rate

Oxidative degradation produces carboxylic acids which are one of the undesirable degradation products and may have a negative impact on the CO₂ separation energy of post combustion capture system. 30wt% MEA solutions mixed with carboxylic acids were regarded as a simulated solution for degraded MEA and effect of the additives on heat of CO₂ absorption, equilibrium CO₂ loading and CO₂ absorption rate were experimentally evaluated by using a differential reaction calorimetry (DRC) apparatus, a pressurized vessel to obtain vapor liquid equilibrium (VLE) data and a gas-liquid contactor, respectively. At the range of CO₂ loading from 0.0 to 0.3 mol-CO₂/mol-amine, the heat of CO₂ absorption of the simulated solution increased by around 10% compared to the normal MEA solution. Moreover, the changing-point of the heat of CO₂ absorption of the simulated solution moved to a leanerCO₂ loading compared to the normal solution. Result of a 13C-NMR analysis also indicated the change in reaction mechanism. At the absorber condition, the equilibrium CO₂ loading of the simulated solution decreased by 20% in comparison with the normal solution, where it decreased by 10% at the stripper condition and therefore the cyclic CO₂ loading also decreased. Both CO₂ absorption rates decreased linearly but in different gradients with increasing CO₂ loading. Higher pH in the simulated solution kept higher CO₂ absorption rate, which is consistent with the result of pH measurement.