Experimental Studies for Development of a Purification Process for Single and Mixed Amine Solvents

Abstract

Amine solvents used for the removal of CO2 from flue gas are subject to solvent degradation, which results from the reaction of impurities in the gas stream. This leads to the formation of degradation products, which could lead to many operational problems such as changes in the solvent absorption capacity and physical properties. Amine thermal (distillation) or non-thermal (ion-exchange or electrodialysis) reclamation are usually used to purify the solvents. In post-combustion CO2 1- The reclamation process might not effectively handle single or blended amine solvents. The solvent recovery could be low while its content in the waste stream could be high. The high consumption for water and energy cannot be justified. capture, thermal purification seems to be the only feasible method due to its ability to remove all types of degradation products. However, thermal reclamation has suffered from some challenges as follows: 2- Blended solvent could be difficult to purify due to the complicated nature of amine mixture with the degradation products. 3- The recovered solvent could be contaminated with light degradation products that have a closer boiling point to amine or are even lighter than amine. To develop an efficient reclamation process, laboratory investigation was carried out for monoethanolamine (MEA) and monoethanolamine/methyldiethanolamine (MEA/MDEA). MEA is considered a reference solvent while MEA/MDEA is a potential candidate solvent for CO2 capture. A number of degradation products were selected to create artificially-degraded solvents. The laboratory work was intended to address three issues: understanding the impact of degradation, testing batch thermal reclamation and activated carbon treatment of contamination in recovered solvent. The impact of degradation studies revealed that the degradation products have a noticeable impact on the solvent physical properties and absorption capacity. The measurement of density and refractive index showed proportional increases with degradation level. Moreover, the solvent absorption capacity diminished with increase of their concentrations. Process simulation of a CO2 In the thermal reclamation study, recovery of single and blended solvents was maximized to greater than 90-95% under deep vacuum. MEA was recovered in one step while MEA/MDEA was recovered in one or two steps. Optimum solvent recovery varied based on the degradation level and test conditions (temperature and pressure). capture plant with ProTreat shows that the plant suffers from the presence of heat stable salts (HSSs). Recovered single or blended solvents exhibited at least some level of contamination; however, MEA solvent had less contamination than MEA/MDEA which depended on the types of degradation products selected for each system and the reclamation conditions. Adsorption treatment with three activated carbon types to remove the contamination was successful in the case of MEA/MDEA (50-60% removal), while the contamination removal for the MEA solvent was unsatisfactory (<10%). Three industrial samples of degraded lean amine solvents were thermally purified and treated with adsorption. Almost all degradation products were eliminated in the two treatment steps, showing the new hybrid reclamation process (thermal at increased vacuum plus activated carbon) is a feasible method in treating industrial solvents.