Reclaiming degraded mixed monoethanolamine and N-methyldiethanolamine solvent in carbon dioxide capture process

Abstract

In this work, the effect of thermosiphon on vacuum distillation of degraded amine solutions was investigated for the amine reclamation process. A detailed analysis of the feed, the recovered solvent, and the waste streams showed that this novel reclamation process modified with thermosiphon was able to remove most of the undesirable impurities and degradation products and to restore the single degraded solvent to almost its original purity at a high recovery efficiency compared with the original process. Therefore, the thermosiphon was found to increase the recovery efficiency of degraded single amine reclamation at a steady-state. The average rate of products obtained from the enhanced unit was 2.64 mL/min, 6.28 times higher than the rate of product collected from the original unit (0.42 mL/min) at a temperature of 140 °C and vacuum pressure of 20 kPa. However, due to heavy amine in formulated mixed amines, the phenomenon of hindered circulation in thermosiphon occurred to make reclamation efficiency decline considerably. In order to maintain the original recovery efficiency in case of mixed solvents, after eliminating the thermosiphon part, the vacuum distillation temperatures were increased to a maximum of 170 °C close to heavy amine boiling point, by our new feeding mode of opening and closing feed valve intermittently in equal interval of 10 min to increase the evaporation rate of heavy amine at unsteady state. The analysis results showed that most of the undesired degradation products and impurities were removed, and the recovered product had a high weight ratio of MDEA/MEA in the range of 0.45–0.6. The total solvent concentration of the product was close to the feeding solvent concentration. These data will benefit for commercial reclaiming system design for blended amine solvents.