Solvent extraction based reclaiming technique for the removal of heat stable salts (HSS) and neutral degradation products from amines used during the capture of carbon dioxide (CO2) from industrial flue gases

Abstract

This work used a modified OH-aliquat mixed with a new diluent, namely, 2-ethyl-1-hexanol to separate heat stable salts (HSS), namely, formate, glycolate and oxalate as well as neutral degradation products (i.e. imidazole, N-acethylethanolamine, 2-oxazolidone, N-(2-hydroxyethyl)-succinimide) from monoethanolamine (MEA), 2-amino-2-methyl-1-propanol (AMP), and N-methyldiethanolamine (MDEA) and their blends which are amines/amine blends typically used for carbon dioxide (CO2) capture from industrial flue gases. The new diluent, which has a branched-chain structure, increased the extraction performance of the OH-aliquat up to 50% HSS removal from MEA solution compared to our previous straight-chained 1-octanol diluent. The extractant also performed very well in removing HSS from MDEA and AMP with the ease of HSS extraction increasing in the order of AMP < MEA < MDEA for which the oxalate was removed by nearly 100% regardless of the type of amine and concentration. In blended MEA, AMP and MDEA, the extractant had a higher chemical affinity in removing all HSS when compared with single MEA. The extractant could also remove major neutral degradation products found in MEA solution. High temperature and low CO2 loading conditions were found to be favorable in maximizing the ability of the extractant to remove both product types. This finding revealed that the exact location where the amine slipstream should be taken for simultaneous extraction of all degradation products is at the exit point of the lean-rich amine heat exchanger. The regeneration of extractant using sodium hydroxide solution (NaOH) also indicated the reusability of the extractant as long as its reactive molecules remained. The results obtained from this study are being used for further development of the extraction process that can be used as a permanent replacement for conventional reclaiming techniques.