Comprehensive performance of a diethylenetriamine/2-diethylaminoethanol biphasic absorbent for CO2 capture

Abstract

The CO2 capture process based on amine absorption–regeneration is currently the most widely used technology, and the performance of absorbent is the key to this process. Biphasic absorbents have attracted considerable interest because of their strong potential to reduce the regeneration energy consumption and equipment investment costs. The mixed solution of diethylenetriamine (DETA) and 2-diethylaminoethanol (DEEA) has been proven to be a biphasic absorbent, but there is still a lack of comprehensive performance evaluation data. In this study, the ratio of the DETA/DEEA solution was optimized as 2 M DETA + 3 M DEEA, and its phase separation property, reaction mechanism, mass transfer kinetics, and desorption thermodynamics were investigated under various conditions. The comprehensive performance of the solution was then evaluated by further analyzing its oxidative degradation, thermal degradation, and metal corrosion characteristics. On this basis, the capital cost and operation cost of using DETA/DEEA biphasic absorbent were analyzed. Under typical coal-fired flue gas (CO2 concentration 12%), because of the high CO2 absorption capacity and excellent phase separation property, the minimal desorption energy consumption of the DETA/DEEA absorbent decreased to 2.14 GJ/t CO2, a 43.7% decrease compared with that of 5 M monoethanolamine (MEA). Under the same experimental conditions, DETA/DEEA exhibited an oxidative degradation rate of only 2.71%, which was 20.7% of 5 M MEA. In addition, the metal corrosion rate of DETA/DEEA was one order of magnitude lower than that of 5 M MEA. However, under a high CO2 loading, its thermal degradation resistance needed to be improved, and it was clear that the rates of oxidative degradation, metal corrosion, and thermal degradation of the CO2 rich lower phase were higher than those of the CO2 lean upper phase. The capital cost and operational capture cost of the DETA/DEEA biphasic process were approximately $107.8/t CO2 and $31.6/t CO2, respectively, which were 2.5% and 36.4% lower than those of the MEA process. These findings provide a theoretical basis for the industrial application of DETA/DEEA.