A novel diamine non-aqueous absorbent based on N-methyl diethanolamine regulation for energy-efficient CO2 capture

Abstract

Non-aqueous absorbents receive more and more attention due to their low sensible heat and evaporation latent heat. But their low CO₂ desorption efficiency and high desorption reaction heat are still major limits for practical application. Herein, a novel non-aqueous diamine absorbent based on alkanolamine regulation is proposed. In the experiments, monoethanolamine (MEA) was used as the main absorbent for ensuring high CO₂ absorption capacity and absorption rate, while polyethylene glycol 200 (PEG200) was used as a cosolvent to reduce evaporation latent heat. Subsequently, MEA/PEG200 non-aqueous absorbents were composed with three typical secondary/tertiary amines including N-methyldiethanolamine (MDEA), diethanolamine (DEA) and triethanolamine (TEA), respectively, and their regulation effects on CO₂ capture performance were investigated systematically. The results showed that the MEA/MDEA/PEG non-aqueous system exhibited a superior CO₂ desorption performance. The corresponding maximum regeneration efficiency reached up to 82.1%, which was significantly higher than the case without addition of MDEA. It still kept a high CO₂ desorption efficiency (79%) after the 8th regeneration cycle. According to thermodynamic analysis, the desorption reaction heat for the MEA/MDEA/PEG non-aqueous system was only 1.40 GJ per ton CO₂, which was 20% lower than the non-aqueous MEA/PEG200 absorbent. And its total regeneration energy consumption was 1.90 GJ per ton CO₂, which was reduced by 48.1% compared to MEA aqueous solution. FT-IR, ¹³C-NMR and DFT calculations indicated that the introduction of the MDEA regulator would result in a much lower reaction energy barrier between zwitterions and MDEA compared to that between zwitterions and MEA. Besides, it would induce the formation of protonated MDEA (MDEAH⁺), which was much easier for MDEA regeneration.