Effect of H2O on absorption performance of tetraethylenepentamine-ethanol-CO2 two-phase absorbent and its mechanism

There is about 10 vol% water vapor in coal-fired flue gas, and the existence of water has an effect on the phase separation performance of amine-alcohol two-phase absorbent. The effects of a small amount of water on the phase separation performance and mechanism of TEPA-ethanol-CO2 system in the range of 0.2 ~ 2.3M TEPA concentration were investigated. The influences of amine concentration and water content on the absorption rate, absorption loading, absorption capacity, mass fraction of CO2-rich phase and the proportion of CO2 enriched in the CO2-rich phase to total CO2 enriched were studied. The different mechanisms between amine-alcohol-H2O-CO2 system and amine-H2O-CO2 or amine-alcohol-CO2 system were discussed. Fourier transform infrared spectroscopy (FTIR) analyses show that the 1308 cm−1 absorption peak attributes to the superposition of angular vibration frequency of -CH2 and alkylcarbonate. The 1.6M-TEPA-ethanol-14%-H2O system shows the best comprehensive performance, 96.23 vol% CO2 is enriched in the CO2-rich phase, and the average CO2 absorption rate within the first 30 minutes is 2.4 times faster than 0.2M-TEPA-ethanol-14 %-H2O solution. The main products in CO2-rich phase of 1.6M-TEPA-ethanol-14%-H2O system are carbamate, protonated amine and a little alkylcarbonate. In FTIR spectrum, some unreacted ethanol is also found.