Application Of Biphasic System In CO₂ Capture

Global warming has caused many meteorological and climate extreme events,which have had a great impact on human life.Among the greenhouse gases that cause global warming,CO₂ contributes the most.Carbon capture methods have attracted extensive attention.Among them,the chemical absorption system with biphasic behavior has been widely used,due to its advantages of"low requirements for CO₂ partial pressure,significantly reduced regeneration energy consumption and high CO₂ recovery".However,in most of the reported phase change systems,the CO₂ absorption capacity is weak and the absorption time is long.The increase of amine groups in the absorbent helps to improve the CO₂absorption capacity.Based on this,TEPA containing more amino groups is selected to develop a phase change system with high CO₂ absorption capacity.In order to reduce the viscosity of TEPA to obtain higher absorption rate and shorten the absorption time,low viscosity solvent and water are compounded with TEPA.Among the 16 ternary absorption system,TEPA/DGME/H₂O has the best phase transition behavior and pure CO₂ absorption performance.Under the mass ratio of TEPA/DGME/H₂O of 3:3:4,25℃and atmospheric pressure,the absorption capacity of pure CO₂ reaches 2.99 mol CO₂/Kg absorbent within50 mins,of which the volume of CO₂ rich phase accounts for 73%.At 130℃,the desorption rate of the absorbed product is stable at about 97%.After four absorption and desorption cycles,the average single CO₂ load is 2.83 mol CO₂/Kg absorbent.The CO₂ cycle absorption capacity of TEPA/DGME/H₂O in pure CO₂ absorption is about 2.60 times that of traditional 30 wt%monoethanolamine solution.Compared with the reported two-phase system,the absorption time is significantly shortened due to the low viscosity.In order to study the mechanism of CO₂ absorption by phase change system,the TEPA/DGME/H₂O absorption system before absorption,the upper phase after absorption and the lower phase after absorption were sampled and tested by ¹³C NMR.Based on the analysis of the test results,CO₂ first reacts with TEPA to form zwitterionic ion TEPA⁺COO^-,and then zwitterionic ions combine with unreacted TEPA to form TEPACOO^-and TEPAH⁺.At the same time,a small amount of CO₂ dissolved in water reacts with water to produce CO₃^2-and HCO₃^-.The reason for the phase separation is the high solubility of carbamate in water.With the increase of TEPACOO^-,DGME is gradually excluded.The final system is divided into the light phase of DGME with low density and the heavy phase,which contains carbamate,carbonate and bicarbonate,as well as a small amount of DGME.In order to explore the carbon capture performance of TEPA/DGME/H₂O in power plant flue gas,a simulated flue gas（90%N₂,10%CO₂）is designed according to the actual components of flue gas.The experimental results of CO₂capture for simulated flue gas show that the CO₂ absorption capacity of TEPA/DGME/H₂O phase change system can be maintained at 2.70 mol CO₂/Kg absorbent at the simulated flue gas temperature of 55℃.Under the conditions of absorption temperature of 55℃and desorption temperature of 130℃,four absorption and desorption cycle experiments were carried out.The desorption efficiency of residual and new absorption products is always about 97%,and the average single CO₂ load is 2.55 mol CO₂/Kg absorbent.Under the condition of simulated flue gas,TEPA/DGME/H₂O system still shows good absorption performance and cycle stability.Therefore,TEPA/DGME/H₂O system is a kind of phase change absorber with good industrial application prospect.