Application Research Of Ionic Liquids Phase Change Systems In CO₂ Capture

In recent years,the greenhouse effect and global warming have continued to affect people's living environment.The capture of greenhouse gases,especially CO2,is a hotspot for research,in which the regeneration of absorbents contributes the highest energy consumption.The CO2 phase change absorption system can undergo liquid-liquid phase change or liquid-solid phase change after absorbing CO2,and the reaction product is enriched in one phase.The effect of reducing the energy consumption of absorbent regeneration can be achieved by only regenerating the CO2 rich phase.At present,most of the phase change systems studied are mostly amine-based solvents,but these systems usually have problems like amine volatilization and equipment corrosions and the absorption performances need to be improved.In this paper,ionic liquids are used to replace the traditional amines.Ionic liquids CO2 phase change absorption system with good absorption performance,low regeneration energy consumption and little pollution is selected.First,[TETA]Br,[TETA]BF4 and[TETA]NO3 ionic liquids are synthesized,which were respectively compounded with some solvents.After CO2 absorption screening experiment,a total of 7 phase change systems were screened out.The phase change performances of the phase change systems are studied,and it is found that the type of anion of the ionic liquid,the polarity of the organic solvent and the functional group will affect the phase change performances.At the same time,the absorption capacities of the 7 phase change systems and the volumes of the lower phases after phase separations were investigated.Finally,[TETA]Br-PMDETA-H2O was selected for further experimental condition optimization and mechanism testing.The[TETA]Br-PMDETA-H2O system(4M,[TETA]Br and PMDETA molar ratio 3:7)can reach equilibrium within 90 minutes when absorbing pure CO2 at 303 K and the CO2 absorption capacity is 2.631 mol CO2/L.After the phase separation,the upper and lower phases are separated,and the lower phase is regenerated at 423 K.The regeneration efficiency can reach 98.48%.After 4 cycles of absorption and desorption,it can still be maintained above 95%.The CO2 cycle load reaches 8.513 mol CO2/mol ILs.Secondly,this article uses 88%volume fraction of N2 and 12%CO2 to form simulated flue gas,and[TETA]Br-PMDETA-H2O system was applied for flue gas CO2 absorption.Although the CO2 capacity will be reduced by increasing the operating temperature,the CO2 capacity at 323 K can still reach 2.501 mol CO2/L.The absorption and desorption cycle experiments were carried out under the conditions of absorption temperature 323 K and desorption temperature of 423 K.After 3 cycles,the regeneration efficiency can be kept above 96%,and the total CO2 cycle load can reach 6.091 mol CO2/L.Good absorption performance benefits from the mutual promotion of[TETA]Br and PMDETA after mixing.Among them,the highly active amino group in[TETA]Br can react quickly with CO2,PMDETA reduces the overall viscosity of the system so that[TETA]Br is not inhibited,and the reaction of PMDETA and water with CO2 further improves the system's CO2 absorption capacity.Finally,the 13C NMR sprctrums of different solutions during[TETA]Br-PMDETA-H2O absorbing CO2 were analyzed.The CO2 absorption products are mainly enriched in the lower phase.The main products are carbamate,carbonate and bicarbonate.In addition,there are water,[TETA]Br and PMDETA in the lower phase.It is speculated that the mechanism may be[TETA]Br reacts with CO2 to form carbamate,and at the same time,PMDETA and water react with CO2 to generate a small amount of carbonate and bicarbonate.The accumulation of carbamates leads to a decrease in the solubility of PMDETA in water.As the reaction proceeds,PMDETA with a lower density precipitates as the upper phase,and the remaining substances remain in the water as the lower phase.