Design Of Phase Change Absorber And Its Application In CO₂ Capture

With economic and population growth,greenhouse gas emissions,especially CO₂emissions,continue to increase,causing great harm to the natural environment and climate.The capture and utilization of CO₂ have become the focus of researchers.The ionic liquid phase change absorber is proposed for the disadvantages of traditional organic amine absorbers,such as high energy consumption for regeneration,corrosive equipment,easy degradation of amines,and volatile solvents.At the same time,the excellent structural characteristics of ionic liquids make it possible for them to function as absorbents,solvents,and catalysts simultaneously.The paper constructs a green and environmentally friendly ionic liquid phase change absorption system with high absorption capacity and low regeneration energy consumption for capturing CO₂ in power plant flue gas and reusing CO₂ absorption products to achieve a green chemical technology route for CO₂ capture and utilization.This paper synthesized a series of biofunctionalized ionic liquids with good thermal stability and low viscosity.TETA and TEPA with multiple amino active sites were used for the cations.Imidazole（amino active site）and phenol（phenolic hydroxy active site）with different active sites were used for the anions.Firstly,ionic liquid-organic solvent-water absorption systems were designed to study their phase change absorption performance.The results were found that the anionic and cationic structures of ionic liquids and the types of organic solvents had significant effects on CO₂ absorption performance and phase change behavior.The[TEPAH][Im]/DGME/H₂O phase change absorption system with high absorption capacity and small volume share after phase change was screened for the optimization of absorption conditions and mechanism analysis.Under the optimal absorption conditions in a pure CO₂absorption environment(0.5 mol/L[TEPAH][Im],V_DGME:V_H2O=7:3,298.15K),the system absorbs CO₂ and then undergoes a good phase change behavior,producing two phases L-L,the CO₂-enriched phase is the lower phase,accounting for more than 99%of the total load.The volume only accounts for15.6%of the total,a small regeneration volume.It is expected to further reduce the regeneration energy consumption.The system was saturated within 60 min with an absorption capacity of 2.08 mol CO₂/mol ILs,significantly higher than the CO₂ absorption capacity of 30 wt%aqueous MEA solution.Then,the absorption reaction and phase transition mechanism of the[TEPAH][Im]/DGME/H₂O system after CO₂ capture were inferred based on ¹³C NMR analysis and DFT calculation analysis.After the[TEPAH][Im]/DGME/H₂O system captures CO₂,the ionic liquid[TEPAH][Im]reacts with CO₂ to form carbamate.Water reacts with CO₂ to form HCO₃^-/CO₃^2-,and the absorption products obtained are mainly concentrated in the lower phase,and the organic solvent DGME is mainly in the upper phase.Since the solubility of the absorption products in DGME is much lower than that in water,and the density of DGME is relatively small,the absorption products are deposited in the lower phase.To investigate the potential of the[TEPAH][Im]/DGME/H₂O system for industrial application,a simulated of desulfurization flue gas（87.5%N₂,12.5%CO₂）was designed to capture CO₂ at 45°C.The results showed that the system could maintain a high absorption capacity and produce excellent phase change behavior with an absorption capacity of 1.84 mol CO₂/mol ILs.The regeneration efficiency was maintained above 96%after five absorption-desorption cycles at a temperature of 120°C.Finally,the catalytic activity and cyclic regeneration performance of[TEPAH][Im]catalyzed conversion of the absorption product to quinazoline-2,4（1H,3H）-dione was investigated,which can effectively save regeneration energy and directly obtain valuable chemical products compared with absorption desorption or desorption reuse.The effects of reaction time,temperature,and catalyst dosage on the reaction were investigated.The product yield was up to 98%under a molar ratio of 1:4 between 2-aminobenzonitrile and catalyst[TEPAH][Im]at atmospheric pressure,90°C,and 16 h.No significant decrease in catalyst activity occurred after five cycles,indicating that the[TEPAH][Im]ionic liquid has high catalytic activity and stable structure.The results show that the[TEPAH][Im]/DGME/H₂O system designed in this paper to capture and utilize CO₂ is a green,low-cost,non-toxic,and non-hazardous process with easy recovery of the catalyst and has a good promising development.