Development Of Novel MDEA-based Phase Change Absorbents And Study On The Carbon Capture Process

Global warming caused by massive emission of carbon dioxide（CO₂）has become one of the most pressing environmental problems.CO₂ capture and storage technology（CCS）is the key to significantly reducing CO₂emissions.Among them,the chemical absorption method is one of the most mature and suitable technical routes for flue gas CO₂ capture at this stage.The high investment cost and regeneration energy consumption of typical ethanolamine（MEA）capture technology have greatly hindered the application of industrialization.In recent years,phase change absorbents have been widely studied by researchers for their potential advantages of low regeneration energy consumption and flexibility of application.The purpose of this paper is to study the N-methyldiethanolamine（MDEA）with low reaction heat as the main agent,to develop a new type of low energy phase change absorbent,and to explore the phase separation,absorption,reaction mechanism and regeneration energy consumption.The main elements of the research work in this pape aresummarised below:（1）Employing MDEA as the primary agent,adding a small amount of MEA as the activator,and diethylene glycol dimethyl ether（DEGDME）as the phase separation agent to build low energy consumption phase change absorbent.The results showed that the CO₂ rich phase absorption loading of 3M1M2.2D absorbent is 1.79 mol/L,while the CO₂ lean phase absorption loading is almost neglected.The rich phase volume accounts for79.49%of the total volume of the absorbent.（2）A novel low-energy MDEA-based phase change absorbent was developed with MDEA activated by adding a small amount of activator diethylenetriamine（DETA）as main agent and 1-butyl-3-methylimidazole tetrafluoroborate（[Bmim][BF₄]）as phase separation accelerator.Based on the comprehensive evaluation of phase separation behavior,physical parameters,absorption performance and regeneration energy consumption,3M1D1.5B is the best concentration formulation system,its CO₂ rich phase loading can reach 3.01 mol/L with a fractional ratio of 72.22%,and the regeneration energy consumption is as low as 2.11 GJ/t CO₂,which is 45.8%lower compared to 30 wt%MEA,indicating that MDEA-based phase change absorbent has a great advantage in saving energy.（3）The two-phase composition distribution of absorbent was analyzed by ¹³C NMR characterization,and the reaction mechanism of MDEA-based phase change absorbent during CO₂ absorption was clarified.The phase separation mechanism showed that during the initial stage of CO₂ absorption,the activator has a high CO₂ reactivity and first reacts with CO₂ to form carbamate.With the increase of CO₂ absorption loading,MDEA alkalinity participated strongly in the dephosphorization reaction and catalyzed the hydration of CO₂ to produce HCO₃^-/CO₃^2-.CO₂absorption products such as protonated amines,carbamates,and bicarbonates are dissolved in the aqueous phase by strong ionic dipole forces,while physical solvents are excluded from the water phase to form organic phase under salting out effect.In general,the MDEA-based phase change absorbents have good CO₂capture performance and lower regeneration energy consumption,which has important reference significance for selecting high efficiency and low energy consumption CO₂ phase change absorbents.