Study On Carbon Dioxide Cpature Using Nonaqueous 2-(Methylamino) Ethanol-based Absorbent

Chemical absorption using aqueous monoethanolamine（MEA）is the most mature and available method for CO₂ capture.However,large energy consumption required for solvent regeneration and high capture costs still remain major disadvantages of this technology.The use of non-aqueous MEA solvents has been confirmed to play a huge role in reducing energy consumption in our previous work.In this work,2-（Methylamino）ethanol（MAE）-based nonaqueous absorbents were proposed to capture CO₂,and systematically investigated the absorption-desorption performance,absorption mechanism,physicochemical properties,and regeneration energy consumption.Results will provide important support for developing next generation energy-efficient absorbents and demonstrating new capture processes,with great scientific value and practical significance.In this paper,the phase behavior,absorption-desorption performance,and cycling capacity of MAE-based nonaqueous solvents such as ethylene glycol methyl ether（EGME）,ethylene glycol ethyl ether（EGEE）,ethylene glycol butyl ether（EGBE）,diethylene glycol dimethyl ether（DEGDME）,etc.Absorbents were studied in a laboratory rapid screening device and microwave reactor using N₂/CO₂gas mixture to simulate the main components in flue gas,and biogas natural gas,A thermal regeneration device was used to analyze the energy consumption of different absorbents at same desorption conditions and compare with the aqueous MEA system.Physicochemical properties of these absorbents were measured using densimeter and microviscometer at various conditions.Solubility of N₂O and CO₂ in the blends of MEA and glycol ethers was also determined in a vapor-liquid equilibrium apparatus using static methods,and the experimental data were interpreted using thermodynamic models.Reaction mechanisms were revealed by the findings of ¹³C NMR and FT-IR.Under the same experimental conditions,After CO₂absorption by the systems of MAE with EGME,EGEE,and EGBE,the solution was still in a single homogeneous liquid phase.But for the system of MAE and DEGDME,liquid-liquid phase change occurred.In the homogeneous single liquid system,the CO₂loading in different absorbents was found to be about 2.1 mol.kg^-1,and its cyclic capacity was about 1.0mol.kg^-1.The absorption capacity of MAE-based absorbent is slightly lower than aqueous MEA(2.3 mol.kg^-1),but its absorption-desorption cyclic capacity is about twice that of aqueous MEA under the same operating conditions.At 373K,the regeneration energy consumption of the MAE+EGME system is about 56%lower than that of MEA aqueous system and 15%lower than that of nonaqueous MEA.In the case of phase change system,97%of CO₂ was mainly concentrated in the lower phase with a volume percentage of about 50%.For the phase change absorbent,only the CO₂-rich phase was desorbed during solvent regeneration,which significantly reduces the total amount of the solution mass.The absorbents of MAE+EGME and MAE and DEGDME were found to be stable with an average cyclic capacity of 1.0 and 2.8 mol.kg^-1 in several absorption-desorption cycles,respectively.The reaction products of the MAE+EGME system are mainly carbamates and protonated amines.Densities and viscosities of CO₂-free and CO₂-loaded MAE-based nonaqueous systems decreased with the increasing temperature,the densities increase with the increasing mass fraction of MAE in the blends of MAE with EGEE or EGBE,where as they decrease in the blends of MAE with EGME.It is mainly due to the density order of pure solvents.Viscosities of the solution increases with the increase of MAE concentration.Excess molar volumes V^E and viscosity deviationsΔηfor these blends were both negative over the entire range of mole fraction and temperature,which indicated that there was a volume contraction and decrease in viscosity on mixing,and strong intermolecular forces between MAE molecules and organic solvents.Density and viscosity data of CO₂-free systems were represented by fitting to Redlich-Kister equation.The experimental and the calculated from the proposed model matched well with each other,with an average absolute deviation within 0.01%and 1.3%.The semi-empirical model was used to fit the density and viscosity data of the CO₂-loaded solution.The average absolute deviations were 0.15%and 3.0%respectively.Henry’s cofficients of CO₂ in MAE-based nonaqueous systems were estimated by N₂O/CO₂ analogy.The values in these non-aqueous blends increase with increasing temperature.The predictions from the exponential model and experimental data were in good agreement with each other within 2.0%AAD.The CO₂ loadings in the MAE+EGME solution decrease with increasing the temperature at a given CO₂ partial pressure and the CO₂ partial pressures increase with increasing the CO₂ loading at a constant temperature.In comparison with aqueous MEA.CO₂ solubility in these nonaqueous blends was found to be sensitive to the change of temperature resulting in higher cyclic capacity,which is favorable for temperature-swing CO₂ capture process.The cyclic absorption capacity from the solubility curves was in accord with the findings above-mentioned.A semi-empirical model and a Kent-Eisenberg model were proposed to interpret the vapor-liquid equilibrium data for the systems of CO₂/MAE/EGME solution and the AADs were within 20%and 10%respectively.Compared with aqueous MEA,the developed nonaqueous absorbents of MEA with glycol ethers have shown different absorption behaviors and comparative capture performance.In addition,they can reduce significantly the regeneration energy consumption as well as high cyclic capacity and good stability.MAE-based nonaqueous system can offer an alternative strategy to solve the key issues of high regeneration energy consumption for CO₂ capture.Therefore,the proposed absorbents have huge potential in energy-efficient carbon capture process in several industries such as biogas upgrading and natural gas processing.