Study On Physicochemical Properties Of Alkanolamines/2-Alkoxyethanol Carbon Dioxide Absorbents And Their Mass Transfer Performance In A Dixon Ring Packed Column

Chemical absorption is the most widely used and effective technology for the reduction of CO₂ emission.Aqueous monoethanolamine（MEA）is considered to be a benchmark absorbent.However,the high regeneration energy consumption,significant amine loss and corrosion problems are the major barriers to implement large-scale applications.Considering the facts that,the reaction heat of secondary alkanolamines with CO₂ is lower and the 2-butoxyethanol（EGBE）has excellent characteristics such as low specific heat,low viscosity,low volatility and environmental friendliness,further investigation on the proposed novel absorbents and their mass transfer performance in packing column is demanding with practical significance.In this work,the basic physicochemical properties,capture performance and mass transfer performance of the secondary alkanolamines-EGBE of aqueous/water-lean absorbent were studied preliminary.These results will provide important support for further improvement and application demonstration of absorbents.Physicochemical properties of EGBE with 2-（ethylamino）ethanol（EAE）or2-（butylamino）ethanol（BAE）was measured using densimeter and microviscometer at various conditions.The absorption-desorption performance and cycling capacity of water-lean alkanolamines-EGBE solvent were studied in a rapid screening device and microwave desorption reactor.Reaction mechanisms were also revealed by the findings of FT-IR and ¹³C NMR.Solubility of CO₂ in the system of BAE-EGBE was determined in a vapor-liquid equilibrium apparatus using a static method.The mass transfer performance of aqueous MEA,nonaqueous MEA-EGME and BAE-EGBE blends was comprehensively investigated in a packed column with Dixon ring random packing.Densities and Viscosities of EAE and BAE in EGBE solvent decrease with the increasing temperature,but increase sharply with an increase in CO₂ loading.The densities of these systems increase with increasing the EAE concentration but decrease with the increase in BAE 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 were a volume contraction and decrease in viscosity on mixing.These density and viscosity data for EAE-EGBE and BAE-EGBE binary systems were correlated by a Redlich-Kister type equation,and the calculated from the fitting parameters were in good agreement with the experimental data.Property data of EAE-EGBE-CO₂and BAE-EGBE-CO₂ ternary systems were also correlated by the proposed non-dimensional empirical equations.Densities and viscosities for water-lean ternary mixtures decrease with the rising temperature.The densities of the three systems show an increase with the increasing water content.The measured ternary property data were well represented by the proposed equations with Redlich-Kister and Cibulka parameters.CO₂ absorption-desorption performance of these water-lean/free absorbents was investigated and compared under the same operating conditions at near atmospheric pressure.It was found that non-aqueous blends of secondary alkanolamines with EGBE have shown a significant reduction in regeneration energy consumption and good capture performance.The water content in these blends has shown little effect on the CO₂ capture performance.The main products after absorption CO₂ in water-lean solvents were carbamate and bicarbonate species.The CO₂ partial pressures increase with increasing the CO₂ loading at a constant temperature and the CO₂ loadings decrease as the temperature increases at a given CO₂partial pressure.A semi-empirical model was proposed to interpret the vapor-liquid equilibrium data for the systems of CO₂-BAE-EGBE solution.Mass transfer performance of different absorbents in the Dixon ring packed tower was evaluated by the volumetric overall mass transfer coefficient（K_Ga_v）and absorption efficiency（η）.The calculated K_Ga_v andηfor the systems investigated（i.e.aqueous MEA,the MEA-EGME and BAE-EGBE）decrease with the increasing CO₂ loading,and increase with the increasing liquid flow rate.For aqueous MEA system,it was observed that the K_Ga_v increases with the increasing inert gas flow rate.Increasing liquid feed temperature is favorable for enhancing mass transfer performance.It was found that the K_Ga_v decreases slightly with increasing the inert gas flow rate and the liquid feed temperature for nonaqueous MEA-EGME system.For nonaqueous BAE-EGME system,K_Ga_vincreases first and then decreases with an increase in inert gas flow rate.Increasing water content in this water-lean system can improve the mass transfer performance.In addition,the liquid feed temperature had little effect on K_Ga_v.Although non-aqueous absorbents of secondary alkanolamines with EGBE have shown good CO₂ capture performance,the mass transfer behaviors and regeneration energy consumption in packed columns still need to further investigate in future work.