| In recent years,global warming caused by greenhouse gases has become an urgent problem to be solved all over the world.Carbon dioxide(CO2)as the most important greenhouse gas,its capture and storage technology(CCS)has been the focus of attention for researchers.Considering that fossil fuels are still the main energy source at present,CO2 capture from the emission source is the most direct way of carbon emission reduction and control.Among them,the chemical absorption using organic amine aqueous solution is the most widely used method.However,the solvent of most traditional organic amines is water.Since the vaporization enthalpy and the heat capacity of water are much larger than that of the organic solvents,the conventional desorption process needs a large amount of energy to heat and evaporate the water during regeneration,and its regeneration efficiency and reusability are not ideal.In order to reduce the regenerative energy consumption and improve the reusability of absorbents,non-aqueous absorbents come into being.In this work,the switchable ionic liquid of 1,8-diazabicyclo-[5.4.0]-undec-7-ene(DBU)/ethanol and non-aqueous amine of triethylenetetramine(TETA)/ethanol solution were chosen as the CO2 absorbents,and 2-amino-2-methyl-1-propanol(AMP)as a regulatory agent to improve the non-aqueous absorbents for CO2 capture.The variation of viscosity with the absorption loading and temperature,and the absorption/desorption performance of the two non-aqueous absorbents were investigated.In addition,the absorption and desorption mechanisms of non-aqueous absorbents were explored by 13C NMR to clarify the interaction between substances and the mechanism of CO2 capture.Finally,the regulatory mechanism of AMP on the non-aqueous absorbents for CO2 capture was explained sufficiently.The main results are as follows:(1)Weiland equation is applicable to analyze the variation of viscosity for DBU/AMP/ethanol and TETA/AMP/ethanol solutions during the absorption process.The relationship between viscosity and absorption loading(?)and temperature(T)can be expressed as follows:The adjustable parameters of viscosity for the two absorbents are a1=1148.1998,b1=218.6371,c1=21545.2730,d1=-73537.7840,e1=24.6791,f1=-0.0132,g1=-5.7986 and a2=392.4373,b2=0.5380,c2=332807.6296,d2=20848.7584,e2=53.2873,f2=-0.0210,g2=-9.1463,respectively.In addition,the calculated data of the two models satisfactorily fit the experimental data,and the average relative deviations(fs)are 0.02%and 1.97%,respectively.(2)In DBU/AMP/ethanol solution,the optimum molar ratio of DBU and AMP was 1:1,and the optimum concentration of ethanol was 50 wt%.Under the optimum conditions,the absorption loading of DBU/AMP/ethanol solution was 2.98 mol·kg-1 and the viscosity was 13.81 mPa·s.The saturated solution was desorbed at 120 ? for 1.0 h,and the regeneration efficiency was 99.3%.Meanwhile,the regeneration efficiency could still reach 93.5%after the fifth regeneration,which indicated that DBU/AMP/ethanol solution had good reusability.In addition,the absorption and desorption performances of DBU/ethanol and DBU/AMP/ethanol solution were compared.It was found that replacing part of DBU with AMP would slightly reduce the absorption loading,but significantly improve its regeneration efficiency and reusability.(3)The reaction mechanism of DBU/AMP/ethanol solution was explored by 13C NMR.DBU/ethanol solution reacted with CO2 to directly form carbonate of CH3CH2OCO2-,while AMP initially reacted with CO2 to form carbamate,and then the carbamate reacted with ethanol to form CH3CH2OCO2-.During the desorption process,the carbamate and carbonate would react with DBUH-and AMPH+ to release CO2 by heating under the atmospheric pressure.Finally,the products in the DBU/AMP/ethanol solution were decomposed completely.(4)In TETA/AMP/ethanol solution,the optimum molar ratio of TETA and AMP was 1:2,and the optimum concentration of ethanol was 60 wt%.Under the optimum conditions,the absorption loading of TETA/AMP/ethanol solution was 3.71 mol·kg-1 and the viscosity was 198.32 mPa·s.The saturated solution was desorbed at 120 ?for 1.0 h,and the regeneration efficiency was 99.7%.Meanwhile,the regeneration efficiency could still reach 95.4%after the fifth regeneration,which indicated that TETA/AMP/ethanol solution had good reusability.In addition,the absorption and desorption performances of TETA/ethanol and TETA/AMP/ethanol solution were compared.It was found that replacing part of TETA with AMP would significantly improve its absorption loading,regeneration efficiency and reusability.(5)The reaction mechanism of TETA/AMP/ethanol solution was explored by 13C NMR.TETA and AMP both reacted with CO2 to form different kinds of carbamates,and then a part of carbamates reacted with ethanol to form carbonate.During the desorption process,the carbamates and carbonate would react with TETAH+ and AMPH+ to release CO2 by heating under the atmospheric pressure.Finally,the products in the TETA/AMP/ethanol solution were decomposed completely.Compared to DBU/ethanol and TETA/ethanol solutions,the mixture solutions strengthened by AMP had significant advantages in absorption and regeneration performance.The regulatory mechanism of AMP for non-aqueous absorbents could be expressed as follows:On the one hand,AMP reduced the viscosity of the solution and it was beneficial to the absorption of CO2.On the other hand,AMPH+ could act as a good proton donor and promote the decomposition of the reaction product,which was beneficial to the regeneration of saturated solutions.The DBU/AMP/ethanol and TETA/AMP/ethanol solutions both are green and novel non-aqueous absorbents,which provide ideas for the CO2 control and emission reduction technologies.At the same time,they also provide the basic data and theoretical basis for the application of technologies. |
PDF Full Text Request