Study Of Co₂ Capture Using Biphasic Solvent Triethylenetetramine Lysine?[TETAH][Lys]?-Ethanol-Water

In recent years,global warming caused by greenhouse effect has increasingly become one of the most important environmental problems.As the most important greenhouse gas,the control and reduction of carbon dioxide?CO₂?is really urgent.Currently,the most effective carbon dioxide emission reduction technology is carbon dioxide capture and storage technology?CCS?.Chemical absorption based on alkanolamine aqueous solutions appears to be a viable option and is the most widely used examples.But the alkanolamine absorbent also has obvious disadvantages,such as high regeneration energy consumption,easy foaming,solvent volatilization and equipment corrosion and the like.In view of its high energy consumption of regeneration,phase change absorbent emerge as the times require.The absorbent could divide into liquid-liquid or solid-liquid two-phase by means of certain regulation and control after absorption.The CO₂ could concentrate in the rich phase which should been regenerated,in order to reduce the energy consumption of regeneration.The regeneration efficiency was low.And it also has a disadvantage that the high regeneration efficiency only under the condition of N2 stripping.The regenerated gas was the mixture of N2 and CO₂,which was not conducive to obtaining high-purity CO₂ gas for CCS.Amino functional ionic liquid?AFIL?is a new type of high efficient and green absorbent.Because a certain number of amino groups,AFIL could significantly increase the absorption rate and absorption loading.However,in order to reduce the viscosity of the absorbents,AFILs were dissolved in water,which also suffered the high cost and energy penalty of CO₂ capture.Therefore,a new type of phase change AFIL absorbent is proposed in this paper,which has the advantage of high absorption loading of AFIL and the higher energy consumption potential of phase change absorbent.It can also overcome the defect of high viscosity of phase change absorbent.In this work,the amino functional ionic liquid of s triethylenetetramine L-Lysine?[TETAH][Lys]?-ethanol-water was chosen as the CO₂ absorbents.The variation of viscosity with the absorption loading and temperature,and the absorption-desorption performance of the biphasic solvent absorbents were investigated.The absorption-desorption mechanism and phase separation mechanism of the absorbent were analyzed by ¹³ C NMR.Finally,the kinetics of the absorbent was investigated and the energy consumption in the process of regenerating the absorbent was estimated.The energy saving potential of the absorbent could be obtained more intuitively.The main results of this work are as follows:?1?In [TETAH][Lys]-ethanol-water absorbent,the optimum volume ratio of ethanol to water is 6:4,and the concentration of [TETAH][Lys] is 0.5 mol CO₂/mol IL.After absorption saturation,the solution was divided into two phases.The loading of the upper phase was 0.17 mol CO₂/mol IL,and the loading of the lower phase is 2.18 mol CO₂/mol IL.The absorption loading of the lower phase was about 90% of the total loading and the viscosity was only 27.95 m Pa·s.It was found that the CO₂-rich phase could be well regenerated with the addition of ethanol in CO₂-lean phase,and its regeneration efficiency still maintained 91.3% after the 5th regeneration.It indicated that the [TETAH][Lys]-ethanol-water absorbent has good ability of reuse.And a small amount of lean-phase could obviously improve the regeneration efficiency of absorbent.?2?The reaction mechanism of the absorbent was analyzed by ¹³ C NMR: During the absorption,CO₂ reacted with[TETAH][Lys]-ethanol-water solvent to form carbamate,HCO3-/CO32-and ethyl carbonate.Due to the low solubility of the CO₂-products in ethanol and high in water,and the higher density of the CO₂-products than ethanol,the CO₂-products would gradually enrich in the lower phase of the solution,and ethanol was distributed in the upper phase of the mixture.During the desorption process,since the CO₂ product of carbamate was difficult to be desorbed,the regeneration efficiency of the CO₂-rich phase was rather low?66.0%?.With the addition of ethanol,carbamate would firstly react with ethanol to produce ethyl carbonate,and the regeneration efficiency was significantly enhanced because of a higher regenerability of the ethyl carbonate.?3?The kinetic experiments show that the capture of CO₂ by [TETAH][Lys]-ethanol-water absorbent conforms to the zwitterion mechanism,and the mass transfer reaction was a fast pseudo first order reaction.According to Arrhenius equation,the logarithm of the rate constant k2?lnk2?of CO₂ absorbed in [TETAH][Lys]-ethanol-water absorbent and the reciprocal of temperature?1/T?are linearly fitted.The Arrhenius relationship of [TETAH][Lys]-ethanol-water absorbent is obtained as follows: k2,[TETAH][Lys]-ethanol-water=1.9941×10¹⁵exp?-73883.1/T?.The activation energy of chemical reaction is 61.42 k J/mol.The Arrhenius relationship of [TETAH][Lys]-water absorbent is obtained as follows:k2,[TETAH][Lys]-water=8.5293×10¹⁴exp?-7469.4.1/T?.The activation energy of chemical reaction is 62.10 k J/mol.?4?The regeneration energy consumption of [TETAH][Lys]-ethanol-water phase change absorption system was s estimated by thermodynamic experiments.It is found that the regeneration energy consumption of [TETAH][Lys]-ethanol-water solution was only 1.29 GJ/ton CO₂,while that of the [TETAH][Lys]-water solution was 2.00 GJ/ton CO₂.Compared with [TETAH][Lys] water solution,the regeneration energy consumption of phase change absorption [TETAH][Lys]-ethanol-water was 35.5% lower than the former.Compared with the widely used 5M MEA solution,the regeneration energy consumption of [TETAH][Lys]-ethanol-water system could be reduced by 65.78% under the same regeneration conditions,which has obvious energy saving advantages.