Application Of Ionic Liquids To Improve The Aqueous Solutions Of Alkanolamine For CO₂ Capturing

Flue gas of coal-fired power plants is the main source of CO2 emissions. At present the CO2 capture process is mainly alcohol amine method, but this method has some shortcomings:the ethanolamine is volatile, CO2 per tonne makes 0.2-1.6kg absorber lost; the use of solution concentration cannot exceed 20%; the energy consumption is high; the water in the solution will react with CO2 in regeneration which leades to equipment corrosion, etc. Ionic liquids are non-volatile and thermal stable, and they can be used as a new type of green solvent. In this paper, the traditional alcohol amine process was combined with ionic liquid technology, using ionic liquids as a solvent. The MEA/ionic liquid mixed system was optimized to explore the good absorption capacity, low corrosive, high absorption rates and good regeneration performance absorber.In this paper, eight ionic liquids were synthesized:four imidazole ionic liquids [BMIM] [BF4], [BMIM] [PF6], [EMIM] [BF4], [EMIM] [PF6] and four amine-functionalized ionic liquids ethylenediamine formate [EDA][FA], ethylenediamine acetate[EDA][AC],diethylenetriamine formate [DETA][FA], diethylenetriamine acetate [DETA][AC]. They were mixed with MEA in different concentrations and studied the influence of pressure, temperature, length of anion side chain and type of cation on the absorption capacity.The experimental results showed that for imidazole ionic liquid (ILs), 50%ILs+50%MEA (volume fraction) mixture was the best, and in the same concentration the absorption capacity was in order [BMIM][BF4]-MEA>[EMIM][BF4]-MEA>[BMIM][PF6]-MEA>[EMIM][PF6]-MEA;For amine-functionalized ionic liquid,40%ILs+60%MEA(mass fracion)had the highest absorption capacity, the ILs-MEA binary mixture increased 27.4% CO2 mole/litre than ethanolamine solution under 0.1 Mpa. Further study showed how the type of ionic liquids effect the absorption capacity with order [DETA][FA]-MEA>[DETA][AC]-MEA>[EDA][FA]-MEA>[EDA][AC]-MEA, they were all higher than ethanolamine solution. [BMIM][BF4]-MEA compound solution was found higher absorption rate than ethanolamine solution. This was because the insoluble sediments was generated, promoting the positive reaction. Temperature on the reaction system was also investigated:the temperature higher, the reaction rate constant bigger which means faster to reach the chemical reaction balance. On the other hand, temperature also caused decline in the uptakebut, but the impact was not obvious, especially under the condition of low pressure. The compound solution of ILs-MEA system was thermal stable.The regeneration performance of the mixed solution was obtained by cycling four times under vacuum and the recycling regenerative efficiency reach 88%. In addition, the mechanism of CO2 absorption with TILs was assumed.