Synthesis Of Task-specific Ionic Liquid And Its Application For CO₂

The greenhouse effect caused by carbon dioxide has received more and more attentionin recent years. As the major greenhouse gas, potentially contributing to global warming,the capture and separation technologies for CO2, including absorption, membraneseparation, absorption method, biological method, have been discussed. Among thosemethods, absorption has been considered the most mature. Absorption includes thephysical absorption and chemical absorption. The physical absorption presents somedrawbacks such as poor selectivity, low recovery rate and bad economic effects. Whereas,the chemical absorption is considered to be a proved technology for capturing CO2due toits advantages, such as high reactivity, low solvent cost, and especially the high CO2selectivity. However, it shows drawbacks related with its absorption solvent great loss,poor regeneration energy consumption as well as the system corrosion. To address theabove-mentioned questions, a new absorbent is an important role to break the bottleneck inthe utilization of chemical absorption.Ionic liquids(ILS)-organic salts with a low melting point, high thermal stability, highdissolution, adjustable structures, negligible vapor-pressures, nonflammable and asignificant ability to dissolve various chemical compounds have emerged as the reversibleabsorbents for CO2removal. However, the ability that ionic liquids dissolve CO2is lowduring the process of a physical absorption. The performance of ionic liquid in absorbingCO2can be dramatically improved by varying the coupled anion and cation to synthsizetask-special ionic liquid under the condition of chemical absorption.Herein, three imidazole,(methyl,butyl,octyl) were choosed, through the cationic (NH2)and anion(PF6-)functional modification respectively, finally got the task-specific ionicliquids.The structures of these ionic liquids were characterized by IR and HNMR, Thermalstability for each ionic liquid were characterized by thermal gravimetricanalysis(TGA).The experiment conditions、temperature、time、purification methods wereinvestigated and discussed. At the same time, the absorptivity experiment of six task-specific ionic liquid and further discusses the mechanism between functional ionicliquid and CO2.The experimental results have been shown as follows:(1) The six products have been synthesized, and they are1-[(2-aminoethyl)-3-methyllimidazoliumtetrafluoroborate][NH2emim][BF4],[1-(2-aminoethyl)-3-methyllimidazoliumhexafo-rophosphate][NH2emim][PF6],[1-(2-aminoethyl)-3-butylimidazoliumhexafo-rophosphate][NH2ebim][BF4],[1-(2-aminoethyl)-3-butylimidazoliumhexafo-rophosphate][NH2ebim][PF6],1-[(2-aminoethyl)-3-octlyllimidazoliumtetrafluoroborate][NH2eoim][BF4], and[1-(2-aminoethyl)-3-octlyllimidazoliumhexafo-rophosphate][NH2eoim][PF6], respe-ctively.(2) The structures of ionic liquids have been characterized by IR and HNMR.Thermal stability experiments show that the ionic liquids begin to decompose at300℃untildecompose completely at400℃.(3) The yield of six functional ionic liquids are similar. Cationic functional productyield is81%~91%, sequentiality with37%in the neutralization the process. The yield ofion exchange is about25%.(4) The CO2absorption capacity and equilibrium of the six functional ionic liquidshave been obtained. The experiments show that imbibing the functional groups [-NH2]、[BF4-]、[PF6-] into the ionic liquid substantially improves the absorption of CO2. Cation ofTIL play great effect on the absorption amount. In addition, It can been concluded that anequimolar TIL with [PF6-] has higher CO2capture efficiency than that of with [BF4-].(5) Among the six task-specific ionic liquids, the [NH2ebim][PF6] has the highestCO2absorption amount of0.915mol/mol. Absorption experiment with different qualityionic liquids show that the molar ratio of absorption beyond1:2in some cases, whichindicates that there may be two reaction mechanisms between CO2and task-specific ionicliquid. One is that CO2reacts with task-specific ionic liquid at1:1stoichiometry, and theother is1:2.(6) The CO2desorption experiment has been carried out by heating the CO2treatedTIL at80℃for two hours under vacuum. The result shows that the regeneration rate isstill more than90%after the four cycles, which proves that the ionic liquid can be reused.