| Excessive emission of carbon dioxide has caused serious negative effect to global climate environment. However, CO2is not just a major "greenhouse gas" but also an important potential resource. For example, Carbon dioxide can be transformed into environmental-friendly extraction solvent for green chemical industries. Moreover, as a Cl resource, CO2can be some basic chemical materials, such as CO, syngas and methanol[3,8].Thus the research about decarbonization technology is particularly important and urgent. At present,aqueous alkanolamines have been widely used as chemical absorbents for removal carbon dioxide. For example, MEA has been widely used as industrially important absorbent because of its rapid reaction rate while the MEA has a disadvantage due to its degradation through oxidation of the amine,high enthalpy of reaction and it causes operational problem; MDEA has high loading capacity,less regeneration energy, but the absorption rate is low. Ionic liquids (ILs) as good environmentally friendly decarburization absorbent have some special properties such as low vapor, high stability and easy assembly. However, the cost and viscosity of ILs was too high to be used as industrially important absorbent. Therefore, the hybrid of MDEA and IL become a hot research topic in the area of CO2removal.Zhang et al.[6] prepared four amino acid based ILs:tetramethylammonium glycinate([N1111][Gly]), tetraethylammonium glycinate([N2222][Gly]),tetramethylammoniumlysinate([N1111][Lys]) and tetraethylammonium lysinate([N2222][Lys]) and blended them and MDEA to create a new absorbent with the total amine concentration at30w%. They found that adding a certain amount of ILs in MDEA aqueous solution could greatly improve the absorption rate of CO2,and the aqueous solutions of15wt%IL and15wt%MDEA had higher absorption rate and larger uptake capacity than the other IL+MDEA solutions.In practice, large absorption capacity of the absorbent leads to smaller amount of absorbent and size of device, resulting in lower cost in CO2removal.There usually have two kinds of methods to improve the absorption capacity for mixture absorbents, either improve the absorption capacity of main absorption agent or enhance the IL’s.In this work,we have tried to improve the concentration of MDEA in the blended aqueous liquids,and also we synthesized a new kind of IL, dual-cations amino acid ILs, blended with MDEA to explore the effect of carbon structure and two positive charge centers on CO2uptake.In the present work, different amounts of [N1111][Gly] were added in MDEA aqueous solutions of higher concentration (above30wt%) to obtain a series of CO2absorbents. The absorbents prepared were suggested to have large absorption capacity and high absorption rate. By evaluating the absorption performance of CO2in these absorbents, the influence factors of absorption rate and absorption load were determined. The solution formulation with higher absorption rate and larger capacity could also be presented according to the conflicting impact of concentration and viscosity.The absorption mechanism of the amino acid based IL+MDEA aqueous solution would be verified by analyzing the experimental results. Besides, the physical properties necessary to industrial design, such as the density, viscosity and surface tension of the solution, were measured for all the tested solutions.For the first time, dual-cations amino acid ILs were synthesized, in which the cation was equipped with two charges and the anions were functionalized with two appended amine groups. In our work, DILs and their solutions were first applied in the absorption of CO2gas. Then, absorption of CO2in the DIL aqueous solutions and the DIL+MDEA aqueous solutions was investigated respectively to explore the effect of carbon structure and two positive charge centers on CO2uptake. |
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