Enhancement of CO2 capture performance of aqueous MEA by mixing with [NH2e-mim][BF4

Mei Wang,Mingming Wang,Jiale Li,Jianfen Li,Na Rao

doi:10.1039/c7ra11757d

Abstract

Alcohol amine solutions have a high absorption capacity and rate for CO2 capture, however, there are some shortcomings such as high energy-consumption and low stability. To enhance CO2 capture performance of aqueous MEA, a functional ionic liquid ([NH2e-mim][BF4]) was introduced based on the advantages for CO2 capture. Absorbents were prepared with the molar concentration ratio of [NH2e-mim][BF4] to the 30 vol% aqueous MEA of 0 : 10, 1 : 9, 2 : 8, 3 : 7, 4 : 6 and 6 : 4. The density and the viscosity of the investigated absorbents were measured and the effects of the molar fraction of [NH2e-mim][BF4] (nI) and temperature on CO2 absorption performance were investigated. CO2 desorption performance of the solvent at different temperatures was discussed. The stability performance of the absorbent with nI of 2 : 8 (I/M2:8) was examined by five consecutive cyclic tests. The results showed that for pure CO2, the I/M2:8 displayed the highest absorption performance at 303 K under 1 bar: a comparable CO2 absorption capacity of the 30 vol% aqueous MEA and a higher CO2 absorption rate at the later absorption stage. Moreover, with the increase of temperature, CO2 absorption capacity and rate decreased, while CO2 desorption efficiency and rate increased. 393 K was chosen as the optimum desorption temperature with the desorption efficiency of 99.31%. The introducing of IL contributed to CO2 desorption performance of the absorbents significantly. The properties (CO2 absorption capacity, mass loss, density and viscosity) of the I/M2:8 during the cycles suggested that the IL-MEA mixture had an excellent stability performance.

Highlights

393 K was chosen as the optimum desorption temperature with the desorption efficiency of 99.31%
The properties (CO2 absorption capacity, mass loss, density and viscosity) of the I/M2:8 during the cycles suggested that the Ionic liquids (ILs)-MEA mixture had an excellent stability performance
The viscosity of [NH2e-mim][BF4] was 3589.2 mPa s determined by our group,[22,34] while the viscosity of the absorbents was below 10 mPa s with nI of 0–0.6, which showed that the addition of 30 vol% solution reduced the viscosity of absorbents signi cantly

Summary

Introduction

Global warming, caused by excessive emission of carbon dioxide (CO2), has become one of the world's major environmental issues.[1,2,3,4] The reduction of CO2 emissions by the capture of CO2 from ue gases is considered as an effective method to mitigate the greenhouse effect.[5,6,7] Currently, the leading technology involves chemical absorption with aqueous amine solutions (typically 30 vol% amine by volume).[8,9] the commercially available aqueous amine solutions, represented by monoethanolamine (MEA), present many disadvantages including high regenerative energy and degradation in the presence of oxygen.[10,11,12] the volatilization of amines causes environmental pollution and corrosion, as well as raises the cost of operation and amortized installation.[13,14]. Considerable research efforts have been made to study the capture performance of the solvents that could overcome the aforementioned disadvantages. A new kind of solvent was developed by mixing an amine-functionalized IL (1-(1-aminoethyl)-3-methylimidazole uoroborate [NH2e-mim][BF4]), with 30 vol% aqueous MEA solutions to investigate whether there was a synergetic effect on CO2 capture performance. The effects of the molar concentration ratio of [NH2e-mim][BF4] to MEA in the mixture and the temperature on CO2 absorption performance of the solvents were explored. The desorption performance of the solvents at different temperature were discussed. The cyclic stability of the absorbents were evaluated by ve consecutive CO2 absorption–desorption tests

Experimental

Results and discussion

Conclusions