Amr Henni

Abstract:

Anthropogenic CO2 emission is driving global warming, hence causing a drastic change in earth's geological and ecological systems. One of the solutions to reduce CO2 emission is to capture it from large point sources and store in geological strata or use it in enhanced oil recovery (EOR). Among many technologies, amine-based CO2 capture process is the most mature one and it offers high CO2 capture capacity and rapid kinetics. However, high regeneration energy, degradation and corrosion for the amine systems [1] compelled researchers to find alternate solvents. Ionic liquids (ILs) known as green solvents are molten salts at room temperature fulfil those criteria of low regeneration energy, negligible volatility and high thermal stability.[2] But, low CO2 uptake and high viscosity is the hindrance for deployment in CO2 capture operation [3]. To improve CO2 uptake, researcher have deployed strategies of functionalizing ILs with amines then known as task specific ionic liquids (TSILs)[4], but costly synthesis and purification steps, excessive viscosity forming gel like solids upon CO2 uptake are major obstruction for CO2 capture operation. An alternate strategy of blending the amines with ILs have shown promising results, such blended systems retain the desired properties of ILs but exclude the drawbacks of TSILs such as high synthesis cost and high viscosity. Moreover, the regeneration process requires lower energy as ILs replaces water fully or partially without compromising the absorption performance. A number of blended systems have been reported in the literature, however, in search of better blended systems with higher CO2 capacity but lower viscosity, new blended systems comprising of water, amines (Piperazine (PZ)) and ILs (1-butyl-3-methylimidazolium acetate ([Bmim][Ac]) were investigated.
Herein, the concentration of PZ was kept constant at 15 wt.%, while the concentration of ionic liquid (ILs) was varied from 0 to 60 wt.% by replacing the corresponding amount of water. Experiments were conducted up-to a CO2 partial pressure of 300 kPa at (313 and 333) K. In addition, the density and viscosity of all the blended systems were measured for the temperature range of (303 to 333) K at atmospheric pressure. The results indicated that the CO2 uptake in all blended systems increased with the increase in CO2 partial pressure. In addition, CO2 uptake decreases for all systems with an increase in temperature. No significant change in CO2 uptake was observed for the addition of ILs up to 30 wt.% to aqueous PZ, however a dramatic increase in CO2 uptake was observed for ILs concentration of 60 wt.%. Moreover, it was found that the viscosities of the blended systems are significantly lower than the pristine [Bmim][Ac] as well as other functionalized ionic liquids (TSILs) reported in the literature. The results reveal that aqueous PZ + [Bmim][Ac] blended systems have the potential to overcome the drawbacks of IL/TSILs while retaining superior CO2 capture performance.