Solubility studies of carbon dioxide in novel hybrid solvents using a new static synthetic apparatus.

Abstract

The use of alkanolamine solutions in removing acidic gases from natural gas is common in the industry, but such technologies have disadvantages which include amongst others, solvent loss, corrosion and high heat consumption. This study aimed to provide a comprehensive theoretical and experimental investigation of selected fluorinated ionic liquids (ILs) and their use as additives to amine solutions for CO2 absorption, hereby attempting to reduce the disadvantages of amine technology. Solubility measurements of CO2 in five hybrid solvents, viz. (n-methyl-2-pyrrolidone (NMP) + 1-butyl-3-methylimidazolium tetrafluoroborate (bmim[BF4]), monoethanolamine (MEA) / diglycolamine (DGA) + water + 1-butyl-3-methylimidazolium trifluoromethanesulfonate (bmim[OTF]), MEA/DGA + NMP + 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (bmim[TF2N]), were conducted using a new static-synthetic apparatus, designed and commissioned for this project. Additionally, viscosity, density, sound velocity and evaporation rate for the solvents were measured. Overall, replacing the entire water present in the aqueous amine solvents with NMP increased the CO2 solubility, except at low pressures depending on the concentration of amine. Although the addition of IL into the aqueous amine solvents or the water-free NMP-containing amine solvents decreased the CO2 solubility, all the studied hybrid solvents could achieve the maximum loading of CO2 allowed in the industrial amine processes. The addition of IL into the amine solutions decreased the volatile part of the solvent and, in most cases, decelerated the evaporation rate of solvent, while the loss of ILs was almost zero. However, the addition of IL into the amine solvents increased viscosity. The theoretical development of a new thermodynamic approach to predict the aqueous amine + ILs + acidic gases systems was performed. The consistency between modelled results and reliable data reported in the literature demonstrated the validity of the proposed method. The present model was limited to predict gas loading at very low pressures depending on the temperature and initial concentration of amine. This study can be continued in many aspects. It is recommended to investigate the potential of physical solvents to reduce the energy consumption and corrosion rate of amine processes. Additionally, the solubility of H2S and hydrocarbons in the solvents studied in this work can be further investigated as a continuation of this project.