abstract
The acidity/basicity of the reaction media has a substantial influence on the efficiency of many reactive processes: therefore, a new class of acidic or basic ionic liquids is gaining special attention due to the possibility of increasing the efficiency of many processes by a wise manipulation of their properties. The absorption of sour gases is one of the processes that can be enhanced by the basic character of the ionic liquid. The fluorination of the cation or anion can also contribute to the gas solubility enhancement. In this work, these two characteristics are evaluated and compared through the study of gas-liquid equilibrium of two ionic liquids, 1-butyl-3-methylimidazolium dicyanamide ([C(4)mim][DCA]) and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C(4)mim]][Tf(2)N]), with carbon dioxide (CO(2)) at temperatures up to 363 K and pressures up to 74 MPa. A thermodynamic model based on the Peng-Robinson equation of state with the Wong-Sandler mixing rule, using the UNIQUAC model for the activity coefficients, was used to describe the experimental data and for the estimation of the Henry's constants. The solubility of CO(2) in 1-butyl-3-methylimidazolium dicyanamide is much lower than anticipated on the basis of the reported pK(a) of the anion when compared with the acetate anion. No chemisorption is observed and the solvation enthalpy is quite low, ruling out any Lewis acid/base interaction between the anion and the CO(2). The 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid, known to present one of the highest solubilities towards CO(2) due to the presence of fluoroalkyl groups, showed a much larger solubility for CO(2) than 1-butyl-3-methylimidazolium dicyanamide. (C) 2009 Elsevier B.V. All rights reserved.
keywords
ELEVATED PRESSURES; THERMODYNAMIC PROPERTIES; INDUSTRIAL APPLICATION; CO2; TEMPERATURE; SYSTEMS; SOLUBILITY; MIXTURES; PLUS; EQUILIBRIA
subject category
Chemistry; Engineering
authors
Carvalho, PJ; Alvarez, VH; Marrucho, IM; Aznar, M; Coutinho, JAP
our authors
Isabel Maria Delgado Jana Marrucho Ferreira
Full professor
João Manuel Costa Araújo Pereira Coutinho
Vice-Director
Pedro Jorge Marques de Carvalho
Auxiliary Researcheracknowledgements
The authors are thankful for financial support from Fundacao para a Ciencia e a Tecnologia (PTDC/EQU/65252/2006) and Ph.D. grant (SFRH/BD/41562/2007) of Pedro J. Carvalho. The authors would like to acknowledge FAPESP (Fundacao de Amparo A Pesquisa do Estado de Sao Paulo), process # 2006/03711-1. M. Aznar is the recipient of a CNPq fellowship. The authors are also grateful to Catarina M.S.S. Neves for the help with the NMR spectra.