Given the industrial significance of carbon monoxide (CO) in the petrochemical industry as starting material for a vast number of chemicals, its separation and purification in a practical and efficient manner, either for the adjustment of H2/CO ratio or the production of pure H2 and CO, has become of great importance to meet the requirements for downstream processing. High purity CO can be obtained by means of gas-liquid absorption processes that involve the selective and reversible complexation reaction between CO and a complexing agent dissolved in an aromatic hydrocarbon solvent, e.g., toluene, in which other gases are just physically absorbed to some extent. Unfortunately, these are highly energy intensive processes, due to the extreme operating conditions applied, i.e., high pressure and low temperature, and the use of volatile solvents that evaporate during the regeneration. However, it has been recently proved that a suitable combination of an ionic liquid (IL) and a metallic salt based on a transition metal that is capable to complex carbon monoxide molecules, e.g. copper(I), can successfully be employed to develop novel separation processes that are highly selective towards CO over other light gases [1-2]. This separation avoids the use of the volatile solvents typically employed for that purpose, allowing a greener and more sustainable process.
In this contribution, a theoretical semi-predictive approach based on the soft-SAFT equation of state [3] is presented for the first time to model the complexation reaction between carbon monoxide (CO) in a combined ionic liquid (IL) plus a copper(I) metallic salt media in terms of the gas solubility as a function of temperature, pressure and composition. Two different degrees of molecular approximation are tested. In the first approach, the IL-metal salt mixture is treated as a single compound whose parameters are modified according to the concentration of the metallic salt. In the second approach, both compounds are treated as independent species, enhancing the predictive capability of the model. The complexation between CO molecules and the metal salt is reproduced by adding specific cross-association interaction sites that simulate the reaction, in a similar manner as done in a previous contribution for the reaction between the acetate anion and CO2 [4]. The density of the doped IL and the CO solubility are described in quantitative agreement with the experimental data at different operating conditions [5].
Acknowledgments
Financial support from the Spanish Ministry of Economy and Competitiveness (CTQ2015-66078), the Catalan Government (2014SGR-1582) and Fundación Iberdrola España is gratefully acknowledged.
References
[1] G. Zarca, I. Ortiz, A. Urtiaga, Chem. Eng. J. 252, 298-304, 2014.
[2] O.C. David, G. Zarca, D. Gorri, A. Urtiaga, I. Ortiz, Sep. Purif. Technol. 97, 65-72, 2012.
[3] L.F. Vega, F.J. Blas, Mol. Phys. 92, 135-150, 1997.
[4] L.M.C Pereira, M.B. Oliveira, F. Llovell, L.F. Vega, J.A.P. Coutinho, J. Supercrit. Fluids 92, 231–241, 2014.
[5] G. Zarca, I. Ortiz, A. Urtiaga, F. Llovell, AIChE J. sent.
Carbon capture and other industrial applications , Challenges and advances in fluid phase equilibria
