Experimental determination and modeling of enthalpy of solution of carbon dioxide in aqueous solutions of demixing amines

International audienceCarbon Capture and Storage (CCS) is a solid option for CO2 mitigation in the atmosphere. Post-combustion capture processes using chemical solvents are considered as one of the most adequate method for CCS [1]. However, these processes are energy intensive and need to be improved in order to develop an economically viable method to separate CO2 from industrial effluent. For this purpose the DMXTM process [2] using aqueous solutions of demixing amines has been developed by IFP Energies nouvelles over the past few years. The novelty of this solvent is to undergo a liquid-liquid phase separation at a specific temperature and CO2 concentration. Such a phase separation will concentrate CO2 into the water rich phase. Then only this part of the solvent will be heated in the regeneration step of the separation process. The DACOOTA project, supported simultaneously by the French National Agency of Research (ANR) and the Natural Sciences and Engineering Research Council of Canada (NSERC), concerns the understanding of this class of amines for CCS.In this work, the absorption of CO2 in aqueous solutions of 2-methylpiperidine, 3-methylpiperidine and 4-methylpiperidine, has been studied at different temperatures, pressures and amine compositions. These three cyclic amines undergo a Lower Critical Solution (LCST) in aqueous solution [3,4]. The heats of mixing of CO2 in aqueous solutions of amine have been measured by a flow calorimetric technique [5]. The technique makes it possible simultaneous determination of the enthalpies of solution and solubility limits. The experimental enthalpies of solution of CO2 for these three systems {x-methylpiperidine – water – CO2} are compared with data derived from a rigorous thermodynamic model of phase equilibria based on a γ-ϕ approach [6, 7]. Interaction parameters were chosen to be adjustable parameters in this model and were fitted to vapor-liquid equilibrium data. In order to improve the understanding of this class of amine, the influence of the position of the methyl group on the enthalpy of solution of CO2 will be discussed