Modeling the complex phase behavior of methane, ethane and propane in an ionic liquid up to 11 MPa – A comparison between the PR EoS and the GC EoS

• Solubilities of light hydrocarbons in [hmim][TCB] were modeled up to 11 MPa.
• Both VLE (at p < pc) and LLE (at p ≥ pc) were correlated simultaneously.
• The Peng Robinson (PR) and group contribution (GC) EoS were used.
• Both GC EoS and PR EoS accurately describe the phase behavior.
• GC EoS predicts LLE better than PR EoS with parameters fitted to VLE data only.

In this paper, the Peng Robinson equation of state (PR EoS) and a group contribution equation of state (GC EoS) were applied to describe the phase behavior of methane (CH4), ethane (C2H6) and propane (C3H8) in the low-viscosity ionic liquid 1-hexyl-3-methylimidazolium tetracyanoborate ([hmim][TCB]) to pressures up to 11 MPa. Both models were able to satisfactorily correlate the experimental vapor–liquid equilibria (VLE) at low pressure as well as the liquid–liquid equilibria (LLE) at high pressure (above the critical point) by fitting only one temperature-independent parameter. Moreover, excellent agreement with experimental data was found with both EoS when more than one parameter was fitted. The relative absolute average deviation (AARD) of PR EoS was 1.95% for the CH4 + [hmim][TCB], 3.14% for C2H6 + [hmim][TCB], and 5.51% for the C3H8 + [hmim][TCB] systems. The GC EoS exhibited an AARD of 0.91% for the CH4 + [hmim][TCB], 3.10% for C2H6 + [hmim][TCB], and 5.71% for the C3H8 + [hmim][TCB]. Furthermore, both EoS were assessed for their capability to predict the occurrence of the LLE above critical pressure when the parameters were fitted to solely low pressure VLE data. The GC EoS was found to be a more powerful model to predict the phase behavior of C2H6 and C3H8 in the IL beyond the condition range used to fit the parameters.

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