This paper presents a new model to predict the density of biodiesel + petrodiesel mixtures at high pressure and high temperature (HPHT) based on the Murnaghan equation of state, as a function of temperature, pressure, volumetric composition, and petrodiesel and biodiesel densities. This model was validated by using experimental data from the literature, along with a new experimental data set for biodiesel (grape seed, corn, and linseed) + petrodiesel, at high pressure (0.10–100.00 MPa) and high temperature (293.15–413.15 K) in a composition range of 0, 20, 40, 60, 80, and 100%vol. These experimental data were correlated by using the Tammann–Tait equation. From these data, the following derivative properties were determined: isothermal compressibility (κT), isobaric thermal expansibility (αP), internal pressure (p int), and the difference between pressure and volume heat capacities (c p – c v). Deviations obtained from the model proposed in this work (%AARD) were less than 0.50% for biodiesel + petrodiesel density data.

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In this work, high-pressure and high-temperature density data for 1-methyl-3-octylimidazolium trifluoromethanesulfonate [C8C1Im]­[OTf], 1-butyl-1-methylpyrrolidinium dicyanamide [C4C1Pyr]­[DCA], and 1-ethyl-3-methylimidazolium acetate [C2C1Im]­[C1COO] ionic liquids (ILs) were determined at P = (0.2 to 100.0) MPa and T = (298.15 to 398.15) K with steps of 25 K, by using a tube vibration method. It was observed that density increases in the following sequence: [C4C1Pyr]­[DCA] < [C2C1Im]­[C1COO] < [C8C1Im]­[OTf], according to their intermolecular interactions. These experimental density data were correlated by using the Tammann–Tait equation, with the average absolute relative deviation less than 0.0090% for [C8C1Im]­[OTf] and [C2C1Im]­[C1COO] and less than 0.0220% for [C4C1Pyr]­[DCA]. From these data, the following derivative thermodynamic properties were calculated: isothermal compressibility (κT), isobaric expansivity (αp), thermal pressure coefficient (γv), and internal pressure (P i). Furthermore, the densities of the studied ILs were predicted using six different group contribution models. The best agreement between experimental and calculated data was obtained when the model proposed by Paduszynski and Domanska was applied.

Although physicochemical properties are essential to developing new industrial ionic liquid (IL) applications, experimental data must be obtained, especially under high-pressure operational conditions. Therefore, density data were measured for three commercial ILs: methyltrioctylammonium bis(trifluoromethylsulfonyl) imide [(C8)3C1N][NTf2]; 1-methyl-1-propylpiperidinium bis(trifluoromethylsulfonyl) imide [C3C1Pip][NTf2]; and 1-butylpyridinium bis(trifluoromethylsulfonyl) imide [C5Py][NTf2] at high-pressure and wide temperature ranges [P = (0.2 to 100.0) MPa and T = (298.15 to 398.15) K] by the intermediate of a tube vibrating method. The operational range was chosen because it could cover many industrial applications. The structural interaction between the IL cation and the anion is significant in volumetric behavior. It was observed that the density increases in the following order: [C5Py][NTf2] > [C3C1Pip][NTf2] > [(C8)3C1N][NTf2]. The Tammann–Tait equation was used to evaluate the influence of pressure and temperature on density, showing an average absolute relative deviation (%AARD) of less than 0.032% compared to experimental data. From these data, the isothermal compressibility (κT), isobaric expansivity (αp), thermal pressure coefficient (γv), and internal pressure (P i) were calculated. Additionally, IL density was estimated using five different group contribution methods reported in the literature, with better results obtained for Gardas and Coutinho and Paduszyński and Domańska.