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Two different numerical techniques, applying either the SRK or the PC-SAFT equations of state, were used to predict the multiphase behavior exhibited by the ternary systems nitrogen + methane + ethane, nitrogen + methane + propane, and nitrogen + methane + n-butane. The predictions with both equations of state were compared against experimental data in terms of nitrogen mole fractions of the two liquid phases and it was demonstrated that the agreement is good. Furthermore, a procedure similar to that reported by Gregorowicz and de Loos, in conjunction with the SRK equation of state, was introduced. It was applied to predict the K (L1–L2=V) and LCST (L1=L2–V) critical end points at constant temperature for the systems studied, and demonstrated a reliable and robust performance with good convergence characteristics.

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Some of the main problems during vegetable oil hydrotreating are the high heat of reaction released, the huge quantity of expensive hydrogen required, and the high corrosion rates in the equipment. Some insights into the advantages and disadvantages of processing raw vegetable oils or their respective fatty acid methyl esters are given. The ASPEN Plus process simulator was used for the simulation of a hydrotreating process, with two different feedstocks coming from the same plant: raw castor oil and castor oil methyl esters. That process was modeled with two stoichiometric reactors in series. The technical viability of using methyl esters as hydrotreating feedstock for the production of biofuels such as green gasoline and diesel is demonstrated.

The effect of temperature was studied on the synthesis of fatty acid alkyl esters by means of transesterification of waste beef tallow using ethanol and, iso-butanol and 1-butanol at supercritical conditions. These alcohols are proposed for the synthesis of biodiesel in order to improve the cold flow properties of alkyl esters. Alcohol–beef tallow mixtures were fed to a high-pressure high-temperature autoclave at a constant molar ratio of 45:1. Reactions were carried out in the ranges of 310–390 °C and 310–420 °C for ethanol and iso-butanol, respectively; meanwhile, synthesis using 1-butanol was assessed only at 360 °C. After separation of fatty acid alkyl esters, these samples were characterized by nuclear magnetic resonance (NMR) and gas chromatography coupled to mass spectrometry (GC-MS) to quantify yields, chemical composition, and molecular weight. Results indicated that yields enhanced as temperature increased; the maximum yields for fatty acid ethyl esters (FAEEs) were attained at 360 °C, and for fatty acid butyl esters (FABEs) were achieved at 375 °C; beyond these conditions, the alkyl ester yields reached equilibrium. Concerning the physicochemical properties of biodiesel, the predicted cetane number and cloud point were enhanced compared to those of fatty acid methyl esters.