The objective of this work was to study the volumetric and transport properties of mixtures made up of biodiesel and diesel, in order to meet the desirable properties of these formulations for their practical applications. The volumetric and transport properties were analyzed for two pseudobinary mixtures constituted of diesel + beef tallow butyl ester biodiesel and diesel + waste cooking oil methyl ester biodiesel in the whole range of composition at 0.078 MPa. The study of butyl ester biodiesel was motivated by the scarcity of these properties’ data for butyl esters and the improvement of some of its physicochemical properties. The biofuels were previously transesterified from waste materials and alcohols, beef tallow with 1-butanol and cooking oil with methanol. Density measurements were performed in a vibrating tube densimeter from 293.15 to 363.15 K; the kinematic viscosity experiments were carried out in Cannon-Fenske viscometers from 293.15 to 343.15 K. The derived thermophysical properties evaluated were the excess molar volume, the partial molar volume, the thermal expansion coefficient, the dynamic viscosity and the viscosity deviation. The excess molar volumes presented positive and negative values. The Redlich–Kister correlation and the theoretical ERAS (Extended Real Association Solution) model were applied for modelling the excess molar volume. Both approaches resulted in good agreement. For viscosity, the McAllister model was implemented and yielded lower deviations for the butyl ester biodiesel.

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.

The performance of chemical and biological additives in the methane hydrates formation and dissociation processes is of relevance for the development of gas-transport and gas-storage systems. The effect of sodium surfactin, rhamnolipids, and sodium dodecyl sulfate (SDS) on the methane hydrate formation process was assessed in this work at different temperatures and a fixed pressure of 50 bar. The studied parameters were induction time, methane uptake, period to reach 90 percent of the consumed gas, water-to-hydrate conversion, and formation rate. Concentrations for sodium surfactin were 3, 150, 750, 1500, 2000, and 2500 ppm, while rhamnolipids and SDS solutions were analyzed at 1500, 2000, and 2500 ppm. Performance testing of these additives was carried out by means of the isochoric–isothermal method. The experimental setup consisted of an isochoric three-cell array with 300 mL of capacity and magnetic stirring. According to the results, the sodium surfactin promoted the methane hydrate formation since the kinetics were higher and the water-to-hydrate conversion averaged 24.3%; meanwhile, the gas uptake increased as concentration was rising, and the induction time was reduced even at a temperature of 276.15 K.

This study investigates the supercritical transesterification of waste beef tallow using methanol, with carbon dioxide employed as a cosolvent to reduce the operating pressure. The experimental design, guided by response surface methodology, evaluated the effects of reaction temperature (250–360 °C), carbon dioxide/methanol molar ratio (0.000–0.421), and methanol/beef tallow molar ratio (40–50) on conversion and quality during 60 min in a batch reactor. Bulk properties and spectroscopic analyses confirmed that the fatty acid methyl esters (FAMEs) met reference standard values. The results showed that temperature was the most significant factor affecting conversion, while carbon dioxide addition proved beneficial at high methanol-to-fat ratios. The process proved to be a feasible method for producing high-quality biodiesel while lowering required pressure compared with non-cosolvent supercritical systems.