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.

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.

A B S T R A C TIn recent years, numerous studies on lignin hydrotreatment have been published; however, it is crucial to diversify both the type and origin of the lignin being processed. This study describes the production of liquid biofuel from lignin obtained through a Kraft extraction process using forest residues from Mexican Ocote pine (Pinus montezumae Lamb.). The work was carried out in two stages: the first consisted of isolating lignin from forest residues by means of Kraft extraction, and the second involved applying a hydrotreating process to the isolated lignin using a commercial CoMo/γ-Al2O3 catalyst and 1,2,3,4-tetrahydronaphthalene (tetralin) as a hydrogen donor in an isothermal batch reactor. The hydrotreating products were characterized based on their boiling point distribution, and their composition was determined using the ASTM D2887 method. A four-component chemical reaction network, together with its kinetic model, was developed to represent the hydrotreating of lignin obtained from pine wood residues. The model was derived from experiments carried out in a batch reactor operating under isothermal conditions at 380, 400, and 420 °C, with reaction times ranging from 2 to 4 h. Results showed that more severe operating conditions led to higher selectivity toward the kerosene fraction (C9–C13). However, these operating conditions also increased the diesel fraction (C14–C20) and the gasoline fraction (C5–C6), due to the contribution of secondary reactions. Consequently, both the reaction temperature and residence time during hydrotreating should be carefully moderated.

Understanding the relationships between operating conditions and product formation pathways in biomass pyrolysis remains challenging due to the complex interactions among temperature, catalytic effects, and feedstock composition. In this work, principal component analysis (PCA) was applied to investigate the combined influence of temperature and catalyst-to-biomass ratio on the pyrolysis of sugarcane bagasse and Salicornia. To preserve mechanistic interpretability, two complementary analyses were performed: one considering only catalytic experiments and a second integrating both thermal and catalytic conditions. Separate PCA were conducted for product yields, gas and liquid compositions, and solid-phase FTIR features. The results reveal that thermal conditions promote severe cracking and solid carbonization, whereas catalytic operation favors secondary pathways associated with controlled dehydration and partial stabilization of liquid products. Distinct patterns between the two feedstocks were also identified, reflecting their intrinsic compositional differences. Based on the multivariate trends identified, a conceptual reaction scheme is proposed to describe the interplay between thermal and catalytic pathways.