Biomass waste, as raw material for renewable energy, is an attractive alternative since it does not compete with human food supply. An emerging alternative for its treatment is supercritical water gasification (SCWG), due to the high moisture content of some types of biomass. On this regards, guava fruit (Psidium guajava L.) is one of the most wasted agro-food products in Mexico. This motivated us to evaluate gasification of guava waste on dry biomass base under supercritical water conditions for the first time, with the aim of analyzing the impact of moderate temperatures and feed ratios as reaction parameters on gas products. Temperature was varied in the range of 673.15–773.15 K and using a batch reactor loaded with biomass:water (B:W) mass ratios of 1:1, 1:4, and 1:6. Furthermore, the obtained solid, liquid, and gas phase products were characterized. Hydrogen (H₂), carbon dioxide (CO₂), carbon monoxide (CO), methane (CH₄), ethane (C₂H₆), propane (C₃H₈), and butane (C₄H₁₀) were identified in gas phase and quantified by means of a gas chromatograph equipped with a TCD detector. Liquid and solid phase products were subjected to Fourier Transform Infrared spectroscopy analyses. This preliminary research indicated that high temperature operation and high biomass:water mass ratio enhanced gas yields (mol/kg) of about 4.137 for CH₄, 6.705 for CO₂, and 7.743 for H₂; whereas the selectivity and gas efficiency for hydrogen was 65.26% and 58.94%, respectively.

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 anti-depressive and anxiolytic effect of galphimine B (isolated from Galphimia glauca) has been demonstrated by researchers. Therefore, it is necessary to explore extraction techniques that produce materials with adequate quality for pharmaceutical applications. In this work, supercritical extractions of galphimines from Galphimia glauca were performed in the presence of carbon dioxide. Pressure, temperature, particle diameter, and flow rate effects were examined to explore the conditions with the highest yield and the concentration profile of galphimines in the studied interval. The identification of the nor-seco triterpenoids and galphimine B and E was carried out by HPLC analyses. The mathematical modeling of the extraction curves was attained by the approaches proposed by Sovová and Papamichail et al. According to results, the highest yield 2.22% was obtained at 323.15 K, 326 μm, 3 L/min, and 33.75 MPa. Meanwhile, the content of galphimine B in the extract was, on average, 19.5 mg·g⁻¹.