The reaction efficiency of soybean oil transesterification in supercritical ethanol in a continuous catalyst-free process was investigated under different water concentrations. Experiments were performed at 350 °C and 20 MPa, with an oil/ethanol ratio of 1:40. A fatty acid ethyl ester content of 77.5% was obtained at a flow rate of 1.5 mL/min in a water-free system, while the maximum concentration of ethyl esters reached for a water content of 10 wt % was 68.1% at a flow rate of 1.0 mL/min. Decomposition and trans-isomerization of unsaturated fatty acids were significantly affected by the flow rate, with a pronounced reduction in the ratio of C18:2/C16:0 in the final product compared to the starting oil.

This work investigated the effect of temperature on the reaction efficiency of soybean oil transesterification in supercritical ethanol in a continuous catalyst-free process under different water concentrations and at varying substrate flow rates. Experiments were performed in the temperature range from 250 to 325 °C, at 20 MPa, with an oil to ethanol molar ratio of 1:40. Results showed that temperature and substrate flow rates strongly affected the reaction conversion to fatty acid ethyl esters, decomposition, and trans-isomerization of unsaturated fatty acids, mainly for C18:2 and C18:3. It is shown that the synthesis of esters was favored by the addition of water to the reaction medium and the degradation phenomenon decreased as water concentration increased from 0 to 10 wt %.

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The dilatational rheological interfacial properties are important in colloidal systems due to the possibility of studying changes in the interfacial tension because of interface relaxation and diffusion. Information on these properties enables analyses on the interfacial activity and mechanical behavior of surfactants in the interfaces for different colloidal systems such as petroleum emulsions. The determination of elastic modulus is crucial for characterizing the interfacial behavior of films containing asphaltenes at interfaces. In this study, the pendant drop tensiometry technique was used to describe the rheological interfacial properties of asphaltenes extracted from two Brazilian oils at toluene/water and heptol (heptane + toluene)/water interfaces under varying proportions of organic solvents (1:1 and 1.5:1) and asphaltene concentrations. The applicability of adsorption isotherm models for involving Gibbs theory and Langmuir equation was investigated for the systems studied. For systems containing a good solvent (toluene), the attraction between the solvent and asphaltene molecules was stronger due to their high solubility, thereby reducing the interfacial activity of asphaltene molecules. For systems containing poor solvents (heptol 1:1 and 1.5:1), the interaction between the asphaltene and solvent molecules was weak, resulting in an increase in the interfacial activity of asphaltenes. Maximum surface concentrations in excess (Γ ∞ ) of 1.69 × 10 −5 mol/m 2 and 2.77 × 10 −6 mol/m 2 were obtained for petroleums A and B, respectively, resulting in cross-sectional areas of 9.8 and 59.9 Å 2 , respectively. The dilatational rheological interfacial properties of the systems studied, surface pressure, and elastic modulus depend exclusively on the interfacial coverage. These results are useful to understand how asphaltene adsorption processes occur at fluid/fluid interfaces at the microscopic level.