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 %.

No abstract

No abstract

No abstract

No abstract

This work studied the effect of the addition of free fatty acids (FFAs) at various proportions to different vegetable oils (soybean oil, rice bran oil, and high oleic sunflower oil) on the efficiency of their conversion to ethyl esters by a continuous supercritical ethanolysis. When the continuous reactor was operated at 300 °C and 20 MPa with soybean oil using an alcohol/oil molar ratio of 40:1, an ester content of 53% was obtained. Under identical conditions but processing soybean oil with 10% of FFAs, the ester content rose to 91%. A similar favorable effect of the addition of FFAs on the efficiency of the process was observed when processing rice bran oil and high oleic sunflower oil. Processing oils from different origins lead to different ester contents in the final product because of the occurrence of decomposition phenomena at different extents depending upon oil composition and stability. Results showed that the addition of FFAs is a useful tool for favoring alcoholysis against decomposition, with the consequence of a substantial increase in process efficiency.

This work reports the production of fatty acid methyl esters (FAMEs) and fatty acid ethyl esters (FAEEs) by means of waste fried oil (WFO) transesterification using methanol and ethanol at supercritical conditions, in a continuous catalyst-free process. Transesterification experiments were performed from 573 to 623 K, at 10, 15, and 20 MPa, with oil/alcohol molar ratios of 1:20, 1:30, and 1:40 and water addition to alcohol of 0, 5, and 10 wt %. The extent of the reaction was explored using a novel parameter, convertibility, which corresponds to the maximum ester content attainable from the feedstock (92.1%). The highest FAME and FAEE contents achieved were 81.7 and 82.2%, respectively. Results show that transesterification of WFO in methanol was more efficient than that in ethanol, the temperature had the strongest influence, and the addition of water considerably improved the ester yield.