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In this study, research was performed on the interesterification reaction of cotton oil with methyl acetate, using potassium methoxide as catalyst, in the presence of ultrasonic waves. In order to obtain a better understanding of the process variables behavior, a response surface methodology was used along with statistical methods. The experiments were performed with molar ratio varying from 1:8 to 1:24, catalyst percentage of 0.1 to 1.3% (weight), ultrasonic nozzle amplitude varying from 30% to 90% (180 to 540 W) and vibration pulse varying from 50% to 90%. Process variables were optimized with the optimal molar ratio of 1:14.87, catalyst concentration of 1.17%, ultrasonic probe amplitude of 67.64% and vibration pulse of 67.30%. The average conversion of triglycerides was found to be 98.12% at the optimal conditions. The experimental data were adjusted to the second-order irreversible reaction approximation model, under optimized conditions, with temperatures of 30, 40 and 50 ºC. Lastly, in comparison to the conventional methodology, a significant increase of 14% of triglycerides conversion utilizing ultrasonic waves was observed.

The search for new sources of energy requires more and more interaction between the economical and technological viabilities associated with social development, increasing, in this manner, the interest in raw materials that generate regional development. Thus, this work analyzed the viability of ethyl esters production (biodiesel) from Gossypium hirsutum L. (cottonseed oil) without the use of a catalyst, in a continuous supercritical reactor. The reactions occurred at a tubular reactor, under 15 MPa and 20 MPa of pressure, reaction time (3.75–50 min), molar ratio of oil:alcohol (1:30–1:50), and temperature (250–400 °C). The maximum yield obtained was 75.05 % at 375 °C, under 20 or 15 MPa of pressure, molar ratio of oil:ethanol 1:40, and reaction times 30 and 40 min, respectively. A significant influence of the temperature on yield in esters was verified, but there was also thermal degradation under high temperatures, which caused a decrease in the ester's yield. The high content of polyunsaturated acids present in cotton oil possibly hampered the process of transesterification in long periods of reaction time and high temperatures.

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