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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.

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A mathematical model of an isothermal semibatch bubble reactor has been developed to describe the esterification reaction of free fatty acids with superheated alcohol vapor. The proposed model accounts for the effects of mass transfer followed by chemical reaction in the liquid phase. The fluid physical properties are calculated by published correlations, and the partition coefficient of alcohol vapor was estimated based on thermodynamic models of vapor−liquid equilibria. Experimental data of acid-catalyzed esterification of oleic acid with superheated ethanol vapor at different conditions of temperature and gas superficial velocities were used to estimate the liquid side mass transfer coefficients and kinetic parameters. The results obtained showed that the model satisfactorily fits the experimental data for all operating conditions and was also able to simulate and predict experimental results for intermediate conditions with a coefficient of determination R 2 of 0.987. In addition, the estimated values of the mass transfer coefficient agreed with data reported in the literature for gas−liquid reactors.

Oiticica is a feedstock with energetic potential for biofuel due to the presence of high oil content in its almond (54-60%). In this work, biodiesel from oiticica was produced by methyl transesterification using alkaline catalysts. Fatty acid methyl ester (FAME) obtained at 32 °C, with 1.5% of KOH and 2h of reaction time was higher (92%) than that with NaOH (85%). At the temperature of 50 °C, no difference between the catalysts was found, both resulting in a conversion of 91%. The best acid index was obtained with 1% of NaOH (0.40 mg KOH g -1 oil at 50 °C) and the best value of viscosity (9.61 mm 2 s -1 ) with 1.5% of KOH at 50 °C. Oiticica oil and biodiesels exhibited high viscosities due the predominance of unsaturated compounds. Thermogravimetric analysis demonstrated to be a feasible technique, when compared to chromatography, in terms of time of analysis, conversion of the esters, and reagent consumption. All the biodiesels presented an oxidation temperature of 90 °C via Pressure Differential Scanning Calorimetry (PDSC).

A semi-batch bubble reactor has been developed to produce fatty acid ethyl ester (biodiesel) by acid-catalyzed esterification of oleic acid with superheated ethanol vapor. In this paper, the effects of reaction temperature (110, 130 and 150°C), ethanol volumetric flow rate (1.35, 2.50 and 3.65 mL/min) and vapor bubble size on the reactor performance were evaluated. The results demonstrated that temperature and volumetric flow rate have significant effects on the chemical reaction, gas phase solubility and mass transfer limitations. In addition, the free fatty acid conversion velocity was increased by approximately 56% when a microporous stainless-steel tube was employed to generate and distribute the vapor bubbles inside the reactor, which allowed the process to reach 95% conversion in approximately 40 minutes for the operating temperature of 150°C and volumetric flow rate of 2.5 mL/min.

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