In this study, the noncatalytic production of ethyl esters from used frying oil (UFO) in a continuous process was evaluated under supercritical conditions. Experiments were performed with the objective of evaluating the effect of the addition of water, a co-solvent (n-hexane), and ethyl esters to the reaction medium, applying different temperatures and keeping the oil:ethanol mass ratio (1:1), pressure (20 MPa), and residence time (40 min) fixed. The results demonstrated that the formation of fatty acid ethyl esters (FAEE) is favored at higher temperatures. The addition of 5 wt % water increased the yield, while no significant effect (p > 0.05) was noted with the addition of 10 wt % water. The addition of cosolvent and ethyl esters in the range investigated plays a vital role in maximizing the FAEE yields for most conditions studied. The presence of water and cosolvent reduced the degree of fatty acids decomposition, while the addition of ethyl esters increased this parameter. The effect of the residence time was investigated applying the best conditions observed and good reaction yields (>85 wt %) were achieved under different conditions.

-This study evaluated the potential of macauba pulp oil (MPO) as a feedstock for continuous ester production using ethanol under pressurized conditions. Experiments were performed in order to obtain data for the effect of process variables on ethyl ester (FAEE) and free fatty acid (FFA) conversion in a catalyst-free process. From the results, it appears that the MPO to ethanol mass ratio and the pressure were the variables with more favorable effect on the evaluated response variables. The addition of n-hexane caused an increase in the production of esters; however, this had a negative effect on FFA conversion. The addition of water was unfavorable for oil processing with high acidity. In this process, esterification and transesterification occur simultaneously, and the high FFA content in MPO provides high yields (85 wt% of esters; 93% FFA conversion) at low temperature, since the esterification reaction rate is higher than the transesterification. The decomposition of fatty acids was evaluated and levels <5% were observed under the evaluated experimental conditions.

ResumoO biodiesel (ésteres de ácidos graxos) tem atraído considerável atenção como combustível renovável, biodegradável e não tóxico. Tal ponto justifica o crescente interesse no desenvolvimento de tecnologias referentes à produção deste biocombustível em diversos países e no âmbito nacional. Com a grande variedade de substratos para a produção deste biocombustível, aumenta-se o interesse no estudo da reação de esterificação, como um processo prévio a transesterificação quando os substratos apresentam elevada acidez. O objetivo do presente trabalho foi investigar o processo de esterificação de ácidos graxos livres (AGL) em óleos residuais de fritura, avaliando o efeito da temperatura (50, 65 e 80ºC), razão molar AGL:etanol (1:20, 1:40 e 1:60) e concentração de catalisador argila KSF (5, 10 e 20% em relação a massa de AGL), mantendo-se fixo o tempo de reação em 1 hora. Os resultados obtidos demonstram que o aumento da razão molar AGL:etanol e a temperatura de reação favorece a conversão da reação, sendo que conversões na ordem de 80% dos AGL podem ser alcançadas dentro da faixa de estudo das variáveis selecionada.Palavras-chave: ácidos graxos livres; óleos residuais de fritura; esterificação.