Effect of Additives in the Reaction Medium on Noncatalytic Ester Production from Used Frying Oil with Supercritical Ethanol

Abstract

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 ...