Experimental study and kinetic modeling of waste frying soybean oil hydrolysis in subcritical water

This work reports experimental kinetic data in addition to conventional and modified mathematical models for predicting free fatty acid production from refined and waste frying soybean oils in subcritical water. The experiments were performed in batch mode until 220 min of reaction, at an oil to water mass ratio of 1: 4 and temperatures of 250 and 275 degrees C. The proposed modified kinetic model presented a good agreement with the experimental data, with a mean absolute error of 2.17% between experimental data of free fatty acid yields and calculated values (the conventional model presented an error of 2.41%). The experimental data used in the model parameter estimation were obtained from the hydrolysis of refined oil and frying oil used on a single frying procedure. The modified kinetic model was also used to predict the hydrolysis of a mixture of waste frying oils submitted to more than one cycle of frying (results not used for parameter estimation), and a mean error of 3.04% was observed when comparing the calculated values to experimental data (the conventional model presented an error of 4.98%). It was observed that the effect of frying is positive and statistically significant in the hydrolysis kinetics, which can justify the use of the proposed modified model for predicting yields of free fatty acids from oils submitted to different home frying cycles.