Predicting the higher heating values of waste frying oils as potential biodiesel feedstock

In the literature, there are several empirical models to estimate the higher heating values of vegetable oils and biodiesel fuels. In this study, five of these models found in the literature were used to estimate the higher heating value of waste frying oils. When some models are used to estimate HHVs of waste frying oils, the relative errors were found up to 5% compared to the values obtained experimentally. Therefore, a new empirical formula based on the fatty acid composition was developed to predict the HHV of waste frying oils. For this purpose, 35 samples taken from different facilities producing waste frying oils (fast-foods, fish restaurants and hospital restaurants) were analyzed and their properties (such as viscosity, density, iodine value, saponification value, HHV and fatty acid distributions) were determined. Subsequently, to develop an empirical formula, a regression analysis was performed between the HHVs and fatty acid compositions of the waste frying oils. When the experimentally determined and estimated values were compared, it was proven that the new empirical formula gave precise results. By using this model, the mean absolute and relative errors were found around 148.40 kJ/kg and 0.37%, respectively.