Kinetics and optimization of biodiesel production from rapeseed oil over calcined waste filter cake from sugar beet processing plant

Abstract

A low-cost, highly active CaO-based catalyst was prepared from waste filter cake (WFC) from a sugar beet processing factory by calcination in air at 900 °C for 2 h, referred to as the calcined filter cake (CFC). It was used to catalyze the rapeseed oil transesterification with methanol under mild reaction conditions (methanol-to-oil molar ratio of 9:1, catalyst loading of 4–10 %, and reaction temperature of 40–60 °C). Rapeseed oil was characterized regarding the physicochemical properties and fatty acid profile. Low free fatty acid content (about 2.0 mg KOH/g) allowed the direct use of the base CFC catalyst for rapeseed oil transesterification. Rapeseed oil has more unsaturated fatty acids (about 93 %), with oleic acid as the most abundant, than saturated fatty acids (about 7 %). A simplified model combining the changing mechanism of the reaction and the triacylglycerols mass transfer limitation successfully describes the kinetics of transesterification. A good agreement between the model and the experiment was proved by the mean relative percentage deviation for the conversion degree of only ± 7.43 % (based on 42 data). The apparent reaction rate constant follows the Arrhenius equation with the activation energy of 51.9 kJ mol−1. The FAME content higher than 96.5 % can be obtained in wide ranges of the catalyst amount (4–10 %) and the reaction time (about 45–70 min). The following conditions were optimum: the reaction temperature of 59.2 °C, the catalyst loading of 9.1 % (based on the oil weight), and the reaction time of 47 min.