Optimization of biodiesel production from waste cooking oil using waste-based CaO/Zeolite catalyst

Abstract

Lignite coal fly ash collected from Serbian thermal power plants was converted into value-added zeolite-like material using a Teflon-lined hydrothermal reactor in an alkali activation process at 150 ºC for 24 h. The obtained material was used in the synthesis of zeolite supported chicken eggshell calcium oxide catalyst for biodiesel synthesis from waste cooking oil using earlier established procedures. The study aimed to coupled optimization of catalyst synthesis parameters (CaO loading and calcination temperature) and biodiesel synthesis process (CaO concentration in the reaction mixture). The influence of calcination temperature in the catalyst activation stage was monitored by X-ray diffraction and FT-IR spectroscopy, whereas the reaction progress by the HPLC analysis. The analyzed calcination temperature range was within 450 ºC and 950 ºC, CaO loading in the range of 10 wt% - 50 wt%, whereas CaO concentration in the reaction mixture was within 2 wt% and 10 wt%. It is shown that calcination temperature strongly influences the final catalyst form, whereby the temperature higher than 700 ºC leads to the destruction of the initial zeolitic support and interaction of CaO with the melted glassy silicate phase making less-active or non-active calcium silicate phases. The highest fatty acid methyl esters content (>97 wt.%) was obtained using a catalyst with 44 wt.% of CaO and calcined at 523 ºC under the following reaction conditions, reaction temperature of 60 ºC, methanol to oil molar ratio of 1/12, catalyst concentration of 8.8 wt.%, and reaction time of 90 min.