Synthesis of biodiesel via methanolysis of waste frying oil by biowaste-derived catalyst: process optimization and biodiesel blends characterization

Heterogeneously catalyzed transesterification reaction is known to be the most appropriate process for producing biodiesel from triglyceride-containing feedstock as it ensures catalyst reusability and easy product separation, lowers production costs, and makes biodiesel affordable. This work investigates the influence of calcination temperature (700–1000 °C) on the performance of CaO catalyst obtained from eggshells for biodiesel synthesis from waste frying oil (WFO). The prepared CaO catalyst was characterized using various techniques (TGA/DTA, N2 adsorption–desorption isotherm (BET), FTIR, CO2-TPD, XRF, XRD, and SEM). Taguchi optimization method with an orthogonal array was used to investigate the effect of process parameters (time, catalyst amount, methanol/oil ratio, and temperature). Reaction time was observed to be the most influential variable according to the design. Under the optimal transesterification conditions (i.e., at 50 °C for 3 h using WFO/methanol molar ratio of 1:10 with catalyst dosage of 0.75 wt.%), the biodiesel yield attained 90.81% when eggshell derived-catalyst calcined at 850 °C (CEG-850) was used. The remarkable performance of the CEG-850 could be attributed to its high basic strength (749 μ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\upmu$$\end{document}mol/g), improved surface area (15.4 m2/g), and dominance of basic sites on its surface. The blended fuel with 10% by volume biodiesel (B10) exhibited improved fuel properties compared to blended fuel with 50% by volume biodiesel (B50), which confirmed the suitability of a low-level biodiesel blend in the diesel engine. More than 54% biodiesel yield was achieved after the seventh cycle, depicting better stability.