Clean biodiesel production approach using waste swan eggshell derived heterogeneous catalyst: An optimization study employing Box-Behnken-response surface methodology

It is crucial to develop an environmentally benign and extremely potent heterogeneous catalyst for biodiesel production to meet the current fossil fuel scarcity. The current study employs waste swan (Anser cygnoides) eggshells as a reusable heterogeneous catalyst for transesterification of castor (Ricinus communis) oil to produce biodiesel. X-ray diffraction analysis, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy, and energy dispersive X-ray, Brunauer Emmett Teller, X-ray fluorescence, thermogravimetric analysis was utilized to analyse crystal structure, chemical composition, and surface morphology of the swan eggshell-derived calcium oxide (CaO) catalyst. The CaO catalyst (calcined at 900 degrees C, 3 h) has average crystal size of 17.18 nm, specific surface area of 10.50 m2/g, average pore volume of 0.00372 cm3/g, and average pore diameter of 14.19 nm. Box-Behnken design-response surface methodology with four input variables and three levels viz. calcination time (2 h, 3 h, and 4 h), calcination temperature (800 degrees C, 900 degrees C, and 1000 degrees C), reaction temperature (50 degrees C, 60 degrees C, and 70 degrees C), and reaction time (1 h, 1.5 h, and 2 h) was used to optimize biodiesel synthesis processes. Highest biodiesel yield of 95.64% was achieved at predicted optimal input parameters of calcination time 3 h, calcination temperature 915.7 degrees C, reaction temperature 60.4 degrees C, and reaction time 1.5 h. The synthesized biodiesel was analysed using gas chromatography-mass spectrometry and FTIR analysis which confirms the formation of methyl ester groups. The physicochemical properties of castor biodiesel have specific gravity (at 15 degrees C) of 0.86, Kinematic viscosity (at 40 degrees C) of 5 mm2/s, flash point of 165 degrees C, calorific value of 40 MJ/Kg, acid value of 0.49 KOH/g, and density (15 degrees C) of 0.89 g/cm3 which meet ASTM D6751 and EN 14214 standards. Swan eggshell CaO catalyst offers several appealing characteristics, including availability, ease of preparation, and capability to reused without significant catalytic activity loss (above 85 % biodiesel yield even after the fourth consecutive usage).