A novel CaO-based catalyst obtained from silver croaker (Plagioscion squamosissimus) stone for biodiesel synthesis: Waste valorization and process optimization

A new catalyst was synthesized from the South American Silver Croaker’s stone − the Silver Croaker is a fish widely consumed in Brazil and the stone is a residue from the fish’s head. The stone and the bio-based catalyst obtained from it were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, X-ray fluorescence, thermogravimetric analysis, surface area, and soluble alkalinity. It was confirmed that the stone is composed of aragonite (calcium carbonate) and the catalyst obtained by calcination of calcium oxide (CaO). The catalytic activity was evaluated by transesterification reactions. The process was optimized by surface response methodology based on Box – Behnken design. Methanol:oil molar ratio of 11.8, 5.33 wt% of catalyst, 175 min of reaction time, and 67.85 °C were identified as optimal conditions, reaching conversions close to 99% and ester content of 97.4%. The catalyst derived from silver croaker stone was reused 5 times while maintaining its high performance. Thus, a new application was given to this little-known waste, showing its potential as a catalyst in the synthesis of biodiesel. [Display omitted] •The Silver Croaker’s stone was characterized for the first time.•The new bio-based catalyst (CaO) showed high catalytic activity.•The transesterification process was optimized by RSM based on BBD.•Soybean oil to biodiesel conversions close to 99% were obtained.•The catalyst was reused 6 times, maintaining its good activity (conversions > 90%).