article · Scientific Reports
Discarded chicken eggshells can be converted into a porous calcium oxide catalyst to produce fatty acid ethyl esters from waste cooking oil using ethanol. Calcination at 900 degrees Celsius for three hours created high basicity within the catalyst structure. Optimised reaction conditions achieved a maximum ester yield of 94.86 per cent at 77 degrees Celsius, reducing the free fatty acid content from 1.07 per cent to 0.11 per cent. The resulting fuel satisfied ASTM D6751 and EN 14214 standards, with oxidative stability improved using an additive. Testing diesel blends containing between five and twenty per cent of this biofuel demonstrated engine performance comparable to conventional diesel. At full load, the twenty per cent blend decreased emissions of carbon dioxide by 6.7 per cent, carbon monoxide by 19.0 per cent, and particulate matter by 40.9 per cent.
Replacing petroleum fuels with cleaner alternatives helps tackle transport emissions while offering productive uses for common waste streams. Utilizing discarded eggshells and waste cooking oil addresses two waste disposal challenges simultaneously. Furthermore, substituting ethanol for conventional methanol offers a greener, renewable pathway to manufacture biodiesel that complies with existing international fuel specifications and functions directly in standard diesel engines.
This applied and tested technology offers potential applications for biofuel manufacturers and waste management facilities seeking to convert food waste into marketable fuels. Because the resulting blend meets international standards and functions in diesel engines with marked reductions in particulate emissions, it holds value for transport operators. Commercialisation would require moving from laboratory-scale testing to scaled pilot production and long-term engine durability trials.
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A sustainable waste-to-energy strategy has been developed for the production of fatty acid ethyl esters (FAEE) from waste cooking oil using a heterogeneous CaO catalyst derived from discarded chicken eggshells. The process combines dual waste valorization with enhanced renewable energy production by employing ethanol instead of methanol. Catalyst characterization revealed that a hydration–dehydration treatment generated a highly porous CaO structure, with Ca–O vibrational bands observed at 598 and 545 cm⁻¹, and a maximum basicity of 4.23 mmol g⁻¹ achieved after calcination at 900 °C for 3 h. Optimization using response surface methodology resulted in a maximum FAEE yield of 94.86% at 77 °C, with an ethanol-to-oil molar ratio of 14.65:1 and a catalyst loading of 7.42 wt%. The activation energy was determined to be 94.73 kJ mol⁻¹. The produced FAEE met ASTM D6751 and EN 14,214 specifications, reducing free fatty acid content from 1.07% to 0.11% and exhibiting improved oxidative stability with 500 ppm of tert-butylhydroquinone (TBHQ). Furthermore, engine performance testing of FAEE-diesel blends (B5–B20) demonstrated comparable performance to conventional diesel fuel. At 40% load, brake power increased from 1.95 kW (B0) to 2.00 kW (B20), while brake thermal efficiency decreased slightly from 19.2% to 18.2%, and brake-specific fuel consumption rose from 0.51 to 0.59 kg/kWh. At full load, B20 reduced emissions of CO₂, CO, and particulate matter by 6.7%, 19.0%, and 40.9%, respectively, with a modest increase in NOx emissions. These findings confirm the strong potential of eggshell-derived CaO catalysts for sustainable biodiesel production.
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DOI: 10.1038/s41598-026-65237-6
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