From tannery waste to sustainable fuel: An integrated optimized experimental-simulation approach for biodiesel synthesis with mass- heat synergy and comprehensive financial feasibility analysis

The tannery industry produces significant leather fleshing waste (LFW), posing environmental concerns. This study explores LFW for sustainable biodiesel production. Extracted oil was degummed to enhance quality, reducing viscosity by 29 % and acid value by 18 %, then transesterified using calcium oxide. Process parameters—molar ratio, catalyst loading, and temperature—were optimized via response surface methodology (RSM), achieving a 96.38 % yield under optimal conditions (9:1 molar ratio, 6 wt% CaO, 60 °C, 3 h). The quadratic model (R² = 0.999) showed high predictive accuracy. Aspen Plus simulation confirmed scalability, and heat/mass integration improved efficiency—cutting energy demand by 51.9 % and enabling methanol reuse by 66 % through recycling. The biodiesel met ASTM/EN standards, with a cetane number of 64.2 and a higher heating value of 44.1 MJ/kg. Economic analysis showed strong feasibility: $42.81 million NPV, 39 % IRR, and 3.69-year payback. This work demonstrates LFW's potential as a cost-effective and eco-friendly biodiesel source.