Transesterification of waste cooking oil using pyrolysis residue supported eggshell catalyst

The present study focusses on synthesis and characterization of eggshell supported pyrolysis residue (char) as a heterogeneous base catalyst for transesterification of waste cooking oil (WCO). The influence of structural, compositional, and morphological properties on catalytic activity to optimize reaction time, methanol: oil molar ratio (6:1, 9:1, 12:1, 15:1 and 18:1), and catalyst concentration (10, 20, and 30 mass%) in biodiesel production from WCO were evaluated. The particle size distribution of pyrolysis residue, calcined eggshell, and the synthesized catalyst was in the range of 0.06 to 14 μm. The decomposition of eggshell revealed a two-stage mass loss from 300 to 900 °C indicating the formation of CaO and CO₂ from CaCO₃. WCO methyl ester with higher conversion rate over 95% was observed at 65 °C using 10 mass% catalyst concentration with methanol to oil molar ratio of 12:1 in 3 h. The calorific value of WCO methyl ester was 38.4 MJ kg^-1, with kinematic viscosity of 4.5 cSt, and had lower thermal stability when compared to raw WCO. The estimated apparent activation energy for WCO, and WCO methyl ester was 133.1 and 63.9 kJ mol^-1, respectively. The synthesized catalyst displays improved surface area and catalytic activity in comparison with unsupported eggshell catalyst.