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Keywords:

  • Heterogeneous catalyst;
  • Kinetic study;
  • Reusability;
  • Transesterification;
  • Waste cottonseed oil

Potassium fluoride impregnated CaO/NiO has been prepared by wet impregnation method in nano particle form as supported by powder XRD, scanning electron microscopy, and transmission electron microscopy studies. Brunauer–Emmett–Teller surface area and basic sites measurement studies have been performed to establish the effect of potassium fluoride impregnation on catalyst surface morphology and basic strength. CaO/NiO impregnated with 20 wt% potassium fluoride was used as solid catalyst for the transesterification of waste cottonseed oil having up to 5.8 wt% free fatty acid content. The variables used for the transesterification were, KF impregnated on CaO/NiO, catalyst concentration, reaction temperature, and methanol to oil molar ratio. Reaction parameters have been optimized to achieve the least reaction period for the completion of the reaction. Complete transesterification (>99% FAMEs yield) of waste cottonseed oil with methanol (1:15 molar ratio) required 4 h in the presence of 5 wt% catalyst (with respect to oil) at 65°C. Reusability study suggests that catalyst could be recycled for four successive runs without significant loss in activity. A pseudo first order kinetic equation was applied to evaluate the kinetic parameters and under optimized conditions first order rate constant and activation energy was found to be 0.023 min−1 and 41.2 kJ/mol, respectively. Few physicochemical properties of the prepared biodiesel sample have also been studied and compared with standard values.

Practical applications: In India, application of edible vegetable oils for biodiesel production is prohibited to avoid food versus fuel situation. Application of waste cottonseed oil (WCO) for biodiesel production could circumvent this problem. However, homogeneous alkali catalyst could not be employed due to the presence of high free fatty acid contents in such feedstock. In this context present study demonstrates the impregnation preparation of KF impregnated CaO/NiO and its application as reusable solid catalyst for the transesterification of WCO.