In recent years, reductions in limited resources of fossil fuels and the high volume of pollution from fuels have led researchers to pay special attention to alternative fuels. Biodiesel is one of the alternative fuels to replace diesel fuel. Higher operating cost, which is due to the use of more expensive raw materials, is the main issue hindering biodiesel production. In this study, it was tried to significantly reduce feed costs through using waste cooking oil as well as KOH catalyst based on calcined cow bone at a temperature of 800 °C. In addition, a T-shaped microreactor was used to reduce the reaction time, which reduced the residence time of the reaction to about 1.5 min. The experiments were designed via Box-Behnken method and experiments were performed to investigate and optimize the effects of the variables of calcined cow bone to KOH ratio, oil to methanol volume ratio, residence time, and reaction temperature on the purity of biodiesel. The results showed that the maximum purity of biodiesel, i.e., 97.21 % was obtained using calcined cow bone to potassium hydroxide ratio of 4.07:1 g/g, oil to methanol volume ratio of 2:1 vol:vol, residence time of 85 s, and temperature of 63.53 °C. Then, using toluene (10 wt. % based on oil) as a co-solvent under optimal conditions, the purity of the produced biodiesel increased to 99.56 %. Finally, the catalyst was reused at the optimum conditions for seven times. The result shows a slight decline in FAME % in catalyst reusability process.
