Sulfonated carbon microspheres were successfully used as catalysts for biodiesel production from waste cooking oil. The catalyst
demonstrated good catalytic activity with 96.5% and 89.6% yield at
a reaction temperature of 110C, reaction time of 2 h, and catalyst
loading of 10 wt% for with and without treatment waste cooking
oil, respectively. Meanwhile, the catalytic stability needs to be
improved due to the leaching of sulfonic acid; however, the sulfonated carbon microsphere catalyst is still of interest as an environmentally benign, low-cost catalyst.