A novel carbon-based solid acid catalyst was prepared by the sulfonation of incompletely carbonized cassava stillage residue (CSR) with concentrated sulfuric acid, and employed to catalyze the esterification of
methanol and free fatty acids (FFAs) in waste cooking oil (WCO). The effects of the carbonization and the
sulfonation temperatures on the pore structure, acid density and catalytic activity of the CSR-derived catalysts were systematically investigated. Low temperature carbonization and high temperature sulfonation can cause the collapse of the carbon framework, while high temperature carbonization is not
conducive to the attachment ofASO3H groups on the surface. The catalyst showed high catalytic activity
for esterification, and the acid value for WCO is reduced to below 2 mg KOH/g after reaction. The activity
of catalyst can be well maintained after five cycles. CSR can be considered a promising raw material for
the production of a new eco-friendly solid acid catalyst