•Green and practical synthetic approaches with easy operation.•Excellent activity and selectivity.•Homogeneous catalyst with a self-separation feature.•The catalyst is reusable up to ten times without any significant loss of activity.An eco-friendly and readily accessible 2,2,6,6-tetramethylpiperidinium triflate was found as highly-selective and self-separated catalyst for esterification under solvent-free condition. The X-ray crystallography revealed that it formed a ‘hydrophobic wall’ which could effectively eliminate the generated water from the reactive sites. Moreover, it could precipitate from the reaction system with excellent recovery ratio (>99%) and be reused for ten times without any significant loss of activity.

A SO3H and NH2+ functional carbon-based solid acid was used as a highly active heterogeneous catalyst for the transesterification of various carboxylic methyl esters with alcohols under mild conditions. It also showed high catalytic performance for transesterification of triolein with methanol or isopropanol. Furthermore, it was able to catalyze simultaneous esterification and transesterification of rice oil and butter respectively, the yields of biodiesel obtained were up to 94%, and the catalyst could be easily recovered and reused more than ten times without loss of activity, which indicated the carbon-based solid acid was a potential catalyst for the biodiesel industry.