Enhanced esterification of carboxylic acids with ethanol using propylsulfonic acid-functionalized natural rubber/hexagonal mesoporous silica nanocomposites

• NR/HMS-SO3Hs were applied as solid acid catalysts in esterification reactions.
• NR/HMS-SO3Hs had wormhole-like structure, high mesoporosity and hydrophobicity.
• NR/HMS-SO3Hs exhibited a superior catalytic performance to SAC-13 and HMS-SO3Hs.
• Hydrophobicity of NR reduced the poisoning effect of H2O added into the reaction.
• NR/HMS-SO3H can be regenerated by washing and reused in the esterification.

Propylsulfonic acid-functionalized natural rubber (NR)/hexagonal mesoporous silica (HMS) nanocomposites (NR/HMS-SO3H) with different acid contents were prepared via an in situ sol–gel process, and then applied as heterogeneous acid catalysts in the esterification of model carboxylic acids and palm fatty acid distillate (PFAD) with ethanol. The NR/HMS-SO3H composites exhibited a wormhole-like framework with enhanced wall thickness, high mesoporosity, and enhanced hydrophobicity. The NR/HMS-SO3H composites exhibited a superior catalytic performance compared to a commercial Nafion/silica composite solid acid catalyst (SAC-13) and conventional propylsulfonic acid-functionalized HMS (HMS-SO3H). The NR/HMS-SO3H catalyst can be regenerated and reused in the esterification.

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