Ahmad Nasir Pulungan, Junifa Layla Sihombing, Agus Kembaren, Dian Wardana, Annisya Dwi Putri Zulmi, Dika Fahreza, Immanuel Veron Silitonga, Rahayu Rahayu
This study investigates the catalytic specificity of sulfonated palm kernel shell (PKS)-derived biochar for the esterification of free fatty acids (FFA) in high-acid crude palm oil (HACPO). Biochar was prepared by pyrolysis (500 °C, 5 h, N2), activated with KOH (2 M, 1:4 w/v, 90 °C, 5 h) and HCl (1 M, 1:4 w/v), and sulfonated with concentrated H2SO4 (1:4 mass ratio, 100 °C, 5 h). Comprehensive characterization using FTIR, XPS, XRD, and N2 physisorption revealed that KOH activation generated substantial microporosity (BET surface area 251.85 m2/g), which was subsequently blocked by the grafted –SO3H groups after sulfonation, causing the surface area to collapse to 4.95 m2/g. XPS confirmed the exclusive presence of covalently bound aromatic –SO3H groups (S 2p at 168.7 eV) with no residual sulfate impurities. The resulting catalyst exhibited a competitive acid site density of 2.80 mmol g⁻1 and achieved an 84.44% FFA conversion at a 4 wt % catalyst loading. Notably, the near-complete loss of internal porosity confined the active acid sites predominantly to the external particle surface, creating a catalyst that is highly specific toward FFA esterification while showing negligible activity for triglyceride transesterification. This pore-blocking-driven substrate selectivity establishes a clear structure–activity relationship and highlights the potential of PKS-derived sulfonated biochar as a selective solid-acid catalyst for high-FFA feedstock pretreatment. © Akadémiai Kiadó Zrt 2026.
Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Negeri Medan, Jl. Willem Iskandar Pasar V Medan Estate, Medan, 20221, Indonesia; Department of Chemistry, Faculty of Science and Technology, Universitas Samudra, Langsa, 24416, Indonesia
