The use of a sulfonated soaked palm seed cake (SPSC-SO3H) derived catalyst for the production of biodiesel from palm fatty acid distillate (PFAD) (the byproduct obtained during palm oil production) has been demonstrated. The activated carbon material from the soaked palm seed cake (SPSC) was sulfonated and then used for the esterification of PFAD (containing 85% of free fatty acid (FFA), 10% of triglycerides, 3% of diglycerides, 0.3% of monoglycerides and some traces of impurities). The synthesized SPSC-SO3H catalyst was characterized using powder X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscope (FESEM), NH3-temperature programmed desorption (NH3-TPD), N2 physisorption and thermogravimetric analysis (TGA). The SPSC-SO3H catalyst showed higher acid density (12.08 mmol g−1) and surface area (483.07 m2 g−1). The optimized reaction conditions, i.e. 9:1 methanol/PFAD molar ratio; 60 °C reaction temperature; 2.5 wt.% of the SPSC-SO3H catalyst and 2 h of reaction time was employed to achieve FFA conversion (98.2%) and FAME yield (97.8%). The SPSC-SO3H catalyst underwent eight reaction cycles and catalytic activity was dropped by 24% during recyclability study. The SPSC-SO3H catalyst demonstrates a promising and effective application for biodiesel synthesis especially for feedstocks containing high free fatty acid content.

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Palm waste biochar (PWB) catalysts were synthesized as bio-based catalysts using different sulphonation methods. (NH4)2SO4, ClSO3H, and H2SO4 were applied to functionalize PWB and appraise the discrepancies between the sulfonic agents, as they affect the esterification reaction in terms of fatty acid methyl ester (FAME) yield and conversion while using palm fatty acid distillate (PFAD) as feedstock. The PWB was first soaked in phosphoric acid (H3PO4) for 24 h and then pyrolized at 400 °C for 2 h in tube furnace. Afterwards, sulphonation was done with different sulfonic agents and characterized with thermo-gravimetric analysis (TGA), Brunauer-Emmett-Teller (BET), Fourier transform infrared (FT-IR), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray (EDX), and temperature programmed desorption–ammonia (TPD-NH3). The three synthesized catalysts showed high free fatty acid (FFA) conversions of 90.1% for palm waste biochar-ammonium sulfate (PWB-(NH4)2SO4), 91.5% for palm waste biochar-chlorosulfonic acid (PWB-ClSO3H), and 97.4% for palm waste biochar - sulphuric acid (PWB-H2SO4), whereas FAME yields were 88.6% (PWB-(NH4)2SO4), 89.1% (PWB-ClSO3H), and 96.1% (PWB-H2SO4). It was observed that PWB-H2SO4 has the best catalytic activity, which was directly linked to its high acid density (11.35 mmol/g), improved pore diameter (6.25 nm), and increased specific surface area (372.01 m2 g−1). PWB-H2SO4 was used for the reusability study, where it underwent eight reaction runs and was stable until the seventh run. PWB-H2SO4 has shown huge promise for biodiesel synthesis, owing to its easy synthetic process, recyclability, and high catalytic activity for waste oils and fats.

Sulfonated kenaf seed cake (SO3H-KSC) catalyst, was synthesized to aid biodiesel production from palm fatty acid distillate (PFAD). It was chemically activated with phosphoric acid for an impregnation period of 24 h in order to enhance the porosity and the specific surface area of kenaf seed cake (KSC). After the carbonization and sulfonation, the resultant catalyst was characterized with powder X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscope (FESEM), NH3-temperature programmed desorption (NH3-TPD) and thermogravimetric analysis (TGA). The SO3H-KSC catalyst was amorphous in nature and had an acid density of 14.32 mmol/g, specific surface area of 365.63 m2/g, pore volume of 0.31 cm3/g and pore diameter of 2.89 nm. At optimum esterification conditions--reaction time 90 mins, temperature of 338 K, methanol:PFAD molar ratio of 10:1 and catalyst concentration of 2 wt.%—a free fatty acid (FFA) conversion of 98.7% and fatty acid methyl esters (FAME) yield of 97.9% was achieved. The synthesized SO3H-KSC catalyst underwent five reaction cycles while maintaining a fatty acid methyl esters (FAME) yield and free fatty acid (FFA) conversion of >90%. Thus, the SO3H-KSC catalyst was shown to be an excellent application of bio-based material as a precursor for catalyst synthesis for esterification of PFAD.

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