Synthesis of sulfonated bio-based catalysts for the esterification of palm fatty acid distillate

The synthesis of sulfonated of bio-based catalysts from palm seed cake (PSC), sugarcane bagasse (SCB) and kenaf seed cake (KSC), for the esterification of palm fatty acid distillate (PFAD), have been demonstrated in this work. The derived biomass materials were subjected to different levels of pretreatment that is triggered by the chemical activation period over ortho-phosphoric acid. The pretreated biobased materials were calcined at different temperatures in a nitrogen controlled atmosphere for about 2 to 5 h at 400 OC. The average SULFONATION time and temperature were between 5 to 12 h and 230 ᵒC. Whereas, the volume of the sulfonating agents used were between 100 – 250 mL in concentrated form. The synthesized biobased catalysts were further characterized in terms of their active acid sites using the ammonia-temperature programmed desorption (NH3-TPD), field emission scanning electron microscopy (FESEM) to confirm the morphology, the Brunauer, Emmett and Teller (BET) analysis to ascertain the surface area definition. To ensure the attachment of the functional group (–SO3H) attachment, the fourier transform infrared (FTIR) analysis was carried out, while the thermal stability of the catalyst was checked using the thermogravinometric analysis (TGA) and X-ray dispersion (XRD) to validate the amorphous nature of the catalysts. These catalysts; sulfonated - soaked palm seed cake (SPSC-SO3H), kenaf seed cake (SO3H-KSC) and sugarcane bagasse (SCB-SO3H), showed enhanced catalytic properties. The SPSC-SO3H had an acid density of 12.08 mmol/g and a specific surface area of 483.07 m²/g while the SO3H-KSC had an acid density of 14.32 mmol/g, specific surface area of 365.63 m²/g and the SCB-SO3H recorded an acid density of 5.63 mmol/g and specific surface area of 298.34 m²/g and this is as a result of the pretreatment processes, highlighting the novelty of this work. The palm waste biochar was further used for the appraisal of sulfonation processes, where three corresponding catalysts were appraised; ammonium sulphate – palm waste biochar (PWB- (NH4)2SO4) catalyst, chlorosulfonic–palm waste biochar (PWB-ClSO3H) catalyst and sulfuric – palm waste biochar (PWB - H2SO4) catalyst. The optimized esterification reaction conditions for SPSC-SO3H were 60 ᵒC reaction temperature, 2 h reaction time, 9:1 methanol:PFAD molar ratio and 2.5 wt % catalysts weight, with a- free fatty acid (FFA) conversion of 98.2 % and fatty acid methyl ester (FAME) yield of 97.8 %. Whereas, for SO3H-KSC catalyst, 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.%—an FFA conversion of 98.7% and FAME yield of 97.9% was achieved. For the SCB-SO3H, at optimum reaction conditions of; reaction time 1.5 h, reaction temperature 60 °C, catalyst loading 2 wt.% and methanol:PFAD molar ratio 10:1; a FAME yield of 98.6% was achieved. The SCB-SO3H was used for six reaction cycles. The fuel properties of produced biodiesel where appraised and compared with biodiesel EN 14214 and ASTM D-6751 standard limits. The PFAD methyl ester was further blended with petro-diesel from B0, B3, B5, B10, B20 and B100, on volumetric basis. The blends were characterized by TGA, DTG and FTIR. With acid value of 0.42 (mg KOH/g), iodine value of 63 (g.I2/100g), kinematic viscosity of 4.31 (mm²/s), the PFAD methyl ester has shown good fuel potential, as all of its’ fuel properties were within the permissible international standards for biodiesel. Overall, the synthesized biobased catalysts have shown impressive thermal stability, high specific surface area, improved pore diameter and pore volume, high yield and conversions and ability to run multiple reaction cycles. Sulfuric acid have also been proven to be a good sulfonating agent and the palm biomass showed better properties as a precursor than kenaf and sugarcane bagasse. These catalysts have also demonstrated a great potential to catalyze high FFA feedstock such as PFAD for the production of biodiesel while also maintaining good reusability. The success of the biobased catalysts is attributed to the attachment of sulfonic group (-SO3H) on the surface of the biobased materials. The fuel properties of the synthesized biodiesel also showed great positive outcome as the blends show similar fuel properties as compared to the petroleum fuel.

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