Single-step esterification of crude karanj (Pongamia pinnata) oil to fatty acid methyl esters over mesostructured SBA-16 supported 12-molybdophosphoric acid catalyst

• Fatty acid methyl esters (FAME) were synthesized via karanj oil esterification.
• Molybdophosphoric acid anchored onto SBA-16 catalyst facilitated the reaction.
• 82.2% of FAME yield was achieved at 140 °C and after 5 h.
• The superior catalytic activity is most likely relevant to the Keggin anion density.
• Catalyst surface acidity plays a prominent role in promoting the catalytic activity.

Fatty acid methyl esters (FAME) are synthesized via the single step esterification of non-edible feedstock, crude karanj oil (CKO), of high level of free fatty acids (FFAs about 20%) with methanol over series of solid acid catalysts prepared by anchoring molybdophosphoric acid (MP, 5 to 25 wt.%) onto SBA-16 support. The prepared catalysts were intensively characterized for their intrinsic physicochemical and textural properties using BET surface area, NH3-TPD, XRD, SAXS, FT-IR, SEM and EDX. Characterization results revealed that the intact MP Keggin structure was preserved in the final catalyst after the thermal treatment at 220 °C. The catalyst with 15 wt.% MP (MP-S-16(15)) exhibited a peerless catalytic activity achieving 82% of FAME yield using a molar ratio of methanol to CKO of 1:8 at 140 °C and after 5 h. The effect of different operational parameters such as MP concentration in the final catalysts, reaction temperature, molar ratio of methanol to CKO, catalyst wt.% and reaction time were investigated over the MP-S-16(15) catalyst toward the maximum FAME yield. The stability of the catalytic activity was examined through leaching and reusability tests. As such, the MP-S-16(15) catalyst was recycled through four consecutive batch runs to understand its stability.