Transesterification of soybean oil on guanidine base-functionalized SBA-15 catalysts

SBA-15 functionalization with the guanidine base 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) was used to prepare TBD-grafted catalysts for the soybean oil transesterification reaction. The structural and textural features of both the support and the catalysts were investigated by X-ray diffraction, transmission electron microscopy, and nitrogen physisorption. CHN analysis and FTIR characterization were also carried out on the catalysts before and after reaction. Potentiometric titration was also used to confirm CHN analysis data for the fresh catalysts. Mild conditions (atmospheric pressure and 343 K) were chosen for catalytic testing in a batch reactor. The influence of the base content and the reaction time on the methyl esters yield was investigated. All the catalysts were found active for the soybean oil conversion. Comparison with the catalytic behaviour of a commercial TBD-grafted polymer showed a superior performance of the functionalized SBA-15 catalysts. The higher the functionalization extent, the higher the activity, just a few hours being required for a 100 mol% methyl esters yield. Over such a short reaction time leaching was observed to occur only to an extremely low extent, which makes possible to reuse the catalysts after a regeneration step consisting in a simple NaOH treatment of the recovered samples. During such treatment the catalyst base sites – poisoned (through protonation) by the free fatty acids – are freed, and their activity is restored.