Transesterification of soybean oil catalyzed by Sr-doped cinder

•Sr-doped cinder catalyst was prepared and used for biodiesel synthesis.•A 99% of triglycerides conversion was achieved under optimal reaction conditions.•SrAl2Si2O8 and Sr5Al8O1 are determined as dominant compounds which are responsible for high catalytic activity.•Catalyst exhibits high activity and can be easily recovered and regenerated.•The Sr-doped cinder catalyst is used in 14 repeated runs.

The Strontium doped cinder was prepared using the wet impregnation method and analyzed as catalyst for biodiesel synthesis. Different procedure for cinder impregnation were investigated (temperature and duration of catalyst calcinations, the concentration of SrCl2 solution) and optimal condition was established: impregnation 20 g of cinder 2–5 mm particles with 0.2 M SrCl2 solution followed by calcinations at 1000 °C for 4 h. The Sr-cinder activity was tested at 90–200 °C using 1–5% mass of catalyst with different molar ratio of methanol to soybean oil (from 9 to 36). The maximum triglycerides (TG) conversion of 99.0% with the Fatty Acid Methyl Esters (FAME) yield of 97.1% was obtained by using 4% catalyst at 180 °C, for 1 h, and methanol/oil molar ratio 24:1. Influence of free fatty acid (FFA) and water in soybean oil on catalyst activity was analyzed, too. The catalyst could be used for 14 times with TG conversion and FAME yield above 90% and 80% respectively. The Sr-doped cinder catalysts before and after transesterification were characterized using BET surface area, basic strength, X-ray diffraction (XRD), scanning electron microscopy (SEM) and ICP-AAS. Results showed that the formation of SrAl2Si2O8 and Sr5Al8O17 complexes should be the main reason for the catalytic activity of prepared catalyst. Slow decrease of catalyst activity during its repeated use is result of Sr–Al-glycerolate formation in reaction between Sr–Al complexes and glycerol.

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