New catalysts for biodiesel additives production

Mesoporous silicate and metallosilicate (Al or Nb) materials of SBA-15 type were prepared in the presence of MPTMS, i.e. (3-mercaptopropyl)trimethoxysilane, and hydrogen peroxide. The samples prepared were characterised by different techniques (N2 adsorption/desorption, XRD, XRF, elemental analysis, thermal analysis, FTIR, UV–Vis) and applied as catalysts in glycerol esterification with acetic acid. The impact of different factors such as temperature, glycerol to acetic acid molar ratio, and metal concentration on the course and yield of glycerol esterification was examined. The role of niobium in the formation of sulphonic species was considered and discussed. The most important finding is that niobium source present in the SBA-15 synthesis gel together with MPTMS and H2O2 improves the efficiency of –SH oxidation towards sulphonic species and increases the stability of the modifier (oxidised MPTMS), which results in increased activity and selectivity of the catalysts to triacetylglycerol in esterification of glycerol.

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► Niobium species in NbSBA-15 enhance the effectiveness of active centres formation.
► Presence of niobium stabilizes the sulphur containing modifier.
► Niobiosilicate effectively directs the esterification of glycerol towards triacetylglycerol.
► Active phase is not leached during the reaction allowing reuse of the catalysts.