(655a) Catalytic Etherification of Glycerol to Glycerol Oligomers in the Presence of Alumina Supported Ca/Sr Mixed Oxides

In this work, the solvent-less
etherification of glycerol to oligomers using alumina supported Ca and Sr
catalysts was studied. These catalysts were obtained with impregnation of
strontium and calcium onto γ-alumina (γ-Al₂O₃)
in Sr(NO₃)₂ and Ca(NO₃)₂ solutions. The evidence for synergistic
effects between active Ca and Sr species was demonstrated by etherification
tests over a series of Ca-Sr-Al catalysts with varied Ca-to-Sr molar ratios. Effect of calcination temperatures of these supported catalysts,
from 600 °C to 900 °C, on the resultant reusability and conversion efficiency
of glycerol to oligomers and the selectivity of linear and branched oligomer to
cyclic ones were investigated. The catalyst properties
were characterized by various
instruments including BET, TPD, XRD and SEM, and the ICP-OES analysis was performed to confirm the leaching of the
metal species in the liquid phase of the reaction mixture. With Ca and Sr
supported on γ-alumina catalyst, the catalyzed etherification reactions
were carried out at 250 °C with 2.5 wt% Ca/Sr/γ-alumina calcined at 900 °C
in nitrogen atmosphere. Under optimal impregnation conditions, a conversion
efficiency of glycerol 80 % glycerol could be obtained after 10-h reaction. Moreover,
a selectivity near 70% of di- and tri-glycerol in linear and branched forms
over the cyclic form could be achieved.