Selective oligomerization of glycerol over mesoporous catalysts

In the general context of the development of the use of agricultural products for nonfood applications, particularly in the field of glycerol valorization (coproduct of triglyceride hydrolysis and methanolysis processes), the selective etherification of glycerol to di- and triglycerol was studied. Part of this study consisted in the synthesis and the modification, by different techniques, of cesium containing mesoporous solids of the MCM-41 type in order to make them active, selective and stable catalysts for the target reaction. The catalytic results obtained show that the impregnation method gives the highest activity. Concerning the selectivity of the modified mesoporous catalysts, the best values to (di- + tri-) glycerol (>90%) are obtained over solids prepared by the impregnating or the grafting methods. The cesium-impregnated catalysts can be reused without loss of selectivity. In the presence of lanthanum- or magnesium-containing catalysts, the glycerol dehydration to acrolein is important, whereas this unwanted product is not formed when cesium is used as promoter. Moreover, when compared to homogeneous catalysts, the mesoporous solids induce a different regioselectivity. Finally, as far as the catalyst leaching and stability is concerned, the best results are obtained with the grafted solids, which retain their structure and their specific area after the promoter addition or incorporation. Such property is not observed over impregnated catalysts.