In recent years, use of glycerol as a renewable raw material for the chemical industry has received considerable attention. One interesting reaction is the catalytic oligomerization of glycerol yielding highly hydrophilic molecules. The resulting oligo-glycerols are an interesting class of chemicals that exhibit a broadrange of applications in various industrial sectors such as cosmetic, food and pharmaceutic industries It is a difficult reaction mainly because of the difficulty to closely control the reaction selectivity. Oligomerization of glycerol can be heterogeneously or homogeneously-catalyzed either by bases or acids. Under basic conditions, high temperature are generally required (T > 220°C) leading to the competitive dehydration or dehydrogenation of (oligo)glycerol. On the other hand, under acid conditions, side dehydration of (oligo)glycerol to readily polymerizable substrates occurs which represent an important limitation of this route. In this study we screen various homogeneous acid catalysts and Aquivion®PFSA PW98 a solid superacid catalyst. Under optimized conditions, a mixture of oligoglycerol with an average degree of oligomerization of 3.4 was obtained at a glycerol conversion of 80% in the presence of metal triflates catalyst. At such conversion, the selectivity to oligoglycerols was higher than 90%. In the presence of Aquivion®PFSA PW98 wasnearly fully selective to oligoglycerols up to 80% conversion of glycerol was selectively converted to and Aquivion®PFSA PW98 was found highly robust and was sucessfully recycled at least 10 times.
