Glycerol polymerization over stable and selective calcium hydroxyapatite

High catalytic activity and large availability of Ca-based catalysts make them particulartly attractive for the glycerol polymerization reaction. However, this kind of catalyts usually suffers from a poor stability under the reactions conditions. We present herein the use of Ca-hydroxyapatites (HAps), a very abundant Ca source in the nature, as glycerol polymerization catalysts combining high performance in terms of selectivity and high resistance to deactivation by leaching. We have synthesized, characterized and tested Ca-rich, stochiometric and Ca-deficient HAps. The two latter ones were fully selective to triglycerol at a glycerol conversion of 15 %, at 245 °C after 8 h in the presence of 0.5 mol.% of catalyst. Under the same reaction conditions, the Ca-rich HAp was highly selective to di- and triglycerol (88 %) at a glycerol conversion of 27 %. All the catalysts proved to be stable with negligible Ca species leaching according to the ICP-OES results.