Novel catalysts derived from hydrothermally synthesized phyllosilicates for the selective preparation of glycerol ethers or esters

Novel catalysts derived from hydrothermally synthesized
phyllosilicates for the selective preparation of glycerol ethers or esters

S. VALANGE, M.V. SIVAIAH, J. BARRAULT and S. PETIT

Institute of Chemistry, Naturals and Materials, IC2MP/UMR CNRS 7285, Catalysis and Renewables, ENSIP, 1 rue Marcel Doré, 86022 Poitiers, France

The increasing availability of glycerol coupled to its high functionalization possibilities makes it one of the most promising platform chemicals of the near future. In fact glycerol is the by-product with the largest economic impact in the modern oleochemical industry, being formed in numerous processes. Among the large panel of applications, the selective synthesis of polyglycerols (PGs) followed by polyglycerol esters (PGEs) preparation is gaining more importance. These products, because of the possibility of controlling their hydrophilic-lipophilic balance (HLB) are of great interest in cosmetics, food and pharmaceutical industry. The synthesis of PGs starting from glycerol and esterification of PGs are generally carried out in the presence of homogeneous basic catalysts (eg. Na2CO3). However, active solid base catalysts that are selective and easily recovered/recycled are better suited for environmentally friendly catalytic processes. Recently, alkaline earth based oxides/hydroxides have been emerging as heterogeneous catalysts for the etherification of glycerol to polyglycerol. For example, Mg supported or incorporated in MCM-41-based materials were successfully used as catalysts for this reaction, despite significant amount of acrolein (side product) was generated for some of them. Moreover, rather long reaction times were necessary for Mg incorporated MCM-41 catalysts to reach a significant glycerol conversion even at high temperature (260 °C). Very recently, it was also observed that alkali earth based oxides readily reacted with glycerol, which resulted in the formation of the corresponding metal-glyceroxide phases during glycerol etherification reaction.
We therefore evaluated the ability of hydrothermally synthesized Mg-containing phyllosilicates as novel catalysts to increase the catalytic performances (selectivity and stability) for glycerol etherification to polyglycerols. Such phyllosilicates (PS) are layer structured materials and are mostly represented as 1:1 or 2:1 phases. In 1:1 phyllosilicates, each layer consists in one tetrahedral sheet (with tetracoordinated cations) and one octahedral sheet (with hexacoordinated cations). In the case of 2:1 phyllosilicate type, the octahedral sheet sandwiched in between two tetrahedral sheets.
We will show that these new Mg-based phyllosilicates, in particular the 1:1 analogs, are more active in the selective synthesis of glycerol ethers or esters than the previously used catalysts, while keeping a high selectivity to a (di-tetra glycerol) fraction. We will also demonstrate that such Mg 1:1 PS phases are reusable, which is also a crucial property in catalysis.

Acknowledgements
This work was supported by ANR under the NANOCAT consortium (ANR-06-MAPR-0023-01). The author (MVS) gratefully acknowledges the CNRS/ANR for the awarding of postdoctoral fellowship.