Diglycerin und höhere Oligomere des Glycerins als Synthesebausteine

High Functionality Polyether Polyols Based on Polyglycerol

Polyglycerol (PGL) is a polyhydroxyl compound obtained by selfcondensation of glycerol in the presence of alkaline catalysts. It is a very attractive polyol as a starter for the synthesis of polyether polyols for rigid polyurethane foams. It is liquid, easy to handle and has a very high average functionality of 4—20 (or more) hydroxyl groups/mol. By propoxylation of PGL or PGL—sucrose mixtures, we obtained new polyether polyols with very high functionalities, which are very difficult or impossible to obtain by other methods. A new technology for PGL-based polyether polyols preparation was investigated. In the first step the self-polycondensation of glycerol to PGL in the presence of potassium hydroxide or potassium methoxide as a catalyst was carried out. In the second step, the crude alkaline PGL was alkoxylated with PO without removing the catalyst, followed by purification of the resulting polyether polyols. Rigid polyurethane foams prepared from the synthesized PGL-based polyether polyols and crude MDI displayed good physical and mechanical properties, excellent dimensional stability, and low friability.

Glycerol upgrading over zeolites by batch-reactor liquid-phase oligomerization: heterogeneous versus homogeneous reaction

Glycerol upgrading to diglycerols in the presence of basic (Na+ or Cs+) ion-exchanged (FAU or BEA) zeolite catalysts was studied in a liquid-phase batch rector at 260 degrees C under normal pressure. Homogeneous NaHCO3 and CsHCO3 catalysts were studied for comparison. All the catalysts, including NaHCO3 and CsHCO3, displayed the same conversion-selectivity relationship. The selectivity to linear diglycerols decreased at higher conversions/reaction times owing to the consecutive formation of higher oligomers, with preferential further conversion of alpha,alpha'-diglycerol. The maximum yield of linear diglycerols was limited to about 30 %. The activities of the zeolites followed the order X>Y>Beta, independent of the alkali ion present. Catalysis by the zeolites starts with an induction period attributed to a slow leaching of alkaline cations from the zeolite. Thereafter, the reaction is characterized by a progressive loss of the microporous structure of the zeolite and increasing overlap of heterogeneous and homogeneous catalysis, where, primarily, the activity depends on the cation content of the zeolite.