Tuning of diglycerol yield and isomer distribution in oligomerization of glycerol supported by DFT-calculations

Diglycerol (DG) is a useful compound for food, cosmetic and chemical applications being available from cheap glycerol of biodiesel manufacture. Homogeneous catalyzed conversions led to a distribution of the three isomers (58(alpha alpha') : 35(alpha beta) : 7(beta beta'); glycerol conversion (X) = 55%, DG yield (Y-DG) = 40%; 7 h). This can be shifted in favor of alpha beta-DG by using basic zeolites (e.g. CsX, 24(alpha alpha') : 52(alpha beta) : 24(beta beta'); X = 70%, Y-DG ca. 45%; 8 h). Otherwise, acidic Nafion(R) catalyst revealed 69(alpha alpha') : 27(alpha beta) : 4(beta beta') distribution (X = 93%, Y-DG ca. 68%; 24 h) using a falling film reactor under reduced pressure. (C) 2011 Elsevier B.V. All rights reserved.