Polyol Preparation by Liquefaction of Technical Lignins in Crude Glycerol

This work reports a study of polyol synthesis through liquefaction of technical lignins in crude glycerol by means of ¹H and ³¹P NMR spectroscopy. The polyols are intended for preparation of polyurethane foam; thus, it is important to know how different lignin types as well as crude glycerol influence and contribute to the final polyol hydroxyl contents. Polyols prepared from organosolv lignin, kraft lignin and lignosulphonate had hydroxyl numbers suitable for rigid foam of 435, 515 and 529 mgKOH/g, respectively. The polyols differed in composition with glycerol, showing significant variation. During liquefaction the glycerol content was mostly reduced through bonding with lignin, and to a lesser extent monoacylglycerol and diacylglycerol formation through transesterification with fatty acid ethyl esters. It is concluded that crude glycerol can potentially replace petroleum-derived polyols as liquefaction solvent and that different types of technical lignin have a strong impact on the resulting bio-based polyol hydroxyl contents.