Quantitative solid state NMR analysis of residues from acid hydrolysis of loblolly pine wood

The composition of solid residues from hydrolysis reactions of loblolly pine wood with dilute mineral acids is analyzed by ¹³C Cross Polarization Magic Angle Spinning (CP MAS) NMR spectroscopy. Using this method, the carbohydrate and lignin fractions are quantified in less than 3 h as compared to over a day using wet chemical methods. In addition to the quantitative information, ¹³C CP MAS NMR spectroscopy provides information on the formation of additional extractives and pseudo lignin from the carbohydrates. Being a non-destructive technique, NMR spectroscopy provides unambiguous evidence of the presence of side reactions and products, which is a clear advantage over the wet chemical analytical methods. Quantitative results from NMR spectroscopy and proximate analysis are compared for the residues from hydrolysis of loblolly pine wood under 13 different conditions; samples were treated either at 150 °C or 200 °C in the presence of various acids (HCl, H₂SO₄, H₃PO₄, HNO₃ and TFA) or water. The lignin content determined by both methods differed on averaged by 2.9 wt% resulting in a standard deviation of 3.5 wt%. It is shown that solid degradation products are formed from saccharide precursors under harsh reaction conditions. These degradation reactions limit the total possible yield of monosaccharides from any subsequent reaction.