The production of fuels and chemicals from biomass in liquid phase processes requires depolymerization of the polymeric feedstock. One of the most common approaches for this is hydrolysis in aqueous phase using acid or base catalysts. In the present work different acids (H₂SO₄, H₃PO₄, HNO₃, HCl, TFA) are compared as homogeneous catalysts for biomass hydrolysis. The influence of the proton concentration and the coordination of the corresponding anions to the biomass are investigated. The dissolution yield increased strongly with increasing temperature. In contrast, the effect of the acid concentration was surprisingly small.

A key focus of this work is the characterization of the non-hydrolyzed solid residue by ¹³C CP MAS NMR spectroscopy. The use of physical mixtures of cellulose and lignin as calibration standards allowed for quantification of the carbohydrate and lignin fractions in the solid residue. The quantitative spectroscopic results are confirmed by proximate analysis, which includes the determination of the lignin and saccharide content by the Klason method and HPLC after complete hydrolysis, respectively. In addition to being a fast and easy analysis method for the determination of the carbohydrate and lignin contents in biomass residues, ¹³C CP MAS NMR provides information about chemical modifications of the residues. It was shown that the formation of aliphatic side products becomes a significant reaction pathway at 473 K. The results are suggested to be quite useful for optimizing the process conditions for acid hydrolysis of woody biomass.

The aqueous phase was analyzed by LC. As expected, high concentrations of sugars were found after all reactions. The extent of degradation increased strongly with increasing temperature and increasing acid concentration (decreasing pH of the aqueous phase). The most important degradation pathway, yielding furfural and 5-hydroxymethyl furfural (HMF), will be discussed.