Systematic diffusion-ordered spectroscopy for the selective determination of molecular weight in real lignins and fractions arising from base-catalyzed depolymerization reaction mixtures

The valorization of biorefinery downstream lignin fractions is a key issue in increasing the sustainability of second-generation biofuels. The development of reliable methodologies for the selective determination of the apparent masses of the poly(hydroxy)-aromatic ethers arising from lignin depolymerization reaction is crucial. Diffusion-ordered spectroscopy (DOSY) has been tested to estimate the molecular weight in downstream biorefinery lignins and base-catalyzed depolymerization reaction mixtures. Excellent correlation was found in the calibration of molecular weight and diffusion coefficients with standards. DOSY permitted the selective estimation of the apparent masses of different fractions in the lignin and in the depolymerization reaction mixtures, providing a more profound knowledge of the reaction mixture composition than that obtained with traditional size-exclusion chromatography (SEC). Excellent correlations have been achieved in the estimation of the apparent masses of poly(hydroxy)-aromatic ethers between SEC and DOSY. This permits a reliable estimation of the molecular weight of different fractions in the lignin and in the depolymerization product, which is essential for their further applications.