Interactions between cellulose and lignin during pyrolysis: Evolutions of condensed-phase functional groups and gas-phase volatile fraction

Understanding cellulose-lignin interactions during biomass pyrolysis is important to improve the overall product distribution and quality. In the current study, the condensed-phase cellulose-lignin interactions during biomass pyrolysis from 100 degrees to 600 degrees C were systematically investigated with in-situ diffuse reflectance infrared Fourier transform spectroscopy and modified perturbation correlation moving-window two-dimensional correlation spectroscopy. It was found that compared to the individual component pyrolysis, the decomposition peak, evident by thermogravimetric analysis, of cellulose-lignin co-pyrolysis became wider and shifted to higher temperature range. The cellulose-lignin interactions further promoted the formations of char, and H2O, CH3/ CH2, C--O, aromatic-containing compounds. With simultaneous IR identification of gaseous products and condensed-phase remaining, the detailed interaction mechanism was elucidated as: 1) hydrogen donation from cellulose hydroxyl to lignin C alpha could promote the lignin rearrangement at low temperature range through quinone methide structure; 2) the reactive species from homolytic cracking of lignin could abstract hydrogen from CH/CH2 groups of cellulose to generate phenolic compounds; 3) dehydration reactions of cellulose was therefore enhanced to promote char formation.