Signatures of Biologically Driven Hemicellulose Modification Quantified by Analytical Pyrolysis Coupled with Multidimensional Gas Chromatography Mass Spectrometry

Biomass storage conditions are a major source of feedstock quality variability that impact downstream preprocessing, feeding, handling, and conversion into biofuels, chemicals and products. Microbial activity in the stored biomass can result in heating that can modify or degrade the cell walls of the biomass, changing its characteristics. Analytical pyrolysis has been used to characterize biomass, but at temperatures typically used (∼600 °C), the differentiation of samples having different storage histories is subtle or nonexistent. In this study, lower-temperature (400 °C) pyrolysis was used to show large differences in corn stover samples that had experienced different biological heating histories, indicated by pyrolysis products that were identified and, in several cases, quantified using two-dimensional gas chromatography/mass spectrometry. Pyrolysis of the samples originating from biomass that had experienced biological heating during storage generated small oxygenates such as furfural, 5-methyl furfural, and 2-(5H)-furanone with efficiencies that were as much as ten times greater than those measured for samples that were not significantly heated. Most of the pyrolysis products with enhanced efficiencies were C5 oxygenates, suggesting formation from hemicellulosic precursor polymers in the corn stover. The findings suggest that biological heating disrupts the cell wall structure, fragmenting the hemicellulose or cellulose chains and generating more polymer termini that have a higher efficiency in the generation of oxygenates at lower temperatures. Further, analytical pyrolysis conducted at lower temperatures may be a beneficial strategy for improved biomass cell wall characterization and the provision of insights to understand and manage the feedstock variability and inform harvest and storage best management practices.