Physico-Chemical Evolution in Lignocellulosic Feedstocks During Hydrothermal Pretreatment and Delignification

Lignocellulosic feedstocks are potential resources for renewable fuels. However, the cross-linked and hydrophobic lignin makes the biomass recalcitrant to acids and enzymatic conversion. This study investigates the effect of hydrothermal pretreatment and delignification on lignocellulosic biomass from forestry (pinewood), agriculture (wheat straw) and energy crop systems (timothy grass). In order to understand their physico-chemical properties, the pretreated and delignified feedstocks were characterized through carbon-hydrogen-nitrogen-sulfur analysis, thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, atomic force microscopy, Fourier transform infrared spectroscopy and Raman spectroscopy. Hydrothermal pretreatment caused remarkable loss of hemicelluloses (up to 68.4%) and intense lignin re-localisation. Delignification of feedstocks led to significant removal of lignin by 95.9% and exposed the interwoven cellulose fibers. As a result of the removal of hemicelluloses and lignin, cellulose concentration increased by 28.4% in hydrothermally treated feedstocks and 61.4% in delignified feedstocks, respectively. The amplification in cellulose content in delignified feedstocks suggested enhanced accessibility of cellulolytic enzymes for improved bioconversion.