Impact of cellulose properties on its behavior in torrefaction: commercial microcrystalline cellulose versus cotton linters and celluloses extracted from woody and agricultural biomass

Abstract

Biomass composition on cellulose, hemicelluloses and lignin determinates its behavior in torrefaction (200–350 °C, default-oxygen atmosphere). Up to now, commercial microcrystalline cellulose was typically used to represent cellulose behavior in biomass torrefaction models based on macromolecular components. The objective of this work is to evaluate the impact of cellulose properties on its behavior in torrefaction, so as to identify the most suitable cellulose sample for modelling. To do this, five extracted celluloses from woody and agricultural biomass, commercial microcrystalline cellulose (Avicel) and four cotton linters tailored to different degrees of polymerization (DP) were considered. Cellulosic samples were deeply characterized in terms of fiber analysis, molar mass distribution (MMD), hydrodynamic behavior (SEC-RALS) and allomorphic structure. Cellulosic samples were torrefied in a thermogravimetric analysis up to two temperatures, leading to partial (300 °C) and total (350 °C) cellulose degradation. Extracted celluloses and Avicel cellulose degradation profiles showed strong differences at 300 °C. Polymer MMD, dispersity and the presence of residual hemicellulose sugars, especially xylose, strongly impacted cellulose degradation through torrefaction. Extracted celluloses presented high purity, narrow MMD and high DP, but a cellulose II structure due to mercerization. This cellulosic allomorph was shown to be more reactive, but it led to an identical final solid mass loss. The observed hydrodynamic behavior and the probable preservation of cellulose amorphous areas from native cellulose may also influence polymer structural behavior in torrefaction. Finally, at least one-order-of-magnitude DP variation was shown to be required to see an impact in cellulose degradation profile through torrefaction.