Evaluation of chlorine dioxide as a supplementary pretreatment reagent for lignocellulosic biomass.

Chlorine dioxide (ClO2) is a bleaching reagent used in paper industry. Two different types of pretreatment methods were investigated incorporating ClO2 as a secondary reagent: (a) alkaline followed by ClO2 treatment; (b) dilute-sulfuric acid followed ClO2 treatment. In these methods, ClO2 treatment has shown little effect on delignification. Scheme-a has shown a significant improvement in enzymatic digestibility of glucan far above that treated by ammonia alone. On the contrary, dilute-acid followed by ClO2 treatment has shown negative effect on the enzymatic hydrolysis. The main factors affecting the enzymatic hydrolysis are the changes of the chemical structure of lignin and its distribution on the biomass surface. ClO2 treatment significantly increases the carboxylic acid content and reduces phenolic groups of lignin, affecting hydrophobicity of lignin and the H-bond induced association between the enzyme and lignin. This collectively led to reduction of unproductive binding of enzyme with lignin, consequently increasing the digestibility.

Effect of thermal pretreatment on equilibrium moisture content of lignocellulosic biomass.

The equilibrium moisture content (EMC) of raw lignocellulosic biomass, along with four samples subjected to thermal pretreatment, was measured at relative humidities ranging from 11% to 97% at a constant temperature of 30 °C. Three samples were prepared by treatment in hot compressed water by a process known as wet torrefaction, at temperatures of 200, 230, and 260 °C. An additional sample was prepared by dry torrefaction at 300 °C. Pretreated biomass shows EMC below that of raw biomass. This indicates that pretreated biomass, both dry and wet torrefied, is more hydrophobic than raw biomass. The EMC results were correlated with a recent model that takes into account additional non-adsorption interactions of water, such as mixing and swelling. The model offers physical insight into the water activity in lignocellulosic biomass.