Kinetics of Strong Acid Hydrolysis of a Bleached Kraft Pulp for Producing Cellulose Nanocrystals (CNCs)

Abstract

Cellulose nanocrytals (CNCs) are predominantly produced using the traditional strong acid hydrolysis process. In most reported studies, the typical CNC yield is low (approximately 30%) despite process optimization. This study investigated the hydrolysis of a bleached kraft eucalyptus pulp using sulfuric acid between 50 and 64 wt % at temperatures of 35–80 °C over time periods of up to 240 min for the production of CNCs. The experimental design captured the feature of the coexistence of a variety of reaction products, such as CNC, cellulosic solid residue (CSR), glucose, and xylose, in the product stream for accurate kinetic modeling to improve the CNC production yield. The kinetic model describing the solubilization of cellulose fibers used three phenomenological reactions, namely, hydrolysis of xylan to form xylose, depolymerization of cellulose to CNCs, and hydrolysis of cellulose to form glucose, each of which can be described by pseudohomogenous first-order kinetics. The concept of “degrees of hydroly...