Modelling of reaction kinetics in production of hydroxy carboxylic acids by alkaline degradation of cellulosic waste

Abstract

The reaction kinetics in alkaline degradation of cellulosic materials to monomeric compounds at elevated temperatures was studied. The target compounds are hydroxy carboxylic acids, preferably glucoisosaccharinic acid (GISA), that are valuable platform chemicals. This methodology, which focuses on depolymerizing cellulosic materials and transforming them into hydroxy carboxylic acids, has not been explored in existing literature. To this end, a rigorous mathematical model was developed that considers phenomena at macroscopic level (transformation of crystalline cellulose into amorphous) and at microscopic level (cleavage of glycosidic bonds). Experimental cellulose degradation data in 10 wt-% NaOH and 20–200 °C was correlated with the model. The agreement between the model results and the experimental data confirmed that the process obeys the proposed reaction pathway. Around 80 % of degradation occurs during the reactor warming up period. Analysis of rate constants indicates that GISA is not degraded into smaller hydroxy acids (SHA) at the temperatures studied. Instead, monosaccharides are converted into SHA as soon as they are produced. Conversion of crystalline cellulose into amorphous form was identified as the rate determining step.