Alkaline Pulping of Hemp Woody Core: Kinetic Modelling of Lignin, Xylan and Cellulose Extraction and Degradation

Abstract

The kinetics of alkaline degradation of lignin, xylan and cellulose in relation to pulp yield were studied for hemp woody core to support development and optimization of a non-polluting alkaline pulping process. Shavings of hemp woody core were impregnated at room temperature with various sodium hydroxide concentration (0.25-2 M NaOH) and delignified isothermally at various reaction temperatures (150-180°C) in a flow-through reactor. Extraction and degradation of xylan from hemp woody core was strongly depending on the NaOH concentration used. Consequently, to attain a certain lignin content, lower NaOH concentrations result in higher pulp yields. Extended pulping diminished the differences in pulp yields, due to further xylan degradation. The kinetics of lignin, xylan and cellulose degradation were modelled as a function of reaction time, temperature and NaOH concentration. The combined models resulted in a pulp yield model for hemp woody core, suitable for process optimization purposes. Degradation kinetics of perennial wood can be modelled similarly, which was illustrated using literature data on spruce and poplar.