Chip scale modelling of the kraft pulping process by considering the heterogeneous nature of the lignocellulosic feedstock

This article focuses on a multiscale modelling approach to describe the delignification of softwood during the kraft pulping process. A framework for modelling the lignocellulosic feedstock on a fibre scale which considered the fundamental chemical components of wood as a distributed variable is re-assessed and extended to include chip-level phe-nomena such as diffusion limitations and initial component distributions within a soft-wood chip mixture. A new description of the wood chip is presented using a finite volume discretisation along one spatial dimension by simultaneously considering the anisotropic structural differences of the wood. Additionally, based on literature data, a distinction between the softwood chips' early-and latewood regions with their differences in den-sities and chemical composition is suggested. The presented model framework uses published sub-models for kinetics, diffusion etc. The validation and estimation of the remaining parameters are conducted from experimental data that quantifies the kappa number distribution of individual softwood fibres after kraft pulping. The investigation hypothesises a Gaussian distribution for the initial chemical component distribution within wood chips from a well-defined region. In contrast, a Log-normal distribution is used to describe the initial chemical distribution within a softwood chip mixture. The established sub-models for the kraft pulping process's kinetics and mass transfer phe-nomena could not predict the experimental data satisfactorily. However, modifying the sub-models by including a change in lignin reactivity and a temperature dependency of the lignin reactivity decline during the delignification progress could predict the essence of the observed experimental kappa number distribution.& COPY; 2023 The Author(s). Published by Elsevier Ltd on behalf of Institution of Chemical Engineers.

Automated summary

This article focuses on a multiscale modelling approach to describe the delignification of softwood during the kraft pulping process. The model framework considers the chemical components of wood, diffusion limitations, and initial component distributions within a softwood chip mixture. The sub-models for the kinetics and mass transfer phenomena of the kraft pulping process were modified to better predict the experimental data.