A multi-scale model for diffusion of large molecules in steam-exploded wood

Patric Kvist,Tobias Gebäck,Anders Rasmuson

doi:10.1007/s00226-020-01185-2

Abstract

In this paper, multi-scale modeling was used to resolve diffusion in steam-exploded wood at tracheid scales including sub-micrometer features of bordered pits. Simulations were performed using the lattice Boltzmann method with high-resolution X-ray tomography image data as the input for the microstructure. The results show an effective method for utilizing a variable diffusion coefficient to implement two length scales. This circumvents the need to resolve the bordered pits in detail, which requires massive computing power. Instead, the effective diffusion coefficient for one bordered pit is used as input for this model. Results based on the present model are comparable to experimental data. This methodology can be extended to more structural features at the microscale of wood, such as latewood and the cell wall. Obtaining a map of different diffusion coefficients based on features and scale gives a better overall understanding of diffusion and the importance of mass transport with regard to the pretreatment of wood.

Highlights

A challenge for society today is to revert from and find alternatives to the fossilbased industry and aim for sustainable solutions
Pretreatment steps are required to make the cell wall more accessible for enzymes (Azhar et al 2011); the treatment must not be too harsh in order for the biopolymers not to degrade
The diffusion coefficient inside the space of the pits was based on a previous study by the authors (Kvist et al 2017), where the effect of steam explosion on a bordered pit was investigated

Summary

Introduction

A challenge for society today is to revert from and find alternatives to the fossilbased industry and aim for sustainable solutions. The dependence of the diffusion coefficient on multi-scale implementation of bordered pits in the microstructure of wood was investigated by utilizing lattice Boltzmann simulations. The diffusion coefficient inside the space of the pits was based on a previous study by the authors (Kvist et al 2017), where the effect of steam explosion on a bordered pit was investigated. Three more surfaces were created in the selected region of interest by increasing the threshold level of the image input data, increasing the number and size of the bordered pits This enabled a comparison of the importance of porosity and the size of the pits for the simulated results, while keeping the microstructure of the tracheids relatively constant. In the open pore space in the lumina, the coefficient will be the same, or 2 times, 4 times, and 10 times larger than that of the pit

Results and discussion

Conclusion

Compliance with ethical standards