A diffusion model for the impregnation of lignocellulosic materials

Chip impregnation is essential to achieve a uniform distribution of active chemicals throughout the wood matrix prior to rapid pulping. To determine the rate at which chemicals penetrate the wood chips through the radial and axial directions, an impregnation-diffusion model was developed based on experimental data. The diffusion coefficient—a function of both temperature and pressure—increases with pressure at a power of 0.38 in the radial direction and 0.54 in the axial direction. The coefficient increases exponentially with temperature, following an Arrhenius-type correlation. Activation energy for radial and axial thermal diffusion was 2.8 and 3.2kJ/g·mole, respectively, while the frequency factors were 2.7 x 10–7 and 113.3 x 10–7 cm2/s/K1/2, respectively. The results indicate that impregnation of chemicals proceeds readily via axial diffusion and is not strongly dependent on temperature.