A DIFFUSION-MODEL FOR THE IMPREGNATION OF LIGNOCELLULOSIC MATERIALS

Chip impregnation is essential to achieve a uniform distribution of ac tive chemicals throughout the wood matrix prior to rapid pulping. To d etermine the rate at which chemicals penetrate the wood chips through the radial and axial directions, an impregnation-diffusion model was d eveloped based on experimental data. The diffusion coefficient-a funct ion of both temperature and pressure-increases with pressure at a powe r of 0.38 in the radial direction and 0.54 in the axial direction. The coefficient increases exponentially with temperature, following an Ar rhenius-type correlation. Activation energy for radial and axial therm al diffusion was 2.8 and 3.2 kJ/g.mole, respectively, while the freque ncy factors were 2.7 x 10(-7) and 113.3 x 10(-7) cm(2)/s/K-1/2, respec tively. The results indicate that impregnation of chemicals proceeds r eadily via axial diffusion and is not strongly dependent on temperatur e.