Diffusion of Soluble Lignin out of Chips During Magnesium Bisulfite Pulping, 2000 Pulping / Process & Product Quality Conference Proceedings

J. Li, A. R. van Heiningen--The diffusion of degraded, soluble lignin in wood chips during magnesium bisulfite pulping was simulated numerically by solving the unsteady, one-dimensional diffusion with reaction equation. The effective diffusion coefficient of the soluble lignin was obtained by comparison with experimental results of the lignin concentration in solution for Magnefite cooks performed on wood shavings and regular black spruce chips. The calculated diffusion coefficients at 155, 165 and 175°C are 2.78 x 10 -10 , 6.67 x 10 -10 and 1.39 x 10 -9 m 2 /s respectively. The strong temperature dependence suggests that the diffusion of soluble lignin in wood chips during magnesium bisulfite pulping can be described by an ’activated’ diffusion mechanism. The activation energy of diffusion was found to be 128 kJ/mol. The implications for controlling magnesium bisulfite cooking by measurement of the dissolved lignin concentration in the cooking liquor are discussed.