Delignification and degelation: Analogy in chemical kinetics

Structurally and kinetically, chemical pulping can be treated as a degelation process. Kinetics derived from the empirical power law is rejected on the grounds that lignin is a polymer. Using an extended version of the Flory–Stockmayer theory and a kinetic expression derived by Whittle, the delignification kinetics is expressed in terms of opposing unimolecular–bimolecular reactions. The quantity replacing lignin concentration is the “extent of reaction” defined in the theory. Parameters used in this reaction are estimated, and the time dependence of the undissolved lignin fraction can be calculated. The calculated delignification curve is shown to be in good agreement with experimental results.