1D Multiscale Modeling of Delignification Rate in Hardwood Chips during Kraft Pulping

Journal article, 2026

This paper introduces a multiscale 1D model to describe the delignification inside hardwood chips during kraft pulping. The proposed approach combines our previously developed model encompassing the kinetics of lignin reaction and the transport of lignin fragments inside fiber walls (microscale) with the transport of alkali across the chip (macroscale). Validation was performed using experimental measurements of local lignin content inside birch chips subjected to batch kraft cooking. The results showed it was possible to capture the delignification behavior of the least accessible fibers by focusing on modeling the lignin removal along the thickness of the chip. Additionally, sensitivity analysis indicated the model was heavily influenced by parameters governing the availability of alkali at the chip macroscale. Moreover, similar to what has been reported for softwoods, the model suggests that a virtually uniform delignification could only be achieved under the studied conditions when using thin chips (thickness <2 mm).