This work explores the interplay between reaction and mass transfer kinetics during kraft pulping of birch wood meal. A novel delignification model has been developed, incorporating molecular weight-based diffusivities alongside traditional reaction kinetics to describe delignification at the cell wall level. Laboratory-scale reactor experiments provided pulping data for model validation at a range of industrially relevant process conditions. The developed model successfully described the delignification behavior during both constant and transient process conditions. By fitting the model to experimental data, the calculated rate constants (for both reaction and diffusion) revealed that the rate of delignification at the cell wall level is controlled by the diffusion of dissolved lignin. The results provide a plausible explanation to the slow rate of delignification at the end of the cooking operation. Furthermore, the reaction rate may also be limited by the access to OH^– within the cell wall even during wood meal pulping.

中文翻译：

---

细胞壁水平 Kraft 脱木素的异质扩散和反应模型


这项工作探讨了桦木粉牛皮纸制浆过程中反应动力学和传质动力学之间的相互作用。已经开发了一种新的脱木素模型，将基于分子量的扩散率与传统反应动力学相结合，以描述细胞壁水平的脱木素。实验室规模的反应器实验为在一系列工业相关工艺条件下的模型验证提供了制浆数据。开发的模型成功地描述了恒定和瞬态工艺条件下的脱木素行为。通过将模型与实验数据拟合，计算的速率常数（对于反应和扩散）表明细胞壁水平的脱木素速率受溶解木质素扩散的控制。结果为烹饪操作结束时缓慢的脱木素速度提供了一个合理的解释。此外，即使在木粉制浆过程中，反应速率也可能受到细胞壁内 OH^– 的接近的限制。