H2O2 bleaching in mixed triploid poplar and acacia woodchips high-yield pulping process with substitution of 50 wt% NaOH by MgO and its kinetics study
2021
Liu, Xin | Zhang, Bo | Hou, Qingxi | Wang, Xiaodi | Chen, Yunjing | Tao, Zhengyi
In the present work, the H₂O₂ bleaching with the substitution of 50 wt% NaOH by MgO as the alkali source in the high-consistency (HC) retention stage of mixed triploid poplar (Populus tomentosa Carr.) and acacia (Acacia confusa Merr.) woodchips P-RC APMP (preconditioning followed by refiner chemical treatment, alkaline peroxide mechanical pulp) was conducted. Meanwhile, the related bleaching reaction kinetics was well established. The obtained high-yield pulp presented a higher bleaching yield, improved bulk, favorable brightness and physical properties in comparison with the obtained pulp using 100 % NaOH as the alkali source. Most importantly, the chemical oxygen demand (COD) of the bleaching effluent was greatly decreased. The established bleaching kinetic equation is as following: dwdt=K[H2O2]3.63[NaOH]1.08[MgO]0.57[Na2SiO3]0.05w−1.89K= A·e–E/RT where the activation energy E =57.2 kJ/mol. It demonstrates that the bleaching reaction rate greatly depends on the concentration of primary bleaching reagents. The magnitude of the dependent extent is [H₂O₂] > [NaOH] > [MgO] > [Na₂SiO₃]. The rapid rise of the pulp brightness increment occurred in the first 35 min in the bleaching reaction.
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