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

Abstract

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.