Enhancement of TCF and ECF Bleaching Processes by Urea and Enzymatic Pretreatments: Optimization of a Laccase-Mediator Pretreatment

Abstract

A TCF bleaching sequence consisting of a urea pretreatment stage (U), laccase-mediator system stage (L), alkaline extraction stage (E), and hydrogen peroxide bleaching stage (P) was used to study the effect of five independent variables on the dependent variables pulp properties, hydrogen peroxide consumption, and residual enzyme activity. Results showed that the most influential variable was L stage pulp consistency, followed by mediator and laccase dosages. On the other hand, oxygen pressure did not have a significant effect. The optimal UL partial sequence significantly enhanced the EP bleaching sequence: 49.8% vs. 33.4% delignification, up to 65.6% ISO vs. 56.3% ISO bleached brightness, and 50.3% vs. 89.9% peroxide consumption in the P stage. The ULE partial sequence also improved an ECF bleaching sequence (ULED0E1D1)

Modelling and optimization of the last two stages of an environmentally-compatible TCF bleaching sequence

“…Hence, bleaching accomplishes the following objectives: (i) to modify the reactivity of the cellulose in the resulting dissolving pulp; (ii) to meet customer requirements that utilize the dissolving pulp; and (iii) to increase brightness and purity of the dissolving pulp (Liu et al 2016;Chen et al 2016). There are numerous bleaching sequences employed to improve pulp reactivity and adjust pulp viscosity, such as chlorinebased bleaching (Gangwar et al 2016), elemental chlorine free (ECF) (Bodhlyera et al 2015;Li et al 2015;Yao et al 2016), catalytic bleaching (Kumar Chenna et al 2016;Afsahi et al 2018); total chlorine free (TCF) (Li et al 2015;Zhou 2015;Veisi and Mahdavi 2016), and bio-bleaching with enzymes, such as cellulases (Duan et al 2017;Hutterer et al 2017), endoglucanase (Quintana et al 2015a), xylanase (Hutterer et al 2017;Zhao et al 2017), or laccase (García-Fuentevilla et al 2015;Quintana et al 2015b).…”