Singlet Oxygen Pulp Bleaching via Peracetate Oxidant
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Solution Overview
Problem
Current pulp bleaching methods using chlorine and chlorine dioxide are inefficient, environmentally hazardous, and costly, causing damage to cellulose fibers and generating harmful byproducts, while lacking effective methods for delignification and brightening on smaller scales and in a chlorine-free manner.
Innovation Solution
The use of a ROS formulation that generates singlet oxygen, combined with alkaline peroxide stages, to reduce chlorine dioxide usage and achieve brighter pulp grades with increased pulp yield and fiber strength, employing a bleach sequence that includes singlet oxygen stages followed by alkaline peroxide and other bleaching agents to selectively oxidize and extract lignin without damaging cellulose fibers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If chlorine dioxide is used for bleaching and delignification, then brightness is improved, but fiber strength and yield deteriorate due to non-selective oxidation
Solution Approach 1:
The patent changes the chemical state of oxygen from triplet ground state to singlet excited state, creating a fundamentally different oxidant with selective reactivity. Singlet oxygen selectively oxidizes lignin phenolic structures while sparing cellulose, achieving brightness improvement without the fiber strength deterioration caused by conventional chlorine dioxide oxidation
Solution Approach 2:
The patent employs singlet oxygen, a highly reactive oxidant form, generated through photooxidation of photosensitive dyes. This strong oxidant achieves rapid and selective delignification and brightening of pulp fibers, outperforming conventional oxidants in both speed and selectivity while preserving fiber integrity
2Illumination intensity
If conventional ECF bleaching processes are used, then brightness is achieved, but environmental harm increases due to AOX formation
Solution Approach 1:
The patent replaces harmful chlorine-based oxidants with singlet oxygen generated through photooxidation. This conversion eliminates the formation of absorbable organic halogens (AOX) and other harmful byproducts, transforming the bleaching process from environmentally damaging to environmentally benign while maintaining effective brightness achievement
Solution Approach 2:
The patent fundamentally changes the oxidant parameter from chlorine-based compounds to singlet oxygen, which does not form halogenated byproducts. This parameter change eliminates AOX formation entirely while achieving the same brightness improvement through selective lignin oxidation
3Loss of substance
If extended delignification exposure time is used, then lignin removal is improved, but cellulose fiber damage increases
Solution Approach 1:
The patent changes the chemical reactivity parameter by using singlet oxygen instead of triplet oxygen or radical oxidants. Singlet oxygen exhibits selective reactivity toward lignin phenolic structures with minimal attack on cellulose, enabling extended delignification exposure without the fiber damage that would result from non-selective radical oxidation
Solution Approach 2:
The patent introduces photosensitive dyes as intermediaries that absorb light energy and transfer it to ground state oxygen, generating singlet oxygen in situ. This intermediary mechanism enables controlled, selective oxidation of lignin while protecting cellulose fibers from direct exposure to harmful radical species
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly reduces chlorine dioxide use by up to 97%, achieves pulp brightness of 85% ISO or greater, increases pulp yield, preserves fiber strength, and minimizes environmental impact by reducing AOX formation and water consumption, making it suitable for smaller-scale pulp processing.
Implementation Method 1
The disclosure more particularly relates to methods of bleaching, brightening, and delignifying pulp fibers involving the use of peracetate oxidant solutions to provide singlet oxygen
Data Source
AI summary
In some embodiments, a method may include treating pulp. The method may include contacting a wood pulp with a singlet oxygen source. The method may include contacting the wood pulp with an alkaline peroxide source. The singlet oxygen source may include a peracetate oxidant solution and generating a reactive oxygen species. The peracetate oxidant solution may include peracetate anions and a peracid. In some embodiments, the peracetate solution may include a pH from about pH 10 to about pH 12. In some embodiments, the peracetate solution has a molar ratio of peracetate anions to peracid ranging from about 60:1 to about 6000:1. In some embodiments, the peracetate solution has a molar ratio of peracetate to hydrogen peroxide of greater than about 16:1. The peracetate oxidant solution may provide enhanced treatment methods of bleaching, brightening, and delignifying pulp fibers involving the use of peracetate oxidant solutions.