Multi-Stage Bleaching Process for High Brightness Pulp
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Solution Overview
Problem
Current recycling technologies face challenges in efficiently processing lower-grade waste papers, such as curbside waste, due to contamination with mechanical pulp and various inks, leading to increased costs and difficulties in achieving premium brightness for products like bath tissue and paper towels.
Innovation Solution
A multi-stage bleaching process using magnesium hydroxide in combination with hydrogen peroxide and oxygen, followed by a peroxide activating agent to convert residual peroxide into peracetic acid, and a final reductive bleaching stage, effectively increases pulp brightness while reducing chemical consumption and fiber damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional bleaching technologies are used on curbside waste paper, then the process can handle the volume of lower-grade fibers, but the resulting pulp brightness is insufficient for premium products
Solution Approach 1:
The bleaching process is divided into multiple sequential stages (oxidative bleaching with hydrogen peroxide and magnesium hydroxide, peroxide activation to form peracetic acid, and reductive bleaching with sodium borohydride or sodium hydrosulfite). Each stage targets specific contaminants and achieves incremental brightness improvement, allowing the complex task of brightening heavily contaminated curbside waste paper to be managed through manageable steps that collectively produce premium brightness pulp
Solution Approach 2:
Magnesium hydroxide serves as an intermediary substance that facilitates the activation of residual hydrogen peroxide into peracetic acid, a more effective bleaching agent. This intermediary step transforms the bleaching capability of the system, enabling the conversion of moderately brightened pulp into high brightness pulp suitable for premium products without requiring excessively complex direct treatment methods
2Illumination intensity
If aggressive chemical treatments are applied to achieve high brightness, then premium brightness pulp can be produced, but fiber damage and chemical consumption increase
Solution Approach 1:
The process utilizes controlled changes in chemical parameters (pH, oxidizing/reducing agent concentrations, temperature) across different bleaching stages. The oxidative stage operates under controlled alkaline conditions with hydrogen peroxide and magnesium hydroxide, followed by peroxide activation, then transitions to a reductive stage with sodium borohydride or sodium hydrosulfite. These parameter changes enable effective brightness improvement while controlling fiber damage through staged, moderate treatments rather than single aggressive applications
Solution Approach 2:
The process converts the potentially harmful effect of residual hydrogen peroxide into a benefit by activating it with magnesium hydroxide to form peracetic acid, a more effective bleaching agent. Additionally, the reductive bleaching stage uses reducing agents that not only remove residual color but also help protect fibers from oxidative damage, effectively converting what could be harmful chemical residues into beneficial treatment mechanisms that improve both brightness and fiber integrity
3Illumination intensity
If conventional bleaching processes are used, then standard pulp can be produced, but the cost increases due to high chemical consumption
Solution Approach 1:
The process enables self-service bleaching by utilizing hydrogen peroxide that remains in the pulp from the oxidative stage and activating it in-situ with magnesium hydroxide to form peracetic acid. This eliminates the need to add separate large amounts of additional bleaching chemicals, as the system uses its own residual chemicals to continue the brightening process, thereby reducing overall chemical consumption while achieving premium brightness
Solution Approach 2:
Instead of discarding the hydrogen peroxide residual from the oxidative bleaching stage, the process recovers and utilizes it by activating with magnesium hydroxide to form peracetic acid for further bleaching. This recovery approach converts what would be waste chemical into a valuable intermediate that continues to contribute to brightness improvement, reducing the need for additional chemical inputs
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 process allows for the production of premium or near-premium brightness pulps from lower-grade fibers, reducing costs and improving the efficiency of the bleaching process by minimizing fiber damage and chemical usage, enabling the use of more widely available and cost-effective recycled fibers.
Implementation Method 1
contacting the cellulosic admixture with magnesium hydroxide in combination with hydrogen peroxide and oxygen
Implementation Method 2
contacting the brightened pulp with a peroxide activating agent and thereby converting the residual peroxide into peracetic acid
Implementation Method 3
treating the brightened pulp with a reductive bleaching composition
Data Source
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AI summary
This present invention relates to methods for preparing premium or near-premium brightness pulps for towel and tissue applications from fiber sources comprising substantial amounts of lignin-containing pulp and chemical pulp while controlling fines, scale and anionic trash. These methods use alkaline hydroxide in combination with peroxide and oxygen for initial bleaching stages followed by treatment with a peroxide activating agent to convert residual peroxide in the pulp into peracetic acid followed by a final reductive bleaching stage.