Low-Temperature Peroxy Bleaching of Recycled Pulp
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Solution Overview
Problem
Conventional bleaching processes for cellulosic pulps, especially those using recycled wastepaper, are costly and inefficient in achieving high brightness, particularly with the decline in availability of high-quality recycled materials and the increase in low-quality mixed paper, which often contains contaminants and requires expensive biocide programs to prevent microbial growth during storage.
Innovation Solution
A low-temperature, extended-duration bleaching method using peroxy compounds, specifically hydrogen peroxide, at temperatures between 110-135°F (43-57°C) with retention times of 6-90 hours and pH levels of 9.5-12.5, integrated into a multi-stage process to enhance bleaching efficiency and inhibit microbial growth, thereby reducing the need for pressurized bleaching and capital costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional bleaching processes are used with high-quality recycled materials, then high brightness can be achieved, but the cost increases and availability decreases
Solution Approach 1:
The patent applies parameter changes by operating at lower temperatures (10-50°C instead of conventional higher temperatures) and extended retention times (1-24 hours instead of shorter times), which fundamentally alters the bleaching kinetics to achieve high brightness from low-quality recycled materials at reduced cost
Solution Approach 2:
The patent employs preliminary action through pre-treatment stages before the main bleaching process, including washing, refining, and conditioning of the recycled pulp to remove contaminants and prepare the fiber structure for more efficient bleaching, thereby enabling cost-effective processing of low-quality materials
2Ease of manufacture
If conventional bleaching processes are used with low-quality mixed paper, then cost is reduced, but brightness achievement becomes difficult
Solution Approach 1:
The patent segments the bleaching process into multiple sequential stages (e.g., washing, refining, bleaching, drying) with specific conditions for each stage, allowing progressive treatment of low-quality materials to achieve high brightness that would be impossible in a single conventional stage
Solution Approach 2:
The patent implements continuous bleaching action over extended retention times (1-24 hours) with maintained optimal conditions throughout, ensuring progressive and complete decolorization of low-quality recycled materials rather than relying on short intensive pulses
3Illumination intensity
If extended duration bleaching is used, then brightness gain increases, but processing time increases
Solution Approach 1:
The patent changes key parameters including temperature (10-50°C), pH level (9.5-12.5), and retention time (1-24 hours) to optimize the bleaching reaction rate, achieving high brightness gain within a practical time frame rather than requiring excessively long processing times
4Loss of substance
If low temperature bleaching is used, then peroxide consumption decreases, but bleaching rate slows
Solution Approach 1:
The patent compensates for the slower reaction rate at low temperatures by implementing continuous bleaching action over extended retention times (1-24 hours), maintaining optimal pH and temperature conditions throughout to ensure complete and efficient peroxide utilization without waste
Solution Approach 2:
The patent adjusts multiple parameters simultaneously including temperature (10-50°C), pH (9.5-12.5), and retention time to optimize the balance between reaction rate and peroxide efficiency, achieving high brightness gain with minimal peroxide consumption
5Productivity
If multi-stage processes are integrated, then bleaching efficiency increases, but process complexity increases
Solution Approach 1:
The patent segments the bleaching process into distinct functional stages (washing, refining, bleaching, drying) that can be implemented sequentially in existing equipment, achieving high efficiency through staged treatment without requiring completely new complex system architecture
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 method achieves high brightness gains with low peroxide consumption, effectively decolorizing brown fibers and inhibiting microbial growth, allowing for the production of high-brightness pulps from low-brightness recycled paper with reduced operational and capital expenses, and can be easily integrated into existing bleaching operations.
Implementation Method 1
A low-temperature, extended-duration bleaching method using peroxy compounds, specifically hydrogen peroxide
Implementation Method 2
pH levels of 9.5-12.5
Data Source
AI summary
A high efficiency bleaching method for cellulosic pulp includes: (a) providing a charge of aqueous cellulosic pulp to a bleaching vessel at a consistency of from 10% to 30% along with a peroxy bleaching agent and an alkaline agent effective to adjust pH of the charge to 9.5 to 12.5; and (b) bleaching the aqueous cellulosic pulp in the bleaching vessel while maintaining a bleaching temperature of from 110° F. (43° C.) to 135° F. (57° C.) and a pH of the charge from 9.5 to 12.5 for an extended bleaching retention time. The bleaching method is advantageously used to bleach low brightness recycle pulp, and/or as part of a multistage process with bleaching stages of lesser duration, and/or as a high peroxy efficiency, low dose bleaching process or in connection with concurrently storing and bleaching pulp.