Paper Pulp Bleaching Process Eliminates Intermediate Washing
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Solution Overview
Problem
Conventional paper pulp bleaching processes using chlorine dioxide result in high consumption, formation of chlorate ions, and generation of organochlorine compounds, leading to environmental pollution and reduced delignification efficiency, while requiring intermediate washing steps that increase water and chemical usage.
Innovation Solution
A process that combines chlorine dioxide with hydrogen peroxide in an alkaline medium, optionally followed by acidification, eliminating the need for intermediate washing steps and optimizing the bleaching sequence (DalkP) to reduce chlorine dioxide consumption, chlorate formation, and water usage, while maintaining bleaching efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If chlorine dioxide is used in conventional bleaching processes, then delignification efficiency is improved, but chlorate ion formation increases and environmental pollution worsens
Solution Approach 1:
The patent converts the harmful chlorate ion formation into a beneficial process by operating at controlled pH levels where chlorate ions formed can be subsequently reduced by hydrogen peroxide addition, transforming an environmental liability into a manageable intermediate state that ultimately improves effluent quality
Solution Approach 2:
The patent changes the pH parameter control strategy, maintaining pH between 6.5-7.5 during chlorine dioxide treatment and then adjusting to pH 2-4 in subsequent stages, which optimizes the balance between delignification efficiency and chlorate ion formation rates
2Reliability
If intermediate washing steps are implemented between bleaching stages, then chemical reagent effectiveness is improved, but water consumption and process complexity increase
Solution Approach 1:
The patent merges the washing function into the pH adjustment steps by using acidification with sulfuric acid to simultaneously achieve pH control and removal of residual chemicals, eliminating separate washing operations and reducing water consumption while maintaining reagent effectiveness
Solution Approach 2:
The pH adjustment steps serve multiple functions: controlling chemical reaction conditions, removing residual bleaching agents, and preparing for subsequent treatment stages, thereby replacing dedicated washing steps and reducing overall process complexity
3Object-generated harmful factors
If chlorine dioxide consumption is reduced, then environmental pollution is decreased, but delignification efficiency deteriorates
Solution Approach 1:
The patent implements continuous delignification through sequential treatment stages (D1-D3) with optimized pH control and hydrogen peroxide supplementation, maintaining effective lignin removal throughout the process while reducing peak chlorine dioxide consumption and associated pollution
Solution Approach 2:
The patent uses a composite chemical treatment system combining chlorine dioxide, hydrogen peroxide, and sulfuric acid in specific sequences and concentrations, where each component complements the others to achieve delignification with reduced overall chemical consumption and pollution
4Reliability
If pH is maintained at alkaline levels during bleaching, then hydrogen peroxide effectiveness is improved, but chlorate ion formation increases
Solution Approach 1:
The patent applies periodic pH adjustment, alternating between alkaline conditions for hydrogen peroxide treatment and acidic conditions for chlorine dioxide stages, optimizing both reagent effectiveness and chlorate ion suppression at different process intervals
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 reduces chlorine dioxide usage, chlorate ion formation, water consumption, and chemical oxygen demand, while maintaining optical and mechanical properties of the final paper pulp, and significantly decreasing the generation of pollutants in effluents.
Implementation Method 1
different chemical reagents such as delignification agents (oxygen, chlorine dioxide or hydrogen peroxide) are generally used to generate oxidation, decoloration and nearly complete dissolution of the lignin in the paper pulp
Implementation Method 2
The hydrogen peroxide acts by delignification (i.e. oxidation, then solubilization of the depolymerized lignin) or by decoloration
Implementation Method 3
The hydrogen peroxide acts by delignification (i.e. oxidation, then solubilization of the depolymerized lignin) or by decoloration (oxidation of lignin with a decrease in the conjugation of the lignin molecule)
Implementation Method 4
hypochloric acid (HClO) is generated during the reaction between the chlorine dioxide and the lignin
Implementation Method 5
Chlorate ions are formed from chlorite ions (ClO2−), and hypochloric acid (HClO) is generated during the reaction between the chlorine dioxide and the lignin
Data Source
AI summary
The present invention relates to a method for bleaching an unbleached or pre-bleached paper pulp comprising at least the following consecutive steps: a) preparing an unbleached or pre-bleached paper pulp having a pH of at least 8, b) bringing the paper pulp obtained at the end of step a) into contact with chlorine dioxide, c) when the pH of the paper pulp obtained from step b) is lower than 10, adding at least one Brønsted base to the paper pulp, d) adding hydrogen peroxide to the paper pulp obtained at the end of step c), e) maintaining the paper pulp obtained at the end of step d) in a first bleaching tower, f) optionally, adding sulphuric acid to the paper pulp obtained at the end of step e) and maintaining the obtained paper pulp in a second bleaching tower, the method dispensing with the need for a step of washing the paper pulp before the end of step e), and, if applicable, before the end of step f).