Bleaching Pitch Control Using pH-Switchable Cationic Polymers
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Solution Overview
Problem
Existing methods for pitch control during bleaching of cellulosic fibres in pulp manufacturing face challenges due to the formation of agglomerates and deposits caused by pitch and pitch-like substances, which are not effectively removed by talc, especially neutral substances like sterols and betulinol, and there is a need for alternatives to reduce inorganic material content in the pulp.
Innovation Solution
Employing a cationic polymer with hydrolysable cationic functional groups that interact with pitch and pitch-like substances at acidic pH, allowing their effective removal during alkaline extraction stages, thereby reducing agglomeration and minimizing inorganic material content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If talc is used as a pitch control agent to reduce tackiness of pitch and pitch-like substances, then agglomeration is reduced, but inorganic material content increases and some pitch substances remain bound
Solution Approach 1:
The patent changes the chemical nature of the pitch control agent from inorganic (talc) to organic (polymer), and specifically uses a polymer whose charge state changes with pH. The polymer is cationic at acidic pH to bind pitch, but becomes neutral at alkaline pH to release pitch, enabling effective pitch control without inorganic material accumulation
Solution Approach 2:
The polymer pitch control agent is designed to be temporary in its function - it binds pitch during the acidic bleaching stage but deliberately releases it during the alkaline extraction stage so that both the polymer and bound pitch can be removed together with the extraction liquor, leaving no residual inorganic material
2Object-generated harmful factors
If talc is used to bind pitch substances during acidic bleaching, then deposit formation is reduced, but pitch removal efficiency is insufficient for neutral substances
Solution Approach 1:
The patent exploits the pH-dependent charge state change of the polymer to achieve both binding and release functions. At acidic pH the polymer is cationic and binds pitch effectively preventing deposits. At alkaline pH the polymer becomes neutral, releasing the bound pitch so it can be removed with the extraction liquor, thereby achieving both deposit prevention and effective pitch removal
3Ease of operation
If inorganic pitch control agents are used, then pitch management is improved, but occupational safety risks increase due to asbestos contamination
Solution Approach 1:
The patent replaces permanent inorganic pitch control agents with an organic polymer that performs its function temporarily and then degrades or can be removed. The polymer binds pitch during processing but releases it during alkaline extraction, allowing both to be washed away, eliminating the need for persistent inorganic additives and associated safety risks
Solution Approach 2:
The polymer acts as a temporary intermediary between pitch substances and the aqueous environment. It facilitates pitch management during acidic conditions but deliberately relinquishes this role under alkaline conditions, transferring the pitch back to the aqueous phase for removal, thus avoiding the need for permanent inorganic intermediaries
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
The cationic polymer effectively removes neutral pitch and pitch-like substances, reducing agglomeration and inorganic material content, enhancing pulp quality and suitability for various applications, particularly in carboxymethyl cellulose production.
Implementation Method 1
a cationic polymer with hydrolysable cationic functional groups that interact with pitch and pitch-like substances at acidic pH
Implementation Method 2
hydrolysable cationic functional groups that interact with pitch and pitch-like substances at acidic pH, allowing their effective removal during alkaline extraction stages
Data Source
AI summary
The invention relates to a method for pitch control and/or removal during bleaching of cellulosic fibres. Cellulosic fibres are obtained from a pulping process and formed into an aqueous cellulosic fibre suspension, and bleaching of the cellulosic fibre suspension is performed in a bleaching process comprising at least one acidic stage, where pH of the cellulosic fibre suspension is <6. A pitch control agent is added to the cellulosic fibre suspension before the acidic stage, wherein the pitch control agent comprises at least one cationic polymer comprising cationic functional groups which are hydrolysed at pH 9.0