Phosphonate Polymers for Calcium Sequestration in Kraft Pulping
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Solution Overview
Problem
The Kraft pulping process faces challenges in achieving high pulp yield and reducing rejects due to undissolved lignin and metal interference, leading to increased costs and operational difficulties.
Innovation Solution
A composition and process utilizing polymers with phosphonate or phosphinate components, along with nitrogen and sulfur functionalities, are used to bind calcium and prevent repreciptitation of lignin and extractives, addressing the issue of metal interference and scaling in the pulping process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional Kraft pulping process is used to cook wood chips, then lignin is dissolved to free cellulosic fibers, but calcium and metals form sticky precipitates that block flow channels and cause scaling
Solution Approach 1:
The patent introduces phosphonate-containing polymers as intermediary substances that mediate between calcium/metal ions and the pulping process. These polymers bind to metal ions through chelation, preventing them from forming harmful precipitates with lignin and hemicellulose, while allowing the pulping reaction to proceed effectively
Solution Approach 2:
The patent converts the harmful effect of calcium and metals (which form scaling precipitates) into a beneficial outcome by using phosphonate polymers to selectively bind these metals. This prevents the metals from interfering with the pulping process and causing equipment scaling, while the bound metals can be easily removed in the black liquor
2Productivity
If digestion time is increased to maximize pulp yield, then more lignin is dissolved, but metal interference increases and causes hydrolysis of wood sugars and cellulose
Solution Approach 1:
Phosphonate-containing polymers act as intermediaries that bind to metal ions (particularly calcium, copper, and iron) present in the cooking liquor and wood chips. This sequestration prevents metals from catalyzing unwanted hydrolysis reactions of sugars and cellulose, maintaining process stability even during extended digestion times required for maximum pulp yield
3Productivity
If calcium is present in cooking liquor to assist pulping, then lignin dissolution is enhanced, but calcium forms tenacious scales in high heat transfer areas
Solution Approach 1:
The phosphonate polymers serve as intermediary agents that preferentially bind to calcium ions in the cooking liquor. This prevents calcium from reacting with lignin and hemicellulose to form insoluble precipitates that would deposit on heat transfer surfaces, while still allowing sufficient calcium to remain in solution to facilitate effective pulping
Solution Approach 2:
The patent changes the chemical state of calcium from free ions that form insoluble scales to calcium complexed with phosphonate groups. This parameter change in calcium's chemical environment prevents scale formation on heat transfer surfaces while maintaining calcium's beneficial role in the pulping process
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 results in lower processing costs, easier operational procedures, and increased pulp yield by controlling calcium and other metals, reducing rejects and scaling, and improving the quality of pulp production.
Implementation Method 1
The polymers, which have phosphonate or phosphinate components along the backbone of the carbon chain, bind calcium and prevent repreciptitation of lignin and extractives
Implementation Method 2
sodium sulfide is added to the medium that is used to cook the wood chips and produce pulp
Implementation Method 3
The reaction conditions present during the cook, or digestion, cause lignin, the amorphous polymeric binder found in wood fibers, to be hydrolyzed
Implementation Method 4
White liquor solubilizes the pulp and removes the lignin from the wood fibers
Data Source
AI summary
In general, the present disclosure is directed to compositions and processes to increase pulp yield, reduce extractives, and reduce scaling in a chemical pulping process. In one particular embodiment, for instance, the present disclosure is directed to a composition comprising a surface active agent, an alkaline mixture, at least one polymer, the polymer having a linear backbone segment having two ends, at least one phosphorus component, the phosphorus component chemically linked along the linear backbone segment of the polymer, and at least one end component, the end component chemically linked to one or both ends of the linear backbone segment of the polymer.