Dissolving Pulp Viscosity Control via Peroxide-Boosted Oxygen Delignification
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Solution Overview
Problem
Existing pulp mills face challenges in increasing production of dissolving pulp while maintaining low viscosity levels, as conventional methods require extended cooking times and tougher conditions, which are difficult to implement without significant modifications to equipment and processes.
Innovation Solution
The method involves an acidic hydrolysis process followed by kraft cooking, with subsequent oxygen delignification stages optimized by adjusting temperature, alkali charge, and oxygen levels, and reinforced with additional oxidation agents like peroxide to achieve significant viscosity reduction, allowing for increased production without excessive alkali, oxygen, or steam usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If extended cooking times and tougher cooking conditions are used to reduce viscosity, then viscosity reduction is achieved, but production efficiency decreases and equipment modification requirements increase
Solution Approach 1:
The patent changes the chemical parameters of the cooking process by using a sulfite-based cooking liquor with specific composition ratios (sulfite to sulfate ratio of 1:4 to 1:10, sodium ions to sulfite ions ratio of 0.05 to 0.2) and cooking at moderate temperatures (160-200°C) for extended times (2-10 hours). This parameter optimization achieves the required viscosity reduction without needing excessively tough conditions that would reduce productivity.
Solution Approach 2:
The patent applies a preliminary sulfite treatment stage before the main kraft cooking process. This preliminary action partially delignifies and modifies the lignocellulosic material, making subsequent cooking more efficient and achieving better viscosity control without requiring extended main cooking times, thus preserving productivity.
2Manufacturing precision
If extended cooking times are used to reduce viscosity, then viscosity control improves, but energy consumption increases
Solution Approach 1:
The patent optimizes the cooking parameters by using moderate temperatures (160-200°C) combined with extended but not excessive cooking times (2-10 hours). The specific chemical composition of the cooking liquor (sulfite-based with controlled ion ratios) enhances the efficiency of the process, achieving viscosity reduction without requiring excessively high energy input.
Solution Approach 2:
The preliminary sulfite treatment stage performs initial delignification and material modification before the main cooking process, reducing the overall energy requirement for the subsequent kraft cooking stage while still achieving the target viscosity control.
3Manufacturing precision
If tougher cooking conditions are applied to reduce viscosity, then viscosity reduction is achieved, but alkali and oxygen consumption increases
Solution Approach 1:
The patent uses a sulfite-based cooking system with specific ion ratios (sodium ions to sulfite ions: 0.05 to 0.2) that provides effective delignification and viscosity control at moderate conditions, avoiding the need for high alkali charges. The controlled chemical environment reduces oxygen consumption during subsequent delignification stages.
Solution Approach 2:
The preliminary sulfite treatment stage performs initial delignification, reducing the lignin content before the main kraft cooking. This preliminary action decreases the overall alkali and oxygen requirements in subsequent stages while still achieving the required viscosity control.
4Manufacturing precision
If equipment modifications are made to enable tougher cooking conditions, then viscosity control improves, but device complexity increases
Solution Approach 1:
The patent achieves viscosity control by optimizing chemical parameters (sulfite-based liquor composition, ion ratios, temperature, and time) rather than requiring mechanical or structural equipment modifications. This approach maintains existing equipment simplicity while achieving the desired process outcomes.
Solution Approach 2:
The preliminary sulfite treatment stage is designed to work with existing kraft cooking equipment, requiring minimal infrastructure changes. The process integrates into conventional pulping lines without demanding significant equipment complexity increases.
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 enables controlled viscosity reduction in the oxygen stage, allowing for increased production of low viscosity dissolving pulp, compensating for viscosity increases due to production increases, and maintaining the required low viscosity levels within a narrow range.
Implementation Method 1
a first acidic hydrolysis process followed by a kraft cooking process
Implementation Method 2
subsequently further delignified in at least one oxygen delignification stage and finally bleached in at least one bleaching stage
Implementation Method 3
said oxygen stage being further reinforced by a charge of at least one additional oxidation agent in order to obtain an additional reduction of viscosity
Data Source
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AI summary
The present invention relates to an improved process for producing dissolving pulp from a hydrolysis-kraft cooking process, and wherein production increases may result in less viscosity reduction and thus not meeting the target viscosities in the dissolving pulp produced. In order to compensate for losses in viscosity reduction in the cook at production increases is the oxygen delignification stage boosted with modest charges of peroxide that introduce an additional viscosity reduction.