Dissolving Pulp Process via Cold Caustic Extraction
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Solution Overview
Problem
Conventional kraft processes for manufacturing dissolving pulp suffer from low yields and high residual hemicellulose content, which affects the quality and utility of the pulp for textile applications, and are not optimized for industrial-scale production.
Innovation Solution
A process incorporating a cold caustic extraction (CCE) step with high alkali concentration and temperature, followed by oxygen delignification and dewatering, which allows for efficient removal of xylan and alkali, resulting in high-yield dissolving pulp suitable for industrial-scale production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If conventional kraft process with prehydrolysis is used, then lignin is removed effectively, but hemicelluloses are degraded and transferred into acid condensate resulting in low yield
Solution Approach 1:
The invention changes the pH parameter from acidic (conventional prehydrolysis) to alkaline conditions (cold caustic extraction with 70-100 g/l alkali concentration). This parameter change prevents hemicellulose degradation while still achieving effective removal, thereby maintaining high dissolving pulp yield.
Solution Approach 2:
The invention introduces cold caustic extraction as an intermediary step between kraft cooking and final pulp production. This intermediary process uses alkaline conditions to selectively remove hemicelluloses without the harsh degradation that occurs in acidic prehydrolysis, serving as a bridge that preserves both yield and purity.
2Manufacturing precision
If cold caustic extraction with high alkali concentration is applied, then xylan and alkali are efficiently removed, but process complexity increases
Solution Approach 1:
The invention merges the cold caustic extraction step with the existing kraft process workflow, integrating it between cooking and bleaching. By combining this selective extraction with standard industrial operations and utilizing readily available white liquor, the process achieves high xylan removal without proportionally increasing overall system complexity.
Solution Approach 2:
The process utilizes white liquor (a byproduct of the kraft process) as the extracting agent in the cold caustic extraction step. This self-service approach recycles internal process materials, reducing the need for additional chemicals and simplifying the overall process by using resources already present in the system.
3Productivity
If conventional kraft process is used, then industrial scale production is achieved, but residual hemicellulose content remains high affecting textile application quality
Solution Approach 1:
The invention segments the pulp purification process into distinct stages: kraft cooking for lignin removal, followed by cold caustic extraction for hemicellulose removal, and finally bleaching. This segmentation allows each step to target specific impurities independently, achieving high pulp purity suitable for textile applications while maintaining industrial scale production capabilities.
Solution Approach 2:
The invention maintains continuous operation by integrating the cold caustic extraction step into the existing kraft process flow without interrupting production. The process uses continuous counterscurrent washing and maintains steady-state operation, ensuring both high pulp purity and sustained industrial-scale productivity.
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 process increases the yield of dissolving pulp, reduces residual hemicellulose content, and produces a pulp with improved quality for textile applications, while being economically viable and adaptable to industrial-scale conditions.
Implementation Method 1
adding industrial white liquor with high ionic strength to the pulp obtained from step d), wherein said pulp has a xylan content of 8 weight % or more and wherein the temperature is lowered and kept at 65° C. or lower for 5 minutes or more
Implementation Method 2
removing 90% or more of the alkali and dissolved xylan as a liquor flow from the pulp obtained from step e) by dewatering the pulp
Implementation Method 3
oxygen delignifying the pulp obtained from step c)
Implementation Method 4
removing 90% or more of the alkali and dissolved xylan as a liquor flow from the pulp obtained from step e) by dewatering the pulp
Data Source
AI summary
The invention relates to processes for manufacturing pulp and more specifically to improved processes for manufacturing dissolving pulp. The processes have primarily been developed to be used in connection with large scale kraft processes, i.e. they have been designed to be incorporated into a plant. A liquor derivable from the process and comprising xylan, lignin, alkali and water is also disclosed as well as a dissolving pulp produced by the process.