Sodium Dithionite in Sulfate Pulping for Yield and Odor Control
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Solution Overview
Problem
Current methods for obtaining cellulose from lignocellulosic materials, such as sulfite and sulfate digestion, face challenges in achieving high pulp yield with low lignin content while minimizing malodorous emissions, particularly in the sulfate process.
Innovation Solution
The addition of small amounts of salts of dithionous acid, such as sodium dithionite, during the sulfite or sulfate digestion processes improves pulp yield and delignification, reducing lignin content and malodorous emissions like mercaptans.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If sulfite or sulfate digestion is used to obtain cellulose from lignocellulosic material, then cellulose production is achieved, but lignin content in the pulp remains high and pulp yield is limited
Solution Approach 1:
The patent applies parameter changes by modifying the chemical composition of the cooking liquor through the addition of sodium dithionite. This chemical additive changes the delignification mechanism and efficiency, enabling higher pulp yield with lower lignin content. The sodium dithionite introduces new chemical parameters (reducing agents) that enhance the breakdown of lignin while preserving cellulose.
Solution Approach 2:
The patent uses a composite cooking liquor system that combines traditional sulfite or sulfate digestion chemicals with sodium dithionite. This composite approach integrates multiple chemical mechanisms (sulfonation, reduction, and complexation) to achieve superior delignification and pulp yield compared to single-chemical systems.
2Productivity
If sulfate digestion is used to obtain cellulose, then cellulose production is achieved, but malodorous emissions (mercaptans) are generated
Solution Approach 1:
The patent converts the harmful effect of mercaptan emissions into a benefit by using sodium dithionite as a reducing agent that suppresses mercaptan formation. The sodium dithionite modifies the chemical environment to prevent the formation of malodorous compounds while maintaining efficient delignification, effectively turning a harmful byproduct issue into a controlled process advantage.
Solution Approach 2:
The addition of sodium dithionite changes the chemical parameters of the cooking process, specifically the redox potential and sulfur species distribution. These parameter changes suppress the formation of mercaptans while maintaining effective lignin removal, thereby reducing malodorous emissions without sacrificing productivity.
3Object-affected harmful factors
If traditional sulfite or sulfate digestion is used, then delignification occurs, but brightness of the pulp is insufficient
Solution Approach 1:
The patent applies parameter changes by introducing sodium dithionite, which modifies the chemical mechanisms of lignin removal. This additive enhances both the efficiency of lignin degradation and the brightness of the resulting pulp through its reducing properties, which prevent chromophore formation and improve light reflectivity of the cellulose fibers.
Solution Approach 2:
The composite cooking liquor containing sodium dithionite combines multiple delignification mechanisms that work synergistically to remove lignin more effectively and produce brighter pulp. The combination of traditional sulfite/sulfate chemicals with sodium dithionite creates a multi-functional system that addresses both lignin removal and brightness enhancement.
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 enhances pulp yield and brightness while reducing the concentration of malodorants in the off-gas, specifically mercaptans, during the sulfate cooking process.
Implementation Method 1
The addition of small amounts of salts of dithionous acid, such as sodium dithionite, during the sulfite or sulfate digestion processes improves pulp yield and delignification
Implementation Method 2
reducing the concentration of malodorants in the off-gas, specifically mercaptans
Data Source
AI summary
A method of producing cellulose from lignocellulosic material by sulfite digestion or sulfate digestion in the presence of a salt of dithionous acid comprises using the salt of dithionous acid in an amount from 0.1 to 4.0 wt. % based on the amount of oven-dry lignocellulosic material.