Acid-Base Treatment for Mechanical Pulp Brightness and Calcium Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Mechanical pulp production faces challenges in maintaining brightness and reducing calcium carbonate dissolution due to conflicting pH requirements and impurities in circulating process waters, leading to suboptimal bleaching agent usage and calcium ion accumulation.
Innovation Solution
An acid-base treatment process is applied to mechanical pulp suspensions, where the pH is initially reduced with a strong acid by 0.5-4 units to 4-6 and then increased with a weak base by 0.5-3 units to below 8, optimizing brightness and reducing calcium ion levels without excessive calcium carbonate dissolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the pH of mechanical pulp is reduced with acid to minimize brightness loss, then brightness is improved, but calcium carbonate dissolution increases
Solution Approach 1:
The patent applies preliminary action by reducing the pH with acid before the pulp suspension contacts calcium carbonate-containing process waters or fillers. This pre-acidification ensures that when the suspension later encounters calcium carbonate, the pH is already optimized to minimize both brightness loss and excessive calcium carbonate dissolution, allowing the system to operate at a higher pH than traditionally used without suffering brightness loss.
Solution Approach 2:
The patent segments the pH control into two distinct stages: first, acid treatment to reduce pH and improve brightness; second, operation at the resulting lower pH to maintain brightness while reducing calcium carbonate dissolution. This segmentation allows optimization of brightness without immediately triggering excessive calcium carbonate dissolution, as the system operates at the acidified pH level.
2Illumination intensity
If the pH is lowered to improve brightness, then brightness loss is reduced, but the pH becomes too low for optimal chemical performance
Solution Approach 1:
The patent applies preliminary action by reducing the pH with acid before the pulp suspension contacts calcium carbonate-containing process waters or fillers. This pre-acidification ensures that when the suspension later encounters calcium carbonate, the pH is already optimized to minimize both brightness loss and excessive calcium carbonate dissolution, allowing the system to operate at a higher pH than traditionally used without suffering brightness loss.
3Productivity
If process waters with neutral pH are used to dilute unbleached mechanical pulp, then dilution is effective, but brightness loss increases
Solution Approach 1:
The patent applies preliminary action by pre-acidifying the pulp suspension before it contacts neutral pH process waters. This ensures that when dilution occurs, the pulp is already at a pH optimized for brightness retention, preventing the brightness loss that would normally occur when neutral pH water raises the pulp pH.
4Productivity
If circulating process waters are reused for dilution to reduce water discharge, then water efficiency improves, but brightness loss and calcium ion accumulation increase
Solution Approach 1:
The patent applies preliminary action by pre-acidifying the pulp suspension before it contacts circulating process waters containing accumulated impurities. This ensures that the pulp enters the water circulation system at an optimized pH, minimizing brightness loss and reducing calcium ion accumulation even when using water with high impurity content.
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 process effectively maintains pulp brightness, reduces bleaching agent usage, and minimizes calcium carbonate dissolution, improving the overall efficiency and quality of mechanical pulp production.
Implementation Method 1
the pH of said suspension is first reduced with a strong acid by 0.5-4 pH units to a pH between 4 and 6
Implementation Method 2
then the pH of said suspension is increased with a weak base by 0.5-3 units to a pH below 8
Data Source
Figure 1
AI summary
The invention relates to a process for making paper, wherein a pulp suspension, which comprises mechanical pulp, is thickened in a dewatering device and is thereafter diluted with water and pumped to a storage tank, then diluted again and made in to paper. According to the invention, the pulp suspension is subjected to an acid - base treatment after the dewatering device. The pH of the suspension is first reduced with a strong acid by 0.5 -4 pH units to a pH between 4 and 6 and then the pH of the suspension is increased with a weak base by 0.5 -3 units to a pH below 8. The invention also relates to the use of an acid - base treatment in a process for making paper, wherein a pulp suspension, which has been thickened in a dewatering device, is subjected to an acid - base treatment for improving the process and/or the product. The invention provides improvements in the brightness of the pulp suspension and/or reduces the need for bleaching agent. The invention also decreases the dissolution of calcium carbonate filler in the process.