Oxygen Nanobubble Bleaching for Faster Cellulose Delignification
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Solution Overview
Problem
Existing oxygen-assisted bleaching processes in chemical pulp production face inefficiencies due to the sparing solubility of oxygen in water, leading to slow reaction rates and incomplete lignin removal, particularly in oxygen delignification stages, where large gas bubbles form and fail to react effectively with lignin.
Innovation Solution
Introduce oxygen in the form of nanobubbles with diameters between 20 nm and 1 μm, which remain stable and penetrate fibers, acting as a reservoir for oxygen to sustain the reaction with lignin, using porous materials to generate nanobubbles directly in the reactor or feed conduits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If oxygen is introduced in conventional forms (large gas bubbles), then the oxygen supply is simple, but the reaction rate with lignin is slow and oxygen dissolution is insufficient
Solution Approach 1:
The oxygen gas is segmented into extremely fine bubbles with diameters of 1 μm or less (preferably 0.1 to 10 μm) by passing it through a porous plate before introduction into the reactor. This segmentation increases the total surface area of oxygen contact with the suspension, enhancing dissolution and reaction efficiency without requiring complex oxygen delivery systems
Solution Approach 2:
A porous plate is used as the oxygen introduction structure to generate fine bubbles. The porous material divides the oxygen stream into numerous small bubbles, achieving effective oxygen dissolution and distribution throughout the suspension while maintaining a simple introduction apparatus
2Productivity
If large gas bubbles are used for oxygen introduction, then the apparatus is simple, but the gas bubbles rise rapidly and pass through the reactor without reacting
Solution Approach 1:
By segmenting oxygen into fine bubbles (1 μm or less diameter), the rise speed of individual bubbles is dramatically reduced due to increased drag and decreased buoyancy forces. This allows bubbles to remain suspended in the reactor longer, increasing residence time and reaction efficiency with lignin
Solution Approach 2:
The patent utilizes fluid dynamics principles by introducing oxygen through a porous plate to create a dispersed bubble suspension rather than large rising bubbles. The fine bubble distribution creates a more uniform two-phase flow regime that enhances mass transfer and reaction efficiency
3Quantity of substance
If oxygen is introduced to achieve maximum distribution, then oxygen dissolution improves, but excessively large gas bubbles form that slow the reaction rate
Solution Approach 1:
The porous plate segments oxygen into the finest possible bubbles (1 μm or less), achieving both maximum distribution throughout the suspension and maintaining small bubble size. This simultaneous achievement of wide distribution and small bubble diameter optimizes both oxygen availability and reaction kinetics
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
Enhances the efficiency of oxygen utilization by ensuring uniform distribution and direct contact with lignin, improving the bleaching process by maintaining a stable oxygen supply and increasing the reaction rate.
Implementation Method 1
nanobubbles having an average diameter between 20 nm and 1 μm... which remain stable and penetrate fibers, acting as a reservoir for oxygen to sustain the reaction with lignin
Implementation Method 2
using porous materials to generate nanobubbles directly in the reactor or feed conduits
Data Source
AI summary
In a process/an apparatus for producing bleached cellulose in which a lignin- and cellulose-containing suspension is subjected to at least one process step for oxygen-assisted bleaching in a reactor, such as alkaline oxygen delignification, oxygen-enhanced extraction or oxygen-enhanced peroxide bleaching, the oxygen required for the oxygen-assisted bleaching is supplied to the reactor at least partially in the form of oxygen-containing nanobubbles. The small size and high stability of the nanobubbles allow uniform distribution of the oxygen in the suspension and a comparatively long exposure time. The efficiency of the bleaching is thus substantially increased.