Lignin Purification via pH Adjustment and Large-Pore Membrane Filtration
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Solution Overview
Problem
Current methods for lignin purification from black liquor, such as ultrafiltration, face challenges like modest fractionation results, membrane fouling, and the need for costly acid washing, which limit the efficiency and feasibility of lignin utilization in industrial scales.
Innovation Solution
A two-stage method involving pH reduction to form a lignin precipitate suspension, followed by large-pore membrane filtration of lignin agglomerates, which avoids the use of small-pore ultrafiltration membranes and acid washing, allowing for the separation of purified lignin salt by retaining lignin agglomerates while removing small molecular components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If ultrafiltration is used to purify lignin from black liquor, then lignin concentration is increased, but membrane fouling occurs and flux rate continuously declines
Solution Approach 1:
The patent applies preliminary action by adjusting the pH of black liquor to 9-10.5 before ultrafiltration to precipitate lignin. This pre-treatment step modifies the lignin's solubility and aggregation state, preventing membrane fouling before the filtration process begins, thereby maintaining stable flux rate while achieving lignin concentration.
Solution Approach 2:
The patent changes the pH parameter from the typical high alkalinity condition (pH>12) to a controlled range of 9-10.5. This parameter change alters the charge state and aggregation behavior of lignin molecules, enabling effective concentration without causing membrane fouling, thus resolving the contradiction between lignin concentration and flux rate stability.
2Manufacturing precision
If ultrafiltration is used to fractionate lignin by molecular mass, then high molecular mass lignin is enriched, but the process is difficult to operate due to membrane fouling
Solution Approach 1:
The patent applies preliminary action by adjusting the pH of black liquor to 9-10.5 before ultrafiltration to precipitate lignin. This pre-treatment step modifies the lignin's solubility and aggregation state, preventing membrane fouling before the filtration process begins, thereby maintaining stable flux rate while achieving lignin concentration.
Solution Approach 2:
The patent changes the pH parameter from the typical high alkalinity condition (pH>12) to a controlled range of 9-10.5. This parameter change alters the charge state and aggregation behavior of lignin molecules, enabling effective concentration without causing membrane fouling, thus resolving the contradiction between lignin concentration and flux rate stability.
3Reliability
If conventional ultrafiltration membranes are used, then filtration is achieved, but inorganic salts and organic compounds compromise membrane performance
Solution Approach 1:
The patent applies preliminary action by adjusting the pH of black liquor to 9-10.5 before ultrafiltration to precipitate lignin. This pre-treatment step modifies the lignin's solubility and aggregation state, preventing membrane fouling before the filtration process begins, thereby maintaining stable flux rate while achieving lignin concentration.
Solution Approach 2:
The patent changes the pH parameter from the typical high alkalinity condition (pH>12) to a controlled range of 9-10.5. This parameter change alters the charge state and aggregation behavior of lignin molecules, enabling effective concentration without causing membrane fouling, thus resolving the contradiction between lignin concentration and flux rate stability.
4Manufacturing precision
If Lignoboost process is used for lignin purification, then purified lignin is obtained, but significant expenditure in process equipment and addition of sulphuric acid is required
Solution Approach 1:
The patent changes the pH parameter from the typical high alkalinity condition (pH>12) to a controlled range of 9-10.5. This parameter change alters the charge state and aggregation behavior of lignin molecules, enabling effective concentration without causing membrane fouling, thus resolving the contradiction between lignin concentration and flux rate stability.
Solution Approach 2:
The patent extracts and removes the problematic acid washing step from the conventional Lignoboost process. By using pH adjustment to 9-10.5 followed by ultrafiltration, the process achieves lignin purification without requiring sulphuric acid addition and extensive equipment, thereby reducing device complexity while maintaining purification effectiveness.
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 method effectively enriches and purifies lignin, reducing membrane fouling and chemical usage, resulting in a more efficient and cost-effective production of purified lignin salt with improved chemical balance in the pulp mill.
Implementation Method 1
subjecting the alkalilignin agglomerate colloid to large-pore membrane filtration
Implementation Method 2
separation of purified lignin salt by retaining lignin agglomerates while removing small molecular components
Implementation Method 3
decreasing the spent liquor pH to form a lignin precipitate suspension
Data Source
AI summary
The invention is directed to a method for producing a purified lignin salt from alkaline spent liquor from the chemical cooking of lignocellulosic raw materials. The method comprises the steps of decreasing the spent liquor pH to form a lignin precipitate suspension; filtering the lignin precipitate to form a lignin filter cake and a filtrate; mixing the lignin filter cake into a dilution liquid to form an alkalilignin agglomerate colloid; subjecting the alkalilignin agglomerate colloid to large-pore membrane filtration; and recovering a purified lignin salt concentrate.