Multistage Nanofiltration Concentrate Processing to Reduce Monovalent Ions
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Solution Overview
Problem
Existing nanofiltration systems face challenges in achieving complete separation of monovalent ions from brine, resulting in high monovalent ion content in the final concentrate, necessitating improved methods to lower this content and enhance separation efficiency.
Innovation Solution
A nanofiltration system with at least three stages and concentrate staging, incorporating a recirculation pump, pH adjustment, and temperature control units to manage pH between 2 to 7 and temperature between 20°C to 60°C, along with optional deionized water dilution, to optimize the separation process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If nanofiltration membrane is used to separate monovalent ions from brine, then divalent and multi-valent ions are retained effectively, but monovalent ion content in the final concentrate remains relatively high
Solution Approach 1:
The system divides the nanofiltration process into multiple stages (at least three stages) with concentrate staging between them. Each stage processes the concentrate from the previous stage, progressively reducing monovalent ion content through sequential separation steps rather than attempting complete separation in a single stage.
Solution Approach 2:
The system adjusts operating parameters including pH control (using acid or base to adjust feed pH) and temperature control (heating or cooling the feed) to optimize membrane performance. These parameter changes enhance the membrane's ability to reject monovalent ions while maintaining divalent ion retention.
2Productivity
If multiple-stage nanofiltration system with concentrate staging is implemented, then recovery rate is improved, but monovalent ion content in final concentrate increases
Solution Approach 1:
The concentrate stream is segmented and processed through multiple sequential stages rather than being discharged after a single stage. This segmentation allows progressive concentration of divalent ions while continuously removing monovalent ions at each stage, achieving both high recovery and low monovalent content.
Solution Approach 2:
The system maintains continuous processing of the concentrate stream through all stages without interruption. The concentrate from each stage is immediately fed to the next stage, ensuring continuous separation action that progressively reduces monovalent ion content while maximizing water recovery.
3Manufacturing precision
If pH adjustment is applied to optimize separation, then monovalent ion rejection is improved, but system complexity increases
Solution Approach 1:
Chemical intermediaries (acids or bases) are introduced to adjust the pH of the feed stream. This pH adjustment serves as an intermediary step that modifies the ionic environment to enhance membrane selectivity, improving monovalent ion rejection without requiring fundamental changes to the membrane or system architecture.
4Manufacturing precision
If temperature control is implemented to enhance separation, then membrane performance is improved, but energy consumption increases
Solution Approach 1:
Temperature is adjusted as a controllable parameter to optimize membrane performance. By heating or cooling the feed stream to specific temperature ranges, the membrane's selective properties are enhanced, improving separation efficiency. The temperature control allows the system to operate at optimal conditions without requiring excessive energy input.
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 method effectively reduces the monovalent ion content in the final concentrate, improving the separation efficiency of monovalent ions from divalent or multivalent ions, achieving a lower concentration of monovalent ions in the final concentrate compared to the brine input.
Implementation Method 1
Nanofiltration (NF) is a membrane separation technology between osmosis and ultrafiltration. The cutoff relative molecular weight of a nanofiltration membrane may be between 200 and 2000 and the membrane pore size may be around 1-2 nm.
Implementation Method 2
A nanofiltration membrane can effectively retain bivalent and multi-valent ions and organics with a relative molecular weight greater than 200, while most of monovalent inorganic salts can pass through.
Implementation Method 3
recirculating a first portion of the concentrate produced by the last stage to the last stage
Implementation Method 4
controlling the feed liquid in a pH range of 2 to 7
Implementation Method 5
controlling the feed liquid in a temperature range of 20 °C to 60 °C
Implementation Method 6
deionized water is fed through an inlet of a stage of a membrane system to dilute the feed stream to the stage
Data Source
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AI summary
This specification describes a method for lowering the content of monovalent ions in a final concentrate of a nanofiltration system relative to a brine and a corresponding nanofiltration system. The nanofiltration system comprises at least three stages of nanofiltration, wherein the concentrate from each segment flows into the next segment. A feed stream is sent into one stage to generate a concentrate stream, and a first portion of the concentrate stream is recirculated to the one stage. The pH of the feed stream is controlled in a range of 2-7. The temperature of the feed stream is in a range of 20-60°C. The feed stream includes the recirculated concentrate stream and at least part of a concentrate generated from an upstream stage. The method and the system described herein can reduce the concentration of monovalent ions in the final concentrate during a nanofiltration separation process.