Guanidine-Based Nanofiltration Membrane for Alkaline Ion Rejection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing nanofiltration membranes struggle to effectively reject multivalent ions over a wide pH range due to decreased protonation of amino or imidazole groups under alkaline conditions, limiting their separation efficiency.
Innovation Solution
A guanidine-based composite nanofiltration flat-sheet membrane is developed by introducing 1,3-diaminoguanidine hydrochloride onto the membrane surface, enhancing the positive charge and maintaining protonation over a wide pH range through interfacial polymerization with trimesoyl chloride, forming a dense separation layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If amino or imidazole groups are introduced into NF membranes to enhance rejection of divalent ions, then rejection rate of divalent ions improves under acidic conditions, but separation efficiency deteriorates under alkaline conditions due to decreased protonation
Solution Approach 1:
The patent changes the chemical parameter of the functional groups on the membrane surface from amino/imidazole groups (lower pKa) to guanidine groups (higher pKa). This parameter change enables the membrane to maintain protonation and positive charge under alkaline conditions, thereby maintaining high rejection rates for divalent ions across a wider pH range including alkaline conditions.
Solution Approach 2:
The patent creates a composite nanofiltration membrane by combining a polyethersulfone (PES) base membrane with a functional layer containing guanidine groups. This composite structure integrates the mechanical strength and selectivity of the PES membrane with the enhanced protonation capability of guanidine groups, achieving both structural integrity and improved chemical adaptability under alkaline conditions.
2Measurement precision
If the pore size of NF membrane is maintained at 0.5-2.0 nm for nanofiltration, then separation capability for charged particles is improved, but rejection rate of multivalent ions deteriorates under alkaline condition due to electrostatic interaction changes
Solution Approach 1:
The patent changes the surface charge parameter of the membrane by introducing guanidine groups with higher pKa values. This enables the membrane surface to maintain positive charge under alkaline conditions, reversing or mitigating the negative electrostatic interaction that occurs with conventional membranes, thereby maintaining high rejection rates for multivalent ions across different pH conditions.
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 membrane achieves a rejection rate of over 96% for divalent ions like MgSO4 and operates stably in alkaline conditions, with a simple and cost-effective preparation process, maintaining high performance across a pH range of 8-9.
Implementation Method 1
the positive charge of membrane surface can be enhanced under alkaline condition, thereby achieving effective rejection of positively charged multivalent ions such as Mg2+ over a wide pH range
Implementation Method 2
Due to electrostatic interaction, the rejection rate of multivalent ions by NF membrane decreases with increasing pH
Implementation Method 3
The surface or interior of NF membrane contains charged groups, and the Donnan effect enables the NF membrane to separate charged particles and have a high rejection rate in particular for multivalent ions
Data Source
AI summary
The present invention belongs to the technical field of membrane-based water treatment and relates to a novel guanidine-based composite nanofiltration (NF) flat-sheet membrane, and a preparation method and application thereof. The present invention provides a method for preparing a guanidine-based composite NF flat-sheet membrane, where a dense separation layer is formed on the surface of a polyethersulfone ultrafiltration membrane through polymerization reaction between the amino group of 1,3-diaminoguanidine and the acyl chloride group of trimesoyl chloride. Under suitable reaction conditions, the guanidine-based composite NF membrane obtained according to the present invention enables effective separation of multivalent ions over a wide pH range, with a rejection rate of over 96% for 1000 ppm of MgSO4 solution, and can operate continuously and stably in a mixed ions solution with a wide pH.