Composite Polyamide Membrane with Pendant Carboxylic Acid Groups
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Solution Overview
Problem
Current composite polyamide membranes used in fluid separations, such as reverse osmosis and nanofiltration, face challenges in achieving optimal performance due to limitations in salt rejection and flux rates, particularly with the addition of new additives that enhance membrane performance.
Innovation Solution
The method involves applying polyfunctional amine and acid halide monomers to a porous support for interfacial polymerization, with the inclusion of a carboxylic acid monomer and a tri-hydrocarbyl compound, which increases the solubility of water and selectively catalyzes the hydrolysis of the polyfunctional acyl halide, resulting in a modified polymer structure that improves membrane performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional acyl halide monomers are used in interfacial polycondensation, then membrane formation is achieved, but salt rejection and flux rates are suboptimal
Solution Approach 1:
The patent modifies the chemical structure of the acyl halide monomer by incorporating carboxylic acid functional groups at specific positions (meta or para relative to the acyl halide group). This structural parameter change creates pendant carboxylic acid groups in the polyamide layer that enhance salt rejection through electrostatic interactions while maintaining adequate flux rates.
Solution Approach 2:
The invention creates a composite polyamide layer combining the polyfunctional amine backbone with pendant carboxylic acid groups introduced through the specialized acyl halide monomer. This composite structure integrates both the structural framework needed for membrane formation and the functional groups required for enhanced salt rejection, achieving improved performance in both salt rejection and flux compared to conventional monomers.
2Reliability
If complexing agents are added to improve membrane performance, then salt rejection increases, but the complexity of the coating solution increases
Solution Approach 1:
The patent extracts the complexing agent function from separate additives and integrates it directly into the acyl halide monomer structure itself. The carboxylic acid groups are built-in structural elements rather than added complexing agents, simplifying the coating solution while achieving the same performance enhancement.
Solution Approach 2:
The invention merges the structural role of the acyl halide monomer with the functional role of complexing agents by incorporating carboxylic acid groups into the same molecular structure. This combination eliminates the need for separate complexing agent additives while achieving enhanced salt rejection performance.
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 approach leads to membranes with lower solute passage and higher flux rates compared to similar membranes without these additives, specifically enhancing salt rejection and permeability in reverse osmosis and nanofiltration applications.
Implementation Method 1
increases the solubility of water
Implementation Method 2
selectively catalyzes the hydrolysis of the polyfunctional acyl halide
Data Source
AI summary
A method for making a composite polyamide membrane comprising the step of applying polyfunctional amine and acid halide monomers to a surface of a porous support and interfacially polymerizing the monomers to form a thin film polyamide layer. The method further includes the step of conducting the interfacial polymerization in the presence of: a carboxylic acid monomer comprising an aliphatic or aromatic moiety substituted with single carboxylic acid functional group and at least one acyl halide functional group, and a tri-hydrocarbyl compound.