Composite Polyamide Reverse Osmosis Membrane with Large Open Spaces
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Solution Overview
Problem
Reverse osmosis membranes used for desalination face challenges in achieving high water flux and salt rejection, particularly at lower pressures, due to osmotic pressure and fouling issues, which limit their effectiveness in brackish water and tap water treatment.
Innovation Solution
A composite polyamide reverse osmosis membrane is fabricated using a microporous support coated with an aqueous solution containing a monomeric polyamine and aliphatic sulfonic acid, followed by an organic solution with an amine-reactive reactant, and dried at controlled temperatures to create a polyamide layer with large open spaces, enhancing water flux and salt rejection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional polyamide membranes are used for desalination, then salt rejection is achieved, but water flux is limited due to osmotic pressure and membrane fouling
Solution Approach 1:
The patent employs a microporous polysulfone support membrane with controlled porosity (40-60% pore volume) as the base layer. The porous structure allows high water permeability while maintaining mechanical strength, enabling water flux >35 gfd at low pressures (65 psi) without compromising the overall membrane integrity for salt rejection
Solution Approach 2:
The patent creates a composite membrane structure by coating the microporous polysulfone support with a polyamide layer formed through interfacial polymerization. This composite approach combines the high porosity and mechanical strength of polysulfone with the selective salt rejection properties of polyamide, achieving both high water flux and effective desalination
2Productivity
If higher operating pressures are applied to increase water flux, then more water passes through the membrane, but osmotic pressure increases making the process less efficient
Solution Approach 1:
The patent fundamentally changes the membrane's physical parameters by creating a thin polyamide layer (50-250 nm) on a highly porous support, reducing the overall membrane thickness from conventional values to <2 μm. This parameter change allows water to pass through with minimal pressure requirement (65 psi), achieving flux >35 gfd without the need for high-pressure operation that would increase energy consumption
3Productivity
If the polyamide layer is made thinner to increase water permeability, then water flux improves, but mechanical strength and fouling resistance deteriorate
Solution Approach 1:
The patent segments the membrane into two functional layers: a thin polyamide layer (50-250 nm) for selective separation and high water permeability, and a thick microporous polysulfone support (100-150 μm) for mechanical strength and structural integrity. This segmentation allows the thin active layer to provide high water flux while the robust support maintains fouling resistance and mechanical durability
4Productivity
If conventional interfacial polymerization is used without additives, then membrane formation is simple, but flux enhancement and fouling resistance are insufficient
Solution Approach 1:
The patent introduces polysulfone as an intermediary substance that serves multiple functions: it forms the microporous support structure, acts as a coating material for the thin-film active layer, and provides fouling resistance. This intermediary material enables flux enhancement and improved durability without significantly complicating the interfacial polymerization process
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 resulting membrane exhibits extremely high water flux (>35 gfd) and high salt rejection (>97%) at low pressures, with a polyamide layer thickness and surface roughness optimized for high permeability and mechanical strength.
Implementation Method 1
an interfacial synthesis method for making the reverse osmosis membrane
Implementation Method 2
reverse osmosis membrane
Implementation Method 3
Osmotic pressure works against the reverse osmosis process
Implementation Method 4
dried at controlled temperatures
Data Source
AI summary
A composite polyamide reverse osmosis membrane comprising a polyamide layer; where the polyamide layer has a thickness in the range of 50-250 nm, and large open spaces (i.e., free volumes); where the open spaces are defined by a ratio of water flux, Jw, (gfd) divided by the average surface roughness, Ra, (nm) of the polyamide layer; wherein the composite polyamide reverse osmosis membrane has the ratio of Jw/Ra>0.35 gfd/nm when tested at 65 psi, using an aqueous solution containing 250 ppm of NaCl; and a microporous support with a thickness ranging from 100-150 μm. The present invention also relates to processes of fabricating the composite polyamide reverse osmosis membrane.