Bilayer Polyamide Membrane Salt Rejection

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Solution Overview

Problem

High-performance composite reverse osmosis membranes for seawater desalination face challenges due to variability in manufacturing processes, leading to inconsistent salt rejection and selectivity, which can result in membranes falling below desired performance levels.

Innovation Solution

The development of bilayer polyamide composite membranes, where a rigid, crosslinked aromatic polyamide base layer is overlaid with a flexible, crosslinked aliphatic polyamide layer, enhancing salt rejection characteristics and reducing salt passage by up to 60% compared to monolayer polyamide compositions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a monolayer aromatic polyamide membrane is used, then salt rejection is achieved, but manufacturing variability causes performance inconsistency

Engineering Contradiction:

Improvesalt rejection consistencyVSAvoidmembrane performance uniformity

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The single polyamide layer is segmented into two distinct layers: a base layer of aromatic polyamide and a top layer of aliphatic polyamide. This segmentation allows each layer to perform specific functions - the aromatic base layer provides structural integrity and baseline salt rejection, while the aliphatic top layer enhances selectivity and compensates for manufacturing defects, thereby improving overall reliability and reducing performance inconsistency.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention uses a composite bilayer structure combining aromatic polyamide and aliphatic polyamide. This composite material approach leverages the complementary properties of both polymers - the rigidity and chemical stability of aromatic polyamide with the flexibility and defect-tolerance of aliphatic polyamide - to create a membrane that maintains consistent salt rejection performance despite manufacturing variability.

Inventive Principle:

Principle #40Composite materials

2Manufacturing precision

If manufacturing conditions are strictly controlled, then membrane quality improves, but process complexity and cost increase

Engineering Contradiction:

Improvemembrane quality consistencyVSAvoidmanufacturing process complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The aliphatic polyamide top layer acts as a cushioning layer that compensates for potential manufacturing defects in the aromatic polyamide base layer. By incorporating this additional layer, the design preemptively addresses quality issues that might arise during manufacturing, reducing the need for extremely tight process control while maintaining high membrane quality consistency.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Solution Approach 2:

The invention changes the chemical composition parameter by introducing a second polyamide type (aliphatic) with different properties than the base layer (aromatic). This parameter change in material composition provides a buffer against manufacturing variability, allowing the process to tolerate wider parameter fluctuations while still producing consistent quality membranes.

Inventive Principle:

Principle #35Parameter changes

3Productivity

If membrane thickness is reduced for higher flux, then productivity increases, but salt rejection may deteriorate

Engineering Contradiction:

Improvewater fluxVSAvoidsalt rejection

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The bilayer structure applies local quality differentiation where the aromatic polyamide base layer provides the primary separation function with appropriate thickness for salt rejection, while the aliphatic polyamide top layer (typically thinner) enhances selectivity and provides a defect-tolerant surface. This local optimization allows the membrane to maintain high salt rejection even with reduced overall thickness, thereby supporting higher water flux and productivity.

Inventive Principle:

Principle #3Local quality

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 bilayer polyamide membranes demonstrate superior salt rejection and reduced salt passage, maintaining high performance even under variable manufacturing conditions, effectively addressing the inconsistency issues in existing membrane technologies.

Implementation Method 1

a rigid, crosslinked, aromatic polyamide serving as a base layer is overlaid by a second layer of a crosslinked aliphatic polyamide

Methodology Applied

Scientific EffectInterfacial polymerization: Chemical Bonding

Implementation Method 2

the same having a second layer made by reaction of a polymeric aliphatic polyamine with a polyacyl halide

Methodology Applied

Scientific EffectInterfacial polymerization: Chemical Bonding

Implementation Method 3

reverse osmosis membranes for water treatment, and more particularly to improved composite reverse osmosis membranes for use in desalination

Methodology Applied

Scientific EffectReverse osmosis: Reverse Osmosis

Data Source

PatentUS11684895B2Bilayer polyamide desalination membrane

Publication Date: 2023.06.27 NL CHEMICAL TECHNOLOGY

AI summary

A composite reverse osmosis membrane having a semipermeable bilayer polyamide composition comprising a base layer containing a rigid crosslinked aromatic polyamide and a top layer containing a flexible aliphatic polyamide is disclosed, the two layers in combination providing reduced salt passage in reverse osmosis desalination of brackish waters and of seawater.