Osmotic Membrane Composite Support Layer
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Solution Overview
Problem
State-of-the-art reverse osmosis membranes are unsuitable for desalinating feed solutions with salt concentrations above 50,000 ppm due to the high hydraulic pressure required, which compromises membrane integrity and leads to severe internal concentration polarization.
Innovation Solution
A counter-flow reverse osmosis membrane with a composite support layer comprising an electrospun-fiber sub-layer and a phase-inversion sub-layer, optimized to balance mechanical strength and porosity, allowing for reduced osmotic pressure gradients and lower hydraulic pressures, thereby preventing membrane strain and enhancing water flux.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high hydraulic pressure is applied to overcome osmotic pressure for desalination, then water production rate increases, but membrane mechanical integrity is compromised
Solution Approach 1:
The support layer is segmented into two distinct sub-layers: a porous sub-layer (5-20 μm thick) providing mechanical strength, and a highly porous sub-layer (10-50 μm thick) with >90% porosity to minimize concentration polarization. This segmentation allows each layer to specialize in one function, resolving the contradiction between strength and low polarization.
Solution Approach 2:
The membrane uses a composite structure combining different materials: polyamide active layer, polysulfone or polyethersulfone for the porous support layer, and a highly porous material for the second sub-layer. This composite approach enables simultaneous achievement of mechanical strength, chemical stability, and low concentration polarization.
2Productivity
If support layer porosity is increased to reduce internal concentration polarization, then water flux improves, but mechanical strength decreases
Solution Approach 1:
The support layer is divided into two functional zones: the first sub-layer (5-20 μm) with moderate porosity (40-70%) provides mechanical strength, while the second sub-layer (10-50 μm) with high porosity (>90%) minimizes concentration polarization. This segmentation resolves the contradiction by assigning different porosity levels to different functional requirements.
Solution Approach 2:
Different regions of the support layer have different porosity characteristics tailored to their specific functions. The region closer to the active layer has moderate porosity for strength, while the region farther away has high porosity for reducing polarization, optimizing both mechanical and transport properties locally.
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 fine balance between mechanical strength and low internal concentration polarization, enabling efficient desalination of high-salt solutions without compromising the membrane, allowing for increased water production while maintaining membrane integrity.
Implementation Method 1
The osmotic membrane can be fabricated by electrospinning an electrospun-fiber sub-layer, casting a phase-inversion sub-layer on the electrospun-fiber sub-layer
Implementation Method 2
casting a phase-inversion sub-layer on the electrospun-fiber sub-layer
Implementation Method 3
The water production rate (J) is a function of the applied hydraulic pressure, as shown in the following equation: J=A(ΔP−Δπ), where A is the pure water permeability constant of the membrane; ΔP is the hydraulic pressure gradient; and Δπ is the osmotic pressure gradient
Implementation Method 4
An RO membrane is generally used for the removal of dissolved ions, e.g., sodium, calcium, magnesium, chloride, bromide, etc.
Implementation Method 5
The membrane can have both a low structural parameter and high mechanical strength so as to make the CFRO process feasible. The membrane can achieve a fine balance between having sufficient mechanical strength and exhibiting a low internal concentration polarization in the support layer.
Data Source
AI summary
An osmotic membrane comprises an active layer and a composite support layer. The active layer selectively allows passage of water molecules but rejects at least some dissolved ions. The composite support layer includes a side that is bonded to the active layer and comprises an electrospun-fiber sub-layer and a phase-inversion sub-layer.