Microporous PVDF Membrane for High-Pressure Membrane Distillation
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Solution Overview
Problem
Existing membranes for membrane distillation and microfiltration face challenges in maintaining high water vapor permeability while preventing water permeation, especially under high pressure, due to structural changes in pore sizes and mechanical instability.
Innovation Solution
A hydrophobic flat membrane made from vinylidene fluoride polymer with a microporous, sponge-like structure across 80% of its thickness, featuring island-shaped pores on one surface and a network structure on the other, with a weight-average molecular weight between 300,000 to 500,000 daltons and a polydispersivity greater than 5.5, ensuring isotropic pore distribution and high mechanical strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the membrane uses a conventional pore structure for microfiltration, then water removal capability is improved, but water vapor permeability deteriorates
Solution Approach 1:
The membrane employs different pore size distributions in different regions: larger pores (1-10 μm) in the support layer provide mechanical strength and water filtration, while smaller pores (0.1-1 μm) in the selective layer enable water vapor permeability. This spatial differentiation of pore qualities resolves the contradiction between water removal and vapor transmission.
2Quantity of substance
If the membrane pores are enlarged to increase water vapor permeability, then water vapor transmission is improved, but mechanical stability deteriorates
Solution Approach 1:
The membrane is segmented into two functional layers: a support layer with larger pores providing mechanical integrity, and a selective layer with smaller pores providing vapor permeability while maintaining structural stability. This segmentation allows each layer to optimize its function without compromising the other.
3Reliability
If the membrane uses a dense structure to prevent water permeation, then selectivity is improved, but water vapor permeability deteriorates
Solution Approach 1:
The membrane utilizes a hierarchical porous structure with two distinct pore size ranges. The support layer pores (1-10 μm) prevent liquid water permeation through capillary pressure, while the selective layer pores (0.1-1 μm) allow water vapor transmission. This porous material design achieves both selectivity and vapor permeability simultaneously.
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 high mass flows for water vapor without water breakthrough and exhibits excellent mechanical stability, including high breaking strength and elongation, suitable for both membrane distillation and microfiltration applications.
Implementation Method 1
a hydrophobic membrane in the form of a flat membrane made from a vinylidene fluoride polymer
Implementation Method 2
For the vapor phase, i.e. for water vapor, however, the membrane is permeable and water vapor can permeate the pores of the membrane
Implementation Method 3
the hydrostatic pressure on the side of the membrane on which the water to be treated is located must be lower than the permeation pressure, that is, the pressure at which permeation of the water through the membrane begins to take place
Implementation Method 4
a microporous supporting layer having a sponge-like, open-pored pore structure that is substantially isotropic across the wall thickness
Implementation Method 5
The process is a thermally driven separation method in which the separation—as with conventional distillation—takes place due to a phase change
Implementation Method 6
water vapor can permeate the pores of the membrane
Implementation Method 7
results in condensation on the permeate side of the membrane of the water molecules permeating through the membrane
Data Source
AI summary
Hydrophobic flat membrane made from a vinylidene fluoride polymer with a wall, a first surface, and a second surface. The membrane has on its first surface a network structure with open pores and on its second surface a continuous skin in which pores are formed, and adjacent to the skin of the second surface a supporting layer with an isotropic pore structure across the wall thickness, wherein the supporting layer extends over at least 80% of the wall thickness and wherein the pores of the supporting layer have an average diameter of less than 1 μm. The weight average of the molecular weight MW of the vinylidene fluoride polymer lies in the range from 300 000 to 500 000 daltons, and the polydispersivity MW/MN is greater than 5.5.The pores in the skin of the second surface have a closed perimeter in the plane of the skin and an average ratio of the extension in the direction of the longest axis thereof to the extension in the direction of the shortest axis thereof of at most 5. The pores in the first surface and second surface have an essentially isotropic distribution of their orientation. The porosity of the membrane lies in the range from 50 to 90 vol. % and the wall thickness in the range from 50 to 300 μm. The membrane has a maximum separating pore diameter dmax in the range from 0.05 to 1.5 μm.