Polyimide/PES Blend Hollow Fiber Membrane for Gas Separation
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Solution Overview
Problem
Current gas separation membranes, particularly those used for hydrogen purification and biogas purification, face challenges in achieving both high selectivity and permeability, which are essential for efficient gas separation processes such as H2/CH4, He/CH4, and CO2/CH4 separations, due to limitations in material properties like mechanical stability and chemical resistance.
Innovation Solution
A new asymmetric polyimide/PES blend hollow fiber membrane is developed, combining polyethersulfone (PES) and polyimide polymers with specific repeating units, which form molecular-level blends without phase separation, enhancing both intrinsic gas permeability and selectivity. The membrane structure includes a thin selective skin layer on a porous support, achieved through a dry-wet phase inversion technique using solvents like N-methylpyrrolidone and 1,3-dioxolane, and optionally coated with materials like polysiloxane for improved performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a thin selective skin layer is used to improve selectivity, then gas separation selectivity is improved, but mechanical strength and stability deteriorate
Solution Approach 1:
The patent uses a composite structure combining polyimide and polyethersulfone (PES) polymers to create a membrane that achieves both high selectivity and mechanical strength. The polyimide provides selectivity for gas separation while the PES component enhances mechanical stability and chemical resistance, resolving the contradiction between thin skin layer selectivity and mechanical strength.
Solution Approach 2:
The patent creates an asymmetric membrane structure with a thin selective skin layer (less than 50 nm) on one side and a thicker support layer on the other side. The thin skin layer provides high selectivity for gas separation while the thicker support layer provides mechanical strength, effectively applying local quality to different regions of the membrane.
2Measurement precision
If polymer backbone stiffness is increased to improve selectivity for small molecules, then selectivity for H2/CH4 and He/CH4 is improved, but permeability for larger molecules deteriorates
Solution Approach 1:
The patent combines polyimide (with stiff backbone for small molecule selectivity) and polyethersulfone (with more flexible backbone) to create a composite membrane. This allows the membrane to maintain selectivity for small molecules like H2 and He while improving permeability for larger molecules compared to pure polyimide membranes.
3Temperature
If polyimide is used to improve thermal stability and selectivity, then thermal stability and selectivity are improved, but chemical resistance and mechanical stability deteriorate
Solution Approach 1:
The patent creates a composite membrane where polyimide provides thermal stability and selectivity, while polyethersulfone (PES) contributes superior chemical resistance and mechanical stability. The PES component compensates for the chemical vulnerability of polyimide, creating a balanced membrane material with both thermal and chemical stability.
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 polyimide/PES blend membrane exhibits higher selectivities and permeabilities compared to individual polyimide or PES membranes, effectively separating gas pairs like H2/CH4, He/CH4, and CO2/CH4, with a super thin selective skin layer less than 50 nm, resulting in high permeance and selectivity for various gas separation applications.
Implementation Method 1
Separation is based on a solution-diffusion mechanism. This mechanism involves molecular-scale interactions of the permeating gas with the membrane polymer. The mechanism assumes that in a membrane having two opposing surfaces, each component is sorbed by the membrane at one surface, transported by a gas concentration gradient, and desorbed at the opposing surface.
Implementation Method 2
each component is sorbed by the membrane at one surface, transported by a gas concentration gradient, and desorbed at the opposing surface
Implementation Method 3
The PA is the product of the gas flux and the selective skin layer thickness of the membrane, divided by the pressure difference across the membrane
Data Source
AI summary
A low cost, high selectivity asymmetric polyimide/polyethersulfone (PES) blend hollow fiber membrane, a method of making the membrane and its use for a variety of liquid, gas, and vapor separations such as deep desulfurization of gasoline and diesel fuels, ethanol/water separations, pervaporation dehydration of aqueous/organic mixtures, CO2/CH4, CO2/N2, H2/CH4, He/CH4, O2/N2, H2S/CH4, olefin/paraffin, iso/normal paraffins separations, and other light gas mixture separations. The polyimide/PES blend hollow fiber membrane is fabricated from a blend of a polyimide polymer and PES and showed surprisingly unique gas separation property with higher selectivities than either the polyimide hollow fiber membrane without PES polymer or the PES hollow fiber membrane without PES polymer for gas separations such as for H2/CH4, He/CH4, H2S/CH4, CO2/CH4 separations.