Cross-linked Polybenzoxazole Membranes for Gas Separation
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Solution Overview
Problem
Current polymer membranes for gas separation face limitations in selectivity and permeability, with high permeability often leading to reduced selectivity and vice versa, and are prone to plasticization and solvent swelling, while inorganic molecular sieve membranes are costly and mechanically unstable.
Innovation Solution
Development of high-performance cross-linked polybenzoxazole and polybenzothiazole polymer membranes with UV cross-linkable functional groups and pendent functional groups, thermally converted and exposed to UV radiation for enhanced selectivity and stability, eliminating the need for molecular sieves and pretreatment systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If polymer membranes are designed to achieve high permeability, then gas flux increases, but selectivity decreases
Solution Approach 1:
The patent uses composite polymer structures combining polybenzoxazole or polybenzothiazole with cross-linking agents to create a membrane that achieves both high permeability and high selectivity. The cross-linked network structure provides selective pathways while maintaining open channels for gas transport, resolving the traditional trade-off between flux and selectivity.
Solution Approach 2:
The patent modifies the polymer membrane parameters by introducing cross-links through UV irradiation or chemical agents, changing the free volume distribution and chain mobility. This parameter change enables the membrane to maintain high permeability while achieving superior selectivity that cannot be obtained with conventional linear polymer structures.
2Reliability
If polymer membranes are designed to achieve high selectivity, then gas separation purity increases, but permeability decreases
Solution Approach 1:
The cross-linked composite structure creates a dual-function membrane where the cross-linked network provides selectivity through its ordered architecture while the resulting free volume maintains high permeability. This composite approach inverts the traditional selectivity-permeability trade-off.
Solution Approach 2:
The cross-linking creates local regions of high density and order within the polymer matrix, providing selective sites for gas separation, while simultaneously creating interconnected free volume channels that maintain high permeability. This local quality differentiation resolves the contradiction between selectivity and permeability.
3Ease of manufacture
If conventional polymer membranes are used, then manufacturing is simple, but thermal stability and contaminant resistance are insufficient
Solution Approach 1:
The patent incorporates cross-linkable functional groups into the polymer structure during synthesis, and performs cross-linking as a preliminary step before membrane deployment. This preliminary action of cross-linking locks in thermal stability and contaminant resistance while maintaining ease of manufacture through standard polymer processing techniques.
Solution Approach 2:
The patent replaces physical blending or surface coating methods with chemical cross-linking to achieve thermal stability. The cross-linked chemical bonds provide inherent thermal resistance without complicating the manufacturing process, as cross-linking can be performed in-situ during membrane formation.
4Area of stationary object
If membrane area is reduced to decrease capital cost, then equipment size decreases, but separation performance may be compromised
Solution Approach 1:
The cross-linked polymer membrane achieves superior intrinsic permeability and selectivity parameters compared to conventional membranes. This parameter enhancement allows the membrane to achieve the required separation performance with significantly reduced area, directly reducing capital cost while maintaining or improving productivity.
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 cross-linked membranes exhibit improved selectivity and permeability, resistance to solvent swelling and plasticization, and sustained performance over time, reducing the need for costly pretreatment systems and minimizing membrane area and footprint.
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
The high performance cross-linked polybenzoxazole and polybenzothiazole polymer membranes described in the current invention comprise polybenzoxazole or polybenzothiazole polymer chain segments wherein at least a part of these polymer chain segments are cross-linked to each other through possible direct covalent bonds by exposure to UV radiation.
Data Source
AI summary
In the present invention high performance cross-linked polybenzoxazole and polybenzothiazole polymer membranes and methods for making and using these membranes have been developed. The cross-linked polybenzoxazole and polybenzothiazole polymer membranes are prepared by: 1) first synthesizing polyimide polymers comprising pendent functional groups (e.g., —OH or —SH) ortho to the heterocyclic imide nitrogen and cross-linkable functional groups in the polymer backbone; 2) fabricating polyimide membranes from these polymers; 3) converting the polyimide membranes to polybenzoxazole or polybenzothiazole membranes by heating under inert atmosphere such as nitrogen or vacuum; and 4) finally converting the membranes to high performance cross-linked polybenzoxazole or polybenzothiazole membranes by a crosslinking treatment, preferably UV radiation. The membranes can be fabricated into any convenient geometry. The high performance cross-linked polybenzoxazole and polybenzothiazole polymer membranes of the present invention are suitable for a variety of liquid, gas, and vapor separations.