Self-Cross-Linkable Polyimide Membranes for Gas Separation
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Solution Overview
Problem
Current polymer membrane technologies for gas separation, such as cellulose acetate, face limitations in selectivity, permeability, and stability, and require costly pretreatment systems to prevent liquid condensation, which increases the overall cost and footprint of membrane systems, especially in offshore natural gas upgrading projects.
Innovation Solution
The development of polybenzoxazole (PBO) membranes from self-cross-linkable aromatic polyimide polymers containing hydroxyl and carboxylic acid functional groups, which are cross-linked to prevent densification during thermal rearrangement, resulting in membranes with high permeability and selectivity for gas separation applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If aromatic polyimide membranes are thermally rearranged to convert to PBO membranes, then CO2 permeability is improved (greater than 100 Barrer), but the membrane structure densifies which reduces gas permeance
Solution Approach 1:
The patent applies preliminary action by introducing carboxylic acid functional groups into the polyimide membrane before thermal rearrangement. These groups undergo cross-linking reactions during the thermal treatment process (200-300°C), creating a cross-linked network structure that prevents excessive densification when the membrane is subsequently heated to higher temperatures (350-500°C) for PBO conversion. This preliminary structural modification enables the membrane to maintain both high CO2 permeability and acceptable gas permeance.
Solution Approach 2:
The patent creates a composite structure by combining polyimide chains with cross-linked carboxylic acid groups within the same membrane matrix. The cross-linked regions act as structural anchors that prevent densification, while the polyimide segments provide the necessary flexibility and gas transport pathways. This composite approach allows simultaneous achievement of high CO2 permeability through PBO formation and maintained gas permeance through cross-linking prevention of collapse.
2Reliability
If pretreatment systems are added to remove water and heavy hydrocarbons, then membrane performance stability is improved, but system cost increases by 10 to 40%
Solution Approach 1:
The patent changes the operational parameters of the membrane system by enabling it to function effectively at higher temperatures (350-500°C) where water and heavy hydrocarbon condensation is minimized. The thermal stability of the cross-linked PBO membrane allows operation in conditions that inherently reduce the need for aggressive pretreatment, thereby lowering system costs while maintaining performance stability.
Solution Approach 2:
The patent extracts the pretreatment function from the overall system by designing a membrane that can tolerate and operate in the presence of water and heavy hydrocarbons without requiring their complete removal beforehand. The cross-linked PBO membrane structure provides inherent resistance to these contaminants, effectively removing the need for separate pretreatment systems and reducing overall system complexity and cost.
3Object-affected harmful factors
If pretreatment systems are installed to lower dew point, then liquid condensation is prevented, but system footprint increases by 10 to 50%
Solution Approach 1:
The patent changes the operational temperature parameter to 350-500°C, where the dew point of natural gas is significantly lower, eliminating liquid condensation issues without requiring large pretreatment systems. The thermally stable cross-linked PBO membrane structure maintains its integrity and performance at these elevated temperatures, enabling condensation-free operation in a compact footprint.
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 PBO membranes exhibit significantly improved CO2 and H2 permeance and selectivity, reducing the need for costly pretreatment systems and minimizing membrane system footprint, making them suitable for efficient gas separation in various industrial applications.
Implementation Method 1
cross-linking the self-cross-linkable aromatic polyimide polymer membrane to form a self-cross-linked aromatic polyimide polymer membrane by heating the membrane at 250° C. to 300° C.
Implementation Method 2
thermal heating the self-cross-linked aromatic polyimide polymer membrane at a temperature from about 350° to 500° C. to convert the self-cross-linked aromatic polyimide polymer membrane into a PBO membrane
Implementation Method 3
The PBO membranes exhibit significantly improved CO2 and H2 permeance and selectivity
Data Source
AI summary
A method for separation of liquid mixtures with a polybenzoxazole (PBO) membrane from a self-cross-linked aromatic polyimide polymer membrane is provided.