6FDA-Based Co-Polyimide Membranes for Sour Gas Separation
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Solution Overview
Problem
Current natural gas treatment technologies, such as amine absorption and pressure swing adsorption, face challenges with high energy requirements and capital costs, and existing membrane materials for sour gas separations, like rubbery polymeric membranes, exhibit low CO2/CH4 separation capability and mechanical instability.
Innovation Solution
Development of hexafluorodianhydride (6FDA)-based aromatic co-polyimide membranes with specific monomers like 4,4′-(Hexafluoroisopropylidene)diphthalic anhydride, 9,9-bis(4-aminophenyl) fluorene (CARDO), and 2,3,5,6-tetramethyl-1,4-phenylenediamine, which enhance gas separation properties through copolymerization and chemical modifications, resulting in high selectivities and permeabilities for CO2/CH4 and H2S/CH4 separations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If rubbery polymeric membranes are used for sour gas separations, then mechanical flexibility is improved, but CO2/CH4 separation capability and mechanical stability deteriorate
Solution Approach 1:
The patent employs composite membrane structures combining rubbery polymer layers with glassy polymer layers or inorganic fillers. This composite approach allows the membrane to achieve both mechanical flexibility from the rubbery phase and high CO2/CH4 separation capability from the glassy phase or inorganic components, resolving the contradiction between ease of operation and reliability
2Reliability
If conventional amine absorption processes are used for natural gas treatment, then acid gas removal capability is improved, but energy requirements and capital costs increase
Solution Approach 1:
The patent replaces the mechanical/thermal amine absorption process with a membrane-based separation system that operates at near-ambient conditions. The membrane selectively transports acid gases through its structure based on size exclusion and solubility differences, eliminating the need for energy-intensive heating, cooling, and solvent circulation required by conventional amine processes, thus resolving the contradiction between reliability and energy consumption
3Reliability
If glassy polyimide membranes are used for acid gas separations, then CO2/CH4 separation capability is improved, but mechanical stability at high temperatures deteriorates
Solution Approach 1:
The patent creates composite membranes by incorporating inorganic fillers (such as metal oxides, zeolites, or ceramic particles) into the glassy polyimide matrix. These inorganic components provide enhanced mechanical stability and thermal resistance while the polyimide matrix maintains the selective transport pathways for CO2/CH4 separation, thus resolving the contradiction between reliability and strength
4Strength
If membrane thickness is increased to improve mechanical strength, then mechanical stability is improved, but gas permeability deteriorates
Solution Approach 1:
The patent employs porous membrane structures with controlled pore sizes and distributions. The porous architecture provides mechanical reinforcement through the pore walls and framework while maintaining high gas permeability through the interconnected pore channels. This allows the membrane to achieve both mechanical stability and high productivity by utilizing the pore structure rather than relying solely on increased thickness
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 6FDA-based co-polyimide membranes demonstrate improved thermal stability, mechanical strength, and resistance to penetrant-induced plasticization, achieving high CO2/CH4 selectivities and permeabilities, even at high H2S concentrations, with reduced energy needs and lower operational costs compared to conventional methods.
Implementation Method 1
These high glass transition temperature (Tg) (Tg>about 300° C.) materials develop certain acid gas separation capability based on size selectivity
Implementation Method 2
CO2 permeability is in a range of about 175-239 Barrer and CO2/CH4 selectivity is up to about 39
Implementation Method 3
the presence of a CF3 group in the polymer results in chain stiffness, which causes certain membranes incorporating 6FDA to separate molecules based on steric bulk more effectively. The CF3 group also leads to increased permeability due to inhibition of chain packing
Implementation Method 4
9,9-bis(4-aminophenyl) fluorene-(CARDO-) type aromatic co-polyimide membranes... at least three distinct moieties polymerized together
Data Source
AI summary
Co-polyimide membranes for separating components of sour natural gas where embodiments can include at least three distinct moieties polymerized together, the moieties including a 2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) based moiety; a 9,9-bis(4-aminophenyl) fluorene (CARDO) based moiety; and 2,3,5,6-tetramethyl-1,4-phenylenediamine (durene diamine) based moiety.