Polyimide Membrane Blend for Hydrogen-Carbon Monoxide Separation
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Solution Overview
Problem
Current membrane technologies for separating hydrogen from synthesis gas, particularly for the Fischer-Tropsch reaction, face challenges in achieving optimal H2/CO ratios due to non-selective separation and energy-intensive cryogenic processes, with issues like membrane plasticization by carbon dioxide and inefficient nitrogen rejection.
Innovation Solution
A non-porous polyimide-based membrane blend of BTDA-DAPI and BTDA-TDI/MDI is used for asymmetric membranes, providing high selectivity and productivity in hydrogen separation from gas mixtures, including nitrogen, carbon dioxide, and water, while maintaining membrane integrity and increasing selectivity with water presence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If cryogenic processes are used to separate hydrogen from synthesis gas, then hydrogen separation can be achieved, but energy consumption increases significantly
Solution Approach 1:
The patent replaces the mechanical cryogenic separation system with a membrane-based separation system using polyimide materials. The membrane process operates at ambient or near-ambient temperatures, substituting the energy-intensive mechanical cooling system with a thermodynamically favorable permeation process that requires minimal external energy input.
Solution Approach 2:
The patent changes the operating temperature parameter from cryogenic conditions to ambient or near-ambient temperatures. This parameter change fundamentally alters the separation mechanism from condensation-based to permeation-based, dramatically reducing energy consumption while maintaining effective hydrogen separation.
2Productivity
If conventional polyimide membranes are used for hydrogen separation, then hydrogen removal can be achieved, but carbon dioxide plasticization decreases membrane selectivity
Solution Approach 1:
The patent employs composite polyimide membrane formulations that combine multiple polyimide components or incorporate cross-linking structures. This composite approach creates a more robust membrane matrix that resists plasticization by carbon dioxide while maintaining high hydrogen permeability and selectivity.
Solution Approach 2:
The patent modifies the local chemical structure and physical properties of the membrane material to create regions with enhanced resistance to carbon dioxide swelling. This localized structural optimization allows the membrane to maintain its selective transport properties even in the presence of plasticizing gases.
3Reliability
If membrane separation is used to adjust H2/CO ratio in synthesis gas, then the optimum ratio for Fischer-Tropsch reaction can be achieved, but high selectivity and productivity are required which current membranes cannot provide
Solution Approach 1:
The patent optimizes multiple parameters including membrane composition, operating temperature, pressure differential, and gas flow rates to achieve both high selectivity and high productivity. By carefully controlling these parameters, the membrane system can simultaneously deliver the required H2/CO ratio adjustment and the necessary separation efficiency for industrial Fischer-Tropsch applications.
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 a remarkably high hydrogen/carbon monoxide selectivity, effectively removing hydrogen to adjust the H2/CO ratio, minimizing nitrogen passage, and reducing carbon dioxide plasticization, thus optimizing the synthesis gas for reactions like methanol synthesis and Fischer-Tropsch processes.
Implementation Method 1
contacting the gas mixture with a non-porous polyimide-based membrane to obtain a hydrogen rich permeate and a hydrogen lean retentate
Implementation Method 2
the presence of water surprisingly increases the selectivity of the membrane while maintaining the productivity
Implementation Method 3
one or more components may exhibit a strong interaction with the membrane material, which can plasticize the membrane. This holds especially for carbon dioxide
Data Source
AI summary
A process for the extraction of hydrogen from a gas mixture including hydrogen and carbon monoxide and optionally nitrogen, carbon dioxide, lower hydrocarbons and/or water, by contacting the gas mixture with a non-porous polyimide-based membrane, especially with the selective side of an asymmetric membrane, to obtain a hydrogen rich permeate and a hydrogen lean retenate, the polyimide-based membrane being a specific mixture of two polyimids. This specific membrane shows a very high hydrogen/carbon monoxide selectivity. The process is especially suitable for the upgrading of synthesis gas obtained by partial oxidation and/or reforming of hydrocarbonaceous feedstream for use in hydrocarbon synthesis reaction as the Fischer-Tropsch reaction.