Carbon Molecular Sieve Membranes for Nitrogen Methane Separation
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Solution Overview
Problem
Current nitrogen rejection technologies for natural gas are costly and energy-intensive, particularly for small-scale operations, and existing membrane technologies struggle to achieve high selectivity and permeability for nitrogen/methane separation, limiting their effectiveness in removing nitrogen from natural gas to meet pipeline specifications.
Innovation Solution
Development of carbon molecular sieve membranes (CMSM) derived from pyrolyzed polyimide precursors, which are subjected to high temperatures in an inert atmosphere to achieve high nitrogen/methane selectivity and permeability, utilizing the difference in kinetic diameters and sorption coefficients to enhance diffusion selectivity and permeability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional polymer membranes are used for nitrogen/methane separation, then the membrane structure is simple and easy to manufacture, but the nitrogen permeability and selectivity are insufficient to meet pipeline specifications
Solution Approach 1:
The patent applies parameter changes by controlling pyrolysis temperature (600-900°C) and duration to transform the polymer precursor membrane into a carbon molecular sieve membrane with optimized pore structure. This thermal treatment parameter change creates the desired balance between nitrogen permeability (≥3.0 Barrers) and selectivity (≥5.0) while maintaining manufacturing feasibility through a single-step pyrolysis process
Solution Approach 2:
The patent utilizes phase transitions during pyrolysis where the polymer precursor undergoes thermal decomposition and phase transformation into carbonized structure. This phase transition from organic polymer to carbon molecular sieve fundamentally changes the membrane's permeability and selectivity properties, enabling it to meet pipeline specifications while maintaining structural integrity
2Productivity
If cryogenic distillation is used for nitrogen removal, then the methane recovery rate is high (about 98%), but the energy consumption is high and pretreatment complexity increases
Solution Approach 1:
The patent replaces the mechanical cryogenic distillation system with a membrane separation system based on molecular sieve principles. This substitution eliminates the need for complex cooling equipment, condensers, and reboilers, significantly reducing energy consumption while maintaining high methane recovery through selective nitrogen permeation through the carbon molecular sieve membrane
Solution Approach 2:
The patent employs carbon molecular sieve membrane with controlled porous structure (pore size 0.3-0.8 nm) that enables size-sieving mechanism for nitrogen/methane separation. The porous structure allows nitrogen molecules to pass through while retaining methane, achieving high recovery rates without the energy-intensive cryogenic conditions required by traditional distillation
3Adaptability or versatility
If pressure swing adsorption or liquid absorption is used for nitrogen removal, then the process is suitable for small throughputs, but the technology maturity and reliability are lower compared to cryogenic distillation
Solution Approach 1:
The patent employs a disposable-like membrane module that can be easily replaced rather than requiring complex PSA or liquid absorption systems. The membrane module provides reliable nitrogen removal for small throughput applications with simpler infrastructure, achieving comparable reliability to mature technologies while being specifically optimized for small-scale deployments where cryogenic distillation would be overly complex
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 CMSM achieves nitrogen/methane selectivity of at least 5.0 and permeability of at least 3.0 Barrers, exceeding the performance of traditional polymer membranes and enabling efficient nitrogen removal from methane streams with lower energy consumption and capital costs, suitable for small-scale operations.
Implementation Method 1
diffusion selectivity in carbon molecular sieve membranes
Implementation Method 2
carbon molecular sieve membranes (CMSM)
Implementation Method 3
subjecting a polymer precursor membrane to a pyrolysis temperature of at least about 675° C. in an inert atmosphere
Data Source
AI summary
The various embodiments of the disclosure relate generally to carbon molecular sieve membranes (CMSM) and their associated fabrication processes for the separation of nitrogen/methane gas mixtures, and more particularly to CMSM that maintain high nitrogen-methane selectivity and high gas permeabilities. Methods for removing nitrogen from a nitrogen methane mixture gas via the use of the CMS membranes and gas enrichment devices using the same are also disclosed.