Defect-Free CMS Membrane via Pyrolysis for Gas Separation
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Solution Overview
Problem
Current carbon molecular sieve (CMS) membranes suffer from defects such as pinholes, leading to reduced hydrogen permeance and selectivity, particularly for the separation of gases like H2, CO2, and liquids like water and alcohols, due to their high porosity and roughness, which compromises their efficiency in separating gas and liquid mixtures with small kinetic diameter differences.
Innovation Solution
A defect-free ultrathin CMS membrane is developed using a polyimide precursor, specifically Alfa Aesar polyimide, supported on an α-Al2O3/γ-Al2O3 composite structure, with a mesoporous intermediate layer and optimized pyrolysis conditions to create a thin, crack-free carbon layer with precise pore sizes, enhancing gas and liquid separation capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional CMS membranes are used with high porosity and roughness, then gas permeability is improved, but separation selectivity deteriorates due to defects like pinholes
Solution Approach 1:
The patent applies local quality by creating distinct regions within the membrane structure: a dense defect-free selective layer (50-200 nm thick) for high selectivity, and a porous support layer for mechanical strength and additional permeability. This local differentiation allows the membrane to simultaneously achieve high gas permeability through the porous support and high separation selectivity through the dense selective layer, resolving the contradiction between productivity and reliability.
Solution Approach 2:
The patent employs composite materials by combining a defect-free carbon molecular sieve membrane layer with a porous support structure (such as alumina or stainless steel). This composite construction allows the dense CMS layer to provide high separation selectivity while the porous support provides mechanical integrity and contributes to overall gas permeability, thus resolving the contradiction between selectivity and permeability.
2Reliability
If membrane thickness is reduced to improve separation efficiency, then selectivity is improved, but mechanical strength deteriorates
Solution Approach 1:
The patent applies segmentation by dividing the membrane into two functional segments: a thin defect-free selective layer (50-200 nm) for high separation efficiency and a thicker porous support layer for mechanical strength. This segmentation allows each layer to optimize its specific function, with the thin selective layer providing high selectivity and the porous support providing structural integrity, thus resolving the contradiction between separation efficiency and mechanical strength.
Solution Approach 2:
The patent uses a thin film approach by creating an ultrathin defect-free carbon molecular sieve membrane layer (50-200 nm) that provides high separation efficiency. This thin film is then supported on a mechanically robust porous substrate, allowing the membrane to achieve high separation performance while maintaining sufficient mechanical strength through the support structure.
3Stability of the object's composition
If pyrolysis temperature is increased to improve membrane stability, then chemical stability is improved, but pore size uniformity deteriorates
Solution Approach 1:
The patent applies parameter changes by optimizing the pyrolysis temperature range (600-900°C) and holding time (1-4 hours) to achieve the desired balance between chemical stability and pore size uniformity. By carefully controlling these thermal processing parameters, the patent produces a defect-free carbon membrane with consistent micropore structure and high chemical stability, resolving the contradiction between stability and manufacturing precision.
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 resulting CMS membrane exhibits high hydrogen permeance and selectivity for gases like H2/CO2, H2/N2, and H2/CH4, and effective dehydration of aqueous alcohol mixtures, surpassing previous CMS membranes in separation performance and durability, with reproducible results across multiple samples.
Implementation Method 1
Carbon molecular sieve membranes are typically prepared by pyrolysis (carbonization) of various types of polymer precursors in vacuum or inert atmosphere. After decomposition of the thermally unstable polymeric components, a thermally stable carbon framework is formed
Implementation Method 2
The molecular sieve mechanism relies on size exclusion to separate gas mixtures. Pores within the membrane have a strictly controlled size relative to the kinetic diameter of the gas molecules. This allows the smaller gas molecules to diffuse at much higher rates than the larger gas molecules.
Implementation Method 3
Knudsen separation is based on certain gas molecules passing through membrane pores small enough to prevent all of the gas from passing through.
Implementation Method 4
A thin layer of γ-Al2O3 is provided as an intermediate layer between the support and the CMS membrane
Data Source
AI summary
Disclosed are a CMS membrane, characterized in that it is obtainable by pyrolysis of a polyimide composed of the monomers 1-(4-aminophenyl)-1,3,3-trimethyl-2H-inden-5-amine and 5-(1,3-dioxo-2-benzofuran-5-carbonyl-2-benzofuran-1,3-dione of the following formulae:preferably by pyrolysis of the polyimide having the CAS number 62929-02-6, and a supported CMS membrane comprising a CMS membrane obtainable from a polyimide by pyrolysis and a porous support, characterized in that a mesoporous intermediate layer is provided between the CMS membrane and the porous support.Further disclosed are a process for preparing the supported membrane, the use of the membranes for separating gas mixtures or liquid mixtures, an apparatus for gas separation or for liquid separation, and the use of the polyimide for preparing a CMS membrane by pyrolysis.