Asymmetric PVDC Membrane Carbonization for Gas Separation
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Solution Overview
Problem
Asymmetric carbon molecular sieve membranes derived from polyvinylidene chloride (PVDC) copolymers face structural collapse and thickening issues during carbonization, limiting their productivity and separation efficiency, especially for gases with similar molecular sizes like hydrogen/ethylene and ethane/propylene.
Innovation Solution
A method involving the formation of an asymmetric PVDC copolymer membrane by heating it to a pretreatment temperature of 100°C to 180°C, followed by pyrolysis from 350°C to 1700°C to create a carbon molecular sieve membrane, which stabilizes the microstructure and maintains the separation layer thickness, preventing structural collapse and enhancing separation efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If asymmetric resin membranes are pyrolyzed to form CMS membranes, then gas separation performance is improved, but structural collapse and thickening of the dense separating layer occur due to consolidation or sintering during carbonization
Solution Approach 1:
The patent applies parameter changes by carefully controlling pyrolysis temperature (350-1700°C) and atmosphere (inert or reducing conditions) to achieve carbonization while minimizing structural collapse. The asymmetric membrane structure is preserved through optimized thermal treatment parameters that convert the resin to carbon without excessive consolidation
Solution Approach 2:
The patent employs preliminary action by first forming a stable asymmetric resin membrane structure with a dense separating layer supported by a porous substrate, then applying controlled pre-treatment before pyrolysis. This preliminary structural preparation prevents collapse during the subsequent carbonization process
2Ease of manufacture
If PVDC copolymer is pyrolyzed to form carbon molecular sieve, then micropore structure is created for gas separation, but larger pores are formed reducing separation efficiency for small molecules
Solution Approach 1:
The patent controls pore size by adjusting pyrolysis temperature and holding time. Lower temperatures (350-600°C) produce smaller micropores suitable for separating small gas molecules, while higher temperatures create larger pores. The patent optimizes these parameters based on the target gas separation application
Solution Approach 2:
The patent employs feedback control by characterizing the micropore structure (using techniques like gas adsorption, mercury intrusion, or microscopy) after pyrolysis, then adjusting pyrolysis conditions in subsequent batches to achieve the desired pore size distribution for optimal separation performance
3Strength
If asymmetric membrane structure is used to maintain structural integrity, then membrane strength is improved, but productivity is compromised due to the need for thicker separating layers
Solution Approach 1:
The patent utilizes asymmetry by designing a membrane with a thin dense separating layer (0.1-10 μm) supported by a thicker porous support layer (10-100 μm). This asymmetric structure provides both the separation function in the thin layer and the mechanical strength from the thick support, optimizing both productivity and structural integrity
Solution Approach 2:
The patent applies local quality by giving different regions of the membrane different properties: the separating layer has high density and low porosity for gas separation, while the support layer has high porosity (30-70%) and appropriate mechanical strength for structural support, allowing each region to optimize its specific function
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 method effectively produces carbon molecular sieve membranes that maintain desirable productivity and separation efficiency for gases with similar molecular sizes, such as hydrogen/ethylene and ethane/propylene, without structural collapse, and can be used in gas separation modules for efficient gas separation.
Implementation Method 1
heating it to a pretreatment temperature of 100°C to 180°C
Implementation Method 2
pyrolysis from 350°C to 1700°C
Data Source
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AI summary
An asymmetric polyvinylidene chloride copolymer membrane is made by a method using a dope solution comprised of a polyvinylidene chloride copolymer and a solvent that solubilizes the polyvinylidene chloride copolymer that is shaped to form an initial shaped membrane. The initial shaped membrane is then quenched in a liquid comprised of a solvent that is miscible with the solvent that solubilizes the polyvinylidene chloride copolymer but is immiscible with the polyvinylidene chloride copolymer to form a wet asymmetric polyvinylidene chloride copolymer membrane. The solvents are removed from the wet membrane to form the asymmetric polyvinylidene chloride (PVDC) copolymer membrane. The membrane then may be further heated to form a carbon asymmetric membrane in which the porous support structure and separation layer of the PVDC membrane is maintained. The asymmetric carbon membrane may be useful to separate gases such as olefins from their corresponding paraffins, hydrogen from syngas or cracked gas, natural gas or refinery gas, oxygen/nitrogen, or carbon dioxide and methane.