Polydimethylsiloxane Membrane for CO2 Permeability and Nitrogen Selectivity
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Solution Overview
Problem
Existing gas selective permeable composite membranes, such as those made from organosiloxane compounds, have limitations in gas separability of carbon dioxide from nitrogen and gas permeability.
Innovation Solution
A gas separation membrane composed of a first layer made of organopolysiloxane and a second layer of a polydimethylsiloxane derivative with a specific substituent X, where the molecular descriptor α MOL of the substituent X satisfies α MOL < 0, enhancing carbon dioxide permeability and separability from nitrogen.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If organosiloxane compound membranes are used, then gas permeability is maintained, but gas separability of carbon dioxide from nitrogen is insufficient
Solution Approach 1:
The patent modifies the molecular structure parameters of the siloxane compound by introducing specific substituents (fluoroalkyl groups, aromatic rings, heterocyclic rings) at controlled substitution rates (1-50%). This changes the physical and chemical parameters of the membrane material, including free volume, polarity, and molecular size distribution, thereby simultaneously improving both gas permeability and selectivity
Solution Approach 2:
The patent creates composite membrane structures by combining siloxane base polymers with various functional additives including metal organic frameworks (MOFs), zeolites, and grafted functional groups. This composite approach allows the membrane to exhibit both the high permeability of siloxane and the selective separation properties of the added materials
2Manufacturing precision
If membrane thickness is reduced to improve selectivity, then gas separability improves, but mechanical strength and stability deteriorate
Solution Approach 1:
The patent applies local quality modification by creating functional gradients within the membrane structure. The substituent distribution is optimized to create regions with different properties: high substituent concentration zones for selectivity and lower concentration zones for mechanical integrity. This allows thin membrane design while maintaining both selectivity and strength
Solution Approach 2:
The patent divides the membrane into multiple functional layers or segments with different compositions. The support layer provides mechanical strength while the selective thin layer (containing the modified siloxane with specific substituents) provides separation performance. This segmented structure decouples the conflicting requirements of strength and selectivity
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 high carbon dioxide permeability and selective separation from nitrogen, with improved gas separability and permeability, suitable for applications like direct air recovery of carbon dioxide from the atmosphere.
Implementation Method 1
a gas separation membrane that selectively separates carbon dioxide from a mixed gas containing the carbon dioxide and nitrogen by allowing the carbon dioxide to permeate
Data Source
Figure 1
AI summary
Provided is a gas separation membrane that selectively separates carbon dioxide from a mixed gas by allowing the carbon dioxide to permeate. The gas separation membrane includes: a thin film made of a polydimethylsiloxane derivative that includes a main chain formed of a siloxane bond and a methyl group bonded to silicon atoms contained in the siloxane bond, with a part of the methyl group being substituted with a substituent X. A molecular descriptor αMOL of the substituent X calculated based on the following Formulae (1) and (2) satisfies the following Formula (3). αMOL=∑iNαAi [In the above Formula (1), i is a natural number that changes from 1 to N. N is the number of atoms excluding hydrogen atoms contained in the substituent X.] αAi=rAirC−1 [In the above Formula (2), rAi is a covalent bond distance of atoms excluding the hydrogen atoms contained in the substituent X. rC is the covalent bond distance of an sp3 orbital of the carbon atoms.] αMOL<0