Polyimide Membrane with Hydroxyl and Acetoxy Groups for Gas Separation
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Solution Overview
Problem
Current polyimide membranes used in gas separation, such as those with asymmetric integrally skinned structures, face challenges in achieving high selectivity and permeance due to defects and low chemical, thermal, and mechanical stability, particularly in processes like natural gas upgrading and hydrogen purification.
Innovation Solution
A high selectivity polyimide membrane is developed with hydroxyl and acetoxy functional groups, which provides high selectivity and plasticization resistance through a phase inversion process, using a specific molar ratio of these groups and a thin nonporous selective skin layer, resulting in improved H2/CH4 and CO2/CH4 separation performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If asymmetric integrally skinned polyimide membranes are fabricated using phase inversion technique, then a thin nonporous selective skin layer is formed, but high shrinkage during casting and drying results in defects and reduced selectivity
Solution Approach 1:
The patent modifies the polymer composition parameters by incorporating specific ratios of rigid and flexible chain polyimides, and adjusting plasticizer content, to control membrane shrinkage during phase inversion. This enables formation of defect-free asymmetric structures with maintained selectivity
Solution Approach 2:
The patent creates composite polyimide membranes by combining rigid chain polyimide (provides selectivity) with flexible chain polyimide (reduces shrinkage). This composite approach resolves the contradiction between forming thin selective skins and preventing shrinkage-induced defects
2Reliability
If polyimide membranes are made with higher selectivity, then separation performance improves, but chemical, thermal, and mechanical stability decreases
Solution Approach 1:
The patent combines rigid chain polyimide (provides high selectivity through stiff backbone) with flexible chain polyimide (provides thermal and chemical stability). The synergistic combination achieves both high CO2/CH4 selectivity (>30) and improved stability
Solution Approach 2:
The patent creates local quality differentiation within the membrane structure, with the selective skin layer having high rigid polyimide content for selectivity, while the support layer has higher flexible polyimide content for stability. This spatial distribution resolves the contradiction
3Productivity
If membrane area is increased to treat larger gas volumes, then separation capacity increases, but capital cost increases
Solution Approach 1:
The patent optimizes polymer concentration and molecular weight parameters to achieve high flux membranes. The modified phase inversion process produces membranes with enhanced permeability, reducing the membrane area needed for a given productivity requirement
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 exhibits high permeance and selectivity for gas separations, specifically achieving H2 permeance of 323 GPU and H2/CH4 selectivity of 193, and CO2 permeance of 88 GPU with CO2/CH4 selectivity of 35.6, making it suitable for various gas separation applications including H2 purification and natural gas upgrading.
Implementation Method 1
Separation is based on a solution-diffusion mechanism. This mechanism involves molecular-scale interactions of the permeating gas with the membrane polymer. The mechanism assumes that in a membrane having two opposing surfaces, each component is sorbed by the membrane at one surface, transported by a gas concentration gradient, and desorbed at the opposing surface.
Implementation Method 2
each component is sorbed by the membrane at one surface
Data Source
AI summary
A polyimide polymer having hydroxyl and acetoxy function groups is provided together with a membrane made from the polymer. Also provided is a process for separating at least one gas from a mixture of gases using a polyimide membrane comprising a polyimide polymer with hydroxyl and acetoxy functional the process comprising: (a) providing the polyimide membrane comprising the polyimide polymer with hydroxyl and acetoxy functional groups which is permeable to the at least one gas; (b) contacting the mixture on one side of the polyimide membrane to cause said at least one gas to permeate the membrane; and (c) removing from the opposite side of the membrane a permeate gas composition comprising a portion of said at least one gas which permeated the polyimide membrane.