Sulfonated Block Copolymer Membrane Sulfonation Process
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Solution Overview
Problem
Existing methods for sulfonating aromatic-containing block copolymers in non-halogenated solvents face challenges such as polymer precipitation and gelation, especially when using C2 to C8 acyl sulfates, which result in residual carboxylic acids that cause internal stresses and offensive odors in membranes.
Innovation Solution
A process involving sulfonation of precursor block polymers with C2 to C8 acyl sulfates in non-halogenated aliphatic solvents, followed by conversion of residual carboxylic acids to C1 to C4 alkyl esters, reducing their concentration to less than 2.0 wt%, thereby preventing membrane defects and odors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If sulfonation is performed using C2 to C8 acyl sulfates in non-halogenated solvents, then high sulfonation levels can be achieved without halogenated solvents, but residual carboxylic acids are formed that cause internal stresses and offensive odors in membranes
Solution Approach 1:
The patent converts the harmful residual carboxylic acid byproducts into beneficial alkyl esters by reacting them with alcohols. This transformation eliminates the offensive odor and internal stress problems caused by free acids while maintaining the sulfonation benefits of using C2 to C8 acyl sulfates in non-halogenated solvents.
Solution Approach 2:
The patent changes the chemical form of the carboxylic acid byproduct from free acid to alkyl ester through esterification reaction. This parameter change in molecular structure fundamentally alters the properties of the byproduct, transforming it from harmful to benign or desirable.
2Productivity
If polymer concentration is increased to improve productivity, then membrane production efficiency increases, but polymer precipitation and gelation occur
Solution Approach 1:
The patent introduces an intermediary substance (alcohol) that mediates between the polymer and the carboxylic acid byproduct. The alcohol reacts with the acid to form ester, preventing the acid from causing precipitation or gelation at high polymer concentrations, thus enabling improved productivity without sacrificing solution stability.
3Stability of the object's composition
If halogenated solvents are used to prevent polymer precipitation, then polymer solubility is maintained, but environmental and safety concerns arise
Solution Approach 1:
The patent converts the harmful effect of carboxylic acid byproducts (which would normally require halogenated solvents to manage) into a beneficial esterification process. This allows the use of safe non-halogenated solvents while maintaining polymer solubility and preventing precipitation through the ester formation mechanism.
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
This approach enables high sulfonation levels without polymer precipitation or gelation, producing membranes with improved wet strength, dimensional stability, and reduced residual acid-related issues, such as internal stresses and odors.
Implementation Method 1
reacting the precursor block polymer with a C2 to C8 acyl sulfate in a reaction mixture further comprising at least one non-halogenated aliphatic solvent to form a sulfonated block polymer
Implementation Method 2
reacting the residual carboxylic acid with a C1 to C4 alcohol or mixture thereof in a molar ratio of alcohol to residual carboxylic acid of at least 0.9:1 to form the corresponding alkyl esters of the carboxylic acid
Data Source
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AI summary
The present invention relates to an improved method for making sulfonated block copolymers and to methods for making membranes from such block copolymers. In particular, the present invention relates to an improved method for making sulfonated block copolymers having at least two polymer end blocks that are resistant to sulfonation and at least one polymer interior block that is susceptible to sulfonation where the sulfonation agent is C2 to C8 acyl sulfate. In the improved process the residual carboxylic acid formed from the C2 to C8 acyl sulfate is converted to C1 to C4 alkyl esters by contacting the residual carboxylic acid with at least a 0.9: 1 molar ratio of a C1 to C4 alcohol to residual carboxylic acid, resulting in an improved sulfonated block copolymer solution. The present invention further relates to the use of such sulfonated block copolymer solutions to prepare various membranes and other articles.