Polyamide Nanofiltration for PET Chemical Recycling
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Solution Overview
Problem
Current membrane purification methods fail to selectively separate and recover terephthalic acid or its salt and diol from aqueous solutions containing both, which are essential components in the chemical recycling of polyethylene terephthalate (PET).
Innovation Solution
A method utilizing a polyamide-based nanofiltration membrane with a molecular weight cutoff of 150 to 500, operated at a pH of 7.0 or more and a temperature between 30°C and 45°C, to selectively separate and recover terephthalic acid or its salt and diol through filtration, followed by acidification to crystallize the terephthalic acid.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If membrane purification is used to separate terephthalic acid and diol from aqueous solution, then separation and recovery can be achieved, but selective separation of both components simultaneously is not possible
Solution Approach 1:
The patent applies parameter changes by adjusting pH to 7.0 or more (making the solution alkaline) to convert terephthalic acid into its salt form, which fundamentally alters the separation behavior of the membrane. This parameter change enables the membrane to selectively pass terephthalate ions while retaining diol, achieving simultaneous separation of both components that was not possible under neutral or acidic conditions.
2Productivity
If conventional membrane purification is used, then filtration can be performed, but selective recovery of both terephthalic acid and diol cannot be achieved
Solution Approach 1:
The patent changes the pH parameter to alkaline conditions (pH 7.0 or more) to convert terephthalic acid into terephthalate ions. This parameter change enables both high productivity through efficient filtration and high separation selectivity, as the membrane can now selectively pass terephthalate ions while retaining diol molecules, allowing simultaneous recovery of both components.
Solution Approach 2:
The patent replaces conventional mechanical separation methods with a chemically-enhanced membrane filtration system. By substituting the separation mechanism from purely physical size-based filtration to a combination of chemical state control (ionization) and membrane selectivity, the system achieves superior separation of both components with high productivity.
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 allows for the efficient and selective recovery of terephthalic acid or its salt and diol, enabling their independent reuse as polymer raw materials, thereby enhancing the recycling efficiency and reducing energy and greenhouse gas emissions.
Implementation Method 1
a polyamide-based nanofiltration membrane can be used as a separation membrane in a membrane purification process in which terephthalic acid or a salt thereof and diol are selectively separated and recovered
Implementation Method 2
filtrating an aqueous solution including terephthalic acid or a salt thereof and a diol through a polyamide-based nanofiltration membrane to recover the terephthalic acid or the salt thereof from a non-permeated liquid
Implementation Method 3
a step (C) of acidifying the non-permeated liquid in the step (A) to crystallize the terephthalic acid
Data Source
AI summary
An aqueous solution comprising terephthalic acid or a salt thereof and a diol is filtered across a polyamide nanofiltration membrane, and terephthalic acid or a salt thereof can be selectively separated and recovered from the non-permeated solution side and the diol can be selectively separated and recovered from the permeated solution side. The selectively separated and recovered terephthalic acid or salt thereof or diol can each be independently reutilized as a polymer starting material, e.g., for a polyester.