BHET Monomer Purification via Segmented Depolymerisation Reactors
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Solution Overview
Problem
Conventional PET recycling methods produce low yields of high-quality BHET monomers due to the presence of dimers and trimers, leading to inefficiencies and the need for additional purification steps, and often result in recycled PET products with unwanted impurities like isophthalic acid, which complicates polymerization processes.
Innovation Solution
A method using a series of depolymerization reactors and protic solvents like water to achieve a high proportion of BHET monomers with low dimer and trimer content, allowing for the omission of conventional purification steps and the production of BHET products with minimal isophthalic acid, enabling simplified polymerization processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional depolymerisation methods are used to recycle PET, then BHET monomers can be produced, but significant amounts of dimers and trimers are also produced which reduces polymer quality and requires additional purification steps
Solution Approach 1:
The invention uses a series of three depolymerisation reactors arranged in sequence, where each reactor performs a specific stage of depolymerisation. The first reactor converts PET to BHET, the second converts dimers to BHET, and the third converts trimers to BHET. This segmentation of the depolymerisation process into distinct stages allows for high selectivity and minimizes the formation of unwanted oligomers, thereby producing high-purity BHET monomer without requiring additional purification steps.
Solution Approach 2:
The invention performs preliminary depolymerisation of dimers and trimers in the second and third reactors before the final polymerisation step. By pre-converting these unwanted oligomers into BHET monomers in advance, the system ensures that only high-purity monomers enter the final polymerisation reactor, eliminating the need for post-depolymerisation purification steps.
2Manufacturing precision
If multiple purification steps are added to remove dimers and trimers, then BHET purity improves, but process complexity and energy consumption increase
Solution Approach 1:
The invention performs preliminary depolymerisation of dimers and trimers in the second and third reactors before the final polymerisation step. By pre-converting these unwanted oligomers into BHET monomers in advance, the system ensures that only high-purity monomers enter the final polymerisation reactor, eliminating the need for post-depolymerisation purification steps.
Solution Approach 2:
Instead of treating dimers and trimers as harmful impurities to be removed, the invention converts them into beneficial BHET monomers through additional depolymerisation reactors. The unwanted oligomers become valuable feedstock, increasing overall monomer yield while maintaining high purity, thereby turning a problem into a solution.
3Ease of manufacture
If recycled BHET contains isophthalic acid impurities, then the polymerisation process becomes more complex and requires additional control steps
Solution Approach 1:
The segmented three-reactor system allows for controlled depolymerisation at different stages, with each reactor operating under optimized conditions to minimize side reactions. This segmentation prevents the formation of isophthalic acid impurities by maintaining precise control over the depolymerisation process throughout all three stages.
Solution Approach 2:
The invention converts the potential harm of incomplete depolymerisation (which would leave oligomers) into a benefit by using those same reactors to also convert any formed isophthalic acid impurities back into BHET monomers through the controlled action of the catalyst system in each reactor stage.
4Productivity
If conventional single-reactor depolymerisation is used, then process simplicity is maintained, but BHET yield is less than 80% with significant oligomer production
Solution Approach 1:
The invention uses a series of three depolymerisation reactors arranged in sequence, where each reactor performs a specific stage of depolymerisation. The first reactor converts PET to BHET, the second converts dimers to BHET, and the third converts trimers to BHET. This segmentation of the depolymerisation process into distinct stages allows for high selectivity and minimizes the formation of unwanted oligomers, thereby producing high-purity BHET monomer without requiring additional purification steps.
Solution Approach 2:
The three-reactor system operates continuously with the effluent from each reactor feeding into the next, maintaining continuous useful action throughout the depolymerisation process. This continuous conversion of PET and its oligomers into BHET monomers maximizes productivity while maintaining high purity, as the process never stops converting unwanted materials into valuable monomers.
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 results in a high-purity BHET product that can be used directly in polymerization reactions without additional purification, simplifying the process and reducing energy and time requirements, while producing PET products suitable for high-grade applications like transparent bottles.
Implementation Method 1
PET may be depolymerised using a glycolysis agent such as ethylene glycol to form BHET monomers
Implementation Method 2
a depolymerised mixture may be obtained which contains a very high proportion of BHET monomer and relative low amounts of dimer and trimer
Data Source
AI summary
The present invention relates to a method for preparing polymers, in particular to a method for preparing a polymer comprising constitutional units derived from bis(2-hydroxyethyl) terephthalate (BHET). The BHET used in the method is a high quality recycled BHET product, which allows plastic preparation methods in which the BHET is used to be simplified.