PET Depolymerization via Reactive Distillation for High BHET Yield
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Solution Overview
Problem
Existing methods for depolymerizing polyethylene terephthalate (PET) do not efficiently produce bis-2-hydroxyethyl terephthalate (BHET), limiting its availability for recycling into new PET production.
Innovation Solution
A method involving reactive distillation to produce a solution of sodium or potassium glycolate, which is then used to react with PET, resulting in a higher proportion of BHET in the cleavage products.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional methods (mixing glycol with alkali metal hydroxide) are used to produce glycolate solution, then the process is simple and easy to operate, but the yield of BHET is low and not suitable for efficient recycling
Solution Approach 1:
The patent changes the chemical parameters of the glycolate solution preparation by using reactive distillation instead of simple mixing. This involves changing the reaction conditions, temperature profiles, and chemical composition parameters to achieve high BHET yield while maintaining operational feasibility through established distillation technology
Solution Approach 2:
The reactive distillation process enables continuous production of glycolate solution with high BHET content. The process maintains continuous reaction and separation operations, ensuring steady supply of high-quality cleavage products for PET recycling without interruption or batch processing limitations
2Productivity
If reactive distillation is used to produce glycolate solution, then the BHET proportion in cleavage products is high, but the process requires more complex equipment and operation
Solution Approach 1:
The patent uses an intermediary approach by introducing a distillation column as a mediator between the reaction zone and product collection. This intermediary equipment enables selective separation and concentration of BHET-containing phases, achieving high yield while distributing the manufacturing complexity across standard industrial equipment components
3Adaptability or versatility
If conventional glycolate preparation methods are used, then the equipment required is simple, but the BHET obtained cannot be efficiently reused in PET production
Solution Approach 1:
The patent modifies the chemical and physical parameters of the glycolate solution through reactive distillation to achieve optimal BHET purity and concentration. These parameter changes enable the produced BHET to be directly adapted for PET polymerization processes, improving both reusability and recycling efficiency simultaneously
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 enhances the yield of BHET, making it more suitable for direct reuse in PET production and facilitating efficient recycling of PET materials.
Implementation Method 1
converting MAOR and glycol in a reactive distillation to obtain a solution SAP comprising glycol and MA glycolate
Implementation Method 2
reacting the solution SAP with PET to give a mixture M1 comprising bis-2-hydroxyethyl terephthalate (BHET)
Data Source
AI summary
The present invention relates to a method for the depolymerization of polyethylene terephthalate (PET), in which method PET is reacted with sodium glycolate or potassium glycolate which has been obtained via reactive distillation, to form a mixture M1 comprising bis(2-hydroxyethyl) terephthalate (BHET). The method according to the invention is characterized in that BHET forms a particularly high proportion of the cleavage products in the mixture M1. As a result, the method according to the invention provides a high yield of BHET, which can be used directly to produce PET again. The present invention therefore also relates to a method for recycling PET, in which method the BHET that is obtained in the method for the depolymerization of PET and, if necessary, has been further purified from M1, is repolymerized to form PET.