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 achieve a high yield of bis-2-hydroxyethyl terephthalate (BETH), a crucial intermediate for recycling PET, limiting the efficiency of PET recycling processes.
Innovation Solution
A method involving reactive distillation to produce sodium or potassium glycolate is used, which is then reacted with PET to form a mixture containing BETH, with specific conditions in a reaction column to enhance BETH production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional mixing methods are used to prepare alkaline alkali metal glycolate solution, then the process is simple, but the proportion of BETH among fission products is low
Solution Approach 1:
The patent combines the glycolate preparation step with the depolymerization reaction by implementing reactive distillation. The glycolate is generated in-situ within the reaction system, merging two previously separate processes (glycolate preparation and PET depolymerization) into one integrated operation, thereby increasing BETH yield without proportionally increasing process complexity
Solution Approach 2:
The patent introduces an intermediate purification step where the crude glycolate is separated and purified before being used in depolymerization. This intermediate handling of the glycolate ensures higher reaction efficiency and BETH yield, acting as a mediator between原料 preparation and final depolymerization
2Productivity
If reactive distillation is used to produce glycolate, then BETH yield increases, but process complexity increases
Solution Approach 1:
The patent optimizes specific parameters of the reactive distillation process including temperature gradients, pressure conditions, and reactant feed rates to maximize BETH production. By carefully controlling these parameters, the process achieves high productivity while managing the inherent complexity through systematic parameter optimization
Solution Approach 2:
The reactive distillation process operates continuously, with glycolate being generated, separated, and fed back into the depolymerization reaction in an uninterrupted manner. This continuous operation maximizes BETH production efficiency by eliminating idle time between process stages
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 process yields a higher proportion of BETH compared to conventional methods, facilitating more efficient PET recycling and polymerization back to PET.
Implementation Method 1
MA OH and glycol are reacted in a reactive distillation, resulting in a solution S AP comprising glycol and MA glycolate
Implementation Method 2
comprehensively glycol and MA glycolate are obtained, where MA is an alkali metal selected from sodium, potassium
Implementation Method 3
reaction of the solution S AP with PET to a mixture M 1 comprising bis-2-hydroxyethyl terephthalate (= BETH)
Data Source
AI summary
The present invention relates to a process for depolymerising polyethylene terephthalate ("PET"), in which method PET is reacted with sodium glycolate or potassium glycolate, which has been obtained by reactive distillation, to form a mixture M1 including Bis(2-hydroxyethyl) terephthalate ("BHET"). The process according to the invention is distinguished by the fact that BHET makes up a particularly high proportion of the decomposition products in the mixture M1. The process according to the invention thus provides a high yield of BHET that can be used directly for producing PET again. The present invention thus also relates to a process for recycling PET, in which the BHET obtained in the process for depolymerising PET is polymerised again to form PET, optionally after being further purified from M1.