PET Depolymerization Using 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), a key reactant for producing new PET, as a significant proportion of other by-products are formed.
Innovation Solution
A method involving reactive distillation to produce a solution of sodium or potassium glycolate, which is then reacted with PET to yield a mixture predominantly comprising BHET, using a reactive rectification column to enhance the production of BHET.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional methods are used to depolymerize PET, then the depolymerization process can be completed, but the yield of BHET is low and other by-products are formed
Solution Approach 1:
The patent changes the chemical parameters of the glycolate solution by using reactive distillation to produce a solution with specific composition (containing glycol, glycolate, and water in controlled ratios). This parameter change in the reactant solution leads to improved BHET yield and reduced by-product formation during PET depolymerization
Solution Approach 2:
The patent replaces conventional mechanical mixing methods with reactive distillation technology to produce the glycolate solution. This substitution of the solution preparation method enables better control over solution composition and improves the subsequent depolymerization efficiency
2Quantity of substance
If reactive distillation is used to produce glycolate solution, then the BHET yield is significantly improved, but the process complexity increases
Solution Approach 1:
The patent merges the functions of reaction and distillation into a single reactive distillation unit. This combination of operations allows simultaneous production of glycolate solution and separation of components, reducing the need for separate equipment and simplifying the overall process despite the advanced technology used
Solution Approach 2:
The reactive distillation column serves multiple functions: it acts as a reaction vessel for glycolate formation, a separation device for water-glycol-glycolate mixture, and a source of controlled reactant solution. This multi-functionality reduces process complexity by eliminating the need for multiple separate units
3Quantity of substance
If the glycolate solution is produced by reactive distillation, then the quality and composition of the solution is improved, but the energy consumption increases
Solution Approach 1:
The patent converts the energy-intensive nature of distillation into a benefit by using the heat of vaporization to drive the reaction and simultaneously achieving separation of components. The energy input for distillation is justified by the high-quality solution produced and the avoidance of energy-intensive subsequent purification steps
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
The method significantly increases the yield of BHET, allowing for its direct use in producing new PET and facilitating efficient recycling of PET by polymerizing BHET back to PET.
Implementation Method 1
converting MAOH 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
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.