PET Depolymerization with Electrolytic Glycolate 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), which is crucial for recycling PET, as they yield lower proportions of BHET in the cleavage products.
Innovation Solution
A method involving electrolytically produced alkali metal glycolate, particularly sodium or potassium glycolate, is used to react with PET in an electrolysis cell with specific chamber configurations and solid-state electrolyte ceramics to enhance the production of BHET in the mixture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional methods (methanolysis or hydrolytic methods) are used to cleave PET, then the process can be performed with simple equipment, but the yield of BHET is low and recycling efficiency is poor
Solution Approach 1:
The patent changes the chemical parameters by using electrolytically produced alkali metal glycolate instead of conventional methanol or water-based methods. This parameter change in the reaction medium fundamentally improves BHET yield while managing the increased process complexity through controlled electrolysis conditions
Solution Approach 2:
The patent replaces conventional chemical cleavage methods with an electrolytic system that uses electrical energy to drive the formation of alkali metal glycolate in situ. This substitution of the cleavage mechanism enables higher BHET production by controlling the electrochemical reactions and avoiding side products
2Productivity
If electrolytically produced alkali metal glycolate is used to react with PET, then BHET yield is significantly increased, but the process requires complex electrolysis cell equipment
Solution Approach 1:
The patent performs preliminary action by generating the alkali metal glycolate solution in advance through electrolysis before the actual PET cleavage reaction. This preliminary preparation of the reactive species enables the subsequent PET glycolysis to proceed with high BHET selectivity and efficiency
Solution Approach 2:
The patent uses alkali metal glycolate as an intermediary substance that mediates between the PET polymer and the electrolytic system. This intermediary facilitates the cleavage reaction while ensuring high BHET yield, effectively bridging the gap between the electrolysis process and the desired chemical transformation
3Reliability
If the electrolysis cell uses a dividing wall with solid-state electrolyte ceramic, then ion selective transport is achieved, but the device structure becomes more complex
Solution Approach 1:
The patent applies local quality by incorporating solid-state electrolyte ceramic materials with specific ion conductive properties into the dividing wall structure. This localized use of specialized materials enables selective ion transport (e.g., Na+ or K+ conduction) while maintaining the overall structural integrity of the electrolysis cell
Solution Approach 2:
The patent employs composite materials in the dividing wall construction, combining solid-state electrolyte ceramics with appropriate structural supports and sealants. This composite approach achieves reliable ion-selective transport while managing the mechanical and chemical stability requirements of the complex device structure
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 method significantly increases the yield of BHET, allowing for its direct use in PET production and subsequent recycling by polymerizing BHET back to PET, thus addressing the inefficiencies of conventional methods.
Implementation Method 1
producing a solution L1 of MA glycolate in glycol, where MA is an alkali metal cation, especially selected from lithium, potassium, sodium, preferably selected from potassium, sodium, and most preferably sodium, in an electrolysis cell E(1)
Implementation Method 2
the dividing wall W comprises at least one alkali metal cation-conducting solid-state electrolyte ceramic FA in such a way that the alkali metal cation-conducting solid-state electrolyte ceramic FA encompassed by the dividing wall W makes direct contact with the interior IKK on the SKK side via the surface OKK
Data Source
AI summary
The invention relates to a method for depolymerising polyethylene terephthalate (“PET”), in which PET is reacted with electrolytically prepared alkali metal glycolate, in particular sodium or potassium glycolate, to form a mixture M1 comprising bis(2-hydroxyethyl) terephthalate (“BHET”). The method according to the invention is characterised in that BHET accounts for a particularly high proportion of the breakdown 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 for renewed PET production. The present invention also relates to a method for recycling PET, in which the BHET obtained in the method for depolymerising PET is polymerised again to PET, optionally after further purification from M1.