BHET Monomer Purity via Water Extraction in Terephthalate Depolymerization
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Solution Overview
Problem
Current methods for depolymerizing terephthalate polymers into reusable raw materials often result in impurities like 2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl]terephthalate (BHEET) and diethylene glycol (DEG), which contaminate the bis(2-hydroxyethyl)terephthalate (BHET) monomer, affecting its quality and purity, especially in applications where high purity is required, such as food and medical uses.
Innovation Solution
A method involving a reaction mixture of terephthalate polymer and ethylene glycol with a catalyst, such as a metal-containing particle, to form BHET and BHEET, followed by monitoring and adjusting the mass fraction of BHEET in the depolymerized product stream to below a predetermined limit, ensuring high purity BHET production through separation and reusing the BHET-depleted stream as solvent, thereby reducing impurities like BHEET, DEG, and other soluble non-volatile impurities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If glycolysis is used to depolymerize terephthalate polymer, then conversion of polymer to monomer is high, but impurities like BHEET and DEG are formed that reduce monomer purity
Solution Approach 1:
The patent extracts and removes impurities (BHEET and DEG) from the reaction mixture through a two-phase separation system. Water is added to create phases where impurities preferentially partition into one phase, allowing separation from the BHET monomer. This extraction process resolves the contradiction by maintaining high conversion while removing purity-reducing impurities.
Solution Approach 2:
The patent changes physical parameters (temperature, phase composition) to control the distribution of impurities. By adjusting the water content and temperature during the separation step, the solubility and partitioning behavior of BHEET and DEG are modified, enabling their removal while preserving BHET monomer purity and yield.
2Reliability
If strict purity rules are applied for food and medical applications, then health safety is ensured, but more complex purification processes are required
Solution Approach 1:
Water acts as an intermediary substance that facilitates the separation of impurities from the BHET monomer. By introducing water to create a two-phase system, impurities are transferred to the aqueous phase while BHET remains in the organic phase, achieving high purity suitable for food and medical applications without requiring complex multi-step purification equipment.
3Manufacturing precision
If phase separation is used to separate BHET from catalyst and oligomers, then separation efficiency is improved, but BHEET and DEG remain as dissolved impurities
Solution Approach 1:
The patent applies extraction by adding water to create a two-phase system where BHEET and DEG are selectively transferred to the aqueous phase. This secondary extraction step follows the initial phase separation, removing dissolved impurities that remained after catalyst and oligomer separation, thereby reducing total impurity content in the BHET monomer.
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 ensures the production of high-purity BHET monomer with reduced impurities, meeting the stringent requirements for subsequent polymerization and ensuring the quality of the recycled material for various applications, including food and medical uses.
Implementation Method 1
providing a catalyst being capable of catalyzing degradation of the polymer into oligomers and/or monomers
Implementation Method 2
One preferred way of depolymerization is glycolysis, which is preferably catalyzed. Typically, as a result of the use of ethylene glycol a reaction mixture comprising at least one monomer comprising bis (2-hydroxyethyl) terephthalate (BHET) may be formed.
Implementation Method 3
At the end of the depolymerization process, water is added and a phase separation occurs. This enables to separate a first phase comprising the BHET monomer from a second phase comprising catalyst, oligomers and additives.
Implementation Method 4
heating the reaction mixture and depolymerizing the polymer in the reaction mixture using the catalyst
Data Source
AI summary
A method and reactor system for depolymerizing a terephthalate polymer into reusable raw material are described, as well as a raw material obtainable by the method. The method inter alia comprises providing the polymer and a solvent such as ethylene glycol as a reaction mixture in a reactor. A heterogeneous catalyst, such as a metal containing particle, and/or a homogeneous catalyst is provided in the reaction mixture and the reaction mixture heated to depolymerize the polymer. Monomer comprising bis-(2-hydroxyethyl)-terephthalate (BHET), and 2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl]terephthalate (BHEET) as byproduct are formed. The BHET is recovered from a depolymerized product stream exiting the reactor and a BHET-depleted stream is formed. A mass fraction of BHEET in the depolymerized product stream and/or in the BHET-depleted stream is monitored and adjusted to below a predetermined limit value of the BHEET-mass fraction in the depolymerized product stream.