BHET Monomer Purification via Segmented Depolymerisation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional methods for recycling polyethylene terephthalate (PET) result in low yield and high loss of raw material due to the presence of dimers and trimers, and require additional steps for IPA analysis and adjustment, reducing efficiency and preventing direct use of BHET in integrated recycling and polymerization processes.
Innovation Solution
A method involving a series of depolymerization reactors to produce a high-purity BHET monomer by using ethylene glycol and a catalyst system, followed by crystallization, dissolution in a protic solvent, and impurity removal, allowing for direct use in polymerization without further purification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional depolymerisation methods are used to recycle PET, then BHET monomers are produced, but the yield is less than 80% with significant amounts of dimers and trimers produced
Solution Approach 1:
The depolymerisation process is divided into multiple sequential stages with progressively lower temperatures. The first stage operates at higher temperature to break down PET into BHET monomers, while subsequent stages operate at lower temperatures to prevent dimer and trimer formation. This segmented approach to temperature control resolves the contradiction by maximizing monomer yield while minimizing unwanted oligomer production.
Solution Approach 2:
The invention changes the temperature parameter throughout the depolymerisation process. By dynamically adjusting temperature from higher initial values to progressively lower values in subsequent stages, the process optimizes BHET monomer production while suppressing dimer and trimer formation. This parameter change strategy directly addresses the yield versus material loss contradiction.
2Manufacturing precision
If purification steps are added to remove dimers and trimers, then BHET quality is improved, but the process complexity and time increase
Solution Approach 1:
The purification action is built into the depolymerisation process itself through the multi-stage temperature control. By preventing dimer and trimer formation during the depolymerisation stages rather than removing them afterward, the process achieves high BHET purity without requiring separate purification equipment or steps. This preliminary prevention approach resolves the contradiction between purity and process complexity.
3Manufacturing precision
If IPA analysis and adjustment steps are added, then recycled PET quality is improved, but the efficiency and energy consumption increase
Solution Approach 1:
The invention extracts IPA from the waste PET feedstock before the depolymerisation process begins, through washing or extraction steps. By removing IPA upfront, the need for subsequent analysis and adjustment steps is eliminated, maintaining high recycled PET quality while preserving process efficiency and reducing energy consumption.
4Manufacturing precision
If dimers and trimers are removed from the depolymerisation mixture, then BHET quality is improved, but considerable amounts of PET raw material are lost
Solution Approach 1:
The invention applies preliminary anti-action by preventing dimer and trimer formation in the first place through controlled multi-stage depolymerisation. By maintaining progressively lower temperatures in subsequent stages, the process prevents the harmful formation of oligomers that would otherwise need to be removed. This approach improves BHET quality while avoiding the material loss associated with removing formed oligomers.
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 achieves a high-purity BHET product that can be used directly in polymerization, reducing material loss and energy consumption, and enabling the production of high-grade recycled PET suitable for applications like transparent bottles.
Implementation Method 1
depolymerising PET in the presence of ethylene glycol and a catalyst system to form a depolymerised mixture comprising bis(2-hydroxyethyl) terephthalate (BHET)
Implementation Method 2
crystallising a precipitate comprising BHET from the depolymerised mixture
Implementation Method 3
dissolving the precipitate in a protic solvent to form a solution comprising BHET
Data Source
AI summary
The present invention relates to a method for preparing polymers, in particular to a method for preparing recycled polymers from polyethylene terephthalate (PET). The method comprises producing a high quality BHET product which is used as a monomer feedstock in an integrated polymerisation process.