Waste Polyester Recycling via Melted-State Alcoholysis
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Solution Overview
Problem
Existing methods for recycling waste polyester, such as the alcoholysis method, face challenges with long depolymerization times and high dosages of alcoholysis agents due to solid-liquid heterogeneous reactions.
Innovation Solution
A method that involves pretreating waste polyester by dewatering and deoxygenating, then melting and feeding it into an alcoholysis tank with ethylene glycol as the alcoholysis agent, allowing for a homogeneous liquid-liquid reaction that shortens depolymerization time and improves product purity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If solid polyester is used for alcoholysis reaction, then the reaction can be carried out, but the reaction time becomes long and the process becomes complex
Solution Approach 1:
The patent changes the physical state parameter of polyester from solid to liquid by pre-melting it before alcoholysis reaction. This parameter change enables homogeneous liquid-liquid reaction, significantly reducing depolymerization time from hours to minutes while maintaining reaction effectiveness
Solution Approach 2:
The patent applies preliminary action by melting polyester and performing preliminary alcoholysis before the main reaction. This preliminary processing reduces the viscosity and molecular weight of polyester chains, making the subsequent main alcoholysis reaction faster and more efficient
2Productivity
If large amount of alcoholysis agent is used, then the reaction can proceed well, but the cost and equipment complexity increase
Solution Approach 1:
The patent changes the physical state of the reaction system from solid-liquid heterogeneous to liquid-liquid homogeneous by pre-melting polyester. This enables better mixing and reaction efficiency with reduced alcoholysis agent dosage, lowering both cost and equipment requirements for separation processes
Solution Approach 2:
The patent extracts and removes moisture and oxygen from waste polyester before reaction. This preliminary purification prevents side reactions and improves reaction efficiency, allowing reduced alcoholysis agent dosage while maintaining high reaction efficiency
3Ease of manufacture
If solid-liquid heterogeneous reaction is used, then the process is simple, but the reaction time is long and productivity is low
Solution Approach 1:
The patent changes the physical state parameter of polyester from solid to liquid through pre-melting. This transforms the reaction from solid-liquid heterogeneous to liquid-liquid homogeneous, maintaining process simplicity while dramatically improving productivity by reducing reaction time from hours to minutes
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 reduces depolymerization time, enhances the purity and yield of Bis(2-hydroxyethyl) terephthalate (BHET), and improves the efficiency of subsequent transesterification to produce Dimethyl Terephthalate (DMT).
Implementation Method 1
the alcoholysis of waste polyester with ethylene glycol (EG) into bishydroxy terephthalate (BHET) or oligomers
Implementation Method 2
the melted waste polyester, further ethylene glycol as an alcoholysis agent, and alcoholysis catalyst undergo depolymerization reaction in the alcoholysis tank to obtain alcoholysis product
Implementation Method 3
methanol as a transesterification agent, a transesterification catalyst and the alcoholysis product undergo transesterification reaction in the transesterification tank, to produce dimethyl terephthalate
Implementation Method 4
melting waste polyester to obtain melted waste polyester and feeding the melted waste polyester to the alcoholysis tank
Data Source
Figure 1
AI summary
A method for recycling waste polyester, in particular to a method for recycling waste polyester by a modified alcoholysis method to recycle waste polyester to prepare dimethyl terephthalate (DMT), is provided and belongs to waste polyester recycling technology field. The waste polyester after dewatering and deoxygenation treatment is used as a raw material, in the step of feeding in melted state the alcoholysis agent is added in the melted waste polyester for preliminary alcoholysis, and the alcoholysis agent is ethylene glycol. On one hand, alcoholysis reaction occurs when the waste polyester raw material are melted, and at the same time, the viscosity of the melted material is reduced. Thus, the melted material remains melted at the alcoholysis temperature and is not easy to solidify again after entering the alcoholysis tank, ensuring that the alcoholysis is carried out under homogeneous conditions.