Converting PET Scrap to PBT Copolymers via Depolymerization
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Solution Overview
Problem
Current methods for utilizing polyethylene terephthalate (PET) scrap are inefficient, as they either incinerate or bury it, and existing processes for converting PET into polybutylene terephthalate (PBT) are limited, failing to effectively utilize PET scrap due to issues like diethylene glycol contamination and inability to produce PBT with desired ethylene glycol content and melting temperatures.
Innovation Solution
A process involving reacting PET with ethylene glycol or propylene glycol, followed by 1,4-butanediol in the presence of a catalyst and basic compounds, under controlled temperature and pressure conditions, to form a modified random polybutylene terephthalate copolymer with specific molecular weights and residues, allowing for the production of PBT-like materials from PET scrap.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If PET is converted to PBT using conventional processes, then PBT material is produced, but diethylene glycol contamination occurs and purification is required
Solution Approach 1:
The patent extracts and removes diethylene glycol contamination through purification steps including filtration and washing processes. The method specifically targets and separates the harmful diethylene glycol byproduct from the PBT product stream, enabling direct use of converted material without extensive purification.
Solution Approach 2:
The patent introduces intermediate processing steps between PET conversion and final PBT product. These intermediate steps include controlled hydrolysis and selective precipitation processes that prevent diethylene glycol formation or facilitate its removal, acting as mediators to break the direct contamination pathway.
2Loss of substance
If PET scrap is utilized through incineration or landfilling, then waste disposal is achieved, but resource waste and environmental harm occur
Solution Approach 1:
The patent implements a recovery process that transforms discarded PET scrap into valuable PBT material. Instead of incineration or landfilling, the process chemically converts the scrap polymer into a different but useful polymer, recovering valuable resources and eliminating waste disposal needs.
Solution Approach 2:
The patent changes the chemical parameters of PET scrap through controlled hydrolysis and repolymerization conditions. By adjusting temperature, pressure, catalyst concentration, and reaction time parameters, the process transforms the chemical structure of PET into PBT, enabling resource recovery from waste material.
3Manufacturing precision
If PET is converted to PBT with complete replacement of ethylene glycol, then pure PBT is produced, but melting temperature control and performance properties are compromised
Solution Approach 1:
The patent applies partial replacement of ethylene glycol with controlled amounts retained in the final PBT product. Rather than complete removal, the process maintains optimal residual ethylene glycol levels that preserve desired melting temperature and performance properties while still achieving sufficient purity for application requirements.
Solution Approach 2:
The patent controls melting temperature by adjusting reaction parameters including hydrolysis degree, repolymerization temperature, and catalyst selection. These parameter changes enable precise control over the final PBT's crystalline structure and thermal properties, balancing purity requirements with performance specifications.
4Quantity of substance
If existing PET to PBT conversion processes are used, then PBT material is produced, but the processes are complex and require multiple purification steps
Solution Approach 1:
The patent merges multiple process steps into integrated reaction-purification sequences. The hydrolysis, repolymerization, and initial purification steps are combined into a continuous process flow, reducing the number of separate equipment units and simplifying the overall process complexity while maintaining production efficiency.
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 process enables the production of PBT materials with performance properties similar to virgin PBT, including high melting temperatures and reduced diethylene glycol content, effectively utilizing PET scrap and reducing waste, while also lowering carbon dioxide emissions and energy consumption.
Implementation Method 1
reacting (i) a polyethylene terephthalate component with a diol component selected from the group consisting of ethylene glycol, propylene glycol, and combinations thereof, in a reactor at a pressure that is at least atmospheric pressure in the presence of a catalyst component at a temperature ranging from 190°C to 250°C, under conditions sufficient to depolymerize the polyethylene terephthalate component into a first molten mixture
Implementation Method 2
adding 1,4-butanediol to the first molten mixture in a reactor in the presence of a catalyst component and a basic compound at a temperature ranging from 190°C to 240°C, under conditions that are sufficient to form a second molten mixture containing oligomers containing butylene terephthalate moieties
Implementation Method 3
increasing the temperature of the second molten mixture under subatmospheric conditions and agitation to a temperature from 240°C to 260°C, thereby forming a modified random polybutylene terephthalate copolymer
Data Source
AI summary
The invention relates to a process for making modified polybutylene terephththalate random copolymers from a polyethylene terephthalate component. The invention relates to a three step process in which a diol component selected from the group consisting of ethylene glycol, propylene glycol, and combinations thereof reacts with a polyethylene terephthalate component under conditions sufficient to depolymerize the polyethylene terephthalate component into a first molten mixture; and where the first molten mixture is combined with 1 ,4-butanediol under conditions that create a second molten mixture that is subsequently placed under subatmospheric conditions that produce the modified polybutylene terephthalate random copolymers. The invention also relates to compositions made from the process.