Recycled BHET Purification for Thermal-Resistant Polyester Feedstock

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Solution Overview

Problem

Existing methods of recycling waste polyester result in bis(2-hydroxyethyl) terephthalate products with impurities such as acetate-based and diethylene glycol ester compounds, which degrade thermal resistance and quality in polymer production.

Innovation Solution

A process to depolymerize waste polyester, controlling the peak area fractions of acetate-based ester compounds to 1.0% or less and diethylene glycol ester compounds to 2.0% or less, using high-performance liquid chromatography, through cooling crystallization and pressure filtering.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If glycolysis is performed at high temperatures to depolymerize waste polyester, then depolymerization efficiency is improved, but by-products such as diethylene glycol esters and acetate-based esters are generated, deteriorating product purity

Engineering Contradiction:

Improvedepolymerization efficiencyVSAvoidproduct purity

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The patent applies parameter changes by carefully controlling the glycolysis reaction temperature and time parameters to optimize the balance between depolymerization efficiency and by-product formation. By adjusting these parameters, the process achieves effective waste polyester decomposition while minimizing the generation of diethylene glycol esters and acetate-based esters.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs extraction principles through the purification process that specifically removes harmful by-products (diethylene glycol esters and acetate-based esters) from the reaction mixture. This selective removal of disturbing components from the system achieves high-purity BHET while maintaining efficient depolymerization.

Inventive Principle:

Principle #2Taking out (Extraction)

2Speed

If acetate catalyst is used in glycolysis reaction, then reaction rate is improved, but acetate-based ester compounds are formed as by-products, accumulating during ethylene glycol recovery and reuse

Engineering Contradiction:

Improvereaction rateVSAvoidpurity of recycled bis(2-hydroxyethyl) terephthalate

Core Design Contradiction:

SpeedVSManufacturing precision

Solution Approach 1:

The patent converts the harmful effect of acetate catalyst by-products into a manageable issue through systematic purification. The acetate-based ester compounds that inevitably form during catalysis are identified and removed through the purification process, transforming the harmful accumulation problem into a controlled removal step that enables catalyst reuse.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent introduces an intermediary purification process between the glycolysis reaction and the final product that mediates the presence of acetate-based ester by-products. This intermediary step separates the beneficial catalytic function from the harmful by-product accumulation, allowing continued use of acetate catalysts while maintaining product purity.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Ease of manufacture

If physical recycling methods are used for waste polyester, then recycling process is simple, but purity cannot be guaranteed

Engineering Contradiction:

Improverecycling process simplicityVSAvoidpurity of recycled material

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The patent replaces mechanical/physical recycling methods with a chemical recycling approach (glycolysis). This substitution transforms the simple but ineffective physical process into a chemically-based system that provides both effective waste polyester decomposition and high-purity product recovery through controlled chemical reactions and systematic purification.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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

The process ensures high purity of bis(2-hydroxyethyl) terephthalate, maintaining thermal resistance characteristics and producing high-quality polyester resins by effectively removing low-weight organic substances.

Implementation Method 1

cooling crystallization

Methodology Applied

Scientific EffectCrystallization: Crystallisation

Implementation Method 2

pressure filtering

Methodology Applied

Scientific EffectFiltration: Filter (physical)

Data Source

PatentUS12509412B2Polymerizable raw material comprising recycled bis(2-hydroxyethyl) terephthalate and method for preparing the same

Publication Date: 2025.12.30 SK CHEMICALS CO LTD

AI summary

A polymerization raw material obtained by the depolymerization of waste polyester is disclosed. The polymerization raw material contains recycled bis(2-hydroxyethyl) terephthalate in which the contents of acetate-based ester compounds and diethylene glycol ester compounds are adjusted to specific levels. The polymerization raw material is excellent in purity and quality, and free from the problem that thermal resistance characteristics deteriorate in the polymerization of a polymer from the recycled monomer.