Recycled Ethylene Glycol Purification for BHET Acetate Control
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Solution Overview
Problem
The accumulation of acetate-based compounds in ethylene glycol during the continuous glycolysis process for producing bis(2-hydroxyethyl) terephthalate leads to a decrease in the quality of the final product, as these compounds have similar boiling points to ethylene glycol and are difficult to separate effectively.
Innovation Solution
A process involving depolymerization of waste polyester using glycolysis, followed by distillation to separate ethylene glycol, removal of acetate-based compounds through side draw purging in a multi-stage distillation column, and reuse of purified ethylene glycol for continuous glycolysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ethylene glycol is reused in continuous glycolysis process, then cost efficiency is improved, but acetate-based compounds accumulate and product quality deteriorates
Solution Approach 1:
The patent extracts and removes acetate-based compounds from the recycled ethylene glycol through a distillation column. The side draw purging technique specifically targets and removes these harmful compounds from the circulation stream, preventing their accumulation while allowing the ethylene glycol to be reused.
Solution Approach 2:
The patent changes the operational parameters of the distillation column, specifically implementing side draw purging at optimized positions and flow rates. This parameter adjustment enables selective removal of acetate-based compounds while maintaining efficient ethylene glycol recovery and reuse.
2Manufacturing precision
If side draw purging is implemented to remove acetate-based compounds, then product purity is improved, but process complexity increases
Solution Approach 1:
The patent segments the distillation column into multiple stages with side draws positioned at specific heights. This segmentation allows targeted removal of acetate-based compounds from different zones of the column, achieving high product purity through distributed purification points rather than a single complex separation stage.
3Manufacturing precision
If multi-stage distillation is used to separate acetate-based compounds, then separation effectiveness is improved, but energy consumption increases
Solution Approach 1:
The patent implements continuous side draw purging throughout the distillation process, maintaining constant removal of acetate-based compounds as they form. This continuous action prevents compound accumulation and reduces the need for additional reprocessing, optimizing energy utilization across the multi-stage 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
This process ensures the production of bis(2-hydroxyethyl) terephthalate with excellent purity and quality by preventing the concentration of acetate-based compounds, resulting in high-purity ethylene glycol that can be reused multiple times.
Implementation Method 1
it has been possible to do so by side draw purging at a specific fraction from the stages with the highest concentration of acetate-based compounds in a multi-stage distillation column
Implementation Method 2
side draw purging at a specific fraction from the stages with the highest concentration of acetate-based compounds
Data Source
AI summary
A method for producing bis(2-hydroxyethyl)terephthalate is disclosed. In the method, by recovering and reusing ethylene glycol with an acetate removed, after the glycolysis of a waste polyester, an acetate is not concentrated even though ethylene glycol is reused in a continuous process, leading to bis(2-hydroxyethyl)terephthalate with excellent purity and quality.