MEG Purification from PET Depolymerization Using Resin and Distillation
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Solution Overview
Problem
Existing methods for purifying mono-ethylene glycol (MEG) from depolymerized polyesters, such as PET, fail to effectively remove impurities like dicarboxylic acid salts and other inorganics, resulting in MEG that is not suitable for further reuse in high-quality plastic products.
Innovation Solution
A multi-step process involving evapo-condensation, resin treatment, and distillation is employed to purify MEG, including evapo-condensation to separate salts and impurities, followed by contacting the overhead fraction with a strong anion exchange resin, and finally distilling to obtain highly pure MEG.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If distillation is used to purify MEG from depolymerization solution, then MEG can be recovered, but impurities such as dicarboxylic acid salts and inorganics remain in the recovered MEG
Solution Approach 1:
The purification process is divided into multiple sequential steps: evapo-condensation to remove bulk impurities, followed by distillation to separate MEG from remaining impurities based on boiling point differences. This segmentation allows each step to target specific impurity types, achieving both high recovery and high purity
Solution Approach 2:
A fractionation column acts as an intermediary device between the crude MEG solution and the final purified product. The column provides multiple theoretical plates that facilitate repeated vaporization-condensation cycles, progressively separating MEG from impurities with different volatilities
2Device complexity
If simple distillation is used for MEG purification, then the process is simple, but the MEG purity is insufficient for high-quality plastic production
Solution Approach 1:
The purification system is segmented into distinct functional units: evaporator, fractionation column with multiple trays, condenser, and collection system. Each unit performs a specific separation function, and the modular design allows the process to achieve high purity without excessive overall complexity
Solution Approach 2:
The process exploits phase transitions (liquid-vapor-liquid) repeatedly through the fractionation column. Each tray in the column represents a phase transition cycle that enhances separation efficiency, allowing high purity to be achieved through natural physical processes rather than complex mechanical means
3Manufacturing precision
If extensive purification steps are added to remove all impurities, then MEG purity increases, but the process becomes too complex and costly
Solution Approach 1:
The process optimizes key parameters such as heating temperature, pressure, and distillation rate to maximize separation efficiency at each stage. By carefully controlling these parameters, the system achieves high purity MEG recovery without requiring excessive purification steps or complex equipment
Solution Approach 2:
Impurities are selectively extracted and removed at different stages: bulk inorganics are removed in the evapo-condensation stage, while organic impurities are separated in the distillation stage. This staged extraction approach achieves comprehensive purification without treating all impurities with the same complex method
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 achieves MEG purity comparable to petrochemical standards, suitable for repolymerization, with low color values and impurity levels, enabling the reuse of MEG in high-quality plastic products.
Implementation Method 1
Submitting said depolymerization solution to at least one evapo-condensation step to obtain a bottom fraction and a condensed overhead fraction
Implementation Method 2
Submitting said depolymerization solution to at least one evapo-condensation step to obtain a bottom fraction and a condensed overhead fraction
Implementation Method 3
Contacting the condensed overhead fraction obtained in step (a) with a resin, to obtain a solution
Implementation Method 4
Submitting the solution obtained in step (b) to at least one distillation step to obtain a distillate
Data Source
AI summary
The present invention relates to a process for purifying and recovering the mono-ethylene glycol (MEG) from a solution obtained from the depolymerization of at least one polyester having at least one unit of MEG. This solution is preferably obtained from an enzymatic depolymerization under alkaline conditions of polyethylene terephthalate (PET) included in a plastic product. The invention also relates to a process for recycling a polymer-containing material, such as plastic product, comprising at least one polyester having at least one unit of MEG, such as PET, and recovering the monomers thereof.