BHET Recovery From Recycled Polyester Through Two-Stage Crystallization
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Solution Overview
Problem
Conventional methods for recycling PET fabrics into bis(2-hydroxyethyl) terephthalate (BHET) suffer from poor recovery quality, low recovery rates, and high energy consumption due to complex purification procedures and impurity removal processes.
Innovation Solution
A method involving chemical depolymerization with ethylene glycol, followed by dissolution in water, and a two-stage crystallization process with controlled cooling rates to achieve high purity and recovery rates of BHET, utilizing activated carbon for impurity adsorption and controlled crystallization temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional purification procedures using activated carbon or ion exchange resin are used to remove impurities, then impurity removal is achieved, but the recovery rate and recovery quality of BHET deteriorate
Solution Approach 1:
The patent changes the fundamental parameter of the purification approach by replacing chemical adsorption methods (activated carbon, ion exchange resin) with a physical crystallization method. By controlling temperature parameters during crystallization, the patent achieves both impurity removal and high recovery rate (95% or higher) without the trade-off present in conventional methods
Solution Approach 2:
The patent utilizes the phase transition of BHET from dissolved state to crystalline state through controlled cooling. This phase transition enables separation of BHET from impurities that remain in the mother liquor, achieving both purification and high recovery rate simultaneously
2Object-affected harmful factors
If conventional purification procedures are used to remove impurities, then impurity removal is achieved, but the recovery quality (hue) of BHET deteriorates
Solution Approach 1:
The controlled crystallization process exploits phase transition to selectively precipitate pure BHET crystals while leaving impurities in the liquid phase. This results in high recovery quality with excellent hue, as the crystalline structure naturally excludes impurity molecules
Solution Approach 2:
The patent extracts pure BHET in crystalline form from the reaction mixture, leaving impurities behind in the mother liquor. This extraction through crystallization achieves superior recovery quality compared to adsorption methods that may co-adsorb desirable components
3Object-affected harmful factors
If conventional purification procedures are used to remove impurities, then impurity removal is achieved, but energy consumption increases
Solution Approach 1:
The patent utilizes the exothermic nature of crystallization and the natural cooling curve of the system to minimize external energy input. The phase transition from dissolved to crystalline state occurs with controlled cooling, reducing the need for energy-intensive purification steps
Solution Approach 2:
The crystallization process is designed to proceed with minimal external intervention after the initial cooling is started. The system self-organizes into crystalline structures, automatically separating pure BHET from impurities without requiring additional energy input for filtration or regeneration of adsorbents
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
Improves BHET recovery quality and rate to at least 85% purity and 99.0%, with a good hue and reduced energy consumption.
Implementation Method 1
using a chemical de-polymerization liquid to chemically depolymerize the recycled polyester fabric, so as to form a de-polymerization product mainly containing bis(2-hydroxyethyl) terephthalate (BHET)
Implementation Method 2
dissolving the BHET in water to form a aqueous phase liquid
Implementation Method 3
utilizing activated carbon for impurity adsorption
Implementation Method 4
cooling the aqueous phase liquid from the dissolution temperature to a first crystallization temperature, so as to crystallize at least a part of the BHET from the aqueous phase liquid
Data Source
AI summary
A method for improving a recovery rate of recycled bis(2-hydroxyethyl) terephthalate (BHET) is provided, which includes: providing a recycled polyester fabric; using a chemical de-polymerization liquid to chemically depolymerize the recycled polyester fabric, so as to form a de-polymerization product containing BHET; dissolving the BHET in water to form a aqueous phase liquid; cooling the aqueous phase liquid from a dissolution temperature to a first crystallization temperature, so as to crystallize at least a part of the BHET; and cooling the aqueous phase liquid from the first crystallization temperature to a second crystallization temperature, so as to crystallize at least another part of the BHET.