Polycarbonate Monomer Recovery Through Two-Step pH Crystallization
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Solution Overview
Problem
Existing chemical recycling methods for polycarbonate-based resins face challenges such as the use of harmful chemicals, high temperature and pressure requirements, low yield, and economic disadvantages, which affect the efficiency and quality of the recycling process.
Innovation Solution
A method involving a two-step pH adjustment process followed by crystallization to recover high-purity aromatic diol compounds from polycarbonate-based resins, using mild conditions and avoiding distillation, thereby enhancing yield and optical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If alcohol decomposition using base catalyst is used for chemical recycling of polycarbonate, then the decomposition process is simplified, but harmful methanol is used or high temperature and pressure conditions are required with low yield
Solution Approach 1:
The invention changes the pH parameter from highly basic (pH 13 or more) to a milder range (pH 8-12) through controlled acidification. This parameter change enables the decomposition process to proceed without requiring harmful chemicals or extreme conditions, while maintaining high aromatic diol compound yield and eliminating the need for distillation
Solution Approach 2:
The invention uses readily available, inexpensive acids (such as hydrochloric acid or sulfuric acid) for pH adjustment instead of expensive or harmful catalysts. These common chemicals enable the recycling process to be economically viable while avoiding the environmental and health issues associated with traditional base catalysts
2Manufacturing precision
If pH adjustment to 8-12 followed by further adjustment to less than 4 is performed, then aromatic diol compound crystals are effectively recovered, but additional processing steps are required
Solution Approach 1:
The invention utilizes phase transition through controlled pH changes to precipitate aromatic diol compound crystals. By adjusting pH to 8-12 first, then to less than 4, the aromatic diol compound transitions from dissolved state to crystalline precipitate, enabling effective recovery without requiring distillation or other complex separation equipment
Solution Approach 2:
The pH adjustment process is segmented into two distinct stages: first adjusting to pH 8-12 to initiate controlled precipitation, then further adjusting to pH less than 4 to complete crystal formation. This segmentation allows for better control of the precipitation process and easier filtration, achieving high purity without overly complex equipment
3Productivity
If conventional chemical recycling methods are used, then polycarbonate can be decomposed, but high operational costs and environmental harm occur
Solution Approach 1:
The invention converts the typically harmful highly basic conditions (pH 13 or more) into a benefit by systematically acidifying to pH 8-12 and then to less than 4. This controlled conversion of extreme conditions into moderate conditions enables high-yield aromatic diol compound recovery while eliminating environmental harm and reducing operational costs by avoiding distillation
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 method achieves high-purity aromatic diol compound recovery with improved yield and reduced environmental impact, eliminating the need for distillation and reducing operational costs.
Implementation Method 1
subjecting a polycarbonate-based resin to a depolymerization reaction
Implementation Method 2
adjusting the pH of the depolymerization reaction product having a pH of 13 or more to be 8 to 12
Implementation Method 3
adding a crystallization solvent to the depolymerization reaction product whose pH is adjusted to less than 4 and recovering the formed aromatic diol compound crystals
Data Source
AI summary
A method for preparing a monomer composition for synthesizing recycled plastic, a monomer composition for synthesizing recycled plastic, a recycled plastic using the same, and a molded product using the same. The method includes the steps of: subjecting a polycarbonate-based resin to a depolymerization reaction; adjusting the pH of the depolymerization reaction product having a pH of 13 or more to be 8 to 12; adjusting the pH of the depolymerization reaction product whose pH is adjusted to 8 to 12 to be less than 4; and adding a crystallization solvent to the depolymerization reaction product whose pH is adjusted to less than 4 and recovering the formed aromatic diol compound crystals.