PET Pellet Crystallization Without Reheating
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Solution Overview
Problem
Existing solid state polycondensation (SSP) processes for polyester resins, particularly PET, face issues with high crystallinity leading to reduced removal efficiency of acetaldehyde and molecular weight increasing reaction rates due to re-heating of PET pellets, causing agglomeration and sintering, which affects gas and solid flow distribution.
Innovation Solution
A process and apparatus that quenches molten PET particles into solid form without re-heating, using a cooling liquid to form pellets, followed by crystallization in a bin with hot inert gas contact, ensuring crystallization occurs from core to surface, thereby avoiding the formation of an extra crystalline layer that hinders diffusion and reaction rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If PET particles are re-heated during solid state polycondensation, then molecular weight increasing reaction can proceed, but crystalline layer forms on surface blocking diffusion and reducing reaction rates
Solution Approach 1:
The patent applies preliminary crystallization action before the solid state polycondensation reaction. By pre-crystallizing the PET particles to achieve desired crystallinity (30-70%) before feeding to the SSP reactor, the process eliminates the need for re-heating during reaction, preventing crystalline layer formation that would block diffusion and reduce reaction rates.
Solution Approach 2:
The patent changes the temperature parameter profile by conducting crystallization at elevated temperatures (100-200°C) before the SSP reaction. This parameter change allows the particles to achieve sufficient crystallinity without forming a surface crystalline layer that would hinder diffusion during the subsequent polycondensation process.
2Stability of the object's composition
If high crystallinity is achieved in PET particles, then particle stability improves, but removal efficiency of acetaldehyde and molecular weight increasing reaction rates decrease
Solution Approach 1:
The patent performs crystallization as a preliminary step before the solid state polycondensation reaction. By pre-crystallizing particles to achieve 30-70% crystallinity, the process stabilizes particle structure while maintaining porosity and surface properties necessary for efficient acetaldehyde removal and high reaction rates during the subsequent SSP process.
3Speed
If PET particles are quenched in cooling liquid, then immediate solid formation occurs, but crystallization may start in cooling liquid causing agglomeration
Solution Approach 1:
The patent optimizes the cooling liquid temperature parameter to a specific range (0-50°C) to control the crystallization process. This parameter change allows rapid solid formation while preventing excessive crystallization in the cooling liquid, maintaining particle homogeneity and preventing agglomeration.
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 approach minimizes crystalline layer formation, enhancing the diffusion of by-products and molecular weight increasing reactions, reducing energy consumption and improving the homogeneity and quality of PET pellets, resulting in significant operational and energy savings.
Implementation Method 1
cutting the molten PET particles into pellets while quenching with a cooling liquid
Implementation Method 2
contacting the solid PET particles with hot inert gas
Implementation Method 3
crystallization of the particles takes place, resulting in a temperature increase and crystallization of the PET particles which forms from core to surface
Implementation Method 4
crystallization of the particles takes place, resulting in a temperature increase
Data Source
AI summary
The present subject matter claims a process and apparatus for forming, crystallizing and increasing the molecular weight of polymer particles which does not require re-heating the polyethylene terephthalate (PET) pellets after they are cut and crystallized in the under water cutting (UWC) section. In the existing solid state polycondensation (SSP) technologies where an UWC is used, high crystallinity of the PET pellets can occur, by cooling and re-heating the PET pellets, which results in reduced removal efficiency of by-products, such as acetaldehyde (AA) and furthermore also a reduction of the reaction rates of molecular weight increasing reactions.