Polyester Crystallization Using Low Dew Point Gas
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Solution Overview
Problem
Current methods for producing highly condensed polyesters in the solid state face challenges such as high energy expenditure, oxidative damage, and excessive acetaldehyde content, particularly in the production of packaging materials like bottles, due to the use of high temperatures and expensive gases like nitrogen.
Innovation Solution
A method involving crystallization of polyester materials in the presence of a gas with a dew point of ≤−10° C, using a fluidised bed reactor and shaft crystallizer, which controls viscosity and acetaldehyde content without the need for expensive gases or high temperatures, allowing for the production of granulates with high intrinsic viscosity and low acetaldehyde levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high temperatures (up to 230°C) are used for solid-state polycondensation to increase intrinsic viscosity, then the acetaldehyde content is reduced, but severe thermo-oxidative breakdown of the polyester occurs
Solution Approach 1:
The patent applies nitrogen atmosphere during solid-state polycondensation to prevent oxidative damage. The nitrogen gas creates an inert environment that eliminates oxygen, thereby preventing thermo-oxidative breakdown of the polyester chains while still allowing the polycondensation reaction to proceed at elevated temperatures for acetaldehyde removal.
Solution Approach 2:
The patent optimizes the temperature profile and nitrogen flow rate parameters to achieve the desired balance. By controlling the temperature to not exceed 230°C and maintaining appropriate nitrogen atmosphere conditions, the process removes acetaldehyde effectively while minimizing polymer degradation.
2Object-affected harmful factors
If nitrogen gas is used to prevent oxidative damage during solid-state polycondensation, then the polyester quality is improved, but the production costs increase significantly
Solution Approach 1:
The patent uses air instead of nitrogen gas for the fluidized bed crystallization step, which is a preliminary treatment before solid-state polycondensation. This substitution of expensive nitrogen with free air reduces costs while still achieving the desired crystallization effect. The nitrogen is then used only in the essential polycondensation step where it is truly needed.
Solution Approach 2:
The patent divides the processing into two distinct stages: fluidized bed crystallization using air (low cost) and solid-state polycondensation using nitrogen (high cost but necessary). This segmentation allows the expensive nitrogen to be used only where absolutely necessary for preventing oxidative damage, while the less critical crystallization step uses cheaper air.
3Manufacturing precision
If large amounts of dry air with dew point of −40 to −80°C are used to remove acetaldehyde, then the acetaldehyde content is reduced, but oxidative damage to the granulate cannot be excluded
Solution Approach 1:
The patent replaces dry air with nitrogen gas during the solid-state polycondensation step. Nitrogen creates an inert atmosphere that prevents oxidative damage while still allowing acetaldehyde to be removed through the polycondensation reaction. The nitrogen atmosphere eliminates the oxygen that would cause oxidative degradation.
Solution Approach 2:
The patent changes the gas composition parameter from air (21% oxygen) to nitrogen (0% oxygen), fundamentally altering the chemical environment to prevent oxidation while maintaining the temperature and pressure conditions necessary for acetaldehyde removal.
4Manufacturing precision
If temperatures above 220°C are used with air as carrier gas to increase intrinsic viscosity, then the processing is simplified, but severe oxidative damage occurs
Solution Approach 1:
The patent uses nitrogen gas instead of air as the carrier gas during solid-state polycondensation. This inert atmosphere allows the process to operate at temperatures above 220°C to achieve the desired intrinsic viscosity increase without suffering from oxidative damage that would occur with air.
Solution Approach 2:
The patent changes the carrier gas from air to nitrogen, which fundamentally alters the chemical environment to prevent oxidation. This allows temperature parameters to be optimized for viscosity increase without the constraining factor of oxidative degradation.
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 method simplifies the production process, reduces energy costs, minimizes oxidative damage, and achieves the required high quality standards for polyester granulates, enabling the production of high-strength polyester materials with low acetaldehyde content suitable for packaging applications without the need for additional solid-state polycondensation.
Implementation Method 1
crystallisation is carried out in the presence of a gas with a dew point (Tp) of (less than or equal to) ≦approximately −10° C.
Implementation Method 2
using a fluidised bed reactor and shaft crystallizer
Data Source
AI summary
The invention relates to a continuous or discontinuous method for the production of highly condensed polyesters in the solid state, comprising a crystallization of a polyester material, wherein the crystallization is carried out in the presence of a gas with a dew point of (less than or equal to) ≦approximately −10° C. The invention also relates to a method for the production of polyester formed bodies using the polyester material obtained for the production of bottles, films and high strength threads.