Polyalkylene Terephthalate Melt Polymerization for Low Acetaldehyde
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Solution Overview
Problem
Conventional methods for producing polyalkylene terephthalate (PArT) with high polymerization degree and low acetaldehyde content are inefficient, requiring complex equipment, high energy, and generating foreign matter that affects the quality of molded articles, while also being costly and difficult to maintain.
Innovation Solution
A method involving the polymerization of a prepolymer with 70 mol% or more ethylene terephthalate units, allowing it to fall along a support under specific conditions, and introducing inert gas to reduce pressure and promote polymerization, resulting in a high-quality PArT with reduced acetaldehyde content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If solid phase polymerization is used to produce high polymerization degree PArT, then the polymerization degree is improved, but the process complexity and energy consumption increase significantly
Solution Approach 1:
The invention changes the physical state parameter of the polymer from solid to liquid during polymerization. By conducting melt polymerization instead of solid phase polymerization, the process achieves high polymerization degree while avoiding the complexity of solid handling, multiple heating/cooling cycles, and extended processing times associated with solid phase methods.
Solution Approach 2:
The invention utilizes the phase transition of the polymer from solid to liquid state by heating above the melting point. This phase transition enables the polymer to be processed in a molten state where molecular mobility is high, facilitating rapid polymerization and simplifying the overall process while achieving high polymerization degree.
2Manufacturing precision
If solid phase polymerization is used to produce high polymerization degree PArT, then the polymerization degree is improved, but the energy consumption increases enormously
Solution Approach 1:
The invention changes the temperature parameter to maintain the polymer in a molten state throughout polymerization. By keeping the temperature above the melting point, the process eliminates the need for repeated heating and cooling cycles required in solid phase polymerization, significantly reducing energy consumption while achieving high polymerization degree.
3Manufacturing precision
If solid phase polymerization is used, then high polymerization degree is achieved, but powder polymer is generated that acts as foreign matter affecting molded article quality
Solution Approach 1:
The invention changes the physical state parameter to liquid/molten during polymerization. This prevents the formation of powder polymer that occurs in solid phase processes. The molten state ensures uniform polymerization throughout the material without generating discrete powder particles that would act as foreign matter and compromise molded article quality.
4Manufacturing precision
If strict conditions with high temperature or high shearing are applied to melt processed high crystallinity pellets, then high-quality polymer is produced, but the molded article quality deteriorates significantly
Solution Approach 1:
The invention performs polymerization in the melt state before molding, achieving high polymerization degree and quality in a single step. This preliminary polymerization eliminates the need for subsequent high-temperature or high-shearing processing of high crystallinity pellets, thereby preventing the deterioration of molded article quality that would result from such strict processing conditions.
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 enables the stable, cost-effective production of high-quality PArT with high polymerization degree and low acetaldehyde content, suitable for beverage containers, without the need for solid phase polymerization, thus improving productivity and reducing energy consumption.
Implementation Method 1
polymerizing the prepolymer under reduced pressure, while allowing the prepolymer to fall along the surface of a support
Implementation Method 2
polymerizing the prepolymer under reduced pressure
Data Source
AI summary
The present invention provides a method of producing polyalkylene terephthalate, which comprises: introducing a prepolymer of polyalkylene terephthalate that is in a molten state comprising 70 mol % or more of ethylene terephthalate or 1,4-butylene terephthalate repeating units and having an intrinsic viscosity [η] between 0.2 and 2 dl/g through a feed opening to a polymerization reactor; discharging the introduced prepolymer from holes of a perforated plate; and polymerizing the prepolymer under reduced pressure, while allowing the prepolymer to fall along the surface of a support that is open towards the outside at a temperature between the [crystalline melting point−10° C.] of the prepolymer or higher and the [crystalline melting point+30° C.] of the prepolymer or lower under the conditions represented by a formula S1/S2>1, wherein S1 is the surface area of falling polyalkylene terephthalate, and S2 is the area where the support is in contact with polyalkylene terephthalate.