Polyester Granule Production via Hot Die Cutting and Dry Air Drying
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Solution Overview
Problem
Conventional processes for producing polyester granules from high-viscosity melts face issues such as rapid hydrolysis, insufficient crystallization control, high water losses, and uncontrollable isothermal drying, leading to degradation and quality inconsistencies.
Innovation Solution
The process involves hot die cutting at water temperatures of 70° C to 95° C with a liquor ratio of 8 to 12:1, retaining liquor until the pre-dryer, and rapid water separation within 10 seconds, followed by efficient drying using a stirred centrifuge and preheated dry air to minimize hydrolysis and residual moisture, while using a specifically designed drying/degassing device to control water vapor and volatile by-products.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If conventional water cooling and steam drying processes are used, then rapid hydrolysis occurs reducing degree of polycondensation by up to 20%, but the process is simple and fast
Solution Approach 1:
The patent changes the temperature parameter from conventional cooling (below melting point) to heating above melting point (160-200°C), and changes the atmospheric parameter from steam atmosphere to dry air atmosphere, thereby preventing hydrolysis while maintaining processing efficiency
Solution Approach 2:
The patent replaces the steam atmosphere with dry air atmosphere in the drying chamber, creating an inert environment that prevents hydrolytic degradation of the polyester granules while still achieving effective drying
2Productivity
If intensive contact with hot water and steam is used for drying, then drying efficiency is high, but severe hydrolysis occurs reducing degree of polycondensation
Solution Approach 1:
The patent replaces steam atmosphere with dry air atmosphere in the drying chamber, creating an inert environment that prevents hydrolytic degradation while still achieving effective drying through controlled air circulation and temperature
Solution Approach 2:
The patent replaces the mechanical steam injection system with a dry air circulation system, eliminating the source of hydrolysis (steam) while maintaining drying capability through forced air convection
3Strength
If high temperature processing is used to increase viscosity, then molecular weight increases, but hydrolytic degradation susceptibility increases
Solution Approach 1:
The patent uses dry air atmosphere during the heating and processing stages to prevent hydrolytic degradation, allowing the polyester to be heated to high temperatures for viscosity increase without exposure to moisture that would cause degradation
4Stability of the object's composition
If conventional cooling below melting point is used, then crystallization occurs preventing agglomeration, but energy consumption is high and process complexity increases
Solution Approach 1:
The patent inverts the conventional approach by heating above melting point instead of cooling below melting point, using the molten state itself to prevent agglomeration rather than relying on crystallization, thereby simplifying the process
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 reduces the degree of polycondensation to less than 2%, achieves low acetaldehyde content, and produces granules with low crystallinity, suitable for direct use in bottle and film applications, reducing reheating needs and minimizing degradation products, with improved control over drying and crystallization.
Implementation Method 1
the die, from which the polymer is extruded, is in direct contact with the cutting and water chamber, with a circulating flow of water constantly cutting the round to oval shaped 'pellets' produced by a simple blade crown passing the die holes conveyed away, whereby the heat of fusion is removed
Implementation Method 2
The chips/water mixture is separated and the surface water is removed in a stirred centrifuge
Implementation Method 3
In this area, crystallization sets in and by installing a horizontal crystallization trough downstream, degrees of crystallization of > 38% are achieved
Implementation Method 4
the still hot 'pellets' can be further annealed at a constant temperature for further drying and outgassing of disruptive reaction by-products of the polyesters in a storage container for a few hours with a slight flow of a carrier gas
Data Source
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AI summary
The present invention relates to a method for the continuous production of polyester granules low in hydrolysis made of high-viscosity polyester melts, characterized in that the decrease in the degree of polycondensation from the polyester melt to the polyester granule is less than 2%. The invention further relates to a polyester granule produced by said method, and to a device for the production of the granule.