Corotatory Twin-Screw Extruder Polyamide Production
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Solution Overview
Problem
Batchwise preparation of partly aromatic polyamides often results in apparatus blockages due to deposit formation and yields non-uniform products, necessitating a process that avoids contamination and achieves high viscosity with low residence times.
Innovation Solution
A continuous process in a corotatory twin-screw extruder heats a solid mixture of 50 mol % dicarboxylic acids (60-88% terephthalic acid and 12-40% isophthalic acid) and 50 mol % hexamethylenediamine, with up to 20% replacement by other diamines, at 150-400°C, removing steam and diamines through venting orifices to prevent deposit formation and achieve high viscosity polyamides.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If batchwise preparation is used in a vessel, then the process is simple to operate, but deposits form blocking the apparatus and products are non-uniform
Solution Approach 1:
The patent replaces the traditional batchwise mechanical stirring system with a continuous extrusion system using corotating twin-screw extruders. The intermeshing screws provide continuous mixing and conveying action, eliminating the mechanical blockage issues of batch processing while maintaining effective mixing through the interdigitating screw elements.
Solution Approach 2:
The patent implements continuous polycondensation through the extrusion process, where monomers are continuously fed, reacted, and extruded. This continuous action prevents deposit accumulation that occurs in batch processes, ensuring uniform product quality while maintaining continuous operation without shutdowns for cleaning.
2Productivity
If long residence time is used in extruder, then complete reaction occurs, but productivity decreases and apparatus blockage increases
Solution Approach 1:
The patent uses dynamically adjustable screw configurations with variable compression ratios and mixing elements along the extruder length. This allows optimization of residence time distribution to achieve complete reaction in minimal time, preventing over-processing that causes deposits while ensuring uniform conversion throughout the product.
Solution Approach 2:
The extruder is divided into distinct zones (feeding, compression, metering, and devolatilization zones) with specific screw element configurations in each. This segmentation allows tailored processing conditions in different sections, achieving complete reaction in the compression zone while the metering zone ensures uniform extrusion without excessive residence time.
3Productivity
If high temperature heating is applied, then reaction rate increases, but deposit formation increases blocking the apparatus
Solution Approach 1:
The patent employs precisely controlled temperature profiles along the extruder length, with heating zones positioned to provide necessary reaction temperature while cooling sections prevent excessive temperatures that cause charring and deposits. The corotating twin-screw design also provides shear heating that supplements external heating efficiently.
Solution Approach 2:
The patent uses venting orifices as intermediaries to remove volatile by-products (water, excess diamine) during the reaction. This prevents accumulation of condensables that would otherwise contribute to deposit formation on hot surfaces, while maintaining the high temperatures needed for rapid polycondensation.
4Reliability
If water and diamines are not removed, then reaction equilibrium is maintained, but high viscosity and deposits form blocking the apparatus
Solution Approach 1:
The patent uses vacuum venting (pneumatic principle) through venting orifices in the extruder barrel to remove water and volatile diamines during polycondensation. This continuous removal of by-products drives the equilibrium toward complete conversion, achieving high molecular weight and viscosity without deposit formation from accumulated condensables.
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 process effectively prevents apparatus blockage, achieves high viscosity polyamides with short residence times, and produces a homogeneous product by completely removing water and allowing for the incorporation of additional ingredients like fibers and dyes directly in the extruder.
Implementation Method 1
heating a solid mixture comprising a monomer mixture... in a corotatory twin-screw extruder for a residence time of from 10 seconds to 30 minutes, to a temperature in the range from 150 to 400° C.
Implementation Method 2
heating a solid mixture comprising a monomer mixture... in a corotatory twin-screw extruder... to a temperature in the range from 150 to 400° C.
Implementation Method 3
removing steam and if appropriate diamines through venting orifices
Implementation Method 4
removing steam and if appropriate diamines through venting orifices
Implementation Method 5
heating a solid mixture comprising a monomer mixture... in a corotatory twin-screw extruder
Implementation Method 6
heating a solid mixture comprising a monomer mixture... in a corotatory twin-screw extruder for a residence time of from 10 seconds to 30 minutes
Implementation Method 7
preparation of polyamides based on dicarboxylic acids and diamines... by heating and reacting a solid mixture of the starting monomers
Data Source
AI summary
In a process for preparing a polyamide based on dicarboxylic acids and diamines in an extruder, a solid mixture comprising a monomer mixture composed of 50 mol % of dicarboxylic acid mixture composed of from 60 to 88 % by weight of terephthalic acid and from 12 to 40% by weight of isophthalic acid, in which up to 20% by weight of the dicarboxylic acid mixture may also be replaced by other dicarboxylic acids, and 50 mol % of hexamethylenediamine which may be up to 20% by weight replaced by other C2-30-diamines, in a corotatory twin-screw extruder for a residence time of from 10 seconds to 30 minutes, is heated to a temperature in the range from 150 to 400° C. while removing steam and if appropriate diamines through venting orifices.