Polyamide 6 Pelletizing With In-Line Dimer Extraction
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Solution Overview
Problem
Existing methods for producing polyamide 6 pellets are inefficient in removing cyclic dimers, require extensive energy for water evaporation, and suffer from excessive foaming and complex processes, leading to high costs and lengthy production times.
Innovation Solution
A method involving underwater pelletizing with an aqueous ε-caprolactam solution at controlled pressure and temperature, followed by a vertical vessel extraction, allows for rapid removal of cyclic dimers and oligomers, eliminating the need for intermediate drying and reducing process steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If wet extraction process with hot water is used to remove e-caprolactam and oligomers, then extraction efficiency is improved, but energy consumption increases due to evaporation of large amounts of water
Solution Approach 1:
The patent extracts only the necessary components (cyclic dimers and oligomers) from the polyamide 6 pellets using a superheated steam treatment, rather than using large amounts of water for extraction. This selective extraction approach removes harmful substances while minimizing the need for subsequent water evaporation, thereby reducing energy consumption while maintaining extraction efficiency
Solution Approach 2:
The patent uses superheated steam at temperatures above 100°C to extract cyclic dimers and oligomers from polyamide 6 pellets. By changing the extraction medium from water to superheated steam and operating at elevated temperatures and pressures, the process achieves effective extraction without requiring large volumes of water that would need to be evaporated, thus reducing energy consumption
2Productivity
If conventional underwater pelletization is used, then pellet production is achieved, but excessive foaming occurs when extractable content exceeds 4% by weight, impeding granule cleansing
Solution Approach 1:
The patent applies increased pressure (≥4 bar) during underwater pelletization to suppress foaming. By changing the pressure parameter, the process can tolerate higher extractable content (up to 10% by weight) in the pelletization water without excessive foaming, thereby maintaining productivity while enabling effective extraction of harmful substances
3Manufacturing precision
If extraction process with residence times of several hours is used, then thorough extraction is achieved, but production time increases
Solution Approach 1:
The patent performs extraction of cyclic dimers and oligomers during the pelletization process itself, before the conventional separate extraction step. By conducting preliminary extraction under pressure with superheated steam during pelletization, the process achieves thorough removal of harmful substances while significantly reducing the total production time
Solution Approach 2:
The patent combines the pelletization process with the extraction process by using superheated steam treatment during pelletization to remove cyclic dimers and oligomers. This merging of processes eliminates the need for separate lengthy extraction steps, achieving thorough extraction while reducing overall production time
4Loss of substance
If large evaporators are used to cope with extraction fluid, then water recovery is achieved, but plant design becomes spacious and costly
Solution Approach 1:
The patent extracts cyclic dimers and oligomers using superheated steam, which condenses and can be directly recovered and reused. This approach eliminates the need for large evaporators required in conventional water extraction processes, thereby achieving water recovery while simplifying plant design and reducing space requirements
Solution Approach 2:
The patent recovers and reuses the extraction medium (superheated steam) by condensing it after extraction. This recovery process is more compact and efficient than evaporating large amounts of water, reducing both the size and complexity of the plant design while maintaining effective substance recovery
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 results in polyamide 6 pellets with low residual dimers, enabling direct use in solid state polymerization, reducing energy consumption, and minimizing process time and costs.
Implementation Method 1
extraction of cyclic dimers and oligomers from the pellets; the fluid in the underwater pelletizing system and the vertical vessel comprises an aqueous solution of ε-caprolactam
Implementation Method 2
rapid removal of cyclic dimers and oligomers
Implementation Method 3
the fluid in the underwater pelletizing system and the vertical vessel comprises an aqueous solution of ε-caprolactam
Implementation Method 4
the tapered bottom section of the vertical vessel is cooled
Implementation Method 5
the tapered bottom section of the vertical vessel is cooled
Implementation Method 6
a pressure between 4 bar and 12 bar is maintained in the underwater pelletizing system and the vertical vessel
Implementation Method 7
Since a content of about 4% by weight of extractables in the pelletization water raises its boiling point, also some degrees above 100° C. are possible without increased pressure
Implementation Method 8
after sedimentation by gravity into the tapered bottom section of the vertical vessel, the pellets together with residual amounts of the fluid are conveyed by the screw and/or the rotary gate valve through the pipe
Implementation Method 9
after sedimentation by gravity into the tapered bottom section of the vertical vessel
Data Source
AI summary
A method for the production of polyamide 6 pellets. The method includes, among other things, providing a melt of polyamide 6, feeding the melt into an underwater pelletizing system being operated with a fluid and producing pellets from the melt, transporting the pellets from the underwater pelletizing system with the fluid into an upper side of a vertical vessel having a cylindrical section and a tapered bottom section connected to a pipe comprising a screw and/or a rotary gate valve for conveying the pellets, and extracting of cyclic dimers and oligomers from the pellets, where the fluid is circulated between the underwater pelletizing system and the vertical vessel wherein a fraction thereof is withdrawn from circulation and the residual amounts of fluid leaving the vertical vessel with the pellets via the pipe and the withdrawn fraction are replenished with fresh fluid.