Polyamide Melt Polymerization Reactor Stirring Control
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Solution Overview
Problem
The production of polyamide with a diamine component having 70 mol% or more of p-xylylenediamine and a dicarboxylic acid component with 70 mol% or more of C6 to C18 aliphatic dicarboxylic acid in the absence of solvent faces challenges with deposition of solid matter in the reaction tank vapor section and vapor pipe, leading to product quality issues and reduced productivity due to incorporation of unmelted solid matter.
Innovation Solution
A batch process involving direct melt-polymerization in a reactor equipped with specific stirring blades, maintaining a vapor phase temperature of 200°C or higher, and controlling the stirring-related Froude number to suppress deposition, ensuring the stirring blades do not contact the vapor phase section, and using a pressure condition of 0.2 to 0.5 MPa to manage the reaction effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If directly melt-polymerizing a diamine component with 70 mol% or more of p-xylylenediamine and a dicarboxylic acid component with 70 mol% or more of C6 to C18 aliphatic dicarboxylic acid in the absence of solvent, then productivity is improved and water removal is eliminated, but deposition of solid matter occurs in the reaction tank vapor phase section and vapor pipe
Solution Approach 1:
The patent controls the temperature of the vapor phase section to be 200°C or higher, which changes the thermal parameter to prevent deposition. By maintaining elevated temperature in the vapor phase section, the solubility of the nylon salt and oligomers in the water vapor increases, preventing them from depositing on the vapor phase section and vapor pipe surfaces.
Solution Approach 2:
The patent applies a heating measure beforehand to the vapor phase section to prevent deposition before it occurs. By pre-heating the vapor phase section to 200°C or higher, the system creates conditions where the nylon salt and oligomers remain soluble and do not deposit, thus cushioning against the harmful effect before it manifests.
2Manufacturing precision
If increasing the p-xylylenediamine content to 70 mol% or more, then product quality is improved, but water solubility of the formed salt decreases leading to deposition
Solution Approach 1:
The patent changes the temperature parameter of the vapor phase section to 200°C or higher, which fundamentally alters the solubility characteristics of the nylon salt in water vapor. At this elevated temperature, even with high p-xylylenediamine content forming salts with low water solubility at room temperature, the salt remains soluble in the hot vapor phase, preventing deposition.
Solution Approach 2:
The patent utilizes the phase transition and temperature-dependent solubility of water. By maintaining the vapor phase section at 200°C or higher, water remains in vapor phase with high capacity to dissolve the nylon salt. This phase state and temperature condition prevent the salt from transitioning to solid deposited form.
3Object-generated harmful factors
If maintaining vapor phase section at 200°C or higher, then deposition is suppressed, but energy consumption increases
Solution Approach 1:
The patent applies heating locally and selectively only to the vapor phase section where deposition occurs, rather than heating the entire reactor system. This localized heating approach maintains the necessary 200°C or higher temperature in the vapor phase section to suppress deposition, while minimizing energy consumption by not unnecessarily heating other parts of the system.
Solution Approach 2:
The patent segments the reactor into different thermal zones, with the vapor phase section maintained at 200°C or higher specifically to prevent deposition, while other sections operate at lower temperatures. This segmentation allows the system to achieve deposition suppression with minimal energy input by applying heat only where it is functionally necessary.
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 effectively reduces deposition in the reaction tank vapor phase and vapor pipe, enhancing productivity and maintaining high product quality by minimizing the incorporation of unmelted matter, thus ensuring consistent polyamide production.
Implementation Method 1
One generally and widely known example of the process for producing a polyamide through polycondensation of a dicarboxylic acid component and a diamine component
Implementation Method 2
the temperature of the formed polymer is elevated at the melting point of the polymer or higher
Implementation Method 3
the thus-formed nylon salt and oligomers are generally dissolved in water which is generated through polycondensation between the dicarboxylic acid component and the diamine component
Implementation Method 4
stirring the contents of the reaction tank, from the start of adding the diamine component until after completion of the addition and before the start of pressure falling
Implementation Method 5
reacting the diamine component with the dicarboxylic acid component under a pressure condition of 0.2 to 0.5 MPa (Abs)
Data Source
Figure 1~2
AI summary
The present invention is directed to a process for producing a polyamide, which process includes directly melt-polymerizing a diamine component including 70 mol% or more of p-xylylenediamine and a dicarboxylic acid component including 70 mol% or more of a C6 to C18 aliphatic dicarboxylic acid, in the absence of solvent in a batch-type reactor equipped with a stirring blade, the process including: (1) reacting the diamine component with the dicarboxylic acid component under a pressure condition of 0.2 to 0.5 MPa (Abs); (2) maintaining a vapor phase section of a reaction tank of the reactor at 200°C or higher during reaction; (3) stirring the contents of the reaction tank, from the start of adding the diamine component until after completion of the addition and before the start of pressure falling, such that the stirring-related Froude number represented by a specific formula is adjusted to 0.0002 to 0.15; and (4) employing a stirring blade having no structural body in the horizontal direction or having a structural body in the horizontal direction, which body does not come into contact with the interface between the reaction mixture and the vapor phase section during stirring. In the polyamide production process, deposition of solid matter in the reaction tank vapor section and in a vapor pipe is suppressed, and incorporation into the product of unmelted solid matter originating from the deposits is reduced.