Dynamic Single-Screw Devolatilizer for Low-Shear Volatile Removal
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Solution Overview
Problem
Existing devolatilization methods for polymers, particularly single-screw and twin-screw devolatilizers, face limitations in mass transfer interface generation, operational flexibility, and high shear stress, leading to inefficient volatile removal and quality degradation.
Innovation Solution
A dynamic single-screw devolatilizer with a novel screw-housing structure and internal components, including rear venting, stripping, and devolatilization sections, enhances mass transfer interfaces and operational flexibility, allowing for efficient volatile removal with low shear stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a twin-screw dynamic devolatilizer is used to increase mass transfer interface area, then devolatilization efficiency is improved, but shear stress increases causing polymer degradation and color changes
Solution Approach 1:
The screw channel is divided into multiple flow paths through the use of distribution rings with multiple slots or pores, segmenting the polymer melt flow to increase the total interfacial area between polymer and gas phases without requiring high shear stress from intense mechanical mixing
Solution Approach 2:
The patent introduces a radial dimension to mass transfer by using distribution rings with slots or pores that create polymer melt films extending radially, increasing the interfacial area from a single-point contact to a distributed two-dimensional interface throughout the screw channel
2Duration of action of stationary object
If a static devolatilizer is used to increase interfacial area, then devolatilization time is extended, but surface renewal rate remains low making it unsuitable for high viscosity systems
Solution Approach 1:
The patent combines static residence time extension with dynamic surface renewal by using the rotating screw to continuously refresh the polymer-gas interface through axial movement and melt circulation, maintaining both extended contact time and high renewal rate
3Device complexity
If a single-screw devolatilizer is used, then structure is simple, but mass transfer interface area is limited reducing devolatilization efficiency
Solution Approach 1:
The patent introduces localized structural features (distribution rings with slots or pores) at specific positions within the screw channel to create high interfacial area regions without fundamentally complicating the overall single-screw structure, maintaining simplicity while dramatically improving efficiency
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
The method effectively reduces volatile concentrations from 5-10% to 10-200 ppm, improves mass transfer efficiency, and reduces equipment costs by adjusting the mass transfer interface area and operational flexibility.
Implementation Method 1
conveying and compressing polymer materials by the screw downstream a devolatilization section
Implementation Method 2
The heat and mass transfer efficiency of flash devolatilization is high, mainly controlled by thermodynamic phase equilibrium
Implementation Method 3
devolatilization is controlled by molecular diffusion at the polymer-gas interface
Implementation Method 4
increasing the mass transfer interface area between polymer melt and gas phase and promoting surface renewal are effective means to improve devolatilization efficiency
Implementation Method 5
The heat and mass transfer efficiency of flash devolatilization is high, mainly controlled by thermodynamic phase equilibrium
Implementation Method 6
the system rapidly generates a large number of bubbles under low pressure conditions, and expands due to liquid-phase mass transfer and bubble aggregation
Implementation Method 7
the twin-screw dynamic devolatilizer disclosed in EP patent application no. 2168743 and U.S. patent application no. 2020/0215738 utilizes a kneading section to apply shear stress to the polymer melt through kneading elements, thereby diverting the melt stream in the screw channels and generating the required mass transfer interface area for devolatilization
Data Source
AI summary
The present application discloses a continuous dynamic and efficient devolatilization method for a polymer/volatile system based on high mass transfer interfaces, including the following steps: providing a dynamic single-screw devolatilizer, feeding a polymer solution to the devolatilizer, wherein the polymer solution includes polymer and volatile substances with small molecule weight, and the volatile substances include organic solvents, residual monomers, water or reaction by-products; conveying and compressing polymer materials by the screw downstream a devolatilization section, and extruding the polymer materials out of the dynamic single-screw devolatilizer directly; or providing a side-feeding extruder downstream of the devolatilization section and feeding plastic additives into a devolatilized polymer melt, and then melt blending the plastic additives with the devolatilized polymer melt at an end of the dynamic single-screw devolatilizer before exiting the dynamic single-screw devolatilizer.