Polymer Deodorization via Twin-Screw Extrusion and Countercurrent Air
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Solution Overview
Problem
Current deodorization processes for polymeric materials, such as polyolefins and polystyrene, are inadequate in achieving high-level deodorization requirements, particularly for recycling purposes, as they fail to effectively remove impurities that cause unpleasant odors during processing.
Innovation Solution
A process involving a twin-screw extruder and a single-screw extruder, followed by granulation and countercurrent air flow, where a mixture of polymeric materials and water is processed at specific temperature and LID ratios to produce deodorized granules with reduced water content and improved odor removal, achieving enhanced deodorization rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional single-screw extruder is used for deodorization, then device complexity is reduced, but deodorization effectiveness is insufficient
Solution Approach 1:
The deodorization process is segmented into two distinct stages: first a twin-screw extruder performs initial deodorization and drying, then a single-screw extruder with degassing devices completes the deodorization. This segmentation allows each extruder type to be optimized for its specific function, achieving high deodorization effectiveness while managing overall system complexity
Solution Approach 2:
The patent introduces an intermediary drying stage where polymeric material is dried before entering the single-screw extruder. This intermediary step prepares the material for effective degassing and deodorization in the second stage, ensuring optimal performance of the deodorization process
2Quantity of substance
If polymeric material is dried before processing, then water content is reduced, but energy consumption increases
Solution Approach 1:
The patent performs preliminary drying action in the twin-screw extruder before the main deodorization process. By removing excess water beforehand, the subsequent deodorization stage operates more efficiently with lower energy requirements, as the material is already in an optimal moisture state for degassing
Solution Approach 2:
The process maintains continuous action by integrating drying and deodorization in a sequential flow without interruption. The twin-screw extruder continuously dries the material while the single-screw extruder continuously deodorizes it, eliminating idle time and optimizing energy utilization throughout the process
3Productivity
If post-consumer polymeric material is processed, then recycling rate increases, but impurity content increases
Solution Approach 1:
The patent employs strong oxidizing conditions in the extrusion process, using oxygen-containing atmosphere and elevated temperatures to oxidize and remove odorous contaminants from post-consumer polymeric material. This accelerated oxidation effectively eliminates unpleasant odors while preserving the polymeric material for recycling
Solution Approach 2:
The process utilizes parameter changes including temperature variation (180-260°C in twin-screw, 180-260°C in single-screw), moisture content control (1-3% water in final product), and atmospheric composition to transform and remove impurities from post-consumer material, achieving both high recycling rates and acceptable material quality
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 process achieves a deodorization rate improvement of 40% to 90% compared to conventional methods, with reduced energy consumption by allowing wet material processing and improved granule quality, as verified by dynamic olfactometry tests.
Implementation Method 1
feeding a mixture of polymeric material and water... to a twin-screw extruder kept at a temperature between 180 and 260 °C, extruding from said twin-screw extruder a melt
Implementation Method 2
twin-screw extruder... extruding from said twin-screw extruder a melt consisting of 97 to 99% wt.% of polymeric material and 3 to 1 wt.% of water
Implementation Method 3
feeding said melt to a single-screw extruder... kept at a temperature between 180 and 260 °C... provided with at least two degassing devices
Implementation Method 4
single-screw extruder... kept at a temperature between 180 and 260 °C
Implementation Method 5
feeding said extruded product to a granulator which produces granules of polymeric material containing not more than 0.3 wt.% of water
Implementation Method 6
feeding said granules of polymeric material to the top of a silo provided with a vertical axis feeding device, in countercurrent with a flow of air having a temperature between 80 and 90 °C
Implementation Method 7
silo provided with a vertical axis feeding device, in countercurrent with a flow of air
Data Source
Figure 1
Figure 2
AI summary
The process comprises the steps of feeding a mixture of polymeric material and water, wherein the polymeric material constitutes from 75 to 95 wt.% and the water from 25 to 5 wt.% of the mixture, to a twin-screw extruder (14) having an L/D ratio between 1.25 and 1.50 and kept at a temperature between 180 and 260 °C; extruding from the twin-screw extruder (14) a melt consisting of 97 to 99 wt.% of polymeric material and 3 to 1 wt.% of water; feeding the melt to a single-screw extruder (16) having an L/D ratio between 20 and 32 and kept at a temperature between 180 and 260 °C, so as to obtain an extruded product; feeding the extruded product to a granulator (20) which produces granules of polymeric material containing no more than 0.3 wt.% of water; feeding the granules of polymeric material to the top of a silo (24) provided with a vertical axis feeding device (34), in countercurrent with a flow of air having a temperature between 80 and 90 °C and a flow rate between 4 and 13 m3/kg of granules of polymeric material; and obtaining deodorized granules of polymeric material.