Lactide Recovery via Depolymerization Catalyst and Vent Chamber
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Solution Overview
Problem
Current methods for recovering lactide from polylactic acid on an industrial scale face challenges such as temperature control issues in extruders, leading to racemization and impurity formation, and the formation of resin masses that clog vent chambers and reduce efficiency.
Innovation Solution
A method involving the depolymerization of polylactic acid in a vent chamber under controlled temperature and pressure conditions without a carrier resin, using a depolymerization catalyst to prevent racemization and avoid resin mass formation, with a trapping apparatus to recover the gasified lactide.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If depolymerization is executed in an extruder with carrier resin, then the polylactic acid can be conveyed and processed, but the carrier resin forms resin masses that float on the screw conveyer passage and clog the vent chamber, preventing lactide volatilization and reducing recovery efficiency
Solution Approach 1:
The invention extracts and removes the carrier resin from the system entirely. Instead of using carrier resin to convey polylactic acid, the patent employs a screw conveyor specifically designed to convey the molten polylactic acid directly from the extruder to the vent chamber, eliminating the source of resin mass formation and vent-up problems
Solution Approach 2:
The invention introduces a screw conveyor as an intermediary device between the extruder and vent chamber. This screw conveyor acts as a dedicated transport mechanism that conveys molten polylactic acid without introducing carrier resin, thereby preventing resin mass formation while maintaining efficient material flow
2Productivity
If the extruder temperature is increased to facilitate depolymerization, then the depolymerization reaction is enhanced, but the racemization is accelerated and the purity of the obtained lactide decreases
Solution Approach 1:
The invention segments the processing into two distinct stages: (1) extrusion and conveying at controlled temperature to avoid racemization, and (2) depolymerization at high temperature in the vent chamber where racemization does not affect product quality since the lactide is immediately vaporized and separated. This segmentation allows each stage to operate at optimal temperature without compromising overall product purity
Solution Approach 2:
The screw conveyor acts as an intermediary that rapidly transports the molten polylactic acid from the extruder to the vent chamber, minimizing the residence time at intermediate temperatures where racemization could occur. This rapid transfer enables the system to achieve high depolymerization rates while maintaining lactide purity
3Ease of operation
If the carrier resin is melted and compressed in the extruder, then the polylactic acid and depolymerization catalyst can be conveyed, but upon pressure reduction in the vent chamber, the carrier resin expands and turns into resin mass that covers the molten mixture and prevents lactide volatilization
Solution Approach 1:
The invention completely removes the carrier resin from the process system. The screw conveyor is designed to convey molten polylactic acid directly without any carrier resin, eliminating the expansion and resin mass formation problems that occur when carrier resin undergoes pressure reduction in the vent chamber
Solution Approach 2:
The invention uses a disposable, single-purpose screw conveyor designed specifically for conveying molten polylactic acid. This dedicated conveying mechanism performs its function efficiently and is then discharged into the vent chamber where depolymerization occurs, avoiding the need for carrier resin that would require repeated heating and cooling cycles
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 allows for the recovery of highly pure lactide by preventing racemization and eliminating resin mass-related issues, enhancing efficiency and preventing vent-up, making the process suitable for industrial-scale implementation.
Implementation Method 1
depolymerizing the polylactic acid by the heating in the presence of a depolymerization catalyst
Implementation Method 2
decomposing the polylactic acid and reusing it. This method comprises depolymerizing the polylactic acid by the heating
Implementation Method 3
the lactide of a low molecular weight (which is 144) formed by the depolymerization of the polylactic acid has a boiling point of as high as 255°C under the standard atmospheric pressure. Therefore, upon feeding a melt-kneaded product that contains the polylactic acid and the depolymerization catalyst into the vent chamber maintained under a reduced pressure, the lactide that is formed can be recovered in a gasified form
Data Source
Figure 1
Figure 2~3
AI summary
A method of recovering lactide comprising throwing a polylactic acid and a depolymerization catalyst into an extruder 1 communicated with a vent chamber 3 maintained under a reduced pressure, melt-kneading the polylactic acid and the depolymerization catalyst together in the extruder 1, feeding the melt-kneaded product thereof into the vent chamber 3, depolymerizing the polylactic acid in the vent chamber 3, gasifying the formed lactide and recovering the gasified lactide from the vent chamber 3.