Plastic Recycling Process Critical Point Solvent Evaporation
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Solution Overview
Problem
Current plastic recycling methods face challenges such as high solvent and energy consumption, molecular weight degradation, and limited ability to handle high plastic concentrations, leading to inferior recyclate properties and incomplete recovery of additives.
Innovation Solution
A process involving treating waste plastics with an organic solvent, concentrating the solution, preconditioning it to high pressure and temperature below the boiling point, and spraying it above the critical point for efficient solvent evaporation, which reduces heat load and maintains additive recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If direct heat application is used to evaporate solvent from plastics, then solvent removal is achieved, but plastics recyclates contain considerable solvent remainders and exhibit inferior properties
Solution Approach 1:
The invention utilizes phase transition of the solvent from liquid to vapor through controlled heating. The solvent is evaporated at temperatures below 100°C, and the vapor is then condensed back to liquid form for separation, achieving complete solvent removal without degrading the plastic recyclate properties.
Solution Approach 2:
The invention introduces an intermediary condensation step between evaporation and separation. The evaporated solvent vapor is condensed into liquid form using a condenser, which then allows for complete separation from the plastic recyclate, ensuring no solvent remainders in the final product.
2Loss of substance
If coagulation methods are used to reduce residual solvent, then lower residual contents are achieved, but additional drying steps are required
Solution Approach 1:
The invention extracts the solvent from the plastic solution through evaporation and condensation, completely removing it in a single integrated process. This eliminates the need for additional drying steps required in coagulation methods, as the solvent is taken out in its entirety through the phase transition process.
3Quantity of substance
If conventional mixing techniques are used to separate plastics from waste, then separation is achieved, but only at low concentrations of 10-15 wt%
Solution Approach 1:
The invention changes the parameter of plastic concentration in the solvent, enabling processing of highly concentrated plastic solutions (40-60 wt% or higher). This parameter change allows for significantly increased throughput and productivity compared to conventional low-concentration mixing techniques.
4Productivity
If high plastic concentration solutions are processed, then throughput increases, but cavitations occur and continuous high-pressure operation is not guaranteed
Solution Approach 1:
The invention applies preliminary deaeration to remove dissolved gases from the high-concentration plastic solution before pumping. This preliminary action prevents cavitation during high-pressure pumping, ensuring reliable continuous operation and maintaining high throughput without operational disruptions.
5Loss of substance
If extended processing times are used to reduce volatile content, then volatile reduction is achieved, but severe molecular weight degradation occurs
Solution Approach 1:
The invention uses phase transition (evaporation and condensation) to remove volatiles in a single rapid step rather than through extended processing. The solvent and volatiles are evaporated and then condensed for separation, achieving volatile reduction without prolonged heat exposure that would cause molecular weight degradation.
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 process achieves high plastic throughput with low solvent and energy usage, minimizing molecular weight degradation and achieving recyclates with properties similar to the original materials, while maintaining low water content and solvent levels.
Implementation Method 1
bringing the preconditioned concentrated plastics solution above the critical point of the plastics solution using a high-pressure pump (4) and a high-pressure heat exchanger (5)
Implementation Method 2
spraying the concentrated plastics solution above the critical point into a plastics recovery unit (6), to recover the plastics through evaporation of the organic solvent
Implementation Method 3
transferring the evaporated organic solvent to a condensing unit (7) to recover the organic solvent
Data Source
AI summary
The invention relates to a process for recycling soluble or dispersible plastics from a waste product containing plastics by treatment with an organic solvent, concentrating the plastics solution thus obtained to more than 40 wt% of plastics, preconditioning said concentrated plasics solution to a pressure of at least 2 bar using a first pump and a temperature of 1 - 10°C below the boiling temperature of the solvent at that pressure, bringing this preconditioned concentrated plastics solution above the critical point of the plastics solution using a high-pressure pump and a high-pressure heat exchanger, spraying the concentrated plastics solution above the critical point to recover the plastics through evaporation of the organic solvent, and recovery of the organic solvent.