Polyamide-Polyester Separation via Alcohol Solvent Filtration
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Solution Overview
Problem
Current separation processes for polyamides and polyethylene terephthalate in waste streams are cumbersome, costly, and generate waste streams like salts, and are not robust against additives and impurities, making them inefficient and impractical for large-scale recycling.
Innovation Solution
A process involving reducing the density of mixed polymers through fluffing, adding an alcohol with a boiling point above 100°C that may contain up to 25% water, heating to dissolve polyamide, and then filtering with a mesh size between 0.5-2 μm to separate polyamide from polyester, allowing for efficient recovery and reuse of polyamide while keeping the process simple and cost-effective.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If highly pure glycerol is used as solvent and water is excluded, then polyamide dissolution and separation is achieved, but process complexity and cost increase due to multiple heating and precipitation cycles
Solution Approach 1:
The patent changes the solvent composition parameter by using an alcohol-water mixture instead of highly pure glycerol, and adjusts the temperature parameter to allow precipitation at lower temperatures. This single-step approach achieves separation without requiring multiple heating and cooling cycles, thus reducing process complexity while maintaining separation effectiveness.
2Ease of manufacture
If water and glycerol mixture is used as solvent, then process is simpler, but corrosion and hydrolysis occur at high temperature
Solution Approach 1:
The patent uses a cheaper alcohol-water mixture that can tolerate water presence, accepting some corrosion as a trade-off for process simplicity and cost reduction. The alcohol solvent system is more forgiving of water content compared to glycerol, enabling a simpler single-step process.
3Manufacturing precision
If precipitation starts around 160°C, then polyamide separates, but it precipitates onto polyester fibres hindering separation
Solution Approach 1:
The patent changes the temperature parameter by using a lower precipitation temperature achieved through alcohol-water mixture solvent system. This prevents premature precipitation onto polyester fibres while still achieving effective polyamide separation, solving the deposition problem.
4Temperature
If higher pressures are applied to keep water liquid above boiling point, then precipitation can occur at higher temperature, but process becomes less practical for low density waste material
Solution Approach 1:
The patent changes the pressure parameter by operating at atmospheric pressure instead of high pressure. The alcohol-water mixture allows precipitation to occur at lower temperatures without requiring pressurization, making the process practical for low-density waste materials that would be difficult to handle under high pressure.
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 method effectively separates polyamide from polyester, is robust against additives and impurities, reduces waste, and allows for the reuse of polyamide and further processing of polyester, making it suitable for large-scale recycling of materials like carpet waste.
Implementation Method 1
dissolving the polyamide at an elevated temperature in a solvent selected from the group consisting of a substantially anhydrous ethylene glycol, propylene glycol, and aliphatic carboxylic acid having from 2 to 6 carbon atoms
Implementation Method 2
combining the polyamide solution with an additional quantity of substantially the same solvent at a temperature sufficiently below the temperature of the solution to quench the solution and cause the polyamide to precipitate
Implementation Method 3
filtering with a mesh size between 0.5-2 μm to separate polyamide from polyester
Data Source
AI summary
The present invention is in the field of an improved separation process for mixed polymers, typically provided in a waste stream, comprising a polyamide (PA) and a polyethylene terephthalate (PET). The process comprises providing a composition having a density of 50-500 gr/dm3, adding an alcohol to the composition heating the mixture to a temperature above 150° C., cooling by adding hot water, filtering with a first filter, filtering with a second filter to recover the polyamide, and recovering the polyester for further processing for depolymerization.