Polypropylene Solvent Recycling With Supercritical Purification
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Solution Overview
Problem
Existing recycling methods for polypropylene plastics are inefficient in removing impurities such as additives, colorants, and metals, leading to limited economic upgrading and high energy consumption.
Innovation Solution
A process involving dissolution of polypropylene plastics in a light hydrocarbon solvent at specific temperatures and pressures, followed by purification steps including insoluble matter separation, washing, extraction, and adsorption, culminating in a supercritical separation to obtain purified polypropylene with minimal impurities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If mechanical recycling is used to sort and reuse plastic waste, then the purity of the polymer stream is improved, but the impurities trapped in the polymer matrix (additives, colorants, metals) are not sufficiently removed
Solution Approach 1:
The patent extracts impurities from the polymer matrix by dissolving the polymer in a solvent system, allowing impurities to be separated from the polymer solution through filtration and extraction steps, thereby removing trapped additives, colorants, and metals that mechanical sorting cannot eliminate
Solution Approach 2:
The patent introduces a solvent system as an intermediary medium to facilitate the removal of impurities. The solvent dissolves the polymer while allowing impurities to be separated through various treatment steps, acting as a mediator between the polymer and impurities for effective removal
2Adaptability or versatility
If chemical recycling via pyrolysis is used to reform monomers, then the plastic waste can be converted into useful chemicals, but the energy consumption is high due to high temperature treatments
Solution Approach 1:
The patent changes the operational parameters from high-temperature pyrolysis to lower-temperature dissolution conditions (around 25-50°C), fundamentally altering the energy requirements while achieving effective polymer degradation and impurity removal through solvent-based processes
Solution Approach 2:
The patent replaces the thermal-mechanical pyrolysis process with a chemical dissolution approach using solvent systems, substituting high-temperature thermal energy with chemical interactions that occur at much lower temperatures, thereby reducing energy consumption
3Object-generated harmful factors
If dissolution and purification methods are used to treat plastic waste, then impurities can be removed from the polymer, but the process complexity and cost increase
Solution Approach 1:
The patent segments the purification process into distinct functional steps: dissolution, filtration of insoluble matter, extraction of soluble impurities, and solvent recovery. This segmentation allows each step to be optimized independently and facilitates easier implementation compared to single-step complex processes
Solution Approach 2:
The patent implements solvent recovery and reuse mechanisms, discarding only the minimal amount of solvent needed for each cycle while recovering and reusing the bulk solvent. This reduces waste, lowers costs, and simplifies the overall process by eliminating the need for complete solvent disposal and replacement
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 effectively recovers purified polypropylene with low impurity content, suitable for reuse in new plastic products, while reducing energy consumption and solvent use, thus enhancing economic viability and resource conservation.
Implementation Method 1
a dissolution step involving placing the plastic feedstock in contact with a dissolution solvent, comprising at least one hydrocarbon-based compound having a boiling point of between −15 and 100° C., at a dissolution temperature of between 150° C. and 250° C. and a dissolution pressure of between 1.0 and 18.0 MPa absolute, to obtain at least one crude polymer solution
Implementation Method 2
c) a solvent-polymer separation step, using at least one supercritical separation section operated at a temperature of between 160 and 300° C. and at a pressure (Psupercritical) of between 2.7 and 10.0 MPa absolute, followed by at least one solvent recovery section
Data Source
AI summary
The present invention relates to a process for purifying a plastic feedstock comprising polypropylene, involving:a) dissolving the plastic feedstock in a dissolution solvent comprising a hydrocarbon-based compound having a boiling point of between −15° C. and 100° C., at a dissolution temperature of between 150° C. and 250° C., a dissolution pressure of between 1.0 and 18.0 MPa absolute, to obtain a crude polymer solution;b) purifying the crude polymer solution, comprising:b1) separation of the insoluble matter;b2) washing, with a dense solution;b3) extraction, with an extraction solvent; and/orb4) adsorption of the impurities; and thenc) solvent-polymer separation, using a supercritical separation section, at a temperature of between 160 and 300° C. and a pressure of between 2.7 and 10.0 MPa absolute, followed by at least one solvent recovery section, to obtain purified polypropylene.