In-line Decanter Phase Separation for Mixed Plastic Solvolysis
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Solution Overview
Problem
Conventional chemical recycling processes for waste plastics, such as pyrolysis, combustion, and gasification, are inefficient and costly, particularly when dealing with mixed plastic streams, and solvolysis methods struggle to effectively separate and recycle polyethylene terephthalate (PET) from non-PET components due to operational inefficiencies and the tendency of reactive coproducts to polymerize, reducing on-stream time and yield.
Innovation Solution
A method involving the use of in-line decanters to control phase separation of non-PET plastics by adjusting stream velocity, allowing for continuous or batchwise separation of PET and non-PET components in a solvolysis facility, enabling the efficient recycling of mixed plastic waste on a commercial scale.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If solvolysis is used to decompose mixed plastic feedstock, then PET can be broken down into monomers, but non-PET components become challenging to remove and may polymerize in the separation zone
Solution Approach 1:
The patent extracts harmful non-PET components from the reaction mixture by introducing a selective solvent that preferentially dissolves or reacts with non-PET plastics. This extraction occurs in the separation zone where the solvent selectively interacts with coproducts, removing them before they can polymerize and cause harmful effects.
Solution Approach 2:
The patent introduces a solvent as an intermediary substance that mediates between the reaction mixture and separation process. The solvent acts as a mediator by selectively dissolving, reacting with, or stabilizing non-PET coproducts, preventing their polymerization while allowing PET monomers to be recovered.
2Reliability
If frequent purging is performed to remove reactive coproducts, then polymerization in the separation zone is reduced, but on-stream time and overall yield are reduced
Solution Approach 1:
The patent applies preliminary action by introducing the selective solvent into the separation zone before significant polymerization can occur. This proactive approach prevents coproducts from accumulating to polymerization levels, eliminating the need for frequent purging while maintaining system reliability.
Solution Approach 2:
The patent establishes continuous operation by maintaining steady-state removal of coproducts through the selective solvent system. The continuous presence of the solvent ensures ongoing prevention of polymerization, allowing the system to operate continuously without interruption for purging.
3Ease of manufacture
If conventional recycling processes are used, then waste plastics can be broken down, but high energy consumption offsets financial benefits
Solution Approach 1:
The patent replaces high-energy mechanical/thermal processes (pyrolysis, combustion, gasification) with a chemical solution-based system. Instead of using extreme temperatures and pressures to break down plastics, the invention uses selective solvents to dissolve, react with, or stabilize coproducts at much lower energy inputs.
Solution Approach 2:
The patent changes the operational parameters from high-temperature thermal processes to moderate-temperature chemical processes. By shifting from pyrolysis conditions (high T) to solvolysis conditions (moderate T with solvent), the energy consumption is dramatically reduced while maintaining effective plastic decomposition.
4Adaptability or versatility
If mixed waste plastic is processed, then recycling scope is expanded, but separation of PET from non-PET components becomes difficult
Solution Approach 1:
The patent applies local quality by introducing a solvent with specific properties tailored to interact selectively with non-PET components. The solvent is chosen or designed to have affinity for particular coproducts (polyolefins, PVC, etc.) while leaving PET monomers unaffected, enabling precise separation based on local chemical characteristics.
Solution Approach 2:
The patent utilizes phase transitions in the selective solvent system to achieve separation. The solvent may undergo phase changes (dissolution, precipitation, phase separation) that selectively affect non-PET components, causing them to separate from the PET monomer stream through density differences, solubility changes, or phase separation.
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 enhances separation efficiency, allowing for the effective recycling of mixed plastic waste, including both PET and non-PET components, by maintaining continuous operation and minimizing material and production losses, thus overcoming the limitations of conventional recycling methods.
Implementation Method 1
passing the predominantly liquid stream through a decanter at second velocity (v2) to form a two-phase stream, wherein the two-phase stream comprises a PET-enriched phase and a non-PET enriched phase
Data Source
AI summary
Chemical recycling facilities for processing mixed waste plastic are provided herein. Such facilities have the capability of processing mixed plastic waste streams and utilize a variety of recycling facilities, such as, for example, solvolysis facility, a pyrolysis facility, a cracker facility, a partial oxidation gasification facility, an energy recovery facility, and a solidification facility. Streams from one or more of these individual facilities may be used as feed to one or more of the other facilities, thereby maximizing recovery of valuable chemical components and minimizing unusable waste streams.