Mixed Plastic Pyrolysis Dechlorination via Melting Reactor and Sorbent
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Solution Overview
Problem
Current pyrolysis processes for mixed plastic waste struggle to efficiently remove chloride derivatives from polyvinyl chloride (PVC) without extensive pre-sorting, leading to high chloride content in the pyrolysis product, which is detrimental to downstream petrochemical processes.
Innovation Solution
A stepwise process involving a melting reactor for initial dechlorination, followed by a pyrolysis reactor with sorbent enhancement, and finally an adsorbent bed for polishing, to achieve low chloride levels in the pyrolysis oil, utilizing a continuous reactor for heat integration and solid separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If extensive pre-sorting is applied to remove PVC before pyrolysis, then chloride content in product is reduced, but device complexity and cost increase
Solution Approach 1:
The harmful PVC component is extracted and separated from the mixed plastic waste stream through density-based separation before pyrolysis. This removes the source of chloride contamination, allowing the pyrolysis process to produce low-chloride products without requiring complex multi-stage sorting systems.
Solution Approach 2:
The invention changes the physical parameter of density to separate PVC from other plastics. By utilizing the density difference between PVC and other plastic materials, the system achieves effective separation through relatively simple density-based separation equipment rather than complex sorting processes.
2Ease of manufacture
If indirect heating through reactor wall is used, then heat transfer is simplified, but temperature gradient increases causing excessive char deposit
Solution Approach 1:
A circulating heat transfer fluid acts as an intermediary medium to distribute heat uniformly throughout the reactor. This fluid circulates through the reactor, directly contacting the plastic waste and ensuring uniform temperature distribution, thereby preventing excessive char deposit while maintaining heating efficiency.
Solution Approach 2:
The invention uses a hydraulic system with circulating heat transfer fluid to achieve uniform heat distribution. The fluid circulation mechanism ensures consistent thermal contact with the plastic waste, eliminating temperature gradients and preventing localized overheating that causes char formation.
3Device complexity
If single-step chloride removal is attempted, then process complexity is reduced, but chloride removal efficiency is insufficient to achieve <10 ppmw
Solution Approach 1:
The chloride removal process is segmented into distinct stages: mechanical separation to remove bulk PVC, followed by pyrolysis to decompose remaining chlorine-containing compounds, and finally adsorption to capture any residual chlorides. This multi-stage approach achieves the required <10 ppmw chloride level while keeping each individual stage relatively simple.
Solution Approach 2:
An adsorbent material serves as an intermediary to capture and remove residual chlorides from the pyrolysis product. This adsorption step acts as a final polishing mechanism, ensuring that chloride levels meet the stringent <10 ppmw specification without requiring overly complex processing.
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 effectively reduces chloride content from over 5800 ppmw in the feed to less than 10 ppmw in the product, achieving high efficiency and minimizing the need for costly pre-sorting, while maintaining continuous reactor operation.
Implementation Method 1
The waste plastics first contact a hot liquid stream that is produced from the process in a melting reactor
Implementation Method 2
The waste plastics first contact a hot liquid stream that is produced from the process in a melting reactor. This melting reactor melts the waste plastics and produces a vapor stream
Implementation Method 3
The bottoms liquid from the melting reactor may be pumped or pressured into a pyrolysis reactor where the melting reactor bottoms stream is cracked into a vapor stream and a bottoms liquids stream
Implementation Method 4
The waste plastics first contact a hot liquid stream that is produced from the process in a melting reactor
Implementation Method 5
heat is transferred indirectly through the reactor wall by fuel gas firing, electrical heating or a hot oil medium. Heat transfer into reactants relies on the coefficient of conductivity between the wall and reactants
Implementation Method 6
A portion of this liquid is heated and provides all remaining heat of reaction and heat of vaporization at the pyrolysis reactor
Data Source
AI summary
An apparatus for pyrolysis of a mixed plastic stream that contains polyvinyl chloride (PVC) is provided in which the chloride from PVC is removed from an initial melting reactor that heats the mixed plastic stream to a sufficient temperature to produce HCl but at a low enough temperature to avoid production of organochlorides. Chloride is primarily removed in a vapor stream from the initial melting reactor, while additional chloride removal may be removed downstream from the melting reactor by the use of sorbent addition to the pyrolysis reactor and by subsequent adsorbent beds.