Multistage Plastic Pyrolysis With Intermediate HCl Removal
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Solution Overview
Problem
Non-biodegradable waste materials pose environmental challenges when disposed of in landfills, and recycling them is economically challenging due to the need for different processing methods and the presence of high halogen contents in pyrolysis oils, which can cause stress cracking and corrosion in cracking equipment.
Innovation Solution
A multistage dehalogenation system and process involving physical sorting, melting, and two-stage pyrolysis with intermediate HCl removal to produce pyrolysis oil with reduced halogen content, allowing for the production of pyrolysis oil suitable for large-scale production facilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If physical sorting of waste materials is performed to achieve pure, single-composition waste volumes, then the quality and consistency of pyrolysis feedstock is improved, but the device complexity and processing cost increase
Solution Approach 1:
The waste plastic feedstock is divided into different stages of processing: initial sorting, melting/separating, and two-stage pyrolysis. Each stage handles specific components, with the first stage removing easily separable halogen-containing plastics and the second stage processing the remaining mixed plastics, thereby achieving composition stability without requiring complete initial sorting
Solution Approach 2:
A preliminary dehalogenation step is performed before pyrolysis by heating the plastic-containing feed to release halogen-containing waste streams. This preliminary action removes halogens from the feedstock before the main pyrolysis process, preventing stress cracking and corrosion issues downstream while avoiding the need for complex sorting to eliminate halogen-containing plastics
2Productivity
If high halogen content pyrolysis oil is produced from waste plastics, then the productivity and economic viability of recycling is improved, but the reliability of cracking equipment deteriorates due to stress cracking and corrosion
Solution Approach 1:
The system performs preliminary dehalogenation by heating the plastic-containing feed to a temperature sufficient to release halogen-containing waste streams before pyrolysis. This preliminary removal of halogens prevents subsequent stress cracking and corrosion in cracking equipment while maintaining high productivity
Solution Approach 2:
An intermediate HCl removal step is introduced between the first and second pyrolysis stages. This intermediary process captures and removes HCl and other halogen-containing compounds that are released during pyrolysis, preventing them from contaminating the pyrolysis oil and causing equipment damage downstream
3Reliability
If expensive metallurgy is used to prevent stress cracking and corrosion in cracking equipment, then the reliability and lifespan of equipment is improved, but the manufacturing cost increases
Solution Approach 1:
The invention converts the potentially harmful halogen-containing compounds into a separable waste stream. By heating the feedstock to release halogens before pyrolysis, the harmful substances are extracted and removed, transforming them from a threat to equipment into a manageable byproduct that can be disposed of or treated separately, thereby avoiding the need for expensive corrosion-resistant metallurgy
4Device complexity
If a single-stage pyrolysis process is used, then the device complexity is reduced, but the ability to remove halogen effectively deteriorates
Solution Approach 1:
The pyrolysis process is segmented into two distinct stages: a first pyrolysis stage that operates at specific conditions to release halogen-containing compounds, and a second pyrolysis stage that processes the dehalogenated material. This segmentation allows effective halogen removal while keeping each individual stage relatively simple in design
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 removes halogen-containing compounds from recycled plastic feedstocks, reducing the need for expensive metallurgy and preventing stress cracking, while producing a pyrolysis oil with desirable aromatic and alkane contents for downstream use.
Implementation Method 1
heating said plastic-containing feed to a temperature sufficient to thereby release a halogen-containing waste stream and form a dehalogenated feed
Implementation Method 2
pyrolyzing at least a portion of said dehalogenated feed to thereby form a pyrolysis effluent comprising a pyrolysis oil
Data Source
AI summary
A pyrolysis method and system are provided that utilizes a multistage dehalogenation method to effectively remove halogen-containing compounds that are present in an initial recycled plastic feedstock. More particularly, the multistage dehalogenation system and process may involve physical sorting the plastic feedstock, melting and separating the feedstock, and subjecting the feedstock a two-stage pyrolysis with intermediate HCl removal.