Waste Plastics Dechlorination via Thermal Vacuum Pyrolysis
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Solution Overview
Problem
The presence of chlorine atoms in post-consumer mixed waste plastics streams, primarily from polyvinyl chloride (PVC), poses challenges in processing due to corrosion issues and interference with catalytic activity, making it difficult to meet the specifications required for chemical recycling and feedstock use in refinery and chemical facilities.
Innovation Solution
A process involving the dechlorination of waste plastics by heating the PVC-containing stream to 250-350°C under vacuum or inert gas sweep, evacuating hydrogen chloride, and separating partially unsaturated PVC to produce a dechlorinated stream with reduced chlorine content, allowing for safer and more efficient processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If waste plastics containing PVC are processed directly into chemical feedstock, then chemical recycling can be achieved, but chlorine atoms cause corrosion to equipment and interfere with catalytic activity
Solution Approach 1:
The patent applies preliminary dechlorination action before the waste plastics enter chemical recycling processes. By heating the waste plastics to 250-350°C under vacuum or inert gas sweep to remove hydrogen chloride, the harmful chlorine atoms are eliminated in advance, preventing corrosion and catalytic interference during subsequent chemical processing
Solution Approach 2:
The patent extracts and removes hydrogen chloride from the waste plastics stream through thermal degradation under vacuum or inert gas conditions. This extraction of the harmful chlorine-containing compound separates it from the main plastic matrix, allowing the remaining dechlorinated plastic to be processed in chemical recycling facilities
2Quantity of substance
If dechlorination is performed by thermal degradation, then chlorine content can be reduced, but the process requires precise temperature control and vacuum/inert gas conditions
Solution Approach 1:
The patent utilizes parameter changes by heating waste plastics to specific temperature ranges (250-350°C) under controlled atmospheric conditions (vacuum or inert gas). These parameter changes enable thermal degradation that selectively removes hydrogen chloride while maintaining control over the degradation process to achieve desired chlorine reduction levels
3Object-generated harmful factors
If PVC is thermally degraded to remove chlorine, then hydrogen chloride is released, but this requires energy input and creates corrosive byproducts
Solution Approach 1:
The patent converts the harmful effect of thermal degradation (energy input and corrosive byproduct release) into a beneficial process by controlling the degradation to specifically remove chlorine atoms. The hydrogen chloride released during degradation is captured and removed from the system, transforming the energy input into a useful dechlorination function rather than purely destructive thermal breakdown
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 reduces chlorine content in waste plastics to below 25 ppm, enabling their use in chemical and refinery processes without causing corrosion or interfering with catalytic activity, thus improving process continuity and equipment longevity.
Implementation Method 1
subjecting the waste plastics in the reactor vessel to a temperature of ≥250° C. and ≤350° C., preferably for a period of 5-30 minutes, under applying a vacuum, preferably of ≤35 mbar, or using an inert gas sweep
Implementation Method 2
under applying a vacuum, preferably of ≤35 mbar
Implementation Method 3
using an inert gas sweep
Data Source
AI summary
A process involving the steps in this order of: providing a waste plastics stream (A) comprising polyvinyl chloride (PVC); (i) supplying the waste plastics stream (A) to a reactor vessel; (ii) subjecting the waste plastics in the reactor vessel to a temperature of ≥250° C. and ≤350° C., preferably of ≥275° C. and ≤325° C., preferably for a period of 5-30 minutes, under applying a vacuum, preferably of ≤35 mbar, or using an inert gas sweep, and evacuating the generated hydrogen chloride (B) from the vessel, wherein the PVC is partially dechlorinated to form a waste plastics stream (C) comprising partially unsaturated PVC; (iii) removing the waste plastics stream (C) comprising partially unsaturated PVC from the reaction vessel; and (iv) separating the partially unsaturated PVC from the waste plastics stream to form a dechlorinated waste plastics stream (D).