Maximum Contamination Tolerance Levels
Maximum contamination tolerance levels and technical solutions for four key contaminants in depolymerisation feedstock — PVC content, moisture, other polymers, and ash/dirt — the go/no-go specifications for feedstock acceptance.
Parameter | Max. Tolerance (Typical) | Solution |
PVC Content | < 0.1% (1000 ppm) | Infrared (NIR) Sorting or Manual Pick. |
Moisture | < 2.0% | Industrial Drying / Pre-heating. |
Other Polymers | < 5.0% (e.g., PE caps in PET) | Sink-Float separation or Filter Screening. |
Ash/Dirt | < 1.0% | Pre-washing or Cyclone Separation. |
Beyond definitions
Planning to start a Plastic (Chem) business?
Get the full business understanding — capex, regulations, machinery, vendor questions, and risk checks before you commit capital.
How to read this table
- Max Tolerance is the upper limit at which the process can still operate — material above these limits should be rejected or require additional pre-treatment before it enters the reactor.
- PVC content tolerance is the strictest of the four — 0.1% (1,000 ppm) is a hard limit; exceeding it causes catalyst poisoning that takes significant time and cost to remediate.
- Solution column describes the standard technical intervention for each contaminant type.
About this table
Depolymerisation is a molecular-level process — the quality of the output monomer is directly determined by the quality of the input feedstock. Contaminants that a mechanical recycler might tolerate in small quantities become critical problems in a depolymerisation reactor, where they can poison catalysts, corrode reactor walls, contaminate the monomer product, or cause safety incidents. This table specifies the maximum tolerance levels for four key contaminant categories and the technical solutions used to bring incoming feedstock within specification.
PVC (Polyvinyl Chloride) content is the most dangerous contaminant for a depolymerisation plant. At just 0.1% (1,000 ppm), PVC decomposes during the reaction and releases hydrochloric acid (HCl) — which corrodes reactor stainless steel walls and 'poisons' metal catalysts by converting active metal sites into inactive metal chlorides. The only solution is to prevent PVC from entering: Near-Infrared (NIR) optical sorting, which identifies PVC by its unique spectral signature, is the standard pre-processing technology. Manual picking is used where NIR is not available. Moisture content above 2% wastes energy because the water must be evaporated inside the reactor, and causes foaming in certain reaction types. Industrial dryers (rotary drum or oven) are used to bring moisture below the 2% threshold before feeding.
Other polymer contamination — for example, HDPE bottle caps mixed with PET flakes — can be tolerated up to 5% because the separation steps (sink-float, filtration) in the pre-treatment stage remove most cross-polymer contamination. Above 5%, yield losses become commercially significant. Ash and dirt content above 1% acts mechanically (sand and grit erode pumps and valves) and chemically (silica can interfere with some catalyst systems). Pre-washing and cyclone separation are used to bring ash content below the tolerance level.
Key insights
- PVC tolerance of less than 0.1% (1,000 ppm) is the strictest limit in the table — even small amounts of PVC cause hydrochloric acid release that corrodes reactor walls and destroys catalysts.
- NIR optical sorting for PVC removal is essential, not optional — manual picking alone is insufficient to reliably hold PVC content below 1,000 ppm in a high-volume operation.
- Moisture tolerance of less than 2% requires pre-drying of incoming feedstock — this is an operating cost that must be factored into feedstock acceptance economics.
- Other polymer contamination up to 5% is acceptable because sink-float separation (PET sinks, HDPE floats in water) naturally removes most cross-contamination in the washing stage.
Methodology & sources
Contamination tolerance levels are representative of typical depolymerisation (glycolysis/hydrolysis) process specifications as of 2024. Actual limits depend on specific reaction chemistry, catalyst type, and target monomer purity grade. PVC tolerance in particular varies by catalyst — some catalyst systems have tighter limits than the 1,000 ppm shown here. Confirm with your process licensor before finalising feedstock acceptance criteria.
Related data tables
Feedstock Acceptance/Rejection Criteria
A four-parameter feedstock acceptance decision table for a depolymerisation plant — showing Acceptable, Conditional (with price discount), and Rejected thresholds for PET content, PVC contamination, moisture, and colour.
Feedstock Cost vs. Yield by Type
A comparison of four PET-type feedstocks for depolymerisation — clear bottles, coloured PET, polyester textiles, and multi-layer packaging — showing estimated yield percentage, cost profile, and the reason for yield loss in each case.
Feedstock Quality Parameters & Business Impact
Six feedstock quality parameters that determine depolymerisation plant profitability — polymer purity, moisture content, PVC contamination, bulk density, ash/dirt content, and organic residue — with ideal ranges and business consequences.