Chemical recycling breaks plastic waste down at the molecular level, typically through pyrolysis, so it produces an oil or gas feedstock rather than a reprocessed solid material. This matters for mixed and contaminated waste streams that mechanical recycling cannot handle economically because sorting quality is poor. The patent evidence here focuses specifically on upgrading that pyrolysis oil, removing chlorine and other contaminants, and protecting downstream refinery catalysts, rather than on the mechanical sorting or shredding steps that precede it.

Chlorine in mixed plastic waste, largely from PVC and other chlorinated polymers, deactivates the catalysts used in downstream hydrotreating and steam cracking, which is why chlorine removal is one of the three technical problem areas this dataset is built around. The most-cited filings in this set, several sharing the title around alkali-enhanced hydrothermal purification, are aimed directly at this problem. A staged guard-bed and main-bed hydrotreating approach, as seen in the representative filing, is one documented way to isolate and remove chlorine before it reaches the higher-temperature main catalyst bed.

Filing activity in this dataset concentrates heavily around SK Innovation and its affiliate, which co-file at a scale well above any other pairing recorded, largely around hydrotreating and oil-purification technology. National oil interests such as Saudi Aramco and waste-to-fuel specialists such as Neste also appear among the named assignees, reflecting both refiner and specialist-processor interest in taking pyrolysis oil as usable feedstock. Recent-year momentum across the named assignees in this data is flat, which is consistent with the broader post-2024 filing slowdown.

The recorded trend shows filings rising from near zero in 2017 to a peak of 38 in 2024, then easing off through the most recent partial year. However, publication typically lags actual filing by around eighteen months, so the apparent 2025-2026 decline is likely an artefact of incomplete data rather than a genuine drop in R&D activity. A more reliable read on whether the field has actually cooled will only be possible once later filing years are fully published.

The core refining subclass, C10G, covers all 73 families in this dataset, so it offers little room for a clean first claim. Secondary areas including catalysis (B01J), separation processes (B01D) and mass-balance certification tracking carry far fewer filings relative to the core, and specific sub-areas such as chlorine speciation sensing upstream of hydrotreating or catalyst regeneration after chlorine poisoning appear thin. These are the areas worth a freedom-to-operate check before assuming the space is occupied.