Extractive distillation adds a high-boiling, non-volatile solvent (an entrainer) to alter the relative volatility of the components being separated, without forming a new azeotrope with either. Azeotropic distillation instead introduces an entrainer that deliberately forms a new azeotrope with one component, which is then removed overhead or via a side stream. Both techniques exist because ordinary fractional distillation cannot separate mixtures whose components share very close boiling points or an existing azeotrope. The patent literature in this dataset covers both routes, with entrainer selection and solvent recovery as the recurring claim elements in each.

Filing in this space is concentrated among a small group of refiners and process-technology licensors, with the strongest documented co-assignee relationship linking a technology firm to a national refiner (48 shared filings). Beyond that top tier, ownership fragments into a long tail of single-filing entrants, which is typical of a mature separations technology. Recent-year filing counts have dropped to zero across every named leader tracked in this dataset, suggesting the field is in a consolidation phase rather than an expansion one.

Filings peaked at 73 in 2019, held near 65 at the 2022 midpoint, and have fallen sharply since, with only 8 recorded in the most recent partial year. Part of that drop is a data artefact: publication typically lags filing by about 18 months, so the last one to two years will always look thinner than they eventually turn out to be. Even allowing for that lag, the broader shape is a technology whose core claim space — entrainer selection, solvent recovery, energy reduction — has already been heavily filed, leaving less new ground for incremental patents.

The IPC composition shows sharp drop-offs outside the two dominant classes: C07C and B01D together account for the large majority of records, while B01J (catalysis), C01B (inorganic compounds), C02F (wastewater treatment) and C07B (general organic methods) each hold fewer than 40 records in this corpus. That imbalance points to thinner prior art around catalytic entrainer regeneration, wastewater-integrated solvent recovery, and extractive separations applied to inorganic or heterocyclic feedstocks. Thin coverage is not proof of open space, though — it warrants a targeted freedom-to-operate search rather than an assumption that no one has filed there.

US20210053893A1, filed by China Petroleum & Chemical Corporation and published in February 2021, claims a two-column extractive distillation process for separating aromatic hydrocarbons: a hydrocarbon mixture enters an extractive distillation column mid-height, an extraction solvent enters near the top, and the benzene-containing overhead raffinate (3-40% by mass) is routed to a second extraction column for a further liquid-liquid extraction with the same solvent. The claims are specific to this two-column configuration and the stated benzene concentration range in the intermediate raffinate. Someone designing a single-column aromatic extraction process, or one operating outside that concentration band, would sit outside its direct scope, though a full claim chart is needed to confirm freedom to operate.