Black Liquor Recovery Patents: Leaders & Filing Trends 2026
A data-backed view of black liquor recovery patents: who leads filings, how the technology splits across pulp processing, incineration and water treatment, and where filing activity is concentrated.
Filing growth = 2021 (34 records) → 2024 (15); 2024 is the last year we treat as complete. Top-5 share = the 5 largest assignees ÷ all 1,607 records in scope (CR5), not the ranked leaders only.
What the black liquor recovery patent record shows
Black liquor recovery sits at the intersection of pulping chemistry and energy recovery: spent cooking liquor is evaporated, burned and reconstituted into usable chemicals, and the patent record tracks that chain closely. Across 1,607 records filed or published between 2015 and 2026, the dominant technical center of gravity is pulp production and treatment itself, with incineration, wastewater handling and separation technologies forming smaller, more contested rings around it. The filing curve peaked in 2021 and has since declined through the last complete year of data, a pattern consistent with a field that built out its core claims in the previous decade and is now filing more selectively.
Receiving-office data shows the field is filed heavily through national mills-driven jurisdictions — the United States, Canada, Finland and Sweden — alongside European and PCT routes, reflecting where kraft pulp capacity and recovery-boiler engineering are concentrated.
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Filing trends and technology composition
The trend and classification charts below are drawn directly from the 1,607 records in scope; the technology shares intentionally sum to more than 100% because most records carry more than one IPC classification.
A 2021 peak followed by a decline through the last complete filing year
Filings rose to 34 in 2021, the high point of the period, then fell to 15 by 2024 — a 56% decline across that three-year span. Because publication typically lags filing by around 18 months, 2025 and 2026 figures are still incomplete and should not be read as confirming a continued slide.
Publication lags filing by roughly 18 months, so 2025 onwards are still filling in. Growth rates on this page therefore end at 2024; running them to the last bar would understate the field.
Pulp treatment dominates; incineration and water treatment trail well behind
D21C (pulp production and treatment) appears in 86.1% of the 1,607 records, far ahead of F23G incineration (8.6%), C02F water treatment (7.6%) and the remaining classes, each under 6%. That gap indicates most inventive effort still targets the core recovery cycle rather than the downstream energy or effluent stages.
Shares are the percentage of the 1,607 records in scope. A patent can carry several IPC classes, so the shares add up to more than 100%.
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Try EurekaThe most-cited records in this landscape
GB1217833A — Improved cellulosic pulp process
Filed by Electric Reduction Company of Canada, this 1970 filing describes digesting cellulosic material with white liquor, separating and washing the resulting black liquor, then routing it through a chemical recovery system: evaporation to a solid residue, burning that residue, dissolving it in water to form green liquor, and causticizing it back into usable cooking liquor.One of the earliest fully-documented recovery-cycle claims in the dataset, illustrating the evaporate-burn-dissolve-causticize sequence that later filings still build around.
| # | Publication no. | Patent title | Citations |
|---|---|---|---|
| 1 | US5595628A | Production of pulp by the soda-anthraquinone process (SAP) with recovery of the cooking chemicals | 314 |
| 2 | US4764596A | Recovery of lignin | 246 |
| 3 | US4943349A | Process for preparing a sheet material with improved on-machine retention | 148 |
| 4 | US5788812A | Method of recovering furfural from organic pulping liquor | 123 |
| 5 | WO2007111605A1 | Cellulose-solvent-based lignocellulose fractionation with modest reaction conditions and reagent cycling | 114 |
| 6 | US4011129A | Pulp mill recovery system | 85 |
| 7 | US4024229A | Production of polysulfide with PTFE coated catalyst | 82 |
| 8 | US4619733A | Pollution free pulping process using recycled wash effluent from multiple bleach stages to remove black liquo… | 77 |
| 9 | US20110294991A1 | Process for recovering lignin | 76 |
| 10 | US6176971B1 | Heat economy enhancements for the recovery and use of energy obtained from spent cooking liquors | 69 |
Citation counts reflect influence within the searched corpus and skew toward older filings; they are not a measure of current commercial importance.
Each row carries its publication number; clicking a row searches Eureka by that number.
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Three patterns stand out once the ranking, the trend and the classification data are read together.
No single owner controls the field
The leading assignee holds 74 records out of 1,607, and even the top five combined reach only 17.7% of all records in scope. That leaves a long tail of single- and few-filing entrants, which is unusual for a century-old industrial process and suggests recovery-cycle engineering keeps generating incremental, ownable improvements rather than settling around a handful of blocking patents.
Activity has pulled back from its 2021 high
Filings peaked at 34 in 2021 and had fallen to 15 by 2024, a 56% decline over three years. That is the last year the data can be treated as complete; 2025 and 2026 are still filling in given typical publication lag, so the true trajectory past 2024 is not yet visible.
Core pulping claims dominate; energy and effluent stages trail
D21C outweighs every other subclass by a wide margin, while incineration (F23G, 8.6%), water treatment (C02F, 7.6%) and separation processes (B01D, 4.7%) each cover a small minority of records. Filing density in D21C signals occupied claim space, not that the underlying chemistry is settled.
The most-cited work skews toward older foundational filings
The top-cited record, on the soda-anthraquinone process with cooking-chemical recovery, and the second-ranked lignin recovery patent both predate the current filing window by decades. High citation counts here reflect long exposure to later searches, not that these remain the newest state of the art.
Eureka can read the same corpus for gaps instead of for coverage: under-claimed branches adjacent to pulp & papermaking: black liquor recovery patent landscape, with the prior art for and against each one.
| Assignee | Co-assignee | Shared families |
|---|---|---|
| Paprican (Pulp and Paper Research Institute of Canada) | Kvaerner Canada Inc. | 13 |
| Paprican (Pulp and Paper Research Institute of Canada) | Eco-Tec Limited | 9 |
| Andritz Oy (Finland) | VEHMAA JANNE | 5 |
| Kvaerner Pulping AB | SNEKKENES VIDAR | 4 |
| Andritz Oy (Finland) | TERVOLA PEKKA | 4 |
| Andritz Oy (Finland) | PIKKA OLAVI | 4 |
| Kvaerner Pulping AB | LINDSTROM MIKAEL | 3 |
| Kvaerner Pulping AB | OLSSON KRISTER | 2 |
Only 10 co-assignee pairs appear in the dataset, and the strongest pairing links two Canadian pulp-and-paper research bodies; most assignees in this field file independently rather than through joint ownership.
Where to take this analysis
The dataset points to a field with settled core claims and a thinner set of adjacent branches still open for new filing.
Map the white space around the recovery boiler
Incineration, water treatment and separation processes each sit under 10% of records despite being mechanically inseparable from the recovery cycle. That gap is worth testing against current mill retrofit and emissions-control priorities.
Explore white space in EurekaTrack the post-2024 filing signal as it fills in
The 2021-2024 decline is confirmed, but 2025-2026 data is still incomplete due to publication lag. Re-run the trend once those years mature before drawing conclusions about a continued slowdown.
Set up a filing alert in EurekaCheck freedom-to-operate against the long tail
With the top five assignees holding only 17.7% of records, freedom-to-operate work in this space means clearing many small portfolios rather than one or two dominant blockers.
Run a clearance search in EurekaCommon questions on black liquor recovery patents
The assignee ranking covers 100 companies, and no single one dominates: the leader holds 74 records out of 1,607, while the top five combined reach only 17.7% of all records in scope. That means the field has a long tail of smaller filers alongside a handful of larger, pulp-and-paper-equipment-focused holders. For freedom-to-operate purposes, this spread means clearance work has to look well beyond the largest few names.
Filings peaked at 34 in 2021 and fell to 15 by 2024, a 56% decline over that three-year window, which is the most recent period that can be treated as complete. Data for 2025 and 2026 is still incomplete because publication typically lags filing by around 18 months, so it is too early to call the trend beyond 2024 a continued decline. The safest reading is that the field cooled off its 2021 high, not that it has stopped moving.
Pulp production and treatment, IPC class D21C, appears in 86.1% of the 1,607 records in scope, far outweighing every other classification. Incineration and waste burning (F23G) covers 8.6%, water and wastewater treatment (C02F) covers 7.6%, and separation processes, catalysis and steam generation each sit under 6%. Because records often carry multiple classifications, these figures describe density of claim activity rather than a strict market breakdown.
GB1217833A, filed by Electric Reduction Company of Canada, describes the core black liquor recovery sequence: digesting pulp with white liquor, separating and washing the resulting black liquor, evaporating it, burning the residue, dissolving it into green liquor and causticizing that back into usable cooking liquor. It is a representative early filing of the evaporate-burn-dissolve-causticize cycle that much later patent activity in this dataset still builds around. It is useful as a reference point for understanding the baseline process rather than as a currently enforceable blocking claim, given its age.
The most-cited record in the dataset is US5595628A, covering the soda-anthraquinone process with cooking-chemical recovery, cited 314 times, followed by US4764596A on lignin recovery at 246 citations. Both predate the current filing window by a considerable margin, which is typical: citation counts accumulate over time and favour older records regardless of their current commercial relevance. Newer filings should be judged on their technical claims, not on citation counts alone, since they simply have not had time to accumulate the same exposure.
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Disclaimer. This page is generated from Patsnap Eureka data drawn from a limited snapshot of global patent and scientific-literature records, and is provided for general information and reference only.
Patent data carries inherent limitations: recent filings (typically the most recent 18–24 months) are under-counted due to standard publication lag; counts may be reported at either a patent-family or a patent-record basis and are not always directly comparable; classification, applicant-name, and citation data may contain errors, duplicates, or omissions; and the underlying search query defines and constrains the scope shown. As a result, the analysis may be incomplete or inaccurate and may not reflect the full technology landscape.
Nothing on this page constitutes an exhaustive prior-art, novelty, freedom-to-operate, or validity search, nor does it constitute legal, financial, investment, or professional advice, and it should not be relied upon as such. Any patent, commercial, or strategic decision should be verified independently and reviewed with qualified patent, legal, and domain professionals. Patsnap makes no warranties, express or implied, as to the accuracy, completeness, or fitness for any particular purpose of the information presented.
Machine translation. Assignee and organisation names originally recorded in Chinese, Japanese or Korean have been rendered into English by an AI translation step so that the tables stay readable. These renderings are best-effort and may not match a company’s registered English name; the original name is what the underlying patent record carries, and it is what any Eureka query launched from this page uses.