How a Special Carbon-Fluorine Catalyst Makes Chlorine and Caustic Soda
This patent describes using a unique carbon-fluorine compound as a catalyst in a special type of electrolysis cell to make chlorine and caustic soda more efficiently by preventing hydrogen gas from forming.
Original patent title: “Cathode electrocatalysts for solid polymer electrolyte chlor-alkali cells”
This patent describes using a unique carbon-fluorine compound as a catalyst in a special type of electrolysis cell to make chlorine and caustic soda more efficiently by preventing hydrogen gas from forming. Granted to PPG Industries in 1981 with 14 claims and 47 forward citations, and it is now in the public domain.
Coverage
What does this patent actually cover?
The patent improves the chlor-alkali process, which creates chlorine and sodium hydroxide (caustic soda) from salt water. Instead of a traditional cathode that produces hydrogen gas, this invention uses a "solid polymer electrolyte" cell (ClaimclaimA numbered sentence at the end of a patent that legally defines what the inventor owns. The most important section.Read more → 1). The key improvement involves placing a specific catalyst, an "intercalation compound of carbon and fluorine" (Claim 1, 8), on the cathode side. An "oxidant," such as oxygen (Claim 5), is fed to this side. This setup "substantially eliminates hydrogen evolution" (Claim 1), meaning less hydrogen gas is made, which saves energy. For example, a cell could use this carbon-fluorine catalyst (like CFx where x is between 0.25 and 1.0, Claim 6) to convert oxygen and water into hydroxide ions, boosting efficiency.
The gap
What does this patent NOT cover?
- Electrolysis cells that produce hydrogen gas at the cathode as the primary cathodic reaction.
- Cathode depolarization methods that do not use an "intercalation compound of carbon and fluorine" as the catalyst.
- Chlor-alkali processes that do not use a solid polymer electrolyte to separate the anolyte and catholyte compartments.
- Cathodes that do not receive an external oxidant feed to prevent hydrogen evolution.
- Catalysts that are not specifically carbon-fluorine intercalation compounds, or the specific oxidant complexes mentioned in claimclaimA numbered sentence at the end of a patent that legally defines what the inventor owns. The most important section.Read more → 11.
These exclusions are unique to PatentBrief — derived from the actual claim language, not patent-office boilerplate.
Key facts
What made this novel
The noveltynoveltyThe requirement that an invention be different from anything publicly known before its priority date.Read more → lies in using a specific "intercalation compound of carbon and fluorine" as the cathode catalyst in a solid polymer electrolyte cell, combined with feeding an oxidant, to specifically prevent hydrogen gas formation. This targeted approach to cathode depolarization with a novel catalyst material was not obvious.
The Patent Drawing
Schematic visualization of the patent's claim structure. Hand-drawn diagrams in progress for each landmark patent.
Where you've seen this
Real-world examples
Industrial chlor-alkali plants
Membrane electrolysis cells
Electrolytic cells using oxygen depolarized cathodes
Why it matters
The bigger picture
The chlor-alkali industry is a massive global market, producing essential chemicals for everything from water treatment to plastics. This patent aimed to make that process more energy-efficient by avoiding hydrogen production, a significant energy drain. Energy efficiency is a constant goal in heavy industrial processes, directly impacting production costs and environmental footprint.
Filed
February 23, 1979
Granted
March 3, 1981
Market context
Who's building on this
Companies in this space
Companies involved in industrial electrochemistry and chemical manufacturing, such as Olin, Westlake Chemical, and Dow Chemical, continually research and implement more efficient chlor-alkali technologies. Developers of advanced membrane materials and catalysts for fuel cells or electrolyzers might also draw on similar principles.
Market impact
This patent contributed to the ongoing drive for energy efficiency in the chlor-alkali industry. By proposing a specific catalyst for oxygen-depolarized cathodes, it offered a pathway to reduce the significant electricity consumption of these plants, potentially lowering production costs and environmental impact. While not creating a new market, it aimed to improve an existing, critical industrial process.
Claim 1 — Plain English
What this patent covers
The patent improves the chlor-alkali process, which creates chlorine and sodium hydroxide (caustic soda) from salt water. Instead of a traditional cathode that produces hydrogen gas, this invention uses a "solid polymer electrolyte" cell (Claim 1). The key improvement involves placing a specific catalyst, an "intercalation compound of carbon and fluorine" (Claim 1, 8), on the cathode side. An "oxidant," such as oxygen (Claim 5), is fed to this side. This setup "substantially eliminates hydrogen evolution" (Claim 1), meaning less hydrogen gas is made, which saves energy. For example, a cell could use this carbon-fluorine catalyst (like CFx where x is between 0.25 and 1.0, Claim 6) to convert oxygen and water into hydroxide ions, boosting efficiency.
The clever bit
The novelty lies in using a specific "intercalation compound of carbon and fluorine" as the cathode catalyst in a solid polymer electrolyte cell, combined with feeding an oxidant, to specifically prevent hydrogen gas formation. This targeted approach to cathode depolarization with a novel catalyst material was not obvious.
What it does not cover
- Electrolysis cells that produce hydrogen gas at the cathode as the primary cathodic reaction.
- Cathode depolarization methods that do not use an "intercalation compound of carbon and fluorine" as the catalyst.
- Chlor-alkali processes that do not use a solid polymer electrolyte to separate the anolyte and catholyte compartments.
- Cathodes that do not receive an external oxidant feed to prevent hydrogen evolution.
- Catalysts that are not specifically carbon-fluorine intercalation compounds, or the specific oxidant complexes mentioned in claim 11.
Patent timeline
Application submitted to the patent office
Application published, typically 18 months after filing
Patent officially issued
Patent enters public domain
This patent is in the public domain
See the Freedom to Build guide — what is free to use, what is not, and how to cite this patent.
PatentBrief Score
Impact Score
Moderate
Citation count
34/40
Moderately cited
Claim breadth
9/20
Moderate scope
Recency
0/20
Older than 20 years
Assignee scale
0/20
Independent or smaller assigneeassigneeThe entity that owns the patent — usually the inventor's employer or a company.Read more →
PatentBrief Impact Score — based on citation count, claim breadth, recency, and assignee scale. Not a legal assessment.
Heuristic Value Estimate
What this patent might be worth
$32K – $104K
Midpoint $65K · expired or expiring · industry ×2.4
Heuristic only — blends forward/backward citation counts, claim scope, time remaining, litigation history, and CPC-derived industry baseline. Real valuations need a professional appraisal.
Patent Claims
0 independent claims · 1 dependent
Claims are the legal boundaries of the patent. An independent claim stands alone. A dependent claim adds limitations to its parent, narrowing — but not broadening — the scope.
The original legal language
Original claims
14 claims as filed with the patent office.
Concepts involved
Citations
Patent lineage
Cite this patent
Welch, C. N. (1981). How a Special Carbon-Fluorine Catalyst Makes Chlorine and Caustic Soda (U.S. Patent No. 4,253,922). U.S. Patent and Trademark Office. https://patentbrief.org/patent/us/4253922/cathode-electrocatalysts-for-solid-polymer-electrolyte-chlor-alkali-cells
Auto-generated from the patent record. Double-check author order and the issue date against the official USPTO document before submitting.
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Common Questions
Frequently Asked Questions
What does How a Special Carbon-Fluorine Catalyst Makes Chlorine and Caustic Soda cover?
This patent describes using a unique carbon-fluorine compound as a catalyst in a special type of electrolysis cell to make chlorine and caustic soda more efficiently by preventing hydrogen gas from forming.
Who owns patent US 4253922?
PPG Industries owns this patent, granted in 1981.
When does this patent expire?
This patent has expired and is now in the public domain — anyone can use the invention freely.
What is patent US 4253922 cited by?
This patent has been cited by 47 later patents that build on its ideas.
What problem does this patent solve?
The chlor-alkali industry is a massive global market, producing essential chemicals for everything from water treatment to plastics. This patent aimed to make that process more energy-efficient by avoiding hydrogen production, a significant energy drain. Energy efficiency is a constant goal in heavy industrial processes, directly impacting production costs and environmental footprint.
What does this patent NOT cover?
Electrolysis cells that produce hydrogen gas at the cathode as the primary cathodic reaction.
Patent monitoring