Ionic-Liquid Greases vs PFAS Rules: The FSI Anion Problem

What ILs do in grease (conductivity, friction, starvation delay)

Ionic liquids — molten salts that are liquid near room temperature — entered grease research for three practical reasons. They are ionic, so they carry charge and can be tuned to conduct. They adsorb on metal and build low-shear boundary layers, so friction and wear can drop in the right base oil. And they change oil-bleed and re-wetting behaviour, which is why component-level tests show them delaying starvation in oscillating bearings. None of this is magic; it is ions, polarity and solubility. An IL is an additive with a cation and an anion, and the anion decides both the tribology and the regulatory file.

What the filing is evidence for

WO 2024/017518 A1 — since granted in the US as US 12,612,575 B2 (28 April 2026) — is evidence that IL–grease combinations have moved from journal papers into claim drafting: it puts 0.5–80 wt% of an ionic liquid with a bis(fluorosulfonyl)imide (FSI) anion into ester or polyglycol greases. Read it as a map of what one applicant claimed, including that very broad treat range and those base-oil families. We cite it as prior art; we do not reproduce its claims, and nothing here is a freedom-to-operate opinion.

Which anions are PFAS-class

Here is the tension. FSI — N(SO2F)2 — is a fluorinated imide anion. Its better-known cousin TFSI carries CF3 groups and sits squarely inside the common OECD-based PFAS definitions. FSI itself carries S–F bonds rather than perfluoroalkyl carbon chains, and whether it falls inside a given PFAS rule depends on which definition that rule adopts; fluorine policy is moving, and several proposed frameworks are broader than today's. The honest formulation takeaway is not a legal classification — it is that 'ionic liquid grease' is not automatically PFAS-free, and an anion you cannot name is an anion you cannot defend to a customer's EHS team. Fluorinated anions also hydrolyse toward fluoride under abuse conditions, which is a handling and corrosion question before it is a marketing question. When in doubt, ask the supplier for the full chemical name and CAS number of the anion — the name decides the file.

What it is not evidence for

The patent is not evidence that FSI greases are banned, and it is not evidence they are safe to sell as 'PFAS-free' — both would be legal claims we do not make. It is not evidence of performance in your base oil: ester and polyglycol are the claimed families, and Indian Group II shelves behave differently. And a 0.5–80 wt% claim range is not a recommendation; at the high end you are pricing an electrolyte, not a grease.

Halide-free, non-fluorinated IL research (boronium, phosphonium phosphate)

The research literature has already moved partway around the fluorine problem. Boronium-cation ionic liquids with non-fluorinated anions, and phosphonium phosphate ILs — the trihexyl(tetradecyl)phosphonium family with dialkyl-phosphate anions are the workhorse examples — show antiwear and friction behaviour without a single C–F bond. These are screening directions, not commodity drums: cost, purity and supply all lag the fluorinated incumbents, and halide residue from IL synthesis is its own corrosion story that has to be specified on the incoming QC sheet.

What a formulator changes on the bench

An IL screen at Lubechem starts with the anion, not the brochure:

• Documents first: anion identity, halide content, water content and the supplier's own PFAS-position statement — filed before any grease is made.
• Solubility ladder: 0.5–2 wt% in your actual base oil (ester, PAO, Group II), with clarity and separation checks after heat-and-freeze cycling.
• Tribology and corrosion together: four-ball wear (D2266) and SRV friction beside copper corrosion (D4048) and rust (D1743), because an ion that plates out nicely can also strip a cage.
• Hydrolysis check: water-aged samples re-tested, since fluorinated anions that release fluoride change both the corrosion picture and the EHS file.

How Lubechem would screen an IL additive for an Indian blender

For an Indian blender the questions arrive in a specific order. Can you buy the IL twice, from a supplier who will put the anion on the CoA? Does it survive monsoon humidity in an open kettle? Does the duty actually need it — conductivity for an e-motor grease, starvation delay for an oscillating joint — or is it decoration on a commodity drum? And can the customer's export market ask for a PFAS declaration, which is increasingly the real gate for food-adjacent and EU-bound products?

The design-around question

The design-around question: the granted claims cover an FSI-anion IL in ester or polyglycol grease across a very wide treat range — so the legitimate design space is a non-fluorinated anion (phosphate, borate, alkylsulfate families), a different cation (phosphonium, ammonium, boronium), or a base oil outside the claimed families. Which of those gives you the conductivity or starvation benefit you actually need at 1–2 wt%? That is bench chemistry. Whether it clears US 12,612,575 B2 or its family members in your sales territories is a patent attorney's question, and it stays there.

What Lubechem will and will not claim

Lubechem Consultant is an independent formulation house in New Delhi, led by Er. Manoj Kumar and practising since 2010. WO 2024/017518 A1 and US 12,612,575 B2 are cited as prior art so a chemist can read the source; they are not Lubechem products, we do not reproduce claims, and we give no freedom-to-operate or regulatory-clearance opinions. We also do not print 'PFAS-free' on anything until the anion, the supplier declaration and the customer's market definition all line up — that is a documentation exercise, not a slogan.

If an IL-grease paper or sales deck is on your desk, send it with the duty brief. The first deliverable is the anion name and a screening plan, not a purchase order.

How to use this filing as prior art — not as a recipe

Literature and prior art

Citations below are orientation, not a freedom-to-operate opinion. Lubechem does not copy claimed compositions and does not treat a patent as a product endorsement.

1. WO 2024/017518 A1; US 12,612,575 B2 (granted 28 Apr 2026) — cited as prior art or literature, not as a product Lubechem sells
2. EU REACH lithium-hydroxide classification trajectory — labelling and supply, not a ban on every lithium grease
3. NLGI High-Temperature Performance Limit discussion — operating temperature is not drop point
4. NSF H1 / ISO 21469 — incidental food contact, not a licence to invent ingredients

Related formulation pages

• Ev Motor Bearing Grease India
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