Patents

Celanese v. ITC: The On-Sale Bar Survives the AIA for Secret Processes

The Federal Circuit held that selling a product made by a secret process starts the on-sale clock against a later patent on that process — and the America Invents Act did nothing to change it.

March 28, 2026
An industrial chemical processing facility at dusk
Celanese sold the sweetener Ace-K for years before patenting the secret process used to make it. Shutterstock
Educational content, not legal advice. This article explains general legal concepts. It does not create an attorney–client relationship. For your specific situation, consult a licensed attorney.

Celanese International Corp. v. International Trade Commission, No. 22-1827 (Fed. Cir. Aug. 12, 2024), resolves a question that the Leahy-Smith America Invents Act (AIA) was widely thought to have reopened: whether an inventor who quietly sells a product made by a secret process may later obtain a valid patent on that process. The unanimous panel — Judges Reyna (author), Mayer, and Cunningham — said no. Affirming a final determination of the International Trade Commission in Investigation No. 337-TA-1264, Certain High-Potency Sweeteners, the court held that pre-AIA precedent on the on-sale bar carried forward unchanged into 35 U.S.C. § 102 as amended. A patentee’s own pre-critical-date sales of products made by a secret method invalidate later claims to that method, even though the sales disclosed nothing about it.

At a glance

  • Case: Celanese International Corp. v. International Trade Commission, No. 22-1827 (Fed. Cir. Aug. 12, 2024)
  • Panel: Reyna (author), Mayer, Cunningham; unanimous; ITC determination affirmed
  • Tribunal below: U.S. International Trade Commission, Inv. No. 337-TA-1264
  • Patents: U.S. Patent Nos. 10,023,546; 10,208,004; and 10,266,095 — all directed to processes for making acesulfame potassium (“Ace-K”), an artificial sweetener
  • Statute: Post-AIA on-sale bar, 35 U.S.C. § 102(a)(1)
  • Holding: A patentee’s pre-critical-date sale of a product made by a secret process triggers the on-sale bar against later claims to that process; the AIA did not displace pre-AIA on-sale-bar law
  • Status: Final; the Federal Circuit denied rehearing, and the case stands as precedent

The facts: a long-sold product, a late-filed process patent

The relevant facts were stipulated and stark. Celanese manufactured Ace-K abroad using a process it kept as a trade secret. Well before the critical date of its asserted patents, Celanese sold Ace-K made by that secret process in the United States. Only later did it file the applications that matured into the ‘546, ‘004, and ‘095 patents, each claiming the process itself. When Celanese asserted those process patents at the ITC against importers of competing Ace-K, the respondents raised the on-sale bar: Celanese had commercialized the fruits of its invention before filing, so the statute should foreclose a patent.

The administrative law judge agreed, and the Commission affirmed, holding the asserted claims invalid under § 102. Celanese appealed, betting that the AIA’s rewording of § 102 had quietly abrogated a doctrine that had governed for the better part of a century.

Anticipation, the on-sale bar, and the pre-AIA baseline

Section 102 polices novelty. It denies a patent to anyone who was not the first to invent something genuinely new, and it sets out categories of prior art and statutory bars that defeat a claim. The on-sale bar is a statutory bar in the truest sense: it operates against the inventor’s own conduct, regardless of whether anyone else knew of the invention. Its purpose, as the Supreme Court reaffirmed in Pfaff v. Wells Electronics, Inc., 525 U.S. 55 (1998), is to prevent an inventor from commercially exploiting an invention beyond the statutory term — first profiting in secret, then resetting the monopoly clock with a patent.

Under pre-AIA law, the Federal Circuit and its predecessor court drew a sharp, and to many counterintuitive, distinction. A third party’s secret use of a process generally did not count as invalidating prior art; secrecy meant the public gained nothing. But when the patentee was the one exploiting the invention commercially, the calculus flipped. The Second Circuit’s seminal opinion in Metallizing Engineering Co. v. Kenyon Bearing & Auto Parts Co., 153 F.2d 516 (2d Cir. 1946) (L. Hand, J.), held that an inventor who used a secret process to make and sell products forfeited the right to patent that process — the secrecy benefited only the inventor, and allowing a later patent would extend the de facto monopoly. The Federal Circuit absorbed that principle, and decisions such as D.L. Auld Co. v. Chroma Graphics Corp., 714 F.2d 1144 (Fed. Cir. 1983), confirmed that a patentee’s sale of products made by a secret method triggers the on-sale bar against claims to the method itself. The product on the market need not embody or reveal the process; the inventor’s commercial exploitation is the trigger.

The AIA argument: did “available to the public” rewrite the rule?

Celanese’s appeal rested entirely on the AIA’s redrafting of § 102. The pre-AIA statute barred a patent if the invention was “on sale in this country, more than one year prior to the date of the application.” The AIA replaced that with a single clause: a patent is barred if “the claimed invention was patented, described in a printed publication, or in public use, on sale, or otherwise available to the public” before the effective filing date. § 102(a)(1).

Celanese seized on two changes. First, the shift from “invention” to “claimed invention,” which it argued tied the bar to whether the process as claimed had been made available, not merely a product made by it. Second, and more forcefully, the new catch-all phrase “otherwise available to the public.” Reading “on sale” through that residual clause, Celanese contended that only sales making the invention available to the public could bar a patent. A secret-process sale disclosed nothing about the process, so — on this reading — it should fall outside the reframed bar.

The Federal Circuit rejected the argument root and branch. It treated the move from “invention” to “claimed invention” as a clerical refinement carrying no substantive freight. More importantly, the court refused to let the “otherwise available to the public” tag rewrite the established meaning of the discrete term “on sale” that precedes it. The decisive authority was the Supreme Court’s own reading of the same statutory language. In Helsinn Healthcare S.A. v. Teva Pharmaceuticals USA, Inc., 586 U.S. 123 (2019), the Court held that the AIA did not alter the meaning of “on sale,” and that “a sale or offer of sale need not make an invention available to the public” to trigger the bar. Congress, the Court reasoned, had reenacted a settled term of art and is presumed to have adopted its established judicial construction. Celanese applied that logic directly: if a secret sale to a third party can be invalidating under the AIA (as Helsinn held), then a patentee’s own secret-process sale — the a fortiori case under Metallizing — must be as well. The on-sale bar of pre-AIA law survives intact.

Open questions

Celanese settles the headline question but leaves several edges unresolved. It does not squarely address how the bar applies when a third party, rather than the patentee, both holds the process as a secret and sells the resulting product — the classic asymmetry between inventor-secrecy and third-party-secrecy was not directly tested on these facts. The opinion also leaves room to argue over what counts as a “sale” of a product “made by” the process in more attenuated supply chains, including foreign manufacture followed by importation, where the territorial reach of § 102’s “on sale” language post-AIA (which dropped “in this country”) interacts with extraterritorial sourcing. Finally, the court declined Celanese’s invitation to treat the catch-all clause as a limiting principle; whether some future “on sale” scenario might genuinely turn on public availability — for instance, a transfer that is arguably not a commercial sale at all — remains open for the right facts.

Implications

  • Trade-secret-then-patent strategies are foreclosed for the process owner. An inventor cannot commercialize products made by a secret method for years and then patent the method. The commercial-exploitation clock starts at the first qualifying sale, regardless of confidentiality.
  • Choose early between secrecy and patenting. For a manufacturing process, the realistic options are to keep it a trade secret indefinitely or to file before commercial sales of the resulting product — not to do both in sequence.
  • The AIA did not soften the on-sale bar. Celanese, reinforcing Helsinn, confirms that confidential and even non-disclosing sales remain invalidating. Practitioners should not rely on “otherwise available to the public” as a safe harbor for secret transactions.
  • Diligence must look at the patentee’s own conduct. Validity analyses and freedom-to-operate opinions on process patents should probe the patentee’s pre-filing commercial history, not just third-party prior art.
  • ITC respondents have a potent invalidity tool. Where a complainant’s product predates its process patents, the on-sale bar offers a clean, often stipulable, path to a no-violation determination.

Frequently asked questions

Does the product sold have to reveal the secret process for the bar to apply? No. That is the core of the holding. Under Metallizing and now confirmed under the AIA, the patentee’s commercial sale of a product made by the process triggers the bar even if the product discloses nothing about how it was made. The trigger is the inventor’s commercial exploitation, not public disclosure of the method.

Would the result differ if a third party — not the patentee — used the secret process? Likely yes, at least on classic pre-AIA principles, which distinguished an inventor’s secret commercialization (forfeiting) from a third party’s secret use (generally not invalidating prior art). Celanese involved the patentee’s own sales and did not need to resolve the third-party scenario, so that asymmetry remains the governing framework until a future case tests it.

Could the Supreme Court revisit this? It is possible but unlikely to change the outcome. Celanese rests directly on the Supreme Court’s own 2019 decision in Helsinn, which held that the AIA preserved the established meaning of “on sale.” Absent a circuit split or a sharply different fact pattern, the doctrine appears stable.

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