On April 28, 2025, the U.S. Supreme Court declined to hear Celanese International Corp.’s challenge to a Federal Circuit decision which found the company’s patent on the process to create the artificial sweetener used in Coke Zero to be invalid. The Federal Circuit decision affirmed a holding from the U.S. International Trade Commission which initially deemed the patent invalid due to the on-sale bar.

The underlying issue in the case is whether Celanese’s patent, which covers an improved process for making acesulfame potassium (Ace-K), was invalid due to the on-sale bar. The on-sale bar prohibits a patent applicant from obtaining patents for an invention that the applicant or predecessor used or had offered for sale more than a year before filing the patent application. Celanese argued that the Ace-K process itself was never on sale, that the process was only used to create an end product (Coke Zero) that went on sale and that it had used the process in secret, not publicly. The appellant argued that, although the Courts had long ruled that processes that were performed in private for creating a product that was then offered for sale qualified under the old patent statutes, the 2011 America Invents Act changed all this and created a new standard for the on-sale bar.

Both the U.S. International Trade Commission and the U.S. Court of Appeals for the Federal Circuit rejected this argument, concluding that Celanese’s use of the process to create Ace-K for a product that was on sale was sufficient to trigger the on-sale bar. In affirming the ITC ruling, the Federal Circuit held that, had Congress intended to create such a significant change in the law, it was incumbent upon Congress to have made that change explicit, which it did not do.

The National Association of Manufacturers filed an amicus brief in support of Celanese’s position, arguing that the Federal Circuit’s broad interpretation of the on-sale bar was out of step with international intellectual protection standards.