## Facts

- Celanese owned a European patent covering a method of removing iodide impurities from acetic acid using a silver-loaded ion-exchange resin “guard bed.”
- BP operated large-scale acetic-acid plants and used silver-loaded resin guard beds that were found (in earlier proceedings) to infringe Celanese’s patent.
- After establishing validity and infringement, Celanese elected an equitable account of BP’s profits rather than an inquiry as to damages.
- Two BP plants were relevant: one was overall loss-making during the period; the other generated profits.
- The remedy dispute focused on whether Celanese could claim profits from BP’s sale of low-iodide acetic acid, or only profits attributable to the patented guard-bed feature within a larger production process.

## Issues

1. Whether an account of profits requires proof of actual profits from the infringing use, such that no recovery is available for a plant that was overall loss-making.
2. Whether profits from the profitable plant had to be apportioned to reflect the patented guard bed as only one component of a broader, profit-generating industrial process.
3. What method could fairly estimate the share of profits attributable to the patented feature where precise incremental profit evidence was difficult to isolate.
4. Whether corporation tax could be deducted in calculating profits to be disgorged.

## Decision

- The court held that no profits were payable for the loss-making plant because there were no actual profits on which an account could be taken.
- For the profitable plant, the court rejected a claim to the plant’s full profits and required apportionment to the infringing contribution.
- The court apportioned profits by using the guard bed’s relative capital value as a proxy, attributing 0.6% of the plant’s total profits to the infringement.
- The court allowed BP to deduct corporation tax in determining the net profits subject to the account.
- The resulting sum was a small award (a few hundred thousand pounds), far below Celanese’s claimed figures.

## Legal Principles

- An account of profits in patent infringement is restitutionary, not punitive; the claimant recovers only profits actually derived from the infringement.
- If the relevant undertaking generated no overall profit, an account of profits yields nothing; the court will not construct hypothetical profits to substitute for an absence of realized gain.
- Where the patented invention is one part of a larger profitable process, the court will apportion profits between infringing and non-infringing contributions rather than award the whole enterprise profit.
- In evidentially difficult apportionment exercises, the court may use a practical proxy (including relative capital cost/value) to estimate the infringing share.
- “Profit” for an account may be calculated on a net basis permitting deduction of corporation tax (and, by implication, necessary expenses) to identify profit actually retained.

## Conclusion

The Patents Court limited the account of profits to BP’s actual net profits attributable to the infringing guard-bed process, awarding nothing for a loss-making plant and only 0.6% of profits (net of tax) for the profitable plant based on a capital-value apportionment.


Celanese Int'l Corp. v. BP Chems. Ltd., [1999] R.P.C. 203 (Pat. Ct. 1999)