## Facts

- Ralph M. Parsons Co. owned U.S. Patent No. 3,752,877 covering an effluent (tail) gas treating method used with the Claus sulfur-recovery process; Union Oil Co. of California licensed the technology.
- The Claus process removed most sulfur from gas streams, leaving residual sulfur species in the effluent, including sulfur dioxide, elemental sulfur, carbonyl sulfide, and carbon disulfide.
- The patented method treated Claus effluent by converting sulfur species to hydrogen sulfide through hydrogenation and hydrolysis steps, followed by sulfur recovery, achieving very high overall sulfur removal when combined with Claus.
- Environmental Designs, Ltd. and its general partner, the Trentham Corporation, announced construction of an effluent gas treating plant using the “Trencor process.”
- Parsons and Union contended the Trencor process practiced the patented method; Environmental and Trentham asserted noninfringement and challenged the patent’s validity and enforceability.

## Issues

1. Whether the asserted patent claims were invalid as obvious under 35 U.S.C. § 103.
2. Whether the patent was unenforceable for fraud/inequitable conduct based on alleged nondisclosure of internal company materials to the PTO.
3. Whether the Trencor process infringed claims 1–8 and 12 of the patent.

## Decision

- The Federal Circuit affirmed the judgment of the district court.
- The claims were held nonobvious under § 103, applying the Graham factors and crediting objective evidence such as industry skepticism, long-felt need, and commercial success.
- The patent was not rendered unenforceable because the alleged undisclosed internal materials were not shown to be material prior art and intent to deceive was not proven.
- The Trencor process was found to literally infringe; the court rejected attempts to read unrecited limitations into the claim language.
- The injunction and the damages award of $14,000 were left intact.

## Legal Principles

- Obviousness under 35 U.S.C. § 103 is determined using the Graham framework: scope/content of prior art, differences from the claims, level of ordinary skill, and objective indicia.
- Objective indicia of nonobviousness (including commercial success, long-felt need, and industry skepticism) are part of the obviousness analysis and must be considered with the other evidence.
- Inequitable conduct requires proof of both materiality and intent to deceive the PTO; nondisclosure of internal information not shown to be material to patentability does not, by itself, establish unenforceability.
- Infringement analysis begins with the claims as written; courts should not import limitations from the specification or other sources into otherwise unambiguous claim language.

## Conclusion

The Federal Circuit upheld the validity and enforceability of a tail-gas sulfur-treatment patent and affirmed literal infringement, emphasizing that objective indicia can strongly support nonobviousness and that inequitable conduct demands clear proof of materiality and intent.


Envtl. Designs, Ltd. v. Union Oil Co. of Cal., 713 F.2d 693 (Fed. Cir. 1983)