Conoco v. Energy & Environmental International

Transitional Phrase “Consisting Of” Is Not Absolute In The Exclusion of Unrecited Limitations. 

(Fed. Cir. 2006, 05-1363)

Conoco originally brought suit against EEI alleging infringement of U.S. Patent Nos. 5,244,937 (the 937 patent) and 6,172,151 (the 151 patent).  The case came to the CAFC from the District Court for the S.D. of Texas which held that EEI had literally infringed the 937 patent and infringed under the doctrine of equivalents the 151 patent.  The CAFC affirmed the findings of infringement and upheld the ruling of the district court.

The technology of the patents relate to processes for making drag reducing agents (“DRA”) that are injected into oil and gas pipelines to reduce pumping friction. By reducing such friction, liquid may be pumped more efficiently. The DRAs of the invention are aqueous suspensions of high molecular weight polymers.

The issues on appeal were the district court’s construction of various claim terms, with one issue in particular relating to the transitional phrase “consisting of.”  Specifically, EEI alleged that the Conoco’s use of “consisting of” in the claims limited the scope to exclude products performing only the recited steps of the patent “and nothing else.” EEI further contended that the district court erred by allowing the accused process’s suspension medium to include MIBK, a non-alcohol, in spite of the limitation that the suspending medium consist of water or a water-alcohol mixture.  

The transitional phrase “consisting of” is a term of art in patent law with its own construction.  See MPEP § 2111.03.  The phrase “consisting of” signifies restriction and exclusion of unrecited steps or components. See MPEP § 2111.03. However, the CAFC notes that although “consisting of” is a term of restriction, the restriction is not absolute.  For instance, the BPAI has interpreted “consisting of” to “close the claim to the inclusion of materials other than those recited except for impurities ordinarily associated therewith.”  Additionally, the transitional phrase “consisting of” does not exclude additional components or steps that are unrelated to the invention.

In light of this construction, the CAFC recognized that MIBK is a common impurity found in industrial alcohols.  Regardless of EEI’s assertions that MIBK was being purposefully added, “the intentional addition of a component does not change its status as an ‘impurity normally associated therewith.'”  Interestingly, the court acknowledged that the purpose with which a material is added, e.g. if the MIBK had been added for a purpose related to the invention (prevent agglomeration, stability, etc.), effects a conclusion on whether the material is an impurity or not. 

Based in part on findings that MIBK has little to no effect on the invention and could normally be found as an impurity to prevent a liquor tax from being applied (i.e. the use is unrelated to the purpose of the invention), the CAFC holds that the district court did not clearly err in the construction of the claims.