Patents by Inventor Roger K. Clifford

Roger K. Clifford has filed for patents to protect the following inventions. This listing includes patent applications that are pending as well as patents that have already been granted by the United States Patent and Trademark Office (USPTO).

  • Solvent extraction process for recovering bitumen from tar sand
    Patent number: 4676889
    Abstract: Bitumen recovered from tar sand by direct solvent extraction followed by washing of the sand tailings with countercurrent solvent flow and a solvent/aqueous phase separation step to recover solvent and residual bitumen.
    Type: Grant
    Filed: February 27, 1984
    Date of Patent: June 30, 1987
    Assignee: Chevron Research Company
    Inventors: C. Richard Hsieh, Roger K. Clifford