Appeal No. 96-1165
Application 08/060,422
concentration of the reducing gas (col. 1, lines 57-62). According to Wheelock, the reducing gas can be
carbon monoxide or hydrogen or preferably a mixture thereof (col. 5, lines 44-51).
It is known in the art, as evidenced by Kertamus, that sulfur dioxide in the presence of char or coke
can be converted to sulfur and carbon monoxide (col. 1, line 67 to col. 2, line 2; col. 2, lines 58-64). While
Kertamus ultimately burns the elemental sulfur so produced, Kertamus discloses and suggests a simple one
step chemical means for converting sulfur dioxide to elemental sulfur. Gorin’s process is more complex in
that it involves two steps. The sulfur dioxide produced from the oxidation of calcium sulfide is divided into
two parts; one part is treated in a first vessel with carbon monoxide and hydrogen and the product of this
reaction is combined with the remaining sulfur dioxide and subjected to a Claus reaction in a second vessel.
We find that the simpler chemistry of Kertamus would have motivated a person having ordinary skill in the
art to replace the more complicated chemical process disclosed by Gorin for converting sulfur dioxide to
elemental sulfur.
As for the carbon monoxide by-product of the conversion process, it is well known in the chemical
arts that an effluent containing by-products from a process can be recycled back through the process. See
Ex parte Brown, 65 USPQ 531 (Bd. App. 1945). This is evidenced by the teachings of Gorin.
Moreover, the motivation for recycling by-products can be based on both economic as well as
environmental factors, and need not be expressly suggested or taught by the prior art. See In re
Thompson, 545 F.2d 1290, 1294, 192 USPQ 275, 277 (CCPA 1976); In re Clinton, 527 F.2d 1226,
1229, 188 USPQ 365, 367 (CCPA 1976). Accordingly, we find that recycling of carbon monoxide to
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