Appeal No. 1997-4399
Application 08/505,338
that “continuous absorption of the sulphur containing compounds may be achieved through the removal
of the absorbed sulphide ions in the aqueous solution by oxidation with an oxygen containing gas,”
wherein the “principal oxidation product is the thiosulphate ion with lesser amounts of sulphate and
sulphite ions as well as minor amounts of elemental sulphur” (col. 2, lines 34-48; emphasis supplied).
While Murray teaches that it is “critical . . . that the pH of the aqueous alkaline solution is maintained
about 9.0 and above throughout the absorption” (col. 3, lines 31-43), it is clear from the reference that
the disclosed process “substantially increase hydrogen sulphide absorption by maintaining the
equilibrium partial pressure of the hydrogen sulfide [sic] at a level near zero . . . by reducing the effective
concentration of sodium sulfide [sic] . . . [which is] kept at a level near zero by the oxidation of the
hydrogen sulfide [sic] absorbed in the solution” (col. 3, lines 62-73). We find that Anderson discloses a
process (col. 4, lines 29-39), without stating the pH at which it is conducted, that is similar to the
process which Murray acknowledged to be in the prior art.
Upon comparing the claimed invention with the applied combination of references, we cannot
agree with the examiner’s position that one of ordinary skill in this art would “by-pass the oxidation step
. . . of Murray” in order to obtain a “sulphide solution” that can be used to prepare “white liquor” as
suggested by Anderson in a similar process (answer, e.g., pages 5-6 and 10-13). Indeed, as appellants
point out in their brief, there is no apparent suggestion, teaching or motivation in the combined teachings
of the references which would have led one of ordinary skill in this art to delete the oxidation step taught
by Murray to be necessary for the “continuous” absorption of hydrogen sulphide. We also fail to find in
the applied references any apparent suggestion, teaching or motivation to modify the prior art process
acknowledged by Murray to be inefficient by using multiple stages of circulating carbonate-containing
alkaline solutions, each maintained at a pH of about 9-12, to achieve the amount of total sulphide
content specified in appealed claim 1. Thus, on this record, we must conclude that the examiner’s
position is based on impermissible hindsight. See generally, Dow Chem. Co., supra.
We have considered the apparatus encompassed by appealed claim 9 with respect to the
specific structure recited therein, that is, without respect to the material intended to be worked on by the
unpatentable over Kent in view of Kignell (answer, page 2).
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