Application of Brown

• Citation: 173 USPQ 685,459 F.2d 531
• Decision Date: 18 May 1972
• Docket Number: Patent Appeal No. 8621.
• Parties: Application of David BROWN and Alfred Saffer.
• Court: United States Court of Customs and Patent Appeals

173 USPQ 685, 459 F.2d 531 (1972)

Application of David BROWN and Alfred Saffer.

Patent Appeal No. 8621.

United States Court of Customs and Patent Appeals.

May 18, 1972.

William C. Long, David Dick, New York City, attorneys of record, for appellants.

S. Wm. Cochran, Washington, D. C., for the Commissioner of Patents. Fred W. Sherling, Washington, D. C., of counsel.

Before RICH, ALMOND, BALDWIN and LANE, Judges, and RAO, Judge, United States Customs Court, sitting by designation.

BALDWIN, Judge.

This appeal is from the decision of the Patent Office Board of Appeals affirming the examiner's rejection of claims 7-19 in appellant's application.¹ No claims have been allowed.

The Invention

The invention relates to catalysts for vapor phase partial oxidation of ethylene to ethylene oxide. Claims 7 and 15, the only independent claims in the case, read as follows:

7. A process for preparing a silver-supported catalyst for the improved production of ethylene oxide, said process comprising the steps of

(a) forming an aqueous solution of silver salt,

(b) immersing completely in said solution a carrier of inert, porous particles characterized by an average diameter not larger than about 3/16 inch, an average pore diameter of about 10 to 70 microns, and a surface area less than about one square meter per gram,

(c) impregnating said particles with said solution by soaking said particles therein for a period of at least about 5 minutes at a temperature of about 90° to 95°C, thereby permitting capillary action to fill effectively the pores of said particles with said solution,

(d) separating the impregnated particles from the remainder of said solution,

(e) drying the separated particles, whereby said silver salt is deposited uniformly throughout the pores of said particles, and

(f) activating the dried particles by heating them in air at a temperature sufficient to decompose the deposited silver salt. letters (a), (b), etc. supplied.

15. An oxygen-activated catalyst for use in the controlled catalystic sic oxidation of ethylene to ethylene oxide, said catalyst comprising about 5 to 25% by weight of silver, said silver being the thermal decomposition product of a pore solution-deposited silver salt uniformly distributed throughout the pores of inert, porous particles having an average diameter not larger than about 3/16 inch, an average pore diameter of from 10 to 70 microns, and a surface area less than about one square meter per gram.

Claim 8 places the temperature of step (f) at 200-300°C. Claim 9 recites that the solution formed in step (a) is 25-80% silver. Claim 10 specifies that the solution is formed in step (a) by adding silver oxide to an aqueous carboxylic acid solution. In claim 11 the carboxylic acid is lactic acid. Claim 12 adds an oxidizing agent to the solution to prevent premature reduction of the silver salt. Claim 13 adds an alkaline earth promoter to the solution. Claim 14 recites further specifics of the drying step (e). Product claims 16-19 depend on claim 15. Claim 16 recites a particle size of 1/16-3/16 inch. Claim 17 recites an apparent porosity of 48-54%. Claim 18 recites a surface area of 0.1 to 0.2 square meters. Claim 19 requires the particles to contain silica-alumina.

Appellants allege that their catalysts have both high selectivity and high productivity. Selectivity is a measure of the ability of a catalyst to prefer the partial oxidation reaction of ethylene over the total oxidation of ethylene to carbon dioxide. It is reported as the percentage of ethylene molecules oxidized which become ethylene oxide. A catalyst with high productivity produces a large amount of ethylene oxide per unit of catalyst and per unit of time.

The References

Aries² produces a catalyst for oxidation of ethylene to ethylene oxide by "impregnating the porous carrier with a solution of a silver salt of an organic acid and separating the excess liquid therefrom, * * * drying the impregnated carrier, then decomposing the silver salt by direct heat under controlled conditions." Aries does not describe at any length the physical characteristics of his carriers. His impregnation takes place at between about 100 and 125°C for 1-4 hours. The catalyst is activated by heating at from 300-500°C for a period of 12 to 18 hours in an inert gas. The solution employed can contain 25-75% silver salt. The preparation of the solution by adding silver oxide to a lactic acid solution is disclosed. The addition of an oxidizing agent to prevent premature reduction of the silver salt is disclosed. In his discussion of the prior art, Aries discloses the previously known method of applying the silver compound to the carrier in the form of a paste or slurry.

McClements et al. (McClements)³ discloses a method of coating a carrier with a silver catalyst by using a paste or slurry. The silver compound paste is coated on the support, dried and then activated:

That the silver catalyst must be activated by converting the silver oxide thermally to metallic silver is known. This is generally accomplished on commercial scale by treating the catalyst in large trays for several hours in a forced draft hot air oven at about 400°C.

McClements found improved results if the activation temperatures were only 250-340°C. McClements is also relied on for his statements about carriers:

Any of the known carriers employed in the production of silver surface catalysts used for catalyzing olefin to olefin oxide reactions may be used. Silica, fused alumina refractory materials, and beryllium oxide, including Alusite and Alundum, of a convenient size, say 1/8" to 1/2", preferably 3/8", may be used as the carrier.

McClements also supports the use of a barium promoter material.

Ameen⁴ is primarily relied on for his discussion of the physical characteristics of carriers:

So far as it is known, the prior art catalysts made from commercially available alumina have varying degrees of porosity which may be as much as 65% with a large number of small pores averaging in diameter about 2-30 microns. According to the present invention, the number of pores is considerably reduced and the remaining pores enlarged to diameters within the range of about 80-200 microns, preferably 100-150 microns, while maintaining a relatively high porosity of about 40-50 percent.

While he does use the word impregnate in describing his catalyst deposition process, it is clear from a reading of the whole patent that he uses a slurry coating technique. He states that his catalyst pellets "may be as large as 1/4-1/2" in diameter."

Hill⁵ discusses both the impregnation and the slurry methods of silver deposition. He uses the impregnation method, activating the catalyst by heating in the presence of hydrogen. Hill mentions that the carrier "alundum" is a mixture of Al2O3 and SiO2.

The Rejection

All the claims were rejected under 35 USC 103 as unpatentable over Aries combined with McClements et al. and Ameen. In the examiner's opinion the Ameen and McClements patents rendered it obvious to use a support having the physical characteristics recited in the claims and to use the Aries impregnation method. The examiner also considered that it would have been obvious to activate the Aries catalysts by heating in air at a temperature within the terms of the present claims in view of McClements.

The examiner also entered a rejection of product claims 15-19 under "35 U.S. C. 102 or at least 35 U.S.C. 103" as unpatentable over any of McClements, Hill, Ameens or Aries. The examiner considered that the claims do not recite "any characteristic which is not possessed by the supported silver catalysts disclosed by the references or which is unobvious to one of ordinary skill in the art."

The board generally adopted the examiner's reasoning. It pointed out that the physical characteristics discussed by Ameen, which overlap those recited in the claims, are those of the commercially available supports employed in prior art catalysts, which it would clearly be obvious to use. The board was also of the opinion that since Aries teaches his impregnation step as a cure for some of the difficulties encountered in the slurry deposition processes exemplified by McClements, it would have been obvious to substitute the Aries impregnation step for the slurry deposition steps in the McClements process.

Opinion

I. The Process Claims

After a thorough review of the references of record,⁶ we disagree with the examiner and the board that the proposed substitutions of activation steps would have been obvious to one of ordinary skill in the art. The Aries patent states and reiterates several times that the organic silver salt should be activated in an inert atmosphere. He warns against the use of a hydrogen atmosphere, because that decreases the selectivity of the catalyst. He most strenuously warns against the possibility of combustion:

The method of reduction is extremely important as an excessive amount of heat caused by the combustion of the organic material will result in a poor catalyst.

The only atmosphere utilized in his examples is an inert nitrogen atmosphere. In sum, the Aries patent itself teaches against the proposed combinations.

The solicitor argues:

The teaching of Aries that combustion should be avoided is not a warning that simple oxidation should be avoided, as interpreted by appellants (Br. 12-13). Of course, an "instance of burning" or consumption should be avoided. Moreover, the artisan of ordinary skill would be free to evaluate and question the teachings of Aries that nitrogen activation gives better results than activation in air or hydrogen. If air activation is best as argued by appellants, no reason appears as to why this would not readily be determined by the artisan of ordinary

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