Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Reexamination Certificate
2002-04-08
2004-06-15
Silverman, Stanley S. (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
C502S347000, C549S534000, C549S536000, C549S537000
Reexamination Certificate
active
06750173
ABSTRACT:
BACKGROUND OF THE INVENTION
1.Field of the Invention
The present invention relates to silver catalysts for the oxidation of ethylene to ethylene oxide, and especially to the preparation of catalyst supports or carriers having improved properties such that catalysts comprising the carriers have enhanced utility.
2. Description of the Prior Art
Processes for the production of ethylene oxide involve the vapor phase oxidation of ethylene with molecular oxygen using a solid catalyst comprised of silver on a support such as alumina. There have been efforts by many workers to improve the effectiveness and efficiency of the silver catalyst for producing ethylene oxide. U.S. Pat. No. 5,051,395 provides an analysis of these efforts of various prior workers.
U.S. Pat. Nos. 3,962,136, 4,010,115 and 4.012,425 describe the use of alkali metal promoters such as cesium to improve silver ethylene oxide catalysts.
Among the many prior teachings in this area is that of U.S. Pat. No. 4,007,135 (see also UK 1,491,447) which teaches variously silver catalysts for the production of ethylene and propylene oxides comprised of a promoting amount of copper, gold, magnesium, zinc, cadmium, mercury, strontium, calcium, niobium, tantalum, molybdenum, tungsten, chromium, vanadium, and/or preferably barium, in excess of any present in immobile form in the preformed support as impurities or cements (column 2, lines 1-15), silver catalysts for the production of propylene oxide comprising a promoting amount of at least one promoter selected from lithium, potassium, sodium, rubidium, cesium, copper, gold, magnesium, zinc, cadmium, strontium, calcium, niobium, tantalum, molybdenum, tungsten, chromium, vanadium and barium, in excess of any present in immobile form in the preformed support as impurities or cements (column 2, lines 16-34), as well as silver catalysts for producing ethylene oxide or propylene oxide comprising (a) a promoting amount of sodium, cesium, rubidium, and/or potassium, and (b) magnesium, strontium, calcium and/or preferably barium in a promoting amount (column 3, lines 5-8).
U.S. Pat. No. 5,057,481, and related U.S. Pat. No. 4,908,343 are concerned with silver ethylene oxide catalysts comprised of cesium and an oxyanion of a group 3b to 7b element.
U.S. Pat. No. 3,888,889 describes catalysts suitable for the oxidation of propylene to propylene oxide comprised of elemental silver modified by a compound of an element from Group 5b and 6b. Although the use of supports is mentioned, there are no examples. The use of cesium is not mentioned.
European Patent 0 266 015 and U.S. Pat. No. 4,766,105 deal with supported silver catalysts promoted with rhenium and a long list of possible copromoters.
U.S. Pat. No. 5,102,848 deals with catalysts suitable for the production of ethylene oxide comprising a silver impregnated support also having thereon at least one cation promoter such as cesium, and a promoter comprising (i) sulfate anion, (ii) fluoride anion, and (iii) oxyanion of an element of Group 3b to 6b inclusive of the Periodic Table.
U.S. Pat. No. 5,486,628 describes a silver catalyst promoted with alkali metal, rhenium and a rare earth or lanthanide component.
U.S. Pat. No. 5,011,807 is concerned with an ethylene oxide catalyst comprised of silver, alkali metal, a transition metal, and sulfur on alumina support.
The support of choice in the preparation of silver ethylene oxide catalysts has in the past been a solid inorganic material such as alumina, silica, or titania based compounds, or combinations thereof. Alpha alumina which may contain silica has been an especially preferred carrier.
Various patents have focused on the pretreatment of such carriers to improve the utility thereof. U.S. Pat. No. 5,102,848, for example, shows repeated alpha alumina support washing with 90° C. deionized water prior to deposition of the catalyst components. In the same patent, the carrier was also washed with HF solution at 25° C. In both cases there was no claim or demonstration of the effect of carrier washing on the catalyst's stability.
Later U.S. Pat. No. 6,103,916 similarly shows washing alpha alumina support with 90° C. water repeatedly prior to deposition of the catalytic components in ethylene oxide catalyst preparation.
The prior art has disclosed that the presence of either sodium or lithium will have a profound effect on the performance of the silver catalyst. The claims of different patents, however, are not in agreement regarding the effect of these two alkali metals.
The prior art has been inconsistent about the effect of sodium on the catalytic performance of the silver catalyst. For instance, several patents have disclosed the importance of the presence of a minimum amount of Na on the surface of the carrier:
1. U.S. Pat. No. 4,740,493 states that the carrier should have at least 50 ppm of soluble Na ion, see claims 1 and 5.
2. U.S. Pat. No. 4,414,135 states, in the first claim, the advantage of a catalyst containing at least 1000 ppm Na, in addition to Cs.
3. EP 0247 414 B2 discloses, in the first claim, the prerequisite of having a carrier containing at least 0.08% and up to 2% sodium. In addition, it is taught that the silver impregnating solution should also contain Na, along with K or Cs.
By contrast, the claims of the following patents have disclosed the importance of lowering the amount of surface sodium:
1. U.S. Pat. No. 4,368,144 states that better performance is obtained with carriers that contain no more than 0.07% Na.
2. WO 00/15333, 15334, 15335 disclose improvement of the properties of the carrier by lowering the concentration of ionizable species, especially Na and silica, using boiling de-ionized water. The patents disclose that it is preferred to lower the concentration of Na and silica by at least 5%.
In the preferred Na removal method, the carrier is repeatedly immersed in boiling water.
3. U.S. Pat. No. 6,103,916, EP 0937 498A1 claim that catalyst performance is improved when the carrier is washed by boiling in pure water until the water resistivity is more than 10,000 &OHgr;.cm.
Lithium has repeatedly been mentioned as an example of the alkali metals that can be added to improve the selectivity of the catalyst. It has been mentioned along with Na, K, Rb and Cs, with Cs as the preferred promoter alkali metal. In few cases, however, Li was added to Cs as a co-promoter, e.g. U.S. Pat. Nos. 4,272,443, 4,278,562, 4,212,772 and EP 0384 312 B1. Also, EP 0624 398 B1 discloses the addition of Li to the silver impregnating solution, along with the other promoters: Cs, W and Na (example 2).
Several patents have indicated that Li and Na are similar in their effect on the catalyst's performance:
1. U.S. Pat. No. 4,916,243 discloses using combinations of a Cs salt and a salt of any of the other alkali metals.
2. U.S. Pat. No. 4,820,675 discloses using combinations of a Cs salt and a salt of any of the other alkali metals. Addition of Li to Cs was augmented with addition of Na, column 7, and experiment 7-28, column 25.
3. U.S. Pat. No. 4,212,772 indicates that Na and Li are equivalent with respect to their influence on the catalyst's life, and selectivity, and that their mixtures, in all proportions gave favorable influence, column 2 line 49.
4. WO 00/15333, 15334, 15335 disclose improving the carrier via removing “ionizable species” from its surface. These ionizable species include sodium, cesium and lithium.
Treating the carrier with Li before use is known and has been disclosed in the following cases:
1. U.S. Pat. No. 5,705,661 discloses that the carrier was pretreated by impregnation with Li and Cs provided that at least 100 ppm Li will be present in the finished catalyst. The pretreatment was based on soaking the carrier in a water solution containing both Li and Cs carbonates, followed by drying.
2. EP 0716 884 B1 discloses the preference for pre-depositing a pre-dopant of at least one alkali metal, Li, K, or Cs. The pre-doping procedure involves vacuum impregnating the carrier for three minutes and then drying the carrier at a temperature of up to 1000° C. The amount
Bornn Errrol
Rizkalla Nabil
Zulauf Charles W.
Long William C.
Scientific Design Company, Inc.
Silverman Stanley S.
Strickland Jonas N.
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