Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Reexamination Certificate
2001-11-06
2003-06-17
Dunn, Tom (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
C502S344000, C502S348000, C502S300000, C502S340000, C502S325000, C502S302000, C502S216000, C502S208000, C502S202000, C502S224000
Reexamination Certificate
active
06579825
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a catalyst with improved catalytic properties, particularly a catalyst suitable for the preparation of epoxides.
BACKGROUND OF THE INVENTION
Methods have been described for lowering the total concentration of soluble species in the bulk of a catalyst carrier. These methods generally involve a process by which the carrier is manufactured in such a way so as to lower the concentration of those species throughout the bulk of the carrier. These approaches limit the formulation of carriers, often times with undesirable consequences such as high carrier density.
U.S. Pat. No. 4,797,270 discloses water washing to reduce the sodium content of an alumina powder. The pH of the wash water may need to be adjusted for extraction of other metals and Japanese patent JP56164013 discloses the use of a low pH (acid) to extract uranium and thorium from a calcined &agr;-alumina raw material.
U.S. Pat. Nos. 4,361,504 and 4,366,092 suggest that ethylene oxide catalyst be water washed after the deposition of silver or silver/gold on the carrier. EP-211521 discloses washing of a catalyst with hot water to remove basic materials left on the catalyst from a silver impregnation process or the physical deposition of alkali metals. U.S. Pat. No. 4,367,167 discloses a process for a supported catalyst wherein an impregnated support is immersed in an inert water immiscible organic solvent containing a dissolved aliphatic amine. U.S. Pat. No. 4,810,689 discloses depositing a silver compound, decomposing the silver compound to silver in the presence of an alkali metal compound, removing organic deposits by washing and introducing fresh alkali metal by impregnation during or after the washing stage. U.S. Pat. Nos. 4,186,106 and 4,125,480 disclose washing with an inert liquid after deposition of the catalytic metal and before deposition of a promoter material.
The prior art remains concerned with the total amount of impurities; i.e., impurities throughout the bulk. Unfortunately, the impurity removal techniques taught typically attack the carrier itself. It has surprisingly been found that controlling the solubilization rate of certain species found on a carrier surface results in a catalyst with improved catalytic properties.
SUMMARY OF THE INVENTION
According to the invention, there is provided a catalyst carrier comprising a material having a sodium solubilization rate no greater than 5 ppmw/5 minutes.
Another embodiment of the invention provides a catalyst comprising a carrier having a sodium solubilization rate no greater than 5 ppmw/5 minutes; and one or more catalytically reactive metals deposited on said carrier. A further embodiment of the invention provides a catalyst suitable for the vapor phase production of epoxides comprising a carrier having a sodium solubilization rate no greater than 5 ppmw/5 minutes; and one or more catalytically reactive metals deposited on said carrier.
A further embodiment of the invention provides a catalyst suitable for the vapor phase production of oxiranes from olefin and oxygen comprising a carrier having a sodium solubilization rate no greater than 5 ppmw/5 minutes; and catalytically reactive silver deposited on said carrier.
DETAILED DESCRIPTION
It has been found that carriers which have a controlled solubilization rate, in particular controlled sodium and/or soluble silicate solubilization rates, provide catalysts with improved catalytic properties, such as activity, selectivity and activity and/or selectivity performance over time. Controlling the solubilization rate is believed to work to improve the properties of most catalysts, no matter how impure the bulk carrier material. Further, controlling the solubilization rate will work for organic or inorganic carriers.
The typical carrier of the invention has a sodium solubilization rate in boiling water which is controlled to be no greater than 5 ppmw/5 minutes. As used herein, boiling water is deemed to have a temperature of 100° C. “Solubilization rate” as used herein refers to the measurable solubilization rate of the sodium in a solution after the carrier is placed in the solution for a specified time and at a ratio of boiling solution to carrier of 3:1. Thus, a solubilization rate in boiling water of 5 ppmw sodium/5 minutes is the amount of sodium measured in the water after the carrier has been in the boiling water for five minutes.
Carriers are commonly inorganic materials such as, for example, alumina-, silica-, or titania-based compounds, or combinations thereof, such as alumina-silica carriers. Carriers may also be made from carbon-based materials such as, for example, charcoal, activated carbon, or fullerenes. Ionizable species typically present on the inorganic type carriers include sodium, potassium, aluminates, soluble silicate, calcium, magnesium, aluminosilicate, cesium, lithium, and combinations thereof. Of particular concern are the ionizable anionic species present on the surface, particularly ionizable silicates. The solubilization rate of silicates may be measured by inductively coupled plasma (ICP) techniques and the amount of silicon species on a surface may be measured by x-ray photoelectron spectroscopy (XPS); however, since sodium is soluble in the same solutions that silicates are soluble in, the solubilization rate of sodium becomes a simpler check of the ionic species removal and it has been chosen as the indicator to define the present invention. Another measurement technique is to measure the electrical conductivity of the treatment solution.
Control of the solubilization rate may be obtained by a multiple of means. The raw materials for the carrier can be tightly controlled, for example. Or the surface of the carrier may be treated. As used herein, the “surface” of the carrier is that area of the carrier which may be measured by BET analysis. Specifically, the surface of the carrier is the site at which reaction takes place. Lowering the concentration of ionizable species on the surface of the carrier has been found to be an effective and cost efficient means of achieving the desired sodium solubilization rate. An “ionizable” species is a species which is capable of being rendered ionic, where the term “ionic” or “ion” refers to an electrically charged chemical moiety.
Lowering the surface solubilization rate of ionizable species may be accomplished by any means (i) which is effective in rendering the ionizable species ionic and removing the species, or (ii) which renders the ionizable species insoluble, or (iii) which renders the ionizable species immobile; however, use of aggressive medias is discouraged as these medias tend to dissolve the carrier, extract too much material from the bulk, and generate acidic or basic sites in the pores. Acids, which are considered aggressive media, will remove the cations on a carrier but are fairly ineffectual in removing the undesirable anions, such as silicates. Effective means of lowering concentration include washing the carrier; ion exchange; volatilizing, precipitating, or sequestering the impurities; causing a reaction to make the ionizable species on the surface insoluble; and combinations thereof. The bulk carrier may be treated, or the raw materials used to form the carrier may be treated before the carrier is manufactured. Even greater improvements in solubilization rate control are seen when both the carrier raw materials and the finished carrier are treated.
To make a catalyst from the carrier, the carrier is typically impregnated with metal compound(s), complex(es) and/or salt(s) dissolved in a suitable solvent sufficient to deposit or impregnate a catalytically effective amount of metal on the carrier. As used herein, “catalytically effective amount” means an amount of metal that provides a measurable catalytic effect. For example, a catalytically effective amount of metal when referring to an olefin epoxidation catalyst is that amount of metal which provides a measurable conversion of olefin and oxygen to alkylene oxide. In addition, one or more promoters may also be deposited on the c
Dunn Tom
Ildebrando Christina
Shell Oil Company
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