Chemistry of hydrocarbon compounds – Aromatic compound synthesis – Having alkenyl moiety – e.g. – styrene – etc.
Reexamination Certificate
2001-06-22
2002-11-26
Dang, Thuan D. (Department: 1764)
Chemistry of hydrocarbon compounds
Aromatic compound synthesis
Having alkenyl moiety, e.g., styrene, etc.
C585S374000, C585S624000, C585S660000
Reexamination Certificate
active
06486370
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a hydrocarbon dehydrogenation process using a layered catalyst composition at select operating conditions for increased catalyst stability.
BACKGROUND OF THE INVENTION
Platinum based catalysts are used for numerous hydrocarbon conversion processes. In many applications promoters and modifiers are also used. One such hydrocarbon conversion process is the dehydrogenation of hydrocarbons, particularly alkanes such as isobutane which are converted to isobutylene. For example, U.S. Pat. No. 3,878,131 (and related U.S. Pat. Nos. 3,632,503 and 3,755,481) discloses a catalyst comprising a platinum metal, a tin oxide component and a germanium oxide component. All components are uniformly dispersed throughout the alumina support. U.S. Pat. No. 3,761,531 (and related U.S. Pat. No. 3,682,838) discloses a catalytic composite comprising a platinum group component, a Group IVA (IUPAC 14) metallic component, e.g., germanium, a Group VA (IUPAC 15) metallic component, e.g., arsenic, antimony, and an alkali or alkaline earth component all dispersed on an alumina carrier material. Again all the components are evenly distributed on the carrier.
U.S. Pat. No. 6,177,381 describes a dehydrogenation process using a layered catalyst composition. Example 7 of U.S. Pat. No. 6,177,381 describes testing of Catalysts A, B, E, and F for dehydrogenation activity using a hydrocarbon feed. A water concentration of 2000 ppm based on hydrocarbon weight was injected. The deactivation rates of Catalysts A, B, E, and F were 0.052, 0.032, 0.050, and 0.033° F./hr, respectively.
Although these deactivation rates are relatively low, other dehydrogenation processes are sought that have even lower deactivation rates.
SUMMARY OF THE INVENTION
An improved dehydrogenation process using a layered catalyst composition which exhibits excellent stability at a critical combination of catalyst properties and operating conditions is disclosed. When the thickness of the outer layer of the layered catalyst is in the range of from 40 to 150 microns, the loading of the platinum group metal in the entire layered catalyst is in the range of from about 5 to about 22 gram-mole of the platinum group metal per cubic meter of the entire layered catalyst, and the concentration of the platinum group metal in the outer layer of the layered catalyst is from about 0.02 to about 0.26 gram-mole of the platinum group metal per kilogram of the outer layer, then excellent stability results, provided that the amount of water passed to the layered catalyst is less than 2000 wt-ppm, and preferably less than 100 wt-ppm, and more preferably less than 10 wt-ppm based on the amount of hydrocarbon passed to the layered catalyst. This result was unexpected because previously it had been thought that such high amounts of platinum-group metal in the outer layer would adversely affect stability. However, it is now recognized that even dehydrogenation processes using catalysts that have relatively high amounts of platinum-group metal in the outer layer can be operated at low water concentrations and thus achieve excellent catalyst stability.
In addition, the process disclosed exhibits better selectivity than processes of the prior art, in terms of total selectivity to normal olefins.
In a broad embodiment, this invention is a hydrocarbon dehydrogenation process comprising contacting a hydrocarbon stream with a layered composition under dehydrogenation conditions to give a dehydrogenated product. The layered composition comprises an inner core and an outer layer bonded to the inner core. The outer layer comprises an outer refractory inorganic oxide and has a thickness of from about 40 to about 150 microns. The outer layer also has, uniformly dispersed thereon, at least one platinum group metal and at least one promoter metal, where the concentration of the at least one platinum group metal in the outer layer is from about 0.02 to about 0.26 gram-mole of the platinum group metal on an elemental basis per kilogram of the outer layer. The layered composition has a loading of the at least one platinum group metal of from about 5 to about 22 gram-mole of the platinum group metal on an elemental basis per cubic meter of the layered composition. The layered composition further has dispersed thereon at least one modifier metal. The inner core and the outer refractory inorganic oxide comprise different materials. The dehydrogenation conditions comprise a weight of water passed to the layered composition based on the hydrocarbon weight passed to the layered composition of less than 2000 ppm.
Other objects and embodiments are described in the detailed description of the invention.
INFORMATION DISCLOSURE
U.S. Pat. No. 6,177,381 describes a dehydrogenation process using a layered catalyst composition. The entire teachings of U.S. Pat. No. 6,177,381 are incorporated herein by reference.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a dehydrogenation process that uses layered catalyst composition. The layered catalyst composition comprises an inner core composed of a material which has substantially lower adsorptive capacity for catalytic metal precursors, relative to the outer layer. Some of the inner core materials are also not substantially penetrated by liquids, e.g., metals including but not limited to aluminum, titanium and zirconium. Examples of the inner core material include, but are not limited to, refractory inorganic oxides, silicon carbide and metals. Examples of refractory inorganic oxides include without limitation alpha alumina, theta alumina, cordierite, zirconia, titania and mixtures thereof A preferred inorganic oxide is alpha alumina.
These materials which form the inner core can be formed into a variety of shapes such as pellets, extrudates, spheres or irregularly shaped particles although not all materials can be formed into each shape. Preparation of the inner core can be done by means known in the art such as oil dropping, pressure molding, metal forming, pelletizing, granulation, extrusion, rolling methods and marumerizing. A spherical inner core is preferred. The inner core whether spherical or not has an effective diameter of about 0.05 mm to about 5 mm and preferably from about 0.8 mm to about 3 mm. For a non-spherical inner core, effective diameter is defined as the diameter the shaped article would have if it were molded into a sphere. Once the inner core is prepared, it is calcined at a temperature of about 400° C. to about 1500° C.
The inner core is now coated with a layer of a refractory inorganic oxide which is different from the inorganic oxide which may be used as the inner core and will be referred to as the outer refractory inorganic oxide. This outer refractory oxide is one which has good porosity, has a surface area of at least 50 m
2
/g, and preferably at least 150 m
2
/g, an apparent bulk density of about 0.2 g/ml to about 1.0 g/ml and is chosen from the group consisting of gamma alumina, delta alumina, eta alumina, theta alumina, silica/alumina, zeolites, non-zeolitic molecular sieves (NZMS), titania, zirconia and mixtures thereof. It should be pointed out that silica/alumina is not a physical mixture of silica and alumina but means an acidic and amorphous material that has been cogelled or coprecipitated. This term is well known in the art, see e.g., U.S. Pat. Nos. 3,909,450; 3,274,124; and 4,988,659, all of which are incorporated by reference. Examples of zeolites include, but are not limited to, zeolite Y, zeolite X, zeolite L, zeolite beta, ferrierite, MFI, mordenite and erionite. Non-zeolitic molecular sieves (NZMS) are those molecular sieves which contain elements other than aluminum and silicon and include silicoaluminophosphates (SAPOs) described in U.S. Pat. No. 4,440,871, ELAPOs described in U.S. Pat. No. 4,793,984, MeAPOs described in U.S. Pat. No. 4,567,029 all of which are incorporated by reference. Preferred refractory inorganic oxides are gamma and eta alumina.
A preferred way of preparing a gamma alumina is by the well-known oil drop method which is
Bozzano Andrea G.
Broerman Andrew W.
Lawson R. Joe
Rende Dean E.
Steigleder Karl Z.
Dang Thuan D.
Moore Michael A.
Paschall James C.
Tolomei John G.
UOP LLC
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