Compositions – Gaseous compositions – Carbon-oxide and hydrogen containing
Reexamination Certificate
2000-12-22
2003-04-08
Langel, Wayne A. (Department: 1754)
Compositions
Gaseous compositions
Carbon-oxide and hydrogen containing
C502S174000, C502S209000, C502S213000, C502S226000, C502S227000, C502S229000, C502S302000, C502S303000, C502S328000, C502S330000, C502S335000, C502S337000
Reexamination Certificate
active
06544439
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a novel catalyst composition comprising a crystalline metal oxide component, a method of making the composition, and a hydrocarbon conversion process using the composition. More specifically, the invention relates to a phosphate- or vanadate-based crystalline catalyst with nickel incorporated into the crystalline metal oxide framework, deposited thereon, or both. The catalyst is used for the production of synthesis gas from light hydrocarbons (e.g. methane).
BACKGROUND OF THE INVENTION
The combustion stoichiometry of methane gas at 1000° F. is highly exothermic and produces CO
2
and H
2
O according to the following reaction:
CH
4
+2O
2
→CO
2
+2H
2
O (−190.3 kcal/g mol CH
4
)
The formed gases are not useful for the production of valuable chemical compounds, and the stability of these products complicates their conversion to more desirable products. Also, further processing is problematic due to the high temperatures generated in the combustion reaction, presenting problems with respect to downstream reactors and catalysts.
In contrast, useful gases, known as synthesis gases or syngases, are produced from the coversion of methane and light hydrocarbons to a mixture containing CO and H
2
. Conventional syngas-generating processes include the gas phase partial oxidation process (U.S. Pat. No. 5,292,246), the autothermal reforming process (U.S. Pat. No. 5,492,649), and various other processes involving CO
2
or steam reforming. These reactions are all significantly less highly exothermic than combustion, and the choice of a particular route depends primarily on the desired product composition, as determined by its end use. Syngas is typically used to produce methanol, ammonia, or heavier hydrocarbon fuels through Fisher-Tropsch technology.
The partial oxidation of hydrocarbons can generally proceed according to several pathways, depending upon the relative proportions of the hydrocarbons and oxygen in the reaction mixture as well as the conditions used. In the case of methane, for example, the following reactions are possible:
2CH
4
+2O
2
→2CO+2H
2
+2H
2
O (−64 kcal/g mol CH
4
)
2CH
4
+1.5O
2
→2CO+3H
2
+H
2
O (−34.9 kcal/g mol CH
4
)
or
2CH
4
+O
2
→2CO+4H
2
(−5.7 kcal/g mol CH
4
)
The last reaction is the most desirable in terms of both the quality of the syngas produced and the minimization of liberated heat to protect the apparatus and catalyst bed from thermal damage. A further benefit of this pathway is a reduced formation of steam and corresponding increased yield of hydrogen and carbon monoxide. When combined with the reforming reaction, this reaction product provides a high quality syngas. Therefore, partial oxidation is usually optimal when the carbon to oxygen molar ratio (C:O ratio) in the feedstock gas mixture is maximized. Unfortunately, the improvements in product quality at high C:O ratios are largely offset by a greater tendency of coke formation reactions limiting the partial oxidation catalyst life. As a result, operation is normally constrained to C:O ratios that are lower than ideal for product quality purposes, but that provide reasonable catalyst stability. By lower product quality it is meant that downstream operational costs, such as those associated with recycling unconverted syngas, are increased.
In the autothermal reforming process, the methane and oxygen-containing feeds are mixed and reacted in a diffusion flame. The oxidized effluent is then typically passed into a steam reforming zone where the effluent is contacted with a conventional steam reforming catalyst. The catalyst may be present as a simple fixed bed or impregnated into a monolith carrier or ceramic foam. The high temperature in the catalytic reforming zone places great demands on the reforming catalyst in terms of its ability to substantially retain its catalytic activity and stability over many years of use. As in the partial oxidation process, catalyst coking problems associated with autothermal reforming normally require operation at sub-optimal conditions in terms of the feed stock composition and product quality. Specifically, the level of steam injection required to suppress coking is beyond that dictated solely by concerns about optimizing product quality and minimizing utility costs. In terms of the rate of catalyst coke formation, the molar C:H
2
O ratio for steam reforming is analogous to the C:O ratio used in partial oxidation. Higher values generally mean a greater coking tendency.
According to the autothermal steam reforming process of U.S. Pat. No. 5,492,649, the production of high amounts of carbon or soot in the diffusion flame oxidation step is avoided by mixing the methane gas with the oxidizer gas while swirling the latter at the injection nozzle to provide a large number of mixing points in the diffusion flame. However, this process still causes partial oxidation in the diffusion flame, resulting in over-oxidation and an excessively high temperature effluent. The heat generated can damage the steam reforming catalyst as well as the face of the injector. Published Canadian Patent Application No. 2,153,304 teaches that the formation of soot is avoided or reduced by actually reducing the steam to carbon molar feed ratio, combined with increasing the steam reforming temperature to between 1100-1300° C., and/or introducing the gaseous hydrocarbon feed in increments.
The prior art dealing with partial oxidation and reforming is concerned with overcoming undesired side reactions that lead to the formation of catalyst coke. However, the methods employed have largely been confined to process adjustments, such as those discussed in Canadian Patent Application 2,153,304. As mentioned previously, however, the manipulation of reaction compositions and conditions often restrains partial oxidation and reforming operations to the extent that product quality suffers and/or larger equipment and utilities are imposed.
In terms of adjusting catalyst properties to limit coke formation under a wide range of conditions, it is well known that the use of noble metals (e.g. Pt) provides a solution. However, noble metal-containing catalysts are generally cost prohibitive for industrial applications. Instead, catalysts used in the various types of steam reforming processes normally contain a metal component selected from uranium, Group VII metals, and Group VIII metals. These metals may be combined or used with other metals such as lanthanum and cerium. Generally, the metals are supported on thermally stable inorganic refractory oxides. Preferred catalyst metals are the Group VIII metals, particularly nickel. In the case of nickel, essentially any nickel-containing material has been found useful, e.g. nickel supported on alpha-alumina, nickel aluminate materials, nickel oxide. Preferably, supported nickel-containing materials are used.
Support materials include alpha-alumina, aluminosilicates, cement, and magnesia. Alumina materials, particularly fused tabular alumina, are particularly useful as catalyst support. Preferred catalyst supports may be Group II metal oxides, rare earth oxides, alpha-alumina, modified alpha-aluminas, alpha-alumina-containing oxides, hexa-aluminates, calcium aluminate, or magnesium-alumina spinel. In some cases, catalysts are stabilized by addition of a binder, for example, calcium aluminum oxide. It is preferred to maintain a very low level of silicon dioxide in the catalyst, e.g. less than 0.3 wt-% to avoid volatilization and fouling of downstream equipment. The shape of the catalyst carrier particles may vary considerably. Raschig rings 16 mm in diameter and height, and having a single 6-8 mm hole in the middle, are well known in the art. Other physical forms, such as saddles, stars, beads, and spoked wheels are commercially available.
Catalysts comprising calcium nickel phosphates used in dehydrogenation applications are disclosed in U.S. Pat. No. 3,595,808, where a crystalline hydroxyapatite phase has been known to r
Bauer John E.
Lewis Gregory J.
Gooding Arthur E.
Langel Wayne A.
Molinaro Frank S.
Tolomei John G.
UOP LLC
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