Chemistry: fischer-tropsch processes; or purification or recover – Group viii metal containing catalyst utilized for the...
Reexamination Certificate
1999-09-21
2001-08-21
Richter, Johann (Department: 1621)
Chemistry: fischer-tropsch processes; or purification or recover
Group viii metal containing catalyst utilized for the...
C518S700000, C502S314000, C502S327000, C502S331000, C502S332000, C502S336000, C502S338000, C502S301000, C420S077000, C420S089000, C420S090000, C420S091000, C420S590000
Reexamination Certificate
active
06277895
ABSTRACT:
BACKGROUND OF INVENTION
This invention pertains to skeletal iron catalyst and its preparation and use in Fischer-Tropsch and similar slurry-phase synthesis processes. More particularly, such skeletal iron catalyst utilized in slurry phase synthesis processes for H
2
+CO feedstreams has increased attrition resistance and improved catalyst/product liquid separation, while providing increased selectivity for producing C
2
-C
5
light olefin products.
Slurry phase Fischer-Tropsch (F-T) synthesis process technology is an important known route for indirect coal liquefaction for synthesis of liquid fuels from H
2
+CO feedstreams. Precipitated iron is currently a commonly used catalyst for such Fischer-Tropsch processes. However, precipitated iron catalysts are undesirably fragile and break down easily under reaction conditions into very fine particles, so that separation of such fine catalyst particles from reaction product waxes is difficult to accomplish and results in inferior product quality and significant catalyst loss. Such catalyst problems hinders commercial use of the process. For overcoming this problem, improved skeletal iron catalysts made according to this invention are provided by utilizing caustic extraction and/or leaching non-ferrous metals from specific iron metal alloy particles, and such skeletal iron catalysts have good particle strength and attrition resistance. Literature studies on such catalysts to date have focused on improvement of catalyst activity in simple gas-solid hydrogenation reaction system. Utilization of such improved skeletal iron catalyst in slurry-phase or three-phase gas-liquid-solid Fischer-Tropsch reaction processes fully realizes the advantages of such skeletal iron catalysts. By utilizing such improved skeletal iron catalysts, commercial slurry-bed Fischer-Tropsch synthesis to produce clean hydrocarbon transportation fuels from syngas feedstreams is greatly facilitated.
Light olefins C
2
− to C
5
− are key component materials in the petrochemical industry as important feedstocks and building blocks for the synthesis of a variety of chemical/petrochemical products. Conventionally, such light olefins are produced by thermal cracking of hydrocarbons ranging from ethane to vacuum gas oils, but not produced directly from natural gas which is essentially methane (CH
4
). Such thermal cracking is practiced under high temperatures (1,500-1,600° F.), thus requiring costly construction materials and consuming huge amounts of energy for feedstream heating and reaction. A commercially practiced technical route for making light olefins from natural gas is to first convert natural gas via steam reforming into a mixture of hydrogen and carbon monoxide, called synthesis gas or syngas. The current technology of converting syngas into olefins is a two-step catalytic conversion, the first step being catalytic conversion of syngas to methanol, followed by conversion of methanol into olefins. A unique catalyst/technology would be to directly convert synthesis gas into light olefins, without the necessity of an additional step for making methanol as an intermediate material. The skeletal iron catalyst, promoted with other metal ingredients and used in a fixed bed or in slurry-bed reactor system with liquid paraffin as the liquid medium, can advantageously convert syngas directly into light olefins C
2
−-C
5
− under mild conditions in a temperature range of 180-350° C. and a pressure range of 0.5-5.0 mPa.
Thus, this invention provides a unique skeletal iron catalyst having high activity for catalyzing the conversion of syngas feeds to a broad range of hydrocarbon products, and has high selectivity towards light olefins formation in a slurry-phase catalytic reactor system under mild conditions conventionally used in Fischer-Tropsch synthesis, so that the hydrocarbon product is rich in olefins.
SUMMARY OF INVENTION
This invention provides a unique skeletal iron catalyst material advantageously suitable for use in either fixed bed or slurry-phase Fischer-Tropsch synthesis processes for H
2
+CO feedstreams for producing clean liquid transportation fuels and light olefin products. The particulate skeletal iron catalyst contains at least 50 wt % iron and preferably 60-90 wt. % iron with remainder being smaller percentages of a non-ferrous metal selected from the group including aluminum, antimony, nickel, tin and zinc and a promotor metal selected from the group of calcium, copper, chromium, magnesium, and potassium. The final skeleton iron catalyst should have a surface area of 10-100 m
2
/g and average pore diameter of about 10-40 nm.
The unique skeletal iron catalyst material of this invention is made using a preparation method, which includes providing an iron powder mixed with a suitable non-ferrous metal powder selected from aluminum, antimony, silicon, tin, or zinc sufficient to provide 20-80 w. % iron, together with 0.01-5 wt. % of a promotor metal powder selected from calcium, copper, chromium, magnesium, or potassium. The mixed metal powders are heated and melted together to form an iron alloy precursor material which is then pulverized to 0.1-10 mm (100-10,000 micron ) particle size, followed by extracting and/or leaching the major portion of the non-ferrous metal from the iron using a suitable caustic solution of NaOH or KOH, and leaving mainly the iron portion as the skeletal iron catalyst material. The catalyst may be further pulverized and has smaller particle size surface area of 20-100 m
2
/g and an average pore diameter of 10-40 run.
The preparation method and pretreatment procedures for this skeletal iron catalyst are relatively simple and inexpensive. This skeletal iron catalyst has good particle strength and attristion resistance, and activity equivalent to that of precipitated iron catalyst because during reactions H
2
is easily absorbed in its skeletal structure, and produces larger yields of lower-molecular-weight liquid fuel range hydrocarbons and smaller amounts of wax products. Also, in F-T synthesis processes it is easier to separate the skeletal iron catalyst from the reactor liquid medium and product, and thus achieves high recovery of the catalyst and thereby provides hydrocarbon liquid products essentially free of catalyst fines.
Although the skeletal iron catalyst of this invention is useful in either fixed bed or slurry bed type F-T reactors, its use in slurry bed reactors is preferred. For use in fixed bed catalytic reactors, the catalyst particle size should be 1.0-10 mm, and for use in slurry bed type reactors the catalyst particle size should be 0.1-5 mm. For Fischer-Tropsch synthesis process utilizing this skeleton iron catalyst, useful reaction conditions are 0.5-2.5:1 H
2
/CO molar ratio, 200-500° C. temperature, 0.5-5.0 mPa pressure.
DESCRIPTION OF INVENTION
The skeletal iron catalyst of this invention is made utilizing the following basic steps:
1. Catalyst Preparation. Mix iron powder and a non-ferrous metal powder selected from aluminum, antimony, silicon, tin or zinc in proportion of 20-80 wt. % iron and also add 0.01-5 wt % of promotor metal powder selected from calcium, copper, chromium, magnesium or potassium into a suitable furnace such as an electric induction furnace and mix together such as by magnetic stirring. Then melt the mixed powders under inert gas protection to form an iron alloy material, cool the iron alloy to room temperature and pulverize it to provide 0.1-10 mm particle size precursor material. Contact the iron alloy particles with 10-50% NaOH or KOH caustic solution in a stirred container under inert gas protection of argon, hydrogen or nitrogen; maintain reaction temperature 30-95° C. for 2-150 minutes to provide a desired substantial degree of extraction and/or leaching a major portion of the non-ferrous portion, and leaving particles containing mainly ∝ -Fe and some Fe
3
O
4.
Adding the iron alloy powder to the caustic solution is usually preferred rather than the reverse order, as it results in skeletal iron catalyst having larger pore size. The skel
Lee Lap-Keung
Li Guohui
Lu Yijun
Zhou Jinglai
Zhou Peizheng
Hydrocarbon Technologies, Inc.
Parsa J.
Richter Johann
Wilson Fred A.
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