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Patent Issued for Fischer-Tropsch Catalysts (USPTO 9242229)

By a News Reporter-Staff News Editor at Journal of Engineering -- According to news reporting originating from

Alexandria, Virginia
, by VerticalNews journalists, a patent by the inventors Koranne, Manoj M. (
Clarksville, MD
); Rytter, Erling (Trondheim, NO); Eri, Sigrid (Ranheim, NO); Borg, Oyvind (Trondheim, NO), filed on July 29, 2011, was published online on January 26, 2016.

The assignee for this patent, patent number 9242229, is GTL.F1 AG (

Zurich
, CH).

Reporters obtained the following quote from the background information supplied by the inventors: "Conversion of natural gas to liquid hydrocarbons ('Gas To Liquids' or 'GTL' process) is based on a 3 step procedure consisting of: 1) synthesis gas production; 2) synthesis gas conversion by Fischer-Tropsch ('FT') synthesis; and 3) upgrading of FT products (wax and naphtha/distillates) to final products.

"The Fischer-Tropsch reaction for conversion of synthesis gas, a mixture of CO and hydrogen, possibly also containing essentially inert components like CO.sub.2, nitrogen and methane, is commercially operated over catalysts containing the active metals Fe or Co. Iron catalysts are best suited for synthesis gas with low H.sub.2/CO ratios (<1.2), e.g. synthesis gas produced from coal or other heavy hydrocarbon feedstock, where this ratio is considerably lower than the consumption ratio of the FT-reaction (2.0-2.1).

"To achieve sufficient catalytic activity, it is customary to disperse a catalytically active metal on a catalyst carrier, often referred to as the support material. In this way, a larger portion of the metal is exposed as surface atoms where the reaction can take place. Typically, support materials are alumina, silica and titania based. In addition, different promoters are also added to further increase catalytic activity, and typical promoters may be rhenium, ruthenium and platinum. The F-T process can be carried out either in a fixed bed reactor or a slurry bed reactor. In case of a slurry bed process, the catalyst particles are suspended in oil with gaseous reactants being bubbled into the reactor. For either process to be economically viable, the catalyst must exhibit good performance for a long period of time without significant loss in catalytic activity. Typically, catalyst deactivates because of one or more of the following issues: (a) poisoning of the active catalytic metal (e.g. cobalt), (b) loss of catalytic metal surface area (e.g. via sintering), © loss of active metal species due to reaction with support, and (d) attrition.

"The attrition of the catalyst, i.e. issue (d) above, is primarily dependent on the strength of the support for the catalytically active metal. Using slurry bed catalysts are subjected to a number of collisions either with other particles or with the reactor walls. This causes the catalyst particles to 'attrit' or break into smaller particles. Smaller particles are not retained in the reactor, and as a result the activity declines absent continuous addition of fresh catalyst. In order to enhance performance of the catalyst and to improve the catalyst life, a support must therefore exhibit high attrition resistance.

"High surface area alumina is commonly used as a catalyst support for F-T. Supports having high surface area provide the necessary support for dispersing catalytic sites throughout the catalyst. High surface area aluminas are conventionally prepared by calcining an aluminum hydroxide composition such as boehmite. Calcined, high surface area alumina per se, however, does not exhibit good attrition resistance. Indeed, it is also largely believed that aluminas after calcination cannot be easily bound into hard particles. Hence, there is a tendency to use boehmite aluminas as support precursors, which are slurried in water and 'peptized' in the presence of an acid such as nitric or hydrochloric acid, followed by drying and calcinations to give attrition resistant particles. This alternative presents its own problem because these peptized boehmitic aluminas slurries gel at high solids content and need to be diluted before drying and calcination. Processing the alumina at high solids content is desirable not only to get high production rates, but also to yield a strong particle of desired particle size upon spray drying.

"In addition, and as reference with respect to issue © above, high surface area alumina supports react with active metal precursor of cobalt to form Co-aluminate spinel upon calcination. This transforms the active Co metal to 'inactive' spinel Co-aluminate and thus decreases the catalyst activity.

"In order to prevent Co-aluminate spinel formulation, divalent metals like Ni, Zn, and Mg can be added to an alumina support to form the spinel phase 'a priori' and thus prevent the formation of inactive Co-aluminate. The divalent metal aluminate spinels are formed upon high temperature calcinations above 650.degree. C. Such spinel materials do not exhibit high strength, however, and can easily break into smaller particles. In other words, such spinel phase-based particles generally do not have sufficient attrition resistance.

"It has been shown that if the spinels compositions are calcined at very high temperatures, in excess of 1100.degree. C., the attrition resistance improves significantly (see WO 2005/072866 A1 or US 2007/0161714). In addition to requiring high calcination temperatures, it is also apparent that high levels of divalent metals are needed to attain the good attrition resistance. Typically, the divalent compound is in excess of 10 wt % (as metal) in loading.

"It has also been shown that, as a result of high temperature calcinations, the support pore diameter shifts to high pore modes. Catalysts made from these high temperature calcined spinel supports therefore have high selectivity to high hydrocarbons in addition to the aforementioned attrition resistance. The practical use of these supports, however, is limited due to expensive processing steps, and large amounts of expensive divalent metal compounds added as dopants. Furthermore, large amount of divalent dopant compounds poses the risk of leaching out of the spinel structure and adversely affecting the catalyst activity."

In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventors' summary information for this patent: "It is an object of the present invention to provide a method of producing such a catalyst with a high resistance to attrition and at a lower cost, minimizing the amount of costly components and costly processing steps.

"Certain aspects of the present invention are concerned with aluminium oxide, as a support material.

"According to one aspect of the invention, there is provided a method of producing a modified aluminium oxide supported catalyst, which comprises the following steps: an initial step of forming a slurry by mixing aluminium oxide and a metal compound capable of forming a spinel phase and a soluble compound of trivalent aluminium; a shaping step in which solid material from the slurry is shaped into a solid precursor material; a first calcination step in which the precursor material is calcined at a temperature of at least 700.degree. C. to produce a modified aluminium oxide support material including a metal aluminate spinel phase compound formed by the metal capable of forming a spinel phase and the aluminium oxide; an impregnation step in which the modified aluminium oxide support material is impregnated with a source of catalytically active metal; and a second calcination step in which the impregnated modified aluminium oxide support material is calcined at a temperature of at least 150.degree. C. to produce the modified aluminium oxide supported catalyst.

"Preferably, the aluminium oxide is selected from the group consisting of gamma alumina, delta alumina, theta alumina, eta alumina, rho alumina and mixtures thereof. Preferably, the aluminium oxide predominantly comprises gamma alumina. Preferably, the gamma alumina is prepared by heating boehmite alumina at a temperature sufficient to convert boehmite alumina to gamma alumina. Preferably, the boehmite alumina is heated to a temperature in the range of 400.degree. C. to 700.degree. C.

"The metal capable of forming a spinel phase with aluminium oxide will hereinafter be referred to as 'the spinel forming metal' and is a divalent.

"Preferably, the source of the spinel forming metal comprises a source of cobalt, zinc, copper, magnesium, calcium, manganese, nickel or iron. Preferably, the source of the spinel forming metal is a soluble metal salt and is preferably selected from the group consisting of zinc nitrate, nickel nitrate, and magnesium nitrate. Preferably the amount of spinel forming metal added is in the range of 1 to 50 wt %, expressed as the wt % of the spinel forming metal based on the total weight of modified support preferably 2 to 20 wt %, more preferably 3 to 12 wt %.

"A soluble compound of trivalent aluminium is combined in the slurry of alumina and the spinel forming metal. Preferably, the soluble compound of trivalent aluminium is selected from the group consisting of aluminium nitrate, aluminium chlorohydrol, aluminium sulphate, aluminium chloride, aluminium acetate, aluminium formate.

"Preferably, mixing the slurry reduces the particle size of solids in the mixture to a median particle size that is less then than ten microns, preferably without significant gelling. The mixing may be conducted in a mill. Preferably, the mixing reduces the particle size of solids in the mixture to a median particle size in the range of 1 to 5 .mu.m.

"Preferably, the first calcination step is carried out at a temperature in the range of 700 to 1300.degree. C., more preferably at a temperature in the range of 700 to 1050.degree. C., preferably 900 to 1050.degree. C. Optionally, the product from the first calcination step, further comprises alpha alumina.

"Optionally, before the shaping step, the solid material is washed at least once. Preferably the washing is performed with water containing less than 300 ppm calcium and/or less than 300 ppm sodium. Preferably, the material from the slurry is dried at a temperature in the range of 100 to 400.degree. C. to form particles having a median particle size in the range of 20 to 100 microns, prior to the first calcination. Preferably, the drying is carried out in a spray drier. Preferably, the forming step is selected from the group consisting of spray-drying, peletization and extrusion.

"The first calcination step may be carried out in several calcination steps, each of which covers a part of the temperature range up to the maximum temperature.

"A preferred embodiment is constituted by a method in which the modified aluminium oxide support is produced by: combining aluminium oxide selected from the group consisting of gamma alumina, delta alumina, theta alumina, eta alumina and mixtures thereof, a 2-valent and/or soluble compound of a spinel forming metal, or mixture of metals, and a soluble compound of trivalent aluminium selected from the group consisting of aluminium nitrate, aluminium chlorohydrol, aluminium sulphate, aluminium chloride and mixtures thereof; reducing the particle size of the solids in the mixture to a median particle size of less than ten microns; drying the mixture at a temperature in the range of 100 to 400.degree. C.; and calcining the dried mixture at a temperature in the range of 700 to 1300.degree. C.

"Preferably, in this method, the particle size of solids in the mixture is reduced to a median particle size in the range of 1 to 5 microns, the mixture is dried at a temperature in the range of 100 to 400.degree. C., and the dried mixture is calcined at a temperature in the range of 700 to 1050.degree. C. Preferably, the aluminium oxide is gamma alumina, the spinel forming metal compound is a metal nitrate salt and the trivalent aluminium is aluminium nitrate. Preferably, the method includes drying the mixture at a temperature in the range of 100 to 400.degree. C. to form particles having a median particle size in the range of 20 to 100 microns prior to the first calcination step.

"Another important step in the catalyst preparation is the impregnation with catalytically active metal. A number of different procedures have been described in the literature, including the case of alternative solvents and chemicals. Preferably, in the present invention, the impregnation step comprises an incipient wetness treatment in which an aqueous solution of the catalytically active metal is mixed with the modified support material until the pores are filled and the impregnated modified support material is then dried, prior to the second calcination step.

"The preferred procedure involves aqueous incipient wetness with solutions of cobalt nitrate (Co(NO.sub.3).sub.2) and perrhenic acid (HReO.sub.4). Alternatives include using cobalt acetate(s), cobalt halide(s), cobalt carbonyl(s), cobalt oxalate(s), cobalt phosphate(s), cobalt (hexa)amine salt(s), organic cobalt compounds, ammonium perrhenate, rhenium halide(s), rhenium carbonyl(s), industrial metal salt solutions and organic solvents. However, the impregnation technique may encompass all available methods besides incipient wetness, such as precipitation, impregnation from slurry with surplus liquid, chemical vapor deposition, etc.

"Impregnation may be in a single or multiple steps from a mixed aqueous solution of appropriate metal salts, generally of cobalt nitrate and perrhenic acid. Preferably, the impregnation technique is by the pore filling or 'incipient wetness' method that implies that the solution is mixed with the dry support until the pores are filled. The definition of the end point of this method may vary somewhat from laboratory to laboratory, giving an impregnated catalyst that has a completely dry appearance to one which appears sticky or snow-like. However, in no instance is there any free flowing liquid present. Preferably, the amount of aqueous solution used in the impregnation is 0.05-2 times larger than the measured pore volume of the catalyst support.

"The impregnated catalyst is dried, preferably at 80-120.degree. C., to remove water from the catalyst pores before being calcined at preferably 200-600.degree. C.

"There are several variations to these procedures that will not affect the essence of the invention. The calcinations in the present case are preferably performed in a stationary oven with a certain temperature ramping speed of 2.degree. C./min. It should be understood that the ramping speed could be varied and that any standard or specially designed calcination equipment could be applied by adjusting the conditions properly. Examples of such calcination equipment are continuous or batch-wise operated rotational calciners and conveyor belt type calciners.

"Preferably, after impregnation the cobalt content of the impregnated modified support material is in the range of 3 to 60 wt %, measured as the metal weight of the total catalyst after reduction, preferably 5 to 30 wt %, more preferably 8 to 18 wt %. Preferably, the impregnated modified support material is calcined at a temperature in the range 200 to 600.degree. C. Preferably after the second calcination step, the supported catalyst material is activated. Preferably, the activation step comprises reduction of a substantial portion of the catalytically active metal compound present to the metal, preferably more than 60%, more preferably more than 70%. Preferably, the reduction is carried out by treating the catalyst material with a reducing gas. Preferably, the reducing gas is selected from the group consisting of hydrogen, carbon monoxide and a mixture thereof, optionally mixed with an inert gas. Preferably, the reduction is carried out at an activation temperature in the range 20 to 500.degree. C., more preferably in the range 250 to 400.degree. C.

"Preferably, prior to impregnation, the modified support has an ASTM attrition modified value of less than 10%, preferably less than 5%, more preferably less than 2%.

"The present invention extends to a catalyst produced by a method according to the present invention, which comprises a support derived from aluminium oxide in the presence of a soluble compound of trivalent aluminium, the aluminium oxide being modified by the presence of a spinel phase formed from the aluminium oxide and spinel forming metal, and impregnated with a catalytically active metal, whereby the spinel is substantially homogeneously distributed throughout the aluminium oxide and the catalytically active metal is absorbed on to the surface of the modified support particles.

"Preferably, the source of spinel forming metal is soluble compound. The spinel forming metal preferably comprises nickel or zinc and the catalytically active metal is preferably cobalt. Preferably, the cobalt content of the catalyst is from 5 to 30% by weight, preferably 8 to 18% by weight. The catalyst may include a promoter, preferably up to 3% by weight. Preferably, the promoter is selected from rhenium and platinum.

"The present invention also extends to a process for the production of hydrocarbons which comprises subjecting H.sub.2 and CO gases to a Fischer-Tropsch synthesis reaction in a reactor in the presence of the catalyst of the present invention.

"Preferably, the Fischer-Tropsch synthesis reaction is a three-phase reaction in which the reactants are gaseous, the product is at least partially liquid and the catalyst is solid. Preferably, the reaction is carried out in a slurry bubble column reactor. Preferably, the H.sub.2 and CO are supplied to a slurry in the reactor, the slurry comprising the catalyst in suspension in a liquid including the reaction products of the H.sub.2 and CO, the catalyst being maintained in suspension in the slurry at least partly by the motion of the gas supplied to the slurry.

"Preferably the reaction temperature is in the range 190 to 280.degree. C., preferably 210 to 250.degree. C., and the pressure is in the range 10 to 60 bar, preferably 15 to 35 bar. Preferably the ratio H.sub.2/CO of the gases supplied to the Fischer-Tropsch synthesis reactor is in the range 1.1 to 2.2, preferably 1.5 to 1.95, and the superficial gas velocity in the reactor is in the range 5 to 60 cm/s, preferably 20 to 40 cm/s.

"Preferably, the product of the Fischer-Tropsch synthesis reaction is subsequently subjected to post-processing. The post-processing may include de-waxing hydro-isomerization, hydro-cracking and combinations of these.

"The present invention is generally but not exclusively concerned with Co-based catalysts, in particular, supported Co-based catalysts. A variety of products can be made by the FT-reaction, but from supported cobalt, the primary product is long-chain hydrocarbons that can be further upgraded to products like diesel fuel and petrochemical naphtha. Byproducts can include olefins and oxygenates.

"The present invention may be carried into practice in various ways and will now be illustrated in the following non-limiting examples."

For more information, see this patent: Koranne, Manoj M.; Rytter, Erling; Eri, Sigrid; Borg, Oyvind. Fischer-Tropsch Catalysts.

U.S.
Patent Number 9242229, filed July 29, 2011, and published online on January 26, 2016. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=9242229.PN.&OS=PN/9242229RS=PN/9242229

Keywords for this news article include: Cobalt, Chemistry, GTL.F1 AG, Heavy Metals, Hydrocarbons, Aluminium Oxide, Aluminium Nitrate, Organic Chemicals, Transition Elements.

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