Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C5/00—Preparation of hydrocarbons from hydrocarbons containing the same number of carbon atoms
  • C07C5/32—Preparation of hydrocarbons from hydrocarbons containing the same number of carbon atoms by dehydrogenation with formation of free hydrogen
  • C07C5/373—Preparation of hydrocarbons from hydrocarbons containing the same number of carbon atoms by dehydrogenation with formation of free hydrogen with simultaneous isomerisation
  • C07C5/393—Preparation of hydrocarbons from hydrocarbons containing the same number of carbon atoms by dehydrogenation with formation of free hydrogen with simultaneous isomerisation with cyclisation to an aromatic six-membered ring, e.g. dehydrogenation of n-hexane to benzene
  • C07C5/41—Catalytic processes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
  • B01J23/16—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
  • B01J23/24—Chromium, molybdenum or tungsten
  • B01J23/28—Molybdenum
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
  • B01J27/20—Carbon compounds
  • B01J27/22—Carbides
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B32/00—Carbon; Compounds thereof
  • C01B32/90—Carbides
  • C01B32/907—Oxycarbides; Sulfocarbides; Mixture of carbides
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
  • C01G39/00—Compounds of molybdenum
  • C01G39/02—Oxides; Hydroxides
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C5/00—Preparation of hydrocarbons from hydrocarbons containing the same number of carbon atoms
  • C07C5/02—Preparation of hydrocarbons from hydrocarbons containing the same number of carbon atoms by hydrogenation
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C5/00—Preparation of hydrocarbons from hydrocarbons containing the same number of carbon atoms
  • C07C5/22—Preparation of hydrocarbons from hydrocarbons containing the same number of carbon atoms by isomerisation
  • C07C5/2206—Catalytic processes not covered by C07C5/23 - C07C5/31
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2002/00—Crystal-structural characteristics
  • C01P2002/20—Two-dimensional structures
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2006/00—Physical properties of inorganic compounds
  • C01P2006/12—Surface area
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C2527/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
  • C07C2527/20—Carbon compounds

Definitions

• the invention relates to a catalyst for chemical or petrochemical reactions, based on metallic oxycarbons with large specific surface, its preparation process and its use.
• This catalyst is particularly suitable for the refining and transformation of petroleum products, in particular for the isomerization of saturated hydrocarbons, for the hydrogenation and the decyclization of cyclic and aromatic hydrocarbons, and has improved catalytic properties, in particular the specific speed.
• catalysts based on Mo oxycarbide are of major interest since they always offer a high selectivity, in particular even when the conversion rates are high. In addition, they are much cheaper and less sensitive to poisons than conventional Pt catalysts.
• the inventors therefore asked themselves the question of improving the catalytic activity of this type of catalyst by seeking in particular to increase, in petrochemical reactions, the specific speed reduced to the unit of weight of catalyst.
• a first aspect of the invention is a modified molybdenum oxycarbide with a high specific surface, characterized in that it is prepared from a molybdenum oxide M0O3 having a structure essentially comprising platelets having a preferential orientation.
• the most favorable oriented plane of M0O3 to obtain a more efficient oxycarbide is the plane (010) with a preferential development in direction (001).
• Said plates generally have a length in the direction of the preferred orientation of at least 1 ⁇ m; it is remarkable that they can reach or exceed 10,000 ⁇ m.
• the thickness of the plates is generally at least 0.1 ⁇ m and their width at least 0.5 ⁇ m; the latter can sometimes reach 6000 ⁇ m. They are generally of the monocrystalline type, more or less agglomerated.
• the BET specific surface area of this oxycarbide is greater than 5 m 2 / g, generally 20 m 2 / g and can even reach 90 m 2 / g and is clearly greater than that of the starting oriented MO 3.
• Another aspect of the invention is a process for obtaining modified molybdenum oxycarbide of high specific surface, characterized in that one starts from usual polycrystalline molybdenum oxide, or optionally from a molybdenum compound (by example of ammonium heptamolybdate) which is transformed into oxide, said molybdenum oxide is heat treated by sublimation-condensation at a temperature between 500 and 800 ° C. in an enclosure under an atmosphere of oxidizing gas for at least 5 hours to obtain an oriented recrystallized oxide, which is then treated under a current of a mixture of hydrocarbon and hydrogen to give a modified molybdenum oxycarbide.
• a molybdenum compound by example of ammonium heptamolybdate
• the sublimation-condensation stage is usually carried out under a static atmosphere or under a stream of dry or wet oxidizing gas at low speed, said gas possibly being air.
• a recrystallization of the molybdenum oxide is thus carried out on site, without appreciable transfer of material.
• This material is usually a refractory, for example alumina, but preferably a carbide with a large specific surface such as pure or doped SiC.
• the recrystallized oxide obtained is an oxide with an oriented structure mainly comprising monocrystalline wafers of elongated shape having a preferential orientation.
• the preparation of the oxycarbide from the recrystallized oxide is carried out according to the methods described in the patents cited above.
• Another aspect of the invention is the use of this modified molybdenum oxycarbide with a large specific surface prepared from oriented M0O3 as a catalyst in petrochemical reactions in particular for the isomerization of hydrocarbons or their hydrogenation, in particular that of aromatics to obtain a high selectivity at high conversion rate.
• Such catalysts according to the invention exhibit a clearly improved activity compared to the usual polycrystalline molybdenum oxycarbide.
• their specific speed can reach almost 10 times that of the MoOC obtained from polycrystalline M0O3; in other words, for the same reaction, the quantity of catalyst required is more than 10 times lower.
• the specific speed is also higher, sometimes at least 4 times, than that obtained with the usual catalysts based on Pt on zeolite.
• the catalyst according to the invention can be prepared as it is (that is to say in bulk) or supported, for example, on an SiC support with a high specific surface, as has already been said.
• a first method of preparation consists in heating under a low current of air a polycrystalline M0O3 powder as it is at a temperature preferably between 650 and 750 ° C. for a period ranging from 5 to 240 h.
• the molybdenum oxide used can be replaced either by a precursor salt (heptamolybdate), or by a metal powder or metal plates which are oxidized.
• the molybdenum oxide after this treatment is in the form of powder or platelets having the preferred orientation desired.
• the air stream can be replaced by any other oxygen-containing gas.
• the gas flow generally of low speed, can either be used in the form of dry gas or contain water vapor.
• the synthesis can also be carried out under a static atmosphere of air or a mixture of oxygen with an inert gas.
• a second method of preparation consists of heating not a powder of polycrystalline M0O3 but an intimate mixture of polycrystalline MOO3 and grains of SiC.
• the treatment is identical to that described in the first method of preparation.
• the resulting product consists of SiC grains covered by M0O3 plates oriented preferentially.
• a third method of preparation consists in impregnating a support based on SiC with a solution containing a molybdenum salt, for example a heptamolybdate solution.
• a molybdenum salt for example a heptamolybdate solution.
• the support is then dried in an oven at 120 ° C for 12 hours and then calcined under air flow. The temperature rose from the ambient to the calcination temperature (650-750 ° C) with a slope of 60 ° Cmin- 'then kept at this temperature for an additional 24 hours.
• the gas mixtures used are identical to those used in the first two methods.
• the oxidizing gas used is generally air, but can be pure oxygen or more or less diluted by an inert gas. It is not necessary to dilute the oxygen too much and preferably a gas containing at least 10% oxygen is used.
• the gas mixture can be used in anhydrous form or containing water vapor as has already been said; - the treatment temperature must be between 500 ° C and 800 ° C. It has been shown that at a temperature below 500 ° C, the treatment to be effective, should have an unacceptable duration while the temperatures above 800 ° C cause too strong evaporation of the product; - the duration of treatment is more than 5 hours; it is usually between 24 and 72 hours when the treatment is carried out in the presence of humid air, and between 48 and 120 hours in the presence of dry air. However, it may be higher, the performance of the catalyst increasing with the duration of the treatment.
• Example 1 This example illustrates first obtaining molybdenum oxide (M0O3) as it is oriented according to the invention, using the first method, then modified molybdenum oxycarbide as such in order to catalyze isomerization of n-heptane.
• the oriented oxide was prepared in the following way: a mass of 1000 mg of polycrystalline MOO3 was introduced into a quartz tube located inside a tubular furnace. The whole was swept by a stream of dry air (10 cm 3 min- '). The oven temperature was raised from ambient to 680 ° C with a speed of 20 ° C min- '. The temperature was maintained for a period of 100 h. The oven temperature was then lowered to room temperature still under air flow. At ambient temperature, the oriented or monocrystalline oxide M0O3 obtained was extracted from the oven and stored in a glove box to be subsequently transformed into a modified oxycarbide according to the invention.
• FIG. 1 gives the selectivity for n-heptane (i-Cz) isomers in% as a function of the conversion of said n-C7.
• the BET specific surface is 80 m 2 / g.
• the number of n-heptane molecules transformed is very low during the first hour of the reaction. After approximately 2 hours under a flow of n-heptane and hydrogen at 350 ° C., the catalyst begins to be active, which indicates a significant modification of its surface. This activation corresponds to the reduction and the carburetion of molybdenum oxide oriented to reactive modified oxycarbide, by reaction with the reaction mixture (n-heptane / hydrogen), as in the case of a polycrystalline molybdenum oxide.
• the selectivity for C7 isomers is very important from the start of the reaction and remains greater than 95%.
• the isomeric products formed are essentially composed of monobranched molecules (2-methyl hexane and 3-methyl hexane) and dibranched (dimethylpentanes) while cyclic molecules are formed in very small quantities ( ⁇ 1%).
• FIG. 1 shows that the selectivity for isomers of n-C7 remains very high whatever the conversion of the reaction.
• This example illustrates first of all obtaining oriented Mo oxide according to the invention, supported on a support based on SiC, using the third method, then modified molybdenum oxycarbide supported on said SiC to catalyze the isomerization of n-heptane.
• Granules of SiC with a BET specific surface area of 19 m 2 / g were impregnated with an aqueous solution of ammonium heptamolybdate and then calcined at 350 ° C. for 2 hours to decompose heptamolybdate into MOO3 oxide.
• Such an oxycarbide supported on SiC offers the advantage of greater solidity (abrasion resistance, mechanical strength, etc.), better conditions of use (no plugging of reactors, etc.) and a better efficiency of use (less quantity used compared to the product treated).
• Example 2 illustrates the results obtained with a molybdenum oxycarbide as modified according to the invention using an intermediate oriented oxide obtained in the presence of a humid oxidizing atmosphere.
• the method of Example 1 was used in which the stream of dry air was replaced by a stream of moist air of 30 cm 3 / min at 3% (by volume) of water vapor;
• the oriented oxide was obtained after 48 h of treatment and was then transformed into oxycarbide then used for the isomerization of n-heptane, as in Example 1.
• Example 4 modified oxycarbide / oxycarbide prior art
• Example 6 This example illustrates the use of molybdenum oxycarbide as modified according to the invention in the hydrogenation and decyclization reaction of benzene.
• the modified oxycarbide catalyst is obtained from oriented M0O3 (in the form of platelets) synthesized in the presence of dry air in Example 1 and is used in the hydrogenation and decyclization reaction of benzene.
• the reaction temperature and the working pressure are 350 ° C. and 60 bar respectively.
• the results obtained are reported in Table 6.
• the catalyst is first activated at 6 bars under a mixture of n-heptane / hydrogen (see Example 3) and then placed under a mixture of benzene / hydrogen at 60 bars.

Landscapes

• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Inorganic Chemistry (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
• Catalysts (AREA)
• Low-Molecular Organic Synthesis Reactions Using Catalysts (AREA)
• Carbon And Carbon Compounds (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=9505213

Family Applications (1)

Country Status (9)

Cited By (1)

Families Citing this family (1)

Family Cites Families (5)

• 1997
  • 1997-03-21 FR FR9703726A patent/FR2760979B1/fr not_active Expired - Fee Related
• 1998
  • 1998-03-19 EP EP98914949A patent/EP0968054A1/de not_active Withdrawn
  • 1998-03-19 WO PCT/FR1998/000551 patent/WO1998042438A1/fr not_active Ceased
  • 1998-03-19 BR BR9808399-6A patent/BR9808399A/pt not_active Application Discontinuation
  • 1998-03-19 KR KR1019997008646A patent/KR20010005583A/ko not_active Withdrawn
  • 1998-03-19 JP JP54324898A patent/JP2001517152A/ja active Pending
  • 1998-03-19 CA CA002284883A patent/CA2284883A1/fr not_active Abandoned
  • 1998-03-20 ZA ZA982404A patent/ZA982404B/xx unknown
• 1999
  • 1999-09-20 NO NO994561A patent/NO994561L/no unknown

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events