FR2999569A1 - NON-OXIDIZING DESYDROGENATION PROCESS USING A MANGANESE OXIDE CATALYST ON AN ALUMINUM SUPPORT - Google Patents

Abstract

The invention relates to a process for the non-oxidative dehydrogenation of aliphatic, naphthenic or olefinic compounds employing a catalyst comprising an active phase comprising a manganese oxide and an alumina support, the BET specific surface area of said catalyst being between 1 and 300 m 2 / g, the total pore volume of said support being between 0.1 and 2 ml / g, the manganese element of said active phase being at a degree of oxidation greater than zero, the mass content of the active phase. , relative to the metallic manganese, relative to the total mass of the final supported catalyst being between 2% and 20% by weight, said process operating at a temperature of between 0 ° C. and 750 ° C., a pressure of between 0.1 and 10 bar absolute and hourly volume velocity (VVH) for the hydrocarbon feedstock to be dehydrogenated between 1 and 1000 h-1, in the gas phase and in the presence or absence of water vapor.

Description

The dehydrogenation process makes it possible to convert the saturated or monounsaturated compounds of the petroleum fractions to the corresponding alkenes or polyunsaturated compounds while avoiding parasitic reactions such as cracking or skeletal isomerization.

The object of the invention is to propose the use of an improved performance catalyst comprising an alumina-supported manganese oxide in processes for non-oxidative dehydrogenation of saturated or monounsaturated hydrocarbon compounds present in petroleum fractions or derived from biomass, preferably in a non-oxidizing olefin dehydrogenation process, very preferably in a non-oxidative butene dehydrogenation process. In the following, groups of chemical elements are given according to the CAS classification (CRC Handbook of Chemistry and Physics, publisher CRC press, editor-in-chief D.R.

Lide 81st edition, 2000-2001). For example, group VIII according to the CAS classification corresponds to the metals of columns 8, 9 and 10 according to the new IUPAC classification. PRIOR ART The catalysts for dehydrogenation of hydrocarbon compounds are generally based on metal oxides of groups VIB and VIII of the periodic table of elements, in particular based on iron or chromium oxides. The active phase of the catalysts is either in bulk form or in the form of particles deposited on a support which may be a refractory oxide in the form of beads, extrudates, trilobes or in forms having other geometries. The metal content, the size and the nature of the particles of the metal oxide active phase, as well as the textural and structural properties of the support are among the criteria that have an importance on the performance of the catalysts. Oxidative and non-oxidative dehydrogenations do not follow the same reaction scheme. Indeed, the non-oxidative dehydrogenation reaction produces, in addition to an olefin, dihydrogen while in the oxidative dehydrogenation reaction, the reactant reacts with oxygen to give the corresponding olefin and water. These two reactions being different, the catalysts that are effective for the latter are not, obviously, identical.

The present invention aims at providing the use of catalysts comprising a manganese oxide on an alumina support in non-oxidizing dehydrogenation of hydrocarbons.

Indeed, and surprisingly, the type of catalyst according to the invention makes it possible to achieve improved performances in the non-oxidative dehydrogenation of hydrocarbons. It is indeed known from the literature (A. Miyakoshi, A. Ueno, M. Ichikawa, Applied Catalysis A: General, 216, pp. 137-146, 2001) that a mass catalyst based on manganese oxide MnO (95 wt%) and potassium oxide (5 wt%), achieves only low conversions and poor selectivities with respect to the non-oxidative dehydrogenation of ethylbenzene to styrene.

In addition, studies from the literature indicate that manganese catalysts are particularly studied in the oxidative dehydrogenation of 1-butene (VV Krishnan, SL Suib, J. Catal., 184, pp. 305-315, 1999), ethane and propane (Q. Ge, B. Zhaorigetu, C. Yu, Li W., H. Xu, Catal. Lett., 68, pp. 59-62, 2000) or cyclohexane (H. Zhu , Q. Ge, W. Li, X. Liu, H. Xu, Catal. Lett., 105, pp. 29-33, 2005).

It is also known from US Pat. No. 4,370,259 that it may be advantageous to use a manganese and phosphorus-based catalyst optionally on a refractory oxide support for the oxidative dehydrogenation of hydrocarbons.

Thus, the prior art does not make it possible to deduce that the use according to the invention of catalysts supported on alumina comprising a manganese oxide in non-oxidizing dehydrogenation of hydrocarbons may have an advantage. SUMMARY OF THE INVENTION The dehydrogenation process makes it possible to convert the saturated or monounsaturated compounds of the petroleum or biomass cuts to the corresponding alkenes or polyunsaturated compounds while avoiding parasitic reactions such as cracking or skeletal isomerization.

The invention relates to a non-oxidizing hydrocarbon dehydrogenation process using a catalyst comprising a manganese oxide supported on alumina. DETAILED DESCRIPTION OF THE INVENTION The invention relates to a process for the non-oxidative dehydrogenation of aliphatic, naphthenic or olefinic compounds using a catalyst comprising an active phase comprising a manganese oxide and an alumina support, the BET specific surface area. a catalyst being between 1 and 300 m 2 / g, the total pore volume of said support being between 0.1 and 2 ml / g, the manganese element of said active phase being at a degree of oxidation greater than zero, the the mass content of the active phase, relative to the metallic manganese, relative to the total mass of the final supported catalyst being between 2% and 20% by weight, said process operating at a temperature of between 0 ° C. and 750 ° C., a pressure of between 0.1 and 10 bar absolute and a hourly volume velocity (VVH) for the hydrocarbon feedstock to be dehydrogenated between 1 and 1000 h -1, in the gas phase and in the presence or absence of water vapor. Said aliphatic, naphthenic or olefinic compounds may come from petroleum fractions or be derived from biomass. Preferably, said process is a non-oxidizing olefin dehydrogenation process, very preferably a non-oxidizing olefin C 4 dehydrogenation process. Hydrocarbon conversion processes such as steam cracking or catalytic cracking are operated at high temperatures and produce a wide variety of unsaturated molecules such as ethylene, propene, linear butenes, isobutene, pentenes and unsaturated compounds containing up to about 15 carbon atoms. To allow the use of these different cuts in petrochemical processes such as polymerization units, the unsaturated molecules must comply with very strict purity constraints.

Thus, the monounsaturated and polyunsaturated compounds used in the preparation of polymers have a high added value. As a result, direct dehydrogenation methods for saturated or monounsaturated molecules are developed to access these products more specifically. On the same principle, unsaturated compounds derived from the dehydration of ex-biomass products can be used.

Thus, for example, the gasoline cut (7 to 10 carbons) may have the following average composition: of the order of 60% by weight of paraffins, of the order of 30% by weight of naphthenes and of the order of 10% weight in aromatics. The reforming process makes it possible to dehydrogenate cyclohexane to benzene. Ethylbenzene, produced by alkylation of benzene, can also be catalytically dehydrogenated to give predominantly styrene. This route is the preferred route for obtaining styrene as the essences of the steam cracker contain only 3 to 5% by weight of styrene. Steam crackers using ethane feed produce only 1 to 2% by weight of butadiene relative to the ethylene production capacity. However, a crude C4 cut obtained from a refinery may have the following average composition: 35% by weight of isobutane, 20% by weight of n-butane, 14% by weight of isobutene, 30% by weight of n-butenes and about 1% by weight distributed between C3 and C5. Here again the dehydrogenation of butanes and / or butenes to butadiene is suitable for the production of butadiene. Thus, the dehydrogenation process is advantageous for obtaining monounsaturated or polyunsaturated products that are not very present in steam cracker cuts. The non-oxidizing dehydrogenation is carried out in the gas phase, in the presence of water vapor or not, preferably in the presence of water vapor. Indeed, a reaction in the presence of water vapor makes it possible to limit the endothermicity of the reaction and to increase the cycle time of the catalysts by limiting the formation of coke. In addition, low pressures are preferred for thermodynamic reasons since they allow for higher conversions at equal temperatures. In this case, the dilution with water vapor also makes it possible to lower the partial pressure of saturated or monounsaturated compounds to be dehydrogenated.

The operating conditions generally used for the non-oxidative dehydrogenation reactions are as follows: a temperature of between 0 ° C. and 750 ° C., preferably between 400 ° and 700 ° C. A pressure of between 0.1 and 10 bar absolute, preferably between 0.2 and 3 bar absolute. A hourly volume velocity (V.V.H.) for the hydrocarbon feed to be dehydrogenated between 1 and 1000 h -1, preferably between 125 and 500 h -1. V.V.H. is the hourly flow rate of charge in m3 / h at 25 ° C, 1 atm divided by the volume of catalyst. For a dehydrogenation reaction without dilution with water vapor, the pressure is generally between 0.1 and 0.4 bar absolute, the temperature between 500 and 700 ° C and the hourly volume velocity (VVH) is between 50 and 500 h-1.

For a dehydrogenation reaction with a dilution with water vapor, the pressure is generally between 1 and 4 bar absolute, the temperature between 500 and 700 ° C, the hourly volume velocity (VVH) is between 100 of 1000 h- 1 and the vapor / (saturated or monounsaturated compounds to be dehydrogenated) molar ratio between 1 and 50, preferably between 5 and 30. The nonoxidative dehydrogenation process according to the invention uses a catalyst comprising a manganese oxide on a support. alumina A1203.

The alumina support can be obtained by any method known to those skilled in the art. The specific surface of the catalyst (measured by the Brunauer method, Emmett, Teller, the BET method as defined in S.Brunauer, PHEmmett, E.Teller, J. Am., Chem Soc., 1938, 60 (2), pp 309-319) is between 1 and 300 m 2 / g, preferably between 21 and 150 m 2 / g. The total pore volume of said support is between 0.1 and 2 mL / g, preferably between 0.2 and 1.5 mL / g. The support may contain impurities up to a few hundred ppm, such as sodium, potassium, magnesium, chlorine, sulphates, titanium oxide or even silicon oxide.

The active phase of the catalyst is a manganese oxide which element can be at any oxidation state greater than zero. Preferably, the degree of oxidation of the manganese on the catalyst will be +2, +3, +4 or a mixture of these oxidation levels.

The mass content of the active phase, relative to the metallic manganese, relative to the total mass of the final supported catalyst is between 2% and 20% by weight, preferably between 5% and 15% by weight. The active phase of manganese oxide being amorphous or crystallized. The catalyst may optionally comprise a Group IA element. Preferably Li, Na or K, even more preferably K. When it comprises, the element content of Group IA is between 0.1 and 5%, preferably between 0.5 and 2%. According to the invention, the catalyst is advantageously in the form of balls, trilobes, extrudates, pellets, or irregular and non-spherical agglomerates, the specific shape of which may result from a crushing step. Very advantageously, said catalyst is in the form of beads or extrudates. Even more advantageously, said catalyst is in the form of beads. The use of the catalyst according to the invention and the conditions of its use must be adapted by the user to the reaction and to the technology used.

The preparation of the catalyst can be carried out by any method known to those skilled in the art. For example, a preferred method of obtaining may be the dry impregnation of a manganese precursor in solution in the porosity of an alumina support.

The first step is to prepare a solution of manganese precursor. Any compound containing the manganese element may be used. Preferably the precursor will be manganese nitrate, manganese carbonate, manganese acetate, manganese acetylacetonate, manganese bromide, manganese chloride, manganese fluoride, manganese formate, manganese manganese iodide, manganese sulfate. Preferably, the manganese precursor is manganese nitrate or manganese carbonate.

A volume of solution adapted to the porosity of the support and in a concentration of manganese precursor adapted to the desired final content in the active phase is thus impregnated on the alumina support.

The impregnated catalyst is generally dried in order to remove all or part of the water introduced during the impregnation, preferably at a temperature between 50 and 250 ° C, more preferably between 70 ° C and 200 ° C . The drying is carried out in air, or in an inert atmosphere (nitrogen for example).

The catalyst is then calcined, generally under air. The calcining temperature is generally between 250 ° C and 900 ° C, preferably between about 350 ° C and about 750 ° C. The calcination time is generally between 0.5 hours and 16 hours, preferably between 1 hour and 5 hours. Optionally, the catalyst obtained at the end of the calcination step may undergo a gas stream treatment comprising between 25 vol% and 100 vol% of a reducing gas. The reducing gas is preferably hydrogen. This step is preferably carried out at a temperature of between 50 ° C. and 450 ° C. Said reduction can be carried out in situ or ex situ, that is to say after or before the catalyst is loaded into the reactor. It is preferably carried out in situ, ie in the reactor where the catalytic conversion is carried out. This possible reduction can enable said catalyst to be activated and to form manganese oxide particles at oxidation levels lower than those of the oxides formed after the calcination step. All or part, that is to say more than 90% by weight of the manganese, remains at a degree of oxidation greater than 0.

The impregnation of the precursor of the active phase may be carried out in one or more successive impregnations. If it is made in several successive impregnations, then the stages of drying and calcination will be repeated. Optionally, a member of Group IA of the Periodic Table of Elements may be added by impregnating a solution containing a hydroxide, chloride, bromide, carbonate salt of the element. If a group IA element is thus deposited by dry impregnation, the drying and calcination steps are then repeated.

EXAMPLES The invention is illustrated by the following examples without limiting its scope.

EXAMPLE 1 Catalyst A (implementation not in accordance with the invention) Catalyst A (not in accordance with the invention) is a catalyst based on chromium and potassium oxide supported on a gamma-alumina. It differs from the invention by the nature of the active phase.

In order to prepare 100 g of catalyst, an aqueous solution of chromium nitrate Cr (NO 3) 3 is prepared by dilution of 34.2 g of chromium nitrate nonahydrate (Aldrich) in demineralized water. The total volume of the aqueous solution prepared corresponds to the pore volume of a commercial alumina support of 140 m.sup.2 g.sup.-1 and a total pore volume of 1 ml.sup.g-1. The alumina support is in the form of a ball having a diameter between and 4 mm.

This solution is then impregnated on 90.1 g of the alumina support. The solid obtained is dried under air at 120 ° C. and then calcined for 2 hours at 650 ° C. under a stream of air with a flow rate of 1 L.h -1 (g of catalyst).

This solid is then dry-impregnated with an aqueous solution in which 1.69 g of K 2 CO 3 (Aldrich) were dissolved in 86 ml of demineralized water. The catalyst A obtained contains 8% by weight of Cr metal (12% by weight in Cr203 form), and 1% K relative to the weight of the dry catalyst. The BET specific surface area of Catalyst A is 124 rT12.g-1. Catalyst B (According to the Invention) Catalyst B (according to the invention) is a catalyst comprising a manganese oxide supported on a gamma-alumina. In order to prepare 100 g of catalyst, an aqueous solution of manganese nitrate Mn (NO3) 2 is prepared by diluting 42.4 g of manganese nitrate tetrahydrate (Aldrich) in demineralized water. The total volume of the aqueous solution prepared corresponds to the pore volume of a commercial alumina support of 140 m2.g-1 and a total pore volume of 1 ml.g-1. The alumina support is in the form of a ball having a diameter of between 2 and 4 mm.

This solution is then impregnated on 91.42 g of the alumina support. The solid obtained is dried under air at 120 ° C. and is then calcined for 2 hours at 650 ° C. under a stream of air with a flow rate of 1 L.h -1 (g of catalyst) -1.

The catalyst B obtained contains 8.4% by weight of Mn metal (10.9% by weight in MnO form) relative to the dry catalyst mass. The BET specific surface area of Catalyst B is 278 m 2 g -1.

EXAMPLE 3 Nonoxidative Dehydrogenation Process of 1-Butene The catalysts are subjected to a dehydrogenation test of 1-butene in 1,3-butadiene in a 20 mm diameter fixed bed reactor. The volume of the catalytic bed is 40 cc diluted to a ratio 1/3 with silicon carbide particle size 1.5 mm. A preheating zone at the inlet of the reactor makes it possible to obtain a uniform temperature.

When the reactor is heated, a stream of nitrogen and steam water is injected until the set point is reached. The beginning of the test phase starts when the nitrogen flow is replaced by the flow of 1-butene (Air Liquide 99%).

The 1-butene VVH is fixed at 200 h-1, a flow rate of 2 NL.h-1 controlled by a mass flow meter. The volume ratio H 2 O / 1-butene is set at 20. The pressure is maintained at 1 barg and the temperature of the catalytic bed is 650 ° C. After separation of the hydrocarbons and the steam at room temperature and pressure, the gas is analyzed by gas chromatography. The first analysis is performed 5 minutes after the start of the test, then every 20 minutes. By the first analysis of the effluents at t = 5 minutes, the conversion of 1-butene and the selectivity to 1,3-butadiene (in percentage) are calculated. The results obtained for catalysts A (not according to the invention) and B (in accordance with the invention) are reported in Table 1. Table 1: 1-Butene conversions and selectivity to 1,3-butadiene The implementation The use of catalyst B in the non-oxidizing dehydrogenation of 1-butene according to the invention induces improved performances compared to catalyst A, the use of which is not in accordance with the invention. Catalyst Conversion (%) Selectivity (%) Catalyst A (non-compliant) Catalyst B (according to the invention) 32 10 15 2. 20 3. 25 4. 5. 30 6.

Claims (1)

REVENDICATIONS1. A process for the non-oxidative dehydrogenation of aliphatic, naphthenic or olefinic compounds employing a catalyst comprising an active phase comprising a manganese oxide and an alumina support, the BET specific surface area of said catalyst being between 1 and 300 m 2 / g, the total pore volume of said support being between 0.1 and 2 ml / g, the manganese element of said active phase being at a degree of oxidation greater than zero, the mass content of the active phase, relative to the metallic manganese , relative to the total mass of the final supported catalyst being between 2% and 20% by weight, said process operating at a temperature between 0 ° C and 750 ° C, a pressure between 0.1 and 10 bar absolute and a hourly volume velocity (VVH) for the hydrocarbon feed to be dehydrogenated between 1 and 1000 h -1, in the gas phase and in the presence or absence of water vapor. Process according to Claim 1, carried out in the absence of steam, at a pressure of between 0.1 and 0.4 bar absolute, a temperature of between 500 and 700 ° C. and a VVH of between 50 and 500 h. 1. Process according to Claim 1, carried out in the presence of water vapor, at a pressure of between 1 and 4 bar absolute, a temperature of between 500 and 700 ° C., a VVH of between 100 and 1000 h -1, and a molar ratio. steam / (saturated or monounsaturated compounds to be dehydrogenated) between 1 and 50. Process according to one of claims 1 to 3, wherein the BET specific surface area of said catalyst is between 21 and 150 m2 / g. Process according to one of Claims 1 to 4, in which the total pore volume of said support is between 0.2 and 1.5 ml / g. Process according to one of claims 1 to 5, wherein the manganese element of said active phase is at an oxidation state of +2, +3, +4 or as a mixture of these oxidation levels.7. Process according to one of claims 1 to 6, wherein the mass content of said active phase, relative to the metal manganese, relative to the total mass of the final supported catalyst is between 5% and 15% by weight. 8. Method according to one of claims 1 to 7, wherein said catalyst comprises a group IA element, the content is between 0.1 and 5%. 9. The method of claim 8 wherein said group IA element is Li, Na or K. 10. The method of claim 8 wherein said group IA element is K. 11. Process according to claim 1 Claims 1 to 10 for non-oxidative dehydrogenation of C4 olefins.