FR3022802A1 - ALPHA ALUMINUM IRON OXIDE CATALYST AND ITS IMPLEMENTATION IN A PROCESS FOR THE DEHYDROGENATION OF MONOINSATURE HYDROCARBONS COMPRISING FROM 4 TO 5 CARBON ATOMS - Google Patents

Abstract

The invention relates to a catalyst whose active phase comprises iron oxide, advantageously comprises platinum, and is free of alkaline and alkaline earth elements, supported on alpha alumina. The invention also relates to a process for the dehydrogenation of unsaturated hydrocarbons comprising from 4 to 5 carbon atoms using a catalyst whose active phase comprises iron oxide, advantageously comprises platinum, and is free of alkaline elements and alkaline earth, supported on alpha alumina.

Description

The dehydrogenation process makes it possible to convert the monounsaturated compounds comprising from 4 to 5 carbon atoms of the petroleum fractions to the corresponding polyunsaturated compounds while avoiding the parasitic reactions such as cracking or skeletal isomerization.

An object of the invention is to provide an improved performance catalyst comprising an alpha alumina supported iron oxide, said catalyst also possibly comprising platinum.

Another object of the invention is to propose the use of an improved performance catalyst comprising an alpha alumina supported iron oxide in a process for the dehydrogenation of monounsaturated hydrocarbons comprising from 4 to 5 carbon atoms, said catalyst possibly being also include platinum.

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 Dehydrogenation catalysts for hydrocarbon compounds are generally based on metal oxides of groups VIB and VIII of the periodic table of elements, especially 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.

It is known from the literature (DE Stobbe et al., Surf Stud Sci., Catal., 75c, p2337, 1993) that the addition of potassium is desirable for the use of iron oxide as a catalyst for dehydrogenation of 1-butene or ethylbenzene. Indeed, it is the KFeO2 species which is designated as the active phase for this type of reaction. On the other hand, Mr.

Muhler et al (J. Catal. 126, p339, 1990) emphasize the important role of the K-O-Fe3 + moiety as the active center of iron oxide dehydrogenation catalysts.

FR 1,218,700 discloses the implementation of a catalyst based on metal oxides such as iron oxide on an alumina support of 20 to 150 m 2 / g, said alumina may be alpha or gamma type. This patent teaches that a support with a surface of the order of 80 m 2 / g gamma alumina type is suitable. It also indicates that the metal oxide is converted into the course of reaction, and that the term "catalyst" is therefore not suitable. Because of its participation in the reaction, this "contact mass" must be regenerated frequently. On the other hand, it is known from the literature (S. Henry Inami et al., J. Catal., 13, p397, 1969) to use catalysts based on gold, palladium and their alloys for butene dehydrogenation reaction to 1,3-butadiene. S. Bocanegra et al. (Ind Eng Eng Chem Res 49, p4044, 2010) propose the use of platinum-based catalysts and tin or lead supported MgA1204 for the dehydrogenation of n-butane. In addition, J. M. McNamara et al. studied dehydrogenation of butane on platinum catalyst on gamma alumina (SBET = 180m2 / g). However, the use of these catalysts often involves cracking and coking phenomena having a negative impact on the reaction performance. Finally, S. Kobayashi et al. have described the use of Pt-based catalysts or a Pt-Sn alloy on a Fe203-Al2O3 support prepared by co-precipitation. The catalysts resulting from these studies are different from the catalysts according to the invention since the iron oxide is introduced into the matrix of the support thus developing fewer active surface sites, whereas according to the invention the iron oxide is deposited on a pre-formed alumina support thus inducing the formation of iron oxide particles located on the surface of the alumina support.

On the other hand, the specific surfaces developed by the catalysts disclosed in this prior art are greater than those developed by the catalysts according to the invention, involving potentially higher surface acidities and penalizing the performance of the process.

It is also known to those skilled in the art that a high specific surface area of the support allows good dispersion of the active phase and therefore good catalytic performance. However, it has been discovered that, surprisingly, a carrier having a low specific surface area makes it possible to obtain active and stable catalysts.

Surprisingly, the catalyst comprising an active phase comprising iron oxide, and advantageously comprising platinum, free of alkaline and alkaline earth elements according to the invention makes it possible to achieve improved dehydrogenation performances of monounsaturated hydrocarbons. comprising from 4 to 5 carbon atoms by the use of a low surface area alpha alumina support. SUMMARY OF THE INVENTION The invention relates to a catalyst whose active phase comprises iron oxide, advantageously comprises platinum, and is free of alkaline and alkaline earth elements, supported on alpha alumina. The invention also relates to a process for the dehydrogenation of monounsaturated hydrocarbons comprising from 4 to 5 carbon atoms using a catalyst whose active phase comprises iron oxide, advantageously comprises platinum, and is free of alkaline elements and alkaline earth, supported on alpha alumina. The catalyst according to the invention has good stability, with performance maintained for at least 24 hours, which does not require frequent regeneration when it is used in the process according to the invention. DETAILED DESCRIPTION OF THE INVENTION The invention relates to a catalyst comprising an active phase, which comprises iron oxide and is free of alkaline and alkaline earth elements, and an alpha alumina support, the total pore volume of said with a support ranging from 0.1 to 1.2 ml / g, the BET specific surface area of said catalyst being between 1 and 19 m 2 / g, the iron 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 iron, relative to the total mass of the catalyst being between 2% and 20% by weight. The invention also relates to a process for the dehydrogenation of monounsaturated hydrocarbons comprising from 4 to 5 carbon atoms using the catalyst according to the invention, said process operating at a temperature of between 300 ° C. and 750 ° C., a pressure comprised between between 0.1 and 10 bar absolute and a hourly volume velocity (VVH) of between 1 and 1000 h -1, in the gas phase and in the presence or absence of water vapor. Said monounsaturated hydrocarbon can come from petroleum cuts or be derived from biomass.

Said monounsaturated hydrocarbons advantageously comprise from 4 to 5 carbon atoms, preferably 4 carbon atoms. Very preferably, said unsaturated hydrocarbons are butene.

Said active phase also advantageously comprises platinum, said platinum being at an oxidation degree equal to 0, the platinum mass content relative to the total mass of catalyst being between 0.01 and 2% by weight.

In a preferred embodiment, said active phase is made of iron oxide and is free of alkaline and alkaline earth elements. In another preferred embodiment, said active phase consists of iron oxide, platinum, an additional element of the groups VA and VIA of the periodic table of the elements, advantageously tin, and is free of alkaline elements. and alkaline earth. Hydrocarbon conversion processes such as steam cracking or catalytic cracking are operated at high temperature and produce a wide variety of unsaturated molecules such as ethylene, propene, linear butenes, isobutene, 1,3-butadiene linear pentenes, isopentenes, isoprene and unsaturated molecules containing up to about 15 carbon atoms. To allow the use of these different sections 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. Steam crackers using ethane as the feedstock produce only 1 to 2% by weight of butadiene relative to the ethylene production capacity, whereas a crude C4 cut from a refinery can have the following average composition: 35% wt. isobutane, 20% by weight of n-butane, 14% by weight of isobutene, 30% by weight of n-butenes and approximately 1% by weight distributed between C3 and C5.

Thus, the butene dehydrogenation process is useful for obtaining 1,3-butadiene.

The 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 to butene. The operating conditions generally used for the dehydrogenation reaction of monounsaturated hydrocarbons comprising from 4 to 5 carbon atoms are as follows: a temperature of between 300 ° 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 4 bar absolute. A hourly volume velocity (V.V.H.) for the monounsaturated hydrocarbon feed to be dehydrogenated between 1 and 1000 h -1, preferably between 100 and 800 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 in m3.

For a dehydrogenation reaction without dilution with water vapor, the pressure is generally between 0.1 and 0.4 bar absolute, the temperature between 400 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 400 and 700 ° C, the hourly space velocity (VVH) is 100 of 1000 h- 1 and the steam / hydrocarbon molar ratio between 1 and 50, preferably between 5 and 30. The process for the dehydrogenation of monounsaturated hydrocarbons comprising from 4 to 5 carbon atoms according to the invention uses the catalyst according to the invention, said catalyst comprising an active phase, which comprises iron oxide and is free of alkaline and alkaline earth elements, and an A1203 alpha alumina support. Said active phase also advantageously comprises platinum.

Said alpha alumina support can be obtained by any method known to those skilled in the art. The specific surface of the catalyst (measured by the method Brunauer, Emmett, Teller, i.e. BET method as defined in S.Brunauer, P.H.Emmett, E.Teller, J.

Am. Chem. Soc., 1938, 60 (2), pp 309-319.) Is between 1 and 19 m 2 / g, preferably between 1 and 15 m 2 / g and more preferably between 1 and 10 m 2 / g. The total pore volume of said support is between 0.1 and 1.2 ml / g, preferably between 0.2 and 0.7 ml / g.

Said active phase of the catalyst according to the invention comprises iron oxide, the iron element being in any degree of oxidation greater than zero. Preferably, the degree of oxidation of the iron on the catalyst will be +2, +3 or a mixture of these oxidation levels.

The mass content of said active phase, relative to metallic iron, relative to the total mass of the catalyst is between 2% and 20% by weight, preferably between 5% and 15% by weight. Said active phase of iron oxide is amorphous or crystallized. Said active phase also advantageously comprises platinum metal. In this case, the platinum mass content relative to the total mass of the catalyst is between 0.01 and 2% by weight, preferably 0.05 to 1% by weight. It can advantageously furthermore comprise an additional element of groups VA and VIA of the periodic table of elements. Said additional element is preferably tin. The mass content of the additional element, relative to the metal element, relative to the total mass of the catalyst is between 0.01 and 5% by weight, preferably between 0.05 and 2% by weight. Said catalyst according to the invention 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 preparation of said catalyst according to the invention 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 an iron precursor in solution in the porosity of an alpha alumina support.

Another preferred embodiment may be the dry impregnation of a platinum precursor in solution and then an iron precursor in solution in the porosity of an alpha alumina support.

The first step is to prepare an iron precursor solution. Any compound containing the iron element may be used. Preferably the precursor will be iron nitrate, iron carbonate, iron acetate, iron acetylacetonate, iron bromide, iron chloride, iron fluoride, iron formate, iron iron iodide, iron sulphate. Preferably, the iron precursor is iron nitrate or iron carbonate. A volume of solution adapted to the porosity of the support and in an iron precursor concentration adapted to the desired final content in the active phase is thus impregnated on the alpha 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. drying is carried out under air, or under 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. In the case where said active phase also comprises platinum, the second step consists in preparing a platinum precursor solution. Any compound containing the platinum element may be used. Preferably the precursor will be hexachloroplatinic acid, ammonium chloroplatinate, ammonium hexabroroplatinate, ammonium hexachloroplatinate, bromoplatinic acid, chloroplatinic acid, hexahydroxyplatinic acid. Preferably, the platinum precursor is hexachloroplatinic acid.

A volume of solution adapted to the porosity of the support and in a platinum precursor concentration adapted to the desired final content in the active phase is thus impregnated on the alpha 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. drying is carried out under air, or under 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, an additional element of groups VIA and VA of the periodic table of the elements can be added. The precursor of the additional element can be added to the platinum and / or iron precursor solution, or impregnated onto the support from a precursor solution of the single element at any stage of the precursor solution. preparation. When the element is tin, any compound containing the tin element may be used. Preferably, the precursor is tin oxalate, tin acetate, tin acetylacetonate, tin sulfate, tin chloride, tin bromide, iodide tin, tin fluoride. Very preferably, the tin precursor tin chloride.

Very preferably, the tin precursor tin chloride. After impregnation of the additional element, drying and calcination steps as presented just before are performed. The impregnation of the precursors 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, 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. The 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 may enable said catalyst to be activated and to form iron oxide particles at lower oxidation states than the oxides formed after the calcination step. All or part, that is to say more than 90% by weight of the iron, remains at an oxidation state greater than 0. In the case where the active phase comprises platinum, this reduction makes it possible to obtain the metal platinum. . The impregnation of the precursor of the active phase can 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.

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

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

In order to prepare 100 g of catalyst, an aqueous solution of iron nitrate Fe (NO 3) 3 is prepared by dilution of 32.52 g of iron nitrate nonahydrate (Aldrich,> 98%) in demineralized water. The total volume of the aqueous solution prepared corresponds to the pore volume of a commercial gamma alumina support of 142 m 2 g -1 and a total pore volume of 1.1 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 86 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 flow of air with a flow rate of 1 L.h.h. (g of catalyst) -1. This impregnation / drying / calcination step is repeated a second time by again using 32.52 g of iron nitrate nonahydrate (Aldrich,> 98%) in demineralised water. The total volume of the aqueous solution prepared for this second impregnation corresponds to 95% of the pore volume of the initial support of commercial gamma alumina. This solid is then dry-impregnated with an aqueous solution in which 1.77 g of K 2 CO 3 (Aldrich,> 99%) have been dissolved in a volume of demineralized water corresponding to 90% of the pore volume of the gamma alumina support. The catalyst A obtained contains 9% by weight of Fe metal (13% by weight in Fe 2 O 3 form), and 1% by weight K (1.2% by weight in the form of K 2 O) relative to the dry catalyst mass.

The BET specific surface area of catalyst A is 120 rd.g-1.

Catalyst B (not according to the invention) Catalyst B (not in accordance with the invention) is a catalyst comprising an iron oxide supported on a gamma-alumina. It differs from the invention only by the nature of the support.

In order to prepare 100 g of catalyst, an aqueous solution of iron nitrate Fe (NO 3) 3 is prepared by dilution of 32.52 g of iron nitrate nonahydrate (Aldrich,> 98%) in demineralized water. The total volume of the aqueous solution prepared corresponds to the pore volume of a commercial gamma alumina support of 142 m 2 g -1 and a total pore volume of 1.1 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 87 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 flow of air with a flow rate of 1 L.h.h. (g of catalyst) -1. This impregnation / drying / calcination step is repeated a second time by again using 32.52 g of iron nitrate nonahydrate (Aldrich,> 98%) in demineralised water. The total volume of the aqueous solution prepared for this second impregnation corresponds to 95% of the pore volume of the initial support of commercial gamma alumina. The catalyst B obtained contains 9% by weight of Fe metal (13% by weight in Fe 2 O 3 form) relative to the dry catalyst mass.

The BET specific surface area of catalyst B is 124 rd.g-1. Example 3 Catalyst C (in Accordance with the Invention) Catalyst C (in accordance with the invention) is a catalyst whose active phase consists of iron oxide supported on an alpha alumina. In order to prepare 100 g of catalyst, an aqueous solution of iron nitrate Fe (NO 3) 3 is prepared by dilution of 21.68 g of iron nitrate nonahydrate (Aldrich,> 98%) in demineralized water. The total volume of the aqueous solution prepared corresponds to the pore volume of a commercial alpha alumina support of 5 m 2 g -1 and a total pore volume of 0.51 ml / g. 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 87 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 flow of air with a flow rate of 1 L.h.h. (g of catalyst) -1.

This impregnation / drying / calcination step is repeated a second time again using 21.68 g of iron nitrate nonahydrate (Aldrich,> 98%) in demineralised water. The total volume of the aqueous solution prepared for this second impregnation corresponds to 95% of the pore volume of the initial support of commercial alpha alumina. This impregnation / drying / calcination step is repeated a third time again using 21.68 g of iron nitrate nonahydrate (Aldrich,> 98%) in demineralised water. The total volume of the aqueous solution prepared for this second impregnation corresponds to 90% of the pore volume of the initial support of commercial alpha alumina. The catalyst C obtained contains 9% by weight of Fe metal (13% by weight in Fe 2 O 3 form) relative to the weight of the dry catalyst.

The BET specific surface area of catalyst C is 7 rd.g-1. EXAMPLE 4 Catalyst D (not in Accordance with the Invention) Catalyst D (not in accordance with the invention) is a catalyst comprising platinum supported on gamma-alumina as prepared in the prior art (S. Kobayashi et al., Catalyst Application A: General, 417, p306, 2012). It differs from the invention by the nature of the support and the active phase. Catalyst D is composed of 1% by weight of platinum as the active phase and a carrier at 12% by weight Fe2O3 and 87% by weight of gamma alumina. The specific surface of catalyst D is measured at 162 m 2 / g. EXAMPLE 5 Catalyst E (Not in Accordance with the Invention) Catalyst E (not in accordance with the invention) is a catalyst comprising platinum supported on a mixed support of iron oxide and gamma-alumina as prepared in the prior art ( JM McNamara et al., Catal.Text, 81, p583, 2003). It differs from the invention by the nature of the support and the active phase.

Catalyst E is composed of 0.66% by weight platinum as the active phase and a gamma alumina support. The specific surface of catalyst E is measured at 175 m 2 / g.

Example 6 Catalyst F (in Accordance with the Invention) Catalyst F (in accordance with the invention) is a catalyst comprising platinum and an iron oxide supported on an alpha alumina.

In order to prepare 100 g of catalyst, an aqueous solution of iron nitrate Fe (NO 3) 3 is prepared by dilution of 21.6 g of iron nitrate nonahydrate (Aldrich,> 98%) in demineralized water. The total volume of the aqueous solution prepared corresponds to the pore volume of a commercial alpha alumina support of 5 m.sup.2 g.sup.-1 and a total pore volume of 0.51 ml.sup.-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 87 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 flow of air with a flow rate of 1 L.h.h. (g of catalyst) -1.

This impregnation / drying / calcination step is repeated a second time again using 21.6 g of iron nitrate nonahydrate (Aldrich,> 98%) in demineralised water. The total volume of the aqueous solution prepared for this second impregnation corresponds to 95% of the pore volume of the initial support of commercial alpha alumina. This impregnation / drying / calcination step is repeated a third time by again using 21.6 g of iron nitrate nonahydrate (Aldrich,> 98%) in demineralised water. The total volume of the aqueous solution prepared for this second impregnation corresponds to 90% of the pore volume of the initial support of commercial alpha alumina. The solid obtained is then impregnated to dryness with an aqueous solution in which 0.36 g of H 2 PtCl 6 H 2 O (AldrichTM,> 37% Pt basis) were dissolved in a quantity of demineralized water corresponding to 90% of the pore volume of the support. alumina.

The solid obtained is dried under air at 120 ° C. and then calcined for 2 hours at 450 ° C. under a stream of air with a flow rate of 1 L.h.h. (g of catalyst) -1. The catalyst F obtained contains 0.14% by weight of Pt and 9% by weight of Fe metal (13% by weight in Fe 2 O 3 form) relative to the weight of the dry catalyst. The BET specific surface area of the catalyst F is 6 rd.g-1. Example 7 Catalyst G (in Accordance with the Invention) Catalyst G (according to the invention) is a catalyst comprising platinum and tin and an iron oxide supported on alpha alumina. In order to prepare 100 g of catalyst, an aqueous solution of iron nitrate Fe (NO 3) 3 is prepared by dilution of 21.6 g of iron nitrate nonahydrate (Aldrich,> 98%) in demineralized water. The total volume of the aqueous solution prepared corresponds to the pore volume of a commercial alpha alumina support of 5 m.sup.2 g.sup.-1 and a total pore volume of 0.51 ml.sup.-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 87 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 flow of air with a flow rate of 1 L.h.h. (g of catalyst) -1. This impregnation / drying / calcination step is repeated a second time again using 21.6 g of iron nitrate nonahydrate (Aldrich,> 98%) in demineralised water. The total volume of the aqueous solution prepared for this second impregnation corresponds to 95% of the pore volume of the initial support of commercial alpha alumina.

This impregnation / drying / calcination step is repeated a third time by again using 21.6 g of iron nitrate nonahydrate (Aldrich,> 98%) in demineralised water. The total volume of the aqueous solution prepared for this second impregnation corresponds to 90% of the pore volume of the initial commercial alpha alumina support. The solid is then impregnated dry with an aqueous solution in which 0.24 g of SnCl 2 (AldrichTM purity> 99%) were dissolved in a quantity of demineralized water corresponding to 90% of the pore volume of the alumina support.

The solid obtained is dried under air at 120 ° C. and then calcined for 2 hours at 450 ° C. under a stream of air with a flow rate of 1 L.h.h. (g of catalyst) -1. The solid obtained is then impregnated to dryness with an aqueous solution in which 0.36 g of H 2 PtCl 6 H 2 O (AldrichTM,> 37% Pt basis) were dissolved in a quantity of demineralized water corresponding to 90% of the pore volume of the support. alumina. The solid obtained is dried under air at 120 ° C. and then calcined for 2 hours at 450 ° C. under a stream of air with a flow rate of 1 L.h.h. (g of catalyst) -1.

The catalyst G obtained contains 0.13% by weight of Pt, 0.15% by weight of Sn and 9% by weight of Fe metal (13% by weight in Fe 2 O 3 form) relative to the weight of the dry catalyst. The BET specific surface area of catalyst G is 7 rd.g-1.

Example 8 Process for the dehydrogenation of 1-butene The catalysts are subjected to a dehydrogenation test of 1-butene in 1,3-butadiene in a fixed bed reactor with a diameter of 20 mm. The volume of the catalytic bed is 10 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 along the catalytic zone. Before the catalytic test, the catalysts D, E, F and G are treated in situ under a flow of hydrogen with a V.V.H. 500 h -1 with a temperature rise of 300 ° C / h and a plateau at a final temperature of 450 ° C for 2 hours.

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 VVH is set at 125 h-1, a flow rate of 1.25 NL.11-1 controlled by a mass flow meter. The volume ratio H 2 O / 1-butene is set at 16. The pressure is maintained at 1 barg and the temperature of the catalytic bed is 550 ° C.

After separation of the hydrocarbons and the steam in a separator maintained at 9 ° C. and at ambient pressure, the gas is aialysed by gas chromatography. The first analysis is performed 5 minutes after the start of the test, then every 40 minutes. The results obtained for the catalysts A, B (not in accordance with the invention) and C (according to the invention) are reported in Table 1. The 1-butene conversion and the selectivity to 1,3-butadiene are calculated. (in percent by mass) at 5 minutes and 240 minutes.

Catalyst Converter Conversion (%) Conversion (%) Selectivity (%) Selectivity (%) (at 5 min) (at 240 min) (at 5 min) (at 240 min) Catalyst AI 22 I 3 50 0 not compliant Catalyst B non-compliant Catalyst C Catalyst C 30 896 according to the invention Catalyst D 30 356 0 non-conforming Catalyst E 24 6 I 75 I 37 non-conforming Catalyst F 28 2291 90 according to the invention II Catalyst G 29 25 93 93 According to the invention Table 1: Conversions of 1-butene and selectivity to 1,3-butadiene The implementation of catalyst C in dehydrogenation of 1-butene according to the invention leads to a lower initial conversion than non-catalytic catalysts. conforms, but greater stability, with performance in terms of conversion to 240 min higher. The performances in terms of selectivity and stability are superior to those obtained with catalysts A and B whose implementation is not in accordance with the invention.

The use of the catalysts F and G in dehydrogenation of 1-butene according to the invention induces improved performances in terms of selectivity and stability with respect to catalysts A, B, D and E, the implementation of which is not according to the invention.

20 I 2.7 34 0 25

Claims (7)

REVENDICATIONS1. Catalyst comprising an active phase, which comprises an iron oxide and is free of alkaline and alkaline earth elements, and an alpha alumina support, the total pore volume of said support being between 0.1 and 1.2 ml / g, the BET specific surface area of said catalyst being between 1 and 19 m2 / g, the iron element of said active phase being at a degree of oxidation greater than zero, the mass content of the active phase, referred to metallic iron , relative to the total mass of the catalyst being between 2% and 20% by weight. Catalyst according to Claim 1, in which the BET specific surface area is between 1 and 15 m 2 / g. 3. Catalyst according to claim 1, wherein the BET specific surface area is between 1 and 10 m2 / g. 4. Catalyst according to one of claims 1 to 3, wherein the total pore volume of said support is between 0.1 and 1.2 mL / g. 5. Catalyst according to one of claims 1 to 4, wherein the iron element of said active phase is at an oxidation state of +2, +3 or a mixture of these oxidation levels. 6. Catalyst according to one of claims 1 to 5, wherein said active phase comprises platinum, said platinum being at a degree of oxidation equal to 0, the mass content of platinum relative to the total mass of catalyst being between 0.01 and 2% by weight. The catalyst of claim 6, wherein said active phase further comprises an additional element of groups VA and VIA of the periodic table of elements, the mass content of the additional element, referred to the metal element, relative to the total mass of the catalyst is between 0.01 and 5% by weight, preferably between 0.05 and 2% by weight. The catalyst of claim 7, wherein said active phase is iron oxide, platinum, an additional element of groups VA and VIA of the Periodic Table of Elements. Catalyst according to one of claims 1 to 5, wherein said active phase consists of iron oxide. Process for the dehydrogenation of monounsaturated hydrocarbons comprising from 4 to 5 carbon atoms using a catalyst according to one of claims 1 to 9, said process operating at a temperature of between 300 ° C. and 750 ° C., a pressure of between 0.1 and 10 bar absolute and a hourly volume velocity (VVH) for hydrocarbons between 1 and 1000 h -1, in the gas phase and in the presence or absence of water vapor. Process according to Claim 10, carried out in the absence of water vapor, at a pressure of between 0.1 and 0.4 bar absolute, a temperature of between 400 and 700 ° C. and a VVH of between 50 and 500 h. 1. Process according to Claim 10, carried out in the presence of water vapor, at a pressure of between 1 and 4 bar absolute, a temperature of between 400 and 700 ° C, a VVH of between 100 and 1000 h -1, and a molar ratio The process according to one of claims 10 to 12 wherein said monounsaturated hydrocarbons are butene. 5 9. 10. 10 15 11. 12. 20 13.