WO1998024742A1

WO1998024742A1 - Method for oxygen dehydrogenation of alkanes into alkenes

Info

Publication number: WO1998024742A1
Application number: PCT/FR1997/002121
Authority: WO
Inventors: Gilles Descat
Original assignee: Elf Atochem S.A.
Priority date: 1996-12-03
Filing date: 1997-11-25
Publication date: 1998-06-11
Also published as: FR2756558B1; FR2756558A1; AU5229098A

Abstract

The invention concerns a method of oxygen dehydrogenation of a C1-C12 alkane, linear, branched or cyclic, leading to the corresponding alkene consisting in contacting in vapour phase said alkane with molecular oxygen or a gas containing molecular oxygen, at a temperature between 200 and 800 °C, under pressure ranging from atmospheric pressure up to 6 bars, and in the presence of a catalyst. The method is characterised in that it consists in using as catalyst at least a mineral and porous substance with crystalline phase, having a hexagonal arrangement of pores of uniform dimension of at least 1.3 nm in diameter and having, after calcination, a hexagonal electronic diffraction pattern which can be indexed with a value of d100 greater than 1.8 nm, said substance having the following composition: (Me)x.(SiO2)y.(Al2O3)z, (Me = metal selected among V, Mn, Fe and Co; x, y and z represent the mass percentages of the substances Me, SiO2 and Al2O3 in the active mass respectively, and comply with the following relationships: 0.1 % ≤ x ≤ 20 %; 40 % ≤ y ≤ 100 %; 0 ≤ z ≤ 40 %).

Description

PROCESS FOR THE OXIDE DEHYDROGENATION OF ALKANES TO ALKENE

The present invention relates to a process for the oxidationhydrogenation of alkanes to alkenes.

The transformation of alkanes into alkenes is thermodynamically limited. The presence of oxygen makes it possible to displace the equilibrium by transforming hydrogen into water. However, the reactivity of the alkene formed with oxygen being higher than that of the starting alkane, this results in a high selectivity in combustion products. We know from the American patent

US-A-3 856 881, a process for the dehydrogenation, inter alia, of alkanes to alkenes, this process consisting in bringing into contact in vapor phase, at a temperature of more than 250 "C, a mixture of the compound or compounds to be dehydrogenated and from 0.2 to 2.5 moles of oxygen per mole of the compound or compounds to be dehydrogenated, with a catalyst composition comprising a crystalline spinel of the general formula M ₂ V0 ₄ , MV ₂ 0 ₄ , between V ₂ 0 ₄ and M ₂ V0 ₄ or mixtures thereof, where M represents in particular Mn, Zn, Co. It is also known from the American patent

US-A-4,046,833, a process for dehydrogenation of C ₃ -C ₈ paraffinic hydrocarbons to the corresponding monoolefins, this process consisting in contacting the paraffin with molecular oxygen on a catalyst, at a temperature d about 400 ^* -700 ^* C, under a pressure of about 1-3 atmospheres, the molar ratio of paraffin to oxygen being about 1: 0.04 to 1: 10; said catalyst having the composition:

^A a ^v b ^A1 c ° x

in which A can be one or more of the metals chosen from Groups IIA, IIB, VIB and VIII of the Periodic Table; 0 <a <3; 0.25 <b <5; 0.5 <c <25; and x is a number determined by the valence requirements of the metals of A, vanadium and aluminum, said catalyst being subjected to a heat treatment in the presence of oxygen. The Applicant Company has now discovered that, by the use of mesoporous systems as catalysts for the oxidationhydrogenation of alkanes, the selectivity for alkenes was improved compared to the use of microporous structures for these catalysts. The use of vanadium type catalysts incorporated in a mesoporous structure makes it possible to avoid confinement between the alkene and the oxygen, and therefore improves the selectivities for alkene.

Furthermore, the invention offers the complementary advantage of a higher activity of the proposed catalyst compared to the vanadium catalysts already known for catalyzing this same reaction: thus the catalyst used in the present invention makes it possible to operate at temperatures 400 - 450 'C, therefore lower than the temperatures of 500 - 600' C of previous catalysts.

The present invention therefore firstly relates to a process for the oxyhydrogenation of a linear, branched or cyclic C _1-12 alkane, in particular C ₁ _ ₆ , leading to the corresponding alkene, said process comprising the setting in vapor phase contact of said alkane with molecular oxygen or a gas containing molecular oxygen, at a temperature between 200 and 800 ° C, especially between 250 'C and 650 "C, more particularly between 400 and 450 'C, under a pressure ranging from atmospheric pressure up to 6 bars, in particular up to 3 bars, and in the presence of a catalyst, characterized in that at least one material with phase is used as catalyst crystalline, mineral, porous, having a hexagonal arrangement of pores of uniform size at least 1.3 nm in diameter and having, after calcination, a hexagonal electronic diffraction pattern which can be indexed with a value greater than 1.8 nm, said m with the following composition:

(Me) _χ - (Si0 ₂ ) _y . (Al ₂ 0 ₃ ) ₂ where:

Me represents a metal chosen from V, Mn, Fe and Co; x, y and z represent the mass percentages in the active mass of the materials Me, Si0 ₂ and Al ₂ 0 _{3 respectively} , and satisfy the following relationships:

0.1% <x <20%, in particular 0.2% <x <10%, • 40% <y <100%, in particular 80% <y <100%, 0% <z <40%, in particular 0% <z <20%.

The material with a crystalline phase has in particular a pore diameter of between 1.3 nm and 20 nm, preferably between 1.5 nm and 10 nm. The preparation of the catalyst useful in the process of the invention is known from American patent US-A-3,556,725. It belongs to the family of compounds designated as being silicas of low apparent density. In accordance with other characteristics of the process of the present invention, the oxyhydrogenation is carried out with an apparent contact time of between 0.2 and 30 seconds, and with a molar ratio of alkane to oxygen of between 0, 5 and 5, in particular between 0.5 and 2.

The following Examples illustrate the present invention without, however, limiting its scope. The structuring agent cetyltrimethylammonium bromide is designated by the abbreviation CTMABr.

Example 1

(a) Preparation of catalyst V _{4 4} (SiQ ₂ ) _{Q5 6}

A first solution is prepared by mixing 0.0033 mole of sodium vanadate (FLUKA) and 0.1 mole of Si0 ₂ in the form of a colloidal solution (LUDOX AS 40). A second solution is prepared by dissolving

0.01 mole of CTMABr in 2.8 moles of distilled water. The pH is adjusted to 11 by adding NaOH. After stirring for 1/2 hour, the second solution is slowly added to the first with vigorous stirring. A gel is obtained which is transferred to an autoclave, which is then placed in an oven at 150 ° C. for 6 days. By filtration and washing, a solid is recovered which is dried. The elementary analysis provides the following composition:

If: 31.7% V: 3.1%. The X-ray diffraction spectrum, shown in Figure 1, is consistent with that described in the literature for these silicas of low apparent density.

The solid is then calcined for 6 hours at 500 ° C. in order to remove the structuring agent CTMABr before use.

(b) Oxydhydro enation of propane to propene

5 cm ³ of the solid catalyst as obtained in paragraph (a) are placed in a reactor 12 cm in diameter. The reactor is immersed in a bath of molten salts maintained at temperature. A gas flow of 4.6 Nl / h consists of 17.4% propane and 82.6% air, preheated to 200 ° C., is injected onto the catalyst. The temperature of the reactor is gradually increased to 420 ° C., the temperature at which the reaction balance is carried out. Analysis of the effluent reveals a conversion of propane of 24% and a selectivity to propene of 20%.

Example 2 (a) Preparation of the catalyst V- ^ ₃ l i0 ₂ l _{98 7}

A first solution is prepared by mixing 0.1 mole of sodium silicate (26% Si0 _{2 solution} ) and 0.002 mole of vanadyl sulfate. This solution is stirred for 3 hours. A second aqueous solution containing 0.05 mole of CTMABr is prepared by adjusting the pH to 11 by adding sodium hydroxide.

The mixture of the two solutions is stirred for 1 hour at room temperature and this mixture is placed in an oven at 100 ° C. for 6 days. After filtration and washing, a solid is recovered which is dried. The elementary analysis comprises the following composition: Si: 11.7% V: 0.34%.

The X-ray diffraction spectrum, shown in Figure 2, is consistent with that described in the literature for these silicas of low apparent density.

(b) Oxydhydro enation of propane to propene

The procedure is as in Example 1 (b) using, as catalyst, the solid obtained in paragraph (a) above. The conversion of propane is 3% and the selectivity to propene is 40%.

Example 3 (a) Preparation of the catalyst: Co _{5 Q} (SiQ ₂ ) _{g5 0}

A first solution is prepared by mixing 0.1 mole of sodium silicate (26% Si0 _{2 solution} ) and 0.02 mole of CTMABr. This solution is stirred for 1 hour.

A second aqueous solution containing 0.0033 mole of cobalt acetate is prepared. The mixture of the two solutions is stirred for

3 hours at room temperature and this mixture is placed in oven at 100 ° C for 3 days. After filtration and washing, a solid is recovered which is dried.

Elementary analysis provides the following composition: Si = 14.2% Co = 1.6%.

The X-ray diffraction spectrum, shown in Figure 3, is consistent with that described in the literature for these silicas of low apparent density. The solid is then calcined for 6 hours at 500 ° C. in order to remove the structuring agent CTMABr before use.

(b) Oxydhydroαénation of propane to propene

5 cm ³ of the solid catalyst as obtained in paragraph (a) are placed in a reactor 12 cm in diameter. The reactor is immersed in a bath of molten salts maintained at temperature. A gas flow of 4.6 Nl / h, consisting of 17.4% propane and 82.6% air, preheated to 200 ° C. on the catalyst, is injected onto the catalyst. Increasing the reactor temperature gradually to 420 ^° C, at which temperature the reaction balance is performed. Analysis of the effluent reveals a conversion of propane to 12.1% and a selectivity to propene of 8.9%.

Example 4 (a) Preparation of the catalyst; Fe _{5 1} SÀ0 _{2 g4 9}

A first solution is prepared by mixing 0.1 mole of sodium silicate (26% Si0 _{2 solution} ) and 0.033 mole of ferric chloride. This solution is stirred for 30 minutes.

A second aqueous solution containing 0.02 mole of CTMABr is prepared. The mixture of the two solutions is stirred for

4 hours at room temperature and this mixture is placed in oven at 80 ° C for 2 hours. After filtration and washing, a solid is recovered which is dried.

Elementary analysis provides the following composition: Si = 15.5% Fe = 1.8%.

The X-ray diffraction spectrum, shown in Figure 4, is consistent with that described in the literature for these silicas of low apparent density. The solid is then calcined for 6 hours at 500 ° C. in order to remove the structuring agent CTMABr before use.

(b) Oxydhydrogenation of propane to propene

5 cm ³ of the solid catalyst as obtained in paragraph (a) are placed in a reactor 12 cm in diameter. The reactor is immersed in a bath of molten salts maintained at temperature. A gas flow of 4.6 Nl / h, consisting of 17.4% propane and 82.6% air, preheated to 200 ° C. on the catalyst, is injected onto the catalyst. The temperature of the reactor is gradually increased to 420 ° C., the temperature at which the reaction balance is carried out. Analysis of the effluent reveals a conversion of propane of 3.4% and a selectivity to propene of 10.2%.

Example 5 (a) Preparation of the catalyst: Mn ₄ g (SiQ ₂ ) _g5 .

A first solution is prepared by mixing 0.1 mole of sodium silicate (26% Si0 _{2 solution} ) and 0.033 mole of manganese acetate. This solution is stirred for 30 minutes.

1 hour at room temperature and this mixture is placed in oven at 80 ° C for 24 hours. After filtration and washing, a solid is recovered which is dried.

Elementary analysis provides the following composition: If ≈ 15.7% Mn = 1.8%.

The X-ray diffraction spectrum, shown in Figure 5, is consistent with that described in the literature for these silicas of low apparent density. The solid is then calcined for 6 hours at 500 ° C. in order to remove the structuring agent CTMABr before use.

(b) Oxydhydrogenation of propane to propene

5 cm ³ of the solid catalyst as obtained in paragraph (a) are placed in a reactor 12 cm in diameter. The reactor is immersed in a bath of molten salts maintained at temperature. A gas flow of 4.6 Nl / h, consisting of 17.4% propane and 82.6% air, preheated to 200 ° C. on the catalyst, is injected onto the catalyst. The temperature of the reactor is gradually increased to 420 ° C., the temperature at which the reaction balance is carried out. Analysis of the effluent reveals a conversion of propane of 20.0% and a selectivity to propene of 11.4%.

Example 6

(a) Preparation of the catalyst V- ^ g (SiQ ₂ ) ₅ (A1 ₂ 0 ₃ ) ₃ -

A first solution is prepared by mixing 0.1 mole of Si0 ₂ in the form of a colloidal solution

(Ludox AS40), 0.0025 mole of pseudoboehmite and 0.0033 mole of sodium vanadate. This solution is stirred for

1 hour.

A second solution is prepared by dissolving 0.01 mole of CTMABr in 2.8 moles of distilled water. The pH is adjusted to 11 by adding NaOH. The mixture of the two solutions is stirred for 3 hours at room temperature and this mixture is placed in an oven at 150 ° C. for 6 days. After filtration and washing, a solid is recovered which is dried. Elementary analysis provides the following composition: Si = 40.9% Al = 1.5% V = 1.8%.

The X-ray diffraction spectrum, shown in Figure 6, is consistent with that described in the literature for these silicas of low apparent density.

The solid was then calcined for 6 hours at 500 ^° C to remove the structuring CTMABr before use.

(b) Oxidehydroqénation of propane to propene 5 cm ³ of the solid catalyst as obtained in paragraph (a) are placed in a reactor 12 cm in diameter. The reactor is immersed in a bath of molten salts maintained at temperature. A gas flow of 4.6 Nl / h, consisting of 17.4% propane and 82.6% air, preheated to 200 ° C. on the catalyst, is injected onto the catalyst. The temperature of the reactor is gradually increased to 420 ° C., the temperature at which the reaction balance is carried out.

Analysis of the effluent reveals a conversion of propane of 13.3% and a selectivity to propene of 21.1%.

Claims

1 - Process for the oxidationhydrogenation of a linear, branched or cyclic alkane at ^c ₁ _ ₁₂ , leading to the corresponding alkene, said process comprising bringing said alkane into contact with the vapor phase with molecular oxygen or a gas containing molecular oxygen, at a temperature between 200 and 800 ° C., under a pressure ranging from atmospheric pressure up to 6 bars, and in the presence of a catalyst, characterized in that the catalyst used is , at least one material with a crystalline, mineral, porous phase, having a hexagonal arrangement of pores of uniform size at least 1.3 nm in diameter and having, after calcination, a hexagonal electronic diffraction diagram which can be indexed with a d ₁₀₀ value greater than 1.8 nm, said material having the following composition:

(Me) _χ . (Si0 ₂ ) _y . (Al ₂ 0 ₃ ) ₂ where:

Me represents a metal chosen from V, Mn, Fe and Co; - x, y and z represent the mass percentages in the active mass of the materials Me, Si0 ₂ and A1 ₂ 0 _{3 respectively} , and satisfy the following relationships:

0.1% <x <20%

40% <y <100% • 0 <Z <40%.

2 - Method according to claim 1, characterized in that the crystalline phase material has a pore diameter between 1.3 nm and 20 nm.

3 - Method according to claim 2, characterized in that the crystalline phase material has a pore diameter between 1.5 nm and 10 nm.

4 - Method according to one of claims 1 to 3, characterized in that x, y and z satisfy the following relationships: • 0.2% <x <10% 80% <y <100% 0% <z < 20%. 5 - Method according to one of claims 1 to 4, characterized in that the starting alkane is chosen from alkaneε in ₁ _ _& .

6 - Method according to one of claims 1 to 5, characterized in that one conducts the oxyhydrogenation at a temperature between 250 'C and 600' C, in particular between 400 and 450 'C.

7 - Method according to one of claims 1 to 6, characterized in that the oxyhydrogenation is carried out under a pressure ranging from atmospheric pressure to 3 bars.

8 - Method according to one of claims 1 to 7, characterized in that one conducts the oxyhydrogenation with an apparent contact time between 0.2 and 30 seconds.

9 - Process according to one of claims 1 to 8, characterized in that the oxyhydrogenation is carried out with a molar ratio of alkane to oxygen of between 0.5 and 5. 10 - Process according to claim 9, characterized in that the oxyhydrogenation is carried out with a molar ratio of alkane to oxygen of between 0.5 and 2.