Mesoporous mixed oxide catalyst comprising silicon

Abstract

A mesoporous mixed oxide catalyst that comprises silicon and at least one metal M that is selected from the group that consists of the elements of groups 4 and 5 of the periodic table and mixtures thereof, with the mass of metal M being between 0.1 and 20% of the mixed oxide mass.

Claims

1. A catalyst comprising a mesoporous mixed oxide that comprises silicon and at least one metal M that is selected from the group consisting of tantalum, niobium, zirconium, and mixtures thereof, with the mass of metal M being between 0.1 and 20% of the mixed oxide mass, with said mixed oxide being a solid mixed oxide of both silicon and metal M, having M-O—Si bonds, said mixed oxide having a specific surface area of at least 600 m.sup.2/g, a pore volume of at least 1 ml/g and a mean diameter of the pores of between 4.5 and 17 nm, the specific surface area being a B.E.T. specific surface area that is determined by nitrogen adsorption in accordance with the ASTM D 3663-78 standard established from the BRUNAUER-EMMETT-TELLER method, the pore volume V corresponding to the volume that is observed for the partial pressure P/P.sup.0.sub.max of the nitrogen adsorption-desorption isotherm determined by the Barrett-Joyner-Halenda model, the diameter of the mesopores ϕ being determined by the formula 4000.V/S.sub.BET.

2. The catalyst according to claim 1, further comprising a metal M′, with said metal M′ being a metal that is selected from the group consisting of the elements of groups 11 and 12 of the periodic table and mixtures thereof, with the mass of metal M′ being between 0.1 and 20% of the mixed oxide mass.

3. The catalyst according to claim 2, in which said metal M′ is selected from the group consisting of silver, copper, zinc and mixtures thereof.

4. The catalyst according to claim 1, in which said mixed oxide is mesostructured.

5. The catalyst according to claim 1 that is shaped in the form of balls, pellets, granules, or extrudates, or rings.

6. The catalyst according to claim 5, further comprising at least one porous oxide material that has the role of a binder, with said porous oxide material being silica, magnesia, clays, titanium oxide, lanthanum oxide, cerium oxide, boron phosphates, or mixtures of at least two of the oxides.

7. A method for preparation of the catalyst according to claim 1 via metallo-organic modern sol-gel by precipitation/gelling that comprises at least the following: (a) dissolution of at least one alkoxide precursor of formula Si(OR).sub.4-aR′.sub.a, where R═H, methyl, ethyl and R′ is an alkyl chain or a functionalized alkyl chain of the element Si in aqueous, organic or aquo-organic medium, optionally in the presence of an acid or a base, so as to form an optionally colloidal solution, (b) addition to the solution that is obtained during (a) of at least one precursor of the metal M, in the pure state or dissolved in a suitable medium with said solution that is obtained from the operation (a), such that said medium does not demix or precipitate when it is brought into contact with the solution obtained from (a) under the conditions of (b), (c) precipitation of the Si-based mixed oxide, at least the metal M by the addition of an acid, a base, or by application of a specific reaction temperature, (d) filtration followed by optional washing cycles or evaporation of the suspension that is obtained during (c), (e) at least one heat treatment of mixed oxide that is obtained in (d) so as to obtain said catalyst.

8. The method for preparation of the catalyst according to claim 7, in which said heat treatment (e) is drying followed by calcination, with said drying being carried out in an oven in a temperature range of 20 to 200° C. during a period of less than 72 hours, with said calcination being carried out in air in an oven in a temperature range of 300 to 800° C. during a period of less than 24 hours.

9. A process for the production of 1,3-butadiene from a feedstock that comprises at least ethanol, comprising contacting said feedstock with a catalyst according to claim 1, at a temperature of between 300 and 400° C., a pressure of between 0.15 and 0.5 MPa, and a volumetric flow rate of between 0.5 and 5 h.sup.−1.

10. The process according to claim 9, in which the temperature is between 320° C. and 380° C.

11. The process according to claim 9, in which the pressure is between 0.15 and 0.3 MPa.

12. The process according to claim 9, in which the volumetric flow rate is between 1 and 4 h.sup.−1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 represents a diagrammatic depiction of the process.

(2) The invention is illustrated by means of the following examples.

EXAMPLES

Example 1

Preparation of the Catalyst A Based on 2% Ta/SiO.SUB.2 .(2% by Weight of Ta in Relation to the Silica Mass) that is Obtained by Dry Impregnation of the Tantalum Precursor that is Associated with the Surface of a Davisil 636 Commercial Silica (for Comparison Purposes)

(3) 2.68 g of tantalum ethoxide (Ta(OCH.sub.2CH.sub.3).sub.5) is diluted in 96 ml of ethanol. This solution is quickly added drop by drop and mixed with 60 g of the Davisil 636 silica (SBET≈500 m.sup.2/g, Vp≈0.9 ml/g and ϕ≈7 nm, grain size: 200-500 microns) until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in an ethanol-saturated atmosphere for 3 hours, dried at 100° C. for 24 hours. The catalyst A is obtained by calcination of the solid that is dried in air at 550° C. for 4 hours.

Example 2

Preparation of the Mixed Oxide Catalyst Ta—Si B Comprising 2% by Weight of Metal Ta in Relation to the Silica Mass, Obtained via the Metallo-Organic Modern Sol-Gel Path (According to the Invention)

(4) 12.5 ml of a 68% (by volume) nitric acid solution is added to a solution that contains 55 ml of tetraethyl orthosilicate (TEOS, Si(OCH.sub.2CH.sub.3).sub.4) and 150 ml of ethanol at ambient temperature. The whole mixture is left to stir for 30 minutes. 0.66 g of tantalum ethoxide (Ta(OCH.sub.2CH.sub.3).sub.5) is then added drop by drop under inert conditions to the preceding mixture. 50 ml of a 14% (by volume) ammonia solution is then added. The operation of the system is disrupted, and a gel forms. 19 ml of ethanol is then added to make possible additional stirring for 3 hours. The final gel is filtered, washed with ethanol, and then dried at 100° C. for 24 hours. The catalyst K is obtained by calcination of the solid that is dried in air at 550° C. for 4 hours. The catalyst B that is obtained is characterized by the following textural data: S.sub.BET=710 m.sup.2/g, Vp=1.42 ml/g and ϕ=11.7 nm.

Example 3

Preparation of the Catalyst C Based on 2% Nb/SiO.SUB.2 .(2% by Weight of Nb in Relation to the Silica Mass) that is Obtained by Dry Impregnation of the Niobium Precursor that is Associated with the Surface of the Davisil 636 Commercial Silica (for Comparison Purposes)

(5) 4.24 g of niobium oxalate and pentahydrated ammonium oxalate is diluted in 80 ml of water. This solution is quickly added drop by drop and mixed with 50 g of the Davisil 636 silica (SBET≈500 m.sup.2/g, Vp≈0.9 ml/g and ϕ≈7 nm, grain size: 200-500 microns) until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in a water-saturated atmosphere for 3 hours, dried at 100° C. for 24 hours. The catalyst C is obtained by calcination of the solid that is dried in air at 550° C. for 4 hours.

Example 4

Preparation of the Mixed Oxide Catalyst Nb—Si D that Comprises 2% by Weight of Metal Nb in Relation to the Silica Mass that is Obtained via the Metallo-Organic Modern Sol-Gel Path (According to the Invention)

(6) 12.5 ml of a 68% (by volume) nitric acid solution is added to a solution that contains 55 ml of tetraethyl orthosilicate (TEOS, Si(OCH.sub.2CH.sub.3).sub.4) and 150 ml of ethanol at ambient temperature. The whole mixture is left to stir for 30 minutes. 0.96 g of niobium ethoxide Nb(OCH.sub.2CH.sub.3).sub.5) is then added drop by drop under inert conditions to the preceding mixture. 50 ml of a 14% (by volume) ammonia solution is then added. The operation of the system is disrupted, and a gel forms. 19 ml of ethanol is then added to make possible an additional stirring for 3 hours. The final gel is filtered, washed with ethanol, and then dried at 100° C. for 24 hours. The Nb—SiO.sub.2 powder that is obtained is then calcined in air at 550° C. for 4 hours. The catalyst D that is obtained is characterized by the following textural data: S.sub.BET=790 m.sup.2/g, Vp=1.02 ml/g and ϕ=6.7 nm.

Example 5

Preparation of the Catalyst E Based on 1% Zn/2% Ta/SiO.SUB.2 .(1% by Weight of Zn and 2% by Weight of Ta in Relation to the Silica Mass) that is Obtained by Dry Impregnation of the Tantalum and Zinc Precursors that are Associated with the Surface of the Davisil 636 Commercial Silica (for Comparison Purposes)

(7) 2.27 g of hexahydrated zinc nitrate is diluted in 80 ml of water. This solution is quickly added drop by drop and mixed with 50 g of the Davisil 636 silica (SBET≈500 m.sup.2/g, Vp≈0.9 ml/g and ϕ≈7 nm, grain size: 200-500 microns) until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in a water-saturated atmosphere for 3 hours, dried at 100° C. for 24 hours. The intermediate solid is obtained by calcination of the solid, which is dried damp (20% water) at 550° C. for 4 hours.

(8) 1.34 g of tantalum ethoxide (Ta(OCH.sub.2CH.sub.3).sub.5) is diluted in 96 ml of ethanol. This solution is quickly added drop by drop and mixed with 30 g of the previously prepared solid until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in an ethanol-saturated atmosphere for 3 hours, dried at 100° C. for 24 hours. The catalyst E is obtained by calcination of the solid, which is dried in air at 550° C. for 4 hours.

Example 6

Preparation of the Mixed Oxide Catalyst Ta—Si—Zn F that Comprises 1% by Weight of the Metal Zn and 2% by Weight of the Metal Ta in Relation to the Silica Mass that is Obtained, Synthesis of the Mixed Oxide Ta—Si via the Metallo-Organic Modern Sol-Gel Path and Dry Impregnation of Said Mixed Oxide by the Associated Zinc Precursor (According to the Invention)

(9) 12.5 ml of a 68% (by volume) nitric acid solution is added to a solution that contains 55 ml of tetraethyl orthosilicate (TEOS, Si(OCH.sub.2CH.sub.3).sub.4) and 150 ml of ethanol at ambient temperature. The whole mixture is left to stir for 30 minutes. 0.66 g of tantalum ethoxide (Ta(OCH.sub.2CH.sub.3).sub.5) is then added drop by drop under inert conditions to the preceding mixture. 50 ml of a 14% (by volume) ammonia solution is then added. The operation of the system is disrupted, and a gel forms. 19 ml of ethanol is then added to make possible an additional stirring for 3 hours. The final gel is filtered, washed with ethanol, and then dried at 100° C. for 24 hours. The catalyst K is obtained by calcination of the solid that is dried in air at 550° C. for 4 hours.

(10) 0.91 g of hexahydrated zinc nitrate is diluted in 56 ml of water. This solution is quickly added drop by drop and mixed with 20 g of the mixed oxide Ta—Si (SBET≈710 m.sup.2/g, Vp≈1.42 ml/g and ϕ≈11.7 nm) until wettability of the surface of the latter (dry impregnation) is observed. The solid is then placed in a water-saturated atmosphere for 3 hours, dried at 100° C. for 24 hours. The catalyst F is obtained by calcination of the solid, which is dried in air at 550° C. for 4 hours.

(11) Definition of the Terms

(12) pph (g/g.sub.cath):

(13) $\mathrm{pph}=\frac{\mathrm{mass}\mathrm{flow}\mathrm{rate}\mathrm{of}\mathrm{the}\mathrm{feedstock}\left(g/h\right)}{\mathrm{catalyst}\mathrm{mass}\left(\mathrm{gcat}\right)}$ Conversion (% by weight):

(14) $\mathrm{conversion}=100*\left(1-\frac{\begin{array}{c}\mathrm{mass}\mathrm{flow}\mathrm{rate}\mathrm{of}\mathrm{exiting}\mathrm{ethanol}+\\ \mathrm{mass}\mathrm{flow}\mathrm{rate}\mathrm{of}\mathrm{exiting}\mathrm{acetaldehyde}\end{array}}{\begin{array}{c}\mathrm{mass}\mathrm{flow}\mathrm{rate}\mathrm{of}\mathrm{entering}\mathrm{ethanol}+\\ \mathrm{mass}\mathrm{flow}\mathrm{rate}\mathrm{of}\mathrm{entering}\mathrm{acetaldehyde}\end{array}}\right)$ Productivity (g.sub.c/g.sub.M/h)

(15) $\mathrm{productivity}=\frac{\mathrm{mass}\mathrm{flow}\mathrm{rate}\mathrm{of}\mathrm{carbon}\mathrm{belonging}\mathrm{to}\mathrm{butadiene}\left(\mathrm{gc}/h\right)}{\mathrm{catalyst}\mathrm{mass}\left(\mathrm{gM}\right)}$ Selectivity (% C):

(16) $\mathrm{selectivity}=\frac{\mathrm{mass}\mathrm{flow}\mathrm{rate}\mathrm{of}\mathrm{carbon}\mathrm{belonging}\mathrm{to}\mathrm{butadiene}\left(\mathrm{gc}/h\right)}{\begin{array}{c}\mathrm{mass}\mathrm{flow}\mathrm{rate}\mathrm{of}\mathrm{carbon}\\ \mathrm{belonging}\mathrm{to}\mathrm{the}\mathrm{converted}\mathrm{feedstock}\end{array}}$
Description of the Catalytic Test Unit

(17) The reactor that is used in the following examples consists of a stainless steel tube that is 20 cm long and 10 mm in diameter. The reactor is first loaded with carborundum and then with the catalyst that is diluted in carborundum and finally with carborundum. The carborundum is inert relative to the feedstock and does not influence the catalytic results; it makes it possible to position the catalyst in the isothermal zone of the reactor and to limit the risks of material and heat transfer problems. The temperature of the reactor is controlled with a tubular furnace with three heating zones. The liquid feedstock (mixture of ethanol and acetaldehyde in a ratio R) is injected via a double-piston HPLC pump. The liquid stream is evaporated in the lines that are heated by a tracer before entering into the reactor and is homogenized by passing into a static mixer. The products that are formed during the reaction are kept in the vapor phase so that they can be analyzed on-line by gas chromatography (PONA and Carboxen 1010 capillary columns) to make possible the most precise identification of the hundreds of products formed. The catalyst is activated in situ under nitrogen at the test temperature. The specific operating conditions are described in the following examples.

(18) Catalytic Test Protocol

(19) For all of the catalysts that are prepared according to the examples that are described below, the test conditions have been as follows: The test for transformation of the alcoholic feedstock was carried out at a temperature [sic] at a pressure of 0.15 MPa with a start-up temperature of 340° C. The feedstock flow rate (and therefore the pph) is adjusted for each catalyst so as to obtain initially (at 340° C.) the desired conversion level. The temperature is gradually increased to compensate for the deactivation of the catalyst and to keep a butadiene productivity level stable. The test is stopped from the time when the test temperature exceeds 375° C. At the end of each test, the catalyst is regenerated by calcination in air. The regeneration conditions were selected so as to be the most representative of industrial regeneration. The conditions of the regeneration step are described in detail in Table 1, and the regeneration is carried out according to the diagram that is shown in FIG. 1, which illustrates the diagrammatic depiction of the circulation of the streams during various phases. After a first period under a stream of nitrogen that makes it possible to evacuate the residues of volatile compounds that are present in the reactor and on the catalyst, air is introduced into the unit to initiate the regeneration of the catalyst. This air is diluted using a partial recycling of the exiting gas (recycling rate=5), gas that consists of an N2, CO2 and H2O mixture as well as the oxygen that has not reacted. During this phase (periods 1-4), the temperature is gradually increased so as to burn the coke while managing the exotherm of the reaction. Finally, the residual coke is burned completely after a last step in pure air (period 5). The unit is then rendered inert under N2 so as to be able to begin the next test.

(20) In a diagrammatic manner, FIG. 1 shows the circulation mode of fluids during the regeneration phase.

(21) TABLE-US-00001 TABLE 1 Operating Conditions of the Step for Regenerating Catalysts Gas Return Nitrogen Air Flow Flow Rate Flow Rate Rate Duration Initial Final Rate of Q1 Q2 Q3 of the Periods Temperature Temperature Climb (l/h/gcat) (l/h/gcat) (l/h/gcat) Stage Phenomenon 1 200° C. 350° C. 20° C./h 1.4 0 0.6  5 h Calcination 2 350° C. 480° C. 20° C./h 1.4 0 0.6  5 h of Coke 3 480° C. 540° C. 20° C./h 1.4 0 0.6 10 h Calcination 4 540° C. 590° C. 20° C./h 1.4 0 0.6 10 h of Hard Coke 5 580° C. 590° C. — 0 0 2 10 h 6 580° C. 230° C. 100° C./h  1.4 0.6 0  2 h Rendering Inert

(22) The catalytic test/regeneration sequence is repeated 20× so as to be able to extrapolate the service life of the catalyst. In the following examples, the former will correspond to the number of cycles that the catalyst can undergo before its productivity level reaches a critical level, set at half its starting level, i.e., on the level of the catalyst that was just prepared.

Example 7

Comparison of the Ta—Si Mixed Oxide Catalyst System and Impregnated Ta/Si Catalyst

(23) In this example, the ethanol/acetaldehyde ratio of the feedstock is set at 2.5 mol/mol, the beginning test temperature at 340° C., and the pressure at 0.15 MPa. For each catalyst, the feedstock flow rate is set to obtain a 45% conversion. Maintaining butadiene productivity on the cycle is ensured by a regular increase in the temperature of the reactor. The losses in productivity between each cycle reflect the rate of aging of the catalyst.

(24) TABLE-US-00002 Number of Cycles Productivity Productivity Loss in Extrapolated during the after 20 Productivity before Reaching 1st Cycle Cycles after 20 Minimum Example Catalyst (g/g.sub.Ta/h) (g/g.sub.Ta/h) Cycles Productivity 1- For A- 2% 37 22 41% 21 Comparison Ta/SiO.sub.2 Purposes 2 B- 2% 31 26 16% 65 Ta—SiO.sub.2

Example 8

Comparison of the Nb—Si Mixed Oxide Catalyst System and Impregnated Nb/Si Catalyst

(25) In this example, the ethanol/acetaldehyde ratio of the feedstock is set at 2.5 mol/mol, the beginning test temperature at 340° C., and the pressure at 0.15 MPa. For each catalyst, the feedstock flow rate is set to obtain a 30% conversion. Maintaining butadiene productivity on the cycle is ensured by a regular increase in the temperature of the reactor. The losses in productivity between each cycle reflect the rate of aging of the catalyst.

(26) TABLE-US-00003 Number of Cycles Productivity Productivity Loss in Extrapolated during the after 20 Productivity before Reaching 1st Cycle Cycles after 20 Minimum Example Catalyst (g/g.sub.Nb/h) (g/g.sub.Nb/h) Cycles Productivity 1- For C- 2% 30 12 60% 15 Comparison Nb/SiO.sub.2 Purposes 2 D- 2% 22 18 18% 70 Nb—SiO.sub.2

Example 9

Comparison of the Ta—Si—Zn Mixed Oxide Catalyst System and Impregnated Ta/Zn/Si Catalyst

(27) In this example, the ethanol/acetaldehyde ratio of the feedstock is set at 24 mol/mol, the beginning test temperature at 340° C., and the pressure at 0.15 MPa. For each catalyst, the feedstock flow rate is set to obtain a 55% conversion. Maintaining butadiene productivity on the cycle is ensured by a regular increase in the temperature of the reactor. The losses in productivity between each cycle reflect the rate of aging of the catalyst.

(28) TABLE-US-00004 Number of Cycles Productivity Productivity Loss in Extrapolated during the after 20 Productivity before Reaching 1st Cycle Cycles after 20 Minimum Example Catalyst (g/g.sub.Ta/h) (g/g.sub.Ta/h) Cycles Productivity 1- For E- 1% Zn/2% 12 8 33% 30 Comparison Ta/SiO.sub.2 Purposes 2 F- 1% Zn-2% 11 10 10% 100 Ta—SiO.sub.2

(29) In Examples 7 to 9, it is observed that the mixed catalyst oxide according to the invention has a better stability than the catalyst that has a similar formulation, but for which the active phase has been deposited on the substrate.