JP2009039679A - Catalyst, its production method, and alkene production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-performance alkane oxidative dehydrogenation catalyst using a V-Mg compound and to provide a method for highly efficiently producing an alkene by alkane oxidative dehydrogenation using the catalyst. <P>SOLUTION: An alkene is produced by oxidatively dehydrogenating an alkane by using a catalyst containing at least a palladium compound and magnesium orthovanadate (Mg<SB>3</SB>V<SB>2</SB>O<SB>8</SB>). It is possible to more efficiently produce an alkene by performing the step of reactivating the catalyst by a non-regular operation. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a catalyst for producing alkene by oxidative dehydrogenation of alkane and a method for producing the same, and a method for producing alkene by oxidative dehydrogenation of alkane using the catalyst.

  Technology for producing alkenes, which are basic compounds, from inexpensive alkanes is also very important industrially. Among these, in view of the growing demand for propylene used as a raw material for various materials, a method for producing propylene from propane is likely to become more important in the future.

  A catalyst for dehydrogenating alkanes to produce alkenes has been actively studied. In particular, the method for producing alkenes by oxidative dehydrogenation of alkanes is a dehydrogenation reaction under oxidizing conditions, and therefore there is a problem that the dehydrogenated product undergoes oxidation to generate carbon dioxide, which is difficult. It is a high reaction. For example, the reaction in which propane is oxidized and dehydrogenated to become an alkene is represented by the following formula (1).

C ₃ H ₈ + 0.5O ₂ → C ₃ H ₆ + H ₂ O (1)
As for the production method of alkane oxidative dehydrogenation catalyst and alkene, particularly propane oxidative dehydrogenation catalyst and propylene production method, a method using a composite oxide catalyst composed of vanadium and magnesium (Non-patent Document 1), vanadium and magnesium And a method using a catalyst containing vanadium produced using polyvanadic acid as a raw material (Patent Document 1).
Japanese Patent No. 3826161 Journal of Catalysis, 123, 417-435 (1990) Bulltin of the Chemical Society of Japan, 75, 181-186 (2002)

In Non-Patent Document 1, a composite oxide catalyst composed of vanadium and magnesium has been proposed. Magnesium pyrovanadate (α-Magnesium pyrovanadate; α-Mg ₂ V ₂ O ₇ ), magnesium orthovanadate (Magnesium orthovanadate; Mg ₃ V ₂ O ₈₎ and magnesium metavanadate (β-magnesium metavanadate; β- MgV 2 O 6) has been studied. Among these, magnesium pyrovanadate (α-Mg ₂ V ₂ O ₇ ) is suitable for the oxidative dehydrogenation of propane, and magnesium orthovanadate (Mg ₃ V ₂ O ₈ ) has a strong tendency to complete oxidation, and magnesium metavanadate ( (β-MgV ₂ O ₆ ) describes that propylene selectivity is not so high.

In Non-Patent Document 2, oxidative dehydrogenation reaction under the condition where a small amount of tetrachloromethane (TCM) coexists in β-MgV ₂ O ₆ , α-Mg ₂ V ₂ O ₇ and Mg ₃ V ₂ O _8. As compared with the case where TCM does not coexist, α-Mg ₂ V ₂ O ₇ shows an approximately 2-fold improvement in activity. However, it is described that the activity gradually decreases due to excessive generation of chlorinated chemical species on the catalyst surface.

Patent Document 1 describes that a catalyst containing V ₂ O ₅ produced using polyvanadic acid as a raw material is suitable for oxidative dehydrogenation of propane. However, the composite oxide catalyst of magnesium and vanadium (V-Mg composite oxide catalyst) is effective for oxidative dehydrogenation of propane and butanes, but it is difficult to form a uniform phase in the calcination step in catalyst preparation. However, it is described that it has not reached an industrially feasible level.

Thus, it is known that V-Mg composite oxide, especially magnesium pyrovanadate (α-Mg ₂ V ₂ O ₇ ) is highly active for propane oxidative dehydrogenation. However, the performance of magnesium orthovanadate (Mg ₃ V ₂ O ₈ ) and magnesium metavanadate (β-MgV ₂ O ₆ ) is not sufficient, and various compounds having vanadium and magnesium such as V-Mg composite oxides. In order to use (V-Mg compound) as a catalyst, further improvement was necessary.

  Accordingly, an object of the present invention is to provide a high-performance alkane oxidative dehydrogenation catalyst using a V-Mg compound, and to provide a method for producing alkene with high efficiency by oxidative dehydrogenation of alkane using the catalyst. It is to provide.

  The present inventor has found that both the activity of oxidative dehydrogenation of propane and the selectivity of propylene are improved by using a catalyst obtained by adding a palladium compound to a V-Mg compound.

Therefore, the present invention is a catalyst for producing alkenes by oxidative dehydrogenation of alkanes, which contains at least a palladium compound and magnesium orthovanadate (Mg ₃ V ₂ O ₈ ).

  In addition, the present invention is a method for producing the above catalyst, wherein palladium nitrate is used as a palladium raw material, and ammonium metavanadate is used as a vanadium raw material.

  Furthermore, the present invention is a method for producing an alkene, characterized in that an alkane is oxidatively dehydrogenated using the above catalyst. Moreover, it is preferable to have the process of reactivating the said catalyst by unsteady operation. These methods are suitable for a method for producing propylene by oxidative dehydrogenation of propane.

  According to the present invention, a higher-performance alkane oxidative dehydrogenation catalyst than before can be provided, and alkene can be produced with high efficiency by oxidative dehydrogenation of alkane using this catalyst.

The catalyst of the present invention is a catalyst containing at least a palladium compound and magnesium orthovanadate (Mg ₃ V ₂ O ₈ ). Thus, the presence of vanadium, magnesium, and palladium improves both the activity of propane oxidative dehydrogenation and the selectivity of propylene. There are ortho, pyro, and meta forms of magnesium vanadate. In the present invention, it is important to include magnesium orthovanadate.

The palladium compound is not particularly limited, but is preferably a compound in which divalent magnesium in the MgO ₆ octahedron in Mg ₃ V ₂ O ₈ is substituted with divalent palladium. In this case, the catalyst contains a and Mg ₃ V ₂ O _8, and Mg ₃ V ₂ O ₈ obtained by replacing at least a portion of the divalent magnesium divalent palladium. Moreover, palladium oxide may exist as a palladium compound in the catalyst. Mg ₃ V ₂ O _{8 obtained} by substituting at least a part of divalent magnesium with divalent palladium can be represented by Pd _x Mg _{3 -x} V ₂ O ₈ .

The content of palladium, relative to the number of moles of Mg in Mg ₃ V ₂ O _8, preferably at least 0.1 mol%, more preferably at least 0.5 mol%, more preferably at least 1.0 mol% . The palladium content is preferably 20 mol% or less, more preferably 15 mol% or less, and even more preferably 10 mol% or less. If the palladium content is low, the ability to give lattice oxygen may not be sufficiently exhibited. When the content of palladium is large, there may be a significant decrease in activity due to the metal palladium or palladium oxide having a large particle diameter covering the surface of Mg ₃ V ₂ O ₈ .

  The palladium raw material used when producing the catalyst of the present invention is preferably palladium nitrate, more preferably an aqueous palladium nitrate solution, and further preferably an aqueous palladium nitrate solution obtained by adding nitric acid to an aqueous palladium nitrate solution. The concentration of palladium nitrate in the aqueous palladium nitrate solution or the aqueous palladium nitrate solution can be appropriately selected from 1 to 50% by mass, for example.

The vanadium raw material used when producing the catalyst of the present invention is preferably ammonium metavanadate (NH ₄ VO ₃ ). Since NH ₄ VO ₃ has low solubility in water, a small amount of aqueous ammonia solution can be added to promote dissolution.

The magnesium raw material used for producing the catalyst of the present invention is preferably magnesium hydroxide (Mg (OH) ₂ ). Mg (OH) ₂ can also be prepared by decomposing MgCl ₂ .6H ₂ O with an alkali such as NaOH.

  The catalyst can be prepared by the following method. First, a solution or dispersion obtained by dissolving or dispersing each raw material in water is mixed and heated and stirred. Subsequently, after evaporating water to dryness, the obtained powder is dried. Then, a catalyst is prepared by performing calcination. Drying may be performed, for example, at 70 ° C. to 150 ° C. for 6 hours to 48 hours. Firing may be performed at 150 ° C. to 900 ° C. for 3 hours to 100 hours, for example.

In order to form a magnesium orthovanadate (Mg ₃ V ₂ O ₈ ) phase in the catalyst, for example, two or more calcination steps may be performed at different temperatures. The firing temperature is gradually changed from a low temperature to a high temperature. For example, the Mg ₃ V ₂ O ₈ phase can be formed by firing at 550 ° C. for 6 hours, 625 ° C. for 49 hours, 640 ° C. for 60 hours, 750 ° C. for 15 hours, and 800 ° C. for 15 hours. . However, the maximum firing temperature is preferably 750 ° C. or lower in consideration of the influence of sintering of the catalyst during high-temperature firing.

  It is preferable to sufficiently grind the solid during each calcination step to suppress non-uniform catalyst components during calcination. For grinding, a mortar, a ball mill, or the like can be used, and either a manual type or an automatic type can be used.

The catalyst can be appropriately analyzed by confirming the Mg ₃ V ₂ O ₈ phase and analyzing various physical properties by XRD, XPS, nitrogen gas adsorption, FT-IR, ⁵¹ V-MAS-NMR and the like.

  In the alkene production method of the present invention, alkane is oxidatively dehydrogenated using the above catalyst. As the raw material alkane, ethane, propane, n-butane, isobutane and the like can be used. Among these, it is suitable for oxidative dehydrogenation of propane. The alkene produced is an alkene in which two adjacent hydrogen atoms of the alkane to be oxidatively dehydrogenated are dehydrogenated to form a double bond. For example, propylene is obtained by oxidative dehydrogenation of propane.

  The alkane oxidative dehydrogenation reaction is usually carried out using a fixed bed flow reactor. The source gas is supplied as a mixed gas of alkane / oxygen / nitrogen (or helium), for example. There is no restriction | limiting in the gas flow rate to supply, It can adjust suitably with catalyst activity, a catalyst filling amount, contact time, pressure loss, etc. When air is used as the oxygen source, impurities such as carbon dioxide in addition to nitrogen are mixed in a minute amount, but there is no problem. Helium may be used as a balance gas when pure oxygen is used as an oxygen source.

In the alkane oxidative dehydrogenation reaction of the present invention, the reaction can be carried out using lattice oxygen in the catalyst without circulating oxygen, or oxygen can be mixed with the alkane and allowed to flow. In the absence of oxygen, although there is a drawback that catalyst deterioration due to lattice oxygen extraction is accelerated, sequential oxidation is less likely to occur, so that the alkene selectivity is improved. When oxygen is mixed with alkane, CO ₂ generation due to complete oxidation of alkane increases when oxygen is excessive. Therefore, the alkane / oxygen which is the flow ratio (partial pressure ratio) of alkane and oxygen is preferably 0.5 or more. 1.0 or more is more preferable, and 2.0 or more is more preferable.

  There is no restriction | limiting in particular in reaction pressure, Either a normal pressure or pressurization is possible. The reaction temperature is not particularly limited, but is set appropriately in consideration of the fact that the reaction does not proceed at a low temperature and a homogeneous reaction involving no catalyst occurs at a high temperature. Generally, in the propane oxidative dehydrogenation reaction, the reaction proceeds efficiently at 400 ° C. or higher, but at 500 ° C. or higher, the homogeneous gas phase reaction becomes remarkable.

Here, when the present inventor confirmed the recovery behavior of lattice oxygen in the case of performing reoxidation treatment after extracting lattice oxygen from the catalyst by reduction treatment, in magnesium orthovanadate (Mg ₃ V ₂ O ₈ ) It has been found that the crystal structure changes from monoclinic to triclinic in magnesium pyrovanadate (α-Mg ₂ V ₂ O ₇ ) while lattice oxygen recovers and the structure also recovers. That is, towards the α-Mg ₂ V ₂ O ₇ for the oxidative dehydrogenation of an alkane is higher activity than Mg ₃ V ₂ O _8, found the following Mg ₃ V ₂ O ₈ for redox It was found that the stability was higher than that of α-Mg ₂ V ₂ O ₇ .

The ability to give lattice oxygen is expected to be highly active against the oxidative dehydrogenation of alkanes, but the life of the catalyst is particularly important when the recovery of lattice oxygen is poor and the crystal structure changes. Is inevitable. Further, in the catalyst of the present invention containing a palladium compound and magnesium orthovanadate (Mg ₃ V ₂ O ₈ ), lattice oxygen was more easily given due to the effect of palladium, and a decrease in the activity with time was observed.

Therefore, the present inventor has found a method for reactivating the catalyst by unsteady operation. That is, it is activated by reoxidizing a catalyst that has deteriorated or began to deteriorate due to the extraction of lattice oxygen. By doing so, the performance of the catalyst can be maintained in a good initial state, and the alkene can be produced with higher efficiency. This method is effective in the case of using a catalyst that easily gives lattice oxygen and easily deteriorates with time due to reduction. In particular, since Mg ₃ V ₂ O ₈ is highly stable against redox, this method is effective when a catalyst containing a palladium compound and Mg ₃ V ₂ O ₈ is used.

  It is effective to carry out the reoxidation until the alkene yield reaches 60% of the initial reaction. As the gas used for reoxidation, air, oxygen diluted with an inert gas such as nitrogen or helium, and pure oxygen can be used. The oxygen concentration in the reoxidized gas obtained by diluting oxygen with an inert gas is preferably 4% by volume or more.

  In the case of a single tube reactor, the unsteady operation is a method in which the source gas to be supplied is switched to a reoxidation gas, reoxidation is performed for a certain period of time, and then the oxidative dehydrogenation reaction is performed again by switching to the source gas. . In the case of a parallel reactor, when a decrease in yield is observed in one reactor (A), the reaction is started by switching the supply of the source gas to the other reactor (B) and In this method, reoxidation gas is supplied to the reactor (A) to perform reoxidation, and the reactor (A) and the reactor (B) are used while being switched. The former makes it impossible to produce alkanes during the reoxidation process, while the latter makes it possible to produce alkanes even during the reoxidation process. Which unsteady operation is used can be appropriately selected depending on required productivity and cost.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to the examples.

(Analysis of raw materials and products)
The analysis of raw materials and products was performed by gas chromatography. The number of moles of supplied alkane is A (mol), the number of moles of consumed alkane is B (mol), the number of moles of generated alkene is C (mol), and the number of carbons of the generated CO and CO ₂ alkanes is the standard. The alkane change rate X (%), the alkene selectivity S (%), the CO selectivity S (CO), and the CO ₂ selection, where D is the number of moles The rate S (CO ₂ ) and the alkene yield Y (%) are each expressed by the following formulas.

X = 100 × B / A (%)
S = 100 × C / B (%)
S (CO) = 100 × D / B (%)
S (CO ₂ ) = 100 × E / B (%)
Y = X × S / 100 = 100 × C / A (%)
[Example 1]
(Catalyst preparation)
60 ml of distilled water was added to 3.34 g of ammonium metavanadate (manufactured by Wako Pure Chemical Industries, Ltd.), and 2.28 ml of 25% by mass ammonia water was added while stirring with a stirrer. Further, 2.38 g of magnesium hydroxide (manufactured by Kanto Chemical Co., Inc.) and 0.94 g of an aqueous palladium nitrate solution (manufactured by NE Chemcat, Pd: 24.41% by mass) were simultaneously added to the aqueous solution. The solution was evaporated to dryness by heating and stirring, and the resulting solid was dried at 75 ° C. overnight. The obtained solid was ground in a mortar for 30 minutes and then baked at 550 ° C. for 6 hours in a box-type electric furnace. After standing to cool, the obtained solid was ground in a mortar for 30 minutes and then calcined again at 700 ° C. for 10 hours in a box-type electric furnace to obtain a catalyst. The powder X-ray diffraction (XRD) pattern of the obtained catalyst is shown in FIG. According to this, the obtained catalyst contains palladium oxide (PdO) and Mg ₃ V ₂ O ₈ . Further, although it could not be confirmed by XRD, it is estimated that Pd _x Mg _3-x V ₂ O ₈ is also contained. The palladium content of the catalyst was 5 mol%.

(Catalytic activity test)
0.5 g (10 to 20 mesh) of catalyst in a fixed bed flow type reactor (made of quartz glass, catalyst filling part (center part): φ8.5 mm × 30 mm, other glass tubes (both ends): φ3.5 mm, reaction) Tube total length: 250 mm), and both ends were fixed with quartz wool. The temperature inside the reaction tube was heated to 450 ° C. while flowing helium at 25 ml per minute. After reaching 450 ° C., the flow gas was switched to oxygen and flowed at 25 ml / min for 1 hour to pretreat (oxidize) the catalyst. After completion of the pretreatment, helium (25 ml / min) was allowed to flow for 10 minutes while maintaining the reaction temperature (450 ° C.), and then propane (4.3 ml / min, 14.4 kPa) and oxygen (1.2 ml / min) The raw material gas diluted with helium gas was circulated so that the total flow rate was 30.0 ml / min at 4.1 kPa), and oxidative dehydrogenation of propane was performed for 45 minutes. At this time, the propane conversion was 11.8%, the propylene selectivity was 61.4%, and the propylene yield was 7.2%. The catalyst activity test results are shown in Table 1.

[Example 2]
A catalyst preparation and a catalyst activity test were performed in the same manner as in Example 1 except that the catalyst activity test was performed at a flow rate of oxygen constituting the raw material gas of 2.4 ml (8.2 kPa) per minute. At this time, the propane conversion was 16.4%, the propylene selectivity was 35.6%, and the propylene yield was 5.8%. The catalyst activity test results are shown in Table 1.

[Example 3]
A catalyst preparation and a catalyst activity test were performed in the same manner as in Example 1 except that the catalyst activity test was performed at a flow rate of oxygen constituting the raw material gas of 3.6 ml (12.3 kPa) per minute. At this time, the propane conversion was 21.5%, the propylene selectivity was 32.4%, and the propylene yield was 7.0%. The catalyst activity test results are shown in Table 1.

[Example 4]
A catalyst preparation and a catalyst activity test were performed in the same manner as in Example 1 except that the catalyst activity test was performed at a flow rate of oxygen constituting the raw material gas of 0.6 ml (2.1 kPa) per minute. The propane change rate at this time was 9.6%, the propylene selectivity was 71.3%, and the propylene yield was 6.8%. The catalyst activity test results are shown in Table 1.

[Example 5]
A catalyst preparation and a catalytic activity test were performed in the same manner as in Example 1 except that the catalytic activity test was performed without circulating oxygen constituting the raw material gas. At this time, the propane conversion was 7.5%, the propylene selectivity was 91.6%, and the propylene yield was 6.9%. The catalyst activity test results are shown in Table 1.

[Example 6]
A catalyst preparation and a catalyst activity test were performed in the same manner as in Example 1 except that the catalyst activity test was performed with a reaction time of 105 minutes. At this time, the propane conversion was 8.8%, the propylene selectivity was 49.2%, and the propylene yield was 4.3%. The catalyst activity test results are shown in Table 1.

[Example 7]
A catalyst preparation and a catalyst activity test were conducted in the same manner as in Example 2 except that the catalyst activity test was conducted with a reaction time of 105 minutes. At this time, the propane conversion was 14.4%, the propylene selectivity was 28.4%, and the propylene yield was 4.1%. The catalyst activity test results are shown in Table 1.

[Example 8]
A catalyst preparation and a catalyst activity test were performed in the same manner as in Example 3 except that the catalyst activity test was performed with a reaction time of 105 minutes. At this time, the propane conversion was 18.8%, the propylene selectivity was 24.2%, and the propylene yield was 4.5%. The catalyst activity test results are shown in Table 1.

[Example 9]
A catalyst preparation and a catalyst activity test were performed in the same manner as in Example 4 except that the catalyst activity test was performed with a reaction time of 105 minutes. At this time, the propane conversion was 6.8%, the propylene selectivity was 64.9%, and the propylene yield was 4.4%. The catalyst activity test results are shown in Table 1.

[Example 10]
A catalyst preparation and a catalyst activity test were performed in the same manner as in Example 5 except that the catalyst activity test was performed with a reaction time of 105 minutes. The propane conversion rate at this time was 4.6%, the propylene selectivity was 95.7%, and the propylene yield was 4.4%. The catalyst activity test results are shown in Table 1.

[Comparative Example 1]
(Catalyst preparation)
The catalyst was calcined for 6 hours at 550 ° C., 49 hours at 625 ° C., 60 hours at 640 ° C., 15 hours at 750 ° C. and 15 hours at 800 ° C. without adding an aqueous palladium nitrate solution. Catalyst preparation was carried out in the same manner as in Example 1. In addition, the solid grinding | pulverization was performed like Example 1 between each baking process. The powder X-ray diffraction (XRD) pattern of the obtained catalyst is shown in FIG.

(Catalytic activity test)
A catalytic activity test was conducted in the same manner as in Example 1 except that the catalyst prepared by the above method was used. At this time, the propane conversion was 5.0%, the propylene selectivity was 58.1%, and the propylene yield was 2.9%. The catalyst activity test results are shown in Table 1.

[Comparative Example 2]
A catalyst activity test was conducted in the same manner as in Example 6 except that a catalyst was prepared in the same manner as in Comparative Example 1 and the catalyst was used in the catalyst activity test. At this time, the propane conversion was 5.0%, the propylene selectivity was 60.5%, and the propylene yield was 3.0%. The catalyst activity test results are shown in Table 1.

[Example 11]
A catalyst was prepared in the same manner as in Example 1, and a catalytic activity test (first time) was conducted in the same manner as in Example 1 using the catalyst. At this time, the propane conversion was 13.4%, the propylene selectivity was 57.9%, and the propylene yield was 7.8%. Thereafter, the gas flowing into the reactor while being maintained at 450 ° C. was switched to oxygen, and the gas was recirculated at 25 ml / min for 1 hour to reoxidize the catalyst. Further, the flow gas was switched to the raw material gas having the same composition as in Example 1 and flowed under the same conditions, and the catalytic activity test (after reoxidation) was performed for 45 minutes. At this time, the propane conversion was 11.8%, the propylene selectivity was 56.8%, and the propylene yield was 6.7%. The results of the catalytic activity test are shown in Table 2.

[Comparative Example 3]
A catalyst was prepared in the same manner as in Comparative Example 1, and the catalyst activity test (first time, after reoxidation) and reoxidation were performed in the same manner as in Example 11 except that the catalyst was used. The propane change rate in the first test was 4.9%, the propylene selectivity was 61.0%, and the propylene yield was 3.0%. Moreover, the propane change rate in the test after reoxidation was 6.7%, the propylene selectivity was 64.1%, and the propylene yield was 4.3%. The results of the catalytic activity test are shown in Table 2.

It is a powder X-ray diffraction (XRD) pattern of the catalyst obtained in Example 1 (A) and Comparative Example 1 (B).

Claims (5)

A catalyst for producing an alkene by oxidative dehydrogenation of alkane, which contains at least a palladium compound and magnesium orthovanadate (Mg ₃ V ₂ O ₈ ).   The method for producing a catalyst according to claim 1, wherein palladium nitrate is used as a palladium raw material, and ammonium metavanadate is used as a vanadium raw material.   A method for producing an alkene, which comprises oxidatively dehydrogenating an alkane using the catalyst according to claim 1.   The method for producing an alkene according to claim 3, further comprising a step of reactivating the catalyst by an unsteady operation.   The method for producing alkene according to claim 3 or 4, wherein propylene is produced by oxidative dehydrogenation of propane.

Images