WO2004071657A1

WO2004071657A1 - Process for the regeneration of mixed oxide catalysts

Info

Publication number: WO2004071657A1
Application number: PCT/EP2004/000939
Authority: WO
Inventors: Achim Fischer; Andreas Martin; Angelika BRÜCKNER; Ursula Bentrup; Christoph Weckbecker; Klaus Huthmacher
Original assignee: Reilly Industries, Inc.
Priority date: 2003-02-12
Filing date: 2004-02-03
Publication date: 2004-08-26
Also published as: DE10305650A1

Abstract

The invention relates to a process for the regeneration of mixed oxide catalysts that are used in ammonoxidation for the production of nitriles, by passing an oxidizing agent over the catalyst at elevated temperature. The invention relates in particular to catalysts that contain compounds of the elements antimony, vanadium, silicon, titanium and oxygen and optionally of one or more alkali metals.

Description

Process for the Regeneration of Mixed Oxide Catalysts

Field of the Invention

The present invention relates to a process for the regeneration of mixed oxide catalysts that are used in ammonoxidation for the production of nitriles by passing an oxidizing agent over the catalyst at elevated temperature. The invention relates in particular to catalysts that contain compounds of the elements antimony, vanadium, silicon, titanium and oxygen and optionally one or more alkali metals.

Background of the Invention

Several processes are known for the production of cyanopyridines by reacting the corresponding methylpyridines with ammonia and oxygen at an elevated temperature in the gaseous phase. These processes differ as regards the conditions of the reaction and the composition of the catalyst. Of the processes and catalysts, only those that exhibit a good selectivity and service life and at the same time have a high space-time yield are appropriate for use on an industrial scale.

From EP 0 726 092 Bl it is known that the requirements can be met by catalyst systems of the general empirical formula

in which

X¹ denotes silicon, the Si being obtained from the highly dispersed silicon dioxide used in the production and at least one layer silicate,

X² denotes at least one of the elements of the alkali metal series, b = 0.5 - 2 c = 3 - 10 d = 2 - 20 e = 0.01 - 2

f = number of atoms necessary to achieve stoichiometric saturation of the remaining components and calculated from the valences and relative proportions .

From EP 0 059 414 Bl it is known that catalysts for the production of 3-cyanohydrin can be obtained having a good selectivity and high space-time yield from layer lattice silicates, highly dispersed silicon dioxide and oxygen-containing compounds of the elements iron, titanium, copper, cobalt, manganese and nickel, wherein the atomic ratio of antimony to vanadium is greater than 1. These catalysts contain layer lattice silicates and highly dispersed silicon dioxide in a total amount of 10 to 60 wt.-%, with the proviso that the quantitative ratio of layer lattice silicate to silicon dioxide is 20 to 1 to 0.25 to 1. The catalysts have a BET surface of 5 - 50 m²/g, a macropore volume of 0.1 - 0.8 cm³/g and a mean pore radius of 1 to 8 x 10^"7 cm.

With this type of catalysts the activity decreases only after several years' use. This deactivation is manifested by the fact that the conversion and/or product yield decrease. The deactivation can be compensated only to a limited extent. For this, reaction parameters such as temperature, pressure, residence time or composition of the reaction mixture must be matched to the altered activity of the catalyst. A matching of these parameters inevitably means however that the process can continue to be operated only inefficiently, uneconomically and/or not at all, with the result that the spent catalyst has to be replaced by a fresh catalyst. A process for the regeneration of the described catalysts is not hitherto known.

Instead, the catalyst has to be produced anew.

The object of the present invention was to provide a process for the regeneration of the spent catalysts and to achieve once again with. the regenerated catalysts high yields and high selectivities such as are described for example in EP 0 059 414 Bl and EP 0 726 092 Bl .

From JP 63 208 575 A (DERWENT AN 88-283060) catalysts based on antimony oxides and vanadium oxides are known, which in addition contain oxides of the alkali metal K and of the alkaline earth metals Cs, Rb and Tl and aluminum oxide as carrier. A process has now been found by means of which a deactivated catalyst can be regenerated at elevated temperatures using a gaseous oxidizing agent.

Summary of the Invention

The present invention provides a process for the regeneration of a heterogeneous mixed oxide catalyst that is employed in the production of nitriles by ammonoxidation in the gaseous phase and whose composition is based on antimony oxides and vanadium oxides, characterized in that an oxygen-containing gas free of reducing compounds is passed at a temperature of 300°C to 900°C, in particular 350°C to 680°C, over the catalyst.

Description of the Invention

The catalyst preferably contains at least one further oxide of the elements iron, copper, titanium, cobalt, manganese, nickel and optionally several carrier substances and optionally compounds of one or more alkali metals or alkaline earth metals. The catalyst was preferably employed in processes for the production of 3-cyanopyridine by catalytic reaction of 3-methylpyridine and ammonia and oxygen at elevated temperature.

The deactivated catalyst is treated for a period of 2 to 48 hours, in particular 7 to 20 hours, preferably 8 to 14 hours, with a gaseous oxygen-containing oxidizing agent.

As oxidizing agents there may be used pure oxygen, oxygen diluted with inert gases, especially air or compounds such as hydrogen peroxide or N₂0 that release oxygen on decomposition.

The regeneration may be carried out in a pressure range from 1 to 10 bar (absolute) , preferably 1 to 4 bar (absolute) . The oxygen equivalent of the regenerating gas that is added should be in the range from 5 to 35 vol.-%, advantageously 15 to 25 vol.-% of the total amount of the gas. The remainder consists of inert compounds such as for example nitrogen.

Si0₂ or layer lattice silicates are particularly suitable as carrier substances for the catalyst, though Ti0₂ or aluminum oxide may also be employed.

The process is particularly suitable for the catalysts known from EP 0 726 092 Bl and EP 0 059 414 Bl .

For the production of the catalysts known from EP 0 059 414 Bl antimony and vanadium as well as the elements iron, copper, titanium, cobalt, manganese and nickel are used, conveniently as compounds with oxygen, in elementary form, or as compounds that can be converted into compounds containing oxygen, preferably as oxides, as . , ammonium salts of their oxygen-containing acids, or as nitrates .

The quantitative ratios are chosen so that in the catalysts the atomic proportion of antimony is greater than that of vanadium. The atomic ratios of antimony to vanadium are conveniently between 1.1 to 1 and 50 to 1, preferably between 1.1 to 1 and 25 to 1. Suitable atomic ratios of antimony to iron, cobalt, copper, manganese and nickel, individually or jointly, may be 2 to 1 to 20 to 1, preferably 3 to 1 to 10 to 1. However, the atomic proportions of iron, cobalt, copper, manganese and nickel, individually or jointly, should not exceed the proportion of vanadium. Suitable atomic ratios of antimony to titanium are 1 to 3 to 8 to 1, preferably 1 to 2 to 4 to 1.

A mixture of layer lattice silicate and highly dispersed silicon dioxide is added to the thus formulated catalyst substances, so that the proportion of the mixture in the catalysts is 10 to 60 wt.-%, preferably 20 to 40 wt.-%. The quantitative ratio of layer lattice silicate to highly dispersed silicon dioxide is, in parts by weight, 20 to 1 to 0.25 to 1, preferably 10 to 1 to 1 to 1.

The highly dispersed silicon dioxide may be obtained in any suitable way, for example by pyrolysis of silicon compounds or by precipitation from solutions of silicon compounds. The silicon dioxide conveniently has a BET surface of about 50 to 500 m²/g, preferably 100 to 300 m²/g.

A process for the production of catalysts is known from EP 0 726 092 Bl, in which there are used antimony, vanadium, titanium as well as silicon and elements of the alkali metal series, conveniently as compounds with oxygen, in elementary form or in the form of compounds that can readily be converted into oxygen-containing compounds, such as nitrates, oxalates or carbonates, one or more of the substances optionally being in the form of a solution or slurry. The solution thus obtained and containing solids fractions is boiled while stirring and maintained initially at a low pH between 0 and 2 , preferably between 0.5 and 1.5. Towards the end of this boiling phase the reaction mixture is cooled, the pH is raised with a base, preferably ammonia, and adjusted to a value between 3 and 6, preferably 4 and 5, and reboiled. The suspension thus obtained may be directly processed further after cooling to < 50°C. To this end it is dried in a spray dryer at temperatures between 200°C and 700°C at rotational speeds between 20, 000 and 60,000 rpm. The grain size can be specifically adjusted depending on the temperature and rotational speed. The powder is separated in a cyclone.

_*

The powder that is thereby obtained may be directly processed further. The complicated stages of drying, grinding and intermediate calcination are omitted in this procedure.

The finished catalysts generally have a BET surface of about 5 to 50 m²/g, a macropore volume of about 0.1 to 0.8 cm³/g and a mean pore radius of about 1 to 8 x 10^"7 cm. Their bulk density is about 0.9 to 1.4 kg/1. Depending on their shape and size, they are employed in a fixed bed or in a fluidized bed.

Before the regeneration a catalyst present in the form of a molded article is generally ground unless it already exists in finely particulate form. It may however also be regenerated as a molded article.

The present invention also provides a process for the production of 3-cyanopyridine by reacting 3-methylpyridine with ammonia and oxygen at elevated temperatures, followed by the regeneration of the catalysts described above.

Processes for producing 3-cyanopyridine include for example the processes described in EP 0 059 414 Bl, EP 0 070 395 Bl. and EP 0 726 092 Al.

According to EP 0 059 414 Bl the reaction of 3-methyl- pyridine with ammonia and oxygen to form 3-cyanopyridine is conventionally carried out in the gaseous phase. The reaction conditions may be chosen within a broad range. The reaction is mainly carried out without the use of pressure or under a slight excess pressure of up to about 3 bar, at temperatures between about 320°C and 460°C, preferably at temperatures between 340°C and 440°C. The necessary oxygen is advantageously added in the form of air, and steam is also mixed in with the gases. The quantitative ratio of 3-methylpyridine to ammonia, oxygen or air and optionally steam may be chosen within wide limits. In general it is convenient to employ, per mole of 3-methylpyridine, about 2 to 10 moles, preferably 3 to 8 moles, of ammonia, about 10 to 40 moles, preferably 25 to 35 moles, of air, and about 2 to 10 moles, preferably 3 to 8 moles, of steam. Conveniently about 1 to 2 moles of . 3-methylpyridine per liter bulk volume of the catalyst and per hour are fed into the reactor.

After the regeneration the initial activity of the catalyst is restored. It is surprisingly found that, despite, the temperature conditions prevailing during the conversion of 3-methylpyridine to 3-cyanopyridine, the oxidative regeneration of the catalyst with oxygen-containing gases can be successfully achieved with the simultaneous presence of oxygen in the gaseous phase.

In the examples, % denotes wt.-% unless otherwise specified. The following terms are employed in the following examples:

Conversion = (moles of converted hydrocarbon/moles of employed hydrocarbon) l00%

Yield = (moles of produced product/moles of employed hydrocarbon) l00%

GHSV = Gas Hourly Space Velocity = (volume of gas fed in/time x bulk volume of the catalyst) [1/hl = 1/h]

Selectivity = (yield/conversion) x 1-00 Example 1 (according to EP 0 059 414 Bl)

23.3 kg of antimony trioxide, 4.7 kg of ammonium metavanadate, 12.8 kg of titanium dioxide, 11.7 kg of montmorillonite and 5.8 kg of highly dispersed silicon 5 dioxide with a surface of 200 m²/g were made into a slurry in 140 1 of water. 16.4 1 of 54% strength nitric acid were then added. The mixture was slowly heated to boiling point, 7 1 of water were added and the mixture was kept for 2 hours at the boiling point, following which the mixture

10. was adjusted to a pH of 4.6 with ammonia, cooled, heated to 300°C in a cylinder dryer and ground in a pin mill to a grain size of below 0.5 mm. 4500 g of the catalyst mixture prepared in this way were thoroughly mixed with 225 g of graphite and 1700 g of a 20% aqueous urea solution and then

15 formed into extruded articles of 3 mm diameter. The extruded articles were heated in the stream of air, more precisely kept for 15 hours at 120°C, 2 hours at 550°C, 1 hour at 650°C and 3 hours at 770°C. The bulk density of the catalyst was 1.05 kg/1, the BET surface was 18 m²/g,

20 the macropore volume was 0.28 cm³/g and the mean pore radius was 2.7xl0^"7 cm.

Example 2

A catalyst was used that had been produced according to Example 1. 1485 1 of gaseous mixture, referred to 1 liter

25 of catalyst, were added per hour. The gaseous mixture contained, per mole of 3-methylpyridine, 6 moles of ammonia, 30 moles of air and 9 moles of steam. The gaseous mixture was added, preheated, to a tubular reactor. The tubular reactor was maintained at 340°C. The product gas

30 was analyzed by means of gas chromatography. 82% of the methylpyridine used had been converted. The yield of 3-cyanopyridine referred to the 3-methylpyridine used was 75 mole %. Example 3 (deactivated catalyst)

A catalyst that had been produced according to Example 1 and had become deactivated after several years' use was employed. 1485 1 of gaseous mixture, referred to 1 liter of catalyst, were added per hour. The gaseous mixture contained, per mole of 3-methylpyridine, 6.1 moles, of , ammonia, 29.7 moles of air and 8.9 moles of steam. The gaseous mixture was added, preheated, to the tubular reactor. The tubular reactor was kept at 350°C. The product gas was analyzed by means of gas chromatography. 24.7% of the methylpyridine used had been converted. The yield of 3-cyanopyridine referred to the 3-methylpyridine used was 24 mole %.

Example 4 (oxidative treatment of a deactivated catalyst)

2400 1 of air were added over a period of 12 hours at a temperature of 600°C to 1 liter of the deactivated catalyst from Example 3. The reaction was then carried out at 350°C, as described in Example 3. 92% of the methylpyridine' employed had reacted. The yield of 3-cyanopyridine referred to the 3-methylpyridine employed was 88 mole %.

Example 5 (oxidative treatment of a deactivated catalyst)

2400 1 of air were added over a period of 12 hours at a temperature of 600°C to 1 liter of the deactivated catalyst from Example 3. The reaction was then carried out, as described in Example 2, at a reaction temperature of 377°C. 96% of the methylpyridine used had reacted. The yield of 3-cyanopyridine referred to the 3-methylpyridine employed was 93 mole %.

Claims

What is claimed is:

1. Process for the regeneration of a mixed oxide catalyst that has been used in the production of nitriles by ammonoxidation in the gaseous phase and whose composition is based on antimony oxides and vanadium oxides, wherein an oxygen-containing gas free of reducing compounds is passed over the deactivated catalyst at a temperature of 300°C to 900°C.

2. Process according to claim 1, wherein the catalyst additionally contains at least one of the compounds of the elements iron, copper, titanium, cobalt, manganese, nickel with oxygen and optionally compounds of one or more alkali metals or alkaline earth metals.

3. Process according to claims 1 and 2, wherein the catalyst contains silicon dioxide and/or layer lattice silicates.

4. Process according to claim 1, wherein the oxygen- containing gas free of reducing compounds is passed over the catalyst at a temperature of 350°C to 680°C.

5. Process according to claim 1, wherein mixed oxide catalysts that have been used in the production of cyanopyridines from methylpyridines , ammonia and oxygen, are regenerated.

6. Process according to claim 1, wherein oxygen, air or N₂0 and H₂0₂ as donor substance are used as oxidizing agent for the regeneration.

7. Process according to claim 1, wherein the oxygen is added in a percentage volumetric proportion of 5 - 35 vol.-%, preferably 15 - 25 vol.-%, to the regenerating , gaseous mixture.

8. Process according to claim 1, wherein the gas is passed over at a pressure of 1 to 10 bar, preferably 1 to 4 bar.

9. Process according to claim 1, wherein the gas is passed for 2 to 48 hours, in particular 7 to 20 hours, over the deactivated catalyst.

10. Process for the production of 3-cyanopyridine by reacting 3-methylpyridine with ammonia and oxygen using a heterogeneous mixed oxide catalyst based on antimony oxides and vanadium oxides and for the subsequent regeneration of the deactivated catalyst, wherein oxygen-containing gas free of reducing compounds is passed at a temperature of 300°C to 900°C, preferably 350°C to 680°C, over the deactivated catalyst.

11. Process according to claim 10, wherein the deactivated catalyst is left in the reactor used for the production of the 3-cyanopyridine and is regenerated in si tu .