There have been various proposals for the direct amination of aromatic compounds such as benzene using oxidic catalysts ; see for example CA 553 988, US 2 948 755, GB 1 327 494, and GB 1 463 997. Thus CA 553 988 proposes a vapour phase process using oxides of chromium, molybdenum, tungsten or niobium in combination with platinum, or reducible metal oxides such as oxides of iron, nickel, cobalt, tin, antimony, bismuth or copper. US 2 948 755 discloses a mixed gas/liquid phase process using a mixture of a Group Vlb metai, especiaiiy molybdenum, chromium or tungsten, and an easily reduced oxide, especially copper, iron, nickel, silver or gold.

GB 1 327 494 and GB 1 463 997 disclose processes employing a sealed autoclave wherein high pressures, e. g. above about 300 bar, are achieved using nickel/nickel oxide, or nickel/nickel oxide/rare earth oxide catalysts.

We have found that vanadium oxides are particularly suitable catalysts. Vanadium forms a number of oxides : it is believed that the most active species has a composition corresponding to a mixture of \/205 and V204. It is therefore desirable to operate the process under such conditions that the average valency state of the vanadium is below 5. This may be achieved by limiting the amount of oxygen present in the reaction mixture.

Accordingly the present invention provides a process for the production of an aromatic amine comprising contacting a gaseous mixture containing an aromatic compound and ammonia at an elevated temperature with a catalyst composition comprising at least one oxide of vanadium, there being, per mole of the aromatic compound, at least one mole of ammonia and a sub- stoichiometric amount of a hydrogen sink.

The aromatic compound is preferably an aromatic hydrocarbon, i. e. it is free from substituents other than hydrocarbyl groups, e.g. alkyl groups. Particularly suitable aromatic hydrocarbons are benzene, toluene and xylenes. Benzene is preferred.

In the present invention, at least one mole of ammonia per mole of aromatic compound is employed. Preferably there are 1. 1 to 120 moles, particularly 2 to 60 moles, most preferably 2 to 10 moles of ammonia per mole of aromatic compound.

The reactionofthe aromatic compound and ammonia is effected in the presence of a - hydrogen sink. The reaction is believed to be where Ar - H represents an aromatic compound and"H-sink"represents a hydrogen sink, i. e. a material capable of reacting with the hydrogen produced by the reaction of the aromatic compound and ammonia. The stoichiometric amount of hydrogen sink is thus that which would react with 2 hydrogen atoms for each molecule of aromatic compound employed. In the present invention, the amount of hydrogen sink used is sub-stoichiometric. Preferably the amount of hydrogen sink is

from 1 to 50%, particularly 2 to 50%, of the stoichiometric amount relative to the aromatic hydrocarbon. The hydrogen sink normally comprises a source of available oxygen, but may also contain other elements capable of reacting with hydrogen. Unless such other elements are also present, the stoichiometric amount of available oxygen is thus one atom of available oxygen per molecule of the aromatic compound, i. e. one gram atom of available oxygen peur mole of the aromatic compound. Preferably there are used from 0. 02 to 0. 5, more preferably from 0. 04 to 0. 5, particularly 0. 1 to 0. 5, gram atoms of available oxygen per mole of the aromatic compound.

Some or all of the hydrogen sink is available oxygen provided by the reduction of the vanadia from the higher valency, i. e. pentavalent, state to the lower valency, i.e. tetravalent, state, i. e.

Where the hydrogen sink is only the available oxygen so provided by the vanadia, there should thus be less than one mole, preferably less than 0. 5 mole, of vanadium pentoxide per mole of aromatic hydrocarbon. Unless excessive amounts of catalyst are employed, or the catalyst is subjected to regeneration by oxidation to the pentavalent state, the amount of reaction, i.e. yield per unit amount of catalyst, is therefore limited. It is therefore preferred to provide an additional hydrogen sink to react directly, i. e. to augment the hydrogen sink provided by reduction of the vanadia catalyst, and/or to provide a source of available oxygen for regeneration of the catalyst.

The additional hydrogen sink preferably is an oxygen-containing gas which may contain free gaseous oxygen or may have the oxygen in combined form. Using gaseous oxygen, preferably air, as a source of available oxygen, the overall reaction is believed to be 2Ar-H+2NH3+02->2Ar-NH2+2H20 so that the stoichiometric amount of oxygen is 0. 5 mole per mole of aromatic compound. Since some of the hydrogen sink is provided by the reduction of the vanadia, the amount of free oxygen fed to the reaction should be such that the total available oxygen fed to the reaction is sub- stoichiometric. Normally, the amount of free oxygen fed to the reaction is in the range 0. 01 to 0. 2, preferably 0. 02 to 0. 2, particularly 0. 05 to 0.2, moles of oxygen per mole of aromatic compound.

As indicated above, the oxygen-containing gas may contain oxygen in combined form. For example, the oxygen-containing gas may be, or contain, carbon dioxide or carbon monoxide. Here the oxygen-containing gas provides a hydrogen sink in the form of carbon in addition to the available oxygen. Thus it is believed that the reaction with carbon monoxide as the oxygen- containing gas is so that the stoichiometric amount of carbon monoxide is one mole of carbon monoxide per 3 moles of aromatic compound. Similarly, where the oxygen-containing gas is, or contains, carbon dioxide, the overall reaction can be represented as

so that the stoichiometric amount of carbon dioxide is one mole of carbon dioxide per 4 moles of aromatic compound. With methanol as the oxygen-containing gas, the reaction is believed to be so that the stoichiometric amount of methanol is one mole of methanol per mole of aromatic compound.

Surprisingly it has been found that little direct oxidation of the ammonia to nitric oxides or of the aromatic compound to carbon dioxide occurs. Indeed nitrogen oxides may be used as the oxygen-containing gas. Thus the reactions using nitrogen oxides are believed to be so that the stoichiometric amounts are one mole per moie of aromatic compound.

Although steam is not suitable as a hydrogen sink as it does not contain available oxygen, the presence of steam is not precluded, although its presence is not preferred except as a reaction product.

The process is preferably operated continuously, particularly with recycle of unreacted gases after separation of the product amine.

The process is preferably operated at a pressure below 20 bar abs. , more preferably below 10 bar abs. , particularly at a pressure in the range 1 to 7 bar abs. , most particularly between 2 and 5 bar abs. The reaction is effected at an elevated temperature, preferably at a temperature below 600°C, more preferably in the range 200-550°C, particularly in the range 300-500°C, more particularly between 350 and 450°C.

The vanadium oxides may be supported on a suitable inert support material : suitable supports include non-reducibte oxidic materials such as silica, zirconia. titania. atumina or calcium aluminate cement. The supports may contain stabilising additives as is known in the art. Alumina is the preferred support, particularly transition aluminas such as delta, theta or gamma alumina, especially those having a BET surface area of at least 100 m2/g, e.g. 100-200 m2/g. Typicaily the catalyst contains 1-15, preferably 5-15% by weight of vanadia, expressed as V205. Alternatively the catalyst may be unsupported, i. e. composed essentially of vanadia together with any activity promoters as described hereinafter, possibly with a small proportion, e. g. up to 10% by weight-ef the catalyst of a suitable binder such as a calcium aluminate cement or a clay.

The catalyst may be in any suitable physical form, for example powder, pellets, extrudates, or may be monolithic, e. g. a honeycomb structure. The physical form of the catalyst will depend on whether the process is designed to employ a fixed bed catalyst or a moving bed.

Where a supported catalyst is employed, the catalyst may be made by co-precipitation of the support and a suitable vanadium compound or by precipitation of a vanadium compound in the presence of the support, e. g. with the latter suspended in the medium in which the precipitation is effected. Alternatively the catalyst may be formed by coating the support with a suspension

containing a vanadium compound. Preferably the catalyst is produced by impregnation of the support with a solution of a vanadium compound, e. g. ammonium metavanadate. The composition is then heated if necessary to convert the vanadium compound to the oxidic state. The catalyst composition may also contain other components such as activity promoters. Examptes of additives include compounds of alkali metal, such as potassium, e. g. in amounts of 1 to 5% by weight (expressed as the alkali metal oxide M2O where M represents an alkali metal) of the catalyst, which may be useful to minimise the deposition of carbon during use of the catalyst, and/or noble metals such as platinum, and/or compounds of transition metals such as chromium, manganese, iron, cobalt, nickel or copper in amounts of up to 1 %, e.g. 0.05 to 0. 2%, by weight (expressed as the metal) of the catalyst.

As indicated above, it is believed that the most active state of the vanadia catalyst is a partially reduced state. Hence, prior to use, it may therefore be desirable to reduce the vanadia to the active state. This may be effected with a suitable reducing gas, such as hydrogen or carbon monoxide. Generally it is necessary to effect the reduction at temperatures above about 400°C. In some cases, the aromatic compound itself may exert sufficient reducing power, and/or sufficient of the ammonia fed may crack at the operating temperature to provide hydrogen to effect the reduction. If an oxygen-containing gas, which may be substantially pure oxygen, enriched air, un- enriched air, or preferably air in admixture with an inert diluent, e.g. nitrogen, is co-fed with the aromatic compound and ammonia, this will tend to oxidise the vanadium to a higher oxidation state.

By limiting the proportion of oxygen-containing gas relative to the aromatic compound, the extent of such oxidation may be decreased. Thus the valency state of the vanadium may be controlled by controlling the proportion of oxygen-containing gas and/or by controlling the proportion of an inert diluent, e. g. nitrogen, which has the effect of modifying the partial pressure of the oxygen- containing gas.

Alternatively, or additionally, the oxidation state of the vanadium may be controlled by feeding hydrogen or another reducing gas such as carbon monoxide, continuously, or intermittently, in a controlled manner to maintain the vanadium oxide in the desired state.

The process is preferably operated at a space velocity, i. e. total gas volume (expressed at NTP) fed per hour per volume of catalyst in the range 100 to 10,000 h-'.

During use, carbon is liable to be deposited on the catalyst as a result of side reactions, - e. g. decomposition of the aromatic compound. Such deposited carbon tends to de-activate the catalyst. Such deposited carbon may be removed by regenerating the catalyst by contact with air or oxygen at an elevated temperature in the absence of the aromatic compound. Such regeneration may be effected periodically, e. g. by employing two or more beds of catalyst so that one or more beds are on reaction duty while another is being regenerated, or continuously by employing a moving bed wherein part of the bed is on reaction duty while another part is undergoing regeneration. For example the catalyst may be provided in the form of a rotating bed which during one rotation passes through a zone wherein deposited carbon is burnt off, possibly a

reduction zone where the catalyst is reduced to a lower valency state and then the reaction zone.

In such an arrangement the catalyst is preferably in the form of a coating of vanadia on a monolithic honeycomb support.

Alternatively a flowing, e. g. ftuidised powder, catalyst may be employed.

In a preferred form of the invention, using a moving catalyst bed, the catalyst is cycled through a plurality of stages, inctuding a reaction stage wherein the vanadia is reduced to the tetravalent state and the amine is formed, e. g. and then an oxidation stage wherein the vanadia is oxidised to the pentavalent state it may be desirable to reduce part of the vanadia to the tetravalent state before the reaction stage.

It has been noticed that when the catalyst is used for the amine-forming reaction, in some cases a relative large proportion of byproducts may initially be formed. This is believed to be the result of the presence of some"over-active"sites. Accordingly it is preferred that such"over-active" sites are subject to a reaction before contact of the catalyst with the aromatic compound. For example, if a catalyst that has been used for the reaction and is largely in the tetravalent state, the catalyst is preferably oxidised to the pentavalent state and then subjected to partial reduction before contact with the aromatic compound.

A process operated in stages may also be applied to other catalysts having a variable oxidation state or that may be readily reduced to the elemental form, e. g. iron, cobalt, nickel, chromium, manganese, copper, platinum, silver and gold.

Accordingly the present invention also provides a process for the production of an aromatic amine by contacting a gaseous mixture of an aromatic compound and ammonia at an elevated temperature with a catalyst composition comprising at least one metal that can be oxidised from a lower valency state to a higher valency state, said process comprising a plurality of stages including a reaction stage wherein the catalyst in the higher oxidation state is reacted with the aromatic compound and ammonia to form the amine with the reduction of the catalyst to said lower valency state, and a subsequent oxidation stage wherein the catalyst is contacted with an oxygen- containing gas to oxidise said-catalyst to the higher valency, i. e. oxidation, state : Preferably, in such a process, at least one mole of ammonia is used per mole of aromatic compound. While an excess of oxygen may be employed for the oxidation stage to ensure that the catalyst is oxidised to the higher vaiency state, the amount of oxygen-containing gas, if any, employed in the reaction stage is preferably sub-stoichiometric relative to the aromatic compound.

Indeed, may be desirable that the catalyst is partially reduced to the lower valency state before the reaction stage.

In a preferred form of the invention it may be desirable to introduce the reactants sequentially. Thus the catalyst in the higher oxidation state may first be contacted with ammonia

and then the thus treated catalyst contacted with the aromatic compound. The ammonia is adsorbed onto the catalyst and the aromatic compound reacts with the adsorbed ammonia at the same time effecting reduction of the catalyst to the lower valency state. The catalyst is then contacted with the oxygen-containing gas, before and/or after separating the product amine and any unreacted ammonia and aromatic compound, to effect oxidation to the higher valency state.

The sequence of processes, using vanadia as the catalyst, is as follows A process employing sequential introduction of the reactants may be effected in a batch process or in a continuous process using a moving bed of catalyst. Alternatively a semi-continuous process may be adopted where there is periodic reversal of flow of the reactants through the catalyst bed. Thus the process may be operated cyclically wherein, in a first stage, ammonia and the aromatic compound are fed through the catalyst bed in a first direction, then in a second stage, an oxygen-containing gas is fed through the catalyst bed in the direction opposite to the first direction, then in a third stage, ammonia and the aromatic compound are fed through the catalyst bed in the direction opposite to the first direction, and in a fourth stage the cycle is completed by feeding an oxygen-containing gas through the catalyst bed in the first direction. Preferably, in each of the first and third stages, ammonia is first fed through the catalyst bed and then the mixture of ammonia and the aromatic compound is fed through the catalyst bed.

Examples of embodiments of the invention are illustrated by reference to the accompanying drawings in which Figures 1 and 2 are a diagrammatic flowsheets of alternative fluidised vanadia catalyst systems, and Figures 3a to 3d illustrate a process using a fixed catalyst bed with flow reversal. Figure 4 is a cross section of a reactor for use in a variant of the flowsheets of Figures 1 and 2.

Referring to Figure 1, a reaction vessel 10 is provided with means (not shown) to remove a vanadia catalyst in a small particle form, e. g. a powder of average size 50-500 pm, from its lower end, and to return the catalyst particles, via line 12, to the upper end. A gas containing free oxygen, -e.g. air, is fed to the vessel at the lower end of the vessel via line 14 and effects fluidisation of the catalyst particles and also effects removal of any deposited carbon by combustion, the carbon dioxide produced passing up through the reaction vessel 10. The oxygen also effects oxidation of the vanadium in the catalyst to the pentavaient state in this region of the vessel (designated A in Figure 1). Part way up the reaction vessel ammonia and the aromatic compound, e. g. benzene, are introduced via line 16 and pass up the vessel, reacting to form the amine, i. e. aniline where the aromatic compound is benzene. This reaction region of the vessel is designated B. At the upper end of the vessel, in the region designated C, the excess of aromatic compound and ammonia effect reduction of the catalyst, having the vanadium in the pentavalent

state, recycled to the top of the vessel to give the vanadium in a valency state below 5 so that the catalyst is in the active state when it contacts the mixture of oxygen, aromatic compound and ammonia passing up the reaction vessel. At the top of the vessel the mixture of gaseous products, viz. the amine, water, excess aromatic compound and ammonia, nitrogen and carbon dioxide, is removed and sent, via line 18, to a separation unit (not shown) wherein the product amine is separated. The excess of the aromatic compound and ammonia can also be separated and recycled to line 16. The vessel is maintained at the requisite temperature by preheating the feeds thereto.

In the alternative arrangement of Figure 2, two vessels are employed. In the first vessel 20, the catalyst is fluidised in the lower part D of the vessel by an oxygen-containing gas, e. g. air, fed to the bottom of the vessel via line 22. The aromatic compound and ammonia are also fed to the bottom of the vessel via line 24. The catalyst is taken from the bottom of the vessel via line 26, and fed to the lower end of a column 28 to the bottom of which an oxygen-containing gas, e. g. air, is fed via line 30. The oxygen-containing gas fed to column 28 serves to oxidise the catalyst to the pentavalent state and to transport it to the upper end of the column from whence it is fed, via line 32, to the top of the vessel 20. The excess of oxygen-containing gas is exhausted from the top of column 28 via line 34. The upper portion E of vessel 20 has an enlarged cross section compared to the lower portion D so that, while the catalyst is fluidised in the lower portion D, it"rains"down through the upper portion E. Reduction of the catalyst takes place in the upper portion E. The product stream leaves the top of vessel 20 via line 36.

The arrangement of Figure 2 may also be adapted to provide for sequential introduction of the reactants. Thus the aromatic compound is introduced to the lower portion of zone D via line 24, and ammonia introduced at a location part way up zone D via line 38. In this embodiment, the oxygen-containing gas injected via line 22 may be omitted and an inert gas, e. g. nitrogen, may be fed via line 22 to the bottom of zone D to effect the fluidisation. Alternatively the aromatic compound, preferably in admixture with an inert diluent such as nitrogen, may be fed via line 22 to effect fluidisation.

In the arrangement of Figures 3a to 3d, the catalyst is disposed as a fixed bed in a vessel 40 provided with a number of inlet ports and with outlet ports at each end of the vessel and the process operated cyclically. - During a first period, as shown in Figure 3a, ammonia is fed to one (first) end of the vessel via line 41 a and passes through the catalyst bed and leaves the vessel at the opposite (second) end via line 42b. While continuing to supply ammonia via line 41 a, introduction of the aromatic compound to the first end of the vessel is then commenced via line 43a. The reaction proceeds with the reduction of the catalyst to the lower valency state, and the products are removed from the second end of the vessel through line 42b.

After a period of time, as shown in Figure 3b, the flows of ammonia and aromatic compound via lines 41 a and 43a are stopped and an oxygen-containing gas is introduced through

line 44b at the second end of the vessel and passes through the catalyst, effecting oxidation thereof to the higher oxidation state, and feaves via line 42a at the first end of the vessel.

During a third period, as shown in Figure 3c, the flow of oxygen-containing gas is stopped and ammonia is fed to the second end of the vessel via line 41 b and the flows through the bed leaving the vessel via line 42a at the first end of the vessel. Then the flow of aromatic compound is commenced via line 43b at the second end of the vessel. The reaction proceeds and the products leave the first end of the vessel via line 42a.

After a further period of time, as shown in Figure 3d, the flows of ammonia and aromatic compound via lines 41 b and 43b are stopped and an oxygen-containing gas is introduced through line 44a at the first end of the vessel and passes through the catalyst, effecting oxidation thereof to the higher oxidation state, and leaves via line 42b at the second end of the vessei. After oxidation of the catalyst, the cycle is complete and can be repeated.

In a process of this type, a number of catalyst-containing vessels may be employed in parallel but out of phase so that product formation is continuous. Instead of having separate ports, at each a single port can be employed with valves to effect switching between the various streams.

In the variant shown in Figure 4, the reactor comprises a cylindrical vessel 50 provided with an internal baffle in the form of an open-ended hollow cylinder 51. Air is introduced at the lower end of the vessel via ports 52 and 53 to effect fluidisation of the catalyst and circulation of the latter up through the cylinder 51 and then back down through the annulus 54 between the outer shell of the vessel 50 and the exterior surface of the cylinder 51.

A mixture of benzene and ammonia are supplied to the lower end of the annulus 54 via ports 55, and ammonia is supplied, via port 56 into the upper part of the interior of the cylinder 51.

The products are removed via outlet port 57.

In this embodiment, the reaction of the benzene and ammonia is effected in the annulus 53 and the catalyst leaving the reaction zone at the lower end of the annulus and passing up through the cylinder 51 is oxidised by the air flowing up through the cylinder 51. In the upper part of cylinder 51, the catalyst is reduced by the ammonia injected through port 56, so that the catalyst leaving the inner cylinder 51 at the top thereof is in the active state. Instead of using ammonia to effect the reduction of the catalyst, an alternative reducing gas, for example hydrogen, may be introduced through port 56. Where the amount of air required to effect circulation and fluidisation is such that too much oxygen would be introduced, the gas used to effect fluidisation and/or circulation may be an inert gas such as nitrogen and the requisite amount of oxygen may be introduced via port 52. Thus nitrogen may be introduced via ports 53 and air through port 52.

The invention is illustrated by the following examples.

Example 1 y-alumina extrudates (AL 3992-etc) of about 2-3 mm length and having a BET surface area of 180 m2/g were impregnated with an aqueous solution of ammonium metavanadate, dried, and calcine at 550°C for 3 h to give a catalyst containing 8% by weight of vanadia, expressed as

Vz05. 12. 68 g of the catalyst was placed in a fixed bed reactor of 1 cm intemal diameter. The reactor was heated to about 450°C and the catalyst was reduced to V204 by passing a mixture of hydrogen and nitrogen through the bed for 16 h.

A mixture of benzene, ammonia and oxygen diluted with nitrogen in moiar proportions of 3 moles of ammonia, 0. 05 moles of oxygen, and 2. 45 moles of nitrogen per mole of benzene was then continually passed through the catalyst bed at a space velocity of 300 h''at a temperature of 450°C at a pressure of about 9 bar abs.

The reaction products were then cooled below 10°C, and the organic phase collected for analysis. The maximum amount of aniline produced, expressed as a percentage of all carbon- containing products (excluding unreacted feed components), was about 71% by weight.

At the termination of the experiment, after 48 hours, the catalyst had the vanadium in the valency state 5. It was observed that the activity increased with time and then decreased, passing through a peak corresponding to a vanadium valency state between 4 and 5.

Example 2 A vanadium oxide/alumina catalyst was prepared as described in Example 1 and the oxidation state before and after reduction was determined. The catalyst as prepared was examined by X-ray diffraction (XRD) and the only vanadium oxide phase detected was that of V205. The reduction of the catalyst was studied by thermogravimetric analysis (TGA), the catalyst being heated in a stream of 5% hydrogen in nitrogen was compared to heating in a stream of nitrogen. A weight loss of 1 % was detected between 410 and 535°C when the sample was heated in the hydrogen-containing stream. This corresponded to the loss of one oxygen atom from each V205 unit, i. e. reduction from V205 to V204.

The extent of re-oxidation was also determined by pulsing oxygen over a reduced catalyst.

Thus immediately after reduction at 500°C, a catalyst was subjected to aliquots of dioxygen while the catalyst bed was still at 500°C. The amount of dioxygen adsorbed was determined and hence the ratio of O(ads):V2 was calculated and found to be 1. 1 : 1.

Example 3 A catalyst was prepared as described in Example 1. The catalyst was reduced at 450°C in flowing hydrogen/nitrogen for 16 h. The catalyst was cooled to 400°C and the gas flow was then switched to a gas flow-containing ammonia/benzene/oxygen having a moiar-ratio-of 150:-24: 1, at a pressure of 2 bar abs. and a space velocity of 300 h-'. The variation of aniline yield with time is shown in the Table below.

Example 4 A catalyst was prepared as described in Example 1. The catalyst was reduced at 450°C in flowing hydrogen/nitrogen for 16 h. The catalyst was cooled to 350°C and the gas flow was then switched to a gas flow containing ammonia/benzene/oxygen having a molar ratio of 17 : 8 : 1, at a pressure of 2 bar abs. and a space velocity of 300 h-'. The variation of anitine yield with time is shown in the following table. Time (min) Aniline yield (arbitrary units) Example 3 Example 4 5 0 - 10 8 38 18 28 20 2342 13 41 41 5436 4 62 28 2 75 15 1 82 17 - 92 12 1015 109 2 - 120 1 -

Example Silica spheres (Fuji Sylisia, Q10) of about 5 mm diameter and having a BET surface area of 300 m2/g were impregnated with an aqueous solution of ammonium metavanadate, dried, and calcine at 873 K for 3 h to give a catalyst containing 12% by weight of vanadia, expressed as V205. The catalyst was subjected to a flow of benzene, ammonia, and oxygen in the ratio 1 : 3 : 0. 05.

The contact time was 3. 5 s, the temperature 723 K, and the pressure 7. 5 bara. Under these conditions the initial molar selectivity, based on carbon containing products was 17%. as the run continued the selectivity increased to give a molar, selectivity of 87%.

Examp!e6.

The catalyst in Example 5 was subjected to different ammonia ratios. When the benzene : ammonia : oxygen ratio was 1 : 100 : 0. 05 the selectivity increased from 87% to 96%.

Example 7 The catalyst in Example 5 was subjected to sequenced flows, such that individual flows of benzene, ammonia, and oxygen were passed over the catalyst. The initial sequencing rate was such that each flow was on-line for 15 s. The test was then repeated with a sequencing rate of 9 s.

In both cases aniline was produced. The production of aniline was equivalent to the continuous flow system with a 15 s sequence, however with the shorter time sequence, the yield was increased by 30%.

Example 8 In a calculated example of the invention using the flowsheet of Figure 1 to produce aniline at a rate of 10 kmol/h, the catalyst consists of particles of vanadia supported on alumina of average size 250 pm. The catalyst contains 8% by weight of vanadia expressed as Vz05 and is circutated via line 12 at a rate of 12640 kg per hour (approx. 5.6 kmol/h of vanadia expressed as Vz05). Air is fed via line 14 at 25°C and at a pressure of 3 bar abs. A mixture of benzene and ammonia (5 motes of ammonia per mole of benzene) is fed at 3 bar abs and at 210°C via line 16. For simplicity it is assumed that no carbon is deposited on the catalyst so that in the oxidation zone A, the catalyst is simpty oxidised to the pentavalent state and no carbon dioxide is formed. In the reduction zone C, part of the vanadia is reduced to the tetravalent state. It is assumed that some oxidation/reduction occurs in zone B, but that most of the catalyst leaving the bottom of zone B is in the tetravalent rate and is oxidised in zone A to the pentavalent state. The calculated flow rates and temperatures are set out in the following table. Component flow rate (kmol/hr) Location Temp ( C) °2 N2 C6H6 NH3 C6HsNH2 l-120 14 255. 620. 9 A (top) 4722. 820. 9 16 210 - - 27. 8 138. 9 - - B (top) 411 0. 0 20. 9 17. 8 128. 9 10. 0 10. 0 18 472 0. 0 21. 3 17. 8 128. 2 10. 0 11. 1 Example 9 In a calculated example of the invention using the flowsheet of Figure 2 to produce aniline at a rate of 10 kmol/h, the catalyst consists of particles of vanadia supported on alumina of average size 250 um. The catalyst contains 8% by weight of vanadia expressed as V205 and is circulated via line 32 at a rate of 12639 kg per hour (approx. 5.6 kmol/h of vanadia expressed as V205). Air is fed to vessel 20 via line 22 at 330°C and at a pressure of 5 bar abs. A mixture of benzene and ammonia (5 moles of ammonia per mole of benzene) is fed at 5 bar abs. and at 200°C viå line 24.

Air is fed to the base of column 28 at 330°C and at a pressure of 5 bar abs. For simplicity it is assumed that no carbon is deposited on the catalyst so that in the cotumn 28, the catalyst is simply oxidised to the pentavalent state and no carbon dioxide is formed. In the reduction zone E, part of the vanadia is reduced to the tetravalent state. It is assumed that some oxidation/reduction occurs in zone D, but that most of the catalyst leaving the bottom of zone D is in the tetravalent rate and is oxidised in column 28 to the pentavalent state. The calculated flow rates and temperatures are set out in the following table. Temp Component flow rate (kmol/hr) Location s'"P------ ( C) °2 N2 C6H6 NH3 C6HsNH2 H2O 22 3302. 810. 5 24 200 - - 27. 8 138. 9 - - D (top) 416 0.0 10.5 17.8 128.9 10.0 10.0 36 397 0.0 10.8 17.8 128.2 10.0 11.1 30 330 52.0 195.6 34 397 49.2 195.6 The temperature of the catalyst leaving the zone D via line 26 is 375°C.