FR2720741A1 - Prepn. of aliphatic carboxylic acids and aldehyde(s) - Google Patents

Abstract

A process for the prepn. of aliphatic acids and aldehydes contg. at least 2C, and their mixt., by the controlled oxidn. of the corresp. alcohols in the presence of a catalyst comprising an active phase on an inert support. The active phase is based on V, Ti and O2, making up 0.10-0.15% of the catalyst.

Description

PROCESS FOR THE PREPARATION OF ALIPHATIC CARBOXYCIC ACIDS,

  AUPHATIC ALDEHYDES, OR THEIR MIXTURE,

  BY HOUSEHOLD OXIDATION OF THE CORRESPONDING ALCOHOLS

  The present invention relates to a process for the preparation of aliphatic carboxylic acids, aliphatic aldehydes, comprising at least two carbon atoms, or a mixture thereof. The process according to the invention consists in carrying out a controlled oxidation of the corresponding alcohol with a source of oxygen, in the presence of a catalyst comprising an inert support and an active phase based in particular on titanium, vanadium and oxygen, the latter representing 0.1 to 15% by total weight

of the catalyst.

  More particularly, the present invention is suitable for the preparation of acetic acid, acetaldehyde, or a mixture thereof, by gentle oxidation of rethanol with

  a source of oxygen, in the presence of such a catalyst.

  Obtaining carboxylic acids or aliphatic aldehydes, by gentle oxidation of the corresponding alcohol, in liquid or gas phase, are methods

known to those skilled in the art.

  However, it can be seen that the implementation of these methods has drawbacks. Thus, in the case where one proceeds in the liquid phase, according to certain modes, the catalyst is in the homogeneous phase, which leads to difficulties in separating the catalyst subsequently. According to other modes, the reaction is not carried out with a catalyst but with a compound used in proportions

  stoichiometric, oxidation reagent which is consumed during the reaction.

  As regards gas phase oxidations, and in particular the preparation of acetic acid from ethanol, two-stage processes are known, which are currently used on an industrial scale. First, an ethanol dehydrogenation reaction is carried out in the gas phase by reaction on a fixed bed of a catalyst based on copper and silica, at a temperature of the order of 250 to 300 C. It is also possible to carry out an oxidative dehydrogenation

  of this compound at 500 ° C., by passage over a fixed bed of a silver-based catalyst.

  In a second step, the acetaldehyde thus obtained is transformed into acetic acid by oxidation in air, in the liquid phase, at a temperature of the order of 60 C under a pressure of about 2.5 bar absolute. The catalyst used in this second

  step is based on cobalt and / or manganese.

  The disadvantage of this type of process, except for the main fact that it comprises two stages, resides in the fact that it gives at best an overall yield of the order of 90%. It is also known to prepare carboxylic acids to flavor corresponding alcohols in the gas phase in a single step. Thus, one can cite the process for the manufacture of acetic acid from ethanol in the presence of a catalyst based on heterogenized palladium, deposited on a mixed compound of titanium, phosphorus and oxygen. However, this process does not make it possible to obtain a sufficiently high selectivity for acetic acid formed and the productivity is very low. Finally, the synthesis

of this catalyst seems difficult.

  The object of the present invention therefore consists in proposing a method for the direct synthesis of aliphatic carboxylic acids comprising at least two carbon atoms from the corresponding alcohol, in one step, for which the alcohol conversion rate and the selectivity for carboxylic acid are as high as possible, while using a catalyst of simple composition and easy to prepare. In order to solve a problem of this type, it has been described in French patent application 94 01923, a catalyst based on vanadium, titanium and oxygen as constituents of the active phase. The performance of this type of catalyst, used in a controlled oxidation reaction of ethanol to acetic acid, is

  improved over the performance of conventional catalysts used.

  It has now been found that the catalyst used in the process according to the invention, comprising an inert support with an active phase based on titanium, vanadium and oxygen and whose vanadium content is reduced, exhibits intrinsic activity increased, without any decrease in acid selectivity being observed. In addition, the process according to the invention is carried out at temperatures

  low, of the order of 100 to 300 C.

  Furthermore, it has been found that the process according to the invention makes it possible to obtain, depending on the more or less reducing nature of the reaction medium, the corresponding aldehyde,

  selectively, or a mixture of acid and aldehyde.

  Another advantage of the process according to the invention lies in the fact that the productivity is even higher when the operating conditions are favorable for the production of a carboxylic acid / aldehyde mixture than when it is used in

  conditions for the selective production of one or other of the compounds.

  The fact that two different compounds are produced poses no problem in itself. Indeed, these two compounds are easily separable and it is possible, if

  we only want to get the acid, to recycle the aldehyde produced.

  These and other objects are achieved by the present invention which therefore relates to a process for the preparation of aliphatic carboxylic acids, aliphatic aldehydes, these two compounds comprising at least two carbon atoms, or of their mixture, by phase reaction gaseous of the corresponding alcohol, with a source of oxygen, in the presence of a catalyst comprising an active phase and an inert support, said active phase being based on vanadium, titanium and oxygen, and

  representing 0.1 to 15% by weight of the catalyst.

  It has therefore been found that the catalyst used in the process according to the invention makes it possible to obtain a practically quantitative transformation of ralcool,

  with very high acid or aldehyde selectivity.

  In addition, it has been found that the selectivity in combustion products is significantly reduced compared to what is commonly obtained according to known methods. Finally, as a direct consequence of the improved selectivity of the reaction, the

  quantity of by-products is lowered.

  All these factors combined in particular result in simplifying the

  subsequent separation of the acid or aldehyde produced.

  In addition, as indicated above, the method according to the invention

  has the advantage of being very productive, in comparison with known methods.

  Another advantage of the present invention is that the process is carried out under mild conditions in temperature and pressure, and simplified due to the

  possibility of carrying out the reaction in air.

  Finally, as already mentioned, the catalysts used in the process of the invention are simple compositions, comprising little or no

  noble metal, and which can also be prepared using simple methods.

  But other advantages and characteristics of the invention will appear more

  clearly on reading the description and the examples which follow.

  For convenience, the catalyst used in the invention will

first be described.

  As already mentioned, the catalyst comprises an active phase with

an inert support.

  According to a first variant of the invention, the active phase is diluted in the

  inert support (mass catalyst).

  According to a second variant, the active phase is coated or dispersed at the

  surface of the inert support (coated catalyst).

  The active phase of the catalyst is based on vanadium, titanium and oxygen.

  In the following description, the vanadium will be designated by V205 and the

  proportions in this element will be expressed in relation to this same compound.

  The amount of vanadium in the active phase of the catalyst, therefore expressed as V205, is between 0.1 and 30% by weight. It should be noted that contents outside this range are not excluded although they do not provide additional advantages. According to a more particular embodiment of the invention, the catalyst used in the present invention comprises an active phase whose content of

  vanadium, expressed as V205, is between 0.2 and 15% by weight.

  The titanium present in the active phase can be either in the form of

  TiO2 anatase, rutile, brookite or even bronze (symbolized (B)), or their mixtures.

  Preferably, the allotropic form of the titanium oxide is chosen from the

  anatase, rutile forms, or mixtures thereof.

  The titanium oxide used in the composition of the catalytic phase also has a specific surface, measured according to the B.E.T. , between 1 and

  m2 / g. More specifically, the specific surface is between 10 and 120 m2 / g.

  According to a particular embodiment of the invention, the amount of active phase

  0.2 and 10% by weight of the catalyst is included.

  It has in fact been found in a completely surprising manner that such small amounts of active phase in the catalyst make it possible to obtain a very high selectivity.

  high in the desired product, as well as high productivity.

  Furthermore, the active phase of the catalyst used in the present invention can

include at least one dopant.

  The dopant is chosen from the following: Na, K, Rb, Cs, Mg, Ca, Sr, Ba, La, Zr, Nb, Cr, Mo, W, Mn, Re, Fe, Ru, Co, Ni, Pd , Cu, Ag, Zn, Cd, B, AI, Ga, In, Ti, Si,

Ge, Sn, P, As, Sb and Bi.

  Usually, the amount of dopant in the active phase is between 0.01 and 20 atomic% relative to vanadium. Preferably, the amount of dopant

is 0.5 to 10 atomic%.

  The active phase of the catalyst used in the present invention can be

  obtained by any method known to those skilled in the art.

  It is possible, for example, to envisage manufacturing said active phase by mixing the oxides of the elements constituting the active phase or of compounds capable of transforming into oxide when they are brought to high temperatures. The mixture is then subjected to a calcination step, optionally followed and / or preceded by a

grinding said mixture.

  Another suitable method for the preparation of the active phase consists in carrying out the following steps: - a mixture is prepared based on the constituent elements of the active phase; - one or more of said elements is optionally precipitated; - the possibly treated mixture is dried;

- the dried product is calcined.

  By constituent elements, we mean not only vanadium and titanium but

  also the dopant (s) added if necessary to the composition of the active phase.

  Usually the building blocks are used in the form of a solution

or a suspension.

  Advantageously, the dispersing (or solubilizing) medium is fine, although any other type of dispersant (or solvent) is possible. As such, we can cite

  in particular alcohols, such as methanol, ethanol, isopropanol, tert-butanol.

  The constituent elements of the active phase entering into the composition of the aforementioned mixture, are generally used in the form of salts of inorganic acids

  or organic, or in the form of compounds such as oxides or their derivatives.

  All the acids or oxide derivatives indicated are suitable for the preparation of the mixture insofar as these can decompose into oxide of the

corresponding elements.

  As examples of salts of inorganic acids suitable for the preparation of the abovementioned mixture, there may be mentioned, inter alia, nitrates, sulfates,

  halides comprising one or more halogens, ammonium salts.

  As examples of salts of acids or organic esters, mention may be made of

  formate, oxalate, tartrate, acetate, acetylacetonate, ethylhexanoate.

  As indicated previously, it is also possible to use oxides or their derivatives; these compounds can be used in the form of particles, or

  dissolved, in particular by adding an acid or a base to said mixture.

  By oxide derivatives is meant compounds of the type of oxyhalides, alkoxides, aryloxides, glycoxides in particular

  It should be noted that all of these compounds can be used alone or as a mixture.

  By way of examples of compounds comprising vanadium, suitable for the implementation of this method of preparation, there may be mentioned, without intending to be limited, vanadyl sulfate, ammonium metavanadate, vanadium oxyhalides such as , in particular, VOCI3, (V02) CI, VOCI, VOBr, VOBr2, VOF3, VOF2, VF4, VBr2, V12, vanadyl acetylacetonate, vanadyl oxalate, metavanadic acid, vanadium hexacarbonyl, vanadium oxide triisopropoxide, the oxides of

  vanadium such as, for example, V205, V7013, VO, VO2, V203, V307.

  As a compound comprising titanium, mention may be made of compounds of the TiX4 type with X representing a halogen and more particularly chlorine, compounds of the Ti (OR) 4 type with R representing an alkyl group and more particularly the

  ethyl, isopropyl or sec-butyl radicals.

  Also suitable for the implementation of the invention titanium oxide under its

  various allotropic forms, that is to say in anatase, rutile, brookite or (B) form.

  As regards the compounds based on a dopant, these are chosen from potassium chlorides, potassium acetate, rubidium chlorides, niobium chloride or oxychloride, niobium oxalate, cesium sulfate, cesium acetate, iron sulfate, iron acetate, chromium chlorides or chlorates, chromium nitrates, chromium acetate, chromium acetylacetonate, dimethylbdate ammonium, metatungstate and ammonium paratungstate, oxides and alkyloxides, such as ethoxide, zirconium, silver oxide Of course, this list

  cannot be considered as limiting.

  The temperature at which the mixing of the constituent elements is carried out is usually between 20 ° C. and the boiling point of the dispersant or

solvent chosen.

  In general, the concentration of said mixture varies between 0.1 and 5 M. The amounts of the various constituent elements are used so as to obtain a composition corresponding to the proportions of V205 and of doping, if necessary

indicated above.

  According to a first particular embodiment, the drying of the

mixture obtained.

  Drying can be carried out in two stages: the first consisting in evaporating the solvent or dispersant from the mixture, until dry, the second in drying the paste thus obtained. Generally, the first step is carried out at a temperature varying from 20 to

  i 00 C for the time necessary to obtain a non-flowing paste.

  Evaporation is usually carried out with stirring.

  The resulting paste is then dried, in a second step, under a preferably non-reducing atmosphere, such as oxygen or air for example,

  for an average duration of 15 hours.

  The drying temperature is usually around 120 C.

  It should be noted that other drying methods can be envisaged, such as for example, the drying of the suspension by atomization in any type.

  of apparatus known to those skilled in the art.

  According to a second particular embodiment, a step of precipitating at least one of the constituent elements present in dissolved form is carried out,

  prior to drying described above.

  Said elements can be precipitated, either simultaneously or successively

  In addition, all or part of these may be precipitated during this operation.

  In the latter case, the first and second steps can be carried out as many times as necessary so that the product to be dried contains all the constituent elements.

  of the active phase in precipitated form.

  All the compounds can be used as precipitating agent insofar as they combine with one or more constituent elements, in the form of a compound insoluble in the medium chosen and insofar as the resulting insoluble compound

  provides access to the oxide of the combined element (s).

  Conventionally, the agent or agents used are chosen, among others, from bases such as ammonia in particular, or from inorganic or organic acids, such as hydrochloric acid or even citric acid. It is to highlight that

  water can constitute a precipitating agent suitable for the implementation of the invention.

  Obviously the choice of precipitating agents is not limited to this single list,

given as an indication.

  Usually, precipitation is carried out with stirring.

  The temperature at which it is carried out, generally varies between 20 C and the

  boiling point of the chosen solvent.

  Finally, the precipitation step (s) can if necessary be followed by ripening steps. These consist in leaving the precipitate in suspension, with stirring,

  for a period varying from 30 minutes to approximately 4 hours.

  The ripening temperature is within the temperature range

indicated above.

  The products obtained according to each of the abovementioned modes are then subjected to a

calcination step.

  This is carried out, in a conventional manner, under a non-reducing atmosphere.

  Advantageously, air is used, but oxygen could just as easily be used.

  The calcination temperature is usually between 200 and 1200 "C.

  Generally, the duration of the operation varies between 1 and 24 hours.

  Before and / or after the calcination step, the dried product

  may undergo a grinding or deagglomeration stage.

  The catalyst used in the process according to the present invention

  further includes an inert support.

  As has been specified before, the catalyst can be in the form of a mass catalyst, that is to say that the active phase is mixed with the

inert support.

  According to a second embodiment of the invention, the catalyst is located under the

  coated form, that is to say that the active phase is on the surface of the inert support.

  A preferred embodiment of the invention consists of catalysts of the coated type.

  The nature of the inert support is not critical, except that it must be inert to

  with reagents under the selected reaction conditions.

  As materials which can be used as inert catalyst support, mention may be made of: silica, alumina, silica-alumina, sintered clay, magnesia, magnesium silicate, diatomaceous earth. These types of support can be used in porous form or not. Preferably, the support used is in little or non-porous form. If necessary, these can be glazed in order to

make such.

  Ceramic materials, such as cordierite, alumina, muUite, porcelain, silicon nitride, boron nitride, silicon carbide, can also be used

as an inert support.

  In the particular case of silicon carbide, preferably a

  inert support with an apparent porosity of at least 10%.

  Preferably, the inert support of the catalyst used according to the invention is

  chosen from clay, silicon carbide.

  The catalyst is in the form of beads or rings. By rings we mean hollow objects whose section is circular, parallelepiped, ellipsoidal among others. We can also consider any other type of complex structure obtained

  by extrusion of the inert for example (cross, star, etc.).

  The size of the balls or rings is in particular between a few micrometers and ten millimeters. It should be noted that this depends on the mode of implementation of the catalyst. Thus, by way of indication, a catalyst used in a fixed bed has a particle size distribution generally between 0.5 and 6 mm. The particle size of the particles of a catalyst used in a fluidized or moving bed is usually between 5 and 700 microns, and preferably between 5 and

microns for 80% of the particles.

  According to a particularly advantageous embodiment of the invention, the

  catalyst support is in the form of rings.

  The catalyst according to the invention can be obtained according to any known method of

the skilled person.

  Here and for the remainder of the description, the term “phase precursor” is understood

  active, the mixture of the constituent elements of this phase in all the states prior to the calcination step described previously. Thus, according to a first embodiment, the inert support is brought into contact, preferably in the form of rough particles, and the active phase or its precursor, in a high shear mixer (LODIGE type devices) or in a

  granulation device (drageers, in the form of a drum or plate).

  The operation is generally carried out at a temperature varying between 20 and 150 C for the time necessary for coating the inert support with the desired amount of

  active phase, more particularly in air, for at least 30 minutes.

  The particles thus obtained are usually calcined at a temperature between 300 and 600 C, preferably between 450 and 500 C.

  The duration of the calcination is generally at least 3 hours.

  A second possible method of manufacturing the catalyst consists in

  application of the impregnation technique.

  According to this technique, the inert support is impregnated with a suuion of the

  active phase or with a suspension or solution of its precursor.

  The impregnation step is followed by a drying step, usually carried out at a temperature between 100 and 200 ° C., in air, for at least

minutes.

  We can then repeat the impregnation-drying cycle and end it by

calcination in air.

  The calcination temperature is between 400 and 600C for one

ten hours.

  A possible variant consists in carrying out a calcination between the o'J the impregnation-drying cycles. According to a third mode of preparation of the catalyst, the required quantity of inert support is added to the mixture of at least one of the constituent elements of the active phase. The mixture thus obtained is then treated in accordance with the various modes of reactivation of the process for preparing the catalytic phase, as described above, namely the stages of possible precipitation, drying and

cacination.

  Of course, all these methods of preparation are given for information only and

  cannot in any case constitute an exhaustive list.

  As mentioned previously, the present invention relates to a process for the preparation of aliphatic carboxylic acids, aliphatic aldehydes, these two types of compounds comprising at least two carbon atoms, or their

  mixture, from an aliphatic alcohol comprising at least two carbon atoms.

  According to a preferred embodiment of the indication, the process is particularly suitable for the preparation of acetic acid, acetaldehyde, or their mixture, by reaction in the gas phase, of ethanol with an oxygen sourcew in the presence of a

  catalyst as defined above.

  There are no special conditions regarding the quality of the alcohol used. However, for obvious questions of separation of formulated J, it is preferred to use an alcohol having a purity of at least 90%. A so-called technical alcohol, that is to say comprising a few percent of water, is therefore suitable

the realization of the invention.

  The controlled oxidation reaction of the alcohol is carried out in the presence of a source of oxygen. This can be based on pure oxygen or diluted in an inert gas, such as helium, argon or nitrogen. According to a particular embodiment of the invention, the reaction is carried out

  oxidation using air as the oxygen source.

  A variant of the process consists in using a gas mixture comprising, in addition to

the other constituents, water.

  The composition of the gaseous mixture, alcohol, oxygen source and water, can

vary within wide limits.

  Unless otherwise stated, all the percentages indicated below are expressed

  in mole percent of the gas mixture.

  Generally, the alcohol content in the gas mixture is between 0.5 and 30%. Preferably, the composition of the gas mixture is such that ron

  is outside the explosive domain.

  According to a variant, the alcohol content in the mixture is between 0.5 and

3% or between 10 and 30%.

  Preferably, the alcohol content is between 1 and 3% or between 10 and

20%.

  The oxygen content in the gas mixture used is between

0.5 and 20%.

  According to a more particular embodiment, the oxygen content in the

  gas mixture varies between 2 and 20%.

  The water content in the gas mixture used is between 0 and%.

  Preferably, the water content in the above mixture is from 0 to 20%.

  The water / alcohol molar ratio in the mixture is more particularly understood

between 0.5 and 10.

  The complement to 100% being constituted by the inert gas mentioned previously. According to a first embodiment of the invention, the reaction of

  under conditions such that essentially the carboxylic acid is obtained.

  According to this first mode, the molar ratio between oxygen and alcohol is higher

  to 1. More particularly, the molar ratio is between 1.1 and 10.

  According to a second embodiment of the invention, the reaction of the

  conditions such that the product obtained essentially is aldehyde.

  In this case, the molar ratio of oxygen to alcohol is less than 1. More

  in particular, said ratio is between 0.1 and 0.8.

  According to a third embodiment of the invention, the reaction conditions

  are such that a mixture of the carboxylic acid and of aldehyde is obtained.

  This variant is implemented with a molar oxygen / alcohol ratio of about 1. The gas mixture is therefore brought into contact with the catalyst according to the invention. The device in which the method according to the invention is implemented is one of the conventional devices for catalytic reactions in the gas phase; these

  the latter can be used continuously or discontinuously.

  Thus, the reaction can be carried out in the presence of a catalyst in a fixed, fluidized bed.

or transported.

  The processing temperature is generally between 100 and 300 C and

  more particularly between 120 and 280 C.

  The total pressure of the reaction gas mixture generally varies between 0.5 and 3

absolute bar.

  The feed flow of the reactants, relative to the volume of the catalytic bed is

between 360 and 10,000 h-1.

  The separation of the acid or aldehyde formed is carried out in a conventional manner.

  It should be noted that it is simplified compared to conventional methods in so far as, according to the first and second embodiments explained above, the selectivity of the oxidation reaction to carboxylic acid or to aldehyde is very

  high, and since the alcohol conversion is practically complete.

  Consequently, the separation of the acid or of the aldehyde consists essentially only in separating these products from the other compounds, essentially under

gaseous form, and water.

  The acid or aldehyde formed are therefore separated from each other, if necessary, and from gaseous by-products, in the usual manner. It is therefore possible to carry out cooling and then condensation of a mixture comprising acid and / or aldehyde, water. The carboxylic acid can be separated from the aldehyde / water mixture by fractional distillation. he

  can be separated from water by liquid-liquid extraction or fractional distillation.

* The aldehyde is finally separated from the water by fractional distillation.

  Concrete but nonlimiting examples of the invention will now be presented.

EXAMPLES

  In the following examples, the performance of the catalysts is calculated as follows: - conversion of ethanol (% mol) conv. ethanol = (# mole ethanol entered - # mole ethanol released) X 100 (# mole ethanol entered) - oxygen conversion (% mol) conv = (# mole 0 entered - # mole O, output) 100 (# mole 02 between) - selectivity of product X (acetic acid. acetaldehyde, combustion products) (% mol) sel. X- number mole ethanol converted to X100 (number mole ethanol entered - number mole ethanol released) EXAMPLE 1 comparative Preparation of the catalyst 1 g of TiO02 (i.e. 1.125 mol), having a BET surface area equal to 100 μg (marketed by Rhône- Poulenc) are introduced into a bezel and dry impregnated

  per 200 cm3 of a vanadyle oxalate solution.

  The solution used comprises 28.89 g of oxalic acid dihydrate (i.e. 229.26 mmol) and 12.86 g of commercial V205 from JANSSEN (i.e. 70.6 mmol) in water.

  The product thus obtained is calcined in air at 500 ° C. for 3 hours.

  The composition of the calcined product has 12.5% by weight of V205 and a ratio

V / Ti of 0.126.

  g of the active phase thus prepared are deposited on 100 g of clay beads with an average diameter of 5 mm (marketed by Rhône-Poulenc) by coating with

  bezel, using an aqueous glucose solution.

  The product is then calcined in air at 500 ° C. for 3 hours.

  The final active phase content of the catalyst is 18% by weight.

  The amount of V205 in the catalyst is 2.2% by weight.

EXAMPLE 2:

  Preparation of catalyst 2: 90 g of TiO2 (i.e. 1.125 mol), having a BET surface area equal to 100 m2 1g (marketed by Rhône-Poulenc) are introduced into a bezel and impregnated to dryness

  per 130 cm3 of a vanadyle oxalate solution.

  The solution used comprises 17.59 g of oxalic acid dihydrate (i.e. 140 mmol)

  and 8.47 g of commercial V205 from JANSSEN (i.e. 46.5 mmol) in water.

  The product thus obtained is calcined in air at 500 ° C. for 3 hours.

  The composition of the calcined product has 8.6% by weight of V205 and a ratio

V / li of 0.083.

  An inert support consisting of 7 mm silicon carbide cylinders is introduced into a rotary oven, preheated to a temperature between 200 and 250 ° C.

  outer diameter and 9 mm in height, with an apparent porosity of 36%.

  An amount of active phase obtained previously is sprayed onto the support so as to obtain a catalyst comprising 5% by weight of active phase by

  based on the total weight of the catalyst.

  Calcination is carried out at 500 ° C. in air for 3 hours.

  A catalyst is then obtained comprising 5% by weight of active phase and a

V / Ti ratio of 0.083.

EXAMPLE 3

  Use of catalysts 1 and 2 for the selective preparation of acetic acid The catalyst (20 cm3) is introduced into a continuous stainless steel reactor with a fixed bed, equipped with heating by fluidized sand bath and two on-line chromatographs, one operating with a flame ionization detector and the other with a thermocondometric detector.

  The feed gases are controlled by mass flow meters.

  Ethanol and water are introduced in liquid form via a

dosing pump (HPLC GILSON).

  The feed flow (expressed in mol%) consists of:

  ethanol / 02 / H20 / N2 = 2.5 / 18.5 / 5/74.

  The hourly volume speed is 6400 h-1.

  The reactor pressure is kept constant at 1.7 bar absolute.

  selectivity productivity catalyst V205 T conversion (% (gAcOH / Ih) (g) (C) (%) AcOH COx

1 0.443 185 87 96 4 360

2 0.054 220 95 94 3 384

  V205 represents the amount of V205 in the reactor.

  This table clearly shows that the catalyst 2 according to the invention is more productive, because with a quantity of vanadium considerably reduced than the catalyst 1, one

  achieves higher acetic acid productivity.

EXAMPLE 4

  Use of catalyst 2 for the selective preparation of acetaldehyde The conditions are similar to those of the previous example except that: - the feed stream (expressed in mol%) consists of: ethanol / 02 / H20 / N2 = 30/10/20/40, - the hourly volume speed is 3200 h-1, - the pressure is maintained at 1.7 bar absolute,

  - the processing temperature is 170 to 200 C.

  The catalyst performances are as follows: ethanol conversion: 21% (theoretical conversion: 33%) selectivity: Acetaldehyde: 90%, Acetic acid: 3%,

Products of combustion: 4%.

  acetaldehyde productivity: 350 g / I / h.

EXAMPLE 5

  Use of catalyst 2 for the preparation of acetic acid and acetaldehyde The conditions are similar to those of Example 3 except that: - the feed stream (expressed in mol%) consists of: ethanol / 02 / H20 / N2 = 14/14/16/56, - the hourly volume speed is 2000 h-1, - the pressure is maintained at 1.7 bar absolute, - the processing temperature is 205 C, the catalyst performance are as follows: ethanol conversion: 68% selectivity: acetic acid: 44%, acetaldehyde: 39%,

Products of combustion: 12%.

  acetic acid productivity: 220 g / Vh,

acetaldehyde: 150 g / Vh.

  This example clearly shows that under these conditions, the process according to the invention is very productive since it makes it possible to obtain a cumulative productivity in acid equivalent

acetic acid of 425 g / h / l.

Claims (14)

  1 / Process for the preparation of aliphatic carboxylic acids, aliphatic aldehydes, comprising at least two carbon atoms, or of their mixture, by gentle oxidation of the corresponding alcohols, with a source of oxygen, characterized in that one carries out the reaction in the presence of a catalyst comprising an active phase with an inert support, said active phase being based on vanadium,   of titanium and oxygen, and representing 0.1 to 15% by weight of the catalyst.   2 / Method according to the preceding claim, characterized in that a   catalyst whose active phase represents 0.2 to 10% by weight of the catalyst.   3 / Method according to any one of the preceding claims, characterized in that   that a catalyst is used whose active phase has an amount of vanadium, expressed in V205 of between 0.1 and 30% by weight of the active phase, and   preferably between 0.2 and 15% by weight.   4 / Method according to any one of the preceding claims, characterized in that   that a catalyst is used whose active phase comprises at least one dopant chosen from Na, K, Rb, Cs, Mg, Ca, Sr, Ba, La, Zr, Nb, Cr, Mo, W, Mn, Re, Fe, Ru, Co, Ni, Pd,   Cu, Ag, Zn, Cd, B, AI, Ga, In, TI, Si, Ge, Sn, P, As, Sb and Bi.   / Method according to the preceding claim, characterized in that the dopant content is between 0.01 and 20 atomic% relative to the vanadium, and preferably 0.2 to 10 atomic%.   6 / A method of preparation according to any one of the preceding claims,   characterized in that a catalyst is used whose inert support is chosen from clay, silicon carbide.   7 / A method according to any one of the preceding claims, characterized in that   that a catalyst is used whose active phase is mixed with the inert support.   8 / A method according to any one of claims 1 to 6, characterized in that one   uses a catalyst whose active phase is coated or dispersed on the surface of the inert support.   9 / A method according to any one of the preceding claims, characterized in that   that a catalyst is used which is in the form of a ball or rings.   / Method according to any one of the preceding claims, characterized in that   that the reaction is carried out with a gas mixture comprising 0.5 to 30 mol% of alcohol.   11 / A method according to any one of the preceding claims, characterized in that   that the alcohol used is ethanol.   12 / A method according to any one of the preceding claims, characterized in that   that is used as the source of oxygen for air or oxygen.   13 / A method according to the preceding claim, characterized in that one carries out the   reaction with a gas mixture comprising 0.5 to 20 mol% of oxygen.   14 / A method according to any one of the preceding claims, characterized in that   that a gas mixture comprising water is used.   15 / A method according to the preceding claim, characterized in that one uses a   gas mixture comprising 0 to 40% by mole of water and preferably 2 to 20%.   16 / A method according to any one of the preceding claims, characterized in that   that a gas mixture is used comprising a diluent gas chosen from rare gases or nitrogen.