FR2779427A1 - METHOD FOR DEHYDROGENATING AN ORGANIC COMPOUND USING A CATALYST COMPRISING A PEROVSKITE - Google Patents

Abstract

The invention concerns a method for dehydrogenating an organic compound characterised in that it consists in using a catalyst comprising an ABO3 type structure perovskite. It is particularly useful for dehydrogenating ethylbenzene for preparing styrene. Said method consists in using in particular perovskites wherein B represents at least an element selected from the group comprising manganese, iron, cobalt and chromium and A represents at least a rare earth.

Description

PROCESS FOR DEHYDROGENATION OF AN ORGANIC COMPOUND USING

  A CATALYST COMPRISING A PEROVSKITE

RHODIA CHEMISTRY

  The present invention relates to a process for dehydrogenation of a compound

  organic using a catalyst comprising a perovskite.

  Dehydrogenation processes are used in the preparation of several organic compounds. Mention may very particularly be made of the process for preparing styrene which uses the dehydrogenation of ethylbenzene in the presence of water. These dehydrogenation reactions must be catalyzed to

  obtain acceptable yields and selectivities from an industrial point of view.

  As catalysts which can be used for this reaction, systems based on iron oxide and potassium carbonate for example or mixed systems of oxides are known, these systems being able to be doped with elements such as

  molybdenum, vanadium, cerium or tungsten.

  The object of the invention is to provide new catalysts for the

dehydrogenation.

  To this end, the process according to the invention for the dehydrogenation of a compound

  organic is characterized in that a catalyst is used comprising a perovskite.

  While the catalysts of the prior art require a more or less complex formulation to obtain the catalytic composition based on the active elements concerned, the catalyst used in the present invention may be present in the form of

  form of a single phase of simpler preparation.

  Other characteristics, details and advantages of the invention will also appear

  more fully on reading the description which follows, as well as the various

  concrete but non-limiting examples intended to illustrate it.

  The process of the invention applies in particular to dehydrogenation reactions in which at least one C-C single bond is transformed into a C = C double bond. Mention may in particular be made of the reactions allowing the preparation of dienes from ethylenic carbides, for example the preparation of chloroprene from 2-chloro-butene-1 and 3-chloro-butene-1 or else the dehydrogenation of butene-1 to obtain the butadiene. Mention may also be made of the dehydrogenation of aromatic hydrocarbons, such as the transformation by dehydrogenation of alkyl aromatic compounds into alkylene aromatic compounds, for example the dehydrogenation of alkylbenzene to allylbenzene. We can quote everything

  particularly the dehydrogenation of ethylbenzene for the preparation of styrene.

  The dehydrogenation reactions are carried out in a known manner. In the case of the dehydrogenation of ethylbenzene for the preparation of styrene, the following operating conditions may be indicated, by way of nonlimiting example. The reaction is carried out at a temperature generally between approximately 500 and approximately 700 C. It can be carried out at atmospheric pressure or at a lower pressure or even under pressure. It is preferred to carry out the process continuously. Water or steam can be used with the reagent to help remove carbonaceous residue from the catalyst. The catalyst is preferably used in a fixed bed, in

one or more reactors.

  Within the meaning of the present invention, the term perovskite is understood to mean compounds having the ABO3 type structure in which A represents a substituted or unsubstituted element, coordinated with 12 oxygen atoms and B a substituted or unsubstituted element, coordinated with 6 atoms of oxygen. This ABO3 type structure must be understood, here

  and for the whole of the description, in the broad sense, that is to say that it corresponds to the

  structure of the products in which the elements A and B can be partially substituted as well as the lacunar structures, structures which can be represented by the formula A1.xA'xB1 yB'yO3.d in which A 'and B' represent the respective substituents of A and B, x and y verify the relations 05x <1, 05y <1, d can be zero or verify the relation -0,155d <+0.5, the incomplete structures corresponding to those in which d is different from 0. The structure is generally of cubic type but the cubic mesh can be more or less deformed according to the quantity and the

nature of the substituent.

  It is advantageous to use a perovskite of which a constituent element is capable of exhibiting, in part, at least two different oxidation states. This constituent element may thus be present in the perovskite in a first oxidation state, for example in state 11, and another part of this same element may be present or may be liable to appear in another state of oxidation for example in state III, the passage of a part of the element from one oxidation state to another taking place as a function of the operating conditions under which the catalyst is used. We can of course use a perovskite with several elements

of that type.

  According to a particular variant of the invention, a perovskite is used in which the aforementioned element, likely to present in part at least two different oxidation states is mainly element B. This element likely to present in part at least two different oxidation states, can be more particularly chosen from the group comprising manganese, iron, cobalt and chromium. More particularly, it is possible to use a perovskite in which the iron and the cobalt are present in combination, the iron possibly

  in particular be in majority atomic proportion with respect to cobalt.

  According to another variant, a perovskite is used of which at least one constituent element is a rare earth. Said element may be the aforementioned element A. By rare earth is meant the elements of the group constituted by yttrium and the elements of the periodic classification with atomic number included inclusively between 57 and 71. The

  rare earth may be more particularly lanthanum or cerium.

  The invention also relates to the combination of the embodiments and variants which have just been described above, that is to say the use of perovskites comprising a rare earth and an element capable of having at least two states at least of different oxidation, the rare earth and said element possibly being the

elements A and B respectively.

  Perovskites in which a constituent element, more particularly element A, is substituted by an alkali such as sodium or potassium, an alkaline earth metal such as magnesium,

  strontium, calcium, barium or by tin, cadmium or lead.

  By way of example, the following perovskites can be mentioned: LaCrO3, LaMnO3, La (Cr, Mn) O3, Gold and Mn can be in any respective proportions, LaCoO3, (La1 lx, Srx) MnO3, (La1.x, Srx) CrO3 with 0 <x <1, La (Fe, Co) O3, Fe and Co can be in any respective proportions, (Lal.x, Srx) (Fe, Co) O3 with

  0cx <1, or also the perovskites of the SrFeO3_d type, (La, Sr) CoO3.d.

  According to another variant of the invention, a catalyst is used comprising a support and a supported phase. The support is a perovskite as described above. The supported phase is a phase capable of catalyzing the dehydrogenation reaction. This supported phase can for example be based on an alkali compound and an iron compound. The alkali can be potassium. Such a phase is advantageous in the case of the dehydrogenation of ethylbenzene for the

preparation of styrene.

  The invention also relates to a catalytic composition comprising a perovskite for the implementation of a dehydrogenation process. Which was

  described above concerning perovskite applies here to the definition of the composition.

  This composition can be in various forms such as granules, beads, cylinders or honeycomb of variable dimensions, this composition being in this case shaped by known methods of forming catalysts, for example

  extrusion, compaction, granulation in a bezel or in a rotary kiln.

  The perovskites used in the context of the invention can be prepared by

any known method.

  Perovskites can thus be prepared by solid / solid reaction, that is to say by mixing powdered oxides and calcination at high temperature, or by co-precipitation from a salt solution with a precipitating agent (a base for example) in a discontinuous or continuous mode, followed by a heat treatment of the precipitate obtained at a temperature sufficient to obtain the desired phase, this temperature generally being at least 500 C. We can also mention the

sol-gel methods.

  Mention may however be made more particularly of the preparation process which follows.

  This process uses as starting materials the salts or the soils of the constituent elements of the perovskites. By constituent elements is meant the elements A, B and

  their possible substituents entering into the perovskite of the type described above.

  The choice between salt and soil may be made according to the availability of the products, their stability and, as regards the salts, their temperature.

fusion and decomposition.

  Salts of organic or inorganic acids can be used.

  All the inorganic or organic acids are suitable for carrying out the process insofar as they form soluble salts in the reaction mixture, which can be an aqueous and organic medium, with the constituent elements of perovskite. However, the nitrates, chlorides or

  sulfates, as salts of inorganic acids. Nitrates are the preferred salts.

  Concerning the salts of organic acids, the salts are generally chosen

  of saturated aliphatic carboxylic acids or the salts of hydroxycarboxylic acids.

  As saturated aliphatic carboxylic acids, mention may be made of formates,

acetates, propionates.

  As for hydroxycarboxylic acids, citrates are usually used.

  The concentrations of the various salts of the elements in the reaction medium are adjusted according to the stoichiometry of the desired final perovskite and are generally

between 0.05 and 5M.

  The elements are brought together by mixing the soil (s) and / or

salt solutions.

  We work in conditions such as to avoid precipitation of salts, this

  which therefore implies that one is at a sufficiently acidic pH.

  In addition, it is necessary to be in a field of concentration of the elements such that there is no appearance of a gel, but obtaining a mixture of the elements in a liquid phase or a homogeneous suspension of the soil elements in the solution of other elements. This is achieved by playing on the dilution of said elements.

  The suspension or mixture thus obtained is then dried.

  This drying is carried out according to any known method.

  Preferably, however, the mixture is spray dried.

  This atomization can be done using any conventional atomizer, for example with a turbine or a nozzle. In this case, the inlet temperature of the gases at the start of drying is usually between 200 and 300 ° C., for example close to 250 ° C., the outlet temperature may vary between 120 and 200 ° C. An air pressure of between by

example between 2 and 3 bars.

  According to a particular embodiment, said mixture is dried by injection of

  the latter in a gas having a sufficient speed to atomize it.

  Thus, according to a particular embodiment of the invention, the drying is carried out in a "flash" reactor, for example of the type developed by the Applicant and described in particular in French patents 2 257 326, 2 419 754, 2 431 321. In this case, the hot gases are driven in a helical movement and flow in a vortex well.The suspension is injected along a trajectory coincident with the axis of symmetry of the helical trajectories of the gases, which allows the momentum to be transferred perfectly from the gases to the particles of this suspension. Furthermore, the residence time of the particles in the reactor is extremely short, it is generally less than 1/10 of a second, which eliminates all

  risk of overheating due to too long contact with gases.

  Depending on the respective flow rates of the gases and of the suspension, the gas inlet temperature is between 400 and 900 C and more particularly 600-800 C, the

  temperature of the dried solid between 150 and 300 C.

  Regarding the flash reactor mentioned above, we can refer

  in particular in FIG. 1 of French patent application no. 2 431 321.

  Said reactor consists of a combustion chamber and a

  contact composed of a bicone or a truncated cone, the upper part of which diverges.

  The combustion chamber opens into the contact chamber through a passage

reduced.

  The upper part of the combustion chamber has an opening

  allowing the introduction of the combustible phase.

  On the other hand, the combustion chamber comprises an internal coaxial cylinder, thus defining inside thereof a central zone and an annular peripheral zone and having perforations lying for the most part towards the upper part of said chamber. This preferably comprises at least six perforations distributed over at least one circle, but preferably over several circles spaced axially. The total area of the perforations located in the lower part of the chamber can be very small, of the order of 1/10 to 1/100 of the area

  total of the perforations of said internal coaxial cylinder.

  The perforations are usually circular and have a very small thickness. Preferably, the ratio of the diameter of these to the thickness of the wall is at least 5, the minimum thickness of the wall being only limited by mechanical requirements. Finally, a bent pipe opens into the reduced passage, the end of which opens

in line with the central area.

  The gas phase animated by a helical movement (thereafter helical phase) is composed of a gas, generally air, introduced into an orifice made in the annular zone, preferably this orifice is located in the part

lower of said zone.

  In order to obtain a helical phase at the reduced passage, the gas phase is preferably introduced at low pressure into the aforementioned orifice, that is to say at a pressure less than 1 bar and more particularly at a pressure included

  between 0.2 and 0.5 bar above the pressure existing in the contact chamber.

  The speed of this helical phase is generally between 10 and 100

  m / s and preferably between 30 and 60 m / s.

  Furthermore, a combustible phase which may in particular be methane or natural gas, is injected axially through the aforementioned opening in the central zone to

  a speed of about 100 to 150 m / s.

  The combustible phase is ignited by any known means, in the region where the

  fuel and the helical phase are in contact.

  Thereafter, the imposed passage of the gases in the reduced passage is done according to a set of trajectories confused with families of generators of a hyperboloide. These generators rest on a family of circles, of small rings located near and below the reduced passage, before diverging in

all directions.

  The substance to be treated is then introduced in the form of a liquid through the pipe.

cited above.

  The liquid is then divided into a multitude of drops, each of them being transported by a volume of gas and subjected to a movement creating a centrifugal effect. The ratio between the natural momentum of the helical phase to that of the liquid must be high. In particular, it is at least 100 and preferably included

between 1,000 and 10,000.

  The amounts of movement at the level of the reduced passage are calculated as a function of the inlet flow rates of the gas and of the substance to be treated, as well as of the section of said passage. An increase in flow rates leads to a magnification of the drop size. Under these conditions, the proper movement of the gases is imposed in its direction and its intensity on the drops of the substance to be treated, separated from each other in the zone of convergence of the two streams. The speed of the liquid is further reduced to the minimum necessary to obtain a

continuous flow.

  The ratio of the mass of the liquid and the gas is obviously chosen as a function of several factors such as the temperature of the fluid and the operation at

  perform, such as spraying the liquid.

  It should be noted that this representation and operation of the 'flash' reactor does not

  are only an example and that other realizations and functioning are possible.

  After drying of the mixture comprising the soils and / or the salts of elements

  constituent of perovskite, the recovered powder is calcined.

  The purpose of this calcination is to remove anions, for example nitrates

  present in the dried product. It also aims to form the desired phase.

  The calcination is carried out at a temperature varying between approximately 450 C and approximately 1200 C, preferably between approximately 570 C and approximately 1200 C. The calcination can be carried out in particular in air and / or under an air / oxygen mixture in atmosphere

static or under scanning.

  The duration of the calcination is usually between 15 minutes and 10

  hours depending on the temperature and the type of oven used.

  It should be noted that a grinding step prior to calcination is not necessary. However, it would not be departing from the scope of the present invention to carry out a

such operation.

  In the case of the variant where perovskite is used as a support for a catalytic phase, the deposition of the catalytic phase can be done for example by impregnation. Examples will now be given

EXAMPLE 1

  This example concerns a perovskite of formula Lao, 6Sro, 4CoO3.

  Solutions of lanthanum nitrate, strontium nitrate and cobalt nitrate in the stoichiometric proportions of

expected composition.

  A mixture of these solutions is formed and the mixture obtained is dried in a 'flash' reactor of the type described above under the following conditions: gas inlet temperature 750 0C, gas outlet temperature 230 0C, solid temperature

dried 1500C.

  A portion (300g) of the product obtained is calcined in a static oven at 1000 C with a temperature rise of 5 C / min and a level of 2h15 min. After calcination the product is compacted by uniaxial pressing (30T) then crushed and

sieved between 1.6 and 2.4mm.

  Perovskite is then used under the conditions which are given below.

  below for the dehydrogenation of ethylbenzene.

EXAMPLE 2

  This example relates to a perovskite of formula La0,6Sr0o, 4Fe0,8Co0,203.

  The same procedure is used as in Example 1, using in addition

iron nitrate solution.

EXAMPLE 3

  This example relates to a perovskite of formula La0,5Sr0,5MnO3.

  The same procedure is used as in Example 1, using in one

manganese nitrate solution.

EXAMPLE 4

  Perovskite is used in the form of a powder obtained in Example 2. The product is impregnated dry as follows. 70g of the product are placed in a 120mm diameter glass crystallizer. 21.8 ml of a solution of iron citrate and potassium acetate are added thereto (100 ml of this solution contain 35.42 g of iron citrate and 24.28 g of potassium acetate). The addition is done drop by drop, homogenizing with a spatula. The impregnated product is then dried for 16 hours at

   0C and calcined for 1 hour at 800 C. The powder obtained is pelletized and crushed to 1.6-

  2.4mm. The products obtained according to the preceding examples are implemented from the

next way.

  A reactor is used which is a 316L stainless steel tube, with a total length of 240mm with an inlet for the reagents and an outlet for the products formed. The system is equipped with two chromatographs, one fitted with an FID detector (column

  filled with silocel + 10% FFAP), the other with a catharometer (column filled with HAYESEP A).

  The reactor is heated by a fluidized sand bath oven.

  The reactor is loaded with 27.3 g of catalyst, ie a volume of approximately 20 cm 3.

  The temperature is adjusted to 580 ° C. and a mixture of water and ethylbenzene is sent to the reactor via a vaporizer with a respective flow rate of 27.2 cm 3 / h for water and 15.63 cm 3 / h for ethylbenzene. The tracer gas is nitrogen sent with a flow rate of 3.281 / h. Conversion and selectivity are measured after

h of test.

  The results are given in the table below.

  Salt. means selectivity. Product Conversion from Sel. C8HR Sel. C7H8 Sel. CCHF Sel. CH4 Sel. CO + CO2 ethylbenzene%%%%%% Ex. 1 12.2 84.1 2.2 5.6 2.6 5.5 Ex. 2 33.9 89.0 3.5 4, 4 1, 1 2.0 Ex. 3 26.8 89.9 1.8 5.8 1.2 1.2 Ex. 4 38.5 94.7 3.9 0.6 0.1 0.6

Claims (13)

  1- Process for dehydrogenation of an organic compound, characterized in that a catalyst is used comprising a perovskite. 2- A method according to claim 1, characterized in that a catalyst is used comprising a perovskite of which a constituent element is capable of having, in   part, at least two different oxidation states.   3- A method according to claim 2, characterized in that a catalyst is used comprising a perovskite of ABO3 type structure in which A represents a substituted or unsubstituted element, coordinated with 12 oxygen atoms and B a substituted or unsubstituted element, coordinated with 6 oxygen atoms, the aforementioned element, capable of having, in part, at least two different oxidation states, being mainly element B. 4- Method according to claim 2 or 3, characterized in that use is made of a catalyst comprising a perovskite in which the above-mentioned element, capable of exhibiting, in part, at least two different oxidation states, is chosen from the group   including manganese, iron, cobalt and chromium.   - Method according to one of the preceding claims, characterized in that one uses   a catalyst comprising a perovskite of which at least one constituent element is a   rare earth, this element possibly being the aforementioned element A.   6- Method according to one of the preceding claims, characterized in that one uses   a catalyst comprising a perovskite in which a constituent element, more particularly element A, is substituted by an alkali, an alkaline-earth, by tin, cadmium or lead.   7- Process according to claim 5, characterized in that a catalyst is used comprising a perovskite in which the rare earth is chosen from lanthanum and cerium.   8- Method according to one of the preceding claims, characterized in that one uses   a catalyst comprising a perovskite of which constituent elements are iron in combination with cobalt.   9- Method according to one of the preceding claims, characterized in that one uses   a catalyst comprising a lacunar perovskite.   10- Method according to one of the preceding claims, characterized in that one uses   a catalyst comprising the above-mentioned perovskite as support and a supported phase capable of catalyzing the dehydrogenation reaction, more   particularly based on an alkali and iron.   11- Method according to one of the preceding claims, characterized in that one uses   a catalyst comprising the above-mentioned perovskite, this perovskite having been obtained by a preparation process in which a mixture comprising salts and / or soils of the constituent elements of perovskite is formed, said mixture is dried and   calcines the dried product, the drying possibly being carried out by atomization.   12- A method according to claim 11, characterized in that a catalyst is used comprising a perovskite having been obtained by a preparation process in which the above-mentioned mixture is dried by injection of the latter along a path coincident with the axis of symmetry of a helical flow and gas vortex well   hot ensuring spraying, then drying of said mixture.   13- Method according to one of claims 1 to 10, characterized in that one uses a   catalyst comprising the aforementioned perovskite, this perovskite having been obtained by a process of preparation by co-precipitation from a salt solution with a   precipitating agent then heat treatment of the precipitate obtained.   14- Method according to one of the preceding claims for the dehydrogenation of   alkyl aromatic compounds into alkylene aromatic compounds.   15- Method according to one of the preceding claims for dehydrogenation of   ethylbenzene for the preparation of styrene.   16- Catalytic composition comprising a perovskite, for the implementation of the   method according to one of the preceding claims.