FR2497795A1 - CATALYST OF OXIDESHYDROGENATION - Google Patents

Abstract

THE INVENTION CONCERNS AN IMPROVEMENT OF THE PROCESS FOR THE CATALYTIC CONVERSION OF ISOBUTYRIC ACID INTO METHACRYLIC ACID BY THE REACTION OF OXIDEHYDROGENATION IN WHICH AN IRON PHOSPHATE CATALYZER IS IN CONTACT WITH A GASEOUS SUBSTRATE SUPPLY CURRENT ACID AND OXYGEN AT A TEMPERATURE BETWEEN APPROXIMATELY 300 AND 550C. THE IMPROVEMENT ACCORDING TO THE INVENTION CONSISTS OF CARRYING OUT THE SAID REACTION OF OXIDESHYDROGENATION IN THE PRESENCE OF A MODIFIED IRON PHOSPHATE CATALYST HAVING THE FOLLOWING EMPIRICAL FORMULA, IN ATOMS-GRAMS: FEMPO IN WHICH M BOREISI REPRESENTS A MET. ALUMINUM, GALLIUM AND INDIUM AND IN WHICH X REPRESENTS THE NUMBER OF OXYGEN ATOMS BOUND WITH THE OTHER ELEMENTS IN THEIR RESPECTIVE STATES OF OXIDATION IN THE CATALYST.

Description

The present invention relates to a method for

  conversion of isobutyric acid to methacrylic acid by oxy-

  dehydrogenation. The process is equally applicable to the functional equivalents of isobutyric acid such as propionic acid and methyl isobutyrate. There is a considerable number of prior art techniques aimed at the oxidation hydrogenation of monocarboxylic acids.

  lower saturates to prepare the corresponding up-unsaturated acids

  dent. The first works indicated in this field consist in thermally performing the oxidized hydrogenation indicated by vapor phase reaction of the acidic substrate with iodine and oxygen. This

  attempt did not receive much attention as a potential pathway

  It is actually viable to industrially perform the basic reaction.

  This, it is understood, especially since the iodine is expensive, present

  extremely corrosive properties and causes serious problems.

  in the achievement of full recovery of quantities

  relatively large amounts of iodine needed in the process.

  As is widely indicated by the prior art succes-

  the heterogeneous catalytic method for carrying out the oxidation-hydrogenation reaction is considered to be more interesting from the point of view of potential industrial application. In the most recent main prior art, the activity was centered on

  the use of two types of catalytic compositions for this purpose.

  One of these types generally comprises heteropolyacids, which are

  typically characterized by 12-molybdophosphoric acid optionally containing vanadium and / or tungsten in a similar structural arrangement. The other type of catalyst contains

  systems having in common a matrix of calcined iron phosphate.

  The iron phosphates subjected to calcination exist in the form of numerous phases or crystalline species. Although it is believed that the oxidation / reduction pair involved in the main reaction is attributable to iron phosphate, the species or species catalytically active), have not been identified. However, there is evidence that the presence of an additional metal component in

  the preparation serves to facilitate the formation of the catalytic species

  actively active. For example, US Pat. No. 3,948,959 discloses, inter alia, that an alkaline or alkaline earth metal

  as an additional metal component is effective for this purpose.

  The present invention therefore represents an extension of this aspect

  particular of the current state of the art.

  The invention relates to a catalytic process for carrying out the oxidative dehydrogenation of isobutyric acid to form methacrylic acid. The process of the invention consists in bringing into contact a heterogeneous catalyst at a temperature of 300-550 ° C. with a combined charge of said isobutyric acid and dilute gaseous oxygen, characterized in that said catalyst is calcined iron phosphate further containing aluminum metal as a modifying or doping agent. Other elements of group IIa, boron, gallium and indium can serve as modifying or doping component. According to the broadest aspect of the invention, the envisaged catalyst is defined by the empirical formula in grams of FeM, ollP1, in which M is aluminum, boron, galliurm or indium and x is the number oxygen scavengers bound to the other metals in their respective states of oxidation in the catalyst. It has been found that the aluminum-modified iron phosphate catalyst is active for long periods of time. Unlike iron phosphate catalysts which lose their activity over time, the aluminum-modified catalyst has shown in studies

  for a duration of 100 hours that it keeps its activity.

  There are a number of applicable techniques

  for the preparation of the catalyst useful in the practice of the invention.

  Among these, the easiest methods include the preparation of an integral composition prior to calcination. This can be done easily using the so-called slurry method or the precipitation method. In the latter method, an aqueous solution of salts of the metals in question and phosphoric acid is first prepared and then neutralized with a suitable base to precipitate the mixed metal phosphates. It is advantageous to wash the precipitate thoroughly to separate all traces of water-soluble substances and then to dry prior to calcination. Alternatively, ammonium phosphate may be added to the solution of the metal salts to directly precipitate the metal phosphates. As has been indicated, any water-soluble iron or aluminum salts can be used. However, due to the solubility characteristics of nitrates, among other things,

these salts are preferred.

  The so-called slurry method is even more suitable for use and for this reason it is the preferred method in the invention. According to this procedure, the aqueous solution of the iron and aluminum salts is obtained together with the phosphoric acid. The solution is heated continuously until the mass can no longer be stirred. The residue is then broken up and heated again at a moderately high temperature of about 120C until complete drying. Then the product is sieved and calcined. The appropriate calcination temperatures are roughly 400 to 1000 ° C, and preferably

they are from 400 to 85 ° C.

  According to one or other of these techniques, it is possible to

  a supported catalyst. For example, in the slurry method, colloidal silica or colloidal alumina or any other form of either may be added before the water content is removed. When colloidal alumina is used it can also be used as an additional source of the aluminum cations which give the improved activity and long catalyst life observed in the iron phosphate catalyst

  modified with aluminum according to the present invention.

  Supports such as alumina, silica, titanium oxide, etc. can be added before the water content is removed. The support

  may also be impregnated in a metal phosphate solution

  liquefied and dried. The impregnation and drying steps should be repeated until the desired number of dried metal phosphate layers are obtained. Similarly, in the alternative method described, it is possible to carry out the precipitation of phosphates

  metal in the presence of suspended particles of the intended support.

  In a typical commercial catalyst preparation, a spray drying technique is used in which the slurry is introduced into the spray dryer and the

  solid product is then tableted or extruded and calcined.

  The catalyst compositions of the invention can be used in a fluid bed reactor, a stirred tank reactor or a fixed bed type reactor. Because of the convenience associated with using a fixed bed reactor in an operation

  on a small scale, this reactor is illustrated in the examples below.

  In the preferred mode of operation, the feed to the reactor comprises a preheated gaseous mixture of the molecular oxygen substrate, steam and an inert gaseous diluent. A preheating temperature is generally observed in the range of about 300 to 350 ° C. A wide range of applicable reaction temperature is 250 ° -5,500 ° C., more generally a temperature of 350 ° to 45 ° C.

gives the optimal treatment.

  The molar ratio of molecular oxygen to the substrate is 0.2 to 1.5, preferably 0.5 to 1.0. Although steam is not required to effect the reaction, its presence in the feed improves the yield of the desired product. A molar ratio

  applicable water to the substrate in the load is about 1 to 75.

  The optimum ratio is more in the range of about 10 to 30.

  Another important parameter is the concentration

  substrate in the load. Expressed in moles percent, the

  The concentration of the substrates considered varies widely from 0.1 to 20.

  As is common in such reactions, the yield of the desired product is an inverse function of the concentration. From the point of view of obtaining a reasonable flow rate combined with an acceptable yield, the concentration of the substrate in the feed is about 3-6 mol%. The concentration is controlled by the amount of water and inert gas present in the feed stream. The preferred gaseous diluent is nitrogen although other gases such as carbon monoxide, helium, argon, etc. are also suitable. Of course, if the desired concentration of the substrate allows it, air represents

a suitable dilute oxidant.

  Another applicable parameter is the duration of contact. The duration of contact is defined as the volume of catalyst divided by the flow rate of the gaseous load in volume / second at the

  reaction temperature. The volume of catalyst is the volume

  occupied by the catalyst in the reactor. In this sense, the term "catalyst" includes not only the modified iron phosphate itself, but also the solid diluent or the carrier if appropriate. As a result, usable contact times range from 0.05 to 50 seconds and more generally from 0.1-20.

  seconds. The reaction is carried out under atmospheric pressure.

  - The following examples illustrate the invention without

however, limit its scope.

EXAMPLE; 1

  The purpose of this example is to illustrate the slurry method described above for preparing a catalyst useful in

  the practice of the invention. 122 g of nonionic iron nitrate are dissolved

  hydrated with 11.33 g of aluminum nitrate nonahydrate in 250 ml of water, 42.4 g of concentrated phosphoric acid are added with stirring to the solution of metal salts. The solution is then stirred and heated until the mass of the water is evaporated. The resulting paste is further dried at 1250 ° C until it can be comminuted, after which the solid is broken up into 1.25 cm pieces and

  less and calcined for 16 hours in a stream of air at 450C.

  The calcined material is milled and passed through a mesh size of 0.84-1.68 mm prior to use. The empirical formula in grams of mixed phosphates of calcined iron and aluminum is as follows: FeAI P O 0.11 1.1 x

EXAMPLE 2

  This example illustrates the preparation of an aluminum-modified iron phosphate catalyst having a ratio of

  phosphorus / aluminum greater than that of the catalyst of Example 1.

  610.0 g of iron nitrate nonahydrate are dissolved with 62.6 g of aluminum nitrate nonahydrate in 1.2 liters of distilled water. We

  add 250 g of concentrated phosphoric acid. The rest of the operating mode

  is as shown in Example 1. The empirical formula in atoms

  grams of mixed phosphates of calcined iron and aluminum is as follows: FeAl 01P O440x

EXAMPLE 3

  The present example illustrates the preparation of an aluminum-modified iron phosphate catalyst of empirical formula, in gram atoms, FeAl 05P1 05Ox 128.6 g of iron nitrate nonahydrate is dissolved with 5.86 g of nitrate of iron. Aluminum nonahydrate in 250 ml of distilled water. 50.0 g of concentrated phosphoric acid are added. The rest of the procedure is as indicated

in example 1.

EXAMPLE 4

  The present example illustrates the preparation of an aluminum modified iron phosphate catalyst of empirical formula in grams FeA 10 P10 O1. This catalyst has the same 0.1.1 1.1 x empirical formula as the catalyst of Example 1. It differs from it.

  however, in that the preparation avoids the use of additional water

  mentary. The catalyst of Example 4 is prepared by mixing 610 g of iron nitrate nonahydrate and 56.65 g of aluminum nitrate nonahydrate. This mixture is heated until melting and then added to

  stirring 212 g of 85% phosphoric acid. The rest of the operating mode

is as in example 1.

EXAMPLE 5

  This example illustrates the preparation of a

  Gallium-modified iron phosphate lyser having the following empirical formula in atom-atoms: FeGaO 11 Pox. 71.0 g of iron nitrate nonahydrate are dissolved with 5.0 g of gallium nitrate nonahydrate in 100 ml of water. 24.8 g of concentrated phosphoric acid are then added. The rest of the procedure is comine to

Example 1

EXAMPLE 6

  This example illustrates the preparation of a

  Gailium-modified iron phosphate lysate having the following empirical formula in grams: FeGa O1P1,440x. 71.0 g of iron nitrate nonahydrate are dissolved with 5.0 g of gallium nitrate nonahydrate in 100 ml of water and 29.3 g of concentrated phosphoric acid are then added. The rest of the operative mud is like

in example 1.

EXAMPLE 7

  This example illustrates the preparation of a

  Iron phosphate lyser which is not modified by the addition of another metal. 101 g of iron nitrate nonahydrate are dissolved in

  ml of water. 29.1 g of concentrated phosphoric acid are then added.

  The remainder of the procedure is as indicated in Example 1. The empirical formula for calcined iron phosphate is as follows, in

gram atoms: FePO.

X

2 497795

EXAMPLE 8

  This example illustrates the use of the

  catalytic section of the preceding examples in carrying out the oxidative dehydrogenation of isobutyric acid (AIB). The reactor and the general mode of implementation of the reaction are the same for each of the listed tests. The catalyst is diluted by

  quartz flakes (1 part by volume of the catalyst for 4 parts

  by volume of quartz flakes) and loaded into a conventional up-and-down tubular reactor. The tests are carried out at 400-4250C. The procedure involves feeding with a preheated mixture of isobutyric acid oxygen, nitrogen and steam a stainless steel tube 1.27 cm in outer diameter (9.5 mm internal diameter) and about 45 cm long containing the test catalyst as a 15 ml bed maintained at the reaction temperature used in the particular test. The ratio of water to isobutyric acid in the feed is from 1 to 1, the ratio of oxygen to isobutyric acid is 1: 1 and the duration of contact is of the order of 0.4 to 0, 5 seconds. These ratios lead to a feed mixture containing 4 moles / isobutyric acid, 78 mole% water, 4 mole 7 oxygen and

14 mole% nitrogen as diluent.

  The preheater consists of a tube of stainless

  dable of length similar to that of the reactor but filled with glass beads. The condensed organic product is collected and analyzed by gas chromatography. The gaseous products are

  analyzed separately by gas chromatography.

  The relevant results observed for the individual tests are shown in the table below. The results obtained in selectivity and in conversion are also indicated in said table. The conversion represents the molar ratio

  from the substrate consumed to that charged to the reactor. Selectivity

  for methacrylic acid (AM &) represents the molar ratio of methacrylic acid found in the effluent to AIB

consumed in the reaction.

  The catalyst prepared as described in Example 1

  and used as described in Example 8 to carry out the oxideshydro-

  Isobutyric acid generation worked for 100 hours without

  show signs of deactivation.

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Claims (5)

  In a process for the catalytic conversion of   isobutyric acid to methacrylic acid by the reaction of oxy-   dehydrogenation in which an iron phosphate catalyst is contacted with a gaseous feed stream containing said acid substrate and oxygen at a temperature between about 300 and 550 C, the improvement of performing said   oxidation-hydrogenation reaction in the presence of a phosphorus catalyst   modified iron phate having the following empirical formula,   grams: FeM ol-1 P_20x in which M represents a metal selected from boron, aluminum, gallium and indium and wherein x represents the number of oxygen atoms bound to the other elements   in their respective oxidation states in the catalyst.   2. Improvement according to claim 1, characterized in that M is aluminum.   3. Improvement according to claim 1, characterized in that the modified iron phosphate catalyst has the formula   next in atoms-gram: FeA10,050_, 11P1,0o1,50x.   4. Improvement according to claim 1, characterized in that M is gallium.   5. Improvement according to claim 4, characterized in that the modified iron phosphate catalyst has the formula   next in grams: FeGa, 11P1, 1,50x.