NO146707B - PROCEDURE FOR THE PREPARATION OF Saturated Aldehydes by Oxidation of Propylene or Isobutylene in the Presence of an Oxidation Catalyst - Google Patents

Description

A large number of catalysts are known to be effective in the oxidation of propylene and isobutylene. This invention relates to a process in which such known catalysts are used in a new way for the production of unsaturated aldehydes from the aforementioned olefins.

By an oxidation reaction that is carried out during use

of a stationary catalyst bed, very significant problems with heat generation occur at high feed rates due to the exothermic nature of the reaction. In order to allow the heat developed to be dissipated, in the past it has been necessary to resort to economically unfavorable measures such as low temperatures,

small throughput rates, small amounts of catalyst and small diameter of the reactor tubes.

A solution is proposed in US patent no. 3,801,634

on the problem of heat generation in a continuous process for the production of acrylic acid by catalytic oxidation of propylene with elemental oxygen in a reactor tube containing a fixed, stationary catalyst. The reaction is carried out in two steps,

as the propylene is essentially oxidized to acrolein in a first step, and the acrolein is further oxidized to acryl

acid in a second step. To counteract overheating, the activity of the catalysts in the two stages is adjusted by diluting the catalysts with inert material, so that the activity at the intake of the individual reactor tubes is reduced to approx. 25 - 75%

of full activity. The mixing of inert material is adapted so that the activity of the catalysts in the longitudinal direction of the reactor tubes increases gradually until the activity reaches 100% at a certain distance from the outlet end of the reactor tubes. The dilution of the catalysts is carried out either by mixing shaped catalyst with shaped inert material during the filling of catalyst in the reactor, or by mixing the catalyst and the inert material beforehand in powder form and then shaping and placing them in the reactor tubes.

Although the method described in the aforementioned US patent helps to make the oxidation reactions more efficient by enabling an increase in the reactant throughput per unit of reactor volume, it is cumbersome and requires great care when filling the catalysts into the reactor tubes. The present invention is aimed at solving the aforementioned

problem in a more economically acceptable way.

With the help of the invention, a method is thus provided for the production of unsaturated aldehydes by reacting a mixture of propylene or isobutylene with molecular oxygen in a reactor where the reactants flow through one or more parallel connected tubes which are surrounded by a heat transfer medium and in which there is a fixed, stationary oxidation catalyst, in which the active catalytic material consists of mixed oxides containing the metals Fe, Bi and Mo, the catalytic material preferably having the composition:

where A is an alkali metal, an alkaline earth metal, Sm, Ta, Tl, In, Ga, B, P, As, Sb or a mixture thereof,

B is nickel, cobalt, magnesium, manganese or a mixture thereof, a is a number from 0 to 8,

b is a number from 0 to 20,

c is a number from 0.1 to 10,

d is a number from 0.01 to 6, and

x is the number of oxygen atoms required to satisfy the valence requirements of the other elements present.

The new method is distinguished by the fact that two catalysts are used in each of one or more of the tubes in the reactor, the first catalyst being "a catalyst consisting of an essentially inert carrier with an outer surface and a coating of a catalytic material which adheres strongly to the outer surface of the support, and the second catalyst is a catalyst consisting essentially of the catalytic material, and in that

the catalysts are arranged in the tubes of . the fixed bed reactor on

such a way that the first catalyst comes into contact with the reactants first, and the second catalyst comes into contact with the reactants after the contact with the first catalyst.

With the method according to the invention, the temperature regulation of the exothermic reaction becomes very convenient, while at the same time a high conversion of the olefins is achieved.

Among the preferred catalysts, the particularly preferred catalysts contain nickel, cobalt, magnesium, manganese or a mixture of two or more of these. The catalysts containing potassium are likewise advantageous.

The essential feature of the method according to the invention is the use of two catalysts, each of which exists in its own physical form. The first catalyst is a coated catalyst, and the second catalyst essentially consists of the catalytic material itself.

The term "inert carrier" as used above denotes a carrier material which, when placed in the reactor alone and used under the reaction conditions for the oxidation, gives less than 10% conversion to the desired aldehyde per review. The inert support can be any material that is not active during the oxidation reaction. Examples of such mainly inert carrier materials are silicon dioxide, aluminum oxide, "Alundum", silicon carbide, boron phosphate and zirconium oxide. The inert carrier must

be at least partially porous. The carrier can be in the form of particles of dimensions 0.1 cm or larger. Although there is no theoretical upper limit to the size, the inert carrier particles usually have a diameter of less than 2 cm.

The term "catalytic material" used here denotes the active catalytic components, which may optionally contain a carrier material, such as silicon dioxide, dispersed in the active components.

The catalytic material can be placed on the inert carrier by partially wetting the carrier with water or other liquid and the partially wet carrier material is then brought into contact with a powder of the active catalytic material, preferably using a rolling motion. When using this method, the catalytic material forms a strongly adherent coating on the carrier material. In the preferred preparation of the first catalyst, carriers are used which are in the form of spherical particles, so that a first catalyst of this form is obtained.

The relative quantity ratios between the inert carrier and

the catalytic material can vary greatly. The coating of catalytic material can be relatively thin or relatively thick. In a preferred embodiment of the method according to the invention, a first catalyst containing from 5 to 60% by weight of the catalytic material is used.

The second catalyst essentially consists of the catalytic material itself. As mentioned, this catalyst can contain a carrier material dispersed in the catalyst. It is this type of catalyst that has usually been used alone in oxidation reactions. Various forms of this second catalyst, such as tablets, spheres and pellets, are known.

In a preferred embodiment of the method according to the invention, the catalytic material used in the first catalyst and the catalyst material used in the second catalyst are essentially the same material. Thereby, any adverse effect of one active ingredient on another is eliminated.

The relative quantity ratios between the first catalyst and the second catalyst can vary within wide limits. A sufficiently large amount of the first catalyst should be used to regulate the reaction temperature, and a sufficiently large amount of the second catalyst should be used to ensure a high conversion of the olefin (approx. 90%). In a preferred embodiment of the method according to the invention, the first catalyst is used in an amount which fills from 10 to 80% by volume of the reactor tube.

The method according to the invention is carried out according to the parameters known in the art. The reactants, catalysts, reaction conditions, etc., are the same as for methods known in the art. The molar ratio between molecular oxygen and olefin is from 0.7 to 4. The reaction can be carried out at atmospheric pressure or at subatmospheric or superatmospheric pressure. The temperatures vary from 200° to 600°C, with temperatures from 300° to 500°C being preferred. The contact time can be up to 20 seconds.

In the attached drawing, fig. 1 a side view of

an acrolein reactor with solid, stationary catalyst, while fig. 2 shows a top plan view of the acrolein reactor.

From fig. 1 it will be seen that the reactor consists of an outer jacket 1 which contains a number of tubes 2. Each tube contains a first catalyst 3 and a second catalyst 4 in such a way that the reactants first come into contact with the first catalyst.

The reactants are introduced through pipeline 5 to the distribution chamber 6, from where the reactants are distributed evenly on the pipes 2. The products are collected in a collection chamber 7 and conveyed there-

from to extraction and purification operations (not shown) through pipeline 8.

The reactor is equipped with a stirrer 9 which stirs a heat transfer fluid 10. The heat transfer fluid 10 is cooled by means of a heat exchange system 12, 13, 14 and 15 and is fed back to the reactor jacket.

Comparison example A and examples 1 and 2 - Comparison between tableted catalyst used alone and coated, respectively tableted catalyst used together.

A reactor was constructed for the use of solid, stationary catalyst, with a -4 m long reaction zone, using stainless steel tubes of internal diameter 2.7 mm.

A catalyst with the composition 87.5% KQ 1Ni2 5Co^ ^Fe3BiPQ 5~ Mo o and 17.5% SiC) was prepared according to US patent document 3,746,657. The catalyst was freed of nitrogen at 425°C, formed into tablets of 0.5 cm diameter and calcined. Another catalyst of the same composition (as far as the active ingredient is concerned), but without silicon dioxide, was prepared and coated on "Alundum" spheres of diameter 0.32 mm. This coating was accomplished by partially wetting the "Alundum" beads with water, contacting the beads with a powder of the catalytic material in a rolling motion, and drying the coated carrier beads. The coated catalyst contained 33.3% by weight of the catalytic material. The coated catalyst was calcined for 2 hours at 538°C.

Comparative example A

The entire reaction zone of a reactor was filled with it

tableted catalyst alone. None of the coated catalyst was used. Attempts to provide a stable acrolein reaction were made using a variety of initiation methods. None of these initiation methods succeeded in maintaining a stable reaction. In each case, an uncontrollable increase in temperature occurred, and the reaction was interrupted for safety reasons. It was determined that the tableted catalyst could not be used alone in this reactor under satisfactory reactant feed rates.

Example 1-2

The same reactor as in comparative example A was filled with a coated catalyst and a tableted catalyst,

according to the invention. The first half of the reaction tube nearest the reactor inlet was filled with the coated catalyst, and the second half of the reaction tube was filled with the tableted catalyst. This catalyst system was operated using a propylene/air/steam feed of 1/.5/ 6. For the experiment, example 1, which was carried out at a temperature of 345°C and a space velocity of 1500 parts by volume, denoted reactants at standard temperature and pressure conditions per hour per volume fraction reactor volume occupied by the catalyst, the conversion to useful products (measured as the number of moles of acrolein and acrylic acid produced times 100 and divided by the number of moles of propylene fed in) was 90.8%. Of the propylene feed, 96.3% was converted. In the experiment designated example 2, where a temperature of 355°C and a space velocity of 1700 were used, the yield in a single pass was 89.4% with 95.5% propylene conversion. This example 2 gave the greatest production rate in a given period of time. In both cases, the product contained more than 80% acrolein.

Example 3 - Deviating pipe diameter and other coating percentage.

A reaction tube with an internal diameter and length of 2 cm

4 m was filled 1/3 with coated catalyst towards the inlet and 2/3

with tableted catalyst in the rest of the tube. Using a temperature of 355°C, a propylene/air/steam feed rate of 1/8.6/6 and a space velocity of approx. 1300, the single-pass conversion to useful products was 90.0% with a propylene carryover of 95.5%. The difference between the temperature of the bath and the temperature of the catalyst was 58°C.

In the same way as shown in the example above, isobutylene is used instead of propylene in the feed, whereby methacrolein and methacrylic acid are formed. When, in the same way as shown for the given catalyst, other catalysts are used which are known to be applicable in the oxidation of olefins, in coated form and in combination with the essentially pure catalytic material, similarly beneficial oxidation processes are achieved.

Claims (5)

1. Process for the production of unsaturated aldehydes by reacting a mixture of propylene or isobutylene with molecular oxygen in a reactor where the reactants flow through one or more parallel connected tubes which are surrounded by a heat transfer medium and in which there is a fixed, stationary oxidation catalyst , in which the active catalytic material consists of mixed oxides containing the metals Fe, Bi and Mo, the catalytic material preferably having the composition: where A is an alkali metal, an alkaline earth metal, Sm, Ta, Tl, In, Ga, B, P, As, Sb or a mixture thereof, B is nickel, cobalt, magnesium, manganese or a mixture thereof, a is a number from 0 to 8, b is a number from 0 to 20, c is a number from 0.1 to 10, d is a number from 0.01 to 6, and x is the number of oxygen atoms required to satisfy the valency requirements of the other elements present, characterized by the fact that two catalysts are used in each of one or more of the tubes in the reactor, wherein the first catalyst is a catalyst consisting of a substantially inert support with an outer surface and a coating of a catalytic material which adheres strongly to the outer surface of the support, and the second catalyst is a catalyst consisting substantially of the catalytic material, and by that the catalysts are arranged in the tubes of the fixed bed reactor in such a way that the first catalyst comes into contact with the reactants first, and the second catalyst comes into contact with the reactants after contact with the first catalyst. 2. Method according to claim 1, characterized in that essentially the same material is used as the catalytic material of the first catalyst and as the catalytic material of the second catalyst. 3. Method according to claim 1 or 2, characterized in that a first catalyst containing 5 - 60% catalytic material is used. 4. Method according to claims 1-3, characterized in that the first catalyst is used in an amount which fills from 10 to 80 percent by volume of the reactor tube or tubes. 5. Method according to claims 1-4, characterized in that the first catalyst is used in the form of spherical particles.