NO147068B - PROCEDURE FOR THE PREPARATION OF ACRYLIC ACID AND METACRYLIC ACID BY REPLACING PROPYLEN OR ISOBUTYLENE WITH MOLECYCLES OXYGEN - Google Patents

Description

The oxidation of propylene or isobutylene to acrylic acid

or methacrylic acid has been carried out in two fixed-bed reactors containing two different catalysts to obtain the best yields. Combining the two catalysts in one reactor has not been considered advisable because the second catalyst attacks the olefin in such a way that by-products are formed. Thus, before the desired conversion can take place, unwanted by-products are formed rather than the desired unsaturated acids.

Different catalysts that are effective for the conversion

of propylene or isobutylene, are well known. Representative patents that provide examples of such catalysts include: US Patents 2,941,007, 3,248,340, 3,639,269, 3,362,998,

3,629,148, 3,576,764 and 3,171,859, Dutch Patent 769,689, Belgian Patents 767,659, 774,905 and 777,476 showing bismuth molybdate and other molybdate catalysts, US Patents 3,428,674, 3,431,292, 3,543,854, 616,642 and 3,551,470 which show for-

various uranium catalysts effective in producing the unsaturated aldehydes from propylene and isobutylene, and other catalysts effective in this olefin oxidation, are represented by US patents 3,264,225, 3,197,419, 3,200,081, 3,282. 982, 3,468,958 and 3,408,400, Dutch Patent 7,018,091

and British Patent 1,091,961.

The other catalysts that are used in the invention,

are also known. Catalysts representative of the second catalyst according to the invention are represented by US patents 3,567,773 and 3,567,772, Belgian patent 773,851, Dutch patent 7,205,595, Canadian patent 893,145, Belgian patent 77 4,329, German patent 2 . 217 . 77 4 and German patent 2,214,480

which shows oxidation of unsaturated aldehyde oxidation catalysts using catalysts containing at least molybdenum. Other catalysts for the production of acids are known from US patents 2,881,214, 2,881,213, 2,881,212 and 3,395,178, German patent 2,046,411, Japanese patent 72/11969 and Belgian patent 784,263. From BRD official document. 2,126,534, it is known to produce acrylic acid or methacrylic acid in one step by oxidizing propene or isobutene in gas phase with molecular oxygen in the presence of a two-component oxidation catalyst in a solid layer.

But the combination of the two catalysts in a reactor in a fluidized-bed oxidation of the olefin to the acid is not known. Moreover, one could not expect in industry the very desirable yields of acrylic acid and methacrylic acid which are obtained according to the present invention.

One of the advantages of using a fluidized-bed reactor is that you get a uniform temperature throughout the reaction zone compared to a fixed-bed reactor system where it is possible to achieve a temperature gradient.

The mentioned BRD official document 2,126,534 mentions in particular

that the catalysts have different optimum temperatures for each of the two different oxidation processes that take place. With the present method, one would expect that two catalysts with different optimum temperatures would not work as well in a fluidized bed as in a solid bed where it is possible to achieve a desired temperature profile. A temperature profile 1 can in reality be considered an inherent feature of a fixed-bed reactor system. It is thus unexpected that a high yield is achieved by using a fluidized bed with two different catalysts, when one takes into account that it would be reasonable to expect that the special conditions of a fluidized bed would be unfavorable for the two-catalyst system used in the method according to the invention.

According to the present invention, a method is provided for the production of acrylic acid and methacrylic acid by reacting propylene or isobutylene with molecular oxygen at an elevated temperature in the presence of an oxidation catalyst,

by using as an oxidation catalyst a catalyst containing two different catalysts, the first catalyst being one which is particularly effective in the oxidation of propylene or isobutylene to acrolein or methacrolein, and the second catalyst being one which is particularly effective in the oxidation of acrolein or methacrolein to acrylic acid or methacrylic acid. The method is characterized by the fact that the reaction is carried out in a fluidized-bed reactor in which oxidation

the catalyst is kept in a substantially undivided reaction

zone in such a way that the oxidation catalyst can be moved to any point in the reaction zone. With the method according to the invention, surprisingly high conversions to useful acid products are achieved per passage.

As stated above, the present invention is a progress

method for producing acrylic acid or methacrylic acid from propylene or isobutylene using process conditions, reactant feeds and reaction parameters that lie within the ranges described in the literature. The problem with the present invention is the use of a fluidized bed reactor which uses an oxidation catalyst containing two different catalysts.

Fluidized-bed reactors which are suitable for use in the method according to the present invention are well known.

In a broad sense, these reactors contain a layer of fines

particles of the oxidation catalyst, which are expanded by the flow of reactants through the catalyst. In the preferred embodiment of the invention, the oxidation ion catalyst in fluidized

bed reactor a particle size of less than about 300 microns, and during operation of the reactor the bed volume of the oxidation catalyst is 5 to 50% greater than the volume of the unexpanded bed.

The fluidized-bed reactor can essentially have any design that is compatible with the method according to the invention. A main criterion is that there is a

substantially undivided, reaction zone in the fluidized-bed reactor. In this reaction zone, the reactants form the desired products in the presence of the oxidation catalyst. An important aspect of this reaction zone is that the oxidation catalyst can be moved through the entire reaction zone. In the current design of a fluidized bed reactor, there are of course areas where the movement of the oxidation catalyst is significantly greater than the movement in other areas. It is also not necessary for all catalyst particles to move equally through the entire layer. This limitation instead implies that the particles of the oxidation catalyst during normal operation of the fluidized bed reactor are capable of being moved to any point in the reaction zone.

The fluidized-bed reactor can be an open-bed reactor where there are little or no restrictions with respect to the flow of the oxidation catalyst, or the fluidized-bed reactor can be constructed with a sieve trough, such as those described in US Patent 3.2 30.2 46 for improving the contact between the reactants and the catalyst while at the same time allowing relatively free movement of the oxidation catalyst through the entire reaction zone. In addition to the possible use of sieve trays, most reactors will use cooling coils in the reactor so that a heat transfer fluid is indirectly brought into contact with hot gases developed by the exothermic reaction. All these reactor modifications provide a substantially undivided reaction zone as required by the method according to the present invention.

The second main aspect of the present invention is the special oxidation catalyst that is used. As indicated, there are not one, but two different catalysts. The first catalyst is selected from the group of such catalysts known to be particularly effective in the conversion of propylene or isobutylene to acrolein or methacrolein. The second catalyst is selected from such catalysts which are particularly effective in the oxidation of acrolein or methacrolein to acrylic acid or methacrylic acid.

The first catalyst is, as indicated, effective in the production of acrolein or methacrolein from the corresponding olefin. Broadly speaking, these catalysts are capable of selectively attacking propylene or isobutylene at the α-carbon atom which has no double bond. In each olefin, the catalyst abstracts 2 hydrogen atoms from an α-carbon atom and inserts oxygen in their place to form the carbonyl compound. Catalysts capable of performing this function are

well known, see e.g. the patents listed in the introduction to the description. All such catalysts can be used as the first catalyst in the oxidation catalyst. These catalysts are oxides in the oxidation state determined by the environment. By the term "oxides" is meant oxides, mixed oxides, oxide complexes, solutions in the solid state and other such structures.

Preferred catalysts which are used as first catalyst are those which contain at least one oxide of molybdenum. Of these catalysts, those which contain at least the oxides of bismuth and molybdenum are preferred, and those which have the following formula are preferred.

where

A is an alkali metal, an alkaline earth metal, Zn, Cd, Tl, In, Nb,

Ta, a rare earth metal or mixtures thereof,

B is nickel, cobalt, manganese or mixtures thereof,

D is phosphorus, arsenic, antimony, boron, tungsten, chromium, vanadium

or mixtures thereof,-

and where

a and c are numbers from 0 to 10,

b is a number from 0 to 20,

e is a number greater than zero but less than 10,

d is a number from zero to about 5, and

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

Of these catalysts described by the formula, the catalysts where b is not zero are preferred, because of the particularly desirable results that are obtained by using them. Beneficial catalysts can also be prepared by adding

at least some tellurium instead of bismuth in the above formula.

A particularly preferred first catalyst has the composition KQ 5 Ni 2 5 Co 45 Fe 3 Bi.^ PQ Moi 2 °x' where x is as indicated above.

The other catalyst present in the oxidation catalyst is the catalyst that forms the acid from the aldehyde. This catalyst can be selected from any catalyst capable of introducing oxygen into the carbonyl portion of the aldehyde to form the corresponding acid. Representative examples of these catalysts are known and are indicated in the patents mentioned in the introduction to the description. These catalysts are thus oxides that contain a number of oxygen atoms determined by their surroundings.

Those catalysts are preferred which contain at least an oxide of molybdenum, and such catalysts which contain at least vanadium and molybdenum are of particular interest, and those catalysts described by the following formula are particularly preferred:

where

E is Sn, Cu, Ge, Sb, Bi, Te, Mn, Fe, Mg, Zn, Ni or

mixtures thereof,

G is W, Cr or mixtures thereof, and

J is V, P, Sb, Co or mixtures thereof,

and where

g and h are from zero to 20,

i is from greater than zero to 20, and

x is the number of oxygen atoms required to satisfy

the valence requirements of the other elements present.

In the formula, such catalysts are preferred where G is tungsten and J is vanadium, and such catalysts containing tungsten, vanadium and tin, i.e. G is tungsten, J is vanadium and E is tin, are particularly preferred, and such catalysts containing tungsten , vanadium, tin and at least one of copper, nickel, iron, cobalt or manganese, i.e. G is tungsten, J is vanadium,

E is a mixture of tin and at least one of copper, nickel, iron, cobalt or manganese, is of particular interest because of the highly desirable catalytic effect on the reaction according to the invention.

A particularly preferred second catalyst has the composition 2 V3 Moi2 where x is as stated above.

Of great interest with regard to the second catalyst

with the formula, are also such catalysts which contain copper as one of the constituents. This is the case in the formula when E is at least copper.

The two catalysts comprising the oxidation catalyst used in the method according to the present invention are such as are known in the industry. Although the particular production method is important for the catalytic activity, this is not the point of the invention, and the production methods for certain catalysts are shown in the examples.

As stated above, the oxidation catalyst used in the method according to the invention contains two different catalysts. In a preferred embodiment of the present invention, the oxidation catalyst comprises a physical mixture of separate particles of the first catalyst and separate particles of the second catalyst. One can easily imagine other techniques for bringing the various catalysts into a simple fluidized-bed reactor. E.g. the catalyst addition may comprise particles containing a mixture of the two catalysts.

Another important aspect of the oxidation catalyst is the relative amounts of the two different catalysts. In a preferred embodiment of the invention, it has been found that a substantially complete conversion of the reactants to the acids with a low yield of aldehydes can be obtained by starting from an oxidation catalyst that contains more than about 95% by weight of the first catalyst that is used to oxidize the olefin to the aldehyde. This catalyst mixture is used under given conditions, and the second catalyst (the catalyst that converts aldehydes to acids) is added until a desirable low (less than 5%) concentration of aldehydes is obtained. Alternatively, a relatively high concentration of aldehydes can be recovered in the reactor effluent, for use as aldehyde or for use as recycled feed to the fluidized bed reactor.

In the preferred embodiment of the invention, the second catalyst makes up 5 to 40% by weight of the active ingredients in the oxidation catalyst, and 10 to 30% by weight is more preferred. These concentrations give small yields of unwanted by-products, such as acetic acid, and high yields of acrylic acid and methacrylic acid.

Although the oxidation catalyst usually contains only

two catalysts, the invention also takes into account that more than two catalysts can be used by choosing more than one catalyst from one or both groups of catalysts or by using another catalyst that has no harmful effect on the reaction according to the present invention. It is also technically possible, in addition to the active catalysts, to add to the oxidation catalyst a solid special diluent to improve fluidization, to act as an agent to moderate the heat of reaction or for other purposes.

As stated above, the process conditions, reactant conditions and reaction parameters used in the invention are essentially the same as in industry. The temperature during the reaction is usually between 200 and 600°C, with temperatures of from 300 to 500°C being preferred. Atmospheric, subatmospheric or superatmospheric pressure can conveniently be used.

Although the quantity ratio of molecular oxygen can be varied within wide limits, the molar ratio between molecular oxygen and olefin is usually 1 to 4. Expressed as air, this means that 5 to 20 volumes of air are used per volume of olefin. In addition to the reactants, it can conveniently be taken in the feed

with inert dilution gases, such as steam, nitrogen and carbon dioxide, to improve temperature regulation and increase the selectivity of the acid.

The other aspects of the method according to the invention are not critical. Specific features for carrying out the reaction are shown in the specific embodiments. The important factor in the method according to the invention is that it has been discovered that the use of two different catalysts mixed in a fluidized bed reactor gives surprisingly high yields of acrylic acid and methacrylic acid.

Specific designs

Example - Production of acrylic acid.

A first catalyst useful in the preparation

of acrolein from propylene and which has a composition of 90.<4%> Kq 5Ni2 5Co4 5Fe3Bi1PQ 5Mo120x °g 9.6% Si02' was prepared in the following way:

1645 g of Fe (N03) 3-9H20, 986 g of Ni (N03)_2• 6H20, 1777 g of Co(N03)2-6H20 and 658 g of Bi(N03)3-5H20 were melted and 13.7 g of KN03 were added dissolved in an equal amount by weight of water. 6325 g of (NH 2 )g<Mo>^O 24-4H 2 O was separately dissolved in water, and 7 8.2 g of 85% H 3 PO 4 and 397 g of silicon dioxide were added. The metal nitrates and molybdenum slurry were combined and the mixture placed in a high speed mixer for a few seconds. The resulting material was spray dried and calcined for 4 hours at 540°C. The catalyst was sieved to give the following particle distribution: 25% below 44 microns, 70% between 44 and 88 microns and 5% between 88 and 106 microns.

A second catalyst which is particularly useful in the production of acrylic acid from acrolein and which has the composition 62% VI1 2V3Moi2°x °g 38% SiO2 was prepared as follows: Water was heated in a stainless steel vessel to a temperature of 75°C . 3923 g of (NH4)6Mo?<0>24.4H20, 606 g of (NH4)6W7<0>24•6H20 and 650 g of NH4V03 and 7,604 g of silicon dioxide were added to the water. The mixture was spray dried and heated for four hours at 400°C and sieved to give the same particle sizes as the first catalyst.

A fluidized bed reactor was constructed from a pipe

of stainless steel with an internal diameter of 3.8 cm and with an inlet opening for the reactants at the bottom and an outlet opening for the products at the top. Inside the reactor and at intervals in the longitudinal direction of the reactor were 12 sieve troughs. The sieve troughs were constructed and installed in such a way that the catalyst particles were able to move through the entire reaction zone.

A physical mixture of 500 g of the first catalyst

and 55.5 g of the second catalyst was loaded onto the reactor to give a total catalyst addition approximately 0.5 meters high. Under an air stream, the catalytic layer was brought to a temperature of 340°C.

A stream of the reactants with a propylene:air:steam molar ratio of 1:10.1:5 was fed over the catalyst at a linear velocity of 4.2 cm/sec, and the propylene weight per weight unit with catalyst per hour (WT) was 0.031. The reaction was carried out at a temperature of 340°C, and the waste gases were cleaned with water. The reactor was pretreated for 30 minutes and the product was collected for 15 minutes. The product was analyzed by gas-liquid chromatography. The percentage conversion per passage defined as the molar amount of a certain product obtained x 100 divided by the molar amount allowed propylene, was calculated. The conversion per passage to acrylic acid was 75.6% and the conversion per passage to acrolein was 9.8%. The conversion per passage to acrylic acid and acrolein was thus 85.4%. Less than 0.05% acetic acid was found in the product. The acrolein formed could be recycled or more of the second catalyst could be added to eliminate the formation of acrolein.

In a preferred preparation with some of the catalysts, the molybdenum oxide is reduced with a finely divided metal, such as tungsten.

In the same way as shown above where the catalysts were combined with a silica support, the catalysts can also

have a support of other materials such as alumina, titanium oxide, zirconium oxide, alunum, calcium phosphate or any other support suitable for use with the present catalysts.

Comparison experiment

A catalyst with the composition 82.5%

, Ni„ ,Co. cFe-,BiP^ cMo,o0 and 17.5% SiO„ were used as

0.1 2.5 4.5 3 0.5 12 x ^ 2

first catalyst. A catalyst of 62% Wv _V,.Mo 0 and.

38% SiO 2 was used as the second catalyst. These catalysts were ground and sieved to give a particle size of 10-20 mesh. A mixture of the catalysts containing 90% of the first catalyst and 10% by weight of the second catalyst was prepared and introduced into the reaction zone in a 20 cm 3 reactor prepared by

a stainless steel pipe. A mixture of propylene/air/steam in the proportions 1/11/4 was passed over the catalyst at a temperature of 343°C and with a contact time of 2.5 seconds. The product was analyzed by gas-liquid chromatography. The conversion rate per passage to acrylic acid was 57.1% and to acrolein 31.6%. The amount of acetic acid formed was 0.9%. The conversion to acrylic acid per passage was thus significantly worse than that achieved in the above example.

Claims (7)

1. Process for the production of acrylic acid and methacrylic acid by reacting propylene or isobutylene with molecular oxygen at an elevated temperature in the presence of an oxidation catalyst, by using as oxidation catalyst a catalyst containing two different catalysts, the first catalyst being one which is particularly effective in the oxidation of propylene or isobutylene to acrolein or methacrolein, and the second catalyst is one which is particularly effective in the oxidation of acrolein or methacrolein to acrylic acid or methacrylic acid, characterized by carrying out the reaction in a fluidized-bed reactor in which the oxidation catalyst is kept in a substantially undivided reaction zone in such a way that the oxidation catalyst can be moved to any point in the reaction zone. 2. Method according to claim 1, characterized in that the oxidation catalyst has a particle size of less than about 300 microns and that the volume of the layer during operation of the reactor is about 5 to 50% greater than the volume of the non-expanded layer. 3. Method according to claim 1, characterized in that said first catalyst has the composition K0 5Ni2 ^Co4 j-Fe^Bi-^Q 5Moi2°x' where x is the number of oxygen atoms needed to satisfy the valence requirements of the other elements which is present. 4. Method according to claim 3, characterized in that said second catalyst consists of the composition W^. 2V3Mc'i2(~)x' ^where x is antaH oxygen atoms needed to satisfy the valency requirements of the other elements present. 5. Method according to any of the preceding claims, characterized in that the oxidation catalyst comprises a physical mixture of separate particles of the first catalyst and separate particles of the second catalyst. 6. Method according to any one of claims 1 to 4, characterized in that the first catalyst and the second catalyst are contained in the same particle. 7. Method according to any one of the preceding claims, characterized in that enough of the second catalyst is present in the oxidation catalyst to keep the concentration of acrolein in the product at less than about 5%.