GB1586173A

GB1586173A - Catalysts suitable for use in making acrylic acid from acrolein

Info

Publication number: GB1586173A
Application number: GB3459279A
Authority: GB
Original assignee: Dow Chemical Co
Current assignee: Dow Chemical Co
Priority date: 1977-07-11
Filing date: 1977-07-11
Publication date: 1981-03-18

Description

(54) CATALYSTS SUITABLE FOR USE IN MAKING ACRYLIC ACID FROM ACROLEIN (71) We, THE DOW CHEMICAL COMPANY, a Corporation organised and existing under the laws of the State of Delaware, United States of America, of Midland, County of Midland, State of Michigan, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention is directed to the oxidation of aldehydes, particularly acrolein, to the corresponding acid, and to certain novel catalysts useful in such an oxidation process.

In the process of making acrylic acid, the most widely used processes are those which oxidize propylene or acrolein to acrylic acid. Many different combinations of metal oxides have been used as catalysts for these processes. Most of these catalysts contain molybdenum oxide as the principal component. Some of the catalysts are effective in oxidizing the propylene directly to acrylic acid although this is frequently a function of the conditions under which the catalyst is used; others oxidize acrolein to the acid. In either case, any acrolein not converted, or acrolein made in the process of oxidizing propylene to acrylic acid, may be recycled to the feed stream and subsequently oxidized to form the acrylic acid.

In addition to molybdenum oxide, the catalysts of the prior art contain many other metals (usually as their oxides) which promote the catalytic effect of the molybdenum. The transition metals of Group VIII of the periodic chart, including iron, cobalt and nickel, have been employed in many such catalysts. Others selected from various groups of metals of the periodic chart have been employed. Thus, for example, titanium, vanadium, chromium, tungsten and manganese in groups IVB, VB, VIB and VIIB are known to be useful.

The art known to us as being closest to that of the present invention is found in United States Patents 3,775,474; 3,833,649 and 3,886,092 which teach the use of Mo, V, Cr, Cu and Win various combinations. None of these teaches the use of tantalum, titanium or niobium as taught by the present invention, nor does the instant catalyst composition contain the tungsten taught by the above three United States patents.

It has now been discovered that with the catalysts and processes of the present invention there have been obtained improved conversions of the reactants and improved selectivities to the desired products.

According to the present invention there is provided a catalyst for the oxidation of an unsaturated aldehyde containing 3 to 6 carbon atoms to the analogous acid which contains oxides of molybdenum, vanadium, chromium, copper and at least one of an oxide of tantalum, titanium and niobium wherein the atomic ratios of the metals are as follows: Mo lsVs-loCro.2-2Cu2-sMo.l-3 wherein Mis tantalum, titanium, niobium or a mixture of two or more thereof, but which does not contain tungsten.

A preferred catalyst is one in which the atomic ratios of the metals are as follows: Mols V5-7 Cro.7-o.s Cu2.4 2.s My.5.2.

The catalysts of the invention may additionally contain silicon as its oxide in an atomic ratio of 1-5, preferably 2-3.

The efficiency of the catalysts made from any particular combination of metals apparently is affected by the manner in which the catalysts are made, and whether or not they are supported or in pelleted form. The porosity and surface area of either the pellet or the support are important to the performance of the catalyst and will determine to some extent the amount of catalytic material employed on the support. It is extremely important in the preparation of the catalyst to obtain uniform distribution of the various oxides contained therein, otherwise the effect of the combination may be lost. The molybdenum and the various promotor metals are added as their soluble salts. usually in acid solution. They are sometimes mixed together in the same solution. but because of possible problems with premature precipitation which would cause non-uniformity in the finished catalyst the metals are most frequently made up in separate solutions which are in turn added together under the proper controlled conditions. Generally, the final pH of the solutions is slightly on the acid side, at pH 6-6.5. The solvent is then evaporated from the solution of the catalyst components in the presence of a support in order to burden the support. when a support is used. If not supported. the components are dried and pelleted.

The total amount of catalytic oxides burdened on the support is preferably from 13% to 30% by weight based on the combined weight of catalyst and support. A particularly preferred burden is from 18%to 23%. The preferred support is alumina and the surface area of the preferred support should be not more than 2 m2/g with a porosity of 35-65 %.90% of the pores being in the diameter range of 50-1500 microns.

According to a further aspect of the present invention there is provided a process for the vapor phase oxidation of an unsaturated aldehyde, particularly acrolein, to the analogous acid which comprises using as the oxidation catalyst a catalyst of the present invention.

The unsaturated aldehyde may be one which has been prepared by the vapor phase oxidation of an olefin in which a gaseous mixture of the olefin and oxygen is introduced over a catalyst which comprises oxides of cobalt. iron. bismuth, molybdenum and potassium wherein the atomic ratios of the metals are as follows: Co4.4-7.o Fe -2Bi l -2Mo lsKo.os-e 2 but which does not comprise tungsten. In particular. the catalyst may be one as described and claimed in our co-pending Application No. 29072/77 (Serial No. 1586172) out of which the present application is divided.

In a particular aspect of the present invention there is provided a two-stage process of oxidizing propylene to acrylic acid comprising: (A) passing a gaseous mixture of propylene and oxygen together with an inert diluent over a catalyst as described above. particularly one of Application No. 29072/77 (Serial No.

1586172). and (B) passing the effluent from (A) over a catalyst of the present invention.

The parameters of feed composition. flow rate. temperature and pressure are well known to the prior art. Thus the aldehyde is usually present in the feed stream from 1-10 volume %. the remainder being molecular oxygen (0.8 to 21 vol ,70) and inert gas. Steam is frequently used as the inert gas although since air is usually employed as the source of oxygen. nitrogen is also present as an inert gas component. Suitable temperatures employed are within the range of 200-400"C and a pressure of from 1-10 atm. is commonly used. Contact times are usually from 0.4 to 15 seconds depending upon the temperature employed and the efficiency of the particular catalyst.

The tantalum pentoxide which may be employed as a component is insoluble and difficult to incorporate into the catalyst mixture and as a result is generally slurried in a solution of the other components. A particularly preferred method of making the solution of catalyst components is to employ the tantalum pentoxide as a colloidal suspension. The commercially available oxide powder is first run through a colloidal mill prior to mixing with the silica (when silica is employed) and then added to the remaining components as described in Example 1 below. The use of the finely divided colloid produces a superior catalyst.

The present invention will now be further illustrated by way of the following Examples.

Example 1 - Preparation of Catalyst A first solution was prepared by heating 1400 ml of distilled water to which was added 172.7 g of ammonium molybdate. 43.9 g of ammonium meta-vanadate. and 6.0 g of ammonium dichromate. A second solution was prepared by adding 43.9 g of cupric nitriate to 75 ml of distilled water which had been acidified with 3 ml. of concentrated nitric acid. A third solution was prepared by adding 27.5 g of colloidal tantalum pentoxide to 28.3 ml of 30% colloidal solution of silica.

The second solution was added drop-wise to the first solution with stirring and heating.

Upon completion of this addition. the third solution was added to the other two with continued heat and stirring. The carrier support. 1/4 inch (0.64 cm) spheres of alumina. was preheated in an oven at 150"C and then added to the composite solution above with continued heating and stirring to remove the excess water. When most of the water had been removed. the carrier was placed in an oven at 150"C for I hour to dry it. The dried catalyst was then calcined for a period of about 6-1/2 hours, the temperature being gradually increased from about 200 to 400"C over a period of about 1-1/2 hours. The temperature was then maintained at 4000C for the remainder of the time. The finished catalyst was removed and cooled prior to use. The catalyst prepared as above contained about 19.2 wt. % of the metal oxides on the catalyst support, and the atomic ratios of the metals were Mo g 5V5.7Cro.73Cu2.76Ta I .89Si2.59.

Example 2 In the manner of Example 1, another catalyst was prepared in which titanium was substituted for tantalum. After the first two solutions had been combined as in Example 1, 7.3 g of titanium dioxide were added to the combination solution while heating and stirring was continued. The remaining steps of making the catalyst were carried out as above. The catalyst contained 19.2 wt. % of the metal oxides on the support and had the following atomic ratio of metals: Mo IsV5.76Cro.72CU2.79Ti 1.39.

Example 3 - Utilization of Catalyst.

The catalyst of Example 1 was placed in a stainless steel reactor made of a 1-inch (2.54 cm) tube 10 feet (3.05m.) long within a concentric pipe which contained a heat exchange fluid for temperature control. The feed to the reactor contained 5.6 mole % acrolein, 30 mole % nitrogen (as diluent) and oxygen, the oxygen to acrolein mole ratio being 1.48. Temperature in the reactor was 300"C. Contact time was 2.9 seconds. This feed stream when passed through the reactor over the above catalyst resulted in a conversion of 99% of the acrolein and gave a selectivity to acrylic acid of 93.4% with 4.4% going to carbon oxides. In like manner, catalysts of varying compositions were tested. The mole % acrolein in the feed of each of the following Examples was in the range of from about 4.5 to about 5.5 %. The results are shown in Table III.

TABLE III Reactor Contact Example Catalyst Components Temp. Time Conv. Selectivity Number Mo V Cr Cu Ta Nb Si ( C) (sec) (% Acrn.) % A A % Carbon Oxides 4 15 6.67 0.93 3.22 2.2 -- 2.92 280 3.5 95 89 9.6 5 15 5.7 0.72 2.76 1.89 -- -- 289 2.5 95.1 94.8 5.2 6 15 5.7 0.72 2.76 1.89 -- 2.59 300 2.9 99.5 93.0 6.0 7 15 5.7 1.09 2.76 1.89 -- -- 301 2.2 89.8 91.2 8.8 8 15 5.71 0.74 2.76 -- 1.78 4.2 283 3.7 96.0 88 9.5 9* 15 5.47 0.71 2.64 1.82 -- 2.9 276 3.2 98 91 9.0 10 15 7.48 1.51 2.75 -- 1.14 -- 280 3.1 89.4 88.1 10.2 11** 15 5.75 0.73 2.78 1.89 -- -- 289 2.2 94.9 96.3 3.7 * Only 2.6 mole % acrolein was employed in the feed stream ** Catalyst was made employing a colloidal form of tantalum Example 12 In the manner of Example 2 other catalysts were prepared containing different amounts of titanium. These were tested as in Example 3 and the results given in Table IV. All components are the same as in Example 2 except titanium the atomic ratio of which is given in the column labeled (x).

TABLE IV (molt Vs.76 Cr0.72 Cu2.79 Ti(x)) Reactor Contact Temp Time Conv. Selectivity Catalyst (x) (NoC) (sec) % Acrn. % AA % Carbon Oxs.

A 0.99 291 3.43 87.7 94.0 5.9 B 1.19 291 3.45 94.6 93.8 6.2 C 1.39 290 3.57 99.2 95.2 5.4 D 1.46 280 3.59 98.5 95.0 5.0 E 1.85 291 2.62 98.7 94.2 5.8 F 2.18 294 3.51 97.3 93.8 6.2 G 3.0 291 3.3 98.4 92.2 6.9 Example 13 In a preferred preparation of the catalyst, a first solution was prepared by heating 6000. m. of distilled water to which was added 1427.6 g. of ammonium molybdate, 362.8 g. of ammonium meta-vanadate, and 49.0 g. of ammonium dichromate. A second solution was prepared by adding 363 g. of cupric nitrate to 150 ml. of distilled water which had been acidified with 20 ml. of concentrated nitric acid. A third solution was prepared by adding 226.4 g. colloidal tantalum pentoxide. less than 1 micron in size, to 500 ml. of water.

Upon the completion of this addition, the third solution is added to the other two with continued heat and stirring. The carrier support, 1/4 inch (0.64 cm.) spheres of alumina, was preheated in an oven at 1500C and then added to the composite solution above with continued heating and stirring to remove the excess water. When most of the water had been removed, the carrier was placed in an oven at 1500C for 1 hour to dry it. The dried catalyst was then calcined for a period of about 6-1/2 hours, the temperature being gradually increased from about 200 to 4000C over a period of about 1-1/2 hours. The temperature was then maintained at 400"C for the remainder of the time. The finished catalyst was removed and cooled prior to use. The catalyst prepared as above contained about 22.3%wit.

% of the metal oxides on the catalyst support, and the atomic ratios of the metals were MolsVs.7sCro.73Cu2.7sTal.s.

The above catalyst, when employed to oxidize acrolein in the manner of Example 3, gave a 99.8 %conversion of acrolein and a selectivity of 96.5%to acrylic acid.

Example 14 A catalyst for the oxidation of propylene to acrolein was employed in conjunction with a catalyst for the oxidation of acrolein to acrylic acid in sequential operation in the following manner: A metal oxide composition containing atomic metal ratios of MolsCo6.7Fe.3sBi.3Ko.o formed into pellets 1/4 inch (0.64 cm.) diameter and 1/4-inch (0.64 cm.) thick was placed into a first column which was a stainless steel tubular reactor 12 ft. (3.66 m.) tall and 1-1/4 inch (3.2 cm.) diameter. A conduit connected this first column with a second column 19 ft.

(5.8 m.) long x 1-1/2 inch I.D. (3.81 cm.) of the same stainless steel into which was packed the supported catalyst of Example 13. Each column was heated by means of a heat exchange fluid flowing through an outer concentric tube. To the first column was fed a gas stream containing 5.3 mole percent propylene. 9.4 mole percent oxygen, and balance nitrogen at a pressure of 28.7 psig (2.13 kg./cm.2) and a flow rate of 12.5 Ib/hr (5.67 kg./hr.) to obtain a contact time of 2.19 seconds. The feed was preheated to a temperature of 325"C and the first reaction column was maintained at 331 C. The exit stream was passed through the conduit to the second column which was maintained at 279"C. Contact time in the second column was 4.87 seconds. The exit gases from the second column were quenched and the noncondensible gases were recycled to the first column. Conversion of propylene was 98.3 % and yield to acrylic acid was 89%.

Claims

WHAT WE CLAIM IS: 1. A catalyst suitable for use in the oxidation of an unsaturated aldehyde containing 3 to 6 carbon atoms to the analogous acid which contains oxides of molybdenum, vanadium, chromium. copper and at least one of an oxide of tantalum. titanium and niobium wherein the atomic ratios of the metals are as follows: MolsVs-loCro.2-2Cu2-sMo.l-3 wherein M is tantalum, titanium, niobium or a mixture of two or more thereof, but which does not contain tungsten.
2. A catalyst as claimed in claim 1 which additionally contains silicon as its oxide in an atomic ratio of 1-5.
3. A catalyst as claimed in claim 1 wherein the atomic ratios of the metals are as follows: MolsVs-7Cro.7-o.8Cuz.4-2.8M1.5-2.
4. A catalyst as claimed in claim 3 which additionally contains silicon as its oxide in an atomic ratio of 2-3.
5. A catalyst as claimed in any one of the preceding claims which is supported.
6. A catalyst as claimed in claim 5 wherein the support is alumina having a surface area of not more than 2 m2/g and a porosity of 35-65%, 90% of the pores being of from 50-1500 microns in diameter.
7. A catalyst suitable for use in the oxidation of an unsaturated aldehyde containing 3 to 6 carbon atoms to the analogous acid substantially as hereinbefore described in any one of Examples 1,2 and 4 to 13.
8. A method of making a catalyst as claimed in claim 1 substantially as hereinbefore described.
9. A method of making a catalyst as claimed in claim 1 substantially as hereinbefore described in any one of Examples 1,2 and 13.
10. A catalyst which has been made by a method as claimed in claim 8 or claim 9.
11. A process for the vapor phase oxidation of an unsaturated aldehyde to the analogous acid which comprises using as the oxidation catalyst a catalyst as claimed in any one of claims 1 to 7 and 10.
12. A process as claimed in claim 1 1 wherein the unsaturated aldehyde is acrolein.
13. A process as claimed in claim 11 or claim 12 wherein the unsaturated aldehyde has been prepared by the vapor phase oxidation of an olefin in which a gaseous mixture of the olefin and oxygen is introduced over a catalyst which comprises oxides of cobalt, iron, bismuth, molybdenum and potassium wherein the atomic ratios of the metals are as follows: Co.-.oFe I-2Bi 1-2Mo 15K0.o5.o.2 but which does not comprise tungsten.
14. A process as claimed in claim 11 or claim 12 wherein the unsaturated aldehyde is that claimed in claim 21 of our co-pending Application No. 29072/77 (Serial No. 1586172).
15. A process for the vapor phase oxidation of an unsaturated aldehyde to the analogous acid substantially as hereinbefore described in any one of Examples 3 to 13.
16. An acid which has been prepared by a process as claimed in any one of claims 11 to 15.
17. A two-stage process of oxidizing propylene to acrylic acid comprising: (A) passing a gaseous mixture of propylene and oxygen together with an inert diluent over a catalyst which comprises oxides of cobalt, iron, bismuth, molybdenum and potas sium wherein the atomic ratios of the metals are as follows: Co4.4-7.0Fe1-2Bi1-2Mo15K0.05-0.2 but which does not comprises tungsten, and (B) passing the effluent from (A) over a catalyst as claimed in any one of claims 1 to 7 and 10.
18. A two-stage process of oxidizing propylene to acrylic acid comprising: (A) passing a gaseous mixture of propylene and oxygen together with an inert diluent over a catalyst as claimed in any one of claims 1 to 7 and 14 of our co-pending Application No.29072/77 (Serial No. 1586172), and (B) passing the effluent from (A) over a catalyst as claimed in any one of claims 1 to 7 and 10.
19. A two-stage process of oxidizing propylene to acrylic acid substantially as hereinbefore described in Example 14.
20. Acrylic acid which has been prepared by a process as claimed in any one of claims 17 to 19.