AU596425B2

AU596425B2 - A dehydrogenation catalyst having improved moisture stability and a process for making the same

Info

Publication number: AU596425B2
Application number: AU74577/87A
Authority: AU
Inventors: Stanley E. Moore
Original assignee: Dow Chemical Co
Current assignee: Dow Chemical Co
Priority date: 1985-02-20
Filing date: 1987-06-22
Publication date: 1990-05-03
Anticipated expiration: 2007-06-22
Also published as: AU7457787A

Description

A

593425

AUSTRALIA

Patents Act COMPLETE SPECIFICATION

(ORIGINAL)

Class Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: 'S do CkCLl--nt 'men;ment corntains t Priority I lton 49 and e Under pri tirN g s correct for Related Art: I APPLICANT'S REFERENCE: 33,488B-F Name(s) of Applicant(s): The Dow Chemical Company A ddress(es) of Applicant(s): 2030 Dow Center, Abbott Road, S. Midland, Michigan 48640, UNITED STATES OF AMERICA.

'Address for Service is: PHILLIPS ORMONDE FITZPATRICK Patent and Trade Mark Attorneys 367 Collins Street C Melbourne 3000 AUSTRALIA complete Specification for the invention entitled: A DEHYDROGENATION CATALYST HAVING IMPROVED MOISTURE STABILITY AND A PROCESS FOR MAKING THE SAME Our Ref 58955 POF Code: 1037/1037 The following statement is a full description of this invention, including the best method of performing it known to applicant(s): ,'Ia 6003q/l 1 c -i -1a- A DEHYDROGENATION CATALYST HAVING IMPROVED MOISTURE STABILITY AND A PROCESS FOR MAKING THE SAME Promoted iron oxide catalysts have been known for many years as dehydrogenation catalysts. They are especially useful in the manufacture of styrene by the dehydrogenation of ethylbenzene. Most of the catalysts now in commercial use employ minor amounts of promoters, e.g. salts or oxides of chromium, manganese, bismuth, tungsten, or molybdenum, with chromium being l' the preferred minor component, together with compound of potassium, e.g. potassium oxide or carbonate. The last component gives the catalyst a self-regenerative property enabling its use for long periods of time without significant loss in activity. More recent improvements include the incorporation of minor amounts 'of vanadium, cerium, and of modifiers (such as carbon black or graphite and methyl cellulose) which affect the pore structure of the catalysts. None of these improvements has dealt with the physical integrity of the catalysts. Improved stability to moisture is desirable while maintaining high activity and high yield.

33,488B-F -1- -2- Catalyst life of dehydrogenation catalysts is often dictated by the pressure drop across a reactor, the increase of which lowers both the yield and conversion to the desired vinyl aromatic. For this reason, the physical integrity of the catalyst is of major importance.

In recent years catalysts with higher amounts of potassium have been used, e.g. 20 percent or more, up to 48 percent of potassium calculated as the oxide.

Thus, in U.S. 4,503,163, catalysts are disclosed which contain 13 to 48 percent and preferably 27 to 41 percent by weight of a potassium promoter compound, t' calculated as potassium oxide. Such catalysts are self 15 regenerative catalysts which perform well at lower Ssteam to oil ratios, e.g. ratios of The economic advantages of using less steam are obvious. Associated with the higher amounts of potassium used in such catalysts has been an increase in physical degradation due to moisture and "wet steam" during start-up conditions and plant upsets. This physical degradation can cause increased pressure drop due to coking, 0, plugging, and reduction of the void volume in the catalyst bed.

Calcination process being practiced by the industry at present are either low temperature calcination processes producing catalyst which can 30 operate at low steam to oil ratios, but is not moisture stable, or high temperature calcination processes producing catalysts which are moisture stable but cannot operate adequately at low steam to oil ratios.

It would be desirable if a catalyst could be prepared which had both high activity and resistance to 33,488B-F -3moisture and which can operate at low steam to oil ratios. A method has now been discovered which will provide such a catalyst.

Dehydrogenation catalysts of the present invention are no different with respect to chemical composition and are made from the same constituents as those of the prior art. Thus, red or yellow iron oxides can be used and the promoter materials are likewise those known to the art. Promoter compounds incorporated into the catalyst are K 2 Cr 2 7

K

2

CO

3 Cr 2 0 3

V

2 0 5 and Co(OH) 2 or other compounds of these metals such as, for example, acetates, nitrates and i" oxalates which are reducible to their oxides. Other 15 metal compounds which may be added as promoters include r compounds of aluminum, cadmium, cerium, magnesium, manganese and nickel, provided they can be calcined to the oxide.

20 In addition to the catalytic components, binders and porosity agents are employed in the mixture from which the catalyst is made. A refractory cement is usually employed as a binder and carbon-containing 25 materials, such as graphite and methyl cellulose, may be used to provide porosity which is obtained when they are pyrolyzed during the manufacturing process.

The process of the present invention is a twostep calcination process. It employs tablets or 1 1 30 pellets of the catalytic components, which materials have been dried subsequent to being pelletted or tabletted. The first step in the process is conducted at a temperature in the range of from 2500 to 600°C in which the carbonaceous materials (porosity agents) are burned out. Temperatures below 25 0 C will not 33,488B-F -3- -4completely oxidize the carbonaceous materials and temperatures above 600 0 C can cause the reduction of iron oxide as the organics burn. Above 350 0 C it becomes necessary to purge the catalyst environment with air in order to prevent the reduction of iron.

The-chemical reactions taking place during the first calcination step can be described as follows: Cellulose pyrolization 02 CxHyOz CO 2

H

2 0 Graphite or carbon pyrolization 15 C 0 2 CO CO 2 t The second step in the calcination process, which can follow the first without any cooling, calcines the catalyst at temperatures in the range of from 700 0 C to 800 0 C. During this calcination step, the carbonate or carbonates present are converted to the corresponding oxides.

a* The chemical reactions and transformations occurring during the second calcination step can be SI S described as: Potassium carbonate decomposition

S'

1 30 K 2 CO K 2 0 CO 2 Potassium ferrite formation Fe 2 0 3

K

2 Fe 2 0 4 KFe 5 0 8 Clay dehydroxylation and dehydration 33,488B-F -4- Potassium silicate formation from potassium-clay interaction Removal of the evolved CO 2 from the vicinity of .he catalyst during the second step by providing a gas flow over the catalyst, e.g. air, shortens the time needed for carbonate decomposition. The shorter the time required for this second step, the more active the resulting catalyst. This shorter time also provides a more moisture stable catalyst with no loss in activity over the moisture unstable catalyst containing the same catalytic components. The Figure shows the relationship between the percent CO 2 in the atmosphere O above the catalyst during the calcination step and the 15 time at that temperature required to provide a o o moisture-stable catalyst. While only two temperatures are shown, the higher temperatures should provide an Pros area of stability delineated by a line paralleling the 20 two lower temperature indicia. 20 The preferred temperature for the first step is s. within the range of from 350' to 6000C and for the second step from 7500 to 790°C.

25 *2 The length of time necessary for the calcination in each step will vary with the temperature employed, the higher temperatures requiring shorter times. Generally, however, from 30 minutes to 4 hours is sufficient time for the first step and from 30 t minutes to 60 minutes for the second step. The amount of CO 2 evolved and its rate of removal affects the time needed to complete this step. The time is shortened if the gases (oxidation products and 002) are simultaneously removed as they evolve. This is enpecially true in the second step where there is an 33,488B-F -6equilibrium existing between the carbonate in the catalyst and the CO 2 in the atmosphere surrounding the catalyst.

The present invention will now be more fully described with reference to the accompanying examples.

It should be understood, however, that these examples are illustrative only and should not be taken in any way as a restriction on the generality of the invention as described above.

Examples 1 to 8 In a representative example of making the .o 15 catalyst, K 2 C0 3 is provided in an aqueous solution to °B which K 2 Cr 2 07 is added. This solution is then mixed 4o^ into a dry blend of Fe 2 0 3 graphite, cement, clay and °o o methyl cellulose to form a. slurry which is fed to a spray drier. The slurry normally contains 50 percent 20 water, but may contain as little as 20 percent, or as much as 70 percent. A preferred water content is from O. 40 to 60 percent. The spray dried material, which is o V" fed to a tabletting machine, usually contains <1 0" percent water. Details of such a process are described 25 in U.S. 4,139,497.

A 30 Alternatively, the mixture can be fed as a paste directly to a pelleting machine, in which case the water content is from 8 to 12 percent. This paste is formed as a slurry with 20 to 30 percent water and subsequently dried to an extrudable mass which contains the above correct water content. This alternate process is described more fully in U.S. 3,849,339 and U.S. 3,703,593.

33,488B-F -6- -7- The present invention is directed to a method of calcining such pelleted or tabletted catalyst precursors. Table I shows the composition of a number of different catalysts before calcining.

The calcining of the compositions of Examples 1-7 in Table I was done by heating the catalyst pellets in a furnace up to 6000C over a period of approximately one-half hour. The pellets were held at this temperature for 2 hours, then the temperature in the furnace was raised to 7600C over a period of approximately one-quarter hour and then maintained at that temperature for one-half hour. The catalyst of Example 8 was calcined in the same way except that the 15 1 temperature of the first step was 595'C and that of the t second step was 7900C.

St Sf s a a 3 t 4 t S 33,489B-F -7- '0 CO 0 090 C a 0 0 CC C 6 I. 0 0 0 S 0 #0

C

0*S S *oa 00a CCC C 00 0 C C C C 0e~ e Example TABLE I Comnone ts 1% Wt. I Fe 2

O

3

K

2 C0 3 K 2 Cr 2

O.

1 Cement Graphite Clay 46.7 45.7 44.9 7 46.5 48.7 34.7 46.5 34.6 33.9 33.2 33.9 34.5 36.0 34.2 34.7 0.9 0.8 0.8 0.8 0.9 0.9 0.9 0.9 4.4 4.2.

4.1 4.2 4.3 4.5 4.5 4.3 6.0 4.2 4.1 4.2 4.3 4.5 4.5 4.3 4,5 8.4 8.3 8.4 0.0 0.0 8.9 8.5 Cellulose 0.9 0.8 0.8 0.8 0.9 0.9 0.9 0.9 Other 2. 0 ZrO 2 2.0 KHS0 4 3.8 H 3 P0 4 2.0 KH 2

PQ

4 8.6 Ti0 2 4.5 K 2

B

4 0 7 11.4 MgO -9- The catalysts were tested for moisture stability and for their effectiveness as dehydrogenation catalysts as follows: DEHYDROGENATION REACTION The catalysts shown in Table I, aftercompleting the two-step calcination, were placed in a laboratory reactor made of 1 inch (25.4 mm) OD pipe, 36 10 inch (915 mm) long and wrapped with beaded electrical heaters and insulated. A preheater section containing an inert column packing material preceded the catalyst bed. This assured that the ethylbenzene and water were in the vapor phase, mixed well and heated to the 15 reaction temperature prior to contact with the catalyst. A volume of 70 ml of catalyst was provided to the reactor. Different weight ratios of steam to ethylbenzene (steam/oil, or S/O) are indicated for Examples 1-8 in Table II and Example 9 in Table III.

20 Each catalyst was allowed a minimum of 14 days operation as a break-in period before conversions and yields were recorded. Each of these catalysts gave adequate conversion and selectivity for the dehydrogenation of ethylbenzene to styrene.

MOISTURE TEST C The moisture stability of the catalysts was q measured by the following method: Twenty pellets or tablets were placed in deionized water (sufficient to cover) and left standing for thirty minutes after which they were visually inspected for retention of shape and form. The number retaining their original form was noted and recorded as a percentage of the total used in test, i.e. 20 tablets. For any given catalyst to the test, iie. 20 tablets. For any given catalyst to 33,-488B-F -9r i i pass the moisture test it must maintain 90 percent or greater of its original form.

Table II shows the results of moisture stability tests of the catalyst compositions from Table I after the first and second calcination steps along with the activity and selectivity as determined using the dehydrogenation reaction on each of these catalysts determined after the second calcination. The activity of the catalyst is indicated by the temperature necessary to achieve a conversion of 50 percent, i.e.

the lower the temperature, the higher the activity.

TABLE II re CATALYST ACTIVITY AND MOISTURE STABILITY 1 t I sF~ 14 ri r I r MOISTURE TEST 50 PERCENT CONVERSION EXAMPLE Step Step 2 i A A Ar Failed Failed Failed Failed Failed Failed Failed Failed Passed Passed Passed Passed Passed Passed Passed Passed Temp. °C 588 589 601 594 605 603 612 593 Selectivity 93.6 93.8 93.2 93.7 95.0 94".7 95-. 0 94.2

S/O**

1.4 1.2 1.4 1.2 4, 4 4 4 4, percent Conversion is the weight ratio ethylbenzene.

of steam to oil, i.e. water to Example 9 The catalyst of Example 8 was calcined for 2 hours at 595°C, but at different timed intervals for the 33,4888-F -rr~ -11second step at a temperature of 790°C. Table III shows the effect of time on the activity and selectivity of the catalyst in dehydrogenating ethylbenzene and the moisture stability of the catalyst. The temperature is that required to give 50 percent conversion.

TABLE III

CONVERSION

TIME

OF SECOND MOISTURE TEST 1 CALCINATION After Step 2 Temp. C 12 min.

16 min.

20 min.

Failed Passed Passed Selectivity 94.0 93.6 93.7 s/o It I Comparative Example A (one-step process) Catalyst pellets having the composition of Example 8 (Table I) were heated to the desired calcination temperature over a period of approximately Sone-half hour and then maintained at that temperature for different periods of time. The temperatures and lengths of time of calcination together with results of S 25 the moisture and dehydrogenation tests are given in Table IV. The weight ratio of steam to hydrocarbon, i.e. water to ethylbenzene, was 1.0. Since one of the catalysts failed the moisture test, it was not tested 3 0 for dehydrogenation.

S 33,488B-F -11j_ -12- TABLE IV MOISTURE TEST CALCINATION (Single Step) 50% CONVERSION Temp. Time Temp.

C) (hrs.) Select.

700 3 Failed 700 4 Passed 591 93.3 800 1-1/2 Passed 605 <93.0 S Comparing the results in Example 10 with those of Example 8 in Table II, one sees that while the calcination using the two steps of the invention 2 requires substantially the same temperature for conversion as that using one step at 700°C for four hours, the selectivity is nearly one percentage point difference. This is a significant advantage for the process of the invention. The difference is even more apparent when the comparison is made with the catalyst employing one step calcination at 8000C. Here, both temperatures at conversion 50 percent and selectivity show an advantage for the process of the invention.

44 30 Example 11 and Comparative Example B In yet another experiment, the percent CO2 in the atmosphere above the catalyst being calcined was measured during the second step at temperatures of 7500C and 760°C during timed intervals and moisture stability determined for catalysts calcined for the different 33,488B-F -12- -13lengths of time and temperatures. The results are shown in the Figure. Note that at 0 percent C02, it was necessary to heat the catalyst for 12.5 minutes at 760°C, but a longer time of 21 minutes was required at 750°C. At 5 percent C02, 20 minutes heating was required at 7600C, but between 32 and 33 minutes was required at 750°C to obtain a moisture stable catalyst.

This shows the importance of removing the CO2 as it is evolved from the catalyst and of keeping the CO 2 concentration in the atmosphere above the calcined catalyst as low as possible.

A test of two commercial scale catalysts having the same composition was conducted, one being calcined 1 at 597°C (Comparative Sample B) and the other at 5950C, followed by further calcining at 785°C in accordance with the process of the present invention (Example 11).

Results are shown in Table V: TABLE V Comparative t. Property Example 11 So Sample B Average Crush 29.6 psi 33.4 psi Strength (0.2 MPa) (0.23 MPa) t Attrition 0.19 0.76 Water Stability* 0% 100% Average Reactor 597 593 Temperature Conversion 50 Selectivity 94.0 94.2 *The water stability test was performed as previously described.

33,488B-F -13- Ii 14 The sacrifice of some degree of attrition in a catalyst having high water stability is acceptable since the breaking up of pellets due to water is much more severe than that caused by handling the catalyst in shipping and/or reactor loading operations.

44 t It 4 4 *4 4 II 1* 4 .CL 33,488B-F -14- 1~7

Claims

2. A process claimed in claim 1 wherein the products of oxidation in the first step and the carbon dioxide of the second step are removed simultaneously as they are evolved from said mass.
3. A process as claimed in claim 1 or claim 2 wherein steps 1 and 2 are conducted at temperatures within the ranges of 2500 to 600 0 C and 7000 to 800 0 C, respectively. to 60 Ca
4. A process as claimed in claim 2 or claim 3 wherein the removal of evolved products of oxidation is accomplished oo6 T S by a flow of gas over said mass,
5. A process as claimed in claim 4 wherein the flowing 0 gas is air. a a
6. A process as claimed in any one of the preceding claims wherein the temperature of steps 1 and 2 are 3500 to 600 0 C and 7500 to 790 0 C, respectively.
7. A process as claimed in any one of the preceding claims wherein the time of calcination is from 30 minutes to 4 hours for step 1 and from 10 to 60 minutes for step 2.
8. An iron oxide-containing dehydrogenation catalyst prepared by a process wherein a metal, salt, oxide, acetate, nitrate, or oxalate of chromium, manganese, bismuth, tungsten, vanadium, cobalt, aluminum, cadmium, cerium, magnesium, nickel or molybdenum is employed as a promoter, organic materials are employed as porosity control agents and the constituents are combined, formed into a particular mass and calcined at temperatures sufficient to oxidize the organic material and convert the carbonate to an oxide, characterized in that the calcining process is conducted in two steps, wherein said particulate mass is heated in a first step to a temperature sufficient to oxidize said organic materials and thereafter heated in a second step to a temperature sufficient to convert substantially all carbonates present to the corresponding oxides.
9. An iron oxide-containing dehydrogenation catalyst as claimed in claim 8 wherein the products of oxidation in the first step and the carbon dioxide of the second step are removed simultaneously as they are evolved from said mass. An iron oxide-containing dehydrogenation catalyst as claimed in claim 8 or claim 9 wherein steps 1 and 2 are conducted at temperatures within the ranges of 2500 to 0O 0 0C 600 0 C and 7000 to 800 0 C, respectively.
11. A process according to claim 1 substantially as hereinbefore described with reference to any one of the Examples. o 12. An iron oxide containing dehydrogenation catalyst according to claim 8 substantially as hereinbefore described with reference to any one of the Examples. DATED: 18 January 1990 PHILLIPS ORMONDE FITZPATRICKAO S- ttorneys for: E DOW CHEMICAL COMPANY Fw/ -16-