CA1106351A - Dehydrogenation catalyst tablet and method for making same - Google Patents

Abstract

ABSTRACT
Non-supported, fixed bed catalyst tablets made by spray drying a slurry of the components into microspheres followed by tabletting the microspheres under high pressure in apparatus such as punch and die sets. The catalysts formed according to the process of this invention have better catalytic performance and/or crush strength than do conventionally made pel-lets such as extrudates.

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Description

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IMPROVED DEHyDRoGENArrIoN cATALys~r TABLET AND METHOD FOR MAKING SAME
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Non-supported, fixed-bed catalyst pellets are used in many chemical processes. Among these are pro-cesses for dehydrogenation, hydrogenation, and oxidationof organics. Dehydrogenation processes using such fixed--bed, non-supported catalysts include the dehydrogenation of ethylbenzene to produce styrene, of ethyl toluene to produce vinyl toluene, and of butane or butene to produce ~ ~0 butadiene.
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Hydrogenation processes which use such fixed--bed, non-supported catalysts include such processes as ~ that for producing saturated hydrocarbons from olefins.
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Oxidation processes which use such fixed-bed, non-supported catalyst pellets include such processes as those for making aldehydes and acids from saturated and unsaturated hydrocarbons, e.g., acrylic acid from pro-pylene.

For the sake of conciseness, the word "pel-lets" is hexeinafter used as a generic term to includethose spray dried tablets made by the process of this !
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invention as well as other forms of pe].lets made by such processes as ex-trusion, i.e., extrudates. "Tablet"
is defined to be any pellet made by the process of this " lnventlon.

In the past, improvements in the catalytic performance and/or crush strength of non-supported cata-lyst pellets for the processes referred to above, have generally been obtained by chanying the formula-tion of componen-ts. Typically such ~on-supported catalyst pel-lets are made by extnlding a paste of components through cylindrical dies to form moist cylinders having a diam-eter of from about 1/16 inch to about 1/2 inch (0.16--1.27 cm). As these cylinders exit from the extruder they are usually either chopped into predetermined lengths or allowed to break of their o~n weight, forming cylindrical pellets (extrudates) having a length of from about 1/8 inch (0.32 cm) to about one inch (2.54 cm).
, Methods other than extrusion have been taught for forming non-supported catalyst pellets. For example U.S. Patent 1,680,807 ~August 14, 1928) teaches the for-` mation of catalyst pellets by compression of a multiplic-- ity of fine particles of catalytic material, which parti-cles are not naturally coherent in the dry state. Spray drying of fluid bed catalysts is known. See U.S. Patents ~ .
2,768,145 (Tongue et al. 1956) and 1,680,807 (Scultze 1928). Spray drying catalyst materials on catalyst car-riers or supports is known. See U.S. Patent 2,435,379 (Archibald 1948).
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The present invention is directed to a method ;~ 30 for making an unsupported fixed-bed catalyst tablet, said - ~ method characterized by ,~

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- 3 -(a) spray drying a slurry of catalyst source - constitutents into microspheres; and (b) forming the catalyst tablet by subjecting ; a selected amount of the microspheres to a compres-sive pressure.

The present invention is also directed to method for making an improved unsupported fixed-bed catalyst , tables characterized by :
(a) forming microspheres from a slurry of catalyst source constituents of the oxides of iron, ` potassium, and chromium by spray drying a slurry containing these catalyst source constituents;
' (b) forming a catalyst tablet by subjecting a preselected amount of the microspheres to a compressive pressure of at least 3000 psi (212 - kg/cm2); and (c) calcining the tablet at a temperature greater than 500C.

For some unknown reason these combinations of steps produce a catalyst tablet having superior cata-lytic performance and/or crush strength qualities.

,~ The present invention is also directed to catalyst tablets made by the processes described immediately above.

It should be noted that the phrase "a slurry of catalyst source components" is used above in the spray drying step as opposed to "a slurry of catalyst components". This is done to point out that sometimes the constituents used ln making up the slurry for spray drying are not the same components as those found in the final formualtion of the catalyst tablets to be used.
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Often after adding the constituents together, or in subsequent steps in making the catalyst pellets, chemical changes occur in these constituents. Thus dierent con-stituents other than those started with often appear in the final catalyst pellet formulation. Of course, there are also catalyst slurry formulations which are not changed.
This invention is applicable to both. Hence, as used hereinafter the phrase "catalyst source constituents" is defined to mean not only those constituents which appear in one form in the slurry and another form in the finished catalyst tablet, but also to those constituents that appear in the same form in both the slurry and the inished tablet.
For example K2C03 is a source for K20 if the K2CO3 is con-verted to K20. Also K20 itself is a source of K20 by this definition.
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:' .~ T~e tablets made by the claimecl process are useful in various organic chemical processes, including dehydrogenation, hydrogenation, andoxidation processes.

;;~ In many applications the catalyst tablets must ~ be further treated to be useful. For example, dehydro-; genation catalyst tablets often must be calcined, while oxidation catalyst tablets often must be heated in the ~ presence of hydrogen or a hydrogen source.
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The present invention, is also additionally directed to a method for.making an unsupported fixed-. bed catalyst tablet for use in the dehydrogenation of ethylbenzene to styrene characterized by :: (a) spray drying a slurry into microspheres, with said mircorspheres having an average diameter of from 20 microns to 2~0 microns and a moisture content no greater than 5 weight percent, with . said slurry being comprised of water and catalyst - source constituents of the oxides of iron, potassium, . and chromium, and with said slurry having a water : content of from 20 weight percent of 70 weight percent;
(b) forming a substantially cylindrically shaped ~ tablet from a preselected amount of said microspheres by subjecting these microspheres to a compressive pressure of at least about 22,000 psi (1550 kg/cm2), said tablet having a diameter of from l/8 inch (0.32 cm) .to l/2 inch (1.27 cm); and ; (c) calcining the tablet at a temperature of at least 500C.

The method of making these tablets has found use in making fixed-bed, non-supported, dehydrogenation catalyst tablets for use in the known process of dehydrogenation of .
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- 4a -' of alkyl aromatics, e.g., those aromatics having alkyl ; groups containing from two to eight carbon atoms, and ; particularly dehydrogenation of ethylbenzene to styrene.
This process comprises passing at an elevated tempera-ture, ethylbenzene mixed with steam over catalyst tablets, said catlayst tablets containing at least oxides of iron, ~ potassium and chromium.
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-~ To specifically illustrate the process by which these new catalyst tablets are made as well as the un-' ex~ected improvement in catalystic performance and crush ....
strength of the tablets made by this process, the discussion `' and examples given below refer to a catalyst tabletting ` process, and the tablets made by this process, which are used in the dehydrogenation of ethylbenzene to produce styrene.
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Typically, styrene is made in a dehydrogenation reactor by passing ethylbenzene and steam at an elevated ~ temperature through a bed of catalyst pellets. These `~ pellets are comprised of oxides of iron, potassium and chromium.

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a~ formirlg a paste comprised of water, lub-. ricant, binders and cata:Lyst source constituents of the oxides of iron, potassium, and chromium;
(b). extruding the paste into cylindrical pel-lets haviny a diameter o:E from about 1/8 inch (0.32 1 cm) to about 3/16 inch (0.48 cm) and a length of from about 1/8 inch ~0.32 cm) to abou-t 3/4 inch ~ 10 (1.90 cm); and .: (c) calcining the pellets at a temperature . of from ahout 50QC to about 1200C.

~roducing catalyst tablets utilizing the . method of this invention can be accomplished. by:

.~ 15 (a) forming a slurry capable of being spray .; dried comprised of water and catalyst source con-stituents of oxides of iron, potassium and chromium;
(b) spray drying the slurry to form micro-~ spheres;
- 20 (c) forming a catalyst tablet from a selected .: amount of the spray dried microspheres by compressing the microsplleres; and . (d) calcining the tablet at a temperature of ~ at least 500C.
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These s-teps will now be elaborated upon in the : following discussion.

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SLURRY FORMATI ON
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In forming a slurry suitable for spray drying, any method can be used which gets the catalyst formation components into an a~ueous solution, aqueous suspension, or both.
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The amount of wa-ter present in the slurry is not critical. This amount depends only on the opera-ting - capabilities of the particular spray dryer used. A slurry containing from about 20 weight percent to about 70 weight percent water is found satisfactory for nearly all spray ; dryers. A range o about 40 weight percent to about 60 weight percent water is preferable for most disk type spray dryers.
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- The oxides of iron, chromium, and potassium which are found to be necessary in the final catalyst tablet can be provided in other chemical forms in the : slurry, such as, for example, potassium carbonatè, potas-sium dichromate and ferric oxide. These other chemical ~ forms, however, must be convertible -to the oxides during ; ~0 the remainder of the process of making the tablets. The calcining step is usually the step in which these other forms of iron, potassium, and chromium are converted to the oxides, Fe203, Cr203, and K20. It is immaterial in what form the elements of iron, potassium, chromium, and oxygen occur in the slurry preparation step so long as they can be changed to the oxides themselves in the finished catalyst tablet.

` In preparing pellets by the old method of extrusion (i.e., preparing extrudates), it is known that the water-insolub].e constituents of the slurry should be ground or otherwise converted into powdered particles.
.;~ Usually this powder is available commercially. The same :`
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~7--water-insoluble powdered ingredients used in the process i of producing extruda-tes are used in the process of this ~ invention. For the comparative runs given below, for each diame-ter pellet of each :Eormulation, the inyredients used were from the same source. This was done so that .there would be no variation in the test results due to variations in the source materials.
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SPRAY DRYING
Spray drying is a process long known as a pro-cess for producing very small, discontinuous, spherical particles from a slurry feed, the particles being micro-spheres usually having a diameter no grea-ter than about 500-1,000 microns for most formulations from most spray dryers. For a general description of spray dryers and their operation, see Perry's Chemical Engineers' Hand-book, John H. Perry, editor, Third Edition, McGraw-~Iill Book Co., Inc., New York, Toronto, and London, pages 838-8~ (1950).

Spray dryers are class.ified into three gen-eral categories, centrifugal disk, pressure nozzles, and two-fluid nozzles. Any of these are suitable for use in the process of this invention, but the disk type is pre-ferred for large-scale commercial operations.
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,; Neither -the moisture content nor the parti-cle si~e distribution of the microspheres made by the - spray drying step of this invention are critical limi-tations. ~owever, there are practical limitations that the particular spray dryer being used imposes upon these two parameters, and the microspheres' diameters should not be of the same order of magnitude as the finished non-supported catalys-t tablets desired to be produced.

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I~aving the diameter of the spray dried micro-spheres approach -the siæe of the finished tablets poses no problem generally. This is so because the diameter or size of the smallest tablet contemplated by this 5 invention is about 1/]6 inch t0.16 cm) while the ].argest microspheres usually produced by co~mercial spray dryers are on the order of only about 500-1,000 microns. This size microsphere is within the operable limits for making the tablets contemplated by this invention. It was found that better catalytic performance of the catalyst tablets was achieved when the diameter of about 80 percent of the microspheres was greater than about 20 microns. It is ~: preferable to have a particle size distrihution of the spray dried microspheres such that about 80 percent of the microspheres have diameters which lie in a range of from about 20 microns to about 200 microns, and more preferable if this range is from about 20 microns to about 100 microns. Smaller microspheres caused the equipment used in the tabletting step to bind and exhibit exkreme wear. The larger siæes caused no perceptible problems.

Variations in moisture con-tent of the spray dried microspheres was not critical for the catalytic performance of the finished tablets. ~oisture content of the microspheres had more of an effect on the opera-tion of the particular spray dryer and auxiliary equip-,.
ment used. A moisture content of from about æero weight ~- percent to about 5.0 weight percent produced catalytic tablets which were satisfactory in their catalytic per-formance and crush strength as well as for operation of the equipment. Large moisture contents caused poor flow properties.
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COMP~ESS~ON I~l'.'O TABLETS
After spray drying the slurry into micro-spheres, the next step in the process of this invention is to form relatively large tablets from these micro-spheres by subjecting predetermined amounts of thesemicrospheres to a compressive pressure. This compressive pressure is not critical, but should be grea-t enough to produce tablets having sufficient crush streng-th to withstand the physical loads and attrition to which they will ultimately be subjected. Usually such compressive - pressures are best achieved in punch and die equipment.

As a general rule, the greater the table-tting pressure used, the greater will be the crush strength of the tablets. l'ablets with adequate strength were made using a compressive tabletting pressure as low as about 3,000 psi ~212 kg/cm2). It is generally preferred to use a compressive pressure of greater than about 15,000 psi ; (1060 kg/cm2). It is more preferred to use a compressive - pressure of from about 22,000 psi (1550 kg/cm2) to about ~; 20 45,000 psi (3180 kg/cm2) and most preferable to use a compressive pressure of from about 28,000 psi to 3~,000 psi (1980-26~0 kg/cm2). The higher pressures of these latter two pressure ranges are chosen as a compromise ` between acceptable tablet crush strengths and catalytic performance and the pressure operating limits of the equipment used. No upper limit was found for the compxes-sive pressure, however. Compressive pressures greater than about 130,000 psi (9160 kg/cm2) were used in a laboratory test run which produced very good tablets, but ; 30 ~lown commercial equipment was not available for large--scale manufacture of tablets made with this large a pressure.

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Subjection of the spray dried material to com-~- pressive pressures grea-ter than from abou-t 3,000-15,000 psi (212~1060 kg/cm ) is herein also referred to as "tab-le-tting". The pellets formed by such tabletting are herein also referred to as "-tablets" to distinguish them from those pellets formed by extrusion, herein also ~: referred to as extrudates.

In the tablet-ting step of the process, the molds or dies are chosen with shapes such that the tab-lets formed will have the desired size and shape.

The most preferred shape for fixed-bed, non--supported catalyst pellets produced by any method is - spherical. Ade~uate dies to produce such spherical ~ shapes, however, were not readily available at the time ; 15 the experiments which follow herein were conducted.
Thus no examples are shown for making spherical shaped fixed-bed, self-supporting catalyst tablets. This shape, ; however, is certainly within the scope of this inven-tion as are other non-cylindrical shaped pelle-cs, such as ellipsoids, cubes, star shapes, frustoconical shapes and hollow cylinders.

Generally cylindrically shaped tablets are easier to make and those with convex ends are preferable.
There is no critical size limit for these tablets. Cata lytic performance tends to fall off as the diameter of the tablets varies from about 3jl6 inch (0.48 cm) in the ~ styrene reactors tested. The diameter of these cylindri-:`~ cal tablets can be from about l/16 inch (0.16 cm) to about one inch ~2.54 cm). Preferably the diame-ter is from about 1/8 inch (0.32 cm) to about 1/2 inch (1.27 cm), with a more preferred diameter being from about l/8 inch 18,324-F

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(0.32 cm) to 1~4 inch (0.64 cm). The most preferred diameter is 3/16 inch (0.48 cm). The length of the cylin-ders can be from abou-t 1/16 inch (0.16 cm) up to about one inch (2.54 cm). It has been found, however, that less attrition and mechanical breakage of the tablets occur if the tablets are made so that their length is approximately the same as their diameter.

CALCINING
Following the compression of the microspheres to form tablets, these tablets are usually calcined.
Typically calcining is carried out at a temperature of from about 500C to about 1200C for a time of from abou-t 1 or 2 to abou-t 20 hours. Calcining can be carried out in a special calcining chamber or in the reactor itself.
This calcining step for the tablets formed by the method of this invention is carried out in virtually the same manner as has heretofor been done for the calcining o~
: extrudates.
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Examples of Making Spray Dried Table-ts by the Method of this Invention A slurry was made as follows: To 1411 U.S.
gal (5330 1) of water were added the following water-~soluble solid constituents in the amounts given: 5600 lb (254~ kg) of K2CO3-3/2H2O, 839.5 lb (381 kg) of K2Cr2O7, ; 25 and 839.5 lb (381 kg) of V2O5. To this solution was added the following water-insoluble solid components in powdered form in the amounts given and in particle size distribu-tion given: 14,573 lb (6610 kg) of Fe2O3 powdered particles ranging in size from about 3 microns to about 49 microns, 30 5883 lb (2670 kg) of Fe2O3 H2O powdered particles ranging in size from about 2 microns to about 52 microns, 869 lb 18,324-F

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; (395 kg) of Portland cement ranging in size frorn about 2 microns to 55 microns, 4278 lb (1943 kg) of methyl cel-lulose (a binder) powdered particles rangin~ in size from about 3 microns to about 250 znicrons; and 4145 lb (1880 kg) of graphite powdered particles ranging in size from about 1 micron to about 13 microns.

Additional water was added -to the above slurry so there was a solids to water ratio of 0.94:1 in the resulting slurry.
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This suspension was then fed as the ~eed to the feed inlet pump of a centrifugal rota-ting disk type spray dryer a-t a tempera-ture of 30C. The model used had an atomizing disk wheel 5 inches (12.7 cm) in diam-eter which was located near the top of the drying cham-ber of the spray dryer. The drying chamber was conical in shape and supported vertically wi-th the larger por-` tion above the smaller portion. Its largest diameter was ~ 7 feet (2.14 m) and its height was 12 feet (3.66 m). The ; flow of the ~rying air was concurrent to the downward 20 falling of the microspheric particles.
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The rate of the feed to the atomizer disk was 0.77 U.S. gal/min (2.91 l/mj. The disk was rotated at a speed of ~1,600 rpm. The inlet temperature of the drying air was 260C while its outlet temperature was 2S 149C.

The dried microspheres were exhausted fromthe spra~ drying chamber of the spray dryer into its bag filter collector. The microspheres were observed to be both of the ruptured surface and smooth surface type. They had a particle size distribution of from 5 microns to about 27 microns diameter with moisture of less than 1 weight percent.
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.3-The microspheres were then fed to a -tablekting machine having 0.200 inch (O.Sl cm) inside diameter dies and were compressed with punches at a pressure of 36,400 psi (2570 kg/cm2~.

The tablets produced by the tabletting machine were cylindrical in shape. They were 0,210 inch (0.52 cm) in diameter and 0.180 to 0.290 inch long (0.46-0.74 cm).
They had an average crush strength of 29 lb (13.2 kg) as measured by a hardness tester instrument.

The tablets were then calcined in a kiln at tempera-tures rangin~ from 683~C to 732~C with an average temperature of 703C for 1 to 1.5 hours. Following cal-cination, the tablets were observed to have an average relative crush strength of 27 lb (12.2 kg) measured by the same instrument used above to measure the uncalcined tablets.

~ The calcined tablets were then analyzed and s found to contain Fe2O3 - 70.2 wt. %; K2O - 4.6 wt. %;
K2CO3 - 10-6 wt. %; Cr203 - 2-8 wt. %; V2O5 - 4.0 wt. %;
cement - 3.3 wt. %; carbon - 4.3 wt. %.

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;~ Examples and Comparative Runs Eighteen experiments were made so that nine pairs of comparisons could be made between the catalytic performance and crush strength of catalyst tablets made -~ 25 by the method o the present invention and the catalytic performance and crush streng-th of catalyst extrudates ~ made by conventional extrusion.
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In each pair of experiments made, the cata-lyst pellets (tablets and extrudates) were made from the same formulation and had the same diameter. Three dif-~ ferent formulations were used and three different diam-;; 5 eters for the catalyst pellets were used for each formu~
lation. Two different methods of pellet preparation were used for each diameter. The comparisons rnade are between those pairs of experiments in Table II whose catalyst pel-lets were made from the same formulation and have the same diameter.
., In all of these experiments ethyl bezene (EB) was dehydrogenated to form styrene. Data are assemblèd in Table II.
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The three different formulations used are well-known, useful dehydrogenation catalysts. The par-ticular cons-tituents of these formulations and their weight ratios (excluding free water) are given in Table I.
These specific formulations are herein referred -to as F-~l, F-2, and F-3.

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The three diEferent pellet diameters chosen for testing each formulation were 1/8 inch (0.32 cm), 3/16 inch (0.48 cm) and 1/2 inch (1.27 cm). In the past, conventional catalyst pellet diameters have ranged from 5 about 1/8 inch (0.32 cm) to a~out 1/4 inch (0.64 cm).
It is known that smaller diameter pellets are normally more active and have greater crush strength than larger ; ones. Lar~er diameter pellets have the advantage of producing less pressure drop in the reactor, which allows the use of a lower absolute pressure than would he per-mit-ted otherwise. This in turn increases the conversion of the ethylbenzene. Thus a compromise has been utilized in the past between using a smaller catalyst pellet which ~; has greater catalytic activity, and using a larger cata-lyst pellet which allows a lower operating pressure.
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With the present invention such a compromise still has to be made, but by this invention, larger cata-lyst pellets can be used with less loss in cataly-tic activity and crush strength as was experienced before when using conventionally made extruded pellets.

In the examples and comparative runs below pellet crush strength was determined on an average value of 20 pellets (tablets and extrudates~ from each of the 18 batches of pellets made using a hardness tester instru-ment. This instrument gives a reading proportional tothe total force, in units of pounds force (kg/force), required to crush the pellets.

The two different methods of catalyst prepa-ration used for each diameter of each formulation were (1) the conventional method of extruding a paste into pellet extrudates and then calcining the extrudates, and , .

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(2) spray dr~ing a slurry containing the catalyst consti-tuents, sufficiently compressing the microspheres in a tabletting machine to form tablets of the same diameters and formulations as the extrudates, and then calcining the tablets. A detailed elaboration of these two methods ` for preparing the catalyst extrudates and tablets is given following Table II.

The extrudates and tabletted pellets pre-pared for each diameter of each formulation were tested for performance in mini-reactors. The reactor used for both the 1/8 inch (0.32 crn) and 3/16 inch ~0.48 cm) extrudates and spray dried tablets was a part of a 35 inch long (0.89 m), 1 inch diameter (2.54 cm), 316 stainless steel pipe. The reactor used for the 1/2 inch (1.27 cm) diameter extrudates and spray dried tab-lets required a 1.5 inch (3.81 cm) diameter pipe. Other-wise the mini-reactors were the same.
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The pipes for both of these mini-reactors were ~rected upright. Both reactors were fitted with a beaded wire heater and heater control means to control the temperature in their reactor zones and were well insulated. In every experiment, in either size reactor, ` the catalyst pellets were installed in the mini-reactors to form a catalyst bed 7 inches high (17.8 cm). Beneath the catalyst bed, but still in the pipe, 11 inches ~27.9 cm) of spacers were installed to support -the catalys-t pellets. Above the catalyst bed, but still in the pipe, a 17-inch (43.2 cm) section of the pipe was used as a preheater and mixing zone. This zone contained porce-lain saddles for column packing.
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The preheater section al.so had a beaded wire heater wrapped around it as did the heater for the reac-tor section of the pipe described above.
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Into this preheater there was fed 99 percen-t pure ethylbenzene (EB) and water. As t.he EB and water fed through the preheater stage they were heated to a temperature approaching reactlon temperature. This tem-perature is above the vapor forming phase of the EB and the water. The porcelain saddles and boiling action of the EB and water caused the EB and water to become a well mixed vapor mixture. In this vapor s-tate the mix-ture entered the reactor zone of the pipe in which were located the catalyst pellets (extrudates or tablets).

The li~uid hourly space velocity (LHSV) (LHSV
is defined as the volume flow of fluid per hour divided by the volume of catalyst present) of the E~-steam mix-ture was maintained at 1.0 vol/vol/hour. The weight ratio of the steam used to the EB used was maintained at 2.0:1.

For each batch of pellets tested, the oper-ating temperature for the reactor was kept constant for each of the runs of a particular formulation, i.e., all the F-l formulation experiments were made at 575C, the F-2 at 610C and the F-3 at 600C. Conversion data are given in Table II.

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rd --I I I I I I I I I I I I I I I I I I
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O
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a) Z H ~d ~d ~ P
rd ~I N ~ ~ .~ d 3 ~ a)rd ~ ~ a)rd O rd au~0 0 rd O
Fil ~ d P~ p~ rd Q~
~ 0 X 0 X o x o x o x o x o x o X o x n ~ J~
F~ 1 C~ F~ t~ FL~ C~ F~ F~ C) F~ U F;l ~ C) F~ ~I N
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. ., From Table II it can be seen that the crush strength of the spray dried tablets prepared by the - method of this invention was as good or better than that of the conventionally made extrudates for a given formu-lation and a given diameter. Further, it iS seen tha-t in every case the tablet made by the method o this inven-tion produced a higher conversion o ethylbenzene to sty-~ rene.

-~ The extrudate pellets of the three formula-tions used were made by the conventional eXtrllSion method.
This me-thod is as follows:
.
First the soluble components used for making the extrudates for each particular batch were dissolved in water. The water-insoluble components were in powder ; 15 form and were thoroughly mixed.

; The water-soluble constituents of the formula-tions in Table I are K2CO3 3/2H2O, K2Cr2O7, and V2O5.

The small particles of water-insoluble con-- stituents of the formulation being used wexe then added to the solution of water-soluble constituents of tha-t formulation and thoroughly mixed to orm a slurry having about 75 weight percent solid material. This solid material percentage is calculated by considering both the soluble and insoluble material as solid. -~
;~
Next the resulting mixed slurries were dried in an oven at 110C ~mtil the free water con-tent of each mixture was down to 10 to 12 weight percent so that a paste was formed.

.
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.
. . . .

.. . . .

.
.. :

:' The paste for each formulation and each of -the three diameters used was then extruded using a com-merical type pellet mill.

The extruda-tes formed by this pellet mill varied in length from 1/8 inch (0.32 cm) to 1/2 inch (1.27 cm) for each of the three diameter pellet extru-dates produced, with the larger diameter pellets tending to have the longer lengths. rrhese lengths were formed as the continuous extrusions of pas-te exiting from -the pellet die was cut by a knife.
, The pelle-t extrudates were then calcined at a temperature of about 700C-900C for 3 hours.

The different batches of spray dried tablets - made for the comparative runs of Table II were made by first forming the cons-tituents of the particular formu-lation into a water slurry in the same way -the mixture used to form the paste for the conventional extrudate pellets above was made. Thus, the water-soluble consti-tuents were added to water and this solution was thor--; 20 oughly mixed with the water-insoluble components obtained from the same source from which the insoluble constituents , were obtained. The slurry contained about 35 weight per-; cent solid material. The weight percent of the solid material of the sluxry was calculated as including the water-soluble as well as the water-insoluble consti-tuents.

~;~ The slurry was fed to a laboratory disk type ~ ~ spray drier where it was led from a reservoir to the top ; of the atomizer wherein it was passed down a feed tube `~ to an atomizer wheel. The slurry entered the interior 3Q of the wheel and because of the high rotational speed of ~,.',. . .
.. ~ . .
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.
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the wheel (40,000 rpm), it is flung outward at a high ; rate of speed in droplet form. These droplets produced a very fine, uniform mist. This mist entered the drying chamber of the atomizer from -the periphery of the atomizer whee]. The atomizer wheel had a diameter of 63 milli-meters. The drying air at the drying chamber inlet was maintained at 210C and the outlet temperature in the cyclone filter was maintained at 90C. The feed rate to the atomizer was maintained at about 1000 grams/hour.
The spray dried microspheres produced for all the experi-mental runs using spray dried tablets contained about 2 percent moisture. Their diameters ranged from about 10 microns to about 50 microns with most of the microspheres having a dic~meter close to 30 microns. Under an electron ; 15 microscope some of these microspheres appeared to be of the hollow xuptured type.

These microspheres were then fed to a manu-ally operated pellet press having dies with the same : inside dia~leter as that desired for the tablets, i.e., 1/8 inch (0.32 cm), 3/16 inch tO.48 cm), and 1/2 inch ~1.27 cm). The dies used were filled with the spray dried microspheres. Sufficient amounts of microspheres were used in the dies so that the length and diameter of the tablets formed were the same. The tablets were cylindrical in shape with ends which were slightly convex.
'.
Eollowing the tabletting of the spray dried microsphere the formed tablets were then calcined in the same way as were the conventionally made extrudates above, i.e., these spray dried tablets were heated at a tempera-ture of about 700C to about 900C for about 3 hours.
-The crush strength of these spray dried tab-lets used in Table II were measured fol'owing the cal-cining of the spray dried tablets.
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,, .
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Claims (8)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for making an unsupported fixed--bed catalyst tablet said method characterized by (a) spray drying a slurry of catalyst source constituents into microspheres; and (b) forming the catalyst tablet by subjecting a selected amount of the microspheres to a compres-sive pressure.

2. The catalyst tablets made by the process of Claim 1.

3. The process of Claim 1 wherein the micro-spheres axe subjected to a compressive pressure of at least 3000 psi (212 kg/cm2).

4. A process as in Claim 1 wherein following the compression of the microspheres into tablets, the tab-lets are calcined at a temperature of at least 500°C for a time of at least one hour.

5. The calcined tablets made by the process of Claim 4.

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6. A method for making an improved unsup-ported fixed-bed catalyst tablet characterized by (a) forming microspheres from a slurry of catalyst source constituents of the oxides of iron, potassium, and chromium by spray drying a slurry containing these catalyst source constituents;
(b) forming a catalyst tablet by subjecting a preselected amount of the microspheres to a compressive pressure of at least 3000 psi (212 kg/cm2); and (c) calcining the tablet at a temperature greater than 500°C.

7. The catalyst tablet made by the process of Claim 6.

8. A method for making an unsupported fixed--bed catalyst tablet for use in the dehydrogenation of ethylbenzene to styrene characterized by (a) spray drying a slurry into microspheres, with said microspheres having an average diameter of from 20 microns to 200 microns and a moisture con-tent no greater than 5 weight percent, with said slurry being comprised of water and catalyst source constituents of the oxides of iron, potassium, and chromium, and with said slurry having a water con-tent of from 20 weight percent of 70 weight percent;
(b) forming a substantially cylindrically shaped tablet from a preselected amount of said microspheres by subjecting these microspheres to a compressive pressure of at least about 22,000 psi (1550 kg/cm2), said tablet having a diameter of from 1/8 inch (0.32 cm) to 1/2 inch (1.27 cm); and (c) calcining the tablet at a temperature of at least 500°C.

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