CA1074773A

CA1074773A - Dehydrogenation catalyst and process

Info

Publication number: CA1074773A
Application number: CA254,619A
Authority: CA
Inventors: Gregor H. Riesser
Original assignee: Shell Canada Ltd
Current assignee: Shell Canada Ltd
Priority date: 1975-07-03
Filing date: 1976-06-11
Publication date: 1980-04-01
Also published as: DE2629635C3; BE843682A; IT1064096B; JPS527889A; FR2315995B1; NL186898B; FR2315995A1; DE2629635A1; GB1539551A; IN143710B; JPS5713335B2; AU500742B2; DE2629635B2; AU1548776A; BR7604302A; NL7607155A

Abstract

A B S T R A C T

The invention relates to a catalyst containing iron, chromium, potassium and vanadium compound, which has been modified by the addition of a small amount of cobalt compound and to the use of the catalyst in the dehydrogenation of hydrocarbons.

Description

This invention relates to improved catalysts for the dehydrogenation of hydrocarbons and to a process for the dehydroge-nation of hydrocarbons such as the production of vinyl aromatic hydrocarbons from alkyl substituted aromatic hydrocarbons and the production o~ mono olefins and diole~ins from the corresponding more saturated aliphatic hydrocarbons.
The vinyl benzenes and butadienes play a particularly inportant role in the preparation of synthetic rubbers, plastics and resins. The polymerization of styrene for example with various comonomers such as butadiene to produce synthetic rubbers is well kno~n as is the polymerization of styrene to produce polystyrene resins.
Styrene and butadiene are typically produced from ethyl benzene and butylene, respectively, by dehydrogenation over solid catalysts in the presence of superheated steam, and preferably at temperatures ranging from 500 to 700C. The class of catalysts found to be the most effective for this process is a potassium oxide (carbonate) promoted, chromium oxide stabilized iron oxide.
Considerable research has gone into attempting to improve the

2~ activity and selectivi~y of this class of catalysts. Any improvement which results in either increasing the selectivity (moles of desired product produced per mole of reactant reacted) or the conversion (moles of reactant reacted per mole of starting material) .

7~3 without lowering the other is economically attractive since the result is that the yield (moles of desired product produced per mole of reactant) of the product has been increased. Any increase in the numerical value o~ the yield results in a more efficient operation with more reactant be-.ng converted into the desired product. In commercial operations many of which produce millions of poundsof product per year, an increase of only 1 or 2 percentage points in the selectivity can result in a substantial net increase in the plant production or a substantial savings of starting materials.
The addition of vanadium pentoxide is known to improve the selectivity of the above described iron-chromium-potassium oxide catalysts. Such catalysts containing vanadium pentoxide were disclosed in U.S. Patent Specifications 3,351,683 and 3,084,125.
Addition of cobalt to a typical iron-chromium-potassium oxide catalyst has been disclosed in U.S. Patent Specification 3,291,75&.
Further it is disclosed in sai.d specification t~at the replacement of all or a substantial portion of the iron oxide in these catalysts by cobaltous ferrite effects a noticeable increase in the catalyst ..
activity, and also that at lower cobaltous ferrite levels the .
activity of the catalysts decreases to that of the conventional iron oxide catalyst, It has now been found that when small amounts of cobalt compound~are added to dehydrogenation catalysts comprising iron 2~ oxide, chromium oxide,potassium oxide and vanadium pentoxide~ :

. ~

~37~7~73 the yield to unsaturated hydrocarbons from corresponding more satu-rated materials is improved. In particular, yield to styrene from ethyl benzene and butadiene from butylene is improved. In particular, thecatalyst of this invention is useful for the pro-duction of olefins ~rom the corresponding more saturated aliphatic hydrocarbons, and specifically for the production of butadiene Prom butylene or isoprene from amylene. The catalyst of this invention is further of use in producing alkenyl aromatic hydrocarbons from alkyl aromatic hydrocarbons particularly loNer alkenyl aromatic hydrocarbons from lower alkyl aromatic hydrocarbons, in which the lower alkyl groups have from two to six carbon atoms, and speci-r.ically the catalyst is useful for the production of styrene from ~thyl benzene.
- According to the invention the catalyst comprises (a) r 9~.~
1~ ~ from 50 to ~ and preferably from 55 to 90 percent by weight of iron compound, measured as ferric oxide, (b) from 5 to 30 and preferably from 6 to 25 percent by weight of potassium compound, measured as potassium oxide, (c) from 1 to 6 and preferably from 1.5 to 5 percent by weight of chromium compound, measured as chromium oxide, (d) from 1 to 6 and preferably from 2 to 5 percent by weight of vanadium compound, measured as vanadium pentoxide and (e) from 0.1 to 10, preferably from 0.1 to 5, more preferably from 0.3 to 4, and most preferably from 0.5 to 3 percent by weight of a cobalt compound~ measured as cobaltous oxide.

- . ': . :

~7~77~

Variances within the general composi~ion described above depend in part on whether the catalyst is used to produce vinyl aro-matic compounds or olefinic compounds.
Catalysts for the production of vinyl aromatic compcund~
such as styrene from ethyl benzene and alpha-methyls~yrene from ~ ~Z,~
I cumene typical~.y contain from 75 to 3~ and preferably from 80 to 90 percent by weight of iron compound measured as ferric oxide, from 5 to 20 and preferably ~rom 6 to 15 percent by weight of potassium compound measured as potassium oxide, from 1 to 6 and preferably from 1.5 to 5 percent by weight of chromium compound measured as chromium oxide, from 1 to 6 and preferably from 2 to 5 percent by weight of vanadium compound measured as vanadium pentoxide and from 0.1 to 10 and preferably from 0.1 to 5 and more preferably from 0.3 to 4 and most preferably from 0.5 to 3 percent by weight of a cobalt compound measured as cobaltous oxide. The production of dienes from mono-olefins is also possible with these catalysts. :~
Gatalysts for the producticn of dienes from mono-olefins such as, for example, isoprene from amylene or butadiene from butylenetypically contain from 50 to 75 and preferably from 55 to 70 percent by weight of iron compound measured as ferric oxide, from 15 to 30 and preferably from 20 to 30 percent by weight of potassium compound measured as potassium oxide, from ~ to 6 and preferably from 1.5 to 5 percent by weight of chromium compound measured as chromium oxide, from 1 to 6 and preferably ~7~L773 from 2 to 5 percent by weight of vanadium compound measured as V205 and from 0.1 to 10, preferably from 0.1 to 5~ more preferably from 0.3 to 5, even more preferably from 0.3 to 4.0 and most preferably from 0.5 to 3 percent by weight of a cobalt compound measured as cobaltous oxide. The production of vinyl-aromatic compounds from alkyl substituted aromatlc hydrocarbons is also possible with these catalysts.
Many forms of iron oxide can be used in preparation of the catalyst of this invention. Typically, iron oxides employing catalyst preparations o$ this sort are usually a synthetically produced, powdered red, red-brown, yellow or black pigment.
The red or red-brown pigments are highly pure ferric oxide, while the black pigment is the magnetic form, ferrosoferric oxide (Fe3O4),which is usually found in the catalyst;under various reaction conditions. The yellow iron oxides consist of the monohydrated form of ferric oxide. These oxides are prepared by various methods, e.g., oxidation of iron compounds, roasting, `
precipitation, calcination, etc. A suitable form of iron compound is the mono-hydrated yellow iron ox;de. Particularly suitable are pigment grade red iron oxides of purities exceeding ~8% wt. These red oxides have surface areas ranging from 2 to 50 m2/gram and particle sizes from 0.1 to 2 microns.
It is known that the most selective catalysts are those having surface areas be]ow 10 m2/gram, and in many cases below 5 m2/gram. If iron oxides have surface areas in excess of this ,. ". . .

.
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, . . : . .

requirement the surface area can be reduced by precalcining the iron oxides at temperatures exce~ding 700C for a period of time ranging from one-half hour to several hours.
The strength of the catalysts can be improved by adding binding agents such as calcium aluminate and portland cement.
~lowever, catalyst strength can also be improved by calcining the extruded pellets at temperatures ranging from about 700C
to about 1000C. Calcination at these temperatures can alleviate the use of binding agents.
While most of the above methods result in catalysts having the desired surface area, they also result in catalysts having a relatively high density. It has been found that catalysts h~vin~ a highly porous structure and a low surface area are highly active in catalytic dehydrogenation. Various methods 1~ have beenemployed to form highly porous catalysts. For example, combustible materials, such as sawdust, carbon, wood flour, etc.
have been added during catalyst formation, and then burned out after the pellet has been formed. Many of these porosity-promoting aids alsoas3ist in facilitating extrusion of pellets, for ~0 ~xample, the use of graphite and aqueous solutions of methyl cellulose.
The po.assium p~omoter is added to the catalyst in various for-ms. For example, it may be added as the oxide, or as other compounds which are convertible, at least in part, under ~5 dehydrogenation conditions~ to the oxides, such as the hydroxides, ~7~773 the carbonates,,the bicarbonates, the phosphates, the borates and the acetates. A particularly preferred potassium compound is potassium carbonate.
The chromium compound is added to the catalyst in the form of chromium oxide or in the ~orm of chromium compounds which decompose upon calcination to chromium oxide, as for example, chromium nitrfltes, hydroxides and acetates.
Vanadium is added to the catalyst as vanadium pentoxide or as salts or other compounds thermally decomposable to the oxides, such as sulfates, oxysulfates, sulfides or vanadates.
Cobalt is added to the catalyst as the oxide, or as compounds decomposable to the oxide such as hydroxides, nitrates, acetates and oxalates.
The catalyst o~ this invention is compounded in a variety of ways. One method is to ballmill together a mixture of the desired oxides, adding a small amount of water, and extruding the paste formed to Produce small pellets, which are then dried and calcined at temperatures above 500C. Another method is to dissolve the components together, spray dry these components to form a resulting powder, calcine the powder into the resultant oxides, and then add suf~icient water to ~orm a paste and extrude into pellets, dry and calcine. Another procedure would involve precipitating those materials which are precipitatable, such as iron and chromium, as the resultant hydroxides~ partially de-watering the resultant precipitate~ adding soluble salts of . ~ , ~ , . . . . .
' `: . - ' . ': . ': .' . ' .
.. . . , .. .,: .. . .

g potassium and vanadium, and then subsequently extrudirg, drying and calcining the resultant pellets. A preferred method is to dry-blend powders of iron oxide, chromium oxide, cobalt carbonate and vanadium pentoxide and potassium carbonate, add water, optionally containing potassium carbonate in solution, and then mull and pelletize the mixture, subsequently substantially drying and then calcining the pellets at a temperature ranging from about bOOC to about 1000C to form the final product.
Alternatively, the vanadium pentoxide is dissolved in the potassium carbonate solution, rather than dry-mixed with the iron oxide, chromium oxide and cobalt carbonate.
The optimum size of the pellets produced will vary according to the need of various process. Catalyst pellets having a diameter of from 0,3 to 1,O~cm, and from 0,3 to 1,6 cm in length are typical.
The smaller diameter catalysts are generally more active but provide increased pressure drops.
The dehydrogenation reaction is usually carried out at reaction temperatures of about 500-700C. However, higher or lower temperatures may be used. The use of at,mospheric, sub-atmospheric, or super-atmospheric pressure is suitable.
However, it is preferable to operate at as low a pressure as is feasible, and atmospheric or subatmospheric pressure is preferred. The process of the invention may be carried out in batch, semi~continuous, or continuous operation~ with cont~nuous operation being preferred. The catalyst is employed in the form of a fixed bed, or in fluidized or suspended form.

~L~7~7~3 It is preferable to utilize a fixed bed. The reaction may be carried out in single stage reactors or by staging in series reactors.
The reactors may be of various designs, e.g., downflow reactors, radial reactors, etc.
With the use of the catalyst of this invention, it is desirable to add steam to the reactant feed to aid in the removal Or carbonaceous residues from the catalyst. The reaction feed contains from 2-30 moles of steam for everymol~ of feed. Ca-talysts having higher potassium contents are usuallyemployed at lot~e~ ~eed to steam ratios. Feed to steam ratios of from about 1:9 to about 1:~8 are desirable. Good results are obtained with feed to steam ratios of about 1:12.
The contact time of the reactatnt gas with the catalyst is usually defined in terms of gaseous-hourly-space velocity (volumes of hydrocarbon reactant per volume of catalyst per hour, i.e., GHSV), The GHSV according to this invention may vary from about 10 to 3,000 and is preferably adjusted within this range to effect the degree of conversion desired for the particular feed in question.
Example I
Part A. A catalyst in accord with this invent,ion was prepared by dry-blending cobalt carbonate, vanadium pentoxide~ chromium oxide, potassium carbonate with red oxide having a surface area of 5 m2/gram and an average particle size of 1 micron.
2'i W~ter is then added and the mixture is mulled and pelleted.

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1~37~773 The pellets were dried at 200C for 1/3 of an hour and then calcined at about 1000C ~or about 50 minutes. This catalyst is denoted as I-A in Table I which gives the resultant composition.
Thiscatalyst was tested ~or activity and selectivity in the dehydrogenation of ethylbenzene to styrene by placing the catalyst pellets in a ~ixed reactor having a volume of 100 cc and passing a preheated mixture of steam and ethyl-benzene at a molar ratio of 12:1 into the catalyst bed which was maintained at the temperature needed to effect the desired conversion of ethylbenzene. This temperature is dependent upon the activity of the catalyst. A pressure of about 0 to 4 cm of water was used and the liquid hourly space velocity of ethylbenzene was varied from about o.65 to about 1.8h 1. The effluent vapors were analyzed for styrene, ethylbenzene, benzene and toluene. These results were converted to activity and selectivity and are recorded in Table I.
Part B. A catalyst composition not in accord with this invention was prepared and tested in a manner similar to that of catalyst Part A above. This catalyst is denoted as I-B and contains only iron oxide, potassium oxide and chromium oxide.
This catalystand its test results are shown in Table I.
~0 Part C. A catalyst composition not in accord with this invention was prepared and tested in a manner similar to that of part A above. This catalyst is denoted I~C and has the composition of a vanadium-promoted iron/chromium/potassium oxide catalyst.
This catalyst and its test results are shown in Table I.

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~7~77~

Part D. A catal~st composition not :;n accord with this invention was prepare(l and tested in a manner similar to that of part A above. This catalyst is denoted as I-D and has the composition of a cobalt-promoted iron-chromium-potassium oxide catalyst. This catalyst and its results are shown in Table I.
From Ta~le I it can be noted that the addition of CoO to à vanadium-promoted catalystproduces a synergistic effect whereas the addition of cobalt to the iron-chromium-potassium oxide catalyst does not provide any activation.
In Tabie I and hereinafter T(7o) is used to represent the temperature in C at 70 percent conversion, and S(7o) is used to represent the selectivity at 70 percent conversion.

TABLE 1: DEHYDROGENATION CATALYSTS

-15Catalyst %w K20 %w Cr203 %w V205 %w Co0 %w Fe203 T(70) (7o) I-A 9.6 2.5 3.0 1.6 Balance616 91.4 I-B 9.6 2.5 __ __ Balance599 87.6 I-C 9.6 2.5 2.8 -~ Balance630 90.8 I-D 9.6 2.5 -- 1.6 Balance600 86.3 - :~ . , : . .

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-Example II
Catalysts in accord with this invention having varying potassium contents and containing in addition 1.6%w Co0,

3.0~w V205, 2.5%w Cr203 and balance Fe203 were prepared and tested in a manner similar to that of part A in Example I.
The results are shown in Table II. The optimum potassium oxide content is about 12.5 percent by weight although greater and lesser amounts are satisfactory.

TABI,E II: OPTIMI~ATION OF POTASSIUM CONTENT
ON DEHYDROGENATION CATALYSTS

Catalysts%w K20 (7o) (70) II-A 7.5 615 90.2 II-B 9.6 611 91.5 II-C 11.0 606 91.2 II-D 12.5 602 91.8 II-E 14.0 612 91.9 II-F 16.0 617 91.8 - lL! _ Exam~le III
Different catalysts with varying concentrations of cobalt and vanadium were prepared and tested in a manner similar to that of Part A, Example I. These results are shown in Table III.
If both cobalt and vanadium concentrations are high, the catalyst significantly loses selectivity.

TABLE III; DEHYDROGENATION CATLYSTS WITH
VARYING COBALT-VANADIUM CONCENTRATIONS

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l t %w K20%w Cr203%w V20_ % 2 3 (7 III-A 9.6 2.5 1.5 0.8 Balance 613 90.0 III-B 9.6 2.5 3.0 1.6 Balance 611 91.4 III-C 9.6 2.5 3.0 5. Balance 611 90.1 III-D 9.6 2.5 3.0 10.0 Balance 603 89.4 III-E 9.6 2.5 3.0 15.0 Balance 606 88.8 III-F 9.6 2.5 12.0 6.4 Balance Almost inactive~ :
gave 26% conversion `
at 597C
III~G 9.6 2~5 1.6 1.6 Balance 613 90.4 III-H 9.6 2.5 1.6 3.2 Balance 612 90.5 ,, ,: , ...... ... . . . . . . ..

Claims

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

1. A catalyst comprising:
(a) from 50 to 92.9 percent by weight of an iron compound, measured as ferric oxide, (b) from 5 to 30 percent by weight of a potassium compound, measured as potassium oxide, (c) from 1 to 6 percent by weight of a chromium compound, measured as chromium oxide, (d) from 1 to 6 percent by weight of a vanadium compound, measured as vanadium pentoxide, and (e) from 0.1 to 10 percent by weight of a cobalt compound, measured as cobaltous oxide.

2. A catalyst as claimed in claim 1 comprising (a) from 55 to 90 percent by weight of an iron compound (b) from 6 to 25 percent by weight of a potassium compound, (c) from 1.5 to 5 percent by weight of a chromium compound, (d) from 2 to 5 percent by weight of a vanadium compound, and (e) from 0.1 to 5 percent by weight of a cobalt compound.

3. A catalyst as claimed in claim 2, comprising from 0.3 to percent by weight of cobalt compound.

4. A catalyst as claimed in claim 3, comprising from 0.5 to 3 percent by weight of colbalt compound.

5. A process for the dehydrogenation of a hydrocarbon which comprises contacting the hydrocarbon in the presence of steam with a catalyst comprising:
(a) from 50 to 92.9 percent by weight of an iron compound, measured as ferri oxide, (b) from 5 to 30 percent by weight of a potassium compound, measured as potassium oxide, (c) from 1 to 6 percent by weight of a chromium compound, measured as chromium oxide, (d) from 1 to 6 percent by weight of a vanadium compound, measured as vanadium pentoxide, (e) from 0.1 to 10 percent by weight of a cobalt compound, measured as cobaltous oxide.

6. A process as claimed in claim 5 in which the catalyst comprises:
(a) from 55 to 90 percent by weight of an iron compound, (b) from 6 to 25 percent by weight of a potassium compound, (c) from 1.5 to 5 percent by weight of a chromium compound, (d) from 2 to 5 percent by weight of a vanadium compound, and (e) from 0.1 to 5 percent by weight of a cobalt compound.

7. A process as claimed in claim 6 in which the catalyst comprises from 0.3 to 4 percent by weight of a cobalt compound.

8. A process as claimed in claim 7 in which the catalyst comprises from 0.5 to 3 percent by weight of a cobalt compound.

9. A process as claimed in claim 5 wherein the hydrocarbon to be dehydrogenated is a monoolefin.

10. A process as claimed in claim 5 wherein the hydrocarbon to be hydrogenated is an alkyl substituted aromatic hydrocarbon.

11. A process as claimed in claim 9 wherein the monoolefin is butylene or amylene.

12. A process as claimed in claim 10 wherein the alkyl substituted aromatic hydrocarbon is ethylbenzene.