US2678923A - Reforming catalyst - Google Patents

Description

Patented May 18, 1954 REFORMING CATALYST Rowland 0. Hansford, Woodbury, N. J assignor to Socony-Vacuum Oil Company, Incorporated, a corporation of New York No Drawing. Application March 19, 1951, Serial No. 216,460

2 Claims. 1

This invention relates to new reforming catalysts characterized by the combination, in a single catalyst composition, of the catalytic prop erties of isomerization and of aromatization. More particularly, the present invention is concerned with new reforming catalysts containing chromia and fluorine.

As is well known to those familiar with the art, unsaturated hydrocarbons, as a class, possess octane number ratings that are higher than those of the corresponding saturated hydrocarbons, and aromatic hydrocarbons, as a class, possess octane number ratings that are higher than those of aliphatic and naphthenic or alicyclic hydrocarbons, saturated and unsaturated, although the octane number ratings of certain aliphatic hydrocarbons are as high or even higher. In general, therefore, the conversion of saturated hydrocarbons into unsaturated hydrocarbons through dehydrogenation, and the conversion of aromatizable aliphatic and alicyclic hydrocarbons into aromatic hydrocarbons through dehydrogenation or cyclization or both, i. e., dehydrocyclization, depending upon the type of aromatizable hydrocarbon, are expedients whereby the low-octane hydrocarbons are converted into the corresponding higher-octane hydrocarbons. The reactions involved are well known and several processes, involving these reactions, have been proposed for the purpose of producing gasolines having improved antiknock properties from petroleum naphthas. These operations are generically referred to as reforming and the conditions of temperature, pressure (including hydrogen pressure), and residence time are referred to as reforming conditions.

Most of the proposed reforming processes involve the use of catalysts. Depending upon the type of reaction or reactions which they primarily promote, the reforming catalysts have been termed aromatization catalysts, dehydrogenation catalysts, dehydrocyclization catalysts, etc. Indeed, these catalysts also promote crack: ing, thereby producing normally gaseous hydrocarbons and carbonaceous deposits on the catalysts.

Controlled or selective cracking is advantageous from two standpoints. In the first place, it increases the yields of desired product, through the conversion of the higher-boiling constituents of the charge stocks into fractions boiling within the gasoline boiling range F. to 400 F.) and by decreasing the conversion of fractions boiling within the gasoline boiling range into normally gaseous hydrocarbons. In the second place, it further increases the octane number rating of the reformed gasoline through the formation of unsaturated hydrocarbons. Excessive and. uncontrolled cracking, on the other hand, although increasing the formation of unsaturated hydrocarbons, increases the amounts of normally gaseous hydrocarbons and of carbonaceous deposits with concomitant losses in the yields of desired product and rapid deactivation of the catalyst. Accordingly, as is well known to those familiar with the art, the performances of reforming catalysts are ordinarily compared on the basis of octane number rating-gasoline yield relationships.

Chromia on alumina is typical of the reforming catalysts of the prior art. Its function in reforming operations is as a dehydrogenationdehydrocyclization catalyst. It does not promote isomerization to any great extent and is not selective in its cracking activity. Thus, in a typical reforming operation in which a chromia on alumina reforming catalyst is employed, a saturated gasoline, such as, for example, a straight run gasoline, which comprises a mixture of paraffinic and alicyclic hydrocarbons, is subjected to reforming conditions, whereby the aromatizable alicyclic hydrocarbons are dehydrogenated into aromatic hydrocarbons and the aromatizable paraffinic hydrocarbons are dehydrocyclized into aromatic hydrocarbons. The improved octane number rating of the reformed gasoline obtained from such an operation may be attributed, therefore, primarily, to the formation of the aromatic hydrocarbons.

It is well known that chromia on alumina catalysts are among the most active of the dehydrocyclization catalysts. This high activity is obtained at low pressures, such as atmospheric, and at temperatures of the order of 900-1000 F.

It is also well known that when dehydrocyclization catalysts, such as chromia-alumina, are employed under hydrogen pressure, the dehydrocyclization activity is preferentially decreased, compared to the dehydrogenation of naphthenes containing six-membered rings. In spite of this, it has become common practice to use such catalysts under hydrogen pressure in order to gain the advantage of reduced coke deposition. Such operations are predicated upon striking a balance between the practical ad.- vantages of reduced coke formation and the decreased aromatization, especially the reduced dehydrocyclization, obtained under hydrogen pressure.

As stated hereinbefore, the octane number ratings of certain aliphatic hydrocarbons are as high or even higher than those of aromatic hydrocarbons. These aliphatic hydrocarbons are highly-branched, a structure ordinarily obtained through isomerization of the corresponding, less highly-branched aliphatic hydrocarbons. Accordingly, a reforming catalyst which promotes isomerization reactions is manifestly highly desirable.

It has now been discovered that it is possible to combine, in a relatively inexpensive reforming catalyst, the properties of aromatization and isomerization. It has been found, as set forth in copending application for patent Serial No. 218,291, filed on March 29, 1951, by Carlos L. Gutzeit, that compositions containing chromia, specified amounts of fluorine, and alumina promote aromatization and isomerization reactions in operations involving relatively high hydrogen pressures.

The use of halogens, including fluorine, in destructive hydrogenation catalysts is well known. While such catalysts contain both a hydrogenating component and a cracking com ponent (the halogen), and hence, are dual catalysts like those contemplated herein, they are otherwise dissimilar and are unsuitable for aromatization reforming. Metal fluorides, including chromium fluoride, have been employed as cracking catalysts. However, it has been observed generally that even small amounts of a halogen, including fluorine, are injurious to the dehydrocyclization activity of chromia-alumina catalysts.

From a theoretical standpoint, the catalysts of the present invention are capable of producing gasoline in the highest yield for a given octane number rating. This follows from the fact that these catalysts effect the conversion of cyclo- 'hexanes and of alkyl cyclopentanes into aromatic hydrocarbons with a smaller increase in density than is the case in the dehydrocyclization of aromatizable paraffinic hydrocarbons and, also, effect the isomerization of paraffinic hydrocarbons with concomitant increase in octane number rating and with substantially no volume change.

Accordingly, it is an object of this invention to provide improved reforming catalysts. Another object is to provide efficient aromatizationisomerization catalysts suitable for use under hydrogen partial pressures sufficient to reduce coke deposition appreciably. A more specific object is to provide a reforming catalyst containing chromia, specified amounts of fluorine, and alu mina. Other objects and advantages of the present invention will become apparent to those skilled in the art from the following description.

Broadly stated, the present invention provides a reforming catalyst comprising a combination of specified amounts of chromia with specified amounts of fluorine, supported on an active alumina base.

In accordance with the teachings of the prior art, it has been found that, in aromatization reforming at atmospheric pressure, the fluorinecontaining chromia-alumina catalysts are inferior to the fluorine-free chromia-alumina catalysts. Also in accordance with the prior art, it has been found that, in reforming operations involving the use of fluorine-free chromia-alumina catalysts, hydrogen pressure tends to suppress aromatization activity, so that it is necessary to increase temperature and/or apparent contact time in order to maintain the conversion by such catalysts at a reasonable level. Such compensatory octane level with reduced coke formation can be achieved at pressures of up to 200 pounds per square inch gauge and a hydrogen-to-naphtha mole ratio varying between about 2:1 and about 10:1, respectively, with only minor disadvantages in the octane number rating-gasoline yield relationship. However, at pressures of 500 pounds per square inch gauge and higher, using hydrogen dilutions falling within the same range of variations referred to hereinbefore, and under conditions of negligible coke formation, the fluorinefree chromia-alumina catalysts are not sufficiently active, in reforming operations, to be commercially feasible.

On the other hand and as stated hereinbefore, it has now been found, as set forth in copending application for patent Serial No. 218,291, filed on March 29, 1951, by Carlos L. Gutzeit, that under hydrogen pressure, the addition of small amounts of fluorine to conventional chromia-alumina reforming catalysts improves their activity. Indeed, tests have shown that within reasonable limits, the effectiveness of fluorine in this respect increases as the pressure is increased. Thus, for example, the addition of small amounts of fluorine to a chromia-alumina catalyst (mol ratiozCrzozzAlzoaz :24z'76) using a hydrogen-tonaphtha mol ratio of 4 1, causes slight inferiority at atmospheric pressure, slight superiority at 200 pounds per square inch gauge, and marked superiority at 500 pounds per square inch gauge. At pressures of 500 pounds per square inch gauge and higher, the coke deposition is negligible, thereby permitting continuous operation for long periods without interruption for oxidative regeneration to remove carbonaceous material.

The improvement in activity of the fluorinecontaining chromia-alurnina catalysts under hydrogen pressure appears to be due to a superposition of isomerization activity on the dehydrogenation activity of the chromia-alumina catalysts. Under optimum conditions of dehydrocyclization, such as at atmospheric pressure, this isomerization action causes only a small part of the octane number rating increase but causes a marked increase in coke formation, resulting in an over-all deleterious effect. Under increased hydrogen pressure, where dehydrocyclization is diminished and coke formation becomes small or negligible, the isomerization contributes a very considerable part of the over-all octane number rating increase, and the over-all activity of the catalyst for aromatization reforming is increased.

Isomerization-aromatization catalysts may be considered to be bifunctional catalysts, one function being that of cracking-isomerization and the other that of dehydrogenation, although these functions need not be entirely separate and distinct. The catalysts contemplated herein belong to the class wherein such functions are distinct and can be separately controlled. by a judicious selection of the active components. The fluorine or acid component functions as the cracking-isomerization promoter while the chromia component functions as the dehydrogenation promoter. While the alumina component is not strictly non-catalytic, it may, as a approximation be considered to be merely an activating support which acts as a high surfacearea carrier for the catalytically active material and to prevent crystallization, migration or vola tilization of active components. Therefore, the ratio of fluorine to chromia must be selected so that the fluorine component will produce isomerization but only negligible cracking, while the chromia component must promote the dehydrogenation of the aromatizable alicyclic hydrocarbons at the relatively high space velocities necessary to effect selective isomerization with the fluorine component.

In view of the foregoing, the reforming catalysts contemplated herein comprise combinations of from about 5% by weight to about 70% by weight of chromia, calculated as Cl'zCa, with from about 0.1% by weight to about 2.9% by weight of fluorine, and the balance, an active alumina base. More particularly preferred, however, are combinations of from about 105% by weight to. about by weight of chromia, calculated as CI'2O3, with from about 0.2% by weight to about 1.5% by weight of fluorine, and the balance, an active alumina base.

There appears to be nothing critical in the method of preparing the catalysts of the present invention. In general, any method of catalyst preparation known to the prior art can be utilized. For example, the catalysts can be prepared by adding chromic acid, and hydrogen fluoride, in predetermined amounts, to an alumina base, followed by washing, drying, comminution and colcination undo" conditions to y ld products which have relatively high sure-cc areas. Or, alumina pellets can be impregnated, initially, with an aqueous solution of ammonium fluoride followed by washing, drying and calcining, and, subsequently, with an aqueous solution of chromic acid also followed by washing, drying and calcining, the amounts of fluorine and of chromia in the final catalyst being controlled by using calculated amounts of ammonium fluoride and of chromic acid based on the weight of alumina and just enough water, in each case, to be completely absorbed by the pellets. The order of impregnation. may be reversed or be combined in one impregnation step. Or, commercially available or previously prepared chromia-alurnina 'alyst, bead o-r pellet form such as those described in application for patent Serial No. 201,537, filed by Stover and Wilson on December 14, 1950, can be impregnated with an aqueous solution of ammonium fluoride, the amounts of fluorine in the final catalyst being controlled by using calculated amounts of ammonium fiuodde and just enough water to be substantially completely absorbed by the beads or pellets.

Whatever the method of preparation employed, it is important to effect the calculation in a hydrogen atmosphere. The chrornia-fluorine combination has been found to be unstable under oxidizing conditions, either during catalyst preparation or during oxidative regeneration. Therefore, unless the catalyst is maintained in reducing atmosphere, fluorine is lost. By way of non-limiting examples, the drying can be efiected at temperatures of from about 386 to about 900 F., and the calcination, at temperatures varying between about 900 F. and about 1200 Ft,

for a period of time of about one hour to about 10 hours.

It will be apparent to those skilled in the art that mlmerous compounds can be used as sources for the various components of the catalysts contemplated herein. Thus, for example, fluorine can; be introduced as dry hydrogen fluoride, aqueous hydrofluoric acid or an aqueous solution of ammonium fluoride (NHiF or NHlF-HF). Aqueous solutions of chromic acid, ammonium bichromate, or chromium acetate can be used as sources of chromia.

Any of the commercially available aluminas of high surface area, such as gel-type alumina or activated aluminas consisting principally of gamma-alumina, can be used to prepare impregnated catalysts of the type contemplated. herein. Or, precipitated alumina can be prepared in accordance with any known procedure suitable for the production of high surface area alumina utilizable as a catalyst support. Thus, for example, aluminum hydroxide can be initially precipitated using aqueous solutions of aluminum nitrate, aluminum sulfate or aluminum chloride and the hydroxides or carbonates of ammonium, sodium or potassium. Residua1 sodium or potassium ions can be reduced to negligible amounts by base-exchange with ammonium salts. Traces of residual sulfate, nitrate or chloride ions are not harmful.

Precipitation using a. slight excess of alkali at a pH, not exceeding 10 or using dilute solutions, of the order of 0.1 molar or less, simplifies or facilitates the washing out of anions. Freezing and thawing the gelatinous, hydrous alumina converts it to a more easily fllterable or centriiugable material and lowers its water-content, thereb facilitatin washing. The addition of ammonium hydroxide or of neutral salts, such as ammonium nitrate to the wash water facilitates the removal of. other ions and prevents peptization of the alumina toward the end of the washing operation.

The catalysts can be used in any of the conventional forms such as powder, pills, spheres, extrudates or irregular fragments, all of a size suitable for the reaction. system to be employed. As stated hereinbefore, the catalysts of the present invention, due to their instability under oxidative conditions, are adapted for use in continuous reforming operations without interruption for oxidative regeneration.

Any mixture of hydrocarbons suitable as a charge stock to a reforming operation can be used with the catalysts of this invention. As is well known, petroleum naphthas, particularly those having a boiling range of from about F. to about 450 F. and a relatively low octane number rating, are the conventional charge stocks for reforming processes. Accordingly, the charge stock can be an intermediate type naphtha, i. 9., one containing an average distribution of hydrocarbon types (paraflins, oleiins, naphthemes and aromatics) or one which is excep tio-nally high in paraflins, naphthenes or arcmatics.

As set forth in the copending application for patent, Serial No. 218,291, filed on March 29, by Carlos L. G-utzeit, the temperatures to be used in the process utilizing the catalysts of the present invention, vary between about 900 F. and about 1050 F, preferably, between about 975 F. and about 1025 F. The total pressures vary between about 260 pounds per square inch gauge and about 750 pounds per square inch gauge, preferably, between about 400 pounds per square inch gauge and about 600 pounds per square inch gauge. The moi ratios of hydrogen to naphtha vary between about 1:1 and about :1, respectively, preferably, between about 3:1 and about 6:1 respectively. The liquid hourly space velocities vary between about 0.5 and about 5 and, preferably, between about 2 and about 4.

The following detailed examples are for the purpose of illustrating the catalysts contemplated herein and to indicate the advantages and characteristics thereof. It must be appreciated, however, that the invention is not to be construed as being' limited to the specific catalysts, methods of catalyst preparation, and the specific manipulations and conditions set forth in the examples. As those skilled in the art will readily understand, numerous modifications and variations therein, all within the purview of the foregoing discussion, are possible and, accordingly, must be considered to be encompassed by the scope of the present invention.

EXAMPLES 1-27 All the catalysts were prepared by impregnation of chromia-alumina beads obtained in accordance with the procedure disclosed in application for patent Serial No. 201,537, filed by Stover and Wilson on December 14, 1950, referred to hereinbefore.

Briefly, the procedure comprises rapidly mixing a solution of sodium aluminate (containing the equivalent of 2.65 mols A1203 per liter) with a solution of chromic acetate (containing the equivalent of 0.75 mol C12O3 per liter) in a mixing nozzle to form a chromia-alumina hydrosol. The hydrosol flows over a divider to form droplets and these fall through a column of oil. During the descent through the column of oil, the hydrosol droplets assume a spherical shape before setting to a firm hydrogel, thereby producing spherical hydrogel beads. The beads are then aged in an aqueous solution of ammonium sulfate, washed free of anions, dried in steam and, finally, calcined at a temperature of 100W F. These beads approximate the composition:

CrzOazAlzOszwlflo (mol ratio) The catalysts of Examples 7, 2, 1.1, 12, 13, 14, 15, 1'7, 18, 19, 20, 21, 22, 23, 24, 25, 26 and 27 were prepared by treatment of dry, calcined beads with aqueous solutions containing the calculated amounts of ammonium fluoride, assuming complete absorption, in just enough water to wet the beads. The catalysts of Examples 2, 3, 4 and 5 were prepared from wet hydrogel beads by impregnation with aqueous solutions containing the calculated amounts of ammonium fluoride, assuming complete absorption, in just enough water to cover the beads. For example, 955 grams of wet beads, containing 143 grains of solids or 1.25 mols CrzOs:AlzOz:24:'l8, and equivalent to 150 cc. dry beads, were covered with 650 ml. 01 solution containing the required amount of ammonium fluoride, allowed to soak overnight and then drained.

In both types of preparation, the wet beads were dried overnight at temperatures of Bil-100 C. in an air-circulation drying oven, then calcined in a hydrogen stream at gradually increasing temperatures up to 1100 F. over a 6-hour Initial boiling point 158 F. 16% At 175 F. 50% At 190 F. At 212 F. End point 248 F. CFRR octane number, clear 58.5

For convenience the pertinent data are set forth in Tables I, II, III and IV.

Table I.-Dchydr0cyclizati0n of normal heplune with chroma-alumina AVERAGE OF THREE TESTS WITH REGENERATED CATALYSTS [loniperaturc=932 F.; liquid hourly space vclocity=1; length of tests=2.5 hours] Catalyst Composition Conversion Toliililene of Example Product tane to No. Fluorine, wt Toluene,

Chronna Alumina wt. perwt. percent cent Table II.-.iromatization reforming of light Oklahoma City naphtha AVERAGE OF TWO RUNS WITH REGENERATED CATA- LYSTS, ONE-HOUR TESTS [Pressure=atmospheric; temperature=L000 F.; Liquid hourly space vclocity=1.]

Catalyst: 033%; sears 24:76 Percent F Example N0. 6 Example N o. 7

Yield, Based on wt. Percent Recovery:

Gas, wt. percent 17.6 12.6 Coke, wt. percent 10. 9 11.2 CyFrce Gasoline, Vol.

percent 69. 1 72. 6 CFRR Octane Number,

Clear 87 80. 5

[Hydrogen pressure=200 pounds per square inch gauge; temperaturo=l,000 F.;liquid hourly space velocity=1;hydrogen:naphthav mol ratio =5zi Example No. 8 Example N0. 9

Yield, Based on 100 wt. porcent Recovery:

Gas, wt. percent 19. 4 30. 5 Coke, wt. percent 0.1 0.3 OzFree Gasoline, Vol.

percent 78. 3 67. 2 CFRR Octane Number,

Clear 81. 5 86 9 10 Table III .Aromattzation reforming of light Oklahoma City naphtha [Pressure =200 pounds per square inch gaugelteniperature=lflofi F.; hydrogen: naphtha, mol ta o= .l

- Products Based on 100 Wt. Catalyst Composition Percfmt Recovery 1izLtlquid gFRR our y ctane Example In 0. Fluorine, 1 Space Coke (Jr-free Number,

Ohromia Alumina wt. perrelomty wt. pergasolme lear pelcent wt. percent cent cent Table I V.Aromatization reforming of light Oklahoma City naphtha [Pressure=500 pounds per square inch gauge; hydrogen: naphtha, rncl rct1o=4:1.]

Products Based on 100 Wt. Octal st Composition Percent Recovery T Ililquild OFRB NY emperour y Octane Example Fluorine ature, F. vsiiace G t n k t (la-glee Nullnber,

I j, eoci y as w e0 e w ase ine v ear Ghwmu Alumina 3 percent pcrc cnt :vt. per

cent

The data set forth in Table I illustrate the decrease in activity for dehydrocyclization of nheptane produced in chron1ia-aluniina catalysts by the addition of small amounts of fluorine. This is in accordance with the prior art.

The results of the runs set forth in Table I1 show the efiect of the addition of small amounts of fluorine on the activity of chroniia-aliunina catalysts in aromatization reforming. As expected, when. the catalysts are used at atmospheric pressure, the most favorable condition for dehydrocyclization, the addition of fluorine causes a sharp drop in the octane number rating of the gasoline product. However, when the catalysts are usee nder hydrogen pressure, the situation is reversed and the fluorine-containing catalysts produce the higher octane number ratings.

The data set forth in Table 111 further illustrate the favorable effect, under hydrogen pressure, of fluorine on the octane number rating-gasoline yield relationship. It will be noted that this relationship increases as the fluorine-content of the chromia-alumina catalysts is increased.

Finally, the results of the runs set forth in Table IV show the enfect of the addition of fluorine on the activity of chromia-alumina catalysts under relatively high hydrogen pressure. Under these conditions, dehydrocyolization is almost completely suppressed, so that the non-promoted catalyst shows an increase in octane number rating of only eight units. Three fluorine-com taining catalysts were used. One in Examples Nos. 17, 18, 19 and 20, another in Examples Nos.

the necessity for or-zidative regeneration.

What is claimed is:

1. A11 .proved dehydrogenation-dehydrocyclization catalyst to be used under hydrogen pressures of at least about 200 pounds per square inch, which comprises about 10% by Weight to about 35% by weight or" chromia, calculated as chromium eesuuioxide, from about 0.2% by weight to about 1.5% by weight of fluorine, and the balance alumina.

2. An improved dehydrogenation-dehydrocycli- 1 zation catalyst to used under hydrogen pressures of at least about 200 pounds per square inch, which comprises about 32% by Weight of chroznia, calculated as chromium sesquioxide. from about 0.2% by weight to about 1.5% by Weight of fluorine, and the balance alumina.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,221,165 Goldsby Nov. 12, 1940 2,322,622 Fischer et a1. June 22, 1943 2,348,624 Hillrnan May 9, 1944 2,443,285 Webb et a1. June 15, 1948 2,479,109 I-Iaensel Aug. 16, 1949

Claims (1)

1. AN IMPROVED DEHYDROGENATION-DEHYDROCYCLIZATION CATALYST TO BE USED UNDER HYDROGEN PRESSURES OF AT LEAST ABOUT 200 POUNDS PER SQUARE INCH, WHICH COMPRISES ABOUT 10% BY WEIGHT TO ABOUT 35% BY WEIGHT OF CHROMIA, CALCULATED AS CHROMIUM SESQUIOXIDE, FROM ABOUT 0.2% BY WEIGHT TO ABOUT 1.5% BY WEIGHT OF FLUORINE, AND THE BALANCE ALUMINA.