US2917566A - Isomerization of n-paraffin hydrocarbons - Google Patents

Description

United States Patent ISOMERIZATION OF N-PARAFFIN HYDROCARBONS Norman L. Carr, Crystal Lake, 111., assignor to The Pure Oil Company, Chicago, Ill., a corporation of Ohio No Drawing. Application October 31, 1956 Serial No. 619,404

10 Claims. ((31:260-683-66) This invention relates to the isomerization of saturated, aliphatic and alicyclic hydrocarbons or mixtures thereof. It is more directly concerned with an isomerization process in which is employed a solid catalyst for promoting the efficiency of the isomerization reaction.

A considerable onus is placed on petroleum refiners because of the increasing octane requirements of modern, high-speed, high-compression, internal combustion engines, and the competitive market to provide suitable gasoline motor fuels for use in these engines. In formulating a gasoline motor fuel, a major portion of the composition consists of gasolines derived from the catalytic cracking of petroleum gas oil fractions. The remainder of the composition can be from light virgin distillates employed without further treating; however, it is desirable to upgrade these light distillate naphthas to produce higher octane blending stocks. To effect this end, a variety of refining processes such as reforming, isomerization, alkylation, or polymerization can be used with attendant advantages. Isomerization of suitable feed stocks produces high-octane-number, branch-chain parafiins which can be incorporated in gasoline blends to promote a more eflicient utilization of tetraethyl lead. Isomerized parafiinic blending stocks are desirable because of their very low sensitivity. Sensitivity is a critetion of a gasolines ability to perform under road conditions, and is the difference between the research octane number (CRC Designation F-1-545) and the motor octane number (CRC Designation F2-545). The sensitivity of several gasolines is shown in Table I:

TABLE I Octane values of representative blending stocks 1 Containing 3 cc. of tetraethyl lead/gallon.

refractory, metal oxide catalyst which can be employed for extended periods without regeneration. A further object of this invention is to provide a promoted, refractory metal oxide, isomerization catalyst which is susceptible to regeneration for re-use. An additional object of this invention is to provide an isomerization process for upgrading light petroleum naphthas predominantly containing C -C saturated hydrocarbons to produce high-octane-number blending agents for use in the formulation of high-grade, gasoline motor fuels.

In copending application, entitled Isomerization Catalyst and Process, Serial No. 619,376, filed October 31, 1956, by Norman L. Carr there is described a composite isomerization catalyst of increased stability and high activity which comprises a refractory, mixed-oxides base composited to evince acidic properties and hydrocarbon cracking activity, e.g., silica-alumina, having incorporated therein a hydrogenation agent such as metallic nickel. According to the invention described therein, it has been found that in order to provide a catalyst of maximum efliciency, it is necessary to condition the composite catalyst prior to use by means of a plural-step preconditioning process employing a sequential oxidation and hydrogenation treatment. Essentially, the conditioning process which has been found to be uniquely elfective can be divided into two parts; namely, (A) the catalyst preparation carried out substantially in accordance with the prior art, and (B) the preconditioning steps which have been found to be exceptionally and distinctively efiective for inducing high activity and stability by imparting resistance to permanent depreciation in activity. In the pre-conditioning phase of the invention described in the copending application, the silica-alumina hydrogenation agent composite, after being prepared and activated substantially in accordance with the teachings in the prior art, is further subjected to an oxidizing atmosphere maintained at a temperature of 650750 F. Following this oxidation, the oxidized catalyst is contacted with'hydrogen at the same temperature as that at which the oxidation was carried out to reduce the components of the composition to their most reducible stage at these reduction conditions and produce a composite catalyst of high activity which is resistant to degeneration. Included among the catalyst compositions which were prepared in accordance with the invention described in the copending application are metallic-nickel-containing composites. It has now been found that the eifectiveness of metallic-nickel-containing catalysts of this type can be further enhanced by incorporating molybdena in the catalyst composition. According to this invention, superior catalysts which are rela-' tively sulphur resistant, have exceptionallyv long active lives, and have superior activities and selectivities, are

provided by incorporating small amounts of molybdena in the composition consisting of nickel supported on a refractory, mixed oxides basecomposited to evince acidic properties and hydrocarbon cracking activity. In em:

Another advantage in the use of isomerization processes for upgrading gasoline blending stocks is the excellent octane-yield relationship which permits the production of high-octane-number hydrocarbon fractions or light naphtha distillates without incurring concomitant losses in yields due to the formation of undesirable byproducts.

Although extensive work has been done in investigating the isomerization of parailinic hydrocarbons employing anhydrous aluminum chloride catalysts in a liquid-phase process, the use of solid catalysts for promoting this reaction in vapor phase has become important because of the advantages which accrue in their use. It is therefore an object of this invention to provide a solid catalyst having high-activity and selectivity for-the isomerization of saturated; aliphatic and alicyclic hydrocarbons. Another object of this invention is to provide a promoted,-

ploying these catalysts in a vapor-phase isomerization process, the treatment of saturated aliphaticand/or alicyclic-hydrocarbon-containing feed stocks is carried out under the following conditions:

Temperature, F.- 600-700 Pressure, p.s.i.g. 1000 Liquid volume hourly. space velocity 0.1-2.0 Hydrogen/hydrocarbon mol ratio 0.5-4.5

In preparing the supported nickel-molybdena catalysts employed in this invention, conventional catalyst pre'paration techniques can be employed such as those discussed in Catalysis I, Emmett, Reinhold, 1954, at page 315, et seq. Althoughprecipitation and gel formation can be employed for-specific catalyst preparations-,"th'e' simplest'an'd preferred method of producingthe supported Patented Dec. 15, 19.59

of this invention involves the technique of impregnating the refractory, mixed oxides used as supports, with nickel and molybdena. In this method of preparation, the required quantity of. a powdered or granular, refractory, mixed oxides support is admixed with an aqueous solution containing the promoting constituents which are then precipitated into tthe pores of the support. After filtering and drying, the catalyst is agglomerated into pellets of suitable size and subsequently activated by heating the catalyst to an elevated temperature in a stream of hydrogen for a time sufficient to elfect the reduction of the reducible constituents to their maximum state of reduction under the conditions of the activation. It is to 'be understood that the preparation and activation of the catalyst is to be supplemented by subjecting the catalyst activated in this manner to the pre-conditioning technique described in the co pending application cited supra. Additional methods for preparing a supported nickel-molybdena catalyst for pelleting and activation include, but are not limited to, the following catalyst preparation techniques.

A suitable refractory, mixed oxides base is impregnated by immersion in an aqueous, solution of a decomposable molybdenum salt, such as ammoniacal ammonium paramolybdate. The impregnated carrier is dried and heated to temperatures sufficient to decompose the molybdenum salt to molybdic oxide, M The support, impregnated with molybdic oxide, is thereafter slurried in an aqueous solution of a decomposable nickel salt, such as nickel nitrate. After drying, the resulting mass, impregnated with decomposable nickel salt, is heated to an elevated temperature sufficient to decompose the nickel salt to form nickel oxide. This two-step impregnation process can alternatively be carried out by first introducing into the refractory, mixed oxides support the nickel salt, and thereafter following an appropriate sequential treatment to introduce the molybdic oxide into the catalyst composition.

The incorporation of the nickel and molybdena promoting agents in the mixed oxides support can also be carried out employing co-p'recipitation techniques which involve the precipitation of a decomposable nickel compound from an aqueous solution of a nickel salt, such as nickel nitrate or nickel sulfate, by the addition of an aqueous solution of ammonium molybdate. This preparation can be carried out on a suitable, mixed oxides carrier by first impregnating the carrier with either the nickel or molybdenum salt, and thereafter contacting the thus-impregnated carrier with the other salt. However, an aqueous impregnation solution, preferably containing a slight excess of ammonia, can be prepared by dissolving a water-soluble salt of nickel and a water-soluble molybdenum salt in an aqueous ammoniacal solution. The carrier is then immersed in the impreg'nationsolution, which is adsorbed thereon. The impregnated silicacontaining carrier is then dried and calcined to decompose the adsorbed metal compounds. In another sugnickel-molybdena catalyst going catalyst preparations employ a carrier in finished form as the support, it is to be understood that the precipitation of the nickel and molybdenum promoters can be effected on carriers in the undried, hydrous gel form. Although a variety of catalyst preparation methods can be employed, the manipulative steps must be such that unconditioned, virgin catalyst, which is thereafter preconditioned in accordance with this invention, will comprise nickel and molybdena supported on a refractory, mixed oxides base composited to evince acidic properties and hydrocarbon cracking acivity, in which the nickel is present substantially in the metallic state and the molybdena is present in the lowest oxide form. Accordingly, in the preparation of the unconditioned, virgin catalyst, elevated temperatures which bring about the complete reduction of the molybdena to the metallic state are to be avoided. Thereafter, the virgin catalyst is preconditioned in accordance with the technique described above.

As a specific example, a nickcl-rnolybdena-silicaalumina catalyst employed in the isomerization process of this invention was prepared as follows: An ammoniacal solution of para-molybdate was prepared by dissolving 32 grams of ammonium heptamolybdate gested technique for incorporating the molybdenum constituent in the cracking catalyst carrier, the carrier is impregnated with an aqueous solution of molybdenum pentachloride, and, upon drying and calcining the impregnated base, molybdenum trioxide is formed. Thereafter, the nickel constituent may be incorporated in any suitable manner, such as the above-described two-stage impregnation technique. See also various techniques suggested in US. Patent 2,739,133 for combining molybdena with the selected carrier. The amounts of nickel and molybdenum salts employed are dependent uponthe respective amounts of nickel and molybdenum desired in the finished catalyst as will hereinafter be considered. The preferred quantities are the stoichiometric amounts necessary to form theoretically nickel molybdate. -Because the amounts of nickel and molybdenum in the final composition vary within a preferred range,

other concentrations can be used. Although the forein 270 ml. of distilled water to a salt content of about 11% by weight. To this solution was added 20 cc. of concentrated ammonium hydroxide to provide an NH OH/ H O ratio of about 0.075/1. An 18 weight percent solution of nickel nitrate was prepared by dissolving 58.7 grams of Ni(NO .6H O in 270 ml. of water, and the molybdenumand nickel-containing solutions were separatelyheated to about 176 F. and admixed. To this mixture was added 360 grams of silica-alumina, sufiicient to yield a finished catalyst containing 10% of nickel molybdate. The composition of the commercially prepared silica-alumina 1 was:

Component: Wt. percent A1 0 23.12 Na O 0.02 Fe 0.02 80., 0.25 SiO- 76.59

1 0 8: G3,, October 17, 1955, at page 121 et seq.

The resulting slurry was mixed for one hour at 176 F., and then was filtered, washed with water, and dried for 16 hours in an oven at 230 F. to provide a green composite containing 10% NiMoO on the silica-alumina support. To initially activate the catalyst, 167 grams of green catalyst was inserted in a reactor and heated rapidly to 400 F. with 10 s.c.f.h. hydrogen flowing through the reactor. The temperature of the catalyst was raised, at a rate of F. per hour, to 975 F. employing a hydrogen rate of 10 s.c.f.h. This hydrogen rate and temperature was maintained for one hour after which the hydrogen rate was reduced to 4 s.c.f.h. and held for 18 hours at 975 F., i.e., until no ammonia was detected in the off gas. The catalyst was then cooled to 800 F. with the same hydrogen rate, and purged with nitrogen to remove the hydrogen from the reactor. Following the initial activation the catalyst was pre-conditioned in accordance with the technique described in the copending application, cited supra. In this instance the catalyst was oxidized with dry air flowing at a rate of 3 s.c.f.h. until the hot zone passed through the reactor. The oxidized catalyst was purged with nitrogen and reduced with hydrogen for 20 minutes at a rate of 10 c.f.h./ 200 ml. of catalyst at 775-800 F. To initiate the onstream period, the reactor pressure was increased to 350 .p.s.i.g. and the catalyst cooled to 620-630" F. Based on total composition, the finished catalyst contained 2.7% by weight of nickel and 4.4% of molybdenumpresent as M00 supported on a silica-alumina carrier having a nominal silica/alumina concentration ratio of 75/25 based only on the carrier composition. Other nickelmolybdena-silica-alumina catalysts were similarly prepared using a carrier having a nominal silica-alumina concentration ratio of 50/50 based only on carrier composition. To demonstrate the effectiveness of the catalyst compositions of this invention, the comparative data shown in Table II were obtained in which the superiority of preconditioned nickel-molybdena-containing catalysts over preconditioned nickel-containing-catalysts preconditioned in the same manner is shown.

TABLE II Liquid 1 Degener- Preconditloned Catalyst Composition Recovery Activity ation 8 (wt. per- Rating Time, cent) hours Ni (2.7 wt. percent), M (4.4 wt. percent), 75/25 Silica/alumina 96 70 4 210+ Ni (2.7 wt. percent), M0 (4.4 wt

cent), 75/25 Silica/alumina-.. 96 65 400 (2.7 wt. percent), M0 (4.4 cent), 50/50 Silica/alumina... 97 66. 5 4 550+ Ni (5 wt. percent) 75/25 Silica/alumina. 93 75 55 Ni (5 wt. percent), 75/25 Silica/alumina. 93 73. 2 40 Ni (5 wt. percent), Kicselguhr wt.

percent) with 90% 75/25 Silica] alumina support 93 70 4 1 The conditions under which the liquid recoveries and activity ratings listed were obtained were as follows: Pressure 350 p.s.i.g.; temperature about 660 F.: Ji /hydrocarbon mole ratio 3.5; and liquid volume hourly space velocity-1.0 v./v./hr.; charge characteristics:

Component:

n-Pentanc .volume percent. 27. 9 n-Hexane do. 26. 5 n-Heptane" .do 25 6 Cyelohexanedo 20.0 Gravity, API. 75.0-75.9 R1. (Na 1. 3840-16830 Research Octane Number (CRO Designation 2 Activity miih''is'iifidlfifi'isiifdfifi'iumber (on o Designation Fl-545) of the liquid product obtained from an isomerization process operated under the foregoing operating conditions and employing Aromatics, vol. percent- 2 ASTM test:

LB. P 90 b The run was discontinued at this timcphoweve'r, the research octane of the isomerate had not yet decreased to below 76. The catalyst support here, labeled 50/50, was a nominal 50% alumina and was composed of 35% H-4l alumina and 65% 75/25 silica/alumina in admixture. From Table II it is seen that by incorporating small amounts of molybdena in a nickel-promoted, silica-containing catalyst there is attained an extended catalyst life without depreciation in activity or selectivity of the catalyst. Catalysts of this nature have commercial importance because processes in which they are used can be operated for extended periods of time without shutting the process down for catalyst regeneration.

It also has been found that the objectives of this invention are best achieved if the catalysts employed in the subject isomerization process have the compositions within the following ranges:

1 Based on total catalyst composition.

The nickel and molybdena are incorporated in a refractory, mixed oxides base composited to evince acidic properties and hydrocarbon cracking activity. Because isomerization reactions are acid catalyzed, a variety of acidic mixed-oxide bases can be employed including, but not t0 SIO2A1203, SIOFZIOZ, SiO2TiO2, SIO2B203, A1203-ZI'O2, Al O BeOAl O -B O SiO2 CI'O, B203 TiO2, SiO2A1203-ZI'O2, Al O --BeO, acid-treated clays, etc. The mixed oxides used in forming the base can be either in chemical or physical combination.

To demonstrate the advantages obtained in employing compositions containing nickel and molybdena within the preferred concentration ranges listed above, an investigation of various nickel-mo]ybdena-silica-alumina catalysts was carried out. In this evaluation, the following operating conditions were used:

The synthetic-naphtha feed stock processed under these conditions had the same characteristics as that described in Table II above. Run data obtained using various catalyst compositions are presented in Table IV.

TABLE IV Liquid Activity Ni 1 Mo 1 SIOg/A1g03 2 Recovery, Rating v. percent 1 Based on total catalyst composition.

2 Based only on carrier composition.

Hydrocracking was the main reaction. Hot zones caused operational ditficulties and liquid recoveries were very low at high conversion conditions. The results show that low levels of nickel (3%) and molybdenum (1%) produce the best octane-yield when the metals are combined on the 75/25 silica/alumina support, employed at or near high conversions and high selectivity. The results also clearly define the high activity and low selectivity of the catalysts comprising the 50/50 silica/alumina. In employing catalysts containing less than the preferred concentration ranges of nickel and molybdena, it was found that, although these catalysts had a high initial activity rating, the activity diminished more rapidly than the preferred compositions, a result experienced employing a 1.5Ni----1.2Mo(as MoO )75/25 silica-alumina catalyst.

According to this invention, it has been shown that isomerization catalysts comprising nickel-molybdena supported on refractory, mixed oxides bases composited to evince acidic properties and hydrocarbon cracking activity, in which the respective constituents are preferably present in the amounts defined herein, and when activated and preconditioned in accordance with the technique described in copending application, cited supra, provide excellent catalysts for use in the isomerization of hydrocarbons. These catalysts have long active lives, are resistant to sulfur degeneration, and possess other important catalyst properties. These catalysts are employed under the following isomerization conditions:

Space velocity, 1v./hr./v. 0.1 to about 2.0, with 0.3

to 1.2 preferred. Hydrogen/hydrocarbon mole 0.5 to 4.5, with 0.5 to 3.5

ratio. preferred.

The feed stocks which can be isomerized include saturated aliphatic and alicyclic hydrocarbons having 4 to 8 carbon -7 atoms per molecule, and/or mixtures thereof. The process is especially adaptable for the upgrading of light petroleum distillates having a boiling range of about 90 to 200 F., and the pentane through heptane traction of natural gasoline.

Although the foregoing invention is specifically illustrated, there are modifications in the various phases of this invention which will be obvious to those skilled in the art. It is well to note in this regard that in the initial preparation of the catalyst as well-as in the preconditioning phase it is preferred that successive steps of oxidation and reduction not be carried out without employing an intermediate purge step to avoid the deleterious etfect on the catalyst due to the presence of water vapor or the possibility of forming explosive mixtures of oxygen and hydrogen. This purging, which can be carried out by using an inert gas, evacuation of the process vessel, or both, ordinarily is conventional practice which does not infiuence'the characteristics of the catalyst. Accordingly this invention is limited only in the manner set forth in the following claims. This application is a continuation in part of the copending application of Norman L. Carr, Serial No. 551, 854, filed December 8, 1955, now abandoned.

What is claimed is:

1. A method of preparing a highly active, reactivatable, virgin isomerization catalyst which comprises incorporating in an acidic, mixed-oxides hydrocarbon cracking catalyst support about 0.5-3.0 wt. percent of nickel in the form of a nickel compound and 1.0-5.0 wt.

percent of molybdenum as a molybdenum compound which is decomposable to molybdenum oxide, heating the catalyst to a temperature above about 900 F. and circulating a reducing gas thereover, thereby producing a catalyst composition containing nickel in substantially the metallic state and molybdenum oxide in the most reduced form of the oxide, subjecting the reduced virgin catalyst to an oxidizing atmosphere at a temperature of about 650 to 850 F., for a time sufiicient to oxidize completely the oxidizable constituents of the catalyst composition, and thereafter contacting the oxidized catalyst composition with substantially pure hydrogen, substantially free of O and CO, at 650-800 F. for a time sufficient to substantially completely reduce the reducible components of the oxidized catalyst to the lowest valence state under the stated conditions.

2. A'method in accordance with claim 1 in which the catalyst support is arefractory acidic composite of silica and at least one refractory oxide of the group consisting of alumina, zirconia, titania, beryllia, chromia, and boria.

3. A method in accordance with claim 1 in which the catalyst support is an acidic silica-alumina composite containing 50-90% wt. silica and 50-10% wt. alumina.

4. A method in accordance with claim 1 in which the catalyst support consists of silica-alumina containing about 75% wt. silica and wt. alumina and the resulting catalyst contains about 3% wt. nickel and 1% wt. molybdenum.

5. A method in accordance with claim 1 in which the catalyst support consists of silica-alumina containing about wt. silica and 25 wt. alumina and the resulting catalyst contains about 2.7% wt. nickel and 4.4% wt. molybdenum.

6. A process for isomerizing a charge stock consisting essentially of n-parafiin hydrocarbons containing 4 to 8 carbon atoms per molecule in admixture with hydrogen at a hydrogeu/ hydrocarbon mol ratio of about 0.5 to 4.5, a liquid hourly space velocity of about 0.1 to 2.0, a pressure of -1000 p.s.i.g., and a temperature of 600- 700 F., by contact with a catalyst produced and activated in accordance with the process defined in claim 1.

7. A process for isomerizing a charge stock consisting essentially of n-parafiin hydrocarbons containing 4 to 8 carbon atoms per molecule in admixture with hydrogen at a hydrogen/hydrocarbon mol ratio of about 0.5 to 4.5, a liquid hourly space velocity of about 0.1 to 2.0, a pressure of 150-1000 p.s.i.g., and a temperature of 600- 700 F., by contact with a catalyst produced and activated in accordance with the process defined in claim 2.

8. A process for isomerizing a charge stock consisting essentially of n-parafiin hydrocarbons containing 4 to 8 carbon atoms per molecule in admixture with hydrogen at a hydrogen/hydrocarbon mol ratio of about 0.5 to 4.5, a liquid hourly space velocity of about 0.1 to 2.0, a pressure of 150-1000 p.s.i.g., and a temperature of 600- 700" F., by contact with a catalyst produced and activated in accordance with the process defined in claim 3.

9. A process for isomerizing a charge stock consisting essentially of n-paraflin hydrocarbons containing 4 to 8 carbon atoms per molecule in admixture with hydrogen at a hydrogen/hydrocarbon mol ratio of about 0.5 to 4.5, a liquid hourly space velocity of about 0.1 to 2.0, a pressure of 150-1000 p.s.i.g., and a temperature of 600- 700 F., by contact with a catalyst produced and activated in accordance with the process defined in claim 4.

10. A process for isomerizing a charge stock consisting essentially of n-paraffin hydrocarbons containing 4 to 8 carbon atoms per molecule in admixture with hydrogen at a hydrogen/ hydrocarbon mol ratio of about 0.5 to 4.5, a liquid hourly space velocity of about 0.1 to 2.0, a pressure of 150-1000 p.s.i.g., and a temperature of 600- 700 F., by contact with a catalyst produced and activated in accordance with the process defined in claim 5.

References Cited in the file of this patent UNITED STATES PATENTS 2,687,370 Henricks Aug. 24, 1954 2,718,535 'McKinley et al Sept. 20, 1955 FOREIGN PATENTS 487,392 Canada Oct. 21, 1952

Claims (1)

1. A METHOD OF PREPARING A HIGHLY ACTIVE, REACTIVATABLE, VIRGIN ISOMERIZATION CATALYST WHICH COMPRISES INCORPORATING IN AN ACIDIC, MIXED-OXIDES HYDROCARBON CRACKING CATALYST SUPPORT ABOUT 0.5-3.0 WT. PERCENT OF NICKEL IN THE FORM OF A NICKEL COMPOUND AND 1.0-5.0 WT. PERCENT OF MOLYBDENUM AS A MOLYBDENUM COMPOUND WHICH IS DECOMPOSABLE TO MOLYBDENUM OXIDE, HEATING THE CATALYST TO A TEMPERATURE ABOVE ABOUT 900*F. AND CIRCULATING A REDUCING GAS THEREOVER, THEREBY PRODUCING A CATALYST COMPOSITION CONTAINING NICKEL IN SUBSTANTIALLY THE METALLIC STATE AND MOLYBDENUM OXIDE IN THE MOST REDUCED FORM OF THE OXIDE, SUBJECTING THE REDUCED VIRGIN CATALYST TO AN OXIDIZING ATMOSPHERE AT A TEMPERATURE OF ABOUT 650* TO 850*F., FOR A TIME SUFFICIENT TO OXIDIZE COMPLETELY THE OXIDIZABLE CONSTITUENTS OF THE CATALYST COMPOSITION, AND THEREAFTER CONTACTING THE OXIDIZED CATALYST COMPOSITION WITH SUBSTANTIALLY PURE HYDROGEN, SUBSTANTIALLY FREE OF O2 AND CO, AT 650*-800*F. FOR A TIME SUFFICIENT TO SUBSTANTIALLY COMPLETELY REDUCE THE REDUCIBLE COMPONENTS OF THE OXIDIZED CATALYST TO THE LOWEST VALENCE STATE UNDER THE STATED CONDITIONS.