US3047491A - Method of isomerizing and demethanating c-c u-paraffins - Google Patents

Description

July 31, 1962 Filed Dec.

c PRODUCTION RATE, MOLES/HR/ CATALYST x 10 N. CARR 3,047,491

METHOD OF ISOMERIZING AND DEMETHANATING 0 -0 n-PARAFFINS 25, 1957 s Sheets-Sheet 2 825'-875 AT 22 mm.

OVER-ALL ACTIVITY DECLINES IN THIS TIME RANGE 5 IO 20 3O 4O 50 I00 TREATMENT TIME (HOURS) (IN H AFTER l6 HR. DRY REDUCTION) FIG. 3

INVENTOR.

-\ NORMAN L. CARR ATTORNEY July 31', 1962 N. L. CARR 3,047,491

METHOD OF ISOMERIZING AND DEMETI-IANATING C -C n-PARAFFINS Filed Dec. 23, 1957 s Sheets-Sheet s PREFERRED TIME RANGE AT THESE COND 8' X- BUTANE PRODUCTION RATE 0- ISO- PENTANE 0 IO 20 3O 4O 5O 60 TIME IN CONTACT WITH CONDITIONING HYDROGEN (HOURS) FIG. 4

INVENTOR.

ATTORNEY 3,047,491 Patented July 31, 1962 3,047,491 METHOD 6F EUMERIZENG AND DEMETHA- NATKNG (C -Q n-PARAFFHNS Norman L. Carr, Crystal Lake, llh, assignor to The Pure Qil Company, Qhicago, Ill., a corporation of Ohio Filed Dec. 23, 1957, Ser. No. 704,615 3 Claims. (Cl. 268-136) This invention relates to the isomerization of isomerizable C C hydrocarbons. It is more specifically directed to the upgrading of light petroleum naphthas containing predominantly straight-chain paraffin hydrocarbons for the production of high-octane-number blending stocks.

In the production of gasoline-type motor fuels, a number of processes are employed in an integrated refining operation for the production of various blending stocks which are formulated into a finished gasoline. The normally liquid virgin distillates boiling within the range of 100-400 F. have either been used per se or subjected to thermal or catalytic reforming, or hydroforming, to produce blending stocks of improved octane numbers. It is preferred, however, in preparing feed stocks for use in reforming or hydroforming operations, to use the heavier fractions boiling within the gasoline range because the low-boiling fractions containing predominantly C C straight-chain paraffinic hydrocarbons are not receptive to reforming. Due to the demand for highoctane, gasoline-type motor fuels needed by increasingly powerful internal combustion engines, isomerization has become important as the best method for raising the octane level of the straight-chain paratfinic C C hydrocarbons. Accordingly, the increased performance requirements of gasoline have become the basis for the extensive commercial application of isomerization.

Although the isomerization reaction predominates in a catalytic isomerization process, disproportionation and cracking side-reactions are of such a magnitude that prac tical commercial utilization of the isomerization process is hindered. The problem of hydrocracking and disproportionation becomes especially serious when isomerizable, saturated hydrocarbons of higher molecular weight are processed in the presence of isomerization catalysts which are effective at temperatures Within the range of GUN-800 F. Another problem relating to the molecular Weight of the isomerization feed stock is the difliculty which is experienced in forming gem-substituted C and C parafiinic hydrocarbons. These types of isomerization reaction products are preferred because the highly branched forms of hydrocarbons provide marked increases in octane number.

Isomerization is a reversible reaction the rate of which can be considerably influenced by the presence of catalytic agent. Although earlier investigators of the isomerization reaction employed Friedel-Crafts-type catalysts, more recent development work in this field has been carried out employing solid catalysts. It has been found that catalysts compositions comprising a major portion of a refractory, mixed oxides base, composited to evince acidic properties and hydrocarbon cracking activity, and a small amount of a hydrogenation agent are effective for promoting the efficiency of the isomerization reaction. (Vide Isomerization of Saturated Hydrocarbons in the Presence of Hydrogenation-Cracking Catalysts, Ciapetta, et 211., Industrial and Engineering Chemistry, 45, 147 et seq.) Specific catalysts are prepared by incorporating a small amount of a hydrogenation agent in a refractory, mixed oxides base. Specific hydrogenation agents include the elemental group IV or group VIII metals, such as iron, platinum, cobalt, and nickel, their oxides, and their salts, including molybdates, tungstates, chromates, and borates, as Well as the oxides of chromium, molybdenum and tungsten, alone or in admixture. Because they are susceptible to permanent loss of activity with continued use, extensive work has been carried out to improve the activity and life of these catalysts by specific preconditioning treatments. In U.S. patent application Serial No. 619,376, filed October 31, 1956, now [1.8. Patent No. 2,917,565, there is described a multiple-step preconditioning process employing a sequential oxidation and reduction treatment. Essentially, this preconditioning process involves a two-part manipulative technique, viz., (a) the catalyst preparation carried out in accordance with the prior art, and (b) the preconditioning process of oxidizing and reducing which was found to be exceptionally and distinctively effective for inducing high activity and stability by imparting resistance to permanent depreciation in activity. Although the overall effect of this catalyst preconditioning method has been to provide a stable catalyst which is useful in improving the octane number rating of feed stocks boiling Within the gasoline range, investigation of the reaction products has shown that the method increased the propensity of the catalyst to promote undesired near-middle hydrocracking of the individual paraffinic constituent molecules as distinguished from desired demethylation. In specific instances, the rate of isopentane hydrocracking is increased in absolute magnitude as well as relative to normal pentane hydrocracking.

It is, therefore, the primary object of this invention to provide a catalyst conditioning method which will modify the catalytic properties of an isomerization catalyst, composed of a refractory, mixed oxides base composited to evince acidic properties and hydrocarbon cracking activity, and a small amount of a hydrogenation agent, to enhance the effectiveness of the catalyst composition in promoting isomerization reactions as its principal activity, and in preferentially promoting demethylation reactions as its secondary activity. It is another object of this invention to provide a conditioned isomerization catalyst to accelerate the isomerization of saturated hydrocarbons at temperatures Within the range of about 600-800 F. Still another object of this invention is to provide a conditioned solid isomerization catalyst which effectively promotes the isomerization and selective demethylation of feed stocks consisting of saturated hydrocarbons having 58 carbon atoms per molecule. These and other objects will become more apparent from the following detailed description of this invention, and accompanying drawing, of which:

FIGURE 1 is a flow diagram of a typical isomerization process employing the principles of this invention;

FIGURE 2 is a flow sheet diagramming the process steps employed in preparing the conditioned catalysts of this invention;

FIGURE 3 is a graphical presentation of the critical conditions of this invention; and

FIGURE 4 is a graphical illustration of the effect of time of treatment on isomerization and methylation under specified conditions.

According to this invention, the utility of isomerization processes involving the treating of C C hydrocarbons is enhanced by employing a solid catalyst which is conditioned in such a manner as to promote isomerization, as the principal reaction, and preferentially promote demethylation, as a subordinate but' concomitant reaction. The catalyst which is conditioned in accordance with this invention is a solid comprising a major amount of mixed oxides base, composited to evince acidic properties and hydrocarbon cracking activity, and a minor amount of a hydrogenation agent. The catalysts susceptible to conditioning according to this invention are prepared by conventional techniques and commonly are activated by methods wherein the final activation step involves subjecting the composition to a reducing step which reduces the reducible constituents of the composition to their lowest state of valency attainable at the reducing conditions imposed. The catalyst in this conditionis effective for producing motor fuel components of increased octane numbers, but its use in this form gives rise to certain disadvantages. Conditioning the catalyst before use according to this invention significantly mitigates these disadvantages. Similarly, catalysts of this kind which have become degenerated during use in hydrocarbon processing, when regenerated by conventional techniques also are effective in promoting reactions which yield products of increased octane numbers, but they possess similar disadvantages. The conditioning method of this invention is also effective in improving these catalysts.

In general, the hydrogenation agents employed in the catalysts defined above fall into the distinct categories of base and noble metals. Notable among useful basemetal-containing isomerization catalysts are those in which nic (e1, or nickel in combination with molybdena, is the hydrogenation agent. Among the noble-metal-containing isomerization catalysts are those in which palladium or platinum is the hydrogenation agent. In its broadest aspect, this invention is based upon my discovery that catalysts containing either of these types of hydrogenation agent can be conditioned to provide a unique process in which isomerizable C -C hydrocarbons are converted to more valuable products through predominantly isomerization and demethylation reactions. However, I also have discovered that different techniques are required to condition each of these types of catalysts for the attainment of desired activity and specificity of reaction-promoting propensity. I have discovered further that the attainment of these characteristics in base-metalcontaining catalysts is critically dependent upon the manner in which the catalysts, in reduced condition, are subjected to treatment with a moistureand hydrogen-containing gas. On the other hand, the attainment of this characteristic in noble-metal-containing catalysts is critically dependent upon the manner in which the catalyst is subjected to a first treatment with moisture-and oxygencontaining gas and a second treatment with a dry, hydrogen-containing gas.

Specifically, the method which I have found to be uniquely effective in conditioning a base-metal-containing catalyst requires that substantially all of the catalyst constituents first be at their highest state of oxidation, and that the catalyst be free of contaminants and moisture. Thus, freshly-prepared, virgin catalysts, which commonly are pelleted and dried after compounding, are susceptible to conditioning Without further pretreatment. Catalysts which have become degenerated by previous use in processing hydrocarbons must be first subjected to oxidation. I have found that satisfactory oxidation can be accomplished by contacting the catalyst with a dry mixture of inert gas and oxygen, containing oxygen at a partial pressure of 30-500 mm. Hg, at a temperature of 800-875 F. for a time suflicient to oxidize carbonaceous deposits on the catalyst and the oxidizable constituents of the catalyst composition. The oxygen-containing gas preferably is dry, but may contain Water vapor at a partial pressure up to about 10 mm. Hg Without serious deleterious effect.

The resulting base-metal-containing catalyst, in oxidized state, is subjected to a conditioning method which consists of the following sequential steps: (1) Purge.0xygen and combustion products are removed from the catalyst bed by purging With inert gas, or by evacuation to a low absolute pressure in the range of 10 mm. Hg.

(2) Reducli0n.-The reducible constituents of the composition then are reduced in a three-stage sequence wherein (a) The oxidized catalyst is contacted with a flowing stream of substantially dry, hydrogen-containing gas at a temperature of about 600-975 F. for a period suflicient 4- to remove water, generated by the reduction reaction, from the catalyst bed;

(17) The catalyst is contacted further with dry hydrogen, either by continuing flow or shutting in the catalyst for 15-30 hours While temperature is maintained at 900-975 F, and pressure at 0-600 p.s.i.g.;

(c) The reduced catalyst then is contacted with flowing, moistureand hydrogen-containing gas at a temperature of about 800-975 F. for a period of about 5-50 hours. The gas should contain Water equivalent to a partial pressure in mm. of Hg of about 15-100 and preferably 20-30.

The method which I have found to be effective in conditioning noble-metal-containing catalysts consists of the following sequential steps:

(1) Purge-The catalyst bed is purged with an inert gas for a time sufiicient to displace gaseous hydrocarbons and/or hydrogen therefrom.

(2) Oxidati0n.-The catalyst is contacted with an oxygen-containing inert gas, containing oxygen at a partial pressure of 10-500 mm. Hg and water vapor at a partial pressure of 0-90 mm. Hg, at a temperature of 825-975" F. for 1-20 hours. Temperature, Water-vapor partial pressure, and length of treatment are critically interrelated in this step. At an oxidation temperature of 825 F, the water-vapor partial pressure must be in the range of 20-90 mm. Hg and the length of treatment must be about 20 hours. At an oxidation temperature of 975 F., the water-vapor partial pressure must be in the range of 0-15 mm. Hg, and the length of treatment must be limited to about 1 hour.

(3) Purge.Oxygen, combustion products, and moisture then are removed from the catalyst bed by purging With inert gas, or by evacuation to a subatmospheric pressure in the range of 10 mm. Hg, absolute.

(4) Reduction-The reducible constituents of the oxidized catalyst composition then are reduced to the greatest extent possible by passing a stream of dry, hydrogencontaining gas through the catalyst bed for l-30 hours at a temperature of 850-950 F. and a pressure of 15- 750 p.s.i.g. While dry gas is preferred, water-vapor partial pressures as high as 10 mm. Hg can be employed without serious deleterious effect.

In carrying out a catalyst preparation in accordance with this invention, the preconditioning steps may be carried out in a separate processing system, or an active catalyst prepared in accordance with the prior art can be disposed in the isomerization reactor and the preconditioning carried out as a preliminary to introducing the isomerization feed into the reaction system. This latter method of preconditioning is preferred in order to avoid changes in catalyst composition which may inadvertently occur in handling the preconditioned catalyst prior to its being placed in the reaction system.

Catalysts which may be preconditioned in accordance with this invention are composite compositions comprising a refractory, mixed oxides base composited to evince acidic property and hydrocarbon cracking activity, having incorporated therein a small amount, i.e., 0.1 to about 10% of a hydrogenation agent. Specific examples of the refractory, mixed oxides base include but are not limited to silica-alumin, silica-zirconia, silicatitania, silica-boria, alumina-zirconia, alumina beryllia, alumina-boria, silica-chromia, boria-titania, silica-alumina-zirconia, silica-alumina-beryllia, and acid-treated clays. The hydrogenation agent which is employed can be a group VIII metal, oxide of a poiyvalent metal of group V, VI and VII, or group VIII, metal, and metal salts of the oxyacids of polyvalent metals of groups V, VI and VII. Specific examples of suitable hydrogenation agents, include but are not limited to cobalt, nickel, platinum, tungsten oxide, molybdenum oxide, chromium oxide, manganese oxide and vanadium oxide; and cobalt, nickel and platinum salts of the oxyacids of tungsten, molybdenum, chromium, vanadium or manganese, e. nickel tungstate, cobalt molybdate, nickel molybdate. It has been found that silica-alumina catalyst carriers containing 50-87% silica and 5013% alumina, having incorporated therein 02 to of the hydrogenation agent, particularly nickel, nickel molybdate, palladium or plati' num, have superior activities and are preferred.

This invention, as applied to a base-metal-containing catalyst, was demonstrated by experiments in which catalyst compositions containing 2.7% wt. nickel and 4.7% wt. molybdenum (present as molybdena) as the hydrogenation agent, on a support consisting of 75% wt. silica and 25% wt. alumina (a conventional, commercial cracking catalyst) were used. Such catalysts can be prepared as follows:

A solution of 32 grams of ammonium heptamolybdate and 20 cc. of concentrated ammonium hydroxide in 270 ml. of distilled water is heated to 176 F. To this solution, with stirring, is added 58.7 grams of nickel nitrate in 270 ml. of water. After dissolution, 360 grams of commercial fluid cracking catalyst, containing 75% wt. silica and 25% wt. alumina, are added. The mixture is stirred for about minutes, after which the impregnated solid material is filtered from the supernatant liquid and washed with five 670 ml. portions of distilled water. The catalyst cake then is dried for 16 hours at 230 F. and pelleted.

In one series of experiments, virgin catalysts were subjected to conditioning according to my method, as follows:

EXAMPLE I A batch of freshly-prepared, pelleted, dried catalyst was placed in the reaction vessel of a pilot-plant unit for evaluating catalysts and process variables, and was slowly heated in a flowing stream of dry hydrogen to a temperature of 975 F, at which temperature it was held for 29 hours while continuing the how of hydrogen. Then the catalyst temperature was lowered to 825 F, and water vapor was added to the hydrogen to bring its vapor pressure to 22 mm. Hg. This condition was maintained for hours, after which the catalyst bed was cooled further to 705 F. for an isomerization processing test. The test was conducted using normal pentane as the feed stock, with dry hydrogen being added at a hydrogen/hydrocarbon mol ration of 1/ 1. Hydrocarbon space velocity was 2.8 v./hr./v. Pentane conversion was 50.7 mol percent, isopentane yield was 45.9 mol percent, and n-pentane-isopentane selectivity was 90.6%. Adjusted to operation at a space velocity of 3.3 vol./hr./vol., conversion was 45.9 mol percent, and isopentane yield 41.1 mol percent. In this experimental test, the rate of butane production was 9.6 10 g.-mole/ hr./ g. catalyst. The amount of butane and methane formed by demethylation exceeded the amount of ethane and propane formed through middlemolecule cracking by 360%.

When a similar catalyst composition, which had been activated 'by oxidation and reduction according to conventional practice, was tested at these same conditions, the test had to be terminated soon after processing was initiated because hydrocracking, which is highly exothermic, was so great that catalyst temperatures rapidly and uncontrollably increased.

EXAMPLE II The used catalyst of Example I was regenerated, after being purged free of gaseous hydrocarbons and hydrogen by flowing nitrogen through it. While continuing nitrogen flow, the catalyst was cooled to about 700 E, whereupon a small amount of air was added to the nitrogen to burn carbonaceous deposits and other contaminants from the catalyst surfaces. Burning was evidenced by a rise in temperature at the so-called flame-front which progressed through the catalyst bed from the inlet and to the exit end. When no further evidence of temperature rise was noted, indicating that burning had been completed, the catalyst bed was heated to about 975 F. and dry air,

same as given in Example III.

without dilution, was passed through the system for about one hour to assure completion of oxidation.

The system then was again purged with nitrogen and the catalyst was reduced by being contacted at 975 F. with flowing dry hydrogen for a period of about 24 hours. After being reduced, the catalyst was conditioned by being contacted with wet hydrogen, containing water vapor at a partial pressure of 30 mm. (Hg), at 875 F. for 18 hours. The conditioned catalyst then was used in an isomerization test wherein normal pentane and hydrogen, at a hydrogen/pentane mol ratio of 1, were passed through the catalyst bed at a pentane space velocity of 3.3 vo1./hr./vol. of catalyst. Catalyst temperature was 702 F., and pressure was 500 p.s.i.g.

In this test, n-pentane conversion was 43.8 mol. percent, isopentane yield was 40.4 mol percent, and n-pentane-toisopentane selectivity was 92.2%. The rate of butane production was 7.6 10 gm.-mole/ hr./ gram of catalyst, and the amount of butane and methane formed by demethylation cracking exceeded the amount of ethane and propane formed through middle-molecule cracking by When a similar catalyst is regenerated and reactivated by conventional methods in which reduction is achieved with dry hydrogen, the resulting catalyst is so hot, i.e., the extent of exothermic hydrocracking is so great, that the catalyst cannot be used. Uncontrollable temperature increases occur in the catalyst bed.

EXAMPLE III A second batch of freshly prepared and pelleted catalyst, having the same composition, was conditioned as in Example I, except that the conditioning was at 825 'F. for 50 hours with hydrogen containing water vapor at a partial pressure of 22 mm. (Hg). In testing the catalyst with normal pentane as the feed, space velocity was 3.3 v./hr./v., hydrogen/hydrocarbon mole ratio was 1, and catalyst temperature was 702 F.

In this test, pentane conversion was 41.0 mol percent, isopentane yield was 37.8 mol percent, and selectivity was 92.3%. Butane production rate was 7.9, 10 gm.- mole/ hr./ gram of catalyst, and the amount of butane and methane produced was 520% greater than the amount of propane and ethane.

EXAMPLE IV The used catalyst of Example III was regenerated and conditioned by the method of Example II, except that the conditioning with wet hydrogen consisted of two steps. In the first step the catalyst was contacted with hydrogen containing water vapor at a partial pressure of 22 mm. (Hg) at 975 F. for 16 hours. In the second step the cat alyst was contacted with hydrogen containing water vapor at a partial pressure of 22 mm. (Hg) at 800 F. for 3 hours. In the isomerization test, normal pentane and hydrogen, at a hydrogen/pentane mole ratio of 1, were passed through the catalyst bed at a pentane space velocity of 3.3 vo1./hr./vol. of catalyst. Catalyst temperature was 702 F. and pressure was maintained at 500 p.s.i.g. Normal pentane conversion was 41.7 mol percent, isopentane yield was 39.2 mol percent, and selectivity was 93.9 percent. Butane production rate was 5.6 10 gm.-mole/ hr./ gram catalyst and butane-methane production exceeded ethane-propane production by 150%.

EXAMPLE V Another portion of freshly-prepared and pelleted catalyst, having the same composition, was conditioned as in Examples I and III, except that the conditioning was conducted for 20 hours at 875 F., using hydrogen which contained water vapor at a partial pressure of 22 mm. (Hg). Isomerization test conditions were essentially the Pentane conversion was 43.7 mol percent, isopentane yield was 39.9%. Butane production rate was 10.1 10 gm.-mole/hr./gram of 7 catalyst, and butane-methane production exceeded propane-ethane production by 440%.

EXAMPLE VI Example V was repeated with another portion of catalyst, except that the conditioning consisted of contacting the catalyst at 825 F. for five hours with hydrogen which contained water vapor at a partial pressure of 23 mm. (Hg). Test conditions were similar to those of Example III. Normal pentane conversion was 45.5 mol percent, isopentane yield was 36.9 mol percent, and selectivity was 81.1%. Butane production rate was 27 1O gm.-mole/ hr./ gram of catalyst, and butane-methane production exceeded ethane-propane production by 610%.

EXAMPLE VII In another experiment, a portion of catalyst having the composition of the catalysts used in Examples IVl was conditioned by being contacted at 900 F. with hydrogen which contained water vapor at a partial pressure of 22 mm. (Hg). Contact was maintained for hours. In a test run at 648 F., and 500 p.s.i.g., normal heptane was isomerized over this catalyst at a space velocity of 1.1 vol./hr./vol., with a hydrogen/ hydrocarbon mol ratio of 1.2. Normal heptane conversion was 76.7 mol percent, isoheptane yield was 49.3 mol percent, and hexane yield was 14.7 mol percent. Thus, it can be seen that this conditioned catalyst was active in promoting isomerization and demethylation.

For greater clarity, the results of these experiments are listed in Table I. The critical interrelationship of the effects of temperature, length of time, and water vapor partial pressure on butane production rate are shown in FIG- URE 3. The effects of these variables on isopentane yield and demethylation are shown graphically in FIGURE 4. It can be seen that when the catalyst is conditioned by contact with hydrogen-containing water vapor at a partial pressure of 22 mm. (Hg) at 825 F., the length of time of contact has a profound effect on isopentane yield and demethylation.

of solution used being compatible with the absorptive capacity of the support. Hydrochloric acid is necessary to keep the palladium salt in solution at room temperature in the concentrations required. Alternatively, heating to about 180 F. will keep the palladium salt in solution. After having been dried and pelleted, the green catalysts are decomposed, i.e., the palladium chloride is decomposed and reduced to metallic palladium by contact with hydrogen at an elevated temperature. Following this decomposition step, the catalysts conventionally are activated by oxidation followed by reduction at elevated temperatures. The catalysts are regenerated after use by again being oxidized and reduced at elevated temperatures, the oxidizing step being employed primarily to burn carbonaceous and other contaminating deposits from the catalyst. I have found that the isomerization and demethylation propensities of such catalysts are critically dependent upon the conditions to which the catalyst is subjected in these oxidizing steps.

The demonstration experiments were as follows:

EXAMPLE VIII A previously-used, degenerated portion of the described catalyst was oxidized at 850 F. by passing nitrogen, containing oxygen at a partial pressure of 35 mm. (Hg) and water vapor at a partial pressure of 90 mm. (Hg), through the catalyst bed for one hour. Then the bed was purged free of oxygen by passing nitrogen through it, and the catalyst was reduced at 850 F. by passing hydrogen containing water vapor at a partial pressure of 90 mm. (Hg) through the bed for hours.

An attempt was then made to use the catalyst in the isomerization of normal pentane, in the presence of hydrogen at a hydrogen/hydrocarbon mol ratio of 1.7, at 750 F., 395 p.s.i.g., and at a pentane space velocity of 3.0 vol./hr./vol. of catalyst. The catalyst was so hot, i.e., exothermic hydrocracking reactions caused such a rapid uncontrollable temperature rise, that operation was impossible. The isopentane yield was only about 6%.

Table I.Is0merizati0n and Demethylation of Pentane Over a Base M earl-Containing Catalyst Example 1 2 3 4 Treatment Conditions in hydrolime, hr 20 18 50 16 Ternp., 825 875 825 975 H1O partial pressure mm.

Hg 22 30 22 22 Run Conditions:

mp., F 705 702 IEU/HC mol ratio. 1 LV V 2.8 3.3 Pressure, p.s.i.g 500 500 Results:

nC Conv., mol percent 50. 7 45. 9) 43.8 i-O Yield, mol percent 45. 9 (41.1) 40. 4 Selectivity, percent 90.6 04 Production Rate, g.m01/hr./g.

cat. 10 9.6 M01 ratio: (0 +6 4 6 2 5 6.2 (o3+o2) 2 5 Percent more (CH-C1) formed than (02+03), (mole basis) 360 150 520 150 1 Corrected to LVHSV=3.3.

r a freshly dried support with a solution of palladium chlo- EXAMPLE IX The hot catalyst of Example VIII then was subjected to oxidizing conditions at 850 F., after having been evacuated to about 10 mm. Hg, absolute to remove water, by passing a dry air-nitrogen mixture through the bed for 1 hour. After oxidation, the catalyst bed was again evacuated for 15 minutes, and was then subjected to reduction at 850 F. by passing dry hydrogen through it for 1.5 hours.

After this treatment, the catalyst was again used in isomride in about one-normal hydrochloric acid, the volume erizing normal pentane at the same conditions employed in Example VIII. Normal pentane conversion was 28.4 mol percent, isopentane yield was 21.1 mol percent, and butane and lighter yield was 7.3 mol percent. The catalyst had been made operable by this treatment, but its activity was uneconomically low.

EXAMPLE X The catalyst of Example IX then was subjected to the method of this inventon, in which it was oxidized at 850 F. by passing nitrogen, containing oxygen at a partial pressure of 35 mm. (Hg) and water vapor at a partial pressure of 15 mm. (Hg), through the bed for 1 hour. Then, after being purged with nitrogen, the catalyst was reduced by contact with dry hydrogen at 850 F. for 1 hour. When the catalyst was employed in the isomerization of normal pentane at the conditions of the previous examples, normal pentane conversion was 62 mol percent, isopentane yield was 45 mol percent, butane yield was 11.5 mol percent, and propane and lighter yield was only 4.5 mol percent. Thus, my method had rendered the catalyst very active, reasonably selective in promoting isomerization as the primary reaction, and very selective in promoting demethylation as the predominant side reaction.

To employ the preconditioned catalyst prepared in accordance with this invention in an isomerization process, a suitable isomerization feed stock is processed in a reaction system employing operating conditions within the following range:

While the isomerization process employing the preconditioned catalyst of this invention can be utilized as a separate unit in the processing of selected isomerization feed stocks, it is preferred that the process be employed in an integrated refining operation wherein the primary objective is the upgrading in-octane number of light petroleum distillates boiling in the gasoline range. In this instance, in order to improve the octane number of a full-boiling-range gasoline, the isomerization process can be employed in conjunction with a reforming operation. In this operation the full-boiling-range gasoline is initially fractionated to produce a low-boiling range fraction and a high-boiling-range fraction. The low-boiling-range fraction, having a boiling range of about 100250 F. and consisting predominantly of straight-chain paraifinic hydrocarbons, is contacted in an isomerization process employing the preconditioned catalyst of this invention. The higher-boiling fraction is thereafter processed in a catalytic reforming or hydroforming process which aromatizes and cyclizes the constituents of the higher-boiling range fraction. The reformate from the reforming step is then treated in a refining operation, such as solvent extraction, to remove the aromatic constituents which were produced in the reforming operation. The paraflinic constituents of the reformate which are produced in the course of the reforming operation are then recycled for subsequent processing in the isomerization zone of the combination, isomerization-reforming, integrated unit. If preferred, it may also be desirable to utilize a plurality of isomerization zones containing catalysts and operating under reaction conditions which are conducive to the processing of separate feed stocks at maximum efliciency. In other words, the low-boiling fraction boiling within the gasoline range may be further fractionated to produce separate cuts which are rich in C C C or C paraffinic hydrocarbon constituents. The separate streams can then be fractionated in separate reaction systems which are operated under conditions which will provide optimum effect with regard to upgrading in the octane number of the selected feed stocks. It is apparent that other manipulative techniques may be utilized in carrying out the instant invention, which is directed primarily to a preconditioned catalyst and process for the isomerization of C C saturated hydrocarbons.

In carrying out an isomerization process of this nature, low-boiling, saturated, hydrocarbon-containing feed stocks are employed. Such stocks include normal paraffins containing not more than about 8 carbon atoms per molecule, or naphthenic hydrocarbons, as well as mixtures of these hydrocarbons which are found in straight-run, light, petroleum distillates boiling between about 250 F. Such light petroleum distillates include straight-run gasolines which are obtained in the fractionation of crude petroleum oil, as well as natural gasoline. In carrying out the isomerization process, conventional contact equipment and product recovery systems can be employed. A typical installation is shown in FIGURE 1. A light naphtha distillate rich in saturated hydrocarbons is passed via lines 10 to heating coil 11. Hydrogen admitted to the system through line 12 is then mixed with the naphtha feed and the combined feed is heated to reaction temperature in coil 11 before being introduced into the reactor 15, which contains catalyst preconditioned in the manner previously described. The reaction efiluent leaves reactor 15 through line 16 and is sent to a highpressure separator 17 to effect a separation of the liquid isomers, which are discharged from the reaction system through line 18, from the oif-gas, which leaves separator 17 by means of line 19 and is sent to knockout drum 20 wherein any entrained isomerization liquid is recovered. The gaseous efliuent is withdrawn to line 21. Because this efliuent is rich in hydrogen, provision is made for recycling a portion of this gas to the reactor by means of line 22 which interconnects with the hydrogen feed line 12. The gas which is not used for the recycle operation is passed via line 23 to an absorbing section (not shown), where any remaining hydrocarbon fractions boiling in the gasoline range are recovered.

During the isomerization reaction the proconditioned catalyst of this invention may become contaminated with various materials which lower its catalytic activity. When the activity falls below the desired level it is regenerated in the manner previously described, and as illustrated in FIGURE 2.

FIGURE 3 graphically shows the effect of time, tem perature and water partial pressure during hydrogen conditioning on rate of demethylation. With increase in time, demethylation rate decreases rapidly and then levels off, whereas isomerization selectivity and activity increases to a maximum and then falls off slowly. For short conditioning periods the activity of the catalyst is high, but the isomerization selectivity of the catalyst is low and demethylation selectivity is high. Increase in moisture content of the conditioning hydrogen also decreases the demethylation rate. Therefore, if the object is to promote isomerization with minimum amount of demethylation, the catalyst s hould be conditioned with Water vapor pressures above 20 mm. of Hg, and the time of conditioning should be at least 15 hours. On the other hand, if it is desired to promote demethylation together with isomerization, as for example, in the processing of heptane-rich stock, the conditioning time should be short and preferably at the lower temperature range, as demonstrated by Example 6 and the graphs in FIGURE 3.

FIGURE 4 shows the preferred time range for conditioning a catalyst at 825 F. with hydrogen containing water at 22 mm. of Hg partial pressure in order to obtain maximum isomerization selectivity and activity. Below 10 hours, isomerization selectivity and yield fall oif sharply. Conditioning times above 20 hours adversely affect isomerization yield without having any material effect on demethylation.

Although the invention has been described as being particularly adaptable to use in connection with a reaoazam forming operation, it can be employed in conjunction with other types of refining processes in order to provide an integrated refining operation for the upgrading of petroleum distillate stocks to produce a finished gasoline having a high octane number rating. It is, therefore, intended that the following invention be limited only in the manner described in the appended claims.

This application is a continuation-impart of my copending patent applications, now United States Patents 2,917,565 and 2,917,566, having efiective filing dates of December 8, 1955.

What is claimed as my invention is:

1. A method of isomerizing and demethan-ating C -C n-paraflins which comprises passing a mixture of hydrogen and C -C parafiins in a hydrogen/hydrocarbon mol ratio of 0.5-6.0/1, at a pressure of 50-1000 p.s.i.g., and temperature of 600-800 F., over an isomen'zation catalyst consisting essentially of a promoter selected from the group consisting of nickel, reduced nickel molybdate,

and reduced nickel phosphate supported on an acidic 2O oxidizable constituents of the catalyst, removing oxygen and combustion products from the catalyst, subjecting the oxidized catalyst to reduction with a dried hydrogen at 850-975 F. for a' time, in the range from about 15-30 hours, sufiicient to reduce completely all reducible catalyst components, followed by contacting the reduced catalyst with hydrogen containing water vapor at a partial pressure of 15-100 mm. Hg, at a temperature of 800-975 F. for a time, in the range from about 5 to 50 hours, sufli- II cient to condition the catalyst so that the isomerization reaction is substantially free of exothermic hydrocracking. 2. A method in accordance With claim 1 in which the catalyst comprises nickel molybdate on silica-alumina.

3. A method in accordance With claim 1 in Which the water partial pressure in the hydrogen treating gas is about 20-30 mm. Hg.

References Cited in the file of this patent UNITED STATES PATENTS 2,671,763 Winstrom et al Mar. 9, 1954 2,870,085 Love Jan. 20, 1959 2,879,232 Malo et al Mar. 24, 1959 2,882,241 Slyngstad et a1 Apr. 14, 1959 2,906,697 Hall et al Sept. 29, 1959 2,968,631 Carr et al Jan. 17, 1961

Claims (1)

1. A METHOD OF ISOMERIZING AND DEMETHANATING C5-C8 N-PARAFFINS WHICH COMPRISES PASSING A MIXTURE OF HYDROGEN AND C5-C8 PARAFFINS IN A HYDROGEN/HYDROCARBON MOL RATIO OF 0.5-6.0/1, AT A PRESSURE OF 50-1000 P.S.I.G., AND TEMPERATURE OF 600*-800*F., OVER AN ISOMERIZATION CATALYST CONSISTING ESSENTIALLY OF A PROMOTER SELECTED FROM THE GROUP CONSISTING OF NICKEL, REDUCED NICKEL MOLYBDATE, AND REDUCED NICKEL PHOSPHATE SUPPORTED ON AN ACIDIC SILICA-ALUMINA HYDROCARBON CRACKING CATALYST, CONTAINING 50-87% WT. SILICA, SAID CATALYST HAVING BEEN PRECONDITIONED TO INCREASZE CATALYST ACTIVITY AND SELECTIVITY FOR ISOMERIZATION BY OXIDIZING THE CATALYST WITH A DRY MIXTURE OF AN INERT GAS CONTAINING OXYGEN AT A PARTIAL PRESSURE OF 30-500 MM. HG, AT A TEMPERATURE OF ABOUT 800*-875* F., FOR A TIME SUFFICIENT TO COMPLETELY OXIDIZE THE OXIDIZABLE CONSTITUENTS OF THE CATALYST, REMOVING OXYGEN AND COMBUSTION PRODUCTS FROM THE CATALST, SUBJECTING THE OXIDIZED CATALYST TO REDUCTION WITH A DRIED HYDORGEN AT 850*-975*F. FOR A TIME, IN THE RANGE FROM ABOUT 15-30 HOURS, SUFFICIENT TO REDUCE COMPLETELY ALL RESDUCIBLE CATALYST COMPONENTS, FOLLOWED BY CONTACTING THE REDUCED CATALYST WITH HYDROGEN CONTAINING WATER VAPOR AT A PARTIAL PRESSURE OF 15-100 MM. HG, AT A TEMPERATURE OF 800*-975* F. FOR A TIME, IN THE RANGE FROM ABOUT 5 TO 50 HOURS, SUFFICIENT TO CONDITION THE CATALYST SO THAT THE ISOMERIZATION REACTION IS SUBSTANTIALLY FREE OF EXOTHERMIC HYDROCRACKING.

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