US3099617A - Pretreatment of catalyst employed in the hydrocracking of hydrocarbons - Google Patents

Description

United States Patent Office Patented July 30, 1963 poration of California No Drawing. Filed Aug. 4, 1960, Ser. No. 47,368

12 Claims. (Cl. 208-109) This invention relates to the catalytic hydrooracking of high-boiling hydrocarbons to produce therefrom lower boiling hydrocarbons, boiling for example in the gasoline range. The invention is directed specifically to certain novel methods for improving the overall activity of sulfided hydrocracking catalysts, for improving their selectivity of conversion, and for increasing the ratio of isoparafiins to normal paraffins produced during hydr-ocracking. Briefly, the basic novel feature of the invention involves a pretreatment step wherein the catalyst, before being sulfided, is treated under hydrocracking conditions with a hydrocarbon feedstock which is substantially free from sulfur. Following the pretreatment step, the catalyst is then sulfided, either by direct treatment with hydrogen sulfide, or by treatment with feeds containing decomposable sulfur compounds. It has been discovered that substantial improvements in overall activity, selectivity, and isoparaflin to normal parafiin ratios in the product are obtainable where the pretreatment with sulfur-free feed is employed, as compared to the case where the catalyst is directly sulfided, as by contacting with hydrogen sulfide or a sulfur-containing feedstock.

It is a principal object of this invention to improve the overall activity of sulfided hydrocracking catalysts for converting high-boiling hydrocarbons to lower boiling hydrocarbons. A further object is to improve the selectivity of conversion to gasoline in catalytic hydrocracking processes. Still another object is to improve the antiknock quality of hydrocracked gasolines by increasing the ratio of isoto normal paraflins in the product. A concomitant objective with the foregoing involves decreasing the rate of catalyst deactivation attributable to the deposition of coke and other deactivating deposits. This latter objective flows from the improvements in activity and selectivity, which permits the use of lower temperatures with reduced coking rates.

The pretreated and sulfided catalysts of this invention may be employed for the hydrocracking of substantially any mineral oil fraction boiling above the conventional gasoline range, i.e., above about 300 F., and usually above about 400 F, and having an end-boiling-point up to about 1000 F., but preferably not greater than about 750 F. These feedstocks may be sulfur-free, or they may contain up to about by weight of sulfur, in the form of organic sulfur compounds. If it is desired to maintain the catalyst in a completely sulfided state, feedstocks containing between about 0.01% and 5% by weight of sulfur may be used, or a small proportion of H 5 may be recirculated in the recycle gas. Specific feedstocks contemplated comprise straight-run gas oils and heavy naphth'as, coker distillate gas oils and heavy naphthas, deasphalted crude oils, cycle oils derived from catalytic or thermal cracking operations and the like. These feedstocks may be derived from petroleum crude oils, shale oils, tar sand oils, coal hydrogenation products and the like. Specifically, it is preferred to employ oils having an end-boiling-point between about 400 and 650 R, an API gravity between about 20 and 35, and containing at least about 30% by volume of acid soluble components (aromatics plus olefins).

In their initial form, prior to the pretreatment step, the hydrocracking catalysts employed herein comprise a major proportion of a solid refractory oxide cracking component plus a minor proportion, e.g., about l20% by weight, of a sulfidab'le heavy metal hydrogenating component. Suitable sulfidable hydrogenating components include the oxides or other compounds of the transitional metals, particularly'those of groups VB and VIII, or mixtures thereof, or the corresponding free metals. Particularly desirable components consist of the oxides of chromium, molybdenum, tungsten, iron, cobalt, nickel, platinum or palladium, and especially cobalt and/or nickel. The cracking component on which these materials are deposited may consist for example of synthetic coprecipitated silica-alumina, silica-zirconia, silicatitania, silica-titania-zirconia, silica-alumina-zirconia, silica-magnesia, and the like. Acid-activated montmorillonite clays may also be employed. Any of these carriers may be further activated by the incorporation of small amounts of acidic materials such as fluorine or chlorine.

A particularly preferred group of catalysts for the hydr-ocracking reaction consists of a coprecipitate-d base composed of 10-65% silica, 15-65% titania, and 15-65% zirconia, on which is deposited, as by impregnation or coprecipitation, a minor amount, from about 0.5% to about 20%, of a group VlB or group VIII metal promoter, e.g., a sulfide of chromium, molybdenum, tung: sten, cobalt, nickel, or any combination thereof. Alternatively, even smaller proportions, between about 0.05% and 1.0% of the metals platinum, palladium, rhodium or iridium may be employed. The sulfides of other transitional metals may also be used, but to less advantage than the foregoing.

In preparing the preferred catalysts, it is desirable to coprecipitate all four components from aqueous solution under prevailingly alkaline conditions, i.e., at a pH between about 6 and 12. The alkaline coprecipitated catalysts are considerably more active than catalysts coprecipitated under acidic conditions. To effect alkaline coprecipitation, an aqueous solution of acidic titanium and zirconium salts, e.g., the sulfates, may be poured with stirring into an alkaline solution of a soluble silicate, e.g., sodium silicate. The desired promoter, e.g., nickel, may be included as a soluble salt with the titanium-zirconium solution. Following coprecipitation, the wet gel is washed exhaustively, base-exchanged with an ammonium salt to remove all alkali metals, dried and finally calcined at e.g. 6001200 F.

With any of the above-described hydrocracking catalysts, following the final calcining step, it is normally desirable to subject them to a reducing step wherein hydrogen or a hydrogen-containing gas is passed over the catalyst at temperatures of about 500 to 1000 F. for one to five hours. However, the prereduction step is ordinarily not necessary herein because the sweet-feed pretreatment step will ordinarily accomplish the desired reduction.

The hydrocarbon feedstock to be employed for the pretreatment step may comprise any hydrocarbon, or mixture of hydrocarbons, which is susceptible of being cracked in the presence of hydrogen upon the particular catalyst employed. Its sulfur content should be below about 0.01% by weight, and preferably below about 0.001%. Suit-able feedstocks for the pretreatment step include for example sulfur-free naphthas, gasolines, gas oils, kerosene, etc. Preferably, a portion of the same feedstock which is ultimately to be hydrocracked is utilized for the pretreatment step. If such feedstock contains more than about 0.01% sulfur, it will of course be necessary to subject it to a desulfurization'treatment, as by hydrofim'ng, before using it in the pretreatment step.

The conditions of pretreatment may be the same as those employed in the subsequent hydnocracking operation, but this is not essential, for any conditions of pressure and temperature may be employed at which the pretreatment feed undergoes a substantial hydrocracking. Temperatures between about 500 and 1000 F. may be used, and preferably between about 600 and 850 F. Hydrogen is normally included with the feed to the pretreatment step in ratios between about 200 and 10,000 s.c.f./bbl. of feed, and at total pressures between about and 5,000 p.s.i.g., preferably between about 500 and 3,000 p.s.i.g. Space velocities may vary between about OJ]. and 10. The foregoing conditions are not intended to be limiting in scope, but merely to indicate permissible operating ranges, and it will be understood that the conditions should be correlated with each other so that whatever the feedstock and catalyst being used, there will be a substantial hydrocracking taking place. Any degree, i.e., time, of pretreatment under the foregoing conditions will effect some improvement in the activity and efiiciency of the catalyst when subsequently sulfided and used for hydrocracking, but it is preferred to continue the pretreatment for at least about one hour, and up to about 100 hours or more, under conditions involving the conversion of about 70 volume-percent of the feed to products boiling below the initial boiling point of the feedstock.

Following the sweet-feed pretreatment step, the catalyst may be utilized directly for hydrocracking a sulfur-containing feed, or it may be subjected to a presulfiding step wherein hydrogen sulfide (preferably diluted with other gases such as hydrogen, nitrogen, methane, etc.), or some other decomposable sulfur compound such as carbon disulficle, is contacted with the catalyst in. order to effect a substantially complete s-ulfiding of the composition. In some cases it is bound that a separate presulfiding operation is desirable, in preference to allowing the sulfiding to proceed concurrently with hydrocracking of a sulfurcontaining feed. However, the sweet-feed pretreatment appears to minimize any resulting differences in activity between the catalysts which are separately presulfided, or sulfided during hydrocracking.

Hydrocr-acking conditions to be employed herein (following the pretreatment step) fall within the following ranges:

TABLE 1 I Operative Preferred Temperature, F 600-800 Pressure, p.s.i.g 750-2 000 HZ/Oll ratio, soriBB 2, 000-: 000 LHSV o. 5-5

The lower temperature ranges from about 400 to 600 F. are norm-ally operable only for the catalysts which contain an added halogen component. Those skilled in the art will understand that the combination of conditions selected should be correlated with the particular feedstock and catalyst used, to obtain the desired conversion per pass, normally between about and 70% by volume of the feed. Ordinarily, about 500 to 3,000 s.c.f. of hydrogen per barrel of gasoline produced is consumed during the hydrocracking. Conversion is measured in terms of volumes of original feed converted per volume of feed taken, times 100.

The following examples are cited to illustrate the invention and the results obtainable, but are not to be construed as limiting in scope.

Example 1 Two comparative experimental hydrocracking runs were carried out; in run A thesweet-feed pretreatment of this invention was employed, while in run B the catalyst was directly sulfided by contacting with a sulfur-containing feedstock. In each run, the catalyst contained about 4% of nickel, coprecipitated as the hydrous oxide upon a cracking base containing silica, zirconia, and titania in the weight ratio :of 20:50:30 (all four components were coprecipitated from aqueous solution at a pH of about 8.5). The resulting coprecipitated catalyst was then drained, washed and dried and calcined at 900 F. for about 5 hours. Following the calcining treatment, the catalyst was reduced in a flowing stream of hydrogen for 2 hours at 730 F.

The feedstock utilized in both runs was a coker distillate gas oil boiling between about 430 and 550 R, which had been subjected to a previous hydrofining treatment. This hydrofined feedstock contained less than 1 part per million nitrogen, and about 0.002% by weight of sulfur, and had a gravity of 372 API. This feedstock was hence essentially free of sulfur, and was utilized as such for the pretreatment portion of run A. The feed utilized throughout in run B, and for the portion of run A following the pretreatment step, consisted of the same feedstock to which had been added 2% by volume of carbon disulfide. The conditions employed throughout for hydrocracking and for pretreatment were the same, viz, pressure 1,500 p.s.i.g., average bed temperatures 730 F.; hydrogen feed rate 8,000 s.c.f. per barrel of feed; liquid hourly space velocity 2.0. The pretreatment in run A consisted in feeding the low-sulfur feedstock over the catalyst for 26 hours. Following the pretreatment in run A, the carbon disulfide-containing feed was subjected to hydrocracking over the respective catalysts for total run lengths amounting to several days in each case. The results [of the respective runs were as follows:

TABLE 2 Run A Bun B (catalyst (no pl'epretreated) treatment) Total conversion, vol. percent of feed 1 54. 8 44.0 Yields, vol. percent of feed:

To 0 gasoline 62. 6 50. 4 To 06+ gasoline- 46. 2 36.8 10 RVP gasoline 54. 7 45.8 Product characteristics:

A. 10 RVP gasoline: Research octane (+3 ml. TEL) 90. 7 90.8 B. 0 gasoline, vol. percent:

Total paralfins 38 24 Isoparaifins 34 13 n-Paraflins 4 11 Total naphthenes 44 55 Total aromatics 18 21 1 Conversions and yields based on CSz-free feed,

It will thus be apparent that the pretreated catalyst gave markedly superior results in terms of overall conversion and yields. Moreover, the isoto normal paratfin ratio in the C gasoline from the pretreated catalyst run was 8.5, as compared to a ratio :of 1.2 in the corresponding product from run B, demonstrating a remarkable superiority of the pretreated catalyst in this respect.

Example 11 Following the runs described in Example I, the respective catalysts were then employed for hydrocrackin-g the same feed (containing 2 volume-percent of carbon disulfide), under the same conditions except that a higher temperature of 760 F. was employed. The results were as follows:

1 Efficiency equals percent of total feed converted which was recovered as gasoline.

It is thus apparent that at higher temperatures, there is still an improvement in overall conversion, and a marked improvement in conversion efficiencies to the desired products.

Upon continuing the foregoing runs under the same conditions, but using in each case the original CS -free feed, the rehative superiority of the pretreated catalyst of Run A is again observed, with respect to activity, selectivity and iso/nor mal parafiin ratio.

When other hydrocracking catalysts such as nickel sulfide or cobalt sulfide supported on silica-alumina, are substituted in the foregoing examples, generally similar differential results are obtained, with respect to the effect of the pretreatment upon conversions, efficiencies, and isoto normal paraffin ratios. It is therefore not intended that the invention should be limited to the details described above since many variations may be made by those skilled in the art without departing from. the scope or spirit of the following claims.

I claim:

1. An improved process for the hydrocracking of a mineral oil feedstock which comprises: contacting said feedstock plus added hydrogen with a hydrocracking catalyst under hydrocracking conditions, said catalyst comprising a sulfided transitional metal hydrogenating component supported on a solid refractory oxide cracking base, said catalyst having been subjected before sulfiding to a pretreatment contacting with a hydrocarbon pretreatment feedstock containing less than about 0.01% by weight of sulfur, said pretreatment contacting having 'been carried out under hydrocracking conditions at a temperature between about 500 and 1,000 F. and in the presence of at least about 200 s.c.f. of hydrogen per barrel of pretreat ment feed.

2. A process as defined in claim 1 wherein said pretreatment was continued for between about 1 and 100 hours under hydrocracking conditions adjusted to convert about 5 to 70 volume-percent of the sulfur-free feed to products boiling below the intial boiling point of said sulfur-free feedstock.

3. A process as defined in claim 1 wherein said hydrocracking catalyst is essentially a silica-Zirconia-titania hydrocracking base containing a minor proportion of a hydrogenating promoter selected from the class consisting of the sulfides of nickel and cobalt.

4. A process as defined in claim 1 wherein said mineral oil feedstock contains between about 0.01 and 5% by weight of sulfur.

5. A process as defined in claim 1 wherein said mineral oil feedstock is a cracked oil boiling between about 400 and 650 F., and containing between about 0.01 and 5% by weight of sulfur.

6. A process as defined in claim 1 wherein said hydrocracking of mineral oil feedstock is carried out at a temperature between about 600 and 800 F., a pressure betweeen about 750 and 2,000 p.s.i.g., a hydrogen to oil ratio between about 2,000 and 10,000 -s.c.f. per barrel of feed, and at a space velocity between about 0.5 and 5.

7. A process for converting a gas oil feedstock boiling between about 400 and 750 F. to gasoline-boiling-range hydrocarbons, which comprises subjecting said feedstock to catalytic hydrocracking in the presence of added hydrogen and a hydroc-racking catalyst and under hydrocracking conditions, said hydrocracking catalyst comprising a minor proportion of a sulfided transitional metal hydrogenating component, and a major proportion of a solid refractory oxide cracking base, said hydrocracking catalyst having been subjected before sulfiding to a hydrogen-reduction treatment, and to a pretreatment contacting with a hydrocarbon pretreatment feedstock containing less than about 0.01% by weight of sulfur, said pretreatment contacting having been carried out under hydrocracking conditions at a temperature between about 500 and 1,000" F. and in the presence of at least about 200 s.c.f. of hydrogen per barrel of pretreatment feed.

8. A process as defined in claim 7 wherein said hydro gen-reduction treatment and said pretreatment contacting are carried out simultaneously.

9. A process as defined in claim 7 wherein said hydrogen-reduction treatment is carried out prior to said pretreatment contacting.

10. A process as defined in claim 7 wherein said pretreatment was continued for between about 1 and 100 hours under hydrocracking conditions adjusted to convert about 5 to volume-percent of the sulfur-free feed to products boiling below the initial boiling point of said sulfur-free feedstock.

11. A process as defined in claim 7 wherein said hydrocracking catalyst is essentially a silica-zirconia-titania hydrocracking base containing a minor proportion of a hydrogenating promoter selected from the class consisting of the sulfides of nickel and cobalt.

12. A process as defined in claim 7 wherein said gas oil feedstock contains between about 0.01 and 5% by weight of sulfur.

References Cited in the file of this patent UNITED STATES PATENTS Doumani July 28, 1959

Claims (1)

1. 7. A PROCESS FOR CONVERTING A GAS OIL FEEDSTOCK BOILING BETWEEN ABOUT 400* AND 750*F. TO GASOLINE-BOILING-RANGE HYDROCARBONS, WHICH COMPRISES SUBJECTING SAID FEEDSTOCK TO CATALYTIC HYDROCRAKING IN THE PRESENCE OF ADDED HYDROGEN AND A HYDROCRACKING CATALYST AND UNDER HYDROCRACKING CONDITIONS, SAID HYDROCRACKING CATALYST COMPRISING A MINOR PORPORTION OF A SULFIDED TRANSITIONAL METAL HYDROGENATING COMPONENT, AND A MAJOR PROPORTION OF A SOLID REFRACTORY OXIDE CRACKING BASE, SAID HYDROCRACKING CATALYST HAVING BEEN SUBJECTED BEFORE SULFIDING TO A HYDROGEN-REDUCTION TREATMENT, AND TO A PRETREATMENT CONTACTING WITH A HYDROCARBON PRETREATMENT, FEEDSTOCK CONTAINING LESS THAN ABOUT 0.01% BY WEIGHT OF SULFUR, SAID PRETREATMENT CONTACTING HAVING BEEN CARRIED OUT UNDER HYDROCRACKING CONDITIONS AT A TEMPRATURE BETWEEN ABOUT 500 AND 1,000*F. AND IN THE PRESENCE OF AT LAST ABOUT 200 S.C.F. OF HYDROGEN PER BARREL OF PRETREATMENT FEED.