US2761817A - Hydrodesulfurization process with precoditioned catalyst - Google Patents

Description

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United States Patent Ufifice 2,761,817 Patented Sept. 4, 1956 HYDRODESULFURIZATION PROCESS WITH PRECONDITIONED CATALYST Sumner B. Sweetser, Cranford, and Stanley 0. Bronson H, Mountainside, N. J., assignors to Esso Research and Engineering Company, a corporation of Delaware N Drawing. Application June 21, 1954, Serial N0. 438,362

8 Claims. (Cl. 19628) The present invention concerns an improved process for the desulfnrization of petroleum fractions that contain relatively large amounts of sulfur. It particularly relates to a desulfurization process in which a petroleum fraction containing in excess of about 1.5 wt. per cent sulfur is hydrodesulfun'zed in the presence of a cobalt molybdate-type catalyst. It especially concerns a method of presulfiding a cobalt molybdate catalyst in situ so that the catalyst is markedly more active in its ability to desulfnzize a high-sulfur content feed stock. The catalyst of particular interest to the present invention is cobalt molybdate impregnated on alumina.

It is well known in the petroleum industry to reduce the sulfur content of a petroleum fraction by subjecting the fraction to a hydrodesulfurization operation. In this process, a sulfur-containing petroleum fraction is contacted with a catalyst such as cobalt molybdate on alumina at a temperature of about 650 to 800 F. and a pressure of about 100 to 1000 p. s. i. g. The petroleum fraction is fed to the hydrodesulfurization zone at a rate of about 0.25 to 3.0 volumes of feed per hour per volume of catalyst. Hydrogen-containing gas is also passed through the zone at rates of between 500 and 5000 s. c. f./-bbl. of feed. Under these conditions some hydrogen is generally consumed by the process. Hydrogen consumption rates are usually in a range of 75 to 700 s. c. f./bbl. of feed and may be even as high as 1000 s. c. f./bbl. of feed. The hydrogen consumed in the process is considered to react with unsaturated compounds in the feed to form more saturated compounds and with sulfur to form hydrogen sulfide.

The hydrodesulfurization process may be employed on petroleum fractions that exist within the desulfurization zone in the liquid and/ or vapor phase. Thus, petroleum fractions including naphtha, fuel oil, kerosene, gas oil, diesel fuel, jet fuel and the like may be subjected to a hydrodesulfurization operation. Similarly, feed stocks derived from cracking operations may be employed as well as straight-run fractions that are derived directly from a crude oil.

The hydrodesulfurizati-on process causes sulfur compounds within a petroleum fraction to react with hydrogen to form hydrogen sulfide. The hydrogen sulfide and other gaseous components are separated from. the product stream and handled as desired. In many instances, the gaseous components are scrubbed with an ethanolamine solution which serves to remove any hydrogen sulfide therefrom.

As the hydrodesulfurization process proceeds, the catalyst may gradually deactivate and in such a case, it will have to be periodically regenerated by burning oi the carbon deposited on the catalyst. This is done by passing an oxygen-containing gas through the catalyst at a temperature of between 800 to 1100 F. and a pressure of between 0 to 400 p. s. i. g. The regenerating gas may contain about 1 to 21 volume per cent oxygen obtained fromlair and is generally diluted with either recycled flue gas or steam. The main problem in such a regeneration is the economic removal of the heat of burning. A longer interval between necessary regeneration permits a slower burning rate and consequently less expensive provisions for heat removal. It thus follows that any gainin catalyst initial activity which permits a longer operation between necessary regenerations, will be particularly desirable.

To date, it has not been the practice to presulfide a cobalt rnolybdate catalyst before employing the catalyst to desulfurize a petroleum feedstock. This has been particularly true in those instances where the feedstock contains more than about 0.15 wt. per cent sulfur. When the feedstock contains less than this amount of sulfur, it has been an occasional practice to presulfide the catalyst by first contacting it with a petroleum fraction containing more sulfur than the feedstock itself. Specifically, petroleum fractions containing from about 0.25 to 0.50 wt. per cent sulfur and especially about 0.50% have been used for this purpose.

The presulfiding or activating step has been generally carried out at temperatures of about 550700 F., pressures of about 100 to 1000 p. s. i. g. and feed rates of about 0.5-2 volumes of feed per hour per volume of catalyst. The duration of the presulfiding step has been governed by the fact that a catalyst of the cobalt molybdate type is generally most active when it is partially sulfided. When sulfiding under the conditions described above, it has been usually desirable to employ sulfiding times between about 12 and 48 hours duration.

Up to the present time, presulfiding of a cobalt molybdate catalyst has not been employed when the catalyst is to be used in the hydrodesulfurization of petroleum feedstocks that contain in excess of about 0.15% sulfur. Instead, such a feedstock is contacted directly with the cata lyst under conventional hydrodesulfurization conditions. This procedure has been especially true for feedstocks that possess in excess of 1.5% to 2% sulfur.

As mentioned earlier, the present invention is concerned with the hydrodesulfurization of high-sulfur content petroleum fractions that contain in excess of about 1.5% by weight sulfur. It is particularly concerned with petroleum fractions which contain about 2 to 6 Wt. per cent sulfur; and it is a particular object of the invention to render cobalt-molybdate type catalysts more active for the desulfurization of such feed stocks. It is a further object of the present invention to provide a means for increasing the activity of cobalt-molybdateon alumina for desulfurizing .a high sulfur content petroleum fraction in a hydrodesulfurizatiou operation which utilizes an activated cobalt molybdate-type catalyst. As described earlier, particularly elfective catalysts for this purpose are formed by the impregnation of alumina with cobalt mclybdate. Such catalysts are Well known in the art and are conventionally prepared, for example, by impregnating alumina with an ammoniacal solution of cobalt and molybdenum salts. The catalyst is dried and decomposed to convert the cobalt and molybdenum salts to the oxides.

Before employing a catalyst of the type described above in the hydrodesulfurization of a high-sulfur feedstock, the

catalystin accordance with the present inventionis first contacted and presulfided with a petroleum fraction which contains about 0.2 to 1.0 wt. per cent sulfur and preferably about 0.5 wt. per cent sulfur. The hydrocarbon fraction may boil in a range of about 300 to 700 F., and it is preferred that the fraction boil from about 330 to 550 F. The fraction may contain straight-run hydrocarbons as well as hydrocarbons that are derived from cracking operations. It is preferred, however, that the petroleum fractions be characterized by possessing from about to 110 mgs. of mercaptan sulfur per 1111. Straight run fractions that contain about 99 mgs. of mercaptan sulfur per 100 ml. have been found to be especially effective.

In accordance with the present invention, a cobalt molybdate on alumina catalyst is presulfided by contacting it with a hydrocarbon fraction of the type described immediately above. It is preferred that the hydrocarbon fraction be passed through the catalyst at a feed rate between about 0.5 and 2.0 volumes of feed per hour per volume'of catalyst. A particularly preferred feed rate is about 1.0 v./h./v. An operating temperature of about 550 to 650 F. and an operating pressure of about 100 to 250 p. s. i. g. may be employed. It is particularly preferred that an operating temperature of about 600 F. and a pressure of about 200 p. i. g. be employed. The hydrocarbon fraction may be in the liquid andor vapor phase during the presulfiding step; and it may be passed upflow or downflow through the bed. Particularly effective results have been obtained with about 80% of the fraction in the vapor phase within the reaction zone and with downflow operation.

When the presulfiding operation is'initiated, it has been observed by chemical analyses that the product stream generally shows very little desulfurization. After a short period of time, however, the catalyst begins to combine with the sulfur in the presulfiding feed; and analyses of the product stream reveal a gradually increasing degree of desulfurization taking place. After about 12 to 36 hours of the presulfiding operation, it has been found that the degree of desulfurization of the presulfiding feed reaches an equilibrium value. In other words, the sulfur content of the product stream settles out at a substantially constant value. At this point the catalyst, which may contain from 15% to 65% by weight of the sulfur that would be required if all of the cobalt molybdate were converted to the thiomolybdate, is activated; and the desulfurization operation is commenced.

During the presulfiding operation it is desired that a hydrogen rate to the reaction zone of about 500 to 3000 s. c. f./bbl. of feed be utilized. It is particularly preferred that a hydrogen rate of about 1000 s. c. f./bbl. be used.

Following the presulfiding step, a feed stock to be desulfurized is passed through the bed of presulfided catalyst. As mentioned earlier, a catalyst which'has' been presulfided according to the present invention, is particularly effective for use in the hydrodesulfurization of petroleum fractions that contain in excess of about 1.5 wt. per cent sulfur and especially about 2 to. 4.5 wt. per cent sulfur. Such a feed stock is passed through the presulfided catalyst at a rate of about 0.253.0 volumes of feed/hour/volume of catalyst (v./hr./v.) at a temperature of about 650800 F. and a pressure of about 1!00l000 p. s. i. g. A hydrogen feed rate of about 500-5000 s. c. f./bbl. of feed should. be employed.

Regeneration of the catalyst may be required periodically, depending largely upon the nature of the feed stock. Some feed stocks such as straight-run distillate petroleum fractions cause very little or no degradation of the catalyst; and the catalyst may be employed in such, cases for months without regeneration. Indeed, frequently no rcgeneration is required. Feed stocks derived from cracking or coking operations, on the other hand, degrade a catalyst much more rapidly, and more frequent regenerationsvare therefore necessary. Even in these instances, however, the catalyst need almost never be regenerated more than once a week. But whenever a catalyst is regenerated, it is generally desirable to reactivate the catalyst by the present presulfiding procedure before it is returned to hydrodesulfurization service. A

The present invention may be better understood by reference to the following examples which illustrate specific examples of the invention'and preferred modes of carrying out the same.

Example I A conventional cobalt molybdate on alumina catalyst in the form of A x 4 cylindrical pills was charged to a reaction zone. Here the pills were presulfided by contact with a West Texas light straight-run heating oil.

The heating oil had a boiling range of about 330530 F., an A. P. I. gravity of about 39, a sulfur content of about 0.5 wt. per cent and contained about 99 mgs. of

mercaptan sulfur per 100 ml. The heating oil was passed through the catalyst in a downflow operation at 600 F., 200 p.- s. i. g. and 1 v./hr./v. for a period of 24 hours.

The 24 hour time had been selected on the basis of preoil, the catalyst was then contacted in a downfiow manner with a coker gas oil possessing a boiling range of 430- 1050 R, an API gravity of about 15, and a sulfur content of about 4 wt. per cent. The coker gas oil was derived by conventional fluid coking at 1000 F. of a 1050 F.+ residuum from a West Texas crude. The

residuum comprised about of the total crude;

It will be noted that the feed rate of the various liquid fractions to the catalyst zone is expressed in this example and throughout the present description in terms of volumes of liquid/hour/volume of catalyst. A hydrogenfeed rate of about 3500 s. c. f./bbl. of coker gas oil was employed during the hydrodesulfurization reaction. The reaction additionally was carried out at a temperature of 750 F., a pressure of 400 p. s. i. g. and feed rate of 0.5 v./h r./v. As a result of this treatment, the sulfur content of the coker gas oil was reduced from the initial value of 4 wt. per cent to a value of about 0.40 wt. per cent.

. required.

realized in Example 1.

Example 11 those presented in Example I. In this instance, however,

the catalyst was not first activated by treatment with'the straight-run heating oil. Instead, it was initially and directly contacted with the coker gas oil. In the absence of the pretreatment with the virgin heating oil, the coker gas oil experienced a sulfur reduction to a value of only 0.49 wt. per cent instead of the 0.40 wt. per cent value It is apparent from these data that the presulfiding step employing the Virgin heating oil is .very effective in increasing the activity of the catalyst.

Example III In this example, samples of a West Texas heavy straight-run gas oil of 24.4 API gravity and a 500 to 1050 F, boiling range were hydrosulfurized over a cobalt molybdate on alumina catalyst (of the type in Examples I and II) with and without pretreatment with a West Texas light straight-run heating oil. Thus, in a first procedure a sample of the heavy gas oil was passed directly and downflow through a bed of the catalyst at 700 F., 400 p. s. i. g., 1.0 v./hr./v. and at a hydrogen rate of 1500 s. 'c. f./bbl. of feed. Under these conditions the heavy gas .oil experienced a sulfur reduction from 2.1 wt. per cent sulfur to 0.16 wt. per cent sulfur. The gas oil further experienced an increase in gravity up to a value of 28.7 API.

In a second treating procedure, the catalyst was first contacted for 24 hours with a West Texas light straightrun heating oil (39 API, 330540 F. boiling range and 0.5 wt. per cent sulfur and 99 mgs. of mercaptan sulfur perl00 ml.) at 600 F., 200 p. s. i. g., 1 v./hr./v. and 1000 s. c. f./bbl. hydrogen rate. Following this pretreatment procedure, the catalyst was then contacted with The run was terminated before regeneration was another portion of the West Texas heavy straight-run gas oil under the same hydrodesulfurization conditions described earlier in this example. In this instance, however, the heavy gas oil realized a sulfur reduction to 0.11 wt. per cent sulfur, thereby demonstrating the marked eflectiveness of the presulfiding procedure in increasing the activity of the catalyst.

The foregoing examples are intended to illustrate specific applications of the present invention. It will be understood that the present invention is not to be limited, however, in its scope to these particular examples. Thus, it will be noted that the presulfiding and hydrodesulfurizing reactions of the present invention may be employed using fixed beds, moving beds or fluidized beds of catalyst. Such modifications of the invention are considered to be well within the ability of persons skilled in the art to realize.

It will further be appreciated that the catalyst may be employed in structural forms other than the x 75 cylindrical pills presented in the examples. Furthermore,

the catalyst may contain a small amount of silica to stabilize it in a manner known to those skilled in the art.

It will further be realized that the present invention may be used in combination with other petroleum refining processes such as catalytic processes including hydroforming, platforming, cracking, and the like. It is particularly contemplated that gas oil fi'actions derived from the present desulfurization process be employed as feed stocks to catalytic cracking operations.

Piping, pumps, valves, instruments, heat exchangers,

furnaces and other equipment conventionally employed to operate hydrodesulfurization processes may be utilized without departing from the spirit or scope of the present invention. Similarly, the hydrogen utilized in the present process may be derived from any of the production sources that are contemplated for use in connection with hydrodesulfurization processes.

What is claimed is:

1. In the catalytic hydrodesulfurization of a petroleum feedstock containing from 2-6 wt. per cent sulfur with the aid of a cobalt molybdate-type catalyst, the improvement of which comprises contacting the catalyst at about 300-700" F. and 100-250 p. s. i. g. for about 12-36 hours with about 0.5 to 2.0 v./hr./v. of a petroleum fraction which boils within the range of about 330-550 F. and which contains about 0.5 wt. per cent sulfur, said fraction further being characterized by containing about 90-110 mgs. of mercaptan sulfur per 100 ml. of said fraction, said preactivating being carried out in the presence of about 1000 s. c. f. of Hz/bbl. of fraction and thereafter treating a petroleum feed stock containing from 2 to 6 wt. per cent sulfur in contact with said reactivated catalyst under hydrodesulfurizing conditions at temperatures above about 650 F.

2. In the hydrodesulfurization of petroleum feedstocks which contain about 24.5 wt. per cent sulfur by means of a cobalt molybdate-type hydrodesulfurization catalyst,

the improvement which comprises contacting the catalyst with a petroleum fraction that boils within the range of about 330-550 F., said fraction containing about 0.5 wt. per cent sulfur and about 99 mgs. of mercaptan sulfur per 100 ml., said fraction being contacted with said catalyst at about 600 F. and 200 p. s. i. g. at 1.0 v./hr./v. in the presence of about 1000 s. c. f. of hydrogen per barrel of petroleum fraction for about 12-36 hours and thereafter treating a petroleum feed stock containing from 2 to 6 wt. per cent sulfur in contact with said reactivated catalyst under hydrodesulfurizing conditions at temperatures above about 650 F.

3. Process as defined in claim 2 in which the fraction used for preactivating the catalyst consists of straight-run hydrocarbons and the feed stock consists of cracked hydrocarbons.

4. Process as defined in claim 1 in which the sulfided catalyst contains from 15 to wt. per cent of the sulfur theoretically required to change the cobalt molybdate to cobalt thiomolybdate.

5. Process as defined in claim 2 in which the presulfiding is carried out for a period of about 24 hours.

6. The method of catalytically hydrodesulfurizing a high-sulfur content petroleum feedstock with a cobalt molybdate-type catalyst which comprises in combination presulfiding the catalyst in a reaction zone at about 550-650 R, 100-250 p. s. i. g. and 0.5-2.0 v./hr./v. with a first petroleum fraction which boils Within the range of about 300-700 F. and which contains about 0.2 to 1.0 wt. per cent sulfur, said fraction being further characterized by containing about -100 mgs; of mercaptan sulfur per ml. of fraction, said catalyst being sulfided in the presence of about 500 to 3000 s. c. f. of Hz/bbl. of fraction until the degree of desulfurization of the fraction reaches an equilibrium value, thereafter passing a second petroleum fraction comprising the highsulfur feedstock containing in excess of 1.5 wt. per cent sulfur through the presulfided catalyst at a rate of about 0.25 to 3.0 v./hr./v., a temperature of 650-800 F. and a pressure of 100-1000 p. s. i .g. in the presence of from 500-5000 s. c. f. of Ha/bbl. of feedstock.

7. A process as defined in claim 6 in which the said first petroleum fraction contains about 0.5 wt. per cent sulfur and the feedstock contains about 2 to 4.5 wt. per cent sulfur.

8. A process as defined in claim 7 in which the said first petroleum fraction contains about 99 mgs. of mercaptan sulfur per 100 m1. of said fraction.

References Cited in the file of this patent UNITED STATES PATENTS 2,143,078 Lyman et al. Jan. 10, 1939 2,337,358 Szayna Dec. 21, 1943 2,604,438 Bannerot July 22, 1952 2,647,857 Home Aug. 4, 1953 2,656,302 Porter et al. Oct. 20, 1953

Claims (1)

1. IN THE CATALYTIC HYDRODESULFURIZATION OF A PETROLEUM FEEDSTOCK CONTAINING FROM 2-6 WT. PER CENT SULFUR WITH THE AID OF A COBLAT MOLYBDATE-TYPE CATALYST, THE IMPROVEMENT OF WHICH COMPRISES CONTACTING THE CATALYST AT ABOUT 300-700* F. AND 100-250 P. S. I. G. FOR ABOUT 12-36 HOURS WITH ABOUT 0.5 TO 2.0 V./HR./V. OF A PETROLEUM FRACTION WHICH BOILS WITHIN THE RANGE OF ABOUT 330 550* F. AND WHICH CONTAINS ABOUT 0.5 WT, PER CENT SULFUR, SAID FRACTION FURTHER BEING CHARACTERIZED BY CONTAINING ABOUT 90-110 MGS, OF MERCAPTAN SULFUR PER 100 OF SAID FRACTION, SAID PERACTIVATING BEING CARRIED OUT TO THE PRES ENCE OF ABOUT 1000 S. C. F. OF H2/BBL OF FRACTION AND THEREAFTER TREATING A PETROLEUM FEED STOCK CONTAINING FROM 2 TO 6 ET. PER CENT SULFUR IN CONTACT WITH SAID REACTIVATED CATALYST UNDER HYDRODESULFURIZING CONDITIONS AT TEMPERATURES ABOVE ABOUT 650* F.