US3528910A - Hydrotreating process utilizing alkyl disulfide for in situ catalyst activation - Google Patents

Description

United States Patent C U.S. Cl. 208216 4 Claims ABSTRACT OF THE DISCLOSURE A process for activating and initiating reaction on a nickel-molybdenum hydrotreating catalyst, which provides superior aromatic saturation and nitrogen and sulfur removal, is provided by the steps of treating the catalyst with hydrogen at low pressure while heating to about 350 F., pressurizing to about 300-2500 p.s.i.g. and sulfiding with a hydrocarbon stock containing about 1 to 5% disulfide sulfur with a hydrogen flow rate of about 1000-2500 s.c.f./b., at a temperature of about 675- 700 F., taking care that the temperature does not exceed 750 F. at any point in the reactor. Processing is then initiated with a substantial excess of hydrogen for the first 24 to 72 hours.

This invention relates to a process for the catalytic hydrotreating of hydrocarbon oils of at least 90% by volume boiling above about 300 C. More particularly, it relates to a process for the catalytic hydrotreating of hydrocarbon oils containing aromatic unsaturated constituents and sulfurand nitrogen-bearing compounds. Most particularly, it relates to a process whereby the activity of the hydrotreating catalyst is enhanced both for the hydrogenation of unsaturated constituents and the removal of sulfur and nitrogen atoms.

Various high boiling hydrocarbons have been hydrotreated under varying conditions of temperature, pressure, and contact time, depending on the particular catalyst and the particular oil feed, to effect a substantial conversion of the oil to lower boiling products. When carried out with this result, such operation is referred to as destructive hydrogenation or hydrocracking. This invention does not relate to such hydrotreating processes. While hydrocracking is desired in some processes, there are cases where it is undesirable and is avoided, e.g. in the hydrotreating of lubricating oil and the like.

Hydrotreating under conditions where not more than of the feed oil is converted to lower boiling products is often referred to as non-destructive hydrogenation or hydrotreating. There is usually at least a small amount of lower boiling material unavoidably produced due to the extraction of sulfur and nitrogen atoms from the sulfurand nitrogen-bearing compounds which are normally present in the feed, but lower boiling material is not desired. It is to such non-destructive hydrotreating processes that the present invention relates.

The non-destructive hydrogenation of hydrocarbon oils may be efiected in several ways. In one type of operation, for example, hydrocarbon oils containing aromatic unsaturated constituents and sulfurand nitrogen-bearing compounds are hydrotreated with a catalyst containing a metal or metal oxide which is capable of extracting and reacting with sulfur in the oil. The catalyst also serves to promote hydrogenation of unsaturated constituents and to remove nitrogen from the oils. In this type of process, which may be called regenerative, the process is stopped as soon as the metal has been substantially converted to the sulfide (as manifested in the appearance of hydrogen sulfide in the reactor efiluent), the catalyst is regenerated or roasted to convert the metal sulfide back to the active oxide or metallic form, and a new process period is then started. The process periods between successive regenerations of the catalyst are normally quite short. Since it is necessary to free the catalyst of oil preceding each regeneration, it is only practical to operate this type of process when treating low boiling, easily volatilized feeds or to ensure that the feed oil, if heavy, is completely volatilized by the use of a large amount of gas. This invention does not relate to such regenerative processes.

The more preferred type of hydrotreating process is one in which the oil and hydrogen gas are passed substantially continuously in contact with a fixed bed of a suitable hydrotreating catalyst. The processes to which the present invention relates are of this type, usually referred to as non-regenerative processing. And regeneration is only required after a relatively long period of continuous use, usually measured in a plurality of weeks or months.

The catalysts found suitable for the non-regenerative hydrotreating processes comprise one or more metals selected from Group VIII of the periodic chart of the elements and one or more metals of Group VI, and ordinarily are supported on an alumina or silica-alumina base. The metals may have been prepared initially in their metallic form or in the form of compounds with oxygen or sulfur. During use, however, they are present in an activated form as sulfides. Thus, the catalyst may be prepared from the metal sulfides, or it may be sulfided prior to use, or it may become sulfided during the initial stages of the process itself.

This process relates to hydrotreating catalysts comprising nickel and molybdenum as the active metal component. The particular catalysts are well known and are available commercially, as, for instance, American Cyanamids HDS-3 or HDS-3A, in the form of nickel and molybdenum oxides on an alumina or silica-alumina base. Such catalysts, when activated by conversion of the metal oxides to sulfides, are highly active both in the hydrogenation of aromatic constituents and in the removal of sulfur and nitrogen from the feed.

The nickel-molybdenum hydrotreating catalysts are significantly more sensitive than other hydrotreating catalysts, such as for instance cobalt-molybdenum or cobalttungsten, to the activation processes ordinarily employed to convert the metals to their sulfides. Difliculties are encountered in achieving full activity of the nickel-molybdenum catalysts, in that the nickel oxide component is readily reduced to the metallic form and, as such, is rendered almost incapable of conversion to the sulfide necessary to obtain the fullest activity. The activation processes known for the activation of nickel-molybdenum hydrotreating catalysts include sulfiding with a stream of hydrogen sulfide gas; a mixture of hydrogen sulfide and hydrogen; a mixture of hydrogen and a mercaptan, a sulfide, or a disulfide; a high sulfur content hydrocarbon stream; and the sulfur containing hydrocarbon feed to be processed. None of these processes has proved completely satisfactory in achieving the full activity of the catalyst and are decidedly inferior to the activation process of this invention, particularly in accomplishing saturation of aromatic carbon rings to the fullest extent.

In the process of the present invention, the catalyst is activated by contacting it in the hereinafter prescribed manner first with hydrogen alone and then with a mixture of hydrogen and a distillate of medium viscosity containing from about 1 to about 5 percent of disulfide sulfur. The particular sulfiding medium is not, however, alone sufl'icient in order to most effectively activate the catalyst.

3 It is additionally necessary to maintain process conditions within certain prescribed limits.

The process of the present invention comprises first purging the caltalyst bed of air. Ordinarily, the reactor containing the catalyst bed is evacuated and then the system is purged with nitrogen until the oxygen content is reduced to less than about 2%. Once the reactor system is purged, the nitrogen is displaced with hydrogen or a hydrogen-rich gas. The reactor is then heated to a temperature of about 350 F., preferably in as short a time as possible, at a hydrogen flow rate relative to a feed of processing stock or sulfiding medium at 0.4 WHSV of from about 1000 to 2500 s.c.f./b., and at a pressure not greater than about 50 p.s.i.g. When the temperature has reached about 400 F., the system is pressurized to about 300 to 2500 p.s.i.g. with the hydrogen gas. It is necessary not to create a pressure of greater than about 50 p.s.i.g. before attaining the 400 F. temperature to avoid entrapping water absorbed or adsorbed on the catalyst which will cause sintering and preclude satisfactory activation of the catalyst. When the reactor is fully pressurized at about 400 F., the sulfiding stock is cut in. The sulfiding stock preferably has a viscosity of about 30 to 100 S.S.U. at 100 F. and is a distillate containing from about 1 to 5 weight percent sulfur as disulfide compounds, e.g. R-S-S-R where R may be a methyl, ethyl, butyl or higher radical, or a mixture of such compounds. The feed should be passed through the reactor at about 0.25 to 1.0 WHSV and the hydrogen gas should be maintained at about the same rate of flow as before, or at 1.5-3 times the rate of consumption. The temperature is gradually increased at about 100 F. per hour from about 400 F. to about 675700 F., taking care that the temperature does not exceed 725 F. at any point in the reactor. Once the desired temperature is attained, the processing is continued for at least 6 hours, and preferably for 24 hours or even longer. The sulfiding medium is then cut out and the stock to be processed is fed at a WHSV of 0.2 to 5.0. The hydrogen rate is set at from about 300 to 5000 s.c.f./b. at the operating pressure of the process, or at least about twice the rate of consumption, and the temperature is maintained at the 675 F. to 700 F. range. Processing is continued under these conditions for at least about 48 hours, and preferably about 72 hours before conditions are altered to normal operating levels for the hydrotreating process.

When conducted as described, the process provides a nickel-molybdenum hydrotreating catalyst of exceptional activity, both for providing aromatic saturation and for the removal of sulfur and nitrogen.

EXAMPLES I-III A hydrotreating HDS-3A catalyst comprising 2.3 weight percent nickel oxide and 15.6 weight percent molybdenum oxide on an alumina support was activated by three different sulfiding processes. After activation, the catalyst from each process was utilized for hydrotreating a medium viscosity, non-waxy lube distillate feed, processed at 700 F. 0.25 WHSV, and with 1500 s.c.f./b. of hydrogen at 1500 p.s.i.g. The pertinent characteristics of the feedstock appear in Table I In the first process, the catalyst was reduced for 2 hours at 500 F. with hydrogen gas at atmospheric pressure with a flow of 20 s.c.f. of hydrogen per kilogram of catalyst. After the H reduction, the catalyst was treated with hydrocarbon feedstock at 700 F., 1500 p.s.i.g., and at 1.0 WHSV in the presence of 1500 s.c.f./b. for 193 hours of conditioning under process conditions, the reaction product was tested for catalyst activity reported below in Table I as process 1.

A second catalyst charge was purged with nitrogen and then pressurized to 80 p.s.i.g. with hydrogen. Under 10 s.c.f. of hydrogen per hour per kilogram of catalyst, the temperature was raised to 400 F. and 0.2 s.c.f. of

H S per hour per kilogram of catalyst was injected into the hydrogen stream for 24 hours. At the end of the sulfiding processing, the charge was conditioned for 24 hours with feedstock at 700 F., 1500 p.s.i.g., at 1.0 WHSV with 1500 s.c.f./b. of hydrogen and the product was tested with the results reported on Table I. under process 2.v

In the third process, after a nitrogen purge at low temperature, the catalyst charge was treated with hydrogen to bring the temperature to 400 F. with a flow rate of 10 s.c.f. hydrogen per kilogram of catalyst at atmospheric pressure. At the 400 F. temperature, the system was pressurized to 1500 p.s.i.g. and a light gas oil stock containing 5% disulfide sulfur at 0.4 WHSV and the hydrogen rate was adjusted to 1500 s.c.f./ b. The temperature was increased at F. per hour to a maximum of 700 F. and the processing was continued for 24 hours, and the sulfiding stock was then replaced with the hydrocarbon feed, the space velocity changed to- 0.25, and conditioning was continued for 48 hours before processingconditions were further altered. The hydrotreated stock was then tested and appears in Table I as process 3.

EXAMPLES IV-VI Three catalyst samples of a commercially available hydrotreating catalyst of nickel and molybdenum oxides on an alumina base were activated in the following manner. After purging with nitrogen, the catalyst beds were heated to 400 F. with a flow of 20 s.c.f. of hydrogen per kilogram of catalyst atmospheric pressure. The systems were then pressurized to 1500 p.s.i.g. and a light gas oil sulfiding stock containing 1.85% disulfide sulfur was passed through the reactor at 1.0 WHSV with 1500 s.c.f./ b. hydrogen. The temperature was increased at 100 F. per hour to 700 F. Two of the catalyst samples were permitted to exceed 750 F. for a short time during the sulfiding process, while the third was not allowed to exceed 725 F. at any time. The sulfiding was continued for 48 hours for the first overheated sample, reported as 4 in Table II, and the sample maintained at below 725 F reported as 6 in Table II. The remaining overheated sample, number 5 in Table II, was processed for 144 hours. At the conclusion of the sulfiding step, a medium viscosity, non-waxy lube distillate was introduced as feed on each catalyst and was processed at 700 F., 1500 p.s.i.g. and 0.25 WHSV with 1500 s.c.f./b. hydrogen. After 12 hours on stream, inspection tests on the nitrogen stripped product (to remove H 8) showed the results reported in Table II.

Comparison of the results of runs 4 and 5 with those of run 6 indicate the necessity of maintaining the catalyst at temperatures below 750 F. during the sulfiding step.

Even the increased processing time in run 5 did not serve to improve the activity of the overheated catalyst sample.

EXAMPLES VII-IX In the following Table III, a light, non-waxy lube distillate of about 60 SUS at 100 F. containing 5% disulfide sulfur was utilized as indicated as sulfiding stock. The feedstock processed was the same as in Table II, as were conditions of feedstock processing.

TABLE III Activation process 7 8 9 sulfidingprocess conditions:

WHS ,lb. /hr./lb. c 1.0 0. 25 0.40

Pressure, p.s.i.g 1, 500 1,500 1, 500

H2 rate, s.c.f.[b 2, 500 2, 500 1, 560

Temperature, F 650 650 650 Sulfiding time, hrs 48 48 48 Activity test:

Gravity, API 26. 27. 9 29. 0

Refractive index, no 1. 4860 1. 4827 1.4790

Specific dispersion 102. 6 105. 1 101. 0

Sulfur content, p.p.m 10 10 Nitrogen content, p.p.m 1. 8 2. 7 1. 8

Hydrogen content, wt. percent 13. 36 13. 31 13. 52

A comparison of the results indicates less than optimum activity in run 8. The lower space velocity in this run results possibly in exposure of the catalyst in the lower part of the bed to hot hydrogen which reduces nickel and/or molybdenum to the metallic form, rather than formation of the sulfide. In run 9, where a near optlmum is achieved, the hydrogen rate is balanced with the space velocity and sulfur content.

EXAMPLE X Example X illustrates a further requirement in the activation of the catalyst for hydrotreating, i.e., the manutenance of the hydrogen gas rate considerably in excess of the rate of consumption for a period of 24 to 72 hours after the initiating of feedstock processing at the conclusion of the sulfiding process. Hydrogen starvation has proved to permanently damage catalyst activity and aromatic saturation and nitrogen removal will be less than optimum. In Table IV, two processing runs are shown, utilizing the feed of Table II on two catalysts sulfided under identical conditions.

A comparison of the two runs, wherein the hydrogen gas rate is the only significant process variable, indicates about the same flush hydrocracking activity, as measured by API gravity, and sulfur removal. Run B, however, shows significantly better aromatic saturation and nitrogen removal.

It is claimed:

1. A process for hydrotreating a hydrocarbon stock in a system including a catalyst comprising nickel and molydenum oxides on a base selected from the group consisting of alumina and silica-alumina disposed in a hydrotreating zone comprising the steps of (a) contacting the catalyst in said hydrotreating zone with a flow of hydrogen gas while heating the catalyst to a temperature of about 350 F. with the pressure being not greater than about 50 p.s.i.g,

(b) increasing the pressure to about 300 to 2500 p.s.i.g,

(c) contacting said catalyst with hydrogen and a hydrocarbon gas oil or lube distillate sulfiding stock containing from about 1 to 5 weight percent sulfur as alkyl disulfide, the alkyl groups of which have 1 to 4 carbon atoms, at a WHSV of from about 0.25 to 1.0, a pressure of from about 300 to 2500 p.s.i.g, and a temperature of from about 675 to 700 F. with hydrogen at a flow rate of from about 1000 to 2500 s.c.f./b., said temperature never exceeding 750 F. in any part of the system, with the sulfiding step being maintained for a period of from about 24 to 72 hours,

((1) stopping the sulfiding stock, and

(e) passing said hydrocarbon feedstock in contact with said catalyst and hydrogen at a hydrogen flow rate of at least about 300 to 5000 s.c.f./b. for at least about 48 hours.

2. The process of claim 1 wherein the temperature of the sulfiding step never exceeds 725 F.

3. The process of claim 1 wherein the hydrocarbon feedstock which is subjected to hydrotreating is a hydrocarbon oil having at least by volume boiling above about 300 C.

4. The process of claim 1 wherein the hydrocarbon sulfiding stock has a viscosity of about 30 to S.S.U. at 100 F.

References Cited UNITED STATES PATENTS 3,016,347 1/ 1962 OHara.

3,109,804 11/1963 Martin 208216 3,114,701 12/1963 Jacobson et al 252439 3,239,450 3/ 1966 Lindquist et a1. 252--439 3,256,205 6/1966 Constabaris et a1. 252-415 3,291,751 12/1966 Buss 252439 3,364,150 1/1968 Hughes 252 439 DELBERT E. GANTZ, Primary Examiner G. J. CRASANAKIS, Assistant Examiner US. Cl. X.R. 208--254; 252-439