US3912621A - Hydro desulfurization of heavy petroleum oil at higher temperatures and space velocities - Google Patents

Abstract

Heavy hydrocarbon oils are effectively desulfurized with minimum hydrogen consumption by being contacted with a hydrodesulfurization catalyst under desulfurization conditions including a temperature between 750*F. and 850*F. and a space velocity between 3 and 10 v/v/hr.

Description

United States Patent [191 Kravitz et al.

[ Oct. 14, 1975 HYDRO DESULFURIZATION OF HEAVY PETROLEUM OIL AT HIGHER TEIVIPERATURES AND SPACE VELOCITIES [75] Inventors: Stanley Kravitz, Fishki11;Jitendra A.

Patel, Beacon, both of NY.

[73] Assignee: Texaco Inc., New York, NY.

[22] Filed: Dec. 7, 1973 [21] Appl. No.1 422,631

2,840,513 6/1958 Nathan 208/216 2,878,193 3/1959 Scott, Jr 208/216 2,880,171 3/1959 Flinn et a1..... 208/216 2,897,143 7/1959 Lester et a1 208/216 3,464,915 9/1969 Paterson et al. 208/216 Primary ExaminerDe1bert E. Gantz Assistant Examiner-G. J. Crasanakis Attorney, Agent, or Firm-T. H. Whaley; C. G. Ries; Robert Knox 57 ABSTRACT Heavy hydrocarbon oils are effectively desulfurized with minimum hydrogen consumption by being contacted with a hydrodesulfurization catalyst under desulfurization conditions including a temperature between 750F. and 850F. and a space velocity between 3 and 10 v/v/hr.

6 Claims, N0 Drawings HYDRO DESULFURIZATION OF HEAVY PETROLEUM OIL AT HIGHER TEMPERATURES AND SPACE VELOCITIES This invention relates to the desulfurization of petroleum fractions. More particularly, it is concerned with the catalytic hydrodesulfurization of heavy petroleum oils under conditions whereby the throughput and desulfurization of a unit are increased and the hydrogen consumption in the desulfurization procedure is reduced.

The catalytic desulfurization of petroleum hydrocarbons has been well known in the industry for many years. It has been discussed quite thoroughly in Petroleum Processing November 1956, pages 116-138. The literature discloses reaction conditions using fixed beds of catalysts in the broad ranges of temperatures of from 400-900F., pressures of from 50-5000 psig, hydrogen rates of from 20020,000 standard cubic feet per barrel (scfb) and space velocities of 01-20 volumes of oil per volume of catalyst per hour (v/v/hr.)

Experience has shown that in the commercial desulfurization of heavy oils such as vacuum gas oils and heavier stocks, that is, oils having an initial boiling point of about 625F. or higher, using fixed beds and conventional desulfurization catalysts, the start-of-run temperature using fresh or freshly regenerated catalyst will be between about 625 and 650F. and the end-ofrun temperature will be about 750F., a gradual increase being made to compensate for loss of activity of the catalyst throughout the onstream period. Pressures range generally between about 500 and 1000 psig with hydrogen rates of about 500-2000 scfb. Ordinarily in conventional commercial units the space velocity is controlled to obtain the desired amount of desulfurization with 85-90% desulfurization being considered as the most practical from an efficiency standpoint.

It has been generally accepted in the industry that high temperatures result in shortened catalyst life due to loss of activity on the part of the catalyst through deposition of carbon and, in the case of residuecontaining charge stocks, metal-containing compounds on the surface of the catalyst particles. It has also been generally accepted that hydrogen consumption is a function of the amount of desulfurization and that as the percentage desulfurization increases so does the amount of hydrogen consumed. It is also a general belief in the industry that, other things being equal, a decrease in space velocity is required to obtain an increase in desulfurization.

For ecological reasons, it has become necessary for refineries to treat more and more petroleum fractions to reduce the sulfur content thereof thus making desulfurization costs enormous, not only in the amount of equipment that must be built but also in the costs of processing the various petroleum fractions, not the least of which is the cost of hydrogen consumed. It has been ascertained that process improvements leading to a reduction in hydrogen consumption of 100 scfb of an increase in desulfurization from 90 to 95% or a reduction in pour point of 40F. would result in a great economic improvement over current operations.

According to our invention, the efficiency of a hydrodesulfurization unit is improved by contacting a sulfurcontaining petroleum oil having an initial boiling point of at least about 625F. with a desulfurization catalyst at a temperature between 750 and 850F., a pressure between about 500 and 3000 psig and a space velocity between 3 and 10, preferably 4-8 v/v/hr. in the presence of added hydrogen in an amount between about 500 and 5000 scfb.

The feed used in the process of our invention is a heavy petroleum oil fraction having an initial boiling point of at least about 625F. Non-limiting examples of such feeds are gas oils such as vacuum gas oils, atmospheric residua, vacuum residua, coker distillates, coal tar distillates and gas oils obtained from shale, tar sand and the like.

The hydrogen used in the process of our invention may be obtained from any suitable source such as reformer by-product hydrogen, hydrogen produced by the partial oxidation of carbonaceous or hydrocarbonaceous materials followed by shift conversion and CO removal or electrolytic hydrogen are satisfactory. The hydrogen should have a purity of at least 50% and preferably at least 65% by volume.

The catalyst used in the process of our invention generally comprises a Group VIII metal such as an iron group metal or compound thereof optionally composited with a Group VI metal or compound thereof on a refractory inorganic oxide support. Suitable Group VIII metals are particularly nickel and cobalt used in conjunction with tungsten or molybdenum. Preferably, the metals are in the form of the oxide or sulfide. Advantageously the iron group metal is present in an amount between about 1.5 and 10% by weight of the catalyst composite and the Group VI metal is present in an amount between about 5 and 30% also based by weight on the catalyst composite. Examples of refractory inorganic oxides which may be used as a support are silica, alumina, magnesia, zirconia and the like or mixtures thereof. In a preferred embodiment the support is composed for the most part of alumina with a minor amount, e.g. up to about 15 wt. silica.

The catalyst is used as a fixed bed of particles which may be in the form of spheroids, pellets or cylindroids. Advantageously, the catalyst particles greatest dimension ranges between about and 1/16 of an inch. Preferably, the catalyst particles are in the form of cylindroids having a maximum dimension of one-quarter inch. The reactant flow through the catalyst bed is concurrent and may be either up or down. In commercial installations the hydrogen and the oil usually are passed downwardly through the catalyst bed.

As mentioned above, the space velocity and temperature used in our process are considerably higher than those conventionally used in commercial installations.

The following examples are submitted for illustrative purposes only and should not be construed as limitations on the invention.

EXAMPLE I A West Texas-New Mexico sour vacuum gas oil having a sulfur concentration of 1.85 wt. (x-ray) is passed in upward flow through a fixed bed of cylindrical pellets of a catalyst comprising approximately 3 wt. cobalt, 12 wt. molybdenum, 83.0 wt. alumina, 2-4 wt. silica and having a surface area of 290 m lg, a pore volume to 0.63 cc/g and an average pore diameter of 82.5A. Desulfurization is effected by passing hydrogen upwardly through the catalyst bed with the feed at a rate of 1500 scfb recycle hydrogen and 500 scfb fresh hydrogen at a pressure of 800 psig. The space velocities and temperature and other data appear below.

Run 1 represents typical commercial operation. is approximately ten times as great as the catalyst deac- TABLE I Run No. l 2 4 5 Temperature F. 670 670 750 800 850 Space velocity v/v/hr. l 4 4 4 4 Wt. 7c sulfur in product (x-ray) 0.22 0.63 0.18 0.06 0.05

% Desulfurization 88 66 9O 97 97 Hydrogen consumption, scfb 450 213 350 310 340 It can be seen from the above data that not only can greater desulfurization be effected at a higher temperature and a higher space velocity than are used in conventional hydrogen desulfurization but it was also found that quite unexpectedly between 750 and 850F. hydrogen consumption was lower than at other temperatures. This is not insignificant as a reduction in hydrogen consumption of 130 scfb during conventional operation means a saving of more than 1,000,000 cubic feet of hydrogen per day in a 10,000 barrel per day desulfurization unit, which by todays standards is of modest size. Many commercial desulfurizationn units have a capacity in excess of 20,000 barrels per day. In addition by making changes in the size of pumps, compressors, heaters and other auxiliary equipment the capacity of a conventional unit can be quadrupled. Either of these features represents a tremendous saving in the cost of desulfurizing a petroleum fraction at a time when the petroleum industry is being called on to desulfurize more and more petroleum fractions.

The results of Runs 1, 2, 3 and 4 show the effectiveness of the combination of high space velocity, high temperature and high linear velocity. In Run 1, the linear velocity is 1 16 whereas in Runs 2-5, it is 454. Run 1 shows good desulfurization but high hydrogen consumption. Run 2 shows low hydrogen consumption but a product containing more than 0.5 wt. sulfur. Runs 3 and 4 with temperatures of 750 and 800F., space velocities of 4 and high linear velocities show desulfurization to a level below 0.2 wt.

EXAMPLE II This example is a substantial repeat of Example I using the same charge stock and reactor, the significant difference being in the use ofa space velocity of 8. Reaction conditions and other data are tabulated below:

TABLE 2 Pressure, psig 800 Temperature, F. 800 Hydrogen rate, SCFB 2000 Product Sulfur, wt. (x ray) 0.18 desulfurization 90.3 Hydrogen consumption, SCFB 260 tivation rate at a pressure of about 800 psig when the reaction conditions encompass the high temperature and high space velocities of our invention.

EXAMPLE III In this example, the same catalyst and charge stock used in the previous examples are used with the same reactor. Reaction conditions and other data are tabulated below.

TABLE 3 Run No. 7 8 Pressure, psig 400 800 Temperature, F. 800 800 Space velocity, v/v/hr. 4 4

Recycle Hydrogen, SCFB 1500 1500 Fresh hydrogen, SCFB 400 500 Product sulfur, wt. 0.22 0.06 desulfurization 88.1 96.7 Hydrogen consumption, SCFB 220 310 Loss in activity, 4.7 0.4

per barrel per pound of catalyst These data show 88% desulfurization with a hydrogen consumption of only 220 scfb. However, at 400 psig the catalyst deactivation rate is considerably greater than at 800 psig.

EXAMPLE IV TABLE 4 Run A B Pressure, psig 800 800 Temperature, F. 825 800 Space velocity, v/v/hr 4 8 Hydrogen rate, scfb 2000 2000 Product sulfur, wt. 0.18 0.28 Desulfurization 91.8 87.2 Hydrogen consumption, scfb 315 290 These data show that a nickel-molybdenum catalyst is substantially equivalent to a cobalt-molybdenum catalyst.

Various modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, and therefore, only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. A method for effecting at least about 90% desulfurization of a petroleum oil having an initial boiling point of at least about 625F. with a hydrogen consumption of between 220 and 350 scfb which com- 3. The process of claim 1 in which the catalyst comprises cobalt and molybdenum.

4. The process of claim 1 in which the catalyst comprises nickel and molybdenum.

5. The process of claim 1 in which the catalyst comprises nickel and tungsten.

6. The process of claim 1 in which the space velocity is between 4 and 8 v/v/hr. and the hydrogen consumption is between about 260 and 350 scfb.

Claims (6)

1. A METHOD FOR EFFECTING AT LEAST ABOUT 90% DESULFURIZATION OF A PETROLEUM OIL HAVING AN INITIAL BOILING POINT OF AT LEAST ABOUT 625*F. WITH A HYDROGEN CONSUMPTION OF BETWEEN 220 AND 350 SCFB WHICH COMPRISES CONTACTING SAID OIL IN THE PRESENCE OF ADDED HYDROGEN WITH A CATALYST COMPRISING AN IRON GROUP METAL, OXIDE OR SULFIDE THEREOF AND A GROUP VI-B METAL, OXIDE OR SULFIDE THEREOF ON ALUMINA CONTAINING 2-15 WT. % SILICA AT A TEMPERATURE BETWEEN 750* AND 850*F. A PRESSURE BETWEEN ABOUT 500 AND 800 PSIG AND A SPACE VELOCITY BETWEEN ABOUT 3-10 V/V/HR. AND RECOVERING FROM THE DESULFURIZATION ZONE EFFLUENT A PETROLEUM OIL OF REDUCED SULFUR CONTENT.

2. The process of claim 1 in which the petroleum oil is a vacuum gas oil.

3. The process of claim 1 in which the catalyst comprises cobalt and molybdenum.

4. The process of claim 1 in which the catalyst comprises nickel and molybdenum.

5. The process of claim 1 in which the catalyst comprises nickel and tungsten.

6. The process of claim 1 in which the space velocity is between 4 and 8 v/v/hr. and the hydrogen consumption is between about 260 and 350 scfb.