Hydrodesulfurization process for the production of low-sulfur hydrocarbon mixture

Abstract

Low-sulfur content hydrocarbon mixture and fuel oil blend below 0.2 or below 0.1 wt. % sulfur are obtained by hydrodesulfurizing vacuum gas oil under a hydrogen partial pressure of 300 - 800 psig. with a select high activity desulfurization catalyst. Further embodiments include the hydrodesulfurization of sulfur-containing vacuum residuum and (1) mixing portions of the desulfurized hydrocarbon residuum with the vacuum gas oil feed or (2) blending fuel oil from portions of the desulfurized vacuum gas oil and desulfurized vacuum residuum product. Further process steps include (3) deasphalting of vacuum residuum or (4) hydrodesulfurizing vacuum residuum with delayed coking of at least a portion of the product.

Description

BACKGROUND OF THE INVENTION

The present invention relates to the production of hydrocarbon mixtures of low-sulfur content. More particularly, it relates to deep hydrodesulfurization of vacuum gas oils obtained from reduced-crude fractions of sulfur-containing crude oils and the production of hydrocarbon mixtures such as fuel oil, fuel oil blending stock, kerosene, diesel and fluid catalytic cracker feeds having low sulfur contents. In an especial aspect of the invention fuel oil blends having a low sulfur content are produced in an integrated hydrodesulfurization process from vacuum gas oil and vacuum residuum fractions of sulfur-containing reduced-crude oils. Other advantages obtained from the use of the present unique hydrodesulfurization process will be evident from the descriptions and examples herein.

Petroleum hydrocarbons are being used up at an ever increasing rate. New crude discoveries have not been sufficient to maintain the unproduced reserve. As a result, crude oils heretofore avoided where possible because of undesirable properties, especially those with high sulfur contents and those also containing heavy metal contaminations, must now be used as feeds for petroleum refineries. Asphaltenes frequently are found in combination with the metal contaminants and these together with sulfur and the metals are a source of serious processing and cost problems in the refining of such crude oils.

The dwindling world supply of crude oil makes it imperative that the refiners secure every last drop of useful hydrocarbon from a crude; and the need to do better in protecting the environment, for example by removing sulfur from combustion fuels, has made it evident that new and better processing methods and more select catalysts are needed. Better yields and reduced sulfur contents must be achieved. In particular, improvements in the processing of a vacuum gas oil from a reduced-crude feedstock are needed which in concert achieve:

1. A DEEPER DESULFURIZATION OF VACUUM GAS OILS, ESPECIALLY FOR THE 350.degree.F. and higher boiling point hydrocarbon mixtures (atmospheric pressure) to at least to a sulfur content (weight percent) below about 0.2, preferably below 0.1, and most preferably below about 0.05;

2. THE USE OF A HYDRODESULFURIZATION PROCESS TEMPERATURE WHICH IS LESS THAN 850.degree.F.;

3. a longer operating cycle for the catalyst in the hydrodesulfurization of a vacuum gas oil, e.g., a cycle of at least 30 months;

4. a select high activity vacuum gas oil hydrodesulfurization catalyst capable of deeper [item (1) above] sulfur removal and suitable for use with a combined feedstock, i.e., a mixture of vacuum gas oil and of vacuum-residuum gas oil, and the like;

5. a vacuum gas oil hydrodesulfurization process performance permitting integration thereof with concurrent vacuum residuum hydrodesulfurization means for the substantial reduction of fuel oil pool sulfur content levels to new low levels, for example below 1 weight percent, and even to below 0.3 weight percent;

6. a lower hydrogen gas consumption per unit of processed reduced-crude oil; and

7. fuel oil products having acceptable stabilities.

SUMMARY OF THE INVENTION

In a broad embodiment, the present invention is a process for producing from a sulfur-containing reduced-crude feedstock, for example, an Arabian crude having a sulfur content above 1 weight percent, calculated as elemental sulfur, various valuable products, including a low sulfur 350.degree.F.+ material suitable for use as a fuel oil or fuel oil blend stock, an FCC charge stock, kerosene or diesel fuel. In the process the reduced-crude is separated into at least one vacuum gas oil fraction, which may boil in the range 600.degree.-1100.degree.F., and a vacuum residuum fraction. The vacuum gas oil fraction is contacted with a select high activity desulfurization catalyst and hydrogen gas in a hydrodesulfurization zone at mild hydrodesulfurization conditions, and from the hydrodesulfurizing reaction zone is withdrawn a product having a sulfur content below 0.2 weight percent.

In a further embodiment:

1. at least a portion of said vacuum residuum fraction is contacted with a vacuum residuum hydrodesulfurization catalyst and hydrogen in a second hydrodesulfurization zone under vacuum residuum hydrodesulfurization conditions;

2. a sulfur-reduced vacuum residuum is withdrawn from said second zone and passed to a vacuum fractionator;

3. a 350.degree.-1050.degree.F. boiling range hydrocarbon mixture is withdrawn from said fractionator; and

4. prior to the hydrodesulfurization of said vacuum gas oil fraction in said first hydrodesulfurization zone, at least a portion of said withdrawn 350.degree.-1050.degree.F. hydrocarbon mixture is admixed with said vacuum gas oil.

By mild hydrodesulfurization conditions, as used herein, is meant the employment of process conditions, including:

1. a hydrogen partial pressure in the range 300 to 800, preferably 350-650 psig; and

2. a temperature in the range 550.degree. to 850.degree.F.

The vacuum residuum fraction may be subjected to further processing as desired.

More specific embodiments of the present invention include:

1. The use of the 350.degree.F. plus boiling fraction of the sulfur-reduced vacuum gas oil produced as described above as a blend stock for upgrading a sulfur-reduced vacuum residuum fuel oil;

2. The use of all or a portion of a sulfur-reduced vacuum gas oil produced as described above as a feed for a fluid catalytic cracker (FCC) unit, particularly the 650.degree.F. plus boiling fraction;

3. The production of a C.sub.4 plus boiling range sulfur-reduced vacuum gas oil produced as described above, separating the resulting sulfur-reduced vacuum gas oil by fractional distillation into:

a. a butane fraction;

b. a C.sub.5 -350.degree.F. fraction with a sulfur content less than 0.01, e.g., 0.005, weight percent; and

c. a 350.degree.-1050.degree.F. fraction with a sulfur content less than 0.1 weight percent, separating the 350.degree.-1050.degree.F. fraction by fractional distillation into a 350.degree.-650.degree.F. fraction with a sulfur content less than 0.05 weight percent, separating the 350.degree.-650.degree.F. product by fractional distillation into a kerosene plus diesel boiling range fraction with a sulfur content less than 0.05 weight percent, and into a 650.degree.F. plus boiling feed for an FCC unit; and

4. Still further embodiments of the present invention will be evident from the Figures below and the description.

By a reduced-crude feedstock or oil, as used herein, is meant the residue or bottoms fraction normally obtained in the topping by distillation of a whole crude, i.e., a topped whole crude. Usually the distillation is an atmospheric distillation, but it may be carried out, if desired, and as known in the art, under a moderately subatmospheric pressure.

The reduced-crude feedstocks contemplated for use herein vary widely depending upon the crude oil which is topped to obtain them. In general, reduced-crude feedstocks obtained from whole crude oils having a 1 weight percent sulfur content or higher are satisfactory and reduced-crude feedstocks obtained from these whole crude oils are contemplated for use herein. The whole crude oil may have smaller relative amounts of sulfur and still yield satisfactory reduced-crude feedstocks. However, as the sulfur impurity in the whole crude oil becomes less, the economic and process advantages of the present process also become less. Preferably, asphaltene and metal contents of the whole crude oil from which the reduced-crude feedstock is obtained are low, but these factors are of secondary importance. Reduced-crude feedstocks obtained from whole crude oils which contain relative amounts of asphaltenes, and metals as normally present in a whole crude, are satisfactory and contemplated for use herein provided that the amount of sulfur in the whole crude is about 1 weight percent or higher. There is no particular prerequisite as to the form of the sulfur in the reduced crude. That is, the form of the sulfur in the reduced crude may vary widely and is dependent upon the natural condition of the sulfur in the whole crude which is topped to produce the feedstock. Sulfur contents, as expressed throughout the description, are calculated as elemental sulfur.

If the meatls content tends to lead to an undesirable catalyst fouling rate, a prior removal in large part may be carried out by ordinary methods (see, for example, U.S. Pat. No. 3,696,027). Also, see the paper "Isomax Process For Residuum and Whole Crude", by S. G. Paradis, G. D. Gould, D. A. Bea and E. M. Reed, Chemical Engineering Progress [Volume No. 67, No. 8, Pages 57-62 (1971)].

The vacuum gas oils satisfactory for use in the present invention are those ordinarily obtained by the fractional distillation at a subatmospheric pressure of a reduced-crude oil having the characteristics as described above and these are contemplated for use herein. The pressures employed for these fractionations are below 1 atmosphere, usually in the range 0.06-0.25 atmosphere, and the resulting vacuum gas oils and vacuum residua are useful and contemplated for use as described in the present disclosure. The vacuum gas oils preferred herein have an initial boiling point (ASTM-D1100) between 350.degree.F. and about 850.degree.F. and an end boiling point in the range 1000.degree.to 1100.degree.F., preferably above 1000.degree.F. The vacuum residua, on the other hand, employed herein are the bottoms fractions from the aforementioned fractional distillation of reduced-crudes under vacuum. These are contemplated for use herein. Preferred vacuum residua have an initial boiling point of about 1000.degree.F.

The process herein, that is using a select high activity hydrodesulfurization catalyst and mild hydrodesulfurization conditions, is especially satisfactory for the production in good yield of a low-sulfur content fuel oil from a sulfur-containing vacuum gas oil. Surprising advantages include:

1. a hydrocarbon product mixture having a sulfur content in the range, broadly, of 0.005 to 0.2 weight percent, particularly 0.1 to 0.005, and most particularly 0.1 to 0.05;

2. a run cycle, hrs., in the range 8,000 to 30,000, usually greater than 24,000; and

3. a hydrogen consumption which is in general less than required in a conventional process.

Other advantages are the production in excellent yield of a fuel oil of good stability, in an operation which is carried out with substantially reduced costs, operational, catalyst and the like, relative to those for a conventional hydrodesulfurization process. Still further advantages in which the above-described hydrodesulfurization process is integrated with other process steps will be evident from the description and Figures below.

SELECT HIGH ACTIVITY HYDRODESULFURIZATION CATALYSTS

By a select high activity hydrodesulfurization catalyst, as used herein, is meant a solid composite comprising a Group VIII component, a Group VI component and alumina, having an average pore diameter in the range 65-150 A., and a pore volume in the range 0.3 to 1 cc per gram. Excellent results have been obtained with catalysts of the foregoing description which:

1. comprise cobalt, molybdenum, and alumina;

2. have an average pore diameter in the range 80-120 A. and with at least 50 percent of the pores having a pore diameter in the range 65-150 A. (see U.S. Pat. No. 3,684,688 for background details with respect to average pore diameter determinations and other references):

3. have an atomic ratio of cobalt to molybdenum in the range 0.3 to 0.6, preferably about 0.4;

4. have a pore volume at least 0.5 cc per gram; and

5. are sulfided, either prior to use or during process operation.

Particularly good results have been obtained when the catalyst further contains phosphorus, and in a preferred form of the catalyst titanium also is present. Use of titanium-containing alumina during catalyst preparation is an excellent procedure. Good results may be obtained when nickel is used in place of the cobalt.

Select hydrodesulfurization catalysts, as herein, have a high metals acceptance capability, have especially low fouling rates, and hiwh hydrodesulfurization activity under the mild desulfurization conditions of the process of the present invention. For reasons of cost, the density of the catalyst composite should be in the range below about 60 pounds per cubic foot, preferably below 50 pounds. The size of the composite should be in the range one-eighth to one-fortieth inch, preferably one-sixteenth to one-thirty second inch.

An especially suitable select high activity hydrodesulfurization catalyst, as defined herein, may be prepared by the steps comprising:

1. calcining an alumina (no previous calcination experience above about 1700.degree.F.) support at a temperature in the range 1400.degree. to 1700.degree.F.;

2. impregnating the calcined alumina with an aqueous solution of a cobalt salt and a heteropolyphosphomolybdic acid; and

3. sulfiding the composite prior to use by ordinary means or in situ in use by contacting of a sulfur containing feed, as herein, with the composite under hydrodesulfurizing conditions.

DESCRIPTION OF THE DRAWINGS

FIGS. 1-4 are process flow diagrams schematically indicating preferred embodiments of the process of the present invention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Referring now to FIG. 1, a reduced-crude feedstock, a 650.degree.F.+ Kuwait residuum is fed at a rate of 50,000 barrels per operating day (BPOD) via line 1 to crude oil vacuum fractionation zone 2. In addition to a reduced-crude oil, other sulfur-containing hydrocarbon sources such as shale oils, tar sand oils and oils derived from coal can be fed to fractionation zone 2. Fractionation zone 2 consists basically of a typical vacuum distillation unit, as used in the petroleum refining art. In zone 2 the Kuwait residuum is separated into an overhead fraction, a vacuum gas oil, in an amount of 30,000 BPOD and a bottoms fraction, a vacuum residuum (1,050.degree.F. plus true boiling point cut) in an amount of 20,000 BPOD. The vacuum gas oil is withdrawn from fractionator 2 via line 3 and passed to mild hydrodesulfurization reactor 4 and the vacuum residuum is withdrawn from fractionator 2 via line 5 and passed to vacuum residuum hydrodesulfurization reactor 13. In reactor zones 4 and 13 the respective feeds, vacuum gas oil, or vacuum residuum, are mixed with hydrogen and hydrodesulfurized under mild or vacuum residuum hydrodesulfurization conditions, respectively. The hydrogen is obtained from a suitable source. For example, hydrogen is produced in hydrogen plant 7 by steam reforming about 1,800 BPOD of naphtha, which is introduced to hydrogen plant 7 via line 6. The produced hydrogen is withdrawn from hydrogen plant 7 via line 8 in an amount of about 34 million standard cubic feet per day (MSCFD). Via lines 8 and 9, 12 MSCFD of the hydrogen is delivered to reactor 4 and via lines 8 and 12, 22 MSCFD of the hydrogen is delivered to reactor zone 13.

In reactor 4, the mild hydrodesulfurization zone, the vacuum gas oil is mixed with hydrogen (2000 standard cubic feet (SCF)/barrel of vacuum gas oil) and contacted with a select high activity desulfurization catalyst which is a sulfided solid composite:

1. containing cobalt, molybdenum, phosphorus and alumina;

2. having an average pore diameter of about 100 A. with at least 50% of the pores having a pore diameter in the range 65 to 150 A.;

3. having an atomic ratio of cobalt to molybdenum of about 0.4; and

4. having a pore volume of about 0.5 cc per gram.

The contacting is at a hydrogen partial pressure of about 400-500 psig, a total pressure of about 600-800 psig, a temperature of about 700.degree.-800.degree.F., and at a liquid hourly space velocity (LHSV) of about 2-3. The contacting of the vacuum gas oil feed, as described above, results in the production of naphtha, a low-sulfur fuel oil having a sulfur content of about 0.15 weight percent, and a light hydrocarbon gas-H.sub.2 S mixture. The naphtha is removed from reactor 4 via line 14 at a rate of about 400 BPOD and the fuel oil is removed from reactor 4 via line 19 at a rate of about 29,800 BPOD. The light gas-H.sub.2 S mixture is withdrawn from reactor 4 via line 16 and is passed to a conventional gas and sulfur recovery unit, 27, for processing.

In reactor 13, the vacuum residuum introduced via line 5 and the hydrogen (about 4000 SCF per barrel of vacuum residuum) introduced via line 12 are mixed and contacted with a satisfactory vacuum residuum hydrodesulfurization catalyst, for example a sulfided composite of cobalt, molybdenum, phosphorus, alumina and titania having the nominal (i.e., calculated as the indicated oxides) composition as follows:

Weight Percent ______________________________________ CoO 2.5 MoO.sub.3 10.0 Al.sub.2 O.sub.3 62.5 TiO.sub.2 15.0 P.sub.2 O.sub.5 10.0 ______________________________________

under suitable vacuum residuum hydrodesulfurization conditions, for example a temperature of about 700.degree.-800.degree.F., a total pressure of about 2000 psig, a hydrogen partial pressure of about 1500 psia, and an LHSV of less than 0.5. The treatment of the vacuum residuum in reactor 13 results in the production of naphtha and a sulfur-reduced vacuum residuum as the principal products and a light gas fraction comprising low molecular weight hydrocarbons and hydrogen sulfide. The naphtha is removed from reactor 13 via line 15 at a rate of about 100 BPOD. The light gas stream containing hydrocarbons and hydrogen sulfide is withdrawn from reactor 13 via line 17 and passed to a conventional gas and sulfur recovery unit 27 via lines 17 and 18.

The sulfur reduced vacuum residuum produced in reactor 13 is withdrawn via line 23 and is passed to a vacuum fractionator 24 for separation into a bottoms product and an overhead fraction. The bottoms product is withdrawn from fractionator 24 via line 26 at a rate of 14,000 BPOD and comprises a 1,050.degree.F. plus boiling residuum which contains about 1.2 percent sulfur.

From vacuum fractionator 24 the overhead fraction comprising 350.degree.-1,050.degree.F. boiling range hydrocarbons having a sulfur content of about 0.15% is withdrawn via line 20 at a rate of 6,300 BPOD. A low sulfur fuel oil pool is produced by the integrated process, as represented in FIG. 1, in an amount of about 36,100 BPOD. Thus, a fuel oil blend is produced by mixing at least a portion of the 350.degree.F.-1050.degree.F. hydrocarbon mixture obtained by fractionating the hydrodesulfurized vacuum residuum product stream with at least a portion of the 350.degree.F.+ effluent fraction of the product from the vacuum gas oil hydrodesulfurization reactor, the blend having sulfur content below about 0.2 weight percent, or, below about 0.1 weight percent. This fuel oil pool or blend has a good stability and is an excellent synthetic replacement for the virgin low sulfur content fuel oils presently available in the market.

Alternatively, at least a portion of the low sulfur product from the mild hydrodesulfurization zone 4 may be used as a charge stock for a fluid catalytic cracker.

Referring now to FIG. 2, a reduced-crude is processed substantially in the manner as described for that portion of the process of FIG. 1 which is enclosed within the dotted lines except:

1. more detail is given with respect to some of the auxiliary elements, and

2. the heavier fraction of the desulfurized vacuum gas oil is fractionated after withdrawal from low pressure separator 62 via line 67.

The withdrawn gas oil is passed to fractionator 68 via line 67 for separation into a naphtha fraction, a kerosene plus diesel oil fraction and a desulfurized fuel oil product.

Referring now to FIG. 3, a reduced-crude feed, a 650.degree.F. plus boiling Kuwait residuum is delivered via line 85 at a rate of 50,000 barrels per operating day (BPOD) to vacuum fractionator 86 for separation into a vacuum gas oil and a 1050.degree.F. plus boiling vacuum residuum. Via line 89 vacuum gas oil having a sulfur content of about 2.8 weight percent is withdrawn from vacuum fractionator 86 at a rate of about 30,000 BPOD. Via line 87 the vacuum residuum is withdrawn from fractionator 86 at a rate of about 20,000 BPOD and is passed to vacuum residuum hydrodesulfurization reactor 88. In reactor 88 the vacuum residuum is mixed with hydrogen, which is introduced to reactor 88 via line 84, and desulfurized by contact with a catalyst having the following nominal composition, weight percent and characteristics:

Average Pore Diameter, A. 130-190 Pore Volume, cc per gram 0.5 CoO 2.5 MoO.sub.3 10.0 TiO.sub.2 15 P.sub.2 O.sub.5 10.0 Al.sub.2 O.sub.3 Remainder

under the following conditions:

Average Bed Temperature, .degree.F. 700-800 Pressure, psig 2000 Space Velocity, V/V/Hr. < 0.5 Hydrogen Rate, SCFB 4000 Hydrogen Purity, Volume Percent 90

Hydrogen sulfide and light hydrocarbon gases produced by the desulfurization in reactor 88 are withdrawn from the reactor via line 92 and delivered via lines 92, 110 and 111 to gas and sulfur recovery unit 114 for processing. Via line 93 sulfur-reduced vacuum residuum having a sulfur content of about 0.7% is withdrawn from reactor 88 and is delivered via lines 93 and 98 to coker fractionator 94 for separation into a C.sub.5 + coker gas oil and a bottoms fraction, a coker feed. The coker feed is withdrawn from fractionator 94 via line 35 and passed to delayed coker 96. Delayed coker 96 is a conventional coke-forming unit which converts the feed to a metallurgical grade coke product and a vaporized hydrocarbon, a coker effluent. The coker effluent is withdrawn from the unit 96 via line 97 and passed to the coker fractionator via lines 97 and 98. Coke having a sulfur content below 2 weight percent and a metals content below 150 ppm of vanadium is withdrawn from coker 96 via line 99 at a rate of about 450 short tons per day.

Two overhead hydrocarbon fractions are withdrawn from coker fractionator 94, the first a C.sub.4 .sup.- fraction and the second the C.sub.5 + coker gas oil. Via line 100 the C.sub.4 .sup.- light hydrocarbon fraction is withdrawn from fractionator 94 and passed via lines 100, 110 and 111 to gas and sulfur recovery unit 114. Via line 103 the C.sub.5 + coker gas oil is withdrawn from fractionator 94 at a rate of about 18,800 BPOD. This gas oil having a sulfur content of about 0.8% sulfur is mixed with the vacuum gas oil by joining lines 103 and 89, is line mixed and passed via line 104 to mild hydrodesulfurization reactor 106. In reactor 106 the combined vacuum gas oil and coker gas oil feed is mixed with hydrogen and contacted with a select high activity desulfurization catalyst in the manner described for the process of FIG. 1 with the production of naphtha and low sulfur content fuel oil. The naphtha is separated by fractionation and withdrawn from reactor 106 via line 107 at a rate of 3,200 BPOD. Fuel oil having a sulfur content of 0.15 weight percent is withdrawn from reactor 106 via line 109 at a rate of 46,100 BPOD.

The hydrogen sulfide and light hydrocarbon containing gas streams withdrawn from reactors 88 and 106 and from coker fractionator 94 are passed to gas and sulfur recovery unit 114 via the lines indicated in the Figure and in unit 114 using ordinary recovery methods the hydrogen sulfide is converted to sulfur and the light hydrocarbons are separated into a sweet fuel gas product. The former is withdrawn from unit 114 via line 115 at a rate of about 305 short tons per day and the sweet fuel gas is withdrawn from unit 114 via line 116 at a rate of 1,510 BPOD.

Delayed cokers or furnace type coking units heat the residuum or other hydrocarbon feedstock to coking temperatures rapidly and little reaction occurs while the charge is in the furnace. Effluent from the furnace discharges at about 850.degree.F. to 1000.degree.F. (see, for example, U.S. Pat. No. 2,727,853, U.S. Pat. No. 2,727,853). U.S. Pat. No. 2,988,501 and U.S. Pat. No. 3,027,317 disclose coking ahead of hydrodesulfurization and U.S. Pat. No. 3,684,688 disclose coking afterwards.

The integrated process of FIG. 3 has many process advantages, including:

1. A practical process by which can be produced at least about a 93 liquid volume percent yield of low sulfur fuel oil product from a high sulfur content reduced-crude oil; and

2. A practical means for disposing of high sulfur-content by-product, e.g., producing metallurgical grade coke and additional fuel oil range gas oil.

Referring now to FIG. 4, a reduced-crude feed, a 650.degree.F. plus boiling Arabian light residuum is delivered via line 124 at a rate of 50,000 barrels per operating day (BPOD) to vacuum fractionator 125 for separation into a vacuum gas oil and a 1050.degree.F. plus boiling vacuum residuum. Via line 126 vacuum gas oil having a sulfur content of about 2.8 weight percent is withdrawn from vacuum fractionator 125 at a rate from about 34,500 BPOD. Via line 127 vacuum residuum having a sulfur content of 4.1 weight percent is withdrawn from fractionator 125 at a rate of about 15,500 BPOD and is passed to asphalt removal unit 128 for separation of the vacuum into asphalt or tar and an asphalt-reduced residuum, a solvent deasphalted oil. The separation is asphalt removal unit 128 is carried out using conventional solvent deasphalting methods, for example, butane-pentane solvent deasphalting or the like.

Asphalt or tar having a sulfur content of about 6.1% is withdrawn from unit 128 via line 144 and passed to gasification unit 145 for gasification and separation into a sulfur-containing fraction comprising hydrogen sulfide and into a synthetic natural gas fraction substantially free of sulfur. The gasification is effected by conventional process methods, for example, by the Texaco Partial Oxidation Process or the Shell Gasification Process.

Asphalt-reduced residuum (solvent deasphalted oil) having a sulfur content of about 3.5 weight percent is withdrawn from unit 128 at a rate of about 12,400 BPOD and combined with vacuum gas oil by joining lines 129 and 126 and the combined feeds are line mixed and passed via line 130 to mild hydrodesulfurization reactor 132. The combined vacuum gas oil and asphalt reduced residuum feed mixture is mixed with hydrogen in reactor 132 and desulfurized under mild hydrodesulfurization conditions in the manner described for the corresponding portion of the process of FIG. 1 to produce naphtha, low-sulfur fuel oil and by-product streams containing hydrogen sulfide. Naphtha is separated by fractionation and withdrawn via line 133 from reactor 132 at a rate of about 380 BPOD. Via line 134 low-sulfur fuel oil having a sulfur content of about 0.05 weight percent is withdrawn at a rate of 46,700 BPOD.

In gas and sulfur recovery unit 139 hydrogen sulfide and hydrogen sulfide plus light hydrocarbon effluent streams from reactor 132 and gasification unit 145 are separated into a sweet fuel gas fraction and a sulfur fraction. Via line 140 sweet fuel gas is withdrawn from unit 139 at a rate of about 230 BPOD. Via line 143 sulfur is withdrawn from unit 139 at a rate of about 240 short tons per day. When the gasification unit comprises a partial oxidation gasification coupled with a methanation stage, a synthetic natural gas product can be recovered having about a heating value of about 930 Btu/SCF.

If the asphalt-reduced vacuum residuum is not mixed with the vacuum gas oil and the hydrodesulfurized vacuum gas oil is back blended with the asphalt-reduced vacuum residuum, the resulting fuel oil blend has a sulfur content of 0.5 weight percent. Such a high value can be acceptable and useful for some areas and for some purposes. The product from the integrated process, the 0.05 weight percent fuel oil, is of course an excellent and highly desirable product having particular reference to desirable environmental protection requirements.

The integrated process of FIG. 4 has many process advantages, including:

1. A practical process by which can be produced at least about a 93 liquid volume percent yield of low sulfur fuel oil product from a high sulfur, high asphaltene crude, for example, an Arabian light atmospheric reduced-crude oil; and

2. A practical means for:

a. disposing of high sulfur content asphalt (tar), and

b. producing needed synthetic natural gas using ordinary gasification and sulfur recovery means.

VACUUM RESIDUUM HYDRODESULFURIZATION CATALYSTS

A satisfactory vacuum residuum desulfurization catalyst for use in the present invention must have a high metals acceptance capability, a good stability, and a low fouling rate. A suitable vacuum residuum desulfurization catalyst for use herein has an average pore diameter in the range from about 100 to 200 A., preferably 130 to 190 A., and comprises a composite of the oxides and/or sulfides of a Group VIII metal, preferably cobalt, of molybdenum and phosphorus and of a refractory metal or mixed metal oxide, preferably alumina. For reasons of operating convenience, a catalyst sizing in the range from about 1/8 inch to about 1/40 inch is preferable.

VACUUM RESIDUUM HYDRODESULFURIZATION CONDITIONS

Conditions suitable for use for the hydrodesulfurization of a vacuum residua, as herein, vary widely and depend in the main upon the particular feed. In general, satisfactory conditions include the indicated and primary process parameters within the ranges as noted below:

Temperature, .degree.F. 600 to 850.degree.F., preferably 600 to 800 Pressure, psig 1000 to 2500, preferably 1500 to 2200 LHSV < 1, preferably < 0.5

and the use of a hydrogen-containing gas, preferably a gas having a hydrogen content of at least 75 volume percent.

Representative reduced-crude feeds suitable for use herein include those obtained from Middle Eastern crudes, such as Arabian light, Kuwait, Arabian medium, Iranian heavy (especially for solventing deasphalt route) and Iranian light crude oils, and the like high sulfur content crude oils; others are California crude, Alaskan North Slope crude, and the like, as well as blends of crude oils, that is crude oils and crude oil blends, in general, which have a sulfur content of at least about 1 weight percent.

EXAMPLE 1

In the manner described for the process of FIG. 1, encircled portion, a 615.degree.-1050.degree.F. TBP vacuum gas oil from an Arabian medium or a Kuwait-type crude containing 2.8 weight percent sulfur was hydrodesulfurized. The yields and product properties were:

Raw Feed Liquid Products Kuwait By-Product K/D Option.sup.(1) VGO Butanes C.sub.5 -350.degree.F. 350.degree.F. Plus 350-650.degree.F. 650.degree.F. Plus Yield, LV% 0.1 3.5 97.5 21.5 76.0 Inspections Gravity, .degree.API 22.6 48 28 36 26 Aniline Point, .degree.F. 173 ASTM Distillation, .degree.F. D1160 D1160 D86 D1160 ST/5 605/-- 350/-- 385/-- 615/-- 10/30 685/745 590/690 450/510 670/745 50 815 760 560 805 70/90 905/1005 845/960 580/625 880/980 95/EP -- /1100 1000/1065 -- /670 1020/1065 Sulfur, Wt. % 2.8 <0.005 0.02 <0.005 0.05 Nitrogen, ppm 600 110 Pour Point, .degree.F. 105 90 0 95 Viscosity, CS at 122.degree.F. 40 25 3.0 40 __________________________________________________________________________ .sup.(1) Where kerosene and diesel fuel are desired as an option and is separated from the 350.degree.F. plus product, the yields of fuel oil, etc. are as listed under the by-product option.

The low sulfur oils produced by the process herein, particularly by the hydrodesulfurization of a vacuum gas oil under mild hydrodesulfurization conditions using a select high activity desulfurization catalyst, are advantageous feedstocks for hydrocracking for the production of more valuable lower molecular weight products. Typical operating conditions for catalytic hydrocracking include a temperature between 500.degree. and 900.degree.F., a pressure between 100 and 10,000 psig, a hydrogen rate between 100 and 10,000 SCF per barrel of feed, and the use of a catalyst typically comprising a Group VIB and/or Group VIII hydrogenation component and a cracking component, for example amorphous silica-alumina on a crystalline zeolitic molecular sieve.

HYDROGEN CONSUMPTION

The amount of hydrogen required to produce a low-sulfur content fuel oil under the mild hydrodesulfurization conditions as herein varies depending upon the sulfur content of the vacuum gas oil to be treated. On the basis of sulfur content of the vacuum gas oil, at least about 40 standard cubic feet of hydrogen is required per pound of sulfur to be removed in order to reduced the sulfur content to at least 0.2 weight percent. In Table I below is given comparative examples illustrating sulfur removal, hydrogen consumption and resulting product parameters for the desulfurization of vacuum gas oil from an Arabian light crude oil.

TABLE I __________________________________________________________________________ DESULFURIZATION OF ARABIAN LIGHT VACUUM GAS OIL VGO FEED PRODUCTS __________________________________________________________________________ H.sub.2 Consumption, SCF/Bbl 183 240 277 400 H.sub.2 Consumption, SCF/Lb Sulfur Removed 38.6 39.6 42.5 56.5 Inspections (350.degree.F.+ Product Inspections) Sulfur, Wt. % 2.3 0.79 0.43 0.16 0.05 Nitrogen, ppm 650 535 500 420 180 .degree.API 24.6 27.0 27.7 28.5 29.3 Nickel, ppm 0.11 0.03 0.02 Nil Nil Vanadium, ppm 0.39 Nil Nil Nil Nil Distillation, ASTM D-1160, .degree.F. IBP/5 508/599 462/579 511/583 464/573 424/549 10/30 635/724 611/707 623/712 614/707 596/700 50 803 780 782 776 763 70/90 846/982 860/970 868/963 851/952 848/953 95/EP 1009/1044 1012/1037 994/1044 997/1040 998/1041 Product Yields C.sub.1 -C.sub.4, Wt. % 0.04 0.12 0.30 0.35 C.sub.5 -350.degree.F., LV % 0.6 0.7 0.7 0.8 350.degree.F.+, LV % 99.3 99.3 99.4 100.1 __________________________________________________________________________

Although various specific embodiments of the invention have been described and shown, it is to be understood that they are meant to be illustrative only and not limiting. Certain features may be changed without departing from the spirit or essence of the invention. It is apparent that the present invention has broad application to the hydrodemetalization and hydrodesulfurization of hydrocarbons. Accordingly, the invention is not to be construed as limited to the specific embodiments illustrated but only as defined in the following claims.

Claims

What is claimed is:

1. A process for producing a low-sulfur hydrocarbon mixture by desulfurizing a hydrocarbon feedstock, said feedstock being a reduced-crude obtained froma whole crude oil having a sulfur content of at least about 1 weight percent, which comprises:

1. separating said feedstock into a vacuum gas oil fraction and a vacuum residuum fraction;

2. contacting at least a portion of said vacuum gas oil fraction with a select high activity desulfurization catalyst and hydrogen gas in a first hydrodesulfurization zone under a hydrogen partial pressure in the range 300 to 800 psig, said catalyst comprising a sulfided composite containing cobalt, molybdenum, phosphorus and alumina and a pore volume of at least 0.5 cc per gram of said composite, said pores having an average pore diameter in the range 80 to 120A with at least 50 percent of said pores having a diameter in the range 65 to 150A, and said composite having an atomic ratio of cobalt to molybdenum in the range 0.3 to 0.6; and

3. withdrawing from said first hydrodesulfurization zone an effluent, the 350.degree.F.+ portion thereof having a sulfur content below 0.2 weight percent, calculated as elemental sulfur.

2. A process as in claim 1 wherein said 350.degree.F.+ portion has a sulfur content in the range 0.005 to 0.2.

3. A process as in claim 1 wherein said 350.degree.F.+ portion has a sulfur content in the range of 0.005 to 0.1.

4. A process as in claim 1 wherein:

1. at least a portion of said vacuum residuum fraction is contacted with a vacuum residuum hydrodesulfurization catalyst and hydrogen in a second hydrodesulfurization zone under vacuum residuum hydrodesulfurization conditions, said vacuum residuum catalyst comprising a composite of oxides and/or sulfides of a Group VIII metal, molybdenum, titanium, phosphorus and alumina said composite containing pores, and said pores having an average pore diameter in the range from 100 to 200A and said vacuum residuum hydrodesulfurization conditions comprising a temperature in the range 600.degree. to 850.degree.F., a pressure in the range 1000 to 2500 psig, a liquid hourly space velocity in the range below about 1 and the use of a gas having a hydrogen content of at least about 75 volume percent;

2. a sulfur-reduced vacuum residuum is withdrawn from said second zone and passed to a vacuum fractionator;

3. a 350.degree.C.-1050.degree.F. boiling range hydrocarbon mixture having a sulfur content below about 0.15 weight percent is withdrawn from said fractionator; and

4. a fuel oil blend is produced by mixing at least a portion of said 350.degree.F.-1050.degree.F. hydrocarbon mixture with at least a portion of said 350.degree.F.+ portion, said blend having a sulfur content below about 0.2 weight percent.

2. a sulfur-reduced vacuum residuum is withdrawn from said second zone and passed to a coker fractionator;

3. a bottoms fraction is withdrawn from said coker fractionator and passed to a coker;

4. a metallurgical grade coke is withdrawn from said coker;

5. an overhead fraction is withdrawn from said coker fractionator; and

6. prior to the hydrodesulfurization of said vacuum gas oil fraction in said first zone, at least a portion of said overhead fraction withdrawn from said coker fractionator is admixed with said vacuum gas oil.

5. A process as in claim 4 wherein said blend has a sulfur content below about 0.1 weight percent.

6. A process as in claim 1 wherein:

1. at least a portion of said vacuum residuum fraction is contacted with a vacuum residuum hydrodesulfurization catalyst and hydrogen in a second hydrodesulfurization zone under vacuum residuum hydrodesulfurization conditions, said vacuum residuum hydrodesulfurization conditions comprising a temperature in the range 600.degree. to 850.degree.F., a pressure in the range 1000 to 2500 psig, a liquid hourly space velocity in the range below about 1 and the use of a gas having a hydrogen content of at least about 75 volume percent;

2. a sulfur-reduced vacuum residuum is withdrawn from said second zone and passed to a vacuum fractionator;

3. a 350.degree.F.-1050.degree.F. boiling range hydrocarbon mixture is withdrawn from said fractionator; and

4. prior to the hydrodesulfurization of said vacuum gas oil fraction in said first hydrodesulfurization zone, at least a portion of said withdrawn 350.degree.F.-1050.degree.F. hydrocarbon mixture is admixed with said vacuum gas oil fraction and the resulting mixture is fed to the first hydrodesulfurization zone.

7. A process as in claim 1 wherein:

1. at least a portion of said vacuum residuum fraction is contacted with a vacuum residuum hydrodesulfurization catalyst and hydrogen in a second hydrodesulfurization zone uner vacuum residuum hydrodesulfurization conditions, said conditions comprising a temperature in the range 600.degree. to 850.degree.F., a pressure in the range 1000 to 2500 psig, a liquid hourly space velocity in the range below about 1 and the use of a gas having a hydrogen content of at least about 75 volume percent;

8. A process as in claim 1 wherein:

1. at least a portion of said vacuum residuum fraction is passed to an asphalt removal unit and separated into an asphalt fraction and an asphalt-reduced fraction;

2. said asphalt fraction is withdrawn from said unit, and

3. prior to the hydrodesulfurization of said vacuum gas oil fraction in said first zone, at least a portion of said asphalt-reduced fraction is admixed with said vacuum gas oil.

9. A process as in claim 1 wherein said phosphorus and molybdenum are incorporated into the catalyst in the phosphomolybdate form.

10. A process as in claim 1 wherein said catalyst also contains titanium.

11. A process in claim 1 wherein the pores of said catalyst have an average pore diameter of about 100A.

12. A process for producing a low-sulfur hydrocarbon mixture by desulfurizing a hydrocarbon feedstock, said feedstock being a reduced-crude obtained from a whole crude oil having a sulfur content of at least about 1 weight percent, which comprises:

1. separating said feedstock into vacuum gas oil fraction and a vacuum residuum fraction;

2. contacting at least a portion of said vacuum gas oil fraction with a select high activity desulfurization catalyst and hydrogen gas in a first hydrodesulfurization zone under a hydrogen partial pressure in the range 300 to 800 psig, said catalyst consisting essentially of a sulfided composite containing cobalt, molybdenum, phosphorus, titanium and alumina, and having pore volume of at least 0.5 cc per gram of said composite, said pores having an average pore diameter in the range 80 to 120A with at least 50 percent of said pores having a diameter in the range 65 to 150A, and said composite having an atomic ratio of cobalt to molybdenum in the range 0.3 to 0.6; and

3. withdrawing from said first hydrodesulfurization zone an effluent, the 350.degree.F.+ portion thereof having a sulfur content below 0.2 weight percent, calculated as elemental sulfur.

13. A process as in claim 12 wherein the pores of said catalyst have an average pore diameter of about 100A.

14. A process as in claim 12 wherein:

1. at least a portion of said vacuum residuum fraction is contacted with a vacuum residuum hydrodesulfurization catalyst and hydrogen in a second hydrodesulfurization zone under vacuum residuum hydrodesulfurization conditions, said vacuum residuum catalyst comprising a composite of oxides and/or sulfides of a Group VIII metal, molybdenum, titanium, phosphorus and alumina said composite containing pores, said pores having an average pore diameter in the range from 100 to 200A, and said vacuum residuum hydrodesulfurization conditions comprising a temperature in the range 600.degree. to 850.degree.F., a pressure in the range 1000 to 2500 psig, a liquid hourly space velocity in the range below about 1 and the use of a gas having a hydrogen content of at least about 75 volume percent;

2. a sulfur-reduced vacuum residuum is withdrawn from said second zone and passed to a vacuum fractionator;

3. a 350.degree.f.-1050.degree.F. boiling range hydrocarbon mixture having a sulfur content below about 0.15 weight percent is withdrawn from said fractionator; and

4. a fuel oil blend is produced by mixing at least a portion of said 350.degree.F. -1050.degree.F. hydrocarbon mixture with at least a portion of said 350.degree.F.+ portion, said blend having a sulfur content below about 0.2 weight percent.

15. A process as in claim 12 wherein:

1. at least a portion of said vacuum residuum fraction is contacted with a vacuum residuum hydrodesulfurization catalyst and hydrogen in a second hydrodesulfurization zone under vacuum residuum hydrodesulfurization conditions, said vacuum residuum hydrodesulfurization conditions comprising a temperature in the range 600.degree. to 850.degree.F., a pressure in the range 1000 to 2500 psig, a liquid hourly space velocity in the range below about 1 and the use of a gas having a hydrogen content of at least about 75 volume percent;

2. a sulfur-reduced vacuum residuum is withdrawn from said second zone and passed to a vacuum fractionator;

3. a 350.degree.F.-1050.degree.F. boiling range hydrocarbon mixture is withdrawn from said fractionator; and

4. prior to the hydrodesulfurization of said vacuum gas oil fraction in said first hydrodesulfurization zone, at least a portion of said withdrawn 350.degree.F.-1050.degree.F. hydrocarbon mixture is admixed with said vacuum gas oil fraction and the resulting mixture is fed to the first hydrodesulfurization zone.

16. A process as in calim 12 wherein:

1. at least a portion of said vacuum residuum fraction is passed to an asphalt removal unit and separated into an asphalt fraction and an asphalt-reduced fraction;

2. said asphalt fraction is withdrawn from said unit, and

3. prior to the hydrodesulfurization of said vacuum gas oil fraction in said first zone, at least a portion of said asphalt-reduced fraction is admixed with said vacuum gas oil.

17. A process as in claim 12 wherein said phosphorus and molybdenum are incorporated into the catalyst in the phosphomolybdate form.