US3509044A - Hydrodesulfurization of petroleum residuum - Google Patents

Description

A ril 28, 1970 c. E. ADAMS Em 09,0

HYDRODESULFURIZATION OF PETROLEUM RESIDUUM Q Filed June 26. 1967 FIG.I I71 I I I CATALYST A TEMP (F) NECESSARY FOR 55% S REMOVAL FROM SAFANIYA ATM. RESID.

O 5 IO I5 4O 5O DAYS ON OIL FIG. 2

o CoO-MoO ON BASE o NiO-MoO ON BA'SE RELATIVE VOLUME ACTIVITY AFTER 7 DAYS WT. /o SILICA IN ALUMINA BASE PATENT ATTORNEY INVENTORS United States Patent 3,509,044 HYDRODESULFURIZATION OF PETROLEUM RESIDUUM Clark E. Adams and William T. House, Baton Rouge, La., assignors to Esso Research and Engineering Company,

a corporation of Delaware Filed June 26, 1967, Ser. No. 648,604 Int. Cl. Cg 23/02, 23/04 US. Cl. 208216 10 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a process for the hydrodesulfurization of petroleum residuum. More particularly the invention relates to the hydrodesulfurization of petroleum residuum in the presence of a catalyst having a support material characterized by a critical silica content and pore size distribution.

The process of the invention is applied to a petroleum residuum feedstock. The three major characteristics of residua other than molecular weight which distinguish them from distillates are that residua contains l) asphaltenes and other high molecular weight, aromatic structures which severely inhibit the rate of hydrodesulfurization, and cause catalyst deactivation, (2) ash forming constituents such as metallo-organic compounds which result in catalyst contamination and interfere with catalyst regeneration, and (3) a relatively large quantity of sulfur which gives rise to objectionable quantities of S0 and 80;, upon combustion in industrial furnaces.

Hydrodesulfurization has long been recognized as a means of removing sulfur from residual oils and asphalts. In addition to sulfur removal, hydrodesulfurization processes generally result in improvement in other properties of residual fuels by nitrogen removal and metals removal. In spite of these benefits, the commercial application of hydrodesulfurization to residua to produce improved residual fuels has been minimal. Low economic incentives for improved fuel oil properties and high operating costs associated with the relatively high pressure required, the high hydrogen consumption and short catalyst life have hindered the utilization of such processes.

The principal object of the present invention is to reduce the sulfur content of petroleum residuum without significantly changing the properties of the oil. The process is centered on nondestructive hydrodesulfurization as distinguished from destructive hydrogenation or hydrocracking. Thus, conversion to gas and light ends is minimized. Another object of this invention is to provide a process specifically designed to treat a feed consisting entirely of petroleum residuum as distinguished from naphthas, gas oils or residua containing added diluents. In most cases satisfactory processes and catalysts have been developed for the lighter materials and diluted feedstocks.

Another object of this invention is to provide a hydrodesulfurization process for petroleum residua which is economically feasible in view of the low return available from the marketing of the treated residuum as residual fuel oil. Cost studies have shown that the key factors are catalyst activity and catalyst activity maintenance. Therefore the specific object of the invention is to provide a process 3,509,044 Patented Apr. 28, 1970 which is carried out at moderate pressure, temperature and other conditions with a catalyst which features low cost and high activity maintenance. Further objects and advantages of the invention will be apparent from the following description which discloses certain nonlimiting embodiments.

Summarizing briefly, the objects of the invention are attained by hydrodesulfurizing petroleum residua at moderate conditions in the presence of a catalyst comprising an oxide or sulfide of nickel or cobalt and an oxide or sulfide of molybdenum or tungsten deposited upon a support material consisting essentially of 1 to 6 wt. percent silica and 94 to 99 'Wt. percent alumina. The catalyst has a maximum pore volume and surface area in pores 30 to 70 A. in diameter.

In the drawings, FIGURE 1 is a graph comparing the temperature increase requirement of one of the catalysts of the invention compared to that of a typical prior art catalyst and FIGURE 2 is a graph relating relative catalyst activity to the quantity of silica in the catalyst.

The process feedstock is a petroleum residuum obtained from distillation or other treating or separation process. From 30 to 100% of the feed boils have 900 F. The process is designed to treat a residuum without any preprocessing; however, when the metal content of the oil is greater than about 500 to 1000 p.p.m. it may be necessary to employ a metals removal step such as HF treatment or solvent precipitation with propane, butane, mixtures of propane and butane, pentane, hexane or naphtha. The petroleum residuum can be a blend of high boiling materials such as atmospheric bottoms, vacuum bottoms, deasphalted oil, visbreaker products, heat soaked materials, gas oil cuts, etc. The feedstocks of the invention contain relatively large amounts of sulfur, asphaltenes, metals and ash. Some of these materials or conversion products thereof deposit on the hydrodesulfurization catalyst when hot oil is brought in contact with the catalyst surface.

The feedstocks treated have the following properties and inspections:

TABLE I.PROPERTIES OF PETROLEUM RESIDUA Feed of Example 3 Broad Narrow (Safaniya range range Atm0s.Resid.

Percent boiling above 900 F 30-100 50-100 6 Gravity, API 5-25 10-20 15. 4 Viscosity, SFS at 122 F 50-5, 000+ 100-1, 000 309 Sulfur, Wt. percent 1-8 3-6 4. 0 Nitrogen, wt. percent... 0-1 0 001-0. 5 0.26 Metals (p.p.m.), total 20-1, 000 -500 127 Vanadium (p.p.m.) 10-500 30-300 84 Nickel (p p m 5-200 10-100 32 Asphaltenes, wt. p 1-20 2-10 7. 2 Pour point, F 0-200 25-100 45 The composition and characteristics of the support is a most important aspect of the invention and the quantity of silica is critical. Hydrodesulfurization catalyst supports containing silica have been suggested in the past. However, silica was included in the support when the feedstock was gasoline or light gas oil or when a significant amount of hydrocracking was desired. It was felt that the presence of any significant amount of silica in the hydrodesulfurization of residuum would cause significant cracking with consequent coke make and catalyst fouling. Thus, it was entirely unexpected that relative catalyst activity could be greatly improved by the presence of a critical quantity of silica in the catalyst support.

The support can be prepared by precipitating the oxides or hydrated oxides of aluminum and silicon from aqueous solutions of water salts of these metals. For example, suitable proportions of the water soluble salts of aluminum such as the sulfate, chloride or nitrate and suitable proportions of water soluble silicon salts such as sodium silicate are precipitated from solution by adjusting the pH of the solution with acidic or basic material. The precipitate is washed and otherwise treated to remove impurities as necessary. The support can be impregnated with the metals while it is wet or after drying and calcining.

A preferred method of preparing the catalysts is to treat alkaline aqueous aluminate solutions which contain predetermined amounts of silica with acidic reagents to precipitate an aluminosilicate in the hydrous form. A slurry produced by this technique is then dried by known methods to furnish a preferred catalyst support of this invention.

The supports of the types prepared above are then impregnated with metals which promote a hydrodesulfurization reaction.

The catalyst containing all the active ingredients is then (1) dried and extruded, or (2) dried to remove excess moisture, impregnated and extruded, or (3) dried to remove excess moisture, extruded, dried and then impregnated.

The preferred alkaline aqueous aluminate solution is a solution of sodium aluminate. It is understood that other alkali metal aluminates can be used except they are not preferred from an economic standpoint.

The acidic reagents which can be used are the mineral acid salts of aluminum, e.g., aluminum halides, nitrates, and sulfates. Also useful are the well-known mineral acids themselves, e.g., hydrochloric, nitric, sulfuric acids, and the like.

The conditions for preparing the support are so controlled that the finished support has an apparent bulk density of less than 0.70 g./cc. It is further characterized as being opaque as distinguished from glassy in appearance (indicating that a large quantity of the alumina is in a crystalline form). The catalyst is extrudable.

In preparing these preferred catalytic materials the following illustrates preferred conditions.

Using the above general reaction conditions, the support resulting from the reaction is in the form of a dilute slurry. This slurry may then be concentrated and subjected to spray-drying operations at temperatures ranging between 200-2000 F., preferably 200-500" F.

Using conventional techniques known to the catalyst art, the spray-dried material may be subjected to Water washing to remove excess alkali metal ions and sulfate ions. The support can then be impregnated with the catalytic metals and extruded or pilled or otherwise formed into any desired physical form.

The aforementioned silica-alumina hydrogels can b composited with other synthetic and/or semi-synthetic aluminas, silica gels, and/or other silica-alumina-clay hydrogel compositions for the purpose of adjusting the alumina and/or silica present during impregnation. It is essential that the silica content of the catalyst be maintained in the range of 1-6 Weight percent, preferably 1.5-5 Weight percent. The resulting catalyst, when calcined, should have a total surface area greater than 150 m. /g. and the pore volume is preferably greater than 0.25 cc./g. as measured by the BET procedure with nitrogen.

The active metallic components in the finished catalyst are a Group VI-B salt, specifically a molybdenum salt or tungsten salt selected from the group consisting of molybdenum oxide, molybdenum sulfide, tungsten oxide, tungsten sulfide, and mixtures of these and" a Group VIII-B salt, specifically a nickel or cobalt salt selected TABLE III.CATALYST COMPOSITION Broad Preferred range range (wt. percent) (wt. percent) Nickel or cobalt (as oxide) 1-15 2-10 Tungsten or molybdenum (as oxide) 5-25 10-20 Silica 1-6 1. 5-5 Alumina 93-52 86-64 The structure of the catalyst is also an important aspect of the invention. In the hydrodesulfurization of petroleum residue a criticality of pore size has been found With respect to activity maintenance. It has been found that pores having a pore diameter in the 30-70 A. range are of critical importance with heavy residual feeds. Evidently pores of smaller diameter than about 30 A. are ineffective in desulfurizing the high molecular weight molecules present in residues and pores of largerdiameter than about A. are rapidly deactivated. Thus a maximum of surface area should be present in pores having a pore diameter in the 30-70 A. range. Catalysts having good activity and activity maintenance for hydrodesulfurization of residue are characterized by the following relationship between pore diameter in A., pore volume in cc./g. and surface area in mF/g. for pores over the range of 30-70 A. in diameter.

4X 10 Pore Volume (ca/gt) The pore volume distribution of a catalyst as defined by this invention is measured by nitrogen adsorption isotherm where the volume of nitrogen adsorbed is measured at various pressures. This technique is described in Ballou, et al., Analytical Chemistry, vol. 32, April 1960, pp. 532- 536. The pore diameter distributions for the examples of the invention were obtained using a Model No. 4-4680 Adsorptomat manufactured by the American Instrument Company, Silver Spring, Maryland. One skilled in the art can select catalyst manufacturing process steps and process conditions Within the specific ranges disclosed herein to prepare catalysts having the required pore di ameter, pore size distribution, pore volume, and surface area.

EXAMPLE 1 The following illustrates a typical catalyst preparation.

Three solutions are prepared, e.g., A, B, and C:

Ingredient Amount Solution A Water 36 gallons.

Sogigm silicate solution, 28% 113 cc.

1 2. Sodium aluminate 23.5% 5,323 cc.

A1203 solution. 48% gluconlc acid solution 76 cc. Solution B 98% H2804 850 cc. into 4.5 gallons water.

Solution 0.-..-- 9.5% alum solution 3.3 gallons.

1 Total A1203 in s0luti0n-1.3

EXAMPLE 2 A silica-alumina support is prepared in the manner set forth in Example 1 and is composited with suitable quantities of molybdenum oxide and cobalt carbonate by impregnation. The slurry is filtered and dried to provide a catalyst (dry weight basis containing 3.5% cobalt oxide, 12.0% molybdenum oxide, 1.7% SiO and the balance alumina). This catalyst is hereinafter referred to as Catalyst B. The support can be impregnated with the other hydrogenation metals of the invention, i.e., nickel and tungsten in the same manner.

A commercial catalyst was selected for the purpose of obtaining comparative data. It contained 3.5 weight per cent cobalt oxide, 12.5 weight percent molybdenum oxide, 0.2 weight percent SiO and the balance alumina. This catalyst is designated hereinafter as Catalyst A.

The hydrodesulfurization reaction is carried out in a conventional reactor of the fixed bed, moving bed or fluidized bed type. A slurry or ebbulating bed can also be used. Considering the nature of the feedstock, the reaction conditions are relatively mild. The oil is contacted in the liquid phase. Typical conditions are as follows:

TABLE IV.REACTION CONDITIONS Broad range Preferred range Temperature, F 500-825 650800 Pressure, p.s.i.g 5002, 500 1, 000-1, 800 Space velocity, v/v., 0. 2'5. 0. -2. 0 Hydrogen rate, s.c.f./bbl 500-7, 500 1, 000-5, 000

a manner set forth earlier in this specification. FIGURE 1 sets forth the temperature increase requirement (TIR) for runs with Catalyst A and Catalyst B. The TIR for Catalyst B is 017 F./day, showing a very low activity decline. Catalyst A exhibited the usual initial high activity decline then lined out at a TIR of 1.7 F./day. Thus Catalyst B has an activity maintenance ten times better than that of Catalyst A. This result was completely unexpected because the two catalysts demonstrated no such difference in the hydrodesulfurization of distillates.

Runs with Catalyst B demonstrate the following improvements: (1) greatly improved catalyst life, (2) lower pressure operation (1500 vs. 2200 p.s.i.g. which was previously considered necessary for good catalyst life), and (3) lower gas rates (1500 vs. 3000 s.c.f./bbl. also previously considered necessary for good catalyst life). In addition the new catalyst shows about half the metals laydown usually experienced with petroleum residuum feeds. These improvements make residuum hydrodesulfurization by our process attractive from a cost standpoint. Kuwait atmopsheric residuum (3.8 wt. percent S) was desulfurized over Catalysts A and B at 800 p.s.i.g., 1 v./v./hr., 1500 s.c.f. H per barrel of feed for Catalyst B and 3000 s.c.f. H per barrel for feed for Catalyst A, and initial temperature of 685 F. The initial desulfurization was 66% for Catalyst B and 42% for Catalyst A in spite of the higher gas rate for Catalyst A. After days the desulfurization with Catalyst B was still 50% at 685 F., whereas it was only 34% for the Catalyst A at 700 F. It is obvious that Catalyst B has higher activity and much better activity maintenance with this feedstock.

EXAMPLE 4 Table V shows the relative activity of a number of hydrodesulfurization catalysts. All runs were carried out on Safaniya atmospheric residuum (4.0% S) at the following conditions: 1500 p.s.i.g., 725 F., 3000 s.c.f. Hg/ bbl., 1 v./v./hr., cc. catalyst.

TABLE V Rel. Vol. Act. for Day Composition (alumina plus the Bulk Catalyst following materials), wt. percent density 1 7 14 21 A 3.5 CoO, 12.5 M003, 0.2 S102 0.66 1 100 58 43 36 B.. 3.5 C00, 12.0 M00 1.7 SiOz 0. 180 140 115 110 C 0. 65 150 115 100 1).. 1.0 160 113 105 E 0.88 160 113 F .0 0. 88 94 70 63 60 G .5 0. 59 280 105 65 50 H .5 COO, 12.5 M003, 8.6 S102 0.57 280 80 50 35 I .0 N10, 31.0 M003, 14.0 SiO2 0. 54 45 J 4.0 NiO, 15.0 M003, 03 S102 0. 59 70 40 S in iced.

EXAMPLE 3 A pilot plant'unit containing 200 cc. of catalyst was used in this example. The oil was passed down through the catalyst bed.

The catalyst was calcined overnight at 1200 F. and then sulfided using 5 wt. percent carbon disulfide in a light petroleum distillate. Sulfiding was carried out at 1 v./v./hr., 1500 p.s.i.g., and 1500 s.c.f./b. The reactor was held at 500 F. for two hours and then raised to 750 F. and held there for 16 hours. The temperature was lowered to near 700 F. and feed was cut in. The feedstock was a Safaniya residuum having the properties set forth in Table I. Side-by-side comparative runs were made to give a direct comparison to measure the activity decline of the catalysts. The pressure was 1500 p.s.i.g., the space velocity was 1 v./v./hr., and the hydrogen rate was 1500 s.c.f./bbl. The reactor temperature was increased as necessary to obtain 55% desulfurization of the residuum. Catalyst A was selected for comparison because it was effective in hydrodesulfurization of distillate stocks. It contained 3.5 wt. percent C00 and 12.5 wt. percent M00 on a support containing 0.2 wt. percent SiO and the balance alumina. Catalyst B is prepared in The relative volume activity of the catalysts employed in the process of the invention, i.e., catalysts B, C, D, E, F, and G is far superior to the activity of the prior art catalysts, i.e., A, H, I, and I. It can be seen that silica content is critical. In the drawing, FIGURE 2 shows the criticality of silica in the range of 1 to 6 in the catalyst base in attaining high activity and activity maintenance. Since catalyst are sold by the pound, we prefer the catalysts having the lowest metals content and bulk density which will give superior activity maintenance, i.e., catalysts like Catalyst B.

The catalysts employed in the process of the invention have excellent surface area stability and they are effectively regenerated by conventional techniques at temperatures ranging from 6001000 F.

EXAMPLE 5 Catalysts A and B of the first two examples have some similar properties as shown by lines 1-5 of Table VI, below. For example, the overall surface areas are nearly equivalent. However, the nature of the surface areas are considerably different. Catalyst A has a surface area in 30 to 70 A. pores of 86 square meters per gram. Catalyst B has a surface area in 30 to 70 A. pores of 174 square meters per gram. The relatively large number of pores in the 30 to 70 A. range of Catalyst B seems to be one of the reasons for its extended life in processing residua.

TAB LE VI Cat. A Cat. B Cat. E

Surface area, m. /g- 253 266 271 Pore volume, cc./g 0. 58 0. 50 0. 24 Bulk density, g./c 0. 63 0. 71 0. 88 Pellet density, gJcc- 1.10 1.20 Pellet strength 11. 16. 5 S102, wt. percent 0. 2 2.0 3. 9 CaMoOr, wt. percent (by X-ray). 2 0 0 Surface area in 30-70 A. pores, Mz/g- S6 174 136 Relative wt. activity at day 21 36 91 67 After 21 days of operation at the conditions set forth in Examples 4 and 5, Catalyst B had a weight activity of 91 compared to a weight activity of only 3 6 for Catalyst A. Weight activity is determined by Relative Vol. Activity Bulk Density of Reference Catalyst Bulk Density of Test Catalyst In a series of comparative runs, Catalyst B proved to have at least five times as much catalyst life as Catalyst A. Similarly Catalysts C and E which are nickel-molybdenum type catalysts had a high relative weight activity. Thus a surface area in 30-70 A. pores of at least 100 m. /g., preferably 100-300 m. g. provides excellent activity and activity maintenance.

It is well 'known that hydrodesulfurization of residua can be improved by subjecting the feed to such pretreating steps as deasphalting, deasphaltening, dilution, metals removal, etc.; however, usually the cost of the multistep processes cannot be justified. The process of this invention provides adequate sulfur removal without any other major treating steps unless the feed has a very high metals content.

The catalysts of this invention are sufiiciently active so that hydrodesulfurization reaction pressures in the range of 800 to 1500 p.s.i.g. are satisfactory depending upon feedstock. Prior art processes require pressures of 2500 to 3000 p.s.i.g. and a high treat gas recycle because of the low activity of the catalyst. Furthermore, they require 25 more investment and higher operating costs to achieve the same throughput. With respect to temperature, hydrodesulfurization above 825 F. is not practical because of excessive gas make and hydrogen consumption. The process of the invention operates well at lower temperatures. Conversion to light ends, gasoline and other light stocks is less than about 15 wt. percent based on the feedstock.

What is claimed is:

1. A process for the hydrodesulfurization of petroleum residuum containing -100 wt. percent of materials boiling above 900 F., 1-8 Wt. percent sulfur, 210-1000 p.p.m. metals and 1-20 Wt. percent asphaltenes comprising contacting said residuum in the liquid phase at a temperature of 650-800 F. and a pressure of 500-2500 p.s.i.g. in the presence of 500-7500 s.c.f./b. of hydrogen and a hydrodesulfurization catalyst consisting essentially of a molybdcnum salt selected from the group consisting of molybdenum oxide and molybdenum sulfide and a nickel or cobalt salt selected from the group consisting of nickel oxide, cobalt oxide, nickel sulfide, cobalt sulfide and mixtures thereof deposited on a support material comprising silica stabilized alumina, said catalyst being characterized by having a maximum of its surface area in pores having pore diameters in the 30 to A. range.

2. Process according to claim 1 in which the catalyst is 10-20 Wt. percent molybdenum oxide and 2-10 Wt. percent cobalt oxide deposited on the said support.

3. Process according to claim 2 in which the metal oxides are sulfided prior to use.

4. Process according to claim 1 in which the catalyst is 10-20 wt. percent molybdenum oxide and 2-10 Wt. percent nickel oxide deposited on the said support.

5. Process according to claim 4 in which the metal oxides are sulfided prior to use.

6. A process for the nondestructive hydrodesulfurization of a feedstock consisting essentially of petroleum residuum containing 3-6 wt. percent sulfur comprising contacting said residuum in essentially the liquid phase at a temperature of 650 to 800 F., and a pressure of 1000 to 1800 p.s.i.g. in the presence of 1000 to 5000 s.c.f./b. of hydrogen and a hydrodesulfurization catalyst consisting essentially of a molybdenum salt selected from the group consisting of molybdenum oxide and molybdenum sulfide and a Group VIII-B salt selected from the group consisting of nickel oxide, cobalt oxide, nickel sulfide, cobalt sulfide and mixtures thereof deposited on a support material comprising silica stabilized alumina, said catalyst being characterized by a maximum of pores having diameters in the range of 30-70 A.

7. Process according to claim 6 in which the surface area in 30-70 A. pores is at least m. g.

8. Process according to claim 6 in which the surface area in 30-70 A diameter pores is in the range of 100 to 300 m. g.

9. Process according to claim 6 in which less than 15 wt. percent of the feed is converted to gas and light ends.

10. Process according to claim 6 in which the silica content of the support is 1.5-5 wt. percent.

References Cited UNITED STATES PATENTS 2,983,676 5/1961 Howland 208-216 2,988,501 6/1961 *Inwood 208-216 3,169,918 2/1965 Gleim 208-216 3,340,180 9/1967 Beuther et al 208-216 3,393,148 7/1968 Bertolacini et al 208-216 3,425,934 2/ 1969 Jacobson et a1. 208-216 DELBERT E. GANTZ, Primary Examiner G. J. CRASANAKIS, Assistant Examiner US. Cl. X.R.

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