US3392112A - Two stage process for sulfur and aromatic removal - Google Patents

Description

United States Patent 3,392,112 TWO STAGE PROCESS FOR SULFUR AND AROMATIC REMOVAL Paul G. Bercik, Glenshaw, and Alfred M. Henke, Springdale, Pa., assignors to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware N0 Drawing. Filed Mar. 11, 1965, Ser. No. 439,077

14 Claims. (Cl. 208-210) This invention relates to a method of manufacturing highly stable hydrocarbon oils of a quality equal to or better than the present best super-refined oils, and more particularly to a method of preparing such oils from sulfurcontaining oils that are normally unstable to light and heat by a two-stage hydrogenation process.

There is in the pertoleum industry a class of specialty products having exceptionally rigorous quality standards, particularly as to color, odor and stability. Examples of such products are white oils, or light pertoleum oils of lubricating viscosity used for pharmaceutical purposes, pharmaceutical paraflin waxes, petrolatums, i.e., oil-microcrystalline wax petroleum jellies and charcoal lighter fluid. Not only are the color, odor and stability standards of these specialty products extremely high, but also they are unique among petroleum products in general in that these standards must be achieved without the use of inhibitors, since these latter materials might be injurious to health or safety.

The specialty products referred to above, as well as other specialty oils that do not involve health or safety factors, have customarily been produced previously by drastic sulfuric acid treatment followed by clay filtration of suitable stocks, which, in turn, are obtained by fractional distillation, solvent refining, or a combination of these. However, these prior method are not entirely satisfactory in that product yields are relatively low and in that they form relatively large quantities of ditficultly disposable by-products, such as acid sludges, sulfonated oils, spent clay, etc. It has also been proposed to prepare highly stable lubricating oils by hydrogenation in one or two stages. Such processes are advantageous in that they result in improved yields and minimum byproducts, bnt they have not been fully satisfactory to produce a wide range of products of the very highest quality.

' The present invention relates to a process for manufacturing petroleum specialty products having very high quality standards as to color, odor and uninhibited stability, and having remarkable inhibitor response, together with unusually high product yields, While minimizing by-product production. It has now been found that such products can be manufactured by a novel, twostage, catalytic hydrogenation procedure involving a firststage hydrogenation of a sulfurcontaining petroleum hydrocarbon charge stock with a sulfur-resistant hydrogenation catalyst to produce an intermediate product of sufliciently low sulfur content that the activity of a sulfursensitive second-stage catalyst with respect to removal of heteroatoms and aromatics will not be adversely affected, and then subjecting the intermediate product to a secondstage catalytic hydrogenation with a highly active, sulfursensitive, hydrogenation catalyst comprising reduced metallic nickel composited with a diatomaceous earth support. More particularly, in accordance with the process of this invention, a sulfur-containing hydrocarbon oil charge stock is subjected to a first-stage hydrogenation by contact with hydrogen and a sulfur-insensitive hydrogenation catalyst, at a temperature in the range of about 600 to 825 F., preferably about 650 to 775 F., at a pressure in the range of about 750 to 5000 p.s.i.g. preferably about 1000 to 3500 p.s.i.g. at a space velocity "ice in the range of about 0.1 to 5.0, preferably 0.5 to 3.0 liquid volumes of oil per volume of catalyst per hour, While maintaining a hydrogenzoil ratio of 1000 to 20,000, preferably about 2000 to 10,000 standard cubic feet per barrel of oil, to form the aforesaid low-sulfur intermediate product. An example of a suitable sulfur-resistant catalyst is the oxide or sulfide of a nickel-tungsten hydrogenation component composited with an alumina or silicaalumina support, but other sulfur-resistant metals of the left-hand column of Group VI of the periodic system and of Group VIII of the periodic system and sulfur-resistant sulfides and oxides thereof can be used, either in unsupported form or supported on carriers which may or may not themselves possess catalytic activity. The partly hydrogenated, low-sulfur, intermediate first-stage product is then subjected to an exhaustive second-stage hydrogenation by contact with hydrogen and the highly active sulfur-sensitive reduced nickel on diatomaceous earth hydrogenation catalyst, at a temperature in the range of about 450 to 750 F., preferably about 525 to 690 F., at a pressure in the range of about 750 to 5000 p.s.i.g., preferably about 1000 to 3500 p.s.i.g., at a space velocity in the range of about 0.1 to 5.0, preferably about 0.5 to 3.0 liquid volumes of oil per volume of catalyst per hour, while maintaining a hydrogenzoil ratio in the range of about 1000 to 20,000, preferably about 2000 to 10,000 standard cubic feet per barrel of oil, to produce a highly stable product boiling in the same range as the aforesaid intermediate product and containing extremely small proportions of sulfur, nitrogen, oxygen and aromatics. I i

While the exact mechanism of the herein-disclosed process is not fully understood, it is thought that the process may depend for its success upon its unique ability to remove to an exhaustive degree cyclic compounds, including aromatic hydrocarbons as well as cyclic compounds containing heteroatoms, that is, cyclic sulfur-, nitrogenand oxygen-containing compounds, along with any olefinic compounds, from the low-sulfur, first-stage products. As a result, the oils treated in accordance with this invention are less susceptible to oxidation and are therefore more stable than oils from which the aboveindicated compounds have been removed less exhaustively. Although all hydrocarbons are subject to oxidation when exposed to sufficient oxygen and sufiiciently high temperatures, the aromatic hydrocarbons, other than some naphthalene and anthracene derivatives, are generally considered to be most readily oxidizable, possibly because of the activating influence of the ring structure and/or because of the sensitivity of the hydrogen atoms attached to the carbon atoms in side-chains adjacent the ring structure. In addition, most all petroleum oils contain sulfur in at least a few tenths percent, which amount may correspond to several percent sulfur compounds in view of the high proportion of the hydrocarbon part of the molecule relative to sulfur. The sulfur content of hydrocarbon oils, at least of the heavier oils, is thought to be present in aromatic or naphthenic type compounds, where sulfur replaces carbon in the ring, as in thiophene type derivatives. Nitrogen, when present, is probably present as complex derivatives of cyclic compounds such as pyridine and quinoline, just as oxygen is probably present at least in part in the form of complex derivatives of phenol and possibly naphthol, and/or complex oxy-aromatics, all of which resemble aromatic hydrocarbons in structure and behavior. It is hypothesized that the herein disclosed process may function by virtue of the unique ability of the second-stage hydrogenation catalyst exhaustively to remove aromatic hydrocarbons and oxygen-, sulfurand nitrogen-heteroatoms from similarly behaving compounds contained in the intermediate products of the process, once the sulfur content of the first-stage charge stock has been reduced in the first stage of the process to the degree that they will not rapidly deactivate the catalyst sites that are responsible for the exhausive aromatics hydrogenation and heteroatom-removing properties of the catalyst.

' Any petroleum hydrocarbon fraction capable of yielding a product of the desired boiling range following treatent in both stages of the herein-disclosed process can be used as the charge stock to the first stage of the process. When any reduction in viscosity obtained in the first stage is insignificant, the charge to the first stage can comprise an oil of the same boiling range as the final product. Thus, when the desired final product is a white oil or other oil in the lubricating range of viscosities, the charge to the first stage can be a light or medium lubricating distillate, of which raw lubricating distillates having viscosities of about 100 SUS and 250 SUS at 100 F. are examples, respectively. Alternatively, the charge stock can be the rafiinate resulting from solvent treatment of a light or medium neutral distillate oil with a selective solvent such as furfural. When the final product is to be charcoal lighter fluid, the charge stock can advantageously comprise alkylate bottoms, that is, the material obtained from a sulfuric acid or hydrogen fluoride alkylation process that boils above the gasoline range. A mixture of paraffin slack wax, microcrystalline waxes and oil forms a suitable charge when the final product is a petrolatum. Paraflin wax obtained by solvent dewaxing of waxy lubricating distillates is a suitable charge for producing pharmaceutical waxes. When it is desired to have some cracking take place in the first stage, as in the production of high viscosity index oils by hydrotreating, the charge stock should be an oil that is heavier than the desired final product. Thus, heavy, unpressable distillate forms a suitable charge stock for the production of a highly stable lubricating oil product of medium viscosity.

The charge stock to the second stage of the process can be the entire product obtained from the first stage. However, the invention is not limited to this procedure, as the intermediate product can be subjected to further refining, for example, a topping operation or a solvent dewaxing treatment, prior to introduction into the second stage. Also, all or a portion of the intermediate product from the first stage can be mixed with one or more oils obtained from an external source, prior to introduction into the second stage of the process. It is important for purposes of the present invention that the sulfur content of the second-stage product be reduced to a sufficiently low level as not to affect adversely the heteroatom removing and aromatic hydrogenation activity of the secondstage catalyst, which properties are responsible for the unique effectiveness of the second-stage catalyst to produce the super refined products described herein. The actual maximum quantity of sulfur that can be tolerated in the charge to the second stage will vary with the sulfur content of the hydrogen circulated in the second stage. In general, the sulfur content of the hydrogen and the oil, calculated as p.p.m. of oil, should not exceed about 10 p.p.m. for each 1000 s.c.f. of hydrogen per barrel of oil.

As previously indicated, a wide variety of hydrogenation catalysts can be used in the first stage of the process. Thus, there can be used sulfur-resistant metals of Group Via of the periodic system, metals of Group VIII of the periodic system, their oxides, sulfides, and mixtures of any of these that possess suflicient hydrogenating activity to remove most of the sulfur that is capable of rapidly deactivating the second-stage catalyst for purposes of exhaustive heteroatom removal and aromatics reduction. Naturally, the greater the hydrogenating activity of the first-stage catalyst, the better, since the ultimate goal of the process is exhaustive hydrogenation. An example of a preferred first-stage catalyst is nickel-tungsten sulfide. Examples of other catalysts that can be used are nickel tungstate, tungsten sulfide, nickel sulfide, nickel oxide,

molybdenum sulfide, cobalt molybdate, nickel molybdate and mixtures thereof with cobalt molybdate. These catalysts can be employed in unsupported form or they can be composited with porous carriers of high surface area, which may or may not themselves possess catalytic activity. Examples of such carriers are activated aluminas, silica gel, synthetic silica-alumina composites, synthetic silicamagnesia composites, activated clays or the like. The hydrogenating component can constitute about 10 to 65 percent of the composite catalysts. The finished catalysts can also contain combined fluorine, preferably in amounts in the range of about 0.2 to 2.5 percent by weight. Although many of the foregoing catalysts are excellent hydrogenation catalysts, as such, none has been found that is sufiiciently effective alone to achieve the exhaustive hydrogenation obtained by the present invention, even when employed in successive stages, let alone in a singlestage hydrogenation. Thus, a sulfided nickel tungsten catalyst which had been found to produce superior results for purposes of the first-stage hydrogenation of the pres ent invention, when tested for use as the second-stage catalyst, was found to be incapable of achieving a fully satisfactory level of heteroatom and aromatics removal, at least within the constraints of the equipment employed and practical space velocities.

From what has been said, it will be appreciated that the nature of the catalyst for the second stage of the process is very important. In this instance, only reduced nickel composited with a diatomaceous earth such as kieselguhr can be used. The nickel component can comprise about 10 to 65 percent, preferably 25 to 50 percent, of the composite catalyst. The reduced nickel on diatomaceous earth catalysts disclosed herein apparently exhibit an unusual and unique ability to remove heteroatoms and aromatics to an exhaustive degree, provided the sulfur content of the stock has been previously reduced to a level that will not adversely affect the heteroatomand aromatics-reducing properties of the catalyst. The unique effectiveness of the herein-disclosed second-stage catalysts with respect to feed stocks of the class disclosed herein is shown by the fact that they have been found to be markedly superior as compared to other hydrogenation catalysts, even catalysts as closely related thereto as other highly active nickel hydrogenation catalysts, such as Raney nickel.

The above-indicated firstand second-stage catalysts can be prepared in any suitable way. For example, they can be prepared by impregnation of the desired carrier with a water solution of one or more water soluble salts of the desired catalytic metals, drying and calcining. In the case of the reduced metal catalysts, the calcined catalysts can be prereduced by contact with hydrogen at elevated temperature and pressure. In the case of the sulfided catalysts, the prereduced catalysts can be presulfided with hydrogen sulfide, carbon disulfide, mercaptans, or sulfur containing oils. Alternatively, the calcined catalysts can be sulfided directly in known manner.

As previously indicated, hydrogenation is effected in the first stage at temperatures in the range of about 600 to 825 F., at pressures in the range of about 1000 to 5000 p.s.i.g., preferably about 2500 to 3500 p.s.i.g., at space velocities in the range of about 0.1 to 5.0, while maintaining hydrogenzoil ratios in the range of about 1000 to 20,000, preferably about 2000 to 10,000 standard cubic feet per barrel of oil. When it is desired that some cracking of carbon-to-carbon bonds accompany hydrogenation in the first stage, we employ temperatures in the upper'portion of the indicated range, for example, 675- to 775 F., together with space velocities in the lower portion of the range, for example, 0.5 to 1.5. Conversely, when little or no cracking is desired in the first stage of the process, less severe conditions of temperature and space velocity, for example, 650 to 750 F. and 1.5 to 3.0 LHSV, can be used with good results. Unless otherwise indicated, pressures referred to herein are hydrogen partial pressures.

In the second stage of the process, wherein no cracking, but only exhaustive hydrogenation, is desired, relatively low temperatures of the order of about 450 to 750 R, preferably about 525 to 690 F., can be used in conjunc- The catalyst in this stage was prereduced nickel deposited on a kieselguhr base, which catalyst contained 48 percent nickel. The catalyst in calcined form was prereduced at 750 F. and under one atmosphere of hydrogen pressure tion with pressures, space velocities and hydrogenzoil ra- 5 for 4 hours while maintaining a gas space velocity of 490 tios of the same order of magnitude as used in the first volumes (at standard temperature and pressure) of gas stage. per volume of catalyst per hour. The crude petrolatum The products of the first-stage hydrogenation are char charge stock and the products obtained from both the acten'zed chiefly by a low sulfur content, usually not more first and second stages were evaluated for initial color, than about 100 p.p.m. Depending upon the amount of 10 ultraviolet light absorptivity, iodine number, aniline cracking taking place in the first stage, these products point, nitrogen, sulfur and oxygen content, ultraviolet may also exhibit somewhat higher API gravities and relight stability and sunlight stability. Ultraviolet light abdued viscosities. Typically, these products will also show sorptivity is an indication of unsaturation, in this case a marked reduction in oxygen and nitrogen content, as principally the kind of unsaturation present in aromatic compared with the charge stock. ring structures, wherein the lower the ultraviolet light The products of the second-stage hydrogenation will absorptivity, the lower the aromatic content of the sambe characterized by extremely low sulfur content, for exple. Iodine number is also indicative of aromatic conample, less than 50 p.p.m., preferably less than ppm, tent, with lower iodine numbers corresponding to lower extremely low oxygen content, for example less than 100 aromatic content. Aniline point is the temperature at p.p.m., preferably less than 50 p.p.m., and extremely low 0 which a measured sample of test material becomes fully nitrogen content, for example, less than 100 p.p.m., prefsoluble in a measured quantity of aniline. The higher the erably less than 50 ppm, and especially less than 30 aniline point, the lower is the aromatic content of the p.p.m. More importantly, these products will exhibit exsample. The ultraviolet light stability test measures the ceptionally low indicia of aromatics content, as measured stability of the sample in a fused quartz container on exby iodine number, aniline point, or other equivalent indiposure to ultraviolet light radiation in a standard Evcia. The products of the second-stage hydrogenation can eready C-3B carbon arc solarium unit. The stability of show a reduction in viscosity, and accordingly it may be the test sample is measured in this test, and also in the desirable to subject such products to a topping treatment, sunlight stability test, by comparison of the color of the when the viscosity of the final product is important, as in sample before and after exposure to light radiation by the case of lubricating oils. The products of the second either or both of the ASTM D1500 (ASTM color) test stage may also be subjected to additional further procand the ASTM D-156 (Saybolt color) test. On the AST M essing, for example, dewaxing, clay treatment, or the like, color scale colors may vary from L 0.5 (lighter than the if desired. 0.5 ASTM color standard) for the lightest color to 8.0 The process of this invention can be more readily for the darkest color. On the Saybolt color scale, colors understood by reference to the following specific embodivary from +30 (lightest) to 16 (darkest). The sunments. light stability test was carried out by exposure of the test Example 1 sample to sunlight during 25 days of storage on a window- In this example a crude undecolorized petrolamm was Slll, while the sample is in contact with the atmosphere. subjected to a two-stage hydrogenation process in accord- The mspectlons on the charge Stock, the firstfstage ance with the present invention. The first-stage hydrogena- Producf and the secondfsfage product are Set forth the fion was carried out at F 3000 hydrogen following table. In addition, for purposes of comparison, pressure, and a liquid hourly space velocity of 1,5 whil there are also set forth the inspections on a commercial maintaining a hydrogenzoil ratio of about 4000 standard fifllshed petfolatllnt P p r m an quivalent charge cubic feet of hydrogen per barrel of oil. The catalyst emstock by sulfuric acid treatment and clay filtering.

TABLE I Crude First Second Acid Treated Finished, Acid Inspection Petrolatum Stage Stage First Stage Treated and Charge Product Product Product Clay Filtered Petrolatum Gravity: API 31. 5 1 32. 6 33. 5 31.9 gislcosity, SUS 210 F 51.3 51. 1 50. 2 51, 2 O l i'sTM 13-1500 L 3. 5 L 0. 5 L o. 5 L0 ASTM D-l56 +10 L+30 UV Absorptivity, D2008 0. 68 0. 0. 02 Q 03 Iodine Number 6. 9 2. 5 0. 4 3 Aniline Point, F. 241 245. 8 248. 1 243 Total Nitrogen, p p 1.70 30 2 30 Sulfur, p.p.rn. 1, 200 40 20 1, 300 Oxygen, p.p.m 360 50 50 UV Light Stability, 8 hr.: Color before exposure:

ASTM D1500 L 0. 5 ASTM D-l56 +4 Color after exposure:

ASTM D-1500 L 2. 0 ASTM D-156 2 15 Sunlight Stability, days 25 Color before exposur ASTM D-1500- L 0. 5 ASTM Dl56 +4 Color after exposure:

ASTM 13-1500 L 1. 5 ASTM D-156 +28 1 Average. 2 Darker.

ployed was presulfided nickel tungsten on an alumina base, which catalyst contained 6 percent nickel and 19 percent tungsten. The second stage of the process was carried out at 575 F., 3000 p.s.i.g. hydrogen pressure and space velocity of 0.5, while maintaining a pure hydro- Examination of the results set forth in Table I indicates a partial reduction in nitrogen and oxygen and a drastic reduction in sulfur content was obtained in the first-stage hydrogenation. In addition, the color of the first-stage product was improved and the aromatic congeruoil ratio of 5000 standard cubic feet per barrel of oil. 7 tent was reduced as indicated by the reduction in ultraviolet light absorptivity and iodine number and the increase in aniline point. As will also be seen, the product of the second-stage treatment exhibited a still further color improvement and stability concurrently with a reduction in the product to negligible quantities of nitrogen, sulfur, oxygen and aromatics. Comparison of the product obtained by acid treating of the first-stage product demonstrates that a markedly more stable product is obtained by the exhaustive hydrogenation treatment of this invention, as compared with acid treatment. Comparison of the product obtained from the second-stage hydrogenation with the typical finished petrolatum obtained by acid treatment and clay filtering shows that the product obtained by the two-stage hydrogenation process of this invention is markedly superior to the conventional product from the standpoint of color, oxygen, sulfur and nitrogen content, aromatics content and stability as measured by exposure to ultraviolet light radiation.

Example 2 In this embodiment, a lubricating oil fraction having a viscosity of approximately 70 Saybolt Universal Seconds at 100 F. suitable for use as a white oil charge stock was subjected to two stage hydrogenation in accordance with the herein-disclosed invention. The first stage of the process was carried out with the same catalysts and at the same conditions employed in the first stage of the process described in Example 1, except that in this instance the reaction temperature was 700 F. The second stage of the process was also carried out with the same catalyst and at the same operating conditions as the second stage of the process described in Example 1, except in this instance the pure hydrogenzoil ratio was maintained at 4000 standard cubic feet per barrel of oil. The untreated charge stock and the products from the first and second stages were evaluated in the same manner as the charge stock and products in Example 1. In addition, these materials were also evaluated in accordance with ASTM test procedures for carbonizable substances, passage of which is used as an indication of suitability of the test material for pharmaceutical purposes. For purposes of comparison, a finished treated white oil prepared by acid treatment and clay filtration of a charge stock equivalent to that employed in the present example was also evaluated. The results of these evaluations are presented in the following table.

8. reduction in ultraviolet light absorptivity and iodine number and an increase in the aniline point. This product was not fully satisfactory as such for-use as a white oil as evidenced by' failure of the carbonizable substances test and as evidenced by the initial color of the product as well as the color after exposure to ultraviolet light and sunlight. Comparison of the second-stage product with the product from the first stage shows a marked improvement in initial color and a-reduction to negligible proportions of oxygen, sulfur, nitrogen and aromatics content. The quality of this product was significantly better than the product'from the first-stage hydrogenation as evidenced by passage of the carbonizable substances test, lighter initial color and greater stability to ultraviolet light and sunlight. Comparison of the second-stage product with the white oil by acid treating andclay filtration shows that the product obtained by two-stage hydrogenation is superior from the standpoint of lower sulfur, nitrogen and aromatics content.

Example 3 In this embodiment, the bottoms product boiling above 400 F. obtained from distillation of the product obtained by sulfuric acid alkylation of olefins to form alkylate boiling in the gasoline range is subjected to two-stage hydrogenation in accordance with the herein-disclosed process using the conditions described in Example 1 except that in the second stage of the process a reaction temperature of 500 F., a space velocity of 3.0 and a'hydrogenzoil ratio of 2000 standard cubic feet per barrel of oil is used. The product of this process is suitable for use as a charcoal lighter fluid and the initial odor of the product is acceptable for this purpose. The stability of the product is demonstrated by storage for twelve weeks at a temperature of 130 F. after which time the odor is found to be unchanged.

Example 4 In this embodiment, a kerosene distillate is subjected to two-stage hydrogenation in accordance with the present TABLE II First Stage Second Stage Acid Treated and Inspection Charge Stock White Oil White Oil Clay Filtered White Oil Gravity, API 33. 3 1 35. 2 36.0 36. 4 Viscosity, SUS 100 F 71. 8 68. 6 65. 7 69. 6 Color:

ASTM D1500 L 1.0 ASTM D-l 16 +16 +30 L+30 UV Absorptivity, ASTM D2008 2. 37 0. 14 0. 02 0. 09 Iodine Number 8. 5 1. 9 0. 2 1. 2 Aniline Point, F 210.0 211 212 216. 7 Total Nitrogen, p.p.m- 30 30 0. 2 30 Sulfur, p.p.m- 500 40 500 Oxygen .p. 260 50 50 carbonizable Substances Passes Passes D-fi12 Fails Fails Passes Passes UV Light Stability 8 hr.:

Color before exposure:

ASTM D-1500 L 1. 0 L 0.5 ASTM D15fi 13 +14 L+30 L+30 Color after exposure:

ASTM D-1500 L 2. 0 L 1. 0 ASTM D-l 56 +20 +25 Sunlight Stability: Days 25 25 Color before exposure:

ASTM D-1500 L 0. 5 ASTM D-156 +14 Color after exposure:

ASTM D-1500 L 1. 0 ASTM D456 1 Average.

Examination of the results presented in the foregoing table for the product of the first-stage hydrogenation shows a marked reduction in the sulfur content of the oil, a marked reduction in the oxygen content and a reduction in the aromatics content of the oil as evidenced by a 500 Rand a hydrogenzoil ratio of'2000 s.c.f./bbl. The second-stage product is subjected to the Aviation Turbine Fuel Thermal Stability Test ASTM D-1660. Under the procedure of this test the fuel is subjected to temperatures and conditions similar to those occurring in some aviation turbine engines. Thus, fuel is pumped at predetermined rates through a preheater section which simulates the hot fuel line sections of the engine as typified by an engine fuel-oil cooler. It then passes through a heated filter section which represents the, nozzle area or small fuel passages in the hot section of the engine where fuel degradation products may become trapped. A precision sintered stainless steel filter in the heated filter section traps fuel degradation products formed during the test. The extent of the buildup is noted as an increased pressure drop across the filter, and, in combination with the deposit condition of the preheater, is used as an assessment of the thermal stability of the fuel. The preheater deposits are rated in accordance with the scale ranging from for no deposits to 4 for'the heaviest deposits. After subjecting the second-stage product to the conditions of the test using a preheater temperature of 700 F. and a filter tempera ture of 800 F. for hours, no pressure differential across the test filter is observed and the preheater deposits are given a rating of 2 which corresponds to a barely visible discoloration.

Example 5 In still another embodiment of the invention a transformer oil stock that had been subjected to a first-stage hydrogenation in accordance with the present invention at 1000 p.s.i.g., 1.40 LHSV, at a temperature of 625 F., a hydrogenzoil ratio of about 2400 s.c.f./bbl., and using a presulfided nickel-cobalt-molybdenum on alumina catalyst, was further subjected to a second-stage hydrogenation at 575 F., at a pressure of 3000 p.s.i.g., at a space velocity of 0.5 in the presence of 4000' s.c.f. hydrogen per barrel of oil, using a prereduced, 48% nickel on kieselguhr catalyst. The product obtained from the first stage was compared with that portion (196.6 of the product boiling above 554 F. for stability in accordance with the ASTM D-l3l3 Sludge Test, and a standard transformer oil oxidation test, both in uninhibited form and after inhibition with 0.15% by weight of a commercial antioxidant, 2,6-di-t-butyl-p-cresol.

The results of these tests are indicated below:

Comparison of the above indicated results shows a marked improvement in inhibitor response for the secondstage product as compared with the first-stage product. This is particularly remarkable in view of the fact that the unhibited sludging tendencies of the second-stage product were found to be greater than those of the uninhibited first-stage product.

The importance of the use of nickel on diatomaceous earth as the second-stage hydrogenation catalyst was demonstrated by hydrogenating with dififerent catalysts duplicate samples of a medium neutral lubricating oil distillate that had been subjected to a first-stage hydrogenation in accordance with the herein-disclosed process. Both samples were hydrogenated under identical conditions of 3000 p.s.i.g. hydrogen pressure and 650 F., for identical periods of four hours, at maximum reaction pressure. In one instance the second-stage catalyst described in Examples 1 to 4 was utilized in a proportion sufiicient to provide 2.0 parts by weight of reduced nickel or 1000 parts by volume of feed stock. In the other instance metallic nickel in the form of Raney nickel was used in the same proportion as the hydrogenation catalyst. The products obtained from the hydrogenation of each of the samples were evaluated for aromatics content, ultraviolet light stability and heat stability. The heat stability evaluation was carried out by determining the time required for an oil sample maintained at 240 F. and in contact with a copper strip to increase its ASTM color by one and two numbers. The results of these tests were as set forth in the following table.

Comparison of the results set forth in the preceding table shows a marked superiority for the products obtained from second-stage hydrogenation with nickel on kieselguhr as compared with products obtained with the same charge stock under the same second-stage conditions using Raney nickel as the catalyst. Thus, the products obtained from the nickel on kieselguhr hydrogenation were found to have a lower aromatics content as evidenced by the higher aniline point, lower ultraviolet light absorptivity and lower iodine number and as evidenced by the superior stability of such products on exposure to ultraviolet light and heat.

The unique coaction of the herein-disclosed reduced nickel on kieselguhr second-stage catalyst with the firststage hydrogenated product has been further shown by comparison of the products obtained by subjecting a Texas lubricating distillate having a viscosity of about 3200 SUS at F. to a first-stage hydrogenation at 728 F., 1000 p.s.i.g., an LHSV of 1.5, while maintaining a hydrogemoil ratio of 4000 s.c.f. per barrel, in the presence of a presulfided 25% nickel tungsten on alumina catalyst, and then subjecting duplicate portions of the first-stage reactor efiluent to separate, second-stage hydrogenations at 575 R, an LHSV of 1.5, 1000 p.s.i.g., while maintaining a hydrogenzoil ratio of 4000 s.c.f./bbl., in

' the presence of the first-stage catalyst on the one hand,

and in the presence of the prereduced 48% nickel on kieselguhr second-stage catalyst on the other hand. The second-stage products boiling above 700 F. were compared for color, nitrogen content, aromatics content,

iodine number and viscosity index. The results of these tests are shown in the table below.

TABLE V Ni W Sec- N i-Kiesel- Inspections First Stage and Stage guhr Second Product Product Stage Product Color, ASTM D-1500 3. 5 1. 5- 1. 0- Nitrogen:

Total, p p m 180 100 Basic, p p m... 65 44 Aromatics, percent 31. 6 18. 4 Iodine No 7. 5 5. 7 Viscosity Index. 44 47 From the foregoing results it will be seen that the nickel on kieselguhr second-stage catalyst disclosed herein is uniquely selective for low-sulfur hydrogenated oils, in that this catalyst produced an oil that was markedly superior from the standpoint of color, nitrogen content, aromatics content and viscosity index.

The specific examples set forth herein are illustrative only and it will be appreciated that similar results can be obtained by the use of other first-stage hydrogenation catalysts, e.g., nickel-molybdenum sulfide, sulfided cobalt molybdate, and sulfided nickel-cobalt molybdate on alumina, silica gel, or silicia-alumina, and by sulfided nickel-tungsten on silica-alumina, by the use of other 11 feed stocks disclosed herein, e.g., kerosene and parafiin wax, and by the use of other firstand second-stage reaction conditions. dt will also be understood that the products of the first and second stages may be subjected to further refining treatment, as by topping, acidtreating, clay filtration, or the like.

We claim:

1. A process comprising contacting a sulfur-containing petroleum fraction that is normally unstable to heat and light and that is selected from the group consisting of an alkylate fraction boiling above the gasoline range and straight run fractions consisting of lubricating oil distillate, transformer oil stock, white oil stock and petrolatum in a first stage with hydrogen and a sulfur-resistant hydrogenation catalyst at hydrogenation conditions to produce a partly hydrogenated product the sulfur content of which is sufliciently small that it will not adversely affect the activity for removal of heteroatoms and aromatics of a second hydrogenation catalyst referred to hereinafter, thereafter contacting the partly hydrogenated product in a second stage with hydrogen and said second hydrogenation catalyst consisting essentially of reduced metallic nickel composited with a diatomaceous earth, at hydrogenation conditions, including a pressure of at least 2500 p.s.i.g., so selected as to produce a product characterized by improved stability, an extremely small heteroatom content and an iodine number of not greater than 0.71.

2. A process comprising contacting a sulfur-containing petroleum fraction that is normally unstable to heat and light and that is selected from the group consisting of an alkylate fraction boiling above the gasoline range and straight run fractions consisting of lubricating oil distillate, transformer oil stock, white oil stock and petrolatum in a first stage with hydrogen and a sulfur resistant hydrogenation catalyst comprising at least one hydrogenation component selected from the group consisting of metals of Group VIa and Group VIII of the Periodic System, and oxides and sulfides thereof, at a temperature in the range of about 600 to 825 F., at a pressure in the range of about 750 to 5000 p.s.i.g., and at a space velocity in the range of about 0.1 to 5.0 liquid volumes of charge stock per volume of catalyst per hour, while maintaining a hydrogen:charge stock ratio in the range of about 1000 to 20,000 s.c.f./bbl., to produce a partly hydrogenated product the sulfur content of which is sufficiently small that it will not adversely affect the activity for removal of heteroatoms and aromatics of a second hydrogenation catalyst referred to hereinafter and such that the total sulfur content of the combined charge stock and hydrogen feed to a second hydrogenation stage referred to hereinafter, calculated as p.p.m. sulfur in the charge stock, will be not more than about p.p.m. for each 1000 s.c.f. of hydrogen per barrel of charge stock, thereafter contacting the partly hydrogenated oil product in said second stage with hydrogen and said second hydrogenation catalyst consisting essentially of reduced metallic nickel composited with a diatomaceous earth, at a temperature in the range of about 450 to 750 F., at a pressure in the range of 2500 to 5000 p.s.i.g., at a space velocity in the range of about 0.1 to 5.0 liquid volumes of charge stock per volume of catalyst per hour, while maintaining a hydrogen:charge stock ratio of about 1000 to 20,000 s.c.f./'b'bL, the combination of conditions being selected to produce a product characterized by improved stability, an extremely small heteroatom content and an iodine number of not greater than 0.71.

3. The process of claim 2 wherein the charge stock to the first hydrogenation stage is a lubricating oil distill-ate.

4. The process of claim 2 wherein the charge stock to the first hydrogenation stage is a transformer oil stock.

5. The process of claim 2 wherein the charge stock to the first hydrogenation stage is a white oil stock.

6. The process of claim 2 wherein the charge stock to the first hydrogenation stage is a petrolatum.

7. The process of claim 2 wherein the charge stock to the first hydrogenation stage is an alkylate fraction boiling above the gasoline range.

8. A process contacting a sulfur-containing petroleum fraction that is normally unstable to heat and light and that is selected from the group consisting of an alkylate fraction boiling above the gasoline range and straight run fractions consisting of lubricating oil distillate, transformer oil stock, white oil stock and petrolatum in a first stage with hydrogen and a sulfur-resistant hydrogenation catalyst comprising at least one hydrogenation component selected from the group consisting of metals of Group V141 and Group VIII of the Periodic System, and oxides and sulfides thereof at a temperature in the range of about 650 to 775 F., at a pressure in the range of about 1000 to 3500 p.s.i.g., and a space velocity in the range of about 0.5 to 3.0 liquid volumes of charge stock per volume of catalyst per hour, While maintaining a hydrogen:charge stock ratio in the range of about 2000 to 10,000 s.c.f./'bbL, to produce a partly hydrogenated product the sulfur content of which is such that the total sulfur content of the combined charge stock and hydrogen feed to a second hydrogenation stage referred to hereinafter, calculated as p.p.m. sulfur in the charge, will not be more than about 10 p.p.m. for each 1000 s.c.f. of hydrogen per barrel of charge stock, thereafter contacting the partly hydrogenated oil product in said second stage with hydrogen and a second hydrogenation catalyst consisting essentially of reduced metallic nickel composited with a diatomaceous earth, at a temperature in the range of about 525 to 690 1 at a pressure in the range of 2500 to 3500 p.s.i.g., at a space velocity in the range of about 0.5 to 3.0 liquid volumes of charge stock per volume of catalyst per hour, while maintaining a hydrogen:charge stock ratio of about 2000 to 10,000 s.c.f./bbL, the combination of conditions being selected to produce a product characterized by improved stability, an extremely small heteroatom content and an iodine number of not greater than 0.71.

9. A process comprising contacting a sulfur-containing petroleum fraction that is normally unstable to heat and light and that is selected from the group consisting of .an alkylate fraction boiling above the gasoline range and straight run fractions consisting of lubricating oil distillate, transformer oil stock, White oil stock and petrolatum in a first stage with hydrogen and a sulfur-resistant hydrogenation catalyst containing a sulfided combination of nickel and tungsten as the hydrogenating component composited with an alumina support, at a temperature in the range of about 650 to 775 F., at a pressure in the range of about 1000 to 3500 p.s.i.g., and a space velocity in the range of about 0.5 to 3.0 liquidvolumes of charge stock per volume of catalyst per hour, while maintaining a hydrogen:charge stock ratio in the range of about 2000 to 10,000 s.c.f./bbl., to produce a partly hydrogenated product the sulfur content of which is such that the total sulfur content of the combined charge stock and hydrogen feed to a second hydrogenation stage referred to hereinafter, calculated as p.p.m. sulfur in the charge, will not be more than about 10 p.p.m. for each s.c.f. of hydrogen per 'barrel of charge stock, thereafter contacting the partly hydrogenated oil product in a seocnd stage with hydrogen and a second hydrogenation catalyst consisting essentially of reduced metallic nickel composited with kieselguhr, at a temperature in the range of 2500 to 3500 p.s.i.g., at a space velocity in the range of about 0.5 to 3.0 liquid volumes of charge stock per volume of catalyst per hour, while maintaining a hydrogen:charge stock ratio of about 2000 to 10,000 s.c.f./bbL, the combination of conditions being selected to produce a product characterized by improved stability, a sulfur content of less than 20 p.p.m., a nitrogen content of less than 13 5O p.p.m., an oxygen content of less than 50 p.p.m. and an iodine number of not greater than 0.71.

10. The process of claim 9 where the charge stock to the first hydrogenation stage is a lubricating oil distillate.

11. The process of claim 9 where the charge stock to the first hydrogenation stage is a transformer oil stock.

12. The process of claim 9 where the charge stock to the first hydrogenation stage is a white oil stock.

13. The process of claim 9 where the charge stock to the first hydrogenation stage is petrolatum.

14. The process of claim 9 where the charge stock to the first hydrogenation stage is an alkylate fraction boiling above the gasoline range.

References Cited UNITED STATES PATENTS 3,175,970 3/1965 Bercik et a1. 208264 1,908,286 5/1933 Dorrer 260-667 2,671,754 3/1954 De Rosset et a1. 20897 3,006,843 10/1961 Archibald 208264 3,236,764 2/1966 Den Herder et al. 208210 OTHER REFERENCES Gruse and Stevens: Chemical Technology of Petroleum, 3rd edition; McGraW-Hill, New York, N.Y., 1960; pp. 506-512, especially pp. 507 and 510.

S. P. JONES, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,392 ,112 July 9, 1968 Paul G. Bercik et a1.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below: Columns 5 and 6, TABLE I, fourth column, line 1 thereof,

"33.5" should read 33.6 same table, fifth column, line 16 thereof, "L 0.25" should read L 0.5 Columns 7 and 8, TABLE II, second column, line 7 thereof, "210.0" should read 201.0 same table, fourth column, line 9 thereof, 50" should read 20 Column 10, TABLE IV, first column, line 11 thereof, "Hrs. to 3 color increase" should read Hrs. to 2 color increase Signed and sealed this 16th day of December 1969.

(SEAL) Attest:

Edward M. Fletcher, Jr.

Attesting Officer Commissioner of Patents

Claims (1)

1. A PROCESS COMPRISING CONTACTING A SULFUR-CONTAINING PETROLUEM FRACTION THAT IS NORMALLY UNSTABLE TO HEAT AND LIGHT AND THAT IS SELECTED FROM THE GROUP CONSISTING OF AN ALKYLATE FRACTION BOILING ABOVE THE GASOLINE RANGE AND STRAIGHT RUN FRCTIONS CONSISTING OF LUBRICATING OIL DISTILLATE, TRANSFORMER OIL STOCK, WHITE OIL STOCK AND PETROLATUM IN A FIRST STAGE WITH HYDROGEN AND A SULFUR-RESISTANT HYDROGENATION CATALYST AT HYDROGENATION CONDITIONS TO PRODUCE A PARTLY HYDROGENATED PRODUCT THE SULFUR CVONTENT OF WHICH IS SUFFICIENTLY SMALL THAT IT WILL NOT ADVERSELY AFFECT THE ACTIVITY FOR REMOVAL OF HETEROATOMS AND AROMATICS OF A SECOND HYDROGENATION CATALYST REFERRED TO HEREINAFTER, THEREAFTER CONTACTING THE PARTLY HYDROGENATED PRODUCT IN A SECOND STAGE WITH HYDROGEN AND SAID SECOND HYDROGENATION CATALYST CONSISTING ESSENTIALLY OF REDUCED METALLIC NICKEL COMPOSITED WITH A DIATIOMACEOUS EARTH, AT HYDROGENATION CONDITIONS, INCLUDING A PRESSURE OF AT LEAST 2500 P.S.I.G., SO SELECTED AS TO PRODUCE A PRODUCT CHARACTERIZED BY IMPROVED STABILITY, AN EXTREMELY SMALL HETEROATOM CONTENT AND AN IODINE NUMBER OF NOT GREATER THAN 0.71.