US2779711A - Refining of lubricating oils - Google Patents

Description

2,779,711 Patented den. 29, 1957 lice 2,779,711 REFINING F LUBRICATING OILS Louis A. Goretta, Hammond, Ind., assignor to Standard Gil Company, Chicago, Ill., a corporation of Indiana No Drawing. Application February 7&8, 1955, Serial No. 491,199

4 Claims, (Cl. 196-24) This invention relates to improvements in lubricating oil refining and more particularly provides a process for treating raw distillate lubricating oil stocks in the presence of hydrogen and a catalyst.

Conventional lubricating oil refining requires one or more extraction operations with acid or a selective solvent usually followed by clay treating in addition to the standard distillation and dewaxing or deasphalting operations. The availability of cheap by-product hydrogen from catalystic reforming plants has created a great deal of interest in the use of hydrogen treating processes, so called hydrofinishing processes, as an alternative to conventional extraction and clay treating. Treatment of lubricating oil stocks under mild conditions of hydrogenation improves color, viscosity index, and in general contributes to the stability of the oil. In practice however, it has been found necessary to operate on partially refined stocks, i. e. lubricating oil distillates which have been first extracted with acid or a solvent and preferably have been treated for removal of wax, in order to avoid costly stock losses while attaining the desired improvement in color and stability. Thus, in the present state of the art, hydrogenation of lubricating oil stocks is in general limited to finishing operations without eliminating expensive acid treating and/ or solvent extraction. When unextracted or raw stocks are subjected to hydrogenation, the severity of treatment required with conventionally available catalysts results in excessive production of light ends which must be separated from the treated product to meet flash and viscosity specifications.

A particular problem with raw feeds is color instability of the treated oils. Although a satisfactory initial color is obtained, meeting specifications, there is excessive degradation in color quality upon storage. For example, where a conventionally refined oil of 1.5 to 2.5 NPA color (ASTIvl-D155-45T) may darken upon aging at 100 C. for 24 hours to 2.0 to 3.0, a hydrogenated oil may darken to 3.0 to 3.5 or 4.5 or 5.0 NPA. It is undesirable to have the color darken more than /2 NPA upon aging.

I have discovered that a raw distillate lubricating oil stock can be economically processed to a stable product under selective conditions by use of an alkalized hydrogenation catalyst. The most suitable catalyst is alkalized cobalt oxide-molybdenum oxide-alumina, but alkalized molybdenum oxide-on-alumina' and alkalized chromium oxide-on-alumina also appear to have value. Other Wellknown hydrogenation catalysts, however, such as platinum-on-alumina and tungsten-nickel sulfide appear to be distinctly marginal. Surprisingly, the alkalized molybdenum and chromium oxide type hydrogenation catalysts do not appear to afford any significant advantage in processing extracted or partially refined lubricating oil stocks. But in processing Waxy or unextracted lubricating oil stocks, the alkalized catalysts of the invention produce light colored oils of satisfactory color specification and stability where the less selective corresponding unalkalized catalysts do not. Moreover, the production of light ends in the hydrogenation process is substantially reduced, by from about 25 to upwards of 50 percent, resulting in substantial savings of valuable lubricating oil stock.

In the practice of the invention, the feed is a raw distillate lubricating oil stock having a viscosity which may range up to that of the SAE-40 range. Advantageously, however, the invention is applied to stocks in the viscosity range of SAE 10 and 20 oils. The feed stock is not treated by preliminary extraction with acid or solvent and advantageously is a waxy distillate, i. e. has not been subjected to a preliminary dewaxing operation. The preheated stock together with hydrogen is passed in contact with a bed of particle form hydrogenation catalyst, e. g. a cobalt oxide-molybdenum oxide-alumina catalyst which has been alkalized by incorporation of an oxide or salt of an alkali metal or alkaline earth metal, e. g. 4 percent potassium oxide. The catalyst is disposed in the form of a fixed bed of pellets, pills or beads, and the feed is passed, advantageously down-flow, through the catalyst bed. A temperature in the range of about 650 to 850 F., preferably about 800 to 825 F., and a pressure of about 500 to 2500 p. s. i. g., preferably about 11000 to 1500, are maintained. The space velocity may be varied in the range of about 0.5 to 10 L. H. S. V., controlling the severity of treatment. The hydrogen rate is in the range of about 1,000 to 6,000 cubic feet per barrel although hydrogen consumption is low and ordinarily should not exceed about 200 to 400 cubic feet per barrel. After the feed has been subject to contact with the catalyst under the above hydrogenation conditions, unreacted hydrogen is separated. The unreacted hydrogen may berecycled or may be diverted to other purposes such as refinery fuel depending upon the design of the facilities. The treated oil is steam or vacuum stripped to remove light ends formed in the process.

The process of the invention permits the processing of raw waxy stocks directly without preliminary dewaxing and solvent extraction. Specification products may be obtained by selective treating at severities low enough to minimize stock losses, thus protecting the economic gains made by quality improvement and elimination of conventional acid and/or solvent refining methods. Processing waxy stocks provides a further advantage in improving the yield and quality of parafiin waxes produced by subsequent dewaxing operations.

The catalysts used with the process of the invention are conveniently any of the conventionally available chromium oxide-alumina, molybdenum oxide-alumina and cobalt oxide-molybdenum oxide-alumina hydrogenation and reforming catalysts, after selective promotion with an alkaline substance. A particularly suitable alkali is potassium hydroxide, but other alkali metals such as sodium and lithium, for example, may be employed, advantageously in the form of their oxides or hydroxides, but also in the form of other Water soluble salts such as borates, nitrates, carbonates, bicarbonates, acetates, sulfates, phosphates and the like. An example of the last named which is particularly suitable is disodium hydrogen phosphate. Oxides and salts of the alkaline earth metals also have values, for example calcium oxide or calcium bicarbonate.

The simplest method for incorporation of the alkali promoter is by impregnation with an aqueous solution of the soluble alkali in the desired concentration. The catalyst is then dried and calcined at an elevated temperature, e. g. 800 to 1200 F., for use. Alternatively, the alkali promoter may be incorporated in the catalyst composition at any desired stage in its preparation before drying and calcining. The concentration of alkaline promoter may be in the range of 0.5 to about 10 mol percent, but there is an optimum concentration of alkali promoter for each catalyst composition for color stabilization and minimum stock losses. Sincethe optimum concentration depends upon the nature of thefeed stock and correlation with process conditionsin addition to. catalyst composition; it

is necessary to resort to screening tests to determine the best catalyst composition for a given operation. In gen: eral, a concentration of about 2 to 4 mol percent of alkali promoter appears to give the best results, particularly with potassium.

The starting hydrogenation catalysts may be made by several methods. For example, alumina either in the form of a synthetic alumina gel or an activated alumina or bauxite can be impregnated with an aqueous solution of a salt of the metal giving the desired active oxide upon drying and calcination. Also the catalyst can be prepared by err-precipitation of the alumina base material with the molybdenum oxide or chromium oxide from a mixture of :aqueous solutions of corresponding salts. The resulting composites are dried, extruded or pelleted, and calcined. The cobalt oxide-molybdenum oxide-alumina catalyst, which represents a preferred form of catalyst for practicing the invention, may be prepared by impregnating a molybdenum oxide-alumina catalyst, or the catalyst may be prepared by co-precipitation from a mixed aqueous solution of soluble salts. The concentration of metal oxides may be varied quite widely in the finished catalyst although in the case of the molybdenum oxide catalysts, the concentration of molybdenum oxide ordinarily will be less than about mol percent. The proportion of cobalt also may vary but usually will be in the range of about 1 mol percent to 6 mol percent. It may be in the molecular proportions for formation of cobalt molybdate in the co-precipitated type catalyst if desired. The following examples illustrate specific aspects of the invention.

EXAMPLE I The catalyst was prepared by dissolving 22 grams of potassium nitrate in 85 cc. of water and impregnating 200 grams of a commercially available (Oronite) cobalt oxide-molybdenum oxide-alumina catalyst with the resulting solution. The catalyst contained 3.6 percent C00, 11.2 percent M003 and 4 percent K20. The catalyst was dried and calcined at 1000 F. for one hour.

An SAE-10 parafiin distillate from a pipe still running Mid-Continent crude oil Was used as the feed stock. The feed had an initial NPA color of 2.5; after aging for 24 hours at 100 C., the NPA color was 4.5. The feed was passed with hydrogen at a rate of 2810 set/barrel over a bed of 6 to 14 mesh catalyst pellets. The reaction conditions were controlled at a temperature of 800 E, a pressure of 1000 p. s. i. g. and a space velocity of 5.27 L. H; S; V. The reactor efiluent was vacuumed stripped to a pot temperature of 400 F. at 2 to 2 /2 mm. The treated oil had an initial color of 1.6 NPA and an aged color of 2.4.

The light ends off the treated oil, constituting 2.73 percent of the feed, turned dark on standing at room temperature for only a few hours. Similar discoloration of light ends produced by treating with a conventional cobalt oxide-molybdenum oxide-alumina catalyst or a nickeltungsten sulfide catalyst has not been observed. Hence, the color forming bodies responsible for instability appear to have been preferentially attacked by the alkalized catalyst and eliminated with the light ends.

By comparison, treatment with unalkalized, or conventional, cobalt oxide-"molybdenum oxide-alumina catalyst is less eifective in color improvement under similar conditions and, with respect to color stabilization, is exceedingly unreliable. Also the production of light ends is considerably higher, being in the range of 9 to 13.5 percent under the comparable conditions.

EXAMPLE II In the first series of runs, an SAE-10 waxy distillate was passed over a bed of the pelleted catalysts at a temperature of 800 F., a pressure of 1000 p. s. i. g. of hydrogen and a space velocity of 5 L. H. S. V. in the second series of runs. an SAE-ZO unextracted distillate Was treated under the same conditions with a 4 percent K20 on the chromia-alumina catalyst. The results of the two series of runs are tabulated below in Tables 1 and 2.

Table I NPA Color Percent K20 in Catalyst Initial Aged Table II NPA Color Initial i Aged Feed 2. 3 7. 5 Product 2. o l 3. 7 J) i4.. n#

EXAMPLE III A disodium phosphate-cobalt oxide-molybdenum oxidealurnina catalyst containing 4 mol percent C00, 6 mol percent M003, 5 mol percent NAZHPQ; and mol percent alumina was prepared by co-preeipitating an aqueous solution of mixed salts of cobalt, molybdenum and aluminum with disodium phosphate, drying and calcining. An unextracted SAE-lO parafifin distillate having an initial NPA color of 2.8 and an aged color of 8 NPA was treated over the catalyst at 800 E, 1000 p. s. i. g., 5+ 1.. H. S. V. and 3000 cubic feet of hydrogen per barrel. The treated product had an initial NPA color of 1.7 and an aged NPA color of 2.7. Approximately 7 percent light ends were separated when the product was stripped to the initial flash point of the feed before the color determinations.

I claim:

1. A process for producing color stable lubricating oil by hydrogenating an unrefined distillate lubricating oil stock derived from a mixed-base crude oil which is characterized by color instability which process comprises contacting the stock with cobalt oxide-molybdenum oxidealumina hydrogenation catalyst which has been alkalized by incorporation of about 0.5 to 10 mol percent of an alkali selected from the group consisting of compounds of alkali metals and alkaline earth metals, in the presence of hydrogen at a temperature in the range of about 650 to 850 F., :a pressure in the range of about 500 to 2500 p. s. i. g. and a space velocity in the range ofv about 0.5 to 10 W. H. S. V.

2. The process of claim 1 in which the catalyst is alkalized by incorporation of about 2 to 4 mol percent of potassium oxide.

3. The process of claim 1 in which the catalyst is stabilized by incorporation of about 2 to 4 mol percent disodium phosphate.

4. The process of claim 1 in which the unrefined distillate lubricating oil stock is in the viscosity range of about SAEl0 and SAE-ZO oils.

References Cited in the file of this patent UNITED STATES PATENTS 2,441,297 Stirton May 11, 1948 2,442,372 Smith et al. June 17, 1947 2,608,521 Hoog Aug. 26, 1952 2,697,064 Brown Dec. 14, 1954 2,697,683 Engel et al. Dec. 31, 1954 OTHER. REFERENCES Jones: The Oil and Gas Journal, Nov. 1, 1954.

Claims (1)

1. A PROCESS FOR PRODUCING COLOR STABLE LUBRICATING OIL BY HYDROGENATING AN UNREFINED DISTILLATE LUBRICATING OIL STOCK DERIVED FROM A MIXED-BASE CRUDE OIL WHICH IS CHARACTERIZED BY COLOR INSTABILITY WHICH PROCESS COMRISES CONTACTING THE STOCK WITH COBALT OXIDE-MOLYBDENUM OXIDEALUMINA HYDROGENATION CATALYST WHICH HAS BEEN ALKALIZED BY INCORPORATION OF ABOUT 0.5 TO 1 0 MOL PERCENT OF AN ALKALI SELECTED FROM THE GROUP CONSISTING OF COMPOUNDS OF ALKALI METALS AND ALKALINE EARTH METALS, IN THE PRESENCE OF HYDROGEN AT A TEMPERATURE IN THE RANGE OF ABOUT 650* TO 850* F., A PRESSURE IN THE RANGE OF ABOUT 500 TO 2500 P.S.I.G. AND A SPACE VELOCITY IN THE RANGE FO ABOUT 0.5 TO 10 W.H.S.V.