US3208931A

US3208931A - Refining of petrolatum

Info

Publication number: US3208931A
Application number: US166261A
Authority: US
Inventors: Frederick C Wood
Original assignee: Union Oil Company of California
Current assignee: Union Oil Company of California
Priority date: 1962-01-15
Filing date: 1962-01-15
Publication date: 1965-09-28
Anticipated expiration: 1982-09-28

Description

Sept. 28, 1965 Y F. c. woon 3,208,931

REFINING OF PETROLATUM Filed Jan. l5, 1962 United States Patent O 3,208,931 REFlNING F PETROLATUM Frederick C. Wood, Fullerton, Calif., assigner to Union Oil Company of California, Los Angeles, Calif., a corporation of California Filed Jan. 15, 1962, Ser. No. 166,261 7 Claims. (Cl. 208-27) This invention relates to the refining of waxes including microcrystalline waxes, petrolatums, and slack waxes. More particularly, this invention relates to a two-stage hydrogenation treatment of said wax fractions to achieve a high degree of color improvement and to impart color stability to the waxes.

Recently, hydrofining has been suggested as a method for refining of petroleum waxes. In such hydrofining, relatively mild conditions are prescribed to prevent any possible isomerization or cracking of the wax fraction. Thus, low temperatures, i.e., about 400 to 700 F., and high pressures, .e., about 1000 to 3000 p.s.i. are prescribed. Because of the low temperatures employed, relatively low space velocities, i.e., about 0.1 to about l are necessary to effect the refining. Contrary to the results described by the prior art for such hydrofining, I have found that in many instances, a satisfactorily decolorized wax product cannot be obtained with the suggested hydrofining treatment. I have also discovered that the wax product so obtained, even when decolorized to an initially satisfactory color, darkens upon storage to an unmarketable product.

It is an object of this invention to prescribe a hydroning method which will achieve a satisfactory decolorization of crude waxes.

It is also an object of this invention to prescribe a hydrofining method which Will impart a high degree of color stability to the wax product.

Other and related objects will be apparent from the following discussi-on of the invention.

Briefly, the invention prescribes a two-stage hydrofining of waxes wherein the first stage is performed under sufficiently severe conditions to remove the major portions of color bodies and the subsequent stage is performed under mild conditions to impart a color stability to the product.

In a preferred embodiment, the second stage simply comprises a continuation of the first stage wherein the reactants are quenched by the introduction of a cool retially improved contacting efficiency. Preferred solvents are those boiling in the kerosene range; however, naphtha, light mineral oils, jet fuel fractions, etc., can also be used, in amounts between 0 and about 80 volume percent solvent, preferably between about l0 and about 50 volume percent. The slack wax, slack wax distillates and petrolatums are mixtures of a heavy oil and microcrystalline wax and generally contain between about and 95 percent of the latter. The wax feedstocks used herein ordinarily have an initial boiling point above about l000 F. and are dark brown to black in color as determined by the standard ASTM test method, D-lSOO. This test meth-od provides a classification from 0.5 to 8.0, 0.5 corresponding to a pale yellow and 8 corresponding to a dark brown coloration. Commonly, the wax feedstocks are darker than 8 when measured by this test method. The principal objective of the hydrofining treatment is to reduce the color to a maximum of about 1.5 to 2.0 to meet the anticipated requirements of the Foo-d and Drug Administration for waxes used in food packaging containers.

The micro wax feedstocks are commonly derived from a crude oil residuum by conventional deasphalting and propane dewaxing of the deasphalted material. The propane dewaxing yields a crude slack wax which is subjected to a vacuum distillation to recover the high grade paraffin waxes as wax distillate stocks. The vacuum distillation bottoms commonly contain between about 30 to about 90 percent microcrystalline waxes and are referred to as petrolatums. As previously mentioned, the Wax distillates and slack wax bottoms (petrolatums) can be advantageously refined by my invention. The wax distillates can be be hydroiined prior to or after the deoiling step as desired. It is also within the scope of my invention to hydrofine the foots oil Iproduct from the deoiler as this hydrocarbon oil frequently contains color bodies which prevent its use as a paraftinic blending stock, base stock for halogenation, etc., in the production of halogenated, particularly chlorinated hydrocarbons.

The hydrofining operation is carried out in a conventional reactor with a fixed bed of granular catalyst. The feed-stock and recycle gas streams are preheated to the desired hydrofining temperature and then introduced into the reactor in a downflow concurrent or countercurrent technique.

The following table summarizes the reaction conditions in the first and second stages of the treatment.

TABLE 1 First Stage Second Stage Condition Broad Preferred Most Broad Preferred Most Preferred Preferred Temperature, F 600-800 675-775 725-755 400-700 450-600 500-550 Space Rate, v./v./l1r 0. l-l. 5 0. 2-0. 5 0. 25-0. 5 0. 2-l0 0. 5-5 l-4= Pressure, p.s.i.g 500-1, 500 800-1, 200 800-1, 200 500-1, 500 800-1, 200 800-1, 200 Gas Rate, S.o.f./bbl 500-10, 000 l, 000-2, 000 1, 000-2, 000 500-10, 000 3, 000-7, 000 3, 000-7, 000

It is understood of course that se-lection of the necessary conditions t-o obtain the desired severity in each of the hydrofining stages is within the skill of the art. Various processing techniques can greatly affect such selectio-n, e.g., use of a flooded bed technique generally will provide more severe processing than conventional downflow because of the greater residence time of the feedstock in the reactor. With such iiooded bed techniques, .it is within the scope of the invention to employ slightly milder conditions than set forth in Table l.

Conventional hydrofining catalysts are used herein, including in general any of the Group VIB and/or Group VIII metals, their oxides or sulfides, either as such or preferaibly distributed upon a-n abs-orbent oxide carrier such as alumina, titania, Zirconia, silica, aluminum silicates, clays, etc. Particularly suitable catalysts for the first stage a-re the various sulfur resista-nt catalysts which comprise a combination of an iron group metal, oxide or sulfide with a Group VIB metal oxide or sulfide supported upon activated alumina, or activated alumina stabilized by the addition of a small proportion (3A15 of silica gel. l

The total hydrogenating components of the catalyst can comprise between about 4 and about 25 percent by weight of the finished catalyst. Preferred catalystsl a-re the cobalt molybdate type, which contain between about 1 and about 5 percent cobalt oxide or sulfide and between about 5 and about 20 percent molybdenum oxide or sulfide. Preferably, the catalyst is subject t-o a presulfiding technique in order to convert the active hydrogenating components substantially completely to the sulfide form. The catalyst is employed in subdivi-ding form, e.g., pellets between about 1/16 and 1A inch or as 8 t-o about'20 mesh granules.

The catalyst for the second stage treatment preferably is the same sulfur-resistant type as disclosed for the first stage of hydrofining; however, if desired, catalysts hav- .ing a higher hydro-genation activity can be used in the second stage such as the various Group VIII metals, eg., nickel, particularly the noble metals, eg., platinum, palladium, rhodium, etc. The active metals are distributed on various supports, preferably those supports which are finely divided a-nd have a high surface area, e.g., silica gel, alumina gel, titania, zirconia, activated clays, various crystalline metalo aluminosilica zeolites such as the H, X, Y type molecular sieves, etc. In the preferred downflow processing, the second stage of hydrofining merely comprises a quenched extension of the first stage. In this embodiment, the second stage catalyst preferably is the same sulfur resistant type as employed in the first stage. In concurrent downliow processing, this is achieved by introducing the preheated feed and recycle gas into the top of the reactor and permitting it to flow downwardly through the cat-alyst bed. Cool recycle gas is introduced near the exit portion of the bed so as to quench the wax to the desired low temperature severity conditions necessary to impar-t the color stability to the product. In general, the oool recycle quench gas can be introduced at the midportion of the catalyst bed, at the last 5 percent of the bed, or at any increment therebetween. Preferably the exit t-o about 40 percent of the bed is quenched.

In ldownfiow countercurrent contacting, the hot recycle gas stream is introduced at the base of the reactor and the feed liows downwardly, countercurrent to this gas stream. The invention as applied to this processing technique comprises the introduction of the main hot Yrecycle gas stream at the midportion of the catalyst bed, Iat the last 5 percent increment of catalyst bed, or at any increment therebetween including the preferred 10 to 40 exit portion. The cool quench gas is introduced at the lbase of the reactor and permitted to flow through the entire catalyst bed.

A third processing technique comprises concurrent flow in the first stage and countercurrent flow in the quenched zone. In this embodiment, the preheated hydrocarbon feed and hot hydrogen or recycle gas stream are introduced at the top of the reactor and fiow downwardly therethrough. Intermediate the hydrocarbons travel through the reactor, the hot gas stream is withdrawn. The liquid hydrocarbons continue their downward flow countercurrent to the upward fiow of a co-ol quench, hydrogen-rich, gas stream which is introduced at the base of the reactor. The quench gas joins the hot recycle gas at the intermediate point and is withdrawn from the reactor therewith. As with they previously described techniques, the quench zone can comprise the exit 5 t-o about 50 percent of the catalyst bed, preferably between about the exit l0 to about 40 percent.

It is, of course, apparent that in either upflow or down- Afiow processing, separate reactors can be used f-or the two hydro-fining steps. The use of separate reactors, while increasing the capital investment, provides a flexible process which permits a wide variance of space rates and recycle gas rates in each of the contacting zones. When separate reactors are employed, the intermediate efiiuent from the first reactor can be processed directly into the second reactor or, preferably, the eiuent is separated int-o the vapor and liquid phases and the liquid phase is introduced into the second stage reactor together with the desired amount of cool recycle hydrogen.

The following examples are presented to illustrate my invention.

' Example] In this and subsequent examplesa 28-foot reactor, 2 inches in diameter, was employed ina downflow technique. The refined product removed from the bottom of the reactor was passed to a vapor liquid separator from which a liquid product was removed and passed to a stripping vessel for the removal .of hydrogen sulfide.

' The liquid product was passed downwardly through a packed stripping tower countercurrent to the flow of nitrogen.

A cobalt molybdate catalyst, 1A; inch pellet size, was placed in the reactor and presulfided by passing hydrogen over the catalyst at p.s.i.g. while slowly adding hydrogen sulfide to the hydrogen gas to obtain a 3 percent hydrogen sulfide concentration at the reactor inlet. Throughout the presulfiding p-rocedure the catalyst temJ perature was maintained below 400 F. When the temperature wave passed through the catalyst bed, the reactor was heated to the desired temperature while maintaining the hydrogen sulfide-hydrogen circulation. The hydrogen sulfide addition was continued until no further adsorption of hydrogen sul-fide was observed.

Thereafter, the reactor was employed for the hydroiining of a wax by introducing a petrolatum containing about 11.13 weight percent oil into the top of the reactor with a hydrogen containing yrecycle gas in the desired quantities. The feedstreams were preheated to the desired reaction temperature. The initial series of runs were made to determine the required severity of hydrofining to obtain a satisfactorily decolorized product. The reactor pressure was maintained through the series of runs at 1000 p.s.i.g.; the hydrogen rate was maintained at about 2000 stand-ard cubic feet per barrel of feed and the liquid hourly space velocity was maintained at about 0.3 volume per volume per h-our. The decolorization results are illustrated by FIGURE 1 which is a plot of the product colors so obtained as a function of the reactor temperature. At the preferred tempera-ture, about 750 F., the sulfur content was reduced from about 0.421 to about 0.04 weight percent; the nitrogen content from about 980 to about parts per million.

The preceding demonstrates that relatively severe hydrofining temperatures are necessary to obtain a product having a color less than about 3 on the ASTM scale and that the art recommended range of about 400-600 F. is insufficient to effect a satisfactory decolorization. While FIGURE 1 illustrates that temperatures in excess of about 775 F. can be expected to further improve the color of the product, such temperatures are generally prohibited by the degree of isomerization and cracking of the wax. The extent of this secondary reaction is indicated by the percent conversion of the feed to oil and is depicted by the dashed line in FIGURE 1. Generally, conversionsV greater than about 10 weight percent of the feed are to be avoided because of the loss of wax and greater deoiling capacity which will be needed to deoil the wax stock, Accordingly, temperatures less` than about 775 F., preferably less than about 755 F., are to be employed.

Although FIGURE 1 illustrates that the initial color of the waX effluent from the reactor is below about 3 and can be obtained below about 2, a satisfactorily decolorized material, the sample rapidly darkens upon storage to an unmarketable material,

Example 2 In the reactor previously described, a petrolatum stock containing about 11.3 weight percent oil with a color greater than about 8.0 on the ASTM scale was hydroned at a temperature of 750 F. and at 1000 p.s.i.g. pressure. The recycled gas rate was about 2000 s.c.f. per bbl. of feed. The space rate of the feed through the reactor was varied from about 0.2 to about 0.5 volumes per volume per hour. The product collected from the hydrogen sulde stripper was analyzed for color and the results obtained are depicted in FIGURE 2. These results indicate that decreasing the space rate from about 1 to about 0.5 greatly improves the decolorizing efliciency of the process. Preferably, space rates between about 0.5 and about 0.25 are employed.

The reactor effluent was also analyzed for oil `content and the conversion to oil is depicted by the dashed line of FIGURE 2. The results indicate that the conversion to oil is greatly affected by space rates and that any decrease in space velocity substantially increases the conversion of wax to oil. Accordingly, it is preferred to employ no lower space rates than are necessary to obtain the desired color improvement, i.e., no less than about 0.25 volumes per volume per hour. As with temperature, no improvement in color stability was observed throughout the range of space velocities investigated.

Example 3 The preceding examples amply demonstrate the need for improvement on wax hydroning treatments. Specifically, a need exists to provide an improvement in the initial color of the reactor efliuent and to impart a color stability to such efliuent. The following examples demonstrate how my invention achieves these goals.

The aforedescribed reactor was modified so as to permit the introduction of a quench stream of recycle gas into the lower (exit) percent portion of the bed. The remainder of the bed was maintained at 750 F. and 1000 p.s.i.g. pressure.

The petrolatum was passed downwardly through the reaction vessel at an overall space velocity of 0.3 volumes per volume per hour. Quench gas was introduced at the lower l0 percent portion of the catalyst bed t0 quench the reactants to 650, 600 and 500 F. in successive experiments. The following table summarizes the results:

TAB LE 2 Color Sulfur Nitrogen Temperature, Second Stage Initial 11 Single stage hydroiinng at 750 F. (no quench). b After 84 hours storage at 185-200 F.

Example 4 The point of quench gas introduction was moved upwardly to provide a second stage catalyst bed which comprised about 40 percent of the total catalyst. Table 3 summarizes the reaction conditions in each of the hydrolining stages and the results obtained thereby.

TABLE 3 Run 1 2 3 First Stage:

Temperature, F. 750 750 750 Space Rate, v./v./hr 0.3 0.48 0. 48 Pressure, p.s.i.g 1,000 1,000 1, 000 Gas Rate, soil/bbl" 2, 000 2, 000 2, 000 Color, D-1500 2. 6 2. 9 Second Stage:

Temperature, F 600 600 .500 Space Rate, v./v./hr 0.81 0.81 Pressure, p.s.i.g 1, 000 1,000 Gas Rate, s.c.f fbbl.. 8, 500 12,000

Color De1500- Initial l. 8 1. 6 After 2 days at 185-200 F-.- 2. 7 2. 0 After 30 days at l85200 F 3. 1 2. 9

The results demonstrate that a marked color improvement and increased color stability can be achieved by employing a second stage low temperature hydroning treatment of a severely hydroned wax stock.

As apparent to those skilled in the art, Various modifications of the invention can be employed without departing therefrom. Thus, separate reactors and distinct catalyst beds can be employed for each of the hydrofining stages. My invention is intended to be ycovered by the method series of steps and their obvious equivalents set forth in the following claims.

I claim:

1. A method for obtaining a decolorized wax product having a high degree of color stability which comprises: subjecting a wax stock selected from the class consisting of slack wax bottoms and petrolatum and characterized by color instability on storage to catalytic hydroning with added hydrogen in contact with a hydroning catalyst at a temperature between about 700 and about 775 F., a liquid hourly space rate between about 0.1 and about 1.0 and a pressure between about 500 and about 1500 p.s.i.g. to obtain a substantially decolorized wax stock in a iirst stage, withdrawing said wax stock from said first stage, admixing said wax stock with a cold hydrogen gas in a quantity sucient to reduce the temperature of said wax stock to about 450 and 600 F. and thereafter subjecting said substantially decolorized wax stock to mild hydrogenation with a hydrogenation catalyst a second stage at a temperature between about 450 and 600 F. to obtain said product.

2. In a method for decolorization of a wax stock selected from the 4class consisting of slack wax bottoms and petrolatum and characterized by color instability on storage wherein said wax stock is subjected to hydroning conditions with hydrogen and a bed of hydrofning catalyst at a temperature between about 675 and about 775 F., the improved method of improving the decolorization and the color stability of said stock which comprises quenching said waX stock by introducing a cold hydrogen-containing gas stream in quantity suflicient to reduce the temperature of said stock to between about 7 400 and about 600 F., said introduction of said cold gas being at a point intermediate of the travel of said stock through said bed to provide a mild catalytic hydro# genation of said wax. y

3, The method for obtaining a decolorized microcrystalline wax having a high degree of color stability which comprises subjecting a reactant stream comprising a wax containing stock characterized by color instability on storage and hydrogen to hydroning conditions with a bed of hydroning catalyst at a temperature of 675 to about 775 F., quenching said reactant stream at a point intermediate its travel through said bed of catalyst by introducing a cold recycle gas stream into said bed at said point in a quantity sufcient to provide a nal hydrogenation zone having a temperature between about 400 and about 600 F. and aspace velocity between about 0.1 and about 1.0 liquid volumes per volume per hour to impart a color stability to said wax and thereafter deoiling the decolorized wax stock to obtain said microcrystalline wax.

4. The method of claim 3 wherein said space velocity in said final hydrogenation zone is between about 0.25 and about 0.5.

5. The method of claim 3 wherein said catalyst is a sulided -composite of cobalt Aoxidey and molybdenum oxide supported on a carrier which is essentially activated alumina.

6. The method of claim 3 wherein said reactant stream comprises said wax stock and a light petroleum distillate diluent.

7. The method of claim 3 wherein said stock is petrolat'um.

References Cited by the Examiner UNITED STATES PATENTS 2,587,149 2/52 Gwynn 208-303 2,846,356 8/58 Mills et al. 208-27 2,985,579 5/ 61 Heinemann et al. 208-27 `2,998,377 8/61 Beuther et al. 208-27 3,022,245 2/62 Sparset a1 208-26 3,052,622 9/ 62 Johnson et al 208-27 3,089,841 5/ 63 Berkowitz et a1 208-27 A FOREIGN PATENTS 851,969 10/ 60 Great Britain.

797,744 7/ 58 Great Britain.

ALPHONSO D. SULLIVAN, Primary Examiner.

Claims

1. A METHOD FOR OBTAINING A DECLORIZED WAX PRODUCT HAVING A HIGH DEGREE OF COLOR STABILITY WHICH COMPRISES: SUBJECTING A WAX STOCK SELECTED FROM THE CLASS CONSISTING OF SLACK WAX BOTTOMS AND PETROLATUM AND CHARACTERIZED BY COLOR INSTABILITY ON STORAGE TO CATALYTIC HYDROFINING WITH ADDED HYDROGEN IN CONTACT WITH A HYDROFINING CATALYST AT A TEMPERATURE BETWEEN ABOUT 700* AND ABOUT 775*F., A LIQUID HOURLY SPACED RATE BETWEEN ABOUT 0.1 AND ABOUT 1.0 AND A PRESSURE BETWEEN ABOUT 500 AND ABOUT 1500 P.S.I.. TO OBTAIN A SUBSTANTIALLY DECOLORIZED WAX STOCK IN A FIRST STAGE, WITHDRAWING SAID WAX STOCK FROM SAID FIRST STAGE, ADMIXING SAID WAX STOCK WITH A COLD HYDROGEN GAS IN A QUANTITY SUFFICIENT TO REDUCE THE TEMPERATURE OF SAID WAX STOCK TO ABOUT 450* AND 600*F. AND THEREAFTER SUBJECTING SAID SUBSTANTAILLY DECOLORIZED WAX STOCK TO MILD HYDROGENATION WITH A HYDROGENATION CATALYST A SECOND STAGE AT A TEMPERATURE BETWEEN ABOUT 450* AND 600*F. TO OBTAIN SAID PRODUCT.