Production Of Technical White Mineral Oil

Abstract

Technical grade white mineral oil is produced by a series of steps including treating a mineral lubricating oil distillate with hydrogen in the presence of a sulfur-resistant catalyst (e.g., nickel molybdate on alumina) under hydrorefining conditions. The hydrogenated oil is hydroisomerized and hydrocracked by contact with hydrogen in the presence of a silica-alumina and crystalline-aluminosilicate-containing catalyst having about 0.1 to 5 weight percent of a platinum group metal. The resulting product is further contacted with hydrogen under aromatic saturation conditions in the presence of a platinum group metal-containing hydrogenation catalyst (e.g., platinum on alumina).

Description

This invention relates to a process for the production of technical grade white mineral oil from raw, waxy mineral oil distillates. More particularly, this invention concerns a hydrorefining, hydroisomerization-hydrocracking, aromatic saturation, catalytic conversion process for the production of technical grade white mineral oil in increased yields and at reduced operating costs.

Conventional refining techniques employed in producing technical grade white lubricating oils from raw, waxy distillates involve, for example, solvent treating, solvent dewaxing, and severe acid treating. These conventional refining techniques suffer from many shortcomings. For example, acid treating and solvent extraction have the inherent disadvantage of producing relatively low value byproduct sludge or extracts, and solvent dewaxing is a relatively costly operation due to high refrigeration requirements and low filter rates. Other techniques, such as urea adduction, encounter great difficulties as a continuous process for refining raw, waxy lubricating oil distillates.

The present invention concerns a hydrorefining, hydroisomerization-hydrocracking, aromatic saturation process wherein a raw, waxy, lubricating oil distillate having a high pour point, and a high aromatic content is converted into a technical grade white mineral oil in increased yields and at reduced operating coats. According to the process of the present invention the raw, waxy, lubricating oil distillate is contacted in a first stage with hydrogen in the presence of a desulfurization-denitrogenation type catalyst under hydrorefining conditions and treated in a second stage with hydrogen in the presence of a hydroisomerization-hydrocracking catalyst. The oil of lubricating viscosity in the second stage product is further contacted in a third stage with hydrogen under aromatic saturation conditions to produce high quality technical grade white mineral oil.

The mineral lubricating oil distillates to be treated by the process of the present invention are raw, waxy lubricating oil distillates which may even represent the complete distillate lubricating oil fraction derived from a waxy crude oil. The lubricating oil distillates useful as feedstocks in the present invention often possess a viscosity in the range of about 35 to 90 SUS at 210.degree. F., an aromatic carbon content of about 15 to 30 percent, a pour point of at least about 70.degree. F., and boil primarily in the range of about 600.degree. to 1,200.degree. F.

The hydrorefining treatment in the first stage of the present process is conducted at temperatures of about 600.degree. to 800.degree. F., preferably about 675.degree. to 725.degree. F. The other reaction conditions generally can include pressures of about 500 to 3,000 p.s.i.g., preferably about 2,000 to 3,000 p.s.i.g.; weight hourly space velocities (WHSV) of about 0.2 to 2, preferably about 0.25 to 0.5; and molecular hydrogen to feed oil ratios of about 1,000 to 5,000 SCF/B, preferably about 1,500 to 2,500 SCF/B.

According to my method the hydrogenated oil from the first hydrogenation stage is subjected to a second hydrogenation operation in which the catalyst is such that hydroisomerization and hydrocracking are effected. Thus, temperatures in the second stage range from about 600.degree. to 950.degree. F., with temperatures of about 650.degree. to 800.degree. F. being preferred. Other reaction conditions can include pressures of about 500 to 3,000 p.s.i.g., preferably about 2,000 to 3,000 p.s.i.g., weight hourly space velocities of about 0.25 to 2, preferably about 0.25 to 0.5, and molecular hydrogen to feed oil ratio of about 1,000 to 5,000 SCF/B, preferably about 2,000 to 3,000 SCF/B.

The aromatic saturation of the product of lubricating viscosity made in the second stage is in the third stage of the operation of this invention, and is conducted at a temperature of about 450.degree. to 700.degree. F., preferably about 550.degree. to 600.degree. F. Other reaction conditions can include a pressure of about 500 to 3,000 p.s.i.g., preferably about 2,000 to 3,000 p.s.i.g., a weight hourly space velocity of about 0.2 to 2, preferably about 0.25 to 0.5, and a hydrogen to feed oil rate of about 1,000 to 5,000 SCF/B, preferably about 2,000 to 3,000 SCF/B.

The desulfurization-denitrogenation type catalysts used in the first stage of the present process can be the sulfur-resistant, nonprecious metal hydrogenation catalysts, such as those conventionally employed in the hydrogenation of heavy petroleum oils. Examples of suitable catalytic ingredients are tin, vanadium, members of Group VIB in the Periodic Table, i.e. chromium, molybdenum and tungsten, and metals of the iron group, i.e. iron, cobalt and nickel. These metals are present in catalytically effective amounts, for instance, about 2 to 30 weight percent, and may be in elemental form or in combined form such as the oxides or sulfides, the sulfides being preferred. Mixtures of these materials or compounds of two or more of the oxides or sulfides can be employed, for example, mixtures or compounds of the iron group metal oxides or sulfides with the oxides or sulfides of Group VIB constitute very satisfactory catalysts. Examples of such mixtures or compounds are nickel molybdate, tungstate or chromate (or thiomolybdate, thio-tungstate or thiochromate) or mixtures of nickel or cobalt oxides with molybdenum, tungsten or chromium oxides, As the art is aware and as the specific examples below illustrate, these catalytic ingredients are generally employed while disposed upon a suitable carrier of the solid oxide refractory type, e.g., a predominantly calcined or activated alumina or other base exerting little cracking effect. Commonly employed catalysts have about 1 to 10 percent of an iron group metal and 5 to 25 percent of a Group VIB metal (calculated as the oxide). Advantageously, the catalyst is nickel molybdate supported on alumina. Such preferred catalyst can be prepared, for instance, by the method described in U.S. Pat. No. 2,938,002.

The platinum group metal-containing hydroisomerization-hydrocracking catalyst used in the second stage of the method of the present invention, unlike the catalyst employed in the first stage, is not normally sulfur-resistant and contains a major amount of an amorphous silica-alumina composite, containing for instance, about 5 to 45, preferably about 10 to 20, weight percent alumina on a dry basis; about 3 to 25, preferably about 5 to 10, weight percent of a hydrogen-exchanged crystalline alumino-silicate having a silica-to-alumina mole ratio greater than 3:1; and a catalytic amount, say about 0.1 to 5, preferably about 0.3 to 2, weight percent of a platinum group metal. The catalyst may also contain a small amount, e.g., less than about 1 weight percent of halide such as chloride or fluoride. If desired, a small amount, for instance about 5 to 20 or more weight percent of a suitable binder material, for example, alumina hydrogel, may be added to the second stage catalyst composition especially if the catalyst is formed by extrusion.

The platinum group metals include such group VIII metals as, for example, platinum, palladium, rhodium, or iridium. The platinum group metal may be present in the metallic form or as a sulfide, oxide or other combined form, The metal may interact with other constituents of the catalyst, but if during use the platinum group metal is present in the metallic form, then it is preferred that it be so finely divided that it is not detectable by X-ray defraction means, i.e. that it exists as crystallites of less than about 50 A. in size.

The amorphous silica-alumina composite employed in the second stage catalyst of the process of the invention is usually synthetically precipitated. The silica-alumina can be prepared by any desired method and several procedures are known in the art. For instance, a hydrogel can be prepared by coprecipitation or sequential precipitation by either component being the initial material precipitated with at least the principal part of the silica or alumina being made in the presence of the other, Generally the alumina is precipitated in the presence of a silica gel. It is preferred that the silica-alumina hydrogel be made by forming a silica hydrogel by precipitation from an alkali metal silicate solution and an acid such as sulfuric acid. Then alum solution may be added to the silica hydrogel slurry. The alumina is precipitated by raising the pH into the alkaline range by the addition of an aqueous sodium aluminate solution or by the addition of a base such as ammonium hydroxide. Other techniques for preparing the silica-alumina are well known in the are, and these techniques may be used. In the final catalyst the silica-alumina is present in xerogel or catalytically active form due to treatment at elevated temperatures as by calcination of the hydrogel.

The crystalline aluminosilicate component of the second stage catalyst may be synthetic or naturally occurring and has a pore size of about 8 to 15 A., preferably about 10 t0 14 A. Usually, with a given material, the pores are relatively uniform in size and often the crystalline alumino-silicate particles used to make the catalyst are primarily less than about 15 microns in size, preferably less than about 10 microns. In the crystalline aluminosilicate, the silica-to-alumina mole ratio is greater that 3:1 and is usually not above about 12:1, preferably being about 4 to 6:1. The aluminosilicate is at least about 50 percent, preferably at least about 75 percent, hydrogen-exchanged. That is about 50 percent of the metal cations, e.g. sodium, present in the aluminosilicate are replaced by hydrogen. Hydrogen exchange is commonly carried out by exchange of the cations of the synthetic or naturally occurring aluminosilicates with ammonium ions, for instance through contact with an aqueous solution of ammonium chloride or other water-soluble ammonium compound and subsequently calcining the aluminosilicate.

One method of preparing the second stage catalyst is by combining the silica-alumina hydrogel and the hydrogen-exchanged crystalline aluminosilicate and drying the mixture, for instance at temperatures of about 230.degree. to 600.degree. F., to convert the silica-alumina hydrogel to the xerogel form. The crystalline aluminosilicate may, if desired, be hydrogen-exchanged after it is combined with the silica-alumina hydrogel. The dried material can be calcined, for instance, at a temperature of the order of about 700.degree. to 1500.degree. F., preferably about 800.degree. to 1,100.degree. F. The platinum group metal may be added before or after the calcination, by, for example, ion exchange or impregnation, In any event, after the platinum group metal is added, the catalyst can be dehydrated and activated at the calcination temperature described above.

An available method for adding the platinum group metal by ion exchange comprises treating the silica-alumina-crystalline alumino-silicate mixture with an aqueous solution containing complex water-soluble, metal-amine cations, both organic and inorganic, of the metal to be deposited in the crystal structure. These complex cations ion-exchange with the cations present in the crystalline aluminosilicate. The exchange material is then removed from the solution, dried and activated or calcined, for example, by heating the material up to a temperature of about 250.degree. C. in a flowing stream of inert dry gas or vacuum. The activation may be effected at a temperature below the temperature at which the complex cations are destroyed. The activated material may then be subjected to heat treatment to a temperature not exceeding about 650.degree. C. and preferably not exceeding about 500.degree. C. in vacuum or inert atmosphere whereby the complex cation is destroyed and the platinum group metal is reduced in the material. Should the thermal treatment be insufficient to reduce the metal of the complex cations to the elemental state, chemical reduction either alone or in combination with thermal reduction may be employed. Alkali metals such sodium are suitable reducing agents for this purpose. Throughout the operation excessive temperatures and extremes of acidity are to be avoided since they may tend to destroy the crystal structure of the silica-alumina-crystalline aluminosilicate mixture.

The platinum group metal may also be added by impregnation. The silica-alumina-crystalline aluminosilicate mixture, for example, either with or without previous evacuation, may be soaked in either a dilute or concentrated solution, usually aqueous chloroplatinic acid, ammonium hexathio-cyanoplatinate (IV) or hexathiocyanate platinic acid, often in an amount just sufficient to wet the material and be completely absorbed. Also, if desired, the solution may be incorporated into the silica-alumina-crystalline aluminosilicate during the formation of the latter.

Either before of after dehydration, the catalyst can, if desired, be formed into macrosized particles by -inch or extruding. Generally, these particles are about 1/32 inch to 1/2 inch in diameter and about 1/16-inch to 1-inch or more in length. Although these macrosized particles are usually formed after dehydration and before calcination, this, of course is optional and can be done at any time found most convenient.

The catalyst employed in the third, or aromatic-saturation stage of the present invention is a platinum group metal-containing hydrogenation catalyst. This catalyst, like the catalysts of the second stage, is distinguished from the catalysts of the first stage in that it is not normally considered to be sulfur-resistant. The catalyst includes catalytically effective amounts of the platinum group metals mentioned above. Often, the platinum group metal is present in an amount, for example, of about 0,01 to 2 weight percent, preferably about 0.1 to 1 weight percent. The platinum group metal may be present in the metallic form or as a sulfide, oxide, or other combined form. As in the case of the second stage catalyst, the metal may interact with other constituents of the catalyst but if during use the platinum group metal is present in metallic form, then it is preferred that it be so finely divided that it is not detectable by X-ray diffraction means, i.e. that it exists as crystallites of less than about 50 A. size. Of the platinum group metals, platinum is preferred. If desired, the catalysts employed in the third stage of the process of the invention, like the catalysts used in the first stage, can be prereduced prior to use by heating in the presence of hydrogen, generally at temperatures of about 600.degree. to 800.degree. F.

Although various solid refractory type carriers known in the art may be utilized as a support for the third stage platinum group metal, the preferred supports have no substantial cracking effect on the hydrocarbon feeds. Most advantageously, the support is composed predominantly of alumina of the activated or calcined type. The alumina base is usually the major component of the catalyst, generally constituting at least about 75 weight percent on the basis of the catalyst and preferably at least about 85 to 99.8 percent. The alumina catalyst base can be an activated or gamma family alumina, especially gamma or eta alumina, such as those derived by calcination of amorphous hydrous alumina, alumina monohydrate, alumina trihydrate or their mixtures. A catalyst base advantageously used is a mixture predominating in, or containing a major proportion of, for instance about 65 to 95 weight percent, of one or more of the alumina trihydrates, bayerite, nordstandite or gibbsite, and about 5 to 35 weight percent of alumina monohydrate (boehmite), amorphous hydrous alumina or their mixtures. The alumina base can contain small amounts of other solid oxides such as silica, magnesia, natural or activated clays (such as kaolinite, montmorillonite, halloysite, etc.), Titania zirconia, etc., or their mixtures.

The addition of the platinum group metal to the alumina or other solid refractory type carrier can be accomplished employing, for example, the impregnation methods described above in connection with the second stage hydroisomerization-hydrocracking catalyst. Also, as in the case of the catalyst of the second stage, the platinum-group metal hydrogenation catalysts used in the third stage of the process of the invention may be employed in the form of macrosized particles generally having a diameter of about 1/32-inch to 1/2-inch and a length of about 1/16-inch to 1inch or more.

The process of the present invention is illustrated in detail by the following example.

EXAMPLE

A raw, waxy, mixed base lubricating oil distillate having an .degree.API gravity of 23.8; a flash point of 510.degree. F., a viscosity of 82.4 SUS at 210.degree. F.; a pour point of 120+.degree. F. and an aromatic carbon content of about 21 percent, was contacted with hydrogen in the presence of a calcined nickel molybdate on alumina catalyst at a temperature of 700.degree. F., a pressure of 2,500 p.s.i.g., a weight hourly space velocity of 0.25 and a hydrogen rate of 1,500 SCF/B of oil. The catalyst, which contained 2.3 percent nickel and 15.6 percent molybdenum as the oxide, was pretreated with hydrogen sulfide at 350.degree. F. for two hours using one SCF-H.sub.2 S/hr./100 grams of catalyst. The hydrotreated product thus formed was flashed to remove light gaseous products and further treated in a second stage at a temperature of 750.degree. F., a pressure of 2,500 p.s.i.g., a weight hourly space velocity of 0.35 and a hydrogen rate of 2,500 SCF/B of feed in the presence of a calcined platinum-containing, silica-alumina-crystalline aluminosilicate extrudate catalyst. The catalyst contained about 0.5 weight percent platinum, about 7 weight percent of about 90 percent hydrogen-exchanged crystalline aluminosilicate having a pore size of about 13 A. and a silica-to-alumina mole ratio of about 4 to 1, about 82.5 weight percent silica-alumina xerogel containing about 13 weight percent alumina, and about 10 weight alumina added as a hydrogel.

The effluent product from the second stage was steam stripped to remove hydrocracked components boiling below the lubricating oil range, and contacted with hydrogen at a temperature of 550.degree. F., a pressure of 2,500 p.s.i.g., a weight hourly space velocity of 0.25 and a hydrogen rate of 2,7500 SCF/B of feed in the presence of a platinum on alumina catalyst containing 0.6 weight percent platinum. Technical grade white mineral oil was recovered in a yield of about 30 percent by weight.

Claims

It is claimed:

1. A process of producing a technical white mineral oil which comprises contacting a raw, waxy mineral lubricating oil distillate having a viscosity of about 35 to 90 SUS at 210.degree. F., an aromatic carbon content of about 15 to 30 percent, a pour point of at least about 70.degree. F., and boiling primarily in the range of about 600.degree. to 1,200.degree. F., with hydrogen in the presence of a sulfur-resistant hydrogenation catalyst at a temperature of about 600.degree. to 800.degree. F. to provide a hydrorefined oil, contacting said hydrorefined oil with hydrogen in the presence of a hydroisomerization-hydrocracking catalyst comprising a major amount of amorphous silica-alumina composite containing about 5 to 45 weight percent alumina on a dry basis about 3 to 25 weight percent of an at least about 50 percent hydrogen-exchanged crystalline aluminosilicate having a pore size of about 8 to 15 A., and a silica-to-alumina mole ratio greater than 3:1, and about 0.1 to 5 weight percent of a platinum group metal at a temperature of about 600.degree. to 950.degree. F., removing components boiling below the lubricating oil range from the resulting product, and further contacting resulting hydroisomerized-hydrocracked product fraction of lubricating viscosity with hydrogen in the presence of a hydrogenation catalyst comprising a platinum group metal on a support having no substantial cracking effect on said hydroisomerization-hydrocracked product fraction, at a temperature of about 450.degree. to 700.degree. F. to saturate aromatics and produce technical white mineral oil.

2. The process of claim 1 wherein the contact of said mineral lubricating oil distillate with hydrogen and a sulfur-resistant hydrogenation catalyst is conducted at a pressure of about 500 to 3,000 p.s.i.g., a weight hourly space velocity of about 0.2 to 2 and hydrogen feed rate of about 1,000 to 5,000 SCF/B.

3. The process of claim 2 wherein the contact of said hydroisomerized-hydrocracked product fraction with hydrogen is conducted at a pressure of about 500 to 3,000 p.s.i.g., a weight hourly space velocity of about 0.2 to 2 and a hydrogen feed rate of about 1,000 to 5,000 SCF/B.

4. The process of claim 3 wherein the contract of said oil with hydrogen and the hydroisomerization-hydrocracking catalyst is conducted at a pressure of about 500 to 3,000 p.s.i.g., a weight hourly space velocity of about 0.25 to 2 and a hydrogen feed rate of about 1,000 to 5,000 SCF/B

5. The process of claim 1 wherein the platinum group metal of the hydroisomerization-hydrocracking catalyst and of the platinum group metal hydrogenation catalyst is platinum.

6. The process of claim 5 wherein the sulfur-resistant catalyst contains molybdenum and an iron group metal supported on alumina.

7. The process of claim 6 wherein the iron group metal is nickel.

8. A process of producing a technical white mineral oil which comprises contacting in a first stage a raw, waxy mineral lubricating oil distillate having a viscosity of about 35 to 90 SUS at 210.degree. F., an aromatic carbon content of about 15 to 30 percent, and a pour point of at least about 70.degree. F., and boiling primarily in the range of about 600.degree. to 1,200.degree. F., with hydrogen in the presence of a catalytic amount of a sulfided nickel molybdate supported on alumina catalyst at a temperature of about 675.degree. to 725.degree. F., a pressure of about 2,000 to 3,000 p.s.i.g., a weight hourly space velocity of about 0.25 to 0.5 and a hydrogen feed rate of about 1,500 to 2,500 SCF/B to provide a hydrorefined oil, contacting said hydrorefined oil in a second stage with hydrogen at a temperature of about 650.degree. to 800.degree. F. in the presence of a hydroisomerization-hydrocracking catalyst which comprises a major amount of amorphous silica-alumina composite containing about 10 to 20 weight percent alumina on a dry basis, about 5 to 10 weight percent of at least about 75 percent hydrogen-exchanged crystalline aluminosilicate having a pore size of 10 to 14 A., a crystal size of less than about 10 microns and a silica-to-alumina mole ratio of about 4 to 6:1, and about 0.3 to 2 weight percent of platinum, removing components boiling below the lubricating oil range from the resulting product, and further contacting the fraction of the oil of lubricating viscosity from said second stage with hydrogen in the presence of a platinum-alumina catalyst containing about 0.1 to 1 weight percent platinum at a temperature of about 550.degree. to 600.degree. F., a pressure of about 2,000 to 3,000 p.s.i.g., a weight hourly space velocity of about 0.25 to 0.5 and a hydrogen to feed oil rate of about 2,000 to 3,000 SCF/B to saturate aromatics in said fraction, and recovering resulting technical white mineral oil.