Method of Preparing Base Stocks for Lubricating Oil

This invention relates to a method of preparing base stocks for lubricating oil with excellent thermal stability. More particularly, it relates to a method of preparing base stocks for lubricating oil with excellent thermal stability and sunlight stability by maximum utilization of an intermediate product and the neutralized extract.

As a method of preparing base stocks for lubricating oil, it has been known to refine an intermediate product by comparatively mild hydrogenation, so-called hydrofinishing. However, base stocks for lubricating oil with excellent thermal stability can not be obtained by this process. Thus in order to overcome the above defect, as a modified process it has been proposed that hydrofinishing is carried out after extraction of an intermediate product with such a solvent as furfural, phenol, etc., as described in Oil and Gas Journal, Vol. 53, No. 26, p.81-84 (1954). However, according to this process, 20-30 percent of charge stocks are removed as the extract by solvent extraction and thus the product yield is decreased. On the other hand, it has been proposed to obtain base stocks for lubricating oil with excellent thermal stability by only an extraction process. However, according to this process, it is essential to remove undesirable components extensively for thermal stability and thus substantial amounts of desirable materials are moved to the extract. Therefore, further reduction of the raffinate yield, i.e. the product yield, can not be avoided. These extracts are used as a heavy oil and useful components as a lubricating oil are not used effectively.

An object of the present invention is to provide a method of preparing base stocks for lubricating oil with thermal stability by maximum utilization of an intermediate product. More particularly, it relates to provide a method of preparing base stocks for lubricating oil with excellent thermal stability and sunlight stability by utilization of extracts.

A method of the present invention comprises subjecting to hydrofinishing a mixture consisting of 10-60 percent by volume of a neutralized extract prepared by alkaline treating vacuum distillation of an extract obtained through extraction of an intermediate product by a solvent having affinity for aromatic compounds and 90-40 percent by volume of an intermediate product of low total acid value.

An intermediate product in the present invention is a distillate obtained through a vacuum distillation of a topped crude oil which is prepared by removing a light fraction of a crude oil by distillation or a deasphalted oil obtained by deasphalting a residual oil after a vacuum distillation and, if necessary, dewaxing. An intermediate product which is extracted with a solvent may be the same or different from a raw oil for an intermediate product which has a low total acid value. That is, the latter is an oil having a total acid value of lower than 2.0, preferably lower than 0.5, and is (1) an intermediate product having a low total acid value of lower than 2.0, preferably lower than 0.5 or (2) a distillate obtained by alkaline treating vacuum distillation of an intermediate product when the total acid value of said oil is higher than 2.0, or (3) a distillate obtained by alkaline treating vacuum distillation of a topped crude oil. An intermediate product having total acid value of more than 2.0 is not preferred because it causes short catalyst life and undesirable influence on the material of the device. The process of alkaline treating vacuum distillation in the case of (2) and (3) can be carried out in a mixture with prescribed amounts of extracts.

In the present invention, known solvents such as phenol, furfural, dichloroethyl ether, N-methyl-2-pyrolidone, etc. can be used as solvents having affinity for aromatic compounds and a process of extraction can be operated according to conventional methods. The process is carried out normally by countercurrent contact method and components for lubricating oil are obtained from the top of the tower as a raffinate and undesirable components as lubricating oil are removed from the bottom of the tower as an extract and then solvent is recovered with distillation.

To the extract thus obtained, an alkali such as sodium hydroxide, potassium hydroxide etc. is added and then the extract is refined by alkaline treating vacuum distillation. Amounts of alkali added are enough to neutralize petroleum acids (such as naphthenic acids) in the extract.

Thereafter, 10-60 percent by volume of a neutralized extract and 90-40 percent by volume of an intermediate product of low total acid value mentioned above are mixed and the resulting mixture is refined with hydrofinishing. When amounts of the neutralized extract are less than 10 percent by volume, thermal stability of base stocks for lubricating oil obtained by hydrofinishing is insufficient. On the other hand, when amounts of neutralized extract are more than 60 percent by volume, base stocks for lubricating oil obtained do not form precipitates by the thermal stability test (JIS-K-2540), but the increase of total acid value is extensive and thermal stability is practically unsatisfactory.

Hydrofinishing of the mixture can be carried out by conventional methods. Normally, the hydrofinishing is performed using a catalyst which is prepared by holding one or more than two kinds of metals having hydrogenation activity selected from metals belonging to group VIII of the Periodic Table such as Fe, Co, Ni, etc. and metals belonging to group VI of the Periodic Table such as Mo, W, etc. or their oxides or sulfides on alumina, silica-alumina, zeolite, etc. and performed at a temperature of 250.degree.-400.degree. C., a pressure of 50-150 kg/cm.sup.2, a LHSV of 0.5-3.0 per hour, and H.sub.2 /oil; 10-300 Nm.sup.3 /kl.

Base stocks for lubricating oils obtained by the present invention are excellent in thermal stability and sunlight stability and thus can be used preferably for preparation of a lubricating oil. The present invention provides not only base stocks for lubricating oils with excellent thermal stability but also a method of effective utilization of extracts. Therefore, maximum utilization of an intermediate product can be attained according to the present invention.

The present invention is described in detail by means of the following examples.

An extract was obtained by extracting an intermediate product (boiling point: 335.degree.-435.degree. C., viscosity 5.38 cst at 98.9.degree. C.) prepared by distillation under the reduced pressure of a topped crude oil (naphthene base) of Klamono with furfural under the conditions of the ratio of solvent:an intermediate product=3:1 and a temperature of 120.degree. C. Extract yield was 50 percent. Total acid value of the extract was 8.4 (measured by JIS-K-2501 or 2502).

To this extract a neutralization equivalent of sodium hydroxide solution was added and stirred, and after heating and dehydration simple vacuum distillation was performed and the neutralized extract was obtained as the distillate. The residue in the still was about 10 percent. Characteristics of the neutralized extract are shown in Table 1.

A dewaxed distillate was obtained by solvent dewaxing a distillate (boiling point 430.degree.-485.degree. C.) prepared by vacuum distillation of a topped crude oil (naphthene oil) of Kuwait under the conditions of the ratio of solvent (methyl ethyl ketone:toluene=1:1) to the intermediate product=3:1 and a filtration temperature of -20.degree. C.

The dewaxed distillate and the neutralized extract were mixed at the prescribed combination and the resulting mixture was refined with hydrofinishing a using Co--Mo--Al.sub.2 O.sub.3 catalyst (CoO 3.0 weight percent and MoO.sub.3 2.0 weight percent) and under the conditions of a temperature of 320.degree. C., a pressure of 100 kg/cm.sup.2, a LHSV of 1.0 per hour and H.sub.2 / oil 100 Nm.sup.3 /kl. Characteristics of base stocks for lubricating oil thus obtained were measured and results are shown in Table 2.

Topped crude oil (naphthene base) of Tia Juana was subjected to a vacuum distillation and was separated into a first distillate (boiling point: 290.degree.-340.degree. C.), a second distillate (boiling point: 340.degree.-420.degree. C.) and a third distillate (boiling point: 420.degree.-470.degree. C.). These three distillates were solvent extracted with furfural, respectively. The yield and characteristics of the extract are shown in Table 3.

These three extracts were mixed and then the resulting mixture was added to a topped crude oil of Tia Juana at 30 percent by volume. Characteristics of the topped crude oil are shown in Table 4.

To the mixture of extracts and the topped crude oil, the neutralization equivalent of sodium hydroxide was added and then alkaline treating vacuum distillation was performed to obtain three distillates, i.e. the first distillate (boiling point: 300.degree.-335.degree. C.), the second distillate (boiling point: 335.degree.-415.degree. C.) and the third distillate (boiling point: 415.degree.-440.degree. C.).

Subsequently, these raw distillates were finished by hydrofinishing using a Co--Mo--Fe--Al.sub.2 O.sub.3 catalyst (CoO 3.5 weight percent, MoO.sub.3 10.5 weight percent, and Fe.sub.2 O.sub.3 14.0 weight percent) under the conditions of a pressure of 80 kg/cm.sup.2, a temperature of 270.degree. C., a LHSV of 1.0 per hour and H.sub.2 / oil of 60 Nm.sup.3 /kl, respectively. The base stocks for lubricating oil thus obtained had characteristics as shown in Table 5.

For the purpose of comparative study, three distillates obtained by alkaline treating vacuum distillation the above mentioned topped crude oil of Tia Juana with the same conditions as those above without preparing a mixture of extracts were subjected to hydrofinishing with the same condition as above. Characteristics of this product are shown in Table 5.