NO128115B - - Google Patents

Description

Lubricating oil composition, and method for producing this.

The present invention relates to a spreading oil composition

and a method for producing this.

To have good lubricating properties, an oil must have sufficient

suitable viscosity to provide good spreadability even at the highest

ical operating temperatures for the apparatus (e.g. a machine) where

until it is used. At low temperatures, however, visco-

site ok to a level that has an adverse influence at start. This means that the viscosity/temperature relationship must satisfy certain requirements. This relationship is usually expressed using the viscosity index. (The viscosity indication used in the present description refers to values determined using ASTM method D 2270-6^). Furthermore, the oil must meet other requirements, i.e. it must resist oxidation and

have cleansing properties, etc. For this reason, lubricant oils that are used in practice will in most cases consist of lubricant oil composition.

The term lubricating oil composition ions - as -used in this description and in the following claims, denotes compositions which contain, in addition to a base lubricating oil, one or more other base lubricating oils and/or one or more additives. Additives are compounds that are added in small amounts to the lubricating oils to improve their quality (generally used from a few ppm up to 5 wt#, but sometimes up to 15$ or more of additives are used).

In practice, a large number of lubricating oil compositions are produced, so that a large selection of base lubricating oils and additives must be available.

Base lubricating oils and lubricating oils can be classified on the basis of their viscosity index (VI). The division is as follows: Oil with low viscosity index (LVI) with VI less than 30, oil with medium viscosity index (MVI) with VI from 30 to 90,

Oil with high viscosity index (HVI) with VI from 90 to 120, and oil with very high viscosity index (VHVI) with VI greater than 120.

The production of HVI base oils is normally carried out as described below. A raw mineral, which is a suitable raw material for the production of lubricating oils, is subjected to distillation at atmospheric pressure, whereby a number of distillation fractions and a residual fraction (the so-called "long residue" distillation residue) are obtained. The residual fraction is then subjected to distillation at reduced pressure to separate it into fractions, e.g. in three distillation fractions and a residual fraction (the so-called "short residue" distillation residue).

The fractions obtained by distillation under reduced pressure are normally subjected to a series of refining processes.

These refining processes include the removal of some of the aromatics and paraffins (wax) that the oil contains, and a final step that usually includes an improvement in the color, color stability and oxidation stability of the base peanut oil. When it comes to the residual fraction, it is also necessary to remove the asphalt content. Asphalt is undesirable in lubricating oils and it can also affect later refining processes. The processes for removing asphalt, aromatics and paraffins are referred to in the following as asphalt removal, aromatic extraction and dewaxing, respectively.

Asphalt removal from the residual fraction is normally carried out for aromatic extraction and dewaxing. The process is carried out using propane as an asphalt removal solvent.

Aromatic extraction - which is often carried out using furfural, sulfur dioxide or phenol as extractants - helps to increase the viscosity index and to improve the color stability and oxidation stability of the fractions.

The dewaxing serves to lower the pour point of the fractions. Distillation fractions can contain significant amounts of wax. This wax separates if the oil is cooled below a certain temperature. With further decoupling, more wax will be secreted,

and finally the mixture-of wax and oil will flow with difficulty under some circumstances.

The lowest temperature at which the mixture of wax and oil still flows, when it is examined by a standard laboratory test, is called the pour point. To avoid difficulties when using lubricating oil, the pour point must be below the lowest temperature at which the oil is to be used. Dewaxing can be carried out by decoupling in the presence of a solvent. This dewaxing method is referred to below as solvent dewaxing. Dewaxing is generally carried out at a temperature of approx. 10°C lower than the desired pour point for the dewaxed oil. Dewaxing of an oil by cooling in the presence of a solvent must usually be carried out at approx. -20°C because desirable lubricating oils generally have a pour point below -10°C. Dewaxing can also be carried out using urea. The latter dewaxing method is referred to below as urea dewaxing.

Examples of the above-mentioned final treatment steps are sulfuric acid treatment or oleum treatment, followed by treatment with a solid adsorbent, e.g. clay, or treatment with only a solid adsorbent or a catalytic treatment with hydrogen - also called hydrofinishing.

The production of LVI and MVI base oils usually involves only one or more of the refining operations described above for the production of HVI oils. E.g. LVI oils can be prepared by subjecting a naphthenic distillate to only an acid and clay treatment.

Depending on the boiling point range and viscosity, the base lubricating oils are named as follows: spindle oil (SO, light machine oil (LMO) and medium machine oil (MMO). The residual fraction is usually called bright stock (BS).

It is possible to prepare base oil compositions by mixing individual base oils.

According to the step-by-step method described above, it is not possible to produce VHVI base lubricating oils, because base lubricating oils produced according to this method have a VI that is no higher than 105 or even less.

It will be possible to increase the viscosity index of an oil produced in this way by mixing in a VI-increasing additive. However, such additives can gradually break down while the oil is in use. After a relatively short time, this can lead to a permanent decrease in the viscosity index. Furthermore, the aforementioned breakdown will result in a permanent decrease in the oil's viscosity. This decrease in viscosity and viscosity index impairs the oil's lubricating properties.

Another method previously proposed for the production of VHVI base lubricating oils is a mild hydrogenation of a lubricating oil feedstock. In this way, it is generally possible to increase the viscosity index. However, this method is destructive, so that part of the starting material is transferred to lighter fractions, such as petrol, petroleum and gas oil fractions. The hydrogenated material must therefore be worked up by means of distillation in order to obtain the desired VHVI oil. Furthermore, under harsher hydrogenation conditions, more and more of the volatile components will be formed, so that the resulting amount of VHVI oil that boils in the same destination area is getting smaller and smaller. The viscosity of the VHVI base motor oil also decreases considerably in the latter case. Another disadvantage of hydrogenation is that it must be carried out at very high pressure (approx. 150 atmospheres) and at high temperature.

The present invention relates to a lubricating oil composition which partly consists of a base lubricating oil and which further contains one or more additives and/or one or more conventional lubricating oils or base oils, and which is characterized in that the composition has a viscosity index of at least 125 and contains a base lubricating oil with a viscosity index of at least 135 and which is obtained from adducts between thiourea and a lubricating oil feedstock.

The new lubricating oil composition is produced by a method characterized by one or more base lubricating oils and/or one or more additives being mixed with a base lubricating oil which is produced by treating a base lubricating oil raw material with thiourea, whereby solid thiourea adducts are formed, after which the thiourea adducts are separated from non- adducted oil, the separated adducts are split into a hydrocarbon phase and thiourea, and the latter compound is removed.

It will be necessary to use very little or no viscosity-increasing additives when using existing base oils. This avoids the above-mentioned decrease in viscosity index and viscosity during the use of oils. A spreading oil composition according to

the present invention will therefore fulfill its task in a machine much longer than an oil containing a VI-bending ■additive.

This is particularly desirable for use in diesel engines when you take into account the relatively high temperatures lubricating oils are exposed to in such. One of the advantages is that the hydrocarbon phase formed by cleavage of thiourea adducts has been found to allow the addition of antioxidants better than base oils formed by hydrogenation.

As is known, the formation of solid thiourea adducts is based on the fact that certain organic compounds can form clathrates with thiourea molecules. The adduct hydrocarbons remain unchanged and they are recovered unchanged after cleavage of the adducts. Generally, the present method has the advantage over hydrogen treatment that it is not destructive. It is therefore not necessary for the hydrocarbon phase formed by the adduct splitting to be subjected to distillation.

Another advantage of adduct formation compared to the hydrogen treatment method is that the adducts can be formed at relatively low pressures, e.g. atmospheric pressure or slightly above this, so that it is not required to use equipment for high pressures and temperatures.

The viscosity index of the spreading oil compositions will depend on the VI of the base motor oils or the mixtures of base motor oils and additives. The blended oil will normally be a VHVI oil, if it consists entirely of a base oil or oils formed by a process involving the cleavage of thiourea adducts. The blended oil is normally a VHVI oil or an HVI oil if it consists partly of one or more base oils that are not formed by splitting thiourea adducts. VI in such mixed oils can be increased by adding viscosity index increasing additives. If desired, LVI oil can be used for mixing, and the mixed oil can be an MV I or an LVI oil. The portion of the lube oil composition not formed by cleavage of thiourea adducts may comprise any usable lube oil or base lube oil, eg: a spindle oil, a light machine oil, a medium machine oil or a "bright stock" oil. The premixed oils suitably contain one or more additives. Any additive added lubricating oil compositions consisting of two or more lubricating oils may be added to one or more of the base lubricating oils for which they are blended, and/or the additives may be added to the resulting blended oil.

The lubricating oil composition consisting of cleavage products

from thiourea adducts and one or more additives are very suitable.

The lubricating oil composition according to the present invention is particularly suitable as "multigrade" lubricating oils, i.e. lubricating oils with a wide range of applications. This will be explained in the following.

Lubricating oils for internal combustion engines are classified according to a system established by the American Society of Automotive Engineers. According to this so-called SAE classification, lubricating oils are classified into two groups on the basis of their viscosities at -18°C and 99°C respectively. These groups are winter qualities and normal qualities. Each of the two groups is divided into a number of classes. The classes for winter qualities are denoted by the letter W written with a number in front, for example an oil of type 5W, 10W or 20W. The winter grades have a specified maximum viscosity of

-~18°C. The classes for normal qualities are distinguished only by a number, for example one has an oil of type 20, 30, h0 or $ 0. The normal quality oils must have a viscosity at 99°C within a specified range. In general, oils that meet the requirements of a winter oil will not meet the viscosity specifications of a normal grade oil, and vice versa, oils that meet the requirements of normal grades will not meet the viscosity requirements of a winter grade. Lubricating oils that only fall within an SAE class, (i.e. either

follow the requirements for a normal oil or for a winter oil) are termed single-quality (single-grade) lubricating oils. Examples

. on widely used single grade lubrication oils are SAE-20 and SAE-30 oils. On the other hand, lubricating oils that meet the specifications for both winter quality and normal quality are called multigrade lubricating oils. Examples of multigrade lubricating oils are: 5W/20, 5W/30, 10W/30, IOWAO, lOW/50, 20WA0, 20W/50, 10W/20, 20W/30. For the production of multigrade lubricating oils, base lubricating oils of the type HVI and VHVI are very suitable. The hydrocarbon phase formed by cleavage

of the aforementioned thiourea adducts, is particularly suitable as a base oil because it usually has a very high viscosity index and sufficiently high viscosity. From this, the corresponding multigrade lubricating oil can be obtained by mixing other suitable base lubricating oils and/or suitable additives.

Examples of suitable additives which may be present in lubricating oil compositions according to the present invention are: pour point depressants, antioxidants, anti-corrosion agents, wear-reducing (extended play E.P.) additives, dispersants, thickeners, anti-foaming agents, bactericidal agents and tackifiers. Other additives may also be present, e.g. viscosity index increasing agents.

The additives can be monofunctional, i.e. they are capable of producing one of the beneficial effects, or they can be multifunctional, i.e. they are capable of improving a lubricating oil in several areas at the same time.

Base lubricating oils, i.e. hydrocarbon mixtures from which lubricating oils can be produced, normally have an initial boiling point under atmospheric pressure of at least 3Q0°C. For that reason, it is preferable to prepare the thiourea extracts which one wishes to use as base oils according to the invention, by treating a base oil raw material with an initial boiling point of at least 300°C at atmospheric

pressure in the following way: the basic oil raw material is reacted with thiourea and forms thiourea adducts, then the aforementioned thiourea adducts are separated from unreacted oil, and by splitting the separated adducts a hydrocarbon phase and thiourea are obtained, from which the latter compound is removed. Many different base oil raw materials can be used as starting materials for the production of the cleavage products from the thiourea adducts. These base oil raw materials can be so-called lubricating oil raw materials, i.e. they are suitable for the production of base lubricating oils according to conventional methods, but the base oil raw material can also consist of oil raw materials that are not suitable as starting material in conventional processes for the production of base lubricating oils. The latter type of oil feedstock is particularly attractive from an economic point of view.

Suitable base oil raw material for treatment with thiourea in the production of the cleavage products of the thiourea adducts are the above-mentioned distillation fractions and residual fraction obtained by distillation under reduced pressure. These fractions can be subjected to thiourea treatment without any pretreatment. However, the fractions can also be subjected to pretreatment and the pretreated fractions are then treated with thiourea. After e.g. aromatic extraction and/or dewaxing of the fractions, these can be treated with thiourea. When using the aforementioned residual fraction, the asphalt content must be removed for the thiourea treatment. A mixture of base oil raw materials can also be treated with thiourea.

Other suitable base oil raw materials for treatment with thiourea for the purpose of producing the cleavage products of the thiourea adducts are those produced by a conversion process, e.g. a catalytic cracking process. The mixture of hydrocarbons that leaves the reactor in a catalytic cracking unit is separated into a number of hydrocarbon fractions by means of distillation. One of these fractions, called "heavy cycle oil" and which has an initial boiling point at atmospheric pressure normally above 300°C, is a very suitable base oil raw material. In a similar way, a suitable base oil feedstock can be produced from the mixture of hydrocarbons leaving the reactor in a hydrocracking unit. If desired, lubricating oil fractions produced by means of catalytic hydrogenation can also be used.

Another suitable base oil raw material for the production of the thiourea adducts' cleavage products is obtained by isomerizing wax. By isomerisation of wax is meant here a treatment of the wax under conditions where certain hydrocarbons are transferred to isomeric compounds which have a more branched structure and with little other reactions. The wax may originally originate from a de-waxing process as described above. The isomerization process can be carried out catalytically and follow any suitable method.

The non-adducted wax can be recycled to the isomerization process.

Lubricating oil fractions produced from shale oil are also usable as base oil raw material.

The solid thiourea adducts can be formed by any desired method. The base oil substance with which the adducts are to be formed can be brought into contact with thiourea either in the presence of or without the use of a solvent for hydrocarbons. Use of such a solvent is preferable because treatment of the base oil raw material dissolved in a solvent gives filterable dissolution of the adducts in the solvent, and this is preferable to a solid mass substantially containing adducts. Examples of suitable solvents are those containing one or more n-hydrocarbons, such as propane, pentane, hexane, heptane, octane, nonane, decane, dodecane and especially butane, and also aromatics such as benzene, toluene and xylene. Other examples of suitable solvents are those containing one or more halogenated hydrocarbons, e.g.: dichloromethane, chloroform, 1,2-dichloroethane, n-butyl chloride, trichloroethane, carbon tetrachloride, and also chlorofluorine-substituted hydrocarbons with one or two carbon atoms per . molecule. Very suitable solvents are those which themselves form adducts with thiourea, because this has been found to have a beneficial effect on adduct formation. Examples of such solvents are cyclohexane, chloroform and carbon tetrachloride. Mixtures of two or more solvents for oil can also be used, e.g. a mixture of heptane and toluene.

For the purpose of treating the base oil raw material with thiourea, either with or without an oil solvent, thiourea can be used in a solid state or dissolved in a solvent. Adduct formation occurs fastest when a solvent for thiourea is used. Saturated solutions of thiourea as well as dilute solutions of it can be used. A saturated solution can be used when solid thiourea is not present, but it can also be used in the presence of solid thiourea. Suitable solvents for thiourea are: water, lower monohydric alcohols with no more than five carbon atoms per molecule, such as methanol or ethanol, and polyhydric alcohols, such as glycerol, and glycols such as ethylene glycol, propylene glycol, and butylene glycol. Thiourea dissolves particularly easily in liquid ammonia and methylamine. These solvents also have the advantage that the heat released during the formation of the thiourea adducts can be dissipated by evaporation of liquid ammonia or methylamine. Suitable processes in which liquid ammonia is used form the contents of British Patents Nos. 1,153,930, 1,157,760 and 1,158,110.

Mixed solvents can also be used for thiourea, e.g. a mixture containing water and one or more of the alcohols mentioned above, or water and liquid ammonia, or water, a

alcohol and liquid ammonia.

In order to facilitate the separation, it is preferred to use a solvent for thiourea which forms a secondary phase with the liquid from which the thiourea adducts are to be recovered. The latter liquid must be substantially immiscible with the solvent for thiourea. However, thiourea adducts are quickly formed if the base oil raw material is dissolved in a solvent in which thiourea is slightly soluble, e.g. so that thiourea has a solubility of up to 5% by weight in this. Examples of such solvents are mixtures of acetone and dichloromethane, and of toluene and acetone. On the other hand, such solvents are appropriate for thiourea, where the base oil feedstock is soluble to a certain extent, e.g. up to 5 wt$, since this facilitates adduct formation.

The thiourea adducts, once formed, may be present in the oil phase and/or in any thiourea solution. The solid thiourea adducts can be separated from non-adducted oil in an appropriate manner, e.g. by means of decantation, sedimentation, filtration, centrifugation or by means of liquid cyclones. Separation becomes much easier if the thiourea adducts are pelletized according to the process described in British patent document No. 1. 02^4-A75.

After separation, the adducts must be cleaned by washing with

a relatively inert solvent, such as a normal paraffin, e.g.

pentane, hexane or an aromatic hydrocarbon such as benzene or toluene. The adducts are then split. A number of methods for splitting the adducts are described in the literature. For example the adduct can be cleaved using a hot solvent for thiourea, e.g. ammonia or water, whereby a solvent" phase containing dissolved thiourea and a hydrocarbon phase is formed.

The hydrocarbon phase formed by cleavage of the thiourea adducts may have too high a pour point for use in lubricating oil compositions according to the invention, especially when it is produced from a base oil raw material which is not itself dewaxed.

In such a case, such hydrocarbon phases must be dewaxed. The dewaxing can be carried out using any suitable dewaxing process, e.g. by means of a solvent or by means of urea, or by means of a combination of dewaxing processes. On the other hand, the base oil raw material can be solvent-dewaxed or urea-dewaxed and the dewaxed base oil raw material treated with thiourea, and in such a case, dewaxing of the hydrocarbon phase is not necessary.

However, it is also possible to dewax the base oil raw material as well as the hydrocarbon phase obtained by splitting the thiourea adducts. Both dewaxing steps can be carried out using a solvent.

They can also be carried out using urea. It is also possible to carry out any of the two dewaxing steps using a solvent, and the second step using urea.

Dewaxing can also be carried out in e.g. two steps. E.g. oil that one wishes to dewax can first be partially solvent-dewaxed, and the partially dewaxed oil can then be urea-dewaxed. Alternatively, the oil you wish to dewax can first be partially urea-dewaxed, and the partially dewaxed oil can then be solvent-dewaxed.

Examples of suitable solvents for solvent dewaxing are halogenated hydrocarbons, e.g. a mixture of dichloromethane and 1,2-dichloroethane, and ketones, e.g. methyl isobutyl ketone. Mixtures of ketones and aromatic hydrocarbons can be used, for example: a mixture of methyl ethyl ketone and toluene, or a mixture of acetone and toluene. Another suitable solvent is propane.

The oil to be de-waxed can also be de-waxed even if it is mixed with any other oil that must also be de-waxed.

In urea dewaxing as well as in solvent dewaxing, a solvent which is different from or identical to the oil solvent used in the thiourea treatment can be used. An advantage of using the same solvent is that the oil solution can later be treated directly, without removing the solvent beforehand. E.g. a mixture of acetone and toluene can be used as solvent.

In the event that a base oil raw material is used as starting material in the treatment with thiourea, non-adducted oil from which the thiourea adducts are separated can be used as raw material for the production of oil oils, e.g. oils of the type LVI or MVI.

The mixing of the components included in the production of lubricating oil compositions according to the present invention can be carried out by any suitable, known mixing technique. If additives are to be mixed in, it is often appropriate to prepare a concentrated solution of all or part of the additive (or additives) in a base lubricating oil or in a volatile solvent, and later use the solution for mixing into the base lubricating oil which forms part of the lubricating oil composition according to the invention. If a volatile solvent is used, this can be removed e.g. by evaporation.

The invention will be further illustrated by means of the following examples.

Example 1

From a distillation residue obtained by distillation at atmospheric pressure of an Indonesian-type crude oil, a distillation fraction having a boiling point range between <1>+00°C and ^80°C at atmospheric pressure was obtained by means of distillation under reduced pressure. This distillation fraction was dewaxed using urea in the following way. The distillation fraction was dissolved in 5 parts by volume of dichloromethane. To the formed solution which had a temperature of 30°C, was added a saturated solution of urea in water which had a temperature of 70°C. The saturated urea solution was used in an amount of 2.0 parts by volume per volume fraction distillation fraction. The mixture obtained had a temperature of 32°C. The heat developed during the formation of the urea adducts was led away through evaporation of dichloromethane at pressure lower than atmospheric pressure. After stirring for 30 minutes, the formed urea adducts were separated from the solution by means of filtration. The solution was then separated by means of distillation into a dichloromethane and a urea-depleted distillation fraction. The viscosity index of the latter fraction was 87, and the viscosity at 99°C was 6.8 cS (see Table I).

Then, one part by volume of dewaxed distillation fraction was dissolved in 2.3 parts by volume of a solvent consisting of one part by volume of dichloromethane and one part by volume of acetone. The solution that had formed was added to 70% by weight of powdered thiourea, calculated in relation to the amount of dewaxed distillation fraction, and stirred for 2 hours at 0°C. Then the solid thiourea adducts that had formed (together with possibly unreacted solid thiourea particles) were filtered off and washed out with n-pentane. The washed adducts were cleaved by contact with hot water having a temperature of 80°C. The aqueous thiourea solution was removed and a hydrocarbon fraction having a viscosity index of 1^9 was obtained. The viscosity at 99°C for this fraction was .8 cS and the yield was 17.3 wt.%, calculated in relation to the urea-deoxygenated vacuum distillate fraction. The hydrocarbon fraction had a pour point of +17°C. (See table I under VHVI oil). The aforementioned hydrocarbon fraction (VHVI oil) was dewaxed by dissolving it at 50°C under stirring in a mixture of equal parts by volume of methyl ethyl ketone and toluene, for which three parts by volume of this mixture were used per volume part fraction. Furthermore, the solution was cooled with stirring to a temperature of -30°C, and the wax that separated was removed from the oil by means of filtration. The wax was washed with the aforementioned solvent mixture and the washing solution was added to the filtrate. The solvent was then removed from the filtrate by distillation. The dewaxed oil had a viscosity index of 136 and a pour point of -16°C. Its viscosity at 99°C was M-.8 cS and it was obtained in a yield of 12.5" wt#, calculated on the basis of urea dewaxed vacuum distillate fraction. The said data are also given in Table I under solvent dewaxed VHVI oil.

To the dewaxed oil was added 0.5% by weight of L1-,L1-,-methylene-bis-2,6-di-t-butylphenol (antioxidant). This antioxidant completely dissolved in the oil.

Example II

The experiment described in Example I was repeated, with the difference that the distillation fraction formed by distillation under reduced pressure in this case consisted of a distillation fraction obtained from an Iraqi-type crude oil, and that this fraction was extracted in furfural for urea growth. The boiling point range of the fraction was ^30 to <1>+80°C at atmospheric pressure. The furfural extraction was carried out as follows. One part by volume of a middle distillation fraction was mixed with 2.8 parts by volume of furfural at 80°C. The mixture was then allowed to separate into two phases, i.e. a furfural line-containing phase and a phase containing light machine oil. The light engine oil was treated with thiourea. The results are given in Table I, and show that the viscosity indices for VHVI oil and solvent-dewaxed VHVI oil were 152 and 150 respectively.

To the dewaxed oil was added 1% by weight of basic calcium (C₁₁+-C₁₁g)-alkyl salicylate with a basicity of 200% (an anti-oxidation agent and dispersant). If the basic salt contains M equivalents of metal, and E equivalents of organic acid per 100 g of basic salt, the basicity is given by

( ^ M - 1) x $100. This additive completely dissolved in the oil.

The experiment described in Example I was repeated, with the difference that the distillation fraction in this case consisted of a distillation fraction extracted from a crude oil from Iraq. The boiling point range of the fraction was ^80 - 520°c at atmospheric pressure. The results, which are presented in Table I, show that the viscosity indices for the VHVI oil and solvent-dewaxed VHVI oil were respectively l<!>+5 and IV3. According to the SAE specification, the viscosities at -18°C and 99°C for a 10W/20 multi-grade oil must satisfy the following requirements: 12 poise <(v) _1gOc-^■21+ poise (determined according to ASTM method D 2602) and (<v>k)99<o>c<9.6 cS (see 1968 SAE Handbook, page 32^, Crankcase Oil Viscosity Classification - SAE J 300 a). The dewaxed VHVI oil can be classified as a 10W/20 oil as the viscosities for the oil at -18°C and 99°C were 15 poise and 7.9 cS respectively.

To the dewaxed oil was added 0.5% by weight of methylene-bis-2,6-di-t-butylphenol. This antioxidant completely dissolved in the oil.

EXAMPLE IV

The experiment described in Example I was repeated, with the difference that the distillation fraction in this case consisted of a distillation fraction extracted from an Arabian-type crude oil, and that the distillation fraction was extracted in furfural, as described in Example II, for urea dewaxing. The boiling point range for the distillation fraction was ^30 - ^80°C at atmospheric pressure. The results presented in Table I show that the viscosity index of the VHVI oil and the solvent dewaxed VHVI oil were 11+3 and 135" respectively

To the dewaxed oil was added 1% by weight of the same basic calcium alkyl salicylate that was used in Example II. This additive completely dissolved in the oil.

EXAMPLE V

The experiment described in Example IV was repeated with the difference that in this case a distillation fraction was used which had a boiling point range between h-SO and 520°C at atmospheric pressure. The results are reproduced in table I.

To the dewaxed oil was added 1 part by weight of the same basic calcium alkyl salicylate that was used in Example II. This

additive dissolved completely in the oil.

EXAMPLE VI

The experiment described in Example IV was repeated with the difference that the distillation fraction in this case was extracted from a crude oil of North African type, and that the furfural extracted fraction was not dewaxed with the help of urea, but was solvent dewaxed in the same way as described in Example I. The results are presented in Table I.

To the solvent-dewaxed oil was added 0.5% by weight of k,h'-methylene-bis-2,6-di-t-butylphenol. This antioxidant completely dissolved in the oil.

EXAMPLE VII

From the solvent-dewaxed VHVI oil prepared as described in Example I, two mixtures were prepared with "bright stock" fraction recovered from a crude oil of North African type. One of the mixtures (mixture no. 1) consisted of the raw materials in a weight ratio of 1:1, the other mixture (mixture no. 2) consisted of the raw materials mixed in a weight ratio of 1.5:1. The "bright stock" oil was a residual fraction that had been subjected respectively to asphalt removal, extraction in furfural and and solvent dewaxing, and had a viscosity index of 97» According to the SAE specification, the viscosities at -18°C and 99°C for a multigrade oil of class 20W/30 meet the following requirements:

Both oil mixtures satisfied the specification requirements for a 20W/30 oil, see Table II.

EXAMPLE VIII

The experiment described in Example III was repeated, with the

difference that in this case the thiourea adducts were formed at 25°C and the VHVI oil was not dewaxed. Table III shows that the viscosity index for the VHVI oil is higher when the thiourea adducts are prepared at 25°C and that the yield of the oil is lower.

EXAMPLE IX

From a residual fraction obtained by distillation under atmospheric pressure of a crude oil originating from Iraq, a distillation fraction having a boiling point range between 375 °g <1>+30 °C was separated by means of distillation under reduced pressure (spindle oil). The viscosity of this distillation fraction at 99°C was 3.7 cS. This fraction was treated with thiourea and the adducts formed were split as described in Example I. The hydrocarbon mixture obtained was solvent dewaxed as described in Example I. The resulting oil, obtained in a yield of 11.8% by weight calculated on the amount used spindle oil, had a viscosity index of 136, a viscosity at 99°C of 3.2 cS and had a pour point of -16°C.

To the dewaxed oil was added 0.75% by weight of methylene-bis-2,6-di-t-butylphenol. This antioxidant completely dissolved in the oil.

EXAMPLE X

A bright stock crude oil obtained by deasphalting, furfural extraction and solvent dewaxing of a vacuum distillation residue from a crude oil originating in Iraq had a viscosity index of 9° and a viscosity at 99°C of 32.^9 cS.

The bright stock oil was treated with thiourea and the adducts formed were resolved as described in Example I. The resulting oil (6.0 wt% yield calculated on the basis of bright stock crude) had a viscosity index of 1M+ and a viscosity at 99°C of 13.56 cS.

0.75% by weight of h,h'-methylene-bis-2,6-di-t-butylphenol was dissolved in this base oil. This resulted in a lubricating oil with the same viscosity and viscosity index as the base lubricating oil.

EXAMPLE XI

A "heavy cycle" oil, which was obtained as a distillation fraction with an initial boiling point above 300°C at atmospheric pressure, obtained from hydrocarbons leaving a catalytic cracking reactor, was treated with thiourea, and the adducts were cleaved as described in Example I The hydrocarbons obtained were filtered through a silica gel column and separated into a fraction mainly consisting of aromatic compounds and a fraction mainly consisting of saturated compounds. To the latter fraction was added 0.5 wt% of h1 -methylene-bis-2,6-di-t-butylphenol, and the resulting lubricating oil had a viscosity at 99°C of 2.7 cS and a viscosity index of 137.

EXAMPLE XII

A "bright stock" oil feedstock derived from an Iraqi-type crude oil was hydrocracked, and from the products obtained a spindle oil, a light machine oil, a medium machine oil and an oil from which the asphalt content had been removed were produced. The aforementioned four types of oil were treated with thiourea, and the adducts were cleaved as described in Example I. Table IV shows the viscosity properties of the spindle oil, the light machine oil, the medium machine oil and the oil without the asphalt content. Lubricating oils were prepared from the cleavage products of the thiourea adducts for these oils by dissolving 0.5% by weight of the antioxidation compound -methylene-bis-2,6-t-butylphenol in these.

As will be seen, lubricating oil compositions with very high viscosity indices can be produced in this way.

EXAMPLE XIII

The resistance to oxidation for two lubricating oil compositions according to the invention was determined by means of a method described in British Patent Application No. 2,521/69 (Shaken Circulatory Oxidation Test, SCOT). This test was carried out at 180°C without catalyst.

Base lubricating oils were prepared from a medium engine oil and a light engine oil obtained from Iraqi-type crude oil, by treatment with thiourea and cleavage of the adducts as described in Example I, followed by solvent dewaxing of the resulting hydrocarbon mixture. To the prepared lubricating oils were added respectively: 1 weight$ basic calcium (Cll+ - C-^g) alkyl salicylate, as described in Example II (additive A), or 0.5 weight$ '-methylene-bis-2,6-di -t-butylphenol (additive B).

Table V shows the results. For the sake of comparison. the test results for the following oil types are included: a dewaxed hydrotreated light engine oil obtained from the same Iraqi-type crude oil, and a VHVI oil produced by hydrocracking a "bright stock" waxy raffinate from the same crude oil, followed by dewaxing.

It appears from table V that oils according to the present invention are in all cases more resistant to oxidation than the hydrogenated light machine oil and VHVI oil, when in each case the oils containing the same additive are compared with each other.

Claims (2)

1. Lubricating oil composition which partly consists of a base lubricating oil and which further contains one or more additives and/or one or more conventional lubricating oils or base oils, characterized in that the composition has a viscosity index of at least 125 °g contains a base lubricating oil with a viscosity index of at least 135 °g which is obtained from adducts between thiourea and a lubricating oil feedstock. 2. Process for producing a lubricating oil composition according to claim 1, characterized in that one or more base lubricating oils and/or one or more additives are mixed with a base lubricating oil which is produced by treating a base oil raw material with thiourea, whereby solid thiourea adducts are formed, after which the thiourea adducts are separated from non -adducted oil, the separated adducts are split into a hydrocarbon phase and thiourea, and the latter compound is removed.