GB2028866A

GB2028866A - Lubricating oil formulation

Info

Publication number: GB2028866A
Application number: GB7929439A
Authority: GB
Original assignee: Deutsche Texaco AG
Current assignee: Wintershall Dea Deutschland AG
Priority date: 1978-08-25
Filing date: 1979-08-23
Publication date: 1980-03-12
Also published as: FR2434196A1; JPS5531878A; SE7906634L; DE2837141A1

Abstract

Lubricating oil composition consisting of a petroleum distillate having lubricating properties as main component, which is refined to a content of at most 12 weight per cent of aromatic compounds and at most 1.5 weight per cent of sulphur compounds contains as oxidation inhibitor 1,6-hexanediol-bis-3-(3,5-di- tert.butyl-4-hydroxyphenol)- propionate.

Description

SPECIFICATION Lubricating oil formulation This invention relates to a lubricating oil formulation consisting of a lubrication-active petroleum distillate, which has been refined in the usual way to a content of at most 12% by weight of aromatic fractions and at most 1.5% by weight of sulphur compounds, as its main constituent (base oil) together with small quantities of anti-oxidants and corrosion inhibitors, metal deactivators, rust inhibitors and, optionally, detergents and dispersants, solidification point depressants, high-pressure additives, antifoam agents and other standard additives, the anti-oxidant being a 2,4,6-trialkyl phenol derivative and, more particularly, a 2,6-di-tert.-butyl derivative of phenol.

Lubricating oils generally contain as their main constituent, or base oil, lubrication-active petroleum distillates which has been freed from troublesome constituents to the extent required for the particular purpose for which the lubricating oil is intended by one of the standard refining processes. In the case of lubricating oils which are to be used in the crank case of combustion engines, it is generally sufficient to refine the petroleum distillates (or even residual oils) to a content of at most 12% by weight of aromatic fractions and to a content of at most 1.5% by weight of sulphur compounds.

This is usually done by extracting the petroleum fraction used with selective solvents, such as liquid SO2, furfural, N-methyl pyrrolidone and similar compounds, and subjecting the solvent raffinates obtained to an aftertreatment with sulphuric acid of low concentration, adsorbents, such as fuller's earth, or to mild catalytic hydrogenation (hydrofinishing). Lubricating oil formulations ready for use are produced from the base oils thus obtained, which may also be de-paraffinated, by the addition of small quantities of additives, the type and quantity of these additives being adapted to the properties of the base oil and to the purpose for which the lubricating oil is to be used in such a way that the formulation meets certain requirements or specifications.Additives normally used in lubricating oil formulations are described, for example, in German Auslegeschrift No. 1 956,638 (column 4) or in the Journal "Chemie in unserer Zit",12 (1978), No. 2, pages 57 to 62.

It is known that particularly stringent requirements are imposed in lubricating oil formulations intended for lubricating steam turbines, stationary gas turbines, (air) compressors and similar machines or as hydraulic oils, because in cases such as these lubricating oils are generally circulated and are constantly exposed to the action of steam condensate, atmosphere oxygen and metals at high temperatures.

The minimum requirements for lubricating oils such as these, which will be referred to hereinafter as "turbine oils" for the sake of simplicity, are laid down in DIN 51 51 5. Particularly important properties of turbine oils are their resistance to oxidation 6r ageing, as determined in accordance with DIN 51 587 (or ASTM-D-943), and their anti-corrosion behaviour as determined in accordance with DIN 51 585.

In view of the stringent requirements which are imposed on turbine oils and which in practice go far beyond the minimum requirements of DIN 51 515, the base oils of standard commercially available turbine oil formulations consist of highly refined petroleum fractions which contain at most 7% by weight, generally between 2 and 5% by weight of aromatic fractions and less than 0.8% by weight, generally less than 0.2% by weight, of sulphur compounds.As described for example in the Journal Erdol und Kohle ....",23 (1970), No. 5, pages 281 to 284, more particularly page 282, left-hand column, first and second paragraphs, these base oils require much more rigorous and elaborate refining by treatment with relatively large quantities of concentrated sulphuric acid and/or by penetrating catalytic high-pressure hydrogenation than the base oils of normal lubricating oil formulations.

The difference between conventional turbine oil formulations and these normal lubricating oil formulations lies not only in particularly highly refined base oils, but also in a different combination of additives and auxiliaries which is intended to satisfy the stringent requirements on resistance to oxidation and anti-corrosion behaviour.

German Auslegeschrift No. 1 594,603 describes an oxidation-resistant hydraulic oil which, in addition to a mineral oil raffinate as the base oil, contains a) from 0.1 to 2.0% by weight of a sterically hindered phenol derivative as oxidation inhibitor, b) from 0.001 to 0.5% by weight of an oil-soluble alkyl succinic acid anhydride containing from 6 to 20 carbon atoms in the alkyl group and c) from 0.001 to 2% by weight of a secondary aromatic amine, for example a diphenyl amine derivative, a sulphurized terpene or 1,3,4-thiadiazole polysulphide. Of the phenol derivatives, 2,6-di-tert-butyl-4-methyl phenol is particularly preferred.As shown for example by Table V of this German Auslegeschrift, the presence of all the additives a) to c) is necessary for the resistance of the hydraulic oil to oxidation because they co-operate synergistically with one another.

Another lubricating oil formulation having a high resistance to oxidation, which is particularly suitable for use as a turbine oil, is described in US Patent No. 3,032,502 and, in addition to the base oil, contains from 0.01 to 1.0% by weight of a 2,4,6-trialkyl phenol, preferably 2,6-di-tert.-butyl-4-methyl phenol, from 0.3 to 0.1% by weight of an alkenyl dicarboxylic acid containing at least 10 carbon atoms in the alkenyl group, particularly dodecenyl succinic acid, and from 0.03 to 0.1 % by weight of an aromatic amine, such as phenyl-a-naphthyl amine and the like and, optionally, other standard additives.

The object of the present invention is to provide a lubricating oil formulation of the type mentioned at the beginning which shows outstanding resistance to ageing and corrosion-inhibiting properties and which may be used in particular as a turbine oil complying with DIN 51 515.

The present invention relates to the lubricating oil formulation characterised in the Claims. It has been found that oil-soluble a, co-a Ikane diol bis-esters corresponding to the formula

in which R, to R4 are the same or different and represent alkyl groups containing from 1 to 8 carbon atoms, preferably branched alkyl groups containing from 3 to 5 carbon atoms, R5 is an alkyl group containing from 1 to 4 carbon atoms and n = 1 to 8, provide lubricating oils with surprisingly high resistance to oxidation and with other advantageous properties. Accordingly, these esters may completley replace the hitherto usual 2,4,6-trialkyl phenol derivatives as oxidation inhibiting additives in lubricating oil formulations.

It is preferred to use esters corresponding to the above formula in which R, to R4 each represent a t-butyl group, R5 is a C2- or C3-alkylene group and n = 2 to 6. Mixtures of esters such as these may also be present in the lubricating oil formulation. The particularly preferred a,co-alkane diol bis-ester is 1,6hexane diol-bis-3-(3 ,5-di-tert.-butyl-4-hyd roxy phenol)-propionate.

The lubricating oil formulations according to the invention contain these ester compounds in the quantities normally used for oxidation inhibitors of from 0.01 to 0.75% by weight and more particularly in quantities of from 0.1 to 0.3% by weight. In addition, the formulations preferably contain the usual rust and corrosion inhibitors and also metal deactivators in the usual quantities of from about 0.01 to 0.2% by weight in each case, namely at least one benztriazole additive and an alkyl or alkenyl succinic acid (anhydride). An alkyl guanidine of which the alkyl groups each contain from 8 to 20 carbon atoms is an additive having good anti-corrosion and anti-oxidation properties. It may be used in particular instead of the alkyl or alkenyl succinic acid (anhydride).In addition, the lubricating oil formulations according to the invention may optionally contain the additional additives normally used in the particular field of application, namely anti-foam agents, thickeners, solidification point depressants and the like.

As the following Examples will show, the formulations according to the invention, which contain as the base oil a petroleum distillate highly refined in the usual way to a content of aromatic fractions of at most 7% by weight and to a content of sulphur compounds of at most 0.8% by weight, show excellent ageing behaviour exceeding by far the values laid down in DIN 51 51.5 by virtue of the ester compounds added. The anti-ageing effect of the ester compounds is so good that the requirements laid down in DIN 51 51 5 for turbine and similar oils are exceeded by far even when a normally refined petroleum distillate containing up to 12% by weight of aromatic fractions and up to 1.5% by weight of sulphur compounds is used as the base oil of the formulation.This is surprising because, hitherto, normally refined base oils have generally been used only in normal lubricating oils, but not in turbine oils. However, since the rigorous refinement of petroleum distillates normally requires penetrating solvent extraction, i.e. solvent extraction with a poor yield of raffinate, and treatment of the solvates with relatively large quantities of concentrated sulphuric acid (for example 10 to 1 5% by weight) and fuller's earth and/or drastic catalytic high-pressure hydrogenation and, hence, very considerable expense it must be regarded as a considerable advance that turbine oil formulations performing to specification can also be produced from normally refined base oils.

Another advantage of the present invention lies in the fact that the new diol ester additives are compatible with the other additives normally used in a lubricating oil formulations and do not adversely affect any important properties of the formulation.

The invention is illustrated by the following Examples and Comparison Examples.

Base Oil used: Grade 1 Base Oil: A lubricating oil fraction with a boiling range of 370 to 4900C was separated from a paraffin-basic crude petroleum. A normally refined base oil of ISO viscosity class 46 was produced therefrom by solvent extraction (with furfural), low-temperature de-paraffination of the raffinate with a mixture of methylene chloride and dichloroethane and mild catalytic hydrogenation (hydrofinishing).

Grade 2 Base Oil: A lubricating oil fraction with a boiling range of 370 to 4900C was separated from a paraffin-basic crude petroleum and a highly refined base oil of ISO viscosity class 46 was produced therefrom by solvent extraction with furfural, de-paraffination of the raffinate with a mixture of methylene chloride and dichloroethane and treatment with sulphuric acid and fuller's earth.

Grade 3 Base Oil: A lubricating oil fraction with a boiling range of 370 to 4900C was separated from a paraffin-basic crude petroleum and a highly refined base oil of ISO viscosity class 46 was produced therefrom by solvent extraction with furfural, de-paraffination of the raffinate with a mixture of methylene chloride and dichloroethane and catalytic high-pressure hydrogenation.

The properties of these three grades are shown in Table 2 whilst the compositions of the lubricating oils are shown in Table 1. The test results are set out in Table 2.

TABLE 1 Composition of the turbine oll formulations

Example No. Comparison Example No.

1 2 3 1 2 3 4 5 Base Oll Grade 1 1 2 1 1 2 2 3 1,6-hexane diol-bis-3-(3,5-di-tert.-butyl4-hydroxy phenyl)propionate, % by weight 0.30 0.25 0.30 - - - - 2,6-di-tert.-butyl-4-methyl-1-hydroxy benzene, % by weight - - - 0.30 0.30 0.30 0.30 0.30 Benzitriazole, % by weight 0.017 0.017 0.017 - 0.017 - 0.0117 Dodecyl guanidine, 5 by weight - 0.025 - - - - - Tetraprophenyl suocinic acid, % by weight 0.03 - 0.03 0.03 0.03 0.03 0.03 0.03 TABLE 2 Properties of the base oils and turbine oil formulation

Turbine olls Specification acc. to Values DIN 51515* 1 2 3 1 2 3 4 5 Base oll grade: 1 1 2 1 1 2 2 3 Aromatic content % by weight - 9.0 9.0 7.0 9.0 9.0 7.0 7.0 3.0 Sulphur content % by weight - 0.95 0.95 0.62 0.95 0.95 0.62 0.6 0.03 Viscosity at 40 C mm/s 47.5 47.5 46.2 47.5 47.5 46.2 46.2 48.4 Density at 15 C g/ml max. 0.900 0.884 0.884 0.877 0.884 0.884 0.877 0.877 0.872 Water separation secs. max. 300 97 152 72 105 109 60 76 54 capacity (DIN 51 789) Air separation mins. max. 5 4 4 3 4 4 3 3 2 capacity (DIN 51 381) Corrosive effect on copper according to corrosion DIN 51 759 level 2 1 1 1 1 1 1 1 1 (3 h. at 100 C) without presaurization Corroelon-Inhibiting properties with respect free from to steel acc. to DIN 51685, method A corrosion nn nn nn nn nn nn nn nn Ageing behaviour acc. to DIN 51587 max. 2.0 0.1 0.19 0.17 +) 0.15 0.15 0.13 0.22 neutralisation No. after 1000 h. in mg of KOH/g of oll Neutralisation No. 2 mg of KOH/g of oll is - 3000 3400 4200 816 1248 1272 1824 3250 reached during ageing in acc. with DIN 51587 in hours +) Neutralisation No. 2.0 reached after only 815 hours.

* Part 1 nn = not noticeable The results set out in Table 2 show the following: The lubricating oils of Examples 1 to 3, which contain 1,6-hexane diol-bis-3-(2,6-di-tert.-butyl-4hydroxy phenyl)-propionate, have a high resistance to oxidation by comparison with normal lubricating oils (Comparison Examples 1, 3 and 5). They also show a considerable increase in resistance to oxidation by comparison with lubricating oils which, in addition to the usual additives of a turbine oil, additionally contain a triazole as metal de-activator (Comparison Examples 2 and 4). Comparison of Examples 1 and 2 shows the synergistic effect of the alkyl guanidine.

Claims

1. A lubricating oil formulation consisting of a lubrication-active petroleum distillate, which has been refined in the usual way to a content of at most 12% by weight of aromatic fractions and at most 1.5% by weight of sulphur compounds, as the main constituent, together with a 2,4,6-trialkyl phenol derivative as anti-oxidant characterized in that the 2,4,6-trialkyl phenol derivative is 1,6-hexane diol-bis 3-(3,5-di-tert.-butyl-4-hydrnxy phenol)-propionate.

2. A lubricating oil formulation as claimed in Claim 1, characterized in that it contains from 0.01 to 0.75% by weight and more particularly from 0.1 to 0.3% by weight, based on the formulation as a whole, of the 1 ,6-hexane diol-bis-3-(3,5-di-tert.-butyl-4-hydroxy phenol)propionate.

3. A lubricating oil formulation as claimed in Claim 1 or 2 characterized in that it additionally contains a standard benztriazole additive, an alkyl or alkenyl succinic acid or an alkyl or alkenyl succinic acid anhydride, in a quantity of at least 0.01 to 0.2% by weight, based on the formulation as a whole.

4. A lubricating oil formulation as claimed in any of Claims 1 to 3, characterized in that it additionally contains an alkyl guanidine, in which the alkyl group contains from 8 to 20 carbon atoms, in a quantity of at least 0.01 to 0.05% by weight, based on the formulation as a whole.

5. A lubricating oil formulation as claimed in any of Claims 1 to44, characterized in that the base oil is a petroleum raffinate containing at most 7% by weight of aromatic fractions and at most 0.8% by weight of sulphur compounds.

6. The use of the lubricating oil formulation claimed in any of Claims 1 to 5 as a turbine oil (according to DIN 51 515).

7. A lubricating oil formulation as claimed in Claim 1 and substantially as hereinbefore described with reference to any of Examples 1 to 3.