DE1063739B - Neutral ester based lubricants - Google Patents

Description

GERMAN

The invention relates to improvements in lubricants based on neutral esters or ester mixtures with a low content of compounds which have a - ■ C-S - C or - C - Se - C group contain, in particular liquid lubricants of the aforementioned type, which are suitable for a wide temperature range and the most diverse operating conditions must be suitable.

There has been a significant need for lubricants for use in internal combustion engines for some time or other devices where high temperatures come into question, are suitable, for example of lubricants for the lubrication of gas turbines, in particular propeller turbines, in which the lubricant has to lubricate not only the bearings, but also the reduction gear and in which the Lubricant also at low or very low temperatures, for example down to -40 ° C or to about -60 ° C, must remain stable and fluid.

It has been suggested as a lubricant (especially for use at low temperatures suitable) to use certain diesters of aliphatic dicarboxylic acids with branched-chain aliphatic alcohols; a number of such esters are in the journal ^ Industrial and Engineering Chemistrytf, April 1947, Pp. 484 to 497.

Recent improvements in the design of gas turbines have to do with lubricants Requirements even higher. The lubricants are now expected to work at high Temperatures, for example in the order of 200 ° C., have good resistance to oxidation and at the same time no corrosive effect on metals, as they are used in the construction of gas turbines, e.g. steel, copper, brass, magnesium, aluminum and cadmium-plated or cadmium-plated steel. the Lubricants must also be used to lubricate the reduction gear in the turbines for propeller drive have high resilience.

It is also already known from German patent application W14895 IVc / 23c that one can use di-oxyaryl thioether the above-mentioned esters can be added with advantage to their resistance to oxidation at high temperatures to improve.

Other examples of effective antioxidants are phenothiazine and some of its derivatives as described are in the journal Industrial and Engineering Chemistry *, December 1950, at pages 2479 to 2489.

Another group of antioxidants that are found to be quite effective at high temperatures are the relatively high molecular weight dialkyl selenides.

Although these additives all contribute more or less to the oxidation of synthetic lubricants

Lubricant based
neutral ester

Applicant:
CC Wakefield & Company Limited,
London

Representative: Dr. M. Eule, patent attorney,
Munich 13, Kurfürstenplatz 2

Claimed © Priority:
Great Britain May 14, 1956 and May 8, 1957

John Scotchford Elliott and Eric Descamp Edwards,
London,

have been named as inventors

of the ester type, they still suffer from the disadvantage that they tend to decompose at high temperatures, in which case products are formed which have a corrosive effect on copper-containing metals and silver. For example, the phenothiazine-containing synthetic lubricants of the ester type can, under certain conditions at elevated temperatures, cause undesirable and considerable tarnishing of copper and copper-containing metals or silver, while the di-oxyaryl thioethers react with copper and copper-containing metals to form copper derivatives, which at very high temperatures, e.g. B. in the order of 280 ° C, tend to decompose with the formation of copper sulfides. In German patent specification 949 589 it was pointed out that the corrosive action of the dioxyaryl thioethers on copper-containing metals can be reduced by adding certain basic aliphatic, alicyclic or heterocyclic amines to the mixture. However, the action of these compounds is not satisfactory at the high temperatures mentioned above.
There are also ester-based lubricants known which, in addition to thiodiarylamines, additions of bis (aminoaryl) alkanes, such as. B. tetramethyldiamino-diphenylmethane included (French patent 1082950). But even such lubricants are not yet completely satisfactory.

909 SO8 / 395

I 063

It has now surprisingly been found that in synthetic lubricants of the ester type Corrosion effect if they contain one or more antioxidants from the classes mentioned above, largely prevented by adding certain heterocyclic compounds even at high temperatures can be.

As a result, lubricants based on neutral esters or mixed esters contain a low amount Content of compounds which have a - C - S - C or - C - Se - C group, according to the invention an organic heterocyclic compound, soluble in the lubricating oil base, containing 2 or 3 nitrogen atoms and has a carbon double bond in a heterocyclic five-membered ring.

Surprisingly, it has been shown in comparative tests that such lubricants are also superior to the lubricants described in French patent specification 1,082,950. For this purpose, strips of copper foil with the approximate dimensions of 50.8 x 12.7 mm, which had been made shiny by means of carborundum, were inserted into test tubes partially filled with the oil to be tested, the copper strips being completely immersed in the oil. The ίο test tube was then placed in a beaker filled with oil and heated to 200 ° C in an oven.

Duration of the test 24 hours. In all cases, di- (2-ethylhexyl) sebacate was used as the basis. Here the following resulted:

attempt
No. Phenothiazine
in'/. Secondary inhibitor Inhib
stoffin ° / o Appearance of the Cu strip 1 0.5 none Thick black flaky deposit on and over that
Interface 2 1.0 none the same 3 0 Benzotriazole 0.5 Flaky black at the interface; very dark brown
black spots over it 4th 0.5 the same 0.05 Smooth black spots over the interface; Interface
black, a little powdery 5 0.5 the same 0.2 Smooth brown spots over the interface; the latter
as with 4 6th 0.5 Tetramethyl diamino
diphenyl methane 0.05 Thick black flaky deposit on and over that
Interface 7th 0.5 the same 0.2 the same 8th 0.5 the same 0.5 As with 7, but a slightly smaller deposit above
half of the interface

The term "neutral ester" used throughout here is intended to refer to esters with an acid number of not Get over 1 mg KOH per gram.

It is already known to use compounds of the type used according to the invention for aqueous cleaning or add wetting agent-containing systems to the discoloration caused by such washing solutions to avoid on metals. From this, however, it was in no way to be inferred or suggested that Compounds of this type have remarkable anti-corrosion properties in ester lubricants, which - C - S - C or --X - Se - C groups Contain antioxidants. In particular, it could not be inferred from this that compounds of this type were the Also prevent the corrosive effect of compounds consisting of - C - S - C or - C - Se - C groups exhibiting antioxidation in ester lubricants at higher temperatures.

The esters suitable for use as the lubricant base in accordance with the present invention are im essentially neutral saturated esters of organic carboxylic acids and have a viscosity index of at least 100, a pour point or freezing point of over -40 ° C, a boiling or decomposition temperature of not 315 ° C and a flash point not below 176 ° C Of course you can use ester mixtures, in which individual esters have a freezing point of over -40 ° C and a viscosity index of less than 100, provided that the mixture itself has the desired properties.

The preferred esters have the general formula COOR ₁

XOOR ₂

In this formula, R denotes a saturated aliphatic or cycloaliphatic hydrocarbon radical with 2 to 8 carbon atoms. R ₁ and R ₂ are identical to or different from one another, namely branched-chain alkyl or alkyl-substituted cycloalkyl radicals having at least 4 carbon atoms. Examples of the radical R are (CH ₂ ) _n , where η is an integer from 2 up to 8, and

CH ₂

- CH CHXH ₂ -
\ /
C.

/ \
CH ₃ CH ₃

While most of the esters falling into the above group have both a high viscosity index and have a low pour point, there are some among them, such as B. the di- (1,3-dimethyl-butyl) adipate and the di- (3-methyl-butyl) sebacate, which have relatively high freezing points, above about -17 ° C, and therefore normally for the invention

15th

would not be suitable for the purpose in view of the fact that they would not be mixed with other esters of lower Freezing point.

It is readily apparent that depending on the conditions under which the lubricant is used different esters can be selected. So z. B. It is made for use at very high temperatures preferred to use the high molecular weight esters, especially the higher branched chain ones Azelaic and sebacic acid diesters.

As already stated, the antioxidants consist of organic compounds with the property to prevent oxidation at elevated temperatures; they contain the group - C - S - C - or - C - Se - C -. Albeit the great mass of connections of this general type, e.g. B. the aliphatic sulfides, certain antioxidant properties have elevated temperatures, many compounds are at really high temperatures, e.g. B. in the The order of magnitude of 175 ° C, as can be found in the lubrication of gas turbines, is limited in this regard.

The preferred antioxidants which are more or less effective at high temperatures include to three different types:

I. Di (oxyaryl) thioethers (cf. German Patent 949 589), in particular the di (oxyphenyl) thioethers, at which the Benzolkerae are not substituted at all or at least only by short-chain alkyl radicals.

II. Dibenzothiazines, preferably dibenzo-1,4-thiazines. The benzo radicals can have further substituents, e.g. B. Alkyl or aryl groups or halogens.

However, the selenium analogues of these compounds can also be used; H. so the dibenzoselenazine.

Typical examples of compounds that fall into this class are

25th

30th

35

Phenothiazine (2,3,5,6-dibenzothiazine),

Phenoselenazine,

Phenothiazon-3,

Phenothiazine-5-oxide,

10-10'-diphenothiazine,

10-benzyl-phenothiazine,

7-benzo- (c) -phenothiazine,

3,7-difluorophenothiazine.

40

45

III. Dialkyl selenides with at least 20 carbon atoms, ζ. Β. Dilauryl selenide and dicetyl selenide.

The antioxidants used in the context of the invention do not have to have a decomposition temperature of xmter 200 ° C and have adequate solubility in the esters in which they are to be dissolved, own.

The organic heterocyclic compounds contained according to the invention are imidazoles, pyrazoles or 1,2,3-triazoles; they contain the groups

-C-NH

C — R resp.

-C-N

-C-NH

respectively.

- C-NH

ι \

I ^ —C — c

.; n

- C -N

60

55

70 where R = H or represents an alkyl, alkenyl or aryl group.

The selected compounds must not boil below 200 ° C, preferably not below 300 ° C or decompose; they must be soluble in the lubricant in the proportions in which they are used should be.

Specific examples of such additives are

Imidazole,
Benzimidazole,
Pyrazole,
Benzotriazole,
2-methyl-benzimidazole,
3,5-dimethylpyrazole,
Indazole.

The largest proportion of the lubricant according to the invention consists of the esters described above. the Antioxidants can be used in proportions of 0.05 up to 5.0%, preferably 0.1 to 2.0%, based on the weight of the finished mass related, can be used. The organic heterocyclic compounds are generally used in relatively small proportions, for example in amounts from 0.01 to 2.0%, preferably 0.05 to 0.5%, based on the weight of the finished mass.

The scope of the invention also includes lubricants which contain a certain proportion of mineral oil. The amount added and the type of mineral oil depend to a large extent on the intended use required pour point; In no case should the proportion of mineral oil be 20%, on the Weight of the finished mass related, exceed.

In one embodiment of the present invention, the dicarboxylic acid diesters are of the type described thickened by the addition of polymeric esters of acrylic or alkyl-substituted acrylic acids, e.g. B. polymerized η-butyl or even higher esters of methacrylic acid. One can use lubricants of this type produce which, in addition to a sufficiently high viscosity, have a very low pour point.

Alternatively, to increase the viscosity of the lubricant, instead of the polymers, the esters of the Acrylic or alkyl-substituted acrylic acids also use polyesters, e.g. B. Polypropylene glycol sebacate different molecular weights.

In another embodiment of the present invention, certain amines can be added to the lubricant incorporate, as described in German Patent 949 589, to make the corrosion more copper-containing To reduce metals and to give the mixture an increased resistance to oxidation.

In general, these amines are used in relatively small proportions, for example 0.01 to 1.0%, preferably 0.05 to 0.5%, based on the weight of the finished lubricant.

In order to increase the load capacity of the lubricants according to the invention, especially when the same to be used for the lubrication of gas turbines, one can add a portion of a lubricant or to add more additives. You can, for example, the lubricant a proportion of incorporate neutral organic phosphate or phosphite esters (cf. German Patent 958 686).

If desired, other additives can also be incorporated, e.g. B. Rust preventives in the form of very small amounts of meta-petroleum sulfonates or other known ones Compounds capable of preventing rust from forming in the presence of water.

Specific preparations which can be used according to the present invention are as Examples are given in the test results tables below.

In a simple test method, strips of copper foil with the approximate dimensions of 50.8 x 12.7 mm, which had been made shiny with carborundum powder, partially filled with the oil to be tested Test tubes inserted, with the copper strips fully immersed in the oil. The test tube was then in

a beaker filled with oil is inserted and heated in an oven.

In a first series of tests, which was carried out according to this procedure, the mixture was set small amounts of various corrosion inhibitors are added. The mixture consisted of di- (3,5, S-trimethylhexyl) sebacate / D. N. S./ with a content of 1.0% of a technical grade of di (3-methyl-4-oxyphenyl) thioether. The results are summarized in Table I.

Table I.

attempt
No. Inhibitor Inhibitor
in Vo Appearance of the copper strip
after 4 hours 1 none dark brown / black, smooth 2 Benzotriazole 0.1 brown precipitate on a light copper background 3 Imidazole 0.1 brown / dark peacock colored 4th Benzimidazole 0.2 very light peacock colored, light brown precipitation 5 Pyrazole 0.3 light brown, white powdery precipitate 6th 3,5-dimethylpyrazole 0.5 light stains 7th Indazole 0.3 heavy greenish-brown powdery precipitate 8th 2-methyl-benzimidazole 0.2 light peacock color Appearance of the copper strip
after 22 hours 1 none black, flaky 2 Benzotriazole 0.1 dark brown 3 Imidazole 0.1 brown / very dark peacock color 4th Benzimidazole 0.2 light peacock colored, medium brown precipitation 5 Pyrazole 0.3 dark brown 6th 3,5-dimethylpyrazole 0.5 soft brown 7th Indazole 0.3 heavy dark brown precipitate 8th 2-methyl-benzimidazole 0.2 light peacock colored with a little dark brown precipitate

All inhibitors were added to D.N.S. + 1.0% di- (3-methyl-4-oxyphenyl) thioether; temperature 150 ° C; Duration of the respective experiments 22 hours.

From Table I it can be seen that all compounds tested were more or less effective in the Prevention of attack by copper through a technical grade of di- (3-methyl-4-oxyphenyl) -thio-

ether or due to impurities contained in the mixture, namely at 150 ° C

A second series of tests was carried out under the same conditions, but at 200 ° C and on Duration of 6 hours; the results are summarized in Table II. In this series of experiments were two tested various mixtures, each with and without the addition of 0.2% benzotriazole.

Table II

attempt
Xr. Composition of the mixture Inhibitor Appearance of the copper strip 9 45% DOS 1
45% DNA
6% polynonyl methacrylate>
3% tri-m-toluyl phosphate
1% p, p-dioxy-diphenyl-thioether is missing light brown spots 10 the same available matte copper paint with something
white precipitate 11 88% di (2-ethylhexyl) adipate
10% polypropylene sebacate
2% di (3-methyl-4-oxyphenyl) thioether
(technical quality)
+ 0.1% dicyclohexylamine is missing dark brown, 10% black 12th the same available medium brown

Temperature 200 ° C; Duration of the experiment 6 hours; inhibitor used 0.2 ° / ₀ benzotriazole. In this table, D. 0. S. means di (2-ethylhexyl) sebacate; the "polynonyl methacrylate" used was poly (3,5,5-trimethyl-hexyl) methacrylate, and the polypropylene sebacate is a commercially available preparation.

A comparison of Runs 9 and 11 in Table II shows that the main cause of tarnishing of copper as a result of the action of di (oxyaryl) thioethers at temperatures of the order of magnitude from 150 to 200 ° C are impurities; the relatively pure compound in experiment 9 only results light brown spots, whereas the compound used in experiment 11 even in the presence of dicyclohexylamine resulted in some blackening. However, an apparent improvement was obtained in both cases through the introduction of benzotriazole.

In a similar experiment with a silver pattern at 200 ° C, a solution of 1% di (3-methyl-4-oxyphenyl) thioether produced in D. O. S. dark spots on the silver, which, however, did not form when one looked at the Mixture added 0.2% benzotriazole.

Antioxidants of the dibenzothiazine type, such as. B. phenothiazine had greater heat resistance than the di- (oxyaryl) -thioethers and left the copper under the conditions of the previous experiment, tarnish only slightly even at 250 ° C (6 hours).

However, it was observed that if the test strips were only partially immersed in the oil, the copper attacked significantly above the oil level, especially at the oil-air interface.

However, this corrosion could be reduced considerably by the inhibitors according to the invention, such as from Table III.

Table III

attempt
No. Composition of the mixture Inhibitor Appearance of the copper strip 13th 56.5% DOS
40% complex ester I.
3% polynonyl methacrylate [
0.5% tech. Phenothiazine J. none black, flaky precipitate
at and above the interface 14th the same Benzimide
azole (0.2%) soft peacock color above the
Oil with a brown line on the
Interface 15th the same Benzotri
azole
(0.05%) soft brown above the oil
with a black line on the
Interface 16 94% ONS 1
5% mineral oil AI
0.25% calcium petroleum sulfonate (20% in mineral oil) [
0.75% 7-benzo- (c) -pheno-thiazine j none heavier dark brown, flaky
Precipitation at the interface
and just about it 17th the same 2-methyl
benzimide
azole (0.05%) soft light brown above the
Oil with a dark line on the
Interface. No precipitation

Temperature 250 ° C; Duration of the experiment 6 hours; the copper strips were partially submerged.

The complex ester shown in Table III was obtained by esterifying 2 moles of a dicarboxylic acid with 2 moles of a branched chain aliphatic alcohol and 1 mole of glycol; O.N.S. stands for 2-ethyl-hexyl-3,5,5-trimethyl-hexyl-sebacate. The mineral oil A was a solvent naphtha refined mineral oil having a viscosity of about 65 Redwood seconds (Redwood I) at 60 ° C. A further series of experiments has now been carried out carried out using the oxidation / corrosion test procedure as described in US Pat ministerial material regulation No. D Eng. / R. D. 2487 (Issue 2 of January 1, 1954), Paragraph 7 · 4. This The test was a combined oxidation and corrosion test to measure the tendency of an oil to develop Corrosive oxidation products at elevated temperatures. The results are in the Table IV summarized, all experiments being carried out at 140 ° C. over a period of 22 hours.

Table IV

attempt
No. Ester or
Ester mixture Additives Cadmium plated steel specimens with
Docking catalyst Weight
modification
mg Color
Pattern e des
Catalyst Acid number
increase
mgKOG / g 18th
19th Di- (3,5,5-trimethyl-
hexyl) sebacate
the same no
0.5% di- (3-methyl-
4-oxyphenyl) thio
ether -252.5
+6 corroded
light yellow light peacock color
light brown 10.0
0.4

909 608/395

Claims (1)

Table IV (continued) Test No.Ester or mixture of esters Cadmium-plated steel specimens with copper catalystAdditivesWeight change mgColor of the sample | Increase in catalyst acid number mg KOG'g20 of the same 0.5% di- (3-methyl-4-oxyphenyl) thioether +0.1% benzimidazole + 0.8 almost clear peacock color 09147 0 / T) i / 9 ätWl hexyl) sebacate 47 % Di- (3,5,5-trimetnyl-hexyl) -sebacate 6% polynonyl-methacrylateΓ) ΟζΟ / Pnlrinm- petroleum-sulfonate-180 light gray glossy 15,822 of the same 0.5% techn. Phenothiazine + 0.2 traces of light peacock-colored spots, dark peacock colors with black spots 023 of the same 0.5% / 0 techn. Phenothiazine 0.2% benzotriazole-1,6 the same peacock color 0.22- 24 di-i2-ethvl-hexvl) - sebacate5.0% tri-m-toluyl phosphate + 1.0% ger. Phenothiazine + 0.2 peacock color very dark brown varnish, almost black in places 0.0625 of the same 5.0% tri-m-toluyl phosphate + 1.0% ger. Phenothiazine + 0.1% benzotriazole light peacock color enhell gold 0 Table IV (continued) Experiment no. Copper specimen with steel catalyst Weight change mgColor of the sample Acid number increase mg KOH / g18 + 1.2 peacock color9.519 + 3.1 brown0.4020-0.8 peacock colorNuU21-1, 4 peacock colored 11.322 + 0.2 dark peacock colored / brown NuU23 + 1.4 light peacock colored 0.1024 + 1.650% matt black precipitate on dark peacock colored background0.0625 + 0.2 light goldenNuU Experiments 18 and 21 show the development of the inhibitor-free diesters and the mixtures based on them very high acid numbers and the resulting severe corrosion of the cadmium-plated or cadmium-plated steel samples. Experiments 19, 22 and 24 show how the increase in the acid number and the corrosion of the cadmium-plated steels can be effectively halted by the presence of antioxidants of the types described, although this is accompanied by an undesirable attack on the copper samples and catalysts, the especially with phenothiazine is very serious. Experiments 20, 23 and 25 show that the incorporation of the inhibitors according to the invention in the mixtures reduces the corrosion of the copper to an extent which can easily be neglected. Patent claims: 1. Lubricants based on neutral esters or ester mixtures and a low content of Compounds which have a - C - S - C- resp.