DE1230511B - Lubricating oil for aircraft gas turbines - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. CL:

ClOm

German KL: 23 c -1/01

Number: 1230 511

File number: R 35053 IV c / 23 c

Filing date: April 29, 1963

Opening day: December 15, 1966

Aviation today places high demands on the properties of lubricating oils for modern Engines. These properties are characterized by good viscosity behavior even with extreme low temperatures, a low pour point and good stability at high temperatures.

Certain esters or ester mixtures that have these properties have been known as lubricants under the name "ester oils" for some time. However, the starting materials for the production of such esters have so far been limited to a relatively small range. It is known that esters of certain polyalcohols with certain monocarboxylic acids, such as. B. the triple argonate of trimethylolpropane, are useful as ester oils, while corresponding esters using other polyalcohols, such as glycerol or pentaerythritol, do not meet the requirements. It is also known to use esters or ester mixtures of certain dicarboxylic acids with monohydric alcohols of chain length from C ₈ to C ₁₀ , optionally with the use of dihydric alcohols, as lubricants. Long-chain sebacic acid, furthermore azelaic acid and adipic acid, come into consideration as the dicarboxylic acid, although the latter two increasingly decline in terms of the properties required as lubricants. Finally, esters of succinic acid had proven to be completely useless because they have a pour point that is much too high and, in addition, because of the strong tendency of this acid to form the anhydride ring, they are thermally unstable.

In the French patent specification 990 983 complex esters are described, which from aliphatic Dicarboxylic acids, polyethylene glycols, aliphatic alcohols and fatty acids are produced and the following Have structure:

Alcohol — dicarboxylic acid — polyethylene glycol—
Fatty acid.

Dicarboxylic acids HOOC - (CH ₂ ) ,! - COOH described, in which η = 0 to 24, and also alkenylsuccinic acids with 4 to 24 carbon atoms in the alkenyl radical, which are produced by the condensation of olefins with maleic anhydride. The glycols can have up to 18 carbon atoms, the polyethylene glycols 4 to 54 and the polypropylene glycols 6 to 63 carbon atoms. The alcohols can be monohydric alcohols from methanol to fatty alcohols and monoethers of mono-, di- and trialkylene glycols and analogous thioalcohols. The suitable fatty acids Lubricating oil for aircraft gas turbines

Applicant:

Rheinpreussen Aktiengesellschaft for
Mining and chemistry,
Homberg (Ndrh.), Baumstr. 31

Named as inventor:

Dipl.-Chem. Dr. Friedrich Engelhardt,

Homberg (Ndrh.);

Dipl.-Ing. Diethelm Heyer, Moers

include acetic acid and its homologues up to stearic acid, also oleic acid and / 9-alkoxypropionic acids and their theoderivatives, such as ß-tstt.-dodecyl mercaptopropionic acid. However, Table 1 on page 4 of the French patent shows that the pour points of the complex esters with an alkenylsuccinic acid with 10 to 18 carbon atoms as a building block are so little low that they by no means correspond to the Mil-L-7808 B standard. The pour point data, however, prove the uselessness of these complex esters as lubricants for turbo-prop and turbo-jet aircraft.
It has now been found that esters of alkylene succinic acids with 4 to 10 carbon atoms in the alkenyl radical and straight-chain or branched alcohols with 6 to 10 carbon atoms, optionally together with other dicarboxylic acid esters or dicarboxylic acid ester mixtures, can be used as lubricating oils for aircraft gas turbines. The favorable properties of the esters used according to the invention are surprising and were not to be expected since, as already mentioned, succinic acid esters cannot be used as ester oils. The invention is based on the knowledge that when succinic acid is modified by alkenyl groups, on the one hand, the pour point of its esters drops sharply and, on the other hand, the tendency for the anhydride ring to regress is greatly inhibited, which ensures the stability of the esters even at high temperatures. In contrast, it was previously of the opinion that such behavior can only be achieved with dicarboxylic acid esters if

609 747/295

when the carboxyl groups are sufficiently spaced apart. '

The following table lists the physical properties of succinic esters with various Alcohols compared to the corresponding esters from alkenylsuccinic acids.

The esters were prepared in a known manner by esterification of the acids with the corresponding alcohols in the liquid phase in the presence of acidic catalysts. All of the esters had an acid number of 0.1 to 0.2 and a base number of 0.4 to 0.5.

As can be seen from the table, the differences between the succinic acid esters and the corresponding alkenylsuccinic acid esters considerably with regard to their physical properties.

The viscosity of the succinic acid esters at 99 ° C is well below the range required Specification in contrast to the corresponding alkenyl succinic acid esters. The same is true in Temperature range of 38 ° C.

Alkenylsuccinic esters have viscosities at -40 ° C within the required specifications, with the succinic acid esters they are Cannot be measured at all, as the substances are crystalline in this temperature range.

Serious differences can also be seen in the pour points, where the succinic acid esters are completely outside the required specifications, except for ester no. 4. The pour points of the alkenyl succinic acids are in their entirety in accordance with the specification requirements.

cSt at 99 ° C cSt at 38 ° C cSt at -40 ° C Pour point
⁰ C 1.86 6.15 crystalline -22 2.63 9.52 crystalline + 3 crystalline substance 2.18 8.05 unknown -65 2.20 8.28 1320 -65 3.06 12.61 2040 -65 3.10 12.60 7800 -62 3.02 14.88 unknown -65 2.20 15.54 2200 -65 3.59 17.15 3100 -64 4.20 21.00 7100 -63 4.35 30.14 unknown -49

Succinic acid ester from:

1. n-Hexanol .........

2. n-octanol

3. n-octanol / n-decanol

4. 2-ethylhexanol

Isobutenyl succinic acid ester from:

1. n-hexanol

2. n-octanol

3. n-octanol / n-decanol

4. 2-ethylhexanol

Diisobutenylsuccinic acid ester from:

1. n-hexanol

2. n-octanol

3. n-octanol / n-decanol

4. 2-ethylhexanol

The physical properties of succinic esters of various alcohols compared to the corresponding ones Esters from alkenyl succinic acids.

. A wide variety of alkenyl succinic anhydrides can be used to produce the esters, which are prepared by known processes by adding olefins to maleic anhydride can. Naturally, the properties of the esters depend to a large extent on the size and type of the Alkenyl group dependent. This on the other hand must expediently back to the chain length of the alcohols used must be matched. Alkenylsuccinic acids have proven to be particularly advantageous Alkenyl groups of 4 to 10 carbon atoms have been proven. This applies equally to branched as well as to straight chain alkenyl groups. Various types can also be used as the alcohol component as long as they are reasonably matched to the alkenyl groups of the acids. here alcohols with carbon numbers between 6 and 10 are both branched and straight-chain turned out to be advantageous. Mixed esters or mixed esters of alkenylsuccinic acid can also advantageously be used use. So it is possible to use mixed esters of an alkenylsuccinic acid with a Alcohol mixture or mixed ester from an alcohol with an alkenyl succinic acid mixture or else mixed esters from a mixture of alcohols and alkenylsuccinic acids can also be used. Man can also use other components, such as B. other dicarboxylic acids such as adipic acid or Sebacic acid, or glycols or glycol mixtures. It is also possible to use those used according to the invention To combine esters or ester mixtures with esters of another type, for example with esters of Polyalcohols with monocarboxylic acids.

The production of the esters or ester mixtures, for which no protection is claimed here, takes place after known processes without or in the presence of acidic catalysts, optionally with concomitant use of entrainers for the reaction water. In the following some examples of the invented

properly used ester given:

example 1

2.2 moles of isooctanol are mixed with 1 mole of isobutenylsuccinic anhydride, obtained by addition of isobutylene to maleic anhydride, in the presence of catalytic amounts of H ₂ SO ₄ in the temperature range from 140 to 180 ° C. with azeotropic distillation of the resulting reaction water-isooctanol mixture and continuous recycling of what has been distilled off Isooctanol is esterified in the reaction vessel until the acid number of the product has fallen to about 0.4 mg KOH per gram. After washing with

The excess alcohol is removed by applying a thin lye and washing it several times with water distilled off by vacuum. This product has the following properties:

Pour point: -65 ⁰ C

Kinematic viscosity temperature, ⁰ C

90 60 30th -50 3.54 cSt 6.70 cSt 16.60 cSt 12,000 cSt

10

These physical data are well in the range of the conditions of the US specification MIL-L-7808 D, which are specified for lubricants in aircraft gas turbines.

Example 2

According to Example 1, a neutral diester of isooctenylsuccinic anhydride (adduct of maleic anhydride and diisobutylene) and n-octyl alcohol. This product has the following properties:

Pour point: -65 ° C «5

Kinematic viscosity temperature, ⁰ C

30 The thermal stability can therefore be described as good.

Example 3

According to Example 1, a mixed ester is made from isooctenylsuccinic anhydride and an alcohol mixture of n-hexyl alcohol and n-octyl alcohol in a ratio of 1: 1.

This mixed ester has the following properties:

Setting point: -70 ⁰ C

Kinematic viscosity
Temperature, ⁰ C

90 60 30th -50 4.45 cSt 8.50 cSt 21.0 cSt 11 800 cSt

These values are also in the range of the US specification MIL-L-7808 D.

stability

After heating the ester in 28O ⁰ C for 12 and 24 hours the percentage viscosity change at 6O ⁰ C is

% Change in viscosity

after 12 hours +3.5

after 24 hours +4.9

90 60 30th -50 3.83 cSt 7.30 cSt 18.4 cSt 12 400 cSt

35 stability

The following change in viscosity results under the conditions of Example 2

% Change in viscosity

after 12 hours +5.0

after 24 hours +6.9

Claims (1)

Claim: Use of esters from alkenylsuccinic acids with 4 to 10 carbon atoms in the alkenyl radical and straight-chain or branched alcohols having 6 to 10 carbon atoms, optionally together with other dicarboxylic acid esters or dicarboxylic acid ester mixtures as lubricating oils for aircraft gas turbines. Considered publications:
German Auslegeschriften No. 1 031 917.1 056 314; U.S. Patent No. 2,937,993;
British Patent Nos. 722 634, 821941; French patent specification No. 990 983,1275 283. 609 747/295 12. «6 © Bundesdruckerei Berlin