DE961283C - Process for stabilizing the low temperature viscosity of synthetic lubricating oils - Google Patents

Description

The invention relates to a method for stabilizing a lubricating oil which is suitable for lubrication of aircraft gas turbine engines and a substantial proportion of a synthetic one Contains lubricating oil.

A lubricant for aircraft turbines must essentially have the following properties: Good High temperature resistance, good viscosity-temperature properties and good load capacity as well as a low viscosity at low temperatures combined with a low vapor pressure at high temperatures Temperatures. These properties cannot be obtained simultaneously using any economical petroleum refining process. However, it has been proposed to use mixtures which approximate these properties to produce a major proportion of certain synthetic esters. Especially diesters and complexes Esters or mixtures thereof can have properties approaching these desirable ones.

The synthetic lubricant base preferably used in practicing the invention contains a major proportion of compounds of the general composition:

R ₂ OOCR ₁ COOR ₂ ', R ₂ OOCR ₁ COOR ₄ OOCr ₃ , R ₃ COOR ₄ OOCR ₃ ',

R ₃ COOR ₄ (OOCR ₁ COOR ₄ ^ OOCr ₃ '

Here, R ₁ and R ₁ 'are residues of dicarboxylic acids, such as HOOCR ₁ COOH, R ₂ and R ₂ ' are the residues of monohydric alcohols, such as R ₂ OH, R ₃ and R ₃ 'are the residues of monocarboxylic acids, such as R ₃ COOH, and R ₄ and R ₄ 'are the residues of glycols, such as HOR ₄ OH. # is equal to ι to 6, but not necessarily an integer, and indicates the average composition of a mixture of compounds as a fraction. The monovalent alcohol

ao holes are preferably aliphatic alcohols, ether or Thioether alcohols.

It is desirable that the hydrocarbon chain of the radical R _{2 be} somewhat branched; the alcohols obtained after the oxo synthesis are particularly effective.

As R ₂ generally has 4 to 18 carbon atoms and contains sulfur and oxygen only in thioether or ether bonds. The monocarboxylic acids are preferably aliphatic acids with up to 22 carbon atoms, the glycols preferably members of the alkylene or polyalkylene glycol series, the polyethylene glycols from diethylene glycol to decaethylene glycol or diols of the composition HO (GH ^) _n OH, where η is 3 to 12 is, are particularly valuable. The esters should have a molecular weight and a structure such that the resulting mixture has a viscosity of 1 to 20, preferably 3 to 10, cSt at 98.9 °.

When using ester-based lubricant mixtures, especially mixtures that contain more than about 20 percent by volume complex esters have been found to be a disadvantage that these mixtures tend to thicken when stored at low temperatures. The cause of this thickening is not completely clear, in any case this is not desired.

The invention aims to significantly reduce this thickening at low temperatures.

A complex ester is understood here to mean an ester which has three or more ester groups in contains linear chain.

It has now been found that salts of strong organic bases reduce the low temperature viscosity of lubricating oils able to stabilize on the basis of synthetic esters.

The strong organic bases preferably have the general composition:

NO'

R '"HN —C — NSJR"

Herein R ', R "and R'" are aliphatic hydrocarbon groups expediently not more than 10 carbon atoms, in particular not more than 4 carbon atoms, or hydrogen. A particularly preferred organic Base is guanidine.

Other salts can also be used, such as the quaternary ammonium salts of the general one Composition:

R ₄ -NR ₂

Here, R ₁ , R ₃ , R ₃ and R _{4 are} aliphatic ^ hydrocarbon groups of preferably not more than 10, in particular not more than 4, carbon atoms; and X is an anion, preferably carbonate, sulfate, chloride or acetate.

Compounds which can be used according to the invention are, for example, guanidine carbonate, sulfate and acetate.

According to the invention, a small percentage of a salt of a strong organic base, preferably an oil-insoluble salt thereof, is added to a synthetic lubricating oil mixture, in particular a mixture of a complex ester and a diester, the mixture is heated to over 100 ° and nitrated. The upper temperature limit is essentially determined by the stability of the synthetic lubricating oil and can easily be determined for each lubricating oil by means of preliminary tests. Generally it can be said that temperatures are less suitable than 220 ^0, if the heating time is longer than 45 minutes that can be heated to 200 but ⁰ when the heating time 2 ^x / is about ₂ hours.

The proportions of the raw materials used are somewhat dependent on the tendency of the lubricant to become thick and the desired improvement. Generally no more than 7 is used, preferably 0.1 to 5, in particular 1 to 2 percent by weight, based on the total mixture.

The treatment with the salt of the strong organic base is preferably carried out by stirring the mixture, which contains more than 0.1, preferably 0.2 to 2 percent by weight of the salt, based on the total mixture, from 5 to 120, preferably 10 to 60 minutes to over 100, preferably 170 to 190 ⁰ and the reaction mixture is then filtered.

A small amount of a dark colored resinous material usually precipitates from the mixture, and the color of the synthetic lubricating oil mixture is improved.

The treatment does not appear to noticeably increase the viscosity of the mixture at 37.8 ° or the viscosity index affect, as can be seen from the table.

The following example explains an example form of the invention.

example

A mixture of 60 percent by volume of a las is made complex esters and 40 percent by volume dinonyl seba-

cat her. The complex ester was made from nylon alcohol, sebacic acid and polyglycol 200 (predominantly tetraethylene glycol) produced by the half-ester of polyglycol and the acid in a first stage and in a second stage the acidic product formed was esterified with the monohydric alcohol, such as described in British Patent 666,697. The mixture is stirred at 1 percent by weight for 15 minutes Guanidine carbonate heated to 180 °. A small amount, comparable to the amount of salt added, falls Amount of dark brown resinous material, and carbon dioxide is evolved. The reaction mixture is filtered.

The table below shows the effect of this treatment:

Original viscosity
at -40 ⁰ , cSt

Viscosity at -40 ° after

iy hours of storage

-40 ⁰ , cSt

Color value, day Robinson ..
Viscosity at 37.8 °, cSt ..

ASTM. Waste
-40 ⁰ to + 37.8 °

Before the
treatment

II 500

6ο οοο

57.8
ο, 653

After
treatment

Ii 770

12360

13th
6l, 2

0.652

The invention can of course be applied to synthetic lubricating oil blends, which additives such as antioxidants, antiwear agents, and viscosity index improvers.

Claims (6)

Patent claims: 1. Method of stabilizing low temperature viscosity synthetic lubricating oils containing mixed esters, characterized in that one the lubricating oil with the addition of a small amount of an oil-insoluble salt of a strong organic Base heated to over 100 ° and then filtered. 2. The method according to claim 1, characterized in that that the addition of the strong organic base is not less than 0.1, preferably 0.2 to 2 percent by weight (based on the total mixture). 3. The method according to claim 1 and 2, characterized in that the mixture is heated ^{to 170 to 190 0 for 5 to 120, preferably 10 to 60 minutes.} 4. The method according to claim 1 to 3, characterized in that the strong organic base the general composition NO' Il R '"HN —C —NHR" wherein R ', R "and R'" are hydrocarbon groups or hydrogen. 5. The method according to claim 1 to 4, characterized in that the hydrocarbon groups of the organic base contain no more than 10, preferably no more than 4 carbon atoms. 6. The method according to claim 1 to 5, characterized in that the strong organic base Is guanidine carbonate. Considered publications:
U.S. Patent No. 2,620,301. © 609 617/460 8.56 (609 853 3.57)