EP1373443A2

EP1373443A2 - Oxidation-stable hydraulic oil

Info

Publication number: EP1373443A2
Application number: EP02742861A
Authority: EP
Inventors: Frank Bongardt; Ralf Christoph
Original assignee: Cognis Deutschland GmbH and Co KG
Current assignee: Cognis IP Management GmbH
Priority date: 2001-03-29
Filing date: 2002-03-20
Publication date: 2004-01-02
Also published as: WO2002083607A2; US20040147411A1; DE10115829A1; CA2442236A1; WO2002083607A3

Abstract

Oxidation-stable hydraulic oils can be obtained by esterifying polyols with oleic acid and by optionally adding additives, whereby the respective hydraulic oils correspond to the requirements of the thermal oxidation stability test (TOST) in accordance with DIN 51587.

Description

Oxidation stable hydraulic oil

The present application relates to oxidation-stable hydraulic oils which contain certain synthetic esters based on polyols and unsaturated fatty acids and the use of certain additive packages to improve the oxidation stability of hydraulic oils.

Hydraulic systems are used in a large number of technical devices, for example automobiles, trucks, cranes, trains and other means of transport, but also in agricultural devices, ships as well as in industrial companies and in the railway sector. The hydraulic systems generally contain a hydraulic fluid which traditionally contains petrochemical fluids or esters or other oleochemicals as the base fluid. The latter are increasingly preferred due to their biodegradability.

In this context, polyol esters of fatty acids, preferably unsaturated fatty acids, are known from the prior art as suitable base liquids for hydraulic oils. For example, WO 97/39086 discloses esters which are obtained by reacting polyols, including trimethylolpropane, with mixtures of fatty acids, the ratio of short-chain fatty acids to long-chain fatty acids being in the range from 2: 1 to 1:20. The document shows that the esters claimed should have advantageous technical properties, in particular because of their low-temperature compatibility.

In addition to the low-temperature stability, ester systems and hydraulic fluids must also have high oxidation stability, which is particularly important when the hydraulic oil is exposed to high temperatures in the presence of atmospheric oxygen. To achieve this, according to the prior art, antioxidants are added to the hydraulic oils as customary additives. The decisive factor in this case is the so-called modified, "Turbine oxidation stability test", or dryer TOST for short, in accordance with DIN51587, which tests the stability of test oils when aged at 95 ° C in the presence of oxygen. Conventional systems already reach the critical limit of 2.0 mg KOH / g test oil after 170 to about 300 hours. However, since increasingly higher oxidation stability is required, there is a constant need on the part of industry to be able to provide oils which are more stable to oxidation. The attempt to achieve the desired high oxidation stability by adding further antioxidants has so far not been successful. It was therefore the object of the present invention to provide oxidation-stable liquids for use in hydraulic oils which also meet the current requirements with regard to their biodegradability. It has surprisingly been found that selected polyol esters meet the above requirements.

The present application therefore relates to synthetic esters

a) polyols of the general formula (I)

in which R ^{1 represents} a hydrogen atom, a methyl radical or a hydroxyl group, and R ² and R ³ independently of one another represent a methyl radical or a CH2-OH group, with the proviso that at least two hydroxyl groups must be present in the molecule, and

b) unsaturated fatty acids with 16 to 18 carbon atoms

characterized in that the synthetic esters have an iodine number (according to DGF-C-V 11b) from 65 to 100, a saponification number (according to DGf C-V 3) in the range from 160 to 200 and an acid number (according to DGF C-V 2) from a maximum of 3.

The synthetic esters according to the invention are prepared in a manner known per se by reacting the polyols with the unsaturated fatty acids in the presence of suitable catalysts and at an elevated temperature. The reaction products can then be removed from the batch by distillation. Such synthetic esters are particularly preferred which have a kinematic viscosity at 40 ° C. of 40 to 70 mm / sec. and at 100 ° C a kinematic viscosity measured according to DIN 51562 of 5 to 20 mm ² / sec. exhibit. The polyols which are used to prepare the synthetic esters are preferably selected from the group consisting of neopentyl glycol, trimethylolpropane, trimethylolethane and / or pentaerythritol. The use of trimethylolpropane as a starting point for the preparation of the synthetic esters according to the invention is particularly preferred. The fatty acids with 16 to 18 carbon atoms, which together with the polyols according to a) synthetic esters are preferably derived from oleic acid with its different qualities. The esters according to the invention are further characterized in that their acid number measured according to DGF C-V2 at max. 3, preferably ax. 2 mg KOH / g. The iodine number measured according to DGF C-V11B should preferably be in the range from 65 to 100, but in particular in the range from 65 to 90 and very particularly preferably in the range from 70 to 90 mg KOH / g. The saponification numbers measured according to DGF CV should preferably be less than 200 and in particular in the range from 160 to 190 and in particular in the range from 170 to 185 mg KOH / g. The cloud point, measured according to DGF D-Ill 3, is preferably in the range from -40 to -20 ° C. in the esters according to the invention. The water content according to Karl Fischer (DGF C-Ill 13a) is preferably in the range of max. 0.1 and preferably in the range of 0.01 to 0.05. Further characteristic characteristics of the esters according to the invention are the pour point (DIN 3016), which is preferably at most - 30 ° C. The cloud point according to DIN EN 23015 is preferably at most - 20 ° C. The esters according to the invention are not only stable to oxidation but also Stable for several years even at normal storage temperature.

Another object of the present application relates to a process for the preparation of synthetic polyol and complex esters, wherein polyols of the general formula (I) are reacted with so-called oleins at temperatures of> 200 ° C. for at least 3 hours with a nitrogen atmosphere and then in reduced pressure removes the excess fatty acid by distillation. The oleins used in the process according to the invention are technical mixtures of unsaturated and saturated fatty acids which, however, predominantly contain oleic acid. Such oleins are obtained from naturally occurring fats and oils, especially animal oils. Oleins which are obtained by the process of DE 197 36 737 A1 are preferably used for the preparation of the esters according to the invention. Reference is made here in particular to Examples 1, 3, 4, 7, 8 and 9 of DE 197 36737 A1 according to the invention, which are hereby expressly the subject of the disclosure of the present application. According to the invention, such oleins have an iodine number, measured according to DGF CV 11B, in the range from 60 to 130 and a cloud point, measured according to DGF C III, of less than 11 ° C., the oleines furthermore comprising more than 65% by weight of oleic acid and must contain less than 20% by weight of linoleic acid.

The present application further claims a hydraulic oil containing 90 to 99% by weight, preferably 95 to 99% by weight and in particular 97 to 99% by weight of a synthetic ester as described above and 1 to 10% by weight of additives , These additives are the classes known in principle to the person skilled in the art, namely antioxidants, extreme pressure (EP) or anti-wear (AW) additives, corrosion inhibitors, demugators and / or defoamers. Nonferrous metal deactivators may also be present. The additives are in usual quantities, but in total in max. Contain 10% by weight, preferably 1 to 3% by weight, based on the total weight of the hydraulic oil. The EP / AW additives are in amounts of preferably 0.2 to 2.0% by weight, antioxidants in the range of 0.2 to 1.0% by weight, corrosion protection additives in the range of 0.05 to 0.2 % By weight, non-ferrous metal deactivators in the range from 0.05 to 0.5 and antifoam additives defoamers in the range from 0.005 to 0.04% in the hydraulic oils according to the invention. Such hydraulic oils are formulated by mixing the base liquid with the additives, if necessary at elevated temperature.

It has proven to be particularly advantageous to add an additive containing alkylamines, tolyltriazole, alkylphosphate and / or succinic acid semiesters and their derivatives to the hydraulic oils according to the invention. Such additives are preferably contained in a total amount of 0.5 to 2% by weight. The use of an additive package which is commercially available under the trade name Additin RC 9308 has been particularly preferred. This additive contains C12-C14 tertiary alkyl amines, tolyltriazole, tri-n-butyl phosphate and tetrapropylene succinic acid semiesters. The combination of this additive with the synthetic hydraulic oil results in a particularly oxidation-stable end product. Another object of the present application therefore relates to the use of such an additive package to improve the oxidation stability of polyol esters of the above description.

The esters according to the invention and the hydraulic oils formulated therefrom show a surprisingly high stability TOST test. The so-called "dry" TOST test, in which water is no longer present, is used in particular.

Examples

1. Preparation of a TMP Ester According to the Invention:

14.5 kg of trimethylolpropane together with 85.5 kg of an olein, prepared according to the specification from DE 197 36 737 A1, under a nitrogen atmosphere for 4 hours at a temperature of 250

° C warmed and stirred. The pressure was then reduced to less than 20 mbar and the

Excess fatty acid removed.

The TMP ester had the following key figures:

Acid number (DGF C-V 2): 2 mgKOH / g

Saponification number (DGF CV 3): 187 mgKOH / g iodine number (DGF CV 11b): 83 g / 100g kin. Viscosity at 40 ° C (DIN 51562): 42 mm ² / s kin. Viscosity at 1000 ° C (DIN 51562): 9 mm ² / s

2. Test of the application properties of the TMP esters according to the invention.

A hydraulic oil was examined, containing 98% by weight of TMP ester from the 1st and 2% by weight of an additive package, containing C12-14 alkylamines, tolyltriazole, tri-n-butyl phosphate and tetrapropenylsuccinic acid alkyl half-ester (Additin RC 9308 - a commercial product from the company Rhein Chemie).

The above hydraulic oil was subjected to a modified turbine oxidation stability test "TOST" according to DIN 51587 in order to determine the oxidation stability of the hydraulic oil. In a modification of DIN 51587, the test was carried out in the absence of water. The water was replaced with the same amount of test oil. In the test according to DIN 51587, the test oil is aged in the presence of steel and copper wire with the introduction of oxygen at 95 ° C. The end point of aging is either reached at a neutralization number of 2.0 mg KOH / g oil or, if this value has not yet been reached after 1000 h, the value measured after 1000 h is given. In the hydraulic oil according to the invention, the neutralization number was 1.9 after 1000 h. Only after 1414 h was a neutralization number of 2.0 and thus the final state of aging reached.

Claims

claims

1. Synthetic esters from a) polyols of the general formula (I)

b) unsaturated fatty acids with 16 to 18 carbon atoms

2. Synthetic esters according to claim 1, characterized in that the esters have a kinematic viscosity at 40 ° C of 40 to 70 mm ² / s ² and a kinematic viscosity at 100 ° C (measured in each case according to DIN 51562) from 5 to 20 mm ² / s ² have.

3. Synthetic esters according to claims 1 to 2, characterized in that the polyol a) is selected from the group neopentyl glycol, trimethylolpropane, trimethylolethane and / or pentaerythritol.

4. Synthetic esters according to claims 1 to 3, characterized in that component b) is oleic acid.

5. Process for the preparation of synthetic polyolesters, using polyols of general

Formula (I) according to claim 1 with olines at temperatures of> 200 ° C for at least 3 hours under a nitrogen atmosphere to react, and then at reduced pressure

Fatty acid removed by distillation, characterized in that the olein has an iodine number (DGF CV 11b) have in the range from 60 to 130, and a cloud point (DGF D-HI 3) below 11 ° C. and the olines contain more than 65% by weight of oleic acid and less than 20% by weight of linoleic acid.

6. hydraulic oil containing 90 to 99 wt .-% of a synthetic ester according to claim 1 to 5 and s 1 to 10 wt .-% of additives.

7. Hydraulic oil according to claim 6, characterized in that it contains additives selected from the classes of antioxidants, extreme pressure or antiwear additives, corrosion inhibitors, demulsifiers and / or defoamers. 0

8. Hydraulic oil according to claims 6 to 7, characterized in that it contains an additive containing alkylamines, tolyltriazole, alkyl phosphate and / or succinic acid semiesters.

9. Hydraulic oil according to claim 8, characterized in that it contains the additive in amounts of 0.5 to 2.0% by weight.

10. Use of synthetic esters according to claim 1 to 5 as the base liquid in hydraulic oils.

11. Use of an additive package containing alkylamines, tolyltriazole, alkyl phosphate and succinic acid semiesters to improve the oxidation stability of synthetic polyol esters according to claim 1.