RU2794597C2 - Oil for piston compressors - Google Patents

Abstract

FIELD: lubricating oil composition.

SUBSTANCE: oil for a piston compressor containing 2,6-di-tert-butylphenol and tris(2,4-di-tert-butylphenyl) phosphite as an additive to mineral oil and/or synthetic oil used as a base oil is proposed, moreover, naphthenic component in the total amount of base oil is from 17 to 30% in% of C_N by ring analysis according to ASTM D3238, and with a pour point of -25°C or lower.

EFFECT: obtaining oil that can withstand high temperatures and high pressures, forms little sludge and has high stability due to oxidation resistance.

4 cl, 5 tbl, 20 ex

Description

Technical field

The present invention relates to a lubricating oil composition and in particular relates to an oil for reciprocating compressors.

State of the art

A compressor is a machine that compresses air, such as gas, and increases its pressure. These compressors come in three types: piston (reciprocating type), rotary and turbocharger. However, the lubrication points differ depending on the type and, accordingly, the required characteristics of the compressor oil differ.

In a reciprocating compressor, the reciprocating piston compresses the gas in the cylinder, so the compressor oil used for the reciprocating piston is in direct contact with the compressed gas, and therefore is subjected to the high temperature/high pressure of the compressed gas and tends to char easily. If the carbon thus formed sticks to the peripheral part of the valve, there is a risk of valve failure or a risk of fire or explosion due to the accumulation of heat by the adhering coal.

Therefore, a reciprocating compressor oil must have an extremely important characteristic - the ability to not generate coal. In addition, in order to withstand the above high temperature and high pressure, the reciprocating compressor oil must have high temperature/oxidation stability and reduce sludge formation. In addition, when used in cold regions or outdoors, the oil must remain stable even at low temperatures, so the pour point must also be low.

Generally, to make such a compressor oil, phosphorus-based antioxidants, amine-based antioxidants, phenol-based antioxidants, and the like are used as additives, as in JPH11-189781.

The present invention provides a reciprocating compressor oil that can withstand high temperature and high pressure, generate little sludge, and can be used for a long time while maintaining stability because it has been given sufficient oxidation resistance by the choice of base oil and the addition of additives.

The essence of the invention

The inventors have conducted various studies on additives having effective antioxidant properties in compressor oil. As a result, it has been found that 2,6-di-tert-butylphenol and tris(2,4-di-tert-butylphenyl) phosphite are used in combination with very good results. The present invention has been made based on these results.

In other words, the present invention relates to a reciprocating compressor oil in which a combination of 2,6-di-t-butylphenol and tris(2,4-di-t-butylphenyl) phosphite is added to the base oil.

2,6-di-tert-butylphenol is effective as an additive when it is contained in an amount of from 0.5 to 6.0% wt. based on the total amount of compressor oil, and tris (2,4-di-tert-butylphenyl) phosphite is effective when it is contained in an amount of from 0.3 to 2.0% wt. based on the total amount of compressor oil.

In addition, the use of an alkaline earth metal salt of alkylsalicylic acid in combination as an additive is even more effective. The amount of this salt used is preferably from 0.05 to 2.0% wt. based on the total amount of compressor oil.

The compressor oil base oil uses mineral oil and/or synthetic oil, but it is preferred that the base oil contains a relatively high amount of naphthene. The content of naphthene in total base oil is from about 17 to 30%, preferably from 18 to 28%, more preferably from 20 to 25% in % C _N ring analysis according to ASTM D3238.

Detailed Description of the Invention

According to the present invention, even when the oil is used under high temperature and high pressure conditions, it retains excellent antioxidant properties, has low sludge and deposit formation, and can be used stably for a long period of time.

As the base oil, the reciprocating compressor oil of the present invention uses mineral oil or synthetic oil. In the classification of API base oils, base oils of Group 1, Group 2, Group 3, Group 4, etc. are used, but these base oils can be appropriately mixed and used.

As this base oil, it is preferable to use an oil containing a relatively large amount of naphthene, and the content of naphthene in the total base oil is preferably from about 17% to 30% in % C _N ring analysis according to ASTM D3238. In addition, the content of naphthene is preferably 18 to 28%, more preferably 20 to 25%.

As described in the patent literature, the naphthenic base oil has a high solubility in additives and sludges compared to the base oil containing a large amount of paraffin, therefore it is especially useful when used for reciprocating compressor oil, since deposits (charcoal deposits) remain soft even in the carbonized state .

In cases where the proportion of the naphthenic component is small, carbonization tends to take place, and the formed carbon becomes hard, precipitates and sticks, which may lead to compressor failure and the like. On the other hand, since the naphthenic component is highly volatile, if it is in excess, the base oil evaporates during use, and this leads to an undesirable increase in the kinematic viscosity of the lubricating oil. Thus, the content of the naphthenic component in the total amount of the base oil should be in a suitable range, and it is preferable to set the above ratio.

As described above, a base oil is used with the addition of 2,6-di-tert-butylphenol. This 2,6-di-tert-butylphenol is a phenolic substance having the structure shown below.

Chemical formula 1:

This 2,6-di-tert-butylphenol is widely known as an antioxidant and has a similar structure to the commonly used BHT (butylhydroxytoluene) (2,6-di-tert-butyl-4-methylphenol) described below. It lacks a methyl group at the 4th position of the BHT benzene ring.

Chemical formula 2:

In addition, it has a similar structure to 4,4'-methylenebis (2,6-di-tert-butylphenol), which has the following formula, is widely known as an antioxidant and has wide applications.

Chemical formula 3:

As mentioned above, 2,6-di-tert-butylphenol is known as a phenolic substance having a structure similar to BHT and 4,4'-methylenebis(2,6-di-tert-butylphenol) [2, 2', 6,6 '-tetra-tert-butyl-4,4'-methylenediphenol]. However, there is a problem of sublimation, but in the present invention, the authors found that this substance has excellent antioxidant characteristics.

In addition, 4,4'-methylene-bis(2,6-di-tert-butylphenol) degrades slowly and is highly concentrated, and its long-term toxicity to humans or higher animals has not been determined, so it is sometimes included in the list of "Chemicals to Monitor". substances." Therefore, for these reasons, it is desirable to avoid its use.

2,6-di-tert-butylphenol exists in a dimeric state due to the fact that the 4th position of the benzene ring has a hydrogen atom as described above and is difficult to sublimate. In addition, the joint action (synergistic effect) of the additives made it possible to detect the manifestation of the antioxidant function of the dimer.

Such 2,6-di-tert-butylphenol is used in an amount of 0.5 to 6.0% by weight, preferably 1.0 to 5.0% by weight, based on the total amount of compressor oil.

This 2,6-di-tert-butylphenol is used as an additive in combination with tris(2,4-di-tert-butylphenyl)phosphite, which is a phosphoric acid ester antioxidant.

Chemical formula 4:

When used in combination with a phosphoric acid ester antioxidant, a compressor oil having stable high temperature and high pressure resistance for a long period of time can be obtained, further improving the antioxidant performance and reducing sludge formation.

Tris (2,4-di-tert-butylphenyl) phosphite is also used in an amount of 0.3 to 2.0% wt., preferably in the range of 0.5 to 1.0% wt. based on the total amount of compressor oil.

Even more effective is the use of an alkaline earth metal salt of alkylsalicylic acid as an additive in combination with this compressor oil. Alkaline earth metals include calcium, magnesium, and the like, but calcium salicylate is commonly used.

The amount of this salt used is preferably 0.05 to 2.0% by weight, preferably 0.075 to 1.5% by weight. and, more preferably, from 0.075 to 1.0% wt. based on the total amount of compressor oil.

If necessary, the compressor oil may contain known additives, for example, extreme pressure agents, anticorrosive agents, demulsifiers, copper deactivators, antiwear agents, dispersants, friction modifiers, corrosion inhibitors, pour point depressants, antifoam agents, and various other additives. These additives can be added singly or in combination. In this case, an additive package that does not contain antioxidant or detergent dispersants can be used.

The pour point (pour point measured by the method described in JIS K 2269) of the reciprocating compressor oil of the present invention is preferably -30°C or lower, more preferably -35°C or lower. A low pour point indicates that the lubricating oil composition has excellent low temperature characteristics.

Examples

preliminary experiment

First, a preliminary experiment on the selection of an antioxidant was carried out. In the preliminary experiment, the following materials were prepared.

- Base oil 1: Fischer-Tropsch base oil obtained by gas-to-liquid conversion (properties, etc.: kinematic viscosity at 40°C; 17.1 mm ² /s, kinematic viscosity at 100 °C; 4.0 mm ² /s, Viscosity Index, 135, density at 15°C, 0.814 g/cm ³ , % C _A ring analysis according to ASTM D 3238, 0%, % C _N ring analysis according to ASTM D 3238, 8%, and % C _P ring analysis according to ASTM D 3238, 92%)

- Base oil 2: Group I refined mineral oil (properties, etc.: kinematic viscosity at 40°C; 25.1 mm ² /s, kinematic viscosity at 100°C; 4.7 mm ² /s , Viscosity index, 107, density at 15°C, 0.863 g/cm ³ , % C _A ring analysis according to ASTM D 3238, 3% C _N ring analysis according to ASTM D 3238 method, 28% and % C _P ring analysis according to ASTM D 3238, 69%)

- Base oil 3: Group I refined mineral oil (properties, etc.: kinematic viscosity at 40°C; 53.2 mm ² /s, kinematic viscosity at 100°C; 7.6 mm ² /s , Viscosity index, 106, Density at 15°C, 0.875 g/cm ³ , % C _A of ring analysis according to ASTM D 3238, 4%, C _N of ring analysis according to ASTM D 3238, 27% and % C _P of ring analysis according to ASTM D 3238, 69%)

- Base oil 4: Naphthenic base oil (properties, etc.; kinematic viscosity at 40°C; 139.1 mm ² /s, kinematic viscosity at 100°C; 10.8 mm ² /s, Viscosity index; 35 , density at 15°C, 0.918 g/ ^cm3 , % C _{A of} ASTM D 3238 ring analysis, 11%, % C _N of ASTM D 3238 ring analysis, 39% and % C _P of ASTM D ring analysis 3238; 50%)

- Additive 1:2, 6-di-tert-butylphenol

- Additive 2: tris (2,4-di-tert-butylphenyl) phosphite

- Additive 3: calcium salicylate.

- Additive 4: 4,4'-methylenebis-(2,6-di-tert-butylphenol)

- Additive 5: BHT (butylhydroxytoluene) (2,6-di-tert-butyl-4-methylphenol)

- Additive 6: Benzenepropanoic acid, 3,5-bis(1,1-dimethylethyl)-4-hydroxy-C7-C9 branched alkyl ether

- Additive 7: An additive package for compressor oil containing ZnDTP, an anti-corrosion agent, a demulsifier and an antifoam agent.

Then, the following Experimental Examples and Control Experimental Examples were prepared.

Experimental Example 1

1.000% wt. additives 1, 0.500% wt. additives 2 and 0.075% wt. additives 3 were added to the mixed base oil obtained by mixing 24.000% wt. base oil 1, 17.000% wt. base oil 2, 8.410% wt. base oil 3 and 48.330% wt. base oil 4. In addition, to the above mixture was added 0.685% wt. additives 7 and mixed well to obtain the compressor oil of Invention Example 1.

Control Experimental Examples 1 to 3

Compressor oils of Reference Examples 1-3 were obtained by the procedure described in Experimental Example 1 above, except for the use of the compositions shown in Table 1.

Testing the Sample Obtained in the Preliminary Experimental Example

To determine the effectiveness of the above Experimental Example and Control Experimental Examples, the following tests were carried out.

Oxidation Stability Test (Dry-TOST):

The test was carried out at 120°C for 168 hours in accordance with the method of testing for oxidation stability (Dry-TOST method) ASTM D7873.

After this test, a test was carried out at a temperature of 150°C under a pressure of 620 kPa before heating in accordance with JIS K 2514-3 for the rotary vessel oxidation resistance test (RPVOT), and the time from maximum pressure to drop to 175 kPa was measured. (RPVOT value: min). It can be said that the lubricating oil composition has excellent oxidation resistance because the time has been longer.

Further, based on the RPVOT value (min) after the Dry-TOST test, the residual ratio of the RPVOT value (%) was calculated by the following formula.

[Residual ratio of RPVOT value] = [RPVOT value after test/initial RPVOT value] × 100

The following criteria were used to evaluate oxidation resistance.

Residual ratio of RPVOT value is 85% or more

Fine

Residual ratio of RPVOT value less than 85% Badly

The results of preliminary experiments are presented in Table 1.

Table 1

Invention example 1 Test Case 1 Test Case 2 Test Case 3 Base oil 1 24,000 24,000 24,000 24,000 Base oil 2 17,000 17,000 17,000 17,000 Base oil 3 8.410 8.410 8.410 8.410 Base oil 4 48.330 48.330 48.330 48.330 Additive 1 1,000 - - - Additive 2 0.500 0.500 0.500 0.500 Additive 3 0.075 0.075 0.075 0.075 Additive 4 - 1,000 - - Additive 5 - - 1,000 - Additive 6 - - - 1,000 Additive 7 0.685 0.685 0.685 0.685 Total 100 100 100 100 %Cp 71 71 71 71 %Cn 23 23 23 23 % Ca 6 6 6 6 RPVOT new oil
(min) 116 92 106 86 RPVOT after Dry TOST
(min) 120 56 44 28 Residual ratio RPVOT

103

61

42

33

From the data shown in Table 1, it follows that when using 1% wt. 2,6-di-tert-butylphenol (Additive 1) from Experimental Example 1, the RPVOT value after the Dry-TOST test did not decrease from the RPVOT value of fresh oil, the residual RPVOT ratio is good, and the oxidation stability is excellent.

On the other hand, in Control Experimental Example 1, when the same amount of 4,4'-methylenebis(2,6-di-tert-butylphenol) (Additive 4) was used instead of Additive 1 from Experimental Example 1, the RPVOT residual ratio value was low and there were no good results.

In Control Experimental Example 2, when the same amount of BHT (Additive 5) was used instead of Additive 1 from Experimental Example 1, the value of the residual RPVOT ratio was even lower and no good results were obtained.

In Control Experimental Example 3, when the same amount of benzenepropanoic acid, 3,5-bis(1,1-dimethylethyl)-4-hydroxy-C7-C9 branched alkyl ether was used instead of Additive 1 from Experimental Example 1 (Additive 6), the value of the residual RPVOT ratio was even lower, and there were no good results.

In Control Experimental Example 2, sublimation of BHT (additive 5) after the Dry-TOST test showed adhesion to the capacitor.

On the other hand, in Experimental Example 1, no such adhesion was observed, and no problems were confirmed due to sublimation of 2,6-di-tert-butylphenol (Additive 1).

Thus, in compressor oil, 2,6-di-tert-butylphenol has been found to be a preferred antioxidant that does not cause problems with sublimation and oxidation resistance.

This is because 2,6-di-tert-butylphenol exists in a state of dimer formation, since the 4th position of the benzene ring is a hydrogen atom, as described above, and it is difficult to sublimate, and the dimer is 3, 3' , 5, 5'-tetra-tert-butyl-4,4'-diphenoquinone of the following formula. Thus, the manifestation of the antioxidant function of 3,3',5,5'-tetra-tert-butyl-4,4'-diphenoquinone can be detected by the combined action (synergistic effect) of additives.

Chemical formula 5:

Invention Examples and Comparative Examples

Based on the results of the above preliminary experiment, the following materials were prepared for the preparation of Examples and Comparative Examples. In addition, the compressor oil of the present invention will be specifically described below with reference to Examples and Comparative Examples, but the present invention is not limited to them in any way.

- Base oil 1: same as base oil 1 from the preliminary experiment.

- Base oil 2: same as base oil 2 from the preliminary experiment.

- Base oil 4: same as base oil 4 from the preliminary experiment.

- Base oil 5: Fischer-Tropsch base oil obtained by gas-to-liquid conversion (properties, etc.: kinematic viscosity at 40°C; 44.9 mm ² /s, kinematic viscosity at 100°C; 7.7 mm ² /s, Viscosity Index, 142, density at 15°C, 0.828 g/cm ³ ,% C _A of ASTM D 3238 ring analysis, 0%, % C _N of ASTM D 3238 ring analysis, 8% and % C _P of ring analysis according to ASTM D 3238, 92%)

- Additive 1: the same as Additive 1 in the preliminary experiment. (2,6-di-tert-butylphenol)

- Additive 2: same as Additive 2 in the preliminary experiment. (tris(2,4-di-tert-butylphenyl)phosphite)

- Additive 3: same as Additive 3 in the preliminary experiment. (Calcium salicylate)

- Additive 4: the same as Additive 4 in the preliminary experiment. (4,4'-methylenebis(2,6-di-tert-butylphenol))

- Additive 7: the same as Additive 7 in the preliminary experiment. (Compressor oil additive package containing ZnDTP, anti-corrosion agent, demulsifier and defoamer)

The following Inventive Examples and Comparative Examples were prepared.

Invention example 1

1.000% wt. Additives 1 and 0.500% wt. Additives 2 were added to a mixed base oil obtained by mixing 32.485% wt. base oil 1, 17.000% wt. base oil 5 and 48.330% wt. base oil 4. In addition, to the above mixture was added 0.685% wt. Additives 7 and mixed well, resulting in the compressor oil of Invention Example 1.

Invention Examples 2-6

Compressor oils for Invention Examples 2-6 were prepared in the same manner as in Invention Example 1, except for using the compositions shown in Table 2 and Table 3.

Comparative Examples 1-10

Compressor oils for Comparative Examples 1-10 were prepared in the same manner as in Invention Example 1, except for using the compositions shown in Table 4 and Table 5.

Tests

To determine the characteristics of the samples obtained in the Inventive Examples and Comparative Examples, the following tests were carried out.

An ISOT (oxidation resistance test) test was performed in which the test equipment and test method were in accordance with JIS K 2514, the catalyst was immersed in the sample, the sample was stirred with a glass stirrer for 72 hours at 150°C, and oxidized. The acid number after the ISOT test was determined by potentiometric titration. The following evaluation criteria were used.

0.6 mg KOH/g or less

Fine

More than 0.6 mg KOH/g Badly

After the aforementioned ISOT test, the sediment formed in the compressor oil to be tested was filtered using the quantitative method and equipment (filter pore size: 0.8 µm) described in JIS B 9931 (Method for measuring hydraulic oil contamination by mass method). Then the filtered sludge was washed with n-hexane and its amount was determined. The following evaluation criteria were used.

0 mg/100 ml to less than 10 mg/100 ml

Perfect

10 mg/100 ml or more to 70 mg/100 ml or less Fine

More than 70 mg/100 ml Badly

The pour point was measured in accordance with JIS K 2269.

A panel coking test was performed according to the method described in U.S. Federal District Engineering Mutual Statement 791-3462, in which a test oil at a set temperature of 90°C was sprayed with a rotating sprayer onto an aluminum panel heated and maintained at a set temperature of 270°C for 12 hours at intervals of 1 s rotation time / 14 stop time With. This test was conducted to evaluate the deposit inhibiting performance of a test oil, namely cleanliness, by increasing panel weight after testing compared to pre-test weight.

The test results are represented by the weight increase (mg) of the aluminum panel, and the evaluation criteria showing purity at high temperatures were as follows.

0 mg to 20.0 mg

Perfect

More than 20.0 mg to 100.0 mg or less Fine

Over 100.0 mg Badly

The test results are presented in Tables 2-5. It should be noted that in each of the tables, for test results that are not described, tests have been excluded from the results of other tests.

после испытания на устойчивость к окислению (ISOT), при этом оно имело низкую температуру застывания, т.е. -35°C, и демонстрировало хороший результат панельного теста коксуемости (ISOT) и способность выдерживать высокую температуру и высокое давление.As follows from Table 2, when in the Example of the invention 1 used 1% wt. 2,6-di-tert-butylphenol (Additive 1) and 0.5% wt. tris (2,4-di-tert-butylphenyl) phosphite (Additive 2) good results were obtained, i.e. the reciprocating compressor oil showed a slight increase in acid number and a good amount of sludge

after the oxidation stability test (ISOT), while it had a low pour point, i.e. -35°C, and showed a good result in the panel coking test (ISOT) and the ability to withstand high temperature and high pressure.

были получены как для кислотного числа, так и для количества осадка после ISOT. Таким образом, были получены положительные результаты.In Invention Example 2, the amount of Additive 1 and Additive 2 used was approximately doubled compared to Invention Example 1. As a result, good results

were obtained for both the acid number and the amount of sediment after ISOT. Thus, positive results were obtained.

In Invention Example 3, the amount of Additive 1 used was changed to 5.0 wt%, i.e., was 5 times more than in Invention Example 1, and the amount of base oil 1 was reduced accordingly. As a result, even more suitable results were obtained compared to Invention Example 1.

, и характеристики были дополнительно улучшены.In the example of the invention 4, shown in Table 3, to the Example of the invention 1 was added 0.075% wt. calcium salicylate (Additive 3). As a result, we got excellent results in terms of sludge after ISOT.

, and performance has been further improved.

In Invention Example 5, the amount of calcium salicylate was increased to 0.5% wt. compared to Example 4, and even better results were obtained in the panel coking test.

In Invention Example 6, the amount of Ca salicylate was further increased to 1.0% wt. compared to Example 4. As a result, a compressor oil was obtained that showed overall better results.

On the other hand, in the comparative examples shown in Table 4, Additive 1 of Invention Example 1 was used, and Additive 2 was not used. The acid number after ISOT was good, but the amount of sediment was very high; thus, good results were not obtained. In Comparative Example 2, the amount of Additive 1 used was increased to 3.0% wt. compared to Comparative Example 1, but both the acid number and the amount of sediment after ISOT were low, which is undesirable for a reciprocating compressor oil.

In Comparative Example 3, Additive 2 of Invention Example 1 was used, and Additive 1 was not used. The acid number after ISOT was also low and the amount of sediment was also very large, which is not a good result. In Comparative Example 4, the amount of additive 2 used in Comparative Example 3 was increased to 3.0% wt. The acid number after ISOT has improved, but the amount of sediment is still unsatisfactory, which is undesirable.

результат, но результат по кислотному числу и количеству осадка после ISOT был плохим

, что нежелательно.In Comparative Example 5, instead of Additive 1, 1.0% wt. Additives 4, phenolic antioxidant. As a result, the panel test for coking showed good

result, but acid value and sedimentation result after ISOT was poor

, which is undesirable.

), но кислотное число было низким

; таким образом, хороших результатов не было получено.In Comparative Example 6, 1.0 wt% was added to the composition of Comparative Example 5. Additives 2 and 0.075% wt. Additives 3. As a result, the amount of sediment decreased, and the result for this indicator was good (

), but the acid number was low

; thus, good results were not obtained.

. Однако кислотное число после ISOT было низким, а численное значение количества осадка было чрезвычайно низким. Таким образом, этот образец не является предпочтительным в качестве компрессорного масла.In Comparative Example 7, the amount of base oil 4 and base oil 1 from Example 4 was high and amounted to 90.0% wt. and 7.74 wt.%, respectively (both are given on a total basis). The naphthenes content was high and the panel coking test showed excellent results

. However, the acid number after ISOT was low and the numerical value of the amount of sediment was extremely low. Thus, this sample is not preferred as a compressor oil.

. Однако кислотное число после ISOT все еще было низким, и численное значение количества осадка также было чрезвычайно низким. Таким образом, данный состав не привел к получению предпочтительного компрессорного масла.In Comparative Example 8, the amount of base oil 4 and base oil 1 from Comparative Example 7 was 75.0% wt. and 22.74% wt. The naphthenes content was high and the panel coking test showed excellent results

. However, the acid number after ISOT was still low, and the numerical value of the amount of sediment was also extremely low. Thus, this formulation did not result in a preferred compressor oil.

In Comparative Example 9, the amount of base oil 4 from Comparative Example 8 was reduced to 25.0% by weight, and the amount of base oil 5 was increased to 50.0% by weight. The content of naphthenes was low and the panel test for coking showed extremely poor results. Thus, this sample is not preferred as a compressor oil.

In Comparative Example 10, base oil 2 was used instead of base oil 1 and base oil 5 from Example 4, and the amount used was increased to 54.41% wt. The naphthenes content was high, the acid number and sludge count after ISOT and the panel coking test were excellent, but the pour point increased, which led to problems using the oil at low temperature.

It should be noted that the compressor oil from Experimental Example 1 obtained in the above preliminary test can be used in the same manner as in the above Examples.

table 2

Example 1 Example 2 Example 3 Base oil 1 32.485 32.338 28.485 Base oil 5 17,000 16.667 17,000 Base oil 2 - - - Base oil 4 48.330 47.382 48.330 Additive 1 1,000 1.961 5,000 Additive 2 0.500 0.980 0.500 Additive 3 - - - Additive 4 - - - Additive 7 0.685 0.672 0.685 Total 100 100 100 %Cp 71 71 70 %Cn 23 23 24 % Ca 6 6 6 Pour point (°C) -35.0 -35.0 -35.0 Acid number of fresh oil 0.29 0.28 0.36 Acid number after ISOT

0.52

0.35

0.48

Amount of sediment after ISOT

Panel coking test (mg) 54.8

34.7

Table 3

Example 4 Example 5 Example 6 Base oil 1 32.410 31.985 31.485 Base oil 5 17,000 17,000 17,000 Base oil 2 - - - Base oil 4 48.330 48.330 48.330 Additive 1 1,000 1,000 1,000 Additive 2 0.500 0.500 0.500 Additive 3 0.075 0.500 1,000 Additive 4 - - - Additive 7 0.685 0.685 0.685 Total 100 100 100 %Cp 71 71 71 %Cn 23 23 23 % Ca 6 6 6 Pour point (°C) -35.0 -35.0 -35.0 Acid number of fresh oil 0.32 0.47 0.54 Acid number after ISOT

0.53

0.38

0.44

Amount of sediment after ISOT 9.6

2.8

2.0

Panel coking test (mg) 59.5

16.4

1.9

Table 4

Comp. Example 1 Comp. Example 2 Comp. Example 3 Comp. Example 4 Base oil 1 32.985 30.985 32.985 31.985 Base oil 5 17,000 17,000 17,000 16,000 Base oil 2 - - - - Base oil 4 48.330 48.330 48.330 48.330 Additive 1 1,000 3,000 - - Additive 2 - - 0.500 3,000 Additive 3 - - - - Additive 4 - - - - Additive 7 0.685 0.685 0.685 0.685 Total 100 100 100 100 %Cp 71 71 71 71 %Cn 23 23 23 23 % Ca 6 6 6 6 Pour point (°C) -35.0 -35.0 -35.0 -35.0 Acid number of fresh oil 0.32 0.33 0.36 0.38 Acid number after ISOT

0.48

0.65

0.78

0.40

Amount of sediment after ISOT 209.6

242

611.2

174.8

Panel coking test (mg) - - - -

Table 5

Comp.
Etc. 5 Comp.
Etc. 6 Comp.
Pr 7 Comp.
Etc. 8 Comp.
Etc. 9 Comp.
Etc. 10 Base oil 1 32.985 32.985 7.74 22.74 22.74 - Base oil 5 17,000 17,000 - - 50,000 - Base oil 2 - - - - - 54.410 Base oil 4 48.330 48.330 90,000 75,000 25,000 43.330 Additive 1 - - 1,000 1,000 1,000 1,000 Additive 2 - 1,000 0.500 0.500 0.500 0.500 Additive 3 - 0.075 0.075 0.075 0.075 0.075 Additive 4 1,000 1,000 - - - - Additive 7 0.685 0.685 0.685 0.685 0.685 0.685 Total 100 100 100 100 100 100 %Cp 71 71 53 60 81 60 %Cn 23 23 36 31 16 33 % Ca 6 6 eleven 9 3 7 Pour point (°C) -35.0 -35.0 - - - -22.5 Acid number of fresh oil 0.31 0.30 0.35 0.35 - 0.41 Acid number after ISOT

1.09

1.22

2.35

1.60

- 0.34

Amount of sediment after ISOT 297.0

1593.6

916.0

- 4.2

Panel coking test (mg) 51.2

- 9.0

7.1

236.8

2.4

Claims (4)

1. Oil for reciprocating compressor containing 2,6-di-tert-butylphenol and tris(2,4-di-tert-butylphenyl)phosphite as an additive to mineral oil and/or synthetic oil used as base oil, and the naphthenic component in the total base oil is 17 to 30% in % C _N ring analysis according to ASTM D3238, and having a pour point of -25 °C or lower. 2. Oil for a reciprocating compressor according to claim 1, characterized in that the content of the 2,6-di-tert-butylphenol additive is from 0.5 to 6.0% wt., and the content of the tris additive (2,4-di- tert-butylphenyl) phosphite is from 0.3 to 2.0% wt. based on the total amount of compressor oil. 3. Oil for a piston compressor according to claim 1 or 2, characterized in that the compressor oil additionally contains as an additive 0.05% wt. or more and 2.0% wt. or less salt, alkaline earth metal salicylate, based on the total amount of compressor oil. 4. Reciprocating compressor oil according to claim 3, characterized in that the salt, alkaline earth metal salicylate, is Ca salicylate.