Ester for refrigerator oils

Abstract

It is provided an ester for a refrigerator oil and of mixed alcohols and mixed monocarboxylic acids. The mixed alcohols include dipentaerythritol and tripentaerythritol in a mass ratio of 90/10 to 99.7/0.3, and the mixed monocarboxylic acids include n-pentanoic acid and 2-methyl butanoic acid in a mass ratio of 50/50 to 80/20. The ester has a kinematic viscosity of 50 to 150 mm.sup.2/s at 40° C.

Claims

1. An ester for a refrigerator oil and of mixed alcohols and mixed monocarboxylic acids, wherein said mixed alcohols consist of dipentaerythritol and tripentaerythritol in a mass ratio of 90/10 to 99.7/0.3; wherein said mixed monocarboxylic acids consist of n-pentanoic acid and 2-methyl butanoic acid in a mass ratio of 50/50 to 80/20; and wherein said ester has a kinematic viscosity of 50 to 150 mm.sup.2/s at 40° C.

2. A working fluid composition for a refrigerator, said fluid composition comprising said ester for said refrigerator oil of claim 1 and R-32 refrigerant.

Description

EXAMPLES

(1) The present will be described further in detail below.

(2) (Method of Synthesis)

(3) “D-PE” and “T-PE” supplied by KOEI CHEMNICAL Co. LTD., were used as dipentaerythritol and tripentaerythritol. N-pentanoic acid and 2-methyl butanoic acid were synthesized using agents supplied by TOKYO CHEMICAL INDUSTRY CO. LTD.

(4) A thermometer, nitrogen-supplying tube, agitator, Dimroth condenser and oil-water separation tube of a volume of 30 ml were equipped to a four-necked flask of 2 liter. 440 g (1.7 mol) of dipentaerythritol and 23 g (0.06 mol) of tripentaerythritol were charged in the flask. 700 g (6.85 mol) of n-pentanoic acid and 467 g (4.57 mol) of 2-methyl butanoic acid were then added so that the molar ratio of carboxylic acids with respect to hydroxyl group of the charged alcohols was made 1.05. It was finally charged 6.2 g (0.02 mol) or 0.2 mol equivalent of titanium isopropoxide with respect to the hydroxyl groups of the charged alcohols.

(5) The charged reaction solution was heated under nitrogen gas flow at 220° C. until the hydroxyl value of the ester reached 3 or lower. Thereafter, the inside of the reactor was cooled to 200° C. and the pressure was lowered to 80 Torr, so that excessive fatty acids were evaporated until the acid value reached 5 mgKOH/g or lower.

(6) After the reactor was cooled to 85° C., 1.5 equivalent of amount of potassium hydroxide calculated from the acid value was diluted with ion exchange water to produce 10 percent aqueous solution, which was added to the reaction solution, followed by agitation for 1 hour. After the agitation was terminated, it was stood still for 30 minutes so that aqueous layer separated as the lower layer was removed. Then, 20 mass percent of ion exchange water was added to the reaction solution, which was agitated at 85° C. for 10 minutes and stood still for 15 minute to separate the aqueous layer, which was then removed. The operations were repeated until pH of the aqueous layer reached 7 to 8. Thereafter, it was agitated at 100° C. and 30 Torr for 1 hour to remove water. 2 mass percent of active clay was finally added to the reaction solution, which was then stirred under condition of 80° C. and 30 Torr for 1 hour and filtrated to remove the adsorbent, so that the desired ester for the refrigerator oil was obtained.

(7) (Method of Analyzing Composition)

(8) 10 ml of 0.5N KOH ethanol solution was added to the thus obtained ester for the refrigerator oil, which was subjected to decomposition by saponification at 80° C. for 8 hours. Excessive amount of hydrochloric acid was added to the thus obtained sample for the neutralization and 40 ml of hexane and 20 ml of ion exchange water were added, followed by agitation, standing and layer separation.

(9) Hexane was evaporated from hexane layer, to which 2 ml of methanol solution of boron trifluoride was added. The layer was then heated at 60° C. for 30 minutes to perform the methyl esterification and the quantity of mono carboxylic acids was determined by gas chromatography.

(10) Ion exchange water was evaporated at a reduced pressure from aqueous layer, which was then dried by storing in a temperature constant bath at 105° C. for 1 hour. 10 ml of isopropyl alcohol was then used to extract alcohol. Isopropyl alcohol was evaporated and it was performed the trimethylsilylation according to a conventional method. The quantity of the alcohol was determined by gas chromatography.

(11) Color phase: It was measured based on JOCS 2.2.1.4-1996

(12) Acid value: It was measured based on JIS K-0070.

(13) Total acid value: It was measured based on JIS C-2101.

(14) Hydroxyl value: It was measured based on JIS K-0070.

(15) The operations described above were performed and the ratio of the alcohols and carboxylic acids was changed to synthesize esters for refrigerator oils. The thus obtained esters for the refrigerator oils were subjected to analysis of composition. Table 1 summarizes the results of the analysis of the composition, R-value as described above, and color phase, acid value and hydroxyl value of the ester for the refrigerator oil.

(16) TABLE-US-00001 TABLE 1 Mixed alcohols Mixed monocarboxylic Color Total acid Hydroxyl (G C %) Acids (G C %) phase value value diPE triPE nC5 iC5 R (APHA) (mgKOH/g) (mgKOH/g) Ex. 1 95 5 58 42 14 30 0.01 or lower 0.5 Ex. 2 99.7 0.3 64 36 160 30 0.01 or lower 0.4 Ex. 3 91 9 69 31 5 40 0.01 or lower 0.3 Ex. 4 92 8 64 36 6 40 0.01 or lower 0.4 Ex. 5 99 1 78 22 51 30 0.01 or lower 0.3 Ex. 6 93 7 53 47 11 40 0.01 or lower 0.8 Ex. 7 98 2 68 32 20 30 0.01 or lower 0.3 Com. Ex. 1 99.9 0.1 57 43 754 30 0.01 or lower 0.5 Com. Ex. 2 84 16 58 42 4 50 0.01 or lower 0.5 Com. Ex. 3 94 6 28 72 40 50 0.01 or lower 0.9 Com. Ex. 4 95 5 87 13 3 30 0.01 or lower 0.1 (※) diPE: Dipentaerythritol triPE: Tripentaerythritol nC5: n-pentanoic acid iC5: 2-methyl butanoic acid

(17) Each ester for the refrigerator oil was evaluated according to the following methods.

(18) (Kinematic Viscosity)

(19) It was measured based on JIS K-2283.

(20) (Two-Layer Separation Temperature)

(21) The two-layer separation temperature at a low temperature region was measured based on JIS K-2211 and under the condition that the mass ratio of R-32 refrigerant and the ester for the refrigerator oil was 8:2. The thus obtained separation temperatures were evaluated based on the following standard.

(22) ⊚: It is not higher than minus 35° C.

(23) ◯: It is higher than minus 35° C. and not higher than minus 30° C.

(24) Δ: It is higher than minus 30° C. and not higher than minus 20° C.

(25) x: it is higher than minus 20° C.

(26) (Heat Resistance Test: Shield Tube Test)

(27) 2 g of the ester for the refrigerator oil whose water content was adjusted at about 1000 ppm in advance, 3 g of the refrigerant R-32, and each one of metal pieces of iron, copper and aluminum having a length of 10 mm were enclosed and sealed in a thick Pyrex (Registered trade name) tube (total length of 300 mm, outer diameter of 10 mm and inner diameter of 6 mm). This was heated at 200° C. for 10 days and opened to draw the refrigerant. The resultant acid value was measured based on JIS C-2101. The resultant acid value was evaluated based on the following standard.

(28) ⊚: It is not higher than 0.05 mgKOH/g.

(29) ◯: It is higher than 0.05 mgKOH/g and not higher than 0.1 mgKOH/g.

(30) Δ: It is higher than 0.1 mgKOH/g and not higher than 0.15 mgKOH/g.

(31) x: It is higher than 0.15 mgKOH/g.

(32) (Lubrication Test)

(33) Falex Test Pin Wear Amount:

(34) Falex pin wear test was performed based on ASTM D-2670, while R-32 refrigerant was blown into the ester for the refrigerator oil at a rate of 150 ml/min. The temperature of a sample was made 100° C., and running-in operation was performed for 1 minute at a load of 150 pounds, followed by running for 1 hour at a load of 300 pound. The wear amount of the pin after the completion of the operation was measured. The thus obtained wear amount of the pin was evaluated based on the following standard.

(35) ⊚: It is not higher than 8.0 mg.

(36) ◯: It is higher than 8.0 mg and not higher than 10.0 mg.

(37) Δ: It is higher than 10 mg and not higher than 13.0 mg.

(38) x: It is higher than 13.0 mg.

(39) The results of the evaluation were summarized in table 2.

(40) TABLE-US-00002 TABLE 2 Two-layer separation Kinematic temperature Heat resistance test Test of lubrication property viscosity at 40° C. R-32, low Acid value (pin wear (mm.sup.2/s) temperature, (° C.) Evaluation (mgKOH/g) Evaluation amount, mg) Evaluation Ex. 1 74 −37 ⊚ 0.05 ⊚ 7.1 ⊚ Ex. 2 57 −36 ⊚ 0.03 ⊚ 9.3 ◯ Ex. 3 79 −33 ◯ 0.08 ◯ 5.0 ⊚ Ex. 4 79 −33 ◯ 0.03 ⊚ 6.0 ⊚ Ex. 5 52 −33 ◯ 0.05 ⊚ 9.3 ◯ Ex. 6 90 −40 ⊚ 0.08 ◯ 7.0 ⊚ Ex. 7 60 −35 ⊚ 0.04 ⊚ 7.0 ⊚ Com. Ex. 1 59 −38 ⊚ 0.03 ⊚ 14.2 X Com. Ex. 2 105 −35 ⊚ 0.13 Δ 5.0 ⊚ Com. Ex. 3 98 −46 ⊚ 0.04 ⊚ 13.8 X Com. Ex. 4 56 −28 Δ 0.13 Δ 4.0 ⊚

(41) As shown in the examples 1 to 7, according to the present invention, it can be obtained the ester for the refrigerator oil excellent in compatibility with R-32 refrigerant and heat resistant and lubrication properties.

(42) According to the comparative example 1, as the ratio of dipentaerythritol is high, the lubrication property is deteriorated.

(43) According to the comparative example 2, as the ratio of dipentaerythritol is low, the heat resistant property is deteriorated.

(44) According to the comparative example 3, as the ratio of n-pentanoic acid is low, the lubrication property is deteriorated.

(45) According the comparative example 4, as the ratio of n-pentanoic acid is high, the heat resistant property is deteriorated and the two-layer separation temperature is high on the low temperature side.