JP2015140352A - Ester for refrigeration oil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ester which can be used for a machine using R32 coolant, having good lubricity, and higher low temperature stability and heat resistance than before.SOLUTION: Provided is an ester for a refrigeration oil comprising an ester between a mixed alcohol containing pentaerythritol and tripentaerythritol, and a mixed monocarboxylic acid containing 2-methylpropanoic acid and 3,5,5-trimethylhexanoic acid. The ester for refrigeration oil satisfies specific conditions (A), (B), and (C).

Description

  The present invention relates to a lubricating oil for refrigeration oil used in refrigeration equipment using an R-32 refrigerant, and more particularly to a carboxylic acid ester used in the lubricating oil for refrigeration oil.

  Due to the problem of ozone layer destruction, the transition from chlorine-containing chlorofluorocarbon refrigerant (chlorine-containing chlorofluorocarbon refrigerant), which has been used in air-conditioning equipment such as refrigerators and air conditioners, to chlorine-free chlorofluorocarbon refrigerant (alternative chlorofluorocarbon refrigerant) Has been. Due to changes in refrigerants, lubricating oils using synthetic hydrocarbon oils such as mineral oil and alkylbenzene, which have been used as refrigeration oils for chlorine-containing CFC refrigerants, have low compatibility with alternative CFC refrigerants. It has become difficult to fully demonstrate the performance as machine oil.

  For this reason, in order to solve the above-mentioned problems, studies have been made on compounds that exhibit good compatibility with alternative chlorofluorocarbon refrigerants. As a result, polyol ester compounds, polyalkylene glycol compounds and the like have been found as refrigerating machine oils and have been used in place of refrigerating machine oils using conventional mineral oils and synthetic hydrocarbon oils. Among them, the polyol ester is an ester of a neopentyl polyol such as neopentyl glycol, trimethylolpropane, pentaerythritol, and dipentaerythritol and an aliphatic carboxylic acid, and not only has excellent compatibility with an alternative chlorofluorocarbon refrigerant, Widely used because of its electrical insulation and thermal stability suitable for use as refrigerating machine oil.

  In recent years, alternative chlorofluorocarbon refrigerants have a low ozone depletion coefficient, but have a high global warming potential. As for refrigerants used in household refrigerators, there is a shift from R-134a refrigerant having a high global warming potential to hydrocarbon refrigerants such as R-600a refrigerant having a low global warming potential. Since the R-410A refrigerant mainly used as a refrigerant for room air conditioners also has a high global warming potential, vigorous studies have been made on refrigerants as alternatives.

  There are various candidates as alternative refrigerants for the R-410A refrigerant. Among them, the R-32 refrigerant is considered to be promising, and the development of an ester for refrigerating machine oil that is compatible with the R-32 refrigerant is being promoted. In Patent Document 1, as such an ester, an ester using butyric acid or isobutyric acid which is an aliphatic monocarboxylic acid having 4 carbon atoms and a fatty acid having 7 to 9 carbon atoms is proposed. Patent Document 2 discloses pentaerythritol, isobutyric acid, and 3,5,5-trimethylhexanoic acid ester.

WO2012 / 026214 WO2012 / 026303

  R-32 refrigerant is known to exhibit cooling performance superior to R-410A refrigerant due to its temperature characteristics. However, in order to draw out the excellent performance, it is necessary to operate the compressor efficiently at a higher temperature and higher pressure than the R-410A refrigerant. Therefore, the refrigerating machine ester used is required to have higher heat resistance than before.

  Also, in recent years, from the viewpoint of improving energy saving, it has become common to operate equipment flexibly according to the situation efficiently by inverter control, and various parts of refrigeration equipment such as compressors, aggregators, expansion valves, evaporators, etc. The temperature at the time of operation in is from a low temperature to a high temperature in a wider range than before. Since the lubricating oil for refrigerating machine oil circulates in the refrigerating apparatus together with the refrigerant, the lubricating oil for refrigerating machine oil used for equipment using the R-32 refrigerant is required to have higher low temperature stability and heat resistance than before.

  In particular, for low-temperature stability, there is a demand for the ability to remain liquid for a long period of time without causing crystals to precipitate and solidify even when the temperature fluctuates at low temperatures. If precipitation or solidification of refrigeration oil ester crystals occurs at locations where the temperature is low during operation, such as expansion valves and evaporators, not only will the energy efficiency of the equipment be reduced, but the equipment may also be shut down. is there.

  An object of the present invention is to provide an ester for refrigerating machine oil that can be used in equipment using an R-32 refrigerant, and has a higher low-temperature stability and heat resistance than before.

  Therefore, the present inventor has found that an ester having the following characteristics is effective as an ester for refrigerating machine oil to overcome the problem of lubricating oil for refrigerating machine oil for equipment using the R-32 refrigerant as described above. I found it.

That is, the present invention is an ester for refrigerator oil comprising an ester of a mixed alcohol containing pentaerythritol and tripentaerythritol and a mixed monocarboxylic acid containing 2-methylpropanoic acid and 3,5,5-trimethylhexanoic acid. The following (A), (B) and (C) are satisfied.

(A) The mass ratio of 2-methylpropanoic acid in the mixed monocarboxylic acid is 20% by mass to 55% by mass, and the mass ratio of 3,5,5-trimethylhexanoic acid is 45% by mass to 80% by mass. is there.
(B) The mass ratio of tripentaerythritol in the mixed alcohol is 5% by mass or less.
(C) The mass ratio of tripentaerythritol in the mixed alcohol is 0.02 times or more of the mass ratio of pentaerythritol tetra 2-methylpentanoic acid ester in the ester of pentaerythritol and the mixed monocarboxylic acid.

  ADVANTAGE OF THE INVENTION According to this invention, it is the ester for refrigerator oil which can be used for the apparatus which uses R-32 refrigerant | coolant, Comprising: The ester for refrigerator oil which has low-temperature stability and heat resistance higher than before can be provided.

It is a chart which shows the analysis result by the gas chromatography of ester.

  The refrigerator oil ester used in the present invention is an ester of a mixed alcohol containing pentaerythritol and tripentaerythritol and a mixed monocarboxylic acid containing 2-methylpropanoic acid and 3,5,5-trimethylhexanoic acid.

Hereinafter, the conditions (A), (B) and (C) will be sequentially described.
(Condition A)
From the viewpoint of solubility in R-32 refrigerant and long-term low-temperature stability, the mass ratio of 2-methylpropanoic acid in the mixed monocarboxylic acid is 20% to 55% by mass, and 3,5,5- The mass ratio of trimethylhexanoic acid is 45% by mass to 80% by mass. However, this mass ratio is a numerical value when the total amount of the mixed monocarboxylic acid is 100% by mass. Moreover, the mass ratio of each monocarboxylic acid which comprises mixed monocarboxylic acid is based on the preparation amount.

  If the mass ratio of 2-methylpropanoic acid is 20% by mass or more, an ester highly compatible with the R-32 refrigerant can be obtained. From this viewpoint, the mass ratio of 2-methylpropanoic acid is more preferably 25% by mass or more. If the mass ratio of 2-methylpropanoic acid is 55% by mass or less, an ester having excellent low-temperature stability over a long period of time can be obtained. If this exceeds 55% by mass, the content of pentaerythritol tetra-2-methylpropanoate will increase, and if exposed to low temperature conditions over a long period of time, crystals may precipitate or solidify. From this viewpoint, the mass ratio of 2-methylpropanoic acid is more preferably 50% by mass or less.

(Condition B)
It is necessary that the mass ratio of tripentaerythritol in the mixed alcohol is 5% by mass or less. However, this mass ratio is a numerical value when the total amount of the mixed alcohol is 100% by mass. The mass ratio of each alcohol constituting the mixed alcohol is based on the amount charged.

  When the mass% of tripentaerythritol occupying the total amount of mixed alcoholic acid is 5 mass% or less, an ester for refrigerating machine oil having thermal stability that can withstand operation at high temperatures in equipment using R-32 refrigerant is obtained. I can do it. From this viewpoint, the mass ratio of tripentaerythritol in the mixed alcohol is preferably 3% by mass or less, more preferably 2.5% by mass or less, and still more preferably 1% by mass or less.

  Here, the mixed alcohol may consist of pentaerythritol and tripentaerythritol. Alternatively, the mixed alcohol may further contain another pentaerythritol condensate, and typically may contain dipentaerythritol. The mass ratio of the other pentaerythritol condensate in the mixed alcohol, particularly dipentaerythritol, is not particularly limited, but from the viewpoint of obtaining an ester for refrigerating machine oil excellent in long-term low-temperature stability and thermal stability, the ratio is 0. 1 mass% or more is preferable and 0.5 mass% or more is still more preferable. From the same viewpoint, the mass ratio of other pentaerythritol condensates in the mixed alcohol, particularly dipentaerythritol, is preferably 2% by mass or less, and more preferably 1.5% by mass or less.

(Condition C)
The mass ratio of tripentaerythritol in the mixed alcohol is set to 0.02 times or more of the mass ratio of pentaerythritol tetra-2-methylpentanoic acid ester in the ester of pentaerythritol and mixed monocarboxylic acid.

  Since pentaerythritol tetra 2-methylpentanoic acid ester has a high melting point of about 40 ° C., when the amount thereof increases, crystals tend to precipitate and solidify over a long period of time in a low temperature environment. It has been discovered that by adding the predetermined amount of tripentaerythritol to the mixed alcohol, the stability of the entire refrigerating machine ester significantly deteriorates at low temperatures. This makes it possible to obtain an ester for refrigerating machine oil that is excellent in long-term low-temperature stability and does not precipitate and solidify crystals over a long period of time in a low-temperature environment where the temperature changes. From this viewpoint, the mass ratio of tripentaerythritol in the mixed alcohol is 0.03 times or more of the mass ratio of pentaerythritol tetra 2-methylpentanoic acid ester in the ester of pentaerythritol and mixed monocarboxylic acid. Is more preferable, and more preferably 0.05 times or more.

  From the viewpoint of thermal stability at high temperature in equipment using R-32 refrigerant, the mass ratio of tripentaerythritol in the mixed alcohol is such that pentaerythritol tetra-2 in the ester of pentaerythritol and mixed monocarboxylic acid. -It is preferable that it is 0.5 times or less of the mass ratio of methylpentanoic acid ester.

  The mass ratio of tripentaerythritol in the mixed alcohol is calculated from the amounts charged as described above. The mass ratio of pentaerythritol tetra 2-methylpentanoic acid ester in the ester of pentaerythritol and mixed monocarboxylic acid is obtained by analysis using a gas chromatography equipped with an FID detector.

  That is, analysis is performed using a packed column having a length of 1.1 m and an inner diameter of 3.2 mm in which “GC-2014” manufactured by Shimadzu Corporation is used for gas chromatography, and “OV-1” manufactured by GL Sciences is packed in the column. An example of the analysis result is shown in the chart of FIG. In the conditions of the inlet temperature of 320 ° C. and the detector temperature of 330 ° C., the column temperature is raised from 100 ° C. to 320 ° C. at a rate of 10 ° C./min from the start of measurement, and maintained at 320 ° C. for 20 minutes, Such an analysis result can be obtained.

The peak of each product is assigned as follows in order of the retention time.
(1) pentaerythritol tetra-2-methylpropanoate (2) pentaerythritol tri-2-methylpropanoate, mono-3,5,5-trimethylhexanoate (3) pentaerythritol di-2-methylpropanoate, di3 5,5-trimethylhexanoic acid ester (4) pentaerythritol mono 2-methylpropanoic acid, tri-3,5,5-trimethylhexanoic acid ester (5) pentaerythritol tetra-3,5,5-trimethylhexanoic acid ester

From each area of the peaks (1) to (5), the content of pentaerythritol tetra-2-methylpropanoate can be obtained.
Each peak area ratio of (1) to (5) is basically determined by the ratio of 2-methylpropanoic acid to 3,5,5-trimethylhexanoic acid, but whether or not a catalyst is used, the type of catalyst, and reaction conditions , And may vary depending on the type of equipment used for the reaction. In addition, when an operation for processing at a high degree of vacuum is performed under a high temperature condition exceeding 200 ° C. in the purification process, the ratio of each peak changes due to volatilization of the ester component.

  In the present invention, the mixed alcohol and the ester of the mixed carboxylic acid are prepared, and the amount of the mixed alcohol and the mixed carboxylic acid used is such that the hydroxyl value of the resulting refrigerator oil ester is 10.0 mgKOH / g or less, It adjusts so that an acid value may be set to 0.1 mgKOH / g or less. The hydroxyl value is preferably 5.0 mgKOH / g or less, more preferably 2.0 mgKOH / g, and most preferably 1.0 mgKOH / g or less. The acid value is preferably as low as possible, preferably 0.05 mgKOH / g, more preferably 0.02 mgKOH / g or less.

  The ester for refrigerating machine oil of the present invention can be produced by ordinary esterification reaction and transesterification reaction. Specifically, the equivalent ratio of the above-mentioned specific alcohol and carboxylic acid is usually that an excess of the carboxyl group of the carboxylic acid is added to one equivalent of the hydroxyl group of the alcohol, and a catalyst can be added as necessary. Moreover, you may use a solvent as needed, such as when the ratio of 2-methylpropanoic acid is high. The solvent to be used has a boiling point of 100 ° C. to 150 ° C., and a hydrocarbon solvent such as heptane and an aromatic solvent such as toluene are preferable. This is reacted under nitrogen flow at 120 to 260 ° C. for 3 to 15 hours, and when the hydroxyl value becomes, for example, 3.0 mgKOH / g or less, excess carboxylic acid is removed under reduced pressure. Then, ester can be obtained by performing deoxidation by alkali and performing operations such as adsorption treatment and steaming using activated clay, acidic clay and synthetic adsorbent alone or in combination.

  In the lubricating oil composition for refrigerating machine oil of the present invention, at least two kinds of esters for refrigerating machine oil synthesized by the above method can also be used by mixing.

The lubricating oil composition for refrigerating machine oil of the present invention is a known additive, for example, a phenolic antioxidant, a metal deactivator such as benzotriazole, thiadiazole or dithiocarbamate, and an epoxy compound. Alternatively, an additive such as an acid scavenger such as carbodiimide or a phosphorus-based extreme pressure agent can be appropriately blended depending on the purpose.

  Table 1 summarizes the charged composition of the ester used in this example. Moreover, the obtained ester was analyzed by the following gas chromatography, and the contents of pentaerythritol tetra 2-methylpropanoate (PTMP) in the pentaerythritol ester are summarized in Table 1.

Each ester was synthesized according to the following method.
(Synthesis Example 1)
Into a 2 L four-necked flask equipped with a thermometer, a nitrogen inlet tube, a stirrer, a Dimroth condenser tube and a 30 mL oil-water separator tube, alcohol was charged according to the ratio shown in Table 1, and the hydroxyl group of the charged alcohol was The reactor was charged with 2-methylpropanoic acid and 3,5,5-trimethylhexanoic acid in the ratio shown in Table 1 so that the carboxylic acid had a molar ratio of 1.05. Finally, 0.2 mol equivalent of titanium isopropoxide was charged with respect to the hydroxyl group of the charged alcohol.

  The charged reaction solution was heated under a nitrogen stream and reacted at a temperature of 220 ° C. until the hydroxyl group of the ester became 3 or less. Thereafter, the inside of the reactor was cooled to 200 ° C., and the pressure was reduced to 80 Torr, and excess fatty acid was distilled off until the acid value became 5 mgKOH / g or less.

  After cooling the reactor to 85 ° C., 1.5 equivalents of the amount of potassium hydroxide calculated from the acid value is diluted with ion-exchanged water to prepare a 10% aqueous solution, which is added to the reaction solution for 1 hour. Stir. After stopping the stirring, the mixture was allowed to stand for 30 minutes and the aqueous layer separated into the lower layer was removed. Next, 20% by mass of ion exchange water with respect to the reaction solution was added, stirred at 85 ° C. for 10 minutes, allowed to stand for 15 minutes, and then the operation of removing the separated aqueous layer was carried out by adjusting the pH of the aqueous layer to 7 Repeated from 8 to 8. Then, it dehydrated by stirring at 100 degreeC and 30 Torr for 1 hour. Finally, 2% by mass of activated clay was added to the reaction solution, stirred for 1 hour at 80 ° C. and 30 Torr, filtered to remove the adsorbent, and the desired ester was obtained.

(Synthesis Example 2)
Into a 2 L four-necked flask equipped with a thermometer, a nitrogen inlet tube, a stirrer, a Dimroth condenser tube and a 30 mL oil-water separator tube, alcohol was charged according to the ratio shown in Table 1, and the hydroxyl group of the charged alcohol was The reactor was charged with 2-methylpropanoic acid and 3,5,5-trimethylhexanoic acid in the ratio shown in Table 1 so that the carboxylic acid had a molar ratio of 1.07. Then, 10 mass% toluene was prepared with respect to the total preparation mass of alcohol and carboxylic acid. Finally, 0.2 mol equivalent of titanium isopropoxide was charged with respect to the hydroxyl group of the charged alcohol.

  The charged reaction solution was heated under a nitrogen stream, reacted at 150 ° C. for 5 hours, and then reacted at a temperature of 220 ° C. until the hydroxyl group of the ester became 3 or less. The inside of the reactor was cooled to 200 ° C., and the pressure was reduced to 50 Torr, and excess fatty acid and remaining toluene were distilled off until the acid value became 5 mgKOH / g or less.

  After cooling the reactor to 85 ° C., 1.5 equivalents of the amount of potassium hydroxide calculated from the acid value is diluted with ion-exchanged water to prepare a 10% aqueous solution, which is added to the reaction solution for 1 hour. Stir. After stopping the stirring, the mixture was allowed to stand for 30 minutes and the aqueous layer separated into the lower layer was removed. Next, 20% by mass of ion exchange water with respect to the reaction solution was added, stirred at 85 ° C. for 10 minutes, allowed to stand for 15 minutes, and then the operation of removing the separated aqueous layer was carried out by adjusting the pH of the aqueous layer to 7 Repeated from 8 to 8. Then, it dehydrated by stirring at 100 degreeC and 30 Torr for 1 hour. Finally, 2% by mass of activated clay was added to the reaction solution, stirred for 1 hour at 80 ° C. and 30 Torr, filtered to remove the adsorbent, and the desired ester was obtained.

  Examples 1 to 4 and Comparative Examples 1 to 3 were synthesized according to Synthesis Example 1. In addition, Examples 5 to 6 and Comparative Examples 4 to 7 were synthesized according to Synthesis Example 2.

  The obtained ester was analyzed by gas chromatography, and the content of pentaerythritol tetra 2-methylpropanoate (PTMP) in the pentaerythritol ester was measured by the following method. Table 1 summarizes the results.

However, GC-2014 manufactured by Shimadzu Corporation was used for gas chromatography, and analysis was performed using a packed column having a length of 1.1 m and an inner diameter of 3.2 mm packed with OV-1 manufactured by GL Sciences. Under the conditions of inlet temperature 320 ° C. and detector temperature 330 ° C., the column temperature is increased from 100 ° C. to 320 ° C. at a rate of 10 ° C./min from the start of measurement, and measurement is performed under the condition of holding at 320 ° C. for 20 min. A gas chromatography chart as shown in FIG. 1 was obtained. From each peak in order of retention time,
(1) pentaerythritol tetra-2-methylpropanoate (2) pentaerythritol tri-2-methylpropanoate, mono-3,5,5-trimethylhexanoate (3) pentaerythritol di-2-methylpropanoate, di3 5,5-trimethylhexanoic acid ester (4) pentaerythritol mono-2-methylpropanoic acid, tri-3,5,5-trimethylhexanoic acid ester (5) pentaerythritol tetra-3,5,5-trimethylhexanoic acid ester The content of pentaerythritol tetra-2-methylpropanoate (PTMP) in pentaerythritol ester was calculated.

Various measurements of the ester for refrigerator oil performed in the present invention were performed according to the following methods.
Hue: Measured according to JOCS 2.2.1.4-1996.
Acid value: Measured according to JIS K-0070.
Total acid value: Measured according to JIS C-2101.
Kinematic viscosity: Measured according to JIS K-2283.
Hydroxyl value: measured in accordance with JIS K-0070.
Pour point: Measured according to JIS K-2269.

Two-layer separation temperature:
Based on JIS K-2211, the two-layer separation temperature in the low temperature region was measured under the condition that the mass ratio of R-32 refrigerant to ester was 8: 2.
Long-term low-temperature cycle test:
80 g of ester was weighed into a 100 mL screw tube, put into a thermostat set so as to change between −10 ° C. and −30 ° C. every 12 hours, and the appearance of each sample after 1000 hours was visually confirmed. The case where crystals were precipitated or solidified was evaluated as “x”, and the case where no crystals were observed was evaluated as “◯”.

Heat resistance test (shield tube test):
Thick Pyrex (registered trademark) tube (total length 300 mm, outer diameter 10 mm, inner diameter 6 mm) 2 g of the sample whose water content was adjusted to about 1000 ppm in advance, 3 g of refrigerant R-32, and 10 mm long iron, copper, and Each aluminum piece was sealed and sealed. This was heated at 200 ° C. for 10 days, then opened, the refrigerant was taken out, and the acid value was measured according to JIS C-2101.
The above analysis results are summarized in Table 2.

  As shown in the examples, according to the present invention, it is possible to obtain an ester for refrigerating machine oil that is excellent in compatibility with the R-32 refrigerant, and excellent in thermal stability and long-term low-temperature stability.

In Comparative Example 1, since the mass ratio of 2-methylpropanoic acid is low, the two-layer separation temperature is high.
In Comparative Example 2, since the mass ratio of tripentaerythritol is high, the thermal stability is low.
In Comparative Examples 3 and 4, the mass ratio of tripentaerythritol in the mixed alcohol is 0.01 times the mass ratio of pentaerythritol tetra 2-methylpentanoate in pentaerythritol. Not good.
In Comparative Example 5, since the mass ratio of tripentaerythritol is high, the thermal stability is low.
In Comparative Example 6, since the mass ratio of 2-methylpropanoic acid is high, the results of the low-temperature cycle test are not good.
In Comparative Example 7, since the mass ratio of 2-methylpropanoic acid is high and the mass ratio of tripentaerythritol is high, the thermal stability is low and the results of the low-temperature cycle test are not good.

  From the above results, it was confirmed that the ester for refrigerating machine oil shown in the present invention has long-term stability at low temperatures and high heat resistance as an ester used as refrigerating machine oil for R-32 refrigerant. .

Claims (1)

A refrigerating machine ester comprising an ester of a mixed alcohol containing pentaerythritol and tripentaerythritol and a mixed monocarboxylic acid containing 2-methylpropanoic acid and 3,5,5-trimethylhexanoic acid, the following (A) (B) and (C) are satisfied, The ester for refrigerator oil characterized by the above-mentioned.

(A) The mass ratio of 2-methylpropanoic acid in the mixed monocarboxylic acid is 20% by mass to 55% by mass, and the mass ratio of 3,5,5-trimethylhexanoic acid is 45% by mass to 80% by mass. is there.
(B) The mass ratio of tripentaerythritol in the mixed alcohol is 5% by mass or less.
(C) The mass ratio of tripentaerythritol in the mixed alcohol is 0.02 times or more of the mass ratio of pentaerythritol tetra 2-methylpentanoic acid ester in the ester of pentaerythritol and the mixed monocarboxylic acid.

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