JP2010215756A - Method for producing ester lubricating oil for refrigerator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing an ester lubricating oil for a refrigerator that has high quality and high heat resistance. <P>SOLUTION: In producing an ester from a 5-10C alcohol and an aliphatic carboxylic acid having a 5-12C straight chain or branched structure, the reaction is performed until the hydroxyl value of the reaction system attains 5 mg-KOH/g or below and the resulting crude product is treated with use of synthetic zeolite having an average particle diameter of 8-20 μm and a fine pore diameter of 0.4-1.5 nm at a temperature of 60-120°C. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing an ester lubricating oil for a refrigerator, and more particularly to a method for producing an ester lubricating oil for lubricating a compressor for compressing a refrigerant in a refrigeration air conditioner. In particular, the present invention relates to a method for producing an ester lubricating oil for a refrigerator that is used in a working fluid composition for a refrigerator that contains a non-chlorofluorocarbon refrigerant or a natural refrigerant.

  Air conditioning equipment such as room air conditioners and packaged air conditioners, cryogenic equipment and industrial refrigerators, and refrigeration and air conditioning equipment such as hybrid and electric car car air conditioners use chlorine-containing chlorofluorocarbon refrigerants that cause problems such as ozone layer destruction. Instead, conversion to non-chlorofluorocarbon refrigerants such as 1,1,1,2-tetrafluoroethane (R-134a), pentafluoroethane (R-125), difluoroethane (R-32), and mixed refrigerants thereof Is underway. Accordingly, various ester lubricating oils for refrigerators based on polyol esters having high compatibility with non-chlorine fluorocarbons have been proposed.

  Ester lubricating oil for refrigerators has heat resistance and is composed of carboxylic acid having methyl or ethyl branched chain at α-position or β-position and pentaerythritol from the viewpoint of heat resistance and compatibility with non-chlorine fluorocarbons. Hindered esters that are excellent in use have been put into practical use. In recent years, the demand for energy saving performance of refrigerators from the viewpoint of environmental friendliness has increased, and the lubricating oil for refrigerators has been used under severe conditions. That is, there is an increasing demand for improving the heat resistance of esters used in lubricating oil for refrigerators.

  For example, in Patent Document 1 (particularly in Examples), pentamer is used as an ester having high stability even in a compressor that is operated in a thermally severe environment with the use of a refrigerant mixture including difluoromethane (R-32). A lubricating oil for refrigerating machines mainly composed of an ester composed of erythritol, 2-ethylhexanoic acid and a mixed monocarboxylic acid of 3,5,5-trimethylhexanoic acid is disclosed. Patent Document 2 discloses a refrigerating machine oil composition having excellent stability over time, an acidic component reactive additive, an ester of an alcohol having a neopentyl structure and a monocarboxylic acid having a branched structure, water, A refrigerator oil composition containing a hydrochloric acid reactive additive is disclosed.

  In order to improve the heat resistance of the ester lubricating oil for refrigerators, as described above, there are a method for devising the structure of the ester and a method for devising the additive, but the heat resistance of the ester greatly depends on the production method. For this reason, many studies have been conducted on methods for producing esters having high heat resistance. For example, Patent Document 3 discloses a method of adding a Lewis acid catalyst and a phosphorus reducing agent in an esterification reaction as a method for producing an ester having high heat resistance. Patent Document 4 discloses that in order to obtain an ester having heat resistance, unreacted carboxylic acid is captured with an inorganic acid scavenger, and then the remaining carboxylate is adsorbed with an adsorbent. ing.

Japanese Patent Laid-Open No. 10-8084 Japanese Patent Laid-Open No. 2001-226692 JP 2002-193882 A JP 2007-332134 A

  The objective of this invention is providing the manufacturing method for obtaining the ester lubricating oil for refrigerators which has high quality and high heat resistance. In particular, an object of the present invention is to provide a method for producing an ester lubricating oil for a refrigerator that is suitably used for a working fluid composition for a refrigerator that contains a non-chlorine-based Freon refrigerant or a natural refrigerant.

  In order to solve the above-mentioned problems, the present inventors have conducted intensive research. When an ester is obtained from an alcohol having 5 to 10 carbon atoms and an aliphatic carboxylic acid having a linear or branched structure having 5 to 12 carbon atoms, The reaction product is reacted until the hydroxyl value of the reaction system becomes 5 mgKOH / g or less, and the resulting crude product is synthesized using a synthetic zeolite having an average particle size of 8 to 20 μm and a pore size of 0.4 nm to 1.5 nm. It has been found that by performing the treatment at 60 ° C. to 120 ° C., an ester lubricating oil for a refrigerator having high heat resistance can be obtained.

  In addition, after carrying out the treatment with the above-mentioned synthetic zeolite, by further carrying out (1) a neutralization treatment step with an alkaline aqueous solution and / or (2) an adsorption treatment step using an adsorbent, the heat resistance is further increased. It has been found that a high-quality ester lubricating oil for refrigerators can be obtained.

  In the present invention, the ester is preferably composed of a polyhydric alcohol having a neopentyl structure having 5 to 10 carbon atoms and an aliphatic carboxylic acid having a branched structure having 5 to 10 carbon atoms. Further, since the ester lubricating oil for refrigerators obtained by the present invention has high heat resistance, it is preferably used as a base oil for a working fluid composition for refrigerators containing a non-chlorine fluorocarbon refrigerant or a natural refrigerant. .

  The “refrigerator” in the present invention includes a sealed refrigerator such as an electric refrigerator, a refrigerator / freezer showcase, a vending machine, an open refrigerator such as a car air conditioner, a sealed / semi-sealed package such as a room air conditioner and a packaged air conditioner. General industrial refrigerators such as large refrigerators, condensing units, and refrigerator-freezer units are included.

  Since the ester lubricating oil for refrigerators obtained by the production method of the present invention has high quality and high heat resistance, it can be suitably used for a compressor of a refrigerating and air-conditioning apparatus that particularly requires thermal stability. In addition, since the ester lubricating oil for refrigerators obtained by the production method of the present invention is highly compatible with non-chlorine-based chlorofluorocarbon refrigerants and natural refrigerants, it is suitable for working fluid compositions for refrigerators containing these refrigerants. Can be used.

Hereinafter, the present invention will be described in detail.
The manufacturing method of the ester lubricating oil for refrigerators of this invention has the process of obtaining ester from C5-C10 alcohol and C5-C12 aliphatic carboxylic acid which has a linear or branched structure.

  As the reaction raw material, the alcohol having 5 to 10 carbon atoms, a monohydric alcohol or a dihydric or higher polyhydric alcohol is used. Examples of the monovalent alcohol that can be used include those having a linear structure such as 1-pentanol and 1-decanol, 2-ethyl-1-butanol, 2-ethyl-1-hexanol, 3, 5, Those having a branched structure such as 5-trimethyl-1-hexanol are used. From the viewpoint of hydrolysis resistance of ester and low temperature fluidity, alcohol having a branched structure is preferable.

  Examples of the dihydric or higher polyhydric alcohol that can be used include neopentyl glycol, 2-ethyl-2-methyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, and 2-n-butyl- Examples include 2-ethyl-1,3-propanediol, trimethylolethane, trimethylolpropane, trimethylol nonane, pentaerythritol, and dipentaerythritol, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, glycerin, and diglycerin. . Furthermore, from the viewpoint of heat resistance, a polyhydric alcohol (neopentyl polyol) having a neopentyl structure having no hydrogen atom in the β-position carbon of the hydroxyl group is preferably used. Specifically, neopentyl glycol, 2-ethyl-2-methyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 2-n-butyl-2-ethyl-1,3- Examples include propanediol, trimethylolethane, trimethylolpropane, pentaerythritol, and dipentaerythritol.

  Another aliphatic carboxylic acid having a linear or branched structure having 5 to 12 carbon atoms (hereinafter also simply referred to as carboxylic acid) as the other reaction raw material is a linear or branched chain having 5 to 12 carbon atoms. The monocarboxylic acid which has is used. Examples of such monocarboxylic acids include monocarboxylic acids having a linear structure such as pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, and dodecanoic acid, and 2-methylpentanoic acid. Monocarboxylic acids having a branched structure such as 2-ethylhexanoic acid, 3,5,5-trimethylhexanoic acid and neodecanoic acid are used. From the viewpoint of heat resistance, it is preferable to use a monocarboxylic acid having a branched structure having 5 to 10 carbon atoms. In some cases, a dibasic acid having two carboxylic acids can be used. Examples of dibasic acids that can be used include succinic acid, adipic acid, azelaic acid, sebacic acid, and the like.

  In the production of the ester, the above alcohol and aliphatic carboxylic acid are charged into a suitable reactor and reacted. In this case, the ratio of the alcohol to the aliphatic carboxylic acid can be charged so that the carboxylic acid group has a molar equivalent of 1.0 to 1.5 with respect to the hydroxyl group of the alcohol. The reaction temperature is in the range of 150 ° C. to 250 ° C. in order to efficiently remove water generated as the esterification reaction proceeds, and is preferably carried out under a nitrogen stream. Furthermore, the pressure during the reaction can also be carried out under reduced pressure in order to efficiently distill off water. Further, from the viewpoint of heat resistance, it is preferable to sufficiently advance the esterification reaction, and it is preferable to carry out the reaction until the hydroxyl value of the reaction system, that is, the reaction crude product becomes 5 mgKOH / g or less. In addition, said alcohol and aliphatic carboxylic acid can be used individually or in combination of 2 types or more, respectively.

  In the present invention, a catalyst can also be used in order to proceed the reaction efficiently and sufficiently. The catalyst to be used is not particularly limited as long as it has a catalytic effect on the esterification reaction. As such a catalyst, a Bronsted acid or Lewis acid catalyst is generally used. Examples of Bronsted acid include sulfuric acid, p-toluenesulfonic acid, and methanesulfonic acid. Examples of the Lewis acid catalyst include Lewis acid catalysts such as titanium, zirconium and hafnium.

  When the hydroxyl value of the reaction crude product reaches 5 mgKOH / g or less, the remaining alcohol or carboxylic acid can be distilled off under reduced pressure. The temperature and degree of reduced pressure depend on the amount and type of remaining alcohol and carboxylic acid, but it is preferable to carry out at a reduced pressure of 100 Torr or less in the temperature range of 150 to 250 ° C. Moreover, in order to prevent the oxidative degradation of ester as much as possible, it is preferable to carry out under nitrogen stream.

  The manufacturing method of the ester lubricating oil for refrigerators of this invention has the process of processing the obtained crude product with a synthetic zeolite. As synthetic zeolite, sodium silicate and sodium aluminate are used as the main raw materials, and those obtained by mixing and molding alkali metals such as caustic soda and alkaline earth metals as required can be used.

  A synthetic zeolite having an average particle diameter of 8 to 20 μm measured by a laser diffraction / scattering method such as a microtrack method is used. When a synthetic zeolite having an average particle size of less than 8 μm is used, the effect of improving the heat resistance of the ester is not observed, and in some cases, the heat resistance of the ester may be reduced. Moreover, although the heat resistance of ester tends to be improved as the average particle size is large, even if the average particle size exceeds 20 μm, the effect of improving the heat resistance of the ester corresponding to the size of the particle size cannot be obtained.

  The pore diameter of the synthetic zeolite is preferably 0.4 nm or more and 1.5 nm or less. When the pore diameter is less than 0.4 nm, since the molecule to be treated is larger than the pore, the treatment effect is low because the molecule is not taken into the synthetic zeolite. In addition, when the pore diameter exceeds 1.5 nm, not only the molecule to be treated but also an ester having a relatively large molecular size is treated, which may cause deterioration and cannot be used.

  The treatment using the synthetic zeolite is performed at 60 ° C. or higher and 120 ° C. or lower in a nitrogen stream. When the temperature is less than 60 ° C., the activity of the synthetic zeolite is insufficient and the effect of the treatment cannot be obtained. Moreover, when it exceeds 120 degreeC, since the adsorption effect of synthetic zeolite is low, the effect of sufficient processing cannot be acquired. The treatment with synthetic zeolite is more preferably performed at a temperature of 80 ° C. or higher and 100 ° C. or lower. Moreover, in order to promote the effect of the process by synthetic zeolite, it is also effective to carry out under reduced pressure. The lower the degree of decompression, the better, but it is preferable to carry out at 100 Torr or less. The treatment time is about 1 to 6 hours under the above conditions.

  There are no particular restrictions on the method of treatment with synthetic zeolite, a method of adding a predetermined amount of synthetic zeolite directly to a reactor containing an ester, which is a crude product, or a method of filling synthetic zeolite with a predetermined temperature. The method of passing ester through a cylindrical column is mentioned. When a predetermined amount of synthetic zeolite is added directly to the reactor for treatment, the amount of synthetic zeolite added is preferably 0.1% by mass or more and 10% by mass or less based on the ester. If the amount is less than 0.1% by mass, the amount of the synthetic zeolite may be insufficient and the treatment effect may not be exhibited. Even if the amount exceeds 10% by mass, an effect commensurate with the amount added cannot be obtained.

  The shape of the synthetic zeolite is not particularly limited, and the above-mentioned powdery synthetic zeolite or pellets, flakes, beads, or the like formed by adding a binder component can be used.

  In the present invention, an ester lubricating oil for refrigerating machine having higher heat resistance can be obtained by carrying out the following purification treatment step after treatment with synthetic zeolite.

(1) Neutralization treatment step with aqueous alkali solution A prescribed amount of an aqueous alkaline solution is added to the obtained ester, and the mixture is stirred and allowed to stand to discharge the aqueous alkaline solution. As an alkali component, 1 type (s) or 2 or more types of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate can be used. The concentration of the alkaline aqueous solution is preferably 5% by mass to 30% by mass in consideration of the treatment efficiency and hydrolysis of the ester by the alkaline aqueous solution. The amount of the aqueous alkali solution added to the ester is preferably 1 to 2 times equivalent to the acid value of the ester. The treatment temperature is preferably in the range of 60 ° C to 90 ° C.

  Stirring is carried out under the above conditions, and then the stirring is stopped and the mixture is allowed to stand and separate to remove the underlying alkaline aqueous solution. If the alkali component remains with respect to the ester, the heat resistance of the ester is lowered. Therefore, washing with water is performed to sufficiently remove the alkali component. For example, 5% by mass to 30% by mass of water is added to the ester and agitated. The agitation is stopped and the mixture is allowed to stand and separate to remove the lower layer water. It is preferable to repeat this series of operations until the pH of the treated water becomes 7-9. Finally, dehydration is performed to remove moisture in the ester. Although there is no restriction | limiting in particular in the method of dehydration, the water | moisture content in ester can fully be reduced by stirring under reduced pressure at 60 to 150 degreeC.

(2) Adsorption treatment process using an adsorbent An adsorbent is added to the ester to perform an adsorption treatment. Examples of the adsorbent include activated clay, acidic clay, activated carbon, zeolite, activated alumina, diatomaceous earth, silicon dioxide, aluminum oxide, and hydrotalcite. These adsorbents may be used in combination. The amount of adsorbent used is preferably 0.1 to 5% by weight, based on the ester obtained. The adsorption treatment can be performed in a nitrogen stream under a reduced pressure condition of 100 Torr or less in a temperature range of 60 ° C. to 120 ° C. After the adsorption treatment, the adsorbent is removed by filtration.

  As described above, by performing at least one of the purification treatment (1) the neutralization treatment step using an alkaline aqueous solution and (2) the adsorption treatment step using an adsorbent after the treatment using the synthetic zeolite, An ester lubricating oil for refrigerators having higher heat resistance can be obtained. Preferably, after carrying out the treatment using synthetic zeolite, the above-mentioned two purification treatments are performed, whereby an ester lubricating oil for refrigerators having higher heat resistance can be obtained. In addition, when performing said two refinement | purification processes, after performing the neutralization process process with (1) alkaline aqueous solution, it is preferable to perform the adsorption process process using (2) adsorption agent.

  The ester lubricating oil for refrigerators obtained by the production method of the present invention includes known additives such as phenol-based antioxidants, metal deactivators such as benzotriazole, thiadiazole or dithiocarbamate, and epoxy compounds. Alternatively, an additive such as an acid scavenger such as carbodiimide and a phosphorus-based extreme pressure agent can be appropriately blended depending on the purpose.

  Since the ester lubricating oil for refrigerators obtained by the production method of the present invention has high heat resistance, it can be used as a base oil in refrigerator oils. In particular, in a refrigerating and air-conditioning apparatus using a non-chlorofluorocarbon refrigerant, the refrigerating machine according to the present invention is used as a base oil for a working fluid composition for a refrigerating machine for lubricating a rotary compressor or a scroll compressor for compressing the refrigerant. An ester lubricating oil is preferably used.

  The working fluid composition for a refrigerator contains an ester lubricating oil for a refrigerator obtained by the production method of the present invention, and a non-chlorine type chlorofluorocarbon refrigerant or a natural refrigerant. Specific examples of non-chlorofluorocarbon refrigerants include 1,1,1,2-tetrafluoroethane (R-134a), pentafluoroethane (R-125), difluoroethane (R-32), trifluoromethane (R -23), 1,1,2,2-tetrafluoroethane (R-134), 1,1,1-trifluoroethane (R-143a), 1,1-difluoroethane (R-152a), etc., or A mixed refrigerant composed of two or more of these is used.

  Specific examples of the mixed refrigerant include R-407C (R-134a / R-125 / R-32 = 52/25/23 mass%) and R-410R (R-125 / R-32 = 50). / 50 mass%), R-404A (R-125 / R-143 / R-134a = 44/52/4 mass%), R-407E (R-134a / R-125 / R-32 = 60/15) / 25 mass%), R-410B (R-32 / R-125 = 45/55 mass%) and the like. Among these, a refrigerant containing at least one of R-134a and R-32 is particularly preferable.

  Examples of natural refrigerants include hydrocarbon refrigerants and carbon dioxide refrigerants, and examples of hydrocarbon refrigerants include alkanes having 1 to 5 carbon atoms, cycloalkanes, alkenes, and mixtures thereof.

  The working fluid composition for a refrigerator usually has a mass ratio of 10:90 to 90:10 of the ester lubricating oil for a refrigerator according to the present invention and a non-chlorine-based Freon refrigerant or the natural refrigerant. If the mass ratio of the refrigerant is within this range, the working fluid composition has an appropriate viscosity, which is preferable because it has excellent lubricity and high refrigeration efficiency.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not restrict | limited to the following Example.

(Examples 1-15 and Comparative Examples 1-12)
A crude ester product (esters A to H shown in Table 1) was obtained by the following steps using the alcohol and carboxylic acid shown in Table 1. The obtained crude ester product is subjected to the treatments shown in Tables 3 and 4 (treatment with synthetic zeolite, treatment with an alkaline aqueous solution, treatment with an adsorbent shown below) to obtain an ester lubricating oil for a refrigerator. It was. The hues of the resulting ester lubricating oil for refrigerators were all 1 or less in terms of Gardner color, the acid value was 0.01 mgKOH / g or less, and the hydroxyl value was 0.5 mgKOH / g or less. In Tables 3 and 4, “o” in the column of presence / absence of implementation indicates “implemented”, and x indicates “not implemented”.

Each measurement of the ester lubricating oil for refrigerators was performed by the following method.
Hue: Measured in accordance with 2.2.1.3 of the standard oil and fat analysis test method (“Standard oil analysis test method 1996” edited by the Japan Oil and Fat Chemical Society).
Acid value: measured in accordance with JIS C-2101.
Hydroxyl value: measured in accordance with JIS K-0070.

[Ester crude product A]
A 3 L four-necked flask equipped with a thermometer, a nitrogen inlet tube, a stirrer, a cooling tube and an oil / water separation tube was charged with 500 g of pentaerythritol, 283.4 g of n-pentanoic acid, and 1650 g of 3,5,5-trimethylhexanoic acid. After maintaining at 160 ° C. for 6 hours under a nitrogen stream, the reaction water was distilled off at 220 ° C. under normal pressure. After confirming that the hydroxyl value of the reaction system was 5.0 mgKOH / g or less, unreacted carboxylic acid was removed under a reduced pressure of 50 Torr over 1 hour. The obtained ester was cooled to room temperature to obtain 1980 g of a crude ester product having a hydroxyl value of 0.3 mgKOH / g.

[Ester crude product B]
A 5 L four-necked flask equipped with a thermometer, a nitrogen inlet tube, a stirrer, a condenser tube and an oil / water separator tube was charged with 850 g of pentaerythritol, 965.2 g of 2-methylhexanoic acid, and 2171 g of 2-ethylhexanoic acid, and a nitrogen stream. Then, after maintaining at 160 ° C. for 6 hours, the reaction water was distilled off at 240 ° C. under normal pressure. After confirming that the hydroxyl value of the reaction system was 5.0 mgKOH / g or less, unreacted carboxylic acid was removed under a reduced pressure of 50 Torr over 1 hour. The obtained ester was cooled to room temperature to obtain 3070 g of a crude ester product having a hydroxyl value of 0.7 mgKOH / g.

[Ester crude product C to H]
After charging the alcohol shown in Table 1 into a 3 L four-necked flask equipped with a thermometer, a nitrogen inlet tube, a stirrer, a cooling tube, and an oil-water separation tube, 1.2 mol equivalents of carboxylic acid groups with respect to the hydroxyl groups of the alcohol Then, the carboxylic acid shown in Table 1 was charged so that the temperature was raised to 160 ° C. and kept for 6 hours in a nitrogen stream while removing the distilled water. Then, it heated up to 240 degreeC and it reacted until it became the predetermined hydroxyl value shown in Table 1. Finally, unreacted carboxylic acid was removed over 1 hour under reduced pressure of 50 Torr to obtain crude ester products C to H.

[Synthetic zeolite (Zeolite 1-5)]
As zeolites 1 to 5 shown in Table 2, powder products of Wako Pure Chemical Industries, Ltd. product names: synthetic zeolite A-3, synthetic zeolite A-4, synthetic zeolite A-5, and synthetic zeolite F-9 were used. . The average particle size of the synthetic zeolite was measured using a Microtrac particle size distribution measuring device MT3000 manufactured by Nikkiso Co., Ltd. Synthetic zeolite was added to the above-mentioned measuring apparatus in which ethanol was circulated so that the DV value was 0.6 to 0.8, and the average particle diameter of the synthetic zeolite in that state was measured. The pore size of the synthetic zeolite is determined by the mercury injection method [Halenda PP,
J. Am. Chem. Soc., Vol. 73, 373 (1951)]. Table 2 summarizes the pore size and average particle size of the synthetic zeolite used.

[Treatment with synthetic zeolite]
2 g of various synthetic zeolites were added to 200 g of the crude ester product obtained by the above method, and the mixture was stirred for 1 hour under the reduced pressure of 30 Torr under the temperature conditions shown in Tables 3 and 4, and then the synthetic zeolite was removed by filtration.

[Treatment with alkaline aqueous solution]
1.5 equivalents of the amount of potassium hydroxide calculated from the acid value of the crude ester product before treatment was diluted with ion-exchanged water to prepare a 10% by mass aqueous solution, which was added to the crude ester product, and 85 The stirring was carried out at 1 ° C. for 1 hour. Thereafter, stirring was stopped, and the aqueous layer separated into the lower layer was removed by allowing to stand for 30 minutes. Next, 20 mass% ion-exchanged water was added to the crude ester product, the mixture was stirred at 85 ° C. for 10 minutes, allowed to stand for 15 minutes, and then the operation of removing the separated aqueous layer was repeated 5 times. Finally, it was dehydrated by stirring at 100 ° C. and 30 Torr.

[Treatment with adsorbent]
2% by weight of activated clay was added to the crude ester product, and the mixture was stirred at 80 ° C. under a reduced pressure of 30 Torr for 1 hour. Finally, the adsorbent was removed by filtration using a 1 micron filter.

[Heating test of ester lubricant for refrigerator]
The heat resistance of the ester lubricant for refrigerators was evaluated by carrying out a heating test on the ester lubricant for refrigerators. The heating test was performed in an air atmosphere in a thermostatic bath at 180 ° C. for 300 hours, and the hue of the ester lubricating oil for refrigerators after heating (Gardner color number: according to the above standard oil analysis method 2.2.1.3) Compliance) and weight loss rate (%). The above results are summarized in Tables 3 and 4.

  By comparing the results of Examples 1 to 10 and Comparative Examples 1 to 7, using synthetic zeolite having an average particle diameter and a pore diameter specified in the present invention, heat treatment was performed under the temperature conditions specified in the present invention. It was shown that ester lubricating oils for refrigerators having excellent properties can be obtained.

  In addition, the results of Examples 11 to 15 and Comparative Examples 8, 9, 11, and 12 showed that the treatment with synthetic zeolite improved the heat resistance of the ester lubricant for refrigerators. The treatment with the synthetic zeolite shown in the present invention has been shown to improve the heat resistance of the various ester lubricating oils for refrigerators shown in the present invention.

Claims (4)

  When an ester is obtained from an alcohol having 5 to 10 carbon atoms and an aliphatic carboxylic acid having a linear or branched structure having 5 to 12 carbon atoms, the reaction system is obtained until the hydroxyl value of the reaction system is 5 mgKOH / g or less. The resulting crude product is treated at 60 ° C. to 120 ° C. with synthetic zeolite having an average particle size of 8 to 20 μm and a pore size of 0.4 nm to 1.5 nm. Manufacturing method.   2. The method according to claim 1, wherein after the treatment with the synthetic zeolite, (1) a neutralization treatment step with an aqueous alkali solution and / or (2) an adsorption treatment step with an adsorbent is further performed. The manufacturing method of ester lubricating oil for refrigerators as described in any one of.   The refrigeration according to claim 1 or 2, wherein the ester comprises a polyhydric alcohol having a neopentyl structure having 5 to 10 carbon atoms and an aliphatic carboxylic acid having a branched structure having 5 to 10 carbon atoms. A method for producing a machine ester lubricant.   The refrigerator according to any one of claims 1 to 3, wherein the ester lubricating oil for a refrigerator is used in a working fluid composition for a refrigerator containing a non-chlorine fluorocarbon refrigerant or a natural refrigerant. Of producing ester lubricating oil.