JP2000096075A - Lubricant for refrigerator employing ammonia refrigerant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a refrigerator oil excellent in compatibility with ammonia refrigerant, lubricity and stability and used for refrigerators employing ammonia as the refrigerant. SOLUTION: This lubricant for refrigerators comprises at least one kind of polyether represented by the formula X O-(AO1)a-(AO2)b-H}p [X denotes a residue after removing hydroxyl group from a monool or polyol; (AO1)a denotes a polyoxyalkylene group composed by copolymerization of ethylene oxide and propylene oxide and/or butylene oxide; AO2 denotes a >=3C oxyalkylene group; (a) denotes a number of >=2; (b) denotes a number of >=1; (p) denotes the number of valence of X]. In the polyether, (AO1)a is preferably the polyoxyalkylene group composed by random copolymerization of the ethylene oxide and the propylene oxide and/or butylene oxide or the polyoxyalkylene group containing the random copolymerization in a part thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a lubricant for a refrigerator using ammonia as a refrigerant.

[0002]

2. Description of the Related Art Conventionally, a compression refrigerator comprises a compressor, a condenser, an expansion mechanism (expansion valve, etc.) and an evaporator, and its refrigerant is trichlorofluoromethane (R11), dichlorodifluoromethane (R12) or chlorofluoromethane. Chlorine-containing fluorocarbons (fluorocarbon compounds) such as difluoromethane (R22) have been used for a long time. These fluorocarbon compounds cause an international environmental problem of depletion of the ozone layer, the use of which is regulated, and chlorine-free difluoromethane (R32), tetrafluoroethane (R134)
Or R134a), difluoroethane (R152 or R134a).
152a) and the like. However, it has been pointed out that even these fluorocarbon compounds containing no chlorine have an extremely high global warming ability, and may cause environmental problems from a long-term perspective.

[0003] In recent years, hydrocarbons, ammonia and the like have attracted attention as refrigerants that do not cause such environmental problems. These refrigerants are far superior to the chlorofluorocarbon compounds in terms of environmental safety for the global environment and the human body. Further, although these compounds have not been the mainstream as refrigerants, they have been used for a long time.

Until now, since ammonia is not compatible with mineral oil, alkylbenzene, etc., which is a refrigerating machine oil, a refrigerating machine equipped with an oil circulating system at the compressor outlet side to separate and recover the oil and return it to the compressor inlet side again. It has been restricted to use only.
In addition, if the function of the oil circulation equipment is not sufficient, the refrigerating machine oil is taken out into the refrigerating cycle, causing a shortage of lubricating oil in the compressor. May be significantly shortened. Further, since the temperature of the evaporator is low, the high viscosity refrigerating machine oil taken out into the refrigeration cycle may remain in the evaporator and reduce the heat exchange efficiency. For this reason, refrigerators that use ammonia are relatively large and are limited to industrial equipment that can be regularly maintained.

However, in consideration of the above-mentioned environmental problems, ammonia refrigerants have been reviewed. Along with this, refrigerating machine oils that have compatibility with an ammonia refrigerant and do not require an oil circulation facility like a CFC refrigerant have been proposed. For example, EP 0490810 discloses a lubricant comprising a polyalkylene glycol which is a copolymer of ethylene oxide (EO) and propylene oxide (PO) and EO / PO = 4/1. Also, EP
585934 discloses a lubricant comprising a mono- or bifunctional polyalkylene glycol having EO / PO = 2/1 to 1/2. Furthermore, in DE 4404804, the general formula

Embedded image A polyether-based lubricant represented by RO— (EO) _x — (PO) _y —H (R is a C ₁ -C ₈ alkyl group, x = y = 5-55) is disclosed. . In EP 699737, the general formula

Embedded image Z ((CH ₂ CH (R ¹ ) O) _n- (CH ₂ CH)
(R ¹ ) O) _m ) _p- H (Z is C ₆ or more for an aryl group, C for an alkyl group
₁₀ or more, R ¹ is a hydrogen atom, a methyl group or an ethyl group, n =
A lubricant represented by 0 or a positive number, m = positive number, p = valence of Z) is disclosed.

Further, Japanese Patent Application Laid-Open No. 5-9483 and WO
No. 95/12594 discloses a refrigerating machine oil comprising a polyalkylene glycol diether and having excellent compatibility and stability with ammonia.

[0007]

When the above polyalkylene glycol-based compound is used as the refrigerating machine oil of an ammonia refrigerant refrigerator, the bifunctional polyalkylene glycol having two hydroxyl groups has stability and moisture absorption. The problem of poor sex has been pointed out. Further, the above polyalkylene glycol diether has a problem that it has lower compatibility with ammonia than polyalkylene glycol having a hydroxyl group, and is incompatible depending on the structure. In addition, polyalkylene glycol diether has a disadvantage that the production process is complicated because the terminal of the molecule must be blocked with an alkyl group, and thus the terminal is blocked.

[0008] Accordingly, an object of the present invention is to provide a refrigerating machine oil for a refrigerating machine that uses ammonia as a refrigerant having excellent compatibility with an ammonia refrigerant and excellent lubricity and stability.

[0009]

That is, the present invention provides the following general formula (1):

Embedded image _{^{X {-O- (AO 1) a}} - (AO 2) b -H} p (1) [ wherein, X represents a residue obtained by removing hydroxyl groups from a monool or polyol, (AO ¹ ) _a ethylene oxide and represents a polyoxyalkylene group constituted by copolymerization of propylene oxide and / or butylene oxide, AO ² represents the number 3 or more oxyalkylene group having a carbon, a represents a number of 2 or more , B represents a number of 1 or more, and p represents a valence of X. ] A lubricant for a refrigerator using an ammonia refrigerant, comprising at least one kind of polyether represented by the formula:

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the general formula (1), X represents a residue obtained by removing a hydroxyl group from a monol or a polyol. As the monol, for example, methanol, ethanol, propanol, 2-propanol, butanol,
2-butanol, pentanol, 2-pentanol, 3
-Pentanol, isopentyl alcohol, 2-methyl-4-pentanol, hexanol, secondary hexanol, isohexanol, heptanol, secondary heptanol, octanol, 2-ethylhexanol, secondary octanol, isooctanol, nonanol, secondary Nonanol, 1-decanol, isodecyl alcohol, secondary decanol, undecanol, secondary undecanol, 2-
Methyldecanol, lauryl alcohol, secondary dodecanol, 1-tridecanol, isotridecyl alcohol, secondary tridecanol, myristyl alcohol, secondary tetradecanol, pentadecanol, secondary pentadecanol, cetyl alcohol, palmityl alcohol, 2
Grade hexadecanol, heptadecanol, secondary heptadecanol, stearyl alcohol, isostearyl alcohol, secondary octadecyl alcohol, oleyl alcohol, behenyl alcohol, eicosanol, docosanol, tetracosanol, hexacosanol, octacosanol, myricyl alcohol, Lasserol, tetratriacontanol, allyl alcohol, cyclopentanol, cyclohexanol, 2-butyloctanol, 2-butyldecanol, 2-hexyloctanol, 2-hexyldecanol, 2-hexyldecanol, 2-octyldecanol, 2-octyldodecanol, 2-octyltetradecanol, 2-decyldodecanol, 2-decyltetradecanol, 2-decylhexadecanol, 2-do Siltetradecanol, 2-dodecylhexadecanol, 2-dodecyloctadecanol, 2-tetradecyloctadecanol, 2-tetradecylicosanol, 2-hexadecyloctadecanol, 2-hexadecylicosanol Alcohols such as phenol, cresol, ethylphenol, tert-butylphenol, hexylphenol, octylphenol, nonylphenol, decylphenol, undecylphenol, dodecylphenol, tridecylphenol, tetradecylphenol, phenylphenol, benzylphenol, styrenated phenol, p-
Phenols such as cumylphenol are exemplified.

As the polyol, for example, ethylene glycol, propylene glycol, 1,4-butanediol, 1,2-butanediol, neopentyl glycol, 1,6-hexanediol, 1,2-octanediol, 1,8- Octanediol, isoprene glycol, 3-methyl-1,5-pentanediol, sorbite, catechol, resorcin, hydroquinone, bisphenol A, bisphenol F, hydrogenated bisphenol A,
Diols such as hydrogenated bisphenol F and dimer diol; glycerin, trioxyisobutane, 1,2,3-
Butanetriol, 1,2,3-pentanetriol,
2-methyl-1,2,3-propanetriol, 2-methyl-2,3,4-butanetriol, 2-ethyl-
1,2,3-butanetriol, 2,3,4-pentanetriol, 2,3,4-hexanetriol, 4-propyl-3,4,5-heptanetriol, 2,4-dimethyl-2,3 Trihydric alcohols such as 4-pentanetriol, pentamethylglycerin, pentaglycerin, 1,2,4-butanetriol, 1,2,4-pentanetriol, trimethylolethane and trimethylolpropane; pentaerythritol, erythritol,
2,3,4-pentane tetrol, 2,3,4,5-hexane tetrol, 1,2,4,5-pentane tetrol, 1,3,4,5-hexane tetrol, diglycerin, sorbitan Pentahydric alcohols such as adonitol, arabitol, xylitol and triglycerin; hexahydric alcohols such as dipentaerythritol, sorbitol, mannitol, iditol, inositol, darcitol, talose and allose; Examples thereof include polyglycerin and dehydration condensates thereof. p is a valence of X, and a number of 1 to 8 is preferable.

X may be a residue of a compound derived from the above monol or polyol. Examples of such a compound include sodium alcoholate and potassium alcoholate of the above monol or polyol.

Of these, if the valence p of X is too large, the molecular weight of the obtained polyether becomes too large, the viscosity becomes too high, or the compatibility with the ammonia refrigerant is lowered. p is more preferably 1 to 3. In particular, it is most preferable that p is 1, that is, X is a residue obtained by removing a hydroxyl group from a monol. Even if it is a monol, the carbon number of X is preferably 1 to 8, more preferably 1 to 4, since the compatibility with the ammonia refrigerant may decrease when the carbon number is too large. Preferably X is a methyl group.

(AO ¹ ) _a is ethylene oxide and
Represents a polyoxyalkylene group formed by copolymerization of propylene oxide and / or butylene oxide. The polymerization ratio of ethylene oxide and propylene oxide and / or butylene oxide is not particularly limited, but at least ethylene oxide is required in order to impart excellent compatibility with ammonia to the polyether which is a polymerization product. . However, the proportion of too ethylene oxide increases, hygroscopic property and low-temperature characteristics are deteriorated such as pour point, since the powdery solid precipitate, or it may be precipitated oxy occupied in (AO ¹⁾ _a The proportion of ethylene groups is preferably 50% by weight or less,
0 wt% is more preferable, and 30 to 10 wt% is most preferable. For the same reason, the ratio of the number of oxyethylene groups in the molecule of the polyether represented by the general formula (1) used in the present invention is 40% or less based on the total number of oxyalkylene groups. Is preferably 30% or less, and most preferably 20% or less.

The form of copolymerization may be block polymerization, random polymerization or a mixture of block polymerization and random polymerization, but polyoxyalkylene in which (AO ¹ ) _a is entirely composed of block polymerization. If it is a group, the fluidity at low temperature is deteriorated, so that (AO ¹ ) _a may be a polyoxyalkylene group constituted by random polymerization or a polyoxyalkylene group containing at least partly random polymerization. preferable. a represents a number of 2 or more, preferably 2 to 150, more preferably 5 to 1
00.

AO ² represents an oxyalkylene group having 3 or more carbon atoms. Examples of the oxyalkylene group having 3 or more carbon atoms include an oxypropylene group, an oxybutylene group, and an oxyalkylene group having about 5 to 24 carbon atoms, and among them, an oxypropylene group or an oxybutylene group is preferable. b represents a number of 1 or more, preferably 1 to 10. (AO ² ) _b is a (poly) oxyalkylene group composed of one or more oxyalkylene groups having 3 or more carbon atoms.

Since the polyether represented by the general formula (1) used in the present invention has a group represented by (AO ² ) _b -H at the terminal of the structure, it exhibits excellent stability in the presence of an ammonia refrigerant. . In general, when a hydroxyl group bonded to a primary carbon atom is oxidized, it changes to a carboxylic acid via an aldehyde, but the carboxylic acid may form an acid amide in the presence of ammonia, and this may precipitate. On the other hand, the hydroxyl group bonded to the secondary carbon atom only changes to a ketone even when oxidized, and the ketone is more stable than the carboxylic acid in the presence of ammonia. Therefore, the reason why the polyether represented by the general formula (1) used in the present invention can exhibit excellent stability even in the presence of ammonia is obtained by finally adding an alkylene oxide having 3 or more carbon atoms. This is presumed to be because the polyether is a structure in which the hydroxyl group at the terminal of the structure is bonded to a secondary carbon atom. That is, the refrigerator lubricant of the present invention has a problem specific to a lubricant of a refrigerator using an ammonia refrigerant,
This has been solved by specifying the structure of the lubricant as described above.

The molecular weight of the polyether represented by the general formula (1) used in the present invention is not particularly limited, but the molecular weight and the kinematic viscosity tend to be proportional. Has a molecular weight of 300 to 3,0
About 00 is preferable.

The kinematic viscosity of the polyether represented by the general formula (1) used in the present invention is not particularly limited. However, if the viscosity is too low, the sealing property is poor and the lubricating performance may be reduced. The compatibility with ammonia decreases, and the energy efficiency also deteriorates. Therefore, the kinematic viscosity at 40 ° C. is preferably 15 to 200 cSt, and more preferably 20 to 150 cSt.

Ammonia as a refrigerant and polyether represented by the general formula (1) used in the present invention are 99/1 by weight in terms of the cooling capacity of the refrigerant and the sealing property of the lubricant.
It is preferably used in the range of 1/99 to 95/5.
More preferably, it is used in the range of 30/70.

Since the polyether represented by the general formula (1) used in the present invention is a lubricant used in a refrigerator for an ammonia refrigerant, it is preferable that impurities such as moisture and chlorine are as small as possible. Moisture promotes deterioration of lubricants, additives, etc., so the smaller the better, the better, preferably 500 ppm or less, more preferably 300 ppm or less, 100 pp
m or less is most preferable. In general, since polyether has hygroscopicity, caution is required during storage or filling in a refrigerator. However, polyether can be removed by distillation under reduced pressure or by passing through a dryer filled with a desiccant.

Further, chlorine forms an ammonium salt in the presence of ammonia and causes clogging of the capillary. Therefore, the chlorine content is preferably as small as possible, preferably 100 ppm or less, more preferably 50 ppm or less.

Further, in producing the refrigerator lubricant of the present invention containing an oxypropylene group, propylene oxide may cause an allyl group by causing a side reaction. When an allyl group is formed, first, the thermal stability of the lubricant itself decreases. In addition, it forms a polymer and causes sludge, and is liable to be oxidized, thereby generating peroxide. When the peroxide is generated, it is decomposed to generate a carbonyl group, which reacts with the ammonia refrigerant to generate an acid amide, which also causes the clogging of the capillary.
Therefore, the less the degree of unsaturation derived from an allyl group or the like, the better. Specifically, it is preferably 0.04 meq / g or less, more preferably 0.03 meq / g or less, and 0.02 meq / g. It is most preferred that:

The peroxide value is 10.0 meq / kg
Or less, more preferably 5.0 meq / kg or less, and most preferably 1.0 meq / kg. The carbonyl value is 100 ppm by weight.
Or less, more preferably 50 ppm by weight or less, and most preferably 20 ppm by weight or less.

In order to produce such a polyether having a low degree of unsaturation, the reaction temperature when reacting propylene oxide is preferably 120 ° C. or lower, more preferably 110 ° C. or lower. In addition, if an alkaline catalyst is used in the production, an inorganic adsorbent such as activated carbon, activated clay,
Use of bentonite, dolomite, aluminosilicate, or the like can reduce the degree of unsaturation. Further, when the lubricant of the present invention is produced or used, contact with oxygen as much as possible or use of an antioxidant can also prevent an increase in peroxide value or carbonyl value.

The degree of unsaturation, peroxide value and carbonyl value are values measured by a standard fat and oil analysis test established by the Japan Oil Chemists' Society. The outline of the measuring method is shown below. <Method of measuring the degree of unsaturation (meq / g)> A whis solution (ICl-acetic acid solution) was allowed to react with the sample, and the sample was allowed to stand in a dark place. The iodine value was calculated by titration with, and the iodine value was converted to a vinyl equivalent, which was defined as the degree of unsaturation. <Measurement method of peroxide value (meq / kg)> Potassium iodide was added to a sample, the generated free iodine was titrated with sodium thiosulfate, and this free iodine was converted to the number of milliequivalents per 1 kg of the sample. The oxide value was used. <Method for measuring carbonyl value (ppm by weight)>
4-Dinitrophenylhydrazine was allowed to act to generate a chromogenic quinoid ion, the absorbance of this sample at 480 nm was measured, and the carbonyl amount was converted to a carbonyl amount based on a calibration curve previously determined using cinnamaldehyde as a standard substance.

The method for producing the polyether represented by the general formula (1) used in the present invention is not particularly limited, and may be a conventional method for producing a polyether. For example, a mixed alkylene oxide of ethylene oxide and propylene oxide (or butylene oxide) is added to an alcohol such as methanol as a starting material in the presence of an alkali catalyst such as sodium hydroxide or potassium hydroxide at a temperature of 10
After the reaction at 0 to 150 ° C. and a pressure of about 0 to 10 kg / cm ² , an alkylene oxide having 3 or more carbon atoms such as propylene oxide may be reacted.

Other components can be added to the lubricant of the present invention as needed. For example, known refrigerator lubricants such as mineral oil, alkylbenzene, polyalkylene glycol diether, polyalkylene glycol, and polyol ester; and extreme pressure agents such as tricresyl phosphate and triphenyl phosphate; Antioxidants such as ributyl-4-methylphenol, 4,4'-methylenebis-2,6-di-tert-butylphenol, dioctyldiphenylamine, dioctyl-p-phenylenediamine; stabilizers such as phenylglycidyl ether; glycerin mono Additives such as oily agents such as oleyl ether and glycerin monolauryl ether; metal deactivators such as benzotriazole; and foam control agents such as polydimethylsiloxane can be appropriately added. Further, additives such as a detergent / dispersant, a viscosity index improver, a rust inhibitor, a corrosion inhibitor, a pour point depressant and the like can be blended as required. These additives are generally added in an amount of about 0.01 to 10% by weight based on the lubricant of the present invention.

[0029]

The present invention will be described more specifically with reference to the following examples. In the following examples, “parts” and “%” are based on weight unless otherwise specified. EO is an oxyethylene group, PO is an oxypropylene group, BO is an abbreviation of an oxybutylene group, and the symbol “−” between them represents a block copolymer, and “/” is a random copolymer. Represents The following tests were performed on each of the examples and the comparative examples, and evaluations as a lubricant for a refrigerator using an ammonia refrigerant were performed.

(Production Example) In a 3 liter autoclave, 64 g of methanol and 8 g of potassium hydroxide as a catalyst were placed.
Was charged. After dissolving the catalyst, the reaction temperature is 100 to 150 ° C,
At a pressure of 0 to 10 kg / cm ² , 1,548 g of propylene oxide and 388 g of ethylene oxide (weight ratio of 8
/ 2) were reacted. After aging, reaction temperature 100-150 ° C, pressure 0-10kg / c
At m ² , 232 g of propylene oxide was reacted.
After aging, an adsorbent treatment was performed to obtain the lubricant of Example 1.
The lubricants of Examples 2 to 9 and Comparative Examples 1 to 7 shown in Table 1 below were produced in the same manner.

<Compatibility with Ammonia> After 5 ml of each sample and 1 ml of ammonia were sealed in a glass tube, the mixture was cooled from room temperature at a rate of 1 ° C./min, and the temperature at which two layers were separated was measured. Table 1 shows the obtained results. <Falex baking load> In order to evaluate the lubricity of each sample, the Falex baking load was measured in accordance with ASTM-D-3233-73. Table 1 shows the obtained results. <Bomb test> The following tests were performed to evaluate the stability of each sample in an ammonia atmosphere. That is,
300m loaded with iron wire of 1.6mm diameter as catalyst
50 g of each sample was placed in a 1-liter cylinder, pressurized with ammonia to 0.6 kg / cm ² G, and further charged with nitrogen gas.
The pressure was increased to 7 kg / cm ² G. Thereafter, the mixture was heated to 150 ° C. and kept at the same temperature for 7 days. Thereafter, the sample was allowed to cool to room temperature, the pressure was reduced by removing gas, and the pressure was further reduced to remove ammonia from the sample. The total acid value and hue of the sample thus obtained were measured. After the test, the sample was transferred to a 100 ml beaker and left at room temperature for 5 hours.
Changes in appearance were visually observed and evaluated according to the following ratings. Table 1 shows the obtained results. 0: No abnormality (same state as before test). 1: Slight powdery precipitate is seen at the bottom of the beaker. 2: State between score 1 and 3. 3: A powdery precipitate is seen on the entire bottom surface of the beaker. 4: Solidified or lost fluidity at room temperature.

[0032]

[Table 1]

In Table 1, {(PO) / (EO)} represents a random copolymer of propylene oxide and ethylene oxide. G represents a residue obtained by removing a hydroxyl group from glycerin. The unsaturation, peroxide value, and carbonyl value of the samples of Examples 1 to 9 were measured by the methods described above, and the unsaturation was 0.012 meq / g to 0.018.
meq / g, peroxide value is 2.5 meq / kg to 3.2
meq / kg, carbonyl value was 10 to 15 ppm by weight. Further, when the water content was measured using a Karl Fischer moisture meter, all were 300
ppm or less. In addition, * mark is ｛(PO) / (E
O) represents the weight ratio of the part. However, for Example 8 and Comparative Example 5, the portion of {(PO)-(EO)} is shown, and for Comparative Examples 2 and 7, the entire PO / EO ratio is shown.

[0034]

The effect of the present invention is to provide a refrigerating machine oil for a refrigerating machine which uses ammonia as a refrigerant having excellent compatibility with an ammonia refrigerant and excellent lubricity and stability.

Continued on the front page (72) Inventor Goro Yamamoto 7-2-35 Higashiogu, Arakawa-ku, Tokyo Asahi Denka Kako Kogyo Co., Ltd. Japan Energy Co., Ltd.

Claims (5)

[Claims] 1. The following general formula (1): X ｛—O— (AO ¹ ) _a — (AO ² ) _b —H｝ _p (1) wherein X is a monool or a polyol. (AO ¹ ) _a represents a polyoxyalkylene group formed by copolymerization of ethylene oxide and propylene oxide and / or butylene oxide, and AO ² represents an oxyalkylene having 3 or more carbon atoms. A represents a number of 2 or more, b represents a number of 1 or more, and p represents a valence of X. ] A lubricant for a refrigerator using an ammonia refrigerant, comprising at least one kind of polyether represented by the formula: 2. A polyoxyalkylene group in which (AO ¹ ) _a is formed by random copolymerization of ethylene oxide and propylene oxide and / or butylene oxide, or a polyoxyalkylene group partially containing a random copolymer. The lubricant for a refrigerator according to claim 1, which is: 3. The refrigerator lubricant according to claim 1, wherein the polyether represented by the general formula (1) has a kinematic viscosity at 40 ° C. of 15 to 200 cSt. 4. The refrigerator lubricant according to claim 1, wherein the proportion of oxyethylene groups in (AO ¹ ) _a is 50 to 10% by weight. 5. The refrigerator lubricant according to claim 1, wherein the degree of unsaturation of the polyether represented by the general formula (1) is 0.04 meq / g or less.