JP5848465B2 - Frozen oil and composition having hydrocarbon refrigerant - Google Patents

Description

  This application is a U.S. provisional application 61 / 596,376 filed on February 8, 2012 and a US patent application filed on February 5, 2013, the disclosures of which are incorporated herein by reference. Claims the benefit under 35 USC 119 (e) of 13 / 759,139.

  A working fluid containing a polyol ester lubricant composition and a hydrocarbon refrigerant suitable for heat transfer devices, such as refrigeration and air conditioning systems, comprising a mixture of alkyl carboxy esters of neopentyl polyol is provided. The polyol is selected from, for example, trimethylolpropane, pentaerythritol, dipentaerythritol, tripentaerythritol and pentaerythritol oligomers, and the mixture of alkyl carboxy esters has a kinematic viscosity at 40 ° C. of 22-125 cSt and a viscosity greater than 140 It has an index and is characterized by having very high lubricity, excellent load bearing ability and excellent low temperature characteristics.

  Heat transfer devices such as refrigerators, refrigerators, heat pumps and air conditioning systems are well known. Simply put, such a device has a cycle in which an appropriate boiling point refrigerant receives heat from its surroundings, evaporates at low pressure, then condenses into a liquid at a different location and releases the heat to a new surrounding. Work through. In addition to mechanical parts such as compressors, particularly suitable materials are required, such as refrigerants, suitable heat transfer materials, and lubricants that allow operation of the moving parts of the device. The combination of lubricant and refrigerant in the heat transfer device is called the working fluid.

  There are strict requirements for lubricants in these devices. The lubricant must have good low temperature fluidity, be heat stable, provide protection against wear of moving parts such as bearings under load, remove heat from the compressor, The gap must be sealed to efficiently compress the gas from low pressure to high pressure. The frozen lubricant must be compatible with the refrigerant and generally requires good miscibility of the lubricant and the refrigerant under various operating conditions.

  Synthetic ester based lubricants are effective refrigeration lubricants in many systems. U.S. Pat.No. 6,444,626 includes a cooling agent or mixture comprising pentaerythritol, dipentaerythritol, a mixture of tripentaerythritol and tetrapentaerythritol esters, and a mixture of the aforementioned esters and trimethylol polyol esters. Formulation fluids that are well suited for use as lubricants are disclosed. The mixture of pentaerythritol and polypentaerythritol esters of US Pat. No. 6,444,626 is prepared from a starting polyol that is predominantly monopentaerythritol in a two-stage process. The first step is by partially esterifying the polyol under acidic conditions using less carboxylic acid than required for complete esterification under conditions that result in polyol / ester oligomerization. In accordance with the general teachings of US Pat. No. 3,670,013. In the next step, esterification of the hydroxy group is completed.

  The physical properties of the ester mixture, such as viscosity, depend on the type of ester present and the proportion of ester. For example, the higher the amount of di and tripentaerythritol esters, the more the composition will have a higher viscosity than a similar composition with a higher amount of monopentaerythritol esters. For many large scale high performance applications, high viscosity lubricants are desirable.

  The number of carbon atoms and the amount of branching of the carboxylate portion of the ester have a significant effect on viscosity and miscibility with various other components such as refrigerants. U.S. Pat. No. 5,486,302 discloses higher viscosity POE lubricants obtained by esterifying polyols using branched carboxylic acids; unfortunately these The branched chain esters are poorly lubricious for use in certain heat transfer devices.

  U.S. Pat. No. 6,774,093 discloses a frozen lubricant containing an ester similar to the lubricant described in U.S. Pat. If it is much higher, it becomes suitable for use with fluorinated refrigerants.

  Environmental problems, such as ozone layer depletion, replace traditional chlorofluorocarbon refrigerants with new or alternative materials such as carbon dioxide or non-halogenated hydrocarbons. With the increased use of alternative refrigerants, new lubricant compositions are being developed that must be compatible with these alternative refrigerants while meeting the increasing performance requirements.

In co-pending US patent application Ser. No. 12 / 684,315, mono-, di-, tri-, tetra- and higher oligomers of pentaerythritol, at least 25% being an ester of tetrapentaerythritol or higher oligomers. A refrigeration lubricant comprising a mixture of carboxyesters of the same, having the high viscosity and lubricity characteristics required for use with CO ₂ is disclosed. Preference is given to ester mixtures rich in carboxy groups containing 7 or more carbons, for example n-heptylcarboxy. Co-pending US patent application Ser. No. 13 / 080,739 also contains mainly esters of C _3-6 linear carboxylic acids, for example n-pentanoic acid esters, and four pentaerythritol groups. A high viscosity lubricant useful for use with CO ₂ is disclosed, comprising 30% by weight or more of an ester of pentaerythritol oligomer containing the above.

Japanese Patent Application Laid-Open No. 2003-073681 discloses a biodegradable refrigeration working fluid containing isobutane and a polyol ester, the polyester comprising neopentyl glycol, trimethylolpropane and pentaerythritol, and at least one C _4. prepared from ₈ linear carboxylic acids, and has a kinematic viscosity of 5 to 20 mm ² / g at 40 ° C..

Japanese Patent Application Laid-Open No. 2003-041278 discloses a refrigeration oil that is compatible with hydrocarbon refrigerants such as ethane, propane, butane, and isobutane, and includes one or more C _5-10 neopentyl polyols such as neopentyl glycol. , A frozen oil comprising one or more polyol esters made from trimethylolpropane, pentaerythritol and dipentaerythritol, and one or more _C5-9 straight or branched chain carboxylic acids ing. An example having a kinematic viscosity of 30-33 mm ² / g at 40 ° C. is shown.

  US Pat. No. 7,718,083 includes (A) a base oil selected from polyalkylene glycols, polyol esters, polyalphaolefins, alkylbenzenes, and mineral oils; (B) a sulfur content of 35% by weight or less. A refrigerating machine oil is disclosed, comprising: an organic sulfur compound having; (C) a refrigerant composed of at least one selected from carbon dioxide, hydrocarbons, and ammonia.

JP-A-2010-090284 discloses, refrigerator oil comprising a hydrocarbon refrigerant, and esters of polyols with _{C 10 to 20} straight chain carboxylic acid, is disclosed. Japanese Patent Application Laid-Open No. 2010-031134 discloses a compressor in which a refrigerator oil containing propane and pentaerythritol erythritol and / or an ester of dipentaerythritol and C _11-19 carboxylic acid is used as a refrigerant. ing.

  Certain mixtures of polyol esters made from selected polyols and predominantly or exclusively linear carboxylic acids are very effective base oils for use as refrigeration lubricants with hydrocarbon refrigerants. It was found. The polyol ester mixture has a surprising combination of physical properties such as viscosity, lubricity, etc., and an ideal hydrocarbon solubility combination for use with hydrocarbon refrigerants in refrigeration working fluids.

The present invention provides a working fluid comprising a C _1-6 hydrocarbon refrigerant and a polyol ester lubricant, the polyol ester lubricant having a kinematic viscosity at 40 ° C. of 22 to 125 cSt, a viscosity index greater than 140. And predominantly linear alkyl carboxy esters of neopentyl polyol, ie C _5-10 carboxylate esters of neopentyl polyol selected from trimethylolpropane, pentaerythritol, dipentaerythritol, tripentaerythritol and pentaerythritol oligomers And most or all of the alkyl carboxy groups are derived from linear C _5-10 carboxylic acids. Often, the polyol ester lubricant has a pour point of less than -40 ° C according to ASTM D97. The working fluid of the present invention is compatible with standard additives common in the field.

  The polyol ester based on pentaerythritol of the present invention conveniently comprises reacting less than the theoretical amount of carboxylic acid with pentaerythritol to available hydroxyl groups at high temperature under strong acid catalyst to give pentaerythritol, By forming a mixture of partial esters of dipentaerythritol and higher polypentaerythritol, it can be prepared in a two-step process; partial esters are partially esterified with hydroxyl groups, but all It is a polyol compound that is not esterified. The amount and viscosity of oligomerization can be controlled by the length of time the reaction proceeds and is affected by the amount of carboxylic acid added, the temperature, and other reaction parameters that vary readily. After neutralizing the strong acid, the remaining hydroxyl groups are esterified in a second step with additional carboxylic acid using standard means.

The polyol esters of the present invention can also be prepared by simple esterification of one or more polyols, and it is common to blend the individually prepared esters to obtain the polyol ester mixture of the present invention. is there. For example, blends of pentaerythritol-based polyol esters made from the two-stage process described above are blended with, for example, C _5-10 carboxylic acid esters of trimethylolpropane to adjust the viscosity of the lubricant composition. can do.

In many embodiments, the _C5-10 carboxylic acid used to form the polyol ester is selected from _C7-10 carboxylic acids, and a mixture of acids is often used, for example, the acid is n- It can be selected from heptanoic acid, n-octanoic acid and n-decanoic acid.

2 is a Daniel Chart relating kinematic viscosity to temperature, pressure (isobar) and composition (straight line) for a propane solution having the lubricant mixture of Example 1. 2 is a Daniel chart relating kinematic viscosity to temperature, pressure and composition for a propane solution having the lubricant mixture of Comparative Example 1. 6 is a Daniel chart relating kinematic viscosity to temperature, pressure and composition for a propane solution having the lubricant mixture of Comparative Example 2.

i) As refrigerant, _C1-6 hydrocarbons, such as _C1-5 hydrocarbons, such as _C2-5 hydrocarbons, such as ethane, propane, propene, butane, isobutane, butene, isobutene, pentane and iso-pentane, such as , Propane, butane, isobutane, butene and isobutene, or a mixture of said hydrocarbons;
ii) C _5-10 alkyl carboxylate esters of neopentyl alcohol predominantly, for example one or more of C _{5 of} trimethylolpropane, pentaerythritol, dipentaerythritol, tripentaerythritol or pentaerythritol oligomers. _A polyol ester lubricant composition, wherein a majority or all of the alkyl carboxylate is a linear alkyl carboxylate;
A working fluid for a heat transfer device, comprising:
A working fluid wherein the polyol ester lubricant composition has a kinematic viscosity at 40 ° C. of 22-125 cSt, a viscosity index greater than 140. In many embodiments, the polyol ester lubricant has a pour point of less than −40 ° C. as determined by ASTM D97.

In one embodiment, the polyol ester lubricant composition has the formula I

A mixture of
In the above formula, n is an integer of 1-20, such as 1-12, or 1-10,
Each R is independently alkylcarbonyl having 5 to 10 carbon atoms, most of which is straight-chain alkylcarbonyl;
Each R ₁ is independently selected and the R group or substituent of formula II:

Either
The polyol ester lubricant composition comprises at least a) a compound of formula I wherein n is 1 and each R ₁ is independently selected and is an R group, ie a monopentaerythritol ester, and b) a formula Compounds of I (n is 2, each R ₁ is independently selected and is an R group, ie a dipentaerythritol ester);
Including:
For example, the polyol ester lubricant composition comprises at least a) a compound of formula I wherein n is 1 and each R ₁ is independently selected and is an R group, ie, a monopentaerythritol ester.
b) a compound of formula I (n is 2, R ₁ is each independently selected and R group, ie a dipentaerythritol ester), and c) a compound of formula I (n is 3; Each R ₁ is independently selected and is an R group, ie a tripentaerythritol ester);
Including:
For example, the polyol ester lubricant composition comprises at least a) a compound of formula I wherein n is 1 and each R ₁ is independently selected and is an R group, ie, a monopentaerythritol ester.
b) a compound of formula I (n is 2, R ₁ is each independently selected and R group, ie a dipentaerythritol ester), and c) a compound of formula I (n is 3; Each R ₁ is independently selected and is an R group, ie a tripentaerythritol ester);
d) a compound of formula I which is a pentaerythritol oligomer of four or more pentaerythritol monomer groups;
including.

In other embodiments, the polyol ester lubricant composition comprises a mixture of a compound of formula I and an ester of another neopentyl polyol, such as a compound of formula I, and predominantly a straight chain C _{5 of} trimethylolpropane. And mixtures thereof with ₁₀ alkyl carboxylate esters.

In one embodiment, the polyol ester lubricant composition is:
a) about 30 to about 55% by weight, for example about 40 to about 50% by weight, of a compound of formula I, wherein n is 1, each R ₁ is independently selected and is an R group,
b) about 1 to about 20% by weight of a compound of formula I, wherein n is 2, each R ₁ is independently selected and is an R group, eg about 10 to about 20% by weight,
c) about 1 to about 10% by weight of a compound of formula I, wherein n is 3, each R ₁ is independently selected and is an R group, for example about 3 to about 10% by weight,
d) about 25 to about 45% by weight of a compound of formula I which is a pentaerythritol monomer group of 4 or more pentaerythritol oligomers, for example about 30 to about 40% by weight;
A mixture of
Its weight percent is relative to all compounds of formula I present in the lubricant composition, and the mixture can be blended with, for example, the trimethylolpropane ester of the present invention.

  In some embodiments, at least 50%, such as 60%, such as 75% by weight of all esters in the polyol ester lubricant composition is a compound of formula I, and in one embodiment 90% or more Are compounds of formula I. In other embodiments, 50%, 60%, 75%, 90% or more of all esters in the polyol ester lubricant composition are esters of trimethylolpropane.

  Each R is independently an alkylcarbonyl of 5 to 10 carbon atoms, which may be linear or branched, but generally at least 60 mol% of the alkylcarbonyl groups are linear and all 75 mol%, 90 mol%, 95 mol% or more of the alkylcarbonyl chain is linear. Often R is selected from alkylcarbonyls of 7 to 10 carbon atoms, for example R is selected from alkylcarbonyls of 7, 8 and 10 carbon atoms. In one embodiment, at least 50 mol%, such as at least 60, 75, 80 or at least 90 mol% is linear alkylcarbonyl with 7, 8 and 10 carbon atoms. In one embodiment, essentially all of the alkylcarbonyl is a straight chain alkylcarbonyl of 7, 8 and 10 carbon atoms.

  In one particular embodiment, at least 60%, such as at least 70, 80 or at least 90% or more of the esters in the compound of formula I comprise alkanoyl (R is n-heptanoyl).

  The carboxy group of other neopentyl polyol esters, such as trimethylol propane ester, in the lubricant composition is selected from the same alkylcarbonyl as described for R of the compound of formula I.

A compound of formula I that is a pentaerythritol oligomer may be a linear or branched oligomer. For example, an oligomer of formula I (n is 4), ie an oligomer of formula III, can be a linear pentaerythritol tetramer when all R ₁ groups are alkylcarbonyl. However, a number of R ₁ groups can be pentaerythritol groups of formula II, for example when the R ₁ group marked with an arrow is a group of formula II, the result is a branched pentaerythritol pentamer That is, it will be a branched oligomer of 5 pentaerythritol monomer units.

Thus, an oligomer of formula I having 4 or more pentaerythritol monomer units need not have n of 4 or more in formula I. Formula IV is an oligomer of Formula I having 4 pentaerythritol units (n is 3 and one R ₁ group is a pentaerythritol group):

And the compound of formula V is an oligomer of formula I having 5 pentaerythritol units (n is 3 and the two R ₁ groups are pentaerythritol).

  Other compounds similar to the compounds of formula I described above may be present in the working fluid. For example, incomplete esterification results in compounds in which one or more R groups are hydrogen, and higher oligomers that exhibit a higher degree of branching are possible depending on the synthetic method used.

  Mixtures of the above esters can be made by simple esterification of suitable polyols, such as pentaerythritol, dipentaerythritol, and poly (pentaerythritol), which yields individual polyols as starting materials. There is a need.

The polyol ester of the composition of the present invention is conveniently made by a two-stage process incorporating a first step similar to that described in US Pat. No. 3,670,013. In a first step, the molar ratio of carboxyl groups to hydroxyl groups is less than 1: 1, such as about 1: 4 to about 1: at 2, pentaerythritol, strong acid catalyst, and C ₅ -C ₁₀ monocarboxylic acid Alternatively, the acid mixture is charged. Examples of suitable strong acid catalysts include mineral acids such as sulfuric acid, hydrochloric acid and the like, and sulfonic acids such as benzene sulfonic acid, toluene sulfonic acid, polystyrene sulfonic acid, methane sulfonic acid, ethane sulfonic acid and the like. The reaction mixture is then heated to a temperature of about 150 ° C. to about 250 ° C., generally about 170 ° C. to about 200 ° C., while continuously removing water vapor from the reaction vessel, typically by applying a vacuum.

  The carboxylic acid co-distilled with the water vapor is returned to the reactor or replaced by adding a carboxylic acid substitution moiety. Some degree of pentaerythritol oligomerization takes place under conditions that result in a mixture of pentaerythritol, dipentaerythritol, tripentaerythritol and higher polypentaerythritol partial esters. The amount of oligomerization, and thus the viscosity, can be controlled by the length of time that allows the first step reaction to proceed at an elevated temperature. This can be determined by experiments such as checking the viscosity of the reaction mixture or performing a spectroscopic measurement, or recovering a calculated amount of water corresponding to the desired amount of water resulting from the formation of ester groups. The pentaerythritol ether linkage is formed by dimer or oligomer formation.

  Optionally, at the end of the first reaction step, the acid catalyst is neutralized with alkali.

In the second step of the process, esterification of the partial ester is complete. Therefore, a further C ₅ -C ₁₀ monocarboxylic acid or acid mixture, optionally the esterification catalyst is added to the reaction mixture. The additional carboxylic acid is the same or different from that used in the first step and is generally added in an amount that gives a 10-25% excess of carboxyl groups relative to hydroxyl groups. The reaction mixture is then heated to complete esterification under known conditions for ester formation.

  In the second step, a known catalyst such as an acid catalyst, an acid salt, a metal catalyst such as an organometallic catalyst, clay, or the like may be used. Good results have been obtained using tin oxalate and / or activated carbon, and in some cases it was not necessary to add a catalyst to the second step.

  The resulting ester mixture may be used without further purification, or it may be distilled, treated with an acid scavenger to remove traces of acidity, or treated with a moisture scavenger to remove moisture. And / or may be purified using conventional techniques, such as filtration to improve clarity.

  Dipentaerythritol is often present at the beginning of the process, especially since industrial purity pentaerythritol starting materials often contain some of this dimer. Small amounts of other pentaerythritol oligomers may also be present in the starting material.

  For example, according to this process, 25 moles of pentaerythritol are mixed with about 50 moles of n-heptanoic acid. Since pentaerythritol contains four hydroxyl groups, this amount of acid represents only half of the stoichiometric equivalent required for complete esterification. A catalytic amount of sulfuric acid or methanesulfonic acid is also added. Although about 10 millimoles of acid catalyst is often sufficient, there is no limit to the amount of acid used, and higher amounts are common. The mixture is agitated or stirred and heated to about 160 to about 200 ° C., such as about 170 to about 180 ° C., and water is collected, for example, in a Dean-Stark trap. The length of time that the reaction is heated depends on how much polymerization is desired.

  The reaction is then cooled and the acid catalyst is neutralized by the addition of a base, such as sodium hydroxide. Sufficient carboxylic acid to react with the remaining hydroxyl groups, such as additional n-heptanoic acid or a mixture of heptanoic acid and other carboxylic acids, and optional catalyst is added to complete the esterification. The reaction mixture is heated with mixing and water is recovered until the reaction is complete. In this step, depending on whether a catalyst is used and what the catalyst is, the temperature of the reaction will vary, and therefore higher or lower temperatures may be encountered than used in the first step.

  The amount of carboxylic acid included in the initial charge varies greatly as long as it is less than the amount required to esterify all the hydroxy groups present. As noted above, dipentaerythritol and polypentaerythritol are included in the initial charge of the starting material, in which case utilization on the dimer and polymer in determining the amount of carboxylic acid added. The amount of different hydroxyl groups possible must be considered.

  One advantage of this process is that it can start with readily available starting materials. Another advantage is that the degree of oligomerization can be controlled by simply changing the length of time the reaction mixture is exposed to strong acid at high temperatures, thereby effectively controlling the viscosity of the resulting ester composition. Is possible. That is, the longer the reaction time at a high temperature in the first step, the higher the viscosity. Polyol ester compositions containing an ester of formula I as defined above are all conveniently produced by this process.

  The ester product of the previous process may be blended with other neopentyl polyol esters, such as neopentyl glycol and trimethylolpropane esters, to produce a lubricant composition. In other embodiments, the lubricant composition comprises an ester of trimethylolpropane, optionally an ester of another neopentyl polyol that is not a compound of formula I.

  Blend a polyol ester ester with other lubricants such as poly alpha olefins, polyalkylene glycols, alkylated aromatics, polyvinyl ether, mineral oil, other ester-based lubricants, vegetable oils to form a lubricant composition You can also However, a mixture of polyol esters as defined above is the majority or only component of a lubricant composition that is mixed with a hydrocarbon refrigerant to produce a working fluid and uses it with a hydrocarbon refrigerant. Care must be taken when adding other lubricant base stocks so that the desired properties of the polyol ester composition are not compromised.

  The lubricant composition has a viscosity of about 22 cSt to about 125 cSt, more typically 25 cSt to 100 cSt, measured at 40 ° C. without refrigerant, for example, about 25 to about 60 cSt measured at 40 ° C. without refrigerant. Or having a viscosity of about 25 to about 45 cSt.

  It is also important that the viscosity remain as constant as possible over the temperature range commonly encountered. The ester lubricant composition of the present invention also exhibits a consistent viscosity over a wide range of temperatures, as indicated by its high viscosity index, eg, 120 or more, generally 130 or more, eg, 140 or more.

  Because of that particular combination of physical properties, the polyol ester lubricant composition of the present invention is ideally suited for working fluids containing hydrocarbon refrigerants. Other similar polyol ester lubricants have various useful properties, but do not fully demonstrate performance criteria, i.e., are required for hydrocarbon-based working fluids and are found in the ester mixtures of the present invention. It shows neither sexuality nor hydrocarbon miscibility.

  The mixing ratio of the polyol ester lubricant and the refrigerant is not particularly limited, but the lubricant may be present in a ratio of 1 to 500 parts by weight, more preferably 2 to 400 parts by weight per 100 parts by weight of the refrigerant. In one embodiment, the working fluid includes about 5-20% by weight of ester lubricant based on the weight of lubricant and refrigerant.

  In addition to hydrocarbons, the working fluids of the present invention may include other components common in the art, such as additives, other lubricants, and refrigerants.

For example, other refrigerants that may be present in the working fluid include CO ₂ , carbon halide, ammonia, etc., and in many embodiments of the invention, C _1-6 hydrocarbons are the majority refrigerant, Hydrocarbons are often the only refrigerant.

  Examples of the halogenated carbon refrigerant include fluorocarbon and hydrofluorocarbon compounds such as carbon tetrafluoride (R-14), difluoromethane (R-32), 1,1,1,2-tetrafluoroethane (R-134a), 1 , 1,2,2-tetrafluoroethane (R-134), pentafluoroethane (R-125), 1,1,1-trifluoroethane (R-143a) and tetrafluoropropene (R-1234yf). And mixtures containing fluorocarbons, hydrofluorocarbons and / or hydrocarbons are well known and can be used in the working fluids of the present invention.

  Common additives that may also be present in the working fluid include antioxidants, extreme pressure additives, antiwear additives, friction reducing additives, antifoaming agents, profoaming agents, metal inertness Agents, acid scavengers and the like.

  Examples of antioxidants that can be used include phenolic oxidations such as 2,6-di-tert-butyl-4-methylphenol and 4,4′-methylenebis (2,6-di-tert-butylphenol). Inhibitors; p, p-dioctylphenylamine, monooctyldiphenylamine, phenothiazine, 3,7-dioctylphenothiazine, phenyl-1-naphthylamine, phenyl-2-naphthylamine, alkylphenyl-1-naphthylamine, and alkylphenyl-2-naphthylamine Amine antioxidants such as; sulfur-containing antioxidants such as alkyl disulfides, thiodipropionic esters and benzothiazoles; and zinc dialkyldithiophosphates and zinc diaryldithiophosphates.

  Examples of extreme pressure, antiwear, friction reducing additives that can be used include zinc compounds such as zinc dialkyldithiophosphates and zinc diaryldithiophosphates; thiodipropionic esters, dialkyl sulfides, dibenzyl Sulfur compounds such as sulfides, dialkyl polysulfides, alkyl mercaptans, dibenzothiophenes and 2,2′-dithiobis (benzothiazoles); Ash wear-resistant additives; phosphorus compounds such as tricresyl phosphate and triaryl phosphate such as trialkyl phosphate; dialkyl or diaryl phosphate; trialkyl phosphite or triaryl phosphite; Amine salts of alkyl and dialkyl phosphates, such as dodecylamine salts of ter; dialkyl or diaryl phosphites; monoalkyl or monoaryl phosphites; perfluoroalkyl polyethers, trifluorochloroethylene polymers and fluorinated graphite Fluorine compounds; silicon compounds such as fatty acid-modified silicone silicon compounds; molybdenum disulfide, graphite and the like. Examples of organic friction modifiers include long chain fatty amines and glycerol esters.

  Examples of antifoaming and prefoaming agents that can be used include silicone oils such as dimethylpolysiloxane and organosilicates such as diethyl silicate. Examples of metal deactivators that can be used include benzotriazole, tolyltriazole, alizarin, quinizarin and mercaptobenzothiazole. In addition, epoxy compounds such as phenyl glycidyl ethers, alkyl glycidyl ethers, alkyl glycidyl esters, epoxy stearates and epoxidized vegetable oils, organotin compounds and boron compounds may be added as acid scavengers or stabilizers.

  Examples of moisture scavengers include trialkyl orthoformates such as trimethyl orthoformate and triethyl orthoformate, ketals such as 1,3-dioxacyclopentane, and amino ketals such as 2,2-dialkyloxazolidine.

  The working fluid comprising the polyol ester of the present invention and a refrigerant can be used in a wide variety of refrigeration and thermal energy transfer applications. Non-limiting examples range from small window air conditioners, centralized home air conditioners to light industrial air conditioners and large industrial units for factories, office buildings, and apartment buildings. An air conditioner is mentioned. Refrigeration applications include small household appliances such as household refrigerators, freezers, water coolers, vending machines and ice makers, large-scale refrigerated warehouses and ice skating rinks. A grocery store cascade refrigeration and freezer system would also be included in industrial applications. Thermal energy transfer applications include heat pumps and hot water heaters for domestic heating. Applications related to transportation include automotive and truck air conditioning, refrigerated semi-trailers and maritime and rail transport refrigerated containers.

  The types of compressors useful for the above applications can be classified into two broad categories: positive displacement compressors and dynamic compressors. Positive displacement compressors increase the refrigerant vapor pressure by reducing the volume of the compression chamber by the work applied to the compressor equipment. Positive displacement compressors include many styles of compressors currently in use, such as reciprocating compressors, rotary compressors (rolling pistons, rotor blades, uniaxial, biaxial) and orbits (scroll or trochoid). The dynamic compressor continuously increases the vapor pressure of the refrigerant by continuously transferring kinetic energy from the rotating member to the steam and subsequently converting this energy into a pressure increase. Centrifugal compressors operate on these principles.

Preparation of Esters and Comparative Examples Example 1: Polypentaerythritol ester A reactor equipped with a mechanical stirrer, thermocouple, temperature controller, Dean-Stark trap, condenser, nitrogen sparger, and vacuum source was charged with pentaerythritol (2. 88 mol) 392 g, n-heptanoic acid (5.54 mol) 720 g and a strong acid catalyst were charged. The initial charge had a molar ratio of carboxyl groups to hydroxyl groups of 1: 2.08, and the expected amount of water formed by esterifying the initial charge was 5.54 moles or about 100 grams. It was. The mixture was heated to a temperature of about 170 ° C., a vacuum was applied, the water produced in the reaction was collected in a trap, and the collected acid was returned to the reactor.

  After collecting 125 ml of water, the reaction mixture containing pentaerythritol, dipentaerythritol, tripentaerythritol, a partial ester of tetrapentaerythritol, and a higher oligomeric ester of pentaerythritol is cooled to about 134 ° C and n-octane is cooled. An additional 236 of n-heptanoic acid, along with 264.4 g (2.05 moles) of 6: 4 blend of acid: n-decanoic acid and a sufficient amount of alkali to neutralize the strong acid catalyst used in the first step 0.6 g (1.82 mol) was added. The reaction mixture was heated to 240 ° C. for about 8 hours, during which time 173 ml of water was collected, after which the hydroxyl number was KOH 6.4 mg / g.

  The reaction mixture was maintained at 240 ° C. for about another 3 hours, and excess acid was removed under vacuum until the acid number was less than 1.0 mg / g KOH. The mixture was cooled to 80 ° C. and the residual acidity was neutralized with alkali. The viscosity at 40 ° C. was 140 cSt, and the viscosity at 100 ° C. was 19.6 cSt.

  About 275 g of industrial pentaerythritol ester of n-heptanoic acid, n-octanoic acid and n-decanoic acid is added to the reaction product, about 47% monopentaerythritol ester, 14% dipentaerythritol ester, 7% tripentaerythritol ester % And a mixture of 32% esters of pentaerythritol oligomers of 4 or more pentaerythritol monomer groups. The resulting product was dried, filtered, and showed the desired kinematic viscosity of 80 cSt at 40 ° C.

Example 2: Trimethylolpropane ester of caprylic acid A reactor equipped with a mechanical stirrer, thermocouple, temperature controller, Dean-Stark trap, condenser, nitrogen sparger, and vacuum source was charged with trimethylolpropane and about 15 mol%. An excess amount of caprylic acid (which is a 6: 4 blend of n-octanoic acid: n-decanoic acid) was charged.

  The reaction mixture was heated at 240 ° C., a vacuum was applied, the water produced in the reaction was collected in a trap, and the collected acid was returned to the reactor. The reaction was maintained at 240 ° C. until the hydroxyl number dropped to less than 2.5 mg KOH / gram. The reaction was then maintained at 240 ° C. for about another 3 hours and a vacuum was applied to remove excess acid until the acid number was less than 1.0 mg / g KOH. The mixture was cooled to 80 ° C. and the residual acidity was neutralized with alkali. The kinematic viscosity of the polyester product was 19 cSt at 40 ° C. and 4.4 cSt at 100 ° C.

Example 3
The esters of Example 1 and Example 2 were blended at a ratio of 2: 3 to obtain a blended polyol ester having a kinematic viscosity at 40 ° C. of about 32 cSt. The physical properties of the product are shown in Table 1.

Example 4: Pentaerythritol ester of caprylic acid An industrial purity pentaerythritol (pentaerythritol) was added to a reactor equipped with a mechanical stirrer, thermocouple, temperature controller, Dean-Stark trap, condenser, nitrogen sparger, and vacuum source. 90 wt% and dipentaerythritol 10 wt%) and about 15 mol% excess caprylic acid (which is a 6: 4 blend of n-octanoic acid: n-decanoic acid) was charged.

  The reaction mixture was maintained at 240 ° C. for about another 3 hours, and excess acid was removed under vacuum until the acid value was less than 2.5 mg / g KOH. The mixture was cooled to 80 ° C. and the residual acidity was neutralized with alkali. The kinematic viscosity of the polyester product was 31 cSt at 40 ° C. and 6.2 cSt at 100 ° C. The physical properties of the product are shown in Table 1.

Comparative Example 1
Comparative Example 1 is an 84:16 (weight ratio) blend of two polyol esters having kinematic viscosities 7.5 cSt and 44 cSt at 40 ° C. The 7.5 cSt ester is the reaction product of neopentyl glycol and 2-ethylhexanoic acid. The 44 cSt ester is the reaction product of pentaerythritol and 2-ethylhexanoic acid. The physical properties are shown in Table 1.

Comparative Example 2
Comparative Example 2 is an ISO32 grade alkylated benzene commercially available from Virginia KMP Corporation as SPECIAL DUTY AB150. The physical properties of the product are shown in Table 1.

Load bearing performance Extreme pressure bearing performance of lubricants under boundary lubricant conditions (direct contact between metals).

.
A steel journal held in place by brass shear pins is rotated with respect to two fixed V-shaped blocks to obtain a 4-line contact. The specimen and its support jaws are immersed in an oil sample cup for oil lubricant. The journal is driven at 250 rpm and a load is applied to the V-shaped block by means of a nutcracker lever arm and a spring gauge. The brass shear pin is used to actuate the load during the test and continuously apply the ramp load until the brass shear pin shears or the test pin breaks. Torque from the gauge attached to the Falex lubricant tester is reported in pounds (Table 2). The results of load bearing tests demonstrate the superior load bearing performance of the lubricants of the present invention when compared to common branched acid polyol ester lubricants and alkylated benzene lubricants.

Lubricity Performance The lubricity of the lubricant was evaluated using a mini traction machine (MTM) commercially available from PCS Instruments. In this test, the lubricity / friction properties of the lubricant are measured by two different techniques using a rotating ball-on-disk type. In the first mode of operation, all of the lubrication modes such as boundary (metal-to-metal contact), mixed film (fluid film-to-metal mixture contact), elastohydrodynamic (fluid film) and hydrodynamic (fluid film) Over a range, the lubricity is measured. Ball and disk speeds increase simultaneously with a slide-roll-ratio of 50% and the coefficient of friction is measured as a function of constant load and constant entrainment speed. This means that the ball always moves at 50% of the rotating disk speed when the disk speed increases. As the speed of the disc and ball increases, the lubricant moves to the metal-to-metal contact surface, increasing the pressure at the front of the rotating / sliding contact. At some point, the speed is high enough and the pressure is sufficient to entrain the lubricant between the ball contact and the disk contact. At this point, the system is under hydrodynamic lubrication; meaning that lubrication is controlled by the integrity of the film between the ball and disk. A low friction coefficient at a high entrainment speed means that the lubricating performance of the lubricant is excellent. Table 3 shows the coefficient of friction at 40 ° C., 80 ° C. and 120 ° C. at various entrainment speeds for Example 1, Comparative Example 1 and Comparative Example 2.

  In the second mode of operation, the lubricity of the lubricant is evaluated under perfect fluid film conditions (hydrodynamic lubrication). In this test, the coefficient of friction is measured at various slip rates (ie, the ball and disk rotate at different speeds relative to each other) at constant load and temperature. For both modes of operation, testing is generally performed at several different fixed temperatures: in this case 40, 80 and 120 ° C. and a load of 30N. The coefficient of friction is a direct measure of the lubricity of the lubricant; the lower the coefficient of friction, the higher the lubricity of the lubricant. It is important to note that in this test it usually makes sense to compare equivalent ISO viscosity grade lubricants. Table 4 shows the coefficient of friction at various slip rates for Example 1, Comparative Example 1 and Comparative Example 2 at 40, 80 and 120 ° C.

  The coefficient of friction is consistently lower for the lubricant of the present invention relative to the comparative lubricant.

Thermophysical properties of the lubricant / propane mixture Equipment for measuring the viscosity and composition of the lubricant / propane mixture as a function of temperature and pressure includes temperature-controlled circulation loop-containing pumps, mass flow / density meters, high-pressure viscometers, bulk Consists of a lubricant / refrigerant reservoir and a pressure transducer. Thermocouples are located directly at multiple locations in the loop, as well as mass flow meters and viscometers. The loop design allows continuous circulation of the liquid mixture and provides agitation to achieve a rapid vapor-liquid equilibrium. Lubricant was initially charged to the system gravimetrically (± 0.02 g) and the circulation loop was cooled to −10 ° C. Next, propane was charged gravimetrically (± 0.02 g) from a small stainless steel sample cylinder in the amount necessary to obtain the desired bulk propane / lubricant composition. For safety reasons, a vapor space correction was applied to the composition to account for propane in the gas phase, because the loop did not fill to capacity and a small vapor space was present at the top of the bulk reservoir. After being charged into the system, a gear pump was used to circulate liquid through each of the measuring devices. The pressure of the bulk mixture was measured up to ± 0.20 bar. The liquid density was measured to ± 0.002 g / cc using a Micromotion CMF10 mass flow meter. The viscosity of the liquid was measured to ± 1.0% of the value using a Cambridge viscosity high pressure electromagnetic viscometer. Incorporate two high-pressure viewing windows in the viscometer housing to allow liquid miscibility observation and check the mixture for possible phase separation if the bulk mixture pressure is within 1% of the saturated refrigerant pressure can do. Measurements were collected in the temperature range -10 ° C to 120 ° C (± 0.5 ° C), and the composition of propane in the lubricant was 0 to 20 wt%.

  For each lubricant, a Daniel chart was created that relates the kinematic viscosity of the refrigerant / lubricant mixture to temperature, pressure (isobar) and composition (straight) (Figures 1-3). From the comparison of the charts, the propane solution having the lubricant of Example 1 (see FIG. 1) is the propane solution having the lubricant of Comparative Example 1 (see FIG. 2) or the propane solution having the lubricant of Comparative Example 2 (see FIG. 1). 3), it has been demonstrated to exhibit a high kinematic viscosity (ie low dilution) at high temperatures at a given pressure / temperature combination. Furthermore, the lubricant / propane mixtures of the present invention generally have a low viscosity at low temperatures and low refrigerant concentrations (conditions normally observed in compressors at the start of operation). This low viscosity means that the lubricant imparts a low viscous resistance to the compressor, resulting in less energy consumption, particularly at the start of operation.

Claims (10)

i) a C _1-6 hydrocarbon refrigerant;
ii) compounds of formula I

(In the formula, n is an integer of 1 to 12,
Each R is independently alkylcarbonyl having 5 to 10 carbon atoms;
Each R ₁ is independently selected and the R group or substituent of formula II:

Either
At least 80 mol% of all R groups are independently selected from linear alkylcarbonyl having 7 to 10 carbon atoms)
A polyol ester lubricant composition having a kinematic viscosity at 40 ° C. of 22 to 125 cSt, a viscosity index greater than 140,
A working fluid for a heat transfer device, comprising:
The polyol ester lubricant composition is
a) 30-55% by weight of a compound of formula I (n is 1, R ₁ is independently selected and is an R group),
b) 1 to 20% by weight of a compound of the formula I (n is 2, R ₁ is independently selected and is an R group ) ,
c) 1-10% by weight of a compound of the formula I (n is 3, R ₁ is independently selected and is an R group),
d) 25-45% by weight of a compound of formula I which is a pentaerythritol oligomer of 4 or more pentaerythritol monomer groups,
Including
The weight percent is a percentage of the weight of all compounds of formula I present in the lubricant composition;
Working fluid.   The working fluid of claim 1, wherein at least 90 mol% of all R groups are independently selected from linear alkylcarbonyls of 7, 8 and 10 carbon atoms. 2. The refrigerant in which only the C _1-6 hydrocarbon refrigerant is present, and one or more refrigerants selected from the group consisting of ethane, propane, propene, butane, isobutane, butene and isobutene. The working fluid described in 1.   The working fluid according to claim 1, wherein the refrigerant is one or a plurality of refrigerants selected from the group consisting of propane, butane, isobutane, butene, and isobutene.   In addition to components i) and ii), selected from the group consisting of mineral oil, polyalphaolefins, alkylbenzenes, carboxylic acid esters other than compounds of formula I, polyethers, polyvinyl ethers, perfluoropolyethers, and phosphate esters The working fluid of claim 1, further comprising one or more of the following.   Further comprising one or more antioxidants, extreme pressure additives, antiwear additives, friction reducing additives, antifoaming agents, prefoaming agents, metal deactivators, acid scavengers or mixtures thereof. Item 4. The working fluid according to Item 1. The polyol ester lubricant composition comprises a mixture of a compound of formula I and a _C5-10 alkyl carboxylate ester of trimethylolpropane, wherein at least 80 mol% of all alkylcarbonyls of the ester of trimethylol polyol are from 7 to 7 carbon atoms. The working fluid according to claim 1, wherein 10 linear alkylcarbonyls are independently selected.   7. A working fluid according to claim 6, wherein at least 50% by weight of all esters in the polyol ester lubricant composition is a compound of formula I.   7. A working fluid according to claim 6, wherein at least 75% by weight of all esters in the polyol ester lubricant composition is a compound of formula I.   7. A working fluid according to claim 6, wherein at least 90% by weight of all esters in the polyol ester lubricant composition is a compound of formula I.