A LUBRICANT ESTER

Abstract: A lubricant ester having enhanced hydrolytic stability is disclosed. The ester is a mono or diester of 2-ethyl-2-butyl-1,3-propanediol or an alkoxylate thereof and at least one carboxylic acid having 5-10 carbon atoms. The invention in a further aspect refers to a refrigeration working fluid comprising said ester and at least one halocarbon refrigerant.

Description: A LUBRICANT ESTER The present invention relates to a lubricant ester having enhanced hydrolytic stability The ester is in particular intended as lubricant in refrigeration systems The invention refers in a further aspect to a refrigeration working fluid comprising at least two components, whereby at least one is a halocarbon refrigerant and at least one is said lubricant ester Esters and polyesters used as lubricants are well-known in the art and used in a large number of application including automotive and aviation oils, metal working fluids, gear oils, turbo oils, hydraulic fluids and refrigeration lubricants Refrigeration systems such as refrigerators, freezers, air conditioners, heat pumps and the like normally include a circulating and heat transferring refrigerant Lubricants for refrigeration systems must be compatible and miscible within a wide range of temperatures with said refrigerant so that resulting refrigeration working fluids obtain a non-obstructing composition and so that moving parts in the system are properly lubricated The properties and performances of halocarbon refrigerant fluids are well-known and so is also the environmental effects of those containing chlorine, which fluids presently to an increasing extent are replaced by substantially chlorine free compounds such as fluorocarbons Ester and polyester based synthetic lubricants are also well-known products which to a high extent is used as lubricants in various refrigeration systems Many of the presently used refrigeration lubricants, mineral based as well as synthetic, exhibit an overall limited compatibility, miscibility and lubricating ability or most commonly a temperature dependent compatibility, miscibility and lubricating ability, especially at low temperature and in combination with fluorocarbons The development efforts in regard of lubricants for various refrigeration system have for some time, more or less successfully, been focused on obtaining lubricating esters and polyesters being at all temperatures, especially at low temperatures, compatible and miscible with said refrigerants, especially fluorocarbon refrigerants The lubricant must in order to provide proper lubrication over a wide range of temperatures have a low pour point and a high viscosity index The problem of obtaining excellent miscibility at a very wide range of temperatures is most pronounced when chlorine containing halocarbon refrigerants and other heat transfer fluids are replaced with substantially chlorine free fluorocarbons The fluorocarbons considered to be the most interesting and thus in focus for said development are isomers of tetrafluoroethane, such as 1 , 1 , 1 ,2-tetrafluoroethane commonly known as "Refrigerant 134a" The solubility in fluorocarbons is for many esters and polyesters low in general or reduced at low or extremely low temperatures. The solubility in fluorocarbons is often judged by the temperature, the so called miscibility temperature, at which a solution of a compound such as said esters and polyesters in above mentioned "Refrigerant 134a" separates. The miscibility temperature of a 30% by weight solution of a lubricant ester is often to be found within the interval of + 10°C and - 30°C. A synthetic lubricant must be formulated to provide required lubricating properties at a temperature interval as wide as possible. A well performing lubricant should to provide adequate lubricity have as invariable a viscosity as possible over a wide range of temperatures, however, yet being miscible with the refrigerant. Miscibility at very low temperatures is especially difficult to obtain. An increased as well as a decreased viscosity normally negatively influence the lubricating ability of the ester or polyester. A lubricant must, furthermore, in most system exhibit a very high thermal stability and a high flash point. Major drawbacks in the use of lubricating esters and polyesters are that many esters and polyesters have a limited thermal, chemical and especially hydrolytic stability and resistance. These properties are dependent of for instance the choice of raw materials, the purity of said raw materials, the number of ester links and the acid and hydroxyl values. The present invention provides a lubricant ester primarily intended as lubricant in various refrigeration systems, whereby resulting refrigeration working fluids can comprise said ester. The ester can also advantageously be used in automotive and aviation oils, metal working fluids, gear oils, turbo oils, hydraulic fluids. The lubricant ester has an enhanced hydrolytic stability as well as excellent miscibility in halocarbon, especially fluorocarbon, refrigerants. The ester is a mono or preferably a diester of a 2-ethyl-2-butyl- l ,3-proρanediol or alkoxylated, such as ethoxylated, propoxylated, butoxylated or phenylethoxylated, 2-ethyl-2-butyl- - 1 ,3-propanediol and at least one monocarboxylic acid having 5- 10 carbon atoms The superior and excellent properties are quite unexpected and contrary to expected and predicted properties, such as lubricity, compatibility and especially hydrolytic stability compared to other 2,2-substituted 1 ,3-propanediols, such as 2,2-diethyl-l ,3-propanediol and 2-methyl-2-ethyl-l ,3-propanediol Preferred embodiments of the present invention are mono or preferably diesters wherein the carboxylic acid is selected from the group consisting of valeric acid, isovaleric acid, hexanoic acid, isohexanoic acid, heptanoic acid, isoheptanoic acid, octanoic acid, isooctanoic acid, nonanoic acid or isononanoic. Further preferred carboxylic acids are mono, di or trialkyl hexanoic acids, such as 2-methylhexanoic acid, 2-ethylhexanoic acid, 2,2-dimethylhexanoic acid, 3,5,5-trimethylhexanoic acid or mixtures thereof and/or therewith The ester is in the most preferred embodiments a diester wherein the carboxylic acid is isooctanoic acid or 3 ,5, 5-trimethylhexanoic acid Alkoxylation of 2-ethyl-2-butyl- l ,3-propanediol is performed by adding, in accordance with known procedures, an alkylene oxide, such as ethylene oxide, propylene oxide, butylene oxide and/or phenylethylene oxide, to said diols The molar ratio is preferably 1 1 to 1 20 as diol to alkylene oxide In a further aspect the present invention refers to a refrigeration working fluid comprising at least one halocarbon refrigerant, such a fluorocarbon or a chlorofluorocarbon, and in addition thereto said mono or diester The halocarbon s suitably a fluoroethane selected from the group consisting of ) a difluoroethane, such as 1 , 1 -difluoroethane, i) a trifluoroethane, such as 1, 1 , 1-trifluoroethane, ii) a tetrafluoroethane, such as 1 , 1 , 1 ,2-tetrafluoroethane, and v) a pentafluoroethane A refrigeration working fluid comprises normally 1 -60% by weight of the ester and 40-99% by weight of the halocarbon and optionally in addition thereto one or more additives such as stabilisers, antioxidants and the like Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent The following preferred specific embodiments are, therefore, to be construed as merely illustrative and not limitative of the remainder of the disclosure in any way whatsoever Embodiment Examples 1 -8 show Example 1 Preparation of a lubricant ester from 2-ethyl-2-butyl- l ,3-propanediol and isooctanoic acid Example 2 Preparation of a lubricant ester from 2-ethyl-2-butyl- l ,3-propanediol and 3 ,5,5-trimethylhexanoic acid Example 3 Evaluation of the lubricity of the esters of Examples 1 and 2 Example 4 Determination of the compatibility of the esters of Examples 1 and 2 and a fluorocarbon Example 5 Evaluation of hydrolytic stability of the esters of Examples 1 and 2 Example 6 Preparation of a comparative lubricant ester from 2,2-diethyl- l ,3-propanediol and 3,5,5-trimethylhexanoιc acid Example 7 Preparation of a comparative lubricant ester from 2-methyl-2-ethyl- l ,3-propanediol and 3,5, 5-trimethylhexanoic acid Example 8 Hydrolytic stability of the esters according to Example 2, 6 and 7 Example 1 Preparation of a lubricant ester from 2-ethyl-2-butyl- l ,3-propanediol and isooctanoic acid 2 0 moles of 2-ethyl-2-butyl-l ,3-propanediol, 4 8 moles of isooctanoic acid, 45 0 g of heptane and 1 8 g of /?-toluenesulphonic acid were charged in a 4-necked reaction flask equipped with stirrer, pressure gauge, nitrogen inlet, thermometer, cooler and water trap (Dean-Stark) The temperature was during 1 50 minutes raised to 1 50°C The temperature was maintained until the esterification was completed Heptane and unreacted isooctanoic acid were now removed by vacuum distillation Obtained product was finally, at 130°C, neutralised with Ca(OH) 2 > followed by a vacuum evaporation of neutralisation water and by a filtration at 100°C Obtained ester exhibited the following properties Acid value, mg KOH/g 0 07 Hydroxyl value, mg KOH/g 4 Viscosity at 40°C, cSt 15 8 Viscosity index 70 Pour point, °C < - 42 Example 2 Preparation of a lubricant ester from 2-ethyl-2-butyl-l ,3-propanediol and 3,5,5-trimethylhexanoic acid 2 0 moles of 2-ethyl-2-butyl- l ,3-propanediol, 4 8 moles of 3 ,5,5-trimethylhexanoic acid, 47 0 g of heptane and 1 9 g of /?-toluenesulphonic acid were charged in a 4-necked reaction flask equipped with stirrer, pressure gauge, nitrogen inlet, thermometer, cooler and water trap (Dean-Stark) The temperature was during 150 minutes raised to 150°C The temperature was maintained until the esterification was completed Heptane and unreacted 3,5,5-trimethylhexanoic acid were now removed by vacuum distillation Obtained product was finally, at 1 30°C, neutralised with Ca(OH) 2 , followed by a vacuum evaporation of neutralisation water and by a filtration at 100°C Obtained ester exhibited the following properties. Acid value, mg KOH/g 0 05 Hydroxyl value, mg KOH/g 4 Viscosity at 40°C, cSt 23 2 Viscosity index 82 Pour point, °C < - 42 Example 3 The lubricity of the lubricant esters according to the invention (Examples 1 and 2) were evaluated according to ASTM D2266 (4-Ball Wear Test), whereby scar (mm) and acidity increase, ΔTAN (mg KOH/g) were determined Result Example 1 Example 2 Scar, mm 0.66 0 80 Acidity increase, ΔTAN, mg KOH/g + 0 01 + 0 04 The esters according to the invention exhibit a very low scar value implying excellent lubricity and an exceptionally low acidity increase implying excellent stability Example 4 The compatibility of the lubricant esters of Examples 1 and 2 and a fluorocarbon was determined as the temperature (the miscibility temperature) at which a 30% by weight solution of said esters in "Refrigerant 134a" (Solkan 134a, Solvay Fluor und Derivate GmbH, Germany) separates Result Example 1 Example 2 Miscibility temperature, 30% in " 134a", °C - 1 8 - 24 5 The esters according to the invention were at temperatures above the miscibility temperature miscible with "Refrigerant 134a" in all proportions Example 5 The hydrolytic stability of the lubricant esters of Example 1 , 2 and 3 were evaluated according to ASTM D2619-88 ("Coca Cola Test"), whereby ♦ the viscosity change at 40°C, ♦ the acidity increase, ester and water phase, and ♦ the percentage insolubles formed, was determined Result Example 1 Example 2 Viscosity change at 40°C, % + 0 9 - 0 8 Acidity increase, ester phase, mg KOH/g + 0 04 + 0 81 Acidity increase, water phase, mg KOH/g + 0 03 + 0 04 Insolubles, % 0 03 0 06 The results show that the lubricant esters according to the present invention exhibit a superior hydrolytic stability Example 6 (comparative example) Example 2 was repeated with the difference that 2 moles of 2,2-diethyl- 1 ,3- -propanediol was used instead of 2-ethyl-2-butyl-l ,3-propanediol Example 7 (comparative example) Example 2 was repeated with the difference that 2 moles of 2-methyl-2-ethyl- - 1 ,3-propanediol was used instead of 2-ethyl-2-butyl- l ,3-propanediol Example 8 The hydrolytic stability exhibited by esters according to Example 2, 6 and 7 was determined 0 2 g of the ester was dissolved in 50 ml of acetone and 2 mmole of NaOH and 10 ml of water were added The mixture was stored at room temperature and samples were drawn at pre-determined intervals for HPLC determination of released acid and most important unhydrolysed remaining ester Result Released acid, % Remai ining ester , % Time hrs Ex 2 Ex 6 Ex. 7 :x 2 Ex 6 Ex. 7 9 1 8 20 24 79 74 62 15 23 25 27 68 62 43 1 8 25 27 28 64 56 38 22 28 30 30 59 5 1 32 28 3 1 32 32 48 41 24 Above table shows that the 2-ethyl-2-butyl- l ,3-propanediol ester in comparison to other 2,2-substituted 1 ,3 -propanediols, exhibits a substantial and unpredictable increase in hydrolytic stability (up to 100%) with a substantially higher percentage unhydrolysed ester remaining in the prepared mixture

Claims: CLAIMS 1. A lubricant ester for automotive and aviation oils, metal working fluids, gear oils, turbo oils, hydraulic fluids and primarily lubricants in refrigeration systems, whereby resulting refrigeration working fluids can comprise said lubricant ester ch a r a cte ris ed i n, that the ester is a mono or diester of 2-ethyl-2-butyl-l,3-propanediol or alkoxylated 2-ethyl-2-butyl-l,3-propanediol and at least one monocarboxyhc acid having 5-10 carbon atoms 2. A lubricant ester according to Claim 1 c h a ra cte ris ed i n, that alkoxylation is performed by addition an alkylene oxide, such as ethylene oxide, propylene oxide, butylene oxide and/or phenylethylene oxide, to said diol at a molar ratio diol to alkylene oxide of 1 1 to 120 3. A lubricant ester according to Claim 1 or 2 ch a ra ct e ris ed i n, that the monocarboxylic acid is valeric acid, isovaleric acid, hexanoic acid, isohexanoic acid, 2-methylhexanoic acid, 2-ethylhexanoic acid, 2,2-dimethylhexanoic acid, 3,5,5-trimethylhexanoιc, heptanoic acid, isoheptanoic acid, octanoic acid, isooctanoic acid, nonanoic acid and/or isononanoic 4. A lubricant ester according to Claim 1 c h a ra cterised i n, that the ester is a diester wherein the carboxylic acid is isooctanoic acid or 3,5,5-trimethylhexanoic acid. 5. A refrigeration working fluid characterised in, that the fluid comprises at least two components, of which at least one is the lubricant ester of any the Claims 1-4 and at least one is a halocarbon refrigerant, such a fluorocarbon or a chlorofluorocarbon 6. A refrigeration working fluid according to Claim 5 c h ara cte rised i n, that the refrigerant comprises at least one fluoroethane selected from the group consisting of i) a difluoroethane, such as 1,1-difluoroethane, ii) a trifluoroethane, such as 1,1,1-trifluoroethane; iii) a tetrafluoroethane, such as 1,1,1,2-tetrafluoroethane; and iv) a pentafluoroethane. 7. A refrigeration working fluid according to Claim 5 or 6 c h ara c teris ed i n, that the fluid comprises 1-60% by weight of the ester and 40-99% by weight of the halocarbon and optionally in addition thereto one or more additives such as stabilisers, antioxidants and the like.

Inventors: OGEMARK KEITH, SJOEGREEN CARL-AXEL, SOERENSEN KENT, OGEMARK, KEITH, SJOEGREEN, CARL-AXEL, SOERENSEN, KENT
Applicants: OGEMARK KEITH, PERSTORP AB, SJOEGREEN CARL AXEL, SOERENSEN KENT, OGEMARK, KEITH, SJOEGREEN, CARL-AXEL, SOERENSEN, KENT
Application year: 1997
Main classification: C10M105
IPC codes: C09K5, C10M105, C10M107