WO1993014176A1

WO1993014176A1 - Refrigerant compositions

Info

Publication number: WO1993014176A1
Application number: PCT/US1992/010849
Authority: WO
Inventors: Joel F. Carpenter
Original assignee: Ethyl Corporation
Priority date: 1992-01-10
Filing date: 1992-12-15
Publication date: 1993-07-22
Also published as: US5240629A

Abstract

A lubricant comprising at least one ester of an alkanepolyoic acid containing at least four carboxyl groups is used in conjunction with a refrigerant, preferably a fluorohydrocarbon refrigerant, to form a refrigeration composition.

Description

REFRIGERANT COMPOSITIONS

Field of Invention

This invention relates to compositions for use in refrigeration systems and more particularly to such compositions comprising a refrigerant and at least one ester of an alkanepolyoic acid as a lubricant.

Background

Many natural and synthetic materials are known to be useful as lubricants, their utility in particular applications depending on factors such as their stability and viscosity under the conditions of use, their pour points, and their compatibility with any materials with which they will be used.

In refrigeration applications (e.g., home-use or industrial-use refrigerators, freezers, or air conditioners for buildings, automobiles, airplanes, and other vehicles), the need to replace chlorofluorocarbon refrigerants with a refrigerant having lesser ozone-depleting potential has made it important to find lubricants which would be suitable for use with 1,1,1,2-tetrafluoroethane (R-134a), a refrigerant that has been reported to have an ozone depletion potential of zero. Mineral oils, usually the refrigeration lubricants of choice in the past, cannot be utilized in this application because of incompatibility with R-134a.

As shown, e.g., in Jolley, "New and Unique Lubricants for Use in Compressors Utilizing R-134a Refrigerant," pp. 145-152 (a paper presented at the ASHRE/Refrigera- tion/ Compressor Engineering Conference at Purdue, July 1990), oils of various types, including polyalkylene glycols, esters, and amides, have been found to have sufficient compatibility with R-134a to justify further investigation. However, there is still a need for lubricants to be used in this application. U.S. Patent 4,436,641 (Stelz et al.) teaches that di- or triesters of di- or tricafboxylic acids are useful as lubricants in refrigeration compositions containing various rialocarbon refrigerants. - ? -

Summary of Invention

The invention resides in refrigeration compositions comprising a refrigerant and, as a lubricant, at least one ester of an alkanepolyoic acid containing at least four carboxyl groups.

Detailed Description

The refrigerants with which the novel lubricants are employed may be one or more of a wide variety of such materials, e.g., ammonia; alcohols such as methanol and ethanol; glycols such as ethylene and propylene glycols; and hydrocarbons such as methane, ethane, propane (R-290), butane, ethylene, and propylene. However, they are more commonly halocarbons and/or halohydrocarbons such as chlorotrifluorometh- ane, dichlorodifluoromethane, dichlorofluoromethane, chlorodifluoromethane (R-22), l,2,2-trifluoro-l,l,2-trichloroethane, l,l-dichloro-2,2,2-trifluoroethane (R-123), 1,1- dichloro-1-fluoroethane, l-chloro-2,2,2-trifluoroethane, 1 -chloro-l,2,2,2-tetrafluoroethane (R-124),l-chloro-l,l,2,2-tetrafluoroethane,dichloromethane,difluoromethane(R-32), 1,1,2,2,2-pentafluoroethane (R-125), 1,1,2,2-tetrafluoroethane (R-134), 1,1,1,2- tetrafluoroethane (R-134a), 1,1,1-trifluoroethane (R-143a), 1,1-difluoroethane (R-152a). The preferred refrigerants, of course, are the fluorohydrocarbons — especially R-134a — and fluorohydrocarbon mixtures.

Among the refrigerant blends with which the lubricants can be advantageously used are the binary mixtures of R-32 with R-125, R-152a, or R-134a; R-125/R-143a,

R-290/R-134a, and R-22/R-152a binary blends; and ternary blends such as R-22/R-

290/R-125, R-22/R-152a/R-124, R-32/R-125/R-134a, and R-125/R-143a/R-134a.

Esters utilizable as lubricants in the practice of the invention are the esters formed by reacting one or more alcohols with an alkanepolyoic acid, or an anhydride or halide thereof, in the presence of an esterification catalyst. When the acidic reactant is an acid, it is an alkanepolyoic acid containing at least four carboxyl groups and an alkane moiety of at least four carbons, usually 4-10 carbons, such as 1,2,3,4- or 1,2,2,4- butanetetracarboxylic acid, 1,2,3,4,5-pentanepentacarboxylic acid, or 1,2,3,4,5,6- hexanehexacarboxylic acid. The other acidic reactants useful in forming the esters are the anhydride, bromide, and chloride derivatives of such acids. In general, the ester lubricants are the products obtained by reacting 0.5-10, preferably 1-6, and more preferably 2-5 equivalents of one or more alcohols (e.g., alkyl, aryl, cycloalkyl, aralkyl, alkaryl, cycloalkylalkyl, cycloal kylaryl, haloalkyl, halocycloalkyl,

% and haloaryl alcohols containing 1-20 carbons; preferably alkanols and cycloalkanols;

5 and most preferably alkanols containing 1-10 carbons) with an equivalent of the acidic reactant in the presence of an esterification catalyst, such as p-toluenesulfonic acid or methanesulfonic acid. In these esterifications, as is conventional, the reaction may be driven to completion by the use of azeotropic distillation to remove the water of reaction; and the product may be washed with a basic solution to remove the catalyst

10 before blending it with the refrigerant.

The particular ester or ester mixture preferred for use in a refrigeration composition of the invention varies with the refrigerant component of the composition and with the conditions to which the composition is expected to be exposed. In choosing a lubricant for use with any refrigerant, it is important to select one which

15 is completely miscible with the refrigerant throughout the temperature range to which the refrigeration composition is to be exposed and which has a viscosity such as to permit its functioning as a lubricant over that entire temperature range. The optimum lubricant to be used in any instance can be determined by routine experimentation, aided by observation of the following general principles:

20 (1) A low viscosity is most suitable for a lubricant to be used at relatively low temperatures, while lubricants intended for use at relatively high temperatures should have higher viscosities.

(2) The viscosities most suitable for lubricants to be used in refrigeration compositions that are to be exposed to the temperature conditions generally found

25 in refrigeration equipment (i.e., temperatures in the range of -40 ° C to 70 ° C or sometimes even higher temperatures) are apt to be 1-200, preferably 5-30, and most

^* preferably 10-20 mπr - s^"1 at 40 ° C and 0.5-100, preferably 2-20, and most preferably

1-5 mm² - s^"1 at 100 ° C. 4

In the preferred embodiment of the invention wherein the refrigerant .is a

30 fluorohydrocarbon, such as R-134a, or a fluorohydrocarbon-containing mbcture, the preferred ester lubricants are the esters of butanetetracarboxylic acids, especially the tetraalkyl esters of 1,2,3,4-butanetetracarboxylic acid in which the alkyl groups may be the same or different and contain 1-10 carbons.

Refrigeration compositions of the invention typically comprise 0.001-0.7, preferably 0.1-0.5 part of the novel lubricant per part by weight of the refrigerant, and, if desired, they may also contain additives of the type conventionally used in refrigera¬ tion lubricants. In addition to epoxy and other dehydrating agents sometimes employed to prevent corrosion of refrigeration equipment by any water in the refrigeration compositions, such additives include, e.g., oxidation resistance and thermal stability improvers, corrosion inhibitors, metal deactivators, lubricity additives, viscosity index improvers, pour and/or floe point depressants, detergents, dispersants, antifoaming agents, anti-wear agents, and extreme pressure resistance additives, such as those exemplified in U.S. Patent 5,021,179 (Zehler et al.). As in Zehler et al., these additives, when employed, are generally utilized in small amounts totaling not more than 8%, preferably not more than 5%. of the weight of the lubricant formulation. The refrigeration compositions are generally formed prior to use. However, when desired, they may also be formed in situ during operation of the refrigeration equipment. Thus, the refrigerant and the lubricant may be charged to the refrigeration equipment separately, either simultaneously or consecutively in either order, instead of being preblended. The following examples are given to illustrate the invention and are not intended as a limitation thereof.

EXAMPLE 1

Preparation of tetrabutyl 1.2.3.4-butanetetracarboxylate

Charge a suitable reaction vessel with 5.5 lg (23.6 mmols) of 1,2,3,4-butanetetra- carboxylic acid, O.όlg (3.2 mmols) of p-toluenesulfonic acid, and 35g (470 mmols) of butanol. Heat the mbcture to 120 ° C in a hot oil bath and hold at this temperature for 20 hours. Remove the water of reaction and excess reagent by simple distillation, dilute the bottoms product with 50 mL of ethyl acetate, and wash with two 30 mL portions of 3 wt.% aqueous sodium bicarbonate and then with brine. Filter the washed product through cotton and strip the solvent from the product under reduced pressure to provide 10.8g (99%yield) oftetrabutyl 1,2,3,4-butanetetracarboxylate, a light yellow oil. The recovered product is totally misible with R-134a and has a viscosity of 20.3 mπr- s^"1 at 40° C, a viscosity of 3.77 mπr - s^"1 at 100 ° C, and a viscosity index of 50.

EXAMPLE 2 Preparation of tetraethyl 1.2.3.4-butanetetracarboxylate

React 8.0g (34.2 mmols) of 1,2,3,4-butanetetracarboxylic acid with lOOg (217 mmols) of ethanol) in the presence of 0.55g (5.8 mmols) of methanecarboxylic acid by the general procedure of Example 1 to provide 7.4g (62% yield) of tetraethyl 1,2,3,4- butanetetracarboxylate. The product is totally miscible with R-134a and has a viscosity of 30.0 mm² • s^"1 at 40 ° C and a viscosity of 3.59 mm² • s^'1 at 100 ° C.

EXAMPLE 3 Preparation of butyl /isopropyl tetraester of 1.2.3.4-butanetetracarboxylic acid React 6.87g (29.4 mmols) of 1,2,3,4-butanetetracarboxylic acid with a mixture of 20g (270 mmols) of n-butanol and 16.2g (270 mmols) of isopropanol in the presence of 0.64g (3.4 mmols) of p-toluenesulfonic acid by the general procedure of Example 1 to provide 13.2g (99% yield) of a butyl/isopropyl tetraester of 1,2,3,4-butanetetracar- boxylic acid having a butyl/isopropyl ratio of 10.3/ 1. The product, a yellow oil, is totally misible with R-134a and has a viscosity of 21.1 mπr - s^"1 at 40 ° C, a viscosity of 3.83 mπr- s^"1 at 100° C, and a viscosity index of 45.

Claims

1. A refrigeration composition comprising a refrigerant and, as a lubricant, at least one ester of an alkanepolyoic acid containing at least four carboxyl groups and an alkane moiety of at least four carbons.

2. The composition of claim 1 wherein the refrigerant comprises a fluorohydro¬ carbon.

3. The composition of claim 2 wherein the refrigerant is 1,1,1,2-tetrafluoroeth- ane.

4. The composition of claim 1 wherein the ester is a tetraalkyl ester of 1,2,3,4- butanetetracarboxylic acid in which the alkyl groups are the same or different and contain 1-10 carbons.

5. The composition of claim 1 wherein the lubricant/refrigerant weight ratio is 0.001-0.7/1.

6. The composition of claim 5 wherein the lubricant/ refrigerant weight ratio is 0.1-0.5/1.

7. The composition of claim 6 wherein the refrigerant is 1,1,1,2-tetrafluoroethane and the lubricant is a tetraalkyl ester of 1,2,3,4-butanetetracarboxylic acid in which the alkyl groups are the same or different and contain 1-10 carbons.