Refrigerant additive and method for reducing corrosion in refrigeration systems

The addition of a phospholipid to the halogenated hydrocarbon working fluid of a refrigeration system serves to markedly reduce the corrosion of steel exposed thereto.

BACKGROUND OF THE INVENTION 
This invention relates to lubrication of refrigeration systems of the 
closed, hermetically-sealed compression type including halogenated 
hydrocarbon refrigerant and a lubricant, and more particularly to 
additives for the prevention of corrosion in such systems. 
Sealed refrigerating systems employing as a working fluid a combination of 
a halogenated hydrocarbon, a refrigerant and a lubricant are subject to 
wear and corrosion of the metal parts that come in contact with the 
working fluid. Many combinations of refrigerants and lubricants are 
subject to a slow deterioration that results in byproducts corrosive to 
the metal parts and particularly to the ferrous metal components of the 
compressor. Some system designs, and particularly those in which a 
less-than-ambient pressure condition exists, are particularly subject to 
the eventual intrusion of atmospheric oxygen and water. The presence of 
water and oxygen substantially increases the corrosion of the steel 
compressor parts, and particularly the steel shell, producing scale and 
other insoluble materials. These corrosion products are transported into 
and clog the interstices of heat exchange surfaces. This becomes a major 
problem in systems employing heat exchange tubing having porous surfaces, 
in as much as the porosity of these surfaces is rapidly reduced, resulting 
in a very substantial loss in efficiency. 
A variety of approaches have been used to reduce such problems. Improved 
lubricants having better stability and complexity with refrigerants have 
been developed, as shown for example in U.S. Pat. Nos. 3,878,112 and 
4,046,533. Additives such as metallodithiophosphates have been added to 
the working fluid to inhibit the interaction between the refrigerant and 
hydrocarbon lubricants, as shown in U.S. Pat. No. 3,375,197. The transfer 
of copper from heat exchange surfaces to the steel surfaces of the 
compressor by the working fluid can also contribute to the corrosion 
problem, and inhibitors have also been added to the working fluid to 
reduce such interactions, as shown in U.S. Pat. No. 2,975,137. System 
driers have also been devised and are widely used to continuously remove 
moisture from the system. 
Corrosion inhibitors for use with aqueous fluids such as are found in 
adsorption refrigeration systems and the like are widely known. Additives 
are also widely used in non-aqueous lubricant systems for a great variety 
of applications, as well as in hydraulic fluids, transmission fluids and 
the like. In general, such additives are not known for use with 
halogenated hydrocarbon refrigerants, in as much as most are not soluble 
in common refrigerants and many promote decomposition of the refrigerant 
or increase the interaction between refrigerant and lubricant. However, an 
additive having the requisite solubility in refrigerants and effective in 
reducing or preventing corrosion under the conditions found in 
refrigeration systems would be highly useful, particularly for use in 
sealed systems that operate at less than atmospheric in ambient pressures. 
SUMMARY OF THE INVENTION 
Phospholipids such as for example lecithin are effective corrosion 
inhibitors for use with refrigerants. When added to halogenated 
hydrocarbon refrigerants, phospholipids are effective in reducing 
corrosion brought about by the presence of small amounts of water, oxygen 
and corrosive compounds associated with the deterioration or refrigerant 
systems. 
DESCRIPTION OF THE EMBODIMENTS 
Phospholipids, or phosphatides, are naturally occuring phosphate-containing 
glycerides found in animal and vegetable materials. Typical of such 
phospholipids is lecithin, a complex mixture obtained commercially from 
soybeans. Lecithin has many uses in the food industry as an additive and 
preservative, and in industrial applications as an interfacial agent in 
the manufacture of paints, lacquers, inks and the like. In commercial 
practice, the term lecithin refers to a complex mixture of 
acetone-insoluble phosphatides. Lecithin is widely available commercially 
and methods for its manufacture from natural sources are well known. 
Lecithin is soluble in halogenated hydrocarbons commonly used as 
refrigerants, including the chlorofluoromethanes and chlorofluoroethanes. 
Examples of such refrigerants include dichlorofluoromethane, 
dichlorodifluoromethane, chlorodifluoromethane, 
trichloromonofluoromethane, dichlorotetrafluoroethanes, 
trichlorotrifluoroethanes and the like, all of which are used as 
refrigerants in commercial applications. Commercial refrigeration working 
fluids will further comprise a lubricant such as a hydrocarbon oil, as is 
well known in the art. The addition of lecithin to such working fluids in 
an amount effective to inhibit corrosion is readily accomplished by 
dispersing the requisite amount of lecithin in the working fluid, in as 
much as the additive is readily soluble. The amount of lecithin employed 
may vary over a wide range from 0.01 to 10 wt% or more. However, the 
additive is effective at low concentrations, hence will be employed in 
amounts of less than about 1 wt%.

The effectiveness of lecithin in reducing corrosion will be seen from a 
consideration of the following examples: 
EXAMPLE 1 
The effectiveness of lecithin as a corrosion inhibiting additive in 
refrigerants was demonstrated by immersing 2 sq. in. steel coupons in a 
mixture of containing 92 ml of R-113 refrigerant, 7 ml of hydrocarbon oil 
and 0.5 g of lecithin, to which 1.0 ml of 0.01N HCl containing 10 ppm 
ferric ion was added with stirring. The aqueous component separated 
forming a separate phase, insuring saturation of the refrigerant. As 
controls, equivalent mixtures without lecithin were employed. The steel 
coupons were sandblasted, cleaned with a mild soap solution, 
ultrasonically cleaned in isopropanol, dried at 80.degree. C. and stored 
in a dessicator until used. The tests were run by suspending the weighed 
coupons from glass hooks in covered jars containing the refrigerant 
mixture for a period of three weeks. At the end of the test, the coupons 
were removed, cleaned of corrosion product by immersing in 500 ml of 37% 
HCl containing 25 g of SnCl.sub.2 and 10 g of SbCl.sub.3, then cleaned 
with isopropanol, dried and weighed as before. The degree of corrosion was 
determined by weight loss. 
TABLE I 
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Inhibitor Reduction 
type wt % % Remarks 
______________________________________ 
none -- -- ppt 
Lecithin 0.5 90 -- 
DBTD 0.5 50 ppt 
TCP 0.5 75 -- 
______________________________________ 
Note: 
DBTD = dibutyl tin dilaurate; TCP = tricresylphosphate; ppt = precipitate 
formed in working fluid. 
It will be apparent from these data that lecithin was highly effective in 
reducing scale. TCP and DBTD, both compounds known to be useful as 
corrosion inhibitors in other applications, were markedly less effective 
in this system. 
EXAMPLE 2 
Test solutions containing 560 mL of R-11 refrigerant, 50 ml of oil 
(Carpella C from Texaco Company) and varying amounts of lecithin. The 
solutions were placed in covered jars and steel coupons were suspended for 
two weeks at three different levels--(a) in the vapor space, (b) half 
immersed and (c) totally immersed, to demonstrate the effect of varying 
concentrations and immersions on corrosion inhibition. Water was 
introduced into the system twice each week by spraying the coupons with 2 
ml of water. 
The steel coupons were initially prepared by cleaning in trichlorethylene 
and acetone, then drying at room temperature with a stream of nitrogen and 
weighing. At the end of the test, the specimens were cleaned with an 
aqueous soap solution, dipped in HCl, rinsed with water and acetone, dried 
as before and reweighed to determined the corrosion by weight loss. 
TABLE II 
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Exposure Lecithin wt loss Reduction 
Location (wt %) (mg) (%) 
______________________________________ 
vapor 0 34* -- 
1/2 immersion 
0 43* -- 
immersed 0 8* -- 
vapor 0.05 25 26 
1/2 immersion 
0.05 8 81 
immersed 0.05 0 100 
vapor 0.2 22 35 
1/2 immersion 
0.2 7 84 
immersed 0.2 0 100 
vapor 0.5 28 18 
1/2 immersion 
0.5 2 95 
immersed 0.5 1 88 
______________________________________ 
Notes: 
*Ave of 2 runs. 
It will be seen that substantial reduction in corrosion occurs for 
composition containing as little as 0.05 wt% lecithin where partially or 
completely immersed. Corrosion in the vapor space is much less affected by 
lecithin at low concentrations. 
The invention will thus be seen to be a method for inhibiting corrosion in 
refrigerant systems by incorporating into the working fluid an effective 
amount of a phospholipid such as lecithin, and a working fluid for use in 
such systems comprising a halogenated hydrocarbon, a lubricant and a 
phospholipid. It will be understood that further modifications, including 
the addition of further lubricant and wear additives, copper inhibiting 
compounds and the like may be made as will occur to those skilled in the 
art without departing from the spirit and scope of the invention as set 
forth in the appended claims.