Abstract:
A field test kit which uses a single vial is useful in testing acidity in refrigeration oils contaminated with a colored leak detector. This vial contains a pre-measured indicator solution and has sufficient additional volume that the test oil can be added directly to the indicator solution and accurately measured within the vial. After shaking, the mixture quickly separates into two phases. The color of the bottom phase indicates whether or not the acidity of the refrigeration oil exceeds 0.05 acid number.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to test kits for detecting acidity in oils and particularly relates to field test kits for detecting acidity in refrigeration oils which are contaminated with a leak detecting component. 
     2. Review of Prior Art 
     In the refrigeration industry, lubricating oils are tested for acidity as an indication of suitability for continued use and as a means for detecting contamination of the entire refrigeration system. Such tests are set forth in ASTM D664-58 and ASTM D974-64, but the requirements of D664-58 for laboratory equipment makes this procedure unsuitable for field testing, and testing according to D974-64 is not satisfactory with dark colored samples of refrigeration oils because the color changes that are produced by a color indicator such as p-naphtholbenzein solution are obscured by the color of the sample, making it difficult to estimate color changes with sufficient precision. 
     Acid field test kits for use on refrigeration and airconditioning systems have been developed to meet this need and are currently designed to show whether or not the acidity of the refrigeration oil is above an acid number of 0.045 to 0.05, as determined by the color produced by an acid/base indicator in the test kit. New refrigeration oils intended for use in refrigeration systems generally have an acid number of from 0.01 to 0.02 when tested according to conventional ASTM test methods. Such an acid number represents the quantity of base, expressed in milligrams of potassium hydroxide, that is required to titrate all acidic materials in a 1 -gram sample of the oil that are dissociated sufficiently to react to the KOH. According to experience, when a refrigeration oil develops an acid content which corresponds to an acid number of from 0.05 to 0.07, it should be replaced with new oil. 
     There are four acid field test kits which are now in popular use for testing refrigeration and air-conditioning systems. Two of these four field test kits produce a homogeneous mixture after shaking, and two produce a mixture that separates into two phases, the aqueous bottom phase containing the telltale color. The two-phase kits are based upon the method disclosed in U.S. Pat. No. 3,510,260 for forming an aqueous acid solution as an immiscible bottom phase, in which the acidic components are dissolved, with the oil as the top phase. When testing dark oils with a homogeneous-type kit, the color change is obviously likely to be masked. When using the two-phase method, the color change of an indicator solution, such as a one percent solution of phenolphthalein in ethanol, can become easily observable even with a dark oil when the aqueous phase turns from colorless to pink or red. However, if a red-colored leak detector is present as a component of the oil, the color change can be entirely obscured. 
     For example, when the refrigeration oil is contaminated with a leak detector such as the highly colored additive marketed by E. I. Dupont de Nemours and Company as Dytel, the color of the homogeneous mixture is distorted and the test results are no longer reliable. It is believed that the alkylanilino-substituted anthraquinone dyes in U.S. Pat. No. 3,770,640 are sold under the mark, Dytel. Other leak detectors are disclosed in U.S. Pat. No. 3,370,013 as organic dye compounds such as methyl derivatives of azobenzene-4-azo-2-naphthol, phenyl-azo-2-naphthol and methyl derivatives of azo-benzene-4-azo-2-naphthol, phenyl-azo-2-naphthol, and p-diethylaminoazobenzene. 
     One homogeneous-type device, identified as &#34;TKO ACID TEST KIT,&#34; is simplest to use. It employs a single vial, having a capacity of two fluid ounces, containing a purple mixture of alcoholic potassium hydroxide, an acid-base indicator and a solvent mixture comprising benzene and ethyl alcohol or, preferably toluene and isopropanol. By adding refrigeration oil to the mold line on the neck of the test vial, the correct amount of oil that corresponds to the amount of potassium hydroxide is obtained. The vial need be shaken for only a few seconds after addition of the refrigeration oil sample to produce a homogeneous mixture, with no transfers and no delay for separation into distinct phases. If the test sample has an acid number less than 0.045, the color of the mixture in the shaken vial remains purple. If the oil sample has a borderline acidity, the color becomes orange, indicating that changing the oil is desirable. If the oil is definitely too acidic, the color becomes yellow, indicating that the oil must be changed. Unfortunately, if a red leak detector is present as a component of the refrigeration oil, the results are unreliable. 
     Another test kit of the homogeneous type is identified &#34;as `ONE TIME ACID TEST KIT` and consists of a two-fluid ounce vial containing an acid-base indicator in a benzene-ethyl alcohol media (reddish-orange in color). A second vial of approximately 0.5 fluid oz., with a capacity for 15.5 g of fresh refrigeration oil, contains an alcoholic potassium hydroxide solution in benzene. According to the test procedure, the contents of the small vial are emptied into the larger vial producing a violet color. The small vial, which also serves as the measuring vial, is then filled with the test oil and finally emptied into the larger vial. If after shaking for fifteen seconds the color of the resulting homogeneous mixture remains purple-red, the oil is considered to be satisfactory&#34;. However, if the refrigeration oil contains a highly colored leak detector, the homogeneous mixture does not produce the expected test colors so that the kit is not suitable for such contaminated oils. 
     A field test kit of the two-phase type, identified as &#34;UNI-KIT&#34;, consists of three vials and a glass ampoule containing potassium hydroxide solution. The largest vial has a capacity of approximately one fluid ounce and contains dried crystals of phenolphthalein indicator. When the ampoule is broken and its colorless contents emptied into the large vial with the aid of a small piece of rubber tubing for venting the ampoule and obtaining better drainage into the vial, as described in U.S. Pat. No. 3,653,839, the contents become pink. A second vial, containing isopropyl alcohol and toluene, is emptied into the mixture. Using the third vial for measurement, a sample of the refrigeration oil is then poured into the pink mixture, and the large vial is shaken vigorously. The resulting heterogeneous mixture frequently must stand for one to five minutes so that the partially emulsified layers can be separated sufficiently for an accurate color determination. Any pink color remaining in the bottom layer, even very light pink, signifies satisfactory oil. Therefore, if the oil in the top layer contains a leak detector, such as Dytel, which is even slightly miscible with or emulsified in the bottom layer, a slightly pinkish color is observed which could lead to an erroneous pass for an acidic refrigeration oil which is contaminated with the leak detector. 
     The fourth test kit, also of the two-phase type, is marketed as &#34;PHASE II&#34; and consists of a two-fluid ounce bottle, which is partially filled with a solvent solution consisting of benzene, methanol, and toluene, and a 0.5-fluid ounce bottle of neutralization solution. When the contents of the smaller bottle are poured into the large bottle, a purple-colored bottom layer is formed. The smaller bottle is then filled completely with oil to be tested and emptied into the larger bottle. After capping and shaking the larger bottle well, the mixture separates into two phases upon standing for two to three minutes. If the bottom layer loses its purple color, the sample has an acid number of 0.05 or more so that the oil should be replaced. This field test kit is probably the most convenient test kit which is now available for testing refrigeration oil taken from a system contaminated with a leak detector, even though it is subject to some interference from the dye. However, there are several practical drawbacks in that the kit requires the use of two bottles instead of only one bottle, considerable time is lost while waiting for phase separation, and benzene as one component of the solvent mixture is now a suspected carcinogen. 
     Other test kits of interest are described in U.S. Pat. No. 3,528,775 for determining the water content of water-immiscible petroleum products, U.S. Pat. No. 3,449,081 for performing blood tests, and U.S. Pat. No. 1,674,416 for testing alcohol. 
     In the refrigeration and air conditioning fields, no simple and quickly operated field test kit is known that is not obscured by a leak detector in the oil to be tested. Accordingly, an acid field test kit is needed that provides acidity indications that cannot be obscured by a leak detector in oil contaminated therewith, that requires minimum time for field testing, that requires only a single vial so that transferring liquids is not necessary, and that preferably contains no benzene. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of this invention to provide an acid field test kit that is operable within a single bottle or vial for measuring a sample of a refrigeration oil, for carrying out the test precedure, and for obtaining reliable test results as to acidity of the oil. 
     It is also an object to provide an acid field test kit of the two-phase type wherein the phases separate with exceptional rapidity and without emulsification. 
     It is further an object to provide an acid field test kit having components that permit an acidity-related color change to be observed without interference from the color of a leak-detecting component of a refrigeration oil. 
     Therefore, in accordance with the objects and principles of this invention, an acid field test kit of the two-phase type is herein provided which comprises a single vial for storage of the testing solution, for measurement of the oil sample, and for carrying out the test procedure. The testing solution comprises an aqueous bottom layer, which includes a color indicator and which is highly ionic in nature, and a solvent top layer which preferably includes no benzene. In operation, this field test kit requires only one vial, provides fast phase separation, produces distinct colors, and utilizes cyclohexane as the preferred solvent. Fast phase separation into two distinct layers is effected by the highly ionic nature of the aqueous layer. With the test kit of this invention, the single vial is merely filled to the line on its neck and shaken. The layers separate almost immediately, and in a very short time the operator can detect the color of the bottom phase. If its color is blue to blue-green, the oil is satisfactory for further service. If its color is green to yellow-green, the oil is marginal for further use. If its color is distinctly yellow, the oil is bad and unquestionably should be changed. 
     The highly ionic nature of the aqueous layer is principally imparted by a water-soluble inorganic salt as a major component of the testing solution. This salt is preferably sodium chloride at 6-12% of an indicator stock solution by weight. 
     DESCRIPTION OF THE INVENTION 
     The method of preparing acid field test kits in general comprises the preparation of an indicator stock solution according to the following steps which are defined for an indicator, such as thymol blue, which changes color over a pH range of 8.0 to 9.6: 
     A. preparing a concentrated aqueous indicator solution; 
     B. preparing an indicator mixture comprising 20-28 percent by weight of a lower alcohol, 56-79 percent by weight of distilled water, 6-12 percent by weight of a water-soluble inorganic salt, and 0.2-0.3 percent by weight of the concentrated aqueous indicator solution; 
     C. adjusting the pH of the indicator mixture to 9.5 with 1.0 N alkaline hydroxide, preferably as a solution, to form an adjusted mixture; 
     D. adding to the adjusted mixture, to form the indicator stock solution, exactly the amount by weight of additional alkaline hydroxide solution so that the weight ratio of oil to be tested to one milliequivalent of the additional alkaline hydroxide is 1122; and 
     E. protecting the indicator stock solution with nitrogen. 
     Other materials producing an equivalent result can be substituted for the preferred materials. Indicators having a pH range of 8-10, such as phenolphthalein and phenol red, can be substituted for thymol blue to produce different colors. The term, alkaline hydroxide, includes potassium hydroxide, sodium hydroxide, and lithium hydroxide; potassium hydroxide is preferred. The term, water-soluble inorganic salt, includes sodium chloride, calcium chloride, magnesium chloride, sodium bromide, and like materials; sodium chloride is preferred. 
     Using KOH as the alkaline hydroxide in steps C and D on a gram basis, for example, so that one milliequivalent (meq.) is 0.0561 gram, the quantities used in step B are: 600 ml-900 ml of alcohol/meq. KOH, 1400-1950 ml of water/meq. KOH, 135-275 g NaCl/meq. KOH, and 5-7 ml of concentrated aqueous indicator solution/meq. KOH. The preferred levels, as outlined in Example 1 hereinafter, are 751 ml of alcohol/meq. KOH, 1690 ml of water/meq. KOH, 201 g of NaCl/meq. KOH and 6.4 ml of indicator solution/meq. KOH. 
     When KOH is used as a 1.000 N solution in step D, exactly 0.04018 percent by weight is added to the adjusted mixture to form the indicator stock solution. 
     Step C is necessary to neutralize any acidic components arising from the raw materials and to establish a baseline for the indicator which changes from yellow to blue over a pH range of 8.0 to 9.6. By setting the baseline at a pH of 9.5, the color is unmistakably blue. If an indicator such as phenol red had been chosen, the baseline would have been set at pH 8 since it changes from yellow to red over a range of 6.8 to 8.0. 
     The alkaline hydroxide added in step D is critical because the final kit should contain 0.775 mg KOH if KOH is the selected alkaline hydroxide. This amount represents the alkalinity consumed by 15.5 g of test oil with an acid number of 0.05. When properly filled with test solution and test oil, the weight of oil corresponds to 15.5 g. If the test oil is more acidic (acid number &gt;0.05), the KOH is consumed and the kit changes color. If the oil has an acid number below 0.05, the oil does not consume all of the KOH and the kit remains blue. 
     In order to prepare kits of another size and be able to use larger or smaller oil samples, the amount of KOH in the kit would have to be adjusted so as to maintain a level of 20 g of oil/mg of KOH or 14.3 g of oil/mg of NaOH, for example. Whether the potassium hydroxide is added as a 1.0 N solution, or 2.0 N, etc., is not critical so long as the ratios are properly maintained. 
     The method further comprises the preparation of a plurality of test vials, each having a mark thereon to indicate a selected internal volume, according to the following steps: 
     A. adding to each test vial, while protecting its contents with nitrogen, a quantity of a waterimmiscible solvent equalling 22.7 percent of the volume, preferably principally comprising cyclic carbon compounds having no carboxyl groups, alcohol groups, or ether linkages in its side chains, such compounds including benzene, toluene, the xylenes, mesitylene, isopropyl benzene, and cyclohexane, and mixtures thereof; and 
     B. adding to each test vial, while continuing to protect its contents with an inert gas such as nitrogen, a quantity of the indicator stock solution equalling 51.4 percent of the selected internal volume. The remaining capacity of each field test vial equals 25.9% of its total volumetric capacity up to the mark. One or more test vials are included in a field test kit to be used by automobile mechanics and air conditioning and refrigeration servicemen. When carrying out the test procedure in the field, the oil to be tested is filled to this mark, shaken, and allowed to settle and separate into two distinct phases. The color of the aqueous bottom phase is then examined to obtain the test results. 
     This procedure is illustrated with the following examples in which preferred materials and preferred quantities are used. 
    
    
     EXAMPLE 1 
     A plurality of acid field test kits were made according to the following preferred procedure, in which all bottles and vials were clean and dry and all vials had a capacity of two fluid ounces up to a mark thereon, as follows: 
     (1) a concentrated aqueous indicator solution was prepared by dissolving 2.0 g of thymol blue indicator, in two hundred ml. of distilled water; 
     (2) an indicator mixture was prepared under a nitrogen atmosphere by mixing 14.1 liters of isopropyl alcohol, 31.5 liters of distilled water, 3.175 kilograms of sodium chloride, and 120 ml. of the concentrated indicator solution; 
     (3) using a pH meter, the pH of the indicator mixture was adjusted to 9.5 with 1.0 N potassium hydroxide solution, using approximately 2.0-2.3 ml. of the KOH solution; 
     (4) 18.64 ml. of 1.000 N KOH was added to the indicator mixture to form the indicator stock solution which was thereafter protected with nitrogen; 
     (5) exactly 13.4 ml. of cyclohexane was charged to each field test kit vial; 
     (6) while protecting with nitrogen, exactly 30.4 ml. of the indicator stock solution was added to each vial containing cyclohexane, forming two phases of which the bottom layer of each kit was blue with the top layer varying from a slight yellow tint to clear; and 
     (7) each vial was very carefully sealed. 
     EXAMPLE 2 
     Five samples of Suniso 3GS refrigeration oil were treated with oleic acid (Wilmar 110) to produce acid numbers of 0.02, 0.04 and 0.06. Dytel II leak detector was added in normal commercial quantities to each sample. (Suniso refrigeration oils, such as Suniso 3GS, 4 GS, and 5GS refrigeration oils, are naphthenic oils manufactured by the Sun Oil Co.). Five vials made according to Example 1 were filled with the oil samples. The test oil at acid number 0.02 produced a blue bottom layer, the test oil at 0.04 acid number produced a green bottom layer, and the test oil at 0.06 acid number, in triplicate, produced distinctly yellow bottom layers. 
     Other materials producing an equivalent result can be substituted for the preferred materials, such as toluene, benzene, and the xylenes being substituted for cyclohexane, and ethyl alcohol, n-propyl alcohol, and tert-butyl alcohol being substituted for isopropyl alcohol. The volumes and weight ratios of the water, cyclohexane, alcohol, and inorganic salt can be altered from the preferred amounts given hereinbefore without seriously affecting the test results. 
     Because it will be readily apparent to those skilled in the art that innumerable variations, modifications, applications, and extensions of these embodiments and principles can be made without departing from the spirit and scope of the invention, what is herein defined as such scope and is desired to be protected should be measured, and the invention should be limited, only by the following claims.