Patent Application
20080014641
Further advantages of the invention are apparent by reference to the detailed description in conjunction with the figures, wherein elements are not to scale so as to more clearly show the details, wherein like reference numbers indicate like elements throughout the several views, and wherein:
The Karl Fischer test method used to determine a concentration of water in an oil mixture is widely used because of its relative accuracy. However, one of the drawbacks of using the Karl Fischer test method is that certain reaction byproducts and other chemical species within the oil mixture tend to give false high readings of water content. In other words, certain reaction byproducts and other chemical species within the oil mixture effectively masquerade as water. Various embodiments of the invention described herein offer a method and apparatus using spectrochemical analysis in addition to the Karl Fischer test method. More specifically, spectrochemical analysis is used to identify certain masquerading chemical species and calculate a true water concentration of an oil mixture by subtracting the masquerading effects of certain reaction byproducts and other chemical species from Karl Fischer test results, thereby giving a more accurate overall water concentration test result.
Certain chemical classes have been identified by various sources as causing false water readings when the Karl Fischer test method is used to determine a concentration of water in an oil mixture. These general chemical classes include, but are not limited to, aldehydes and ketones, strong amines, ammonia, ferric salts, hydrazine derivatives, hydroxylamine salts, mercaptans, sodium methylate, sulfuric acid, thioacids, and thiourea. Tests were conducted on four additives/contaminants that fall under the chemical classes listed above. The four chemical species tested were magnesium sterate, ferric oxide, diphenyl amine, and zinc dialkyl dithiophosphate (ZDDP). Oil mixtures for magnesium sterate, ferric oxide, and diphenyl amine were tested with 0 ppm additive/contaminant, 500 ppm additive/contaminant, 1000 ppm additive/contaminant, and 2000 ppm additive/contaminant. Six runs per additive/contaminant were made at each of the four listed concentration value (i.e., 0 ppm, 500 ppm, 1000 ppm, and 2000 ppm). The test results suggested that ferric oxide and diphenyl amine had no substantial effect of masquerading as water in the oil mixture. However, the test results for magnesium sterate showed a substantially direct correlation between the concentration of additive/contaminant and the false high concentration measurement of water. The test results for magnesium sterate are shown in Table 1 below.
Based on the test results for magnesium sterate shown in Table 1, a direct correlation between the concentration of magnesium sterate and false high concentration measurements of water is established. More specifically, for approximately every 1000 ppm of magnesium sterate present in the oil mixture, a false high water concentration measurement of 1800 ppm emerges in Karl Fischer test results. An algorithm based on the relationship illustrated by Table 1 allows for false high water concentration measurements based on magnesium sterate to be factored out of a final water concentration measurement. By using spectrochemical analysis techniques. the identity and concentration of magnesium sterate may be calculated and reconciled with corresponding Karl Fischer test results to give a more accurate water concentration measurement.
For example, if a Karl Fischer test result from an oil mixture is 1000 ppm water and spectrochemical analysis reveals that 500 ppm of magnesium sterate is also present in the oil mixture, a calculation may be performed based on the relationship shown in Table 1 to demonstrate that only about 100 ppm of water is actually present in the oil mixture. The other 900 ppm of “water” from the Karl Fischer test result is actually magnesium sterate masquerading as water. The method described above using spectrochemical analysis for correcting false high water concentration measurements when using the Karl Fischer test method can also be used with other chemical species.
Another set of tests were performed on ZDDP to develop an algorithm based on the relationship between the mass percentage of ZDDP and Karl Fischer test results for water concentration (ppm) in an oil mixture. The ZDDP/oil mixtures were tested at values of 0%, 1%, 2%, and 5% ZDDP as shown in Table 2 below. The results of this test, like the results of the test with magnesium sterate, demonstrate a direct correlation between the percentage of ZDDP present in the oil mixture and the water concentration measurement using the Karl Fischer test method. The zinc content (mass %) or the phosphorus content (mass %) of ZDDP molecules can be used as the basis for a comparison with Karl Fischer test results for water concentration. Interestingly, the mass of zinc and the mass of phosphorus in a molecule of ZDDP is substantially the same, causing their relationship with Karl Fischer test results for water concentration to also be very similar.
The general chemical formula for ZDDP is ((RO)2PS2)2Zn wherein the “R” represents a simple alkyl group such as methyl or butyl. When R=methyl, the phosphorus concentration is about 1790 ppm and the zinc concentration is about 1880 ppm. When R=butyl, however, the measured phosphorus concentration is about 1250 ppm and the zinc concentration is about 1320 ppm. When the zinc concentration from ZDDP ranges from about 1320 ppm to about 1880 ppm in an oil mixture, a false reading of about 290 ppm of excess water emerges in Karl Fischer test results for water concentration. Similarly, when the phosphorus concentration from ZDDP ranges from about 1250 ppm to about 1790 ppm in an oil mixture, a false reading of about 290 ppm of excess water emerges in Karl Fischer test results for water concentration. When the zinc concentration ranges from about 440 ppm (correlating to a phosphorus concentration of 430 ppm) to about 640 ppm (correlating to a phosphorus concentration of 620 ppm) in an oil mixture, a false reading of about 100 ppm of excess water emerges in Karl Fischer test results for water concentration.
Zinc concentrations from ZDDP may be measured and relied on independently of phosphorus concentrations for correcting Karl Fischer test results. Similarly, phosphorus concentrations from ZDDP may be measured and relied on independently of zinc concentrations for correcting Karl Fischer test results. In a preferred embodiment, the concentration of zinc and phosphorus may be averaged so that a Karl Fischer test measurement for water concentration may be corrected based on both zinc concentration and phosphorus concentration.
The term “chemical species” used herein is meant to be interpreted broadly including one or more atoms of a pure element or a plurality of atoms of various elements bonded together by chemical bonding including, but not limited to, ionic bonding, covalent bonding, a combination of ionic bonding and covalent bonding, metallic bonding, and hydrogen bonding. The term “Karl Fischer test method” or “Karl Fischer test” is meant to be interpreted broadly to include all test methods known to those skilled in the art that are commonly referred to as or, otherwise, are understood by one of ordinary skill in the art to be Karl Fischer testing methods including, but not limited to, methods using solvents such as pyridine, benzene, and other Karl Fischer solvents known to those skilled in the art.
In one preferred embodiment of the invention, an apparatus is used to perform the method described above. With reference to
The Karl Fischer testing assembly 14 is broadly defined herein as any testing assembly known to those skilled in the art that can be used to perform a Karl Fischer test. The “first sample” as defined above includes only the portion of the oil mixture depleted in the chemical reaction to produce a Karl Fischer result. The “second sample” as defined above includes only the portion of the oil mixture depleted in the spectrochemical analyzer to produce composition data. In a preferred embodiment, the spectrochemical analyzer 18 includes a spectrometer, a spectrograph, or a spectroscope. In another preferred embodiment, the synthesizer 16 includes a computer, and the computer 16 is preferably in communication with a display device 20 for displaying the water content measurement from the computer 16 as shown in
The foregoing description of preferred embodiments for this invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise form disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments are chosen and described in an effort to provide the best illustrations of the principles of the invention and its practical application, and to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.
