Color canceling marking systems

Two or more dyes or markers, including a dye or marker having an absorbance peak in the 400 to 500 nm range and including a dye or marker having an absorbance peak in the 560 to 700 nm range are mixed together in appropriate ratios so when added to a liquid, such as a petroleum fuel, at combined levels of from 5 to 100 ppm, the colors of the dyes and/or markers cancel each other such that a "water-white" liquid still appears "water-white".

The present invention is directed to marking systems for tagging colorless
 liquids, such as "water white" petroleum fuels or "water white" organic
 solvents with two dyes or markers which, at the levels used, each impart a
 slight color, the color of each of which is masked by the color of the
 other.
 BACKGROUND OF THE INVENTION
 It is well known to provide markers (taggants) and packages to the fuel
 industry to aid in identifying taxable vs. untaxed fractions, additive
 packages, brand identification, etc. Until recently, tax evaders
 exclusively mixed similar petroleum fractions, e.g.,. kerosene into #2 oil
 or heating oil into diesel fuel in order to avoid taxation. Recently, a
 new twist has emerged, where common solvents, e.g., xylene, toluene,
 naptha, etc. are being used as fuel diluents to avoid taxation.
 For the supplier marker systems, this has brought about a new challenge. In
 the past, a number of tracer molecules such as described in U.S. Pat. Nos.
 5,156,653, 5,490,872 and 5,737,871 have a pale yellow body color.
 Intrinsic color value of such tracer molecules was described in terms of
 known solid dye such as color index Yellow 56.
 The slight yellow color imparted by such tracer molecules, at the
 application level of the tracer molecule in fuel, typically 5-50 ppm, was
 not considered a problem due to natural yellow coloration associated with
 most petroleum fractions. Consequently, these products were considered
 "silent" or not visibly detectable when applied in the proper manner.
 Other potentially useful tracer molecules might impart a different color.
 For example, tracer molecules described in U.S. Pat. No. 4,209,302 imparts
 a purple color to petroleum fuels. However, if these molecules were used
 in conjunction with a petroleum dye intended to color the petroleum fuel,
 the color of the tracer molecule used, e.g., at a 5-50 ppm level, would be
 masked. In this sense, these molecules could be considered "silent" in
 that a potential cheater would not recognize the inclusion of the tracer
 molecule.
 Tagging of water white solvents at the current normal dosage levels, e.g.,
 5-50 ppm, with colored tracer molecules imparts a definite coloration to
 the such solvents. This is unacceptable to the governments, solvent
 manufacturers and consumers of these products for a variety of reasons.
 Governments reject imparted color due to existing regulations for such
 goods requiring A.P.H.A. or Sarbolt color measurements of zero. Also, the
 integrity of a government sponsored program is compromised because
 imparting color to traditionally water white substances would immediately
 signal to the cheater and remove the element of surprise. The consumer
 would equate coloration of these products with poor quality or
 contamination making manufacturers adamant about maintaining current
 standards for body color.
 SUMMARY OF THE INVENTION
 In accordance with the invention there is provided a plural component
 marking system for colorless liquids, particularly colorless
 water-immiscible liquids such as "water white" petroleum fuels or "water
 white" organic solvents potentially used as adulterants for petroleum
 fuels. The marking system uses two or more markers and/or dyes at
 appropriate relative concentrations such that the combination of colors is
 a grey, which at the low use levels is undetectable to the naked eye and
 thus leaves the liquid within the standards of "water white". The grey
 color of the combination of markers and/or dyes is achieved by balancing
 of red, blue, and yellow color factors. A single marker or dye may provide
 more than one color factor; for example, a purple dye may contribute both
 blue and red color factors. A common dye color for petroleum fuels is
 purple, and a purple dye in combination of a yellow marker may be combined
 to provide a grey color combination. One or more of the markers and/or
 dyes may be used to identify the liquid. The combined level of markers
 and/or dyes used to tag a liquid in accordance with the invention is
 between about 5 and about 100 ppm.
 DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS
 Herein, "ppm" is used conventionally as parts per million by weight.
 The plural component systems according to the invention includes chemicals
 conventionally used as "dyes" and chemicals conventionally used as
 "markers". The term "dyes" is used conventionally in respect to petroleum
 fuels as colorants for the fuel while the term "marker" is intended to
 refer to chemicals which tag the fuel but which are sufficiently invisible
 to the naked eye and/or masked by a dye so as to be non-detectable in the
 petroleum fuel until extracted from the petroleum fuel and identified,
 e.g., by a chromophoric reaction. However, the distinction is somewhat
 blurred because certain "dyes", when used at a sufficiently low level, may
 serve as markers which may be identified by extraction. Also, certain
 "markers" which were originally intended to be identified by extraction
 and chromophoric reaction may be identified directly in the petroleum fuel
 by spectrophotometric methods, e.g., with a Petrospec.RTM. detection
 apparatus sold by Boston Advanced Technologies.
 Although, heretofore, many chemicals used as "markers" were identified as
 "silent" or "colorless" at their intended tagging levels, many such
 chemicals in fact exhibit a slight color even at their intended use
 levels. Heretofore, natural yellow colors in certain petroleum fuels could
 be relied upon to "mask" a slight yellowish color of a marker.
 Alternatively, dyes intended to impart color to petroleum fuels would mask
 the color of low levels of marker compound. The number of suitable
 entirely colorless markers suitable for tagging "water white" liquids is
 quite limited.
 Also, although a wide number of chemicals have been described as suitable
 "markers" for petroleum fuels, only a relatively small proportion of these
 are commercially viable and actually used as petroleum markers. The number
 of commercially viable markers is further reduced by the stricter
 standards for "water white" liquids. With a wide variety of tax
 structures, brand names, and possible adulterants, there exists a need for
 additional marking systems, particularly for "water white" liquids.
 Surprisingly, it is found that a blue-to-purple component(s), typically
 having an absorbency peak in the 600-700 nm range, and a yellow
 component(s), typically having an absorbency peak in the 400-500 nm range,
 may mutually mask their color, the combination appearing "grey" to the
 naked eye and thus undetectable by the naked eye at the total intended use
 level of between about 5 and about 50 ppm.
 Actual combinations of colored components must be determined empirically
 from available markers and dyes. Also, the relative proportions of two
 components must be empirically determined according to their color
 intensity. However, such empirical determination is within the scope of
 the art.
 Compounds generally thought of as "markers" are generally extractable with
 an aqueous solution, either alkaline or acidic, depending upon the
 chemical nature of the "marker". Chromophoric reaction may be with the
 base or acid of the extracting solution or with a color developing
 compound, e.g., a diazo reactant for an aniline marker as described in
 U.S. Pat. No. 4,209,302. Any such extractable marker, when used as part of
 a plural component system in accordance with the invention may be
 similarly identified as heretofore described. Both extractable markers and
 non-extractable dyes may also be detected spectrophotometrically as
 described above. Accordingly a variety of suitable combinations are
 possible including:

first component second component
 a non-extractable dye a non-extractable dye
 an alkaline aqueous extractable marker a non-extractable dye
 an acidic aqueous extractable marker a non-extractable dye
 an acidic aqueous extractable marker an alkaline aqueous extractable
 marker
 A third, forth, etc. component(s) selected from any of the above-mentioned
 types may be added for color balancing. Most systems in accordance with
 the invention, however, will be limited to a combination of two to three
 markers and/or dyes. It is to be understood, however, that many markers
 and dyes are, due to their method of synthesis, actually a mixtures of
 several related chemical compounds. If one of the components is to be
 identified by extraction, either acidic aqueous or alkaline aqueous, the
 extractant should not extract any of the other components of the color
 mixture.
 Examples of components absorbing in the 560 to 700 nm range include:
 Non Extractable Dyes
 Solvent Blue 98
 Solvent Blue 79
 Alkaline Aqueous Extractable Marker
 1-akyl amino-4-hydroxy 9,10 Anthracenedione
 Examples of components absorbing in the 400 to 500 nm range include:
 Non Extractable Dyes
 1-phenyl-3-methyl-4-(alkylphenylazo)-5-pyrazalone
 Solvent Yellow 107
 Solvent Yellow 96
 Solvent Yellow 174
 Solvent Yellow 124
 Solvent Yellow 56
 Acidic Aqueous Extractable Marker
 4-(2-methoxyphenylazo)-1-(3-methoxypropyl-amino)naphthalene
 alkaline aqueous extractable markers
 Phenol, 2,6 Bis(1-methyl-propyl-4-[4-nitro phenyl]-azo
 Phenol, 2,6 Bis(1-methyl propyl)-4-[2-nitro phenyl]-azo
 Phenol, 2,6 Bis(1-methyl-propyl)-4-[3,4di chloro phenyl]-azo
 Phenol, 2,6 Bis(1-methyl-propyl)-4-[2-chloro-4nitro phenyl]-azo
 Disazo dye; phenylazo-n-phenylazo-phenyl-benzamide, alkyl derivative
 Additional examples of marker components for plural component systems in
 accordance with the invention can be found for example, in U.S. Pat. Nos.
 4,209,302, 4,735,631, 5,156,653, 5,205,840, 5,252,106, 5,490,872,
 5,737,871, 5,905,043, the teachings of each of which are incorporated
 herein by reference. Additional examples of dyes useful in the invention
 can be found in U.S. Pat. No. 5,142,030, the teachings of which are
 incorporated herein by reference. Again, because achieving a grey is
 dependent upon color factors of the dye, including blue, yellow, and red
 color factors, color balancing is empirical. The empirical color balancing
 may also take into account any color factors naturally occurring in the
 liquid, e.g., yellow impurities in petroleum fuel.
 While a yellow marker or dye is best masked with a blue or purple, in some
 cases a red dye, such as Solvent Red 164 having a maximum absorbance peak
 at about 520 nm may be added as well.
 In accordance with one aspect of the invention when an alkaline extractable
 marker is used in conjunction with a non-extractable dye in a petroleum
 fuel, the specimen is desirably first extracted with an acidic aqueous
 solution to remove any yellow colored impurities. Thereafter, the marker
 may be extracted with alkaline aqueous solution and identified in a
 conventional manner.

The invention will now be described in greater detail by way of specific
 examples:
 EXAMPLE 1
 A blend of (A) phenol, 2,6-bis(1-methyl propyl-4-[4-nitro phenyl]azo, an
 amine-extractable molecule described in Example 1 of U.S. Pat. No.
 5,156,653; (B) Solvent Red 164; and (C) Solvent Blue 98 at a 94:2.04:3.96
 weight ratio is added at 10 ppm total to xylene. Color is undetectable.
 EXAMPLE 2
 A blend of (A), the reaction product of phenyl-ethyl ethanolamine and
 diazotized aniline described in Examples 1 and 2 of U.S. Pat. No.
 5,737,874; (B) Solvent Blue 98; and (B) Solvent Red 164 are mixed at a
 weight ration of 80:13.4:6.6. At 10 ppm total in xylene, color is
 undetectable. Compound (A) is extractable in acidic aqueous solution.