Field

The present specification concerns marking liquids, especially hydrocarbon liquids, with tracer materials. The present specification in particular concerns marking hydrocarbons which are taxable or liable to be subject to tampering or substitution, such as gasoline and diesel fuels for example.

Background

It is well-known to add tracers to hydrocarbon liquids. A typical application is the tagging of hydrocarbon fuels in order to identify the fuel at a subsequent point in the supply chain. This may be done for operational reasons, e.g. to assist in distinguishing one grade of fuel from another, or for other reasons, in particular to ensure fuel quality, deter and detect adulteration and to provide a means to check that the correct tax has been paid. Apart from fuels, other products, such as vegetable oils may be marked to identify the product produced at a particular source, or certified to a particular standard.

One problem which is known to exist with the marking of fuel liquids in particular is the potential for the tracer to be removed, by evaporation from the fuel, by degradation of the tracer through ageing or exposure to environmental conditions such as heat, sunlight or air or alternatively by deliberate removal of the tracer for unlawful purposes such as for avoidance of tax. Methods for deliberate removal of tracers include adsorption of the tracer onto common adsorbent materials such as charcoal or clays, exposure to radiation, such as ultraviolet light, oxidation etc. A useful fuel tracer therefore needs to be resistant to removal by these common methods and also to more sophisticated treatments such as treatment with acids and/or bases.

Various compounds are known in the art for use as markers for liquid hydrocarbons and other fuels and oils. These include: biphenol ether compounds (W02013/003573); trishydroxyphenyl ethane ethers (WO2014/088898); tetraarylmethane ethers (W02015/171304 and W02015/171305); alkyl trityl phenyl ethers (WO2014/165776); and substituted phenolphthaleins (KR 20110038893).

In addition to the above, WO2012/177614 and WO2012/177632 disclose benzyl ethers of bisphenol A for use as fuel and oil markers according to the following formula: wherein Rl and R2 independently represent hydrogen or C1-C4 alkyl groups, and G represents hydrogen or at least one substituent selected from the group consisting of C1-C18 alkyl and Cl- C18 alkoxy.

It is an aim of the invention to provide tracer compounds and methods of marking hydrocarbon liquids which are more resistant to removal of the tracer than other known tracers or have a similar resistance to removal but are more simple or cheap to manufacture and/or are more readily detectable in hydrocarbon liquids such as fuels.

Summary of invention

The present specification is directed to a method of marking a hydrocarbon liquid comprising adding to said hydrocarbon liquid a tracer compound, the tracer compound having a structure of Formula I:

Formula I wherein Rl, R2, R3, R4, R5 and R6 are the same or different and selected from hydrogen, straight chain, branched or cyclic alkyl groups or aryl groups, and wherein at least one, two, three, four, five, or all six of Rl, R2, R3, R4, R5 and R6 is not hydrogen. It is preferred that the R groups are straight chain, branched or cyclic alkyl group rather than aryl groups with straight chain or branched alkyl groups being most preferred. Alkyl groups are particularly preferred for at least R5. The R groups may be C3 to C20, C4 to C20, C ₆ to C20, or Cg to C20 groups. The R5 groups may be the same or different. In certain examples, the R5 group on the middle aromatic ring is hydrogen. Similarly, the R6 groups may be the same or different. In many examples, R1 and R2 are the same as R3 and R4. Furthermore, for certain applications it is required that the tracer compound consists only of atoms selected from the group carbon, hydrogen, and oxygen.

The substituted tracer compounds as defined above have several advantages as discussed below.

The presence of bulky, non-planar substituent groups, such as alkyl groups, reduces the planarity of the molecule improving its resistance to adsorption. As such, the compounds as described herein have improved resistance to laundering.

In addition to reducing the planarity of the tracer compounds, non-planar alkyl substituents on the aromatic rings can also serve to increase the non-polar nature of the tracer molecule thus helping to protect the molecule and ether linkage from potential reaction with any aqueous reagents which may be used in an attempt to remove the molecule from the fuel.

It has also been found that while functionalization of the core structure with non-planar alkyl groups increases its mass, the molecules are surprisingly quick eluting by gas chromatography for their mass. The combination of higher mass while remaining relatively quick eluting is a very useful combination of properties as it means the tracer molecules elute at least with some of the components of the hydrocarbon liquid in which they are disposed but can still be resolved from those components by virtue of their mass. For example, the tracer molecules as described herein are heavier than most of the components of a typical fuel (gasoline or diesel fuel) but are still readily distinguishable from the fuel components which elute at a similar rate as the tracer molecules.

Furthermore, it can sometimes be the case that prior art tracer molecules operate best in one or other of gasoline and diesel but not both. Due to the combination of properties as outlined above, the substituted molecules as described herein can operate well in both fuels while satisfying the other critical requirement of non-launderability.

Further still, the tracer molecules of the present invention can consist of atoms selected only from the group carbon, hydrogen, and oxygen which is a specified requirement for certain fuel marking applications. Additionally, the tracer molecules do not contain reactive functional groups or fused-ring structures which would otherwise decrease their resistance to laundering.

Finally, the basic core structure enables a family of related tracer molecules to be derived. That is, a suite of molecular tracers can be produced simply by varying the species that is reacted with the biphenol core. The R groups of the biphenol core, while typically being Ci to C20 groups, can be intentionally varied to provide a suite of tracer compounds. As each compound in the family will possess a different mass or affinity to the separation column, they can all be distinguishable from each other by gas chromatography mass spectrometry (GC-MS). Such a suite of tracer compounds is very useful for marking hydrocarbon liquids (e.g. fuels) from different sources and/or for marking a hydrocarbon liquid with a combination of different tracer molecules.

A method of marking a hydrocarbon liquid, such as a gasoline or diesel fuel, is thus provided comprising adding a tracer compound as defined above to the hydrocarbon liquid. The method may further comprise analysing a sample of hydrocarbon liquid of unknown origin to determine whether the sample comprises the tracer compound and thus determine the origin of the hydrocarbon liquid.

Further still, there is also provided a hydrocarbon liquid, such as a gasoline or diesel fuel, comprising a tracer compound as defined above.

Brief Description of the Drawings

For a better understanding of the present invention and to show how the same may be carried into effect, certain embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:

Figure 1 shows the generic structure of tracer compounds as described in this specification; Figure 2 shows the generic structure of a sub-set of tracer compounds as described in this specification;

Figure 3 shows the generic structure of another sub-set of tracer compounds as described in this specification; Figure 4 shows the structure of two commercially available bisphenol core structures which can be used to derive a range of molecules according to the present specification;

Figure 5 shows a reaction scheme for the synthesis of one of the biphenol structures shown in Figure 4;

Figure 6 shows a modified reaction scheme for the synthesis of bisphenol structures in which the terminal aryl rings are alkylated;

Figure 7 shows an example reaction scheme for the synthesis of an ether compound from a biphenol compound; and

Figure 8 shows a more generic reaction scheme for the synthesis of an ether compound from a biphenol compound.

Detailed Description

As described in the summary section, the present specification provides a tracer compound for marking a hydrocarbon liquid, the tracer compound having a structure of Formula I:

Formula I wherein Rl, R2, R3, R4, R5 and R6 are the same or different and selected from hydrogen, straight chain, branched or cyclic alkyl groups or aryl groups, and wherein at least one, two, three, four, five, or all six of Rl, R2, R3, R4, R5 and R6 is not hydrogen.

It is preferred that the R groups are straight chain, branched or cyclic alkyl groups rather than aryl groups with straight chain or branched alkyl groups being most preferred. Alkyl groups are particularly preferred for at least R5. The R5 groups may be the same or different. In certain examples, the R5 group on the middle aromatic ring is hydrogen. Similarly, the R6 groups may be the same or different. In many examples, R1 and R2 are the same as R3 and R4. Furthermore, for certain applications it is required that the tracer compound consists only of atoms selected from the group carbon, hydrogen, and oxygen.

The or each of Rl, R2, R3, R4, R5 and R6 can consist of atoms selected only from the group carbon, hydrogen, and oxygen. As such, for applications which specify that the tracer must only contain carbon, hydrogen, and/or oxygen atoms, embodiments of the tracer compound as described herein can fulfil this requirement.

The tracer compound may have a structure of Formula II as shown in Figure 2 (para substituted on the middle ring):

Alternatively, the tracer compound may have a structure of Formula III as shown in Figure 3 (meta substituted on the middle ring):

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A method of marking a hydrocarbon liquid is provided comprising adding a tracer compound as described herein to the hydrocarbon liquid. The resultant product is a hydrocarbon liquid, such as a gasoline or diesel fuel, comprising the tracer compound. The hydrocarbon liquid may be a pure compound such as hexane or octane or it may comprise a mixture of compounds such as a distillation fraction having a particular range of boiling points. The hydrocarbon liquid may be intended for use as a chemical, a solvent or a fuel. The tracer compounds as described herein are of particular use for marking liquid hydrocarbon fuels such as gasoline and diesel fuels or liquified petroleum gas. In one particular application a low-tax fuel such as an agricultural diesel may be marked in order to detect any subsequent sale and use for purposes such as road-vehicle fuel which would normally be taxed more highly. In such cases unlawful dilution or substitution of a more highly taxed fuel with the low-taxed fuel may be detected by analysis of the highly taxed fuel to determine whether the tracer is present. Therefore, in these cases, it is highly beneficial to use a tracer compound in the low-taxed fuel which is not easily removed, or laundered, from the fuel to a level at which it can no longer be detected. It has been found that compounds as described herein are resistant to removal from hydrocarbon fuels by multiple known methods of fuel laundering. As such, after marking a hydrocarbon liquid, a sample of hydrocarbon liquid of unknown origin can be analysed to determine whether the sample comprises the tracer compound and thus determine the origin of the hydrocarbon liquid.

The tracer compound is added to the hydrocarbon liquid in such an amount as to provide a concentration of the tracer compound which is detectable by readily available laboratory methods capable of identifying the tracer compound in the liquid at the concentrations used. Suitable methods include but are not limited to gas chromatography coupled with a suitable detector such as a mass spectrometer. Typical concentrations are within the range 1 pg/l to 10000 pg/l with the specific amount dependent on the detection method and limit of detection of the particular tracer compound used. The tracer compound may be present at a higher concentration than 1000 pg/l although when the product to be marked is a high-volume commodity such as a motor-fuel, economic considerations usually favour lower levels of tracer compound. The tracer compound may be supplied in the form of a concentrated dosing solution (or master-batch) of the tracer compound in a solvent. In this case the preferred solvent is a liquid which is similar to the liquid to be marked, although a different solvent, e.g. a single or mixed component aliphatic or aromatic solvent, may be used provided the presence of such a solvent can be tolerated in the hydrocarbon liquid to be marked. A preferred solvent is naphtha. The concentrated dosing solution can be added to the hydrocarbon liquid to be marked so as to produce the required final concentration of the tracer compound by dilution. More than one tracer compound may be added to the hydrocarbon liquid. Figure 4 shows the structure of two commercially available bisphenols each of which can serve as the core structure of a range of molecules according to the present specification. As they stand, the molecules in Figure 4 are relatively non-polar. Flowever, they do contain hydroxyl groups which are susceptible to reaction with a Brpnsted-Lowry base, such as a metal hydroxide or carbonate. Reaction with a base would make the core molecule anionic, which could result in greater solubility in an aqueous phase. A greater aqueous solubility means the molecule would partition between fuel and any aqueous layer, which would create a potentially viable method for lowering the concentration of the molecule in the fuel. Reducing the concentration of a fuel marker chemical to a non-detectable level is synonymous with 'laundering' the marker from the fuel.

Both of the molecules in Figure 4 have a mass of 346.5 amu. This is approaching the upper end of the distribution of molecular weights in diesel fuel which means that both bisphenol M and bisphenol P could potentially be used as marker chemicals for fuel without further modification. Flowever, they would be subject to the limitations described in the preceding paragraph.

Alkylation of the hydroxy groups in both these molecules would render them more inert and would increase the mass of the molecules placing it beyond the normal mass of components observed in a diesel fuel. Their molecular mass would also be significantly outside the range of masses observed in gasolines.

A suite of non-launderable molecules can be fabricated based on one or other structures, bisphenol M or bisphenol P. The following description is limited to bisphenol P, but the ideas may be applied to the use of bisphenol M as the core molecule.

Bisphenol P is made using the synthetic step shown in Figure 5 from the reaction of the dicarbinol of 1,4-di-isopropylbenzene and phenol as described in US3393244. An alternative synthesis is described in GB935061 starting from 1,4-di-isopropenylbenzene and phenol. l,4-bis(2-hydroxy-isopropyl)benzene and phenol are readily available. Flowever, there is no reason why Rl, R2, R3, and R4 need be methyl groups nor why a substituted phenol could not be used. This would give rise to the molecule in Figure 6.

Alkylation of bisphenol P by octylbromide with potassium hydroxide in dimethylsulfoxide is described in JP0665479 and shown in Figure 7.

Alternative alkylhalides may be used to give a suite of molecules of formula shown in Figure 8. The substituents Rl, R2, R3, R4, R5, and R6 serve several purposes. They increase the mass of the molecules making them more discernible from the background distribution of molecules in the fuel. They render the molecules more non-polar and so more fuel soluble, resulting in molecules which are harder to extract from the fuel by chemical manipulation. The use of bulky substituents render the molecule less likely to be adsorbed onto activated charcoal which is a common laundering reagent for fuels. Use of different substituents generates molecules of differing boiling point and differing shape and so allow their discrimination from one another by chromatographic techniques, such as gas chromatography or liquid chromatography. This means a plurality of molecules can be created. Detection of the molecules by mass spectrometry is preferred but other techniques can be used. The preferred analysis technique is GC-MS.

While this invention has been particularly shown and described with reference to certain embodiments, it will be understood to those skilled in the art that various changes in form and detail may be made without departing from the scope of the invention as defined by the appended claims.