GB2354070A

GB2354070A - Markers for identifying liquids

Info

Publication number: GB2354070A
Application number: GB9921169A
Authority: GB
Inventors: Duncan William John Mccallien
Original assignee: JOHN HOGG TECHNICAL SOLUTIONS
Current assignee: JOHN HOGG TECHNICAL SOLUTIONS
Priority date: 1999-09-07
Filing date: 1999-09-07
Publication date: 2001-03-14
Also published as: GB9921169D0

Abstract

Liquids e.g. fuels are marked by the addition of a compound that absorbs strongly in the near ultraviolet region of the spectrum. The preferred compounds are porphines or porphyrin derivatives. The markers may be used in conjunction with conventional standard solvent dyes. Detection is typically with a spectrophotomer or fluorimeter.

Description

2354070 Title: A Method for Marking Liquids The present invention concerns

a method for marking liquids, describes some compounds suitable for this method and modes of detection. In particular it is suitable for marking organic solvents such as petroleum based products.

It is often necessary to mark faels for fiscal purposes so as to distinguish between the taxed and untaxed ones or to provide brand identification in organic based liquids. The simplest way of doing this is to colour the material using a solvent soluble dyestuff because the measurement of colour can either be done by eye or by using a spectrophotometer. In some cases a confirmatory marker chemical is also present with the dye. This latter chemical is colourless but becomes strongly coloured on addition of a chemical reagent. Its role is to help ensure that the source of the colour really was the misuse of another grade of fuel and not accidental.

Suitable marker chemicals are usually added to the liquid in tiny amounts (< 50 ppm) and must be chosen so that their properties do not affect those of the bulk liquid. Similarly they must impart negligible cost to the liquid and must be easily detectable should the liquid be diluted to 5-10 % strength with another solvent.

Any marker chemicals added to a liquid must impart little or no discernible colour to the liquid and yet must be readily distinguishable from the liquid either by their chemical reactivity or by their physical properties. So for example US 5498808, EP 0438734, WO 95/00606, US 5205840 and WO 95/10581 all describe the application of acids or bases to hydrolyse or ionise a species so causing it to become strongly coloured and often extractable into an aqueous phase. Similarly the specific reactivity of certain compounds for certain reagents is detailed in WO 95/07460 and WO 96/02613. In all of the above examples the chemical properties of the marker compound when included in the ftiel must be different in at least one 2 aspect from the properties of the fuel and must react rapidly enough for convenient identification of the ftiel. All require the addition of a reagent to the fuel and generally result in permanent changes occurring to the mixture. Despite the widespread use of such systems false positive results can occur from different compounds that coincidentally produce the same colour in the test reaction but which exist naturally in some fuels.

More subtle types of marker chemicals exist that can be detected by their spectroscopic properties alone. The absorbance of materials in the ultraviolet, visible and near infrared regions is particularly easy to measure. Patents WO 94/02570, EP 0484018 and US 5525516 describe the use of compounds with a strong absorption (and sometimes fluorescence) in the near infrared region of the spectrum. Such properties are not usually shown by an organic liquid and especially when they are seen together indicate the presence of the marker.

The aim of the present invention is to provide a method for marking liquids using compounds that can be detected spectroscopically in the near ultraviolet (NUV) region. Some of these compounds can also have a fluorescence in the orange region of the visible spectrum. They offer an advantage over near infrared absorbing compounds as their molar absorption coefficients are typically >10x the size in the appropriate region of the spectrum, thus less than one tenth the quantity can be used for the same ease of detection. In practice this means that concentrations of parts per million or less may be used as opposed to 10's ppm.

This invention concerns the use of compounds which have a pronounced NUV absorption. Such NUV absorbing compounds are added to the liquid at concentrations as to impart little or no colour to the liquid but at a sufficient concentration as to present a characteristic absorbance in the ultraviolet region of the spectrum. Preferably these compounds are chosen so as to have a sharp 3 absorbance just outside the visible region of the spectrum in the NUV region. In many organic liquids there is an absorption window between the visible spectrum and where the liquid begins to absorb strongly in the ultraviolet region. The compounds in this document have very strong and sharp absorbances in this region: they can therefore be detected very easily and at low concentrations.

The preferred compounds of this invention are based on the porphyrin unit. These preferred compounds are particularly suited to use in fuels as they are stable over a six month period and may be used at ppm levels or less. They are preferably added at a rate that imparts no colour to the liquid to be marked. In addition they can also show a characteristic orange fluorescence which provides a secondary means of identifying that the marker is present.

The porphyrins are preferably added to the liquid by means of a concentrated solution as they can be sparingly soluble in non-polar solvents such as petroleum products. Such a concentrate has to be miscible with the fuel and contain the greatest proportion of the porphyrin so as to minimise the quantities of the concentrate required. Preferable formulations are based around commercial blends of aromatic organic solvents such as alkylbenzenes or alkylnaphthalenes with the optional use of polar organic solvents or oxygenated solvents in order to increase the solubility. Polar solvents typically include formamide, N, Ndimethylformamide, N-methylpyrrolidone and cresols. These solvents may be used singly or in blends.

The absorbance of the compound in the organic liquid is chosen to be above 0. 1 (in a 10 min cell) and preferably between 0.5-1.5 absorbance units. A concentrate of 0.1-10% of the porphyrin in an organic solvent blend is preferred. A preferable addition rate of the porphyrin is 1-5 ppm with detection being possible down to less than 50 ppb amounts.

4 The compounds in this present invention may be used in conjunction with standard solvent dyes or other marker chemicals which have been outlined earlier so long as the principal absorbances of the latter are outside the region 390-450 nm. For example the porphyrins may be used in conjunction with typical solvent dyes such as mono and bis-azo dyes, quinoline, methine, xanthene, perylene and anthraquinone based dyes. Alternatively they may be used in conjunction with, or added as a mixture with, marker chemicals that require the addition of basic reagents for the formation of colour such as coumarin, quinizarin and compounds covered by WO 96/32462.

A preferred class of NUV absorbers are porphyrin based. These can absorb sharply from 390 nm into the visible region and can have absorption coefficients (F-) of above 400,000 M-1 cm-1. Thus they can be used at concentrations that impart little or no visible colour to the liquid to be marked but still have an absorbance of up to 2 units in a 10 mm cell. They are preferably used at concentrations of 1-5 ppm.

NUV absorbers based on a porphyrin core are shown in figure I where R', R4, R' and R" are for example hydrogen; substituted phenyl, naphthyl or anthracenyl units where the substituents thereon include R', W, R', R', R', R', R" and R" as defined below or carboxylic or sulphonic acid groups; acetylenyl; vinyl; methoxy; nitro; amino; halo groups; oxo groups or substituents that are in turn bonded to 2 12 further porphyrin units. R, W, R', R6, R', R', R" and R may either be the same or different and may be alkyl chains of CI to C 20 atoms for example methyl, ethyl, propyl, iso-propyl, butyl, iso-butyl, sec-butyl, tert-butyl, pentyl, iso- pentyl, neopentyl, tert-pentyl, hexyl, 2-methylhexyl, heptyl, octyl, 2ethylhexyl, iso-octyl, nonyl, iso-nonyl, decyl, iso-decyl, undecyl, dodecyl, tridecyl, 3,5,5,7tetramethylnonyl, iso-tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, 6 8 octadecyl, nonadecyl, eicosyl. Alternatively substituents R2, R, R', R, R, R9, R" and R" may be hydrogen, carboxylic esters, substituted phenyl, amino, nitro, halo, oxo or vinyl groups. In addition R', R, R', R 6, R8, R9, R" and R" may form with one another one or more fused rings conjugated with the porphyrin core; any of these rings including the central core can possess one or more unsaturated regions. M can be hydrogen, a divalent metal for example copper, zinc, magnesium, cobalt, nickel or a trivalent metal such as iron (III).

A preferred structure is a porphyrin where substituents R1, R', R' and R" are phenyl groups or substituted phenyl groups and R2, R', R', R 6, R 8, R9, R" and R 12 are hydrogen atoms. Such tetra(aryl)porphyrin units are more stable to aerial oxidation, present reasonable solubilities and have high molar NUV absorptivities as they are still planar. Tetra(aryl)porphyrm's can also be synthesised in a standard one-pot reaction: brief details of the synthesis are included in the examples cited. The solubilities of these compounds may be increased by using a mixture of alkyl substituents on the phenyl groups. These preferred porphyrins are shown in figure 2 where R 13, R 14, R 15 and R" are alkyl groups as defined for R2, R3, R', R 6, R', R9, R" and R", hydrogen, carboxylic esters, substituted phenyl, amino, nitro, halo, vinyl, acetylenyl, carboxylic or sulphomic acid groups and where in varies from 05.

The following examples illustrate but do not limit the scope of the invention:

Examplel: 5,10,15,20-tetra-p-tolyl-21,23H-porphyrin (Figure 3) Propionic acid (100 g, 20 equiv.) and p-tolualdehyde (8.09 g, I equiv.) were heated to reflux in a two necked round bottomed flask. Pyrrole (5 g, 1. 11 equiv.) was then added by syringe and the mixture heated for 1.5 hours again to reflux (155'C). After cooling the solution was filtered at a water pump and the purple crystals washed with methanol (100 ml), water (100 ml) and then finally with more methanol. Yield: 1.98 g (17 %). (log & in toluene) = 420 (5.64), 516 (4.31), 550 (4.06), 592 (3.67), 651 (3. 73). A typical concentrate would then contain from 6 0. 1 - I % of the porphyrin in a blend of an aromatic solvent and a polar solvent. The ratio of solvents obviously determines the ultimate concentration accessible, the stability and the miscibility. A preferred ratio contains an equal mixture of an organic solvent blend with a polar solvent such as cresylic acid or Nmethylpyrrolidone.

Example 2: 5,10,15,20-tetra-3,,5-(di-tert-butylphenyl)-21,23H-porphyrin (Figure 4) Propionic acid (20.34 g, 40 equiv.) and 3,5-di-tertbutylbenzaldehyde (1.5 g, I equiv.) were heated to reflux in a two necked round bottomed flask. Pyrrole (0.506 g, 1. 1 equiv.) was then added by syringe and the mixture was heated for 1. 5 hours again at reflux (155'C). A-fter cooling the solution was filtered at a water pump and the purple crystals washed with methanol (50 ml), water (50 ml) and then finally with more methanol. Yield: 0.14 g (8 %).,Ix (log s in toluene) = 421 (5. 71), 516 (4.23), 550 (3.88), 595 (3.51), 650 (3.51). A concentrate of 5% by weight of this porphyrin was prepared in a commercial aromatic solvent blend. A preferred solvent blend is based on mixed alkylbenzenes. This alleviates the necessity of using a polar co-solvent to achieve a high concentration of the porphyrin: some polar aprotic solvents can inhibit the miscibility of the concentrate with certain fuels.

Example 3: mixture of 5,10,15,20-tetra-aryl-21,23H-porphyrins (Figure 5) Propionic acid (199 g, 40 equiv.), benzaldehyde (6.43 g, 0.9 equiv.) and ptolualdehyde (0.805 g, 0.1 equiv.) were heated to reflux in a two necked round bottomed flask. Pyrrole (5 g, 1.10 equiv.) was then added by syringe and the mixture heated for 1.5 hours again at reflux (155'C). After cooling the solution was filtered at a water pump and the purple crystals washed with methanol (100 ml), water (100 ml) and then finally with more methanol (100 ml). Yield: 1.49 g (14 %).,,,x (log & in toluene) = 419 (5.68), 514 (4.28), 548 (3.87), 593 (3.56), 650 (3.40). The mixed porphyrins may be dissolved to make a I % concentrate 7 using a blend of xylenes and a polar protic solvent. A preferred ratio of solvents is 5-40 % cresylic acid with 60-95 % xylenes.

Preferable porphyrin concentrates contain from 0.1-10 % of the porphyrin in an aromatic solvent blend mixed with either a polar or aprotic solvent optionally present. Preferred polar aprotic solvents include Nmethylpyrrolidone and NNdimethylformamide: a useful polar protic solvent is cresylic acid. The ratio of solvents could then vary from 040% of the polar solvent and 60-100 % of a commercial aromatic solvent blend. Such porphyrin concentrates can also be added to organic based solutions which are designed to be miscible with aqueous systems. Thus inherently insoluble porphyrin based NUV absorbers may be used to mark aqueous systems in addition to organic systems. Typical levels for the fmal concentration of the porphyrin in a fuel or other liquid are between 0. 1 and 5 ppm. A preferred concentration of any of the porphyrins in the preceding three examples is 1.5 ppm which typically gives an absorbance at,na, of -1.0 in a liquid such as kerosene, gasoline or diesel. For quantitative determinations of the marker in a fuel by UVNis spectroscopy the sample should be measured against a comparable unmarked sample of the liquid to account for residual background absorption between 390 nm and 450 nm. Usually no further manipulation of the marked liquids is necessary prior to measurement.

NUV absorbing compounds can be used in conjunction with standard solvent dyes that are used for colouring fuel so long as the principle absorption of the latter is outside the 390-450 nm region. Classes of solvent dyes can include mono-azo, bis azo dyes such as solvent red 19, quinoline and methine based dyes, xanthenes such as solvent green 4, perylenes such as solvent green 5 and anthraquinone based dyes such as solvent blue 35.

Similarly porphyrin based NUV absorbing compounds may be used in combination with, or added as a mixture with, marker chemicals which are frequently used in fuels and become coloured on addition of a base. These chemicals include quinizarin, cournarin and compounds that are described in WO 96/32462 where the extracted layer is coloured.

Alternatively the marker compounds described herein often show characteristic fluorescence maxima which may be readily differentiated from the matrix in which they are dissolved even at concentrations < I ppm. The fluorescence is usually in the orange region of the spectrum (> 600 nm) which means that it is readily distinguished from the inherent blue fluorescence of fuels. This offers an alternative method of detection and still allows concentrations of marker chemicals to be used in fuel that impart no colour to the eye.

NUV marker chemicals based on porphyrins therefore can have two properties that may both be detected at sub ppin levels with a spectrophotometer and fluorimeter, which are not a usual characteristic of organic liquids, for example fuels, where the second property serves as confirmation of the chemical in the liquid.

9

Claims

CLAIMS:

1) The use of a compound with a sharp absorbance maximum in the near ultraviolet region of the spectrum as a means of characterising a liquid.

2) A method as outlined in claim 1 wherein the compound or compounds employed are used at levels that impart little or no colour to the liquid to be marked.

3) The use of a UV/ Vis spectrophotometer for detecting the compounds in a liquid as marked in claims I and 2.

4) The use of a fluorimeter for detecting the compounds in a liquid as marked in claims I and 2.

5) The use of a compound as in claims 1, 2 and 3 such that it has an absorption between 0. 1 and 2 units in a standard 10 nun cuvette at its maximum absorbance as measured by UV/ Vis spectroscopy.

6) A method for the addition of the compounds in previous claims to organic liquids as concentrated solutions.

7) A method as in claim 6 where the concentrated solution contains an aromatic solvent blend.

8) A method as in claim 7 where the preferred aromatic solvent blend consists of alkylbenzenes, alkylnaphthalenes or a proprietary blend of such compounds.

9) A method as in claims 6, 7 and 8 where a polar protic or aprotic solvent may also be added to increase the solubility of the marker compound.

10)A method as in claims 6-9 wherein the concentrate contains 0.1-10% of the marker chemical.

I I)A method as in any one of the preceding claims wherein the marker compounds are used at a concentration of 0. 1-5 ppm in the liquid to be marked.

12)A method as in any one of the preceding claims wherein the marker compounds are used in conjunction with a solvent dye.

13)A method as in any of the preceding claims for the use of marking a fuel.

14)The use of a porphine or porphyrin derivative in conjunction with claims 1- 13.

15)A method as in any claims 1-14 wherein the compounds are used in conjunction with colourless marker chemicals which require alkaline conditions for the formation of colour in an extracted layer.

16)The use of a porphyrin or porphine derivative as in claim 14 wherein the 4 general structure is shown in figure 1, where R', R, R' and R" are for example hydrogen; substituted phenyl, naphthyl or anthracenyl units where the substituents thereon include R', R', R', W, R', R', R" and R 12 as defined below or carboxylic or sulphonic acid groups; acetylenyl; vinyl; methoxy; nitro; amino; halo groups; oxo groups or substituents that are in turn bonded to ftuther 2 6 12 porphyrin units. R, R, R', R, R', R', R" and R may either be the same or different and may be alkyl chains of CI to C 20 atoms for example methyl, ethyl, propyl, iso-propyl, butyl, iso-butyl, sec-butyl, tert-butyl, pentyl, iso-pentyl, neopentyl, tert-pentyl, hexyl, 2-methylhexyl, heptyl, octyl, 2-ethylhexyl, iso-octyl, nonyl, iso-nonyl, decyl, iso-decyl, undecyl, dodecyl, tridecyl, 3,5,5,7tetramethylnonyl, iso-tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, 2 5 12 octadecyl, nonadecyl, elcosyl. Alternatively R, W, R, R6, R, R9, R" and R substituents may be hydrogen, carboxylic esters, substituted phenyl, amino, nitro, halo, oxo or vinyl groups. In addition R 2, R', R 5, R 6, R', R9, R" and R 12 may form with one another one or more fused rings conjugated with the porphyrin core; any of these rings including the central core can possess one or more unsaturated regions. M can be hydrogen, a divalent metal for example copper, zinc, magnesium, cobalt, nickel or a trivalent metal such as iron (111).

17)The preferred use of compounds shown in figure 2 where R 13, R 14, R 15 and R 16 are alkyl groups as defined for R2, R', R 5, R 6, R', R', R" and R 12, hydrogen atoms, carboxylic esters, substituted phenyl, amino, nitro, halo, vinyl, acetylenyl, carboxylic or sulphonic acid groups and where in varies from 0-5.

18)The use of a blend of such porphyrins as described in claims 16 and 17.

19)The use of a compound as in claim 16 where R1, R4, R7 and R10 are ptolyl 2 3 6 12 groups, R, R, R', R, R', R9, R", R and M are hydrogen atoms (figure 3).

I I 20)The use of a compound as in claim 16 where R', R4, R' and R'O are 3,5- dl-(tertbutyl)phenyl groups, R2, R', R', R6, R, R', R", R 12 and M are hydrogen atoms (figure 4).

21)The use of a mixture of compounds as described in claims 16 and 18 where RI, W, R7 and R10 are differently substituted aryl groups (being either phenyl or tolyl groups) and R2, R', R, R6, R', R', R", R 12 and M are hydrogen atoms (figure 5).

22)The detection of such compounds as in the preceding claims by means of their fluorescence.