USE IN AN ENGINE

FIELD OF THE INVENTION

The present invention concerns a method of providing a liquid hydrocarbon fuel that is suitable for use in an engine. More particularly, the invention concerns a method of providing a fuel which comprises no more than a prescribed maximum amount of waterborne chloride ions, i.e. CI ^" ions solvated in water. The method of the present invention is particularly suitable for providing a jet fuel for use in a jet engine and a composition, though may also be used to provide fuels suitable for other engines, such as gasoline and diesel for automobiles and trucks.

BACKGROUND OF THE INVENTION

Hydrocarbon fuels which are liquid at ambient handling temperatures, such as kerosene, gasoline and diesel, are often produced at an oil refinery by a continuous process that typically includes a sweetening step, to oxidize any mercaptans in the fuel, followed by a washing step, to reduce or eliminate contaminants remaining in the fuel after sweetening, and a subsequent drying step, to reduce the amount of water retained in the fuel after washing. Drying may involve passing the washed, sweetened fuel through a salt filter, e.g. a salt bed, made of sodium chloride and/or potassium chloride. For example, a jet fuel can be produced by a Merox Treatment Process, such as illustrated in Figure 1 (from http://en.wikipedia.org/wiki/Merox). The use of a salt filter to dry the fuel can substantially eliminate the amount of entrained water and free water retained in the fuel and substantially reduce the amount of dissolved water retained in the fuel. However, salt filtering will not eliminate all water retained in the fuel. IATA Guidelines, that dictate the suitability of jet fuels for fuelling aircraft at airports, currently permit a maximum of entrained and free water content of 30 ppm (mg/1) in a jet fuel at ground level, but the Guidelines do not specify a maximum of water that is dissolved in the jet fuel. Although water is only sparingly soluble in jet fuel, in a hot and humid location, a jet fuel could contain significantly more than 30ppm dissolved water, e.g. up to 100 ppm or more. By virtue of its high solubility in water, the dissolved water can comprise an equivalent amount of dissolved salt. Thus, a commercial grade jet fuel that has been dried by salt filtering will normally comprise a small residual amount of dissolved water and a residual amount of salt dissolved therein. Further, sweetened liquid hydrocarbon fuels which are transported overseas, e.g. in a supertanker, may be potentially contaminated with salt water used as ballast in the ship. When such circumstances may have arisen, it is quite common for the potentially contaminated fuel to be dried by passing the fuel through a filter water separator as the fuel is pumped from the ship to a storage tank. Again, because of the high solubility of salt in water and the fact that filter water separators will not eliminate all water from the fuel, the fuel will retain a residual amount of salt dissolved in residual water.

The presence of excessive amounts of salt in a fuel can be detrimental to the performance of the fuel, as burn efficiency can be reduced, and may be detrimental to the performance of an engine within which the fuel is burnt, as solid deposits may build-up or corrosion occur within the engine over a period of time. Thus, fuels containing an excessive amount of salt are not suitable for use in an engine.

At present, oil refiners measure the amount of salt in a liquid hydrocarbon fuel by techniques that rely upon measuring the amount of chloride ions in the fuel, and a fuel is only considered acceptable when the measured amount of chloride ions in the fuel is at or below a prescribed maximum. The techniques that have been used in the past to measure chloride ions in the fuel tend to be analytical techniques, are time consuming and, in view of the nature of the tests and complexity of the apparatus required to perform them, essentially this requires them to be performed in a laboratory, rather than at the production site. Hence, in a refinery-based situation, these techniques can have the effect of requiring the fuel to be stored whilst tests are undertaken and the fuel determined to be acceptable or not. Examples of such techniques are disclosed in WO2009/123496 and WO2010/133315.

WO2013/150274 discloses a method of determining the suitability of a fuel for use in an engine wherein the fuel may be contaminated with solid particles. The method comprises providing a compound which is soluble in the fuel and which provides a fluorophore when absorbed by, reacted with or coordinated with the solid contaminant particles, forming a mixture of the compound and a test sample of the fuel, exposing the mixture to electromagnetic radiation of such a wavelength that would cause said fluorophore to undergo fluorescence if said fluorophore was present, measuring the amount of fluorescence, comparing that amount of fluorescence against a standard and rejecting or accepting the fuel, as appropriate. This technique cannot be used to determine the suitability of a fuel wherein the fuel may comprise a liquid contaminant, such as residual salt dissolved in residual dissolved water. It is the object of the present invention to provide an alternative method of providing a fuel suitable for use in an engine. Preferably, the method includes a chloride ion measuring technique that does not suffer the problems of techniques previously employed at oil refineries and terminals.

Summary of the invention

The present invention, in its various aspects, is as set out in the accompanying claims. In accordance with one aspect of the present invention, there is provided a method of providing a liquid hydrocarbon fuel that is suitable for use in an engine, said method comprising the following sequential steps:

i) sweetening a liquid hydrocarbon fuel to oxidize any mercaptans in the fuel into more innocuous disulfides;

ii) washing the sweetened liquid hydrocarbon fuel produced in step i) in water to reduce or eliminate contaminants remaining in the fuel after step i);

iii) passing the washed and sweetened liquid hydrocarbon fuel produced in step ii) through a salt filter to reduce the amount of water retained in the fuel after step ii) to an amount at or below a prescribed maximum water content;

characterised in that the method further comprises the following sequential steps:

iv) providing a compound that is a fluorophore, wherein said compound has a first known fluorescence spectrum that is modified in the presence of waterborne chloride ions to provide a second known fluorescence spectrum;

v) contacting a specified amount of said compound with a specified amount of the liquid hydrocarbon fuel produced in step iii) for an amount of time sufficient for any waterborne chloride ions in the fuel to react or coordinate with the compound;

vi) exposing said compound that was contacted with said liquid hydrocarbon fuel in step v) to electromagnetic radiation of a first wavelength;

vii) measuring the amount of fluorescence emitted at a second wavelength by virtue of step vi); viii) comparing the amount of fluorescence measured in step vii) with an amount of fluorescence measured in a similarly tested fuel that contained a prescribed maximum allowable amount of waterborne chloride ions; and

ix) only if the amount of fluorescence measured in step vii) corresponds to the fluorescence emission measured for a fuel that does not comprise more than the prescribed maximum allowable amount of waterborne chloride ions, accepting the fuel as being suitable for use in an engine;

wherein said first wavelength falls within the excitation spectrum of either of said fluorescence spectra but not both, and/or wherein said second wavelength falls within the emission spectrum of either of said fluorescence spectra but not both.

In accordance with another aspect, the present invention provides a method of providing a liquid hydrocarbon fuel that is suitable for use in an engine, said method comprising the following sequential steps:

i) providing in a tank on a ship a mixture of liquid hydrocarbon fuel and sea water;

ii) unloading the mixture of liquid hydrocarbon fuel and sea water from the ship; iii) passing the mixture of liquid hydrocarbon fuel and sea water through a filter water separator to reduce the amount of water retained in the fuel to an amount at or below a prescribed maximum water content;

characterised in that the method further comprises the following sequential steps:

iv) providing a compound that is a fluorophore, wherein said compound has a first known fluorescence spectrum that is modified in the presence of waterborne chloride ions to provide a second known fluorescence spectrum;

v) contacting a specified amount of said compound with a specified amount of the liquid hydrocarbon fuel produced in step iii) for an amount of time sufficient for any waterborne chloride ions in the fuel to react or coordinate with the compound;

vi) exposing said compound that was contacted with said liquid hydrocarbon fuel in step v) to electromagnetic radiation of a first wavelength;

vii) measuring the amount of fluorescence emitted at a second wavelength by virtue of step vi); viii) comparing the amount of fluorescence measured in step vii) with an amount of fluorescence measured in a similarly tested fuel that contained a prescribed maximum allowable amount of waterborne chloride ions; and

ix) only if the amount of fluorescence measured in step vii) corresponds to the fluorescence emission measured for a fuel that does not comprise more than the prescribed maximum allowable amount of waterborne chloride ions, accepting the fuel as being suitable for use in an engine;

wherein said first wavelength falls within the excitation spectrum of either of said fluorescence spectra but not both, and/or wherein said second wavelength falls within the emission spectrum of either of said fluorescence spectra but not both.

Waterborne chloride ions (i.e. CI ^" ions solvated in water) are present in a fuel whenever the fuel has been exposed to water and salt. Though a fuel can be treated to remove a substantial proportion of or eliminate any entrained or free water in it i.e. water that would form a separate, visible aqueous phase if the fuel was left to stand, it is very difficult to remove all the water from the fuel as some dissolved water may be retained in the fuel phase . Water that remains dissolved in the fuel phase e.g. in amounts of up tolOOppm (mg/1) or more, is referred hereinafter as residual water. The residual water does not form a separate aqueous phase when left to strand and is invisible to the human eye in the fuel, so the fuel may appear clear or slightly translucent. Salt is very soluble in water, producing waterborne chloride ions and waterborne metal ions (e.g. Na ⁺ and/or K ⁺ ) in the salt solution. It is very difficult to remove these ions and so waterborne chloride ions are normally retained in the residual water. If the concentration of the solvated chloride and metal ions in the residual water is too high, then the efficiency of a jet engine may be impaired. Detailed Description

Liquid hydrocarbon fuels often become contaminated with various materials such as water, salt, rust particles derived from storage vessels and pipelines and dust particles from vented storage vessels. Several techniques exist to rapidly determine many of these materials using simple analytical techniques that are able to be performed anywhere using simple mobile units. In the case of detection of chloride salts, however, these have historically only been determined using lab based analytical techniques or aqueous based techniques that require extraction into a water phase prior to testing. These are time consuming techniques and cannot be performed at the production site. The present invention allows the potential to perform analysis expeditiously. It also allows the analysis to be performed at the production site.

The present invention relies on reacting a fluorescent material with chloride salts in the fuel phase. The fluorescent material must be preferentially reactive with chloride in order to minimize interference from other chemical species. The reaction can be done using various methods.

One technique involves the introduction of a fuel sample to a liquid fluorescent material, which can be shaken for a given period of time and then placed into a detection unit to evaluate the level of fluorescence. This can be correlated to a calibration graph to determine the amount of chloride in an unknown sample.

A second and more preferred option is to allow a fuel sample to flow through a pre-treated pad, such as a fabric made of woven or nonwoven fibres, treated with the desired fluorescent material. A distinct colour change on the pad will indicate the presence of chloride and the area of colour change (intensity) will be related to the amount of chloride present. This colour change may only be present when a light source of the correct wavelength is applied to the pad. The fluorescent material can have an excitation and emission wavelengths of any suitable value such that determination is simple. Preferentially, the emission wavelength is between 500 and 540 nm and most preferentially between 500 and 520 nm. Typically, the fluorescent material can be any chemical that preferentially reacts with chloride and emits fluorescence at the required wavelength. Such chemicals are typically but not limited to the following: Fluorescent Yellow 13 ISC, Nile Blue A, Trans-Stilbene, Cis-Stilbene, Fluorescent Red Pigment, 6-Methoxy-N-(3-sulfopropyl)quinolinium, N-(Ethoxycarbonylmethyl)-6- methoxyquinolinium bromide, sodium fluorescein, 6-Methoxy-N-ethylquinolinium iodide and Ν,Ν'- Dimethyl-9,9'-biacridinium dinitrate. Other materials will be apparent to those skilled in the art.

In the above aspects of the invention the chloride exists as a contaminant i.e. it is not a desirable component of the liquid fuel or oil. The chloride exists or is introduced as a contaminant in the liquid fuel or oil when e.g. seawater is added to the liquid fuel or oil accidentally or inadvertently, or deliberately as ballast, or saltwater is incorporated such as from salt drying processes. Other mechanisms of contamination will be apparent to those skilled in the art. The term "fluorescent" means the emission of electromagnetic radiation, especially of visible light, stimulated in a substance by the absorption of incident radiation and persisting only as long as the stimulating radiation is continued. The terms "liquid hydrocarbon fuel" and "hydrocarbon oil" are herein used as substantially generic terms for liquids such as diesel; kerosene; gasoline/petrol (leaded or unleaded); aviation fuel; paraffinic, naphthenic, heavy fuel oils, biofuels, waste oils or such as esters, poly alpha olefins (often referred to as synthetic oils) lubricant oils, hydraulic fluids, gear oils etc., and mixtures thereof. The liquid fuels most suitable for practising the present invention are the hydrocarbon fuel oils, most suitably Biodiesel, bioethanol, diesel, kerosene, gasoline/petrol and synthetic fuels such as Fischer- Tropsch type fuels.

The present invention provides a fluorescent material that is reactive to chloride ions present as a contaminant in fuel or hydrocarbon oil. The fluorescent material will have excitation energy of 330 nm to 500 nm and emission energy of 440 nm to 580 nm.

Oil is a hydrocarbon feedstock and can consist of any of the following: diesel, kerosene, gasoline/petrol (leaded or unleaded); paraffinic, naphthenic, heavy fuel oils, biofuels, waste oils or synthetic oils such as esters, poly alpha olefins; etc., and mixtures thereof.

An important area of the invention is for detecting chloride contaminant in fuel or hydrocarbon oil at the refinery allowing rapid determination, which gives a more rapid turnover of fuel usage. Current methods require sampling and testing at external laboratories, which obviously takes time and leads to large quantities of fuel being held until the fuel is approved for use. The detection of the chloride in fuel also allows for a determination of the condition of the salt drier used in the fuel drying process. As the chloride level increases this is an indication that the salt drier is becoming saturated and should be changed.

The fluorescent material is preferably, but not limited to, the following chemical species Fluorescent Yellow 13 ISC, Nile Blue A, Trans-Stilbene, Cis-Stilbene, erythrosin, 6-Methoxy-N-(3- sulfopropyl)quinolinium, N-(Ethoxycarbonylmethyl)-6-methoxyquinolinium bromide, sodium fluorescein, 6-Methoxy-N-ethylquinolinium iodide and N,N'-Dimethyl-9,9'-biacridinium dinitrate. Other chemicals will be apparent to those skilled in the art. The fluorescent material will ideally have an emission wavelength once reacted with the chloride of between 440 nm and 580 nm. More preferably the emission wavelength will be 490 to 530 nm. The fluorescent material should be capable of being made into a liquid form using an appropriate solvent. This liquid form can be used to test a small fuel sample directly or as a means of impregnating the fluorescent material onto a filter pad material that allows the flow of fuel. Any chloride in the fuel will react with the fluorescent material on the pad and show an emission when placed in a suitable test unit. Hand held test units for determining fluorescence are currently available and will be apparent to those skilled in the art.

Two test methods are currently available to utilize this invention. These are given below:

Method 1. This requires a sample of the fuel or oil to be added to a liquid sample of the fluorescent material. The material is then shaken vigorously for a given time frame. After this time the sample is allowed to stand for 1 minute and then placed into an appropriate hand held testing unit. The ratio of fuel to liquid fluorescent can be varied to give the optimum reaction parameters.

Method 2. This requires the pre-preparation of a liquid fluorescent sample that is impregnated on to a suitable filter pad material. This pad is then placed into a suitable holder and a fuel sample allowed to pass through the filter. Any chloride in the fuel will react with the fluorescent sample. Upon completion of the fuel pass the pad is then taken to a hand held test unit where is can be tested for fluorescence. The amount of reduction in fluorescence can be taken as a direct measurement of how much material has reacted and thus gives a determination of chloride content. Alternately, the gain in fluorescence at the emission wavelength of the reacted fluorescent chloride can also be determined and used to derive the chloride concentration.

The permissible limit of sodium chloride concentration varies with fuel type but is typically 500 ppm. All other salts are present in part per billion levels so the chance for interference of this test is minimal. The main interference would come from fluoride ions, which are very uncommon in fuel.

Whilst this method is preferentially aimed at determining chloride content it will be apparent to those skilled in the art that variation of the fluorescent material could lead to determination of other anions that may be present in fuel or hydrocarbon oil. Other than in the operating examples, or where otherwise indicated all numbers expressing quantities of ingredients used herein are to be understood as modified in all instances by the term "about".