GB2546726A

GB2546726A - Method for improving the thermal stability and/or lubricity of fuel

Info

Publication number: GB2546726A
Application number: GB1600366.7A
Authority: GB
Inventors: Assaad Zard William
Original assignee: Palox Ltd
Current assignee: Palox Ltd
Priority date: 2016-01-08
Filing date: 2016-01-08
Publication date: 2017-08-02
Also published as: GB201600366D0

Abstract

A method of improving the thermal stability and/or lubricity of a liquid hydrocarbon fuel, especially at low temperatures. The method comprises the steps of: a) providing a specified amount of liquid hydrocarbon fuel, said liquid hydrocarbon fuel comprising less than 50 ppm water; b) providing at least one surfactant that is capable of dispersing water in said liquid hydrocarbon fuel to provide a stable clear water-in-oil microemulsion wherein the droplet size of the dispersed water phase is no greater than 0.25 µm; c) adding said at least one surfactant to said specified amount of liquid hydrocarbon fuel in an amount sufficient to disperse at least 50 ppm water in said liquid hydrocarbon fuel; and d) dispersing said at least one surfactant in said liquid hydrocarbon fuel, thereby improving the thermal stability and/or lubricity of the liquid hydrocarbon fuel.

Description

METHOD FOR IMPROVING THE THERMAL STABILITY AND/OR LUBRICITY OF FUEL Field of the invention

The present invention relates to improving the thermal characteristics and/or lubricity of liquid hydrocarbon fuel. More particularly the invention is a method for improving the thermal stability and/or lubricity of liquid hydrocarbon fuel at elevated temperatures by dispersing a liquid concentrate in the fuel that removes or substantially reduces the amount of water within the fuel by trapping and stabilising the water within an emulsion.

Background of the Invention

Liquid fuels and other liquid hydrocarbons often become contaminated with water, such as from condensation formed within a vented storage tank. This water can be held as a colloidal dispersion within the fuel or, after sufficient time, may form a separate water phase at the bottom of the storage tank. The presence of this water in fuel can have various detrimental effects on fuel.

International patent application WO 2007/083106 A1 (Palox Offshore S.A.L.) discloses water-in-oil emulsions that contain emulsifying agents (e.g. betaines e.g. cocoamidopropyl betaine) and optionally C6-Ci5 alcohol ethoxylates and C6-C24 alkyl amide oxide. The emulsifying agents improve the physical stability of the oil by scavenging any free-water in the fuel and/or inhibiting the growth of microorganisms in the fuel.

International patent applications WO 2011/095825 A1 (Palox Limited) and WO 2011/0445334 A1 (Palox Offshore S.A.L.) disclose liquid concentrates and their use when added to liquid hydrocarbon fuel form stable water-in-oil-emulsions or water-in-oil-microemulsions that prevent or at least minimise the formation of ice and "apple jelly" in that fuel that is cooled to temperatures in the range of from 0 to -50°C. Liquid hydrocarbon fuel, especially jet fuel, can be contaminated in a fuel tank of a turbine engine aircraft with small quantities of free water from condensation arising from the changes in temperature due to altitude changes. On the ground the fuel/tank temperature can range from about -20 °C to +50 °C (depending on location), whilst in flight it typically ranges from -22 °C to -39 °C. It is believed a Boeing 777 aircraft lost sufficient power to cause an emergency landing at Heathrow in January 2008 due to the formation of ice reducing the flow of fuel from the fuel tanks to the engines (AAIB interim report No 2 G-YMMM).

Extensive testing of these liquid concentrates, water-in-oil-emulsions and water-in-oil-microemulsions by the Applicant led to an unexpected and highly beneficial improvement in the thermal characteristics of fuel, especially at high temperatures, i.e. above 150 °C, preferably above 200 °C but especially above 250 °C.

An improvement in thermal performance of liquid hydrocarbon fuel at high temperature can prevent formation of undesired solid materials that can affect the performance of the engine. Poor thermal stability, for example, can lead to injection nozzles blocking and combustor coking thus operational down time for maintenance. An improvement in lubricity can minimise engine wear.

Statement of the invention

In a first aspect, the present invention provides a method of improving the thermal stability and/or lubricity of a liquid hydrocarbon fuel, said method comprising the steps of: a) providing a specified amount of liquid hydrocarbon fuel, said liquid hydrocarbon fuel comprising less than 50 ppm water; b) providing at least one surfactant that is capable of dispersing water in said liquid hydrocarbon fuel to provide a stable clear water-in-oil microemulsion wherein the droplet size of the dispersed water phase is no greater than 0.25 pm; c) adding said at least one surfactant to said specified amount of liquid hydrocarbon fuel in an amount sufficient to disperse at least 50 ppm water in said liquid hydrocarbon fuel, and d) dispersing said at least one surfactant in said liquid hydrocarbon fuel, thereby improving the thermal stability and/or lubricity of the liquid hydrocarbon fuel.

In a second aspect, the present invention provides a method of refuelling an aircraft with a liquid hydrocarbon fuel which after refuelling has an improved thermal stability and/or lubricity, said method comprising the steps of: a) pumping a specified amount of liquid hydrocarbon fuel into a fuel tank of an aircraft, said liquid hydrocarbon fuel comprising less than 50 ppm water; b) providing at least one surfactant that is capable of dispersing water in said liquid hydrocarbon fuel to provide a stable clear water-in-oil microemulsion wherein the droplet size of the dispersed water phase is no greater than 0.25 pm; c) adding said at least one surfactant to said liquid hydrocarbon fuel in an amount sufficient to disperse at least 50 ppm water in said liquid hydrocarbon fuel during or after said liquid hydrocarbon fuel is pumped into said fuel tank; and d) dispersing said at least one surfactant in said liquid hydrocarbon fuel, thereby improving the thermal stability and/or lubricity of the liquid hydrocarbon fuel.

In a third aspect, the present invention provides a use of at least one surfactant that is capable of dispersing water in a liquid hydrocarbon fuel to provide a stable clear water-in-oil microemulsion wherein the droplet size of the dispersed water phase is no greater than 0.25 pm in a liquid hydrocarbon fuel comprising less than 50 ppm water to improve the thermal properties and/or lubricity when said liquid hydrocarbon fuel is used in an engine, wherein the amount of said at least one surfactant used in said liquid hydrocarbon fuel is sufficient to disperse at least 50 ppm up to 5000 ppm water in said liquid hydrocarbon fuel.

In a fourth aspect, the present invention provides at least one surfactant for use in improving the thermal properties and/or lubricity of a liquid hydrocarbon fuel, said at least one surfactant being capable of dispersing water in a liquid hydrocarbon fuel to provide a stable clear water-in-oil microemulsion wherein the droplet size of the dispersed water phase is no greater than 0.25 pm, said liquid hydrocarbon fuel comprising less than 50 ppm water to when said liquid hydrocarbon fuel is used in an engine, wherein the amount of said at least one surfactant used in said liquid hydrocarbon fuel is sufficient to disperse at least 50 ppm up to 5000 ppm water in said liquid hydrocarbon fuel.

Terms

Terms used in the specification have the following meanings:

The term "free-water" as used herein means water present as a separate visible liquid phase in a two phase liquid fuel and water mixture.

The term "fuel", "liquid fuel" or "liquid hydrocarbon fuel" as used herein means a liquid hydrocarbon that is suitable for burning to power a combustion engine. A fuel in accordance with the present invention includes jet fuel, aviation gasoline, military grade fuel, biofuel, bioethanol, biodiesel, diesel; kerosene; gasoline/petrol (leaded or unleaded); paraffinic fuel, naphthenic fuel, heavy fuel oil,, waste oils or such as esters, poly alpha olefin; and mixtures thereof. The fuel is preferably jet fuel, aviation gasoline, military grade fuel, biodiesel, bioethanol, diesel, kerosene or gasoline/petrol but especially jet fuel.

The term "liquid fuel which is immiscible with water" as used herein means in relation to a liquid fuel, that is not miscible with water at greater than about 0.1% water, preferably at greater than 0.05%, i.e. any admixture of liquid fuel and water above 0.05% separates out on standing in to two phases.

The term "lubricity" as used herein means wear due to excessive friction resulting in shortened life of engine components such as fuel pumps and fuel controls which has sometimes been ascribed to lack of lubricity in an aviation fuel. Lubricity can be measured using ASTM D5001 -10(2014) Standard Test Method for Measurement of Lubricity of Aviation Turbine Fuels by the Ball-on-Cylinder Lubricity Evaluator (BOCLE).

The term "scavenge" as used herein means to act as a scavenger, as defined below.

The term "scavenger" as used herein means a substance added to a chemical reaction or mixture to counteract the effect of impurities, as defined in Collins English Dictionary, Fourth Edition 1998, Reprinted 1999 (twice), HarperCollins Publishers. In the context of the present invention it means to draw water from liquid hydrocarbon fuel into the water phase of a water-in-oil emulsion or water-in-oil microemulsion that is formed within liquid hydrocarbon fuel into which a liquid concentrate comprising at least one surfactant has been added.

The term "stable" as used herein in relation to the water-in-oil microemulsion that is formed during the method of the present invention means that the water phase in the water-in-oil emulsion exists as dispersed droplets having an average particles size of no greater than 0.1 pm in the oil phase for at least 12 months when stored at a constant temperature of 25 °C without stirring.

The term "surfactant" or "microemulsion-forming surfactant" as used herein means any suitable surfactant or mixture of surfactants, which is capable upon simple admixture with a mixture comprising two immiscible phases of a liquid fuel and water of forming a water-in-oil- emulsion or water-in-oil-microemulsion. Formation of the emulsion or microemulsion is substantially spontaneous upon the addition at ambient temperature (e.g. 10-30 °C) of the surfactant(s) to a mixture comprising two immiscible phases of a liquid fuel and water.

The term "thermal stability" as used herein means the stability of a molecule at high temperatures; i.e. above 150 °C, preferably above 200 °C but especially 250 °C. Thermally stable molecules resist decomposition at high temperatures.

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".

Throughout this specification and in the claims that follow, unless the context requires otherwise, the word "comprise" or variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other stated integer or group of integers.

Description of the drawings

The present application includes Figures 1 to 5. In the drawings:

Figure 1 shows the results of the tests described in Example 2 i.e. deposition on the Torque Motor Screen during Advanced Reduced Scale Fuel System Simulator (ARSFSS) testing.

Figure 2 shows the results of the tests described in Example 2 i.e. deposition on the Flow Divider Screen (FDS).

Figure 3 shows the results of the tests described in Example 2 i.e. deposition on the Servo Valves (SV).

Figure 4 shows the results of the tests described in Example 3 i.e. deposition on the Torque Motor Screen during Advanced Reduced Scale Fuel System Simulator (ARSFSS) testing.

Figure 5 shows the results of the tests described in Example 4 i.e. deposition on the combustor nozzle prior to or after testing.

Detailed description of the invention

The present invention provides a method for improving the thermal stability and/or lubricity of liquid hydrocarbon fuel at elevated temperatures by dispersing a liquid concentrate in the fuel that removes or substantially reduces the amount of water within the fuel by stabilising the water within an emulsion.

Water exists in fuel as either free water or dissolved water. The term "free-water" refers to water present as a separate visible liquid phase in a two phase liquid fuel and water mixture. This may arise from entrained water or water that is dissolved in the liquid fuel phase. Dissolved water becomes free water with lower temperatures due to the reduction in solubility of the water in liquid fuel.

In the context of the method of the present invention the free-water exists in or is introduced into the liquid fuel as a contaminant i.e. it is not water, which has been deliberately added to the liquid fuel, such as water, added to a liquid fuel in the preparation of a water-in-oil emulsion or microemulsion. The free-water exists or is introduced as a contaminant in the liquid fuel or water when e.g. water is added to the liquid fuel accidentally or inadvertently, or the water is ambient moisture such as from rain or condensation water derived from changes in humidity levels in the atmosphere whilst the liquid fuel is in a tank vented to atmospheric conditions or in a tank subject to wide temperature changes such as that on an aircraft. In the method of the present invention the free-water is preferably free-water introduced into the liquid fuel oil as ambient moisture. Whilst in extreme conditions the amount of free-water which may be introduced as a contaminant could comprise 0.5% by weight or more of the combined weight of water and liquid fuel, it will be apparent to those skilled in the art that in practice the amount of free-water contaminant will typically comprise significantly less than 0.5 wt% of the combined weight of free-water and liquid fuel. For example, typically the amount of free-water contaminating the liquid fuel will be less than 0.2 wt% and more typically less than 0.1 wt%, such as 0.05 wt% or less, by weight of the combined weight of water and liquid fuel.

In broad terms the method of the first aspect of the present invention comprises four steps.

The first step, step a), of the method of the first aspect of the present invention comprises providing a specified amount of liquid hydrocarbon fuel, said liquid hydrocarbon fuel comprising less than 50 ppm water.

The liquid hydrocarbon fuel is a hydrocarbon feedstock and can consist of any of the following: jet fuel, aviation gasoline, military grade fuel, biofuel, bioethanol, biodiesel, diesel; kerosene; gasoline/petrol (leaded or unleaded); paraffinic fuel, naphthenic fuel, heavy fuel oil,, waste oils or such as esters, poly alpha olefin; and mixtures thereof. The fuel is preferably jet fuel, aviation gasoline, military grade fuel, biodiesel, bioethanol, diesel, kerosene or gasoline/petrol but especially jet fuel.

The concentration of water in the liquid hydrocarbon fuel can be determined by various methods that are well known in the art, for example ASTM D6304 - 07 Standard Test Method for Determination of Water in Petroleum Products, Lubricating Oils, and Additives by Coulometric

Karl Fischer Titration.

In certain preferred embodiments the liquid hydrocarbon fuel additionally comprises one or more components selected from the group consisting of static dissipaters, antioxidants, metal deactivators, leak detector additives, corrosion inhibitors, lubricity improvers, alcohols, ethers and glycols.

The second step, step b), of the method of the first aspect of the present invention comprises providing at least one surfactant that is capable of dispersing water in said liquid hydrocarbon fuel to provide a stable clear water-in-oil microemulsion wherein the droplet size of the dispersed water phase is no greater than 0.25 pm.

The at least one surfactant can be any suitable surfactant or mixture of surfactants, which is capable upon simple admixture with a mixture comprising two immiscible phases of a liquid fuel and water of forming a water-in-oil- emulsion or water-in-oil-microemulsion. It is understood that any water dissolved in the fuel, albeit at very low concentrations, will be stabilised prior to any free water.

Persons skilled in the art will be familiar with such surfactants or surfactant mixtures, for example as disclosed in the aforementioned international patent application WO 2007/083106 Al.

Processes for inhibiting sedimentation, screen clogging and rusting in fuel oil compositions during storage are known in the art, for example as disclosed in US-A-3095286. That said, the addition agents disclosed in US-A-3095286 are not believed to form stable, clear, water-in-oil microemulsions upon admixture with a mixture comprising two visible immiscible phases of a liquid fuel and water. Accordingly, the addition agents disclosed in US-A-3095286 are not considered being stable, clear, microemulsion-forming surfactants within the context of the present invention. More specifically, none of the amic acids of formula (1), (2), (3) or (4) nor their salts of primary amines having between 4 and 30 carbon atoms per molecule as disclosed in US-A-3095286 are considered to be suitable for providing stable clear water-in-oil microemulsions.

In certain preferred embodiments the at least one surfactant is a mixture of surfactants. A preferred mixture of surfactants comprises a Ce-Cis alcohol ethoxylate or a mixture of such ethoxylates. Particularly suitable stable, clear, water-in-oil microemulsion-forming surfactants are amphoteric or comprise a mixture of surfactants including at least one amphoteric surfactant. Preferred amphoteric surfactants are betaines and sulpho betaines, particularly betaines.

Preferred surfactants are emulsifying agents, for example one or more fatty (C8-C24)-amido-(Cr C6) alkyl betaine. Preferably, the fatty (C8-C24)-amido-(Ci-C6) alkyl betaine is a fatty (C10-C20)-amido-(C2-C4) alkyl betaine, more preferably a fatty (Cio-Ci8)-amido-(C3) alkyl betaine, and most preferably a fatty (Cu-Ci7) alkyl amidopropyl betaine, e.g. cocoamidopropyl betaine.

Preferably, from about 0.5 up to about 15% by weight of the emulsifying agents employed in the microemulsion is comprised of the fatty (C8-C24)-amido-(Ci-C6) alkyl betaine. More preferably the fatty (C8-C24)-amido-(Ci-C6) alkyl betaine comprises 0.5 to 8 wt% of the emulsifying agents.

In addition to the fatty (C8-C24)-amido-(Ci-C6) alkyl betaine, the microemulsion preferably includes one or more other emulsifying agents. For example, in certain preferred embodiments the microemulsion additionally comprises a Ce - Cis alcohol ethoxylate comprising from 2 to 12 EO groups, but preferably a mixture of such alcohol ethoxylates is used. The C6 - Ci5 alcohol ethoxylate preferably comprises from 5 to 99 wt%, more preferably 50 to 95 wt%, of the emulsifying agents.

In other preferred embodiments, the microemulsion comprises a (C6-C24) alkyl amine oxide, preferably a (C6-Ci2) alkyl amine oxide. The (C6-C24) alkyl amine oxide preferably comprises from 0 to 15 wt% of the emulsifying agents.

In other preferred embodiments, the microemulsion comprises: i) a fatty (C8-C24)-amido-(Ci-Ce) alkyl betaine; ii) a Οε - Cis alcohol ethoxylate comprising from 2 to 12 EO groups or a mixture of such alcohol ethoxylates, preferably the mixture; and iii) a (C6-Cm) alkyl amine oxide.

Preferably, the emulsifying agent comprises: i) about 0.5 to about 15 wt% fatty (C8-C24)-amido-(Ci-C6)alkyl betaine; ii) about 5 to about 99 wt% Ce - Cis alcohol ethoxylate comprising from 2 to 12 EO groups or a mixture of such alcohol ethoxylates, preferably the mixture; and iii) about 0 to about 15 wt% (Ce-C24)alkyl amine oxide.

In addition to emulsifying agents i) and ii) and/or iii), the microemulsion optionally comprises one or more other emulsifying agents. When present, such other emulsifying agents may comprise from about 0.5 up to about 95 wt% of the emulsifying agents. Such other emulsifying agents are preferably non-ionic emulsifying agents. Examples of such other emulsifying agents useful in the present invention include fatty acid amine ethoxylates (Acid amine ethoxylates are well known to those skilled in the art and are also known as alkanolamide ethoxylates).

Products useful in the present invention may be obtainable by the reaction of ethylene oxide and fatty alkanolamide or the reaction of a fatty acid and an ethoxylated amine, e.g. fatty (Οε-Cm) acid amine ethoxylates comprising from about 2 to 20 EO groups, examples of which include cocomonoethanolamide and cocodiethanolamide.

Where a compound is referred to as being "ethoxylated", we mean it includes at least 2 EO groups. Preferably ethoxylated compounds comprise from 2 to 12 EO groups.

When a mixture of C6-C15 alcohol ethoxylates is employed in the microemulsion, it is preferably a mixture of C9-C14 alcohol ethoxylates, such as a mixture of Cgto Cn alcohol ethoxylates or a mixture of C12-C14 alcohol ethoxylates. The distribution of any of the components in the mixture can range from 0 to 50% by weight, and are preferably distributed in a Gaussian format. Commercially available C6-Ci5 alcohol ethoxylates include relevant products sold by leading chemical companies.

In certain preferred embodiments the emulsifying agent comprises the following: (i) 3 parts by wt cocamidopropyl betaine; and (ii) 97 parts by wt C9-Cn alcohol ethoxylate;

In certain preferred embodiments, the emulsifying agent comprises: (i) 1 part by wt cocamidopropyl betaine; (ii) 8 parts by wt C9-Cu alcohol ethoxylate; (iii) 3 parts by wt Cio-alkyl amine oxide; and iv) 90 parts nonionic fatty (C6-C24)acid amine ethoxylates comprising from about 2 to 20 EO groups.

In certain preferred embodiments the emulsifying agent comprises: (i) 5 parts by wt cocamidopropyl betaine; (ii) 75 parts by wt C6-Ci5-alcohol ethoxylate; (iii) 10 parts by wt Cio-alkyl amine oxide; and iv) 10 parts nonionic fatty (C6-C24) acid amine ethoxylates comprising from about 2 to 20 EO groups.

The emulsifying agents employed in the method of the present invention are liquids at room temperatu re.

In certain preferred embodiments the emulsifying agent comprises: (i) 2 parts cocamidopropyl betaine; (ii) 60 parts C9-Cu alcohol ethoxylate; (iii) 4 parts ethylene glycol; and (iv) 34 parts ethanol.

In certain preferred embodiments, a microemulsion is prepared by mixing: (a) about 99.8 to 99.999 parts, e.g. 99.998 parts, fuel, e.g. a jet fuel; and (b) about 0.0001 to about 0.02 parts, e.g. 0.025 parts, emulsifying agents, wherein the emulsifying agents include i) a fatty (C8-C24)-amido-(Ci-C6)alkyl betaine, and ii) a C6-

Ci5-alcohol ethoxylate comprising from 2 to 12 EO groups or a mixture of such alcohol ethoxylates, preferably the mixture, wherein all parts are by volume.

In some preferred embodiments the emulsifying agent comprises: i) about 0.5 to about 15 wt% fatty (C8-C24)-amido-(Ci-C6)alkyl betaine; ii) about 5 to about 98.5 wt% C6 - Ci5 alcohol ethoxylate comprising from 2 to 12 EO groups or a mixture of such alcohol ethoxylates, preferably the mixture; iii) about 0 to about 15 wt% (C6-C24)alkyl amine oxide; and iv) about 0 to about 94 wt% other emulsifying agent, preferably non-ionic emulsifying agent, more preferably nonionic fatty (C6-C24) acid amine ethoxylates comprising from about 2 to 20 EO groups.

The total amount of emulsifying agent, expressed as active ingredient (a.i.), employed in the present invention constitutes from about 0.0001 to about 0.2 wt% of the microemulsion. Preferably, the amount of emulsifying agent (a.i.) is from about 0.0001 to about 0.05 wt%, more preferably from about 0.0001 to about 0.025 wt% of the microemulsion.

In some preferred embodiments the emulsifying agent comprises an emulsifier composition for preparing a water-in-oil microemulsion. The emulsifier composition comprises a mixture of emulsifying agents i) and ii) and/or iii). The mixture may comprise additional emulsifying agents, such as a fatty acid amine ethoxylate. The mixtures of the present invention are very beneficial, because they may be added to any water-contaminated fuel thereby to distribute the water in the fuel and render it combustible. Without use of the emulsifier composition, it would otherwise be necessary to carefully remove the water before firing up the engine.

Free water in the liquid fuel gives an opportunity for microbial growth. This problem occurs in the base of the fuel tank and in severe circumstances leads to a corrosive sludge that requires a grounding of the aircraft and a cleaning of the tank. Ordinarily the problem is treated with the addition of bioactive material such as the biocide Kathon FP 1.5 (Rohm & Haas) or Biobor JF (Hammonds). Due to environmental and toxicity concerns the use of biocides is being reconsidered with the eventual withdrawal of the use of such chemicals. However, the present invention provides a microemulsion that has very small water droplets dispersed in the liquid hydrocarbon fuel e.g. less than 0.25 pm, but preferably less than 0. 1 pm. The average size for microbial contaminant is approximately 1 pm. Therefore, the microbe cannot survive. Even when excess quantities of water are present the composition of the invention in the fuel phase appears to prevent microbial growth. Whilst the mechanism for this is not fully understood it is believed that the micelles of the composition can reside at the interface of the water/fuel layer and act as a barrier to the microbial material.

The mixture ratios of the oil and water employed in the method of the invention are dependent upon many factors. Generally speaking, the oil comprises at least about 99.8 %, more preferably at least about 99.995%, most preferably about 99.999 % by weight, based on the total weight of the clear aqueous composition or emulsion. Generally speaking, the oil phase comprises no greater than about 99.8 % by weight, and preferably no more than about 99.99 % by weight.

Typically, the microemulsion comprises from about 0.0001 to about 0.50 % by weight of emulsifier, preferably from about 0.0001 to about 0.05 %, and even more preferably from about 0.0001 to about 0.025 %. The emulsifier is most preferably a mixture of emulsifying agents selected to minimise the total amount of emulsifier required to form a microemulsion for a given fluid.

The microemulsion may comprise additional components. These additional components may be incorporated to improve anti-wear, extreme pressure properties or improve cold weather performance. The requirement to add additional components may be dictated by the application area in which the microemulsion is used. Suitable additional components, and the requirement thereof depending on application area, will be apparent to those skilled in the art.

These microemulsions, without other additives, are clear or translucent emulsions.

The droplet size of the dispersed water phase can be determined by various methods that are well known in the art. Typically, emulsion droplet size can be viewed through conventional microscopic techniques or using particle analysis equipment. Notwithstanding that, emulsions can be visually inspected and those that are clear are considered to have an average droplet size of the water phase of the water-in-oil emulsion of no greater than 0.1 pm.

Although the physical nature of the stable clear water-in-oil microemulsion that is formed in step b) of the method of the present is not fully understood, it is believed that the microemulsion comprises an aqueous phase distributed within a non-aqueous phase, wherein that the aqueous phase is distributed in the non-aqueous phase in the form of droplets, possibly micelles, having a size no greater than about 0.1 μη

The water-in-oil microemulsion is stable in the sense that the water phase in the water-in-oil emulsion exists as dispersed droplets having an average particles size of no greater than 0.1 pm in the oil phase for at least 12 months when stored at a constant temperature of 25°C without stirring. The microemulsion is of a continuous fuel phase in which water droplets, having an average droplet size of no greater than or < 0.1 pm is dispersed. The resultant clear translucent microemulsion remains thermodynamically stable when used as a liquid hydrocarbon fuel, for example for use in jet or diesel engines. The droplets in the water-in-oil emulsion may be in the form of micelles.

The third step, step c), of the method of the first aspect of the present invention comprises adding said at least one surfactant to said specified amount of liquid hydrocarbon fuel in an amount sufficient to disperse at least 50 ppm water in said liquid hydrocarbon fuel.

The at least one surfactant is added to the liquid hydrocarbon fuel in an amount sufficient to disperse at least 50 ppm water in said liquid hydrocarbon fuel.

In certain preferred embodiments the at least one surfactant is added to the liquid hydrocarbon fuel in an amount sufficient to disperse at least 100 ppm water in said liquid hydrocarbon fuel.

In certain especially preferred embodiments the at least one surfactant is added to the liquid hydrocarbon fuel in an amount sufficient to disperse at least 200 ppm water in said liquid hydrocarbon fuel.

The dispersal of at least 50 ppm water in the liquid hydrocarbon fuel can be determined by various methods that are well known in the art, for example ASTM D6304 - 07 Standard Test Method for Determination of Water in Petroleum Products, Lubricating Oils, and Additives by Coulometric Karl Fischer Titration.

The fourth step, step d), of the method of the first aspect of the present invention comprises dispersing said at least one surfactant in said liquid hydrocarbon fuel, thereby improving the thermal stability and/or lubricity of the liquid hydrocarbon fuel.

The at least one surfactant is dispersed in the liquid hydrocarbon fuel by any suitable method known in the art, for example direct injection pumping techniques.

The at least one surfactant scavenges water which exists in or is introduced into the liquid fuel thereby to render or retain the liquid fuel in a usable state. This is known from international patent application WO 2007/083106 Al.

The method of the present invention, however, improves the thermal performance of liquid hydrocarbon fuel especially at high temperature, i.e. above 150 °C, preferably above 200 °C but especially above 250 °C, by preventing or at least minimising the formation of undesired solid materials that can affect the performance of the engine. Poor thermal stability, for example, can lead to carbonaceous material depositing and accumulating in the engine system. This can, for example, lead to injection nozzles coming blocked and therefore functionally sub-optimally and eventually not functioning at all. Such effects require operational down time for maintenance.

While not wishing to be bound by theory, it is postulated that this reduction in deposited material arises from an interaction between the inverse micelles of the composition and free radicals formed during engine operation. The presence of water in the micelle may also be beneficial in quenching the radicals formed.

This highly beneficial improvement in the thermal characteristics of liquid hydrocarbon fuel was observed during extensive testing of surfactant-containing liquid concentrates added to liquid hydrocarbon fuel. This improvement was unexpected and therefore surprising. Further testing was conducted to understand the improvement.

Given that the reduction in carbonaceous matter observed in testing (see later Examples) is not a function of detergency as this would just mean transport of that carbonaceous matter to a downstream filter or settlement zone, and is an actual reduction in carbonaceous mass, the mechanism must be one of reduced carbon formation.

The mechanism for carbon formation involves free radical processes so this suggests that the present invention can suppress these.

The microemulsion formed during the method of the present invention forms inverse micelles in fuel with immeasurably low levels of free component molecules, and therefore any mechanism must relate to the inverse micelles.

The carbon reduction is a function of the concentration of the microemulsion in the liquid hydrocarbon fuel and that relates to the number density of inverse micelles. There is therefore a free radical termination process that involves inverse micellar structures. Such structures are very small, about 70 nm, and have a very polar core. In a non-polar, low dielectric medium, ion transfer would be very limited but electron transfer is uninhibited. A fuel with inverse micelles may be able to supply a system that can encourage free radical reduction.

Furthermore, liquid hydrocarbon fuels in which at least one surfactant is dispersed in accordance with the method of the present invention tend to demonstrate improved physical stability over commercially available water-in-oil emulsions, thereby requiring less stirring in storage.

The method of the present invention improves the lubricity of liquid hydrocarbon fuel that can be seen by a reduction in wear in an engine, for example as noted by a reduction in wear scarring. Lubricity can be measured using art known techniques, for example using the Ball-on-Cylinder Lubricity Evaluator (BOCLE) system of lubricity tests i.e. ASTM D5001-10 Standard Test Method for Measurement of Lubricity of Aviation Turbine Fuels by the Ball-on-Cylinder Lubricity Evaluator (BOCLE).

The method of the present invention even improves the lubricity of liquid hydrocarbon fuel in the presence of excess water.

Various modifications and variations of the described methods and uses of the present invention will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described modes for carrying out the invention, which are obvious to those skilled in chemistry or related fields, are intended to be within the scope of the invention.

The present invention will now be further described by way of examples.

EXAMPLES

The following describes the preparation of liquid concentrates and water-in-oil-emulsions that are used in the method of the present invention. This is followed by Examples 1 to 5 that illustrate the method of the present invention.

Reference hereafter to "a water-in-oil microemulsion wherein the emulsion is a clear translucent emulsion" is believed to be analogous to "a water-in-oil emulsion, wherein the average droplet size of the water phase of the water-in-oil emulsion is no greater than 0.1 pm".

In the present examples, the emulsions were visually inspected. Those that were clear were considered to have an average droplet size of the water phase of the water-in-oil emulsion of no greater than 0.1 pm.

In the following examples, all "parts" are parts by weight, unless stated otherwise.

Preparation of liquid concentrates:

Preparation of liquid concentrate 1 A liquid concentrate was prepared by adding the following components in the quantities stated: (i) 97 parts Cg - Cu alcohol ethoxylate and (ii) 3 parts cocamidopropyl betaine.

The components were gently mixed to form a homogenous composition.

Preparation of liquid concentrate 2 A liquid concentrate was prepared by adding the following components in the quantities stated: i) 1 part by wt cocamidopropyl betaine; (ii) 8 parts by wt C9 - Cu alcohol ethoxylate; (iii) 3 parts by wt Cioalkyl amine oxide and iv) 90 parts fatty (C6-C24) acid amine ethoxylates comprising from about 2 to 20 EO groups.

The components were gently mixed to form a homogenous composition.

Preparation of liquid concentrate 3 A liquid concentrate was prepared by adding the following components in the quantities stated: (i) 5 parts by wt cocamidopropyl betaine; (ii) 75 parts by wt Ce - Ci5 alcohol ethoxylate; (iii) 10 parts by wt Cioalkyl amine oxide and iv) 10 parts fatty (C6-C24) acid amine ethoxylates comprising from about 2 to 20 EO groups.

The components were gently mixed to form a homogenous composition.

Preparation of liquid concentrate 4 A liquid concentrate was prepared by adding the following components in parts by volume in the quantities stated: (i) 2 parts cocamidopropyl betaine; (ii) 60 parts Cg - Cu alcohol ethoxylate; (iii) 4 parts ethylene glycol and (iv) 34 parts ethanol

The components were gently mixed to form a homogenous composition.

Preparation of water-in-oil emulsions:

Preparation of water-in-oil emulsion 1 0.01 parts by volume of liquid concentrate 1 was added to jet fuel contaminated with 200 ppm of water. The liquid concentrate was introduced to the oil and water from a micro pipette. The resulting fluid was gently mixed until a clear translucent fluid was observed. The resulting fluid remains physically stable even after more than one year.

Preparation of water-in-oil emulsion 2 0.01 parts by volume of liquid concentrate 2 was added to jet fuel contaminated with 200 ppm of water. The liquid concentrate was introduced to the oil and water from a micro pipette. The resulting fluid was gently mixed until a clear translucent fluid was observed. The resulting fluid remains physically stable even after more than one year.

Preparation of water-in-oil emulsion 3 0.01 parts by volume of liquid concentrate 3 was added to jet fuel contaminated with 200 ppm of water. The liquid concentrate was introduced to the oil and water from a micro pipette. The resulting fluid was gently mixed until a clear translucent fluid was observed. The resulting fluid remains physically stable even after more than one year.

Preparation of water-in-oil emulsion 4 0.01 parts by volume of liquid concentrate 4 was added to jet fuel contaminated with 200 ppm of water. The liquid concentrate was introduced to the oil and water from a micro pipette. The resulting fluid was gently mixed until a clear translucent fluid was observed. The resulting fluid remains physically stable after more than one year.

Thermal stability tests:

Example 1

Liquid concentrate 4 was prepared as described above and added to jet fuel to evaluate any improvement in the thermal properties of jet fuel.

The concentrate was added to jet fuel at a ratio of 0.1 to 99.9 parts by weight. The fluid was then subject to a series of Jet Fuel Thermal Oxidation Tester (JFTOT) thermal stressing tests. ASTM D3241 - 15el Standard Test Method for Thermal Oxidation Stability of Aviation Turbine Fuels. Typically over a series of tests the fluid containing the composition showed an increase in the thermal breakpoint of 5°C.

Example 2

The concentrate was added to jet fuel at a ratio of 0.1 to 99.9 parts by weight. This fluid was used in an aircraft flight simulation fuel-stressing test. The testing was very extensive and incorporated multiple test scenarios. A brief description and summary of the tests and results is given here.

The Advanced Reduced Scale Fuel System Simulator (ARSFSS) is a thermal stability evaluation device that more closely represents and replicates military aircraft fuel system-operating conditions than any other sub-aircraft scale test device in the world. The ARSFSS has been used extensively to evaluate fuels and additives under realistic aircraft fuel system conditions for almost three decades. An ARSFSS test run typically consists of between 65 and 150 missions executed sequentially operating 24 hours per day, 7 days a week. Three major components are examined during these tests for deposition. These are the Torque Motor Screen (TMS), Burner Feed Arm (BFA) and the Fuel Cooled Oil Cooler.

Multiple test scenarios have been completed and in all cases the fluid containing the composition of the invention have demonstrated reduced deposition without any loss in performance indicating an improved thermal stability on all three of the investigated components.

Typical results for deposition on the TMS are shown in Figure 1. Run 125 and 126 show baseline fuel tests and runs 127 and 128 show fuel treated with the aforementioned liquid concentrate 4.

Other components such as the Flow Divider Screen (FDS) and Servo Valves (SV) were looked at and in all cases the fluids containing liquid concentrate 4 showed greater thermal stability see Figures 2 and 3, with the run numbers corresponding to those described above.

The results showed fuel treated with the aforementioned liquid concentrate 4 in accordance with the method of the present invention provides reduced deposition material. This indicated the fuel so treated had improved thermal stability.

Example 3

With the success and unexpected improvement in thermal properties of fuel seen in Example 2 a further series of tests using the fluid from liquid concentrate 4 were carried out to establish whether this improvement was observed should the additive scavenge sufficient water and also the effect of excess quantities of water.

The fluids prepared were subject to the same tests as in Example 2. Again, the fluids all demonstrated superior thermal property performance as measured by deposition on the three components i.e. Torque Motor Screen (TMS), Burner Feed Arm (BFA) and the Fuel Cooled Oil Cooler.

Typical results for the TMS are showed in the Figure 4. Run 136 was fuel with added water, run 137 was excess water in the presence of liquid concentrate 4 and run 138 was fuel only. It can be seen that the deposition on the screen containing the composition was reduced giving it a lighter appearance. This indicated the fuel so treated had improved thermal stability.

The overall results showed that the presence of the liquid concentrate had a positive effect on preventing deposition even in the presence of water in both typical and extreme excess quantities.

Example 4 A further engine test was performed by the United States Air Force testing lab using a T63 test engine operating for 175 hours.

The 175 hour runtime was achieved using a run cycle consisting of 2 minutes of idle, 10 minutes of normal rated power, 2 minutes of idle, 5 minutes of maximum power, 50 minutes of normal rated power, 5 minutes of maximum power, followed with 1 minute of idle. The cycle was 75 minutes in length with 140 cycles required to achieve 175 hours of operation.

Figure 5 shows the deposition on the combustor nozzle. Photograph A shows the combustor nozzle prior to testing. Photograph B shows the combustor nozzle through which only non-treated fuel has passed during the 175 hours of operation. Photograph C shows the combustor nozzle through which fuel treated with liquid concentrate 4 has passed during the 175 hours of operation.

These results showed that the presence of the liquid concentrate in the fuel led to less thermal deposition thus indicating an improvement in the thermal stability of the fuel.

Example 5

As the composition is designed to remove unwanted water from the system the effect this may have on lubricity was investigated. This was done using the Ball-on-Cylinder Lubricity Evaluator (BOCLE) system of lubricity tests. ASTM D5001-10 Standard Test Method for Measurement of Lubricity of Aviation Turbine Fuels by the Ball-on-Cylinder Lubricity Evaluator (BOCLE).

It was found that the presence of liquid concentrate 4 reduced the wear scar diameter from 0.75 mm (neat fuel) to 0.69 mm. This is equivalent to an 8% reduction in wear. Similarly it was found that in the presence of both water (concentrations less than or equal to the composition) and excess quantities of water (concentrations greater than the composition) the wear scars were reduced to 0.69 mm and 0.67 mm respectively. These tests were repeated in ISOPAR M and again showed improvements in reducing the wear scar (0.91 mm for neat fuel to 0.70 mm for 200 ppm water containing fuel in the presence of liquid concentrate 4). Indeed even in the presence of excess water a marked improvement in wear scar (0.73 mm) was observed. This allows lubricity to be maintained even in the presence of large quantities of water.

At present there is no equivalent data of water containing fluids using conventional additives in the literature for comparison purposes. However, recent studies (The Effect of Water on Jet Fuel Additive Performance, by P. Rawson and D. Posselt. Paper presented at IASH 2015 the 14th International Conference on Stability, Handling and Use of Liquid Fuels, Charleston 4-8 October 2015) examining the performance of Jet fuel additives upon interaction with water wash out during fuel handling processes found that lubricity was reduced after water washing for the two unnamed additives used. The work examined the impact of a simple water wash out procedure on two lubricity additive's performance in four Jet fuels. The authors concluded that lubricity additives based on carboxylic acid may be prone to water wash out even with distilled deionised water.

The tests here indicated that liquid hydrocarbon fuel treated in accordance with the method of the present invention had a positive effect on lubricity regardless of water content.

Claims

1. A method of improving the thermal stability and/or lubricity of a liquid hydrocarbon fuel, said method comprising the steps of: a) providing a specified amount of liquid hydrocarbon fuel, said liquid hydrocarbon fuel comprising less than 50 ppm water; b) providing at least one surfactant that is capable of dispersing water in said liquid hydrocarbon fuel to provide a stable clear water-in-oil microemulsion wherein the droplet size of the dispersed water phase is no greater than 0.25 pm; c) adding said at least one surfactant to said specified amount of liquid hydrocarbon fuel in an amount sufficient to disperse at least 50 ppm water in said liquid hydrocarbon fuel, and d) dispersing said at least one surfactant in said liquid hydrocarbon fuel, thereby improving the thermal stability and/or lubricity of the liquid hydrocarbon fuel.

2. The method of claim 1, wherein said at least one surfactant is a mixture of i) at least one (C6-Ci5) alcohol ethoxylate and ii) at least one (C8-C24)alkyl amido (Ci-C6)alkyl betaine.

3. The method of claim 2, wherein the liquid hydrocarbon fuel after addition of said at least one surfactant comprises i) from 45 to 4575 ppm of at least one (C6-Ci5) alcohol ethoxylate and ii) from 5 to 425 ppm of at least one (C8-C24)alkyl amido (Ci-C6)alkyl betaine.

4. The method of any one of the preceding claims, wherein the total amount of said at least one surfactant is sufficient to disperse no more than 5000 ppm water in said liquid hydrocarbon fuel.

5. The method of any one of the preceding claims, wherein the total amount of said at least one surfactant is sufficient to disperse no more than 250 ppm water in said liquid hydrocarbon fuel.

6. The method of claim 4 or 5, wherein said hydrocarbon fuel after addition of said at least one surfactant comprises i) about 160 ppm of at least one (C6-Ci5) alcohol ethoxylate and ii) about 10 ppm of at least one (Cs-C24)alkyl amido (Ci-C6)alkyl betaine.

7. The method of any one of the preceding claims, wherein said liquid hydrocarbon fuel additionally comprises one or more components selected from the group consisting of static dissipaters, antioxidants, metal deactivators, leak detector additives, corrosion inhibitors, lubricity improvers, alcohols and glycols.

8. A method of refuelling an aircraft with a liquid hydrocarbon fuel which after refuelling has an improved thermal stability and/or lubricity, said method comprising the steps of: a) pumping a specified amount of liquid hydrocarbon fuel into a fuel tank of an aircraft, said liquid hydrocarbon fuel comprising less than 50 ppm water; b) providing at least one surfactant that is capable of dispersing water in said liquid hydrocarbon fuel to provide a stable clear water-in-oil microemulsion wherein the droplet size of the dispersed water phase is no greater than 0.25 pm; c) adding said at least one surfactant to said liquid hydrocarbon fuel in an amount sufficient to disperse at least 50 ppm water in said liquid hydrocarbon fuel during or after said liquid hydrocarbon fuel is pumped into said fuel tank; and d) dispersing said at least one surfactant in said liquid hydrocarbon fuel, thereby improving the thermal stability and/or lubricity of the liquid hydrocarbon fuel.

9. Use of at least one surfactant that is capable of dispersing water in a liquid hydrocarbon fuel to provide a stable clear water-in-oil microemulsion wherein the droplet size of the dispersed water phase is no greater than 0.25 pm in a liquid hydrocarbon fuel comprising less than 50 ppm water to improve the thermal properties and/or lubricity when said liquid hydrocarbon fuel is used in an engine, wherein the amount of said at least one surfactant used in said liquid hydrocarbon fuel is sufficient to disperse at least 50 ppm up to 5000 ppm water in said liquid hydrocarbon fuel.

10. At least one surfactant for use in improving the thermal properties and/or lubricity of a liquid hydrocarbon fuel, said at least one surfactant being capable of dispersing water in a liquid hydrocarbon fuel to provide a stable clear water-in-oil microemulsion wherein the droplet size of the dispersed water phase is no greater than 0.25 pm. said liquid hydrocarbon fuel comprising less than 50 ppm water to when said liquid hydrocarbon fuel is used in an engine, wherein the amount of said at least one surfactant used in said liquid hydrocarbon fuel is sufficient to disperse at least 50 ppm up to 5000 ppm water in said liquid hydrocarbon fuel.