EP3078728A1

EP3078728A1 - Viscosity index improvers in fuel compositions

Info

Publication number: EP3078728A1
Application number: EP15162647.0A
Authority: EP
Inventors: Christopher William Clayton
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 2015-04-07
Filing date: 2015-04-07
Publication date: 2016-10-12

Abstract

A fuel additive composition is provided comprising a viscosity index improver (VII) polymer component, wherein the VII polymer is comprised predominantly within a solid particulate phase; and a liquid phase component. The additive demonstrates lower viscosity and can be added to fuel compositions, especially diesel, without significantly altering the overall characteristics of the fuel blend. Fuels comprising the additive composition demonstrate improved performance. Methods of using and making the fuel additive compositions are also provided.

Description

Field of the Invention

The present invention relates to fuel additive formulations that comprise polymeric viscosity index improvers and in particular to the use of viscosity index improver components in automotive gas oil compositions to give improvements in fuel performance.

Background of the Invention

The addition of viscosity index improving (VII) additives to diesel fuel can have significant benefits on engine performance. WO-A-2009/118302 , for example, discloses the use of VII additives, in an automotive fuel composition, for the purpose of improving the acceleration performance of an internal combustion engine into which the fuel composition is or is intended to be introduced. The concentration of the VII additive may be up to 1% w/w, although optimum concentrations are said to be, for instance, between 0.05 and 0.5% w/w, or between 0.05 and 0.25% w/w, or between 0.1 and 0.2% w/w.
VII additives are typically dosed, or added, directly into a fuel component or composition, usually at a refinery. For example WO-A-2012/085263 describes how VII additives are pre-dissolved to form an additive composition or pre-blend, which is subsequently dosed into the fuel component or composition. Pre-dissolution has the perceived advantage of even distribution of the VII additive in the fuel. Furthermore, the blending of base fuel components may not be feasible at all locations, whereas the introduction of additive compositions, in relatively low amounts, can more readily be achieved at fuel depots or at other filling points such as road tanker, barge or train filling points, dispensers, customer tanks and vehicles. WO-A-2009/118302 suggests a number of examples of solvents that may be used to pre-dissolve VII additives in general, including certain fuel components and organic solvents. Nevertheless, incorporation of VII additives into additive formulations remains problematic due to the issues of poor solubility of VII polymers. This can result in the need to use high volumes of solvent which can consequently affect the composition of any subsequent fuel that is to be treated.
Fuels are typically required to comply with fuel specifications (e.g. EN 590) that set thresholds for the concentration of the fuel components comprised within the composition. The inclusion of complex additive mixtures comprising high levels of solvent necessary to improve solubility of VII polymers can be problematic, affecting the compliance of the resulting composition with such specifications and, thus, the commercial utility of such compositions. In addition, transportation of high volumes of VII additive mixtures increases operating costs of resultant fuel mixtures, especially if a substantial portion of the fuel volume is displaced by the presence of additive.
It would be desirable to provide additive compositions comprising VII polymers that comprise the minimal amount of solvent necessary to permit effective dosing of fuels, such as diesel. Thus, this invention aims to overcome or alleviate at least one of the problems associated with the prior art.

Summary of the Invention

It has now surprisingly been found that VIIs may be included at high concentration in additive formulations intended for dosing automotive gas oils (such as diesel fuel) when provided in solid particulate form without contributing to a significant increase in viscosity of the formulation.
Accordingly, in a first aspect of the invention, there is provided a fuel additive composition comprising:

(a) a viscosity index improver (VII) polymer component, wherein the VII polymer is predominantly comprised within a solid particulate phase; and
(b) a liquid phase component.

Suitably, the VII polymer component comprises a block copolymer, which contains one or more monomer blocks selected from ethylene, propylene, butylene, butadiene, isoprene and styrene monomers. In one embodiment, the VII polymer component comprises a polystyrene-polyisoprene stellate copolymer.
In embodiments of the invention the VII polymer component is present within the solid particulate phase at a concentration selected from the group consisting of: greater than 5% w/w; greater than 10% w/w; greater than 15% w/w; greater than 25% w/w; greater than 40% w/w; greater than 50% w/w; greater than 60% w/w; and greater than 25% w/w, based on the total weight of the additive composition. In embodiments of the invention the VII polymer component is present within the solid particulate phase at a concentration selected from the group consisting of: at most 99% w/w; at most 98% w/w; at most 95% w/w; at most 90% w/w; at most 85% w/w; at most 80% w/w; at most 75% w/w; at most 65% w/w; and at most 50% w/w, based on the total weight of the additive composition.
Suitably the liquid phase component comprises a solvent, optionally selected from a hydrocarbon, organic, inorganic, and/or polar solvent. In embodiments of the invention the solvent is present at a concentration sufficient to make up the balance of the additive mixture following selection of the concentration of the solid particulate phase. Optionally, the solvent is present in an amount of at most 95% w/w; at most 90% w/w; at most 85% w/w; at most 75% w/w; at most 60% w/w; at most 50% w/w; at most 40% w/w; and at most 25% w/w based on the total weight of the additive composition.
In embodiments of the invention, the VII polymer component is comprised of solid particles having a diameter selected from the group consisting of: at least 0.01 µm; at least 0.5 µm; at least around 1.0 µm; and at least around 5.0 µm. Suitably, the VII polymer component is comprised of solid particles having a diameter selected from the group consisting of: at most 100 µm; at most 20 µm; at most 10 µm; at most 5 µm; and at most around 1.0 µm.
In a specific embodiment of the invention the mean average particle size of the sold phase VII polymer component is selected to be below the size exclusion of a typical diesel fuel filter.
A second aspect of the invention provides the use of an additive composition as defined herein to increase the kinematic viscosity at 40°C of a diesel fuel composition into which it is intended to be used, wherein the kinematic viscosity at 40°C of the diesel fuel composition comprising the additive composition is in the range of:

(i) up to 4.5 mm²/s;
(ii) between 2.0 mm²/s and 4.0 mm²/s; or
(iii) between 3.0 mm²/s and 3.8 mm²/s.

Optionally the diesel fuel composition comprises a biofuel.
A third aspect of the invention provides a method for manufacturing a fuel additive composition comprising combining a viscosity index improver(VII) polymer component, wherein the VII polymer is comprised predominantly within a solid particulate phase, with a liquid phase component, so as to form a slurry.

Detailed Description of the Invention

In order to assist with the understanding of the invention several terms are defined herein. Unless otherwise defined, terms used in the present disclosure should be taken as having the standard meaning understood in the most relevant art. In the event that a term can only be understood if it is construed by reference to a dictionary, if the term is defined by the Kirk-Othmer Encyclopedia of Chemical Technology, 5th Edition, (2005), (Published by Wiley, John & Sons, Inc.) this definition shall control how the term is to be defined in the claims.
"Viscosity Index" (or VI) is an arbitrary unit used to measure the change of kinematic viscosity with temperature. It is generally used to characterise lubricating oils in the automotive industry. Thus, the Viscosity Index highlights how a liquid's (or lubricant's) viscosity changes with variations in temperature. In general, the viscosity of a liquid decreases as its temperature increases. Many lubricant or fuel applications require the liquid to perform across a wide range of engine conditions: for example, at start-up when the liquid is at prevailing temperature of the environment, as well as when it is running (up to 200 °C /392 °F). The higher the VI, the smaller the relative change in viscosity with temperature. Desirably, a fuel composition will not vary much in viscosity over its typical operating temperature range (i.e. it will have a relatively high VI).
The reference temperatures at which viscosity is measured in accordance with the VI scale were chosen arbitrarily to be 37.8°C and 98.9°C (i.e. 100°F and 210°F). Typically, however, kinematic viscosity measurements are taken at approximately 40°C and/or approximately 100°C, unless otherwise indicated. Conveniently, kinematic viscosity is measured using standardised testing procedures known to the person of skill in the art, such as ASTM D-445 or EN ISO 3104.
VI improvers (also known as VIIs) are additives that increase the viscosity of the fluid throughout the useful temperature range of the VII. The useful operating temperature preferably overlaps at least a portion of the operating temperature range of a fuel composition in an engine.
VIIs are polymeric molecules that are sensitive to temperature. At low temperatures, the molecule chains contract and so do not significantly impact on the fluid viscosity. However, at high temperatures, the chains relax and a relative increase in viscosity occurs; although the actual viscosity will still decrease as temperature increases. Hence, the addition of VIIs serves to slow down rather than halt the rate at which the viscosity decreases. There are many types and structures of VIIs. Higher molecular weight polymers make better thickeners but tend to have less resistance to mechanical shear. On the other hand, lower molecular weight polymers are more shear-resistant, but do not improve viscosity as effectively at higher temperatures and, therefore, may be used in larger quantities to achieve the same effect at a desired temperature.
The fuel compositions to which the present invention relates include automotive gas oils (AGOs) such as diesel fuels for use in automotive compression ignition engines, as well as in other types of engine such as for example marine, railroad and stationary engines, and industrial gas oils for use in heating applications (e.g. boilers). The base fuel may itself comprise a mixture of two or more different diesel fuel components, and/or be additivated as described in further detail below.
The AGO of the present invention may suitably comprise a middle distillate gas oil that comprises liquid hydrocarbons and may typically have a boiling point (EN ISO 3405) within the usual diesel range of 150 to 410°C or 170 to 370°C, depending on grade and use. In general middle distillate gas oil may be organically or synthetically derived. A petroleum derived gas oil may for instance be obtained by refining and optionally (hydro) processing a crude petroleum source. It may be a single gas oil stream obtained from such a refinery process or a blend of several gas oil fractions obtained in the refinery process via different processing routes. Examples of such gas oil fractions are straight run gas oil, vacuum gas oil, gas oil as obtained in a thermal cracking process, light and heavy cycle oils as obtained in a fluid catalytic cracking unit and gas oil as obtained from a hydrocracker unit. Optionally, a petroleum-derived middle distillate gas oil may comprise petroleum derived kerosene fraction. Typically, petroleum derived gas oil will include one or more cracked products, obtained by splitting heavy hydrocarbons. Optionally, according to particular embodiments non-mineral oil based fuels, such as bio-fuels or Fischer-Tropsch derived fuels, may also form or be present in the fuel composition.
The gas oil may also be or comprise a Fischer-Tropsch, or GTL, derived gas oil. In the context of the present invention, the term "Fischer-Tropsch derived" means that a material is, or derives from, a synthesis product of a Fischer-Tropsch condensation process. The term "non- Fischer-Tropsch derived" may be interpreted accordingly. A Fischer-Tropsch derived gas oil or fuel component will therefore be a hydrocarbon stream in which a substantial portion, except for added hydrogen, is derived directly or indirectly from a Fischer-Tropsch condensation process.
The Fischer-Tropsch reaction converts carbon monoxide and hydrogen into longer chain, usually paraffinic, hydrocarbons in the presence of an appropriate catalyst and typically at elevated temperatures (e.g. 125 to 300°C, preferably 175 to 250°C) and/or pressures (e.g. 0.5 to 10 MPa, preferably 1.2 to 5 MPa). Hydrogen to carbon monoxide ratios other than 2:1 may be employed if desired. The carbon monoxide and hydrogen may themselves be derived from organic, inorganic, natural or synthetic sources, typically either from natural gas or from organically derived methane.
A Fischer-Tropsch derived gas oil of use in the present invention may be obtained directly from the refining or the Fischer-Tropsch reaction, or indirectly for instance by fractionation or hydrotreating of the refining or synthesis product to give a fractionated or hydrotreated product. Hydrotreatment can involve hydrocracking to adjust the boiling range (see e.g. GB-B-2077289 and EP-A-0147873 ) and/or hydroisomerisation, which can improve cold flow properties by increasing the proportion of branched paraffins. EP-A-0583836 describes a two-step hydrotreatment process in which a Fischer-Tropsch synthesis product is firstly subjected to hydroconversion under conditions such that it undergoes substantially no isomerisation or hydrocracking (this hydrogenates the olefinic and oxygen-containing components, and then at least part of the resultant product is hydroconverted under conditions such that hydrocracking and isomerisation occur to yield a substantially paraffinic hydrocarbon fuel or gas oil. The desired fraction(s), typically gas oil fraction(s), may subsequently be isolated for instance by distillation. Other post-synthesis treatments, such as polymerisation, alkylation, distillation, cracking- decarboxylation, isomerisation and hydroreforming, may be employed to modify the properties of Fischer-Tropsch condensation products, as described for instance in US-A-4125566 and US-A-4478955 . Typical catalysts for the Fischer-Tropsch synthesis of paraffinic hydrocarbons comprise, as the catalytically active component, a metal from Group VIII of the periodic table of the elements, in particular ruthenium, iron, cobalt or nickel. Suitable such catalysts are described for instance in EP-A- 0583836 .
An example of a Fischer-Tropsch based process is the Shell (TM) "Gas-to-liquids" or "GTL" technology (formerly known as the SMDS (Shell Middle Distillate Synthesis) and described in "The Shell Middle Distillate Synthesis Process", van der Burgt et al, paper delivered at the 5th Synfuels Worldwide Symposium, Washington DC, November 1985, and in the November 1989 publication of the same title from Shell International Petroleum Company Ltd, London, UK). In the latter case, preferred features of the hydroconversion process may be as disclosed therein. This process produces middle distillate range products by conversion of a natural gas into a heavy long chain hydrocarbon (paraffin) wax, which can then be hydroconverted and fractionated.
For use in the present invention, a Fischer-Tropsch derived middle distillate gas oil is preferably any suitable fuel component derived from a gas to liquid synthesis (hereinafter a GTL component), or a component derived from an analogous Fischer-Tropsch synthesis, for instance converting gas, biomass or coal to liquid (hereinafter an XTL component). A Fischer-Tropsch derived component is preferably a GTL component. It may be a BTL (biomass to liquid) component. In general a suitable XTL component may be a middle distillate fuel component, for instance selected from kerosene, diesel and gas oil fractions as known in the art; such components may be generically classed as synthetic process fuels or synthetic process oils.
Middle distillate gas oil components for use in the solvent mixture of the composition according to the present invention will typically have a density in the range of from 750 to 900 kg/m3, preferably from 800 to 860 kg/m3, at 15°C (EN ISO 3675) and/or a kinematic viscosity at 40°C (VK40) of from 1.0, e.g.1.5, to 6.0 mm2/s (VK 40°C as measured by EN ISO 3104). Preferably the VK40 is in the range of from 1.0 to 3.0 mm2/s, more preferably from 1.5 to 2.5 or 2.7 mm2/s; all as measured according to EN ISO 3104).
The gas oil component may preferably contain no more than 5000 ppmw (parts per million by weight) of sulphur, typically from 2000 to 5000 ppmw, or from 1000 to 2000 ppmw, or alternatively up to 1000 ppmw. The composition may, for example, contain at most 500 ppmw, preferably no more than 350 ppmw, most preferably no more than 100 or 50 or even 10 ppmw, of sulphur. The sulphur content may be measured according to EN ISO 20884.
Gas oil may be processed in a hydrodesulphurisation (HDS) unit so as to reduce its sulphur content to a level suitable for inclusion in a diesel fuel composition. The aromatics content of the middle distillate gas oil may preferably be in the range of from 0 to 40% m/m, suitably from 5 to 30% m/m, for example in the range of 10 to 20% m/m. More preferably the aromatics content is in the range of from 10 to 35 % m/m, even more preferably from 15 to 30 % m/m, and especially from 20 to 30 % m/m. The middle distillate aromatics content may be measured according to IP391 and EN12916.
Diesel fuels of an embodiment of the invention will typically contain a base fuel which may typically comprise liquid hydrocarbon middle distillate gas oil(s), for instance petroleum derived gas oils, as described above. Such fuels will typically have boiling points with the usual diesel range of 150 to 410 °C, depending on grade and use. They will typically have a density from 750 to 900 kg/m3, preferably from 800 to 860 kg/m3, at 15 °C (e.g. ASTM D4502 or IP 365) and a cetane number (ASTM D613) of from 35 to 80, more preferably from 40 to 75. They will typically have an initial boiling point in the range 150 to 230 °C and a final boiling point in the range 290 to 400 °C. Their kinematic viscosity at 40 °C (ASTM D445) might suitably be from 1.5 to 4.5 mm /s.
In embodiments of the invention, industrial gas oils will contain a base fuel which may comprise fuel fractions such as the kerosene or gas oil fractions obtained in traditional refinery processes, which upgrade crude petroleum feedstock to useful products. Preferably such fractions contain components having carbon numbers in the range 5-40, more preferably 5-31, yet more preferably 6-25, most preferably 9-25, and such fractions have a density at 15 °C of 650-950 kg/m³, a kinematic viscosity at 20 °C of 1-80 mm /s, and a boiling range of 150-400 °C.
The inclusion of small amounts of high molecular weight polymer or surfactant in high pressure fluids can lead to a reduction in friction as a result in decreasing the turbulence within the fluid as it flows under pressure. This effect is often referred to as an additive turbulence drag-reducing effect, and can be used to increase the flow rate of fluids within pipelines, for example. According to the present invention it has been found that the drag-reducing effect seen when including a high molecular weight polymer can result in a dramatic reduction in viscosity when such polymers are present as VIIs in fuel additive compositions in an emulsion or slurry form. Conventionally, large volumes of solvent and high temperatures have been required in order to ensure adequate solubility of VII polymers in compositions intended for use in dosing AGOs. This solubility problem can lead to complications during subsequent blending with a base fuel, such as a diesel.
VII additives are well-known to the skilled person and suitably include compositions comprising polyolefin polymers, including block copolymer, e.g. which contain one or more monomer blocks selected from ethylene, propylene, butylene, butadiene, isoprene and styrene monomers. A particularly suitable VII additive comprises a polystyrene-polyisoprene stellate copolymer, such as SVTM 200 (ex. Infineum, Multisol and others).
The polymer VII additive is suitably provided in the form of a particulate monomodal, bi-modal or multi-modal mixture. The polymer VII additive is typically present predominantly in sold phase form, which is intended to mean that a majority of the polymer (i.e. greater than 50% by weight) is in solid phase form. Optionally, most of the polymer is present in solid phase form - e.g. greater than 70% by weight of the polymer is in solid phase form. In a specific embodiment of the invention substantially all of the polymer VII additive is in solid phase form in the additive mixture - i.e. less than at most around 5% and at least around 1 % by weight is dissolved in the solvent phase.
According to a specific embodiment of the invention, the polymer VII additive particles may be simply dispersed within the solvent phase. In an alternative embodiment of the invention, some of all of the polymer VII additive particles may be impregnated or 'swollen' with solvent so as to modify the dissolution kinetics of the particles when added to a fuel composition.
Processes for preparing polymer drag reducing agents may involve passing pelletized polymer through a pulveriser or grinder multiple times, optionally recycling the material up to as much as 30 times to achieve sufficient size reduction. Alternatively, polymer particles may be formed by conventional spray drier or atomization techniques. Bi-modal and multi-modal particle size distributions can be important in formulation of additive compositions as particle size can affect viscosity and dosage characteristics of the product. A bi-modal particle size distribution is one that includes two different particle size distributions that show discrete peaks at different sizes, whereas multi-modal distribution refers to a combination of more than two different particle size distributions. Methods for the preparation of bi-modal and multi-modal polymer compositions are described in WO-2013/009553-A .
According to one embodiment of the invention, the VII polymer is provided as polymer particles with a median average diameter of about 100 microns (µm) or less, optionally 50 microns or less. Suitably particle sizes of the order of about at least 20 microns, suitably at least 15 microns, optionally at least 10 microns, up to approximately at most 5 microns, typically at most 2 microns, have utility in the additive compositions of the present invention.
According to one embodiment of the invention, the additive composition comprises solid phase VII polymer particles that are substantially smaller than the size exclusion cut off for a conventional diesel fuel filter. Whilst it is expected that once the additive is introduced into the fuel virtually all of the solid VII polymer will dissolve in the fuel, there is a possibility that a small proportion may not dissolve immediately. Hence, in order to prevent clogging of fuel filters it may be desirable to select a particle size that is smaller than the mesh of the fuel filters. Typical diesel fuel filters have a mesh size of around 15 microns (15 µm), meaning that particles smaller than 15 microns in diameter should pass freely through the filter. Some ultra-fine fuel filters may possess smaller mesh sizes, such as 10 or 5 micron sizes. However, it is unusual for diesel fuel filters to have mesh sizes smaller than 1 micron. Hence, in specific embodiments of the invention the particle sizes for the solid phase VII polymer may be selected on a geographical basis dependent in-part upon local regulations, conventional norms or other requirements for engine fuel filter specifications.
In addition to the polymer VII, the compositions of the present invention may comprise a coating or partitioning agent, e.g., a wax. As used herein, the term "wax" includes any low melting, e.g., <500° C., organic mixture or compound of high molecular weight which is solid at ambient temperature. The contemplated waxes can be natural, i.e., derived from animal, vegetable, or mineral sources, e.g., fatty acid waxes, or synthetic as, for example, ethylenic polymers, waxes obtained from the Fischer-Tropsch synthesis, described previously. Non-limiting examples of suitable waxes that may serve as suitable partitioning agents include paraffin, microcrystalline wax, slack or scale wax, polymethylene wax, polyethylene wax, fatty acid wax, etc. Typically, the waxes used in the compositions of the present invention are hydrocarbon in nature and are powders or particulates at room temperature. In addition to waxes, non-limiting examples of other suitable coating agents include talc, alumina, metal salts of a fatty acid, e.g., metal stearates, silica gel, polyanhydride polymers, etc. It will be understood that the term "coating agent" is intended to and does include components which while not actually coating the VII additive, interact in such a way, be it chemical or physical, which prevents the polymer, when at a desired particle size, from agglomerating to the extent that the agglomerated material constitutes a solid or substantially solid non-dispersible mass - e.g. a slurry. Coating agents may also serve to control or moderate the dissolution kinetics of the polymer particles.
The VII polymer particles may be formed into a slurry or sol together with a suitable liquid phase. In a particular embodiment of the invention polymer particles are dispersed within a solvent of very different viscosity, usually much lower viscosity. Consequently, the majority of the VII polymer does not dissolve in the solvent phase and the viscosity of the resultant additive mixture is not increased greatly beyond that of the liquid phase alone. The invention provides, therefore, the improved ability to package these high viscosity polymeric materials into considerably more concentrated forms yet maintaining acceptably low viscosity of the additive composition even at ambient temperatures.
Suitable solvents for use within the liquid phase of the additive mixture may include, for example an oil such as a mineral oil or Fischer-Tropsch derived hydrocarbon mixture; a fuel component (which again may be either mineral or Fischer-Tropsch derived) compatible with the fuel composition in which the additive is to be used (for example a middle distillate fuel component such as a gas oil or kerosene, when intended for use in a diesel fuel composition); a poly alpha olefin; a so-called biofuel such as a fatty acid alkyl ester (FAAB), a Fischer-Tropsch derived biomass-to-liquid synthesis product, a hydrogenated vegetable oil, a waste or algae oil or an alcohol such as ethanol; an aromatic solvent; any other hydrocarbon or organic solvent; or a mixture thereof. In particular embodiments of the invention, solvents for use in this context are mineral oil based diesel fuel components and solvents, and Fischer-Tropsch derived components such as the "XTL" components referred to herein. Biofuel solvents may also be selected in certain cases. Polar solvents may also be suitable in certain instances given that the actual volume of solvent being utilised is relatively small. Suitable polar solvents may include one or more of the group selected from: water; methanol; ethanol; propanol; butanol; isopropanol; acetic acid; formic acid; ethyl acetate; tetrahydrofuran (THF); acetone; dimethyl sulfoxide (DMSO); and propylene carbonate.
In specific embodiments of the invention, a fuel additive mixture typically contains, in addition to the polymeric VII particulate solid phase, a detergent, and a diesel fuel-compatible diluent as the solvent. The solvent may be a mineral oil, a solvent such as those sold by Shell companies under the trade mark "SHELLSOL", a polar solvent such as an ester and an alcohol (e.g. hexanol, 2-ethylhexanol, decanol, isotridecanol and alcohol mixtures such as those sold by Shell companies under the trade mark "LINEVOL", especially LINEVOL 79 alcohol which is a mixture of C7-9 primary alcohols, or a C12-14 alcohol mixture which is commercially available).
The concentration of the VII polymer in the additive composition may be greater than 5% w/w and at most 95% w/w; greater than 10% w/w and at most 90% or higher w/w; greater than 15% w/w and at most 85% or higher w/w; greater than 25% w/w; greater than 40% w/w; greater than 50% w/w; and greater than 60% w/w, based on the total weight of the additive composition.
The concentration of the VII additive will depend on the desired viscosity of the overall fuel composition, the viscosity of the composition prior to incorporation of the additive, the viscosity of the additive itself and the viscosity of any solvent in which the additive is used. The relative proportions of the VII additive, fuel component (s) and any other components or additives present, in an automotive fuel composition prepared according to the present invention, may also depend on other desired properties such as density, emissions performance and cetane number, in particular density.
The engine in which the fuel composition of the invention is used may be any appropriate engine. Thus, where the fuel is a diesel or biodiesel fuel composition, the engine is a diesel or compression ignition engine. Likewise, any type of diesel engine may be used, such as a turbo charged diesel engine. Similarly, the invention is applicable to an engine in any vehicle.
The remainder of the fuel composition will typically consist of one or more automotive base fuels optionally together with one or more fuel additives, for instance as described in more detail below. Such fuels are generally suitable for use in compression ignition (diesel) internal combustion engines, of either the indirect or direct injection type.
The relative proportions of the fuel mix components such as cetane number enhancers, detergents and dispersants, fuel components and any other components or additives present in a diesel fuel composition prepared according to the invention may also depend on other desired properties such as density, emissions performance and viscosity. Thus, in addition to the VII additive, an AGO or diesel composition prepared according to the present invention may comprise one or more diesel fuel components of conventional type. It may, for example, include a major proportion of a diesel base fuel, for instance of the type described below. In this context, a "major proportion" means at least 75% w/w, and typically at least 90% w/w based on the overall composition, more suitably, at least 95% w/w or even at least 99% w/w. In some cases at least 99.5 % w/w or at least 99.9 % w/w of the fuel composition consists of the diesel base fuel.
In the context of the present invention, "use" of a VII in a fuel additive composition means incorporating the particulate VII polymer into the composition, typically as a blend (i.e. a physical mixture) with one or more solvents and optionally with one or more fuel additives (including a standard additive pack).
The VII containing additive composition is preferably incorporated into the fuel composition before the fuel is introduced into an engine which is to be run on the composition.
Accordingly, the invention provides for an additive composition that may be added to an automotive fuel composition downstream of the refinery. For example, it may be added as part of an additive package containing one or more other fuel additives. This can be particularly advantageous because in some circumstances it can be inconvenient or undesirable to modify the fuel composition to include VIIs at the refinery. The use of relatively low concentrations of downstream VII additives can help to avoid any undesirable side effects: for example, impacting on distillation or cold flow properties, caused by their incorporation into a fuel composition. In addition, the blending of base fuel components may not be feasible at all locations, whereas the introduction of fuel additives, at relatively low concentrations, can more readily be achieved at fuel depots or at other filling points such as road tanker, barge or train filling points, dispensers, customer tanks and vehicles.
Accordingly, the "use" of the invention may also encompass the supply of a VII containing additive composition together with instructions for its use in an automotive fuel composition to achieve one of the benefits of the present invention (e.g. an increase in fuel economy and/or acceleration performance in a particular internal combustion engine or in a particular vehicle). The VII additive composition may therefore be supplied as a component of a formulation which is suitable for and/or intended for use as a fuel additive, in particular a diesel fuel additive. By way of example, the viscosity increasing component or additive may be incorporated into an additive formulation or package along with one or more other fuel additives. The one or more fuel additives may be selected from any useful additive, such as detergents, anti-corrosion additives, esters, poly-alpha olefins, long chain organic acids, components containing amine or amide active centres, and mixtures thereof, as is known to the person of skill in the art.
An automotive fuel composition prepared according to the present invention, or a base fuel used in such a composition may contain one or more fuel additives, or may be additive-free. If additives are included (e.g. added to the fuel at the refinery), it may contain minor amounts of one or more additives. Selected examples or suitable additives include (but are not limited to): anti-static agents; pipeline drag reducers; flow improvers (e.g. ethylene/vinyl acetate copolymers or acrylate/maleic anhydride copolymers); lubricity enhancing additives (e.g. ester- and acid-based additives); dehazers (e.g. alkoxylated phenol formaldehyde polymers); anti-foaming agents (e.g. polyether-modified polysiloxanes); ignition improvers / cetane improvers (e.g. 2-ethylhexyl nitrate (EHN), cyclohexyl nitrate, di-tert-butyl peroxide); anti-rust agents (e.g. a propane-1,2-diol semi-ester of tetrapropenyl succinic acid, or polyhydric alcohol esters of a succinic acid derivative); corrosion inhibitors; reodorants; anti-wear additives; antioxidants (e.g. phenolics such as 2,6-di-tert-butylphenol); metal deactivators; combustion improvers; static dissipator additives; cold flow improvers (e.g. glycerol monooleate, di-isodecyl adipate); antioxidants; and wax anti-settling agents. The composition may for example contain a detergent. Detergent-containing diesel fuel additives are known and commercially available. Such additives may be added to diesel fuels at levels intended to reduce, remove or slow the build-up of engine deposits. In some embodiments, it may be advantageous for the fuel composition to contain an anti-foaming agent, more preferably in combination with an anti-rust agent and/or a corrosion inhibitor and/or a lubricity enhancing additive.
Where the composition contains such additives (other than the viscosity increasing components of the invention), it suitably contains a minor proportion (such as 1% w/w or less, 0.5% w/w or less, 0.2% w/w or less), of the one or more fuel additives, in addition to the viscosity increasing component(s). Unless otherwise stated, the (active matter) concentration of each such additive component in the fuel composition may be up to 10000 ppmw, such as in the range of 0.1 to 1000 ppmw; and advantageously from 0.1 to 300 ppmw, such as from 0.1 to 150 ppmw.
If desired, one or more additive components, such as those listed above, may be co-mixed (e.g. together with suitable diluent) in an additive concentrate, and the additive concentrate may then be dispersed into a base fuel or fuel composition. The viscosity increasing component, particularly the VII may, in accordance with the present invention, be incorporated into such an additive formulation.
The total content of the additives in the fuel composition may be suitably between 0 and 10000 ppmw and more suitably below 5000 ppmw.
As used herein, amounts (e.g. concentrations, ppmw and %w/w) of components are of active matter, i.e. exclusive of volatile solvents/diluent materials.
Another aspect of the invention provides a method of operating an internal combustion engine and/or a vehicle powered by such an engine, which comprises introducing into a combustion chamber of the engine a fuel composition comprising an additive in accordance with the present invention. The fuel composition is preferably introduced for one or more of the purposes described in connection with this invention. Thus, the engine may be preferably operated with the fuel composition for the purpose of improving its fuel economy and/or acceleration performance. The engine is in particular a diesel engine, and may be a turbo charged diesel engine. The diesel engine may be of the direct injection type, for example of the rotary pump, in-line pump, unit pump, electronic unit injector or common rail type, or of the indirect injection type. It may be a heavy or a light duty diesel engine. For example, it may be an electronic unit direct injection (EUDI) engine.
According to another aspect of the invention, there is provided a process for the preparation of an automotive fuel composition, which process involves blending an automotive base fuel with an additive composition comprising a polymeric VII in particulate form such that the polymeric VII dissolves in the fuel composition. The blending may be carried out for one or more of the purposes described herein.
Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.
Thus features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the present invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. Thus, features of the "uses" of the invention are directly applicable to the "methods" of the invention. Moreover, unless stated otherwise, any feature disclosed herein may be replaced by an alternative feature serving the same or a similar purpose.

Claims

A fuel additive composition comprising:
(a) a viscosity index improver (VII) polymer component, wherein the VII polymer is predominantly comprised within a solid particulate phase; and

(b) a liquid phase component.
The additive of Claim 1, wherein the VII polymer component comprises a block copolymer, which contains one or more monomer blocks selected from ethylene, propylene, butylene, butadiene, isoprene and styrene monomers.
The additive of Claim 2, wherein the VII polymer component comprises a polystyrene-polyisoprene stellate copolymer.
The additive of Claims 1 to 3, wherein the VII polymer component is present at a concentration of selected from the group consisting of: greater than 5% w/w; greater than 10% w/w; greater than 15% w/w; greater than 25% w/w; greater than 40% w/w; greater than 50% w/w; greater than 60% w/w; and greater than 75% w/w, based on the total weight of the additive composition.
The additive of Claims 1 to 4, wherein the liquid phase component comprises a solvent, optionally selected from a hydrocarbon or organic solvent.
The additive of claim 5, wherein the solvent is present at a concentration selected from the group consisting of: at most 95% w/w; at most 90% w/w; at most 85% w/w; at most 75% w/w; at most 60% w/w; at most 50% w/w; at most 40% w/w; and at most 25% w/w based on the total weight of the additive composition.
The additive of claims 5 or 6, wherein the solvent is selected from one or more of the group consisting of:
a mineral oil; a Fischer-Tropsch derived hydrocarbon mixture; a fuel component that is compatible with a fuel composition in which the additive is to be used; a poly-alpha olefin; a biofuel such as a fatty acid alkyl ester (FAAB); a Fischer-Tropsch derived biomass-to-liquid synthesis product; a hydrogenated vegetable oil; a waste or algae oil; an alcohol, such as ethanol; an aromatic solvent; or a mixture thereof.
The additive of any preceding claim, wherein the VII polymer component is present in an amount sufficient to increase the kinematic viscosity at 40°C of a diesel fuel composition into which it is intended to be used by:
(i) at least 0.2 mm²/s;

(ii) 0.25 mm²/s to 1.0 mm²/s; or

(iii) 0.32 mm²/s to 0.67 mm²/s;
compared to the viscosity of the fuel composition prior to the addition of the additive.
The additive of any preceding claim, wherein the VII polymer component is comprised of solid particles having a median average diameter selected from the group consisting of: at least 0.01 µm; at least 0.5 µm; at least around 1.0 µm; and at least around 5.0 µm.
The use of an additive composition as defined in any of claims 1 to 8 to increase the kinematic viscosity at 40°C of a diesel fuel composition into which it is intended to be used, wherein the kinematic viscosity at 40°C of the diesel fuel composition comprising the additive composition is in the range of:
(i) up to 4.5 mm²/s;

(ii) between 2.0 mm²/s and 4.0 mm²/s; or

(iii) between 3.0 mm²/s and 3.8 mm²/s.
The use of claim 9, wherein the diesel fuel composition comprises a biofuel.
A method for manufacturing a fuel additive composition comprising combining a viscosity index improver(VII) polymer component, wherein the VII polymer is comprised within a solid particulate phase, with a liquid phase component, so as to form a slurry.
The method of Claim 11, wherein the VII polymer component comprises a block copolymer, which contains one or more monomer blocks selected from ethylene, propylene, butylene, butadiene, isoprene and styrene monomers.
The method of Claims 11 to 13, wherein the liquid phase component comprises a solvent, optionally selected from a hydrocarbon, an organic solvent, an inorganic solvent or a polar solvent.
A method for improving the fuel economy and/or acceleration performance of an engine, or of a vehicle powered by such an engine, the method comprising introducing into a combustion chamber of the engine a fuel composition comprising an additive composition of any of claims 1 to 8.