US20140059923A1

US20140059923A1 - Fuel composition

Info

Publication number: US20140059923A1
Application number: US14/018,766
Authority: US
Inventors: Aldo CAIAZZO; Lionel Clarke; Tor Kit Goh; George Robert Lee; David Alexander Parker; Richard John Price
Original assignee: Shell Oil Co
Current assignee: Shell USA Inc
Priority date: 2012-09-05
Filing date: 2013-09-05
Publication date: 2014-03-06
Also published as: CN104603244A; CN104603244B; EP2892985A1; WO2014037439A1

Abstract

A fuel composition comprising: a diesel base fuel; from 1 to 10% v/v of a fatty acid alkyl ester; and more than 10% v/v of an ether component, the ether component comprising one or more ether compounds having in the range of from 8 to 12 carbon atoms and selected from compounds of formula I

R₁—O—R₂ (I)

wherein R₁and R₂are independently primary or secondary alkyl.

Description

This present application claims the benefit of European Application No. 12183067.3, filed Sep. 5, 2012.

FIELD OF THE INVENTION

This invention relates to diesel fuel compositions comprising certain ethers, their preparation and their use, as well as to the use of certain ethers in fuel compositions for new purposes.

BACKGROUND TO THE INVENTION

Many diesel fuel compositions contain cetane boost components, also known as ignition improvers. The cetane number of a fuel or fuel composition/formulation is a measure of its ease of ignition. With a lower cetane number fuel a compression ignition (diesel) engine tends to be more difficult to start and may run more noisily when cold. There is a general preference therefore for a diesel fuel composition to have a high cetane number, and as such automotive diesel specifications generally stipulate a minimum cetane number.
It is also desirable, in the interest of the environment, to increase the amount of biofuels or biocomponents used in automotive diesel fuels. Biofuels are combustible fuels, derived from biological sources, which result in a reduction in “well-to-wheels” (ie from source to combustion) greenhouse gas emissions. For use in diesel engines, fatty acid alkyl esters (FAMEs), in particular fatty acid methyl esters (FAMEs) such as rapeseed methyl ester, soybean methyl ester and palm oil methyl ester, are the biofuels most commonly blended with conventional diesel fuel components.
It is known in the art that certain (FAAEs), in particular FAMEs, can be used in low concentrations as cetane boost components in diesel fuels.
Currently FAMEs concentrations in light duty automotive diesel are limited to a maximum of 7% v/v, primarily because of transfer of the ester into the vehicle's sump, where its accumulation causes a dilution of, and property changes in, the lubricating oil. This is a consequence of both the high boiling points of FAMEs (typically of the order of 340° C.) and possibly also their polarity. Moreover, due to the incomplete esterification of oils (triglycerides) during their manufacture, FAMEs can contain trace amounts of glycerides which on cooling can crystallise out before the FAMEs themselves, causing fuel filter blockages and compromising the cold weather operability of fuel compositions containing them.
In any event, from the perspective of improving cetane number, it is known that the cetane boosting effect of FAMEs diminishes as the blend ratio of FAME to base fuel is increased. The potential of FAMEs as cetane boost components is thus limited for more than one reason, necessitating additional cetane boost additives, at least in some applications.
It would therefore be desirable to identify alternative cetane boost components for use in diesel fuel compositions, which suffer from fewer of the drawbacks and limitations associated with FAAEs.
It is an object of the invention to address one or more of the limitations associated with prior art cetane boost components.

SUMMARY OF THE INVENTION

It has now been found that certain types of ethers can be particularly advantageous for use in diesel fuel compositions, particularly at high concentrations, due to their effects on cetane numbers in fuel blends.
According in one embodiment of the invention, a fuel composition is provided comprising: a diesel base fuel; from 1 to 10% v/v of a fatty acid alkyl ester; and more than 10% v/v of an ether component, said ether component comprising one or more ether compounds having in the range of from 8 to 12 carbon atoms and selected from compounds of formula I
R₁—O—R₂ (I)
wherein R₁and R₂are independently primary or secondary alkyl.
In another embodiment is provided, a method of increasing the concentration of a biofuel component in a diesel fuel composition comprising blending more than 10% v/v of an ether compounds having in the range of from 8 to 12 carbon atoms and selected from compounds of formula I
R₁—O—R₂ (I)
wherein R₁and R₂are independently primary or secondary alkyl.

DETAILED DESCRIPTION OF THE INVENTION

Ideally such components should be biologically derivable, ie biofuels, and also have minimal transfer into the engine sump and cause minimal dilution of lubricant as a result.
Cetane boost components need to offer a good property fit with fossil-derived diesel fuels, not only in terms of their cetane number but also in terms of volatility, flash point, melting and boiling points and cold flow properties. Flash point in particular can be a handling issue for diesel fuels, and in an overall fuel composition must be above a specified limit to ensure that flammable mixtures of fuel and air do not form within the fuel supply and distribution system. The melting point of a molecule, meanwhile, will directly affect the cloud point and cold filter plugging point of a fuel composition into which it is blended, and these properties must also be controlled in order to allow satisfactory vehicle operability during winter months.
Ideally, an alternative cetane boost component, particularly if it is a biofuel oxygenate component, will have properties—in particular a flash point and melting point—which allow it to be blended into diesel fuel compositions at concentrations above the current 7% v/v limit for FAMEs.
U.S. Pat. No. 5,520,710 in the name of Olah suggests symmetrical or unsymmetrical ethers comprising 2 to 24 carbon atoms as cetane enhancing supplements. The ether supplements are added in an amount of 0.5-10 v/v %, preferably 1-5% v/v. Data provided in U.S. Pat. No. 5,520,710 in relation to dihexyl ether and dioctyl ether suggests that the effectiveness of ethers as cetane boost additives reduces considerably with increasing concentration, e.g. at a concentration of 5% v/v compared to at a concentration of 2% v/v. This work contrasts with that of U.S. Pat. No. 2,221,839 which considers the use of straight-chain aliphatic ethers as fuels or as ignition accelerators for compression ignition engine fuels. One example documents the ignition acceleration activity resulting from incorporating one of 10% v/v n-butyl ether, 25% v/v n-amyl ether, and 25% v/v mono-butyl ether of diethylene glycol. Increase in cetane number is used as an indicator for usefulness as an ignition accelerator.
In US 2002/0134008, it is proposed to provide a diesel fuel formulations of a pre-determined flash point and cetane number increase by including two oxygenate compounds, a first oxygenate of lower flash point than the diesel base fuel and of equal to or higher cetane number, and a second oxygenate having a higher than or equal flash point to that of the diesel base fuel and a higher cetane number. The first oxygenates proposed are selected from monoglyme, diethylether and diisopropylether and are utilised in bulk quantities; the second oxygenate proposed is selected from diglyme, triglyme and dipentylether and is proposed for use in quantities of 10% v/v or less.
Anastopoulos et al in Fuel 81 (2002) 1017-1024 ‘The tribiological behaviour of alkyl ethers and alcohols in low sulphur automotive diesel’ reviews the behaviours of seven alkyl ethers and five alcohols on the lubricity of automotive diesel. Their results led them to the conclusion that alcohols offer the best lubricant potential, as only six of the seven ethers tested provided a benefit and then at concentrations of the order of 750 to 1500 ppm.
According in one embodiment of the present invention there is provided a fuel composition comprising: a diesel base fuel; from 1 to 10% v/v of a fatty acid alkyl ester; and more than 10% v/v of an ether component, the ether component comprising or consisting of one or more ether compounds having in the range of from 8 to 12 carbon atoms and selected from compounds of formula I
R₁—O—R₂ (I)
wherein R₁and R₂are independently C₂to C₁₀primary or secondary alkyl. By ether compounds are meant compounds that contain only one ether group. The term “consisting” wherever used herein also embraces “consisting substantially”, but may optionally be limited to its strict meaning of “consisting entirely”.
Contrary to the trend visible in U.S. Pat. No. 5,520,710, it has been found that C8+ ethers can function highly effectively as cetane boost additives in diesel fuel at high concentrations in excess of 10% v/v e.g. up to 50% v/v. The ether component may be a biofuel and generally does not suffer from the drawbacks associated with FAAEs in the context of lubricant dilution. For example, the ether component is less prone to accumulation in vehicle sumps. The ether component can thus be incorporated into diesel fuel compositions at concentrations significantly higher than the current 7% v/v FAME limit, without build-up of biofuel components in engine oil and whilst maintaining a positive effect on cetane numbers of the overall compositions.
The ether component is to be understood herein as an added component. Preferably, the ether component may be, or be taken to be, the sole source of the ether compound(s) that it consists of in the composition, but this is not essential.
The ether component is defined herein as comprising or consisting of one or more ether compounds having at least 8 carbon atoms (C8+ ether), or at least 9 carbon atoms (C9+ ether), or most preferably at least 10 carbon atoms (C10+ ether). Thus, in preferred embodiments of the invention, the ether component may comprise, or be, C8+ ether, C9+ ether, or C10+ ether. Higher molecular weight ethers tend to have particularly advantageous volatility and cetane properties.
In some embodiments of the invention, the ether compounds of the ether component may comprise at most 12 carbon atoms, or most preferably at most 10 carbon atoms. Ether compounds with a relatively low number of carbon atoms may be preferred for their ease of biological synthesis. C10 ethers, are particularly preferred.
The ether compound(s) of the ether component may be symmetrical or asymmetrical; dialkyl, dicycloalkyl, or alkylcycloalkyl. Symmetrical compounds are preferred. A particularly preferred ether is dipentyl ether (DPE).
Suitably, the ether compound(s) may be selected from compounds of formula I
R₁—O—R₂ (I)
wherein R₁and R₂are independently C₂to C₂₄primary or secondary alkyl, provided that the total number of carbon atoms in formula (I) is as required, e.g. at least 8, 9 or 10, or as defined anywhere hereinabove.
Preferably, R₁and/or R₂may be C₃to C₁₅alkyl, more preferably C₄to C₇. In a particularly preferred embodiment, R₁and/or R₂may be C₅alkyl.
Since the ether component may preferably comprise or consist of symmetrical compounds, R₁and R₂may preferably be the same.
The ether component may comprise or consist of one or more of the ether compounds or ether compound mixtures described hereinabove. Most preferably, the ether component may comprise or consist of dipentyl ether.
The ether component may comprise a mixture of two or more ether compounds as defined hereinabove. For predictability of properties, in some embodiments of the invention, the ether component may comprise at least 50% v/v, or 70% v/v or 90% v/v, or even 95% v/v of any one of the ether compounds or ether compound mixtures described hereinabove.
In some embodiments of the invention, the ether component may be accompanied by a small amount of impurities, for example by-products of ether synthesis that have no substantive effect on the overall properties of the ether component. Such impurities may, for example, be present in an amount of at most about 3%, e.g. as measured by gas chromatography (GC) commonly employed by suppliers such as Sigma Aldrich. In embodiments of the invention, such impurities up to 3% as measured by GC may be considered part of the ether component, in which case the component consists substantially of the ether compounds.
The cetane number of the ether component will typically be higher than the cetane number of the diesel base fuel. Suitably, the cetane number of the ether component may be at least 90, preferably at least 100, or at least 102, most preferably at least 104.
Suitably, the ether component may offer a good property fit with the diesel base fuel, particularly with a view to the composition meeting EN590 or another specification.
The ether component may preferably have a density, measured according to ASTM D 4052, of at least 0.750 g/cm³, more preferably at least 0.770 g/cm³. The density of the ether component may, for example, be at most 0.830 g/cm³.
The ether component may preferably have a flash point, measured according to ASTM D 93, of at least 20° C., more preferably at least 50° C.
The ether component may preferably have a vapour pressure, measured at 25° C., of at most 500 Torr (66661.2 Pa), preferably at most 50 Torr (6666.1 Pa), or even at most 5 Torr (666.6 Pa). The vapour pressure of the ether component may, for example, be at least 0.5 Torr (66.6 Pa).
The ether component may preferably have a boiling point, measured according to ASTM D 86, of at least 40° C., more preferably at least 100° C. The boiling point of the ether component may, for example, be at most 480° C.
The ether component may be prepared by any suitable process known in the art. One well known synthesis is the Williamson ether synthesis, which involves treatment of a parent alcohol with a strong base to form an alkoxide, followed by addition of an appropriate aliphatic compound bearing a leaving group such as halide or sulfonate. This synthesis works particularly well for acyclic, unencumbered open chain primary aliphatic compounds. The Ullmann ether synthesis, which is also well known and based on a similar mechanism, albeit generally in the presence of a catalyst, is particularly suitable for the formation of aryl ethers. Other methods of forming ethers include the electrophilic addition of alcohols to alkenes, e.g. alkoxymercuration of alkenes using mercury trifluoroacetate as catalyst and hydroboration of alkenes followed by oxidation. Further methods of synthesizing ethers, including cyclic and polycyclic systems are described, for example, in U.S. Pat. No. 5,520,710.
On an industrial scale, symmetrical ethers are typically prepared by the dehydration of a parent alcohol. Dipentyl ether, for example, may be prepared by dehydrating 1-pentanol in the presence of sulphuric acid.
The alcohols or other starting materials for the synthesis of ethers may be obtained from any available source. For example parent alcohols, such as amyl alcohol, may be obtained by the hydroformylation of olefins, which may in turn be petroleum derived (see e.g. K Weissermel and H-J Arpe, Industrial Organic Chemistry, Wiley-Vch, p 205). Further alternatives may be i) Markovnikov hydration of olefins in the presence of acids and/or metal catalysts; ii) Anti-Markovnikov addition via the sequence hydroboration/oxidation of alkenes (see e.g. M. G. Loudon, (2002). “Addition Reactions of Alkenes”. Organic Chemistry (Fourth Edition ed.) Oxford University Press pp. 168); iii) the reduction of organic acids (such as but not limited to acids obtained via fermentation), via intermediates aldehydes (see e.g. Y. Li, et al. Huaxue Tongbao (2002), 65(7), 452-457); and iv) deep hydrogenation of furfural through intermediates such as methylfuran and methyl tetrahydrofuran (see e.g. H.-Y. Zheng, et al, Journal of Molecular Catalysis A: Chemical, 246(1-2), 18-23; 2006).
In a preferred embodiment of the invention, the ether component may be a biofuel component, ie derived from a biological source. In such embodiments, the ether component may comprise or consist of ether compounds derived from parent molecules, e.g. alcohols, which are in turn obtained from a renewable carbonaceous feedstock. For example, it is known to obtain alcohols by fermentation, e.g. by distillation of fusel oil. Other biological routes to alcohols, such as pentanol, via fermentation of renewable feedstocks (organic carbon sources) using microorganisms, fungi (such as members of the genus Saccharomyces), protists, algae, bacteria (including cyanobacteria) and archaea are increasingly being proposed. Alternatively, alcohols can be biologically derived via gasification/pyrolysis from renewable carbonaceous feedstock, followed by Fischer-Tropsch synthesis.
In some embodiments of the invention, the ether component may comprise at least about 0.1 dpm/gC of carbon-14. It is known in the art that carbon-14, which has a half-life of about 5700 years, is found in biologically derived materials but not in fossil fuels. Carbon-14 levels can be determined by measuring its decay process (disintegrations per minute per gram carbon or dpm/gC) through liquid scintillation counting.
The concentration of the ether component in the overall fuel composition (or at least in the base fuel/ether component mixture) is preferably 90% v/v or less, more preferably 80% v/v or less, yet more preferably 70 or 60 or 50% v/v or less, based on the total composition/mixture. As a minimum it is more than 10% v/v, or 12% v/v or greater, such as 15% or 25% v/v or greater, or even 30 or 40% v/v or greater, based on the total composition/mixture. The amount of the ether component may represent a balance of the fuel composition: after inclusion of the base fuel component, and any further (optional) components and additives, the ether component may therefore be present in an amount to represent the balance to 100% v/v in the composition.
The diesel base fuel may be any fuel component, or mixture thereof, which is suitable and/or adapted for use in a diesel fuel composition and therefore for combustion within a compression ignition (diesel) engine. It will typically be a liquid hydrocarbon middle distillate fuel, more typically a gas oil. It may be or contain a kerosene fuel component.
It may be petroleum derived. Alternatively it may be synthetic: for instance it may be the product of a Fischer-Tropsch condensation. It may be derived from a biological source.
A diesel base fuel will typically boil in the range from 150 or 180 to 370° C. (ASTM D86 or EN ISO 3405). It will suitably have a measured cetane number (ASTM D613) of from 40 to 70 or from 40 to 65 or from 51 to 65 or to 70.
However, because the ether component has a positive effect on cetane number, a fuel composition according to the invention may include (or may include a greater proportion of) a base fuel which has a relatively low cetane number. This can increase the options available to the fuel formulator. The ether component may therefore be used for the purpose of allowing the inclusion, in a diesel fuel composition, of one or more lower cetane number fuel components (for example diesel base fuels), or of a higher concentration of one or more such fuel components, without, or without undue, detriment to the cetane number of the overall composition. In this context a “lower cetane number” fuel component may for example have a measured cetane number of less than 50, or of less than 45 or 40 or in cases of less than 35. “Without undue detriment to the cetane number” may for example mean without reducing the cetane number by more than 30%, or in cases by more than 20 or 10 or 5 or 1%, of its value if a higher cetane number fuel component (for example, with a measured cetane number of 40 or greater, or of 45 or 50 or greater) were to be used in the fuel composition, at the same concentration, in place of the lower cetane number fuel component. It may entail the overall fuel composition meeting a desired target specification, for example the European diesel fuel specification EN 590.
The diesel base fuel may suitably be present in the composition in an amount of 10% v/v or greater, or 20 or 30 or 40% or 50% v/v or greater, based on the total composition. It may be present in an amount of less than 90% v/v, or up to 85 or up to 80 or 75% v/v, or up to 70 or 65 or 60% v/v, based on the total composition. The amount of the base fuel may represent a balance of the fuel composition: after inclusion of the ether component, the fatty acid alkyl ester, and any further (optional) components and additives, the diesel base fuel may therefore represent the balance to 100% v/v in the composition.
The fuel composition may be prepared by simple blending of its components in any suitable order, and such methods of blending any of the fuel compositions herein are embraced by the invention.
The fuel composition may comprise, in addition to the diesel base fuel, the fatty acid alkyl ester, and the ether component, one or more fuel or refinery additives, in particular additives which are suitable for use in automotive diesel fuels. Many such additives are known and commercially available. The composition may for example comprise one or more additives selected from cetane boost additives, antistatic additives, lubricity additives, cold flow additives, and combinations thereof. Such additives may be included at a concentration of up to 300 ppmw (parts per million by weight), for example of from 50 to 300 ppmw. Due to the inclusion of the ether component, however, it may, as described below, be possible for the composition to contain lower levels of cetane boost additive, or in cases for the composition not to contain such type of additive.
The fuel composition should be suitable and/or adapted for use in a compression ignition (diesel) internal combustion engine. It may in particular be an automotive fuel composition. In further embodiments it may be suitable and/or adapted for use as an industrial gas oil, or as a domestic heating oil.
The fuel composition may suitably comply with applicable current standard diesel fuel specification(s) such as for example EN 590 (for Europe) or ASTM D975 (for the USA). By way of example, the overall composition may have a density from 820 to 845 kg/m³at 15° C. (ASTM D4052 or EN ISO 3675); a T95 boiling point (ASTM D86 or EN ISO 3405) of 360° C. or less; a measured cetane number (ASTM D613) of 40 or greater, ideally of 51 or greater; a kinematic viscosity at 40° C. (VK40) (ASTM D445 or EN ISO 3104) from 2 to 4.5 centistokes (mm²/s); a flash point (ASTM D93 or EN ISO 2719) of 55° C. or greater; a sulphur content (ASTM D2622 or EN ISO 20846) of 50 mg/kg or less; a cloud point (ASTM D2500/IP 219/ISO 3015) of less than −10° C.; and/or a polycyclic aromatic hydrocarbons (PAH) content (EN 12916) of less than 11% w/w. It may have a lubricity, measured using a high frequency reciprocating rig for example according to ISO 12156 and expressed as a “HFRR wear scar”, of 460 μm or less.
Relevant specifications may however differ from country to country and from year to year, and may depend on the intended use of the composition. Moreover the composition may contain individual fuel components with properties outside of these ranges, since the properties of an overall blend may differ, often significantly, from those of its individual constituents.
The fuel composition comprises, in addition to the diesel base fuel and the ether component, a fatty acid alkyl ester, in particular a fatty acid methyl ester (FAME) such as rapeseed methyl ester or palm oil methyl ester. It is further possible for one or more further biofuel components, particularly other than ether or FAME, to be present. The biofuel component may suitably comprise an alcohol, for example ethanol, and/or a fatty alcohol ester, and/or a hydrogenated vegetable oil. The fatty acid alkyl ester may be present in an amount of at least 1% v/v, or 2 or 3 or 4 or 5% v/v, and up to 10 or 7 or 5% v/v, based on the total composition. Typically, the amount of further biofuel component may be at least 1% v/v, or 2 or 3 or 4 or 5% v/v, and up to 30% v/v, or up to 20 or 10 or 7 or 5% v/v, based on the total composition. Due to the inclusion of the ether component, it may, as described below, be possible for the composition to contain lower levels of biofuel components, or in cases for the composition not to contain additional biofuel components.
It has been found that the ether component can significantly boost cetane number when the fuel composition also comprises a a fatty acid alkyl ester.
According to a further aspect of the invention, there is provided the use of an ether component as defined above, in a diesel fuel composition containing a fatty acid alkyl ester, for the purpose of increasing the cetane number of the composition.
If it is desired to include a fatty acid ester or a fatty alcohol ester in a diesel fuel composition, for example in order to increase the biofuel content of the composition, and/or for the lubricity benefits described in US-A-2011/0154728, the present invention can provide for a further cetane boost. In accordance with the invention, the ether component may be used to replace all or part of a fatty acid ester or fatty alcohol ester which was previously, or was intended to be, or would otherwise have been, included in the diesel fuel composition.
The ether component may be used to achieve any degree of increase in the cetane number of the diesel fuel composition, and/or for the purpose of achieving a desired target cetane number, for example a target set by an applicable regulatory standard such as EN 590, or a target set by a user (which includes a handler, keeper or distributor) or potential user of the composition. It may be used to achieve a cetane number increase which is greater than that which would be possible using the same concentration of another biofuel component, in particular of a fatty alcohol ester such as an alkyl acetate, or of a fatty acid alkyl ester such as a FAME. The increase in cetane number will typically be as compared to the cetane number of the composition prior to adding ether component to it.
In the present context, “achieving” a desired target property also embraces—and in an embodiment involves—improving on the relevant target. Thus, for example, the ether component may be used to produce a diesel fuel composition which has a cetane number higher than a desired target standard.
The cetane number of a fuel composition may be determined using any suitable method, for instance using the standard test procedure ASTM D613 (ISO 5165, IP 41) which provides a so-called “measured” cetane number obtained under engine running conditions. Alternatively the cetane number may be determined using the more recent “ignition quality test” (IQT) (ASTM D6890, IP 498), which provides a “derived” cetane number based on the time delay between injection and combustion of a fuel sample introduced into a constant volume combustion chamber. This relatively rapid technique can be used on laboratory scale (ca 100 ml) samples of a range of different fuels.
Alternatively, cetane number may be measured by near infrared spectroscopy (NIR), as for example described in U.S. Pat. No. 5,349,188. This method may be preferred in a refinery environment as it can be less cumbersome than for instance ASTM D613. NIR measurements make use of a correlation between the measured spectrum and the actual cetane number of a sample. An underlying model is prepared by correlating the known cetane numbers of a variety of fuel samples with their near infrared spectral data.
The present invention preferably results in a diesel fuel composition which has a measured cetane number (ASTM D613) of 40 or greater, or of 45 or 50 or 51 or greater, for example of 55 or 60 or 65 or greater, in cases of 70 or 75 or greater.
The invention may additionally or alternatively be used to adjust any property of the diesel fuel composition which is equivalent to or associated with cetane number, for example to improve the combustion performance of the composition (eg to shorten ignition delays, to facilitate cold starting and/or to reduce incomplete combustion and/or associated emissions in a fuel-consuming system running on the fuel composition) and/or to improve fuel economy.
By using the present invention, it can be possible to include in a diesel fuel composition a higher concentration of a biofuel component than would have been predicted to be possible—whilst still achieving a desired target cetane number—based on the properties of the fatty acid/alcohol esters. It can be desirable to increase biofuel concentrations for a number of reasons, for instance to meet regulatory requirements or consumer expectations or more generally to reduce the “well-to-wheels” carbon dioxide emissions associated with the production and use of the fuel. It can also be desirable to increase the concentration of fatty alcohol esters, not only as biofuel components but also, for example, in order to improve the lubricity of a fuel composition containing an acid-based lubricity additive, as described in US-A-2011/0154728. However it would have been thought necessary, in the past, to balance such benefits against the potential reduction in cetane number which would be expected to result from increasing the concentration of a fatty alcohol ester, particularly for those esters having shorter (for example C10 or less) carbon chains. According to the present invention, such benefits can now be achieved with the added option of a cetane number increase and without leading to excessive lubricant dilution.
Thus according to an additional aspect, the invention provides the use of an ether component as defined above, in a diesel fuel composition, for the purpose of increasing the concentration of a biofuel component in the composition, without undue detriment to: the cetane number of the composition; and/or lubricant dilution under engine operating conditions. The biofuel component may, for example, comprise a fatty alcohol ester: the ether component may therefore be used to increase the concentration of fatty alcohol esters in the diesel fuel composition, without or without undue detriment to its cetane number and/or lubricant dilution properties under engine operating conditions. Alternatively, the biofuel component may be taken as including all biologically derived fuel components in the composition. In this way the invention may be used to increase the options available, to the fuel formulator, for increasing the biofuel content of a diesel fuel composition whilst still meeting relevant fuel specifications.
In the present context, “without undue detriment to the cetane number” may for example mean without reducing the cetane number by more than 30%, or in cases by more than 20 or 10 or 5 or 1%, of its original value.
In the present context, “without undue detriment to lubricant dilution under engine operating conditions” may for example mean without increasing at all the lubricant dilution compared to a comparable or identical fuel composition without the ether component. Lubricant dilution may be measured in any suitable manner, e.g. based on gas chromatography (GC) analysis of lubricant sump samples. Expressed in another way, the ether component may be used to enhance or maintain lubricant lifetime during use of the composition, or to maintain or increase the oil drain interval.
In accordance with this embodiment of the invention, the ether component may be used to achieve any degree of increase in the concentration of the relevant biofuel component. In an embodiment, the ether component is used to increase the concentration of the biofuel component whilst at the same time increasing (which again embraces any degree of increase) the cetane number of the diesel fuel composition.
Because the ether component can increase the cetane number of a diesel fuel composition in which it is used, the composition may as a consequence require a lower level of cetane boost additives than might otherwise have been needed in order to achieve a desired target cetane number. This can in turn reduce the cost and complexity of preparing the composition, and/or can provide greater versatility in fuel formulation practices. Thus, a further aspect of the invention provides the use of an ether component as defined above in a diesel fuel composition, for the purpose of reducing the concentration of a cetane boost additive in the composition.
In the context of this embodiment of the invention, the term “reducing” embraces any degree of reduction, including reduction to zero. The reduction may for instance be 10% or more of the original concentration of the cetane boost additive, or 25 or 50 or 75 or 90% or more. The reduction may be as compared to the concentration of the cetane boost additive which would otherwise have been incorporated into the fuel composition in order to achieve the properties and performance required and/or desired of it in the context of its intended use. This may for instance be the concentration of the additive which was present in the composition prior to the realisation that the ether component could be used in the way provided by the present invention, and/or which was present in an otherwise analogous fuel composition intended (eg marketed) for use in an analogous context, prior to adding the ether component to it in accordance with the invention.
The reduction in concentration of the cetane boost additive may be as compared to the concentration of the additive which would be predicted to be necessary to achieve a desired cetane number for the composition in the absence of the ether component.
A cetane boost additive may be any additive which is capable of increasing, or intended to increase, the cetane number of a diesel fuel composition to which it is added, and/or to improve the ignition properties of such a composition when it is used in an engine or other fuel-consuming system. A cetane boost additive may also be known as a cetane improver, a cetane number improver or an ignition improver. Many such additives are known and commercially available; they typically function by increasing the concentration of free radicals when a fuel begins to react in a combustion chamber of a fuel-consuming system. Examples include organic nitrates and nitrites, in particular (cyclo)alkyl nitrates such as isopropyl nitrate, 2-ethylhexyl nitrate (2-EHN) and cyclohexyl nitrate, and ethyl nitrates such as methoxyethyl nitrate; and organic (hydro)peroxides such as di-tert-butyl peroxide. Cetane boosting diesel fuel additives are commercially available for instance as HITEC™ 4103 (ex Afton Chemical) and as CI-0801 and CI-0806 (ex Innospec Inc).
In the context of the present invention, “use” of the ether component in a diesel fuel composition means incorporating the ether component into the composition, typically as a blend (ie a physical mixture) with one or more other diesel fuel components, for example a diesel base fuel and optionally one or more diesel fuel additives. The ether component will conveniently be incorporated before the composition is introduced into an engine or other system which is to be run on the composition. Instead or in addition, the use of the ether component may involve running a fuel-consuming system, typically an internal combustion engine, on a diesel fuel composition containing the ether component, typically by introducing the composition into a combustion chamber of an engine. It may involve running a vehicle which is driven by a fuel-consuming system, on a diesel fuel composition containing the ether component. In such cases the engine is suitably a compression ignition (diesel) engine.
“Use” of the ether component in the ways described above may also embrace supplying the ether component together with instructions for its use in a diesel fuel composition in order to increase the cetane number of the composition. The ether component may itself be supplied as part of a composition which is suitable for and/or intended for use as a fuel additive, in which case the ether component may be included in such a composition for the purpose of influencing its effects on the cetane number of a diesel fuel composition.
In general, references to “adding” a component to, or “incorporating” a component in, a fuel composition may be taken to embrace addition or incorporation at any point during the production of the composition or at any time prior to its use.
In embodiments, the present invention may be used to produce at least 1,000 litres of the ether component-containing fuel composition, or at least 5,000 or 10,000 or 20,000 or 50,000 litres.
A fuel composition prepared or used according to the invention may be marketed with an indication that it benefits from an improvement due to the inclusion of the ether component, in particular a higher cetane number. The marketing of such a composition may comprise an activity selected from (a) providing the composition in a container that comprises the relevant indication; (b) supplying the composition with product literature that comprises the indication; (c) providing the indication in a publication or sign (for example at the point of sale) that describes the composition; and (d) providing the indication in a commercial which is aired for instance on the radio, television or internet. The improvement may be attributed, in such an indication, at least partly to the presence of the ether component. The invention may involve assessing the relevant property (in particular the cetane number) of the composition during or after its preparation. It may involve assessing the relevant property both before and after incorporation of the ether component, for example so as to confirm that the ether component contributes to the relevant improvement in the composition.
Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of the words, for example “comprising” and “comprises”, mean “including but not limited to”, and do not exclude other moieties, additives, components, integers or steps. Moreover 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.
Preferred features of each aspect of the invention may be as described in connection with any of the other aspects. Other features of the invention will become apparent from the following examples. Generally speaking the invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims and drawings). Thus features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. For example, for the avoidance of doubt, the optional and preferred features of the fuel composition, the diesel base fuel, the ether component or the biofuel component apply to all aspects of the invention in which the fuel composition, the diesel base fuel, the ether component or the biofuel component are mentioned.
Moreover unless stated otherwise, any feature disclosed herein may be replaced by an alternative feature serving the same or a similar purpose.
Where upper and lower limits are quoted for a property, for example for the concentration of a fuel component, then a range of values defined by a combination of any of the upper limits with any of the lower limits may also be implied.
In this specification, references to fuel and fuel component properties are—unless stated otherwise—to properties measured under ambient conditions, ie at atmospheric pressure and at a temperature from 16 to 22 or 25° C., or from 18 to 22 or 25° C., for example about 20° C.
The present invention will now be further described with reference to the following non-limiting examples.

Example 1 (Comparative)

Diesel fuel compositions were prepared by blending a diesel base fuel with an ether component consisting of dipentyl ether (DPE).
The base fuel was a zero sulphur diesel fuel (ex Shell), which conformed to the European diesel fuel specification EN 590. It did not contain any detergent or lubricity additives, or any oxygenates such as FAMEs. Its properties are summarised in Table 1 below.

TABLE 1

Property	Units	Test method	Base fuel

Density @ 15° C.	kg/m³	ASTM D 4052	825
VK40	mm²/s	IP 71	2.08
Distillation		ASTM D 86
0%	° C.		172.0
10%			195.6
20%			205.3
30%			215.0
40%			226.7
50%			239.9
60%			254.4
70%			269.6
80%			288.2
90%			311.2
95%			328.6
100%			342
Rec at 250° C.	% v/v		57.5
Rec at 370° C.	% v/v		97.7
Cetane (CRF engine)		ASTM 613	53.8
Derived cetane (IQT)		IP 498	54.1
HFRR (averaged)	μm	ISO 12156	272

The ether component tested consisted of 97% pure (measured by GC) dipentyl ether sourced from Sigma Aldrich. Relevant properties (literature values) for the ether component are as follows: boiling point=188° C.; flash point=57° C.; vapour pressure at 25° C.=1.0 Torr; density=0.791 g/cm³.
The ether component was blended with the base fuel at 2, 5, 10, 15, 30 and 50% v/v. The resultant blends were tested for cetane number using the IQT method specified in Table 1. The results are shown in Table 2.
From the measured cetane numbers of the blends and the diesel base fuel, blending cetane number values were calculated for the ether component as follows.
blending CN _DPE=(CN _comp−(1−x)*CN _diesel)/x
where:

- blending CN_DPEis the blending cetane number of the ether component when used at volume fraction x;
- CN_compis the measured cetane number of the base fuel/ether component blend; and
- CN_dieselis the measured cetane number of the diesel base fuel.

The resultant blend values are also shown in Table 2.

TABLE 2

	Diesel	DPE	CN_comp	Blending
Comp	(% v/v)	(% v/v)	(IQT)	CN_DPE

1	98	2	55.3	99.4
2	95	5	56.6	98.4
3	90	10	58.1	91.4
4	85	15	60.4	94.4
5	70	30	66.6	95.1
6	50	50	76.7	99.0

The blending cetane number of the ether component is a measure of the contribution of the ether component to the measured cetane number of the fuel composition. It can be seen that the blending cetane number of the ether component increases from 91.4 at 10% v/v to 99 at 50% v/v. The effectiveness of the ether component in boosting cetane is thus increased at higher concentrations.

Example 2 (Comparative)

Diesel fuel compositions were prepared, for comparison with those of Example 1, by blending a diesel base fuel with a fatty acid methyl ester (FAME) component.
The diesel base fuel was as in Example 1.
The FAME component consisted of 100% refinery grade palm oil methyl esters (POME).
Relevant properties for the FAME component are as follows: flash point=156° C. (IP 34); viscosity at 40° C.=4.45 mm²/s (IP 71); density=0.877 g/cm³(IP 365).
The FAME component was blended with the base fuel at 2, 5, 10, 15, 30 and 50% v/v. The resultant blends were tested for cetane number using the IQT method specified in Table 1. The results are shown in Table 3.
From the measured cetane numbers of the blends and the diesel base fuel, blending cetane number values were calculated for the FAME component as follows.
blending CN _FAME=(CN _comp−(1−x)*CN _diesel)/x
where:

- blending CN_FAMEis the blending cetane number of the FAME component when used at volume fraction x;
- CN_compis the measured cetane number of the base fuel/ether component blend; and
- CN_dieselis the measured cetane number of the diesel base fuel.

The resultant blend values are also shown in Table 3.

TABLE 3

	Diesel	FAME	CN_comp	Blending
Comp	(% v/v)	(% v/v)	(IQT)	CN_FAME

7	98	2	54.7	69.4
8	95	5	56	86.4
9	90	10	56.5	75.4
10	85	15	57.2	73.1
11	70	30	59.1	70.1
12	50	50	62.4	70.4

The blending cetane number of the FAME component is a measure of the contribution of the FAME component to the measured cetane number of the fuel composition. It can be seen that the blending cetane number of the FAME component decreases from 75.4 at 10% v/v to 70.4 at 50% v/v. The effectiveness of the FAME component in boosting cetane is thus decreased at higher concentrations.

Example 3

Diesel fuel compositions were prepared, according to the invention, by blending a diesel base fuel with an ether component consisting of dipentyl ether and a fatty acid methyl ester (FAME) component.
The diesel base fuel and the dipentyl ether components were as in Example 1. The FAME component was as in Example 2.
The ether and FAME components were blended with the base fuel in the amounts shown in Table 4. The resultant blends were tested for cetane number using the IQT method specified in Table 1. The results are shown in Table 4.
From the measured cetane numbers of the blends and the diesel base fuel, blending cetane number values were calculated for the combined ether and FAME components as follows.
blending CN _DPE+FAME=(CN _comp−(1−x)*CN _diesel)/x
where:

- blending CN_DPE+FAMEis the blending cetane number of the combined ether and FAME components when used at a total volume fraction x;
- CN_compis the measured cetane number of the base fuel/ether component blend; and
- CN_dieselis the measured cetane number of the diesel base fuel.

The resultant blend values are also shown in Table 4.

TABLE 4

	Diesel	FAME	DPE	CN_comp	Blending
Comp	(% v/v)	(% v/v)	(% v/v)	(IQT)	CN_DPE+FAME

13	90	5	5	56	70.4
14	85	5	10	58.7	83.1
15	70	5	25	64	86.4
16	50	5	45	74.5	94.6
17	85	7.5	7.5	58.6	82.4
18	70	15	15	62.9	82.7
19	50	25	25	68.4	82.4

The blending cetane number of the combined ether and FAME components is a measure of the contribution of these components to the measured cetane number of the fuel composition. It can be seen that, at a consistent concentration of the FAME component, the blending cetane number of the combined components increases from 70.4 at 5% v/v ether component to 94.6 at 45% v/v ether component. At equivalent concentrations of ether and FAME components, the blending cetane number of the combined components stays relatively constant, irrespective of concentration.

Example 4

The properties of a diesel fuel composition from Example 1 were examined to determine their compliance with fuel specifications. Table 5 shows the properties of composition 3 from Example 1.

TABLE 5

Property	Units	Test method	Comp 3

Density @ 15° C.	kg/m³	ASTM D 4052	822
VK40	mm²/s	IP 71	1.92
Distillation		ASTM D 86
0%	° C.		174.3
10%			191.6
20%			198.8
30%			207.6
40%			218.1
50%			230.4
60%			246.7
70%			264.7
80%			284.8
90%			309.3
95%			328.3
100%			340.3
Rec at 250° C.	% v/v		61.9
Rec at 370° C.	% v/v		97
Flash point	° C.	ASTM D 93	65
Cetane (CRF engine)		ASTM D 613	56.8
Derived cetane (IQT)		IP 498	58.4
HFRR (averaged)	μm	ISO 12156	445
Cloud point	° C.	IP 219	−14
CFPP (pot A)		IP 309	−35
CFPP (pot B)		IP 309	−35

Example 5

The dilution of diesel engine lubricant with ether component and other biofuel components was examined.
The standardised experimental procedure was as follows:

- A diesel engine was flushed with new lubricant and operated for 16 hours under steady-state conditions. The engine speed and load was then increased to a higher speed/load point at the start of test, after which the lubricant sump temperature reached 120° C.
- The diesel fuel used to run the engine did not contain any biofuels (ie. free of FAME and ether).
- To simulate accumulation of a bio-component transferred from a diesel fuel, known volumes of the ether component and/or FAME component (as in the Examples above) were dosed in separate runs directly into the lubricant sump.
- Samples at the start, end and intermediate time points were collected and analysed.

The components tested were Ether component only, FAME component only, and an equivolume Ether-FAME component mixture. The loss of bio-component (measured as percentage remaining in the lubricant; % remaining) was determined from GC analysis of lubricant sump samples.
The results are shown in Table 6.

TABLE 6

		Ether-FAME component
Ether	FAME	(1:1 v/v)

Time	component	component	FAME %	Ether %
(min)	% remaining	% remaining	remaining	remaining

0	100	100	100	100
60	34.4	—	—	—
120	15.4	—	—	—
180	2.7	—	—	—
240	2	—	—	—
300	0.1	—	—	—
360	0	—	—	—
420	0	94.3	95.5	0

It is observed that the ether component is volatilized from the lubricant in less than 7 hours, whereas the FAME component is persistent. When an ether-FAME mixture is added, the ether component is volatilized in the same manner as when it was present as a single component.

Discussion of Examples

The effectiveness of the ether component in boosting cetane has been found to increase at higher concentrations. This is unexpected, both in view of the behaviour of other cetane boost components such as FAME and in view of the behaviour of the ether component at concentrations below 10% v/v. The ether component has been found to boost cetane effectively in diesel fuel compositions both with and without a FAME component, but provided a significant boost when both components were present.
Furthermore, it was found that any dilution of lubricant by the ether component was rapidly reversible by volatilization under engine operating conditions. Therefore, lubricant performance properties such as protection and durability are not affected. This behaviour of the ether component contrasts with that of FAMEs, which accumulate in the lubricant.

Claims

We claim:

1. A fuel composition comprising: a diesel base fuel; from 1 to 10% v/v of a fatty acid alkyl ester; and more than 10% v/v of an ether component, said ether component comprising one or more ether compounds having in the range of from 8 to 12 carbon atoms and selected from compounds of formula I

R₁—O—R₂ (I)

wherein R₁and R₂are independently primary or secondary alkyl.

2. The fuel composition of claim 1 wherein the ether component comprises symmetrical ether compounds.

3. The fuel composition of claim 1 wherein the ether component comprises dipentyl ether.

4. The fuel composition of claim 1 wherein the ether component has a density of at least 0.770 g/cm³.

5. The fuel composition of claim 1 wherein the ether component has a flash point of at least 50° C.

6. The fuel composition of claim 1 wherein the ether component has a vapour pressure at 25° C. of at most 5 Torr.

7. The fuel composition of claim 1 wherein the ether component has a boiling point of at least 100° C.

8. The fuel composition of claim 1 wherein the ether component is a biofuel component.

9. The fuel composition of claim 1 wherein the ether component is present in an amount of from 15% to 90% v/v.

10. The fuel composition of claim 9 wherein the ether component is present in an amount of from 15% to 50% v/v.

11. The fuel composition of claim 1 wherein the ether component consists of one or more ether compounds having in the range of from 8 to 12 carbon atoms and selected from compounds of formula I

R₁—O—R₂ (I)

wherein R₁and R₂are independently primary or secondary alkyl.

12. The fuel composition of claim 1 wherein the ether component has a density of at least 0.770 g/cm³, a flash point of at least 50° C., a vapour pressure at 25° C. of at most 5 Torr, and a boiling point of at least 100° C.

13. The fuel composition of claim 1 wherein the fuel composition has a measured cetane number of 40 or greater.

14. A method of increasing the concentration of a biofuel component in a diesel fuel composition comprising blending more than 10% v/v of an ether compounds having in the range of from 8 to 12 carbon atoms and selected from compounds of formula I

R₁—O—R₂ (I)

wherein R₁and R₂are independently primary or secondary alkyl.

15. The method of claim 14 wherein the diesel fuel composition contains a fatty acid ester or a fatty alcohol ester.