WO2013083596A1

WO2013083596A1 - New use

Info

Publication number: WO2013083596A1
Application number: PCT/EP2012/074425
Authority: WO
Inventors: Alison Felix-Moore; George Robert Lee; Robert John Price
Original assignee: Shell Internationale Research Maatschappij B.V.; Shell Oil Company
Priority date: 2011-12-05
Filing date: 2012-12-05
Publication date: 2013-06-13

Abstract

Use of a C8 or C8+ alkyl or alkenyl formate, in a diesel fuel formulation, for the purpose of increasing its cetane number. The alk(en)yl formate may in particular be an alkyl formate, for example with an alkyl chain length of from C8 to C12, and may be used to replace, at least partially, another biofuel component of lower cetane number, for example another fatty alcohol ester or a fatty acid ester. The invention may also be used to increase the concentration of a biofuel component in a diesel fuel formulation, without or without undue detriment to its cetane number, and/or to reduce the concentration of a cetane improving additive in the formulation.

Description

NEW USE

Field of the Invention

This invention relates to the use of certain fatty alcohol esters in diesel fuel formulations for new purposes .

Background to the Invention

It is desirable, both in the interests of the environment and to comply with increasingly stringent regulatory demands, to increase the amount of biofuels 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 (FAAEs) , 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.

The properties of a FAAE depend to a large extent on the nature of the carbon chain in the fatty acid moiety, in particular its length and degree of unsaturation. This in turn depends on the oil or fat from which the fatty acid is derived. For example, C18 is the predominant carbon chain length for both soybean and rapeseed oil, although the former has a greater degree of unsaturation.

If a FAAE is to be used as a component of a diesel fuel formulation, two critical physical properties are its melting point {which can limit its concentration in a fuel for use during the winter) and its boiling point (which needs to fall within the typical diesel boiling range) . For typical FAMEs, boiling points become too high for chain lengths above C18, whilst melting points become too high for saturated chains longer than C12. The introduction of unsaturation into a C18 chain can reduce the melting point of the corresponding FAME below 0°C, making it usable as a diesel fuel component, but this is at the expense of reduced oxidative stability during storage and a possibly increased tendency to form

injector deposits.

Currently, FAME 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 formulations containing them.

It would therefore be desirable to identify

alternative biocomponents for use in diesel fuel

formulations, which suffer from fewer of the drawbacks associated with FAAEs. Such components need to offer a good property fit with fossil-derived diesel fuels, in terms for example of their melting and boiling points, cetane numbers, flash points and cold flow properties. Flash point in particular can be a handling issue for diesel fuels, and in an overall fuel formulation 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 formulation 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 biodiesel

component will have properties - in particular a flash point and melting point - which allow it to be blended into diesel fuel formulations at concentrations above the current 7% v/v limit for FAMEs.

At present, the most widely recognised alternatives to FAMEs are bio~alkanes, which can be produced either by hydrotreating vegetable oils or microbial (for instance algal) oils, or via Fischer-Tropsch synthesis of syngas produced from biomass. Other potential alternatives are fatty alcohols and their derivatives, which can be produced by the fermentation of plant-derived sugars using microbial (typically fungal} catalysts. Like fatty acids, such fatty alcohols can have a range of different chain lengths, and a corresponding range of properties such as melting points and boiling points.

Fatty alcohols themselves are potentially suitable for use as diesel fuel components. Alternatively, they can be converted into derivatives such as esters, for example by transesterification with appropriate organic acids. These derivatives are also potential fuel

candidates .

An ester formed by reacting a fatty alcohol with an organic acid such as acetic acid is herein called a "reverse ester". In US-A-2011/0154728, such esters are disclosed for use in improving the lubricity of diesel fuel formulations containing acid-based lubricity additives. A range of alkyl acetates, formed from fatty alcohols of chain lengths between C6 and C12, are tested in the examples and demonstrate lubricity improvement; there is no indication of any advantageous effect on cetane number.

US-A-2005/0118691 describes a preparation route to provide a mixture of levulinic acid esters and formic acid esters, the mixture being necessitated by the difficulty of removal of formic acid from levulinic acid when produced from cellulose-based biomass. The formic acid is formed as a by-product of such processes. In US - A-2005/0118691 the ester mixture is proposed for use as a component of gasoline and diesel fuel compositions and as a 100% biofuel itself. However no fuel formulations are demonstrated in the Examples (where only butyl- and hexyl-formate containing mixtures are disclosed} and the only support for effectiveness in or as a fuel

composition is by way of comparison of oxygen content with MTBE, cf paragraph [0061] and the Tables in Fig. 1A and IB. As such only octane-increasing properties in gasolines for the acid ester mixtures is in any way supported in this document; there is no support for use as a cetane number-enhancing agent for diesel

formulations. Furthermore there is no indication of the amount of formic acid ester in the mixtures; as a

byproduct material it can be expected to be minimal.

It has now surprisingly been found that certain types of reverse ester can be particularly advantageous for use in diesel fuel formulations, due to their effects on cetane numbers in fuel blends.

Statements of the Invention

According to a first aspect of the present invention there is provided the use of an alkyl or alkenyl formate having an alkyl or alkenyl chain length of C8 or greater, In a diesel fuel formulation, for the purpose of

increasing the cetane number of the formulation.

An alk(en)yl formate having an alk(en)yl chain length of C8 or greater will hereafter be referred to as "a C8 or C8+ alk(en)yl formate".

It has surprisingly been found that of the fatty alcohol esters, the C8 and C8+ alk{en)yl formates have particularly high blending cetane numbers, higher than would be expected based on their total carbon content. Their blending cetane numbers are sufficiently high as to enable them to increase the overall cetane number of a typical diesel fuel component (for example a diesel base fuel) with which they are blended. They are thus

particularly suited for inclusion in diesel fuel

formulations.

It has also been found that the C8 and C8+ alk(en}yl formates can be incorporated into diesel fuel

formulations at concentrations significantly higher than the current 7% v/v FAME limit, without reducing the cetane numbers of the overall formulations below the limits currently specified for automotive diesel fuels (the European diesel fuel specification EN 590, for example, requires a measured cetane number of at least 51) .

The invention can thus make possible an increase in the biofuel content of a diesel fuel formulation, but without the above described problems - in particular the build-up of biofuel components in engine oil - which can accompany the incorporation of FAAEs or in particular FAMES.

A further advantage to using a reverse ester as a biodiesel fuel component, as opposed to a more

conventional biofuel component such as a FAME, is that reverse esters can be prepared from fatty alcohols which can in turn be derived, by fermentation, from biological sources such as sugars and lignocellulosic sugars. Such sources are capable of giving higher fatty alcohol yields, per hectare, than the FAME yields which are typically obtainable from plant sources such as palm oil. Thus, the production and use of reverse esters in place of FA Es can reduce environmental pressures due to the deforestation of land in order to grow fuel crops or the replacement of much-needed food crops with fuel crops.

The C8 or C8+ alkyl or alkenyl formate used in the present invention is a fatty alcohol ester (ie a fatty alcohol formate) . In the present context, a fatty alcohol ester (which may also be referred to as a "reverse ester") is a compound of formula Rl-C (0) -0-R2, where Rl is either hydrogen or hydrocarbyl (typically alkyl or alkenyl) and is typically derived from an acid, and R2 is a hydrocarbyl {typically alkyl or alkenyl) group which is derived from a fatty alcohol. An alkyl or alkenyl group may be either straight chain (linear) or branched, in particular straight chain. An alkenyl group will contain one or more, for example either one, two or three, carbon-carbon double bonds.

In a C8 or C8+ alk(en)yl formate, Rl is hydrogen and R2 is an alkyl or alkenyl group containing 8 or more carbon atoms. In a specific embodiment of the invention, the C8 or C8+ alk(en)yl formate is a C8 or C8+ alkyl formate, in which R2 is an alkyl group containing 8 or more carbon atoms.

In a C8 or C8+ alk(en)yl formate, the alkyl or alkenyl group R2 may contain an odd or an even number of carbon atoms, in particular an even number. It may for example be a C8 to C14 alkyl or alkenyl, in particular alkyl, group. It may be a C8 to C12 alkyl or alkenyl group, in particular a C8 to C12 alkyl group, for example selected from octyl, decyl and dodecyl . It may be a CIO to C12 alkyl or alkenyl group, in particular a CIO to C12 alkyl group, for example selected from decyl and dodecyl. In an embodiment, it is a C12 alkyl or alkenyl group, in particular a C12 alkyl group. In an embodiment, it is a CIO alkyl or alkenyl group, in particular a CIO alkyl group.

A fuel formulation prepared or used according to the invention may contain a mixture of two or more C8 or C8+ alk(en)yl formates of the type defined above.

An alk(en)yl formate may be prepared by any suitable process, for example by reacting a fatty alcohol with formic acid. The fatty alcohol and/or the acid, in particular the fatty alcohol, may be derived from a biological source. In an embodiment, the fatty alcohol is the product of a microbial fermentation of one or more sugars. The one or more sugars may be derived from a plant source such as straw (for example wheat straw or rice straw) ; corn and corn products such as corn stover, corn fibre and corn cobs} ; bagasse; sugar cane; wood and wood residues; nut shells; grasses such as switchgrass and miscanthus; paper; cotton seed hairs; plant material from sorted refuse; and mixtures thereof. In an

embodiment, the formic acid is derived from a biological source. Thus, the C8 or C8+ alk{en)yl formate may be a biologically derived product, and thus suitable for use as a biocomponent of a diesel fuel formulation.

The C8 or C8+ alk(en)yl formate may be included in the diesel fuel formulation at a concentration of 0.5% v/v or greater, or of 1 or 2 or 5% v/v or greater, or in cases of 7.5 or 10% v/v or greater. It may be included at a concentration of up to 50% v/v, or of up to 45 or 40 or 35% v/v, or of up to 30 or 25 or 20% v/v, for example from 1 to 25% v/v or from 5 to 25% v/v or from 5 to 20% v/v or from 10 to 20% v/v.

In an embodiment, in particular when the alk(en)yl formate is a C8 to C12 alk(en}yl formate (ie its group R2 is a C8 to C12 alkyl or alkenyl group, more particularly a C8 to C12 alkyl group) , it may be included in the fuel formulation at a concentration of 5% v/v or greater, or of 7.5% v/v or greater, or of 10 or 15 or 17.5% v/v or greater, for example at a concentration of from 10 or 15 or 17.5 to 25% v/v, or of from 10 or 15 or 17.5 to 20% v/ .

It has been found that the best results for a measured cetane improvement when using a C8 alkyl formate is provided by in the range of from 5 to 10% v/v. Where the formate component is a CIO to C12 alkyl formate, then useful measured cetane improvements are given for

concentrations in the range of from 5 to 20% v/v, with the best measured cetane improvement derived from use in a concentration of from 10 to 20% v/v. Measured cetane improvement as noted herein is assessed using the

standard test procedure AST D613.

A fuel formulation prepared or used according to the invention should be suitable and/or adapted for use in a compression ignition (diesel) internal combustion engine. It may in particular be an automotive fuel formulation. In further embodiments it may be suitable and/or adapted for use as an industrial gas oil, or as a domestic heating oil.

The formulation may comprise, in addition to the C8 or C8+ alk(en}yl formate, one or more diesel fuel

components and/or additives, as are known in the art. It may for example comprise a diesel base fuel or mixture thereof .

A diesel base fuel may be any fuel component, or mixture thereof, which is suitable and/or adapted for use in a diesel fuel formulation 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 petroleum derived. It may be or contain a kerosene fuel component.

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. It may be or include an oxygenate such as an alcohol (in particular a CI to C4 or CI to C3 aliphatic alcohol, more particularly ethanol) or a fatty acid alkyl ester, in particular a fatty acid methyl ester (FAME) such as rapeseed methyl ester or palm oil methyl ester. In an embodiment, however, it may be preferred for a formulation prepared or used according to the invention not to include an alcohol or a fatty acid alkyl ester, in particular a FAME.

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 70. However, because the C8 or C8+ alk(en)yl formate has a positive effect on cetane number, a fuel formulation 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 C8 or C8+ alk(en)yl formate may therefore be used for the purpose of allowing the inclusion, in a diesel fuel formulation, of one or more lower cetane number fuel components (for example 4425

- 10 - 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

formulation. 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 formulation, at the same

concentration, in place of the lower cetane number fuel component. It may entail the overall fuel formulation meeting a desired target specification, for example the European diesel fuel specification EN 590.

Where a formulation prepared or used according to the invention comprises a diesel base fuel, its

concentration may be 45% v/v or greater, or 50 or 55 or 60% v/v or greater, or 65 or 70 or 75 or 80 or 85 or 90% v/v or greater. It may be up to 99.5% v/v, or up to 99 or 98 or 95% v/v, or up to 90 or 85 or 80% v/v. The base fuel may represent the major part of the fuel

formulation: after inclusion of the C8 or C8+ alk(en)yl formate, and any further (optional) fuel components and additives, the diesel base fuel may therefore represent the balance to 100%.

A diesel fuel formulation prepared or used according to the invention will 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 formulation may have a density from 820 to 845 kg/m³ at 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 (mmVs) ; 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 (IP 219) 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 m 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 formulation. Moreover a formulation prepared or used according to the invention 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.

A fuel formulation prepared or used according to the invention may comprise 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 formulation may for example comprise one or more additives selected from cetane improvers, 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 C8 or P2012/074425

- 12 -

C8+ alk(en)yi formate, however, it may as described below be possible for the formulation to contain lower levels of cetane improvers and/or lubricity additives, or in cases for the formulation not to contain either such type of additive, or at least not to contain a cetane

improver .

In a specific embodiment, a fuel formulation

prepared or used according to the invention comprises a lubricity additive. A lubricity additive may be defined as any additive which is capable of, or intended to, improve the lubricity of a diesel fuel formulation to which it is added, and/or impart anti-wear effects when such a formulation is used in an engine or other fuel- consuming system.

Where the formulation comprises a lubricity

additive, the lubricity additive may in particular be an acid-based lubricity additive. An acid-based lubricity additive comprises an acid, typically a mono-acid, more typically an organic acid, as its lubricity-enhancing active ingredient. The active ingredient may for example be a carboxylic acid, such as a fatty acid or aromatic acid, in particular the former. Such fatty acids may be saturated or unsaturated (which includes

polyunsaturated) . They may for example contain from 1 or 2 to 30 carbon atoms, or from 10 to 22 carbon atoms, or from 12 to 22 or from 14 to 20 carbon atoms, or from 16 to 18 carbon atoms, such as 18 carbon atoms. Examples include oleic acid, linoleic acid, linolenic acid, linolic acid, stearic acid, palmitic acid and myristic acid. Of these, oleic, linoleic and linolenic acids may be used, in particular oleic and linoleic acids.

Examples of acid-based lubricity additives are known and commercially available, for example as R650^TK (ex Infineum) , products in the Lz 539™ series (ex Lubrizol), and ADX4101B™ (ex Adibis) . Other conventional lubricity additives for use in diesel fuels tend to contain either ester or amide active ingredients, as in for example the ester-based additive R655™ (ex Infineum) and the amide- based additive Hitec™ 4848A (ex Afton) .

Where a formulation prepared or used according to the invention comprises an acid-based lubricity additive, the acid active ingredient may in particular be an organic acid. It may for example be a C16 to C20 organic (typically fatty) acid, such as a C18 fatty acid, as in the additive R650™ (ex Infineum) .

A lubricity additive may be included in a diesel fuel formulation at a concentration of for example 30 ppm or greater, or of 50 or 100 or 120 or 150 ppmw or greater. It may be included at a concentration of up to 1000 ppmw, or of up to 500 or 400 or 300 ppmw, or of up to 200 or 100 or 50 ppmw. It may for example be included at a concentration from 50 to 300 ppmw.

According to a second aspect of the present

invention, there is provided the use of a C8 or C8+ alk(en)yl formate, in a diesel fuel formulation

containing a biofuel component such as a fatty acid ester or a fatty alcohol ester, for the purpose of increasing the cetane number of the formulation.

Thus, if it is desired to include a fatty acid ester or a fatty alcohol ester in a diesel fuel formulation, for example in order to increase the biofuel content of the formulation, and/or for the lubricity benefits described in US-A-2011/0154728, the present invention provides that at least some, or in cases all, of the fatty acid/alcohol ester can be a C8 or C8+ alk(en)yl formate or mixture thereof, since this can lead to a higher overall cetane number than if a different fatty acid/alcohol ester were used instead. In accordance with the invention, therefore, the C8 or C8+ alk{en)yl formate may be used to replace all or part of another 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 formulation.

In an embodiment, the C8 or C8+ alk(en)yl formate is the only fatty acid/alcohol ester which the formulation contains. In an alternative embodiment, the formulation contains a second fatty alcohol ester, other than a C8 or C8+ alk(en}yl formate, and the C8 or C8+ alk(en)yl formate is used in addition to the second fatty alcohol ester. Thus, as described above, the C8 or C8+ alk(en)yl formate can be used to replace all or part of the second fatty alcohol ester, in order to increase the cetane number of the diesel fuel formulation. The second fatty alcohol ester may for example be an alk(en)yl acetate, in particular a C8 or C8+ alk(en)yl acetate, more

particularly a C8 to C12 or CIO to C12 alk(en)yl acetate; it may be an alkyl acetate, in particular a C8 or C8+ alkyl acetate, more particularly a C8 to C12 or CIO to C12 alkyl acetate.

Similarly, in an embodiment the formulation contains a fatty acid ester, in addition to the C8 or C8+

alk(en)yl formate. Thus, the C8 or C8+ alk(en)yl formate may be used to replace ail or part of the fatty acid ester in the formulation, in order to increase its cetane number. The fatty acid ester may for example be a fatty acid methyl or ethyl ester, in particular a FAME; it may in particular have a fatty acid chain length of from C6 to C20, or from C8 to C18, or in cases from C8 to C14 or C8 to C12. In the context of the first and second aspects of the invention, the C8 or C8+ alk{en)yl formate may be used to achieve any degree of increase in the cetane number of the diesel fuel formulation, 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 formulation. 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 another fatty alcohol ester such as an alkyl acetate, or of a fatty acid alkyl ester such as a FAME, more particularly of another such ester which has the same total number of carbon atoms as the C8 or C8+ alk(en)yl formate. The increase in cetane number will typically be as compared to the cetane number of the formulation prior to adding the C8 or C8+ alk(en)yl formate 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 C8 or C8+ alk(en)yl formate may be used to produce a diesel fuel formulation which has a cetane number higher than a desired target standard.

The cetane number of a fuel formulation 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 (KIR) , as for example described in US-A-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

The present invention preferably results in a diesel fuel formulation 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

formulation which is equivalent to or associated with cetane number, for example to improve the combustion performance of the formulation (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 formulation) and/or to improve fuel economy.

By using the present invention, it can be possible to include in a diesel fuel formulation a higher

concentration of a biofuel component (in particular of a fatty alcohol ester or fatty acid ester, more

particularly of a fatty alcohol ester) than would have been predicted to be possible - whilst still achieving a desired target cetane number - based on the properties of other fatty acid/alcohol esters (ie fatty acid/alcohol esters other than C8 or C8+ alk(en)yl formates, in particular C8 or C8+ alkyl formates) . 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 formulation 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 CIO or less} carbon chains. According to the present invention, such benefits can now be achieved with the added advantage of a cetane number increase.

Thus according to a third aspect, the invention provides the use of a C8 or C8+ alkyl or alkenyl formate, in a diesel fuel formulation, for the purpose of

increasing the concentration of a biofuel component in the formulation, without or without undue detriment to the cetane number of the formulation. The biofuel

component may for example comprise a fatty alcohol ester: the C8 or C8+ alk(en)yl formate may therefore be used to increase the concentration of fatty alcohol esters in the diesel fuel formulation, without or without undue detriment to its cetane number. The biofuel component may comprise a fatty acid alkyl ester (in particular a FAME) , in which case the C8 or C8+ alk(en)yl formate may be used to allow an increase in the concentration of fatty acid esters in the diesel fuel formulation, without or without undue detriment to its cetane number. 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 formulation whilst still meeting relevant fuel specifications. In addition it can provide new uses for bio-derived products such as the products of microbial sugar fermentation processes.

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 accordance with this third aspect of the

invention, the C8 or C8÷ alk(en}yl formate may be used to achieve any degree of increase in the concentration of the relevant biofuel component. In an embodiment, the C8 or C8+ alk(en)yl formate 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

formulation.

Thus according to a fourth aspect of the invention, there is provided the use of a C8 or C8+ alkyl or alkenyl formate, in a diesel fuel formulation, for the purpose of achieving a benefit (such as those described above) associated with the use of a biofuel component such as a fatty alcohol ester or fatty acid ester without, or with less, reduction in the cetane number of the formulation, or indeed whilst simultaneously increasing the cetane number of the formulation.

Because a C8 or C8+ alk(en)yl formate can increase the cetane number of a diesel fuel formulation in which it is used, the formulation may as a consequence require a lower level of cetane improving 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 formulation, and/or can provide greater versatility in fuel formulation

practices. Thus, a fifth aspect of the invention provides the use of a C8 or C8+ alkyl or alkenyl formate, in a diesel fuel formulation, for the purpose of reducing the concentration of a cetane improving additive in the formulation.

In the context of this fifth aspect 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 improving additive, or 25 or 50 or 75 or

90% or more. The reduction may be as compared to the concentration of the cetane improving additive which would otherwise have been incorporated into the fuel formulation 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 formulation prior to the realisation that a C8 or C8+ alk{en)yl formate could be used in the way provided by the present invention, and/or which was present in an otherwise analogous fuel formulation intended (eg marketed) for use in an analogous context, prior to adding a C8 or C8+ alk{en)yl formate to it in accordance with the invention.

The reduction in concentration of the cetane

improving 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 formulation in the absence of the C8 or C8+ alk(en)yl formate .

A cetane improving additive may be any additive which is capable of increasing, or intended to increase, the cetane number of a diesel fuel formulation to which it is added, and/or to improve the ignition properties of such a formulation when it is used in an engine or other fuel-consuming system. Ά cetane improving 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 improving diesel fuel additives are commercially available for instance as HI EC™ 4103 (ex Afton Chemical) and as CI-0801 and CI- 0806 (ex Innospec Inc) .

In the context of the present invention, "use" of a C8 or C8+ alk(en)yl formate in a diesel fuel formulation means incorporating the alk(en)yl formate into the formulation, 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 C8 or C8+ alk(en)yl formate will conveniently be incorporated before the formulation is introduced into an engine or other system which is to be run on the formulation. Instead or in addition, the use of a C8 or C8+ alk(en)yl formate may involve running a fuel-consuming system, typically an internal combustion engine, on a diesel fuel formulation containing the alk{en)yl formate, typically by introducing the

formulation 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 formulation containing the alk(en)yl formate. In such cases the engine is suitably a compression ignition (diesel) engine.

"Use" of a C8 or C8+ alk(en)yl formate in the ways described above may also embrace supplying the alk{en)yl formate together with instructions for its use in a diesel fuel formulation in order to increase the cetane number of the formulation. The C8 or C8+ alk(en)yl formate 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 alk(en)yl formate may be included in such a composition for the purpose of

influencing its effects on the cetane number of a diesel fuel formulation.

In general, references to "adding" a component to, or "incorporating" a component in, a fuel formulation may be taken to embrace addition or incorporation at any point during the production of the formulation 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 alk(en)yl formate- 5 containing fuel formulation, or at least 5,000 or 10,000 or 20,000 or 50,000 litres.

A fuel formulation 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

C8 or C8+ alk{en)yl formate, in particular a higher cetane number and optionally improved lubricity. The marketing of such a formulation may comprise an activity selected from (a) providing the formulation in a

container that comprises the relevant indication; (b) supplying the formulation 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 formulation; 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 C8 or C8+ alk(en)yl formate. The

invention may involve assessing the relevant property (in particular the cetane number) of the formulation during or after its preparation. It may involve assessing the relevant property both before and after incorporation of the C8 or C8+ alk(en)yl formate, for example so as to confirm that the C8 or C8+ alk(en)yl formate contributes to the relevant improvement in the formulation.

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. 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 of 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

Diesel fuel formulations were prepared, in

accordance with the invention, by blending a diesel base fuel with three different C8 or C8+ alkyl formates. For comparison, other formulations were prepared by blending the same base fuel with a C6 alkyl formate (ie an alkyl formate in which the alkyl chain contained 6 carbon atoms) , and also with alkyl acetates of corresponding chain lengths.

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.

- Base Fuel Properties

Table 1 - Base Fuel Properties (Continued)

The fatty alcohol esters tested had alkyl chain lengths of C6, C8, CIO and C12. All were sourced from Aldrich, UK, apart from the CIO and C12 alkyl formates, which were sourced from Chiron AS, Stiklestadveien 1, NO- 7041 Trondheim, Norway. Their chain lengths were chosen based on their melting points, boiling points and flash points, which needed to be within, or at least close to, diesel fuel specifications such as EN 590. Relevant properties (literature values) for the selected esters are shown in Table 2 below.

Table 2 - Fatty Alcohol Ester Properties

n/a = not available

From Table 2, the C8 and C8+ alkyl formates appear to be the more suitable for use in diesel fuel

formulations than the C6 alkyl esters. For the C6 alkyl esters, their flash points are likely to limit blend ratios, the EN 590 specification requiring a flash point of 55°C or greater. Each of the Table 2 esters was blended with the base fuel at 5, 10, 15 and 20% v/v. The resultant blends were tested for density, VK40, flash point, cetane number (both measured and derived) , lubricity (HFRR wear scar) , cloud point and cold filter plugging point (CFPP) , using the same test methods as for the Table 1 measurements. The results are shown in Tables 3 and 4, for the formates and the acetates respectively.

Table 3 - Alkyl Formate Blends

Table 4 - Alkyl Acetate Blends

It can be seen from Tables 3 and 4 that from the raw data the alkyl formate components provide an increased cetane value compared with their alkyl acetate analogues, and that the CIO and C12 formates provide a significantly enhanced cetane number at all tested concentrations compared with the C8 formate analogue, and particularly at concentrations of from 10 to 20% v/v. The C8 formate blends yield the best cetane improvement when the C8 formate is used at concentrations of 5 and 10% v/v in the fuel blend.

It is possible to determine an average blending value for each property for each tested formate and acetate component by calculation from the measured values of Tables 3 and 4, which allows a further comparison. Thus from the measured values of Tables 3 and 4, blending values were calculated, for relevant properties, for each of the esters as noted below.

For the properties which can be assumed to blend linearly by volume (density and measured cetane number) , the blending values were calculated as follows.

Density

blending -ecuie =

- (1-x) * Pd±_esei ) I x [1] where :

x is the volume fraction of the relevant ester in the base fuel/ester blend;

blending pmoieouie is the blending density of the ester when used at volume fraction x;

pfaei is the measured density of the base fuel/ester blend; and

Pdiesei is the measured density of the diesel base fuel .

(Measured) Cetane Number

blending C¾_olecttle = ( CN^i - (1-x) * CN^se! ) / x [ 2 ] where :

blending CN_MOx_emi_e is the blending cetane number of the relevant ester when used at volume fraction x; CNfvei is the measured cetane number of the base fuel/ester blend; and

CNcUesei is the measured cetane number of the diesel base fuel.

For the properties which do not blend linearly by volume (flash point, viscosity and cloud point), the blending values were calculated as follows.

Flash Point

FPIttolecule = ( SPIftael ^" * FPIdiesel ) / X [3] where :

FPI_moi_ecule is the blending flash point index of the relevant ester when used at volume fraction x;

FPIfaei is the measured flash point index of the diesel/ester blend; and

FPIoiesei is the measured flash point index of the diesel base fuel;

and

log FPI = -6.1188 + (2414/ ( FP + 230.5556)) [ A ] where FP is the flash point and equation [4] is the Wickey-Chittenden blend rule.

Viscosity (VK40)

νΒΙ_{Λο1βαν1β} = ( VBIfuei - (1-JE) * BIdieea! ) / x [5] where :

VBJjnoiecuie is the viscosity blend index of the relevant ester when used at volume fraction x; VBJfue! is the measured viscosity blend index of the diesel/ester blend; and

VBIdiese is the measured viscosity blend index of the diesel base fuel;

and VBI = 41.10743 - 49.08258 * log{log(VX:) + 0.8)) [6] where Vk is the viscosity in mm²/s at 40°C.

Cloud Point

l_kl Ay

tFormae CPImciecvle = (CBItael ^~ (1^"X) * I^s^) / X [7] where :

CPI_moleaule is the cloud point index of the

ester when used at volume fraction x;

CPI_fuel is the measured cloud point index of the diesel/ester blend; and

CPI_diesei is the measured cloud point index of the diesel base fuel;

and

CPI = ((1.8 * CP + 491.7) /600) ^Λ (1/0.045) * 10⁴ [8] where CP is the cloud point and equation [8] is the

Pauillac blending rule.

To simplify the results, the blending properties for a given ester and fuel property were averaged from the measurements taken at 5, 10, 15 and 20% v/v blend ratios. The resultant blend values are shown in Table 5 below.

Table 5 - 7Average Blend Values (Fatty Alcohol Esters)

Average blending values in diesel base fuel

Alkyl at 5, 10, 15 and 20% v/v chain Cetane Flash Cloud length Density VK40

nximbe jpoint point kg/m³ CN °c mm²/s °C

6 877 44 35 0.67 < -10

8 874 67 > 55 1.08 < -10

10 867 82 > 55 1.55 < -10

12 864 80 > 55 2.19 < -10

Φ 6 871 37 51 0.79 < -10 a 8 868 49 > 55 1.17 < -10

H d> 10

< ϋ 866 47 > 55 1.72 < -10

12 866 73 > 55 2.55 < -10 Ideally, for use as a component of a diesel fuel formulation, the blend properties of an ester should fall within the following ranges:

(i) cetane number > 40;

(ii) flash point > 55°C;

(iii) V 40 2.00 - 4.50 mirt²/s;

(iv) cloud point < -10°C.

It can be seen from Table 5 that the blending cetane numbers of the C8 and C8+ alkyl formates are

significantly higher than those of their acetate

counterparts (for any given alkyl chain length) . Their blending cetane numbers are indeed well above those required for a diesel fuel component. Thus, a C8 or C8+ alkyl formate may be used, optionally in place of another fatty alcohol ester or indeed in place of another biofuel component, to increase the cetane number of a diesel fuel formulation. The invention can thus allow the fuel formulator to include higher levels of biofuel components in diesel fuels, without or without undue detriment to the cetane properties of the fuels. Moreover the

invention can enable greater use to be made of

microbially-generated fatty alcohol derivatives.

Table 5 also shows that in other key respects (flash point and cloud point) , the C8 and C8+ alkyl formates have blending values within the ranges desired of a diesel fuel component. Although their densities and HFRR wear scar results, and in cases their viscosities, may be outside of the ideal ranges, the differences are unlikely to be limiting on blend ratios at ester concentrations of up to 20% v/v. The lubricity of a reverse ester- containing fuel formulation can moreover be improved by the addition of standard lubricity additives, in

particular acid-based lubricity additives. Thus, C8 and C8+ alkyl formates have been shown to have blend

properties which are a good fit with diesel fuel

components .

It appears from the viscosity and density data that the CIO to C12 alkyl formates are likely to be the most suitable candidates for use as diesel fuel components, in particular the C12 alkyl formate. In terms of their effects on cetane number, again the CIO to C12 alkyl formates are the most preferred.

Example 2

For comparison purposes, Example 1 was repeated using a series of fatty acid alkyl esters (FAAEs) in place of the alkyl formates and acetates. The FAAEs were all sourced from Aldrich, UK. The measured properties are shown in Tables 6 and 7, for C6 to C12 methyl alkanoates and C6 to C12 ethyl alkanoates respectively. Table 8 below shows the average blending values, calculated as in Example 1 from the results at 5, 10, 15 and 20% v/v blending ratios for each of the FAAEs. Table 9 shows specifically the blending cetane numbers for the esters at the four different concentrations tested.

Table 6 - Methyl Alkanoate Blends

Table 7 - Ethyl Alkanoate Blends

Table 8 - Average Blend Values (Fatty Acid Esters)

Average blending values in diesel base fuel

lh Mtey Alkyl at 5, 10, 15 and 20% v/v

k_ltAanoae chain

Cetane Flash Cloud length Density VK40

numbex point point kg/m³ CN °C mm²/s °C

6 881 16 35 0.64 < -10

8 876 43 > 55 0.94 < -10

10 872 43 > 55 1.39 < -10

12 871 58 > 55 2.32 < -10

Φ 6

+> 871 26 49 0.75 < -10

>i 0 8 868 62 > 55 1.12 < -10

& d

10 865 59 > 55 1.65 < -10

12 865 82 > 55 2.44 < -10

Table 9 - Blending Cetane Numbers (Fatty Acid Esters)

Total carbon Alkyl Alkyl Methyl

XIO . formate acetate alkanoate

20% v/v

7 40 14

8 23 21

9 61 27

10 48 39

11 74 53

12 57 55

13 78 63

14 72 73

15% v/v

7 47 19

8 35 16

9 60 51

10 52 56

11 73 49

12 59 59

13 74 64

14 71 79

10% v/v

7 34 16

8 49 14

9 66 49

10 48 59

11 87 44

12 61 51

13 86 61

14 70 100

5% v/v

7 58 13

8 40 53

9 82 43

10 50 93

11 94 23

12 14 73

13 84 45

14 80 77 It can be seen from Tables 6 to 9, when compared with the results of Example 1, that the cetane blending properties of the C8 and C8+ alkyl formates are at least as good as, and in most cases better than,, those of FAAEs having corresponding total numbers of carbon atoms. At blend ratios of 10, 15 and 20% v/v, the C8 and C8+ alkyl formates out-perform the FAAEs, and also the alkyl acetates, at any given total carbon number. This is particularly true at a blend ratio of 20% v/v. It is a surprising result, in view of the fact that the other esters tested (both fatty alcohol acetates and fatty acid esters) had broadly similar blending cetane numbers to one another at any given total carbon number.

Note that a total carbon number of n equates to an alkyl chain length of (n-1) carbon atoms in an alkyl formate or a fatty acid methyl ester (methyl alkanoate) , and to an alkyl chain length of (n-2) carbon atoms in an alkyl acetate or a fatty acid ethyl ester {ethyl

alkanoate) .

These examples confirm that a C8 or C8+ alkyl formate may be used to improve the cetane properties of a diesel fuel formulation, and that it can be used in place of other biodiesel components such as FAAEs or indeed other fatty alcohol esters, to give a greater improvement in cetane properties. Thus the present invention is able to provide more optimised methods for formulating

biofuel-containing diesel fuels, in particular to achieve target cetane numbers.

Claims

C L A I M S

1. Use of an alkyl or alkenyl formate having an alkyl or alkenyl chain length of C8 or greater (a "C8 or C8+ alk(en)yl formate"), in a diesel fuel formulation, for the purpose of increasing the cetane number of the formulation as measured by ASTM D613.

2. Use according to claim 1, wherein the alk{en)yl formate has an alk(en)yl chain length of from C8 to C12.

3. Use according to claim 3, wherein the alk{en)yl formate has an alk{en)yl chain length of from CIO to C12.

4. Use according to any one of the preceding claims, wherein the C8 or C8+ alk(en)yl formate has been prepared from a fatty alcohol from a biological source,

5. Use according to any one of the preceding claims, wherein the C8 or C8+ alk(en)yl formate is a C8 or C8+ alkyl formate.

6. Use according to any one of the preceding claims, wherein the C8 or C8+ alk(en)yl formate is included in the diesel fuel formulation at a concentration in the range of from 5 to 25% v/v.

7. Use according to claim 6, wherein the formate is included at a concentration in the range of from 10 to 20% v/v.

8, Use according to any one of the preceding claims, wherein the diesel fuel formulation comprises an acid- based lubricity additive.

9. Use according to any one of the preceding claims, wherein the diesel fuel formulation contains an

additional biofuel component.

10. Use according to claim 9, wherein the diesel fuel formulation contains the C8 or C8+ alk{en)yl formate and a second fatty alcohol ester other than a C8 or C8+ alk{en)yl formate.

11. Use according to claim 9 or claim 10, wherein the diesel fuel formulation contains a fatty acid ester in addition to the C8 or C8+ alk(en}yl formate.

12. Use of a C8 or C8+ alk(en)yl formate, in a diesel fuel formulation, for the purpose of increasing the concentration of a biofuel component in the formulation, without reducing the cetane number of the formulation by more than 30% of its original value, as measured by AST D613.