GB2387175A - Oxidised fuel formulations - Google Patents

Abstract

A method for preparing a fuel formulation comprising oxidising a liquid hydrocarbon fuel and adding to it an oxygenate, in particular a C1 to C6 oxygenate such as methanol and/or ethanol. The oxidation, preferably to an oxygen content of 0.25% w/w or greater, enhances the miscibility of the oxygenate with the fuel. Also provided are fuel formulations prepared using such methods, compositions containing the formulations and their use particularly in automotive fuels. Also disclosed is a method for improving the miscibility of a liquid hydrogen fuel with an oxygenate, by oxidising the fuel.

Description

- 1 FUEL FORMULATIONS

This invention relates to fuel formulations, their preparation and their use.

It is known that the inclusion of oxygenates (oxygen containing compounds) in a fuel can help to reduce 5 particulate and smoke emissions from an engine running on the fuel. Ethanol, particularly when produced by fermentation from biomass, is currently one of the most attractive such components for use in diesel fuels, being available in industrial quantities, relatively inexpensive 10 and non-toxic and also biodegradable.

Biomass derived ethanol is however only poorly miscible with many fuel oils, in particular the gas oil typically used as a base for diesel fuel compositions. Its use as a component of diesel fuel is therefore impractical 15 at levels higher than a few volume percent. Phase separation occurs at low temperatures, preventing proper engine functioning.

The temperature below which phase separation sets in depends on the fuel type and the ethanol concentration.

20 For a typical diesel fuel/ethanol blend it could be around normal room temperature, yet in some countries fuels are required to be operable down to -22 C or below.

A number of solutions to the miscibility problem have been proposed for diesel fuel compositions. For instance, 25 it is known to prepare emulsions of alcohols with gas oil using surface active additives. These emulsions are milky in appearance, need to be prepared by high shear mixing and are thermodynamically only meta-stable. An alternative approach is to use one or more cosolvents to form clear

- 2 alcohol/gas oil mixtures which may be true solutions or microemulsions. These are thermodynamically stable so have no tendency to separate spontaneously. Cosolvents and stabilizers known for use in this way include gasoline, 5 benzene, iso-octane, alcohols and ethyl ether (USA-4509953 and VS-A-6056793), vegetable oils and surface active alcohols (US-A-4557734 and US-A-4526586), acetal, ketals and orthoesters (US-A4395267), esters of fatty acids (Pischinger et al, ASIA Purl. (1982) (482, Veg. Oil Fuels) 10 198-208, and EP-A-0708808), ethoxylated alcohols and their derivatives (US-A-6190427) and nonionic surface active amino alcohols (Satge de Caro et al, Fuel, 80 (2001) 565-574).

Although such technology can widen the range of 15 temperatures over which alcohol/gas oil mixtures are stable, even at relatively high alcohol concentrations, it inevitably increases processing costs.

It is also known to directly oxidise fuels such as gas oils to improve their volumetric energy content and/or to 20 reduce vehicle emissions in use. However this has not to our knowledge been done prior to blending the fuel with another oxygenate such as ethanol. WO-A-01/64817 for instance describes an auto-oxidation process for oxygenating gasoline and diesel fuels, in which oxygen gas 25 is added to a sulphur-free base fuel at a temperature of between 150 and 200 C, followed by removal of impurities such as water. The oxygen content of the product fuel is above 5% w/w. In US-A-4723963, aromatic components of a middle distillate base fuel are selectively oxidised to 30 benzylic alcohols and/or ketones, to improve the cetane number of the fuel. In WO-A-01/32809, paraffinic components of distillate fuel are selectively oxidised,

preferably by hydrogen peroxide in the presence of a catalyst, to reduce particulate emissions on subsequent combustion. Direct fuel oxidation, to the degree effected in many 5 of these prior art processes, can bring its own problems,

notably fuel degradation (darkening and sludge formation, for instance), inferior injector fouling performance, reduced stability and high viscosity.

According to a first aspect of the present invention 10 there is provided a method for preparing a fuel formulation, the method comprising oxidising a liquid hydrocarbon fuel (i) and adding an oxygenate (ii) to the fuel. The oxygenate may be added either before or more preferably after its oxidation.

15 By "hydrocarbon fuel" is meant a combustible material the chemical composition of which consists entirely or essentially (typically = 99.5% w/w) of carbon and hydrogen.

The hydrocarbon fuel may be suitable for, and/or intended for, use in an internal or external combustion 20 engine (de, an automotive fuel), or alternatively in for example a furnace or boiler or any other fuel combustion system. It may for instance be a petrol (gasoline), a kerosene (paraffin) or a gas oil or other distillate fuel.

It is preferably a base fuel suitable for use in an 25 internal combustion engine, either of the spark ignition or in particular of the compression ignition (diesel) type.

It may comprise a mixture of two or more component hydrocarbon fuels.

When the fuel is a base fuel for use in a diesel fuel 30 composition, it will typically be a gas oil comprising one or more liquid hydrocarbon middle distillate fuel oils, in which case it will typically have an initial distillation

- 4 - temperature of about 120 to 200 C (eg, around 150 C) and a final distillation temperature of from 290 to 370 C, depending on its grade and use. Suitable diesel fuels may be derived from various sources including petroleum or s Fischer Tropach synthesis. Base fuels for spark ignition (petrol) engines tend to include primarily the lower boiling gasoline fractions such as those with boiling points from 100 to 150 C.

The fuel may in particular be, or contain a proportion 10 (for instance, 10% v/v or more) of, reaction products of a Fischer-Tropsch methane condensation process such as the process known as Shell Middle Distillate Synthesis (SMDS) such reaction products suitably have boiling points within the typical diesel fuel range (from about 150 to 370 C), a Is density of from about 0.76 to 0.79 g/cm3 at 15 C, a cetane number greater than 72.7 (typically from about 75 to 82), a sulphur content of less than 5 ppmw (parts per million by weight) and a viscosity from about 2.9 to 3.7 centistokes at 40 C.

20 The fuel is suitably a low or ultra low sulphur content fuel, for instance containing at most 500 ppmw sulphur, preferably no more than 100 ppmw, most preferably no more than 60 or 50 or even 10 ppmw.

The fuel preferably contains relatively high levels of 25 saturated components such as paraffinic and naphthenic components. It suitably contains relatively low total levels of aromatic components (for instance 40% w/w or less, preferably 30% w/w or less, more preferably 20% w/w or less or 10% w/w or less). Such fuels can be easier to 30 oxidise, in particular using relatively straightforward air treatment processes. They may also suffer fewer problems

- c 5 - associated with the formation of sludge and/or other undesirable by-products.

The fuel may be additivated (additive-containing) or unadditivated (additive-free). If additivated, it will 5 contain minor amounts of one or more additives selected for example from anti-static agents, pipeline drag reducers, flow improvers (eg, ethylene/vinyl acetate copolymers or acrylate/maleic anhydride copolymers) and wax anti-settling agents (eg, those commercially available under the Trade 10 Marks "PARAFLOW" (eg, PARAFLOW 450, ex Infineum), "OCTEL" (eg, OCTET W 5000, ex Octel) and "DODIFLOW" (eg, DODIFLOW v 3958, ex Hoechst).

The fuel may be oxidised by any method, which will generally involve contacting it with an oxygen donor of 15 some form. The oxidation suitably involves contacting the fuel with oxygen or with an oxygen containing fluid (conveniently air, which may be oxygen enriched). The contacting may for instance be carried out by bubbling the fluid through the fuel, with or without stirring. The 20 oxidation may be carried out at an elevated temperature, for instance from 80 to 300 C, preferably from 100 to 200 C, such as at around 160 C. It may be conducted in the presence of an oxidation promoter such as a peroxide or ozone or of any other appropriate homogeneous or 25 heterogeneous catalyst.

Alternatively, the fuel (or components of it) may be oxidised by reaction with appropriate chemicals.

The most preferred oxidation process is an auto oxidation process, in particular air treatment, in which an 30 oxygen containing gas such as air is passed through the fuel.

- 6 - Known apparatus in which to carry out such processes includes bubbler reactors, film reactors and the like.

Suitable reactors are currently known, for instance, for use in oxidising cyclohexane and ethyl benzene. The s oxidation may be carried out as a batch, semi-batch or continuous process, in known fashion - a batch or semi batch process may facilitate a milder and more selective oxidation but may be more difficult and expensive to operate in particular on a large scale.

10 The degree and selectivity of oxidation achieved will depend on factors such as the nature of the oxygen donor and the way in which it is contacted with the fuel, the operating temperature and pressure and in particular the time period for which the oxidation process continues. It 15 will also depend on the nature of the fuel itself.

The fuel is preferably oxidised (more preferably pre oxidised, ie, prior to blending with the oxygenate (ii)) to an oxygen content of 0.25% w/w or greater, more preferably 0.3% w/w or greater, most preferably 0.5% w/w or 0.8% w/w 20 or 1% w/w or 1.2% w/w or 1.5% w/w or 1.8% w/w or 2% w/w or 2. 5% w/w or greater.

By "oxygen content" is meant the total amount of elemental oxygen in the fuel and/or its component compounds (including any water present, although excluding the 25 subsequently added oxygenate (ii)). It may be measured by any suitable method, for instance using a fast neutron activation (FNA) technique such as ASTM E385-90 (Standard Test Method for Oxygen Content using a 14-MeV Neutron Activation and Direct Counting Technique).

30 Suitably the fuel is only mildly oxidised, for example to an oxygen content of 10% w/w or less, preferably 5% w/w or less, more preferably 3% w/w or less, most preferably

- 7 2.5% w/w or less or 2% w/w or less. Too high a degree of oxidation can degrade the properties and/or performance of the fuel, for instance by reducing its energy content to an undesirable extent or by leading to undue deposition of S sludges, gums or lacquers. Moreover, lower oxidation levels tend to favour formation of primary oxidation products, such as alcohols, over secondary products such as aldehydes, ketones, acids, esters and anhydrides. This will generally be preferred as the primary products tend to 10 have fewer adverse side effects such as corrosion and elastomer incompatibility, and may also function as better cosolvents for the oxygenate (ii) in the formulation of the invention. It is thus preferred that the oxygen content of the IS oxidised fuel be provided to a relatively great extent by alcoholic components (typically secondary and/or tertiary alcohols), as opposed to aldehydes, ketones, acids, esters and acid anhydrides. It may be preferred that alcoholic components contribute at least 30%, more preferably at 20 least 40%, of the overall oxygen content of the oxidised fuel Additives may be included in the fuel in order to increase the selectivity of the oxidation process with these aims in mind.

25 The added oxygenate (ii) in the method of the invention is an oxygen containing compound, preferably containing only carbon, hydrogen and oxygen. It may suitably be a compound containing one or more hydroxyl groups -OH, and/or one or more carbonyl groups C=O, and/or 30 one or more ether groups -O-, and/or one or more ester groups -C(O)O-. It preferably contains from 1 to 6 carbon atoms, more preferably from 1 to 5, most preferably from 1

- 8 - to 4 or from 1 to 3, such as a Cl or C2 compound. Ideally it is biodegradable.

The invention is particularly suitable for use with oxygenates which are poorly miscible with the unoxidized s fuel under normal conditions of use.

The oxygenate is suitably an alcohol, which may be primary, secondary or tertiary. It is in particular an optionally substituted (though preferably unsubstituted) straight or branched chain C1 to C6 alcohol, suitable lo examples being methanol, ethanol, n-propanol and iso propanol. Typical substituents include carbonyl, ether and ester groups. Methanol and in particular ethanol are preferred oxygenates.

Ideally the oxygenate is in an anhydrous or dehydrated 15 form, ie, it is free of or contains less than 0.1% w/w, preferably less than 0.01% w/w, water. Normal fuel grade materials (for instance methanol or ethanol) may for instance be used as the component (ii).

A mixture of two or more such oxygenates may be added 20 to the fuel (i).

The oxygenate is preferably added at a concentration which gives a total oxygen content in the fuel formulation of 5% w/w or greater, more preferably of 8% w/w or greater, most preferably of 10% w/w or greater, such as from 8 to 2s 15% w/w. Typical oxygenate concentrations, in particular where the oxygenate is ethanol, might be up to 40% w/w of the overall formulation, more suitably up to 25 or 30% w/w.

The concentration of the oxygenate in the formulation may be at least 2% w/w, preferably at least 5% w/w, more 30 preferably at least 8% w/w, still more preferably at least 10% w/w, most preferably at least 15 or 20 or 25 or 30% w/w.

- 9 - The oxidised fuel and the oxygenate (ii) are preferably physically blended together. This may be done a period of time (for instance, up to one, two, three, four or six months) after oxidation of the fuel. Where the s oxygenate (ii) is a higher boiling point material such as butanol, however, it may be preferable to blend the fuel and oxygenate prior to oxidizing the blend to the required total oxygen content.

Following or during the oxidation, the method of the lo invention may involve removing water from the fuel, suitably to give a water concentration in the overall formulation of below 0.3% w/w, preferably below 0.25% w/w, more preferably below 0.2% w/w and most preferably below 0.1% w/w. Any water removal process may be used, such as 15 for instance molecular sieve drying or distillation. Since the oxidation process can itself increase the water content of the fuel, it may be preferable to carry out the oxidation at higher temperatures (eg, above 150 C) to encourage water removal during the process, and/or to take 20 steps to reduce reflux of water back into the fuel during the oxidation.

The method may also involve removing secondary oxidation products such as in particular acids from the oxidised fuel. Acids may be removed for example by 2s neutralization with a base such as sodium bicarbonate.

According to a second aspect of the present invention, there is provided a fuel formulation comprising (i) a liquid hydrocarbon fuel which has been oxidised to an oxygen content of 0.25% w/w or greater and (ii) a C1 to C6, 30 preferably a C1 to C3, oxygenate.

The fuel may be oxidised by any suitable method which serves to increase its oxygen content. Preferred methods

- 10 -

are those described in connection with the first aspect of the invention. Thus, a formulation in accordance with the second aspect of the invention is preferably prepared using a method according to the first aspect.

s The fuel may be mixed with the oxygenate (ii) following oxidation, or alternatively the fuel and oxygenate may be mixed prior to oxidising the mixture to an extent sufficient that the formulation has an overall oxygen content equal to at least 0.25% w/w plus the oxygen 10 content of the oxygenate (ii).

Other preferred features of the second aspect of the invention, in particular regarding the nature of the fuel (i) and oxygenate (ii), the oxygenate concentration and the degree of oxidation of the fuel, may be as described in 15 connection with the first aspect of the invention. In particular the oxygenate is preferably a Cl to C3 alcohol, more preferably methanol and/or ethanol.

The fuel formulation of the invention is preferably stable as a single phase solution, more preferably at 0 C 20 or below.

Stability of a formulation is dependent on the miscibility of its components. In formulations according to the invention, the oxidised fuel (i) and the oxygenate (ii) are preferably fully miscible at 0 C or below. By 25 "fully miscible" is meant that the two liquids dissolve in one another to form a single phase solution. Thus, the phase separation temperature ("demising temperature") of the formulation, TSep' is preferably below 0 C. TSep is the temperature at and below which the single phase liquid 30 mixture separates into more than one distinct phase, typically a fuel-rich and an alcohol-rich phase, and/or becomes cloudy (due to the formation of a dispersed

- 11 alcohol-rich phase, or in cases to the precipitation of waxes, sludges, gums, lacquers or other poorly fuel miscible components). It can therefore correspond in some cases to the cloud point temperature. In the present 5 specification, references to the phase separation

temperature are to the temperature at which the first sign of phase separation or cloudiness is detected.

Cloud point and phase separation temperatures may be determined using routine techniques, typically by observing l0 the relevant mixture visually as its temperature is altered and recording its temperature at the point where the phase separation or clouding first occurs. Observations may be made by eye or using for instance apparatus which measures light transmission through the mixture.

IS More preferably, the oxygenate and the fuel are fully miscible at -5OC or below, still more preferably at -7OC or below, most preferably at 10 C or -20 C or even -22 C or -30 C or below.

A formulation according to the invention is preferably 20 free of (especially externally added) surfactants, emulsifiers, stabilizers, solubilising agents and/or cosolvents such as esters, ethers, alcohols (especially higher and/or substituted alcohols), gasoline or benzene.

If it contains such additives, they are preferably present 25 at levels lower than 5% v/v, more preferably lower than 2% v/v or than 1% v/v or than 0.5% v/v or than 0.2% v/v.

The formulation preferably has a water content of below 0.3% w/w, preferably below 0.25% win, more preferably below 0.2% w/w, most preferably below 0.1% w/w. This also 30 applies to the fuel (i) prior to addition of the oxygenate (ii).

- 12 -

A third aspect of the present invention provides a fuel composition which includes a major proportion of a fuel formulation according to the first aspect. This composition is preferably suitable for use as an automotive 5 fuel, more preferably for use in an internal combustion engine in particular of the compression ignition type.

Other preferred features of the third aspect of the invention may be as described in connection with the first and second aspects.

10 The fuel composition, in particular where it is for use as an automotive fuel, may contain a minor proportion of one or more appropriate fuel additives. Typical examples include detergents, lubricity enhancers, anti foaming agents, ignition improvers (cetane improvers), 15 corrosion inhibitors, Deodorants, anti-wear additives, anti-oxidants, metal deactivators and cosolvents such as fatty acid esters and higher alcohols.

By "major proportion" is meant preferably 99% w/w or greater of the fuel composition, more preferably 99.5% w/w 20 or greater and most preferably 99.8% w/w or greater; references to "minor proportion" may be construed accordingly. Such additives are conveniently added to a fuel formulation according to the second aspect of the invention 25 after the oxidised fuel (i) and oxygenate (ii) have been combined. Where the fuel composition has a low (eg, 500 ppmw or less) sulphur content, it is particularly preferred that it contains a lubricity enhancer. In the additivated fuel 30 composition, the lubricity enhancer is conveniently present at a concentration between 50 and 1000 ppmw, preferably between 100 and 1000 ppmw.

- 13 The (active matter) concentrations of other additives in the fuel composition (with the exception of the ignition improver) will each preferably be in the range from O to 20 ppmw, more preferably from 5 to 20 ppmw or from 0 or 5 to 5 10 ppmw, although in some cases additive concentrations of up to 150 or 300 or 500 or even 1000 ppmw may be desirable.

The (active matter) concentration of any ignition improver present will preferably be between O and 600 ppmw and more preferably between O and 500 ppmw, conveniently between 300 lo and 500 ppmw.

According to a fourth aspect of the present invention, there is provided a method of operating a fuel combustion system, which method involves introducing into a combustion chamber of the system a fuel formulation according to the 15 second aspect of the invention and/or a fuel composition according to the third.

The combustion system may be in particular an internal or external, most particularly an internal, combustion automotive engine. Again the engine is preferably a diesel 20 (compression ignition) engine.

The fourth aspect of the invention encompasses a method of operating a machine which is powered by a fuel combustion system, especially a vehicle which is driven by an internal combustion engine.

2s Preferred features of this aspect of the invention, for instance regarding the nature of the fuel, the degree of oxidation, and the nature and concentration of the oxygenate (ii), may be as described in connection with the first, second and third aspects of the invention. In 30 particular, the fuel is preferably oxidised to an oxygen content of 0. 25t w/w or greater.

- 14 According to a fifth aspect of the present invention, there is provided a method for increasing the oxygen content of a liquid hydrocarbon fuel, in particular an automotive fuel such as a diesel fuel, which method 5 involves oxidising the fuel, preferably to an oxygen content of 0.3% w/w or greater, and adding an oxygenate to the fuel preferably post-oxidation. Preferred features of this aspect of the invention may be as described above in connection with the first aspect.

10 The methods of the invention thus allow the oxygen content of a fuel to be increased in two ways at once, not only by direct oxidation of the fuel (which if done to too high a degree could lead to degradation, inferior stability and/or undesirably high viscosity) but also by 15 incorporating an externally added oxygen-contributing additive. The oxygenate can provide most of the oxygen content of the fuel, but a low level of pre-oxidation can allow incorporation of the oxygenate at levels previously thought impractical due to their destabilizing effects. In 20 this sense there appears to be synergy between the two oxygencontributing processes. Moreover not only can the invented formulation suffer reduced fuel degradation because the oxygenate provides most of its oxygen content, but the presence of the oxygenate (in particular ethanol) 2s can also mitigate the problems typically accompanying direct fuel oxidation, since it can act as a solvent for polar materials like sludge, and can lower viscosity.

Ethanol is in addition a known anti-oxidant.

Incorporation of the oxygenate can also reduce 30 combustion-related emissions from the fuel, for instance smoke and/or particulate and/or CO emissions from the use of the fuel in automotive, in particular diesel, engines.

- 15 In many cases it may be used to increase the proportion of biologically derived and/or biodegradable matter in the fuel, an advantage which is assuming increased significance in the automotive industry.

5 A sixth aspect of the present invention provides a method for improving the miscibility of a liquid hydrocarbon fuel with an oxygenate, in particular an alcohol such as methanol or ethanol, which method comprises oxidising the fuel, for instance in the manner described in lo connection with the first aspect of the invention. The fuel is preferably subjected to an auto-oxidation process, and suitably oxidised to an oxygen content of 0.25% w/w or greater, more suitably to an oxygen content of 5% w/w or less. Again, other preferred features may be as described 15 in connection with other aspects of the invention.

This method has particular application to automotive base fuels, especially diesel base fuels.

"Improving the miscibility" includes improving the stability of a mixture of the fuel and oxygenate, for 20 example lowering the cloud point temperature and/or the phase separation temperature of the mixture and/or increasing the concentration of the oxygenate which can be mixed with the fuel to form, at a given temperature, a single phase solution.

25 It may also involve, as has been found possible using the present invention, an improvement in the tolerance of the fuel/oxygenate mixture to water content, ie, a reduction in the destabilizing effect (raising of phase separation temperature) of a given amount of water present 30 in the mixture.

The improvement may be achieved immediately following oxidation of the fuel, and/or after a subsequent period of

- 16 storage of the oxidised fuel. It may be achieved on addition of the oxygenate to the fuel, and/or after a subsequent period of storage of the fuel/oxygenate mixture.

It is preferably achieved without the addition of 5 cosolvents or other oxygenate-solubilising agents, surfactants, emulsifiers or stabilizers to the fuel. In other words, the sixth aspect of the invention preferably allows an improvement in the miscibility of a mixture consisting essentially of the fuel and the oxygenate 10 (preferably methanol and/or ethanol), where "consisting essentially of" means that the mixture contains 5% w/w or less of materials other than the fuel and the oxygenate, preferably 2% w/w or less, more preferably 0.5% w/w or less, most preferably 0.01% w/w or less.

IS The present invention will be further understood from the following illustrative examples, in which the procedure used to oxidise a fuel is generally as follows. An appropriate quantity of the fuel is poured into a bubbler reactor equipped with a reflux separator to remove the 20 water formed in the process. An oxygen containing fluid, in this case dry air,is bubbled into the fuel at the base of the reactor, through a filter such as a P3 filter, to maximise the residence time of the air bubbles in the fuel.

The reactor is heated in a magnetically stirred silicon oil 25 bath and the air is allowed to flow for an appropriate period of time. The air flow is then stopped and the reactor removed from the oil bath and cooled.

An oxygen meter and chart recorder may be used to indicate the progress of the oxidation. However prior to 30 entering the meter, the oxygen depleted air is passed not only through the water cooled condenser but also through a

- 17 cold trap, maintained at for instance -78 C, to remove any remaining water and lighter oxidation products.

The oxygen level in the treated fuel may be analysed for instance using a fast neutron activation (FNA) s technique, as described in the examples below. Infra red (JR) spectroscopy may be used to analyse the components of the oxidised fuel, and Karl Fisher analysis (ASTM E203) to determine its water content.

Example 1 - preparation of oxygenated fuel oil/ethanol 10 bl ends _ Two typical fuel oils were oxidised and then blended with ethanol to produce fuel formulations in accordance with the invention.

Fuel oil A is a low sulphur gas oil typically used as À 15 a diesel base fuel for lower temperature climates. Fuel oil B is an ultra low sulphur diesel base fuel intended for use in more temperate climates. Both have relatively low wax contents and relatively low cloud points; this reduced the risk of phase separation in the ethanol blends, in 20 subsequent tests, being obscured by the separation of wax.

- 18 -

The properties of the two oils are shown in Table 1.

Table 1

Property E'uel Fuel oil A oil B Density @ 15 C (IP 365/ASTM 0.8150 0.8225 D4052) (g/ml) Distillation (IP 123/ASTM D86) IBP ( C) 186.0 193.810 % 207.0 216.3

20 % 214.0 224.2

30 % 222.0 231.1

40 % 229.0 238.2

60 % 242.0 253.4

70 % 248.0 1 262.6

80 % 256.0 273.5

90 % 264.0 287.5

95 % 272.0 297.5

Cetane number (ASTM D613) 54.5 55 Kinematic viscosity @ 40 C 2.030 2.156 (IP 71/ASTM D445) (cSt) Sulphur (ASTM D2622) (mg/kg) <5 5 Cloud point (IP 219) ( C) -32 -26 Cold filter plugging point -37 -27 (IP 309) ( C)

HPLC aromatics (IP 391 Mod): Mono (% w/w) 4.4 34.7 Di (% w/w) <0.1 1.8 Tri (% w/w) <0.1 0.1 Total (% w/w) 4.4 36.6

- 19 The addition of 15% w/w ethanol to either of these base fuels results in the formation of two phases at 20 C, making the blend unsuitable for use as a diesel fuel. 15% w/w is however a typical ethanol concentration for a diesel 5 fuel composition, balancing the desire for low particulate and smoke emissions and a higher proportion of biodegradable material with the need to prevent undue lowering of the cetane number and corresponding loss of performance. 10 The two fuels were air treated using the above described procedure to increase their oxygen contents. 10 g of the relevant fuel was poured into the bubbler reactor through which air was allowed to flow at 25 ml/minute for one hour. The oil bath was maintained at 160 C.

IS Some of the samples were batch processed, others subjected to a continuous flow oxidation in which the base fuel was added to, and the oxidized fuel removed from, a stirred reactor continuously.

The air treated oils were analysed by the standard FNA 20 method ASTM E385-90. Note that this gave total oxygen concentrations, including any water present in the oil.

Minor amounts of volatile materials derived from the oxidation process were collected at the condenser. The major part of the oil remained however in the liquid phase.

25 Fuel formulations in accordance with the invention were prepared by blending (physically mixing) the thus oxygenated oils with absolute ethanol (PA (99.8%), Merck).

Example 2 - stability of the fuel oil/ethanol blends The temperature stability of the blends prepared in 30 Example 1, with respect to their cloud points, was assessed and the results are shown in Tables 2 (fuel oil A) and 3 (fuel oil B) below.

- 20 The cloud point temperatures were determined using Colorant KryoThermostat WK6 baths containing isopropyl alcohol that were capable of reaching -30 to -33 C. The samples were observed visually using 2 ml gas s chromatography glass bottles. The temperature was decreased stepwise and at each temperature the bottles were removed quickly from the bath and shaken to see if they had either turned cloudy or separated into two distinct phases.

The highest temperature at which either of these events 10 occurred was recorded as the cloud point.

The effect of water content on blend stabilities was also assessed. Most samples already contained water formed during the oxidation process; in some cases, the oxidised fuel was dried by molecular sieve to reduce its water 15 content, and in others, water was deliberately added post oxidation.

Table 2

Sample Oxidation Oxygen Ethanol Water Cloud method content (8 content content point w/w) by (% w/w) (a w/w) ( C) FNA Batch 0.91 15 0.06 -10 2 Batch 0.91 15 0.16 8 3 Batch 0.91 15 0.26 18 4 Batch 1.29 15 0.08 -23 5 Batch 1.29 15 0.18 -5 . 6 Batch 1.29 15 0.28 8 7 Batch 1.39 15 0.09 -27 Batch 1.39 _ 15 0.19 -11 9 Batch 1.39 15 0.29 5 10 Batch 1.90 15 0.12 -29 _ 11 Batch 1.90 15 0.22 -15 .. . 12 Batch 1.90 15 0.32 -2 13 Batch 2. 24 15 0.14 -33 14 Batch 2.24 15 0.24 -23 15 Batch 2.24 15 0.34 -10 16 Flow 2.04 15 0.24 -4 17 Flow 2.66 15 0.24 -12 18 Flow 2.66 15 0.34 -2 19 Flow 2.61 13 0.075 -23 Table 3

r Sample Oxidation Oxygen Ethanol Water Cloud method content Content Content point ( w/w) by (8 w/w) (a w/w) ( C) FNA 20 Batch 1.53 15 0.10 21 21 Batch 1.53 15 0.20 -8 22 Batch 1.53 15 0.30 23 Batch 2.10 15 0.13 25 24 Batch 1 2.10 15 0.23 -18 25 Batch 2.10 15 0.33 -8 26 Flow 2.02 15 0. 14 -14 27 Flow 2.02 15 0.24 -2

- 22 These results demonstrate that after the base fuels have undergone a small degree of oxidation, they can be blended with 15% w/w absolute ethanol to form a single phase system which is stable at normal operating 5 temperatures.

It appears that the effect of the oxidation on ethanol miscibility is greater, pro rata, at lower oxidation levels. Although blend stability appears to be compromised by 10 the presence of water, in fact preoxidation of the fuel seems to enhance the water tolerance of the fuel/ethanol blends compared to those of unoxidized fuel/ethanol blends.

At oxygen levels (pre blending) of greater than about 1.9% w/w even water contents of up to 0.3% w/w do not prevent 15 the blend being of practical use in a diesel fuel composition. In normal use, water can enter a blended fuel in several ways: either the fuel or the oxygenate can itself contain water; water can be absorbed from the air which 20 comes into contact with the blend during handling, for instance during filling and emptying of the tank and during the diurnal breathing of storage tanks; it can also enter due to leaks and dirty tanks. It is thus necessary for a fuel blend to be able to tolerate a certain amount of water 2s without undue phase separation during normal storage and use. Since water tends to increase the cloud point temperature of fuel oil/oxygenate blends, it is desirable in accordance with the invention to strip the water from the fuel either during or after oxidation.

- 23 -

Example 3 - stability of further oxidized fuel oil/ethanol by ends Further fuel oil formulations according to the invention were prepared as described in Example 1, using s the gas oil A. Oxidation was carried out for between 30 minutes and 5 hours, and blends of the thus oxygenated oil with absolute ethanol were prepared by calculating, using the oxygen content obtained by FNA, the amount of ethanol required to increase the total oxygen content of 10 the fuel to 10-% w/w. Again the gas oil and ethanol were physically mixed.

The temperature stability of the blends, with respect to their phase separation, was assessed in the manner described in Example 2 and the results are shown in Table 15 4. Samples having the suffix "a" are those to which ethanol had been added to give a total oxygen content of 10% w/w. The stabilities of the oxidised oils alone are also shown. The temperature at which a sample separated into two distinct phases, or became cloudy, is recorded as 20 its phase separation temperature TSep.

- 24 Table 4

Sahel e T=ne air Oxygen Phas e s epara ti on tree ted a t: con ten t of tempera tune 160 C gas oil by Tsep ( C) (hoursJ oxidation (8 w/wJ 28 0 0 <-30

28a 0 _ 20>Tsep >0 29 0.5 i.27 <-30 29a 0.5 -12.5<Tse.<-10 P 30 1.0 2.49 lO<Tsep.<-7.5 30a 1.0 <-30 31 1.5 3.46 -lO<Tsep.<-7.5 31a 1.5 <-30 32 2. 0 4.52 -10<T.<-7.5

32a 2.0 <-30 33 3.0 6.51 -lO<Tsep.<-7.5 33a 3.0 <-30 34 5.5 12.32 lO<Tsep.<-7.5 It can be seen from Table 4 that the non-air treated 5 gas oil alone was stable down to -30 C but that the addition of ethanol to it brought its phase separation temperature well above 0 C (actually to around 15 C), making it unsuitable for use as a diesel fuel.

Air treatment of the gas oil appeared, on its own, to lo reduce stability (samples 29 to 33), but in each case the addition of ethanol restored stability to acceptable levels, resulting in most cases in a phase separation temperature below -30 C. At pre-blending oxygen contents above about 2% w/w, the ethanol blend exhibited superior 15 demixing performance compared to the oxidised oil alone without the ethanol present, there appeared to be some tendency for some of the constituents of the oxidised oil to separate at temperatures below about -10 C. This could indicate a degree of synergism (possibly mutual

- 25 solubilising effects) between the ethanol and components present in the oxidised oil.

The argument for synergism may be supported by the results for sample 34 (no ethanol added since air treatment s alone resulted in > 10% w/w oxygen), which show that merely increasing the oxygen content by air treatment, without the subsequent addition of ethanol, fails to give the beneficial effects of the present invention.

Example 4 - fuel oil/methanol blend 10 A further fuel formulation in accordance with the invention was prepared by oxidising the gas oil A as described in Example 1, to an oxygen content of 1.9% w/w, and blending the thus oxidised fuel with methanol (dehydrated organic synthesis grade, Prolabo).

15 Prior to oxidation, the amount of methanol that could be dissolved as a single phase in the gas oil at 18 C was found to be less than 0.1% v/v.

In the oxidised oil, in contrast, 3.6% v/v methanol could be dissolved to give a single phase solution at 18 C.

20 Again this demonstrates the value of the invented method in increasing significantly the miscibility of an oxygenate with a fuel oil. The methanol/gas oil blend according to the invention is expected to exhibit reduced smoke and/or particulate emissions due to its increased 25 oxygen content.

Claims (10)

1. - 26 C L A I M S

   _ 1. A method for preparing a fuel formulation, the method comprising oxidising a liquid hydrocarbon fuel (i) and adding an oxygenate (ii) to the fuel.
2. 2. A method according to claim l, wherein the oxygenate 5 (ii) is added after oxidation of the fuel.
3. 3. A method according to claim 1 or claim 2, wherein the fuel is an automotive fuel suitable for use in a compression ignition engine.
4. 9. A method according to any one of the preceding claims, lo wherein the oxygenate is added at a concentration which gives a total oxygen content in the fuel formulation of 5% w/w or greater.
5. 5. A method for improving the miscibility of a liquid hydrocarbon fuel with an oxygenate, which method comprises IS oxidising the fuel.
6. 6. A method according to any one of the preceding claims, wherein the fuel is oxidised to an oxygen content of from 0.25% w/w to 3% w/w.
7. 7. A method according to any one of the preceding claims, 20 wherein the oxygenate (ii) is ethanol, methanol or a mixture thereof.
8. 8. A fuel formulation comprising (i) a liquid hydrocarbon fuel which has been oxidised to an oxygen content of 0.25% w/w or greater and (ii) a C1 to C6 oxygenate.

   25
9. 9. A fuel formulation according to claim 8, wherein the oxidised fuel and the oxygenate are fully miscible at -10 C or below.

   - 27
10. 10. A fuel formulation according to claim 8 or claim 9, wherein the oxygenate (ii) is methanol, ethanol or a mixture thereof.