Title : Emulsified Oxygenate Diesel Fuel Composition and Method of preparing an Emulsified Oxygenate Diesel Fuel Composition The present invention relates to an emulsified oxygenate diesel fuel composition consisting of water, an alcohol and an ether together with a water/oil emulsifier and an oil/water emulsifier. The invention further relates to a method of preparing the emulsified fuel composition on board a vehicle for use as fuel in a compression ignition engine.

The most typical example of a compression ignition engine is the Diesel engine operating with high cetane numbered

Diesel fuel. To reduce environmental pollution arising from combustion of Diesel fuel, several attempts have been made in the past to replace Diesel fuel with alternative fuels having a reduced impact on the environment .

Ethers, in particular ethers prepared by dehydration of lower alcohols, such as dimethyl and diethyl ether, have shown to be a superior Diesel fuel. The use of lower ethers as Diesel fuel has been described in a number of publications, e.g. US Patent Nos. 4,892,561, 5,906,664 and 7,449,034.

Despite its clean combustion characteristics and high efficiency in a Diesel engine, the main disadvantage of an ether-based fuel is found in the difficult storage and handling thereof on board vehicles. As an example, dimethyl ether is in the gaseous form at ambient conditions. To transform the dimethyl ether fuel into its more convenient liquid form, the fuel must be stored and handled under pressure .

To avoid storage of ethers on board a vehicle, US patent No. 7,449,034 discloses oxygenated Diesel fuel compositions, which contain a combination of alcohol, ether and water. The fuel compositions are prepared by means of a catalytic dehydration unit on board a vehicle.

Modern Diesel engines are provided with a common rail fuel system. The system consists of a high pressure pump and a fuel accumulation chamber for storing fuel at high

pressures of above 2,000 bars. The accumulation chamber supplies multiple fuel injectors with high pressure fuel. Surplus fuel is withdrawn from the chamber, depressurised and recycled to a fuel buffer tank. During conversion of alcohol into ether, water is

cogenerated, and at a certain level of conversion two liquid phases in equilibrium may be formed. Thus, when operating an engine system on oxygenated diesel fuel prepared on board by dehydration of a primary alcohol fuel phase, phase separation may occur in the buffer tank of the common rail system resulting in an in-homogeneous fuel to the engine.

When phase separation occurs in the buffer tank, slugging in the feed rail system may lead to imbalance in the engine performance . It has now been found that phase separation of an oxygenate diesel fuel is avoided by^adding a water/oil emulsifier together with an oil/water emulsifier to the fuel. Pursuant to this finding, this invention provides an emulsified oxygenate diesel fuel composition comprising water and an ether and optionally an alcohol together with a water/oil emulsifier having an HLB value of between 4 and 6 and an oil/water emulsifier having an HLB value of between 8 and 13.

The term "HLB" is commonly known in the art as a shortage of "Hydrophilic-Lipophilic Balance". The hydrophilic-lipophilic balance of an emulsifier is a measure of the degree to which it is hydrophilic or

lipophilic, said measure being determined by calculating values for the different regions of the molecule as

described by Griffin (Griffin WC: "Classification of

Surface-Active Agents by 'HLB,'" Journal of the Society of Cosmetic Chemists 1 (1949) : 311; and Griffin WC:

"Calculation of HLB Values of Non-Ionic Surfactants,"

Journal of the Society of Cosmetic Chemists 5 (1954) : 259) . The HLB value of an emulsifier is calculated according to the following formula:

HLB = 20 * Mh / where Mh is the molecular mass of the hydrophilic portion of the molecule, and M is the molecular mass of the whole molecule giving a result on an arbitrary scale of 0 to 20. An HLB value of 0 corresponds to a completely hydrophobic molecule, and a value of 20 corresponds to a molecule made completely of hydrophilic components. Other correlations exist for specific molecular types of emulsifiers, said correlations taking into account

variations in e.g. number of . repeating units.

The alcohol of the emulsified diesel fuel according to the invention comprises preferably methanol, ethanol or

mixtures thereof, and the ether comprises dimethyl ether, diethyl ether, methyl-ethyl ether or mixtures thereof.

In the emulsified fuel, the content of water is typically between 10 and 50 wt%, the content of the alcohol between 0 and 25 wt% and the content of the ether between 40 and 90 wt%, which provide an excellent engine performance.

The amount of emulsifier is preferably between 0.05 and 5 vol% based on the total oxygenated diesel fuel product (ether/water/alcohol) , and the ratio of the water/oil emulsifier to the oil/water emulsifier is between 1:2 and 2:1. Preferred water/oil emulsifiers for use in the invention comprise sorbitan oleates, in particular sorbitan

monooctadecanoate, such as sorbitan (Z)-mono-9- octadecenoate being commercially available under the trade mark Span ^® 80. Preferred oil/water emulsifiers comprise alkylphenol ethoxylates, in particular octylphenol ethoxylate being commercially available under the trade mark TRITON™ X-45. An amount of surfactant/emulsifier capable of stabilizing a water in an oil emulsion system (HLB number < 10) is injected into the reactor product stream, preferably at the valve system of the reactor, where the pressure is released or before a restriction after said valve system, or just after the feed pump for the injection system. As a ^' result, sufficient energy is provided for the emulsification of the two liquid phases without any other means. To enable a sufficient mixing, the surfactant must be delivered in a water/ethanol solution or dispersion.

The amount of surfactant can be between 0.05 and 5% based on the total fuel composition e.g. DEE/water/ethanol. The sedimentation and equilibrium phase separation of

DEE/water/ethanol mixtures into two liquid phases appears within minutes. The role of the surfactant is to decrease the rate of static separation and to allow for a rapid and easy re-dispersion after the phase separation, i.e. in case of parking the vehicle. Further the surfactant may add to increase the lubricity which is lacking in diethyl ether containing fuel compositions compared to traditional diesel fuel .

In addition, the invention provides a method of preparing an emulsified oxygenate diesel fuel.

In one embodiment of the invention, the method comprises the steps of contacting an alcohol primary fuel with one or more dehydration catalysts; dehydrating the alcohol to its corresponding ether and water; and adding an amount of a water/oil emulsifier having an HLB value of between 4 and 6 and an oil/water emulsifier having an HLB value of between 8 and 13 to an alcohol primary fuel.

In a further embodiment of the invention, the method comprises the steps of adding an amount of a water/oil emulsifier having an HLB value of between 4 and 6 and a oil/water emulsifier having an HLB value of between 8 and 13 to an alcohol primary fuel; contacting the primary fuel containing the water/oil and oil/water emulsifier with one or more alcohol dehydration catalysts and dehydrating the alcohol to its corresponding ether and water.

EXAMPLES

Example 1 (comparative)

Sorbitan monooleat emulsifier Span ^® 80 was added to a 1:1 weight mixture of ethanol and water and dispersed by shaking. The SPAN concentration was varied from 0.2 to 2.5 wt% of the final mixture. Further 2 weight parts of diethyl ether (DEE) were added, and the mixture was shaken by hand for 2 minutes. After this phase volumes were estimated as a function of time. Rapid creaming was observed (decreasing haze of upper part of test tube) , while a slow formation of the bottom phase appeared.

Example 2

Sorbitan monooleat emulsifier Span ^® 80 and the dispersant TRITON™ X-45 were added in equal amounts to a 1:1 weight mixture of ethanol and water and dispersed by shaking. The Span ^® 80 concentration was varied from 0.2 to 2.5 wt% of the final mixture. Further 2 weight parts of DEE were added, and the mixture was shaken by hand for 2 minutes. No settling of a lower phase was observed within one hour, while a weak creaming of a clear top phase was observed.