The present invention relates to additives for diesel fuels and diesel fuels containing such additives.

When diesel fuels are used in automotive diesel engines deposits can form on various parts of the combustion chamber and piston. One place where deposits can form is on piston crown lands. Deposits in such places are particularly undesirable because it is believed that they may contribute to undesirable polishing of the bore of the engine cylinder.

Various proposals have been made for incorporating additives into fuels, including diesel fuels to reduce deposits. One class of detergent additives proposed for use in fuels are derivatives of long chain hydrocarbons, for example derivatives of polyisobutene. Thus GB 1 405 652 mentions use of amines containing long hydrocarbon groups as additives for fuels. The amines may be made by reacting halogen-substituted hydrocarbons with aliphatic polyamines, which may be cyclic polyamines. Preference is however given to the use of polyethylene polyamines and the preferred fuels are gasolines and aviation turbine fuels. The possibility of using the reaction products of reacting halogenated polyisobutene with polyamines which may contain a piperazine structure is mentioned in US 3 565 804. Preferably the piperazine group is not present.

More recently a favoured detergent additive is based on succinic acid derivatives having a long hydrocarbon chain, usually derived from polyisobutene. However it is desirable to provide alternative diesel fuel additives based on novel chemistry to

provide more choice in the market. Furthermore where possible it is desirable to provide such additives having improved properties.

Bic lie guanidines are known compounds. Thus EP 198 680 discloses a method of making such compounds, for example 1,5,7-triazabicyclo[4,4,0]dec-5-ene. This material is referred to in the specification as TBD. The only use suggested in EP 198 680 for such compounds is as catalysts for various chemical reactions.

According to the present invention a novel chemical compound suitable for use as a diesel fuel additive is a bicyclic guanidine substituted on the amino nitrogen atom by an aliphatic hydrocarbon group containing from 20 to 200 carbon atoms in the molecule.

According to another aspect of the present invention a diesel fuel comprises a major amount of a hydrocarbon fraction having a boiling point in the range 160-380 ^β C at atmospheric pressure and a minor amount of a guanidine substituted on the amino nitrogen atom by an aliphatic hydrocarbon substituent having from 1 to 200 carbon atoms.

A further aspect of the present invention is the use of a guanidine substituted on the amino nitrogen atom by an aliphatic hydrocarbon having from 1 to 200 carbon atoms in a diesel fuel to reduce deposit formation in a diesel engine.

The preferred guanidines are bicyclic guanidines. The preferred bicyclic guanidine is TBD. The TBD may be prepared by any suitable process for example that disclosed in EP 198 680.

The aliphatic substituent preferably contains 1 to 200 carbon atoms, more preferably 10 to 100, most preferably 20 to 60. The aliphatic group is a hydrocarbyl group, preferably derived from a polyisobutene. Such polyisobutenes having various molecular weights are commercially available. They will generally be materials of varying chain length. Where the substituent is derived from a material which is a mixture of homologues of varying chain length then the number of carbon atoms in the substituent for the purposes of this specification corresponds to the average number of carbon atoms. For hydrocarbons for which a weight average molecular weight

is quoted the average number of carbon atoms can be obtained by dividing by the molecular weight of the carbon repeating unit, e.g. for polybutene the average number of carbon atoms is obtained by dividing the molecular weight by 14. The bicyclic guanidines with an aliphatic substituent containing from 20 to 200 carbon atoms are believed to be new compounds.

The novel substituted bicyclic guanidines of the present invention may be prepared by reaction of a chlorinated aliphatic hydrocarbon and a bicyclic guanidine. The chlorinated aliphatic hydrocarbon may contain a quantity of chlorine equivalent to 1 to 5 chlorine atoms per molecule, for example an amount of chlorine equivalent to 1.5 to 2.5 chlorine atoms per molecule.

The quantity of the guanidine derivative used in the diesel fuel may vary over a moderately wide range, and may be for example from 50 to 500, or more preferably 100 to 300 ppm.

The invention will now be described by reference to the accompanying drawings in which Figures 1 and 2 are graphical representations of deposits resulting from heating distillate diesel fuel and by reference to the following experiments, in which comparative tests not according to the invention, are identified by letters and examples of the invention are identified by numbers.

Example 1

Preparation of a chlorinated polyisobutene

The starting material was a polyisobutene supplied by BP Chemicals Limited under the trade name "Hyvis 150". The polyisobutene has the following characteristics:

Viscosity at 100 ^β C 3065 cSt

Pour Point 18°C

Relative Density at 15.5°C 0.911 g/cm ³ Refractive Index 1.503

Bromine No. (gB^/lOOg) 8

Acid No. (mgKOH/g) 0.02

The average molecular weight was 2400. The corresponding average number of carbon atoms was 171.4. The chlorination was carried out in a flask fitted with a

mechanical gas recycle stirrer, a reflux condenser, a thermometer pocket, a chlorine inlet with a sintered plug, and a vent to a chlorine scrubber.

The polyisobutene was added to the flask and the apparatus was flushed with nitrogen before it was heated to 110 ^β C. Chlorine gas was then fed into the apparatus at a rate of about 5 litres per hour measured at ambient temperature and pressure. The chlorination was carried out at atmospheric pressure. The apparatus was weighed before and after the addition of chlorine to indicate the chlorine uptake. Chlorine was fed for nine hours into 0.27 moles of the polyisobutene. A 20g increase in weight was obtained. Analysis showed the presence of 3.4% by weight of chlorine, which was equivalent to 2.4 chlorine atoms per molecule of the polyisobutene. Reaction between the polyisobutene chloride and TBD The apparatus used for this reaction was a two neck flask fitted with a reflux condenser and magnetic stirrer. The polyisobutene chloride produced in the first step was dissolved in xylene and the apparatus flushed with nitrogen. 1,5,7-triaza bicyclo (4,4,0) dec-5-ene (TBD) was added in an amount to give a molar/ratio of 2:1 to the chlorinated polyisobutene after the apparatus was flushed with nitrogen. The mixture was then heated to reflux for 6 hours. The resulting product was then washed with a hot 10% aqueous solution of sodium hydroxide to remove hydrogen chloride liberated in the reaction. The organic layer resulting from the washing step was separated and dried with magnesium sulphate. It was then filtered and evaporated to constant weight on a rotary evaporator to remove the xylene solvent.

The reaction product has a base number of 14.6 mg KOH per gram. This was equivalent to 67% reaction of the chlorine end groups. Evaluation of the Additive in a Diesel Fuel

The substituted TBD from the preceding step was added to a base fuel. The base fuel was a typical winter grade diesel fuel for road vehicles. The amount of additive used was sufficient to give a

content of 100 ppm in the fuel.

The tendency of the fuel to give deposits on piston crown lands was investigated by passing the fuel over the surface of a standard aluminium tube as used in the JFTOT test (ASTMD 3241) maintained at 300°C. The fuel was passed over it on a single pass basis for a period of 2 hours.

At the conclusion of the test the relative thickness of deposits on the tube over a distance of 60 mm was assessed using

SEM/EDAX (Scanning Electron Microscopy/Energy Dispersive Analysis of X ray).

The results are shown in Figure 1, dotted line marked 0. The numeral 0 is for identification only.

Example 2

An experiment was carried out as in Example 1 except that the polyisobutene used was a material sold under the trade name "Hyvis

30". This had the following characteristics:

Viscosity at 100 ^β C 635 cSt

Pour point 4 ^β C

Relative Density at 15.5 ^β C 0.902 g/cm ³ Refractive Index 1.498

Bromine No. (gB^/lOOg) 12

Acid No. (mgKOH/g) 0.03

The average molecular weight was 1300. The corresponding average number of carbon atoms was 92.9. The chlorinated product contained 1.93 chlorine atoms per molecule of the polyisobutene, and 56% of the chlorinated product reacted to give TBD functionalised polyisobutene.

The results are shown in Figure 1, by the solid line marked 6.

Comparative test A The deposit formation resulting from the use of the base fuel without any additive was determined. The results are shown in

Figure 1 by the dotted line marked 9. The amount of deposit was so high that the peak level could not be shown on the graph of the scale used.

Example 3

A methyl substituted TBD was prepared using the general technique as disclosed in Example 1. The result of adding this to diesel fuel is shown in Figure 1, by the continuous line marked 5. A consideration of the results shown in Figure 1 shows that the use of the TBD derivatives results in a reduction in deposit formation. Deposit formation is still high with the methyl derivative, it is lower with the material derived from a relatively long chain polyisobutene, but is lowest with a material derived from a relatively short chain polyisobutene. Example 4

An experiment was carried out as in Example 2 except that a lower accelerating voltage (6 kV instead of 9 kV) was used in the SEM/EDX measurements. The carbon/aluminium ratios (which are an indicator of deposit thickness), along the length of the tube are shown in Figure 2, by the solid line marked 6. Example 5

An experiment was carried out as in Example 4 except that the polyisobutene starting material was a material supplied by BP Chemicals Limited under the trade name "Hyvis 3". This had the following characteristics:

Viscosity at 100 ^β C 57 cSt

Pour Point -21 ^β C

Relative density at 15.5°C 0.869 g/cro ³ Refractive Index 1.487

Bromine No. (gB^/lOOg) 27

Acid No. (mgKOH/g) 0.03

The average molecular weight was 650. The corresponding average number of carbon atoms was 46.4. The chlorinated polyisobutene contained 4 chlorine atoms per molecule, and 65% of the chlorinated material reacted to give TBD functionalised polyisobutene.

The results are shown in Figure 2, by the dashed line marked 1. Comparative Test C A commercially available package for addition to diesel fuels

sold under the designation ECA 12278 was tested as in Example 4.

The results are shown in Figure 2, by the continuous line marked 7.

Comparative Test D

A commercial additive package for diesel fuels sold under the designation H 4340 was tested as in Example 4. The results are shown in Figure 2, by the dotted line marked 8.

It should be noted that the materials in accordance with the invention were used on their own and not as part of a commercially formulated package. Nevertheless significant reductions in deposit formation are obtained, particularly with the product derived from the lower molecular weight polyisobutene.