Compositions and methods and uses relating thereto

1. A composition comprising a diesel fuel and a quaternary ammonium compound of formula (I):

wherein R 0 , R 1 , R 2 and R 3 is each independently an optionally substituted hydrocarbyl group, X is a linking group, R 4 is an optionally substituted alkylene group, R 5 is hydrogen or an optionally substituted alkyl, alkenyl or aryl group, and n is 0 or a positive integer, provided that n is not 0 when R 5 is hydrogen, wherein X is CH 2 CHR or CHRCH 2 wherein R is an alkyl or alkenyl group having 20 to 24 carbon atoms.

2. A method of improving the performance of an engine, the method comprising combusting in the engine a diesel fuel composition comprising as an additive a quaternary ammonium compound of formula (I):

wherein R 0 , R 1 , R 2 and R 3 is each independently an optionally substituted hydrocarbyl group, X is a linking group, R 4 is an optionally substituted alkylene group, R 5 is hydrogen or an optionally substituted alkyl, alkenyl or aryl group, and n is 0 or a positive integer, provided that n is not 0 when R 5 is hydrogen; wherein X is CH 2 CHR or CHRCH 2 wherein R is an alkyl or alkenyl group having 20 to 24 carbon atoms.

3. The composition according to claim 1 wherein HOOCXCOO—(R 4 O) n —R 5 is derived from a hydrocarbyl substituted succinic acid or a hydrocarbyl substituted succinic anhydride.

4. The composition according to claim 1 wherein each R 4 is ethylene or propylene.

5. The composition according to claim 1 wherein R 5 is hydrogen and n is at least 1.

6. The composition according to claim 1 wherein R 5 is an optionally substituted alkyl group having 4 to 40 carbon atoms and n is from 0 to 40.

7. The composition according to claim 1 wherein each of R 1 and R 2 is independently an optionally substituted alkyl group having from 1 to 12 carbon atoms.

8. The composition according to claim 1 wherein R 3 is an alkyl or hydroxyalkyl group having 1 to 10 carbon atoms.

9. The composition according to claim 1 wherein R 3 is selected from the group consisting of:

(1) a polyisobutenyl group having a molecular weight of from 100 to 5000;

(2) an optionally substituted alkylene phenol moiety of formula (A) or (B)

wherein n in structure (A) or (B) is 0 to 4, IV is an optionally substituted hydrocarbyl group, R y is an optionally substituted alkyl, alkenyl or aryl group; and L is a linking group; and

(3) a succinimide moiety of formula:

wherein R z is an optionally substituted hydrocarbyl group and L is a linking group.

10. The composition according to claim 1 wherein R 0 as is a group of formula:

wherein each of R 9 , R 10 , R 11 , R 12 is independently selected from hydrogen or an optionally substituted alkyl, alkenyl or aryl group.

11. The composition according to claim 1 wherein the quaternary ammonium compound is the reaction product of:

(a) a tertiary amine of formula R 1 R 2 R 3 N wherein each of, R 1 , R 2 and R 3 is independently an optionally substituted alkyl group having 1 to 12 carbon atoms;

(b) an epoxide selected from styrene oxide, ethylene oxide, propylene oxide, butylene oxide, epoxyhexane, octene oxide, stilbene oxide, 2-ethylhexyl glycidyl ether, 1,2-epoxydodecane and other alkyl and alkenyl epoxides having 2 to 50 carbon atoms; and

(c) a compound of formula HOOCXCOO—(R 4 O) n —R 5 wherein X is CH 2 CHR or CHRCH 2 wherein R is an alkyl or alkenyl group having 20 to 24 carbon atoms; and

n is more than 1, R 4 is an ethylene or propylene group and R 5 is hydrogen; or

n is 0 and R 5 is a C1 to C20 alkyl group.

12. The composition according to claim 1 wherein the quaternary ammonium compound is the reaction product of:

(a) a tertiary amine of formula R 1 R 2 R 3 N wherein each of, R 1 , R 2 and R 3 is independently an alkyl or hydroxyalkyl group having 1 to 6 carbon atoms;

(b) an epoxide selected from propylene oxide, butylene oxide and 2-ethylhexyl glycidyl ether; and

(c) a compound of formula HOOCXCOO—(R 4 O) n —R 5 which is the reaction product of a succinic acid or anhydride having a C 20 to C 24 alkyl or alkenyl substituent and an alcohol selected from polypropylene glycol having a number average molecular weight of 300 to 800, 2-ethylhexanol and butanol.

13. The composition according to claim 1 further comprising one or more detergents selected from the group consisting of:

(i) a further quaternary ammonium salt additive;

(ii) the product of a Mannich reaction between an aldehyde, an amine and an optionally substituted phenol;

(iii) the reaction product of a carboxylic acid-derived acylating agent and an amine;

(iv) the reaction product of a carboxylic acid-derived acylating agent and hydrazine;

(v) a salt formed by the reaction of a carboxylic acid with di-n-butylamine or tri-n-butylamine;

(vi) the reaction product of a hydrocarbyl-substituted dicarboxylic acid or anhydride and an amine compound or salt which product comprises at least one amino triazole group; and

(vii) a substituted polyaromatic detergent additive.

14. The composition according to claim 1 wherein the composition comprises a mixture of two or more quarternary ammonium salt additives.

15. The method as defined in claim 2 wherein the additive is used as a detergent to combat deposits in a diesel fuel composition in a diesel engine.

16. The method according to claim 2 which is carried out in a diesel engine having a pressure in excess of 1350 bar.

17. The method according to claim 2 which achieves “keep clean” performance.

18. The method according to claim 2 which achieves “clean up” performance.

19. The method according to claim 15 wherein the deposits are injector deposits.

20. The method according to claim 19 wherein the deposits are internal diesel injector deposits.

21. The method according to claim 2 which achieves an improvement in performance of one or more of:

a reduction in power loss of the engine;

a reduction in external diesel injector deposits;

a reduction in internal diesel injector deposits;

an improvement in fuel economy;

a reduction in fuel filter deposits;

a reduction in emissions; or

an increase in maintenance intervals.

22. The method according to claim 21 which provides an improvement in performance in diesel engines having a pressure in excess of 1350 bar and provides an improvement in performance in traditional diesel engines.

23. The composition according to claim 1 which further comprises one or more further additives selected from the group consisting of: lubricity improvers, corrosion inhibitors and cold flow improvers.

24. A method of preparing a fuel composition, the method comprising preparing a quaternary ammonium salt by reacting (a) a tertiary amine of formula R 1 R 2 R 3 N with (b) an acid-activated alkylating agent in the presence of (c) a compound of formula HOOCXCOO—(R 4 O) n —R 5 , and adding the quaternary ammonium salt into the fuel;

wherein R 4 is an optionally substituted alkylene group, R 5 is hydrogen or an optionally substituted alkyl, alkenyl or aryl group, and n is 0 or a positive integer, provided that n is not 0 when R 5 is hydrogen; and

wherein n is a positive integer and/or X is CH 2 CHR or CHRCH 2 wherein R is an alkyl or alkenyl group having 20 to 24 carbon atoms.