Composition and methods and uses relating thereto

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

wherein X is a linking group; Y is O, NH or NR 1 wherein R 1 is H or an optionally substituted hydrocarbyl group; Q + is a moiety that includes a quaternary ammonium cation; A − is an anion; R 2 is an optionally substituted alkylene group; R 3 is hydrogen or an optionally substituted hydrocarbyl group; and n is 0 or a positive integer; provided that n is not 0 when R 3 is hydrogen.

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 salt of formula (I):

wherein X is a linking group; Y is O, NH or NR 1 wherein R 1 is H or an optionally substituted hydrocarbyl group; Q + is a moiety that includes a quaternary ammonium cation; A − is an anion; R 2 is an optionally substituted alkylene group; R 3 is hydrogen or an optionally substituted hydrocarbyl group; and n is 0 or a positive integer; provided n is not 0 when R 3 is hydrogen.

3. The composition according to claim 1 wherein the quaternary ammonium salt additive is prepared by reacting:

(a) a hydrocarbyl substituted dicarboxylic acid or anhydride thereof; with

(b) an alcohol of formula R 3 (OR 2 ) n OH;

(c) a reactive alcohol or amine including a tertiary amino group; and

(d) a quaternising agent.

4. The composition according to claim 1 wherein X is an optionally substituted alkylene or arylene.

5. The composition according to claim 1 wherein n is 0 and R 3 is an optionally substituted alkyl or alkenyl group having 4 to 40 carbon atoms.

6. The composition according to claim 1 wherein each R 2 is ethylene or propylene.

7. The composition according to claim 1 wherein R 3 is hydrogen and n is at least 1.

8. The composition according to claim 1 wherein R 3 is an optionally substituted alkyl group having 4 to 40 carbon atoms and n is from 1 to 40.

9. The composition according to claim 1 wherein Q + is a group having the formula:

wherein R 5 is an optionally substituted alkylene, arylene or alkenylene group and each of R 6 , R 7 and R 8 is independently an optionally substituted hydrocarbyl group.

10. The composition according to claim 9 wherein R 5 is an optionally substituted alkylene group having 1 to 6 carbon atoms, R 6 is C 1 to C 6 alkyl, R 7 is C 1 to C 6 alkyl and R 8 is an unsubstituted C 1 to C 6 alkyl group or a hydroxy substituted C 1 to C 40 alkyl group.

11. The composition according to claim 1 wherein A − is a carboxylate anion.

12. The composition according to claim 1 wherein the quaternary ammonium salt additive is prepared by reacting:

(a) an optionally substituted succinic acid or anhydride thereof;

(b) an alcohol of formula H(OR 2 ) n OH or R 3 OH;

(c) a reactive alcohol including a tertiary amino group; and

(d) a quaternising agent.

13. The composition according to claim 1 wherein the quaternary ammonium salt additive is prepared by reacting:

(a) a succinic acid or anhydride thereof substituted with a C 20 to C 24 alkyl or alkenyl group;

(b) a polypropylene glycol or butanol;

(c) dimethylaminopropanol; and

(d) a quaternising agent selected from the group consisting of: methyl salicylate, dimethyl oxalate and a hydrocarbyl epoxide in combination with an acid.

14. The composition according to claim 1 wherein the diesel fuel composition further comprises one or more detergents selected from the group consisting of:

a 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.

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

16. The method according to claim 2 wherein the engine is a modern diesel engine having a high pressure fuel system.

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 2 which prevents or reduces the occurrence of deposits in the diesel engine, 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; and

an increase in maintenance intervals.

22. The method according to claim 21 which provides an improvement in performance in modern diesel engines having a high pressure fuel system 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.