Gas hydrate inhibitors

1. A method for inhibiting the formation of gas hydrates in systems comprising mixtures of hydrocarbons and water, said method comprising adding to the mixture a quaternary ammonium ester salt of formula I:

wherein

R 1 (CO)— is the residue of a saturated or unsaturated, linear or branched fatty acid containing from 6 to 24 carbon atoms;

R 2 and R 3 are, independently of each other, a butyl or a pentyl group;

R 4 is linear or branched alkyl group having from 1 to 5 carbon atoms;

X can be R 4 SO 4 − , R 4 O(CO)O − , bicarbonate and carbonate;

a can be 1 or 2;

with the proviso that at least 50% of the aliphatic carboxylic acid contains less than 16 carbon atoms.

2. The method of claim 1 , wherein, in the quaternary ammonium ester salt of formula I, R 1 (CO)— is the residue of a saturated or unsaturated, linear or branched aliphatic carboxylic acid wherein at least 60% by weight of said acid contains less than 16 carbon atoms.

3. The method of claim 1 , wherein, in the quaternary ammonium ester salt of formula I, R 2 and R 3 are the same and are a butyl group.

4. The method of claim 1 , wherein, in the quaternary ammonium ester salt of formula I, R 4 is linear or branched alkyl group having from 2 to 4 carbon atoms.

5. The method of claim 4 , wherein R 4 is linear or branched alkyl group having 2 or 3 carbon atoms.

6. The method of claim 1 , comprising adding to the mixture of hydrocarbons and water the quaternary ammonium ester salt of formula I as a composition comprising between 20 and 95% % by weight of said salt, a solvent and other optional additives.

7. The method of claim 6 , wherein the composition comprises between 45 and 90% by weight of said quaternary ammonium ester salt.

8. The method of claim 1 , comprising adding to the mixture of hydrocarbons and water between 0.1 and 8.0% by weight of quaternary ammonium ester salt of formula I.

9. The method of claim 8 , comprising adding between 0.5 and 5.0% by weight of said quaternary ammonium ester salt.