Method of limiting chemical degradation due to nitrogen dioxide contamination

A method of limiting the chemical degradation of a hydrocarbonaceous liquid in service at bulk liquid temperatures of from 60 to 180° C., the degradation being initiated by nitration of the liquid resulting from contamination with nitrogen dioxide in service, comprising:

• preparing, or obtaining a freshly prepared, hydrocarbonaceous liquid suitable for service at bulk liquid temperatures of from 60 to 180° C. and being free of aged components and nitrogen dioxide contamination;
• adding to said hydrocarbonaceous liquid, prior to service at bulk liquid temperatures of from 60 to 180° C., an ionic liquid comprising:
• (i) one or more organic cations each comprising a tetra-alkyl substituted phosphonium cation, and
• (ii) one or more halogen- and boron-free organic anions each comprising an aromatic ring bearing at least two substituent functional groups containing heteroatoms, these functional groups being conjugated with the aromatic ring, and this conjugated system bearing the anionic charge;
• wherein the one or more anions (ii) of the ionic liquid are one or more alkyl-substituted salicylate anions, and wherein the alkyl substituent(s) of each anion are independently selected from alkyl groups containing from 12 to 24 carbon atoms;
• wherein the ionic liquid is added in an amount of 0.1 to 5.0% by weight, per weight of hydrocarbonaceous liquid to thereafter inhibit the nitration of the hydrocarbonaceous liquid in service at bulk liquid temperatures of from 60 to 180° C., in the presence of nitrogen dioxide contamination;
• and
• putting said hydrocarbonaceous liquid into service, wherein the ionic liquid thereby limits the resulting chemical degradation of the liquid.