NAPHTHENIC ACIDS

Naphthenic acids are a mixture of cyclo-paraffins with alkyl side chains ending with a carboxylic group. The low-molecular-weight naphthenic acids (8–12 carbons) are compounds having either a cyclopentane or a cyclohexane ring with a carboxyalkyl side chain. These compounds are normally found in middle distillates such as kerosine and gas oil.

High boiling napthenic acids from the lube oils are monocarboxylic acids, (C_l4-C_l9) with an average of 2.6 rings. Naphthenic acids constitute about 50 wt% of the total acidic compounds in crude oils. Naphthenic-based crudes contain a higher percentage of naphthenic acids. Consequently, it is more economical to isolate these acids from naphthenic-based crudes. The production of naphthenic acids from middle distillates occurs by extraction with 7–10% caustic solution.

The formed sodium salts, which are soluble in the lower aqueous layer, are separated from the hydrocarbon layer and treated with a mineral acid to spring out the acids. The free acids are then dried and distilled.

Using strong caustic solutions for the extraction may create separation problems because naphthenic acid salts are emulsifying agents. Properties of two naphthenic acid types are shown in Table 1.1.

Table 1.1: Properties of two types of naphthenic acids

driers in oil-based paints. Among the diversified uses of naphthenates is the use of aluminum naphthenates as gelling agents for gasoline flame throwers (napalm). Manganese naphthenates are well-known oxidation catalysts.