Method of preparing naphthenic acids

A method for preparing naphthenic acids consisting in that a petroleum fraction boiling out in the temperature range of 250.degree.-350.degree. C. is oxidized with oxygen taken in the quantity of 0.06-0.065 kg/kg per hour at a temperature of 135.degree.-140.degree. C. in the presence of a catalyst consisting of 30-40 percent by weight of manganese naphthenate and 60-70 percent by weight of potassium naphthenate taken in the quantity of 1.2-2.5 percent of the weight of the starting stock;

• the product of the oxidation reaction, which is a mixture of organic oxygen-containing compounds containing naphthenic and hydroxynaphthenic acids, is diluted with an organic solvent taken in the weight ratio of 1:1-1.5 to the reaction mixture which is inert toward said mixture in order to precipitate hydroxynaphthenic acids which are then separated;
• the solution of organic oxygen-containing compounds in said organic solvent is treated with an aqueous solution of sodium hydroxide at a temperature at which said organic solvent boils to separate the obtained aqueous solution of sodium naphthenates from the solution of unsaponifiable organic oxygen-containing compounds in said organic solvent;
• said aqueous solution of sodium naphthenates is treated with diethyl sulphate at a temperature of 90.degree.-95.degree. C. to obtain ethyl naphthenates from which the fraction of ethyl naphthenates boiling out in the temperature range of 75.degree.-170.degree. C. is separated by rectification in vacuum of 3 mm Hg;
• said isolated fraction is treated with an aqueous solution of sodium hydroxide, and the end product is finally isolated from the obtained aqueous solution of sodium naphthenates by treating with organic acids.