Reducing naphthenic acidity in petroleum oil comprises providing oil, supplying oil with water towards radiation emitter, decomposing carboxylic acids to liberate carbon dioxide, separating gas, water and oil phases, and recovering oil

Reducing naphthenic acidity in petroleum oil or its fraction comprises providing the oil supply in water that is emulsified/dispersed in the oil; sending the oil with the water towards a device, which is emitting microwave radiation, where the oil is subjected under the microwave radiations in liquid phase; decomposing carboxylic acids (that is responsible for naphthenic acidity) of x320[deg]C to liberate carbon dioxide; separating the formed gas, water and oil phases using separating device; and recovering the oil having reduced amount of naphthenic acids. Reducing naphthenic acidity in petroleum oil or its fraction comprises: providing the oil supply (0.1-99 wt.%) in water that is emulsified/dispersed in the oil, where the oil contain salts and naphthenic acid content is 0.1-10 mg that are measured by total acid number (TAN) measurement using potassium hydroxide/g; sending the oil with the water towards a device, which is emitting microwave radiation, where the oil is subjected under the microwave radiations in liquid phase at 50-350[deg]C under 0.7-4.5 MPa in which the microwave radiations have influencing distance of 1 mm-30 cm of the oil, in the presence of salts, applied temperature and the high permittivity of the water droplets involve absorption of heat preferably heating water in the place of oil, the naphthenic compounds interface between the droplets, and the oil absorb the heat; decomposing carboxylic acids (that is responsible for naphthenic acidity) of x320[deg]C to liberate carbon dioxide; separating the formed gas, water and oil phases using separating device; and recovering the oil having reduced amount of naphthenic acids, where the oil lack any added solid matter and the tendency of the naphthenic acids to migrate towards the emulsified phase to concentrate the acids in a fraction of the oil with the application of the microwave radiation that allows on a fraction of the oil, which is smaller than the total oil. Procédé de réduction de l'acidité naphténique d'huile de pétrole ou de ses fractions, dans lequel ledit procédé comprend les étapes consistant à :a) fournir une alimentation d'huile de pétrole ou de ses fractions comprenant de l'eau émulsifiée/dispersée dans ladite huile, ladite alimentation contenant des sels et ayant une teneur en acides naphténiques mesurée par TAN comprise entre 0,1 et 10 mg de KOH/g d'huile ;b) envoyer ladite alimentation d'huile de pétrole ou de ses fractions avec l'eau émulsifiée/dispersée vers un disposi