Naphthenic acid (NA) are present in crude oil and lead to corrosion problems within the oil refineries. The objective of this study is to reduce total acid number (TAN) from NA in an environmentally benign way, suppressing the solid deposition using supercritical water (SCW). The reaction was carried out in an 8.8 mL batch reactor fabricated from Hastelloy C-276 with respective design temperature and pressure of 500 degrees C and 50 MPa. The ability of SCW to reduce TAN was explored at temperatures from 400 to 490 degrees C and water partial pressures (WPPs) from 0 to 45 MPa. Experimental results revealed that TAN removal was 83% at a temperature of 490 degrees C, WPP of 45 MPa and reaction time of 90 min. The TAN removal followed first order kinetics, with Arrhenius parameters of activation energy 66 +/- 4 kJ/mol and a pre-exponential factor (1.4 +/- 0.2) x 10(5) s (1). Solid deposition was drastically reduced at WPP of 45 MPa. These results suggest that SCW is capable of reduction of TAN from NA with no use of catalyst or additives. (C) 2011 Elsevier Ltd. All rights reserved.