Non-catalytic reduction of total acid number (TAN) of naphthenic acids (NAs) using supercritical methanol

Naphthenic acid (NA) present in crude oil leads to corrosion problems within oil refineries. The objective of this study is to reduce total acid number (TAN) from NA using a catalyst-free supercritical methanol (SC-MeOH), a process novel in this area. 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 °C and 50 MPa. The ability of SC-MeOH to reduce TAN was explored at temperatures from 300 to 350 °C and methanol partial pressure (MPP) of 10 MPa. Experimental results revealed that TAN removal was 99.77% at a temperature of 350 °C, MPP of 10 MPa and reaction time of 60 min. The TAN removal followed first order kinetics, with Arrhenius parameters of activation energy 5.78 kcal/ mol and a pre-exponential factor 1.56 s− 1. These results suggest that SC-MeOH is capable of reducing TAN from NA with no use of catalyst or additives.

Graphical abstractSupercritical methanol (SC-MeOH) is suitable for reducing total acid number (TAN) of naphthenic acids (NAs) within a short reaction time. (Symbols: □, 300 °C; ○, 325 °C; ∆, 350 °C)Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Supercritical methanol is capable of reducing TAN of naphthenic acids. ► This process benefits from the absence of catalyst and short reaction time. ► TAN reduction of 96.87% TAN is possible at a temperature of 350 °C. ► Overall naphthenic acid removal kinetics follows first order.