Ionic liquid-mediated removal of naphthenic acids from crude oil: Process modelling and optimization

Abstract

The present study demonstrated the efficiency of ionic liquid in the removal of naphthenic acids from crude oil. The crude oil sample was obtained from Belema oil field in Southern Nigeria while tetramethyl ammonium hydroxide pentahydrate (TMAH) ionic liquid was commercially obtained. Liquid-liquid extraction was carried out and the reaction conditions were modelled and optimized using Box-Behnken design of the response surface methodology. Ionic liquid concentration (w/v%), reaction temperature (°C), and reaction time (mins) were selected as the factors while extraction efficiency (%) was selected as the response. The results of the study showed that the highest extraction efficiency of 96.67 % was achieved under reaction conditions of 3 w/v% ionic liquid concentration, 50 °C reaction temperature, and 45 mins reaction time. Owing to R2, adjusted R2, and predicted R2 values generally > 0.90, the model accurately described the deacidification reaction. Optimization results indicated that removal efficiency can reach over 96 % at 2.82 w/v% ionic liquid concentration, 48 °C reaction temperature, and 45 mins reaction time. The characterization of the original and deacidified oils using GC–MS showed reduced concentration of acidic species in the latter. Also, FT-IR of the ionic liquid showed minimal or no variations in functional groups before and after extraction, highlighting a possibility for regeneration of the ionic liquid. The findings of the study showed the use of ionic liquids as green alternatives in the removal of acidic species from crude oil.

Keywords

• Crude oil
• Ionic liquid
• Naphthenic acid
• Response surface methodology
• Total acid number