Oil acidity reduction by extraction with imidazolium ionic liquids: Experimental, COSMO description and reutilization study

Abstract

Crude oil acidity, usually quantified through total acid number (TAN) and mainly due to carboxylic compounds, is a main problem because causes high corrosion rates and fouling during refining process. Reduction of crude oil TAN by means of ionic liquids (ILs) can be due to neutralization (basic ILs) or to extraction (ILs acting as solvent).In this work, a synthetic crude oil (SC, 150 g/mol, TAN equal to 3.8) was treated with [EMIm][EtSO4], [EMIm][SCN], and [EMIm][Cl] in the temperature range 30–120 °C and IL/crude ratio in the range 0.03–1 g/g. TAN reductions were up to 50% at high temperature and IL/SC ratio.Water washing and reuse of [EMIm][SCN] were studied. No structural changes were detected but IL TAN increased and reduced the extraction efficiency, probably due to the strong interaction between IL and acid that makes washing with water not completely efficient. However, the reduction in extraction efficiency was much faster for IL without any treatment and such reuse is not possible.The COSMO-RS model was used for the ILs characterization through the σ-profile and was successfully included in the simultaneous correlation of all the experimental data. COSMO-Therm was used to study the liquid-liquid equilibria and the predictions of the TAN of the organic phase were in fair agreement with the experimental results. However, COSMO-RS was unable to predict the effect of temperature and described a decrease in TAN reduction as temperature increases.Reuse of IL was also modelled with COSMO-RS and the decrease in extraction efficiency was correctly described related to the IL acid content.