# Extraction of Pyrrole from Its Mixture with n-Hexadecane Using Protic Ionic Liquids

## TL;DR

This paper explores using protic ionic liquids to efficiently extract pyrrole, a nitrogen compound, from a fuel mixture, offering a cheaper and less energy-intensive alternative to traditional methods.

## Contribution

The study introduces and validates the use of specific protic ionic liquids for nitrogen compound extraction, supported by COSMO-RS predictions and NRTL model correlation.

## Key findings

- TEA-TSA showed superior selectivity and distribution ratio for pyrrole extraction compared to TEA-SA and TEA-BZ.
- All PILs exhibited strong hydrogen bonding with pyrrole, indicated by negative excess enthalpy values.
- COSMO-RS predictions aligned well with experimental results, confirming PILs' effectiveness in nitrogen compound removal.

## Abstract

The removal of nitrogen compounds from fuel via the conventional method, which is hydrodenitrogenation, is costly and involves catalysts and energy-intensive conditions (600 K and 300 atm). Recently, ionic liquids (ILs) have emerged as a promising alternative solvent for the denitrogenation of fuel oil. However, certain ILs are expensive and challenging to synthesize, prompting the exploration of protic ionic liquid (PIL) substitutes, which offer similar advantages to ILs. This study utilized the conductor-like screening model for real solvents (COSMO-RS) to predict the phase equilibria for three PILs—triethylammonium p-toluenesulfonate (TEA-TSA), triethylammonium salicylate (TEA-SA) and triethylammonium benzoate (TEA-BZ)—which were subsequently validated through experimental investigations. Liquid–liquid extraction experiments were conducted at 298 K and 1 atm, with pyrrole (serving as the model nitrogen compound) concentrations in n-hexadecane (representing the model fuel) ranging from 10 to 50 wt%. Additionally, the NRTL model effectively correlated the experimental tie lines. The obtained data indicated that TEA-TSA exhibited superior selectivity and distribution ratio compared to TEA-SA and TEA-BZ. All the ternary systems tested displayed positive slopes, suggesting a higher affinity of nitrogen compounds for the PIL. Supporting this observation, interaction energy (ΔE) and excess enthalpy (HE) were employed. The predicted outcomes revealed that TEA-TSA had high ΔE, and all PILs exhibited negative values of HE. The HE calculation underscored the significance of strong hydrogen bond interactions between pyrrole and the PIL for successful extraction.