Effect of Cation Structure in Quinolinium-Based Ionic Liquids on the Solubility in Aromatic Sulfur Compounds or Heptane: Thermodynamic Study on Phase Diagrams.

Marta Królikowska,Marek Królikowski,Urszula Domańska

doi:10.3390/molecules25235687

Abstract

Experimental and theoretical studies on thermodynamic properties of quinolinium-based ionic liquids (ILs) based on bis(trifluoromethylsulfonyl)imide anion (namely N-butyl-quinoloinium bis(trifluoromethylsulfonyl)imide, [BQuin][NTf2], N-hexylquinoloinium bis(trifluoromethyl-sulfonyl)imide, [HQuin][NTf2], and N-octylquinoloinium bis(trifluoromethyl-sulfonyl)imide, [OQuin][NTf2]) with aromatic sulfur compounds and heptane, as a model compound of fuel were examined in order to assess the applicability of the studied ionic liquids for desulfurization of fuels. With this aim, the temperature-composition phase diagrams of 13 binary mixtures composed of organic sulfur compounds (thiophene, benzothiophene, or 2-methylthiophene) or heptane and ionic liquid (IL) were investigated at ambient pressure. A dynamic method was used to determine the (solid–liquid) equilibrium phase diagrams in binary systems over a wide composition range and temperature range from T = 255.15 to 365.15 K up to the fusion temperature of ILs. The immiscibility gap with an upper critical solution temperature (UCST) was observed for each binary system under study. The influence of the alkane chain length of the substituent on the IL cation and of the sulfur compounds (the aromaticity of the solvent) was described. The experimental (solid + liquid) phase equilibrium dataset were successfully correlated using the well-known NRTL equation.

Highlights

It has been well-known for many years that sulfur compounds are the third, after carbon and hydrogen, most common elements in crude oil, the combustion of which causes the emission of sulfur dioxide [1]
One can conclude that the mutual solubility in the investigated systems depends on many factors including the length of the alcohol chain in the ionic liquid cation, the length of the alkyl chain in the aromatic sulfur compound, and the aromaticity of the solvent
It was observed that the quinolinium–based ionic liquids (ILs) tested in this work exhibited high solubility in aromatic sulfur compounds and a very low solubility in heptane

Summary

Introduction

It has been well-known for many years that sulfur compounds are the third, after carbon and hydrogen, most common elements in crude oil, the combustion of which causes the emission of sulfur dioxide [1]. The acid rain, arising from dissolved sulfur compounds in atmosphere and water, cause forest degradation, leading to changes in the ecosystem [1]. It is an important target for many countries to limit the content of sulfur-compounds in the fuel. The process of the desulfurization of fuels is an element of both academic and industrial interest. Restrictions at 10 ppm pose a major technological challenge for science

Objectives

Methods

Results

Conclusion