Elsevier

Fluid Phase Equilibria

Volume 395, 15 June 2015, Pages 9-14
Fluid Phase Equilibria

Separation of pyridine from heptane with tricyanomethanide-based ionic liquids

https://doi.org/10.1016/j.fluid.2015.03.027Get rights and content

Highlights

  • The experimental LLE in ternary systems.

  • High solubility of pyridine in [BMIM][TCM], [BMMOR][TCM], and [BMPY][TCM].

  • Extraction of nitrogen-compounds from alkanes.

  • [BMMOR][TCM] may be proposed as entrainer for the denitrogenation of fuel oil.

Abstract

Recent approaches employ three tricyanomethanide-based ionic liquids (ILs) as selective solvents of the extraction of pyridine as a model compound of nitrogen compounds in fuels from heptane at T = 298.15 K and ambient pressure. Experimental data for liquid–liquid phase equilibrium (LLE) were obtained for three ternary systems. The 1-butyl-3-methylimidazolium tricyanomethanide, [BMIM][TCM], 1-butyl-1-methylmorpholinium tricyanomethanide, [BMMOR][TCM] and 1-butyl-1-methylpyridinium tricyanomethanide, [BMPY][TCM] were used due to their immiscibility with gasoline and diesel, negligible vapor pressure, and high selectivity to sulfur- and nitrogen-containing compounds. All of proposed ILs showed similar excellent selectivity with the best Smax = 609.3 for and similar high distribution ratio with βmax = 9.2 for [BMMOR][TCM] in the extraction of pyridine from heptane and much higher to what is currently published for different ILs. Chromatography analysis showed that IL was not present in the heptane layer. This eliminate the process of the separation of the solvent from the raffinate layer. The data obtained have been correlated with the non-random two liquid NRTL model. The experimental tie-lines and the phase composition in mole fraction in the ternary systems were calculated with an average root mean square deviation (RMSD) of 0.004.

Introduction

The emission of sulfur from petrol and diesel oils, which is linked to acid rain phenomena, plays a crucial role in pollution problems of large conglomerates. Commercially, the hydrodesulfurization (HDS) processes are the established method used in some industrial technologies to remove organic sulfur compounds from fuels. However, the aromatic sulfur compounds including thiophene, benzothiophene, methyldibenzothiophenes, 4,6-dibenzothiophenethiols, thioethers, and disulfides are more difficult to convert over HDS catalysts. Therefore, the liquid–liquid extraction (LLE) is proposed for deep desulfurization and denitrogenation by using the extractive solvents with high selectivity of absorption of sulfur and nitrogen compounds at high capacity without affecting the olefin contents. Extraction desulfurization and denitrogenation with ionic liquids (ILs) have the potential for alternative and future complementary technology for deep desulfurization [1], [2], [3], [4]. These new organic solvents are already very well known as a high selective entrainers in many processes. From the beginning the popular 1-ethyl-3-methyl imidazolium tetrafluoroborate, [EMIM][BF4] or 1-butyl-3-methylimidazolium hexafluorophosphate, [BMIM][PF6] were proposed for desulfurization with average removal of sulfur compounds on the level of 13 (wt%) and nitrogen compounds 25 (wt%) [1]. For the denitrogenation of diesel fuel the 1-butyl-3-methylimidazolium sulfate, [BMIM][HSO4], or 1-butyl-3-methylimidazolium methylsulfate, [BMIM][CH3SO4], or 1-ethyl-3-methyl imidazolium ethylsulfate [EMIM][EtSO4] were proposed with high selectivity [2]. The interaction with a diesel model feed with 41 ILs and the extraction possibility of thiophene, or benzothiophene and nitrogen containing heteroaromatic compounds was recently presented in an open literature [4]. The extraction level about 70–86 (wt% for sulfur compounds) and 99 (wt% for nitrogen compounds) was found [4]. The best ILs used in this process were pyridinium and imidazolium-based ILs with dicyanoamide anion, [N(CN)2], or tricyanomethanide, [C(CN)3], [TCM] anion, or thiocyanate, [SCN] anion [4].

The application of many ILs as LLE solvents for petrol desulfurization and/or denitrogenation has already been reported during the last decade [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17]. Two ILs, namely 1-hexyl-3,5-dimethylpyridinium bis(trifluoromethylsulfonyl) imide, [HMMPY][NTf2] and 1-heptyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl) imide, [HMMIM][NTf2] were found to show high extraction selectivity of pyridine from model fuel on the level of 70 and 50 (wt%), respectively [5]. The LLE data for the quaternary mixture of {IL + thiophene + pyridine + pentane} were shown with 1-ethyl-3-methylimidazolium acetate, or ethylsulfate or methylsulfonate with average selectivity and distribution ratio [7]. Acidic ILs were used to desulfurization and denitrogenation of model fuel (hexane, or octane) and the removal of pyridine after 6-stage extraction at T = 298.15 K with 1-butyl-3-methylimidazolium chloride/zinc dichloride, [BMIM]Cl/ZnCl2 was 97.8 (wt%) [17].

The effect of cation and anion of 21 ILs on the desulfurization of model fuel was observed in liquid–liquid phase equilibrium data at T = 298.15 K [18]. The ILs were chosen after many years of experimental work with different ILs from the literature and in our laboratory [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18]. The best extraction of sulfur-compounds was obtained with 1-butyl-1-methylmorpholinium tricyanomethanide, [BMMOR][TCM], 1-buty-3-methylimidazolium tricyanomethanide, [BMIM][TCM] and 1-butyl-1-methylpyridinium tricyanomethanide, [BMPY][TCM] with the selectivity of extraction of thiophene S = 159.7, S = 85.0 and S = 86.3, respectively [18].

The 1-alkylpyrrolidinium-based ILs with different anions have been recently studied in our laboratory in ternary LLE {IL + thiophene + heptane) at T = 298.15 K [13]. The highest selectivity (Smax = 133.4) with high solute distribution ratio (β = 3.47) was found for 1-butyl-1-methylpyrrolidinium tricyanomethanide [BMPYR][TCM] [13].

With these results in the current work we continue our systematic study with focus on denitrogenation of fuels with the best tricyanomethanide-based ILs: [BMIM][TCM], [BMMOR][TCM], and [BMPY][TCM]. We report experimental ternary LLE data for three ILs, which we expected to show high selectivity for the extraction of pyridine from heptane. The extraction selectivity and the solute distribution ratio were determined and discussed from the experimental work.

Section snippets

Experimental

The ILs studied: [BMIM][TCM], [BMMOR][TCM] (CAS No. 1620828-20-7), and [BMPY][TCM] were purchased from IoLiTec (the structure, name, abbreviation and molecular mass are presented in Table 1 [19], [20]) and all solvents used from Sigma–Aldrich (the origins of the chemicals, CAS numbers, purity, water content and densities are listed in Table 1S in the Supplementary material). The samples of ILs were dried for 24 h at 300 K under reduced pressure to remove volatile impurities and trace amounts of

Results and discussion

The extractive denitrogenation performance results are listed in Table 3. The equilibrium compositions of the experimental tie-line ends in three ternary systems {IL (1) + pyridine (2) + heptane (3)} at T = 298.15 K and ambient pressure analyzed by gas chromatography showed that the IL almost has not been found in the raffinate (heptane) layer after LLE experiment. This achievement is very important from an industrial point of view. The “entrainer lost” should not be expected. In the binary {IL (1) + 

Data correlation

The tie-lines of LLE data measured in this study were correlated using the non-random liquid equation, NRTL [21]. The equations and algorithms used for the calculation of the compositions in both phases followed the method described by Walas [22]. The objective function F(P), was used to minimize the difference between the experimental and calculated compositions:F(P)=Σi=1n[x2Iexpx2Icalc(PT)]2+[x3Iexpx3Icalc(PT)]2+[x2IIexpx2IIcalc(PT)]2+[x3IIexpx3IIcalc(PT)]2where P is the set of parameters

Conclusions

The liquid–liquid phase equilibrium data were measured in this study for the extraction of pyridine from heptane exploring three ILs at temperature T = 298.15 K at ambient pressure using a GC for the composition analysis. As a conclusion from all the data presented in this work, it is clear that all ILs showed very optimistic results for the extraction of N-compounds from fuel oils. Thus [BMMOR][TCM] presents the best denitrogenation result and is selected as a representative IL that can be

Acknowledgement

Author E.V. Lukoshko wish to thank for the project MPD 2010/4 “Towards Advanced Functional Materials and Novel Devices-Joint UW and WUT International PhD Programme”.

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