Ind. Eng. Chem. Res. 2008, 47, 8801–8807
8801
Selective Extraction and Identification of Neutral Nitrogen Compounds Contained in Straight-Run Diesel Feed Using Chloride Based Ionic Liquid Li-Li Xie,†,‡ Alain Favre-Reguillon,*,†,§ Stephane Pellet-Rostaing,† Xu-Xu Wang,‡ Xianzhi Fu,‡ Julien Estager,| Michel Vrinat,⊥ and Marc Lemaire*,† ICBMS, Institut de Chimie et Biochimie Mole´culaires et Supramole´culaires, Laboratoire de Catalyse et Synthe`se Organique, 43 bouleVard du 11 noVembre 1918, Villeurbanne, F-69622, France, UMR5246, UniVersite´ Lyon 1., Laboratoire des Transformations Chimiques et Pharmaceutiques, UMR7084, ConserVatoire National des Arts et Me´tiers, 2 rue Conte´, 75003 Paris, France, Research Institute of Photocatalysis, Fuzhou UniVersity, 523 Gong Ye Road, 350002 Fuzhou, P. R. China, Laboratoire de Chimie Mole´culaire et EnVironnement, EA1651, UniVersite´ de SaVoie, Polytech’SaVoie, 73376 Le Bourget du Lac Cedex, France, IRCELYON, 2 aVenue Albert Einstein, CNRS, UMR5256, UniVersite´ Lyon 1, Villeurbanne, F-69626 France
Extraction of neutral nitrogen-containing compounds (N-compounds) has been investigated with chloride based ionic liquids (ILs) with varying cation classes (imidazolium, pyridinium). ILs were first discriminated by their mutual solubility of ILs and model fuel. Low solubility of 1-butyl-3-methylimidazolinium chloride (BMImCl) and 1-octylpyridinium chloride (OcPyCl) in the model fuel was observed. The ILs were then evaluated using a synthetic solution with dibenzothiophene and carbazole as model compounds, and a high selectivity for N-compounds was found. BMImCl and OcPyCl were then evaluated using straight-run diesel feed, containing 13 400 ppm S and 105 ppm N. An extraction of up to 50% of the N-compounds was obtained in one step whereas the sulfur concentration reduction was only 5%. Both ILs can be regenerated using small amount of water. Extracted compounds could be then extracted using toluene. The major constituents were identified by GC-MS. Analysis of the extracted compounds emphasized the selectivity of the extraction process. Furthermore, refractory sulfur-containing compounds (S-compounds) and polyaromatics were also identified in the extract. 1. Introduction The traditional hydrodesulfurization (HDS) process is confronted with a great challenge and need a substantial improvement for the production of ultralow sulfur diesel. Despite the tremendous improvement of the catalysts activity,1 the inhibiting effect on HDS of trace polar compounds and among them nitrogen compounds (N-compounds)2-5 and poly aromatics6 has received much attention of the refiners because government worldwide are mandating substantial sulfur reduction as illustrated in Figure 1. Furthermore, trace polar compounds found in petroleum distillates can affect the stability of the fuel7,8 and can act as pro-oxides causing fouling and gum formation.9 Identification and quantification of N-compounds in gasoline and diesel fuels by chromatographic separation followed by a selective detection have already been reported in the literature.10,11 However, nitrogen analysis represents a considerable challenge because of the huge hydrocarbon matrix interfering with nitrogen analysis, and therefore, a preconcentration step is needed. N-compounds have been concentrated and separated using different procedures.7,10-13 Nitrogen compounds present in middle distillates fuels are present as two classes of polyaromatic heterocycles, namely five membered heterocycles (neutral, i.e. indole 1 and carbazole 2 derivatives) and six membered heterocycles (basic, i.e. pyridine 3, acridine 4, and quinoline 5 derivatives). * Corresponding authors. E-mail:
[email protected] (A.F.-R.) and
[email protected] (M.L.). † Universite´ Lyon 1. ‡ Fuzhou University. § Conservatoire National des Arts et Me´tiers. | Polytech’Savoie. ⊥ IRCELYON.
Removal of N-compounds from hydrocarbon feed by a noncatalytic process has been described in the literature3 and claimed in patents.14-16 Previously, we have shown that π-acceptor molecules covalently attached on hydrophilic support could be used to selectively remove neutral N-compounds from diesel feed by a charge transfer mechanism,3,17 and we demonstrated that such selective removal of nitrogen compounds from gas oil strongly enhanced the further deep desulfurization.2,3 Our method is efficient, but both the cost of the reagents and the low capacity of the polymer used limit the applicability of such a process. Liquid extraction could be an interesting alternative to process hydrocarbon streams. This extraction process is a wellestablished process that can be carried out at around ambient temperature and pressure. However, the recovery of the solvent from the extract and the feed require additional distillation steps to separate the extraction solvent from both the extract and raffinate phases. In contrast to molecular solvents, ionic liquids (ILs) have several advantages: negligible vapor pressure and thermal stability over a wide range of temperature, even if their stability seems to be overestimated.18 Several groups have already explored the application of ILs to replace conventional solvents. ILs have been used for the separation of aromatic from aliphatic hydrocarbon mixtures,19,20 and for the extraction of refractory sulfur compounds21-25 or basic N-compounds.23,26 Although ILs were shown to be very effective in removing refractory sulfur compounds, their sensitivity to moisture (chloroaluminate), low stability of the anions (hexafluorophosphate), and their cost (fluorinated amides) make large scale application difficult. Recently, we have shown that 1-butyl-3methylimidazolinium chloride (BMImCl) exhibits a high affinity toward neutral N-compounds and these compounds could be
10.1021/ie701704q CCC: $40.75 2008 American Chemical Society Published on Web 04/08/2008
8802 Ind. Eng. Chem. Res., Vol. 47, No. 22, 2008
Figure 1. Sulfur specification for on-board fuel as a function of time (data taken from ref 32). Table 1. Composition and Physical Properties of Arabian Light Straight Run density (at 293 K) (g/L) sulfur (ppm) total nitrogen (ppm) basic nitrogen (ppm) aromatics (wt %)
Figure 2. Nitrogen-containing compounds in petroleum.
selectively extracted from hydrocarbon feed.27 Chloride based ILs are easy to prepare and are used for the synthesis of most of commercially available ILs through methathesis reaction. This work is aimed to investigate a liquid-liquid extraction process using chloride based ILs applied to the extraction, isolation, and identification of neutral polar compounds in straight-run feed. The aim of the study was to evaluate the extraction ability of others chloride based ILs that could be compared to BMImCl.27 This study expands on previous work that demonstrated the effectiveness of preliminary treatment of straightrun fuel before HDS.2,3 After back extraction, gas chromatography coupled to mass spectrometry was used for the identification of the extracted compounds. This method might prove to be useful to study the effect of the nitrogen compounds and polyaromatic hydrocarbon on HDS. 2. Experimental Details 2.1. Reagents. The model fuel was prepared by dissolving 179.2 mg (1.07 mmol) of analytical grade carbazole and 86.3 mg (0.47 mmol) of analytical grade dibenzothiophene (DBT) in 100 g of a mixture of toluene/n-dodecane mixture (80/20 weight). The total nitrogen and sulfur content of the solution was 150 ppmw. The single component solutions were prepared by dissolving an appropriate amount of analytical grade compound in 100 g of a mixture of toluene/n-dodecane mixture (weight/weight). The nitrogen or sulfur content of the solutions was 100 ppmw. Arabian Light Straight Run was kindly provided by IFP (Lyon-France) and was used as feedstock. The relevant properties of this oil are summarized in Table 1.
852 13240 105 125 >1.6
0.65
3.30%
1.97%
>1.6
0.75
contacted with the real feed with a mass ratio of 1/10 (BMImCl/ feed). The total concentration of N and S in the feed were analyzed as a function of time. The equilibrium was reached after 1 h of contact at 60 °C in a batch reactor under continuous stirring. The results are presented in Figure 5. At 60 °C, 48% and 58% of the N-compound were extracted from the straight-run feed by BMImCl and OcPyCl, respectively, in a single contact with an IL/feed ratio of 1/10 by weight. Under those conditions, the sulfur level was decreased by less than 5% even if S-compounds concentration was 125 times higher. BMImCl and OcPyCl showed high N/S selectivity, calculated according to eq 3., higher than 20. The relative low N/S selectivity obtained with real feed compared to synthetic solution could be explained by the presence of a large variety of polyaromatic compounds and polyaromatic heterocycles which could compete the extraction of N-compounds. Furthermore, neutral N-compounds in straight-run feed are alkylated and the substitution could prevent specific interaction with chloride anion. The use of a countercurrent operation will increased the separation capacity. The design of a multistage separation process leading to high denitrogenation levels is possible if the regeneration process of the ILs is efficient. Thus the question of regeneration of ILs have been considered. 3.5. Regeneration of the RTIL. Extracted heterocyclic aromatic compounds and coextracted hydrocarbons have a high
8806 Ind. Eng. Chem. Res., Vol. 47, No. 22, 2008
boiling point and the stripping by distillation cannot be reasonably considered. Eβer et al. showed that high boiling point heteroaromatics extracted from diesel feed could not be easily stripped from 1-butyl-3-methylimidazolinium octylsulfate.22 Alternative re-extraction techniques like scCO2 have been reported,31 but their use of multiton scale are questionable. In our case, the regeneration of water miscible ILs could be done using water.24,27 At the end of the extraction, the phase were separated. Without stirring, pentane was added to the IL phase in order to remove adsorbed feed at the interface. After removing pentane, water was added to the IL (water/IL ratio ) 1/2). Water is miscible with the chloride based ILs used (i.e., BMImCl and OcPyCl) and induced segregation of the extracted compounds. These compounds could be recovered using liquid-liquid extraction with toluene. The organic phase was dried with Na2SO4 and toluene was removed under vacuum. The results are showed in Table 3. In both cases, the results obtained by the BMImCl and OcPyCl were similar. Less than 0.8% of the feed was extracted. It should be noticed that under those conditions, more than 50% of N-compounds and less than 5% of S-compounds were extracted. Thus the S/N concentration ratio of the extracted compounds was close to 1.6 and could be compared to the initial ratio of 125. The selectivity of the process was further emphasized by GC-MS analysis of the extracted compounds. N-compounds present in trace quantities could not be analyzed directly by GC-MS analysis because they are masked by other more-dominant species in the feed. However, our process selectively extracted these N-compounds and thus the GC-MS analysis could be used. The GC-MS chromatogram for the extracted compounds by OcPyCl is shown in Figure 6. The chromatogram emphasized the selectivity of this extraction process. Only few alkanes and diaromatics could be identified. Refractory S-compounds could be identified such as dibenzothiophene and alkyldibenzothiophene. Triaromatics and alkylated triaromatics could also been identified as well as neutral N-compounds and among them alkylated carbazoles. 4. Conclusion Chloride based ILs can be considered as a novel medium for liquid/liquid extraction of neutral N-compounds from hydrocarbon feed. Since the chloride based ILs studied showed a very low solubility in the hydrocarbon feed, the loss of the ILs in the rafinate is low. Among the ILs evaluated, BMImCl and OcPyCl tested at 60 °C are the most suitable for the extraction of neutral N-compounds with a high selectivity toward Scompounds. The origin of the selectivity have not yet been elucidated but may be due to hydrogen bounding between the chloride anion (with nonbonding electrons) in combination with the imidazolium or pyridinium cation. This study demonstrates that neutral nitrogen-containing compounds could be selectively removed from straight-run diesel feed using chloride based ILs as a solvent. Furthermore, this extraction process can be extended to the isolation and identification of N-compounds in diesel fuel. Because many performance characteristics of the fuel are related to the presence of trace N-compounds in the fuel, this method provides an important tool for determining the species that could have an active role in many fuel performance aspects, such as storage and thermal stability. Efforts to use the extraction process to HDS and to identify refractory and N-compounds in diesel fuel are ongoing.
Acknowledgment The authors would like to thanks the Ministe`re des Affaires Etrange`res, Ambassade de France en Chine, that partially funded this research through a Ph.D. grant to L.-L.X. Note Added after ASAP Publication: This paper was published on the Web April 8, 2008 with the title “Selective Removal of Nitrogen-Containing Compounds from StraightRun Diesel Feed using 1-Alkyl-3-methylimidazolinium Chloride”. It has been revised, including the title, and the current version was reposted to the Web October 18, 2008. Literature Cited (1) Eijsbouts, S.; Mayo, S. W.; Fujita, K. Unsupported transition metal sulfide catalysts: From fundamentals to industrial application. Appl. Catal. A: Gen. 2007, 322, 58–66. (2) Koltai, T.; Macaud, M.; Guevara, A.; Schulz, E.; Lemaire, M.; Bacaud, R.; Vrinat, M. Comparative inhibiting effect of polycondensed aromatics and nitrogen compounds on the hydrodesulfurization of alkyldibenzothiophenes. Appl. Catal., A 2002, 231, 253–261. (3) Macaud, M.; Sevignon, M.; Favre-Reguillon, A.; Lemaire, M.; Schulz, E.; Vrinat, M. Novel Methodology toward Deep Desulfurization of Diesel Feed Based on the Selective Elimination of Nitrogen Compounds. Ind. Eng. Chem. Res. 2004, 43, 7843–7849. (4) Choi, K.-H.; Korai, Y.; Mochida, I.; Ryu, J.-W.; Min, W. Impact of removal extent of nitrogen species in gas oil on its HDS performance: an efficient approach to its ultra deep desulfurization. Appl. Catal., B 2004, 50, 9–16. (5) Yang, H.; Chen, J.; Briker, Y.; Szynkarczuk, R.; Ring, Z. Effect of nitrogen removal from light cycle oil on the hydrodesulphurization of dibenzothiophene, 4-methyldibenzothiophene and 4,6-dimethyldibenzothiophene. Catal. Today 2005, 109, 16–23. (6) Liu, Z.; Zhang, Q.; Zheng, Y.; Chen, J. Effects of Nitrogen and Aromatics on Hydrodesulfurization of Light Cycle Oil Predicted by a System Dynamics Model. Energy Fuels 2008, 22, 860–866. (7) Link, D. D.; Baltrus, J. P.; Zandhuis, P. Isolation and Identification of Nitrogen Species in Jet Fuel and Diesel Fuel. Energy Fuels 2007, 21, 1575–1581. (8) Bauserman, J. W.; Mushrush, G. W.; Hardy, D. R. Organic Nitrogen Compounds and Fuel Instability in Middle Distillate Fuels. Ind. Eng. Chem. Res. 2008, 47, 2867–2875. (9) Loeffler, M. C.; Li, N. C. Role of nitrogen- and sulphur-containing compounds in the ageing of liquid fuels. Fuel 1985, 64, 1047–1053. (10) Mushrush, G. W.; Beal, E. J.; Hardy, D. R.; Hughes, J. M. Nitrogen compound distribution in middle distillate fuels derived from petroleum, oil shale, and tar sand sources. Fuel Process. Technol. 1999, 61, 197–210. (11) Briker, Y.; Ring, Z.; Iacchelli, A.; McLean, N. Miniaturized method for separation and quantification of nitrogen species in petroleum distillates. Fuel 2003, 82, 1621–1631. (12) Wiwel, P.; Knudesen, K.; Zeuthen, P.; Whitehurst, D. Assessing compositional changes of nitrogen compounds during hydrotreatment of typical diesel range gas oil using a novel preconcentration technique coupled with gas chromatography and atomic emission detection. Ind. Eng. Chem. Res. 2000, 39, 533–540. (13) Oliveira, E. C.; Vaz de Campos, M. C.; Rodrigues, M. R. A.; Perez, V. F.; Melecchi, M. I. S.; Vale, M. G. R.; Zini, C. A.; Caramao, E. B. Identification of alkyl carbazoles and alkyl benzocarbazoles in Brazilian petroleum derivatives. J. Chromatogr. A 2006, 1105, 186–190. (14) Min, W. S.; Choi, K., II; Khang, S. Y.; Min, D. S.; Ryu, J. W.; Yoo, K. S.; Kim, J. H. Method for manufacturing cleaner fuels. WO Patent No. 9967345, 1999. (15) Burkhardt, T.; Nicolaos, A.; Diehl, F. Desulfurization, denitrogenation or dearomatization of a hydrocarbon feedstock by adsorption oVer a solid spent sorbent. Eur. Patent No. 1454976, 2004. (16) Greaney, M. A.; Begasse, J. N.; Lee, M. Acid extraction for denitrogenation of middle distillates and lube oil fractions using spent sulfuric acid from alkylation processes. WO Patent No. 2005056726, 2005. (17) Lemaire, M.; Schulz, E.; Sevignon, M.; Macaud, M.; FavreReguillon, A.; Thomas, M.; Loutaty, R. Polymer-supported π-electron acceptors for charge-transfer-based denitrogenation-desulfurization of petroleum fractions. WO Patent No. 0224836, 2002. (18) Scammells, P. J.; Scott, J. L.; Singer, R. D. Ionic Liquids: The Neglected Issues. Aust. J. Chem. 2005, 58, 155–169. (19) Zhang, J.; Huang, C.; Chen, B.; Ren, P.; Lei, Z. Extraction of Aromatic Hydrocarbons from Aromatic/Aliphatic Mixtures Using Chloro-
Ind. Eng. Chem. Res., Vol. 47, No. 22, 2008 8807 aluminate Room-Temperature Ionic Liquids as Extractants. Energy Fuels 2007, 21, 1724–1730. (20) Arce, A.; Earle, M. J.; Rodriguez, H.; Seddon, K. R. Separation of aromatic hydrocarbons from alkanes using the ionic liquid 1-ethyl-3methylimidazolium bis{(trifluoromethyl) sulfonyl}amide. Green Chem. 2007, 9, 70–74. (21) Bo¨esmann, A.; Datsevich, L.; Jess, A.; Lauter, A.; Schmitz, C.; Wasserscheid, P. Deep desulfurization of diesel fuel by extraction with ionic liquids. Chem. Commun. 2001, 2494–2495. (22) Eβer, J.; Wasserscheid, P.; Jess, A. Deep desulfurization of oil refinery streams by extraction with ionic liquids. Green Chem. 2004, 6, 316–322. (23) Zhang, S.; Zhang, Q.; Zhang, Z. C. Extractive Desulfurization and Denitrogenation of Fuels Using Ionic Liquids. Ind. Eng. Chem. Res. 2004, 43, 614–622. (24) Nie, Y.; Li, C.; Sun, A.; Meng, H.; Wang, Z. Extractive Desulfurization of Gasoline Using Imidazolium-Based Phosphoric Ionic Liquids. Energy Fuels 2006, 20, 2083–2087. (25) Holbrey, J. D.; Lopez-Martin, I.; Rothenberg, G.; Seddon, K. R.; Silvero, G.; Zheng, X. Desulfurisation of oils using ionic liquids: selection of cationic and anionic components to enhance extraction efficiency. Green Chem. 2008, 10, 87–92. (26) Matsumoto, M.; Mikami, M.; Kondo, K. Separation of organic nitrogen compounds by supported liquid membranes based on ionic liquids. J. Japan Petrol. Inst. 2006, 49, 256–261.
(27) Xie, L.-L.; Favre-Reguillon, A.; Wang, X.-X.; Fu, X.; PelletRostaing, S.; Toussaint, G.; Geantet, C.; Vrinat, M.; Lemaire, M. Selective extraction of neutral nitrogen compounds found in diesel feed by 1-butyl3-methyl-imidazolium chloride. Green Chem. 2008, 10, 524–531. (28) Huddleston, J. G.; Visser, A. E.; Reichert, W. M.; Willauer, H. D.; Broker, G. A.; Rogers, R. D. Characterization and comparison of hydrophilic and hydrophobic room temperature ionic liquids incorporating the imidazolium cation. Green Chem. 2001, 3, 156–164. (29) Estager, J.; Leveque, J.-M.; Cravotto, G.; Boffa, L.; Bonrath, W.; Draye, M. One-pot and solventless synthesis of ionic liquids under ultrasonic irradiation. Synlett 2007, 2065–2068. (30) Visser, A. E.; Swatloski, R. P.; Reichert, W. M.; Griffin, S. T.; Rogers, R. D. Traditional Extractants in Nontraditional Solvents: Groups 1 and 2 Extraction by Crown Ethers in Room-Temperature Ionic Liquids. Ind. Eng. Chem. Res. 2000, 39, 3596–3604. (31) Planeta, J.; Karasek, P.; Roth, M. Distribution of sulfur-containing aromatics between [hmim][Tf2N] and supercritical CO2: A case study for deep desulfurization of oil refinery streams by extraction with ionic liquids. Green Chem. 2006, 8, 70–77. (32) www.dieselnet.com (accessed May 2007).
ReceiVed for reView December 13, 2007 ReVised manuscript receiVed February 27, 2008 Accepted February 28, 2008 IE701704Q
