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A Novel Desulfurization Process for Fuel Oils Based on the Formation and Subsequent Precipitation of S-Alkylsulfonium Salts. 3. Denitrogenation Behavior of Light Oil Feedstocks Yasuhiro Shiraishi, Kenya Tachibana, Takayuki Hirai,* and Isao Komasawa Department of Chemical Science and Engineering, Graduate School of Engineering Science, and Research Center for Solar Energy Chemistry, Osaka University, Toyonaka 560-8531, Japan
The denitrogenation behavior of light oils, when occurring during a novel desulfurization process based on alkylation and a subsequent precipitation method, using the alkylating agents (CH3I and AgBF4), has been investigated. Denitrogenation results, obtained for three model nitrogen compounds (aniline, indole, and carbazole) in a xylene solution, were compared with the results for three light oils, of differing nitrogen, sulfur, and aromatic concentration. The nitrogen compounds in the light oils were found to be N-methylated by reaction with the alkylating agents, such that they were removed as precipitates under moderate conditions. By use of this process, the nitrogen contents of all of the light oils were reduced successfully to less than 20% of the corresponding feed concentration, thus demonstrating that the present process is satisfactory for the simultaneous denitrogenation of light oils combined with desulfurization. Although the denitrogenation of aniline and indole compounds from the light oils proceeded effectively, carbazoles and especially those having a large carbon number of alkyl substituents were difficult to be denitrogenized by the present process. This is because the electron density on the nitrogen atom decreases with increasing carbon number of the alkyl substituents on the molecule of the carbazoles. Introduction There has been much recent interest in the desulfurization and denitrogenation of light oils. This is because the sulfur and nitrogen compounds in light oils are converted by combustion to sulfur and nitrogen oxides (SOx and NOx) and, hence, to a major source of acid rain and air pollution. The removal of these compounds from light oils is carried out industrially presently via the catalytic hydrodesulfurization (HDS) process and by simultaneous hydrodenitrogenation (HDN). The HDN of light oil is rather more difficult to achieve than HDS,1-3 such that the production of light oil, with very low levels of both nitrogen and sulfur, therefore requires inevitably the application of rather severe operating conditions and the use of specially active catalysts. An alternative process, able to be operated under moderate conditions and without the added requirements of hydrogen and catalyst, is therefore strongly required. Resulting from this, a new concept for the desulfurization and simultaneous denitrogenation of light oils, based on UV irradiation and liquid-liquid extraction, has been proposed.4-7 A novel desulfurization process for light oils and catalytic-cracked gasoline, based on the precipitation of S-alkylsulfonium salts, produced by the reaction of sulfur-containing compounds with the alkylating agents (CH3I and AgBF4), has also been investigated.8,9 The sulfur compounds in these oils are S-methylated, by the addition of the alkylating agents, and removed as precipitates under moderate conditions. This process enabled the sulfur contents of the light oils and of the * To whom correspondence should be addressed. E-mail:
[email protected]. Fax: +81-6-6850-6273. Tel: +816-6850-6272.
catalytic-cracked gasoline to be decreased successfully to less than 50 and 30 ppm respectively, which are below the regulatory levels presently applied for both Japan and Europe. The denitrogenation behavior of light oils, when occurring simultaneously with desulfurization during the above process, was studied in the present work. Xylene solutions, containing aniline, indole, and carbazole compounds, were used as model solutions, representing the actual light oil, to clarify the denitrogenation reactivities and the products for the nitrogen compounds. The relative denitrogenation reactivities were correlated with electronic parameters, obtained by use of semiempirical molecular orbital (MO) calculation. The proposed process was then applied to the denitrogenation of three types of actual light oil (commercial light oil, CLO; straight-run light gas oil, LGO; light cycle oil, LCO), each with differing nitrogen, sulfur, and aromatic concentrations, such that the applicability of the present process to the practical refining of the light oils could be examined. Following denitrogenation, gas chromatography-atomic emission detector (GC-AED) analysis was used to determine quantitatively the individual residual nitrogen-containing compounds remaining in the light oils, to reveal the reactivity for each compound. Experimental Section 1. Materials and Analysis. The model nitrogencontaining compounds (aniline, indole, and carbazole) and the actual light oils were the same as those used for the previous studies.4,6-8 Three light oils, CLO (nitrogen content, 80 ppm), LGO (160 ppm), and LCO (243 ppm), produced by the fluid catalytic cracking of vacuum gas oil, were supplied by Cosmo Petroleum Institute and were used as the feedstocks for the
10.1021/ie001090j CCC: $20.00 © 2001 American Chemical Society Published on Web 06/22/2001
Ind. Eng. Chem. Res., Vol. 40, No. 15, 2001 3391 Table 1. Properties and Compositions of the Light Oils
density at 288 K (g/mL) total sulfur (wt %) total nitrogen (ppm) basic nitrogen neutral nitrogen saturated hydrocarbona (vol %) aromatic hydrocarbona,b (vol %) one-ring two-ring
commercial light oil (CLO)
straight-run light gas oil (LGO)
light cycle oil (LCO)
0.8313 0.179 80.4
0.8548 1.434 160.0
80.4 76.2
160.0 75.4
0.8830 0.132 243.1 54.7 188.4 33.7
19.5 4.3
14.9 9.7
a According to the JIS-5S-49-97 normal-phase HPLC method.4 aromatics are trace (573
8.11 (d, J ) 7.81 Hz, 2 H), 8.04 (d, J ) 7.81 Hz, 2 H), 7.79 (t, J ) 7.45 Hz, 2 H), 7.73 (t, J ) 7.81 Hz, 2 H), 3.76 (s, 6 H, N+-CH3)
149.9, 132.9, 131.5, 130.9, 123.7, 118.7, 56.9 (N+-CH3)
363-365
8.28 (d, J ) 7.81 Hz, 2 H), 8.23 (d, J ) 8.06 Hz, 2 H), 7.92 (t, J ) 7.08 Hz, 2 H), 7.77 (t, J ) 7.69 Hz, 2 H), 3.32 (s, 3 H, N-CH3)
140.1, 134.8, 131.9, 131.5, 128.4, 125.1, 35.1 (N-CH3)
oil
see Figure 2a
see Figure 2b
379-380
7.55 (d, J ) 8.06 Hz, 1 H), 7.35 (d, J ) 8.30 Hz, 1 H), 7.17 (t, J ) 7.81 Hz, 1 H), 7.12 (d, J ) 3.17 Hz, 1 H), 7.04 (t, J ) 7.45 Hz, 1 H), 6.42 (d, J ) 2.93 Hz, 1 H), 3.74 (s, 3 H, N-CH3)
29.9, 129.3, 121.9, 121.2, 119.8, 118.0, 110.1, 101.1, 33.0 (N-CH3)
N-methylanilinium tetrafluoroborate 2
carbazole
N,N-dimethylcarbazolium tetrafluoroborate 3
N-methylcarbazole 4
indole
mixture (polymerized material)
5
N-methylindole
Figure 1. (a) Reaction pathway for carbazole with alkylating agents and the structure of (b) indoles and (c) carbazoles present in actual light oils.
and a large number of peaks at 2-3 and 1-1.7 ppm, owing to methyl (HR) and methylene (Hβ) protons, respectively. The 13C NMR spectrum shows a large number of peaks at 48-54 ppm, due to methyl carbons of N+-CH3, and at 110-140 and 10-30 ppm, owing to aromatic and methyl carbons, respectively, on the
aromatic or pyrrole ring. These findings suggest strongly that the precipitate obtained from the indole is not the sole product of the corresponding N,N-dimethylindolium salt11 but contains different types of N-CH3 and N+CH3 groups on its macromolecular (polymeric) structure. When N-methylindole (no. 5) was used as the starting material, a similar polymerized material was obtained. Kong et al.12 and Talbi et al.13 have reported that the hydrogen atoms on the C2 and C3 positions of the indole molecule, as shown in Figure 1b, are deprotonated, electrochemically in a LiClO4-acetonitrile solution, to give rise to a highly polymerized product material. The electron density for the unsaturated bond on the C2 and C3 positions of indole is quite significantly large. The hydrogen atoms on the C2 and C3 positions of indole are therefore likely to be deprotonated relatively easily by the addition of the alkylating agents to form a carbonium ion.14 This initiation reaction probably causes a chain indole polymerization to produce the polymerized material. The IR spectrum for the precipitate, obtained from indole, showed a broad absorption band at 3000-3300 cm-1, and the 1H NMR spectrum showed a weak resonance at 1.7-2.0 ppm, as shown in Figure 2a, which is attributable to N-H groups. These findings indicate that indole molecules, having N-H, N-CH3, and N+-CH3 groups, are also involved in the polymer matrixes, during the polymerization. 1.2. Denitrogenation Reactivity. The variation in the denitrogenation yields for the nitrogen compounds in the xylene solution and in the presence of differing quantities of AgBF4 is shown in Figure 3. The denitrogenations of aniline and indole are shown to proceed
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Figure 3. Variation in the denitrogenation yield for the nitrogencontaining compounds (open keys) from a xylene solution with respect to AgBF4 concentration, together with the desulfurization yield for sulfur-containing compounds (closed keys): reaction time, 11 h; temperature, 303 K; [nitrogen compounds]initial ) [sulfur compounds]initial ) 20 mM; [CH3I]initial ) 400 mM. Table 3. Quantities of Carbazoles in (a) Feed Light Oils and in the Oils Obtained Following Denitrogenation in the Presence of (b) 2-Fold and (c) 10-Fold Molar Excess of AgBF4 Based on the Initial Sulfur Concentrations of the Feed Light Oilsa CLO (ppm) species
a
b
c
LGO (ppm) a
b
LCO (ppm) c
carbazole C1-carbazole 1.2 0.1 0 5.2 0.2 0 C2-carbazole 7.2 1.8 0.3 19.3 1.8 0.1 C3-carbazole 29.6 8.7 4.3 58.1 9.2 2.5 C4-carbazole 42.4 15.5 9.3 77.4 14.0 4.1 total carbazoles 80.4 26.1 13.9 160.0 25.3 6.7
a
b
7.1 2.5 40.2 23.1 40.9 27.6 11.6 11.2
c 0.2 2.9 5.9 3.3
99.8 64.4 12.3
[CH3I]initial ) 20-fold molar excess based on the initial sulfur concentration of the feed light oils. a
Figure 2. (a) 1H NMR and (b) 13C NMR spectra for the precipitate obtained by the reaction of indole with alkylating agents.
very effectively, with almost 100% denitrogenation yields being attained. The denitrogenation reactivity of the nitrogen compounds lies in the order aniline > indole > carbazole, and the yield for carbazole is seen to be significantly lower than that for the other compounds. Because the rate of the presently considered SN2 displacement reaction depends on the concentrations both of the alkylating agents and of the nitrogen compound,14,15 the denitrogenation yields are shown to be increased with increasing AgBF4 concentration. The denitrogenation yield for carbazole, in the presence of a 5-fold molar excess of AgBF4, was, however, only 45%, which is lower than the desulfurization yield obtained for the typical sulfur compounds in light oils, such as benzothiophene and dibenzothiophene.8 As shown in Table 3, actual light oils contain a large quantity of carbazoles, with alkyl substituents of carbon number C0-C4 on the C1-C8 positions of the molecule (Figure 1c). It is, therefore, necessary to explain the denitrogenation reactivity of the alkyl-substituted carbazoles. The reactivity for nitrogen compounds of the present nucleophilic substitution usually depends on the electron density on the nitrogen atom.14,15 For carbazole or N-methylcarbazole, the N-methylation reactions with alkylating agents occur in the direction perpendicular to the plane of the molecule, because the hydrogen atom or the methyl group is substituted on the nitrogen atom,
lying parallel to the molecule. The electron densities on the nitrogen atom, lying perpendicular to the plane of the molecule, was therefore calculated by a semiempirical MO method based on their HOMO orbitals, as shown in Figure 4. The relative values of the electron density for carbazole and N-methylcarbazole were 0.6870 and 0.7166 eV, respectively, thus suggesting that Nmethylcarbazole has a higher reactivity for the SN2 displacement reaction than carbazole. This result is consistent with that obtained from the model experiments in the xylene solution, thus indicating that the carbazole compounds, with lower electron density on a nitrogen atom, are more difficult to be denitrogenized, according to the present process. To explain the reactivity of alkyl-substituted carbazoles in detail, the effect of the position of the alkyl substituents, on the electron density of the carbazoles, was then studied. The variation in the electron density of the carbazoles, when a methyl or ethyl group is present on the C1-C4 positions of the molecule, is shown in Figure 5a. In this case, the electron density is decreased by the substitution of both methyl and ethyl groups on all of the positions of the carbazole molecule, with the most marked decrease being observed by substitution on the C4 position. The effect of the structure of the alkyl substituent on the electron density of the carbazoles was then studied. The variation in the electron density, when several alkyl groups of carbon number C3 are present on the carbazole molecule, is
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Figure 4. Calculated energy-level diagram and schematic representation of the electron density on HOMO orbitals for (a) carbazole and (b) N-methylcarbazole.
shown in Figure 5b. The respective electron densities for the carbazoles were calculated, and the average values were summarized. The results show that, when n-propyl groups are present, the electron density values are lower than for isopropyl groups, thus showing that the reactivities of the carbazoles having branched-chain groups are higher than those with straight-chain groups. For the ethylmethyl and trimethyl groups, the electron density is reduced compared with the n-propyl- and isopropylcarbazoles. To obtain a complete picture of the denitrogenation reactivity of the carbazoles, the electron densities for all carbazoles, having alkyl substituents of carbon number C0-C4 on the C1-C8 positions of the carbazole molecule, were calculated. The average values are summarized in Figure 5c and are plotted with respect to the carbon number of the alkyl substituents, m. The results show clearly that the electron density values for the carbazoles decrease with increasing carbon number of the alkyl substituents. The same tendency was also observed, based on the MO calculation, for sulfur compounds in light oils such as benzothiophenes and dibenzothiophenes.8 The above calculation results thus show that, when the present process is applied to the denitrogenation of actual light oils, carbazoles having the large carbon number of alkyl substituents are, therefore, expected to be the most difficult compounds to be denitrogenized. 2. Denitrogenation of Nitrogen-Containing Compounds from Light Oils. 2.1. Denitrogenation of Light Oils. The applicability of the present process to the denitrogenation of actual light oils was then studied. Addition of the alkylating agents to the light oils led to the formation of a dark green viscous liquid at the bottom of the flask, for which elemental analysis showed the precipitates to contain a small amount of nitrogen compounds, as has been described in a previous paper.8 As shown in Figure 6, the 1H NMR spectrum for the precipitates, obtained from the light cycle oil (LCO), showed a weak resonance at 3.30-4.50 ppm, due to methyl protons of N-CH3 and N+-CH3, and the 13C
Figure 5. Variation in the electron density on the nitrogen atom for carbazoles (a) by the substitution of methyl or ethyl group on C1-C4 positions of the carbazole, (b) by the substitution of several alkyl groups of carbon number C3 on the C1-C8 positions of the carbazole, and (c) by the substitution of alkyl groups of carbon number C0-C4 on the C1-C8 positions of the carbazole.
NMR spectrum showed also a weak resonance at 4570 ppm, due to methyl carbons of N+-CH3. The above signals are consistent with those also obtained from the precipitate obtained for the model nitrogen compounds and are shown in Table 2 and Figure 2. The results, therefore, suggest that the resulting precipitates contain
Ind. Eng. Chem. Res., Vol. 40, No. 15, 2001 3395
Figure 7. Variation in the residual percentage of nitrogen in light oils, following denitrogenation in the presence of differing mole ratio quantities of AgBF4 based on the initial nitrogen concentration of the feed light oil: reaction time, 11 h; temperature, 303 K; [CH3I]initial ) 20-fold molar excess for the sulfur content of feed light oils. The numbers (2, 5, and 10) in the figure denote the AgBF4 concentration for the initial sulfur content of the feed light oils. Table 4. Quantities of Indoles in (a) Feed LCO and in the Oils Obtained Following Denitrogenation in the Presence of (b) 2-Fold and (c) 10-Fold Molar Excess of AgBF4 Based on the Initial Sulfur Concentrations of the Feed Light Oilsa LCO (ppm)
Figure 6. (a) 1H NMR and (b) 13C NMR spectra for the precipitates obtained from the denitrogenation of LCO.
nitrogen compounds such as N-methylanilinium, N,Ndimethylpyrrolinium salt, or polymerized materials for indoles, which are removed simultaneously with the sulfur compounds, in accordance with the present process. The variation in the residual percentage of nitrogen in the light oils, following denitrogenation in the presence of various amounts of AgBF4, is shown in Figure 7. The rate of the SN2 displacement reaction here depends on the concentration of both the nitrogencontaining compounds and the alkylating agents,8,9 with the result that the denitrogenation of light oils is accelerated by an increase in the quantity of AgBF4 added. In this way, the nitrogen content of the light oils was thus decreased successfully from 80.4 to 13.9 ppm for CLO, from 160 to 6.7 ppm for LGO, and from 240 to 13.4 ppm for LCO, corresponding to respective AgBF4 concentrations of 98-, 318-, and 20-fold molar excess quantities based on the initial nitrogen concentration of the respective feed light oil. These results show that the present process, when applied to the desulfurization of light oils in the presence of a 10-fold molar excess amount of AgBF4 based on the initial sulfur concentration of the feed light oil, is able to produce a simultaneous decrease in both the sulfur and nitrogen contents to 2% and 17%, respectively, for CLO, 0.3% and 4% for LGO, and 8% and 14% for LCO, based on the respective feed concentrations.8 These results suggest that the
species
a
b
c
indole C1-indole C2-indole C3-indole C4-indole total indoles
3.2 14.8 28.1 27.5 15.0 88.6
0 1.1 6.7 8.2 12.1 28.1
0 0 0 0.4 0.3 0.7
a [CH I] 3 initial ) 20-fold molar excess based on the initial sulfur concentration of the feed LCO.
present process is thus effective for both the desulfurization and simultaneous denitrogenation of light oils. The denitrogenation reactivity for the light oils, as shown in Figure 7, lies in the order LCO > LGO > CLO. This result differs from that obtained in the photochemical denitrogenation of light oils with an order of CLO > LGO > LCO7 and also in the desulfurization of light oils, according to the present process, with an order being LGO > CLO > LCO.8 2.2. Denitrogenation Reactivity of NitrogenContaining Compounds in Light Oils. The variation in the composition of the individual nitrogen-containing compounds in light oils, following denitrogenation, is shown in Tables 3-5. The denitrogenation of anilines and indoles from LCO proceeds effectively, with a ranking order of anilines > indoles > carbazoles. This agrees reasonably well with that obtained for the model compounds in a xylene solution, as shown in Figure 3, and is also the same as that obtained for the HDN3 and photochemical denitrogenation processes.7 The high denitrogenation yield for LCO, as shown in Figure 7, is, therefore, due to the presence of highly reactive nitrogen compounds such as anilines and indoles. The carbazoles are, however, still the most difficult compounds to be denitrogenized by the present process. Figure 8 shows the variation in the residual percentage of carbazoles in all three light oils, following denitro-
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Table 5. Quantities of Anilines in (a) Feed LCO and in the Oils Obtained Following Denitrogenation in the Presence of (b) 2-Fold and (c) 10-Fold Molar Excess of AgBF4 Based on the Initial Sulfur Concentrations of the Feed LCOa LCO (ppm) species
a
b
c
aniline C1-aniline C2-aniline C3-aniline C4-aniline total anilines
0.9 8.1 19.6 7.5 18.6 54.7
0 0 0.8 2.2 5.1 8.1
0 0 0 0 0.4 0.4
a [CH I] 3 initial ) 20-fold molar excess based on the initial sulfur concentration of the feed LCO.
Figure 9. Variation in reactivity ratio, η, for the nitrogencontaining model compounds in a xylene solution and in the presence of aromatic and sulfur-containing compounds. The value for η is defined as the ratio of the obtained denitrogenation yield for nitrogen compounds, both in the presence and in the absence of the hydrocarbon and sulfur compounds as defined in eq 1: reaction time, 11 h; temperature, 303 K; [nitrogen compounds]initial ) 20 mM; [aromatics or sulfur compounds]initial ) 200 mM; [AgBF4]initial ) 10 mM for experiments for aniline and indole and 100 mM for carbazole, respectively; [CH3I]initial ) 200 mM.
to the xylene solution together with 20 mM of each nitrogen compound, for the experiments. The results are summarized in Figure 9, where the reactivity ratio, η,8,9 for each nitrogen compound is defined as
Figure 8. Residual percentage of alkyl-substituted carbazoles in the light oils, following denitrogenation in the presence of 2-fold (open keys) and 10-fold (closed keys) molar excess AgBF4 based on the initial sulfur concentration of the feed light oils, as a function of the carbon number of the alkyl substituents on carbazole, m. The initial amount for each alkyl-substituted carbazole in the light oils is set as 100%. The denitrogenation conditions were identical to those in Figure 7.
genation, for the cases of both 2- and 5-fold excess amounts of AgBF4, based on the initial sulfur content of the feed light oils. The residual percentages of the carbazoles for all feedstocks are seen to increase with an increasing carbon number of the alkyl substituents. This result is consistent with that found by MO calculation, as shown in Figure 5c, thus indicating that, in the proposed process, the highly substituted carbazoles are the most difficult compounds to be denitrogenized, owing to the low electron density on the nitrogen atom. This tendency was also found in previous studies relating to the photochemical denitrogenation of light oils.7 As shown in Table 1, the actual light oils contain high proportions of aromatic hydrocarbons and sulfurcontaining compounds. It is, therefore, necessary to clarify the effect of these compounds on the denitrogenation of light oils and thus to obtain a complete picture of the present process. The effect of these compounds on the denitrogenation in a xylene solution of aniline, indole, and carbazole was, therefore, studied also. In this case, tetralin (tetrahydronaphthalene), naphthalene, benzothiophene, and dibenzothiophene were used as model components, representing the oneand two-ring aromatics and sulfur compounds present in light oils.8 The 200 mM of each compound was added
η ) [denitrogenation yield in the presence of hydrocarbon or sulfur compound]/ [denitrogenation yield in the absence of hydrocarbon or sulfur compound] (1) The values of the reactivity ratio for aniline and indole are reduced only very slightly by the presence of both aromatics and sulfur compounds. The reactivity ratio for carbazole is, however, seen to be decreased significantly by the presence of all four model compounds. This decrease in the denitrogenation yield results because the methylation of the aromatic and sulfur compounds occurs competitively with the N-methylation reaction.8 A much greater decrease in the reactivity ratio for carbazole results in the presence of sulfur compounds than in the presence of aromatics. This is because the S-methylation reaction occurs more easily than the aromatic methylation reaction.8 These results suggest that the present process, therefore, has a much greater difficulty in the denitrogenation of the carbazoles in light oils having high concentrations of aromatic hydrocarbon and sulfur compounds. Conclusion Denitrogenation, when occurring during a novel desulfurization process for light oils based on alkylation and a subsequent precipitation method using alkylating agents (CH3I and AgBF4), has been investigated, and the following results were obtained. (1) Aniline and carbazole, when dissolved in a xylene solution, are methylated by the addition of the alkylating agents to be removed as the corresponding Nmethylanilinium and N,N-dimethylcarbazolium tetrafluoroborates. The precipitate obtained from indole, however, is not the sole product; polymer materials
Ind. Eng. Chem. Res., Vol. 40, No. 15, 2001 3397
formed on the pyrrole ring. The denitrogenation yield, obtained from a xylene solution for these compounds, lies in the order aniline > indole > carbazole. (2) The nitrogen-containing compounds in light oils are removed simultaneously as precipitates with the sulfur compounds, such that the nitrogen contents of the light oils, in the presence of 10-fold molar excess amount of AgBF4 based on the initial sulfur content of the feed light oil, are decreased to less than 20% of the feed concentration. Light cycle oil, containing large amount of anilines and indoles, are denitrogenized more easily than the other light oils. (3) The percentages of the residual carbazoles in light oils, following denitrogenation, increase with increasing carbon number of the alkyl substituent on the carbazole molecule. This is because the electron density of the nitrogen atom, lying perpendicular to the molecules, for carbazoles decreases with increasing carbon number of alkyl substituents on carbazole, as calculated by semiempirical MO methodology. (4) The denitrogenation of aniline and indole from a xylene solution proceeds effectively even in the presence of additional aromatics and sulfur compounds. However, the denitrogenation yield for carbazole is decreased significantly by the presence of these compounds. This results because of the methylation of the aromatics and sulfur compounds with the alkylating agents occurring competitively with the N-methylation reaction for carbazole. Acknowledgment The authors acknowledge the members of the Idemitsu Kosan Co. Ltd. and the Kinuura Research Center for the JGC Corp. for their help in the analyses of the total nitrogen concentration of light oils, and Mr. Yasuto Taki for experimental assistance. The authors are grateful for financial support by a Grant-in-Aid for Scientific Research (Nos. 09555237 and 12555215) from the Ministry of Education, Science, Sports and Culture, Japan, and by the Showa Shell Sekiyu Foundation for Promotion of Environmental Research. Y.S. is grateful to the Research Fellowship of the Japan Society for the Promotion of Science (JSPS) for Young Scientists and to the British Council Grants for JSPS Fellows visiting the United Kingdom.
Literature Cited (1) Gutberlet, L. C.; Bertolacini, R. J. Inhibition of Hydrodesulfurization by Nitrogen Compounds. Ind. Eng. Chem. Process Des. Dev. 1984, 23, 179. (2) Dong, D.; Jeong, S.; Massoth, F. E. Effect of Nitrogen Compounds on Deactivation of Hydrotreating Catalysts by Coke. Catal. Today 1997, 37, 267. (3) Katzer, J. R.; Sivasubramanian, R. Process and Catalyst Need for Hydrodenitrogenation. Catal. Rev.-Sci. Eng. 1979, 20, 155. (4) Shiraishi, Y.; Hirai, T.; Komasawa, I. A Deep Desulfurization Process for Light Oil by Photochemical Reaction in an Organic Two-Phase Liquid-Liquid Extraction System. Ind. Eng. Chem. Res. 1998, 37, 203. (5) Shiraishi, Y.; Hirai, T.; Komasawa, I. Identification of Desulfurization Products in the Photochemical Desulfurization Process for Benzothiophenes and Dibenzothiophenes from Light Oil by Photochemical Reaction Using an Organic Two-Phase Extraction System. Ind. Eng. Chem. Res. 1999, 38, 3300. (6) Shiraishi, Y.; Hirai, T.; Komasawa, I. Photochemical Desulfurization for Light Cycle Oil Using an Organic Two-Phase Extraction System. Solv. Extr. Res. Dev. Jpn. 2000, 7, 11. (7) Shiraishi, Y.; Hirai, T.; Komasawa, I. Photochemical Denitrogenation Process for Light Oils Effected by a Combination of UV Irradiation and Liquid-Liquid Extraction. Ind. Eng. Chem. Res. 2000, 39, 2826. (8) Shiraishi, Y.; Taki, Y.; Hirai, T.; Komasawa, I. A Novel Desulfurization Process for Fuel Oils Based on Formation and Subsequent Precipitation of S-Alkylsulfonium Salts. 1. Light Oil Feedstocks. Ind. Eng. Chem. Res. 2001, 40, 1213. (9) Shiraishi, Y.; Tachibana, K.; Taki, Y.; Hirai, T.; Komasawa, I. A Novel Desulfurization Process for Fuel Oils Based on Formation and Subsequent Precipitation of S-Alkylsulfonium Salts. 2. Catalytic-Cracked Gasoline. Ind. Eng. Chem. Res. 2001, 40, 1225. (10) Naudin, E.; Goue´rec, P.; Be´langer, D. Electrochemical Preparation and Characterization in Non-Aqueous Electrolyte of Polyaniline Electrochemically Prepared from an Anilinium Salt. J. Electroanal. Chem. 1998, 459, 1. (11) Donovan, P. F.; Conley, D. A. Some Organic Tetrafluoroborates. J. Chem. Eng. Data 1966, 11, 614. (12) Kong, S. W.; Choi, K. M.; Kim, K. H. The Properties of Electrochemically Prepared Polyindole Perchlorate. J. Phys. Chem. Solids 1992, 53, 657. (13) Talbi, H.; Maarouf, E. B.; Humbert, B.; Alnot, M.; Ehrhardt, J. J.; Ghanabaja, J.; Billaud, D. Spectroscopic Studies of Electrochemically Doped Polyindole. J. Chem. Phys. Solids 1996, 57, 1145. (14) Lowe, P. A. In The Chemistry of the Sulphonium Group Part 1; Stirling, C. J. M., Ed.; John Wiley & Sons: New York, 1981; Chapter 11. (15) Trost, B. M.; Melvin, L. S., Jr. Sulfur Ylides; Academic Press: New York, 1975; Chapter 2.
Nomenclature n ) carbon number of alkyl substituents on indole m ) carbon number of alkyl substituents on carbazole η ) reactivity ratio of nitrogen-containing compounds defined by eq 1
Received for review December 18, 2000 Revised manuscript received April 25, 2001 Accepted May 8, 2001 IE001090J
