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A Novel Desulfurization Process for Fuel Oils Based on the Formation and Subsequent Precipitation of S-Alkylsulfonium Salts. 4. Desulfurization and Simultaneous Denitrogenation of Vacuum Gas Oil Yasuhiro Shiraishi, 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 simultaneous removal of sulfur- and nitrogen-containing compounds from vacuum gas oil (VGO), based on alkylation and a subsequent precipitation method using alkylating agents (CH3I and AgBF4), has been investigated. Desulfurization and denitrogenation reactivities for various compounds in VGO have been studied by means of field ionization-mass spectrometry (FIMS) and gas chromatography-atomic emission detection (GC-AED), respectively. The sulfur and nitrogen compounds in the VGO were found to be methylated by the addition of the alkylating agents under moderate conditions and were removed successfully as the precipitates of the corresponding S-methylsulfonium and N,N-dimethylcarbazolium tetrafluoroborates. By this means, the sulfur and nitrogen concentrations of the VGO were reduced simultaneously to less than 0.1% and 7.0% of the corresponding feed values, in the presence of a 20-fold molar excess of CH3I and a 10-fold molar excess of AgBF4, respectively, based on the initial sulfur concentration of the feed VGO. The FI-MS and GC-AED analyses revealed that the tetrahydrodibenzothiophenes and carbazoles, especially those having a large carbon number of alkyl substituents, are the most difficult compounds to be removed by the process. Introduction Vacuum gas oil (VGO), one of the heavier petroleum feedstocks, is produced by vacuum distillation of atmospheric residue and is utilized as a main source for the production of catalytic-cracked gasoline and light cycle oil (LCO).1,2 Because VGO contains large amounts of sulfur- and nitrogen-containing compounds, subsequent desulfurization and denitrogenation treatments are necessary in order to protect the environment against sulfur and nitrogen oxide emissions (SOx and NOx). The removal of the sulfur and nitrogen species from VGO is presently carried out via the catalytic hydrodesulfurization (HDS) and simultaneous hydrodenitrogenation (HDN) processes. Both sets of species consist of higher molecular weight compounds than those present in lighter feedstocks such as light oils and gasolines, and their removal is thus significantly more difficult.3-5 Further refining for VGO therefore requires the application of rather severe conditions and the use of specially active catalysts. Resulting from this, the new concept of the desulfurization and simultaneous denitrogenation of VGO, based on a combination of UV irradiation and liquid-liquid extraction, has been investigated and reported.6 Another novel desulfurization and simultaneous denitrogenation process for light oils and catalytic-cracked gasoline has also been investigated, based on alkylation using alkylating agents (CH3I and AgBF4) and subsequent precipitation.7-9 The sulfur and nitrogen compounds in these oils were found to be methylated, by the addition of the alkylating agents, and removed as * To whom correspondence should be addressed. E-mail:
[email protected]. Fax: +81-6-6850-6273. Tel: +816-6850-6272.
the precipitates of the corresponding S- and N-methylated tetrafluoroborates. In this work, the above alkylation and precipitation process has now been applied to the desulfurization and simultaneous denitrogenation of VGO. To examine the applicability of the present process, the desulfurization and denitrogenation efficiencies, obtained for the VGO, have been compared with the results for light oil feedstocks. The relative reactivities for the individual sulfur and nitrogen compounds in the VGO have been examined in detail by means of field ionization-mass spectrometry (FI-MS) and gas chromatography-atomic emission detection (GC-AED) analyses, respectively. The reactivities, for the respective compounds, were then compared with the electron densities on the sulfur and nitrogen atoms, obtained by the semiempirical molecular orbital (MO) calculation method. Experimental Section 1. Materials and Analysis. The VGO, produced by the vacuum distillation of atmospheric residue, was identical to that used in the previous photochemical study.6 The properties of the VGO are summarized in Table 1. The total sulfur and nitrogen concentrations of the VGO were analyzed using an inductively coupled argon plasma atomic emission spectrophotometer (Nippon Jarrell-Ash ICAP-575 Mark II) and a total nitrogen analyzer (Mitsubishi Chemical Industry, TN-05), respectively.6 The concentrations of each of the individual sulfur- and nitrogen-containing compounds in the VGO were analyzed quantitatively by means of FI-MS (JEOL JMS-AX505H) and GC-AED (Hewlett-Packard 6890, equipped with AED G2350A), following fractionation from the VGO using column chromatography and ligand-exchange chromatography, as described in the
10.1021/ie001091b CCC: $20.00 © 2001 American Chemical Society Published on Web 06/22/2001
Ind. Eng. Chem. Res., Vol. 40, No. 15, 2001 3399 Table 1. Properties and Composition of the VGO density at 288 Ka viscosity at 323 Kb hydrogen carbon sulfur nitrogen vanadium nickel saturated fractionc aromaticsc one-ring >two-ring distillation IBP 10 vol % 20 vol % 30 vol % 50 vol % 70 vol % 80 vol %
g/mL mm2/s wt % wt % wt % ppm ppm ppm vol % vol %
0.9194 31.8 13.15 84.48 1.9899 823.0 0.11 VGO, as shown in Figure 2. The VGO, however, contains rather more higher molecular weight sulfur compounds than the BTs and DBTs present in light oils.6 The relatively low desulfurization efficiency for the VGO thus probably results because the desulfurization reactivities for the sulfur compounds in the VGO are lower than those for the BTs and DBTs in light oils. 1.2. Desulfurization Reactivity of Sulfur-Containing Compounds. The desulfurization reactivity of the individual sulfur-containing compounds in the VGO was then studied, in detail, by means of FI-MS. Based on the molecular weight data obtained, the sulfur compounds in the VGO were classified into seven compound fractions, as described previously6 and where
Figure 2. Residual percentage of sulfur in VGO and light oils such as CLO, straight-run LGO, and LCO, following desulfurization in the presence of differing quantities of AgBF4, based on the initial sulfur concentration of the feed oils. The resulting sulfur contents of the oils, following desulfurization, are also shown in this figure. The data for light oils are cited from a previous paper.7 Desulfurization conditions: reaction time, 11 h; temperature, 303 K; [CH3I]initial ) 20-fold molar excess for initial sulfur concentration of the feed oils.
ing to the presence of differing quantities of AgBF4, are shown in Figure 2. The desulfurization yield for the SN2 displacement reaction depends both on the concentrations of the sulfur compounds and on those of the alkylating agents.7 The residual percentage of sulfur in the VGO was, therefore, seen to decrease with the increasing quantity of AgBF4 added. When this process is employed, in the presence of 10-fold molar excess of AgBF4 based on the initial sulfur concentration of the feed VGO, the sulfur content of the VGO was thus decreased to 0.1% of the feed concentration. Compared to this value, the current HDS process is reported as being able to decrease the sulfur content of VGO to 14% of the feed value at the conditions of reaction temperature of 633 K, hydrogen pressure of 8 MPa, and LHSV of 2.0 1/h.12,13 The results, therefore, indicate the present process to be both comparatively more energy-efficient and also more effective for the desulfurization of the VGO, as compared to the HDS process. As shown in Figure 2, the decrease obtained in the residual percentage of sulfur for the VGO is lower than that for straightrun light gas oil (LGO), but higher than that for commercial light oil (CLO) and also for LCO, produced by the catalytic-cracking of VGO, with the desulfurization efficiency obtained lying in the ranking order LGO > VGO > CLO > LCO. The order of the desulfurization efficiency, obtained in the present case, thus differs from that obtained according to the previous photochemical desulfurization process, where the ranking order of CLO > LGO > VGO > LCO was found.6 As described previously,7 the present S-methylation reaction is hindered significantly, by a high aromatic hydrocarbon concentration in the oil and occurs because the methylation of the aromatics by the alkylating agents occurs competitively with the S-methylation reaction. The quantities of aromatics, relative to the sulfur content of the oils, were determined as 17.8 (vol % aromatics/wt % sulfur) for LGO, 16.4 for VGO, 123.5 for CLO, and 502.3 for LCO, giving a ranking order of VGO < LGO < CLO < LCO. This, however, differs from that of the real desulfurization efficiency, where the
MW (molecular weight) ) 14n + U (n ) natural number, U ) even number, -10 e U e 2) (1) and where the sulfur compounds, having the same number of naphthenic and aromatic rings, are involved in each U value. The relationship between the U value and the compound structure is shown in Table 2, according to Aoyagi et al.12,13 and our other previous work.6 The distributions of the sulfur compound fraction, for each value of U, both in the feed and in the treated VGO, following desulfurization in the presence of 10-fold molar excess of AgBF4 based on the initial sulfur content of the feed VGO, are summarized in Figure 3, together with the residual percentage obtained for each sulfur compound fraction. The residual percentage for each sulfur compound fraction is seen to lie in the ranking order U ) -8 > -2 > -6, -10 > 0 > -4 > +2, thus revealing that the sulfur compounds of U ) -8 and -2 are the most difficult compounds to be desulfurized, according to the present process. The sulfur fraction for U ) +2, which is desulfurized most easily, contains mainly alkyl-substituted DBTs, as shown in Table 2a, thus suggesting that the desulfurization reactivities of all of the other sulfur compounds in the VGO are lower than those for the DBTs. The lower desulfurization efficiency obtained for the VGO as compared to that of the LGO, as shown in Figure 2, is therefore caused by the presence of these more refractory sulfur compounds. Parts a-g of Figure 4 show the molecular weight distribution of the individual sulfur-containing compounds, for the respective values of U, both in the feed and in the treated VGO, together with the residual percentage for each compound. Figure 4a shows the distribution of the U ) +2 sulfur compounds, which consist of DBTs (n e 17) and benzothiophenobenzothiophenes (BTBTs, n > 17).6 The residual percentage for these compounds, following desulfurization, is seen to increase with increasing molecular weight of the compounds. The results indicate that the desulfurization of the BTBTs is more difficult than that of the DBTs and that both DBTs and BTBTs, having a large carbon number of alkyl substituents, become increasingly more difficult to be desulfurized. Parts b-g of Figure 4 show the distribution of tetrahydrobenzonaphthothiophenes (THBNTs) for U ) 0, octahydrodinaphthothiophenes (OHDNTs) for U ) -2, benzonaphthothiophenes (BNTs) for U ) -4, tetrahydrodinaphthothiophenes (THDNTs) for U ) -6, tetrahydrodibenzothiophenes (THDBTs) for U ) -8, and dinaphthothiophenes (DNTs) for U ) -10,
Ind. Eng. Chem. Res., Vol. 40, No. 15, 2001 3401 Table 2. Representative Structures and Electron Densities on the Sulfur Atom for the Various Sulfur-Containing Compounds in VGOa
a The respective electron densities were calculated from the sulfur σ orbital, lying parallel to the molecules, as described previously.7
Figure 3. Distribution in the sulfur compound fraction, as defined by the U value, both in the feed and in the treated VGO, following desulfurization in the presence of a 10-fold molar excess of AgBF4 based on the initial sulfur concentration of the feed VGO, and the residual percentage sulfur obtained for each sulfur compound fraction. The sum of the intensity ratio for all of the U values for the feed VGO (total sulfur concentration of the feed VGO) is set as 100%.
respectively. The data show that the low molecular weight compounds are removed effectively for respective values of U, the residual percentage for all of the compounds increases with increasing molecular weight of the compounds. The above results suggest that THDBTs with U ) -8 and OHDNTs with U ) -2 are the most difficult compounds to be desulfurized according to the present
process. This compares with the current HDS process10,11 and also the previously proposed photochemical process,6 where the respective sulfur compound fractions for U ) +2 and -6 are the most difficult compounds to be desulfurized. The residual percentage for all of the sulfur compounds in the VGO, as shown in Figure 4ag, tends to increase with increasing carbon numbers of alkyl substituents on the molecule, thus agreeing with the tendency also observed in the previous photochemical desulfurization for VGO.6 1.3. Relationship between the Desulfurization Reactivity and Electron Density on the Sulfur Atom. A previous study revealed that the desulfurization reactivity for the BTs and DBTs in light oils decreases with decreasing electron density on the sulfur atom (sulfur σ orbital), lying parallel to the plane of the molecules.7 As shown in Figure 5 for BNT (U ) -4) and DNT (U ) -10), these higher molecular weight sulfur compounds have a large electron density distribution on the sulfur atom, lying parallel to the plane of the molecules, as also applies for BTs and DBTs.7 To study the desulfurization reactivity for the sulfur compounds in the VGO in detail, the respective electron densities on the sulfur atom (sulfur σ orbital) for the various compounds in the VGO were calculated by the semiempirical MO method. The results are summarized in Table 2. The values of the electron densities for all of the compounds in the VGO are seen to be lower than that for DBT (U ) +2; Table 2a.i). This result agrees with the real desulfurization reactivity obtained for sulfur compounds, as shown in Figure 3.
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Figure 4. Molecular weight distribution of the differing sulfur-containing compounds, as represented by the respective U values, both in the feed and in the treated VGO, following desulfurization in the presence of a 10-fold molar excess of AgBF4, based on the initial sulfur concentration of the feed VGO, and the residual percentage sulfur obtained for the respective sulfur compounds. (a) U ) +2, (b) U ) 0, (c) U ) -2, (d) U ) -4, (e) U ) -6, (f) U ) -8, (g) U ) -10.
Ind. Eng. Chem. Res., Vol. 40, No. 15, 2001 3403 Table 3. Quantities of Carbazoles, Having Different Carbon Numbers of Alkyl Substituents, in (a) Feed VGO and in the Treated Oils, Following Desulfurization in the Presence of (b) 2-Fold and (c) 10-Fold Molar Excess of AgBF4, Based on the Initial Sulfur Content of the Feed VGO
Figure 5. Calculated energy level diagram and a schematic representation of the electron density distribution for the sulfur σ lone pair orbital for (a) BNT (U ) -4) and (b) DNT (U ) -10).
As shown in Table 2a.i and ii for U ) +2 compounds, the electron density for BTBT is smaller than that for DBT. This result is consistent with the real desulfurization reactivity, as shown in Figure 4a. Comparing the value for DBT (U ) +2; Table 2a.i) with those for BNTs (U ) -4; Table 2d.i-iii) and DNTs (U ) -10; Table 2g.i-vi), the electron densities are seen to decrease with increasing number of aromatic rings added to the DBT molecule, with a resulting order of DBT > BNTs > DNTs. This tendency agrees with the order obtained for the real desulfurization reactivity of U ) +2 > -4 > -10, as shown in Figure 3. The results also revealed that the BNT (Table 2d.i), with one aromatic ring on the C1-C2 position of the DBT molecule (Table 2a.i), and DNT (Table 2g.iv), with two aromatic rings on the C1-C2 and C7-C8 positions of the DBT molecule, are the most difficult compounds to be desulfurized. Comparing the data for THBNTs (U ) 0; Table 2b.i-iii) and BNTs (U ) -4; Table 2c.i-iii), the electron densities for the THBNTs are seen to be lower than those for the BNTs. These results suggest that the addition of the naphthenic ring to the DBT molecule (Table 2a.i) reduces the electron density more greatly than the addition of the aromatic ring and that the methylation reactivity of the THBNT is, therefore, lower than that of the BNT. This result is consistent with the real desulfurization reactivity obtained of U ) -4 > 0, as shown in Figure 3. The results also show that the electron densities of the THBNTs (Table 2b.iv-vi), in which the internal aromatic ring of the BNT molecules is hydrogenated, are greater than those for the THBNTs (Table 2b.i-iii), in which the external aromatic ring of the BNT molecules is hydrogenated. As shown in Table 2c.i-vi for OHDNTs (U ) -2) and in Table 2e.i-vi for THDNTs (U ) -6), the electron densities for these compounds are relatively lower than those for the nonhydrogenated DNTs (U ) -10; Table 2g.i-vi). The real desulfurization reactivity for the THDNTs is, however, comparable with that of the DNTs, as shown in Figure 3. The electron densities for the OHDNTs (Table
species
a (ppm)
b (ppm)
c (ppm)
C1-carbazoles C2-carbazoles C3-carbazoles C4-carbazoles C5-carbazoles C6-carbazoles C7-carbazoles C8-carbazoles C9-carbazoles C10-carbazoles C11-carbazoles total nitrogen
2.9 10.5 22.0 50.7 21.1 59.3 30.6 27.8 26.8 182.8 379.0 823.0
0 0.1 0.4 3.7 2.4 8.4 4.9 6.1 7.2 67.2 171.2 271.6
0 0 0 0.1 0.4 0.3 0.4 0.8 1.4 13.1 41.1 57.6
2c.iv-vi) and for the THDNTs (Table 2e.iv-vi), in which the internal aromatic ring of the DNTs molecule is hydrogenated, are seen to be higher than those for the compounds in which the external ring of the DNTs is hydrogenated. The same real desulfurization reactivity obtained for U ) -6 and -10, as shown in Figure 3, is therefore probably caused by the presence of these highly reactive THDNTs. As shown in Table 2f.i, the electron density for THDBT (U ) -8) is seen to be significantly less than those for the other compounds in the VGO. This result is consistent with the real desulfurization reactivity, as shown in Figure 3. As described previously,7 the methylation reactivity of BTs, having an unsaturated bond on their thiophene ring, is reduced significantly with increasing bond order of the unsaturated bond. As shown in Table 2f.i, THDBT also has an unsaturated bond on the C1′-C4′ position of the molecule (bondorder value of 1.7202, a value which is comparable to that of the BT molecule, 1.7693). The low desulfurization yield for THDBT, as shown in Figure 3, therefore also results owing to the presence of the unsaturated bond on the thiophene ring. The residual percentage for all of the sulfur compounds, as shown in Figure 4a-g, increases with increasing carbon number of alkyl substituents on the molecules. As described previously,7 the electron densities of DBTs and BTs decrease with an increasing carbon number of alkyl substituents. The low reactivity of the highly alkyl-substituted sulfur compounds in VGO, as shown in Figure 4a-g, therefore probably results as a consequence of the reduction in the electron densities of the sulfur compounds, caused by the addition of alkyl substituents, in the same manner as that found for BTs and DBTs. 2. Denitrogenation of VGO. 2.1. Denitrogenation Behavior of VGO. The denitrogenation behavior of VGO, occurring simultaneously with desulfurization, was then studied. A previous GC-AED analysis revealed that VGO contains only alkyl-substituted carbazoles as nitrogen compounds,6 as shown in Table 3. As shown in the 1H NMR spectrum for the precipitate obtained from VGO (Figure 1a), a weak resonance, which is attributable to the methyl protons for N+-CH3, appears at the range of 3.5-4.2 ppm. In the 13C NMR spectrum (Figure 1b), a weak resonance, which is attributable to the methyl carbons for N+-CH3, is observed at 45-70 ppm. These distinctive spectra are also found in the spectra for the precipitates obtained from pure carbazole and light oils.9 These results, therefore, suggest that the carbazoles in VGO are
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Figure 6. Residual percentage of nitrogen in VGO and in the light oils (CLO, LGO, and LCO), following denitrogenation in the presence of differing quantities of AgBF4 based on the initial nitrogen concentration of the feed oils. The resulting nitrogen contents of the oils, following desulfurization, are also shown in this figure. The data for light oils are cited from a previous paper.9 The denitrogenation conditions are identical to those in Figure 2. The numbers (2, 5, and 10) in the figure denote the relative AgBF4 concentration, based on the initial sulfur concentration of the feed oils.
methylated, by the addition of the alkylating agents, and removed successfully as a precipitate of the corresponding N,N-dimethylcarbazolium tetrafluoroborate, together with sulfur-containing compounds. The variations in the residual percentage of nitrogen in the VGO, following denitrogenation in the presence of differing quantities of AgBF4, are shown in Figure 6. The residual percentage of nitrogen decreases with increasing AgBF4 concentration, as was found also in the cases for the desulfurization of the VGO (Figure 2) and the denitrogenation of light oils.9 This is because the denitrogenation yields for the N-methylation reaction depend both on the concentrations of the nitrogencontaining compounds and on those of the alkylating agents.9 In this way, the total nitrogen concentration of the VGO was thus decreased successfully from 843 to 57.6 ppm, using an 86-fold molar excess of AgBF4 based on the initial nitrogen content of the feed VGO. The results show that the present process, when applied to the desulfurization of VGO in the presence of a 10fold molar excess amount of AgBF4 based on the initial sulfur concentration of feed VGO, is able to decrease both the sulfur and nitrogen concentrations simultaneously to 0.1% and 7.0%, respectively, of the feed values. The present process is thus effective for both the desulfurization and simultaneous denitrogenation of VGO, as is also the case for light oils.9 The denitrogenation efficiency for the differing oils, as shown in Figure 6, lies in the ranking order LCO > VGO > LGO > CLO. This order differs from that obtained for desulfurization, with the order then being LGO > VGO > CLO > LCO for the present process and also with the order being CLO > LGO > VGO > LCO for the previous photochemical denitrogenation process.6 2.2. Denitrogenation Reactivity of NitrogenContaining Compounds. VGO, LGO, and CLO contain only alkyl-substituted carbazoles as nitrogen compounds, while LCO also contains anilines (23%) and indoles (36%), which are denitrogenized more easily than carbazoles.6,9 The higher denitrogenation yield for LCO, as shown in Figure 6, therefore results as a
Figure 7. Residual percentage of carbazoles in VGO, with respect to the carbon number of alkyl substituents on carbazole, following denitrogenation in the presence of 2- and 10-fold molar excess quantities of AgBF4 based on the initial sulfur content of the feed VGO. The initial amount of each alkyl-substituted carbazoles in feed VGO is set as 100%.
consequence of LCO containing these highly reactive aniline and indole compounds. The VGO and light oils contain high proportions of aromatic hydrocarbons, as shown in Table 1. As described previously,9 the complete N-methylation reaction for carbazoles is prevented by the presence of aromatics, because the methylation of the aromatics occurs competitively with the N-methylation reaction. The relative quantities of the aromatics, as compared to the nitrogen concentration of the oils, were determined as 0.15 (vol % aromatics/ppm of nitrogen) for LGO, 0.03 for VGO, and 0.30 for CLO,9 with a ranking order of VGO < LGO < CLO. As shown in Figure 6, the order of the denitrogenation yield decreases with increasing aromatics concentration of the oils, thus suggesting that the present process is thus more effective for the denitrogenation of VGO than for the higher aromatic content LGO and CLO. The change in the composition of the carbazoles in the VGO, following denitrogenation in the presence of 2- and 10-fold molar excess of AgBF4 based on the initial sulfur content of the feed VGO, is summarized in Table 3. The residual percentages for the carbazoles, following denitrogenation, are plotted in Figure 7, as a function of the carbon number of alkyl substituents on the carbazole molecule. Following denitrogenation, the residual portion for the carbazoles in the VGO tends to increase with an increase in the carbon number of alkyl substituents, as was also the case for light oils.9 This is because the N-methylation reactivity for the carbazoles increases with an increasing electron density on nitrogen atom and the electron density of the carbazoles decreases with an increasing carbon number of alkyl substituents on the molecule, as described previously.9 These results, therefore, reveal that the highly substituted carbazoles in the VGO are the most difficult compounds to be denitrogenized according to the present process, as was also the case for light oils. This tendency was also observed in the previous photochemical denitrogenation process for VGO and light oils.6 Conclusion A novel process for the desulfurization and simultaneous denitrogenation of fuel oils, based on alkylation using alkylating agents (CH3I and AgBF4) and a sub-
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sequent precipitation method, has been applied to the refining of VGO, and the following results were obtained. (1) The sulfur-containing compounds in the VGO are methylated, by the addition of the alkylating agents, and are removed as a precipitate of the corresponding S-methylsulfonium salts. When this process is employed , the sulfur content of the VGO was decreased successfully to 0.1% of the feed concentration, in the presence of 10-fold molar excess of AgBF4 based on the initial sulfur content of the feed VGO. The desulfurization efficiency for the VGO was higher than that for aromaticrich light oils. (2) FI-MS analysis revealed that the THDBTs, especially those having a large carbon number of alkyl substituents, are the most difficult compounds to be desulfurized. This is because the electron density on the sulfur atom for the THDBTs is significantly lower than that for other compounds. The desulfurization reactivities for all of the sulfur compounds in the VGO are less than those for DBTs, which are present mainly in light oils. (3) The carbazoles in VGO are methylated, by the addition of the alkylating agents, and removed as precipitates of the N,N-dimethylcarbazolium salts, together with sulfur compounds. In this way, the nitrogen content of VGO was decreased successfully to 7.0% of the feed value. The denitrogenation efficiency for VGO is higher than that for aromatic-rich light oils. GC-AED analysis reveals that the carbazoles, especially those having a large carbon number of alkyl substituents, constitute the difficult compounds to be denitrogenized. Acknowledgment The authors acknowledge the members of the Central Analytical Center for Japan Energy Corp. for their help in the separation using ligand-exchange chromatography and FI-MS analyses for the sulfur-containing compounds and Messrs. Yasuto Taki and Kenya Tachibana for their experimental assistance. The authors are grateful for financial support by Grants-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. Nomenclature BT ) benzothiophene BNT ) benzonaphthothiophene BTBT ) benzothiophenobenzothiophene CLO ) commercial light oil DBT ) dibenzothiophene DNT ) dinaphthothiophene
FI-MS ) field ionization-mass spectrophotometer GC-AED ) gas chromatography-atomic emission detector HDN ) hydrodenitrogenation HDS ) hydrodesulfurization LCO ) light cycle oil LGO ) straight-run light gas oil n ) integral number defined in eq 1 OHDNT ) octahydrodinaphthothiophene THBNT ) tetrahydrobenzonaphthothiophene THDBT ) tetrahydrodibenzothiophene THDNT ) tetrahydrodinaphthothiophene U ) even number defined in eq 1 VGO ) vacuum gas oil
Literature Cited (1) Dahl, I. M.; Tangstad, E.; Mostad, H. B. Effect of Hydrotreating on Catalytic Cracking of a VGO. Energy Fuels 1996, 10, 85. (2) Fukase, S.; Maruyama, F. Catalytic Cracking of VGOs Derived from Hydroprocessing (Part 1) Properties of VGO Fractions and Their Catalytic Cracking Characteristics. J. Jpn. Pet. Inst. 1994, 37, 611. (3) Katzer, J. R.; Sivasubramanian, R. Process and Catalyst Need for Hydrodenitrogenation. Catal. Rev.-Sci. Eng. 1979, 20, 155. (4) Girgis, M. J.; Gates, B. C. Reactivities, Reaction Networks, and Kinetics in High-Pressure Catalytic Hydroprocessing. Ind. Eng. Chem. Res. 1991, 30, 2021. (5) Ma, X.; Sakanishi, K.; Mochida, I. Hydrodesulfurization Reactivities of Various Sulfur Compounds in Vacuum Gas Oil. Ind. Eng. Chem. Res. 1996, 35, 2487. (6) Shiraishi, Y.; Hirai, T.; Komasawa, I. Photochemical Desulfurization and Denitrogenation Process for Vacuum Gas Oil Using an Organic Two-Phase Extraction System. Ind. Eng. Chem. Res. 2001, 40, 293. (7) Shiraishi, Y.; Taki, Y.; Hirai, T.; Komasawa, I. A Novel Desulfurization Process for Fuel Oils Based on the Formation and Subsequent Precipitation of S-Alkylsulfonium Salts. 1. Light Oil Feedstocks. Ind. Eng. Chem. Res. 2001, 40, 1213. (8) Shiraishi, Y.; Tachibana, K.; Taki, Y.; Hirai, T.; Komasawa, I. A Novel Desulfurization Process for Fuel Oils Based on the Formation and Subsequent Precipitation of S-Alkylsulfonium Salts. 2. Catalytic-Cracked Gasoline. Ind. Eng. Chem. Res. 2001, 40, 1225. (9) Shiraishi, Y.; Tachibana, K.; Hirai, T.; Komasawa, I. 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. Ind. Eng. Chem. Res. 2001, 40, 3390. (10) Acheson, R. M.; Harrison, D. R. S-Alkylthiophenium Salts. J. Chem. Soc. D 1969, 724. (11) Acheson, R. M.; Harrison, D. R. The Synthesis, Spectra, and Reactions of Some S-Alkylthiophenium Salts. J. Chem. Soc. C 1970, 1764. (12) Aoyagi, I.; Imagishi, T.; Mitani, H. Relative Desulfurization Reactivity of Thiophenes in Vacuum Gas Oil (in Japanese). J. Jpn. Pet. Inst. 1996, 39, 418. (13) Aoyagi, I.; Kobayashi, M.; Tokawa, S.; Mitani, H. Molecular Transformation of Vacuum Gas Oil in Hydrodesulfurization (in Japanese). J. Jpn. Pet. Inst. 1997, 40, 213.
Received for review December 18, 2000 Revised manuscript received April 25, 2001 Accepted May 8, 2001 IE001091B
