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Energy & Fuels 2004, 18, 1220-1225
Rapid Discrimination of Counterfeit Gas Oil Prepared by Mixing Fuel Oil with Sulfuric Acid Using Gas Chromatography-Mass Spectrometry and Gas Chromatography-Atomic Emission Detection Shoji Kurata*,† and Masatoshi Nagai‡ Criminal Investigation Laboratory, Metropolitan Police Department, 2-1-1, Kasumigaseki, Chiyoda-ku, Tokyo 100-8929, Japan, and Graduate School of Bio-applications and Systems Engineering, Tokyo University of Agriculture and Technology, 2-24, Nakamachi, Koganei-shi, Tokyo 184-8588, Japan Received December 29, 2003. Revised Manuscript Received May 21, 2004
A rapid discrimination of counterfeit gas oils prepared by mixing fuel oil A with sulfuric acid (95% H2SO4) was studied by gas chromatography-atomic emission detection (GC-AED) and gas chromatography-mass spectrometry (GC-MS). Sulfuric acid is used for the removal of coumarin as an oil marker. Both the aromatic and sulfur contents in the counterfeit gas oils are reduced by sulfonation. The counterfeit gas oils gradually changed into oils with abundant paraffins. The GC-MS analysis showed no or a slight amount of the condensed polycyclic aromatic compounds in the counterfeit gas oils before the sulfuric content in the oils was reduced to 50 ppm or less on the basis of the sulfur analysis by GC-AED. These sulfur values corresponded to the sulfur content in the authentic gas oils from Japan. Therefore, the combination of GC-MS and GC-AED analyzed the composition of the aromatic compounds and the sulfur content in the oils and rapidly distinguished the counterfeit gas oils from the authentic gas oil.
Introduction Recently, counterfeit gas oils are being prepared by mixing gas oil1,2 with fuel oil A3 (or kerosene) or by mixing fuel oil A with H2SO4. These are then sold without paying the delivery tax on gas oils in Japan. Fuel oil A is one of the heavy oils in Japan and is used for boilers in plant, diesel engines of vessels, and airconditioners. Coumarin is not added to gas oils but is added to fuel oil A and kerosene as an oil marker at 1 ppm in Japan for proof of the delivery tax payment.4 Spectrofluorophotometry has been used as a method of coumarin detection for the rapid analysis of the counterfeit gas oils requiring a few milliliters of sample. However, this analysis is not suitable for the counterfeit gas oils prepared by mixing fuel oil A with H2SO4 * Author to whom correspondence should be addressed. † Metropolitan Police Department, Chiyoda-ku, Tokyo. ‡ Tokyo University of Agriculture and Technology. (1) Gas oil is used as diesel fuels for motor vehicles. Gas oils in Japan are classified into five types of gas oils, primarily for automotive use, by the Japan Industrial Standard (JIS) K-2204 for diesel engine fuels: grade special-No.1 (5 °C or less pour point); No.1 (-2.5 °C or less pour point most popular in Japan); No.2 (-7.5 °C or less pour point); No.3 (-20 °C or less pour point); and special No.3 (-30 °C or less pour point). Each gas oil is separately used on the basis of the regional area in Japan and time of year. (2) Japanese Standards Association, Japan Industrial Standard (JIS) K-2204, JIS Handbook Petroleum (in Japanese), 1999; pp 5354. (3) Japanese Standards Association, Japan Industrial Standard (JIS) K-2205, JIS Handbook Petroleum (in Japanese), 1999; pp 5556. (4) Kurata, S.; Aizawa, N.; Hirano, H.; Nagai, M. Rapid discrimination of oils containing coumarin using three-layer extraction and fluorescence spectrometry (in Japanese), BUNSEKI KAGAKU 2003, 52 (3), 187-194.
because H2SO4 removes coumarin from the fuel oils A by sulfonation. Gas chromatography-flame ionization detection (GC-FID) is useful for the discrimination of the counterfeit gas oils prepared from kerosene but discriminated with difficulty the authentic gas oils from the counterfeit gas oils prepared from fuel oil A because of the very similar peak composition of paraffin. Newly improved analyses have to be urgently developed in lieu of spectrofluorophotometry4 to detect coumarin in the oils. Gas chromatography-atomic emission detection (GC-AED) is superior to GC-FID for the analysis of the sulfur atoms of sulfur compounds in the counterfeit gas oils. Gas chromatography-mass spectrometry (GC-MS) also surpasses GC-FID in the analysis of aromatic compounds in counterfeit gas oils and analyzes only a few microliters of sample, an amount much better than the spectrofluorophotometry for even counterfeit gas oils without coumarin. In a previous study,5 we reported that the GC-MS analysis easily distinguished fuel oil A from the authentic gas oils in the content of the condensed polycyclic aromatic compounds such as naphthalene, phenanthrene, and the derivatives. Fuel oils A are classified into the high-sulfur (approximately 10000 ppm) and low-sulfur (approximately 600 ppm) types. In this study, a new analytical method was developed in combination with GC-MS and GC-AED and applied to the rapid discrimination of counterfeit gas oils. The GC-MS6,7 (5) Kurata, S.; Aizawa, N.; Hirano, H.; Takashima, C.; Nagai, M. Analytical method for discrimination of CGO prepared from fuel oil mixed with sulfuric acid (in Japanese). J. Jpn. Pet. Inst. 2004, 47 (1), 44-53.
10.1021/ef034108m CCC: $27.50 © 2004 American Chemical Society Published on Web 07/02/2004
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Table 1. Calibration Curvesa for Quantification of 14 Compounds
no.
compound
1 2 3* 3 4 5 6 7 8 9 10 11 12* 12 13 14* 14
1,2,4-Trimethylbenzene 1,2,3,4-Tetramethylbenzene d8-Naphthalene Naphthalene 2-Methylnaphthalene Biphenyl 2,6-Dimethylnaphthalene 2,3-Dimethylnaphthalene 4-Methylbiphenyl n-Hexadecane 3,3′-Dimethylbiphenyl Dibenzothiophene d10-Phenanthrene Phenanthrene 4,6-Dimethyldibenzothiophene d10-Pyrene Pyrene
(1,2,4-TrMB) (1,2,3,4-TeMB) (d8-Np) (Np) (2-MNp) (Bp) (2,6-DMNp) (2,3-DMNp) (4-MBp) (n-C16) (3,3′-DMBp) (DBT) (d10-Phe) (Phe) (4,6-DMDBT) (d10-Pyr) (Pyr)
a
mol. wt.
ret. time (min)
120 134 136 128 142 154 156 156 168 226 182 184 188 178 212 212 202
5.77 8.27 8.85 8.9 11.61 11.8 12.19 12.68 13.42 14.58 14.64 16.72 17.08 17.17 19.04 20.75 20.83
Linear calibration curves with more than a 0.98 correlation coefficient ranging from 20 to 500 ng/µL.
analyzed the aromatic compounds in the oils using deuterated compounds as the internal standards. The GC-AED analyzed the sulfur content of counterfeit gas oil prepared by mixing the low-sulfur type of fuel oil A with H2SO4. Experimental Section Materials. d8-Naphthalene, d10-phenanthrene, and d10pyrene (Cambridge Isotope Lab. Inc.) were used as labeled compounds. Naphthalene (98%), phenanthrene (98%), biphenyl (99%), 1,2,4-trimethylbenzene (98%), 1,2,3,4-tetramethylbenzene (98%), 4-methylbiphenyl (98%), 3,3′-dimethylbiphenyl (98%), 2,3-dimethylnaphthalene (98%), 2,6-dimethylnaphthalene (98%), and dibenzothiophene (98%) were purchased from Tokyo Kasei Kogyo Co., Ltd., and used without further purification. Pyrene (98%), 2-methylnaphthalene (98%), sulfuric acid (95%), n-hexane (96%) (Wako Pure Chemical Industries, Ltd.), n-hexadecane (98%) (Kanto Chemical Co.), and 4,6dimethyldibenzothiophene (97%) (Aldrich Chemical Co.) were also used without further purification. A low-sulfur (23 ppm) type of gas oil, grade No.1, which is the most popular in Japan, and a low-sulfur (600 ppm) fuel oil A were obtained from filling stations (A and B oil companies, respectively) in Tokyo, Japan. The sulfur contents in fuel oil A and the gas oil shown in parentheses were determined using a Vario elemental analyzer. Sample Preparation. In a previous paper,5 the mixture of fuel oil A with 95% H2SO4 (1:1) with a mixing time of more than 30 s (150 rpm) was suitable for the complete removal of coumarin from fuel oil A and decolorizing of the dark brown fuel oil A. These sample preparation conditions were used in this study. The artificial counterfeit gas oil (CGO) samples were prepared as follows. Experimental samples (4 mL) were prepared by mixing one part of fuel oil A with one part of H2SO4 (95%) in screw-capped tubes (10-cm × 13-mm id) with shaking (150 rpm) for 3, 10, and 30 min and then stored at room temperature to allow separation into two layers. The upper layer is composed of oil and the lower layer consisted of a residue with H2SO4, i.e., H2SO4-pitch. The obtained upper (6) American Society for Testing and Materials (ASTM), D 5769-98 Standard test method for determination of benzene, toluene, and total aromatics in finished gasolines by gas chromatography/mass spectrometry. Annual Book of ASTM 2000, 05.03, 782-793. (7) Baumard, P.; Budzinski, H. Internal standard quantification method and gas chromatograph-mass spectrometer (GC-MS): a reliable tool for polycyclic aromatic hydrocarbon (PAH) quantification in natural matrixes. Analysis 1997, 25, 246-252.
(r2)
int. std.
slope
intercept
corr. coef. r2
d8-Np d8-Np
0.0028 0.0023
-0.0525 0.0217
0.9921 0.9962
d8-Np d8-Np d8-Np d8-Np d8-Np d8-Np d8-Np d8-Np d10-Phe
0.0099 0.0068 0.0072 0.0057 0.0056 0.0046 0.00014 0.0037 0.0153
0.0655 -0.0998 -0.0981 -0.041 -0.0973 -0.0182 -0.00277 -0.0527 -0.0953
0.9831 0.996 0.9993 0.9903 0.9981 0.986 0.9885 0.9928 0.9992
d10-Phe d10-Pyr
0.0173 0.012
-0.2049 -0.0653
0.992 0.9989
d10-Pyr
0.0131
-0.0308
0.9982
were obtained for all 14 compounds for concentrations
layer was washed with distilled water to remove the H2SO4, and used as a sample. The gas oil and fuel oil A without mixing with H2SO4 were also used as the samples for comparison. An authentic sample is the solution of n-hexane that contained 14 compounds of 1,2,4-trimethylbenzene, 1,2,3,4-tetramethylbenzene, naphthalene, 2-methylnaphthalene, 2,3-dimethylnaphthalene, 2,6-dimethylnaphthalene, biphenyl, 4-methylbiphenyl, 3,3′-dimethylbiphenyl, phenanthrene, pyrene, dibenzothiophene, 4,6-dimethyldibenzothiophene, and n-hexadecane. Elemental Analyzer. The sulfur content in the oils was determined using a Vario TRACE S liquid injection into an elemental analyzer with a UV-fluorescence detector for SO2 formed by combustion of the sulfur compounds at 1150 °C. The carrier gas was an N2/O2-mixture. The sample amounts were 60 µL. GC-MS. The 14 compounds in the oil samples (CGO, fuel oil A, and gas oil) and the authentic samples were quantitatively analyzed using a Shimadzu GC-MS G17A/QP5050A. A fused-silica capillary (30-m × 0.25-mm id × 0.25-µm film thickness DB-5 ms, J&W Sci.) was used throughout as the GC column. The temperature program was 50 to 320 °C at 10 °C/ min and then 10 min at 320 °C. Helium was used as the carrier gas at the constant column flow rate of 1 mL/min. The split ratio was set at 50:1. The quadrupole mass spectrometer was operated in the electron impact (EI) mode (ionization energy 70 eV, interface temperature 230 °C) scanning from 50 to 650 amu in 0.5 s. The oil samples and the authentic samples were injected at 0.1 and 1 µL, respectively. Quantification of 14 Compounds by GC-MS. The solution containing the deuterated compounds as internal standards6-10 was prepared by diluting each d8-naphthalene, d10-phenanthrene, and d10-pyrene in n-hexane to adjust the concentration to 100 ng/µL. An internal standard solution was used both for the preparation and dilution of the authentic samples and as the internal standard for the oil samples to be quantified. To obtain a calibration curve for the quantification of the 14 compounds, an authentic sample was prepared by adding 500 ng/µL of each of the 14 compounds to the internal authentic sample (100 ng/µL of each of the three perdeuterated polycyclic aromatic hydrocarbons (PAHs) in n-hexane). This solution was then diluted with the internal standard solution (100 ng/µL of each of the three perdeuterated PAHs in n-hexane) to produce the concentrations of 20, 50, 100, 200, 300, and 500 ng/µL of the 14 compounds in the solution. Each d8-naphthalene, d10-phenanthrene, and d10pyrene remained at the concentration of 100 ng/µL for all the authentic samples. The peak intensities of the molecular ions
1222 Energy & Fuels, Vol. 18, No. 4, 2004
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Figure 1. Total ion chromatogram ((a)) and mass chromatograms ((b-1) to (b-4)) of GC-MS of 1 µL of n-hexane solution containing 100 ng of each of the 14 compounds with 100 ng of each of the 3 perdeuterated PAHs used as the internal standard compounds. The peak number in the chromatograms corresponds to that in Table 1. (M+‚) for each of the 14 compounds were used to generate the calibration curves for the compounds. The mass-to-charge ratios (m/z) of the compounds corresponded to the molecular weights (mol. wt.) as shown in Table 1. The molecular ion of the compounds except for 1,2,4-trimethylbenzene, 1,2,3,4tetramethylbenzene, and n-hexadecane corresponds to the base peak in the spectra. The 10 compounds except dibenzothiophene, 4,6-dimethyldibenzothiophene, phenanthrene, and pyrene were quantified using d8-naphthalene as the internal standard as shown in Table 1. The contents of phenanthrene and dibenzothiophene were determined using d10-phenanthrene. Pyrene and 4,6-dimethyldibenzothiophene were quantified using d10pyrene. The curves were constructed by plotting the intensity ratio of the compound to the internal standard versus the concentration of the compound. Before the GC injections, 2 mL of the internal standard solutions (200 ng/µL of each of the 3 perdeuterated PAH in n-hexane) were added to 2 mL of the oil samples. Determination of Sulfur Content in the Oil by GCAED. The sulfur content in the oils was determined using a 6890 GC coupled to a G2350A AED. A HP-1 MS capillary column (30-m × 0.32-mm id × 1-µm film thickness) was used for the separation. The temperature of both the injection port and AED transfer line/cavity was 300 °C. The oven temperature was programmed from 80 to 300 °C at the rate of 7 °C/ min and held at 300 °C for 50 min. Helium was used as the
carrier gas with a head pressure of 91 kPa and a total flow of 105 mL/min. The split ratio was set at 35:1. The injection volume of the oil sample was 1 µL. The AED was operated by monitoring two emission lines from the carbon (193 nm) and sulfur (181 nm) elements. Light gas oils11 were used as the standard solution for the determination of the sulfur content in the oils.
Results and Discussion Analysis of 14 Compounds in the Oils by GC-MS. Figure 1 shows the total ion chromatogram ((a)) and (8) Mie`ge, C.; Bouzige, M.; Nicol, S.; Dugay, J.; Pichon, V.; Hennion, M. C. Selective Immunocleanup followed by liquid or gas chromatography for the monitoring of polycyclic aromatic hydrocarbons in urban wastewater and sewage sludges used for soil amendment. J. Chromatogr. A 1999, 859, 29-39. (9) Smith, K. E. C.; Green, M.; Thomas, G. O.; Jones, K. C. Behavior of sewage sludge-derived PAHs on pasture. Environ. Sci. Technol. 2001, 35, 2141-2150. (10) Norlock, F. M.; Jang, J.-K.; Zou, Q.; Schoonover, T. M.; Li, A. Large-volume injection PTV-GC-MS analysis of polycyclic aromatic hydrocarbons in air and sediment samples. J. Air Waste Manage. Assoc. 2002, 52, 19-26. (11) Light gas oil is composed of hydrocarbons (Carbon number is approximately C13-C18) with a distillation range of approximately 250 to 350 °C.
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Table 2. Content of 14 Compounds in n-Hexane Solution by Mixing with Sulfuric Acid content of 14 compounds (ng/µL) time mixing with sulfuric acid no. 1 2 3 4 5 6 7 8 9 10 11 12 13 14
compound 1,2,4-TrMB 1,2,3,4-TeMB Np 2-MNp Bp 2,6-DMNp 2,3-DMNp 4-MBp n-C16 3,3′-DMBp DBT Phe 4,6-DMDBT Pyr
0 min 149 125 88 100 98 91 93 77 174 106 90 79 84 79
3 min (66%)a
99 70 (56%) 55 (63%) 63 (63%) 68 (69%) 57 (63%) 61 (66%) 51 (66%) 138 (79%) 87 (82%) 57 (63%) 55 (70%) 63 (75%) 8 (10%)
10 min
30 min
74 (50%) 46 (37%) 35 (40%) 52 (52%) 56 (57%) 42 (46%) 46 (49%) 42 (55%) 119 (68%) 62 (58%) 54 (60%) 26 (33%) 58 (69%) 0
24 (16%) 0 0 20 (20%) 37 (38%) 12 (13%) 20 (22%) 35 (45%) 118 (68%) 52 (49%) 22 (24%) 24 (30%) 35 (42%) 0
a Percentage in parentheses denotes the ratio of the content of the compounds in n-hexane mixed with sulfuric acid for 3, 10, or 30 min to that in n-hexane.
mass chromatograms ((b-1), (b-2), (b-3), and (b-4)) of 1 µL of the authentic sample containing 100 ng of each of the 14 compounds with 100 ng of three perdeuterated PAHs. The perdeuterated PAHs (peaks 3*, 12*, and 14* in Figure 1) were excellent internal standards for the GC separation of the PAHs since they eluted immediately prior to the nondeuterated PAHs (peaks 3, 12, and 14 in Figure 1).6-10 The data for the calibration curves of all the 14 compounds are shown in Table 1. The concentrations of these compounds outside the calibration concentration range from 20 to 500 ng/µL in Tables 2 and 3 were extrapolated. Table 2 shows the reduction of approximately 100 ng of each of the 14 compounds in the authentic sample by mixing with H2SO4 for 3, 10, and 30 min. n-Hexadecane was the most difficult to remove from the authentic sample and remained at 68% by mixing for 30 min. The biphenyl type of compounds such as biphenyl, 4-methylbiphenyl, and 3,3′-dimethylbiphenyl remained by about 38-49% with mixing for 30 min, indicating that these compounds were more difficult to remove than the other aromatic compounds. Biphenyl and the derivatives are the major PAH compounds in fuel oils A and the gas oils5 and are chiefly produced by the hydrodesulfurization of dibenzothiophene and its derivatives.12-14 Dibenzothiophene and 4,6-dimethyldibenzothiophene were observed to undergo a 58-76% reduction by mixing for 30 min. Furthermore, the benzene derivatives, such as 1,2,4trimethylbenzene and 1,2,3,4-tetramethylbenzene, and the condensed polycyclic aromatic compounds, such as naphthalene and the derivatives phenanthrene and pyrene, were removed quite easily by H2SO4. A reduction of 70-100% was observed by mixing for 30 min. Table 3 shows the content of the 14 compounds in the CGOs by mixing for 3, 10, and 30 min. The 14 com(12) Kwak, C.; Lee, J. J.; Bae, J. S.; Choi, K.; Moon, S. H. Hydrodesulfurization of DBT, 4-MDBT, and 4,6-DMDBT on fluorinated CoMoS/Al2O3 catalysts. Appl. Catal. A 2000, 200, 233-242. (13) Song, C. An overview of new approaches to deep desulfurization for ultra-clean gasoline, diesel fuel and jet fuel. Catal. Today 2001, 96, 211-263. (14) Bataille, F.; Lemberton, J.-L.; Michaud, P.; Pe´rot, G.; Vrinat, M.; Lemaire, M.; Schulz, E.; Breysse, M.; Kasztelan, S. Alkyldibenzothiophenes hydrodesulfurization-promoter effect, reactivity, and reaction mechanism. J. Catal. 2000, 191, 409-422.
Figure 2. Comparison of total sulfur contents in various oils by elemental analyzer (EA) and GC-AED.
pounds in fuel oil A and the gas oil are also shown for comparison. Although n-hexadecane in the solution of the authentic sample decreased with difficulty by mixing with H2SO4 as shown in Table 2, the compound gradually increased with the increasing mixing time. n-Hexadecane increased by approximately 8% with mixing for 30 min. This is probably because n-hexadecane in fuel oil A is more difficult to react with sulfuric acid and is more abundantly contained as the major paraffin component than the other 13 aromatic compounds. The biphenyl type of compounds were reduced by 59-81% with mixing for 30 min. This result indicated that they were difficult to remove in comparison with the other aromatic compounds. After the mixture was held for 10 min, 97-100% of 10 aromatic compounds were reduced and were completely eliminated from fuel oil A after 30 min of mixing except for the biphenyl type of compounds. The CGO samples gradually changed to abundant paraffins oils with the increased mixing time of the fuel oils A with H2SO4. Thus, the CGOs prepared by mixing for more than 10 min were easily distinguished from the authentic gas oil when compared with the 14 compounds of two oils. Analysis of the Sulfur Compounds in the Oils by GC-AED. The total sulfur contents of the various oils measured by the elemental analyzer and GC-AED are shown in Figure 2. Fifty ppm in Figure 2 is the maximum sulfur content of gas oils in Japan.15,16 The total sulfur contents as determined by the elemental analyzer almost agreed with those by GC-AED for both fuel oil A and the gas oil. The total sulfur contents of the CGOs based on the elemental analyzer were slightly higher than those by GC-AED, because a trace of H2SO4 in the CGOs was detected by the elemental analyzer even after washing with water. GC-AED analyzes the total sulfur contents in the CGOs more exactly than the elemental analyzer using the simultaneous measurement of the sulfur and carbon elements. Figure 3 shows chromatograms (a), (b), and (c) of fuel oil A, CGO by mixing for 10 min, and the authentic gas oil, (15) Gas oil has less than a 50 ppm sulfur content which corresponds to the sulfur content of gas oils supplied from April 2003 in Japan, according to a report of the 4th central environmental council in 2000 for the regulation of emission gases from diesel engines. (16) Oh, S. K.; Baik, D. S.; Han Y.-C. Emission characteristics in ultralow sulfur diesel. Int. J. Automotive Technol. 2003, 4 (2), 95100.
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Table 3. Content of 14 Compounds in Fuel Oil, CGO Samples Prepared by Mixing with Sulfuric Acid, and Gas Oil content of 14 compounds (ng/µL) no.
compound
Fuel oil A
CGO-3 min
CGO-10 min
CG-30 min
Gas oil
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1,2,4-TrMB 1,2,3,4-TeMB Np 2-MNp Bp 2,6-DMNp 2,3-DMNp 4-MB p n-C16 3,3′-DMBp DBT Phe 4,6-DMDBT Pyr
1469 449 259 1358 387 668 336 509 19016 678 15 328 91 63
508 (35%)a 121 (27%) 49 (19%) 365 (27%) 385 (99%) 194 (29%) 119 (35%) 465 (91%) 19768 (104%) 599 (88%) 13 (87%) 71 (22%) 33 (36%) 0
0 0 0 41 (3%) 248 (64%) 0 0 362 (71%) 20208 (106%) 147 (22%) 0 0 0 0
0 0 0 0 146 (38%) 0 0 210 (41%) 20498 (108%) 131 (19%) 0 0 0 0
1551 361 15 76 136 63 48 140 19528 211 9 23 8 14
a Percentage in parentheses denotes the ratio of the content of the compounds in fuel oil mixed with sulfuric acid for 3, 10, or 30 min to that in fuel oil.
Figure 3. Chromatograms of GC-AED for sulfur analysis of the oils. (a) Fuel oil A, (b) CGO sample prepared mixing fuel oil A with H2SO4 (1:1) for 10 min, (c) Authentic gas oil. (**Sulfur from a trace of sulfuric acid that remained in the oil even after washing with water.)
respectively, for the sulfur analysis of GC-AED. The peaks in the chromatograms were assigned by comparison with the analytical results of the benzothiophene derivatives and dibenzothiophene derivatives in the gas oil.17-19 The major sulfur compounds in the oils are dibenzothiophene and the alkyl-substituted diben-
zothiophene derivatives. 4,6-Dimethyldibenzothiophene is sterically hindered and is the most difficult to remove.12-14,20 Table 4 shows the content of 19 groups of sulfur compounds in the gas oil, the CGOs by mixing for 3 and 10 min, and fuel oil A. The sulfur compounds with low boiling points such as the benzothiophene
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Table 4. Sulfur Determination in Fuel Oil A, CGO Samples Prepared by Mixing with Sulfuric Acid, and Gas Oil by GC-AEDa Sulfur Content (ppm) Compound C1-Benzothiophene (C1BT) C2-Benzothiophene (C2BT) C3-Benzothiophene (C3BT) C4-Benzothiophene (C4BT) C5-Benzothiophene (C5BT) C6-Benzothiophene (C6BT) DBT C6-Benzothiophene (C6BT) 4-MDBT Methyldibenzothiophene (MDBT) C7-Benzothiophene (C7BT) C8-Benzothiophene (C8BT) C2-Dibenzothiophene (C2DBT) 4,6-DMDBT C2-Dibenzothiophene (C2DBT) C3-Dibenzothiophene (C3DBT) C4-Dibenzothiophene (C4DBT) C5-Dibenzothiophene (C5DBT) C6-Dibenzothiophene (C6DBT) Total (ppm)
retention time (min)
Fuel oil A
CGO prepared by mixing for 3 min
CGO prepared by mixing for 10 min
Gas oil
∼15.7 15.7∼16.6 16.6∼18.6 18.6∼20.7 20.7∼21.8 21.8∼2 2.3 22.6 22.7∼24.3 24.4 24.5∼24.9 25 25.3 25.9 26 26.2∼27.1 27.1∼28.8 28.8∼29.8 29.8∼30.7 30.7∼
13 12 10 11 4 3 9 8 30 22 1 3 9 57 74 157 82 30 129 662
0 0 0 0 0 0 3 0 13 7 0 0 5 23 29 84 53 21 123 361
0 0 0 0 0 0 0 0 0 0 0 0 2 1 6 15 25 13 76 138
0 0 0 0 0 0 0 0 0 0 0 0 3 0 6 3 1 3 16
a The relation between the peak areas (x) of the sulfur compounds by the GC-AED analysis and the sulfur content (ppm) (y) in the oils given by the following formula: y ) 0.1969x.
derivatives were more easily eliminated than the sulfur compounds of the dibenzothiophene derivatives with high boiling points. The total sulfur concentration of the CGOs decreased with the increasing mixing time of fuel oils A with H2SO4. The CGO by mixing for 3 min was almost identical to the authentic gas oil based on the composition of the 14 compounds by GC-MS. The sulfur concentration of 361 ppm in the CGO was greater than the 16 ppm in the authentic gas oils listed in Table 3. The sulfur concentrations of the CGOs by mixing within 10 min were significantly greater than about 9 times the 16 ppm. The sulfur concentration of CGO gradually became similar to that of the authentic gas oil with the decreasing sulfur concentration for a mixing time of more than 10 min. However, the CGOs by mixing for more than 10 min were distinguished from the authentic gas oil because the GC-MS analysis showed no condensed polycyclic aromatic compounds present in the CGOs. (17) Miki, Y.; Sugimoto, Y.; Tanaka, M.; Wu, Z. Analysis of dibenzothiophene derivatives in straight-run and hydrodesulfurized gas oil (in Japanese). J. Jpn. Pet. Inst. 2002, 45(2), 117-122. (18) Ma, X.; Sakanishi, K.; Isoda, T.; Mochida, I. Determination of sulfur compounds in nonpolar fraction of vacuum gas oil. Fuel 1997, 76 (4), 329-339. (19) Segawa, K.; Takahashi, K.; Satoh, S. Development of new catalysts for deep hydrodesulfurization of gas oil. Catal. Today 2000, 63, 123-131. (20) Kabe, T.; Akamatsu, K.; Ishihara, A.; Otsuki, S.; Godo, M.; Zhang, Q.; Qian, W. Deep hydrodesulfurization of light gas oil. 1. Kinetics and mechanisms of dibenzothiophene hydrodesulfurization. Ind. Eng. Chem. Res. 1997, 36, 5146-5152.
Conclusion Sulfuric acid removed coumarin, the aromatics, and sulfur compounds more easily than the paraffins from fuel oil A by sulfonation. Furthermore, H2SO4 was more effective for eliminating the condensed polycyclic compounds from fuel oil A than the noncondensed polycyclic compounds. The CGO samples were gradually changed into oils high in paraffins. The GC-MS analysis showed no condensed polycyclic aromatic compounds such as naphthalene and phenanthrene in the CGO samples before the sulfuric content in the CGO samples was reduced to 50 ppm or less,15,16 which corresponded to the sulfur content in the authentic gas oil, by GC-AED sulfur analysis. Therefore, the CGO by mixing fuel oil A with H2SO4 was rapidly distinguished from gas oil on the basis of the GC-MS analysis of the aromatic compounds and the GC-AED analysis of the sulfur compounds in the oils. This analytical method offers the discrimination of gas oil, gasoline, and fuel oil A with sulfur compounds for environmental preservation. Acknowledgment. The authors thank the Analytical Laboratory of the Cosmo Oil Co. for analysis of the samples by GC-AED and useful discussion. The authors acknowledge the elemental analyses of the sulfur contents in the oils provided by the Technology Division of Nihon SiberHegner K.K. EF034108M
