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Hydrocarbon group-type analysis of high boiling petroleum distillates by HPLC
Journal of Petroleum Science and Engineering 22 Ž1999. 31–36
Hydrocarbon group-type analysis of high boiling petroleum distillates by HPLC Dongmei Qiang, Wanzhen Lu
)
Research Institute of Petroleum Processing, SINOPEC, Beijing, 100083 China Accepted 17 January 1997
Abstract A high performance liquid chromatography ŽHPLC. system was developed for the group-type analysis of high boiling petroleum distillates Ž350–5008C.. By coupling with multi-column switching and gradient elution techniques, the high boiling distillates were separated into saturates, monoaromatics, diaromatics, polyaromatics Ž3–5 rings. and resins Žmore than six condensed-ring aromatics and polar compounds.. Employing moving-wire flame ionization detector for detection and data station for quantitation, the method was characterized by good separation, short analysis time and adaptability to high boiling samples. Its quantitative results showed a high repeatability and were well consistent with mass spectroscopy results for most high boiling distillates. q 1999 Elsevier Science B.V. All rights reserved. Keywords: Hydrocarbon group-type analysis; High boiling petroleum distillates; High performance liquid chromatography ŽHPLC. system
1. Introduction The properties of petroleum and its products are closely related to their chemical compositions. The hydrocarbon compositional information are important for petroleum processing. Group-type analysis is a widely used procedure for obtaining the required information to evaluate petroleum and its products in the petroleum industry. The method normally used for hydrocarbon group-type analysis is the fluorescent indicator adsorption method ŽFIA. and it is well known for its simplicity and ease of operation. However, its poor separation is usually encountered in samples with
)
Corresponding author. Fax: q86-62017429
final boiling points higher than 3158C and dark colored samples ŽLee et al., 1989; Ozubko and Clugstom, 1981.. Gas chromatography coupling with mass spectroscopy ŽGC-MS. has been widely used for hydrocarbon analysis of light fractions in oil industry ŽPetrakis et al., 1983; Disanzo and Giarrocco, 1988; Matisova and Juranyiova, 1991; Beardslay, 1985; Sazonova and Lunskii, 1986.. But the requirement of vaporization of samples limits its application in separation of samples with high boiling point and poor thermostability. Supercritical fluid chromatography ŽSFC. has become a popular analytical tool in petroleum analysis during last few years not only for its ability to analyze thermally unstable and relatively high-molecular-weight compounds, but also because highly efficient and selective capillary columns can be used to achieve unique separations
0920-4105r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 0 - 4 1 0 5 Ž 9 8 . 0 0 0 5 4 - 0
32
D. Qiang, W. Lu r Journal of Petroleum Science and Engineering 22 (1999) 31–36
Žespecially for polycyclic aromatics. ŽNorris and Rawdon, 1984; Apffel and MeNair, 1983; Schwartz and Brownlee, 1986; Disanzo and Yoder, 1991; Levy, 1994; Lundanes and Greibrokk, 1985; Compell et al., 1988; Fields et al., 1988; Ashraf-Khorassani and Levy, 1992.. But the expensive mobile phase-supercritical CO 2 and complicated operation make SFC difficult to apply in production control in refinery. The application of high performance liquid chromatography ŽHPLC. to hydrocarbon group-type analysis of petroleum products was first reported in 1970s. HPLC is characteristic with its high efficiency, high speed, high sensitivity and wide application range. The development and application of HPLC offer a powerful analytical tool for high boiling distillates. Detail studies on HPLC utilizing alumina, silica and various chemically bonded silica stationary phases to analyse petroleum products have been published ŽStevenson, 1971; Suatoni and Swab, 1975; Popl and Dolansky, 1978; Vogh and Thornson, 1981; Matthias, 1984; Pei and Britton, 1983; Grizzle and Sablotny, 1986; Felix and Thoumazeau, 1987; Grizzle and Thomson, 1982; Hsu and McLean, 1991; Pearsonand and Gharfeh, 1986; Dimor et al., 1993; Chen and Steenackers, 1993; Miller, 1982.. But the aromatic-ring number separation of high boiling distillates has been still a difficult task. Traditional open-column chromatography coupled with mass spectroscopic ŽMS. technique is a powerful analytical tool which provides detailed compositional information for alkanes, cycloalkanes and aromatics.
But it is difficult to be received as a routine method by hydrocarbon processing due to its high capital costs, long analysis time and requirement of known calibration coefficients. According to the coordination between double bond and empty d-orbit of silver ion ŽAgq. , using silver bonded silica to separate olefins from saturates using HPLC was reported in earlier years ŽMckay and Latham, 1980; Matsushita and Teda, 1981; Hayes and Anderson, 1987; Hayes and Anderson, 1988; Tao et al., 1995.. In this study, silver sulfonic bonded silica ŽAg-SCX. and cynobonded silica column were used to separate various high boiling distillates into saturates, mono-, di-, poly-aromatics and resin.
2. Experimental section 2.1. Apparatus The HPLC system was operated under the following conditions. 2.1.1. Liquid chromatography HP 1050 pump, HP 1050 autosampler, ŽHewlett Packard.; TL-9300 chromatographic workstation ŽTaili Electronic, Beijing.; Stationary phase, SCX ŽNucleosil 10SA, Macherey-Nagel Germany, 10 mm. exchanged with Agq; column, 10 cm = 3.9 mm i.d.; mobile phase, n-hexane, 1.0 mlrmin; modifier, cyclohexene.
Fig. 1. Valve switching configuration of HPLC system. Ž1. HPLC pump; Ž2. autosampler; Ž3. CN-bonded silica column; Ž4. Ag-SCX column; Ž5. MW-FID detector A, six-port switching valve. Step 1: solid line—for eluting saturates and aromatic classes from Ag-SCX column. Step 2: dotted line—for backflushing resin from CN-bonded silica column.
D. Qiang, W. Lu r Journal of Petroleum Science and Engineering 22 (1999) 31–36
33
Table 1 Solvent elution sequence of HPLC system Elution time Žmin. Configuration Mobile phase 0–3.0 3.0–5.0 5.0–8.0 8.0–9.0 9.0–12.5 12.5–13.0 13.0–17.5
solid line solid line solid line solid line solid line dotted line dotted line
n-hexane 3‰ cyclohexener n-hexane n-hexane 10% cyclohexener n-hexane n-hexane CH 2 Cl 2 n-hexane
Fig. 2. Separation of a lube base oil. Mobile phase: 0–1.0 min, n-hexane; 1.0–6.0 min, 1‰ cyclohexene; )6.0 min, 10% cyclohexene, flow rate, 1 mlrmin.
2.1.2. MW-FID detector (Yuan et al., 1994) Carrier gas, hydrogen and nitrogen; spray gas, air; clean chamber temperature, 8508C; oxidation chamber, 7508C; catalysis chamber, 3508C; FID temperature, 2008C.
weighed into 5-ml volumetric flasks and then diluted to the mark with analytical grade n-hexane Žafter purification.. Same solvent with different volume percentage of cyclohexene was used for the HPLC eluent.
2.2. Procedure
2.2.3. Chromatographic analysis The valve switching configuration was illustrated in Fig. 1. The solvent elution sequences was listed in Table 1. Diluted samples of high boiling distillates were injected into the chromatographic system by autosampler. A CN-bonded silica column was used to retain resin and the Ag-SCX column was used for separation of saturates and different aromatic classes. n-Hexane was used as mobile phase to elute saturates at a flow rate of 1 mlrmin, with different volume percentage of cyclohexene as modifier to displace diaromatics and polyaromatics Žsolid line in Fig. 1.. After elution of polyaromatics, the position of the six-port switching valve was changed as indicated by dotted lines in Fig. 1. Dichloromethane ŽCH 2 Cl 2 . was used for back-flushing resin. The
2.2.1. Preparation of Ag-SCX column A 10 cm = 3.9 mm i.d. column was packed with 10 mm SCX by the classical slurry packing technique. A 1.0-g SCX stationary was suspended in 30-ml cyclohexanol-toluene Ž2:1. and the slurry was forced with petroleum benzene into the chromatographic column under a pressure of 7500 psi. Agq was bonded on the SCX column by in situ flushing with 0.1 molrl aqueous silver nitrate, followed by flushing with de-ionized water, ethanol, tetrahydrofuran and n-hexane. 2.2.2. Sample preparation The petroleum samples were prepared for analysis as follows: different high boiling distillates were
Table 2 Retention time of model aromatic hydrocarbons Hydrocarbon
Retention time Žmin.
Hydrocarbon
Retention time Žmin.
Dodecylbenzen Tetrohydronaphthalene Methylnaphthalene Acenaphthene Fluorene Phenanthrene Anthracene
2.90 3.50 8.35 8.80 8.85 11.50 11.55
Pyrene 1,2-Benzoanthracene 3,4-Benzopyrene 1,2,5,6-Dibenzoanthracene 2,3,6,7-Dibenzoanthracene Coroene Benzofuran
11.60 12.00 11.45 11.50 11.85 15.00 14.25
34
D. Qiang, W. Lu r Journal of Petroleum Science and Engineering 22 (1999) 31–36
3.2. QualitatiÕe analysis
Fig. 3. Separation of a high boiling distillates. ŽThe solvent elution sequence same as that listed in Table 1..
integration of chromatographic peaks was accomplished on TL-9300 workstation. 2.2.4. Quantitation Normalized area percent was used. Since MW-FID detector is a mass detector, the response factor is not related to hydrocarbon type and solvent properties.
3. Results and discussion 3.1. Determination of retention time of model aromatic hydrocarbons The retention time of model aromatic hydrocarbons ŽTable 2. was determined under the chromatographic conditions selected in Section 2. The results listed in Table 2 showed that baseline separation of aromatic classes was achieved by using this HPLC system. Monoaromatics was eluted by n-hexane; diaromatics was displaced by 3‰ cyclohexene and tri-, tetra-, penta-aromatics were displaced by 10% cyclohexene. Coroene and benzofuran were retained on CN-bonded column and backflushed by CH 2 Cl 2 .
A lube base oil was separated by the Ag-SCX column. The eluates in different elution time were collected according to its chromatogram ŽFig. 2.. The UV and MS qualitative analysis of eluates showed that the aromatics were basically separated into mono-, di-, and polyaromatics.
3.3. QuantitatiÕe analysis A series of high boiling distillates were separated by the chromatographic system. The compositions of high boiling distillates were obtained by the normalized area percent according to their chromatogram. Fig. 3 showed the separation of a high boiling distillate. As shown in Fig. 3, saturates, monoaromatics, diaromatics, poly-aromatics and resin in high boiling distillates were obtained a baseline separation in this HPLC system. Table 3 listed the quantitative results of various high boiling distillates by HPLC compared to the results by MS method, which is the combination of traditional open-column chromatography and MS technique. As the results listed in Table 3, close resemblance existed between HPLC results and MS results for straight distillates. But for some special petroleum fractions, such as coking oil and heavy oil from catalytic cracking, their HPLC results deviated from MS results because of their complicated structural compositions. Moreover, the repeatability of quantitative results by HPLC method was very good.
Table 3 Quantitative results of various high boiling distillates by HPLC and MS Žwt.%. Sample components
Straight distillate HPLC
MS
HPLC
MS
HPLC
MS
HPLC
MS
Saturates Monoaromatics Diaromatics Polyaromatics Resin
65.5 10.3 13.2 8.7 2.3
64.5 10.2 13.5 8.9 2.9
78.0 12.7 7.3 1.8 0.2
80.5 11.8 6.4 1.3 0.0
68.3 12.1 10.4 5.2 4.0
68.4 11.8 10.9 5.6 3.3
51.7 12.9 20.2 10.5 4.7
59.8 12.0 14.6 9.8 4.8
DCC, deep catalytic cracking.
HVIS lube base oil
DCC feed stocks
Coking oil
D. Qiang, W. Lu r Journal of Petroleum Science and Engineering 22 (1999) 31–36
4. Conclusion A high performance liquid chromatographic ŽHPLC. system was established for the group-type analysis of high boiling petroleum distillates. By coupling with multi-column switching and gradient elution techniques, a CN-bonded silica column was used to retain resin and a column packed with AgSCX stationary phase was used to separate saturates and different cyclic aromatics. n-Hexane was used as m obile phase, cyclohexene as m odifier, dichloromethane ŽCH 2 Cl 2 . for back-flushing resin. Contents of saturates, monoaromatics, diaromatics, polyaromatics and resin can be obtained within 20 min. The UV and mass spectropic ŽMS. qualitative analysis of the eluates in each chromatographic peak showed that hydrocarbon group-type were well separated. The quantitative results of straight distillates and lube base oil were well consistent with MS results. But for some special petroleum fractions, such as coking oil and heavy oil from catalytic cracking, their HPLC results deviated from MS results because of their complicated structural compositions.
References Apffel, J.A., MeNair, H., 1983. Hydrocarbon group-type analysis by on-line multidimensional chromatography. J. Chromatogr. 279, 139. Ashraf-Khorassani, M., Levy, J.M., 1992. SFC determination of saturates and aromatics in petroleum streams. Am. Lab. 5, 29. Beardslay, J.D., 1985. Fuels, gaseous and liquid. Anal. Chem. 57, 195R. Chen, J., Steenackers, D., 1993. Temperature optimization for the separation of PAHs on micropacked LC ODS columns. J. High Resolut. Chromatogr. 16, 605. Compell, R.N., Djordjevic, N.M., Markides, K.E., Lee, M.L., 1988. Supercritical fluid chromatographic determination of hydrocarbon groups in gasolines and middle distillate fuels. Anal. Chem. 60, 356. Dimor, N., Millina, R., Fresenius, 1993. A new approach to the UV-spectral quantitative analysis of complex mixtures Žpetroleum products.. Anal. Chem. 345, 521. Disanzo, F.P., Yoder, R.E., 1991. Determination of aromatics in jet and diesel fuels by supercritical fluid chromatography with flame ionization detection: a quantitative study. J. Chromatogr. Sci. 29, 4. Disanzo, F.P., Giarrocco, V.J., 1988. Analysis of pressurized
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gasoline-range liquid hydrocarbon samples by capillary column and PIONA analyzer gas chromatography. J. Chromatogr. Sci. 26, 258. Felix, G., Thoumazeau, E., 1987. Hydrocarbon groups type analysis of petroleum products by HPLC on specific stationary phases. J. Liq. Chromatogr. 10, 2115. Fields, S.M., Markides, K.E., Lee, M.L., 1988. Ultraviolet-absorption detector for capillary supercritical fluid chromatography with compressible mobile phase. Anal. Chem. 60, 802. Grizzle, P.L., Sablotny, D.M., 1986. Automated liquid chromatographic compound class group-type separation of crude oils and bitumens using chemically bonded aminosilane. Anal. Chem. 58, 2389. Grizzle, P.L., Thomson, J.S., 1982. Liquid chromatographic separation of aromatic hydrocarbons with chemically bonded Ž2,4Dinitro-anilinopropyl.silica. Anal. Chem. 54, 1071. Hayes, P.C., Anderson, S.D., 1987. Rapid determination of naphthenes in hydrocarbon distillates using on-line column switching high-performance liquid chromatography with dielectric constant detection. J. Chromatogr. 387, 333. Hayes, P.C., Anderson, S.D., 1988. High resolution multidimensional chromatographic analysis of hydrocarbon distillate fuels: matrix simplification using off-line preparative HPLCrDCD with on-column GCrMSD and GCrFID. J. Chromatogr. Sci. 26, 250. H su, C .S., M cL ean, M .A ., 1991. O n-line liquid chromatographyrmass spectrometry for heavy hydrocarbon characterization. Energy Fuel 5, 395. Lee, S.W., Fuhr, B.J., Holloway, L.R., 1989. Development of supercritical fluid chromatographic method for determination of aromatics in heating oils and diesel fuels. Energy and Fuel 3, 80. Levy, J.M., 1994. Fossil fuel applications of SFC and SFE: a review. J. High Resolut. Chromatogr. 17, 212. Lundanes, E., Greibrokk, T., 1985. Group separation of oil residues by supercritical fluid chromatography. J. Chromatogr. 349, 439. Matisova, E., Juranyiova, E., 1991. Analysis of multi-component mixtures by high resolution capillary gas chromatography and combined gas chromatography-mass spectrometry. J. Chromatogr. 552, 301. Matsushita, S., Teda, Y., 1981. Rapid hydrocarbon group analysis of gasoline by high performance liquid chromatography. J. Chromatogr. 208, 429. Matthias, R., 1984. Class separation of aromatic compounds in rock extracts and fossil fuels by liquid chromatography. Anal. Chem. 56, 2538. Mckay, J.F., Latham, P.R., 1980. High performance liquid chromatographic separation of olefin, saturate and aromatic hydrocarbons in high-boiling distillates and residues of shale oil. Anal. Chem. 52, 1618. Miller, R.L., 1982. Hydrocarbon class fractionation with bondedphase liquid chromatography. Anal. Chem. 54, 1742. Norris, T.A., Rawdon, M.G., 1984. Determination of hydrocarbon type in petroleum liquids by supercritical fluid chromatography with flame ionization detection. Anal. Chem. 56, 1767. Ozubko, R.S., Clugstom, D.M., 1981. Comparison of mass spec-
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D. Qiang, W. Lu r Journal of Petroleum Science and Engineering 22 (1999) 31–36
trometry and nuclear magnetic resonance spectrometry for determination of hydrocarbon type. Anal. Chem. 53, 183. Pearsonand, D., Gharfeh, S.G., 1986. Automated high-performance liquid chromatography determination of hydrocarbon types in crude oil residuals using a flame ionization detector. Anal. Chem. 58, 307. Pei, P., Britton, J., 1983. Hydrocarbon type separation of lubricating base oil in multigram quantity by preparative HPLC. J. Liq. Chromatogr. 6, 627. Petrakis, L., Allen, D.T., Gates, B.C., 1983. Analysis of synthetic fuels for functional group determination. Anal. Chem. 55, 1557. Popl, M., Dolansky, V., 1978. Hydrocarbons and porphyrins in rock extracts. Fuel 57, 565. Sazonova, M.L., Lunskii, M.K., 1986. Gas chromatographic determination of the composition of unfractionated natural hydrocarbon mixtures. J. Chromatogr. 364, 267.
Schwartz, H.E., Brownlee, R.G., 1986. Hydrocarbon group analysis of gasolines with microbore supercritical fluid chromatography with flame ionization detection. J. Chromatogr. 353, 77. Stevenson, R., 1971. Rapid separation of petroleum fuels by hydrocarbon type. J. Chromatogr. Sci. 9, 257. Suatoni, J.C., Swab, K.E., 1975. Rapid hydrocarbon group-type analysis by high performance liquid chromatography. J. Chromatogr. Sci. 13, 361. Tao, X.M., Long, Y.Ch., Lu, W.Zh., 1995. The analysis of diesel fuels by high performance liquid chromatography. Chin. J. Chromatogr. 13, 368. Vogh, J.W., Thornson, J.S., 1981. Preparative liquid chromatography for fractionation of petroleum and synthetic crude oils. Anal. Chem. 53, 1345. Yuan, H.F., Yang, M.B., Fen, S.K., 1994. Moving-wire flame ionization detector for hydrocarbon analysis by HPLC, CN 2157519Y, 23, 6, p. 2.
Hydrocarbon group-type analysis of high boiling petroleum distillates by HPLC Dongmei Qiang, Wanzhen Lu
)
Research Institute of Petroleum Processing, SINOPEC, Beijing, 100083 China Accepted 17 January 1997
Abstract A high performance liquid chromatography ŽHPLC. system was developed for the group-type analysis of high boiling petroleum distillates Ž350–5008C.. By coupling with multi-column switching and gradient elution techniques, the high boiling distillates were separated into saturates, monoaromatics, diaromatics, polyaromatics Ž3–5 rings. and resins Žmore than six condensed-ring aromatics and polar compounds.. Employing moving-wire flame ionization detector for detection and data station for quantitation, the method was characterized by good separation, short analysis time and adaptability to high boiling samples. Its quantitative results showed a high repeatability and were well consistent with mass spectroscopy results for most high boiling distillates. q 1999 Elsevier Science B.V. All rights reserved. Keywords: Hydrocarbon group-type analysis; High boiling petroleum distillates; High performance liquid chromatography ŽHPLC. system
1. Introduction The properties of petroleum and its products are closely related to their chemical compositions. The hydrocarbon compositional information are important for petroleum processing. Group-type analysis is a widely used procedure for obtaining the required information to evaluate petroleum and its products in the petroleum industry. The method normally used for hydrocarbon group-type analysis is the fluorescent indicator adsorption method ŽFIA. and it is well known for its simplicity and ease of operation. However, its poor separation is usually encountered in samples with
)
Corresponding author. Fax: q86-62017429
final boiling points higher than 3158C and dark colored samples ŽLee et al., 1989; Ozubko and Clugstom, 1981.. Gas chromatography coupling with mass spectroscopy ŽGC-MS. has been widely used for hydrocarbon analysis of light fractions in oil industry ŽPetrakis et al., 1983; Disanzo and Giarrocco, 1988; Matisova and Juranyiova, 1991; Beardslay, 1985; Sazonova and Lunskii, 1986.. But the requirement of vaporization of samples limits its application in separation of samples with high boiling point and poor thermostability. Supercritical fluid chromatography ŽSFC. has become a popular analytical tool in petroleum analysis during last few years not only for its ability to analyze thermally unstable and relatively high-molecular-weight compounds, but also because highly efficient and selective capillary columns can be used to achieve unique separations
0920-4105r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 0 - 4 1 0 5 Ž 9 8 . 0 0 0 5 4 - 0
32
D. Qiang, W. Lu r Journal of Petroleum Science and Engineering 22 (1999) 31–36
Žespecially for polycyclic aromatics. ŽNorris and Rawdon, 1984; Apffel and MeNair, 1983; Schwartz and Brownlee, 1986; Disanzo and Yoder, 1991; Levy, 1994; Lundanes and Greibrokk, 1985; Compell et al., 1988; Fields et al., 1988; Ashraf-Khorassani and Levy, 1992.. But the expensive mobile phase-supercritical CO 2 and complicated operation make SFC difficult to apply in production control in refinery. The application of high performance liquid chromatography ŽHPLC. to hydrocarbon group-type analysis of petroleum products was first reported in 1970s. HPLC is characteristic with its high efficiency, high speed, high sensitivity and wide application range. The development and application of HPLC offer a powerful analytical tool for high boiling distillates. Detail studies on HPLC utilizing alumina, silica and various chemically bonded silica stationary phases to analyse petroleum products have been published ŽStevenson, 1971; Suatoni and Swab, 1975; Popl and Dolansky, 1978; Vogh and Thornson, 1981; Matthias, 1984; Pei and Britton, 1983; Grizzle and Sablotny, 1986; Felix and Thoumazeau, 1987; Grizzle and Thomson, 1982; Hsu and McLean, 1991; Pearsonand and Gharfeh, 1986; Dimor et al., 1993; Chen and Steenackers, 1993; Miller, 1982.. But the aromatic-ring number separation of high boiling distillates has been still a difficult task. Traditional open-column chromatography coupled with mass spectroscopic ŽMS. technique is a powerful analytical tool which provides detailed compositional information for alkanes, cycloalkanes and aromatics.
But it is difficult to be received as a routine method by hydrocarbon processing due to its high capital costs, long analysis time and requirement of known calibration coefficients. According to the coordination between double bond and empty d-orbit of silver ion ŽAgq. , using silver bonded silica to separate olefins from saturates using HPLC was reported in earlier years ŽMckay and Latham, 1980; Matsushita and Teda, 1981; Hayes and Anderson, 1987; Hayes and Anderson, 1988; Tao et al., 1995.. In this study, silver sulfonic bonded silica ŽAg-SCX. and cynobonded silica column were used to separate various high boiling distillates into saturates, mono-, di-, poly-aromatics and resin.
2. Experimental section 2.1. Apparatus The HPLC system was operated under the following conditions. 2.1.1. Liquid chromatography HP 1050 pump, HP 1050 autosampler, ŽHewlett Packard.; TL-9300 chromatographic workstation ŽTaili Electronic, Beijing.; Stationary phase, SCX ŽNucleosil 10SA, Macherey-Nagel Germany, 10 mm. exchanged with Agq; column, 10 cm = 3.9 mm i.d.; mobile phase, n-hexane, 1.0 mlrmin; modifier, cyclohexene.
Fig. 1. Valve switching configuration of HPLC system. Ž1. HPLC pump; Ž2. autosampler; Ž3. CN-bonded silica column; Ž4. Ag-SCX column; Ž5. MW-FID detector A, six-port switching valve. Step 1: solid line—for eluting saturates and aromatic classes from Ag-SCX column. Step 2: dotted line—for backflushing resin from CN-bonded silica column.
D. Qiang, W. Lu r Journal of Petroleum Science and Engineering 22 (1999) 31–36
33
Table 1 Solvent elution sequence of HPLC system Elution time Žmin. Configuration Mobile phase 0–3.0 3.0–5.0 5.0–8.0 8.0–9.0 9.0–12.5 12.5–13.0 13.0–17.5
solid line solid line solid line solid line solid line dotted line dotted line
n-hexane 3‰ cyclohexener n-hexane n-hexane 10% cyclohexener n-hexane n-hexane CH 2 Cl 2 n-hexane
Fig. 2. Separation of a lube base oil. Mobile phase: 0–1.0 min, n-hexane; 1.0–6.0 min, 1‰ cyclohexene; )6.0 min, 10% cyclohexene, flow rate, 1 mlrmin.
2.1.2. MW-FID detector (Yuan et al., 1994) Carrier gas, hydrogen and nitrogen; spray gas, air; clean chamber temperature, 8508C; oxidation chamber, 7508C; catalysis chamber, 3508C; FID temperature, 2008C.
weighed into 5-ml volumetric flasks and then diluted to the mark with analytical grade n-hexane Žafter purification.. Same solvent with different volume percentage of cyclohexene was used for the HPLC eluent.
2.2. Procedure
2.2.3. Chromatographic analysis The valve switching configuration was illustrated in Fig. 1. The solvent elution sequences was listed in Table 1. Diluted samples of high boiling distillates were injected into the chromatographic system by autosampler. A CN-bonded silica column was used to retain resin and the Ag-SCX column was used for separation of saturates and different aromatic classes. n-Hexane was used as mobile phase to elute saturates at a flow rate of 1 mlrmin, with different volume percentage of cyclohexene as modifier to displace diaromatics and polyaromatics Žsolid line in Fig. 1.. After elution of polyaromatics, the position of the six-port switching valve was changed as indicated by dotted lines in Fig. 1. Dichloromethane ŽCH 2 Cl 2 . was used for back-flushing resin. The
2.2.1. Preparation of Ag-SCX column A 10 cm = 3.9 mm i.d. column was packed with 10 mm SCX by the classical slurry packing technique. A 1.0-g SCX stationary was suspended in 30-ml cyclohexanol-toluene Ž2:1. and the slurry was forced with petroleum benzene into the chromatographic column under a pressure of 7500 psi. Agq was bonded on the SCX column by in situ flushing with 0.1 molrl aqueous silver nitrate, followed by flushing with de-ionized water, ethanol, tetrahydrofuran and n-hexane. 2.2.2. Sample preparation The petroleum samples were prepared for analysis as follows: different high boiling distillates were
Table 2 Retention time of model aromatic hydrocarbons Hydrocarbon
Retention time Žmin.
Hydrocarbon
Retention time Žmin.
Dodecylbenzen Tetrohydronaphthalene Methylnaphthalene Acenaphthene Fluorene Phenanthrene Anthracene
2.90 3.50 8.35 8.80 8.85 11.50 11.55
Pyrene 1,2-Benzoanthracene 3,4-Benzopyrene 1,2,5,6-Dibenzoanthracene 2,3,6,7-Dibenzoanthracene Coroene Benzofuran
11.60 12.00 11.45 11.50 11.85 15.00 14.25
34
D. Qiang, W. Lu r Journal of Petroleum Science and Engineering 22 (1999) 31–36
3.2. QualitatiÕe analysis
Fig. 3. Separation of a high boiling distillates. ŽThe solvent elution sequence same as that listed in Table 1..
integration of chromatographic peaks was accomplished on TL-9300 workstation. 2.2.4. Quantitation Normalized area percent was used. Since MW-FID detector is a mass detector, the response factor is not related to hydrocarbon type and solvent properties.
3. Results and discussion 3.1. Determination of retention time of model aromatic hydrocarbons The retention time of model aromatic hydrocarbons ŽTable 2. was determined under the chromatographic conditions selected in Section 2. The results listed in Table 2 showed that baseline separation of aromatic classes was achieved by using this HPLC system. Monoaromatics was eluted by n-hexane; diaromatics was displaced by 3‰ cyclohexene and tri-, tetra-, penta-aromatics were displaced by 10% cyclohexene. Coroene and benzofuran were retained on CN-bonded column and backflushed by CH 2 Cl 2 .
A lube base oil was separated by the Ag-SCX column. The eluates in different elution time were collected according to its chromatogram ŽFig. 2.. The UV and MS qualitative analysis of eluates showed that the aromatics were basically separated into mono-, di-, and polyaromatics.
3.3. QuantitatiÕe analysis A series of high boiling distillates were separated by the chromatographic system. The compositions of high boiling distillates were obtained by the normalized area percent according to their chromatogram. Fig. 3 showed the separation of a high boiling distillate. As shown in Fig. 3, saturates, monoaromatics, diaromatics, poly-aromatics and resin in high boiling distillates were obtained a baseline separation in this HPLC system. Table 3 listed the quantitative results of various high boiling distillates by HPLC compared to the results by MS method, which is the combination of traditional open-column chromatography and MS technique. As the results listed in Table 3, close resemblance existed between HPLC results and MS results for straight distillates. But for some special petroleum fractions, such as coking oil and heavy oil from catalytic cracking, their HPLC results deviated from MS results because of their complicated structural compositions. Moreover, the repeatability of quantitative results by HPLC method was very good.
Table 3 Quantitative results of various high boiling distillates by HPLC and MS Žwt.%. Sample components
Straight distillate HPLC
MS
HPLC
MS
HPLC
MS
HPLC
MS
Saturates Monoaromatics Diaromatics Polyaromatics Resin
65.5 10.3 13.2 8.7 2.3
64.5 10.2 13.5 8.9 2.9
78.0 12.7 7.3 1.8 0.2
80.5 11.8 6.4 1.3 0.0
68.3 12.1 10.4 5.2 4.0
68.4 11.8 10.9 5.6 3.3
51.7 12.9 20.2 10.5 4.7
59.8 12.0 14.6 9.8 4.8
DCC, deep catalytic cracking.
HVIS lube base oil
DCC feed stocks
Coking oil
D. Qiang, W. Lu r Journal of Petroleum Science and Engineering 22 (1999) 31–36
4. Conclusion A high performance liquid chromatographic ŽHPLC. system was established for the group-type analysis of high boiling petroleum distillates. By coupling with multi-column switching and gradient elution techniques, a CN-bonded silica column was used to retain resin and a column packed with AgSCX stationary phase was used to separate saturates and different cyclic aromatics. n-Hexane was used as m obile phase, cyclohexene as m odifier, dichloromethane ŽCH 2 Cl 2 . for back-flushing resin. Contents of saturates, monoaromatics, diaromatics, polyaromatics and resin can be obtained within 20 min. The UV and mass spectropic ŽMS. qualitative analysis of the eluates in each chromatographic peak showed that hydrocarbon group-type were well separated. The quantitative results of straight distillates and lube base oil were well consistent with MS results. But for some special petroleum fractions, such as coking oil and heavy oil from catalytic cracking, their HPLC results deviated from MS results because of their complicated structural compositions.
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