Analysis of Heavy Oils by FID-TLC (Part 3)

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1 Analysis of Heavy Oils by FID-TLC (Part 3) Preparation of Thin Layer Rods with Chemically Bonded Silica Gels Yojiro YAMAMOTO* and Yoichi OHNO Research Center, Maruzen Oil Co., Ltd., , Gongendo, Satte-cho, Kitakatsushika-gun, Saitama Preparation of thin layer rods using partially chemically bonded silica gels was investigated to develop a rapid method for hydrocarbon type analysis of heavy oils by flame ionization detection-thin layer chromatography (FID-TLC) in which the rods served as the stationary phase. Aminopropyl and cyanopropyl bonded silica gel thin layer rods (Chromarod NH2-SII and Chromarod CN-SII) were prepared. Chromarods composed of 40% chemically bonded layer and 60% silica gel layer had good separability in FID-TLC for hydrocarbon type analysis of heavy oils. Moreover, the observation of Chromarod NH2-SII surface by EPMA suggested that aminopropyl groups were bonded uniformly onto the surface of silica thin layer of the Chromarod. 1. Introduction The development of technology to produce light fraction from heavy oil has become an important subject for research. Characterization of heavy oils and their products is necessary for understanding the reactions in the treatment of heavy oils. Since heavy oil comprises a variety of structurally complex compounds, it is impossible to isolate them. Compositional analysis to determine the contents of the individual fractions with similar chemical properties in heavy oils provides an important characteristic means. Adsorption column chromatography with silica gel1) or with alumina gel2) has been generally used for analyzing the chemical composition of heavy oils. Because the method has such drawbacks as necessitating timeconsuming determinations and use of large quantities of solvents, high performance liquid chromatography (HPLC) has been recently studied for many applications.3)-10) Since Wise et al.5) discovered that alkylamine bonded silica gels had advantage for the separation of aromatic ring compounds, these have been widely used for various hydrocarbon type analysis.8)-10) However, any method using HPLC will have shortcomings in quantitation. The unsatisfactory quantitative analysis of HPLC stems mainly from the difference in the sensitivity of each component in the RI detector or in the UV detector. Although thin layer chromatography also has shortcomings in quantitation, it has, at the same * To whom correspondence should be addressed. time, such advantages as high separability, simple and rapid procedure, and use of small samples. Moreover, some of the problems have been removed by the development of thin layer chromatography with flame ionization detection (FID-TLC), which is now used in many applications.11)-15) We have also developed rapid methods for determination of asphaltene contents in heavy oils16) and analyzing the compositions of them.17) In this study, the preparation of thin layer rods with partially chemically bonded silica gel has been investigated for the purpose of developing a rapid method for hydrocarbon type analysis of heavy oils by FID-TLC in which those rods serve as the stationary phase. 2. Experimental 2.1 Materials For standard samples, n-pentacosane, n-octadecylbenzene, 2,6-dimethylnaphthalene, and 9,10- dimethylanthracene (guaranteed reagents obtained from Tokyo Kasei Kogyo) were used. n- Hexane (liquid chromatography use of Wako Pure Chemical Industries) was used as the developing solvent for FID-TLC. 2.2 Apparatus and Methods FID-TLC Iatroscan TH-10 (Iatron Laboratories Inc.) was used for FID-TLC analysis. Chromarod S and S II (thin layer rod sintered with silica gel) and Chromarod A (thin layer rod sintered with alumina gel) were used as the stationary phase. C-R1A type Datalyzer (Simadzu) was used for treatment

2 of FID data in the same manner as in our previous papers.16),17) Such analytical conditions as the weight of sample loaded in TLC and the combustion conditions in FID were set at the optimum conditions described in our paper.16) Procedures for FID-TLC are as follows. justed to a concentration of 5-10wt% on (2) Develop the rod to 10cm after hanging for 5 minutes in the developing tank containing n-hexane. (3) Dry the rod at room temperature. (4) Determine the components as peak areas in the FID chromatogram Surface Analysis EMX-SM type Electron Probe X-ray Micro Analyzer (Simadzu) was used for the observation of rod surfaces. 3. Results and Discussion 3.1 Preparation of Thin Layer Rods with Chemically Bonded Silica Thin layer rods with aminopropyl or with cyanopropyl bonded silica gel (Chromarod NH2-SII or Chromarod CN-SII) were prepared by the following procedures.18) Chromarod SII was treated with (3-aminopropyl) triethoxysilane or (3-cyanopropyl) trichlorosilane according to the common and convenient method for preparation of bonded phases described in literature.19),20) The upper portion of the rod was then passed through a hydrogen flame to reform the silica gel layer for detection by FID, as shown in Fig. 1. Effect of length of chemically bonded layer in Chromarod on resolution was investigated, since separability is considered to be strongly affected by the layer length. In TLC, resolution (Rs) between adjecent peaks can be calculated from the following equation where (Zx)1 and (Zx)2 are the moved distances of peaks of component-1 and 2, and b1, b2 are the half widths of those peaks, respectively. Relationships between lengths of aminopropyl bonded layer in Chromarod NH2-SII ranging from 0 to 4cm and resolutions (Rs1, Rs2, Rs3) were examined, using a standard mixture prepared from n-pentacosane, n-octadecylbenzene, 2,6- dimethylnaphthalene, and 9,10-dimethylanthracene which were selected as representatives of Saturates (Sa), Monoaromatics (M-Ar), Diaromatics (D-Ar), and Triaromatics (T-Ar), respectively. The results are shown in Fig, 2 in which Rs1 and Rs2 hardly varied with the length of aminopropyl bonded layer, whereas Rs3 increased with its length. From these results, it can be concluded that Chromarods composed of 40% chemically bonded layer and 60% silica gel layer exhibited good separability in FID-TLC for hydrocarbon type a: Thin quartz rod b: Thin layer of silica gel c: Thin layer of chemically bonded silica gel F: Front point Fig. 1 Schematic Picture of Thin Layer Rod of Partially Chemically Bonded Silica Gel Fig. 2 Effect of Length of Chemically Bonded Layer in Chromarod on Resolution

3 1: n-pentacosane, 2: n-octadecylbenzene, 3: 2,6-Dimethylnaphthalene, 4: 9,10-Dimethylanthracene Fig. 3 FID-TLC Chromatograms of Standard Mixture by using Chromarods NH2-SII and CN-SII analysis of heavy oils. Fig. 3 shows FID-TLC chromatograms of the standard mixture by using Chromarod NH2-SII and Chromarod CN-SII. Both chromatograms for each type component give good separability. 3.2 Comparison with Conventional Chromarods Fig. 4 shows FID-TLC chromatograms of the standard mixture by using conventional Chromarods for comparing the chromatograms in Fig. 3. Table 1 shows a comparison of resolution indicated as Rsi (i=1-3) values for Chromarod NH2-SII and Chromarod CN-SII with those for conventional Chromarods. Since the separation of Sa, M-Ar, and D-Ar could not be carried out with Chromarod A because of its inadequate separability, Rsi for Chromarod A was not shown. Table 1 reveals that both Rs2 and Rs3 for Table 1 Comparison of Various Chromarods for Resolutions (Rsi) of Hydrocarbons i=1: Resolution between Sa and M-Ar i=2: Resolution between M-Ar and D-Ar i=3: Resolution between D-Ar and T-Ar Fig. 4 FID-TLC Chromatograms of Standard Mixture by using Chromarods S, SII, and A Chromarod NH2-SII and CN-SII, respectively, are larger than those for conventional Chromarods. This indicates good separation of Sa, M-Ar, D- Ar and T-Ar by FID-TLC with Chromarod NH2- SII and CN-SII, suggesting that Chromarod NH2- SII and Chromarod CN-SII have better separability in FID-TLC than conventional Chromarods for hydrocarbon type analysis of heavy oils. 3.3 Surface of Chromarod Surfaces of both chemically bonded layer (lower portion of the rod) and reformed silica gel layer (upper portion of the rod) of Chromarod NH2-SII were observed with EPMA. The results are shown in Figs. 5 and 6. Secondary electron (SE) s reveal that both s of both layers correspond well with the SE s of the respective layers. Furthermore, ically bonded layer corresponds to SE of its layer, as shown in Fig. 5. It is suggested, therefore, that aminopropyl groups are bonded uniformly onto the surface of chemically bonded layer of Chromarod NH2-SII. 4. Conclusion 1,2,3,4: Described in Fig. 3 Preparation of thin layer rods with partially chemically bonded silica gels was investigated to

4 496 (A) (B) 10um (C) (A): (C): Fig. 5 Surface (D) SE O-Kα of (A) Chemically Bonded (B): Si-Kα (D): C-Kα Layer of Chromarod NH2-SII (B) 10um (C) (D) (A), (B), (C), (D): Described in Fig. 5 Fig. 6 Surface of the 石油学会誌 Reformed Sekiyu Silica Gakkaishi, Gel Layer Vol. 28, of Chromarod No. 6, 1985 NH2-SII

5 develop a rapid method for hydrocarbon type analysis of heavy oils by FID-TLC in which those rods served as the stationary phase. Aminopropyl and cyanopropyl bonded silica gel thin layer rods (Chromarod NH2-SII and Chromarod CN-SII) could be prepared by treating Chromarod SII with (3-aminopropyl) triethoxysilane and (3-cyanopropyl) trichlorosilane. Chromarod composed of 40% chemically bonded layer and 60% silica gel layer exhibited good separability in FID-TLC for hydrocarbon type analysis of heavy oils. References 1) ASTM Part 15, 1289 (1982). 2) Iijima, H., Sekiyu Gakkaishi, 13, 606 (1970). 3) Suatoni, J. C., Suab, R. E., J. Chromatogr. Sci., 14, 535 (1976). 4) Suatoni, J. C., Garber, H. R., J. Chromatogr. Sci., 14, 546 (1976). 5) Wise, S. A., Chesler, S. N., Hertz, H. S., Hilpert, L. R., May, W. E., Anal. Chem., 49, (14), 2306 (1977). 6) Dark, W. A., McGough, R. R., J. Chromatogr. Sci., 16, 610 (1978). 7) Galya, L. G., Suatoni, J. C., J. Liq. Chromatogr., 3, (2), 229 (1980). 8) Chmielowiec, J., George, A. E., Anal. Chem., 52, (7), 1154 (1980). 9) Katoh, T., Yokoyama, S., Sanada, Y., Fuel, 59, 845 (1980). 10) Yokoyama, S., Tsuzuki, N., Uchino, H., Katoh, T., Sanada, Y., Nippon Kagaku Kaishi, 1983, ) Poirier, M. A., George, A. E., ACS, Div. Petrol. Chem., Prep., 27, 973 (1982). 12) Selucky, M. L., Anal. Chem., 55, 141 (1983). 13) Poirier, M. A., George, A. E., J. Chromatogr. Sci., 21, 331 (1983). 14) Sawada, S., Takahashi, T., Saito, K., Matsumura, T., Nenryo Kyokaishi, 63, 128 (1984). 15) Poirier, M. A., Rahimi, R., Ahmed, S. M., J. Chromatogr. Sci., 22, 116 (1984). 16) Yamamoto, Y., Kawanobe, T., Sekiyu Gakkaishi, 27, (3), 269 (1984). 17) Yamamoto, Y., Kawanobe, T., Sekiyu Gakkaishi, 27, (5), 373 (1984). 18) Yamamoto, Y., Patent pending. 19) Majors, R. E., J. Chromatogr. Sci., 18, 488 (1980). 20) Cooke, N. H. C., Olsen, K., J. Chromatogr. Sci., 18, 512 (1980). Keywords Chemically bonded silica, Flame ionization detection, Heavy oil, Hydrocarbon type analysis, Thin layer chromatography

Introduction. Experimental. Bhajendra N. Barman

Introduction. Experimental. Bhajendra N. Barman Hydrocarbon-Type Analysis of Base Oils and Other Heavy Distillates by Thin-Layer Chromatography with Flame-lonization Detection and by the Clay-Gel Method Bhajendra N. Barman Texaco Inc., Research and