I n d . Eng. Chem. Res. 1987, 26, 1822-1824
1822
Tipper, C. F. H., Eds.; Elsevier: Amsterdam, 1969; Vol. 2, Chapter 4. Dunlop, A. K. Corrosion Inhibitors; Nathen, C. C., Ed.; NACE: Houston, 1973; p 76. Flynn, C. M. Chem. Reu. 1984, 84, 31. Grogarty, W. B. J . Pet. Technol. 1983, 35, 1581, 1767. Hobson, D. B.; Richardson, P. J.; Robinson, P. J.; Hewitt, E. A.; Smith, I. J . Chem. Soc., Faraday Trans. 1 1986,82, 869. Johnson, D. A. Some Thermodynamic Aspects of Inorganic Chemistry, 2nd ed.; Cambridge University Press: Cambridge, 1982; Chapter 4. Linek, V.; Tvrdik, J. Biotechnol. Bioeng. 1971, 13, 353. Matsuura, A,; Harada, J.; Akehata, T.; Shirai, T. J . Chem. Eng. Jpn. 1969, 2(2), 199. Miron, R. L. Mater. Perform. 1981, 20(6), 45. Mishra, G. C.; Srivastava, R. D. Chem. Eng. Sci. 1975, 30, 1387. Mishra, G. C.; Srivastava, R. D. Chem. Eng. Sei. 1976, 31, 969. Mitchell, R. W.; Grist, D. M.; Boyle, M. J. J . Pet. Technol. 1980, 32, 904. Mitchell, R. W.; Finch, E. M. J . Pet. Technol. 1981, 33, 1141. Ogden, P. H. Chemicals i n the Oil Industry; Royal Society of Chemistry: London, 1983. Parsons, R. Handbook of Electrochemical Constants; Butterworths: London, 1959; p 69. Patton, C. C. Oilfield Water Systems; Campbell Petroleum Series;
Campbell Petroleum: New York, 1977. Penkett, S. A,; Jones, B. M. R.; Brice, K. A,; Eggleton, A. E. J. Atmos. Enuiron. 1979, 13, 123. Perrin, D. D. Ionisation Constants of Inorganic Acids and Bases in Aqueous Solution, 2nd ed.; IUPAC Chemical Data Series 29; Pergamon: Oxford, 1982; p 101. Richardson, P. J. PhD Thesis, CNAA (Manchester Polytechnic), 1983. Robinson, R. A,; Stokes, R. H. Electrolyte Solutions, 2nd ed.; Butterworths: London, 1959; Chapter 4. Scranton, D. C., Jr. Mater. Perform. 1979, 18(9), 46. Shreir, L. L. Corrosion;Newnes-Butterworth: London, 1976; Vol. 1. Sillen, L. G.; Martell, A. E. Stability Constants of Metal-Ion Complexes, 2nd ed.; Special Publication 17; Chemical Society: London, 1964; p 151 et seq. Snavely, E. S.,Jr. J . Pet. Technol. 1971, 23 (April), 443. Snavely, E. S.; Blount, F. E. Corros. NACE 1969, 25(10), 397. Templeton, C. C.; Rushing, S.S.; Rodgers, J. C. Mater. Perform. 1963, 2(8), 42.
Weast, R. C., Ed. CRC Handbook of Chemistry and Physics, 67th ed.; CRC: West Palm Beach, 1986; p D-151. Wheeler, D. Pet. Eng. 1975, Nou, 68. Received for review June 19, 1986 Accepted May 26, 1987
Detailed Gas Chromatography/Mass Spectrometric Structural Determination of Olefin Oligomerization Products Alan L. Chaffee* CSIRO, Division of Energy Chemistry, Menai, NSW 2234, Australia
Kingsley J. Cavell,+Anthony F. Masters,’ and Robert J. Western CSIRO, Division of Materials Science, Clayton, Victoria 3168, Australia
Reaction gas chromatography/mass spectrometry methods have been applied in determining the molecular structure of individual C7 olefins present in a complex mixture of isomers formed by the cooligomerization of C3 and C4 olefins. The catalytic oligomerization of low molecular weight olefins to higher molecular weight products, useful in the production of plasticizers, lubricants, detergents, fuels, etc., has been practiced commercially for many years (Hobson and Pohl, 1973). There are several processes which employ a range of catalytic types and operating conditions (Sittig, 1978; Chauvin et al., 1974; Freitas and Gum, 1979; Bogdanovic, 1979). These processes lead to different product distributions, as a result of the operation of different reaction pathways and their relative importance under particular conditions. For many applications, high product selectivity is required (e.g., linear a-olefins or branched internal olefins); hence, a detailed definition and understanding of these reaction pathways is required. A novel example of propylene oligomerization over a highly specific nickel catalyst has recently been reported (Masters and Cavell, 1985). In this case, the product distribution was relatively simple. By using gas chromatography (GC) and coinjection of standard compounds, it was demonstrated that eight C, olefins were produced as Current address: Department of Chemistry, University of Tasmania, Hobart, Tas. 7001, Australia. Current address: Department of Inorganic Chemistry, University of Sydney, Sydney, NSW 2006, Australia.
*
0888-5885/87/2626-1822$01.50/0
“primary” products and that four more resulted from subsequent double bond isomerization. In this case, since the mechanism specifically excludes highly branched isomers (such as the 2,2-dimethylbutenes), it was possible to obtain all the necessary standard compounds. Unfortunately, for olefins CnHPn,the number of possible isomers increases rapidly with n so that oligomerization and cooligomerization of even simple olefins can produce complex mixtures which vary in both carbon number and isomer distribution. As isomer complexity and carbon number increase, it becomes increasingly difficult or impossible to obtain all of the necessary standard compounds to facilitate the definitive assignment of GC peaks by coinjection. Conventional electron impact gas chromatography/mass spectrometry (EI-GC/MS) is also of limited value since the E1 mass spectra of many isomeric olefins are nearly identical. The determination of reaction pathways necessarily starts with a detailed and exact characterization of individual components in the product mixture. To help overcome the difficulties outlined above, we have employed a technique of postcolumn reaction (hydrogenation) GC/MS recently described in the literature (Chaffee and Liepa, 1985). This procedure is an ideal aid in assigning definitive molecular structures to individual 0 1987 American Chemical Society
Ind. Eng. Chem. Res., Vol. 26, No. 9, 1987 1823 I
I
1
I
TIC
600
700
800
900
WSC,"
Figure 1. Conventional EI-GC/MS chromatograms of olefin cooligomerization product: (a) total ion chromatogram (TIC), (b) m / z 98 chromatogram (specific for C, alkenes), (c) m / z 100 chromatogram (specific for C7 alkanes).
oligomerization/isomerization products. We demonstrate here its application to a typically complex mixture of C7 olefins formed by cooligomerization of C3 and C4 olefins.
Experimental Section Postcolumn Reaction GC/MS. Full details of the postcolumn reaction GC/MS data system (JEOL DX-300 and DA-5000) have been published elsewhere Chaffee and Liepa, 1985). Briefly, the system consists of a microreactor loaded with Adams catalyst and situated in line in a separately heated zone between the GC column outlet and the mass spectrometer inlet. The effective dead volume of the microreactor is small enough for chromatographic resolution to be only minimally affected. Hydrogen is used as the GC carrier gas to allow hydrogenation within the microreactor. Neat oligomerization product liquids were injected into the gas chromatograph (50/1 split, 300 "C), and the oven was programmed from 10 "C a t 4 "C min-l. The linear carrier gas flow rate was 30 cm s-l. The microreactor and GC/MS interface ovens were maintained a t 300 "C. The mass spectrometer was operated in the electron impact mode (ionizing potential 70 eV, ionizing current 300 PA) by using a source temperature of 200 "C and a date acquisition rate of 1 scan ( m / z 35-600) per second. Oligomerization Liquid. The sample was taken from a series of commercial and laboratory samples used to assess catalytic olefin oligomerization selectivities (Cave11 and Masters, 1983). It was obtained by distillation (C, cut) of a propylene/butene cooligomerization liquid, such as might be used as a feed for plasticizer manufacture.
Results and Discussion Assignment of Skeletal Structures. In conventional EI-GC/MS, individual components are both separated and detected as olefins. With the postcolumn reaction GC/MS technique, components are first separated as olefins and then detected as alkanes. Since the mass spectra of isomeric alkanes are more readily distinguished, the skeletal structure of the individual components can be assigned relatively easily. Figure 1 illustrates the total ion chromatogram (TIC) from a conventional EI-GC/MS analysis of the olefin cooligomerization product. Single ion chromatograms (SICS) for molecular ions of C7 alkenes ( m / z 98, Figure l b ) and C7 alkanes (m/z 100, Figure IC)indicate that >90% of the distillation cut is made up to C7 compounds. With postcolumn reaction GC/MS, the TIC is, of course, identical. However, the m / z 100 SIC (Figure 2a) demonstrates that the C7 olefins have been converted quantitatively to C7 alkanes. Certain ions are characteristic of particular structural features in the alkane isomers, and an examination of selected SICs can lead to a preliminary indication of the isomer distribution (see Figure 2). Nevertheless, definitive assignment of skeletal structures
6ca
500
700
800
Scan
Figure 2. EI-GC/MS chromatograms of cooligomerization product obtained with postcolumn hydrogenation: (a) m / z 100 (specific for C, alkanes), (b) m / z 85 (indicative of 2,4-dimethylpentane and 2methylhexane), (c) m / z 71 (indicative of 3-methylhexane), (d) m / z 57 (indicative of 2,2-trimethylpentane), (e) m / z 56 (indicative of 2,3-dimethylpentane); ( 0 )represents peaks corresponding to the indicated skeletal structures.
700
800
900
TIC
XXH) Scan
Figure 3. Structural assignment of C7 alkenes in cooligomerization product. Table I. Relative Abundance of C7 Skeletons i n Oligomerization Liquid skeleton % abundance 2,3-dimethylpentane 59.9 2,4-dimethylpentane 18.6 3-methylhexane 6.5 2,2-dimethylpentane 4.7 2-methylhexane 9.1 n-heptane 0.3 3-ethylpentane 0.3
requires the analysis of the full mass spectra of each component. This analysis allowed the determination of the skeletal structure of all components identified in Figure 3. A quantitative breakdown of the hydrocarbon skeleton in the present sample is given in Table I. Determination of Double Bond Positions. Once the field of possibilities had been reduced by assignment of the skeletal structure of each component, a comparison of the alkene spectra (obtained without postcolumn hydrogenation) within each skeletal class, together with standard spectra in the EPA/NIH data base (Heller and Milne, 1978) and fragmentation rules developed by Mayer and Djerassi (1971) and Kraft and Spiteller (1969), allowed double bond positions to be assigned to all components present in the mixture. As an example, the spectra of all six components with the 2,3-dimethylpentane skeleton are illustrated in Figure 4. It can be seen that of the six spectra, only two (d and e) are closely similar and assigned to the same structural isomer. Gas chromatography/chemical ionization/mass spectrometry (GC/CI/MS), using reagent gases such as dimethyl ether and vinyl methyl ether, can also be used to determine the presence of specific structural features of isomeric alkenes (Chaffee and Liepa, 1986). Where applicable, these techniques provided support for the structural assignments given in Figure 3 but are not discussed further here.
1824 Ind. Eng. Chem. Res., Vol. 26, No. 9, 1987
Acknowledgment We thank I. Liepa for assisting with the GC/MS analyses.
e s
la
,2
68
Q
:a
TZ
aM/Z
Figure 4. Mass spectra of isomeric alkenes with the 2,3-dimethylpentane skeletal structure: (a) 3,4-dimethylpent-l-ene, (b) 2,3-dimethylpent-1-ene, (c) 2-ethyl-3-methylbut-l-ene, (d) (Z)-2,3-di(f) 2,3-dimethylmethylpent-3-ene, (e) (E)-2,3-dimethylpent-3-ene, pent-3-ene.
Determination of Double Bond Geometry. Many of the structural isomers identified to this point can be further defined in terms of their double bond geometry, that is E-trans or 2-cis. for example, spectra d and e illustrated in Figure 3 are nearly identical and represent a pair of geometric isomers. It has recently been demonstrated that double bond geometry can be determined by GC/CI/MS using isobutane as the reagent gas (Chaffee and Liepa, 1986). This is achieved by comparison of the relative abundance of the isobutane-olefin adduct ion ( M 57)+ and the ( M - 1)' ion in the two spectra (Budzikiewicz and Busker, 1980). Although this method enabled the assignment of geometry in some cases, it was of somewhat limited application since it can be used only in the comparison of geometric isomers where the double bond does not reside at skeletal branching points. For the present it has been necessary to rely on published relative retention times (Sanders and Maynard, 1968; Simekova et al. 1970) in order to assign the geometry of the remaining compounds.
+
Registry No. Propylene, 115-07-1; 1-butene, 106-98-9; 2butene, 107-01-7; isobutene, 115-11-7; 4,4-dimethyl-2-pentene, 26232-98-4; 2,2-dimethylpentane, 590-35-2; 3,4-dimethylpentene, 7385-78-6 2,4-dimethylpentene, 2213-32-3; 2,4-dimethyl-2-pentene, 625-65-0; 2,3-dimethylpentene, 3404-72-6; (E)-2-methyl-3-hexene, 692-24-0; 2-methylhexane, 591-76-4; 2-(methylethyl)butene, 7357-93-9; (E)-5-methyl-2-hexene, 7385-82-2; 3-methylhexane, 589-34-4; (2)-3,4-dimethyl-2-pentene, 4914-91-4; (E)-3,4-dimethyl-2-pentene, 4914-92-5; 2-ethylpentene, 3404-71-5; (E)-3methyl-2-hexene, 20710-38-7; (2)-3-heptene, 7642-10-6; 2methyl-2-hexene, 2738-19-4; (E)-2-hexene, 4050-45-7; 3-ethyl-2pentene, 816-79-5; (2)-3-methyl-2-hexene, 10574-36-4; 2,3-dimethylpentene, 3404-72-6.
Literature Cited Bogdanovic, B. Adu. Organomet. Chem. 1979, 17, 105. Budzikiewicz, H.; Busker, E. Tetrahedron 1980, 36, 255-266. Cavell, K. J.; Masters, A. F. J. Chem. Res. Symp. 1983, 72. Chaffee, A. L.; Liepa, I. Anal. Chem. 1985,57, 2429-2430. Chaffee, A. L.; Liepa, I. Prepr.-Am. Chem. Soc., Diu. Pet. Chem. 1986, 31, 142-144. Chauvin, Y.; Gaillard, J. F.; Quang, D. V.; Andrews, J. W. Chem. Ind. (London) 1974, 375. Freitas, E. R.; Gum, C. R. Chem. Eng. Prog. 1979, 75, 73. Heller, D. R.; Milne, G. W. A., Eds. EPNAJNIH Mass Spectral Data Base; U.S. Department of Commerce; Washington, D.C., 1978. Hobson, G . D.; Pohl, W., Eds. Modern Petroleum Technology; Applied Science: Dorking, 1973. Kraft, M.; Spiteller, G. Org. Mass. Spectropsc. 1969, 2, 865-876. Masters, A. F.; Cavell, K. J. U.S. Patent 4533651, 1985. Mayer, K. K.; Djerassi, C. Org. Mass. Spectrosc. 1971,5, 817-831. Sanders, W. N.; Maynard, J. B. Anal. Chem. 1968, 40, 527-535. Simekova, J.; Pronayova, N.; Pies, R.; Ciha, M. J . Chromatogr. 1970, 51,91-101. Sittig, M. Handbook of Catalyst Manufacture; Noyes Data: Park Ridge, NJ, 1978; p 358. Received for review July 25, 1986 Accepted June 3, 1987
