Aromatization, temperature programmed

Figure 12.22 SFC-GC analysis of aromatic fraction of a gasoline fuel, (a) SFC trace (b) GC ttace of the aromatic cut. SFC conditions four columns (4.6 mm i.d.) in series (silica, silver-loaded silica, cation-exchange silica, amino-silica) 50 °C 2850 psi CO2 mobile phase at 2.5 niL/min FID detection. GC conditions methyl silicone column (50 m X 0.2 mm i.d.) injector split ratio, 80 1 injector temperature, 250 °C earner gas helium temperature programmed, — 50 °C (8 min) to 320 °C at a rate of 5 °C/min FID detection. Reprinted from Journal of Liquid Chromatography, 5, P. A. Peaden and M. L. Lee, Supercritical fluid chromatography methods and principles , pp. 179-221, 1987, by courtesy of Marcel Dekker Inc.

Boylan and Tripp [76] determined hydrocarbons in seawater extracts of crude oil and crude oil fractions. Samples of polluted seawater and the aqueous phases of simulated samples (prepared by agitation of oil-kerosene mixtures and unpolluted seawater to various degrees) were extracted with pentane. Each extract was subjected to gas chromatography on a column (8 ft x 0.06 in) packed with 0.2% of Apiezon L on glass beads (80-100 mesh) and temperatures programmed from 60 °C to 220 °C at 4°C per minute. The components were identified by means of ultraviolet and mass spectra. Polar aromatic compounds in the samples were extracted with methanol-dichlorome-thane (1 3). 

Polymer films were produced by surface catalysis on clean Ni(100) and Ni(lll) single crystals in a standard UHV vacuum system H2.131. The surfaces were atomically clean as determined from low energy electron diffraction (LEED) and Auger electron spectroscopy (AES). Monomer was adsorbed on the nickel surfaces circa 150 K and reaction was induced by raising the temperature. Surface species were characterized by temperature programmed reaction (TPR), reflection infrared spectroscopy, and AES. Molecular orientations were inferred from the surface dipole selection rule of reflection infrared spectroscopy. The selection rule indicates that only molecular vibrations with a dynamic dipole normal to the surface will be infrared active [14.], thus for aromatic molecules the absence of a C=C stretch or a ring vibration mode indicates the ring must be parallel the surface. 

The catalytic coke produced by the activity of the catalyst and simultaneous reactions of cracking, isomerization, hydrogen transfer, polymerization, and condensation of complex aromatic structures of high molecular weight. This type of coke is more abundant and constitutes around 35-65% of the total deposited coke on the catalyst surface. This coke determines the shape of temperature programmed oxidation (TPO) spectra. The higher the catalyst activity the higher will be the production of such coke [1],... 

Figure 3.8 shows an example dataset of mixed hydrocarbons used as a petrochemical feedstock. These are straight-run naphthas which consist of a wide range of alkane, alkene, aromatic and naphthenic hydrocarbons, mainly in the range of C4-C9. The conventional analytical method for naphtha analysis is temperature-programmed gas chromatography (GC), which can provide a full analysis including C-number breakdown, but which is rather slow for process optimisation purposes. 

Bridie et al. [27] have studied the solvent extraction of hydrocarbons and their oxidative products from oxidised and non-oxidised kerosine-water mixtures, using pentane, chloroform and carbon tetrachloride. Extracts are treated with Florasil to remove non-hydrocarbons before analysis by temperature programmed gas chromatography. From the results reported it is concluded that, although each of the solvents extracts the same amount of hydrocarbons, pentane extracts the smallest amount of non hydrocarbons. Florasil effectively removes non hydrocarbons from pentane extracts, but also removes 10-25% of aromatic hydrocarbons. However, as the other solvents are less susceptible than pentane to treatment with Florasil, pentane is considered by those workers to be the most suitable solvent for use in determining oil in water. 

Activity and selectivity of Pt/KL catalysts depend crucially on the method of their preparation. There seems to be a consensus that Pt/KL samples prepared by incipient wetness impregnation display a higher Pt dispersion and a higher aromatization yield than samples prepared by ion exchange. Temperature-programmed reduction shows that in samples prepared by impregnation, followed by calcination, a considerable fraction of the Pt is present as Pf ions, whereas Pt prevails in ion-exchanged samples after calcination (53). 

INITIAL STEPS IN METHANOL CONVERSION AND AN ALTERNATIVE HOMOLOGATION MECHANISM A small amount of methane (ca. 1C%) is formed in methanol conversion, and appears to be one of the first products formed (ref. 11). When a small amount of methanol is sorbed onto ZSM-5 zeolite, the lattice is methylated (ref. 5). Subsequent temperature-programmed desorption gives dimethyl ether and desorbed methanol first, then (at 250-300°C) methane (stable) and formaldehyde (unstable), and finally aromatic products (ref. 22-23). 

Figure 2.22 Graphical measurement of Kovats retention index (/= lOOn ) on a column in the isothermal mode. The number of equivalent carbons n, is found from the logarithm of the adjusted retention time t of X. The chromatogram corresponds to the injection of a mixture of 4 n-alkanes and two aromatic hydrocarbons. The values in italics match the retention times given in seconds. By injecting periodically this mixture the modifications to the Kovats indexes of these hydrocarbons permits the following of the column s performance. The calculations for retention indexes imply that the measurements were effected under isothermal conditions. With temperature programming they yield good results to the condition to adopt an adjusted formula, though this entails a reduction in precision.

Modification of H-ZSM-5 zeolites through solid-state reaction with ZnO was described by Yang et al. [32]. On the basis of XPS results they reported that, upon heat-treatment of a ZnO/H-ZSM-5 mixture, Zn ions migrated from the outer surface into the channels of the zeolite. This finding was supported by TPDA, IR (decrease of acidic Brpnsted sites upon solid-state reaction between ZnO and H-ZSM-5) and temperature-programmed reduction (TPR). The latter showed increased uptake and reducibility after thermal treatment of ZnO/H-ZSM-5 compared to ZnO. Zeolites Zn,H-ZSM-5 exhibited, after reduction in H2, pronounced selectivity in propane aromatization. 

Figure 4. Glass capillary gas chromatograms of aromatic hydrocarbons in New York Bight surface sediments. Analysis conditions 20 m X 0.32-mm i.d. Jaeggi SE-54 column installed in a Carlo Erba Model 2150 gas chromatograph equipped with split/splitless injection helium carrier gas at 0.55 kg/cm2 injection at room temperature, program 80°-240°C at 3°/minute injector and detector at 250°C. Numbered peaks are identified in Table V.

MacLeod et al. (54,55) have found the high resolution achieved by glass capillaries to be extremely useful in identifying the source of oil pollution in marine biota. Two-meter capillaries with rapid temperature programming were excellent for screening, since they could analyze Ci0-C34 hydrocarbons in 7 min vs. 40 min for a 2-m packed column of comparable resolution. High-resolution separations were achieved with a 20-m capillary column. The saturated and aromatic hydrocarbon fractions were separated on a silica gel column first and analyzed separately by capillary GC. Horizontal scale expansion showed 15-40 discrete hydrocarbon components in the intervals between adjacent n-alkane peaks these were found useful in determining the identity of the source oil. 

Figure 1. Capillary GC separations of the aromatic hydrocarbon f tion extracted from rain water. Column was 30 m X 0.35 mm OVim and temperature programmed from 60° to 240°C/min. Carripr...

The potential of M(T 2-H2) moieties in the heterogeneous hydrogenation of aromatics has been demonstrated for [RuH2(H2)2(PCy3)2], which, in temperature-programmed decomposition under hydrogen, has been found to convert benzene into cyclohexane [57]. 

Figure 8 shows the C-GCxGC of a jet juel. In this separation, the oven temperature program rate was reduced from 2°C/min to 1°C /min. As wifli gasoline, the hydrocarbon aromatic classes were readily resolved, and their carbon number distributions are readily distinguishable fiom C7 to C13. As expected, this sample did not contain benzene. Note that cleanly separated compounds at approximately X = 85 min, Y = 90 s (labeled phenolics ) were almost as retained as the di-aromatics (naphthalenes). The O-GCxGC separation (Fig. 9) revealed the presence of oxygen in these compounds, which were identified as phenolics. 

Makromolekulare Chemie 194, No.6, June 1993, p.1545-59 LEVEAR-TEMPERATURE PROGRAMMED PYROLYSIS OF THERMORESISTANT POLYMERS - MASS AND FTIR SPECTROMETRIES. II. AROMATIC POLYESTERS AND COPOLYESTERS Hummel D 0 Neuhoff U Bretz A Duessel H J Koln,Universitat Angewandte Spektrometrie Koeln eV... 

Values of heats adsorption may also be derived from a TPD curve, since a relationship between the temperature corresponding to the peak maximum (Tm) and heating rate, involving also AH for adsorption, has been worked out, and applied in particular to the system ZSM-5/aromatic hydrocarbons [57]. The correct estimation of Tm can depend on the selection of a suitable linear or nonlinear temperature program [62]. 

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