Aromatic hydrocarbons vapor-phase

CoF is used for the replacement of hydrogen with fluorine in halocarbons (5) for fluorination of xylylalkanes, used in vapor-phase soldering fluxes (6) formation of dibutyl decalins (7) fluorination of alkynes (8) synthesis of unsaturated or partially fluorinated compounds (9—11) and conversion of aromatic compounds to perfluorocycHc compounds (see Fluorine compounds, organic). CoF rarely causes polymerization of hydrocarbons. CoF is also used for the conversion of metal oxides to higher valency metal fluorides, eg, in the assay of uranium ore (12). It is also used in the manufacture of nitrogen fluoride, NF, from ammonia (13). 

The feedstocks used ia the production of petroleum resias are obtaiaed mainly from the low pressure vapor-phase cracking (steam cracking) and subsequent fractionation of petroleum distillates ranging from light naphthas to gas oil fractions, which typically boil ia the 20—450°C range (16). Obtaiaed from this process are feedstreams composed of atiphatic, aromatic, and cycloatiphatic olefins and diolefins, which are subsequently polymerized to yield resias of various compositioas and physical properties. Typically, feedstocks are divided iato atiphatic, cycloatiphatic, and aromatic streams. Table 2 illustrates the predominant olefinic hydrocarbons obtained from steam cracking processes for petroleum resia synthesis (18). 

Titov and co-workers, although conceding the validity of the ionic nitration mechanism for liq phase nitrations with coned acids, believe that many nitrations occur via a free-radical mechanism involving the free radicals (at any rate molecules having an unpaired electron) N02, N03, and NO. For vapor phase nitration of hydrocarbons, nitration of side chains of aromatic compds in... 

Pure N204 forms nitrocompds readily at elevated temps with either aliphatic or aromatic hydrocarbons in the gaseous or vapor state. It therefore finds extensive use in the commercial prepn of nitrocompds in both the expls and dye industries (Ref 24). Nitrations can be conducted in either the liq or vapor phase (Ref 8), and the N204 can be used as such or dissolved in an inert solvent such as CC14. Recently, Castorina et al (Refs 19 36) have shown that gamma... 

Mokbel, I., Rauzy, E., Meille, J.P., Jose, J. (1998) Low vapor pressures of 12 aromatic hydrocarbons. Experimental and calculated data using a group contribution method. Fluid Phase Equil. 147, 271-284. 

Yamasaki, H., Kuwata, K., Kuge, Y. (1984) Determination of vapor pressure of polycyclic aromatic hydrocarbons in the supercooled liquid phase and their adsorption on airborne particulate matter. Nippon Kagaka Kaish. 8, 1324—1329. 

STAR [Steam Active Re-forming] A catalytic reforming process for converting aliphatic hydrocarbons to olefins or aromatic hydrocarbons. Hydrocarbons containing five or fewer carbon atoms are converted to olefins. Those containing six or more are dehydrocy-clized to aromatic hydrocarbons. The reactions take place in the vapor phase, in a fixed catalyst bed containing a noble metal catalyst, in the presence of steam. Demonstrated on a semi-commercial scale and offered for license by Phillips Petroleum Company. The first commercial plant was built for Coastal Chemicals in Cheyenne, WY, in 1992 another for Polibutenos Argentinos in 1996. 

A gaseous sample is passed through a solid material, such as silica gel or polyurethane foam (PUF), in a tube. A glass fiber filter is often put in front of the solid support to capture particle-phase constituents, while the vapor-phase compounds are captured on the solid support. This is used for semivolatile analytes, such as polycyclic aromatic hydrocarbons and pesticides. The solid support is then usually extracted in the lab with a solvent (see techniques described later in this chapter), and then the techniques used for liquid samples are followed. 

C. The Detection of Cyclohexene Intermediates The postulate that olefins are released from the surface during the hydrogenation of aromatic hydrocarbons has gained considerable support. Madden and Kemball (89) observed cyclohexene during the early stages of the vapor phase hydrogenation (flow system) of benzene over nickel films at 0° to 50°. The ratio of cyclohexene to cyclohexane diminished with time, and little or none of the alkene was detected if the films were annealed at 50° in a stream of hydrogen. 

Physical Form. Liquid gasoline is a complex mixture of at least 150 hydrocarbons with about 60-70% alkanes, 25-30% aromatics, and 6-9% alkenes. The small-chain, low-carbon-numbered components are more volatile and thus in higher percentages in the vapor phase than the larger and heavier molecules. The concentrations of aromatics, the more toxic of the components, are depleted to about 2% in the vapor phase. The light alkanes, the less toxic components, are enriched to about 90%. Benzene is also present and represents a component of major concern. 

Yamasaki, H., K. Kuwata, and Y. Kuge, Determination of Vapor Pressure of Polycyclic Aromatic Hydrocarbons in the Supercooled Liquid Phase and Their Adsorption on Airborne Particulate Matter, Nippon Kagaku Kaishi, 8, 1324-1329 (1984) (Chem. Abstr., 101, 156747p (1984)). 

Vapor-phase oxidation of toluene to benzaldehyde is a classical subject in the field of partial oxidation. Indeed, it has already been studied with various V- and Mo-based oxide catalysts [1-18]. However, the one-pass yield of benzaldehyde was still lower than that of other oxygenated compounds obtained in oxidation of olefins and aromatic hydrocarbons. For example, the maximum yield of benzaldehyde obtained with Bi-Mo oxides was around 10 mol% [7,11,12],... 

Mobil s High Temperature Isomerization (MHTI) process, which was introduced in 1981, uses Pt on an acidic ZSM-5 zeolite catalyst to isomerize the xylenes and hydrodealkylate EB to benzene and ethane (126). This process is particularly suited for unextracted feeds containing Cg+ aliphatics, because this catalyst is capable of cracking them to light paraffins. Reaction occurs in the vapor phase to produce a PX concentration slightly higher than equilibrium, ie, 102—104% of equilibrium. EB conversion is about 40—65%, with xylene losses of about 2%. Reaction conditions are temperature of 427—460°C, pressure of 1480—1825 kPa, WHSV of 10—12, and a H2/hydrocarbon molar ratio of 1.5—2 1. Compared to the MVPI process, the MHTI process has lower xylene losses and lower formation of heavy aromatics. 

Polycyclic Aromatic Hydrocarbons (PAHs). The most highly studied class of compounds in combustion effluents 1s the PAHs. However, very little information about the amounts present in the vapor phase and on particles in the effluents from the efficient combustion of coal is available. The data in Table II partially fills this informational gap. The amounts in the vapor phase varied according to the firing conditions and the stack temperature that was 170 C. Even 1f all these PAHs were to condense on the particles, the amounts are well below the multiple ng/g quantities present on ambient air particles. 

Alkanes and Aromatics. The distinction between aromatic and poly-cyclic was arbitrarily set at three conjugated six-member rings in Table I. With this definition the alkanes and aromatic hydrocarbons, with 25 entries, dominate the list of identified components. These compounds are also present in the highest concentration in the different effluents. Ordinarily their concentrations were not measured because of a low interest in these kinds of compounds but in those instances where measurements were made, the amounts ranged from 10-1500 ng/M3 in the vapor phase and from 10-90 ng/g on the suspended particles in the stack effluents. These hydrocarbons were not quantitated for any of the fly and grate ash samples. 

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