Aromatics and Naphthenes

Consider the molecule below. From an atomic point of view, an atom common to two structures, aromatic and naphthenic, or aromatic and paraffinic or still further naphthenic and paraffinic will be considered first of ill aromatic, then naphthenic, then paraffinic 2... 

The bitumens are complex mixtures of paraffinic, aromatic and naphthenic hydrocarbons. A small amount of unsaturation is usually present which accounts... 

Paraffinic—the ratio of paraffinic hydrocarbons is high compared to aromatics and naphthenes. 

Like aniline point, the K factor differentiates between the highly paraffinic and aromatic stocks. However, within the narrow range (K = 11.5-12.0), the K factor does not correlate between aromatics and naphthenes. Instead, it relates fairly well to the paraffin content (Figure 2-11). The K factor does not provide information as to the ratio of naphthene and paraffin contents. The ratio of naphthenes to paraffins can vary considerably with the same K values (Table 2-8). 

A petrochemical is any chemical (as distinct from fuels and petroleum products) manufactured from petroleum (and natural gas) and used for a variety of commercial purposes (Table 3.8). The definition, however, has been broadened to include the entire range of aliphatic, aromatic, and naphthenic organic chemicals, as well as carbon black and inorganic materials such as sulfur and anunonia. Petroleum and natural gas are made up of hydrocarbon molecules, which comprise one or more carbon atoms to which hydrogen atoms are attached. Currently,... 

Aliphatic hydrocarbon a hydrocarbon in which the carbon-hydrogen groupings are arranged in open chains that may be branched. The term includes paraffins and olefins and provides a distinction from aromatics and naphthenes, which have at least some of their carbon atoms arranged in closed chains or rings. 

Figure 5.33 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, isoalkane, aromatic and naphthenic... 

Accordingly, work has been done on series of n-paraffins,. isoparaffins, naphthenes, aromatics, and naphthene-aromatics which have been chosen as representative of the major components of petroleum. In addition, olefins, cyclo-olefins, and aromatic olefins have been studied as a means of depicting the important secondary reactions of the copious amounts of unsaturates produced in the majority of catalytic cracking reactions. A silica-zirconia-alumina catalyst was used principally it resembles closely in cracking properties typical commercial synthetic silica-alumina catalysts. 

Bicyclic aromatics and naphthenes are important components of cracking feed stocks. The former, after cracking in the side chains to gasoline and gas, will remain as smaller bicyclic aromatics in the cracked gas oil. The latter will be converted to naphthenes and aromatics distributed in both the gasoline and gas oil, together with aliphatic gas and gasoline components. 

The main reactions of the MTG/MTO process can be summarized as follows the first is the dehydration of methanol to DME on acidic zeolite catalysts. The equilibrium mixture of methanol, DME, and water is then converted to light alkenes, which react further to form higher alkenes, n- and Ao-alkanes, aromatics, and naphthenes by hydrogen transfer, alkylation, polycondensation, isomerization, and other secondary reactions. 

Terms such as paraffinic, naphthenic, naphthenic-aromatic, and aromatic-asphaltic are used in the several classification methods which have been proposed. These terms obviously relate to the molecular structure of the chemical species most prominent in the crude oil mixture. However, such classification is made difficult because the large molecules usually consist of condensed aromatic and naphthenic rings with paraffinic side chains. The characteristic properties of the molecules depend on the proportions of these structures. 

Figure 14.5. Representation of solvent extraction behavior in terms of certain properties rather than direct compositions [Dunstan et aL, Sci. Pet., 1825-1855 (1938)]. (a) Behavior of a naphthenic distillate of VGC = 0.874 with nitrobenzene at 10°C. The viscosity-gravity constant is low for paraffins and high for naphthenes, (b) Behavior of a kerosene with 95% ethanol at 17°C. The aniline point is low for aromatics and naphthenes and high for paraffins, (c) Behavior of a dewaxed crude oil with liquid propane at 70°F, with composition expressed in terms of specific gravity.

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. 

The stability of the products from coal-derived syncrudes must be examined carefully. Many unique compounds are present in these syncrudes peri-condensed aromatics and naphthenes, oxygen compounds, and asphaltene-like hydrocabons. Traces of these compounds may remain in the hydrotreated product and their effect on jet, thermal, and oxidation stabilities cannot be predicted from the behavior of petroleum products. 

This resistance is affected by the crude source and refining process (which in turn affects the relative amounts of paraffinic, aromatic and naphthenic hydrocarbons). Because of these fundamental differences, lubricants respond differently to different additives. The final choice of the additive must be based, therefore, on actual laboratory tests according to ASTM D-2272 and practical tests... 

Taking into account the results reported here on the various fractions, Figure 3 shows structures consistent with the data. Molecular formulae were determined from the elemental analyses of the fractions. Other functionalities and linking units could also satisfy the data however, those shown were considered most likely based on the results and steric and stability considerations. The structures in Figure 3 contain only major features such as the nature of the aromatic clusters, as well as the approximate numbers of aromatic and naphthenic rings per cluster. Functional groups and side chains are indicated only in a qualitative manner. 

The form of the dissolved sulfur has not been characterized properly yet. While stable at ambient temperatures, a substantial amount can be converted to crystalline sulfur at elevated temperatures or by solvent separation. This observation led to the development of a rapid liquid chromatography method to determine elemental sulfur in SA binders. The procedure which has been described previously by Cassidy (17) is based on gel permeation principle and uses a Styragel column and a uv detector. Results showed that 2-14% of the elemental sulfur added reacted chemically with the asphalt. Petrossi (18) and Lee (19), who determined free sulfur by extraction with sodium sulfite followed by titration with iodine, calculated a higher percent of bonded sulfur in sulfur-asphalt compositions. The observed differences are most likely caused by variations in the asphalt composition with regard to polar aromatics and naphthene components as well as by reaction temperature and contact time. 

According to the increase of PS content in HDPE and PS mixture, in Eigure 5.15 the fraction of gasoline components in the liquid products was increased from about 85 wt% (pure HDPE) to about 98 wt% (pure PS) and the rest was kerosene + disel (C13-C24). No heavy oil (> 24) was detected. In the catalytic degradation of pure HDPE without PS, the major product was olefin components whereas the paraffin products as well as the aromatic and naphthene products with a cyclic structure were minor products. According as PS content in the reactant increased from 0 to 20 wt%, the fraction of paraffin... 

It was found that the light-paraffinic-oil-like fractions had olefin and paraffin content without aromatics and naphthenes. These fractions are appeared in solid phase at room temperature due to their hydrocarbon structure with boiling point 250-380°C. 

Analysis of the feedstocks, shown in Table 2, indicates that the density, refractive index and carbon content of the blend naphtha are higher than those of SRN. This was due to higher aromatics and naphthenes, lower alkanes and higher final boiling point. To study the effect of catalyst type on sulfitr compounds selectivity, the feedstock and products were characterized... 

Tower deposition appears stratified, indicating localized fouling. One possible explanation is the preferential precipitation of the heavy ends asphaltenes facilitated by the low solubilizing power" of the local reflux. The reduced fouling effects observed for the higher trays support this hypothesis. Side streams fi-om the less fouled trays contain considerably more aromatics and naphthenes than those drawn from the more fouled trays. 

Zahlsen K, Eide I, Nilsen AM, et al. 1992. Inhalation kinetics of C6 to C10 aliphatic, aromatic and naphthenic hydrocarbons in rat after repeated exposures. Pharmacol Toxicol 71 144-149. 

Cataldo, F. Ultrasound-induced cracking and pyrolysis of some aromatic and naphthenic hydrocarbons. Ultrasonics Sonochemistry 2000, 7, 35. 

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