Petroleum hydrocarbons cycloparaffins

Hydrocarbons, compounds of carbon and hydrogen, are stmcturally classified as aromatic and aliphatic the latter includes alkanes (paraffins), alkenes (olefins), alkynes (acetylenes), and cycloparaffins. An example of a low molecular weight paraffin is methane [74-82-8], of an olefin, ethylene [74-85-1], of a cycloparaffin, cyclopentane [287-92-3], and of an aromatic, benzene [71-43-2]. Cmde petroleum oils [8002-05-9], which span a range of molecular weights of these compounds, excluding the very reactive olefins, have been classified according to their content as paraffinic, cycloparaffinic (naphthenic), or aromatic. The hydrocarbon class of terpenes is not discussed here. Terpenes, such as turpentine [8006-64-2] are found widely distributed in plants, and consist of repeating isoprene [78-79-5] units (see Isoprene Terpenoids). 

Brown and Huffman [85] reported an investigation of the concentration and composition of nonvolatile hydrocarbons in Atlantic Ocean and nearby waters. Sea water samples were taken at depths of 1 and 10 m and the nonvolatile hydrocarbons were identified by mass spectrometric techniques. The results show that the nonvolatile hydrocarbons in Atlantic and nearby waters contained aromatics at lower concentrations than would be expected if the source of the hydrocarbons were crude oil or petroleum refinery products. Hydrocarbons appeared to persist in the water to varying degrees, with the most persistent being the cycloparaffins, then isoparaffins, and finally the aromatics. 

Hydrocarbon compounds can be divided into four major structural forms (1) alkanes, (2) cycloalkanes, (3) alkenes, and (4) arenes. Petroleum geologists and engineers commonly refer to these structural groups as (1) paraffins, (2) naphthenes or cycloparaffins, (3) aromatics, and (4) olefins, respectively and will be referred... 

Naphthenes or cycloparaffins are formed by joining the carbon atoms in ring-type structures, the most common molecular structures in petroleum. These hydrocarbons are also referred to as saturated hydrocarbons since all the available carbon atoms are saturated with hydrogen. Typical naphthenes and their respective physical properties are listed in Table 4.2 and shown in Figure 4.3. 

The cycloalkanes also are known as naphthenes, cycloparaffins, or alicyclic hydrocarbons. In the petroleum industry, this class of hydrocarbons is known as naphthenes. Naphthenes have saturated rings. The general formula for the ring without substituents is CnH2n. This is the same as the general formula for the alkene series however, the structural configurations differ completely and, thus, the physical and chemical properties are not at all similar. 

The principal source of aromatic compounds is coal tar, produced as a by-product in the manufacture of coke. Gas tar, of which much smaller quantities are produced, also contains these same materials. Aromatic hydrocarbons occur in nature in Borneo and other petroleums, and they may be prepared artificially by stripping hydrogen atoms from the cycloparaffins which occur in Caucasus petroleum and elsewhere. They are also produced from paraffin hydrocarbons by certain processes of cracking, and it is to be expected that in the future aromatic compounds will be produced in increasing quantity from petroleum which does not contain them in its natural state. 

Naphtha is divided into two main types, aliphatic and aromatic. Aliphatic naphtha is composed of paraffinic hydrocarbons and cycloparaffins (naphthenes), and may be obtained directly from crude petroleum by distillation. Aromatic naphtha contains aromatics, usually alkyl-substituted benzene, and is very rarely, if at all, obtained from petroleum as straight-run materials often reforming is necessary (Fig. 2). 

Saturated hydrocarbons also occur in petroleum in cyclic form, and will have generic molecular formulas of the form CnH2n (if monocyclic). These cycloparaffins are referred to as naphthenes in the petroleum industry and occur primarily as five, six, and seven-membered rings, with and without alkyl substituents. They also occasionally occur as various combinations of two of these ring systems linked or fused together, in which case their molecular formulas become of the form CnH2n-2 (Eq 18.4). 

Crude Oil. Crude petroleum consists essentially of mixtures of paraffinic, naphthenic, and aromatic hydrocarbons containing from 1 to over 70 carbon atoms per molecule and may contain dissolved gases or solids. The naphthenic hydrocarbons are based on cyclopentane or cyclohexane or on fused C5 and Ce rings. There is no evidence of the existence of C3, C4, C7, or C7+ cycloparaffins in crude oil. Olefins, diolefins, and acetylenes are absent. The aromatics are mainly benzene derivatives naphthalene, tetralin, and their substituted derivatives have been isolated in a few cases. 

The early investigators, by repeated fractional distillation, were able to determine that crude petroleum consisted principally of hydrocarbons. Ultimate analyses had shown that relatively small proportions of sulfur, nitrogen, and oxygen were usually present, probably in the form of derivatives. They were able to identify a number of hydrocarbon types such as paraffins, cycloparaffins, and aromatics, and even to isolate some members of these series in a qualitative way. The state of the art was very well summed up by Hoefer (1888) (65) when he wrote in his book Das Erdol as follows It should be pointed out that up to the present no complete quantitative analysis has been carried out on any crude petroleum, that we must be content rather to discover which are the principal types of hydrocarbons present, which predominate and, qualitatively, to identify the individual members of such series. ... 

Usually crude petroleum is separated into various useful fractions as given in Table 4 12°. Extensive analyses of crude petroleum have shown that there are more than two hundred hydrocarbons, about one-half of which are low-boiling. Of the 175 hydrocarbons isolated from a representative U.S. petroleum sample, 70 can be classified as paraffins, 48 as cycloparaffins and 57 as aromatic. According to Rossini121 the hydrocarbons which occur in abundance greater than 1% by vol are n-hexane (1.8%), n-heptane (2.3%), n-octane (1.9%), n-nonane (1.8%), n-decane (1.8%), n-undecane (1.6%), n-dodecane (1.4%), n-tridecane (1.2%), n-tetradecane (1.0%), methylcyclohexane (1.6%) and l-methyl-3-isopropylbenzene (1.1%) Petroleums from different locations contain essentially the same hydrocarbons, but the proportions in which the different molecules occur vary considerably. 

In a typical separation of a petroleum fraction containing C18-C25 hydrocarbons, an initial silica gel column is used to separate aromatics from paraffins and cycloparaffins. The aromatics are then chromatographed on an alumina column to separate them into groups containing one, two and three rings. Under appropriate conditions, silica gel can separate (i) olefines, paraffins, cycloparaffins... 

Early compositional analyses on petroleum (and lubricating oil base stocks) were focused on quantifying the three major hydrocarbon types present, namely paraffins, naphthenes or cycloparaffins, and aromatics. In that period (the 1920s to the 1950s), the availability of instrumental techniques was essentially nil in terms of our viewpoint today, since spectroscopic methods were in their infancy, as was electronics technology. Accordingly, research workers used the limited tools available at that time—density, refractive index, molecular weight, and elemental analyses. Based on work with model compounds, these led to compositional relationships between structure and these measurements and development of the concepts of VGC, refractivity intercept, and the n-d-M method. 

Naphthenes. A term used in petroleum chemistry to denore certain saturated hydrocarbons, specifically five-and six-carbon cycloparaffins and their alkyl derivatives, Tound in crude petroleum. Sometimes used to include polycyclic members found in the higher-boiling fractions. 

Petroleum. Crude oil mineral oil rock oil coal oil seneca oil. Consists of a mixture of hydrocarbons from C2H6 and up—chiefly of the paraffins, cycloparaffins, or of cyclic aromatic hydrocarbons, with small amounts of benzene hydrocarbons, sulfur, and oxygenated compounds. Occurrence U.S., Mexico, Iran, Russia, Roumania, Poland, Dutch East Indies, etc. 

Isomerization, carbon-carbon bond scission (cracking), and carbon-carbon bond formation (alkylation) are among the most imp>ortant hydrocarbon conversion reactions catalyzed by acids. Zeolites are often used to carry out these reactions during the refining of petroleum. Some of the zeolites are particularly active to convert olefins and cycloparaffins to paraffins and aromatics to produce jet fuel and gasoline. 

Petroleum, or crude oil, is an extremely complex mixture derived like coal from prehistoric vegetation. The components range from gaseous to semi-solid or solid hydrocarbons, with compounds of sulphur, nitrogen, oxygen and various metals as impurities. Distillation gives roughly the fractions shown in Table 12.1. The hydrocarbons are almost entirely saturated paraffins, cycloparaffins (naphthenes) and aromatics/polyaromatics the proportions vary enormously from one source to another. 

Cycloparaffins - par-o-fon (1900) n. Ring compounds of saturated hydrocarbon type based on groupings of methylene radicals (CH2). Typical cycloparaffins are cyclopropane, cyclobutane, cyclopheptane. etc. The cycloparaffins have very good solvent properties, and are constituents of crude petroleum s. 

The precise composition of crude petroleum varies widely from one source to another, but the principal components are always hydrocarbon paraffins (40-75%), cycloparaffins or naphthenes (mainly cyclopentane and cyclohexane derivatives) (20—50%) and aromatic hydrocarbons (5-20%). The first step in petroleum refining is distillation into broad fractions, which typically have the boiling ranges and compositions given in Table 2.1. None of these distillates contain significant amounts of olefins. The lower olefins, ethylene, propylene and butenes are produced principally by subsequent cracking operations. 

The hydrocarbon types found in petroleum are (i) paraffins, (ii) cycloparaffin (naphthenes or cyclohexanes), and (iii) aromatics. Paraffins range from methane to -hexacontane (C60H1225 a microcrystalline wax) of both straight- and branched-chain alkanes. Higher boiling fractions are high in saturated alkanes while commercial paraffin mainly consists of straight-chain... 

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