Naphtha paraffin/aromatic content

The amount of benzene produced in a reformer will depend on the composition of the feed. Every crude oil has naphtha with different PNA (paraffin, naphthene, aromatics) content. In commercial naphtha trading, the PNA content is often an important specification. High naphthene and aromatic content would indicate a good reformer feed. High paraffin content would indicate a good olefin plant feed. 

Reforming. The hydrotreated naphthas were reformed over a conventional platinum reforming catalyst in an attempt to maximize aromatics. The catalyst was Cyanamid AERO PHF-4 (0.3% Pt, 0.6% Cl). The intent was to operate the reformer at constant conditions in order to better compare naphthas. By operating at severe conditions, the expected hydrocracking activity of the catalyst would tend to purify the aromatics by selectively cracking away the paraffins. If the resultant reformate had a suitably high aromatic content, it could be fed directly to a hydrodealkylator. 

With the possible exception of the SRC II straight-run naphthas, these Ce-Co reformates could be fed to a hydrodealkylator without first being extracted. However, it must be noted that hydrocracking, as evidenced by paraffin conversion, was not nearly as active as expected. In the event that a coal-derived naphtha contained a substantial portion of paraffin, particularly C6 paraffin, the aromatic content of the resultant reformate would be significantly less. 

The following four feed parameters were found to be sufficient to characterize naphthas (25) hydrogen content (HF) molecular weight (MW) isoparaffin content (Pi) normal-paraffin content (PN). Other potential parameters were satisfactorily accounted for in the above set. For example, the inclusion of naphthenic and aromatic content as parameters did not significantly improve the yield correlation. 

The aniline (or mixed aniline) (ASTM D-611, IP 2) point helps in characterization of pure hydrocarbons and in their mixtures and is most often used to estimate the aromatic content of naphtha. Aromatic compounds exhibit the lowest aniline points and paraffin compounds have the highest aniline points, with cycloparaffins (naphthenes) and olefins having aniline points between the two extremes. In any homologous series the aniline point increases with increasing molecular weight. 

In addition, a method of petroleum classification has been developed that is based on other properties as well as the density of selected fractions. The method consists of a preliminary examination of the aromatic content of the fraction boiling up to 145°C as well as that of the asphaltene content, followed by more detailed examination of the chemical composition of the naphtha (b.p. <200°C). For this examination, a graph (a composite of curves expressing the relation between percentage distillate from the naphtha, the aniline point, refractive index, specific gravity, and the boiling point) is used. The aniline point after acid extraction is included in order to estimate the paraffin-naphthene ratio. 

The feed composition used for this validation case was characterized as listed in Table 1.2, based on measured naphtha gravity, ASTM-D86 volume versus boiling point, and PINA (paraffin, isoparaffin, naphthinic, and aromatic content) information, plus recycle desulfurization hydrogen stream measurements. The feed is a mix of the naphtha and desulfurization hydrogen streams. This naphtha feed molecular weight is 65.923. 

When simple Hquids like naphtha are cracked, it may be possible to determine the feed components by gas chromatography combined with mass spectrometry (gc/ms) (30). However, when gas oil is cracked, complete analysis of the feed may not be possible. Therefore, some simple definitions are used to characterize the feed. When available, paraffins, olefins, naphthenes, and aromatics (PONA) content serves as a key property. When PONA is not available, the Bureau of Mines Correlation Index (BMCI) is used. Other properties like specific gravity, ASTM distillation, viscosity, refractive index. Conradson Carbon, and Bromine Number are also used to characterize the feed. In recent years even nuclear magnetic resonance spectroscopy has been... 

Another UOP zeolitic process that produces petrochemical feedstocks is the MaxEne process (27). The MaxEne process, another member of the Sorbex family of processes, separates C5 to Cn full-range naphtha into an extract stream containing more than 90 wt-% normal paraffins and a raffinate stream containing over 99 wt-% non-normals, namely isoparaffins plus naphthenic and aromatic hydrocarbons. The high normal-paraffin content of the extract makes it a preferred feedstock for a naphtha steam cracker, and the absence of normal paraffins in the raffinate makes it a preferred feedstock for catalytic reforming. 

Often naphtha is split at about lOO C into a heavy and a light fraction. The light fractions tend to have a higher paraffin content and more attractive to petrochemical operators and the heavy fraetion containing higher levels of naphthenes and aromatics are of interest to refiners for reforming into high octane blend stock. 

Figure 2. The content of a) Cg paraffins and naphthenes b) Cg aromatics c) components and d) Cg. aromatics in the naphthas as a function of the final boiling point (FBP). C8P=Cg paraffins PCP=propylcyclopentane C8CP=ethylmethyl- and trimethyl-cyclopentanes ECH=ethylcyclohexane DMC=dimethylcyclohexane EB=ethylbenzene PX,MX,OX=xylenes.

Naphtha feed is treated as a single pseudo species. Naphthas, used as pyrolysis feedstocks, are mainly composed of paraffins and naphthenes, with lesser amounts of aromatics. Olefin content is usually very small. Consistent with observed pyrolytic behavior of paraffins and naphthenes (15,16,26,27,28), feed decomposition is assumed to follow first-order kinetics. Equation 3 of the reactor model can be simplified as follows. 

Feedstock Properties. One empirical parameter that is used in refineries to rank naphthas as to reformability is the (N-I-2A) parameter, what is the amovmt of naphthenes (N) plus two times the amount of aromatics (A) in the feed. The higher this number is the better the reformate yield for a given octane number of the gasoline. Also, the higher the paraffin content of the feed, the... 

Crude Distillation. Naphthas are qualitatively referred to as lean (high paraffin content) or rich (low paraffin content) with important consequences of their composition on the ease with which they can be reformed to aromatics and high octane gasoline. 

Naphtha is characterized as about thirty components, pure or pseudo (several species of similar structure lumped together). The distribution of these components is chosen to best match measured specific gravity, volume average boiling fractions (ASTM-D86 method), and normal paraffinic, branched paraffinic (iso-parafiins), naphthenic, and aromatics (PINA) contents. 

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