Naphtha, analysis

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. 

Shale Oil Naphthas. (Analysis of small samples by silica gel adsorption method.)... 

Asphaltenes seem to be relatively constant in composition in residual asphalts, despite the source, as deterrnined by elemental analysis (6). Deterrnination of asphaltenes is relatively standard, and the fractions are termed / -pentane, / -hexane, / -heptane, or naphtha-insoluble, depending upon the precipitant used (5,6,49). After the asphaltenes are removed, resinous fractions are removed from the maltenes-petrolenes usually by adsorption on activated gels or clays. Recovery of the resin fraction by desorbtion is usually nearly quantitative. 

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... 

Selecting the naphtha type can be an important processing procedure. For example, a paraffinic-base naphtha is a better feedstock for steam cracking units because paraffins are cracked at relatively lower temperatures than cycloparaffins. Alternately, a naphtha rich in cycloparaffins would be a better feedstock to catalytic reforming units because cyclo-paraffins are easily dehydrogenated to aromatic compounds. Table 2-5 is a typical analysis of naphtha from two crude oil types. 

The impact of the release of liquid products on the environment can, in part, be predicted from knowledge of the properties of the released liquid. Each part of an ocular liquid product from petroleum has its own set of unique analytical characteristics (Speight, 1999, 2002). Since these are well documented, there is no need for repetition here. The decision is to include the properties of the lowest-boiling liquid product (naphtha) and a high-boiling liquid product (fuel oil). For the properties of each product (as determined by analysis) a reasonable estimate can be made of other liquid products, but the relationship may not be linear and is subject to the type of crude oil and the distillation range of the product. 

Hydrocarbon composition is also determined by mass spectrometry, a technique that has seen wide use for hydrocarbon-type analysis of naphtha and gasoline (ASTM D2789) as well as for the identification of hydrocarbon constituents in higher-boiling naphtha fractions (ASTM D2425). 

Although the focus of many tests is analysis of the hydrocarbon constituents of naphtha and other petroleum fractions, heteroatoms compounds that contain sulfur and nitrogen atoms cannot be ignored, and methods for their determination are available. The combination of gas chromatography with element-selective detection gives information about the distribution of the element. In addition, many individual heteroatomic compounds can be determined. 

Figure 5.34 Predictive models for naphtha compositional analysis (PINA).

In 2000 two major petrochemical companies installed process NMR systems on the feed streams to steam crackers in their production complexes where they provided feed forward stream characterization to the Spyro reactor models used to optimize the production processes. The analysis was comprised of PLS prediction of n-paraffins, /xo-paraffins, naphthenes, and aromatics calibrated to GC analysis (PINA) with speciation of C4-C10 for each of the hydrocarbon groups. Figure 10.22 shows typical NMR spectral variability for naphtha streams. Table 10.2 shows the PLS calibration performance obtained with cross validation for... 

J. C. Edwards and P. J. Giammatteo, Detailed hydrocarbon analysis of naphtha by on-line NMR integration of real-time NMR Feed analysis with advanced process control and optimization, Presented at Eastern Analytical Symposium, Somerset, NJ, November 18-21, 2002. 

P.A. Barnard, C. Gerlovich, and R. Moore, The validation of an on-line nuclear magnetic resonance spectrometer for analysis of naphthas and diesels, presented at the ISA Analytical Division Meeting, Calgary, Alberta, Canada, 2003. 

We believe it has been shown that this method for infrared analysis of hydrocarbons collected on charcoal tubes and vapor monitors is a valid and acceptable one. Further work is being done to validate the method for other hydrocarbons such as petroleum naphtha, Stoddard solvent, and other JP aviation fuels. Additionally, work is being done to determine the 3M monitor sampling rate for JP-4. 

We will examine three synthetic fuel scenarios and compare their implications regarding sulfur availability with the current and projected market for sulfur to the year 2000. The analysis will consider three production levels of synthetic fuels from coal and oil shale. A low sulfur Western coal will be utilized as a feedstock for indirect liquefaction producing both synthetic natural gas and refined liquid fuels. A high sulfur Eastern coal will be converted to naphtha and syncrude via the H-Coal direct liquefaction process. Standard retorting of a Colorado shale, followed by refining of the crude shale oil, will round out the analysis. Insights will be developed from the displacement of imported oil by synthetic liquid fuels from coal and shale. 

Under the assumptions of naphtha price and aromatics value stated above, naphtha pyrolysis clearly would be superior to light hydrocarbon pyrolysis at their current feed prices. A similar analysis can probably be made also for gas oil. Thus, if the possible developments discussed above do materialize, the heavier feeds could probably dominate almost all new U.S. ethylene plant construction in the future. 

Properties of the naphthas produced from the syncrudes in the above tests are shown in Table V. Dinaphthenes are found in the 300-350°F naphtha and, surprisingly, in the 250-300°F naphtha. High levels of these compounds can make coal-derived naphthas difficult to reform. ( 9) A combination gas chromato-graphic-mass spectrometric (GC-MS) analysis of the 250-300°F naphtha from hydrotreated Illinois H-Coal found that the dinaphthenes are 8-carbon atom compounds (1.8% octahydropenta-lene) and 9-carbon atom compounds (0.7% bicyclo 3.3.1 nonane, 0.4% methyloctahydropentalene, 1.0% octahydroindenes, and 2.6% unidentified compounds) These dinaphthenes should not yield naphthalene when reformed. If the initial point of the jet fuel is 300°F or less, the 300°F " naphtha should be easy to reform. 

Mathematical models for the pyrolysis of naphthas, gas oils, etc. are relatively empirical. The detailed analysis of such a feedstock is essentially impossible, and all heavier feedstocks have a wide range of compositions. Such heavy hydrocarbons also contain a variety of atoms often including sulfur, nitrogen, oxygen, and even various metal atoms. Nevertheless, certain models predict the kinetics of pyrolysis, conversions, yields, etc. with reasonable accuracy and help interpret mechanistic features. 

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