Inferring Molecular Composition

As mentioned earlier, we must also be able to infer the paraffin, naphthene and aromatic (PNA) composition of each boiling-point range given certain measured bulk properties to completely map feed information to kinetic lumps. The API (Riazi-Daubert) [54, 55] is a popular chemical composition correlation that takes the form  

We present an alternate correlation in Eqs. (4.11) and (4.12). Our correlation extends the original correlation from Riazi [54,55] by including specific gravity (SG) as an additional parameter and providing different sets of correlation coefficients (a, b, c and d) for different boiling-point ranges. 

We use a total of 233 different data points containing laboratory measured chemical composition and bulk property information (distillation curve, density, refractive index and viscosity) for light naphtha, heavy naphtha, kerosene, diesel and VGO. These data points come from various plant measurements made over the six-month period of this study and a variety of light and heavy crude assay data (spanning several years) available to the refinery. 

We can now use the two methods we have developed to propose a technique to use limited feed information to infer lumped composition. This technique is similar to the one given by Hollas et al. [52]. However, we make several changes to account for limited data sets. We outline the technique in the following steps (Changes from the procedure of Hollas et al. [52] are indicated with a ( )  

Use the beta-distribution method to extend partial ASTM D-1160 distillation curves. ( ) 

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Technique to infer molecular composition of FCC feedstock from routine analysis... 

Detailed process to infer molecular composition of feed when little plant information is available... 

In catalysis, infrared (IR) spectroscopy is commonly used to characterize specific adsorbates. Because of the localized nature and particular chemical specificity of molecular vibrations, IR spectra are quite rich in information, and can be used to extract or infer both structural and compositional information on the adsorbate itself as well as on its coordination on the surface of the catalyst. In some instances, IR spectroscopy is also suitable for the direct characterization of solids, especially if they can be probed in the far-IR region (10-200 cm ) [74-76],... 

Solubility and kinetics methods for distinguishing adsorption from surface precipitation suffer from the fundamental weakness of being macroscopic approaches that do not involve a direct examination of the solid phase. Information about the composition of an aqueous solution phase is not sufficient to permit a clear inference of a sorption mechanism because the aqueous solution phase does not determine uniquely the nature of its contiguous solid phases, even at equilibrium (49). Perhaps more important is the fact that adsorption and surface precipitation are essentially molecular concepts on which strictly macroscopic approaches can provide no unambiguous data (12, 21). Molecular concepts can be studied only by molecular methods. 

The haptophyte microalga Emiliania huxleyi produces biomarkers in the form of long-chain (C37, C38, and C39) alkenones (Brassell, 1993). Alkenones are well preserved in marine sediments and their molecular distributions and isotopic composition have been used to infer paleo-temperatures (Brassell, 1993) and pC022 values (Jasper et ak, 1994), respectively. Unsaturation patterns in the alkenone series are related to the growth temperature of the haptophyte algae that produce these compounds (Brassell et ak, 1986 Prahl and Wakeham, 1987), and hold great promise as indicators of absolute ocean paleotemperature. 

There is a series of arsenatophosphates corresponding with each of the three forms of condensed potassium arsenate and phosphate, the transition points and melting point of which vary systematically with composition (see Fig. 10). A chain structure for the a-form of potassium arsenate and arsenophosphate may be inferred from their isomorphism with (KP03)xB. The 7-forms also contain high-molecular anionic chains for, when they are hydrolyzed, monoarsenate and polyphosphates with chain length up to n = 6 are formed, depending on their phosphorus content. No metaphosphate is produced, however. 

When Payne began her work in the 1920s, stellar spectroscopy was a very active area of research. Numerous elemental and molecular lines had been identified in stellar spectra. The lines observed in each star varied with the inferred temperature of the star, which was understood to mean that the elemental abundances varied with temperature. This body of data was the basis for the spectral typing of stars ( , B, A, F, G, , M, L). However, the power source for stars was not understood and it was not clear why the composition of a star should be related to its temperature. In the 1920s, it was also widely believed that the Sun had the same composition as the Earth models considered the Earth to have formed from the outer layers of the Sun. Payne used the new guantum mechanical understanding of atomic structure to show how and why the spectral lines of the different elements varied as a function of stellar spectral type. She demonstrated how the temperature of the stellar surface controls the spectral lines that are observed. Her analysis led to the conclusion that the chemical... 

Curie point pyrolysis mass spectrometry has also been valuable in providing information about the chemical types that are evolved during the thermal decomposition of coal (Tromp et al., 1988) and, by inference, about the nature of the potential chemical types in coal. However, absolute quantification of the product mixtures is not possible, due to the small sample size, but the composition of the pyrolysis, product mix can give valuable information about the metamorphosis of the coal precursors and on the development of the molecular structure of coal during maturation. However, as with any pyrolysis, it is very important to recognize the nature and effect that any secondary reactions have on the nature of the volatile fragments, not only individually but also collectively. 

The different types of mass spectrometers provide a wealth of information going from simple molecular masses of intact components to an inference of the amino acid composition, sequence order, substitution site and nature of posttranslational modifications, and tissue distribution of the molecule of... 

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