Structural parameters asphaltenes

Figure 8. Distribution of structural parameters of asphaltene from Shin-Yubari coal hydrogenation at 450°C (O), H2 100kg/cm2 ( ), H2 75 + CHh 25 ( ),...

Figure 9. Structural parameters of asphaltene from Soya-Koishi coal by CO + H,0 and Ht reduction at 400° C...

Fractionation of an asphaltene by stepwise precipitation with hydrocarbon solvents (heptane to decane) allows separation of the asphaltene by molecular weight. The structural parameters determined using the x-ray method (Table II) show a relationship to the molecular weight (16). For the particular asphaltene in question (Athabasca), the layer diameters (La) increase with molecular weight to a limiting value similar relationships also appear to exist for the interlamellar distance (c/2), micelle height (Lc), and even the number of lamellae (Nc) in the micelle. 

Table II. Structural Parameters of Asphaltene Fractions Derived by the X-ray Method...

Structural information obtained from various methods can usually be represented by a set of structural parameters, S. These parameters are related to the physical and chemical properties of a given substance. A given set of properties, Pjt is unique to a given substance. Therefore, a given set of structural parameters can be used to characterize a given asphaltene ... 

Both structural parameters and properties derived in this manner are in matrix form. Furthermore, the production or genesis of asphaltene must depend on a set of environmental or refinery variables, such as temperature, and pressure. These quantities, tentatively called refinery variables, Rkt can affect the nature of the chemical and physical properties of asphaltenes ... 

Consequently, by studying the structural parameters of asphaltenes, one can directly relate them to refinery variables. The application to engineering problems is that by controlling a given set of refinery variables, the properties of the asphaltenes can be controlled. 

Microstructure. By using a group of structural parameters obtained through a number of physical methods (such as x-ray, NMR, MS, IR, VPO, DTA, densimetric methods, EM, and SAS) and chemical methods (such as oxidation, alkylation, and halogenation), the structure of petroleum asphaltene has been gradually revealed. As an example, the structural parameters of an asphaltene derived from a Laquinillas crude oil from Venezuela (API gravity 20°, Conradson carbon number 13.39, Miocene Age) are listed in Table I. An empirical formula can be deduced. 

Table I. Examples of the Structural Parameters for the Microstructure of a Petroleum-Derived Asphaltene...

We have recently determined the structural parameters and composition of some asphaltene samples obtained from the Synthoil and Exxon Donor Solvent (EDS) liquefaction processes. The particular EDS sample used was sufficiently volatile for analysis by ultrahigh resolution mass spectrometry, so we could obtain very detailed data on its composition in terms of the distribution of individual carbon-number homologs. Information from this approach, integrated with data from NMR, IR, molecular weight determinations, elemental analyses, and separations furnished us with a novel and detailed insight into the nature of these asphaltenes. The excellent agreement observed between composites calculated from the detailed MS data, where available, and the averages determined by NMR, IR, and elemental analyses reinforces the credibility of the approaches used and allows extrapolations to heavier samples that are not amenable to detailed MS characterization. 

Table X. Average Structural Parameters Calculated for Asphaltenes from NMR, GPC, and Elemental Analysis...

Table IV. Average Structural Parameters of Green River Asphaltenes...

Hydrocarbon Structures. Early postulates of asphaltene structure centered around a variety of polymer structures based on aromatic systems (36, 37). More recent information has related to the structural parameters and carbon skeleton of petroleum fractions, and asphaltenes structures have been derived from spectroscopic studies of asphaltenes isolated from various petroleum and bitumen (38-46). 

These NMR methods developed for dilute solutions of the intractable fractions of petroleum asphaltenes [75,91,92] have supported the high average mass measurements of asphaltenes by LD-MS through evaluation of average structural parameters from the NMR spectra. Briefly, for the sample mass data to match the measured... 

Sato, S., Takanohashi, T, Tanaka, R. (2003) Estimation of the structural parameter distribution of asphaltene using preparative GPC technique. ACS Fuel Chem. Div. Preprints, 48 1), 61-62. 

In recent decades, NMR has been used as a tool for the characterization of mixtures, especially the NMR, providing relevant information about the structure of complex systems such as asphaltenes. Simultaneous use of and NMR allows the determination of a series of structural parameters such as fraction of aromatic carbon, the average number of carbons in an alkyl attached to aromatic systems and the percentage replacement of this system (Skoog et al, 2002). 

Vijay, R., Deshpande, A.P., and Varughese, S. 2008. Nonlinear rheological modeling of asphalt using White-Metzner model with structural parameter variation based asphaltene structural build-up and breakage. Appl. Rheol. 18 23214—23228. 

Upgrading of heavy oils and residua can be designed in an optimal manner by performing selected evaluations of chemical and structural features of these heavy feedstocks (Schabron and Speight, 1996). The evaluation schemes do not need to be complex, but must focus on key parameters that affect processability. For example, the identification of the important features can be made with a saturates-aromatics-resins-asphaltene separation (Chapter 3). Subsequent analy-... 

Asphaltene particles are dispersed in saturates and aromatic hydrocarbons (gas-oil) with resins as peptizing agents in asphalt or heavy oil. The interaction between resin and asphaltene micelles is not well understood. In the present study, asphaltene has been dispersed into aromatic hydrocarbons (such as toluene), and the precipitations due to additions of paraffinic hydrocarbons (such as pentane) in the presence of a number of amphiphiles have been studied. These amphiphiles certainly affect the asphaltene precipitation, either by retardation or by enhancement, depending on the structural types and quantities of the amphiphiles. We have found that the nature of resin is that it behaves as an amphiphile, since the polar fractions of resin do contain amphiphiles. The solubility parameter spectra of these asphaltenes are discussed. 

The NMR technique, in particular, provides reliable molecular parameters about characteristics of aromatic rings and aliphatic chains of asphaltene structures (Speight, 1999). 

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