Asphaltene and oil

Suspension Model of Interaction of Asphaltene and Oil This model is based upon the concept that asphaltenes exist as particles suspended in oil. Their suspension is assisted by resins (heavy and mostly aromatic molecules) adsorbed to the surface of asphaltenes and keeping them afloat because of the repulsive forces between resin molecules in the solution and the adsorbed resins on the asphaltene surface (see Figure 4). Stability of such a suspension is considered to be a function of the concentration of resins in solution, the fraction of asphaltene surface sites occupied by resin molecules, and the equilibrium conditions between the resins in solution and on the asphaltene surface. Utilization of this model requires the following (12) 1. Resin chemical potential calculation based on the statistical mechanical theory of polymer solutions. 2. Studies regarding resin adsorption on asphaltene particle surface and... 

Many studies on direct liquefaction of coal have been carried out since the 1910 s, and the effects of kinds of coal, pasting oil and catalyst, moisture, ash, temperature, hydrogen pressure, stirring and heating-up rate of paste on coal conversion, asphaltene and oil yields have been also investigated by many workers. However, few kinetic studies on their effects to reaction rate have been reported. 

Product oils from SYNTHOIL runs carried out at 415° and 450° C and 2,000 and 4,000 psi H2 pressures were analyzed with respect to asphaltene and oil content, elementary compositions (C, E, S, N), ash and physical properties (specific gravity and viscosity). Asphaltenes exert a large effect on the viscosity of the product oil, the viscosity increasing exponentially with asphaltene content. Viscosity of product oil is not only dependent on the amount but also on the molecular weight of asphaltenes present. At 415° C, asphaltenes with a molecular weight of 670 are formed and at 450° C asphaltenes with a molecular weight of 460. 

Mima, M. J. Schultz, H. McKinstry, W. E. Method for the Determination of Benzene Insolubles, Asphaltenes, and Oils In Coal Derived Liquids. ERDA/PERC/RI-76/6, 1976, 15 pp. 

Removal of asphaltenes and preasphaltenes was easier than heteroatoms. At an increase of a hydrogen-to-carbon atomic ratio by 0.16, they were 80% removed. A comparison can be made with Synthoil process product of hydrogen-to-carbon atomic ratio equal to 1.04 which was hydrotreated to hydrogen-to-carbon atomic ratio equal to 1.24. The asphaltenes and preasphaltenes were 77% and 99% removed, respectively (7). Squires (8) concluded that the preasphaltenes can be converted to asphaltenes and oils with very little consumption of hydrogen. Asphaltenes are the major consumers of hydrogen. Although Squires conclusions were based on donor-solvent coal liquefaction, similar results were reported... 

Benzene Insolubles, Asphaltenes, and Oils in Coal-Derived Liquids, PERC/ RI-76/6, NTIS, U. S. Department of Commerce Springfield, VA, 1976. 

The concept of preasphaltenes, asphaltenes, and oils is of historical significance in the development of the science and technology of coal liquefaction (i). This concept is routinely employed in attempts to understand, assess,... 

The phosphotungstate salts cannot be used for equivalent weight determinations, for their characteristically variable composition leads to inconsistent titration results. However, treatment of the salts with aqueous sodium hydroxide led to recovery of the free bases in reproducible amounts. These results show that one-fifth of the high molecular weight asphaltenes and one-third of the preasphaltenes are precipitated as phosphotungstate salts. Considerably less of the unfractionated H-coal vacuum-still bottoms and none of the low molecular weight asphaltenes and oils and resins were separated in this manner. 

Hydrogenation studies were undertaken on the parent iron-tin treated coal (Drum 289) as well as the THF insolubles, preasphaltene, asphaltene and oil derived from a continuous reactor run as previously discussed. Studies with no additional catalyst added (case A) and with the addition of a sulphided nickel molybdate catalyst supported on alumina (case B) were performed. The results are presented in Table 1. The Ni/Mo catalyst in case B did not increase the conversion of the coal or the THF insolubles beyond that for case A because sufficient amounts of iron and tin materials were already... 

Yields of Preasphaltenes and Asphaltenes. Subbituminous coal is converted very rapidly to soluble products in tetralin at 427°C. Figure 1 shows the yields of THF-soluble but pentane-insoluble, benzene-soluble and pentane-soluble products vs. reaction time. These fractions correspond respectively to a mixture of preasphaltenes and asphaltenes, asphaltenes and oils. Of the 78% ultimate yield of THF-soluble products based on the dry coal containing 8.6% ash, 55-60% are formed within 5 to 10 min of reaction time. By 35 min of reaction time, conversion of coal to soluble products is essentially complete. In contrast to the extremely rapid process of conversion of the parent coal to preasphaltenes, the further degradation of preasphaltenes occurs only very gradually, the yield of asphaltenes increasing from 10 to only 25% over a 1-hr reaction time. 

The coal-derived materials are usually classified into preasphaltenes with approximate molecular weight = 1,000 to 2,000, asphaltenes with approximate molecular weight = 400 to 800, and oils with approximate molecular weight = 200 to 300. All three products are soluble in THF, asphaltenes and oils are soluble in benzene, whereas only oils are soluble in pentane. In DCL, some gases are also produced and clearly higher yields of oils are desired... 

Retcofsky et al. The ESR line widths in the coal used by Goldberg et al. were dominated by the narrow component (AH 1 Oe) and no significant changes in the narrow component line width were observed for different fractions. They also noted that the total number of unpaired electrons in the total product is approximately the same as that of the parent coal, with nearly 90 percent of these in the insoluble fraction. This is understandable since asphaltenes and oils have nearly an order of magnitude lower density of free radicals. This suggests that simply measuring total intensity of free radicals in the starting and end material is not likely to provide very useful information. 

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