Asphaltene Cold Lake

These heavy oils already contain large percentages of refractory materials such as asphaltenes, and it would be highly undesirable to increase the amount or degrade the quality of these components. We have, therefore, investigated the effect of heat treatment during distillation on the quantity and physical and chemical properties of asphaltenes. Cold Lake crude was chosen for this study since it is known to be a thermally sensitive material. 

The separations of resins and asphaltenes under comparable conditions done on the fractions from a common source—Athabasca (in some cases Cold Lake) bitumen—have confirmed a number of postulates that have appeared in the recent literature. 

The thermal hydroconversion of Cold Lake asphaltenes was studied initially to provide a basis for evaluation of catalytic effectiveness in subsequent work. Series of thermal runs were made at 335°C, 365°C and 400°C and the reaction products were separated as described previously. Several kinetic models were tried, but after examining the variability of our data, we decided on the simple first-order asphaltene decomposition model shown below ... 

Figure 1. Thermal hydroconversion of Cold Lake asphaltenes at 400°C and 6 MPa H2 asphaltenes ( A) maltenes (O) coke ) model (-).

Figure 3. Arrhenius plot for hydroconversion of Cold Lake asphaltenes 200 ppm molybdenum (A) thermal (0).

Influence of Thermal Processing on the Properties of Cold Lake Asphaltenes The Effect of Distillation... 

Preparation of Asphaltenes. Asphaltenes were obtained by n-heptane precipitation from either Cold Lake crude or vacuum residuum using typical deasphaltening procedures. (i.e. One part of residuum was refluxed for one hour with 10 parts of heptane. 

To provide raw material for this comparative study of untreated and heat-treated oils, asphaltenes from Cold Lake crude (crude asphaltenes) and from Cold Lake vacuum residuum (residuum asphaltenes) were prepared by n-heptane precipitation as described in the Experimental section. The Cold Lake residuum fraction was prepared by Imperial Oil Enterprises, Ltd. at Sarnia, Ontario, Canada. The distillation history of this bottoms fraction indicates that the pot material was subjected to temperatures as high as 314-318°C during atmospheric and vacuum distillation. The length of time at 300°C or higher was about two hours. This is well in excess of what would be experienced in a pipestill and should have provided ample time for any decomposition. It should be noted, however, that since it was possible to maintain the system vacuum at 0.35 mm, the maximum temperature experienced by the residuum was not quite as high as it might be during refinery distillation (e.g. ca 350°C). 

Asphaltene Yields from Cold Lake Crude and Residuum Source % Asphaltenes (On Crude)... 

Aromatic Carbon and Hydrogen Contents of Cold Lake Asphaltenes... 

Figure 3. IR spectrum of Cold Lake crude asphaltenes...

Figure 4. 1R spectrum of Cold Lake residuum asphaltenes... 

ESR Parameters for Cold Lake Asphaltenes Parameter Crude Asphaltenes Residuum Asphaltenes... 

It is apparent from the chemical shifts (g-values), the hyperfine coupling constants (A-values), and the linewidths that the free radicals and vanadyl species are in very similar environments in both samples. It was not possible to obtain meaningful values for the absolute numbers of spins per gram for either species, but estimates of the relative concentrations obtained by measuring peak heights indicate that the vanadyl and free-radical concentrations do not differ significantly between the two asphaltenes. It thus appears that heat treatment of Cold Lake asphaltenes to 320°C does not alter the nature or abundance of paramagnetic centers. 

The characteristics of Cold Lake crude and residuum asphaltenes have been compared by a number of instrumental and physical techniques. The asphaltenes were essentially identical in quality... 

Since the Cold Lake crude used in this investigation has been exposed to the temperature of the pressuized steam used in the oil production, one cannot be certain that some thermal changes had not already occurred in the crude oil. To study this possibility the properties of cold bailed (i.e. recovered without steam injection) Cold Lake crude asphaltenes are being investigated by many of these same techniques and will be described in a future report. 

In many petroleum reservoirs around the world, reservoir fluid composition has been found to very with location and depth. Patel found the viscosity of Athabasca, Peace River, Wabasca and Cold Lake bitumens to vary with depth of the formation. Schulte explained the compositional variations within a hydrocarbon column by gravity segregation phenomenon. However, he found that the extent of variation to be higher with larger aromatic fractions in the hydrocarbon fluid. Hirschberg concluded that the heavy polar components play a key role in compositional and oil viscosity variation and in particular, identified asphaltene segregation to have a dominant effect. Hirschberg found that the... 

Conversion (upgrading) of bitumen and heavy oils to distillate products requires reduction of the MW and boiling point of the components of the feedstocks. The chemistry of this transformation to lighter products is extremely complex, partly because the petroleum feedstocks are complicated mixtures of hydrocarbons, consisting of 10 to 10 different molecules. Any structural information regarding the chemical nature of these materials would help to understand the chemistry of the process and, hence, it would be possible to improve process yields and product quality. However, because of the complexity of the mixture, the characterization of entire petroleum feedstocks and products is difficult, if not impossible. One way to simpHfy this molecular variety is to separate the feedstocks and products into different fractions (classes of components) by distillation, solubility/insolubility, and adsorption/desorption techniques. For bitumen and heavy oils, there are a number of methods that have been developed based on solubility and adsorption. The most common standard method used in the petroleum industry for separation of heavy oils into compound classes is SARA (saturates, aromatics, resins, and asphaltenes) analysis. Typical SARA analyses and properties for Athabasca and Cold Lake bitumens, achieved using a modified SARA method, are shown in Table 1. For comparison, SARA analysis of Athabasca bitumen by the standard ASTM method is also shown in this table. The discrepancy in the results between the standard and modified ASTM methods is a result of the aromatics being eluted with a... 

During the thermal cracking of vacuum residues, maltenes play an important role in the conversion of asphaltenes. Wiehe has shown that in the hydrocracking of CL VB (Cold Lake Vacuum Bottoms), the presence of maltenes in the resid increases (prolongs) the coke induction period significantly. The results were interpreted based on the efiectiveness of maltenes as hydrogen donors to cap free radicals produced by the thermal cracking of asphaltenes. 

Clarke, P. Pruden, B. Asphaltene precipitation Irom Cold Lake and Athabasca bitumen. Pet Sci. Technol, 1998,16(3 4), 287-305. 

Khulbe, K.C., Sachdev, A.K., Maim, R.S., Davis, S. 1984. TGA studies of asphaltenes derived from cold lake (Canada) bitumen. Fuel Process. Technol. 8 259-266. 

Schucker, R.C., Keweshan, C.F. 1980. Reactivity of cold lake asphaltenes. Prepr. Pap. Am. Chem. Soc. Div. Fuel Chem. 25 155-165. 

Rahimi, P.M., Gentzis, T. 2003. Thermal hydrocracking of cold lake vacuum bottoms asphaltenes and their subcomponents. Fuel Process. Technol. 80 69-79. 

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