Characterization of Crude Oil by Real Component Surrogates

Abstract

For characterization of crude oil and its primary fractions, the generation of substitute mixtures (surrogates) containing only real chemical components is a promising approach. The abandonment of pseudo-components, except for the utmost high-boiling fractions, allows for rigorous application of standard thermodynamic models (e.g., activity coefficients and equations of states), increasing reliability of phase-equilibrium calculations and predictive capabilities using process simulators. In this paper, an improved algorithm for characterization of petroleum fractions with real components is developed and applied to characterization of crude oil and its products through generation of substitute mixtures. The capabilities of emulating the separation behavior of crude oil are verified through a comprehensive analysis of a simulation conducted with real components by comparison to real plant data of an operating crude oil distillation unit (CDU). Additionally, a simulation based on the traditional pseudo-component approach is used for comparison. ■ MOTIVATIONCrude oil is a hydrocarbon mixture containing thousands of individual components ranging from light gases to very heavy, high-boiling components. 1 This mixture of a vast number of components with unknown chemical composition has to be processed in the refineries. Because of the increased need for efficiency, a much deeper understanding of the chemical specificity of refinery streams will be necessary for optimization. 2 A molecular-based characterization of the refinery streams can help to achieve this task. 3 A state-of-the-art approach for crude oil characterization is the pseudo-component approach, which is readily available in commercial simulation programs. Pseudo-components are generated on the basis of measured bulk properties, and all further calculations are based on these artificial components. Within the generation of pseudo-components, especially the estimation of their critical data and the acentric factor is arguable and no single commonly accepted method has been established thus far. 3 Another approach to characterize complex hydrocarbon mixtures is the use of real chemical components instead of pseudo-components. One advantage of using real components is the applicability of rigorous thermodynamic models instead of mainly empirical correlations for property estimation, which might be prone to errors. 4 This allows also for the modeling of fractions and mixtures with non-traditional components, e.g., bio-based products, which are not captured in the original pseudo-component approach. Furthermore, such an approach enables use of reaction kinetics or inclusion of key components within the simulation. 3 Moreover, it is possible to define key components within simulations, where calculations can rely on measured pure component data and interaction parameters. Additionally, the real component approach allows for experimental validation of predictions and applied models. ■ INTRODUCTIONPioneering activities in the generation of substitute mixtures for ...

Coarse grained force field for the molecular simulation of natural gases and condensates

“…It is thus natural to consider that the atomistic modelling will follow the EoS modelling approach, i.e. it is compulsory to describe a crude oil as a mixture of a relatively small number of prototypical species or surrogate real molecules 17 . Some key questions still remain to be answered as to the number and nature of discrete elements necessary for a trustworthy representation, the level of fidelity required from the models and the strategies employed to represent the more "unknown" fractions present in heavier crudes.…”

Surrogate Generation and Evaluation for Diesel Fuel

“…6 The surrogate composition is obtained by fitting the selected physical and chemical properties based on experimental data such as the True Boiling Point (TBP) curve according to ASTM D2887, 7 liquid density at a temperature of 15 ℃ according to ON EN ISO 12185 (equivalent to ASTM D4052), and the derived cetane number according to DIN EN 15195 (equivalent to ASTM D6890).…”

“…The strategy of modeling the TBP curve with a small number of real components was based on a method proposed by Riazi and Daubert,19 which has been explained in detail by Reiter et al 6 and Albahri. 21 The idea behind this approach was to model the smooth TBP curve by using a step-wise approximation method, as illustrated in Figure 2.…”

“…The state-of-the-art fitting procedure typically used in this context 6,[22][23][24][25][26] this fitting procedure is…”

“…The normal boiling point, T b i , is used to generate a dimensionless value that can be used to compare with other criteria that might be additionally considered in the objective function. 6,21,23,25 One limitation of this objective function is represented by the fact that different components exhibiting the same temperature difference, ∆T i , unequally contribute to the function value, because the normal boiling point of the component, T b,i , is used in the denominator of eq 1.…”