Influence of High Asphaltene Feedstocks on Processing M. M. Abu-Khader, J. G. Speight To cite this version: M. M. Abu-Khader, J. G. Speight. Influence of High Asphaltene Feedstocks on Processing. Oil &Gas Science and Technology - Revue d’IFP Energies nouvelles, Institut Français du Pétrole, 2007, 62 (5), pp.715-722. 10.2516/ogst:2007049. hal-02005751 HAL Id: hal-02005751 https://hal.archives-ouvertes.fr/hal-02005751 Submitted on 4 Feb 2019 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Oil & Gas Science and Technology – Rev. IFP, Vol. 62 (2007), No. 5, pp. 715-722 Copyright © 2007, Institut français du pétrole DOI : 10.2516/ogst:2007049 Influence of High Asphaltene Feedstocks on Processing M.M. Abu-Khader1 and J.G. Speight2 1 Department of Chemical Engineering, FET, Al-Balqa Applied University, Amman-Jordan 2 CD & W Inc., Laramie, Wyoming 82070, USA e-mail: [email protected] - [email protected] Résumé — Influence des charges élevées d'asphaltène sur le raffinage — Les composants de l’asphaltène sont, par définition, une fraction insoluble obtenue par précipitation depuis le pétrole, l’huile lourde ou le bitume et qui n’a par conséquent pas de structure simple, unique ou de poids moléculaire spécifique. Quand ils sont dispersés dans le pétrole, les composants de l’asphaltène en augmentent de manière importante la viscosité et affectent négativement la productivité des puits et/ou les moyens de raffinage. Du fait de changements dans la composition du pétrole ou de variations de température ou de pression, le pétrole (un système stable dynamique) peut être perturbé et les composants de l’asphaltène sont susceptibles de précipiter. Le but de cette analyse est d’étudier les méthodes au moyen desquelles le dépôt d’asphaltène peut être prévu ou déterminé et les méthodes au moyen desquelles il peut être atténué. Abstract — Influence of High Asphaltene Feedstocks on Processing — Asphaltene constituents are, by definition, a solubility class that is precipitated from petroleum, heavy oil and bitumen and therefore do not have a single, unique structure or specific molecular weight. When dispersed in petroleum, asphaltene constituents appreciably increase petroleum viscosity and adversely affect the productivity of oil wells and/or the means of refining. Owing to the changes in the composition of petroleum as well as variations of temperature, pressure, petroleum (a dynamic stable system) may be disturbed and asphaltene constituents are likely to be precipitated. The purpose of this review is to examine the methods by which asphaltene deposition can be predicted or determined and hence methods by which deposition can be mitigated. 716 Oil & Gas Science and Technology – Rev. IFP, Vol. 62 (2007), No. 5 1 THE NATURE OF PETROLEUM ASPHALTENE 2 ASPHALTENE CONSTITUENTS PROPERTIES CONSTITUENTS A predictive approach based on computer assisted structure Petroleum is a complex mixture of hydrocarbons and het- elucidation and atomistic simulations for the estimation of eroatom organic compounds of varying molecular weights the thermodynamic properties of condensed phase systems and polarity (Speight, 2006 and references cited therein). has been presented (Diallo et al., 1994). The approach A common practice for the purpose of research is to involved the use of molecular mechanics calculations and separate petroleum into four fractions: saturates, aromatics, simulations to estimate the molar volume, density, cohesive resins, and asphaltene constituents (Speight, 2006 and ref- energy, solubility parameter, enthalpy, thermal expansion erences cited therein; Liao and Geng, 2000; Sheu, 2002). coefficient and specific heat at constant pressure of the model The definition of the nonvolatile constituents of petroleum asphaltene structures in volumetric and thermal properties (i.e., the asphaltene constituents, the resin constituents, from molecular dynamic simulations. and, to some extent, part of the oils fraction insofar as non- In addition, the electrokinetic charges on asphaltene con- volatile oils occur in residua and other heavy feedstocks) is stituents are dependent on the solution pH, ionic strength, an operational aid. It is difficult to base such separations on ionic composition and the degree of hardness of the elec- chemical or structural features. This is particularly true for trolyte solution (Kokal et al., 1995). Asphaltene constituents the asphaltene constituents and the resin constituents, for are negatively charged in the neutral pH range. An increase which the separation procedure not only dictates the yield in the ionic strength of the aqueous solution leads to a but can also dictate the quality of the fraction (Speight, decrease in the electrophoretic mobility (and charge) of 2004a). Thus, some aspects of recovery and refining chem- asphaltene constituents. This effect is consistent with the istry, especially the chemistry of the deposition of asphal- compression of the electric double layer by indifferent elec- tene material (degradation or reaction products of the trolytes. It is possible to measure the electrophoretic mobility asphaltene constituents and the resin constituents), can be of asphaltene constituents in non-aqueous solvents with rela- tively high permittivity, for example; nitromethane and proposed by virtue of the studies that have led to further nitrobenzene. Also, the adsorption of asphaltene constituents knowledge of the nature of asphaltene constituents and the on mineral surfaces is influenced by the surface charge on resin constituents and particularly the nature of their inter- asphaltene constituents as well as on the mineral. Adsorption action in crude oil (Speight, 2004b). of asphaltene constituents from toluene solutions on minerals Thus, asphaltene constituents are, by definition, a solu- exhibits Langmuir Type I adsorption isotherms which indi- bility class that is precipitated from petroleum, heavy oil cate mono-layer adsorption. and bitumen by the addition of an excess of a liquid paraf- Based on surface tension, viscosity, dielectric relax- fin hydrocarbon. In addition, the composition of the ation, conductivity, and small angle neutron scattering asphaltene fraction is dependent upon the nature of the measurements, asphaltene molecules exhibit a strong hydrocarbon precipitant, the ratio of the volume of the pre- propensity for self-association and that these aggregates cipitant to the volume of feedstock, to the contact time, and are approximately spherical in shape (Sheu et al., 1991). to the temperature at which the precipitation occurs The conductivity and dielectric relaxation measurements (Speight, 2006 and references cited therein). Simply, suggest that the electron transformation between asphal- asphaltene constituents are high molecular weight, aro- tene molecules is the main mechanism in forming aggre- matic, polar compounds containing carbon, hydrogen, oxy- gates, but these aggregates do not percolate at either high gen, nitrogen, sulfur and some heavy metals such as vana- concentration or high temperature (60°C). dium and nickel. For this reason, the asphaltene Fluorescence depolarization techniques have been used to constituents do not have a single, unique structure or spe- measure asphaltene molecular size, and establish the substan- cific molecular weight. tial difference between asphaltene constituents derived petro- When dispersed in petroleum, asphaltene constituents leum (Buch et al., 2003). The method can be used to track appreciably increase petroleum viscosity and adversely the changes of the asphaltene constituents from a petroleum affect the productivity of oil wells and/or the means of atmospheric residuum subjected to increasing thermal sever- refining. Owing to the changes in the composition of petro- ity of catalytic hydrothermal cracking. leum as well as variations of temperature, pressure, petro- Following from the polarity concept (Speight and Long, leum (a dynamic stable system) may be disturbed and 1996 and references cited therein), it has been reported asphaltene constituents are likely to be precipitated (Goual and Firoozabadi, 2002) that the polarity of asphal- (Speight, 1996; Speight and Long, 1996). tene constituents and resins affects precipitation strongly. The purpose of this review is to examine the methods by For a given petroleum fluid, asphaltene constituents have a which asphaltene deposition can be predicted or determined higher dipole moment than resin constituents. However, and hence methods by which deposition can be mitigated. resin constituents from one petroleum fluid can have a MM Abu-Khader / Influence of High Asphaltene Feedstocks on Processing 717 higher dipole moment than asphaltene constituents from of crude oil towards asphaltene precipitation is better than another petroleum. both the Asphaltene–Resin ratio and the Oliensis Spot Test. While the polarity affects the solubility parameter Also, the author proposed the use of live oil depressurization (Speight, 1999), application of a theoretical model allows as the test for predicting the stability of