Dilution des bruts lourds-Les pétroles bruts lourds ne peuvent être transportés par pipeline sans réduction préalable de leur viscosité. Pour ce faire, la méthode la plus couramment employée est la dilution par des hydrocarbures légers. Dans ce cas, la viscosité du mélange dépend uniquement du taux de dilution et des viscosités et densités respectives de l'huile lourde et du diluant. L'ajout d'un solvant polaire à une solution d'asphaltènes dans du toluène permet d'agir sur la structure colloïdale des asphaltènes. Ceci conduit à une diminution de la viscosité relative de la solution. Des mesures effectuées par diffusion des rayons X aux petits angles indiquent que le rayon de giration des agrégats d'asphaltènes diminue conjointement. De même, en mélangeant des hydrocarbures avec des solvants comportant des groupements polaires, il est montré que l'efficacité de la dilution des bruts lourds est améliorée. La théorie de Hansen peut être utilisée pour sélectionner les solvants les plus efficaces. À taux de dilution constant, une augmentation du paramètre de polarité ou du paramètre représentatif des liaisons hydrogène se traduit par une diminution de la viscosité relative du brut dilué. Néanmoins, les produits comportant de fortes liaisons hydrogène sont généralement plus visqueux que les hydrocarbures. L'effet de leur interaction avec les asphaltènes s'en trouve masqué lorsque les résultats sont exprimés en termes de viscosité absolue. Seuls les solvants polaires donnant peu de liaisons hydrogène permettent d'obtenir une réduction significative de la viscosité du brut dilué. Abstract-Heavy Oil Dilution-Heavy crude oils cannot be transported by pipeline without a prior reduction of their viscosity. This is commonly obtained by blending the oil with light hydrocarbons. In that case, the resulting viscosity of the mixture depends only on the dilution rate, on the respective viscosities and densities of the oil, and of the diluent. The addition of a polar solvent to a solution of asphaltenes in toluene acts on the colloidal structure of the asphaltenes. The relative viscosity of the solution decreases. Small-angle X-ray scattering (SAXS) measurements show that the radius of gyration of the aggregates of asphaltenes decreases too. In the same way, by mixing hydrocarbons and solvents owning polar functional groups in their molecule, it is shown that the efficiency of the dilution of heavy crude oils is enhanced. Hansen's theory can be used to screen the solvent efficiency. At constant dilution rate, the higher the polarity parameter or the hydrogen bonding parameter of the solvent, the greater the relative viscosity reduction of the diluted crude oil. Nevertheless, solvent owning high hydrogen bonding are generally more viscous than hydrocarbons. The influence of their interactions with the asphaltenes is hidden when the results are expressed in absolute viscosity. Only polar solvents giving few hydrogen bonding give a significant reduction of the viscosity of the diluted crude oil. Pipeline Transportation of Heavy Oils...
fax 01-972-952-9435. AbstractHeavy or extra heavy crude oils cannot be transported by pipeline without a prior reduction of their viscosity. This is commonly obtained by blending the oil with light hydrocarbons. In that case, the resulting viscosity of the mixture depends only on the dilution rate, and on the respective viscosities and densities of the oil and of the diluent. Classical diluent are light crudes, condensates, naphtha. Availability of the diluent and its possible recycling needs of course to be taken in account. In this work we have studied the influence of composition of the diluent on the viscosity reduction efficiency. In particular we show that the addition of a polar solvent to a solution of asphaltenes in toluene acts on the colloidal structure of the asphaltenes. The relative viscosity of the solution decreases, as well as the size of the aggregates of asphaltenes. In the same way, by mixing hydrocarbons and solvents owning polar functional groups in their molecule, it is shown that the efficiency of the dilution of heavy crude oils is enhanced. Hansen's theory can be used to screen the solvent efficiency. At constant dilution rate, the higher the polarity parameter or the hydrogen bonding parameter of the solvent, the greater the relative viscosity reduction of the diluted crude oil. Nevertheless, solvent owning high hydrogen bonding are generally more viscous than hydrocarbons. The influence of their interactions with the asphaltenes is hidden when the results are expressed in absolute viscosity. Polar solvents giving few hydrogen bonding give a significant reduction of the viscosity of the diluted crude oil. From an economical point of view, any improvement of the efficiency of the thinner could be a benefit for the process, by reducing the amount of solvent needed to get an acceptable viscosity, and therefore allowing a greater quantity of crude to be transported.
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