Hassan ElBanhawi

About this Book (Preface):-

Refining has the function of transforming crude oil from various origins into a set of refined products in accordance with precise specifications and in quantities corresponding as closely as possible to the market requirements.
Crude oils present a wide variety of physical and chemical properties. Among the more important characteristics are the following:

• distillation curve, which leads to a first classification of light crude oils having high distillate yields as opposed to heavy or extra heavy crudes• distillation curve, which leads to a first classification of light crude oils having high distillate yields as opposed to heavy or extra heavy crudes

• sulfur content (crudes having low or high contents)

• chemical composition, this is used only to characterize particular crudes (paraffinic or naphthenic).

As a whole, a given crude is generally used to make products most of which have positive added values. This is particularly the case for motor fuels and specialty products. However, some of the products could have negative added values, as in the case of unavoidable products like heavy fuels and certain petroleum cokes.
The products could be classified as a function of various criteria: physical properties (in particular, volatility), the way they are created (primary distillation or conversion). Nevertheless, the classification most relevant to this discussion is linked to the end product use: LPG, premium gasoline, kerosene and diesel oil, medium and heavy fuels, specialty products like solvents, lubricants, and asphalts. Indeed, the product specifications are generally related to the end use. Traditionally, they have to do with specific properties: octane number for premium gasoline, cetane number for diesel oil as well as overall physical properties such as density, distillation curves and viscosity.

Chemical composition does not generally come into play, except for the case where it is necessary to establish maximum specifications for undesirable compounds such as sulfur, nitrogen, and metals, or even more unusually, certain compounds or families of compounds such as benzene in premium gasolines. By tradition, the refiner supposedly possesses numerous degrees of freedom to generate products for which the properties but not the composition are specified.
Nevertheless, we are witnessing most recently an important development in petroleum product specifications regarding two main factors:

• product quality improvements, e.g., lubricant bases having a very high viscosity index

• product quality improvements, e.g., lubricant bases having a very high viscosity index

• environmental limits on composition established to reduce emissions overall or to modify them to reduce their impact. This constraint concerns principally the motor and heating fuels.

From complex cuts characterized in an overall manner, there is a transition towards mixtures containing only a limited number of hydrocarbon families or even compounds. This development has only just begun. It affects for the moment only certain products and certain geographical zones. It is leading gradually to a dil!erent view of both refining and the characterization of petroleum products.

Simple conventional refining is based essentially on atmospheric  distillation. The residue from the distillation constitutes heavy fuel, the quantity and qualities of which are mainly determined by the crude feedstock available without many ways to improve it. Manufacture of products like asphalt and lubricant bases requires supplementary operations, in particular separation operations and is possible only with a relatively narrow selection of crudes (crudes for lube oils, crudes for asphalts). The distillates are not normally directly usable; processing must be done to improve them, either mild treatment such as hydrodesulfurization of middle distillates at low pressure, or deep treatment usually with partial conversion such as catalytic reforming. The conventional refinery thereby has rather limited flexibility and makes products the quality of which is closely linked to the nature of the crude oil used.