Requirements for the Determination of Metal Content in Virgin and Crude Oils

4 Requirements for the Determination of Metal Content in Virgin and Crude Oils 

Crude petroleum is a naturally occurring complex material composed mainly of the elements hydrogen, carbon, sulphur, phosphorous and nitrogen, as well as a host of organometallic and free inorganic metal salts or complexes in the crude composition as contamination from the earth s surrounding minerals. The crude oil is present as solid (asphalt), liquid (crude oil) and gas (natural gas). 

The presence of major and trace metals in crude oils and their products is of considerable interest to the oil industry. This interest derives from the association of metals with the geological origin of the cmde and the influence of contamination by metal in the refining or processing of petroleum products, or the effects of metals on the utilisation or performance 

The list of metals detected in petroleum products is considerable and the most common detected are Fe, Na, Ni, V, Cr, Mg, and Si other metals at a lower concentration are Sb, Ar, Be, Cd, Co, Pb, Mn, Hg, Mo and Se. The elements Fe, Ni and V are the most important as they are present in all crudes at a higher concentration than other metals and, as expected, can be extracted from the earth s mineral source. The important requirement of knowledge of metals in crude oils and their products has resulted in a considerable effort to develop analytical methods for accurate measurements of the true concentration of all metals present. 

To evaluate the influence of given metals in oil products it is fortunate that analytical methods are available that are sensitive, accurate and informative. Analytical methods associated with oils involve step-by-step procedures from sample preparation to suitable solutions for measurements against certified standard calibration curves. The sample preparation step is very important in the analysis, and the method used is decided by the concentration of metal present and whether or not it is soluble in the oil or present as particulates. Preparation by simple dilution may not be sufficient for very low concentrations of elements as the dilution may inhibit the ability to measure low levels due to non-detection, precipitation or settling out of the metals of interest. 

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