SARA Separation and Determination of Concentration Levels of Some Heavy Metals in Organic Fractions of Nigerian Crude Oil

Abstract

Nigerian Crude oil samples were obtained from Nigerian Petroleum Development Company (NPDC). The samples were subjected to column chromatography.  Sequential leaching method was used to separate the crude oil into four distinct fractions based on leaching of crude oil with different organic solvents and mixtures. Saturated fraction was extracted with hexane- cyclohexane (1:1v/v), aromatic fraction was extracted with hexane- toluene (7:3v/v), while resin was extracted with tetrachloromethane-trichloromethane (7:3v/v), and asphaltene was extracted with acetonitrile-methanol (1:1v/v). The fractions were digested using sulphuric acid, nitric acid and hydrochloric acid method followed by the detection of metals in the samples using AAS analysis. The elements analyzed were Pb, Cu, Cr, Fe and Ni. The result shows that Fe had the highest concentration while Ni had the least concentration. The concentration (ppm) levels of these elements in the crude oil fraction analyzed range from 0.1307 – 0.4107 for Pb, 0.1796 – 1.1250 for Cu, 2.7420 – 10.1903 for Cr, 11.2962 – 21.8084 for Fe, and 0.0464 – 0.5876 for Ni. It was obvious from this study and previous ones that Nigerian crude oil fractions have low metal content. However, despite their low concentrations they can still be detrimental to the refinery operations and the immediate environment, and therefore, should be removed before refining.

Keywords: Atomic Absorption Spectroscopy, Aromatic, Asphaltenes, Risens, Saturates, Heavy Metals