Determination of volatile and non-volatile nickel and vanadium compounds in crude oil using electrothermal atomic absorption spectrometry after oil fractionation into saturates, aromatics, resins and asphaltenes.
In recent work, it has been shown that electrothermal atomic absorption spectrometry (ET AAS) can be used to differentiate between volatile and non-volatile nickel and vanadium compounds in crude oil. In the present work, the distribution of these two groups of compounds over different fractions of crude oil was investigated. For this purpose two crude oil samples were separated in two steps: firstly, the asphaltenes were precipitated with n-heptane, and secondly, the maltenes were loaded on a silica column and eluted with solvents of increasing polarity. The four fractions of maltenes eluted from silica column were: F1, saturated and light aromatics; F2, polyaromatics; F3, resins; and F4, polar compounds. Fractions F1 and F2 were further investigated using gas chromatography, and all fractions were characterized by CHN analysis, confirming the increase of aromatics in the fractions 2, 3, 4 and asphaltenes. For the determination of Ni and V by ET AAS, oil-in-water emulsions were prepared. The speciation analysis was carried out measuring without chemical modifier (stable compounds) and with 20 microg palladium (total Ni and V) and the volatile fraction was calculated by difference. The limits of detection were 0.02 microg g(-1) and 0.06 microg g(-1), for Ni and V, respectively, based on an emulsion of 2g of oil in 10 mL. The volatile species of Ni and V were associated with fractions F3 and F4, while only thermally stable Ni and V was precipitated in part together with the asphaltenes.
Vale
Maria Goreti R
MG
Instituto de Química, Universidade Federal do Rio Grande do Sul, Av. Bento Gonçalves 9500, 91501-970 Porto Alegre, RS, Brazil.
Silva
Márcia M
MM
Damin
Isabel C F
IC
Sanches Filho
Pedro J
PJ
Welz
Bernhard
B
D005591:Chemical Fractionation / Q000379:methods; D009532:Nickel / Q000032:analysis*; D010578:Petroleum / Q000032:analysis*; D013054:Spectrophotometry, Atomic / Q000379:methods*; D017968:Vanadium Compounds / Q000032:analysis*
D010578:Petroleum; D017968:Vanadium Compounds; D009532:Nickel