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

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

Oil-in-water emulsion

Crude oil fractionation

Electrothermal atomic absorption spectrometry

Nickel and vanadium in crude oil fractions

Palladium modifier

Speciation analysis

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 20μg palladium (total Ni and V) and the volatile fraction was calculated by difference. The limits of detection were 0.02μgg−1 and 0.06μgg−1, for Ni and V, respectively, based on an emulsion of 2g of oil in 10mL. 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.

Talanta

2008-02-15

Vale, Maria Goreti R.

Silva, Márcia M.

Damin, Isabel C.F.

Sanches Filho, Pedro J.

Welz, Bernhard

Journal Article

SPZE9F2P

0039-9140

10.1016/j.talanta.2007.09.009