Simplification of heavy matrices by liquid-liquid extraction, the use of fractionation and GPC-ICP/MS
Résumé
S, N, V and Ni are the most abundant poisonous elements that are naturally present in petroleum.1 The high stabilities of Ni and V in crude oils and heavy fractions suggest that they mainly occur as tetrapyrrole complex-type metalloporphyrins. The predominance of Ni and V compounds compared to other organic metallocompounds is a consequence of the greater stability of nitrogen-vanadium or nickel bonds and their favorable electron configurations, among other factors.2,3 Many studies have been published in the recent years4-6 and most of those shows that conventional analytical approaches require previous fractionation in order to simplify the hydro carbonaceous matrix. A method using liquid-liquid extractions has been developed for matrix simplification and evaluated by gel permeation chromatography hyphenated with inductively coupled plasma and mass spectrometry (GPC ICP MS). In this method, maltenes and asphaltenes are firstly separated, then maltenes were dissolved in n-heptane, and a sequential extraction with acetonitrile (ACN) and dimethylformamide (DMF) was performed. The results show, that it is possible to separate the three V and Ni species of compounds present in maltenes based on their molecular weight (HMW, MMW and LMW). A second extraction procedure dedicated to the asphaltenes fractions is also proposed using ethylacetate, DMF, ACN and acetone. Using such fractionation procedure allows to have 7 simplified fractions that will be very interesting for further investigations with FTICRMS.