Analysis of the Photo Conversion of Asphaltenes Using Laser Desorption Ionization Mass Spectrometry: Fragmentation, Ring Fusion, and Fullerene Formation

The conversion or photo conversion of asphaltenes to polycyclic aromatic hydrocarbons (PAH’s) promoted by a laser source is analyzed using both experimental and theoretical methods. We propose that during measurements performed at an intermediate laser power, fragmentation to afford PAH’s and ring fusion to yield fused PAH’s (FPAH’s) may occur either within molecular clusters (resin case) or within molecular aggregates (asphaltene case) which are vaporized or sublimed after ionization by the laser source. These events change the initial molecular mass distribution (MMD) of the sample to a continuous statistical MMD that can be fitted to a log-normal distribution. At a high laser power, the experimental MMD is converted to a sequence of Cn bands (n is an even number) which are separated by a 24-amu, the characteristic of a mixture of fullerene compounds

Simplification of heavy matrices by liquid-liquid extraction, the use of fractionation and GPC-ICP/MS

International audienceS, 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

Simplification of heavy matrices by liquid-liquid extraction: Part I -How to separate LMW, MMW and HMW compounds in maltene fractions of V, Ni and S compounds

International audienceA method using liquid–liquid extractions has been developed for matrix simplification and evaluated by gel permeation chromatography coupled with inductively coupled plasma and mass spectrometry. In this method, maltenes were dissolved in n-heptane and extractions with methanol (MeOH), acetonitrile (ACN), and dimethylformamide (DMF) were performed. The extraction with ACN is more efficient than that with MeOH for the removal of compounds with low-molecular weights (LMW) containing V (our reference element) and more selective than that with DMF (with this solvent, compounds with LMW and medium-molecular weights (MMW) are extracted). Thus, a sequential extraction was performed by applying ACN to selectively remove LMW compounds, followed by extractions with DMF of the resulting maltene to separate the MMW compounds from the high-molecular weights (HMW) compounds remaining in the final remnant maltene. The results show, for the first time in the literature, that it is possible to separate the three V and Ni species of compounds present in maltenes based on their molecular weights (HMW, MMW, and LMW)

Simplification of Heavy Matrices by Liquid–Solid Extraction: Part II—How to Separate the LMW, MMW, and HMW Compounds in Asphaltene Fractions for V, Ni, and S Compounds

International audienceA method of sequential liq.-​solid extn. (leaching) has been developed to ext. the V, Ni, and S compds. present in asphaltenes (n-​C7) according to their mol. wt. distribution. For the high-​mol.-​wt. (HMW) compds., 2 new families of compds. were extd., labeled as HMW1 and HMW2, where the latter was smaller than HMW1, and together represented ∼85​% of the asphaltene mass according to the mass balance obtained after the extns. The compds. assocd. with HMW1 were asphaltenes that were insol. in hot DMF, while the compds. assocd. with HMW2 were sol. in DMF but insol. in the 2nd leaching step based on hot acetone. The 3rd family of obtained compds. was the medium-​mol.-​wt. (MMW) compds., which were sol. in hot acetone but insol. in MeCN (ACN)​. The last fraction to be obtained was the low-​mol.-​wt. compds., which were sol. in ACN. The results reported here represent a new method that allows the extn. of different types of aggregated asphaltenes according to their mol. wts. With respect to the temp. and no. of extn. steps, an increase in both parameters increased the extn. efficiency

Suppression of Phase Separation as a Hypothesis to Account for Nuclei or Nanoaggregate Formation by Asphaltenes in Toluene

International audienceHere, the concept of suppression of phase separation is proposed to account for the solubility behavior of asphaltenes at high dilution in toluene under ambient conditions. Nuclei formation at concentrations near 90 mg L–1 is the consequence of reaching A1 fraction solubility, and phase separation is suppressed by the intercalation of sufficient A2 in these nuclei or nanoaggregates. Presumably, such intercalation leads to media penetration of the nuclei periphery, hindering the growth and allowing for nuclei dispersion as a kinetic unit. Trapped compounds (TCs) or compounds trapped by asphaltene clusters were isolated, and their elemental analysis showed that they were neither resins nor asphaltenes. The information available regarding the A1 and A2 asphaltene subfractions is revised and complemented with new thermogravimetric analysis, simulation distillation (SimDis) curves, microcarbon Conradson, softening points, and nanoparticle results involving size-exclusion microchromatography. In general, physical results, such as solubility, SimDis, aggregation, and the softening point, differ substantially, whereas structural results, such as elemental analysis, DBE, and 13C nuclear magnetic resonance spectra, are similar. These results suggest that minor structural differences strongly affect the solubility, softening point, and other physical characteristics