The
size distributions of sulfur (S), vanadium (V), and nickel (Ni) compounds
in four crude oils, two residues, and their saturate, aromatic, resin,
and asphaltene (SARA) fractions were determined using gel permeation
chromatography (GPC) coupled to inductively coupled plasma high-resolution
mass spectrometry (ICP HR MS). The results show trimodal distributions
of V, Ni, and S compounds in the crude oils and residues. V and Ni
compounds are present in both resins and asphaltenes. Trimodal distributions
are clearly apparent in the resins but not apparent in the asphaltenes.
In the latter, the predominant compounds have a high molecular weight
(HMW), even when the solution of asphaltenes is diluted by 40000-fold.
In the resins, compounds with a medium molecular weight (MMW) were
expected; however, HMW compounds were observed, indicating that nanoaggregates
or large molecules exist in both the asphaltenes and resins. Low-molecular-weight
(LMW) compounds are predominantly present in the resins and do not
represent more than 22% of V and Ni present in crude oil. These compounds
appear to have molecular weights similar to simple metalloporphyrins.
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 were dissolved in n-heptane (HEP), and extractions with methanol (MeOH), acetonitrile (ACN) and dimethylformamide (DMF) were performed. The extraction with ACN is more efficient than that of MeOH for the removal of
The
aggregation and adsorption of asphaltenes is of great interest
due to their negative effects on the oil industry. Asphaltenes form
aggregates, even at low concentrations, producing groups of molecules
with different molecular weights in equilibrium. Using GPC ICP HR
MS, the different molecular weight fractions are separated. By monitoring
the signals of S, V, and Ni ions, typical mass profiles are obtained.
The V profile of asphaltene in toluene shows three zones corresponding
to low, medium, and high molecular weight fractions in equilibrium.
The present study describes the development of a method to study the
adsorption of asphaltenes on SiO2 nanoparticles using GPC-ICP
HR MS. Samples of asphaltenes in toluene were analyzed before and
after adsorption onto nanoparticles (NPs). At low concentrations,
the adsorption of larger aggregates predominates. The adsorption onto
NPs increases the proportion of vanadium in the low molecular weight
fraction of the solution.
A method of sequential liquid-solid extraction (leaching) has been developed to extract the V, Ni and S compounds present in asphaltenes (n-C 7) according to their molecular weight distribution. For the high molecular weight (HMW) compounds, two new families of compounds were extracted, labeled HMW1 and HMW2, where the latter was smaller than HMW1, and together represented approximately 85% of the asphaltene mass according to the mass balance obtained after the extractions. The compounds associated with HMW1 were asphaltenes that were insoluble in hot dimethylformamide (DMF), while the compounds associated with HMW2 were soluble in DMF but insoluble in the second leaching step based on hot acetone. The third family of obtained compounds was the medium molecular weight (MMW) compounds, which were soluble in hot acetone but insoluble in acetonitrile (ACN). The last fraction to be obtained was the low molecular weight (LMW) compounds, which were soluble in ACN. The results reported here represent a new method that allows the extraction of different types of aggregated asphaltenes according to their molecular weights. With respect to the temperature and number of extraction steps, it was observed that an increase in both parameters increased the extraction efficiency.
This work describes the carbonylation of hex-1-ene, cyclohexene, 2,3-dimethyl-but-1-ene and 2-methylpent-2-ene, their quaternary mixture and a real Venezuelan naphtha, catalyzed by a rhodium(I) [Rh(cod)(4-picoline) 2 ] (PF 6 ) (cod = 1,5-cyclooctadiene) complex immobilized on poly(4-vinylpiridine) (P(4-VP)) in contact with methanol under carbon monoxide atmosphere. The conversion (%) of olefins to carbonylated products for the individual olefins decreases in the order: hex-1-ene (63) [ cyclohexene (58) [ 2,3-dimethyl-but-1-ene (50) [ 2-methyl-pent-2-ene (31), under the following conditions: 0.5 g of P(4-VP) for [Rh] = 2 wt.% (1 9 10 -4 mol), 10 mL of CH 3 OH, [olefin] = 1 9 10 -2 mol, S/C = 100, P(CO) = 33 atm at 110°C for 24 h. Other products such as H 2 and CO 2 coming from the catalysis of the water-gas shift reaction are observed.
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