Characterization of petroleum saturates (Exxonmobil)

CATEGORY: CRUDE OIL ANALYSIS
PATENT
Characterization of petroleum saturates (Exxonmobil)
Publication number US20130206980 A1
Publication type Application
Application number US 13/832,564
Publication date Aug 15, 2013
Inventors
Anthony S. Mennito, Kuangnan Qian
Original Assignee
Exxonmobil Research And Engineering Company
Abstract
A method for characterizing the saturates portion of a petroleum or hydrocarbon sample that includes compounds with boiling points of 1000° F. (538° C.) or higher includes use of laser desorption ionization (LDI) to desorb and vaporize petroleum saturates into the gas phase. After ionization, the saturate compounds cations can be detected using mass spectrometry. The mass spectrum generated from the ionized saturated compounds is then characterized by assigning molecular formulas to any “detected” masses that exhibit a peak with an intensity greater than a defined signal to noise threshold. After making the molecular assignments, the abundance of each assigned molecule can be determined based on the signal magnitude of the peaks in the mass spectrum. The assigned molecules and the corresponding abundances can then be grouped based on a variety of factors.
FIELD OF THE INVENTION
This invention provides methods for characterizing compounds within a petroleum fraction, such as saturate compounds.
BACKGROUND OF THE INVENTION
Petroleum samples are complicated hydrocarbon mixtures containing paraffins, cyclic paraffins (naphthenes), multi-ring aromatics, and various heteroatomic hydrocarbons (most commonly O, S, and N). Virgin petroleum crude oils contain molecules of a wide boiling point range from highly volatile C4 hydrocarbons to nonvolatile asphaltenes. Analysis of petroleum composition of various boiling ranges is valuable for improving the operation of many subsequent processes.
According to at least some conventional definitions, a vacuum gas oil (VGO) is a crude oil fraction that boils between about 343° C. (about 650° F.) to 538° C. (about 1000° F.). A vacuum residuum (VR) is a residuum obtained by vacuum distillation of a crude oil and boils above a temperature about 538° C.
U.S. Pat. No. 6,275,775 describes methods for correlating properties determined by conventional methods with measurements made using a chromatography technique. The described methods start by determining properties for a set of sample compounds using a conventional method, such as using an ASTM method for determining cetane. The reference set of compounds are then characterized using chromatography combined with another spectroscopic technique to characterize the compounds relative to boiling point. The two measurements for the reference compounds are then used to build a model. An unknown sample is then measured using the chromatography and spectroscopic technique, and the model is used to determine the correlated property value for the unknown sample in relation to a predicted boiling point profile for the unknown sample.
An article in the Journal of the American Society for Mass Spectrometry by Chen et al (pg 1186-1192, vol. 12, issue 11, November 2001) describes using matrix assisted laser desorption ionization for generation of ions of polyethylene waxes for detection using mass spectrometry. The article describes use of a copper or cobalt matrix with a silver nitrate solution for forming ions of the wax.
SUMMARY OF THE INVENTION
In an embodiment, a method for characterizing a hydrocarbon sample is provided. The method includes obtaining a hydrocarbon sample comprising at least about 90 wt% of saturate compounds; forming saturate-ion adducts by laser desorption ionization in the presence of a soft Lewis acid; detecting the saturate-ion adducts using mass spectrometry with a resolving power of at least about 10,000, the detected saturate-ion adducts comprising a mass spectrum which is a list of accurate masses and intensities of the corresponding masses; selecting the detected saturate-ion adducts based on Kendrick mass defect values so that Kendrick mass defect values of between about 0.150 to about 0.400 are retained; assigning molecular formula to the selected saturate-ion adducts in the mass spectrum; and determining weight percentages for compounds in the petroleum or hydrocarbon sample based on the intensities of the saturate-ion adducts.
In another embodiment, a method for developing a model of composition for a heavy hydrocarbon sample is provided. The method includes separating a heavy hydrocarbon sample having a T5 boiling point of at least about 350° C. to form a plurality of composition groups, including at least one saturates group; measuring a weight percentage for composition groups formed by separation of the heavy hydrocarbon sample; determining elemental formulas and relative amounts for compounds within separated composition groups using mass spectrometry, the ions for the mass spectrometry being formed using a soft ionization method; and calculating a model of composition for the heavy hydrocarbon sample based on the measured weight percentages for the composition groups, the determined elemental formulas for compounds within the separated composition groups, and the determined relative amounts for compounds within the separated composition groups, wherein the ions for the mass spectrometry of the at least one saturates group are formed using laser desorption ionization.
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