Method for reconciling a model of composition (Exxonmobil)

CATEGORY: CRUDE OIL ANALYSIS
PATENT
Method for reconciling a model of composition (Exxonmobil)
Publication number US20130325362 A1
Publication type Application
Application number US 13/832,747
Publication date Dec 5, 2013
Also published as WO2013181349A2
Inventors
Roland B. Saeger, Kaiyuan He
Original Assignee
Exxonmobil Research And Engineering Company
Abstract
Method for determining the composition of a material, including obtaining a reference model of composition (MoC) of the material based on a molecular formula distribution of the material, and reconciling, using at least one computer processor, the reference MoC to match at least one target property of the material, is provided. The reference MoC can be expressed as a combination of molecular lumps with associated reference percent. The reconciliation can be carried out using by constrained optimization of information entropy, and the optimization can be performed on a more coarse-grained basis relative to the reference MoC.
BACKGROUND
1. Field of the Invention
The present application generally relates to methods for obtaining models of composition to compensate limitations of measurement techniques currently available.
2. Description of Related Art
Petroleum streams are complex mixtures of hydrocarbons containing enormous numbers of distinct molecular species. These streams include a variety of hydrocarbon streams from processes directed to the petroleum molecular composition. For example, virgin petroleum crude oils can contain molecules of a wide boiling point range from highly volatile C4 hydrocarbons to nonvolatile asphaltenes. The streams are extremely complex, and have numerous distinct molecular species. As such, any molecular approximation of the composition is essentially a model, that is, a model of composition (MoC). Analysis of petroleum composition of various boiling points is necessary for inputs to many subsequent processes.
Fourier Transform Ion Cyclotron Resonance (FTICR) mass spectrometry, together with a suitable ionization method, can be used can be used in constructing an initial estimate of the composition of a petroleum stream. Ionization methods used in conjunction with FTICR include Atmospheric Pressure Photoionization (APPI) and negative and positive ion electrospray (N-, PESI).
Despite FTICR's ultra-high mass resolution, this technique alone cannot provide sufficient information to construct an accurate model of composition beyond certain thresholds. For example, none of the identified ionization methods can efficiently ionize molecules in complex hydrocarbon mixtures that boil above 1250° F. Thus, known techniques cannot provide sufficient information to construct a Heavy Hydrocarbon Model of Composition (HHMoC) that is consistent with all features of the petroleum stream. HHMoC, as used herein, refers to a model of composition for a vacuum residuum (also known as resid) stream, i.e., petroleum streams that boil above 1000° F. In at least some resid streams, at least 50 weight percent of the molecules are known to boil above 1250° F. Thus, current ultrahigh resolution APPI-FTICR-MS (or N-, PESI-FTICR-MS) data does not lead to accurate estimates of molecular property distributions on the entire resid, or the entire resid fraction. Examples of FTICR-MS data based on the current technique are disclosed in available literature. See, e.g., McKenna, A. M., et al., “Heavy Petroleum Composition. 1. Exhaustive Compositional Analysis of Athabasca Bitumen HVGO Distillates by Fourier Transform Ion Cyclotron Mass Spectrometry: A Definitive Test of the Doduszynski Model,” Energy & Fuels, v. 24, pp. 2429-2938, 2010.
Furthermore, APPI-FTICR-MS has poor ionization efficiency for molecules that boil above 1250° F. Relative to high-temperature Simdis measurements, FTICR severely under-predicts the amount of material boiling above 1250° F. Hence, it is not uncommon for FTICR to be unable to detect approximately 40 weight percent of the highest boiling material of a resid.
Complex hydrocarbon streams (e.g. crude petroleum, refinery intermediate and product streams) that boil below 1000° F. can be reconciled to High Detail Hydrocarbon Analysis (HDHA) or petroleum assays. Before the development of the HHMoC research analytical protocol, ExxonMobil researchers generated models-of-composition of resid streams. See e.g., Van Geem, K. M., et al., “Challenges of Modeling Steam Cracking of Heavy Feedstocks”, Oil & Gas Science and Technology—Rev. IFP, v. 63, pp. 79-94, 2008; Jaffe, S. B., H. Freund, and W. N. Olmstead, “Extension of Structure-Oriented Lumping to Vacuum Residua”, IEC Chem. Res., 44, pp. 9840-9852, 2005. Researchers at Institute Petrole de Francais (IFP, Lyon, France) and at the University of Ghent (Belgium) reconciled models-of-composition to HDHA-like analytical protocols. See Hudebine, D., J. J. Verstraete, “Molecular Reconstruction of LCO Gasoils from Overall Petroleum Analyses”, Chem. Eng. Sci., v59, pp. 4755-4763, 2004. To date, there has not been public disclosure of models of composition reconciled to analytical protocols capable of analyzing petroleum streams with boiling points in the realm of HHMoC research analytical protocol (above 1000° F.).
Therefore, there is a need for a system and method to obtain model of composition that accurately describe the composition of resids at higher boiling points for HHMoC applications.
SUMMARY OF THE INVENTION
The purpose and advantages of the present application will be set forth in and apparent from the description that follows, as well as will be learned by practice of the disclosed subject matter. Additional advantages of the disclosed subject matter will be realized and attained by the method and system particularly pointed out in the written description and claims hereof, as well as from the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the application, as embodied and broadly described, the disclosed subject matter includes a method for determining the composition of a material from a petroleum stream. The method includes obtaining a reference model of composition (MoC) for the material having a boiling point above about 1000° F. at atmospheric pressure, the reference MoC including a combination of molecular lumps having determined reference percent for each of the molecular lumps. The reference MoC is then reconciled using at least one computer processor to match at least one selected target property of the material to obtain a reconciled MoC representative of the composition of the material.
In some embodiments, the reconciled MoC includes updated percent for each of the molecular lumps. In some embodiments, the reconciling is performed under a constraint of the updated percent for each of the molecular lumps satisfying a set of property balance criteria regarding the at least one selected target property. In certain embodiments, each of the determined reference percent in the reference MoC is expressed as a function of the attributes of a Heavy Hydrocarbon Model of Composition (HHMoC) protocol.
In certain embodiments, the reference MoC of the material is based on a molecular formula distribution obtained the following method: obtaining an initial molecular formula distribution within a predetermined threshold for a sample of the material; identifying a correlation between two or more molecular properties of the initial molecular formula distribution; extrapolating, using at least one processor, the initial molecular formula distribution beyond the predetermined threshold along the correlation to construct an extrapolated molecular distribution; and renormalizing the extrapolated molecular formula distribution based on renormalization data obtained from the sample to generate a renormalized molecular formula distribution. The initial molecular formula distribution can include a fraction molecular formula distribution for each of a plurality of fractions, each of which can be a liquid chromatographic fraction selected from one of DAO saturates, DAO ARC1, DAO ARC2, DAO ARC3, DAO ARC4, DAO sulfides, DAO polars, asphaltenes, DAO aromatics, and DAO. The predetermined threshold is boiling point temperature of 1250° F. the renormalized molecular formula distribution include the determined reference percent of the molecular lumps in the reference MoC as defined by a HHMoC protocol. The method can further include blending the renormalized molecular formula distribution with the initial molecular formula distribution.
In some embodiments, reconciling the reference MoC is carried out by constrained optimization which comprises adjusting the reference percent of each of the molecular lumps to the updated percent. The at least one selected target property includes total weight of resid in the material, weight percentage of a fraction on total resid basis, or weight percentage of an element, such as hydrogen, sulfur, nitrogen, nickel, vanadium, of a fraction on total resid basis, the fraction being one of the fractions defined by a HHMoC protocol.
In exemplary embodiments, reconciling the reference MoC comprises adjusting the reference percent on a coarse-grained basis relative to the reference MoC. In particular embodiments, adjusting the reference percent comprises using a coarse-grained index related to a unique combination of attributes of fraction, hydrogen deficiency class, and molecular type as defined by a HHMoC protocol.
The at least one selected target property can be measurable by an analytic technique. For example, the analytic technique can be selected from one of super critical fluid chromatography, sulfur simulated distillation, simulated distillation, N and S elemental analysis, H-NMR and GC-Flame Ionization Detection.
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