Structural Characterization of Different Asphaltenes of Kuwaiti Origin

Abstract

Asphaltenes obtained by precipitation from crude Kuwaiti oils have been analyzed by proton magnetic resonance (¹H-NMR), carbon-13 nuclear magnetic resonance (¹³C-NMR) and Infrared (IR) spectral techniques. The molecular weight and elemental analysis were also determined. These combined analytical data were used for the characterization of these Kuwaiti oils. The asphaltenes molecular weights range from approximately 4200–6500 with an H/C ratio of 0.91–1.1 with an average 45–71% aromatic carbons. The average side chain length was of 4–6 carbons. It can also be concluded that the asphaltenes under investigation contain 5–9 sets of condensed aromatic rings joined together by bridges of alkyl chains or other hetero atoms and the average number of each of these sets of condensed aromatic rings is nearly 7. There are a number of alicyclic rings and condensed alicyclic rings in asphaltene. The IR spectra showed main molecular groups including OH, NH, SH, C=O and aliphatic and aromatic C-H′s.     

Structural Characterization of Asphaltenes and Ethyl Acetate Insoluble Fractions of Petroleum Vacuum Residues

Asphaltenes and insoluble fractions of vacuum residues (VRs) of two Indian crude oils (viz. Heera and Jodhpur) of different specific gravity were obtained by precipitation of VRs in n-hexane, n-heptane, and ethyl acetate, and also by subsequent reprecipitation of n-heptane and ethyl acetate soluble fractions by n-pentane. The effect of various solvents on average molecular structure of asphaltenes and insolubles was studied using nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared spectroscopy (FTIR), and size exclusion chromatography (SEC). The asphaltenes and insolubles of Jodhpur VR have higher amounts of high molecular weight species with a high concentration of condensed and substituted aromatic rings, branched and/or short alkyl side chains, oxygen and nitrogen functionalities, compared to that of Heera VR. Ethyl acetate insolubles comprise a higher number of substituted aromatic structures, branched aliphatic structures, complex average unit structures, nitrogen and oxygen functionalities, and high molecular weight (MW) species as compared to hexane and heptane asphaltenes. Heptane insolubles consist of more naphthenic rings condensed with aromatic rings than C6A and EAI.     

Structural Aspects of Crude Oil Derived Asphaltenes by NMR and XRD and Spectroscopic Techniques

Asphaltene samples obtained from crude processed at two Indian refineries were characterized for chemical composition and structure by nuclear magnetic resonance (NMR), X-ray diffractometry (XRD), fluorescence spectroscopic techniques, and chromatographic (column and GPC) techniques. Estimation of NMR average structural parameters were obtained by combined ¹H, NMR ¹³C, NMR DEPT-45, and QUAT pulse sequence spectral editing techniques. The macrostructure and crystalline parameters of these samples were obtained by XRD. The nature of the functional groups have been obtained by IR technique. A combined NMR and XRD parameters were used to estimate the size of average aromatic structural units. Asphaltenes from one of the crudes (ASP-A) was found to be highly pericondensed, highly substituted, and higher molecular size compared to ASP-B asphaltene molecules. The number of aromatic sheets per unit sheets are 3.7 and 2.5 in the sample ASP-A and ASP-B, respectively. Both the asphaltene molecules in the samples have periodically and systematic arrangement of aromatic sheets in the unit sheet. The number of aromatic rings per unit sheet in ASP-A and ASP-B are 6.0 and 5.0, respectively. The fluorescence spectral studies has also exhibited λ_max (the wavelength of maximum intensity) at 505 and 509 nm confirming to pericondensed higher polycondensed aromatic ring system in both the samples. The analysis of liquid chromatographic fractions of these samples show that each sample is composed of several polycondensed aromatic systems where unit sheet of ring sizes vary from 1.8 to 6.3 with varying molecular sizes. These structural parameters allowed a model structure of the asphaltenes to be constructed.     

Structural Studies on Residual Fuel Oil Asphaltenes by RICO Method

Structural characterization of asphaltenes isolated from Saudi Arabian heavy and medium crude oils was undertaken by using ruthenium ion catalyzed oxidation (RICO) method. The RICO method was capable to convert aromatic carbons selectively into carbon dioxide and carboxylic acids and esters group while leaving aliphatic and naphthenic structures of asphaltenes essentially unaffected. Detailed analyses of RICO products of both Arab heavy and Arab medium asphaltenes were conducted using FT-IR, ¹³C-NMR, IC, GPC, and GC-MS techniques. These analyses indicate that the aqueous phase fraction (water-soluble products) obtained from RICO reaction of asphaltenes consists of aliphatic dicarboxylic acids and aromatic poly carboxylic acids with longer alkyl chains. The ¹³C-NMR and GC-MS analyses of organic phase products of asphaltenes indicate that this fraction contains large amount of aliphatic carboxylic acids with longer alkyl groups. The oxidation products of both Arab heavy and Arab medium asphaltenes were found to be dominated by a homologous series of straight chain monocarboxylic acids suggesting that the normal alkyl chains are major and important constituents of the chemical structure of both asphaltenes.     

Behavior and Role of Asphaltenes in a Two-stage Fixed Bed Hydrotreating Process

Residue upgrading processes are very important for the production of distillates and low sulfur fuel oils. Among those, fixed bed technologies are very efficient for deep desulfurization of petroleum residue heavy oils, even for highly asphaltenic feeds. This work analyzes the effects of the operating conditions on the evolution of asphaltenes and on their inhibition effect during the hydrodesulfurization reactions. Residue hydrotreating experiments were performed on a pilot plant and asphaltene fractions were investigated using size exclusion chromatography (SEC), ¹³C nuclear magnetic resonance (NMR), liquid chromatography, and elemental analyses. Besides the overall decrease in asphaltenes yield, significant changes in the average structure of the asphaltenes were also observed.     

Characterization of Asphalt Fractions by NMR Spectroscopy

Abstract

Petroleum asphalt was separated into saturates, naphthalene aromatics, polar aromatics, and asphaltenes using the Corbett method. These asphalt fractions were characterized by H-1 and C-13 nuclear magnetic resonance spectroscopy (NMR). The spectra of saturates illustrate only traceable quantities of aromatic hydrogen and aromatic carbon. Naphthalene aromatics, polar aromatics, and asphaltenes all have broad bands in the aromatic regions of both H-1 and C-13 NMR spectra. These broad bands demonstrate the presence of polycondensed aromatic rings present in the structure of naphthalene aromatics, polar aromatics, and asphaltenes. Based on available literature, numerous NMR resonance bands are identified. The quantitative estimations for various kinds of protons and carbons in the asphalt fractions are compared.     

CHANGES IN THE COMPOSITION AND PROPERTIES OF THE VACUUM RESIDUES AS A RESULT OF VISBREAKING

Two vacuum residues of heavy petroleum blends and residues of the products of their visbreaking, on a commercial unit, were investigated by means of column chromatography, cryoscopic analysis, elemental analysis, NMR spectroscopy, etc. An increase in the contents of asphaltenes and saturated, increase in asphaltenes/polar components ratio, and decrease in the aromatics contents during visbreaking were observed for both kinds of feed. The N/C ratio increased, the S/C ratio did not change significantly. Most of the nickel and vanadium were concentrated in the asphaltenes and aromatics. The length of the paraffinic chains of the saturated decreases during visbreaking from about 50 to 30 carbon atoms. The number of carbon atoms per alkyl chain and the number of naphthenic rings in the average molecule of the aromatics decreased, whereas the number of aromatic rings increased. About 2/3 of the total aromatic carbon in the aromatics are non-bridged. The average asphaltenes molecule contains about 36-38 aromatic rings (mostly condensed), 5-7 naphthenic rings and 12-16 alkyl substituents having relatively short (n = 5-6) chains. Two contrary processes, relating asphaltenes, take place during visbreaking: 1) cracking of asphaltenes, which results in a decrease in their content and molecular weight, decrease in the number of the side chains and their length, and increase in asphaltenes aromaticity; 2) asphaltenes formation from the polar components of the feed. The resulting process may be expressed both in a decrease and in an increase in the asphaltenes content. Reactions of condensation of the asphaltenes precursors (resins, etc.) prevail for the light stocks. For heavier stocks, cracking of the asphaltenes plays a more significant role, and the increase in asphaltenes content takes place mainly due to concentrating them in the visbreaking residue as a result of the distillation of the visbroken product.     

固态13C-NMR法表征渣油沥青质的结构组成

以长庆常压渣油、胜利减压渣油和加拿大减压渣油为原料,研究了正庚烷沥青质的结构及组成,根据固态13C NMR分析结果,计算了沥青质分子的平均结构单元参数,并模拟出了沥青质的结构单元模型。结果表明,沥青质分子由4个左右的结构单元组成,每个结构单元包括5～7个缩合芳香环。沥青质中的饱和碳以环烷碳为主,并包含少量的短烷基侧链,沥青质的n(HS)/n(CS)在16左右。对于平均相对分子质量较大、具有较短烷基侧链和较少取代基的沥青质分子,由核磁共振氢谱计算其结构参数时,采用重油计算过程的假设--芳香环烷基侧链上α位及β位和β位以远的氢/碳比为2(x=y=2)是不合理的,可能会导致计算结果与沥青质的真实结构存在较大的误差。     

CHANGES IN THE COMPOSITION AND PROPERTIES OF THE VACUUM RESIDUES AS A RESULT OF VISBREAKING

ABSTRACT

Two vacuum residues of heavy petroleum blends and residues of the products of their visbreaking, on a commercial unit, were investigated by means of column chromatography, cryoscopic analysis, elemental analysis, NMR spectroscopy, etc. An increase in the contents of asphaltenes and saturated, increase in asphaltenes/polar components ratio, and decrease in the aromatics contents during visbreaking were observed for both kinds of feed. The N/C ratio increased, the S/C ratio did not change significantly. Most of the nickel and vanadium were concentrated in the asphaltenes and aromatics. The length of the paraffinic chains of the saturated decreases during visbreaking from about 50 to 30 carbon atoms. The number of carbon atoms per alkyl chain and the number of naphthenic rings in the average molecule of the aromatics decreased, whereas the number of aromatic rings increased. About 2/3 of the total aromatic carbon in the aromatics are non-bridged. The average asphaltenes molecule contains about 36-38 aromatic rings (mostly condensed), 5-7 naphthenic rings and 12-16 alkyl substituents having relatively short (n = 5-6) chains. Two contrary processes, relating asphaltenes, take place during visbreaking: 1) cracking of asphaltenes, which results in a decrease in their content and molecular weight, decrease in the number of the side chains and their length, and increase in asphaltenes aromaticity; 2) asphaltenes formation from the polar components of the feed. The resulting process may be expressed both in a decrease and in an increase in the asphaltenes content. Reactions of condensation of the asphaltenes precursors (resins, etc.) prevail for the light stocks. For heavier stocks, cracking of the asphaltenes plays a more significant role, and the increase in asphaltenes content takes place mainly due to concentrating them in the visbreaking residue as a result of the distillation of the visbroken product.     

CHARACTERIZATION OF VARIOUS BITUMEN SAMPLES FROM TAR SANDS

We have investigated twenty three bitumen samples obtained using different separation methods such as: ultracentrifugation, Dean-Stark extraction, solvent extraction employing vigorous agitation, hot water separation and the Solvent Extraction Spherical Agglomeration technique. These samples were extracted from oil sand feedstocks of different grades, Suncor sludge pond tailings and mineral agglomerates obtained from the Solvent Extraction Spherical Agglomeration process. All of the bitumen samples were examined on a comparative basis using various analytical techniques. These included: fractionation into asphaltenes and maltenes; elemental analyses; molecular weight determination using vapour pressure osmometry and gel permeation chromatography, infrared, proton and 13C nuclear magnetic resonance spectroscopy. Proton and ¹³C n.m.r. spectroscopic data were used to determine the distribution of various types of hydrogens and carbons in the samples. These data were also used to derive various molecular parameters in order to investigate average molecular structures of different bitumen samples and some of their asphaltene fractions.     

VARIATION IN THE CHEMICAL NATURE OF ASPHALTENES WITH THE PROCESS, THE COAL AND THE REACTION CONDITIONS

Average structure data for twelve asphaltenes are reported, based on ¹³C- and H- n.m.r. spectroscopy combined with elemental, molecular weight and functional group analyses. The asphaltenes were from supercritical gas extraction, flash pyrolysis and hydrogenation of a brown and a bituminous coal. The effect of the reaction temperature and, for hydrogenation, the catalyst and solvent on the nature of the asphaltene produced was studied. The asphaltene obtained from supercritical gas extraction of the brown coal at 350°C was the least aromatic (f_a = 0.44) with the highest H/C atomic ratio (1.16) and probably consists mainly of single ring aromatlcs with about half of the aromatic sites substituted. A significant proportion of the carbon in this asphaltene is in long alkyl chains and the hydroxyl content is high. Whereas, the asphaltenes produced by hydrogenatlon of the bituminous coal at 450°C were far more aromatic with more highly condensed but less substituted aromatic ring systems and few, if any, long alkyl chains, together with a lower hydroxyl content. The asphaltenes obtained from the brown coal are less aromatic with less condensed aromatic ring systems but a higher degree of aromatic substitution than those produced from the bituminous coal under the same conditions. The asphaltenes formed at 450°C had lower H/C atomic ratios, molecular weights and degree of aromatic substitution, but higher aromaticities Ohan those produced at 35O°C or 400°C under like processing conditions. The asphaltene produced in the presence of both stannous chloride catalyst and tetralin was less aromatic than when either of these species was absent.     

Preparative Subfractionation of Petroleum Resins and Asphaltenes. II. Characterization of Size Exclusion Chromatography Isolated Fractions

In the first study of this series, resins and asphaltenes from stable and unstable crude oils have been separated by size exclusion chromatography in three molecular mass ranges (MM: high, medium, and low). In the present study, the isolated fractions were further characterized in order to correlate several of their structural properties with crude oil tendency to solid deposition. Elemental analysis (C, H, S, N), infrared spectrophotometry (IR), and proton nuclear magnetic resonance (¹H NMR) were the characterization techniques performed in order to meet the objective. Hydrogen deficiency and aromaticity appear to be the main parameters governing the intrinsic stability for the studied samples. Oxygen compounds were observed to be more abundant within fractions isolated from unstable oils, particularly in resins and in the low MM range fractions both from resins and asphaltenes. However, causes for the presence of these oxygenates remain open to further study. Experimental evidence gathered during this work suggest the possibility of small compounds acting like natural dispersants of the larger components present in complex mixtures like asphaltenes.     

Thermodynamic Properties of Asphaltenes Through Computer Assisted Structure Elucidation and Atomistic Simulations. 1. Bulk Arabian Light Asphaltenes

This article describes a new method for estimating the thermodynamic properties of asphaltenes. To illustrate this methodology, we used a computer assisted structure elucidation software (SIGNATURE) to generate an ensemble of 10 isomers for Arabian Light (AL) asphaltenes compatible with (i) analytical data from elemental analysis, FT-IR spectroscopy, 1-D ¹H/¹³C solution NMR and vapor pressure osmometry and (ii) literature data on the molecular composition of asphaltenes. The 10 model isomers were packed into a 3-D periodic cell to form the condensed phase model for the fraction of bulk AL asphaltenes with a number average molar mass (M_n) approximately equal to 1280 Dalton. This cell was subsequently used in molecular dynamics (MD) simulations to estimate the molar volume, density, enthalpy, specific heat at constant pressure, solubility parameter, and isothermal compressibility of the AL asphaltene fraction. The results of the MD simulations compare favorably with the available experimental data.     

Structural Description of Polyaromatic Nucleus in Residue

The proton nuclear magnetic resonance spectroscopy （1H-NMR）, the synchronous fluorescence spectrometry （SFS） and the ruthenium ions catalyzed oxidation （RICO） method were used to determine the chemical structure of polyaromatic nucleus in Oman residue fractions. The results of 1H-NMR analyses showed that the average numbers of aromatic rings in the aromatics, resins and asphaltenes units were 3.2, 5.6 and 8.2, respectively. SFS was used to investigate the distribution of aromatic rings in residue fractions, the main distribution range of aromatic rings in aromatics, resins and asphaltenes were 3 4 rings, 3--5 rings and more than 5 rings, respectively. The aromatic network in residue fractions was oxidized to produce numerous carboxylic acids. The types and content of benzenepolycarboxylic acids, such as phthalic acid, benzenetricarboxylic acids, benzenetetracarboxylic acids, benzenepentacarboxylic acid and benzenehexacarboxylic acid disclosed the condensed types of aromatic nuclei in the core. The biphenyl fraction （BIPH）, the cata-condensed fraction （CATA）, the peri-condensed fraction （PERI） and the condensed index （BCI） were calculated based on the benzenepolycarboxylic acids formed. The results implied that there was less biphenyl type structures in all residue fractions. The aromatics fraction was almost composed of the cata-condensed type system, and the asphaltenes fraction was wholly composed of the peri-condensed type system, while in the resins fraction co-existed the two types, herein the peri-con- densed type was predominant over the cata-condensed type. Based on the analytical results obtained in the study, the components --aromatics, resins and asphaltenes -- were given the likely structural models.     

Investigation of the Molecular Structure of Turkish Asphaltenes

Abstract

Molecular structure of asphaltenes prepared from four Turkish crude oils with different origin were characterized by elemental analysis, proton nuclear magnetic resonance (¹H NMR), gel permeation chromatography (GPC) by X-ray diffraction (XRD) and by Fourier transform infrared spectroscopy (FTIR). The X-ray diffraction method was used to investigate the crystallite and aromaticity parameters of the asphaltenes. Average distance between the aromatic sheets, average distance between the aliphatic chains, average diameter of the cluster, and average number of aromatic sheets per stack parameters were calculated for the asphaltenes. The combined NMR, FTIR, molecular weight, elemental content, and XRD results have been used to calculate hypothetical structure of the Turkish asphaltenes.     

煤液化油模型分子结构的研究

对神华煤在连续液化装置的加氢液化油(试样1#)和实验室获得的液化油(试样2#)进行了模型分子结构的研究。通过元素分析、平均相对分子质量的测定、核磁共振谱图和傅里叶变换红外光谱的分析,得到了两种液化油的平均分子结构式和相关的结构参数,并利用这些参数推测了模型分子的结构。实验结果表明,试样1#和试样2#的平均相对分子质量分别为228,299;平均分子式分别为C17H23N0.1S0.006O0.02和C23H21N0.02S0.002O0.1;试样1#的模型分子结构以含一个芳香环的部分氢化芳烃为主体;试样2#主要以含3~4个芳香环的缩合芳烃为结构单元;两种试样芳香环上均存在取代基,但取代基的碳数不一样,且存在少量氮和氧形成杂环。     

Investigation of Asphaltene Precipitation Process for Kuwaiti Reservoir

Abstract

As part of an Enhanced Oil Recovery (EOR) research program, Asphalting precipitation processes were investigated for a Kuwaiti dead oil sample using different hydrocarbons and carbon dioxide as precipitants at the ambient and high pressure of 3000 psig conditions. The hydrocarbons used as precipitants were ethane (C2), propane (C3), butane (C4), normal pentane (n-C5), normal hexane (n-C6), and normal heptane (n-C7). The equipment used for this investigation was a mercury-free, variable volume, fully visual JEFRI-DBR PVT system with laser light scattering. The minimum critical value of precipitants concentration for the oil sample has been identified at the ambient and high-pressure conditions for each precipitant. Our investigation has revealed that for this oil sample the most powerful asphaltene precipitant were CO₂ followed by C2, C3, C4, n-C5, n-C6, and n-C7. Moreover, the effect of pressure and temperature on the asphaltene precipitation has been investigated experimentally for CO₂, n-C5, n-C6, and n-C7. The precipitation and redissolution of asphaltene upon the addition and removal of CO₂ and light alkanes (C2–C4), at 3000 psig and ambient temperatures, have shown evidence of reversibility of asphaltene precipitation. A comprehensive fluid characterization analysis for the oil sample has been performed including, physical properties of crude oil, compositional, molecular weight (Mw), and SARA analyses. Advanced analytical techniques such as 1H and 13C NMR and IR spectrometers have been utilized to investigate the molecular structure of the asphaltene for this sample. It was concluded that the asphaltene molecules for this oil contain 120 total aromatic carbons with 42 aromatic rings, 114 naphthenic rings, and 5–7 sets of condensed aromatic rings.     

Structural Aspects of Crude Oil Derived Asphaltenes by NMR and XRD and Spectroscopic Techniques

Abstract

Asphaltene samples obtained from crude processed at two Indian refineries were characterized for chemical composition and structure by nuclear magnetic resonance (NMR), X-ray diffractometry (XRD), fluorescence spectroscopic techniques, and chromatographic (column and GPC) techniques. Estimation of NMR average structural parameters were obtained by combined ¹H, NMR ¹³C, NMR DEPT-45, and QUAT pulse sequence spectral editing techniques. The macrostructure and crystalline parameters of these samples were obtained by XRD. The nature of the functional groups have been obtained by IR technique. A combined NMR and XRD parameters were used to estimate the size of average aromatic structural units. Asphaltenes from one of the crudes (ASP-A) was found to be highly pericondensed, highly substituted, and higher molecular size compared to ASP-B asphaltene molecules. The number of aromatic sheets per unit sheets are 3.7 and 2.5 in the sample ASP-A and ASP-B, respectively. Both the asphaltene molecules in the samples have periodically and systematic arrangement of aromatic sheets in the unit sheet. The number of aromatic rings per unit sheet in ASP-A and ASP-B are 6.0 and 5.0, respectively. The fluorescence spectral studies has also exhibited λ _max (the wavelength of maximum intensity) at 505 and 509 nm confirming to pericondensed higher polycondensed aromatic ring system in both the samples. The analysis of liquid chromatographic fractions of these samples show that each sample is composed of several polycondensed aromatic systems where unit sheet of ring sizes vary from 1.8 to 6.3 with varying molecular sizes. These structural parameters allowed a model structure of the asphaltenes to be constructed.     

不同重油的正戊烷及正庚烷沥青质性质对比

以中东减压渣油（MEVR）、加拿大油砂沥青（VTB）、辽河稠油减压渣油（LHVR）、委内瑞拉常压渣油及减压渣油（VAR、VVR）等5种重油为原料，利用溶剂沉淀法制备正戊烷及正庚烷沥青质，采用元素组成、GPC、1H-NMR、13C-NMR、XRD、SEM等分析方法和手段进行沥青质性质评价以考察其差异性。结果表明，五种重油的C5沥青质、C7沥青质在含量、分子结构、平均结构单元数目、分子大小、微观结构形态等方面差异明显。沥青质芳碳率在0.47~0.54之间，VTB、LHVR沥青质中参与有序堆积结构的芳香碳较少，而MEVR，VAR，VVR沥青质中该部分芳香碳则相对较多。     

Structural Characterization of Asphaltenes from Raw and Desulfurized Vacuum Residue and Correlation Between Asphaltene Content and the Tendency of Sediment Formation in H-oil Heavy Products

Asphaltenes obtained from raw vacuum residue from Russian (Ural) petroleum have been characterized by means of elemental analysis and ¹H proton nuclear magnetic resonance (NMR) and compared with asphaltenes separated from the residue desulfurized in the H-oil process. The latter have much lower molecular weight and more aromatic character. In high-temperature conditions of fractionation of the whole H-oil product and in the presence of catalyst dust carried away from reactors, asphaltenes tend to condense, dehydrogenate, and separate from the desulfurized oil as a coke-like sediment. Some correlations have been found between the asphaltene contents of raw and desulfurized residue and the tendency of sediment formation in desulfurized residual oil that causes serious operating problems in H-oil units.