Structural Studies on Residual Fuel Oil Asphaltenes by RICO Method

Abstract

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.     

钌离子催化氧化法研究沥青质经加氢处理后的变化

 利用钌离子催化氧化方法研究了渣油中沥青质的化学结构，定量测定了与沥青质芳香核相连的烷基侧链和烷基桥链的分布，推断了沥青质中芳香环系的缩合形式，讨论了沥青质组分在加氢处理过程中的结构变化规律。结果表明，渣油组分中都存在C1～C27的烷基侧链，并且主要是正构烷基侧链，也存在与两个芳香核相连接的C2～C16烷基桥链，它们的浓度随链长增加而下降。沥青质的氧化产物中检测出从邻苯二甲酸到苯六甲酸的一系列苯多甲酸。沥青质芳香核结构中存在着渺位缩合、迫位缩合和联苯结构，其中联苯结构较少。沥青质可以看作纯粹的迫位缩合。随着加氢处理深度的增加，沥青质组分的化学结构发生变化，芳香结构较大的芳香核在沥青质中富集，使得沥青质组分中的芳香结构逐渐增多，芳香核缩合程度逐渐增加。     

Structural Changes of Sub-fractions in Residue Hydrotreating Products by Ruthenium Catalyzed Oxidation

Abstract

Structure of aromatics, resins, and asphaltenes in petroleum residue was undertaken by using ruthenium ion catalyzed oxidation. The distribution of alkyl side chains and bridges connected to aromatic rings was quantified, and the condensed type of aromatic rings was deduced. The structural changes of fractions in residue during hydrotreating were discussed. The results showed that fractions have abundant alkyl side chains (C₁–C₂₇), mainly n-alkyl side chains, attached to aromatic carbons, and polymethylene bridges connected to at least two aromatic ring systems are also present. The molar concentrations of these alkyl groups are declined as the increase of chain length. Cata-condensed, peri-condensed, and biphenyl-type aromatic unit structures coexist in fractions, while the proportion of biphenyl type structure is relatively small. The aromatic structure of aromatics is mostly cata-condensed, while for resins the proportion of cata-condensed and peri-condensed type aromatic structures is comparable, and structure of asphaltene is mostly peri-condensed. The chemical structure of fractions in residue changed due to the increase of hydrotreating degree. The enrichment of large aromatic units made asphaltene have more aromatic structures and higher condensed degree.     

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.     

东营凹陷草桥油田生物降解原油沥青质钌离子催化氧化研究——生标分布及地质意义

运用钌离子催化氧化技术(RICO)研究了渤海湾盆地东营凹陷草桥油田生物降解原油沥青质.原油沥青质RICO产物主要包括一元酸、二元酸、三环萜烷酸、藿烷酸、伽马蜡烷酸、孕甾烷酸、甾烷酸等,键合在沥青质芳核结构中的生物标志物以特定碳位与沥青质结合.草桥生物降解原油沥青质RICO产物中具有较高的伽马蜡烷酸/C₃₀藿烷酸比值,具有完整的4-甲基、4,4-二甲基甾烷酸系列,表明原油为沙四段、沙三段的混源油;生标酸异构化参数低表明原油成熟度不高.沥青质钌离子催化氧化技术对于强烈生物降解原油的油-油对比、油-源对比提供了一种新的途径.      

塔里木盆地原油沥青质钌离子催化氧化及油源

运用钌离子催化氧化(RICO)技术研究了塔里木盆地轮南、塔河、哈得逊地区及TD2井原油沥青质。其RICO产物包括一元酸、二元酸、支链酸、三环萜烷酸、藿烷酸、甾烷酸和4-甲基甾烷酸。键合在沥青质中的烷基侧链和生物标志物不易遭受生物降解作用,特别是甾烷与饱和烃中分布相似。沥青质的RICO研究结果表明,中、上奥陶统烃源岩为轮南、塔河、哈得逊原油的主力烃源岩。沥青质RICO技术为严重生物降解原油的油源对比提供了一种新的途径。图5表3参12     

大港减压渣油超临界萃取残渣极性组分的化学结构特征

 将大港减压渣油超临界萃取（SFEF）的残渣利用中性Al2O3色谱柱进行四组分（SARA）分离，得到饱和分、芳香分、胶质和沥青质。然后对其中的芳香分、胶质和沥青质3个极性组分进行钌离子催化氧化反应（RICO）选择性降解，生成的混合物分离处理后，非挥发性羧酸用CH2N2-乙醚溶液酯化，挥发性羧酸用苯甲酰甲基溴酯化。采用GC-MS、GC、FT-IR等手段对这些酯化产物进行定性和定量分析，检测到各组分的降解产物含有一系列的一元正构脂肪酸、α,ω-二元正构脂肪酸和多种芳羧酸，以此可了解各组分的结构特征。结果表明，3个组分的RICO产物中，芳环上的正构烷基侧链含量和连接两个不同芳碳的聚亚甲基桥含量均随着碳链增长都呈递减趋势。沥青质组分的芳核中迫位缩合结构比芳香分要多，而芳香分中的联苯和渺位缩合结构比沥青质中的比例要大，胶质中各种结构的分布介于两者之间。     

STRUCTURAL FEATURES OF ATHABASCA BITUMEN RELATED TO UPGRADING PERFORMANCE

ABSTRACT

Using a combination of instrumental and chemical methods many new classes of compounds appearing as homologous series have been detected in Athabasca oil sand bitumen and in the chemical and thermal degradative products of asphaltene and the heavy ends of maltene. In general, the volatile portion of the maltene is rich in cyclic terpenoid structures and devoid in aliphatic compounds or normal alkane-derived cyclic molecules while the asphaltene fraction and heavy ends of maltene are abundant in normal alkyl-substituted aromatics, thianes, thiolanes, thiophenes, benzo- and dibenzothiophenes

Ru(VM)-catalyzed oxidation permitted the quantitative estimation of the n-alkyl groups attached to aromatic carbons and of n-alkyl bridges between two aromatic units and their concentration distribution according to chain length. It also showed the presence of a large naphthenic core containing cyclic sulfides, which, during oxidation, were converted to their sulfones.     

Mass Spectrometry of Metalloporphyrins in Egyptian Oil Shales from Red Sea Area

Abstract

Metalloporphyrins, extracted from asphaltene and maltene fractions of some Egyptian oil shales (Abu-Shegeili, El-Beida, El-Nakheil, and Abu-Tundub in the Red Sea area) by means of adsorption column chromatography and TLC, were subjected to mass spectrometry in order to elucidate the structure of different types of VO, Ni, or Fe porphyrins. Metalloporphyrins were not detected in maltene or asphaltene fractions of Abu-Shegeili oil shale. The mass spectra appeared as a truncated series of mass numbers, which is characteristic of geo-porphyrins in sediments or oil shales. The data indicated that the five types of porphyrins (Etio, DPEP, BEtio, BDPEP, and THBD) with carbon numbers ranging from C₂₀ to C₅₀ were present in considerable detection levels. Based on mass spectrometric data, the major components of metalloporphyrins (VO, Ni, or Fe) were identified and their chemical structures were suggested. The occurrence and distribution of VO, Ni, and Fe porphyrins were interpreted from a geochemical point of view, particularly maturation levels and oil-gas potentials of kerogens.     

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

ABSTRACT

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.     

PARTICLE SIZE,SOLVENT, OXYGEN,TEMPERATURE AND PRESSURE EFFECTS ON THE CONTENTS OF INSOLUBLE FRACTIONS FROM SOLID VACUUM RESIDUA

ABSTRACT

n-Heptane insoluble contents were determined for an extraheavy-oil vacuum residue, one petroleum and one coal pitch as a function of particle size. This variable was found to affect the yields of insoluble material, aspect which was also observed during extractions carried out with aromatic and halogenated solvents. The precision of results was observed to be independent on the operators. A study was carried out to determine the effect of sample drying time on fraction yields. It was found that maltene fractions were strongly dependent on this variable, whereas asphaltene fractions were totally independent

Predissolution in aromatic solvents proved worthless from the repeatability point of view. However, predissolution of the oil residue in CH₂Cl₂ followed by filtration and asphaltene precipitation with simultaneous solvent removal, was deemed to be a suitable technique to remove mineral matter and isolate asphaltenes in a single step

Sample oxidation during asphaltene precipitation and isolation was detected by gravimetric and spectroscopic techniques. This fact is very important since common precipitation techniques do not address this issue

Preliminary accelerated extraction experiments carried out with pitch samples at high temperature and pressure, revealed that this approach can be a very interesting research tool to investigate solubility properties.     

Changes in Sub-fractions Properties during Hydrotreating of Residue

Abstract

One atmosphere residue was hydrotreated (HDT) in a pilot plant at constant conditions. The properties of the HDT products from a series of reactors and their sub-fractions were characterized by H/C, sulfur, nitrogen, carbon residue, nickel, vanadium, and VPO apparent molecular weight. The removal levels of sulfur, nitrogen, carbon residue, nickel, and vanadium were 84.9 m%, 51.4 m%, 62.8 m%, 84.8 m%, and 94.0 m%, respectively. The removal increment of contaminants in reactors was very different during HDT. The ranking of sulfur and nitrogen contents in sub-fractions was asphaltene > resin > aromatic > > saturate; however, the distribution of sulfur in sub-fractions was aromatic > resin > > asphaltene > saturate, while that of nitrogen was resin > > aromatic > asphaltene. Average carbon residue was removed in reactors. Nickel and vanadium were removed mainly in hydrodemetalization reactors.     

POLAROGRAPHIC CHARACTERIZATION OF AROMATIC STRUCTURES IN COAL LIQUID PRODUCTS

ABSTRACT

Reducible aromatic species in coal liquid products from five major processes (Synthoil, FMC COED, HRI H-Coal, PAMCO SRC, and Catalytic Inc. SRC) together with solvent elution chromatography fractions of a selected asphaltene has been evaluated. The half-wave potentials measurments are found to be consistant with other methods. The total polarographic reduction of measurement per average molecule for Synthoil solvent fractions, as measured by diffusion constant (i_d /C), increases in the following manner: gas oil → resin → asphaltene → carbene → carboid. The same trend was observed when color indices (I) and refractive indices (n ₂₅) were individually studied.     

Thermal Degradation of Asphaltene and Infrared Characterization of Its Degraded Fractions

Abstract

Petroleum asphaltene and its thermally degraded fractions are characterized using thermal analysis and infrared spectrometry, respectively. Thermal analysis of asphaltene has demonstrated that heating rate is important in studying thermal degradation of asphaltene. Asphaltene goes through three stages of mass reduction under thermogravimetric analysis from 25 to 1,000°C at a heating rate of 1°C/min and below. The products from thermal degradation of asphaltene at three different temperature intervals are collected. The collected fractions are characterized using a Fourier transform infrared spectrometer. The fraction collected between 220 and 350°C demonstrates similar infrared spectrum to that of asphaltene, however, with less aromatic properties. The fraction collected between 350 and 450°C resembles the undegraded asphaltene most based on the infrared spectra obtained. The fraction collected between 450 and 650°C demonstrates a spectrum that is totally different from those of the undegraded asphaltene and the other two fractions. In addition, a high degree of oxidation is observed on all of the three degraded fractions of asphaltene.     

The Prediction of Asphaltene Precipitation from Crude-Oils

Abstract

Asphaltene precipitation is undesirable deposition that causes difficult problems in oil production and transportation. A molecular thermodynamic model is proposed for predicting the asphaltene precipitation under live oil conditions and at a wide range of pressures and different solvent ratios. In this model, it is assumed that the precipitation phenomenon is a reversible process, and an equation of state is employed for phase behavior prediction. The vapor and liquid equilibrium calculations are performed separately and sequentially. The characterization of unknown-heavy fraction of petroleum (C₇₊) is obtained by the generalized molar mass distribution model, in which C₇₊ is represented by four pseudocomponents. The two heaviest pseudocomponents of C₇₊ are identified as asphaltenic components, are also considered as precipitating components. The model is verified by its ability to prediction of asphaltene precipitation in different thermodynamic conditions. It has been shown that the calculated results are in good agreement with the experimental data.     

Docking of An Asphaltene Molecular Model on A Fe2O3 Surface,An Ab Initio Simulated Annealing

Abstract

The docking of an asphaltene molecular model over the (1000) hematite surface is analyzed through the use of ab initio molecular dynamics simulation techniques where the Density Functional Theory (DFT) forces were obtained using the Harris functional approach. The (1000) hematite surface is modeled by a supercell slab lattice of 225 atoms with a  =  b lengths of 25.17 Å; on the c -direction an empty gap space and Fe-O-Fe-Fe-O atomic sequence was built. This structure was thermally stabilized at 400K. The asphaltene-hematite surface interaction was simulated with an annealing process at 400K during 555 fs, and then a geometry optimization process was carried out on the final annealed configuration in order to stabilize the asphaltene-surface system. We find an attractive interaction between the asphaltene and the Fe₂O₃ which is located mainly at the asphaltene aromatic region. Finally, we have obtained cohesion energy of ?417 kcal/mol, indicative of quimisorption energy on the basis of a Harris functional treatment.     

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.     

CHARACTERIZATION OF THE STRUCTURAL FEATURES OF OXIDIZED BEYPAZARI LIGNITE USING DECONVOLUTED SOLID STATE 13C NMR SPECTRA

ABSTRACT

The solid state ¹³C NMR method have been used to investigate the structural changes occurred in Beypazari lignite while oxidizing at 150°C in a dynamic air atmosphere. Least squares curve fitting techniques have been used to resolve the overlapping bands in the 0-220 ppm region of the 13_c NMR spectra. Measurements of the relative intensities of the functional groups observed in the oxidized coals were used to follow the progress of air oxidation. Oxidation reactions seemed to decrease the total intensities of both aliphatics and aromatics, though the reduction in aliphatics was more pronounced. The relative intensities of the total aliphatics decreased from 1.0 to 0.9 and 0.6 in the original and lignites oxidized for 12 and 312 hours, respectively. The relative intensities of Ar-C-C in the 130-148 ppm region for the same set of samples were 1.0, 0.9 and 0.8. The least-squares bands resolved in the carbonyl region were at 175 ppm and 190 ppm in the original lignite; at 180 ppm (carboxylic acids), 195 ppm (meta substituted ketones) 210 ppm (di orto substituted ketones) in the lignite oxidized for 12 hours and at 170 ppm (esters), 180 ppm, 200 ppm (aldehydes) and 210 ppm in the lignite oxidized for 312 hr. Carbonyl intensity increased from 1.0 in the original lignite to 2.3 and 3.3 in the oxidized lignites. The intensity of aromatic ethers increased from 1.0 in the original lignite to 1.9 and 1.6 for the oxidized samples. The mechanism of oxidation ether. Aldehydes are easily oxidized to carboxylic acids in the presence of air by the free radical formation of a peroxy acid. The carboxylic acid formed by disproportionation reactions between the peroxy acid and aldehydes might combine with phenols to produce esters as it was observed in the present work. The presence of high free radical concentration in the oxidation atmosphere probably caused to abstract hydrogen atoms from the aromatic structures thus degrading aromatics to produce hydroperoxides which acted later as it was described above. The gradual degradation of aromatic structures observed in the present study indicated that the oxidation reactions of the aromatic rings should less probable when compared to the oxidation of aliphatic structures.     

AN EXPERIMENTAL STUDY OF THE EFFECT OF PARAFFINIC SOLVENTS ON THE ONSET AND BULK PRECIPITATION OF ASPHALTENES

ABSTRACT

Asphaltene onset concentration and bulk deposition were measured for a typical live reservoir oil titrated with n-C₆H₁₄, n-C₅H₁₂, n-C₄H₁₀, C₃H₈, C₂H₆, CH₄ and CO₂ at 100° C (212 ° F) and 29.9 MPa (4340 psia). The concentration of titrant at asphaltene onset was observed to decrease approximately in a linear fashion with decreasing molecular weight of the paraffinic solvent; CH₄ did not induce any asphaltene precipitation. Bulk deposition experiments were performed using a solvent: oil volume ratio of 10:1; the results indicated that the weight percent of asphaltenes precipitated increased exponentially with decreasing molecular weight of the paraffinic solvents. More importantly, the asphaltene molecular weight showed a maximum for n-C₄H₁₀ precipitated asphaltenes. Possible explanations for this unusual result are presented.     

13C-N.M.R. STUDIES OF A FLASH PYROLYSIS TAR AND A SUPERCRITICAL GAS EXTRACT USING MODERN PULSE SEQUENCES

ABSTRACT

The oil and the asphaltene obtained from a flash pyrolysis tar of an Australian sub-bituminous coal and the oil and asphaltene from a supercritical gas extract of an Australian bituminous coal were studied by ¹³;c-n.m.r. apectroscopy using modern pulse sequences which distinguish between primary (CH₃), secondary (CH₂), tertiary )CH( and quaternary (C) carbons. The oil from the flash pyrolysis tar was further separated into three fractions by elution chromatography and these were also studied. All the samples studied contained considerable amounts of long unsubstituted aliphatic chains. In the flash pyrolysis tar, a sizeable proportion of the long chains had a CH = CH₂ end group pertaining to both 1-alkenea and those chains attached to aromatic rings (w-aryl-1-alkenes), but this was much less in the supercritical gas extract. From the quaternary and tertiary carbon subspectra, it appears that the division of the aromatic carbon signal at 129-130 ppm between aromatic CH and C carbons is not valid for polar fractions of coal liquids. Though these pulse sequences are very useful for obtaining information on well resolved signals, broad featureless signals often found in coal liquids pose considerable problems.