Aggregation and solubility behavior of asphaltenes and their subfractions

Asphaltenes from four different crude oils (Arab Heavy, B6, Canadon Seco, and Hondo) were fractionated in mixtures of heptane and toluene and analyzed chemically, by vapor pressure osmometry (VPO), and by small angle neutron scattering (SANS). Solubility profiles of the asphaltenes and their subfractions indicated strong cooperative asphaltene interactions of a particular subfraction that is polar and hydrogen bonding. This subfraction had lower H/C ratios and modestly higher N, V, Ni, and Fe contents than the less polar and more soluble subfraction of asphaltenes. VPO and SANS studies indicated that the less soluble subfractions formed aggregates that were considerably larger than the more soluble subfractions. In general, asphaltene aggregate size increased with decreasing solvent aromaticity up to the solubility limit, beyond which the aggregate size decreased with heptane addition. The presence of a low wavevector Q feature in the scattering curves at 25 degrees C indicated that the individual aggregates were flocculating; however, the intensity of the feature was diminished upon heating of the samples to 80 degrees C. The solubility mechanism for Canadon Seco asphaltenes, the largest aggregate formers, appears to be dominated by aromatic pi-bonding interactions due to their low H/C ratio and low nitrogen content. B6 and Hondo asphaltenes formed similar-sized aggregates in heptol and the solubility mechanism is most likely driven by polar interactions due to their relatively high H/C ratios and high nitrogen contents. Arab Heavy, the least polar asphaltene, had a H/C ratio similar to Canadon Seco but formed the smallest aggregates in heptol. The enhancement in polar and pi-bonding interactions for the less soluble subfraction indicated by elemental analysis is reflected by the aggregate size from SANS. The less soluble asphaltenes contribute the majority of species responsible for aggregation and likely cause many petroleum production problems such as pipeline deposition and water-in-oil emulsion stabilization.     

沙特常压渣油超临界流体萃取分馏宽馏分中含硫化合物的分子表征

采用超临界流体萃取分馏(SFEF)装置,将沙特中质原油常压渣油(SZAR)按照分子大小和极性强弱进行多级萃取分馏,得到四个宽馏分和一个萃余残渣。考察了四个宽馏分沸程分布、密度、残炭值、黏度、相对分子质量、硫和氮含量以及结构族组成等基本性质均随萃取压力的变化趋势。采用甲基衍生化作用使含硫化合物转化为含有极性的甲基硫盐,结合正离子模式下的电喷雾(ESI)电离源的傅里叶变换离子回旋共振质谱(FT-ICR MS)分析各馏分中所包含的含硫化合物的分子组成。结果表明,超临界萃取分馏技术可以将馏分按照分子大小进行分离,且对于非烃类化合物具有富集作用。各个馏分中含量最高的均为包含一个硫原子的S1类化合物,且二苯并噻吩(DBE=6)类含量最高。馏分越重,S1、S2类化合物含量越高、种类越繁多、且缩合程度更高,包含的更多的大分子含硫化合物。     

Interfacial rheology of petroleum asphaltenes at the oil-water interface

A biconical bob interfacial shear rheometer was used to study the mechanical properties of asphaltenic films adsorbed at the oil-water interface. Solutions of asphaltenes isolated from four crude oils were dissolved in a model oil of heptane and toluene and allowed to adsorb and age in contact with water. Film elasticity (G') values were measured over a period of several days, and yield stresses and film masses were determined at the end of testing. The degree of film consolidation was determined from ratios of G'/film mass and yield stress/G'. Asphaltenes with higher concentrations of heavy metals (Ni, 330-360 ppm; V, 950-1000 ppm), lower aromaticity (H/C, 1.24-1.29), and higher polarity (N, 1.87-1.99) formed films of high elasticity, yield stress, and consolidation. Rapid adsorption kinetics and G' increases were seen when asphaltenes were near their solubility limit in heptane-toluene mixtures (approximately 50% (v/v) toluene). In solvents of greater aromaticity, adsorption kinetics and film masses were reduced at comparable aging times. Poor film forming asphaltenes had yield stress/G' values ((1.01-1.21) x 10(-2)) more than 4-fold lower than those of good film forming asphaltenes. n-heptane asphaltenes fractionated by filtering solutions prepared at low aromaticity (approximately 40% toluene in mixtures of heptane and toluene) possessed higher concentrations of heavy metals and nitrogen and higher aromaticity. The less soluble fractions of good film forming asphaltenes exhibited enhanced adsorption kinetics and higher G' and yield stress values in pure toluene. Replacing the asphaltene solutions with neat heptane-toluene highlighted the ability of films to consolidate and become more elastic over several hours. Adding resins in solution to a partially consolidated film caused a rapid reduction in elasticity followed by gradual but modest consolidation. This study is among the first to directly relate asphaltene chemistry to adsorption kinetics, adsorbed film mechanical properties, and consolidation kinetics.     

煤基和石油基C7-沥青质的结构特征及缔合行为

采用核磁(NMR)、小角散射分析(SAXS)、X射线光电子能谱(XPS)、改进的B-L法等手段,研究了煤基C7-沥青质(CT-asp)和石油基C7-沥青质(M-asp)两类沥青质的化学组成、官能团和分子结构等组成结构特征以及差异性,进而通过极性溶剂中沥青质稳定参数研究两类沥青质的缔合行为和聚集体尺寸以及两者之间的氢键和酸碱作用。结果表明,CT-asp分子芳香环数较少且有较多短烷基侧链,且芳香度较高,较高含量氧杂原子以芳香醚和酚羟基赋存形态为主;而M-asp的芳香核尺寸和平均相对分子质量明显高于CT-asp,芳香环数虽较多且有较多长烷基支链,且芳香度较小;两类沥青质缔合聚集程度关联物质的量比(n_(CT-asp)/n_(M-asp))及其分子结构特征,源于杂原子官能团的氢键和酸碱作用是两类沥青质缔合的主要作用力。     

Isolation and analysis of peptidic fragments of alpha-gliadin using reversed-phase high-performance liquid chromatography

Peptidic fragments of alpha-gliadin were obtained by peptic-tryptic-pancreatic (PTP) digestion of the alpha-gliadin fraction isolated by ion-exchange chromatography on a sulphopropyl-Sephadex C-50 column. The proteolytic digest was fractionated by ultrafiltration into three subfractions, PTPa1-PTPa3. The subfraction PTPa2 was then analysed and individual peaks were separated using reversed-phase high-performance liquid chromatography (RP-HPLC) using a gradient of acetonitrile in 0.1% trifluoroacetic acid and a Separon SGX-C18 sorbent. A 100-mg amount of the PTPa2 subfraction was separated in a single analysis by preparative RP-HPLC and twenty peaks were obtained for further characterization. The molecular mass in range 300-3000 was established for individual peptidic fragments by gel-permeation chromatography on a TSK-G2000 SW column.     

Pyrolysis/gas chromatography/mass spectrometry of asphaltene fractions

Two n-heptane-precipitated asphaltene samples, characterized by elemental analysis and nuclear magnetic resonance spectrometry, were fractionated according to relative molecular size by gel permeation chromatography (GPC). Both the whole asphaltene samples and their fractions were analysed by pyrolysis/gas chromatography/mass spectrometry. The data obtained from the pyrograms (average side-chain length, aromaticity index, sulphur compounds vs. aliphatic compounds, presence of SO₂ and CO₂) demonstrated that, in the case of asphaltenes, GPC fractionation results in the separation of different chemical structures ranging from lower molecular mass, highly aromatic and polar compounds to higher molecular mass, less polar and aromatic compounds.     

Interaction between asphaltenes and fatty-alkylamine inhibitor in bulk solution

In the present work, the mechanism of interaction between asphaltenes and a commercial fatty-alkylamine inhibitor was investigated by a combination of techniques. The “macro” properties, like the asphaltene precipitation onset and the amount of asphaltenes precipitated, were measured by near-infrared (NIR) and UV-vis spectroscopy, respectively, while the interaction enthalpy between asphaltenes and inhibitor was measured by isothermal titration calorimetry (ITC). Asphaltenes subfractions and derivatives were also used to identify the mechanism.

ITC indicated that only a small fraction (～6%) of asphaltenes interacts strongly with the inhibitor. The proportion of interacting species was found to be higher in irreversibly adsorbed asphaltenes subfraction. These 6% are mostly composed of acidic asphaltenes, as indicated by measurements involving ester asphaltenes. However, the measurement of precipitation onset and amounts precipitated for whole and ester asphaltenes indicated that the acid–base interaction was not the main interaction responsible for the inhibitory action. Other type(s) of interaction is/are responsible for the inhibition properties of the inhibitor, which are not detected by ITC. The nature of other interactions is not known for the moment, but it was shown that irreversibly adsorbed asphaltene fraction contains a higher concentration of the functionality (ies) responsible for the “other” type of interaction.     

Non-Exponential 1H and 2H NMR Relaxation and Self-Diffusion in Asphaltene-Maltene Solutions

The distribution of NMR relaxation times and diffusion coefficients in crude oils results from the vast number of different chemical species. In addition, the presence of asphaltenes provides different relaxation environments for the maltenes, generated by steric hindrance in the asphaltene aggregates and possibly by the spatial distribution of radicals. Since the dynamics of the maltenes is further modified by the interactions between maltenes and asphaltenes, these interactions—either through steric hindrances or promoted by aromatic-aromatic interactions—are of particular interest. Here, we aim at investigating the interaction between individual protonic and deuterated maltene species of different molecular size and aromaticity and the asphaltene macroaggregates by comparing the maltenes’ NMR relaxation (T1 and T2) and translational diffusion (D) properties in the absence and presence of the asphaltene in model solutions. The ratio of the average transverse and longitudinal relaxation rates, describing the non-exponential relaxation of the maltenes in the presence of the asphaltene, and its variation with respect to the asphaltene-free solutions are discussed. The relaxation experiments reveal an apparent slowing down of the maltenes’ dynamics in the presence of asphaltenes, which differs between the individual maltenes. While for single-chained alkylbenzenes, a plateau of the relaxation rate ratio was found for long aliphatic chains, no impact of the maltenes’ aromaticity on the maltene–asphaltene interaction was unambiguously found. In contrast, the reduced diffusion coefficients of the maltenes in presence of the asphaltenes differ little and are attributed to the overall increased viscosity.     

抚顺烟煤吡啶抽出物ZM2馏份结构表征

本文采用了多种现代结构分析方法(FTIR,~1H-、~(13)C-NMR,FDMS,MS/MS)对抚顺烟煤吡啶抽出物的正庚烷不溶、正庚烷/苯(1∶1)可溶馏份(ZM2馏份)进行了详细的结构解析,得到了其平均分子量、分子量分布及其中30种化合物的分子结构,为研究抚顺烟煤的结构提供了有价值的信息。     

Asphaltenes Flocculation in Light Crude Oils: A Chemical Approach to the Problem

This article describes the state‐of‐the‐art of the phenomena associated to the flocculation and precipitation of asphaltenes as well as the solutions used to prevent this kind of phase behavior problem in a Brazilian light (42⁰ API) crude oil. A discussion on how to diagnose this light crude tendency to flocculate its low concentration (0.3%) asphaltenes and on the approach to (chemically) mitigate the phenomena also are provided. To address the problem a comprehensive study was carried out as follows: 1) Scoping trials to assess the so‐called asphaltenes deposition envelope (ADE) of the crude, a key parameter to design the chemical injection system and to production management. To accomplish that a mono‐phase crude oil sample was collected and tests were performed on a PVT cell equipped with a solid detection system. These PVT results enabled us to evidence the reversibility of the asphaltenes flocculation process—above the bubble point pressure—which is in agreement with the Hildebrand theory for macromolecules in hydrotopic solutions and; 2) A suite of field experiments to address the following issues: asphaltenes flocculation inhibitor dosage optimization; how to collect inhibitor‐free oil samples for well site evaluation; adaptation of the existing analytical methods for well site analysis and: setting up guidelines against which measure the inhibitor performance in this low‐asphaltenes concentration crude oil.

The engineered solutions that ended up being developed from this comprehensive study are now incorporated to Petrobras flow assurance solutions portfolio.     

Quartz Crystal Microbalance Monitoring of Asphaltene Adsorption/Deposition

Adsorption and deposition of asphaltenes onto differently coated (hydrophilic surfaces: silica, titanium, alumina, and a noncommercial tailor‐made FeO_x) quartz crystals from heptane/toluene (1∶1) and toluene solutions have been studied with the quartz crystal microbalance method with dissipation measurements (QCM‐D). The results show that the adsorbed mass is related to the solubility state of asphaltenes (aromaticity of the solvent), their origin (aggregate size in solution) and very little to the hydrophilicity of the investigated crystal. Adsorption/deposition of asphaltenes depends on their solubility. We found two cases: Either the asphaltenes are solubilized, or the asphaltenes are partly solubilized and partly precipitated. In the former case, asphaltenes are bounded very tightly to the surface and poorly for the latter. The change in solution composition due to decrease in asphaltene solvency causes formation of a variety of asphaltenes species. The results also were compared and discussed in relation to adsorption onto particles, determined with the UV depletion method. The study shows that QCM‐D method is a very useful tool to study the mechanisms and the effects of solvency of asphaltenes. We discuss and compare the different techniques.     

Acid-base characterization of molecular weight fractionated humic acid

Acid-base properties of molecular weight fractionated humic acids (HAs) were investigated by the acid-base potentiometric titration. The acidic group contents (C(A(t))) and the average values of apparent pK (pK(app)) were evaluated by applying a modified Henderson-Hasselbalch equation to the experimental titration curves. The average values of pK(app) of the fractionated and unfractionated HAs were about 4.1-4.4, and the distribution of pK(app) values could be represented by the relationships between alpha and pK(app) plots in the range 2-8. The C(A(t)) values increased with a decrease in molecular size, as did the aromaticity. This suggests that the acidic group contents are related to the aromaticity of the HA.     

Identification of dimethyl- and ethylphenanthrenes in HPLC-fractions of rock and coal extracts by capillary gas chromatography and high resolution spectrofluorometry at 15K

Summary Total-aromatics fractions from an oil shale and a coal extract were fractionated in a three-step HPLC procedure. C₂-phenanthrenes in the triaromatic subfraction from the first step were tentatively identified on the basis of retention indices and GC-MS data. Successive fractionation of triaromatics on reverse-phase columns yielded 20 subfractions that were amenable to a positive identification of individual C₂-phenanthrene isomers by using high resolution spectrofluorometry. Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984     

Asphaltene precipitation from latin american heavy crude oils. Effects of solvent aromaticity and agitation on particle size reduction

Asphaltenes from three crudes were precipitated with a mixture of n-heptane and toluene, the size of the particles formed under different solvent mixtures and different agitation regimes were studied. The kinetic size reduction of aggregates formed with an excess of precipitant agent is followed, contrary to other published studies where the kinetic followed is of growing particles. It was found that the particle size of precipitated asphaltenes decreases as precipitant aromaticity increases and agitation energy rises, which indicates the formation of aggregates bonded by weak forces, since the agitation applied was not of high energy, except for the ultrasonic device.     

Fractionation of cigarette smoke condensate for chemical and biological testing

Large-scale fractionation of cigarette smoke condensate (CSC) was carried out by gel filtration and silicic acid column chromatography, and selected fractions and their subfractions were tested for tumorigenicity by mouse-skin bioassay. The weak-acid fraction was separated into four subfractions, the polynuclear aromatic hydrocarbon (PAH) fraction into two subfractions, and the polar neutral lipid fraction into three subfractions. Also, combinations of subfractions were examined for synergic effects and portions of all active material were subjected to chemical analyses by gel filtration, column, thinlayer and gas chromatography, and ultraviolet and mass spectrometry. A weak-acid subfraction (F-63) in which catechol was concentrated, and which comprized 3.27% CSC was shown to be tumorigenic, as were combinations of this sub fraction with the active PAH (F-67) sub fraction and a polar, neutral lipid (F-70) sub fraction, representing 0.01 and 0.05% CSC, respectively. The results indicated that catechol may be a potent cocarcinogen and that the PAH in CSC interact with other components to exert a tumorigenic effect.     

Biocatalytic removal of nickel and vanadium from petroporphyrins and asphaltenes

Asphaltenes from a crude oil rich in heavy metals (Castilla crude oil) were fractionated and partially characterized. Biocatalytic modifications of these fractionated asphaltenes by three different hemoproteins: chloro-peroxidase (CPO), cytochrome C peroxidase (Cit-C), and lignin peroxi-dase (LPO) were evaluated in both aqueous buffer and organic solvents. The reactions were carried out in aqueous buffers, ternary systems of toluene: isopropanol: water, and aqueous-miscible organic solvent solutions with petroporphyrins as substrate. The petroporphyrins were more soluble in the ternary systems and aqueous miscible-organic solvent systems than in the aqueous buffer systems. However, only the CPO-mediated reactions were effective in eliminating the Soret peak in both aqueous and organic solvent systems. The effects of CPO-mediated reactions on the release of the metals complexed with the porphyrins and asphaltenes were also determined. Chloroperoxidase was able to alter components in the heavy fractions of petroleum and remove 53 and 27% of total heavy metals (Ni and V, respectively) from petroporphyrin-rich fractions and asphaltenes     

Asphaltene self-association and water-in-hydrocarbon emulsions

The configuration of asphaltenes on the water-oil interface was evaluated from a combination of molar mass, interfacial tension, drop size distribution, and gravimetric measurements of model emulsions consisting of asphaltenes, toluene, heptane, and water. Molar mass measurements were required because asphaltenes self-associate and the level of self-association varies with asphaltene concentration, the resin content, solvent type, and temperature. Plots of interfacial tension versus the log of asphaltene molar concentration were employed to determine the average interfacial area of asphaltene molecules on the interface. The moles of asphaltenes per area of emulsion interface were determined from the molar mass data as well as drop size distributions and gravimetric measurements of the model emulsions. The results indicate that asphaltenes form monolayers on the interface even at concentrations as high as 40 kg/m(3). As well, large aggregates with molar masses exceeding approximately 10,000 g/mol did not appear to adsorb at the interface. The area occupied by the asphaltenes on the interface was constant indicating that self-associated asphaltenes simply extend further into the continuous phase than nonassociated asphaltenes. The thickness of the monolayer ranged from 2 to 9 nm.     

Characterization of asphaltenes precipitated with three light alkanes under different experimental conditions

Asphaltene precipitation plays an important role in both oil production and refining processes. In this paper, asphaltenes are precipitated from a heavy oil sample under different experimental conditions by using three different light alkanes, i.e., propane, n-pentane, and n-heptane. A variety of analytical techniques are applied to characterize the precipitated asphaltenes and deasphalted heavy oil (i.e., maltenes), such as the density and viscosity measurements, vapour-pressure osmometry, freezing-point osmometry, scanning electron microscope (SEM) imaging, nuclear magnetic resonance (NMR) measurement, and simulated distillation for compositional analysis. It is found that the yields and properties of the precipitated asphaltenes and remaining maltenes strongly depend on the specific precipitant tested and the liquid precipitant-to-oil volume ratio used. The asphaltene yield decreases as the carbon number of an alkane increases, while it increases monotonically and finally reaches a plateau if the liquid precipitant-to-oil volume ratio increases up to 20–40 for n-pentane and n-heptane, respectively. As a result, n-heptane-precipitated asphaltenes (C₇-asphaltenes) have the highest molecular weight and aromaticity among the three kinds of precipitated asphaltenes. C₇-asphaltenes are bright and black particles, whereas n-pentane-precipitated asphaltenes (C₅-asphaltenes) are dull and brown powders. Propane-precipitated asphaltenes (C₃-asphaltenes) together with some amount of co-precipitated resins are found to be highly viscous and semi-solid like immediately after the flashed-off process but become more and more liquid-like afterward. Compositional analysis results of the original heavy crude oil and three different maltenes indicate that the carbon numbers of most precipitated asphaltenes are higher than C₅₀.     

Radiation-induced effects on alternative fuels

Solvent refined coal (SRC) produced from Indiana V feed coal was X-ray irradiated at different doses. The gases evolved from the irradiated sample consist mainly of methane, whose concentration is shown to depend on the irradiation dose. The condensed matter left after gas extraction was fractionated by column liquid chromatography into five non-polar fractions (saturated, monoaromatic, diaromatic, triaromatic and polyaromatic hydrocarbons); one of intermediate polarity (resins); and two polar (asphaltenes and asphaltols) fractions. The relative distribution of these radiolytic products depends upon the dose delivered with the concentration of hydrocarbons increasing remarkably with the dose.