Solid Petroleum Asphaltenes Seem Surrounded by Alkyl Layers

In this review, a comprehensive analysis of recent results obtained in our laboratory and published in the literature is presented, which points toward the existence of alkyl layers surrounding precipitated asphaltene solids. A micellar model for asphaltenes has been proposed, which explains many of the experimental determinations carried out to date with these compounds. The model considers the existence of alkyl moieties surrounding the inner aromatic cores. Faster dissolution kinetics of asphaltenes modified by coprecipitated waxes has been explained by the enhanced incorporation of alkane-surrounded particles into the eluent employed in the dissolution experiments. Finally, asphaltene volumetric changes brought by organic solvents have recently been studied, and can be explained by the existence of an alkyl layer prone to the incorporation of solvent molecules. This paper will discuss these aspects that seem to support the model long time ago postulated by Yen and coworkers.     

Abiotic Degradation of Petroleum Asphaltenes

Chemistry and Technology of Fuels and Oils - The literature data on the abiotic degradation of asphaltenes are the subject of a systematic review. Such degradation may proceed under natural...     

Adsorption of Phenol by Nitro and Amino Derivatives of Petroleum Asphaltenes

Chemistry and Technology of Fuels and Oils - The sorption properties of native and modified petroleum asphaltenes with respect to phenol were studied under static conditions. The asphaltenes were...     

Variation in Composition of Subfractions of Petroleum Asphaltenes

Boscan asphaltenes were precipitated from the crude oil using mixtures of toluene and heptane at temperatures of 24, 50, and 80°C. Another process of extracting solid n-heptane asphaltenes (24°C) using the same solvent systems and temperatures was also investigated. Asphaltene yield is different by the two processes at similar conditions although both increases in temperature or toluene content lead to lower solid yield. This way the asphaltene continuum was investigated from incipient flocculation to total n-heptane precipitated asphaltenes. The asphaltenes were analyzed using elemental analysis, fluorescence spectroscopy, vapor pressure osmometry, and HPLC size exclusion chromatography. The distribution of porphyrins was also measured using absor-bance spectroscopy. The asphaltenes were found to follow a regular trend in elemental ratios, H/C and N/C, indicating increased aromaticity and nitrogen content as the solid yield decreases. Also the molecular weight was seen to increase. Size exclusion chro-matograms and fluorescence spectra were found to be different comparing solids from the two separation processes. This indicates that the asphaltene fractions obtained by extraction of solid asphaltenes are altered relative to asphaltenes obtained by ordinary precipitation. The porphyrin concentration was found to diminish rapidly with solid yield decrease in both precipitation and extraction experiments, the latter fractions, however, containing significantly less asphaltenes indicating an adsorption step in the coprecipitation of porphyrins. Soluble fractions were found to exhibit relatively low molecular weights and an apparent lack of indications of association up to a point of solubles exceeding 50 % of the total asphaltenes. The-latter have implications for the further understanding and experimental investigation. of the associating nature of asphaltenes such as concentration effects during analytical characterization.     

Variation in Composition of Subfractions of Petroleum Asphaltenes

ABSTRACT

Boscan asphaltenes were precipitated from the crude oil using mixtures of toluene and heptane at temperatures of 24, 50, and 80°C. Another process of extracting solid n-heptane asphaltenes (24°C) using the same solvent systems and temperatures was also investigated. Asphaltene yield is different by the two processes at similar conditions although both increases in temperature or toluene content lead to lower solid yield. This way the asphaltene continuum was investigated from incipient flocculation to total n-heptane precipitated asphaltenes. The asphaltenes were analyzed using elemental analysis, fluorescence spectroscopy, vapor pressure osmometry, and HPLC size exclusion chromatography. The distribution of porphyrins was also measured using absor-bance spectroscopy. The asphaltenes were found to follow a regular trend in elemental ratios, H/C and N/C, indicating increased aromaticity and nitrogen content as the solid yield decreases. Also the molecular weight was seen to increase. Size exclusion chro-matograms and fluorescence spectra were found to be different comparing solids from the two separation processes. This indicates that the asphaltene fractions obtained by extraction of solid asphaltenes are altered relative to asphaltenes obtained by ordinary precipitation. The porphyrin concentration was found to diminish rapidly with solid yield decrease in both precipitation and extraction experiments, the latter fractions, however, containing significantly less asphaltenes indicating an adsorption step in the coprecipitation of porphyrins. Soluble fractions were found to exhibit relatively low molecular weights and an apparent lack of indications of association up to a point of solubles exceeding 50 % of the total asphaltenes. The-latter have implications for the further understanding and experimental investigation. of the associating nature of asphaltenes such as concentration effects during analytical characterization.     

石油沥青质化学结构模型研究进展

主要介绍了近年来石油沥青质化学结构模型的研究成果,从分子量、稠合芳核缩合度及缩合方式等方面描述了石油沥青质基本结构模型,从缔合层次及分子间力等方面描述了沥青质缔合结构模型。     

Characterization of Petroleum Asphaltenes by Size Exclusion Chromatography, UV-fluorescence and Mass Spectrometry

The molecular weight of petroleum asphaltenes remains the subject of debate. Our previous work using size exclusion chromatography with 1-methyl-2-pyrrolidinone (NMP) as eluent, combined with mass spectrometry and fluorescence spectroscopy has indicated molecular masses up to 40,000 u. The present work investigates the asphaltene fraction of Kuwaiti crude oil. The asphaltene was separated into several NMP-soluble fractions and an insoluble residue. The evidence from size exclusion chromatography (SEC) and UV-fluorescence spectroscopy (UV-F) shows that the molecular size range and the size of the aromatic chromophores increased with increasing insolubility in NMP. A steady increase in the sizes of the range of chromophores was shown by UV-fluorescence in going from the maltene fraction, via the asphaltene sample to the NMP-insoluble residue, using chloroform as solvent. Laser-desorption mass spectra showed very wide mass ranges for the whole asphaltene and the NMP-insoluble residue of asphaltenes, with a signal up to m/z 200,000 and slightly more ion intensity at high masses for the residue compared to that from the asphaltene.     

Maltenes and Asphaltenes of Petroleum Vacuum Residues: Physico-Chemical Characterization

Abstract

Solvent separation is frequently applied to petroleum vacuum residues to reduce the coke-forming tendencies of these materials. This process is capable of removing all or a substantial amount of asphaltenes from feedstocks that are destined for further processing and thus applied as the first step of refining. Maltenes and asphaltenes obtained from vacuum residues of Heera (HVR) and Jodhpur (JVR) Indian crude oils using n-hexane, n-heptane, and soluble and insoluble fractions obtained using ethyl acetate, were characterized for elemental analysis, molecular weight, conradson carbon residue (CCR), specific gravity, and pour points. The resulting degree of removal of asphaltenes ranged from 10–28 wt% of the HVR and 25–50 wt% of the JVR. The increasing trend of the American Petroleum Institute (API) gravity and the decreasing trend of CCR and pour point are observed with the increase in removal of asphaltenes.     

Maltenes and Asphaltenes of Petroleum Vacuum Residues: Physico-Chemical Characterization

Solvent separation is frequently applied to petroleum vacuum residues to reduce the coke-forming tendencies of these materials. This process is capable of removing all or a substantial amount of asphaltenes from feedstocks that are destined for further processing and thus applied as the first step of refining. Maltenes and asphaltenes obtained from vacuum residues of Heera (HVR) and Jodhpur (JVR) Indian crude oils using n-hexane, n-heptane, and soluble and insoluble fractions obtained using ethyl acetate, were characterized for elemental analysis, molecular weight, conradson carbon residue (CCR), specific gravity, and pour points. The resulting degree of removal of asphaltenes ranged from 10-28 wt% of the HVR and 25-50 wt% of the JVR. The increasing trend of the American Petroleum Institute (API) gravity and the decreasing trend of CCR and pour point are observed with the increase in removal of asphaltenes.     

Nitration of Petroleum Asphaltenes with Concentrated Nitric Acid under Various Conditions

Chemistry and Technology of Fuels and Oils - The relationships of the reaction of the of tar asphaltenes with concentrated nitric acid were studied under various quantitative, temperature, and time...     

石油沥青质超分子聚集及解聚研究进展

石油沥青质组成复杂,氢/碳原子比低,硫、氮等杂原子含量高,给石油开采、运输和加工处理带来困难,究其原因是石油沥青质分子结构复杂,极易发生超分子聚集,形成聚集体。目前对沥青质超分子聚集的认识越来越广泛,并被石油化学工作者广泛接受。沥青质超分子聚集是通过电荷转移作用、偶极作用以及氢键作用形成沥青质分子之间的缔合,这些弱相互作用在石油体系的分子间普遍存在,实现沥青质聚集体的解聚是重质油高效轻质化的基础。研究表明,采用化学方法改变沥青质分子结构或采用物理方法改变沥青质物理状态,均能在一定程度上使得沥青质聚集体解聚。     

渣油加氢处理后沥青质组成和结构的变化

采用IR、NMR、XPS等分析手段及钌离子催化氧化(RICO)法,考察了不同加氢反应温度下渣油沥青质组成和结构的变化。结果表明,随着加氢反应温度的升高,沥青质结构中硫质量分数降低,而氮质量分数增加,芳碳率提高;沥青质结构中出现较大的芳香核,芳香环上的取代侧链和芳环间的桥链均变短,分别由C₂₉降至C₁₇、C₂₁降至C₇;沥青质RICO产物中的苯多酸由苯甲酸、苯二甲酸为主逐渐变化为以苯四甲酸至苯六甲酸为主,说明沥青质中的群岛型结构有向大陆型结构转化的趋势。加氢温度升至450℃后,沥青质的组成和结构已基本稳定,说明渣油加氢适宜温度为450℃。     

Effect of Asphaltenes on the Thermal Properties of Petroleum and Bitumen Emulsions

The thermal properties and characteristics of the molecular structure of petroleum and bitumen emulsions were investigated by viscometer and Rayleigh light scattering. The viscosity, structural properties, and character of the intermolecular interactions in the emulsions are determined by the temperature of formation of these media. Formation at critical temperatures close to 36 – 38°C initiates a structural phase transition that alters the size and activity of molecular aggregates of asphaltenes. These aggregates serve as binder material in three—dimensional supramolecular structures containing wax microcrystals. The long (up to several months) memory of the emulsions concerning the conditions of formation is due to the strength of the three—dimensional structures that contain not only hydrogen but also covalent bonds.     

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.     

Correction to: Nitration of Petroleum Asphaltenes with Concentrated Nitric Acid under Various Conditions

Chemistry and Technology of Fuels and Oils -     

Preparative Subfractionation of Petroleum Resins and Asphaltenes. I. Development of Size Exclusion Separation Methodology

A preparative chromatographic separation methodology for petroleum resins and asphaltenes was developed. Size exclusion was the chosen separation mechanism, carried out with commercial polymeric columns. Several parameters were optimized in order to achieve repeatable and quantitative separations. Asphaltenes and resins isolated from stable and unstable crude oils were studied. Differences in the relative fraction distribution were observed for resins separated from unstable oils.     

Preparative Subfractionation of Petroleum Resins and Asphaltenes. I. Development of Size Exclusion Separation Methodology

Abstract

A preparative chromatographic separation methodology for petroleum resins and asphaltenes was developed. Size exclusion was the chosen separation mechanism, carried out with commercial polymeric columns. Several parameters were optimized in order to achieve repeatable and quantitative separations. Asphaltenes and resins isolated from stable and unstable crude oils were studied. Differences in the relative fraction distribution were observed for resins separated from unstable oils.     

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

Abstract

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.     

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.     

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.