ELECTROPHORETIC MOBILITY AND STABILIZATION OF ASPHALTENES IN LOW CONDUCTIVITY MEDIA

ABSTRACT

The electrophoretic mobilities of asphaltenes in n-heptane and ethanol were determined. The asphaltenes studied show a positive charge in both solvents. However, the magnitude of the charge is considerably lower in n-heptane than in ethanol. It is concluded that although the electrostatic forces are presented in both solvents, the van der Waals’ atractive forces are the main responsable for the flocculation of asphaltene particles. The addition of a well known asphaltene stabilizer, dodecyl benzene sulphonic acid (DBSA), decreases the electrophoretic mobility of asphaltene particles in ethanol until a constant positive value is reached. This means that the neutralization of the positive charges of the asphaltene particles is not complete, probably due to the limited adsorption of the DBSA on asphaltene surface and also, to the presence of charges inside the asphaltene particles that are not accessible to the DBSA.     

ELECTRICAL CONDUCTIVITY OF ASPHALTENES IN ORGANIC SOLVENTS

Conductivities of asphaltenes were measured as a function of concentration in solvents of varying permittivity. The molar conductivity was calculated assuming the molecular weight of asphaltenes to be 1000 g/mol

The Fuoss conductivity model was fitted to the experimental data with two free parameters i.e. the association constant and the molar conductivity at infinite dilution. The experimental data show indication of ion-pairs and strong dipole-ion interaction. Accordingly, the measurements were consistent with the model for ion pairs as given by Fuoss and multibody interaction theory given by Petrucci

At low concentration the asphaltenes consist mainly of free ions, as the concentration increases ion pairing leads to a decrease of the molar conductivity. At higher concentration ion-dipole interaction may lead to an increase of the molar conductivity, as is seen in some of the solvents. At even higher concentrations some indications of aggregation are observed

The results indicate that part of the asphaltenic fraction is ionized and behave as ions in solvents of low dielectric constant.     

ELECTRICAL CONDUCTIVITY OF ASPHALTENES IN ORGANIC SOLVENTS

ABSTRACT

Conductivities of asphaltenes were measured as a function of concentration in solvents of varying permittivity. The molar conductivity was calculated assuming the molecular weight of asphaltenes to be 1000 g/mol

The Fuoss conductivity model was fitted to the experimental data with two free parameters i.e. the association constant and the molar conductivity at infinite dilution. The experimental data show indication of ion-pairs and strong dipole-ion interaction. Accordingly, the measurements were consistent with the model for ion pairs as given by Fuoss and multibody interaction theory given by Petrucci

At low concentration the asphaltenes consist mainly of free ions, as the concentration increases ion pairing leads to a decrease of the molar conductivity. At higher concentration ion-dipole interaction may lead to an increase of the molar conductivity, as is seen in some of the solvents. At even higher concentrations some indications of aggregation are observed

The results indicate that part of the asphaltenic fraction is ionized and behave as ions in solvents of low dielectric constant.     

PEPTIZATION AND COAGULATION OF ASPHALTENES IN APOLAR MEDIA USING OIL-SOLUBLE POLYMERS

The asphaltene fraction of crude oil contains a variety of acidic and basic functional groups. During oil production and transportation, changes in temperature, pressure or oil composition can cause asphaltenes to precipitate out crude oil through the flocculation among these polar functional groups. In this study, two types of oil-soluble polymers, dodecylphenolic resin and poly (octadecene maleic anhydride), were synthesized and used to prevent asphaltenes from flocculating in heptane media through the acid-base interactions with asphaltenes. The experimental results indicate that these polymers can associate with asphaltenes to either inhibit or delay the growth of asphaltene aggregates in alkane media. However, multiple polar groups on a polymer molecule make it possible to associate with more than one asphaltene molecule, resulting in the hetero-coagulation between asphaltenes and polymers. It was found that the size of the asphaltene-polymer aggregates was strongly affected by the polymer-to-asphaltene weight (or number) ratio. At low polymer-to-asphaltene weight ratios, asphaltenes keep flocculating with themselves and with polymers until the floes precipitate out of solution. On the other hand, at high polymer-to-asphaltene weight ratios, asphaltene-polymer aggregates peptized by the extra polymer molecules can remain fairly stable in the solution.     

PEPTIZATION AND COAGULATION OF ASPHALTENES IN APOLAR MEDIA USING OIL-SOLUBLE POLYMERS

ABSTRACT

The asphaltene fraction of crude oil contains a variety of acidic and basic functional groups. During oil production and transportation, changes in temperature, pressure or oil composition can cause asphaltenes to precipitate out crude oil through the flocculation among these polar functional groups. In this study, two types of oil-soluble polymers, dodecylphenolic resin and poly (octadecene maleic anhydride), were synthesized and used to prevent asphaltenes from flocculating in heptane media through the acid-base interactions with asphaltenes. The experimental results indicate that these polymers can associate with asphaltenes to either inhibit or delay the growth of asphaltene aggregates in alkane media. However, multiple polar groups on a polymer molecule make it possible to associate with more than one asphaltene molecule, resulting in the hetero-coagulation between asphaltenes and polymers. It was found that the size of the asphaltene-polymer aggregates was strongly affected by the polymer-to-asphaltene weight (or number) ratio. At low polymer-to-asphaltene weight ratios, asphaltenes keep flocculating with themselves and with polymers until the floes precipitate out of solution. On the other hand, at high polymer-to-asphaltene weight ratios, asphaltene-polymer aggregates peptized by the extra polymer molecules can remain fairly stable in the solution.     

INTERMOLECULAR FORCES IN AGGREGATES OF ASPHALTENES AND RESINS

In order to determine the forces acting in the asphaltene and resin molecular aggregates, an analysis of the origin of the intermolecular interactions in organic molecules was made. The results showed that the forces present in the aggregates of asphaltenes and resins were only those originated in the van der Waals, Coulombic (electrostatic), charge transfer and induction plus the exchange-repulsion interaction. No other forces were found to be significant in these aggregates that are formed by molecules containing well-known atomic groups. Molecular orbital calculations in resins and model asphaltene suggested that charge transfer is small or negligible in their aggregates. Although the H bonds present could be quite strong, other intermolecular interactions should not be disregarded in the analysis of the energy of their aggregates.     

INTERMOLECULAR FORCES IN AGGREGATES OF ASPHALTENES AND RESINS

ABSTRACT

In order to determine the forces acting in the asphaltene and resin molecular aggregates, an analysis of the origin of the intermolecular interactions in organic molecules was made. The results showed that the forces present in the aggregates of asphaltenes and resins were only those originated in the van der Waals, Coulombic (electrostatic), charge transfer and induction plus the exchange–repulsion interaction. No other forces were found to be significant in these aggregates that are formed by molecules containing well-known atomic groups. Molecular orbital calculations in resins and model asphaltene suggested that charge transfer is small or negligible in their aggregates. Although the H bonds present could be quite strong, other intermolecular interactions should not be disregarded in the analysis of the energy of their aggregates.     

低渗油藏非线性渗流规律数学模型及其应用

中国已探明未动用的2.4×10⁹t低渗透石油地质储量成为石油工业发展的重要潜力。低渗透非线性渗流是开发低渗透油气田所需解决的重要基础问题,也是现代渗流力学的前沿研究方向之一。根据实验结果,首次提出了低渗透非线性渗流规律的连续函数模型,为使低渗透非线性渗流的研究从定性分析到定量分析奠定了基础。基于此模型建立了低渗透非线性定常和非定常渗流数学模型。导出了非线性定常渗流压力分布和产量公式,运用影响半径的概念和平均质量守恒的方法导出了非线性非定常渗流压力分布和影响半径公式。根据实验得到的参数及建立的模型进行了算例分析,得出了非线性定常渗流压力分布、非定常渗流压力分布及影响半径发展的规律,并将其与按线性渗流规律计算的结果进行了对比,结果表明二者差别明显,在进行低渗透油气田开发计算时,应考虑非线性渗流的影响。     

低渗透多孔介质中气体滑脱行为研究

研究和讨论了气体滑脱的物理机制,推导了气体在多孔介质中流动包括滑脱速度在内的新方程,并且从实验得到了和理论分析一致的结果.     

塔河常压渣油中不同沥青质的组成与结构研究

以塔河常压渣油为原料,正戊烷、正己烷和正庚烷为溶剂,分离制得3个沥青质试样C5-As,C6-As,C7-As,采用SEM,XRD,FT-IR,TG-DTG等方法,分析表征了其表面形态、晶体结构、官能团结构和热解性能等。结果表明：随着溶剂碳链的增加,C5-As,C6-As,C7-As试样的收率逐渐减小,其值分别为33.57 %,26.98 %,21.12 %; 3个试样依次表面逐渐粗糙,粒径递减;芳香片层数和芳构化程度增加;芳环取代度降低,缩合度增大;热稳定性增强,残炭增加。     

MOLECULAR SIZE AND STRUCTURE OF ASPHALTENES

Fluorescence depolarization measurements are used to determine the size of asphaltene molecules and of model compounds for comparison. Mean molecular weights of 750 amu have been found for petroleum asphaltenes. A strong correlation is established between the size of fused rings in asphaltene molecules and the overall size of these molecules, showing that asphaltenes have one or perhaps two fused ring systems per molecule. Coal asphaltene molecules are found to be much smaller than petroleum asphaltenes.     

MOLECULAR SIZE AND STRUCTURE OF ASPHALTENES

Fluorescence depolarization measurements are used to determine the size of asphaltene molecules and of model compounds for comparison. Mean molecular weights of 750 amu have been found for petroleum asphaltenes. A strong correlation is established between the size of fused rings in asphaltene molecules and the overall size of these molecules, showing that asphaltenes have one or perhaps two fused ring systems per molecule. Coal asphaltene molecules are found to be much smaller than petroleum asphaltenes.     

THE EFFECT OF LOW TEMPERATURE OXIDATION ON THE CHEMICAL AND PHYSICAL PROPERTIES OF MALTENES AND ASPHALTENES DERIVED FROM HEAVY OIL

The chemical changes that occur when the maltene and asphaltene fractions (separated from heavy oil) are subjected to low temperature oxidation (LTO) in the presence and absence of water have been investigated by a combination of classical separation techniques and analytical pyrolysis. In general, it is observed that water has a mitigating effect on the destructive nature of LTO. A detailed analysis of the pyrolytic products suggests that the presence of water reduces the ease with which oxygen reacts with sulfides to give sulfones and thereby supresses the formation of coke. An analysis of the data indicates that most of the coke produced results from LTO of the asphaltenes; only a small portion originates in the maltenes.     

THE EFFECT OF LOW TEMPERATURE OXIDATION ON THE CHEMICAL AND PHYSICAL PROPERTIES OF MALTENES AND ASPHALTENES DERIVED FROM HEAVY OIL

Abstract

The chemical changes that occur when the maltene and asphaltene fractions (separated from heavy oil) are subjected to low temperature oxidation (LTO) in the presence and absence of water have been investigated by a combination of classical separation techniques and analytical pyrolysis. In general, it is observed that water has a mitigating effect on the destructive nature of LTO. A detailed analysis of the pyrolytic products suggests that the presence of water reduces the ease with which oxygen reacts with sulfides to give sulfones and thereby supresses the formation of coke. An analysis of the data indicates that most of the coke produced results from LTO of the asphaltenes; only a small portion originates in the maltenes.     

减压渣油中胶状沥青状物质的化学结构研究

利用对芳香碳有高选择性转化能力的钌离子催化氧化法研究了减压渣油中轻、中、重胶质和戊烷沥青质的化学结构,定量了与芳香环相连的正构烷基侧链和桥链的分布,并了芳香环系的缩合型式,结果表明,这些石油重质组分中均存在碳数为Ｃ１￣Ｃ３０的与芳香 相连的正构烷基侧链,其摩尔浓度随链长的增加而下降,也存在由正构烷基桥连接的至少具有两个芳香环系的芳香性分子,在芳香结构中存在着渺位缩合,迫位缩合以联苯型结构,其中联苯     

STABILIZATION OF COAL PARTICLE SUSPENSIONS USING COAL LIQUID DERIVED SUSPENDING MEDIA

ABSTRACT

A liquid we derived from coal, and a liquid produced from Exxon donor solvent (EDS) vacuum gas oil served to stabilize coal particle suspensions. In one case the liquids were used like commercial stabilization additives for coal-petroleum oil mixtures (COMs) with poorer but comparable results. In the other case the idea of using the coal liquid itself as the suspending medium (in place of petroleum oil) was considered, with encouraging results.

Arguments suggest interparticle repulsion enhances the stability of coal particles in coal liquid derived suspending media.     

PYROLYSIS AND LIQUEFACTION OF BRAZILIAN COAL AND COAL-DERIVED ASPHALTENES

ABSTRACT

The present work describes a study of the liquefaction and pyrolysis of a Southern Brazilian mineral coal and its derived asphaltenes, using conversion systems developed in our laboratory.

The results show that significant quantities of the intermediate polarity fraction named resins is obtained through the pyrolysis of coal, while after the liquefaction process higher quantities of the higher fractions was found. A model is proposed to explain the liquefaction and pyrolysis processes of both coal and coal-derived asphaltenes.     

THE INFLUENCE OF PRESSURE ON THE ASPHALTENES CONTENT AND COMPOSITION IN OILS

The objective of this work was to investigate the effect of pressure on the concentration of the dissolved asphaltenes in a heavy oil. The asphaltenes content was determined in oil samples, produced at reservoir temperature and different pressures ranging from the initial reservoir pressure to the atmospheric one, using the standard IP143/90 method. Additionally, the content of nine trace metals in the asphaltenes, produced at each pressure step was studied by Total Reflection X-Ray Fluorescence (TXRF). It was found that the amount of the dissolved asphaltenes in oil decreases as pressure falls from the initial reservoir pressure down to bubble point pressure and subsequently increases as the pressure is reduced further. A positive correlation was observed between the concentration of several metals (Ni, V, Cr, Mn) and the dissolved asphaltenes content.