Investigation of Molecular Weight and Aggregation of Asphaltenes in Organic Solvents Using Surface Tension Measurements

The physico-chemical behavior of asphaltene is very useful to assist prediction and control the mechanisms of asphaltene deposition during the production of petroleum fluids. It has been realized that the first step in the formation of precipitated asphaltene particles is the self-aggregation mechanism to form colloidal particles or pseudo-micelles in several solvents. In this work, the critical micelle concentration (CMC) of two asphaltene fractions extracted from vacuum residues (VR) were obtained by surface tension measurements, using aromatic solvents. The molecular weight (1094-565 g/mol), calculated from average radii of the asphaltene molecules adsorbed at the air-solvent interface, are also in agreement with the values for small aggregates reported using small angle X-ray scattering.     

Structural Relaxation Behaviors of Three Different Asphaltenes Using MD Calculations

For asphaltene obtained from vacuum residues of three different kinds of crude oils (Khafji, Maya, and Iranian-Light), the energy-minimum conformation calculated by molecular mechanics-dynamics simulations showed that aggregated structures of asphaltene molecules through noncovalent interactions are the most stable conformation. Changes of aggregated structures by heating or solvent treatment were investigated by using the molecular dynamics calculation. For Khafji and Iranian-Light asphaltenes, the simulation showed that the aggregated structure was dissociated at 673K, while for Maya asphaltene the dissociation behavior was not observed, showing that Maya asphaltene seems difficult to be dissociated by heating, compared to other asphaltenes. In contrast, the simulation of relaxation of the Maya aggregates in quinoline showed that at 573K a part of aggregates was dissociated more easily than Khafji and Iranian-Light asphaltenes. These results above suggest that the effects of heating and solvent treatment on the structural relaxation of asphaltene aggregates can be different.     

Estimation of the Surface Tension of a Pure Liquid

Abstract

Pure component method for surface tension estimation is presented as is a method based upon critical properties and molecular weight of pure components. This method is judged most accurate when estimated values are compared with experimental determinations. The purposed correlation is valid for polar and nonpolar components with an acceptable percent error.     

Estimation of the Surface Tension of a Pure Liquid

Pure component method for surface tension estimation is presented as is a method based upon critical properties and molecular weight of pure components. This method is judged most accurate when estimated values are compared with experimental determinations. The purposed correlation is valid for polar and nonpolar components with an acceptable percent error.     

Molecular Weight Measurement of UG8 Asphaltene Using APCI Mass Spectroscopy

Abstract

Asphaltene molecular weight has been a controversial issue in the past several decades and continues on nowadays. From industrial application point of view, asphaltene molecular weight is important for setting up a heavy oil refining strategy so that the process is efficient and economically viable. If the measured average molecular weight of asphaltene is high and is the true molecular weight, then substantial amount of energy will be needed, in order to break the molecule into light products during refining process. This is likely not an economical option. On the other, if the measured high molecular weight is due to self-association and the true molecular weight is low (e.g., less than 1500 Da), it will be energetically attractive to refiners to develop heavy oil cracking technology. Vapor pressure osmometry (VPO) has been routinely used for measuring molecular weight. However, it measures the apparent molecular weight and is likely not the true molecular weight. In order to unambiguously measure the molecular weight, it is necessary to develop a convincing technology and a reliable experimental procedure that allows one to measure the molecular weight accurately and consistently. We chose the Atmospheric Pressure Chemical Ionization (APCI) technique and Atmospheric Pressure Photo Ionization (APPI) to measure UG8 asphaltene. Both APCI and APPI have mild ionization processes and have been applied to many unstable drug compounds such as proteins and peptides with reliable outcomes. In addition, we measured the sample on two APPI instruments to compare the results. We also demonstrated how one can choose wrong set of operating parameters and lead to erroneous results. The relevant parameters for APCI and APPI are temperature, voltage, and sample concentration. We chose 0.01 mg/mL as the concentration, much below any known critical aggregation concentration. As for temperature and ionization voltage, we varied systematically varied (T = 300–600°C; V = 30–150 V) in order to demonstrate the consistency of the methods and how one can easily make mistake. Through these measurements, an average molecular weight of 400 to 900 Da was obtained for UG8 asphaltene.     

Molecular Weight Measurement of UG8 Asphaltene Using APCI Mass Spectroscopy

Asphaltene molecular weight has been a controversial issue in the past several decades and continues on nowadays. From industrial application point of view, asphaltene molecular weight is important for setting up a heavy oil refining strategy so that the process is efficient and economically viable. If the measured average molecular weight of asphaltene is high and is the true molecular weight, then substantial amount of energy will be needed, in order to break the molecule into light products during refining process. This is likely not an economical option. On the other, if the measured high molecular weight is due to self-association and the true molecular weight is low (e.g., less than 1500 Da), it will be energetically attractive to refiners to develop heavy oil cracking technology. Vapor pressure osmometry (VPO) has been routinely used for measuring molecular weight. However, it measures the apparent molecular weight and is likely not the true molecular weight. In order to unambiguously measure the molecular weight, it is necessary to develop a convincing technology and a reliable experimental procedure that allows one to measure the molecular weight accurately and consistently. We chose the Atmospheric Pressure Chemical Ionization (APCI) technique and Atmospheric Pressure Photo Ionization (APPI) to measure UG8 asphaltene. Both APCI and APPI have mild ionization processes and have been applied to many unstable drug compounds such as proteins and peptides with reliable outcomes. In addition, we measured the sample on two APPI instruments to compare the results. We also demonstrated how one can choose wrong set of operating parameters and lead to erroneous results. The relevant parameters for APCI and APPI are temperature, voltage, and sample concentration. We chose 0.01 mg/mL as the concentration, much below any known critical aggregation concentration. As for temperature and ionization voltage, we varied systematically varied (T = 300-600°C; V = 30-150 V) in order to demonstrate the consistency of the methods and how one can easily make mistake. Through these measurements, an average molecular weight of 400 to 900 Da was obtained for UG8 asphaltene.     

凝胶色谱法测定7000F平均分子量及分子量分布

根据７０００Ｆ在凝胶色谱柱上的淋洗特点,确定了测定其分子量及分子量分布试验条件,采用示差和粘度双检测凝色谱系统,利用谱适校正方法,不需要Ｍａｒｋ常数Ｋ、α值,可直接测定数均分子量,重均分子量,粘均分子量并给出分子量分布曲线。     

Surface Tension Estimation of Binary System of Several Organic Liquids

Abstract

One of the most striking demonstrations of the intermolecular forces is the tension at the surface of a liquid. Recently, a new expression for the surface tension prediction of a binary liquid system. Using the proposed equation, surface tensions are predicted within an overall 2.5 AAD%, which is better than the other available prediction methods.     

沥青组分和分子量分布规律

根据冲洗溶剂的量和极性直接将沥青分成不同的组分，详细考察了沥青组分分布情况，并用VPO法测定了各组分的分子量，考察了沥青组分中分子量的分布规律。沥青组分分布及分子量分布规律的研究，对于深入了解沥青的粘附性能具有重要意义。     

丁基橡胶相对分子质量分布的影响因素研究

以二氯金刚烷为引发剂,烷基氯化铝为共引发剂,在低温-100～-90℃条件下进行了丁基橡胶的淤浆聚合研究,探讨了共引发剂酸性及浓度,链转移剂和链终止剂等对丁基橡胶的产率、相对分子质量及其分布的影响情况.研究结果表明,共引发剂的酸性增强,不仅有利于提高产率,也有利于加宽产物的相对分子质量分布。当以二氯乙基铝(EADC)为共引发剂时,通过改变EADC的浓度,可以调整产物中高相对分子质量级分和较低相对分子质量级分含量的变化,提高EADC浓度有利于增加高相对分子质量级分的相对分子质量和含量,而降低EADC浓度有利于增加低相对分子质量级分的含量,从而可以在一定范围内调整产物的相对分子质量及其分布。在丁基橡胶聚合体系中,外加微量链转移剂或链终止剂对产物相对分子质量分布没有明显的调节作用,但即使是极微量的链终止剂,也会导致单体转化率大幅度下降,不利于反应。     

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.     

利用表面张力过渡工艺提高管道焊接的根焊质量

本文介绍一种用于管道根焊的新工艺。与其他工艺相比，表面张力过渡工艺（STT）不仅可以获得极好的根焊质量，而且具有相当的焊接速度，对焊工也无更高的操作技巧要求。STT是一种类似于短路过渡或短弧过渡的新过渡方式，其重要的特点是焊接电流与送丝速度无关，因此可以更好地控制热量输入而得到合适的熔深，并消除普通工艺可能产生的冷搭接现象，同时使焊接飞溅减少了90％、烟尘减少了50％～70％。     

RI/VI联用测定聚乙烯相对分子质量及其分布

150℃测试温度下，以1，2，4-三氯苯为溶剂，采用示差折光指数器，毛细管黏度计双检测器联用凝胶渗透色谱技术测定了聚乙烯的相对分子质量及其分布。与常规凝胶渗透色谱法对比，该方法不仅能直接得到聚乙烯较精确的相对分子质量和分布形态，同时可以得到聚乙烯的特性黏数分布。     

Molecular Weight Determination of Asphaltenes from Colombian Crudes by Size Exclusion Chromatography (SEC) and Vapor Pressure Osmometry (VPO)

Abstract

Characterization of Colombian asphaltenes isolated from feedstocks to refining units was carried out during this study, emphasizing the determination of their average molecular weights (MW). Experimental conditions used for vapor pressure osmometry (VPO) and size exclusion chromatography (SEC) were investigated aiming to select the most suitable set up that affords the best representative values. SEC was observed to provide the most reasonable MW values, after analysis improvements were achieved by using realistic calibration curves got with phthalocyanines, compounds that closely mimic component structures within oil and asphaltenes fractions. MWs displayed by Colombian vacuum residua asphaltenes fall within the range 1,700 ± 200 Daltons, reported previously for asphaltenes from different reservoirs worldwide.     

高分子量和窄分布聚醚多元醇的合成

介绍了高活性多组分双金属氰化物（ＤＭＣ）络合催化剂的制备及主／助催化剂体系的确立。用低分子聚和起始剂,合成出高性能的二官能团聚醚和三官能团聚醚。研究了环氧化物进料速率、聚合反应温度、乙氧基封端和粗醚精制等对产物性能的影响。     

聚碳酸酯的分子量分布与热降解

除了用Ｍｗ，Ｍｎ和Ｍｗ／Ｍｎ表征聚碳酸酯（ＰＣ）分子量大小和分布宽度外，还采用了（Ｍｐ－Ｍ１０）和（Ｍ９０－Ｍｐ）来表征低分子量和高分子量尾端所延伸的宽度，并以两尾端的起始分子量作为参考参数。其中Ｍｐ为分子量微分分布曲线峰位分子量，而Ｍ１０和Ｍ９０则为累积分布曲线中１０％和９０％处的分子量。研究了这些参数与聚碳酸酯热降解的关系，发现除数均分子量外，高低分子量尾端部分与ＰＣ热稳定性关系密切，尤其是低分子量尾端分布状态和起始分子量大小，对ＰＣ热稳定性更为敏感。这与ＰＣ端ＯＨ基相对浓度同ＰＣ热降解率的关系相一致。     

提高聚丙烯酰胺（PAM）相对分子质量和溶解性的措施

讨论了聚合体系中单体含量、引发主有关杂质等对提高PAM相对分子质量的影响,并从聚合添加剂、干燥添加剂、溶解添加剂的应用角度,综述了提高PAM产品溶解速率的方法。     

Characterization of Functional Groups of Asphaltenes in Vacuum Residues Using Molecular Modelling and FTIR Techniques

Asphaltenes are components of crude oil, and their average chemical structures are characterized with difficulty. This study shows that simple Fourier transform infrared (FTIR) analysis spectroscopy could be adapted to the determination of aromatic hydrogens in asphaltenes and resins and elucidation of their average molecules. The work demonstrates the existence of a linear correlation in the infrared (IR) intensities of the symmetric and asymmetric aromatic hydrogens in methyl substituted arenes, in the 2,900 to 3,100 cm^-1 region and of the out-of-plane deformation in the 700 to 900 cm^-1 region.     

丁苯乳液聚合中配方和聚合条件对分子量及分子量分布的影响

讨论了高转化率丁苯乳液聚合中，叔十二碳硫醇（ＴＤＭ）的用量和加入方式、聚合温度、引发剂用量等对共聚物分子量及分子量分布的影响，对单体转化率、门尼粘度、物件与分子量和分子量分布的关系也作了研究。