热改质过程中渣油结构及其重组分溶剂化变化规律研究

以委内瑞拉减压渣油为原料,采用微型反应釜,研究了其在410℃、2.0 MPa氮气初压下,不同反应停留时间的热改质过程生成油的化学结构组成及其重组分溶剂化变化规律。通过1H-NM R技术研究了热改质过程生成油中沥青质和重胶质不同化学位移归属氢的转化路径;并结合改进的Brown-Ladner法分析了热改质过程生成油中沥青质和重胶质的平均分子结构参数变化;采用蒸汽压渗透法考察了热改质过程生成油中沥青质和重胶质在甲苯溶液中所形成的复合超分子结构的平均相对分子质量。结果表明,随着热改质程度的加深,沥青质和重胶质的H/C原子比减小,供氢能力逐渐下降,沥青质和重胶质的芳香环共轭程度和fA在体系生焦后(45 min)显著提高;沥青质的聚集趋势相关值在热改质15 min前变化不大,15 min后显著增强,而重胶质在整个热改质过程中,其聚集趋势相关值的增势较为缓和;沥青质和重胶质的聚集趋势相关值差异逐渐增大,15 min时增加了1.5%、25 min时增加了50.8%、45 min时增加了142.3%,表明沥青质和重胶质的结构差异越来越明显;重胶质溶剂化沥青质的能力逐步减弱,体系的溶剂化参数从0时的32.9%逐步降到15 min时的29.5%、25 min时的14.1%和45 min时的9.6%;热改质生成油的斑点实验等级逐渐增加,体系的胶体稳定性逐渐降低。     

Plasmachemical Modification of Asphaltenes and How It Influences Their Aggregation Behavior

The properties of asphaltenes have been changed by modification in water plasma. The polarity of the asphaltenes was found to increase with plasma treament times up to 10 minutes. At longer treatment times the polarity decreases again. Nevertheless, aggregation studies showed earlier onset of precipitation for asphaltenes with longest plasma exposure time.     

On the determination of molecular weight distributions of asphaltenes and their aggregates in laser desorption ionization experiments

Molecular weight distributions (MWD) of asphaltenes and their aggregates have been investigated in laser desorption ionization (LDI) mass spectrometric experiments. A systematic investigation of the dependence of the measured MWD on the asphaltene sample density and on the laser pulse energy allows the assignment of most probable molecular weights within 300-500 amu and average molecular weights of 800-1000 amu for the monomeric asphaltenes, as well as for the estimation of the contribution from asphaltene clusters in typical LDI measurements. The results serve to reconcile the existing controversy between earlier mass spectrometric characterizations of asphaltenes based on laser desorption techniques by different groups. Furthermore, the MWD measurements performed on particularly dense samples yield an additional differentiated broad band peaking around 9000-10,000 amu and extending over 20,000 amu, not observed previously in LDI experiments, thereby revealing a strong propensity of the asphaltenes to form clusters with specific aggregation numbers, which is in qualitative agreement with previous theoretical predictions and with the interpretation of measurements performed with other techniques.     

Limitations and Applicability of the Interfacial Shear Rheology in the Study of Monolayer Films at the Air-Water Interface

This article studies the applicability of a new technique in determining the interfacial shear rheology properties of surface active compounds relevant to the petroleum industry. It presents the theory behind the determination of the rheological parameters and the results of tests performed on a set of petroleum related compounds (asphaltenes, tetra-acid model compound, fatty acid, and surfactant). It is concluded that this technique is not mature enough to determine the properties of the studied compounds.     

Thermal Conversion of Heavy Oil Systems and Analysis of Structural Changes of their High Components with PMR Method

Heavy oil systems are thermolyzed with different ratios of amount of resins and asphaltenes: 3.4, 3.8, 5.3, and 12.4. The change in yield and composition of gaseous, liquid and solid products of thermolysis is shown depending on the ratio of the resin: asphaltenes. In the liquid products of thermolysis, resins content decreases and s the amount of asphaltenes and oils increases. According to PMR spectroscopy, the distribution of protons is compared in the secondary resin and asphaltene molecules of the initial samples and the thermolysis products. It is shown that the relative content of hydrogen aromatic rings in the molecules of asphaltenes is higher, and for β- and γ- positions relative to the aromatic rings and heterofunction, it is lower than in the resin molecules.     

Experimental Investigation of Asphaltenes Flocculation Threshold in Crude Oils Using Different Methods: Comparative Study

Despite some recent progress trustworthy methods to predict the flocculation onset in crude oils are still needed. In this article, different experimental methods, like the density measurement method, the optical and the spot techniques based on the mixture of crude oil + toluene or cyclohexane + n-heptane, respectively, are applied to assess changes of aggregation occurring in crude oil under influence of physical and chemical factors as well as under variable temperature conditions. The solubility parameters of Hildebrand have also been used to predict the flocculation threshold. It turned out that the findings achieved by the spot method and the optical technique are in excellent agreement with break points of the reduced density curves obtained by the density measurement method for crude oils of different geographical origins. Using the solubility parameters of Hildebrand leads to comparable results. All these achievements confirm the density measurement method as a new possibility for reliably determining the flocculation onset in crude oils systems. With respect to temperature effects, changes of the oil microstructure could be detected as function of the temperature by means of the differential scanning calorimetry. In particular the thermal curves behavior of certain crude oils confirmed the existence of aggregation processes.      

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.     

Solvent desorption of asphaltenes from solid surfaces

The main goal of this paper is to compare the ability of different organic solvents to desorb asphaltenes from stainless steel surfaces. The asphaltenes were extracted from a North Sea crude oil by precipitation. The organic solvents are characterized based on their Hansen solubility parameters (HSPs). The adsorption of asphaltenes was followed by means of a Quartz Crystal Microbalance with Dissipation (QCM-D). The asphaltene desorption efficiency of the solvents tested varied between 20% and 70%, with pyridine as the most efficient solvent. Carbon disulfide was found to be a poor desorption solvent, indicating the importance of solvent polarity. A simple model based on the HSPs seemed to give a good quantitative explanation of experimental desorption experiments.     

Effect of Surfactant on the Growth of Onset Aggregation of Some Egyptian Crude Oils

This work pertains to study the asphaltenes aggregates' settling behavior of crude oil in absence and presence of oil‐soluble surfactants including long‐chain fatty acid in the form of amidation and estrification. First, the onset points as a function of light absorbed asphaltenes aggregates were quantified before and after adding asphaltenes dispersants using ultra violet spectroscopy, and the photograph fractal‐like aggregate structures were quantified using Carl Zeiss Trinocular microscope. Second the shear rates against shear stress induced aggregation were also measured in absence and presence of different concentrations of asphaltenes dispersants using Brookfield digital rheometer model LVDV‐III⁺. The results reviled that the asphaltenes aggregates are found to depend on toluene–heptane ratios. In absence of dispersant the accumulated and aggregates clusters of asphaltenes are formed at heptane: toluene ratio of 50∶50. Whereas, in the presence of dispersant the asphaltenes are solvated at heptane: toluene ratio of 60∶40, followed by appearance of stronger and dots aggregates clusters at a ratio of 70∶30, and finally, a larger aggregates growing at heptane: toluene ratio of 80∶20. The dispersant solvates the asphaltenes and maintains them in solution, while their surface activity remains high. This means that the dispersant apparently functioned well in decreasing the degree of flocculation and precipitation beyond the critical micelle concentration (CMC) of asphaltenes at 0.0027 g/L. Also, the reduction in the viscosity in presence of dispersant suggests that the asphaltenes aggregates are highly porous and very fragile.     

钼(VI)配合物催化氧化降解沥青砂中重组分过程研究

针对沥青砂的重组分,探讨了催化氧化沥青砂降解反应体系有机相和残余相中有机物的量随反应时间、催化剂及氧化降解体系的变化规律。结果表明,钼（VI）配合物［(MoO2)(C5H7O2)2］催化剂对沥青砂的氧化降解是非常有效的,催化降解反应与氧化剂、氢质子供体有关。在［(MoO2)( C5H7O2)2］/t-BuOOH/H3PO4体系中,沥青砂有机相中沥青质转化率为10.7%,残余相中沥青质转化率为20%。TLC-FID分析证明,沥青砂中沥青质的减少主要生成胶质和饱和烃,降解产物的得率为11.7%。