Precipitation, fractionation and characterization of asphaltenes from heavy and light crude oils

Asphaltenes of Maya and Isthmus crude oils were precipitated, fractionated and characterized in this work. Isolation of asphaltenes was performed by following the ASTM D3279 method, which uses n-heptane for solvent precipitation. Asphaltenes were separated into three fractions by Soxhlet extraction with a binary solvent system of toluene and n-heptane. C, H, O, N, S, and Ni and V contents were determined in asphaltenes and in their fractions by elemental analysis and atomic absorption, respectively. VPO aggregate weight and NMR measurements were also performed in all samples. Important differences in properties of unfractionated asphaltenes and asphaltenes fractions were observed. Some of these differences were attributed to impurities in the unfractionated asphaltenes.     

The zeta potential and surface properties of asphaltenes obtained with different crude oil/n-heptane proportions

We have investigated some surface properties of asphaltenes precipitated from crude oil with different volumes of n-heptane. According to the crude oil/n-heptane proportions used, asphaltenes are identified as 1:5, 1:15 and 1:40. Zeta potential results indicate that the amount of n-heptane determines the electrokintetic behaviour of asphaltenes in aqueous suspensions. Asphaltene 1:5 exhibits an isoelectric point (IEP) at pH 4.5 whereas asphaltenes 1:15 and 1:40 show an IEP at about pH 3. Surface charge on asphaltenes arises from the dissociation of acid functionalities and the protonation of basic functional groups. The presence of resins remaining on the asphaltene molecules may be responsible for the different IEP of asphaltene 1:5. Both sodium dodecyl sulfate (an anionic surfactant) and cetylpyridinium chloride (a cationic surfactant) were found to adsorb specifically onto asphaltenes. They reverse the sign of the zeta potential under certain conditions. These surfactants may be potential candidates to aid in controlling the stability of crude oil dispersions. Critical micelle concentration, interfacial tension measurements, and Langmuir isotherms at the air-water interface confirm the different nature of asphaltene 1:5, which also showed more solubility and a larger molecular size.     

Molecular size of asphaltene fractions obtained from residuum hydrotreatment

Previously, fluorescence depolarization techniques (FD) have been shown to measure asphaltene molecular size, thereby establishing the substantial difference between asphaltenes derived from crude oil vs from coal. Here, FD is used to track the changes of the asphaltenes from a petroleum atmospheric resid feedstock that has been subjected to increasing thermal severity of catalytic hydrothermal cracking. Changes in asphaltene properties with increasing cracking are readily observed and understood. In addition, asphaltene molecular size is measured for various asphaltene solubility fractions in binary solvent mixtures of toluene with either n-heptane or acetone; a strong dependence is found of asphaltene properties on the particular solvent mixtures in accord with recent publications.     

Deasphaltization and demetalling of heavy crude oils and distillation residues with CO2

Deasphaltization of heavy crude oils and distillation residues may reduce the metal content of these oils to such an extend that the upgrading of deasphaltized oil in a catalytic process becomes economically feasible. Experimental results of deasphaltization of Boscan crude from Venezuela, using subcritical and supercritical carbon dioxide as deasphaltizing agent, are presented. Deasphaltization and demetalling with CO₂ in the supercritical state is more effective. Under favorable conditions, the deasphaltized oil contains practically no asphaltenes and the metal content is reduced by 690 wt-%. The influence of n-heptane or n-pentane addition to the crude, which lowers viscosity and promotes flocculation, is also discussed. Furthermore, a multistage deasphaltization process is more efficient than a single stage process.     

Reactions of Athabasca asphaltenes and heavy oil with metal chlorides

The interactions of Athabasca asphaltenes and heavy oil with metal chlorides are described. The asphaltenes are converted to insoluble, presumably higher molecular weight, products which contain substantial amounts of chemically bound chlorine. The heavy oils were converted partly into insoluble products; both this fraction and residue oils contained chemically bound chlorine. Statistical structure analysis aided by infra-red spectrographic and nuclear magnetic resonance examination of the soluble portion of the reacted heavy oils suggests that inter- and intramolecular condensation by dehydrogenation and dealkylation accompany chlorination.     

Heavy crude oil asphaltenes as a nanofiller for epoxy resin

Asphaltenes are harmful components of heavy crude oils and require rational utilization after oil refining or deasphalting. Asphaltenes are macromolecules containing various functional groups that self-assemble to nanoscale aggregates and can be used as nanofillers for polymers. In this research, mixtures of asphaltenes with the diglycidyl ether of bisphenol A were considered. The solubility of asphaltenes in this epoxy resin, the rheological properties of the mixtures, and the effect of asphaltenes on the curing with 4,4′-diaminodiphenyl sulfone were studied. In addition, the glass transition temperature, strength, and adhesion characteristics of the asphaltene-filled cured composites were evaluated. The dual role of asphaltenes in polymer modification was demonstrated: the asphaltenes simultaneously plasticize and reinforce the polymer matrix, and the transition from predominant plasticization to strengthening occurs with an asphaltene content at 20 wt%. The dual reinforcement/plasticization effect occurs because epoxy composites contain both nanosized and microsized particles of asphaltenes due to the partial dissolution of asphaltenes in the epoxy resin and the decrease in their solubility during high-temperature curing.     

Characterization of Doba-Chad heavy crude oil in relation with the feasibility of pipeline transportation

A heavy crude oil was characterized in view of the recent commercial exploitation of Doba oilfield in landlocked Chad from where the crude oil is extracted and expected to be routed to the Atlantic shore through pipeline transportation. The elemental composition of Doba feedstocks is 86.25% C, 12.10% H, 0.25% N, 0.14% S and 1.16% O. Atmospheric distillation indicated an initial boiling point at 85 °C, a 10 vol% fraction distilling before 250 °C and an onset of crude thermal cracking at 300 °C. Crude API gravity is 18.8° API, corresponding to a specific gravity of 0.94 at 15.6 °C. The Doba crude oil was found to exhibit non-elastic purely viscous Newtonian behavior over the temperature range typical of crude transportation by pipeline. The crude was fractionated into 97.4% maltenes (n-pentane solubles), 1.8% asphaltenes (n-pentane insolubles), and 0.1% toluene insolubles. The maltenes were subsequently split into four sub-fractions: 45.0±1.2% saturates (MF1), 11.0±0.3% mono and diaromatics (MF2), 26.8±1.2% polyaromatics (MF3), and 12.8±0.8% polars (MF4). FT-IR characterization and proton nuclear magnetic resonance identification of the maltenic and asphaltenic fractions provided evidence of the chemical nature of the different fractions. The high values of the kinematic viscosity of crude oil (184.4cSt at 50 °C) and deasphalted crude oil (152.4cSt at 50 °C) suggest that partially upgrading the oil would be necessary to comply with the viscosity specifications recommended for crude transportation by pipeline.     

Effect of heavy asphaltene on stability of residual oil

An asphaltene fractionation method was developed in order to investigate the effect of heptane (n-C7) insoluble asphaltene (C7-asphaltene) on residual oil stability. C7-asphaltene was separated into heavy and light fractions by a new method using a binary solvent system of toluene and heptane (n-C7). It was found that the heavy fraction of C7-asphaltene in residual oil, extracted by this method, consisted of highly condensed polynuclear aromatics. Our new fractionation method and the Heithaus stability evaluation method were applied to hydroprocessed residual oils. The peptizability of heavy fraction of C7-asphaltene defined by the Heithaus method decreased in accordance with structural condensation of that fraction. On the other hand, light fraction of C7-asphaltene was considered to influence the peptizing power. We proposed a new conceptual model: light asphaltenes would perform as peptizing material as well as resin, and heavy asphaltene would be peptized in oil. This model introduced from our new asphaltene fractionation method could be more effective for understanding the destabilization phenomenon of residual oil.     

Effects of asphaltene content on the heavy oil viscosity at different temperatures

Asphaltene content plays an important role in determining the high viscosity of heavy oil. This paper presents an experimental and theoretical study of the specific effects of asphaltene content on the heavy oil viscosity at different temperatures. In the experiment, a deasphalted heavy oil is obtained by using a standard ASTM method to precipitate asphaltenes from a crude heavy oil. Then eleven reconstituted heavy oil samples are prepared by adding the precipitated asphaltenes into the deasphalted heavy oil at a different asphaltene content each time. The viscosities of such reconstituted heavy oil samples with different asphaltene contents are measured at six different constant temperatures by using a cone-plate viscometer. Theoretically, two viscosity models for a colloidal dispersion system are applied to find the best fit to the experimental data by using non-linear regression. The following four important parameters are thus determined to characterize the reconstituted heavy oil samples: the solvation constant, shape factor, intrinsic viscosity, and maximum packing volume fraction. The detailed non-linear regression results show that the state of asphaltene particles in the heavy oil changes with the asphaltene content and temperature and that this state change strongly affects the heavy oil viscosity.     

油砂沥青质对油砂沥青中甲苯残留的影响

利用热重质谱联用仪（TG-MS）分析了三种油砂沥青（印尼油砂沥青、伊朗油砂沥青、加拿大油砂沥青）中的甲苯残留以及油砂沥青质含量对油砂沥青中甲苯残留的影响,并在此基础上,进一步研究了油砂沥青质中的甲苯残留。结果发现,不同油砂沥青中甲苯残留量存在一定差异,其中印尼油砂沥青中的甲苯残留量最多。进一步对沥青质质量分数分别为10%、19%、30%的油砂沥青样品进行热重质谱实验,发现随着油砂沥青中沥青质含量的增加,甲苯的残留量会成倍增加。以加拿大油砂沥青质为例,研究了油砂沥青质对溶剂残留的影响,发现油砂沥青质具有对甲苯分子的夹带能力,导致甲苯分子在超过自身沸点40℃以上才能从沥青质中分离出来。油砂沥青中其他组分的存在也会加剧沥青质对甲苯的夹带作用。此外,研究还发现,在350~650℃时,油砂沥青质可以热解产生甲苯,而且油砂沥青中的沥青质含量越高,热解生成的甲苯越多。     

Enhanced heavy oil recovery through interfacial instability: A study of chemical flooding for Brintnell heavy oil

This study is aimed at developing an alkaline/surfactant-enhanced oil recovery process for heavy oil reservoirs with oil viscosities ranging from 1000 to 10,000 mPa s, through the mechanism of interfacial instability. Instead of the oil viscosity being reduced, as in thermal and solvent/gas injection processes, oil is dispersed into and transported through the water phase to production wells.Extensive emulsification tests and oil/water interfacial tension measurements were conducted to screen alkali and surfactant for the oil and the brine samples collected from Brintnell reservoir. The heavy oil/water interfacial tension could be reduced to about 7 × 10⁻² dyn/cm with the addition of a mixture of Na₂CO₃ and NaOH in the formation brine without evident dynamic effect. The oil/water interfacial tension could be further reduced to 1 × 10⁻² dyn/cm when a very low surfactant concentration (0.005-0.03 wt%) was applied to the above alkaline solution. Emulsification tests showed that in situ self-dispersion of the heavy oil into the water phase occurred when a carefully designed chemical solution was applied.A series of 21 flood tests were conducted in sandpacks to evaluate the chemical formulas obtained from screening tests for the oil. Tertiary oil recoveries of about 22-23% IOIP (32-35% ROIP) were obtained for the tests using 0.6 wt% alkaline (weight ratio of Na₂CO₃ to NaOH = 2:1) and 0.045 wt% surfactant solution in the formation brine. The sandpack flood results obtained in this project showed that a synergistic enhancement among the chemicals did occur in the tertiary recovery process through the interfacial instability mechanism.     

分子水平重油生焦规律研究进展

阐述了重油缩合生焦规律分子水平的研究进展,主要从重油中四组分的分子组成与生焦的关系以及重油模型化合物生焦的研究两方面进行了概述。研究表明,对于重油各族组分来说:适量的饱和分有助于提升生焦质量;芳香分环数越多生焦越明显,生焦质量越差;中、重胶质和沥青质易生焦,生焦质量差;杂原子会降低生焦质量,但各个杂原子的危害程度不同。而对于各个重油模型化合物来说:甲苯极难发生热缩合反应;萘、菲、蒽、芘的热缩合反应难度逐渐降低;二甲基萘由于侧链的作用,生焦质量比萘要差;1,2,4,5-四甲基苯由于其特殊的空间构型较易缩合生焦且生焦质量很好;杂原子模型化合物单独生焦质量越差,则其在加入到芳烃中之后对体系的生焦质量危害越大。随着超高分辨质谱技术的发展,为更加细致深入研究芳烃热缩合反应生焦机理提供了可能。     

Reduced coke formation and aromaticity due to chloroperoxidase-catalyzed transformation of asphaltenes from Maya crude oil

The transformation of the porphyrin-free asphaltene fraction from a heavy Maya crude oil was catalyzed by chloroperoxidase from Caldariomyces fumago (CPO) in a ternary system with low water content of 6.3%. The total turnover number (TTN) in this system was determined for lyophilized CPO in the presence of sucrose as cryoprotector and for a covalent bioconjugate with chitosan. The covalent conjugation of CPO with chitosan increased the TTN by 10-fold. Fluorescence due to aromatic groups decreased by 24% in treated asphaltenes, indicating significant changes after the biotransformation. On the other hand, the solubility profile indicated that transformed asphaltenes are less soluble in toluene and more prone to precipitate in the presence of hexane, compared to untreated asphaltenes, which could be related to the introduction of polar atoms. Energy-dispersive X-ray spectroscopy (EDS) showed that the content of chlorine increased six-fold on an atomic basis. Finally, enzymatically transformed asphaltenes are more reactive and thus generate less coke, as evidenced by thermal degradation under nitrogen atmosphere.     

Preparation and evaluation of double-hydrophilic diblock copolymer as viscosity reducers for heavy oil

In this work, a series of double-hydrophilic diblock copolymers of N-acryloylmorpholine (NAMO) and N,N-dialkylacrylamide are prepared as the additives for viscosity reduction, which could effectively interact with the asphaltenes and resins. The viscosity reduction effects of the types of N,N-dialkylacrylamide monomer (N,N-dimethyl acrylamide & N,N-diethyl acrylamide) and degree of polymerization (DP) of poly(N,N-dialkylacrylamide) block in copolymers on heavy oil are tested with heavy oils with different viscosities. These viscosity reducers can work with small dosages (>25 mg L⁻¹). The interfacial tension between oil and water is significantly weakened, and the aggregating structures of asphaltenes and resins are disassembled into smaller aggregates and covered with polymers with the addition of copolymers. The re-establishment of aggregates among polar components seems to be prevented, and the stability of the heavy oil/water emulsions is greatly enhanced as a result. All these results provide the prerequisites for water-soluble diblock copolymers working as viscosity reducers for various heavy oils.     

Polycardanol's potential to deasphalt crude oil: Influence of polymer conversion degree,molar mass,and structure

Cardanol is a natural material that acts to stabilize asphaltenes in crude oil. However, its derivative, polycardanol, obtained via cationic polymerization, has divergent behaviour, with reports of its acting both as asphaltenes stabilizer and flocculant. Recently, it was demonstrated that the reaction conditions influence the conversion rates, structures, and molar masses of the products from synthesizing polycardanol initiated with BF₃ · O(C₂H₅)₂. Seeking to elucidate the influence of these variables on the phase behaviour of asphaltenes, in this work six products, previously synthesized and characterized, had their performance evaluated by asphaltenes precipitation onset, using n-heptane titration and monitoring by near-infrared spectroscopy, using asphaltenes model systems (C5I and C7I) at 1.00 wt./vol.% in toluene. All the products had the ability to flocculate asphaltenes and have potential for deasphalting process. Flocculation efficiency increased with rising molar mass, higher reaction conversion degree, and presence of lateral hydrocarbon chains. The most efficient structures were not affected by the presence of unreacted cardanol. This indicated that the reaction does not require a purification step. Aged cardanol was also able to produce flocculant polymer, indicating that the distillation of cardanol is not required. The cost to obtain a product without needing reagent distillation becomes lower.     

Fullerenic structures derived from oil asphaltenes

The handling and properties of heavy oils are becoming an increasingly important problem. Even though petroleum is the widest used source of fuels and it has been studied for decades, its complex nature is still an enigma in several ways. A reasonable approach to a definition of a crude oil is a colloidal fluid formed by several dispersed phases from gases (light hydrocarbons) to solids (heavy paraffins and asphaltenes). Through all these years of research, applications have been found for almost all classes of components in crude oil except for some of the solid phases such as asphaltenes. Very heavy petroleum is a non-newtonian liquid with a viscosity of ≈10⁶ Poise, and an average molecular weight of 600 amu. The solids that are toluene soluble but heptane insoluble are called asphaltenes and are the most aromatic fraction with the highest molecular weight of unconverted petroleum. In the present work, we applied high resolution transmission electron microscopy (HREM) and energy dispersive spectrometry (EDS) in the study of asphaltenes. It was found that when the asphaltenes are well separated from the resins the sample consists of a carbon structure containing S, V, Si, related to fullerenic carbon. During observation in the microscope it was possible to see the formation of fullerenes such as onions and C₂₄₀ @ C₆₀ structures. The fact that they decomposed under further irradiation suggests that they are metastable structures. Since the heteroatoms are still present they are likely to cause instability to the structure. Not only does our result indicate the possibility of obtaining fullerenes from crude oil but it also suggests the asphaltene molecule, when it is resin free, might be a precursor of fullerenic structures.     

Geochemical characterization of solid residues, bitumen and expelled oil based on steam pyrolysis experiments from Irati oil shale, Brazil: A preliminary study

Steam pyrolysis experiments were performed on immature samples from the Irati oil shale, Paraná Basin, Brazil, using a maximum temperature of 350 °C with up to 98 h exposure time at that temperature. The objectives were to study geochemical and petrographical changes in the source material during stepwise increase in maturity, in steam conditions, comparing the properties of expelled oil with the bitumen retained in the solid residue after experimentation.Petrographical and geochemical parameters such as vitrinite reflectance and T_max, indicated an increase in maturity related to the exposure time of the organic matter to the maximum temperature. However, biomarker ratios such as 22S/(22S + 22R) C₃₁ and C₃₂ homohopanes, 20S/(20S + 20R) and αββ/(αββ + ααα) C₂₉ sterane, which are considered to be indicators of organic matter maturity levels, did not reach their equilibrium values. Some biomarkers frequently used as indicators of specific sources and/or paleoenvironments of deposition such as hopane/sterane ratio, and the concentrations of C₂₇ and C₂₉ steranes showed significant variations related to the stage of maturity. Based on the evaluation of Rock-Eval parameters, the transformation ratios in steam pyrolysis conditions reached levels higher than 80% in samples having 9 and more hours of exposure time to maximum temperature. Bitumen was found to be enriched in components of heavier molecular weight (resins and asphaltenes), whereas the expelled oils contained higher quantities of aliphatic and aromatic components. At relatively low maturity levels the n-alkane distribution of expelled oils indicate a somewhat higher maturity level when compared to the n-alkane distribution of the bitumen retained in the source rock, whereas at higher maturity levels the n-alkane distribution for the expelled oil and for the bitumen is very similar.     

［(MoO2)(acac)2］/t-BuOOH/H3PO4催化氧化体系对稠油中重组分的降解作用

针对稠油的重组分，探讨了催化氧化稠油降解反应体系中稠油黏度、平均分子量随反应时间、催化剂及氧化降解体系的变化规律.研究了各种条件下油层矿物在反应中的作用.实验结果表明，［(MoO₂)(acac)₂］催化剂对稠油的氧化降黏是非常有效的，其催化降解反应与氧化剂、氢质子供体以及油层矿物有关.在［(MoO₂)(acac)₂］/t-BuOOH/H₃PO₄/油层矿物体系中，稠油沥青质降解率达到81%，稠油黏度由原始的117.2 Pa·s下降到55.8 Pa·s，下降率为52.4%，平均相对分子质量下降了100.TLC-FID分析证明，稠油中的沥青质减少主要生成胶质、芳烃和饱和烃，这种理化性质的改变促进了稠油体系的稳定，对稠油开采、运输以及后处理工艺将起到推动作用.     

On-column precipitation and re-dissolution of asphaltenes in petroleum residua

A new automated separation technique was developed for measuring the distribution profiles of the most polar, or asphaltenic components of an oil, using a continuous flow system to precipitate and re-dissolve asphaltenes. Methods of analysis based on this new technique were explored. One method based on the new technique involves precipitation of a portion of residua sample in heptane on a polytetrafluoroethylene-packed (PTFE) column. The precipitated material is re-dissolved in three steps using solvents of increasing polarity: cyclohexane, toluene, and methylene chloride. The amount of asphaltenes that dissolve in cyclohexane is a useful diagnostic of the thermal history of an oil, and its proximity to coke formation. For example, about 40% (w/w) of the heptane asphaltenes from unpyrolyzed residua dissolves in cyclohexane. As pyrolysis progresses, this number decrease to below 15% as coke and toluene-insoluble pre-coke materials appear. Currently, the procedure for the isolation of heptane asphaltenes and the determination of the amount of asphaltenes soluble in cyclohexane spans three days. The automated procedure takes one hour. Another method uses a single solvent, methylene chloride, to re-dissolve the material that precipitates in heptane on the PTFE-packed column. The area of this second peak can be used to calculate a value which correlates with gravimetric asphaltene content. Currently the gravimetric procedure to determine asphaltenes takes about 24 h. The automated procedure takes 30 min. Results for four series of original and pyrolyzed residua were compared with data from the gravimetric methods. Methods based on the new on-column precipitation and re-dissolution technique provide significantly more detail about the polar constituents oils than the gravimetric determination of asphaltenes.     

沥青质/胶质影响稠油乳状液稳定性的研究

对稠油乳状液的稳定性进行了研究,研究发现,沥青质和胶质作为天然的乳化剂,对稠油乳状液的稳定性有较大的影响,沥青质的分散性是影响乳状液油水界面膜强度的重要因素,胶质是沥青质的良溶剂,和沥青质具有强的协同作用,同时发现在稠油中添加溶解剂对沥青质的分散性有较大的改善,从而增强了稠油乳状液的稳定性。研究认为,胶质含量为4%,沥青质含量为0.5%的情况下,乳状液稳定性较好,并且随着两者的大量增加或者减少,都不利于稠油乳状液的稳定性。