沥青质和胶质对乳状液稳定性的影响

利用光学显微镜-摄像-录像-计算机图象处理系统研究了大庆原油的沥青质和胶质对乳状液稳定性的影响.结果证实,原油乳状液的稳定性与沥青质和胶质浓度有关,沥青质和胶质的分散状态是决定界面膜强度或刚性进而决定乳状液稳定性的关键.当沥青质浓度在0.3%～0.5%（质量分数）,胶质浓度在1%～2%（质量分数）范围时,乳状液水珠聚并的比例随表面活性物质浓度的增加而降低;当沥青质浓度增大到0.7%（质量分数）,胶质浓度增大到3%（质量分数）后,聚并水珠的比例随表面活性物质浓度的增加而增加,形成的乳状液的液滴数量也减少.     

Distribution of polyalkyl-substituted C<Subscript>14</Subscript>-C<Subscript>16</Subscript> bicyclo[4.4.0]decanes (Sesquiterpanes) in the thermolysis products of tars and asphaltenes from petroleum of different genotypes

The mild thermolysis of resins and asphaltenes from petroleum of different genotypes was performed. It was found that the same C₁₄-C₁₆ polyalkyl-substituted bicyclo[4.4.0]decanes were formed as a result of the thermolysis of resins and asphaltenes. The relative concentration of the thermodynamically more stable isomer 2,3,3,7,7-pentamethylbicylo[4.4.0]decane in the thermolysis products of resins was higher than that in the thermolysis products of asphaltenes and close to equilibrium concentrations. Simultaneously, the amount of the thermodynamically less stable isomer 1,2,3,7,7-pentamethylbicylo[4.4.0]decane generated in the thermolysis products of asphaltenes was greater than that in the thermolysis products of resins, and its relative concentration was far from equilibrium concentrations. The degree of the maturity of organic matter, which was evaluated based on the relative thermodynamic stability of C₁₅ sesquiterpanes in the thermolysis products of resins and asphaltenes, increased in the order asphaltenes-resins-petroleum.     

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。     

pH值对原油乳状液稳定性的影响

研究了pH值对原油乳状液稳定性的影响, 测定了胶质和沥青质在油水界面上的聚集和铺张情况, 不同pH值下油水界面张力以及胶质和沥青质模拟乳状液的稳定性变化, 并且完成了不同pH值下的乳状液化学破乳以及电场破乳实验。沥青质相对胶质更易在界面上聚集和铺展, 形成高黏弹性的界面膜。pH值为酸性或碱性时都能有效降低油水界面张力, 增加乳状液稳定性, 使其化学破乳脱水困难, 而破乳实验也验证了这一观点。随着pH值从2增加到10, 胶质模拟乳状液和沥青质模拟乳状液稳定性变化大, 变化趋势则刚好相反, 胶质模拟乳状液稳定性增加, 油水分离速度减慢;沥青质模拟乳状液稳定性减弱, 体系电导率0.21～1.8mS/cm。因此pH<7时, 沥青质稳定能力强, 而胶质稳定能力弱, 电脱水过程中电脱装置正常工作;pH>7时, 结果相反, 表明电脱装置短路现象与沥青质、胶质稳定能力变化相关。     

Effect of Resins on Asphaltene Self‐Association and Solubility

In previous studies, asphaltenes and resins have been treated as two distinct fractions of a crude oil. The asphaltenes were assumed to be the only self‐associating fraction. However, there is evidence that resins also participate in this self‐association. In this study, molar masses of mixtures of asphaltenes and resins were measured with vapour pressure osmometry. Precipitation from the same mixtures dispersed in solutions of toluene and pentane were also measured. The data were modelled with previously developed self‐association and precipitation models. Model results with asphaltenes and resins characterized as a single distribution and as individual components are compared. The data and the modelling suggest that asphaltenes and resins are better characterized as a single distribution of self‐associating components.     

Asphaltenes and resins from the Orinoco basin

Elemental analyses, molecular weights (by vapour pressure osmometry and gel permeation chromatography), ¹³C and ¹H nuclear magnetic resonance precipitation and interfacial studies are reported for asphaltenes and resins from crude oils from the Orinoco basin. No major structural differences were found between coprecipitated resins and those remaining in the maltenes. The high number average molecular weights (⁻M_n) of asphaltenes (by v.p.o.) in benzene, 15000-7500, were reduced to ≈2000 after methylation or when measured in pyridine. The results from structural studies indicate the presence of a large number of aliphatic rings in the asphaltenes.     

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.     

Asphaltenes as a tackifier for hot-melt adhesives based on the styrene-isoprene-styrene block copolymer

The use of heavy crude oil asphaltenes and resins (termed asphaltenes) as the components of hot-melt adhesives based on the styrene-isoprene triblock copolymer was considered. The rheological, thermophysical, strength, and adhesive characteristics of the mixtures containing from 10 to 40 wt% of asphaltenes were studied. The addition of 10 to 20 wt% of asphaltenes enhanced the strength and adhesive properties of the mixtures and only slightly changed their rheology. The higher concentrations of asphaltenes reduced the viscosity of the mixtures but did not lead to improved characteristics of the adhesives. The ambiguous effect of asphaltenes is probably due to their uneven distribution between the microphases of the block copolymer as well as their ability to act both plasticizers and reinforcing particles depending on temperature. A comparison of asphaltenes and conventional tackifiers based on hydrocarbon resins revealed their comparable effect on the properties of the block copolymer.     

Permeability reduction by asphaltenes and resins deposition in porous media

The deposition of crude oil polar fractions such as asphaltenes and resins in oil reservoir rocks reduce considerably the rock permeability and the oil production. In the present work, a crude oil and various core samples were extracted from Rhourd–Nouss (RN) reservoir rock. Afterwards, core flow experiments were carried out in the laboratory to investigate permeability reduction that causes formation damage. The core permeability damage was evaluated by flooding Soltrol, through the sample and measuring the solvent permeabilities, K_i and K_f, respectively, before and after injection of a given pore volume number of the crude oil.The data indicate that upon flooding the crude oil through the porous medium, considerable permeability reduction, expressed as the ratio (K_i − K_f)/K_i, and ranging from 72.4% to 98.3% were observed. The permeability reduction is found to result from irreversible retention of asphaltenes and resins in the porous core sample. However, no correlations could be established between the depth of the well, the core porosity, the core mineral compositions determined by X-ray analysis, and the permeability damage factors. In addition, effluents flowing away from RN wells were collected and analysed at various periods, after carrying out aromatic solvents squeezes. The amount of saturates, aromatics, resins, and asphaltenes (SARA analysis), of the crude oil, the deposited crude oil fraction, and the effluent’s residues were measured and compared. The asphaltenes weight percent was found to increase from 1.56% for the crude oil to 11.42% for the deposited oil fraction, and was in the range 1.37–2.36% for the effluent’s residues. Such results indicate that the deposited oil fraction and the effluent’s residues consist mainly of asphaltenes and resins.     

Investigations on Romashkino asphaltic bitumen. 3. Fractionation of asphaltenes using ion-exchange chromatography

The fractionation of asphaltenes originally separated¹ from Romashkino asphaltic bitumen has been achieved by means of stepwise anion- and cation-exchange chromatography through macroreticular resins. The fractionation procedure and yields of the fractions are given. A detailed structural analysis has been made of original asphaltenes and their acid- and base-free fraction using elemental and densimetric analyses, gel-permeation chromatography and proton magnetic resonance spectroscopy. Inverse gas-liquid chromatography has also been used to detect the chemical functionality of the asphaltene fractions. Results are presented to show the effect of ion-exchange resins treatment upon the composition of asphaltenes, noting that molecular weight as well as chemical structure changes appreciably.     

Effect of styrene on properties of vinyl ester resins,I

The paper describes the effect of styrene on the properties of bis(methacryloxy) derivatives of epoxy resins (vinyl ester resins). The styrene concentration in the resin was systematically varied between 20–60 wt.-%. The curing characteristics of vinyl ester resins changed only marginally on dilution with styrene. Dilution with styrene resulted in a decrease in tensile modulus and increase in elongation of neat resin castings and glass fibre reinforced laminates. The glass transition temperature of laminates was determined by dynamic mechanical analysis and was found to decrease with increasing styrene content.     

Solubility Parameter from an Acoustic Method: Temperature Effect and Applications to Petroleum

The thermodynamic information relating cohesive energy and internal pressure is explored in order to calculate the solubility parameter for hydrocarbons, some of its mixtures, and crude oils taking into account the effect of temperature. Single-phase data of pure hydrocarbons and some of their binary and ternary mixtures, such as speed of sound, density, and heat capacity at constant pressure, are used to adjust the proposed models. Finally, the results are compared with an experimental method recently presented by us in a previous publication. This evaluation demonstrates that the proposed methods are robust for highly saturated oils. Moreover, a general expression including SARA (percentage by weight of saturates S, aromatics A, resins R, and asphaltenes As) composition is proposed to predict the solubility parameter of oils with high content of resins and asphaltenes.     

Thermal dissolution of mechanically activated Barzas sapromyxite coal with benzene under supercritical conditions

The results of the thermal dissolution of Barzas sapromyxite coal in benzene under supercritical conditions in a flow system are reported. It was found that the mechanical pretreatment of coal under intense impact bending conditions resulted in an increase in the yield and a change in the group composition of the liquid products: in the high-temperature region of the process, the concentration of high-molecular-weight components (preasphaltenes, asphaltenes, and resins) increased.     

The Stability of Water‐in‐Crude and Model Oil Emulsions

The critical electric field (cef) technique has been utilized to measure the stabilities of a variety of water‐in‐model oil and petroleum emulsions. The cef method allows for a fast, reproducible, and quantitative gauge of emulsion stability. Here, we have used cef to measure the stability of water‐in‐heptane‐toluene‐asphaltene emulsions and confirmed the importance of solvation of asphaltenes and the state of asphaltene aggregation to emulsion stability. Emulsion stability increased with the concentration of soluble asphaltenes near the point of precipitation. Droplet sizes were measured with optical microscopy in order to calculate interfacial areas and film thicknesses. It was found that film thickness increased with asphaltene concentration up to the solubility limit, above which increased concentration had little effect, and cef increased with interfacial film thickness up to a monolayer coverage of asphaltene aggregates, above which film thickness had a much smaller effect. These findings were applied to a cef investigation of water‐in‐ppetroleum emulsions to develop correlations of the stability of water‐in‐ccrude oil emulsions. A strong correlation (coefficient = 0.95) was found for cef with the product of asphaltene concentration and the difference in hydrogen to carbon atomic ratios of the asphaltenes and petroleum solvent. The development of a kinetic model and its fit to experimental data revealed the effects of asphaltene chemistry, solvency, and resin concentration on the adsorption and consolidation of emulsion stabilizing interfacial films.     

Effect of Binary Surfactant Mixtures on the Stability of Asphalt Emulsions

The interfacial tension (IFT) of different asphalt components (aromatics, waxes, resins and asphaltenes) as 10% solutions in kerosene against different surfactant solution systems has been measured. The data revealed that both asphaltenes and waxes increased the IFT while aromatics and resins decreased it. The former two components are believed to destabilize asphalt emulsions, on the other hand, the latter two components facilitate asphalt emulsion formation and stability. A correlation between the rheological properties of the prepared asphalt emulsions by different binary and single surfactants mixtures and the stability of the emulsion was investigated. The flow curves of the different emulsion formulations clarified that the rheograms were found to attain plastic properties. The yield values, τ_B and plastic, and apparent viscosities, ξ_pl and ξ_app respectively, were determined from these plots. The results showed that the enhancement of the rheological properties of the asphalt emulsions using different binary surfactant systems were in the following order: dodecyl benzene sulfonic acid sodium salt (DDBS-Na)/decyl phenol ethoxylate e.o.= 15 (DPE-15)>1,1′ (lauryl amido)-propyl ammonium chloride (LAPAC)/DPE-15>DPE-15>DDBS-Na>LAPAC. On the other hand, the order of emulsion stability is as follows: LAPAC>DDBS-Na/DPE-15>DPE-15>DDBS-Na. The effect of the aqueous phase salinity up to 5% NaCl concentration on the stability of asphalt emulsions stabilized by different surfactant solutions systems is discussed. © 1997 SCI.     

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.     

Demetallization of heavy oil through pyrolysis: A reaction kinetics analysis

By tracking the transfer of vanadium and nickel in pyrolysis products, a seven-lump reaction kinetic model for pyrolysis-based demetallization of heavy oil was established. During pyrolysis, the demetallization of heavy oil is achieved by condensing metal-rich resins and asphaltenes to coke. The condensation of oil components originally contained in heavy oil differs greatly in reaction behavior, having the activation energy between 167 and 361 kJ/mol. As the pyrolysis progresses, the newly formed heavy components show a condensation behavior close to that of the light components. Limited by high activation energy and low initial fraction, the condensation of asphaltenes to coke and the resulting removal of metals contained in asphaltenes are hindered. Meanwhile, the condensation of light components has a major contribution to coke formation. An increase in reaction temperature accelerates the demetallization, but hardly changes the yield and component distribution of liquid products at the same metal removal rate.     

Sorption of gas condensate components by solid high-molecular-mass compounds of the gas-condensate field

The main mechanisms of sorption and desorption of saturated vapors of gas condensate fractions by asphaltenes and resins from the Orenburg oil-gas condensate field (OOGCF) was considered. These substances showed a high sorption capacity for mixtures of vaporized C₅-C₁₀ hydrocarbons in the temperature range of 50–70°C. Vapor sorption by asphaltenes is accompanied by their considerable swelling. The desorption of hydrocarbons from asphaltenes and resins proceeds much faster than their sorption. First, the lightest components (C₆ and C₇ hydrocarbons) are desorbed. Then, their relative amount in the desorbate gradually decreases while the amount of the heavier hydrocarbons octane, nonane, and decane increases. A possible mechanism of sorption of hydrocarbon vapors by asphaltenes is discussed.     

Effect of SO42− on catalytic activity of Fe2O3 for hydrocracking of coal

The catalytic activity of Fe₂O₃for the hydrocracking of a bituminous coal at 673K increases when a small amount of SO₄^2? is included in the catalyst. The effect of SO₄^2? is marked in the formation of resins, stronger polar compounds and asphaltenes.     

Effect of dilution on branching and gelation in living copolymerization of monomer and divinyl cross-linker: Modeling using dynamic lattice liquid model (DLL) and Flory-Stockmayer (FS) model

The effect of dilution on random living copolymerization of vinyl- and divinyl monomers with fast initiation and slow propagation was simulated and compared with the experiments. Two Monte Carlo simulation methods have been used: one, purely statistical, based on the Flory-Stockmayer (FS) theory and the second using the dynamic lattice liquid model (DLL). The results were compared with experiments using atom transfer radical polymerization (ATRP), one of controlled/living radical polymerization methods. Molecular weights, polydispersities and the crosslinking/cyclization of macromolecules were analyzed as a function of conversion and time for various solvent concentrations and initiator crosslinker/monomer ratios. The results obtained by the DLL method are in good agreement with the experiment, showing an increase of conversion and time at gel point with dilution, i.e., with the increase of solvent concentration. The FS theory was found to be unable to reproduce even qualitatively the dilution effect on gelation. It is shown that intrachain crosslinking becomes more and more important with increasing solvent concentration, preventing macroscopic gelation at high dilutions, even if the number of crosslinks per primary chain is much greater than one (Flory criterion).DLL simulations give an insight into the mechanism of crosslinking processes near the gel point (leading to gelation) and/or microgel formation when solvent concentration is too high. At very high solvent concentration polymerization is slow and side effects like deactivation of radicals become important. Taking such effects into account, the simulation gives better agreement with the experimental data.