Relationship between solvent-derived and compound-class fractions in coal-derived distillates and vacuum still bottoms

High-boiling SRC-1 process-derived distillable liquids and nondistillable vacuum still bottoms (VSB) from Wyodak and Kentucky 9/14 coals were separated into solvent-derived and compound-class fractions using Chromatographic techniques. The fractions were characterized using infrared spectrometry, proton nuclear magnetic resonance spectrometry, field ionization mass spectrometry, and elemental analysis. Emphasis was placed on the determination of the composition of oils and asphaltenes. Results showed that oils and asphaltenes consist of the same compound classes: hydrocarbons, nitrogen compounds, and hydroxyl aromatics. The main differences between the oil and asphaltene fractions are in concentrations of compound classes. It was found that oils are rich in hydrocarbons while asphaltenes are rich in hydroxyl aromatics. Also, oils and asphaltenes contain compounds of the same homologous series, and molecular weight is not a factor which differentiates oils and asphaltenes. Components in VSB oils have higher molecular weights than components in distillate asphaltenes. Molecular structure rather than molecular weight is a major parameter that determines solubility of coal-derived liquids.     

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.     

Precipitation of asphaltenes from solvent-diluted heavy oil and thermodynamic properties of solvent-diluted heavy oil solutions

Ratios of n-heptane (hep) to toluene (tol) affect the solubility of the asphaltenes in heavy oil extraction processes. Consequently phase changes and time after mixing n-heptane and heavy oil in toluene are important for understanding produced emulsions. The kinetics of phase change when n-heptane is added to toluene-diluted heavy oils, and the thermodynamic properties of partially deasphalted heavy oils were studied. The methods used were monitoring precipitation in time using light microscopy, quantitative asphaltenes analysis by near infrared spectroscopy, refractive index and densities measurements, and calculated solubility parameters of mixtures. At critical mass ratios of hep/tol from 1.37 to 2.0 in diluted heavy oil the precipitated asphaltene particles were observed under the microscope after lag times from 2 h to instantly. Lag times were longer at low initial oil concentration. The floc growth time decreased as heavy oil concentration in toluene increased. The growth patterns in time appeared as dots to beads (strings) to clusters (fractal-like flocs). Final wt% precipitated asphaltenes vs. mass fraction (hep+tol)/heavy oil followed sigmoidal relationships. Curves showing wt% soluble asphaltenes vs. mass fraction hep/tol after 24 h initially followed the same shape as time zero curves and diverged at the onset ratios of hep/tol. Slope for precipitated asphaltenes vs. solubility parameters curve showed a break at 16.4 MPa^1/2. Linear correlations were established for concentrations of soluble asphaltenes in residual oils and density, for refractive index and density and for refractive index and solubility parameter. The latter correlation was in accordance with Lorenz-Lorentz theory. These equations provided a means by which oil density, refractive index and solubility parameter can be predicted when these measurements are difficult to measure practically.     

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.     

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.     

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.     

Group structure characteristics of the liquid thermolysis products of vitrinites of different ranks

The results of the group structure analysis of asphaltenes, resins, and hydrocarbons in the liquid products obtained upon the thermolysis of vitrinites of different ranks are presented. The molecular weights of components decreased with the degree of vitrinite conversion: aromatic structures were predominant among ring compounds, and the lengths of alkyl substituents decreased. The molecules of asphaltenes predominantly consisted of two-block structures, whereas tars and oils mainly exhibited a single-block organization; in all cases, the alkyl substituents of aromatic rings had a length of C₁–C₄.     

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.     

Oxidation of a bitumen

Oxidation of a bitumen with air or oxygen in the presence of a diluent significantly increases the asphaltene content and noticeably reduces the asphaltene solubility. It is suggested that one of the main factors influencing the solubility of the asphaltenes, aside from possible polymerization of asphaltenes and resins, is incorporation of oxygen groups, e.g. hydroxyl, into the asphaltenes, and consequent changes in polarity sufficient to influence asphaltene deposition.     

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.     

Modeling the phase behavior in binary mixtures involving blowing agents and thermoplastic resins

The thermophysical properties of mixtures of thermoplastic resins and blowing agents, together with the knowledge of the solubilities of these components, are the basis for the manufacturing of plastic foams. In this work, the solubilities of blowing agents trichlorofluoromethane, dichlorodifluoromethane, chlorodifluoromehane, and 1,2‐dichloro‐1,1,2,2‐tetrafluoroethane in thermoplastic resins poly(styrene), high density poly(ethylene), low density poly(ethylene), poly(propylene), poly(vinyl chloride), poly(carbonate) and poly(propylene oxide) were modeled by using the Perturbed Chain‐Statistical Associating Fluid Theory (PC‐SAFT) and the Sánchez‐Lacombe equations of state (EoS), fitting a single temperature‐dependent binary interaction parameter. PC‐SAFT is a theoretically based equation of state with three pure component parameters that describe efficiently the thermodynamics of complex systems. Earlier works with this EoS have already predicted the phase coexistence properties of various refrigerants and higher order alkane series compounds, along with their mixtures. The pure component parameters for the blowing agents were obtained by regression of vapor pressure and liquid density data, while the pure component parameters for the thermoplastic resins were obtained by regression of pure liquid PVT data. The parameter estimation was performed by using a modified maximum likelihood method. The solubility results obtained with both EoS have been compared; the results from PC‐SAFT showed a higher accuracy in terms of solubility pressure deviations. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

一个新的溶解度参数

基于液体混合的热力学模型,为非电解质溶液导得了1个比Scatchard-Hilde-brand正规溶液理论更加严格的过量Gibbs自由能表示式.据此,定义了1个新的溶解度参数,它等于液体的内聚能密度除以内压的开方根.对35个二元液体混合物的过量Gibbs自由能预测结果表明,预测值与实验值的偏差大多优于SHFH理论,特别是碳氟与碳氢化合物的溶液,对于这类溶液,正规溶液及其修正形式SHFH理论是不适用的.     

Investigation of solubility in plasticised rubber systems for tire applications

Oligomer resins and process oils are indispensable for rubber technology in order to achieve high-performance tyres on wet roads and ultralow energy consumption with acceptable manufacturability. This study investigates the solubility of oligomer resins, oils and elastomers using differential scanning calorimetry and describes its implication on rubber compound hysteresis loss. Owing to the configurational entropy of mixing, resin molecular weight strongly influences miscibility within binary resin/oil, ternary resin/oil/elastomer and filled rubber compounds. Similarity of chemical structure plays a role in miscibility linked to enthalpic effects. Among Hansen solubility parameters, the polar component correctly ranks the compatibility of resins with oils and elastomers. It has been shown that increased solubility among the resin–oil–elastomer system provides better balance of predicted rolling resistance and wet grip of tread compounds. Therefore, optimisation of rubber properties relies on the adequate selective use of process oils and resins according to their chemical structure and molecular weight.     

Determination of multi-properties of residual oils using mid-infrared attenuated total reflection spectroscopy

Several physical and chemical parameters (such as saturates, aromatics, resins, and asphaltenes, element contents, density, viscosity, and carbon residue) are necessary to characterize residual oils. The combined use of mid-infrared (MIR) attenuated total reflection (ATR) spectroscopy and multivariate calibration allows those parameters to be estimated accurately. In order to improve the prediction results, samples from different processing units require different calibration models relative to the spectral similarities. This paper builds a strategy to classify and discriminate different types of residual oils by use of partial least square regression. The calibration models for the physical and chemical parameters of three types of residual oils were developed, respectively. The consistencies between the MIR predicted and reference values testify to the creditability of the proposed method.     

Estimation of supercritical fluid-liquid solubility parameter differences for vegetable oils and other liquids from data taken with a stirred autoclave

Fujishiro and Hildebrand developed a procedure for determining the solubility parameter difference between the components of a partially miscible binary mixture, knowing the molar volumes of the components and the composition of each phase. Using this procedure, the solubility parameter differences between supercritical carbon dioxide (SCCO2) and each of three vegetable oils and four hydrogen bonding liquids have been determined. For the vegetable oils the solubility parameter differences at 72 C over the pressure range 5,000–10,000 psi were low, of the order of 2.0, and decreased only slightly with increasing pressure. For the hydrogen-bonding liquids at 52 C, over the same pressure range, the solubility parameter differences were much larger, of the order of 4 to 7 units, and independent of pressure except for ethylene glycol for which the difference increased from 5.7 to 6.7 from 5,000 to 10,000 psi.     

A method to predict solubility of hydrogen in hydrocarbons and their mixtures

Knowledge of solubility of hydrogen in hydrocarbon systems is important in design and operation of units and equipments in petroleum and coal processing plants for upgrading fuels quality. In this paper a method based on regular solution theory is proposed for prediction of solubility of hydrogen in hydrocarbons, petroleum fractions and coal liquids at different conditions of temperature and pressure. Hydrogen solubility parameter is calculated through solvent type or its molecular weight. Evaluation of results shows that the method can predict solubility data within the same range of accuracy as those calculated from an EOS or other models while this method is simpler and does not require critical properties of solvent which in most cases cannot be estimated accurately. For more than 400 data points and for systems consisting pure hydrocarbons, coal liquid and petroleum fractions the AAD for the proposed model from estimating solubility of hydrogen and Henry's constant for pressures up to 160 bar was about 5%. The proposed method is applicable to fractions with molecular weight ranging from 70 to 650 which is equivalent to carbon number ranging from 6 to 46. The temperature and pressure ranges are 283-623 K and 1-160 bar, respectively. Solubility range is from 0.01 to 26 mol%.     

The significance of chemical markers in the bioprocessing of fossil fuels

Biochemical conversion of crude oils is a multi-step process proceeding through a series of biochemical reactions. These reactions can be characterized by a set of chemical markers which are associated with the chemical composition of crude oils. Reactions with heavy crude oils indicate that there is an overall decrease in the concentration and chemical speciation of organic sulfur compounds, and a redistribution of hydrocarbons and organometallic species. The contents of trace metals in the crude oils, such as nickel and vanadium, also decrease. Further, heavy ends of crudes, containing the asphaltenes and the polar nitrogen, sulfur, and oxygen containing fractions, as well as the organometallic compounds and complexes, are biochemically converted to lower molecular weight chemical species. In the studies reported in this paper, microorganisms used to mediate such reactions were thermophilic ( > 60°C) and pressure tolerant (up to 2500 psi). These organisms are also capable of biochemical conversion of bituminous and lignite coals in an analogous manner to their action on crude oils and follow similar trends characterized by chemical markers. For example, X-ray absorption near-edge structural (XANES) analyses of biotreated crude oils and low grade coals show that biochemical reactions lead to decreases in organic sulfides and thiophenes with a concurrent increase in sulfoxide contents. Chemically related constituents present in heavy crude oil fractions and low grade coals are the asphaltenes. Asphaltenes are complex structures containing heteroatoms and metals involved in inter- and intra-molecular bridges and stereochemical configurations. The chemical markers associated with the biochemical conversion of oils and coals indicate multiple biochemical processes involving chemical reactions at sites containing heteroatoms and metals leading to a breakdown of the structure(s) to smaller molecular weight units. Thus, using chemical markers as diagnostic tools, the extent and the efficiency of fossil fuel bioconversion may be predicted and monitored, allowing for better cost-efficient field trials. Recent results in this area will be presented and discussed in this paper.     

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.     

Surface properties of heavy petroleum distillation residues

Heavy residues of the distillation of oils from different origins and their main constituents (oil, asphalt, resins and asphaltenes) were analysed using various methods: elemental analysis, potentiometry for acid and base content measurement, i.r. spectroscopy for H bonding capacity determination, a spot test for the evaluation of the flocculation tendency of the constituents and either liquid contact angle measurements on compressed powders or inverse gas chromatography for the assessment of the surface free energy of the solid constituents of the residues. The properties of the heavy residues are quite different. In particular, the surface properties depend on the molecular composition (functional group content) of the residues but also on the degree of association of polar and less polar constituents. Clearly the weight ratio of resins and asphaltenes is a significant factor for the surface properties and the stability of heavy residues.     

Characterization of lignite low-severity depolymerization products

Oils and asphaltenes derived from direct extraction and several mild depolymerization processes have been studied. The asphaltenes have been fractionated by column adsorption chromatography (with deactivated silica gel) and benzene, THF and MeOH were used in sequence as eluothropic series. Clear chemical separation between one aromatic and two polar fractions has been obtained, giving high percentages recovery. The fractions have been characterized by VPO, FT-IR, ¹H-NMR and elemental analysis. Several structural parameters of oils have been calculated. These oils can be assimilated to equivalent average hydrocarbons having between 10 and 20 carbon atoms and an aromatic carbon percentage oscillating between 47 and 66%. In general, the degree of substitution in aromatic rings is low and the presence of phenolic groups is limited. The majority of the carbons are aromatic and these rings show low degrees of condensation.