PARTICLE SIZE, SOLVENT, OXYGEN, TEMPERATURE AND PRESSURE EFFECTS ON THE CONTENTS OF INSOLUBLE FRACTIONS FROM SOLID VACUUM RESIDUA

n-Heptane insoluble contents were determined for an extraheavy-oil vacuum residue, one petroleum and one coal pitch as a function of particle size. This variable was found to affect the yields of insoluble material, aspect which was also observed during extractions carried out with aromatic and halogenated solvents. The precision of results was observed to be independent on the operators. A study was carried out to determine the effect of sample drying time on fraction yields. It was found that maltene fractions were strongly dependent on this variable, whereas asphaltene fractions were totally independent

Predissolution in aromatic solvents proved worthless from the repeatability point of view. However, predissolution of the oil residue in CH₂Cl₂ followed by filtration and asphaltene precipitation with simultaneous solvent removal, was deemed to be a suitable technique to remove mineral matter and isolate asphaltenes in a single step

Sample oxidation during asphaltene precipitation and isolation was detected by gravimetric and spectroscopic techniques. This fact is very important since common precipitation techniques do not address this issue

Preliminary accelerated extraction experiments carried out with pitch samples at high temperature and pressure, revealed that this approach can be a very interesting research tool to investigate solubility properties.     

Investigation of Asphaltene Precipitation Process for Kuwaiti Reservoir

Abstract

As part of an Enhanced Oil Recovery (EOR) research program, Asphalting precipitation processes were investigated for a Kuwaiti dead oil sample using different hydrocarbons and carbon dioxide as precipitants at the ambient and high pressure of 3000 psig conditions. The hydrocarbons used as precipitants were ethane (C2), propane (C3), butane (C4), normal pentane (n-C5), normal hexane (n-C6), and normal heptane (n-C7). The equipment used for this investigation was a mercury-free, variable volume, fully visual JEFRI-DBR PVT system with laser light scattering. The minimum critical value of precipitants concentration for the oil sample has been identified at the ambient and high-pressure conditions for each precipitant. Our investigation has revealed that for this oil sample the most powerful asphaltene precipitant were CO₂ followed by C2, C3, C4, n-C5, n-C6, and n-C7. Moreover, the effect of pressure and temperature on the asphaltene precipitation has been investigated experimentally for CO₂, n-C5, n-C6, and n-C7. The precipitation and redissolution of asphaltene upon the addition and removal of CO₂ and light alkanes (C2–C4), at 3000 psig and ambient temperatures, have shown evidence of reversibility of asphaltene precipitation. A comprehensive fluid characterization analysis for the oil sample has been performed including, physical properties of crude oil, compositional, molecular weight (Mw), and SARA analyses. Advanced analytical techniques such as 1H and 13C NMR and IR spectrometers have been utilized to investigate the molecular structure of the asphaltene for this sample. It was concluded that the asphaltene molecules for this oil contain 120 total aromatic carbons with 42 aromatic rings, 114 naphthenic rings, and 5–7 sets of condensed aromatic rings.     

SUPERCRITICAL PROPANE SEPARATION OF DEASPHALTED OIL AND CARBON-PRECURSOR PITCH FROM HEAVY PETROLEUM RESIDUUM

ABSTRACT

The feasibility of the use of a petroleum vacuum-distillation residuum as a feedstock for carbon applications was investigated using a semicontinuous supercritical propane (C3H8) extraction system. Experiments were carried out under different conditions to ascertain the effects of system pressure and temperature on the yields of extracted oils and the properties of residual pitches. The extraction residue obtained near the critical temperature and over the critical pressure of propane solvent showed appropriate properties as a precursor pitch for carbon materials, representing superior yields, high asphaltene contents, low toluene insolubles and the adequate softening point of 401-424 K. The extraction yields of deasphalted oil were increased as the system pressure was increased corresponding to the increased density of propane solvent. No difference in the yields and properties of residual pitches were observed at the experiments performed in the vicinity of the critical temperature of propane.     

STRUCTURAL CHARACTERIZATION OF GUDAO ASPHALTENE BY RUTHENIUM ION CATALYZED OXIDATION

ABSTRACT

Structural characterization of Gudao asphaltene was undertaken by using ruthenium ion catalyzed oxidation (RICO ) which is capable of converting aromatic carbons selectivety to carbon dioxide and/or carboxyUc groups while leaving aliphatic and alicyclic structures essentially unaffected. The oxidation products were dominated by a homologous series of straight chain monocarboxyfic acids ( C₂ -C₃₅) indicating that normal alkyl chains are important constituents of the asphaltene. A series of α,ω; -dicarboxylic acids (C₄ - C₂₆) were also detected and determined, confirming the presence of poh/methylenc mokties linking two aromatic units. Relative high yields of benzenepenta- and hexacarboxyhc acids fonned in the RICO of Gudao asphaltene clearly indicate that substantia] aromatic structures of this asphaltene are peri-condensed.     

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.     

Structural Changes of Sub-fractions in Residue Hydrotreating Products by Ruthenium Catalyzed Oxidation

Abstract

Structure of aromatics, resins, and asphaltenes in petroleum residue was undertaken by using ruthenium ion catalyzed oxidation. The distribution of alkyl side chains and bridges connected to aromatic rings was quantified, and the condensed type of aromatic rings was deduced. The structural changes of fractions in residue during hydrotreating were discussed. The results showed that fractions have abundant alkyl side chains (C₁–C₂₇), mainly n-alkyl side chains, attached to aromatic carbons, and polymethylene bridges connected to at least two aromatic ring systems are also present. The molar concentrations of these alkyl groups are declined as the increase of chain length. Cata-condensed, peri-condensed, and biphenyl-type aromatic unit structures coexist in fractions, while the proportion of biphenyl type structure is relatively small. The aromatic structure of aromatics is mostly cata-condensed, while for resins the proportion of cata-condensed and peri-condensed type aromatic structures is comparable, and structure of asphaltene is mostly peri-condensed. The chemical structure of fractions in residue changed due to the increase of hydrotreating degree. The enrichment of large aromatic units made asphaltene have more aromatic structures and higher condensed degree.     

Molecular Dynamics Simulation of Structural Relaxation of Asphaltene Aggregates

Abstract

For asphaltene obtained from vacuum residue of Khafji crude oil, the energy-minimum conformation calculated by molecular mechanics–dynamics simulations showed that aggregated structures of asphaltene molecules through noncovalent interactions are more stable. Changes induced in aggregated structures by pretreatment with solvents were investigated using molecular dynamics calculations. The simulation showed that in quinolin at 573 K, some staking interactions could be disrupted, while, in 1-methylnaphthalene it was not observed. Autoclave experiments showed that the coke yield after pyrolysis at 713 K was decreased when the asphaltene was pretreated with quinoline at 573 K for 1 h, compared to the yield without the pretreatment. While, in the case of pretreatment in 1-methylnaphthalene, the coke yield did not change significantly. The simulation's results above can be related to the difference in coke yield between two solvents; in quinoline some aromatic–aromatic stacking interactions could be disrupted and mobility of molecules was increased. This resulted in prevention of the asphaltenes from polymerizing, as in condensation reactions among aromatic rings. Consequently, the coke yield after the pretreatment with quinoline was decreased.     

PHYSICAL AND CHEMICAL CHARACTERIZATIONS OF ASPHALTENES FROM DIFFERENT SOURCES

ABSTRACT

Asphaltenes and resins are two of the several, but important, heavy organics present in petroleum fluids. Asphaltenes are operationally defined as the non-colatile and polar fraction of petroleum that is insoluble in n-alkanes (i.e., n-pentane). Conversely resins are defined as the non-colatile and polar fraction of petroleum that is soluble in n-alkanes (i.e., n-pentane), and aromatic solvents (i.e., toluene), and insoluble in ethyl acetate. A commonly accepted view in the petroleum chemistry is that crude oil asphaltenes form micelles which are stabilized by adsorbed resins kept in solution by aromatics. Two key parameters that control the stability of asphaltene micelles in a crude oil are the ratio of aromatics to saturates and that of resins to asphaltenes. When these ratios decrease, asphaltene micelles will coalesce and form larger aggregates. The precipitation of asphaltene aggregates can cause problems such as reservoir plugging and wettability reversal.     

ASPHALTENE PRECIPITATION AND SOLVENT PROPERTIES OF CRUDE OILS

ABSTRACT

Improved prediction of the onset of asphaltene precipitation may be achieved using refractive index (RI) to characterize crude oils and their mixtures with precipitants and solvents. Experimental measurements of RI for mixtures of several crude oils with the precipitant n-heptane, are reported at ambient conditions. Theoretical developments are described that will permit extension of these observations to reservoir conditions

Measurements of RJ at the onset of precipitation have shown that the onset occurs at a characteristic RI for each oil/ precipitant combination, supporting the premise that precipitation is dominated by London dispersion interactions and thus, that RI can be used to predict the onset of precipitation. Reports in the literature showing that the onset of precipitation occurs at constant solvent-to-precipitant ratios provide additional confirmation

The theory is developed on the assumption that London dispersion forces dominate aggregation and precipitation of asphaltenes. The interaction energy of asphaltene molecules or aggregates in a medium of oil can be expressed as a function of the difference between the RI of asphaltene and oil. The RI of live crude oil during pressure depletion can be calculated from the RI of the stock tank oil, the molar refraction of the separator gas, the formation volume factor B_o and the solution gas/ oil ratio R_s     

The Chemical Composition of Solubility Classes from Athabasca Bitumen Pitch Fractions

Abstract

As the Canadian supply of light crudes diminishes, refineries have necessarily been required to deal with more difficult to process oilsands bitumen and heavy oils. Nearly 50% of bitumen consists of a residuum that cannot be easily upgraded. A better understanding of the chemistry of this material is the key to achieving overall optimal yields of commercially useful products. In recent years, the application of supercritical fluid extraction (SCFE) with pentane has been successful in separating the bitumen residuum into a number of narrow fractions based on solubility parameters and molecular weight. In combination with advanced characterization techniques this approach has proved to be useful in elucidating the complexity of bitumen chemistry. To provide further insights into the chemistry of bitumen pitch we now extend this established approach to the solubility classes (saturate, aromatics and resins) derived from the bitumen fractions, or front-cuts, separated during the SCFE process with pentane. The amount of the saturate class present in the front-cuts decreases rapidly with cumulative yield. In the same range, resin content increases continuously while aromatic content passes through a maximum. No asphaltene is present in the front-cuts; this component is separated in the pentane insoluble end-cut fraction during SCFE. Both aromatics and resins from the front-cuts show a trend for increasing aromatic content and decrease in H/C atomic ratios at higher cumulative yields. This is a reflection of increasing number of aromatic rings, with a higher degree of condensation and decreasing degree of substitution, for larger and more complex molecules. In terms of structural parameters and molecular sizes we find relatively minor differences between the corresponding aromatic and resin fractions in each front-cut. The most noteworthy difference between these SARA classes lies in the significantly higher nitrogen contents of the resin class.     

Changes in Sub-fractions Properties during Hydrotreating of Residue

Abstract

One atmosphere residue was hydrotreated (HDT) in a pilot plant at constant conditions. The properties of the HDT products from a series of reactors and their sub-fractions were characterized by H/C, sulfur, nitrogen, carbon residue, nickel, vanadium, and VPO apparent molecular weight. The removal levels of sulfur, nitrogen, carbon residue, nickel, and vanadium were 84.9 m%, 51.4 m%, 62.8 m%, 84.8 m%, and 94.0 m%, respectively. The removal increment of contaminants in reactors was very different during HDT. The ranking of sulfur and nitrogen contents in sub-fractions was asphaltene > resin > aromatic > > saturate; however, the distribution of sulfur in sub-fractions was aromatic > resin > > asphaltene > saturate, while that of nitrogen was resin > > aromatic > asphaltene. Average carbon residue was removed in reactors. Nickel and vanadium were removed mainly in hydrodemetalization reactors.     

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

Abstract

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.     

Solid Petroleum Asphaltenes Seem Surrounded by Alkyl Layers

Abstract

In this review, a comprehensive analysis of recent results obtained in our laboratory and published in the literature is presented, which points toward the existence of alkyl layers surrounding precipitated asphaltene solids. A micellar model for asphaltenes has been proposed, which explains many of the experimental determinations carried out to date with these compounds. The model considers the existence of alkyl moieties surrounding the inner aromatic cores. Faster dissolution kinetics of asphaltenes modified by coprecipitated waxes has been explained by the enhanced incorporation of alkane-surrounded particles into the eluent employed in the dissolution experiments. Finally, asphaltene volumetric changes brought by organic solvents have recently been studied, and can be explained by the existence of an alkyl layer prone to the incorporation of solvent molecules. This paper will discuss these aspects that seem to support the model long time ago postulated by Yen and coworkers.     

MICROSCOPIC INVESTIGATION OF THE ONSET OF ASPHALTENE PRECIPITATION

ABSTRACT

A microscopic study of the onset of asphaltene precipitation is reported. The onset conditions can be quantified by measurement of mixture refractive index, together with microscopic observations of particulate formation in mixtures of oil and precipitant, with or without added solvents. For isooctane mixtures with a variety of hydrocarbon solvents and a crude oil from Alaska, the onset of precipitation occurs over a narrow range of solution refractive index. Addition of polar solvents or different precipitating agents can shift the refractive index at which precipitation begins. Refractive index decreases when a crude oil is diluted by precipitant, as in this study, or when changes in temperature and pressure alter the relative molar volumes of species in the oil. If it falls below some critical value, resin/asphaltene aggregates that had been in stable dispersion become unstable and precipitate. These observations provide a method of screening solvents to differentiate between those that prevent precipitation mainly by maintaining a higher mixture refractive index and others that may participate in or disrupt asphaltene/resin interactions.     

Hydrotreating of Furrial Crude Oil Using NiMoS Supported on Alumina: Study of the Asphaltene and Their Fractions in Cyclohexane

Abstract

The Furrial crude oil originated in northern Monagas State. This shows problems such as the colloidal instability of the asphaltenes fraction present in them, causing its precipitation. This work is oriented to achieve an interpretation of the colloidal behavior of the asphaltenes through the study of the effect of the hydrotreating reactions (HDT) on the asphaltenes of the Furrial crude oil, using NiMoS/γ-Al₂O₃ as a catalyst. The results obtained after HDT reactions were analyzed to know the percentage of asphaltene and their fractions in cyclohexane, the measurement of flocculation thresholds and molecular weights by the VPO technique, and ¹³C NMR as well as the determination of the total sulfur content. Appreciable changes on the asphaltene of the Furrial crude oil and its fractions in cyclohexane after HDT, under conditions used, were observed. In general terms, the amount of asphaltene diminished and the percentage of distribution for insoluble fraction in cyclohexane (IFC) and for soluble fraction in cyclohexane (SFC) was affected causing an increase in the stability of the asphaltene. The asphaltene and IFC were observed to be a pronounced variation of the molecular weight average in number, in comparison with SFC. ¹³C NMR spectra indicate that the hydrotreated asphaltene shows structural change, and IFC presents a variation of the percentage of sulfur minor in comparison to SFC.     

The Structural Characterization of Saturate,Aromatic, Resin,and Asphaltene Fractions of Batiraman Crude Oil

Abstract

The structural characterization of fractions of Batiraman crude oil, which is the heavy crude oil from a field in the southeastern part of Turkey, was investigated. Batiraman crude oil and its saturate, aromatic, resin, and asphaltene (SARA) fractions were seperated. Treatment of crude oil with n-heptane provided the separation of asphaltene. Maltene was collected by evaporating the n-heptane from the filtrate. Then, maltene was separeted into saturates, aromatics, and resins by SARA technique. Maltene was separated into saturate, aromatic, and resin fractions using column chromatography. SARA fractions were quantified on a weight percent basis. Fractions of Batiraman crude oil were characterized by elemental analysis, proton nuclear magnetic resonance (¹H NMR) analysis, electrospray ionization mass spectrometry (ESI-MS), and Fourier transform infrared (FTIR) spectroscopy techniques.     

DIMETHYL SULPHOXIDE-A SOLVENT FOR THE STUDY OF COALS

ABSTRACT

Dimethyl sulphoxide (DMSO) has been found to be a very good solvent for the study of Tow rank coals. Chemical studies of a Texas lignite, its DMSO soluble fraction obtained under ambient conditions, the DMSO insoluble residue and its humic acids have been carried out. Physico-chemical techniques such as Fourier transform infrared spectrometry (FTIR), and ¹³C cross-polarization/magic angle spin (¹³C CP/MAS) NMR spectrometry and chemical methods such as pertri fluoroacetic acid oxidation and the determination of acidic group concentrations have shown that the DMSO-soluble portion possesses a chemical structure which is similar to both that of the neat lignite and of the DMSO-insoluble residue. The humic acids are highly aromatic and acidic in nature. Preliminary data obtained through the use of ²⁵²Cf plasma desorption mass spectrometry (²⁵²Cf PDMS) suggests the existence of a common species in both the DMSO extract and the humic acids.     

DISTRIBUTION OF BIOMARKERS IN HIGHLY WEATHERED PETROLEUM RESIDUE FROM MEDITERRANEAN WATERS

ABSTRACT

The aliphatic and aromatic fractions of a beach tar sample from the Mediterranean coast of Sidi Kreir, 37Km west of the city of Alexandria was analyzed by GC and GC/MS techniques. A complete analysis was carried out to investigate chemical composition changes, fate of weathered oil residue and possible source identification. The distribution of sterane, hopane, mono-and triaromatic steroids, C₂ - and C₃ - phenanthrenes and dibenzothiophenes and chrysenes, however, had remained unaltered by weathering. The beach tar possessed geochemical features consistent with a marine carbonate or evaporite source depositional environment under normal saline, reducing conditions. The GC fingerprints pointed to heavy fuel oil as a possible source for the tar sample.     

AN EXPERIMENTAL STUDY OF THE EFFECT OF PARAFFINIC SOLVENTS ON THE ONSET AND BULK PRECIPITATION OF ASPHALTENES

ABSTRACT

Asphaltene onset concentration and bulk deposition were measured for a typical live reservoir oil titrated with n-C₆H₁₄, n-C₅H₁₂, n-C₄H₁₀, C₃H₈, C₂H₆, CH₄ and CO₂ at 100° C (212 ° F) and 29.9 MPa (4340 psia). The concentration of titrant at asphaltene onset was observed to decrease approximately in a linear fashion with decreasing molecular weight of the paraffinic solvent; CH₄ did not induce any asphaltene precipitation. Bulk deposition experiments were performed using a solvent: oil volume ratio of 10:1; the results indicated that the weight percent of asphaltenes precipitated increased exponentially with decreasing molecular weight of the paraffinic solvents. More importantly, the asphaltene molecular weight showed a maximum for n-C₄H₁₀ precipitated asphaltenes. Possible explanations for this unusual result are presented.