CHARACTERIZATION OF HEAVY RESIDUA BY AAPPLICATION OF A MODIFIED D 2007 SEPARATION AND ELECTRON PARAMAGNETIC RESONANCE

Seven atmospheric residua (343^°C + [ 65O^°F + ]) were separated into saturate, aromatic, resin, and asphaltene fractions for detailled assessment of feed structure. The weight percent distribution of the fractions revealed two groupings of the residua. One grouping exhibited 20 wt % saturate composition, while the other only 10 wt %. The residua also exhibited high polar content (resin and asphaltene fractions) consisting of over 40% of the total residua. These results are related to the sulfur composition of the residua, and Indicate a fundamental relationship between the aromatic content and sulfur content. Discussion of the accuracy of the separation technique Is also Included.

The vanadium binding sites In the separated fractions were investigated by EPR spectroscopy. The resin and asphaltene fractions all appear to be dominated by 4N and N 0 2S coordination spheres. Discussion of this technique is also included.     

EFFECTS OF ASPHALTENE PRECIPITATION AND REPRECIPTION ON THE METAL-CONTAINING COMPOUNDS IN HEAVY RESIDUA

Boscan vacuum residuum (VR) has been separated into isooctane insoluble asphaltenes and isooctane soluble maltenes. The asphaltenes were dissolved in a minimum of toluene and were further separated by two additional reprecipitations using isooctane as the precipitating solvent. We examined the fractions, including the recovered isooctane soluble material, by size exclusion chromatography (SEC) with inductively coupled plasma (ICP) emission spectroscopy to determine the effects, if any, the reprecipitations have on the size distribution of the metal-containing compounds.

The asphaltene fractions show little change in size upon reprecipitation, but removal of a small amount of the metal components does occur. The first reprecipitation produces isooctane soluble material which is very similar in size to the original maltene fraction. However, the second reprecipitation removes small amounts of material in the size range of the asphaltenes. When the amounts were weight balanced, the resulting separation did little to effect the overall maltene and asphaltene size profiles.     

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.     

EFFECTS OF ASPHALTENE PRECIPITATION AND A MODIFIED D 2007 SEPARATION ON THE MOLECULAR SIZE OF VANADIUM-AND NICKEL-CONTAINING COMPOUNDS IN HEAVY RESIDUA

Boscan vacuum residuum (VR), and Maya atmospheric residuum (AR), were separated into operationally defined components by an isooctane asphaltene precipitation followed by a modified D 2007-80 separation of the isooctane soluble material. These collected fractions were examined by size exclusion chromatography (SEC) with element specific detection employing inductively coupled plasma emission spectroscopy (ICP) to investigate the effect the separation has on the the V and Ni compounds. The V and Ni SEC-ICP profiles of the asphaltene fractions indicated some of the metal-containing molecules are substantially larger in size than those observed in the residua. The asphaltene precipitation appears to cause an increase in molecular size through agglomeration of smaller constituents, and accomplishes only limited size separation of the metal-containing compounds.

The resin fraction, the polar fraction obtained by modified D 2007-80 chromatography of the isooctane soluble portion, contained much of the smaller size molecules of the feeds. The agglomeration seen in the SEC-ICP profiles of the asphaltene fraction was not apparent in any of the resin fraction profiles.     

STUDIES ON LARGE CRUDE OIL ALKANES. II. ISOLATION AND CHARACTERIZATION OF AROMATIC WAXES AND WAXY ASPHALTENES.

Isolation of very large alkane components as described in the first paper within this series, fail in some cases. This work describes two non-routine isolation procedures applied to two different non-typical petroleum fractions. The first one comprises a chromatographic approach applied for the separation of alkanes from alkylaromatic compounds derived from paving asphalt waxes. The second separation procedure was developed for the isolation of alkane fractions associated with asphaltenes that precipitated during long crude oil storage periods, resulting in highly insoluble organic composites

In the first case, the isolated fractions were characterized by spectroscopic and chromatographic methods. The evidence showed that long chain naphtheno-aromatic molecules behave like waxy asphalt components, which interact by unusual mechanisms with solid sorbents. Their chromatographic behavior was found to be between typical alkanes and typical aromatics. This behavior is caused by the simultaneous presence of three functionalities

The second sample type was characterized by spectroscopic methods only. The results permitted to assess that the waxy composite from crude oil tank sediments precipitated selectively, including highly aromatic and long alkyl chain asphaltenes as well as very large n-alkanes.     

SOLVENT DEMETALLIZATION OF ATMOSPHERIC AND VACUUM RESIDUES

The effectiveness of various solvents for the removal of heavy metals, particularly vanadium and nickel via the removal of asphaltene from atmospheric and vacuum petroleum residues are presented The solvent deasphalting was carried out at 29§C The solvents used in this investigation were pentane, hexane, heptane, petroleum ether, ethyl acetate and butyl acetate and the degree of refining was studied by evaluating the properties of the refined residue.

Results obtained show that the removal of the heavy metals decreases with increase in the carbon number of the hydrocarbon solvents, and also decreases with the increase in the molecular weight of the acetate solvents. The percentage removal of vanadium was higher than that of nickel irrespective of the solvents used and ethyl - acetate gave the highest removal of the metals.     

THE EFFECT OF ASPHALT COMPOSITION ON THE FORMATION OF ASPHALTENES AND THEIR CONTRIBUTION TO ASPHALT VISCOSITY

Interactions among asphalt components have significant effects on the performance of asphalt binder. To understand those interactions, four asphalts, SHRP AAA-I, AAD-I, AAF-I, and AAG-I, were fractionated into three generic fractions according to Corbett's procedure and reblended into asphaltenes/aromatics/saturates ternary mixtures in various ratios. Mixtures were oxidatively aged with atmospheric air at temperatures of 87.7, 93.3, and 98.8°C for 5 to 33 days. The changes in chemical composition and physical properties were monitored using fourier transform infrared spectroscopy (FT-IR) and dynamic mechanical rheometry

The formation of asphaltenes is a major factor in the hardening of asphalt with aging. The data collected in this study indicate that the saturate content in the maltene phase has a profound impact on the contribution that asphaltenes have on the viscosity of aged asphalt. The data also suggest that the aromatics fraction is solely responsible for the formation of asphaltenes as an asphalt oxidizes.     

ELECTRICAL CONDUCTIVITY OF ASPHALTENES IN ORGANIC SOLVENTS

Conductivities of asphaltenes were measured as a function of concentration in solvents of varying permittivity. The molar conductivity was calculated assuming the molecular weight of asphaltenes to be 1000 g/mol

The Fuoss conductivity model was fitted to the experimental data with two free parameters i.e. the association constant and the molar conductivity at infinite dilution. The experimental data show indication of ion-pairs and strong dipole-ion interaction. Accordingly, the measurements were consistent with the model for ion pairs as given by Fuoss and multibody interaction theory given by Petrucci

At low concentration the asphaltenes consist mainly of free ions, as the concentration increases ion pairing leads to a decrease of the molar conductivity. At higher concentration ion-dipole interaction may lead to an increase of the molar conductivity, as is seen in some of the solvents. At even higher concentrations some indications of aggregation are observed

The results indicate that part of the asphaltenic fraction is ionized and behave as ions in solvents of low dielectric constant.     

ASPHALTENE PRECIPITATION AND SOLVENT PROPERTIES OF CRUDE OILS

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     

MODIFICATIONS INDUCED BY VISBREAKING ON COMPOSITION AND STRUCTURE OF ATMOSPHERIC RESIDUES

The atmospheric residues, the corresponding visbroken residues and the related asphaltenes have been characterized by elemental analysis, liquid and gel permeation chromatography (LC, GPC), nuclear magnetic resonance (NMR) and pyrolysis/gas chromatography/mass spectrometry ( Py/GC/MS) before and after the thermal process. The results show that visbreaking (VB) increases the aromaticity (Car) of the residues and decreases their resins/ asphaltenes ratio. A relationship between δC_ar and resins/as-phaltenes ratio has been found.

The cracking of aliphatic chains which takes place during the thermal process produces asphalthenes with lower molecular weight and more condensed aromatic structures. The rise up to 60% of the ratio of aromatic to paraffinic carbon (C_ar/C_p ( greatly affects the solubility of VB asphaltenes in a oily medium.     

PYROLYSIS AND LIQUEFACTION OF BRAZILIAN COAL AND COAL-DERIVED ASPHALTENES

The present work describes a study of the liquefaction and pyrolysis of a Southern Brazilian mineral coal and its derived asphaltenes, using conversion systems developed in our laboratory.

The results show that significant quantities of the intermediate polarity fraction named resins is obtained through the pyrolysis of coal, while after the liquefaction process higher quantities of the higher fractions was found. A model is proposed to explain the liquefaction and pyrolysis processes of both coal and coal-derived asphaltenes.     

CHARACTERIZATION OF HEAVY RESIDUA BY AAPPLICATION OF A MODIFIED D 2007 SEPARATION AND ELECTRON PARAMAGNETIC RESONANCE

ABSTRACT

Seven atmospheric residua (343^°C + [ 65O^°F + ]) were separated into saturate, aromatic, resin, and asphaltene fractions for detailled assessment of feed structure. The weight percent distribution of the fractions revealed two groupings of the residua. One grouping exhibited 20 wt % saturate composition, while the other only 10 wt %. The residua also exhibited high polar content (resin and asphaltene fractions) consisting of over 40% of the total residua. These results are related to the sulfur composition of the residua, and Indicate a fundamental relationship between the aromatic content and sulfur content. Discussion of the accuracy of the separation technique Is also Included.

The vanadium binding sites In the separated fractions were investigated by EPR spectroscopy. The resin and asphaltene fractions all appear to be dominated by 4N and N 0 2S coordination spheres. Discussion of this technique is also included.     

THE CONCEPT OF ASPHALTENES REVISITED

Petroleum asphaltenes are defined as material insoluble in pentane or heptane and the nature of the molecular species that constitute asphaltenes has been a well researched subject over the past three decades. These investigations have led to a general consensus of the majority of researchers that asphaltenes contain condensed aromatic systems carrying alkyl, cycloalkyl, and heteroatom substituents. A variety of molecular models has been developed which have been used to explain the behavior of asphaltenes in feedstocks during recovery and processing operations

However, an alternate concept introduced the idea that asphaltenes can be defined as a complex mixture of organic compounds of varying molecular weight and polarity. This allows asphaltenes to be described more fully in terms of their behavior during processes and properties in products, such as asphalt

Thus, the concept can be used to explain, even predict, the incompatibility of asphaltenes with the other petroleum constituents as well as the deposition of asphaltic material on reservoir rock and the occurrence of sediments during refinery operations.     

VISCOSITY AND SOLUBILITY OF MIXTURES OF BITUMEN AND SOLVENT

The solubilities of three bitumen samples (Suncor, Syncrude and Lloydminster) in five solvents were examined and prediction on the various bitumen-solvent mixture viscosities were made with Cragoe equation. By calculating the Cragoe constant 'a' for each mixture and using the average value in the Cragoe equation the prediction accuracy of the equation was improved by over 60%. Bitumen-naphtha mixtures showed the best viscosity prediction characteristics.

The solubility of the asphaltenes in the bitumen was highest in toluene among the five solvents However, naphtha, showed a moderate solvating power, which negligibly varied over the range of composition studied. Therefore naphtha, a solvent derived from bitumen was recommended as the most appropriate solvent for reducing the viscosity bitumen.     

减压渣油微观相结构特性的分子模拟

选用4种模型化合物代表减压渣油四组分(SARA),采用分子动力学模拟了减压渣油微观相结构,发现不同结构分子间相互作用的差异是减压渣油微观非均匀分布的本质原因,并通过电子分布特性分析了不同结构分子间相互作用差异的本质原因。沥青质分子间强相互作用使得沥青质分子自缔合形成聚集体;而多个胶质分子与沥青质分子的强相互作用封闭了沥青质分子自身进一步发生相互作用的活性位;同时,与胶质分子、饱和烃分子具有强相互作用的芳香烃分子将沥青质 胶质分子形成的聚集体分散在由芳香烃 饱和烃分子构成的连续相内,其中芳香烃分子更靠近胶质分子。因此,增加沥青质、饱和烃分子的含量会促进沥青质聚集,降低减压渣油稳定性;增加胶质、芳香烃分子的含量会阻碍沥青质聚集,提高减压渣油稳定性。     

CHARACTERIZATION OF ASPHALTENES AND RESINS FROM PROBLEMATIC MEXICAN CRUDE OILS

Asphaltenes and resins have been separated from four mexican oils suffering from the deposition of asphaltenic material during recovery operations. A SARA separation of the oils was performed and the resins and asphaltenes further analyzed. Characterization methods employed were FTIR, elemental composition both of CHNSO, and trace metals and molecular weight determination using size exclusion chromatography. NMR techniques were applied to two asphaltene samples. The overall scope of the work was to get a better understanding of the nature of the asphaltene stability at a molecular level in these problematic oils. Separation of resin in two fractions indicates that there is no long alkyl chains in these as given by FTIR, which may be the cause of the lack of stability along with the large difference in bubble point and reservoir pressure.

     

CHARACTERIZATION OF ASPHALTENES AND RESINS FROM PROBLEMATIC MEXICAN CRUDE OILS

Asphaltenes and resins have been separated from four mexican oils suffering from the deposition of asphaltenic material during recovery operations. A SARA separation of the oils was performed and the resins and asphaltenes further analyzed. Characterization methods employed were FTIR, elemental composition both of CHNSO, and trace metals and molecular weight determination using size exclusion chromatography. NMR techniques were applied to two asphaltene samples. The overall scope of the work was to get a better understanding of the nature of the asphaltene stability at a molecular level in these problematic oils. Separation of resin in two fractions indicates that there is no long alkyl chains in these as given by FTIR, which may be the cause of the lack of stability along with the large difference in bubble point and reservoir pressure.     

FRCTIONATION AND CHARACTERZATION OF SULFUR COMPOUND IN PETROLEUM DISTILLATES

A procedure For the fractionation and the characterization of sulfur containing compounds in petroleum distillates is descrloea. The method is based on a enromatograonic separation using aiumina columns ceated with silver nitrate (Ligand Exchange enromatography) which permits the seperation of molecules containing aromatic sulfer itniocnenic compounds from the sulfiaes

The subsequent gc analysis using selective atomic emission oetector allows the Quantification of the two types of sulfur as well as the quantification of the major sulfur -containing compounds n each fraction

The result of the application of theis procedure on an Egyption gas-oil from Belaym crude are reported.     

POLYMER SOLUBILITY THEORY PREDICTS EFFICIENCY OF RESIDUAL OIL EXTRACTION BY POLAR SOLVENTS

Light paraffinic solvents (C2 to C7) have traditionally been utilized by the petroleum refining industry to extract oils from crude distillation residua. Extracted oils constitute feedstock to lubricants manufacture and, to a lesser extent, additional cracking stock. More recent literature reveals a growing interest in polar, non-hydrocarbon partially oil-soluble solvents such as alcohols, ketones, and esters of lower carboxylic acids. In this work, articles and patents which report the separation of residua into asphalt and extracted oil by means of polar solvents are briefly reviewed, and the separation performance of same of those solvents is correlated to the solute-solvent interaction parameter (ϰ) in the Flory-Huggins theory of polymer solubility. The three dimensional solubility parameter (δ) approach is followed to estimate ϰ for the solvents of interest at the appropriate operating conditions. The saturate, aromatic, and polar compounds fractions of a bitumen are characterized by solubility parameters equal to the values of δ of the solvents or mixtures thereof used by the standard ASTM D-2007 chromatographic fractionation of the deasphaltenated oil (DAO). A mean value of ϰ is found for every DAO-solvent pair, treatment ratio and temperature. For each solvent considered, yields of extracted oil at varying operating conditions (temperature, pressure, solvent /feed ratio) are found to be well correlated to ϰ, in according with theoretical predictions that the lower a value of ϰ a solvent has for a given solute, the better it dissolves the solute and the higher the yield.

It is suggested that this type of approach could supply criteria to select solvents and operating conditions for applications requiring high yields (to produce additional cracking stock) or lower yields but high rejection of metals and heteroatoms (e.g. for lube oil bases extraction).     

OXIDATION KINETICS OF ASPHALT CORBETT FRACTIONS AND COMPOSITIONAL DEPENDENCE OF ASPHALT OXIDATION

This paper investigates the oxidation kinetics of asphalt generic fractions and the contribution of each individual fraction to the oxidation of the whole asphalt. Polar aromatic (PA) and naphthene aromatic (NA) fractions of five Strategic Highway Research Program (SHRP) core asphalts (AAA-1, AAD-1, AAF-1, AAG-1 and AAM-1) were prepared and aged at multiple conditions to obtain their kinetic parameters. Aromatics/saturates/asphaltenes blends of four of the five asphalts were also aged to deduce the influence of saturates and asphaltenes.

Carbonyl growth in the PA and NA fractions as a result of oxidation follows a similar profile as the whole asphalts. The kinetic parameters of the NA fractions occur in two groups, one with high reaction order and activation energy, and the other with low values of each. The kinetic parameters of the PA fractions all fall into the low-values group. Although the PA fraction is the most reactive portion in an asphalt, its kinetic parameters (reaction order and activation energy) may be much different from those of its parent asphalt. Saturates have only a dilution effect. The data indicate that the addition of asphaltene increases the oxidation rate. The data also indicate that the PA and NA fractions age faster in a separated state than in a mixed state. This study shows that the kinetic characteristics of an asphalt are determined not only by the kinetic characteristics of the fractions but also by the interactions and molecular associations between the fractions.