Identification of nitrogen functional groups in Athabasca bitumen

Reactions of resins, asphaltenes and model nitrogen compounds with acetic anhydride and with trifluoroacetic anhydride yield compounds which provide indications that the predominant nitrogen functional groups in resins and asphaltenes (from Athabasca bitumen) exist as imino groups of the carbazole-type. Evidence for this was obtained from infrared and F¹⁹ nuclear magnetic resonance studies.     

TGA studies of asphaltenes derived from cold-lake (Canada) bitumen

The pyrolysis of the asphaltene fraction from Cold-Lake, Canada, bitumen in a nitrogen environment in the temperature range 20–845°C has been studied by TGA. A rate equation for the decomposition of asphaltenes was derived and a second order decomposition of asphaltenes was observed. The apparent activation energy and the Arrhenius constant for the decomposition of the asphaltenes were calculated and found to be 56.5 kcal/mol and 5.2 × 10¹⁸g^?1 min^?1, respectively.     

Investigation of hydrogen bonding by oxygen functions in Athabasca bitumen

A study has been made of the role played by the oxygen functions in hydrogen-bonding interactions which occur between the asphaltene and resin entities of Athabasca bitumen. The results show that hydrogen bonding occurs readily between these fractions and allows feasible representation of the manner by which the asphaltenes are peptized by the resins.     

Pyrolysis and Pt(IV)- and Ru(III)-ion catalyzed pyrolysis of asphaltenes in organic geochemical investigation of a biodegraded crude oil (Gaj, Serbia)

This paper is aimed at investigating the origin and geological history of the biodegraded Gaj (Serbia) crude oil, based on comparison of biomarkers, particularly alkylaromatics, in crude oil maltene fraction, with those in the liquid raw asphaltene pyrolysis products. The content of asphaltenes in crude oils being generally very low, expecting a higher yield of pyrolysate, pyrolysis of raw asphaltenes was also carried out in the presence of Pt(IV)- and Ru(III)-ions. The used metal ions demonstrated positive effects on the yields of total liquid pyrolysate and corresponding hydrocarbons. Occluded maltene and asphaltene pyrolysis products showed that metal ions had considerably stronger effect on maturation changes in naphthalene and phenanthrene rings than in polycyclic alkanes. The values of maturity parameters observed in maltenes and pyrolysates suggested this crude oil to have been expelled from the source before the “oil window” maximum. The investigated sample of the Gaj crude oil was shown to be in the 4th stage of biodegradation scale and to have originated from source rocks poor in clays, most probably carbonates, with significant contribution of algae to oil precursor biomass, deposited under a stratified saline water column.     

Thermal cracking and combustion kinetics of asphaltenes derived from Fosterton oil

Thermal behavior of crude oil (Fosterton) asphaltenes mixed with reservoir sand was investigated using thermogravimetric analysis (TGA), in nitrogen and air atmospheres for different heating rates up to 800 °C. In this study, four sets of TGA runs were performed to examine the thermal behavior of Fosterton asphaltenes and the coke derived from the asphaltenes. The parameters studied were heating rate (10, 15 and 20 °C min^− 1) and the type of purge gas (N₂ and air) employed for the process of thermal degradation of asphaltenes. Distributed activation energy model (DAEM) has been applied to study the asphaltene pyrolysis kinetics. It was observed that the activation energy was distributed from 46.16 to 72.17 kJ/mol, for the conversion range of 0.1 to 0.4. The general model for nth order reaction was used to obtain the kinetic parameters of coke oxidation reaction from the TGA data. From the model, the calculated activation energy, E, was 93.46 kJ/mol and the pre-exponential factor was 9.59 × 10⁵ min^− 1 for the coke combustion. The apparent order of combustion reaction gradually increased from 0.7 to 0.8 for different temperatures.     

Comparative reactivities of coal asphaltenes during hydropyrolysis

Comparisons have been drawn in the relative reactivities of three coal asphaltenes during hydropyrolysis. All were derived from hydrogen donor-solvent extracts of bituminous coal, but had different hydrotreatment histories and different carbon contents (87.1, 91.9 and 90.8 wt% for asphaltenes 1, 2 and 3, respectively). The hydropyrolyses were carried out in the presence of CoO–MoO₃ catalyst and gaseous hydrogen at 8.7 MPa. For two of the asphaltenes (1 and 2) systematic comparisons were made for different reaction times at 425°C; for all three asphaltenes comparisons were made for l h of hydropyrolysis at 425°C. The general pattern of asphaltenes conversion indicated that more pentane-soluble product was produced from asphaltene isolated from straight coal extract (asphaltene 1). For the asphaltenes isolated from hydrotreated extracts, the extent of conversion to liquids was limited when the carbon content was high (asphaltene 2) although the pattern of conversion was similar in the other hydrotreated asphaltene (asphaltene 3). The aliphatic content of the liquid products formed was low, and the distribution of hydrogenated species in the highly aromatic liquid products indicated that complete hydrogenation of the polyaromatics produced in pyrolysis is difficult. Altogether the aliphatics made up ≈ 10 wt% of the asphaltene 1 hydropyrolysate. Aromatic hydrocarbons made up 90% of the liquid product. Phenanthrene, pyrene and anthracene were prominent, and the largest component in the mixture was phenanthrene which, together with other polyaromatics such as fluoroanthene, dominated the liquid product.     

Molecular size and weight of asphaltene and asphaltene solubility fractions from coals, crude oils and bitumen

The molecular weight of asphaltenes has been a controversy for several decades. In recent years, several techniques have converged on the size of the fused ring system; indicating that chromophores in virgin crude oil asphaltenes typically have 4-10 fused rings. Consequently, the molecular weight debate is equivalent to determining whether asphaltenes are monomeric (one fused-ring system per molecule) or whether they are polymeric. Time-resolved fluorescence depolarization (FD) is employed here to interrogate the absolute size of asphaltene molecules and to determine the relation of the size of the fused ring system to that of the corresponding molecule. Coal, petroleum and bitumen asphaltenes are compared. Molecular size of coal asphaltenes obtained here by FD-determined rotational diffusion match closely with Taylor-dispersion-derived translational diffusion measurements with UV absorption [1]. Coal asphaltenes are smaller than petroleum asphaltenes. N-methyl pyrrolidinone (NMP) soluble and insoluble fractions are examined. NMP soluble and insoluble fractions of asphaltenes are monomeric. It is suggested that the ‘giant’ asphaltene molecules reported from SEC studies using NMP as the eluting solvent may actually be the expected flocs of asphaltene which are not soluble in NMP. Data is presented that intramolecular electronic relaxation in asphaltenes does not perturb FD results.     

Pyrolysis of SCG extract coal asphaltenes: Gas chromatographic-mass spectroscopic study of the n-pentane soluble fraction

The asphaltene fraction from a super-critical gas (SCG) extract of bituminous coal was pyrolysed under nitrogen at temperatures from 200 to 450 °C, and the resultant pyrolysate re-fractionated into four conventional solubility classes (n-pentane-soluble, benzene-soluble, pyridine-soluble and pyridine-insoluble). The present work describes the characterization of the n-pentane-soluble fraction by combined gas chromatography-mass spectrometry. Preliminary studies indicated that asphaltenes, conventionally isolated, occlude significant amounts of pentane-soluble material and a multiple precipitation procedure for generating a ‘clean’ asphaltene was accordingly adopted. A very complex mix of pentane-soluble material was generated from the asphaltenes at the ≈2–4% level throughout the entire pyrolysis temperature range. The products identified included (1) n-alkanes (2) alkylbenzenes (3) alkylnaphthalenes (4) indanes (5) biphenyls (6) phenols and (7) other minor constituents such as fluorene and phenanthrenes. They were separated by capillary g.c. and identified either by co-injection of standards or from their mass spectral properties using comparison with a computer accessed library of mass spectral data. The major products of pyrolysis of SCG asphaltenes are benzene-insoluble fractions (including pyridine-insolubles); the formation of these is associated with the reduction of phenolic content of the asphaltene pyrolysand.     

Behavior of tar sand bitumen with paraffinic solvents and its application to separations for athabasca tar sands

A study was made of the dissolution of tar sand bitumen using low-molecular-weight paraffinic solvents at essentially ambient temperatures. The experimental data were obtained using the spinning disc technique, liquid-fluidized beds, and direct particle-size analysis of the insolubles. The results are consistent with a mechanism where the paraffins leach the soluble oil from the bitumen and leave behind a porous network of insoluble asphaltenes. This phenomenon of oil diffusing through an asphaltene layer was modeled using Fick's law for unsteady-state diffusion. An understanding of the mechanism of bitumen extraction with paraffins and also the effect of fluid mechanics in the tar sand system have been applied to obtain a novel separation of deasphalted oil and asphaltenes from Athabasca tar sands. This new separation technique has the potential of simplifying downstream processing for the bitumen and also of avoiding environmental problems associated with the present tar sand extraction technology.     

Langmuir and Langmuir‐Blodgett Asphaltene Films at Heptane‐water Interface

Monolayer characteristics of subfractions and unfractionated whole asphaltenes from Athabasca oil sands bitumen were studied at heptane‐water interface. The transferred Langmuir‐Blodgett films of asphaltenes were characterised with atomic force microscopy and contact angle measurements. Monolayers prepared from the three asphaltene samples are found to behave similarly at heptane‐water interface. The high molecular weight asphaltene monolayer is the most expanded one whereas the low molecular weight asphaltene monolayer is the most condensed one. An asphaltene monolayer behaves differently at an airwater interface to a heptane‐water interface. The presence of the bulk heptane phase renders the interfacial asphaltene monolayer more flexible as compared to that at air‐water interface.     

Studies on the evolution of asphaltene structure during hydroconversion of petroleum residues

The evolution of asphaltenes has been studied under hydroconversion conditions with an ebullated bed on a Buzurgan (Middle East) feedstock. A bench unit was used to produce effluents in residue conversion conditions ranging from 55 to 85 wt.%. In those conditions, asphaltene conversion ranged 62–89 wt.%. Asphaltenes from the feedstock and unconverted asphaltenes have been characterized using Size Exclusion Chromatography to evaluate asphaltene size, and ¹³C Nuclear Magnetic Resonance to evaluate the evolution of the average molecular structure parameters of asphaltenes. Results obtained were compared to results obtained at moderate residue conversion levels in a fixed bed.

The work clearly shows that unconverted asphaltene evolution is continuous. Unit size decreases with increasing conversion while the aromaticity of the asphaltenes increases due to dealkylation. Our results suggest that the remaining asphaltenes are dissociated in smaller aggregates around 50% conversion. Below this level, asphaltene evolution may be related to dissociation mechanisms. Above 50% conversion, the chemical structure of asphaltene units still significantly evolves through dealkylation mechanisms, leading to fairly condensed structures that remain at high conversion. Based on these results, an attempt was conducted to interpret the evolution of unconverted asphaltenes as a function of residue conversion level using a simple molecular reconstruction method.     

Separation and characterization of clay from Athabasca asphaltene

Athabasca bitumen separated from the associated mineral matter by Soxhlet extraction contains fine clay particles and inherent ash. Empirical relations have been developed to estimate the percentage of clay and inherent ash present in the asphaltene fraction which concentrates in large measure the mineral constituents present in the bitumen. The ash level, Y, of the asphaltenes is related to the weight per cent of clay, C_t, by an expression of the form Y = 0.872C_t + 0.582. The ash level of the asphaltene fraction is also correlated with the infrared absorbance. A, at 1032 cm^?1 which gives an approximate empirical relation of the form A = 0.0648Y + 0.294. Greater accuracy at low ash levels can be achieved by measuring A at 1040 cm^?1 above the base line drawn from 960 to 1140 cm^?1. This results in the equation A = 0.0709Y + 0.0124 when a standard KBr pellet thickness of 0.833 mm and concentration of 2 mg asphaltene per 300 mg KBr is used. X-ray diffraction used to characterize the clay minerals shows decreasing crystallinity as the particle size diminishes. The infrared absorbance of this mineral matter indicates decreasing intensity of the band at 2930 cm^?1, associated with adsorbed and occluded organic matter, relative to the two characteristic clay bands at 3697 and 3620 cm^?1 as the particle size decreases. Trace element analysis of the asphaltene inherent ash, by inductively coupled argon plasma, shows the major metallic constituents to be vanadium, nickel and iron with minor amounts of calcium, potassium, aluminium and sodium.     

Pyrolysis and oxidation of heavy fuel oils and their fractions in a thermogravimetric apparatus

Using the derivative thermogravimetric technique, an investigation was made of the pyrolysis and oxidation of some heavy fuel oils and their separate paraffinic, aromatic, polar and asphaltene fractions. The thermal behaviour of fuel oil can be interpreted in terms of a low-temperature (< 400 °C) phase involving the volatilization of paraffinic and aromatic fractions, and a high-temperature phase in which the polar and asphaltene fractions pyrolyse and leave a particulate carbon residue. In an oxidizing atmosphere, the first phase (< 400 °C) consists of the simultaneous evaporation and oxidation of paraffinic and aromatic fractions. The second phase (400–550 °C) consists mainly of pyrolysis of oxidized polar materials, the asphaltenes, with a final phase involving the burning of the carbonaceous residue formed in the second stage.     

Mesophase formation in coal-derived liquid asphaltene

The carbonaceous mesophase transformation in two coal-derived liquid asphaltenes, Catalytic Incorporated and FMC-COED, has been studied using Fourier-Transform infrared spectroscopy (FTIR) and X-ray diffraction analysis. The Catalytic Incorporated asphaltene forms a coarse, deformed mesophase and the FMC-COED asphaltene forms a fine, isotropic mesophase. The FMC-COED asphaltene has more oxygen and aliphatic functional groups than that of the Catalytic Incorporated. FTIR analysis shows that oxygen remains in the pyrolysis residues in carbonyl and ether groups for both asphaltenes, but there appears to be more ether in the FMC-COED residues. The aliphatic functional groups in the FMC-COED asphaltene appear to crack off and react with the molecules in the pyrolysate and suppress mesophase growth.     

E.s.r. of Alberta tar sand bitumen and thermally hydrocracked products

A study of the vanadium and free radical species present in Athabasca bitumen and thermally upgraded products from a hydrocracking pilot plant was carried out. The samples were separated into asphaltene, chloroform resin, tetrahydrofuran resin and oil components, and the fractions studied by electron spin resonance. All samples except the oil fraction contained vanadyl (VO²⁺) ions and free radicals. It was found that even mild thermal treatment of bitumen produced considerable redistribution of vanadyl groups among the fractions, whereas at the severest hydrocracking conditions 94 wt% of all vanadyl groups were associated with the asphaltene fractions compared with only 58.5 wt% in the original bitumen. As the hydrocracking severity increased, the asphaltene vanadyl concentration initially increased above the value for unreacted bitumen and then decreased to a lower value. On the other hand, the resin vanadyl concentration decreased continuously and more rapidly than asphaltene vanadyl concentration. This indicates that vanadyl groups associated with the resin fractions are less stable than those associated with the asphaltenes and also suggests that transfer of vanadyl groups from the resin fractions to asphaltene predominates at low severity while removal of vanadyl groups predominates at high severity. The average spin Hamiltonian parameters showed that the chemical environment of vanadyl ions in the THF resins was significantly different from the vanadyl environment in the other two fractions.     

Liquid Chromatographic fractionation of oil-sand and crude oil asphaltenes

Asphaltenes extracted from Alberta oil sands (Athabasca, Cold Lake, and Peace River) and crude oils (Taber South and Fenn-Big Valley) were fractionated by sequential elution solvent chromatography (SESC) involving 10 organic solvents on a silica column. Athabasca asphaltenes and SESC fractions were further studied by elemental analysis, i.r., u.v., and n.m.r. spectroscopy. Incomplete extraction of maltenes from the oil-sand bitumens increased the yields of the first two SESC fractions, the saturates and aromatics, of oil-sand asphaltenes relative to the crude oil asphaltenes. About 55 wt% of the asphaltenes elute in fractions 3–5. Two distinct molecular types are present in the asphaltenes; namely, lower functionality species with lower heteroatom content and the higher functionality species with higher heteroatom content. Compounds eluting in fractions 3–10 are predominantly polynuclear aromatics with alkyl substituants and probably bridged by cycloalkanes. The extent of bridging as well as the location, number and type of heteroatoms determines the fraction in which each compound appears. Complexity of compounds eluting increases with time: earlier fractions are composed of smaller-size polynuclear aromatic centers and contain heteroatoms in predominantly ring locations, whereas later fractions contain a larger proportion of complex species and more functional heteroatom groups.     

Influence of thermal processing on the properties of Cold Lake asphaltenes. 2. Effect of steam treatment during oil recovery

Cold-bailed (untreated) Cold Lake crude asphaltenes have been compared to steam-stimulated Cold Lake crude and Cold Lake vacuum residuum asphaltenes by elemental analysis, vapour pressure osmometry, gel permeation chromatography, infrared spectroscopy, and thermogravimetric analysis. The results of these analyses indicate that the steam stimulation procedure used to produce Cold Lake crude asphaltene results in significant changes in all of the measured characteristics except molecular weight. These changes include a decreased $\text{H}\text{C}$ ratio, alterations in the carbon skeleton and functional groups, an increased percentage of aromatic carbon (as determined by ¹³C n.m.r.), and decreased volatiles evolution during thermogravimetric analyses. The changes occurring during steam stimulation, which are implied by these physical measurements, include side-chain dealkylation and/or aromatization of hydroaromatic rings and loss or alteration of some heteroatomic functional groups. Polymerization leading to high-molecular-weight materials was not observed.     

Hydrocracking of Athabasca bitumen over binary metal oxide (SiO2MoO3 and CoO/SiO2MoO3) catalysts

The hydrocracking of Athabasca bitumen was studied over SiO₂MoO₃ (80: 20wt%), 2.92 and 5.54 wt% CoO on SiO₂MoO₃, and commercially available CoOMoO₃/Al₂O₃ catalysts at temperatures in the range 648–698 K for 2 h under an initial hydrogen pressure of 7.0 M Pa in a batch reactor. The reaction products were separated into coke, asphaltenes, resins, aromatics, saturates and gases. The severity of cracking increased with increased reaction temperature. At 698 K, asphaltene and resin yields were low (0.59 and 13.22 wt%, respectively) and gas yields high (40.5 wt%). SiO₂MoO₃ and CoO/SiO₂MoO₃ catalysts showed higher activity than commercial CoOMoO₃/Al₂O₃ catalyst in the conversion of heavy fractions (asphaltenes and resins) and in the formation of light fractions (saturates and aromatics).     

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.     

Investigation of glass transition temperatures of Turkish asphaltenes

Asphaltenes are a major concern in production operations, due to their role in conversion of vacuum residues by processes such as coking, catalytic cracking and hydroconversion. Six Turkish asphaltenes were characterized by elemental content, proton NMR, carbon NMR, GPC, DSC. Differential scanning calorimetry (DSC) provides parameters for comparing the glass transition temperatures, endothermic behavior of asphaltene and a hypothetical melting temperature of the asphaltenes which is within the range of the pyrolysis temperature of asphaltenes. The glass transition temperatures points (T_g) of asphaltenes were determined using DSC. Hypothetical melting point temperature (T_m) of the asphaltenes was also calculated. Among all the asphaltenes tested, Bati Raman showed much higher glass transition temperatures than the others.