Formation of coke during thermal hydrocracking of Athabasca bitumen

The formation of two structurally different cokes during thermal hydrocracking of Athabasca bitumen is attributed to differences in coking properties of the asphaltenes and the deasphalted heavy oils. The grain-mosaic coke structure formed from the asphaltenes may be ascribed to the presence of crosslinkage groups derived from the phenolic character of this fraction of the bitumen. Carbonization of the deasphalted heavy oils of the bitumen results in a flow-type coke structure. These two cokes appear to form independently of each other and can therefore be readily identified in samples collected from the reactor.     

Kinetics of the thermo-oxidative and thermal cracking reactions of Athabasca bitumen

The thermo-oxidative and thermal cracking reactions of Athabasca bitumen were examined qualitatively and quantitatively using differential thermal analysis (DTA). Reaction kinetics of low temperature oxidation (LTO) and high temperature cracking (HTC) were determined. The rate of the LTO reaction was found to be first order with respect to oxygen concentration. The activation energy and the Arrhenius pre-exponential factor were 64 MJ kg^?1 mol^?1 and 10^5.4 s^?1, respectively. The effects of atmosphere, pressure, heating rate and support material on the thermal reactions of bitumen were studied. In general, it was found that partial pressures of oxygen > 10% O₂ favoured exothermic oxidation reactions. High pressure increased the rates of LTO and HTC as well as the exothermicity of these reactions. A major contribution of this study to thermal in-situ processes is that heating rate can be used effectively to control the extent of low temperature oxidation and hence fuel availability during in-situ combustion. Low linear heating rates (2.8 °C min^?1) favoured low temperature oxidative addition and fission reactions. The reaction products readily formed coke and combusted upon heating. High linear heating rates (24.5 °C min ^?1) led to rapid oxidation reactions in the high temperature zone; the high temperature and the energy released during oxidation appeared to promote combustion. Finally, when sand was used as the support material there appeared to be a catalytic effect in both LTO and HTC reactions.     

Sulphoxidation of Athabasca bitumen

Treatment of Athabasca bitumen with sulphur dioxide proceeds mainly by oxidation, with sulphonation occurring to a lesser extent. The evidence indicates that when a bitumen is treated with oxygen, esters are the main products which must be hydrolysed in order to increase the emulsifying power of these materials. The use of sulphur dioxide also results in ester formation, but some formation of sulphonic and carboxylic functions may actually remove the necessity for a separate hydrolysis step to generate these emulsifying compounds that are presumed to be beneficial for in situ recovery of the bitumen.     

Chemical composition of Athabasca bitumen

A detailed analysis has been carried out on the deasphaltened Athabasca bitumen using two different series of Chromatographic separations followed by i.r., u.v., n.m.r. and computerized GC/MS studies of the separated fractions: saturates (22–25%), monoaromatics (10.3–10.8%), diaromatics (4.6–5.3%), polyaromatics and non-specific polar compounds (28.6%), acids (16.5%), bases (7.8%), and neutral nitrogen compounds (1.6%). The acyclic paraffin content of the maltene is low: straight-chain paraffins and the isoprenoids, phytane and pristane, are present in very low concentrations. Polycyclic saturates represent about 90% of the saturate fraction. The presence of C-27 and C-29–C-35 hopanes of the 17(h):21β(H) series and C-21–C-30 steranes was established. The mono- and diaromatic fractions were analysed by computerized mass spectrometry. The monoaromatic fraction contains alkylbenzenes, naphthenebenzenes and dinaphthenebenzenes in a ratio of 1.0:1.7:1.3. The ratio for naphthalenes, acenaphthenes + dibenzofurans and fluorenes in the diaromatic fraction is 1:0.9:0.5.     

Molecular weight distribution of Athabasca bitumen

A sample of whole Athabasca bitumen has been fractionated by preparative g.p.c. The weights of the fractions have been determined and their molecular weights measured by several methods. In contrast to previously published data, consistent results were obtained using different solvents (THF, be-nzene/water) and using different techniques (v.p.o., f.p.d. and g.c.-m.s.). This has resulted in an accurate definition of the molecular weight distribution of Athabasca bitumen.     

Oxidation reaction kinetics of Athabasca bitumen

The oxidation reaction kinetics of bitumen from Athabasca oil sands have been investigated in a flow-through fixed bed reactor using gas mixtures of various compositions. The system was modelled as an isothermal integral plug-flow reactor. The oxidation of bitumen was found to be first order with respect to oxygen concentration. Two models were examined to describe the kinetics of bitumen oxidation. In the first, the Athabasca bitumen is considered to be a single reactant and the oxidation reaction a single irreversible reaction. The activation energy for the overall reaction was found to be 80 kJ mol^?1. This model is limited to calculating the overall conversion of oxygen. Because the fraction of oxygen reacting to form carbon monoxide and carbon dioxide increases with temperature, a more sophisticated model was proposed to take this into account. The second model assumes that the bitumen is a single reactant and that the oxidation of bitumen may be described by two simultaneous, parallel reactions, one producing oxygenated hydrocarbons and water, the other producing CO and CO₂. The activation energy for the first reaction was found to be 67 kJ mol^?1, and for the second, 145 kJ mol^?1. This more sophisticated model explains the result that at higher temperatures more oxygen is consumed in the oxidation of carbon, because this reaction has a higher activation energy than the reaction leading to the production of oxygenated hydrocarbons and water. This model can also predict the composition of the product gases at various reaction conditions.     

Catalytic (Mo) upgrading of Athabasca bitumen vacuum bottoms via two-step hydrocracking and enhancement of Mo-heavy oil interaction

Athabasca bitumen vacuum bottom (ABVB) was fractionated into 66.9% maltenes (n-pentane-solubles), 32.2% asphaltenes (n-pentane-insolubles), and 0.9% coke (toluene-insolubles). The maltenes were subsequently split into four sub-fractions: 5.6% saturates (MF1), 2.6% mono and diaromatics (MF2), 38.2% polyaromatics (MF3), and 20.3% polars (MF4). Yield maximization of the desirable light MF1 and MF2 sub-fractions was explored according to three catalytic (Mo) scenarios: (i) a one-step ABVB hydrocracking with light products recovery; (ii) two-step process consisting of ABVB hydrocracking followed by the hydrocracking of the maltenic MF3+MF4 sub-fractions; and (iii) one-step ABVB hydrocracking with specific pretreatment procedures to enhance contacting between Mo-based catalyst and the heavy oil. The products yield distribution was mapped according to a severity parameter combining temperature and time. Coke and gas formation increased with increased severity while asphaltenes and total maltenes decreased. For scenario (i), the optimum severity factor for the highest light products yield was 7.2. At this severity the ensemble of saturates, plus mono and diaromatics reached 32.7%. For scenario (ii), the optimum severity factors were 6.9 and 7.0 for the first and second hydrocracking steps, respectively, resulting in a total light products yield of 45.4%. In scenario (iii) where options such as increasing the catalyst concentration, removal of oil-borne coke before hydrocracking and ultrasonic mixing, the maximum MF1+MF2 yield reached 50.8% on raw ABVB weight basis at a severity factor of 7.2.     

Plasticizing effectiveness of hydrocarbons in Athabasca bitumen

The plasticizing effectiveness of hydrocarbons in Athabasca bitumen (i.e. the extent of reduction in viscosity of the bitumen caused by hydrocarbons) depends on the molecular structure of the hydrocarbon and the molecular interaction between hydrocarbon and bitumen. High molecular weight branching, and aromatic and alicyclic rings, decrease the plasticizing effectiveness of the hydrocarbon. The plasticizing effectiveness decreases with an increase in the solubility parameter, which may be considered as a measure of molecular interaction.     

Catalytic desulphurization of Athabasca bitumen using hydrogen donors

The use of hydrogen-donor diluents while catalytically hydrocracking Athabasca bitumen has been studied. No improvement in sulphur removal, nitrogen removal or catalyst life was obtained from their use, contrary to reports in the literature. When the results were compared on the basis of constant reactor size and constant bitumen feed rate, the hydrogen-donor diluents were found to have a negative effect. Variations in the boiling-point range, sulphur content and nitrogen content of the donors only produced marginal changes. It was concluded that hydrogen-donor diluents are not effective processing aides, and therefore should not be used during the catalytic hydrocracking of Athabasca bitumen.     

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.     

Catalytic hydrocracking of bitumen at mild experimental condition

Mo-containing catalysts were prepared by impregnation method using silica-based porous supports and their physical properties were characterized by BET, XRD and TEM. Catalytic hydrocracking of bitumen extracted from oil sand was carried out in a high pressure reactor using Athabasca oil sand over 5 wt% Mo containing catalyst supported on SiO₂, MCF(Meso Cellular Foam) and SBA-15, respectively, under the conditions of 200 °C, 20 h and 10 atm of H₂ gas. Catalytic hydrocracking activity was estimated by analyzing H/C mole ratio based on EA data, and TGA was employed to compare the thermal behavior of bitumen before and after reaction. Upon hydrocracking over Mo/MCF catalyst, H/C was increased from 1.50 (bitumen itself) to 1.66.     

Separation and characterization of bitumen from Athabasca oil sand

Separation and chemical analysis was investigated using bitumen samples from Athabasca oil sand in Alberta. Fractionation according to solubility and polarity has been used to separate bitumen into its fractions. The solvent de-asphaltening was performed by n-pentane solvent (solubility fractionation), and the polarity fractionation using Fuller’s earth allows maltene to separate into SARA components (saturates, aromatics, resins and asphaltenes). The SARA components are analyzed comprehensively using elemental analysis (EA), Fourier-transformed infrared (FTIR), ultraviolet-visible spectroscopy (UV-vis), high performance chromatography (HPLC) and thermogravimetric analysis (TGA). EA (C, H, N, S), heavy metals (Ni, V) concentrations, FT-IR and UV-vis tests provided the explanation of chemical composition. From IR spectra, maltene and saturates/aromatics (sat/aro) contained more aliphatic compounds than resin or asphaltene. Also, IR spectrum of sat/aro was similar to crude oil and VGO (vacuum gas oil). Different UV signal data clearly indicates the contribution of aromatic constituents in the fractions. Using optimized analysis conditions of HPLC, we successfully separated the peaks for bitumen and its fractions. The characteristic peak pattern of SARA (saturates, aromatics, resins, asphaltenes) fractions was observed, and also the peak pattern of sat/aro was similar to that of crude oil and VGO. However, TGA results revealed that thermal behavior for sat/aro was similar to that of crude oil but different from that of VGO. Also, from the comparison between decomposition temperature of TGA and boiling point, their correspondence was found.     

A new reaction model for aquathermolysis of Athabasca bitumen

Aquathermolysis of bitumen occurs when it is thermally cracked in the presence of water. Current in situ technologies for bitumen production, such as Cyclic Steam Stimulation and Steam‐Assisted Gravity Drainage, inject high pressure, high temperature steam in the reservoir to heat the bitumen which in turn lowers its viscosity enabling flow to a production well. Thus, the major physical effect of steam is the heating of bitumen which mobilises it. Beyond physical interactions, chemical effects also result: steam heating produces acid gases, such as carbon oxides, sulphur dioxide and hydrogen sulphide along with small amounts of hydrogen and methane. For steam‐based in situ bitumen recovery processes, nearly all analyses, including simple drainage theories and thermal reservoir simulations, focus solely on the physical processes: heat transfer, fluid flow and thermodynamic equilibrium. However, steam chambers are also underground reactors: bitumen aquathermolysis occurs due to high temperatures and water saturation. Here, we describe a new in situ aquathermolysis reaction scheme for Athabasca bitumen to predict hydrogen, methane, carbon oxides, hydrogen sulphide and other heavy molecular weight hydrocarbons. Reaction parameters were fitted against one experimental data set and validated against other independent experimental data sets, both from the literature. Our results indicate that, to more accurately predict gas compositions and rates, the effects of aquathermolysis should be taken into account in reservoir modelling. © 2012 Canadian Society for Chemical Engineering     

A new kinetic model for pyrolysis of Athabasca bitumen

Pyrolysis of bitumen is a key contributor to gas production in in situ combustion and in situ gasification recovery processes, yet a detailed reaction scheme, that includes a breakdown of products into the most abundant gas components, that is simple enough to be used in detailed thermal‐reactive simulation models, does not exist. Here, we present a novel reaction scheme for pyrolysis of Athabasca bitumen that was developed and calibrated against four experimental data sets (65 data points) over a temperature range from 130 to 422°C. The new model was then verified by comparing its thermogravimetric behaviour against published literature. © 2012 Canadian Society for Chemical Engineering     

Effect of low-temperature oxidation on the composition of Athabasca bitumen

The effect of low temperature oxidation on the composition of Athabasca bitumen was examined. Oxidation temperatures in the range 125–135 °C and extents of oxidation up to 100mg $\text{O}{}_2\text{g}$ bitumen were investigated. The aromatics concentration was observed to decline steadily and the concentration of asphaltenes to increase, during oxidation. The saturates were unaffected by low-temperature oxidation. The resins concentration displayed a strange behaviour, first dropping and then increasing to a maximum and again dropping as oxidation proceeded.     

The production of low-sulphur liquids and coke from Athabasca bitumen

Hydrocracking of the Athabasca bitumen using a batch process produces liquid fuel streams that are highly aromatic. The results suggest that the use of hydrogen causes stabilization of the reactive intermediates rather than saturation of the thermal products. Furthermore, the liquid products are low in sulphur and asphaltics; coke with less than 2.5% sulphur is also produced.     

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.