Water‐Based Bitumen Recovery from Diluent‐Conditioned Oil Sands

Important process development aspects leading to more efficient bitumen recovery from diluent‐conditioned oil sands by water‐based methods are discussed. Bitumen viscosity of 0.5–2 Pa·s is required at the processing temperature and can be reduced to this level by bitumen dilution with an organic solvent. Oil sand porosity, however, poses a restriction on the amount of diluent that can be accepted by the oil sand. Also oil sand‐diluent conditioning time is an important process parameter and can vary from a few minutes for oil sands with low‐viscosity bitumen to several hours if viscosity of the bitumen is high. Additionally, the bitumen separation efficiency during digestion and flotation can be enhanced by reducing the bitumen/water interfacial tension through addition, for example, of tripolyphosphate to the aqueous phase.     

Understanding Water‐Based Bitumen Extraction from Athabasca Oil Sands

The current state of knowledge on the fundamentals of bitumen recovery from Athabasca oil sands using water‐based extraction methods is reviewed. Instead of investigating bitumen extraction as a black box, the bitumen extraction process has been discussed and analyzed as individual steps: Oil sand lump size reduction, bitumen liberation, aeration, flotation and interactions among the different components that make up an oil sand slurry. With the development and adoption of advanced analytical instrumentations, our understanding of bitumen extraction at each individual step has been extended from the macroscopic scale down to the molecular level. How to improve bitumen recovery and bitumen froth quality from poor processing ores is still a future challenge in oil sands processing.     

Preparation of bitumen from oil sand by ultracentrifugation

Ultracentrifugation was investigated as a means to obtain solvent-free bitumen from oil sand. The bitumen from three oil sands of varying grades was separated by placing the sands in specially designed tubes and centrifuging for 2 h at 198 000 at 20 °C. For all grades of oil sand, approximately 70% of the bitumen was recovered. The recovered bitumen was compared to the residual remaining on the sand, and to that extracted by the conventional Soxhlet technique. The ultracentrifuged bitumen contained some emulsified water and a small amount of fine solids. The solvent-extracted material was water-free, but contained a small amount of residual solvent and fine solids. The ultracentrifuge caused some fractionation of the bitumen, resulting in a product slightly enriched in asphaltene components compared to the solvent-extracted material. The residual bitumen remaining on the sand was correspondingly slightly depleted in asphaltenes. However, as evidenced by gas Chromatographic simulated distillation data, ultracentrifugation did retain the light (180–220 °C) components of the bitumen which were lost during the solvent removal step following solvent extraction. Other analyses such as density, viscosity and elemental composition verified that ultracentrifugation resulted in some fractionation of bitumen components.     

Bitumen Recovery with Oily Air Bubbles

Air‐kerosene bubbles were used in a novel laboratory scale pipeline loop to assess the extraction performance of poor processing oil sand ores. The addition of kerosene to air, whereby producing oily bubbles, substantially enhanced bitumen recovery from poor processing oil sand ores. The oily bubbles were added in a pipeline loop during bitumen liberation from the sand grains. The bitumen recovery from poor processing ores with the addition of the oily bubbles to the conditioning slurry becomes comparable to that of good processing ores. The present findings can be of substantial benefit to the oil sands industry.     

Solvent screening for non‐aqueous extraction of Alberta oil sands

Non‐aqueous extraction of bitumen from oil sands has the potential to reduce fresh water demand of the extraction process and eliminate tailings ponds. In this study, different light hydrocarbon solvents, including aromatics, cycloalkanes, biologically derived solvents and mixtures of solvents were compared for extraction of bitumen from Alberta oil sands at room temperature and ambient pressure. The solvents are compared based on bitumen recovery, the amount of residual solvent in the extracted oil sands tailings and the content of fine solids in the extracted bitumen. The extraction experiments were carried out in a multistage process with agitation in rotary mixers and vibration sieving. The oil sands tailings were dried under ambient conditions, and their residual solvent contents were measured by a purge and trap system followed by gas chromatography. The elemental compositions of the extraction tailings were measured to calculate bitumen recovery. Supernatants from the extraction tests were centrifuged to separate and measure the contents of fine solid particles. Except for limonene and isoprene, the tested solvents showed good bitumen recoveries of around 95%. The solvent drying rates and residual solvent contents in the extracted oil sands tailings correlated to solvent vapour pressure. The contents of fine solids in the extracted bitumen (supernatant) were below 2.9% for all solvents except n‐heptane‐rich ones. Based on these findings, cyclohexane is the best candidate solvent for bitumen extraction, with 94.4% bitumen recovery, 5 mg of residual solvent per kilogram of extraction tailings and 1.4 wt% fine solids in the recovered bitumen. © 2012 Canadian Society for Chemical Engineering     

A New Device to Determine Bitumen Extraction from Oil Sands

The Batch Extraction Unit (BEU) has been in use since the 1970's for studying the extraction of bitumen from oil sand. The present study investigates an alternative method for estimating bitumen recovery, based on visualization of oil sand slurry undergoing digestion. A Couette flow device is loaded with known amounts of oil sand and water. Air is bubbled through the oil sand slurry, while it is subjected to controlled chemical conditions and shear environment. Images of the slurry are captured at various time intervals and then analyzed using image analysis software, which selects black areas based on the gray scale intensities of the area in view. The variation of the black area with time is used as a measure of bitumen recovery. The technique provides quick estimates of final recovery, while enabling kinetic studies of the liberation and recovery processes. The experimental set‐up offers great flexibility in selecting conditions for the digestion of oil sands.     

Effect of weathering on oil sands processability

Effect of weathering on oil sand processability was studied using a good processing ore, a laboratory weathered ore and a naturally weathered ore. The laboratory weathered ore was prepared by weathering the good processing ore in an oven under controlled conditions to study the nature of ore weathering. It was found that the bitumen recovery, bitumen flotation rate, and bitumen froth quality were greatly reduced due to ore weathering. It was also observed that the fresh bitumen coating on a silicon surface could recede and liberate from the silicon surface easily even in a warm water of 35°C. However, after weathering of the bitumen coating, its liberation became more difficult and effective liberation of bitumen from the silicon surface could only occur at higher temperature of 65°C. The current study further confirms that weathering enhanced adhesion of bitumen with solids, causing difficulties for bitumen liberation from sand grains and hence poor processability of weathered ores.     

Characterization of Circle Cliffs oil sands of Utah

In the continuing characterization studies of Utah oil sands, this article was focused on the Circle Cliffs deposits which occur in the southeastern region of Utah. The bitumen was separated from the oil sand using a toluene extraction method. The extracted bitumen was fractionated using the modified SARA method and its fractional composition was compared to the other bitumens obtained from the Uinta Basin deposits. This comparison indicated that Circle Cliffs bitumen was unique among the Utah oil sand bitumens, particularly with respect to the chemical composition of its resin fraction, but showed resemblance with the Canadian Athabasca bitumen in some features. The effect of resin composition on the bitumen viscosity is discussed. Mineralogical analysis was performed on the solids, which indicated relatively large proportions of carbonate and kaolinite minerals. The undesirable effect of these minerals in the modified hot-water processing of Circle Cliffs oil sands is briefly discussed.     

Processibility of Athabasca Oil Sand Using a Laboratory Hyd ro t ransport Extraction System (LHES)

A novel laboratory scale apparatus has been developed and used to assess the extraction performance of oil sands under conditions analogous to current industrial processes. The apparatus can be used to investigate independently, the liberation of bitumen from the sand as well as air‐bitumen attachment and bitumen recovery. Experiments show that lower operating temperatures have a detrimental effect on bitumen recovery and controlled air addition is beneficial for recovery. The liberation of bitumen from sand grains has been found to proceed faster than air attachment and bitumen recovery, making the flotation the ratelimiting step in the extraction process. The potential benefit of staged air injection into hydrotransport pipelines as a possible process aid is discussed.     

油砂沥青超声波减粘工艺研究

油砂沥青粘度较大,自然状态下不易流动,严重影响了管道输送及加工,针对目前油砂沥青研究中存在的问题,采用超声波进行了减粘的实验研究。实验综合考察了超声波作用时间、温度、超声波频率、超声波功率等因素对减粘效果的影响。实验结果表明,在适当的超声作用时间(20 min)、适宜的温度(30℃)、适宜的超声波频率(20 kHz)和超声波功率(250 W)的条件下,油砂沥青的减粘率可达80%以上。经超声波处理后的油砂沥青粘度略有恢复,但仍远低于处理前的粘度,超声波减粘效果良好。     

Role of mineral flotation technology in improving bitumen extraction from mined Athabasca oil sands: I. Flotation chemistry of water‐based oil sand extraction

The role of surface hydrophobicity in water‐based oil sand extraction is examined from the perspective of mineral flotation separation. Although anionic carboxylates (sulphonates) released from bitumen are helpful for charging bitumen and liberating bitumen from sand grains, their presence in oil sand slurries tends to make bitumen and bubbles less hydrophobic. In addition, solid hydrophobization under oil sand extraction conditions can occur through different mechanisms of carboxylate adsorption. It is the hydrophobized fine solids that present challenges for achieving a high bitumen recovery with a good froth quality, due to their competition with bitumen for attachment to bubbles. While chemisorption of carboxylates contributes to hydrophobization of heavy minerals present in oil sands, carboxylate adsorption activated by hydrolyzed metal cations alters silica and clays from hydrophilic to hydrophobic. Different adsorption mechanisms of calcium on silica, clays, and other minerals are analyzed to explain why fine solids of varying mineralogy in combination with calcium affect bitumen extraction differently. Metal ions that activate solid hydrophobization under oil sand extraction conditions are identified from dynamic attachment of solids from mature fine tailings (MFT) to bitumen. To mitigate the effect of fines on oil sand extraction, selective flocculation of fine solids is recognized as especially feasible for bitumen flotation recovery from oil sand middling streams. Future research in reducing or eliminating caustic addition, understanding the role of inorganic anions, and searching for feasible techniques for treating MFT based on different mineralogy and surface properties, are briefly discussed.

     

Understanding weathering of oil sands ores by atomic force microscopy

Effect of weathering on colloidal interactions between bitumen and oil sands solids was studied by atomic force microscopy (AFM). The change in bitumen chemistry due to weathering was found to have a negligible effect on the interactions of bitumen with solid particles. However, the increase in solid surface hydrophobicity due to ore weathering reversed the long‐range interaction forces between bitumen and solids from repulsive to attractive with a corresponding increase in adhesion force. The measured force profiles between bitumen and various solids can be well fitted with the extended DLVO theory by considering an additional attractive force. The attractive long‐range force and increased adhesion force make the separation of bitumen from solids more difficult and the attachment of fine solids on liberated bitumen easier, thereby leading to poor bitumen liberation and lower aeration efficiency. Such changes account for the observed poor processability of the weathered ores. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Wettability alteration of solid surface to enhance the bitumen liberation and the water-based processability of weathered oil sands

Weathering often induces bituminous materials adsorbing on the sand grains and leads to poor processability of the oil sands. Chemical and microbial pre-treatment of the prepared weathered ore model and a weathered oil sand ore were carried out to improve the solids surface wettability so as to facilitate the bitumen liberation and recovery. It was found that although all the cetyl trimethylammonium bromide (CTAB), sodium dodecylbenzene sulphonate (SDBS), and microbial culture medium could greatly decrease the surface tension of the solution, the CTAB treatment failed to improve the bitumen liberation, while the SDBS and microbial treatment significantly accelerated the bitumen liberation from the silicon substrates. The wettability analysis showed that the improved bitumen liberation could be attributed to the alteration of the solids surface wettability from hydrophobic to hydrophilic by the SDBS and microbial treatment. Inconsistent with the findings of the bitumen liberation, floatation tests of a weathered ore showed that the CTAB pre-treatment only gave a low bitumen recovery of 33%, while the SDBS and microbial pre-treatment improved the processability of the ore. In particular, the microbial treatment was more effective at removing the adsorbed organics from the solids and improved the surface hydrophilicity, resulting in a much better bitumen recovery of 95%. This work provides a way to improve the processability of the weathered ore by altering the solids surface wettability.     

Application of microbial enhanced oil recovery technology in water‐based bitumen extraction from weathered oil sands

When using the water‐based extraction processes (WBEPs) to recover bitumen from the weathered oil sands, very low bitumen recovery arisen from the poor liberation of bitumen from sand grains is always obtained. Application of microbial enhanced oil recovery (MEOR) technology in WBEPs to solve the poor processability of the weathered ore was proposed. It was found that processability of the microbial‐treated weathered ore was greatly improved. The improved processability was attributed to the biosurfactants production in the culture solution, alteration of the solids wettability, degradation of the asphaltene component, and the decrease of the bitumen viscosity, which collectively contributed to the bitumen liberation from the surface of sand grains. Although it still has many issues to be solved for an industrial application of the MEOR technology in oil sands separation, it is believed that the findings in this work promote the solution to the poor processability of the weathered ore. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2985–2993, 2014     

Characterization of organic‐coated solids isolated from different oil sands

Solids isolated from weathered oil sands ores and those having low‐ and high‐fine solids content were studied. The organic matter (OM) adsorbed on the solids was found insoluble in most common solvents, contributing significantly to the change of solid surface properties. The surface properties of these solids were found to affect the entire process cycle of obtaining synthetic crude oil from surface‐mined oil sands using a water‐based extraction process, and managing the existing tailings ponds. In this study, the low‐fine solids ore possessed the lowest amount of organic‐coated solids and highest bitumen recovery. Siderite and pyrite, which tend to concentrate in the hydrocarbon phase were observed in the isolated solids from the weathered and high‐fine ores but were absent in the low‐fine ores. In all the ores studied, the solids from the bitumen froth possess less quartz, and more carbonates compared with solids from the tailings. Elemental analysis by energy dispersive X‐ray spectroscopy (EDX) and elemental analyser revealed the presence of more transition metals (iron and titanium), and carbon in the solids obtained from the bitumen froth when compared with those from the tailings. Infrared (IR) spectroscopy study substantiated the results obtained by X‐ray diffraction and elemental analysis. IR spectra showed a likely association between OM and carbonates in the organic‐coated solids isolated from bitumen froth. More organic‐coated solids were found in weathered oil sands than in other types of ores and observed to reduce bitumen recovery from oil sands.     

Separation and Characterisation of Problematic Solids from Athabasca Oil Sands and Waste Unit Samples

Traditionally, Athabasca oil sands have been classified by bitumen and fines (<44 µm) contents. However, these markers do not always identify ores with poor processing characteristics. Consequently, there is a need to discover other characteristics to define problem ores. Here we describe a separation scheme for oil sands solids fractions based on their physical and surface properties. Clay material (<3 µm) and its ultra‐fine (<0.3 µm) component are of particular interest. Settling tests on ultra‐fine clay suspensions confirm that this fraction is the major cause of sludging during primary bitumen separation. Waste units, or barren oil sands, are shown to be a major source of this component.     

Bitumen—sand interaction in oil sand processing

Bitumen—sand interaction was studied as a function of pH, particle size, temperature and solvent addition to bitumen. Sand particles can be easily detached from the bitumen surface at pH> 6. At pH < 6, strong attachment between bitumen and sand is observed. The bitumen—sand interaction is also particle-size dependent: the finer the particles, the stronger the attachment. The detachment of coarse particles from bitumen can be achieved by increasing the alkalinity of the solution, but not for fine particles, indicating that the particle size is one of the critical factors affecting liberation of bitumen from sand. Increasing temperature has two effects: it is not only reduces the viscosity to facilitate bitumen liberation, but also increases the electrostatic repulsion between sand and bitumen. This is confirmed by the DLVO theory and is in agreement with the batch extraction results on real oil sands.     

水基提取技术用于油砂分离的研究进展

油砂作为一种重要的非常规油气资源,其分离技术的研究近些年来引起了国内科研工作人员的重视。介绍了目前世界上最重要的油砂分离技术--水基提取技术的基本原理及影响油砂分离的重要影响因素,阐述了油砂结构、特性与水基提取分离的重要关系及分离条件对沥青回收率的重要影响作用,同时探讨了原子力显微镜用于油砂水基分离过程中相关微观机理研究的重要应用,最后对水基提取技术用于油砂工业生产的流程进行了简单介绍。     

Effect of molecular weight and charge density on the performance of polyacrylamide in low‐grade oil sand ore processing

The effect of charge density and molecular weight (MW) of partially hydrolyzed polyacrylamide (HPAM) polymers on their performance in processing low‐grade oil sand ores was investigated. Bitumen extraction and tailings settling tests were carried out and an atomic force microscope (AFM) was used to directly measure the bitumen‐solid and solid‐solid interaction forces. It was found that HPAM polymers with a low MW acted as dispersants in the bitumen extraction process, resulting in low bitumen recovery and slow tailings settling but improved froth quality. In contrast, the use of HPAM polymers with a high MW improved both bitumen recovery and tailings settling but deteriorated froth quality. To achieve high bitumen recovery and fast tailings settling, a HPAM polymer must have a low to medium charge density (～30%) and a high MW (17.5 million Daltons). A stronger clay‐bitumen adhesion force normally resulted in a lower bitumen recovery. Fast tailings settling was achieved in the presence of a strong solid‐solid adhesion force.     

Fines/Water Interactions and Consequences of the Presence of Degraded Illite on Oil Sands Extractability

The chemical composition of the aqueous phase in oil sand slurries influences bitumen recovery from oil sands, especially those containing greater than 10% fines. The composition is controlled by a combination of mixing and dilution, ion exchange with clay surfaces and precipitation of divalent ions as carbonate minerals. Elevated levels of soluble potassium in the oil sand, which appear to be a marker for degraded illite or smectitic clays, are associated with depressed bitumen recovery. These clays have a swelling character and can contribute divalent ions to the slurry by ion exchange between the clay mineral surfaces and the process water.