Extraction of tar sands

Partition Coefficients of nonvl-phenyl-poly-(ethoxy)-ethanol (NPE) Surfactants. The solubility of surfactants in water and hydrophobic solvents is well documented (11,12,22), but only a few attempts at measuring partition coefficients between immiscible liquids have been reported (2,4,9,10). Partition coefficients of surfactants are of theoretical interest because of their relation to observed surfactant properties such as emulsification, wetting and detergency. Partition coefficients (K ) may be also of considerable practical value for predicting surfactant recov and recycling in industrial processes. For example, in the cold water extraction of tar sand, an effective surfactant with a high Kp could be efficiently recycled in the process water and would not follow the bitumen into the upgrading stream. 

Figure 5. Solvent-aqueoussurfactant extraction of tar sand with Triton and Makon surfactants. Surfactant added to initial aqueous phase.

Figure 7. Solvent-aqueous-surfactant extraction of tar sand vs, partition coefficient for Makon surfactants added to solvent (kerosene)...

Figure 10, Aqueous-surfactant extraction of tar sand (composite extraction index) vs, adhesion tension against various solids for Tween surfactants (0.02% w/v). Symbols as in Figure 8.

Extraction of tar sands with benzene or toluene yields a bitumen fraction and a mineral fraction. Further treatment of the bitumen with heptane or n-pentane yields asphaltenes and petrolene, which are the insoluble and soluble fractions, respectively. Depending on the source, these fractions contain varying amounts of vanadium (117,118). 

Bitumen. There are wide variations both in the bitumen saturation of tar sand (0—18 wt % bitumen), even within a particular deposit, and the viscosity. Of particular note is the variation of density of Athabasca bitumen with temperature, and the maximum density difference between bitumen and water (70—80°C (160—175°F)) hence the choice of the operating temperature of the hot-water bitumen-extraction process. 

On a commercial basis, tar sand is recovered by mining, after which it is transported to a processing plant, where the bitumen is extracted and the sand discharged. For tar sands of 10% wt/wt bitumen saturation, 12.5 metric tons of tar sand must be processed to recover 1 m (6.3 bbl) of bitumen. If the sand contains only 5% wt/wt bitumen, twice the amount of ore must be processed to recover this amount. Thus, it is clear that below a certain bitumen concentration, tar sands caimot be processed economically (19). 

Canada s Montreal oil refinery, has operated successfully since 1986. A variation for treating extracts from tar sands was developed by Petro-Canada Exploration and the Department of Energy Mines and Resources and piloted in Canada in the 1980s. Another variation, for making diesel fuel from vegetable oils, was piloted in Vancouver in 1992. 

Canadian oil sand processing plants have been developed by Syncrude and Suncor for extraction and upgrading of tar sand bitumen into fuel. Aboveground surface mining and in-situ methods have been developed to recover raw material. Bitumen recovery from surface mined oil sand requires conditioning in order to free the bitumen from the sand matrix. 

Panzer t al. (5) extracted Athabasca tar sand in two steps, the first with compressed n-pentane (Tc = 570 K, Pc = 3.37 MPa) and the second with compressed benzene (Tc = 563 K, Pc = 4.92 MPa). At 533-563 K and 2.0-7.7 MPa, n-pentane extracted 95% of the maltenes and asphaltenes from the tar sand, whereas at atmospheric pressure only 75% was extracted. Further extraction with benzene at 633 K and 2.0 MPa removed the remaining higher molecular weight asphaltenes. This indicates that the chemical nature of the dense gas is important in some applications. 

The organic matter in these tar sands resembles most crude oils in several respects. Metals always are concentrated in asphaltene fractions. Extracts from tar sands which are high in sulfur content usually have ratios of vanadium-to-nickel greater than unity, while those which are low in sulfur tend to have vanadium-to-nickel ratios less than unity. An exception to this generalization is the Edna, California tar sands, which yield extracts that are high in sulfur content but have vanadium-to-nickel ratios of less than unity. 

The hydrogen sulfide is now easily separated from the liquid hydrocarbon stream by distillation, and is then converted to elemental sulfur, another product of tar sands operations, via the Claus process. The stabilized liquid hydrocarbon stream is the synthetic crude oil product of tar sands extraction plants. 

In this way the useful petroleum fractions are recovered from the surface or near surface exposures of tar sand by the two currently operating hot water process extraction plants in Alberta. The production of synthetic crude oil by Alberta tar sand processors has risen from 28 million barrels (ca. 4 million tonnes) in 1978, to 77.3 million barrels (ca. 10.5 million tonnes) in 2003, which now supplies about 13% of Canada s current crude oil requirements [48]. Other processes for bitumen recovery from minable sands, such as preliminary partial sand removal with the help of cold water, followed by direct coking of the whole of the bitumen/solid residue, and solvent extraction methods have both been tested but are apparently not attractive for commercial development [49]. 

The pour point is the lowest temperature at which the bitumen will flow. The pour point for tar sand bitumen can exceed the natural temperature of tar sand deposits. It is important to consider because for efficient production a thermal extraction process to increase the reservoir temperature to beyond the pour point temperature must supply supplementary heat energy. Elements related to pour point are depth, bitumen viscosity, original reservoir temperature, and atomic hydrogen/carbon ratio. 

Synthetic Fuel. Solvent extraction has many appHcations in synthetic fuel technology such as the extraction of the Athabasca tar sands (qv) and Irish peat using / -pentane [109-66-0] (238) and a process for treating coal (qv) using a solvent under hydrogen (qv) (239). In the latter case, coal reacts with a minimum amount of hydrogen so that the solvent extracts valuable feedstock components before the soHd residue is burned. Solvent extraction is used in coal Hquefaction processes (240) and synthetic fuel refining (see Coal conversion processes Fuels, synthetic). 

Asphalt (bitumen) also occurs in various oil sand (also called tar sand) deposits which occur widely scattered through the world (17) and the bitumen is available by means of various extraction technologies. A review of the properties and character of the bitumen (18) suggests that, when used as an asphaltic binder, the bitumen compares favorably with specification-grade petroleum asphalts and may have superior aging characteristics and produce more water-resistant paving mixtures than the typical petroleum asphalts. 

The dense fluid that exists above the critical temperature and pressure of a substance is called a supercritical fluid. It may be so dense that, although it is formally a gas, it is as dense as a liquid phase and can act as a solvent for liquids and solids. Supercritical carbon dioxide, for instance, can dissolve organic compounds. It is used to remove caffeine from coffee beans, to separate drugs from biological fluids for later analysis, and to extract perfumes from flowers and phytochemicals from herbs. The use of supercritical carbon dioxide avoids contamination with potentially harmful solvents and allows rapid extraction on account of the high mobility of the molecules through the fluid. Supercritical hydrocarbons are used to dissolve coal and separate it from ash, and they have been proposed for extracting oil from oil-rich tar sands. 

These are found in crude petroleum including bitumen in the Athabasca tar sands of Northern Alberta. They contain a complex mixture of saturated polycyclic live- and six-membered cycloalkanes with alkane and alkanoic acid substituents. Attention has been directed to the degradation of both commercially available products, and those that are produced during bitumen extraction. Although the former were degradable (Clemente et al. 2004), the higher molecular mass components of the latter were much more recalcitrant (Scott et al. 2005). 

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