Coke Distillation Bitumens

A plot of the TGA curve versus the temperature of the distillation bitumen B80 (sample 6) and its colloidal components is shown in Fig. 4-37. The curves of the bitumen, the dispersion medium, and the petroleum resins difler very little from each other up to 450 °C. The differences shown by the curves in the temperature range above 500 °C represent the coke residue. The curve of the asphaltenes is shifted towards higher temperatures due to a higher particle mass and also has a considerably higher coke residue. 

Table 4-64 Means x of the coke residue for distillation bitumens ...

The total colloids (petroleum resins and asphaltenes) can be correlated quite well with the coke residues R600 and RSOO (Fig. 4-54 and 4-55). There is no difference between the distillation and the blown bitumens. Correlation of the maxima of the reaction rate DTG with the colloid content gives two straight lines for the distillation bitumens (independent of the origin of the samples) and a third line for the blown bitumens (Fig. 4-56). No other correlations with the colloid content were found, nor were any expected. 

The asphaltenes are responsible for the formation of coke residue due to their high content of condensed aromatic ring systems. This is shown by the correlation of the coke residues / 600 or RSOO with the contents of asphaltenes (Fig. 4-60). Independent of the origin of the samples, two straight lines result for the distillation bitumens, whereas the data of the blown bitumens fit a third line with a steeper slope. Correlation of the maxima of the reaction rate DTG upon the concentration of asphaltenes presents a similar picture (Fig. 4-61). 

Recovering the bitumen is not easy, and the deposits are either strip-mined if they are near the surface, or recovered in situ if they are in deeper beds. The bitumen could be extracted by using hot water and steam and adding some alkali to disperse it. The produced bitumen is a very thick material having a density of approximately 1.05 g/cm. It is then subjected to a cracking process to produce distillate fuels and coke. The distillates are hydrotreated to saturate olefinic components. Table 1-8 is a typical analysis of Athabasca bitumen. ... 

This difficulty in translating what appears to be a simple technique in a beaker to a viable continuous process contributed to the failure of many subsequent pilot plants. It was not until 1967 that the first commercial plant was put on stream, using giant bucket wheel excavators to mine the sand, the hot water process to separate the oil, centrifuging of the froth to remove solid and water contaminants, delayed coking of the bitumen to produce a sour distillate product, followed by hydrofining to produce a "synthetic crude oil. 

Technologies for upgrading heavy crude oils such as heavy oil, bitumen, and residua can be broadly divided into carbon rejection and hydrogen addition processes (Chapter 8). Briefly, carbon rejection processes are those processes in which a carbonaceous by-product (coke) is produced along with distillable liquid products. On the other hand, hydrogen addition processes involve reaction of the feedstock with an external source of hydrogen and result in an overall increase in H/C ratio of the products as well as a decrease in the amount of coke produced. 

Both of the Canadian plants use the technique of hot water extraction to remove the bitumen from the tar sand. In this procedure the tar sand, steam, sodium hydroxide, and hot water are mixed and tumbled at a temperature of around 90°C. Layers of sand pull apart from the bitumen in this process. Additional hot water is added and the bitumen-sand mixture is separated into two fractions by gravity separation in cells in which the bitumen rises to the top and is skimmed off, while the sand settles to the bottom. The upgrading of the bitumen to a synthetic crude is then accomplished by oil refinery procedures including coking, in which carbon is removed by thermal distillation and hydrotreating. 

Water and often fine sand and silt are held in various crude oils in permanent emulsions. Particularly crudes obtained by secondary methods and those from tar sands where water or steam are used contain water and mineral matter emulsified therein by the surface forces on small particles and drops. Azeotropic distillation removes the relatively small amount of water, using the solvent as an entrainer which dilutes the crude. This allows the mineral matter to be separated easily without using centrifuges with their substantial cost and wear, free of organic material, so it may be discarded with-out hazards of fire or odors the bitumen to be recovered for such use or cracked to give volatile fractions and coked to an ash-free coke the water to be obtained as distilled water for reuse. 

The nonvolatile residuum is used to produce road asphalt (sometimes referred to as bitumen) as well as a variety of asphalt grades for roofing and waterproofing. It is produced to certain standards of hardness or softness in controlled vacuum distillation processes. Asphalt is a residuum and cannot be distilled even under the highest vacuum because the temperatures required to volatilize the residuum promote the formation of coke. Asphalts have complex chemical and physical compositions that usually vary with the source of the crude oil. 

Data calculated from that for composite synthetic crude obtained after coking and Unifining of extracted bitumen, from Bachman and Stormont [2]. Before Unifining (hydrogenation) mean density of the composite stream would be somewhat higher, and sulfur content would be about 3%. Proportions of distillate components are approximate carbon content quoted is the coke residue on pyrolysis of bitumen. 

The Conradson coke residue in the non-distillable part of the samples (CCR/ND) 100 is in the limits from 23 to 33 % for vacuum residues, bitumens, and atmospheric residues. The statistics result in a mean x = 27.3 % and a coefficient of variation V = 9.6 % (relative). The products from conversion processes scatter from 33 to 58 %. The furfural extract (sample 24) stands out because it does not possess any coke residue. 

The Conradson coke residue in the simulated vacuum residue ((CCR/SVR) 100) for the vacuum residues and bitumens has a mean value x2l.6%( y= 7.01% relative). For the atmospheric residues the mean amounts to x = 13.8 % ( + y = 8.7 % relative). The products from conversion processes (samples 19, 20, and 22) have extremely high values demonstrating that they have been distilled exhaustively, whereas the distillate of the residue of a cat-cracker, sample 25, exhibits the extremely low value of 4.4 %. 

Recently, major synthetic oil producers in Western Canada have switched from atmospheric bottoms to vacuum resids for processing bitumen. This raises the question of what impact this change might have on the coke induction period during thermal processing of these materials. To address this question, Athabasca bitumen (+343°C) was fractionated using Distact distillation into four distillates and resids.The selected boiling point cuts were 525°C, 575°C, 625°C, and 675°C. The coke induction periods of bitumen... 

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