US20100101980A1

US20100101980A1 - Extraction of bitumen from oil sands

Info

Publication number: US20100101980A1
Application number: US12/260,313
Authority: US
Inventors: John E. Stauffer
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-10-29
Filing date: 2008-10-29
Publication date: 2010-04-29
Also published as: CA2681857A1; US9169441B2; US20120074045A1

Abstract

Carbon disulfide is used as a solvent to extract bitumen from oil sands in an anhydrous countercurrent flow process that is compatible with existing procedures for upgrading bitumen. The solution is then fractionated to separate the carbon disulfide from the bitumen product. The bitumen is then treated with hydrogen to decompose the remaining carbon disulfide. The process should provide high yields and meet environmental concerns.

Description

FIELD OF THE INVENTION

A process is provided for the extraction of bitumen from oil sands employing carbon disulfide as a solvent. In the process, oil sands are contacted with carbon disulfide to dissolve the hydrocarbon contained in the sands. Next, the resulting solution of hydrocarbon is fractionated to separate the carbon disulfide from the product, the bitumen is treated with hydrogen to decompose the remaining carbon disulfide.

BACKGROUND OF THE INVENTION

Oil sands are growing in importance as a source of petroleum. Oil sands are found in various parts of the globe, but the most significant deposits occur in northern Alberta, Canada, along the Athabasca River. The composition of oil sands is a mixture of quartz, clay, water and about ten percent heavy oil with a consistency of tar and known in the industry as bitumen.
The accepted practice for extracting bitumen from oil sands is to mix the sands with hot water and caustic to form an oil emulsion that is siphoned off from the solids. The mineral tailings are discarded after about 95 percent of the oil has been recovered. The extracted oil is upgraded by one of two processes to produce a synthetic crude oil that is suitable for refining at a later stage.
While current technology is workable, it has some drawbacks, particularly as practiced on a large scale. Water pollution is caused by the discharge of substantial quantities of wastewater. The energy efficiency of the process is poor. Lastly, the required investment in plant and equipment is considerable.
The object of the present invention is to provide an improved bitumen extraction process which is more cost-effective, meets environmental concerns and provides a product of the highest quality. This object, as well as other features and advantages of the present invention, will be apparent from the following description which is based on the single drawing figure that is included.
Other applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawing.

SUMMARY OF THE DISCLOSURE

The present invention comprises three steps for the extraction of bitumen from oil sands. First, the oil sands are mixed with carbon disulfide to dissolve the oil and extract it from the solid material. Second, the solution of oil is fractionated to recover the oil and separate the carbon disulfide. Third, the recovered oil is treated with hydrogen to destroy vestiges of carbon disulfide dissolved in the oil.
The process is carried out for the most part under anhydrous conditions. In this manner, water pollution from the discharge is tailings is avoided. Additionally, the recovery of oil is enhanced. Finally, by recycling carbon disulfide to the extraction steps, its consumption is kept to a minimum.

BRIEF SUMMARY OF THE DRAWING

The description herein makes reference to the accompanying drawing wherein like reference numerals refer to like parts throughout the several views and wherein:

FIG. 1 is a block diagram showing three steps of the process, including extraction, fractionation, and hydrotreating.

DETAILED DESCRIPTION OF THE PROCESS

The oil contained in oil sands is a heavy, viscous hydrocarbon mixture not unlike tar. With the nomenclature of bitumen, this oil contains molecules with twenty or more carbon atoms. By contrast, light sweet crude, the premium feed to refineries, is mostly made up of compounds with five to twenty carbon atoms. Bitumen is further characterized by its content of aromatic compounds in addition to aliphatic hydrocarbons. Bitumen also contains substantial quantities of bound sulfur.
Given the nature of bitumen, this raw material presents difficult problems in its recovery from oil sands. As already mentioned, the prior art depends on forming a water-oil suspension that is separated from the solids by flotation. Alternatively, bitumen can be heated to a high temperature, in excess of 538° C., to reduce its viscosity to a point where it will flow. This approach is used for in-situ recovery of oil from oil sands that lie too deep in the ground to be dug up by strip mining.
For this invention, I use carbon disulfide as a solvent for the bitumen. Carbon disulfide is an excellent solvent for this purpose: it is completely miscible with hexane as well as xylene. Up to 20 gm. of paraffin wax and as much as 40 gm. of naphthalene can be dissolved in 100 gm. of carbon disulfide at 20° C.
The low viscosity of carbon disulfide is also an advantage. At 20° C., its viscosity is 0.32 centipoises. This value compares with about 20,000 centipoises and up for bitumen. The viscosities of solutions can be determined by experiment or calculated from standard formulas. Further enhancing its ability to extract bitumen, carbon disulfide can be employed in countercurrent equipment.
The cost of carbon disulfide is a major concern even though the reuse of solvent is assumed. To mine substantial quantities of oil sands cost-effectively requires that the solvent used, be cheap. Fortunately, carbon disulfide can be synthesized from plentiful materials that are found in the oil sands deposits. It can be produced in an electric furnace from elemental sulfur and petroleum coke. Alternatively, it can be formed from carbonyl sulfide, which in turn is made from sulfur dioxide and carbon monoxide.
The solution of bitumen in carbon disulfide is fractionated to recover the bitumen. This step is most easily accomplished by distillation. Bitumen has a high boiling point whereas carbon disulfide boils at 46.25° C. under 1 atmosphere pressure. Notwithstanding the ease of separation, some residual carbon disulfide can be expected to remain in the bitumen.
Because of tightened specifications for petroleum products, including gasoline and diesel fuel, there is a need to reduce sulfur values to a minimum. Such a requirement can be met through hydrotreating. This step entails the reaction of the bitumen stream with hydrogen at elevated temperatures, in the range of 200° C. to 300° C. A catalyst may or may not be used. Cobalt compounds, including cobalt-molybdenum alloys, have been found to be effective in this application.
The reaction that takes place when carbon disulfide is created with hydrogen is shown by the following equation.
CS₂+4 H₂→CH₄+2 H₂S
where CS₂is carbon disulfide, H₂is hydrogen, CH₄is methane, and H₂S is hydrogen sulfide. The thermodynamics for this reaction is extremely favorable under operating conditions so that it goes to completion.
The hydrotreating step can be integrated into the upgrading of bitumen. Because bitumen is so viscous, it cannot be pumped or processed in its existing state. Therefore, one of two processes is generally employed to reduce its viscosity: coking and hydrotreating. Both measures can be taken. The result is a synthetic crude oil that is acceptable for further processing.
A better understanding of the present invention can be gained by reference to FIG. 1. Oil sands, the ore process in the process, and the carbon disulfide are fed to extractor 1. The resulting solution is passed to fractionator 2, while the tailings are discarded. Bitumen from unit 2 is hydrotreated in upgrader 3 to produce synthetic crude oil. The carbon disulfide from the fractionator 2 is recycled to extractor 1.
Making improvements in the processing of oil sands is particularly urgent because the industry is expanding at a breakneck pace. Practices that have been accepted in the past cannot deliver the results demanded by current conditions. The present invention is ideal for meeting the tremendous growth that is forecast.

EXAMPLE

The viscosity of a solution of bitumen in carbon disulfide was calculated using the following expression:
log Φ=x _Alog Φ_A +x _Blog Φ_B
where Φ is fluidity, the reciprocal of the coefficient of viscosity, and x is the mole fraction.
For a solution in which the mole fraction of bitumen is 0.1, the viscosity equals 0.90 centipoises. This result compares with the viscosity of 1.0 centipoises for water.

Claims

1. A process for the extraction of bitumen from oil sands comprising the steps of:

dissolving the bitumen in carbon disulfide to produce a solution;

fractionating the resulting solution to recover bitumen and carbon disulfide; and

hydrotreating the recovered bitumen to remove remnants of carbon disulfide.

2. A process according to claim 1 in which the extraction step is achieved by countercurrent flow of carbon disulfide and oil sands.

3. A process according to claim 1 in which the fractionation is achieved by distillation.

4. A process according to claim 1 in which hydrotreating is conducted in the presence of a cobalt catalyst.