EXTRACTION OF BITUMEN FROM OIL SANDS

EXTRACTION DE BITUME DES SABLES BITUMINEUX

English 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 treated in a thermal reaction to reduce viscosity and then fractionated to recover the bitumen.

French Abstract

Du disulfure de carbone est utilisé comme solvant pour extraire du bitume de sables bitumineux dans un procédé à débit à contre-courant anhydre qui est compatible avec les procédures existantes pour valoriser du bitume. La solution est alors traitée dans une réaction thermique pour réduire la viscosité et ensuite fractionnée pour récupérer le bitume.

Claims

What is claimed is
1. A process for the extraction of bitumen from oil sands comprising
the steps of
(a) contacting the oil sands with carbon disulfide to put the bitumen into
solution,
(b) separating the oil sands from the solution,
(c) hydrotreating the solution as a thermal reaction in the presence of a
cobalt-containing catalyst to reduce viscosity, and
(d) fractionating the reduced viscosity solution to recover the bitumen
6

Description

= CA 02773021 2012-03-30
TITLE
EXTRACTION OF BITUMEN FROM OIL SANDS
FIELD OF THE INVENTION
[0002] 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
treated to reduce viscosity, and then fractionated to recover the bitumen.
BACKGROUND OF THE INVENTION
[0003j 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.
f00041 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
refilling at a later stage.

CA 02773021 2012-03-30
=
100051 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.
[0006] 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.
[00071 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
[00081 The present invention comprises 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. Next, the solution is treated to reduce viscosity, and
finally the solution is
fractionated to recover the bitumen. The treatment to reduce viscosity is
preferably carried out
by way of a thermal reaction.
[0009] The process is carried out for the most part under anhydrous
conditions. In this
manner, water pollution from the discharge in 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
[0010] The description herein makes reference to the accompanying drawing
wherein
like reference numerals refer to like parts throughout the several views and
wherein:
2

CA 02773021 2012-03-30
109111 Fig. 1 is a block diagram showing three steps of the process,
including extraction,
fractionation, and hydrotreating.
DETAILED DESCRIPTION OF THE PROCESS
100121 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.
100131 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.
100141 For this process, 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.
100151 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.
100161 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
3

CA 02773021 2012-03-30
=
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.
100171 The solution of bitumen in carbon disulfide is ultimately
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.
[00181 Because of the high viscosity of the solution, it is preferably
treated before
fractionating. This can be done through hydrotreating. This step entails the
reaction of the
bitumen solution with hydrogen at elevated temperatures, in the range of 2000
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.
[0019] The reaction that takes place when carbon disulfide is treated
with hydrogen is
shown by the following equation.
CS2 + 4 II2 CH4 + 2 H2S
where CS2 is carbon disulfide, H2 is hydrogen, Cl-I4 is methane, and 112S is
hydrogen sulfide.
The thermodynamics for this reaction is extremely favorable under operating
conditions so that it
goes to completion.
[0020] The hydrotreating step is 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.
[0021] A better understanding of the process 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 hydrotreator 2, while the tailings are
discarded. Bitumen from unit
4

CA 02773021 2012-03-30
2 is fractionated at unit 3 to produce synthetic crude oil. The carbon
disulfide from the
fractionator 3 is recycled to extractor 1,
[00221 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
100231 The viscosity of a solution of bitumen in carbon disulfide was
calculated using the
following expression:
log (I) = xA log + Xg log (Dg
where (1) is fluidity, the reciprocal of the coefficient of viscosity, and x
is the mole fraction.
(00241 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.

Representative Drawing