Note: Descriptions are shown in the official language in which they were submitted.
-- ~101~4Q
LOA TEMPERATURE SEPARATION OF BITUMEN FROM OILSANDS
The present invention relates to the recovery of
bitumen from oilsands (tar sands) by a novel procedure.
Tar sands or oilsands comprise a mixture of bitumen,
minerals and water of variable bitumen content.
Surficial deposits of such tar sands located in the
Athabasca region of Alberta, Canada are being exploited
on a commercial scale at this time. In such deposits,
the bitumen content varies up to about 18 wt% and
averages about 12 wt%, water is usually about 3 to about
6 wt% and the mineral content, predominantly quartz,
ranges from about 84 to about 86 wt%.
At the present time, there is one commercial
procedure for the recovery of bitumen from these
deposits, known as the "hot water" process, involving
interconnected steps of feed conditioning, bitumen
separation, waste disposal and bitumen concentrate
cleaning. There are several disadvantages to the hot
water process and attempts have been made to improve the
process.
A major requirement in the economic recovery of
bitumen from Alberta oilsands is now seen to be the
separation of the sand fraction at low temperature. This
separation would enable the sand to be discarded close to
the mining site, and also would minimize heat loss
associated with the rejection of the sand fraction.
Several "cold water" processes have been proposed, the
most recent being the OSLO Cold Water Extraction (OCWE)
process, as described in U.S. Patent No. 4,946,597. In
the OWCE process, oil sand is slurried with water under
attrition scrubbing conditions. After dilution with
additional water and addition of kerosene as a
conditioning agent and methyl isobutyl ketone as a
frothing agent, bitumen is removed in a Denver-type
flotation cell. Results indicated that attrition times
of around 20 minutes at 5°C and 10 minutes at 15°C, at
high mixing speeds (2400 rpm) and high solids content
2101240
2
(about 70%), were necessary to effect bitumen recoveries
of 90% or greater from mid-grade oil sand.
The Alkali Recycle Process, originally proposed at
the Alberta Research Council in the late 1970~s and
described in U.S. Patent No. 4,409,091, incorporates a
separation step in which bitumen is freed from oilsand
matrix by emulsification at high temperatures under
shearing conditions with 0.1$ sodium hydroxide solution.
The bitumen emulsion is broken by the addition of calcium
hydroxide and the bitumen recovered by flotation.
Dispersed clays then are flocculated and converted to
rapidly dewaterable calcium forms by the addition of
further amounts of calcium hydroxide. In both steps,
sodium hydroxide is recovered through ion exchange and
made available for recycle. This procedure is described
in "The Recovery of Water and Alkali Used in Heavy Oil
and Oil Sands Extraction" by M.A. Kessick, Fuel, 6~
(1983), 1297. One potential improvement to this process
would be the removal of clean sand, and possibly useful
bitumen recovery, at low temperatures. The invention
described herein demonstrates that both goals can be
accomplished.
In this invention, rapid separation of the coarse
mineral fraction from Alberta oilsand can be accomplished
at low temperatures by attrition in dilute alkali (e. g.
0.1% sodium hydroxide solution). Bitumen recoveries in
the order of 90 to 95% then can be achieved by flotation.
The procedure can be integrated into a process that
provides for recycle of the alkali and that may also
provide opportunity for effective hydraulic mining of
oilsands.
Accordingly, in one aspect of the present invention,
there is provided a method for the recovery of bitumen
from oil sands, which comprises effecting attrition of
the oil sand in the presence of dilute alkali metal
hydroxide solution to form a slurry of bitumen in the oil
2~0~240
3
sands having a pH of at least about 11.5 and to separate
the bitumen contained in the oil sands from its mineral
content; optionally separating the slurry from a sand
phase; diluting the resulting slurry with further
quantities of dilute alkali metal hydroxide solution to
form an aqueous medium in which bitumen is separable by
flotation from minerals while maintaining the pH of the
slurry at least about 11.5; and floating bitumen from the
aqueous medium to effect separation of the bitumen from
minerals.
The first step of the process of the invention
involves effecting attrition of the oil sands in the
presence of dilute aqueous sodium hydroxide solution in
sufficient quantity to provide a slurry having a pH of at
least about 11.5, preferably about 11.8 to about 12.2, so
as to effect separation of the bitumen contained in the
oil sands from its mineral content. Such attrition
preferably is effected at relatively low temperatures,
generally below about 60°C, preferably below about 30°C.
The attrition step results in the formation of an oil-in-
water emulsion of the bitumen of varying quality.
Quantities of sodium hydroxide used in the attrition
step may vary from about 0.05 to about 0.5 wt% of NaOH of
oil sand. The concentration of sodium hydroxide in the
aqueous solution contacting the oil sand may vary up to
about 0.5 wt% NaOH and usually is in the range of about
0.1 to about 0.2 wt%.
As a result of the attrition step, the clay content
of the oil sand tends to become dispersed in the slurry
and remains suspended, while the sand separates readily
from the slurry. It is preferred to settle out the sand
from the slurry, so that it may remain at the mining
site, which may be surficial or subterranean.
Alternatively, sand separation may be effected in the
flotation operation described below. In addition, the
2101240
4
slurry may be allowed to stand to permit some of the clay
present in the slurry to deposit therefrom.
The second step of the process involves diluting the
slurry with aqueous sodium hydroxide solution to a
consistency such that the bitumen may be separated from
the clay and other minerals, such as residual sand, by
flotation using a flotation cell. Such addition of
aqueous sodium hydroxide solution is effected to maintain
the pH of the slurry at the same or approximately the
same value while diluting the slurry. In general, the
slurry is diluted to a solids content of about 5 to about
30 wt% using aqueous sodium hydroxide solution generally
of NaOH concentration less than about 0.5 wt% and usually
about 0.1 to about 0.2 wt%.
In the case of low grade oil sands, the recovery of
bitumen from the slurry can be improved by the addition
of small amounts of organic solvent, such as kerosene.
The quantity of kerosene or other suitable organic
solvent, such as diesel fuel or naphtha, usually varies
from about 0.1 to about 1.0 wt% on bitumen, preferably
about 0.4 to about 0.6 wt%.
In addition, the recovery of bitumen from a slurry
formed from low grade oil sands may be further improved
by the addition of small quantities of slaked lime to the
aqueous medium resulting from an initial flotation and by
effecting a further flotation step. The quantity of
slaked lime which may be used in this regard usually
varies from about 0.05 to about 1.0 wt% on initial
bitumen content, preferably about 0.1 to about 0.4 wt%.
A tendency for bitumen and solids to reaggregate
upon dilution has been observed for high bitumen content
oil sands, resulting in a high solids content of the
recovered bitumen. The addition of a small quantity of
a non-ionic surfactant to the dilute sodium hydroxide
solution used in the grinding and dilution steps prevents
such reaggregation from occurring.
2101240
Non-ionic surfactants particularly useful in this
regard are alkylphenol ethoxylates of the general
formula
5 R - ~ ~ - p - ( ~~ZC ) ~~ ~Z~zCH
where R may be nonyl (Igepal CO series) and n is between
1 and 100. Compounds with higher values of n have been
' found to be more effective at lower temperatures. The
quantity of such non-ionic surfactant which may be used
is from about 0.02 to about 1.0 wt% on bitumen,
preferably about 0.08 to about 0.3 wt%.
The flotation of the bitumen from the diluted slurry
to effect separation of the bitumen may be effected using
any commercially available flotation equipment, generally
using air as the flotation gas, with the bitumen being
skimmed from the surface. The flotation operation
results in separation of the bitumen from minerals,
mainly clay and any sand not previously separated
following the attrition step.
The bitumen phase is separated from the surface of
the liquid in the flotation equipment and then may be
forwarded to an upgrading operation.
The clay suspension then may be dewatered to recover
the sodium hydroxide solution, which may be recycled for
use in the attrition and/or dilution steps. A
flocculating agent, such as slaked lime, may be added to
the aqueous phase to promote settling of the clay. In
addition, the separation may be assisted by
centrifugation,freeze-thaw techniques and/or filtration
.
The recovered aqueous sodium hydroxide solution may
contain calcium ions, if used during the flotation
operation and/or in settling the clay. If such solution
is to be recycled for reuse, it is preferred to remove
such calcium ions by suitable softening, using, for
* Trademark
A
2101240
6
example, sodium carbonate. Makeup quantities of sodium
hydroxide may be added to the recycle stream.
The invention is illustrated by the following
Examples:
Example 1:
In a first series of experiments, oil sand (100 g)
was slurried with 50 mL of 0.1% sodium hydroxide at
approximately 4°C (refrigerator temperature) and at 22°C
(room temperature) using a laboratory stirrer operating
at 1500 rpm. Both low grade oil sand (LGOS, 7.4%
bitumen, 85.0% solids, by Dean and Stark analysis) and a
high grade oil sand (HGOS, 12.8% bitumen, 84.1% solids)
were processed. Although the stirring time used was two
minutes for all tests, at 4°C fluid slurry formation
seemed essentially complete in about 30 seconds, and at
22° in less than 10 seconds. For the runs at 4°C, 0.058
of kerosene was added and conditioning continued for one
minute.
The slurry then was added to approximately 800 mL of
0.1% sodium hydroxide solution, which was either at room
temperature or which had been cooled to 4°C, in a
laboratory scale Denver cell. Flotation was carried out
for three minutes to produce a "primary" product. In the
case of the low grade oil sand, when appearance of the
primary product in the froth had ceased, a small amount
(0.02 g) of calcium hydroxide was added. After agitating
the slurry for one minute, flotation was continued for a
further three minutes, to produce a "secondary" product.
This flotation sequence was essentially the same as that
reported by Chakrabarty et al, Proceedings of the 2nd
World Congress on Chemical Engineering, Montreal, October
1981.
The sand was removed from the flotation cell, dried,
and analyzed for residual bitumen by Soxhlet extraction.
During the 4°C runs, the bitumen product also was
collected for analysis. After standing at room
2~.012~0
temperature for approximately one hour, the drained
bitumen was dried and analyzed for solids content. This
was carried out by diluting a known mass with toluene and
centrifuging, followed by two washings with toluene and
centrifugation. The solids were quantitatively removed
from the centrifuge tubes, dried and weighed.
Residual bitumen contents of the extracted sand
are listed in the following Table 1:
21~124~
M d' C1 01
ro
e-1 . . . .
IA
O O O O
r~
.,.~
N
41
O
b
G
C 0.,~
O O
O O O O
ro
U
G
O
C
~.J
o
ro
O ~
r~
f,.~
W O
~
N N
O 11
'~
N
N 4J
'd
U!
~!,
x x ~
.,.,
a
0
~ a~
.-1N r1 d'
z
.~
2101240
9
At 22 °C, brown bitumen emulsions were visibly formed
after attrition for about 10 seconds. These emulsions
destabilized on dilution by the 800 mL of 0.1% NaOH in
the flotation cell, and the bitumen was removed as a
compact layer from the froth. No addition of frothing
agent or conditioning agent was necessary in this
procedure.
At 4°C during the initial attrition, the bitumen
seemed to separate from the matrix as large flecks. The
separation was effectively complete after about 30
seconds, as indicated by the fluidity of the slurry.
Conditioning of this slurry prior to flotation with
500ppm of kerosene (based on oil sand) was found
necessary at this temperature in order to obtain a
tractable product. On adding the conditioned slurry to
the 800 mL of 0.1% NaOH in the float cell, the flecks
rose to the surface of the froth and coagulated to a
compact mass that was easily removed with a spatula. At
this low temperature, some oil sand was not broken down
by the attrition and remained as lumps. These were
removed from the sand before analysis by a number 18
screen. For Run 1 they amounted to 4.6% of the original
oil sand and for Run 3, 1.6% of the original oil sand,
indicating the problem is more pronounced for high grade
oil sand. It is expected that an improved attrition
device would reduce these percentages.
It was found, as in the previous work of Chakrabarty
et al., that addition of calcium hydroxide produced
further separation of bitumen in the case of the low
grade oil sand, causing a visible reappearance of bitumen
in the froth after "primary" production had ceased. This
was not the case for the high grade oil sand where all
the bitumen appeared to be recovered as "primary"
product.
Since a consistent drainage procedure was not
employed for the bitumen product, the solids content on
2~oiz~o
a dry basis is considered to provide the best estimate of
the bitumen quality. In the case of the high grade oil
sand processed at 4°C, the dry bitumen was found to
contain 16.0% solids. For the low grade oil sand
5 processed at 4°C, the dry primary bitumen product
contained 23.2% solids and the dry secondary bitumen
product contained 49.3% solids. These values correspond
to solids rejections of ca. 98% for both grades of oil
sand. It was determined that the secondary product was
10 initially associated with about three times as much water
as the primary product. The secondary product in the
case of the low grade oil sand contained approximately
16% of the total bitumen recovered.
Although no attempt was made to measure actual
bitumen recovery and to calculate detailed mass balances
in these preliminary experiments, the low residual
bitumen contents of the extracted sands indicate that,
even at 4°C, 90% or better recoveries can be expected
from low grade oil sand, and 95% or better from high
grade oil sand. At 4°C, the quality of the primary
bitumen product appears to be sufficiently good enough
to be acceptable for standard cleanup procedures prior to
upgrading. The secondary product from the low grade oil
sand at this temperature could require additional
processing.
example 2:
Oil sand (100 g) was slurried with 50 mL 0.125%
sodium hydroxide at 22°C or with 50 mL of 0.125 wt%
sodium hydroxide containing l0 ppm. of Igepal CO 730 at
4°C, using a laboratory stirrer with a toothed circular
blade operating at 1500 rpm. The 4°C grinding was
carried out in a refrigerated room. Stirring time was
increased to 4 minutes at this temperature to ensure all
the oil sand was broken down in the slurry. The slurry
then was added to 800 mL of 0.125 wt% sodium hydroxide
solution at 22°C or to 800 mL of 0.125 wt% sodium
2101241
11
hydroxide containing 10 ppm. of Igepal CO 730 which had
been cooled to 4°C. In the case of low grade oil sand,
500 ppm. (by mass, based on oil sand) of kerosene added
to the diluted slurry improved the production and quality
of the froths. The additions were carried out in a
laboratory scale Denver cell, and the resulting
suspension stirred without air for 2 minutes. Flotation
then was started and carried out in the laboratory for
approximately 3 minutes to produce a "primary" froth. In
these experiments, the sand was not removed prior to
flotation, although this may be carried out with a
suitable settling and washing step, if necessary, in
commercial operation.
At the completion of this first flotation stage,
0.02 g calcium hydroxide was added and the slurry
agitated for 1 minute without air. Flotation then was
carried out for another 3 minutes to produce a
"secondary" froth. After this second stage, flotation
was complete, the tailings remaining were flocculated to
the point of clarification by addition of a further 0.02
to 0.04 g calcium hydroxide. In the case of the lower
temperature experiments, the final temperature of the
tailings had risen by this time to approximately to°C.
Bitumen that had adhered to the sides of the cell
and to the impeller assembly during the first stage
flotation was removed with toluene after the contents of
the cell had been decanted, and was included with drained
primary froth as "primary" product. The partially
processed slurry then was returned to the cell, and
calcium hydroxide added and the second stage flotation
carried out. The same bitumen recovery procedure was
repeated for the "secondary" product.
Primary and secondary bitumen products slurried in
toluene were filtered through weighed Soxhlet thimbles,
and Soxhlet extractions then carried out for
approximately 5 hours using previously weighed flasks.
z~o~~~o
12
The thimbles then were dried and weighed and the solids
determined by difference. The toluene then was distilled
from the filtrate and the remaining bitumen dried in the
flask at 110°C, and its weight determined by difference.
Clear supernatant was decanted from the settled
tailings. The supernatant typically had a pH of 12 and
was suitable for recycle after makeup with sodium
hydroxide, and after addition of 10 to 100 ppm sodium
carbonate to remove any excess free calcium ion. The
tailings, consisting of sand and flocculated clays, were
filtered under vacuum and partially dried in a nitrogen
stream at ca. 80°C. They then were analyzed for bitumen
content by Soxhlet extraction.
Percent bitumen recovery for each stage was
calculated as:
(A/B) x 100
where A was the mass recovered as primary or secondary
froth and B was the total mass recovered from the primary
and secondary froths and the tailings. The results
obtained are set forth in the following Tables II and
III.
z~mz~o
13
O d' M 1p
G4 00 M M
mct
b
rl N
O
dP
O ~"~ ~ !L1
N 00 N
N r-i N
O O O
ro
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b
_
U
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~
U ~ O ri N O
U N
U w
p'~
z ~ o M
w
N
rr r-1
O
O
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r1
0
N N N O
G! ~ O
N
O
~ N N N dP ~ j,~,
dp
l~ N O
O ~
i~ u1
ro
tc1 U ,C
d O O O +~
O O
cron a a~ x 3
H a x
2~ Q~240
14
ao ~ o
b ~. N '-r n 0)
-~i N O
r~
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dP ~ d
N t'1 1p
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W n ' ' U
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N i-1 N fl
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ro . . w
v
c,~ ~ rl
i N
r
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U U G ''ao vo
O O w ,W a ~ 3 N
O ~ ~ N ,~ r-1
t.. N N rl
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N Ar a .C N T1
C ~ vo o m 'b fl
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w ~ . . .
~r ~O N N H Q
N d' 01 E..~rl
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ro
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'"~* ~~-1 d w
ri ,~-I ~".,
4l G~ld
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-~ ~ x G~!O
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d' sr er ~ .tiE3~ W
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2~~~z4o
In summary of this disclosure, attrition in the
presence of dilute sodium hydroxide solution followed by
dilution with additional hydroxide solution and flotation
is a most effective method for the low temperature
5 removal of bitumen from oil sand. This low temperature
bitumen separation also may be fully integrated with the
alkali recycle process concept. The rapidity of the
slurry formation also indicates that hydraulic techniques
using dilute alkali at ambient temperatures may be
10 employed for surface mining of oil sand, and that
sufficient agitation may be provided to effect initial
bitumen separation from the oil sands matrix.
Modifications are possible within the scope of this
invention.
