Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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METHOD FOR REMOVING FINE SOLIDS FROM AN AQUEOUS BITUMEN-
CONTAINING STREAM
The present invention relates to a method for
removing fine solids from an aqueous bitumen-containing
stream, in particular as obtained during an oil sands
extraction process.
Oil sands are found in large amounts in many countries
throughout the world, but in extremely large quantities in
Canada. Such oil sands, also known as bituminous sands or
tar sands, contain naturally occurring mixtures of sand,
clay minerals, water, and a dense and extremely viscous
form of petroleum, technically referred to as bitumen (or
also "tar" due to its similar appearance, odour, and
colour). Oil sands are mined via open-pit mining and (hot)
water is typically used to extract the hydrocarbon content,
the bitumen, from these oil sands and the clay minerals.
After removal of the bitumen, the bitumen-depleted slurry
generally containing various mixtures of coarse solids,
sand, silt, clay and water is generally considered oil sand
tailings. Because of the presence of fine clay minerals, the
produced slurry generally is a suspension that settles
slowly. Part of the water is recycled, but a substantial
amount is fed into so-called tailing ponds (lakes of fine
particles suspended in water) to further settle. As the
process consumes a lot of water (up to about 5 volume units
of water to produce each volume unit of crude oil) very
large tailing ponds have already been created.
Once sufficient settling in the tailing ponds has taken
place (which can take a very long time) the supernatant
water layer (also called "clear zone tailing water") may be
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recycled in the oil sand extraction process. The recycling
of the supernatant water layer is hampered by high solids
loading and high dissolved calcium (and magnesium) content
of the water. The high solids loading and the presence of
bitumen in the water causes a lot of problems in the
extraction process (such as fouling of heat exchangers),
while the high dissolved calcium (and magnesium) content of
the water is detrimental to the oil sand extraction
efficiency.
The internet showed on 25 September 2012 the Program
of the Separation Technology 2012 conference as organised
by TEKNA. One presentation (by one of the inventors of
the present application) was scheduled for 26 September
2012, had as title "Heavy oil and sand issues" and was to
discuss the use of ultra-filtration membrane, dynamic
filtration and self-cleaning filtration as alternative
technologies to tailing ponds and the extraction of
bitumen in an alternative way (not solvents). However,
the presentation did not take place.
It is an object of the present invention to solve,
minimize or at least reduce the above problems.
It is a further object of the present invention to
provide an alternative method for removing fine solids
from an aqueous bitumen-containing stream, in particular
as obtained during an oil sands extraction process.
It is another object of the present invention to
provide a method of reducing the dissolved calcium
content of an aqueous bitumen-containing stream.
One or more of the above or other objects may be
achieved according to the present invention by providing
a method for removing fine solids from an aqueous
bitumen-containing stream, in particular as obtained
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during an oil sands extraction process, the method at
least comprising the steps of:
(a) providing an aqueous bitumen-containing stream;
(b) subjecting the aqueous bitumen-containing stream to
membrane separation using a ceramic membrane, thereby
obtaining a bitumen-depleted permeate stream and a
bitumen-enriched retentate stream.
It has surprisingly been found according to the
present invention that ceramic membranes efficiently
remove fine solids from an aqueous bitumen-containing
stream without severe fouling of the membranes. According
to the present invention, 'fine solids' refer to
particles having a particle size of less than 1 lam. Also,
it has been found that ceramic membranes efficiently
remove dissolved calcium (and magnesium, sodium,
potassium) content(s), solids and TOC (Total Organic
Carbon) without severe fouling of the membranes. This is
contrary to what would have been expected in the field,
as membrane technology is regarded as very prone to
fouling, in particular when used for hydrocarbon-
containing (let alone bitumen-containing) feed streams.
An important advantage of the method according to the
present invention is that the removal of bitumen and
other undesired components can be achieved in a simple
and economical way. This is of particular interest in the
processing of an aqueous bitumen-containing stream as
obtained from an oil sands extraction process.
A further advantage of the present invention is that
no chemical additives (such as flocculants) have to be
used for the removal of the fine solids (and reduction of
the dissolved calcium content, if the case).
The aqueous bitumen-containing stream is not limited
in any way (in terms of composition, phase, etc.), but
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will typically be an aqueous bitumen-containing stream as
obtained in an oil sands extraction process. Alternative
sources of the aqueous bitumen-containing stream may be
such aqueous streams as obtained in shale gas production,
SAGD (Steam-Assisted Gravity Drainage) processes, etc.
Examples of aqueous bitumen-containing streams as
obtained in an oil sands extraction process that may be
suitably processed using the method of the present
invention are "clear zone tailing water" (i.e. the
supernatant water layer obtained after settling of a
tailing pond), "recycle water" (e.g. water originating
from the oil sands extraction process, to be used
elsewhere in the process), "thickener overflow" (i.e. an
aqueous stream containing solids (clay and sand) and
relatively high levels of bitumen).
Preferably, the aqueous bitumen-containing stream
comprises at least 85 wt.% water, preferably at least 90
wt.%, more preferably at least 95 wt.%, even more
preferably at least 97 wt.%. Also, the aqueous bitumen-
containing stream preferably has a turbidity of from 20
to 5000 NTU (normal turbidity unit), preferably less than
1500 NTU, as determined according to APRA 213013 (using a
HACH 2100N Turbidimeter, as obtainable from Hach Company
(Loveland, Colorado, USA)).
Usually, the aqueous bitumen-containing stream
comprises at least 5 ppm bitumen, typically at least 10
ppm, more typically at least 15 ppm, even more typically
at least 20 ppm. Typically, the aqueous bitumen-
containing stream comprises at most 500 ppm bitumen. The
person skilled in the art will readily understand what is
meant by "bitumen" (viz. natural occurring bitumen);
hence this is not further explained in detail here.
Typically, bitumen is oil having a viscosity greater than
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10,000 cP under reservoir conditions and an API gravity
of less than 100 API.
Typically, the aqueous bitumen-containing stream has
a pH in the range from 3.0 to 9.0, preferably above 5.0
and more preferably above 7.0, and preferably below 8.5,
more preferably below 8Ø Also, the aqueous bitumen-
containing stream usually has a dissolved calcium content
of at least 10 ppm, typically at least 20 ppm as
determined according to ASTM D1976-12 (using ICP-AES),
and typically less than 100 ppm Ca, typically less than
60 ppm and more typically less than 50 ppm. Further, the
aqueous bitumen-containing stream typically contains
(again as determined according to ASTM D1976-12):
- less than 50 ppm dissolved Mg, typically less than 30
ppm and more typically less than 25 ppm;
- less than 1000 ppm dissolved Na, typically less than
800 ppm and more typically less than 500 ppm;
- less than 50 ppm dissolved K, typically less than 30
ppm and more typically less than 25 ppm.
Furthermore, the aqueous bitumen-containing stream
usually has a Total Organic Carbon (TOC) of at least 10
ppm, typically at least 20 ppm, as determined according
to APHA 5310A (whilst using HC1 as preservative rather
than H3PO4 or H2SO4). Typically, the aqueous bitumen-
containing stream has a TOC of at most 1000 ppm,
preferably at most 800 ppm, more preferably at most 500
ppm. This TOC value includes the amount of bitumen
present in the aqueous bitumen-containing stream.
The ceramic membrane as used in the membrane
separation of step (b) is not limited in any way. As
ceramic membranes and processes for the preparation
thereof are known, these are not discussed in full
detail.
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Preferably, the ceramic membrane has a mean pore size
of at most 500 nm, preferably at most 100 nm, more
preferably at most 50 nm, even more preferably at most
5.0 nm, yet even more preferably at most 1.0 nm. The mean
pore size of membranes as used in accordance with the
present invention having a mean pore size of above 10 nm
is determined according to ASTM F316-03 (2011). The mean
pore size of smaller membranes (<10 nm) as used in in
accordance with the present invention is determined by
Permporometry. Permporometry has been described in Cao,
G.Z. et al., "Permporometry study on the size
distribution of active pores in porous ceramic
membranes.", Journal of Membrane Science, 1993, 83(2),
pages 221-235. Typically, the ceramic membrane has a
molecular weight cut-off (MWCO) of from 250 to 10,000,000
Da (g/mol) as determined according to the article of Lee,
S. et al., "Determination of membrane pore-size
distribution using the fractional rejection of non-ionic
and charged macromolecules", Journal of Membrane Science,
2002, 201, pages 191-201. Preferably, the ceramic
membrane has a molecular weight cut-off (MWCO) of below
10,000.
The ceramic membrane may be composed of various
inorganic materials, such as alumina, titania, zirconia,
silica, SiC, etc. and is preferably composed of Ti02,
Zr02, gamma-alumina, Si02, or SiC or combinations
thereof. Preferably, the ceramic membrane comprises at
least 50 wt.% inorganic material, preferably at least 60
wt.%, more preferably at least 70 wt.%, even more
preferably at least 80 wt.%, yet even more preferably at
least 90 wt.%, or even 100 wt.%. The ceramic membrane may
be coated, grafted and/or impregnated.
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The ceramic membrane is not limited to any form or
size and can be in the form of a monolith, multichannel
tubes, hollow fibers, etc. Suitable ceramic membranes are
e.g. the Inopor nano TiO2 membranes, obtainable from
Inopor GmbH (Veilsdorf, Germany); a 1000 kDa membrane
obtainable from Orelis Environemt SAS (Salindres,
France); and a 1000 kDa membrane obtainable from TAMI
Industries (Nyons, France).
The membrane separation of step (b) can be performed
in many different ways. Preferably, the aqueous bitumen-
containing stream has a temperature during step (b) of at
least 0 C, preferably at least 10 C, more preferably at
least 15 C, even more preferably at least 20 C and
typically below 100 C, preferably below 90 C. Further it
is preferred that the aqueous bitumen-containing stream
has a pressure during step (b) of at least 0.5 bara,
preferably at least 5 bara, more preferably at least 10
bara and typically at most 50 bara. Typically the Trans
Membrane Pressure (TMP) over the ceramic membrane is at
least 0.5 bar, preferably at least 1 bar, more preferably
at least 2 bar or even as high as at least 5 bar or at
least 10 bar.
Also, it is preferred that during step (b) a cross-
flow velocity along the surface of the membrane of at
least 1.0 m/s is used, preferably at least 1.5 m/s, more
preferably at least 2.0 m/s and typically at most 5.0
m/s.
As a result of the membrane separation in step (b), a
bitumen-depleted permeate stream and a bitumen-enriched
retentate stream is obtained.
Typically, the bitumen-depleted permeate stream
comprises at most 20 ppm bitumen, preferably at most 10
ppm, more preferably at most 5 ppm. Preferably, the
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dissolved calcium content of the permeate stream, as
determined according to ASTM D1976-12, is reduced by at
least 50%, preferably at least 60%, when compared with
the aqueous bitumen-containing stream. Typically, the
permeate stream has a dissolved calcium content of below
800 ppm, preferably below 500 ppm, even more preferably
below 100 ppm. Also, the permeate stream preferably has a
Total Organic Carbon (TOC) of at most 25 ppm, preferably
at most 10 ppm, as determined according to APHA 5310A
(whilst using HC1 as preservative rather than H3PO4 or
H2SO4). Further, the permeate stream preferably has a
turbidity of at most 5 NTU (normal turbidity units),
preferably at most 1 NTU, as determined according to APHA
2130B (using a HACH 2100N Turbidimeter, as obtainable
from Hach Company (Loveland, Colorado, USA)). Also, the
permeate stream preferably has a recovery of at least
50%, preferably at least 90%, more preferably at least
95% when compared with the volume of the aqueous bitumen-
containing stream; if the flow of the aqueous bitumen-
containing stream would be 1.0 m3/hr, a 95% recovery for
the permeate would result in a flow of 0.95 m3/hr for the
permeate and 0.05 m3/hr for the retentate.
Typically the permeate stream is substantially
particle-free. The permeate stream will typically be
reused as a recycle stream in the oil sands extraction
process or sent to a tailings pond; before being used as
a recycled stream it may be subjected to several further
processing steps, if desired. As a mere example, the
permeate stream may be subjected to an ion-exchange resin
to remove even more ions, if desired.
Typically, the bitumen-enriched retentate stream
comprises at most 1000 ppm bitumen, preferably at most
500 ppm, more preferably at most 200 ppm.
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Usually, the bitumen-enriched retentate stream (which
is typically solids-enriched) will be disposed of and
e.g. combined with a tailings stream as generated
elsewhere in the oil sands extraction process or sent to
e.g. a filter press.
If desired, the ceramic membrane may be backflushed
now and then to remove blockages of the ceramic membrane,
e.g. once every 30 minutes. During backflushing,
typically an overpressure of at least 1 bar, preferably
at least 2 bar, more preferably at least 5 bar, even more
preferably at least 6 bar is applied. If needed, the
ceramic membrane may be periodically chemically cleaned;
however, it has been found that no aggressive chemical
cleaning is needed and that mild chemical cleaning once a
month suffices, if at all needed.
The person skilled in the art will readily understand
that many modifications may be made without departing
from the scope of the invention. Further, the person
skilled in the art will readily understand that, while
the present invention in some instances may have been
illustrated making reference to a specific combination of
features and measures, many of those features and
measures are functionally independent from other features
and measures given in the respective embodiment(s) such
that they can be equally or similarly applied
independently in other embodiments.
The present invention is described below with
reference to the following Example, which is not intended
to limit the scope of the present invention in any way.
Example 1
An aqueous bitumen-containing stream (99.0 wt.%
water) as obtained from an oil sands tailings pond was
provided as a feed stream. The feed stream was subjected
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to membrane separation using two M14-19-25-L Inopor TiO2
ceramic nanomembrane modules, having a mean pore size of
0.9 nm, obtainable from Inopor GmbH (Veilsdorf, Germany);
molecular weight cut-off 450Da) thereby obtaining a
bitumen-depleted permeate and a bitumen-enriched
retentate. "M14-19-25-L" refers to 14 multichannels per
module, 19 bore multichannels, outer diameter of 25 for
the multichannel. As an L (length) of 1200 mm was used,
this resulted in 3.51 m2/module.
The following conditions were used during the
membrane separation:
- Temperature feed stream: 20 C
- Pressure feed stream: 1 bara
- TMP over ceramic membrane: 10 bar
- Cross-flow velocity: 2.0 m/s
- Recovery (of the permeate when compared with the
volume of the feed stream): 50%
- Backflush cycle: 30 seconds every 15 minutes.
The properties of the aqueous bitumen-containing
(feed) stream, the bitumen-depleted permeate and the
bitumen-enriched retentate are given in Table 1 below.
The permeate appeared as a clean, transparent liquid. The
ceramic membrane required mild chemical cleaning (1%
citric acid) only once every 10 weeks; further cleaning
(with 1% citric acid) was performed when the flux dropped
below 10 lmh (litres/m2/hr) at 10 bar TMP.
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Table 1
Feed stream Permeate Retentate
Ca dissolved' 21.3 5.0 32.2
[PPri]
Mg dissolved' 11.7 3.0 17.4
[PPrn]
K dissolved' 16.3 8.8 21.3
[PPrn]
Na dissolved' 324 318 418
[PPITO
T0C2 [ppm] 43.7 1.5 69.2
Turbidity3 24 0 22
[NTU]
pH 7.50 7.60 7.45
lASTM D1976-12
2Total Organic Content, according to APHA 5310A (whilst using HC1 as
preservative rather than H3PO4 or H2SO4). The bitumen content (not
determined separately) was part of this TOC.
3APHA 2130B, (using a HACH 2100N Turbidimeter, as obtainable from
Hach Company (Loveland, Colorado, USA))
Discussion
Example 1 surprisingly shows that when a ceramic
membrane is used to remove fine solids from an aqueous
bitumen-containing stream (such as obtained from an oil
sands tailing pond), dissolved calcium content (and
content of Mg, K, Na), turbidity, Total Organic Carbon
(including bitumen) are effectively reduced without
severe fouling of the ceramic membranes. This is a
surprising result as membrane technology has typically
been regarded as prone to fouling when used for
hydrocarbon-containing (let alone bitumen-containing)
feed streams, especially when using highly selective
membranes for reducing the dissolved calcium content by
50%.
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As can be seen, the dissolved calcium content of the
permeate stream is reduced by at least 75%, when compared
with the aqueous bitumen-containing stream.
