CA2101240C - Low temperature separation of bitumen from oilsands - Google Patents

Abstract

Bitumen is recovered from oil sands in an ambient temperature procedure in which the oil sands first are subjected to attrition in the presence of an aqueous sodium hydroxide solution to form a slurry of pH at least about 11.5. Sand, freed from bitumen, usually is separated from the slurry, which then is diluted with further quantities of aqueous sodium hydroxide solution while maintaining the pH value, so as to provide the bitumen in a form which can be separated from the aqueous phase by flotation. The bitumen is floated off from the aqueous phase comprising a clay suspension and then forwarded to an upgrading operation. A second bitumen flotation also may be effected following addition of calcium hydroxide to the remaining aqueous phase. The clay suspension may be flocculated and dewatered and the resulting sodium hydroxide solution recycled to the attrition and/or dilution steps.

Description

-- ~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 (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 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 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.

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

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:

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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 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 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 O d' M 1p mct b rl N

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O O O

ro ~i b _ U
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U N
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~ N N N dP ~ j,~, dp l~ N O
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d O O O +~
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cron a a~ x 3 H a x 2~ Q~240 ao ~ o b ~. N '-r n 0) -~i N O
r~

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r ~ ~ ~ S~~N
U U G ''ao vo O O w ,W a ~ 3 N
O ~ ~ N ,~ r-1 t.. N N rl O O

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U ~ o p +~d ro o 0 3 H .N
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w 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.

Claims (16)

1. 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 at a temperature less than about 60°C to form a slurry of bitumen in the oil sands having a pH of at least about 11.5 and to separate the bitumen contained in the oil sands from its mineral content, 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 said slurry at least about 11.5, and floating bitumen from the aqueous medium to effect separation of said bitumen from minerals.

2. The method of claim 1 wherein said slurry is separated from a sand phase prior to said dilution step.

3. The method of claim 1 or 2 wherein said alkali metal hydroxide is sodium hydroxide.

4. The method of claim 3 wherein said aqueous sodium hydroxide solution which is used in sufficient quantity to provide a slurry of pH of about 11.8 to about 12.2.

5. The method of claim 4 wherein said dilute aqueous sodium hydroxide solution has an NaOH content of less than about 0.5 wt%.

6. The method of claim 5 wherein the aqueous sodium hydroxide solution has an NaOH content of about 0.1 to about 0.2 wt%.

7. The method of claim 4 wherein about 0.05 to about 0.5 wt% NaOH on oil sand is used in said attrition step.

8. The method of any one of claims 1 to 7 wherein about 0.02 to about 1.0 wt% of a non-ionic surfactant is present in the aqueous sodium hydroxide solution.

9. The method of claim 8 wherein said non-ionic surfactant comprises an alkylphenol ethoxylate present in an amount of about 0.08 to about 0.3 wt%.

10. The method of any one of claims 1 to 9 wherein said oil sand is a low grade oil sand and an organic solvent in an amount of about 0.1 to about 1.0 wt% on bitumen is added to said slurry.

11. The method of any one of claims 1 to 10 wherein said dilution step is effected to a slurry solids content of about to about 30 wt%.

12. The method of any one of claims 1 to 11 wherein, following said flotation step, the floated-off bitumen is collected from the surface of the remaining aqueous medium and upgraded.

13. The method of any one of claims 1 to 12 wherein the remaining aqueous medium comprising a clay suspension and residual bitumen is treated with about 0.05 to about 1.0 wt%
of calcium hydroxide, based on initial bitumen content, subjected again to flotation and the floated-off bitumen is collected from the surface of the remaining aqueous medium and upgraded.

14. The method of claim 13 wherein the remaining aqueous medium comprising a clay suspension is dewatered by the addition of calcium hydroxide and a resulting aqueous sodium hydroxide solution is recycled to said attrition and/or dilution step.

15. The method of claim 14 wherein excess calcium hydroxide is present during said dewatering step and said resulting aqueous sodium hydroxide solution is treated with sodium carbonate to remove calcium ions prior to said recycle.

16. The method of any one of claims 1 to 15 wherein the attrition step is effected at a temperature below about 30°C.