Process for the recovery of bitumen from an oil sand

Abstract

The present invention relates to a process for the recovery of bitumen from an oil sand comprising the following phases in succession: (a) mixing an oil sand with a diluent capable of reducing the viscosity and density of the bitumen contained in said oil sand, obtaining a first mixture (slurry) comprising diluted bitumen; (b) mixing said slurry with a basic aqueous solution (BAS) possibly containing salts to increase its ionic strength, capable of removing said diluted bitumen from said oil sand containing it, obtaining a second mixture (BAS-slurry) which can be separated into (i) a liquid phase comprising said diluted bitumen, a fraction of oil sand free of the bitumen removed and water; (ii) a sediment comprising the remaining fraction of said oil sand free of the bitumen removed, water and residual hydrocarbons which can be eliminated by subsequent washings; (c) separating a liquid phase comprising said diluted bitumen removed, from said BAS-slurry mixture; (d) recovering, from said liquid phase separated in phase (c), the removed diluted bitumen contained therein.

Claims

1. A process for recovery of bitumen from an oil sand, the process comprising, in the following order: (a) mixing an oil sand with a diluent capable of reducing a viscosity and density of the bitumen contained in the oil sand, in order to obtain a first mixture, which is a slurry comprising diluted bitumen; (b) mixing the slurry with a basic aqueous solution (BAS) having an ionic strength within the range of 0.5-1, optionally comprising a salt to increase an ionic strength thereof, wherein the basic aqueous solution is capable of removing the diluted bitumen from the oil sand, in order to obtain a second mixture of a BAS slurry which is separated into (i) a liquid phase comprising the diluted bitumen, a fraction of oil sand free of the bitumen removed and water; and (ii) a sediment comprising a remaining fraction of the oil sand free of the bitumen removed, water and residual hydrocarbons which can be eliminated by subsequent washings; (c) separating the liquid phase comprising the diluted bitumen from the BAS-slurry; and (d) recovering, from the liquid phase separated in the separating (c), a removed diluted bitumen contained therein.

2. The process according to claim 1, comprising, before the mixing (a), a rough crushing (a) and optionally a fine crushing (a) of the oil sand.

3. The process according to claim 2, wherein the fine crushing (a) occurs simultaneously with the mixing (a).

4. The process according to claim 2, wherein a part of the liquid phase comprising the removed diluted bitumen separated in phase (c) is recycled to the mixing (a), the fine crushing (a), or both.

5. The process according to claim 1, wherein the diluent is a hydrocarbon compound or a mixture of hydrocarbon compounds having a minimum boiling point higher than 60 C. and a maximum boiling point below 300 C.

6. The process according to claim 1, wherein the diluent is at least one selected from the group consisting of toluene, xylenes, kerosene, diesel, and naphtha.

7. The process according to claim 1, wherein the liquid phase (b) is realized under one or more of the following conditions: a temperature ranging from 60 to 90 C.; a pH of the basic aqueous solution within the range of 9-10.5; and mixing with peripheral rate ranging from 0.5 to 1 m/min.

8. The process according to claim 1, wherein a sand/diluent (S/D) weight ratio ranges from 10:1 to 15:1.

9. The process according to claim 1, wherein a bitumen/diluent (B/D) weight ratio ranges from 2:1 to 1:2.

10. The process according to claim 1, wherein a water/oil sand (W/S) weight ratio ranges from 0.4:1 to 6:1.

11. The process according claim 1, wherein a contact time between the diluent, the basic aqueous solution, and the oil sand ranges from 15 minutes to 120 minutes.

12. The process according to claim 1, wherein clean recycled sand is added to the first mixture comprising the diluted bitumen before the slurry is mixed with the basic aqueous solution.

13. The process according to claim 1, wherein water of the liquid phase remaining at the end of the separation of the diluted bitumen removed in the recovering (d), is at least partially recycled to the mixing (b) and employed for the preparation of the BAS.

14. The process according to claim 1, wherein the bitumen to be recovered has a viscosity ranging from 10,000 to 36,000 mPa.Math.s measured at 120 C., shear rate 100 s.sup.1 and a density ranging from 4 to 7 API degrees.

15. The process according claim 1, wherein the oil sand is oil-wet, water-wet or an oil sand with a mixed wettability.

16. The process according to claim 1, wherein the diluent is at least one selected from the group consisting of kerosene and diesel.

17. The process according to claim 1, wherein the diluent is kerosene.

18. The process according to claim 1, wherein clean recycled sand, which is water-wet, is added to the first mixture comprising diluted bitumen before the slurry is mixed with the basic aqueous solution.

Description

EXAMPLES

(1) The effectiveness of the process of the present invention was verified in the recovery of bitumen from two different types of oil sand.

(2) The physico-chemical characteristics of the oil sands tested are indicated in Table 1.

(3) TABLE-US-00001 TABLE 1 Sand A Sand B BITUMEN Weight percentage of bitumen 12.5 12 Viscosity of bitumen 5375 155 at 140 C. (shear rate 100 s.sup.1) API of bitumen 5.5 10.5 P-value 4.1 6.7 AN (acid number) 7-9 (mg KOH/g) SAND Quartz 90-100 85 (weight %) Orthoclase 0-5 15 (weight %) Clays <5 0 (weight %)

(4) The process according to the present invention was applied using kerosene as diluent. In phase (b) the SAB was added in a W/S (water/sand) ratio equal to about 4/1.

(5) The experimental tests were carried out in a glass reactor having a capacity of 1.5 l, equipped with a sloping blade stirrer for moving the sand on the bottom of the vessel.

(6) Recovery Test

(7) Table 2 indicates the operative conditions of the recovery test carried out on the two different types of oil sand.

(8) The tests were carried out on 150 g samples of sand, selecting a temperature for the digestion-removal treatment of 90 C. and a mixing rate of 4 rpm. The results of the recovery test, in terms of yield of bitumen extracted, are indicated in Table 2.

(9) TABLE-US-00002 TABLE 2 t contact Yield* Test Sand SAB pH S/D ratio (min) (%) 1 B 9.5 (NaOH) 150/20 60 6 2 B 10.0 (NaOH) 150/20 60 16 3 B 10.5 (NaOH) 150/20 60 90 4 B 11 (Na.sub.2CO.sub.3) 150/15 60 77 5 A 11 (Na.sub.2CO.sub.3) 150/15 30 84 *= percentage of bitumen recovered referring to the total quantity of bitumen contained in the sand.

(10) Tests with Recirculation of the Diluent

(11) Tests were carried out to verify the effectiveness of the re-use of a fraction of the diluent-bitumen mixture obtained at the end of phase (c) in order to reduce the consumption of fresh diluent.

(12) For this purpose, a synthetic mixture was prepared, consisting of bitumen (60% by weight) and kerosene (40% by weight), which was used as diluent in phase (a) of the process.

(13) The specific operative conditions adopted and extraction yields of the bitumen are indicated in Table 3. The tests were carried out on 150 g samples of sand, at a treatment temperature (digestion-removal) of 90 C.

(14) TABLE-US-00003 TABLE 3 Fresh dil- MR vs. Sand uent MR bitumen t Yield Test Sand pH (g) (g) (g) % rpm (min) (%) 6 B 11.2 150 6 33.3 178 2 60 74 7 B 11 150 5 15 80 4 60 69 8 B 11 150 8 7 37 4 120 87 MR = recirculation mixture

(15) From Table 3, it can be deduced that the best results in terms of extracted bitumen yield are obtained with recirculation percentages in the order of 40% by weight (calculated as weight of the recirculation mixture with respect to the weight of the bitumen to be extracted).

(16) Tests carried out using the recirculation mixture only, on the contrary, provided low recovery yields of the bitumen.

(17) Tests in the Presence of Salt

(18) The effectiveness of the extraction process was also verified with a variation in the ionic strength of the SAB. The ionic strength of the SAB, in fact, influences the wettability of the sand and consequently the recovery yield of the bitumen.

(19) The specific operative conditions adopted and extraction yields of the bitumen are indicated in Table 4. The tests were carried out on 150 g samples of sand, at a treatment temperature (digestion-removal) of the sand of 90 C. The ionic strength of the aqueous medium, modified by the addition of NaCl, was equal to 0.6 (typical value of seawater).

(20) TABLE-US-00004 TABLE 4 %. of fines S/D t Yield in the water %. Test Sand pH ratio rpm (min) (%) phase* bitumen* 9 B 10 (NaOH) 150/20 4 60 16 3 B 10.5 (NaOH) 150/20 4 60 90 0.3 0.8 10 B 10 (NaOH + 150/20 4 60 82 0.08 0.03 NaCl) 11 B 10 (Na.sub.2CO.sub.3) 150/20 4 60 18 12 B 10 150/20 4 60 88 (Na.sub.2CO.sub.3 + NaCl) 13 A 10 150/15 4 60 87 (NaOH + NaCl)

(21) The tests showed that the presence of NaCl allows high recovery yields (>80%) at lower pH values (10 rather than 10.5), to be obtained with respect to the tests carried out without salt.

(22) An additional positive effect of the presence of the salt is the reduction in suspended solids (fine products) and emulsified bitumen in the aqueous solution which appears much more limpid and easy to separate from the bitumen. The salinity of the water also favours separation as it increases the difference in density between the phases.