OA17039A - Process for the recovery of bitumen from an oil sand. - Google Patents

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.

Description

The présent Invention relates to a process for the recovery of bitumen from an oil sand.

More specifically, the présent invention relates to a process for the recovery of bitumen from an oil sand extracted by mining, said process being particularly suitable for recovering bitumens having a high viscosity and low API degrees.

It Is known that many hydrocarbon reserves currentîy available consist of water-wet or oilwet oil sands, oil rocks, oil shales, containing so-called unconventional oils (or its precursors as in the case of oil shales), I.e. extra heavy oils or bitumens. These unconventional oils hâve an extremely high density, generally lower than 15’ API, and an extremely high kinematlc viscosity, generally higher than 10,000 Cst, said kinematic viscosity being measured at the original température of the réservoir, at atmospheric pressure, in the absence of gas: consequently said unconventional oils do not flow spontaneousiy under the réservoir conditions.

Oil sands are generally characterized by their mineralogy and also by the liquid medium which Is in contact with the minerai particles of said oil sands.

Water-wet oil sands, for example, comprise minerai particles surrounded by a water layer, usually known as connate water. The oils contained In these water-wet oil sands are generally not in direct contact with the minerai particles, but rather form a continuous matrix around the granules. A relatively thin film of water encloses these minerai particles.

Oil-wet oii sands, on the other hand, can include small quantifies of water, but the minerai particles are generally not surrounded by said water and the oils contained therein are in direct contact with said minerai particles. In the case of oil-wet oil sands, the extraction of oils is consequently more difficult with respect to the extraction ôf the same from water-wet oil sands.

Both water-wet oil sands and oil-wet oil sands generally contain a high percentage, about 90%, of minerai particles (prevalently quartz) having an average dimension ranging from 0.1 mm to 6 mm and can also be extremely acid (for example, with a pH lower than 4) depending on the mineralogy of these oil sands.

There are also oil sands with a mixed wettability having Intermediate wettability characteristics between water-wet and oil-wet oii sands.

Various technologies are known in the state of the art for exploiting oil sands and for the extraction of the bitumen contained therein.

The recovery process of bitumen from oil sands extracted via mining called Clark Hot Water Extraction Process (CHWEP) Is the most widely-used process In Canada among those currentîy opéra tive.

The Canadian sands of the Athabasca région are typically sands of the water-wet type.

In the CHWEP process, the oil sand extracted is first subjected to a conditioning phase,

-117039 which provides the vigorous mixing of the oil sand with water in the presence of NaOH, at a pH of about 9-10.

A slurry typically having a volume ratio bitumen/water/inorganic solids equai to about 60/30/10 is obtained from the mixing, which is generally realized at a température within the range of50-85 *C.

The slurry is then fed to a séparation vessel, where it is left to settle with the formation of three superimposed layers (phases).

The first layer consiste of a froth containing almost ail of the bitumen origlnally présent In the oil sand. This layer can be separated from the surface of the slurry by skimming.

The second iayer consiste of sand which settles on the bottom of the séparation vessel.

The third iayer which Is separated is an intermediate viscous layer (mlddlings) containing dispersed day partides and entrapped bitumen. This iayer Is generally sent to a floatation step for a further recovery of bitumen.

The froth containing bitumen, part of the solids (day, sand and sllt) and entrapped water, Is sent to a second treatment unit for the recovery of the bitumen (froth treatment or de-frothing). In this second unit, the froth is heated, In order to eiiminate the entrapped air, and treated with an organic solvent to reduce the density of the bitumen and facilitate Its séparation from the water in the subséquent centrifugation phase.

The bitumen is separated either by dilution with naphtha or using a paraffinic solvent The choice of the type of solvent dépends on the quality of the bitumen to be obtained from the process; the concentration of inorganic resldues and water In the bitumen extraded dépends, In fact, on the type of froth treatment used.

In the case of treatment with naphthas, the froth is diluted with the latter to reduce the density and vlscosity of the bitumen in order to promote the coalescence of water in émulsion. The séparation of the bitumen is obtained by centrifugation.

The bitumen obtained with naphtha treatment is low-quality as it contains hlgh concentrations of solids and cannot be processed directly In refineries. it must be treated, on the contrary, before upgrading to eiiminate residual naphtha, asphaltenes and solids, with a conséquent slgnificant ioss of bitumen (up to 10-15% by weight of the bitumen originally présent). Treatment with naphtha, however, has advantages in terms of yieîd to bitumen (higher than that with paraffinic treatment) and investment costs. High volumes of water, however, are required.

In the case of treatment with paraffinic solvent, dilution with the solvent (typically hexane) reduces the density and vlscosity of the bitumen and causes flocculation of the water in émulsion and suspended solids; the séparation is then effected by decanting.

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Over a certain concentration, the paraffinic solvent also induces the partial précipitation of the asphaltenes présent in the bitumen, favouring the entrapment of water and solids in aggregates that can be easlly separated.

The product obtained with treatment with paraffinic solvent (de-asphalted bitumen) Is of a higher quality than that obtained with treatment with naphtha and can be introduced onto the market.

Treatment with paraffinic solvent is also used for obtaining a bitumen with spécifications which are such as to allow it to be processed In refineries (ebullated-bed hydrocracking).

Although the CHWEP process for the extraction of bitumen from Canadian oil sands offers numerous advantages, there are also various disadvantages.

The main disadvantages of the CHWEP process are:

- consumptîon of huge quantifies of water (2.5-4 units per unit of bitumen):

- production of enormous quantifies of tailings (1-2 m³ per m³of bitumen produced);

- production of high quantifies of CO₂, even if lower than that of insitu recovery processes.

A further and important critical aspect of the CHWEP process is represented by tailing ponds (I.e. artificiel iakes where sand processing waste-products accumulate) into which the aqueous solutions containing entrapped fine solids and hydrocarbons derivlng from the extraction process, are sent. In the tailing ponds, the séparation (sédimentation) of water and bitumen from the suspended solids requires years, sometimes décades, thus creating a serious environmentai problem. Canadian sands are In fact characterized by high clay contents (20-30% by weight).

A further critical aspect lies in the fact that the wastewater of the CHWEP process contains high levels of hydrocarbon, which is toxlc, non-recoverable and with a high COD [Chemical Oxygen Demand) value; this makes tailing ponds substantially anoxie and Incapable of sustaining animal and plant life.

The above drawbacks evldently make the CHWEP process extremely costly and with a high environmentai impact.

The CHWEP process also has signîficant disadvantages with respect to flexibility of use. This process, in fact, can technically be applied only for the extraction of bitumen from water-wet oil sands and/or for the recovery of bitumen having a relatively low viscosity and API degrees higher than 8.

In the case of oil-wet sands or sands with a mixed wettability and containing bitumen having a high viscosity and reduced API degree, on the contrary, the CHWEP process Is difficult to apply, unless signîficant variations In the process conditions are applied in order to favour the séparation of the bitumen (for example, Increase in the pH and increase In the recovery températures).

Considering these difficulties, bitumen extraction processes are known In the state of the art

-317039 which hâve been specifically developed for the treatment of oil sands in which the CHWEP process does not provide good results.

These processes, alternative to the CHWEP process, are based on the use of water-solvent and/or diluent mixtures; extraction processes with a singie solvent are also known.

The processes of the known art, however, hâve bitumen extraction yields which are not always satisfactory or, as in the case of processes with solvent alone, require process schemes/project solutions capable of guaranteeing the almost complété recovery of the solvent and control of the energy costs, both factors jeopardizing the commercial application of the process. To date there are no operative commercial plants employing solvent alone processes but only small pilot/demonstrative plants are known.An objective of the présent Invention is to overcome the drawbacks of the known art.

In particular, an objective of the présent Invention is to find a process for the recovery of bitumen from oil sands In which the conventional CHWEP process is not effective.

An objective of the présent invention therefore relates to a process for the recovery of bitumen from an oil sand comprising the following phases in succession:

(a) mlxing 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 siurry 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 sédiment comprising the remaining fraction of said oil sand free of the bitumen removed, water and resldual hydrocarbons which can be eliminated by subséquent 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.

The fraction of oll sand free of said removed bitumen présent in the above liquid phase (i) is only a minimum part of the oil sand treated. Most of this sand, In fact, forms the sédiment (ii).

The process, object of the présent invention can be used for treating oil sands of a varying lithological nature, containing bitumens of a varying chemical nature and concentration.

The process, object of the présent invention, is particulariy suitable for recovering bitumen from oll sands in which the CHWEP process is not effective(for example, due to the wettability

-417039 characteristics of the sand and/or particularfy high viscosity of the bitumen to be extracted).

The process, object of the présent Invention, is suitable, for example, for recovering bitumen from oil-wet oil sands, oil sands having a mixed wettability and consolidated sands having a large particle-size, such as sands containing high percentages of quartz (higher than 85% by weight) and low percentages of days (lower than 5% by weight). The process of the présent invention, however, can also be advantageously applied to water-wet oil sands, such as the Canadian sands In which days are présent in a quantity of about 20-30% by weight.

For the purposes of the présent invention, the term bitumens Indicates both the bitumens and extra heavy oils présent In the solid matrix of oil sands. The bitumens and heavy oils are generally called unconventional oils.

The content of bitumen in the oii sands that can be treated with the process of the présent invention typically varies within the range of 3-15% by weight with resped to the weight of the oii sand to be treated.

With the process of the présent invention, bitumens having a high viscosity, generally within the range of 10,000-36,000 mPas (measured at 120’C, shear rate 100 s'¹) and a high density, typically within the range of 4-7 “API, can be recovered from oil sands. These bitumens are characterized by a high content of asphaltenes (15-40% by weight) and a high addity (Acid Number between 3 and 14 mg KOH/g).

The process of the présent invention Is based on a réduction in the viscosity and density of the bitumen entrapped in the oil sand and its subséquent transfer from the surface of the grains of the sand matrix.

The réduction in viscosity of the bitumen is obtained by mixing the oil sand with a suitable diluent compound under continuous stirring (pre-conditioning phase (a)).

The transfer of the bitumen from the oii-sand matrix (digestion phase (b)), on the other hand, Is obtained by the addition of hot alkaline water to the sand/diluent (sluny) mixture obtained in the pre-conditioning phase.

Before subjecting the oil sand to the pre-conditioning phase (a), the oil sand is preferably subjected to crushing.

For a better understanding of the characteristics of the présent invention, référencé is made in the following description to figure 1, which illustrâtes a block scheme of the process according to the présent invention.

With référencé to figure 1, a charge of oil sand 1 is subjected to a first rough crushing (block MG) to obtain grains having dimensions In the order of 1-2 cm.

The stream of roughly crushed sand 2 obtained with said first crushing is subjected to a second crushing (block DIL-MF of figure 1) to obtain a further dimensional réduction in the grains to dimensions in the order of 5-10 mm (fine crushing, phase (a”)).

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The rough crushing phase (a*) and fine crushing phase (a) can be effected with the help of equipment known in the art such as, for example, hammer mills, knife milIs, or the like.

In a particularly preferred embodiment, the fine crushing, phase (a) is realized contemporaneously with the pre-conditioning phase (a).

It has been observed, In fact, that the presence of the diluent during the fine crushing favours the disaggregation of the rough fragments and formation of a homogeneous polyphasé system.

Single hydrocarbon compounds or mixtures thereof, such as toluene, xylenes, kerosene, diesel, naphtha or mixtures thereof, can be used as diluents in the pre-conditioning phase.

The diluent used In phase (a) has a minimum boiling point higher than 60 ’C and a maximum boiling point lower than 300 ’C.

Preferred diluents are kerosene and diesels as they contain aromatic fractions that avold the précipitation of asphaltenes in the pre-conditioned bitumen. These diluents, moreover, are produced by the same refineries that will treat the extracted bitumen.

Moreover, kerosene is a particularly preferred diluent due to its lower density, which facilitâtes the séparation of the bitumen.

In the pre-conditioning phase (a), the oil sand is mixed with the diluent compound In suitable weight ratios.

The quantity of diluent mixed with the sand to be treated must be sufficient for wetting the sand and diluting the bitumen entrapped therein, in order to lower its viscosity and density and favour Its release.

Furthermore, the quantity of diluent used dépends on the viscosity of the bitumen and température at which the mixing Is effected.

The diluent is generally added to the oil sand in a *S/D (sand/diluent) ratio ranglng from 10:1 to 15:1 (weight ratio).

Generally, for bitumens having a viscosity higher than 10,000 mPa'S, the B/D ratio between the bitumen présent In the oil sand and diluent added in phase (a) varies from 2:1 to 1:2 (weight ratio).

The diluent used in the pre-conditioning phase (a) advantageously at least partly consists of the hydrocarbon fraction recovered at the end of phase (c) (stream 4), which contains extracted bitumen mixed with the diluent used in phase (a). The remaining part of diluent necessary In phase (a), on the other hand, consists of fresh diluent (stream 3).

The mixing of the oil sand with the diluent is realized at a température ranging from 60 ’C to 80 ’C also depending on the quantity of diluent used.

In the pre-conditioning phase, the rôle advantageously exerted by the diluent in favouring -617039 the expulsion of the gases entrapped In the empty spaces of the sand matrix, with positive effects on the quality of the bitumen extracted from the process, is known art; the gas, if présent In the subséquent digestion phase, upon being released, can in fact entrain drops of water, sand, etc. into the diluted product.

The mixing of phase (a) is realized with equipment known to experts in the field or specificaliy conceived for this operation.

In a preferred embodiment of the process, in the pre-conditioning phase (a), dean recycled sand wet with water (stream 11) is added to the diiuted oii sand, before entering the removal phase with water (phase (b)). The clean recycled sand (stream 11) Is a fraction of clean sand treated at the outlet of the bitumen extraction process (stream 12).

The slurry 5 obtained in the pre-conditioning phase (a) is fed to the subséquent digestion phase (b) (block DiG-SP).

in phase (b), a basic aqueous solution (SAB) (stream 6) is added to the sluny to favour the release of drops of bitumen and diluent from the sand matrix. The action of the hot SAB causes the progressive shifting of the organic phase from the sand matrix and its substitution with the aqueous phase.

The digestion phase (b) Is realized In a mixer of the type known to experts in the field, or specificaliy conceived for this operation, keeping the sand under continuous stirring.

The release degree of the bitumen from the sand, after removal caused by the hot water added, dépends on various factors, among which the vîscosity of the diluted bitumen (the release is less if the température Is not adéquate), the différence In density between diluted bitumen and SAB and the bitumen-sand and water-sand Interface tension. The sand-oii-water wetting angle and interface tension are in tum influenced by the pH and ionlc strength of the SAB.

In the digestion phase (b), the water Is used In a water/sand (W/S) ratio ranging from 0.4:1 a 6:1 by weight.

The SAB is prepared by dissolution in water of a basic compound, such as, for example, a hydroxide, a carbonate or a bicarbonate of an alkaline or alkaline-earth métal (for example NaOH, Na₂CO₃, NaHCOa).

in the digestion phase (b), the SAB added to the slurry has a température within the range of 60*0-90*0.

The pH of the SAB must be sufficiently high as to neutraiize the acidity of the sands and bitumen, but at the same time avoid the formation of stable émulsions, favoured by high pH values. Preferably, the pH of the SAB ranges from 9 to 10.5.

Another factor which Influences the yield of the extraction process Is the Ionie strength of the SAB. It has been observed, In fact, that the presence of high concentrations of Ions In the SAB reduces the formation of both suspended solids and emulsified bitumen in the sIurry-SAB.

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When the SAB has a high ionic strength, the siurry-SAB Is much more limpid and the séparation ofthe solid phase (sédiment) from the remaining liquid phase is easier.

Furthermore, when using a SAB with a high Ionie strength, the différence In density between the sédiment and liquid phase increases.

The SAB preferably has an ionic strength varying within the range of 0.5 -1.

Further factors influencing the extraction yîeld of the bitumen are the mixing rate and duration (contact time) ofthe digestion phase (b).

The mixing rate must favour the contact between the aqueous phase and the organic phase surrounding the sand, in order to aliow the bitumen bound to the sand to be replaced by water. The stirring Is preferably slow, i.e. realized with a peripheral mixing rate ranging from 0.5 to 1 m/min. The stirring must ailow the whoie mass of sand to enter Into close contact with the diluent, In the pre-conditioning phase, and with the basic aqueous SAB solution, In the digestion phase. Slow stirring in these two phases not only keeps the energy consumption low but aiso avoids the formation of froths or émulsions which are dîfficult to treat for the séparation of the organic phase. Furthermore, at the above mixing rates, the reiease and entrainment of fine solids are reduced.

The contact time dépends on the type of oil sand to be treated and on the time necessary for the water to substitute the diluted bitumen on the grains of sand. The contact time is greater for oil-wet sand and sands having a mixed wettability, whereas it is less for water-wet sands. The contact time generally ranges from 15 to 120 minutes.

This time Is also characterized, in oil-wet sands, by an Induction period associated with the perforation of the film of diluted bitumen on the part of the water, to aliow its substitution on the sand partides. This time can be significantly reduced by the addition of dean recycled and waterwet sand. The siurry-SAB mixture obtained In phase (b) is a mixture that can be separated into various phases. If left to settle, In the absence of stirring, the siurry-SAB mixture Is separated Into two phases (i) and (ii):

(i) Is a liquid phase 7, In tum consisting of two Immiscible phases:

- a first oily phase containing the bitumen removed in phase (b), the diluent, a smali fraction ofoil sand free of removed bitumen (thatconsisting ofthefines! solid particles);

- a second aqueous phase substantially consisting of a layer of water;

(ii) is a sédiment 10, comprising most of the treated oil sand, free of the diluted bitumen removed in the digestion phase (b), water and residuai hydrocarbons that can be recovered with consecutive washings.

If left to decant (block DEC), the liquid phase 7 Is In tum separated Into a supematant hydrocarbon phase 8 comprising the diluent and removed bitumen, and an intermedlate aqueous phase 9 comprising, In dispersion, the fine fraction of treated oil sand (free of removed bitumen). The supematant hydrocarbon phase 8 can be recovered with techniques known to experts in the -817039 field. The supematant hydrocarbon phase Is preferably recovered by decanting.

Finally, as already mentioned, the supematant hydrocarbon phase 8 can be, at least partlally, recirculated to the pre-conditionlng phase (a) (stream 4) and possibly crushing phase (phases (a) and (a)) to reduce the concentration and consequently overall consumptions of diluent.

The total quantity of diluted bltumen that can be recirculated to phases (a) and (a) of the process ranges from 0.5 to 10 times by weight with respect to the weight of bitumen contained in the oil sand to be treated.

The Intermediate aqueous phase 9 and sédiment 10 separated In phase (b) of the process are subjected to traditional séparation and purification processes (block SEP-PUR) in order to:

- reduce the concentration of hydrocarbons and fine solids, In the aqueous phase;

- elimlnate the hydrocarbons présent In the sédiment, In order to fullfill the spécifications for disposa! without danger for the environment.

At the end of the extraction process and subséquent séparation and purification phases (SEP-PUR) ,dean sand is obtained, free of the bitumen origlnally contained therein and water purified of hydrocarbons and residual fine solids of the process.

The dean sand (stream 12) and purified water (stream 13) are continuously eliminated from the process.

The dean sand 12, possibly without the recyded fraction 11, is destined for the reconstruction of the site from which it was extracted or for disposai.

When recycled, the dean sand (stream 11) impregnated with water, can be added to the diluted oil sand (slurry 5) before beginnlng phase (b) of the process. The clean recycled sand (stream 11) Is a small part of the oil sand that Is continuously discharged from the process (stream 12).

In a preferred embodiment of the process of the présent Invention, a fraction of the purified water, coming from the séparation and purification phases (SEP-PUR), is recyded back to the extradion process (stream 14), where It is used for preparing the SAB used In phase (b) (block DIG-SP). The purified water can also be advantageously used for washlng the sand after extradion of the bitumen.

The process of the présent Invention has varions advantages with resped to the processes known In the state of the art for extrading bitumen from oil sands. In particular, with resped to the Canadian CHWEP process, the process of the présent Invention has the following advantages:

- more effident and rapld dewaterlng processes,

- Improvement In the bitumen’s quality,

- redudion of solid/fine sédiments In the extraded bitumen,

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- réduction of bitumen losses,

- lower energy consumptions,

- high recycling of the aqueous phase and absence of tailing ponds.

The following embodiment examples are provided for purely Illustrative purposes of the présent Invention and should not be considered as lïmiting the protection scope defined In the enclosed daims.

EXAMPLES

The effectiveness of the process of the présent invention was verifïed In the recovery of bitumen from two different types of oil sand.

The physico-chemlcal characteristics of the oil sands tested are indicated in Table 1.

Table 1

	Sand A	Sand B
BITUMEN
Weight percentage of bitumen	12.5	12
Viscosity of bitumen at 140 ’C (shearrate 100 s'1)	5375	155
’API of bitumen	5.5	10.5
P-vaiue	4.1	6.7
AN (acid number) (mg KOH/g)	7-9
SAND
Quartz (weight %)	90-100	85
Orthodase (weight %)	0-5	15
Ciays (weight %)	<5	0

The process according to the présent 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.

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The experimental tests were carried out in a glass reactor having a capacity of 1.5 I, equlpped with a sloping blade stirrer for moving the sand on the bottom of the vessei.

Recovery test

Table 2 Indîcates the operative conditions of the recovery test carried out on the two different types of oil sand.

The tests were carried out on 150 g samples of sand, selecting a température 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 bltumen extracted, are Indicated In Table 2.

Table 2

Test	Sand	SAB pH	S/D ratio	t contact (min)	Yield* (%)
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 (Na2CO3)	150/15	60	77
5	A	11 (Na2CO3)	150/15	30	84

• = percentage of bitumen recovered referring to the total quantity of bitumen contained In the sand.

Tests with recirculation of the diluent

Tests were carried out to verify the effectiveness of the re-use of a fraction of the diluentbitumen mixture obtalned at the end of phase (c) In order to reduce the consumption of fresh diluent.

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.

The spécifie 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 température (digestion-removal) of 90*C. Table 3

Test

Sand

PH

Sand (g)

Fresh diluent

MR (g)

MR vs. bitumen %

rpm

t (min)

Yield (%)

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				(9)
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

From Table 3, it can be deduced that the best résulté in terms of extracted bltumen yield are obtained with recirculation percentages In the order of 40% by weight (calculated as weight of the 5 recirculation mixture with respect to the weight of the bitumen to be extracted).

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

Tests in the presence of sait

The effectiveness of the extraction process was also verified with a variation In the ionic 10 strength of the SAB. The Ionie strength of the SAB, In fact, influences the wettabilîty of the sand and consequently the recovery yieid ofthe bitumen.

The spécifie operative conditions adopted and extraction yields of the bitumen are indicated ln Table 4. The tests were carried out on 150 g samples of sand, at a treatment température (digestion-removal) of the sand of 90Ό. The Ionie strength of the aqueous medium, modified by the 15 addition of NaCI, was equal to 0.6 (typical value of seawater).

Table 4

Test	Sand	PH	S/D ratio	rpm	t (min)	Yield (%)	%. Of fines in the water 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 + NaCi)	150/20	4	60	82	0.08	0.03

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11	B	10 (Na2CO3)	150/20	4	60	18
12	B	10 (Na2CO3 + NaCI)	150/20	4	60	88
13	A	10 (NaOH + NaCI)	150/15	4	60	87

The tests showed that the presence of NaCI 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 sait.

An additional positive effect of the presence of the sait is the réduction in suspended sollds 5 (fine products) and emulsified bitumen In the aqueous solution which appears much more limpld and easy to separate from the bitumen. The salinity of the water also favours séparation as It încreases the différence in density between the phases.

-1317039 contaïned therein.

2. The process according to the previous claim, comprising, before phase (a) , a rough crushing phase (a') and optionally a fine crushing phase (a) of said oil sand.

3. The process according to the previous claim, wherein said fine crushing phase (a'') is realized simultaneously with said mixing phase (a).

4. The process according to any of the previous daims, wherein a part of said liquid phase comprising said removed diluted bitumen separated in phase (c) is recycled to said phase (a) and/or said phase (a'').

5. The process according to any of the previous daims, wherein said diluent is selected from hydrocarbon compounds or mixtures 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 the previous claim, wherein said diluent is selected from toluene, xylenes, kerosene, diesel, naphtha or mixtures thereof.

7. The process according to any of the previous daims, wherein the basic aqueous solution (BAS) is added to the slurry at a température ranging from 60 to 90°C and it has a pH within the range of 9-10.5.

8. The process according to any of the previous daims, wherein the sand/diluent (S/D) weight ratio ranges from 10:1 to 15:1.

9.

The process according to any of the previous daims, wherein the bitumen/diluent (B/D) weight ratio ranges from 2:1 to 1:2.

10. The process according to any of the previous daims, wherein the water/oil sand (W/S) weight ratio

-217039 ranges from 0.4:1 to 6:1.

11. The process according to any of the previous daims, wherein the contact time between said diluent,

BAS and said oil sand ranges from 15 minutes to 120 minutes.

12. The daims, process wherein according to clean recycled any of the previous sand (water-wet) is added to the diluted oil sand before entering said removal phase (b) with water

13. The	process	according	to	any	of	the p	»revious
daims,	wherein	the water of	said	liquid	phase
remaining	at the	end of the	séparation of	said	diluted
bitumen	removed	in said	phase	(d)	1 '	is at	least
partially	recycled to said	phase	(b)	and	used	for the
préparation of said BAS.
14. The	process	according	to	any	of	the previous
daims, ’	wherein	the bitumen to	be	recovered	has a

36,000 mPa.s measured from 10,000 to viscosity ranging at 120°C, shear rate 100 s^-1 and a density ranging from to 7 API degrees.

15. The process according to any of the previous daims, wherein said oil sand is oil-wet, water-wet or an oil sand with a mixed wettability.

Claims (1)

1. 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) having a ionic strength of the basic aqueous solution within the range of 0.5-1, 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 sédiment comprising the remaining fraction of said oil sand free of the bitumen removed, water and residual hydrocarbons which can be eliminated by subséquent washings;

wherein the mixing is carried out with a stirring peripheral rate ranging from 0.5 to 1 m/min;

(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