CA2024519C - Solvent and water/surfactant process for removal of bitumen from tar sands contaminated with clay - Google Patents

Abstract

This invention involves the separation of clay-contaminated bitumen from sand with a solvent. The bitumen is dissolved with an organic solvent such as condensate from a natural gas well. The clay is separated from the dissolved bitumen and the solvent is recovered and recycled. The sand is washed with water containing a carefully selected, nonanionic surface active agent to remove residual bitumen and solvent. Prior removal of the clay precludes it from unduly contaminating the water.

Description

2 FROM TAR SANDS CONTAMINATED WITH CLAY

4 Backqround Field of the Invention 6 This invention relates to a process for recovering bitumen 7 from tar sand and, more particularly, to a low temperature, 8 solvent extraction step followed by a water process step for 9 recovering bitumen from tar sands contaminated with clay, the water process step including the use of a specific surface active 11 agent to preclude contamination of the water with either bitumen 12 residue or clay.

14 Related Application This application is a continuation-in-part application of my 16 copending application Serial Number 07/297,670 filed 17 January 17 1989 for PROCESS FOR REMOVAL OF BITUMEN FROM TAR SANDS
18 CONTAMINATED ~ITH CLAY.

The Prior Art 21 The term "tar sand" refers to a consolidated mixture of 22 bitumen (tar) and sand. Alternate names for tar sands are "oil 23 sands" and "bituminous sands", the latter term being more 24 technically correct in that the sense of the term provides an adequate description of the mixture. The sand constituent of tar ~' , .

1 sand is mostly alpha quartz, as determined from x-ray diffraction 2 patterns, while the bitumen or tar constituent of the tar sands

3 consists of a mixture of a variety of hydrocarbons and

4 heterocyclic compounds. This bitumen, if properly separated from the sands, may be upgraded to a synthetic crude oil suitable for 6 use as a feedstock for the production of liquid motor fuels, 7 heating oil, and/or petrochemicals.
8 About 65 percent of all of the known oil in the world is 9 contained in tar sand deposits or heavy oil deposits. Tar sand fields occur throughout the world with the exception of the 11 continents of Australia and Antarctica. Significantly large tar 12 sand deposits have been identified and mapped in Canada, 13 Columbia, Trinidad-Tobago, Venezuela, and the United States. The 14 Canadian tar sand deposits, known as the Athabasca tar sands, are located in the province of Alberta, Canada and are currently 16 being developed. The reserves of bitumen in the Athabasca tar 17 sands alone has been estimated to be approximately 900 billion 18 barrels.
19 In the United States, approximately 24 states contain known tar sand deposits. However, about 90 to 95 percent of the mapped 21 tar sand deposits are located within the State of Utah and are 22 estimated to include at least 25 billion barrels of oil. While 23 the Utah tar sand reserves appear small in comparison with the 24 enormous potential of the Athabasca tar sands, the Utah tar sand reserves represent a significant energy resource when compared to 26 the United States crude oil proven reserves (approximately 31.3 ,, 1 billion barrels) and with the United States crude oil production 2 of almost 3.0 billion barrels during 1976. Utah tar sand deposits 3 occur in six major locations along the eastern edge of the state 4 with the bitumen content varying from deposit to deposit as well as within a given deposit. Current information available 6 indicates that Utah tar sand deposits average generally less than 7 10 percent bitumen (by weight), although deposits have been found 8 with a bitumen saturation of up to about 17 percent (by weight).
9 Athabasca tar sands and Utah tar sands are both also characterized by the presence of clay as a contaminant. The clay 11 is finely divided and dispersed throughout the tar sand deposits, 12 so that it represents a significant obstacle to the efficient 13 processing of tar sands. The commercial processing of the 14 Athabasca tar sands has created vast settling ponds where clay-contaminated water is held to allow the clay to settle.
16 Experience has shown that the clay is so extremely fine that it 17 remains suspended in the water for long periods. A further 18 problem is that significant quantities of bitumen are carried 19 into these settling ponds where it agglomerates and floats on the surface of the water to represent a pollution hazard, 21 particularly for migratory waterfowl, and the like.
22 Tests have also determined that the Utah tar sands lacks 23 connate water so that the bitumen is bonded directly to the sand 24 grains. This bitumen is also at least one order of magnitude or at least ten times more viscous than bitumen obtained from 26 Athabasca tar sands. Accordingly, the processing of Utah tar ~ 202~519 . ., ~.

1 sands involves both displacement of the bonded bitumen from the 2 sand grains followed by subsequent phase disengagement of the 3 more viscous bitumen from the residual sand phase. Attempts to 4 use conventional hot water processes that have been successfully applied to the Athabasca tar sands have been unsuccessful for 6 processing Utah tar sands. This failure is readily apparent in 7 light of the recognized differences in both the physical and 8 chemical nature of the Utah tar sands.
9 A more comprehensive discussion of the athabasca tar sands may be found in the literature including, for example (1) E.D.
11 Innes and J.V.D. Tear, "Canada's First Commercial Tar Sand 12 Development," Proceedings of the Seventh World Petroleum 13 Congress, Elsevier Publishing Co., 3, p. 633, (1967); (2) F.W.
14 Camp, The Tar Sands of Alberta Canada, 2nd Edition, Cameron Engineering, Inc., Denver, Colorado (1974); and (3) J. Leja and 16 C.W. Bowman, "Application of Thermodynamics to the Athabasca Tar 17 Sands," Canadian Journal of Chemical Engineerinq, 46 p. 479 18 (1968).
19 Additionally, the following U.S. Pa~ents are a few of the patents which have been granted for apparatus or processes 21 directed toward obtaining bitumen from tar sands: U.S. Pat. Nos.
22 1,497,607; 1,514,113; 1,820,917; 2,871,180; 2,903,407; 2,927,007;
23 2,965,557; 3,159,562; 3,161,581; 3,392,105; 3,401,110; 3,553,099;
24 3,560,371; 3,556,980; 3,605,975; 3,784,464; 3,847,464; 3,875,046;
3,893,907; 4,096,057; 4,120,776; 4,160,720; 4,337,143; and 26 4,410,417. With the exception of U.S. Pat. Nos. 3,605,975, "- 2024~19 1 4,120,776, and 4,160,720, each of the foregoing patents have been 2 directed toward processing any tar sand, but, in particular, 3 Athabasca tar sands.
4 From the foregoing it is clear that extensive progress has been made in separating bitumen from tar sands, particularly with 6 regard to the Athabasca tar sands. To date no commercially 7 feasible process has been used on the Utah tar sands other than 8 the simple mining, crushing, and blending of the Utah tar sands 9 into an asphalt cement which, when combined with a gravel aggregate, forms an asphalt-based concrete highly suitable for 11 use as a paving material.
12 In view of the foregoing, it would be a significant 13 advancement in the art to provide a process for recovering 14 bitumen from clay-contaminated tar sands. An even further advancement in the art would be to recover bitumen from clay-16 contaminated tar sands using a readily available solvent that can 17 be recovered and recycled. Importantly, the process should 18 include a water process step along with the careful use of 19 specific surface active agents to preclude contamination of the water with residual bitumen or clay. Such a novel process is 21 disclosed and claimed herein.

23 Brief Summary and Objects of the Invention 24 This invention relates to a novel, low-temperature process whereby chunks of clay-contaminated tar sand are treated with a 26 readily available solvent. The solvent breaks down the chunks 2~245 19 . ..

1 and forms a slurry of tar sand and solvent. Upon agitation, the 2 solvent removes a substantial portion of the bitumen from the 3 sand to form a liquid phase containing solvent and bitumen. A
4 significant fraction of the clay is also recovered in the solvent/bitumen phase. The resulting liquid phase is drawn off 6 and processed by centrifugation to separate the clay from the 7 solvent and bitumen. The solvent is then removed from the 8 bitumen by distillation. The bitumen-contaminated sand phase is 9 washed with water to which a carefully selected surface active agent has been added in order to recover a second liquid phase of 11 bitumen, solvent, and clay. Advantageously, most of the clay 12 has been removed with the first liquid phase so that very little 13 clay remains to contaminate the water during the water washing 14 process. Great care is exercised in the selection of a surface active agent that will not emulsify the residual bitumen into the 16 water so that the water remains relatively clear.
17 It is, therefore, a primary object of this invention to 18 provide improvements in the process for recovering bitumen from 19 clay-contaminated tar sands.
Another object of this invention is to provide a novel 21 process for removing clay from tar sand by recovering the clay 22 from solvent used to remove bitumen and clay from the tar sand.
23 Another object of this invention is to provide a novel 24 process for the solvent recovery of bitumen from clay-contaminated tar sands using a readily available solvent, the 26 process including a water wash for recovering additional bitumen 1 and solvent from the sand.
2 Another object of this invention is to incorporate a 3 carefully selected surface active agent in the water wash 4 process, the surface active agent having the characteristic of not emulsifying the residual bitumen into the water.
6 Another object of this invention is to remove residual 7 bitumen from sand grains that are essentially free of connate 8 water without emulsifying the bitumen and thereby trapping 9 residual clay in the residual bitumen so as to maintain a relatively clear water.
11 Another object of this invention is to provide a low-12 temperature process for recovering bitumen from a clay-13 contaminated tar sand.
14 Another object of this invention is to provide a process for producing a clean sand from a clay-contaminated tar sand.
16 These and other objects and features of the present 17 invention will become more readily apparent from the following 18 description in which preferred and other embodiments of the 19 invention have been set forth in conjunction with the accompanying drawing and appended claims.

22 Brief Description of the Drawinq 23 The drawing is a schematic flow diagram illustrating a 24 presently preferred embodiment of the novel process of this invention for recovering bitumen from a clay-contaminated tar 26 sand while separating out the clay and producing a clean sand.

1 Detailed Description 2 The invention is best understood by reference to the drawing 3 wherein like parts are designated by like numerals throughout in 4 conjunction with the following description.
s 6 General Discussion 7 Numerous processes for recovering bitumen from tar sand are 8 described in both the patent and technical literature. In 9 general, these references are directed to either the Athabasca tar sands or the Utah tar sands. The processes range among 11 thermal processes, solvent processes, and water processes or a 12 combination of these processes. Interestingly, few of the 13 available references discuss the presence of clay`in the tar sand 14 although clay is now recognized as the primary reason that many of these processes are not commercially feasible. For example, 16 any process that relies on the use of water, with or without 17 additives, will result in clay-contamination of the water. This 18 contamination requires extensive separation processes in order to 19 recover and recycle the water since environmental restrictions prohibit the discharge of clay-contaminated water. A further 21 problem is that surface active agents are designed to cause the 22 bitumen to become dispersed or otherwise emulsified in the water 23 phase. This, in turn, creates significant problems because it 24 not only produces a bitumen/water mixture that is difficult to separate, but it also liberates the clay from the bitumen into 26 the water phase.

1 Thermal processes also encounter problems when clay is 2 present in the tar sand to any appreciable amount. In 3 particular, the extremely fine particle size of the clay means 4 that it will be carried over into the gaseous phase, for example, from any type of thermal, fluidized bed process. Additionally, 6 there is an inherent risk that the clay may sinter on hot 7 surfaces during any coking process involving coked tar sand.
8 Advantageously, the process of the present invention uses a 9 solvent to disintegrate chunks of tar sand, dissolve substantially all of the bitumen therefrom, while, 11 simultaneously, remove the clay in the bitumen/solvent phase.
12 The resulting solvent, bitumen, and clay phase is processed in a 13 centrifuge to remove the clay so that the remaining 14 solvent/bitumen mixture can be separated through a simple distillation process. Residual bitumen with entrapped clay and 16 solvent is removed from the sand in a low-temperature process 17 using water to which a specific type of surface active agent has 18 been added. This water wash cycle may be repeated several times 19 to assure essentially complete removal of the bitumen and solvent from the sand while the particular surface active agent precludes 21 emulsification of the residual bitumen in the water.
22 Importantly, the surface active agent is selected so as to 23 disengage the bitumen from the sand grains without emulsifying 24 the bitumen. This step is particularly critical for Utah tar sand since they are characterized by the lack of connate water so 26 that the highly viscous bitumen is bonded directly to the sand 202451g 1 grains.
2 The selection of the appropriate surfactant in the water 3 wash step of this process is critical to the success of the 4 process. The wrong surfactant can emulsify residual bitumen leaving a highly contaminated water with bitumen and clay 6 dispersed throughout. This problem exists in the current 7 processing technology practiced in the extraction of bitumen from 8 the Athabasca deposits. If one were to practice this same 9 technology on Utah tar sands, it would not only be impractical due to the high water discard rate in a desert environment but 11 also violate all the laws dealing with clean waters.
12 Importantly, the surfactant or surface active agent must be 13 able to separate bitumen from sand grains that are characterized 14 by the absence of connate water without simultaneously emulsifying the bitumen into the wate~ phase. Additional 16 surfactant requirements include its being nontoxic to plant 17 growth so that residual surfactant entrained in the spent sand 18 will permit the sand to be ecologically revegetated during 19 reclamation of the excavation site. A further feature is that the surfactant must be biodegradable and the degradation products 21 must not be toxic to plant life for the reasons stated 22 hereinbefore.
23 Surfactants can be categorized in three general categories:
24 Cationic, Anionic, and Nonionic. I have discovered that a very narrow range of nonionic surfactants provides the necessary 26 characteristics that make this process feasible. Table I sets `` ` 2~245i9 ~ .

1 forth a run of experiments on residual tar sands that had been 2 cleaned with solvent to remove ninety percent of the bitumen.
3 The purpose of the experiment was to demonstrate how this 4 material was wetted by water alone and water to which had been added surface active agents from various types of surface active 6 agents.
7 Table II outlines my discovery that a surfactant selected 8 from primary or linear alcohols of the ethoxylate family with a 9 narrow range of carbon atoms in the primary alcohol chain provides optimal separation. The number of ethoxy groups on the 11 carbon atoms in the chain are also selected within a relatively 12 narrow range since the greater the number of ethoxy groups on the 13 surfactant molecule, the more soluble the bitumen will be in 14 water. This must be balanced with the fact that the higher number of ethoxy groups causes an increased rate of disengagement 16 of the bitumen from the sand grains.
17 Correspondingly, the lower range of carbon atoms in the 18 surfactant provides a faster release of bitumen from the sand 19 grains. For example, a surfactant with eight carbon atoms results in a very fast release of bitumen from the sand, much 21 faster than a surfactant with 12 or 15 carbon atoms. However, an 22 undesirable feature is that surfactants of this type also form 23 emulsions between the released bitumen and the water, an event 24 that must be avoided in order to make this process economically feasible.

- 2~2~51~

.

Table I

Aqueous Medium Results 1. Water (only) Not wetted 2. Water with base Wetted slowly 3. Water with 0.5% Not wetted Cationic surfactant 4. Water with anionic Wetted slowly surfactant (wetting due to solution being basic)

5. Water nonionic Wetted immediately surfactant (alcohol ethoxylate) .

1 Another important limitation is the amount of the surfactant 2 in the water phase. For example, a surfactant of this invention 3 having eight carbon atoms and three ethoxy groups in a 4 concentration range of three to four percent will produce a complete emulsion. I have found that the maximum allowable

6 concentration of surfactant suitable for the practice of this

7 invention must not exceed about one-half percent, by volume.

8 This must be carefully monitored during the recycle of the water

9 so that the makeup stream of surfactant does not create excess surfactant. This is important since a certain fraction of 11 surfactant will be lost with the bitumen phase and some will be 12 carried away by the damp sand.
13 The conclusion to be derived from an analysis of the results 14 displayed in Table II is that the two to three ethoxylate units provide a superior surface active agent as long as the clay 16 floaters do not present interface separation problems during 17 continuous processing. The advantage of this surfactant range is 18 that there is no water contamination problem.
19 Ethoxylate units in the six to eight range present clean interfaces but requires at least ten minutes settling time before 21 the water can be reused. This time requirement may or may not 22 adversely affect the continuous processing strategy. Greater 23 than eleven ethoxylate units renders the surfactant unusable.
24 Another study was conducted to determine the rate at which the bitumen/solvent residue separates from the sand phase during 26 the water-wash cycle. Comparisons were made using alcohols with Table II
Behavior of Nonionic Primary Alcohol - Ethoxylates (E.O. Units) with Varying Surfactant Concentrations 2 E.O. units The water layer Lots of clay regardless of clear, no color floaters at both concentration interfaces 3 E. O. units Same as above Same as above regardless of concentration 6 E.O. units .5% Water layer Settles out, light brown few clay floaters .3% Water layer colorless Settles out, few clay floaters 7 E.O. units .5% Water layer Very few clay light brown floaters1 .3% Water layer colorless Very few clay floaters 8 E.O. units .5% Water layer At end of 10 minutes light black no clay floaters2 .3% Water layer At end of 10 minutes dark brown no clay floaters2 11 E.O. units Water layer is black- Too dark to tell black, with no observed change within one hour 1 Settled out leaving a clear solution within 5 minutes settling time.
2 The black layer in the water contains oil and clay. A layer of fine, tan clay settles out as the solution clears up. This clearing takes place within 10 minutes.

1 eight, twelve and fifteen carbon atoms, C-8, C-12, and C-15, 2 respectively, and with ethoxylate units ranging between three and 3 eight. The studies found that the C-12 and C-15 alcohols were 4 identical with both three and seven ethoxylate units, the seven ethoxylate units being faster. Surprisingly, the C-8 alcohol 6 produced the fastest and cleanest separation with the greater 7 number of ethoxylate units. The results of this study are 8 summarized in Table III.
9 In conclusion, the C-8 alcohol with six to eight ethoxylate units appears to be the ideal surface active agent for this 11 process. This surfactant gave the best rate of recovery, a clean 12 separation of phases with no clinging clay/bitumen in the 13 water/bitumen interface. Additionally, this surfactant gave the 14 highest percentage of bitumen recovery with the least number of process steps. However, great care must be taken to assure that 16 even this surface active agent is maintained at less than 0.5 17 percent, by volume, since even at three percent, by volume, this 18 surfactant produces a complete emulsion.
19 The action involved with this surfactant appears to be the displacement or phase disengagement of the bitumen from the sand 21 grains with the water/surfactant solution. Importantly, the 22 absence of connate water between the sand grains and the bitumen 23 appears to be the primary requirement for the specificity of the 24 surface active agent particularly when this requirement is coupled with the equally important requirement that the surface Table III
Comparison of Carbon Atoms in Alcohol Chain Length with Number of Ethoxylate Units % of Bitumen left on sand after l Alcohol Ethoxylate minute surfactant Chain Units Results wash C-8 6 Very large oil 14%
drops (1/4 in.) Separation completè in 30 seconds C-8 8 Very large oil 18%
drops (1/4 in.) Separation complete in 30 seconds C-15 7 Oil drops (1/8 in.) 33%
work way out for 4-5 minutes C-lS 3 Oil drops (1/8 in.) 36%
without agitation still coming out after 10 minutes ,, i - 202~519 1 active agent does not cause an emulsification of the bitumen into 2 the water phase.

4 The Preferred Embodiment Referring now more particularly to the drawing, a schematic 6 of the basic elements of the novel progress of this invention is 7 shown generally at 10 and includes a stripper 20, a water washer 8 30, a centrifuge 40, a distillation column 50, an oil/water g separator 60 and a bitumen storage 70. Tar sand 12 is introduced into stripper 20 through a coarse screen 13 which prevents 11 excessively large pieces of tar sand 12 from entering stripper 20 12 where they could possibly damage an auger 24 at the bottom of 13 stripper 20. The lower end of stripper 20 is constricted by a 14 throat 22 which directs downwardly falling sand into auger 24.
Auger 24 is rotated as indicated by arrow 25 to transfer sand 16 from stripper 20 to water washer 30.
17 Solvent 14 is an organic solvent such as hexane, pentane, 18 gasoline, or the like, and is introduced into stripper 20 19 adjacent throat 22. Solvent 14 is added in the ratio of about 20 to 30% by weight of-Utah tar sand, and as such, becomes saturated 21 with bitumen upon vigorous agitation. Solvent 14 flows upwardly 22 through tar sand 12 where it not only breaks up the agglomerated 23 pieces of tar sand 12 but also dissolves bitumen which, in turn, 24 carries away clay that is interspersed in the bitumen. Solvent 14 dissolves the bitumen so that the resulting first liquid phase 26 16 includes bitumen dissolved in solvent and suspended clay.

-- 202451g 1 Stripped sand from stripper 20 is directed by auger 24 into 2 water washer 30 where it falls downwardly and is agitated by an 3 upwardly flowing stream of water/surfactant 34 and gas 36 from a 4 compressor 37. Gas 36 is selected from any suitable gaseous medium that does not contain oxygen. Suitable gases include 6 nitrogen, carbon dioxide, methane, or the like. The combination 7 of water/surfactant stream 34 along with gas 36 creates a highly 8 agitated slurry of sand inside water washer 30. The result is 9 that residual bitumen is removed by water and surfactant 34 and carried upwardly into an oil/water separator 60 as a 11 water/bitumen stream 66.
12 A surfactant 33 is mixed with water 32 to produce the 13 desirable ratio of surfactant to water in water/surfactant stream 14 34. Importantly, surfactant 33 is carefully selected from a range of surface active agents so as to provide a surfactant that 16 is nontoxic to plant growth so that spent sand from this process 17 can be readily revegetated with no adverse environmental effects.
18 It is also important that surfactant 33 is biodegradable for the 19 same reasons. However, the most important feature of surfactant 33 is that it will not emulsify oil in water but is an oil 21 surfactant that helps displace the residual bitumen and bitumen-22 solvent residue from the sand without emulsifying the bitumen.
23 Surfactant 33 also aids in the formation of bitumen/solvent 24 droplets within the water~surfactant phase 34. These droplets are large enough that they will rise out of the sand and water 26 phase. The more active the surfactant 33 the larger the droplets ~o~519 1 and the faster the separation process.
2 The sequence involved in water washer 30 may be repeated 3 in additional stages if it is determined that a single pass 4 through water washer 30 is insufficient to remove residual bitumen. An auger 38 at the base of water washer 30 is turned as 6 indicated by arrow 39 to remove clean sand 80 from water washer 7 30.
8 The mixture of gas and water/bitumen stream 66 is introduced 9 adjacent the lower end of oil/water separator 60 where it is agitated by additional gas 36. Residual bitumen and solvent are 11 separated float to the surface where it is removed from oil/water 12 separator 60 as a second liquid phase 62. The second liquid 13 phase 62 joins the first liquid phase 16 where they are processed 14 by centrifuge 40. Water 64 is removed from oil/water separator 60 and recycled as water 34 back into water washer 30 after being 16 supplemented with make up water 65 and surfactant 33.
17 First liquid phase 16 is joined by second liquid phase 62 18 and they are both introduced into centrifuge 40. Suspended clay 19 is separated out as clay 42 while the resulting solvent/bitumen stream 44 is directed to distillation column 50.
21 Distillation column 50 is a simple distillation process for 22 separating solvent 52 from bitumen 54. Heat 56 provides 23 sufficient thermal energy for distillation column to cause 24 solvent 52 to become separated from bitumen 54. Solvent 52 is recycled back to stripper 20 where it is blended with make up 26 solvent 15, if any is required to compensate for solvent carried 202~51g 1 over with bitumen 54, to become solvent stream 14. Bitumen 54 is 2 directed to bitumen storage 50.
3 The following examples are merely illustrative of the 4 process of the present invention and are not intended to be restrictive in any manner in setting forth the novel process of 6 this invention.
7 Example 1 8 Approximately one kllogram of tar sand obtained from the 9 Asphalt Ridge tar sand deposit near Vernal, Utah, was placed in a two liter vessel. The tar sand was in rough chunks, each chunk 11 about 10 cm in diameter. Solvent in the amount of 210 grams was 12 added to the vessel after which the vessel was sealed. The 13 solvent completely disintegrated the chunks of tar sand in about 14 35 seconds without agitation. The resulting slurry was then vigorously agitated by shaking the vessel after which the liquid 16 phase was decanted. The liquid phase consisted of 89 grams 17 solvent, 77 grams bitumen and 76 grams clay for a total weight of 18 242 grams.
19 Water (400 ml.) containing 0.5% (by weight) of the specially selected surfactant of this invention was added to the sand 21 residue in the vessel. The vessel was shaken vigorously to 22 agitate the sand and water slurry. At this point the sand 23 appeared to be clean although there were some residual oil 24 droplets that worked their way out of the sand if the sand were lightly agitated so as to remain loose. There were three 26 distinct, separable layers having very definite interfaces. The l top layer consisted of solvent and bitumen with a limited 2 quantity of clay, a middle layer of water slightly cloudy from 3 small amounts of clay and a lower layer of sand containing a 4 limited amount free oil (bitumen/solvent).
The sand was washed again using an additional 100 ml of 6 water and agitated by bubbling a gas through the mixture. The 7 sand at this stage appeared clean and was analyzed to reveal that 8 at least 94.5% of the bitumen had been removed. The remaining 9 bitumen was present as small droplets interspersed in the sand and could be removed by subsequent washing.
11 The solvent-rich bitumen from each of the prior steps was 12 combined and introduced into a centrifuge where it was processed 13 at 5,000 g's for lO minutes. The clay portion was removed 14 through this centrifugation process so that the bitumen (after distillation to remove the solvent) contained only 0.7% clay (by 16 weight).
17 Example 2 18 To provide a preliminary indication of the effect of 19 temperature upon this process, all materials were cooled in ice water so that the temperature of the process was between 4C and 21 6C. The same process was used as in Example 1, above. Large, 22 approximately 10 cm, chunks of tar sand (1058 grams) were used to 23 fill the stripper chamber. Solvent, 234 grams, was added to the 24 chamber where it took 2.3 minutes for the solvent to soak into the chunks causing them to collapse into a stirrable slurry. The 26 container was agitated by shaking it for thirty seconds. A

1 portion (106 grams) of the solvent-bitumen-clay mixture was 2 removed and was found to contain 44 grams solvent, 34 grams 3 bitumen and 28 grams clay.
4 Chilled ice water (400 ml) containing 0.5~ (by weight) of the specially selected, nonfoaming surfactant was added and the 6 vessel shaken vigorously for one minute. The sand phase was 7 relatively clean and contained numerous small oil droplets which 8 required three additional washing cycles to produce a clean sand 9 free of oil droplets. The bitumen was 94.7% (by weight) removed during this experimental run. Importantly, the surface active 11 agent was carefully selected so as to disengage the bitumen from 12 the sand grains without emulsifying the bitumen into the water 13 phase.
14 The partial removal of solvent from the first step left extra clay which could not be removed easily. The layer of 16 suspended clay particles was partially in the solvent/bitumen 17 phase and partially in the water phase. This clearly 18 demonstrates the importance of removing the major portion of the 19 clay with the solvent phase.
The foregoing combined liquid phases were removed from the 21 vessel and an additional aliquot of solvent was added to the sand 22 residue. The mixture was agitated by shaking slightly and in 23 about thirty minutes the remaining clay particles had settled to 24 the bottom resulting in a very clean separation between the solvent-bitumen phase and the water phase. The water phase was 26 very cloudy due to the extra clay present. After several hours - 202~519 without agitation the clay had settled out of the cold water 2 leaving a slightly cloudy water layer over a clean layer of clay 3 on the bottom.
4 The solvent-bitumen phases from the first and second steps were combined and processed by centrifugation at 5000 g's for ten 6 minutes. The bitumen contained residual clay of 0.5% (by 7 weight).
8 Example 3 9 Using the same equipment, 1143 grams of 13% (by weight)

10 bitumen-content, Utah tar sands were contacted with 234 grams of

11 solvent. After 135 seconds the tar sand had collapsed into a

12 slurry in the absence of agitation. The mixture was then

13 vigorously agitated for one minute by shaking the vessel. The

14 solvent-bitumen-clay phase (215 grams) was decanted and analyzed

15 to contain (by weight) 57% solvent, 31% bitumen, and 12% clay.

16 Water (2100 ml) containing the carefully selected surface

17 active agent 0.5% (by weight) was added to the vessel and

18 agitated vigorously by shaking for one minute. Excellent

19 separation into clean sand and water was obtained upon standing.

20 Medium size oil droplets of solvent-dissolved bitumen were

21 observed interspersed in the sand. The bitumen droplets were too

22 heavy to float to the surface of the water. The addition of 40

23 grams of solvent gave the droplets of bitumen sufficient upward

24 mobility to float on the surface of the water. The resulting

25 layers of solvent-bitumen on top of the water layer had a very

26 clean separation. Importantly, the surface active agent was 2Q2~519 1 carefully selected so that it effectively disengaged the bitumen 2 from the Utah tar sand without emulsifying it into the water.
3 The oil/water mixture was poured off the sand and allowed to 4 stand to provide an excellent, separable interface. The resulting solvent-bitumen phase contained (by weight) 56%
6 solvent, 37% bitumen, and 7% clay.
7 A second washing with 100 ml of ice water was shaken 8 vigorously with the sand and resulted in the medium-size oil 9 droplets being broken into numerous smail droplets. These small droplets remained in the sand and did not float to the surface of 11 the water. The addition of 0.5 ml of the specific surface active 12 agent of this invention followed by shaking created the formation 13 of large droplets of oil. Light agitation of the sand using gas 14 bubbles allowed these large droplets to move out of the sand and float to the surface where they could be skimmed from the water.
16 A repeat washing and agitation of the sand resulted in 17 additional oil being recovered. A third washing produced no 18 additional oil recovery. The bitumen recovery rate was 97% (by 19 weight). The solvent recovery was 88% since no steps were taken to recover solvent carried over in the sand or to preclude losses 21 through evaporation.
22 The solvent used in this process was obtained from the 23 numerous natural gas wells in the vicinity of the tar sand 24 deposits. The solvent was condensate collected at the well head and is frequently referred to as "casing head gas" or "drip gas".
26 This solvent consists generally of about 20% pentane, 70% hexane, 2~2~519 1 and 10~ heavier compounds (by weight) ranging between C5 to Cg 2 hydrocarbons.
3 The present invention may be embodied in other specific 4 forms without departing from its spirit or essential characteristics. The described embodiments are to be considered 6 in all respects only as illustrative and not restrictive. The 7 scope of the invention is, therefore, indicated by the appended 8 claims rather than by the foregoing description. All changes 9 which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Claims (16)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for removing bitumen from a tar sand contaminated with clay comprising:
obtaining a tar sand consisting of bitumen and clay mixed with sand;
introducing said tar sand into a stripper vessel;
dissolving said bitumen with a solvent, said solvent also removing said clay from said sand into a liquid medium formed with said solvent and bitumen;
removing said liquid medium from said sand; and washing said sand with water to which a nonionic surface active agent has been added to remove residual bitumen from said sand, said surfactive agent comprising a linear alcohol having carbon atoms within the range on the order of about eight to fifteen carbon atoms and ethoxylate units on the carbon atoms within the range on the order of about two to eight ethoxylate units, said surfactant being present in said water in an effective amount less than about 0.5 percent, by volume.

2. The process defined in claim 1 wherein said dissolving step comprises obtaining said solvent from a condensate from a natural gas source.

3. The process defined in claim 1 wherein said dissolving step comprises obtaining said solvent from a group consisting of organic solvents.

4. The process defined in claim 1 wherein said removing step includes separating said clay from said liquid medium.

5. The process defined in claim 4 wherein said separating step includes recovering said solvent from said liquid medium by evaporating said solvent from said bitumen thereby recovering said solvent and producing bitumen.

6. The process defined in claim 5 wherein the recovering step includes recycling said solvent to said stripper vessel and amending said solvent with additional solvent.

7. The process defined in claim 4 wherein said separating step includes removing said clay from said liquid medium by centrifugation of said liquid medium.

8. The process defined in claim 1 wherein said adding step includes agitating said sand in said water by passing a gas upwardly through said sand.

9. The process defined in claim 1 wherein said agitating step is followed by removing said residual bitumen from said water by passing said water and residual bitumen into an oil/water separator, said residual bitumen floating to the surface of said oil/water separator.

10. A process for recovering bitumen from a tar sand having a bitumen, clay, and sand content comprising:
obtaining a tar sand having a bitumen, clay, and sand content;
sizing said tar sand and introducing said sized tar sand into a stripper vessel;
stripping said clay and said bitumen from said sand by dissolving said bitumen with a solvent, said clay, bitumen and solvent forming a liquid medium, and leaving a sand residue;
removing said liquid medium from said sand residue;
separating said clay from said liquid medium;
recovering said bitumen from said liquid medium by evaporating said solvent from said bitumen; and washing said sand residue with water to which a carefully selected nonanionic surfactant has been added in an effective amount less than about 0.5 percent, by volume, said surfactant comprising a linear alcohol having carbon atoms within the range on the order of about eight to fifteen carbon atoms and ethoxylate groups within the range on the order of about two to eight ethoxylate groups.

11. The process defined in claim 10 wherein said stripping step includes obtaining said solvent as a condensate from a natural gas well head.

12. The process defined in claim 10 wherein said separating step includes removing said clay from said liquid medium by centrifugation of said liquid medium.

13. The process defined in claim 10 wherein the recovering step includes recycling said solvent to said stripper vessel and amending said solvent with additional solvent.

14. The process defined in claim 10 wherein said adding step includes agitating said sand in said water by passing a gas upwardly through said sand.

15. The process defined in claim 10 wherein said agitating step is followed by removing said residual bitumen from said water by passing said water and residual bitumen into an oil/water separator, said residual bitumen floating to the surface of said oil/water separator.

16. A process for recovering bitumen from a tar sand having a clay contaminant in the bitumen comprising:
mining a tar sand having a sand bonded by a bitumen and clay matrix;
screening said tar sand to remove large pieces of tar sand while introducing the tar sand into a stripper;
obtaining a solvent from a wellhead of a natural gas well, the solvent comprising a hydrocarbon condensate;
dissolving said bitumen by introducing said solvent into said stripper, the solvent releasing said sand from said bitumen and said clay and forming a liquid medium with said bitumen and said clay;
removing said clay from said liquid medium by processing said liquid medium in a centrifuge;
separating said solvent from said bitumen by evaporating said solvent in a distillation column;
recycling said solvent to said stripper;
washing said sand in a washer by passing water and a gas upwardly through said sand in said washer, said water including a carefully selected, nonanionic surface active agent, said surface active agent being present in an effective amount less than about 0.5%, by volume, and comprising a linear alcohol having carbon atoms within the range on the order of about eight to fifteen carbon atoms and ethoxylate groups within the range on the order of about two to eight ethoxylate groups, said water removing residual bitumen from said sand;
floating said bitumen from said water by passing said water into an oil/water separator;
recycling said water back to said washer; and discharging sand from which bitumen has been removed from said washer.