Process for recovery of solvent from tar sand bitumen

There is described a process based on unit operations conventionally employed but modified to enable the use of chlorinated solvents, particularly methylene chloride as the preferred solvent for extraction of the bitumen from the tar sands or shale. The process in general constitutes: PA0 I. an extraction operation wherein the tar sand is contacted with the chlorinated solvent, particularly methylene chloride, to extract (dissolve) the bitumen from the sand; PA0 II. a separation of the sand from the solvent bitumen extract; PA0 III. (a) recovery of the bitumen free of extractant; (b) recovery of the sand free of extractant.

BACKGROUND OF THE INVENTION 
In the United States there are about 550 tar sand occurrences known to 
exist in 22 states. These deposits are estimated to contain up to 50 
billion barrels of crude. By far the most important deposits are the 
near-surface tar sands of Utah, which are estimated to contain 22-29 
billion barrels of petroleum with 96% of the oil occurring in sandstone 
rock in six major deposits. Of the 50 billion barrels of the identified 
U.S. tar sand reserves, about 10% (5 billion barrels) are located close 
enough to the surface to be mined by conventional open pit techniques and 
extracted at the mine site. 
A variety of techniques have been proposed for the surface extraction of 
bitumen from tar sands; e.g., hot or cold water with flotation, 
water-solvent mixtures, and solvent extraction. Of these techniques, water 
separation has an advantage in that the equipment requirements are 
relatively simple and it is an established, commercial method for the 
processing of Canadian tar sands. However, the water wet nature and 
bitumen composition of the Athabasca tar sands is unique; and, 
consequently, it has not been possible to directly apply the Canadian 
technology to U.S. tar sands. 
Water separation processes are essentially mechanical methods. They suffer 
from the disadvantage in both the low efficiency of displacement of the 
bitumen from the sand and the poor flotation behavior of the released 
bitumen which latter is strongly influenced by changes in bitumen 
viscosity within a particular ore body. Water processes also require 
significant volumes of water which must be recycled to approach economical 
operation. Consequently, methods for minimizing the formation of oil/water 
emulsions and means of treating fine-clay/water suspensions are generally 
required. Efficient water recycle is not only important in order to avoid 
costly environmental problems, but it is also scarce and generally closely 
regulated in those areas of the U.S. where most tar sand deposits are 
located. 
Water-solvent processes are chemical dissolution methods which offer the 
potential advantage of diminishing the energy associated with a sand 
drying operation, but suffer many of the disadvantages of the water 
extraction process with regards to clarifying and recylcing large volumes 
of water. Difficult to break water/oil/solvent emulsions also present a 
significant problem. 
Solvent extraction appears to be especially suited for the surface 
extraction of the oil-wet tar sands found in the U.S. However, essentially 
all the developmental work which has previously taken place for the 
solvent extraction of tar sands has been carried out using hexane and 
similar light petroleum hydrocarbon solvents. These types of chemical 
extractants are not good solvents for bitumen. The asphaltenic content of 
bitumen (normally in the range of 15-25%) is not readily soluble in 
aliphatic hydrocarbon solvents. Consequently, slow dissolution rates, poor 
extraction efficiencies, column plugging due to reprecipitated 
asphaltenes, and the expense and difficulty required in recycling large 
volumes of such extremely hazardous solvents has discouraged many workers 
from pursuing a solvent extraction process approach for the recovery of 
bitumen from tar sands. The properties of several commercially-important 
chlorinated solvents could obviously overcome many of the objections 
inherent in the use of hydrocarbon solvents; however, they are generally 
perceived as not suitable for this application because of both their 
thermal and hydrolytic instability at elevated temperatures and consequent 
corrosion potential. 
There are myriads patents which disclose processes for recovering bitumen 
from tar sands and oil-shale as well as unique and conventional solvent 
systems for use in particular processes having modified steps both in 
treatment and solvent recovery. Exemplary of these patents are Hastings, 
U.S. Pat. No. 4,311,561; L. I. Hart et al., U.S. Pat. Nos. 4,054,506 and 
4,054,505; R. G. Murray et al., U.S. Pat. Nos. 4,120,775 and 4,176,465; T. 
A. Pittman, et al., U.S. Pat. Nos. 3,856,474 and 4,029,568; G. B. 
Karnofsky, U.S. Pat. No. 4,239,617; C. D. Smith et al., U.S. Pat. No. 
3,941,679; E. W. Funk et al., U.S. Pat. No. 4,347,118; D. 0. Hanson, U.S. 
Pat. Nos. 4,139,450 and 4,071,433; H. E. Alford, et al., U.S. Pat. No. 
4,067,796; H. W. Gagon, U.S. Pat. No. 4,342,639; and J. A. Gearhart, U.S. 
Pat. No. 4,315,815, as well as the references cited during prosecution and 
those referenced referred to in developing the background of the invention 
in each patent. 
In general these patents describe techniques where sand is contacted in a 
series of extraction tanks and columns, with or without agitation, or 
where the sand is placed in a perforated container or a conveyor belt and 
the solvent is sprayed on the top and allowed to percolate through the bed 
of sand. In most cases, these techniques are designed to increase the 
extraction efficiency of the solvents being used. The other aspect most 
often mentioned are techniques to remove the solvent from the sand after 
the extraction stage; e.g., water displacement of the solvent from the 
extracted sand, multifluid bed driers, etc. Sands are conveyed between the 
various stages of these processes by accepted commercial practices; i.e., 
screw, slurry pumps, conveyor belts, etc. 
Hastings (U.S. Pat. No. 4,311,561) teaches a countercurrent multistage 
vessel process. The last vessel in the series is filled with hot water as 
a means of removing entrained solvent from the sand prior to disposal. 
Hart, et al. (U.S. Pat. Nos. 4,054,506 and 4,054,405) teaches a method of 
using ultrasonics to enhance the recovery of bitumen from tar sands. 
Murray, et al. (U.S. Pat. No. 4,120,775) teaches a tar sand extractor 
design in which the leached tar sand is classified into fine and course 
fractions. The fine sand stays with the miscella, while the course 
fraction falls to the bottom where it is collected for removal from the 
extractor (fine sand retention permits easier washing and draining). In a 
second patent (U.S. Pat. No. 4,176,465), they teach a method for drying 
sand in a device designed to utilize the latent heat of vaporization of 
solvent vapors of the condensing solvent to preheat the sand entering the 
drier. 
Pittman, et al. (U.S. Pat. No. 3,856,474) teaches an apparatus for 
extracting bitumen from tar sands by spraying solvent on tar sand conveyed 
on a perforated moving belt. Primary emphasis is on the design of the 
conveyor belt. In U.S. Pat. No. 4,029,568, they teach the use of 
high-pressure sprays, from 1-100 psi, with their conveyor belt extraction 
system. Their preferred solvents are methyl chloroform, trichloroethylene 
and perchloroethylene, because of "their high solvent effect, low boiling 
point, low specific heat and low heat of vaporization". 
Karnofsky (U.S. Pat. No. 4,239,617) teaches a process to recover oil from 
diatomaceous earth through contacting the ore with a hydrocarbon solvent 
in a series of countercurrent extraction stages. The solvent is removed 
from the spent diatomite by first contacting it with water and secondly 
with steam. The oil-solvent solution is evaporated in multiple-effect 
evaporators followed by steam stripping. 
Smith, et al. (U.S. Pat. No. 3,941,679) teaches a method using 
trichlorofluoromethane for the in situ and surface extraction of tar 
sands. 
Funk, et al. (U.S. Pat. No. 4,347,118) teaches a process using C.sub.5 to 
C.sub.6 hydrocarbons. A two-stage process where a concentrated 
bitumen-solvent solution is separated in a classifier as an overflow and 
the course sand underflow is sent to a countercurrent extraction column 
for further extraction before entering a series of fluid bed driers. The 
patent emphasizes the use of multistaged fluid bed drying for complete 
removal of the solvent. 
Hanson, et al. (U.S. Pat. No. 4,139,450) teaches a countercurrent 
extraction method for wet sands where the water is removed with hot 
solvent vapors prior to the extraction process. In U.S. Pat. No. 
4,071,433, they use a technique where tar sand is slurried with oil, the 
course sand separated by centrifuge and the fine sand, oil, bitumen stream 
is fed directly to a coker. 
Alford, et al. (U.S. Pat. No. 4,067,796) teaches a process involving a 
conditioning step with an alkaline aqueous solution followed by the 
extraction and separation of the tar sand with a hydrocarbon solvent, in a 
vessel which also contains water, thus forming two immiscible liquid 
phases for ease of sand separation. 
Gagon (U.S. Pat. No. 4,342,639) teaches the extraction of tar sand with a 
halogenated solvent wherein the extracted sand is separated from the 
bitumen solvent solution by feeding the oil-solvent-sand slurry onto a 
conveyor system partially submerged in water. A halogenated solvent is 
important, because the oil-solvent solution must be heavier than water in 
order to affect separation. 
Gearhart (U.S. Pat. No. 4,315,815) teaches a method of separating a solvent 
from bitumen by pressure reduction at elevated temperatures followed by 
steam stripping. A device to accomplish this is also described. 
None of the above patents address the need to insure the complete removal 
of the solvent from the extracted bitumen prior to further refining. This, 
of course, is not a major need when nonhalogenated solvents are used as 
the extracting solvent, as most of the above patents so specify. However, 
even those who specify a halogenated solvent, e.g., Pittman, et al., 
Smith, et al., and Gagon, essentially ignore the solvent-bitumen 
separation problem. They specify technology such as flash distillation, a 
conventional evaporator and ambient temperature evaporation (thought to be 
applicable for summer desert environments) for solvent-bitumen separation. 
The concern for residual chlorides in crude oil or bitumen feeds to a 
refinery is universal throughout the petroleum industry. Past experience 
with chloride-contaminated crude oil refinery feed has been extremely 
negative; e.g., causing major corrosion damage to various refinery units 
as well as causing process upsets due to catalyst poisoning. Consequently, 
the use of chlorinated solvents for either bitumen or crude oil extraction 
is generally not considerable feasible. 
It is difficult to remove solvents, even the low boiling methylene 
chloride, to contents much below 100 ppm by conventional techniques. With 
hydrocarbon solvents such low levels are acceptable because they are 
recoverable in the bitumen refinering process. However, it is not 
acceptable to have halogenated hydrocarbon contents in bitumen over 100 
ppm and preferably not over 10 ppm, because the chloride is corrosive to 
refinery equipment and can harm catalysts used in the refining process. 
Therefore, a procedure is needed to reduce the chlorinated hydrocarbon 
content in the extracted bitumen to less than 10 ppm. 
BRIEF DESCRIPTION OF THE INVENTION 
In accordance with the present invention a process based on unit operations 
conventionally employed but modified to enable the use of chlorinated 
solvents, particularly methylene chloride as the preferred solvent for 
extraction of the bitumen from the tar sands or shale. The process in 
general constitutes: 
I. an extraction operation wherein the tar sand is contacted with the 
chlorinated solvent, particularily methylene chloride, to extract 
(dissolve) the bitumen from the sand; 
II. a separation of the sand from the solvent bitumen extract; 
III. (a) recovery of the bitumen free of extractant; (b) recovery of the 
sand free of extractant.

DETAILED DESCRIPTION OF THE INVENTION 
In greater detail, reference is had to FIG. 1 which illustrates a simple 
flow diagram of the essential elements of the process. Tar sand is fed 
into a mixer-extractor (1) into which solvent is also fed by line (3) from 
the rinser stage (2). Fresh solvent is fed to the rinser (2) from storage 
indicated by line (4). The extracted sand leaves the mixer-extractor (1) 
through line (5) and enters the rinser (2). The rinsed sand leaves the 
rinser (2) through line (6) and enters the drier (7). The clean, dry sand 
leaves the drier by line (8) for disposal. A portion of the 
solvent-bitumen solution (miscella) leaving the rinser (2) through line 
(3) is withdrawn through line (9) where it enters a fines removal step 
(e.g. a centrifuge) (10). Upon exiting the fines removal (10) the 
miscella, via line (12), enters a solvent recovery system having a 
distillation stage (13) where most of the extraction solvent is removed 
through line (14), condensed and forwarded to storage via line (20). In a 
second stage of the recovery system (13), the bitumen substantially free 
of solvent, falling from the first stage is mixed with a stripper diluent 
which comes from storage via line (11) and from recycle line (18). In a 
flash tank (19) the bitumen-stripper-residual solvent mixture is subjected 
to a high temperature flash distillation to remove residual extraction 
solvent and most of the stripper-diluent as overhead, which overhead is 
lead via line (16) to condensor (17), wherein the two components are 
condensed and introduced via line (18) to line (15) into still (13). The 
bitumen product (21) containing a small percentage of stripper-diluent 
solvent, for viscosity control, is then sent to upgrading. 
As previously described, the preferred overall process involves a 
single-stage extraction vessel where the bitumen is rapidly and completely 
dissolved. A highly concentrated bitumen-solvent solution (miscella) 
overflows from a solids separation device and a high boiling 
stripper-diluent solvent is added, preferably after fines removal and bulk 
solvent removal, to assist in residual solvent removal in a stripper 
stage. The miscella is first distilled in such a fashion that preferably 
about 98% of the extraction solvent is rapidly vaporized off and sent back 
to the extraction stage via storage. The remaining extraction solvent 
bitumen mixture is mixed with the stripper-diluent and when the 
temperature of this mixture begins to exceed the boiling point of the 
stripper-diluent (SD) solvent, the residual solvent is carried overhead 
with most of the SD. This overhead is condensed and may be flashed to 
separate the low boiling solvent from the SD and the SD recycled with 
make-up SD to supply the stripper diluent to the second stage of the 
solvent recovery step or both SD and solvent may be returned to the 
solvent recovery step in the SD line (15) to the second stage. Three to 
four percent of the stripper-diluent is left in the bitumen to control its 
viscosity and give it an acceptable pumpability for subsequent processing. 
The course sand from the extraction vessel is rinsed with fresh solvent 
prior to drying with a combination of indirect heat, direct steam 
impingement and aeration. The clean sand is suitable for any use since it 
is substantially free of solvent and tar. 
The chlorinated solvents, as a class, exhibit solvency properties between 
those of oxycarbon and hydrocarbon solvents and generally have a good 
solvency for the waxes, resins and greases that are found in common 
industrial operations and are preferable to hydrocarbon solvents in the 
disclosed process. It was still surprising to find that methylene chloride 
exhibited such a superior solvency for all the various tar sand ores which 
were screened. Therefore, methylene chloride is the preferred solvent and 
has the added advantage of being environmentally more acceptable than the 
other chlorinated solvents which as a class are safer than the hydrocarbon 
solvents. 
A spectrum of tar sand samples were evaluated to determine if factors such 
as tar sand source, grade, oil or water wet nature, viscosity 
characteristics of the contained bitumen, etc. had a significant affect on 
extraction rates, efficiencies and complexity of subsequent processing 
steps. 
The results of some of these screening tests are shown in Table 1. These 
simple room temperature washing experiments illustrate the unusual 
solubility which methylene chloride has for tar sand bitumens. The same 
extraction efficiency was obtained for the water-wet (Athabasca) and the 
oil-wet (Kentucky and Utah) sands. The grade (2.84% Raven Ridge through 
12.30% Athabasca) also had no effect on extraction efficiencies. The 
viscosity of the contained bitumen (Sunnyside approx. 10.sup.7 poise or PR 
Springs approx. 10.sup.3 poise) also did not appear to be a factor. 
TABLE I 
______________________________________ 
Multiple Washings with Methylene Chloride 
(Ambient Temperature) 
Wt % carbon on sand 
As Residual carbon/stage 
Wt. % sand 
received 
1 2 3 4 in slurry 
______________________________________ 
Kentucky 5.35 0.60 0.19 0.21 -- 20 
Utah 
PR Springs 
9.42 2.01 0.06 0.50 0.33 50 
Raven Ridge 
2.84 0.40 0.16 0.19 -- 15 
Sunnyside 
4.73 1.04 0.79 0.27 0.11 33 
Athabasca 
12.30 2.05 0.58 0.21 0.21 33 
(high grade) 
Diatomite 
14.84 9.87 6.61 5.34 5.58 30 
McKittrick 
______________________________________ 
Bitumen is soluble in methylene chloride in substantially all proportions. 
Solutions with concentrations above 70% bitumen have been prepared in the 
laboratory. This unusual solvency for bitumen also manifests itself in 
extractions rates. FIG. 3 illustrates this point. Methylene chloride 
containing 20% by weight bitumen initially achieved 100% extraction in a 
matter of minutes for the water-wet, medium-grade, Athabasca sand as shown 
in FIG. 3. These rates, of course, greatly simplify the design of the 
extraction stage for any proposed solvent extraction process. Other tests 
indicate similar results, as with oil-wet, low grade Kentucky sand. 
It is to be understood that single stage extraction efficiency drops off 
significantly at miscella concentrations in excess of about 40%. If 
greater than about 40% weight solutions are used the extractions will 
require longer extraction time or continue in the rinser stage wherein 
more stages may be required to achieve commercially acceptable extraction. 
The phenomenum is a result of viscosity increase in the greater than about 
40% concentration as clearly shown in FIG. 4. 
Although solvency is important, several other solvent properties also have 
to be considered in evaluating a solvent for a commercially-viable solvent 
extraction process. These considerations include safety, health effects, 
and potential environmental impact. Methylene chloride gives the best 
balance of properties relative to the above concerns; i.e., it behaves as 
a nonflammable solvent, it has the greatest solvency power of all the 
solvents evaluated (bitumen dissolves completely and very rapidly with a 
minimum of agitation regardless of the source or grade of tar sand being 
extracted), it has a workplace safety standard (TLV of 100 ppm) which can 
be achieved with good work practices, and it is one of five solvents which 
the EPA has determined to have insignificant photochemical reactivity and 
consequently its emissions may not have to be controlled under State VOC 
emission regulations. The other chlorinated sovlents, perchloroethylene 
and trichloroethylene are less acceptable than methylene chloride from an 
environmental stand point, requiring extra care in leak proof equipment. 
Methyl chloroform another environmentally acceptable chlorinated solvent 
has a problem in that it is more readily hydrolyzed in a process where 
water is present in the quantities here encountered. 
Methylene chloride can be stripped from the bitumen fairly easy using air 
or steam stripping or the addition of a high boiling stripper-diluent, the 
latter is a preferred technique as hereinafter disclosed. Here again, the 
advantage of methylene chloride over the other chlorinated hydrocarbons is 
evidenced as the higher boiling solvents consume more energy and/or are 
more readily hydrolyzable and can't be readily steam stripped. 
If air or steam stripping is employed an additional step will be required 
to recover the solvent in an efficient manner. Present commercial 
techniques employ refrigerated coils, mineral oil absorption or carbon 
absorption. The refrigerated coils method is expensive to run and very 
inefficient. Carbon absorption and mineral oil absorption can be efficient 
depending on the volume and velocity of the solvent-laden air being 
stripped. However, both methods depend on steam stripping to recover the 
solvent from the absorbing media, i.e., mineral oil or activated carbon. 
Consequently, all methods in a sense, except refrigeration, involve a 
steam stripping step for solvent recovery. 
In a steam stripping operation, the saturated water-solvent vapor is fairly 
easy to condense, and the separation of the condensed immiscible water and 
solvent phases can also be readily accomplished. However, this technology 
when applied to the recovery of chlorinated solvents must take into 
account that chlorinated solvents at high temperatures can be extensively 
hydrolyzed, forming hydrogen chloride. This can cause not only extensive 
damage to the distillation system, but the resultant corrosion product, 
FeCl.sub.3, also will act as a catalyst and accelerate the hydrolysis 
reaction. 
Another consideration is that all commercially available chlorinated 
solvents contain metal inhibitors and acid acceptors, which both slow the 
hydrolysis reaction and minimize the corrosive effect of the hydrochloric 
acid generated upon decomposition. These additives, in most cases, are 
water soluble and, consequently, depleted during the water-solvent 
separation stage, particularly when the ratio of water to solvent is large 
as is typical for a steam stripping operation. The depletion of the 
inhibitor system in the solvent sent back to recycle will require 
inhibitor addition to prevent corrosion damage throughout the extraction 
process unless the vapor portion of the solvent is feed for recycle before 
steam is used. A preferred technique is to use a two stage non-steam 
solvent removal process, one in which the solvent is removed without 
contact of the solvent with steam. This is accomplished by a simple 
distillations of the major portion of the solvent followed by a second 
step which uses a a high-boiling stripper diluent (S-D) solvent (in place 
of steam) to remove the residual solvent. 
This latter technique, as presently envisioned also serves several other 
purposes. It is fairly easy to control, since it involves only a volume 
addition of the S-D solvent to the solvent-bitumen solution (miscella) 
preferably subsequent to the major solvent removal by simple distillation. 
With the proper S-D solvent, essentially complete removal of residual 
solvent is accomplished by monitoring the temperature of the exiting 
bitumen product stream. 
Bitumens vary considerably in viscosity, depending on their source. In the 
U.S., bitumens with viscosities of 10.sup.7 to 10.sup.3 poise are normal. 
Since these products may have to be transported considerable distances to 
a refinery for upgrading, they should be pumpable upon delivery. This can 
be accomplished by leaving a few percent of the S-D solvent in the bitumen 
as a viscosity modifier. Ideally, in order to minimize costs, it is 
desirable to choose a S-D solvent which has an acceptable boiling point to 
strip out all residual chloride and is a natural product stream generated 
during the bitumen upgrading process. A solvent of this nature can easily 
be recycled between the extraction and upgrading plants. 
A third purpose which the S-D solvent serves is that it is a mechanism to 
guarantee the recovery of inhibitor and acid acceptor additives normally 
contained in commercial chlorinated solvents, without the solvent 
contacting any water. 
In a tar sand extraction process, the conditions which are most likely to 
lead to the hydrolytic and thermal decomposition of an improperly 
inhibited chlorinated solvent are those generally present in the 
distillation and recovery section of the process. Consequently, this is 
the portion of the process which will require the most protection. The 
stripper diluent technology is designed to give excellent flexibility, by 
adding to the S-D solvent a high boiling inhibitor, which inhibitor will 
be confined by the recovery of the stripper-diluent to the second stage 
distillation section of the solvent recovery process. The conventional 
inhibitors designed to boil with the solvent of course go overhead with 
the bulk solvent removal to protect it in the lower temperature sections 
of the process. 
Most tar sand extraction techniques which have previously been considered 
are multistaged, agitated tank processes. This comes about since many of 
the solvents proposed for use have limited solvency for bitumen and 
dissolution occurs incompletely and at a relatively slow rate. 
Consequently, large volume ratios of solvent to sand are required, and by 
necessity a fairly dilute miscella is fed to the distillation system. 
Because bitumen is soluble in methylene chloride in all portions excellent 
dissolution rates, even with essentially no agitation present or 
achievable. This permits the use a single mixing-extraction stage with a 
minimum volume of solvent in which the dissolution of the bitumen occurs 
thereby to producing a higher bitumen concentration in the extracting 
solvent. 
A preferred embodiment of the present invention for a continuous tar sand 
extraction is shown in FIG. 2 of the drawings: 
As shown in the drawings, FIG. 2, crushed tar sand is fed, as by a 
vibratory or belt feeder, to one end of a mixer-extractor (illustrated as 
a pugmill). Solvent (methylene chloride) containing some bitumen (a 
portion of the stream from the sand rinser) is fed at the same end of the 
mixer-extractor and moves co-current with the sand moving in the 
mixer-extractor. 
The sand and solvent moving through the mixer-extractor are directed to the 
low end of an inclined screw which is employed as a preferred design for 
the rinser. The solvent, containing 35-40% by weight bitumen exiting the 
rinser is partially sent to the mixer-extractor and partially directed to 
a fines removal system, e.g. a centrifuge multi media filter or the like. 
Fresh solvent is fed to the rinser at the high end of the inclined screw 
and flows downwardly countercurrently through the sand to rinse any 
remaining bitumen from the sand and dilute the miscella generated in the 
mixer extractor. The sand is delievered to a drier, preferably as 
illustrated a heated hollow screw drier (TORUS DISC), wherein with the aid 
of steam as a scavenger gas, the residual solvent associated with the sand 
is removed. The sand exits to a clean sand pile. 
The solvent with preferably 35 to 40% by weight bitumen, miscella, is 
subjected to a fine solids a removal as aforestated. The miscella is then 
forwarded to a multistage solvent recovery system. The top portion of the 
tower removes the bulk of the solvent with rectification. In the lower 
section the bitumen which has substantially all of its solvent removed in 
the upper stages is preferably mixed with from about one (1) to about 100 
percent of a hydrocarbon material (SD) having a boiling point higher than 
the solvent which will act as a stripping agent for removing residual 
solvent. The stripping agent is added after the bulk solvent removal to 
assist in the final methylene chloride removal and to enable the solvent 
free bitumen to be pumpable. Thus, the stripping agent acts as a viscosity 
control for the bitumen after bulk solvent removal. As aforestated, the 
stripper-diluent (SD) should preferably be a constitutent of the upgraded 
bitumen thus introducing no impurity or material which must be removed 
during the upgrading stage. 
Following the bulk removal of the solvent, in for example, a sieve tray 
distillation column, and addition of SD the bitumen/residual solvent in 
the second stage, a trace of SD and substantially all of the residual 
solvent are boiled off. The bitumen then has only traces of solvent 
remaining, preferably less than 10 ppm, but retains sufficient SD to be 
pumped to the upgrading step: SD content can conveniently be controlled by 
flashing off any excess added to aid in solvent stripping. 
The bitumen-free sand leaving the inclined screw rinser is fed to a drier. 
Some drainage takes place in the screw, however, solvent hold up on the 
sand will generally be on the order of 20-30 weight percent. For 
desolventizing purposes, we have chosen the heated hollow screw drier, 
called the TORUSDISC, marketed by Bepex Corp. This choice was based on 
cost and efficiency. Although, from our experience the desolventizers 
currently used by the oilseed extraction industry appear to be equally 
effective. 
Drying experiments carried out in the TORUS DISC using solvent-extracted 
Kentucky tar sands in order to obtain the information required for sizing 
and scale-up, utilized a hot oil system and sand feed initially containing 
approximately 25 percent by weight methylene chloride was desolventized 
fairly rapidly approaching a final residual solvent level of 100 ppm. The 
addition of a 12 lb/hr steam sparge accelerated solvent removal, and 
residual solvent levels approaching 1 ppm were fairly easily achieved. In 
order to avoid any chance for groundwater contamination due to the 
leaching of solvent from the backfilled sand a 1 ppm or less solvent level 
is a reasonable and achievable objective. 
The solvent vapors exiting the desolventizer carry with them a considerable 
portion of fine sand particles which require separation therefrom to 
enable the solvent to be recycled. These vapors with the attendant fines 
are quenched in a water jet which exits into a large container, a solids 
separator, wherein the sand wet with water falls to the bottom as does the 
major part of the water, is withdrawn and the bottoms stream split, part 
to recycle to the jet and part to a water stripper wherein steam strips 
the residual solvent from the water. This water containing fine sand 
particles can be combined with coarser sand from the desolventizer and 
used as land fill. The solvent vapors, and unquenched steam from the 
desolventizer, pass through a demister and are joined with the vapors from 
the stripper, condensed and sent to a water separator. The solvent from 
the separator is recycled to the process and the water used as a principal 
source of water to the jet in the solids separator. 
In practice a vent collecting system is associated with the process units. 
The preferred vent collecting system is an absorber/stripper operation 
wherein the vents which contain various constituents of the process as 
well as large volumes of air and other inert gases carried into the 
process with the tar sand and/or generated or released during the various 
steps of the process are absorbed in an oleogeneous liquid, for example, a 
mineral oil, which absorbs the hydrocarbons and chlorinated solvents, 
allowing the non-condensible and inert gases (N.sub.2, O.sub.2, H.sub.2, 
etc.) to pass to the atmosphere. The rich oil is sent to a stripper where 
heat is applied, preferably steam, to strip the volatiles from the oil. 
The vapors go to a phase separator and the condensate, principally the 
methylene chloride, added back to the process. 
While each unit operation has been described illustrating a preferred 
embodiment of equipment it is to be understood that various pieces of 
mechanical apparatus may be used in accordance with the present invention 
to accomplish the unit operations necessary to effectuate the results 
herein described. For example vibrating pan screw or belt feeders, the 
latter with or without vibratory assists may be used to feed the tar sand 
to the extractor-mixer. The extractor mixer may be a pug null, tumbler 
(sag mill), with or without vibratory assists where appropriate. A 
mixer-settler may be used for both the mixer, initial extraction and 
rinsing steps. Rinsers such as inclined screws, percolation beds and 
vacuum belts may be used with good results. Centrifuges, filters and 
settlers may be used for fines removals. Various means for vapor recovery 
include, oil absorbers, carbon absorption and incineration. 
Suitable stripping diluents (SD) include the intermediate boiling 
hydrocarbon fractions such as mineral spirits, Stoddard Solvent, xylene, 
kerosene and #2 diesel oil, preferably one or more of those hydrocarbon 
fraction employed or produced in the upgrading process. Other hydrocarbon 
blends of suitable boiling range can be employed. Pure components such as 
ethyl benzene can be likewise utilized. 
These intermediate hydrocarbons will assist the removal of the commercially 
available chlorinated hydrocarbons, methylene chloride, 
1,1,1-trichloroethane, trichloroethylene and perchloroethylene. 
The amount of the hydrocarbon added can vary from about 1% by weight to 
about 99% by weight based on the methylene chloride employed. Preferably, 
however, 2 to 15% by weight and most preferably 5-7% by weight are 
employed. However, when the bitumen is to be sent to an upgrading unit 
nearby it may be advantageous to employ 40-100% added SD depending on the 
process. 
No particular pressure is more advantageous than another, merely raising or 
lowering the boiling temperatures and bearing on the economics. 
It is also to be understood that while the described solvent recovery 
process has particular utility to removal of chlorinated hydrocarbons from 
the bitumen, the procedure may also be used to recover chlorinated 
hydrocarbons from crude oils or other oleogeneous liquids. 
In carrying out the process of the present invention air or inert gas 
stripping may also be used to strip chlorinated solvent residuals, 
although significant solvent loses or increased cost of operation is 
incurred. Recovery of the solvent from such inert gas stream requires 
cryogenic temperatures or alternate absorption equipment, such as carbon 
or mineral oil absorbers. Steam as a stripping agent is likewise 
effective. However, the resultant contamination of the solvent and bitumen 
with water is undesirable. 
EXAMPLE 1 
A laboratory distillation was carried out to establish the effect of a 
stripper-diluent in recovery of the methylene chloride, using ethyl 
benzene (136 degrees C. boiler) as the added intermediate boiling 
hydrocarbon. A laboratory scale still, was charged with a mixture of 
72.33% wt. methylene chloride, 12.65% wt. Asphalt Ridge bitumen and 15.02% 
wt. ethyl benzene. After boiling was established and the bulk of the 
solvent removed, the pot temperature began to exceed 40.degree. C. At this 
point, pot temperatures were recorded as a function of residual methylene 
chloride in the bitumen. The data table (Table II) below lists boiling 
range and residual methylene chloride. Note the distinct drop in methylene 
chloride concentration as the boiling point of ethyl benzene is reached. 
TABLE II 
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METHYLENE CHLORIDE RECOVERY FROM -ASPHALT RIDGE BITUMEN 
Residual Methylene 
Bottoms Boiling 
Chloride in Bitumen 
Range (.degree.C.) 
wt. % 
______________________________________ 
40-109 6.8952 
109-124 2.7286 
124-139 0.5507 
139-146 0.00005 
146-168 0.00001 
168-186 0.00001 
186-206 N.D.* 
______________________________________ 
*Not Detectable 
For comparison to alternate technologies, additional distillations were 
performed with the same apparatus, bitumen and extraction solvent as well 
as with nitrogen as a stripping aid. 
EXAMPLE 2 
A similar distillation was carried out except nitrogen stripping was used. 
A mixture containing 85.2% methylene chloride and 14.8% Asphalt Ridge 
Bitumen was charged to the distillation device. Once the boiling point of 
methylene chloride was exceeded, nitrogen was sparged into the bitumen 
mass at a rate of 0.13 cu. ft. per lb. of bitumen per minute. 
TABLE IV 
______________________________________ 
METHYLENE CHLORIDE RECOVERY FROM 
ASPHALT RIDGE BITUMEN 
Residual Methylene 
Bottoms Boiling 
Chloride in Bitumen 
Range (.degree.C.) 
wt. % 
______________________________________ 
40-128 3.8505 
128-151 1.22 
151-175 0.6153 
175-192 0.0365 
192-201 0.0032 
______________________________________ 
EXAMPLE 3 
An additional distillation of methylene chloride from Kentucky bitumen was 
made using an intermediate boiling hydrocarbon blend as the S-D. The 
intermediate boiling hydrocarbon blend chosen is a commercial aromatic 
hydrocarbon solvent SC-100 distributed by CHEM CENTRAL, Chicago. The 
boiling range of the solvent is 155.degree.-173.degree. C. and the 
chemical makeup is 98% aromatics. To 63 grams of bitumen was added 25 
grams of SC-100 and 250 grams of methylene chloride. The resulting mixture 
containined 7.4% chaser solvent, 18.6% bitumen and 74% methylene chloride 
by weight. As the vapor temperature exceeds the initial boiling 
temperature of the SC-100 (155.degree. C.) methylene chloride level in the 
bottoms was non-detectable. 
TABLE V 
______________________________________ 
Methylene Chloride Recovery from Kentucky Bitumen 
Temperature, .degree.C. 
Wt % Methylene Chloride 
Bottoms Vapor in Bitumen 
______________________________________ 
90 50 23.1 
180 110 0.099 
230 168 N.D.* 
300 170 N.D. 
______________________________________ 
*Not Detected 
COMATIVE EXAMPLE 
For comparison purposes a direct distillation of a mixture containing 86.4% 
methylene chloride and 13.6% Asphalt Ridge Bitumen was run. Boiling range 
vs. wt % solvent in the bottoms is listed below. Note that although the 
bottoms temperature exceeds 4 times the boiling point of methylene 
chloride, considerable amounts of solvent remains. 
TABLE III 
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METHYLENE CHLORIDE RECOVERY FROM 
ASPHALT RIDGE BITUMEN 
Residual Methylene 
Bottoms Boiling 
Chloride in Bitumen 
Range (.degree.C.) 
wt. % 
______________________________________ 
40-89.5 20.2117 
89.5-122 6.4450 
122-144 4.8513 
144-163 2.1583 
163-184 1.6544 
184-200 0.5413 
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