Recovery of hydrocarbon values from low organic carbon content carbonaceous materials via hydrogenation and supercritical extraction

Hydrocarbon values are recovered from low organic carbon content materials via treatment with hydrogen and extraction with supercritical solvents.

BACKGROUND OF THE INVENTION 
Methods for recovering hydrocarbons from naturally-occurring deposits, such 
as tar sand and oil shale, are the objects of renewed commmercial 
interest. 
Deposits of oil shale and tar sands have been located on the North American 
Continent in Canada and in the western, mid-western, and eastern regions 
of the United States. 
OBJECTS OF THE INVENTION 
It is one object of the invention to provide a process for extracting 
hydrocarbons from low organic carbon content deposits. It is another 
object of the invention to extract hydrocarbons from low organic carbon 
content deposits via hydrogenation and supercritical solvent extraction. 
It is still another object of the invention to extract hydrocarbons from 
low organic carbon content deposits by simultaneous hydrogenation and 
supercritical solvent extraction. 
THE INVENTION 
According to one aspect of the invention, oil shale is preheated with 
hydrogen, optionally in the presence of a hydrogen-donor compound, and 
hydrocarbon values are recovered therefrom via supercritical solvent 
extraction. 
In accordance with another aspect of the invention, oil shale is subjected 
to supercritical solvent extraction while in the presence of hydrogen and 
an optional hydrogen donor. 
THE LOW ORGANIC CARBON CONTENT MATERIALS 
By "low organic carbon content materials" is meant carbonaceous materials 
in which organically bound carbon constitutes about 25 weight percent or 
less of the material. Suitable materials include oil shale, tar sands, oil 
sands, and similar deposits. Coal, lignite, and other materials which 
contain more than 25 weight percent organically bound carbon are not 
included in the invention. 
Some of the largest known deposits of suitable materials are found in the 
Athabasca region of Alberta, Canada, and in the Western, Mid-Western, and 
Eastern United States. The invention is particularly effective for 
treating Eastern Oil shales, such as Kentucky shales. 
THE HYDROGEN CONTACTING STEP 
The hydrogen contacting can be carried out using: 
(1) hydrogen alone, 
(2) hydrogen donor compound alone, or 
(3) hydrogen and hydrogen donor compound together. 
Methods (1) and (3) are preferred. Method (3) is most preferred. 
When hydrogen is employed, it is supplied at a pressure within the range of 
750-10,000 psig and at a temperature within the range of 
200.degree.-475.degree. C. Hydrogen gas is introduced at a rate of 
100-10,000 scf/ton of carbonaceous feed, preferably at 500-5000 scf/ton. 
The hydrogen donors used in the invention include compounds which are 
compatible with the extracting solvents and which, at supercritical 
conditions, aid in the extraction of hydrocarbons from the low organic 
carbon content materials. 
Suitable hydrocarbon donors include tetralin, tetrahydroquinoline, and 
o-cyclohexylphenol. Tetralin is preferred. 
Optionally, the contacting step is carried out by preheating the tar sand 
or oil shale to a temperatures in the range of 100.degree. to 600.degree. 
C., preferably 250.degree. to 475.degree. C. Any suitable temperature can 
be used. Generally, the temperature to which the material is heated is 
within 0.degree. to 50.degree. of the temperature at which the solvent 
extraction will take place. Usually, a temperature of about 350.degree. to 
475.degree. C. is employed. 
If desired, the hydrogen contacting step can be conducted in the presence 
of conventional hydrogenation catalysts. Useful catalysts contain one or 
more of the metals of Groups VIb and VIII, their oxides, and salts. 
Suitable metals include tungsten, cobalt, molybdenum, nickel, iron, 
platinum, palladium, and combinations thereof. Optionally, a catalyst 
support, usually containing one or more of silica, alumina, and metal 
oxides, can be employed. 
After the hydrogen contacting step, the hydrogen and/or hydrogen donor 
compound may be removed, if desired. Typical processes for their removal 
include flashing, fractionation and distillation. Chemical separation may 
be used, but care must be exercised to avoid the addition of the agents 
which would be deleterious in subsequent operations. 
In other embodiments, the hydrogen and/or hydrogen donor compound remains 
in the treatment zone during supercritical solvent extraction. 
If desired, conventional processing operations can be employed before or 
after the hydrogen contacting step. 
THE SUPERCRITICAL SOLVENT EXTRACTION 
The critical temperature for a substance is the temperature above which it 
cannot be liquefied by an increase in pressure. The critical temperature, 
then, depends upon the identity of the particular solvent being used. The 
supercritical temperatures employed in the invention will generally lie 
within a range between the critical temperature of the solvent and about 
100.degree. C. above its critical temperature. 
In general, useful extraction temperatures will be in the range of 
100.degree. C. to 600.degree. C., with a preferred range of about 
250.degree. C. to 475.degree. C. 
The pressure at which the supercritical extraction takes place depends upon 
the identity of the solvent employed. The pressures used during the 
extraction step of the invention will range from the critical pressure of 
the solvent to 10,000 psi or higher. Preferably, the pressures employed 
will be between 750 psi and 3000 psi. 
The liquid hourly space velocity (LHSV) employed will usually range from 
about 0.5 to 10. A LHSV of about 1 to 2 is preferred. Note that the space 
velocity can be denoted in units v/v/hr or v.sub.c /f.sub.c /hr wherein 
v.sub.f is the volume of liquid introduced in one hour, v.sub.c is the 
volume of the extraction vessel, and hr is hours. 
The solvents used as extractants are organic compounds containing about 2 
to 20 carbon atoms. When aromatic solvents are used, they contain from 6 
to about 12 carbons, preferably 6 to 10 carbons. Among the useful aromatic 
solvents are benzene, toluene, xylene, and naphthalene. Toluene is a 
preferred aromatic solvent. 
Other aromatic compounds and heterocyclic compounds can be wholly or 
partially substituted for the hydrocarbons discussed above. Examples are 
furan, pyridine, thiophene, and derivatives thereof. 
Suitable non-aromatic extractants include cyclic and acyclic compounds 
containing two to about 20 carbon atoms. Useful cyclic compounds include 
cycloalkanes and substituted forms thereof. Cyclohexane and methyl 
cyclohexane are contemplated for use. 
Among the acyclic compounds which are preferred are alkanes containing from 
5 to 11 carbon atoms. Hexanes and heptanes, particularly n-heptane, are 
most preferred. Both branched- and straight-chain compounds are useful. 
Mixtures of any of these solvents can be employed. 
SIMULTANEOUS HYDROGEN CONTACTING AND SOLVENT EXTRACTION 
In one embodiment of the invention, the carbonaceous material is contacted 
with hydrogen, and an optional hydrogen donor compound, in the presence of 
one or more supercritical solvents. As was pointed out above, the 
supercritical parameters depend upon the identity of the solvent employed. 
When both hydrogen and hydrogen donor compound are present, the amount of 
hydrogen donor compound present is between 0.5 and 10%, preferably between 
1 and 5% by weight of the solvent. The quantity of hydrogen used will 
range from 100-10,000 scf/ton of oil shale, preferably 500-5000 scf/ton. 
The solids and fluids produced can be separated by conventional methods. 
Useful devices include cyclones, filters, settling devices, or 
combinations thereof. 
The fractions within the fluid phase can be separated via one or more 
conventional cooling, pressure reduction (flashing), or distillation 
steps. Combined methods are also operable. 
The organic product from the supercritical solvent extraction may be 
separated into 2 or more fractions which can be classified as "heavy" or 
"light" according to the molecular weight of the compounds therein. These 
fractions can be collected by conventional means, such as distillation. 
If desired, one or more of the organic extract fractions can be subjected 
to further treatment in order to enhance its suitability for subsequent 
use.

EXAMPLES 
The following examples illustrate the utility of the invention in 
efficiently recovering hydrocarbon values from oil shales. 
EXAMPLES 1-5 
The following five runs were made on coarse Eastern (Kentucky) oil shale 
(containing 13.3% organic carbon) in which 750 g of shale was extracted 
with 2100 g of n-heptane solvent at 410.degree. C. and 1950 psig 
(supercritical conditions). 
______________________________________ 
Tetra- Spent 
lin, Extract Products, 
Shale 
Sam- Hydro- Wt. % Wt. % of Sample Organic 
ple gen of Sol- Heavy Light Carbon, 
No. (scf/ton) 
vent Extract 
Extract 
Gas H.sub.2 O 
% 
______________________________________ 
1 0 0 7.4 2.8 4.3* 1.7 8.28 
2 0 0 5.7 1.8 1.1 0.7 6.94 
3 0 0 5.4 0.2* 1.3 1.2 8.40 
4 0 1.0 8.5 1.5 1.4 1.7 7.26 
5 1250 1.0 11.2 1.2 2.7 2.3 4.78 
______________________________________ 
*Believed erroneous 
The above data indicate that the inclusion of a minor amount of tetralin in 
paraffinic solvent results in a substantial increase in heavy extract 
yield, and the further introduction of hydrogen increases heavy extract 
yield even further. The degree of organic carbon extraction is also 
indicated by the amount remaining on the spent shale. 
It is believed that other hydrogen donor compounds would produce similar 
increases in heavy extract yield. 
EXAMPLES 6-15 
The following ten runs were made on coarse oil shale in which 750 g of 
sample was preheated to 410.degree. C. (with the pretreating gas, if any) 
then solvent extracted with 2100 g of solvent, with or without hydrogen, 
at 1950 psig (1500 psig for Western shale samples). 
__________________________________________________________________________ 
Extracts Products, 
Gas 
Wt. % of Sample 
Flow 
Sample 
Pretreatment Heavy 
Light Rate 
No. Gas Solvent Extract 
Extract 
Gas 
H.sub.2 O 
(scf/ton) 
__________________________________________________________________________ 
Eastern 
Shale 
6 None toluene 4.7 [3.0]* 
1.6 
2.0 
-- 
7 Nitrogen 
n-heptane 
4.4 0.8 2.3 
3.0 
2,500 
8 None n-heptane + H.sub.2 
5.8 1.1 4.1 
2.1 
2,500 
9 Hydrogen 
n-heptane 
6.4 1.0 2.7 
1.9 
No flow 
10 Hydrogen 
n-heptane 
7.1 1.0 2.9 
2.4 
1,200 
11 Hydrogen 
n-heptane 
8.5 1.7 2.5 
2.5 
2,500 
12 Hydrogen 
n-heptane + H.sub.2 
8.4 0.4 2.8 
2.5 
2,500 
13 Hydrogen 
n-heptane + H.sub.2 
8.9 1.0 2.6 
4.0 
5,000 
Western 
Shale 
14 None n-heptane 
12.1 -- 
15 Hydrogen 
n-heptane 
14.2 No flow 
__________________________________________________________________________ 
*Believed to be in error (too high). 
Note that the ratio of heavy fraction to light fraction increases 
dramatically when hydrogen treatment is employed both before and during 
solvent extraction. 
Reasonable variations and modifications which become apparent to those 
skilled in the art can be made in the present invention without departing 
from the spirit and scope thereof.