CA1108081A - Extraction of oil from oil shale and tar sand - Google Patents

Abstract

EXTRACTION OF OIL FROM OIL SHALE AND TAR SAND

Abstract of the Disclosure The present invention is related to a method for extracting oil from oil shale and tar sand. More particu-larly, the present invention is concerned with such extrac-tion which is carried out by means of a retorting process at a temperature between about 700°-1200°F. wherein the heat therefor is generated through microwave energy.

Description

Background of the Invention Oil shale has been recognized as a potential source for large quantities of gasoline, jet fuel, diesel fuel, and non-condensable petroleum gas with the concurrent recovery of such byproducts as coke, pitch, asphalt, ammonia, sulfur, and specific organic chemicals. Additional processing has been devised to produce aluminum and soda ash. Oil shale deposits are found on~all continents and have a common process of formation, ~iz., the co-sedimentation of silt and algae in ancient lakes. Oil shales ha~e a generally laminar appearance having dark brown layers corresponding to algae-rich periods and light brown layers indieating algae-lean periods. Strictly speaking, oil shale is not a shale nor does i~ contain oil. Rather, it is a marlstone with a laminar strùcture thereby exhibiting natural cleavage planes like a shale. The mineral or lnorganic content can vary widely, but the organic component commonly contains two heteroatomic polymers -- about 10% by weight bitumen which ~ is soluble in numerous organic solvents, and about 90% by ,` weight kerogen which is insoluble in most organic solvents.Oil shalès are ine-grained and normally contain over 33% by - 30 weight mineral material.
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Kerogen can vary in composition with different shales.
However, analyses thereof have determined a general classi-fication, in weight percent, of about 65-90% carbon, 7-13%
hydrogen, 0.1-3% nitrogen, 0.1-9% sulfur, and 0,75-27%
oxygen. A typical kerogen molecule has been deemed to be a polymer with a molecular weight well above 3000. The structure thereof has been calculated to be highly naphthenic (alicyclic) with closely associated aromatic and nitrogen and sulfur heterocyclic ring systems randomly distributed.
The inorganic component consists principally of such silicate minerals and clays as hydromica, montmorillonite, nahcolite, dawsonite, and trona along with quartz, dolomite, and/or calcite.
Oil shale deposits exhibit a wide range of physical characteristics and quality with respect to oil production.
Thus, low grade shales may yield only 10-25 gallons of oil per ton, whereas shales are known which can yield up to 100 gallons of oil per ton. However, shales from which 30-35 gallons o oil per ton can be derived are widespread and are considered to be very practical for commercial exploitation.
The primary factor inhibiting the commercial development " of oil shale resources in the United States has been the high cost of production relative to the costs encountered via alternative sources of liquid petroleum. Thus, it i5 simply easier and cheaper to drill for and pump out liquid crude oil than to mine oil shale and extract the oil there-from.
- The standard procedure for extracting shale oil is to crush the shale and heat in a retort at atmospheric pressure at about 700-1000F. (371-538C.). Kerogen decomposes at those temperatures to yield three carbonaceous products in ~ ~ 8 ~ ~ ~

the following approximate amounts, the relative proportions varying with the pyrolysis temperature and, to a lesser extent, with the organic content of the shale: (1) oil, about 63% by weight which forms as a vapor at retort temp-eratures and is subsequently condensed; (2) non-condensable hydrocarbon gases, about 15~/o by weight; and (3) a coke-like ~ixed-carbon residue which remains in the pores of the retorted shale, about 13% by weight. The remaining 9% of the decomposition products is water vapor.
The pyrolysis of oil shale is complex and is believed to involve the ~ollowing sequence of first order kinetic reactions:
Kerogen ~ Gas ~ Rubberoid Rubberoid ~ Oil + Bitumen-Bitumen ~ Oil + Semicoke ~ Semicoke ~ High Molecular Weight Oil ~ Coke $ High Molecular Weight Oil ~ Gas + Oil Both the non-condensable gases and the carbon residue can be burned to produce heat for processing the raw shale and the modern retort designs take advantage of this fact. As a matter of fact, the high alkane content of the gases sug-gests their use in the wide variety of applications pre-sently employing natural gas.
The ~rude shale oils derived from the conventional retorting process are generally de~ined by petroleum stand-- ards as low gravity, high nitrogen, moderate sulfur oils.
~; When retorted in oxygen-rich atmospheres, e.g., air, the ~` resulting shale oil has such a high viscosity that ît cannot be transported through a pipeline in the normal manner as petroleum crude oil. Hence, the pour point, i.e., the lowest temperature at which the oil will flow, is higher ... ....

than 70F. for shale oils, but below 40F. for petroleum crudes.
Tar sands, oil sands, bitumen-bearing rocks~ oil impregnated rocks, and bit~minous sands are terms which have been employed more-or-less interchangeably to describe hydrocarbon-bearing deposits whic~ are distinguished from the more conventional oil and gas reservoirs by the high viscosity, i.e., the thick or glutinous character, of the hydrocarbon. The hydrocarbon is not recoverable in its natural state through conventional oil well drilling tech-niques. However, oils from tar sands are chemically similar to some crude oils - upgrading is necessary to convert them to a refinery feedstock. Many Utah tar sand oils, particu-larly from the Uinta Basin, are similar to gocd grade paraf-finic oils.
The Athabaska tar sands of Alberta, Canada constitute one of the largest sources of synthetic oil in the world.
The deposits consist of a mixture of sand, mineral matter, water, and crude bitumen, the latter comprising about 50% by ~0 weight of the total mixture and being a heavy, black, asphaltic-naphthenic base hydrocarbon which is very viscous and contains sulfur, nitrogen, and a trace of metals. Films of water, crude bitumen, and some gas, normally air, are present between the grains. Synthetic crude oil from tar sands, the ultimate product from bitumen recovery and upgrading 9 can be refined to produce gasoline, jet fuel, and other petroleum products.
In general~ the pyrolysis of tar sand is believed to involve the following reactions:

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Bitumen ~ Oil & Semicoke Semicoke ~ High Molecular Weight Oil & Coke High Molecular Weight Oil ~ Gas & Oil Normally, the pyrolysis of tar sand requires a somewhat hi~her temperature than that required for oil shale to proceed reasonably rapidly. Therefore, whereas temperatures as low as 700F. can be operable, the time required or the reactions to proceed to completion becomes impractically long. Accordingly, temperatures between about 1000-1200F~
(538-649C.) are much to be preferred.

Summary of the Invention Heat can be generated in certain materials through exposure to microwave radiation. Microwaves are part of the electromagnetic spectrum with wave lengths ranging between 1 mm. to 1 m., corresponding to frequencies of 300,000 MHz to 300 MHz. Such range lies between infrared radiation and radio waves. The 2450 MHæ frequency generated by a magnetron tube is the one most often used for practical applications.
The Federal Communicatiolls Commission (FCC) has assigned ~our bands for microwave industrial heating in which there is no limit to the permitted radiation. These bands are centered around 915 MHz, 2450 MH~, 5800 MHz, and 22,000 MH~.
Industrial power sources are presently available at only the first two frequencies.
Thus the present invention provides a method for extracting oil from oil shale or tar sand which consists of subjecting said oil shale or tar sand in particulate form while contained within a distilling apparatus to microwave energy for a sufficient length of time at about 8a~

700-1200F to volatilize the organic portion therefrom, said distilling apparatus in at least those portions in contact with said oil shale or tar sand being constructed from glasses, glass-ceramics, and/or ceramics having low alkali metal contents and that absorb very little microwave radiation or being lined with a metal that reflects microwaves, and thereafter to condense the oil fraction from said organic portion.
Our invention is founded in the discovery that oil shale and tar sands are materials which absorb microwaves to ; a sufficient extent to generate the necessary heat to decompose and distil the kerogen and bitumen components to yield a crude oil which can have a low pour point. By careful ~, ~' -- 5 (~) ,, ~ , ...... .

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selection it is possible to choose a material for the con-taining and distilling apparatus (e.g. a retort) which absorbs very little microwave radiation when compared with the oil shale and tar sand. Glasses, glass-ceramics, and ceramics having low alkali metal contents are illustrative thereof. In this manner energy is not wasted in heating the environment. `A metal lined retort is acceptable in accord-ance with the conventional reflectivity of metal in micro-wave oven cavities.
The use of microwave energy permits the continuous and uniorm heating of the oil shale and tar sand, thereby reducing the overall expenditure o energy to extract the oil phase. Although a unit of power from the microwave frequency is much more costly than a unit of power from conventional heating, the efficiency factor is much higher.
Thus, the ef~iciency ~actor will customarily range from about 2-6 times that for conventional gas-fired equipment.
Microwave heating substantîally reduces warmup heating since the flow rate of heat into the heating mass is not determined by a temperature gradient or by heat convected, conducted, or radiated to the produ~t. Furthermore, the utilization o microwave heating greatly diminishes heat loss by conduction and radiation. Because heat is generated in the product by electromagnetic waves, heating can be instantly started and stopped. The degree of product heat-ing is a function of the electric power level applied, which can be rapidly adjusted to control the temperature.

Description of Preferred Embodiments Tables I and II record approximate analyses, in weight percPnt, of representative samples of oil shale taken from , ~he Green River ~ormation in Colorado and the Sunnyside deposit in Utah.

TABLE I
Green River Oil Shale Organic Matter 15.5%
.~; Composition of Organic Portion ~ Carbon 76.1 f Nitrogen 2.5 Hydrogen ~0.8 Sulfur 1.2 Oxygen and other 9.4 light elements Mineral Content 84.5% :;
Composition of Mineral Portion Dolomite ~CaMgC03] 32 Calcite [CaCO3] 16 Quartz 15 Illite l9 Low-Albite [NaAlSi3O83 10 Adularia [KAlSi3O8] 6 ~:
Other clays 2 TABLE II
Sunnyside Oil Shale Organic Matter 14.6%
Compositîon of Organic Portion Carbon 78.5 Hydrogen 10.1 Nitrogen 2.2 Sulfur 1.0 Oxygen and other 8.2 30 . light elements Mineral Content 85.4%
Composition of Mineral Portion Carbonates t principally 48 Dolomite Feldspars 20 Quartz 12 Analcite [NaAlH2Si2O7] 4 Clays, principally Illite 16 A laboratory microwave oven, Model SMA-1-60, distributed by Despatch Oven Company, Minneapolis, Minnesota, was employed in the following examples. The oven had a variable power output (1-2000 watts), an interior volume of about 92,700 cm3, and generated waves having a frequency of 2450 MHz.
~ The appended drawing provides a diagrammatic representa-; tion of a cross section of the oven interior showing the apparatus utilized in the subse~uently-described work. The oven interior is generally depicted at 1 with a turntable 2 resting on the bottom thereo~. The oil shale or tar sand 3 was crushed and placed within a retort 4 fabricated from PYREX~ brand glassware. The oil shale was crushed to pass a 20 mesh United States Standard Sieve (841 microns) and the tar sand to pass a 60 mesh Sieve ~250 microns). The arm of retort 4 passed through cork 5 into a PY~EX~ brand glass vessel 6 which acted as a collecting container for the oil.
PYREX~ brand glassware is generally known to absorb only about 1-2% of incident microwave radia~ion. Volatile mate-rial was removed from the collecting v~ssel 6 by means of - TYGON~ tubing 7, marketed by Norton Chemical Process Products Division, Akron, Ohio. Water vapor was collected in a liquid nitrogen trap (not shown) for analysis. The volatile hydrocarbon gases were permitted to escape and their presence :' noted by the additional loss of weight over and above that o the water.
A sample size of at least lS0 cm3 of the crushed shale was utilized to secure suf~icient microwave absorption for practical microwave processing in the oven. To prevent possible damage to the oven from ovèrheating where small samples were employed, an additional load of 1 kg. of a high PbO, lead alkali silicate glass 8 was placed within the oven. The use of a load was a safety precaution only and would not be required where a large volume of shale is fired.

Example I

About 150 cm3 (126~2 grams) of the Green River oil shale were placed in retort 4 and the retor~ and collecting vessel 6 positioned as shown in the appended drawing.
TYGON~ tubing 7 was connected to the water trap.
An initial power of 800 watts output was applied for three minutes. Therea~ter, the power was increased to 1400 watts and that output was maintained for 15 minutes. A
temperature o about 850F. was achieved within the sample interior in that cycle, as measured by means of a chromel~
alumel thermocouple sheathed in double bore alumina and connected to an ELECTRONIK~ 194 Chart Recorder distributed by Honeywell, Inc., Fort Washington, Pennsylvania. The power was then cut off.
About 14 ml. of a black, viscous, heavy oil were found in the delivery tube and collecting vessel and about 2 ml.
o water were present in the liquid nitrogen trap. A gross analysis of the various residues is set out in Table III.
(It must be recognized that the presence of the ambient air _g_ , in the oven resulted in some oxidation of hydrocarbons in the gaseous phase.) This type of oil shale will average about 25-30 gallons of oil/ton of shale.

TABLE III
Products from the Pyrolysis Reaction ~t.% of Organi~ Wt.% of Total Carbonaceous Product Constituent in Shale Raw Shale Oil (density 0.958g/cc) 6S 10.7 Non-condensable gases 15 2.3 Fixed carbon residue 10 1.9 Water vapor 10 1.7 ` As can be seen, about 15% of the organic matter was lost as volatile hydrocarbons (mostly alkanes, alkenes, and oxidation products), in addition to about 10% H2O. Of course, in commercial practice those hydrocarbons would be collected, separated, or stored or, if desired, could be burned as fuel for other operations.
Gas chromatographic analysis of the oil indicated the presence of about 40 different organic compounds. Inrared spectrographic analysis of the material determined the pre-sence o a significant amount of oxidized matter, including numerous organic acids. Such material is amenable to con-ventional petroleum refining techniques.

Exam~le II

About 150 cm3 (131 grams) of the Sunnyside oil shale were placed in retort 4 and the apparatus connected together in like manner to Example I. Because of the composition of this shale, it was necessary to preheat the sample to 100C.

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in a conventional electric furnace before processing in the microwave oven in order to obtain sufficient absorption of microwave energy in a reasonable period of time. This prac-tice would not be necessary where a large volume of the material is processed within a microwave operated retort.
- An initial power output of 1000 watts was applied for five minutes and, thereaf~er, the power was increased to 1500 watts for 15 minutes to complete gasification and liquefaction of the shale. A temperature of 920F. was read within the shale interior. Again, a black, viscous, heavy oil was observed in the delivery tube and collecting vessel, in an amount of about 16 ml., and about 2 ml. water was collected in the liquid nitrogen trap. A gross analysis of the various re`sidues is reported in Table IV. This type o oil shale will generally yield about 28-35 gallons of oil per ton of shale.

TABLE IV
Products from the Pyrolysis Reaction Wt.% of ~rganic Wt.~/o of Total Carbonaceous Product Constituent in Shale Raw Shale Oil (density 0.958 g/cc) 63 10.0 Non-condensable gases 15 1.8 Fixed carbon residue 13 2.2 Water vapor 9 1.6 Gas chromatographic analysis of the oil detected about 44 different organic compounds therein. Infrared spectro-graphic analysis thereof indicated a makeup of product similar to that observed in the pyrolyzed Green Riv~r shale material of Example I.

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Reduced microwave energy levels for the retorting can be achieved by blending the oil shale material with a good microwave dielectric material. For purposes of this inven-tion, the dielectric constant of the added material will preferably be at least about 10 at 25C. The following examples are illustrative of that practice.

Example III

Pellets consisting of 48 volume % Li~TiO3 and 52 volume % Li4Ti5O12 were formed which, at 25C., exhibited a dielec-tric constant of 25.6 and a loss tangent of 2.6 x 10-4. A
mixture consisting of 45 grams of the lithium titanate blend having a grain size passing a 40 mesh United States Standard ,Sieve (420 microns~ and 105 grams of Sunnyside oil shale passing a 20 mesh United States Standard Sieve was placed in retort 4 and subjected to a microwave process similar to that described in Example I. The final mixture comprised 30 volume % of the lithiu~ titanate blend and 70 volume % of shale.
Apparently complete extraction of the oil component was achieved a~ter an initial exposure at 800 watts for five minutes and then 1200 watts for 10 minutes. A tempera~ure of 900F. was observed in the shale interior.
An analysis of the oil phase indicated a product simi-lar to that resulting from Example II.

Example IV

A run similar to that described in Example III was made wherein the good microwavP dielectric material consi'sted o a glass having the composition, in weight percent, of 15%
Cu20, 15% CuO, 20% A1203, and 50% SiO2. The glass exhibited, . ,... .. ~

at 25C., a dielectric constant of 20 and a loss tangent of

2.5 x 10-4. A mixture comprising 68 grams of the glass and 129 grams Sunnyside oil shale (15 volume % glass, 85 volume % shale) was charged into retort 4.
The extraction of oil from the shale appeared to be complete upon an initial treatment at 800 watts for five minutes followed by 1400 watts for five minutes. A tempera-ture of 980F. was reached within the shale.
Subsequent analysis of the collected oil indicated a product similar to that obtained in Examples II and III.
It is believed that the addition of the microwave dielectric material leads to the development of hot spots throughout the dielectric material - shale mixture. The heat transferred therefrom assists in the vaporization and distillation, consequently significan~ly reducing the retorting time required. It will be appreciated that the microwave dielectric material added will, desirably, be readily removable from the shale residue. Hence, for example, the material will be non-melting so that the particles thereof can be readily removed from the shale residue.

Example V

About 150 cm3 (128 grams) of Athabaska tar sand were placed in retort 4 and the apparatus assembled in the manner described in Example I. An initial power of 800 watts output was applied for 10 minutes and, subsequently, the power was i.ncreased to 1500 watts and maintained at that output for 15 minutes. ~ temperature of about 1000F. was recorded within the interior of the sample.

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A black, very vlscous, heavy oil remained in ~he delivery tube and collecting vessel. About 6% H20 and about 5% of non-condensable gases were observed.
The ive working examples provided above must be viewed as illustrative, rather than limitative. For example, whereas each example employed the same frequency of micro-wave radiation, it will be appreciated that other wavelengths within the range of 1 mm to 1 m can also be operable. As a matter o fact, the 2450 MHz frequency generated within the microwave oven employed in the above examples may not be optimum for the various oil shales or tar sands. The deter-mination of the optimum, however, is well within the technical ingenuity of the worker of ordinary skill in the art. But, as was noted above, the FCC has drastically limited the scope of microwave frequencies which can be employed.
Therefore, from a practical point o view, one is limited to the four above-cited bands in the United States. Also, the power output applied to the above examples was limited by the oven employed. It is believed apparent that higher ~0 power concentrations would reduce the time required for volatiliæation and liquefaction. Such would be very import~
ant in commercial applications where tons, instead of grams, o oil shale or tar sand would form the retort charge.
Hence, the time required for the process is a function of the volume of the shale or tar sand charge and the microwave energy applied thereto. Accordingly, whereas an exposure ~ime of at least five minutes may be required at a power o 500 watts for a small volume of susceptible material, such could be ar less where an output of 10,000 watts or 100,000 watts was employed on a larger volume of susceptible mate-rial. Nevertheless, again, the understanding of the relationship existing between time of treatment, the volume of the charge, and the microwave energy applied is believed to be well within the technical capability of the worker of ordinary skill in the art.
Furthermore, the microwave pyrolysis methods described above must not be dee~ed to be exclusive in the sense of totally replacing existing conventional techniques. Rather, the microwave may be utilized to augment or supplement conventional practices. Such circumstances are, of course, apparent to those versed in the techniques of retorting oil shale or tar sand.

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Claims (7)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method for extracting oil from oil shale or tar sand which consists of subjecting said oil shale or tar sand particulate form while contained within a distilling apparatus to microwave energy for a sufficient length of time at about 700°-1200°F to volatilize the organic portion therefrom, said distilling apparatus in at least those portions in contact with said oil shale or tar sand being constructed from glasses, glass-ceramics, and/or ceramics having low alkali metal contents and that absorb very little microwave radiation or being lined with a metal that reflects microwaves, and there-after to condense the oil fraction from said organic portion.

2. A method according to claim 1 wherein said microwaves have wavelengths ranging between about 1 mm. to 1 m.

3. A method according to claim 2 wherein said microwaves have a frequency of about 2450 MHz.

4. A method according to claim 3 wherein said microwave energy is at least 500 watts.

5. A method according to claim 4 wherein said length of time to volatilize the organic portion is at least 5 minutes.

6. A method according to claim 1 wherein the microwave dielectric material is added to said oil shale or tar sand.

7. A method according to claim 6 wherein said microwave dielectric material has a dielectric constant of at least about 10 to 25°C.