U.S. patent number RE31,363 [Application Number 06/233,734] was granted by the patent office on 1983-08-30 for method for reducing the nitrogen content of shale oil with a selective solvent comprising an organic acid and a mineral acid.
This patent grant is currently assigned to Occidental Research Corporation. Invention is credited to Carole S. Stover.
United States Patent |
RE31,363 |
Stover |
August 30, 1983 |
Method for reducing the nitrogen content of shale oil with a
selective solvent comprising an organic acid and a mineral acid
Abstract
A method is disclosed for reducing the nitrogen content of shale
oil by selectivity removing therefrom nitrogen-containing
compounds. The nitrogen content of shale oil is reduced by
contacting the shale oil with a sufficient amount of a solvent
which is selective toward the nitrogen-containing compounds present
in the shale oil. The solvent is a mixture comprised of an organic
acid and a mineral acid. The organic acid is selected from the
group consisting of organic acids, and substituted organic acids,
particularly acetic, formic and trichloroacetic acids and mixtures
thereof; the mineral acid is selected from the group consisting of
hydrochloric acid, nitric acid, nitrous acid, sulfuric acid,
sulfurous acid, phosphoric acid and mixtures thereof.
Inventors: |
Stover; Carole S. (Van Nuys,
CA) |
Assignee: |
Occidental Research Corporation
(Irvine, CA)
|
Family
ID: |
26730882 |
Appl.
No.: |
06/233,734 |
Filed: |
February 12, 1981 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
052636 |
Jun 27, 1979 |
04209385 |
Jun 24, 1980 |
|
|
Current U.S.
Class: |
208/254R |
Current CPC
Class: |
C10G
21/06 (20130101) |
Current International
Class: |
C10G
21/06 (20060101); C10G 21/00 (20060101); C10G
017/04 () |
Field of
Search: |
;208/254R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Gantz; Delbert E.
Assistant Examiner: Chaudhuri; O.
Attorney, Agent or Firm: Christie, Parker & Hale
Claims
What is claimed is:
1. A method for reducing the nitrogen content of shale oil by
removing nitrogen-containing compounds from shale oil, comprising
the steps of:
extracting the shale oil with an immiscible selective solvent
system for the nitrogen-containing compounds comprising an organic
acid and a mineral acid; and
separating the immiscible selective solvent system containing
nitrogen-containing compounds from the shale oil having a reduced
nitrogen content.
2. A method as recited in claim 1 wherein the organic acid is
selected from the group consisting of formic acid, acetic acid,
trichloroacetic acid and mixtures thereof.
3. A method as recited in claim 1 wherein the mineral acid is
selected from the group consisting of hydrochloric acid, nitric
acid, nitrous acid, sulfuric acid, sulfurous acid, phosphoric acid
and mixtures thereof.
4. A method as recited in claim 1 wherein the ratio of the organic
acid to the mineral acid in the selective solvent is from about
.[.1:5 to about 1:60.]. .Iadd.60 :1 to about 5:1.Iaddend..
5. A method as recited in claim 1 wherein the selective solvent
contains less than about fifty percent water.
6. A method as recited in claim 1 wherein the ratio of shale oil to
selective solvent system comprises from about 0.20 to about 10
parts by weight shale oil to one part by weight selective
solvent.
7. A method for reducing the nitrogen content of shale oil by
removing nitrogen-containing compounds comprising the steps of:
extracting the shale oil at least once with an immiscible selective
solvent system for nitrogen-containing compounds comprising an
organic acid selected from the group consisting of formic acid,
acetic acid, trichloroacetic acid and mixtures thereof and a
mineral acid selected from the group consisting of hydrochloric
acid, nitric acid, nitrous acid, sulfuric acid, sulfurous acid,
phosphoric acid and mixtures thereof;
separating the selective solvent system containing the
nitrogen-containing compounds from the shale oil having a reduced
nitrogen content by phase separation; and
recovering the selective solvent by separating the selective
solvent from the nitrogen-containing compounds.
8. A method as recited in claim 7 wherein the recovered selective
solvent is recycled for extracting nitrogen-containing compounds
from shale oil containing nitrogen-containing compounds.
9. A method as recited in claim 7 wherein the extraction is
conducted batchwise in at least three successive batch
extractions.
10. A method as recited in claim 7 wherein the extraction is
conducted by a continuous countercurrent extraction.
11. A method as recited in claim 10 wherein the recovered selective
solvent system is recycled for the continuous countercurrent
extraction.
12. A method as recited in claim 7 wherein the organic acid is
selected from the group consisting of formic acid, acetic acid and
mixtures thereof.
13. A method as recited in claim 7 wherein the mineral acid is
selected from the group consisting of hydrochloric acid, phosphoric
acid and mixtures thereof.
14. A method as recited in claim 7 wherein the ratio of organic
acid to mineral acid is from .[.1:5 to 1:60.]. .Iadd.60:1 to
5:1.Iaddend..
15. A method as recited in claim 7 wherein the ratio of organic
acid to mineral acid is from .[.1:15 to 1:40.]. .Iadd.40:1 to
15:1.Iaddend..
Description
BACKGROUND OF THE INVENTION
The method herein relates to reducing the total nitrogen content of
shale oil by extracting nitrogen-containing compounds from the
shale oil with solvent comprising a mixture of an organic acid and
a mineral acid.
More particularly, this application relates to a method for
reducing the nitrogen content of shale oil produced in either an
above ground or an in situ oil shale retort.
The term "oil shale" as used in the industry is, in fact, a
misnomer; it is neither shale nor does it contain oil. It is a
sedimentary formation comprising marlstone deposits with layers
containing an organic polymer called "kerogen" which, upon heating,
decomposes to produce liquid and gaseous products. The formation
containing kerogen is called "oil shale" herein and the liquid
product produced upon decomposition of kerogen is called "shale
oil".
Kerogen is considered to have been formed by the deposition of
plant and animal remains in marine and nonmarine environments. Its
formation is unique in nature. Alteration of this deposited
material during subsequent geological periods produced a wide
variety of organic materials. Source material and conditions of
deposition were major factors influencing the type of final product
formed.
Kerogen samples, found in various parts of the world, have nearly
the same elemental composition. However, kerogen can consist of
many different compounds having differing chemical structures. Some
compounds found in kerogen have the structures of proteins while
some have structures of terpenoids, and others have structures of
asphalts and bitumens.
Shale oils produced from oil shale are generally high molecular
weight, viscous organic liquids, of predominantly hydrocarbonaceous
oxygen, nitrogen and sulfur or containing organic compounds. The
shale oils are of varying linear, branched cyclic aromatic
hydrocarbon and substituted hydrocarbon content with high pour
points, moderate sulfur content and relativley high nitrogen
content. As the composition of shale oil depends upon the
composition of the kerogen within the oil shale formation, the
composition of the shale oil can vary from one geographic location
to another. The shale oil produced from an oil shale formation can
vary also between strata within the oil shale formation. The
nitrogen content of shale oil can also vary dependent upon the
geographical location of the oil shale deposit from which the shale
oil is produced. Such a variance in nitrogen content in different
georgraphical locations can be attributed to differences in the
environment during the time of the deposition of the organisms
which, upon lithification, became oil shale. Such a variance can
also be attributed to the different types of organisms in the
separate geographical locations which were deposited to form the
organic substance in the oil shale and any organisms within the
formed deposited layer which acted upon such deposited material to
provide the kerogen within the oil shale formation.
The nitrogen content in shale oil is attributable to basic
nitrogen-containing compounds and nonbasic nitrogen-containing
compounds. The relative percentages of the basic and nonbasic
nitrogen compounds comprising the total nitrogen content of a shale
oil can also vary depending upon the particular shale oil.
The nitrogen content of shale oil is generally up to about two
percent by weight. The average nitrogen content of shale oil
recovered by in situ retorting of oil shale from the Piceance Creek
Basin of Western Colorado is on the order of about 1.4 percent by
weight.
The presence of nitrogen in shale oil presents many problems in
that the nitrogen can interfere with the transportation and use of
the shale oil. Deleterious effects brought about by the presence of
nitrogen in shale oil are decreased catalyst life in
dehydrogenation, reforming, hydrocracking and catalytic cracking
reactions, decreased chemical stability of products, and decreased
color stability of products. Another problem with the presence of
nitrogen in shale oil is that it is undesirable to transport
nitrogen-containing shale oil through pipelines which are also used
for transporting petroleum products of possible pollution of such
products with residual nitrogen-containing shale oil in the
pipeline. Generally such petroleum products contain a very low
nitrogen content. The relatively high nitrogen content in the shale
oil can pollute the pipelines making them undesirable and
uneconomical for transporting such low nitrogen-containing
petroleum products. In addition, high nitrogen content in shale oil
can cause clogging of pipelines due to self-polymerization brought
about by the reactivity of the nitrogen-containing compounds in
shale oil. Some corrosion can occur thus damaging a pipeline used
to transport shale oil.
Product stability is a problem that is common to many products
derived from shale oil with the major exception of the asphalt cut
and those products that have undergone extensive hydrotreating.
Such instability, including photosensitivity, is believed to be
resultant, primarily from the presence of nitrogen-containing
compounds.
It is, therefore, desirable to reduce the nitrogen content of shale
oil to increase the utility, transportability, and stability of the
shale oil and the products derived from such shale oil.
Due to the undesirable nature of nitrogen in organic fluid streams,
such as fluid streams produced in the recovery and refining of
petroleum, coal and oil shale, many processes have been developed
to reduce the nitrogen content to an acceptable level. The level of
acceptability for the nitrogen content is generally based upon the
use of the particular stream.
In U.S. Pat. No. 3,719,587 to Karchmer et al. a process is
disclosed for removing basic nitrogen-containing compounds from
coal naphtha. The basic nitrogen compounds are removed by washing
the naphtha with water or with a dilute aqueous solution of a
strong acid. The dilute acid solutions are disclosed as from 0 to
10 weight percent of the acid such as sulfuric acid, hydrochloric
acid, phosphoric acid and acetic acid.
U.S. Pat. No. 2,848,375 to Gatsis discloses a process for removing
basic nitrogen compounds from organic substances by washing with a
weak acid in combination with a polyalcohol. The weak acid used is
boric acid in combination with a polyhydroxy organic compound which
has hydroxyl groups on adjacent carbons.
U.S. Pat. No. 2,741,578 to McKinnis teaches that mineral oils can
be treated to recover the nitrogen bases by extracting the mineral
oils with a selective solvent for the nitrogen bases. The selective
solvents are organic hydroxy compounds. Organic hydroxy compounds
which can be used are the compounds which have a pH greater than
6.5.
U.S. Pat. No. 2,035,583 to Bailey discloses a process for the
separation and recovery of nitrogen bases from mineral oils. In the
process, the mineral oil is extracted with a solvent for the
nitrogen bases. Acceptable solvents are liquid sulfur dioxide,
furfural, aniline, nitrobenzene and isobutyl alcohol. However, due
to the solubility of desirable mineral oils, such as aromatics and
olefines, the process also includes extracting the resultant
extract with dilute aqueous acids to recover the nitrogen bases
from the first extract. The nitrogen bases are then recovered from
the aqueous solution by adding an inorganic base to precipitate the
nitrogen bases.
U.S. Pat. No. 2,035,102 to Stratford et al. discloses a process for
improving the color and viscosity of petroleum oils. In the process
an oil is extracted with a selective solvent in combination with an
acid. The selective solvent can be phenol, nitrobenzene, furfural
or liquid sulfur dioxide. The acid is preferably an inorganic acid
but can also be an organic acid such as picric, acetic, oxalic,
citric and benzene sulfuric acids.
U.S. Pat. No. 2,541,458 to Berg discloses a process for recovery of
nitrogen bases from hydrocarbon fractions. In the process the
fraction is extracted with a volatile acid or nonvolatile acid salt
in combination with a mutual solvent for the acid and the
hydrocarbon fraction. The mutual solvents include low boiling
alcohols and ketones. The extraction is conducted in the presence
of water to avoid loss of the volatile acids.
U.S. Pat. No. 2,309,324 to McAllister et al. discloses a method for
removing nitrogen bases from water-insoluble organic solvents,
mineral oils and hydrocarbon fractions. In the process the mineral
oil is extracted with an aqueous, weak acid solution. The weak
acids are classified as acids having dissociation constants below
10.sup.-3. The aqueous acid solutions are prepared by dissolving
from 15 to 90 weight percent of an acid in water. Upon extraction
of the oil, two phases are formed. The aqueous phase contains the
acid and absorbed nitrogen bases. The other phase consists of the
organic substance from which at least a portion of the nitrogen
bases has been removed.
Many of the processes described in the above processes do not
address themselves to the removal of nonbasic nitrogen compounds
which can be present in organic fluids. Additionally, many of the
above described processes are not specific for treatmet of shale
oil and the relatively high nitrogen content found in shale oil.
Still further, none of the above processes are specific for
lowering the nitrogen content for shale oil produced by in situ
retorting of oil shale.
SUMMARY OF THE INVENTIONS
The present invention is directed to a method for the refining of
shale oil wherein the nitrogen content of the shale oil is reduced
by extracting nitrogen-containing compounds from the shale oil with
a solvent system comprising a mixture of an organic acid and a
mineral acid. The organic acid can be selected from formic acid,
acetic acid and trichloroacetic acid; the mineral acid can be
selected from hydrochloric acid, nitric acid, nitrous acid,
sulfuric acid, sulfurous acid and phosphoric acid. In the preferred
embodiment the acids comprising the solvent are concentrated, i.e.,
mixed with less than fifty percent water by weight. In the most
preferred embodiment water is present only up to about fifteen
percent by weight.
Shale oil produced by the retorting of oil shale is a liquid
product which predominantly contains liquid hydrocarbons and some
substituted liquid hydrocarbons such as nitrogen substituted
hydrocarbons. A solvent which selectively substantially dissolves
the nitrogen-containing compounds present in shale oil is added to
the shale oil in an amount sufficient to dissolve such
nitrogen-containing compounds. The amount of selective solvent
system that is sufficient depends upon the solubility of such
nitrogen-containing compounds in the extractant and amount of such
nitrogen-containing compounds in the shale oil. The selective
solvent system can also dissolve or otherwise retain some of the
non-nitrogen-containing compounds present in shale oil. For this
reason, during an extraction of the shale oil with a selective
solvent some desirable compounds can be lost in the extractant.
Therefore, the amount of selective solvent system used is also
determined by balancing nitrogen extraction capabilities of the
selective solvent against the amount of non-nitrogen-containing
compounds also extracted. Selective solvent systems which are
useful in extracting the nitrogen-containing compounds comprise a
mixture of an organic acid selected from the group consisting of
formic acid, acetic acid and trichloroacetic acid and mixtures
thereof and a mineral acid selected from the group consisting of
hydrochloric acid, nitric acid, nitrous acid, sulfuric acid,
sulfurous acid, phosphoric acid and mixtures thereof. The mole
ratio of the organic acid to the mineral acid is from about .[.1:5
to about 1:60, preferably from about 1:15 to about 1:40.].
.Iadd.60:1 to about 5:1 preferably from about 40:1 to about
15:1.Iaddend..
In the preferred embodiments both the organic acid and the mineral
acid are concentrated, i.e., the solvent will contain less than
about fifty percent water, by weight. Such selective solvent
systems do not dissolve or otherwise remove the liquid hydrocarbons
present in the shale oil to any appreciable extent. Further, such
selective solvent systems are sufficiently insoluble in shale oil
that a multiple layer system is provided when mixed with shale oil.
Layer separation provides a separation of nitrogen-containing
compounds from shale oil.
DETAILED DESCRIPTION OF THE INVENTION
This invention relates to the refining of shale oil and, more
particularly, to the reducing of nitrogen content of shale oil.
As used herein, the term "crude shale oil" refers to the liquid
product that is recovered from retorting of oil shale. The term
encompasses liquid products formed during the retorting of oil
shale either through aboveground retorting processes or in situ oil
shale retorting processes which products have not undergone any
further processing other than water removal or emulsion breaking.
The term "processed shale oil" is used herein to indicate a crude
shale oil which has undergone some processing, such as, for
example, sulfur removal, fractionation, and the like. As used
herein, the term "refined shale oil" refers to a crude shale oil or
a processed shale oil which has been processed through the method
of this invention to reduce the nitrogen content of such shale oil.
The "refined shale oil," therefore, has a lower nitrogen content
than the crude shale oil or processed shale oil undergoing the
method herein disclosed.
In a preferred practice of this method, the method is utilized for
refining shale oil produced from in situ retorting of oil shale. An
in situ oil shale retort can be formed by many methods, such as
those disclosed in U.S. Pat. Nos. 3,661,423; 4,043,595; 4,043,596;
4,043,597; and 4,043,598, all of which are incorporated herein by
this reference.
In preparing an in situ oil shale retort, formation from within the
boundaries of a retort site is excavated to form at least one void,
leaving a remaining portion of unfragmented formation within the
boundaries of the retort being formed. The remaining portion of
unfragmented formation is explosively expanded toward such a void
to form a fragmented permeable mass of formation particles
containing oil shale within the retort boundaries.
After the fragmented mass is formed, the final preparation steps
for producing liquid and gaseous products are carried out. These
steps include drilling a plurality of feed gas inlet passages
downwardly to the fragmented mass so that an oxygen-supplying gas
can be supplied to the fragmented mass during retorting operations.
Alternatively, the upper ends of blasting holes used in forming the
fragmented mass can be cleaned and used for introducing gas to the
retort. The fragmented mass connects to a product removal drift at
the lower end of the fragmented mass.
During retorting operations, formation particles at the top of the
fragmented mass are ignited to establish a combustion zone. An
oxygen-supplying gas, such as air, is introduced to the combustion
zone through the inlet passages. The oxygen-supplying gas
introduced to the fragmented mass maintains the combustion zone and
advances it downwardly through the fragmented mass. Combustion gas
produced in the combustion zone passes through the fragmented mass
to establish a retorting zone on the advancing side of the
combustion zone wherein kerogen in the fragmented mass is converted
to liquid and gaseous products. As the retorting zones moves
downwardly through the fragmented mass, liquid and gaseous products
are released from the fragmented formation particles. A sump in a
portion of a drift connected to the lower end of the fragmented
mass collects liquid products produced during operation of the
retort. Off gas is also withdrawn through such drift to above
ground.
Although the process disclosed herein of reducing the nitrogen
content of shale oil is primarily discussed in relation to shale
oil produced from the in situ retorting of oil shale, the process
can be practiced on shale oil produced by other methods of
retorting. Many of these methods for shale oil production are
described in Synthetic Fuels Data Handbook, compiled by Dr. Thomas
A Hendrickson, and published by Cameron Engineers, Inc., Denver,
Colo. For example, other processes for retorting oil shale include
those known as the TOSCO, Paraho Direct, Paraho Indirect, N-T-U,
and Bureau of Mines, Rock Springs, processes.
The TOSCO retorting process is described on pages 75 and 76 of the
Synthetic Fuels Data Handbook and the U.S. patents mentioned
therein, including U.S. Pat. No. 3,025,223. Generally speaking,
this process involves preheating minus 1/2 inch oil shale to about
500.degree. F. in a fluidized bed. Pyrolysis is completed in a
rotating drum heated by ceramic balls which are separately heated
in a ball-heating furnace.
The Paraho process is described at pages 62, 63, 84 and 85 of the
Synthetic Fuels Data Handbook and the U.S. patents referred to
therein. The Paraho process employs a vertical kiln through which
ground oil shale moves downwardly as gas moves upwardly. Combustion
air can be admitted into the bed of oil shale particles for direct
heating of oil shale by combustion within the bed. This process is
referred to as Paraho Direct. The kiln can also be arranged so that
recycled gas can be heated externally, then injected into the bed
of oil shale for indirect heating of the oil shale. Such a process
is referred to as Paraho Indirect.
The N-T-U process is a batch process as described at page 59 of the
Synthetic Fuels Data Handbook and the U.S. patents referred to
therein. In the N-T-U process, a retort is filled with a batch of
oil shale particles and ignited at the top. Combustion is supported
by air injection and a combustion zone is passed downwardly through
the stationary bed of shale. Recycled gas from the bottom of the
retort is mixed with the combustion gas to modulate temperatures
and provide some of the fuel requirement.
The Bureau of Mines, Rock Springs process is described in the
Synthetic Fuels Data Handbook and also in Paper No. SPE-6067
prepared for the 51st Annual Technical Conference and Exhibition of
the Society of Petroleum Engineers of AIME, held in New Orleans,
October 3-6, 1976, by R. L. Wise, et al. Such a process is also
described in U.S. Pat. No. 3,346,044, among others. Generally
speaking, this process involves fracturing of an underground oil
shale formation with the fractures propped open with sand.
Injection and production wells are drilled into the formation. A
combustion zone is moved from an injection well towards one or more
production wells for retorting oil shale in the fractured
formation.
Nitrogen is removed from shale oil in the method herein by mixing
the shale oil with a selective system solvent which is selective to
nitrogen-containing compounds present in the shale oil. Upon mixing
the selective solvent system with the shale oil,
nitrogen-containing compounds are extracted from the shale oil and
are dissolved in or absorbed by the selective solvent. Selective
solvents which are useful in extracting nitrogen-containing
compounds from shale oil comprise a mixture of an organic acid and
a mineral acid. Preferably the organic acid is selected from the
group consisting of formic acid, acetic acid, trichloroacetic acid
and mixtures thereof, and the mineral acid is selected from the
group consisting of hydrochloric acid, nitric acid, nitrous acid,
sulfurous acid, sulfuric acid, phosphoric acid and mixtures
thereof.
The ratio of organic acid to mineral acid in the selective solvent
is from about .[.1:5 to about 1:60, preferably from about 1:15 to
about 1:40.]..Iadd.60:1 to about 5:1, preferably from about 40:1 to
about 15:1.Iaddend..
It is preferred, although not essential to the practice of the
invention thgt the acids comprising the selective solvent be
concentrated; as such, the selective solvent should contain less
than about fifty percent water, preferably less than about fifteen
percent water. Some water though, on the order of at least one
percent, is necessary to make the selective solvent immiscible with
the shale oil and to prevent any appreciable dissolving of the
shale oil in the selective solvent. The amount of water should also
be sufficient to prevent any appreciable loss of the selective
solvent in the shale oil.
Removal of nitrogen compounds from shale oil with a concentrated
organic acid is taught in co-pending application Ser. No. 52,637,
the disclosure of which is incorporated herein by this reference.
Since organic acids are relatively weak their ability to interact
with the more non-basic nitrogen compounds is limited. The
selective solvent of the present invention, with the addition of a
strong acid makes a greater quantity of acidic protons available
for ionization of the nitrogen compounds and, thus for extraction
into the more polar solvent phase. That is, the selective solvent
system of the present invention enhances removal of
nitrogen-containing compounds from shale oil by combining the
protonating effect of the mineral acid with the solubilizing effect
of the organic acid.
The combination of a strong acid with the organic acid provides a
greater quantity of acidic protons for ionizing the
nitrogen-containing compounds thereby making such protonating
nitrogen-containing compounds more susceptible for extraction into
the polar solvent phase. Therefore, more nitrogen-containing
compounds can be removed from shale oil by using a selective
solvent system which is a mixture of an organic acid and a mineral
acid than by using an organic acid alone.
Preferred organic acids are formic acid and/or acetic acid;
preferred mineral acids are hydrochloric and/or phosphoric
acid.
Extraction of the shale oil with the selective solvent can be
performed in batch or continuous extraction processes using
cocurrent or countercurrent extraction techniques. In liquid phase
batch extracting there can be employed a series of multi-stage
batch extractions to improve overall efficiency of the extraction
and to optimize nitrogen-containing compound removal. Similarly,
countercurrent extraction can also be conducted utilizing
countercurrent extractors arranged in series to optimize the
nitrogen-containing compound removal.
The amount of selective solvent system that is required for
extracting nitrogen-containing compounds from shale oil depends
upon the nitrogen content in the shale oil and the solubility of
such nitrogen-containing compounds in the selective solvent. THe
ratio of shale oil to selective solvent system can be from about
0.20 to about ten parts by weight shale oil to one part by weight
selective solvent. Generally, a significant excess of the selective
solvent system is utilized to insure the highest probability of
encountering the nitrogen-containing compounds with the selective
solvent and thereby solvation of the nitrogen-containing compounds
with the selective solvent.
Along with nitrogen removal from the shale oil through extraction
with the selective solvent system, there is some inherent loss of
shale oil by the extraction procedure. For example, some of the
shale oil is carried away in the extractant following the
separation. The most efficient separation process is a process
which removes the greatest amount of nitrogen-containing compounds
with little accompanying shale oil loss. Separation efficiency can
be determined by measuring the nitrogen concentration in the oil in
the extract phase. The higher the nitrogen concentration in the
extracted oil the more efficient is the process. Every time a
nitrogen atom is removed from shale oil by the extraction process,
the organic molecule on which that nitrogen is bonded must go with
it. The maximum efficiency of the process is thereby limited by the
molecular weight distribution of the nitrogen-bearing compounds in
the shale oil and can be approached by preventing non-nitrogen
compounds from dissolving in the selective solvent and by
selectively dissolving smaller nitrogen-containing molecules.
Nitrogen removal by extraction with the selective solvent system
herein was found to be independent of the temperature at which the
extraction process was conducted. The extraction process is
conducted by combining the selective solvent extractant with either
a crude or a processed shale oil. The selective solvent and shale
oil are thoroughly intermixed to provide for rapid achievement of
equilibrium. Such intermixing can be conducted, for example, by
agitation in the batchwise and continuous extraction techniques or
by the current flow in the counter-current extraction
techniques.
Following the contact phase of the extraction process the selective
solvent extractant is separated from the shale oil. The separation
is possible due to the immiscibility of the selective solvent
system and shale oil. The immiscibility of the selective solvent
system and shale oil provides liquid-liquid phase formation
whereupon one phase comprises substantially nitrogen-free shale oil
and the other phase comprises substantially selective solvent and
nitrogen-containing compounds. The two phases are separated by
decanting, withdrawing the lower phase or by other conventional
liquid-liquid separation techniques. To facilitate complete
separation of the two phases of the mixture an emulsion breaker can
be added to the mixture.
The nitrogen content of shale oil can be lowered by conducting
successive extractions of the shale oil with selective solvent
system. Successive extractions can be conducted in the batchwise
operation by separating the shale oil raffinate from the selective
solvent pregnant with nitrogen-containing compounds after an
initial extraction. The shale oil raffinate can then be extracted
with fresh selective solvent system. Such successive extractions
can be continued until the nitrogen content in the raffinate shale
oil has been lowered to the desired level. Successive extractions
can be conducted in countercurrent operation by transferring the
shale oil raffinate effluent from one countercurrent extraction
column into a second countercurrent extraction column against a
flow of fresh selective solvent system.
After the pregnant selective solvent phase is separated from the
shale oil raffinate having a reduced nitrogen content, the
selective solvent can be recovered. The selective solvent is
recovered by separating the nitrogen-containing compounds from the
selective solvent. For example, some of the nitrogen-containing
compounds that are basic can be precipitated from the selective
solvent by adding a stronger base or the nitrogen-containing
compounds can be extracted from the selective solvent in another
extraction process. In another method the selective solvent can be
volatilized and recovered to separate it from the
nitrogen-containing compounds. The selective solvent so recovered
can be recycled for use in subsequent extracting steps to reduce
the nitrogen content of the other shale oils.
The extracted oil can also be useful because of its high nitrogen
content. For example, the extracted oil can be used in the
production of nitrogen compounds and various chemical intermediates
containing nitrogen. When the selective solvent is volatilized, the
residue can be used as an asphalt which provides good adhesive
properties because of its nitrogen content and capabilities to
cross-link through such nitrogen present.
The following examples illustrate the method herein described for
reducing the nitrogen content of shale oil.
EXAMPLE 1-3
In the examples 1-3, extractions were made using concentrations of
both formic acid and acetic acid. The shale oil was brought into
contact with an aqueous solution of either formic or acetic acid.
The two phases were agitated thoroughly to provide a high
probability of the nitrogen-containing compounds in the shale oil
encountering the formic acid or acetic acid.
Complete separation of the two phases formed was brought about by
centrifuging the mixtures. An emulsion breaker was added when
needed. Following separation, the phases were both analyzed for
nitrogen, water, and organic acid content. Second and third stage
extractions were carried out by contacting the raffinates (shale
oil phase) of the previous extraction step with fresh selective
solvent system. Mass and component balances were maintained around
each separate stage.
Tables I and II summarize the data from examples 1-3 using acetic
acid and formic acid as the sole solvents. The extractions were
carried out using three separate extraction stages. The component
weight ratios in each stage are indicated in the Tables. The water
present in the samples in the aqueous acid solutions and the shale
oil is combined to provide the indicate water ratio.
The amount of nitrogen remaining in the raffinate shale oil is
calculated for the shale oil in the raffinate corrected to zero
water and acid content. The shale oil recovered in the raffinate
excludes water and acid and is calculated as weight percentage of
initial shale oil for each stage and is cumulative over the total
extraction. This figure is normalized to 100 percent shale oil mass
balance by dividing by the total percentage of shale oil recovered
in both the selective solvent and raffinate phases. The nitrogen
content of the extracted shale oil, i.e., the nitrogen content in
the pregnant selective solvent phase, is derived from analysis of
the extract solution following separation from the raffinate but
without isolation of the shale oil from the selective solvent. The
higher the value of this number the greater the efficiency of the
separation, i.e., the greatest amount of nitrogen-containing
compounds were removed with the least amount of shale oil removal
in the extract. The oil dissolved in the solvent phase indicates
the weight percent concentration of shale oil, whether nitrogen
bearing or not, dissolved in the selective solvent for each
extraction step.
The nitrogen contents of the phases were determined by modified
Kjeldahl procedure. Karl Fisher titration was used to obtain water
concentrations. Acetic acid and formic acid concentrations were
derived from pH curves of sodium hydroxide titrations of the
samples. The shale oil composition of each phase was obtained by
subtracting the water and acid weight percent concentrations from
100 percent. The accuracy of the composition analysis ratios was
correlated by mass balance determinations on the components.
EXAMPLES 4-9
These experiments were carried out using hydrochloric acid in
combination with acetic acid or formic acid as the selective
solvent for nitrogen-containing compounds.
The results of the experiments show that using hydrochloric acid
with the organic acid can remove more nitrogen-containing compounds
than when acetic or formic acid is used alone. The amount of low
nitrogen-containing shale oil recovered is significantly increased
over that which is expected for the organic acid extraction
alone.
The experiments were carried out by weighing the shale oil and the
selective solvent system into a separatory funnel. The mixture was
thoroughly shaken to effect contact between the nitrogen-containing
compounds present in the shale oil and the selective solvent of
organic acid in combination with hydrochloric acid. The shale oil
used contained 1.3 percent nitrogen. The acetic acid utilized was
glacial acetic acid. The formic acid used in the experiments was
concentrated formic acid which was 89.9 weight percent formic acid.
The hydrochloric acid was a 37.7 weight percent concentrated
hydrochloric acid. No additional water was added to the system.
Following through intermixing, the mixture was centrifuged to bring
about phase separation and the selective solvent layer was
subsequently collected. Fresh selective solvent was then added to
the raffinate and the extraction repeated. The first and second
stage extract solution and raffinates were analyzed for water,
organic acid, hydrochloric acid, and nitrogen contents. The results
of these extractions in the experiments are listed in the following
Table III. The relative quantities used in each extraction are
given in mole ratios. The amount of water is not shown but was
inferred from the amount of hydrochloric acid and formic acid. An
average molecular weight of 250 molecular weight units (M.W.U.) was
assumed for the shale oil. The nitrogen concentrations for the
raffinate and extract were calculated for the shale oils with
residual selective solvents removed. The shale oil recovery figures
were normalized to shale oil mass balances of 100 percent. The last
column lists the solubility of the shale oil in the selective
solvent phase.
TABLE I
__________________________________________________________________________
ACETIC ACID EXTRACTION DATA Oil Recovered in Oil Dissolved N
Content of Raffinate, Wt. % N Content of in Solvent Phase Example
System Weight Ratios Raffinate Oil Each Cumu- Extracted Oil Wt. %
of No. Oil:H.sub.2 O:Acetic Oil:Solvent Stage Wt. % Stage lative
Wt. % Solution
__________________________________________________________________________
1 3.6:1:4.2 1:1.4 1 0.699 88.77 -- 6.48 6.94 5.1:1:8.2 1:1.8 2
0.464 91.63 77.90 3.37 6.08 7.4:1:10 1:1.5 3 0.452 97.63 76.06 6.57
1.52
__________________________________________________________________________
TABLE II
__________________________________________________________________________
FORMIC ACID EXTRACTION DATA Oil Recovered in Oil Dissolved N
Content of Raffinate, Wt. % N Content of in Solvent Phase Example
System Weight Ratios Raffinate Oil Each Cumu- Extracted Oil Wt. %
of No. Oil:H.sub.2 0:Formic Oil:Solvent Stage Wt. % Stage lative
Wt. % Solution
__________________________________________________________________________
2 1.9:1:1.0 1:1.1 1 0.643 92.26 -- 5.47 7.69 1.8:1:1.2 1:1.2 2
0.387 94.47 87.16 4.91 4.49 1.6:1:1.1 1:1.3 3 0.324 96.30 83.93
4.96 2.42 3 1.3:1.0:1 1:1.5 1 0.533 92.74 -- 5.42 5.54 1.7:1:1.2
1:1.3 2 0.516 95.50 88.57 1.59 3.14 1.4:1:1.2 1:1.6 3 0.503 96.08
85.09 1.59 2.52
__________________________________________________________________________
TABLE III
__________________________________________________________________________
ORGANIC ACID-HCl EXTRACTIONS Oil Recovered in Mole Ratios Nitrogen
in Nitrogen Raffinate, Wt. % Nitrogen Content Oil Dissolved in
Experiment of Components Raffinate Oil Removed Each Cumu- of
Extracted Solvent Phase No. Stage Oil:Acid:HCl (Wt. %) (Wt. %)
Stage lative Oil (Wt. %) (Wt. % of
__________________________________________________________________________
Solution) Acetic Acid-HCl 4 1 5.9:17:1 0.256 80.3 70.98 2.35 29.9 2
6.3:20:1 0.112 91.4 90.29 64.09 1.42 11.19 5 1 3.5:15:1 0.151 88.4
70.02 3.59 23.59 2 2.8:16:1 0.109 91.6 88.64 62.06 0.53 7.83 6 1
2.0:8.1:1 0.173 86.7 72.89 3.03 19.24 2 1.8:9.3:1 0.089 93.2 -- --
-- -- 7 1 0.59:1.3:1 0.432 66.8 84.40 5.50 12.20 2 0.49:1.6:1 0.393
69.8 93.83 79.20 0.98 4.10 8 1 0.39:0.36:1 0.430 66.9 90.57 8.33
8.76 Formic Acid-HCl 9 1 0.59:1.7:1 0.370 71.5 88.84 8.34 9.38 2
0.51:1.3:1 0.320 75.4 94.97 84.37 1.16 3.82
__________________________________________________________________________
* * * * *