U.S. patent number 3,847,800 [Application Number 05/385,894] was granted by the patent office on 1974-11-12 for method for removing sulfur and nitrogen in petroleum oils.
This patent grant is currently assigned to KVB Engineering, Inc.. Invention is credited to Arthur F. Diaz, Eugene Daniel Guth.
United States Patent |
3,847,800 |
Guth , et al. |
November 12, 1974 |
METHOD FOR REMOVING SULFUR AND NITROGEN IN PETROLEUM OILS
Abstract
A method for the removal of sulfur and nitrogen components from
petroleum oils is disclosed. The unwanted sulfur and nitrogen is
oxidized to the extent that the resultant compounds exhibit
preferential solubility characteristics in some solvent with
respect to the oil. The oxidation step involves reacting the sulfur
and nitrogen compounds present with an oxide of nitrogen. In
particular instances, pretreatment of the oil to remove active
groups which cause undesirable side reactions or removal of low
sulfur fractions prior to the oxidation step will increase the
efficiency of the process. The oil containing the oxidized forms of
sulfur and nitrogen is then mixed with a selective solvent, which
is immiscible in the oil and in which the sulfur and nitrogen
compounds will dissolve. Methanol is the presently preferred
solvent. Separation of the oil from the methanol-oxidized compound
solution may be effected in a gravity separator. The oxidant gas
may be regenerated by the addition of oxygen and recirculated. The
oxidized sulfur and nitrogen compounds may be decomposed in a
hydrolysis reaction with a dilute base to separate inorganic
sulfate and sulfite, and nitrate and nitrite compounds from the
hydrocarbon parts of the compounds.
Inventors: |
Guth; Eugene Daniel (Palos
Verdes, CA), Diaz; Arthur F. (University City, CA) |
Assignee: |
KVB Engineering, Inc. (Justin,
CA)
|
Family
ID: |
23523298 |
Appl.
No.: |
05/385,894 |
Filed: |
August 6, 1973 |
Current U.S.
Class: |
208/236;
208/208R; 208/254R; 208/289 |
Current CPC
Class: |
C10G
27/04 (20130101); C10G 27/12 (20130101); C10G
53/14 (20130101) |
Current International
Class: |
C10G
27/12 (20060101); C10G 27/04 (20060101); C10G
27/00 (20060101); C10G 53/14 (20060101); C10G
53/00 (20060101); C10g 019/08 () |
Field of
Search: |
;208/254,236,289,207,205,232,211 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Gantz; Delbert E.
Assistant Examiner: Nelson; Juanita M.
Attorney, Agent or Firm: Spensley, Horn & Lubitz
Claims
I claim:
1. The method of reducing sulfur and nitrogen compound
concentrations in petroleum oil which comprises:
a. exposing petroleum oil to an oxidizing gas containing one or
more oxides of nitrogen chosen from the following list: NO.sub.2,
N.sub.2 O.sub.3, N.sub.2 O.sub.4, N.sub.2 O.sub.5, whereby sulfur
and nitrogen compounds in said petroleum oil will be oxidized:
b. mixing said petroleum oil with a solvent selected from the group
consisting of methanol, methanol-water mixtures,
methanol-ethanol-water mixtures and methanol-inorganic salt
solutions, said solvent being substantially immiscible with said
oil but being a solvent for said oxidized sulfur compounds, said
oxidized sulfur compounds dissolving in said solvent; and
c. separating said oil from said solvent solution.
2. The method of claim 1 where said oxidizing gas further contains
an inert gas.
3. The method of claim 1 where said oxide of nitrogen chosen is
NO.sub.2.
4. The method of claim 3 where said oxidizing gas contains about
1-20 percent NO.sub.2 and about 70 to 98 percent N.sub.2.
5. The method of claim 4 where said petroleum oil is exposed to
said oxidizing gas at a temperature of 50.degree. to 350.degree.
F.
6. The method of claim 5 where said exposure is for less than 20
minutes.
7. The method of claim 1 where an oxide of nitrogen in said
oxidizing gas is formed by reacting NO with O.sub.2.
8. The method of claim 7 where said oxidizing gas contains NO,
NO.sub.2 and O.sub.2.
9. The method of claim 8 where said oxidizing gas further contains
an inert gas.
10. The method of claim 9 where said oxidizing gas is comprised
of:
1-9 percent by volume NO+NO.sub.2, 1-19 percent by volume O.sub.2,
and the balance nitrogen.
11. The method of claim 10 where said petroleum oil is exposed to
said oxidizing gas at a temperature of 50.degree. to
350.degree.F.
12. The method of claim 11 where said exposure is for less than 20
minutes.
13. The method of claim 1 where said solvent is methanol.
14. The method of claim 1 where said separation is performed by
gravitational settling.
15. The method of claim 14 where said oxidizing gas further
contains an inert gas.
16. The method of claim 14 where said oxide of nitrogen chosen is
NO.sub.2.
17. The method of claim 16 where said oxidizing gas contains about
1-20 percent NO.sub.2 and about 70 to 98 percent N.sub.2.
18. The method of claim 17 where said petroleum oil is exposed to
said oxidizing gas at a temperature of 50.degree. to
350.degree.F.
19. The method of claim 18 where said exposure is for less than 20
minutes.
20. The method of claim 14 where an oxide of nitrogen in said
oxidizing gas is formed by reacting NO with O.sub.2.
21. The method of claim 20 where said oxidizing gas contains NO,
NO.sub.2 and O.sub.2.
22. The method of claim 21 where said oxidizing gas further
contains an inert gas.
23. The method of claim 22 where said oxidizing gas is comprised
of:
1-9 percent by volume NO+NO.sub.2, 1-19 percent by volume O.sub.2,
and the balance nitrogen.
24. The method of claim 23 where said petroleum oil is exposed to
said oxidizing gas at a temperature of 50.degree. to
350.degree.F.
25. The method of claim 24 where said exposure is for less than 20
minutes.
26. The method of claim 1 including the steps in which said solvent
stream is further treated after said separation:
a. evaporating said solvent from said solvent solution;
b. exposing the residue of said solvent solution to air and a
dilute mixture of an inorganic base and water whereby said oxidized
sulfur compounds will react to form inorganic sulfur compounds and
a hydrocarbon fraction; and
c. separating said hydrocarbon fraction from said inorganic sulfur
compounds.
27. The method of claim 1 and further including the step of heating
said oil, prior to exposure to said oxidizing gas, to a temperature
of from 300.degree. to 600.degree.F for from 2 to 20 hours.
28. The method of claim 1 and further including the step of mixing
a reactant with said oil prior to exposure to said oxidizing gas,
said reactant being chosen from the following: water, hydrogen,
ammonia.
29. The method of claim 1 and further including the step of heating
said oil, prior to exposure to said oxidizing gas, to a temperature
of 800.degree.F at atmospheric pressure.
30. The method of claim 1 and further including the steps of
heating said oil, prior to exposure to said oxidizing gas, to a
temperature of 1,000.degree.F in a vacuum.
31. The method of claim 1 and further including the steps of:
a. mixing said oil with methanol;
b. allowing said oil to separate from said methanol; and
c. decanting said methanol from said oil, said steps being taken
prior to exposure of said oil to said oxidizing gas.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of removing unwanted sulfur and
nitrogen compounds from petroleum oils.
2. Prior Art
The presently used method for performing the function of the
present invention involves the use of a high temperature-high
pressure process to desulfurize hydrocarbon fuels using hydrogen,
and an acid extraction process for the removal of basic nitrogen
compounds. The old methods have major disadvantages. Hydrogen is a
valuable material, made in refineries by pyrolyzing (heating to
decompose) hydrocarbon materials or through combustion to form
carbon monoxide which is subsequently reacted catalytically with
water at high temperature. In any case, it is costly to use
hydrogen to remove sulfur (as hydrogen sulfide) from fuels. The
reaction of hydrogen is nonselective in that some of the hydrogen
will react with the oil to saturate hydrocarbon molecules
(aromatics, olefins) in addition to the desired reaction forming
hydrogen sulfide. This means that a large quantity of hydrogen is
required to desulfurize hydrocarbon fuels.
The second disadvantage of the present method for sulfur removal is
that it requires a heterogeneous catalyst. The surface of the solid
catalyst tends to become fouled, particularly when residual oils
are desulfurized, and this makes the old method inefficient or
inoperable with some residual fuels.
The third disadvantage of the present method for sulfur removal is
that it requires high temperatures and high pressures for
desulfurizing fuels. The reaction conditions make it necessary to
use expensive equipment for the old process.
Several other methods of removing sulfur from hydrocarbons have
been proposed and are known to the applicant but these have not
become commercially popular.
U.S. Pat. No. 1,968,842 issued to Malisoff proposes to treat the
sulfur containing oil with a solution of an alkali in an organic
solvent. The alkali reacts with mercaptans in the oil forming
sulfur compounds which are more soluble in the solvent than in the
oil.
The Malisoff patent is directed specifically to sulfur in the form
of mercaptans in the oil and does not deal in any way with the
broad range of sulfur and nitrogen compounds susceptible to the
method of the present invention.
U.S. Pat. No. 3,267,027 issued to Fierce discloses reacting light
petroleum distillates with NO.sub.2 followed by washing with an
aqueous caustic and finally a water wash. The temperature of the
reaction is limited to 35.degree.C. This process also is directed
primarily to the removal of mercaptans and thus also has limited
applicability.
"Sweetening" of petroleum oils has also been known to applicant as
having been proposed by several people, and is a related process.
While not considered directly applicable, the most pertinent of
these is U.S. Pat. No. 3,224,618 issued to Dimond. Again, the
process considers only mercaptans and proposes to convert any
mercaptans present in hydrocarbons to disulfides by reacting the
mercaptans with oxygen in the presence of an oxide of nitrogen. The
resulting disulfides are not as odorous as the mercaptans and thus
the treated oil is considered sweet.
The major disadvantage of the old method for nitrogen removal is
that it achieves only partial nitrogen removal. Specifically, it
removes only some of the basic nitrogen compounds.
While in concept the old methods can be used to desulfurize and
partially denitrogenate fuels they lead to large economic
penalties. In some cases the cost of desulfurizing may exceed the
cost of the fuel.
A low cost simple method of removing sulfur and nitrogen from
petroleum fuels is mandatory if current and projected air pollution
regulations are to be met. Accordingly, the general purpose of the
present invention is to provide such a low cost process. The
process is low cost since it is carried out at low pressures and
temperatures, that is, the process equipment is inexpensive
compared to the equipment required for high pressure, high
temperature processes. Further, the process uses only low cost
chemicals (i.e., oxygen, nitrogen oxides an methanol, the latter
two being recycled) to remove substantially all of the sulfur and
nitrogen from the fuels. The process has broad applicability since
it can be used to treat liquid petroleum distillates (diesel oil,
jet fuel) as well as residual oils. The process makes it possible
to upgrade hydrocarbon fractions from initially low value-high
sulfur and nitrogen materials to produce high value-low sulfur and
nitrogen materials for use particularly as fuels. The process
significantly increases the quantity of fossil fuels available to
use within the current air pollution regulations and makes possible
a large future reduction in the oxides of sulfur and oxides of
nitrogen emissions by fuel users.
SUMMARY OF THE INVENTION
The present invention is a process based on the selective oxidation
of the sulfur and nitrogen compounds in liquid petroleum oil.
Petroleum oil is used herein to signify diesel oil, jet fuel,
furnace oil, residual oil, crude oil, topped crude oil, and similar
hydrocarbon mixtures. Oxygen is used to regenerate the gas phase
oxidizers (oxides of nitrogen containing two or more oxygen atoms,
e.g., NO.sub.2) which are recycled. The process can be carried out
batch-wise or continuously as desired. A batch of oil can be placed
in a vessel and treated with the gas phase oxidizer to oxidize the
sulfur and nitrogen compounds or the oil can be continuously pumped
through a reactor in which the oxidation is accomplished. For
example, the oxidizing gas may be passed upward through a vessel
while the oil passes downward. The vessel may be packed with a
material (like Berl saddles) which permits the two flows to occur
without interference or a large pressure drop. The reacted oil is
extracted with a suitable solvent to separate the oxidized sulfur
and nitrogen compounds. The extraction can also be carried out
continuously or batch-wise. At this point, a major fraction of the
oil has low sulfur and nitrogen content and is solvent stripped and
removed from the process for use.
One difficulty which may occur in this process is that some oils
may tend to react non selectively during the oxidation step and
form undesirable polymers and coke. This problem may be obviated by
preheating the feed oil to 300.degree. to 600.degree. F for some
time, typically 2 to 20 hours to permit the reactive groups in the
oil to combine with parts of the other hydrocarbon molecules and
thus become less active. An alternate pretreatment procedure is to
react the oil with a reactant such as water, hydrogen, or ammonia
to remove the active groups in the oil.
The solvent containing dissolved sulfur and nitrogen compound and a
fraction of dissolved oil can be separated from its solute either
by evaporating the solvent or cooling the mixture to a temperature
where the oxidized sulfur and nitrogen compounds have low
solubility. The solvent is then recycled through the process.
Finally, the sulfur and nitrogen may be separated from the solute,
for example, by hydrolysis or pyrolysis.
The process consumes oxygen and energy and produces a low sulfur,
low nitrogen oil having physical properties similar to the feed, a
lighter oil fraction (from the solute) and inorganic sulfur as
sulfite or sulfate ions and inorganic nitrogen as nitrate and
nitrite ions or nitrogen. The process steps are all carried out at
near ambient pressure and temperatures below about 300.degree. F so
the equipment, tanks, piping, etc., are all inexpensive compared to
those needed for a high temperature, high pressure process.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a block diagram of the process of the present
invention.
FIG. 2 is a block diagram of the oxidizing gas recirculating
system.
FIG. 3 is a block diagram of a first pretreatment step.
FIG. 4 is a block diagram of an alternative pretreatment step.
DETAILED DESCRIPTION
The general functions to be accomplished in the removal of sulfur
and nitrogen compounds from petroleum oils are:
1. Oxidation. Sulfur and nitrogen exist in petroleum oils in
various forms as mercaptans, disulfides, sulfides, amines, and
other organic nitrogen compounds having one or more carbon bonds.
By exposing feed oil containing such compounds to a gas which
includes one or more oxides of nitrogen, these compounds are
oxidized into sulfoxides aminoxides or similar compounds which can
easily be removed from the oil. The useful oxides of nitrogen for
this process are those containing two or more oxygen atoms, e.g.,
NO.sub.2, N.sub.2 O.sub.3, N.sub.2 O.sub.4, N.sub.2 O.sub.5. The
prior art (e.g., U.S. Pat. No. 3,244,618) discusses the oxidation
or mercaptans in petroleum oils into disulfides for the purpose of
"sweetening" the oils. Disulfides, while not having the
objectionable odor of mercaptans, are, unfortunately, not easily
separated from the oil and thus the oxidation step contemplated by
the method of this invention is intended to oxidize the sulfur
compounds into a higher state which exhibits low solubility in oil,
but relatively good solubility in some other solvent so that the
compounds can be subsequently removed by the process of
preferential solubility.
2. Mixing. The oxidized oil is mised with a suitable solvent, such
as methanol, which is immiscible with the oil, but in which the
oxidized sulfur and nitrogen compounds readily dissolve. Methanol
is not the only possible solvent, but is presently preferred since
it embodies the characteristics desired in a suitable solvent. The
desired characteristics are as follows:
a. Immiscibility in oil;
b. A solvent for oxidized sulfur and nitrogen compounds;
c. Low boiling point to simplify separation from sulfoxides,
aminoxides, etc. and oil.
d. does not readily form an emulsion with the oil;
e. density substantially different from the oil for ease in
separation;
f. Low cost-comparable to oil;
g. Does not degrade fuel properties of the oil.
The significance of items (f) and (g) is that small amounts of
solvent which cannot economically be separated from the final oil
stream will not either increase the cost of the product or render
it less desirable as a fuel.
3. Separation. The different densities of the oil and the solvent
allow separation of the oil (with reduced sulfur and nitrogen
content) from the solvent (in which the sulfur and nitrogen
compounds are dissolved) by gravitational settling or contrifuging.
The resulting oil has a low sulfur and nitrogen content as is
necessary to meet the present stringent requirements for fuels.
While the solvent is generally immiscible with the oil, a small
part of the oil will inevitably dissolve in the solvent along with
the oxidized sulfur and nitrogen compounds. This oil may be
recovered by distilling off the solvent (which is then reused), and
removing the sulfur and nitrogen compounds by decomposition in a
hydrolysis or pyrolysis reaction, as further described below.
It will be appreciated that the three basic steps outlined above
may be supplemented by other steps, such as pretreatment of the
oil, in some circumstances. For example, one difficulty which may
occur in the process is that some oils may tend to react non
selectively during the oxidation step and form undesirable polymers
and coke. This problem is obviated by preheating the feed oil to
300.degree. to 600.degree. F for some time, typically 2 to 20 hours
to permit the reactive groups in the oil to combine with parts of
the other hydrocarbon molecules and thus become less active. An
alternate pretreatment procedure is to react the oil with a
reactant such as water, hydrogen, or ammonia to remove the active
groups in the oil.
In order to improve the efficiency of the process, oils which have
a high volatility portion (such as an untopped crude oil) can be
topped at temperatures up to 800.degree.F, at atmospheric pressure,
or 1,000.degree.F., in vacuum, before processing. In general, the
high volatility portion of the oil is low in sulfur. Also, oils
having a methanol soluble portion can be treated with methanol
first to separate the methanol soluble portion.
Referring now to FIG. 1 where a block diagram of one preferred
embodiment of the process of this invention is shown in the form of
a continuous process. It will be understood that the steps of this
process leading to the removal of unwanted sulfur and nitrogen
compounds from oil can be accomplished by batch processing as well
as by the continuous process described. The process can also be a
combination of batch and continuous, for example, the pretreatment
steps, if utilized, can be done batch-wise while the remainder of
the process is continuous. Other combinations of batch and
continuous processing are also possible and practical within the
spirit of the present invention. The process, as illustrated in
FIG. 1, does not include any pretreatment steps, it being assumed
that such steps are either unnecessary or already performed on the
particular oil being processed.
Pump 10 pumps the oil from its previous location, not shown, into
the top of reactor 11. The reactor preferably operates at near
atmospheric pressure since this results in simple and relatively
inexpensive processing equipment. No particular advantage is to be
gained by increasing the pressure of the system, but to some extent
a somewhat higher than room temperature can be of advantage. A
higher temperature will tend to cause the reaction in which
mercaptans become disulfides to proceed further converting the
disulfides into sulfoxides. Typical temperatures which are
desirable range from about 50.degree. to 350.degree. F. As the
temperature increases some undesirable side reactions such as
polymerization and coke formation begin to occur. The process
temperature should not be so high nor the time of application so
long that these side reactions become a problem.
The reactor is the vessel which provides contact between the feed
oil and the oxidizing gas allowing the reaction to take place. It
can take many forms, but in the particular embodiment being
described, is a relatively tall cylindrical vessel in which the oil
is introduced at the top and the oxidizing gas at the bottom. The
oil flows downward due to gravity, flowing over baffles, or other
packing which provide a large surface over which the oil can flow.
The oil flows in thin layers so that a large surface of oil is
presented to the oxidizing gas. A typical reactor 11 may be packed
with Berl saddles 12, which occupy about 50 percent of the reactor
volume, leaving open spaces through which the oxidizing gas can
pass in contact with the oil on the surface of the saddles. Other
forms of reactor to obtain intimate contact between the oil and
oxidizing gas may, of course, be used, for example, agitated
vessels. The volume of the reactor is a function of the volumetric
flow rate of the oil and usually ranges from about 10 to 100 times
the hourly oil flow rate.
The flow of oil is such that the flowing oil remains in the reactor
for up to about 20 minutes at temperatures up to about 350.degree.
F., the time and temperature being enough to allow the sulfur and
nitrogen compounds in the oil to oxidize as needed to form the
compounds which will preferentially dissolve in the solvent used,
but not so hot or so long as to cause polymerization or side
reactions. The use of too high a temperature tends to cause
polymerization of the oil and is thus not desirable, while overlong
exposure to the oxidant allows other unwanted side reactions to
occur which are also undesirable.
The oxidizing gas is comprised of oxides of nitrogen. It can be a
single oxide, or a mixture of nitrogen oxides. The oxides which
have been found to be useful are NO.sub.2, N.sub.2 O.sub.3, N.sub.2
O.sub.4, and N.sub.2 O.sub.5, A potential problem exists if the
oxidizing gas is used undiluted in that a possible explosive
mixture with the petroleum vapors may be formed within the reactor.
To prevent this, it is preferable to dilute the oxidizing agent
with some relatively inert gas such as nitrogen. Typically the gas
used is 1 to 20 percent oxidizer, the balance being inert or, as
will be discussed below, partly oxygen and partly inert, the oxygen
being utilized in a regenerating cycle for the oxidizer. Presently,
a preferred composition of oxidizing gas is 1 to 9 percent by
volume NO + NO.sub.2, 1 to 19 percent by volume O.sub.2 with the
balance N.sub.2. The function of the NO in the system will be
discussed below.
Since the unwanted sulfur and nitrogen compounds appear in the oil
in various forms, no single reaction can be presented which
describes the process whereby these compounds are oxidized, however
the following reactions, among others, are probably involved.
R.sub.2 s + no.sub.2 .fwdarw. r.sub.2 so + no
r.sub.2 s + no.sub.2 .fwdarw. r.sub.2 so.sub.2 + no
rsh + 2no.sub.2 .fwdarw. rsooh + 2no
the oxidizing gas is introduced at inlet 13 located near the bottom
of the reactor and flows upward through the reactor contacting the
oil which is flowing over the surfaces of the Berl saddles 12. The
oxidizer flows out through outlet 14. It will be found to be most
economical to reconstitute the oxidizer and continuously recycle
the gas through the reactor. The procedure for accomplishing this
will be discussed below.
At the same time that sulfur compounds in the oil are being
oxidized, organic nitrogen compounds present in the oil having one
or more carbon bonds (e.g., amines, saturated aliphatic compounds
or parts of an aromatic ring) also react with the oxygen present to
form an oxidized form of the compound. Typical reactions could be
as follows: ##SPC1##
R.sub.3 n + no.sub.2 .fwdarw. r.sub.3 no + no
the oxidized compounds formed are soluble in methanol and are thus
susceptible to removal from the oil in the process as described
below.
The oil containing the oxidized sulfur and nitrogen compounds flows
out of the bottom of reactor 11 and is pumped by pump 19 to mixer
20 where it is mixed with a solvent, which is preferably methanol,
pumped into mixer 20 by pump 21 from solvent storage tank 22. A
quantity of solvent about 1 to 5 times the volume of oil insures
that substantially all of the soluble components in the oil
dissolve in the solvent. The solvent must be selective, that is,
one in which the oxidized sulfur and nitrogen compounds are soluble
but in which the oil itself is not soluble. Methanol is the
presently preferred solvent but other solvents such as
methanol-water mixtures, methanol-ethanol-water mixtures, and
methanol-inorganic salt (e.g., sodium chloride, potassium chloride
and calcium chloride) solutions can be used.
The mixer may be a stirred vessel or simply a static mixer in which
the flow streamlines are broken up by the shape of the vessel or by
obtructions therein. Again the mixing may be done at atmospheric
pressure and the temperature is not critical but is preferably
between 80.degree. and 150.degree. F, the upper temperature limit
being the boiling point of solvent.
After the oxidized compounds are dissolved in the solvent, the
mixture flows to separator 23 where the fluid is brought
essentially to rest and the lighter liquid, which in the case of a
methanol-diesel oil system is the methanol, rises to the top and
the oil sinks to the bottom.
The desulfurized and denitrogenated oil flows out of a bottom tap
24 of separator 23 while the solvent carrying the oxidized sulfur
and nitrogen compounds in solution is decanted from tap 25 at the
top of separator 23. The separator is preferably maintained at 1
atmosphere pressure and between 80.degree. and 150.degree. F.,
neither condition being critical. Separation of the fluids occurs
in about 10 to 30 minutes and a separator vessel with sufficient
volume to hold 10 to 30 minutes of flow would be satisfactory. A
continuous flow from taps 24 and 25, keeping the line of
demarcation between the oil and the methanol solution about in the
middle of the vessel allows the separation to take place and
prevents contamination of the separator output streams.
Any residual solvent remaining in the oil leaving tap 24 is removed
in holding tank 26 which is maintained at a relatively high
temperature, for example, 160.degree. F which causes the solvent to
vaporize. The vaporized solvent flows to condenser 27 where it is
condensed and is then added to the solvent in solvent tank 22.
The solvent stream, including the dissolved sulfur and nitrogen
compounds, as well as a small fraction of oil (generally 2 to 5
percent of the initial oil volume), flows from separator 23 through
outlet 25 to the solvent still 29, which is maintained at a high
enough temperature to evaporate the solvent. The solvent vapor is
condensed in condenser 27 and the distilled liquid solvent then
flows to tank 22 for recycling.
The residue of the solvent distillation, containing sulfur and
nitrogen compounds, oil, and some amount of solvent is passed
through a holding tank 30, maintained at over the boiling point of
the solvent, where the last vestiges of solvent are stripped from
the liquid and recovered in condenser 27.
The high sulfur, high nitrogen oil remaining as the residue can
either be used as is, for applications where the high sulfur and
nitrogen content is unimportant, or the oil can be further
processed in decomposer 31 which subjects the oil to a pressure of
1 to 5 atmospheres at 150.degree. to 300.degree. F for 5 to 30
minutes in the presence of air and a dilute inorganic base such as
sodium hydroxide. The ensuing hydrolysis reaction decomposes the
oxidized sulfur and nitrogen compounds forming hydrocarbons and
sulfite or sulfate compounds and nitrite or nitrate compounds.
As previously mentioned, it is desirable to recirculate the
oxidizer gas continuously for reasons of economy. FIG. 2 shows how
this may be accomplished.
Assuming that the oxidizing gas being used is the presently
preferred mixture previously referred to (NO.sub.2, O.sub.2 and
N.sub.2), the reaction in the reactor reduces the NO.sub.2 to NO
while oxidizing the sulfur and nitrogen compounds in the oil. As
the NO.sub.2 is being reduced, it is replenished to a large extent
by the reaction of NO and O.sub.2 present to maintain an
equilibrium of NO.sub.2, NO, and O.sub.2 as follows:
NO + 1/2 O.sub.2 .revreaction. NO.sub.2.
Thus the net reaction with the compounds in the oil results in
consumption of oxygen. At the same time the oil will emit some
vapors which tend to contaminate the oxidant gas, notably CO and
CO.sub.2. In order to maintain the composition, therefore, it is
necessary to somehow remove the contaminants. This may be
conveniently done by venting a small fraction (typically 1 to 5
percent) of the circulating gas and to replace the vented portion
with makeup gas. This gas is shown in FIG. 2 as being vented at
bleed 35 and makeup oxygen and NO are shown being supplied at 36
and 37. While in the preferred embodiment described, makeup gas is
NO and O.sub.2 which are reacted as will be presently described to
form NO.sub.2, it will be clear to those skilled in the art that
the oxidizing and makeup gases may be any one or more of the higher
oxides of nitrogen previously mentioned and in such case it would
not be necessary to provide the NO reacting means. Pump 17
circulates the oxidizer in the system. The rate of circulation is
not critical, the most desirable rate depending on the temperature
of the reactor, the quality of the contact of the oxidant with the
oil and the length of time the oil is in contact with the gas. The
order of magnitude of the circulation is 10 to 20 moles of oxygen
per mole of sulfur and nitrogen removed.
NO reactor 18 is a heated vessel maintained at 200.degree. to
450.degree. F. in which the NO and O.sub.2 react forming NO.sub.2
so that the gas stream entering reactor 11 will be rich in
NO.sub.2, the primary oxidant. NO reactor 18 is preferably of a
size which allows the gas to remain in it for 1 to 3 minutes in
order that the desired reaction take place.
After leaving NO reactor 18, the gas having the desired composition
enters reactor 11 through inlet 13. After exiting through outlet
14, the gas is fed through oil trap 33 and filter 34 before any
portion of the gas is vented through bleed 35. The purpose of these
units is to help clean up the circulating gas and to prevent oil
vapors or solid particles from being vented to the atmosphere. It
may be necessary in order to comply with anti-pollution statutes,
to further treat the bleed stream 35 before allowing it to escape
to the atmosphere.
As is well known to those skilled in the art, petroleum products
have very complicated structures and contain varying impurities and
fractions. For this reason it is not possible to describe a single
inflexible process for handling all such products. The process as
has been described to this point is general and it will be noted
that the parameters given are subject to wide variation to
accommodate a particular oil product to be processed. Even this
latitude may not be enough in some cases, however, and a
pretreatment of the oil may be desirable in order to fully utilize
the capabilities and efficiency of the method.
Some oils may tend to react non selectively during the oxidation
step and form undesirable polymers and coke. For such products, a
pretreatment as illustrated in FIGS. 3 or 4 might be found
advantageous.
In the embodiment shown in FIG. 3, a pump 43 drives oil from a
reservoir or other source, not shown, into prereactor 40. The
prereactor 40 is maintained at an elevated temperature of
300.degree. to 600.degree. F and is of sufficient size to that oil
will remain in the prereactor for from 2 to 20 hours. During
residence in the prereactor 40, reactive groups in the oil combine
with parts of other hydrocarbon molecules and become less active.
The purpose of this step is to reduce undesirable side reactions in
the oxidation step which follows. Active groups in the oil, unless
disposed of in some manner, may tend to react nonselectively in the
oxidation reactor to form undesirable polymers and coke. By
pretreating the oil to reduce the activity of these groups, the
side reactions can be held to a minimum.
An alternate pretreatment is illustrated in FIG. 4 where that
portion of the apparatus used in the pretreatment step only is
shown.
In addition to pump 44 pumping feed oil, a pump 41 pumps a suitable
reactant, such as water, hydrogen, or ammonia, into prereactor 42.
Prereactor 42 need not be heated but agitation means, not shown,
should be supplied to insure good mixing of the feed oil and the
reactant. The reactant reacts with the active groups in the feed
oil thereby reducing the amount of active material in the oil.
Other pretreatments which might be used to improve the efficiency
of the sulfur/nitrogen reduction process include topping oils which
have a high volatility portion by heating the feed oil to
800.degree. F at atmospheric pressure or 1,000.degree. F in vacuum.
In general, the high volatility portion of oil is low in sulfur and
removing such portion before processing will increase the
efficiency of the process. An oil which contains a methanol soluble
portion can be treated with methanol first to separate the soluble
portion.
After any pretreatment process or processes, the oil is fed to
reactor 11 and processed in the manner previously described.
In Tables I and II a group of test results are presented indicating
the efficacy of the invented method using methanol as the solvent.
As can be seen, up to 97 percent of the sulfur and 93 percent of
the nitrogen present are removed.
TABLE I
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DIESEL OIL TESTS Initial Wt. % S-0.21; Initial Wt. % N-0.035 Sample
Oxidation Temp. .degree.F Oxidizer.sup.1 Extraction % S.sup.2 %
N.sup.3 Time Conc. Vol. Solv/ Removed Removed Vol. % NO Vol. Oil
__________________________________________________________________________
Batch Reactor Tests 17-3 21 hrs. 150 5 0 0 17-2 21 hrs. 150 5 4 76
17-1 17 hrs. 150 5 4 76 16-1 6 hrs. 150 5 4 66 19-1 6 hrs. 105 7 4
76 14 19-2 27 hrs. 105 7 4 97 13-2 2 hrs. 205 5 5 57 13-3 5 hrs.
205 5 3 76 14-1 8 hrs. 205 5 1 43 Continuous Reactor Tests 21-1 10
min. 85 5 4 43 22 22-2 3 min. 200 2 3 29 26-1 12 min. 200 10 3 48
41-1 12 min. 170 10 3 72 91 41-3 12 min. 170 10 3 72 93 20-4 12
min. 170 10 3 81
__________________________________________________________________________
1. The treating gas was prepared by mixing air and nitrogen oxide
(NO) an heating the mixture to 250.degree.F for 30 seconds before
passing the gas through the reactor. 2. Analyzed by ASTM Method
D1266-70 with an acidimetric determination. 3. Analyzed by the
Kjeldahl method.
TABLE II
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RESIDUAL OIL TESTS Process Conditions Initial Oxidation Oxidizer
Extraction Sample Type of Oil Wt. % S,Wt. % N Time Temp.
Conc..sup.2 Vol. Solv/ Final.sup.1 Removal .degree.F Vol.% NO Vol.
Oil Wt. % S Wt. % % S %
__________________________________________________________________________
N Batch Reactor Tests 7-3 High Sulfur 2.2 3 hrs. 225 10 4 1.8 14
Stock 32-2 Topped Alaskan 0.36 7 hrs. 210 10 4 .13 64 Crude 10-1
Kern County 1.0 2 hrs. 200 4 .30 70 Stock Continuous Reactor Tests
42-2 High Sulfur 2.2 2.45 4 mins. 275 10 5 .3 1.34 86 45 Stock 37-3
Topped Alaskan .36 8 mins. 150 10 5 .16 56 Crude
__________________________________________________________________________
1. Sulfur determined by ASTM Method D 1266-70; Nitrogen by the
Kjeldahl method. 2. The treating gas was prepared by mixing air and
nitrogen oxide (NO) an heating the mixture to 250.degree.F for 30
seconds before passing the gas through the reactor.
In Table I results for diesel oil treatment show the effects of
temperature of oxidation, reaction time, catalyst concentration and
solvent volume on sulfur removal. It has been seen that substantial
reductions in sulfur and nitrogen content can be made using the
invented method under widely varying conditions. In Table II the
results for a variety of residual oils show that the method removes
sulfur and nitrogen from these fuels.
In treating the high sulfur oil remaining from the residue in Test
41-1 at 250.degree.F and one atmosphere for 30 minutes using an
equal volume of 10 percent sodium hydroxide in water with air
passing through the oil at the rate of 4 volumes per minute per
volume of oil the sulfur content of said oil was reduced 62 percent
and the nitrogen was reduced 48 percent.
What has been described is a novel method for reducing the sulfur
and nitrogen content of petroleum oil. Various modifications will
be apparent to those skilled in the art and are considered to be
within the spirit of the invention as set forth in the appended
claims.
* * * * *