Note: Descriptions are shown in the official language in which they were submitted.
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IMPROVED METHOD OF REMOVING HYDROGEN SULFIDE
Cross-Reference to Related Applications
None.
Statement Regarding Federally Sponsored Research or Development
Not Applicable.
Background of the Invention
This invention relates generally to the treatment of sour gas and liquid
hydrocarbon to remove or reduce the levels of hydrogen sulfide therein. The
toxicity of hydrogen
sulfide in hydrocarbon streams is well known in the industry and considerable
expense and
efforts are expended annually to reduce its content to a safe level.
In large production facilities, it is generally more economical to install a
regenerative system for treating sour gas streams. These systems typically
employ a compound
used in an absorption tower to contact the produced fluids and selectively
absorb the hydrogen
sulfide and possibly other toxic materials such as carbon dioxide and
mercaptans. The absorption
compound is then regenerated and reused in the system. Typical hydrogen
sulfide absorption
materials include alkanoIamines, PEG, hindered amines, and other species that
can be
regenerated.
Nonregenerative scavengers for small plant hydrogen sulfide removal fall into
four
general categories: 1) aldehyde based, 2) metallic oxide based, 3) Caustic
based, and 4) other
processes. In the removal of hydrogen sulfide by nonregenerative compounds,
the scavenger
reacts with the hydrogen sulfide to form a nontoxic compound or a compound,
which can be
removed from the hydrocarbon. For example, when formaldehyde reacts with
hydrogen sulfide, a
chemical compound known as formthionals (e.g., trithiane) is formed.
Prior Art aldehyde scavengers typically include low molecular weight aldehydes
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and ketones and adducts thereof. The low molecular weight aldehydes may also
be combined
with an alkyl or alkanoIamine as disclosed in US Patent 4,748,011. Other
aldehyde derived
scavengers include the reaction product of low molecular weight alkanolamines
and aldehydes as
disclosed in US Patent 4,978,512. PCT Application WO 92/01481 discloses a
method of
reducing sulfides in a sewage gas using certain tri-substituted-hexahydro-s-
triazines. German
reference DE4027300 discloses a regenerative solvent for removing H2S and
mercaptans. US
Patent 5,347,004 discloses the use of 1,3,5 alkoxyallcylene hexahydro
triazines. PCT Application
WO 91 US 5232 discloses hydroxyalkyl triazine scavengers, specifically an
N,1\1',N"-tris(2-
hydroxyethyphexahydro-s-triazine. US Patent 5,774,024 discloses the
combination of an alkyl
triazine scavenger and quaternary ammonium salt, where the quaternary ammonium
salt enhances
the effectiveness of the alkyl-triazine..
Thus there is clear need and utility for an improved method of scavenging
hydrogen sulfide from hydrocarbon fluids. The art described in this section is
not intended to
constitute an admission that any patent, publication or other information
referred to herein is
"prior art" with respect to this invention, unless specifically designated as
such. In addition, this
section should not be construed to mean that a search has been made or that no
other pertinent
information as defined in 37 CFR 1.56(a) exists.
Brief Summary of the Invention
At least one embodiment of the invention is directed towards a method for
removing hydrogen sulfide from a hydrocarbon fluid. The method comprises
contacting the fluid
with an effective amount of sulfide scavenger formulated with a nitroxide
promoter. The amount
of nitroxide promoter is sufficient to accelerate the scavenging action of the
scavenger in
comparison to the scavenging action of the scavenger in the absence of the
nitroxide promoter.
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Detailed Description of the Invention
For purposes of this application the definition of these terms is as follows:
"Alkyl-triazine" means a molecule according to the formula:
r
,
Rc N
R2
Where RI, R2, R3 are Alkyl groups such as methyl, ethyl, propyl, isopropyl, t-
butyl, etc. or are
substituted alkyl groups such as CI-12CH2OH, and RI, R2, R3 can all be the
same group or one or
more different groups. Alkykriazines include but are not limited to the
triazines disclosed in US
Patent 5,744,024.
"Hydrocarbon fluid" means a liquid or gas predominantly comprising organic
to material including but not limited to kerosene, crude oil, distillate
fuels, fuel oil, heating oils,
diesel fuel, gasoline, jet fuel, bunker fuel oils, and any combination
thereof.
"Methyltriazine" means an alkyl-triazine in which RI, R2, and R3 are all
methyl
groups.
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"Nitroxide" means a composition of matter according to the formula:
R3 - N
R2
where Ri R2 and R3 are any alkyl group containg 1 ¨30 carbon atoms and
includes cyclic
compounds.
"Non-Regenerative Scavenger" means a scavenger, which is consumed by the
process of scavenging.
"Regenerative Scavenger" means a scavenger, which is not consumed by the
process of scavenging.
"Promoter" means a composition of matter that in and of itself does not
scavenge,
but when combined with a known scavenger, significantly increases the
effectiveness of the
scavenger.
"Salt" means a compound comprising an anion and a cation which usually ionizes
in solution.
"Scavenger" means a composition of matter, such as but not limited to alkyl
triazines, useful in reducing the amount of some other composition of matter,
such as but not
limited to hydrogen sulfide, in a fluid medium.
In the event that the above definitions or a description stated elsewhere in
this
application is inconsistent with a meaning (explicit or implicit) which is
commonly used, in a
dictionary, or stated in a source incorporated by reference into this
application, the application
and the claim terms in particular are understood to be construed according to
the definition or
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description in this application, and not according to the common definition,
dictionary definition,
or the definition that was incorporated by reference. In light of the above,
in the event that a term
can only be understood if it is construed by a dictionary, if the term is
defined by the Kirk-Othrner
Encyclopedia of Chemical Technology, 5th Edition, (2005), (Published by Wiley,
John & Sons,
Inc.) this definition shall control how the term is to be defined in the
claims.
In at least one embodiment, the amount of hydrogen sulfide in a hydrocarbon
fluid
is reduced by the introduction of an alkyl-triazine scavenger with a nitroxide
promoter. The
promoter increases the effectiveness of the alkyl-triazine scavenger.
Nitroxide is superior to the
prior art quarternay ammonium salt promoters because nitroxide is a single
component and does
not contain halides such as chloride.
The effectiveness of a nitroxide as a promoter is unexpected because it is a
single neutral
compound. In at least one embodiment the promoter is from 1-25% of the
scavenger-promoter
containing composition.
In at least one embodiment, at least a portion of the triazines are
synthesized
is according to the process described in US Patent 5,744,024.
In at least one embodiment the ntiroxide is mixed with a solution of alkyl
triazine
where the solvent can be water and the nitroxide bearing solution is
introduced into the
hydrocarbon fluid. In at least one embodiment the nitroxide introduction is
simultaneous to the
alkyl-triazine introduction. The properties of the ntiroxide promoter are such
that it is highly
effective in a number of different hydrocarbon fluids.
One advantage of the use of the nitroxide promoter with a scavenger over the
prior art scavengers is that the nitroxide promoter is not a salt (it is not a
combination of an anion
and a cation) and therefore lacks halides and in particular lacks chloride.
In at least one embodiment a scavenging formulation is used in a
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hydrocarbon stream. The formulation comprises a solvent, alkyl-triazine, and
nib-oxide.
The solvent is selected from the list consisting of water, alcohol, aromatic
solvent, a
solvent that mutually solvates alkyl-triazine, and nitroxide and any
combination thereof.
The formulation can be introduced into the hydrocarbon stream by mechanical
means
including but not limited to injection pumps or any mechanism disclosed in US
Patents
5,744,024 and 5,840,177. In the context of gaseous hydrocarbon fluids, the gas
may be
passed through an absorption tower containing a scavenging formulation.
In at least one embodiment the hydrocarbon fluid is in a liquid state. In at
least one embodiment the hydrocarbon fluid is in a gaseous state.
EXAMPLES
The foregoing may be better understood by reference to the following
example, which is presented for purposes of illustration and is not intended
to limit the
scope of the invention.
Samples of sour hydrocarbon streams (fuel oils) were tested to determine
the efficiency of the triazine formulated with promoter versus the triazine
formulated
without a promoter. The samples were comparatively treated with various
dosages of
methyltriazine scavenger, methyltriazine scavenger with a promoter, and the
amounts of
residual II2S for the various samples were recorded. Table 1 compares the
inventive
composition at different concentrations, Table 2 compares promoted scavenger
with non-
promoted scavenger, and table 3 compares methyltriazine with and without
promoter over
time.
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Table 1: Comparison of promoter at 3 different concentrations
in vacuum gas oil for 2 hours at 60 C
Dose H2S Percent Dose
Sample # Treatment (ppm) (ppm) Reduction Ratio
Untreated 0 200 0
Methyltriazine +
1 2.5% nitroxide 60 100 50 0.3
Methyltriazine +
2 5% nitroxide 60 120 40 0.3
Methyltriazine +
3 10% nitroxide 60 130 35 0.3
Table 2; Comparison of promoted and non-promoted triazine,
in kerosene for 2 hours
Dose H2S Percent Dose
Sample # Treatment (ppm) (ppm) Reduction Ratio
Untreated 0 1300
Methyltriazine +
5% Quaternary
1 ammonium 260 70 95 0.2
Methyltriazine I-
2 5% nitroxide 260 90 93 0.2
3 Methyltriazine 260 120 91 0.2
Untreated 0 950
Methyltriazine +
5% Quaternary
1 ammonium 284 30 97 0.3
Methyltriazine +
2 5% nitroxide 284 70 93 0.3
3 Methyltriazine 284 80 92 0.3
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Table 3: Comparison of alkyl-triazine with and without promoter over time In
kerosene
Dose H2S Percent Dose Time
Sample # Treatment (ppm) (ppm) Reduction Ratio (min)
.
Untreated 0 1200 0 0
Methyltriazine
1 + nitroxide 400 300 75 0.3 15
Methyltriazine
2 + nitroxide 400 200 83 0.3 30
Methyltriazine
3 + nitroxide 400 85 93 0.3 60
Methyltriazine
4 + nitroxide 400 75 94 0.3 90
Methyltriazine
+ nitroxide 400 75 94 0.3 120
Untreated 0 600 0.3 0
1 Methyltriazine 200 250 58 0.3 15
2 Methyltriazine 200 230 62 0.3 30
3 Methyltriazine 200 110 82 0.3 60
4 Methyltriazine 200 60 90 0.3 90
5 Methyltriazine 200 70 88 0,3 120
The vapor space hydrogen sulfide levels were measured according to the
procedure described by ASTM D5705-03. The test procedure was modified for
tables 2
and 3 by performing the test in kerosene at room temperature, which was
approximately
5 22 C instead of 60 C.
This data demonstrates that the presence of the nitroxide enables the
methyltraizine scavenger to reduce the levels of H2S faster than
methyltriazine does
without the promoter.
While this invention may be embodied in many different forms, there are
shown in the drawings and described in detail herein specific preferred
embodiments of
the invention. The present disclosure is an exemplification of the principles
of the
invention and is not intended to limit the invention to the particular
embodiments
illustrated. Furthermore,
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the invention encompasses any possible combination of some or all of the
various
embodiments described herein and incorporated herein.
The above disclosure is intended to be illustrative and not exhaustive. This
description will suggest many variations and alternatives to one of ordinary
skill in this art. All
these alternatives and variations are intended to be included within the scope
of the claims where
the term "comprising" means ''including, but not limited to". Those familiar
with the art may
recognize other equivalents to the specific embodiments described herein which
equivalents are
also intended to be encompassed by the claims.
All ranges and parameters disclosed herein are understood to encompass any and
to all subranges subsumed therein, and every number between the endpoints.
For example, a stated
range of "1 to 10" should be considered to include any and all subranges
between (and inclusive
of) the minimum value of 1 and the maximum value of 10; that is, all subranges
beginning with a
minimum value of 1 or more, (e.g. 1 to 6.1), and ending with a maximum value
of 10 or less,
(e.g. 2.3 to 9.4, 3 to 8, 4 to 7), and finally to each number 1, 2, 3, 4, 5,
6, 7, 8, 9, and 10 contained
within the range.
This completes the description of the preferred and alternate embodiments of
the
invention. Those skilled in the art may recognize other equivalents to the
specific embodiment
described herein which equivalents are intended to be encompassed by the
claims attached hereto.
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