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 alkanolamines, 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
and ketones and adducts thereof. The low molecular weight aldehydes may also be combined
with an alkyl or alkanolamine as disclosed in US Patent 4,748,01 1. 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 ¾ S and mercaptans. US
Patent 5,347,004 discloses the use of ,3,5 alkoxyalkylene hexahydro triazines. PCT Application
WO 9 1 US 5232 discloses hydroxyalkyl triazine scavengers, specifically an N,N',N"-tris(2-
hydroxyethyl)hexahydro-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. 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 CF § 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.
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:
Where Rl R2, R are Alkyl groups such as methyl, ethyl, propyl, isopropyl, t-butyl, etc. or are
substituted alkyl groups such as CH2CH2OH, and Rl R , R3can all be the same group or one or
more different groups. Alkyl-triazines 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
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 Rl R2, and R3 are all methyl
groups.
"Nitroxide" means a composition of matter according to the formula:
R2
where Ri R 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
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-Othmer
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
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
hydrocarbon stream. The formulation comprises a solvent, alkyl-triazine, and nitroxide.
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 ¾ S for the various samples were recorded. Table 1 compares the inventive
composition at different concentrations, Table 2 compares promoted scavenger with nonpromoted
scavenger, and table 3 compares methyltriazine with and without promoter over
time.
Table : Comparison of promoter at 3 different concentrations
in vacuum gas oil for 2 hours at 60 °C
Dose H2S Percent Dose
Sample # Treatment (ppm) (ppm¾ 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 1300
Methyltriazine +
5% Quaternary
ammonium 260 70 95 0.2
Methyltriazine +
5% nitroxide 260 90 93 0.2
Methyltriazine 260 120 9 1 0.2
Untreated 950
Methyltriazine +
5% Quaternary
ammonium 284 30 97 0.3
Methyltriazine +
5% nitroxide 284 70 93 0.3
Methyltriazine 284 80 92 0.3
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 4 0.3 90
Methyltriazine
5 + 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 AST D5705-03. The test procedure was modified for tables 2
and 3 by performing the test in kerosene at room temperature, which was approximately
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. All patents, patent applications, scientific papers, and any other referenced
materials mentioned herein are incorporated by reference in their entirety. Furthermore,
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
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 nge.
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.
Claims
1. A method of reducing the amount of hydrogen sulfide in a hydrocarbon fluid comprising
contacting the fluid with an effective amount of a composition, the composition comprising a
sulfide scavenger and a nitroxide promoter wherein 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.
2. The method of claim 1 wherein the scavenger is an alkyl-triazine.
3. The method of claim 1 wherein the hydrocarbon fluid is liquid.
4. The method of claim 1 wherein the method results in no halides being added to the
hydrocarbon fluid.