CA2805402C - Improved method of removing hydrogen sulfide - Google Patents

Abstract

The invention provides a method of removing hydrogen sulfide from hydrocarbon fluids. The method involves using a nitroxide molecule to promote a sulfide scavenger such as alkyl-triazine. The nitroxide effectively accelerates the scavengers activity. This allows for the avoidance of the introduction of halides into the hydrocarbon stream.

Description

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 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.

2 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

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.

3 "Nitroxide" means a composition of matter according to the formula:

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

4 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

5 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.

6 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

7 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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Claims (5)

CLAIMS:

1. A method of reducing the amount of hydrogen sulfide in a hydrocarbon fluid comprising contacting gaseous hydrocarbon fluid with an effective amount of a composition as the gaseous hydrocarbon fluid passes through an absorption tower, the composition comprising solvent, 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, wherein the scavenger is an alkyl-triazine and the solvent comprises water and wherein the nitroxide promoter is a composition of matter according to the formula:
where R1 R2 and R3 are any alkyl group containing 21 - 30 carbon atoms.

2. The method of claim 1 wherein the method results in no halides being added to the hydrocarbon fluid.

3. The method of claim 1 wherein the alkyl-triazine is methyltriazine.

4. The method of claim 1 wherein the solvent also comprises at least one of: alcohol, aromatic solvent, and any combination thereof.

5. The method of claim 1 wherein R1 R2 and R3 are any alkyl group containing 26 - 30 carbon atoms.