Background of the Invention
This invention relates to the use of zinc octoates as hydrogen sulfide scavengers.
Petroleum asphalt is produced as a residue of a thermal separation refinery process. The thermal
separation process causes thermal cracking to occur which frequently causes hydrogen sulfide to
be present in the asphalt stream. In fact, thermal cracking continues in the asphalt even after the
asphalt has left the vacuum distillation section of the operation, particularly at high temperature.
In order to permit the safe loading, handling, and storage of the asphalt, it is necessary to reduce
the hydrogen sulfide to safe levels in the asphalt. This has been done in the past by weathering of
the hot asphalt for sufficient time for the hydrogen sulfide to be reduced to safe levels. This not
only takes a considerable amount of time (several days), but it releases hydrogen sulfide to the
vapor space in the storage, which could create hazardous conditions. Moreover, recent emphasis
on environmental regulations in Europe stresses the limits on the hydrogen sulfide content of vent
gas.
Other efforts to avoid these problems involve operating the vacuum distillation
tower at a lower temperature to reduce thermal cracking in the residue. Lower temperature
operation is achieved by increasing the flow of asphalt in a quench loop. This, however, is less
efficient than operating at higher temperatures and decreases throughput and thermal recovery.
Other related methods of addressing this situation are described in European Patent Specification,
Publication No. 0121377 and European Patent 000 421 683 A1.
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US Patent 5,000,835 describes using metal carboxylates as hydrogen scavengers.
This patent describes the reaction between metal carboxylates with 6 to 24 carbon atoms. In
these metal carboxylates, the carbonyl group functions as a carrier for the oppositely charged
metal and places the metal into a form which is soluble in an organic environment and able to
make contact with dissolved hydrogen sulfide. When the metal in the metal carboxylates reacts
with dissolved hydrogen sulfide, the two form insoluble metal sulfides, which eliminate the toxic
and corrosive properties of the hydrogen sulfide. While this patent does mention the use of zinc
octoate, which is oil soluble and readily available it also notes that zinc octoate is less effective
than other metal carboxylates.
Thus there is clear need and utility for an improved method of using zinc octoate
as a hydrogen sulfide scavenger. 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 C.F.R. § 1.56(a) exists.
Brief Summary of the Invention
At least one embodiment of the invention is directed towards a method for
removing sulfides from viscous petroleum streams such as asphalt, crude oil, and oil slurry. The
method comprises the step of adding to the stream an effective amount of a zinc octoate, wherein
the molar ratio of zinc complexed with octanoic acid is not 1:2. The zinc octoate may be an oxo
zinc octoate and it may be a tetranuclear oxo zinc octoate. The molar ratio of zinc to octanoic
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acid may be greater than 1:2. The zinc octoate may be added in a fluid with a viscosity less than
that of a similar fluid with a 1:2 molar ratio of zinc to octanoic acid.
At least one embodiment of the invention is directed towards a method for
removing sulfides from a petroleum stream with a fluid containing a molar ratio of zinc to
octanoic acid of 2.1:3, 1.97:3, or a range of between 2.1:3 to 1.97:3. The dosage of zinc octoate
added to the organic liquid may be from 1 to 2000 ppm. The addition may reduce at least 50% of
the sulfides. The zinc octoate may be added in a low viscosity fluid in which zinc metal content
comprises between 5% and 20% by weight of the fluid.
Brief Description of the Drawings
A detailed description of the invention is hereafter described with specific
reference being made to the drawings in which:
FIG. 1 is a graph showing the viscosity of various zinc octoates as hydrogen
sulfide scavengers. The lower the viscosity of the material the easier it is to add and disperse into
the asphalt
Detailed Description of the Invention
Zinc octoate is an 8-carbon carboxylic acid (specifically 2 ethyl hexanoic acid) in
which a zinc ion coordinates with the oxygen atoms of the acid. Because zinc has a +2 charge
and carboxylic acid has a –1 charge, it was previously assumed that all zinc octoates must have a
1:2 ratio of zinc moieties to carboxylic acid. As represemted in FIG. 1, these 1:2 zinc octoates,
tend to polymerize and form highly viscous materials, which makes their practical usefulness as a
hydrogen sulfide scavenger very limited.
In at least one embodiment a zinc octoate is used which has a non 1:2 acid to zinc
ratio. In an oxo zinc carboxylate, one or more oxygen atoms are bonded with two or more zinc
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atoms and the formed oxo-zinc group is the zinc species that becomes complexed with the
carbonyl group of the carboxylic acid. In at least one embodiment the oxo-zinc group is a
tetranulcear oxo-zinc in which four zinc atoms are bonded with one oxygen group and forms a
2:3 ratio of zinc to carboxylic acid.
In one embodiment, the ratio of zinc to carboxylic acid ratio ranges from 1.97:3
to 2.1:3.
This ratio facilitates the reaction of all of the zinc and prevents the appearance of
haze, which is indicative of residual unreacted zinc oxide.
The use of these non 1:2 ratio zinc octoates imparts a number of advantages.
Firstly the resulting octoate has more zinc atoms to be present per mol of octoate. Because the
zinc atoms are the primary impetus of removing the sulfides, concentrating more zinc per mol
increases the effectiveness of the octoate. Secondly as shown in FIG. 1, non 1:2 ratio zinc
octoates have lower viscosities than 1:2 octoates resulting in an octoate which is more applicable
and which can have a concentration that is more effective than more viscous zinc octoates. The
lower viscosity is quite an unexpected result as one would think that a complex that binds more
molecules together would have a higher viscosity, yet the test results demonstrate that when in
this 2:3 ratio a lower viscosity results. FIG. 1 illustrates this reduced viscosity relative to
temperature for the tetra oxo and polymer forms of zinc octoate prepared in an aromatic solvent.
The chemical structure of tetranuclear oxo zinc octoate is:
μ-Zn4O-μ-(O2C8H15)6
EXAMPLES
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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.
A number of samples were prepared in the same aromatic solvent. The
various samples were tested for vapor space H2S levels using Draeger Tubes. Table I
illustrates the sample’s effectiveness after heating for 2 hours at temperatures of 315 –
325 °F. Table II illustrates that the inventive composition is highly effective even after
shorter time periods.
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TABLE I
H2S Level (ppm)
Test
No.
Additive
Description
Additive Treat in
Asphalt (ppm)
No
Treatment
With
Treatment
1 5.5% Iron Octoate 99 4500 3250
2 5.5% Iron Octoate 301 4500 2700
3 5.5% Iron Octoate 702 3500 425
4 5.5% Iron Octoate 1769 3500 40
5
17% Zinc Octoate
tetrameric complex 100 4500 2250
6
17% Zinc Octoate
tetrameric complex 291 4500 1100
7
17% Zinc Octoate
tetrameric complex 541 3500 75
8
17% Zinc Octoate
tetrameric complex 695 3500 30
9
17% Zinc Octoate
tetrameric complex 1744 3500 0
10
17% Zinc Octoate
tetrameric complex 988 5000 10
11
13% Zinc Octoate
polymeric complex 996 5000 30
12
6.5% Zinc Octoate
polymeric complex 979 5000 775
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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
TABLE II
H2S Level (ppm)
Test
No.
Additive
Description
Additive Treat in
Asphalt (ppm) Time
No
Treatment
With
Treatment
1
17% Zinc Octoate
tetrameric complex 1013 1 min 5000 100
2
17% Zinc Octoate
tetrameric complex 998 30 min 5000 35
3
17% Zinc Octoate
tetrameric complex 991 2 hours 5000 20
4
17% Zinc Octoate
tetrameric complex 994 4 hours 5000 5
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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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I/We Claim
1. A method removing sulfides from petroleum streams, the method comprising the step of
adding to the organic liquid an effective amount of a zinc octoate, wherein the molar ratio of zinc
complexed with octanoic acid is not 1:2.
2. The method of claim 1 wherein the zinc octoate is an oxo zinc octoate.
3. The method of claim 1 wherein the zinc octoate is tetranuclear oxo zinc octoate.
4. The method of claim 1 in which the molar ratio of zinc to octanoic acid is greater than
1:2.
5. The method of claim 1 in which the zinc octoate is added in a fluid and the viscosity of
the fluid is less than the viscosity of a similar fluid with a 1:2 molar ratio of zinc to octanoic acid.
6. The method of claim 1 wherein the petroleum stream is one selected from the list
consisting of: asphalt, crude oil, oil slurry, and any combination thereof.
7. The method of claim 1 in which the molar ratio of zinc to octanoic acid is 2.1:3.
8. The method of claim 1 in which the molar ratio of zinc to octanoic acid is 1.97:3.
9. The method of claim 1 in which the molar ratio of zinc to octanoic acid is from 2.1:3 to
1.97:3.
10. The method of claim 1 in which the dosage of zinc octoate added to the organic liquid is
from 1 to 2000 ppm.
11. The method of claim 1 in which the added zinc octoate reduces at least 50% of the
sulfides.
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12. The method of claim 1 in which the zinc octoate is added in a low viscosity fluid and zinc
metal content comprises between 5% and 20% by weight of the fluid.