U.S. patent application number 11/180910 was filed with the patent office on 2005-12-01 for method and composition to decrease iron sulfide deposits in pipe lines.
This patent application is currently assigned to Synergy Chemical, Inc.. Invention is credited to Mattox, Mark Andrew, Valente, Edward J..
Application Number | 20050263739 11/180910 |
Document ID | / |
Family ID | 26978488 |
Filed Date | 2005-12-01 |
United States Patent
Application |
20050263739 |
Kind Code |
A1 |
Mattox, Mark Andrew ; et
al. |
December 1, 2005 |
Method and composition to decrease iron sulfide deposits in pipe
lines
Abstract
The levels of iron sulfide present in a conduit, such as a
pipeline, are reduced by contacting the conduit, on an inner
surface, with a composition obtained from an aqueous solution
containing at least one compound of Formula (I) 1 and at least one
amine or corresponding ammonium derivative in the presence of a
solvent, wherein X is an anion of valency n. Preferably, the pH of
the solution is about 8. Alternatively, the method employs a
composition comprising tris(hydroxymethyl)phosphine (TRIS) and at
least one amine or corresponding ammonium derivative. The amine
preferably is ammonia or a primary alkylamine. The compositions
readily complex and thereby dissolve deposits of iron(II) sulfide,
removing them from the conduit.
Inventors: |
Mattox, Mark Andrew; (Foley,
AL) ; Valente, Edward J.; (Clinton, MS) |
Correspondence
Address: |
FOLEY AND LARDNER
SUITE 500
3000 K STREET NW
WASHINGTON
DC
20007
US
|
Assignee: |
Synergy Chemical, Inc.
|
Family ID: |
26978488 |
Appl. No.: |
11/180910 |
Filed: |
July 14, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11180910 |
Jul 14, 2005 |
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10218905 |
Aug 15, 2002 |
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60312647 |
Aug 15, 2001 |
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60373381 |
Apr 17, 2002 |
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Current U.S.
Class: |
252/175 ;
514/129 |
Current CPC
Class: |
C23G 1/26 20130101; C23F
14/02 20130101; C23G 1/24 20130101; C11D 11/0041 20130101; C09K
2208/20 20130101; F16L 58/1009 20130101; B08B 9/032 20130101; Y10S
210/912 20130101; Y10T 137/0391 20150401; C11D 7/06 20130101; C09K
8/528 20130101; C10G 75/04 20130101; C23G 1/18 20130101; C11D 7/36
20130101 |
Class at
Publication: |
252/175 ;
514/129 |
International
Class: |
A61K 031/66; C02F
005/08 |
Claims
1. A method of decreasing the level of iron sulfide in a conduit
that has an internal surface, comprising (a) contacting said
internal surface with a first composition, obtained by a process
comprised of combining at least one compound of Formula (I): 4with
at least one amine or ammonium derivative thereof in the presence
of an aqueous solvent, wherein X is an anion of valency n, whereby
a second composition is obtained; and (b) removing from said
conduit said second composition.
2-24. (canceled)
25. A method of decreasing the level of iron sulfide in a conduit,
comprising: (a) contacting said conduit with a composition
comprising tris(hydroxymethyl)phosphine (TRIS), at least one amine
or ammonium derivative thereof, and a solvent whereby a second
composition is obtained; and (b) removing from said conduit said
second composition.
26-43. (canceled)
44. A composition obtained by a process comprised of combining at
least one compound of Formula (I): 5with at least one amine or
ammonium derivative thereof selected from the group consisting of
alkylamines, dialkylamines, and the conjugate acids thereof in the
presence of an aqueous solvent, wherein X is an anion of valency
n.
45. The composition of claim 44, wherein X is selected from the
group consisting of chloride, bromide, iodide, lower alkyl
carboxylates, bisulfite, bisulfate, hydrocarbyl sulfonates,
dihydrogenphosphate, nitrate, hexafluorophosphate, sulfate,
sulfite, monohydrogenphosphate, and phosphate.
46. The composition of claim 44, wherein said compound is selected
from tetrakis(hydroxymethyl)phosphonium sulfate and
tetrakis(hydroxymethyl)pho- sphonium chloride.
47. (canceled)
48. The composition of claim 44, wherein said amine or ammonium
derivative is selected from the group consisting of alkylamines and
the conjugate acids thereof.
49. The composition of claim 48, wherein said alkylamine or
conjugate acid thereof is selected from the group consisting of
methylamine, ethylamine, propylamine, isopropylamine, butylamine,
tertbutylamine, and the conjugate acids thereof.
50. The composition of claim 49, wherein said alkylamine is
methylamine.
51. The composition of claim 44, wherein the molar ratio of
phosphorus not in X to nitrogen in said amine or ammonium
derivative thereof is from about 1:1 to about 15:1.
52. The composition of claim 51, wherein said molar ratio is from
about 1.5:1 to about 8:1.
53. The composition of claim 52, wherein said molar ratio is about
2.5:1.
54. The composition of claim 44, wherein said solvent is water or a
mixture comprising water and an alcohol.
55. The composition of claim 54, wherein said alcohol is
methanol.
56. The composition of claim 54, wherein said solvent is water.
57. The composition of claim 54, wherein the pH of said solvent is
between about 4.5 to about 10.
58. The composition of claim 54, wherein said pH is between about 6
to about 9.
59. The composition of claim 58, wherein said pH is about 8.
60. The composition of claim 44, wherein said compound is present
in an amount between 1 to 90% by weight of said composition.
61. The composition of claim 60, wherein said compound is present
in an amount of 5% by weight of said composition.
62. The composition of claim 61, wherein said compound is present
in an amount of 1% by weight of said composition.
63. The composition of claim 44, wherein said amine or ammonium
derivative thereof comprises between 0.05 to 2.0% by weight of said
composition.
64. A composition comprising tris(hydroxymethyl)phosphine (TRIS),
at least one amine or ammonium derivative thereof selected from the
group consisting of alkylamines, dialkylamines, and the conjugate
acids thereof, and a solvent.
65. (canceled)
66. The composition of claim 64, wherein said amine or ammonium
derivative is selected from the group consisting of alkylamines and
the conjugate acids thereof.
67. The composition of claim 66, wherein said alkylamine or
conjugate acid thereof is selected from the group consisting of
methylamine, ethylamine, propylamine, isopropylamine, butylamine,
tertbutylamine, and the conjugate acids thereof.
68. The composition of claim 67, wherein said alkylamine is
methylamine.
69. The composition of claim 64, wherein the molar ratio of TRIS to
amine or ammonium derivative thereof is from about 1:1 to about
15:1.
70. The composition of claim 69, wherein said molar ratio is from
about 1.5:1 to about 8:1.
71. The composition of claim 70, wherein said molar ratio is about
2.5:1.
72. The composition of claim 64, wherein said solvent is water or a
mixture comprising water and an alcohol.
73. The composition of claim 72, wherein said alcohol is
methanol.
74. The composition of claim 72, wherein said solvent is water.
75. The composition of claim 64, wherein TRIS is present in an
amount between 1 to 90% by weight of said composition.
76. The composition of claim 75, wherein TRIS is present in an
amount of 5% by weight of said composition.
77. The composition of claim 76, wherein TRIS is present in an
amount of 1% by weight of said composition.
78. The composition of claim 64, wherein said amine or ammonium
derivative thereof comprises between 0.05 to 2.0% by weight of said
composition.
79. A composition obtained by a process comprised of combining at
least one compound of Formula (I): 6with at least one amine or
ammonium derivative thereof and at least one other amine or
ammonium derivative thereof in the presence of an aqueous solvent,
wherein X is an anion of valency n.
80. The composition of claim 79, wherein X is selected from the
group consisting of chloride, bromide, iodide, lower alkyl
carboxylates, bisulfite, bisulfate, hydrocarbyl sulfonates,
dihydrogenphosphate, nitrate, hexafluorophosphate, sulfate,
sulfite, monohydrogenphosphate, and phosphate.
81. The composition of claim 80, wherein said compound is selected
from tetrakis(hydroxymethyl)phosphonium sulfate and
tetrakis(hydroxymethyl)pho- sphonium chloride.
82. The composition of claim 79, wherein said amine or ammonium
derivative and other amine or ammonium derivative are selected from
the group consisting of ammonia, alkylamines, dialkylamines,
alkylenediamines, cycloalkylamines, and the conjugate acids
thereof.
83. The composition of claim 82, wherein said amine or ammonium
derivative is selected from the group consisting of ammonia and
alkylamines.
84. The composition of claim 83, wherein said amine is selected
from the group consisting of methylamine, ethylamine, propylamine,
isopropylamine, butylamine, tertbutylamine, 1,2-diaminoethane,
1,3-diaminopropane, cyclopropylamine, cyclobutylamine,
cyclopentylamine, cyclohexylamine, and the conjugate acids
thereof.
85. The composition of claim 84, wherein said amine is selected
from the group consisting of methylamine and 1,2-diaminoethane.
86. The composition of claim 82, wherein said other amine or
ammonium derivative is selected from the group consisting of
ammonia and ammonium chloride.
87. The composition of claim 82, wherein said amine or ammonium
derivative is selected from the group consisting of methylamine and
1,2-diaminoethane and said other amine or ammonium derivative is
selected from the group consisting of ammonia and ammonium
chloride.
88. The composition of claim 79, wherein the molar ratio of
phosphorus not in X to nitrogen in said amine or ammonium
derivative thereof and said other amine or ammonium derivative
thereof is from about 1:1 to about 15:1.
89. The composition of claim 88, wherein said molar ratio is from
about 1.5:1 to about 8:1.
90. The composition of claim 89, wherein said molar ratio is about
2.5:1.
91. The composition of claim 79, wherein said solvent is water or a
mixture comprising water and an alcohol.
92. The composition of claim 91, wherein said alcohol is
methanol.
93. The composition of claim 91, wherein said solvent is water.
94. The composition of claim 91, wherein the pH of said solvent is
between about 4.5 to about 10.
95. The composition of claim 94, wherein said pH is between about 6
to about 9.
96. The composition of claim 95, wherein said pH is about 8.
97. The composition of claim 79, wherein said compound is present
in an amount between 1 to 90% by weight of said composition.
98. The composition of claim 97, wherein said compound is present
in an amount of 5% by weight of said composition.
99. The composition of claim 98, wherein said compound is present
in an amount of 1% by weight of said composition.
100. The composition of claim 79, wherein said amine or ammonium
derivative thereof and said other amine or ammonium derivative
thereof comprises between 0.05 to 2.0% by weight of said
composition.
101. A composition comprising tris(hydroxymethyl)phosphine (TRIS),
at least one amine or ammonium derivative thereof,and at least one
other amine or ammonium derivative thereof in the presence of a
solvent.
102. The composition of claim 101, wherein said amine or ammonium
derivative and other amine or ammonium derivative are selected from
the group consisting of ammonia, alkylamines, dialkylamines,
alkylenediamines, cycloalkylamines, and the conjugate acids
thereof.
103. The composition of claim 102, wherein said amine or ammonium
derivative is selected from the group consisting of ammonia and
alkylamines.
104. The composition of claim 103, wherein said amine is selected
from the group consisting of methylamine, ethylamine, propylamine,
isopropylamine, butylamine, tertbutylamine, 1,2-diaminoethane,
1,3-diaminopropane, cyclopropylamine, cyclobutylamine,
cyclopentylamine, cyclohexylamine, and the conjugate acids
thereof.
105. The composition of claim 104, wherein said amine is selected
from the group consisting of methylamine and 1,2-diaminoethane.
106. The composition of claim 102, wherein said other amine or
ammonium derivative is selected from the group consisting of
ammonia and ammonium chloride.
107. The composition of claim 102, wherein said amine or ammonium
derivative is selected from the group consisting of methylamine and
1,2-diaminoethane and said other amine or ammonium derivative is
selected from the group consisting of ammonia and ammonium
chloride.
108. The composition of claim 101, wherein the molar ratio of
phosphorus not in X to nitrogen in said amine or ammonium
derivative thereof and said other amine or ammonium derivative
thereof is from about 1:1 to about 15:1.
109. The composition of claim 108, wherein said molar ratio is from
about 1.5:1 to about 8:1.
110. The composition of claim 109, wherein said molar ratio is
about 2.5:1.
111. The composition of claim 101, wherein said solvent is water or
a mixture comprising water and an alcohol.
112. The composition of claim 111, wherein said alcohol is
methanol.
113. The composition of claim 111, wherein said solvent is
water.
114. The composition of claim 101, wherein TRIS is present in an
amount between 1 to 90% by weight of said composition.
115. The composition of claim 114, wherein TRIS is present in an
amount of 5% by weight of said composition.
116. The composition of claim 115, wherein TRIS is present in an
amount of 1% by weight of said composition.
117. The composition of claim 101, wherein said amine or ammonium
derivative thereof and said other amine or ammonium derivative
thereof comprises between 0.05 to 2.0% by weight of said
composition.
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS
[0001] This application claims benefit of priority to U.S.
provisional applications Ser. No. 60/373,381, filed Apr. 17, 2002,
and No. 60/312,647, filed Aug. 15, 2001.
BACKGROUND OF THE INVENTION
[0002] This invention relates to methods and compositions to
decrease or remove iron sulfide deposits in or on a conduit of a
gas stream.
[0003] Hydrogen sulfide (H.sub.2S) is a pernicious, naturally
occurring contaminant of fluids that is encountered, for example,
during the manipulation of oil or gas. The corrosive nature of
H.sub.2S typically leads to the accumulation of particulate iron
sulfide, which can become easily entrained in hydrocarbons as well
as in glycol, salts, and other contaminants, forming intractable
deposits on the surfaces of conduits such as pipelines. Such
deposits present a significant problem to the oil and gas
industries because the pipelines must be cleaned physically.
Additionally, the iron sulfide deposits hinder accurate
determinations of pipeline structural integrity, which can be
assessed by instrumentation known as SMART PIGS.
[0004] A limited repertoire of techniques has been available for
reducing or removing iron sulfide deposits from pipelines. U.S.
Pat. No. 5,820,766 to Gevertz et al., for example, describes the
use of inorganic bromates or iodates to oxidize fluid-entrained
sulfides to solid elemental sulfur, which must be mechanically
collected and removed from a pipeline. A byproduct of this
mechanical cleaning is a sludge that can be flammable and must be
disposed of in a landfill. U.S. Pat. No. 4,370,236 to Ferguson
discloses a method in which iron sulfide is removed from a gas
stream by washing it with a mixture of a hydrocarbon and water. The
resultant aqueous phase contains soluble and particulate iron
sulfide which must be removed by further physical and chemical
processing steps. For example, see U.S. Pat. No. 6,153,100.
[0005] An alternate approach as informed by general chemical
principles is to solubilize iron sulfide in water. Iron (II) and
iron (III) ions generally form relatively water-insoluble compounds
at neutral pHs. Such iron compounds begin to precipitate from
aqueous solution at pH values of 5 or greater. For example, iron
(II) precipitates from neutral solutions at pH 7 and oxidizes to
iron (III) hydroxide in the presence of oxygen. Thus, the usual
method to render a water insoluble iron (II) or iron (III) compound
soluble in water is to treat the solid in an aqueous mixture with a
strong mineral acid which lowers the pH, thereby dissolving the
iron compound. In the case of iron (II) sulfide, however, this
method results in the evolution of hydrogen sulfide, and if in
sufficient amount (greater than 437 cm.sup.3/L at 0.degree. C.) to
its release as a toxic gas from the solution. An additional
disadvantage of using of strong mineral acids to clean pipelines is
that most pipes are made of steel or iron, which are susceptible to
attack by strong acids, thereby producing corrosion, deterioration,
and pitting. Furthermore, such attack also produces hydrogen gas,
which is flammable and explosive in air.
[0006] Yet another approach to the removal of iron sulfide is
disclosed in PCT publication WO 02/08127, which describes the use
of aqueous compositions of tris(hydroxymethyl)phosphine or a
corresponding phosphonium salt (collectively, "THP") below or well
below neutral pH. The '127 PCT publication discloses, however, that
the use of THP, at the pH required to rapidly complex iron sulfide,
is fraught with practical barriers, including the formation of an
insoluble polymer, when THP is formulated with ammonia as a
co-reagent, and the oxidation of THP to the non-complexing
tris(hydroxymethyl)phosphine oxide. In light of these problems, the
'127 PCT publication discloses that iron sulfide can be chelated by
amino carboxylic acids or amino phosphonic acids in formulations
with THP. According to the publications, the use of THP in the
absence of ammonium ion or ammonia provides a small synergistic
effect on iron sulfide dissolution. Because the acid co-reagents
are expensive, however, their use is undesirable when large
quantities are necessary to remove iron sulfide deposits.
[0007] Accordingly, there is a continued need in the art for an
improved method of removing iron sulfide deposits that employs
safe, readily available and inexpensive materials, which requires
minimum mechanical intervention, and that avoids chemical pitfalls,
such as polymeric precipitates, of prior art methods.
SUMMARY OF THE INVENTION
[0008] To address these and other needs, the present invention
provides a composition obtained by a process comprised of combining
at least one compound of Formula (I) 2
[0009] with at least one amine or ammonium derivative thereof in
the presence of an aqueous solvent. In Formula (I), X is an anion
that has a valency of n, the number of phosphonium cations present.
Preferably, the pH of the aqueous solvent is adjusted to between
about 4.5 and about 10, more preferably between about 6 and about
9. Still more preferred is a pH of about 8.
[0010] In accordance with another aspect, the invention provides a
method of decreasing the level of iron sulfide in a conduit. The
inventive method comprises contacting the conduit with the
composition described above, forming a second composition, and then
removing the second composition from the conduit. This approach
derives in part from the unexpected discovery that the composition
readily solubilizes iron sulfide.
[0011] Yet another aspect of the present invention concerns a
composition comprising tris(hydroxymethyl)phosphine (TRIS), at
least one amine or ammonium derivative thereof, and a solvent.
[0012] This invention also provides a method for decreasing the
level of iron sulfide in a conduit, by contacting the conduit with
the composition of TRIS, as described above, to form a second
composition, and then removing the second composition from the
conduit.
[0013] The present invention can be implemented in relation to a
variety of conduits, such as dry gas conduits and processed fluid
conduits. Furthermore, the invention contemplates both the
continuous administration of compositions of the present invention
and intermittent administration, i.e., a batch process.
[0014] In one embodiment of the invention, the anion X of Formula
(I) is monoanionic, dianionic, or trianionic. Thus, acceptable
anions are selected from but are not limited to chloride, bromide,
iodide, lower alkyl carboxylates, bisulfite, bisulfate, hydrocarbyl
sulfonates, dihydrogenphosphate, nitrate, hexafluorophosphate,
sulfate, sulfite, monohydrogenphosphate, and phosphate. Preferred
anions include chloride and sulfate, and preferred compounds of
Formula (I) thus are tetrakis(hydroxymethyl)phosphonium chloride
and tetrakis(hydroxymethyl)ph- osphonium sulfate.
[0015] Amines that are particularly useful in the practice of this
invention include but are not limited to ammonia, alkylamines,
dialkylamines, alkylenediamines, and cycloalkylamines.
Additionally, the conjugate acids of these amines are also
efficacious. Preferably, the amine is ammonia or an alkylamine.
More preferably, the amine is ammonia or methylamine. A preferred
conjugate acid is ammonium chloride.
[0016] The present invention typically involves the use of a
solvent. Specifically, for a composition and method that employ
compounds of Formula (I), the solvent is an aqueous solvent.
Preferred solvents include but are not limited to water and
alcohols. The solvent also may comprise two or more solvents, such
as water and an alcohol. A preferred alcohol is methanol.
[0017] For compounds of Formula (I) and for TRIS, as well as for
amine or ammonium derivatives thereof, relative amounts and
concentrations employed according to the present invention can vary
widely. According to one aspect of the invention, the amount of a
compound of Formula (I) or TRIS ranges from about 1% to about 90%
(w/w), preferably 5% (w/w), and more preferably 1% (w/w). In
another aspect of the invention, the amount of amine or ammonium
derivative thereof can vary between about 0.05% to about 2.0%
(w/w). The amounts are all based upon the total weight of the
composition. The relative amounts of the components of the
compositions are adjusted according to the molar ratio of
phosphorus to nitrogen. For compositions that comprise one or more
compounds of Formula (I), this molar ratio is based upon the molar
amount of phosphorus contained in the phosphonium ions of Formula
(I). For the compositions that instead comprise TRIS, the molar
ratio is simply based upon the molar amount of TRIS. In either sort
of composition, the molar ratio of phosphorus to nitrogen can vary
between about 1:1 to about 15:1. Preferably, the molar ratio is
about 1.5:1 to about 8:1. The most preferred molar ratio is about
2.5:1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] The present invention effectively decreases the levels of
iron sulfide in conduits, such as processed fluid pipelines and dry
gas pipelines. The iron sulfide may be in a gas stream or, for
example, on the surface of a conduit of a gas stream. The conduit
retaining or containing the iron sulfide must be brought into
contact with a composition of this invention, whereby iron sulfide
forms a soluble complex that can be easily removed from the
conduit. The invention is performed at or near neutral pH and,
hence, is non-corrosive to pipes and other conduits.
[0019] Composition
[0020] The compositions of this invention are particularly
effective at complexing and solubilizing iron sulfide. According to
one aspect of the invention, this result is readily achieved by
providing one or more compounds of Formula (I) in admixture with at
least one amine or ammonium derivative thereof. The anion X
balances the net positive charge of one or more 3
[0021] phosphonium cations. Typically, n in Formula (I) is 1, 2, or
3. Thus, X is typically a monoanion, dianion, or trianion,
respectively.
[0022] While any routinely accessible anion X can be used, it is
preferred that X is chosen such that compounds of Formula (I) are
soluble in water, alcohols, or in mixtures thereof. Thus, suitable
monoanions include halides such as chloride, bromide, and iodide.
Also contemplated are lower alkyl carboxylates, wherein the term
"lower alkyl" refers to a straight or branched C.sub.1-C.sub.6
alkyl group. Exemplary lower alkyl carboxylates are methyl
carboxylate (i.e., acetate), ethyl carboxylate, and propyl and
iso-propyl carboxylates. Other monoanions include sulfur-based
anions such as bisulfite, bisulfate, and hydrocarbyl sulfonates.
Hydrocarbyl sulfonates are anions of the formula RS(O).sub.2O.sup.-
wherein R is a lower alkyl or aryl group. Examples of hydrocarbyl
sulfonates include, but are not limited to, methylsulfonate,
benzenesulfonate, para-toluenesulfonate, and the isomers of
xylenesulfonate. Still other suitable monoanions include nitrate
and hexafluorophosphate.
[0023] Dianions X include sulfate, sulfite, and
monohydrogenphosphate. An acceptable trianion is phosphate.
[0024] Compounds of Formula I are commercially available or can be
obtained routinely by known syntheses. For example, particularly
preferred compounds of Formula (I) are
tetrakis(hydroxymethyl)-phosphoniu- m sulfate and
tetrakis(hydroxymethyl)phosphonium chloride, both of which are
available commercially, for example, from Rhodia (Cranberry, N.J.),
Nippon Industries (Tokyo, Japan), and Cytec Industries (Mobile,
Ala.). Tetrakis(hydroxymethyl)phosphonium sulfate is normally
available as an aqueous acidic solution having a pH of between 1
and 4. Other compounds of Formula (I) bearing different anions X
can be prepared straightforwardly by the well-known reaction
between phosphine and formaldehyde in the presence of an aqueous
acid HX as described, for example, in the procedure of U.S. Pat.
No. 4,044,055 to Katz et al.
[0025] The amine or its ammonium derivative, which is combined with
one or more compounds of Formula (I), can be selected from a
variety of amines and their conjugate acids. It is preferred but
not essential that if the amine or its conjugate acid is a solid,
then it should be soluble in the solvent employed in the
composition of this invention. Similarly, if the amine or its
conjugate acid is a liquid, then it is preferably miscible with the
solvent. One suitable amine is ammonia.
[0026] Primary amines, such as alkylamines, are particularly
efficacious in the practice of this invention. Exemplary
alkylamines include, but are not limited to, methylamine,
ethylamine, normal- and iso-propylamines, and normal- and
tert-butylamines. Other primary amines include alkylenediamines,
such as 1,2-diaminoethane and 1,3-diaminopropane. Still other
exemplary primary amines are cycloalkylamines, such as
cyclopropylamine, cyclobutylamine, cyclopentylamine, and
cyclohexylamine.
[0027] Ammonium derivatives of these amines can also be used. An
ammonium derivative is the conjugate acid of an amine. A conjugate
acid of an amine is obtained by the formal addition of an acid to
that amine. Suitable acids include inorganic acids such as HCl,
HBr, HI, and phosphoric acid, and organic acids such as carboxylic
acids. Thus, the present invention contemplates a variety of
ammonium derivatives. Particularly preferred ammonium derivatives
include ammonium chloride, ammonium nitrate, methylammonium
chloride, and ethylammonium chloride.
[0028] According to certain embodiments of this invention, the
composition is made by combining suitable amounts of at least one
compound of Formula (I) and at least one amine or ammonium
derivative thereof in the presence of an aqueous solvent. The order
of addition of the reagents can be varied, although it is preferred
that the amine or ammonium derivative is added to a solution of a
compound of Formula (I) wherein the pH has been adjusted as
described below. Particularly preferred solvents include water and
an alcohol. Alternatively, mixtures of water and an alcohol can be
used. Exemplary alcohols include methanol, ethanol, and
isopropanol.
[0029] In preferred embodiments, the amount of a compound of
Formula (I) is about 5% (w/w), or even as little as 1% (w/w), based
on the total weight of the composition. A sufficient amount of
amine or ammonium derivative thereof varies from about 0.05 to
about 2.0% (w/w) based on the total weight of the composition.
[0030] The pH of the mixture described above optionally is adjusted
to a value between about 4.5 to about 10. Alternatively, solid
compounds of Formula (I) can be dissolved in or solutions thereof
diluted with an aqueous solvent in which the pH already has been
adjusted to between about 4.5 to about 10. In either instance, the
addition of an appropriate acid or base will effect the desired pH
adjustment. Suitable acids include hydrochloric and sulfuric acids.
Suitable bases include sodium and potassium hydroxides, and organic
bases such as triethylamine.
[0031] For embodiments that employ commercially available aqueous
solutions of tetrakis(hydroxymethyl)phosphonium sulfate, the pH
must be raised. This is accomplished by adding a suitable base to
the mixture. The pH can be maintained by the use of a buffer. In an
exemplary procedure, 0.1 mole of acetic acid is dissolved in less
than 0.5 liters of water and is adjusted to pH 5 by adding 2.0
molar sodium hydroxide, and the mixture is diluted with water to a
volume of nearly 1 liter, readjusted to pH 5 with sodium hydroxide,
and finally brought to a volume of 1.0 liter. Alternatively, one
may employ sodium or potassium acetate and acetic acid such that
the total amount of acetate ion from either source amounts to 0.1
mole, dilute the resulting solution to nearly 1 liter, adjust the
pH to 5 with acetic acid, and dilute the solution to exactly 1.0
liter. Other buffers, such as phosphate and citrate, are
serviceable in the prescribed pH range. Additionally, nitriloacetic
acids can be used as buffers. Exemplary acids include
nitrilotriacetic acid (NTA) and
ethylenediamine-N,N,N',N'-tetraacetic acid (EDTA).
[0032] As mentioned above, the present invention is generally
effective at complexing iron sulfide over a wide pH range. The
inventor has discovered that the rate of iron sulfide complexation
increases with increasing pH. Thus, the preferred pH is about 6 to
about 9, and the most preferred pH is about 8. To illustrate, in
laboratory experiments utilizing an aqueous solution of 0.015M
FeSO.sub.4, 0.03M NH.sub.4.sup.+ and 0.06M
tetrakis(hydroxymethyl)phosphonium sulfate buffered to a pH of 4.5,
the rate of iron complexation at 22.degree. C. was 0.5 hour. The
rate decreased to 0.01 hour for an analogous solution at a pH of
about 5.0. For these determinations, the rate is defined as the
time required to raise the absorbance of the solution at 500 nm to
1.0.
[0033] Without wishing to be bound by any particular theory or
principle, the inventor believes that compounds of Formula (I),
particularly when exposed to aqueous solutions having elevated pH,
furnish tris(hydroxymethyl)phosphine (TRIS). A convenient method
for the production of TRIS is thus realized by adjusting the pH of
an aqueous solution of tetrakis(hydroxymethyl)phosphonium sulfate
to pH 8 by the addition of sodium or potassium hydroxide, whereby
95% of phosphorus in the resultant solution is in the form of
water-soluble TRIS. This transformation has been described in the
art. See K. A. Petrov et al., Zhurnal Obshchei Khimii 32 (1962)
553. Alternatively, TRIS may be synthesized in the reaction between
phosphine, formaldehyde, and potassium tetrachloroplatinate. See
U.S. Pat. No. 3,030,421 to Reuter et al.
Tris(hydroxymethyl)phosphine also is available commercially, for
example, from Strem Chemicals, Inc. (Newburyport, Mass.).
[0034] Another embodiment of this invention, a composition of TRIS,
derives in part from the surprising discovery that the reaction
products of TRIS and at least one amine or ammonium derivative
thereof are effective scavengers of iron sulfide in a conduit.
According to the invention the amine or its ammonium derivative, as
described above, is combined with TRIS in a solvent to form a
solution. If an ammonium derivative is utilized in an aqueous
solvent, then it is preferable, although not necessary, to elevate
the pH of the solution.
[0035] The composition can be prepared by two primary routes. In
one embodiment, TRIS is first prepared from an aqueous solution of
a compound of Formula (I), such as
tetrakis(hydroxymethyl)phosphonium sulfate or chloride, by the
known method described above. The resultant solution, which
contains TRIS, is combined directly with an amine or ammonium
derivative, or solutions thereof, to form the composition. In an
alternative embodiment, a solution of pure TRIS in a solvent can be
combined with an amine or ammonium derivative. Preferably, the
amine is ammonia or a primary amine such as methylamine or
ethylamine. Methylamine is most preferred. The preferred solvents
are those which dissolve TRIS. Polar solvents, such as alcohols or
alcohol-water mixtures, are preferred solvents.
[0036] In preferred embodiments, the composition contains TRIS in
an amount of about 5% (w/w), or even as little as 1% (w/w), based
on the total weight of the composition. A sufficient amount of
amine or ammonium derivative thereof varies from about 0.05 to
about 2.0% (w/w) based on the total weight of the composition.
[0037] The methods and compositions of this invention are effective
for a range of relative amounts of compounds of Formula (I) or TRIS
and an amine or ammonium derivative thereof. The molar ratio of
phosphorus, as contained in the phosphonium ions of Formula (I) or
in TRIS, to nitrogen in the amine or ammonium derivative, can vary
from about 1:1 to about 15:1. A preferred molar ratio is about
1.5:1 to about 8:1. Still more preferred is a molar ratio of about
2.5:1.
[0038] If the amine is ammonia or if the ammonium derivative is an
ammonium salt (e.g., NH.sub.4Cl), then a polymeric precipitate may
be observed in the course of determining the optimum ratio.
Nevertheless, even under optimum ratio conditions and the resultant
formation of a precipitate, the precipitate eventually dissolves to
yield a composition exhibiting diminished but evident iron sulfide
dissolving ability. Alternatively, the precipitate can be avoided
altogether, with no deleterious effect on the eventual removal of
iron sulfide, by using a higher-than-optimal phosphorus:nitrogen
molar ratio. Additionally, use of a primary amine as described
above does not lead to the polymeric precipitate and, hence,
provides a surprising advantage over prior-art compositions that
lead to the precipitate. Moreover, if ammonia and an alkylamine are
employed simultaneously, the tolerance for ammonia without
formation of a precipitate is improved in the pH range useful for
this invention, producing solutions which are also efficacious in
iron sulfide dissolution. Thus, those compositions of the invention
that are comprised of alkylamines provide an advantage in the form
of complexation of iron sulfide associated with water effluent that
is entrained with ammonia.
[0039] The compositions of the present invention optionally
comprise one or more additives, which render the compositions
applicable to a wide range of conduits wherein iron sulfide
deposits present a problem. The additives include surfactants;
biocides, such as glutaraldehyde and
2,2-dibromo-3-nitrilopropionamide (DBPNA); water dispersants;
demulsifiers; scale inhibitors; corrosion inhibitors; anti-foaming
agents, oxygen scavengers such as diethylhydroxylamine (DEHA); and
flocculants.
[0040] Surfactants include anionic, amphoteric, cationic, and
non-ionic surfactants, which generally contain a hydrophilic moiety
and hydrophobic substituents such as alkyl, alkenyl, cycloalkyl,
cycloalkenyl, aryl, alkaryl, arylalkyl, and polyaryl groups of 6 to
24, preferably 10 to 20, and more preferably 12 to 18 carbon atoms.
The hydrophobic substituents also include polymeric moieties, such
as polysiloxanes and polyoxypropylenes.
[0041] Examples of anionic surfactants include sparingly
water-soluble salts of sulfonic or mono-esters of sulfuric acid,
such as alkylbenzene sulfonates, alkyl sulfates, alkyl ether
sulfates, olefin sulfonates, alkane sulfonates, alkylphenol
sulfates, alkylphenol ether sulfates, alkylethanolamide sulfate,
alkylethanolamidether dulfate, and alpha sulfo fatty acids or the
corresponding esters each containing from 6 to 24 carbon atoms.
[0042] Other exemplary anionic surfactants are soaps such as
linoleates, alkyl ether carboxylates, palmitates, resinates,
oleates, and stearates; and alkyl sulfosuccinates such as sodium
di-2-ethylhexylsulfosuccinate and sodium dihexylsulfosuccinate,
acyl taurides, isethionates, alkyl ether sulfosuccinates, acyl
sarcosinates, and alkyl sulfosuccinates.
[0043] The anionic surfactant may be an anionic phosphate ester,
alkyl phosphonate, alkyl amino- or iminomethylene phosphonate. Each
of these surfactants generally contain at least one hydrophobic
substituent described above. Ether-bearing surfactants contain one
or more glyceryl, oxyethylene, oxypropylene, and oxybutylene
groups.
[0044] While preferred anionic surfactants are sodium salts, other
salts of commercial import include those of lithium, potassium,
calcium, and magnesium. Still other salts are those of ammonia,
monoethanolamine, diethanolamine, triethanolamine, lower
alkylamines, alkyl- and hydroxyalkyl-phosphonium.
[0045] Non-ionic surfactants include tertiary acetylinic glycols,
polyethoxylated alcohols, polyethoxylated mercaptans,
polyethoxylated carboxylic acids, polyethoxylated amines,
polyethoxylated hydroxyalkyl amides, polyethoxylated alkyl phenols,
polyethoxylated glyceryl esters, and the propoxylate or mixed
ethoxylated and propoxylated derivatives thereof. Polymeric
non-ionic surfactants include block copolymers of polyoxypropylene
and polyethylene, and copolymers of polyoxybutylene and
polyoxyethylene or polyoxybutylene and polyoxypropylene.
[0046] Amphoteric surfactants include any water soluble surfactant
compound comprised of a hydrophobic moiety, such as a C.sub.6-20
alkyl or alkenyl group, and a hydrophilic moiety containing an
amine or quaternary ammonium group and a carboxylate, sulfate, or
sulfonic acid. Exemplary amphoteric surfactants include betaines,
such as imidazoline betaines. Others include alkyl amine ether
sulfates, sulfobetaines, and quaternary amine or quaternized
imidazoline sulfonic acids and salts thereof. Still other suitable
surfactants include Zwitterionic surfactants such as N-alkyl
taurines and carboxylate amido amines. Specific examples include,
but are not limited to, 2-tallow alkyl, 1-tallow amido alkyl,
1-carboxymethyl imidazoline and 2-coconut alkyl, and
N-carboxymethyl-2-(hydroxyalkyl)imidazoline.
[0047] Cationic surfactants useful in the present invention include
alkylammonium salts having at least 8, preferably 10 to 30, and
more preferably 12 to 24 aliphatic carbon atoms. Particularly
preferred cationic surfactants are tri- and tetraalkylammonium
salts. Typically, the cationic surfactant will bear one or two
aliphatic chains of 8 to 20 carbons apiece, and two or three short
alkyl groups of one to four carbon atoms apiece. Specific examples
include dodecyl trimethyl ammonium salts and benzalkonium salts
bearing one long and two short alkyl groups.
[0048] Other useful cationic surfactants include N-alkyl pyridinium
salts wherein the alkyl groups has 8 to 22, and preferably 10 to
20, carbon atoms.
[0049] The cationic surfactant may also be an alkaryl
dialkylammonium salt. The alkyl groups each have from one to four
aliphatic carbon atoms, and the alkaryl groups is, for example, an
alkyl benzene group having 8 to 22 carbon atoms.
[0050] Still another class of cationic surfactants include alkyl
imidazoline salts, such as alkyl methyl hydroxyethyl imidazolinium
salts. Examples include alkyl methyl hydroxyethyl imidazolinium
salts, alkyl benzyl hydroxyethyl imidazolinium salts, and
2-alkyl-1-alkylamidoethyl imidazoline salts.
[0051] Certain amido amines are useful as cationic surfactants.
These are formed by reacting a fatty acid, ester, glyceride, or
amide forming derivative thereof, with a di- or poly-amine.
Exemplary polyamines are ethylene diamine and diethylene
triamine.
[0052] The cationic surfactant includes an anion, which may be any
anion that confers water-solubility to the surfactant. Suitable
anions include, but are not limited to, those anions X in Formula
(I) described above.
[0053] The foregoing surfactants also include polyfluorinated
derivatives thereof. Particularly preferred surfactants of this
class include polyfluorinated alkyl sulfates and polyfluorinated
quaternary ammonium salts.
[0054] The surfactants of this invention are preferably those which
can be used as wetting agents. Wetting agents lower the surface
tension between water and a hydrophobic solid surface, such as the
interior surface of a pipeline.
[0055] The amounts of a surfactant in the compositions of this
invention can vary widely. Typically, the surfactant is present in
an amount relative to the weight of a compound of Formula (I) or
TRIS of about 50:1 to about 1:200, preferably about 20:1 to about
1:100, and most preferably about 10:1 to about 1:50. Particularly
preferred ratios are from about 2:1 to about 1:15.
[0056] Scale and corrosion inhibitors that are useful in this
invention include, but are not limited to, phosphonates, such as
1-hydroxyethane-1,1,-diphosphonate, polymaleates, polyacrylates,
polymethyacrylates, polyphosphates, phosphate esters, soluble zinc
salts, nitrates, sulfites, benzoates, tannin, ligninsulfonates,
benzotriazole and mercaptobenzothiazole amines, imidazolines, and
quaternary ammonium compound resins.
[0057] An exemplary class of flocculants is polyacrylamide
dispersants. Anti-foaming agents include acetylinic diols,
silicones, and polyethoxylated derivatives thereof. Exemplary
biocides include tin compounds and isothiazolones.
[0058] The compositions of this invention may also comprise
non-surfactant biopenetrants, such as those described in U.S. Pat.
No. 4,778,813. Exemplary non-surfactant biopenetrants include
poly[hydroxyethylene(dimet-
hyliminio)ethylene(dimethyliminio)methylene dichloride],
poly[hydroxyethylene(dimethyliminio)-2-hydroxypropylene(dimethyliminio)me-
thylene dichloride], and
N-3-(dimethylammonio)propyl]-N-3-(ethyleneoxyethy-
lenedimethylammonio)propyl]urea dichloride.
[0059] An alternative class of non-surfactant biopenetrants are
hydrotropes, which, in concentrations of about 1% or higher,
increase the water solubility of sparingly or moderately soluble
solutes. Exemplary hydrotropes are water soluble glycol ethers,
such as diethylene glycol monomethyl ether. Other hydrotropes
include lower alkylaryl sulfonate salts of sodium, potassium,
ammonium.
[0060] When present in a composition of this invention, the
non-surfactant biopenetrant can be used in an amount of less than
about 50%, preferably less than about 20%, more preferably less
than about 10%, and most preferably less than about 5% (w/w) based
on the weight of a compound of Formula (I) or TRIS in the
composition.
[0061] The foregoing additives preferably are combined with
pre-formed compositions of this invention. For example, a compound
of Formula (I) or TRIS is combined with an amine or ammonium
derivative, as described above. Then one or more additives are
added to the resultant composition. The additives can be added as
pure compounds or as commercially available preparations thereof,
such as aqueous solutions.
[0062] The compositions of the present invention can be prepared in
advance and stored until needed. The compositions are moderately
sensitive to oxygen. Therefore, it is preferred but not essential
that the compositions be purged with and stored under an atmosphere
of an inert gas, such as dinitrogen. Alternatively, the
compositions simply may be stored under an atmosphere of an inert
gas or even in tightly closed and nearly full containers, to
minimize the volume of air in the container headspace.
[0063] Method of Decreasing Levels of Iron Sulfide
[0064] The methods of the present invention are highly effective in
solubilizing iron sulfide. This object is achieved by contacting a
conduit containing iron sulfide with a composition of this
invention to form a second composition, and then removing the
second composition from the conduit.
[0065] The methods are broadly applicable to conduits that are
contaminated or otherwise obstructed with iron sulfide deposits.
The conduits include any vessel that can carry water, gas, or other
fluids. Examples of conduits include but are not limited to
pipelines, valves, filters, filtering devices, tanks, storage
facilities. Conduits that are of particular relevance in the oil
and gas industries are pipelines, which can carry dry gas,
processed fluid, or both. Thus, a particular advantage of the
present invention in this context is that the pH of the
compositions introduced into the pipelines can be adjusted and
controlled, thereby effecting the easy manipulation, maintenance,
and removal of the compositions. The invention also contemplates
the treatment of water and aqueous systems, such as tank waters,
that are contaminated with iron sulfide. In this context, removal
of iron sulfide will decrease the tendency for obstruction of
filtering devices by iron sulfide, and thereby decrease the need
for the conventional strong mineral acid treatments which typically
result in the concomitant attack of iron pipes and other iron
containment systems.
[0066] The compositions of this invention can be introduced into
conduits by any means, or combination of means, necessary to bring
the compositions into contact with iron sulfide deposits. The
compositions can be introduced continuously or intermittently,
i.e., batch-wise, into operating gas or fluid pipelines, for
example. Alternatively, batch introduction is effective for offline
pipelines, which have been temporarily taken out of service for
cleaning. Industrial procedures include pigging, which is effective
for the treatment of pipelines. The compositions can even be
introduced into pipelines following the conventional pigging
procedure to remove residual iron sulfide. Additionally, the
compositions can be used in the ongoing treatment of such pipelines
to maintain low levels of iron sulfide.
[0067] While the use of any particular composition of this
invention is effective in removing iron sulfide from conduits, the
optimum molar ratio of phosphorus to iron for a given composition
is about 5:1. The optimum molar ratio can depend somewhat upon the
amine or ammonium derivative contained in the composition, and is
easily determined by routine experimentation. For example, a
phosphorus to iron ratio of 4:1 is particularly effective for
compositions of TRIS and ammonia, giving solutions that appear pink
to magenta, depending on concentration of complexed iron sulfide. A
phosphorus to iron ratio of 5.1:1 is most effective for
compositions of TRIS and methylamine, which typically yield iron
sulfide complexes ranging in color from salmon-orange to deep
orange-brown, depending on the concentration of complexed iron
sulfide. Molar ratios that deviate from an optimum ratio can be
readily employed, however, wherein complexation and dissolution of
iron sulfide will occur, albeit at slower rates. In any event, the
solutions of solubilized iron sulfide, once formed, increasingly
become pale yellow as the iron slowly oxidizes if exposed to air,
but nevertheless remain homogeneous.
[0068] The following examples are given to illustrate the present
invention. It should be understood, however, that the invention is
not to be limited to the specific conditions or details described
in these examples.
EXAMPLE 1
Composition Generated from Tetrakis(hydroxymethyl)phosphonium
sulfate (THPS) and Ammonium Chloride
[0069] A. Tetrakis(hydroxymethyl)phosphonium sulfate (THPS) is
obtained commercially as a 75-90 weight % aqueous solution with pH
that varies below 4. The following procedure yielded 1000 g of a 5%
aqueous composition able to complex iron sulfide. 66.6 grams of 75
weight % THPS (in water) and 0.5 grams ammonium chloride were
combined, diluted with 90 grams of water, and then mixed. A
sufficient amount of a 30% weight aqueous solution of sodium or
potassium hydroxide was added to raise the pH to about 6.5. The
total weight of the product was brought to 1000 grams by adding
water, whereupon the pH was remeasured. After dilution, pH can be
readjusted slightly, if necessary, to the desired value.
[0070] In this example, water can be replaced with methanol in
varying amounts to produce solutions with as little as 0% water and
as much as 95% water, depending upon the overall relative amounts
of THPS and water in the solutions. More concentrated compositions
can be prepared by simply limiting the amount of water or alcohol
used to dilute the reactant solution.
[0071] B. Commercial quantities of the composition were prepared by
following this procedure. Twenty-six (26) gallons of
tetrakis(hydroxymethyl)phosphonium sulfate as a 75% aqueous
solution were diluted to a total of nearly 380 gallons with
deionized water. The resultant acidic solution was adjusted to a pH
of 7.7 with 40% aqueous potassium hydroxide, and the volume was
brought to 390 gallons with deionized water. After mixing well,
ammonium chloride (0.47 lbs) was added and the resultant mixture
was thoroughly dissolved with stirring. The pH required
readjustment to pH 7.7 with a small amount of 40% aqueous potassium
hydroxide. The resultant composition was stored in nearly filled
sealed containers, under an optional blanket of dinitrogen.
EXAMPLE 2
Composition Generated from Tetrakis(hydroxymethyl)phosphonium
sulfate (THPS) and Methylamine
[0072] Following the procedure in Example 1, a 5% by weight
composition was prepared by 1) combining 6.66 g of
tetrakis(hydroxymethyl)phosphonium sulfate in the form of its 75%
aqueous solution by weight with enough water to make 90 mL of
solution, 2) adding concentrated (12M aqueous KOH) caustic to form
TRIS (95% conversion) at a pH of 7.7, 3) diluting with water to 100
mL, 4) adding 0.263 grams of methylamine, and 5) mixing. The mole
ratio of TRIS to amine in this mixture is 2.6:1.
EXAMPLE 3
Determination of Optimum Ratio of Reactants to Iron
[0073] The following determinations demonstrate how the relative
molar amounts of TRIS and an amine source affect optimum iron (II)
complexation. In these determinations, iron (II) sulfate
heptahydrate, a water soluble-iron (II) compound, was selected as a
convenient standard iron source. TRIS was generated using the
general procedures set forth in Examples 1 and 2.
[0074] The complex formed from TRIS, ammonia, and iron (II)
exhibits an absorbance maximum in the vicinity of 490 nm. To find
the optimum ratio of reactants, the absorbances of various
compositions of the complexing components were measured. The
optimal molar ratio of the components [TRIS, ammonia, iron (II)]
was observed to be 20:8:5.
[0075] A similar trial using methylamine gave a complex with an
absorption maximum at 473 nm, and an optimal ratio (in moles) of
26:10:5 for [TRIS, methylamine, iron (II)].
EXAMPLE 4
Complexation of Insoluble Iron Sulfide
[0076] Iron (II) sulfide was precipitated from aqueous solution by
combining a soluble iron (II) compound and a soluble sulfide in
equimolar proportions in sufficient amounts as to exceed the
solubility of iron (II) sulfide. In this example, the combination
of 1.65 mL of an 0.172M solution of iron (II) sulfate heptahydrate
and 1.65 mL of an 0.172M solution of sodium sulfide nonahydrate in
a solution with total volume of 50.0 mL resulted in the
precipitation of 25 mg black iron (II) sulfide, or a dispersion of
about 500 mg iron (II) sulfide per liter of solution.
[0077] A. Complexation of Iron Sulfide in a Dispersion
[0078] 20 mL of the 5% by weight aqueous composition prepared in
Example 2 was agitated with 25 mg iron sulfide in a total of 50 mL
water. The ratio of TRIS:methylamine was calculated to be 26:10.
The iron (II) sulfide dissolved at 22.degree. C. at an initial rate
of about 1800 ppm/hr to about 33 ppm/hr when either the composition
or iron sulfide became depleted.
[0079] Alternatively, 20 mL of the aqueous composition of Example 1
was agitated with the iron sulfide dispersion. Within 30 minutes,
all of the iron sulfide had been dissolved, as confirmed by a
steady increase in the solution absorbance at about 500 nm.
[0080] B. Complexation of an Iron Sulfide Deposit on a Filter
[0081] The iron (II) sulfide dispersion prepared as above was
filtered onto a cloth filter by suction. The cloth with entrained
iron sulfide was placed into contact with 50 mL of 0.1 molar
citrate buffer in water at pH 5 and 20 mL of the composition of
Example 1, and shaken. The cloth filter was rendered completely
free of precipitate in less than 20 hours, during which the
absorbance of the surrounding solution at 500 nm increased.
EXAMPLE 5
pH Dependence of Forming Compositions that Complex Iron (II)
[0082] This example shows that the compositions and methods of the
present invention that employ tetrakis(hydroxymethyl)phosphonium
sulfate (THPS) are pH-dependent.
[0083] For each entry in the following table, a stock solution
containing FeSO.sub.4 (0.015M), NH.sub.4.sup.+ (0.030M), THPS
(0.06M) and phosphate buffer (0.1M) were used at 22.degree. C.
Initial solutions are essentially colorless. The 0.1M phosphate
buffer was used to stabilize the pH at which each trial was
performed.
1 TABLE 1 Time (h) to reach Absorbance pH of 1.0 at 500 nm 1.2
(unbuffered) too slow to be detected 2.68 buffered 26 2.82 buffered
12.5 2.97 buffered 3.5 4.54 buffered 0.5 4.96 buffered 0.01
[0084] The results show that iron sulfide complexation occurs much
more rapidly for compositions prepared from THPS at increasing pH.
At pH values above 5, complexation rates continue to accelerate,
and at pH 7.5, for example, full complexation is complete within a
few seconds.
EXAMPLE 6
Pig Pill Batch Procedure
[0085] This example shows how a pipeline containing iron sulfide
deposits can be cleaned using a composition and method of this
invention.
[0086] A pig is launched into a pipeline and set at a known
location in the pipeline. A sufficient amount of the aqueous
composition prepared as in Example 1 is injected into the line. A
second pig is launched to form a column of fluid between the two
pigs that will cover the entire circumference of the pipeline wall.
The pig pill is launched moving at six miles per hour depending on
the control of pressure used to move the pigs. A third pig with a
carrier fluid can be launched for additional cleanup of any loose
particulate left behind. Samples can be taken at the pig receiver
to evaluate if additional pigging is necessary.
EXAMPLE 7
Non-Pigging Procedure
[0087] This procedure may be necessary for pipelines with
particularly severe iron sulfide buildup or if a pipeline is not
equipped with pig receivers and launchers. Some type of separation
or holding vessels may be necessary up the line. An aqueous
composition of this invention is injected into the pipeline on a
continuous basis upstream of the iron buildup. Flow rate and
pressure are monitored, and samples are taken when possible. The
iron sulfide deposits are removed through the continuous flow of
the composition through the pipeline.
EXAMPLE 8
Batch and Pig Procedure
[0088] The aqueous composition of Example 1 is introduced
batch-wise into a pipeline via gravity feed or injection depending
upon the internal pressure of the pipeline. A pig is then launched
following the batch treatment with the aqueous composition to move
the solution along the line. For best results, the pig should be
moved at six miles per hour. Samples can be taken at the pig
receiver to evaluate if additional pigging is necessary. All
volumes of composition used are based on length, inside diameter of
the pipe, and the severity of dust, slug, or buildup in the
pipeline. The pig type can be chosen based on the severity of the
buildup in the line.
[0089] Although the present invention has been described and
illustrated with respect to preferred embodiments and a preferred
use thereof, it is not to be so limited since modifications and
changes can be made therein which are within the full scope of the
invention as set forth in the appended claims.
* * * * *