Note: Descriptions are shown in the official language in which they were submitted.
CA 02827471 2015-04-07
ANTI-AGGLOMERATE GAS HYDRATE INHIBITORS FOR USE IN PETROLEUM
AND NATURAL GAS SYSTEMS
BACKGROUND
[0001] The systems and methods described herein pertain to the production of
petroleum products and natural gas, and particularly to compositions effective
as anti-
agglomerate low dosage gas hydrate inhibitors ("LDHI's") for the prevention of
gas hydrate
plugs.
[0002] Gas hydrates are solids that may form during hydrocarbon production, in
particular in pipelines and other equipment, that may impede or completely
block flow of
hydrocarbons. These blockages not only decrease or stop production,
potentially costing millions
of dollars in lost production, but are also very difficult and dangerous to
mediate. Unless properly
handled, gas hydrates may explode, rupturing pipelines, damaging equipment,
endangering
workers and putting at risk the ocean environment.
[0003] Gas hydrates may form when water molecules become bonded together after
coming into contact with certain "guest" gas molecules. Hydrogen bonding
causes the water
molecules to form a regular lattice structure that is stabilized by the guest
gas molecules. The
resulting crystalline structure precipitates as a solid gas hydrate. Guest
molecules can include any
number of molecules, including carbon dioxide, methane, butane, propane,
hydrogen, helium,
freons, halogens, and noble gases.
[0004] Thermodynamic, anti-agglomerate, and kinetic inhibitors are three
general
classes of hydrate inhibitors. Thermodynamic inhibitors are most commonly
used.
Thermodynamic inhibitors, such as methanol and ethylene glycol must typically
be used at high
concentrations to be effective, concentrations that may present environmental
concerns. For
instance, methanol is used in concentrations of up to 50% methanol to water
ratio, with glycol as
much as 30% glycol to water. Methanol presents other challenges, as it is
flammable and can be
corrosive. Thus, thermodynamic inhibitors are often not appropriate for many
drilling operations,
particularly environmentally-sensitive drilling operations.
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[0005] Kinetic inhibitors and anti-agglomerate inhibitors typically function
at lower
concentrations than thermodynamic inhibitors and are therefore termed LDHI's.
Kinetic hydrate
inhibitors are polymers that may prevent or delay the nucleation of hydrates.
Thus the kinetic
hydrate inhibitors limit hydrate crystal size and growth such that hydrate
plugs are not allowed to
form in tubular goods. However, kinetic hydrate inhibitors are capable of
handling only low-to
moderate subcooling ¨ typically subcooling of about 10 - 25 F (subcooling is
the difference
between the operating temperature of the hydrocarbon system and the
temperature at which
hydrates would form at the same operating pressure). Thus, kinetic hydrate
inhibitors may not be
suitable in deep and ultra-deep wells, where subcooling may be greater than 30
F.
[0006] Anti-agglomerate gas inhibitors are typically more cost effective than
thermodynamic inhibitors, as they may be used in much lower concentrations and
are typically
useful in environments with greater subcooling than would be appropriate for
kinetic inhibitors.
However, many of the traditional anti-agglomerate LDHI's contain residual
halides, such as HC1,
HBr, and the like, and residual organic halides. Residual halides have been
know to cause
corrosion and stress corrosion cracking ("SCC") in metal piping and production
equipment. One
example of a commonly used anti-agglomerate LDHI is quaternary anti-
agglomerates containing
residual organic halides, such as Kelland, 2006. As an example, Milburn et al.
U.S. Patent No.
6,444,852 entitled "Amines Useful in Inhibiting Gas Hydrate Formation",
describes anti-
agglomerate ether-containing amine compounds that are quaternized with a
halide. Especially in
the case of organic halides, they can be very toxic and environmentally
unfriendly. This is
particularly true when the inhibitors are applied continuously. In addition,
traditional anti-
agglomerate LDHI's may break down and become less effective when exposed to
high
temperatures above 250 F.
[0007] What is needed is an anti-agglomerate LDHI that does not contain
residual
halides in sufficient quantities to present an inappropriate risk of corrosion
or stress cracking and
that is less toxic and more environmentally friendly than the traditional
LDHI's.
SUMMARY
[0008] The present disclosure relates generally to the field of gas and oil
production.
Other uses may also be made of same. In particular, compositions and methods
for inhibiting the
formation of gas hydrate plugs are described.
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[0009] Compositions are described which are anti-agglomerate low dosage
hydrate
inhibitors ("AA-LDHI"s) that are made without the use of organic chlorides or
halides to
minimize residual organic halides other resultant inorganic halides that are
respectively highly
toxic and corrosive. Examples of such halides include HF, HO, HBr, HI, and the
like. These
new AA-LDHI's can be injected continuously without concern for high corrosion
rates or stress
corrosion cracking of injection equipment and production metal goods caused by
residual halides
such as HC1, HBr, and the like. While the compositions are structurally
similar to quaternary
amines, they are reaction products of organic acids and organic amines that
eliminate or
substantially reduce residual inorganic or organic halides (MX), and/or
residual hydrogen halides
(HC1, HBr, HI, and the like). Inorganic halides (MX), and/or residual HX are
often created as
byproducts when quaternary salts are produced using chlorinated or halogenated
alkylating
agents. These agents typically include benzyl chloride, bromide, iodide, or
the like, of the
structure R-X wherein R is any organic structure. This byproduct formation is
due to their
reaction with water either during or after the reaction. In the current
compositions, instead of a
halide anion being associated with the quaternary ammonium cation, an organic
acid anion is
present. This is a significant difference that distinguishes the described
compositions from other
anti-agglomerate compounds. In some preferred embodiments, the anti-
agglomerate low dosage
hydrate inhibitors are mixtures of organic reaction products of organic acids
and organic amines,
including but not limited to those including fatty acids and fatty amines.
[0010] The described compositions effectively inhibit the formation of gas
hydrates in
petroleum and natural gas production systems without the negative effects
associated with
residual chlorides or other halides, such as high corrosion rates, stress
cracking, and potential
high toxicity.
BRIEF DESCRIPTION OF DRAWINGS
[0011] Figure 1 shows a general structure of a quaternary ammonium salt having
a
chloride or other halide anion, wherein le, R2, le, and R4 are generally and
independently H or
C1-C40, and X is generally F, Cl, Br, I, other halides, or similar suitable
substituents.
[0012] Figure 2 shows general structures (a) and (b) of organic reaction
products of
organic acids and organic amines having an organic anion, wherein R', R2, and
R3 are
independently H or C1-C40, including all alkyl and aryl structures and
isomers, and wherein R4
is C1-C40, including all alkyl and aryl structures and isomers.
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[0013] Figure 3 shows a preferred embodiment of a general structure of the
reaction
product of a coconut oil based amine and a fatty coconut oil based acid,
wherein ri is 8-12.
[0014] Figure 4 shows the results of a comparison of the effectiveness of four
anti-
agglomerate compositions based on rating criteria.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0015] The current anti-agglomerate compositions include mixtures of reaction
products
of non-halide-containing inorganic acids and/or organic acids with organic
amines. The reaction
products are structurally similar to other quaternary amine halide analogs,
but the reaction
products lack acid halides, inorganic halides, and organic halides. Certain
embodiments include
mixtures of reaction products of organic acids and organic amines, including
an anti-agglomerate
low dosage hydrate inhibitor that is free of acid halides, inorganic halides,
and organic halides
and that can be injected continuously with minimized concern for corrosion,
stress corrosion
cracking, or highly toxic reactants or reaction products.
[0016] Figure 1 shows a traditional example of a quaternary ammonium salt
utilizing a
halide as an anion. The quaternary ammonium cation is that portion of the
molecule that has a
positive charge, NRIR2R3R4+. The term quaternary amine is often used to refer
to the positively
charged quaternary ammonium compound. In a quaternary ammonium cation, Ri, R2,
RI, and R4
can be any number of suitable constituents, including hydrogen (H), methyl
(CH3), ethyl
(CH2CH3), acetyl (COCH3), other alkyl or aryl groups of varying lengths and
structures, and
others. Some of the R constituents may also be connected to each other. Those
of skill in the art
with the benefit of this disclosure will understand the varying natures of the
R constituents.
[0017] In the reaction or manufacturing processes to form quaternary ammonium
halides for use as AA-LDHIs, it is common to form hydrogen halides and organic
alcohols due to
residual water present during and left over in the reaction mixtures. This is
due to the reaction of
R-X with HOH (H20) to form ROH and HX. This is generally due to having to use
an excess of
RX to drive the reaction. In some cases as much as 1% of the RX (e.g. benzyl
chloride and the
like) is found in the final reaction mixture that eventually converts to HX
(HC1 and the like) and
ROH and mixtures thereof. In some cases it has been found that acid corrosion
inhibitors are
required to mitigate the acid corrosion caused by the residual HC1. In
addition, the residual RX
can prove to have some severe acute and chronic toxicity.
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[0018] In one embodiment of the present disclosure, the anti-agglomerate LDHI
is the
reaction products of organic acid and organic amines. Reaction products of
organic acids and
organic amines are formed when certain organic acids are partially
neutralized, giving them at
least a partial negative charge that enables them to serve as anions in a
salt. Figure 2 shows some
general examples of reaction products or organic acids and organic amines
having the structure
R1R2R3HN v(R4C00) or RIR2R3FIN+(R4Ph0), wherein R1, R2, and R3 are
independently H or
C1-C40, wherein R4 is C1-C40, and wherein Ph is any phenyl group. The
substituents C1-C40
include all alkyl and aryl structures and isomers within these embodiments. In
these examples,
the negatively charged anions are anions created by partial or complete
neutralization of acids.
Certain embodiments can include reactions or mixtures that include varying
ratios of the organic
acid, organic amine, and the resulting salt of the reaction of the organic
acid and amine. In
certain embodiments of the present disclosure, approximately stoichiometric
amounts of the
organic acid and amine are used to create the resultant salt. In other
embodiments of the present
invention, molar ratios of the reactants are adjusted so as to create a
surplus of free organic amine
in the resultant reaction product. Typically, the excess amine is less than
about 1% (by mol) of
the reaction product.
[0019] The compounds that can be used as cations with the desired acid anions
can be
any suitable non-halide-containing amines. As discussed with regard to Figure
1, RI, R2, and R3,
can be any suitable substituents, including hydrogen (H), methyl (CH3), ethyl
(CF2CH3), acetyl
(COCH3), and other alkyl or aryl groups of varying lengths. Some of the R
substituents may also
be connected to each other and can include oxygen, nitrogen, and the like.
Those of skill in the
art with the benefit of this disclosure will understand the varying natures of
the R substituents
within the cation. Examples of suitable cations include, but are not limited
to ammonia,
methylamine, di methylamine, tri methylamine, ethylamine, di ethylamine, tri
ethylamine, n-
propylamine, di-n-proplyamine, tri-n-propylamine, monoethanolamine, di
ethanolamine, diethyl
ethanaol amine, methyl ethanol amine, tri ethanol amine, methyl diethanol
amine, propyl
ethanolamine, ethyl diethanol amine, di methyl amino propyl amine, di propyl
ethanol amine, di-
n-butyl amine, di butyl propanol amine, dibutyl ethanolamine, morpholine,
piperazine, octyl
amine, dimethyl octyl amine, decyl amine, di methyl decyl amine, lauryl amine,
dimethyl
laurylamine, myristyl amine, dimethyl palmityl amine, stearyl amine, di methyl
stearyl amine, di-
stearyl amine, N,N dibutyl coco amido propylamine, N,N dimethyl coco amido
propylamine
cocoamine, cocodiamine, dimethyl cocoamine, tallowamine, tallow di amine, di
methyl tallow
amine, soya amine, dimethyl soya amine, di dodecyl mono methylamine, fatty
imidazolines, fatty
amido-amines, fatty amines, and mixtures thereof
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[0020] The compounds that can be used as anions with the cations discussed
above can
also be any suitable non-halide-containing acids. As discussed with regard to
Figure 1, R4 can be
any suitable constituents, including hydrogen (H), methyl (CH3), ethyl
(CH2CH3), acetyl
(COCH3), and other alkyl or aryl groups of varying lengths, and can include
oxygen, nitrogen,
and the like. Examples of suitable anions include formic acid, acetic acid,
lactic acid, cyanuric
acid, angelic acid, propionic acid, butyric acid, aspartic acid, glycolic
acid, adipic acid, maleic
acid, citric acid, phthalic acid, anthranilic acid, octanoic acid, lauric
acid, benzoic acid, salicylic
acid, fumaric acid, oxalic acid, succinic acid, acrylic acid, cinnamic acid,
azelaic acid,
neodecanoic acid, benzilic acid, pelargonic acid, stearic acid, dimer acid,
trimer acid, varying
ratios of dimer-trimer acid blends, methane sulfonic acid, dodecyl benzene
sulfonic acid, para-
tolunene sulfonic acid, oleic acid, tall oil fatty acid, linoleic acid,
abietic acid, rosin acid,
napthenic acid, carboxylic acids and anhydrides thereof, phenols, sulfonic
acids, sulfuric acid,
phosphoric acid, nitric acid or mixtures thereof. Those of skill in the art
with the benefit of this
disclosure will understand the varying natures of the R constituent within the
anion.
[0021] As those of skill in the art with the benefit of the present disclosure
will
appreciate, certain salts made in accordance with the present disclosure will
have superior
performance characteristics to other salts. As described in U.S. Patent No.
5,460,728 to Klomp et
al., compounds suitable for use as AA-LDHI's will have at least some of the
following
characteristics:
Inhibit hydrate crystal growth;
Emulsify into the hydrocarbon phase, thereby keeping the concentration of
water available for hydrate forming at the conduit wall small;
Concentrate near the water-hydrocarbon interfaces, where hydrate
formation is most pronounced, thereby raising the local concentration of ions
to
freezing-point depressing level;
Modify the structure of water near the hydrocarbon-water interface in such
a way that the formation of hydrate crystals is hindered;
Impeded further access of water molecules to the hydrate crystal after
attachment of the subject compound to the hydrate crystals;
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Prevent agglomeration of hydrate crystals by making their surface
hydrophobic;
Adhere to the conduit wall, thereby preventing the adhesion of hydrates
thereto.
[0022] Examples of salts that meet one or more criteria above include the
reaction
product of a 1:1 molar ratio of benzoic acid and dimethyl palmitoyl amine, a
2:1 molar ratio of
phthalic anhydride and cocodiamine, and a 2:1 molar ratio of salicylic acid
and cocodiamine.
[0023] Certain reaction products of organic acids and organic amines derived
from
coconut oil have the structure [CH3(CH2),(CH3)2HN+][CH3(CH2),C00-]. Figure 3
shows a
general representation of these possible reaction products of a coconut oil
based amine and acid
in which n can be varied from, for example, 8 to 12. This is an exemplary
embodiment that in no
way limits the scope of the anti-agglomerate compositions overall.
[0024] Reaction products of organic acids and organic amines are more
advantageous
than traditional AA-LDHIs made from alkyl or aryl halides in several respects.
In the reaction or
manufacturing processes to form quaternary ammonium halides for use as AA-
LDHIs it is
common to form hydrogen halides and organic alcohols due to residual water
present during and
left over in the reaction mixtures. The reactants and reaction products in the
current AA-LDHI
compositions are not as corrosive as the likes of HC1 or HX, do not cause
halide stress cracking,
and are not as toxic. Because of these advantages, the anti-agglomerate
compositions can be
injected continuously into petroleum and natural gas systems. Methods of
continuous injection
include via umbilical or cap string. Batch applications are also suitable. The
anti-agglomerate
compositions can be applied at a concentration of about 0.05% to about 10%,
and preferably at
about 0.2% to about 1.5%.
[0025] Without wanting to be bound by theory, anti-agglomerate compositions
comprised of mixtures of reaction products of organic acids and organic amines
work by helping
to emulsify water in oil. It is generally agreed that anti-agglomerate LDHI
molecules need
hydrocarbon to function and tend to emulsify water as an internal emulsion
phase. This limits the
growth and size of hydrate crystals to a form and size that does not allow the
hydrates formed to
plug production equipment.
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[0026] The current anti-agglomerate compositions have distinct advantages over
those
anti-agglomerate compositions already commercially available, as all of these
compositions
contain residual chlorides. One advantage is the difference in corrosivity,
which stems from the
basic differences in corrosivity between inorganic acids such as HX or HC1 and
that of organic
acids. The pKa associated with HX is much less than that associated with COOH.
The current
AA-LDHIs potentially resolve long term corrosion issues present with chlorides
or HC I that are
formed or are inherent in the quat type products typically used where
continuous anti-
agglomerate injection is required. Chloride stress corrosion cracking or
hydrogen penetration is
accelerated by the trace I IC I formed in the reaction of R-Cl/R-X in quat
manufacturing that has
proven to be an issue in continuous versus batch use of quat based AA-LDHI.
Testing has shown
that the current anti-agglomerate compositions are equal to if not superior to
the industry
standard in performance. In addition, the current, non-quat anti-agglomerate
compositions have
greater oil solubility for reduction of water quality issues. This leads to
increased "greenness" or
environmental compatibility by partitioning more to the oil phase. The current
compositions also
lack certain inherent chronic or carcinogenic toxicity characteristics
associated with residual RC I,
RX, and other organic chloride or halide found in traditional AA-LDHls,
including vinyl chloride,
benzyl chloride, alkyl bromides, and the like.
[0027] Further, AA-LDHIs made in accordance with the present disclosure have
better
stability at higher temperatures than traditional AA-LDHIs. In certain
applications, it may be
necessary for the AA-LDHI to be subjected to temperatures in excess of 250 F.
Certain
traditional AA-LDHIs, such as those made from quatenary amines, are known to
degrade at
higher temperatures, resulting in a reduction of efficiency in controlling
hydrates. Those AA-
LDHIs made in accordance with the present disclosure retain efficacy after
exposure to
temperatures in excess of 250 F.
[0028] In addition, unlike traditional AA-LDHls, AA-LDHs made in accordance
with
the present disclosure, function as corrosion inhibitors. Corrosion in the
production from oil and
gas often is often as a result of the presence of water in the production
equipment, either
produced from the formation, from condensation, or from water injected into
the well, for
instance, for lift assist. Hydrogen sulfide (H2S) and carbon dioxide (CO2) are
often present in
produced fluids, which can, in the presence of water, form acids such as
sulfuric and carbonic
acids (respectively). Oxygen, when present, may also contribute to corrosivity
and is sometimes
a contaminant in the water used for injection.
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[0029] The AA-LDHIs of the present disclosure may, in addition to serving as
AA
LDHIs, may function as corrosion inhibitors by contacting and coating the
exposed metal of the
oil and gas production equipment and piping. The exposed metal, after being
coated, by the
corrosion inhibitor, prevents subsequent corrosion of the surface by the
corrosive agents in the
hydrocarbon stream.
[0030] Corrosion inhibitors are normally delivered to through an umbilical to
the oil and
gas production equipment and piping. The additional use of the AA-LDHIs of the
present
disclosure as corrosion inhibitors has the benefit of both reducing costs to
the driller by
eliminating an additional on-site chemical, but also by eliminating the
umbilical used to deliver
the traditional corrosion inhibitor.
EXAMPLE 1
[0031] Four AA-LDHIs made in accordance with the present disclosure were
tested and
compared to determine their effectiveness to prevent formation of hydrate
crystals in gas
production systems. The four AA-LDHIs tested were benzoic acid/dimethyl
palmitoyl amine
mixed in a 1:1 molar ratio, maleic anhydride/dimethyl palmitoyl amine mixed in
a 1:1 molar
ratio, methanesulfonic acid/cocodiamine mixed in a 2:1 molar ratio, phthalic
anhydride/cocodiamine mixed in a 2:1 molar ratio, and salicylic
acid/cocodiamine mixed in a 2:1
molar ratio. A rocking cell test was performed on each of the four AA-LDHIs.
[0032] The AA-LDHIs were tested in a bank of high pressure rocking cells. Each
cell is
outfitted with clear sapphire tubes housed and sealed in a Hastelloy body. The
sapphire tubes
allow for visual observation of the pressurized, cooled fluids inside the
cell. The cells were
isolated from each other and were equipped with pressure transducers and
proximity sensors. A
magnetic ball provided agitation as the cells are rocked back and forth at a
predetermined angle
and rate. The cells were submerged in a temperature controlled bath consisting
of glycol and
water.
[0033] The temperature and rocking was pre-programmed and automated. Each cell
was
pressurized independently and the pressure in monitored and recorded, along
with the
temperature data and signals from the proximity sensors.
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[0034] The Four AA-LDHIs were tested under conditions which simulate a typical
offshore pipeline in the Gulf of Mexico (GOM). Steady-state, shut-in and re-
start processes were
replicated. Test fluids (hydrocarbons and gas) were representative GOM are
shown in Table I.
Table 1. Test Fluids
Hydrocarbon: Light GOM condensate
Aqueous: 3.5% NaC1 brine
Structure II hydrate forming
Gas: composition
The gas composition was similar to GOM Green Canyon, a structure II hydrate
former:
Table 2. Type II Gas Composition
Component mol-%
Nitrogen 0.39%
Methane 87.26%
Ethane 7.57%
Propane 3.10%
iso-Butane 0.49%
n-Butane 0.79%
iso-Pentane 0.20%
n-Pentane 0.20%
CA 02827471 2015-04-07
[0035] Tests were all conducted at constant volume. Inhibitor concentration
varied from
1-5 vol-% based upon the total amount of water. The cells were initially
pressurized at 20 C to
2200 psig. Rocking was initialized at 15 rocks/min and an angle of 25 off
horizontal. At
constant temperature of 20 C the cells were rocked for 2 hours to mix the
fluids and allow for the
gas to saturate the fluids. The temperature was then ramped down continuously
to 4 C over a
period of 2 hours while rocking.
[0036] After reaching 4 C, the cells were rocked for 12 hours at which time
they were
"shut-in". This phase consists of stopping the rocking with the cells in a
horizontal position,
simulating a pipeline shut-in. At the end of the shut-in period, rocking was
re-started and the
cells rocked for 2 hours. This was followed by a temperature ramp from 4 C to
20 C over a 2
hour period. Finally the cells were rocked at 20 C for 2 hours. The final
pressure was observed in
order to insure the cells did not leak.
[0037] The performance of the chemicals was graded according to the following
scale:
1. Stuck ball, low liquid level, large agglomerations or solid crystals,
visible
deposits on tube
2. Ball is free but resists rolling, moderate to little change in liquid
level, large solid
crystals, agglomerations that break up with agitation, no visible deposits on
tube
3. Ball is free, no change in liquid level, viscous liquid, small
dispersible
agglomerations or crystals, no visible deposits on tube.
4. Ball is
free, no change in liquid level, low viscosity, fine easily dispersed
crystals, no large crystals
5.
Ball is free, no change in liquid level, little to no change in viscosity, no
visible
deposits on tube or cylinder, extremely fine easily dispersible crystals.
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[0038] Figure 4 shows the results of the performance ranking.
Hydrate Inhibitor Rank
1:1 benzoic acid/dimethyl palm itoyl amine 5
1:1 maleic anhydride/dimethyl palmitoyl amine 1
2:1 methanesulfonic acid/cocodiamine 2
2:1 phthalic anhydride/cocodiamine 5
2:1 salicylic acid/cocodiamine 4
[0039] Although the invention has been described with reference to specific
embodiments, this description is not meant to be constructed in a limited
sense. Various
modifications of the disclosed embodiments, as well as alternative embodiments
of the invention,
will become apparent to persons skilled in the art upon reference to the
description of the
invention. It is, therefore, contemplated that the appended claims will cover
such modifications
that fall within the scope of the invention, or their equivalents.
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REFERENCES CITED
Kelland, Malcom A. "History of the Development of Low Dosage Hydrate
Inhibitors."
Energy & Fuels, An American Chemical Society Journal, vol. 20, May/June 2006.
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