Note: Descriptions are shown in the official language in which they were submitted.
CA 02603022 2007-09-25
Y:\CE101\3310 CA\Spec & Claims\Amended Spec & Claims 070925.wpd
FORMULATION FOR HYDROGEN SULPHIDE SCAVENGING FROM
HYDROCARBON STREAMS AND USE THEREOF
FIELD
The present invention relates to a formulation comprising triethylene glycol
for the reduction
of hydrogen sulphide levels in hydrocarbon streams. Additionally, the present
invention
relates to a method for reducing hydrogen sulphide levels in hydrocarbon
streams while
alleviating solid dithiazine deposit buildup.
BACKGROUND
It is well known in the industry that hydrogen suiphide is a toxic gas that
poses a threat to
public health and safety. In addition there are serious environmental concerns
about the
combustion of fuels that contain hydrogen sulphide since sulfur dioxide is
formed upon
combustion of said fuels which if released into the atmosphere produce acid
rain. Currently,
many regulations exist regarding the upper limits of hydrogen sulphide in
various gas and
liquid hydrocarbon streams such as pipeline gas. Considerable expense and
efforts are
made annually to reduce or eliminate the levels of hydrogen sulphide in gas
and liquid
hydrocarbon streams for both safety and environmental reasons.
A large number of non-regenerative chemical formulations exist in the market
place for
removal of hydrogen sulphide. One important group of these chemical scavengers
is based
on aidehyde and amine reaction products, particularly triazines. Formulations
can consist
of low molecular weight aldehydes such as formaldehyde but can also consist of
ketones
and various adducts thereof. Amines used to produce triazines in
priorformulations include
alkylamines as disclosed in U.S. Pat. No. 5,674,377, alkanolamines as
disclosed in U.S.
Pat. No. 4,978,512 and in some cases a combination of amines can be used as
disclosed
in U.S. Pat. No. 5,347,004 and U.S. Pat. No. 5,554,349.
Scavengers based on aidehyde and amine reaction products such as that
disclosed in U.S.
Patent No. 4,978,512 have been shown to be effective at removing hydrogen
sulphide from
hydrocarbon streams in in-line injection systems, hydrogen sulphide scrubber
systems or
chemical solvent systems. If glycol is added to the formulation, water can
additionally be
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removed. Depending upon the amount of water present, the glycol content can be
as high
as 90%.
Despite the fact that US Patent No. 4,978,512 states that contacting a gas
stream with the
reaction products of formaldehyde and monoethanolamine provides a selective
and almost
instantaneous reaction with the sulphides present in the gas stream, producing
no
precipitate solids or deleterious environmental effects, it was found that
under field
conditions, serious problems arose with regard to formation of crystals. This
is because the
product of the reaction between the reaction product and hydrogen sulphide
produces
diathiazine. Under optimal conditions, such as those found in the laboratory,
a two phase
system is produced, with the dithiazine, methanol and reaction byproducts
forming one
liquid layer and water and various other components forming a second liquid
layer. In
temperatures of about 20 C or lower, under field conditions, solid dithiazine
crystals can
form in the dithiazine layer. These precipitate out of the layer, thus causing
plugging
problems in processing equipment, storage vessels, truck tanks or disposal
wells. As was
stated in US Patent 6,582,624, "It is believed that the presence of
contaminants in field
applications offers numerous nucleation sites to initiate and promote
crystaiiization."
The problems associated with crystalline dithiazine could be avoided by
substituting a minor
amount of monoethanolamine with diglycolamine as disclosed in Canadian Patent
No.
02333794. Again, a two phase system was produced after the reaction with
sufficient
quantities of hydrogen sulphide. The top layer consisted of an aqueous liquid
phase
containing water and other reaction components and impurities, while the
bottom layer
which primarily consisted of dithiazine, was in the form of a liquid at
operating temperatures
between about -5 C and 20 C. At temperatures below about -5 C, the layer
became an
amorphous solid.
More recently, methods for removal of hydrogen sulphide have been undertaken
at higher
temperatures. It was found that at temperatures above about 20 C and more
typically in the
range of 30 C and above, a new problem arose. The dithiazine layer, which had
remained
liquid at normal operating temperatures that were below about 20 C, became a
brownish,
amorphous solid at the higher temperatures. The amorphous solid formed after
exposure
to high temperatures leads to solid deposit buildup and equipment blockages.
As would be
known to one skilled in the art, one cause of this amorphous solid is a high
operating
temperature, and another, separate cause is a low operating temperature. The
low
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temperature leads to a coalescing of the crystals, much like ice crystals
forming a block of
ice.
The amorphous dithiazine solids are characterized by an amorphous and "mushy"
consistency. It is believed that a number of factors can contribute to the
formation o{-
dithiazine solids in the field including conditions that lower the solubility
of dithiazine in the
dithiazine/methanol layer, conditions that strip methanol from the dithiazine
layer and
overspending the scavenger solution.
The formation of amorphous dithiazine is extremely problematic since
substantial deposits
can form blockages in chemical storage tanks, bulk truck tanks, gas processing
equipmen;
and in produced water disposal wells. Clean up procedures are often time
consuming anc:~
requires equipment to be taken off-line or shut down. This makes cleaning up
solic
dithiazine deposits an expensive venture.
As an alternative approach, US Patent 7,078,005 discloses a process for the
reduction or
elimination of hydrogen sulphide that does not use triazine, and in fact,
teaches away from
the use of amines that result in triazines in the reaction products. The
hydrogen sulphide
scavenging formulation is derived by the reaction of a carbonyl group-
containing compounc'
with an alcohol, thiol, amide, thioamide, urea or thiourea. The carbonyl group-
containing
compound is preferably formaldehyde, and preferably the product is derivable
by reactior;
of formaldehyde with an amine-free alcohol or urea selected from ethylene
glycol, propylene
glycol, glycerol, diethylene glycol, triethylene glycol, ethyl alcohol, n-
butanol, a sugar, a low
molecular weight polyvinyl alcohol, castor oil fatty acid and urea. More
especially, the
scavenger product is used with an amine, especially monoethanolamine.
There remains a need for a formulation that is effective at removing hydrogen
sulphide from
gas and liquid hydrocarbon streams that avoids the problem of amorphous and
crystalline
dithiazine solid deposit buildup. It is an object of the present invention to
overcome the
deficiencies in the prior art.
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SUMMARY
The current invention provides a solution to the problem of dithiazine solid
deposit buildup
observed with triazine-based scavengers used for the removal of hydrogen
sulphide from
hydrocarbon streams. In an attempt to reduce the formation of the amorphous
solids that
build up at the higher operating temperatures (approximately 30 C),
triethylene glycol was
added initially to the reaction products of monoethanolamine, diglycolamine
and
formaldehyde. Aftercontacting the hydrocarbon stream, a spent productwas
produced that
consisted substantially of a single phase. Any amorphous dithiazine solids
that formed
where suspended in the single phase, and the remainder of the dithiazine was
in solution.
Further testing showed, surprisingly, that a scavenging formulation comprising
triethylene
glycol and the reaction products of monoethanolamine and formaldehyde produced
a spent
product that formed a substantially single phase, with the dithiazine either
in solution or
suspended in the phase and minimal crystalline dithiazine. Thus in accordance
with the
present invention, there is provided chemical formulation comprising
triethylene glycol and
the reaction products of monoethanolamine and formaldehyde, for the removal of
hydrogen
sulphide from hydrocarbon streams.
In one embodiment of the invention, a hydrogen sulphide and mercaptan
scavenging
formulation for reducing dithiazine solids is provided. The formulation
comprises triethylene
glycol and the reaction products of reacting a first amine and an aldehyde.
In another embodiment of the invention, a hydrogen sulphide and mercaptan
scavenging
formulation for reducing high temperature-induced dithiazine solids is
provided. The
formulation comprises triethylene glycol and the reaction products of reacting
a first amine
and an aldehyde.
In another embodiment of the invention, a hydrogen sulphide and mercaptan
scavenging
formulation for reducing dithiazine solids in high temperature applications is
provided. The
formulation comprises triethylene glycol and the reaction products of reacting
a first amine
and an aidehyde.
In another embodiment of the invention, a hydrogen sulphide and mercaptan
scavenging
formulation for reducing dithiazine solids and not for dehydrating hydrocarbon
streams is
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CA 02603022 2007-09-25
provided. The formulation comprises triethylene glycol and the reaction
products of reacting
a first amine and an aldehyde.
In one aspect of the invention, the first amine is monoethanolamine and the
aldehyde is
formaldehyde.
In another aspect of the invention, the weight of triethylene glycol is about
15% to about
95%.
In another aspect of the invention the weight of triethylene glycol is about
15% to about
50%.
In another aspect of the invention the weight of triethylene glycol is about
15% to about
25%.
In another aspect of the invention the reaction products comprises 2-[3,5-bis-
(2-hydroxy-
ethyl)-[1,3,5]triazinan-1-yi]-ethanol.
In another aspect of the invention, the formulation further comprises a second
amine.
In another aspect of the invention the second amine is diglycolamine.
In another embodiment of the invention, a scavenging formulation is provided
comprising
a mixture of triethylene glycol, and at least one triazine.
In another embodiment of the invention, a method for reducing the levels of
hydrogen
sulphide and mercaptans in hydrocarbon streams is provided. The method
comprises
contacting said streams with a formulation comprising triethylene glycol and
the reaction
products of reacting a first amine and an aldehyde, and reacting said reaction
products with
hydrogen sulphide is provided, thereby reducing the levels of hydrogen
sulphide,
mercaptans and solid dithiazine deposits.
In another embodiment of the invention, a method for reducing the levels of
hydrogen
sulphide and mercaptans in high temperature hydrocarbon streams is provided.
The
method comprises contacting said streams with a formulation comprising
triethylene glycol
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and the reaction products of reacting a first amine and an aldehyde, and
reacting said
reaction products with hydrogen sulphide, thereby reducing the levels of
hydrogen sulphide,
mercaptans and solid dithiazine deposits.
In one aspect of the method the first amine is monoethanolamine and the
aidehyde is
formaldehyde.
In another aspect of the method, the weight of triethylene glycol is about 15%
to about 95%.
In another aspect of the method, the weight of triethylene glycol is about 15%
to about 50%.
In another aspect of the method, the weight of triethylene glycol is about 15%
to about 25%.
In another aspect of the invention, the method further comprises reacting a
second amine
with the first amine and the aldehyde to produce the reaction product.
In another aspect of the method, the second amine is diglycolamine.
In another aspect of the method, the hydrocarbon stream is a gaseous or liquid
stream.
In another aspect of the method, the hydrocarbon stream is a sour natural gas
stream.
In another aspect of the method, the level of hydrogen sulphide is reduced to
a level of
about 16 ppm or less.
In another aspect of the method, the hydrogen sulphide level is reduced to
zero.
In another aspect of the method, the step of contacting reacts the formulation
with hydrogen
sulphide to form a spent formulation comprising a single phase.
In another aspect of the method, the step of contacting reacts the formulation
with hydrogen
sulphide to form a spent formulation comprising dithiazine.
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In another aspect of the method, the step of contacting reacts the formulation
with hydrogen
sulphide to form a spent formulation comprising dithiazine wherein the
dithiazine may be
either a suspended amorphous solid or dissolved in the single phase.
In another aspect of the method, the step of contacting reacts the formulation
with hydrogen
sulphide to form a spent formulation comprising dithiazine, wherein the
dithiazine deposits
are minimized or eliminated.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a graphical representation of the hydrogen sulphide scavenging
performance of
a triazine based scavenging formulation of the prior art.
Figure 2 is a graphical representation of the hydrogen sulphide scavenging
performance of
a scavenging formulation of the present invention which contains a 1:1 molar
ratio of total
amine to formaldehyde and 24% by weight of triethylene glycol.
Figure 3 is a graphical representation of the hydrogen sulphide scavenging
performance of
a scavenging formulation of the present invention which contains a 1:1.5 molar
ratio of total
amine to formaldehyde and 20% by weight of triethylene glycol.
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DESCRIPTION
Definitions
Mercaptans: Mercaptans are a group of sulphur containing organic compounds in
which the
sulphur has replaced an oxygen of a hydroxyl group in the corresponding
oxygenated
compound. For example, but not limited to, methyl mercaptan, in which the
oxygen in
methanol has been replaced, mercaptanol, in which one oxygen in ethanol has
been
replaced, and cyclohexyl mercaptan, in which the oxygen in cyclohexanol is
replaced.
Sulphides: Sulphides include HS-, which is variously called hydrogen sulphide
ion,
hydrosulphide ion, suifhydryl ion, or bisulphide ion, and H2S, hydrogen
sulphide.
Dithiazine solids: Dithiazine solids include amorphous solids and crystalline
dithiazine.
High temperature: High temperature in the present context is any temperature
above about
C, more specifically in the range of 30 C and above.
High temperature-induced dithiazine solids: High temperature-induced
dithiazine solids are
defined as amorphous solids and crystalline dithiazine produced at
temperatures above
20 about 20 C, more specifically in the range of 30 C and above
Detailed Description
The formulation of the present invention can be used to scavenge hydrogen
sulphide and
mercaptans from a variety of hydrocarbon streams, including liquid hydrocarbon
streams
and sour natural gas. The formulation can be contacted to hydrocarbon streams
by various
methods including but not limited to simple mixing, inline injection and with
a contact
scrubber tower. The scavenger formulation of the present invention can be used
to reduce
the levels of hydrogen sulphide to levels below 16 ppm and as low as 0 ppm.
The reaction of hydrogen sulphide with the scavenging formulation of the
present invention
produces a spent formulation characterized by a single liquid phase that does
not contain
crystalline dithiazine solids. Any dithiazine that results from the scavenging
solution reacting
with hydrogen sulphide will be suspended or dissolved in solution and solid
dithiazine
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deposit buildup will be minimized or eliminated. Examples of the embodiment of
the
invention are outline by Examples 2 to 9.
Example 1
As a reference sample, a solution was prepared from 56.2 wt% Formalin (37.5%
formaldehyde; 25% methanol), 41.6 wt% monoethanolamine, and 2.2 wt%
diglycolamine
was formulated. The molar ratio of total amines to formaldehyde was
approximately 1:1.
The scavenger solution was subjected to a hydrogen sulphide scavenging
capacity test
which was performed by passing a feed gas with a known hydrogen sulphide
concentration
at a known rate through a specified volume or mass of scavenger while the
outlet hydrogen
sulphide level was measured as a function of time. The test used 57.14 grams
of the
scavenger formulation maintained at 50 C during the duration of the test and
an inlet gas
comprised of approximately 18.4% hydrogen sulphide balanced with carbon
dioxide. These
conditions were used to strip methanol from the spent solution.
The results of this capacity test are presented in Figure #1 and shows that
breakthrough
occurred at 95 minutes. The breakthrough point was determined as the time
required for
the detection of H2S in the outlet stream. The capacity test was continued
beyond
breakthrough until the molar concentration of hydrogen sulphide in the outlet
gas reached
15.5% which is approximately 84% of the hydrogen sulphide content of the inlet
feed gas.
The spent solution at 20 C produced from the reaction of hydrogen sulphide
with the
scavenger solution had two distinct phases: a clear yellow liquid and an
amorphous
dithiazine solid deposited on the bottom of the reaction vessel. The
dithiazine solid was
characterized by a sticky and mushy consistency and it took considerable
effort to remove
the deposit from the reaction vessel.
Although the conditions used in the capacity test represent a worse case
scenario in terms
of "overspending" the scavenger solution since continuing to use a scavenging
solution until
well after breakthrough is not typical in the field, it clearly illustrates
the problem that can
arise from the deposition of amorphous dithiazine solids.
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Example 2
A scavenger solution was formulated from 41.9 wt% Formalin (37.5%
formaldehyde; 25%
methanol), 32.4 wt% monoethanolamine (MEA), 1.7 wt% diglycolamine (DGA) and 24
wt%
triethylene glycol (about 25 wt% triethylene glycol). The solution was blended
by adding the
formalin and triethylene glycol to the MEA/DGA mixture. The molar ratio of
total amines to
formaldehyde was approximately 1:1.
The scavenger solution was subjected to a hydrogen sulphide scavenging
capacity test.
70.53 grams of scavenger formulation was used with an inlet gas consisting of
approximately 18.6% hydrogen sulphide and 81.4% carbon dioxide. The
temperature was
maintained at 50 C throughout the duration of the test. The results of this
capacity test are
presented in Figure #2 and shows that breakthrough occurred at 95 minutes. The
breakthrough point was determined as the time required for the detection of
H2S in the outlet
stream. The capacity test was continued beyond breakthrough until the molar
concentration
of hydrogen sulphide in the outlet gas reached approximately 14.7% which is
approximately
80% of the hydrogen sulphide content of the inlet feed gas.
The heavily overspent solution which resulted from the scavenging capacity
test was an
opaque yellow single phase liquid at 20 C. The solution was thought to be
opaque due to
an over saturation of dithiazine in the spent solution.
The physical stability of the solution was first tested by allowing the
solution to sit for an
extended period of time (over a week) at approximately 20 C to observe
whether dithiazine
would settle out of the solution and form deposits on the bottom of the sample
container.
Interestingly, dithiazine did not settle out of the solution and no deposits
were formed, in
fact, the solution was so stable that it could be centrifuged at 3500 rpm for
30 minutes
without observing the formation of a dithiazine layer or deposit. The
stability of the solution
was also tested at low temperatures, a condition which is known to bring about
the formation
of dithiazine solids. A portion of the sample was placed in a scintillation
vial and cooled in
a fridge to a temperature of approximately 2 C. Visually, the solution
appeared the same
as that at 20 C but was slightly more viscous. The temperature of the
solution was then
lowered to approximately -30 C by placing the sample in the freezer for 72
hours. Although
the solution was noticeably more viscous at this temperature, the solution did
not freeze and
was considered "pump-able". Most importantly, even at these low temperatures,
a condition
which can cause the formation of amorphous deposits, dithiazine did not settle
out of
CA 02603022 2007-09-25
solution and did not form solid deposits. These results were a stark contrast
from those
described in Example 1 wherein solids were formed at a much higher temperature
(20 C).
Clearly, the results demonstrate the potential of the formulation disclosed in
the present
invention to alleviate solid amorphous dithiazine buildup.
Example 3
A scavenger solution was formulated from 51.4 wt% Formalin (37.5%
formaldehyde; 25%
methanol), 27.2 wt% monoethanolamine (MEA), 1.4 wt% diglycolamine (DGA) and 20
wt%
triethylene glycol. The molar ratio of total amines to formaldehyde was
approximately 1:1.5.
The scavenger formulation was subjected to a hydrogen sulphide scavenging
test. The test
used 57.14 grams of the scavengerformulation and an inlet gas comprised of
approximately
18.7% hydrogen sulphide balanced with carbon dioxide. The temperature was
maintained
at 50 C throughout the duration of the test. The results of this capacity
test are presented
in Figure #3 and shows that breakthrough occurred at 106 minutes. The capacity
test was
continued beyond breakthrough until the molar concentration of hydrogen
sulphide in the
outlet gas reached approximately 14.8%. The resulting spent solution can be
considered
heavily overspent similar to that outlined in Example 2.
The spent solution was an opaque, yellow, single layered liquid similar to
that observed in
Example 2. No solid dithiazine settied out of the solution upon allowing the
spent solution
to sit for 24 hours at 20 C. Nitrogen gas was then bubbled through the spent
solution at a
rate of 250 mL/minute for 24 hours in order to simulate a high gas velocity
which strips
methanol out of spent solution. A small quantity of dithiazine began to settle
out of the
solution; however, unlike other forms of dithiazine such as that described in
Example 1 or
that observed in the field, this dithiazine was dispersed back into the spent
solution by
gentle agitation. The dithiazine in the present spent solution was not sticky
or thick and was
considered to still be "pump-able" which represents a marked improvement over
the
reference sample.
Example 4
A scavenger solution was formulated from 51.4 wt% Formalin (37.5%
formaldehyde; 25%
methanol), 27.2 wt% monoethanolamine (MEA), 1.4 wt% diglycolamine (DGA) and
15%
wt% triethylene glycol. It was determined that this concentration of TEG was
approximately
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the minimum concentration needed to maintain the reacted chemical in a uniform
solution.
Example 5
The scavenger formulation disclosed in Example 3 was subjected to a scavenging
capacity
test using an inlet gas containing approximately 18% hydrogen sulphide and 82%
carbon
dioxide. The test was stopped after the level of hydrogen sulphide in the
outlet gas reached
approximately 1%. The spent solution produced by this test is more
representative of field
conditions relative to those outlined in Examples 2 and 3 since using a
scavenging solution
until well after breakthrough is not typically experienced in the field.
The capacity test produced a clear yellow single-phased spent solution. The
stability of said
solution was first tested by bubbling nitrogen through it at a rate of 250
mUminute for 72
hours. The spent solution turned slightly turbid over the course of the
experiment but no
solid dithiazine formed. This solution was then cooled to approximately -25 C
for an
extended period of time and although the solution did not freeze, the
viscosity increased
slightly and turned milky white. The change in appearance is thought to be due
to dithiazine
solids beginning to form in the solution; however, no dithiazine settled out
of solution and
no solid deposits were formed. This process was found to be completely
reversible since
the milky white characteristic appearance disappeared after the temperature
was increased
to 20 C.
Example 6
A scavenger solution was formulated from 51.4 wt% Formalin (37.5%
formaldehyde; 25%
methanol), 27.2 wt% monoethanolamine (MEA), 1.4 wt% diglycolamine (DGA) and
15%
wt% triethylene glycol. The scavenger formulation was field tested and shown
to be
effective in inhibiting formation of solid deposits.
Example 7
A scavenger solution was formulated from 51.4 wt% Formalin (37.5%
formaldehyde; 25%
methanol), 27.2 wt% monoethanolamine (MEA), 1.4 wt% diglycolamine (DGA) and
20wt%
triethylene glycol. The scavenger formulation was field tested and shown to be
effective in
inhibiting formation of solid deposits.
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Examale 8 Field Test Results
In a specific application in southern Alberta, the operating conditions were
consistent with
a hydrogen sulphide concentration of 1100 ppm, pressure of 620 kPag, operating
temperature of 45 to 50 C and a carbon dioxide rich stream with a flowrate of
4 to 5
MMscfd. The previous process involved partially filling a contact vessel with
a formulation
comprising of formalin (37.5 wt% formaldehyde) and amine (monoethanolamine and
2-(2-
aminoethoxy) ethanol blend). After 18 days of operation, the outlet hydrogen
sulphide
content exceeded the allowable limit and arrangements were made to change out
the
reacted liquid scavenger. In the process of trying to remove the reacted
product from the
vessel, it was observed that there was a significant amount of solid material
that was orange
and yellow in colour with the consistency of wet mud. Samples of the solid
material were
collected and identified through laboratory analysis as being predominantly
dithiazine; a
reaction by-product of triazine and hydrogen sulphide.
An upper manway on the contactor was opened after the vessel was drained of
all
pumpable liquid. The contactor was observed to contain a 2 to 4 inch layer of
solid
dithiazine on the walls of the vessel. In addition, a significant amount of
solid dithiazine was
observed to remain in the bottom section and on the inlet gas dispersion bars.
Arrangements were made to wash the contactor out with hot caustic, drain and
ventilate the
vessel, and then visually inspect the internals. Once this 24 hour process was
completed,
some solid dithiazine material remained in the vessel; particularly in the
bottom and on the
gas distributor. The remainder of the solid dithiazine was manually removed
from the
contactor.
Efforts were successfully made in the laboratory to duplicate the formation of
the analyzed
solid dithiazine by completing capacity tests under similar operating
conditions as the
processing plant. Initial tests were completed with products that were
formulated with
reduced formalin to amine ratios. Although a slight reduction in solids
formation was
observed with smaller formalin to amine ratios, a significant amount of a
"pasty" solid
(identified as dithiazine) continued to be formed. The second phase of the
evaluation was
to assess the effects of modifying the formulation with various additives to
improve the
solubility of the generated dithiazine. It was through these tests with
various additives that
the benefits of triethylene glycol were realized.
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A formulation comprising of an 80 wt% triazine blend (the reaction products of
95% MEA
and 5% DGA) and 20 by wt% triethylene glycol was manufactured and loaded into
the
contact vessel. The processing system operated for 3 weeks with the
triethylene glycol
enhanced product with no detection of newly formed dithiazine solids. The
processing
facility continues to operate with no formation of dithiazine solids;
recovered reaction
product is a low viscosity, pumpable liquid solution. With the triethylene
glycol enhanced
liquid scavenger formulation, this particular facility has attained a record
number of
operating days with no unscheduled down time. As would be known to one skilled
in the art,
the gas stream contained hydrogen sulphide. Accordingly, the formulation and
method is
effective in removing hydrogen sulphide from the gas stream and inhibiting the
formation of
dithiazine solids.
Example 9
To determine whether other glycols could act as a suitable co-solvent two
additional
scavenger formulations were subjected to a capacity test using an inlet gas
containing
approximately 18% hydrogen sulphide and 82% carbon dioxide. The capacity tests
were
stopped after the level of hydrogen sulphide in the outlet gas reached
approximately 4%.
The two formulations each consisted of a 1:1.5 molar ratio of amines to
formaldehyde, with
one formulation containing 15% ethylene glycol, and the second formulation
containing 20%
diethylene glycol (DEG). The spent solutions of both formulations produced
large quantities
of sticky dithiazine solids that were deposited on the walls of the vessel.
These results
indicate that amorphous dithiazine deposits cannot be controlled or prevented
by the
addition of ethylene glycol or diethylene glycol, suggesting that the effect
is specific to the
addition of triethylene glycol in approximately the quantities disclosed.
Example 10
A scavenger composition was formulated from 56.6% wt% Formalin
(37.5%formaidehyde;
10-15% methanol), 28.4% monoethanolamine (MEA) and 15% triethylene glycol. The
scavenger composition was subjected to a scavenging capacity test at 20 C
using an inlet
gas containing approximately 18.5% hydrogen sulfide and 81.5% carbon dioxide.
The test
was stopped after the level of hydrogen sulfide in the outlet gas reached
approximately 3%.
The spent solution consisted of a single phase and more importantly, neither
crystalline nor
amorphous dithiazine solids formed at 20 C. The spent solution was further
tested by
cooling the solution to -10 C and then -25 C for extended periods of time.
Although these
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CA 02603022 2007-09-25
are conditions that are known to promote the formation of dithiazine solids,
neither
crystalline nor amorphous dithiazine solids formed at these sub-zero
temperatures. These
results demonstrate that the alleviation of problems associated with
dithiazine solid deposit
buildup do not require the presence of a second amine but instead can be
attributed to the
presence of triethylene glycol in the triazine formulation. Accordingly, the
results indicate
that the range of triethylene glycol used in the presence of the reaction
products of
monoethanolamine, diglycolamine and formaldehyde would be equally as
applicable to the
formulation made without diglycolamine (about 15% to 25%).
In summary, it has been found that formulations containing monoethanolamine,
formaldehyde and triethylene glycol produce a spent product which consists of
a single
liquid phase. Any amorphous dithiazine solids which may or may not form will
be
suspended in solution and solid deposits on equipment which could lead to
blockages are
minimized or eliminated.
Without being bound to one particular theory, it is believed that spent
solutions of the
present invention consist of a single liquid phase for the reason that
triethylene glycol acts
as a co-solvent for water, methanol, dithiazine and the other reaction
byproducts. The spent
solution retains a single phase even after high temperature conditions since
the co-solvent
is nonvolatile and is not stripped out of the formulation. In situations when
the scavenger
solution is normally spent as in Example 4, the dithiazine remains dissolved
in the spent
formulation. However, as the temperature decreases the solubility of
dithiazine in the spent
formulation also decreases and amorphous dithiazine solids begin to form; this
is observed
as an increase in the turbidity of the solution. Alternately, in situations
where the scavenger
solution is heavily overspent, excess amorphous solids are formed from the
insoluble
dithiazine. It has been found that depending on the ratio of triethylene
glycol to total amines
and formaldehyde, the amorphous dithiazine solids can be kept as a suspension
which
subsequently eliminates solid dithiazine deposit buildup. In fact, the ratio
of triethylene
glycol to total amines and formaldehyde can be altered to produce different
desired effects
depending on the application.
The foregoing is a description of an embodiment of the invention. As would be
known to
one skilled in the art, variations are contemplated that do not alter the
scope of the
invention. For example, the percentage of triethylene glycol could be greater
than 24%, for
example, 30%, or 35%. The limiting factor is the cost of triethylene glycol
and at the present
CA 02603022 2007-09-25
time, a percentage above about 24% is considered to be uneconomical. Further,
it should
be understood that the amount of triethylene glycol will vary depending on the
application,
field conditions and desired effect, however, as would be known to one skilled
in the art, as
the triethylene glycol content is increased above a threshold the scavenging
capacity of the
formulation decreases thus less dithiazine is produced.
16
