Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PROCESS FOR REMOVING HYDROGEN SULFIDE IN CRUDE OIL
FIELD OF THE INVENTION
This invention relates generally to methods for removing hydrogen sulfide and
more particularly, to removing hydrogen sulfide from crude oil.
BACKGROUND OF THE INVENTION
Crude oil may contain hydrogen sulfide, which is highly corrosive in the
presence
of water and poisonous in very small concentrations. The risk of exposure to
hydrogen
sulfide from handling crude oil is a health and safety concern during storage,
transportation (shipping, truck or pipeline) and processing of the crude oil.
Hydrogen sulfide scavengers are used to remove hydrogen sulfide from the crude
oil. Typical hydrogen sulfide scavengers are triazines and aldehydes. However,
triazines
release amines into the liquid hydrocarbon media and residual triazines
thermally
decompose to release additional amines into the liquid hydrocarbon media and
may pose
additional health concerns. The free amines can form salts, which deposit on
the
processing equipment and cause corrosion. Aldehydes can have slower reaction
kinetics
and may have incomplete hydrogen sulfide scavenging.
What is needed is an improved scavenger for removing hydrogen sulfide from
crude oil.
BRIEF DESCRIPTION OF THE INVENTION
In one embodiment, a method for reducing the amount of hydrogen sulfide
present in crude oil includes adding a hydrogen sulfide scavenger composition
to the
crude oil to capture the hydrogen sulfide, migrating the captured sulfides to
an aqueous
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phase and removing the aqueous phase from the crude oil, wherein the hydrogen
sulfide
scavenger composition includes glyoxal and a quaternary ammonium salt.
The various embodiments provide an improved hydrogen scavenging process for
crude oil that quickly captures hydrogen sulfide and does not generate amine
byproducts.
DETAILED DESCRIPTION OF THE INVENTION
The singular forms "a," "an" and "the" include plural referents unless the
context
clearly dictates otherwise. The endpoints of all ranges reciting the same
characteristic are
independently combinable and inclusive of the recited endpoint. All references
are
incorporated herein by reference.
The modifier "about" used in connection with a quantity is inclusive of the
stated
value and has the meaning dictated by the context (e.g., includes the
tolerance ranges
associated with measurement of the particular quantity).
"Optional" or "optionally" means that the subsequently described event or
circumstance may or may not occur, or that the subsequently identified
material may or
may not be present, and that the description includes instances where the
event or
circumstance occurs or where the material is present, and instances where the
event or
circumstance does not occur or the material is not present.
In one embodiment, a method for reducing the amount of hydrogen sulfide
present in crude oil includes adding a hydrogen sulfide scavenger composition
to the
crude oil to capture the hydrogen sulfide, migrating the captured sulfides to
an aqueous
phase and removing the aqueous phase from the crude oil, wherein the hydrogen
sulfide
scavenger composition includes glyoxal and a quaternary ammonium salt.
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The crude oil may be any type of crude oil containing hydrogen sulfide. Any
amount of hydrogen sulfide in the crude oil may be reduced and the actual
amount of
residual hydrogen sulfide will vary depending on the starting amount. In one
embodiment, the hydrogen sulfide levels are reduced to 150 ppm by weight or
less, as
measured in the vapor phase, based on the weight of the crude oil. In another
embodiment, the hydrogen sulfide levels are reduced to 100 ppm by weight or
less, as
measured in the vapor phase, based on the weight of the crude oil. In another
embodiment, the hydrogen sulfide levels are reduced to 50 ppm by weight or
less, as
measured in the vapor phase, based on the weight of the crude oil. In another
embodiment, the hydrogen sulfide levels are reduced to 20 ppm by weight or
less, as
measured in the vapor phase, based on the weight of the crude oil.
The hydrogen sulfide scavenger composition is added to the crude oil in any
conventional manner. In one embodiment, the scavenger composition is injected
into the
crude oil by a conventional in-line injection system and may be injected at
any point in-
line suitable to allow the scavenger to mix with the crude oil, such as in a
pipeline or in a
tanker. The scavenger composition can be added to the crude oil in a
continuous manner
or can be added in one or more batch modes and repeated additions may be made.
The scavenger composition is added to the crude oil in any amount sufficient
to
reduce the levels of hydrogen sulfide in the crude oil. In one embodiment, the
scavenger
composition is added in an amount of from about 1 ppm to about 3000 ppm by
weight,
based on the weight of the crude oil. In another embodiment, the scavenger
composition
is added in an amount of from about 10 ppm by weight to about 2000 ppm by
weight,
based on the weight of the crude oil. In another embodiment, the scavenger
composition
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is added in an amount of from about 50 ppm by weight to about 1500 ppm by
weight,
based on the weight of the crude oil. In another embodiment, the scavenger
composition
is added in an amount of from about 100 ppm by weight to about 1200 ppm by
weight,
based on the weight of the crude oil.
The hydrogen sulfide scavenger may be added neat or diluted with water or
solvent and may be formulated or blended with other suitable materials or
additives.
The hydrogen sulfide scavenger composition captures and neutralizes hydrogen
sulfide in the crude oil by incorporating the sulfur into an inert ringed
compound. The
ringed compound is non-hazardous and is attracted to a water phase and
migrates to a
water phase away from an oil phase.
The hydrogen sulfide scavenger composition comprises glyoxal and a quaternary
ammonium compound. Glyoxal is a water-soluble aldehyde and may include
oligomers
of glyoxal. Glyoxal is commercially available. The glyoxal is catalyzed with a
quaternary ammonium salt, which improves the efficacy of the scavenger
composition
and enhances removal of hydrogen sulfide. The catalyst may be any suitable
quaternary
ammonium salt. In one embodiment, the catalyst has formula I:
R1R2R3R4N X- I
wherein R1, R2, R3 and R4 are each independently an alkyl group having from 1
to 30
carbon atoms, an aryl group having from 6 to 30 carbon atoms or an arylalkyl
group
having from 7 to 30 carbon atoms; and X is a halide, sulfate, nitrate or
carboxylate. The
alkyl groups and the aryl groups may be substituted or unsubstituted.
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In one embodiment, R1 is an alkyl group having from 1 to 24 carbon atoms. In
one embodiment, R2 is an alkyl having from 1 to 24 carbon atoms, an aryl group
having
from 6 to 24 carbon atoms or an arylalkyl group having from 7 to 24 carbon
atoms.
In one embodiment, R3 and R4 are each, independently, an alkyl group having
from 1 to 24 carbon atoms. In another embodiment, R3 and R4 are each,
independently,
an alkyl group having from 1 to 4 carbon atoms.
The alkyl group includes, but is not limited to, methyl, ethyl, propyl,
isopropyl,
butyl, isobutyl, pentyl, hexyl, decyl or dodecyl. The aryl group may be
phenyl. The
arylalkyl group include may be benzyl. The halide may be chloride, bromide or
iodide.
The sulfate may be a methyl sulfate. The nitrate may be a bisulfate nitrate.
The
carboxylate may be acetate.
In one embodiment, the quaternary ammonium salt is alkyl benzyl ammonium
chloride or benzyl cocoalkyl (Cuz-C18) dimethylammonium chloride. In another
embodiment, the quaternary ammonium salt includes, but is not limited to
dicocoalkyl
(C12-C18) dimethylammonium chloride, ditallowdimethylammonium chloride,
di(hydrogenated tallow alkyl) dimethyl quaternary ammonium methyl chloride,
methyl
bis (2-hydroxyethyl cocoalkyl (C12-C18) quaternary ammonium choride,
dimethyl(2-
ethyl) tallow ammonium methyl sulfate, n-dodecylbenzyldimethylammonium
chloride, n-
octadecylbenzyldimethyl ammonium chloride, n-dodecyltrimethylammonium sulfate,
soya alkyltrimethylammonium chloride or hydrogenated tallow alkyl (2-
ethylhyexyl)
dimethyl quaternary ammonium methylsulfate.
In one embodiment, the quaternary ammonium salt is present from about 0.01 to
about 15 percent by weight based on the amount of glyoxal. In another
embodiment, the
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quaternary ammonium salt is present from about 1 to about 10 percent by weight
based
on the amount of glyoxal.
The scavenger composition is attracted to an aqueous phase and the captured
sulfides will migrate into an aqueous phase. If an emulsion is present, the
captured
sulfides can be migrated into the aqueous phase from the crude oil and removed
with the
aqueous phase. If no emulsion is present, a water wash can be added to attract
the
captured sulfides. In one embodiment, the hydrogen sulfide scavenger
composition is
added before the crude oil is treated in a desalter, which emulsifies the
hydrocarbon
media with a water wash to extract water soluble contaminants and separates
and
removes the water phase from the crude oil.
In one embodiment, a water wash is added in an amount suitable for forming an
emulsion with the crude oil. In another embodiment, the water wash is added in
an
amount of from about 1 to about 50 percent by volume based on the volume of
the
emulsion. In another embodiment, the wash water is added in an amount of from
about 1
to about 25 percent by volume based on the volume of the emulsion. In another
embodiment, the wash water is added in an amount of from about 1 to about 10
percent
by volume based on the volume of the emulsion. In one embodiment, the amount
of
crude oil is present in an amount of from about 50 to about 99 percent by
volume based
on the volume of the emulsion. In another embodiment, the crude oil is present
in an
amount of from about 75 to about 99 percent by volume based on the volume of
the
emulsion. In another embodiment, the crude oil is present in an amount of from
about 90
to about 99 percent by volume based on the volume of the emulsion.
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The water wash and crude oil are emulsified by any conventional manner. In one
embodiment, the water wash and crude oil are heated and thoroughly mixed to
produce
an oil-in-water emulsion. In one embodiment, the water wash and crude oil are
heated at
a temperature in a range of from about 90 C to about 150 C. The water wash and
crude
oil are mixed in any conventional manner, such as an in-line static mixer or
an in-line
mix valve with a pressure drop of about 0.2 to about 2 bar depending on the
density of
the crude oil. The emulsion is allowed to separate, such as by settling, into
an aqueous
phase and an oil phase. In one embodiment, the aqueous phase is removed. In
another
embodiment, the aqueous phase is removed by draining the aqueous phase.
Demulsifiers may be added to aid in separating the water from the crude oil.
In
one embodiment, the demulsifiers include, but are not limited to, oxyalkylated
organic
compounds, anionic surfactants, nonionic surfactants or mixtures of these
materials. The
oxyalkylated organic compounds include, but are not limited to,
phenolformaldehyde
resin ethoxylates, alkoxylated polyols and amines, such as Pluronic block co-
polymers.
The anionic surfactants include alkyl or aryl sulfonates, such as
dodecylbenzenesulfonate.
These demulsifiers may be added in amounts to contact the water from about 1
to about
1000 ppm by weight based on the weight of the crude oil. Combinations of
additives
may be used, but the total amounts of additives added should be in the range
of from
about 1 to about 1000 ppm by weight based on the weight of the crude oil.
In order that those skilled in the art will be better able to practice the
present
disclosure, the following examples are given by way of illustration and not by
way of
limitation.
EXAMPLES
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EXAMPLE I
Hydrogen sulfide scavenging tests were performed on a crude oil containing 500
ppm hydrogen sulfide in the liquid phase from a Texas refinery in Valero.
Testing was
performed using the modified ASTM 5705-95 test that measures vapor phase H2S
two
hours after treatment (140 F) via dragger tube. Results are shown in Table 1.
Table 1
Sample H2S Scavenger Residual H2S (ppm)
1000 m
CE-1 MEA' triazine 400
CE-2 Triazine 8411 C2 120
CE-3 MMA triazine + CatalySt4 200
CE-4 MEA' triazine + Catal st4 200
CE-5 Glyoxal 950
1 Glyoxal + Catal st4 140
'MEA is monoethanol amine
2Triazine 8411 C is available commercially from Clearwater, Inc as Sulfa-Clear
8411 C.
3MMA is monomethyl amine
4Catalyst is cocoalkyldimethylbenzyl ammonium chloride (Arquad DMCB-80) at
1.6%
by weight treatment level (actives basis) based on the weight of the triazine
or glyoxal.
Sample 1 has comparable results to the use of a triazine in reducing hydrogen
sulfide, but the catalyzed glyoxal can be removed in an aqueous phase;
whereas, the
triazine remains with the oil and can generate amines upon further processing.
The
catalyzed glyoxal sample shows significant improvement over glyoxal; whereas,
catalyzing the triazine does not improve the performance of the triazine..
EXAMPLE 2
The concentration of the hydrogen sulfide in the vapor phase was determined at
different levels of treatment dosages after 1 hour and 2 hours for samples 1
and
comparative examples CE-1 and CE-3, as shown in Table 2.
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Table 2
Dosages CE-1 CE-3 Sample 1 CE-1 CE-3 Sample 1
(ppm) H2S level H2S level H2S level H2S level H2S level H2S level
(p pm) @ (p pm) @ (p pm) @ (p pm) @ (p pm) @ (ppm) @ 2
1 hour 1 hour 1 hour 2 hours 2 hours hours
0 500 500 500 500 500 500
500 160 100 60 120 80 20
1000 20 20 20 5 5 5
The samples reduce and control the hydrogen sulfide level. Sample 1 has
comparable results to CE-1 and CE-3. However, Sample 1 can be removed in an
aqueous
phase and does not generate amines like the triazine samples will.
EXAMPLE 3
5 g of H2S was bubbled into a 2L flask containing 1L of a commercially
available
raw crude sample containing <25gg/ml of hydrogen sulfide initially. The flask
was
equipped with a mechanical stirrer and a condenser with a caustic trap. The
crude oil was
stirred at room temperature for 1 hour. The H2S concentration in the H2S-
infused crude
was 3940 gg/ml.
A demulsifier was added to the H2S-infused crude oil in the amounts shown in
Table 3.
5% by volume wash water was mixed with glyoxal and cocoalkyldimethylbenzyl
ammonium chloride, as shown in Table 3, and added to the H2S-infused crude
oil. The
wash water was mixed with the H2S-infused crude oil at 4000 rpm for 2 seconds,
grids
on, and heated to 130 C at a pressure of 4 psi to form an emulsion.
The emulsion was allowed to sit for 32 minutes to separate the water phase
from
the crude oil. A water drop reading was performed to test the emulsion
separation and is
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shown in Table 4. The water phase was removed from the separated emulsion and
observed for clarity as shown in Table 3.
Table 3
Sample Demulsifier' Treatment3 Mean Water Drop Separated Water Clarity
(hpm)2 (hpm)2 (ml)
Blank 0 0 2.73 Clear
CE-8 6 0 4.50 Clear
2 6 100 4.50 Slightly cloudy
3 12 100 4.48 Slightly cloudy
4 6 250 4.75 Cloudy
5 12 250 4.70 Cloudy
6 6 500 4.75 Cloudy
7 12 500 4.75 Cloudy
IDemulsifier is an alkoxylated alkylphenol formaldehyde available commercially
from
General Electric Company.
2 Doses based on 100 ml total volume.
3Treatment is glyoxal and cocoalkyldimethylbenzyl ammonium chloride at 1.6% by
weight treatment level (actives basis) based on the weight of the glyoxal.
Table 4: Water Drop Reading in ml
Sample 1 min 2 min 4 min 8 min 16 min 32 min Mean water drop
(ml) (ml) (ml) (ml) (ml) (ml) (ml)
Blank 0.4 1.8 2.7 3.5 4 4 2.73
CE-8 1.8 4 4.7 5.5 5.5 5.5 4.50
2 1.8 4 4.7 5.5 5.5 5.5 4.50
3 2 4 4.7 5.2 5.5 5.5 4.48
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4 3 4 5 5.5 5.5 5.5 4.75
3 4 4.7 5.5 5.5 5.5 4.70
6 3 4 5 5.5 5.5 5.5 4.75
7 3 4 5 5.5 5.5 5.5 4.75
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The increasing cloudiness in the separated water at higher levels of hydrogen
sulfide treatment indicates the presence of captured hydrogen sulfide products
that were
removed with the water. Also, the hydrogen sulfide scavenger does not
negatively
impact the separation of the emulsion.
While typical embodiments have been set forth for the purpose of illustration,
the
foregoing descriptions should not be deemed to be a limitation on the scope
herein.
Accordingly, various modifications, adaptations and alternatives may occur to
one skilled
in the art without departing from the spirit and scope herein.
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