Note: Descriptions are shown in the official language in which they were submitted.
CA 02755746 2014-05-20
QUATERNARY AMMONIUM-BASED MERCAPTAN SCAVENGER
COMPOSITION
TECHNICAL FIELD
[0002] The present invention relates to methods and compositions for
scavenging of mercaptans in hydrocarbon fluids and more particularly to the
use
of quaternary ammonium hydroxides and/or quaternary ammonium alkoxides as
mercaptan and/or H2S scavengers.
TECHNICAL BACKGROUND
[0003] Hydrocarbon fluids, such as crude oil, crude oil emulsions,
oilfield
condensate, petroleum residua and even refined fuels often contain a variety
of
mercaptans, including mercaptans of relatively low molecular weight. In the
drilling, production, transport, storage, and processing of hydrocarbon
stocks, the
mercaptans encountered can cause many problems ranging from malodors to
metal corrosion. Because of the volatility of mercaptans of relatively low
molecular
weight (for example, methyl mercaptan, CH3SH, ethyl mercaptan, CH3CH2SH and
propyl mercaptan, CH3CH2CH2SH), they tend to evolve into vapor spaces, where
their offensive odors create problems in and around storage areas and
throughout
pipelines and shipping systems used for transporting the hydrocarbon.
[0004] Various additives have been employed in efforts to alleviate these
problems. For example, choline or choline hydroxide has been found to
alleviate
hydrogen sulfide evolution and to scavenge mercaptans. See, for example, U.S.
Pat. Nos. 4,594,147 to Roof et al., 4,867,865 to Roof and 5,183,560 to Roof et
al.
However, choline and choline hydroxide are not well suited for many uses and
media, such as in crude oil. Although choline and choline hydroxide might
scavenge mercaptans in such media, they also form a volatile and malodorous by-
product with the sulfur compounds indigenous to such media. Accordingly, the
use
of choline and choline hydroxide to control odors associated with light
CA 02755746 2011-10-24
weight mercaptans is self-defeating in media such as crude oil. Thus, the
cited
patents to Roof and Roof, et al. fail to address this problem and instead
describe
the use of choline or choline hydroxide in the more refined fuel oils.
[0005] European application 0 538 819 A3 to Roof et al. describes the use of
oil-soluble quaternary ammonium compounds of the formula:
R2 R4 R5
I 1 1
R2¨N+¨C¨C-0-
I
R. 1 7 1 R
i
to scavenge various sulfur compounds, including mercaptans, from certain oils,
especially high boiling, heavy residual fuels. These compounds, prepared under
anhydrous conditions, are what are described herein as "internal ions"; i.e.,
the
positive charge on the nitrogen and the negative charge on the oxygen result
in
overall electrically neutral compounds without the presence of counter ions
such
as halides. The European application stresses the significance of the oil
solubil-
ity of these compounds, noting that they are more oil soluble than choline
base
and so disperse through the oil being treated more thoroughly to decrease the
concentration of undesirable sulfur compounds more effectively. Nevertheless,
the compositions of the European application suffer from certain
disadvantages.
For example, compositions that are produced in higher yields, yet still at low
cost, and that reduce mercaptan concentrations more effectively are still
desired.
[0006] U.S. Pat. Nos. 5,840,177 and 6,013,175 relate to methods for scaveng-
ing mercaptans in hydrocarbon fluids using quaternary ammonium hydroxides.
[0007] Other chemistries and methods for removing mercaptans from hydro-
carbons include caustic (NaOH solutions) and cobalt with caustic (MEROXTm
process of UOP, Merichem processes).
[0008] There is a continuing need in the liquid fuel industry for treating
liquid
hydrocarbon stocks and wet or dry gas mixtures containing mercaptans using
new compositions and methods.
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SUMMARY
[0009] There is provided, in one non-limiting embodiment a method for scav-
enging H2S and/or mercaptans in a hydrocarbon fluid that involves adding to
the
hydrocarbon fluid an effective scavenging amount of an aqueous scavenging
composition. The scavenging composition includes an additive selected from the
group consisting of a quaternary ammonium hydroxide, a quaternary ammonium
alkoxide, and mixtures thereof, in the presence of a metal in an oxidation
state of
3+ or greater. The additive reacts with H2S and/or mercaptans in the fluid.
There
is an absence of an oxidizing agent.
[0010] The quaternary ammonium hydroxide has the formula selected from
the group consisting of R1R2R3N+OH OH-, R1R2R3N+CH2CHR5OH OH- and
R1R2R3R4N+OH-, and the quaternary ammonium alkoxide has the formula
W
R2R3-1-<4O-, where:
R1 and R2 are independently selected from the group consisting of alkyl
groups of from 1 to about 18 carbon atoms, aryl groups of from 8 to
about 18 carbon atoms and alkylaryl groups of from 7 to about 18
carbon atoms,
R3 is selected from the group consisting of alkyl groups of from 2 to about
18 carbon atoms, aryl groups of from 6 to about 18 carbon atoms
and alkylaryl groups of from 7 to about 18 carbon atoms, provided,
however, that R2 and R3 may be joined to form a heterocyclic ring
including the N and optionally an oxygen atom, and
R4 is selected from the group consisting of H, alkyl groups of from 2 to
about 18 carbon atoms, alkylaryl groups of from 7 to about 18
carbon atoms, ¨(CH2CH20)nH, where n is from 1 to about 18,
¨(CH2CHO)m(CH2CH20)pH,
CH3
where m and p are independently selected from integers from 0 to
about 18, except that the sum m+p is less than or equal to 18, and
¨CHR5CHR6Y, where R5 and R6 are independently selected from
the group consisting of hydrogen, alkyl groups of from 1 to about
3
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18 carbon atoms, aryl groups of from 6 to 18 carbon atoms
and alkylaryl groups of from 7 to 18 carbon atoms, and Y is
a non-acidic group selected from the group consisting of ¨
OH, ¨SR7 and ¨NR7R8, where R7 and R5 are
independently selected from the group consisting of
hydrogen, alkyl groups of from 1 to 18 carbon atoms, aryl
groups of from 6 to 18 carbon atoms and alkylaryl groups of
from 7 to 18 carbon atoms, and
R5 is selected from the group consisting of hydrogen, alkyl groups
of from 1 to 18 carbon atoms or alkylaryl groups of from 7 to
18 carbon atoms.
[0011] Further, there is provided in another non-restrictive version a
hydrocarbon
composition that has a reduced H2S and/or mercaptan presence which includes a
hydrocarbon fluid, H2S and/or mercaptans, and an effective scavenging amount
of
an aqueous scavenging composition. The composition includes an additive
selected from the group consisting of a quaternary ammonium hydroxide, a
quaternary ammonium alkoxide, and mixtures thereof, in the presence of a metal
in
an oxidation state of 3+ or greater. The quaternary ammonium hydroxide has the
formula R1R2R3N+OH 0H, R1R2R3N+CH2CHR5OH OH- and/or R1R2R3N1+0H- and
the quaternary ammonium alkoxide has the formula R1R2R3R4N+0-, where R1, R2,
R3, and R4 are as defined above. At least some of the additive in the
hydrocarbon
composition has reacted with the H2S and/or mercaptan. Again, there is an
absence of an oxidizing agent.
[0011a] In accordance with an aspect of the present invention there is
provided a
hydrocarbon composition having a reduced H2S and/or mercaptan presence, the
composition comprising:
a hydrocarbon fluid;
H2S and/or mercaptans;
an aqueous scavenging composition comprising an effective scavenging
amount of an additive selected from the group consisting of a quaternary
ammonium hydroxide, a quaternary ammonium alkoxide, and mixtures thereof, in
the presence of a metal in an oxidation state of 3+ or greater, where the
quaternary
ammonium hydroxide has a formula selected from the group consisting of
-1-2
K K R3N+OH 0H, R1R2R3N+CH2CHR5OH OH- and R1R2R3R4N+OH-, and mixtures
thereof and the quaternary ammonium alkoxide has the formula R1R2R3R4N+0-,
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where:
R1 and R2 are independently selected from the group consisting
of alkyl groups of from 1 to 18 carbon atoms, aryl
groups of from 8 to 18 carbon atoms and alkylaryl
groups of from 7 to 18 carbon atoms,
R3 is selected from the group consisting of alkyl groups of from 2
to 18 carbon atoms, aryl groups of from 6 to 18 carbon atoms and
alkylaryl groups of from 7 to 18 carbon atoms, provided, however,
that R2 and R3 may be joined to form a heterocyclic ring including
the N and optionally an oxygen atom,
R4 is selected from the group consisting of hydrogen, alkyl groups of
from 2 to 18 carbon atoms, alkylaryl groups of from 7 to 18 carbon
atoms, ¨(CH2CH20)nH, where n is from 1 to 18,
¨(CH2CHOWCH2CH20)pH,
CH3
where m and p are independently selected from integers from 0 to
about 18, except that the sum m+p is less than or equal to about
18, and
¨CHR5CHR6Y, where R5 and R6 are independently selected from
the group consisting of hydrogen, alkyl groups of from 1 to 18
carbon atoms, aryl groups of from 6 to 18 carbon atoms and
alkylaryl groups of from 7 to 18 carbon atoms, and Y is a non-
acidic group selected from the group consisting of ¨OH, ¨SR7
and ¨NR7R8, where R7 and R8 are independently selected from
the group consisting of hydrogen, alkyl groups of from 1 to 18
carbon atoms, aryl groups of from 6 to 18 carbon atoms and
alkylaryl groups of from 7 to 18 carbon atoms, and
R5 is selected from the group consisting of hydrogen, alkyl groups of
from 1 to 18 carbon atoms or alkylaryl groups of from 7 to 18 carbon atoms.
where at least some of the additive has reacted with the H2S and/or mercaptan,
and where there is an absence of an oxidizing agent.
[0011 b] In accordance with a further aspect of the present invention there is
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provided a hydrocarbon composition having a reduced H2S and/or mercaptan
presence, the composition comprising:
a hydrocarbon fluid selected from the group consisting of crude oil, oil
field condensates, residual fuels, petroleum distillates, light
hydrocarbons, aromatic solvents, paraffinic solvents, dry gas streams,
fuels = comprising oxygenated compounds, biodiesel, and mixtures
thereof;
H2S and/or mercaptans;
an aqueous scavenging composition comprising an effective scavenging
amount of an additive selected from the group consisting of a
quaternary ammonium hydroxide, a quaternary ammonium
alkoxide, and mixtures thereof, in the presence of a metal in an
oxidation state of 3+ or greater selected from the group consisting
of Co(+3), Fe(+3), Cr(+6,+3), Ni(+3), Ce (+3,+4) and combinations
thereof, where the quaternary ammonium hydroxide has a formula
selected from the group consisting of R1R2R3N+OH OH-,
R1R2R3N+CH2CHR5OH OH- and R1R2R3R4N+OH-, and mixtures
thereof and the quaternary ammonium alkoxide has the formula
R1R2R3R4N+0-, where:
R1 and R2 are independently selected from the group consisting
of alkyl groups of from 1 to 18 carbon atoms, aryl groups of from 8
to 18 carbon atoms and alkylaryl groups of from 7 to 18 carbon
atoms,
R3 is selected from the group consisting of alkyl groups of from
2 to 18 carbon atoms, aryl groups of from 6 to 18 carbon atoms
and alkylaryl groups of from 7 to 18 carbon atoms, provided,
however, that R2 and R3 may be joined to form a heterocyclic ring
including the N and optionally an oxygen atom,
R4 is selected from the group consisting of hydrogen, alkyl
groups of from 2 to 18 carbon atoms, alkylaryl groups of from 7 to
18 carbon atoms, ¨(CH2CH20)nH, where n is from 1 to 18,
¨(CH2CHO)m(CH2CH20)pH,
CH3
where m and p are independently selected from integers from 0 to
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about 18, except that the sum m+p is less than or equal to 18, and
¨CHR5CHR6Y, where R5 and R6 are independently selected from
the group consisting of hydrogen, alkyl groups of from 1 to 18
carbon atoms, aryl groups of from 6 to 18 carbon atoms and
alkylaryl groups of from 7 to 18 carbon atoms, and Y is a non-
acidic group selected from the group consisting of ¨OH, ¨SR7 and
¨NR7R8, where R7 and R8 are independently selected from the
group consisting of hydrogen, alkyl groups of from 1 to 18 carbon
atoms, aryl groups of from 6 to 18 carbon atoms and alkylaryl
groups of from 7 to 18 carbon atoms, and
R5 is selected from the group consisting of hydrogen, alkyl groups of
from 1 to
about 18 carbon atoms or alkylaryl groups of from 7 to 18 carbon
atoms
where at least some of the additive has reacted with the H2S and/or mercaptan
and
where there is an absence of an oxidizing agent.
[0011c] In accordance with a further aspect of the present invention there is
provided a method for scavenging H2S and/or nnercaptans in a hydrocarbon
fluid,
comprising adding to the hydrocarbon fluid an aqueous scavenging composition
comprising an effective scavenging amount of an additive selected from the
group
consisting of a quaternary ammonium hydroxide, a quaternary ammonium
alkoxide, and mixtures thereof, in the presence of a metal of an oxidation
state of
3+ or greater, where the quaternary ammonium hydroxide has a formula selected
from the group consisting of R1R2R3N+OH OH-, R1R2R3N+CH2CHR5OH OH- and
Ri R2R3¨KN4- .
+ 0 Fr, and mixtures thereof and the quaternary ammonium alkoxide has
the formula R1R2R3R41\1+0-, where:
R1 and R2 are independently selected from the group consisting of
alkyl groups of from 1 to 18 carbon atoms, aryl groups of from 8 to
18 carbon atoms and alkylaryl groups of from 7 to 18 carbon
atoms,
R3 is selected from the group consisting of alkyl groups of from 2 to
18 carbon atoms, aryl groups of from 6 to 18 carbon atoms and
alkylaryl groups of from 7 to 18 carbon atoms, provided,
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however, that R2 and R3 may be joined to form a heterocyclic ring
including the N and optionally an oxygen atom,
R4 is selected from the group consisting of hydrogen, alkyl groups of
from
2 to 18 carbon atoms, alkylaryl groups of from 7 to 18 carbon
atoms, ¨(CH2CH20),H, where n is from 1 to 18,
¨(CH2CHOWCH2CH20)pH,
CH3
where m and p are independently selected from integers from 0 to
about 18, except that the sum m+p is less than or equal to 18, and
¨CHR5CHR6Y, where R5 and R6 are independently selected from
the group consisting of hydrogen, alkyl groups of from 1 to 18
carbon atoms, aryl groups of from 6 to 18 carbon atoms and
alkylaryl groups of from 7 to 18 carbon atoms, and Y is a non-
acidic group selected from the group consisting of ¨OH, ¨SR7 and
¨NR7R8, where R7 and R8 are independently selected from the
group consisting of hydrogen, alkyl groups of from 1 to 18 carbon
atoms, aryl groups of from 6 to 18 carbon atoms and alkylaryl
groups of from 7 to 18 carbon atoms, and
R5 is selected from the group consisting of hydrogen, alkyl groups of
from 1 to 18 carbon atoms or alkylaryl groups of from 7 to 18
carbon atoms;
where there is an absence of an oxidizing agent.
DETAILED DESCRIPTION
[0012] As defined herein mercaptans are thiols and are defined as any of a
group
of organic compounds resembling alcohols, but having the oxygen of the
hydroxyl
group replaced by sulfur Hydrogen sulfide (H2S) may also be scavenged by the
methods and additives herein, and while not technically a mercaptan may be
understood as included among the species being scavenged. It will thus be
understood that when "nnercaptan" is discussed, H2S is included as a species
that
will also be scavenged herein.
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[0013] It has been unexpectedly discovered that certain quaternary ammo-
nium hydroxides and alkoxides are surprisingly effective mercaptan scavengers
that scavenge H2S and mercaptans, particularly low weight mercaptans selec-
tively in preference to higher weight mercaptans. These additives are believed
to
react with the H2S and/or mercaptans in the fluid. It has been further unexpec-
tedly discovered that these quaternary ammonium hydroxides and alkoxides
have their scavenging ability improved in the presence of a high oxidative
state
metal, such as cobalt, which may act as a catalyst when combined with the
quaternary ammonium hydroxides and/or alkoxides. The exact mechanism by
which the methods herein operate is not known, and it may be that the presence
of a high oxidative state metal is not "catalytic" in the strict chemical
sense; the
inventors herein do not wish to be limited by any particular explanation.
[0014] It will also be appreciated that it is not necessary for all of the
H2S
and/or mercaptan present in the hydrocarbon to be reacted and/or removed for
the compositions, additives, and methods herein to be considered successful.
The compositions and methods have accomplished a goal when the amounts of
H2S and/or mercaptan are reduced as a consequence of being contacted with
the compositions described herein.
[0015] The efficacy of the hydroxides and alkoxides is especially
surprising in
view of the findings that the hydroxides are significantly more effective
scaven-
gers than compounds differing only in the counter ion (i.e., it is other than
hy-
droxide), and that in some non-limiting cases the hydroxides are even more
effective mercaptan scavengers than the corresponding internal ions (i.e.,
R3N+R'0- where R3N+R'OH OH- is the hydroxide).
[0016] The selectivity of the hydroxides reduces the waste that would other-
wise be encountered in scavenging higher molecular weight mercaptans unne-
cessarily, and so permits scavenging of the less desirable mercaptans with
relatively small amounts of the hydroxides. And, even though the European
application noted above stresses the importance of the oil-solubility of its
compounds to their efficacy, the superior efficacy of the hydroxides in
scaveng-
ing mercaptans in hydrocarbons has been found even though the hydroxides
CA 02755746 2011-10-24
would be expected to be significantly less oil-soluble than their
corresponding
internal ions.
[0017] Moreover, it has been found that in some non-restrictive embodiments
introducing oxygen such as by sparging the treated fluid with air increases
the
scavenging activity. However, in another non-limiting embodiment, the composi-
tions and methods herein may be practiced in an absence of an oxidizing agent,
in particular in the absence of an added oxidizing agent. As defined herein,
oxidizing agents include, but are not necessarily limited to air, molecular
oxygen
(02), and/or oxygen-containing gas and mixtures thereof.
[0018] The quaternary ammonium hydroxide has the formula R1R2R3N+OH
OH-, R1R2R3N+CH2CHR5OH OH- or R1R2R3R4N+OH-, and the quaternary
ammonium alkoxide has the formula R1R2R3R4N+0-. R1 and R2 are indepen-
dently selected from the group consisting of alkyl groups of from 1 to about
18
carbon atoms, aryl groups of from 8 to about 18 carbon atoms and alkylaryl
groups of from 7 to about 18 carbon atoms.
[0019] R3 is selected from the group consisting of alkyl groups of from 2
to
about 18 carbon atoms, aryl groups of from 6 to about 18 carbon atoms and
alkylaryl groups of from 7 to about 18 carbon atoms, provided, however, that
R2
and R3 may be joined to form a heterocyclic ring including the N and
optionally
an oxygen atom.
[0020] R4 is selected from the group consisting of H, alkyl groups of from
2 to
about 18 carbon atoms, alkylaryl groups of from 7 to about 18 carbon atoms,
¨(CH2CH20)nH, where n is from 1 to about 18,
¨(CH2CHO)m(CH2CH20)pH,
CH3
where m and p are independently selected from integers from 0 to about 18,
except that the sum m+p is less than or equal to 18, and ¨CHR5CHR6Y, where
R5 and R6 are independently selected from the group consisting of hydrogen,
alkyl groups of from 1 to about 18 carbon atoms, aryl groups of from 6 to
about
18 carbon atoms and alkylaryl groups of from 7 to about 18 carbon atoms, and Y
is a non-acidic group selected from the group consisting of ¨OH, ¨SR7 and
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¨NR7R8, where R7 and Re' are independently selected from the group consisting
of hydrogen, alkyl groups of from 1 to about 18 carbon atoms, aryl groups of
from 6 to about 18 carbon atoms and alkylaryl groups of from 7 to about 18
carbon atoms. In one non-restrictive version, R4 is ¨(CH2CH20)nH or
¨CHR5CHR6Y, where n, R5, R6 and Y are defined as above.
[0021] R5 may be hydrogen, alkyl groups of from 1 to about 18 carbon atoms
or alkylaryl groups of from 7 to about 18 carbon atoms.
[0022] In
choline base, each of R1, R2 and R3 is methyl. It now has been found
that if one of R1, R2 and R3 is longer than methyl, scavenging may be carried
out
even in crude oil without the volatile, malodorous scavenging by-products
trimethylamine generated with use of the choline base. Accordingly, R3 has
been
designated as the radical having at least two carbon atoms. In some non-
limiting
forms, R1 and R2 are alkyl groups of eighteen or fewer carbon atoms and in
other
non-restrictive embodiments lower alkyl groups of six carbons or fewer, espe-
cially three carbons or fewer and, alternatively, methyl groups. In another
non-
limiting embodiment, R3 is a fatty group, such as from about eight to about
eighteen carbon atoms, on the other hand about ten to about fourteen carbons
atoms, such as a coco- group. However, alternatively, R3 may be a benzyl group
or substituted aryl groups, for example, alkylbenzyl groups such as methyl
benzyl, or, less desirably, even may be an alkyl group of at least about two
carbon atoms. In other non-restrictive embodiments, R2 and R3 may be joined to
form a heterocyclic ring including the N and optionally an oxygen atom. In the
latter case, a morpholine may be formed. Such ring products have been found to
be less effective than some other products and may be more difficult to
prepare
by oxyalkylation of a tertiary amine.
[0023] R4, as noted, corresponds to the formula ¨(CH2CH20)nH, where n is an
integer from one to about eighteen, the formula
¨(CH2CHO)m(CH2CH20)pH,
CH3
where m and p are integers from zero to about eighteen (independently selected
except that m+p is less than or equal to about eighteen), or the formula
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¨CHR5CHR6Y, where R5 and R6 and Y are defined as above. Inclusion of such
R4 groups in the quaternary compound has been found to increase the perform-
ance of the compound as a mercaptan scavenger significantly over that of tetra-
alkyl quaternary compounds. In one non-limiting embodiment, R4 corresponds to
the formula ¨CHR5CHR6Y, where R5 and R6 are hydrogen or lower alkyls of
fewer than about six carbon atoms, in one non-restrictive version hydrogen,
and
Y is ¨OH.
[0024] However, when the quaternary compound is prepared by reacting a
tertiary amine with an alkylene oxide to form a quaternary compound where R4
is
¨CH2CH2OH, quaternary compounds are also formed where R4 is the ether or
polyether group ¨(CH2CH20)nH. Thus, a composition containing quaternary
compounds where R4 is ¨(CH2CH20)nH often also contains quaternary
compounds where R4 is the ether or polyether group ¨(CH2CH20)nH. Generally,
however, if the quaternary compound is prepared by oxyalkylating a tertiary
amine, the amine is reacted with the alkylene oxide in a molar ratio of about
1:1
so that, while some amine remains unreacted thereby leaving some alkylene
oxide available for polyether formation, typically the ether or polyether
chains
that do form are short; n being mostly one, two or three.
[0025] The quaternary ammonium hydroxides described herein may be
prepared by a variety of known techniques that will be readily apparent to
those
of ordinary skill in the art. For example, the quaternary ammonium hydroxides
may be prepared by ion exchange techniques from readily available quaternary
ammonium halides, such as quaternary ammonium chlorides. By such tech-
niques, the quaternary ammonium halides may be passed through an ion
exchange column for exposure to an ion exchange resin, exchanging the halide
ion for OH- ions (or Y- ions where Y is as defined above and does not corres-
pond to OH) from the column. Thus, according to this method for producing the
hydroxide, the halide R1R2R3R4N+Z-, where R1, R2, R3 and R4 are as defined in
the broader definition above and Z- is a halide, is brought into contact with
an ion
exchange resin bearing hydroxide ions to form R1R2R3R4N+ OH-.
[0026] Alternatively, the quaternary ammonium hydroxides described herein
may be prepared by oxyalkylation of tertiary amines in the presence of water.
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Techniques for oxyalkylation of tertiary amines have been described, for
example, in the European patent application noted above, but the European
application requires the reaction to be carried out under anhydrous
conditions.
Anhydrous conditions were necessary for the formation of the internal ions of
the
European application. This reaction gives the quaternary ammonium alkoxides
discovered to be useful herein. Quaternary ammonium ethoxides are formed
when ethylene oxide is reacted with tertiary amines to give
R1R2R3N+CH2CHR40- where R4 is H, and R1, R2 and R3 are as defined
previously.
[0027] The hydroxides have been discovered to be beneficial. Such
compounds are formed when the oxyalkylation is carried out in the presence of
water. And, surprisingly, it has been discovered that the reaction carried out
in
the presence of water results in yields of the quaternary ammonium hydroxide
product that are significantly higher than the yields of quaternary ammonium
internal ion resulting from the reaction carried out under anhydrous
conditions.
Moreover, carrying out the reaction in the presence of water allows the use of
less oxide per amine than called for in the non-aqueous reaction of the
European
application of Roof et al. (that is, a 1:1 molar ratio may be employed as
opposed
to bubbling the oxide through the amine as called for by Roof et al.). In
addition,
the aqueous reaction proceeds much faster than does the non-aqueous reaction
and so the quaternary product may be formed in much less time. Where Y of R4
is a non-acidic group other than OH-, a similar reaction may be carried out
with,
for example, an alkylene sulfide or alkyleneimine instead of an alkylene
oxide.
[0028] Thus,
it has been discovered that if the oxyalkylation reaction is carried
out in the presence of water, the resulting quaternary ammonium hydroxides not
only are more effective mercaptan scavengers in certain non-limiting cases
than
are the internal ions (the quaternary ammonium alkoxides) that would have been
produced had the reaction taken place in the absence of water, but also are
produced in higher yields than the internal ions would have been.
[0029] Accordingly, in more detail, where R4 of the quaternary ammonium
hydroxide R1R2R3R4N+ OH- is hydroxyethyl or hydroxypropyl, or if R4 is an
ether
or polyether group as described above, the hydroxide may be prepared by
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= CA 02755746 2011-10-24
reacting a tertiary amine such as of the form R1R2R3N with an alkylene oxide,
in
the presence of water. The alkylene oxide may be propylene oxide, but ethylene
oxide is useful in one non-limiting embodiment. In alternative embodiments
where the quaternary ammonium compound R1R2R3R4N+ is not a hydroxide, but
R4 corresponds to the formula ¨CHR5CHR6Y, where R5 and R6 are defined
above and Y is a non-acidic group corresponding to the formula ¨SR' or
¨NR7R8, an alkylene sulfide or alkyleneimine, respectively, may be substituted
for the alkylene oxide and otherwise the same procedures may be followed.
[0030]
R1, R2 and R3 of the tertiary amine are as defined above. In one non-
limiting embodiment, however, R1 is methyl and alternatively R2 is also
methyl.
Although R2 and R3 may be joined to form a heterocyclic ring including the N
and
optionally an oxygen atom, such as to form a morpholine derivative, such
compositions have been found to be more difficult to oxyalkylate without the
offset of producing more potent scavengers and so in some configurations, R2
and R3 are not joined. In one non-restrictive version, R3 is a fatty group of
from
about six to about twelve carbon atoms.
[0031] The reaction may be carried out in an aqueous solvent. For example,
the solvent may comprise about 50% by weight to about 95%, by weight alcohol
such as isopropanol or, in one useful embodiment, methanol, and about 5% by
weight to about 50% by weight water. A typical solvent formulation, therefore,
might comprise, by weight, two parts solvent to one part water.
[0032] The active ingredients may make up about 70% by weight of the
reaction mixture (the remaining 30% being solvent). In one non-limiting method
of preparation, the tertiary amine is stirred in the solvent and the system is
pressurized with alkylene oxide added in a molar ratio of about 1:1 to the
amine.
Generally, the molar ratio is in the range of from about 1:1 to about 1.5:1
alkylene oxide to amine. The reaction is carried out at a temperature
typically
under about 70 C., in one non-limiting embodiment about 40 C. to about 50 C.,
with continuous stirring and its completion is signaled by a drop in pressure
to
about atmospheric. The resulting mixture, aside from unreacted solvent, is a
combination of the quaternary compounds where the R4s are of the formulae
¨CH2CH2OH and ¨(CH2CH20)nH, where n is as defined above, unreacted
CA 02755746 2011-10-24
amine, and glycols formed from reaction of the alkylene oxide and water. Other
quaternary ammonium hydroxides where R4 corresponds to the formula
¨(CH2CHO)m(CH2CH20)pH,
CH3
or the formula ¨CHR5CHR6Y where m, p, R5, R6 and Y are as defined above,
may be prepared by similar techniques that will be readily apparent to those
of
ordinary skill in the art.
[0033] It has been unexpectedly discovered that the quaternary ammonium
hydroxides and quaternary ammonium alkoxides described herein have
improved H2S and/or mercaptan scavenging properties when they are in the
presence of a metal of a high oxidation state. As used herein, "high oxidation
state" means the metal is present in a primary valence that is capable of
being
reduced without forming the element. Typically this is an oxidation state of
3+ or
greater for most metals of interest. In one non-limiting embodiment these
metals
are believed to act as catalysts in some way, but the inventors do not wish to
be
limited to any particular theory. Alternatively, the metals may function as an
oxidizer. Metals of high oxidation state suitable to give the desired effect
include,
but are not necessarily limited to, Co(+3), Fe(+3), Cr(+6,+3), Ni(+3), Cu(+2),
Ce
(+3,+4) and combinations thereof.
[0034] In
another non-restrictive version, the compositions and methods here-
in may be practiced in the absence of a catalyst on a basic support. In
particular,
in a non-limiting embodiment, the methods and compositions described are
practiced in the absence of a metal chelate on a solid base, such as those
described in U.S. Pat. No. 5,286,372. Such solid bases may be metal oxides, a
layered double hydroxide and mixtures thereof.
[0035] The metals may be present as water or oil soluble salts and complexes.
Specific, non-limiting examples of metals suitable for use in the compositions
and methods herein include, but are not limited to DBM 830, which consists of
a
mixture of aqueous caustic, water, dimethylethanolamine, monoethanolamine,
formaldehyde, nonionic surfactants (nonyl phenol ethoxylate) and Merox
catalyst
(cobalt phthalocyanine complex) available from UOP.
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[0036] The resulting additive, be it quaternary ammonium hydroxide or quater-
nary ammonium alkoxide may be added to the hydrocarbon fluid to be treated by
standard techniques, such as by injection or simple pouring and it may be dis-
persed throughout the fluid by stirring or other agitation. Enough of the
additive
should be added that is effective to scavenge at least a portion of the H2S
and/or
mercaptan. The additive is incorporated at a level sufficient to scavenge the
H2S
and/or mercaptans to a desired degree and will depend on the mercaptan
content of the medium and the corresponding stoichiometry. However, typical
additive levels may be on the order of about 20 to about 10,000, in one non-
limiting embodiment from a lower threshold of about 100 independently to an
upper threshold of about 5,000, ppm based on the weight of the medium to be
treated, alternatively from a lower threshold of about 500 independently to an
upper threshold of about 1000 ppm.
[0037] The amount of metal in the hydrocarbon fluid may range from about 10
to about 1000 ppm, alternatively up to about 500 ppm, based on the hydrocar-
bon fluid. In one non-limiting embodiment, the formulations of the aqueous
scavenging composition may have from 0.1 to 5 wt% of the additive being metal
with the remainder being alkoxide/hydroxide.
[0038] The medium may be any hydrocarbon fluid, and a liquid is expected to
be most common, although dry gas mixtures containing mercaptans may also be
treated. For example, excellent results have been obtained from treatment of
crude oil, petroleum residua and fuels such as kerosene. It should be
recognized
that while the fluids are referred to as hydrocarbon fluids, in some cases
(for
example, crude oil emulsions), hydrocarbons may make up less than half of the
fluid by weight. The product is particularly useful for treatment of crude oil
in that
it does not add an additional malodorous compound as has been associated with
the use of choline to treat crude oil. More specifically, the hydrocarbon
fluids to
which the method herein may be applied include, but are not limited to, crude
oil,
oil field condensates (e.g. naphtha, etc.), residual fuels, petroleum
distillates
(e.g. gasoline, kerosene, diesel, etc.) light hydrocarbons (e.g. propane,
butane,
etc.), aromatic solvents (e.g. toluene, xylene, etc.) and paraffinic solvents
(e.g.
pentane, heptane, etc.), renewable fuels such as biodiesel, and mixtures
thereof.
12
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Further, the hydrocarbon fluids may contain oxygenated compounds such as
alcohols, esters, glycols, ethers and the like and mixtures thereof.
[0039] In addition, even significantly greater degrees of scavenging have
been
found to result if the medium is first oxygenated such as by aeration prior to
addition of the mercaptan scavenger. However, in other non-limiting embodi-
ments, an oxidizing agent, such as air or oxygen, is not used. Although the
inventors do not wish to be bound by any particular theory, it is believed
that the
mechanism by which this scavenging occurs is according to the following
reaction sequence where R1R2R3R4N+ OH- is the scavenger and RSH is the
mercaptan:
RiR2R3R4.,
N OH- + RSH RS- R1R2R3R4N+
2 RS- + 02 RSSR (disulfide)
[0040] Thus, increasingly improved results have been noted as the amount of
oxygen added such as by aerating or bubbling air into the medium increases to
100% of the stoichiometry of this reaction scheme. Addition of air in an
amount
beyond 100% has not been found to improve scavenging much more than that
associated with addition of 100% of stoichiometry. However, as noted, in some
non-limiting embodiments, there is an absence of an added oxidizing agent,
such
as air, molecular oxygen and the like.
[0041] Effective scavenging may be carried out at the ambient temperature of
the hydrocarbon fluid (e.g., about 20 C. for stored crude oil, residuum or
fuel),
but the performance of the scavenger has been found to be improved at higher
temperatures such as about 50 C. to about 75 C. The scavenger tends to
decompose at even higher temperatures, such as at about 100 C. However, the
decomposition at such temperatures occurs relatively slowly while the time for
the reaction between the scavenger and the mercaptans is relatively short,
generally requiring only several hours to reduce the mercaptan level substan-
tially. Thus, the scavenger may still be employed at such elevated
temperatures
with good results.
13
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[0042] It has been found that
the scavenging additives herein remove
H2S first, and then start removing or reacting with the mercaptans. The
quaternary ammonium scavengers herein have been found to react
selectively with the lower molecular weight mercaptans without imparting
to the system an odor of its own. More particularly, for example, the
scavengers have been found to scavenge methyl mercaptan in
preference to ethyl mercaptan and to scavenge ethyl mercaptan in
preference to n-propyl mercaptan and to scavenge n-propyl mercaptan in
preference to n-butyl mercaptan, and so forth. It also has been observed
that the scavengers react selectively with linear mercaptans over
branched mercaptans. Thus, the scavengers enable removal of the most
volatile mercaptans, which are the greatest contributors to odor
problems, with limited waste of scavenger on side reactions with less
volatile mercaptans. It is believed that adding the high oxidation state
metal helps speed the scavenging of lower mercaptans as well as
improves the removal of higher mercaptans (i.e. through 012 or dodecyl
mercaptans).
[0043] The following examples
describe certain specific, non-limiting
embodiments of the methods and compositions. Other embodiments are
within the scope of the invention and will be apparent to one skilled in the
art from consideration of the specification or practice of the methods and
compositions as disclosed herein. It is intended that the specification,
together with the examples, be considered exemplary only. In the
examples, all percentages are given on a weight basis unless otherwise
indicated.
EXPERIMENTAL
[0044] Mercaptan Scavenger A was made according to the methods
of U.S. Pat. Nos. 5,840,177 and 6,013,175, mentioned above, assigned
to Baker Hughes Incorporated. Mercaptan Scavenger A
was a
quaternary ammonium hydroxide prepared from dimethyl soya amine
and ethylene oxide.
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[0045] As shown in Table I, Mercaptan Scavenger A was used alone and
together with DBM 830, also used alone, in the indicated dosages. The initial
mercaptan proportion was 533 ppm. The liquid phase mercaptan (RSH) propor-
tion after 24 hours and after 5 days was noted. The hydrocarbon used in this
testing was Caspian Pipeline Crude containing an unknown mix of naturally
occurring mercaptans with an additional 205 ppm of C3 mercaptan (i.e. 1-
propanethiol; CH3CH2CH2SH) artificially added.
TABLE I
Reduction of RSH Portion Using Scavenger and Cobalt
Dosage Liquid Phase RSH
Ex. Additive ppm 24 hrs 5
days,
1 blank 0 533 ppm 529
ppm
2 Scavenger A 1000 498 ppm 426
ppm
3 DBM 830 1000 346 ppm 159
ppm
4 Scavenger A + DBM 830 500 + 500 276 ppm 112
ppm
Scavenger A 2000 308 ppm 185 ppm
6 DBM 830 2000 291 ppm 107
ppm
7 Scavenger A + DBM 830 1000+1000 273 ppm 61
ppm
[0046] It may be seen from Table I that the mercaptan levels using both
Scavenger A and DBM 830 (Examples 4 and 7) are reduced to a greater extent
as compared with adding the reductions obtained from the Examples using
Scavenger A alone (Examples 2 and 5) or those using DBM 830 alone
(Examples 3 and 6). It may be seen that in all Examples, whether calculated as
an absolute reduction in ppm units, or as a percentage of the starting RSH
content, the reduction in mercaptan is synergistic, that is, greater than
would be
expected from adding the effects of the two components together. This result
is
unexpected.
[0047] Among the several advantages of the methods herein, may be noted
the provision of a method for scavenging mercaptans more effectively and
efficiently than in conventional methods, the provision of such method that
CA 02755746 2014-09-24
scavenges selectively for light weight.mercaptans versus heavier weight
mercaptans, and the provision of such method that does not tend to
generate new malodorous compositions.
[0048] Further evidence of the surprising combined benefit of a
quaternary ammonium compound with a metal of an oxidation state of 3+
or greater is seen in Examples of 8, 9 and 10 of Table 11 below. Example 9
using 1000 ppm of Mercaptan Scavenger A reduces the headspace H2S
from 542 ppm to 475 ppm.
However, Example 10, which uses 500 ppm of Mercaptan Scavenger A
and 500 ppm of Co+3 (10% solution) reduces the headspace H2S from
542 ppm to 329 ppm.
TABLE II
Reduction of H2S Portion using Scavenger A and Cobalt
Ex. Additive Dosage (ppm) Headspace H2S (ppm)
8 Blank 0 542
9 Scavenger A 1000 475
Scavenger A + Co( 10% soln.) 500 + 500 329
[0049] In the foregoing specification, the methods and compositions
have been described with reference to specific embodiments thereof. It
has been demonstrated as effective in providing methods and
compositions for reacting with and reducing the H2S and/or mercaptan
proportions in hydrocarbons, particularly crude oil. However, it will be
evident that various modifications and changes can be made thereto
without departing from the scope of the methods and compositions as set
forth herein. Accordingly, the specification is to be regarded in an
illustrative rather than a restrictive sense. For example, specific
combinations of quaternary ammonium hydroxide, quaternary ammonium
alkoxide, high oxidation state metal, and other compo-nents falling within
the claimed parameters, but not specifically identified or tried in a
particular composition or under specific conditions, are anticipated to be
within the scope of these methods and compositions.
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[0050] The words "comprising" and "comprises" as used throughout the
claims, is to be interpreted to mean "including but not limited to" and
"includes
but not limited to", respectively.
[0051] The present compositions and methods may suitably comprise, consist
of or consist essentially of the elements disclosed and may be practiced in
the
absence of an element not disclosed. For instance, a hydrocarbon composition
may consist of or consist essentially of a hydrocarbon fluid, H2S and/or
mercap-
tans, and an aqueous scavenging composition, as recited in the claims. Simi-
larly, methods for scavenging H2S and/or mercaptans in a hydrocarbon fluid may
consist of or consist essentially of adding to a hydrocarbon fluid containing
these
materials an effective scavenging amount of the additives, as the additives
are
defined in the claims.
17
