U.S. patent application number 17/806135 was filed with the patent office on 2022-09-22 for contaminant removal process.
This patent application is currently assigned to Taminco BVBA. The applicant listed for this patent is Taminco BVBA. Invention is credited to Robin Jacques Matton, Stijn Simonne Paul Van de Vyver, Klaas Victor.
Application Number | 20220297052 17/806135 |
Document ID | / |
Family ID | 1000006391404 |
Filed Date | 2022-09-22 |
United States Patent
Application |
20220297052 |
Kind Code |
A1 |
Van de Vyver; Stijn Simonne Paul ;
et al. |
September 22, 2022 |
CONTAMINANT REMOVAL PROCESS
Abstract
Disclosed is a process comprising: step a) contacting a feed
stream comprising a contaminant with an absorbent stream in a
counter-current flow to produce a contaminant depleted product
stream depleted in the molar quantity of the contaminant relative
to the molar quantity of said contaminant in the feed stream, and a
contaminant enriched absorbent stream enriched in the molar
quantity of the contaminant relative to the molar quantity of said
contaminant in the absorbent stream; and step b) treating the
contaminant enriched absorbent stream to form a gaseous stream
comprising said contaminant and a regenerated absorbent stream lean
in the molar quantity of said contaminant relative to the molar
quantity of said contaminant in the contaminant enriched absorbent
stream; herein said absorbent stream comprises at least 15 wt. % of
at least one compound (A) of general formula (I) or a mixture (M)
comprising at least one compound (B) of general formula (II) and at
least one compound (C) of general formula (III).
Inventors: |
Van de Vyver; Stijn Simonne
Paul; (Gent, BE) ; Matton; Robin Jacques;
(Merelbeke, BE) ; Victor; Klaas; (Beveren,
BE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Taminco BVBA |
Gent |
|
BE |
|
|
Assignee: |
Taminco BVBA
Gent
BE
|
Family ID: |
1000006391404 |
Appl. No.: |
17/806135 |
Filed: |
June 9, 2022 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16968903 |
Aug 11, 2020 |
11383197 |
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PCT/EP2019/053555 |
Feb 13, 2019 |
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17806135 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C10L 2290/12 20130101;
B01D 2257/304 20130101; C10L 2290/541 20130101; C10L 3/103
20130101; B01D 53/1493 20130101; B01D 2257/308 20130101; B01D
2257/504 20130101; B01D 2252/20468 20130101; B01D 53/1456
20130101 |
International
Class: |
B01D 53/14 20060101
B01D053/14; C10L 3/10 20060101 C10L003/10 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 14, 2018 |
EP |
18156822.1 |
Claims
1-15. (canceled)
16. A mixture (M) comprising at least one substituted 2-pyrrolidone
of general formula (II) [compound (B), herein after], herein below,
and at least one amine compound of general formula (III) [compound
(C), herein after], herein below: ##STR00010## wherein: each of R',
equal to or different from each other and at each occurrence, is
independently selected from H or CH.sub.3 j is an integer in the
range from 0 to 3 each of R.sub.3, R.sub.4, R.sub.5 and R.sub.6,
equal to or different from each other and at each occurrence, is
independently selected from H or CH.sub.3; q is an integer in the
range from 0 to 1; p is an integer in the range from 1 to 6; with
the proviso that when p=1 and q=0 then R.sub.3 and R.sub.4 are
CH.sub.3 and when p+q=2 then at least one of R.sub.3, R.sub.4,
R.sub.5 or R.sub.6 is CH.sub.3; each of R.sub.7, R.sub.8 and
R.sub.9, equal to or different from each other and at each
occurrence, is independently selected from H, C.sub.1-10 alkyl,
C.sub.1-10 alkoxyalcohol or a C.sub.1-10 alkanol group; with the
proviso that at least one of R.sub.7, R.sub.8 or R.sub.9 is a
C.sub.1-10 alkoxyalcohol or a C.sub.1-10 alkanol group.
17. A composition comprising the mixture (M) as defined in claim
16.
18. An absorbent stream comprising the mixture (M), as defined in
claim 16.
19. (canceled)
20. A contaminant enriched absorbent stream comprising at least one
absorbed contaminant selected from hydrogen sulfide (H.sub.2S),
carbon dioxide (CO.sub.2), carbon oxysulfide (COS), carbon
disulfide (CS.sub.2), disulfides or mercaptans, the absorbent
stream comprising: i. at least 15 wt. %, relative to the total
weight of the absorbent stream, of at least one substituted
2-pyrrolidone of general formula (I) [compound (A), herein after]:
##STR00011## wherein: each of R.sub.1 and R.sub.2, equal to or
different from each other and at each occurrence, is independently
selected from H or CH.sub.3; each of R, equal to or different from
each other and at each occurrence, is selected from H or CH.sub.3;
i is an integer in the range from 0 to 3; o is an integer in the
range from 2 to 6; n is an integer in the range from 0 to 4; m is
an integer in the range from 0 to 4; or, ii. a mixture [mixture
(M), herein after] comprising at least one substituted
2-pyrrolidone of general formula (II) [compound (B), herein after],
herein below, and at least one amine compound of general formula
(III) [compound (C), herein after], herein below: ##STR00012##
wherein: each of R', equal to or different from each other and at
each occurrence, is independently selected from H or CH.sub.3 j is
an integer in the range from 0 to 3 each of R.sub.3, R.sub.4,
R.sub.5 and R.sub.6, equal to or different from each other and at
each occurrence, is independently selected from H or CH.sub.3; q is
an integer in the range from 0 to 1; p is an integer in the range
from 1 to 6; with the proviso that when p=1 and q=0 then R.sub.3
and R.sub.4 are CH.sub.3 and when p+q=2 then at least one of
R.sub.3, R.sub.4, R.sub.5 or R.sub.6 is CH.sub.3; each of R.sub.7,
R.sub.8 and R.sub.9, equal to or different from each other and at
each occurrence, is independently selected from H, C.sub.1-10
alkyl, C.sub.1-10 alkoxyalcohol or a C.sub.1-10 alkanol group; with
the proviso that at least one of R.sub.7, R.sub.8 or R.sub.9 is a
C.sub.1-10 alkoxyalcohol or a C.sub.1-10 alkanol group.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an improved process for
removing contaminants, in particular to an improved removal of
mercaptans in the presence of other contaminants such as H.sub.2S
and CO.sub.2, from non-aqueous process streams, primarily gases but
also including liquids.
BACKGROUND OF THE INVENTION
[0002] The removal of contaminants such as hydrogen sulfide
(H.sub.2S), carbon dioxide (CO.sub.2), carbon oxysulfide (COS),
carbon disulfide (CS.sub.2), disulfides and mercaptans, from a wide
variety of feed streams, in particular gaseous feed streams, is
known to be important.
[0003] Such feed streams occur for example in the processing of
natural gas. The gas from natural gas fields mainly comprises
methane and may further comprise significant amounts of
contaminants such as carbon dioxide, readily up to 70% volume,
hydrogen sulfide, mercaptans and carbon oxysulfide. These
contaminants may therefore need to be removed to reduce further
transportation costs as compressed gas, to mitigate risk of
corrosion in downstream systems and pipelines, to adjust the
heating value of the gas in order to suit the consumer needs,
and/or to enable the liquefaction of the natural gas into liquefied
natural gas, LNG, a means of transport of increasing use to bring
natural gas from a remote winning location to the gas consumption
market.
[0004] Contaminant removal is also important in refinery streams
such as the liquefied petroleum gas (LPG) fraction, the off-gases
from fluid catalytic cracking (FCC), the hydrotreater off-gases,
and the refinery gas usually contain significant amounts of
mercaptans and/or H.sub.2S, and in some also CO.sub.2 may be
present. The distillation fractions intended for the different fuel
pools need to be desulfurized to alleviate the acid rain problem
caused by SOx emissions in the flue gas after combustion. Several
of these liquid fractions are therefore subjected to
hydrodesulfurization, a refinery step which converts the heavier
sulfur compounds into gaseous H.sub.2S. In a so-called Claus plant,
the H.sub.2S which is collected from all these sources may then be
converted into elemental sulfur, which has become a product of
commerce, for instance as feedstock for the production of sulfuric
acid.
[0005] Furthermore, contaminant removal may be important in the
production of synthesis gas, consisting primarily of H.sub.2, CO
and possibly also N.sub.2, a gas which is in various forms an
important chemical building block but also an important
intermediate in the conversion of energy from solid carbon
containing streams, such as solid waste streams, tar sands, oil
shale and the like. It is usually desirable to remove mercaptans,
H.sub.2S and CO.sub.2 from the synthesis gas, because mercaptans
and H.sub.2S may be an undesirable reactant therein and/or lead to
emission of sulfur oxides (SOx) upon combustion, undesirable in
view of the acid rain concerns and because the CO.sub.2 may for
instance act as a disturbing inert in the downstream process.
[0006] However, the simultaneous and efficient removal of
mercaptans, H2S and CO2 remains an important challenge, more so in
view of the increasingly stringent environmental and technical
requirements and the drive for a continuous cost reduction of gas
processing plants.
[0007] The removal of contaminants from gases, and to a lesser
extent also from organic liquids such as for instance LPG streams,
is typically performed by washing the stream with an absorbent
solution, usually at a relatively low temperature to favour the
absorption of the contaminant. A major portion of the contaminant
is absorbed in the absorbent solution, and the rich absorbent
solution is then routed to a regeneration step for being
regenerated. The lean absorbent solution from the regeneration step
is then usually cooled and recycled to the absorption step. A
typical absorbent solution contains absorbents of a basic nature,
and amine compounds have been preferred over alternatives such as
hot potassium carbonate. Even more preferred were alkanolamines. A
conventional absorbent is for instance 2-hydroxyethyl amine, also
known as monoethanol amine (MEA). The contaminants absorbed react
with the alkanolamine present in solution according to a reversible
exothermic reaction. With MEA, typically two molecules of MEA are
required to absorb one molecule of CO.sub.2. More complex,
sterically hindered amines, including tertiary amines, were found
to provide improved stoichiometry.
[0008] These types of solvents which undergo a chemical reaction
with the contaminants and thereby form thermally regenerable salts,
are often called chemical solvents in this context. Alkanolamines
derived from primary, secondary and/or tertiary amines are the most
widely used chemical solvents. The most frequently used amines are
derived from ethanolamine, especially monoethanol amine (MEA),
diethanolamine (DEA), triethanolamine (TEA), diisopropanolamine
(DIPA) and methyldiethanolamine (MDEA). A disadvantage of such
chemical solvents is that in the regeneration step, the chemical
bond between the solvent and the contaminant needs to be broken
which requires a large amount of energy. Especially the
regeneration of solutions of primary and secondary alkanolamines
consumes large volumes of steam. Since mercaptans are weaker acids,
their removal by chemical solvents will not be efficient when
H.sub.2S and CO.sub.2 are present because the latter react more
quickly with the alkanolamines. Therefore, mercaptans can react
chemically with alkanolamines but they are in competition with
H.sub.2S and CO.sub.2.
[0009] As an alternative to chemical solvents, so-called physical
solvents are often used for the capture of minor sulfuric
components such as mercaptans. Physical solvents rely on a physical
absorption process, the contaminants dissolve and thus are
physically absorbed in the physical solvent. The energy of the bond
with the contaminant is typically smaller than with most of the
typical so-called chemical solvents. Typical physical solvents are
sulfolane and its derivatives, aliphatic acid amides,
N-methyl-2-pyrrolidone (NMP), methanol and mixtures of
dialkylethers of polyethylene glycols (Selexol.RTM., Union
Carbide).
[0010] A mixture of a chemical and a physical solvent, so-called
hybrid solvents, can be employed as well. Such hybrid solvents can
achieve very low contaminant specifications in a single treating
step through a combination of bulk contaminant removal by the
physical solvent and stringent purification by the chemical
solvent.
[0011] A well-known commercial hybrid solvent is the Sulfinol.RTM.
solvent (Shell.RTM.) which is often used to treat refinery,
natural, and synthesis gases. The Sulfinol.RTM. solvent is a
mixture of sulfolane, an alkanolamine (either DIPA or MDEA), and
water. The solution with DIPA, referred to as Sulfinol.RTM.-D, is
usually selected when complete removal of H.sub.2S and CO.sub.2 as
well as deep removal of COS is required. The Sulfinol.RTM.-D
solvent is used in most of the Sulfinol plants in operation
worldwide. The solution with MDEA, referred to as Sulfinol.RTM.-M,
is usually used for selective removal of H.sub.2S in the presence
of CO.sub.2 and is capable of partial removal of COS. U.S. Pat. No.
4,085,192 describes a process for the selective removal of H.sub.2S
by using such a Sulfinol.RTM. type solvent comprising an
alkanolamine and sulfolanes. The Sulfinol.RTM. solvents shows a
good absorption capacity for H.sub.2S, CO.sub.2 as well as
mercaptans, however, it also shows co-absorption of valuable
hydrocarbons. Co-absorption of hydrocarbons should be avoided to
reduce hydrocarbon losses in the separated contaminants.
[0012] US 2016/0288046 A1 relates to processes for removal of
acidic sulfur constituents from fluid streams by using aqueous
mixtures of an amine constituent and a physical solvent. The amine
constituents are generally tertiary amines, such as notably
3-dimethylamino-1, 2-propanediol (DMAPD),
3-diethylaminopropane-1,2-diol,
2-hydroxymethyl-2-dimethylaminopropane-1,3-diol or
2-hydroxymethyl-2-diethylaminopropane-1,3-diol and sterically
hindered amines such as
2-hydroxymethyl-2-methylaminopropane-1,3-diol and
2-methyl-2-hydroxyethylaminopropanol. Preferred physical solvents
include mono-functional and di-functional alcohols having a
dielectric constant of lower than about 20, such as
methoxytriglycol (MTG), methoxydiglycol (MDG), ethoxytriglycol,
butoxytriglycol and mixtures thereof or glycol ethers such as
methyl capped poly-ethylene glycol ethers and methyl capped
polypropylene glycol. US 2016/0288046 A1 is mainly concerned with
the removal of acidic sulfur constituents, in particular selective
removal of H.sub.2S from a gas stream comprising other
contaminants, for example N.sub.2, CO.sub.2, O.sub.2H.sub.6,
C.sub.3H.sub.8, H.sub.2, CO, H.sub.2O, COS, HCN, NH.sub.3, O.sub.2,
and/or mercaptans. In US 2016/0288046 A1, it was found that the
dielectric properties of the amine constituent and the physical
solvent was important. Hybrid solvents with a low permittivity are
most preferred. No mention is made about the amount of
co-absorption of hydrocarbons.
[0013] U.S. Pat. No. 8,313,718 discloses a process for removing
H.sub.2S and CO.sub.2 from a hydrocarbon gas stream also containing
a mercaptan by using an absorption (scrubbing) composition
comprising a solution of a chemical solvent or physical solvent or
mixture thereof and an effective amount of a mercaptan inclusion
compound, such as cyclodextrin, calixarene, cucurbituril, a
cryptand or mixtures thereof. Alkanolamines including for example
monoethanolamine (MEA), diethanolamine (DEA), triethanolamine
(TEA), diisopropylamine (DIPA), diglycolamine (OCA) and
methyldiethanolamine (MDEA) are mentioned as chemical solvents.
Cyclotetramethylene sulfone, aliphatic acid amides, N-alkylated
pyrrolidones such as N-methylpyrrolidone and corresponding
piperidones, methanol and mixtures of dialkylethers of polyethylene
glycols are mentioned as useful physical solvents. U.S. Pat. No.
8,313,718 demonstrates that the addition of such mercaptan
inclusion compounds increases the removal of mercaptans. A
significant drawback of the process of U.S. Pat. No. 8,313,718 is
that it requires a composition with an extra ingredient on top of
the conventional hybrid solvent, which in turn creates extra raw
material costs. No mention is made about the amount of
co-absorption of hydrocarbons.
[0014] U.S. Pat. No. 5,413,627 discloses a process for the
selective removal of sulfur compounds such as H.sub.2S, COS,
CS.sub.2 and thiols in the presence of at least one of H.sub.2,
N.sub.2, Ar, CO.sub.2, CO and aliphatic hydrocarbons using a
physical scrubbing agent. A heterocylic compound is used as a
suitable physical scrubbing agent which need to have five or more
ring atoms, of which 2 atoms are heteroatoms, one of which is
nitrogen and the other of which is oxygen or nitrogen. The nitrogen
atom present in the ring is/are either double bonded or single
bonded but, if single bonded, the nitrogen is organo-substituted. A
wide variety of scrubbing agents are disclosed. The physical
scrubbing agent may further be used in a physically active
scrubbing agent composite with compounds selected from a long list
of various heterocycles. U.S. Pat. No. 5,412,627 is mainly
concerned with the removal of sulfur compounds such as H.sub.2S in
the presence of CO.sub.2 and not with the effective simultaneous
removal of mercaptans. No mention is made about the amount of
co-absorption of hydrocarbons.
[0015] US 2009/0299122 A1 proposes a process for producing purified
hydrocarbon gas which does not incur the risk of significant losses
of hydrocarbon products. First the gas stream is partly purified by
cooling the gas stream and removing any solidified and/or liquefied
contaminants. The partly purified gas is then compressed and the
compressed partly purified gas is further contacted with an
absorbing liquid. The absorbing liquid may comprise an amine
compound, such as alkanolamines, and may further comprise a
physical solvent. According to US 2009/0299122 A1 suitable physical
solvents include tetramethylene sulphone and derivatives, amides of
aliphatic carboxylic acids, N-alkyl pyrrolidone, in particular
N-methylpyrrolidine, N-alkyl piperidones, in particular N-methyl
piperidone, methanol, ethanol, ethylene glycol, polyethylene
glycols, mono- or di(C.sub.1-C.sub.4)alkyl ethers of ethylene
glycol or polyethylene glycols. It should be mentioned that US
2009/0299122 A1 does not describe any working examples. Therefore,
US 2009/0299122 A1 does not provide any experimental evidence of an
effective simultaneous removal of mercaptans and other contaminants
such as H.sub.2S and CO.sub.2 together with a reduced risk of
significant losses of hydrocarbon products.
[0016] In the prior art, the solvent N-methyl-2-pyrrolidone (NMP)
is often recommended as a physical solvent. However, NMP is under
scrutiny because of concerns over its potential health effects. NMP
has increasingly attracted attention as environmental regulators,
first in California and more recently in the European Union, have
sought to exercise control over the solvent primarily in markets
where it represents an inhalation hazard. Furthermore, NMP is now
known to cause reproductive toxicity (it is considered as being
reprotoxic) and is being labeled in the EU as "reprotoxic category
2" as from the 1st of December 2010. Formulations containing
>0.3% of NMP have to be labelled as such. Consequently, the use
of the solvent is restricted to professional users. NMP has been
placed on the REACH "Substance of Very High Concern" (SVHC) list
and will expectedly, sooner or later, be put under authorization or
restriction.
[0017] Therefore, there remains a need for a less toxic, more
economical and a more environmentally friendly absorbent solution
which is able to absorb mercaptans efficiently in the presence of
other contaminants such as H.sub.2S and CO.sub.2 while maintaining
an excellent performance in a conventional absorption-regeneration
cycle and which further exhibits a negligible co-absorption of
hydrocarbons.
SUMMARY OF THE INVENTION
[0018] The inventors have now surprisingly found that it is
possible to provide an improved process fulfilling the
above-mentioned needs.
[0019] The present invention provides a process comprising:
[0020] step a) contacting a feed stream comprising a contaminant
with an absorbent stream in a counter-current flow to produce a
contaminant depleted product stream depleted in the molar quantity
of the contaminant relative to the molar quantity of said
contaminant in the feed stream, and a contaminant enriched
absorbent stream enriched in the molar quantity of the contaminant
relative to the molar quantity of said contaminant in the absorbent
stream; and
[0021] step b) treating the contaminant enriched absorbent stream
to form a gaseous stream comprising said contaminant and a
regenerated absorbent stream lean in the molar quantity of said
contaminant relative to the molar quantity of said contaminant in
the contaminant enriched absorbent stream;
wherein said absorbent stream comprises: [0022] i. at least 15
weight percent (wt. % herein after), relative to the total weight
of the absorbent stream, of at least one substituted 2-pyrrolidone
of general formula (I) [compound (A), herein after]:
##STR00001##
[0022] wherein: [0023] each of R.sub.1 and R.sub.2, equal to or
different from each other and at each occurrence, is independently
selected from H or CH.sub.3; [0024] each of R, equal to or
different from each other and at each occurrence, is selected from
H or CH.sub.3; [0025] i is an integer in the range from 0 to 3;
[0026] o is an integer in the range from 2 to 6; n is an integer in
the range from 0 to 4; m is an integer in the range from 0 to 4;
or, [0027] ii. a mixture [mixture (M), herein after] comprising at
least one substituted 2-pyrrolidone of general formula (II)
[compound (B), herein after], herein below, and at least one amine
compound of general formula (III) [compound (C), herein after],
herein below:
##STR00002##
[0027] wherein: [0028] each of R', equal to or different from each
other and at each occurrence, is independently selected from H or
CH.sub.3 [0029] j is an integer in the range from 0 to 3 [0030]
each of R.sub.3, R.sub.4, R.sub.5 and R.sub.6, equal to or
different from each other and at each occurrence, is independently
selected from H or CH.sub.3; [0031] q is an integer in the range
from 0 to 1; p is an integer in the range from 1 to 6; with the
proviso that when p=1 and q=0 then R.sub.3 and R.sub.4 are CH.sub.3
and when p+q=2 then at least one of R.sub.3, R.sub.4, R.sub.5 or
R.sub.6 is CH.sub.3; [0032] each of R.sub.7, R.sub.8 and R.sub.9,
equal to or different from each other and at each occurrence, is
independently selected from H, C.sub.1-10 alkyl, C.sub.1-10
alkoxyalcohol or a C.sub.1-10 alkanol group; with the proviso that
at least one of R.sub.7, R.sub.8 or R.sub.9 is a C.sub.1-10
alkoxyalcohol or a C.sub.1-10 alkanol group.
[0033] The present invention further provides for a composition
comprising the mixture (M).
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] FIG. 1 shows a schematic diagram of an apparatus suitable
for removing contaminants from a gas stream.
DETAILED DESCRIPTION
[0035] The present invention will be described in the following
with respect to particular embodiments and with reference to
certain drawings but the invention is not limited thereto but only
by the claims. Any drawings described are only schematic and are
non-limiting. In the drawings, the size of some of the elements may
be exaggerated and not drawn on scale for illustrative purposes.
The dimensions and the relative dimensions do not necessarily
correspond to actual reductions to practice of the invention.
[0036] Furthermore, the terms first, second, third and the like in
the description and in the claims, are used for distinguishing
between similar elements and not necessarily for describing a
sequential or chronological order. The terms are interchangeable
under appropriate circumstances and the embodiments of the
invention can operate in other sequences than described or
illustrated herein.
[0037] Moreover, the terms top, bottom, over, under and the like in
the description and the claims are used for descriptive purposes
and not necessarily for describing relative positions. The terms so
used are interchangeable under appropriate circumstances and the
embodiments of the invention described herein can operate in other
orientations than described or illustrated herein.
[0038] The term "comprising", used in the claims, should not be
interpreted as being restricted to the means listed thereafter; it
does not exclude other elements or steps. It needs to be
interpreted as specifying the presence of the stated features,
integers, steps or components as referred to, but does not preclude
the presence or addition of one or more other features, integers,
steps or components, or groups thereof. Thus, the scope of the
expression "a device comprising means A and B" should not be
limited to devices consisting only of components A and B. It means
that with respect to the present invention, the only relevant
components of the device are A and B. Accordingly, the terms
"comprising" and "including" encompass the more restrictive terms
"consisting essentially of" and "consisting of".
[0039] As used in the foregoing and hereinafter, the following
definitions apply unless otherwise noted.
[0040] The term "alkyl"--alone or in combination means an
alkane-derived radical, for example, CF-G alkyl defines a straight
or branched alkyl radical having from F to G carbon atoms, e.g.
C1-4 alkyl defines a straight or branched alkyl radical having from
1 to 4 carbon atoms such as for example methyl, ethyl, 1-propyl,
2-propyl, 1-butyl, 2-butyl, 2-methyl-2-propyl, 2-methyl-1-propyl.
An alkyl group may be a straight chain alkyl or branched alkyl.
[0041] The term "alkanol"--alone or in combination means any alkyl
group comprising one or more hydroxyl (--OH) functional groups, for
example C.sub.F-G alkanol defines a straight or branched alkanol
having from F to G carbon atoms, e.g. C.sub.1-4 alkanol defines a
straight or branched alkanol having from 1 to 4 carbon atoms. An
alkanol group may be monohydric, dihydric, trihydric, or polyhydric
and may be a straight chain alkanol or a branched chain
alkanol.
[0042] The term "alkoxyalcohol"--alone or in combination means an
organic compound of general formula X--O--Y, wherein X is an alkyl
group substituted by --O--Y and wherein Y is an alkanol group. For
example, C.sub.F-G alkoxyalcohol defines an alkoxyalcohol having
from F to G carbon atoms in total, e.g. C.sub.1-4 alkoxyalcohol
defines an alkoxyalcohol group having from 1 to 4 carbon atoms such
as for example ethoxyethanol, methoxyethanol, ethoxymethanol,
methoxymethanol.
[0043] The term "alkanolamine" is intended to denote an amine
compound comprising at least one alkanol group and wherein further
substituents are selected among H, alkyl or alkanol groups. In this
context, a primary alkanolamine comprises one alkanol group and two
hydrogens bonded to the nitrogen atom, a secondary alkanolamine
comprises at least one alkanol group and at least one hydrogen
bonded to the nitrogen atom, a tertiary alkanolamine comprises at
least one alkanol group and no hydrogen bonded to the nitrogen
atom.
[0044] The term "at least one substituted 2-pyrrolidone of general
formula (I)" is intended to denote one or more than one substituted
2-pyrrolidone of general formula (I). Mixtures of substituted
2-pyrrolidones of general formula (I) can also be used for the
purpose of the invention. The term "at least one substituted
2-pyrrolidone of general formula (II)" is intended to denote one or
more than one substituted 2-pyrrolidone of general formula (II).
Mixtures of substituted 2-pyrrolidones of general formula (II) can
also be used for the purpose of the invention. The term "at least
one amine compound of general formula (III)" is intended to denote
one or more than one amine compound of general formula (III).
Mixtures of amine compounds of general formula (III) can also be
used for the purpose of the invention.
[0045] It is understood that the term "quantity" relates to the
property of being measurable in terms of amounts. The term
"quantity" may denote the mass or weight or moles or any physical
or in any case numerical parameter, unless otherwise specified,
able to indicate at least, at quantity level, the presence either
of a contaminant or of a mixture of contaminants.
[0046] Within the context of the present invention, the expression
"contacting a feed stream comprising a contaminant with an
absorbent stream in a counter-current flow" is intended to denote
that an absorbent stream is contacting a feed stream comprising a
contaminant in such a way that said absorbent stream and said feed
stream are approaching each other in an opposite direction. It is
further understood that the angle at which said streams approach
each other may deviate from 180.degree..
[0047] Within the context of the present invention, at least one of
the streams is a mobile stream. Therefore, at least the following
three situations may occur: a static feed stream is contacted with
a mobile, flowing absorbent stream is; a mobile, flowing feed
stream is contacted with a static absorbent stream; or a mobile,
flowing feed stream is contacted with a mobile, flowing absorbent
stream. The term "at least one stream" is intended to denote one or
more than one stream.
[0048] As discussed above, in the prior art, the solvent
N-methyl-2-pyrrolidone (NMP) is often recommended as a physical
solvent. The Applicants have now found that only specific
substituted 2-pyrrolidones of general formula (I) and of general
formula (II), as detailed above, characterised by having notably
specific selections of o, n and m in formula (I) and p and q in
formula (II), as defined above, can provide absorbent streams which
are more efficient in removing mercaptans from a feed stream
compared to NMP, as evidenced by the examples below.
[0049] The Applicants believe that in terms of chemical structure,
the elongation of the chain attached to the nitrogen of the
substituted 2-pyrrolidone of formula (I) or (II) according to the
present invention to a total of at least four carbon atoms, appears
to yield absorbent streams which are more efficient in removing
mercaptans from a feed stream. As a further advantage, compounds
with an elongated chain such as N-n-butyl-2-pyrrolidone were found
to be non-reprotoxic.
[0050] The Applicants have further found that the specific
selection of o, n and m in formula (I) and p and q in formula (II),
as defined above, in terms of chemical structure also restricts the
chain length of the chain attached to the nitrogen of the
substituted 2-pyrrolidone of formula (I) or (II) according to the
present invention, and appears to yield absorbent streams which
maintain a low tendency towards co-absorption of hydrocarbons. This
brings the advantage that less valuable hydrocarbon compounds are
lost in the separated contaminants and further brings a higher
process selectivity towards the contaminants.
[0051] In a preferred embodiment of the process according to the
present invention, in compound (A) of general formula (I) i is an
integer in the range from 0 to 1, more preferably in compound (A)
of general formula (I) i is 0.
[0052] In a preferred embodiment of the process according to the
present invention, each of R1 and R2 in compound (A) of general
formula (I) are H.
[0053] In a preferred embodiment of the process according to the
present invention, in compound (A) of general formula (I) o is an
integer in the range from 2 to 5, more preferably o is an integer
in the range from 2 to 4, even more preferably o is an integer
selected from 2 or 3.
[0054] In a preferred embodiment of the process according to the
present invention, in compound (A) of general formula (I) n is an
integer in the range from 0 to 3, more preferably n is an integer
in the range from 0 to 2, even more preferably n is an integer
selected from 0 or 1, most preferably in compound (A) of general
formula (I) n is 0.
[0055] In a preferred embodiment of the process according to the
present invention, in compound (A) of general formula (I) m is an
integer in the range from 0 to 3, more preferably m is an integer
in the range from 0 to 2, even more preferably m is an integer
selected from 0 or 1, most preferably in compound (A) of general
formula (I) m is 0.
[0056] In a preferred embodiment of the process according to the
present invention, in compound (B) of general formula (II) j is an
integer in the range from 0 to 1, more preferably in compound (B)
of general formula (II) j is 0.
[0057] In one embodiment of the process according to the present
invention, each of R.sub.5 and R.sub.6 in compound (B) of general
formula (II) is H, each of R.sub.3 and R.sub.4 in compound (B) of
general formula (II) equal to or different from each other and at
each occurrence, is independently selected from H or CH.sub.3, q is
1, p is an integer in the range from 1 to 6; with the proviso that
when p+q=2 then at least one of R.sub.3, R.sub.4, R.sub.5 or
R.sub.6 is CH.sub.3.
[0058] In a preferred embodiment of the process according to the
present invention, each of R3, R4, R5 and R6 in compound (B) of
general formula (II) is H, q is 1 and p is an integer in the range
from 2 to 6.
[0059] In a more preferred embodiment of the process according to
the present invention, each of R.sub.3, R.sub.4, R.sub.5 and
R.sub.6 in compound (B) of general formula (II) is H, q is 1 and p
is 2, 3 or 4, more preferably p is 2.
[0060] In one embodiment of the process according to the present
invention, each of R7, R8 and R9 in compound (C) of general formula
(III), are independently selected from H, C1-5 alkyl, C1-5
alkoxyalcohol or C1-5 alkanol group; with the proviso that at least
one of R7, R8 or R9 is a C1-5 alkoxyalcohol or C1-5 alkanol
group.
[0061] In another embodiment of the process according to the
present invention, each of R7, R8 and R9 in compound (C) of general
formula (III), are independently selected from H, C1-5 alkyl or
C1-5 alkanol group; with the proviso that at least two of R7, R8 or
R9 are a C1-5 alkanol group.
[0062] In yet another embodiment of the process according to the
present invention, each of R7, R8 and R9 in compound (C) of general
formula (III), are independently selected from C1-5 alkyl or C1-5
alkanol group; with the proviso that at least one of R7, R8 or R9
is a C1-5 alkanol group. In a preferred embodiment of the process
according to the present invention, each of R7 and R8 in compound
(C) of general formula (III) are an C1-5 alkanol group and R9 is
selected from a C1-5 alkyl or C1-5 alkanol group.
[0063] In a more preferred embodiment of the process according to
the present invention, each of R.sub.7 and R.sub.8 in compound (C)
of general formula (III) are an C.sub.1-5 alkanol group and R.sub.9
is a C.sub.1-5 alkyl group. More preferably, each of R.sub.7, and
R.sub.8 are an C.sub.1-4 alkanol group and R.sub.9 is a C.sub.1-4
alkyl group. Even more preferably, each of R.sub.7, and R.sub.8 are
an C.sub.1-3 alkanol group and R.sub.9 is a C.sub.1-3 alkyl
group.
[0064] In compounds (A) of the absorbent stream as used in step a)
of the process according to the present invention, preferably
R.sub.1 and R.sub.2 are H and i is 0. Preferred compounds (A) are
thus selected from those of formula (I-a) herein below:
##STR00003##
wherein: [0065] o is an integer in the range from 2 to 4; n is an
integer selected from 0 or 1; m is an integer selected from 0 or
1.
[0066] Typical compounds (A) suitable for use in step a) of the
process of the present invention may include, but are not limited
to, dimethylaminopropyl-2-pyrrolidone (DMAP-2-pyrrolidone),
dimethylaminoethyl-2-pyrrolidone (DMAE-2-pyrrolidone),
diethylaminopropyl-2-pyrrolidone (DEAP-2-pyrrolidone) or a mixture
of two or more thereof.
[0067] More preferably, in compounds (A) comprised in the absorbent
stream as used in step a) of the process according to the present
invention, o is an integer in the range from 2 to 4; n is 0 and m
is 0. More preferred compounds (A) are thus selected from those of
formula (I-b) herein below:
##STR00004##
wherein: [0068] o is an integer in the range from 2 to 4.
[0069] According to a preferred embodiment of the process according
to the present invention, the compounds (A) are selected from those
of formula (I-c) or formula (l-d) herein below:
##STR00005##
[0070] The inventors have found that compound (A) as specified
herein, as comprised in the absorbent stream in step a) of the
process according to the present invention, can simultaneously act
as a physical solvent and as a chemical solvent, thereby forming a
so-called hybrid solvent on its own. Without being bound to this
theory, the inventors believe that the pyrrolidone ring in compound
(A) offers an increased ability to dissolve mercaptans while the
tertiary amine substituent on the pyrrolidone ring in compound (A)
can react with other contaminants such as CO.sub.2 and
H.sub.2S.
[0071] The inventors have further found that when compound (A) is
used in the absorbent stream, a minimum amount of 15 wt. % of
compound (A), relative to the total weight of the absorbent stream,
is required to achieve an effective removal of mercaptans in the
presence of other contaminants such as H.sub.2S and CO.sub.2.
[0072] In compounds (B) comprised in the mixture (M) as used in
step a) of the process according to the present invention,
preferably R.sub.5 and R.sub.6 are H and j is 0. Preferred
compounds (B) are thus selected from those of formula (II-a) herein
below:
##STR00006##
wherein: [0073] each of R.sub.3 and R.sub.4, are independently
selected from H or CHs; [0074] q is 1; p is an integer in the range
from 2 to 6.
[0075] Typical compounds (B) suitable for use in step a) of the
process of the present invention may thus include, but are not
limited to, specific N-alkyl 2-pyrrolidones such as
N-n-butyl-2-pyrrolidone, N-sec-butyl-2-pyrrolidone,
N-isobutyl-2-pyrrolidone, N-tert-butyl-2-pyrrolidone,
N-n-pentyl-2-pyrrolidone, N-sec-pentyl-2-pyrrolidone,
N-tert-pentyl-2-pyrrolidone, N-3-pentyl-2-pyrrolidone,
N-isopentyl-2-pyrrolidone, N-neopentyl-2-pyrrolidone,
N-n-hexyl-2-pyrrolidone, N-n-heptyl-2-pyrrolidone,
N-n-octyl-2-pyrrolidone, or a mixture of two or more thereof.
[0076] The inventors have found that in terms of chemical
structure, elongation of the carbon chain attached to the nitrogen
of the pyrrolidone ring in compound (B) as used in step a)
according to the present invention, to at least four carbon atoms
yields absorbent streams which are more effective in removing
mercaptans from a feed stream compared to NMP, as evidenced by the
examples below and furthermore are non-reprotoxic. The inventors
have further found that compounds (B) according to the present
invention, in which the carbon chain attached to the nitrogen of
the pyrrolidone ring is restricted to at most 8 carbon atoms,
maintain a low tendency towards co-absorption of hydrocarbons.
[0077] More preferably, in compounds (B) comprised in the mixture
(M) as used in step a) of the process according to the present
invention, R.sub.3, R.sub.4, R.sub.5 and R.sub.6 are H and j is 0.
More preferred compounds (B) are thus selected from those of
formula (II-b) herein below:
##STR00007##
wherein:
[0078] p is an integer in the range from 2 to 6.
[0079] According to one embodiment of the process according to the
present invention, the compounds (B) are selected from those of
formula (II-c) to formula (II-g) herein below:
##STR00008##
[0080] According to a preferred embodiment of the process according
to the present invention, the compounds (B) are selected from those
of formula (II-c) to formula (II-e), as specified here above.
[0081] According to a more preferred embodiment, the compound (B)
in the absorbent stream as used in step a) of the process according
to the present invention, is a compound of formula (II-c):
##STR00009##
[0082] In compounds (C) comprised in the mixture (M) as used in
step a) of the process according to the present invention,
preferably each of R.sub.7, R.sub.8 and R.sub.9, are independently
selected from H, C1-4 alkyl, C1-4 alkoxyalcohol or C1-4 alkanol
group; with the proviso that at least one of R.sub.7, R.sub.8 or
R.sub.9 is a C1-4 alkoxyalcohol or C1-3 alkanol group.
[0083] Typical compounds (C) suitable for use in step a) of the
process of the present invention may include primary, secondary and
tertiary alkanolamines such as, but not limited to,
monoethanolamine (MEA), diethanolamine (DEA), triethanolamine
(TEA), monomethylmonoethanolamine (MMEA), diethylmonoethanolamine,
diisopropanollamine (DIPA), diglycolamine (DGA), and
methyldiethanolamine (MDEA) or a mixture of two or more
thereof.
[0084] Preferably, the compounds (C) comprised in the mixture (M)
as used in step a) of the process of the present invention are
chosen among tertiary alkanolamines such as notably,
triethanolamine (TEA), diethylmonoethanolamine and
methyldiethanolamine (MDEA). More preferably, the compounds (C)
comprised in the absorbent stream as used in step a) of the process
of the present invention is methyldiethanolamine (MDEA).
[0085] The inventors have found that even in the presence of a
compound (B) and comprised in a mixture (M) as used in step a) of
the process according to the present invention, tertiary
alkanolamines rarely form irreversible components with impurities.
Furthermore, tertiary alkanolamines comprised in a mixture (M)
bring the advantage to be more stable thermally and chemically
under typical operating conditions and usually they require less
energy to be regenerated.
[0086] In certain embodiments, the compound (C) comprised in the
mixture (M) as used in step a) of the process according to the
present invention is diglycolamine (DGA).
[0087] A non-limitative example of a commercially available
tertiary alkanolamine is AdapT.RTM. 100 which is available from the
Eastman Chemical Company.
[0088] It is further understood that all definitions and
preferences as described for compound (A) and compound (C) above
equally apply for this embodiment and all further embodiments, as
described below.
[0089] As said above, the absorbent stream in step a) of the
process according to the present invention comprises at least 15
wt. %, relative to the total weight of the absorbent stream, of at
least one compound (A) of general formula (I), as detailed
above.
[0090] Advantageously, the weight percent of the compound (A)
comprised in the absorbent stream as used in step a), relative to
the total weight of the absorbent stream, is equal to or greater
than 20 wt. %, preferably equal to or greater than 25 wt. %,
preferably equal to or greater than 30 wt. %, preferably equal to
or greater than 35 wt. %, preferably equal to or greater than 40
wt. %, preferably equal to or greater than 45 wt. %, preferably
equal to or greater than 50 wt. %, preferably equal to or greater
than 55 wt. %, preferably equal to or greater than 60 wt. %,
preferably equal to or greater than 65 wt. %, preferably equal to
or greater than 70 wt. %, preferably equal to or greater than 75
wt. %, preferably equal to or greater than 80 wt. %, preferably
equal to or greater than 85 wt. %, preferably equal to or greater
than 90 wt. %, preferably equal to or greater than 95 wt. %,
preferably equal to or greater than 98 wt. %.
[0091] It is further understood that, the upper value of the weight
percent of the compound (A) comprised in the absorbent stream as
used in step a), relative to the total weight of the absorbent
stream, is not particularly limited but is advantageously equal to
or less than 99 wt. %, preferably equal to or less than 95 wt. %,
preferably equal to or less than 90 wt. %, preferably equal to or
less than 85 wt. %.
[0092] As explained above, the inventors have found that compounds
(A) can simultaneously act as a physical solvent and as a chemical
solvent. Therefore, compounds (A) can be used as a solvent as a
part of the absorbent stream or as an absorbent stream as such.
[0093] In one embodiment, the absorbent stream in step a) of the
process according to the present invention consists essentially of
compounds (A) of general formula (I), as detailed above.
[0094] For the purpose of the present invention, the expression
"consists essentially of" is intended to denote that any additional
ingredient is present in an amount of at most 5 wt. %, preferably
at most 2 wt. %, relative to the total weight of the absorbent
stream. For example, any additional ingredient, different from
compound (A), as detailed above, is present in an amount of at most
5 wt. %, preferably at most 2 wt. %, relative to the total weight
of the absorbent stream.
[0095] The inventors have further found that when the compound (A),
as detailed above, is further mixed with a compound (C) of general
formula (III), as detailed above, good results were also
obtained.
[0096] According to a preferred embodiment, the absorbent stream in
step a) of the process according to the present invention comprises
at least 15 wt. %, relative to the total weight of the absorbent
stream, of at least one compound (A) of general formula (I), as
detailed above, and further comprises at least one compound (C) of
general formula (III), as detailed above.
[0097] Advantageously, the at least one amine compound (C) of
general formula (III) is comprised in the absorbent stream in an
amount corresponding to a weight ratio of the compound (C) to the
compound (A) of at least 0.5:1, preferably at least 0.75:1, more
preferably at least 1:1, even more preferably at least 1.5:1, yet
even more preferably at least 1.75:1. It is further understood that
a weight ratio of the compound (C) to the compound (A) in the
absorbent stream is generally at most 5:1, preferably at most 4:1,
more preferably at most 3.5:1, more preferably at most 3:1, more
preferably at most 2.5:1.
[0098] According to certain embodiments of the present invention,
the absorbent streams as used in step a) of the process of the
present invention may further comprise water.
[0099] When water is present in the absorbent stream, then the
water is present in the absorbent stream in an amount of at least
0.5 wt. %, preferably of at least 5 wt. %, preferably of at least
10 wt. %, more preferably at least 15 wt. %, even more preferably
at least 20 wt. %, and even more preferably at least 22 wt. %,
relative to the total amount of all components of the absorbent
stream.
[0100] It is further understood that the water is present in the
absorbent stream in an amount of at most 85 wt. %, preferably of at
most 70 wt. %, more preferably at most 60 wt. %, even more
preferably at most 50 wt. %, more preferably at most 40 wt. %, even
more preferably at most 30 wt. %, more preferably at most 28 wt. %,
relative to the total amount of all components of the absorbent
stream.
[0101] According to a more preferred embodiment, the absorbent
stream in step a) of the process according to the present invention
comprises a composition [composition (C), herein after], comprising
at least 15 wt. % of at least one compound (A) of general formula
(I), as detailed above, relative to the total weight of the
composition (C), at least one compound (C) of general formula
(III), as detailed above, and water.
[0102] Advantageously, the water is comprised in composition (C) in
an amount corresponding to a weight ratio of the water to the
compound (A) of at least 0.25:1, preferably at least 0.3:1, more
preferably at least 0.4:1, even more preferably at least 0.6:1, yet
even more preferably at least 0.9:1. It is further understood that
the weight ratio of the water to the compound (A) in the
composition (C) is generally at most 4:1, preferably at most 3:1,
more preferably at most 2.5:1, even more preferably at most 2:1,
even more preferably at most 1.5:1, even more preferably at most
1.1:1.
[0103] Advantageously, the weight percent of the compound (A)
comprised in the composition (C) as used in step a), relative to
the total weight of the composition (C), is advantageously equal to
or greater than 18 wt. %, preferably equal to or greater than 20
wt. %, more preferably equal to or greater than 21 wt. %, even more
preferably equal to or greater than 22 wt. %.
[0104] It is further understood that, the upper value of the weight
percent of the compound (A) comprised in the composition (C) as
used in step a), relative to the total weight of the composition
(C), is not particularly limited but is advantageously equal to or
less than 50 wt. %, preferably equal to or less than 40 wt. %, more
preferably equal to or less than 35 wt. %, even more preferably
equal to or less than 30 wt. %, even more preferably equal to or
less than 29 wt. %, most preferably equal to or less than 28 wt.
%.
[0105] Advantageously, the weight percent of the compound (C)
comprised in the composition (C) as used in step a), relative to
the total weight of the composition (C), is advantageously equal to
or greater than 2 wt. %, preferably equal to or greater than 5 wt.
%, preferably equal to or greater than 10 wt. %, more preferably
equal to or greater than 20 wt. %, even more preferably equal to or
greater than 30 wt. %, yet even more preferably equal to or greater
than 40 wt. %, most preferably equal to or greater than 45 wt.
%.
[0106] It is further understood that, the upper value of the weight
percent of the compound (C) comprised in the composition (C) as
used in step a), relative to the total weight of the composition
(C), is advantageously equal to or less than 85 wt. %, preferably
equal to or less than 80 wt. %, more preferably equal to or less
than 75 wt. %, more preferably equal to or less than 70 wt. %, more
preferably equal to or less than 65 wt. %, even more preferably
equal to or less than 60 wt. %, yet even more preferably equal to
or less than 55 wt. %.
[0107] It is further understood that all definitions and
preferences as described for compound (B) and compound (C) above
equally apply for this embodiment and all further embodiments, as
described below.
[0108] As said above, the absorbent stream in step a) of the
process according to the present invention may comprise a mixture
(M), as detailed above.
[0109] According to one embodiment of the process according to the
present invention, the at least one compound (B) of general formula
(II) is advantageously comprised in the mixture (M) in an amount
corresponding to a weight ratio of the compound (B) to the compound
(C) of at least 0.05:1, preferably at least 0.1:1, more preferably
at least 0.2:1, more preferably at least 0.3:1, more preferably at
least 0.35:1, even more preferably at least 0.4:1, yet even more
preferably at least 0.45:1. It is further understood that a weight
ratio of the compound (C) to the compound (A) in the mixture (M) is
generally at most 2:1, preferably at most 1.5:1, more preferably at
most 1:1, more preferably at most 0.75:1 even more preferably at
most 0.65:1, yet even more preferably at most 0.55:1.
[0110] In a preferred embodiment of the process according to the
present invention, the weight percent of the compound (B) comprised
in the mixture (M) as used in step a), relative to the total weight
of the mixture (M), is advantageously equal to or greater than 5
wt. %, preferably equal to or greater than 10 wt. %, more
preferably equal to or greater than 15 wt. %, more preferably equal
to or greater than 18 wt. %, more preferably equal to or greater
than 20 wt. %, even more preferably equal to or greater than 22 wt.
%, yet even more preferably equal to or greater than 25 wt. %.
[0111] It is further understood that, the upper value of the weight
percent of the compound (B) comprised in the mixture (M) as used in
step a), relative to the total weight of the mixture (M), is
advantageously equal to or less than 50 wt. %, preferably equal to
or less than 45 wt. %, more preferably equal to or less than 40 wt.
%, more preferably equal to or less than 35 wt. %, more preferably
equal to or less than 30 wt. %, even more preferably equal to or
less than 29 wt. %, most preferably equal to or less than 28 wt.
%.
[0112] In a preferred embodiment of the process according to the
present invention, the weight percent of the compound (C) comprised
in the mixture (M) as used in step a), relative to the total weight
of the mixture (M), is advantageously equal to or greater than 2
wt. %, preferably equal to or greater than 5 wt. %, preferably
equal to or greater than 10 wt. %, more preferably equal to or
greater than 20 wt. %, even more preferably equal to or greater
than 30 wt. %, yet even more preferably equal to or greater than 40
wt. %, most preferably equal to or greater than 45 wt. %.
[0113] It is further understood that, the upper value of the weight
percent of the compound (C) comprised in mixture (M) as used in
step a), relative to the total weight of the mixture (M), is
advantageously equal to or less than 85 wt. %, preferably equal to
or less than 80 wt. %, more preferably equal to or less than 75 wt.
%, more preferably equal to or less than 70 wt. %, more preferably
equal to or less than 65 wt. %, even more preferably equal to or
less than 60 wt. %, yet even more preferably equal to or less than
55 wt. %.
[0114] According to one embodiment, the absorbent stream as used in
step a) of the process according to the present invention consists
essentially of: [0115] 15 wt. %-40 wt. % of at least one compound
(A) of general formula (II), as defined above, [0116] 30 wt. %-65
wt. % of at least one compound (C) of general formula (III), as
defined above, [0117] 15 wt. %-40 wt. % of water, all wt. % are
relative to the total weight of the absorbent stream.
[0118] It is further understood that in this embodiment, any
additional ingredient, different from compound (A), as detailed
above, compound (C), as detailed above, and water, is present in an
amount of at most 5 wt. %, preferably at most 2 wt. %, relative to
the total weight of the absorbent stream.
[0119] Preferably, the mixture (M) as used in step a) of the
process according to the present invention further comprises
water.
[0120] In this preferred embodiment of the process according to the
present invention, the weight percent of the compound (B) comprised
in the mixture (M) as used in step a), relative to the total weight
of the mixture (M), is advantageously equal to or greater than 5
wt. %, preferably equal to or greater than 10 wt. %, more
preferably equal to or greater than 15 wt. %, more preferably equal
to or greater than 18 wt. %, more preferably equal to or greater
than 20 wt. %, even more preferably equal to or greater than 22 wt.
%.
[0121] It is further understood that the upper value of the weight
percent of the compound (B) comprised in the mixture (M) as used in
step a), relative to the total weight of the mixture (M), is
advantageously equal to or less than 50 wt. %, preferably equal to
or less than 45 wt. %, more preferably equal to or less than 40 wt.
%, more preferably equal to or less than 35 wt. %, more preferably
equal to or less than 30 wt. %, even more preferably equal to or
less than 28 wt. %.
[0122] In a preferred embodiment of the process according to the
present invention, the weight percent of the compound (C) comprised
in mixture (M) as used in step a), relative to the total weight of
the mixture (M), is advantageously equal to or greater than 2 wt.
%, preferably equal to or greater than 5 wt. %, preferably equal to
or greater than 10 wt. %, more preferably equal to or greater than
20 wt. %, even more preferably equal to or greater than 30 wt. %,
yet even more preferably equal to or greater than 40 wt. %, most
preferably equal to or greater than 45 wt. %.
[0123] It is further understood that the upper value of the weight
percent of the compound (C) comprised in the mixture (M) as used in
step a), relative to the total weight of the mixture (M), is
advantageously equal to or less than 70 wt. %, preferably equal to
or less than 65 wt. %, more preferably equal to or less than 60 wt.
%, even more preferably equal to or less than 55 wt. %.
[0124] According to one embodiment of the process according to the
present invention, the water is typically added to mixture (M) in
an amount corresponding to a weight ratio of the water to the
compound (B) of at least 0.25:1, preferably at least 0.3:1, more
preferably at least 0.4:1, even more preferably at least 0.6:1, yet
even more preferably at least 0.9:1. It is further understood that
a weight ratio of the water to the compound (B) in the absorbent
stream is generally at most 4:1, preferably at most 3:1, more
preferably at most 2.5:1, even more preferably at most 2:1, yet
even more preferably at most 1.1:1.
[0125] Good results were obtained when the weight percent of the
compound (B) comprised in the mixture (M) as used in step a),
relative to the total weight of the mixture (M), is from 10-35 wt.
%, the weight percent of the compound (C) in the mixture (M) as
used in step a), relative to the total weight of the mixture (M),
is between 30-65 wt. % and the weight percent of the water
comprised in the mixture (M) as used in step a), relative to the
total weight of the mixture (M), is from 15-40 wt. %.
[0126] According to a preferred embodiment, the absorbent stream as
used in step a) of the process according to the present invention
comprises: [0127] 10 wt. %-35 wt. % of at least one compound (B) of
general formula (II), as defined above, [0128] 30 wt. %-65 wt. % of
at least one compound (C) of general formula (III), as defined
above, [0129] 15 wt. %-40 wt. % of water, all wt. % are relative to
the total weight of the absorbent stream.
[0130] According to another embodiment, the absorbent stream as
used in step a) of the process according to the present invention
consist essentially of: [0131] 10 wt. %-35 wt. % of at least one
compound (B) of general formula (II), as defined above, [0132] 30
wt. %-65 wt. % of at least one compound (C) of general formula
(III), as defined above, [0133] 15 wt. %-40 wt. % of water, all wt.
% are relative to the total weight of the absorbent stream.
[0134] It is further understood that in this embodiment, any
additional ingredient, different from compound (B), as detailed
above, compound (C), as detailed above, and water, is present in an
amount of at most 5 wt. %, preferably at most 2 wt. %, relative to
the total weight of the absorbent stream.
[0135] If desired, the absorbent stream may further comprise an
accelerator for the reaction of the absorbent stream with at least
one of the contaminants, in particular for the reaction with carbon
dioxide. The accelerator brings a clear improvement to the kinetics
of the system, absorption rates are faster, loading amounts are
higher, absorbent stream/feed stream ratios are lower, design of
the plant may be smaller and the regeneration heat requirement may
be lower, resulting in less cooling capacity. A lower absorbent
stream/feed stream ratio, may result in a smaller design of the
plant, absorber as well as regenerator. Alternatively, when using
the same absorbent stream/feed stream ratio, an often considerably
larger amount of contaminants may be removed.
[0136] Advantageously, the weight percent of the accelerator as
comprised in the absorbent stream as used in step a), relative to
the total weight of the absorbent stream, is from 0.1 to 20 wt. %,
preferably at least 0.5 wt. %, preferably at least 1 wt. %,
preferably at least 1.5 wt. %, preferably at least 2 wt. %,
preferably at least 2.5 wt. %, and either alternatively or in
combination therewith at most 18 wt. % by weight, preferably at
most 16 wt. %, preferably at most 14 wt. %, preferably at most 12
wt. %, preferably at most 10 wt. %, preferably at most 9 wt. %,
even more preferably at most 8.5 wt. %.
[0137] Typical accelerators suitable for use in the absorbent
stream as used in step a) of the process of the present invention
may thus include, but are not limited to, amines, alcohols,
ketones, vinyl alcohols, vinyl ketones, ether alcohols, ether
ketones, glycols, polyethylene glycols, polypropylene glycols,
ethylene glycolpropylene glycol copolymers, glycol ethers,
thioglycols, thioalcohols, sulfones, sulfoxide, N-alkylated
2-pyrrolidones, N-alkylated piperidones,
cyclotetramethylenesulfones, N-alkylformamides, N-alkylacetamides,
alkyl phosphates, alkylene carbonates and/or dialkyl carbonates.
More preferred candidates are monoethanol amine (MEA), diethanol
amine (DEA), monomethyl ethanolamine (MMEA), piperazine,
2-methylpiperazine, N-methyl piperazine, N-ethyl piperazine,
N-hydroxyethyl piperazine (HEP), N-(2-aminoethyl) piperazine,
homopiperazine, piperidine and morpholine. Most preferred as
accelerator is piperazine.
[0138] In general, the feed stream comprises at least one
contaminant selected from mercaptans, hydrogen sulfide (H2S),
carbon dioxide (CO2), carbon oxysulfide (COS), carbon disulfide,
(CS2), and disulfides.
[0139] In particular, the feed stream comprises mercaptans and at
least one other contaminant selected from H2S, CO2, COS, CS2 and
disulfides.
[0140] We have found that mercaptans are removed efficiently from
feed streams even in the presence of other contaminants such as
H.sub.2S and CO.sub.2. The inventors have found that compound (B)
as specified herein, can act as a physical solvent while compound
(C) as specified herein, can act as a chemical solvent, thereby
forming a so-called hybrid solvent. The inventors believe that the
pyrrolidone ring in compound (B) offers an increased ability to
dissolve mercaptans while the amine compound (C) is able to react
with other contaminants such as CO.sub.2 and H.sub.2S.
Alternatively, the compound (A) as specified herein, can
simultaneously act as a physical solvent and as a chemical solvent,
thereby forming a so-called hybrid solvent on its own. The
inventors believe that the pyrrolidone ring in compound (A) offers
an increased ability to dissolve mercaptans while the tertiary
amine substituent on the pyrrolidone ring in compound (A) can react
with other contaminants such as CO.sub.2 and H.sub.2S.
[0141] It is understood that in the step a), the molar quantity of
the contaminant in the contaminant depleted product stream,
relative to the molar quantity of the contaminant in the feed
stream, is reduced. Furthermore, the molar quantity of the
contaminant in the enriched absorbent stream, relative to the molar
quantity of the contaminant in the absorbent stream, has been
increased.
[0142] The molar quantity of the contaminant in the contaminant
depleted product stream, relative to the molar quantity of the
contaminant in the feed stream, is reduced by at least 5%,
preferably at least 10%, more preferably at least 20%, even more
preferably at least 30%, yet even more preferably at least 40% and
most preferably at least 50%.
[0143] The molar quantity of the contaminant in the enriched
absorbent stream, relative to the molar quantity of the contaminant
in the absorbent stream, has been increased by at least 5%,
preferably at least 10%, more preferably at least 20%, even more
preferably at least 30%, yet even more preferably at least 40% and
most preferably at least 50%.
[0144] The molar quantity of mercaptans in the contaminant depleted
product stream, relative to the molar quantity of mercaptans in the
feed stream, is reduced by at least 5%, preferably at least 10%,
more preferably at least 20%, even more preferably at least 30%,
yet even more preferably at least 40% and most preferably at least
50%.
[0145] Typical feed streams as used in step a) of the process
according to the present invention, such as natural gas or refinery
gas streams and synthesis gas, may comprise valuable hydrocarbons
such as olefins and alkanes, for example methane, ethane, propane,
butane, pentane, hexane, heptane and octane.
[0146] It is understood that in the enriched absorbent stream
produced in step a) of the process of the present invention, the
molar quantity of hydrocarbons, relative to the molar quantity of
the hydrocarbons in the feed stream remains low.
[0147] In one embodiment of the process according to the present
invention, the feed stream comprises carbon dioxide, and the amount
of CO2 in the feed stream to step a) is at least 5 volume % [vol.
%, herein after], preferably at least 10 vol. %, preferably at
least 15 vol. %, preferably at least 20 vol. %, preferably at least
25 vol. %, preferably at least 30 vol. %, preferably at least 35
vol. %, preferably at least 40 vol. %, preferably at least 45 vol.
%, preferably at least 50 vol. %, preferably at least 55 vol. %,
preferably at least 60 vol. %, preferably at least 65 vol. %.
[0148] In one embodiment of the process according to the present
invention, the feed stream comprises hydrogen sulfide, and the
amount of hydrogen sulfide in the feed stream to step a) is at
least 1 vol. %, preferably at least 5 vol. %, preferably at least 8
vol. %, preferably at least 10 vol. %, preferably at least 12 vol.
%, preferably at least 15 vol. %, preferably at least 18 vol.
%.
[0149] In one embodiment of the process according to the present
invention, the feed stream comprises carbon oxysulfide, and the
amount of carbon oxysulfide in the feed stream to step a) is at
least 0.1 ppmv, preferably at least 0.5 ppmv, preferably at least 1
ppmv, preferably at least 5 ppmv, preferably at least 10 ppmv,
preferably at least 15 ppmv, preferably at least 20 ppmv,
preferably at least 30 ppmv, preferably at least 40 ppmv,
preferably at least 50 ppmv, preferably at least 100 ppmv,
preferably at least 150 ppmv, preferably at least 200 ppmv,
preferably at least 300 ppmv, preferably at least 400 ppmv,
preferably at least 500 ppmv, preferably at least 1000 ppmv,
preferably at least 1500 ppmv, preferably at least 2000 ppmv,
preferably at least 3000 ppmv, preferably at least 4000 ppmv,
preferably at least 5000 ppmv, preferably at least 6000 ppmv,
preferably at least 7000 ppmv, preferably at least 8000 ppmv,
preferably at least 9000 ppmv, preferably at least 10000 ppmv. The
applicants have found that the absorbent streams according to the
present invention are particularly effective for removing
mercaptans.
[0150] In a more preferred embodiment of the process according to
the present invention, the feed stream comprises mercaptans, and
the amount of mercaptans in the feed stream to step a) is at least
0.1 parts per million by volume [ppmv, herein after], preferably at
least 0.5 ppmv, preferably at least 1 ppmv, preferably at least 5
ppmv, preferably at least 10 ppmv, preferably at least 15 ppmv,
preferably at least 20 ppmv, preferably at least 30 ppmv,
preferably at least 40 ppmv, preferably at least 50 ppmv,
preferably at least 100 ppmv, preferably at least 150 ppmv,
preferably at least 200 ppmv, preferably at least 300 ppmv,
preferably at least 400 ppmv, preferably at least 500 ppmv,
preferably at least 600 ppmv, preferably at least 700 ppmv,
preferably at least 800 ppmv, preferably at least 900 ppmv,
preferably at least 1000 ppmv, preferably at least 1100 ppmv,
preferably at least 1200 ppmv, preferably at least 1300 ppmv,
preferably at least 1400 ppmv, preferably at least 1500 ppmv,
preferably at least 2000 ppmv, preferably at least 3000 ppmv,
preferably at least 4000 ppmv, preferably at least 5000 ppmv,
preferably at least 6000 ppmv, preferably at least 7000 ppmv,
preferably at least 8000 ppmv, preferably at least 9000 ppmv,
preferably at least 10000 ppmv. The applicants have found that the
absorbent streams according to the present invention are
particularly effective for removing mercaptans.
[0151] It is further understood that the term "mobile, flowing feed
stream" may refer to a liquid or a gaseous mobile, flowing feed
stream.
[0152] In one embodiment of the process according to the present
invention, the feed stream is a gaseous, mobile, flowing feed
stream which is contacted with a liquid static absorbent stream.
This embodiment is clearly illustrated in the examples below which
were performed on lab-scale.
[0153] In another embodiment of the process according to the
present invention, the feed stream is a liquid or gaseous mobile,
flowing feed stream which is contacted with a liquid mobile,
flowing absorbent stream. This embodiment is clearly illustrated in
absorption tower 1 in FIG. 1, which inherently includes the two
stream separations in the tower top and in the tower bottom.
[0154] In an embodiment of the process according to the present
invention, step a) is performed at a pressure of at least 1 bar
gauge, preferably at least 5 bar gauge, preferably at least 10 bar
gauge, more preferably at least 15 bar gauge, even more preferably
at least 20 bar gauge, yet more preferably at least 25 bar gauge.
The applicants have found that the absorbent streams according to
the present invention are particularly effective and efficient
under these higher pressures as specified.
[0155] In an embodiment of the process according to the present
invention, step a) is performed at a pressure of at most 150 bar
gauge, preferably at most 120 bar gauge, more preferably at most
100 bar gauge, even more preferably at most 90 bar gauge. The
applicants have found that higher pressures do not bring much
further improvements of performance of the step a). The applicants
have found that, if the feed stream needs to be pressurized in
order to prepare it for the step a), that further compression
energy to reach pressures above the specified levels is usually not
justified by the additionally obtainable benefits.
[0156] In an embodiment of the process according to the present
invention, step a) is performed at a temperature of at least
10.degree. C., preferably at least 20.degree. C., more preferably
at least 30.degree. C., even more preferably at least 40.degree.
C.
[0157] In an embodiment of the process according to the present
invention, step a) is performed at a temperature of at most
90.degree. C., preferably at most 80.degree. C., more preferably at
most 70.degree. C., even more preferably at most 65.degree. C.
[0158] In one embodiment, the process according to the present
invention further comprises a step c) in which at least part of the
regenerated absorbent stream from step b) may be recycled as at
least part of the absorbent stream to step a).
[0159] In an embodiment of the process according to the present
invention, step b) comprises the step of stripping at least a
portion of the contaminant enriched absorbent stream obtained from
step a) in counter-current with a gaseous stream containing water
vapour in a stripping tower, to form a tower bottom liquid stream
which is a first regenerated absorbent stream for the recycling in
step c). The applicants have found that steam stripping as
prescribed is a very efficient method for breaking the bonds
between the contaminant and the absorbent stream, and for
separating the contaminant from the absorbent stream.
[0160] In an embodiment of the process according to the present
invention, step b) comprises the step of flashing at least a
portion of the contaminant enriched absorbent stream obtained from
step a) to a lower pressure for releasing a gaseous stream
containing the contaminant from a liquid stream which is a second
regenerated absorbent stream for the recycling in step c). The
applicants have found that flashing may be an even more efficient
method, as compared to steam stripping, for breaking the bonds
between the contaminant and the absorbent stream, and for
separating the contaminant from the absorbent stream. The
applicants prefer to combine a flashing step with a downstream
regeneration step, which preferably is a steam stripping step.
[0161] In an embodiment of the process according to the present
invention, the second regenerated absorbent stream is recycled to
step a). The applicants have found that the flashing step may
produce a second regenerated absorbent stream which is suitable for
recycling in step c) to step a). This brings the advantage that
this part of the absorbent stream does not necessarily need to be
processed through a more thorough regeneration step, such as by
steam stripping, before it is suitable for participating in the
step a).
[0162] In an embodiment of the process according to the present
invention, in step b) a first regenerated absorbent stream and a
second regenerated absorbent stream are formed for the recycling in
step c), whereby the second regenerated absorbent stream contains
more contaminant than the first regenerated absorbent stream,
preferably step a) being performed in an absorption tower and the
first regenerated absorbent stream being recycled to a top liquid
feed tray in the absorption tower and the second regenerated
absorbent stream being recycled to an intermediate feed tray in the
absorption tower located lower than the top liquid feed tray. The
applicants have found that this embodiment takes full advantage of
the presence of a flashing step, without increasing the risk for
contaminant breakthrough in the step a), because the feed stream in
contact with the second regenerated absorbent stream still has to
pass the zone where it is contacted with the first regenerated
absorbent stream.
[0163] It is further understood that all definitions and
preferences as described above for mixture (M) as used in step a)
of the process according to the present invention, equally apply
for this embodiment and all further embodiments, as described
below.
[0164] Another aspect of the present invention is the mixture (M),
as detailed above.
[0165] Another aspect of the present invention is a composition
comprising the mixture (M), as detailed above.
[0166] A further aspect of the present invention is an absorbent
stream comprising the mixture (M), as detailed above.
[0167] It is another aspect of the present invention to provide a
use of an absorbent stream comprising the mixture (M), as detailed
above or at least 15 wt. % of at least one compound (A), as
detailed above.
[0168] In another aspect, the present invention provides for a
contaminant enriched absorbent stream comprising at least one
absorbed contaminant selected from hydrogen sulfide (H.sub.2S),
carbon dioxide (CO.sub.2), carbon oxysulfide (COS), carbon
disulfide (CS.sub.2), disulfides or mercaptans, the absorbent
stream comprising the mixture (M), as detailed above or at least 15
wt. % of at least one compound (A), as detailed above.
[0169] FIG. 1 is a schematic diagram of an apparatus for removing
contaminants according to the process of the present invention from
a gaseous feed stream. As shown in FIG. 1, gas feed is led to an
absorption tower 1 through a contaminant containing gas-feed inlet
4. In a packed portion 2, the gaseous feed stream placed in the
absorption tower 1 is brought into contact in a counter flow with
an absorbent stream fed from a nozzle 7, and the contaminant is
absorbed and removed from the gas by the absorbent stream, and the
contaminant depleted gas is discharged through a contaminant
depleted gas-discharge outlet 5. The absorbent stream fed to the
absorption tower 1 absorbs the contaminant, and is led to a heat
exchanger 14 and a heater 8 and heated and led to a regeneration
tower 15. In the regeneration tower 15, the absorbent stream flows
through a nozzle 16 and a packed portion 17 toward the lower
portion of the tower. During this time, contaminant is removed to
regenerate the absorbent stream. A part of the absorbent stream in
the bottom of the regenerator tower is routed over reboiler 27 to
generate a vapour stream for stripping the absorbent stream coming
down the tower. The regenerated absorbent stream is led by a pump 9
to the heat exchanger 14 and an absorbent stream cooler 26 and fed
back to the absorption tower 1 through an absorbent stream feed
inlet 6.
[0170] On the other hand, in the upper portion of the regeneration
tower 15, the contaminant removed from the absorbent stream is
brought into contact with a reflux water fed from the nozzle 18,
and cooled by a regeneration tower reflux condenser 23, and, in a
reflux drum 21, the gaseous contaminant is separated from the
reflux water formed by condensing water vapour accompanying the
contaminant, and may be led to a contaminant recovery step through
a recovered contaminant line 22. The reflux water is fed by a
reflux water pump 20 to the regeneration tower 15.
EXAMPLES
[0171] The invention will be now described in more details with
reference to the following examples, whose purpose is merely
illustrative and not intended to limit the scope of the
invention.
General Procedure for Determination of the Absorption
Capacities
[0172] All experiments were performed using 30 g of an absorbent
stream. Lab-scale absorption experiments were carried out by
contacting a feed stream gas mixture comprising 1000 ppmv (parts
per million by volume) n-butane and 1000 ppmv methyl mercaptan
(CH.sub.3SH) in nitrogen with the various absorbent streams, at a
temperature of 40.degree. C. and a pressure of 2 bar. The
experimental absorption apparatus was comprising a double-walled
tubular absorber with a diameter of 7 mm, equipped with a
thermocouple and heated by a water bath. The pressure inside the
absorber was maintained at a constant pressure using a
back-pressure regulator mounted downstream of the tubular absorber.
The gas flow rate was 5.1 Lh.sup.-1, and the outlet gas passed
through a condenser to avoid evaporation of water from the
absorber. When the feed stream gas mixture was passed in an upward
direction through the absorbent stream, the resulting contaminant
depleted product stream gas was depleted in n-butane and methyl
mercaptan until the contaminant enriched absorbent stream became
saturated. The composition of the outlet gas was analysed at
regular intervals using an Agilent 7890B Gas Chromatograph (GC)
equipped with a split injector and a flame ionization detector
(290.degree. C.). A capillary Rtx-Volatile Amine Column with
dimensions of 60-meter.times.0.32-mm ID was employed. The GC oven
temperature was set at 40.degree. C. and gas samples were injected
with a split ratio of 100:1. OpenLAB Chromatography Data Systems
software was used for data acquisition and data processing. Once at
room temperature, the absorber was opened, contents transferred to
a glass jar, and sampled for GC analysis to determine the
composition. The absorbent streams were evaluated in five
consecutive absorption-regeneration cycles whereby regeneration was
performed by heating the solvents for 90 minutes at temperatures of
at least 80.degree. C. and a gas flow rate of 5.1 L h.sup.-1. Data
of the first two cycles were not incorporated into the analysis in
order to make sure that the absorption apparatus was fully
equilibrated.
[0173] To compare the performance of the different absorbent
streams, the concentration of methyl mercaptan and n-butane in the
outlet gas was followed in time. As long as the absorbent streams
were not saturated, the concentration of methyl mercaptan and/or
n-butane in the outlet gas was zero. Once the absorbent streams
were nearing saturation, the outlet concentrations of methyl
mercaptan and/or n-butane (in ppmv) started to increase (i.e.
breakthrough). For the different absorbent streams, this
breakthrough took place at a different time. The solvent loadings
were approximated by integrating the areas above these respective
"breakthrough" curves (i.e. the ppmv concentration of methyl
mercaptan or n-butane in the outlet gas as a function of time (in
minutes)) and by subtracting the amount of gas used to fill the
head space of the absorber. The amount of absorbed methyl mercaptan
and n-butane was calculated by writing:
n a .times. b .times. s .times. o .times. rbed = A .times. R
.times. E .times. A above .times. curve * V 1 .times. 0 .times. 0
.times. 0 * 6 .times. 0 * 1 .times. 0 - 6 8 . 3 .times. 1 .times. 4
.times. 3 * 1 .times. 0 .times. 1 .times. 3 .times. 2 .times. 5 2
.times. 7 .times. 3 . 1 .times. 5 * 1 m ##EQU00001##
wherein {dot over (V)} is the flow rate of the gas phase
(NLh.sup.-1) and m the total mass of absorbent stream (g).
[0174] The list of used materials according to the invention can be
found in Table 1.
TABLE-US-00001 TABLE 1 List of products and description Description
Compound (A) according to the invention DMAP-2-pyrrolidone
Dimethylaminopropyl-2-pyrrolidone DMAE-2-pyrrolidone
Dimethylaminoethyl-2-pyrrolidone Compound (B) according to the
invention N-tert-butyl-2-pyrrolidone N-tert-butyl-2-pyrrolidone
N-butyl-2-pyrrolidone N-butyl-2-pyrrolidone N-octyl-2-pyrrolidone
N-octyl-2-pyrrolidone Compound (B) according to the invention MDEA
Methyldiethanolamine Reference compound Sulfolane Sulfolane
2-Pyrrolidone 2-Pyrrolidone N-methyl-2-pyrrolidone
N-methyl-2-pyrrolidone
Absorption Performance
Example 1-2
[0175] The absorbent stream of Examples 1-2 was a mixture (M) which
was prepared by mixing 25 wt. % of a compound (B), with 50 wt. % of
MDEA (i.e. compound (C)), and 25 wt. % of water. The absorption
performance data and the specific compounds (B) that were used are
summarized in Table 2 below.
Example 3-4
[0176] The absorbent stream of Examples 3-4 was a composition (C)
which was prepared by mixing 25 wt. % of a compound (A), with 50
wt. % of MDEA (i.e. compound C), and 25 wt. % of water. The
absorption performance data and the specific compounds (A) that
were used are summarized in Table 2 below.
Comparative Examples 5-7
[0177] The absorbent streams of Comparative Examples 5 to 7 were
prepared according to the same procedure as Examples 1 to 2 except
that a reference compound was used which was not a compound (B)
according to general formula (II). Specifically, in Comparative
Example 5, sulfolane was used, in Comparative Example 6,
2-pyrrolidone was used and in Comparative Example 7,
N-methyl-2-pyrrolidone was used. The absorption performance data of
Comparative Example 5 were considered as a reference since the
absorbent stream comprising sulfolane is similar to the well-known
commercial Sulfinol.RTM.-M solvent. The absorption performance data
are summarized in Table 2 below.
TABLE-US-00002 TABLE 2 Reference or CH.sub.3SH concentration
n-Butane concentration compound (A) (mmol kg.sup.-1 solvent) (mmol
kg.sup.-1 solvent) Name or compound (B) 1 2 3 1 2 3 Example 1
N-Butyl-2- 4.11 5.64 5.50 0.35 0.33 0.37 pyrrolidone Example 2
N-Octyl-2- 4.09 4.13 N.D. 0.47 0.45 N.D. pyrrolidone Example 3
DMAP-2- 4.10 4.44 4.16 0.31 0.26 0.31 pyrrolidone Example 4 DMAE-2-
4.12 4.21 4.13 0.34 0.25 0.35 pyrrolidone Comparative Sulfolane
3.64 3.66 3.67 0.30 0.26 0.35 Example 5 Comparative 2-Pyrrolidone
3.17 3.00 3.05 0.23 0.20 0.28 Example 6 Comparative N-Methyl-2-
3.54 3.68 4.02 0.34 0.26 0.27 Example 7 pyrrolidone
[0178] For comparison purposes, it should be noted that the
reference absorbent solution of Comparative Example 5 comprising
sulfolane, could capture 3.64-3.67 mmol CH.sub.3SH and 0.26-0.35
mmol C.sub.4H.sub.10 per kg solvent (Table 2). In the case of
N-butyl-2-pyrrolidone (Example 1), CH.sub.3SH loadings of between
4.11-5.64 mmol and C.sub.4H.sub.10 loadings of between 0.33-0.37
mmol per kg solvent, were observed. Under the same conditions, the
results also indicate that the CH.sub.3SH absorption capacities of
N-octyl-2-pyrrolidone (Example 2), DMAP-2-pyrrolidone (Example 3),
and DMAE-2-pyrrolidone (Example 4) were comparable or superior to
those of the reference absorbent solution of Comparative Example 5
comprising sulfolane. We inferred that these specific substitutions
on the amide nitrogen of the pyrrolidone ring positively impact the
interactions of the absorbent stream with the mercaptans while a
low co-absorption of hydrocarbons (such as n-butane) is maintained.
Table 2 further indicates that the CH.sub.3SH absorption values of
the absorbent streams according to the present invention (Examples
1-4) were comparable or superior to those of the comparative
absorbent solutions of Comparative Examples 5-7.
Example 8
[0179] The absorbent stream of Example 8 was a mixture (M) which
was prepared by mixing 30 wt. % of N-butyl-2-pyrrolidone (i.e.
compound (B)), with 50 wt. % of MDEA (i.e. compound (C)), and 25
wt. % of water. The absorption performance data are summarized in
Table 3 below.
Comparative Example 9
[0180] The absorbent stream of Comparative Example 9 was prepared
according to the same procedure as Example 8 except that 30 wt. %
of sulfolane was used which was not a compound (B) according to
general formula (II). The absorption performance data are
summarized in Table 3 below.
[0181] Table 3 shows typical absorption data (n.sub.absorbed) for
three consecutive absorption-regeneration cycles for the reference
absorbent stream of Comparative Example 9 comprising 30 wt. %
sulfolane and the absorbent stream according to the invention
comprising 30 wt. % of n-butyl-2-pyrrolidone (i.e. compound B)
(Example 8).
TABLE-US-00003 TABLE 3 Reference CH.sub.3SH concentration n-Butane
concentration or com- (mmol kg.sup.-1 solvent) (mmol kg.sup.-1
solvent) Name pound B 1 2 3 1 2 3 Example 8 N-Butyl- 8.46 7.75 7.58
0.43 0.46 0.36 2-pyrrol- idone Comparative Sulfolane 5.22 4.91 5.35
0.33 0.33 0.37 Example 9
Example 10
[0182] The absorbent stream of Example 10 was a mixture (M) which
was prepared by mixing 15 wt. % of N-butyl-2-pyrrolidone (i.e.
compound (B)), with 50 wt. % of MDEA (i.e. compound (C)), and 25
wt. % of water. The absorption performance data are summarized in
Table 4 below.
Comparative Example 11
[0183] The absorbent stream of Comparative Example 11 was prepared
according to the same procedure as Example 10 except that 15 wt. %
of sulfolane was used which was not a compound (B) according to
general formula (II). The absorption performance data are
summarized in Table 4 below.
[0184] Table 4 shows typical absorption data (n.sub.absorbed) for
three consecutive absorption-regeneration cycles for the reference
absorbent stream of Comparative Example 11 comprising 15 wt. %
sulfolane and the absorbent stream according to the invention
comprising 15 wt. % of n-butyl-2-pyrrolidone (i.e. compound B)
(Example 10).
TABLE-US-00004 TABLE 4 Reference CH.sub.3SH concentration n-Butane
concentration or com- (mmol kg.sup.-1 solvent) (mmol kg.sup.-1
solvent) Name pound B 1 2 3 1 2 3 Example 10 N-Butyl- 4.76 5.11
4.61 0.33 0.36 0.40 2-pyrrol- idone Comparative Sulfolane 4.08 4.21
4.08 0.20 0.24 0.24 Example 11
[0185] The effect of a different concentration of compound B was
studied by varying the ratio of the different absorbent stream
components (Example 8 and 10) and by comparing the results with a
reference absorbent stream comprising sulfolane (Comparative
Examples 9 and 11). The absorbent solutions according to the
invention comprising N-butyl-2-pyrrolidone showed a consistently
higher solubility of CH.sub.3SH compared to the reference absorbent
solutions of the Comparative Examples while the co-absorption of
n-butane remained low.
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