Note: Descriptions are shown in the official language in which they were submitted.
CA 02426770 2003-04-23
WO 02/34863 PCT/USO1/32211
REMOVAL OF MERCAPTANS FROM HYDROCARBON
STREAMS USING IONIC LIQUIDS
Field of the Invention
The present invention is in the field of organic chemistry, in particular
removal of
mercaptans from hydrocarbon streams.
Baclcgronnd of the Invention
There are many product streams in petroleum chemistry which axe contaminated
with
mercaptans (RSH). These compounds are odorous and tend to be corrosive and
toxic. They
contribute to acid rain, and also tend to poison a number of catalysts used in
hydrocarbon
conversions. Accordingly, it is important to remove mercaptans from many
hydrocarbon streams,
or at least convert them to less toxic and corrosive compounds such as
disulfides (RSSR') where R
and R' can be different hydrocarbon groups. An excellent review of the
traditional methods of
removing mercaptans and hydrogen sulfide from petroleum streams is found in
Chemical
Technology of Petroleum by William A. Gruse and Donald R. Stevens, 3rd
Edition, McGraw-Hill
Book Company, Inc., pages 30I-304.
Mercaptans are commonly removed using a "sweetening" or "extractive
sweetening"
process. This type of process generally involves reacting mercaptans (RSH)
with caustic solutions
(NaOH) to form water and mercaptides (NaSR). The mercaptides are then
oxidized, usually with
air, to form disulfides (RSSR'), which regenerates the caustic. The disulfides
are for the most part
immissible in the caustic and can be separated by density differences. The
disulfides can either be
disposed of or, in some cases, blended with the original product stream.
The caustic is generally recycled until it reaches a low enough concentration
where it is no
longer effective at adsorbing the mercaptans. The concentration of caustic
decreases in part
because the water formed in the reaction of the mercaptan with caustic
generates water, which
remains with the caustic. Dissolved water in the crude oil can also cause a
decline in the
concentration of the caustic. The result is that the caustic must continuously
be disposed of and
replaced.
It is particularly difficult to remove low molecular weight mercaptans such as
ethyl and
methyl mercaptan from crude oils. These mercaptans must be reduced to a few
ppm for them to be
acceptable for shipping on tankers. When caustic solutions are mixed with
crude oil, emulsions
often form. To avoid direct mixing of caustic with crude, the light portion of
the crude can be
CA 02426770 2003-04-23
WO 02/34863 PCT/USO1/32211
distilled, the mercaptans removed, and the product blended with the crude.
This option requires
using expensive distillation facilities to remove the light portion of the
crude.
The oxidation of the mercaptides to disulfides and regenerated caustic can be
done with a
variety of oxidants (air, pure oxygen, enriched air, chemical oxidants such as
hydrogen peroxide)
or mixtures thereof. However, air is the most commonly used oxidant because of
its low cost. The
oxidation of the mercaptides can be done without a catalyst, but the reaction
tends to be slow. It is
generally preferred to incorporate a catalyst to accelerate the oxidation of
the mercaptides. These
catalysts are typically metals, and the most common metals are lead (typically
as PbS), copper
(typically as a copper chloride), or a phthalocyanine complex of copper, iron,
nickel or cobalt,
preferably cobalt. The preparation and use of phtalocyanine complexes for
mercaptan oxidation is
described in U.S. Pat. No. 5,880,279: U.S. Pat. No. 5,849,656, U.S. Pat. No.
5,741,415, and U.S.
Pat No. 5,683,574 to Mazgarov et al. A particularly effective pthalocyanine
complex involves
cobalt phthalocyanine complexes with electron withdrawing substituents on the
phthalocyanine
ring. Particularly effective electron withdrawing substituents include a
halogen (preferably
chlorine) and sulfate groups as described in U.S. Pat. No. 5,880,279.
The extraction of the mercaptans and the oxidation of the mercaptides can be
done in one
or two stages. The advantage of the use of one stage is primarily lower cost,
but the disadvantages
include the mixing of the oxidant and petroleum product, and the blending of
the mercaptan
reaction product disulfides with the petroleum product. The advantages of use
to two separate
stages is the avoidance of mixing the oxidant and the petroleum product, and
the separation of the
disulfide reaction product, but the disadvantage is higher cost.
Mercaptans can be removed from whole crudes by contacting the crude oil with a
caustic
mixture that includes a cobalt phthalocyanine complex and air, as described in
U.S. Pat No.
5,683,574. The cobalt phthalocyanine complexes are selected to avoid formation
of emulsions.
The caustic/cobalt phthalocyanine solution simultaneously adsorbs the
mercaptans and reacts them
to form disulfides, which remain iii the crude. The caustic and phthalocyanine
complexes can be
partially recovered using a separation system. However, this technology has
various technical
limitations. For example, the introduction of air directly in with the crude
causes concerns over
safety, and when nitrogen from the air is released from the crude, light (Cd-)
hydrocarbons are also
purged. This not only results in a loss of crude, but also causes a safety
hazard and a disposal
problem. Also, since the reaction is essentially stoichiometric, the amount of
caustic and cobalt
catalyst that must be used increases, often to the point where it is not
economically viable to treat
the crude.
CA 02426770 2003-04-23
WO 02/34863 PCT/USO1/32211
It would be advantageous to have efficient methods for removing mercaptans
from
hydrocarbon streams without creating a waste caustic stream, preferably
without introducing air to
the hydrocarbon streams. The present invention provides such methods.
Summary of the Invention
Methods for removing mercaptans from hydrocarbon streams, preferably crude
oil, are
provided. The methods involve forming a solution of a basic metal salt such as
sodium hydroxide
in an ionic liquid, preferably a non-water reactive ionic liquids, and
contacting the ionic liquid
solution with a hydrocarbon stream in a manner which contacts mercaptans in
the hydrocarbon
stream with the basic metal salt. The resulting mercaptide salts are either
dissolved or dispersed iii
the ionic liquid, dissolved in the reaction water, or precipitated. Generally
they are dissolved in
the ionic liquid. The resulting de-sulfurized hydrocarbon feedstream can be
separated from the
ionic liquid, for example by distillation, decantation or gravity separation.
The caustic can be recovered by oxidizing the mercaptides to form disulfides,
preferably
using air or oxygen. The oxidation can be promoted by a catalyst, preferably a
metal
phthalocyanine complex where the metal is preferably cobalt and the
phthalocyanine ring includes
halogens, preferably chlorine, as described in U.S. Pat. No. 5,880,279. The
catalyst can be fixed
on a solid support or, alternatively, dissolved or dispersed in the ionic
liquid.
The disulfides are non-ionic and tend to be insoluble in the ionic liquids.
Accordingly, the
disulfides can be readily removed, for example via distillation, decantation
or gravity separation.
Additionally, the disulfides can be removed by stripping with steam, air or
other suitable gas
streams, or by extraction in a suitable solvent, for example a hydrocarbon
solvent. The de-
sulfurized ionic liquid can then be recycled.
The reaction water produced by the reaction of caustic and mercaptans tends to
be
insoluble in the ionic liquids. The water can also be removed by distillation,
decantation or gravity
separation. If the mercaptide is not particularly soluble in the reaction
water, the water can be
removed by decantation or gravity separation before the oxidation step. The
basic metal salt can
be kept reasonably concentrated in the ionic liquid without unwanted dilution
in water using the
methods described herein.
The mercaptan-containing hydrocarbon stream can be in the gas phase or in the
liquid
phase. The flow of hydrocarbon stream over/through the ionic liquid can be,
for example, co-
current, counter-current, or staged in stirred tanks, with countercurrent
being preferred.
It should also be recognized that this approach is effective in removing
hydrogen sulfide
from petroleum products.
CA 02426770 2003-04-23
WO 02/34863 PCT/USO1/32211
Brief Description of the Drawings
Figure 1 is a schematic illustration of a mercaptan removal process using the
method
described herein.
Detailed Description of the Tnvention
Methods for removing mercaptans from hydrocarbon streams, preferably crude
oil, are
provided. As used herein, the term "adsorption" is used to describe the
movement of mercaptans
out of hydrocarbon streams and into ionic liquids in the form of mercaptides.
Mercaptans
Mercaptans are C1_so mercaptans (carbon-containing compounds that contain a -
SH
group), more preferably Cr_io (cyclic, linear, branched and aromatic)
mercaptans. They may
include other functional groups, such as hydroxy groups, carboxylic acid
groups, heteroatoms, and
the like, provided that such groups do not react with either the base
(typically sodium hydroxide)
or the ionic liquid.
Hydrocarbon Feedstreams
The hydrocarbon feedstreams include crude oil feedstreams and natural gas
feedstreams.
The hydrocarbon stream can include a C6- fraction. The hydrocarbon stream can
include more
than about 50% by weight methane, ethane, propane, butane or combinations
thereof.
Where the hydrocarbon feedstreams include relatively high levels of sulfur
impurities, and
the feedstream is amenable to hydrotreatment or other means well known to
those of skill in the
art, such as extractive Merox, such methods can be used to reduce the level of
sulfur impurities,
and residual mercaptans can be removed using the methods described herein.
Basic Salts
The basic salts can be virtually any base capable of reacting with mercaptans
to form
mercaptides. Examples include alkali metal and alkaline earth hydroxides,
carbonates and
bicarbonates. Sodium hydroxide is a preferred basic salt.
The concentration of the basic salt in the ionic liquid is typically at least
about 0.5 moles
of salt per liter of solvent, and preferably at least about 2 moles of salt
per liter of solvent.
It does not matter whether the salts are dissolved or merely suspended in the
ionic liquids
for them to function as intended. It is preferred, however, to select
combinations of ionic liquids
4
CA 02426770 2003-04-23
WO 02/34863 PCT/USO1/32211
and basic salts that form a solution rather than a suspension, as the solids
in suspensions tend to
settle and become non-available for the reaction.
The salts are able to react with the mercaptans at a variety of
concenfirations. At relatively
high concentrations, the mercaptides may precipitate from solution. If this
precipitation is not
S desirable, more dilute solutions/dispersions should be used. However, this
precipitation may be
desirable and allow one to separate various mercaptides by precipitation and
subsequent filtration.
The extent of mercaptan removal is a least 10%, preferably more than SO% and
most
preferably more than 90%. The product disulfides can be either produced as a
separate stream or
blended with the hydrocarbon product. Methods of measuring mercaptans in
petroleum products
include gas chromatography (especially when coupled with a sulfur sensitive
elemental detector).
ASTM D3227 can also be used to measure mercaptans in gasoline, jet and
distillate boiling range
products. If quantitative measurements of mercapans are not possible (for
example in heavy crude
oils), the extent of mercaptan removal can be judged by an unprovement in the
copper strip
corrosion test (ASTM D130) of at least one value.
1S
Ionic Liquids
Ionic liquids axe organic compounds that are liquid at room temperature. They
differ from
most salts in that they have very low melting points. They tend to be liquid
over a wide
temperature range, and are not soluble in non-polar hydrocarbons. Depending on
the anion, they
tend to be immiscible with water, and are highly ionizing (but have a low
dielectric strength).
Ionic liquids have essentially no vapor pressure. Most are air- and water-
stable, and they are used
herein as a catalyst and/or solvent for the Diels-Alder reaction between the
dime and the
dienophile.
The properties of the ionic liquids can be tailored by varying the canon and
anion. Ionic
2S liquids and their commercial applications are described, for example, in J.
Chem. Tech.
Biotechnol., 68:351-3S6 (1997); Chew. Ind , 68:249-263 (1996); J. Phys.
Condensed Matte,
S:(supp 34B):B99-B106 (1993); Chemical and Engineering News, March 30, 1998,
32-37;
.I. Mater. Chena., 2627-2636 (1998); and Chern. Rev., 99:2071-2084 (1999), the
contents of which
are hereby incorporated by reference.
3 0 Many ionic liquids are formed by reacting a nitrogen-containing
heterocyclic ring,
preferably a heteroaromatic ring, with an alkylating agent (for example, an
allcyl halide) to form a
quaternary ammonium salt, and performing ion exchange or other suitable
reactions to form ionic
liquids. Examples of suitable heteroaromatic rings include pyridine,
substituted pyridines,
imidazole, substituted imidazoles, pyrrole and substituted pyrroles. Suitable
substituents include,
CA 02426770 2003-04-23
WO 02/34863 PCT/USO1/32211
for example, straight, branched, or cyclic alkyl groups, preferably a methyl
group, allcyl chains
containing a terminal alcohol group, alkyl groups containing heteroatoms such
as oxygen, nitrogen
and/or sulfur. The substituents can be in any position on the heteroaromatic
ring, but in the case of
pyridine, is preferably in the para (or 4) position.
These rings can alkylated with virtually any straight, branched or cyclic
Cl_ZO alkyl group,
but preferably the alkyl groups are Cl_16 groups, since groups larger than
this tend to produce low
melting solids rather than ionic liquids. Various triarylphosphines,
thioethers, and cyclic and non-
cyclic quaternary ammonium salts have also been used. Counterions which have
been used
include chloroaluminate, bromoaluminate, gallium chloride, tetrafluoroborate,
tetrachloroborate,
hexafluorophosphate, nitrate, trifluoromethane sulfonate, methylsulfonate, p-
toluenesulfonate,
hexafluoroantimonate, hexafluoroarsenate, tetrachloroaluminate,
tetrabromoaluminate, perchlorate,
hydroxide ion, copper dichloride anion, iron trichloride anion, zinc
trichloride anion, as well as
various lanthanum, potassium, lithium, nickel, cobalt, manganese, and other
metal ions.
Certain low melting solids can also be used in place of ionic liquids,
depending on the
particular separation to be effected. Low melting solids are generally similar
to ionic liquids but
have melting points between room temperature and about 212°C or are
liquid under the process
conditions. The use of low melting solids can be preferred if the density of
the products and the
ionic liquid are similar and it becomes difficult to phase separate products
from the ionic liquids.
In such a case, the low melting solid can be crystallized and separated from
the products. As used
herein, the term "ionic liquid" is intended to include low melting solids
unless otherwise specified.
The ionic liquids can either be neutral, acidic or basic. However, relatively
acidic ionic
liquids (chloroaluminate salts) tend to be water-reactive, whereas neutral
ionic liquids (for
example, tetrafluoroborate or hexafluorophosphate salts) tend to be non-water
reactive. Since
water is generated, it can be preferable to use non-water reactive ionic
liquids, particularly if large
amounts of mercaptans are to be removed. Neutral ionic liquids are also
preferred if the
hydrocarbon stream includes acid-sensitive components, for example normal
alpha olefins, which
are prone to isomerization.
In one embodiment, a library of ionic liquids is prepared, for example by
preparing
various alkyl derivatives of the quaternary ammonium cation, and/or varying
the associated anions.
The acidity of the ionic liquids can be adjusted, for example by varying the
molar equivalents and
combinations of Lewis acids.
Methods for Removing Mercaptans from Hydrocarbon Streams
The methods involve forming a solution of a basic metal salt such as sodium
hydroxide in
6
CA 02426770 2003-04-23
WO 02/34863 PCT/USO1/32211
an ionic liquid, preferably a non-water reactive ionic liquids, and
contaetiiig the ionic liquid
solution with a hydrocarbon stream in a manner which contacts mercaptans in
the hydrocarbon
stream with the basic metal salt. The resulting mereaptide salts are either
dissolved or dispersed in
the ionic liquid, dissolved in the reaction water or precipitated. Preferably
they are dissolved in the
ionic liquid. The resulting de-sulfurized hydrocarbon feedstream can be
separated from the ionic
liquid, for example by distillation, decantation or gravity separation.
If low sulfur products are desired, it is important that contact with air be
minimized during
this step to avoid oxidation of the mercaptides to disulfides, which may
dissolve back into the
hydrocarbon stream. Contact with air can be minimized, for example by reacting
the mercaptans
with the basic metal salts in an inert atmosphere, for example nitrogen or
argon.
If low sulfur products are not relevant but reduction of mercaptans is
desired, the
hydrocarbon stream, the ionic liquid incorporating the basic metal salt, and
an oxidant can be
contacted simultaneously. In this case the product disulfide will be
incorporated into the product.
A catalyst to promote generation of the basic metal salt can also be
incorporated as well (either
dissolved in the ionic liquid, dispersed in the ionic liquid or supported on a
solid). In one
embodiment, Iow melting solids are used in place of ionic liquids, and the
desulfurized
hydrocarbon feedstream is recovered following precipitation of the low
meltilig solid. In this
embodiment, the low melting solid must be a liquid at the temperature at which
the mereaptans are
adsorbed, to permit contact of the mereaptans with the basic salt.
Methods for Oxidizin Mercaptides in Ionic Liquids
The caustic can be recovered by oxidizing the mercaptides to form disulfides,
preferably
using air or oxygen. The oxidation can be promoted by a catalyst, preferably a
metal
phthalocyanine complex where the metal is preferably cobalt and the
phthalocyanine ring includes
halogens, preferably chlorine. The preferred catalyst is described in U.S.
Pat. No. 5,880,279. The
catalyst can be fixed on a solid support or, alternatively, dissolved or
dispersed in the ionic liquid.
The disulfides are non-ionic, and tend to be insoluble in the ionic liquids.
Accordingly,
the disulfides can be readily removed, for example via distillation,
decantation or gravity
separation. Additionally, the disulfides can be removed by stripping with
steam, air or other
suitable gas streams, or by extraction in a suitable solvent, for example a
hydrocarbon solvent.
The resulting de-sulfurized ionic liquids can be recycled.
The water formed by reacting hydroxide ions with mercaptans tends to be
insoluble in the
ionic liquids. The water can also be removed by distillation, decantation or
gravity separation.
Recantation and gravity separation may tend to remove caustic and/or
mercaptide salts from the
7
CA 02426770 2003-04-23
WO 02/34863 PCT/USO1/32211
ionic liquid. Accordingly, distillation, preferably under reduced pressure, is
a prefewed method for
removing the water. Alternatively, if the mercaptide is not particularly
soluble iii the reaction
water, the reaction water can be removed before the oxidation step. The basic
metal salt can be
kept reasonably concentrated in the ionic liquid without unwanted dilution in
water using the
methods described herein.
The mercaptan-containing hydrocarbon stream can be in the gas phase or in the
liquid
phase. The flow of hydrocarbon stream over/through the ionic liquid can be,
for example, co-
cument, counter-current, or staged in stirred tanks, with countercurrent being
preferred.
The method is shown in more detail in Figure 1. As shown in Figure 1, a
hydrocarbon with
mercaptan (RSH) impurities is introduced to a contactor (10) that contains a
non-water reactive
ionic liquid and caustic. The resulting mercaptide is then either dispersed or
dissolved in the ionic
liquid, precipitated, or dissolved in the resulting aqueous phase. The
reaction mixture is sent to a
separator (20) where a purified hydrocarbon stream can be separated. The ionic
liquid and,
optionally, reaction water are sent to an oxidation reactor (30) where
disulfide is formed and
caustic is regenerated. The disulfide and reaction water can then be removed,
regenerating the
ionic liquid and caustic. The regenerated ionic liquid and caustic are then
recycled to the contactor
( I 0).
Combinatorial Chemistry Approaches
A combinatorial approach can be used to identify optimum ionic liquids and/or
basic salts
for removing mercaptans from various hydrocarbon streams. An advantage to the
combinatorial
approach is that the choice of ionic liquid, basic salt and the like can be
tailored to specific
applications.
The scale of the mercaptan removal in combinatorial chemistry is preferably in
the range
of about 1 mg to 200 g, more preferably between one mg and 10 g, although the
scale can be
modified as desired depending on the equipment used. Those of skill in the art
can readily
determine appropriate sets of reactions and reaction conditions to generate
and/or evaluate the
libraries of interest.
The ionic liquids can be laid out in a logical fashion in mufti-tube arrays or
mufti-well
plates in the form of arrays of ionic liquids. Preferably, the ionic liquids
all have a central core
structure and have various modifications that permit the identification of
structure-activity
relationships with which to determine optimum compounds for a particular use.
The basic metal
salts or combinations thereof can also be laid out in a logical fashion, for
example in arrays. In a
preferred embodiment, an A x B array is prepared with various combinations of
ionic liquids and
CA 02426770 2003-04-23
WO 02/34863 PCT/USO1/32211
basic metal salts. However, it is also possible to evaluate a single ionic
liquid with a plurality of
metal salts, optionally at different concentrations, and then repeat the
process as desired with a
plurality of different ionic liquids.
The ability of the particular combination of ionic liquid and metal salt at
performing a
desired mercaptan removal can be measured and correlated to specific
combinations. The array
can be ordered in such a fashion as to expedite synthesis and/or evaluation,
to maximize the
informational content obtained from the testing and to facilitate the rapid
evaluation of that data.
Methods for organizing libraries of compounds are well known to those of skill
in the art, and are
described, for example, in U.S. Patent No. 5,712,171 to Zambias et al. Such
methods can readily
be adapted for use with the ionic liquids and basic metal salts described
herein.
By screening multiple synthetic variations of a core molecule, the selection
of the optimal
candidate is more a function of the data collection method than the "rational"
basis for selecting a
useful ionic liquid and/or metal salt. The desired physical and chemical
properties for the ionic
liquid, when used as a solvent or dispersing agent for a particular metal
salt, and for removing a
1 S particular mercaptan from a particular hydrocarbon stream, can be rapidly
optimized, and directly
correlated with the structural changes within a particular array or sub-array.
The ionic liquids are typically formed by first forming a desired (cyclic, non-
cyclic or
aromatic) quaternary ammonium salt, and then combining the salt with an
appropriate anion
precursor (typically a metal salt such as aluminum chloride, zinc chloride,
sodium
hexafluorophosphate, sodium tetrafluoroborate, hexafluorophosphoric acid,
tetrafluoroboric acid
and the like). Side products salts can be removed, for example by filtration
or, in cases where the
anion precursor was an acid, the acid side products such as HCI can be removed
by extraction or
by gently heating the ionic liquid under vacuum.
The mercaptan removal using the ionic liquids/metal salts in the libraries
generally involve
2S contacting appropriate mixtures of mercaptans and hydrocarbons with the
ionic liquids/basic metal
salts in the tubes or wells in the mufti-tube rack or mufti-well plate, and
allowing the mercaptide
formation to take place. The formation of the mercaptide, and desulfurization
of the hydrocarbon
stream, can be analyzed, for example by GC by following mercaptan removal. The
presence or
absence of mercaptans can be evaluated, for example using GC, to determine the
success of the
particular combination of ionic liquid and basic metal salt.
Robotic arms and mufti-pipet devices are commonly used to add appropriate
reagents to
the appropriate tubes in mufti-tube racks or wells in mufti-well plates.
Preferably, the chemistry is
performed in an inert atmosphere to avoid oxidation of mercaptides to form
disulfides before the
9
CA 02426770 2003-04-23
WO 02/34863 PCT/USO1/32211
desulfurized hydrocarbon stream is removed. This can be done, for example, by
covering the
tubes with a rubber septum to avoid contamination, and adding the reagents via
injection.
In one embodiment, the mercaptan removal is caxried out via computer control.
The
identity of each of the ionic liquids and basic metal salts can be stored in a
computer in a "memory
map" or other means for correlating the data regarding the chemical reactions
to the ionic liquids in
the multi-tube racks or multi-well plates.
Alternatively, the chemistry can be performed manually, preferably in multi-
tube racks or
mufti-well plates, and the information stored, for example on a computer.
Any type of mufti-well plate or mufti-tube array commonly used in
combinatorial
chemistry can be used. Preferably, the number of wells or tubes is in excess
of 30, and there is a
tube in at least 60 percent of the positions in each mufti-tube array. The
shape of the rack is not
important, but preferably, the rack is square or rectangular. The tubes can be
made, for example,
from plastic, polymers, glass or metal such as stainless steel, depending on
the type of anions used
in the ionic liquid or in the metal salt.
Any type of liquid handler that can add reagents to, or remove reagents from,
the wells
and/or tubes can be used. Suitable liquid handlers are prepared, for example
by Tecan. Many
involve the use of robotic arms and robotic devices. Suitable devices are well
known to those of
skill in the art of combinatorial chemistry, and include those by Zymart,
Gilson, Hamilton, Bodhan
and Tecan.
Any device that can take samples from the individual wells and/or tubes and
analyze the
resulting hydrocarbon phase can be used. Preferably, the device is a
chromatographic device such
as an analytical or preparative scale HPLC, GC or column chromatography,
although other devices
can be envisioned depending on the chemistry performed. Since the ionic liquid
is non-volatile,
the sample is preferably taken from the hydrocarbon phase, which is immiscible
with the ionic
liquid.
Preferably, in those embodiments in which a chromatographic column (HPLC, GC
or
column chromatography) is used, the device has the ability to identify when
the compound of
interest is eluting from the column. Various means have commonly been used to
identify when
compounds of interest are eluting from a column, including LTV, IR, TLC, GC-
MS, FID, NMR,
ELSD, nitrogen detection and the like. Any of these means and others known to
those of skill in
the art can be used, alone or in combination. However, when petroleum
chemistry is being
evaluated, the product stream often does not include LTV-active compounds. In
this type of
embodiment, the analytical equipment preferably includes an ELSD detector.
CA 02426770 2003-04-23
WO 02/34863 PCT/USO1/32211
The entire eluent from the chromatographic columns described above can be sent
through
an appropriate detector and then to a mass spectrometer. When sample
collection is desired, it can
begin when the LTV or mass spectrometry signal indicates the presence of the
eluting compound,
and can end when the UV signal indicates that the compound has finished
eluting from the
column. Mass spectrometry can verify that the eluted compound is really the
compound of
interest. In some embodiments, it is preferred to use a combination of GG and
MS, particularly if
the mercaptans and various hydrocarbon components elute from the GC column at
similar rates.
The device preferably includes a computer system capable of storing
information
regarding the identity of the ionic liquids, metal salts and the product
streams obtained when
combinations of ionic liquids and basic metal salts are used to remove the
mercaptans. Software
for managing the data is stored on the computer. Relational database software
can be used to
correlate the identity of the ionic liquids, the metal salts, and the
analytical data from each product
stream. Numerous commercially available relational database software programs
are available, for
example from Oracle, Tripos, MDL, Oxford Molecular ("Chemical Design"), mBS
("Activity
Base"), and other software vendors.
Relational database software is a preferred type of software for managing the
data obtained
during the processes described herein. However, any software that is able to
create a "memory
map" of the ionic liquids in the tubes and correlate that information with the
information obtained
from the chemical reactions can be used. This type of software is well known
to those of skill in
the art.
The present invention will be better understood with reference to the
following non-
limiting example.
Example: Synthesis of Neutral Ionic Liquids
A variety of quaternary amine ionic liquid precursors were prepared as
follows.
1-Methylimidazole was measured into a stainless-steel autoclave along with a
slight molar excess
of 1-chlorobutane. The autoclave was sealed, pressurized with 75 prig of
nitrogen, and heated to
90°C for 18 h. The autoclave was then cooled to room temperature and
the contents were placed
on a rotary evaporator at 95°C for several hours to remove any
unreacted chlorobutane and 1-
methylimidazole. A 1H NMR of the product indicated the formation of 1-butyl-3-
methylimidazolium chloride (bmim+Cl-). The reaction was repeated with 1-
chlorohexane to give
1-hexyl-3-methylimidazolium chloride (hmim''-Cl-). This general procedure was
repeated with
pyridine to give the ionic liquid precursors N-butylpyridinium chloride
(butpyr+Cl-) and
11
CA 02426770 2003-04-23
WO 02/34863 PCT/USO1/32211
N-hexylpyridinium chloride (hexpyr+Cl-), although a higher reaction
temperature (130°C) was
required to achieve high yields.
Two different procedures were used for conducting an anion exchange reaction
to give a
neutral ionic liquid. In one procedure, the precursor is dissolved in acetone
and reacted with the
sodium salt of the desired anion (NaBF4 or NaPF6). In the other procedure, the
precursor is
dissolved in water and reacted with the acid form of the anion (HBF4 or HPF6).
The precursor
hmirri Cl- was used make the ionic liquid hmim+PF6 by both procedures. The
miscibility of the
resulting ionic liquid with water was greatly influenced by the route of
synthesis. The ionic liquid
made by the acid route was immiscible with water, while the ionic liquid made
using the sodium
salt was miscible with water. While not wishing to be bound to a particular
theory, it is believed
that this change in miscibility with water is due to the presence of residual
NaCI in the liquid made
via the salt route.
The acid procedure was then used to generate a variety of ionic liquids using
the
precursors synthesized above, as well as additional precursors purchased from
commercial
suppliers. These reactions are summarized in Table I . Not all of the
combinations resulted in the
formation of room temperature ionic liquids. Highly symmetric canons (Me4N+)
and cations with
long alkyl chains (Cl6NMe3k) tend to give solid products with high melting
points (>100°C). The
reactions that did not result in room temperature ionic liquids are shown in
Table 2.
12
CA 02426770 2003-04-23
WO 02/34863 PCT/USO1/32211
Table 1. Neutral Ionic Liquids
Ionic Liquid PrecursorAnion Source Ionic Liquid
bmim+CI- HBF4 bmim+ BF4
bmim+Cl- HPF6 bmim+ PF6
hmim+Cl- NaBF4 hmim+ BF4
hmim+CI- HBF hmim+ BF4
hmim+Cl- NaPF6 hmim+ PF6
hmim+Cl- HPF6 ' hmim+ PF6
hexpyr+Cl- HBFd hexpyr+ BFd
hexpyr+Cl- HPF6 Hexpyr+ PF6 (mp = 38.7
1C)
(CaHI~)3MeN+Cl- HBF4 (C$HI~)3MeN+ BFd (mp
=
58.8C)
(CaHI~)sMeN+Cl- HPF6 (CsHn)3MeN+ PF6
Bu2Me2N +CI- HBF Bu2Me2N + BF4- (mp =
75.1 1C)
bmim = 1-butyl-3-methylimidazolium
hexpyr = N-hexylpyridinium
hmim = 1-hexyl-3-methylimidizolium
Table 2. Reactions which did not result in room temperature ionic liquids
Ionic Liquid PrecursorAnion Source Solid Product
Me3NI~C1- HBF4 Me3NH+BF4- (mp =
183C)
Me3NH+CI- HPF6 Me3NH +PF6
Me4N+Cl- HPF6 MedN+PF6
Me4N'~Cl- NaBF4 Me4N+BF4
BuzMezN +Cl- HPF6 BuZMe2N+PF6 (mp
=
154.5C)
(GI6H33)Me3N+Cl HBFq (C16H33)Me3N+BFq_
(C16H33)Me3N+Cl- HPF6 (C16H33)Me3N+PF6
(mp =
131.7C)
hexPPh3+Br NaPF6 HexPPh3+PF6
hexPPh3 = hexyltriphenylphosphonium
13
