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An ionic liquid process for mercury removal from natural gas


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Efficient scrubbing of mercury vapour from natural gas streams has been demonstrated both in the laboratory and on an industrial scale, using chlorocuprate(ii) ionic liquids impregnated on high surface area porous solid supports, resulting in the effective removal of mercury vapour from natural gas streams. This material has been commercialised for use within the petroleum gas production industry, and has currently been running continuously for three years on a natural gas plant in Malaysia. Here we report on the chemistry underlying this process, and demonstrate the transfer of this technology from gram to ton scale.
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Cite this: Dalton Trans., 2015, 44,
Received 23rd October 2014,
Accepted 11th February 2015
DOI: 10.1039/c4dt03273j
An ionic liquid process for mercury removal
from natural gas
Mahpuzah Abai,
Martin P. Atkins,*
Amiruddin Hassan,
John D. Holbrey,*
Yongcheun Kuah,
Peter Nockemann,
Alexander A. Oliferenko,
Natalia V. Plechkova,
Syamzari Rafeen,
Adam A. Rahman,
Ran Ramli,
Shahidah M. Shari,
Kenneth R. Seddon,*
Geetha Srinivasan*
and Yiran Zou
Ecient scrubbing of mercury vapour from natural gas streams has been demonstrated both in the lab-
oratory and on an industrial scale, using chlorocuprate(II) ionic liquids impregnated on high surface area
porous solid supports, resulting in the eective removal of mercury vapour from natural gas streams. This
material has been commercialised for use within the petroleum gas production industry, and has currently
been running continuously for three years on a natural gas plant in Malaysia. Here we report on the chem-
istry underlying this process, and demonstrate the transfer of this technology from gram to ton scale.
Mercury is a natural component of the earths crust, and
through a number of natural and anthropogenic cycles is
released into the environment as a toxic pollutant.
All forms
of mercury viz. elemental mercury and oxidised, Hg(I) and Hg(II)
are intrinsically toxic.
One of the main sources of environ-
mental pollution by mercury is from fossil fuels, either during
combustion of coal or emitted from natural gas.
Many natural
gas fields contain mercury released from mercury-containing
ores through secondary geothermal processes. Natural gas
fields typically contain mercury, in either elemental or
combinations of elemental and organometallic forms, in con-
centrations in the range <0.15000 μgm
depending on geo-
graphical location and geology. Although these concentrations
are usually relatively low, for a typical gas processing plant
treating 250 MMSCFD (million standard cubic feet per day =
28 300 m
) of natural gas, the cumulative quantities can be
significant and can lead to problems through accumulation
via condensation and amalgamation. High mercury concen-
trations in oil and gas production correlate with regions of
high mercury emission to the environment (see Fig. 1).
Mercury can be extremely corrosive, causing destructive
damage to process equipment, particularly aluminium heat
exchangers, through liquid metal embrittlement.
example, an explosion in 1973 at the Skikda liquefied natural
gas plant in Algeria led to 27 fatalities and financial losses of
$1 billion due to catastrophic failure of an aluminium heat
exchanger through reaction with mercury contaminants.
Mercury control and treatment within the oil and gas
supply chain is increasingly recognised as important, both to
protect equipment and personnel from deleterious exposure,
and in order to comply with increasingly stringent discharge
regulations. For natural gas processing, mercury control usually
signifiesthe use of fixed-bed scrubbers containing a solid adsor-
bent that can capture mercury vapour either through adsorp-
tion, amalgamation, or oxidation followed by adsorption. The
Fig. 1 Global mercury transport, indicating the major areas of emission
(in red) taken from United Nations Environment Programme, Global
Mercury Assessment.
CCDC 1029551. For crystallographic data in CIF or other electronic format see
DOI: 10.1039/c4dt03273j
PETRONAS Research Sdn. Bhd., Lot 3288 & 3289, OJalan Ayer Itam,
Kawasan Institusi Bangi, 43000 Kajang Selangor, Malaysia
QUILL, The Queens University of Belfast, Belfast, BT9 5AG, UK.
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most common approaches employ commercially available
scrubbers, as shown in Table 1, incorporating sulfur, metal
oxides/sulfides, or metals (particularly silver) as active agents on
porous alumina, zeolite, or activated carbon supports.
Sulfur-impregnated activated carbons are probably the most
widely used adsorbents for mercury control within the gas
industry. Impregnation of sulfur into activated carbons over-
comes some of the slow kinetics of the reaction of mercury
with elemental sulfur under ambient conditions. Vidićand co-
workers have proposed that this is may be due to the involve-
ment of sulfur allotropes with greater number reactive end
However, activated carbons are not as mechanically
robust as oxide supports such as alumina or silica, and there-
fore suer from attrition which shortens their operational life-
Mercury capture from gas using copper(II) chloride
impregnated on carbon as a chloridesource has been
however the resulting mercury(II) chloride was
incompletely captured and leached under high pressure
Ionic liquids
have also been explored for liquid/liquid par-
titioning of mercury, as mercury(II), from water,
using hydrophobic ionic liquids containing pendant sulfur
Subsequently, it was shown that mercury(II) can
partition into unfunctionalised hydrophobic ionic liquids.
The eective involatility of most ionic liquids means that
gasliquid contacting scenarios can be considered without
contaminating process gas streams. Pinto and co-workers have
reported the use of ionic liquids to capture elemental and oxi-
dised mercury from combustion flue gases, combining the
ionic liquid with permanganate(VII) as an oxidant.
and Holbrey
have suggested using ionic liquids containing
perhalide anions for the oxidative dissolution of metals, and
Sasson and co-workers
have reported using similar ionic
liquid systems as liquid scrubbers to remove mercury from
power-plant combustion gas. However, the corrosive nature of
these highly oxidising ionic liquids (analogous to chlorine or
bromine) to metals such as iron may place restrictions on their
Building on previous work developing ionic liquid
approaches to oxidative dissolution,
and selective extrac-
tion and separations,
we considered whether ionic liquids
incorporating metal complexes might oxidise elemental
mercury, leading to the formation of stable anionic mercurate(II)
species. Such anions should then become integral com-
ponents of a new, more complex, ionic liquid system,
would also be non-volatile. Here, we report on the investigation
of chlorocuprate(II)-based ionic liquids for the direct oxidation
of elemental mercury,
and the use of these ionic liquids in a
solid-supported ionic liquid phase (SILP)
for reactive capture
of mercury from gas streams, which has led to the scale-up
and deployment on industrial plants in Malaysia.
Hg NMR spectra were measured using a Bruker 500DRX
spectrometer with a 1 M solution of HgCl
(Sigma Aldrich) in
as an internal standard (1501 ppm relative to Hg-
and deuterium lock.
IR spectroscopy was carried out
using a Perkin Elmer Spectrum 100 FT-IR spectrophotometer
with a Universal diamond Attenuated Total Reflectance (ATR)
top plate.
Mercury solubility in ionic liquids was measured by dissol-
ving an accurately weighed sample of the ionic liquid phase
(ca. 0.05 g) in water (10 cm
), removing the small quantity of
precipitate produced by filtration, and then diluting to 50 cm
followed by subsequent dilution of a 1 cm
aliquot to 50 cm
A sample (<50 μL) calculated to contain less than 1000 ng
mercury was then analysed for mercury using a Milestone
DMA-80 direct mercury analyser. Based on the sample size,
initial mass of ionic liquid used for the contact test, and
mercury content determined, the wt% of water soluble
mercury present in the ionic liquid was calculated.
Mercury capture from the carrier gas by SILPs was tested
using an accelerated breakthrough test rig constructed in-
house, incorporating a mercury generator and Sir Galahad ana-
lyser (PS Analytical). SILPs (and commercial activated carbons
for comparison) were crushed and sieved using a 300500 μm
mesh. Adsorbents (30100 mg) were packed into a thermo-
stated glass column of diameter 1 mm. Mercury removal from
test gas streams (nitrogen and methane) was examined using a
high flow rate (600 cm
) and high mercury content
(2000 ng l
) in the carrier gas; the outlet mercury concen-
tration was monitored continuously.
A suitable crystal of [N
] was selected and mea-
sured on a Rigaku Saturn724+ (2 × 2 bin mode) diracto-
meter. The crystal was kept at 120.0 K during data collection.
Using Olex2,
the structure was solved with the ShelXS
ture solution program using Direct Methods and refined with
the ShelXL refinement package using Least Squares minimis-
ation. Crystal Data for C
CuN (M= 370.27 g mol
monoclinic, space group P2
/n(no. 14), a= 9.2771(4) Å, b=
15.6784(5) Å, c= 12.5521(5) Å, β= 100.016(2)°, V= 1797.88(12)
,Z=4,T= 120.0 K, μ(MoK
) = 1.647 mm
= 1.368 g
, 21 158 reflections measured (5.98° 2Θ54.96°), 4122
unique (R
= 0.0469, R
= 0.0382) which were used in all cal-
culations. The final R
was 0.0377 (>2σ(I)) and wR
was 0.0951
(all data).
Table 1 Various mercury removal systems for natural gas streams
Active compound Support/
medium Fate of mercury
Sulfur Carbon/
alumina HgS
Metal sulfide Carbon/
alumina HgS
Silver Zeolite AgHg amalgam
Thiol/oxidising agent/
chelating agent Scavenger
solution Soluble Hg(II)
Metal oxide/sulfide Metal oxide HgO/HgS
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Results and discussion
Synthesis and characterisation of copper(II) ionic liquids
Chlorocuprate(II) ionic liquids were prepared by combining
1-butyl-3-methylimidazolium chloride ([C
mim]Cl), 1-ethyl-3-
methylimidazolium chloride ([C
mim]Cl), or tributylmethyl-
ammonium chloride ([N
]Cl, (ex. Sigma Aldrich) with copper(II)
chloride (either anhydrous or dihydrate, ex. Sigma Aldrich) in
methanol in either a 1 : 1 or 2 : 1 molar ratio, followed by
solvent removal under reduced pressure, and then in vacuo at
80 °C. It is convenient to define the ionic liquid systems by the
mole fraction χ
, which is defined by χ
where n
is the number of moles of CuCl
and n
is the
number of moles of cation. The resulting ionic liquids formed
as dark yellow-brown liquids which, in all cases, slowly solidi-
fied on standing at room temperature. Additionally, a 1 : 2 : 1
cholinium chloridediethylene glycolCuCl
O deep eutec-
was prepared as a dark green liquid. The ionic liquids
were characterised by DSC, TGA, microanalysis, electronic
absorption and vibrational spectroscopy, Karl Fischer titration
and surface analysis by SEM/EDAX.
Small single crystals were isolated from the bulk solidified
] ionic liquid (1 : 1 CuCl
]Cl), and analysed
by X-ray crystallography. The structure confirmed the presence
of a dimeric copper(II) dianion with four-coordinate copper
centres separated by 3.33 Å (Fig. 2). Li et al.
have reported
that [C
mim]Cl/copper(II) chloride mixtures form [CuCl
chlorocuprate(II) anions even in the presence of substantial
concentrations of water. It was thus not anticipated that
copper speciation would dier in ionic liquids formed with
anhydrous or hydrated copper(II) chloride. Crystal structures of
many chlorocuprate(II) salts with a variety of organic cations
have been previously reported,
and are dominated by salts of
the discrete tetrachlorocuprate(II) anion, which can vary in
structure from tetrahedral to square planar, with many inter-
mediate geometries.
Reaction of copper(II) ionic liquids with mercury
Because the dominant form of mercury in natural gas is
elemental, tests were conducted to determine the solubility of
Hg(0) in the ionic liquids by heating a droplet of mercury
(Sigma Aldrich) with the ionic liquids at 60 °C overnight in a
sealed vial. No precautions to exclude air were made during
sample loading. In each case, a colour change was observed in
the ionic liquid, with the characteristic brown colour of the
chlorocuprate(II)-based systems changing to (i) a clear pale
green ionic liquid at χ
= 0.33, or to (ii) a pale orange-yellow
ionic liquid with precipitation of a pale grey-white solid at
= 0.50, as shown in Fig. 3. After heating, the size of the
mercury drops remaining in the vials had visibly reduced and
the mercury content in ionic liquid phase was determined by
mercury analysis. The results are shown in Table 2.
Over 15 wt% mercury dissolution was observed (Table 2) for
each of the chlorocuprate(II) ionic liquids tested, as deter-
mined from the water soluble mercury content of diluted ali-
quots of the ionic liquids. Reactive dissolution with similar
end results was observed for the ionic liquids prepared from
anhydrous and hydrated copper(II) chloride. A similar ability to
dissolve mercury was observed for both χ
= 0.33 and 0.50,
although the apparent outcomes of the dissolution process
appear to be slightly dierent. The amount of mercury that
was solubilised by the ionic liquids can be expressed by the
molar concentration ratio [Cu(II)
] : [Hg(II)
] (in Table 2) from
the initial concentration of copper in the ionic liquids and
mass of mercury extracted. In all cases, a small excess of
unreacted copper(II) in solution was apparent due to the
residual paler brown colouration. This would imply that one
Fig. 2 Cation and anion within the unit cell of [N
]; d¯(CuCl)
2.19, d¯(CuCl)
=2.32,d¯(CuCu) = 3.33 Å.
Fig. 3 The reaction of an excess of liquid mercury with 1-butyl-3-
methylimidazolium chlorocuprate(II) ionic liquids at 60 °C. The top three
photographs correspond to χ
= 0.33 and the bottom three to χ
= 0.50. At χ
= 0.33, (a) the initial ionic liquid mixture transforms to
(b), a partially decolourised solution after mixing with Hg(0) for 5 min
and then to (c) after extended mixing. At χ
= 0.50, (d) the initial ionic
liquid mixture transforms through (e) after mixing with Hg(0) for 5 min
to (f), a clear, largely decolourised ionic liquid phase containing a ne,
grey-white precipitate after extended mixing.
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mole of mercury was required to reduce two moles of copper:
The simplest mechanisms that can be proposed for this
reaction, depending on the stoichiometry of the chlorocuprate(II)
ionic liquids, are shown in eqn (1)(3).
The changes in colour of the copper(II)-containing ionic
liquids after reaction with mercury are consistent with
reduction to copper(I). Bolkan and Yoke,
described copper(I)
systems ([C
mim]ClCuCl; 0.33 < χ
< 0.67) as having
colours that varied from pale yellow to light green with increas-
ing χ
, and that darken rapidly in air and become paramag-
netic as copper(II) is formed.
In eqn (1), all the products are anionic, and will incorporate
into the ionic liquid. eqn (2) and (3) represent two contrasting
interpretations of the observed reaction. In eqn (2), copper(I)
chloride precipitates and in eqn (3), mercury(II) chloride pre-
cipitates. In the former case, the remaining solution contains
both mercury(II) and copper(I) species; in the latter case, there
will be no mercury in solution.
In eqn (2), it is speculated that the speciation of mercury is
. There is no evidence that this would be the
speciation as it may be a monomeric species
or a polymeric
but the balance of probability is that it is likely to be
Whatever the speciation, it does not aect the
validity of the following arguments.
Examples of
Hg NMR spectra taken from {[C
= 0.50) + Hg(0)} and {[C
0.33) + Hg(0)} systems are shown in Fig. 4. Well defined
NMR signals were obtained in each case, but with dierent
chemical shifts. For χ
= 0.33, this peak was found at
1106 ppm (relative to 1 M HgCl
in dmso); for χ
= 0.50,
the peak appeared at 1140 ppm. These positions are consist-
ent with the formation of chloromercurate(II) anions,
the mercury is in the environment of four chlorine atoms. The
lower field peak is assigned to [HgCl
and the higher peak
to [Hg
. As it is known that [HgCl
has a peak at
1197 ppm,
this suggests that the mercury complex anion
formed is dimeric rather than monomeric. This provides
strong support for the reaction schemes outlined in eqn (1)
and (2). Eqn (3) has been eliminated as it would imply the
absence of mercury in solution. The formation of a precipitate
from the reaction of liquid mercury with the [C
= 0.50) ionic liquid combined with the presence of
chloromercurate(II) anions in solution as shown from
NMR spectroscopy supports the reaction mechanism in eqn
(2) at this composition and the precipitation of CuCl as
the reaction shifts the ionic liquid towards chloride deficient,
i.e. acidic, compositions. While little is known about the phase
behaviour of chloromercurate(II) ionic liquids with χ
the limiting point for homogeneity in chlorocuprate(I) systems
is χ
= 0.67,
that is, with the copper : chloride ratio of 2 : 3.
Copper(II) supported ionic liquids in the laboratory
The above results from the reactions of the copper(II) ionic
liquids with elemental mercury give a good indication that
they might be the basis of an absorption scrubber. This would
combine the thermodynamically favourable oxidation of
mercury(0) to mercury(II) by the copper(II), followed by com-
plexation (and hence stabilisation) by the liberated chloride
ions. Although in the laboratory, it is clearly possible to
develop a mercury scrubber based on an ionic liquid system in
the fluid state, the eciency of passing natural gas through a
viscous liquid system would prevent its scale-up for an indus-
trial process. The logical way forward was to coat a dispersed
solid with a selected and optimised ionic liquid to form a class
of materials now recognised as a supported ionic liquid phase
This would lead to good contact between the gas and
the ionic liquid, high throughput flow, and mechanical
strength. A typical SILP is shown in Fig. 5.
Further, most mercury removal units used in the oil and
gas industry are fixed-bed scrubbers, and so a SILP approach
Table 2 Solubility of bulk elemental mercury in metal-containing ionic
liquid system at 60 °C (averages of three measurements)
Ionic liquid composition wt% mercury
dissolved in IL [Cu(II)
O (1 : 1) 22.1 ± 1.4 2.6
(2 : 1) 21.3 ± 2.3 2.2
(2 : 1) 15.9 ± 0.3 2.4
O (2 : 1) 15.2 ± 0.1 2.3
16.9 ± 0.1 3.0
Chol = cholinium; EG = diethylene glycol.
Fig. 4
Hg NMR (23 °C, neat, 89.57 MHz) spectra of the ionic liquids
obtained from the reaction mixtures of (a) [C
] + Hg(0) (red
trace) and (b) [C
] + Hg(0) (blue trace). The peak at
1501 ppm is the reference peak.
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to heterogenise the ionic liquids would be a natural fit with
standard industrial practice. SILPs, which incorporate high
surface area thin-films of ionic liquids within a porous solid
scaold, have many advantages for ecient gasliquid contact-
ing when a static liquid phase (i.e. as a catalyst or adsorbent) is
SILPs containing the chlorocuprate(II) ionic liquids at 10 wt%
loading were prepared by the incipient wetness method,
adding solutions of the respective ionic liquids in methanol to
porous silica beads, followed by drying overnight at 80 °C.
After drying, the SILPs were orange-yellow (see Fig. 5), in con-
trast to the characteristic green of the methanolic solutions of
the copper salts. ATIR spectra of SILPs showed no vibrational
bands that could be assigned to methanol or to water, other
than that residual on the silica surface (Fig. 6).
Mercury adsorption from gas streams was tested by passing
a mercury-containing gas (either N
or CH
) through a fixed
bed of adsorbent, and comparing the inlet and outlet mercury
concentrations. The more ecient the adsorbent is at
removing mercury from the gas, the longer the time it takes
for mercury to be detected at the outlet. The time from injec-
tion to detection is defined as the breakthrough time. Over the
course of the measurements, the inlet mercury concentration
was held at the high level of 2000 ng l
in order to accelerate
the breakthrough tests. In packed adsorbent beds with no
channelling, the outlet mercury concentration follows the
ideal (and observed) profile illustrated in Fig. 7. The outlet
concentration remained constant at less than 0.2 ng l
to breakthrough, which was characterised by a rapid increase
in its concentration. The breakthrough time was defined as
the time at which mercury capture from the gas stream
decreased to below 99.5% capture eciency ([Hg]
Characteristic mercury outlet profiles obtained under test
conditions for a sulfur-impregnated activated carbon (ca.10wt%
sulfur) and for a chlorocuprate(II) containing SILP (10 wt%
area and 0.83 cm
pore volume) are shown in Fig. 7.
Under the conditions defined in Fig. 7, the selected SILP
remained active for 35 h until breakthrough, which corres-
ponded to a mercury uptake of ca. 2.5 wt% (2.52 mg, 1.27 ×
mol). This 100 mg SILP sample contained 2.71 × 10
moles of copper(II), and so the breakthrough point represents
93% mercury capture eciency based on the proposed capture
mechanism requiring oxidation by two copper(II) centres. The
activated carbon, in contrast, showed poorer performance,
with a breakthrough of 12.7 h, which is equivalent to 0.9 wt%
mercury capture on the support. This was lower than antici-
pated, although this may be due to the extremely short resi-
dence times in these accelerated screening tests. Thus, in a
laboratory test rig, the SILP outperformed the activated carbon
by a factor of 3, which was very encouraging for moving from
laboratory to pilot plant.
Fig. 5 An example of a SILP containing chlorocuprate(II) ionic liquid
impregnated porous 4 mm diameter silica spheres.
Fig. 6 ATR IR spectra comparing a silica support (red) and SILPs pre-
pared with overnight drying at 80 °C (blue) or drying in vacuo (orange),
illustrating the absence of additional OH stretching frequencies in the
SILPS that could be attributable to methanol or water. Peaks at 2965
and 2882 cm
derive from the ionic liquid cation.
Fig. 7 Mercury breakthrough curves for the capture of mercury vapour
from dinitrogen gas ([Hg]
= 2000 ng l
,ow rate = 600 cm
T= 25 °C) using 0.10 g samples of (a) a sulfur-impregnated activated
carbon and of (b) a 10 wt% [N
= 0.50) SILP on
porous silica (135 m
surface area and 0.83 cm
pore volume).
Similar results were obtained using methane as the carrier gas.
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Ionic liquids containing dierent cations ([N
and [C
) were tested, resulting in similar breakthrough
performance which appears to correlate with the total amount
copper(II) within the tested samples (Fig. 8). At higher load-
ings, a reduction in mercury capture performance was
observed, presumably through plugging of the support
through pore filling. This could be partially alleviated by chan-
ging to supports with large pore geometries.
After exhaustive extraction in contact with mercury-contain-
ing gas streams, the SILPs change colour from orange to pale
green. This transformation is comparable to the colour
changes observed after reaction of the neat ionic liquids with
liquid mercury (Fig. 5). As a useful laboratory application,
Fig. 9 shows a bed of chlorocuprate(II)-containing SILP used as
a mercury trap on the o-gas line from a PSA Sir Galahad
mercury analyser in our laboratory. The mercury breakthrough
front can be clearly seen at the sharp transition from spent
(pale green) absorbent to active (yellow-orange) material.
Interestingly, Haumann and co-workers
have also recently
reported the use of chlorocuprate(II)-containing SILPs for gas
absorption applications. They investigated ammonia capture
from air taking advantage of the strong coordination of
nucleophilic amines to copper, and suggested their potential
uses in broadband filters for breathing apparatus.
Copper(II) supported ionic liquids at scale
The laboratory results demonstrated that ecient and compre-
hensive scrubbing of mercury vapour from gas streams could
be achieved with excellent capture kinetics. The accelerated
breakthrough screening used residence times in the order of
50 ms in the test rig, and breakthrough times correlated with
theoretical maximum mercury capacities based on the mecha-
nisms detailed in eqn (1) and (2). Following on from these
small-scale laboratory tests, larger batches (ca. 100 g) of chloro-
cuprate(II) SILPs were prepared and tested in a 200 cm
scale slipstream scrubber on-site at a Gas Processing Plant in
Malaysia. The pilot trials (over 60 days) yielded a gas stream
with mercury outlet concentrations of <0.01 μgm
(Fig. 10),
at least one order of magnitude below the sales specification
for the natural gas.
This allowed a smooth transition to full plant implemen-
tation using 30 m
of a SILP (see Fig. 11). After three years of
continuous operation, the outlet mercury concentration from
the plant remained low, meeting the plant outlet specifica-
tions. This represents a remarkable success of transferring lab-
oratory chemistry to full scale plant operation in a remarkably
fast implementation (less than four years). The SILP is now
commercialised via a marketing licensing agreement between
PETRONAS and Clariant.
Fig. 9 Example of a chlorocuprate(II)-containing SILP used as a
mercury trap on the o-gas line from a PSA Sir Galahad mercury analy-
ser in our laboratory. The mercury breakthrough front can be clearly
seen at the sharp transition from spent (pale green) to active (yellow-
orange) absorbent. The packed bed contains ionic liquid impregnated
on two dierent silica supports; spherical beads and extrudates.
Fig. 10 Results from a pilot trial (over 60 days) of a copper(II) containing
SILP in a slipstream scrubber (200 cm
) for mercury removal from
natural gas on-site at a Gas Processing Plant in Malaysia, showing the
mercury outlet concentrations after passing through commercial
material (blue diamonds) and SILPs (red squares). The average extraction
eciency was 99.998%. The green line indicates specication for sales
quality gas (0.1 μgm
Fig. 8 The change in mercury breakthrough time for SILPs containing
dierent cations ([N
) as a function of ionic
liquid loading in the SILP, expressed as wt% copper. Compared to the
results shown in Fig. 7, the experimental sample sizes here are reduced to
30 mg, with all other conditions identical ([Hg]
,ow rate =
600 cm
,T= 25 °C), which results in a corresponding decrease in
the breakthrough time.
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We have demonstrated that it is possible to develop in the lab-
oratory, processes with industrial applicability. Starting at the
gram scale, the translation of the ionic liquid chemistry into a
SILP material that was scaled to full industrial implementation
within four years has been exemplified. The fundamental
chemistry (namely oxidative dissolution and complexation of
mercury into the ionic liquid as a stable anionic mercurate(II)
species) does not change with the scale of the process and the
ability to digest large quantities of mercury (up to 20 wt%),
coupled with ecient gas-contacting, made possible by for-
mation of a SILP, underpins the successful development of
these materials as commercially competitive solid phase
mercury adsorbents in the natural gas industry.
We are indebted to our many colleagues at PETRONAS for
their funding and discussions about this work. We would also
like thank Chemviron Carbon, Ltd. for supplying activated
carbon samples for testing, and thank the EPSRC UK National
Crystallography Service at the University of Southampton for
the collection of the crystallographic data.
Notes and references
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2 G. Liu, Y. Cai, N. ODriscoll, X. Feng and G. Jiang, Overview
of Mercury in the Environment, in Environmental Chemistry
and Toxicology of Mercury, ed. G. Liu, Y. Cai and
N. ODriscoll, John Wiley & Sons, Hoboken, New Jersey,
2011, pp. 112.
3 S. M. Wilhelm and N. Bloom, Fuel Process. Technol., 2000,
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of SILP on production plant
gas feeds to (c) full-scale mercury removal units with 20 m
of SILP at a gas processing plant site.
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... Based on this, the total amount of mercury present in both gaseous and liquid states is quantified, and its potential effects are evaluated to ensure human health, occupational safety, and environmental sustainability. 21,22 Other strategies include the removal of mercury through sorbents bed that comprise of either granular or pelletized materials (such as metal oxide, zeolite, activated carbon, alumina, and a reactive component bonded to support) for the identification, quantification, and removal of mercury. 23,24,25 The review of the literature reveals numerous studies on the sources, types, concentrations, toxicity, exposure, and impacts of mercury on human health, occupational safety, and environmental sustainability. ...
Full-text available
Introduction: Mercury is a highly toxic and persistent contaminant found in food and parts of the environment. Over the years, global research on mercury poison has soared owing to concerns about its effects on human health, occupational safety, and environmental sustainability. Although numerous studies have identified and examined the various types, sources, toxicity, exposure, and impacts of mercury, comprehensive studies on the research landscape and scientific developments on the subject areas are currently lacking. Therefore, this paper shows a bibliometric analysis (BA) and literature review (LR) of the top publications, funders, organisations, and countries working on Mercury research worldwide. Methods: The research landscape on the subject area was examined by BA from 1995 to 2021, whereas the scientific developments were highlighted through LR. Results: Results showed that mercury research has gained global prominence since the discovery of the Minamata disease in 1956. The most prolific mercury researchers, institutions, and funders are from the United States, Japan, Brazil, Canada, and China, whereas the publications on Mercury research doubled over the period. The top source titles for publications on Mercury are Neurotoxicology, Science of the Total Environment, and Environmental Health Perspectives. However, Micheal Aschner (US) and Takashi Yorifuji (Japan) are the most prolific researchers. Co-occurrence analysis revealed that mercury, methyl mercury, fish, toxicity, and Minamata disease are the most cited keywords, which shows the correlation nexus between fish consumption and mercury poisoning. Conclusion: The LR showed that mercury research is widely investigated due to global concerns about its impact on human health, safety, and the environment.
... Others suggest that mercury migrates into the oil and gas reservoirs from source rocks and metal-rich fluids. This migration process may be encouraged by secondary processes such as geological and geothermal activities (Abai et al., 2015;Yan et al., 2017). Several authors believe that regions with higher tectonic and geological activity are responsible for higher mercury content within natural gas reservoirs (Gallup, 2014;Lang et al., 2012;Yan et al., 2017) because of increased interactions with metal-rich fluids, mineral material, and formation waters (Filby, 1994). ...
Many oil and gas fields are nearing production cessation and will require decommissioning, with the preferred method being complete infrastructure removal in most jurisdictions. However, decommissioning in situ, leaving some disused components in place, is an option that may be agreed to by the regulators and reservoir titleholders in some circumstances. To understand this option's viability, the environmental impacts and risks of any residual contaminants assessed. Mercury, a contaminant of concern, is naturally present in hydrocarbon reservoirs, may contaminate offshore processing and transmission infrastructure, and can biomagnify in marine ecosystems. Mercury's impact is dependent on its speciation, concentration, and the exposure duration. However, research characterising and quantifying the amount of mercury in offshore infrastructure and the efficacy of decontamination is limited. This review describes the formation of mercury-contaminated products within oil and gas infrastructure, expected exposure pathways after environmental release, possible impacts, and key research gaps regarding the ecological risk of in situ decommissioned contaminated infrastructure. Suggestions are made to overcome these gaps, improving the in situ mercury quantification in infrastructure, understanding environmental controls on, and forecasting of, mercury methylation and bioaccumulation, and the cumulative impacts of multiple stressors within decommissioned infrastructures.
... Although different methodologies have been proposed for the Cl − removal from various real samples (Pierce et al., 2007;Sabbaghi et al., 2012;Hou et al., 2013;Wu et al., 2013;Lavela et al., 2015;Sun et al., 2019), but (to the best of knowledge) these methods have not been suitable, especially because of altered problems such as sophisticated matrix and irreversible fouling effect(s) of the NGC. On the other hand, other systems such as sorbent-based mercuric filters (Yan, 1987;Yang et al., 2007;Abai et al., 2015;Liu et al., 2020) have frequently high cost, small efficiency, and often need high temperature. Hence, current study introduces a nano-emulsion as extractant phase (extraction solvent) for efficient and simultaneous removal of the Cl − and Hg(0) using liquid-liquid extraction (LLE) methodology. ...
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This research introduces an oil-in-water (O/W) nano-emulsion (oil-water- CHClF 2 ) as the reusable extractant phase using liquid–liquid extraction methodology for the removal efficiency of Cl− and Hg(0) [between 90% and ∼100%, deepening on the nature of the natural gas condensate (NGC)] at a brief separation time (<3.0 min). The achieved safety of the NGC using this nano-emulsion results in efficient reduction in the corrosion rate during testing iron-based fragments (vs. the untreated ones as controls) and increase in the NGC economic value. Another advantage of the synthesized nano-emulsion is its capability and catalytic mediating behavior to efficiently separate and synthesize highly pure dicopper chloride trihydroxide nanoparticles. The synthesized nanoparticles were characterized by different analytical methods such as Fourier transform infrared spectrometry, X-ray diffraction, X-ray photoelectron spectrometry, and direct visualization by some electron microscopies. Direct synthesis, fast synthetic time (<3.0 min), high purity (>99%), and scalability are the main advantages of this synthetic method. This nanoparticle is not only safe but also is efficiently applicable in different industries, especially as an eco-friendly agricultural pesticide for different plants and tress such as pistachio. Consequently, this method is accepted as direct, simple, low-cost, and scalable conversion of some upstream industries with the downstream ones. All these possibilities are attributed to the intermediate transport properties of the introduced O/W nano-emulsion. At this condition, this reagent plays role as a recycled motor for the NGC purification and conversion of these impurities into the safe and usable products. To the best of knowledge, this research is considered as the first report that shows application of this O/W medium for both chloride and mercury removal from the NGC and its direct use as top element in the synthesis of eco-friendly nanoparticles. This system is applicable in some parts of the fuel and oil centers of the “Middle East.”
The enzymatic reaction is highly respected from an environmentally‐friendly point‐of‐view. Optimization of the reaction media and supporting materials of enzymes must be investigated in parallel with the effort to develop new enzymes. Lipases are frequently used for organic syntheses as synthetic tools even industry because of their acceptance of having a broad range of substrates, stability, and availability. We have investigated the possibility of ILs as both a solvent and activating or stabilization agent of enzymes, in particular, lipase as a model enzyme. ILs allowed recyclable use of a lipase and significant acceleration of transesterification, and also enhanced the stability and reaction activity of a lipase by immobilization through a lyophilization process. We discuss how we enhanced the enzyme capability using the IL engineering focusing on lipase‐catalyzed reactions, i. e., realization of the recyclable use of an enzyme, how ILs mediated the enhanced reaction rate, and improved the stability of the enzyme. Ionic Liquids allowed recyclable use of lipases, improved stability and acceleration of the lipase‐catalyzed reactions, in particular, using the IL‐coated‐enzyme through the immobilization of alkyl‐PEG sulfate IL via lyophilization process.
The detection and removal of the environmentally harmful substance methyl mercury (MeHg) have become an increasingly important issue due to its devastating effects on human tissues and organs. Hybrid systems of 1-ethyl-3-methylimidazolium tetrafluoroborate (C2mim BF4) ionic liquid (IL) and (ZnO)n nanoclusters with n = 2-12 are potential candidates for adsorbing and sensing of MeHg. We are using density functional theory (DFT) calculations to better understand this functionality by calculating the bond orders, HOMO-LUMO energy gaps (Eg), and electronic projected densities of states (PDOS). With adsorption energy of -1.84 eV, IL/(ZnO)4 reveals the strongest interaction with MeHg among IL/(ZnO)n hybrid systems owing to Hg-O polarized covalent bonding. The adsorption process' spontaneity/feasibility is validated by the negative values of ΔH and ΔG, which also suggest that the process is exothermic and energetically favorable. The adsorption of MeHg molecules causes alterations in Eg, and PDOS, demonstrating the hybrid structures' sensing ability. Increasing the alkyl chain length results in maximum adsorption energy of MeHg over the C10mim BF4/(ZnO)4 (-1.98 eV). Our results point the way to the implementation of multi-functional IL/(ZnO)n hybrid systems for sensing and adsorbing hazardous MeHg in the environment based on low-cost, rapid, and sensitive sensors.
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Ionic liquids (ILs) show remarkable performance in enhancing the naphthenic acid extraction efficiency and decreasing the extraction time. However, the ultrasonic-assisted IL-based extraction of naphthenic acid is merely addressed previously. Therefore, this study investigated the impact of essential ultrasonic parameters, including amplitude and time, on naphthenic acid extraction using different ILs, and the system was optimized for maximum extraction. The IL 1,8-diazobicyclo[5.4.0]-undec-7-ene (DBU) with thiocyanate anions revealed the highest efficiency in extracting naphthenic acid from a model oil (dodecane) at optimized conditions, and the experimental liquid-liquid equilibrium data were obtained at atmospheric pressure for the mixture of dodecane, [DBU], thiocyanate, and naphthenic acid. In addition, the influence of the chain length of the cation (hexyl, octyl, or decyl) on the extraction efficiency was also evaluated by determining the distribution coefficients, and the conductor-like screening model for real solvents (COSMO-RS) study was carried out at infinite dilution. It was found that [DBU-Dec] [SCN] gives the best extraction efficiency and has a distribution coefficient of 9.2707 and a performance index of 49.48. Based on these values, ILs can be ordered as follows: [DBU-Dec] [SCN] > [DBU-Oct][SCN] > [DBU-Hex][SCN] in the decreasing order of performance index 49.48, 41.58, and 28.13. Moreover, non-random two liquid and Margules thermodynamic models were employed to investigate the interaction parameters between the components. Both models showed excellent agreement with the experimental results and could successfully be used for ultrasonic-assisted IL extraction of naphthenic acid.
X-ray absorption spectroscopy (XAS) has been employed to carry out structural characterization of the local environment around mercury after the dissolution of the HgCl2 molecule. A combined EXAFS (extended X-ray absorption fine structure) and XANES (X-ray absorption near edge structure) data analysis has been performed on the Hg L3-edge absorption spectra recorded on 0.1 M HgCl2 solutions in water, methanol (MeOH), acetone and acetonitrile. The Hg-Cl distance determined by EXAFS (2.29(2)-2.31(2) Å) is always comparable to that found in the HgCl2 crystal (2.31(2) Å), demonstrating that the HgCl2 molecule dissolves in these solvents without dissociating. A small sensitivity of EXAFS to the solvent molecules interacting with HgCl2 has been detected and indicates a high degree of configurational disorder associated with this contribution. XANES data analysis, which is less affected by the disorder, was therefore carried out for the first time on these systems to shed light into the still elusive structural arrangement of the solvent molecules around HgCl2. The obtained results show that, in aqueous and MeOH solutions, the XANES data are compatible with three solvent molecules arranged around the HgCl2 unit to form a trigonal bipyramidal structure. The determination of the three-body Cl-Hg-Cl distribution shows a certain degree of uncertainty around the average 180° bond angle value, suggesting that the HgCl2 molecule probably vibrates in the solution around a linear configuration.
Thermoresponsive ionic liquids (TR-ILs) are room temperature liquid salt electrolytes with dynamic physical properties which have been hailed as potential solutions to inefficiencies in energy storage and material separations. That potential is hindered by the sensitivity of TR-IL phase separation to chemical structure. An accurate assessment of the effect of ion structure on molecular bonding is required for rational design as bonding changes translate to bulk material behavior. We systematically modify the structure of TR-ILs which exhibit either lower critical solution temperature (LCST) or upper critical solution temperature (UCST) phase separation to isolate the effect of specific types of bonding on eight tetrabutylphosphonium benzoate derived ILs through COSMO-RS sigma profile analysis and variable temperature (VT) ¹H NMR. Our results reveal that in addition to Hydrogen bonding, cation conformational flexibility, functional group availability, cation–anion coordination strength and directionality of hydrogen bonds play key roles in governing the IL phase separation behavior. © 2017 Elsevier Inc. All rights reserved.
Toxic heavy metals create several hazardous impacts on the environment and human lives. Certain heavy metals like Hg, As, Pb, Cr, Cd, Zn, Co, Ni, and many others have been discussed in this article. This review article discusses several water treatment technologies like reverse osmosis, nanofiltration, ultrafiltration, microfiltration, electrochemical, and physio-chemical processes. Fouling, scaling, and operating costs are the major problems of conventional membrane technologies. Selectivity, single-stage operation, and efficacy make liquid membrane an effective method for separation. Liquid membranes have been an exciting research area for various liquid-liquid and gas-liquid separation processes. In this aspect, modified supported liquid membranes like supported ionic liquid membranes (SILMs) emerge as a strong contender. In SILMs, ionic liquid plays a crucial role as the carrier. Various interesting properties of ionic liquids like negligible vapor pressure, liquid at room temperature, and versatile operations make working in extreme conditions. This paper emphasizes the possibility of various heavy metals that can be removed using SILMs. This paper compares the conventional separation techniques with liquid membranes like a bulk liquid membrane, emulsion liquid membrane, and supported liquid membrane.
This unique book gives a timely overview about the fundamentals and applications of supported ionic liquids in modern organic synthesis. It introduces the concept and synthesis of SILP materials and presents important applications in the field of catalysis (e.g. hydroformylation, hydrogenation, coupling reactions, fine chemical synthesis) as well as energy technology and gas separation. Written by pioneers in the field, this book is an invaluable reference book for organic chemists in academia or industry.
The book that looks at mercury's impact on the planet today. Recent research by the EPA has concluded that one in six women of childbearing age have unsafe levels of mercury in their bodies, which puts 630,000 newborn babies each year at risk of neurological impairment. Mercury poses severe risks to the health of animals and ecosystems around the world, and this book provides the essential information that anyone interested in environmental sciences should know about the fundamentals of the entire mercury cycle. Comprised of four parts that present an overview of mercury in the environment, mercury transformations, transport, and bioaccumulation and toxicology, each chapter of Environmental Chemistry and Toxicology of Mercury includes the basic concepts of the targeted subject, a critical review of that subject, and the future research needs. This book explains the environmental behavior and toxicological effects of mercury on humans and other organisms, and provides a baseline for what is known and what uncertainties remain in respect to mercury cycling. The chapters focus on the fundamental science underlying the environmental chemistry and fate of mercury. This work will be invaluable to a wide range of policy experts, environmental scientists, and other people requiring a comprehensive source for the state of the science in this field.
Novel supported ionic liquid phase (SILP) gas purification materials have been developed to remove ammonia irreversibly from an ambient gas flow of nitrogen (1000 ppm NH3 in N2, wet and dry). In the applied SILP materials, thin films of imidazolium based ionic liquids and ionic solutions of metal complexes, namely [C8C1Im][NTf2], [C8C1Im][NTf2]/Cu(NTf2)2, [C8C1Im][NTf2]/Co(NTf2)2 and [CnC1Im]Cl/CuCl2 (n = 2, 4, 8), were dispersed onto the large surface area of polymer-based spherical activated carbon supports. For the [CnC1Im]Cl/CuCl2 (n = 2, 4, 8) based SILP materials the use of a humid gas flow significantly enhances NH3 absorption as demonstrated by a clear increase of breakthrough times. The irreversibility of the ammonia sorption and the broadband capability (e.g. Cl2, H2S and cyclohexane) of the prepared SILP absorber materials are reported and compared to typical standards for gas purification adsorber materials (ABEK regulations).
The crystal structure of the title compound, {(C8H12N)[HgCl3]}n, exhibits alternating organic and inorganic layers, which inter­act via N—H⋯Cl hydrogen bonding. In the inorganic layer, an infinite one-dimensional anion chain is formed by [HgCl3]− subunits.
CuCl2-impregnated sorbents were employed to remove elemental mercury from flue gas. Three carriers including neutral Al2O3, artificial zeolite, and activated carbon have been investigated in this research. The performances of these prepared sorbents have been tested in a bench-scale fixed-bed reactor under different simulated flue gas atmospheres and temperatures (333–573 K). CuCl2-impregnated activated carbon showed the best adsorption ability. However, CuCl2-impregnated neutral Al2O3 and zeolite have demonstrated an adsorption rate similar to that of CuCl2-impregnated activated carbon in the early stage of the tests (5 min), and they achieved relatively high mercury oxidation efficiencies. These non-carbon sorbents could remarkably enhance the technoeconomical properties of mercury removal in coal-fired power plants and have great potentials in industrial application. The appropriate mercury capture temperature for these sorbents is 333–473 K. The possible mechanisms of elemental mercury oxidation have been discussed.
The structure of (Et4N)2[Hg4Cl10] contains dinuclear [Hg2Cl6]2− anions and HgCl2 mol­ecules, with definite interactions so that the anion can also be formulated as [Hg4Cl10]2−. Alternatively the compound can be written as (Et4N)2[Hg2Cl6][HgCl2]2. Charge balance is achieved by ordered [Et4N]+ cations. An inversion centre is situated at the centre of the [Hg2Cl6]2− anions.
The system trihexyl(tetradecyl)phosphonium ([P66614]Cl)/mercury chloride (HgCl2) has been investigated by varying the stoichiometric ratios from 4:1 to 1:2 (25, 50, 75, 100, 150, and 200 mol % HgCl2). All investigated compositions turn out to give rise to ionic liquids (ILs) at room temperature. The prepared ionic liquids offer the possibility to study the structurally and compositionally versatile chloromercurates in a liquid state at low temperatures in the absence of solvents. [P66614]2[HgCl4] is a simple IL with one discrete type of anion, while [P66614]{HgCl3} (with {} indicating a polynuclear arrangement) is an ionic liquid with a variety of polyanionic species, with [Hg2Cl6](2-) apparently being the predominant building block. [P66614]2[Hg3Cl8] and [P66614][Hg2Cl5] appear to be ILs at ambient conditions but lose HgCl2 when heated in a vacuum. For the liquids with the compositions 4:1 and 4:3, more than two discrete ions can be evidenced, namely, [P66614](+), [HgCl4](2-), and Cl(-) and [P66614](+), [HgCl4](2-), and the polynuclear {HgCl3}(-), respectively. The different stoichiometric compositions were characterized by (199)Hg NMR, Raman- and UV-vis spectroscopy, and cyclic voltammetry, among other techniques, and their densities and viscosities were determined. The [P66614]Cl/HgCl2 system shows similarities to the well-known chloroaluminate ILs (e.g., decrease in viscosity with increasing metal content after addition of more than 0.5 mol of HgCl2/mol [P66614]Cl, increasing density with increasing metal content, and the likely formation of polynuclear/polymeric/polyanionic species) but offer the advantage that they are air and water stable.
Ionic liquids with chlorometallate anions may not have been the first ionic liquids, however, it was their development that lead to the recognition that ionic liquids are a distinct, and useful, class of (functional) materials. While much of the phenomenal interest and attention over the past two decades has focussed on 'air and water stable' ionic liquids, research and application of chlorometallate systems has continued unabated albeit largely out of the main spotlight. The defining characteristic of chlorometallates is the presence of complex anionic equilibria, which depend both on the type and on the concentration of metal present, and leads directly to their characteristic and individual properties. Here, we review the experimental techniques that can be applied to study and characterise the anion speciation in these ionic liquids and, using recent examples, illustrate how their applications base is evolving beyond traditional applications in Lewis acidic catalysis and electrochemistry through to uses as soft and component materials, in the ionothermal synthesis of semiconductors, gas storage systems and key components in the development of biomass processing.
Solvents and solutions are ubiquitous in chemistry. For instance, in synthesis the solvent allows reagents to mix intimately so that reactions between these may occur. Consequently, understanding how solutes behave in solutions has been one of the major themes of chemistry throughout its history. Ionic liquids (liquid salts) are an exciting recent addition to the range of available solvents. Here we show that these solvents interact with dissolved salts to give solutions that are completely different from those of salts in either traditional organic solvents or water. Observations of these ideal salt solutions will require new models of solvation and polarity and have the potential to lead to new chemical processes.