Canadian Patents Database / Patent 3043671 Summary
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|(12) Patent Application:||(11) CA 3043671|
|(54) English Title:||REMOVAL OF ARSENIC FROM FLUE-GAS|
|(54) French Title:||ELIMINATION DE L'ARSENIC DES GAZ DE COMBUSTION|
- Bibliographic Data
- Representative Drawing
- Admin Status
- Owners on Record
|(51) International Patent Classification (IPC):||
|(72) Inventors :||
|(73) Owners :||
|(71) Applicants :||
|(74) Agent:||MACRAE & CO.|
|(74) Associate agent:|
|(86) PCT Filing Date:||2017-12-05|
|(87) Open to Public Inspection:||2018-06-14|
|(30) Availability of licence:||N/A|
|(30) Language of filing:||English|
|Patent Cooperation Treaty (PCT):||Yes|
|(86) PCT Filing Number:||PCT/EP2017/081435|
|(87) International Publication Number:||WO2018/104257|
|(85) National Entry:||2019-05-13|
|(30) Application Priority Data:|
The divulged invention concerns a process for the removal of arsenic oxides inprocessexhaust gases, comprising the step of passing the exhaust gases through a supported ionic liquid phase bed,characterized in that the ionic liquid comprises one or more cations from the list consisting of substituted phosphonium, ammonium, imidazolium, pyrrolidinium, and pyridinium, and one or more anions from the list consisting of chloride, bromide, and carboxylate. Compared toa bed of active carbon, theionic liquid soaked active carbon bed according to the invention allows for an estimated doubling of thearsenic adsorptioncapacity of the bed, while also considerably enhancingthe kineticsofadsorption.
La présente invention concerne un procédé d'élimination d'oxydes d'arsenic des gaz d'échappement de procédé, comprenant l'étape consistant à faire passer les gaz d'échappement à travers un lit de phase liquide ionique supporté, caractérisé en ce que le liquide ionique comprend un ou plusieurs cations de la liste constituée par le phosphonium substitué, l'ammonium, l'imidazolium, le pyrrolidinium et le pyridinium, et un ou plusieurs anions de la liste consistant en chlorure, bromure et carboxylate. Par rapport à un lit de charbon actif, le lit de charbon actif imbibé de liquide ionique selon l'invention permet un doublement estimé de la capacité d'adsorption d'arsenic du lit, tout en améliorant considérablement la cinétique d'adsorption.
1. Process for the removal of As2O3 and/or As2O5 in process exhaust gases,
step of passing the exhaust gases through a supported ionic liquid phase bed,
that the ionic liquid comprises one or more cations from the list consisting
phosphonium, ammonium, imidazolium, pyrrolidinium, and pyridinium, and one or
from the list consisting of chloride, bromide, and carboxylate.
2. Process according to claim 1, wherein the substituted phosphonium cation
to formula [Pm n o p]+, and the substituted ammonium cation is according to
formula [Nm n o p]+,
wherein the substituents are hydrocarbon chains containing m, n, o, and p
carbon atoms each,
with the proviso that m+n+o+p > 10 when the anion is a halide, and m+n+o+p <
30 when the
anion is a carboxylate.
3. Process according to claims 1 or 2, characterized in that the
carboxylate is an unbranched,
unsaturated monocarboxylate, containing 1 to 8 carbon atoms.
4. Process according to any one of claims 1 to 3, wherein the supported
ionic liquid phase
comprises a support phase from the list consisting of alumina, silica, and
5. Process according to claim 4, whereby the support phase has a BET of
6. Process according to any one of claims 1 to 5, whereby the weight ratio
phase to ionic liquid weight ratio is between 3 : 1 and 50 : 1.
7. Process according to claim 6, wherein the process exhaust are off-gases
metallurgical smelting process, characterized in that the supported ionic
liquid phase is recycled
to that process.
CA 03043671 2019-05-13
Removal of arsenic from flue-gas
The present invention concerns a gas cleaning process, specially adapted for
the removal of
traces of arsenic oxides in exhaust gases, in particular in off-gases from
processes or coal burning processes.
Arsenic is present in many minerals, concentrates, and recycled metal-bearing
Arsenic and many arsenic compounds are also relatively volatile at high
Consequently, most metallurgical operations produce arsenic bearing gases, in
pyrometallurgical processes are applied. Examples are burning of coal, or the
metals such as copper and lead, using smelting processes. Emissions from
converters can cause health problems in the work place and/or result in
elevated levels of toxic
pollutants such as lead and arsenic in the immediate vicinity of the smelter.
According to known processes, the major part of the arsenic in gas streams can
by condensation, filtration, or adsorption on active carbon.
Condensation and filtration allow for arsenic abatement down to about 0.2 to
0.8 mg/Nm3 in the
gas phase. Hydrated lime Ca(OH)2 can be injected in the gas, thereby not only
condensation surface, but also adsorbing the arsenic by forming a Ca ¨ As
precipitate. A further
reduction of arsenic down to 0.05 mg/Nm3 is then typically obtainable.
A more complete elimination of arsenic is however desired in view of the eco-
toxicity of this
metal and of its compounds. Moreover, typical industrial operations involve
release of huge volumes of gases, thus exacerbating the environmental issue.
A known process for the further reduction of arsenic is passing the gas
through a bed of active
It has been recognized that the effectiveness of arsenic adsorption on active
with increasing temperature. The gas stream has therefore to be cooled down to
100 C. Unfortunately, the adsorption kinetics at this temperature are rather
slow. A sufficient
contacting time between active carbon and gas can only be achieved by using a
bed, which therefore needs to contain a large quantity of active carbon. This
results in bulky and
expensive equipment. The active carbon is moreover not effectively utilized,
as it never gets
saturated in arsenic during its normal operational life.
CA 03043671 2019-05-13
It is the aim of the present divulgation to propose a scheme to solve the
above problems, in
particular to accelerate the adsorption kinetics of arsenic compared to active
allowing for the abatement of arsenic down to less than 0.01 mg/Nm3. This
scheme makes use
of a bed of SILP (Supported Ionic Liquid Phase), i.e. a porous carrier
typically prepared by
soaking a carrier phase in a selected ionic liquid.
Processes for the capture of metals or their oxides using supported ionic
liquid phases have
been described before. They are however not optimized for the elimination of
.. US20140001100 discloses a process for the capture of elemental mercury from
fluid using ionic liquids. Suitable ionic liquids comprise an organic cation,
a metal cation, and an
anion. The ionic liquid is believed to perform a dual function. First, the
metal cation part of the
ionic liquid oxidizes the mercury. The oxidized mercury, being destabilized in
environment, is then efficiently captured in the ionic liquid.
U520070123660 similarly concerns a process for the capture of gaseous forms of
oxidized mercury, but also of lead, zinc and cadmium. Use is made of a
combination of a ligand
and of an ionic liquid. Oxidizing agents are added when elemental species need
to be captured.
A process is hereby divulged for the removal of arsenic oxides in process
comprising the step of passing the exhaust gases through a supported ionic
liquid phase bed,
characterized in that the ionic liquid comprises one or more cations from the
list consisting of
substituted phosphonium, ammonium, imidazolium, pyrrolidinium, and pyridinium,
and one or
more anions from the list consisting of chloride, bromide, and carboxylate.
By process exhaust gases are meant gases from metallurgical smelting processes
or from other
Preferably, the substituted phosphonium cation is according to formula [Pm no
p]+, and the
substituted ammonium cation is according to formula [Nm no p]+, wherein the
hydrocarbon chains containing m, n, o, and p carbon atoms each, with the
m+n+o+p > 10 when the anion is a halide, and m+n+o+p <30 when the anion is a
The hydrocarbon chains substituents of the cation are preferably unbranched
The anions are preferably unbranched, unsaturated monocarboxylates, containing
1 to 8 carbon
CA 03043671 2019-05-13
The most preferred ionic liquid is [P66614] Cl. This product is commercially
CYPHOS IL 101.
The process is most suitable for removing arsenic oxides comprising As203
Preferably, the supported ionic liquid phase comprises a support phase from
the list consisting
of alumina, silica, and activated carbon. A support phase having a BET of more
than 50 m2/g is
desired. A weight ratio of support phase to ionic liquid weight between 3: 1
and 50: 1 is most
The advantages are of the disclosed process and corresponding equipment are:
- the volume of the adsorption bed can be reduced;
- the cleaning apparatus itself can be more compact;
- the pressure drop across the adsorption bed can be reduced.
The investment can therefore be lower than when using active carbon, and the
Such a SILP may also adsorbs elements other than arsenic which may also be
present in the
gas phase, such as Zn, Hg, Cd, Pb, Sb, and Se, dependent upon the precise
selected. For example, the ionic liquid identified as trihexyl-tetradecyl-
[P6 6 6 14] Cl lends itself well for the capture of As, but also of Pb, Cu,
Cd, Se and Zn. There is
also clear evidence for the uptake of Sb and Se when using 1-butyl-3-
acetate [C4C1im] [C1CO2]. These ionic liquids were tested using an active
The supporting substrate should be highly porous and should be wetted by the
liquid. Typical candidates are silica, alumina, titanium oxide, zirconium
oxides, activated carbon,
porous polymers, zeolites, and metal-organic frameworks.
When targeting the adsorption of arsenic, ionic liquids susceptible to
amounts of it are clearly preferred.
When the arsenic-contaminated exhaust gases originate from a metallurgical
the spent SILP can be directly recycled to that process. A capture mechanism
ahead of the
SILP adsorption step is then needed to avoid the accumulation of the metals
captured by the
SILP. The recycled SILP could even be considered as a valuable reaction agent.
This would be
the case, e.g. when dealing with an active carbon substrate and a
CA 03043671 2019-05-13
needing a reducing agent. Similarly, silica or alumina substrates could
usefully be recycled to a
process needing fluxing for the formation of a slag.
In a first example, the increase in capacity of the SILP is demonstrated.
For the preparation of activated carbon-based SILP, activated carbon WS 490
Carbon is used. One part by weight of the ionic liquid is dissolved in nine
volume parts of
methanol. The solution is added to nine part by weight of activated carbon and
left overnight to
ensure complete adsorption. The solvent is removed in three steps: 1.5 h at 45
300 mbar, 1.5 h at 65 C and 300 mbar, and 1.5 h at 65 C and 250 mbar.
Using this method, batches of SILP are produced using ionic liquids [P66614]
Cl and [C4C1irn]
The BET is measured to characterize the specific surface of the obtained SILP
this analysis, the pore volume and the pore size is determined using BJH
determinations are performed using nitrogen for the untreated activated carbon
(AC) as well as
for the above-prepared SILP samples. This is reported in Table 1.
Table 1: BET results for untreated activated carbon (AC) and for SILPs
Material Pore volume (cm3g-1) Pore area (m2g-
AC (uncoated) 0.78 1191.8
AC with 10 wt.`)/0 [P6 6 6 14] Cl 0.63 1021.4
AC with 10 wt.% [C4C1im] 0.68 1088.7
The pore size of all three materials are also recorded. In all three materials
smaller than 40 A are dominant. This demonstrates the persistence of the pore
coating of the activated carbon with the ionic liquids. However, the fraction
of these small pores
is slightly reduced after coating. It is therefore assumed that the ionic
liquid covers the inner
pores of the activated carbon.
Ionic liquids are selected according to their capacity to dissolve As203. This
list is reported in
Table 2, along with the saturation limit as function of temperature.
CA 03043671 2019-05-13
Table 2: As203 solubility in selected ionic liquids
Ionic liquid 50 C 70 C 80 C
wt.% mol% wt.% mol% wt.%
[P2 2 2 8] CI - - - - 4.94
[P4444] Cl - - - - 5.95
[P4446] Cl 1.13 1.82 3.50 5.58 5.43
[P4448] Cl -- -- - -- 3.86
[P66614] Cl 1.63 4.17 3.02 7.55 9.13
[P88810] Cl 0.68 1.85 - - 7.10
[P88818] Cl 2.31 2.31 - - 28.4
[N8881] Cl 1.54 3.08 - - 6.24
[P2 2 2 14] [HCO2] 8.08 9.77 11.5 24.12 14.8
[P4444] [HCO2] 5.88 11.9 14.9 16.71 18.3
[P2 2 2 8]  21.5 28.7 23.2 30.72 23.3
[P2 2 2 14]  7.03 12.5 10.6 18.38 13.9
[C2C1im]  18.2 16.1 25.7 22.94 26.8
[C4C1im]  12.2 12.2 28.4 28.48 34.7
[C8C1im]  11.9 14.8 19.6 23.87 19.6
It can be derived from Table 1 that the coating layer of the selected ionic
liquids is capable of
adsorbing about 10 kg of As203 per tonne of SILP. Assuming that the active
5 will also contribute to the capacity of adsorption, the total capacity of
the SILP can be estimated
to be double the capacity of the active carbon alone. This increase of
capacity is a first
advantage of soaking the active carbon in a selected ionic liquid.
In a second example, the enhanced adsorption kinetics is shown.
In a first step, two adsorption columns are prepared, one filled with un-
soaked activated carbon
to be used as a reference, the filled other with activated carbon soaked in
[P66614] Cl as
described in Example 1. Each column comprises a small amount of glass wool at
followed by a steel mesh and 10 g of adsorption material. Two additional
layers of adsorption
material are added, each separated by a steel mesh. Each layer has an average
1.63 cm. A steel mesh and glass wool is added on the top layer so as to
stabilize the adsorption
bed. The internal diameter of the column is about 4.2 cm.
CA 03043671 2019-05-13
In a second step, As203 bearing gas is fed to the columns. To this end, a side
sampled from the off-gases produced by a lead blast furnace. After a first
dust filter, the gas is
divided into three parallel streams. One stream is directly passed through to
a cascade of
washing bottles for the analysis of the inlet concentrations. The analysis of
the As203 in the
washing bottles allows for the determination of the input concentration. The
other two are
passed through the respective adsorption columns. Each column outlet is
to a separate cascade of washing bottles. Each cascade is followed by a drying
column and a
pump where the gas flow rate is adjusted to 3 L/min for each stream. The
temperature of the
gas entering the columns is about 140 C. The experiment is conducted for 48
As summarized in Table 3, it is observed that the output arsenic concentration
is reduced by a
factor of 3 when ionic liquid soaked active carbon is utilized instead of un-
soaked active carbon.
As the operating conditions are identical, and as the levels are far below
saturation effects, it is
believed that the ionic liquid provides for accelerated adsorption kinetics.
This is a second
advantage of soaking the active carbon in a selected ionic liquid. This
advantage prevails even
when substrates other than activated carbon are used, such as silica or
Table 3: Arsenic adsorption and yield
Column Input concentration Output concentration
mg/Nm3 mg/Nm3 (0/0)
None (pass through) 0.45 0.45 0.
AC (un-soaked) 0.45 0.0059 98.7
AC with 10 wt.% [P6 6 6 14] Cl 0.45 0.0013 99.7
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|Forecasted Issue Date||Unavailable|
|(86) PCT Filing Date||2017-12-05|
|(87) PCT Publication Date||2018-06-14|
|(85) National Entry||2019-05-13|
|Abandonment Date||Reason||Reinstatement Date|
|2021-06-07||FAILURE TO PAY APPLICATION MAINTENANCE FEE|
Last Payment of $100.00 was received on 2019-10-08
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