U.S. patent application number 10/541847 was filed with the patent office on 2006-04-13 for magnetic activated carbon and the removal of contaminants from a fluid streams.
Invention is credited to DavidW Mazyck.
Application Number | 20060076229 10/541847 |
Document ID | / |
Family ID | 32713480 |
Filed Date | 2006-04-13 |
United States Patent
Application |
20060076229 |
Kind Code |
A1 |
Mazyck; DavidW |
April 13, 2006 |
Magnetic activated carbon and the removal of contaminants from a
fluid streams
Abstract
Magnetic activated carbon and the removal of contaminants from a
fluid stream using the magnetic activated carbon is described. The
magnetic activated carbon is preferably magnetic powdered activated
carbon and may contain titania. The magnetic activated carbon (10)
may be used to remove contaminants such as mercury from fluid
streams including flue gases (20) from a combustion plant.
Inventors: |
Mazyck; DavidW;
(Gainesville, FL) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
SUITE 800
WASHINGTON
DC
20037
US
|
Family ID: |
32713480 |
Appl. No.: |
10/541847 |
Filed: |
January 12, 2004 |
PCT Filed: |
January 12, 2004 |
PCT NO: |
PCT/US04/00615 |
371 Date: |
July 12, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60439429 |
Jan 13, 2003 |
|
|
|
Current U.S.
Class: |
204/157.3 ;
422/186.3; 95/27 |
Current CPC
Class: |
B01D 2253/102 20130101;
B01D 53/8665 20130101; B01D 53/10 20130101; B01J 20/28009 20130101;
Y10S 95/901 20130101; B01D 53/02 20130101; B01J 20/20 20130101;
B01D 2257/602 20130101; B01D 2255/802 20130101; B01D 2257/60
20130101; B01J 20/06 20130101; B01J 23/745 20130101; B01D 53/32
20130101; B01J 35/0033 20130101; B01J 35/004 20130101; B01J 21/18
20130101 |
Class at
Publication: |
204/157.3 ;
422/186.3; 095/027 |
International
Class: |
B01D 53/00 20060101
B01D053/00 |
Claims
1. A method for removing a contaminant from a fluid stream,
comprising contacting the fluid stream with a composite of
activated carbon and a magnetic material whereby the contaminant is
adsorbed on the magnetized activated carbon, and removing the
magnetized activated carbon having the mercury adsorbed thereon
from the fluid stream.
2. The method according to claim 1, wherein the contaminant is
mercury.
3. The method according to claim 1, wherein the composite further
comprises a photocatalyst and further comprising the steps of
exposing the photocatalyst to excitation energy to provide hydroxyl
radicals on the surface thereof.
4. The method according to claim 3, wherein the photocatalyst is
TiO.sub.2.
5. The method according to claim 3, wherein the photocatalyst is
present in the composite in an amount of less than about 10% by
weight based upon the total weight of the photocatalyst and
composite of activated carbon and magnetic material.
6. The method according to claim 5, wherein the photocatalyst is
present in the composite in an amount of less than about 7% by
weight based upon the total weight of the photocatalyst and
composite of activated carbon and magnetic material.
7. The method according to claim 6, wherein the photocatalyst is
present in the composite in an amount of less than about 5% by
weight based upon the total weight of the photocatalyst and
composite of activated carbon and magnetic material.
8. The method according to claim 1, further comprising the step of
recycling the magnetized activated carbon removed from the fluid
stream back into contact with the fluid stream.
9. The method according to claim 1, wherein the fluid stream is
flue gas from a combustion plant.
10. The method according to claim 9, wherein the combustion plant
is a coal combustion plant or a waste combustion plant.
11. The method according to claim 1, wherein the activated carbon
is injected into the fluid stream under pressure.
12. The method of claim 1, wherein the activated carbon is powdered
activated carbon.
13. The method of claim 1, wherein the magnetic material is
selected from the group consisting of magnetite, maghemite,
hematite and goethite.
14. The method according to claim 1, wherein the composite contains
activated carbon and magnetic material in a weight ratio of less
than about 5:1.
15. The method according to claim 14, wherein the composite
contains activated carbon and magnetic material in a weight ratio
of less than about 4:1.
16. The method according to claim 14, wherein the composite
contains carbon and magnetic material in a weight ratio of less
than about 3:1.
17. A composite, comprising activated carbon and a magnetic
material.
18. The composite according to claim 17, wherein the activated
carbon is powdered activated carbon.
19. The composite according to claim 17, wherein the magnetic
material is selected from the group consisting of magnetite,
maghemite, hematite and goethite.
20. The composite according to claim 17, further comprising a
photocatalyst.
21. The composite according to claim 20, wherein the photocatalyst
is selected from the group consisting of TiO.sub.2, ZnO and
SnO.sub.2.
22. The composite according to claim 21, wherein the photocatalyst
is TiO.sub.2.
23. The composite according to claim 20, wherein the photocatalyst
is present in an amount of less than about 10% by weight based upon
the total weight of the photocatalyst and composite of activated
carbon and magnetic material.
24. The composite according to claim 23, wherein the photocatalyst
is present in an amount less than about 7% by weight based upon the
total weight of the photocatalyst and composite of activated carbon
and magnetic material.
25. The composite according to claim 24, wherein the photocatalyst
is present in an amount of less than about 5% by weight based upon
the total weight of the photocatalyst and composite of activated
carbon and magnetic material.
26. The composite according to claim 17, wherein the composite
contains activated carbon and magnetic material in a weight ratio
of less than about 5:1.
27. The composite according to claim 26, wherein the composite
contains activated carbon and magentic material in a weight ratio
of less than about 4:1.
28. The composite according to claim 26, wherein the composite
contains activated carbon and magnetic material in a weight ratio
of less than about 3:1.
Description
[0001] This application claims benefit of Provisional Application
No. 60/439,429 filed Jan. 13, 2003; the disclosure of which is
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention is directed to activated carbon for purifying
flue gas, which can be separated magnetically from fly ash and,
more specifically, magnetic powdered activated carbon (MPAC) having
an enhanced affinity for flue gas constituents such as Hg, the iron
on the surface of the carbon catalyzing the oxidation of elemental
Hg. The present invention also relates to further enhancing Hg
capture by using a photocatalyst (e.g., TiO.sub.2, ZnO, SnO.sub.2)
that may be added to the carbon's surface which when irradiated
with UV light creates hydroxyl radicals. The hydroxyl radicals
oxidize elemental Hg which adsorbs more readily than elemental
Hg.
[0004] 2. Description of the Related Prior Art
[0005] Amongst the numerous hazardous air pollutants (HAPs)
currently regulated by the EPA, elemental mercury and mercury
containing compounds have recently been highlighted as significant
due to their increasing rate of release, and the lack of adequate
control technologies. Although the resulting quantity in the
environment is usually low, it can transfer to various organisms,
and then magnify up the food chain. For example, the concentration
of accumulated mercury in some fish can reach levels that are
millions of times greater than that in the water. The consumption
of such fish by humans, and the resulting buildup of mercury in
various tissues may lead to serious neurological and developmental
effects such as losses of sensory or cognitive ability, tremors,
inability to walk, convulsions, and even death. Methylmercury, the
most common form of organic mercury, is almost completely
incorporated into the blood stream, and can be transferred through
the placenta and into all of the tissues of the fetus, including
that of the brain. Because of the health concerns related to eating
mercury contaminated fish, bans on fishing in certain regions such
as in the Great Lakes have resulted in considerable losses to the
economy.
[0006] The EPA has estimated that nearly 87% of the anthropogenic
mercury emissions are from sources such as waste (as in
waste-to-energy facilities) and fossil fuel combustion (as in
coal-fired power plants). Recognizing this, control technologies
have been employed in an effort to capture and dispose of the
mercury found in combustion exhaust gases. Currently, powdered
activated carbon (PAC) injection into the flue gas stream is the
best available control technology for mercury removal. However,
understanding that an estimated 3 kg of activated carbon is needed
to remove 1 g of mercury, to meet regulations it is anticipated
that PAC injection will cost between $2 and $5 billion annually.
Furthermore, PAC's low mercury adsorption efficiency, low
applicable temperature range, slow adsorption rate, and lack of
adequate regeneration technologies, all have sparked an interest in
modifying the material to either decrease costs or improve uptake
in hopes for optimization.
[0007] Another shortcoming in using PAC injection systems is the
accumulation of the waste PAC in the fly ash. Fly ash, the fine
particulate fraction of the Coal Combustion Byproducts (CCBs)
(i.e., noncombustible inorganics and uncombusted carbon), is
collected from flue gas and then commonly sold for the production
of concrete and other materials. By using fly ash instead of the
lime, cement, or crushed stone materials that are typically used,
energy and resources are conserved. However, when the typical fly
ash collection devices are coupled with PAC injection systems, the
quality of the collected fly ash deteriorates because of the large
fraction of carbon in the ash; consequently, revenue generation by
selling the fly ash becomes impossible. Current research geared
towards separation technologies has yet to find an adequate method
to isolate the PAC from the fly ash. Therefore, a method that can
easily separate PAC from the fly ash offers the potential to (a)
maintain the quality of the fly ash for subsequent use, (b) reuse
the PAC, and (c) recover the Hg for various applications.
SUMMARY OF THE INVENTION
[0008] In accordance with the present invention, there is provided
a method for removing a contaminant or contaminants from a fluid
stream. The method includes contacting the fluid stream with a
composite of activated carbon and a magnetic material whereby the
contaminant is adsorbed on the magnetized activated carbon, and
removing the magnetized activated carbon having the mercury
adsorbed thereon from the fluid stream. Preferably, the contaminant
is mercury, and the composite preferably further comprises
titania.
[0009] The method of the present invention preferably includes
further the step of recycling the magnetized activated carbon
removed from the fluid stream back into contact with the fluid
stream, the fluid stream preferably being flue gas from a
combustion plant, more preferably, a coal combustion plant or a
waste combustion plant, wherein the activated carbon is preferably
injected into the fluid stream.
[0010] The present invention also includes a composite of activated
carbon and a magnetic material. The composite preferably further
includes a photocatalyst. The activated carbon is preferably
powdered activated carbon, and the magnetic material is preferably
either magnetite, maghemite, hematite or goethite
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 represents a schematic summarizing the steps of
injecting, capturing, and recycling the MPAC in accordance with the
present invention;
[0012] FIG. 2 represents a schematic of the test stand that was
used to collect the data herein in accordance with the present
invention;
[0013] FIG. 3 represents a breakthrough curve highlighting several
activated carbon magnetic composites and their performance for
capturing Hg from flue gas in accordance with the present
invention;
[0014] FIG. 4 represents a comparison of several activated carbon
magnetic composites manufactured from different activated carbon
precursors in accordance with the present invention; and
[0015] FIG. 5 represents a breakthrough curve highlighting the
effect of TiO.sub.2 addition to the magnetic composites for
capturing Hg from flue gas in accordance with the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0016] The challenge of separating the PAC fraction from the fly
ash is addressed by engineering magnetic PAC (MPAC) through iron
impregnation/precipitation into the carbon's porous matrix or on
its surface. The magnetic PAC particles, after cycling through the
flue gas, can be collected, for example, by a magnetic drum before
it accumulates with other particulate matter. Not only will this
allow for separation of the MPAC and hence use of the fly ash for
concrete production, it will also provide a method by which the
MPAC composite can be recycled. Because of the short contact time
between the flue gas and the carbon particle (mere seconds), only a
fraction of the carbon's surface is actually utilized in removing
mercury. Recycling the MPAC to fully exploit its adsorption
capacity before disposal offers a plausible means to decrease the
mass of PAC that would be required on an annual basis to meet
regulations. Eventually, the adsorption capability of the MPAC in
accordance with the present invention, may become diminished in
which case it will be recognized that the MPAC could then be
replaced with fresh MPAC. In any event, in addition, iron, (e.g.,
Fe.sub.2O.sub.3) can oxidize mercury (e.g., to HgO), which not only
adsorbs better, but it itself serves as a sorption site for
elemental Hg. Therefore, the efficacy for the recycled MPAC to
perform even better than its first time use is very real. In other
words, Hg captured during the second cycle could exceed Hg captured
during the first time use. If so desired, prior to reinjection of
the MPAC, the sorbed Hg could be recovered thermally or chemically
by conventional technologies, as would be appreciated by one of
ordinary skill in the art. In summary, the MPAC composite in itself
will promote conservation of resources and a significant reduction
in expenditures.
[0017] In a preferred embodiment of the present invention, the MPAC
is coated with titanium dioxide (TiO.sub.2) which provides for even
greater Hg capture. Hydroxyl radicals, which are very powerful
oxidants, can be generated on the surface of TiO.sub.2 under UV
radiation which enhances mercury uptake by oxidizing elemental Hg.
Thus, adsorption increases with each exhaustion/UV-enhanced
regeneration cycle. In other words, oxidized Hg (e.g., HgO) serves
as sorption sites for elemental Hg. Therefore, oxidation of
elemental mercury in accordance with the present invention and with
titania and UV increases the mercury uptake over the reinjection
cycles. In the case where electrostatic precipitators are installed
in coal-fired power plants, the energy required to excite titania's
electrons which leads to hydroxyl radical formation is present. For
bag house installations, UV lamps near about 365 nm would be
required. Thus, when a photocatalyst is incorporated into the MPAC
in accordance with the present invention as will be discussed in
more detail below, hydroxyl radicals are suitably provided on the
surface of the photocatalyst by exposing the photocatalyst to
excitation energy in the form of, for example, UV radiation or
electrostatic energy. As would be recognized by one of ordinary
skill in the art, UV radiation includes invisible radiation
wavelengths from about 4 nanometers, on the border of the x-ray
region, to about 380 nanometers, just beyond the violet in the
visible spectrum.
[0018] In accordance with the present invention, activated
carbon/iron composites are prepared by dispersing iron salts in
deionized water already containing a slurry of powdered activated
carbon. When followed by NaOH addition, chemical precipitation
occurs implanting the iron on to and in the pores of the activated
carbon. Preferably, a combination of salts are used to prepare the
composite in accordance with the invention. However, it will be
understood that the use of one iron salt is within the scope of the
invention. The iron salts are preferably a combination of
FeCl.sub.3 (ferric chloride) and FeSO.sub.4 (ferric sulfate)
because they are inexpensive, and can be added in various ratios
(i.e., about 1:99 to about 99:1) to achieve the desired magnetic
species (e.g., magnetite (Fe.sub.3O.sub.4), maghemite
(.gamma.-Fe.sub.2O.sub.3), hematite (.alpha.-Fe.sub.2O.sub.3), and
goethite (.alpha.-FeO(OH))). (Unless otherwise noted, all ratios
expressed herein are weight ratios.) Other iron salts and magnetic
species suitable for use in the present invention will be apparent
to one skilled in the art. Preferably, the weight ratio of chloride
salt to sulfate salt is greater than about 1:1, most preferably
about a 2:1 ratio of FeCl.sub.3 to FeSO.sub.4. In some situations,
however, a ratio of chloride salt to sulfate salt of greater than
about 3:1 may be desired, as would be appreciated by one of
ordinary skill in the art, such as when one desires to increase the
chloride loading on the carbon surface since chloride is known to
chemically bond mercury.
[0019] To achieve a desired activated carbon/iron composite ratio
in accordance with the invention, activated carbon may be added by
adjusting its weight in order to obtain activated carbon/iron oxide
weight ratios of preferably less than about 5:1, more preferably
less than about 4:1, even more preferably less than about 3:1, and
most preferably an activated carbon/iron oxide weight ratio of
about 1:1. For example, a composite in accordance with the present
invention may be suitably prepared by the addition in solution of
FeCl.sub.3, FeSO.sub.4 and activated carbon. The carbon and iron
solution may then be mechanically mixed, and then NaOH added
dropwise to increase pH to a level whereby the iron oxides
precipitated. The material may then be dried. It will be recognized
that heating at high temperatures (i.e., greater than about
150.degree. C.) in inert environments or reducing environments can
enhance magnetite formation. It is within the scope of this
invention to realize that iron in its variety of forms and chemical
formulas could also be added to the carbon via chelation or vapor
phase adsorption.
[0020] Titania and other photocatalysts (e.g., ZnO, SnO.sub.2) are
well known for creating hydroxyl radicals (OH) when irradiated with
UV light. These OH radicals are strong oxidizing species that can
oxidize organic and inorganic compounds. Although this is well
known, there is no evidence currently available that describes the
benefits of adding titania to a magnetic carbon composite. The
titania (available as titania precursors (e.g., titania iso prop
oxide) or nano-sized titania (e.g., P-25 by Degussa)) or other
photocatalyst may be added to the magnetic carbon composite in
accordance with the present invention via boil deposition,
hydrolysis, mechanofusion, or sol gel methods. For example, during
the boil deposition procedure, the activated carbon may be mixed
with the titania while the water is driven off through evaporation.
To achieve a 1% titania weight loading (based upon the total weight
of the titania and activated carbon), for example, about 100 mg of
activated carbon may be mixed with about 1% by weight titania.
Preferably, the titania loading is less than about 10% by weight,
more preferably less than about 7% by weight, and most preferably
less than about 5% by weight, based upon the total weight of the
titania and MPAC, to avoid blocking adsorption sites.
[0021] It will be appreciated that while the present invention is
described in connection with the removal of mercury from flue gas,
the present invention is not limited to the removal of mercury from
flue gas and may be used to remove other materials, specifically,
contaminants such as, for example, sulfur and nitrogen containing
compounds, VOCs (volatile organic compounds), and SOCs (synthetic
organic chemicals) as defined by the Environmental Protection
Agency, can be removed from fluid streams by the process in
accordance with the present invention. Further, the present
invention is described here in connection with the use of PAC.
However, it will be understood that the use of granular activated
carbon is also within the scope of the present invention.
[0022] In addition, by the term "composite" as used herein, is
meant a complex material or a composition of material in which the
activated carbon and magnetic material combine to produce a
material with properties that are not present in either the
activated carbon or magnetic material alone. While not wishing to
be bound by theory, it is believed that there may be come chemical
or physical bonds such as, for example, Van der Waals forces, that
bond the activated carbon and magnetic material. In any event, by
the term "activated carbon" as used herein, is meant powdered or
granular carbon used for purifying by adsorption. Also, by the term
"PAC" or "powdered activated carbon" is meant activated carbon 90%
of which passes through a 325-mesh sieve (45 .mu.m).
[0023] Referring now to FIG. 1, there is shown schematically a coal
fired plant operated in accordance with the present invention.
Indeed, every coal-fired power plant is different, with this
difference primarily depending upon the plant's capacity rating.
In, for example, a coal-fired power plant (approximately 300 MW),
with flue gas temperatures around 270.degree. F. and a volumetric
flow rate of approximately 1 million acfm (actual cubic feet per
minute), the magnetic PAC particles 10, instead of PAC, are
injected into the flue gas 20 at a rate of about 10 lb/hr to about
100 lb/hr, which depends upon the flue gas composition and
temperature as well as the effluent mercury target, just upstream
of the existing air pollution control device (APCD) 30. The
injection of the MPAC includes forcing the MPAC into the flue duct
via a dilute phase pneumatic injection system, like those used in
municipal solid waste facilities. The commingled fly ash and MPAC
exit the APCD (e.g., through an electrostatic precipitator, bag
house) and collect on to a conveyor belt 40, which transports the
mixture to the next processing station. Here, the magnetic
particles are collected, for example, on an electromagnetic drum 50
similar to those used conventionally in coal processing/washing
plants where they are used to collect magnetite that is added to
the coal processing water to modify the water's density. When the
electricity to the drum is interrupted, MPAC can be scraped from
the drum using a blade towards a hopper whereby it can be recycled
for reinjection, disposed, or processed to recover the sorbed
mercury.
[0024] The invention will now be discussed in connection with
certain experiments conducted in accordance with the present
invention. The experiments are described in the following as well
as in summary form in the following figures and tables.
EXAMPLE 1
Preparation of Activated Carbon/Iron Composite
[0025] The production of a 1:1 composite sample would be made
through the addition of 6 g of FeCl.sub.3, 3 g of FeSO.sub.4, and 9
g of activated carbon. The carbon and iron solutions are then
mechanically mixed for at least 30 minutes. Afterwards,
approximately 50 mL or thereabouts of NaOH (ca. 5 mol/L) is added
drop wise to increase the pH to approximately 10, which
precipitated the iron oxides. Afterwards, the sample is oven dried
at 105.degree. C. for 12 hours to decrease the total moisture
content to less than 3%. The sample is then transferred to a
desiccator and permitted to cool to room temperature.
EXAMPLE 2
Preparation of Activated Carbon/Iron Composite with
Photocatalyst
[0026] To 100 g of a 1:1 composite sample of activated carbon/iron
composite prepared in accordance with Example 1 is added 1% by
weight of titania (i.e., 1 mg) in accordance with the following
procedure. 100 g of the 1:1 activated carbon/iron composite is
added to 250 mL of deionized water and mechanically mixed for 60 s
to disperse the composite in the fluid. Next, 1 g of Degussa P-25
TiO.sub.2 is added and the suspension is continually stirred. After
another 60 s, a hot plate is turned on to increase the temperature
of the solution to 150.degree. C. and this temperature is
maintained until the majority of the water is evaporated. Next, the
sample is transferred to a 105.degree. C. gravity drying oven for
24 hours. The sample is then transferred to a desiccator and
permitted to cool to room temperature.
EXAMPLE 3
Removal of Hg
[0027] Bench-scale studies were performed in the apparatus shown in
FIG. 2, which consisted of a small column reactor whereby high
grade nitrogen gas from reservoir 100 was passed through an
elemental mercury reservoir 110 to create a mercury vapor laden air
with less than 45 ppb of Hg. The mercury vapor was joined with a
heated water vapor line (70% RH, 275.degree. F.) from H.sub.2O
bubbler 120 and the combination was flowed downward through the
packed bed glass column from the top to minimize channeling or
selective flow through the column. The parameters of the column are
summarized in Table 1 below. Prior to adsorption testing,
approximately 1 g of MPAC was mixed with a 140.times.200 mesh
sieved quartz sand ( 1/20 carbon to sand ratio) and then heated to
the desired temperature (275.degree. F.) for a minimum of 30
minutes. Breathing grade air was used as a dilution flow to lower
the readings to an acceptable range for the Ra-915+Zeeman Mercury
Spectrometer (Ohio Lumex) 140. The effluent stream from the column
was passed through the mercury analyzer 140 and mercury
breakthrough curves were generated by computer 150 for comparison
of the composite PAC samples. It will be understood that
appropriate flow meters 160 and 170, as well as bypass line 180 are
provided to control and facilitate the transport of the various
materials. TABLE-US-00001 TABLE 1 Carbon Column Design Parameter
Value Length (inches) 7.25 Diameter (inches) 1.0 Volume (mL) 93.3
Volume of media (mL) 19.3 carbon/sand ratio (g) 1/20 Gas flow rate
(L/min) 0.32 Gas temp. (.degree. F.) 275 H.sub.20 (%) 70 Average
influent mercury (ppb) 45 Residence time (s) 3
[0028] Beginning with a commercially available coal-based activated
carbon, several magnetic carbon composites were produced via the
method of Example 1 discussed above. These composites and their
virgin counterpart were compared for their ability to remove
elemental Hg. FIG. 3 demonstrates that a synergy exists when iron
is loaded on to the carbon, for the 1:1 iron loaded carbon never
experienced breakthrough (i.e., the effluent elemental Hg
concentration never surpassed zero). The phenomena can be explained
as the iron oxidizing the elemental Hg to its oxidized form (e.g.,
HgO), which not only sorbs better to activated carbon, but also
serves as a sorbent for elemental Hg. (The 1:1 data was replicated
seven times.) The 2:1 carbon performed about the same as the virgin
carbon. This too is surprising since its surface area (Table 2) is
about 3 times less than its virgin counterpart. Note that the 1:1
carbon also has a surface area about 2.5 times less than its virgin
counterpart. The remaining data follows the same trend whereby the
3:1 out performs the 4:1 and the 5:1 composites for capturing Hg.
The performance for the composites decreases as the ratio of carbon
to iron increases because there is less iron present to catalyze
the conversion (i.e., oxidation) of elemental mercury to oxidized
mercury.
[0029] The BET surface areas for the carbon/iron composites were
just discussed, and even though iron addition to the carbons
severely decreased the carbons' surface area, performance for the
2:1 and 1:1 composites were equal to or better than the virgin
carbon, respectively. The 1:1 composite had slightly more surface
area than the 2:1 because the iron itself contributes to the total
surface area of the composite, and there is more iron present with
the 1:1 composite compared to the 2:1 sample. Table 2 below also
lists the magnetic strengths for the composites. As the magnetic
strength increases, the ease at which the composites are separated
also increases. As shown, the virgin carbon was not magnetic at
all. The composites followed the trend whereby the 1:1 carbon was
the most magnetic (i.e., 109 milligauss) followed by the 2:1, 3:1,
4:1, and then the 5:1. TABLE-US-00002 TABLE 2 BET Surface Magnetic
Strength Carbon Area (m.sup.2/g) (mgauss) Virgin 917 0 1:1 Carbon
to Iron Ratio 357 121 2:1 Carbon to Iron Ratio 290 53 3:1 Carbon to
Iron Ratio 282 46 4:1 Carbon to Iron Ratio 255 28 5:1 Carbon to
Iron Ratio 256 11
[0030] Suitable activated carbon for use in the present invention
is available commercially and FIG. 4 demonstrates that several
commercially available carbons can be magnetized using a 1:1 ratio.
Moreover, the degree of magnetization is different between the
carbons. The commercially available carbon that was prepared with a
chemical activation process was the most magnetic (264 milligauss),
followed by the physically activated coal-based carbons (198, 172,
and 121 milligauss), with the physically activated wood-based
carbon being the least magnetic (89 milligauss). The suppliers of
the carbons are Westvaco, Calgon, Carbochem, NORIT, and
Acticarb.
[0031] In accordance with the present invention, when TiO.sub.2 is
added to the magnetic carbon composite, elemental mercury can be
oxidized so that it is more adsorbable when irradiated with UV
light. FIG. 5 demonstrates that both the 3:1 and 2:1 composites
exhibited better performance with the addition of 1% TiO.sub.2 and
UV irradiation. For example, the effluent concentration for the 2:1
composite with UV performed more than 2 times better than when the
UV was absent. The titania was added to the MPAC via boil
deposition by adding Degussa P-25 TiO.sub.2 (1 wt %) to a beaker
containing deionized water and the preferred mass of MPAC. The
suspension was mechanically stirred at 105.degree. C. until all of
the water evaporated thereby implanting the titania to the
carbon.
[0032] There are no other known inventions whereby activated
carbons are magnetized and coated with a photocatalyst such as
TiO.sub.2 whereby the performance for mercury capture of the
activated carbon improves after each cycle.
[0033] Coal-fired power plants are faced with stringent air
emissions regulations, and PAC injection is currently the best
available technology as deemed by the EPA. However, because it is
expensive and contaminates the fly ash, a means to recycle the PAC
can reduce operating costs while maintaining a salable fly ash. The
invention described herein would facilitate these coal-fired power
plants to meet regulations at a fraction of the projected
costs.
[0034] Although the present application has been described in
connection with the preferred embodiments thereof, many other
variations and modifications will become apparent to those skilled
in the art without departure from the scope of the invention.
* * * * *