U.S. patent application number 11/071632 was filed with the patent office on 2006-09-07 for mercury removal sorbent.
Invention is credited to Joseph B. Cross, Glenn W. Dodwell, Marvin M. Johnson, Edward L. II Sughrue, Jianhua Yao.
Application Number | 20060198774 11/071632 |
Document ID | / |
Family ID | 36944299 |
Filed Date | 2006-09-07 |
United States Patent
Application |
20060198774 |
Kind Code |
A1 |
Cross; Joseph B. ; et
al. |
September 7, 2006 |
Mercury Removal sorbent
Abstract
A composition comprising a vanadium oxide compound and an alkali
metal promoter loaded onto a porous support material is disclosed.
Methods of making and using the composition to remove heavy metals
or heavy metal containing compounds from a fluid stream are also
provided. Such methods are particularly useful in the removal of
mercury and mercury compounds from flue gas streams produced from
the combustion of hydrocarbon-containing materials such as coal and
petroleum fuels.
Inventors: |
Cross; Joseph B.;
(Bartlesville, OK) ; Dodwell; Glenn W.;
(Bartlesville, OK) ; Johnson; Marvin M.;
(Bartlesville, OK) ; Sughrue; Edward L. II;
(Bartlesville, OK) ; Yao; Jianhua; (Bartlesville,
OK) |
Correspondence
Address: |
ConocoPhilips Company - I.P. Legal
PO BOX 2443
BARTLESVILLE
OK
74005
US
|
Family ID: |
36944299 |
Appl. No.: |
11/071632 |
Filed: |
March 3, 2005 |
Current U.S.
Class: |
423/210 ;
502/344; 502/400 |
Current CPC
Class: |
B01D 2253/108 20130101;
B01D 53/8665 20130101; B01D 2257/602 20130101; B01D 2253/104
20130101; B01J 20/0214 20130101; Y10S 210/914 20130101; B01D
2259/414 20130101; B01D 2253/102 20130101; B01J 20/06 20130101;
Y10S 502/516 20130101; B01J 20/3204 20130101; B01J 20/3236
20130101; B01D 53/02 20130101; B01D 2253/112 20130101 |
Class at
Publication: |
423/210 ;
502/344; 502/400 |
International
Class: |
B01J 23/22 20060101
B01J023/22 |
Claims
1. A composition comprising a porous support material including a
vanadium oxide compound and an alkali metal vanadate incorporated
thereon, therein, or thereon and therein.
2. A composition in accordance with claim 1 wherein said vanadium
oxide compound comprises V.sub.2O.sub.5, a hydrate of
V.sub.2O.sub.5, a peroxo complex of vanadium oxide, or mixtures
thereof.
3. A composition in accordance with claim 1 wherein said alkali
metal vanadate is lithium vanadate.
4. A composition in accordance with claim 1 wherein said porous
support material is selected from the group consisting of amorphous
silica-alumina, a zeolite, a material comprising meta-kaolin,
alumina, expanded perlite, and combinations thereof.
5. A composition in accordance with claim 1 wherein said porous
support material comprises at least about 50% by weight of the
total weight of said composition.
6. A composition in accordance with claim 1 wherein said
composition comprises from about 0.5-40% by weight vanadium.
7. A composition in accordance with claim 1 wherein said porous
support material has a surface area of at least about 75
m.sup.2/g.
8. A composition in accordance with claim 1 wherein said
composition comprises from about 0.5-50% by weight of said alkali
metal vanadate.
9. A composition in accordance with claim 1 wherein the weight
ratio of vanadium oxide to alkali metal vanadate is from about 10:1
to 1:10.
10. A composition in accordance with claim 1 wherein said
composition further comprises a quantity of an alkali metal
hydroxide.
11. A composition in accordance with claim 10 wherein said alkali
metal hydroxide is lithium hydroxide.
12. A porous sorbent composition comprising a porous support
material impregnated with a vanadium oxide compound and an alkali
metal promoter selected from the group consisting of lithium
hydroxide, lithium vanadate, and mixtures thereof.
13. A composition in accordance with claim 12 wherein said vanadium
oxide compound comprises V.sub.2O.sub.5, a hydrate of
V.sub.2O.sub.5, a peroxo complex of vanadium oxide, or mixtures
thereof.
14. A composition in accordance with claim 12 wherein said porous
support material is selected from the group consisting of amorphous
silica-alumina, a zeolite, a material comprising meta-kaolin,
alumina, expanded perlite, and combinations thereof.
15. A composition in accordance with claim 12 wherein said porous
support material comprises at least about 50% by weight of the
total weight of said composition.
16. A composition in accordance with claim 12 wherein said
composition comprises from about 0.5-40% by weight vanadium.
17. A composition in accordance with claim 12 wherein said porous
support material has a surface area of at least about 75
m.sup.2/g.
18. A composition in accordance with claim 12 wherein said
composition comprises from about 0.5-50% by weight of said alkali
metal promoter.
19. A composition in accordance with claim 12 wherein the weight
ratio of vanadium oxide to alkali metal hydroxide is from about
10:1 to 1:10.
20. A method for forming a sorbent material comprising: (a) mixing
a vanadium oxide compound and an alkali metal hydroxide promoter
with at least one porous support material.
21. A method in accordance with claim 20 wherein said method
further comprises: (b) dispersing said vanadium oxide and said
promoter in a first aqueous solution prior to step (a).
22. A method in accordance with claim 21 wherein said first aqueous
solution comprises from about 0.5-70% by weight of said vanadium
oxide compound and from about 0.05-50% by weight of said
promoter.
23. A method in accordance with claim 21 wherein said method
further comprises: (c) dispersing said porous support components in
a second aqueous solution prior to step (a).
24. A method in accordance with claim 20 wherein said promoter is
lithium hydroxide.
25. A method in accordance with claim 20 wherein said at least one
porous support material is selected from the group consisting of
amorphous silica-alumina, a zeolite, a material comprising
meta-kaolin, alumina, expanded perlite, and combinations
thereof.
26. A method in accordance with claim 20 wherein at least a portion
of said alkali metal hydroxide promoter reacts with at least a
portion of said vanadium oxide compound to form an alkali metal
vanadate.
27. A method of removing at least one heavy metal or heavy metal
containing compound from a fluid stream, said method comprising the
step of: (a) contacting said fluid stream with a porous support
material having incorporated onto, into, or onto and into a
vanadium oxide compound and an alkali metal promoter for sorption
of at least a portion of said at least one heavy metal or heavy
metal containing compound.
28. A method in accordance with claim 27 wherein said vanadium
oxide incorporated support material oxidizes said heavy metal into
an oxidized heavy metal species or heavy metal containing
compound.
29. A method in accordance with claim 27 wherein said porous
support material is selected from the group consisting of amorphous
silica-alumina, a zeolite, a material comprising meta-kaolin,
alumina, expanded perlite, and combinations thereof.
30. A method in accordance with claim 27 wherein said vanadium
oxide compound comprises V.sub.2O.sub.5, a hydrate of
V.sub.2O.sub.5, a peroxo complex of vanadium oxide, or mixtures
thereof.
31. A method in accordance with claim 27 wherein said promoter is
selected from the group consisting of lithium vanadate, lithium
hydroxide, and mixtures thereof.
32. A method in accordance with claim 27 wherein said contacting
step results in a pressure drop in said fluid stream of less than
about 20 psia.
33. A method in accordance with claim 32 wherein said contacting
step results in a pressure drop in said fluid stream of less than
about 10 psia.
34. A method in accordance with claim 27 wherein said fluid stream
has a temperature between about 50-400.degree. F. during said
contacting step.
35. A method in accordance with claim 27 wherein said fluid stream
comprises at least one heavy metal or compound containing a heavy
metal selected from the group consisting of arsenic, beryllium,
lead, cadmium, chromium, nickel, zinc, mercury, and barium.
36. A method in accordance with claim 35 wherein said at least one
heavy metal is mercury.
37. A method in accordance with claim 27 wherein said vanadium
oxide incorporated support material comprises finely divided
particles that are suspended in said fluid stream during said
contacting step, pelletized particles placed in a fixed or
fluidized bed, monoliths, or combinations thereof.
38. A method in accordance with claim 27 wherein said contacting
step results in the sorption of at least about 80% by weight of the
at least one heavy metal or heavy metal containing compound
contained in said fluid stream.
39. A method in accordance with claim 27 wherein said vanadium
oxide incorporated support material is capable of sorbing at least
about 1 atom of said heavy metal per every 5 atoms of vanadium.
40. A process for the removal of at least one heavy metal or heavy
metal containing compound from a flue gas stream produced by the
combustion of a hydrocarbon-containing fuel comprising the steps
of: (a) contacting said flue gas stream with a first sorbent
material comprising a porous support having incorporated onto,
into, or onto and into a vanadium oxide compound and an alkali
metal promoter for sorbing at least a portion of said at least one
heavy metal or heavy metal containing compound present in said flue
gas stream; and (b) contacting said flue gas with a second sorbent
material different from said first sorbent material for sorbing at
least a portion of said at least one heavy metal-containing
compound not sorbed during step (a).
41. A process as recited in claim 40 wherein said second sorbent
material comprises a material selected from the group consisting of
porous zeolite materials, amorphous carbons, and combinations
thereof.
42. A process as recited in claim 41 wherein said amorphous carbons
are selected from the group consisting of activated charcoal,
activated carbon, and combinations thereof.
43. A process as recited in claim 41 wherein said porous zeolite
material comprises ZSM-5 zeolite.
44. A process as recited in claim 40 wherein said flue gas stream
comprises at least one heavy metal or compound containing a heavy
metal selected from the group consisting of arsenic, beryllium,
lead, cadmium, chromium, nickel, zinc, mercury, and barium.
45. A process as recited in claim 44 wherein said at least one
heavy metal is mercury.
46. A process as recited in claim 40 wherein said vanadium oxide
compound comprises V.sub.2O.sub.5, a hydrate of V.sub.2O.sub.5, a
peroxo complex of vanadium oxide, or combinations thereof.
47. A process as recited in claim 40 wherein step (a) results in a
pressure drop in said flue gas stream of less than about 20
psia.
48. A process as recited in claim 40 wherein said flue gas stream
has a temperature between about 50-400.degree. F. during step
(a).
49. A process as recited in claim 40 wherein said vanadium oxide
incorporated support material comprises finely divided particles
that are suspended in said flue gas stream during step (a),
pelletized particles placed in a fixed or fluidized bed, monoliths,
or combinations thereof.
50. A process as recited in claim 40 wherein step (a) results in
the sorption of at least about 80% by weight of said at least one
heavy metal or heavy metal containing compound contained in said
flue gas stream.
51. A process as recited in claim 40 wherein step (b) results in
the removal of at least about 80% by weight of said at least one
heavy metal compound from the flue gas stream leaving step (a).
52. A process as recited in claim 40 wherein said alkali metal
promoter is selected from the group consisting of lithium vanadate,
lithium hydroxide, and mixtures thereof.
53. A process as recited in claim 40 wherein prior to step (a) said
process includes removal of at least about 50% by weight of all
NO.sub.x and SO.sub.x present in said flue gas.
54. A process as recited in claim 40 wherein said flue gas stream
comprises less than about 400 ppm NO.sub.x and less than about 800
ppm SO.sub.x immediately prior to step (a).
55. A process as recited in claim 40 wherein said vanadium oxide
incorporated support material oxidizes said heavy metal into an
oxidized heavy metal species or heavy metal containing compound
during step (a).
Description
[0001] The invention relates to a composition and method for
removing heavy metal contaminates from fluid streams. In one
aspect, the invention relates to a method of preparing such
composition. In yet another aspect, the invention relates to a
process for removing heavy metal contaminates, such as mercury and
mercury compounds, from flue gas streams produced from the
combustion of hydrocarbon-containing materials.
BACKGROUND OF THE INVENTION
[0002] Heavy metals are released during the combustion process of
many fossil fuels and/or waste materials. These heavy metals
include, for example, arsenic, beryllium, lead, cadmium, chromium,
nickel, zinc, mercury, and barium. Most of these heavy metals are
toxic to humans and animals. In particular, elemental mercury and
mercury compounds such as mercury chlorides are thought to
compromise the health and mental acuity of young children and
fetuses.
[0003] Furthermore, there is every indication that the amount of
mercury, and possibly of other heavy metals, now legally allowed to
be released by those combusting various fossil fuels and/or waste
materials, including coal burning powerplants and petroleum
refineries, will be reduced by future legislation. While a variety
of adsorbents are available for capture of heavy metals (in
particular mercury), these adsorbents tend to have low capacities
and are easily deactivated by other components in the gas stream,
such as sulfur oxides. Thus, there exists a need for a material
that removes elemental mercury from gas streams and has a high
capacity for retaining mercury as a nonvolatile compound.
SUMMARY OF THE INVENTION
[0004] It is an object of the present invention to provide an
improved vanadium material with a high capacity for sorbing heavy
metals and heavy metal compounds.
[0005] A further object of this invention is to provide a method
for making an improved vanadium material by incorporating a
vanadium oxide compound and an alkali metal hydroxide promoter with
a porous support material.
[0006] Another object of this invention is to provide a process for
removing heavy metals or heavy metal compounds from a fluid stream
by contacting the fluid stream with an improved vanadium
material.
[0007] Yet another object of this invention is to provide an
improved vanadium material which when used in the removal of heavy
metals results in the oxidation of the heavy metal to an oxidation
state greater than zero.
[0008] It should be understood that the above-listed objects are
only exemplary, and not all the objects listed above need be
accomplished by the invention described and claimed herein.
[0009] In accordance with a first embodiment of the invention, the
inventive composition comprises a porous support material including
a vanadium oxide compound and an alkali metal vanadate incorporated
thereon, therein, or thereon and therein.
[0010] In accordance with a second embodiment of the invention, the
inventive composition comprises a porous support material
impregnated with a vanadium oxide compound and an alkali metal
promoter selected from the group consisting of lithium hydroxide,
lithium vanadate, and mixtures thereof.
[0011] In accordance with a third embodiment of the invention, the
inventive composition can be prepared by the method of: (a) mixing
a vanadium oxide compound and an alkali metal hydroxide promoter
with at least one porous support material.
[0012] In accordance with a fourth embodiment of the invention, the
inventive composition can be used in the removal of at least one
heavy metal or heavy metal containing compound from a fluid stream
by (a) contacting the fluid stream with a porous support material
having incorporated onto, into, or onto and into a vanadium oxide
compound and an alkali metal promoter for sorption of at least a
portion of the at least one heavy metal or heavy metal containing
compound.
[0013] In accordance with a fifth embodiment of the invention, the
inventive composition can be used in the removal of at least one
heavy metal or heavy metal containing compound from a flue gas
stream produced by the combustion of a hydrocarbon-containing fuel
by: (a) contacting the flue gas stream with a first sorbent
material comprising a porous support having incorporated onto,
into, or onto and into a vanadium oxide compound and an alkali
metal promoter for sorbing at least a portion of the at least one
heavy metal or heavy metal containing compound present in the flue
gas stream; and (b) contacting the flue gas with a second sorbent
material different from the first sorbent material for sorbing at
least a portion of the at least one heavy metal-containing compound
not sorbed during step (a).
[0014] Other objects and advantages of the invention will become
apparent from the detailed description and the appended claims.
BRIEF DESCRIPTION OF THE FIGURES
[0015] A preferred embodiment of the present invention is described
in detail below with reference to the attached figures,
wherein:
[0016] FIG. 1 is a graph of mercury uptake versus mercury
breakthrough for a lithium promoted V.sub.2O.sub.5 sorbent on a
porous support compared to a conventional activated charcoal
sorbent; and
[0017] FIG. 2 is a graph of the mercury removal efficiency for a
lithium promoted V.sub.2O.sub.5 sorbent on a porous support.
DETAILED DESCRIPTION OF THE INVENTION
[0018] Compositions according to the present invention generally
comprise a porous support material with a vanadium oxide compound
and an alkali metal promoter incorporated thereon, therein, or
thereon and therein. Preferably, the vanadium oxide compound
comprises V.sub.2O.sub.5, a hydrate of V.sub.2O.sub.5, a peroxo
complex of vanadium oxide or combinations thereof. However, it is
within the scope of the invention for the vanadium component to
have any oxidation state greater than zero.
[0019] An alkali metal promoter is employed to increase the
effectiveness of the vanadium oxide in sorbing heavy metals.
Preferably, the alkali metal promoter is an alkali metal hydroxide
such as lithium hydroxide. As discussed below, during formation of
the inventive compositions, it is possible for at least a portion
of the alkali metal hydroxide promoter to react with at least a
portion of the vanadium oxide compound to form an alkali metal
vanadate such as lithium vanadate. Hydrates of alkali metal
hydroxides can also be used such as lithium hydroxide monohydrate.
However, it is within the scope of the present invention for the
promoter to be an elemental alkali metal, an alkali metal compound,
or an ionic alkali metal species. Unless otherwise specified, the
term "promoter" refers to any such alkali metal composition whether
it was originally added to the inventive sorbent or whether it was
formed in situ.
[0020] The vanadium oxide compound and promoter are loaded onto a
porous support material. Preferably, the support material is
selected from the group consisting of amorphous silica-alumina, a
zeolite, a material comprising meta-kaolin, alumina, expanded
perlite, and combinations thereof. It is most preferable to employ
a silica-alumina support material such as meta-kaolin in
conjunction with expanded perlite, however, it is possible that the
support may comprise pure alumina or calcined alumina.
[0021] The porous support material generally comprises at least
about 50% by weight of the total composition, preferably between
about 50-99% by weight, more preferably between about 75-95% by
weight, and most preferably between about 80-90% by weight. In
order to maximize the sorptive capacity of the composition, the
support material preferably has a surface area of at least about 75
m.sup.2/g, more preferably at least about 100 m.sup.2/g, and most
preferably at least about 150 m.sup.2/g.
[0022] The overall composition preferably comprises from about
0.5-40% by weight vanadium. Unless otherwise specified, the phrase
"by weight vanadium" is defined as the elemental weight of vanadium
present in the composition. More preferably, the composition
comprises from about 1-35% by weight vanadium, and most preferably
from about 2-25% by weight.
[0023] The composition preferably comprises from about 0.5-50% by
weight of the alkali metal promoter, more preferably from about
1-30% by weight, and most preferably from about 5-25% by weight.
The weight ratio of vanadium oxide to promoter is preferably within
the range of about 10:1 to 1:10, more preferably between about 5:1
to 1:5, and most preferably between about 4:1 to 1:1.
[0024] The sorbent material is formed by mixing a vanadium oxide
compound and an alkali metal promoter with at least one porous
support. The vanadium oxide compound and promoter should be
intimately contacted with the support so that the vanadium oxide
compound and promoter become incorporated onto, into, or onto and
into the support.
[0025] One avenue for accomplishing this intimate mixing is to
dispense the vanadium oxide and promoter in a first solution. Water
is a preferred solvent for forming this solution, however, any
solvent capable of dissolving both the vanadium oxide and promoter
may be used. When dispersed in an aqueous solution, the vanadium
oxide comprises from about 0.5-70% by weight of the solution, more
preferably between about 5-60% by weight, and most preferably from
about 10-50% by weight. Similarly, when dispersed in an aqueous
solution, the promoter comprises from about 0.05-50% by weight of
the solution, more preferably from about 0.5-40% by weight, and
most preferably from about 1-30% by weight. At the same time, the
porous support is dispersed in a second solution, with water being
a preferred solvent.
[0026] If an alkali metal hydroxide is selected as the promoter
that is mixed with the vanadium oxide compound, generally, at least
a portion of the alkali metal hydroxide reacts with at least a
portion of the vanadium oxide compound to form an alkali metal
vanadate, also referred to herein as a "promoter."
[0027] The first and second solutions are then mixed together
thereby loading the vanadium oxide and promoter onto, into, or onto
and into the support. The mixture is then dried, and preferably,
the resulting sorbent material is in a granular or powder form. It
is possible that the porous support used is not in a finely divided
form prior to mixing with the vanadium oxide and promoter solution.
If such is the case, it is preferable to crush and sieve the dried
sorbent material to an acceptable particle size for a given
application. The sorbant material may also be pelletized, formed
into monoliths, or incorporated into a foam in order to render it
suitable for a specific application.
[0028] The inventive sorbent material is particularly useful in the
removal of heavy metals and heavy metal containing compounds from
fluid streams, especially flue gas streams produced by the
combustion of hydrocarbon-containing materials such as coal and
petroleum fuels. As noted above, such fluid streams are often
contaminated with at least one heavy metal or compound containing a
heavy metal selected from the group consisting of arsenic,
beryllium, lead, cadmium, chromium, nickel, zinc, mercury, and
barium. In one aspect, methods of removing heavy metal and heavy
metal containing compounds from fluid streams comprise providing a
sorbent composition according to the present invention and
contacting the stream with the inventive sorbent.
[0029] Flue gas, such as that created by the combustion of
hydrocarbon-containing compounds, generally comprises at least
about 10% by weight N.sub.2, more preferably at least about 50% by
weight, and most preferably between about 75-90% by weight. Flue
gas also generally comprises less than about 10% by weight of
uncombusted hydrocarbons, more preferably less than about 5% by
weight, and most preferably less than about 1% by weight. As
described below, in a particularly preferred application, the flue
gas will have already been treated for removal of NO.sub.x and
SO.sub.x prior to any heavy metal removal process as the presence
of high levels of NO.sub.x and SO.sub.x compounds may lead to
fouling of the heavy metal removal sorbents. Generally, the flue
gas comprises less than about 800 ppm of SO.sub.x compounds such as
SO.sub.2, more preferably less than about 500 ppm, and most
preferably less than about 400 ppm. Also, the flue gas preferably
comprises less than about 400 ppm NO.sub.x such as NO and NO.sub.2,
more preferably less than about 250 ppm, and most preferably less
than about 150 ppm. Flue gas may also comprise between about
2.5-10% by weight O.sub.2, between about 1-5% by weight CO.sub.2,
and between about 5-20% by weight H.sub.2O.
[0030] Preferably, the pressure drop associated with the contacting
step should not exceed more than about 20 psia. More preferably,
the pressure drop in the fluid stream is less than about 10 psia,
and most preferably less than about 5 psia. Typically, flue gas
streams do not flow under high pressures. Therefore, if the
pressure drop is too great, back pressure is created and can affect
the combustion process by which the flue gas is created. The
arrangement of the sorbent material in the vessel in which
contacting occurs can assist in minimizing this pressure drop.
Preferably, the sorbent material comprises finely divided particles
that are suspended in the fluid stream during the contacting step.
Alternatively, the sorbent material may be positioned in a
fluidized bed, placed in a packed bed column, formed into
monoliths, or incorporated into a foam. With the latter
arrangements, pressure drop may become much more of a concern and
may require the use of fans or other equipment to increase the
pressure of the flue gas stream.
[0031] The fluid stream containing the heavy metal contaminant
preferably has a temperature of between about 50-400.degree. F.
during the contacting step, more preferably between about
100-375.degree. F., and most preferably between about
200-350.degree. F. The temperature of the fluid stream at the
contacting stage is in part affected by upstream processes such as
particulate removal systems (i.e., cyclones), other contaminant
removal systems, heat exchange systems, etc. The contacting step
results in the sorption of at least about 80% by weight of the
heavy metals contained in the fluid stream, more preferably at
least about 90% by weight, even more preferably at least about 95%
by weight, and most preferably at least about 98% by weight. As
previously stated, the vanadium oxide incorporated support material
exhibits a high capacity for sorbing heavy metals and heavy metal
containing compounds. Preferably, the vanadium oxide material is
capable of sorbing at least about 1 atom of a heavy metal per every
5 atoms of vanadium. More preferably, the ratio of heavy metal
atoms sorbed to vanadium atoms is at least about 1:3, and most
preferably 1:1.
[0032] The sorbent material also exhibits the ability to oxidize
the elemental heavy metal into a heavy metal containing compound
such as a heavy metal oxide or chloride. Using mercury as an
example, the sorbent material oxidizes mercury into various
oxidized species such as Hg.sup.+1, Hg.sup.+2, or mercury compounds
such as HgO, HgCl, and HgCl.sub.2. At times, due to system
inefficiencies or sorbent saturation, some of these heavy metal
containing compounds may desorb or break free from the sorbent
material. In that case, it can be particularly useful to employ a
downstream heavy metal compound removal system in conjunction with
the above-described sorbent system. In the heavy metal compound
removal system, the gaseous product stream is contacted with a
separate adsorbent in an adsorption zone. The adsorbent can be any
adsorbent capable of adsorbing a heavy metal; however, preferred
materials for removing the heavy metal compounds include those
having a hydrophobic surface with pore openings of less than about
10 .ANG., and high pore volumes. More preferably, the adsorbent
comprises, consists of or consists essentially of a material
selected from the group consisting of a zeolite, amorphous carbon
and combinations thereof. The amorphous carbon can be an activated
carbon and/or activated charcoal. Exemplary zeolites include those
with 8-12 member ring openings, and particularly ZSM-5 zeolite.
Furthermore, the material may be in the form of granules, pellets,
monoliths, powders that are collected on filters, or combinations
thereof. A treated gaseous product stream is withdrawn from the
adsorption zone and contains less than about 20 weight %,
preferably less than about 10 weight %, and more preferably less
that about 5 weight % of the heavy metal in the gaseous feed
stream.
[0033] The heavy metal compound removal system may be contained in
a separate downstream vessel from the vanadium oxide sorbent, or
can be situated along with the vanadium oxide sorbent in a multiple
stage contacting vessel so that the flue gas first contacts the
vanadium oxide sorbent followed by the heavy metal compound removal
sorbent.
[0034] While the vanadium oxide sorbent material exhibits a
relatively high capacity for sorbing heavy metals and heavy metal
containing compounds, its cost is relatively higher than the cost
for conventional heavy metal compound sorbent materials such as
zeolite. Therefore, from an economic standpoint, it may be
desirable to employ a relatively small amount of the vanadium oxide
sorbent compared to the conventional sorbent material. Once the
sorptive capacity of the vanadium oxide sorbent has sufficiently
diminished, it will not be able to sorb sufficient quantities of
the heavy metal containing compounds formed by the catalytic action
of the vanadium oxide sorbent. These heavy metal containing
compounds may then be sorbed by the lesser expensive heavy metal
compound sorbent material located downstream from the vanadium
oxide sorbent.
[0035] The heavy metal compound removal system preferably results
in the sorption of at least about 80% by weight of the heavy metal
containing compounds that break through the vanadium oxide sorbent
material, more preferably at least about 90% by weight, and most
preferably at least about 95% by weight.
[0036] In addition to the vanadium oxide sorbent material becoming
saturated, the overall sorptive efficiency may be affected by the
presence of NO.sub.x and SO.sub.x compounds present in the flue
gas. For example, SO.sub.2 contained in the flue gas stream may be
oxidized to SO.sub.3 and then converted to H.sub.2SO.sub.4 in the
presence of water. The H.sub.2SO.sub.4 then may fill the pores of
the vanadium oxide sorbent thereby decreasing the sorptive capacity
thereof and blocking active catalyst sites. Therefore, it is
preferable to employ an upstream NO.sub.x and SO.sub.x removal
process in order to avoid fouling of the vanadium oxide sorbent
material. Any conventional NO.sub.x and SO.sub.x removal process
would be suitable for use with the present invention. The NO.sub.x
and SO.sub.x removal process should preferably remove at least
about 50% by weight of all NO.sub.x and SO.sub.x present in the
flue gas stream. It is preferable for the flue gas stream
immediately prior to contact with the vanadium oxide sorbent to
comprise less than about 400 ppm NO.sub.x, more preferably less
than about 250 ppm, and most preferably less than about 150 ppm.
Likewise, it is preferable for the flue gas stream immediately
prior to contact with the vanadium oxide sorbent to comprise less
than about 800 ppm SO.sub.x, more preferably less than about 500
ppm, and most preferably less than about 400 ppm.
[0037] The heavy metal compound removal system is capable of
performing effectively even at high flue gas flow rates (i.e.,
greater than 10,000 gas hourly space velocity). The sorbent
material used in the heavy metal compound removal system may be
placed in a fluidized or packed bed vessel, however, as with the
vanadium oxide sorbent material system above, the pressure drop of
the flue gas stream should be minimized to avoid requiring the use
of additional equipment to compensate for the pressure drop.
EXAMPLE
[0038] The following example illustrates preferred sorbent
materials and methods of making the same in accordance with the
present invention. This example should not be taken as limiting the
scope of the present invention in any way.
[0039] In this example, a sorbent material according to the present
invention was prepared by forming a solution comprising 17.816 g of
LiOH.H.sub.2O and 77.229 g of V.sub.2O.sub.5 dissolved in 60 g of
deionized water. A separate dispersion was prepared containing 60 g
of deionized water, 30 g of alumina (DISPAL), 60 g of expanded
perlite, and 20 g of calcined Kaolin or more generally calcined
clay, or more specifically meta Kaolin. The solution and dispersion
were mixed together forming a thick, paste-like material. This
material was extruded through a 1/8 inch die and dried overnight at
248.degree. F. The next day, the extrudate was crushed so as to
form a granular material that could be passed through a 20-40 mesh
sieve.
[0040] The material was then tested for efficacy in removing
elemental mercury entrained in an air stream at a concentration of
approximately 1000 .mu.g/m.sup.3 (ppb w/v). Approximately 0.97 g of
the sorbent was placed in a fixed bed reactor, the temperature of
which was held constant at 300.degree. F. The air flow rate through
the fixed bed reactor was fixed at a gas hourly space velocity of
>10,000 (approximately 200 mL/min). The air stream entering and
exiting the fixed bed reactor was periodically analyzed using a
Jerome Mercury Analyzer.
[0041] FIG. 1 shows the mercury uptake versus the mercury
breakthrough of the sorbent material. For purposes of comparison,
literature data for sulfur impregnated activated charcoal (SIAC), a
conventional sorbent for this application, is also shown. The
lithium promoted V.sub.2O.sub.5 sorbent demonstrated excellent
capacity for sequestering mercury when compared with the SIAC
literature data. FIG. 2 further demonstrates the effectiveness of
the sorbent in removing mercury from the air stream in terms of
efficiency of the sorbent versus mercury uptake. The sorbent
exhibited greater than 95% efficiency over extended test periods.
In sum, the test results indicate that the lithium promoted
V.sub.2O.sub.5 sorbent material has a high capacity for sorbing
mercury and is exceptionally efficient in mercury removal.
* * * * *