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Abstract
The present invention generally relates to a method of thermally reactivating activated carbon via a two-step process: steam followed by pyrolysis; whereby the steam is preferably deoxygenated. Activated carbons reactivated by this method resemble their virgin counterpart's physical characteristics (e.g., BET surface area) and often perform better in water treatment. The present invention also includes a method of reactivating activated carbon via conventional processes (i.e. pyrolysis followed by steam) at low dissolved oxygen (DO) concentrations. The third aspect of the present invention is the activation of carbonaceous material comprising of steam treating the carbonaceous material followed by pyrolysis.
Claims
What is claimed is:
1. A method for reactivating activated carbon, comprising the steps of
steam treating the activated carbon followed by pyrolysis, both the steam
treatment and pyrolysis being conducted at a temperature within the range
of about 400° C. to about 900° C., wherein the steam
treatment comprises treating the activated carbon with steam prepared from
water having a dissolved oxygen content of less than about 9 mg of oxygen
per liter of water.
2. The method according to claim 1, wherein both the steam treatment and
pyrolysis are conducted at a temperature within the range of about
450° C. to about 850° C.
3. The method according to claim 2, wherein both the steam treatment and
pyrolysis are conducted at a temperature within the range of about
650° C. to about 850° C.
4. The method according to claim 3, wherein both the steam treatment and
pyrolysis are conducted at the same temperature.
5. The method according to claim 1, wherein both the steam treatment and
pyrolysis are conducted for a total of about 5 minutes to about 2 hours.
6. The method according to claim 5, wherein both the steam treatment and
pyrolysis are conducted for about 10 minutes to about 60 minutes.
7. The method according to claim 5, wherein the steam treatment and
pyrolysis are conducted for equal amounts of time.
8. The method according to claim 1, wherein the steam treatment comprises
treating the activated carbon with steam prepared from water having a
dissolved oxygen content of less than about 6 mg of oxygen per liter of
water.
9. The method according to claim 9, wherein the steam treatment comprises
treating the activated carbon with steam prepared from water having a
dissolved oxygen content of less than about 5 mg of oxygen per liter of
water.
10. The method according to claim 9, wherein the steam treatment comprises
treating the activated carbon with steam prepared from water havin
a
dissolved oxygen content of less than 1 mg of oxygen per liter of water.
11. The method according to claim 1, wherein the steam treatment comprises
subjecting the activated carbon to a flow of steam of at least about 0.01
pounds of steam per pound of activated carbon.
12. The method according to claim 11, wherein the steam treatment comprises
subjecting the activated carbon to a flow of steam of about 0.05 to about
0.50 pounds of steam per pound of activated carbon.
13. A method for reactivating activated carbon, comprising the steps of
pyrolysis followed by steam treating the activated carbon, both the steam
treatment and pyrolysis being conducted at a temperature within the range
of about 400° C. to about 900° C., wherein the steam
treatment comprises treating the activated carbon with steam prepared from
water having a dissolved oxygen content of less than about 9 mg of oxygen
per liter of water.
14. A method according to claim 13, wherein the steam treatment comprises
treating the activated carbon with steam prepared from water having a
dissolved oxygen content of less than about 6 mg of oxygen per liter of
water.
15. A method according to claim 14, wherein the steam treatment comprises
treating the activated carbon with steam prepared from water having a
dissolved oxygen content of less than about 5 mg of oxygen per liter of
water.
16. A method according to claim 15, wherein the steam treatment comprises
treating the activated carbon with steam prepared from water having a
dissolved oxygen content of less than about 1 mg of oxygen per liter of
water.
17. The method according to claim 13, wherein the steam treatment comprises
subjecting the activated carbon to a flow of steam of at least about 0.01
pounds of steam per pound of activated carbon.
18. The method according to claim 17, wherein the steam treatment comprises
subjecting the activated carbon to a flow of steam of about 0.05 to about
0.50 pounds of steam per pound of activated carbon.
19. The method according to claim 13, wherein both the steam treatment and
pyrolysis are conducted at a temperature within the range of about
450° C. to about 850° C.
20. The method according to claim 19, wherein both the steam treatment and
pyrolysis are conducted at a temperature within the range of about
650° C. to about 850° C.
21. The method according to claim 19, wherein both the steam treatment and
pyrolysis are conducted at the same temperature.
22. The method according to claim 13, wherein both the steam treatment and
pyrolysis are conducted for a combined total of about 5 minutes to about 2
hours.
23. The method according to claim 22, wherein both the steam treatment and
pyrolysis are conducted for a combined total of about 10 minutes to about
60 minutes.
24. The method according to claim 23, wherein the steam treatment and
pyrolysis are conducted for equal amounts of time.
25. A method for activating a carbonaceous material, comprising the steps
of steam treating the carbonaceous material followed by pyrolysis, wherein
the steam treating comprises subjecting the carbonaceous material to steam
prepared from water having a dissolved oxygen content of less than about 9
mg of oxygen per liter of water.
26. The method according to claim 25, wherein the steam treating comprises
subjecting the carbonaceous material to steam prepared from water having a
dissolved oxygen content of less than about 6 mg of oxygen per liter of
water.
27. The method according to claim 26, wherein the steam treating comprises
subjecting the carbonaceous material to steam prepared from water having a
dissolved oxygen content of less than about 5 mg of oxygen per liter of
water.
28. The method according to claim 27, wherein the steam treating comprises
subjecting the carbonaceous material to steam prepared from water having a
dissolved oxygen content of less than about 1 mg of oxygen per liter of
water.
29. The method according to claim 25, wherein the steam treatment comprises
subjecting the carbonaceous material to a flow of steam of at least about
0.01 pounds of steam per pound of carbonaceous material.
30. The method according to claim 29, wherein the steam treatment comprises
subjecting the carbonaceous material to a flow of steam of about 0.05 to
about 0.50 pounds of steam per pound of carbonaceous material.
31. The method according to claim 25, wherein both the steam treatment and
pyrolysis are conducted at a temperature within the range of about
400° C. to about 900° C.
32. The method according to claim 31, wherein both the steam treatment and
pyrolysis are conducted at a temperature within the range of about
450° C. to about 850° C.
33. The method according to claim 32, wherein both the steam treatment and
pyrolysis are conducted at a temperature within the range of about
650° C. to about 850° C.
34. The method according to claim 31, wherein both the steam treatment and
pyrolysis are conducted at the same temperature.
35. The method according to claim 25, wherein both the steam treatment and
pyrolysis are conducted for a total of about 5 minutes to about 2 hours.
36. The method according to claim 35, wherein both the steam treatment and
pyrolysis are conducted for about 10 minutes to about 60 minutes.
37. The method according to claim 36, wherein the steam treatment and
pyrolysis are conducted for equal amounts of time.
38. The method according to claim 25, wherein the steam treating comprises
subjecting the carbonaceous material to steam prepared from water having a
dissolved oxygen content of greater than about 10 mg of oxygen per liter
of water.
39. The method according to claim 38, wherein the steam treating comprises
subjecting the carbonaceous material to steam prepared from water having a
dissolved oxygen content of greater than about 12 mg of oxygen per liter
of water.
40. A method for reactivating activated carbon, comprising the steps of
steam treating the activated carbon followed by pyrolysis, both the steam
treatment and pyrolysis being conducted at a temperature within the range
of about 650° C. to about 850° C. for about 10 to about 60
minutes, wherein the steam treatment comprises treating the activated
carbon with steam prepared from water having a dissolved oxygen content of
less than about 9 mg of oxygen per liter of water.
41. The method according to claim 40, wherein the steam is prepared from
water having a dissolved oxygen content of less than about 6 mg of oxygen
per liter of water.
42. The method according to claim 41, wherein the steam is prepared from
water having a dissolved oxygen content of less than about 5 mg of oxygen
per liter of water.
43. The method according to claim 42, wherein the steam is prepared from
water having a dissolved oxygen content of less than about 1 mg of oxygen
per liter of water.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is directed to a method for activating carbon and thermally
reactivating activated carbon and, more particularly, a technique for
enhancing the thermal reactivation of activated carbon that once served in
water treatment for the removal of taste and odor causing compounds (T&Os;
e.g., 2-methylisobomeol and geosmin), volatile organic compounds (VOCs;
e.g., benzene, xylenes, and toluene), synthetic organic chemicals (SOCs;
e.g., atrazine and lindane), and naturally occurring organic matter (NOM).
2. Description of the Related Prior Art
Activated carbon both in the powdered (PAC) form (generally defined as 90%
passing the 325 mesh) and granular (GAC) form (generally defined as
passing the 8 mesh, but retained on the 30 mesh or passing the 12 and
retained by the 40 mesh) has been used extensively during the past several
decades for the removal of unwanted compounds from drinking water.
Increase in activated carbon use occurred in the late 1970's upon the U.S.
EPA's recommendation of it as being the best available technology (BAT)
for controlling trihalomethanes and, later, SOCs in contaminated ground
water and drinking water. However, GAC has a finite adsorption capacity,
and approaches a point where it cain no longer remove the organics
required to purvey aesthetically pleasing water that also meets the EPA's
stringent water quality standards.
After GAC has exhausted its finite adsorption capacity or when users deem
it necessary, a common practice is to reactivate and return the activated
carbon back to service. Typically, spent activated carbon is reactivated
in a rotary kiln furnace, but also can be reactivated in fluidized bed or
multiple hearth furnaces. Conventional thermal reactivation includes the
following steps as discussed by Suzuki et al. "Study of thermal
regeneration of spent activated carbons: Thermogravimetric measurement of
various single component organics loaded on activated carbons" Chlem Eng
Sci 1978;33(3):271-279. First, the wet carbon is dried at 105° C.
to release water. Second, the GAC is pyrolyzed in a starved gas
environment between 650 and 850° C. During pyrolysis, volatile
compounds that accumulated during operation are released. This step also
causes fragments of adsorbed organic compounds on the GAC surface to form
a carbonaceous char. Finally, the adsorbed char is oxidized and gasified
by exposing the GAC to C02, steam, or a combination of both at 650 to
900° C. The inherent limitation of this oxidation step is that it
gasifies a fraction of the carbon surface while it is gasifying the char.
In other words, some of the carbon is burned during thermal reactivation.
Activated carbon's excellent performance in removing numerous organic
compounds has been proven, but it is common to hear the words "activated
carbon" and "expensive" in the same sentence. Thermal reactivation can
often represent the largest expense associated with using GAC.
Therefore, a method that can reactivate activated carbon that decreases the
mass and volume loss, results in a BET surface area or iodine number (as
measured by ASTM D4607) near its virgin counterpart, and that lasts longer
for removing compounds compared to its virgin counterpart presents an
opportunity to decrease the costs associated with thermal reactivation. In
other words, if mass loss and volume loss could be decreased during
thermal reactivation, then less virgin carbon make-up would be required to
replace the carbon lost during reactivation. If the reactivated carbon
could stay in service for longer periods of time, then reactivation
frequencies would decrease, which would decrease costs because
reactivation cycles would be farther apart. Finally, if the reactivated
carbon's iodine number and/or BET surface area are close to the virgin
counterpart, then the carbon could experience more thermal reactivation
cycles. Similarly, a method that improves the efficacy of activated carbon
for removing unwanted compounds (such as those listed above) presents an
opportunity to improve water treatment.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is a method for reactivating
activated carbon which decreases the mass and volume loss yet results in a
BET surface area or iodine number near its virgin counterpart: the
reactivated carbon lasting longer for removing compounds compared to
conventionally reactivated carbon and, in some instances, its virgin
counterpart.
Another object of the present invention is a method for the development of
an activated carbon superior in removing unwanted compounds to improve
water treatment compared to those that are activated conventionally (i.e.,
pyrolysis followed by steam).
This object and other objects are achieved by a method for reactivating
activated carbon, comprising the steps of steam treating the activated
carbon followed by pyrolysis, both the steam treatment and pyrolysis being
conducted at a temperature within the range of about 400° C. to
about 900° C.
An additional aspect of the invention includes a method for reactivating
activated carbon, comprising the steps of pyrolysis followed by steam
treating the activated carbon, both the steam treatment and pyrolysis
being conducted at a temperature within the range of about 400° C.
to about 900° C., wherein the steam treatment comprises treating
the activated carbon with steam prepared from water having a dissolved
oxygen (DO) content of less than about 9 mg of oxygen per liter of water.
Another aspect of the invention includes a method for activating a
carbonaceous material, comprising the steps of steam treating the
carbonaceous material followed by pyrolysis.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 represents a breakthrough curve comparing conventionally reactivated
carbons reactivated with water containing varying dissolved oxygen
concentrations in accordance with the present invention.
FIG. 2 represents a traditional breakthrough curve comparing conventionally
reactivated, virgin, and steam-pyrolysis reactivated carbons prepared in
the experiments conducted in accordance with the present invention.
FIG. 3 represents a MIB breakthrough curve for spent GAC reactivated using
the present invention at various temperatures (dissolved oxygen=4.5 mg/L)
in accordance with the present invention.
FIG. 4 represents a breakthrough curve comparing spent carbon reactivated
at 750° C. for 15 minutes in steam and 15 minutes in an
inert/starved gas environment at 2 different dissolved oxygen levels
(i.e., 4.5 and 8.3 mgfL) in accordance with the present invention.
FIG. 5 represents a comparison of a wood-based material activated with two
levels of dissolved oxygen (4.5 and 9.8 mg/L) for the removal of T&Os
(i.e. MIB and geosmin) in accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention includes subjecting activated carbon to a two-step
process (herein referred to as steam-pyrolysis) at temperatures equal to
or greater than about 400° C. wherein the steam was produced
preferably by heating deoxygenated water. As used herein the term
pyrolysis refers to heating in an inert/starved gas environment where
further deoxygenation/devolatilization can occur. The activated carbon
reactivated via this method results in a BET surface area or iodine number
near its virgin counterpart, and is capable of processing more bed volumes
compared to conventionally reactivated (pyrolysis followed by oxidation)
activated carbon. In some cases, this deoxygenated steam-pyrolysis
reactivated carbon can outperform its virgin (new) counterpart. In
addition, the steam-pyrolysis reactivated carbon results in a lower mass
and volume loss compared to conventional reactivation.
The first noticeable difference between the reactivation protocol of the
present invention and the conventional reactivation is the reversal of the
pyrolysis and oxidation steps. The steam-pyrolysis technique of the
present invention employs steam followed by pyrolysis, and this technique
is opposite compared to conventional reactivation. While not wishing to be
bound by theory, it is believed that by applying steam first, the organics
that sorbed during treatment can be oxidized easier through steam
gasification rather than first charring the organics through pyrolysis. In
addition, completing the reactivation in the pyrolysis step will further
remove oxygen functional groups that are deleterious to the removal of the
aforementioned organics.
The water gas shift reaction (equation 1 below) is an important reaction
that occurs during the thermal reactivation process. This is because it
controls the quantity of H2 produced, which anneals carbon reactive
sites created from functional decomposition, and thereby prevents
subsequent oxidation, which would improve carbon performance.
CO+H2 O⇄H2 +CO2 (1)
It is further believed that by deoxygenating the water heated for steam
that the water gas shift reaction rate would progress to the right more
quickly. In addition, by removing the oxygen from water, the only oxidant
present in the furnace would be H2 O versus H2 O and liberated
oxygen gas. Water can be deoxygenated by any suitable conventional
technique in the art including, for example, by bubbling with N2 or
by adding chemicals (e.g., sodiumsulfite) to achieve the desired dissolved
oxygen level. On the contrary, under some circumstances it may be
desirable to supersaturate the steam with oxygen in which case bubbling
with pure O2 can increase the water's oxygen content.
In accordance with the general principles of the invention, activated
carbon is thermally reactivated in a two-step process of steam treatment
followed by pyrolysis in an inert/starved gas atmosphere. The steam
treatment and the pyrolysis are both conducted at a temperature of about
400° C. to about 900° C., preferably about 450° C. to
about 850° C., most preferably about 650° C. to about
850° C. Preferably, the steam treatment and the pyrolysis are both
conducted at the same temperature, but if desired they may be conducted at
different temperatures. The steam treatment and the pyrolysis steps may be
conducted for as long as desired. Preferably, both steps are conducted for
a combined total of about 5 minutes to about 2 hours, more preferably,
about 10 to about 60 minutes, most preferably, about 15 minutes to about
30 minutes. The time is preferably split evenly between the steam
treatment and pyrolysis steps. Of course, one of ordinary skill in the art
will recognize that the time may be apportioned as desired. In one aspect
of the invention, at least about half of the time is apportioned to the
steam treatment. Further, for the reasons discussed above, the steam used
in the steam treatment in accordance with the invention is preferably
deoxygenated steam. As used herein, the term "deoxygenated steam" refers
to steam prepared by heating water to a temperature of, for example,
105° C. the water having an oxygen content of less than about 9 mg
of oxygen per liter of water, preferably less than about 6 mg of oxygen
per liter of water, more preferably less than about 5 mg of oxygen per
liter of water, and most preferably substantially free of oxygen, i.e., an
oxygen content of less than 1 mg of oxygen per liter of water.
In accordance with the present invention, the steam treatment includes
subjecting the activated carbon to a flow of steam of at least about 0.01
pounds of steam per pound of carbon, more preferably about 0.05 to about
0.50 pounds of steam per pound of carbon. Further, the pyrolysis may be
conducted in any suitable inert (e.g., nitrogen, argon or helium) or
starved gas environment (e.g., an environment devoid of oxygen). Other
suitable inert, or starved gas, atmospheres will be apparent to one of
ordinary skill in the art. Similarly, as one of ordinary skill in the art
will recognize, the present invention may be carried out in any suitable
conventional apparatus with appropriate accommodation for the reversal of
the order of the steam treatment and pyrolysis steps.
It is within the scope of this invention to conventionally reactivate spent
carbon using water containing low DO (i.e., water having an oxygen content
of less than about 9 mg of oxygen per liter of water, preferably less than
about 6 mg of oxygen per liter of water, more preferably less than about 5
mg of oxygen per liter of water, and most preferably substantially free of
oxygen, i.e., an oxygen content of less than 1 mg of oxygen per liter of
water). In this aspect of the invention, the process conditions including
reactivation temperatures and time, as well as the flow rate of steam,
would be the same as discussed above in connection with reactivation in
which steam treatment is conducted prior to pyrolysis.
Further, it will be recognized that while the present invention has been
described in connection with reactivating activated carbon, it is within
the scope of the present invention to prepare activated carbon, either
powdered or granular, by treating a carbonaceous material in accordance
with the method described herein, including the above discussed
temperatures, times, flow rates, etc. Examples of carbonaceous material
suitable for this aspect of the invention include those that have already
experienced pyrolysis/charring (e.g., carbon recovered from coal fired
power plant's fly ash and bark char from paper mills, and the like). Other
suitable materials would be apparent to one skilled in the art. As
mentioned above, under some circumstances it may be desirable to
supersaturate the steam with oxygen, for example, as in the context of
activating carbon in accordance with the invention, in which case bubbling
the water with oxygen can increase the DO concentration to greater than
about 10 mg of oxygen per liter of water, more preferably to greater than
about 12 mg of oxygen per liter of water. Suitably, the DO concentration
may be up to about 30 mg of oxygen per liter of water, or even up to about
100 mg of oxygen per liter of water under some conditions. It will be
recognized by one skilled in the art that higher DOs are within the scope
of the invention.
The invention will now be described in connection with certain experiments
conducted in accordance with the present invention. The experiments are
described in the following general discussion as well as in summary form
in the following tables and figures.
EXAMPLE 1
Preferably, the pyrolysis and oxidation steps are reversed whereby the
spent GAC experiences steam prior to the inert/starved gas environment.
However, performance gains are achievable if one uses water that contains
low dissolved oxygen water for the steam in the conventional reactivation
process. As an example, 10 g of spent GAC was reactivated conventionally
at 750° C. for 5 minutes (pyrolysis) followed by 10 minutes of
steam (0.2 lb steam/lb carbon), at the same temperature, in a one inch
diameter quartz fluidized bed furnace, using water that contained DO of
4.6, 9.8, and 13.7 mg/L. The spent GAC reactivated with the lower DO water
processed approximately 2000 more bed volumes to the odor threshold
concentration (OTC) compared to that reactivated with water containing
higher DO (FIG. 1). The OTC represents the concentration whereby customers
can detect (taste or smell) MIB in their water. FIG. 1 also shows that the
conventionally reactivated carbon with 9.8 mg/L DO performed similarly to
that reactivated with the low DO to about 3200 bed volumes. After 3200 BV,
the reactivation with the low DO water performed better.
EXAMPLE 2
In general, in accordance with the present invention, spent GAC was
reactivated at 750° C. for 15 minutes in steam (0.2 lbs of steam/lb
of carbon) followed by 15 minutes in N2. Its BET surface area was 950
m2 /g, which was identical to its virgin counterpart, and
considerably greater than the conventionally reactivated activated carbon
(750 m2 /g). In addition, its mass loss (12.1%) and volume loss
(2.3%) were less than the conventionally reactivated carbon (17.3% and
4.1%, respectively). Other temperatures (e.g., 650 and 850° C.) and
times (e.g., 5 to 120 minutes) were likewise investigated, and were
suitable. The carbons reactivated at 650 and 850° C. had high
surface areas (820 and 830 m2 /g) compared to the conventional
reactivation, but the 850° C. reactivated carbon experienced almost
22% mass loss which under some circumstances might be acceptable. In any
event, the process in accordance with the present invention at 750°
C. for 15 minutes in deoxygenated steam and 15 minutes of an inert/starved
gas environment provided optimal results.
The following table represents a summary of experiments conducted in
accordance with the present invention whereby the temperatures for both
steps were identical. More specifically, 6 activated carbon samples
("Utilized F300") were collected from 6 water treatment plants, and each
sample was reactivated with the present invention in triplicate. The data
shown in Table 1 represents an average of these reactivations. In the
table, "Virgin F300" is virgin activated carbon available from Calgon
Carbon Corporation of Pittsburgh, Pa. The experimental protocol identified
as "Conventional Reactivation" included pyrolysis at 850° C. for 5
minutes and oxidation in steam (0.2 lb steam/lb carbon) at 850° C.
for 10 minutes. The experimental protocol identified as "Steam Plus Ramped
Temperature" included steam treatment at 375° C. (45.8 lb steam/lb
carbon) for 1-hr followed by a step in which the temperature was ramped up
to 850° C. in an inert/gas starved environment (which took 20
minutes). The remaining experiments were conducted using a protocol in
accordance with the present invention, including steam treatment (0.2 lb
steam/lb carbon) with deoxygenated steam having an oxygen content of 4-5
mg of oxygen per liter of water followed by pyrolysis in an inert/starved
gas environment for a total of 30 minutes (the time being split evenly
between the steam treatment and pyrolysis steps), with the temperature
being as indicated.
TABLE 1
Comparison of Thermal Reactivation Process Parameters
Percent BET
Mass Percent Volume Surface Area
Protocol Loss Loss (m2 /g)
Virgin F300 NA NA 950
Utilized F300 NA NA 720
Conventional Reactivation 17.3 4.1 750
Steam Plus Ramped 15.9 3.9 830
Temperature
Steam-Pyrolysis (450° C., 5.4 0.6 780
30 minutes)
Steam-Pyrolysis (550° C., 5.4 0.6 750
30 minutes)
Steam-Pyrolysis (650° C., 10.3 2.3 820
30 minutes)
Steam-Pyrolysis (750° C., 12.1 2.3 950
30 minutes)
Steam-Pyrolysis (850° C., 21.9 2.9 830
30 minutes)
Of importance to the thermal reactivation industry is the performance of
the reactivated carbon compared to its virgin counterpart. Therefore, the
conventionally reactivated, virgin, and steam-pyrolysis reactivated
carbons of Table 1 were compared for their performance in removing the
common odorant 2-methylisoborneol (MIB). As illustrated in FIG. 2, the
conventionally reactivated carbon experienced breakthrough at
approximately 1000 bed volumes, and crossed the odor threshold
concentration (OTC) at approximately 2300 bed volumes. The OTC represents
the concentration whereby customers can detect (taste or smell) MIB in
their water. The virgin carbon likewise broke through at ca. 1000 bed
volumes, but did not reach the OTC until ca. 3200 bed volumes. Therefore,
the conventionally reactivated carbon had less capacity for MIB than the
virgin carbon, and performed worse. The concern that arises is that it is
likely that every time this carbon experiences conventional reactivation,
its performance is likely to progressively worsen. The steam-pyrolysis
reactivated carbon (750° C.) out performed both the conventionally
reactivated carbon and its virgin counterpart because the steam-pyrolysis
reactivated carbon did not break through until ca. 3500 bed volumes, and
did not cross the OTC until 5200 bed volumes.
In FIG. 3, the greatest volume of water processed before reaching
breakthrough and the odor threshold concentration was the steam-pyrolysis
reactivated carbon at 750° C. However, this temperature is
dependent upon the nature of the adsorbed organics. For example, the
reactivated carbons in FIG. 4 were capable of processing more water before
breakthrough and surpassing the OTC than those in FIG. 3. For example, the
steam-pyrolysis reactivation with the lower DO water did not experience
breakthrough until 5000 bed volumes, more than 1000 bed volumes more than
the steam-pyrolysis reactivation with the higher DO.
EXAMPLE 3
In accordance with the invention, 3 g of a wood-based material was
activated at 850° C. with steam having a DO concentration of 4.5
and 9.8 mg/L followed by pyrolysis at 850° C. for 15 minutes each
step. Subsequently, the activated carbons were powdered and tested in
batch tests for their ability to either remove MIB or geosmin from two
different raw water sources. FIG. 5 demonstrates that the activated
carbon, which was activated with steam having been prepared with the water
from the lower DO performed better, on a comparison basis, than that which
was activated with steam having the higher DO (i.e., 9.8 mg/L), both
results (i.e., 4.5 and 9.8 mg/L) being favorable/acceptable.
There are no other known inventions whereby activated carbons are thermally
reactivated such that the reactivated carbon resembles its virgin
counterpart with respect to physical properties and performance. There are
no other known inventions where the steam is deoxygenated for either
activation or reactivation.
Water utilities that employ activated carbon must routinely face the costs
and operational challenges associated with removing and replacing carbon
that has lost its capacity for removing contaminants. The invention
described herein would facilitate the water utilities to reactivate their
carbon less frequently.
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.
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