Note: Descriptions are shown in the official language in which they were submitted.
ACl-l
1~7~'76~
GRANULAR ACTIVATED CARBON MANUFACTURE FROM
SUB-BITUMINOUS COAL LEACHED WITH
DILUTE INORGANIC ACID
Background of the Invention
Field of the Invention
This invention relates to granular activated carbon manu-
facture, and more particularly to a new and improved process
for mak;ng granular activated carbon from sub-bituminous coal
leached with d;lute inorganic acid, and to a new and improved
granular activated carbon made by such process and having
properties which make it suitable for use in waste water
treatment and other applicat;ons.
Glossar~ of Terms
In order to facilitate a clear understand;ng of this
l~ invention, various terms of art employed herein are defined
as follows.
Abrasion nùmber - is a measure of the resistance of the
activated carbon granules to degrading on being mechanically ,
abraded. It ;s measured by contacting a sample with steel
balls in a pan on a mach;ne and shaking the contents For a :,
g;ven time and determining the resultant particle size
distribution and hence the mean particle diameter. The
abrasion number is the ratio of the final average (mean)
particle diameter to the original average (mean) particle
diameter (,determined by screen analysis) times lOO.
Activatèd carbon - is carbon which is "activated" by
heating to high temperature prefera61y with steam or carbon
d;oxide as the gaseous activating agent in producing an
internal porous particle structure.
Adsbrption isotherm - is a measurement of the adsorptive
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capacity of an absorbent (viz. granular activated carbon) as
a function of the concentrat;on, or pressure, of the adsorbate
(viz. N2) at a given temperature. It is deFined as the con-
stant temperature relationship between the amount adsorbed
per unit weight of adsorbent and the equilibrium concentration,
or partial pressure.
Apparent density - is the weight per unit volume of
homogeneous granular activated carbon. To assure uniform
packing of the granules during measurement, a vibrating
trough is used to fill the measuring device.
Ash - is a principal mineral constituent of coal, carbon
and pitch. It is normally defined as a weight percent basis
after a given amount of sample is reduced to ash.
Average (mean) particle diameter - is a weighted average
diameter of a granular activated carbon sample. A screen
analysis is run and the average particle diameter is calcu-
lated by multiplying the wei~ht of each fraction by its
average diameter, adding the products~ and dividing by the
total weight of the sample. The average diameter of each
fraction is taken as the size midway between the sieve opening
through which the fraction has passed and the sieve opening
on which the fraction was retained.
Cokin~__alue - is usually expressed as percent residual
carbon obtained when a dry sample of coal, tar or pitch is
vaporized or pyrolized for a specific time at a specific tem-
perature that limits the available oxygen supply (ASTM Method
D-2416~. The coking value, expressed as percent residual
carbon, lndlcates the coke forming properties of the material.
Granular activated carbon - is "activated carbon" which
has a particle size, i.e., "mesh", which is not less than
about 40.
Iodine number - is the milligrams of iodine adsorbed
by one gram of granular activated carbon at an equilibrium
filtrate concentrat;on of 0.02 N iodine. It is measured by
contacting a single sample of carbon with an iodine solution
and extrapolating to 0.02 N by an assumed isotherm slope.
This number can be correlated with the ability of granular
activated carbon to adsorb low molecular weight substances.
Mesh - (or mesh size) is the particle size of granules
as determined by the U.S. Sieve Series or the Tyler Series.
Usually, this term refers to the sizes of the two screens, in
either of the above Series, between which the bulk of a
sample falls. For example, "8/30 mesh" (or "8 by 30 mesh"
or "8 x 30 mesh") means that 90% by weight of the sample will
pass through a No. 8 screen but will be retained on a No. 30
screen. Alternatively, this term re~ers to a maximum particle
size, such as in defining the fineness of powder material.
For example, "65% by weight -325 mesh powder" means that 65%
by weight of a given sample passes through a No. 325 mesh
screen.
Pitch - is a black or dark viscous substance obtained as
a residue in the distillat;on o~ organic materials and
e~pec.ially tars.
Powder - means a particle size, i.e., "mesh", which is
smaller than about 40. The larger the mesh number, the
smaller the si~e.
-Sub-bitùminous coal - is an intermediate stage coal which
_
ranks above lignite and brown coals, but below bituminous coal.
In the as received condition it has, by weight, (1) a proxi-
mate analysis of: from about 10% to about 25% moisture, from
about 35% to about 45% volatile material, ~rom about 2% to
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about 5% ash, and from about 25% to about 45% fixed carbon,
and (2) an ultimate analysis of: from about 65% to about 75%
carbon, from about 4% to about 8% hydrogen, from about 0.5%
to about 2.0% nitrogen, and from about 0.5% to about 1.0%
sulfur.
Surface area - is the amount of surface area per unit
weight of granular activated carbon; it is determined from
the nitrogen adsorption isotherm by the Brunauer, Emmett and
Teller (BET) method, and it is expressed in m2/gram.
Prior Art
Granular activated carbon is particularly useful in waste
water treatment not only because it is highly effective in
purifying the effluent from municipal and industrial sewaye
but also because it can be regenerated for repeated use.
However, in order to accomplish these objectives it must
possess certain properties, namely, a minimum surface area of
about 900 m /gram For adequate adsorption capacity, a minimum
iodine number of about 900 for adequate adsorption of low
molecular weight substances, a maximum ash content (by weight)
of not more than about 12 percent, and preferably not more
than about 8%, for purity, a minimum abrasion number of about
70 and preferably not less than about 80, for adequate hard-
ness in maintaining granular integrity in use and in regenera-
tion, and a minimum apparent density of not less than about
0.46 gram/cc, preferably about 0.48 gram/cc, for obtaining the
dense, closely packed beds and columns needed in waste water
treatment.
These properties can be obtained by making granular
activated carbon from bituminous coal, but until the present
invention it is not known that anyone else has accomplished
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this by d71ute inorganic acid leaching of sub-bituminous coal,
which is considerably cheaper9 as the starting material.
Moreover, when so using bituminous coal, it has been
found necessary not only to mix in pi~ch but also to char the
granulated mixture prior to the devolatilizing and activating
steps. Otherwise, because of the high coking tendency of the
preferred bituminous coals, the ~ranules fuse together during
devolatilization and are thereby rendered unsuitable both for
proper activation and for obtaining the aforesaid desired
properties. Likewise, in the present work herein, it has been
found that this charring step is necessary, whether or not the
granules have been leached with a dilute aqueous solution of
inorganic acid prior to the pitch addition and charring, and
that such acid leaching has little, if any9 bene~icial effect
lS upon either the overall yield of the resulting granular
activated carbon or the aforesaid properties desired.
Furthermore, it has been found herein that granular
activated carbon of the aforementioned properties can not be
produced from sub-bituminous coal when such coal is not sub-
jected to such acid leaching or charr;ng, despite the fact
that such coal usually is not well coking. Although it has
been found herein that sub-bituminous coal can be charred,
without such acid leaching, to produce granular activated
carbon the yield is very low and the properties, at best are
borderline or below the minimum acceptable for granular
activated carbon suitable for use in waste water treatment
and other applications. As a matter of Fact, it has been
found herein that the charring step, originally thought
necessary for so processin~ sub-bituminous coal, can be
eliminated, and that if appropriate dilute inorganic
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acid leaching treatment is employed, this results in signifi-
cant increases not only in yield, but also in the desired
properties. In addition, it has been found herein that,
while a combinat;on of dilute inorganic acid leaching and
carbonaceous binder addition make for optimum yield and pro-
perties, the carbonaceous binder can be eliminated entirely
and still produce a significantly increased yield, as well as
acceptable properties.
Summary of the Invention
¦Accordingly, a general primary objective of the present
invention is (1) to provide a new and improved process for
making granular activated carbon from lower cost sub-bituminous
coal instead of higher cost bituminous coal, and wherein the
charring step necessary for processing bituminous coal is
eliminated, while the overall yield of granular activated
carbon is increased significan~ly by appropriate treatment
o~ sub-bituminous coal by leaching with a dilute aqueous
solution of inorganic acid, with or without the addition of
carbonaceous binder; (2) as well as to provide a new
and improved granular activated carbon made by such
process and having the aforementioned desired properties o~
adsorption (as measured by surface area and iodine number) . .
purity (as measured by ash content), hardness (as measured
by abrasion number~ and density (as measured by apparent
density), which make it suitable for use in waste water
treatment and other applications. To this end9 the invention
includes (1) a process for making gr.anular activated
carbon and comprising: ~orming granules from sub-bituminous ~;~
coal; treating the granules by leaching with a dilute aqueous
solution of inorganic acid, by washing of~ the acid, and by
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drying at least partially to a moisture content of not more
than about 25% by weight, with or without the addition of a
carbonaceous binder; reducing the treated granules to form
powder; compressing the powder to form pellets; reducing the
pellets to reform granules; devolatilizing the reformed
granules; and activating the devolatilized granules; and (2)
granular activated carbon made by such process.
A specific pr;mary object;ve is to provide (l) such
process wherein the sub-bituminous coal has a moisture content
of about lO to about 25% by weight; the acid is selected from
the group consisting of H2S04, ~3P04g HCl and mixtures thereof
at a concentration between about l and about 50% by weight,
preferably between about 1 and about 20~ by wei~ht and at an
aqueous solution to coal ratio of at least about 2/1 by
weight; the treated granules are reduced to powder of more
than about 65% by weight -325 mesh, the reformed granules are
devolatilized, without charring, by heating directly to and at
a temperature higher than the charring temperature in an
oxygen-free atmosphere; and the devolatilized granules are
activated by heating to and at a temperature higher than the
devolatilizing temperature in an atmosphere containing a
gaseous activating agent; and (2~ such granular activated `
carbon made by such process.
Another specific primary objective is to provide (1)
such process wherein the granules are treated by drying
partially to a moisture content of about 10 to about 25~ by
weight, without the addition of a carbonaceous binderi and
(2~ such granular activated carbon made by such process.
Still another specific primary objective is to provide
(1) such process wherein the granules are treated by drying
thoroughly and by mixing with about 5 to about 15~, preferably
about 7 to about 12%, by weight of a carbonaceous binder,
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preferably coal tar pitch; and (2) such granular activated
carbon made by such process.
A more speci~ic primary objective is to provide (1)
such process wherein granules are formed from sub-bituminous
S coal having ~ moisture content of about 10 to about 25% by
weight; the acid concentration is between about 1 and about
10% by weight and the solution to coal ratio is at least
about 4/1 by weight; the reformed granules are devolatilized
by heating to a temperature of about 450C at a rate of
about 300C/hour in an atmosphere of N2 and the volatiles
and by ma;ntaining the devolatilizing temperature for a time
of about 1 hour, and the devolatilized granules are activated
by heating to a temperature of about 800 to about 900C in
an atmosphere of N2 and steam and by maintaining the activa-
ting temperature for a time of about 4 to about 5 hours; in
order to produce an overall yield of granular activated carbon
of about 25 to about 33% by weight, dry basis; and (2) such
granular activated carbon made by such process and having a
surface area of about 900 to about 1100 m /gram, an iodine
number of about 1000 to about 1100, an ash content of about 5
to about 7% by weight, an abrasion numbe`r of about 70 to
about 80, and an apparent density of about 0.46 to about
0.50 gram/cc. ;`i ` `
Another more specific objective is to provide (1) such
process wherein the granules are treated by drying partially
to a moisture content of about 15% by weight without the
addition of a carbonaceous binder; and the overall yield is
about 25 to about 30% by weight, dry basis, and (2) such
granular activated carbon made by such process and having a
surface area of about 900 to about 1100 m2/gram, an iodine
number of about 1000 to about 1l00, an ash content of about
5 to about 7% by weight, an abrasion number of about 70
and an apparent density of about 0.46 to about 0.50 gram/cc.
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Still another more specific objective is to provide (1)
such process wherein the acid is H3P04 and the overall yield
is about 26 to about 30% by weight, dry basis; and (2) such
granular activated carbon made by such process and having a
surface area of about 900 to about 1100 m2/gram, an iodine
number of about 1000, an ash content of about 5 to about 6%
by weight, an abrasion number of about 70, and an apparent
density of about 0.48 to about 0.50 gram/cc.
Yet another more specific primary objective is to pro-
vide (1) such process wherein the granules are treated by
drying thoroughly and by mixing with about 7 to about 12% by
weight of coal tar pitch and the overall yield is about 25
to about 33% by weight, dry basis; and (2) such granular
activated carbon made by such process and having a surface
area of about 900 to about 1100 m2/gram, an iodine number of
about 1000 to about 1100, an ash content of about 5 to about
7% by weight, an abrasion number of about 80, and an apparent
density of about 0.48 to about 0.50 gram/cc.
A further more specific objective is to provide (1)
such process wherein the acid is H3P04 and the overall yield
is about 30 to about 33% by weight, dry basis; and (2) such
granular activated carbon made by such process and having a .
surface area of about 1050 m2/gram, an iodine number of
about 1000 to about 1100, an ash content of about 6% by weiyht,
an abrasion number of about 80, and an apparent density of
about 0.48 to about 0.50 gram/cc.
Additional objectives and advantages of the invention
; will become apparent upon consideration of the following
detailed description and accompanying drawing wherein:
Brief Description of the Drawing
The single figure is a block diagram or flow sheet
illustrating schematically the various steps of the process,
as well as the resulting product, both embodying the
invention.
Description of the Preferred Embodiments
In this detailed description9 reference will be made
to ten Examples, of which Examples 1 and 6-8 relate to and
provide background for the present invention; while Examples
2-5, 9 and 10 are illustrative of the invention per se.
Moreover, the order or sequence of the Examples has been
selected in order to show a progression in experimentation
from Example 1, which represents an at~empt to apply a known
charring technique for making granular activated carbon from :
bituminous coal to sub-bituminous coal, through the inventive
acid leaching techniques of Examples 2-S, to Examples 6 and
7 which compare the results obtained by attempting to
superimpose an inventive acid leaching technique (Example 7)
on a known charring technique (Example 6) for making granular
activated carbon from bituminous coal; to Example 8, which
shows that an inventive acid leaching technique does not work
as well for lignite, and finally to inventive E:xamples 9 and
10 which show the importance of fineness of grinding in pow-
derizing (Example 9) and the workability of HCl (Example 10)
along with H2S04 (Example 4) and H3PO~ (Example 5),
. . .
EXAM~LE 1
~.
CHARRING OF SUB-BITUMINOUS COAL IN
MAKrNG:GR~NULAR ACTIVATED CARBON
In making granular activated carbon from bituminous coal ~ -
it has been found necessary to char the coal granules pricr -.
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'to activation, as will be seen below in Examples 6 and 7.
rhus, this technique was adopted in order to see what sort
of product could be so obtained from sub-bituminous coal.
The starting material for this and each of the ensuing
Examples 2-5, 9 and 10 was a batch of Wyoming sub-bituminous
coal having the following analyses, by weight in the as
received condition:
Proximate Analysis Ultimate Analysis
Moisture17 % Carbon69.8 %
Volatile44 % Hydrogen5.4 ~
Material
Ash 2.05% Nitrogen0.9 %
Fixed 35 % Sulfur 0.55%
Carbon
These analyses are, in general, typical of a sub-
bituminous coal, The as received coal was crushed to a very
fine size such that more than 65% by weight of the material
passed through 325 mesh screen, preferably 75 to 85~ -325 mesh.
The powder was pressed at 40,000 to 80,000 psi pressure into
cylindrical pellets approximately 1/2" high and 1/2" diameter.
The apparent density of these pellets was in the range of
1.1 to 1.2 gramsJcc. The pellets then were granulated to
obtain granules of 6 by 20 mesh with an apparent density in
the range of 0.64 to 0.68 gram/cc. In the course of
experimentation, as will be seen from Examples 2 and 3? it
was found that to obtain compact granules (suitable for
obtaining hard granular actiYated carbonl without the use of
a carbonaceous binder such as coal t~r pitch, the moisture
content of the sub-bituminous coal and the treated granules
is important. Too low a moisture content, i.e., below about
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10% by weight, or too high a moisture content, i.e., above
about 25% by weight, led to poor compaction, and hence
granules that were not hard and dense. Likewise, if the
moisture content of the coal is too great, in the as
received condition, for example as the result of a rainstorm,
it must be dried, before granulating, to the desired moisture
content range. Otherwise, crushing and screening are unduly
dif~icult. In this Example, the 17% by weight content of
the coal was well within the prescribed limits, and hence no
drying was necessary, in the first instance.
600 grams of the granules obtained according to the
procedure described above were loaded into a cylindrical
conta;ner prepared from 5 mesh screen. The container was
mounted onto a cylindrical shaft and the assembly was loaded
into a cylindrical furnace so that the container and the
granules therein were rotated slowly and uniformly inside the
furnace.
The granules then were subjected to a charring treat-
ment wherein the granules were heated in an atmosphere of
air and nitrogen (deficient oxygen) to 200C at the rate oF
100C/hour, and maintained at this temperature for 1 hour.
Dur;ng this process, the granules were slowly and uniformly
rotated (1 to S rpm) so that they were exposed to the oxi-
dizing action of 2 present. During the course of experimen-
tation, it was found that higher temperatures and/or higher
oxygen content in the atmosphere led to poor process control
and eventually a poor product. The loss of weight in the
charring step was in the range of 5 to 10% by wei~ht based
on the dry coal.
The granular material then was subjected to a
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devolatilization process. The granules were loaded into the
furnace described above and heated to 450C at the rate of
300C/hour in an atmosphere free from oxygen (in the present
case an atmosphere composed of N2 and the volatiles given
off by the granules), and maintained at the devolatilizing
temperature for 1 hour and then cooled. Dur;ng the course
of experimentation it was learned that the charring and
devolatilization steps could be carried out sequentially
without cooling down, provided the atmosphere was altered
such that it was nearly free of oxygen during heat up beyond
200C. It also was learned that presence of oxygen at
these higher temperatures led to higher losses, poorer yield
of product and inferior granular product.
The yield of granules after devolatilization was about
60% by weight based on charred granules, and their apparent
density was about 0.6 gram/cc.
Next, the devolatilized granules were loaded into a
cylindrical furnace and were subjected to activation by
heating the granules to 800 to 900C in an atmosphere com-
posed of a carrier gas of N2 and steam and by maintaining
the granules at the activating temperature ~or 4 to 5 hours.
The amount of steam fed in was pre-determined such that it
amounted to 1 to 3 grams of steam/gram of charge/hour.
The yîeld of granular activated carbon from this step
was in the range of 30 to 40% by weight based on devolatilized
material. The granular product has a sur-Face area of 900
to 1000 m2/gram, an ash content in the range of 7 to 10%
by weight, an abrasion number of 60 to 70 and an apparent
density in the range of 0.45 to 0.~8 gram/cc.
The overall yield based on dry coal was 20 to 22% by
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weight and the granules had adsorption properties, ash,
density and hardness which were below or on the borderline
in being acceptable as a granular activated carbon for use
in waste water treatment and other applications.
During the course of experimentation, it was learned that if
the sub-bituminous coal was processed as above, but without
the charring step, the resultant product was soft and had
little activity, thus indicating the importance of charring
the sub-bituminous coal (when processed by itself), even
though such a coal is not very highly coking.
The following Examples 2-5 represent preferred embodi-
ments of the present invention, which is represented
schematically in the drawing. Thus, from a method standpoint~
the inventive process generally includes the steps of
granulating the sub-bituminous coal, which either has, in
the as received condition, the proper moisture content range
of about 10 to about 25% by weight, or is dried, as shown
at the upper right of the drawing, to so control such
moisture content prior to granulating; followed by the steps
..... .. ...
of treating the granules by leaching with a dilute aqueous
solution of inorganic acid, by washing off the acid and by
drying; powderizingi pelletizing; regranulating; devolatiliz-
ing; and activating; all in order to produce the desired
inventive product of granular activated carbon which is
acceptable for use in waste water treatment and other
applications. Examples 2 and 3 represent two preferred
embodiments of such treatment wherein the granules are
leached with dilute aqueous solutions of H2S04 and H3P04
respectively, washed and partially dried to the above noted
proper moisture content range, and preferably to about 15% by
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weight, followed directly by powderizing, etc., without the
addition of pitch, as shown in the drawing. Examples ~ and
5 represent two diFferent and more preferred embodiments of
such treatment wherein the granules are leached with dilute
aqueous solutions of H2S04 and H3P04 respectively, followed
by washing off the acid, by drying thoroughly and by mixing
with pitch, prior to powderizing, etc., as shown at the middle
right side of the drawing.
EXAMPLE 2
DILUTE H2S04 LEACHED SUB-BITUMINOUS COAL GRANULES
(WITHOUT PITCH) IN MAKING GRANULAR ACTIVATED CARBON
A batch of Wyoming sub-bituminous coal having the
analyses described in Example 1 was crushed and screened to
obtain 8 x 30 mesh granules. 300 grams of the granules were
loaded into a 4 liter kettle, and a dilute aqueous acid solu-
tion consisting of 150 cc. of 98% concentrated H2S04 and
2850 cc of water was added to the granules (about 6.5% acid,
by weight, or 5% by volume). The granules and the acid
solution were heated to 80C and maintained a-t this tempera-
ture for 5 hours, while the granules were con-tinuously
stirred. During the course of experimentation, it was learned
that size of granules, temperature of leaching (which is
usually below 100C because of the use of the dilute aqueous
acid solution), time of leaching~ concentration of acid, and
the ratio of dilute aqueous acid solution to coal all have
important effects on further processibility of the coal to
form granular activated carbon. Therefore, the specific
numbers cited in this and the ensuing inventive Examples are -
merely illustrative and not restrictive. For example, both
coarser and finer granules can be employed dur;ng leaching
with corresponding results, with the time of leaching beiny
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longer for coarser particles and shorter for finer ~articles.
The contents of the slurry were allowed to cool, the
solution decanted, and the granules were thoroughly rinsed
such that wash water off the ~ranules analyzed to a pH of 6
to 7. To complete the treatment, the leached granules were
dried partially to an approximate moisture content of 15%,
which is that preferred for good compaction in forming the
pellets and hard, dense granules therefrom, w;thout the use
of a carbonaceous binder.
The treated granules containing roughly 15% by weight o~
moisture were milled into a very fine powder such that more
than 65% by weight of the material passed through 325 mesh
screen, preferably 75 to 85% -325 mesh, as explained in
Example 9 below. The powder was pressed into cylindrical
pellets of 1/2" diameter and 1/2" h~gh using a pressure of
40,00Q to 80,000 psi, the apparent density of the pellets being
in the range 1.1 to 1.2 grams/cc. These pellets were regranu-
lated to obtain 6 x 20 mesh granules having an apparent density
of 0.64 to 0.68 gram/cc. The re~ormed granules were loaded
into a cylindrical furnace and devolatilized as described in
Example 1, which consisted o~ heatlng the granules to ~50C
at 30QC/hour in an atmosphere free of oxygen and holding at
temperature for 1 hour.
During the course of experimentation it was learned that
the charring step described in Example 1 is not necessary to
make hard and adsorptive granular activated carbon. Two
batches of identical material, treated in dilute aqueous acid
solution as described above, were processed, one with a
charring step and the other without. While the yields in
specific process steps varied, the overall yield and activity
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of the granular activated carbon product were the same, indi-
cating that the charring step can be eliminated for this
material. This presumably was a result of the coal being
subjected to the dilute aqueous acid solution leaching treat-
ment.
The devolatilized granules which had an apparent density
of 0.60 gram/cc, were loaded into a cylindrical furnace and
subjected to activation by heating the granules to 800 to
900C in an atmosphere composed of N2 and steam, and by main-
taining the granules at this temperature for 4 to 5 hours.
The amount of steam fed into the furnace was precalibrated
such that it amounted to 1 to 3 grams of steam/gram of charge/
hour.
The resulting overall yield of granular activated carbon,
based on the dry coal, was in the range of 25 to 28% by weight
versus 20-22% for Example 1. The granules had a surface area
of 900 to 1100 m2/gram, as compared to 900 to 1000 for
Example 1, an iodine number of 1000, an ash content of 5 to
6% by weight, as compared to 7 to 10% for Example 1, an abra-
sion number of 70 as compared to 60~70 for Example l, and an
apparent density of 0.46 to 0.48 gram/cc, as compared to 0.45
to 0.48 for Example 1.
Thus, these ~ranules were hard~ very adsorptive, low in
ash and in most respects comparable to the grades of granular
~5 activated carbon preferred for use in waste water treatment and
other applications. Further, it is to be noted that not only
can an acceptable granular activated carbon product be made
from sub-bituminous coal without the use of any carbonaceous
- binder such as coal tar pitch, and without charring, but also
that treatment by leaching with dilute aqueous acid solution
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significantly reduces the ash content while increasing yield
and adsorpt;on, all as compared to Example 1. It also is
noteworthy that a hard granular act;vate~ carbon was prepared
from sub-bituminous coal (with abrasion number of 70) for the
first time without the use of a carbonaceous binder.
EXAMPLE 3
DILUTE H3P04 LEACHED SUB-BITUMINOUS COAL GRANULES
(WITHOUT PITCH) IN MAKING GRANULAR ACTIVATED CARBON
A batch of Wyoming sub-b;tum;nous coal hav;ng the
analyses descr;bed ;n Example 1 was crushed and screened to
obta;n 8 x 30 mesh granules, 300 grams of which were loaded
;nto a 4 liter kettle. A dilute aqueous acid solution con-
sisting of 150 cc. of 75% concentrated H3P04 and 2850 cc. of
water was added to the granules (about 6.5% by weight). The
granules and the acid solution were heated to 80C and main-
tained at this temperature for 5 hours~ while the granules
were continuously stirred. The contents were allowed to cool,
the solut;on decanted~ and the granules were thoroughly rinsed
such that wash water off the granules analyzed to a pH of 6
- 20 to 7. To complete the treatment, the leached and washed
- granules were dried part;ally to an approximate moisture con-
tent of 15%, as ;n Example 2.
The treated granules containing roughly 15% by weight of
moisture were milled into a very -fine powder such that more
than 65% by weight of the material passed through 325 mesh -
screen (65% by weight -325 mesh), preferably 75 to ~5~ -325
mesh.
The powder was pressed into cylindrical pellets of 1/2"
diameter and 1/2" long using a pressure of 40,000 to 80,0no
psi, and the apparent densîty oF the pellets was in the ~ange
1.1 to 1.2 gramslcc. The pellets were regranulated to obtain
1 ~
6 x 20 mesh granules which had an apparent density of 0.58
to 0.62 gram/cc.
The reformed granules were loaded into a cylindrical
furnace and devolatilized as described in Example 1, but with
no charring being necessary prior to such devolatilization.
The devolatilized granules, which had an apparent density of
0.58 to 0.60 gram/cc, were activated in the manner also set
forth in Example 1.
The overall yield of granular activated carbon, based on
the dry coal was in the range of 26 to 30% by weight, versus
20 to 22% for Example 1 and 25 to 2~% for Example 2. The
granules had a surface area of 900 to 1100 m2/gram, versus
~00 to 1000 for Example 1, an iodine number of 1000, an ash
content of 5 to 6% by weight, as compared to 7 to 10% for
Example 1, an abrasion number of 70, as compared to 60 to 70
for Example 1, and an apparent density of 0.48 to 0.50 gram/cc
as compared to 0.45 to 0.48 for Example 1 and 0.46 to 0.48 for
Example 2. The yield and apparent density properties were
slightly higher than those observed in Example 2 (H2S04 leach).
Thus, the resulting granules were hard, very adsorptive,
low in ash, and in most respects comparable to the grades of
granular activated carbon preferred for use in waste water
treatment and other applications. It is to be noted
once again that an acceptable product can be made from sub-
bituminous coal without a carbonaceous binder and without
charring, and that leaching with dilute aqueous acid solution
significantly reduces ash content while increasing yield and
adsorption, as compared to Example 1. As for using H2S04 or
H3P04 as the acid in the aqueous solution, H3P04 is believed
to be more effective in producing a granular activated carbon
_19_ '
7G7
product with higher yield. As becomes evident, the exact
amount of improvement in yield depends upon the specific
leach,ng conditions and other process conditions employed.
EXAMPLE ~
DILUTE H2S04 LEACHED SUB-BITUMINOUS COAL GRANULES
(WITH PITCH) IN MAKING GRANULAR ACTIVATED CARBON
The procedure of Example 2 was followed up to the drying
step, but instead o~ drying partially to about 15% moisture
the granules were dried thoroughly, and then, as shown on the
right side of the drawing, the treatment was completed by
nlixing the granules uniformly with a No. 125 coal tar pitch
having the following properties:
Softening Point 129.2CC
Benzene Insolubles 33.2% by weight `
Quinoline Insolubles 13.1% by weight
Coking Value (Conradson)61.1% by weight
Ash 0.17% by weight
The thoroughly dried granules and pitch were mixed in
the proportion of 90 grams coal and 10 grams pitch (i.e., 10
parts pitch per hundred parts coal, by weight), and this mix-
ture milled into more than 65% by weight -325 mesh powder,
preferably 75 to ~5% -325 mesh, which powder was pressed into
pellets of 1/2" diameter and 1/2" high using a pressure in
the range of 40,000 to 80,000 psi. The bulk density of the
pellets was in the range of 1.1 to 1.2 grams/cc, and they were
granulated to obtain granules of 6/20 mesh and having an
apparent density of 0.68 gram/cc.
600 grams of the granules were loaded into a cylindrical
container and were devolatilized according to the procedure
described in Example 2, without the charring step. The
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7~7
devolatilized granules had an apparent density of 0.62 gram/cc
and a yield of 60% by weight based on the dry coal-pitch mix-
ture.
The devolatilized granules were loaded into a cylindrical
fur~ ce and subjected to activation as also set forth in
Example 2.
The overall yield of granular activated carbon in this
more preferred embodiment of the inventive process, based on
the dry coal pitch mixture was in the range of 25 to 30% by
weight compared to 20 to 22% for Example 1. The granules had
a surface area of 1050 m2/gram, as compared to 900 to 1000
for Example 1, an iodine number of 1000 to 1100, as compared
to 1000 ~or Examples 2 and 3, an ash. content of 6% by weight,
as compared to 7 to 10% for Example 1, an abrasion number of
809 as compared to 60 to 70 for Example 1, and 70 for Examples
2 and 3, and an apparent density of 0.48 to 0.50 gram/cc, as
compared to 0.45 to 0.48 for Example 1 and 0.46 to 0.48 ~or
Example 2 .
Thus, the resulting granules were hard, very adsorptive9
low in ash, and in all respects comparable to the grades of
granular activated carbon preferred for use in waste water
treatment and other applications. It is particularly
noteworthy that, compared to the no acid and the charring
approach of Example 1, the overall yield was considerably
improved when the coal was subjected.to leaching with an ..
aqueous acid solution, followed by mixing with pitch~ with
no charring, while at the same time yielding a product that
was superi~r in adsorption properties, density and abrasion
resistance. As for the H2S04 leaching no pitch procedure o~
Example 2, there was a slight increase in adsorption (iodine
3~7~6~
number3 and a significant increase in abrasion resistance and
apparent density. With respect to the H3PO~ leaching no
pi~ch procedure of Example 3, there was a slight increase in
adsorption (iodine number) and a significant increase in
abrasion resistance.
EXAMPLE 5
DILUTE H3P04 LEACHED SUB-BITUMINOUS COAL (WITH PITCH)
MAKING GRANULAR ACTIVATED r.ARBON
The same procedure as set forth in Example 4 was
followed, except that 75% concentrated H3P04 wa5 substituted
for the H2S04 (making the ac;d about 6.5~ by weight of the
granules). The apparent density of the reformed compacted
granules was 0.65 gram/cc instead of 0.6~, while the
devolatilized granules had an apparent densi-ty o~ 0.59 to
0.61 gram/cc instead of 0.62, and a yield of 60 to 65% by
weight, based on the dry coal pitch mixture instead of 60%.
The overall yie.ld of granular activated carbon in this
most preferred embodiment of the inventive process, based on
the dry coal p;tch mixture was in the range o~ 30 to 33% by
we;ght, as compared to 20 to 22% for Example 1, 25 to 28% for
Example 2, 26 to 30% for Example 3, and 25 to 30% for Example
4. The granules had a surface area of 1050 m2/gram, as com~
pared to 900 to 1000 for Example 1, an iodine number of 1000
to 1100, as compared tn 1000 ~or Examples 2 and 3, an ash
2~ content of 6~ by weiyht, as compared to 7 to 10% ~or Example
1, an abrasion number of 80, as compared to 60 to 70 for Exam-
ple 1, and 70 for Examples 2 and 3, and an apparent density
of 0. 48 to 0. 50 gram/cc, as compared to 0. 45 to 0. 48 for
Example 1 and 0.46 to 0.48 for Example 2.
Thus, the resulting ~ranules were hard, very adsorptive,
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` ~6)7~76~
low in ash and in all respects comparable to the grades of
carbon preferred for use in waste water treatment and other
applications. It is particularly noteworthy that the
overall yield was considerably improved, not only over
Example 1, but also over each of Examples 2, 3 and 4, with a
substantial increase in adsorption, purity, abrasion resis-
tance, and density over Example 1. Likewise, there was a
significant increase in abrasion resistance over Examples 2
and 3, and a significant increase in density over Example 2.
This improved yield of hard, dense, adsorptive granular
activated carbon, obtained by treating sub-bituminous coal
with a dilute aqueous solution of H3P04 is indeed an unexpected
result over the art. Further, such improved yield is believed
to be comparable to that obtainable from the higher valued
bituminous coal, the traditionally preferred raw material.
More importantly, such unexpected result is achieved by
eliminating the charring step believed to be necessary in
the use of bituminous coal.
The next two Examples represent an endeavor to see what
happens when bituminous coal is treated in accordance with
the inventive process, first without dilute acid leaching
(Example 6) and second with dilute acid leaching (Example 7).
EXAMPLE 6
USE OF BITUMINOUS COAL AND PITCH TO
MAKE GRANULAR ACTIVATED CARBON
The starting material was a batch of eastern bituminous
coal having the following analyses by weight:
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Proximate Analysis Ultimate Analysis
As As
Received Dry Received Dr~
% Moisture2.04 - % Moisture2.04
% Ash 1.20 1.26 % Carbon82.30 84.00
% Volatile33.10 33.80 % H 5.20 5.29
Material
a Fixed Carbon 63.60 64.90 % N2 1.30 1.33
% S 0.34 0.35
BTU/lb 14,571 14i874 % Ash 1.23 1.26
These analyses are, in general, typical of eastern bituminous
coals. These coals also are highly coking and low in ash
content. The dried coal was crushed to obtain 8 x 30 mesh
granules which were mixed with No. 125 coal tar pitch oF the
type described in Examples 4 and 5, and in the ratio of 90
grams of coal granules and 10 grams of pitch (10 parts per
hundred by weight).
The mixture was milled into very fine powder so that 65%
of the powder passed through 325 mesh screen. The milled
powder was compressed into pellets 1/2" dlameter and 1/2" high
using a pressure of 40,000 to 80~000 psi. The pellets had a
bulk density of 1.18 grams/cc and were granulated to obtain
6 x 20 mesh granules having an apparent density of 0.65 gram!cc.
600 grams of the granules were loaded into a cylindrical
2~ furnace and were subjected to the charring process substantially
as described in Example 1. However, in this case, ~he
charring consisted of heating the granules from room tempera-
ture to 250C at 100C/hour and maintaining a~ temperature for
2 hours. An atmosphere of 0.5 standard cubic ~eet per hour
at 1 atmosphere and room temperature (SCFH) oF N2 and 0.5
SCFH of air was fed into the furnace while the cylindrical
container was rotating at 1 to 4 rpm.
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~07~7
In the course of experimentation it was found that
heating rate, atmosphere (particularly the amount of oxygen
present), temperature and time at temp~ra~ure were critical
variables that had an important influence on how the granules
were suited for further processing in making hard granular
activated carbon. For example. too small a time (less than
1l2 hour) at temperature or too low a temperature (lower than
200C), in general, led to difficulties in further processing
of the granules. Thus, without proper charring, during the
devolatilization step, the granules fused together and were
unsuitable for proper activation and for obtaining the
desired properties oF granular activated carbon.
When properly charred, as described above, the yield of
the granules was 69% by weight, based on the dry coal pitch
mixture and they had an apparent density of 0.62 gram/cc.
The charred granules then were devolatilized and activated
;n the same manner as described in Example 1.
At the end of the process, hard granular activated carbon
was obta;ned, with an overall yield of 34.0% by weight based
on the dry coal pitch mi~ture. The granules had an apparent
dens;ty of 0.50 gram/cc, an iodine number of 1080, a surface
area of 1040, an ash content oF 2.2% by weight, and an
abrasion number of 80.
Thus, the resulting granules were hard, very adsorptive~
l~w in ash, and ;n all respects very much comparable to the
grades of carbon preferred for use in waste water treat~ent
and other applications. However, it is particularly
noteworthy that hard granular activated carbon could not be
made from this bituminous coal without subjecting the granules
to the charring step described above, prior to devolatilization
... . . .
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: ; :. . . . . :
,
67
and activation. During the course of experimentation, granules
were devolatilized without the charring step and a fused mass
(instead of granules) unsuitable for activation was obtained,
thus indicating the necessity and importance of the charring
step.
EXAMPLE 7
DILUTE H3P04 LEACHED BITUMINOUS COAL AND PITCH
TO MAKE GRANULAR ACTIVATED CARBON
The same proc~dure, as set forth in Example 6, was
followed through the initial granulating step. At this point,
300 grams of the coal granules were loaded into a 4 liter
kettle. A dilute aqueous acid solution consisting of 150 grams
of 75% concentrated H3P04 and 2850 grams of water was added
to the granules (about 6.5% by weight). The mixture was
heated to ~OC and maintained at this temperature for 5 hours,
while the granules were continuously stirred. The contents
were allowed to cool, acid solution decanted and the coal was
thoroughly washed such that the wash water off the granules
analyzed to a pH of 6 to 7.
The leached coal was dried thoroughly, and then was
mixed uniformly with the coal tar pitch of Example ~ in the
same proportions of 90 grams coal and 10 grams pitch. The
mixture was milled into 65% by weight -325 mesh powder, and
was pressed into pellets of 1/2" diameter and ll2" high using
a pressure in the range of 40,000 to 80,000 psi. The bulk
density of the pellets was in the range of 1.1 to 1.2 grams/cc,
and they were regranulated to obtain 6 x 20 mesh granules
having an apparent density at this stage of 0.64 gram/cc.
The reformed granules were loaded into a cylindrical
furnace and were subjected to the charring step described in
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7~7
Example 6, producing a 71% by weight yield and an apparent
density of 0.63 gram/cc. In the course of experimentation,
it was learned that, even for acid leached bituminous coal,
the charring step was necessary as a pre-treating step, in
order to obtain proper granular activated carbon.
The charred granules then were devolatilized and activated
in the manner described in Example 1.
At the end of the activation step, hard granular activated
carbon was obtained, with an overall yield of 35% by weight
based on the dry coal pitch mixture. The granules had an
apparent density of 0.50 gram/cc, a surface area of 1000 m2/
gram, an iodine number o~ 1050; an ash content of 2.4% by
weight, and an abrasion number of 82.
Thus, the granules were hard, very adsorptive, low in
ash and in all respects very much comparable to the grades of
carbon preferred for use in ~aste water treatment and other
applications. At the same time, it is particularly
noteworthy that hard granular activated carbon could not be
made from this bituminous coal without subjecting the granules
to the charring step described above, even though the coal
had been dilute acid leached. In this regard, the result is
ver~y much unlike that ~or sub-bituminous coal, wherein acid
leaching enables one to eliminate the charring step, while
still producing an acceptable product.
Another important and notable feature was that the acid
leaching of bituminous coal with dilute H3P04 did not appear
to significantly alter the yield (from 34 to 35~). In çontrast,
this result was very much unlike that for the sub-bituminous
coal of Example 5 wherein dilute H3P0~ acid leaching of the
3n coal led to substantially improved yield from the 20 to 22%
::
- , ~ .
~76~7
for Example 1 to the 30 to 33% of Example 5, which closely
approximates the 34 and 35% yields of these last two examples.
These two results were indeed unique and unexpected in deal-
ing with sub-bitum;nous coal.
The next Example represents an attempt to apply the
dilute acid leaching technique of the invention to lignite,
which ranks lower than sub-bituminous coal.
EXAMPLE 8
DILUTE H3P04 LEACHED LIGNITE COAL (WITH PITCH)
IN MAKING GRANULAR ACTIVATED CARBON
The starting material in this Example was a batch of
lignite coal having the following analyses by weight:
Proximate Analysis Ultimate Analysis
As As
Received DryReceived
% Moisture 30.3 - % Moisture30.30
% Ash 9.9 14.2 % Carbon 41.50 59.5 :
% Volatile 50.0 71.7 % H 3.15 4.5
Material
% Fixed Carbon 9.8 14.0 % N2 3.50 5.0 :
% S 0.73 1.4
% Ash 9.90 14.2
These analyses are, in general, typical of lignite type
coals, and these coals, in general, have a high ~sh content
compared to other coals. The as received co~l was crushed
to 8 x 30 mesh granules and 300 grams of these granules
were loaded into a 4 liter kettle and 150 cc of concentrated
H3P04 (i5%) and 2850 cc of water were added (6~5% by weight of
3Q acid). The granules and the acid solution were heated to
80C and maintained at this temperature for 5 hours, while the
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767
granules were continuously stirred. The contents were allowed
to cool, the solution decanted, and the granules were
thoroughly rinsed such that the wash water off the granules
analyzed to a pH of 6 to 7. The granules were dried
thoroughly and mixed into lo parts per hundred of coal tar
pitch of the type described in Examples 3 and 4.
This mixture was thoroughly milled such that more than
65% of the powder material passed through 325 mesh screen,
preferably 75 to 85% -325 mesh. The powder was pressed into
cylindrical pellets of l/2" diameter and l/2" high, using a
pressure of 40,000 to 80,000 psi, the apparent density of
the pellets being in the range of 1.1 to 1.2 grams/cc. The
pellets were granulated to obtain 6 x 20 mesh granules having
an apparent density of 0.64 to 0.66 gram/cc. The granules
were loaded into a cylindrical furnace and were devolatilized
as described in Example l. Two batches of granules with
identical processing were devolatilized, one with a charring
step, as described in Example l and the other without a
charring step, as described in Examples 2 to 5. The two
batches were similar in regard to the overall yields qnd ~
activity, indicating that the charring step is not a necessary
requisite for this type of coal.
The devolatilized granules were activated as in Examples
l to 5. The granules had very low apparent density, of 0.30
gram/cc, a surface area of 850, an iodine number of 900. an
ash content of 11.5% by weight, and an abrasion number o~
30. Repeated experiments to optimize the properties, while
showing some improvement, did not produce the preferred
required density of 0.~8 gram/cc or higher, and abrasion
number of 70 or higher. Thus, an acceptable granular
29
7~7
activated carbon which is hard and suitable for waste water
applications could not be produced under the aforementioned
conditions from lignite coal.
Thus, it is patently obvious from this and the foregoing
examples that:
A. Leaching a bituminous coal in dilute aqueous acid
solution did not materially affect the processability o-f
the coal into hard granular carbon or the present yield of
the said carbon ~rom coal, and the dilute acid leaching step
did not eliminate the necessity of a charring step.
B. Leaching a lignite coal in dilute aqueous acid solu-
tion did not result in an acceptable granular activated carbon
where the carbon from lignite was too light and too soft.
C. In contrast, it clearly has been demonstrated in the
preferred inventive embodiments that hard granular carbons
suitable for waste water and other applications can be pro-
duced from sub-bituminous coal for the first time, provided
the said coal is subjected to leaching treatment in dilute
aqueous acid solution (because very hard granular activated
carbon can not be produced from the untreated sub-bituminous
coal), and that such treatment does result in an unexpected
and hence an inventive result of high percent yield of
granular activated carbon from sub-bituminous coal, where the
yield ;s fairly comparable to that from bituminous coal,
particularly comparing Example 5 with Examples 6 and 7.
D. Another indeed unexpected result of the leaching
treatment of sub-bituminous coal in dilute aqueous acid
solution is that the charring step found necessary for treated
and untreated bituminous coal and for untreated sub-bitumjnous
coal can be eliminated in making hard, dense, adsorptive
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. . -
~074767
granular activated carbons from treated sub-bituminous coal.
The next Example is similar to Example 5, but emphasizes
the importance of fineness of grind in powderizing the
treated granul es before pelletizing.
EXAMPLE 9
FINENESS OF POWDER IN USING DILUTE H3P04 LEACHED
SUB-BITUMINOUS COAL (WITH PITCH) IN MAKING
GRANULAR ACTIVATED CARBON
The same procedure, as set forth in Example 5, and as
illustrated at the middle right in the drawing, was followed.
The leached granules were washed with wash water, analyzed
to a pH of 6 to 7 and dried thoroughly before mixing with 10
parts per hundred by weight of No. 125 coal tar pitch. Then
the mixture was divided into 2 equal parts.
The first part was milled to a fine powder which was
about 60 to 65% by weight -325 mesh. The powder was compacted
into pellets of approximately 1/2" hjgh and ll2" diameter under
a pressure of 40,000 to 80,000 psi, and the apparent density of
the pellets was in the range of 1.1 to 1.2 gram/cc. The
pellets were granulated, to 6 by 20 mesh and the density of
the granules was 0.64 to 0.66 gram/cc. The granules were
devolatilized as in Example 5 and the density of granules was
0.57 to 0.59 gram/cc. These granules were activated as
described in earlier Examples 1 and 5, and these activated
~5 granules had a density of 0.44 to 0.47 gram/cc, an iodine
number of 1000 to 1100, a surface area of 900 to lQ50 ~gram,
ash content of 5 to 6% by weight and an abrasion number f
55 to 65. Thus, these granules are considerably softer and
. .
hence are not too suitable for use in waste water applications,
because of possible excessiVe loss of material in use and
regeneration when the granules are not very hard.
-31-
67
The second part was milled to a very fine powder such
that it had a particle size of 75 to 85~ by wei~ht -325 mesh.
The powder was compacted, as above, to a pellet density of 1.1
to 1.2 gram/cc; the pellets were granulated and had a density
of 0.65 to 0.68 gram/cc. The granules wer~ devolatilized as
in Example 5 and the density of granules was 0.60 to 0.62
gram/cc. The granules were activated, as above, and the
apparent density of the activated granules was 0.48 to 0.50
gram/cc. T~e granules had an iodine number of 1000 to 1100, `
surface area of 900 to 1050 m21gram, ash content of 5 to 6Y by
weight and an abrasion number of 80.
Since the granules were subjected otherwise to identical
processing conditions in part 1 and part 2~ it is believed
that the finer grinding of the treated sub-bituminous coal
granules (75 to 85% -325 mesh) resulted in compact granules
and hence a hard granular product. In contrast, as described
in Examples 6 and 7, grinding the bituminous coal to 65%
-325 mesh resulted in a hard granular product.
Thus, the fineness of the grind prior to compaction
required for sub-bituminous coal, as compared to bituminous
coal, is an unexpected requirement which could not have been
deduced from prior art, and hence forms a preferred embod;ment
of the present invention.
The next, and last Example represents the workability
of HCl as the di1ute aqueous acid in the inventive technique.
EXAMPLE l_
DILUTE HCl LEACHED SUB-BITUMINOUS COAL (WITH P~TCH~
IN MAKING GRANULAR ACTIVATED CARBON _ ~ _
A batch of Wyoming sub-bituminous coal having the typjcal
analyses described in Example 1 was crushed and screened to
-32-
- ~ ,
obtain 8 x 30 granules. 300 grams of the granules were loaded
into a ~ liter kettle and a dilute aqueous acid solution
consisting of 300 cc of 37.5% concentrated HCl and 2700 cc
of water was added to the granules (about 5% by volume and
6.5% by weight). The granules and the acid solution were
heated to 80C and maintained at this temperature for 5 hours,
while the granules were continuously stirred.
The contents of the kettle were allowed to cool, the
solution decanted and the granules thoroughly rinsed such
that the waste water off the granules analyzed to a pH of 6
to 7. The granules were dried either: (A) to 15% moisture,
where further processed without a carbonaceous binder, as in
Examples 2 and 3, to a granular activated carbon product, or
(B) to complete dryness, where 10 parts per hundred of pitch
lS were added and processed as in Examples ~ and 5.
The granular coal or coal pitch mixture ~as milled to a
very fine size9 such that more than 65% of the material passed
through 325 mesh, preferably 75 to 85% of material passed
through 325 mesh. The powder was pressed into cylindrical
pellets of 1/2" diameter and 1/2" high using pressure o-F
40,000 to 80,000 psi; the apparent density of the pellets
being in the range 1.1 to 1.2 gram/cc. These pellets were
regranulated to 6 x 20 mesh having an apparent density of
0.60 to 0.65 gram/cc7 and these granules were devolatilized,
without charring 9 and activated, as in Examples 2 to 5.
(A) The resulting overall yield of granular activated
carbon, based on dry coal (pitchless), was 25 to 28~ by weight.
The granules had a surface area of 900 to 1100 m2/~ram~ an
iodine number of 1000 to 1100, an ash content of 5 to 7% by
weight, an abrasion number of 70 and an apparent density of
-33-
'' : '
67
0.46 gram/cc. Compared to Example 1, the y;eld, adsorption
and abrasion resistance were significantly increased, while
the ash content was significantly decreased. Compared to
Examples 2 and 3, the yield and other properties were comparable
to Example 2 (H2S04), while the yield and apparent density
were slightly less than for Example 3 (H3P04).
(B) The resulting overall yield of granular activated
carbon, based on the dry coal pitch mixture, was 25 to 30%
by weight, and the granules had a surface area of 900 to 1100
m /gram, an iodine number o~ 1000 to 1100, an ash content uf
5 to 7% by weight, an abrasion number of 80, and an apparent
density of 0.48 gram/cc. Compared to Example 1, the yield,
abrasion number and apparent density were signi~icantly
increased. As compared to Examples 2 and 3 and (A) above
(pitchless), the abrasion resistance was significantly increased,
and the yield and apparent density were slightly increased
over Example 2 and (A) above. As compared to Examples 4 and
5, the yield was slightly less than for Example 4 (H2S04 with
pitch), and significantly less than for Example 5 (H3P04 with
pitch).
However, in each of (A) and (B) above, as compared to
Example 1, treating the sub-bituminous coal with a dilute
aqueous solution of HCl resulted in higher yield and improved
adsorption, greater abrasion resistance and higher purity,
making such inventive product suitable ~or use in ~aste water
treatment and other applications, while at the same time elimi-
nating the need for the charring step.
It now is seen how the invention accomplishes its various
objectives. Likewise, it is to be understood that while the
invention has been described and illustrated hereln by
-3~- -
. .. ~ . : . . . ~
~Y74~67
reference to certain preferred embodiments, the same are
to be considered as illustrative, rather than as limiting.
-35- - :
, ., , ., ..... " ,, . , ., , , , . , ,. ~, . ..
