CA1074767A - Granular activated carbon manufacture from sub-bituminous coal leached with dilute inorganic acid - Google Patents

Abstract

ACl-l GRANULAR ACTIVATED CARBON MANUFACTURE FROM
SUB-BITUMINOUS COAL LEACHED WITH
DILUTE INORGANIC ACID
Abstract of the Disclosure Granular activated carbon is manufactured from sub-bituminous coal by crushing and screening the as received coal containing about 17% moisture by weight to produce 8/30 mesh granules, which are treated by leaching with a dilute aqueous solution of inorganic acid (H2S04, H3P04, or HCl) at a concentration of about 6.5% by weight and at an aqueous solution to coal ration of about 10/1 by weight, by washing off the acid, and by drying. In one case the granules are dried partially to a moisture content of about 15% by weight without the addition of a carbonaceous binder. In the other case the granules are dried thoroughly and mixed with about 10% by weight of coal tar pitch. The so treated granules are ground to more than 65% by weight -325 mesh powder, preferably 75 to 85% by weight -325 mesh, which is compressed into pel lets of 0.5" diameter and 0.5" long under a pressure of 40,000 to 80,000 psi, and then granulated to obtain 6/20 mesh granules. These granules are devolatilized by heating to 450°C at 300°C/hour in an atmosphere of N2 and the volatiles and by maintaining the temperature for 1 hour, and then activated by heating to 800 to 900°C in an atmosphere of N2 and steam and by maintaining the temperature for 4 to 5 hours.
The overall yield of granular activated carbon is 25 to 33%
by weight of the dry coal, and the activated granules have a surface area of 900 to 1100 m2/gram, an iodine number of 1000 to 1100, an ash content of 5 to 7%, an abrasion number of 70 to 80, and an apparent density of 0.46 to 0.50 gram/cc, which properties make them suitable for use in waste water treat-ment and other applications.

Description

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 ~)7~767 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 ~107~76~

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 ~7~7~7 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 .... . ., : :
.
.. . : - - . .

7Ei7 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 7~7~i7 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, .

~ 7 ~ 7 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.

.

~ 7 ~ 7 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 -.

-1 O- `

. ~, . .

~ 6 ~

'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 - .

~L~7471~7 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 . ~ . . . : . .
-. ... ~ ; .

76'7 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 . - . -, . .

47~7 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 ~74767 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.

(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 ....-. -- . .

7~7 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 ~L07~76~

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 . . . -: : :
::
.. ,. .: , .. , . . ~ .

~ ~7 ~ ~ 7 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.

(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_ ' 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 ~

(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 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.

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, ~22-` ~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).

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:

-23~

~07~

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.

. . ~
- : , . : .

~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 ... . . .

: ; :. . . . . :
, 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.

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 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.

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 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 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 . . -~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.

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.

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 - ~ , 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 '' : ' 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- - :

, ., , ., ..... " ,, . , ., , , , . , ,. ~, . ..

Claims (20)

The embodiments of the invention in which a specific property or privilege is claimed are defined as follows:

1. A process for making hard granular activated carbon and comprising: forming granules from sub-bituminous coal; treating the granules by leaching with a dilute aqueous solution of inorganic acid, by washing off the acid, and by 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; reducing the compressed powder to reform granules; devolatilizing the reformed granules, without charring, by heating directly to and at a temperature higher than the charring tempera-ture in an oxygen-free atmosphere; and activating the devolatilized granules by heating to and at a temperature higher than the devolatilizing temperature in an atmosphere containing a gaseous activating agent.

2. A process as claimed in claim 1, wherein the coal has a moisture content of about 10 to about 25% by weight and an ash content of not more than about 5% by weight.

3. A process as claimed in claim 1, wherein the acid concentration is between about 1 and about 50% by weight and the aqueous solution to coal ratio is at least about 2/1 by weight.

4. A process as claimed in claim 1, wherein the acid concentration is between about 1 and about 20% by weight and the aqueous solution to coal ratio is at least about 4/1 by weight.

5. A process as claimed in claim 1, wherein the acid concentration is about 6.5% by weight and the aqueous solution to coal ratio is about 10/1 by weight.

6. A process as claimed in anyone of claims 3, 4 and 5, wherein the acid is selected from the group consis-ting of H2S04, H3P04, HCl and mixtures thereof.

7. A process as claimed in anyone of claims 3, 4 and 5, wherein the acid is H3P04.

8. A process as claimed in claim 1, wherein the washed granules are dried to a moisture content of about 10 to about 25% by weight, without the addition of a carbonaceous binder.

9. A process as claimed in claim 8, wherein the acid is H3P04, the acid concentration is between about 1 and about 20% by weight, and the aqueous solution to coal ratio is at least about 4/1 by weight.

10. A process as claimed in claim 1, wherein the dried granules are mixed with about 5 to about 15% by weight of carbonaceous binder.

11. A process as claimed in claim 10, wherein the acid is H3P04, the acid concentration is between about 1 and about 20% by weight, and the aqueous solution to coal ratio is at least about 4/1 by weight.

12. A process as claimed in claim 1, wherein the powder is more than about 65% by weight -325 mesh.

13. A process as claimed in claim 1, wherein the powder is compressed to form pellets under a pressure of at least about 40,000 psi.

14. A process as claimed in anyone of claims 1, 12 and 13, wherein the pellets are reduced to reform granules.

15. A process as claimed in claim 1, wherein the reformed granules are devolatilized by heating to a tempera-ture of about 450°C at a rate of about 300°C/hour in an atmosphere of N2 and the volatiles and by maintaining the devolatilizing temperature for a time of about one hour.

16. A process as claimed in claim 1 or 15, wherein the devolatilized granules are activated by heating to a temperature of about 800 to about 900°C in an atmosphere of N2 and steam and by maintaining the activating tempera-ture for a time of about 4 to about 5 hours.

17. Hard granular activated carbon when obtained by the process of anyone of claims 1, 8 and 10.

18. Hard granular activated carbon when obtained by the process of anyone of claims 1, 8 and 9, and having an abrasion number of not less than about 70.

19. Hard granular activated carbon when obtained by the process of claim 10 or 11, and having an abrasion number of not less than about 70.

20. Hard granular activated carbon when obtained by the process of claim 10 or 11, and having an abrasion number of not less than about 80.