Binders and Base Materials for Active Carbon FUNCTIONS OF SUGARS, COAL TAR PITCH, ANTHRACITE, AND CELLULOSE JEROME J. MORGAN AND C. E. FINK1 Columbia University, New York, N . Y .
Activated carbons are made from base materials which generally comprise the larger portion of the raw material and binders which are used to give strength by holding together the particles of base material. When carbonized alone, base materials shrink and give a dull-appearing char; binders swell, become macroporous, and generally yield a lustrous residue. Upon carbonization of briquets made from a mixture of base material and binder, the activity of the char is predominantly that of the binder; after activation the activity of the resulting carbon becomes chiefly that of the base material. Various glucose carbohydrates differ markedly as raw materials for activated carbons; dextrose behaves as a binder, cellulose as a base material, and starch is intermediate. Cellulose is a specially good base material. I t yields carbons of high
general activity and particularly high retentivity. Low density in carbons from cellulose can be avoided, without loss of activity, by briquetting with a binder. Near the end, during the expulsion of volatile matter in the carbonization of cellulose, there is an unusually large drop in the activity of the char for slight losses in weight. This appears to be related to the emission of hydrogen. However, the cellulose char of low activity, even when carbonized to 900' C., can be easily activated. Desirable characteristics of a binder include fluidity on carbonization, relatively small molecular size, and high temperature requirement for carbonization. Base materials should not become fluid or plastic on carbonization, have a large molecule with rigid or oriented structure, and have a long ringchain molecule with oxygen or other volatile in the rings.
A
portion of the original carbon structure. At the same time a high degree of activity generally results. The dehydrating agents most frequently used are zinc chloride, phosphoric acid, and sulfuric acid. MILDOXIDATION.I n mild oxidation the reagents do not seriously attack the carbon but react principally with extraneous matter. Chlorine is a n example of this type of reagent. Mild oxidation has the advantage, which is generally true of the procedures already discussed, of good yield of product because the extraneous materials are selectively removed and a large proportion of the carbon originally present in the raw material is left intact. It has the disadvantage, however, that carbon-to-carbon linkages cannot generally be broken and hence any activation which is dependent on such breakage is impossible. For this reason mild oxidation is frequently followed in practice by "corrosive'' activation. Thus in one process (18) activation with chlorine a t 350" to 600" C. removes most of the residual hydrogen and adsorbed hydrocarbons from a carbonized raw material, and corrosive activation then follows. CORROSIVE OXIDATION.The most drastic form of activation is carried out by so-called corrosive oxidizing agents. These react not only with extraneous matter but with the carbon itself. Reagents are usually air, steam, and carbon dioxide. Air is generally used a t 400" to 600" C., steam and carbon dioxide a t 700" to 950 O C. The latter two have the advantage that the reaction IS endothermic; hence when reaction has taken place a t any one point on the surface, that part is automatically cooled, the tendency is greater for reaction to take place a t some other point, and the likelihood of activation over the whole surface is thus in. creased. ADDITIVES.Carbonaceous and noncarbonaceous additives are used t o help increase activity. As an example of the former, the United States Bureau of Mines finds (16) that the addition of small amounts of starch to coal results in "increase in general activity and particularly in the retentivity". As an example of the latter, the Norit process (85) uses small quantities of salts of the
CTIVATED carbons can be divided into two main classesthose used for adsorption of gases and vapors and thoseused in purification of liquids. For the former a granular material is generally employed, for the latter a powdered material. Activated carbons are usually made by one of the following procedures or combinations of several of them. The raw materials (wood, coconut shells, HEATTREATMEKT. coal, etc.) generally contain hydrogen, oxygen, and other extraneous matter. The major portion is ordinarily driven off by heat. The main purpose of heat treatment is to reduce the proportion of extraneous matter; a t the same time a certain degree of activity results. Heat treatment is also used occasionally to drive off extraneous material not present in the raw material but added during the processing; e.g., in the Urbain process (38) a portion of the phosphorus remaining from a phosphoric acid treatment is removed during subsequent carbonization at 1000 O C. SOLVEKT EXTRACTION. This treatment may be used to remove extraneous matter or to produce activity. Thus in a German process ($3)ash is extracted from brown coal with hydrochloric acid before carbonization and activation; in the process of the West Virginia Pulp and Paper Company (36) acid treatment is used before activation to reduce the ash content of carbonized waste liquor from the sulfite process. The utilization of solvents such as selenium oxychloride is claimed in at least one process (26) to induce activity, supposedly by dissolving hydrocarbons off the surface of the carbonized raw material. Solvent extraction, like heat treatment, is sometimes used to remove extraneous matter not present in the raw material; for example, in the Bayer process (15)zinc from a zinc chloride treatment is removed by washing with hydrochloric acid a'nd water. DEHYDRATING AGENTS. Treating the raw material with a dehydrating agent is another way of removing extraneous matter Especially in those cases in which the raw material contains a considerable proportion of carbohydrates, i t is frequently possible to remove hydrogen and oxygen selectively and retain a large pro1
Present address, Armstrong Cork Company, Lancaster, Pa
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valence forces be linked with one another to produce strength, and the other rcquires that there be great numbers of free primary valence bonds t,oinduce activity. The optimum condition appears to be that in v,-hichthe minimum number of bonds are used t o produce the requisite strength and t'he rest are free, accessible, and 6 0 arranged as to give maximum activity. The name ['base material" is here tiefined as that part of the raw material which is generally present in greater proportion and is expected to contribute in high degree to the act'ivity of the product; the term "binder" means that part x-hich serves to give strengt'h by holding together the particle,? of base material. MATERIALS AND APPARATUS
Figure 1.
Rotary Furnace Used in Carbonizing
alkali and alkaline-earth metals to help produce activity. Materials added for purposes other than producing activity (usually in such large proportion that they cannot strictly be considered "additives") include binders to give mechanical strength and inert substances such as kieselguhr to provide a surface on which the carbonized raw material may deposit. One part of the present investigation dealt with a study of pure chemicals as raw materials for activated carbons. Since activated carbon can bemade from almost any carbon-containing material, many investigations have been directed toviard the utilization of cheap and waste materials, most of which are chemically conglomerate mixtures. A survey of the literature indicated only a few studies on pure chemicals. Hence few data are available to show the fundamental relations betlveen chemical and physical nature of the raw material (molecular structure, molecular size, physical aggolermation, etc.) and character of the resulting carbon. Most of the adsorptivity studies are reviewed by RIcBain (WT),Adam ( I ) , and Brunauer ( 9 ) . Several papers are of particular interest in connection with the study of pure chemicals as rax materials ( S , 4 , 6 , 7,14,18-26,29,.!74). Another part of the investigation dealt with the role of binders in activated carbons, which is important in the preparation of granular carbons. Studies in connection with coke making had indicated that, during carbonization, the binder melts and flows among the particles to be bound and, after cooling, holds them together by a cementing or agglutinating action. Apparently no study had been made of binders in connection with the production of activated carbons in order to learn what happens to the binder during activation, whether the binder tends to contribute to the activity of the product, and what are the desirable characteristics in a binder for making activated carbons. Stillman ( S T ) has discussed binders in general. Binders in relation to activated carbons were reported by the Bureau of Mines (16) with the objective of evaluating American coals. A number of coals were briquetted and made into activated carbons, always with the same binder t o obtain comparable information on the coals. A part of the present investigation included a similar study except that a single coal and a variety of binders were used. The two properties generally required in granulated carbons (activity and mechanical strength) tend to work counter to each other. I n so far as strength is due to specific adhesion (28) and activity to chemical adsorption ( 9 ) ,the one requires that primary
Some of the raw materials arc described sufficiently by their common names ; for others, additional information is included:
COAL. Pennsylvania anthracite containing, on the dry basis, 8.5% volatile combustible matter, 77.97, fixed carbon, and 13.67, ash. COALTARPITCII. Low melting (205-220" F.) and high melting (285-305' F.) pitches, both by cube-in-air method. LIGSITE. A S o r t h Dakota lignite containing 7.07, ash on the dry basis, and the same material steam-treated by the Fleissner process ( 2 4 ~ CELLULOSE.Wood pulp cellulose of approximately the following composition: alpha-cellulose 93.0'%, beta-cellulose 3.2%, gamma-cellulose 3.8%, and ash 0.08%. LIGSIN. Purified fraction of the total lignin removed from hardwoods by the soda pulping process. Ultimate analysis: carbon 64.9%, hydrogen 5.9%, oxygen 29.27,; average molecular weight 870 for the repeating unit of the polymer, each unit of which contains six methoxyl and five hydroxyl groups. Carbonization was carried out in a gas-fired rotary furnace (Figure 1). During carbonization, the furnace was sealed completely except for a small nozzle at one end, through which volatile products could escape. The heating was conducted so that the temperature rise was about 3" C. per minute. When maximum temperature was attained, the furnace was held at t h a t point for exactly 2 hours. The nozzle was then plugged and the furnace allowed to cool. .4ctivation was carried out with superheated steam in a %inch i.d. silica tube surrounded by an electric furnace (Figure 2). Steam was generated in a boiler a t the base of the tube and superheated t o 925" C. while passing through approximately 2 feet of quartz packing. Approximately 100 grams of material were placed above the packing. -4small quantity of quartz chips was placed over the charge t o collect any undefired carbon resulting from gas cracking. The gases evolved passed through the top of the tube to a trap and gas meter. Briquets were made in a Carver laboratory press. They were 1 1 / 8 inches in diameter and "4 inch thick. As an aid to intimate mixing, the raw materials were ground to a fine powder. The coal was ground in a ball mill, andpcreen analysis indicated that more than 95% was finer than 200 mesh and all was finer than 48 mesh. The binders were usually ground with a mortar and pestle. I n a few cases the binder was dissolved in a small amount of solvent, the base material added, and the whole mixed in a Werner and Pfleiderer mixer. Benzene was the solvent when phenol-formaldehyde, polystyrene, and ethylcellulose resins were used as binders; water was the solvent with sugar and dextrin.
February, 1946
INDUSTRIAL AND ENGINEERING CHEMISTRY
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color removed and were reproducible to about “ 2 % . The test is used to predict the utility of a carbon for removing large colorbody molecules from liquids. As used here it gives only a rough classification of the carbons because the brown sugar solution was an arbitrary standard, and Freundlich isotherms, by which a complete evaluation can be made, were not determined. X-RAYPHOTOGRAPHS. A molybdenum anticathode and a powdered sample of carbon, enclosed in a small metallic frame, were used. X-ray photography is useful in showing the nature of crystallization because interference and reinforcement effects as the X-rays pass through the sample result in lines on the film; the intensity of these lines increases with the size of the crystals, and the spacing is dependent on the spacing of the units of the crystal. In general, a carbon which is highly crystallized will not be very active; but lack of activity is not necessarily caused by high degree of crystallization.
All briquets were made a t a pressure of 5000 pounds per square inch, either a t room temperature or a t a temperature approximately equal t o the melting point of the binder used. TESTS ON PRODUCTS
For the mechanical strength test the briquets were tested as such. For bulk density, toluene, and chloropicrin tests the material was ground to 8-14 mesh. For iodine, sugar decolorization, and x-ray tests a finely powdered material was used (over 90% through 200 mesh).
~IECHANICAL STRENGTH.An adaptation of a flexural strength test used in the plastics industry, the briquet was supported by tivo hardened steel blocks held s/4 inch apart by a spacer. Compressive force was applied from above by a rounded knife edge STRENGTH OF BRIQUETS (a bar with a ‘/*-inch flat edge and sides tapering off a t 45”). An hmsler testing machine applied and recorded the force required AFTERCARBONIZATION. Table I shows that carbonization infor breakage. The reproducibility of the test was usually within creased the strength of briquets made with lignin, coal tar pitch, *loyo; errors of this magnitude were not significant because briquets of the widely varying materials used often differed by sugar, and sodium silicate. These binders have relatively small several hundred per cent. Strength is desired in granulated molecules and become fairly fluid on heating. Both coal tar carbons so that they may stand handling in shipment and in use. pitch and lignin give off the major part of their volatile matter a t I n this test the breaking force is not applied in exactly the same higher temperatures than does cellulose, the base material with way as the forces which cause breakage in handling, but a material which requires a large force for breaking in the test should which they formed the strongest carbonized briquets. On the also stand up well in handling. other hand, the strength of the briquets made with polystyrene, BULKDENSITY. The Bureau of Mines test (16) was used, and Pentalyn G, ethylcellulose, and urea-formaldehyde resins was deresults are reproducible within j=2q;b. Density data are imcreased by carbonization, and the strength of carbonized briquets portant for granulated carbons because activity is frequently tested and reported on a weight basis, whereas the apparatus in made with these resins was low. These resins yield large molecules which the carbon is used (gas mask canister or adsorption tower) on heating and do not attain much fluidity. has a definite volume. It appears, therefore, that strength generally increases if the IODINE TEST. The Bureau of Mines method was used, but the molecules of the binder are small, if the binder becomes markedly final result was calculated as per cent of total iodine adsorbed. The reproducibility of the test was within *0.5%. fluid on heating, and if the binder carbonizes a t relatively high TOLUESE TEST. The toluene test (16) not only indicates the temperature. Table I1 shows that the strength of carbonized activity of a carbon toward toluene and similar hydrocarbons briquets depends also upon the activity of the base material. Both but also differentiates between portions of the adsorbate held sugar and coal tar pitch make stronger briquets with cellulose, tightly and loosely. Toluene adsorbed in the first part of the test was designated “total adsorpwhich develops high iodine action” and retained affer tivity, than they do with coal, evacuation, chemical adsorplignin, or carbonize coal tar tion”. The difference between pitch, whose iodine activity is total and chemical adsorption was called ((physical adsorplower. tion”. Per cent retentivity was AFTER ACTIVATION.Tables obtained by multiplying the I and I1 show that thestrength ratio of chemical adsorption to of the briquets after activation total adsorption by 100, and represents the proportion of was in all cases less than after total adsorbate which is held carbonization. The loss in tenaciously by the adsorbent. strength was almost always The reproducibility of the test greater than would be anticiwas within i.275. CHLOROPICRIN TEST. The pated from direct relation to accelerated chloropicrin tube weight loss. test of Fieldner et al. (17) is :eDuring carbonization there producible to about * 2 mincan be either increase or deutes. The method has been used to determine the suitacrease in strength because the bility of a carbon for gas masks. binder is more or less mobile, It differs from other tests used and when unsatisfied bonds are I here in that it is not an equiproduced by loss of volatile, librium test; that is, the test CONDENS47E R€C€/V€R ends when the first traces of the binder will in some cases chloropicrin get through the attach to these points and hold carbon and before it is necesthe material together. At the sarily saturated. Also, the end of the carbonization a activity is expressed on a volume basis, and hence those rather rigid structure is left, carbons having high density and any unsatisfied bonds will frequently show higher formed during activation will activity than in the other tests. contribute to the activity of SUGAR DECOLORIZATION. A 1-gram sample was shaken with the final product; but these 100 ml. of standardbrownsugar bonds usually cannot contact solution a t 70’ C. The solution other unsatisfied bonds and was filtered and compared with add to the strength. Furtherstandards made by diluting portions of the original solution more, some of the carbon with various proportions of disI I chain linkages (residues from tilled water. Results are exthe carbonization and the Figure 2. Steam Activator pressed as per cent of original
tpt
~
INDUSTRIAL AND ENGINEERING CHEMISTRY
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Vol. 38, No. 2 ~
TABLE
I.
-kCTIVI7Y O r CARBONS5 FROM POWDERED C O A L .\\D R I K D E R S
Bulk % Iodine Weight % Lossb Mechanical Strength ~ ~ nemoved ~ ~ i h Activity ~ after Steam Activation before (Dry Basis) in: (Flexural Test) after: after Toluene % color CarSteam Bri- CarAotiSteam Carreten- removed bon Binder Added boniactiquet- bon- Activation, Acti% iodine *luene, ; 9 tivity, from ting izing vating G./Cc. vation removed minutes Total Chem. Phys. 'j& sugar No. (26% b y Wt.) aation vation 43.9 6. 7 0.9 0.7 0 4 0.51 16.7 58.5 21 Iionec 12.0 6.2 64 48.4 30 53 67.1 Low m.p. pitch 13.5 7 3 0.43 4.4 27 14.6 8.0 73 47.7 4 . 5 1 0 . 0 3.8 64.5 High m.p. pitch 12.5 0.38 3.6 23 7.1 13.4 67 13.2 1 7 . 5 57 25 50.0 65.5 Lignin 17.4 1.6 0.42 8.3 16.1 68 46.5 11.5 97 1.5 0 . 3 20 62.2 Ethylcellulose 13.5 0.42 6.8 13.6 74 25.5 133 0.8 43.6 0.42 5.9 23 10. 6 52.0 PolyRtyrene 13. B 0.1 78 52 3.1 10.7 50.4 0.46 29 62.1 Urea-formaldehyde 26.1 1.2 12.3 7.1 80 40 29 0.46 19.7 57.4 33 Phenol-formaldehyde 1 8 . 4 9.7 6.3 64.7 82 $1; 27 36 12.2 0.50 12.4 45.9 62.3 23.0 28 Sugar 8.0 68 8.3 7.1 2.9 61.0 0.48 13.8 43.6 Dextrin 27.5 13.4 26 6.8 72 11.2 0 . 1 0 0 57.1 20 0.40 14.1 50.3 26.2 11.6 6.8 Pentalyn G 76 6.9 44.9 1.2 20 14.8 7.3 8.7 Sodium silicate 9.6 5.3 46.1 0.57 62 a Carbonization carried out by heating to 700' C. and holding for 2 hours. b Steam activation a t 925' C. until indicated weight loss (usually ' / z t o 3/4 hour). c Water used t o aid in briquetting.
:kzl:-
Carbon No. Base Materiala 2 Coal(powdered)
Wt. % Loss (D?y Basis) in Carbonizing ,
..
Binder Added (25% by Yt,) Low m.p. pitch Same
% 10Weight % Lossh Mechanical Strength ~~p dine R ~ (Flexural Test) ~~~~~t~ moved Activity after Steam Activation after: after before Carbonizing Steam Bri- Car- AotiAotiSteam % Chlofovation Actiiodine picrin, - To"Jene, g . / 1 m ! briacti- quet- Pen- ?atquets vation ting izing ing G./Co: vation removed minutes Total Chem. Phys. 13.5 48.4 30 53 7.3 0.43 4.4 67. I 27 22.6 14.6 8.0 (Dry Basis) in: ____
~
13.1 46.6 1 7 . 2 63 18.8 0.36 17.2 84,l 28 29.2 20.6 Cellulose (car81. 1 bonized) Lignin (carbon64.2 Same 14.0 44.2 1 3 . 7 42 12.8 0.37 14.1 59.8 10 18.3 10.4 ized) 16 Hinhm.0. pitch 48.7 Same 14.7 49.6 32 0 C 0.40 5.1 29.4 5 8.2 4.2 CcarbGnGed) 9 Coal (powdered) ... Sugar 23.0 45.9 27 36 :.8 0,5Q 12.4 62.3 28 20.2 12.2 81. 1 Same 18.4 53.2 1 6 . 3 44 2.0 0.31 12.8 91.9 27 36.2 26.7 16 Cellulose (carbonized) a All except coal carbonized prior to,addition of Pinder by heating t o 700' C. and holding for 2 hours: all briquets Carbonized similarly. Steam activation a t 925' C. until indicated weight loss (usually 1/z t o 3/4 hour). c Lost shape on carbonizing so that flexural test could not be made. 13
14
Carbon
Carbonaceous Material 56 Coal (rice size) 57 Lignite 58 Lignite, steamtreated 0.19 43.4 59 Lignocellulose 78.9 0.13 47.6 60 Cellulose 81.1 0.12 77.0 49.2 61 Southernpine 0.22 79.3 50.4 62 Masonite 0.38 73.2 56.2 63 Coconut shell Carbonized by heating t o 700' C. and holding for 2 hours. Steam activation a t 925' C. to indicated weight loss. NO.
5
b
Bulk % Iodine Weight % L o s s h Density Removed (Dry Basis) in: _____ after before CarbonSteam Activation Steam ization activation G./Cc. Activation 0.71 7.8 6.4 40. 2 0.51 13.1 49.4 46.9 0.48 24.6 42.9 49.0 47,6 34.4 33.3 44.4 41.5
linking acrosq from crystallite to crystallite) n-ill be broltcn by {,he corrosive attack of the activating agent,, and hence the activated briquct will be n-eaker than t,he carbonized briquet. That the loss in strengt'h should bc greater than would be anticipated by direct relation to \\-eight loss is probably attributable to the fact that, when the corrosive action destroys one portion of the chain, the effectiveness of the wliole linkage is impaired. Furthermore, as will be shon-n later, there seems to be evidence t,hat the corrosive attack strikes selectively at the binder residues. ACTIVITY OF BRIQUETS
Data in Tables I, 11, and I11 shon AFTER CARBOXIZATYOS. that the activity of thc carbonized product of a mixture of binder and nonbinder is predominantly that of the binder. Thus thc iodine activity of the mixture (carbon 13) of 2593 coal tar pitch binder (hTo. 15) and 75y0 cellulose ( S o . 60) is only 17.2 instead of 27.1, the activity calculated for the mixture if each ingredient contributed its proportional amount. Similarly the iodine activity of the mixture (carbon 2) of coal 1 and coal tar pitch 15 is
TXZG retentivity,
%
64.6
8.6
70.6
7.9
86.8
4.0
51.2
8.0 9.5
60.4 73.7
Activity after Steam Activation
% iodine removed 38.1 48.8 48.3
Ch!or,opicrin, minutes 12 6 7
64.8 85.4 74.7 85.7 91.0
7 14 6 22 42
-To'uene, g./loo g. Total Chem. Phys. 6.5 4.0 2.6 11.0 5.4 5.6 6.9 13.7 6.8 19.8 27.6 23.4 35.4 86.0
11.2 19.9 14.6 19.4 24.0
8.6 7.7 8.8 16.0 12.0
61.5 49.1 50.4
% color removed from sugar GO 74 77
56.6 72.2 82.4 54.8 66.7
88 89 86 93 80
Toluene retentivity,
%
only 4.4, as compared with calculated activity 13.8for the mixture. In carbonization some of the niobilc binder is adsorbed on the outer surfaces of the more rigid fra,inework of the crystallites. It cuts off the activit,y of these more rigid portions and has little activit,y of its own. Thus t'he activity of the mass as a whole is relatively low, so that a t the end of carbonization the activity of a mixture of base material and binder is predominantly characteristic of the binder. AFTERAcTIvaTroK, Data from Tables I, IT, and 111also show that the activity of briquets after activation is predominantly t,hat of t,he basc material. The iodine activity of the mixture (carbon 13) of coal tar pitch 15 and cellulose 60 is 84.1, which is closer t o the activity of the cellulose than 71.5 calculated for the mixture. Also, the activit>yof the mixture (carbon 2) of coal 1 with coal tar pitch 15 is 67.1, which is nearer to that of coal than to the calculated value 51.4 for thc mixture. Table I also shows that, for the different binders used with coal, the activity of the final product is in most cases approximately that of the base material; this becomes more nearly correct if it is considered that activation was not albyays carried to exactly SOYoweight loss.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
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o\
0 0
20 40 Wt-/./GHi-Loss
/N
I
I
6U
80
Acr/vA7/uA5
/QO
+
Figure 3. Activation Weight Loss of Cellulose Carbonized at Various Temperatures
These facts indicate that steam activation tends to remove binder residues preferentially from carbonized mixtures of binder and nonbinder, probablf because the binder residues tend to be nonoriented and disordered. They represent a brush-heap distribution of ‘(bridges” between the more orderly crystallite sections of carbon from the base material. Penetration of the crystallite sections is more difficult for the activating agent than penetration of the nonoriented sections, and hence the latter are more readily available for reaction. Furthermore, brush-heap or amorphous sections are generally considered to be at a higher energy level than oriented crystallite sections and, therefore, tend to be more reactive. Goldfinger, Mark, and Siggia (.24), working with cellulose, found that “diffusion , . is very slow in the crystalline areas and comparatively faster in the amorphous regions”. Kickerson (SI), reporting studies on the hydrolysis and catalytic oxidation of cellulose, stated that noncrystalline portions of cellulosereacted first and explained the rapid evolution of gas in the early part of oxidation as due “to the rapid cleavage of the reactive amorphous or expanded chain network; the final slower rate is attributed t o the dense, less reactive crystalline aggregates or crystallites”. He estimated the proportion of noncrystalline material in wood pulp cellulose to be about 10%.
.
n “0
1
20
40
60
80 100 @
TOTAL W€/GHT LOSS, ( ~ ~ f f 6 O N f Z 4 ? 7 O N &T/VAT/OUJ
Figure 4. Total Weight Loss of Cellulose Carbonized at Various Temperatures
.
bonization, however, the smaller the loss of weight in activation t o give an iodine activity of 90. The saving in material by high temperature carbonization is not so great as would appear from Figure 3 because the higher the carbonizing temperature, the higher the weight loss in carbonization. When iodine activity is plotted against combined weight loss in carbonization and activation (Figure 4),the curves are closer together. I t appears that, as long as both carbonization and activation are used, the resulting activity will be approximately the same for any given total weight loss, regardless of the relative proportions or temperature of carbonization.
TABLE IV. PROPERTIES OF REFERENCE CARBOXS I
Carbon No. Souroe Raw material Mesh size (as received) Bulk density, g./oc. Iodine activity % Chloropiorin t&t min Toluene test, d l 0 0 Total
9.
Chemical Physical Toluene retentivity ? ’7 Sugar deoolorizatioh,
h
I1
I11
Carbide L Carbon (ColumbiaGradeG) Coconut shells 8-14 0.56 86.9 41
Universal Oil Products Petroleum 16-24
h’orit (deoolorising) Vegetable matter Powder
i f .3
62 .$
3212 22.0 10.2 68.3
... ... ...
56
... ...
58
... ... ...
... . ..
85
CELLULOSE CARBONS
1
DENSITY AND VOLUME ACTIVITY.By using a binder with cellulose, its density and activity on a volume basis can be increased without impairment in activity on a weight basis. Carbons 13, 16, and 60 (Tables I1 and 111) show that by use of a binder the volumetric activity toward chloropicrin, iodine, and toluene was approximately doubled. The indications are that, by using higher briquetting pressure, a different proportion of binder, or possibly a different binder, a carbon might be produced which would be as good as and perhaps better than coconut shell carbon 63 (Table 111) and Columbia carbon I (Table IV), the two best carbons in this study. IODINE ACTIVITY AND WEIGHTLoss. Table V gives data on cellulose carbons carbonized a t different temperatures and activated to various degrees. The iodine activities are plotted against weight losses in activation in Figure 3. For a weight loss in excess of 95%, the iodine activity is above 90, regardless of carbonization temperature. The higher the temperature of car-
ACTIVITYOF CELLULOBE CARBONIZED AT 900” C. When cellulose is carbonized to 900” C., the activity of the product is extremely low, according to Table V (carbon 37). Figure 3, however, shows that this material is easily activated. Chaney (11) recommended temperatures below 600 O C. for carbonization if good carbons are to be produced; the British Fuel Research Station (8) indicated the lowest possible temperature for practical carbonization t o be 450” C. The latter work was done entirely with coal, however, and the former apparently does not include cellulose. That this 900” C. char could easily be activated was proof that the loss in activity in passing from a carbonizing temperature of 500” to 900” C. could hardly be due to the formation of large graphitic crystals; moreover, this fact was checked by x-rayphotographs of the cellulose carbons prepared by carbonization a t 500” and 900” C., and compared with a similar photograph of natural graphite. Neither of the cellulose carbohs showed evidence of graphitic lines, and it, must be concluded that the loss in activity
INDUSTRIAL AND ENGINEERING CHEMISTRY
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VoJ. 38, No. 2
TABLE v. Carbon
No. 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
37
38 39
Carbonization Temp., % ' wt. loss C. (dry basis) None 0.0
300
71.0
500
80.0
PROPERTIES O F AkCTIYATED CARBONS FROM C E L L U L O S E Activation" Highest Bulk 9 tEmp., % wt. loss Combined Density, Iodine Toluene Activity, G./100 CJ C. (dry basis) % Wt. Loss G./Cc. Removed Total Chem. Phps. 0.0 0.242 1.8 .... ..). .... 77.2 77.2 0.099 1 6 . 1 .;.. .... ' O.O 86.3 0.098 53.4 .... ~ . ( . .... 717 86.3 858 95.2 95.2 .... 90.2 .... .... 0.143 13.7 71.0 0.0 0.156 56.3 80 9 34.0 0.137 81.4 ... 84.9 817 47 8 0.093 94.0 93.2 859 76.5 900 97 5 99.3 .,.. .... 42.0 2.8 2.0 0.8 80.0 0.161 0.0 21.0 84.2 0.144 71.2 20.9 15.6 5.4 18.9 6.i 86.3 0.138 81.2 26.7 800 31.5 22.6 IO,, 0.121 89.1 33.3 853 50.0 . 90.0 855 60.7 92.1 0.105 90.9 38.0 23.1 14.9 92.8 42.3 23.6 18.7 94.3 0.090 858 71.3 93.1 47.8 24.6 23.2 96.5 0.082 873 82.5
(2:) )::37(
80.7
I
.
.
n
925
,..,
.
.. . I
.
. I . .
j . . I
;'s";)
(;I
7c
....
... ... I
.
900
,&$%t~
0.0 33.0 77.0
80.7 87.1 95.6
0.186 0.139 0.099
3.4 88.4 93.9
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.
.
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Since cellulose activates easily and rapidly, and only 40 grams of material were charged t o the activator in this series, i t was not usually possible an activating temperature of 925' C.; therefore, highest temperature during activation IS reported here. (1
71.5 74.B 73.5 67.8
