926
INDUSTRIAL A N D ENGINEERING CHEMISTRY
VOl. 22, No. 9
The Mechanism of Charcoal Activation' M. E. Barker2 DIWARTYBNT OF CHEMICAL
ENGINEERING, MASSACHUSETTS INSTITUTE
OF
TECHXOLOGY, CAMBRIDGE, MASS.
-
When wood or other carbonaceous substance is dis KUMBER of very held by various investigators tilled out of contact with the air, a primary charcoal interesting t h e o r i e s as to the mechanism by which is formed. This material has a true density of about have been advanced activation of charcoal is ac1.45 and shows no characteristic x-ray diffraction patto explain the increase in adcomplished. In order to work tern. sorptive power developed in out a process of charcoal acUpon activation the true density of the charcoal incharcoals upon activation. t i v a t i o n , the author first creases up to a limiting value of about 2.15 and a Knight, Garner, and McKie studied the mechanism of characteristic x-ray pattern is developed which is simi(58) consider that the incharcoal activation. lar to that produced by graphite in very small particle ternal surface of charcoal is The results obtained dursize. enormously increased during ing this investigation are The increase in density of the charcoal substance activation and the increase given here in Table I in produces an internal shrinkage resulting in the forin surface alone accounts for order to show the increase mation of numerous small spaces within the charcoal the activity developed. Howin adsorptive power due to granule. A crystalline surface is produced. Thus acever, the exact mechanism by activation. tivation produces a more active surface and a very which this increase in surface I n order to account for the large internal surface as well as a large volume of very is obtained is not stated. enormous increase in adsorpsmall capillaries. Chaney (57) considers that tive capacity observed-as, By an ultimate analysis it is shown that the proporthe primary carbonization of for instance, from 11 to 1480 tion of hydrogen and oxygen decreases during activawood substances produces in commercial wood charcoal tion and the proportion of carbon increases. However, the necessary surface and and likewise from 30 for ligin the best activated charcoals there is still present capillary structure to account nite semi-coke to 2715 for the a considerable amount of both hydrogen and oxygen. for fill adsorption obtained in highest activated p r o d u c t I t is believed that these components are present in activated charcoal. At the the various materials were unactivated or primary charcoal which acts as a binder same time certain oily hydros t u d i e d a t e a c h s t a g e of to hold the granule firmly together. carbons are formed and adpreparation by: (a) chemicaI sorbed with great tenacity on analysis, (b) true density dethe active carbon framework. Activation is the only process terminations, ( c ) x-ray powder photographs, (d) the microby which the adsorbed hydrocarbons can be burned away scope and photomicrograph. without, at the same time, burning the active carbon base. Table I-Effect of Activation on Adsorptive Power of Carbon Briggs (36) thinks that primary charcoal is a highly CClr ADSORBED complex polymer formed from cellulose molecular fragments. FROM ASATD; CHARACTER SUBSTANCE TESTED No. T 24 The action of heat and activating agents is such as to attack OF (ALLBONE DRY) C. PER GRAM CHARCOAL these huge molecules a t their most unsaturated points, thus SUBSTANCE eliminating some carbon and most of the hydrogen from the primary charcoal. The result is a huge molecular group Mg. Ironwood 1 22 0.96 Fibrous, hard of carbon atoms, more or less loosely held together, shot Primary ironwood charcoal 2 30 0.89 Hard through and through with holes of atomic dimensions. It Excellent activated ironwood charcoal 3 1160 0.72 Hard, friable is within such spaces as this that adsorption principally granular Commercial wood charcoal 4 11 0.46 Firm, Ebrous takes place. Highest activated wood charcoal@ 5 1480 0.30 Soft friable Sutcliffe (40) says that activation is a process of forming Coconut shell 5 18 1.25 Fib;ous a highly porous material. For color adsorption the pores Coconut shells 7 18 1.20 Hard coconut charcoal 8 47 0.96 Hard should be much larger than for a gas adsorbent charcoal. Primary Excellent activated coconut charcoal 9 0.84 630 Hard Ketzke (39) found that bromine was adsorbed by substitulignite 1.25 10 18 Fair tion in untreated carbon blacks. After heat activation, the Dry Lignite semi-coke 11 1.09 Firm 30 activated lignite charsame amount of bromine was adsorbed, but in this case as Good coal 12 0.89 640 Firm an addition product. He therefore concluded that activa- Highest activated lignite char13 coals 2715 0.31 Friable, tion is a process of increasing the unsaturated condition of granular the charcoal substance. Debeye and Scherer (29) have a Any further activation reduces the granule to a fine powder. shown by x-ray studies that active charcoal is a mass of very small graphite crystal fragments. Ruff, Schmidt, and 01Chemical Analysis brich (%), using x-ray studies, say that active carbon is a A sample of charcoal was weighed into a platinum boat true modification of carbon and, as such, does not have exactly the same lattice structure as graphite. Alm (b?) and.placed in a combustion tube. Dry nitrogen a t 150" C. found that carbon blacks on heating and on activation was passed through the tube and then through an adsorpreadily developed a graphite structure as shown by x-ray tion train for 2 hours. The charcoal was then heated to 300" C. for 2 hours and a good vacuum pulled with a Hivac studies. pump. Two phosphorus pentoxide adsorption tubes were It is thus seen that some very divergent views are now in the train between the combustion tube and the vacuum 1 Received May 12, 1930. From a thesis submitted to the Departpump. After the 2-hour heating period, dry nitrogen was ment of Chemical Engineering, Massachusetts Institute of Technology, again passed through the combustion tube to cool the charin partial fulfilment of the requirement for the degree of doctor of science. coal sample, which was then removed and placed in a dry Present address, Edgewood Arsenal, Edgewood, Md.
A
~~
~~
September, 1930
INDUSTRIAL A S D EXGINEERING CHEMISTRY
927
with the results shown in Tables 11,111, and IV.
I
Mellitic Acid Determination
It will be seen that the composition of active charcoal when computed on the ash- and moisture-free basis corresponds quite closely to the coked sample of primary charcoal and to a charcoal formed somewhat below 1000" C. as shown by Schorger's table (Table 111). The formation of mellitic acid from charcoal does not seem to preclude the presence of graphite when present as very small crystal fragments. It has been generally held in the literature that graphite forms graphitic acid on selective oxidation while charcoal yields mellitic acid. Accordingly, ten samples of 100 grams each of active charcoal from variI ous sources and an equal sample of AquaDag, a colloidal graphite, were treated for the formation of mellitic acid. All the charcoals were almost completely converted to mellitic acid and about 50 per cent of the Aqua-Dag was also converted to the mellitic acid. The residue-in eack case was examined under the microscope. A few flakes of graphite-like materials were observed in the residue of each of the charcoals. Only the larger flakes of Aqua-Dag survived the treatment.
I Figure I Table 11-Analysis
of Primary Ironwood Charcoal SAMPLE
SAMPLE
P n cent
Per cen!
AVERAGE
Per cent
RATIONAL ANALYSIS (AIR-DRY BASIS)
Loss in weight
Increase in weight PzOa tube Adsorbed gases Volatile at 900' C. Carbon in volatile Hydrogen in volatile Oxygen in volatile Residue on coking Hydrogen in residue Carbon ita residue Ash Oxygen (by difference)
2.79 2.80 None 30.44 11.55 3.58 15.31 66.76 0.35 65.10 0.83 0.59
2.88 2.93 None 30.45 11.58 3.57 15.30 66.62 0.32 65.00 0.80 0.46
VLTIMATB ANALYSIS (BONE-DRY BASIS)
Carbon Hydrogen Ash Oxygen Total
stoppered bottle and weighed. The loss in weight was compared with the gain in weight of the phosphorus pentoxide adsorption tube. The difference was called adsorbed gases. The dry sample was then placed in a small combustion tube which in turn was placed in a large combustion tube. Dry heated nitrogen was passed over the sample heated to 900' C. for 10 minutes. Dry oxygen was passed through the outer tube. The gases given up to the nitrogen stream were burned when Lhe oxygen and nitrogen streams mixed. The products of combustion were absorbed and calculated as carbon and hydrogen, and the oxygen obtained by difference. The residue was then burned as in ordinary combustion analysis. Figure 1 shows diagrammatically the set up for outgassing and drying the sample. Figure 2 shows the apparatus for coking. One sample of primary charcoal and three samples of activated charcoal from widely different sources were analyzed,
79.50 4.38 0.85 16.27 100.00
--
2.83 2.87 None 30.45 11.56 3.58 15.30 66.69 0.34 65.05 0.82 0.52
of Wood Charcoals on Ash- a n d MoistureFree Basis (From Schorner (35))
Table 111-Composition
COMPOSITION
TEMPERATURE
\vEIGHT YIELDS OF
OF
FORMATION
c. Wood
200 300 400 500 700 1000
C
Per cent 45.4 52.3 73.2 82.7 89.6 93.7 96.6
Figure 2
H
Per cent 5.9 6.3 4.9 3.8 3.1 2.4 0.6
0
Per cent 48.7 41.4 21.9 13.5 6.7 4.8 2.9
CHARCOAL
Per cenl 100 91.8 51.4 37.8 33.0 28.7 26.5
INDUSTRIA4LAND ENGINEERING' CHEMISTRY
928
Vol. 22, s o . 9
thoroughly outgassed and helium admitted to the container from a measuring buret and the volume of the charcoal substance determined. Cude and Hulett (0) have given explicit directions for determination of densities by liquid submergence, n-liileHoward and Hulett (1.6) and Stamm ( I ? ) have given directions ior determination of densitv bv helium rrreasorement. Table V shows the true densitv of wood and charcoal substances. A marked increase in density of charcoal substance takes place during activation. It is to be noted that helium gives a density for active charcoal just below the true density of graphite. The increase in density with helium over liquids is interpreted as due to the filling u p of the small pores with helium which do not admit the liquids. If the granule density of the charcoal is considered in connection with the true density, it is seen that a considerable increase in pore volume titkes place upon activation and that a large share of this increase is in the form of very small pore sizes which are filled with adsorbed material as shown in Table VI. "
Y t w r s 3-X-Ray
Pinhole Photo!&rmhe
I
X-Ray Studies
Samples of various charcoal materials were powdered to pass a 200-
F i W i e 4-X-Ray Photo of Aqua-Dag
True Density Determinations
mesh screen, loaded in gelatin capsules under 25 pounds load, and x-ray powder photographs made by passing a monochromatic bea,m of x-rays thfough the sample. Figure 3 shows the results obtained by using a pinhole opening, while Figure 4 shows those from a reetaugular slit. In every case a true primary charcoal gave no diffraction rings. Upon activation the diffraction rings of graphite
When a sample of powdered charcoal is heated and subjected to a vacuum, then sealed in a tube and the tube broken under water or other liquid, the p r e s of the charcoal are tilled with the liquid. The sample can be weighed under the liquid and its density determined. Or the saniple can he Tahle IV-Analvala
Loss in weight at 30U0 C. water
Adsorbed g a s volatile at QW',C. Carbon in volntlle Hydrogen in volatile Oxygen in volatile Residue Hydropen in residue Carban m residue Arh in residue Oxysen in residue Copper oxide in rcddue
1.69 1.08
0.M
5.78 2.51 0.09 3.18 92.61 0.51 89. 89 3.73 0.47
...
1.09
1.08 0.61
5.68 2.37
0.11
3.20 92.63 0. 51 88.20 3.68 0.16
...
V L T r x ~ r ANILYSIS e
Carbon
Hydrogen Oxygen Total
95.66 0.64 3.70 100.00
1.69 1.0s 0.61 5.73 2.44 0.10 3.19 92.57 0.51 88.04 3.70 0.31
...
of Aefiwared Charcoals
1.69
0.4s 1.21 5.1s
2.32 0.20 2.66 93.12 0.43 74.06 9.00 4.35
(Asx,WATSE,
...
1.87 0.34 1.33 4.91 2.21 0.18 2.52
93.40 0.48 74.48 9.75 3.84
...
&NLI~ D S O ~ P BOAS D
90.14 0.76 9.10 100.00
1.88 0.41 3.n
5.15 2.27 0.19 2.59 93.26 0.40 74.27 9.37 4.12 5.05
.
0.81
0.28 0.33 2.24 0.90 U,ll
1.23 97.16 0.41 80.13 13.81
2.81
...
0.11
0.60 0.28 0.32 2.29 0.91 0.11
3.M)
97.12 0.42 80.02 13.76 2.91
0.59
0.28 0.34 2.34 0.92
1.31 97.07 0.42 79.02 13.70
...
PRES e ~ s r s )
94.50 0.62 4.8s 100.00
1.27
..
1.VDliSTRIAL A N D EKGINEERING CHEMISTRY
September, 1930
(Courlasy U. S. Bureau of Minci) Figure 5-Sectlon of C O E O ~Shell Y ~ ( X 200) Thin sectioo by transmitted light.
(Cowfrcsy U. S. B U I Cof~Miner) Flgure 5 a S t o n e Cell S t r u c t u r e In C o c o n u t Shells ( x 1000)
Thin s ~ f i o nby transmitted light.
(C0Y"fLIY
u. s.Bureau Of
Miner)
Fl'lgure 6-Sflucture of P r l m a r y Charcoal from C o c o n v t Shell ( X 200) Charcoal formed at SW' C. carbonization. Thin section by transmitted light.
(Courrery
u. s.
Burcold Of Mines)
Figure 7-Steam-Actirafed Coconut-Shell Charcoal ( x 200) Chloropicrin tube tent, 31 minutes. by transmitted light.
This section
(Courlrry U.S. Bur&?%of Mined Figure 7 a - S t e ~ m - A c t l v a t e d Coconut Charcost ( X 1000) Chloropicrin tube test, 31 minutes. br traosmitted light.
appeared. If the activated sample was heated for a prolonged period, the bands became much sharper and narrower, showing that the particle size increased; in which case the adsorptive power decreased. I n Figure 3, picture 2 shows a 37-minute activated coconut charcoal; picture 3 shows the same charcoal after 50 hours heat a t 970" C. The adsorp tive power decreased 40 per cent as a result of this heat treatment. Figure 4 shows Aqua-Dag, a colloidal graphite, after
Coconut Char140) Chloropicrin tlrbe eeit, 5 . 4 minufee. Polished specimen by reflected green light.
Figure 8-Steam-Acdvsfed coal
(x
Flgvre %Red Oak Wood ( X 40) Potirhed specimu, by maacted green
Thin s f f t i o n
(Courlcry U . S. B Y I E ~of%Miner) Figure 7b-AIr-AeN-rated CoCOnUt Charcoal (X 2001 Chloropicrin tnbc mt. !5 minutes. by transmttted light.
929
Thin section
Figure lo-PrImary
Charcoal from Red Oak Wood ( x 40) Slow heating u p t o 850° C. Polished specimen by reflected green light.
i t had been freed from adsorbed ammonia and tannic acid. This photograph shows the peculiar scattering of the x-rays observed by Ramon and Krishnamurti (-31) recently and interpreted by them to mean the presence of more or less loosely attached electrons to the exterior surface of graphite lattice. These photographs and about twenty-five others made during this investigation show that primary charcoal is partly converted into graphite, or graphite-like carbon, present in
Vol. 22, No. 9
INDUSTRIAL AND ENGINEERlNG CHEMISTRY
930
coconut charcoal is carefully carbonized, then activated, the original stone cell structure is retained in the activated eharcoal, an extremely fine granular structure is developed, and a marked pore system is fornied. The same effect is shown in treating oak to form activated charcoal. As shown by the adsorption tests, much better charcoal can be made by preserving the original structure of the wood and finally breaking up these cell structures into active charcoal substances with the formation of a large volume of space present as small capillaries or very thin open spaces. Fi8ure Il-Carbon Dioilde Activated Oak Chsrcosl (x 40) Chloropicrin tube test. 30 minutes. Polished specimen by reflected green lipht.
Figure 12-Specially Prepred Oak Charcoal
Conclusions
( X 1401 Chloropicrin tube test, 45 minutes. Polished IPmimeo by reflected green light.
extremely sinall particle size, whenever a charcoal is activated. Only those substances that gave a pattern like picture 1 of Figure 3 could he readily activated. Microscopic Studies
Figures 5, 6, 7, and 8, respectively, show a section of raw coconut shell, a primary charcoal formed by carbonization of coconut shells a t 800" C., a steam-activated charcoal formed from the primary charcoal shown in Figure 6 , and a charcoal formed by heating coconut shells from 100" C. increasing slowly to 500' C . , then activating with steam a t
sow -"" r-.
On the basis of the foregoing facts, the author concludes that the mechanism of charcoal activation is substantially as follows: (1) The hydrogen and oxygen of is markedlv decreased bv activation. (2) Primary charcoal snbstance having a true density of about 1.45 is partially converted to graphite, or graphitelike carbon of crystalline structure, having a true density of about 2.15. Sufficient primary charcoal remains to act as a hinder in a good granular charcoal. (3) The graphite particles in active charcoal are extremely small and have a large surface energy due to the presence of loosely held electrons on the surface of the graphite latticc. (4) . , Activation increases the interior surface area. aroduces a large volume of very small capillaries, and changes the character of the internal surface. /
Table V-True
Densifies of Wood and Charcoal DENS^^
5"BSTANCB
MHTXOD
IIIVBSTZOATO.
1
A Selected Bibliography on Activated Charcoals
E."".". -.p...-
stamm
I. 536
1.479
J 40
1.44 1.43
1.86 1.85 e)
1.43 1.85 2.15 1.65
~
.... .
__..__.
1
"P
water
Helium Carbon tetrachloride
A i. __.I_" _.
P0.h"..
sulfide Helium
stamm Author Howard and Hulett Howard and Kuleft Author Author Author Cude and Hiilett Howard and Nulett Cude and Hulett
liISTORIC*L
61) Bancroft. "Charcoal before the War," J . Phys. Chcm.. 84, 127, 201, 842 (1920). (21 Burcell. "Deuelopmeot of Active Charcoal." J. 1x0. Exc. CXBM..11. sa (191s). ( 3 ) Hunter, "Charcoal Adsomtion," Phil. Moa.. 141 P6. 364 (1883).
G e n ~ n rINI-ORMATION, ~ Usas
AND
PIIYEICALCIZALIACTBBISTICS
~~~=~~~~~~~~~~~
(4) Army (U. S.1, "Gas Mark Charcoal," U. S. A. SpecifiEation 87-52-12. (51 Chancy. Ray. and St. John, "PrWeriiea d Activated Charcoal Which Fit I t for Industrid Uses." Tmw. A m . Init. Chcm. E m . . 1.5. 309
and l1 shox', respetively, a Of Oak wood, a primary charcoal formed by slowly heating this aood to carbonization, and the same primary charcoal finally activatqd with carbon dioxide a t 825" C. Figure 12 shows a 45-minute charcoal formed by a special treatment from oak wood. The similarity of this material to that shorn in Fignre 8 is very pronounced. Primary charcoal made from coconut shells carbonized a t high temperature has the appearance of l~avingmelted, then so'idified. When this is marked granular structure nnd a fine pore structure are developed. When a
61823). (61 Cude and Hulett, "Some Properties of Charcosi," 1. At". Chem. Soc., 4% 381 (1910). (71 Lamb, Wilson. and Chaoey. "Gas Mnsk Absorbents," 3. IND. E m CSRX.. 11, 420 (isis). (8) Mantc11. "industrial Carbon," Van Nostrand. -propenic9 of Canirfer Charcoal (Unimpregnated)." (a) Chemical Warfere Monogmph 46 ( 2 parts). (10) Petternon. "PmPrrties of Impregnated Canister Chsrcoal," Chemical Warfare Monograph 47 (2 parts).
Ceylon graphite
2.28
_. .
"3
-Abibliography
(JD activated charEo=l handred titles has been compiled by the writer end io panieularly interested in thia subject.
II copy
mDre than two will be forwarded
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
September, 1930 ADSORPTION:FACTS COKCERNING,
AND
METHODS
OF
TESTING
(11) Bliih and Stark, “Concerning Adsorption,” Vieweg (1929). (12) Fieldner et al., “Methods of Testing Gas Mask Adsorbents,” J. IND. ENG. CHBM., 11, 1519 (1919). (13) Harkins and Ewing, “Density of Gas Mask Charcoals,” Proc. Nal. Acad. Sci., 6, 49 (1920). (14) Howard and Hulett, “Study of the Density of Carbon,” ,J. Phys. Chem., 28, 1082 (1924). (15) McBain and Tanner, “Microbalance for Weighing Sorbed Films,” Proc. Roy. SOC., l26(A), 579 (1929). (16) Ruff and Roesner, “Adsorption of Gases by Activated and NonActivated Charcoal,” Ber., 60(B), 411 (1927). (17) Stamm. “Density of Wood Substance a n d Adsorption by Wood,” J . Phys. Chem., 33, 398 (1929). (18) Urbain, “Effect of Size of Pores in Charcoal on Specific Adsorption,” Compf. Rend., 180, 6 3 (1925). THEORIESOF ADSORPTION
(19) Freundlich, “New Conceptions in Colloid Chemistry,” Dutton. (20) Gibbs, “On the Equilibrium of Heterogeneous Substances,” Collected Works of J. Willard Gibbs, Vol. I. p. 65, Longmans. (21) Langmuir, “Theory of Adsorption,” Phrs. Rev., 6, 79 (1915). (22) Langmuir, “Constitution and Fundamental Properties of Solids and Gases,” J. A m . Chem. Soc., 38, 2221 (1916). (23) McBain and du Bois, “Experimental Test of the Gibbs Equation,” Ibid., 61, 3534 (1929). (24) Patrick, “Capillary Theory of Adsorption from Solution,” Trans. A m . Inst. Chem. Eng., 15, (I), 283 (1923). (25) Ruff, “Theories of Adsorption by Active Carbon,” Kolloid-Z., 38, 174 (1926). (26) Smith, “On the Adsorption of Gas by Charcoal,” Proc. Roy. SOC. (London), 12, 424 (1863).
FORMS O F CARBON ,(27) Alm, “X-Ray Investigation of Heat-Treated Amorphous Carbons,” M. I. T. Chemical Engineering Thesis (M. S.), 1927. (28) Bragg, “Carbon Atom in Crystalline Structure,” J. Franklin I n s f . , 198, 615 (1924). (29) Debeye and Scherer, “Study of the Form of Amorphous Carbon,” Physik. Z., 18, 291 (1917). (30) Lowry, “Significance of Hydrogen Content of Charcoals,” J . Phys. Chem., 33, 1332 (1929).
931
(31) Ramon and Krishnamurti, “Graphite Lattice Structure,” Nofure, 124, 53 ~ 9 ) . (32) Ruff, Schmidt, and Olbrich, “Amorphous Carbon and Graphite,” Z . anorg. allgem. Chem., 148, 313 (1925). PREPARATION O F
PRIMARY CHARCOAL
(33) Banks and Lessing, “Influence of Catalysts on Wood Carbonization,” J . Chem. Soc., 126, 2344 (1924). (34) Lichtenberger, “Carbonization of Wood,” Ten Years of Scientific and Industrial Efforts, Chemie et induslrie, Paris. (35) Schorger, “Chemistry of Cellulose and Wood,” McGraw-Hill. THEORYO F CHARCOAL .4CTIVATION
(36) Briggs, “.4dsorption of Gas by Charcoal, Silica Gel, etc.,” Proc. Roy. Soc. (London), 100(A), 88 (1921). (37) Chaney, “Activation of Carbon,” Trans. Elec. Chem. Soc., 36, 91 (1919). (38) Knight, Garner, and McKie, “Area of the Internal Surface of Charcoal,” J . Phys. Chem., 31, 641 (1927). (39) Netzke, Air Activation of Carbon Blacks, Report 3, Problem W-2, M. I. T. Laboratory. (40) Sutcliffe, “Gas Adsorbent us. Decolorizing Charcoal,” Chemistry Induslry, 43, 635 (1924). P R O C E S S OF
ACTIVATIOX
(41) Barnebey and Cheney, “Steam Activation in Tunnel Kiln,” U. S. Patent 1,541,099 (1925). (42) Bayer & Co., “Manufacture of Active Charcoal by Briquetting Charcoal Fines and Chemicals under Pressure,” British Patents 195,390 (1923) and 246,110 (1925). (43) Chaney, “Manufacture of Active’ Carbon (Steam Distillation),” U. S. Patents 1,497,543 and 1,497,544 (1924). (44) Metalbank Co., “Zinc Chloride for Activating Charcoal,” British Patent 238,889 (1924). (45) Mumford, “Briquette Lignite, Dolomite, and a Binder,” U. S.Patents 1,268,181 and 1,287,592 (1918). (46) Sauer, “Heat, Mixed Gases, and Stirring during Activation,” U. S. Patents 1,502,594 (1924) and 1,641,053 (1927). (47) Urbain, “Coal Compressed with Zinc Chloride or Phosphoric Acid, British Patents 257,269 and 257,917 (1927); U. S. Patent 1,610,399 (1926).
Fermentation Products from Cornstalks’ C. S. Boruff with A. M. Buswell ILLINOISSTATE WATERSURVEY,URBANA,ILL.
I
AN earlier paper (1) the writers have called attention to a possible commercial source of methane and carbon dioxide based on the anaerobic fermentation of cellulose and cellulosic materials. I n the digestion of pure cellulose the decomposition goes almost quantitatively to the two gaseous products, carbon dioxide and methane. However, in the fermentation of plant materials, as for instance cornstalks, the decomposition, so far a t least, has not been found to be complete. It is the purpose of this paper to report the analysis of this residue as well as to give the distribution of the different products formed in the digestion. ?;
Experimental Procedure
A 25-liter bottle was fitted up as a small digestion tank. It was arranged with tubes so that cornstalks could be added and withdrawn a t will without opening the tank to the air. -1 mercury-sealed inechanical stirrer served as a means of keeping the bottle contents mixed. To this bottle were added 50 grams of dry cornstalks and 22 liters of overflow liquor from a sewage-disposal plant. This liquor served as an inoculum as well as a suitable source of nitrogen for the bacteria. During the 90-day period of the experiment corn1 Received June 2, 1930. Presented before the Division of Cellulose Chemistry a t the 79th Meeting of the American Chemical Society, Atlanta, Ga., April 7 t o 11, 1930.
stalks were added from time to time and samples of the mother liquid were withdrawn and the volume made up by adding raw sewage. Samples of the cornstalks that settled to the bottom of the tank during the digestion were also withdrawn and composited with those remaining at the end of the experiment. An analysis was made of everything that was put into and taken out of the tank. Table I gives a summary of these data. Figure 1 shows graphically the amounts, as well as the days, on which cornstalks were added. At the end of the experiment the active cornstalks remaining in the tank were separated from the mother liquid by means of a screen filter. These stalks were then washed with distilled water, dried, composited with those drawn during the run, ground, and analyzed (Table 111). The mother liquor and the washings were also analyzed and the data recorded in Table I under the heading “Sludge and Soluble Solids.” Additional data as to the nature of these solids are given in Tables I V and V. A portion of the total solids was extracted with cold water and the water-insoluble sludge analyzed separately (Table V). It might be stated at this point that the ultimate analysis of this material throws little light upon its chemical nature. It possessed humus-like characteristics and probably would be called such by most investigators (8, 10).
