Apr., 1921
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
30 1
The Production of Artificially Dense Charcoal1 By L. F. Hawley SECTION OF
DZRIVED P R O D U C T S . FOREST PRODUCTS
Late in 1917 it was called t o t h e attention of t h e Forest Products Laboratory t h a t coconut shell for making gas-mask charcoal was becoming scarce a n d t h a t a dense charcoal manufactured from a plentiful domestic material would be desirable. T h e writer was acquainted with t h e process in which t h e distillation of briquetted hardwood sawdust was carried out under slight mechanical pressure for t h e purpose of preventing t h e briquets from falling t o pieces during t h e process, a n d i t was thought t h a t by both making and distilling t h e briquets a t much higher pressures an artificially dense charcoal could be produced. S M A I. L-S C A L E A P P A R AT U S
A small “homemade” apparatus was used t o t r y o u t this idea. The briquets were made in a mold 1 1 5 / l s in. in diameter a n d 6 in. deep. By packing t h e sawdust firmly into t h e mold by hand a n d then compressing i n a testing machine, a briquet about 1 in. thick, with a gravity of about 1.08, was produced. These briquets were distilled in a 2.5-in. iron pipe, 2.5 f t . long, held in a 4-in. pipe as a jacket. The outer pipe was heated by a row of Bunsen burners. T h e pressure was furnished by a screw threaded through t h e cap on t h e end of t h e outside pipe and a weight hung over a pulley wheel on t h e end of t h e screw-shaft. When t h e weight descended t o t h e floor, t h e cord was wound around t h e pulley again and in this way fairly constant pressure was maintained. T h e briquets were separated by thin plates of metal t o prevent them from sticking together. With low pressures during distillation t h e shrinkage in diameter of t h e briquet as t h e wood changed t o charcoal was very marked. When distilled under high pressures, however, there was frequently very little change in diameter, but t h e compression in thickness was very marked. It was soon found t h a t fine sawdust (under 20-mesh) was required for best results, a n d t h a t t h e briquetting pressures should be a t least 15 tons per sq. in. T h e pressures obtained on t h e briquets during distillation were difficult t o measure, since so much of t h e force of t h e descending weight was taken u p in friction. The figures mentioned hereafter in connection with this apparatus were computed with a n allowance for friction of one-half of t h e total force. Several species of wood were tried under varying conditions of pressure before and during distillation, a n d a charcoal with maximum apparent density2 of 0.57 was made from maple-wood sawdust briquetted at 50,000 lbs. per sq. in. a n d distilled under 300 lbs. per sq. in. T h e briquets had a density of about 1.10 when first made, but rapidly swelled until t h e density was about 1.09. Apparently there is a stage during t h e distillation when t h e wood or charcoal is slightly plasReceived December 3, 1920. density is an empirical figure showing the weight per cc. of the charcoal between 8- and 14-mesh which can be poured into a tube 113 cm long by 1.41 cm. in diameter under closely specified conditions, 1
* Apparent
L A B O R A T O R Y , >rADISON,
\vISCONSIX
tic and t h e application of t h e proper amount of pressure a t this time increases t h e density of t h e final charcoal. If too much pressure is applied t h e char coal is shattered without increasing t h e density of t h e granules. Not only a high apparent density was required but also a n absorption value after activation, which value, however, varied in general with t h e density of t h e charcoal. The absorption value for chloropicrin’ (designated “ C . P.”), under standard conditions expressed in minutes, was determined for this sample and found t o be 590 min., in comparison with 900 min. for coconut-shell charcoal activated a n d tested under similar conditions. Pine woods with natural rosin binders a n d hardwoods with binders of rosin, hardwood pitch, asphalt, etc., were found t o give higher gravity briquets and charcoal, but t h e C. P. of these charcoals after activation was in no case so high as t h a t obtained from wood briquetted without a binder.
RETORC FOR DISTILLATION OF nRlQUETS
UNDfSR
MECHANICAL PHSSSURE
pipe, B-collars t o hold pipe E in place; C-collar to increase E- 2.5411. pipe; F-bearing thread length through top oI cnp, D-screw; plate G-wheel f o r moving screw D . H-outlet t o condenser
A-4-in.
Further work on untreated woods with or without binders 1%-asstopped by t h e discovery of a material which was very much more promising. I t was found t h a t t h e insoluble residue obtained by hydrolyzing sawdust with dilute acid a n d leaching out t h e sugar2 gave a denser briquet, and a higher yield of a denser charcoal, and t h a t t h e charcoal was more absorbent after activation. The briquets made of 20-mesh dust under a pressure of 35,000 lbs. per sq. in. had a gravity when first made of about 1.21, but in a few hours they swelled t o about 1.18, after which there was very little more swelling. When distilled under a pressure of 300 lbs. per sq. in. (estimated) a t a final maximum temperature of 450’ C., these briquets gave a 40 per cent yield of charcoal with a n ,4.D. of 0.52 and a C. P. of 700. This charcoal resembled anthracite coal3 more t h a n ordinary charcoal; i t had a conchoidal fracture, was hard and shiny, and showed no trace of t h e structure of t h e wood from which i t was made. I n fact, thin pieces under t h e microscope were slightly translucent. SEMICOMMERCIAL A P P A R A T U S
These results were so promising t h a t further small1 THIS JOURNAL. 11 (1919), 519. * “Ethyl Alcohol from Wood Waste,” Met Chem. En# , 16 (1916). 78. T w o plants were producing about 400 tons per day of this material and using it for fuel. 3 I t is, therefore, unnecessary t o assume high pressures or long periods of time t o account for the natural formation of coal. Here is a cabe where a natural carbonaceous material is made into a product resembling coal in luster, density, and hardness with only moderate pressures and in a very short time
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scale work was considered unnecessary, a n d attempts were made t o confirm t h e results i n semicommercial apparatus. T h e Development Division of t h e Chemical Warfare Service finally offered t o construct a n d operate a larger apparatus, and t h e rest of t h e work was carried on a t t h e Defense Laboratory of t h a t Division. A retort 10 f t . long was constructed i n which 4-in. briquets could be distilled, while t h e pressures on t h e briquets could be automatically regulated a t any height desired. It was soon found t h a t t h e optimum pressures a s estimated from t h e results with t h e small apparatus were t o o high and t h a t only about 125 lbs. per sq. in. were required for t h e best results. It was also found t h a t , as might be expected, a much more careful regulation of conditions was required i n t h e larger apparatus t o obtain a satisfactory product. Even with t h e best regulation of t h e temperature t h a t could be obtained a portion of t h e charcoal was unsatisfactory i n density. T h e end surfaces of all t h e briquets next t o t h e plate were hard and dense, b u t t h e center portion of some of t h e m was porous and soft. Since i t seemed t h a t it was only t h e pressure conditions of t h e small-scale work which were not reproduced very closely i n t h e large-scale work (except those conditions due t o t h e size of t h e units), a n attempt was made t o reproduce t h e pressure conditions also. T h e pressure in t h e small-scale work was known t o have been very uneven, since t h e weight would often remain still for a time and t h e n drop several inches. This effect was simulated in t h e larger apparatus by adjusting t h e pressure-control apparatus so t h a t t h e pressure varied over a wide range, dropping from maximum t o minimum slowly and then rapidly running u p t o maximum again. With these pressure conditions i t was possible t o make a much better quality of charcoal. T h e best results were obtained with briquets made of medium-sized commercial hydrolyzed sawdust (between 4- and 43-mesh) , distilled slowly under pressures varying from 80 t o 130 lbs. per sq. in. It was not possible t o make this charcoal quite so hard and homogenous as t h a t made on a small scale with t h e 2-in. briquets, b u t a n A. D. of 0.58 on t h e untreated coal was obtained and a C. P. of 600. There are several possible reasons for t h e less satisfactory results shown by t h e large-scale work: 1-The actual size of the briquets may have been too large to allow a ready escape of the vapors from the center of the briquet to the surface, while at the same time the pressure was applied constantly enough t o get the full effect. This might be the cause of the porous centers of some of the charcoal briquets. 2-The raw material was coarser and not so completely cooked through. 3-There was no way to obtain high pressures in making the briquets, the maximum used being only about 20,000 lbs. per sq. in. &-No other study was made of special activation methods for this charcoal except comparative tests by the same activation methods as were used for coconut-shell charcoal. The wood charcoal having had a maximum temperature of only about 350' C., naturally contained much more volatile matter
Vol. 13, No. 4
than the coconut shell which had been distilled at 900' C., and this may have influenced the activation results. SUMMARY
On a small scale, a charcoal was made from native raw materials which had a n apparent density (A. D.) of 0.62 and a n absorption value for chloropicrin (C. P.) of 700 min., as compared with a standard coconut-shell charcoal value of A. D. 0.63 a n d C. P. 900. On a larger scale (commercial-sized unit) a n A. D. of 0.58 a n d C. P. of 600 were t h e best t h a t could be obtained after incomplete experimental work,
Food Research Institute At the suggestion of Herbert Hoover, a Food Research Institute for the study of all problems of production, distribution, and consumption is to be established at Leland Stanford Junior University, with an endowment of $700,000 provided by the Carnegie Corporation. Under the terms of the agreement, the university agrees to establish a research organization and to appoint three men of science, to be known as directors of the Institute, who will have authority to determine the scientific policies of the institute and the problems to be studied. The directors will head three separate divisions; one will be an expert in the field of physiology and chemistry of nutrition, one in economics and food distribution, and one in the Chemistry of food manufacture and agriculture. There will also be an advisory committee made up of men of national prominence (among them being Mr. Hoover), representing agricultural, consumer, economic, and other groups of the community. The university will appoint seven members, the president of the university and the president of the Carnegie Corporation serving ex-officio. It is the hope of the Carnegie Corporation that eventually the new organization will be known as the Hoover Institute. The institute may receive such specially qualified students as it may be possible to instruct without disadvantage to the primary research purposes of the organization. A small group of fellowships will be available for graduate students. The institute will begin its work July 1, 1921, the Carnegie fund being provided for a period of ten years. After the institute is once established, the Carnegie Corporation will abstain entirely from any direction or control of the work. Classification of Coal for Export A codperative agreement has been effected between the Tidewater Coal Exchange, Inc., of New York and the U. S. Bureau of Mines for the classification of coal shipped for export through the ports of New York, Philadelphia, and Baltimore on a basis of accurate sampling and analysis. The agreement provides for the establishment of limits and tolerances of quality for certain pools and for the maintenance of the quality of the pools within the limits specified. The Bureau of Mines will direct the work of obtaining the technical information required, collecting representative samples of coal as shipped and of mine samples when necessary and making analyses a t the Pittsburgh Experiment Station. The Tidewater Coal Exchange will make classifications on a basis of the analyses and will assign coal to pools within the limits and tolerances as finally published. The general purpose of this classification is to expedite transportation and shipment and to insure the maintenance of certain standards as representative of the quality of American coals shipped from various districts to Europe. The pooling of coals was resorted to in war time by a voluntary organization of coal operators and railroads, and in view of the great saving in the use of freight cars and maritime shipping it has been found desirable t o continue the arrangement.
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