926
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
obtaining in the apparatus would be favorable to such a transformation. The changes may be represented thus: PINENE DIPENTENE--f ISOPRENE Since the first reaction would probably not proceed to a great extent under the conditions of the experiment the yield of isoprene would necessarily be low. It is not probable that either a-pinene or @-pinene can be made to yield directly sufficient isoprene for the commercial production of rubber. However, since good yields of isoprene are possible from dipentene, an attempt to obtain an approximately quantitative conversion of pinene into dipentene is worthy ol further consideration. ,
*
FOREST PRODUCTS LABORATORY MADISOX, WISCONSIX
THE DISTILLATlON OF DOUGLAS FIR AT HIGH TEMPERATURES By BAILEYTREMPER
Inasmuch as the cost of manufacturing illuminating gas from coal and oil is gradually increasing in the small plants, the possible substitution of wood as the raw material is of interest. This is especially the case in sections of this country such as the Pacific Northwest, where thousands of cords of mill waste are destroyed in mill incinerators. For several years an experimental gas plant using sawmill waste has been in operation in this state, and recently several plants have been, or are being, constructed for commercial operation. It is the purpose of this paper to present some of the results obtained in one of these plants, located a t Auburn, Washington. The plant is patterned closely after standard coal-gas installations. Benches of four 9-ft. clay retorts are used. These are connected in turn to a hydraulic main, condenser, exhauster, and dry scrubbers; thence through the station meter to the holder. The big stumbling block in wood-gas manufacture has been the accumulation of tar in the pipes, especially near the offtake. This has been overcome by waterjacketing the standpipes from mouthpiece to bridge pipe. Special design of the mouthpieces provides for drainage of the condensed liquor. Particles of tar and pitch are readily removed by the action of the thin liquor resulting from the condensation of portions of the gas. Trouble from stoppage further on is also minimized. The wood for gas making is bought in 4-ft. lengths. It is tied into bundles of such size that two may be placed side by side in the retort, each retort requiring four bundles. The bench is maintained a t 1400 to 1600" F. Theexhauster is regulated so that there is neither vacuum nor pressure on the retorts. The time of carbonization is one hour and forty to fifty minutes. Both the quantity and the quality of the gas vary with the grade and variety of the wood used. In commercial practice Douglas fir only is used but trial runs were made with red cedar and Western hemlock. Forest wood cut from live trees, seasoned three months, fairly resinous, and weighing 3700 lbs. per cord, an average of the butt of a tree, produced zj,ooo cu. ft. of gas per cord of 128 cu. ft.; 19,000 cu. ft. of this gas had an average heating value of 538 B. t. u. per cu. ft. as determined with a Junkers calorimeter. The average of the entire run was 482 B. t . u. per cu. ft. The maximum heating value during the run was 560 B. t. u. Bark alone from this wood gave 17,000 cu. ft. per cord, averaging 494 B. t. u., with a maximum of 567 B. t. u. From unselected mill waste, thoroughly air-dried, weighing 3300 lbs. per cord, 18,000 cu. f t . of gas were obtained as the average yield per cord during two months' operation. The average heating value of the gas is 470 to 480 B. t. u. I n each run a maximum heating value of about 515 B. t. u. is attained when the run is one-third over. From hemlock mill waste, very wet, and weighing 4000 Ibs. per cord a yield of from 1g.000 to 17,000 cu. f t . of gas with an
Vol. 7,
KO.I I
average calorific value of 414 B. t. u. was obtained. Cedar gave the same yield with a heating value of 460 B. t. u. A typical analysis of the gas as determined with the Morehead apparatus is as follows:
.
.
Carbon dioxide ( C o d . . . . . . . . , . . . , . . . . . . , Illuniinants. Oxygen (02) Carbon monoxide ((20). . . . . . . . . . . . . , . . . . . . Methane (CH4). . . . . . . . . . . , , , . . . , , , . , , , , Hydrogen ( H d . . . . . . . . . . . . . . . , .'. , . . , . . . . . , Nitrogen ( N d . . . . . . . . . . . . , , . , . . , , . . . , , , , , ,
.
.
Per cent 17.4 6.0 0.0 31.5 21.7 18.3
5.1
The calculated heating value of the gas is 500 B. t . u. and the Calorimeter test of the same sample was 509 B. t. u. It will be seen from this analysis that the gas resembles more or less closely carbureted water gas in composition, and it is of value to consider the reactions in the retort in this light. Wood charged into the hot retort soon acquires a coating of charcoal. Water vapor driven out from the wood comes in contact with the hot carbon and is decomposed. Inasmuch as the initial temperature is comparatively low, the layer of charcoal thin, and steam greatly in excess, the formation of carbon dioxide is favored. The resinous and oil-forming portions of the wood, on vaporization, are apparently cracked and partially converted into permanent gases, thus forming the enriching constituents. It has been observed that during the first part of a run there is considerable cooling of the retorts due to evaporation of moisture. During the latter part of the run, the exothermic character of the reaction brings the retorts to their former temperature. Temperatures below 1300OF. do not give as good results as outlined, while, from somewhat incomplete data, it appears that temperatures above 1800' cause the breaking down of the richer constituents of the gas. For bark alone, however, a higher temperature seems suitable, as the gas contains a very high percentage of carbon dioxide when formed a t medium temperatures. Attempts have been made to reduce the high content of carbon dioxide in the gas, which under poor conditions of operation has reached 2 2 per cent. The formation of carbon dioxide is decreased with increase of temperature, but the sample containing 17.4 per cent was generated a t as high a temperature as is practicable in the ordinary bench. It was thought that the carbon dioxide might be reduced by drawing the gas through beds of charcoal in the front part of the retort. The results showed, however, that decomposition of water vapor, under conditions favoring the formation of carbon dioxide, took place to such a n extent that there was no reduction in its amount. In other words, the gas was diluted with a rather poor water gas. The nitrogen content of the gas is due to bench gas working into the retort through small cracks. The more or less porous new retorts do not become coated with carbon as is the case in coal-gas manufacture. This demonstrates the need of extreme care in heating the benches so that the formation of even the finest cracks may be avoided as much as possible. A bench of four 9-ft. retorts will hold a charge of one-fourth cord. Twelve charges can be made in twenty-four hours, giving a gas output of 60,000 cu. ft., or 15,000 cu. f t . per retort, an amount somewhat in excess of coal-gas practice. The by-products of wood-gas manufacture are chiefly tar and charcoal. Wood alcohol, acetic acid, acetone, and part of the tar are largely decomposed under the temperature of distillation, Analysis of the aqueous distillate shows 1.0 to 2.5 per cent acetic acid, 0.2 per cent xood alcohol and acetone, and less than I per cent soluble tar. The yield of tar varies from 14 to 2 2 gallons per cord according to the quality of the wood, the temperature of distillation, and the pressure on the retorts. The tar is much more easily recovered than when produced by low temperature distillation, and settles out in eight hours, carrying less than 5 per cent
Nov.,
1915
T H E J0UR;VAL OF I N D C S T R I A L A N D ENGINEERING C H E M I S T R Y
water. On redistillation it yields 1.5 per cent wood spirits, boiling below 100' C. and 2.j per cent light oils boiling below 560' C. It is completely dehydrated a t I j o o C. This tar sells readily in local markets for I 2 . j cents per gallon. By employing a lower temperature the yield of by-products is increased. n'hile a lower heating value of the gas results, it would still be useful for industrial purposes. Charcoal is obtained a t the rate of 7 0 0 to 800 lbs. per cord, for which a good market does not a t present exist in the S o r t h west. Its quality is impaired by the presence of charcoal from bark, but as the latter is a good producer of gas, it is not feasible to remove it from the sawmill waste. The amount of charcoal obtained is ample to furnish fuel for open-fired benches and with regenerative furnaces an excess would be produced. This excess quantity or the entire amount can be used in water-gas manufacture, as demonstrated by trial runs made in a g-shell Lowe water-gas set a t the plant of the Tacoma Gas Company. The charcoal held its heat so that 3-minute periods of run and blast could- be maintained. The same amount of oil was used as with coke. A yield of 1000 cu. ft. of carbureted gas was obtained from each 25 lbs. of charcoal as opposed to 40 lbs. of coke. The clinker formed was practically negligible and did not show signs of fusion with the generator lining. Whereas one hour out of every eight is generally required for clinkering coke, shaking grates would probably eliminate clinkering entirely, with charcoal. The use of the latter would therefore result in the production of more gas, with a saving in labor and periods of shut-down, as well as increase the life of the furnace. Very little dust was blown into the carburetor and all of it could probably be eliminated by baffles. Kiln-drying of wood to remove the considerable amount of water still held after air-drying would doubtless still further increase the heating value of the gas and the capacity of the retorts, as well as decrease the fuel required. SUMMARY
I-From Douglas fir forest wood, 25,000 cu. f t . of gas with a calorific value of 482 B. t. u. is obtained per cord of 37000 lbs.; 19,000 feet of this gas has a heating value of 538 B. t. u. 2-From Douglas fir mill waste 18,000 cu. f t . of gas with a calorific value of 475 B. t . u. is obtained per cord of 33000 lbs. 3-Enough tar is obtained to pay for the cost of wood a t the plant. 4-The exothermic character of the reaction favors low fuel consumption. j-Water gas can be produced satisfactorily from charcoal a t the rate of 1000 cu. it. per 25 lbs. of charcoal. 6-Wood gas and charcoal are especially available for metallurgical operations a t mines located far from fuel supplies other than wood.
927
ligneous acid by means of a continuously operated electric furnace, containing a catalyzer, which converts the acid directly into acetone without necessitating the intermediate production of the acetate. The raw material consisted of pyroligneous acid obtained by the destructive distillation of Douglas fir mill waste a t the halfcord wood distillation plant designed by the author,' and erected cooperatively by the University of lvashington and the U. s.Forest Service. Before treatment, the pyroligneous acid was distilled in order to separate and recover the turpentine, oils, tar, alcohol, acetone, etc., since i t was thought that these substances might have an injurious effect on the catalyzer and since these byproducts are necessarily separated and recovered in commercial practice, up to the point where the re-distil'ed acid is neutralized with milk of lime for the manufacture of the gray acetate. At this stage, the present practice is to mix the pyroligneous acid with the lime in large tanks until the neutralization is complete, as shown by the color change. The principal acid constituent of pyroligneous acid is acetic acid. 2CHsCOOH
+ Ca(0H)Z --+
(CH&00)2Ca
+
2H20
It is then evaporated to a pasty consistency, dried, and shipped away as "gray acetate of lime" to the acetone plant, where it is destructively distilled in steel retorts, breaking down into acetone and calcium carbonate. .....................
CHsCO . . . 0\
:
-
Fa
CH3 COO
..................
CH3 \cO CH3/
+ CaC03.
The acetone is condensed, washed and refined in column distillation apparatus. APPARATUS
The apparatus used for these experiments is shown in the accompanying illustration. Its operation is as follows : The pyroligneous acid is introduced into the reservoir A and allowed to drop slowly into the round bottom flask B regulated by means of the cock C. The acid in the flask is heated by a carefully regulated burner B , which is so controlled as to cause the liquid to evaporate a t the same speed with which it is dropping into the flask. The acid vapors pass through the tube E into the electric furnace V, which consists of a quartz tube G, surrounded by insulating material J , containing the electric heating element. The interior of the quartz tube is filled with the
AUBURNGAS COMPANY AUEURN,WASHIKGTON
T H E PRODUCTION OF ACETONE FROM PYROLIGNEOUS ACID' By MARC DARRIN
The purppse of the work reported in this paper is to show the yield of acetone that can be obtained from pyro1 REFERENCES-U. S. P a t . (1910). 933,107: Formation of acetone from zinc, barium and magnesium carbonates a t 575' C. l'haum. Z t g . , 54 (1910), 880: Formation of acetone by passing over base heated a t a high temperature a t 300-350 mm. pressure. German P a t . (1910). 214,151. Addition t o patent 198,852: Manufacture under reduced pressure. Ber., 43 (1911). 2821: Acetone a n d ketone formed t o extent of 10% when passed through pumice heated t o 500-600°. Brit. P a t . (1907). 13,263: Generation of acetone. Ger. P a t . (1908). 198,853: Generation of acetone under reduced pressure. Fr. P a t . (1908). Addition t o 6,531 to 361,379: Generation of acetone under reduced pressure.
lip FIG. ACETONE APPARATUS
catalyzer H , and i t is in this region that the conversion takes place. The entrance and exit connections to the heated quartz tube are made by asbestos stoppers, F F. The vapors leaving 1
For design of plant, see THISJOURNAL, 5, 935.
