1'IlE J O Z I R N A L O F I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
924
0.00s
0.01
Fzc. I-SPOIS M ~ o sw i m
TI
o.in
0.0s
(Pencarrrrces GIVIINl brown with black centers
CKZOSOTE A N D LIMPBLACY
Reduced a little oyer one-hrif.
,
Color-Light
...
water Gas Tar Wafer EIardwoodiTar CrraSOie Gas Tar Creosote (Drown and Black) (Dark Brown) (Dark Gray) FTG.II-SPOTS oi- V n n r ~ i i sOILS Usnu FOR WOOD PRESERYINZ Reduced r little "vex one-hail. Colors a* noted
Crude Oil Paramn Base (Pale Gray)
while a n asphaltic base crude oil shows B browner center. No. 4 shows the characteristic dead gray-black of creosote made from hardwood tar. No. 5 is the even dark brown spot of a typical water gas tar: this tar is often used in creosote tar mixtures a t thc present time. No. 6 is the spot of B coal tar with the heavy carbon in the center and the small difliision of the pitchy mass. Thc spots even in Fig. 11 represent only the typical Spots of the various oils used for wood-preserving purposes. In actoal practice, these oils are used in more or less admixture nith each other and a large number of spots can be obtained grading from one of these types t o another. The admixture of tar can be determined roirghly from the size (smaller) and the general character of the spot. The heavy tar does not diffuse with the speed of the lighter cremate oils. CONCLUSIONS
I-The premce or dirt and free carbon in creosote oil is indicated in very minute quantities by this test. 11-If the creosote spot shows a dense black center it will probably be necessar) to run a free carbon analysis to determine if the creosotc passes the free carbon specification. IJI-.-Thc various types of wood-preserving oils can be easily distinguished from each other by this test when they are t N e type samples. IV-In the large number of intermcdiate or mixed commercial oils, the value of this preliminary test will depend on the experience of the one applying it together with the possession of a large number of authentic samples far comparison. On applying this test to a number of oils compounded from known authentic samples it was possible to tell the constituents with a reasonable degree of accuracy. Fuassr PXROD~ICPS Lnaoanronv MADISON.
Val. 7 , No.
Wrscolisnr
ISOPRENE FROM P-PINENE By A . W, SCXOYCCX AND R . SIYRX
Thc discovery during the latter half of the past ccntury of a close relation between isoprene, the terpenes, and caoutchouc has naturally directed considerable attention toward the utilization of the terpenes as a sourcc of isoprene. This relation may be .represented by the following reversible reactions:
(
Coal Tar Dark Brown and Black
CHI
CHa
CH8
C
C
C
I
CH C /\, HzC CHa Dipentcne f 2-Isoprene
I
I
C
E,/>",
I
NC/ I
CHJ (Dimethyl-r,s-Ocladiene-i,5)r
(Caautchauc) It was to be expected that attempts would first be made to utilize a-pinene as a raw material, since, in the form of turpentine, it can be snore easily and cheaply obtained than any of the other terpenes. The results of former experimcnts clearly indirate, however, that only comparatively low yields are possible from turpentine. Tilden,' by passing turpentine through a rcd-hot tube, obtained about 20 cc. of isopienc from a liter of turpentine. By means of his isoprene lamp, HarriesZ obtained about I per cent of isoprenc from commercial pinene and attributed even this small amount to the presence of dipentene in the turpentine employed. IIerty and Graham3 obtained 5.5 per cent (by volume) of isoprene from tltrpentine and 8.0 per cent from 8 iractioti boiling hctwcen 1j5 and 1 5 6 ~ . Thew authors are of the opinion that the isoprene obtainrd from turpentine is not due to dipentene present iii the turpentine as asserted hy Harries, an opinion that we believe is fully justified. Apparently the only trrpenr yielding considerable amounts of isoprene is limonene (dipentene). Harries2 obtained 30 to 50 per e i i t of isopreiic. from comrnercinl limonene while Herty and Graham obtained IZ per ccnt from a limonene fraction. Staudinger and Klevrr' found that by working a t a pressure of about 4 mm., a yield of bo per cent or rrccptionally pure isoprene could be obtaiued from limonene. According to patents held by Schciing and Company,6 con> Chen. N r w r , 46 (18821, 220. 3 Ann.. 383 (19111, 228-9. 3 Tats J o o n ~ ~ 6 r(1914). , 803~4. aer.. 44 (1911). 2212. I ~ e r m n n~ a t e n t260,934; K . stcplmn, IT. s. patent 1,057.68n ( 1 9 1 3 ) (Assixnor to Schering 8- Co.).
'
Nov., 1915
T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
siderably larger yields of isoprene can be obtained from 8-pinene than from a-pinene. As has been previously shown by one of US,^ the oil from the oleoresin of western yellow pine (Pinus ponderosa, Laws.) consists mainly of 8-pinene with small amounts of a-pinene and limonene. Large stands of this species are available for tapping purposes on the Pacific Coast and to our knowledge offers the only cheap source of 8-pinene. Since no data was available on the yields of isoprene to be obtained from 8-pinene, it was determined to investigate this point. The above oil would be additionally promising, owing t o the presence of limonene. It mas found, however, that a-pinene and P-pinene gave approximately the same yield of isoprene when both terpenes were passed through the same apparatus for the purpose of direct comparison, EXPERIMESTAL
The isoprene lamp of Harries2 offers a convenient means of “cracking” terpenes in the laboratory. After considerable experimentation to avoid certain mechanical disadvantages a modified form of apparatus of the type shown in the accompanying Fig. I, A , was employed. The heating coil consisted of a platinum wire ~ j cm. o long wound in the form of a spiral through two parallel rows of holes in the edges of a strip of “transite,” a heatresisting, i n s u l a t i n g material, coniposed of asbestos and cement; the temperature of the wire was regulated by means of a sliding rheostat, the best results being obtained a t a low red heat. The vapors after passing the coil entered the Hopkins condenser where the less volatile portions were condensed and returned to the 8 boiling flask through the trap as indicated. The vapors p a s s i n g through the Hopkins condenser, passed in turn through a second condenser fed with cold water, then through a spiral glass tube surrounded by a freezing mixture of salt and ice, and finally into a receiving flask likewise surrounded by a freezing mixture. FIG.I The turpentine employed was obtained by rectifying ordinary gum turpentine. The /!-pinene employed was obtained by repeated fractionation of the oil of western yellow pine. A t first the boiling was continued until the contents of the flask had completely polymerized, but it was found that practically no isoprene was formed after the first three or four hours. Although great pains were taken to secure complete condensation, it was evident t h a t some of the isoprene escaped with the
7iF
1 2
Schorger, Bull. 119, U. S. Forest Service (1913). A n n . , 383 (1911), 228-9.
925
non-condensable gaseous decomposition products. Immediately after the completion of a run the distillate was fractioned by means of a 12-inch Hempel column, filled with glass beads, and the fraction boiling between 3 j - 3 7 O considered as isoprene. To what extent the crude isoprene was possibly contaminated with trimethylethylene was not determined. The results of some typical runs are given in Table I. TABLEI
Yield of PER CEKTOB ORIGINALisoprene Weight Time Total %.by h-o. ORIGIXALMATERIAL Grams hrs. Residue distillate Loss weight 1 T u r p e n t i n e , , , , , . . , , , , , . 400 6 31.2 35.1 33.2 8.1 2 Turpentine , , . . . . . , . , , , . 283 5.5 46.i 35.3 18.0 10.3 3 8-Pinene (b. p. 162-165O) 300 6 40.0 37.4 22.6 9.4
The production of isoprene in the experiments described above would appear to be due largely to the catalytic effect of the platinum, since a nichrome wire was found to act in a n entirely different manner. I n order to use a long wire in a compact space a nichrome wire was stretched back and forth between perforated disks of transite fastened on a glass rod Fig. I, B. Owing to the great elongation on heating, the wires sagged, thereby causing short circuits. This difficulty was successfully overcome by attaching a section of strong steel door spring to the lower disk to take up the slack in the manner illustrated. When the terpene vapors came in contact with the nichrome wire, heated to the same intensity as the platinum wire, thick deposits of carbon were formed immediately. The wires were short-circuited so quickly by the masses of carbon deposited that i t was impossible to continue the experiment beyond this point. Several experiments were performed by passing the terpene vapors through an iron tube filled with pumice stone and heated in a combustion furnace. With a n apparatus of this type it is difficult to return the unchanged terpenes to the boiling flask. Owing also to the difficulty of temperature control, the terpenes in some cases passed through largely unchanged while in others considerable amounts of tar and members of the naphthalene series were formed from too high temperatures. The results are accordingly not comparable with those obtained with the isoprene lamp. The small yields of isoprene obtained by Tilden were probably due to the small positive catalytic effect of the iron tube. To obtain the desired catalytic effect platinum black was deposited in the pores of the pumice by reduction of potassium chlorplatinate. It was found advisable t o boil the liquid very gently and maintain the tube as nearly as possible a t a barely visible red heat. Some of the results obtained with the tube method are given in Table I1 (no platinum black was deposited in the I). pumice used in Experiment 1-0. TABLEI1
Yield of isoprene PER CENT OF ORIGINAL %,by 10 Residue Distillate Loss weight 1 Turpentine. . . , . . . , , . . , , , . , , 6 . 7 S5.6 7.7 3.5 2 Turpentine . . , . . , , , , , , , . , , , 6 . 0 14.2 19.8 8.0 3 @-Pinene(b. p . 163-166’1.. , , . 3 . 6 64.2 32.2 9.6
..
It will be noted that the yields of isoprene obtained from turpentine are considerably higher than those obtained by Herty and Graham. This may be due t o the employment of a larger catalytic surface in our experiments. COKCLVSIONS
The results obtained show that turpentine and P-pinene under the same conditions yield about the same amount of isoprene, approximately I O per cent. The isoprene obtained from turpentine is certainly not due to the cracking of dipentene or limonene originally present in the turpentine; but the opinion is advanced that the isoprene results indirectly from dipentene. It is a well-known fact that a-pinene can be converted into dipentene by heat; the condition
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
