T H E JOURLVAL O F I - V D l - S T R I A L A N D ELVGINEERING C H E M I S T R Y
3 78 Per cent of natural gas in mixture 4.4 4.0 3.2 2.0
Time of flame in cylinder Seconds
5 5 3 4
P e r cent COP in resultant mixture 1.0 1.0 0.6 0.3
ApproxiPer cent of m a t e cc. of COn from Con f r o m n a t u r a l gas flame gas burned burned 0.15 0.15 0.10 0.10
0.83 0.83 0.50 0.20
100 100 60 25
These results all show appreciable combustion around the flame. This combustion was in all cases greater than is shown by these results on account of the expansion of the gas and the dilution of the remaining gas with air upon contraction before the gas was sampled and analyzed. That partial combustion of such mixtures occurs is shown by the well known lengthening of a lamp flame in air containing fire damp. ANALYSIS O F RESULTS
The experiments here recorded show conclusively t h a t with a high initial ignition temperature a reaction may start in a gas mixture, which, as a whole, may be incombustible because the heat of combustion is not sufficient t o maintain t h e temperature a t t h e kindling point. Hence all of t h e mixture will not burn although t h e reaction may be sufficiently extensive as t o make the mixture appear t o be combustible or explosive. With the source of high temperature employed t o cause ignition acting for only a very brief interval of time, as during t h e fusion of platinum or iron wire, t h e resultant reaction quickly ceases but not until a combustion of gas has occurred, the heat of which is in some cases equivalent t o hundreds of time the energy required t o heat the platinum or iron fuse. T h e heat liberated b y t h e fusion of 0.75 cm. of N o . 34 platinum or iron wire is only a fraction of a calorie. I n a 7.7 per cent mixture of hydrogen this fuse, as has been shown, causes a combustion of 0.4 per cent of hydrogen i n a 30,000 cc. mixture or of 1 2 0 cc. of hydrogen. This liberates about 300 calories of heat. I n the smaller containers a greater percentage of t h e hydrogen was burned. For example, in t h e 1300 cc. cylinder as high as 2 per cent of hydrogen burned or only 2 6 cc. F r o m this i t would appear t h a t when t h e combustion is started from a source of very high temperature, more gas is burned in a large volume of mixture t h a n in a small volume, b u t t h a t t h e greater percentage of t h e gas is burned in t h e smaller mixture. This is a t least partially accounted for by t h e cooling of t h e gas b y the walls of t h e container, especially where small volumes are burned; b u t with large volumes of gas, as in t h e case of t h e two large cylinders holding 13,000 a n d 30,000 cc., respectively, this would be of little effect, a n d in a room full of gas the effect would be entirely negligible. With a continuous source of high temperature, as with a white hot wire, a lamp flame or a running electric spark, t h e reaction produced may be intermittent. The gas immediately around t h e point of ignition burns a n d expands, a n d combustion around t h a t point ceases until another portion of the mixture of gas a n d air has replaced t h e expanded gas a n d products of combustion, whereupon another reaction takes place resulting in a series of combustions or explosions. T h e limits of appreciable ignition or combustion of hydrogen a n d of natural gas in air v a r y with the volume of gas used, t h e source of ignition a n d the style
Vol. 6, NO. 5
of t h e container. I n a 2 0 0 0 cc. open cylinder t h e lower limit obtained for natural gas is about j . j per cent. With hydrogen t h e lower limit for very appreciable ignition was above 7 per cent. I n a closed container t h e lower limit for natural gas using 0.; cm. of No. 34 platinum wire heated white hot, was over j per cent. With a 0 . j cm. platinum or iron wire fused t h e lower limit obtained was 4.7 t o 4.8 per cent. With a j cm. No. 34 wire fused the lower limit obtained mas about 4.3 per cent. With a j cm. No. 36 t a n t a l u m wire fused t h e lower limit was a b o u t 4.3 per cent. With a 0 . 2 ; cm. spark from a n induction coil the lower limit of appreciable reaction was a b o u t 4.3 per cent. With closed containers, 6 t o 7 per cent mixtures of hydrogen a n d air gave vigorous reactions with 0.5 cm. platinum or iron wire fuses. With t h e electric spark, mixtures as low as j per cent gave very noticeable reactions, a n d faint reactions were obtained with mixtures as low as 4.3 t o 4.6 per cent. For t h e same percentage of gas a n d t h e same method of ignition, small volumes of gas gave more vigorous reactions t h a n large volumes, b u t in total amount of gas burned, the combustion obtained in large volumes was greater t h a n t h a t obtained in small volumes. With smaller containers, or with a more powerful spark, or a longer wire fuse, undoubtedly very appreciable reactions can be obtained with mixtures of lower percentages t h a n those given, b u t with ordinary sources of ignition, large volumes of gas will not react appreciably unless t h e mixture is richer in gas t h a n t h e lowest limits obtained in these experiments. However, t h e thermal calculations' based on 850' a n d 700' as the ignition temperature required for explosive mixtures of natural gas a n d of hydrogen with air indicate t h a t mixtures of natural gas in excess of 2 per cent a n d of hydrogen in excess of 5.9 per cent are potentially explosive if conditions favorable t o t h e readtion are present. Some of these conditions, in addition t o a vigorous source of ignition, are unusually high in initial temperature of t h e mixtures of gas a n d air, presence of fine combustible dust, a n d a n increase in t h e pressure of t h e mixture. T h e results of these experiments indicate t h a t a comparatively small excess of hydrogen above t h e theoretical requirement is necessary t o produce a vigorous reaction. Natural gas or methane, on t h e other hand, ignites with such difficulty t h a t , with ordinary methods of ignition, a n appreciable reaction does not occur unless a very large excess of gas is present above t h a t required by the thermal calculation. DEPARTMENT OF METALLURGY OHIOSTATE UXIVERSITY COLUMBUS
DISTILLATIONLUNDER
WOOD DIMINISHED PRESSURE A CONTRIBUTION TO THE PROBLEM OF UTILIZATION OF WOOD WASTE By MAXWELL ADAMSA N D CHARLESHILTON Received Dec. 27, 1913
T h e rapid decrease in the supply of long leaf pine available for t h e production of turpentine a n d t h e immense waste of resinous wood in t h e lumber indus1 THISJOURNAL,
6, 191.
May, 1913
T H E JOURLVVdL O F I N D C S T R I A L A N D E N G I W E E R I N G C H E M I S T R Y
t r y throughout t h e country has stimulated chemists in a n effort t o devise some practical method for t h e extraction of wood turpentiiie from stumps, lapwood a n d mill waste. According t o the Report of t h e Bureau of Chemistry’ there are more t h a n five million cords of waste wood left annually in t h e forests in t h e lumbering of resinous woods. The amount of waste is greatly increased when we a d d t o this the dead and fallen timber of t h e uncut forest. The methods for extracting turpentine from resinous wood, so far proposed, may be classed under four heads: I . Destructive distillation, with or without steam. 2 . Steam distillation. 3. Distillation with hot rosin. 4. Extraction with volatile solvents. These methods have all been tried out with varying degrees of success, b u t i t is somewhat doubtful if any of them have developed beyond t h e experimental stage. The commercial success of a n y method will depend largely upon t h e demand for t h e by-products, a n d t h e utilization of all parts of t h e wood. T h e steam distillation process in conjunction with t h e manufacture of paper pulp appears promising2 and t h e destructive distillation method has often been successful where charcoal, creosote a n d rosin oils are in demand. The method described i n this paper proposes t o improve t h e ordinary destructive distillation process b y controlling t h e temperature a n d diminishing t h e pressure a t which t h e distillation takes place, thereby avoiding superheating a n d a t t h e same time vaporizing t h e turpentine a t a temperature below which i t will not decompose. According t o Violette,s when wood is carefully heated t o I jo’ C. water only is distilled, a n d decomposition begins at about 160’ C. These results will probably vary with t h e kind of wood. I n order t o determine t h e effect of heat upon t h e variety of wood t o be used i n later experiments a sample of western yellow pine, Pinus p o n d e r o s a , was placed i n a flask immersed i n a sulfuric acid b a t h and heated very slowly. Care was taken t h a t t h e temperature of t h e b a t h did not exceed t h a t of t h e interior of t h e flask b y more t h a n five degrees. A t 94’ (the barometric pressure of t h e laboratory being 645 mm.) distillation of water a n d turpentine begins. When kept at 160’ C. for several hours t h e wood t u r n s brown, a n d above this temperature there is abundant evidence of decomposition. Gaseous decomposition begins when a temperature of 2 2 0 ’ C. is reached. hlthough pure turpentine distils at I j j-6”, yet when dry wood is heated only a small percentage of t h e turpentine present is driven off when decomposition begins. This is explained b y t h e fact t h a t ordinary pitch as i t occurs in wood is a solution of rosin and various waxes in turpentine; when a substance is dissolved in a liquid, t h e vapor pressure of t h e solvent is lowered a t all temperatures, and t h e solution must therefore be heated t o a higher temperature t h a n would be required for t h e pure solvent, before distillation begins. 1 2
3
Bull. 159. B u r . of Chem.. Bull. 159. Sadtler’s “Industrial Organic Chemistry,” p . 348.
379
T h e rosin is not volatile; as t h e turpentine distils a n d t h e solution grows more concentrated, t h e vapor pressure is lowered, and t h e boiling point is correspondingly raised, until t h e temperature of decomposition is reached, a n d a large part of t h e turpentine is destroyed before it is vaporized. The presence of water in the wood, however, adds a factor which partly counterbalances this, a n d lowers t h e boiling point
FIG. 1
of the turpentine in t h e mixture. According t o the law of Regnaultl for immiscible liquids, water and turpentine will distil a t the temperature at which t h e sum of their vapor pressures is greater than atmospheric pressure, neither influencing t h e vapor pressure of the other. T h e quantity of each liquid found in the distillate will be proportional t o their vapor densi1
Pogg A n n . . 93, 5 3 7 .
T H E J O U R N A L OF I N D l - S T R I A L A N D ENGINEERING C H E M I S T R Y
3 80
ties a n d can be calculated b y means of Avogadro’s law. A mixture of water a n d turpentine (the barometric pressure in t h e laboratory being 652 m m . ) boils a t
Vol. 6, NO. 5
If we consider the gram molecular volume a t 9 3 ’ as being
‘u-1
liters, a n d assume turpentine 273 t o consist of pinene with a molecular weight of 136,
in FIG.2
93 O C. Water a t this temperature has a vapor pressure of 588 mm. T h e remaining 64 mm. pressure must be due t o t h e turpentine. T h e vapor pressure of
FIG. 3
pure turpentine’ shows t h a t a mixture of it a n d water should boil a t about 91’ C. T h e slight solubility of each in t h e other doubtless lowers t h e vapor tension of both. 1
“Smithsonian Physical Tables,” p. 126.
then t h e mixed vapors will be found t o consist of 18 X j 8 8 136 x 64 = 1 6 . 2 parts of water vapor a n d 6j2 652 1 3 . 3 parts of turpentine vapor. The ratio of t h e weight of water t o turpentine in t h e vapor is approximately I O O t o 80, a n d this is also t h e ratio of their weights in t h e distillate. T h e density of turpentine is 0 . 8 5 , therefore the volume of water a n d t h e volume of turpentine are practically equal when t h e distillation takes place a t atmospheric pressure, b u t t h e proportion of turpentine in t h e distillate should be considerably increased when t h e distillation is carried on under diminished pressure, as is shown b y t h e examination of t h e vapor pressure curves in Fig. I. T h e vapor pressure of turpentine a t 30’ is 6 . 9 mm. a n d t h a t of water a t t h e same temperature is 31.5 m m . ; a total of 38.4 mm. B y applying the preceding method of calculation we find t h a t t h e mixed vapors 18 X 31.5_ -a t 30’ will consist of 1 4 . 7 parts of water 38.4 136 X 6 . 9 = 2 4 . 4 parts of turpentine vapor. vapor a n d 38.4 T h u s the amount of turpentine vaporized is practically double t h a t of the water, when the distillation takes place a t 38 m m . pressure. These results are confirmed b y experiment. When we apply t h e s t e a m distillation method t o t h e extraction of turpentine from wood, t h e proportion of turpentine is very much diminished, a n d t h e distillation temperature is considerably higher, due to the presence of dissolved resins, which have greatly diminished t h e vapor pressure of t h e turpentine. Experiments show t h a t , under t h e most favorable conditions, 1 5 parts of water remove I part of turpentine. The proportion of water, however, varies
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 CHEMISTRY
May, 1914
widely, depending upon t h e rate of distillation a n d t h e size of t h e wood chips. TAnLB
I Expt. No. 1 Press. normal
Expt. No. 2 Press. 35 mm.
c h _
Number of fraction
Temp. of oil b a t h OC.
'
A.. . . ., ,, , . . ,. B, . . .. . . . , . .
c
D
. ...., . , ., ...... .. ....
E. . . .. . .. ,. . . . F.. ....,.. , . , . , G.. ...., . .., ..
100-150 150- 190 190-200 200-220 220-270 270-300 300-330
Temp. of dist. flask OC. 40- 94 94-120 12&140 14G-160 160-180 180-200 200-220
Vol. tdrp. cc.
Vol. water cc.
Vol. turp. cc.
Vol. water cc.
0.0 5.3 4.3 1.4 1.8 2.3 3.1
0.0 4.2 3.2 0.6 1.6 4.0 6.1
i.2 2.8 2.5 1.1 2.1 4.6 6.4
3.1 2.2 1.9 1.5 3.0 3.2 4.1
By decreasing t h e pressure, according t o t h e preceding theoretical considerations, t h e amount of t h e turpentine produced a t a given temperature should be T A B L EI1 Expt. No. 3, press. normal Expt.
KO.4, press. 80 cm.
r
7
Vol. Dist. temp. OC.
Frac. A .. B , .
Up t o 220 220-2.50
crude turp. Cc.
Sp. gr. crude turp.
570 220
0.855 0.882
Vol. Vol. refined crude turp. turp. Cc. Cc. 501 176
920 320
VOl. Sp. gr. refined crude turp. turp. Cc.
0.887 0,934
722 182
considerably increased. Accordingly, a n ordinary distilling apparatus, with a capacity of about 2 0 0 grams of wood shavings, was fitted , u p a n d attached t o a T A B L E111
Variety of wood used Pinus Pinus Pinus Pinus Pinus
Monophylla., . Monophylla.. . Jefryii.. . . . . . . Jefryii. . . . . . , . Jefryii . . . . . . . .
Frac.
A B A B C
Temp. of distil. OC. Up t o 220 220-250 U p to 200 200-220 226250
Time of of distil. 1 hr 30 m, 1 hr. 1 a n d 3 hr 1 hr. 1 hr.
Vol. of ref. turp. obt. a t ord. press. cc. 180 108 100 95 80
Vol. of refined turp. obt. a t 80cm. press.
cc. 250 150 150 105 75
pump capable of maintaining t h e apparatus kt a pressure of 3 j mm. T o avoid superheating, t h e dist-illing flask was placed in a n oil bath. A sample of thoroughly dry, western yellow pine, fairly rich in pitch, was cut into chips, which would pass through
,381
represent t h e extremes of variation. Time being an important factor in determining t h e quantity of distillate obtained from wood, the temperature was raised 2 0 ' in approximately 30 minutes. Time and temperature t h u s being t h e same in both experiments. t h e variation in t h e amount of distillate secured in t h e different fractions must depend upon the pressure. The distillate coming over below 160°, t h e temperature a t which the decomposition of wood begins is 2 0 per cent greater under diminished pressure t h a n t h a t distilling a t ordinary pressure. The fractions coming over, both above and below 160', under diminished pressure are much lighter in color t h a n those distilling a t atmospheric pressure. When t h e temperature reaches z 2 0 O gaseous decomposition begins and diminished pressure can no longer be maint ained. I n order t o repeat t h e above experiments on a larger scale, a double-walled retort, capable of holding about 2 5 kilos of wood, and similar in form t o t h e one described by Pritchard' was constructed. The plan of t h e apparatus is shown in Fig. 2 . Oil is passed through copper coils heated in a gas flame. The hot oil is forced t o circulate through the outside jacket of t h e retort b y means of a small centrifugal pump. By this means t h e temperature is under complete control a n d superheating is avoided. The door, through which t h e retort is filled, is closed with a ground joint, a n d made air-tight by means of set screws. The vapors from t h e retort pass through a condenser into a receiver. which is connected with a Geryk vacuum pump, capable of maintaining t h e entire apparatus, when in operation, a t a pressure of 80 cm. The oil used t o conduct t h e heat t o t h e retort has a flash point of over 3 0 0 ' C. and is capable of withstanding a temperature of 400' C . without cracking, when heated in a closed yessel under pressure. T o test t h e efficiency of the method, a sample of western yellow pine was cut into pieces one foot long a n d about one inch in diameter, thoroughly dried, divided into three equal portions of 2 2 kilos each, and subjected t o t h e following treatment: I. ,Distilled in a retort b y direct heat, without any attempt a t temperature control or fractional separation of
T A B L EI V Temperature N o . of of retort fraction OC. -4. . . . . . . . . . 160-200 B . . . . . . . . . . . 200-240 c . . . . , . . . . . , 240-270 D . . , . . , . , . . . 270-280 E , . . . . . . . . . , 28G290 F . . . . . . . . . . 290-300 G . . . . . . . . . . . 300-360
.
Vol. in Sp. gr. cc. of pyro. of pyro. acid obtained acid 1275 1,002 560 1.013 1.041 885 675 1.053 1045 1.061 975 1.070 920 1 ,073
Per cent Per cent wood acetic alcohol acid in Vol. in cc. of Sp. gr. in pyro. acid pyro. acid t a r obtained of t a r 0.49 0.64 835 0.855 0.91 1.13 280 0.884 1.43 4.01 590 0.930 1.65 5.06 420 0.953 2 . 15 5.48 925 0.993 3.68 4.54 1000 1.025 2.67 2.65 960 1 032
a half inch mesh. The sample was thoroughly mixed a n d 1 7 j grams were used in each experiment, t h e results of which are given in Table I. On account of t h e difficulties of heat control there was some variation in t h e oil b a t h temperatures of Experiments I a n d 2 . The numbers in Column 2
PERC E N T TARDISTILLING Per cent pitch residue below between between 1800 c. 18Oo-24O0 240'-320' i n flask 83.5 2.1 9.6 3.0 27.2 62.5 5.0 4.2 31.1 14.6 12.8 39.6 35.8 16.9 19.2 25.2 44.i 12 5 16.3 13.9 61.4 12.2 14.3 10.1 65 3 11.2 7 4 13.8
t h e crude distillate. 11. Distilled in an retort under atmospheric pressure. 111. a n oil-jacketed retort under a pressure of Method No. I yielded 1606 cc. of t a r was extracted 4 2 4 cc. of a light brown, THISJ O U R S . 4 1 , , 4, 338.
Per cent water in t a r 1.8 2 1 1.9 2.9 2.8 2 0
2.3
oil-jacketed Distilled in 80 cm. from which ill smelling,
T H E J O U R N A L OF 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
382
Vol. 6, N o . 5
TABLE V Variety of wood used in the distillation
Vol. of Per cent pyroligneous wood acid alcohol in in liters pyro. acid
Sugar pine . . . . . . . . . . Yellow pine . . . . . . . . . Stump wood-pine.. . . Red fir . . . . . . . . . . . . . Silver fir . . . . . . . . . . . Millstates.. . . . . . . . . Sage b r u s h . . . . . . . . . .
9.8 12.4 10.9 11.1 10.1 9.6 9.4
0.52 0.55 0.57 0.48 0.51 0.61 3.54
Per cent acetic acid in pyro. acid
Vol. of tar in liters
2.6 2.2 2.4 1.8 2.1 2.7 11.53
1.26 2.09 3.50 1.78 1.23 1.81 1.94
wood turpentine, distilling below 1 7 0 ~ . The results obtained from Experiments 3 a n d 4 are given in Table 11. Sample A is almost colorless and easily purified by distillation, b u t Sample B contains impurities, which can be removed only by alternately washing with caustic soda a n d sulfuric acid a n d redistilling. Experiments 3 a n d 4 were repeated, using samples of other kinds of wood with results given in Table 111. From t h e above results it is evident t h a t t h e yield of turpentine under diminished pressure is from I O to 20 per cent higher t h a n t h a t obtained a t ordinary pressure, using t h e same method of heat control, while i t is double t h a t obtained by t h e common destructive distillation method. I n addition t o this the quality of t h e product is much improved. If, however, as shown b y a number of experiments in this laboratory, t h e wood used is green, a n d contains water in large excess of the volume of turpentine, then the process becomes one of steam distillation a n d the diminished pressure, while bringing t h e distillate over a t a lower temperature, produces no decided increase in the total yield of turpentine. I T h e samples of purified wood turpentine, obtained from each of these varieties of wood, is water white a n d looks like ordinary spirits of turpentine, but t h e y differ from it, a n d from each other, in odor and optical properties. They are under examination in this laboratory in a n effort t o identify the various terpenes present. When t h e temperature of t h e retort reaches 2 j o o , the volume of t h e gases given off is so great t h a t the pump is no longer efficient in reducing the pressure, a n d distillation under diminished pressure becomes impossible. I n order, however, t o determine the total amount and the properties of the different products obtained a t various temperatures from western yellow pine, 2 2 kilos of a sample of dry “light wood” were submitted to distillation in an oil-jacketed retort with results tabulated in Table IV. After the distillation there remained 7 . 8 kilos of charcoal. The time for the distillation of each fraction was one and a half hours a n d the temperature was raised a t almost uniform rate. There are many varieties of wood indigenous to the Pacific coast, concerning the distillation products of which there is no published data. Samples of a number of these varieties, as they occur in the lumber districts of the Sierra Nevada h/Iountains, were submitted t o destructive distillation. The results obtained are set down in Table V. The amount of wood used in each experiment was z j kilos, and the methods
i
Per cent turpentine oil in tar
Per cent creosote oil in tar
Per cent mixed heavy oil in tar
Per cent pitch in tar
Per cent water in tar
Kilos of charcoal
8.5 10.6 18.1 16.1 11.2 9.2
9.0 6.2 9.0 7.8 11.0 8.1 16.2
15 7 20.2 20.4 18.4 18.4 20.7 14.7
56.1 46.9 50.4 47.1 53.1 48.8 15.6
10.2 6.5 2.4 11.2 8.4 11.8 48.0
3.64 4.32 4.09 5.03 4.77 4.53 7.8
...
.
used in the examination of t h e distillate are those described in Allen’s “Commercial Organic Analysis.” SUMMARY
T h e above experiments show t h a t : I. T h e western conifers contain wood turpentine in commercial quantities. 11. Under favorable conditions a cord (4,000 lbs.) of yellow pine will yield 2 5 gallons of wood turpentine. 111. T h e yield of turpentine from a given sample of dry wood can be increased b y distilling under diminished pressure. CHEMICAL LABORATORY UNIVERSITY OF N E V A D A
REXO
THE NATURE OF BASIC LEAD CARBONATE B y EDWINEUSTON Received February 24, 1914
I n a n article’ “ O n the Composition of White Lead,” reasons were presented for t h e assertion t h a t white lead consists of a mixture of normal lead carbonate with a basic carbonate of lead of the composition PbC03.Pb(OH)*. The purpose of t h e present paper is t o consider the nature of t h e combination of the components of this basic carbonate of lead. The existing assumption in text books on pigments is t h a t , in basic carbonate of lead, t h e lead carbonate a n d t h e lead hydroxide are firmly united in actual chemical combination, but the results obtained in the experiments here t o be mentioned indicate rather t h a t the basic carbonate of ‘lead should be considered as among those substances described b y Zsigmondy* as mixtures of colloidal substances which can, under certain conditions, act as chemical compounds. (‘Not only3 have colloid compounds or colloidal mixtures, in which two colloids are united, been erroneously described as chemical compounds, but so also have mixtures or adsorption compounds of crystalloids with colloids.” The fact t h a t the lead hydroxide portion of basic lead carbonate is soluble in ammonium chloride solution but not in cane sugar solution, indicates t h a t the lead hydroxide is not present in mere mechanical mixture a n d yet is not so firmly held as t o be properly considered in chemical combination. Direct evidence t h a t the basic carbonate of lead is a n “adsorption compound” is afforded by the fact t h a t , in more t h a n fifty trials, various samples of white lead a n d of lead carbonate, when treated with basic lead acetate solution a t room temperature b y stirring or agitation, invariably withdrew lead hydroxide from t h e solution a n d correspond1 2 3
THISJOURNAL, March, 1914. “Colloids and the Ultramicroscope,” X. Y., 1909, p. 68. I b i d . , p . 69.
