Aug.. 191j
T H E J O L- R-V-4 L O F I S D 1-S T R I d L 24 S D E S G I i V E E RI1b-G C H E M I S T R I‘
satisfactory results in t h e h a n d s of a n u m b e r of analysts over a rather extended period of time. A new suggestion is offered, namely, t o determine separately t h e free sulfur a n d t h e sulfur remaining after t h e acetone extraction, reporting t h e s u m of t h e t w o quantities as t h e t o t a l sulfur. This procedure eliminates t h e troublesome effect of t h e free sulfur upon t h e determination of t h e t o t a l sulfur. T h e authors wish t o express their appreciation of t h e m a n y suggestions made b y Dr. C. E. Waters, of this Bureau, a n d of t h e assistance given b y t h e Voorhees R u b b e r Lffg. Co., of Jersey City, in permitting u s t o make u p some compounds of known composition i n their factory. B U R E A UO F STANDARDS. WASHINGTON. D.
c.
PRELIMINARY EXPERIMENTS ON THE EFFECT OF TEMPERATURE CONTROL ON THE YIELD OF PRODUCTS IN THE DESTRUCTIVE DISTILLATION OF HARDWOOD By R. C. PALMER] Received April 6, 1915
It is well known t h a t in t h e destructive distillation of wood t h e products methyl alcohol a n d acetic acid are formed b y a decomposition of t h e wood substance a n d t h a t t h e reaction is accompanied b y an evolution of heat. T h e heat supplied b y t h e exothermic character of t h e decomposition when added t o t h e h e a t furnished from some external source, t e n d s t o raise t h e t e m p e r a t u r e at which t h e reaction is t a k i n g place. Increasing t h e t e m p e r a t u r e of t h e wood beyond t h e point where spontaneous decomposition takes place will increase t h e speed or violence of t h e reaction, a n d this condition in t u r n will accelerate t h e r a t e at which t h e temperature is further increased. . There can be no d o u b t t h a t subjecting t h e methyl alcohol a n d acetic acid t o a n excessive temperature at t h e moment of formation m a y result either in a n immediate decomposition of some of these products or m a y prevent their formation from some intermediate products, a n d probably increases t h e tendency for m a n y secondary reactions t o t a k e place. Several facts would seem t o fully substantiate this viewpoint. T h e yield of alcohol a n d acid in t h e destructive distillation of wood is much less t h a n t h e proportion of methoxy a n d acetyl groupings would lead one t o expect. Small scale distillations, where t h e opportunity for secondary decomposition a n d interreactions are minimized b y better control. frequently yield much more acid or alcohol t h a n t h e usual commercial distillations. These f u n d a m e n t a l considerations indicate t h a t t h e speed a n d temperature of t h e destructive distillation reaction have a n i m p o r t a n t effect on t h e formation of alcohol a n d acid. It would seem t h e n t h a t t h e a m o u n t of these products could b e materially increased: I - - - B ~ causing t h e reaction t o t a k e place a t as low a temperature as possible. 2-By decreasing t h e speed of t h e reaction. These t w o methods m a y be in effect t h e same under certain circumstances, owing t o t h e exothermic n a t u r e Chemist in Forest Products, Forest P r o d u c t s L a b o r a t o r y , Madison, Wisconsin.
663
of t h e reaction, since low temperature distillation is a result of slowing down t h e reaction. T h e fact t h a t increasing t h e time of distillation will increase t h e yield of valuable products is generally known in commercial wood distillation practice. Lengthening t h e t i m e of t h e complete process simply means slowing down t h e entire decomposition. I n t h e s t u d y described in this paper, t h e application of t e m p e r a t u r e control t o t h e critical stage of t h e decomposition has shown t h a t a similar result m a y be obtained without increasing t h e time.’ E X P E R I M E S T A I.
I n making a large number of destructive distillations2 in laboratory a p p a r a t u s as a p a r t of studies on t h e relative value of different species of hardwoods. i t became apparent t h a t t h e temperature a t which t h e reaction took place a n d t h e critical stage h a d as much influence on t h e yield of products as t h e theoretical considerations would indicate. A more detailed laboratory s t u d y of t h i s interpretation of temperature control was therefore made. T h e basic principles developed were t h e n applied t o a commercial plant in order t o determine their practicability. T h e experiments were carried ~ on at t h e Forest Products L a b ~ r a t o r y , Madison, Wis.! a n d in t h e plant of t h e Cleveland Cliffs Chemical C o m p a n y , Gladstone, Mich., as a p a r t of a series of studies on methods of increasing t h e yields of valuable products in t h e destructive distillation of hardwoods. This opportunity is t a k e n t o acknowledge t h e assistance a n d m a n y helpful suggestions of Mr. H . C. Merriam, operating superintendent in t h e wood distillation plant of t h e Cleveland Cliffs Iron Company, in conducting t h e commercial experiment a n d interpreting a n d applying t h e results. P A R T I-LABORATORY
.
DISTILLATION
retort used in t h e laboratory studies is shown in Fig. I . This retort (A) held approximately 80 lbs. of wood. T h e oil jacket ( B ) completely surrounded t h e circumference of t h e ret o r t , t h e ends being insulated with heavy asbestos packing. T h e oil was heated b y means of a row of ’ 2 0 Bunsen burners, t h e flame playing largely on t h e side of t h e oil jacket, as in this way it was found t h a t a fairly good natural circulation of t h e h o t oil could be obtained. By means of t h e Bunsen burners t h e temperature of t h e heating medium was controlled fairly easily. T h e temperature within t h e retort was measured in three places: At ( I ) which is close t o t h e inner shell of t h e retort, directly above t h e point where t h e flames play on t h e oil j a c k e t ; t h e temperature a t this point was also approximately t h e highest temperature of t h e oil a t all times; a t ( 4 ) which is a point a t t h e b o t t o m APP.AR.ATTJS-T~~
1 Attention was first called t o t h e effect of “slow a n d fast” distillation on t h e yield oi products b y Sennit, b u t since t h e comparison was made between distillation i r o m t h e cold a n d distillation beginning with red h o t retorts, t h e results could n o t be interpreted t o actual practice. 2 A detailed description of methods of distilling t h e wood a n d analysis of products is given in United States D e p a r t m e n t of Agriculture. Bull. 129, “Yields from the Destructive Distillation of Certain Hardw.oods.” Maintained b y t h e Forest Service, U. S. D e p a r t m e n t of Agriculture. in codperation with t h e University of Wisconsin.
T H E JOCR,VAL O F I i V D l i S T R I A L A M D E,VGINEERING C H E M I S T R Y
664
of t h e retort near t h e inner shell corresponding t o ( I ) ; a n d a t ( 5 ) . t h e center of t h e retort. U S C O N T R O L L E D DISTILLATIOPi-The laboratory retort distillations were made in all cases on pieces of wood approximately 18 in. X 2 l / 2 in. X I i n . sawed from I in. lumber t o insure average material. The raw material consisted of maple, beech, a n d birch. The largest number of tests were made with maple a n d t h e best comparisons obtained with this species. T h e samples tested in comparative runs did not differ more t h a n 2 or 3 per cent in moisture content, and showed from 1 2 t o 1 5 per cent of t h e dry weight as moisture. For t h e purposes of studying t h e effect of control i t was necessary t o have for comparison distillations conducted rapidly a n d a t a comparatively high temperature. The manner of making t h e distillations was as follows: T h e burners were so regulated t h a t t h e maximum temperature of t h e oil was not higher t h a n 270' C. until t h e center of t h e retort reached a t least 1 7 j O C., a t which point i t was considered t h a t t h e moisture in t h e charge was largely distilled off. As soon as t h e center temperature was about 1 7 j ',
C
1701.
7 3 No. 8
tillate. I n t h e laboratory, where t h e temperature difference between t h e heating medium and t h e wood is negligible and t h e variation in temperature in different parts of t h e retort is not great, t h e critical p a r t of t h e distillation may be considered either as t h e period after t h e average temperature has reached 2 7 j ' or after t a r appears in t h e distillate. C O N T R O L L E D DISTILLATIOli-The control of t h e distillation, as interpreted in this study, required t h a t t h e largest possible portion of t h e reaction be completed at t h e lowest possible temperature, or, in other words, t h a t t h e rate of rise of temperature during t h e critical state of t h e reaction should be a t i t s minimum. The control distillations were conducted by regulating t h e burners so t h a t t h e heating medium was not higher t h a n t h e critical decomposition temperature ( 2 7 j t o 3 0 0 ' C.) until t h e temperature in t h e retort a n d t h e rate of flow of distillate indicated t h a t t h e reaction was being stopped. T h e center temperature indictaed a t ( j ) , (Fig. I ) usually passed 2 7 j ' C . a n d reached nearly 3 0 0 ' C. when t h e temperature in ( I ) began t o fall, indicating t h e checking of t h e reaction. The oil bath
d
\
OIL
p7/(-a
1 FIG. E EXPERIMENTAL LABORATORY RETORT
t h e gas was so regulated t h a t t h e oil was raised as quickly as possible t o about 3 j o o C.' a n d t h e distillation allowed t o proceed t o t h e end. T h e distillation practically stopped when t h e center reached its maxim u m temperature a n d began t o fall. I n all cases this maximum in t h e center was higher t h a n t h e temperature of t h e oil (indicated at ( I ) ) showing t h e exothermic character of t h e reaction. T h e exothermic reaction was further indicated b y a rise of.30 t o jo' C. in t h e center after t h e gas was turned off a n d t h e temperature a t ( I ) was falling. A distillation of this kind was comparable in many ways with t h e commercial method of distilling, especially in relation t o t h e rise in temperature during t h e critical p a r t of t h e distillation. T h e exothermic destructive distillation of hardwood begins a t approximately 2 7 5 ' C. a n d this point is indicated by t h e appearance of free t a r in t h e dis-
c.
The tem1 T h e oil used was a high flash cylinder oil, f . p 330° perature was raised above this point by keeping the oil under 15 t o 20 pounds pressure, the pressure being relieved only when the decomposition became excessive as indicated by a rapid rise in pressure.
was t h e n raised as quickly as possible t o 3 j o o C. a n d t h e distillation allowed t o finish. The crude pyroligneous acid liquor obtained in t h e distillations was analyzed for its acetic acid a n d alcohol content b y t h e methods given in "Technologie der Holzverholung," b y M. Klar, p. 3 3 j . RESULTS O F LABORATORY TESTS
The results of t h e laboratory tests are given in Table I. The d a t a are given ( I ) in terms of percentage of wood alcohol a n d acetic acid per unit weight of t h e oven-dry wood distilled a n d ( 2 ) as gallons of 9j per cent alcohol a n d lbs. of 80 per cent acetate of lime per cord of wood. One cord is taken as 80 cu. f t . of solid wood based on actual determination of a commercial cord which equaled 3 4 2 5 lbs. for maple wood containing I j per cent of its dry weight as moisture. From these d a t a t h e effect of controlling t h e distillation is seen t o increase t h e yield of alcohol 45 per cent for maple, 6 per cent for beech, a n d 7 per
Aug., 1 9 1 j
T H E JOLFRNA L O F I L V D C ' S T R I AL A
D E
GI LVE E R I N G C H E M I S T R Y
66 j
trolled distillations a n d curve B t h e average for t h e uncontrolled distillations obtained with maple wood. T h e t a r point has been indicated on each curve a n d t h e
a-The rate a t which t h e distillation has tBken place, indicated b y t h e per cent distillate per degree rise, is slower for A t h a n for B. T h e first 2 0 per cent of distillate after t h e t a r point in curve A came off during a rise in temperature of 2 2 ' while a t a corresponding period in curve B the rise was 3 3 ' . T h e uncontrolled runs given for maple were pushed as fast as possible in order t o give a reaction t h a t would determine t h e extreme effect of this procedure a s compared with especially controlled methods. A number of more normal uncontrolled distillations for this species gave 9 . 0 0 gal. of alcohol per cord a n d 2 j 3 Ibs. of acetate. T h e curve is not shown for these runs: i t lies very nearly between X a n d B b u t with a slope more like curve B. Similar curves for t h e distillations on beech a n d birch have not been shown, b u t these were found t o lie much closer together t h a n t h e curves for maple a n d have only slight differences in rate of distillation (upward slope of curve). It m a y , therefore, be considered t h a t t h e comparatively small increases in yields for these species are explained b y relatively less actual control of t h e distillation as compared t o t h e runs with maple. In t h e case of t h e maple runs t h e yields of alcohol obtained in t h e laboratory tests, particularly those obtained in t h e more normal uncontrolled distillations. are very nearly t h e same as yields from commercial
portion of t h e curve above t h e t a r point, principally t h a t nearest t o it. is considered t h e critical stage oi t h e distillation. F r o m curves X a n d B , it would appear t h a t two things might account for t h e marked increase in alcohol: I-The actual temperature a t which t h e reaction h a s t a k e n place in curve B is from 20 t o jo" C. lower t h a n curve B .
plants, b u t t h e yields of acetate are a b o u t 40 per cent higher t h a n commercial yields. It v d l be noted t h a t t h e small average increase in acetate in t h e controlled runs is due t o a n exceptional run while the yields from t h e other two are actually lower t h a n t w o of t h e u n controlled runs. Neither varying t h e temperature of t h e reaction within t h e limits of t h e laboratory test nor a change in t h e r a t e of distillation appears then
cent for birch, while t h e increase in acetic acid was 2, 9 , a n d j per cent, respectively. I S T E R P R E T A T I O X O F RESULTS-The curves designated X in Fig. 2 show t h e relation between t h e percentage of t o t a l distillate a n d t h e average t e m p e r a t u r e of t h e retort (ai-erage of t h e temperatures indicated a t ( I ) a n d ( j), Fig. I). Curve A is t h e average for t h e conTABLEI-RESTTLTSO F
LABORATORY COSTROL ON Y I E L D S OF
TESTSO N EFFECTO F
'rEMPERATURE
DISTILLATION PRODCCTS YIELDOF ACETIC ACID YIELDOF WOODALCOHOL L~ncontrolled Controlled Uncontrolled Controlled
MAPLE 1 . 5 6 Av.
1.59 1.62 1.59
BEECH 2.01 2.03 2.07 4v. 2.04 BIRCH 1 . 5 9 1.67 Av. 1.63
i.4 T.5 7.6 i.5(a)
2.16 2.36 2.41 2.31
10.2 11.15 11.25 10.90
5.29 5.74 5.91 5.65
240 267 275 261(b)
6.30 5.45 5.52 5.i6
290 251 256 266
9.2 9.28 9.45 9.31 6.95 i.32 i 15
2.15
9.80
5.70 5,i8 5.85 5.77
259 262 266 262 284 281 282
6.28
285
.. .
2.15
... ...
9.80
.
..
,.. . .
6.28 6.96 6.78 6.8;
285 301 7.6 6.58 1,73 1.76 i . i 6.50 292 1.75 7.65 6.54 296 ( a ) T h e average yield from a number of more normal uncontrolled laboratory distillations on maple was 9.00 gallons of alcohol a n d 253 pounds of acetate. ( b ) I n converting t h e acetic acid yields t o acetate of lime, t h e results have been decreased 5 per cent in order t o allow for t h e usual commercial sludge loss.
666
T H E J O U R N A L OF I N D C S T R I A L A N D ENGINEERING C H E M I S T R Y
t o b e t h e cause of t h e high acetate yield. However, it was known t h a t t h e temperature a t which t h e distillation reaction is carried out commercially is much higher t h a n i n t h e laboratory a n d a n application of this fact seemed t o be a possible method of approaching t h e laboratory yield. I n order t o t e s t t h e practical value of these results, i t was, of course, necessary next t o conduct distillations with a commercial retort. T h e commercial test was made ( I ) t o measure t h e yields of alcohol a n d acetate produced b y approaching t h e laboratory t e m perature during t h e critical stage, especially since t h e commercial acetate yield was so much lower t h a n t h e laboratory results; (2) t o determine if t h e increase in yield of alcohol produced by a control of t h e speed of t h e exothermic reaction could be duplicated on a large scale; a n d (3) t o determine t h e economic application of a n y results obtained. P A R T 11-COMMERCIAL
DISTILLATIOS
APPARATUS-A diagrammatic sketch of a commercial retort a n d setting similar t o t h e one used i n t h e test is shown in Fig. 3 . T h e retort held two cars,
FIG.3 - E X P E R I M E N T A L
each having a capacity of 2 l / 4 cords, or a total of 4 l j 2 cords of wood. T h e retort was fired a t t w o points on one side a n d t h e hot gases passed along t h e b o t t o m of t h e retort in opposite directions, u p t h e sides a n d ends beforepassing u p t h e stack. -4 a n d B were pyrometers placed in t h e t o p flue gases a n d t h e average temperature at these points was t a k e n as t h e average temperature of t h e heat being applied t o t h e retort. T h e pyrometer C was located in t h e center of t h e outlet pipe as close t o t h e retort as t h e outer brick casing would permit a n d its readings were assumed t o be t h e average temperature t o which t h e distillation vapors h a d been subjected i n t h e retort. T h e retort was fired with soft coal a n d a t certain periods with t h e uncondensable gases coming from some other retort. T h e experimental retort was one of a b a t t e r y of ten, five of which supplied fuel gas t o t h e other five during a b o u t 7 o u t of 2 4 hours. NANIPULATION-The experiments were made while t h e entire plant was in usual operation a n d in order t o determine t h e yields from t h e single retort t h e distillate was caught in so-gal. barrels. T h e distillate
Vol. 7 , No. 8
was thoroughly mixed in t h e barrels a n d samples of equal volume t a k e n from each. T h e mixed sample, therefore, represented a n average of t h e entire distillate. This sample was analyzed’ for alcohol a n d acetate b y commercial methods of determining t h e yields of products in this manner. T h e total amount of wood for each charge was weighed a n d t h e relative a m o u n t of each species determined a n d moisture samples taken. At t h e outset i t was of course evident t h a t t h e practical value of t h e t e s t depended on introducing no procedure t h a t would reduce t h e efficiency of operation. Since a n increase in t h e time of distilling seemed t h e most likely drawback, i t was decided t o v a r y t h e method of firing or change t h e manner of distillation only so as t o insure t h a t t h e r u n would be finished in t h e usual cycle of 24 hours. Without exception t h e retort was “ p u l l e d ” at t h e e n d of t h a t time. T h e raw material consisted of 93 per cent maple, 4 per cent birch, a n d 3 per cent beech, as a n average. It was in all cases 4-ft. cord wood ranging from 6 t o 8 in. in maximum diameter. F r o m 35 t o 4 j per cent
COMMERCIAL
RETORT
of t h e d r y weight of t h e wood w a s water, which was I O t o 20 per cent more moisture t h a n t h e average distillation wood contains. I n view of t h e necessity of adhering t o t h e 2 4 hour cycle, t h e high moisture content materially shortened t h e time available for temperature control. DIsTILLATIox-Observations of t h e temperatures produced b y t h e usual method of firing were first made a n d t h e yields determined for comparative purposes. With t h e apparent effect of t h e temperature of distillation as a n explanation of t h e high yields of acetate in t h e laboratory, experiments were first made in which t h e critical distillation point was brought as nearly as possible t o t h e laboratory temperature. I n t h e commercial test, where t h e heating medium is necessarily at a much higher temperature t h a n t h a t desired in t h e retort because of t h e large diameter t o be penetrated, t h e critical stage could not be observed, except b y t h e indication of t a r in t h e distillate. All distillations were, of course, made from a hot retort, 1
The methods of analysis were the same as those used in the labora-
tory tests.
Aug..
T H E J O C R S d L O F ISL)CSTRI.-1L . I S D E S G I S E E R I S G C H E M I S T R Y
1 9 1j
t h e previous charge being “pulled ” within t w o hours a t most after finishing. I t was a t once apparent t h a t t h e temperature was not t h e important factor since t h e laboratory yields were not approached I n attempting t o carry t h e distillation within t h e low temperature range of t h e laboratory retort, it was found t h a t t h e critical stage of t h e distillation proceeded very rapidly for a while, b u t h a d t o be pushed hard a t t h e end, in order t o complete t h e r u n in 24 hours. A series of runs was t h e n made in which t h e method of firing was varied in several ways, in order t o produce differences in t h e temperature a t which t h e exothermic reaction took place a n d also l h e r a t e of distillation during t h e critical state. RESULTS OF COXXERCIAL TESTS
T h e results of t h e different distillations on t h e commercial retort are given in Table 11. The different runs were not made consecutively, b u t have been divided into groups including similar tests. T h e results are given both in percentage of t h e unit weight of d r y wood a n d in t h e commercial units, gal. TABLE 11-RESULTS O F COMMERCIAL TESTS TO DETERMINETHE EFFECT OF TEMPERATURE COPTROLO N THE YIELDS OF DISTILLATIOXPRODUCTS Lbs. wood Der cord
4265* 4250 4120 4075 Av. 4160
Wood alcohol
Acetic acid
3025 3025 3010 2910 2982
41.0 40.6 36.9 40.0 39.2
1.70 8.2 1.99 9 . 5 6 2.01 9.63 2.09 9 . 6 i 2.03 9.62
3.75 4.05 3.92 4.03 4.03
187 201 194
2963 2970 3000 2963 29i5
36.5 37.2 44.4 36.9 38.75
2.06 9.73 2.0i 9.8 2 . 1 6 10.32 2.11 9.95 2.10 9.93
4.36 4.34 4 . 15 4.24 4.25
4175‘ 3000 4040 3025 4175 3000 3860(c) 2805 Av. 4130 3008
39.2 33.5 39.2 37.7 37.3
2.18 2.25 2.27 2.30 2.23
4.24 4.39 4.33 4.45 4.32
1
2
3
Av 4
4050* 40701’ 4325 4060 4125
10.42 10.78 10.80 10.27 10.66
Charcoal
194.5
36 4 34.2 35..5 34.7 34.8
53.5fdl 51.75 53.5 50 51.75
213 212 205 20i 209
36.5 37.6 37.2 36.0 36.9
54.25 54.75 .56.25 53.5
209 218 214 205 213.6
.37.8 34.4 37.4 34.7 .36.4
56.5 52 56 49 54.8
188
55.4
*
( u ) T h e moisture content of runs were n o t determined b u t were estimated from runs with corresponding weights per cord t h a t were determined. (0) T h e acetate included I 5 pounds per cord obtained from t h e settled t a r b y distillation. (c) T h i s r u n was not included in t h e average f o r this group a s t h e charge consisted of very badly decayed wood, also shown in t h e light weight per cord. T h e curves for this r u n were t h e same a s t h e average f o r t h e group. T h e yields in per cent of d r y v o o d are seen t o be t h e highest of a n y r u n b u t t h e light weight per cord brought down t h e yields on t h e cord basis. ( d ) Estimated from a number of commercial distillations.
of 9 j per cent wood alcohol a n d Ibs. of 80 per cent acetate of lime per cord. I S T E R P R E T A T I O S O F RESULTS-The results have been interpreted as in t h e laboratory tests by drawing t h e curve showing t h e relation between t h e percentage of total distillate a n d t h e temperature. These curves are shown in Fig. z for comparison with t h e laboratory tests. The curves are numbered t o correspond with t h e groups a n d are t h e average of all t h e runs in t h a t group. The curves designated Y show t h e relation between t h e distillate a n d t h e temperature of t h e vapors (indicated by t h e pyrometer C, Fig. 3) while t h e curves 2 show t h e relation between t h e distillate a n d t h e heat applied t o t h e retort (indicated b y t h e
66;
pyrometers d a n d B , Fig. 3 ) for t h e corresponding groups. The results for t h e different groups are summarized in Table 111. G R O V P I-This is t h e usual commercial method of firing a n d has been described as “fast drying-fast exothermic reaction.”’ The method of firing t o proTABLE111-SUMMARY
OF
EFFECTOF TBXPERATURE CONTROLO N
YIELDS OF PRODUCTS WOODALCOHOL
Laboratory uncontrolled, . . , Laboratorv controlled.. . . . . . Commercial Group I-Fast drying, fast exothermic.. , Commercial Group 2-Slom drying, fast exothermic.. , . Commercial Group 3-Faster drying, slower exothermic t h a n Group 2 . . . . , , , . , , , Commercial Group 4-Fast drying. slow e x o t h e r m i c . ,
ACETATZ
~
TAW
CHARCO~L
...
7.50 10 90
45
261 266
8 2
, ,
187
9.62
1 7 ,3
194.5
9.93
21.1
209
11.8
55.4
30
213.6
11.2
54.8
10.66
...
1 ,
4
53.5 51.75
duce this kind of distillation is clearly indicated in Fig. 2 , curve 21. The temperature of t h e retort is raised continually until t h e destructive distillation point is indicated by t h e flow of distillate a n d t h e appearance of t a r . The fire is t h e n held steady for a while a n d t h e n pushed a t t h e end t o “ m a k e charcoal.” I t should be noted especially t h a t curve Y I is very close t o t h e general slope of B-the uncontrolled laboratory distillation. G R O U P 2-In this group is shorrn t h e effect of bringas possible for ing t h e distillation temperature as IOTT as long a time as t h e cycle would allom. I n curve Y z it is seen t h a t t h e distillation reaction went very rapidly after t h e t a r point was indicated. These runs have been designated as “slow drying--fast exothermic.” I n all cases t h e rise in temperature is clue partly t o t h e exothermic heat a n d partly t o t h e esternal fire b u t in this group much of t h e rapid sloping off of t h e curve is due t o t h e exothermic reaction. I n distillations of this kind t h e b o t t o m of t h e retort became so hot t h a t in practice this procedure would be impractical for continuous operation because of excessive depreciation. Curve 2 2 shows t h e manner of firing. It should be pointed o u t t h a t t h e cold wood in t h e hot retort a t t h e s t a r t takes u p a large amount of heat a n d while t h e temperature of t h e fire was actually being lowered t h e normal quantity of fuel \vas consumed. Compared with Group I , t h e method of distillation showed a n appreciable increase in alcohol a n d acid. G R O C P 3-This group is really a modification of Group z a n d is, therefore, described as “faster dryingslower exothermic reaction t h a n Group 2 . ” This is clearly seen in curve Yg. Curve Z 3 shows t h a t t h e retort was fired b y allowing t h e temperature t o fall slightly during t h e first p a r t of t h e drying stage a n d then keeping t h e fire on a gradual rise until t h e last few hours when the temperature was increased more rapidly in order t o insure good charcoal. Most of t h e curves I‘ up t o t h e t a r point simply indicate t h e removal of moisture f r o m t h e charge. T h e moisture content of t h e different groups was a s follows: ( 1 ) . 41 per cent; (21, 39.2 per cent; (A), 38.75 per cent; (4), 37.3 per cent. These are close enough together t o make t h e curves entirely comparable. An analysis of t h e distillate u p t o t h e t a r point was made f o r one r u n i n G r o u p 3 and indicated 21.9 per cent of t h e total alcohol a n d 28.7 per cent of t h e total acetate obtained in t h e run.
-
T H E J O U R N A L O F I i V D C S T R I A L A N D EIVGIIVEERI-VG C H E M I S T R Y
668
A decided increase in yields over Group 2 is shown. I n t h e light of t h e laboratory curves, this increase must be attributed to t h e slower exothermic reaction rather t h a n t h e effect of temperature. G R O V P 4-The results obtained b y t h e method of distilling used for this group prove conclusively t h e importance of t h e r a t e of distillation on t h e yields of alcohol and acid, since the highest yields are obtained in these runs. As shown by t h e curves, these runs were made by “fast drying and slow exothermic reaction.” Referring t o curve 24, it is seen t h a t t h e drying period was accomplished by a rapid rise in temperature (or steady firing), a n d in this stage t h e distillation curve Y4 parallels curve Y I very closely. The important procedure in achieving this manner of distillation was t h e anticipation of t h e t a r point as indicated in t h e bending back of t h e 2 curve before t h e t a r appeared. I n practice, if t h e distillate can be observed as i t flows from t h e end of t h e condenser, t h e time t o lower t h e temperature of t h e fire would be noted b y t h e first appearance of particles of t a r , which precedes t h e t r u e t a r point b y from one t o two hours. When wood of a uniform moisture content was being used, this method might, however, be replaced by firing at a definite time period. A comparison of curve Y4 with curve A of t h e laboratory-controlled runs indicates t h e similarity of t h e slopes of these curves, especially after t h e t a r point. FuEL-The fuel required in t h e different groups is given in Table IV. TABLEIV-FUEL USED I N COMXERCIAL TESTPER CORDOF \VOOD DISTILLED
Group NO.
Coal Pounds
G a s Total fuel as coal Hours Pounds
Owing t o t h e variation in t h e length of time gas was used, t h e results. as actually measured, are not comparable. On t h e basis of one run made without gas, which required 412 Ibs. of coal per cord, compared with Group I , in which 240 lbs. of coal a n d I O (‘hrs.’’ of gas were used, I hr. of gas was taken as equivalent t o 1 5 lbs. of coal per cord. T h e n on calculating t h e (‘hrs.” of gas into coal for t h e different groups, t h e results are shown i n t h e last column of Table IV under “ t o t a l fuel as coal.’’ On this basis, Group 4, which gives t h e highest yields of alcohol a n d acetate, would require t h e equivalent of about j o lbs. more coal per cord. This would be practically negligible where waste wood was used as fuel, b u t with coal a t $ g . j o per t o n it would amount t o about I O cents per cord additional fuel cost. COMMERCIAL APPLICATIO?;
I n t h e commercial application of temperature control as developed in this preliminary study, a n accurate method of measuring temperature would be required, a n d probably for successful operation also t h e employment of a head fireman. Economically t h e balance is apparently drawn between t h e cost of installing pyrometers, t h e employ of a d a y a n d night
1’01. 7 , SO.8
head fireman for a t least each 5 0 cords per d a y distilled, a n d t h e additional small fue1,cost per cord, as compared with a possible increase in yield of 2 5 lbs. of acetate a n d 2 * / 2 gals. of alcohol per cord. Also t h e control distillations were shown t o be possible within t h e time required for t h e usual cycle of operation. CONCLUSIOSS
I t was shown in t h e small scale distillations t h a t a lowering of t h e temperature of t h e process a n d decreasing t h e speed with which i t took place gave marked increases in t h e yields of alcohol. Also t h e laboratory methods gave much higher yields of acetic acid t h a n those obtained commercially b u t this yield was not greatly affected by varying t h e laboratory methods. I t is now seen in applying these variations in methods of distiliing on a much larger scale t h a t a change in t h e r a t e of distillation produces practically t h e same results on t h e yield of alcohol while t h e actual temperature of t h e reaction is not shown t o be of as great importance. If i t could be shown t h a t t h e formation of alcohol in t h e destructive distillation reaction a n d its probable secbndary decomposition into methane a n d carbon monoxide in t h e presence of t h e hot charcoal is reversible, t h e increase in alcohol b y control of t h e reaction, allowing a n accumulation of t h e end products, would be easily explained. If t h e products after formation are lost by decomposition, t h e greater stability of alcohol after formation as compared t o acetic acid seems evident since t h e large retort which probably involves many interreactions gives practically t h e sa me yields of alcohol as t h e small apparatus while t h e acid yield is much less t h a n t h e laboratory yield. Any process of approaching t h e high laboratory production of acetic acid will probably have t o involve some method of preventing t h e interreactions in t h e large apparatus. It is not improbable t h a t still higher yields t h a n those given can be obtained in t h e commercial plant with t h e application of temperature control alone. Thoroughly air-seasoned wood would require appreciably less time t o enter into t h e destructive distillation stage, t h u s giving a better opportunity t o lengthen t h e period of slow reaction. The drying stage would also not require so high a temperature a t t h e end, t h u s bringing all b u t t h e last portion of t h e reaction into a lower range of temperature. These tests are considered as a preliminary indication of t h e results t h a t may be obtained from this interpretation of temperature control. The s t u d y of this phase is being continued by longer runs comprising a n entire plant. Other phases of directing t h e destructive distillation reaction of wood t o produce maximum yields of products are also being made by t h e United States Forest Products Laboratory. SUMMARY
I-Destructive distillations of hardwood in t h e laboratory on 70-lb. samples indicated t h a t lowering t h e temperature of t h e reaction a n d decreasing t h e speed of t h e distillation a t t h e critical stage increased t h e yield of methyl alcohol 45 per cent.
Aug., 191j
THE JO
R -V.-I L 0F I
D 1-S T RI d L A -VD E -VGI S E E RI S G C H E V I S T R Y
11-The laboratory distillations gave 4 0 per 'cent more acetate of lime t h a n commercial yields, b u t t h e acetic acid was not greatly influenced b y variations in t h e method of distilling. 111-The application of t h e laboratory methods t o a commercial retort holding 4','2 cords of wood indicated possible yields of alcohol 3 0 per cent higher t h a n b y t h e usual methods of firing a n d a n increase of I j per cent in yields of acetate of lime. IY-The best results were obtained b y slow distillation during t h e critical stage rather t h a n b y lowering t h e temperature at which t h e reaction took place. This was accomplished b y rapidly removing t h e moisture content of t h e wood in t h e first stages, a n d t h e n anticipating t h e period when destructive distillation or critical stage began. At this point t h e temperature of t h e fire was decreased. \.'--This method of temperature control gave promise of being entirely applicable in t h e commercial plant. T h e fuel requirements were only slightly higher t h a n t h e usual methods of firing a n d t h e cycle of operation was not changed. . VI-The studies of temperature control have shown t h a t wood alcohol either eshibits sufficient stability in t h e retort or its formation is of a simple enough character t o allow it t o be easily effected a n d t h e a m o u n t recovered greatly increased. Acetic acid, however, is apparently much more subject t o variations in t h e original n-ood decomposition a n d methods of preventing t h e m a n y interreactions going on in t h e complex vapors of a large retort will be required t o secure yields of this product t h a t will more nearly approach t h e theoretically possible yields. FIJREST PRODUCTS IABORATORY, MADISOS, W~scows~s
THE DETERMINATION OF BENZOL IN GAS MIXTURES B y G. A . BURRELLA N D I. 1%'. ROBERTSON Received April 29. 1915
With t h e present great demand for benzol a n d t h e installation of plants a t different places for obtaining t h i s constituent. there has arisen a demand for a rapid method of determining the benzol content of gas mixtures. Hence a scheme follows which t h e authors have used in determining i t in t h e carbureted mixed coal a n d n-ater gas of Pittsburgh. Fig. I illustrates t h e apparatus. T h e bulb contains phosphorus pentoside for removing water vapor. T o s t a r t a determination t h e apparatus is connected t o a vacuum p u m p a n d exhausted of its air: a Gerky pumli will do. The gas mixture is then introduced a t atmospheric. pressure. t h e barometer read. a n d t h e t w o bulbs immersed in a mixture? of solid carbon dioxide a n d acetone or alcohol. After waiting about I O .minutes. as much gas as possible is withdrawn from t h e bulbs b y means of t h e vacuum p u m p . T h e gases removed will be those of high vapor pressure a t -:So C. In t h e case of t h e mixed coal a n d water gas t h e authors worked with. t h e y are C o n , 02,CO, HS, CH4, Nn. CzH,. CzH6, C3H8, C3Hs a n d C4Hs; in fact, Published with the permission of the Director of the Bureau of Mines. This mixture gives a temperature of about - i s 0 C . The solid carbon dioxide. obtained b y releasing the gas from a commercial cylinder, through a cloth towel, is mixed with acetone or alcohol to the consistency of slush.
669
practically all t h e gases except t h e benzol. S e x t t h e stopcock on t h e apparatus is closed, t h e cooling mixt u r e removed. a n d t h e benzol allowed t o vaporize at room temperature. I t s pressure is t h e n read on TABLEI-BENZOL DETERMINATION I N P I T T S B U R G H GAS 7 SAMPLE No. 1 i 4 4 mm. i 4 4 mm. Original pressure of g a s . . . , , . , . , , , 10 mm. 9 mm. Partial pressure oi benzol v a p o r . . . . , loo - 1.34 q X "0 = 1.31 __ P E R C E S T A G E OF B E N Z O L . . . . . . . , . , . . 744 744
t h e side-arm mercury manometer attached t o t h e apparatus. This pressure compared with t h e atmospheric pressure gives t h e percentage of benzol in t h e gas mixture. T h e results of t w o determinations are shown in Table I . T o obtain other d a t a on this method of separation, the distillate from t h e above freezing process was next passed into fuming sulfuric acid. I n t h e case of Sample No. I there was obtained 7 . 3 2 per cent of illuminants, a n d in t h e case of Sample No. 2 . j.39 per cent. T h e total illuminants in t h e Pittsburgh gas. as found by absorption in fuming sulfuric acid. is 8 . 6 7 per cent. In other words, t h e benzol percentages as found when added t o 7 . 3 2 a n d 7.39! respectively, equal 8 . 6 6 a n d 8,.j o per cent, or almost identicaily t h e same quantities as t h e total illuminants in t h e coal gas. Benzene reacts with oxygen as follo\Ts: CeHs 7 . j0, = 6COz 3Hz0. The contraction is 2 . j volumes a n d t h e carbon dioside is 6 volumes. Table I1 shows t h e results of analysis of t h e residual vapor t h a t was held in t h e liquefaction bulb (Fig. I ) when t h e coal gas was cooled a t a temperature of -78' C. Before analysis t h e benzol was diluted with air.
+
+
TABLEII--AKALYSIS
OF B E N Z O L
VAPOR CC
volume taken for analysis.. . , , , . . . , . , , , , , Oxygen added . .. .. .. . .. . .. Total v o l u m e . . . . . . . . . . . . . . , . . . . . . . . , . . l'olume after burning . . . . . . . . . . . . . . . . . . . , . Contraction due to burning . . . . . . . . . . . . . . Volume after KOH absorption., , , . . . . . , , . , , , Carbon dioxide produced b y burning.. , . . . , , . . , ,
.. ,
.. . , . .,
28.29 51 Y I
E?
?i 47
i.>,
4.i6 64.2.5 1 I .47
I t will be observed t h a t t h e ratio of t h e carbon dioxide t o t h e contraction is almost esactly 6 : 2 . j , showing t h a t t h e vapor obtained in t h e benzol deTraces of other termination was principally benzol. easily condensible \-apors m a y have been present b u t apparently in such small quantities as to be negligible. The authors n-ere unable t o find, in t h e literature, t h e vapor pressure of benzol a t -78" C., b u t apparently it is x-ery small. Benzol boils a t 8 0 . I Z O C.: at --zoo t h e vapor pressure is j . 76 m m . ' The a u t h o r s prepared saturated x-apors of benzol b y shaking t h e pure liquid with air. It was a simple matter t o pre1
Landolt and Bornstein Tables, 1906, p. 143; according t o Regnault.
