thermometer i n t o t h e N ORDER to study charge, and a packed beare f f e c t i v e l y the deing, C, to admit the shaft structive distillation of the stirrer, D, which consisted of a two-bladed proof a g r i c u l t u r a l wastes peller-like scraper designed in continuous-feed comto move on the bottom of m e r c i a l - s i z e retorts, it the pot and agitate the was found necessary to charge continuously. A 0.25-horsepower motor, E , have preliminary informawas geared t o operate the tion regarding the influscraper at a speed of slightly ence of distillation temmore than 4 revolutions per peratures on the yields of minute. Vapor outlet A consisted of a half-inch the v a r i o u s p r o d u c t s . (1.3-cm.) brass pipe nipple Previous work (1, 2, 3, 6, surmounted by a brass re6, 8) in this field had not ducing tee with a short included a detailed analyq u a r t e r -inch brass pipe ni ple in the side opening sis of temperature effects; w&ch had a thermometer therefore, it seemed in the top t o record the advisable to make such vapor temperatures. The a study in a small, easily side nipple was connected t o a straight-tube glass concontrolled a p p a r a t u s . denser, F , connected in turn C o r n e o b s , midway bet o a 5-inch (12.7-cm.) tween the light fibrous U-tube vapor trap, G, with materials, such as straws, a gas outlet tube mounted on the condenser side of the and the dense granular T. R. MCELHINNEY, B. M. BECKER, trap. The condensable materials, such as nutAND P. BURKE JACOBS vapors were thus used t o shells, were selected as maintain a seal on the sysU. S. Agricultural By-products Laboratory, suitable material for the tem so that the noncondenIowa State College, Ames, Iowa sable vapors were diverted study. A s m a l l - s c a l e through a 500-ml. scrubbing d i s t i l l a t i o n apparatus flask, H , containing about was constructed in which 1inch of distilled water, and the rate of heating could were then collected over a saturated salt solution in the two bell jars, I and I]. The retort was be easily controlled, the temperature of the distilling material heated electrically by resistance coils surrounding the pot beneath held uniform throughout the mass, and all the products coma 2-inch (5-cm.) la er of asbestos insulation. A rheostat in series pletely recovered. with the heating ecments allowed accurate temperature control.
I
Destructive
Distillation of Corncobs
Effect of Temperature on Yields of Products
Apparatus and Procedure
*
The corncobs used in the various runs were ground and screened to pass a half-inch screen and be retained on a The retort (Figure 1) consisted of a flat-bottomed circular quarter-inch screen, and were ovendried for 15 hours at bronze pot 3.75 inches (9.5 cm.) deep and 9.25 inches (23.5 cm.) in diameter with walls 0.25 inch (6.4 mm.) thick. A flange on 221' F. (105" C.). One pound (454 grams) of the dried the upper edge of the ot was machined to fit a bronze lid which material constituted a charge. After the material had been was provided with a sgeet asbestos ring gasket and held in place sealed in the retort and the stirring started, heat was applied with C-clamps as shown in the drawing. The lid was provided so as to raise the temperature of the charge a t the uniform with a vapor outlet, A , an opening, B, to permit insertion of a rate of about 6" F. (3.3' C.) per minute; this rate of heating had been selected as slow enough to prevent too rapid evolution of gas, with consequent excessive pressure, and fast enough to permit comDestructive distillation of farm wastes has been often pletion of the distillation within a reasonsuggested as one method of commercial utilization. This able time. The same heating curve was followed in each successive run as nearly report characterizes the exothermic reaction which takes as possible. Since the rate of distillation place after the exothermic point is reached for the destrucwas known to influence yields (8), it was tive distillation of corncobs, points out the optimum temdesirable to eliminate this variable. The perature for running this reaction, as applied to this partemperature was gradually raised until ticular material, shows the volumes of gases evolved when a predetermined distillation temperature the reaction temperature is kept at several different points, had been reached. This temperature was maintained until the evolution of and shows the varying composition of these gases and gas had practically ceased, a t which the amounts of other primary products obtained in the time the distillation was considered to destructive distillation of corncobs. These scientific facts be complete. The condenser was then must first be determined by any investigator before he washed with d i s t i l l e d water. This enters into a study of the amount of secondary products water, together with the water from the scrubber, was added to the distillate. recoverable and certainly before an economic evaluation The total distillate was placed in a of destructive distillation as a method for the commercial s t o p p e r e d g r a d u a t e d cylinder and utilization of agricultural wastes can be made. The results allowed to stand in a refrigerator until reported here apply generally to similar agricultural wastes. the insoluble tar had settled out. Then the v o l u m e s of liquor and tar were recorded. The liquor was analyzed for 697
INDUSTRIAL AND ENGINEERING CHEMISTRY
698
VOL. 30, NO. 6
hundred milliliters of the distillate were collected and diluted to 500 ml. in a volumetric flask. This sample was then tested for acetone by the Messinger method ( 7 ) . METHANOL was determined by the method of Zeisel (10). FORMIC ACID was determined by oxidizing it to carbon dioxide by means of mercuric acetate and absorbing the carbon dioxide in a standard solution of barium hydroxide (9). GASES. The scrubbed gases were collected and measured in graduated bell jars over a saturated salt solution. As each jar became full, the gas flow was diverted to the other, and a sample of the gas in the full jar was taken in an ordinary glass gas-sampling pipet. The sample was then analyzed in a standard Fisher gas analyzer. Carbon dioxide, carbon monoxide, illuminants, methane, hydrogen, and oxygen were determined directly: nitrogen - was determined bv difference. VOLATILE MATTERIN CHARCOAL.One gram of charcoal, ground to pass 100 mesh, was heated over a low flame in a closed platinum crucible for 3 minutes. The loss in weight was reported as the volatile matter.
FIGURE 1. DESTRUCTIVE DISTILLATION APPARATUS
acetic acid, acetone, formic acid, methanol, soluble tar, and settled tar. During the course of the run, samples of noncondensable gas from each full calibrated bell jar (approximate capacity, 0.5 cubic foot, or 14.2 liters) were taken for analysis. After each run the retort was allowed to cool before being opened (with air excluded) and the charcoal residue was then taken out, weighed, and tested for volatile matter. A total of ten runs was made, nine of which were used in determining total yields of the various products a t the selected distillation temperature. The tenth run was made after the data from previous runs had been tabulated, for the purpose of watching the changes in the evolved gases during a period of constantly increasing temperature.
Analytical Methods
"
SETTLEDTAR. After the crude distillate had stood for a day or two in a glass-stoppered graduated cylinder in the refrigerator, the volume of settled tar was recorded. The apparent specific gravity of the tar was determined by weighing a small measured volume of the tar, and the percentage yield was computed. SOLUBLETAR. A 100-ml. sample of the clear pyroligneous liquor decanted from the settled tar was distilled from a tared 500-ml. flask in an oil bath. Temperature was main9@ tained a t 140" C . When about 80 ml. of dis8W tillate had been collected, steam was turned into the flqk, and the distillation (at constant volume) continued until a total of 400 ml. of Fm distillate had been collected. The steam was $so then disconnected and distillation continued until the temperature of the liquid inside the Em flask had reached 140" C. The flask was 200 cleaned of oil and weighed with its contents. /PO The residue represented the soluble tar in the 0 0 20 sample. TOTAL ACID. A portion of the distillate from the soluble tar determination was titrated
I
~~
40
60
/YO
80 /W /PO TME/N M~NUTES
/60
/W
200
220 2 p
FIGURE 2. HEATING RATESIS VARIOUS RUNS
TABLEI. EFFECTOF DISTILLATION TEMPERATURE ON YIBLDOF PRODUCTS Run Distn. temp.,
A
F.
Charcoal % of raw material Volatile Aatter in charcoal, % Volatile-free charcoal % of raw material Total (noncondensabie) gas, cu. ft./lb. cobs Heat value of gas:Q Total B. t. u. B.,t. u.,/cu. ft. Acetic acid, yo of raw material Acetone, % ' of raw material Methanol, yo of raw material Formic acid, Toof raw material Settled tar, % of raw material Sol. tar, Yo of raw material a Computed on nitrogen-free basis.
392
68.0 57.9 28.65 0.93
B 430 50.9 40.1 30.5 1.43
107.3 197.3 149 173 4.25 5.38 0.083 0.114 0.14 0.49 0.1685 0.143
.....
1.99
.....
1.15
C 536 40.7 26.2 30.08 2.09
D 556 39.4 24.6 29.78 2.12
E 673 34.4 15.6 29.00 2.35
F 752 32.1 9.1 29.18 2.62
G 813
30.8 6.2 28.88 2.83
271 259.4 472.6 497.3 620 152 211 141 213 245 6.13 6.38 6.60 6.51 6.58 0.266 0.270 0.375 0.352 0.390 0.87 0.76 0.81 0.85 0.57 0.329 0.352 0.325 0.304 0.347 3.27 3.77 6.30 6.54 5.04 3.62 3.29 5.13 4.35 3.52
H 824
I 1000
30.7 6.1 28.88 2.88
29.2 4.6 27.9 2.97
653 256 6.42 0.355 0.56 0.624 6.30 4.21
835 307 6.84 0.240 0.33 0.312 6.54 5.84
INDUSTRIAL AND ENGINEERING CHEMISTRY
JUNE, 1938 70 60
50
40 30
8 20 7
6 5
7 4
S 6 -4
$
5
f
4
4 4
3 2
41
0.9 I
$ne o
$
0.7
0.6 0.5
0.4 0.3 0.2 0./ 0.0
FIGURE 3. VARIATIONOF PRODUCTS WITH DISTILLATION TEMPERATURE
699
was carried out below the exothermic point (approximately 414" F. or 212" C.) but above this temperature a distillation could be completed in a few hours. The yields of products, except charcoal, increase almost proportionately with the temperature of distillation up to about 700" F. (371" C , ) ,but a t higher temperatures the yields do not all follow the same trend. This is particularly noticeable in the case of the gaseous products. Figure 3 shows graphically the effect of temperature on certain of the condensable products and the charcoal. Generally, the optimum distillation temperature for best yields of these products from corncobs is approximately 750" F. (399" C,). CHARCOAL.Table I and Figure 3 show that there is a rapid decrease in the yield of charcoal as distillation temperatures approach 650' F. (287.8" C.). From 560" to 800" F. (287.8" to 426.7" C.) the decrease in yield is much less rapid; from this point on, it is almost negligible. VOLATILE MATTERIN CHARCOAL.This constituent varies inversely with the temperature a t which the charcoal is produced, up to 800" F.; higher temperatures reduce the volatile matter very little. ACETICACID. The acid yield increases fairly rapidly between 392" and 556" F. (200" and 291.1" C.), remains almost constant between 556" and 813" F. (291.1" and 433.9" C,), and increases slowly again as the temperature approaches 1000" F. (537.8" C.). The final increase is possibly due to a secondary reaction a t these temperatures. ACETONE follows the same general trend as acetic acid until 700" F. (371.1" C.) is reached. Further increase of temperature decreases the yield of acetone. METHANOL.The yield of methanol increases rapidly to a maximum a t 536" F. (280" C.), remains fairly constant between 536" and 752" F. (280" and 400" C.), and decreases sharply above this temperature. SOLUBLE TAR. Although the method used for determination of soluble tar is standard (4),it is subject to errors due to traces of moisture left in the flask, presence of dissolved salts, etc. S o t much dependence can be placed upon these results since they fluctuate widely. The results do show a definitely increasing yield. It is believed that the sharp increase a t the
Results 60 Figure 2 shows the similarity of the heating curves for the various runs. The slope is practically uniform to a point so near the predetermined distillation temperature. Table I presents the summarized results 30 from all the runs. The effect of temperature on the yield of various constituents is shown. The charcoal from the lower tempera2 20 ? ture runs, particularly that from run A , was brownish in color and retained the /O physical form of the original corncob par0 ticle. This charcoal was very difficult to q00 450 &W 523 64U 6% itW 7m ~3%850 4 , /a grind because it still possessed much of the ~ m m r M E 2= original toughness of the cob. Somewhere IN GASPRODUCTION AND COMPOSITION DURING RUN FIGURE 4. CHANCE between 390" and 430" F. (198.9" and 221.1 O C.) the distillation temperature reaches the exothermic point and a spontaneous evolution of higher temperatures may indicate a condensation of methano1 gases occurs. The exact thermal decomposition point was and acetone, perhaps with combination with carbon from the not determined because of the time lag of the apparatus. charcoal, as indicated by the decrease in yield of the first two Charcoals from runs made above the exothermic point were named. black and brittle, becoming increasingly easy to grind as the SETTLED TAR. The yield of settled tar seems to vary distillation temperatures increased; in some of the higher directly with the temperature of distillation to 750" F. temperature runs the charcoals were considerably broken up (398.9" C.) and from that point is almost constant. The by the action of the stirring mechanism alone. apparent specific gravity of this tar was found to be 1.135, and A long period was required to complete a distillation if it it did not vary significantly with the temperature of distillation.
8 4
700
INDUSTRIAL AND ENGINEERING CHEMISTRY
GASES. The curvea of Figure 4 were derived from data compiled in Table 11; they were derived by averaging all analyses of the respective fixed volumes (bell jars) of gas secured from each of the runs, at and between the temperatures indicated in the left-hand column. These temperatures are the approximate points a t which unit volumes (bell jars) of gas were accumulated; the variation above or below these
VOL. 30, NO. 6
rises through the exothermic point, with carbon dioxide reaching a maximum a t 474" F. (245.6" C . ) and carbon monoxide, at 514" F. (267.8" C.). Above these temperatures the percentages of both constituents decrease rapidly. The yield of methane above 500" F. (260" C.) increases rapidly. Hydrogen increases slowly to 800" F. (426.7" C.) and increases rapidly thereafter. Nitrogen decreases rapidly, since it is present only as air a t the start of the run and is soon expelled with the evolved gases. The percentage of illupinants was so OF GAS AS TABLE 11. CHANGEIN VOLUMEAND COMPOSITION low that they were omitted from the graph. TEMPERATURE RISESDURING DISTILLATION The curve showing gas evolution per 20" F. , C 0118ti tuent Rate of Qas Evolution, (11" C.) indicates a slow evolution of gas up to Temp. COz CO Hz CHI CnHzn 01 Nz per 20' F." F. % % % % % % % cu. ft. 414" F. (212.2' C.);from this point the curve 414 42.0 14.5 7.0 2.3 0.5 2 . 2 31.5 0.0212 rises very steeply until 515" F. (268.3" C.) is 6.8 0.1520 4.0 1.5 1.0 0 5 474 60.0 26.0 reached, after which it falls off as rapidly as 3.5 0.2120 5.0 2.8 1.5 0.5 514 56.0 31.5 611 54.5 25.0 5.3 41.2 9.5 3.7 4.1 0.5 1.0 0.0761 it rose. This is taken as further evidence that 3.3 0.0672 9.8 14.5 0.6 814 26.9 1000 13.9 5.3 21.6 52.8 3.6 0.5 1.9 0.0300 414" F. is the approximate exothermic temVolume of gas evolved per 20° F. temperature rise at this temperature range. perature for the destructive distillation of corncobs. The volumes of gas from the series of runs are plotted in Figure 5 against the retemperatures was due to slight fluctuations of the respective spective temperatures a t which they were produced to show heating curves. Such unit volumes (bell jars) of gas, evolved that the total volume of gas is increasingly larger with from a series of runs having similar ascending heating curves, higher temperatures of distillation. However, heating above 900" F. (482.2" C.) does not markedly increase the are reasonably comparative. Analyses of gas samples taken after the point when the heat curve of a given run deviated volume, from the common heating curve were omitted in the calculaThe calculated B. t. u.values of the gases (Figure 5 ) from tion or are separately stated. It is apparent that the mxt-ber the various runs are also plotted against the respective temperatures of production to show that gas evolved from a of values making UP the averages in Table 11 and Figure 4 decrease in number with increasing temperatures, and that high-temperature distillation has a higher heat value than are not averages but that of the lower temperature runs, owing to the higher the values given for 1000" F. (537.8" the percentages for a single determination. percentage of methane (as shown in Figure 4). The curve The curves of Figure 4 show that the oxides of carbon Confor B. t. u. per cubic foot shows the actual heat value of the stitute a major portion of the evolved gases as the temperature gas, considering the volumes actually evolved. T a b l e I11 s h o w s the total volume of each gas constituent evolved f r o m runs conducted a t different distilling temperatures. The f i g u r e s f o r carbon dioxide show an increase up t o 824" F. (440" C.), after which t h e r e i s a slight decrease. Carb o n m o n o x i d e follows the same trend, d r o p p i n g off a t 813" F. (433.9' (2.). The methane figures show a n i n c r e a s e , especially from 556" to 1000" F. (291.1" to 537.8" C.). Illuminants are produced in larger quantities a t higher temperatures. The nitrogen figures are nearly constant for the reason explained above. Hydrogen evolution is D/SIILLRT/ON JNIIPEARTuALs markedly increased at IN GAS COMPOSI6. CHANGE AND HEATVALUE OF GASPRODUCED FIGURE FIGURE 5. VOLUME high temperatures. TION DURING RUX AT DIFFERENT TEMPERATURES
-
(1
c.1
"'
JUNE, 1938
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE111. GAS YIELD-DISTILLATION TEMPERATURE DATA Cu. Ft. a t Distn. Temp. of: 392O F. 430° F. 536O F. 556" F. 673O F. 752O F. 813' F. 824' F. 1000' F. 0 452 0.677 1.07 1.12 1.22 1.28 1.29 1.30 1.22 0.744 0.579 0.574 0.495 0.577 0.655 0 194 0.303 0.483
7
Gas
Con
CO
Illuminants 0 002 CHI 0 028 0 051 H Z 0 207 Na
__ 0 93 1.44
-
Total
0.009 0,086 0.071 0.291
0.024 0.081 0.117 0.305
0.026 0.065 0.105 0.292
0.036 0.226 0.183 0.110
0.079 0.236 0.150 0.294
0.043 0.315 0.199 0.296
2.69
2.89
0.060 0.399 0.202 0.329
0.061 0.576 0.211 0.252
-
-
- - -
-
-
2.08
2.10
2.35
2.87
2.89 I
701
distillation of corncobs are obtained if the distillationiscarriedoutat about 700'F. (371.loC,). 4. Greater heat values per unit volume of noncondensable gas are secured at higher temperature distillation. 5. The physical properties of corncob charcoal vary considerably with temperatures of production. 6. The yield of fixed carbon in corncob charcoal is practically constant for all temperatures of distillation.
Acknowledgment I n order to study the change in composition of the gas evolved under progressive heat, a run was made under the identical procedure used in Series A-I to a temperature of 750" F. (398.9" C.). Samples of gas were taken a t every 50' F. (28" C.) temperature rise. The analyses of these samples are plotted in Figure 6 to show the progressive changes in the gas composition as the decomposition reaction proceeds. As might be expected, the general shapeof the curves corresponds closely to those in Figure 4, except that changes in gas composition are accentuated by the analyses of samples taken a t closer intervals of temperature change.
Conclusions 1. 'The exothermic point in the destructive distillation of corncobs is about 414" F. (212.2" C.). 2. The temperature a t which a destructive distillation is carried out has a definite effect on the yields of products. 3. Maximum yields of condensable products from the
The authors wish to express their appreciation to H. D. Weihe for his assistance with the analysis for formic acid and to R. L. Tillson for his assistance with the gas analysis.
Literature Cited (1) Atkinson, F. C.,U. 5. Patents 1,538,505 (1925), 1,572,510 (1926). ( 2 ) Berntson, T.K.,Ibid., 1,516,701(1924). (3) Darling, E.R.,British Patent 341,861 (1928). (4)Klar, M.,"Technology of Wood Distillation," London, Chapman and Hall, 1925. (5) Leon, Antonio de, and Reyes, R. 0. R., Univ.Philippines Nat. and Applied Sci. Bull., 4, 325-31 (1935). (6) Marcusson, J., and Picard, M., Chem.-Ztg., 47, 585 (1937). (7) Messinger, Bey., 21,3666 (1888). (8) Sweeney, 0.R., and Webber, H. A., Iowa Eng. Expt. Sta., Bull. 107 (1931). (9) Weihe, H.D.,and Jacobs, P. B., IND.ENQ.CHEM., Anal. Ed., 8, 44 (1936). (10) Zeisel and Stritar, 2. am2. Chem., 29,359 (1890);42,579 (1903): 43, 387, 394 (1904). RECEIVED February 5, 1938.
Monocalcium Chlorophosphate Reaction Product of
Calcium Chloride and Phosphoric Acid By-product hydrochloric acid may be applied to phosphate rock for the production of monocalcium chlorophosphate, a potential fertilizer material. Compared with the process for producing dicalcium phosphate by neutralizing hydrochloric acid solutions of phosphate rock with milk of lime, an increase of approximately 40 per cent of available phosphate per unit of reagent acid is obtained. The use of milk of lime and the problem of disposing of waste calcium chloride are eliminated.
E. J. Fox A N D K. 0. CLARK Bureau of Chemistry and Soils, U. S. Department of Agriculture, Washington, D. C.
YDROCHLORIC acid obtained as a by-product in the transformation of potassium chloride to other potash salts (4) is applied in several European countries to phosphate rock for the production of agricultural phosphate (6). The conventional method employed produces dicalcium phosphate by neutralization of phosphate rock-hydrochloric acid solutions with milk of lime. Inasmuch as the rock originally contains calcium in excess of that appearing in the finished product, this procedure appears to be illogical and wasteful of both the reagent acid and the added milk of lime. . It seemed desirable therefore to study the phosphate rockhydrochloric acid-water system to determine the possibilities of producing available phosphates with less acid and without the use of additional lime.
H
Decomposition of Phosphate Rock with Aqueous Hydrochloric Acid Tennessee brown-rock phosphate (calcium oxide 46.9 per cent, phosphoric oxide 33.4, fluorine 3.72) was decomposed by hydrochloric acid of various concentrations. The resulting solutions in contact with a n excess of rock a t room temperature (2B"C.) and a t 100" C. were analyzed. In all cases
702
INDUSTHML AND ENGINEERING CHEMISTRY
VOL. 30, NO.6
the formatioil of the precipitate. It was further observed that concentration of the inotlier liquor by evaporation yielded the same 5m .e type of precipitate whether or not phosphate d, L rock was present,. These oliservations led to 1.6 the conclusion that the secondary reaction 0" was between calcium chloride and phosphoric e acid in solution and that phosphate rock as -P .4 such was not involved in the Sonriatioil of the precipitate. eE ' 2 W Preparation of the pure solid product for the pnrpose of identification was attempted 0 I 2 3 4 5 from aquwius, alcoholic, and glacial acetic Gram mobs CoCI2/ Kg. Solution acid solutions of reagent-quality calciuni chloFIGURE1. D n ~ON i DECOXIPOSITION oF PHosmum Rom ride and .~ phosiihoric acid, in addition to filtered liydrochloric acid soliitions of phosphate rock and Iiyrirochloric acid solut,ionsi,f dicalcinm phosphate. On the free acidity and calcinm-, chloride-, and phosphate-ion evaporating t h e solut,ions, hydrnchloric acid was evolved content of the solntions were snbstantially equivalent to mixsinniltaneonsly witb the forinatinn of a snlid phase. tures of calcium chloride and phosphoric acid. These red t s are graphically reprenented in Fignre 1. Broken line a represents the calculated yield of pliosplioric acid, expressed in terrns of gram moles of pliosphoric oxide (P,Os) per gram mole of calcium cliloriiie in solution, based on tlic oalcirnn and phosphorus content of tlia original rock. The close agreement, of lines O A I and 0.4 with line (1 indicates not only that calcium cliloride and phnsphoric acid are the primary products, brit that irr this region reaction in the tem is practically limited to their formation. The increase in the calcium chloriflc-plioslilioricoxide ratio OS the solution at higher concentrations, A ,R,and . 4 A , iirriicates the hnnatioli of a solid nhtue with a lower calciinii (,~i(~e--I~}i(isr~liorii! oxide ratio than the rock. Seuaration of the solid and lianal . .oliasrs was difficult becausd of the liig11 concent,rations OS calcium chloride and phospiraric acid i n the solntions mhicl~were aiimixed with undeeorriposed ruck, insoluble material, and a wlurninous finely dividcd precipitate. Attempts to Erec the solid phiisen from mothcr liqnor by filt,ratioii and wasliing of t,he filter cake wit,h The precipitates ol)tairred were finely divided arid ditiiwater yielded residncs nnd was11 I i i l u ( i ~ ~fhe , conipwition of mkly filteralile, and exiiihited the same tendencies towards which contiuuously varied wit,h the cleflee OS washing. Tile and alc
