March, 1943
INDUSTRIAL AND ENGINEERING CHEMISTRY
of combines (for harvesting) instead of binders, the straw is spread around the field instead of being stacked. Consequently the cost of oollection is out of proportion to the value.” The same is true of most other agricultural cellulosic wastes. The charcoal from wheat straw (1) was extremely light and analyzed: 57.8 per cent fixed carbon, 10.5 volatile matter, 31.7 ash. The potash content of the ash was 2.25 per cent KzO. CORNCOBS.Experimental values on destructive distillation of corncobs have been reported (7). Average values are included in Table 11, converted to the same basis. The collection of corncobs might also be uneconomic.
317
central. Fortunately, the chief product is charcoal which fits well into the economy of many tropical sugar countries where it is used as a domestic fuel. Much better yields of charcoal and lesser yields of acetic acid and of methanol are indicated from bagasse than from hardwoods. The charcoal is bulky and comes as a fine, pulverent material. It is easily made into briquets with a small amount of starch or of molasses, which is another by-product of the same industry. The texture of the charcoal indicates that it might be suitable for activated carbon. It thus seems that bagasse might be profitably carbonized in some locations because of the products, particularly charcoal, and the fact that the valueless bagasse is available a t a single point, the sugar central, in large quantities. The physical nature of bagasse indicates that the advantages of continuous carbonization by the modification of a continuous retort used for wood waste should be realized.
Conclusion
I n the destructive distillation of bagasse it is possible to produce five useful products-namely, acetic acid, methanol, charcoal, combustible gas, and tar. The yields of acetic acid, charcoal, and methanol were great enough to envision the destructive distillation of bagasse on a commercial scale. Bagasse is a waste product already collected a t the sugar central. If the products formed by distillation can be used nearby, as seems possible, transportation costs would be a minimum. Although the regions where bagasse is obtained are mainly agricultural, there is usually some market for acetic acid and methanol as well. The gas produced might be used for the carbonization operation or for fuel a t the sugar
Literature Cited (1) Faith, W. L., private communication. (2) Freeland, E. E., Trans. Am. SOC.Mech. Engrs., 39, 919-20 (1917). (3) Mark, L. S., Mechanical Engineers Handbook, New York, McGraw-Hill Book Co., 1941. (4) Othmer, D. F., IND.ENG.CHEM.,27, 250 (1935). (5) Othmer, D. F., and Schurig, W. F., Ib$d., 33, 188 (1941). (6) Read, W.T., “Industrial Chemistry”, New York, John Wiley & Sons, 1938. (7) Sweeney, 0. R., and Webber, H. A., Iowa Expt. Sta., Bull. 107 (1931).
c
CHLORINOLYSIS ot CHLOROPARAFFINS F F The chlorinolysis reaction has been applied to chlorinated derivatives of ethane, propane, isobutane, butane, hexane, heptane, octane, and tetradecane. Carbon tetrachloride and hexachloroethane are products of the reaction in each case. it seems possible that any polycarbon chloroparaffin can be converted to carbon tetrachloride and hexachloroethanein good yields b y chlorinolysis with an excess of elemental chlorine. .Hexachloroethane may be subsequently converted to tetrachloroethylene, a valuable solvent.
B
Y ANALOGY to such terms as hydrogenolysis, hyrolysis, ammonolysis, and alcoholysis, indicating a chemical reaction in which hydrogen, water, ammonia, or alcohol, respectively, effects a rupture of the molecule undergoing these reactions, the term “chlorinolysis” has been suggested (9) to describe the process of chlorinating an organic compound under conditions which rupture the carbon-carbon bonds to yield chloro compounds with fewer carbon atoms than the starting material. A survey of the literature reveals only a few examples of chlorinolysis in which elemental chlorine was the chlorinating agent. The most significant reference to chlorinolysis with elemental chlorine is that of Grebe, Reilly, and Wiley (4); l’reeent sddress, Visking Corporation, Chioago, Ill.
E. T.
McBee,
H. B. Hass,
and Carl Bordenca‘
PURDUE UNIVERSITY AND PURDUE RESEARCH FOUNDATION, LAFAYETTE, IND.
their’s is a patented process for the preparation of chlorocarbons, principally carbon tetrachloride and tetrachloroethylene, by passing preheated chlorine ahd paraffin hydrocarbons through a bath of molten metal chlorides such as a eutectic mixture of aluminum chloride, ferric chloride, and sodium chloride. According to a patent issued to I. G. Farbenindustrie A.-G. (7), carbon tetrachloride may be prepared by passing aliphatic hydrocarbons of more than one carbon atom or their chlorinated products with chlorine over activated carbon or other substances of large surface area a t 400” to 650” C. The chlorine was 20-40 per cent in excess of the quantity theoretically necessary for the formation of carbon tetrachloride. The high-pressure, high-temperature chlorinolysis of chloropentanes for the production of carbon tetrachloride and hexachloroethane was described by McBee, Hass, and Pierson (9).
INDUSTRIAL AND ENGINEERING CHEMISTRY
318
p
Figure
7.
Vol. 35. No. 3
compounds under investigation were sealed in 1/2-inch ironpipe-size nickel tubes, 4 feet in length, with elemental chlorine in excess of that theoretically necessary for the replacement of all hydrogen atoms. These nickel tubes were then placed in heavy iron pipe for safety and heated to a desired reaction temperature. Chloroheptanes and chlorooctanes were found to give carbon tetrachloride and hexachloroethane when heated a t 250' C. As the temperature is increased, the reaction time for chlorinolysis is decreased. The use of iron equipment instead of nickel was unsatisfactory because of the catalytic reaction of iron and iron chlorides on the decomposition and polymerization of organic chlorides. I n an attempt to shorten the period of chlorinolysis, the use of catalysts was studied briefly. Aluminuni chloride, sulfur dioxide, and benzoyl peroxide were found to be ineffective. A series of experiments was made to determine the applicability of the chlorinolysis reaction to compounds other than chlorinated hydrocarbons. 1-Butoxybutane and pyridine gave hexachloroethane when subjected to chlorinolysis with elemental chlorine. Cyclohexanol yielded hexachlorobenzene when chlorinated a t 265" C.
GAJ MLLAST
Chlorine Pumping Mechanism
There are several references to the chlorinolysis of hydrocarbons and their chlorinated derivatives by chlorinating agents other than elemental chlorine. Eckert and Steiner ( I ) , Mer, and Weith(l0) and Gnehm and Banziger (5)obtained carbon tetrachloride, hexachloroethane, and hexachlorobenzene by chlorinatingavariety of aromatic compounds with antimony pentachloride. Hoffmann (6) reported that hexachlorobutadiene was obtained from the chlorination of trichlorodioxypicoline, CsH4O2NCI3,with phosphorus pentachloride. Hartmann (6) chlorinated certain aliphatic compounds with antimony pentachloride, using iodine as a catalyst, and obtained carbon tetrachloride, hexachloroethane, hexachlorobenzene, and hexachlorobutadiene. Ruoff ( 1 1 ) and Krafft and Mer2 (8) chlorinolyzed a number of aromatic compounds with chlorine in the presence of iodine. The compound CIJ mas believed to be one of the reactants. Shvenberger and Gordon (12 ) obtained carbon tetrachloride and tetrachloroindene by chlorinating naphthalene in the presence of chlorides of the metals of groups I11 and VIII. The chlorinolysis reaction has now been applied to chlorinated derivatives of ethane, propane, isobutane, butane, hexane, heptane, octane, and tetradecane. The chlorinolysis of chloroheptanes (C,H12C14) has been studied extensively, and the effect of varying the conditions of temperature, pressure, and rate of feed of reactants has been determined Chlorinolysis in Sealed Tubes
In evtending the chlorinolysis reaction to various paraffin hydrocarbons, it seemed desirable to carry out initial experiments on a small scale, for it is well known that chlorine forms explosive mixtures with hydrocarbons and certain of the partially chlorinated derivatives. Therefore a series of sealed tube experiments was conducted as a preliminary study of the general applicability of the chlorinolysis reaction. The
Apparatus for Continuous Chlorinolysis
The apparatus (Figures 1 and 2 ) was essentially that described in an earlier publication (9). It was fabricated from ferrous metals with the exception of the reactor and the product condenser which were made of nickel. A dual proportioning pump was used to introduce chlorine and the chloroparaffins continuously into a 1/2-inch iron-pipe-size nickel tube having a capacity of 210 ml. The nickel tube, which was the reactor, was surrounded by a salt bath heated by immersion heaters. The product of the reaction passed from the nickel tube reactor through a water-cooled condenser into a receiver maintained at the same pressure as the reactor. The desired presbure in the system was obtained by filling the reactor and receiver with nitrogen a t the beginning of a n experiment. As the product collected in the receiver, the nitrogen was allon ed to escape slowly to maintain a uniform pressure Safety disks were mounted a t each end of the reactor tube. These disks were made to rupture a t 2000 pounds per square inch pressure. Little difficulty was experienced in pumping liquid chlorine a t pressures as high as 1000 pounds per squarc inch according to the procedure described in the previous publication. This consists essentially of using a cone-type check valve in the chlorine line between the chlorine supply tank and the reactor and maintaining concentrated sulfuric acid in the line connecting the check valve and the pump. By this procedure the chlorine did not come into direct contact with the pump, and hence the problem mas essentially one of pumping sulfuric acid a t high pressure. Application of Chlorinolysis Reaction
I n order t o determine the general applicability of the chlorinolysis reaction it was studied with a variety of chloroparaffins.
Table I. Chlorinolysir of Miscellaneous Chloroparaffins Experiment No. Temperature, C. Pressure, lb./sq. In. Chloroparaffin
RIoles Chlorine, moles Ratio Clz: chloroparaffin Rate of feed min./mole Product, % by weight CCln CzCle Residue
71 400 1000 CzHaC12 0.75 S 11:l 20 72
.28 ..
42 400 750 CsHiCla
1,i
14 8: 1 30 16 84 ,..
65 26 66 400 400 400 750 1000 1000 CaHaC14 Iso-CaHsCls Iso-CaHsClg 0.9 1.0 1.6 18 21 21 23:l 13:l 1S:l 60 75 80 22 78
...
46
.54 ..
42 58
...
32 435 500 C4HvCIl 0.9
10 11:l
72
38 350 500 C4H6Cla 0.8
9:1 28
13
5
GO
SO
27
15
750 CdIaCh 1.5 18 12:l 27
39
67 310 500 CJI6CI4 1.75 19 11:1 20
S 66 26
0.6 99.0 0.5
400
INDUSTRIAL AND ENGINEERING CHEMISTRY
March, 1943
Figure
2.
Chlorinolysis Apparatus
In the chlorinolysis of l,%dichloroethane, carbon tetrachloride and hexachloroethane were obtained as the only products. Presumably it should be possible to maintain conditions which would cause perchlorination without chlorinolysis; but at the conditions given in experiment 71, Table I, 72 per cent of the product was carbon tetrachloride, which was probably formed from the chlorinolysis of hexachloroethane. Therefore, it may be concluded that in the chlorinolysis of compounds with three or more carbon atoms, some of the hexachloroethane which is formed may be further chlorinolyzed .
ExDeriment No. Temperature, C. Pressure Ib./sq. in. C ~ H ~ G Lmoles : Chlorine moles Ratio ci,:C7H1,Cl4 Rate bf feed, min./mole Product, yo by weight CCL CZclS CaC!a Re81due Product, grams
47 400 1000 1.0 20 2O:l 40
48 400 1000 1.0 18:l 25
49 280 1000 0.6 20 33:l 65
29 30
25 29 25 21 427
26 23 34 17 209
26 15 527
18
rial. Carbon tetrachloride and hexachloroethane were the only products of the reaction. No attempt was made to study the effect of varying conditions on the relative proportions of the products. Experiments 26 and 66, Table I, show that an average of 44 per cent of the product was carbon tetrachloride. This relatively high percentage of carbon tetrachloride should be expected from a consideration of the branched-chain structure of the isobutane molecule. Two carbon-carbon cleavages are necessary for the direct formation of hexachloroethane from the chlorinolysis of the isobutane molecule. The series of experiments with tetrachlorobutanes is of particular interest. From experiments 67, Table I, it appears possible t o obtain hexachloroethane with the almost complete exclusion of other reaction products. However, if the temperature and pressure are increased beyond approximately 300" C. and 500 pounds per square inch, respectively, the yield of carbon tetrachloride increases. Chlorinolysis of Chloroheptanes
Polychloroheptanes were selected for a more intensive investigation of the chlorinolysis reaction because they are available from typical paraffin hydrocarbons. A mixture of isomeric heptanes boiling a t 9 6 9 8 " C. a t 750 mm. obtained by fractionation of commercial heptane was used as the starting material. The fraction was chlorinated in the liquid phase, in the presence of light a t about room temperature, to poly-
Table 11. Chlorinolysis of Chloroheptanes 51 52 53 54 50 350 350 450 400 425 1000 1000 1000 1000 1000 0.8 0.8 0.8 1.0 0.7 23 21 18 24 21 26:l 2331 24:l 24:l 33:l 50 44 50 60 60 37 26
.37 .. 231
36 25 20 1s 331
Several experiments were conducted with tetrachloropropanes. The products of chlorinolysis are carbon tetrachloride and hexachloroethane. A change in pressure from 750 to 1000 pounds per square inch had no appreciable effect on the relative proportions of carbon tetrachloride and hexachloroethane in the product. However, the ratio of these two chlorocarbons was affected by varying the exposure time. As would be expected, the yield of carbon tetrachloride increased as the rate of feed of tetrachloropropanes to the reactor was decreased. The average mole ratio of hexachloroethane to carbon tetrachloride for the series of experiments with tetrachloropropanes was about 3:l. Since a satisfactory carbon balance was obtained, it must be concluded that the reaction is more complicated than that of simple cleavage of the carbon-carbon bonds. Presumably there are combinations of free radicals. Otherwise the ratio should not have been greater than one mole of hexachloroethane per mole of carbon tetrachloride. For studying the chlorinolysis of an isobutane derivative, 1,2-dichloro-2-methylpropanewas used as the starting mate-
319
39
40
37 6
26 16 17 258
18 341
39 29 11
21 295
59 300 1000 1.0 32 32:l 50
60 400 1000 0.7 35 5O:l 100
61 400 1000 1.0 30 30:l 40
31 26 32 11 370
37 35 19
34 28 21 17 340
8
310
82 .~
400 750 1.0 28 28:l 40
63 ~~
400 500 0.8
27 34:l 24
31
18
13 44
18 41 22 386
12
450
chloroheptanes with an average composition of C,C14HI2. These polychloroheptanes were then subjected to chlorinolysis (Table 11). EFFECT OF TEMPERATURE. The extent and rate of chlorinolysis are determined by the variables: temperature, rate of feed, pressure, and ratio of reactants. Since it was determined by preliminary experiments that the mole ratio of chlorine to polychloroheptanes had no pronounced effect on the yield of carbon tetrachloride and hexachloroethane, so long as the ratio was maintained above 18:1, respectively,no special attempt was made to regulate accurately the excess of chlorine in the reaction mixture. The use of a large excess of chlorine merely decreases the capacity of the reactor and aids in the discharge of the product from the receiver. Using a rate of feed of 50 minutes per mole of polychloro-
320
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
heptanes (i. e., 50 minutes for one mole of polychloroheptanes to be pumped to the reactor) a t a pressure of 1000 pounds per square inch, a series of experiments was conducted in which the temperature was varied from 280" to450"C. It was found that a t 280" C. a chlorocarbon other than hexachloroethane and carbon tetrachloride constituted 34 per cent of the product; as the temperature was increased to 425" C., the yield of this material decreased to 6 per cent and a maxi-
Vol. 35, No. 3
and hexachloroethane. However, as the rate of feed is increased, or the time required to pump one mole of polychloroheptanes to the reactor is decreased, the yield of carbon tetrachloride and hexachloroethane decreases. Thus a temperature of 400" C. and a pressure of 1000 pounds per square inch are satisfactory for chlorinolysis if the rate of feed to a reactor of 210 mi. capacity is not greater than one mole of polychloroheptanes per hour.
1
I
50
500
PRESSURE
Figure
3. Effect of Temperature on Chlorinolysis of Chloroheptanes
Figure 4. Effect of Rate of Feed of Reactants on Chlorinolysis of Chlorohep tanes
mum yield, 76 per cent, of carbon tetrachloride and hexachloroethane was obtained (Figure 3). This additional chlorocarbon which melts a t 39" C. and boils a t 140' a t 10 mm. was reported (9) to be hexachlorobutadiene, but Fruhwirth (2) proved rather conclusively that it is octachlorocyclopentene. No attempt has been made to identify this material. As the temperature was increased beyond 425" C, a t 1000 pounds per square inch pressure, the yield of carbon tetrachloride and hexachloroethane decreased. Since chlorinolysis presumably takes place most readily when chlorine is in the liquid phase, owing to an effective high concentration of the reactants and an increased contact time, it is possible that at such high temperatures the amount of chlorine in the liquid phase has been decreased to the extent of limiting the reaction As the temperature is increased, it becomes necessary to increase the pressure substantially in the reactor in order to increase the solubility of chlorine in the material being chlorinated and maintain a uniform concentration of chlorine in the liquid phase. EFFECT OF CONTACT TIME. Because of the complexity of the reaction, it is impossible to calculate accurately the exposure time of the reactants in the reactor. However, to obtain data on the effect of exposure time of the reactants on the yields of carbon tetrachloride and hexachloroethane, a series of experiments was performed varying the rate of feed of polychloroheptanes a t 1000 pounds per square inch pressure a t 400" C., with a ratio of chlorine to polychloroheptanes (C7C14H,2)of a t least 18:l. Figure 4 shows that if the polychloroheptanes are pumped to the reactor a t a rate less than one mole of polychloroheptanes per hour (i. e., when more than 60 minutes were required to pump a mole of poiychioroheptanes to the reactor having a capacity of 210 ml.), lhere is no substantial increase in the yield of carbon tetrachloride
750
1000
LBS./SQ.IN.
Figure 5. Effect of Pressure on Chlorinolysis o f Chloroheptanes
EFFECTOF PRESSURE:. Since the chlorinolysis reaction usually proceeds most satisfactorily in the liquid phase, high pressures are employed. The effect of pressure was studied in a series of experiments conducted a t approximately 400" C. and a rate of feed of about one mole of polychloroheptanes per 40 minutes. Figure 5 shows that, as the pressure is increased from 500 to 1000 pounds per square inch, the total yield of carbon tetrachloride and hexachloroethane is increased from 36 t o 62 per cent. Not only is the yield of carbon tetrachloride and hexachloroethane increased by high pressures, but there is also less black, tarry material in the product. The optimum conditions, therefore, for obtaining highest yields of carbon tetrachloride and hexachloroethane from polychloroheptanes are as follows: a pressure of 1000 pounds per square inch, a mole ratio of chlorine to chloroheptanes greater than 18:1,a temperature of 425" C., and a rate of feed not greater than one mole of polychloroheptanes per hour to a reactor of 210 ml. capacity. Literature Cited (1) Eokert and Steiner, Ber., 47, 2629 (1914). (2) Fruhwirth, Ibid., 74B, 1700-1 (1941). (3) Gnehm and Banziger, Ann., 296,64 (1897). (4) Grebe, Reilly, and Wiley, U. S. Patent 2,034,292 (1936). (5) Hartmann, Be?, 24, 1011 (1891). (6) Hoffmann, Ibid., 22,1269 (1889). (7) I. G. Farbenindustrie A.-G., U. S. Patent 2,160,574 (1939). (8) Krafft and Merz, Ber., 8 , 1045, 1296-1302 (1875). (9) McBee, Hass, and Pierson, IND.ENG.CHEM.,33, 181-5 (1941). (10) Merz and Weith, Ber., 16,2882 (1883). (11) Ruoff, Ibid., 9,1483-91 (1876). (12) Shvenberger and Gordon, J. Gen. Chem. (U. S. S. R.), 8, 1355 (1938). ABSTRAOTBDfrom a thesis submitted to the faculty of Purdue University by Carl Bordenca in partial fulfillment of the requirements for the degree of doctor of philosophy.
