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INDUSTRIAL AND ENGINEERING CHEMISTRY
The maximum for chloroform is more than for methylene chloride because the former is more difficultly chlorinated. Four other mole ratios of reactants a t which two of the products have the same mole fraction are: 0.96, 1.83, 2.1, 3.3. EFFECT O F TEMPERATURE
Bath temperatures substantially lower than 440" C. may be used; but the reaction becomes increasingly sluggish as the temperature is decreased, and more and more reactor volume is required. Much higher temperatures may be uscd, provided the momentary concentration of chlorine is maintained low; that is, a large number of jets is used and the exposure time is sufficiently short. There is not much difference in the relative amounts of chloromethanes obtained a t 390", 440", 500", and 550" C., but considerable excess hydrogen chloride was obtained a t 550" C., even with four times the number of jets used a t 440" C. A bath temperature of 440" C., with other conditions as employed in this investigation, is not necessarily a critical point but is within the range of most suitable temperatures. DISCUSSION
The process is very flexible in that almost any desired ratio of chloromethanes may be obtained. It may be made to yield relatively large proportions of the two more costly compounds, methyl chloride and methylene chloride. It has the advantage that any ratio of chlorine to methane may be used in a single pass through a given reactor, and if desired, carbon tetrachloride only can be obtained without the expense of recycling. 'jTable I shows that substantially 95 per cent of the chlorine was accounted for. It is believed that most of the other 5 per
cent can be accounted for as holdup in the apparatus and rectifying column, and as loss in transferring from the receivers to the column. The methane balance was determined in several runs, and in all cases more than 90 per cent was accounted for. Therefore, particularly since there is substantially no carbonaceous material or by-products, it is believed that on a large scale where small losses are less significant the yield of cliloromethanes based on methane would be substantially 100 per cent and based on chlorine, 50 per cent. All of the products of the reaction have important industrial uses, but an outlet for the hydrochloric acid must be assured for the process t o be practical. ACKNOWLEDGMENT
The authors are indebted t o the Ethyl Gasoline Corporation and the Purdue Research Foundation for defraying the expense of this investigation. LITERATURE CITED (1) Chilton and Genereaux, Chem. & M e t . Eng., 37, 755 (1930). (2) Egloff, Schaad, and Lowry, Chem. Rev., 8 , 1 (1931). (3) Ellis, "Chemistry of Petroleum Derivatives", Vol. 1, p. 686 (1934); Vol. 2, p. 726 (1937). (4) Ham and McBee, E. 5.Patent 2,004,072 (1935) ; Canadian Patent 374,241 (1938). (5) Jones, Allison, and Meighan, U. S. Bur. Mines, Tech. Paper 255 (1921). (6) Martinek and Marti, IND. ENG.CHEM., ANAL.ED.,3,408 (1931). (7) Mason and Wheeler, J. Chem. SOC.,1931, 2282. (8) Pease and Walz, J . Am. Chem. Soc., 53,382, 3728 (1931). THIS paper contains material abstracted from B thesis submitted t o the faculty of Purdue University b y C. M. Neher in partial fulfillment of t h e requirements for t h e degree of doctor of philosophy.
Nitration of Methane'. natural gas, freed of a l l hydrocarbons except methane, was nitrated a t atmospheric pressure in the vapor phase w i t h 67 per cent nitric acid at temperatures ranging From 375" to 600" The most favorable conditions found, using a ratio of 9 moles of methane to 1 of nitric acid, are a temperature of 475' C. and an exposure time of 0.18 second. The optimum conversion of nitric acid to nitromethane was 1 3 per cent per pass. The reaction has an activation energy of 52 Calories per mole.
A
Vol. 34, No. 3
.. Thomas Boyd* and
H. B. Hass
Purdue University and Purdue Research Foundation, Lafayette, Ind.
C.
LTHOUGH nitromethane has been known since A and has been readily available for many years as a laboratory product, it first appeared as an industrial chemical 1872
(7)
in May, 1940. That now produced is obtained as a by-product of the nitration of propane ( 3 , 4) a t the Peoria plant of Commercial Solvents Corporation. Because of the long ac1 This paper is the sixteenth in a series on t h e subject of synthesrs from A N D ENGInatural gas hydrocarbons. T h e others appeared in INDUSTRIAL N E E R I N G C H E M I S T R Y , 23, 352 (1931); 27, 1190 (1935); 28, 333, 339, 1178 (1036); 29, 1335 (1937); 30, 67 (1938); 31, 118, 648 (1939); 32, 34, 427 (1940); 33, 176, 181, 185 (1941); 34, 296 (1942). 2 Prerent address, Monsanto Chemical Company, Springfield, Mass.
cessibility of nitromethane, the many researches which have been carried out on it, and its great reactivity, there are many actual and potential commercial outlets for its derivatives. It seemed advisable, therefore, to study possible means of augmenting the supply of nitromethane by a direct attack upon its parent hydrocarbon. The preliminary attempt t o nitrate methane in this laboratory met with failure ( 3 ) because the exposure time was too short for the temperature used. Landon's excellent work on the vapor-phase nitration of methane is disclosed in two patents (6) which describe the process in a ferrous or nonferrous reactor a t exposure times between 1 and 0.005 second under pressures from 1 t o 50 atmospheres. Since the processes of Landon have not so far resulted in commercial success, the subject was re-investigated by the authors. ANALYSIS O F METHANE
Purified natural gas was passed into a flask cooled by liquid air. d sensitive flowmeter on the exhaust side of the receiver showed that practically all of the gas passed into the receiver
INDUSTRIAL AND ENGINEERING CHEMISTRY
March, 1942
was liquefied. About 100ml. of liquid methane were collected and distilled in a low-temperature rectifying column of the Podbielniak type. All of the liquid distilled a t the same temperature. It was concluded that the purified methane contained no other hydrocarbons. This conclusion was confirmed by the fact that no compound boiling higher than nitro-
3
\
A FIGURE 1. GASSCRUBBING TOWERS
methane was found in the product. A run with natural gas containing ethane always yields more than the proportional amount of nitroethane in the nitrated product since the yield of this nitroparaffin per pass is almost three times that of nitromethane (1, 2).
301
phragm valve and provided uniform flow of methane. The flow of carbon dioxide through the nitric acid vaporizer, 30, was controlled and measured similarly to that of methane by a diaphragm valve, 20, and a flowmeter, 18. Themethane was led to reaction chamber 44 (Figure 4) through preheating coil 37 made from 4 meters of 5-mm. Pyrex tubing. The reaction chamber was immersed in an electrically heated bath filled with a 50 mole per cent mixture of sodium nitrate and potassium nitrate, An electrical heating element was wound around the outside of the pot, and immersion heaters (5),along with a thermoregulator, were used to control the temperature of the molten salt. The reaction chamber was constructed with a thermocouple well so that the temperature of the reaction mixture could be determined. The methane inlet tube from the preheater was constricted just above the junction of the nitric acid feed line, 33. The nitric acid was introduced as vapor formed from the constant-boiling mixture (67 per cent nitric acid) by passing carbon dioxide through nitric acid vaporizer 30, a modified form of one described by Rinelli and Willson (8). The vaporizer was immersed in an insulated thermostat filled with Fino1 (a highly refined light lubricating oil) and maintained a t 121' C. A mercury switch, 29, and a relay, 28, were used in conjunction with electrical heaters 25 and 26 to control the temperature of the thermostat. The carbon dioxide-steamnitric acid mixture passed from the vaporizer through a jet and adapter, 45, which caused it to flow into the stream of methane a t an angle of 45'. The products of the reaction were passed through a series of condensers and traps as shown on Figure 5. Receiver 50 was immersed in a water-ice bath, and receivers 52 and 5.3
APPARATUS
The apparatus for purifying natural gas is shown in Figures 1 and 2, and that for carrying out the vapor-phase nitration of methane, in Figures 3,4, and 5. The natural gas was taken from the laboratory supply line and passed through scrubbing tower 40 (Figure l), packed with porous plate chips down which sulfuric acid was allowed to trickle. The gas then passed through caustic scrubbing towers 41 and 42, packed with sodium hydroxide pellets. This scrubbed gas was conducted to compressor 17 (Figure 2), which forced it first through the activated charcoal adsorber 2, and then into the storage tank, 3. Adsorber 2 was constructed so that the charcoal was surrounded by a jacket into which steam or cold water could be passed. During the purification of the natural gas, cold water was passed continuously through the jacket. To regenerate the partially saturated charcoal, the water was drained from the jacket and steam was introduced. At the same time steam from generator 1 was passed through the charcoal for about an hour; then the regenerated charcoal was evacuated with a water aspirator for an hour. The regenerated charcoal was cooled under evacuation by passing water again through the jacket. The vacuum in the adsorber was relieved by using some scrubbed natural gas. The flow of methane was regulated by a diaphragm valve, 21 (Figure 3), and measured by a flowmeter, 19. The resistance coil, 23, was made from 1 meter of 1/2-mm. Pyrex capillary tubing. This caused smoother operation of the dia-
FIGURE
2. COMPRESSOR, ADSORBER;AND STEAM
GENERATOR
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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
Vol. 34, No. 3
nn
FIGURE 3, FLOWMETERS AND REGULATORS
were immersed in a solid carbon dioxide-chloroform-carbon tetrachloride bath. The exhaust gases were allowed to pass up the hood. The flowmeters were calibrated, in situ, against a wet-test gas meter. The volume of gas flowing was measured and the time recorded. According to Whitwell (9),the (volume) X (" K.)O.B/minute was plotted against the difference in the height of the manometer arms. carbondioride
The quantity of 67 per cent nitric acid vaporized per minute for a given manometer arm differential on the carbon dioxide flowmeter was found by passing the gas through acid vaporizer 30 (Figure 4)for a given time; the vaporizer was weighed before and after each run. The products and wash liquors from the receivers (Figure 5) were combined and distilled until 100 ml. of distillate had been collected. The distillate was transferred to another flask. and 100 ml. of water were added. This'mixture was redistilled slowly until the temperature of the distillate rose to 90' C. The bottom layer of the second distillate was separated and distilled in a Podbielniak-type rectifying column, and the amount of nitromethane was determined. The residues from the first two distillations mentioned were combined in a volumetric flask and diluted t o 1 liter. Aliquot portions were titrated with standard sodium hydroxide solution to determine the recovered acid. DISCUSSION
FIGVRE 4. REACTOR
OF DATA
The study of the vapor-phase nitration of methane may be conducted by one of two methods. The first is to maintain the temperature constant, and find the effect of various contact times on the conversion of nitric acid and methane to nitromethane. The second method, which has been followed, is to maintain a constant contact time and determine the conversion of nitric acid to nitromethane for a series of temperatures. The optimum temperature for a given contact time would be determined by plotting the per cent conversion of nitric acid to nitromethane against the
March, 1942
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
303
A mole ratio of methane to nitric acid of 9 to 1 was chosen; i t has been shown (3) that, when the mole ratio of hydrocarbon bo nitric acid exceeds 9 to 1, there is no appreciable effect on the yield from the reaction. By plotting the per cent conversion of nitric acid to nitromethane and the per cent yield of nitromethane based on the nitric acid consumed against the temperature in O C., a series of curves shown in Figure 6 is obtained for different exposure times. The maximum of each of the curves represents the optimum temperature for that exposure time. These maxima are summarized in Figure 7 by plotting the optimum per cent conversion for a given contact time against the common logarithm of that contact time. The curve so obtained shows the optimum contact time for the greatest conversion. If the per cent conversion is plotted against the temperature, a series of curves can be drawn for various exposure times such that the curves approach rapidly and asymptotically a certain temperature a t which 100 per cent conversion FIGURE5. CONDENSERS AND RECEIVERS is obtained, irrespective of the order of the reaction, provided undesirable secondary reactions do not occur. If undesirable secondary reactions occur, their rate will increase with increased temperature. The result will be that the curve obtemperature. The optimum conditions for the process would tained for a constant exposure time will rise rapidly and pass be obtained by plotting the per cent conversion at the optimum through a maximum, beyond which the conversion becomes temperatures'against the contact time. less as the temperature increases. Arrhenius showed that Since the calibration curves for the methane and carbon by plotting the logarithm of the reaction rate constant against dioxide flowmeters are not consistent with each other, it was the reciprocal of the absolute temperature, a straight line desirable to adjust the flowmeter settings so that a constant passes through the points plotted. The reaction rate convolume of gas would flow through the reaction chamber each stant is inversely proportional to the exposure time for a given second. By so doing, the mole ratio of carbon dioxide, methconversion. Therefore, a plot of the logarithm of the expoane, steam, and nitric acid were the same in each experiment, sure time for a given conversion against the reciprocal of the as was also the t i e required. A gas flow was chosen arbiabsolute temperature should give a straight line curve, the trarily which at 27' C. measured as follows: slope of which, multipled by 2.303 R, gives the activation energy for the nitration of methane. I n Figure 8 the common logarithm of the contact time is plotted against the reciprocal Methane 1640-ml. of the temperature in O K. for the optimum per cent converCarbon dioxide 435 Nitrio acid vapor 185 sion a t the corresponding exposure time. The curve is a Steam 325 straight line because the optimum temperature for a given Total 2585 exposure time represents in each case about the same degree of completion of the reaction-i. e., the conditions corresponding t o about 95 per cent consumption of A% ' nitric acid. The curve remesents the relation between contict time, R.5 per cent conversion, and optimum L$COON?%?%WE /ff%C x /O% 55 temperature. For any exposure time between 0.021 and 2.1 secFIGURE 7. OFTIMUMYIELDus. TEMPERATURE onds, the temperature is given
1
1
1
I
/5 I
I
7--+-=-/
' B o - - - = -
I
(//OPT/NU4 .TXJX1000
FIGURE 6. CONVERSION AND YIELD us. TEMPERATURE FOR FOUREXPOSURE TIMES
FIGURE
8. LOGARITHM OF EXPOSURE TIMEUS. RECIPROCAL OF ABSOLUTB~ TEMPERATURE
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INDUSTRIAL AND ENGINEERING CHEMISTRY
which will afford the maximum conversion. The maximum per cent conversion may be found from Figure 7 . The slope of the curve in Figure 8 is 1.14 X lo4degrees, and the activation energy is 52,000 calories per mole.
Vol. 34, No. 3
LITERATURE CITED (1) Hass, H. B., Hibshman, H. J., and Pierson, E. H., IND.ENC. CHEM., 32, 427 (1940). ( 2 ) Hass, H. B., and Hodge, E. B., U. S.Patent 2,071,122 (Feb. 16, 1937); Canadian Patent 382,346 (March 21, 1939). (3) Hass, H. B., Hodge, E. E., and Vanderbilt, B. M.,IXD.ENG. CHEM.,28, 339-44 (1936). (4) Hass, H. B., Hodge, E. B., and Vanderbilt, B. M., U. S. Patent
1,967,667 (July 24, 1934); Brit. Patent 443,707 (June 30,
ACKNOWLEDGMENT
1937) ; Canadian Patent 371,007 (Jan. 4, 1938). (5) Hoskins ICZfg. CO.,Chrome1 Catalog L, Chicago, 1937. (6) Landon, G. K., U. S. Patents 2,161,475 (June 6, 1939); 2,164,774 (July 4, 1939). (7) Kolbe, J. prakt. Chem., 5, 427 (1872). (8) Rinelli, W.R., and Willson, R. S., IND.ENG.CRBM.,ANALED., 12, 549 (1940). (9) Whitwell, J. C., IND. ENQ.CHEM.,30,1157 (1938).
The financial assistance from the Commercial Solvents Corporation, in cooperation with the Purdue Research Foundation, without which this project could not have been undertaken, is appreciated greatly. Thanks are due W. E. Fish and John Hession for their kind assistance in the design and construction of the apparatus.
Studies in Esterification PREPARATION AND PROPERTIES OF STARCH PROPIONATE Darrel
E.
M a c k ' and
R.
Norris Shreve
Purdue University, Lafayette, Ind. tarch tripropionate can b e made by refluxing, w i t h vigorous agitation, starch, propionic acid, and propionic anhydride. There i s some anhydride formation within the starch during the reaction. The acid esterifies about 8.7 times a s fast as the anhydride. The rate equation
S
e
Cl
= -i0g-
K
+
czx 1 I-x
can be used to f o l l o w the reaction, where K i s the rate constant, C l and C2are functions OF the starting concentrations, x is the fraction esterified, and 0 i s the time. The finished product i s soluble in many organic solvents, insoluble in water, and can b e used to give useful protective coatings on metal, wood, paper/ cloth, etc. The sheets prepared of plasticized starch propionate w e r e too weak for practical use.
HE low price of starch at $0.037 per pound (d), together T with the entrance of propionic acid and anhydride into the field of low-price organic reagents, makes the study of the propionic acid ester of starch of considerable interest as a possible cheap film-forming agent. That starch esters have many potential uses is evidenced by the recent appearance of starch acetate on the market ( 3 ) . The product investigated was a propionate corresponding t o a completely esterified starch. Although the less completely esterified starches probably have useful properties they were left for future investigation. 1
Present address, Lehigh University, Bethlehem, Penna.
A11 the reactions were run without catalysts; the possibility was eliminated that they would change or degrade the products in any way, and all runs were thus comparable. It is possible that the various catalysts used by other investigators of starch esters accounts in large part for the discordance of results when their data are compared. Sutra (7) and Reich and Damanski (8) noted that sulfuric acid or phosphoric acid catalysts may degrade the starch. Higginbotham and Richardson ( 2 ) stated that sulfur dioxide plus chlorine catalysts degrade the product, but that pyridine has no effect. The amount of pyridine needed and the difficulty of its recovery make this cat'alyst economically impractical. The writers' own observations show that sodium propionate also tends to decompose the starch. E X P E R I M E N T A L PROCEDURE
The apparatus (Figure 1) consisted of a round-bottom flask of about 100 ml. capacity, fitted with condenser and variablespeed stirrer. It was heated by a controlled-temperature hot oil bath. The reagents were propionic acid (99f per cent), propionic anhydride (98f per cent), and Amaizo Common starch analyzing as follows ( 1 ) : sulfur dioxide, 0.003 per cent; acid, 0.18; total protein, 0.37; ash, 0.10; water-solubles, 0.10; and insolubles. 0.22. The viscositv of the starch was < 100 cc. and its pH was 4.'7. To make a run, the starch was dried to constant weight at 110' C. The reagents were introduced into the flask, the stirrer was turned on, and the oil temperature raised to give the desired reaction temperature. When the run was completed, the flask contents were poured into an evaporating dish, the flask was washed with acetone, and the contents and washings were evaporated to dryness. To make sure that the reaction did not continue during the rocess, drying was carried out at a low temperature (40-50' C.f The residue was then ground in a mortar and dried a t 110' C. t o constant weight. This product was analyzed for ester content according t o the following procedure: One hundred milliliters of c. P . butanol plus exactly 10 ml. of about 4 per cent sodium hydroxide in butanol were heated to boiling in a stirred flask fitt'ed with reflux condenser. One-half gram of sample was then introduced and boiled for about 1.5 minutes. (Less boiling was not sufficient to saponify the ester completely. Longer boiling tended to decompose the liberated starch with the formation of a brown color which masked the end
