CHEMICAL PROCESSES
concentration of unreacted nitrogen dioxide was plotted versus the reaction time. This correlation of the data agreed nearly perfectly with the theory. These reaction rate constants are then the product of a higher order reaction constant and the concentration of cyclohexane. I n order to show the influence of temperature, these reaction rate constants were plotted as the logarithm of reaction rate versus the reciprocal of the absolute temperature. This resulted in a strajght line. From these results, the energy of activation was found to be +26,700 calories per mole of nitrogen dioxide. The expression for the reaction rate constant as a function of temperature is
E
3 , = 54
0 P
9 w
a 3
u.
0
> w
0 >
5840 logla k = 16.72 T where k = reaction rate constant, hours-', and T = absolute temperature, ' K.
-
I 20
This reaction rate constant, k , expresses the rate of reaction in the form -loglo
Figure 7. Ultimate yield of adipic acid by recrystallization of dibasic acids
In using these equations, note that they apply only to mixtures that initially contain 0.13 mole of nitrogen dioxide per mole of cyclohexane.
I n order to determine the kinetics of the reaction between cyclohexane and nitrogen dioxide, the mole ratios of reactants were varied. Six samples were charged with concentrations of about 10, 20, 30, 40, 50, and 74 mole % of nitrogen dioxide a t a reaction temperature of 70" C. Forty minutes after the samples were put in the water bath, the most concentrated mixture detonated violently, This explosion completely demolished the experimental apparatus. I n view of the unexpected explosion, it was decided t o present the data of this investigation at this time. Reaction Rate between Cyclohexane and Nitrogen Dioxide
This reaction is assumed to be pseudo-unimolecular since the cyclohexane was present in large excess. The logarithm of the
0-
- 1.51
where C = moles of NOz per mole of cyclohexane, and 0 = reaction time, hours.
Solid line represents recovery of adipic acid crystals (m.p., 150-152' C.); broken line includes adipic acid estimated to b e in mother liquor
Mononitration of
c = ke
Literature Cited (1) AttanB, E. C . , and Doumani, T. F., IND. ENG.CHEM.,41, 2015 (1949). (2)
Bost, R. W., and Nicholson, F., IND.ENG.CHEM.,ANAL.ED., 7, 190 (1935).
Cavanaugh, R. M., and Nagle, W. M., U. S. Patent 2,343,534 (March 7, 1944). (4) Doumani, T. F., Coe, C. S., and AttanB, E. C., Jr., U. S. Patent 2,459,690 (Jan. 18, 1949). (5) Ibid.,2,465,984(March 29, 1949). (6) Horswell, R. G., and Silverman, L., IND.ENG. CHEM.,ANAL. ED., 13, 555 (1941). (7) Hunter, L.,and Marriott, J. A., J. Chem. SOC.,1936,p. 285. (8) Markownikoff, W.. Ann., 302, 1 (1898). (9) Schorigin, P., and Topchiev, A.,Ber., 67, 1362 (1934).
(3)
RECEIVED for review August 19,1954.
ACCEPTED January 28, 1955.
and p-Nitrotoluene
KENNETH A. KOBE, CHARLES G. SKINNER,
AND HERSHEL
B. PRINDLE
University of Texas, Austin, Tex.
I
DINITROTOLUENES
...
second step of TNT production
F
I
The yield of dinitrotoluenes from both 0 - and p-nitrotoluene has been determined as a function of the process variables-amount and concentration of sulfuric acid, temperature, time, and distribution of sulfuric acid between the mixed acid and the nitrator. Both isomers give essentially quantitative yields of 2,4-dinitrotoluene under the indicated optimum conditions.
OR the past several years a study has been conducted in these laboratories in an effort to define more fully the nitration characteristics of aromatic compounds-Le., benzene, toluene, the xylenes, cumene, and p-cymene (5, 7 , 8, 9, 10). Since 2,4,6-trinitrotoluene is, and has been since World War I, the single most important high explosive, a thorough study of its April 1955
preparation is important. However, there are few published data in the experimental journals concerning the production characteristics of the intermediates. This is probably due to the fact that nearly all the research has been conducted in operating plants. There are available, however, some recipes (which are more or less typical of all aromatic nitration reactions)
INDUSTRIAL AND ENGINEERING CHEMISTRY
785
ENGINEERING. DESIGN. AND PROCESS DEVELOPMENT Table 1.
Typical Laboratory Recipes for Conversion of Mononitrotoluene to Dinitrotoluene
.
Lit. Cited
yt Nitrotoluene, G.
Wt. HESO, in Reactor, G. 109
50
(1)
(la?) (8)
60
157
50
185
Wt. H&Olin Mixed Acid, G. 54.5
Conon. H&O4,
.. ..
that have been used to synthesize dinitrotoluenes in laboratory quantities. These data are incomplete but are presented in Table I since they formed a basis for starting research on the process variables that were studied.
c
50
60
70 WEIGHT
80
PER CENT
100
90
2,4-DlNlTROTOLUENE
Figure 1. Melting point-composition curve for o-nitrotoluene and 2,4.-dinitrotoluene
The nitration of toluene to yield trinitrotoluene ( T N T ) normally is conducted in a two- or three-stage process (11). The initial stage is the mononitration of toluene to yield a mixture of 0-, p-, and some m-nitrotoluene (6). I n a two-stage process the mononitrotoluenes may be converted directly to T N T or toluene may be converted to dinitrotoluene directly and then to the T N T (8). However, in the more conventional three-stage process, mononitrotoluenes are converted t o the dinitrotoluenes before finally being transformed into trinitrotoluenes.
%
97 96
90
Wt. "Os, G. 54.5
G. 0
Temp., O C. 90-100
2b:2
40150
H10,
73.5 27.2
Total Run Time, Min. 180
Yield,
%
High High 91
..
(Finally to 70)
30
of sulfuric acid. These data allowed the operating conditions to be defined in terms of cost of operation and purity of product. The reaction products to be anticipated in the nitration of 0- and p-nitrotoluene differ to some extent since the para derivative is symmetrical and yields only one major product (2,4-dinitrotoluene), whereas the ortho derivative has two points of activation leading to the production of 2,6-dinitrotoluene as well as the 2,4- isomer (3). Since both the latter compounds will yield alpha-TNT on further nitration no distinction icmade between the two in the yield calculations. I n actual plant operations the ultimate concern in all the nitration procedures is the eventual formation of alpha-TNT. Thus, in the mononitration of both toluene and the nitrotoluenes, a quantitative yield of nitration product is desirable. I n this respect no harm is done if some dinitrotoluene is formed during the mononitration of toluene or some trinitrotoluene is formed during the mononitration of 0- and p-nitrotoluene. However, since in this study the primary concern was the operating characteristics of nitration of 0- and p-nitrotoluene t o dinitrotoluenes, the amount of nitric acid utilized was kept a t the theoretical quantity to prevent polynitration. The extent of T N T formation was not determined, but instrumental analysis of several reaction mixtures indicated the amount to be very small.
100
I-
e5
W
Y
90
89
70
, 75 IO0
I 300
200
WEIGHT
500
400
OF SULFURIC ACID IN GRAMS
Figure 3. Effect of amount of sulfuric acid on yield of dinitrotoluenes 200 g. mononitrotoluene; theor. wt. " 0 3 ) 90% HgSO4 (60 parts in reactor and 40 parts in mixed acid); time, 15 min. a t 60' C. 3 0 k '
20
'
40 '
'
I 60
l
I 80
l
I 100
WEIGHT PER CENT p-NITROTOLUENE
Figure 2. Melting point-composition curve for p-nitrotoluene and 2,4-dinitrotoluene
The work reported here was concerned with the second step in the nitration. The yield of dinitrotoluene has been correlated with the process variables used previously-amount and concentration of sulfuric acid, temperature, time, and distribution 786
Experimental
Apparatus and Materials. The sulfuric acid used in this investigation was C.P. reagent grade material which had a minimum analysis of 95.5y0 H2S01. The nitric acid used was technical grade, anhydrous, with a total acidity (as "01) of 100% minimum. The 0- and p-nitrotoluenes were obtained from D u Pont and were used without further purification. Physical properties determined were: p-nitrotoluene, m.p. 51.5' C., reported ( 4 ) 51.7' C.; o-nitrotoluene, n z 1.5476, reported ( 4 ) 1.5474.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Vol. 47, No. 4
CHEMICAL PROCESSES stopped and the reactor removed from the stand and rinsed with several portions of water to remove all adhering organic material. The reaction mixture was subseDinitrotoluene Yield, Time, Run HsSO4, HzSOd, TEmp., Wt., g. Purity, 7% Min. NO. G. C. quently cooled in an ice bath and the or% % 264.0 98 98 10 600 65 10 90 ganic product separated. The solid organic 265,O 98 98 65 11 450 90 IO phase was melted in an equal volume of 65 265.0 98 98 12 10 350 90 264.5 96 96 65 10 250 90 13 hot water and, after being thoroughly agi260.0 95 93 65 14 10 175 90 256.0 83 80 10 125 90 15 65 tated, it was poured immediately into a 92 259,l 16 65 10 .. 175 clean, previously warmed, separatory fun255.3 .. 125 79 17 10 65 76 350 19 10 50 82 235.1 81 nel, and the organic phase mas recovered by 251.0 350 77 20 15 82 50 258.5 io 350 90 21 10 78 82 decantation. 22 10 350 84 65 82 255.6 88 Mzthod of Analysis. I n the mononitra350 91 10 90 262.3 92 23 82 350 91 24 10 92 261.0 92 85 tion of p-nitrotoluene it has been found pos91 25 10 261.0 93 350 78 85 350 91 26 10 65 263.0 91 85 sible to utilize the melting points of the 350 88 27 10 259.0 90 50 85 reaction mixtures as a method for determi96 28 10 264.0 96 350 78 78 96 263.7 96 350 29 10 90 90 nation of purity and yield. The reaction 97 30 65 90 265.7 97 10 350 262.1 95 10 350 95 31 50 90 mixtures were compared with known blends 350 93 32 50 96 262.0 95 10 prepared from pure compounds, for which 96 265.6 96 65 10 350 33 96 96 34 266.0 96 10 350. 96 78 the melting points are presented in Figures 10 350 95 35 96 265.6 95 80 1 and 2. This was possible because 2,4dinitrotoluene resulted from a substitution a t either one of the two active Dositions during The reactor used was a three-necked 1000-ml. flask, with nitration. I n the mononitration of o-nitrotoluene, this was not a built-in set of cooling coils of the same type used previously the since both 2,6- and 2,4-dinitrotoluene are formed, by Kobe and Levin (8). The stirrer was run a t its maximum rate of 4000 r.p.m. in all experiments, and the temperature was controlled b y running steam or cooling water through the coils as needed. No effort was made to exclude air or condense any off gases or water vapor. Table 111. Summarized Data for Nitration of 200 Grams of o-Nitrotoluene Using Theoretical Weight of Nitric Acid Method of Nitration. A mixture of nitrotoluene and sulfuric acid (of the appropriate concentration) was placed in the reactor Dinitroand the stirrer slowly turned to full speed. Steam was passed Run HzSo4~ Temp No % O C G. Min G. % through the inner coils t o bring the mixture within a few degrees 36 450 90 65 15 263 1 95 of the desired reaction temperature after which the steam was 37 350 90 65 15 265 1 99 264 9 98 38 250 90 65 15 disconnected, and cooling water was passed through the same 39 175 90 80 15 258 4 91 40 125 90 80 15 256 0 83 coils. The mixed acid was then introduced through a dropping 41 450 90 65 15 262 9 95 funnel into one neck of the flask. The other neck contained a 42 450 90 65 15 263 0 95 43 350 90 65 15 265 4 99 110' C.thermometer. 44 350 90 65 15 265 4 99 45 350 90 65 15 265.1 99 The time of the run was calculated from the start of addition of 47 250 90 80 15 264.7 98 264.8 98 the mixed acids. It was usually attempted to keep the feed 49 250 90 65 l5 262.5 94 50 190 90 65 15 rate constant and obtain the desired reaction temperature by 51 190 90 65 15 262 3 94 90 80 15 262 7 95 52 190 adjusting the rate of flow of the cooling water. After all the 90 65 15 265 0 98 53 250 nitrating acid had been charged, the reaction was allowed to 54 250 90 65 15 264.7 98 90 65 15 262.5 94 55 190 continue for a n additional 20 minutes, after which it was quenched 56 450 90 65 15 263.0 95 90 80 15 262 5 95 57 450 by addition of several volumes of cold water. The stirrer was 100 90 65 15 265 9
Table 11.
Summarized Data for Nitration of 200 Grams of p-Nitrotoluene Using Theoretical Weight of Nitric Acid
::
-
H2s043
io0
90
80
m
60
50
50
60
70
80
90 50
TEMPERATURE
60 IN
70
80
40 90
'C
Figure 4. Effect of temperature and sulfuric acid concentration on yield of dinitrotoluenes 200 g. mononitrotoluene; theor. wt. " 0 3 ; 350 g. HzS04 (60 ports in reactor and 40 parts in mixed acid); time, 15 min.
April 1955
59 60 62 63 64 65 66 67 68 69 70 71 72 73 75 76 78 79 80 81 82 83 84 85 86 87 88 89 90 91 101 102 103 104 105 106
107 108
350 '350 350 350 350 350 350 350 350 350 350 350 350 350 350 350 350 350 350 350 350 350 350 350 350 350 350 350 350 350 350 350 350 350 350 350 350 350
90 90 90 90 90 90 90 90 90 85 90 85 85 85 85 85 85 85 85 80 80 80 80 80 80 80 80 80 96 96 96 80 80 85 85 85 85
65 50 50 78 78 78 90 90 90 50 78 50 65 65 78 78 90 90 90 90 90 90 78 78 60 65 50 90 50 65 78 78 60 50 80 65 90
INDUSTRIAL AND ENGINEERING CHEMISTRY
15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 16 15 15 16 15 17 l5 19 38 15 15 l5 30 27 15 15 15 15
264.8 266.1 264 9 266 4 265 7 265 8 264.9 265.9 266.5 262.7 265 4 261.8 262 6 261 5 264 2 263 9 264 4 264.6 263 9 243.6 245 7 246 5 242.0 243.9 234 5 227 4 223 2 249 3 264 5 266 4 266 7 248 9 235.4 261.5 262 0 262 4 262 8
98 100 98 101 100 100 98 100 101 95 100 94 95 93 97 97 98 98 97 66 69 72 64 67 52 42 35 75 98 101 101 74 54 93 94 94 95
787
-
ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT Table IV. Effect of Sulfuric Acid Distributed between Reactor and Feed on Mononitration of 200 Grams o-Nitrotoluene with Theoretical Nitric Acid Run No. 100 93 94 65 66 95 96 97
H*SOa, G. 350 350 350 350 350 350 350 350
H804,
Temp.,
90 90
80 80 80 80 80 80 80 80
%
90 90 90 90 90 90
Time Min.' 13 16 16 15 15 15 14 18
c.
100
100
95
95
90
90
85
85
80
60
I / 111 1
70 80
I 84
INITIAL
92
88
SULFURIC
ACID
96 80
84
CONCENTRATION
1
0-NITROTOLUENE
88
IN
92
70 96
PERCENT
Figure 5. Effect of temperature and sulfuric acid concentration on yield of dinitrotoluenes
Dinitrotoluene, G. 267.5 266.4 265.2 265.7 265.8 265.0 264.9 264.7
HzSOd Ratio, % Flask Feed 100 0 80 20 80 20 60 40 60 40 20 80 20 80 0 100
Yield, % 100 99 99 100 100 99 98 98
The data are based on a charge of 200 grams of the mononitro compound and the theoretical amount of nitric acid, unless otherwise stated. o-Nitrotoluene. The optimum weight of sulfuric acid is from 300 to 350 grams as indicated in Figure 3; the yields fall off rapidly below 300 grams. There is no over-all change in yield within reasonable temperature ranges a t the higher sulfuric acid concentrations as indicated in Figure 4. With concentrations of 90 to 95% sulfuric acid there is no appreciable difference between the conversion a t 50' and 90" C. At lower acid concentrations (as 8070), there appears a noticeable temperature effect, the yield increasing rapidly up to 70% conversion a t 90' C. The effect of initial sulfuric acid concentration on the yield of dinitration product is cross plotted a t varying reaction temperatures in Figure 5. The optimum concentration is approximately 90% from 50' to 90" C. The anticipated effect of increasing yield with longer reaction times is shown in Figure 6. Since, a t higher sulfuric acid concen-
200 g. mononitrotoluene; theor. wt. HNOa; 350 g. H2SO4 (60 parts in reactor and 40 parts in mixed acid); time, 15 min. 90 t-
Further, the percentage of these isomers could not readily be ascertained. The analytical technique eventually utilized was developed from an empirical approach-that is, the yield calculations were based on the gain in weight of the reaction mixture. For example, 137.1 grams of mononitrotoluene should yield 182.1 grams of dinitrotoluene or a gain in weight of 45.0 grams in the recovered organic phase from the nitratFn. Assuming, in a given run, a gain in weight of 40.0 grams, the yield would be 40.0/45.0 X 100 = 89%. This method has been checked with p-nitrotoluene where the yield could also be determined from the melting point data, and a reasonable agreement was obtained-usually within 1 %. This was considered adequate to establish optimum conditions. At higher temperatures and sulfuric acid concentrations the results calculated on a weight gained basis gave higher than theoretical results. This was probably because the analytical method cannot take into account side reactions such as sulfonation or oxidation. A study of the ultraviolet spectra of the product obtained with both 0- and p-nitrotoluene on mononitration indicated essentially pure dinitrotoluenes, with no evidence of T N T in sufficient concentration to be observed. This was also true of samples from two runs with o-nitrotoluene examined by infrared techniques. Process Variables
The results of the majority of the runs conducted are presented in Tables 11,111, and IV. These data have been examined and cross plotted to determine the effect of changing process variables on the yield of dinitrated product fromo-and p-nitrotoluene. 788
y
80
W
z n J
?
70
60
50
40
50
1
I
60
60
70
TEMPERATURE
IN
90
OC.
Figure 6 . Effect of time and temperature on ' yield of dinitrotoluenes 200 g. mononitrotoluene; theor. wt. "0s; 80% HzSOd (60 parts in reactor and 40 parts in mixed acid); time, 15 min.
trations the yields were essentially quantitative with even the shortest reaction times, as the 7- t o 15-minute addition period, these data were obtained a t an acid concentration of SOY0, which is less than the optimum. There was observed no difference in the yield of dinitration product relative to the amount of sulfuric acid split between the nitrator flask and the mixed acid feed as shown in Table 111. At both extremes-Le., all the sulfuric acid in the nitrator flask or all in the mixed acid feed-the yield was 100% under optimum conditions. From the standpoint of temperature control and mixing, approximately an even division was desirable because of the design of the nitrator flask.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 47, No. 4
CHEMICAL PROCESSES
$-Nitrotoluene. The optimum sulfuric acid weight per 200gram batch of p-nitrotoluene was the same as that with the ortho derivative-300 t o 350 grams (Figure 3). The optimum reaction temperature was from 65” to 70” C. as shown in Figure 4. A slight decrease in both yield and purity of product occurred a t lower and higher temperatures, using the optimum initial sulfuric acid concentration of 90%. The effect of initial sulfuric acid concentration on the yield a t various temperatures (Figure 5 ) is highest at 90% H2SO4 from 50” t o 90” c. Summary
The quantity of sulfuric acid required for maximum yield of mononitration was found to be practically the same for both 0-and p-nitrotoluene. However, there appeared t o be a broader range in the o-nitrotoluene. For a 200-gram batch of mononitrotoluene, 350 grams of sulfuric acid is optimum when using the theoretical weight of nitric acid. The optimum reaction temperature was practically the same for both isomers, about 65” to 70” C. At these temperatures and above, the reaction rate was essentially instantaneous. The concentration of sulfuric acid required for optimum yield was similar for both 0- and p-nitrotoluene. The minimum strength of sulfuric acid required for a maximum yield is about 90%. It appeared t o make no difference whether the sulfuric acid was added to the nitric acid feed, placed with the mononitrotoluene, or mixed between the two. Both isomers gave nearly quantitative yields under optimum conditions-98% for the p-nitrotoluene isomer and 100yo for the o-nitrotoluene. An infrared study indicated no unreacted material in a reaction mixture of the ortho isomer.
The reaction conditions that gave the maximum yield of dinitrotoluene (based on a 200-gram charge of mononitrotoluene) are: Variable Wt. HzS04, grams Concn. HzS04, grams T e m p , C. Reaction time, rnin.
o-Nitrotoluene 250-350 90 50 15 20
+
p-Nitrotoluene 350 90 15
65 + 20
Acknowledgmeni
The work reported here was sponsored by the Army Ordnance Corps under research contract DAI-23-072-ORD( P)-6. The authors express appreciation for permission t o publish these results. Literature Cited Davis, T. L., “Chemistry of Powder and Explosives,” Vol. I, p. 148, Wiley, New York, 1941. DeBeule, P., “Fabrication du Trinitrotoluene,” Publs. centre de recherches sci. et tech. l’industrie produits explosifs. Gibson, W. H., Duckham, R., and Fairbairn, R., J . Chem. SOC., 1 2 1 , 2 7 8 (1922).
Handbook of Chemistry (N. A. Lange, editor), 8th ed., pp. 618, 1377, Handbook Publishers, Sandusky, Ohio, 1952. Haun, J. W., and Kobe, K. A., IND.EKG.CHEM.,4 3 , 2355-62 (1951).
Jones, W. W., and Russell, >I., J . Chem. SOC.,1947, pp. 921-3. Kobe, K. A., and Brennecke, H. M., IND.ENG.CHEM.,4 6 , 72832 (1954).
Kobe, K. A., and Levin, H., I b i d . , 4 2 , 352-6 (1950). Kobe, K. A , , and WIiIls, J. J., Ibid.,45, 287-91 (1953). Kobe, K. A., and Pritchett, P. W., I b i d . , 44,1398-1401 (1952). Organic Chemistry (H. Gilman, editor), Vol. IV, p. 974, Wiley, NewYork, 1953. Weygand, C., “Organic Preparations,” p. 281, Interscience, New York, 1945. RECEIVED for review May 21, 1954. ACCEPTEDJanuary 14, 1955.
Synthesis of Pyridines SHERMAN
L.
LEVY* AND DONALD F. OTHMER
Polytechnic lnsfifute of Brooklyn, Brooklyn 7 , N.
Y.
The vapor phase reaction of formaldehyde (40%), acetaldehyde, and ammonia at conditions of 360” C., 3 19% excess ammonia, and a total feed rate of 1.1 8 grams per hour per gram of catalyst produced a 48.6% optimum yield of pyridine and picolines. Thermodynamic and kinetic data are given for process design, and a preliminary flow sheet is presented,
N
E W chemical products have recently created a demand for pyridine and its homologs as raw materials therefor. This is greater than the production capacity by classical methods, and an economical. method is desired for their synthesis independent of coke oven operations. Three vapor phase reactions have been reported to yield pyridinic materials: 1. Between acetylene and ammonia over various catalysts with low yields and many side reactions (13-16, 43). 2. Between ammonia and methyl, ethyl, n-propyl, n-butyl, and allyl alcohols (3, 20, 35) over ca1,alysts of the dehydrogenating-dehydrating type. T h e dehydrogenation may give an aldehyde which reacts with ammonia t o give a maximum pyridinic yield of 7 mole yo. 3. Between aliphatic aldehydes and ammonia over dehydrating catalysts, as the second step of (b) (5-7, 8, 14, 62, 84, 37, 29, 30, 34, 40, 42). The reaction between acetaldehyde and ammonia produces a maximum total yield from 30 to 50 mole yo 1
Present address, Chemical Corps School, Fort McClellan, Ala.
April 1955
of pyridines and picolines (14, 30, do), whereas acrolein and ammonia (22, 24, 42) produce a maximum total pyridine and picoline yield as high as 55 mole %. Several other reactions with ammonia are reported-e.g., butadiene ( I C , 4 7 ) and ethylene oxide (31)-but in no case are the yields as promising as for the aldehyde-ammonia reaction. This was chosen as the basis for an attempted synthesis, although quantities of resins are known to be formed by side reactions. These resins are deposited on and rapidly poison the catalyst, especially when acrolein is used. I n order to diminish the troublesome resin formation, a process was used to form the reacting aldehyde in situ (6). There would be continuous formation of the aldehyde in the reaction zone, and if its reaction with ammonia was a t the same rate, the instantaneous aldehyde concentration would be very low, and resin formation would be minimized. The equipment (Figure I ) was constructed mainly of glass. A cylinder of anhydrous liquid ammonia supplied ammonia va-
INDUSTRIAL AND ENGINEERING CHEMISTRY
289
