UNIT PROCESSES
,
that this same effect is superimposed on another that is decreasing the effectiveness of the initiator as pressure increases. A difference curve was obtained by subtracting the ordinates of the dichloro curve from those of the trichloro curve. The negative slope of this difference curve indicates the decrease in initiator efficiency with pressure due to the elimination of the second chlorine atom, This second chlorine elimination is not just a side reaction but is parasitic in nature, since i t uses radicals Fhich might otherwise initiate alkylation, Similar curves and conclusions were obtained when using the isoheptane yield as basis in preference t o the total alkylate yield. An estimate of the difference in initiator consumption can be made from runs 15 and 21 (at pressures of 14,900 and 14,800 pounds per square inch, respectively) where yields with the two initiators were similar. I n run 15, if each molecule of trichloropropane lost two chlorine atoms, 67% of the chlorine fed would have been lost. Table IV shows that 43% was lost, a loss equivalent to decomposition of 65% of the molecules. I n run 21, loss of one chlorine per molecule of dichloropropane would be a loss of 50% of the chlorine fed. Experimentally (Table IV) 20% was lost-a decomposition of only 40% of the molecules. This difference (40 to 65%) is magnified by the fact that smaller percentages of dichloropropane (2.6%) than of trichloropropane (3.1 %) were used in the feed mixtures. The obvious general conclusion is that an initiator that leaves a radical-sensitive fragment is less efficient than one that leaves no such fragment. Acknowledgment
Thanks are accorded t o the Dow Chemical Co. for the fellowship in chemical engineering that one of the authors, J. E. Knap, held for two years and for the help of their spectroscopy laboratory. Thanks are also due the National Bureau of Standards for the spectroscopic standards of the hydrocarbons. literature Cited (1) Barton, D. H. R., J . Chem. Soc., 1949, p. 148. (2) Barton, D. H. R., and Head, A. J., Trans. Faraday Soc., 46, 114 (1950).
(3) Barton, D. H. R., and Howlett, K. E., J . Chem. Soc., 1949, p. 155. (4) Ibid., p. 165. (5) Barton, D. H. R., and Onyon,P. F., Trans. Faraday Soc., 45, 725 (1949). (6) Barton, D. H. R., and Onyon, P. F., J . Am. Chem. SOC.,72, 988 (1950). (7) Ciapetta, F. G., IND. ENG.CHEV.,37, 1210 (1945). (8) Egloff, G., and Hulla, G., “Alkylation of Alkanes,” Vol. I, pp. 637-60, New York, Reinhold Publishing Corp., 1948. (9) Egloff, G., and Hulla, G., Chem. Rev.,37, 323 (1945). (IO) Frey, F. E., and Hepp, H. J., IND. ENQ.CHEY.,28, 1439 (1936). (11) Heigl, J. J., Bell, M. F., and White, J. V., Anal. Chem., 19, 293 (1947). (12) Ipatieff, V. N., Monroe, G. S.,and Fischer, L. E., IXD.ENG. CHEM.,40, 2059 (1948). (13) Ipatieff, V. N., and Schmerling, L., “Alkylation of Isoparaffins”
in “Advances in Catalysis” I, edited by Frankenburg, W. G., Komarewskg, V. I., and Rideal, E. K., p. 27, New York, Academic Press Inc., 1948. (14) Linn, C. B., and Grosse, -4. V., IND. EKG.CHEM.,37, 924 (1945). (15) McAllister, S.H., Anderson, J., Ballard, S. A., and Ross, W.E., J . Org. Chem., 6,647 (1941). (16) Mrstik, A. V., Smith, K. A., and Pinkerton, R. D., Advances in Chem. Ser., No. 5 , 97-108 (1951). (17) N. V. de Bataafsche Petroleum Maatschappij, Dutch Patent 60,768 (March 15, 1948). (18) Oberfell, G. G. and Frey, F. E., Oil Gas J., 38, No. 28, p.150 and No. 29, p. 70 (1939). ENG. CHEM.,38, (19) O’Kelly, A. A,, and Sachanen, A. N., IND. 462 (1946). (20) Pines, H., Grosse, A. V., and Ipatieff, V. iX.,J. Am. Chem. SOC., 64, 33 (1942). (21) Rice, F. O., Ibid., 53, 1959 (1931). (22) Ibid., 55, 3035 (1933). (23) Rice, F. O., and Polly, 0. L., J . Chem. Phys., 6, 273 (1938). (24) Schmerling, L., J. Am. Chem. Soc., 67, 1778 (1945). (25) Sliepcevich, C. M., and Brown, G. G., Chem. Eng. Progr., 46, 556 (1950). (26) Stover, W. A., U. S Patent 2,460,719 (Feb. 1, 1949). (27) Ibid., 2,369,344 (May 3, 1949). (28) Thacker, C. M., Ibid., 2,468,899 (May 3, 1949). (29) Tilicheyev, M. D., and Massine, P. iM.,in Sachanen, A, E., “The Chemical Constituents of Petroleum,” pp. 162-3, Kew York, Reinhold Publishing Corp., 1945. RECEIVED for review January 2, 1953. ACCEPTEDSeptember 2, 1953. This paper is based on a Ph D. thesis at the University of Illinois entitled “High Pressure Reactions in a Flow System” by James Eli K n s p , 1953.
Vapor Phase Nitration FACTORS AFFECTING DEGRADATION TO LOWER NITROPARAFFINS G. BRYANT BACHMAN AND M. POLLACK’ Purdue Universify, lafayeffe,Ind.
A
study of factors leading to lower molecular weight nitroparaffins in the vapor phase nitration of propane has shown that the degree of degradation of the propane is increased by oxygen catalysis and decreased by chlorine catalysis. By proper application of these catalysts considerable control over the distribution of the products of nitration may be achieved. The theoretical correlation of these effects with reaction mechanisms involving free radicals offers a satisfactory explanation of vapor phase nitration processes.
v
phase nitration of a hydrocarbon such as propane leads not only to the nitropropanes (1- and 2-NP) but also to nitroethane (NE) and nitromethane (NM). Normal distribution in the current commercial process is approximately, 1-NP, 25%; 2-KP, 40%; NE, 10%; NM, 25%. Since the demand for the individual nitroparaffins does not necessarily correspond to this distribution, a means of controlling the separate yields would be 1
Present address, Glyco Products Co., Ino., Willismsport. Pa.
April 1954
highly desirable. Furthermore, in the event that production of still higher nitroparaffins (C, and above) should become desirable a means of minimizing the degree of degradation of the original hydrocarbon nitrated would be imperative. We have, therefore, developed methods that give high yields of 1- and 2-NP’s from propane. These methods are believed to be applicable to higher alkanes equally satisfactorily, and to provide means for obtaining nitro compounds not hitherto readily available,
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
713
ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT
(2)
system. If t'his is high the probability is low that a propyl radical \ d l degrade before it reacts with .SOz. There are other considerations which usually make it undesirable t,o use a T high nitrogen dioxide t'o propane ratio, although this may be done with relatively expensive hydrocarbons. Fortunately tho half life of alkyl radicals seems to be sufficiently long to prevent much degradation by this process. Equat'ions 2. 3, and 4 represrnt a series of reactions over d i i c h v e have as yet found no simple means of control. The relat,ive tendencies of alkyl radicals to unite rrit,h ,KOato produce R O S O versus RKOz as well as fact,ors l\-hich influence these tendencics are unknown. However, once the ROKO is formed itd degradation to loxer alkyl radicals appears to be quite rapid (I). L p a tion 4 is rapid compared, for example, to Equation 1. -4lkyl nitrites do not appear in the products of vapor phase nitration although considerable amounts of S O are obtained. The best means of controlling degradation is derivable froin Equations 4, 5, 6, and i . The extent to which oxygen ent'crs the system determines to a marked degree t,he amount of dcgradation that occurs. Elimination of added ox>-gen or air ~vould appear to be desirable for this reason. Hoivever, oxygen is added t o increase the rate of formation of alkyl radicals, which it does by various processee described elseivhere ( 2 , I O ) . A high rate of alkyl radical formation is necessary to maintain a proper balaiice with NOS radicals. The latter do not remain unchanged very long a t nitration temperatures and dissociate to KO 1 / 2 0 2 if sufficient alkyl radicals are not present. These arguments arc based on the assumption that the actual nitration step consists in the combination of alkyl radicals il-ith S O , radicals. If, instead, the principal nitration step involves the reaction of alkyl radicals with nitric acid molecules, then t,he rate of formation of alkyl radicals becomes even more important, because the rate of dissociation of nitric acid is much greater than the rate of dissociation of KO2 radicals under vapor phase nitration condit,ions. 111 either event oxygen is obserl-ed t o increase bot,h the conversions and the degrees of degradation. Oxygen is therefore riot a good catalyst for nitrat,ions in which a high yield of nitro derivatives of the hydrocarbon nitrated is desired. The best x-ay out of t'his dilemma with oxygen is to use another catalyst for alkyl radical format,ion. Halogens, especially chlorine, are cheap enough and active enough to provide the optimum alkyl radical concentration. We have shown I X C viously (6) that combinations of oxygcn and halogens give improved yields of and conversions to nitroparafins. I n all of these experiments, however, considerable amounts of osygc~n 'irere always present, The present 7%-orkwas undertaken to study the catalytic effects of halogens alone and to compare these with results obtained in the presence of added oxygcn. Halogens attack hydrocarbons by chain processes and produce alkyl but not alkoxy radicals. Relatively small amounts of halogen remain combined with carbon, Hence in comparisoii with oxygen, halogens give improved yields based on hydrocarbon. Furthermore, in contradistiiict,ion to oxygen, halogens are regenerated and may cause repeated formation of alkyl radicals. They therefore are rpquired in lower concentrations (about 20% that of oxygen) for the maintenance of an optimum rate of alkyl radical formation
(3)
61*.-b 2c1-
+
Figure 1. 2.
Schematic Druwing - of Vapor Phuse Nitration Equipment
Nitrogen cylinder
3. Flowmeter for nitrogen
4. Surge bottle 5. Manometer to record pressure at inlet of preheater 7. Nitric acid flosk 8. 9. 10. 12.
13. 14. 16. 17. 19. 20. 22. 23.
24. 26.
Cast iron tank (some for reactor) with magnesium oxide insulation Nitric acid iet Preheater Reactor Manometer for recording pressure at exit of reactor Spirol water condenser Propane cylinder Flowmeter for propane Dry ice traps Product flask Chlorine cylinder Flowmeter for chlorine Dry ice flask plus dry ice condenser Wet test meter
The process of nitration in the vapor phase has been shown ( I ) t o proceed very probably through alkyl free radicals. These radicals combine with nitrogen dioxide (,NOS) radicals to produce nitroparaffins. Hovxver, they may also degrade t o Ion er alkyl radicals or react n i t h othei substances present to yield products that also degrade to loner alkyl radicals. Some of the principal . processes by rrhich this may occur are illustrated in Equations 1 through 7 using the 1-propyl radical as an example: CHaCHiCHza CHsCH?CH?*
C H ~ Z C H ? T CHa*
+=
+ .IT02
+
CH3CHICHSONO
CH3CH2CHSOSO -+ CHaCHZCHzO. CHjCHnCR20. CHaCH2CHz. C"jCH&H202*
-+
CH,CH,CH*OzH
CHICHZ. 4- CHzO
+ 02
+HA
+
+
+ *SO
+
CH~CH~CH~OI.
+
CH~CHSCH~OSH . A
CI-I,CH,CH,O*
+ 'OH
(1)
(5) (6) (7)
Reaction 7 is followed by Reaction 4. H A may be nitric acid, a hydrocarbon, an alcohol. or any other hydrogen donor. The loss of propyl radicals through Reaction 1 is controlled in part by the concentration of .NO2 radicals present in the reaction 114
RH
(4) HC1
+ C1*-+Re + HC1
+ O[I1XOa, SO,:
---t
HO. + @I.
These equations, selected Crom the many which occur, illustrat,e the bases for this discussion.
Apparatus The appaiatus is ehona in Figure 1. It is an adaptation of similar equipment described previnlldy ( I ) .
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
V Q ~46, . No. 4
UNIT PROCESSES 45
70
i4
I
‘A\
.::: \
42
64
\
A\
53
+
$m 5 2
6
8 6
36
W P W
62
I-
U
E
2
58
9
39
2
\
33
46
/ 30
40
34
21
0
25.5
0
0.1
0.2 0.3 CWHNOI Ralio
0.4
0.5
Figure 3.
0.6
0 =
Figure 2. Effects of Catalyst Concentrations on Per Cent Conversions to Nitroparaffins Based on Fraction of Nitric Acid Charged
0 = no added oxygen
A =
oxygen to nitric acid ratio = 1
The nitric acid jet calibration is hi hly critical since it measures high viscosity, low volume liquic? flow while all other flowmeters in the system measure low viscosity, high volume gas flow. Furthermore, jets of quite different acid-delivery capacities are required in different experiments and rapid calibration of different jets is desirable. In accordance with the law of Poiseuille, a jet calibrated with distilled water under fixed pressure will deliver a proportional amount of nitric acid under the same or another fixed pressure; the proportionality constant is practically independent of the similar jets used and of small variations in the acid concentrations and is dependent on the pressures applied. With the aid of proportionality nomographs prepared according to this method rapid calibrations were accomplished. Chlorine was introduced as a gas metered into the propane stream through an orifice-type flowmeter. Bromine was introduced as a gas by passing the propane over liquid bromine in two tared containers in series. The rate of flow of bromine was regulated by controlling the temperatures of the bromine containers.
0.1
0.3 0.4 CI~HNOIRatio
0.2
0.5
0.6
Effects of Catalyst Concentrations on Mole Per Cent Yields Based on Propane
no added oxygen
A = oxygen to nitric acid ratio = 1
was analyzed as usual by the mass spectrograph for nitroparaffin distribution. By the use of known prepared nitroparaffin mixtures, i t was shown that the nitroparaffins, nitromethane, nitroethane, 1-nitropropane, 2-nitropropane, and nitrobutane show no significant tendency to codistill with chloroform.
Effects of Various Oxygen-Halogen Combinations
F
Figures 2 and 3 are based on a series of runs with all conditions the same except for the catalyst concentrations. Figure 2 shows the effects on conversions to nitroparaffins based on nitric acid charged, and Figure 3 shows the effects on yield based on propane reacted expressed as mole per cent. Conditions for the runs were as follows:
Product Analysis
Reactor bath temperature = 423 i 1’ C., contact time = 1.75 f 0.10 seconds, propane to nitric acid = 10.8 i 0.5, water to nitric acid = 1.53 f 0.02, surface to volume ratio in the reactor = 300 cm.-l; the variable was the chlorine to nitric acid ratio. In the runs made by the present investigators (solid lines of figures) no oxygen was added to the reaction mixture; the runs made by Bachman and Kohn ( 6 ) (dashed lines of figures) were made in the presence of an oxygen to nitric acid ratio of 1.0.
The product analysis was identical to that described previously (2). Since it was found that small amounts of I- and 2-chloropropanes interfere with the determination of the 1- and 2-nitroproranes by the mass spectrograph, it was necessary to employ chloroform as a low boiling intermediate boiler which would ensure removal of the 1- and 2-chloropropanes. The procedure for the preparation of samples for mass spectrographic analysis was modified as follows, 5 ml. of redistilled chloroform and 2 grams of boric acid were added to the dried ether extract containing the nitroparaffins, and the mixture was heated until no more chloroform distilled. The mixture remaining in the pot
Somewhat higher mole per cent conversions to total nitroparaffins may be obtained with oxygen present (45%) than with it absent (40% in this equipment) although the optimum conversions occur a t quite different concentrations of chlorine in the two cases. On the other hand much higher per cent yields may be obtained in the absence of oxygen (66%) than in its presence (42%). The relative importance of conversions and yields is, of course, determined by the relative costs of the nitrating agent and the hydrocarbon, respectively. Figures 4 and 5 show the effects of catalysts on nitroparaffin distribution measured as mole per cent conversions based on nitric acid (Figure 4) and as mole per cent yields based on
April 1954
INDUSTRIAL AND ENGINEERING CHEMISTRY
715
ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT PO
r
20
10
NM
10
1
NM
0
15
O 20
t
2-NF
10
I
0
0.2
I
0.4 CIdHNOs Ratio
0
I
0.6
0.8
0.1
0.4 CIdHNBa Ratio
0.4
a. 8
Figure 4. Effects of Catalysts on Nitroparaffin Distribution Measured as Mole Per Cent Conversions Based on Nitric Acid
Figure 5. Effects of Catalysts on Nitroparaffin Distribution Measured as Mole Per Cent Yields Bused on Hydrocarbon
0=
0 = no added oxygen
no added oxygen
A
S=
oxygen to nitric acid ratio = 1
hydrocarbon (Figure 5 ) . With oxygen present, the conversions and yields of the lover nitroparaffins are higher, nhile in the absence of oxygen the conversions and jields of the higher Gtroparaffins are higher. The extreme variations in individual nitroparaffin conversions obserwd in a large series of experiments are as follows: Sitroparaffin Obtained ShI
NE
1-NP 2-SP
Conversions, % Yaxinium AIinimuni 49 9 36 6 .. 35 9
45
3
The relative value of catalysis in the presence and in the absence of added oxygen is determined in part by the relative importance of converPion versus yield and in part by the degree of degradation that can be toleiated or is desired in the nitroparafins obtained. On a weight per cent basis the eflects of oxygen and halogcns are also striking. Calculations based on these experiments and others described previously ( 1 ) show that total nitroparaffin conversions may be catalytically increased as much as 32% with oxygen-halogen conlbinations and as much as 46% vith chlorine alone compared to uncatalyxed nitratione. Whereas bromine is more effective than chlorine nhen uscd as a promoter for oxygen catalyzed nitrations ( 6 ) , the reverse is true when oxygen is absent. In fact the first observable effect of bromine alone is a decrease in both conversions and yields. This unexpected effect appears to be due to the fact that bromine, b u t not chlorine, rapidly destroys nitroparaffins. Ilass and coworkers [Riley (Q)] observed that nitroethane and the nitropropanes chlorinated verr sluggishly at teinperatuI es up to 100' C. in the presence of strong illumination. Kitroniethane
716
0
A = oxygen to nitric acid ratio = 1
did not react at all under similar conditions. On the other hand nitromethane, nitroethane, and 1-nitropropane reacted x i t h bromine violently after an initial period of induction and formod large amounts of ammonium and hydroxylammoniurn salts;. The difference in the behavior of chlorine and bromine observed by Rass and Riley is probably attributable to the reducing power of hydrogen bromide relative t o hydrogen chloride. The latter does not reduce nitro groups while the former does. The induction period in the reaction v i t h broinine is necessary for the formation of some hydrogen bromide mhich then reduces t h e nitro compound to substances more readily brominated, rihich in turn produces more hydrogen bromide. The reaction is thercfore autocatalytic. Both bromine and chlorine catalyze the formation of nitroparaffins in the vapor phme process, but bromine alonr is an undesirable catalyst, because it further rcact,s with the nitroparaffins produced and converts t'heni to other products. Conditions were encountered in some of the experiments n-hich resulted in a niarked decrease in the apparent effectivencss of oxygen and chlorine catalysts vhen used individually. After much fruitless investigation these were traced to a new sample of glass woo1 used as a packing in the reactor tubes. Cormpoiidence Kith the Corning Glass Works, suppliers of the old arid new glass wool, indicated that the glass wool P;as troublesolilc, because it contained relatively large amounts of boric oxide. This substance was shown previously (4) to be an anticat)a for nitration. Its use in reactor lubes should be maintained minimuin. as with
in Presence
Nitrib: Aeid
0%~~~~~~$~~
The nitration of a natural gas mixture in the presence of halogens was investigated to see if these catalysts are effective in such
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
Vol. 46,No. 4
UNIT PROCESSES a mixture and to determine the optimum conditions to produce the highest per pass conversion. Such information might be of considerable economic value, as well as of theoretical importance, because of the much lower cost of natural gas as compared with isolated fractions of natural gas. The natural gas employed had the following volume composition when dried, nitrogen, 13.65%; methane, 75.56%; ethane, 6.36%; propane, 3.45%; isobutane, 0.31%; n-butane, 0.6%. The problem vias approached from two standpoints. The first was designed to nitrate all of the hydrocarbons, including the methane, in the presence of a moderate percentage of the inert gas, nitrogen. Hass and Alexander ( 7 ) showed that the ronversion obtained in the nitration of methane in the absence of oxygen is independent of the nitrogen gas concentration up to 30% nitrogen by volume. The second was designed to convert the ethane and propane in the gas as completely as possible to nitroparaffins without attempting to affect the methane, which is considerably more difficult to nitrate. This was equivalent, essentially, to nitrating ethane and propane in the presence of a very high percentage of inert gases. The first approach involved an attempt to nitrate all of the hydrocarbons in the gas including the methane. I n this case the ratio of natural gas to nitric acid was much lower than that used in the second approach. Table I shows that, for the ratio natural gas to nitric acid to water to chlorine of 13.6 i 0.5/1/1.60/0.40 and a contact time of 1.7 to 1.8 seconds, an optimum in conversion of 13.0% was obtained a t 450' C. However, since E-19 (Table 11) shows that a conversion of 12.9% \vas obtained for essentiallv the same ronditions v-ithout added chlorine, it can be stated that essentially no catalytic effect of chlorine was shown with the predominantly methane gas mixture. Run E-21 in Table I1 shows data for a run made a t 450" C. with bromine in the absence of added oxygen. As observed
Table I.
Effect of Reaction Temperature in Nitration of Natural Gas Runs
Re:ctor bath temp., C. Convetsion. %
Table II.
E-24
E-20
E-23
435 i 1 10 5
450 i 1 13 0
460 2~ 1 11.0
Reactants, moles C3Hi HXO3 (69.6 n t . "c) HzO Halogen, Clz On S a t u r a l gas
*
Products, RNOz Conversion (on 3-1, Distribution Rh-02.
'
a
0.475 1
1.60 0.40 1.1 13.8
I 1
Runs E-20
E-27
E-21
E-19
435 i 1 4 5 0 5 1 450 zt 1 450 i 1 1.8 1.8 1.9 1.8 28 28 28 28 300 i. 2
304 i 2
304 i 2
300 % 2
0.459 1 1.60 0.053
0,448
0.483
1.1
0
0.739 1 1.GO 0.21a 0 21.4
14.1
1
1.60 0.39 13.5
1
1.60 0 0 14.0
3 6
7.2
13.0
6.3
12.9
1.85 48.6 17.6
1.57 58.5 26.2
1.91
35.4 38.3
2.25 23.4 28.2
1.86 37.8 38.0
33.8
15.2
26.3
48.4
24.2
0.348
0.211
0.0311
0.231
Table 111. Nitration of Natural Gas in Presence of Catalyst Employing Very High Natural Gas to Nitric Acid Ratios Conditions Reactor bath temp., 0
c.
Contact time, see. Surface/vol. cm. -1 Preheater bath temp., C. Reactants, moles CaHa HXOa (69.6 wt. %) Ha0 Halogen, cla 01
0.360 Bromine instead of chlorine. Calculated as methane.
April 1954
470 9 6
Nitration of Natural Gas with Halogen and/or Oxygen Catalysis
E-25 Conditions Reactor bath temp., c. 450i. 1 Contact time, sec. 1.8 Surface/vol. cm. - 1 28 Preheater bath temp., C. 298 i- 2
%
E-27
earlier in this paper in the nitration of propane, the bromine resulted in a decrease in conversion over that observed at the same temperature (run E-19) in the absence of any catalysts. Run E-25 (Table 11) shows data for a run made with an oxygen to nitric acid ratio of 1.1 and a chlorine to nitric acid ratio of 0.40. The conversion was lowered markedly, to 3.6%b, by the addition of the oxygen. Run E-27 was made employing the optimum chlorine to nitric acid and oxygen to nitric acid ratios found by Bachman and Kohn for the nitration of propane (6). h comparison of this run with run E-24 (Table 11) again revealed that the addition of oxygen to the reaction mixture containing chlorine had a delrterious rffect on the conversion. Samplings of the exhaust gases of natural gas experiments E-I9 (no catalyst employed), E-20 (only chlorine employed as catalyst), and E-25 (chlorine and oxygen employed as catalysts) indicated the presence of 0.2%. 1.2%, and 2 1%, respectively, by volume of olefins. The values, in the cases where catalysts were present, indicate high extent of olefin formation, especially since only approximately 10% of the natural gas mixture was ethane and propane, and these are probably the principal source8 of the olefins formed. The data thus suggest that the ethane and propane in the natural gas mixture &re attacked by the catalysts, but because of the high dilution with methane and nitrogen, the ethyl and propyl radicals are converted to olefins rather than to nitroparaffins. The mass spectrometer analyses (2) for these runs, as well a8 for the subsequent natural gas runs, can only be reported as mole per cent nitromethane, nitroethane and combined 1-nitropropane, 2-nitropropane, and 2-nitrobutane. This was necessary because of interferences in the mass spectrometric measurements, which prevented an accurate determination of the individual components 1-nitropropane, 2-nitropropane, and 2-nitrobutane. HOWevrr, in none of the natural gas experiments did the 2-nitrobutane compose morr than 20 mole % of the combined value of these three components. Compared with the distribution of nitroparaffinsobtainedforpropaneonly, runs E-19, E-20, E-25, and E-27, show that it is principally the methane and ethane in the natural gas mixture that is being nitrated, in spite of the fact that propane is known to be much more readily nitrated than methane or ethane and that the propane to nitric acid ratio in the gaseou.: mixture averaged 0.460 for these runs. Table 111 indicates runs made with verv high natural gas t o nitric acid ratios made in an attempt to obtain much higher conversions by selectively nitrating the propane and ethane only in
Natural gas
E-14
E.15
423 i 3 1.8 28
423 i: 2
295 zt 3
297
37.0 1 6.94
31.1
1.8
28
=3
Runs E-16
E-17
E-20
433 i 2 1.3 28
449 i 1 450 i: 1 1.3 1.8 28 28
298 2~ 4
29G % 4
304 zt 2
24.2 1 5.52 5.7 0 700
0.448 1 1.60 0.39 0 13.5
0
2.5 955
0 2.2 805
24.2 1 5.52 5.7 0 700
8.5
10.8
15.8
14.9
13.0
2.27 22.5 27.6
2.20 24.4 32.0
2.89 3.16 5.23
2.84 3.30 8.95
1.91 35.4 38.3
49.8
43.6
91.7
87.7
26.3
1 6.06
Products, Conversion RNOa (on N),
%
Distribution RNOz. mole % C/N ratio CHsNOa CaHaSOa CaHiNOa a-CaHih 0 2 2-Nitrobutane
INDUSTRIAL AND ENGINEERING CHEMISTRY
717
ENGINEERING. DESIGN. AND PROCESS DEVELOPMENT the natural gas I\-ithout attempting t o nitrate the methane present. -4lthough the propane t o nit,ric acid ratio \?as as high as 37 and the ethane to nitric acid was as high as 68, it was not possible to obtain conversions to nitroparaffins appreciably greater than those in the opt,imum run E-20 in Table I, in which the propane to nitric acid was 0.448 and the ethane to nitric acid was 0.826. The experimental data suggest, the conclusion that in the nitration of a mixture of hydrocarbon gases, the distribution of t,he products of nitration and the over-all conversions do not correspond to v h a t TTould be expected from the nitration of these hydrocarbon components separately.
References (1) Bachman, G. B.. Addison, L.SI.,H e i v e t t , J. V.,Kohn, SIillikan, A,, J . Oro. C'liem., 17, ROO (1952).
(2) Bachman, G . B., .Itvoori, hi. T., arid Pollack, AI,, I b i d . . publication pending. ( 3 ) Rachman, 0. B., I-Iass, 13. 13.. and Addison, L. M., Ibrd., 1 7 , 014 (1952). (1) Bachman, G . B., Hass, 13. 13.. a n d Hev-ett, J. V.,Ib;d., 17, 92s
(1952).
The authors are indebted to the Commercial Solvents Corp. and the Purdue Research Foundation for financial assistance in the form of a fellowship and t o the analytical department of the Commercial Solvents Corp. for the inass spectrographic aiialvsw of the nitroparaffin samples produced in this work.
V.,aud Mllikal1, A. G., I b ; d . , 17, 93.5 (1982). Bachman, G. B., and Kohn, L., Ibid.. 17, 942 (1952). Hass, H. B.,and Alexander, L. G.. Ixu. EKG.CHEM..41, 2266 (1949). Hass, H. E., and Patterson, J. A , Ibid., 30, 67 (1938). Riley, E . , Ph.D. thesis. E'urdue University (1911). Walsh, A. D.. Tmne. F a r u d a ~SOC.,42, 269 (1946).
(5) Rachman, G. B., H e n e t t , 3 . (Gj
(7)
Acknowlledgment
I..,and
(8) (9) (10)
RWEITEDfor review Septemher 1 4 , 1953. ACCEPTEDFebruary 12, 1054. This paper is part of t h e P h . D tliesis of XI. Pollack, Purdue University, I'ebruary 1953.
e FRITZ MEISSNER
GEORGE The
WANNSCHAFF
Firm of J . Meissner, Cologne, G e r m m y
AND
DONALD F. OTHMER Pofyfechnic fnsfifufe, Brooklyn I , N . Y.
This article and the one following are based on the operations of plants which have been built in Germany utilizing this process. At the present time the company is putting additional plants into operation which incorporate a number of improvements. It seemed advisable to sacrifice some detail in the present articles with the expectation of publishing later comparative data between earlier plants operating by this continuous process and these new plants. In continuous processing of nitrotoluenes there is no change of temperatures, pressures, or concentrations of any of the reactants at any point with respect to time, and only a movement of {he reaction components or mass, from point to point, is necessary to control conditions so that they are always at the optimum. Once set, these conditions are more readily maintained t h a n with batch operations, because the reaction is very responsive to minor adjustments. Coytinuous processing equipment i s always filled to optimum capacity; thus the entire heat transfer surface is always operative. The flow of cooling water removes heat exactly as fast as it is generated without changing the reaction temperature and precise and instantly variable proportioning pumps or meters maintain concentrations. Because rates of flow and reaction are always optimum, the size of equipment is only a fraction of that of batch equipment, and the labor of operation is greatly reduced. Only a small amount of the sensitive product is in the plant a i any time.
c
OXTINUOUS nitration of aromatic hydrocarbons has been studied for many decades. The dye firm of hIeieter, Lucius, and Bruning ( l a ) in 1906 patented a continuous inrthod for preparing aromatic mononitro hydrocarbons. The firm \Veiler-ter-Meer ( 1 9 ) >The Westfahlen Explosive A.G. (20), and Tiubierschlry (8) all described apparatus and processes. Uaxter and Beule (3,4) describe processes for the nitration of phenol, also for benzene, toluene, and cresol. The many patents granted clearly showed that continuou. processes would have great advantages, but only relatively small amounts of materials were produced. Especially in the eaplosives industry, which is one of the most conservative of the chemical industries, resistance t o change has been tremendous. The firm of Meissner succeesfully developed and operated on a 00111-
718
niercial scale in 1928 the trc.hiiiqucs of Schmid (2 6). Thereupon a continuous process for nitroglycerin was introduced to the explosives industry, and today 45 continuous working plants for nitroglycerin have been built using this process and the further iiiodifications and refinenleiits that have been added. Four plants that were built as early as 1929 and 1930 are still in production. The advantages demonstrated by the success of the continuous nitration of glycorol encouraged the study of other continuous nitrations. Thus, the firm Meixsner developed procemes arid plants for the continuous nitration of glycol, diglyol. priilawythritol, and aromatic hydrocarbons. This papcr deals, howrver, only with the development of processes for the nitration of aromatic hydrocarbons.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 46, No. 4
