796
INDUSTRIAL AND ENGINEERING CHEMISTRY
Summary The following conclusions can be drawn as to the formation of diniethylaniline by the liquid phase, batch reaction of aniline and methylaniline with methanol, using a sulfuric acid catalyst : 1. The variation in the composition of the amine mixture niih time during t,he methylation of aniline to dimethy1:iniline is represented accurately by R system of first-order, consecutive reactions in which the reaction mte of the first reaction is directly proportional to the concientration of aniline, the reaction rate of the second reaction is directly proportional to the concent ration of methglaniline, and the spcoific- rate constants of thc t\vo reactions are equal. 2. The variation of thr rc ion rate csonstante \\-ith catalyst micentration is represented accurately b y an equation of the form, I; = koe(1 - 0,52), where, z is the fraction of amine present in the form of the sulfuric arid s d t . 3. Temperatures in the neighborhood of 230" C. cause a t least two side reactions to occur: rtwrrangement to nuclear1)- alkylated products, such as diniethyl-1J;-toluidine; and oxidation to give formaldehyde derivatives, such as p,p'-tetrameihyldianiinodiphenylmet,hane. 4. The variation of the reaction rate constants with teniperature is represented accurately by the equation: -12,106
k,
=
6.0 X 101k
*
5. The reaction equilibrium becomes less favorablca
:IS
the
t einperature i 9 increased.
Vol. 42, No. 5
6. The reaction rate constant is only slightly decreased -)k dccreasing the mole ratio of methanol to methylaniline from 3.0 t o
1.5. 7. The equilibrium conversion is increased slightly on
ill-
creasing the mole ratio of methanol l o aniline. 8. The equilibrium conversion is over 99% a t 200" C. using 50% excess methanol. 9. The amount of freeboard lelt in the aut,oclavc has no appreciable effect on either the ratc or the equilibrium of the reaction.
Literature Cited ( 1 ) Groggins, P. H., "Unit Processes in Organic. Synthesis," 31.d cd., p. 598, New York, McGraw-Hill Book Co., 1947. ( 2 ) Hofmann, A. IT.,and hlai~tius,C . A , Ber., 4, 742 (1871). (3) Jones, X*.J., J . SOC. Dyer,s C o i o i ~ r i s i s35, . 43 (1919). (4) Poirrier and Chappat, BidL sue. rhim., 6, 502 (1866). ( 5 ) Spencer, G., and Brimley, .J. E., *J. SOC.Chem. I d . , 64, 53 (1943). (6) Timniermans, J., and Hennaut-lioland, Mme., J . chim. picjl~..32,
501, 589 (1935). (7) U. S. Army Specification, No. SO-ll-3OC, June 17, 194:3, (8) Walter, J., Chem-Ztg., 34, 641 (1910). RECEIVEDSoveinbrr 2. 1949. Abstracted from theses subinittrd to the faculty of Purdue Cniversity by G . S . Vriens in rjartial fulfillment of the requirements for t h e degree oi dortor of philosophy. J u n e 194% and by D. A. \'orel in partial fiilfillnient~ oi t h e reqiiiwriirntii for the degree of inaster of scicnre in chemical engineering, .lime 1948.
Production of aromatic nitriles WILLIAM I. DENTON, RICHARD B. BISHOP, HAMILTON P. CALDWELL, AND HAROLD D. CHAPMAN RESEARCH AND DEVELOPMENT DEPARTMENT, SOCONY-VACUUM LABORATORIES, PAULSBORO, S. J .
A
process for producing aromatic nitriles from alkyl- or alkenyl-substituted aromatic hydrocarbons and ammonia is described. Operating conditions are: atmospheric pressure, catalyst temperature of 975" to 1025" F. (524" to 552" C.), and catalyst of molybdic oxide on activated alumina. Liquid space velocities and reactant ratios may b e varied over a wide range to obtain the desired results. Conversions per pass of 5 to 10 weight YOand ultimate yields of 60 to 85 weight YO of benzonitrile are realized, using toluene as the hydrocarbon charge.
T
HE increased use of nitriles as chcniical intermediates and in
the resin field has result,ed in a demand for cheaper methods of producing these materials. This paper describes a process for the product,ion of aromat,ic nit>iileshy react,ion of ammonia with aromatic hydrocarbons. Known met,hods of preparing aromatic nitriles include: the reaction of an organic acid lvith ammonia over a dchydration catalyst (8); the dehydration of an amide over suitable catalysts or reagents [Japanese acid clay (I ), phosphorus trichloride (0), phosphorus pentachloride ( S ) , and thionyl chloride ( I O ) ] ; and the dehydration of an amnionium salt of an organic acid with heat ( 7 ) or heat plus a catalyst [thoria, silica gel (Sj; phosphorus pentoxide, aluminum sulfate, aluminum phosphate ( 2 ) ; et,c.I. Other methods of preparation are: isomerization of isonitriles by heating to 200" C. ( I O ) , the reaction of cyanogen bromide and an aromatic hydrocarbon in t,he presence of anhydrous aluminum chloride (4), and the condensation of aryl diazonium compounds with potassium cyanide in t,he presence of cuprous cyanide or nickel cyanide ( 5 ) .
Equipment Figure 1 is a schematic flow diagram of the equipment used in this study.
The hydrocarbon was puinped from a graduated cylinder through a preheat,er coil inimersed in a molten salt bath which was maintained a t the desired temperature by electric heaters operated by an automatic controller. The ammonia, tho flow rate of which was measured by a rotameter, was prcheatcd in a similar coil and mixed with the vaporized hydrocarbon prior to entering the reactor. The vapors emerging from the reactor w r e passed through an ice condenser and the liquid product \vas separated from the noncondeiised gases. The liquid product \vas water-n-ashed to remove dissolved ammonia, sampled for infrared analysis, and then distilled to recover nitrile and unreacted hytirocarbon. The lioncondensed gases were measured with a gas meter, sampled for mass-spectrometer analysis, and t h e n vented. Stainless steel reactors of 0.33-, 2-, 8-, and 30-liter capacity were used in this worlr, although experiments have shown that. low-carbon steel may also be used. Bot'h adiabatic and isothermal reactors were investigat'ed, but the majority of the work reported herein was done in isothermal reactors. Adiabatic reactors pcrformed as satisfactorily as isothermal reactor?, except that, a t low space velocities some difficukies i n maintaining uniform temperatures were experienced.
Analysis I n order to facilitate the investigation of the variables involved in this process, it was necessary to develop routine methods or analysis. The noncondensed gases contained chiefly unreacted ammonia, hydrogen, nitrogen, anti lesser amounts of hydrocarbons and water. Inasmuch as mass-spectrometer analysis of known synthetic mixtures gave satisfactory results, this mcthod was adopted for the anslysis of the noncondensed gases. T o simplify the analysis of the liquid product, toluene was tho only hydrocarbon charged in the runs made for the purposc of evaluating process variables. This resulted in a liquid product consisting of toluene and benzonit,rile. Because benzonitrile boils 1,44' F. (80' C.) above toluene, separation by distillation is relatively simple and analysis of lOO-granl samples gave reproducible results. It was further found that infrared analysis of ltnown mixtures of benzonitrile and toluene gave results of the same
May 1950
INDUSTRIAL AND ENGINEERING CHEMISTRY
order of accuracy as those obtained by the distillation method, Therefore, infrared analysis was utilized in most of this work.
797
chain are formed. The chief product is either bensonitrile or a substituted beneonitrile, depending on the initial hydrocarbon used. Styrene reacted with ammonia:
Discussion Basic Reaction. In this process the alkyl or alkenyl group of a substituted aromatic hydrocarbon rcacts with ammonia to produce an aromatic nitrile and hydrogen. Reaction variables are pressure, temperature, space velocity, and molar ratio of reactants. The data indicate that atmospheric pressure, liquid space velocity of about 3, catalyst temperature of about 1000" F. (538"C.), an excess of either reactant, and a catalyst of molybdic oxide on an alumina support are practical reaction conditions. Reactants. The preferred reactants are methyl-substituted benzenes. The reaction of ammonia with toluene may he represented thus :
+ 3H2
Similarly, substituted benzenes with alkyl substituents longci than methyl gave chiefly benzonitrile with smaller amounts of higher molecular weight nitriles.
CN
The reaction is not limited to substituted benzcne rings. Fui. example, methylnaphthalene reacted with ammonia to give naphthoic nitrile:
CC
Runs made using aromatic hydrocarbons with more than one substituent gave a product containing a mixture of mono- and dinitriles.
j.
+ SISP +
6
+ C H I + 2Hl
CHJ
+ YHa +
+ 3Hz
Each individual hydrocarbon requires some modification of the processing conditions from those shown in this paper for toluene and in some cases the conversions per pass are lower. Furthermore, in some cmes more than one product is obtained and, CX therefore, different methods of separation and purification are pequired. It is expected that data on t8hesehydrocarbons will be reported more fully in a subsequent paper. Catalyst. The catalyst used in this process is molybdic oxide on a suitable support such as magnesia, bauxite, or activated alumina. Preliminary reduction of the catalyst with hydrogen or The methyl group was preferentially attacked in compounds ammonia results in a higher initial activity level, but, in practice, containing both a methyl and one or more higher alkyl subthe catalyst will be activated in a relatively short t,ime by stituents. the ammonia used in the process. The activity of molybdic Aromatic hydrocarbons uith an alkenyl substituent are also oxide supported on a carrier, such as activated aluminz, invery reactive in this process. However, only small amounts of creases with increase in molybdic oxide content up to about compounds with the nitrile group attached to a carbon in the side 10 to 20% molybdic oxide, above which HYDROCARBON HYDROCARBON little improvement is RESERVOIR P REHEATER noted. This probably represents the ICE CONDENSER percentage a t which the support has a t least a monolayer of molybdic oxide on the surface. Although catalysts have been used continuously for ROTAMETER SAMPLE FOR M P ss -. 1 as long as 24 hours, SPECTROMETER GAS AMMONIA they remain a t peak c PREHEATER -L activity for only 3 to 6 hours, after which 'r c the conversion to 0 AMMONIA n i t r i l e sloTTly deWATER WASH CYLINDER creases owing to car7 bon deposition on the ;TOR catalyst. The catalyst may be regentUN%EACTED LIQ erated by burning off HYDROCARBON the coke using air NIT~ILE diluted with an inert gas to control reSAMPiE FOR INFRA RED ANALYSIS generation temperatures. Figure 1. Flow Diagram of Nitrile Process
CH3
CH?
II
t
-
-
AyslsG t
-
-
-1
798
INDUSTRIAL AND ENGINEERING CHEMISTRY Table I.
Vol. 42, No. 5
Effect of Catalyst Temperature at Different Space Velocities
W t . % Conversion hlole yo Moles Conversion per per Pass Based on C7Hs per Pressure, ~~~~l Pass Based on Mole NHa Atm. C7Ha NHs charge C?Ha IiHs 2.9 2.9 5.8 A 910 880 1 3.8 2 1 3.2 35 940 935 1 3.8 2 1 5.5 59 5.0 4.9 9.8 78 6.6 6.4 12.8 995 1 3.8 2 1 7.2 1020 63 5.3 5.2 10.4 1060 1050 1 3.8 2 1 5.8 935 1050 1 3.8 2 1 5.9 64 5.4 5.3 10.6 1 3.8 2 940 1100 1 4.2 45 3.8 3.8 7.4 9.6 2.4 14.5 6.2 1000 1 1.25 0.25 1 10.7 B 1020 2.5 0.25 1 11.4 15.4 6.6 10.2 1 1.25 920 1055 13.9 5.9 9.2 2.3 0.25 1 10.3 930 1100 1 1.25 C 1030 925 2 0.8 2 5.0 54 4.6 4.5 8.9 1035 920 5 0.8 2 990 1000 5 0.8 2 5 . 3 57 4 . 9 4 . 7 9 .4 1010 1000 5 0.8 56 4.8 4.6 9.3 1250 1075 5 0.8 1 5.2 a Reactants mixed cold and preheated together. b Contact time calculated on basis of empty reactor with no correction applied for change i n contact time with reaction temperature. Actual free space in catalyst bed is approximately 39%. Temperature, ' F. Preheatera Catalyst
Space Velocity
Contact Timeb, Sec.
~
;
h
TWO MOLES OF TOLUENE TO ONE OF AMMONIA
80
I
800
I
900 CATALYST
1000
1100
1200
TEMPERATURE-'!?
i:! 2:;
i
data indicate that the temperatuie to which ammonia is preheated is critical and that the temperature to which the toluene is heated is not ciitical. It is believed that decomposition of ammonia is the main factor contributing to the decreased yield of nitrile M ith increased preheater temperature. As a check on this theory, thc data presented in Table 11- were obtained by passing eithei ammonia or toluene separately through the unit with the reactoi either empty or containing a catalyst of molybdic oxide on activated alumina as indicated. The data show that without catalyst present, toluene and ammonia are stable up to about 1150" F (621" C.) and 950" F. (510" C.), respectively, but in the piesence of catalysts tolueneisstableup toabout 950" F. (5lO'C ). while ammonia is very unstable over the temperature range studied.
Figure 2. Effect of Catalyst Temperature at Different Space Velocities Table 111. .Effect of Preheater Temperature
Process Variables Temperature. The effect of the catalyst temperature is illustrated in Figure 2 and Table I. These data show that the optimum conversion to nitrile is obtained in the range of 975" to 1025" F. (524"to 552" C.) for liquid space velocities between 1.0 and 5.0. The data also indicate that temperature is less critical at higher space velocities than at lon-er space velocities. The temperature of the preheated reactants is also an important variable in the process. The data presented in Table I1 show that a t constant operating conditions [975" F. (524" C.) catalyst temperature, 1.0 apace velocity, and 2 to 1 molar ratio of ammonia to toluene] preheating ,the mived reactants above 900" F. (482' C.) causes a decrease in conversion to nitrile of about 3% for each 100" F. (56" C.) increase in preheater temperature. Table I11 illustrates the effects obtained by preheating only one of the reactants, and adding the other reactant cold just prior to the time a t n-hich the mixture enters the reactor. These
Tempeiatiire, F. _____
Pieheater Catalyst
(One reactant introduced cold) Wt. 4$ Conversion per Mole % Conveision Pass Based on__ ~~~~l per Pass Ba-ed 03CiHa NHa charge CiHa XHs
A. 800 876 927 976 975 1024 1075 1175
980 978 972 975 976 973 976 974
900 1000 1100,
975 975 975
Ammonia Introduced Cold 7.3 27.0 7.2 26.6 6.7 24.6 24.8 6.7 24.0 6.5 24.6 6.7 24.3 6.6
8.9 8.8 8.1 8.2 8.0 8.1 8 0
4.5 4.4 4.1 4.1 4.0 4.1 4.0
Toluene Introduced Cold 5.9 22.2 23.0 6.2 13.2 3.6
7.2 7.6 4.4
3.7 3.8 2.2
10.0 9.8 9.1 1::i]9.36 8.9 9.1 9.0
B.
8.1 8.5 4.9
Space relocity 1.0. 2 moles of ammonia to 1 of toluene. Catalyst temperature 975O F. Catalyst KF-24 (10% N o O s on alumina). Atmospheric pressure.
Table IV. Effect of Temperature on Thermal and Catalytic Decomposition of Ammonia and Toluene Table 11. Effect of Preheater Temperature (Reactants mixed cold and preheated together) Wt. % Conversion per Mole % Conversion Pass Based on ~~~~l per Pass Based on Temperature, F. Preheater Catalyst CiHa SHs charge C7Ha 5Hs 6.7 8.2 4.1 9.2 21.8 980 800 9.0 4.5 7.4 10.1 27.3 870 977 23.2 6 . 3 7 . 7 3.8 8.6 966 976 3.8 4.6 2.3 14.0 5.2 1077 975 1.6 0 .8 1 . 3 1.8 4 . 9 1170 976 Space velocity 1.0. 2 moles of ammonia t o 1 of toluene. Catalyst temperature 975O F. Catalyst KF-24 (10% MoOa on alumina). Btmospheric pressure.
Temperature, F. Ammonia. Preheater Catalyst c:z;y,t6zt%-a
Toluene, Wt. % Decompositiona
975 1050 1050
980 1050 1050
4.5 11.1 36.5
,
1150 975 1020 1030 1150 1156
1150 980 1050 1055 1150 1150
36.0
, . .
,.
.. ..
, ,
... 1.0 1.0 6.0 1.0 10-13
Catall kt None None KF-24 (10% >IoOa alumina) h-one None None KF-24 Sone I
5 60 U
t-
5 40 2 CL
I- 2 c
0 '
5
I
2
MOLES OF AMMONIA PER MOLE OF TOLUENE
Figure 3.
2
3
4
5
MOLES OF TOLUENE PER MOLE OF AMMONIA
Effect of Molar Ratio
Expressed as weight % conversion
6
7 LIQUID SPACE VELOCITY
Figure 5.
(VOLJHRJVOL)
Effect of Space Velocity
2 mole# of toluene to 1 of ammonia
INDUSTRIAL AND ENGINEERING CHEMISTRY
800
Table VII.
'2,
Temperature, Preheater" Catalyst
Space Velocity
Effect of Pressure
hloles Contact C7Hs per Timeb, hlole
NHB
Seo.
A.
Vol. 42, No. 5
Wt. % Conversion
Based on _per _Pass __ _~ _ ~ Pressure,
Atm.
CiHs
NIII
charge
hIolr % Conversion ~ i e r tPass ~Rasedl o n Cil-I8 SI[,
Conqtant Spare Velocits
uolyiiier~
B.
Constant Contnct 'rime 39 5 0 1.9 0 S 1.0 ii 2.0 0" 13.7 1025 993 3 3 13.7 1.0 1.25 31 2,i 2 7 926 1000 3,; 6.0 1.8 2.0 18.0 920 995 .i . 0 13.7 1.f: 3.0 18 1.6 1.i 3.4 1.9 20 1.7 34.3 13.7 2.0 900 9.3 1005 ( 0 . 4 H.C. imlymer) a Reactant8 niiied cold and preheated together. b Calculated on basis of empty reactor with no correction for change in contact time with reaction teinperat,ure. Actual free space in catalyst is approximately 39%.
ammonia, a ratio which is preferable to one requiring an excesb of ammonia, because it is easier to recover and recycle unreacted toluene than unreacted ammonia. Space Velocity. The effect of space velocity, defined as the volume of liquid reactant pumped per hour per volume of reactor, is shown in Figure 5 and Table VI. From these data it can be seen that the maximum conversion is reached at space velocities of 1.0 to 2.0. However, the conversion per pass falls off relatively slowly as the space velocity is increased. Figure 6 illustrates graphically the effect of space relocity on nitrile production from a reactor of given size. The data presented therein and in Figure 5 indicate that the most economicnl operation would be at a space velocity above 2.0.
Pressure. Data on the effrct of pressure, both a t constant space velocity and a t constant contact time, are listed in Table VI1 and shova graphically in Figure 7 . Bt a given pressure there is very little difference in the conversion per pass obtained at either constant space velocity or constant contact time. I n both cases the conversion per pass falls off almost linearly until a pressure of 10 to 12 atmospheres is reached, after which it levels out a t a relatively low conversion. These data are in agreement with the law of Le Chatelier-Rraun and indicate that subatmospheric pressures are desirable. However, the additional equipment and recovery problems involved in the use of vacuum make it more economical t o use atmospheric pressure.
Conclusions I
L
0
I
2
I
I
I
I
3 4 5 6 7 8 LIQUID SPACE VELOCITY (VOL./HR./VOL.)
I1
9
10
Figure 6. Change i n Nitrile Production of a Given Size Reactor with Space Velocity
Data are presented on a process for the production of aromatic nit,riles. This process involves the reaction of an alkyl-substituteti rtromatic hydrocarbon and ammonia over a molybdic oxide on activated alumina cata,lyst. Aromat,ic hydrocarbons with unsat'urated alkyl groups are applicable, as are substituted polycyclic aromatic rings such as alkylnaphthalenes. Temperature is the most critical variable. The ammonia should not be prehea,ted above 950" F. (510" C.), and t,he catalyst temperature should be maintained a t 975" to 1025' F. (524" to 552" (3.). Space velocity and niolar ratio are not critical variables and may be varied over a \ d e range to secure the desired results. Atmospheric or subatmospheric pressures are preferable, Conversions per pass to aromatic nit,riles of from 5 to 10 weight 7 0 of the toluene charged are realized at ult,imate yields of 60 to 85 weight 7;.(based on toluene used).
Literature Cited 60
.
(1) hbe, Bull. Wasedtc A4pp2ied Chem. SOC., 19, 8 (1933); J . SOC. Chen. Ind., Japan, 36, Supp. binding, 42 (1933).
R U N CONDITIONS ;$5
$2
o
0
CONSTANT CONTACT TIME OF 1 3 7 secs CONSTANT SPACE VELOCITY OF 5 0 IO 0 O'E TEMP E R AT U RE
rc9 UU40
0":
w
z330
a0
?F
zz
Oyz20
0.0
o
4
a
E
16
20
24
28
32
36
40
(2) Deem and Lazier, E. 8.Patent 2,149,280 (1939). (3) Kao, Sen, and Chien, J . Chinese Chem. SOC.,2, 240 (1934). (4) Karrer and Zeller, Helo. Chim. Acta, 2, 482 (1919); 3, 261 (1920). (5) Korczynski and Fandrich, Compt. rend., 183, 421 (1926). (6) Linstead and Lowe, U.S. Patent 2,054,088 (1936). (7) Ralston and Haraood, Ibid., 2,245,545 (1941). (8) Reid, E. E., Am. Chem. J . , 43, 162 (1910); .T. Am. Chem. Soc.. 38, 2120 (1916); 53, 321 (1931). (9) SociBtB pour l'industrie chimique BLle, Swiss Patents 202,545 and 205,159 (1939). (10) Taylor and Baker, "Sidgwiek's Organic Chemiatry of Sitrogen," p. 311, London, Oxford University Press, 1937.
PRESSURE -ATMOSPHERES
Figure 7 .
Effect of Pressure
R E C E I V EJanuary D 12, 1950.
