I N Q U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
July 1951
,
hydrogen can be obtained. At higher temperatures, they? seems to be an initial hydrogenation of asphalt followed by a slox dehydrogenation. At each temperature there is a gradual elimination of sulfur and oxygen with increasing reaction time. On the \Thole, the ultimate compositions of the asphalt fractions are similar to those of the corresponding materials obtained during the kinetic studies on pure aPphalt ( 3 ) . ACKNOWLEDGMENT
The authors are indebted to E. L. Clark for many helpful discussions of the problems involved in this work. James Bayer, Joseph Lederer, and R. A. Friedel also furnished invaluable a & sistance in obtaining the data reported here.
1579
LITERATURE CITED
( 1 ) Pelipetz, M. G., Kuhn, M., Friedman, S., and Storch, H. H . , IND.ENG.CHEM.,40, 1259 (1948). (2) Storch, H. H., Fisher, C. H., Hawk, C. O., and Eisner, A., B u r . M i n e s Tech. Paper 654 (1943).
(3) Weller, S., Pelipetz, M. G., and Friedman, S., IND.ENG.CHEX, 43, 1672 (1951). (4) Weller, 8.. Pelipete, M. G . , Friedman, S., and Storoh, H. H., I b i d . , 42, 330 ( 1 9 5 0 ) .
RECEIVED April 3, 1950. Presented before t h e Division of Gas and Fuel Chemistry, Symposium on Kinetics of Coal Hydrogenation, at the 118th iLIeeting of t,he A M E R I C A N C H E b f I C I L SOCIETY, Chicago, 111. For material supplementary t o this article (tables showing elemenhl balances for all the hydrogenation runq), order Document 31 18 from the American Dooamentation Institute, 1719 Pi St. N.W., Washington 6, D. C., remitting $1 for microfilm (images 1 inch high on standard 35-mm. motion picture film) or $1 for photocopies (6 X 8 inches) readable without optical aid.
Catalytic Reactions of Aromatic Amines J
ALKYLATION WITH ALCOHOLS A. G. HILL', J. H. SHIPP2, AND A. J. HILL Y a l e University, New Haven, Conn.
An
investigation of catalytic vapor phase reactions of aromatic amines, particularly their alkylation with alcohols, was undertaken to explore the advantages in this field of continuoiis low pressure reactions over high pressure batch syntheses, such as that employed for dimethylaniline. Of the many catal>sts tried, aluminum and titanium oxides and phosphoric arid were the most active. While alumina w a s the most efficient for nitrogen alkylation, all these catalysts eEected more nuclear alkylation than had
been anticipated. This led to a study of the rearrangement of alkyl groups from nitrogen to carbon, which was found to be accompanied by extensive disproportionation. Although conversions of primary to tertiary amines exceeding 90% were obtained, more selective catalysts than any here used must be found to permit the vapor phase preparation of N,N-dialkylanilines in a reasonable degree of purity. Means were found for the syntheses from aniline of a wide variety of aromatic amines, including toluidines, xylidines, mesidine, and diphenylamine.
T
washed and ignited. The coconut' charcoal mas a n activated form. Particles were roughly cubical and about 2 mm. on a side. Pumice was screened and part'icles of a size less than 12 mesh were reject8ed. Particles used averaged a,bout 0.55 cc. each. AIXJMINVM OXIDE. Aluminum oxide A was a preparation rcsulting from the action of amalgamated aluminum on water. Coiled strips of condenser aluminum, 99.95 yo pure, were dipped successively in 10% hydrochloric acid and 10% potassium hydroxide until a uniform react'ion over the surface resulted. With a minimum exposure to the air, the metal was washed with distilled water and immersed for 1 minute in a 0.5% solution of mercuric chloride. The coils were then rinsed thoroughly in distilled water, after which they were suspended in distilled water from the lip of a large beaker. Aluminum hydroxide formed on the metal and dropped'to tjhe bottom of the beaker. After filtering, the cake was put int,o pans, cut into l/d-inch cubes, and dried a t room temperature in the air. Aluminum oxide B was prepared in t h e same manner except t h a t it was dried a t an elevated temperature. The temperature was raised from 50" t o 110' C. over a period of 6 hours. Under these conditions, there was little shrinkage in comparison to the considerable shrinkage exhibited in the formation of oxide A4. Oxide A had a particle density of 0.9 and a bulk density of 0.4. Oxide B had a particle density of 0.4 and a bulk density of 0.25. Aluminum oxide C was prepared by precipitating aluminum Iiydroxide on pumice. The pumice was first impregnated ITith aluminum nitrate and then dropped into concentrated ammonium hydroxide containing ammonium nitrate. After standing 24 hours, the pumice was filtered off and thoroughly xvashed. This catalyst was dried a t 105O C. I t contained 5.3 grams of aluminum oxide in a bulk volume of 150 cc. PROMOTED ALUMIKUNOXIDE CATALYSTS.Aluminum oxide promoted with blue oxide of tungsten was prepared by impreggrams of asbestos with a suspension of 15 grams of 1 j.l'roxi+p 13 and 15.5 grams of tungstic acid in 100 ml.
HE production 01 alkylated aromatic amines, such as dimethylaniline, bv the high pressure liquid phase reaction of
alcohols and amines has been well established for many years The corresponding catalytic vapor phase reaction, xhich offers the advantages of continuous operation a t low pressures, has been frequently mentioned but not exhaustively investigated. A wide variety of catalysts has been advocated for this reaction by 8 number of workers (1-4, 9-13), Unfortunately, because of differences in equipment, operating conditions, and analytical techniques, i t is not possible to compare adequately these various catalysts from published results. The purpose of the present investigation was to determine the relative efficiencies of a large number of possible catalysts for the vapor phase formation of dimethylaniline from aniline and methanol. Using the most active catalyst found, a study Mas then made of certain process variables, including an extension of the results to higher alcohols. PREPARATION OF C4TALYSTS
I n general, the catalysts were prepared from reagent grade chemicals. Precipitated catalysts were washed thoroughly t o free them from salts. After careful drying, the usual procedure was to activate the c,atalyst for 1 hour in the reaction tube in a stream of nitrogen a t 360" C. SUPPORTING MATERIALS.In certain instances, asbestos, coconut charcoal, pumice, or silica gel was used as a supporting material. T h e asbestos \r.as in coarse threads, which had been acid 1 Present address, -4inerican Cyanamid Co., Calco Chemical Dirision, Bound Brook, N. ,J. 2 Present address, E. I. du Pont de Nemours & Co.. l n c . , TVilmineton, Del.
INDUSTRIAL AND ENGINEERING CHEMISTRY
1580
of distilled water. After drying a t 105' C., the blue oxide was formed b y reduction in a stream of gaseous methanol at 360' C. for 1hour. An aluminum oxide-copper catalyst was prepared by adding a slight excess of sodium carbonate t o 100 grams of aluminum hydroxide B suspended in 500 ml. of a solution containing 4 grams of copper sulfate pentahydrate. The precipitate was filtered, thoroughly washed, and dried for I hour a t 105" C. Finally it was reduced with hydrogen for 1 hour a t 360" C.
Figure 1.
Vol. 43, No. 7
TRORIUM OXIDE. Thorium oxide waa prepared by precipitating the hydroxide from a solution of 270 grams of thorium nitrate dodtcahydrate in 3 liters of water by the addition of a slight excess of ammonium hydroxide. The precipitate. was washed thoroughly, dried at 105" C., granulated, and made into tablets 7/32 inch in diameter and I/s inch thick. TITANIUM OXIDE. Titanium sulfate was made by heating 540 g r m of titanium oxalate with 736 grams of concentrated sulfuric acid. This product was diluted with 2 liters of water, filtered,
A p p a r a t u s for C a t a l y t i c Vapor Phase Alkylation of Amines w i t h Alcohols
ALUMINUM SALTS. Aluminum phosphate catalyst was prepared by suspending the salt and asbestos in a small amount of water and drying the entire mass at 105" C. Kaolin, a naturally occurring aluminum silicate, was supported on asbestos in a like manner. Aluminum sulfate catalyst was prepared by evaporating a solution of ammonium alum t o dryness on asbestos. CALCIUMSALTS. Calcium phosphate catalyst was prepared by adding 66 grams of diammonium phosphate t o 3 liters of a solution containing 118 grams of calcium nitrate tetrahydrate. T h e resulting precipitate was filtered and washed, supported on asbestos, and dried a t 105' C. Calcium sulfate catalyst was prepared by adding 97 grams of ammonium sulfate t o 3 liters of a solution containing 173.5 grams of calcium nitrate tetrahydrate and then filtering, washing, and drying the precipitate. CHROMIUM OXIDE. Chromium oxide catalyst was prepared by precipitating the hydroxide from the sulfate solution by the addition of ammonium hydroxide. The well-stirred solution was kept slightly alkaline throughout the addition. The precipitate was filtered, washed free from sulfate, dried at 60' t o 105 C., and activated a t 360" C. SILICAGELWITH FERRIC OXIDE. Ferric oxide on silica gel was obtained from Holmes (8). It was in t,heform of irregular cubical lumps averaging about 1 em. on a side. MAGNESIUM OXIDE. Magnesium hydroxide was precipitated by the addition of a slight excess of 10% sodium hydroxide t o 3 liters of a solution of 256.4 grams of magnesium nitrate hexahydrate. The precipitate was filtered, washed thoroughly, and dried, forming particles of about 0.5 cc. each. PHOSPHORIC ACID. Phosphoric acid on charcoal was prepared by heating 100 grams of coconut charcoal and 100 grams of 85% phosphoric acid t o 100" C. This catalyst was heated for 1hour at 360" C. in the reaction tube t o form metaphosphoric acid. Phosphoric acid on asbestos was prepared by heating the acid first t o 360" C. and then supporting 108 grams of the resulting metaphosphoric acid on 30 grams of asbestos. SILICA GEL. Silica gel, obtained from Sifica Gel Corp., Baltimore, Md., was described as a special gel, 105", 8-14 mesh silica gel activated t o 600" F., so as to give an apparent density of about 0.70."
and mixed with concentrated ammonium hydroxide by adding the two simultaneously t o a n initially small volume of water with vigorous stirring. A slight acidity was maintained throughout the addition t o keep iron salts in solution. The precipitate was filtered, washed well, and dried at 105' C., in which form it came out in small lumps about 0.3 cc. in size and having a density of about 0.8 gram per cc. T o a boiling solution of 142 grams BLUEOXIDEOF TUNGSTEN. of Kahlbaum sodium tungstate dihydrate in 2 liters of water was added 6 N hydrochloric acid until the solution became acid. The precipitate was washed free from chloride by decantation and filtration but with some difficulty. The yellow oxide dried in small lumps of 8-14 mesh size at 105" C. Methanol was passed over the yellow oxide at 360" C. a t the rate of 0.8 ml. per minute t o form the blue oxide. A catalyst of blue oxide of tungsten with phosphoric acid was prepared by heating 50 grams of phosphotungstic acid on 25 grams of asbestos t o 360" C. and reducing the tungstic acid in the manner already described. ZINC OXIDE. A solution of 719 grams of zinc sulfate heptahydrate in 2 liters of water was added dropwise t o 94.5 grams of oxalic acid dihydrate in 5 liters of water with vigorous agitation. The precipitated oxalate was filtered, washed free of sulfate with cold water, dried at 105" C. for 2 hours and then made into tablets a/* inch in diameter and I/S inch thick. The oxalate was decomposed and the oxide activated a t 360" C. in the reaction tube. APPARATUS
The apparatus used in this investigation is illustrated in Figure 1. It consisted of three main sections: t h a t for supplying the reactants, the furnace containing the reaction tube, and the a p paratus for collecting the products of reaction. The desired slow, steady stream of alcohol-aniline mixture was fed by displacing it with mercury in the tube, F . The mercury was displaced from tube B by water. Water was fed in above A a t a constant head. The advantage of this procedure v a s that a
INDUSTRIAL AND ENGINEERING CHEMISTRY
July 1951
considerable amount of water could be fed in a t a steady rate and this in turn would displace a much smaller quantity of mercury and, therefore, of the reaction mixture. This device was capable of delivering liquids a t a constant rate of 0.06 ml. per minute, or leas, and was very simple in operation. The furnace, J , was a preheater and vaporized the liquid. The electrically heated furnace, K, surrounded the borosilicate glass reaction tube, L, in which there was inserted a thermocouple, M . The temperature was thermostatically controlled, Products c o n d e a b l e at room temperature, such as the amines, alcohol, and water, were collected in the receiver, N . I n the receiver, &, operated with a dry ice-alcohol bath, dimethyl ether was collected. The noncondensable gases were occasionally, but not regularly, given a scrubbing with dilute hydrochloric acid in the tube, R, and these gases, auch as ethylene, were then collected in the buret, V . An ordinary toy balloon, U,was used to care for small variations in pressure. EXPERIMENTAL PROCEDURE
The usual procedure was to pass 50 ml. of a mixture, containing 6 moles of methanol to 1 mole of aniline, into the reaction tube a t the rate of 0.8 ml. per fninute, whence the material was vaporized and passed over the catalyst. The resulting products were collected and analyzed. The portion of the product which was liquid at room temperature was washed twice with water to remove unchanged alcohol and was then extracted with ether. The ether solution was dried over anhydrous sodium sulfate, after which the ether was removed by distillation. In most of the experiments the product itself was then distilled. ANALYTICAL PROCEDURE
The amine product was analyzed by quantitative acetylation. A weighed sample was reacted with standard acetic anhydride a t 100' C., the exceas anhydride hydrolyzed with water, and the acetic acid formed titrated with standard barium hydroxide solution. The net acetic anhydride was assumed to have reacted with monomethylaniline and the calculation made for per cent monomethylaniline accordingly. Experiments on known mixtures indicated that the ratio of acetic anhydride present to that required for acetylation should be between 1.1 and 1.3 in order to complete nitrogen acetylation of the primary and secondary amines without nuclear acetylation, thus permitting results to be checked within 1% of true values. When the required conditions were met, blank analyses on aniline, methylaniline, and dimethylaniline were as follows: % Monomethylaniline 114.1 (99.2% aniline) 99.4 0.0
Aniline Methylaniline Dimethylaniline
The specific gravities were determined with a pycnometer. RESULTS
EFFECTOF CATALYST.The influence of a large number of catalysts on the interaction of methanol and aniline a t 360' C. was determined. The results are shown in Table I. The space velocity was computed as volumes of gaseous reactants per hour a t standard conditions of temperature and pressure per bulk volume of catalyst bed. The acetylation value, expressed in the tables as per cent monomethylaniline (yoRIIMA), fails to distinguish between primary and secondary amines; hence, the analyses were calculated as per cent monomethylaniline in all cases, even though the products from runs at low conversions contained a considerable amount of aniline. Since the specific gravity decreases in the series aniline, monomethylaniline, dimethylaniline, its value gives a rough indication of the number of methyl groups introduced into the molecule. As a number of the products had lower specific gravities than that of dimethylaniline, it is evident that more than two methyl groups had en-
1581
tered some molecules and, hence, that nuclear alkylation had occurred. This phenomenon of nuclear alkylation and the rearrangements of alkyl groups involved will be discussed in detail in the following paper (6). Since the specific gravity is an indication of the total amount of alkylation, whereas the acetylation value is a function only of nitrogen alkylation, by comparing the specific gravity and the acetylation value of a given product, a qualitative indication may be had as to the selectivity of the catalyst for nitrogen alkylation as compared to carbon alkylation, For example, in the case of titanium oxide as catalyst, a low specific gravity combined with a relatively high acetylation value indicates a high degree of nuclear alkylation. O F ANILINE TABLE I. EFFECTO F CATALYST ON METHYLATION
Space Specific Velocity, Catalyst Aluminum oxide 100 0.942 A lumps 11.8 100 0.942 B: lumps 7.6 100 0.947 21.8 B, powder 100 12.8 0.943 B, tablets 100 0.949 10.7 B,on asbestos 150 36.3 0.961 C, on pumice Phosphoric acid 0.942 On asbestos 100 14.9 150 20.7 0.932 On charcoal Aluminum oxide with tungstic oxide on 100 26.5 0.936 asbestos 100 33.4 0.952 Aluminum oxide with copper Aluminum phosphate on asbestos 100 0.961 37.5 Titanium oxide 130 50.9 0.947 Aluminum sulfate on asbestos 100 61.1 0.969 Kaolin on asbestos 100 71.1 0.985 Tungstic oxide with phosphoric acid on asbestos 100 80.6 0.960 280 82.4 0.988 Tungstic oxide Calcium phosphate on asbestos 100 85.8 0.989 Silica gel 94 86.0 0.983 Silica gel with iron oxide 130 89.4 0.989 Zinc oxide 100 91.5 0.993 Calcium sulfate 102.1 180 1.001 Thorium oxide 103.0 280 1.013 Chromium oxide 100 1,010 104.4 Magnesium oxide 180 109.6 1.011 a Per cent primary and secondary amines calculated a s monomethylaniline. Specific gravity, 25'/4O C.: aniline, 1.017; monomethylaniline, 0.982; dimethylaniline, 0.953.
*
Although there is some variation in the space velocities and in the particle sizesof the catalysts listed in Table I, the results indicate strongly that, of the catalysts examined, only aluminum oxide and phosphoric acid are highly efficient for the alkylation of aniline with methanol under the conditions employed. With the exception of titanium oxide and phosphoric acid, four compounds of aluminum other than the oxide were the most efficient alkylation catalysts found. The case of thorium oxide is a n interesting one. Roy (19) reported a conversion of 7570 of aniline into alkylanilines over thorium oxide at 420' to 430' C. Mailhe and de Godon ( I O ) had also reported thoria to be active in the alkylation of aniline .and other aromatic amines at temperatures of 350' to 450' C. It may be noted from the results reported in Table I t h a t this catalyst was found to be of little or no activity in the methylation of aniline a t 360' C. Work on samples of thorium oxide from the Welsbach Co. and the Rhone-Poulenc Co. confirmed the authors' previous results. This catalyst had little effect even on the alcohol, giving no dimethyl ether and only a negligible volume of gas. Aluminum oxide as a powder was less effective than as lumps or as pellets. However, asbestos was a highly efficient support, a5 only 0.3 as much alumina by weight gave nearly the same conversion as the unsupported catalyst. The supported alumina also gave less nuclear alkylation. Copper oxide decreased the activity of the alumina to which it was added. On the other hand, tungstic oxide greatly increased its activity for nuclear alkylation. The salts of aluminum were much less effective as catalysts for the alkylation of aniline than aluminum oxide itself. The phos-
1582
INDUSTRIAL AND ENGINEERING CHEMISTRY
phate was more active than the sulfate and the sulfate more active than tlhe silicate. Phosphoric acid proved to be an excellent catalyst for alkylation but, in the apparatus used the materlal was handled with difficultyand some of the acid \yas carried along with the product. HoJvever, the loner deiisity values indicat,e more ring alkylation than with alumina, especi:iIly when the acid \\-as supported o n charcoal. Hlue oxide of t,ungstcii \vas notr very etl'ective alone in the niethylat,ion of aniliiir.. i\\7ien promot,ed wit,li phosphoric acid, however, much nucleai alkylation appeared to have t,akeii glace. Titanium oxide \ m s inoderatcly active in the alkylation of miline with methanol. There {viis obtained 50.9% moiiomethylaniline by analysis, hut it was evident that much of thc :tlkylatioti was nuclear, as the density o f the product was less than that of dimethylaniline. Silica gel and silica gel ivith iron oxide were poor catnlysts for alk\-lation. The iioii oxide MIJ :tpparentlp reduced. 111 each there appeared t o be alkylation at first, as a11 aiiiirie layer water layer were i'oi~mcd,but soon the liquid products Liecame homogeneous iind thc catalysts lost any initial activity. Zinc oxide, chromium oxide, :tnd inagiiesiuni oxide exerted little iiifluence on the nlkylation of :iiiiIirii>, They arc1 k n o n ~ it,o bit dehydrogenation c:ital>-i;ts :itid \WIV found t,o d r c ~ i i i i i i o s r tho alcohol to some extent. ut,more iioiicoridc~~~s:ibl~ g OVC'Y tit,atiia; tungstic oxide, aiitl phosphoric ac astiestop. In each of t,liePc c:tscs there as ioui~tlinethJ-I ethcr equivalent t o 0.5 T O 1 inole of the j moles of niethuiiol rharged. TI-ith titania, where the itiiiiiic product nn:tlyzed 51 7Gmononic&ylaniline, methyl c.tlirr I V R P Toriiied cqriivalriil to 1 mole of t h e 5 iiiole: of n1etli:~riolcharged and 0.14 mole of iio~icondensalile gasc's containing 110 carbon dioxidr, 2y0 olefins. 337, c:irhoii monoxide, and 657c residue W A I T formed pw iiiiilc of iiic.thariol charged. in the ciisc of copper 011 aluniiiia cat:ily$t that a s \\-as iiicreueed, by iiicreasiiig the tempelatui~oover' of methyl ether i'orinivl This indicates that tlic cat and prolxihly esi;;ts in equilibriuin vitli t h e ~iiclli:c~iol. c~iniiioycdund(:r stuietl coiiditioii. In iio case did the rat effect diniethylaniliiic. pi~i!paratioiiin :i ~ ~ c ~ : t s o i i i i r1cgrt.i~ l~lc of ~ L I rity. Thc catalyst? \\-ert tcvl I J C W : I U ~ Ctkic litcv : ~ t r i wiiidiratetl Their usefulness in dehytIr:itioi~~.c~iictioiis.The r o u t ' v oc fiuthilr x o r k might, he directed to\r;irti other cat preparations of some o f the effwtivc c:ital> 1 iti thiu \\-ark. SC!lll
Vol. 43, No. 7
phase formation of dimethylaniliric. The apacc velocity was first varied, with the results shom-n in Table 11. The reason for the opt,imum velocity for tertiary amine formation is apparently that above this value there is insufficient contact time for complete reaction to take place while at, lower values nuclear alkylation is favored. This conclupion is substantiated by the specific gravity values which decrease steadily with decreasing space velocity. OF SPACE VELOCITY TABLE 11. EFFECT
*
Space Velocity, Speoific Grai.ity, Hour-' % hlh1.l~' 250:40 c. 228 19 7 0 943 100 7.6 0 942 13 8 D. 937 50 .~ Per cent primary and secondary amines calculated a8 monoillethylaniline.
EFFECT OF TEMPERATCRE. The optimum temperature for the formation of dimrthvlanilirie iTap next determined. The results summarized in Table I11 indicate that a t 350" to 360" C. a maximum conversion t o tertiary amine occurs. The optimum temperature probably depends on the same factors a s did the space velocity-i.e., too low a temperature causes incomplete reaction, whereas too high a temperature results in nuclear alkylation TABLE 111. Temp.,
C.
300 320 340
EFFECT O F TEMPERATURE 7c,hIbIA" 14.6
11.5
9.2 8.5 8.2 9.7 11.4
350
360 370
380
Per cent primary and secondary amines calculated as uionouietliyl-
aniline.
il series of experiinents was C T O F 1t.4TI0 O F R E d C T d N T s . perforined a t 360" C. to determine the effect of varying the ratio of rnet,lianol t,o aniline. The amount of tertiary aniinc appeared t,o iiicreasc with inciwi;.iiig mole ratio of alcohol to aniline until aiiied, as sho\r-n in Table 1 1 7 . Note that the lightly less act,ive t,han otlwr prep;uations of alurninuiii oxide 13.
TABLE IV.
EFFECT OF
N o l e Ratio,
.4looiiol: -4niline
.~T.COHOL--~NII,INE: I L i ~ r o
yc UA1.4"
2 4
27.4
(1 8 10
12.0
11.3 9.6
9 .3 I'er cent primary and 3econdary amines calciilated as ~ i i o n o n ~ e t h y l anilirie. '1
A h ~ ~01.' ~ TOLCIDI . ~ ,~ In~ some ~ preliminary j ~ experiments o n the inoth~~latiori of 0- and p-toluidine over alumina a t 360" ( ' , , pmduct,s eoiitainiiig :tl)out 90% tertiary amine were obtailid. These r e s u l t s indicaiite that tlir rrac-fion may hi! extended t o ii v:ti~icly of aronintic ainiiies. lTsi . Tlic forcgoirig studies \\-ere extended to the use of higher alcohols. Hovxver, t,he results, as indicated hy the iitnouiit of -~-,.~-dia!kvl:inilineformation, w r e cornparativcly poor, l
