AEROGEL CATALYSTS Conversion of Alcohols
K. KEARBY.1 S. S. KISTLER,a AND SHERLOCK SWANN, JR. University of Illinois, Urbana, Ill.
to Amines The conversion of alcohols to amines by reaction with ammonia catalytically in the vapor phase was studied over aerogel catalysts. The best results were obtained over a mixed aerogel of alumina and chromic oxide.
T
HE earliest study of aerogels as catalysts was reported by this laboratory (14)in 1934. It was shown that thoria aerogel was a much better catalyst for the conversion of aliphatic acids and esters into ketones than any catalyst known. This initial success made desirable further studies of aerogels as catalysts. Foster and Keyes (8) showed that silica aerogel and platinized silica aerogel are the equal of any known catalyst for the oxidation of acetaldehyde to acetic acid in the vapor phase. Some work had been carried out in this laboratory on the reaction of alcohols with ammonia in the vapor phase over thoria aerogel (1) to produce amines. Therefore, it seemed of interest to study the behavior of other aerogels. Furthermore, from an industrial standpoint a good catalyst for the conversion of aliphatic alcohols to amines is desirable. The study of aerogels as catalysts for the conversion of alcohols to amines is described in this paper. The alkylation of ammonia by alcohols has been reported extensively, especially in the patent literature, Some of this work (2-7, 11, 19,18-19) is rather contradictory but the majority of it indicates that alumina is the best catalyst. Thoria is recommended by several authors as an active catalyst (16, 17). One investigator (6) reported pure silica gel to be a very active catalyst. A weighted survey of the literature shows that the probable order of decreasing activity is alumina, thoria, and silica.
variable-speed alternating-current motor, equipped with a selfcontained governor to maintain a constant speed at any setting. The glass-mercury displacement system, shown in Figure 1, prevents the pump from contacting the corrosive liquid. Castor oil is pumped from bulb C into bulb D,displacing the mercury in bulb D into bulb B, where it forces the liquid reactants in bulb B into the vaporizer. Simultaneously, as the castor oil is pumped from bulb C, it is replaced with mercury from bulb A , into which is drawn the liquid reactants from flask E on the balance. The amount of liquid delivered in any given time is weighed directly on the balance. When bulb B becomes empty of liquid reactant and filled with mercury, the directions of flow are reversed by giving the four three-way sto cocks, F, G, H , and I , a half turn. B then begins t o fill from ffask E, and the liquid in A is delivered to the vaporizer. In case the stopcocks are not changed in time, the motor is shut off by the relay when the mercury closes the contact above stopcock F . This prevents mercury from being delivered to the hot catalyst chamber or castor oil from being pumped into the upper bulbs. The bulbs have a capacity of 500 cc. Connecting tubing is 8mm. Pyrex, and the stopcocks have Zmm. bores. The rate of passage of ammonia was measured by a flowmeter. The exact amount of ammonia was determined by the difference between the total weight of products condensed in the solid carbon dioxide condenser and the alcohol delivered. The slight losses of hydrogen and methane were neglected. The reactants were delivered to an electrically heated Pyrex coil in which the alcohol was vaporized and preheated. The pre-
Apparatus and Procedure The alcohols were metered by means of a pump which was developed in earlier work for handling corrosive liquids. This pump will deliver at constant rates over the range 0.2 to 15 cc. per minute any liquid which does not react with mercury. The troublesome and less accurate method of running the corrosive liquid or displacing mercury at constant head through a calibrated capillary has usually been used for such work. This pump is described because it was dependable and accurate over a period of about two years. It proved to be a timesaving piece of apparatus, easily adjusted in 1 or 2 minutes to the desired rate of flow and requiring no further attention until the end of the run: Essentially it is a precision gear pump of the type used for viscose. It is driven through suitable reduction gears by a e 1 f
Present address, Standard Oil Development Company, Bayway, N . J. Present address, The Norton Company, Worcester, Mass.
FIGURE 1. LIQUIDMETERINQSYSTEM 1082
SEPTEMBER, 1938
INDUSTRIAL AND ENGINEERING CHEMISTRY
heater was so adjusted that the reactants entered the catalyst chamber within 20" C. of the reaction temperature. The catalyst chamber was the same as the one described previously (14) except for a few modifications. A 4-mm. tube, ring-sealed into the top of the chamber, ran lengthwise down the annular space, permitting temperatures to be measured at any depth in the catalyst bed. The space immediately above and below the catalyst was filled with 2-mm. glass beads. The reactants passed downward through about 18 cm. of the catalyst chamber, ensuring their reaching the reaction temperature before striking the catalyst. To avoid any temperature changes in the catalyst bed caused by the heat of reaction, the reaction temperature was recorded as the temperatufe at which the reactants entered the catalyst. This temperature was kept within 2" C. by an automatic controller.
Analytical Procedure AMYL,AMINES. The products were passed through a liter flask packed in ice and salt to remove the amyl alcohol and amyl amines; then they entered a flask containing 700 cc. of 20 per cent hydrochloric acid a t 50" C. where the excess ammonia was removed. A condenser cooled to 0" C. a t the end of the line condensed the amylene. The condensate in the first trap was acidified with hydrochloric acid, and the amyl alcohol and amylene distilled into the second trap containing the 20 per cent hydrochloric acid held a t 50" C. The amylene passed over to the third receiver where all of it was finally collected. It was determined by weight since its purity was established by fractionation. The amine hydrochlorides containing some ammonium chloride were made strongly alkaline with sodium hydroxide and extracted with two 50-cc. portions of ether. The extract was dried over anhydrous potassium carbonate, and the ether was removed by fractional distillation in a precision column. The residue was weighed as total amines. The amounts were so small that no attempt was made to separate the individual amines. The alcohol recovered was subjected to alkaline hydrolysis to determine its nitrile content, but none was found. BUTYLAMINES. The reaction products passed from the catalyst chamber into a 500-cc. Florence flask surrounded with solid carbon dioxide and acetone. The uncondensed gases then passed through a second solid carbon dioxide trap, a dilute sulfuric acid bubbler, and a gasometer. About 20 cc. of ether were added to the condensed products which were then fractionated in a precision column until pure ether began to distill over. The distillate was passed through two hydrochloric acid absorbers a t 0" C. to absorb the ammonia, and then through a solid carbon dioxide trap to condense the butylene. At the end of the distillation, dissolved butylene was swept from the absorbers and the increase in weight of the solid carbon dioxide trap was taken as the weight of butylene formed. (This product was shown by gas analyses to be fairly pure butylene.) The residue in the distilling flask was acidified with 20 per cent hydrochloric acid and subjected to steam distillation. The residue was extracted with 50 cc. of benzene to remove tarry materials. After the residual benzene had been removed from the aqueous solution by distillation, the solution was cooled in ice and made astrongly alkaline with sodium hydroxide. The amines were separated by salting out with potassium carbonate and extracking with ether. They were then dried and distilled in a small precision fractionating column; butyl Carbitol was used as the residual liquid so that all the tributyl amine could be recovered by distillation. The fractions 45' to 120" C., 120" to 185" C., and 185' to 225' C. were titrated with standard hydrochloric acid as mono-, di-, and tributyl amines, respectively. For the determination of nitrile, an aliquot of the nonbasic products was subjected to acid hydrolysis with sulfuric acid.
1083
The nitrile was determined by titrating the ammonia liberated on adding alkali and distilling. Butyl ether was estimated by fractional distillation of the alcohol residue. BENZYLAMINES. I n the work with benzyl amines the ammonia was allowed to pass off a t room temperature without fractionation. The monobenzyl amine was determined by the Van Slyke method; the tribenzyl amine was titrated after destroying the mono- and diamines with nitrous acid; and the dibenzyl amine was determined by difference.
Preparation of Catalysts A detailed description of the preparation of all the catalysts used would require too much space. A general description of the preparation of aerogels was given by Kistler (la). All of the gels containing alumina were prepared by modifications of the method of Ziese (21). Chlorides of aluminum, chromium, iron, and titanium were allowed to react with ethylene oxide to form pure gels and mixed gels. Thoria was added to such solutions before they set to gels, in the form of a stabilized colloidal solution (90). Silica was added in the form of ethyl silicate which was subsequently hydrolyzed. The alumina precipitate was made by adding ammonium hydroxide to a solution of aluminum nitrate, washing thoroughly, and drying. The catalysts used on runs 1-3 and 4-7 of Table I11 were prepared as follows: To a solution of 332 grams of aluminum chloride hexahydrate and 20.8 grams of chromic chloride hexahydrate in 872 cc. of water were added 150 cc. of glycerol. The solution was cooled to 0" C., and 350 cc. of liquid ethylene oxide were added with stirring. I n 15 hours the solution set to a firm, transparent, green gel which was broken up, extracted thoroughly with methanol, and autoclaved to give the aerogel. The xerogel was prepared by drying the methanol-extracted gel. (Later work has shown that no glycerol is required in preparing this gel.)
TABLBI. CONVERSION OF ISOMERIC BUTYLAND AMYL ALCOHOLSTO AMINBS OVER ALUMINA CATALYSTS Run No.
Aloohol Conver- ConverAloohol NHs sion t o sion to Alcohol Temp. Flow Flow Olefin Amine" O C i Grama per min. % % Alumina Aerogel Catafvsta n-Butyl 325 1.02 1 Traoe 1 5.2 1 350 1.02 1 375 1.02 1 14 1 400 1.02 1 56 2 99 400 1.02 0 0 2 2 sec-Butyl 275 1.05 1 30 2 300 1.05 1 58 2 325 1.05 1 350 1.05 1 70 2 11 2 Aotive amyl 300 1.06 1 32 2 325 1.06 1 62 2 350 1.06 1 Alumina Preoipitateb n-Amyl 275 0.43 0.75 0 300 0.43 0.75 1 325 0.43 0.75 5 6 350 0.43 0.75 1.1 2 Diethyloarbinol 250 0.46 0.51 2.3 2 275 0.46 0.56 4.5 2 300 0.46 0.60 325 0.46 0.60 39 2 350 0.46 0.60 68 2 71 2 375 0.46 0.60 0.8 1 n-Butyl 300 0.79 0.86 325 0.79 0.87 1.6 1 10.1 1 350 0.79 0.88 30 2 375 0.79 0.88 55 8 400 0.79 0.88 sec-Butyl 275 0.83 0.89 4.8 8.2 1 300 0.83 0.92 40 1 325 0.83 0.94 56 2 350 0.83 0.94
-
1 2 3 4 5 6 7 8 9 10 11 12
13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 Q
These values are maximum rather than exact. GO. of catalyst, 7.6 om. deep in all cases.
b 50
.. .... ..
1084
INDUSTRIAL AND ENGINEERING CHEMISTRY ~~~~~
VOL. 30, NO. 9
If a true evaluation of the a c t i v i t y of c a t a l y s t s f o r Conversion t o Aminesc amination were to be arrived Alcohol NHa Space Run No. Aerogel Catalysta Alcohol Temp. Flow Flow Velocitvb MonoDiTotal at, masking of this activity Cl Grama per min. Hr.-1 by olefin formation had to % % % A . Benzyl Alcohols t o Benzyl Amines be eliminated. Benzyl alcoAlumina isample 1) 1 Benzyl 300 1.33 1.00 2061 12.3 5.8 18.2 hol was therefore substituted 3 50 1.39 2 1.oo 2083 49 375 1.37 3 1.00 2076 34:6 19:1 54.3 for the aliphatic alcohols be400 1.43 4d 1.00 2098 24.0 17.5 41.8 cause it cannot be dehySilica (water glass) Benzyl 350 5 1.34 1.00 2066 ,. .. 1.8 375 1.33 1.00 2061 6 .. .. 2.6 drated to olefins readily. The 400 1.33 1.00 2061 7 .... .... 3.5 results with benzyl alcohol 425 1.33 1.00 2061 8 3.0 Benzyl Silica (ethyl silicate) 350 1.43 1.00 9 2098 .. .. Trace are shown in Table IIA. It 375 1.41 1.00 10 2090 .. .. Trace is evident that benzyl alco1.58 1.oo 400 11 2156 . . . . Trace 426 1.58 1.00 12 2156 .. .. Trsoe hol is entirely suitable for 450 0.66 0.50 13 1029 .. .. 1 evaluating the activity of Chromic oxide Benzyl 350 0.68 0.50 14 1035 19.8 2.5 22.5 375 0.68 0.50 15 1035 22.5 0.4 22.9 catalysts for amination. In 400 0.71 1047 0.50 16 .. .. 12.0 425 0.50 0.72 1050 17 .. .. 3.0 contrast to the high recomFerric oxide Benzyl 325 0.50 0.69 1039 18 14.4 .. 14.6 mendation of silica xerogel 350 0.50 0.65 1025 19 .. .. 5.5 375 0.50 1079 20 0.80 .. 2.6 by Brown and Reid (5),this .. 400 0.50 1076 0.79 21 1.4 .. .. work shows that two very Benzyl Thoria 300 0.76 0.80 1538 14.9 22 11.7 26.6 325 0.80 1552 0.80 pure silica aerogels are poor 23 19.7 50.6 25.6 350 0.80 0.82 1560 14.3 24 12.0 26.5 amination catalysts. Pure 375 0.80 0.82 1560 25 .. .. 8.0 Benzyl 300 0.82 0.80 1560 26 33.8 alumina aerogel is a fairly 5.9 40.7 325 0.94 1603 27 34.4 0.80 16.0 51.5 active catalyst. Aerogels of 350 0.80 0.83 1563 28 28.4 9.5 38.1 375 0.82 0.80 29 23.8 1560 6.4 31.0 chromic oxide and ferric oxide 400 0.82 1560 0.80 30 .. .. 15.0 are not so active but give a Benzyl 325 0.84 0.80 1567 27.2 31 17.0 44.5 350 0.80 1567 36.9 0.84 27.0 32 64.0 high ratio of mono- to di375 0.80 0.84 1567 41.8 22.6 33 65.0 400 benzyl amine. Thoria aerogel 1567 34 0.80 0.84 10.4 28.6 39.0 B. Aliphatic Alcohols t o Amines shows high activity, in agreeButyl 375 0.58 0.50 88.4% AlzOa-11.6% CrzOa 1000 18.3 35 14.6 33.6 ment with the early work of Ethyl 375 0.52 0.50 978 13.0 36 3.7 19.6 Sabatier (17). Thoria, howButyl 350 0.85 0.80 1570 90.1% AlzOa-9.9% FezOa 9.2 37 1.9 11.1 1545 375 0.78 0.80 11.8 38 2.2 14.0 ever, catalyzes many other Butyl 350 1563 0.83 0.80 39 89.4% AlzOs-10.6% Ti02 8.6 2.4 11.0 reactions such as dehydro1556 375 0.81 0.80 5.1 40 9.8 14.9 genation, polymerization, and Butyl 350 0.71 0.80 1520 41 33.3% AIzOa-66.6% Si'Oz 3.5 6.8 10.3 1473 350 0.58 0.80 42 4.1 3.8 7.9 decarboxylation, giving a 375 0.73 0.80 1527 43 5.9 3.5 8.6 375 1.52 2919 1.50 44 5.1 3.8 7.9 greater variety of side reacButyl 325 0.82 0.80 1560 12.7 45 2.7 15.4 tions than alumina. It is 350 0.76 0.80 1538 24.5 46 7.2 32.0 375 0.81 1556 0.80 21.8 7.4 47 29.0 apparent from Table IIA Butyl 325 0.70 0.80 1516 48 8.2 5.2 13.4 that alumina and thoria have 1538 350 0.76 0.80 49 2.6 7.1 9.7 1523 0.80 375 0.72 10.6 50 8.3 16.9 the greatest activity, but Butyl 350 0.82 0.80 1560 8.5% AlzOa-91.5% CrzOs 51 8.4 2.8 11.2 that chromic and iron oxides 1549 375 0.79 0.80 10.3 52 2.7 13.0 870 11.8 375 0.37 0.40 4.5 53 16.3 have a more desirable speButyl 325 0.44 0.40 Alumina (sample 2) 791 0.5 54 3 5 4.0 cific activity for the formation 784 345 0.42 0.40 0.6 4.5 55 5.1 1462 350 0.55 0.80 56 3.7 5.8 9.5 of monobenzyl amine. Mixed aerogels of a l u m i n a a n d 50 cc. of asfogel (8-20 mesh particles), 7.6 om. deep. b Space velocity = 00. of reactlng gases (S. T. P.) per cc. of catalyst per hour = (gram moles of reactants x 22,400) chromic oxide and of alumina per cc. of catalyst per hour. c Per cent conversion = per cent of butyl alcohol converted t o amines. and iron oxide were then d 1.7 per cent benzonitrile formed. prepared in the hope that the mixed oxides might retain the high activity of the alumina and the more Discussion of Results specific activity of the other oxides. Alumina was chosen in preference to thoria because the latter gives more side reSince alumina catalysts had been shown to give the best actions and is difficult to prepare as a gel. conversions of alcohols to amines, it was decided to begin The mixed aerogel of alumina and iron oxide gives the the investigation by comparing the behavior of alumina aerohighest ratio of mono- to diamines. The addition of small gel and precipitated alumina as catalysts for the conversion of amounts of chromic oxide causes a considerable increase in isomeric butyl and amyl alcohols to amines. The results of activity. These results seem to contradict the findings of these experiments (Table I) show that the alumina aerogel Shuikin et al. (18), but it must be remembered that these and precipitate were not active enough to convert the alcoinvestigators were not using gel catalysts. A mixed aerogel hols to amines in preference to olefins. Some idea of the of alumina and chromic oxide containing 11.6 per cent of the relative ease of dehydration of the various alcohols (at diflatter is shown to be a good catalyst. The results of Table ferent temperatures) may be gained from the table. ComIIA show to some extent the effect of temperature on the reparison of runs 4 and 5 shows the effect of increasing the action, and this effect is also shown in the results of Tables time of contact. Comparison of runs 6 through 9 with runs IIB and 111. 28 through 31 shows that the aerogel gives greater dehydraThe mixed aerogel of alumina and chromic oxide gave contion in spite of a shorter time of contact. With n-butyl versions to amines sufficiently greater than pure alumina alcohol this greater activity is sufficient to compensate for that it was tried for the amination of n-butyl alcohol. Measthe shorter time of contact only at the highest temperature urable yields of butyl amines were obtained. This reaction of 400' C. TABLE 11. CONVERSION OF ALCOHOLS TO AMINES
e
Q
SEPTEMBER, 1938 ~~
INDUSTRIAL AND ENGINEERING OHEMISTRY
1085
~
OF COMPOSITION OF MIXEDGELSON CONVERSION OF BUTYL ALCOHOL TO AMINES TABLE111. INFLUENCE
Per Cent BuOH Converted to: Total ButyButyl amines lene ether
7
Run No.
Temp.
Catalyst"
a
1 2 3 4
90.6% A1~08-9,36% CrzO3 aerogelb 90.6% AIzOa-9.36% CrzOa xerogelc
5
6 7 8 9 10
!35.3% AlzOa4.7% CrtOa aerogel 81.57, A1~08-18.5%CrzOa aerogel
11
12 13 14 15 16 17
80.5% Ah08-9.5% CrzOa-lO% ThOn
18
90.4% ThOz-9.6% Crz08 aerogel
19 20 21 a
aerogel ThOz aerogel
89.7% & ~ ~ - 1 0 . 3 ThOz ~, aerogel
50 cc. of 8-20 mesh catalyst.
b
cl
375 375 375 375 375 375 335 350 315 350 315 350 315 350 315 350 315 350 315 350 350
BuOH Flow
Space
NHa Flow Grams per min.
2.10 0.970 0.582 2.05 0.961 0.576 0.970 0.935 0.933 0.938 0.928 0.950 0.944 0.977 0.929 1.01 0.962 0.983 0.955 0.968 0.937
Velocity Hr.-1 2598 1934 997 2520 1899 1005 1932 1879 1868 1897 1877 1867 1842 1899 1837 1868 1911 1814 1878 351 1798
1.16 1.00 0.496 1.122 0.978 0.503 0.997 0.976 0.970 0.987 0.976 0.966 0.951 0.980 0.951 0.953 0.991 0.923 0.972 0.00 0.924
Apparent density, 0.185 gram per cc.
was then used to evaluate various other mixed oxide aerogels. (A complete analysis of the products of this reaction requires considerable time. In these preliminary evaluations no comprehensive study of the reaction products, other than the amines, was made.) In the removal of ammonia from the products by distillation, however, a low butylene content was indicated. The results with aliphatic alcohols are shown in Table TIB. The results of Table IIB show that the inclusion of chromic oxide in an alumina gel leads to a marked increase in its activity for the conversion of butyl alcohol to amines. The similar inclusion of titania, silica, and iron oxide in alumina causes a much smaller increase in its activity. The conversions over the pure alumina aerogel in runs 54 to 56 of Table IIB indicate that it is more active than the alumina aerogel used in runs 1 to 5 of Table I. Alumina and chromic oxide form fairly active mixtures over a wide range of compositions. The amine conversions decrease with high chromic oxide contents. Since the mixed alumina-chromic oxide aerogels proved so active, a more thorough study of the effect of composition on activity was desirable. Three more alumina-chromic oxide aerogels with different compositions were prepared; one of them was also prepared as an ordinary gel (xerogel). The results obtained with these catalysts and several other aerogel catalysts are shown in Table 111. The gaseous products, noncondensable at -80" C. and insoluble in dilute sulfuric acid, were measured in all of the runs of Table 111. Table IV shows typical analyses of these products and indicates an average value of about 96 per cent hydrogen. Most of this hydrogen is probably formed by dehydrogenation of butyl amine to butyronitrile and not by the dehydrogenation of the alcohol to the aldehyde. Run 20, in the absence of ammonia, showed only 0.3 times as much hydrogen as run 18 in the presence of ammonia, in spite of the fact that run 20 had a time of contact 5.2 times as long as 18. Run 21 demonstrates that this was not due to a decrease in activity of the catalyst, by duplicating run 18 after making run 20. Additional proof that most of the hydrogen was formed by the dehydrogenation of the amines is shown by nitrile analyses of runs 10 and 18. These analyses show 16.9 and 44.3 per cent nitrile compared with values of 19 and 45 per cent calculated from the amount of hydrogen formed. The values of conversion to butyronitrile in Table I11 have been calculated from the amount of hydrogen formed by the reaction.
C
BuNHz 20.8 29.6 28.2 18.8 25.9 25.6 22.5 22.9 13.9 25.0 18.7 24.6 13.9 10.7 5.1 13.7 3.8 4.7 5.5
.. ..
BuzNH
8.9 8.6 12.5 11.4 9.6 10.2 9.8 7.0 3.3 8.4 4.1 5.0 1.8 4.0 0.88 2.3 0.4 0.8 1.1
30.6 38.7 41.7 31.2 36.4 36.7 33.3 30.7 18.0 33.8 23.7 29.9 16.0 15.0 6.1 16.3 4.4 5.8 6.8
..
..
..
..
