0
A1
inum C V. N. IPATIEFF AND LOUIS SCHMIERLING Unisersal Oil Products Company, Riverside, 111.
38olecular hydrogen at superatmospheric pressure has a surprisingly marked effect on the action of aluminum chloride on alkanes. When n-pentane is heated with pure aluminum chloride at 125 O C. in the presence of hydrogen, no reaction occurs; if nitrogen is used instead of hydrogen, autodestructive alkylation takes place, resulting in the formation of butanes, hexanes, and higher boiling alkanes, and in the conversion of the catalyst to a viscous red liquid. If, on the other hand, the reaction under hydrogen pressure is casried out in the presence of a promoter such a# hydrogen chloride or water, isomerization to isopentane occurs in excellent yield with virtually no side reaction and the catalyst remains crystalline. Hydroperi
does not prevent the autodestructive alky lation of heptaiit. and higher molecular weight alkanes in the presence of pure aluminum chloride. However, if h>drogen chloride is added, destructive hydrogenation occurs and molecular hydrogen is consumed. This reaction has the adsantage over autodestructive alkylation in that it results in a higher ~ i e l dof isobutane and a smaller yield of catalyst complex (low cr layer). \l[oreover, the cataly st complex formed in the presence of hydrogen is more actiie than that formed in its absence, indicating longer catalyst life. Destructive hydrogenation of a Fischer-Tropsch naphtha is described and the effect of changes in cerkain vaviahles is discussed.
HE action of aluminum chloride or aluniinum bromide on alkanes has been discussed by inan)- investigators during the past decade (1, 4,6, 6, 10-15'). Their rcsults mav be summari7rd by stating that, in general, the primary reactions are isomerization and autodestructive alkylation. THe latter reaction is a combination of dealkylation (or cracking) and alkylation and results in the formation of isoparaffins of lower and higher boiling point than the original alkane. Thus, thc reaction of n-hexane with aluminum chloride may be illustrated by the following equations:
With n-heptane, on t,he ot'her hand, either ttutodestruct,ive alkylation or destructive hydrogenation can be made to occur, clepending on whether hydrogen chloride is added as promoter. The literature contains many examples of reaclions in which hydrogen disproportionation occurs in t,he presence of aluminum chloride. The present results shorn7 that aluminum chloride catalyzes hydrogenation reactions with molecular hydrogen.
CH,CH2CH&H2CH2CHj
Z*
(C€f,j iCHCH2CH&HA
iCeHi4 3- [CHB=CH~I
CsHis
EXYERlhIENTAL
( 1)
(3)
Ethylene formed as in Equation 2 inay alkylate lsoalkane (Equation 3) or it may poljmeriae, yielding polymprs xvhich react with the catalyst to produce the addition compounds which make up what is usually referred t o as the lower layer. Because the forination of this catalyst complex is accompanied by hydrogen transfer from one molecule of polymer to another, the hydrocarbon in the lowrr layer is highly unsaturated; the hydrogenated polymer is, of course, recovered as alkane in the upper (hydrocarbon) layer. I n some cases the production of the paraffins of liighei and lox er molecular weight seems to involve diaproportionation of methylene rather than of ethylene or othel olefin. Thus, under oertain conditions, isomerization of n-pentane to inopcntane is accompanied by the formation of butane and hexane. The present paper describes the iesults of an investigation which showed that molecular hydrogen a t superatmospheric pressure markedly modifies the action of aluminum chloride on alkanes. Isomerization lalies place accompanied by more or less destructive hydrogenation, depending on thc reaction conditions and the molecular weight of the paraffin. Catalyst coniplex formation is greatly diminished, thus increasing the life of the catalyst. I n the case of n-pentane, autodestructive alkylation is inhibited, so that little product of higher molecular weight than the original paraffin is obtained; similar use of hydrogen to inhibit cracking during the isomeiization of pentane and hexane has been mentioned briefly in recent publications (8, 15, 16).
CATALYSTS AND REAGENTS. The two types of catalyst used were pure aluminum chloride which \\-as prepared by resubliming technical aluminum chloride a t 190 O C. under hydrogen pressure as described later, and technical aluminum chloride which was a batch of commercially available "sublimed reagent gradc" product which left 15 to 20% by weight of residue Then resublimed. The reagents used were the Phillips Petroleum Company Pure Grade n-pentane (at least 99% n-pentane) ; n-heptane obtained from the California Chemical Company, 11.p. 98.39" C. a t 760 mm.; n*$ 1.38775; and the Xogasin naphtha consisting of IE hydrogenated Ruhr Chemie Kogaein fraction. The crude Kogasin was redistilled and the material boiling chiefly a t 100" to 200" C. and containing about 15% of olefins was hydrogenated a t 100" C. in the presence of (Universal Oil Products) nickel-kieselguhr catalyst to yield a completely saturated product that had an oct,ane number reportcd as "much below zero." A high t,emperat,urePodbielnialr distillation showed that' it consisted principally of normal paraffins in the following approximate percentages by volume: hexane, 2%; heptane, 1070; octane, 13%; nonane, 25'35; decane, 20%; hendecane, 20%; bottoms (chiefly dodecane), 10%. Engler distillation of the naphtha gave: initial boiling point, 210" F.; 10% over, 261" F.; 50% over, 315' F.; 90% over, 367" F.; and end point, 399" I?. APPARATUS ASD PROCEDURE. The experiments on t,he action of aluminum chloride on the paraffins were carried out in an Ipatieff-type rotating autoclave of 850-ml. capacity. The catalyst and the hydrocarbon n-ere weighed into a glass liner equipped with a ground-glass capillary stopper. The open autoclave was flushed n-ith nitrogen and the liner was scaled into it,. Most of the gas was then removed by applying suction with a vacuum oil pump for 2 minutes. Finally, hydrogen chloride (if used) was pressed in from a weighed aluminum cylinder and the pressure mas raised to 100 atmospheres with hydrogen or nitrogen. The autoclave was then heated to the desired temperature f o y , usually, 4 hours, after which it was permitted to set overnight. The gaseous products mere passed successively through x7att:r or soda lime to remove hydrogen chloride, then calcium chloride, a trap immersed in ice water, and a trap immerPed in dry iccacetone mixture. The noneondensable gas was passed through &
2354
December 1948
wet test meter; a sample was collected continuously over salt water, part of the gas being by-passed to the atmosphere. The autoclave was warmed to 45 O C. in order t o stabilize its contents and then was cooled in a n ice bath before it was opened. The hydrocarbon product in the linear was decanted from the catalyst layer, washed with ice water and dried, and its composition was determined by fractionation. I n the experiments with pentane, this liquid product was combined with the material in the traps and analyzed by distillation through a low temperature Podbielniak column. I n the experiments with heptane, the liquid product was distilled through a 14-inch total reflux column (17), the overhead (if any) being combined with the contents of the traps and submitted to the Podbielnialc distillation analysis. The composition of the noncondensable gas was determined by Goeckel analysis; except as noted in the tables, the amount of methane and ethane in the product was usually negligible. RESUBLIMATION OF ALUMINUMCHLORIDE. The technical aluminum chloride was resublimed by heating 100 grams of the material in a glass liner in the rotating autoclave at 190 O C. for 2 hours under 100 atmospheres initial hydrogen pressure. I n some experiments the liner was equip ed with a glass cap in which there was a hole about 0.625 incf in diameter; in others no cap was used. I n both cases, the aluminum chloride sublimed t o the upper part of the liner as a porous maw of large, usually colorless crystals while the nonvolatile residue remained at the bottom as a gray, very fine powder or as a gray, readily powdered cake. The liner was cut in two at a point slightly below the aluminum chloride crvstals and these were then easily removed (in a nitrogen atmosphere). The crystals were powdered in either a mortar or, more satisfactorily, a ball mill. Various samples of technical aluminum chloride were resublimed. T h e amount of residue was from 15 to 20% bv - weight - of material charged. Analysis of a typical residue showed t h a t i t contained 32.8% aluminum and 48.0% chlorine. The aluminum and chlorine content, respectively, d various compounds are: AICI, 20.2 and 79.8700; Al(OH)Ch, 23.5 and 61.7%; Al(OH)&l, 29.0 and 36.7%; AIOC1, 34.4 and 45.1y0; and A1203, 52.9 and 0.0%. Hence, the residue may consist of a mixture of about 85% aluminum oxychloride and 15y0 aluminum hydroxydichloride or of about 90% aluminum oxychloride and loT0 aluminum chloride. That the former composition seems to be the more probable was shown by heating 77 grams of residue (combined from several resublimations) under the resublimation conditions, There were obtained 72 grams of a light gray owdered residue which was so fine that i t flowed like a liquid, a n g l gram of a light gray sublimate at the top of the liner. The latter was soluble in water but did not react violently as does aluminum chloride. The loss in weight (4 grams) corresponds to the hydrogen chloride formed by the decomposition of the hydroxyaluminum dichloride present in the material charged. Analysis of the residue (72 grams) gave 34.8y0 aluminum and 46.270 chloride which indicates the presence of a t least 95% aluminum ox chloride and, hence, supports the theory that, the technical sampgs of aluminum chloride contained about 20 to 25% by weight aluminum hydroxydichloride.
TABLEI.
REACTIONS WITH n-PENTANE
reaction occurred when n-pentane was heated with pure (resublimed) aluminum chloride at 125 o C. under high hydrogen pressure. At least 95% of the n-pentane was recovered and the catalyst retained its crystalline form (experiment 2). If, on the other hand, the reaction was carried out under nitrogen pressure, autodestructive alkylation occurred; over 7070 of the pentane underwent conversion (experiment 1). Butanes, hexanes (including 2,3-dimethylbutane), and higher boiling alkanes were formed and the catalyst was converted t o a viscous red liquid. It must be concluded that although unpromoted pure aluminum chloride is not an isomerization catalyst, i t does catalyze autodestructive alkylation. Furthermore, hydrogen inhibits the latter reaction. EFFECTOF HYDROGEN CHLORIDE. Isomerization of the npentane did take place under hydrogen pressure when hydrogen chloride was used as promoter for the resublimed aluminum chloride. With a mole ratio of promoter to catalyst of 0.73, there was obtained 22.4% of isopentane; there was no appreciable side reaction and the catalyst was recovered unchanged. With a higher ratio-namely, 3.65-a 61% yield of isopentane was obtained; again the catalyst was unaffected and there was virtually no side reaction. On the other hand, use of a similarly high ratio (3.3) and nitrogen instead of hydrogen pressure, resulted in deep-seated autodestructive alkylation; the catalyst was converted to a dark tar (experiment 5). Hydrogen, then, prevents autodestructive alkylation of pentane even under conditions favorable for isomerization. Practical application of this observation of the effect of hydrogen was made (11) in the determination of the equilibrium constants for pentan- at various temperatures. EFFECTOF WATER. The best yield of isopentane was obtained by using water as promoter. Hydrogen again inhibited autodestructive alkylation. A 7ooj, yield of isopentane was obtained when 0.09 mole of water was added to a mixture of 1.39 mole of n-pentane and 0.09 mole of aluminum chloride and the product was heated at 125 C. under hydrogen pressure (experiment 6). The catalyst remained crystalline. EFFECT OF OXYGEN. Trace of oxygen (present as air in the autoclave) may have helped t o promote the isomerization in the presence of resublimed aluminum chloride and hydrogen chloride under hydrogen pressure. Pines and Rackher (IS), using high vacuum technique, have found t h a t isomerization of n-pentane (accompanied by autodestructive alkylation) occurs at 25 O C.
~ S O B I E R I Z A T I O N OF ?$-PENTANE
2
3
NI
€12
HI
100 10 0
100 10 0
100 10 2
100 10 10
100 10 9
...o
16 Liq.
10 Cr.
10 Cr.
10 Cr.
16 Tar
e--
12.9 0 .. 0 0 0 27.6 18.4 5.5 25.4 10.2
, .
0:O
0.0 0.0 2.8 96.6 0.6
0.0 0 0 .. 0 0 0.0 0.0 22.4 77.3 0.3
2355
As can be seen from the results summarized in Table I, little
1
Experiments
Aluminum chloride Atmosphere Reactants g. n-Pentane Aluminum chloride Hydrogen chloride Recovered catalyst Weight, g. Appearanceh Composition of product, mole 7% Methane Ethane Propane Isobutane %-Butane Isopentane n-Pentane Hexanes and higher
cH E M I sT RY
I N D U s T R I A L A N D E N G I NE E R I N G
4
5 HzRcfiublimed Nz
0.0 0 0 ..00 0.5 0.0 61.0 38.0 0.5
4.1 3.5 21.0 28.0 9.8 8.0 17.2 8.4
6
7b
9b
10
H2
H?
HJ
Hz--
KzJ
100 12
50
50
5 0
0
5
50 5 10
12 Cr.
5 Cr.
Cr.5
Cr.5
0.0
..
3i :. o0 1.4 1.4 73.7 18.8 2.1
8 C
.. 0:O 0.0
0.0 0.0
100.0 0.0
0.0 0.0 0.0 0.0 41.0 58.1 0.9
0:O 0.1
0.0 33.5 66.0 0.4
1
100 0
0
15 Liq.
3 9 0 :. 7 47.4 2.8 30.6 3.3 11.37
11 12 Hzf Technical Hz
10 0
363 35 0
. 13 , i
37 Cr.
100
1.8 01 .. 77 0.0 0.0 93.4 2.4 0.0
i:3 2.5 0.0 0.1 84.9 9.2 0.0
13d
HZ
14e
--.
HI
100 10 0
100 10 0
10 Cr.
10 Cr.
10.4 5 0 5 .. 4 1.4 2.5 65.2 10.1 0.0
0.0 0 0 0 .. 0 3.2 3.2 14.2 82.6 0.0
Experiments carried out in glass liners in rotating autoclave Of 850-ml. capacity. Unless otherwise noted, nitrogen or hydrogen was charged to 100 atm. initial pressure and autoclave was heated a t 125O C. f o r 4 hours. b Residual gas in autoclave displaced by two pressurines (to 10 a h . ) with hydrogen and subsequent evacuations with an oil pump (see text). C Air in autoclave not displaced. d Reaction temperature. 150° C. 6 RFaption temperature, 100° C. I Initial pressure, 2 5 atm. 0 Water (1.6 g.) added to the mixture of pentane and catalyst. h Liq. red or red-brown viscous liquid. Cr = white or yellowish crystalline powder. Tar = black tar. i Yellowish powder partially coagulated. f Contains s u b s t a n h amount of 2,3-dimethylbutane identified by photobromination product, 2,3-dibromo-2,3-dinethylbutane, map. 162O C. (sealed tube). a
-
*
INDUSTRIAL AND ENGINEERING CHEMISTRY
2356
a
iri the presence of aluminum chloride provided that oxygen (as iit,tle as 0.007 niole 7 0 of the pentane charge suffices) is present,: when oxygen is absent no reaction occurs. Some air \vas probably present in all the experiments described i n Table I, with the possible exception of experiments 7 and 9. [This inwstigationexcept experiments 7 , 8, and 9-was carried out several gears before the work of Pines and Karkher elucidated t,herole of oxygen in paraffin isomerizations; the oxygen effect has since been described also by Oblad and Gorin ( I O j . 1 In experiments 7 and 9, special precautions were taken t,o have very little. if any, oxygen present; the residual gas in t.he sealed and partially evacuated autoclave was displaced by two preliminary prctssurings with hydrogen and subsequent evacuations. S o react'ion at all occurred when n-pentane was heated Fvit,h resublimed aluminum chloride under hydrogen pressure in t,his presumbably oxygen-free at'inospherc (experiment 7 ; compare experimeiit 2 in which isomerization occurred t o the ext,ent of about 3Yc under the usual conditions). Isomerization did take place under the oxygen-free conditions xvhcn hydrogen chloridc was used as promot'er (experiment 9). Hoxvever, the yield of isopent,ane was 33..5Yc as compared with 6lYc i n the analogous experiment (experiment 4) carried out in t,he usual manner. When no attempt at all was made to displace the air in the autoclave, substantial isomerization (41t7c) occurred even when no hydrogen chloride was added (experiment, 8). The oxygen effect described by Pines and Wackher is t8hus confirmed. At the same time, it may be concluded that the results of the present series of experiments have at least semiquantitative significance despite the comparatively crude apparatus and procedure used. The fact t'hat aluminum chloride-hydrogen chloride catalyzed the isomeriaat'ion even under the oxygen-free conditions indicates the influence of a t least one other factor-for example, the formation of olefins by a cracking reaction. Pines and Nackher (23) sholved that pure n-butane is isomerized in the presence of aluminum chloride-hydrogen chloride, provided that, tho reaction conditions are such as bring about, cracking. They found that' as little as 0.01 niole yb of butene in n-butane viill bring about its isomerization under conditions under which nono occurs with the pure butane. Holyever, yet another effect, seems to have been involved in the present experiments since they lvere carried out under conditions \vhich gave very little cracking-i.e., cracking was inhibited by the presence of hydrogen. TECHNICAL XLumPic~i CHLORIDE.Excellent yields of isopentane accompanied by none 01' the products (hemne oi higherboiling alkanes) of autodestructive alkylation were obtained v,-hen a commercial grade of anhydrous aluminum chloride-i.e., one which left about 15 to 20y0 of residue vhen resublimed-\vas used under hydrogen pressure (experiments 11 to 14). On the other hand, isomerizat,ion of about one third and autodestructive alkylation of almost,all of t'he remaining two t'hirds of the pent>ani: charge occurred when nitrogen \vas substituted for the hydrogen (experiment 10). As wit'h the resublimed aluminum chloride, the catalyst was substantially unchanged when hydrogen was used but, was converted t o a red-brown viscous sludge when nitrogen was employed. The addition of hydrogen chloride as promoter for the cornmercial catalyst was unnecessary. This may have been due to the presence of hydroxyaluminum dichloride, which either is by itself a catalyst for the isomerization or decomposes under the reaction conditions to yield the hydrogen chloride. It' seems probable that the hydrosyaluminum dichloride was formed by the reaction of the commercial aluminum chloride with atmospheric moisture on long standing.
AICI,
+ 1320 +HO,41CI, + " 2 1
Vol. 40, No. 12
Inferential evidence in support of the second equation was obtained from t,he analytical results for the residue obtained by resubliming the commercial catalyst at 180" to 190' C.; the data indicated that t8heresidue had the formula, AlOCI. EFFECTOF TEbIPERATPRE. Destructive hydrogenation of about. 1570 of the n-pent>aneaccompanied if s isomerization when it was heated for 4 hours with commercial aluminum chloride under hydrogen pressure a t a higher temperature, 150" C. (experinlent' 13). Methane, ethane, propane, and butane, but no hcxancs or higher boiling products were formed. The cat'alysl did not undergo any appreciable change. hl a low-er temperature, 100" C., isonirrieation took place to the cxtent of only about' 14co (experiment 1.4j. A small amount, of dest,ructivehydrogenation to butane also occurred. EFFECTOF COKTACT TIME. Tests (not all of w1iic-h are summarized in Table 1) showed that' less than ITo of the n-pentane was isomerized when it) was heated a t 125" C. under hydrogen pressure with the commercial catalyst Cor 0.5 hour or less. Under the same conditions but wilh heating for 2 hours, 55% of isopenta,ne was obtained. A 4-hour cont>arttime yielded a t least S57c of t'he isomer. The effect of shorter contact times a t higher temperatures or of longer contact times at l o n c r temperaturc:s was not, studied in the present investigation. REAC'I'IVNS WITH ra-HEPTAKVE:
Hydrogen had a somewhat different effect on tho action of aluminum chloride on n n-parafin of' higher molecular weight (Table 11). With pure aluminum chloridc, in the absence of added hydrogen chloride, n-heptane underwent autodestructive alkylat,ion a t 1.50" C. regardless o f whether the reaction was carried out under hydrogen or nitrogen pressure. On the other hand, in the presence of added hydrogen chloride: and under hydrogen pressure destructive hydrogenatiori occurred to give a high yield of lower boiling products, particularly isobutane under nitrogen pressure, the heptane i v a , ~autodestiucttively alkylated. When aut,odestruct.ive alkyla,tion oc:currcd: the number of moles of alkane produced per niolc of hcpt,ane was about 1.0 to 1.1; a substantial amount of octane a,nd highcr boiling material was produced. R'hcn drstructivc hydrogonation occurred, the yield \vas about 1.4 to 1.5 moles and very littlt: product of higher molecular weight than heptane Tvas obtained. The use of hydrogen with heptane did not completely prevent rhe formation of catalysl' layer complex regardless of the conditions. However, tjhe complex which was obtained in its presence contained less hydrocarbon and was more active, as indicated by the heat evolved by its rract,ion with watrr.. Thr: catalyst, layer formed under nitrogen pressure v a s a brown tar; that formed under hydrogen was a viscous red or red-brown liquiil if no hydrogen chloride was uscvi and a clear ycllow to yellow-brown fluid if it was used. Grurnmitt, Case, and Mitchell (5) receritl!; showed t h a t the presence of powdered aluminum decreases tho a,mount of catalyst, complex (as well as of isobutane) formed hg the action of aluminum chloride-hydrogen chloride on n-hepta,ne. They point out that t'he hydrogen, which is formed by the reaction of the metal and the hydrogen chloride, m a y reduce olefinic products or olefinic or free radical intermediate protlwts and thus favor the forination of saturated products a t the expense of t'he unsaturated ones which combine with the aluminum chloride. They indicate t h a t this hypothesis suggests t,hat addition of hydrogen during the reaction should alter the product distribution. However, they found that' hydrogen added a t atmospheric pressure to a water promoted r e a d o n had litt'le effect. From the present results, it may be concluded Ihat Grummitt and co-worker8 used too low hydrogen pi'essure. Furthermore, it seems reasonable to conclude t h a t the hydrogen formed by the action of the metal is in more actirc form than is moleciilar hydrogen. ~
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
December 1948
2351
nitrogen instead of hydrogen there was obtained only 270 of condensable gas (compare experiment,. Experiment4 15 16b 17 18 19 20 21C 22d 23 24 and 25). The liquid product recovered from Aluminlrm Chloride ,---Rcsublimed----TechnicalAtmosphere pi2 IIe He Ha Nz H2 Hz He .. the destructive hydrogenation experiment had an Reactants, g. octane number of 59 (the octane number of the n-Heptane loo loa lo'10 lo' loo loo 2oo original naphtha was "much below zero"). The Aluminum chloride 10 10 10 Hydrogen chloride 0 0 0 6 5 0 0 4 : 2 liquid product recovered in the experiment carried Pressure, atm. Initial (room temp.) 100 100 100 100 100 100 100 108 . out under nitrogen pressure still had a n octane Max. a t 150' c. 130 135b 145 125 150 130 130 140 28 Final (room temp.) 100 100 100 75 100 85 85 98 .. number of less than zero. Recovered catalyst 13 44 The increase in octane number was due chiefly 16 15 17 Weight, g. 18 16 14 15 Liq. . . f Tar Liq. Liq. . . f T a r Appearancee Tar Liq. to the presence of isoparaffins which were formed Composition of liquid product, mole ?' & by the isomerization of the products of dePropane 3.2 2.8 20.6 7.2 19.9 13.9 18.0 Butanes 18.6 16.6 21:2 47.5 12.0 46.8 48.5 45.4 35:O atructive hydrogenat>ion. About 6 5 7 , of the Pentanes 20.8 11.3 15.2 21.3 9.0 15.2 18.3 24.2 11.7 liquid product, in experiment 24 boiled below the Hexanes 0.5 1.7 11.1 8.3 6.2 6.1 5.8 1.4 10.7 Heptanes 5 0 . 5 6 1 . 4 45.0 2.3 62.1 9.8 11.9 10.0 38.6 initial boiling point of the charging stock; none Octanes and higher 6.4 6.5 7.5 0.0 3.5 2.2 1.6 1.0 4.0 boiled higher than the original end point. On the hIoles of alkane formed 1.10 1.05 1.01 1.48 0.94 1.49 1.38 1.52 1.07 per mole of heptane other hand, the liquid product from the reaction charge which took place under nitrogen pressure cont'ained a Experiments carried out in glass liners in rotating autoclave of 850-1111. capacity. Unless otherwise noted, autoclave was heated a t 150" C. for 4 hours. 6 Temperature, 125' C. only about 15y0 of material boiling below the Duration, 1 hoiir. rl Duration, 2 hours. Similar results obtained in other experiments in 1 and.4 hours. Tar = dark brown, very viscous liquids, Liq. = red to red-brown initial boiling point of the naphtha charged. viscous liquid. f Yellow t o yellow-brown liquid. Furthermore, i t contained 2% of material boiling above the original end point-Le., autodestructive alkylation had occurred. REACTIONS WITH HYDROGENATED KOGASIN NAPHTHA COI\IPOSITION OF PRODUCT. The composition of the product Having show! that the destructive hydrogenation of n-hept,ane obtained by the destructive hydrogenation of the Kogasin naphin the presence of aluminum chloride results in a n improved tha was determined by the fractionation of the combined materiai from eight batch runs, the average results of which are repreyield of isobutane, it became of interest to apply this reaction to the reforming of paraffinic gasolines-for example, a straight sented by experiment) 26, through a 50-plate column (3). The run gasoline or a synthetic product' of the Fischer-Tropwh type. data presented in Tables IF7 and V and in Figures I and 2 indicate that the compounds formed included butanes (about. 25V0 by It was felt that a useful process could be developed if the gasoline were converted in good yield to isobutane (desired as charging weight of the charge), pentanes (about 22y0), hexanes (about stock for alkylation with olefins) and t'o isopentane and other 100jO),and heptanes (about 7 7 0 ) . The identity of the but>anes and peiitancs is satisfactorily branched-chain parafins. Fischer-Tropsch gasoline is particularly well suited for such a process because it contains little maproved by the boiling points. I n both cases, the iso .compound terial other than aliphatic hydrocarbons. Experiments with was present in about 907, concentration. a Ruhr Cheniie Kogasin naphtha (hydrogenated to convert its The presence of 2,2-dimethylbutane (neohexane) was shown hy olefin content to paraffin) are summarized in Table 111; the the boiling point and refractive index data. It probably reprenaphtha consist,cd chicfly of the n-alkanes boiling between 100" sented about 10 to 15y0 of the hexane fraction. The physical and 200" C. constants also indicated the presence of 2-methylpentanc while The action of aluminum chloride on the Kogasin naphtha was t,hat of 3-methylpentane was not established with certainty. analogous to its action on n-heptane. I n the presence of hyThe hexane isomer present in largest amount was 2,3-didrogen (and hydrogen chloride) a t 75 O C., destructive hydrogenamethylbutane. I t was characterized by means of its crystalline t,ion occurred, yielding 29% by weight' of condensable gas (largely photobromination product, 2,3-dibromo-2,3-dimethylbutane. isobutane). Under the same conditions but in the presence of The plat,eau in the distillation curve (Figure 1) a t 90" C. to-
TABLE 11. ACTIONOF A L U ~ I N UCHLORIDE M ON n-HEPTANE
TABLE111. ACTION OF ALUMISTJXCHLORIDE ---Raactantu, Exyt. b
24 h 25 26i 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43
Atmosphere Hz Na
Hz Ha Nz
He H2 H2
H2 H2
H?
H2 H2 H2
Naphtha 400 400 400 100 100 100 100
100 400 20 100 100 100 100
gram-
AlClSC 40d 40d 40d 10d 104 10 2d 2 8 2
2 5
10 20 10 10 10 10 10
.--Pressure, Initial HC1 (r.t.1 15 1p
Atm.-Max. Final (r.t.1 at T
?
; 1
1 1 3 1 10 1 3 3 15 3 3 1 3 3
100 100 100 100 E2 100 . .m .o 98 H2 u. yo b y weight of hydrocarbon charge. b Expts. carried out in glass liners in rotating autoclave (8E10-111l.capacity, except in expts. 24, 25, and 26 in which a 3515-ml. autoclave was used). Autoclave was rotated at the temwerature shown for 4 hourfi. C Resublimed aluminum chloride unless otherwise noted. d Technical aluminum chloride. e Catalyst layer is red to brown viscous oil. f Octane number, 59. Q Catalyst layer is black viscous tar. 152 Hz
H?
ON
KOGABIN N.4PHTHA
-
Products, %"-------Temp., Hydrocarbon Soncond. Cond. a t Cozd. a t Liq. C. in cat. layer gas -78' C. C. prod. Loss 75 56 1 29 10 52f 2 0 75 0 89h 75 1 28 6 57i 2 175 5e 07 5 21 175 4k 0 5 0 86 1 22 78 5e 8 63 0 75 30 0 0 97 0 125 5Q 92 0 0 lQ 75 0 0 0 98 .. 75 7e 26 0 30 75 20 1 0 98 0 75 3e 1 9 1 80 75 65 3 5 30 50 75 1 45 5 36 75 1 46 12 29 0 23 75 13 e 4 SEI 75 9e 0 24 5 38 1 8e 75 12 0 77 75 17n 3 7 0 73 2 75 3e 30 9 49 h Octane number, "below zero.'' i Average of eight experiments carried out under same conditions. i See Tables 11' and V for distillation and octane number data. k Catalvst laver is brittle. biack coke. 1 Catalyst layer is- mixture of red-oil-and orange-brown solid. m 50 atm. nitrogen and 50 a t m . hydrogen. n. Black fluid. 0 6 g. of aluminum chloride plus 4 g . of catalyst complex (blac,k tar) recovered from expt. 34.
,":
.
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
2358
gether mith the refraction data (Table \ ~ )indicated that about 6570 of the heptane fraction consisted of 2-methylhesane mixed Kith 2,3-dimethylpentane and/or 3-methylhexane. The remainder of the heptane cut was chiefly a mixture of the three heptanes boiling a t about 80" C.-namely 2,2- and 2,4-dimethylpentane and 2,2,3-trimethylbutane. Redistillation of this material and analysis of a middle fraction by means of its Raman spectrum indicated that' it consisted of about 50Cb of 2,4dimethylbutane and about 259; each of the other two compounds. Triptane, then, represented somewhat less than lOy, of the hept,ane product or about, 0.5% by weigh1 of t h e Kogasin charge.
u'
Vol. 40. No. 12
cxperiment (experiment 32, in which the hydrocarbon charge was 400 rather t'han 100 grams) gave similar results. This experiment was performed in order t o determine whether the 8 grams of aluminum chloride would involve the reaction of a t least 80 grams of the naphtha with the formation of about 15 grams 0 1 condensable ga,s. None was obtained. That 2 grams of aluminum chloride can catalyze the dcut,i,uc.tive hydrogenation of the naphtha, provided i'hat them i s proscrit not much more than about 10 times its weight of hydrocarbori. was shown in experiment 33 in which only 20 grains of the naplitha were used. The relative yields of the various products agreoti fairly well with those of the experiments in vhich 5 times the amount of both the charge. and catalyst was used--c.g., in esperiment 29. An almost straight line is obtained when the yield of conderisable gas is plotted against the per cent of aluminum chloride used (Figure 3). The line has a slope of about 55' but, of course, does not, pass through the origin. Therefore, doubling a given catalyst concentration results in somewhat more than tivice t h r s yield of condensable gas. I s is shown below, t,he hydrogen chloride concentration also determines the yield of destructive hydrogenation products; the curve shows the results obtained when t'he hydrogen chloridr is 10 to 20% by wright of the aluminum chloride.
TABLE IV. SUMXARY OF PRODT-CTS OBTAIBED EY DEPTRLC.I IVF, HYDROGENATIOK OF KOGASIX NAPHTWA' Reid Wt. Charge % of
Compound
- 0 2 0
10 20 30 40 50 60 70 Distillate, Vol. yo
Figure 1. Distillation of Product of Destructive Hydrogenation of Kogasin Naphtha
The effect of changes in certain variables 011 the destructive hydrogenation of the Kogasin napht,hn was investigated (Table 111). TEIIPERATURS. An increase in the reaction temperature resulted in increased conversion. When t,he reaction was carried out a t 175' C., less than 25'3 of the naphtha was recovered; condensable gas %-asproduced l o the extent of 67Y0 by weight of the hydrocarbon charge. The catalyst was converted to a brown oil which reacted vigorously when added to water, an indicat,ion that it was still catalytically active. Again, the use of nitrogen instead of hydrogen resulted in thc production of only 5% of condensable gas and more than 85% of the naphtha was recovered. The catalyst was converted to a brittle cokelike material which shored very little reaction with mater. RATIO O F HYDROCARBON TO - 4 ~ u ~ i mCHLORIDE. u~ The amount of aluminum chloride which was used in virtually all of the experiments was 10% by weight of the hydrocarbon charge. Attempts to accomplish the destructive hydrogenation of the Kogasin in the presence of only 2% by weight of the catalyst were unsuccessful. I n experiment 30 using the commercial aluminum chloride at 75 O C., no drop in pressure-i.e., absorpt,ion of hydrogen-occurred nor was any isobutane obtained. 9 black tarry catalyst layer formed. That this result was not due to t'he presence of oxygen compounds or other impusit'ies in the commercial aluminum chloride was shown by carrying out an experiment using the pure aluminum chloride; the result's were practically identical. Further, the use of a higher reaction temperature (125"C., experiment, 31) also did not bring about the formation of isobutane. The only effect of the increased temperature was an increase in the yield of tarry black catalyst layer. T h e use of 297" by weight of aluminum chloride in a large scale
Noncondensable ProDane Isobutane n-Butane Pentaneb Hexane Heptane Residue Hydrocarbon in cataivm layer Loss on washing, etc."c Loss in destructive hydrogenation
Motor OctaneMetdbd No
l.b.,/S~,' V.P In
...
...
1.3 1 3
...
5.1
4.4 3 3
. . I
. .
...
Expmiment 26, see also Table 1. At least 90y0 isopentane. Probably chiefly butane and pentane.
b C
TaBLE 1'. I ) I S T I L L 4 T I O X O F LIQVIDP R O D U C T Ol3TAIXE,ll BY DESTRCCTIVE HYDROGEXATIO~ OF K O Gsix ~ SAPHTFIA"
1 2
5c
6< 7 p 8C
1: 1 l C
18
Residur
Barometric Pressure, Llm.
26.6-28.8
745 . !I
28.8-29.5
3c 4c
12 e 13e 14 15 16 17
Boiling Point,
c.
Fraction
,
29.5-31.4 31.4-44.1 44.1-50. O 50 .O-57 .U 57.0-58.0 58.0-59,: 69.5-60 . 0 60.0-61.7 61,7-67.P 6 7 , 2 - 7 0 18 79.8-85.6 85.6-89.4 89,4-90,5 9 0 , 5 5 9 5 ,B 95.5-106.0 106.0-111.0
..
747 3 750.:
761.3
Vol.,
Yo
n":"
Photobromination h
3 . 4 I . 3560 7 . 1 1,3S48 3 . 3 1.3558 s o crystais 2 . 4 1,3606 N o crvstaln 2 . 6 1.3668 2 . 6 1,3707 3 . 8 1,3720 5 . 5 1 3729 2 . 7 1.3731 3 . 4 1.3738 3 . 7 1.3750 3 . 1 1,3797 3 . 2 1.3856 3 . 0 1.3872 3 . 3 1.3879 2 . 8 1.3881 2 . 9 1 ,3900 1 . 8 1.3940 39.4 1 4104
a Experiment 26 does not include much of pentane.
b Bromine waa added dropwise t o test tube containing 1.O ml. of fraction until color persisted for 5 minutes when illuminated with 1000-watt bulb. Test tub! was inclined on its 6ide:hydrocarbpn ma3 permitted t o evaporate, and formation of crystals noted. C Cuts 3-11 inclusive were combined and redistilled through Ytedman-type column. Results are shown in Figure 2 . d Melting point, 1 6 0 O C. (sealed tube). e Cuts 12 and 13 were combined and redistilied. Material boiling at 78-82' c. (35% of the charge) was analyzed by E. J. Rosenbaum by means of its Raman spectra: he reported t h a t i t consisted of approximately 50% 2,4-dimethyipentane 26% 2 2-dimethyipentane and 25% 2,2,3-trimothylpentane. Remaindth of h y d r k a r b o n boiled a t 75-78' C., n'; 1.3800-1.3817 (4370 of charge) and a t 82-86 C., nz: 1.3857-1.3865 (2070 of charge).
INDUSTRIAL AND ENGINEERING CHEMISTRY
December 1948
a
3
1
1
.
e
2
0
11.40 0
IO 20 30 40 50 60 70 80
2359
ride catalyst is shown in Figure 4 (Table 111). Increasing the amount of hydrogen chloride from 10% by weight of the catalyst to 30Y0 resulted in about 4070 greater yield of condensable gas. Further increase in the amount of promoter to 150% caused an additional 7 5 y 0 increase in yield. I n the experiments in which only 27, of the aluminum chloride by weight of the Kogasin naphtha was used, the hydrogen chloride was varied from 37 to 500% by weight of the aluminum chloride (from 0.75 to 10% by weight of the hydrocarbon). I n all cases, virtually no destructive hydrogenation occurred.
Distillate, Vol. %
Figure 2. Distillation of Pentane-Hexane Fraction Obtained by Destructive Hydrogenation of Kogasin Naphtha
The reason why a low percentage of aluminum chloride will not suffice for the destructive hydrogenation seems to be that excess free aluminum chloride must be present to act as a hydrogenation catalyst to regenerate the aluminum chloride which has formed catalyst-layer complex. I n the presence of large amounts of hydrocarbon all of the catalyst is rapidly converted to tarry complex (presumably by reaction with the more reactive constituents of the naphtha) and none remains to catalyze further reactions between the complex, the hydrocarbon, and the hydrogen. I n the absence of hydrogen, excess aluminum chloride is necessary l o catalyze the reaction between the complex and the hydrocarboni .e., cause autodestructive alkylation. In order to test this idea, the black tarry catalyst layer from experiment 34 in which only 2% by weight of aluminum chloride had been used was heated with the 100 grams of naphtha in the presence of 6 grams of fresh aluminum chloride and hydrogen chloride (experiment 43). T h e catalyst layer which resulted had the red-brown, fluid appearance which is characteristic of the catalyst layers from experiments in which 10% by weight of aluminum chloride is used. Furthermore, the yield of condensable gas was more than would have been obtained with only 6% of catalyst. The catalyst layer, then, does seem to react with paraffins in the presence of aluminum chloride in the predicted manner. RATIO OF HYDROGEN CHLORIDETO ALUMINUMCHLORIDE. The effect, on the yield of condensable gas, of changes in the ratio of the hydrogen chloride promoter to the aluminum chlo-
t
0
248
11,.
20 R 0 6
,
,
,
.
,
,
,
15 30 45 60 75 90 105 120 I35 150 Hydrogen Chloride, Wt. % AlClr
Figure 4. Effect of Hydrogen Chloride Concentration on Yield of Condensable Gas AlCh, 10% of Kogasin
HYDROGEN PRESSURE. Figure 5 shows the effect of the hydrogen pressure on the formation of catalyst layer complex; its effect on the yield of other conversion products is given in the data summarized in Table 111. It will be observed that the amount of catalyst layer decreases with increase in pressure. The hydrocarbon tied up with the aluminum chloride was 13% by weight of the hydrocarbon charge when the reaction was carried out at 25 atmospheres initial pressure, 9 t o 10% at 50 atJmospheres, and 5 to 0% ttt 100 atmospheres. The catalyst layers which were obtained when hydrogen was used were red-brown to brown liquids regardless of the pressure; those formed under nitrogen pressure were black and usually tarry. IJr
I
Initial Hydrogen Pressure, Atm.
Figure 5. Effect of Hydrogen Pressure on Catalyst Complex Formation
> AlCh, Wt.
IO 70
15
20
of Kogasin
Figure 3. Effect of Change in Aluminum Chloride Concentration on Yield of Condensable Gas AlCls/HCl Constant
A further effect of a decrease in the hydrogen pressure was a decrease in the yield of condensable gas. When the naphtha was heated under 50 atmospheres each of hydrogen and nitrogen, the yield of condensable gases was higher than that obtained in the presence of nitrogen alone (compare experiment 42 with experiment 25) but lower than that obtained with hydrogen alone. Furthermore, the black fluid lower layer contained twice as much hydrocarbon as did the red-brown liquid loner layer formed under 50 atmospheres of hydrogen or the black tarry layer obtained under 100 atmospheres of nitrogen.
2360
INDUSTRIAL AND ENGINEERING CHEMISTRY
The effect of a decrease in the hydrogen chloride concentration seems to be greater under 50 atmospheres than under 100 atmospheres initial hydrogen pressure (compare experiment 41 with experiment 40). MECHANISiM O F REACTION
Some insight into the reasons why hydrogen either prevents (as with n-pentane) or decreases (as with heptane or Kogasin naphtha) the formation of catalyst complex may be gained from the results of experiments in which catalyst coniplex was heated under hydrogen pressure. In order to have sufficient niaterial for the experiments, the analogous complex ('7, 9) formed by the polymerization of ethylene was used. Catalyst complex was prepared by polymerizing ethylene (at 20 to 40 atmospheres) pressure in the presence of 100 grams of aluminum chloride and 5 grains of hydrogen chloride a t room temperature. Ethylene was charged and recharged until the pressure no longer dropped below 30 atmospheres. About 140 to 150 grams of ethylene werc usually absorbed, the product consisting of two layers: about 70 to 80 grams of water-\Thite upper layer and about 170 to 180 grams of red-brown, fairly fluid catalyst layer. When 59 grams of such a catalyst coiiiplex was heated in a glasa liner in a rotating autoclave a t 175" C. under 100 atmospheres initial hydrogen pressure, hydrogen was absorbed (the final pressure Kas 85 atmospheres a t room temperature) and moat of the aluminum chloride \vas liberated. .kbout 20 g r a m (of a total of about 32 grams present in the catalyst layer) of crystalline aluminum chloride sublimed t o the top of the liner. The hydrocarbon portion of the complex was converted t,o lo!\-boiling paraffins: ethane and propane, 15 grams; butanei, G grams ; pentanes, 2 grams; higher-boiling, none. Fourteen grams of viscous catalyst layer were recovered. When the complex (46 grams) vas heated a t a lorn-er temperature, 150" C., there was again obtained a substantial yield of low boiling alkanes (ethane, 2.5 grams; propane, 6.5 grams; butanes, 6 grams: and pentanes, 3 grams). Twenty-sev-eii grains of brown, semisolid catalyst layer were recovered: this presumably conbined much free aluminum chloride which did not sublime out a t the lower temperature. IIeating the complex (G4 grains) a t 150" C . but under nitrogen pressure resulted in relatively little cohversion to alkane. About; 4.5 granis of butane and pentane ere obt,ained with little evidence of higher or lower boiling homologs. The recovered catalyst layer (58 grams) was a very viscous black material which on solution in ether yielded a dark brown solution and it black suspended solid (0.9 gram; carbon 1). CONCLUSION
I t may be concluded that when complexes of aluminum chloride with unsaturated compounds are heated with hydrogen, hydrogenat,ion of the unsahrated material occurs and the aluminum chloride is liberated because it cannot form an addition compound with a saturated compound. I t seenis permissible to conclude further that when an alkane is heated with aluminum chloride, under hydrogen pressure, comparatively little complex is obtained, either because all or most of it is hydrogenated to yield alkane and aluminum chloride or because the production of the unsaturated compounds necessary for its formation is prevent,ed. The latter probably occurs in the case of n-pentane. Side reactions leading to the formation of alkanes of lower or higher niolccular veight are suppressed; no olefinic int,ermediates are produced and the aluminum chloride remains unchanged. With n-heptane and higher homologs, on the ot,her hand, crnclting takes place so readily even in the presence of hydrogen t,hat the Tale of olefin fornittion exceeds the rate of hydrogenation. Hence, some catalyst complex is always obtained. Destructive hydrogenation rather than autodestructive alkylation occurs hrcauw
Vol. 40, No. 12
the olefin (or olefin precursor) is converted t o paraffin (by hydrogcnation) instead of high boiling alkanes (by condensation with heptane). Complete deeper insight iiito the mechanism of the reaction does not seem possible a t the present time. It seems probable that an ionic chain reaction ( 2 ) is involved. The primary intcrmediates in the case of the n-alkanes are the sec-alkyl carbonium ions. Migration of an alkyl group ivithin the ion yields (after hydrogen shift) a twt-alkyl ion 15-hich is converted to isoparafin by hydrogen exchange with a molecule of n-alkane which is thus converted to see-alkyl ion and the cycle continues. A conipeting reaction is scission of the alkyl carbonium ion a t t,ht: bond lvhich is in p-position to the eleci.ron-deficient carbon atom; this usually results ultimately in the formation of methylpropane (isobutane). The ot,her product of t,he scission is an olefin (rhich ends up as catalyst complex or as t,he higher molccular weight' paraffinic product, of autodestructive alkylation) unless hydrogen is present under conditions favorable for converting it t o alkane. However, in order to be conipletc a rnechaiiisin which purports to explain the effect of hydrogen on the action of alumiiiuin chloridp on alkanes must' ansxyer the following questions: (1) How does hydrogen inhibit the cracking of ia-penta~it: u,ithout a t the same time inhibiting its isomerization? K OCIA.. tirely satisfactory answer can be given at present,. ( 2 ) Why docs hydrogen chloride have a different effect with n-pentane than with n-heptane and higher homologs? T h r former undcrgoes no change when treated with pure aluminuni chloride undw hydrogen pressure; the latter undergo autodestructive alkylation. If hydrogen chloride is present, t h e pentane is isomerized; the n-hept,ane is destructively hydrogenated. -1s indicated above, the greater tendency of hepi auc l o crack is probably inherent in it3 higher molecular weight. Hydrogen chloride is necessary for destructive hydrogenation, presumably because it involves thc reaction of alkyl aluminiini ,achloride n-it,h hydrogen. LITERATCHE
crrm
(1) Bishop, J. IV.,Burk, K.E., and Lankelma, 13. I?., J . Am. C f ~ c m . Soc., 67, 914 (1945). ( 2 ) Rloch, H. S.,Pines, H., arid Schmerling, L., Zhid., 68, 163
(1946).
(3) Bruun, J. H., and Schicktanz, P. T.. 6. Research S n t 2 . Rzir. Standards, 7,851 (1931). (4) Egloff, G., Hulla, G.. and Komarcwsky, V. I., "Isomerization of Pure Hydrocarbons," Chap. 1 and Table 6, New YoTk, Reinhold Publi3hing Corp., 1942. (5) Grummitt, O., Case, E. N , and Mitchell, C . V., IND. Eso. CHEX., 38,141 (1946). ( A j Grummitt, O., Scnscl, E. E.. Smith, K.12., Burk, 1%.I;,, a,nd Lankelma, H. P., J . Am. Chem. Soc., 67, 910 (1945). ( 7 ) Ipaticff. 5'. N., and GI.OSSC, A. P.,IND. EKG.CHEM.,28, 461
(1836). ( 8 ) Slcdllister. 6 . I € . , IEoes, W. I?., Randlct,t, €1. E., and Carlsoii, G . J., T r a n s . Am. Inst. Chem. Engrs., 42, 33 (1940). (9) Neiiitzeacu, C. D., aiid Dragan, A , , Rer., 66. 1892 (1933). (10) Oblad, 8 . G., mid Gorin, >I, H., Txjn. E S G ~CHEM.,38, 822 (1946).
i l l ) Pines,
(12) (13) (14) (1.6)
(10)
(17)
I%., Kr-etinskas, B., Kassel, L. S., and Ipatieff, V. N., J . Am. Chem. Soc., 6 7 , 631 (1945). Piiieu, H., and Wackher, R . C . , I b i d . , 68, 595 (1946). Ibid.. 68, 599 (1946). Zhid., 68, 1642 (194G'l. Schuit, C. C . A,, Hoog, I%.,an11 \-erheun. J., Rec. trnc. chim., 59, 793 (1940). Swearingen, J. E . , G v k l r r , 11. D., and Nysewarider, C. T V . , Trans. S m . Inst. Chem. Engrs.. 42, 5 7 3 (1946). Thomas, C. L., Uloch. H. 8..aiid Hoekitra, J . , IND.EKG.&T:M., ANIL. ED., 10,153 (19%).
R i c e ~ v ~Nua y 19, 1947. Piesentad before the Division of Pctroleiiiir Chemistry a t the 111th XIeeting of the Atlantic City, ? .I. i.
.&YERICAS C H E ~ ~ K A SLO C I E T Y ,
