Higb-Temperature Alkylation of Aromatic Hydrocarbons A. N. SACHANEN AND A. A. O'ICELLY Socony-Vacuum Oil Company, Inc., Paulsboro, K. J.
Aromatic hydrocarbons-e. g . , benzene and toluene-have been alkylated with olefins at high temperatures of 800' F. and above. This process was performed under atmospheric pressure and in the absence of catalysts, but high pressures and such catalysts as activated clay improved the yields of alkyl aromatics. Toluene is more easily alkylated than benzene at these temperatures. On the other hand, propylene and butylene are stronger alkylating agents than amylene. Under high temperatures the alkyl aromatics produced were partially cracked, forming alkyl aromatics of a lower molecular weight. As a result, alkyl aromatics formed were composed of an entire series of aromatics beginning with toluene and increasing in molecular weight. The alkyl aromatics produced contained 90 per cent or more of purely aromatic hydrocarbons.
Blunck and Carmody ( 1 ) reported on the catalytic alkylation of paraffins with olefins in the presence of double salts of aluminum chloride such as LiAlCL, NaAlC14, etc. The temperature of the process was 155-282" C. (31&540" F.)i. e., on the border between high- and low-temperature alkylation. The data on high-temperature alkylation of aromatics are meager. Patents (4) describe the alkylation of toluene or naphthalene with gaseous olefins a t 300" C. (570' F.) in the presence of chromium or cerium metaphosphate. Schollkopf (11) alkylated naphthalene with ethylene a t 230" C. (445" F.) under a pressure of 10-15 atmospheres in the presence of an activated hydrosilicate catalyst. Ipatieff and Komarewsky (6) described the alkylation of aromatics with paraffins a t a temperature between 700" and 900" F. in the presence of a solid phosphoric acid catalyst. Under these conditions the paraffins decomposed and the decomposition products combined with aromatic hydrocarbons. Thermodynamically the alkylation of aromatic hydrocarbons with olefins is possible a t such comparatively high temperatures as 600' C. (1110" F.). Table I gives freeenergy equations for polymerization of ethylene, alkylation of %butane with ethylene, and alkylation of benzene with ethylene (10). The reaction of alkylation of benzene with formation of m-xylene rather that ethylbenzene has been taken since free-energy data for this isomer only are available.
TABLEI. FREE-ENERGY EQUATIONS OF POLYMERIZATION AND OW-temperature alkylation of aromatic and paraffinic ALKYLATION hydrocarbons with olefins in the presence of acids or Reaction Free Energy metal chlorides has been investigated by several authors CsH4 CzH4 + C4Ha JFo = -24,400 + 32.02' (9). Only a few references describe the high-temperature CaHi CiHm CsH14 AFo -20,200 + 32.47' alkylation processes. CnHr CsHa + CnHs(CH3)z A F o = -26,000 -+ 82.07' Frey and Hepp (3) investigated the alkylation of propane and isobutane with ethylene a t 500-525" C. (930-975" F.) under pressures as high as 4500 pounds per square inch. The A comparison of the data of Table I shows that the thermoreaction time was 4-5 minutes. The relative amount of dynamic probability of alkylation of aromatics is greater than ethylene used was very low, and the reaction took place in that of polymerization or of alkylation of paraffins. Even a t the presence of a large excess of a paraffinic hydrocarbon in atmospheric pressure the values for free energy of alkylation order to minimize polymerization of the olefin. Under these of aromatics are negative up to 547" C. (1017" F.). This indiconditions alkylation was the predominant reaction. With cates t h a t alkylation of aTomatics with olefins may occur a t propane the ethylene reacted to produce pentanes, and with temperatures as high as 500-600" C. (930-11 10"F.) and under isobutane hexanes were formed. At present the high tematmospheric or slightly elevated pressures. perature-pressure alkylation of isobutane with ethylene is being used commercially for the production of neohexane (8). Batch Operation Keith and Ward (7) described experiments on cracking This article describes the results of alkylation experiments pergaseous p a r a f h s and olefins a t 429-453" C. (800-850" F.) formed with bombs (batch process) in which the time of reaction and 800 pounds per square inch pressure. The yield of gasowas rather carefully controlled, as well as experiments conducted line formed was somewhat higher than the quantity of olefins in continuous operation. The batch experiments were carried out in an electricaIIy heated, stainless steel bomb of 2-liter cacapable of being converted into polymers. Thus the authors pacity, furnished by the American Instrument Company. concluded that this excessive yield over olefin present repreAs aromatic hydrocarbons employed in the alkylation experisented alkylation of paraffins. However, according to the rements, carefully redistilled benzene and toluene were used. The sults of Frey and Hepp (S), the pressure used in the above olefins used for the alkylation were propylene, butylene, and amylene. Most of the experiments were performed with amylene experiments should be considered too low for alkylation. 1540
L
+ ++
4
E
December, 1941
INDUSTRIAL AND ENGINEERING CHEMISTRY
since this compound is more convenientlyhandled for bomb operations than the normally gaseous olefins. In continuous operations liquefied cracking still gases containing propylene .and but lenes as well as the corresponding paraliins were used. &e olefins were mixed with the aromatics, usually in a molar ratio of 1:3 to minimize polymerization of the former. The temperature of the bomb experiments varied between 445" and 477 C. (833" and 891" F.). Meanwhile, the pressure varied from 1000 to 3200 ounds per square inch. As a catalyst, activated clay was use$ principally and varied between 5 and 200 per cent by weight with respect to the aromatic-olefin mixture. The recovery of the liquid synthetic products, after reaction, was accepted as equal to the volume actually recovered plus 0.7 times the weight of catalyst used. Blank experiments showed that 1 gram of catalyst retained 0.7 cc. of the synthetic material. Thus, using this correction factor the recovery of liquid products after alkylation varied between 94 and 95 per cent of the original charge. After the alkylation reaction in a bomb had been completed, the latter was cooled by an electric fan and then opened after first relievin any residual pressure. The liquid material was distilled from a fask provided with a fractionating column. The following fractions were taken: Nature of Fraction 1. Olefinic 2. Intermediate 3. Aromatio (benzene or toluene) 4. Alkyl aromatic 6. Residuum
Distillation Temp., ' C. (O F.) Benzene alkylate Toluene alkylate Up t o 45 (113) Up t o 45 (113) 45-70 113-158) 45-100 (113-212) 70-95 158-203) 100-116 (212-241) 95-210 203410) 11e-210 (241-410) Above 210 (410) Above 210 (410)
I
The initial boiling points of 95' C. for alkyl benzenes and 116' C.for alkyl toluenes ensure a sufficient separation of alkyl aromatics, newly formed, from the original aromatics employed. Experiments have shown that after fraction 3 is taken in each of the above cases, the temperature rises rapidly t o that corresponding with newly formed alkylation products. Redistillation of fraction 3 with a n efficient column showed i t t o contain 3 per cent of alkyl aromatics. Nevertheless, since this redistillation in each case would have required a great deal of time, i t was avoided. Therefore, the yields given may be considered as being below the yields actually possible of attainment. Actual maximum yields may thus be 1.5 per cent higher than those submitted. Fraction 4 contained relatively pure aromatic hydrocarbons. The specific gravity of this fraction was approximately 0.870 (60"/60' F.), and the refractive index (60' F.) is of the order of 1.490; these figures correspond closely with those for pure aromatic hydrocarbons of this boiling range-i. e., 110210' The low iodine number (2) of these fractions (less than 20) and their almost complete solubility in concentrated sulfuric acid (95 per cent or more) also show that they consist of comparatively pure aromatic hydrocarbons. High-boiling fractions (i. e., above 210' C.) also have a high specific gravity of 0.870 or more and refractive indices of 1.500 or greater. It is notable that the specific gravity of polymerized olefins boiling above 210' C. is about 0.800 and the refractive index about 1.450 (12). We can thus presume that high-boiling fractions consist chiefly of alkylated aromatics, some of which may have a polycyclic structure. Therefore the total amount of alkylated aromatics obtained in distillation is here accepted as equal t o the sum of fractions 4 and 5 given above. Fraction 5 (the residuum) may contain also some aromatics produced from the olefins employed, which may be cyclized at high temperatures. Polycyclics such as diphenyl may result from the benzene at high temperatures. The amount of alkyl aromatics boiling in the range of motor gasoline-i. e., up t o 210' C. (410" F.)-is accepted as equal to fraction 4.
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were carried out in a specially constructed apparatus consisting of a high-pressure pipe still of one gallon per hour capacity. The reaction chamber consisted of a stainless steel bomb of one-liter capacity. The temperature was measured by a thermocouple placed in a well located inside the reaction chamber. The reagents-i. e., benzene and an olefin-were charged to a preheating coil and then to the above reaction chamber from a pressure charging tank by replacement with ethylene glycol which was pumped with a Bosch pump. The heating of the coil and the reaction chamber was by strip heaters. Figure 1 shows the preheating coil, reaction chamber, and strip heaters of the apparatus; half the heaters are located on the door of the heating case, which are exposed in the photograph. From the reaction chamber the charging stock passes to a condenser and thence to a suitable receiver, amounting to a small gas separator. A reduction valve is placed between the reaction chamber and the condenser. The separation of alkyl benzenes produced in the continuous process was performed in the same manner as described for batch operation. Temperatures as high as 525' C. (977' F.) and pressures up to 2000 pounds per square inch were employed in a continuous process. The reaction chamber was filled with activated clay, and the process took place with a constant excess of this catalyst. The rate was such that the reaction time was approximately 2 minutes. The catalyst was easily re enerated after becoming inactive due to coking. Hundreds o f such regenerations were possible without any noticeable decrease in the alkylating effect. This regeneration process involves removal of gums, coke, etc., from the clay by oxidation with a stream of air a t temperatures of 750" F. and above. Steam was used simultaneously or alternately, to revent too high regeneration temperatures. A typicarexperiment was one in which 10 liters of benzene were mixed with 4.2 liters of liquefied cracking still gases containing 21 per cent ropylene and 17 per cent butylenes. The mixture was processecfin the pressure still a t 525" C. and 1500 ounds per square inch pressure, and gave about 10.5 liters o f synthetic crude. After distillation of the latter there were obtained: 318 cc. of alkyl aromatics boiling from 95" to 150" C. (203' to
c.
Continuous Operation Experiments of once-through flow (continuous) at stmos heric were conducted in an iron tube heated in an egctric urnace. Continuous alkylations at superatmospheric pressures
7
FIGUR 1. ~ PREHEATING COIL,REACTION CHAMBER, AND STRIP HEATER
INDUSTRIAL AND ENGINEERING CHEMISTRY
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302' F.), of specific gravity 0.865, iodine number 12.0; and 1190 cc. boiling between 150" .and 210" C. (202' and 41Oo.F.), of specific gravity 0.873 and iodine number 22.0. In addition, 285 cC. of regiduum boiling above 210' C. were obtained. The theoretical yield (100 per cent) of alkyl aromatics is calculated from the olefin employed, since benzene and toluene are used in excess. Thus the theoretical yield in alkylation of benzene with amylene was calculated according to the equation for reaction: C6Hm f CBHE -t CeH6 - CsHu
This means that even though polyalkyl and lower molecular weight benzenes may be produced by the reaction, the actual yields represent an assumption that none other than primary alkylation reactions occur. Likewise, in the employment of ropylene and butylene, yield calculations were made on a basis of primary propyl- and butylbenzenes as the end product. It should be recalled that the conditions of polymerization of olefins are rather close t o those of alkylation-i. e., temperatures in the neighborhood of 445-477" C. and above, and pressures of 1000 pounds per square inch and higher. Thus the polymerization of olefins may interfere with alkylation of aromatics and reduce the yield of the desired product. Practically, olefin polymerization does not occur to any appreciable extent in the presence of a sufficient excess of aromatics. However, a molar ratio of 3 aromatic to 1 olefin was found necessary to reduce polymerization products t o less than 10 per cent of the total yield. Also, the free energy of alkylation of aromatics is more negative than that of polymerization of olefins under these conditions, and hence the former may become the predominant reaction.
Alkylation Variables Data on the alkylation of benzene and toluene with olefins are summarized in Table I. At 445-477" C. the rate of alkylation is satisfactorily high. The reaction time to produce 20-30 per cent of alkyl aromatics of gasoline boiling range (up to 210" C,.) a t these temperatures is 15-30 minutes and may be lessened by the use of a larger relative amount of catalyst. TABLEI. ALKYLATION OF AROMATICSWITH AMYLENEUNDER VARIEDCONDITIOWS Molar Ratio Catalyst, Aromatic: Amylene ?%y ?
TeT'y- Pressure Lb./Sq.'
R ~ tion Time, Min.
~ Yield0 ~ - Alkyl Aromatics, vO1. %
Boilin t o In. Total 410' % Benzene ~ . ~ ~ . 17 10 1400 90 3:l None 830 443 1100 30 24 18 845 452 5 3:l 1300 30 34 22 3:l 850 454 10 845 452 35 47 31 25 1300 3:l 845 452 1300 30 39 26 50 3:1 1400 15 23 16 845 452 10 3:l 22 300 20 30 29 3:l 845 452 30 44 2700 846 452 15 32 3:l 2700 20 30 42 32 3:l 845 452 3:l 3200 845 452 10 30 40 28 Atm. 5 1-2 10 200 890 477 3:l Toluene 1250 45 65 45 845 452 3:1 3P 2100 45 72 11 845 452 84 3:1 27 19 None 1200 15 3:l 885 474 15 26 15 None 1300 3:l 885 474 18 15 None 1400 890 477 35 5:1 16 None 1300 3:l 880 471 30 34 1200 46 15 52 50 3:l 890 477 200 3:l 890 477 Atm. 22 1-2 32 T h e percentage of alkyl aromatics synthesized with respect t o t h e theoretical yield of amylbenzene or -toluene. O F .
C.
8..
High pressure is not necessarily a prerequisite to thermal alkylation of aromatics. If the relative amount of activated clay is high, the rate of alkylation of benzene and especially of toluene is comparatively rapid, even under atmospheric pressure (Tables I and 11). Nevertheless, moderately high
Vol. 33, No. 12
pressures are very favorable to the process. Above 2400 pounds, however, increase of pressure is not of any advantage since its only effect is to produce a larger proportion of highboiling product without contributing effectively to the increase of total yield. Data show that maximum yields of alkyl aromatics are obtained under pressures of 2400 pounds per square inch for benzene and 2100 pounds for toluene. This negative effect of higher pressures is evidently due to the formation of polyalkyl aromatics. The relative amount of catalyst may be decreased considerably if pressures in the region of 2000 pounds per square inch are employed instead of the 1000-1500 pounds generally sed in these experiments. TABLE11. ALKYLATION OF BENZENE WITH ANYLENE IN PRESENCE OF VARIOUSAMOTXTS OF CATALYST
THE
(850' F.,1300 pounds per square inch, 30 minutes, 3:l molar ratio benEene: amylene) Yielda Alkyl Aromatics Alkyl Aromatics, % Refractive Catalyst, % Boiling index by W t . Total t o 410' F. (6t&OgrF.) (70° F.)
0 T h e percentage of alkyl aromatics synthesized with respect t o the theoretical yield of amylbenzene. 6 T h e reaction time was increased t o 90 minutes.
Thermal alkylation of aromatics with olefins may be performed noncatalytically (Table I), if the pressure is in the neighborhood of 1000-1500 pounds per square inch. The product, however, is colored slightly and is apparently contaminated with nonaromatic materials as shown by its specific gravity. The alkylation process is greatly accelerated by the presence of activated clay; the latter is especially influential in the formation of aromatics in the gasoline boiling range. For example, in the absence of catalyst only 11per cent of lowboiling alkyl aromatics is produced from benzene a t 445" C. and 1400 pounds pressure for a period of 90 minutes, whereas 25 per cent is produced in the presence of 12.5 per cent clay under the same temperature-pressure conditions with a reaction time of only 20 minutes. Noncatalytic alkylation of toluene a t 477" C. and 12001400 pounds pressure for 15 minutes forms about 20 per cent of low-boiling (to 150" C.) alkyl toluenes, whereas 40 per cent is produced in the presence of 15 per cent clay, other conditions being equal. The data of Table I1 demonstrate the influence of the relative amount of catalyst on the rate of alkylation and yields. The yields and aromaticity of the aromatics formed are higher as the amount of catalyst relative to the charge is increased. Toluene is more capable of alkylation than benzene, especially under atmospheric pressure. Other conditions being equal, toluene forms 20-30 per cent of alkyl aromatics boiling up to 210" C., whereas benzene yields only 5 per cent of the theoretical. Under high pressures this difference between benzene and toluene is considerably diminished , and benzene becomes readily alkylated, producing as high as 30 per cent of gasoline-boiling-range alkyl aromatics in one operation. The alkylation of toluene under high pressures converts this compound largely to high-boiling compounds which are of no use in aviation gasoline and of very little use in motor gasoline because of the end-boiling-point specifications of these materials. The alkylating tendency of propylene under pressure is of about the mme order as that of butylene, but both exceed that of amylene (Table 111).
December, 1941
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE111. ALKYLATIONOF BENZENE WITH VARIOUSOLEFINS
'
(840-850' F., 1200-1600 pounds per square inch, 30 minutes) Yield", % by Volume Alkyl Catalyst, Total benzenes boiling Olefin % by Wt. alkyl aromatics to 410' F. 62 Propylene 18 50 59 Butylene 12b 43 34 22 lob Amylene 67 Butylene 12c 53 47 31 Amy1ene 250 a The percentage of alkyl aromatics synthesised with respect to the theoretical yield of amylbensene. b Regenerated catalyst. C Fresh catalyst.
Under the most favorable conditions the total yield of alkyl benzenes may be as high as 67 per cent (all yields are by vol-
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too high for motor gasoline. On the other hand, in a hightemperature catalytic process the same reactants produce chiefly low-molecular aromatics, boiling in the range of aviation and motor gasolines. The distillation curve of the alkyl aromatics formed in hightemperature alkylation depends upon the temperature and the time of reaction. Under quite severe conditions of the process, lighter molecular weight alkyl benzenes such as toluene, ethylbenzene, and xylenes are produced in lesser amount. Figure 2 represents two distillation curves (A. S. T. M.) of alky benzenes boiling up to 210" C. The compounds were formed under the same conditions of temperature and pressure but with different reaction times. While
/oo
I J
INDUSTRIAL AND ENGINEERING CHEMISTRY
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lines, since its octane blending value is 2-3 units higher than that of the aviation cut. On the other hand, this solvent fraction may also be employed as solvent naphtha of very high solvent power. Furthermore, cracking of this SOcalled solvent fraction results in lower boiling aromatics which may be used in the aviation cut. The properties of this solvent fraction are as follows: A. P. I. gravity Boiling range O F. Kauri-butandl No. Aniline point, O C. Color
(O
C)
31.5 300-424 (149-218) 81.8 - 38 Water-white t o very light yellow
This solvent material consists chiefly of propyl-, butyl-, and amylbenzenes. The total amount of unsaturates does not exceed 5 per cent by volume.
Reforming Cracked Gasolines with Benzene Destructive high-temperature alkylation of benzene with high-molecular-weight olefins found in cracked gasolines may also be performed. As a result the octane number and chemical stability of alkylated or reformed gasolines are considerably increased, owing to the formation of stable and high-octane alkyl benzenes. From 10 to 30 per cent of benzene by volume may be used for the alkylation under previously mentioned conditions-i. e., at temperatures around 850-950" F. and a t elevated pressures. The presence of activated clay is also beneficial to this process. The yield of reformed gasoline in the original boiling range is about 76 per cent by volume. Table V gives the results of alkylation of benzene with the olefins contained in two cracked gasolines.
Vol. 33, No. 12
The data of Table V show that cracked gasolines reformed with benzene by alkylation have improved octane numbers and stability. The response to tetraethyllead, however, is relatively poor, The chemical effect, furthermore, of reforming by alkylation is clearly shown by comparison of the chemical composition (in per cent by volume) of vapor-phasecracked gasoline before and after alkylation with 30 per cent benzene. Type of Compound Unsaturates Aromatics Nepht henes Paraffins
Cracked Gasoline 54 11 25 10
After Addition of 30% Benzene 3s
38 17 7
Same after Alkylation 11 58 26 5
Solvent cuts produced from cracked gasolines by alkylation of benzene and boiling between 160' and 210" C. have a very high Kauri-butanol number (83-85).
Acknowledgment We are indebted to J. B. Rather, in charge of General Laboratories, The Socony-Vacuum Oil Company, Inc., for permission t o publish this work, and to C. H. Schlesman, research director, for his helpful suggestions. We wish to acknowledge the able assistance of S. B. Davis in performing some of the experiments connected with this work. Literature Cited (1) Blunck and Carmody, Baltimore Meeting, Am. Chem. Soc., April, 1939. (2) Francis, A. W., IND. EXQ.CHEM.,18, 821 (1926). (3) Frey and Hepp, Ibid., 28, 1439 (1936). (4) I. G . Farbenindustrie, Brit. Patent 316,951 (1928); 323,100 and 327.282 (1929). \ ,
. ~ . ~
TABLE V.
RESULTSOF REFORMING CRACKED GASOLINES BY ALEVLATION
A. P. I. Gravity Compn. of Gasoline Liquid-phase cracked 57.7 Same 3007 hrnaene (before alkylation) 48.1 Same 3 0 d bencene (aftcr alkylation) 41.4 Vapor-phase cracked 46.8 Same 80% benaene (beforealkylatlon) 41.8 Same 3 0 7 beniene (after alkylation) 37.3 Same 1 5 % benzene (before alkylation) 44.7 Same 15% bensene (after alkylation) 41.8 B y t h e Motor method.
+ + + + + +
Octane N0.a With 3 cc. T. E. L. 78.0 82.6 80.7 84.0 86.4 90.0 85.0 90.6
Clear 66.6 72.0 81.6 78.5 81.0 84.0 79.5 81.9
Acid Heat,
F.
> 100
> 100 32 1100
>loo 32 > 100
Ipatieff, "Catalytic Reactions at High Pressures and Tempeiatures", p. 653, New York, Macmillan Co., 1936. Ipatieff and Komarewsky, U. S. Patent 2,098,045 (1937). , Keith and Ward, Oil Gas J . , Nov. 28, 1935. (8) Oberfell and Frey, Ibid., Nov. 23 and 30, 1939. (9) Sachanen. "Conversion of Petroleum", pp. 28, 8 0 , New York. Reinhold Pub. Corp., 1940. (10) Ibid., p. 40. (11) Sch6llkopf, U. 5. Patent 2,115,884 (1938). (12) Waterman, Leendertee, and Makkink, J . I n s t . Petroleum Tech., 22, 333 (1936). ~
30
Q
PREBP~NTED before t h e Division of Petroleum Chemistry a t the 102nd Meeting of t h e American Chemical Society, Atlantic City, N. J.
Drying Heat-Sensitive Substances A Modified Flash-Drying System W. C. RONGSTED, J. B. GOTTFRIED, AND L.
c. SWALLEN
Corn Products Refining Company, Argo, Ill.
T
HIS paper describes a process for drying substances
which are sensitive to heat, and have fusion or solubility characteristics such that a n unworkable mass of dough or liquid is formed if the wet material is warmed appreciably. It applies to cases where material being dried would undergo more or less fusion or be dissolved in residual solvents a t only a slightly elevated temperature. Particular application of this drying system has been made to the preparation of zein. The process for preparing eein
was described by one of the authors (2). This paper gives more details of the drying system and particularly points out the innovations required by the peculiar physical characteristics of zein. Zein is insoluble in water and is precipitated from alcoholic solution when the latter is mixed with wat,er. The doughy character of the zein when first precipitated is lost as soon 8 s sufficient contact has been maintained with cold water to ensure removal of the solvent. However, if the precipitated zein is heated slightly, its plastic and adhesive properties become evident. A temperature of 15" C. (59" F.) is the maximum which can be permitted without a noticeable softening effect, although slightly higher temperatures cause no great difficulty if the factors of time and mechanical action are
