The Liquid Phase Alkylation of Benzene with 1-Octene in the Presence of Hydrogen Fluoride

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P U R D U E UNIVERSITY

T H IS IS TO C E R T IF Y TH A T T H E T H E S IS P R E P A R E D U N D E R MY S U P E R V IS IO N

by

HAROLD EMMONS MARSH. JR._____________________________

E N T IT L E D

THE LIQUID PHASE ALKYLATION OF BEUZBNE WITH______

1-OCTEEE IN THE PRESENCE OF HYDROGEN FLUORIDE______________

C O M P L IE S W ITH T H E U N IV E R S IT Y R E G U L A T IO N S O N G R A D U A T IO N T H E S E S

A N D IS A P P R O V E D B Y M E A S F U L F IL L IN G T H IS P A R T O F T H E R E Q U IR E M E N T S

FO R THE D EG R E E O F

DOCTOR OF PHILPSOPJ

P r o f e s s o r in C h a h g e o f T h e s is

H ead of S cho ol o r D epartm ent

TO T H E L IB R A R IA N :---T H IS T H E S IS IS N O T TO B E R E G A R D E D A S C O N F ID E N T IA L .

R E G I S T R A R F O R M 1 0 —7 - 4 7 —1M

THE LIQUID PHASE ALKYLATION OP BENZENE WITH 1-OCTENE IN THE PRESENCE OF HYDROGEN PLUORIDE

A Thesis Submitted to the Faculty of Purdue University by Harold Emmons Marsh, Jr. In Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy February, 195)0

ProQuest Number: 27714100

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ABSTRACT

Since the year 1877, when Friedel and Crafts (8) reported the first direct alkylation of aromatic compounds, this branch of organic chemistry has been the source of countless fruitful investi­ gations and many industrial achievements.

A great number of

catalysts have been found to be effective for alkylation, the most important ones being the acids, HF, halides, AlCl^ and BF^.

and H^PO^, and the metallic

Hydrogen fluoride was introduced into the

field in 1938 by Simons and Archer (25) • As a catalyst for hydrocarbon alkylations, HF is probably the most useful.

It is cheap and plentiful (25), and it catalyzes

most reactions catalyzed by other agents.

Its effectiveness is

thought to be due mainly to its high acidity, great dehydrating tendency, and its good solvent properties.

It produces fewer

undesirable products (mostly tars) than sulfuric acid (9) and aluminum chloride (25).

Unlike sulfuric acid, it does not undergo

oxidation-reduction reactions (9) and it does not require low tempera­ tures.

Thus cold water instead of refrigeration may be used for

process cooling. A brief summary of the reaction conditions described in the literature for the alkylation of benzene by olefins in the presence of HF includes the following:

temperatures from 0° to

20° C., and at least one mole of catalyst (usually more) for every mole of olefin (21), and a high benzene-olefin ratio to cut down

polyalkylation and polymer formation.

This last can be accomplished

either by a high ratio in the original charge or by slow addition of the olefin to an agitated mixture of benzene and HF. At ordinary temperatures, the alkylation reaction is con­ sidered to be irreversible (7_), and this is borne out by thermo­ dynamic calculation (l6, 23, 22, 31).

Reports are conflicting as

to the location of the reaction; in an early publication (26) Simons expressed the belief that the reaction takes place in the hydrocarbon phase, while Gerhold (9) describes the alkylation of isoalkanes as taking place in the acid phase and at the interface between the two phases.

Francis (7) concludes that the catalyst phase is the

location of the reaction in the case of AlCl^ catalyzed production of ethylbenzene.

The present work also indicates the catalyst

phase as the location of the reaction. The preparations of various octyl benzenes have been reported in the literature (lU, 32, 13, 12, 27, 19).

Only two

investigators employed 1-octene and HF: with toluene (27), and with 2-methylnaphthalene (-IfQ • In this last study by Lottes and Shreve 3? (X9y) HF-octene ratios of less than one and temperatures up to 130° C. were investigated.

Equipment and Procedures

The alkylation of benzene with 1-octene in the liquid phase in the presence of hydrogen fluoride was studied at tempera­ tures ranging from 0° C. to J4.2O0 G.

The major part of the data

concerns the effects of varying temperature and catalyst concentration on the yield of the monoalkylate.

These data were taken in the

temperature range of 0° to 120° C. and with HF-octene ratios ranging from 0.5 to U.O moles per mole.

Attempts at measuring the kinetic

properties of the reaction'at 0° C. were unsuccessful because the reaction was found to be instantaneous.

Some attempts were also

made early in the work to measure equilibrium constants of the monoalkylation reaction at 225° to 1*20° C.

Calculation of equilibrium

constants from the best data available indicated that measurable equilibrium mixtures should exist at temperatures around 225° to 250° C.

These attempts failed because the method used to arrest

the reaction permitted the mixture to cool, and of course the highly mobile reaction proceeded toward the equilibrium of the lower temperatures, which are not measurable by our methods of analysis.

No octene could be found in the products. An enclosed reactor was required to maintain liquid

phases for the high-temperature alkylations, and an open reactor was used for the low-temperature reactions.

The low-temperature

reactor consisted of a 500 ml. beaker constructed of copper with riveted and press-fit joints filled with solder.

A cap for the

beaker was made from a large-diameter rubber stopper.

In it four

holes were bored to accommodate a stirrer bushing, a copper con­ denser, a copper funnel for introducing materials, and a thermo­ couple .

This equipment served satisfactorily for twenty runs.

The reactor was immersed in a water or ice-water bath up almost to the top of the copper beaker.

A small stainless steel propeller,

whose shaft was extended through the bearing in the cap, was driven by a laboratory (worm-gear drive) electric motor.

An auto-trans­

former was employed to regulate the speed, usually to between 500 and 1000 r.p.m.

The temperature was measured by the thermocouple

attached to a millivoltmeter. The high-temperature alkylations were carried out in the bomb of an American Instrument Company rocking autoclave (I4.O6-OID) with a 1000 ml. capacity and cold-tested at 15000 pounds per square inch.

The agitation was effected by the rocking motion.

The

heat was supplied by two electric heaters in the jacket of the auto­ clave, one with a variable auto-transformer for control.

The

temperature was measured by a thermocouple deep in a thermo-well and attached to a Micromax recorder. The procedure for the low-temperature reactions was as follows :

Benzene (with enough chloroform to keep the benzene from

freezing) and HF were introduced into the reactor immersed in an ice bath.

With the stirrer running, the octene was added slowly

from a 50 ml. analytical buret.

Thirty minutes (for data runs)

after half the octene had been added, the reaction was stopped by the addition of concentrated NaOH solution.

The mixture was then

separated, and the hydrocarbon layer was washed with water, dilute HC1 (to dissolve metallic salts that cause emulsions) and then with saturated sodium sulfate.

It was then dried over anhydrous sodium

sulfate. Mixtures with low conversion contain a high percentage of organic fluorides, which cause considerable difficulty in dis­ tillation by liberating HF upon thermal break-down.

Though small

in quantity, this HF etches the distillation column and the vacuum pump and carries over as much as 10 percent of the charge in the form of a fog.

The adoption of a defluorination treatment (20), consist­

ing of refTaxing 100 g. of the hydrocarbon mixture with 25 g. of activated alumina for ten hours, took care of the problem. The analysis of the mixture was accomplished by dis­ tillation.

Careful fractionation was necessary when knowledge of

the proportions of benzene, octene, and the higher alkylates were needed.

However, usually the benzene and octene were stripped off

at atmospheric pressure, and the monoalkylate was carefully fraction­ ated off under vacuum. The procedure for the high-temperature reactions was similar to that described above: chilled bomb.

Benzene, octene and HF were added to the

The bomb was capped and placed in the heater jacket

of the rocking autoclave.

The heat and the rocker were turned on.

Thirty minutes after the reaction temperature was reached, the bomb was removed and held under a stream of water until it was colder than room temperature.

The bomb was then uncapped, and the con­

tents were poured carefully into an agitated bath of ice-water.

The water was separated from the hydrocarbon phase, which was then washed with a small quantity of NaOH solution.

From this point on,

the treatment was the same as that described for low-temperature runs.

Qualitative Results

A great deal of information concerning characteristics of the reaction was obtained during the earlier experiments.

This

information is not quantitative ; however, it - along with other discoveries reported in the literature - serves to aid in the interpretation of the quantitative results of this investigation and is therefore described briefly here. It was found that all of the measurable heat produced at the start of the reaction was caused by a reaction between the 1-octene and the HF. fluoride (10).

This is probably the formation of octyl

The heat could be eliminated by uniting the octene

and HF first and then adding the benzene; however, we were unable to obtain reproduceable results in this manner and the procedure described above for low-temperature reactions was adopted. The small amount of chloroform (20 percent by weight) used to keep the benzene in a fluid state for the 0° G. runs had no great effect on the yields.

However, when as much as 83.3

percent diluent was employed, the yield dropped considerably.

vii.

The first experiments at high temperatures were made with a volume ratio of HF to octene of 1-to-l, because this quantity of catalyst is generally used in petroleum alkylations at room tempera­ ture (20).

It was found that at high temperatures (220° G.) this

caused all of the octene to be converted to tar, probably high-molecularweight polymer. of 78-to-l.

A volume ratio of 1-to-l amounts to a molal ratio

This same ratio at room temperature produced no

measurable quantity of tar, and a ratio as high as 11-to-l at 220° C. produced only a negligible amount. Very poor agreement between the yield values for duplicate runs was encountered at the beginning of the high-temperature pro­ cess variables experiments.

Lottes and Shreve (19) had discovered

that much greater uniformity of results was obtained if the auto­ claves were capped as drained instead of cleaned between alkylations. This procedure was adopted with immediate benefits resulting.

Not

only did this change establish the conditions for good reproduction of results but it also brought about greater yields of monoalkylate than had ever before been obtained - around 90 percent, based on the olefin charged. One run was made at 1*20° C.

The product was more complex

than those obtained at lower temperatures; other alkylates were present.

One cut was identified as cumene on the basis of its

boiling point and molecular weight (cryoscopieally determined.) Experimental values were If?!0 C. and llf> g./mole3 actual values are lf>2.5° C. and 120.19 g./mole.

viii.

Quantitative Results

No extensive work was performed with the variable, time, because all the results of the high- and low-temperature experiments indicate that contact time, in the ranges employed, has no great effect upon the degree of conversion of the octene to phenyloctane and other products.

Two time series of runs were made at 0° G. and

15>° C. under the conditions described for low-temperature alkyla­ tions.

The data from these two series (Table 1 and Figure 1) tend

to substantiate the conclusion that time is not a variable in the conditions employed by us.

The variation in yield of the mono­

alkylate in the lf>° C. series is probably a result of other factors, mainly the method of mixing reagents5 however, the total octene conversion appears to show that a state of equilibrium depending upon the temperature, catalyst concentration, and mixing conditions has been reached in all three cases. Table 1 Effect of Contact Time Run Number 16 17 53 28 27 29

Temperature

HF-0ctene Mole Ratio

0° c. 0 0

3.0 3.0 3.0 3.0 3.0 3.0

15 15 15

Time 1 Min. 5 30 30

60 120

Percent Yield of Monoalkylate 16.5 17.0 15.5 10.8 31.8 20.2

Total % Conversion of Octene ho hh —

68

72.5 75

PER CENT

YIELD OF

0CTYLBEHE6BE

ix.

60

TOTAL CONVERSION OF OCTENE

60

40

MONOALKYLATE

20 x> 0°C

20

Figure 1,

40 TIME

80 60 MINUTES

Effect, of Centre t ïiw*

100

120

X.

The major part of the data from this work concerns the process variables, temperature and catalyst concentration.

Three

temperature series were conducted (0°, 30°, 120° C.) the last two in the rocking autoclave.

A mole ratio of benzene to octene of

5-to-l was maintained, except in the 0° C. runs where one mole of benzene was replaced by one mole of chloroform.

The data are to

be found in Tables 2, 3, and it, and they are plotted in Figures 2 and 3.

The curves of Figure 2 were plotted with the aid of the

method of least squares.

For cross-plotting onto Figure 3, the

data were smoothed by interpolating the slopes of constant catalyst ratio curves like those in Figure 2.

The quantity of data is not

sufficient for accurate statistical analysis.

However, assuming

that the two groups of data for which we have four values were selected at random from a homogeneous universe of data, we can estimate the limits of precision (l).

At 0° C. and with a HF-

octene ratio of 1.5>-to-l, we should expect 90 percent of the yield values to lie between 3.1 and U.2 percent.

At 30° C, and a ratio

of 1.5-to-l, Tie should expect 90 percent of the yield values to lie between 13.It and 16.8.

These theoretical ranges are 1.1 and 3Ji

respectively, and they are lower than some of the others in the data.

xi.

Table 2 Experimental Data for the Effect of Catalyst Concentration at 0° C. Ran Number lt9 2it 30 U8 52 16 17 53 it5 kl

HF-0ctene Mole Ratio 0.5-1 1.5-1 1.5-1 1.5-1 1.5-1 3 -1 3 -1 3 -1 it - i it - i

Percent Yield of Monoalkylate 3 h 3.5 it 3 16.5 17 15.5 89 85.5

Table 3 Experimental Data for the Effect of Catalyst Concentration at 30° C. Run Number 11 ho 38 50 55 56 5U 57 36 i;6

HF-0ctene Mole Ratio

Percent Yield of Monoalkylate

0.5-1 0.5-1 1.5-1 1.5-1 1.5-1 1.5-1 3 -1 3 - 1 it - 1 it - 1

5 It 16 15 lU 15.5 89.5 92.5 90.5 90.5

xii.

Table It Experimental Data for the Effect of Catalyst _________ Concentrationat 120° C.________

Run Number

HF-Octene Mole Ratio

Percent Yield of Monoalkylate

37

0.50-1

7

ljl

0.50-1

lt.5

51

0.75-1

58

0.75-1

lit

U2

1.50-1

16.5

h3

1.50-1

51.5

3k

It -

89

39

It - 1

1

6.5

91.5

xiii.

100

4.0

OF OCTYLBENZENE

60

PER CENT

YIELD

13.0

0

0

20

40

05 60

80

TEMPERATURE °C

2.

Yield versus Temperature

100

120

xiv

100

80

0°

J40

3.0 1.0 20 MOLAL HF-OCTENE RATIO

Figure 3.

Yield W r i u i Catalyst Concentration

4.0

Identification of Alkylates

We believe that we have enough data to assure us that the monoalkylate is a phenyloctane, very probably 2-phenyloctane. We also have considerable evidence for the presence of the dialkylate in our reaction mixture.

The evidence for the identifi­

cation of these compounds can be divided into six categories: (1) the compound expected on the basis of the chemistry involved and on the basis of the work of other investigators with similar compounds5 (2) the appearance of the compound as the fraction expected in distillation analyses ; (3) the agreement of the analysis data with material balances based on the expected com­ pounds 5 (10 the boiling point of the compounds ; (5) molecular weights determined cryoscopically; (6) analysis for carbon and hydrogen. The monoalkylate meets all the above requirements for the formula, G - | a n d meets the first four for the phenyloctane. One value for the boiling point of 2-phenyloctane found in the literature - 125-127° C. at 18 mm. - (6) agrees very well with the vapor pressure curve for our monoalkylate. Figure U.

The

dialkylate meets the first four requirements for dioctylbenzene.

xvi.

4 .0

3 .0 CP

01

m

X A /l

2.0

0.0

2.0

1.0 LOG P

Figore 4.

Vepor Bressmres ef Alkylates

3.0

Discussion

Even though we were unsuccessful in trying to measure equilibrium constants of the monoalkylation reaction, there is little doubt that such equilibriums exist in the presence of sufficient hydrogen fluoride.

The data published by Rossini and

associates (31) with n-alkylbenzenes give validity to our assumption of the temperature range (225-25>0° C. ) in which measurable equi­ librium mixtures might be found.

The fact that our failure was

caused by a much higher rate of reaction than anticipated is established by later experiments.

Strangely enough, our results

indicate that an apparent equilibrium exists in which hydrogen fluoride is one of the major components. Although the results of early experiments and the find­ ings in the literature indicated that the reaction Is instantaneous, an attempt was made to determine the effect of time at low tempera­ ture.

The justification for this action was the theory that if

hydrogen fluoride acts only as a true catalyst, perhaps the experi­ ments referred to had involved amounts of catalyst far in excess of some necessary minimum, and the use of smaller amounts would reduce the rate to a measurable range.

However, although less yield was

obtained under these conditions, showing a decreased catalyst activity, the yield did not vary appreciably with time.

The question is, liVhat happens to the hydrogen fluoride in alkylations of an aromatic compound with an olefin such as octene? Two properties of hydrogen fluoride that seem to be very important to this question are its solvent properties and its tendency to polymerize, even in the vapor state. The book, Hydrofluoric Acid Alkylation, by the Phillips Petroleum Company (20) states that when the acid phase becomes contaminated with dissolved organic compounds to the extent that it contains only completion.

percent HF, the reaction no longer goes to

It must be remembered that they used a continuous

process with a very great excess of HF, a 1-to-l ratio by volume, which corresponds to about an 80-to-l molal ratio of HF to octene in our experiments.

Francis {]_) writes of a selective solvent

action by aluminum chloride catalyst in the éthylation of benzene. Octene is very soluble in hydrogen fluoride by virtue of their reaction to form octyl fluoride, which is soluble in the acid. (10, 11)

An excess of HF causes the olefins to polymerize.

Our

experiments showed very definitely that the reaction between an olefin and hydrogen fluoride is very rapid and gives off a large amount of heat. No data were found on the solubility of benzene in HF; however, the solubility of HF in benzene (2lt) rises from 0.39!? mole percent at 72.8° C. to 6.5)3 mole percent at 21.5>° 0.

It is to be

expected that that magnitude would be the same for benzene in the acid.

The solubilities of isobutane, n-butane, and propane in

hydrogen fluoride have been determined (5).

The isobutane (more

soluble than the others) is soluble to the extent of 0.757 mole percent at 100° C. to 3.5>0 mole percent at 0° C. Jander (15) states that the performance of reactions in nonaqueous solvents, such as HF, depends on solvation and other features.

Klatt (17) relates the high solubility of some com­

pounds in HF to specific addition centers (such as 0-, N-, and double-bonded carbons).

The addition compounds formed are soluble.

Butler and associates (£) report^their belief that a co-association of HF and the tertiary hydrogen atom of isobutane through hydrogen bonding causes the iso-compound to be more soluble than the normal compounds. The detrimental effect of cleaned autoclave walls on the catalytic action of the hydrogen fluoride is certainly important to the question of the activity of the HF.

Simons (25) states

that copper vessels are preferred to iron ones because the FeF^ formed on the walls "is believed to promote tar formation."

The

solubility of FeF^ varies from 16.75 percent at 1*6 percent HF (impurity water) to 1 percent FeF^ at 71 percent HF (30)* data are given for anhydrous HF.

Very likely the clean bomb

surface is attacked by the HF to foim a layer of FeF^ and a little dissolves.

This reaction takes up a large amount of the acid because

the surface is large.

If the bomb is not cleaned out and is not allowed

to vent, the salt remains on the surface to protect it from the next charge.

It is well known that hydrogen fluoride polymerizes in the vapor state, but there is some difference of opinion as to the manner.

One group (18, 2_8) believe that the polymer is a six-

membered ring and that the variations depend upon the equilibrium. The other group (Ij., 3, 2) hold that the polymer is a zig-zag chain of (HF)n, where n varies.

Figure 5 shows the relation between the

apparent molecular weight of liquid HF with temperature.

The data

are from two sources (28, 29). Now, if hydrogen fluoride solvates some of the compounds in our reaction through hydrogen bonding - the tertiary hydrogen of the secondary alkyl group, for example - it is conceivable that this solvation is done also by polymers of HF.

There might even

be a tendency favoring the solvation of the larger polymers, thus causing a shift of polymerization equilibrium. It is difficult to imagine that any specified quantity of hydrogen fluoride molecules needs to be present for simple catalytic action wherein the catalyst molecule is freed after each action. It is true that dissolved organic matter would reduce the activity by mere dilution, but this would result in a slowing down, not a complete arresting of the reaction, and the conversion would still vary with time. However, it is not safe to say that the catalyst layer becomes saturated with products of the reaction and that no more reagents can be dissolved, because the dynamic equilibrium of solution would gradually take care of any unused reactant.

xxl*

NUMBER OF FORMULAR WEIGHTS APPARENT MOLECULAR WEIGHT

5.0

SIMONS & HILDEBRAND — o SOCONY VACUUM •

40

30

II

c

-4 0

50

r i.g'jre 6.

150

100

TEMPERATURE

°C

Apparent Molecular Vfeiçht of H-' ;c: yr;efa

200

aorie

SIMONS & HILDEBRAND SOCONY VACUUM------

50

100

TEMPERATURE

figure 6.

150

eC

Apparent KeleeUar Vfeight of RF fc-vnera

200

It might be proposed that the olefin is entrapped as the fluoride, but that assumption would lead to one of two other con­ clusions that are not compatible with the data.

If the formation

of the octyl fluoride were an irreversible reaction, our problem would be one of kinetics, a race between alkylation and fluoride formation.

However, heating such a reaction mixture from below

room temperature to 120° C. would not increase the yield.

The

other conclusion which might be drawn from such an assumption is that the reaction for the fluoride formation is a reversible one. If this were the case, the equilibrium would continue to shift until all of the octyl fluoride was used up. We suggest that the following actions take place in alkylation reactions under the conditions studied in this investi­ gation. 1.

The reaction takes place in the acid phase.

2.

Hydrogen fluoride catalyzes the alkylation reactions (both mono- and poly-) as long as any is available to do so.

3.

Either octene or octyl fluoride react.

Hydrogen fluoride and octene combine to form octyl fluoride.

it.

As a result of stirring, the various components are distributed between the two phases according to their various solubility equilibriums.

5.

Hydrogen fluoride and its polymers solvate certain molecules present in the mixture (probably the tertiary hydrogens of the secondary alkylbenzene molecules and possibly the benzene molecules dissolved in the HF phase.) Solvating HF groups have, on the average, the apparent molecular weight that is characteristic for the tempera­ ture prevailing*

As a result of the above actions, no more free HF molecules are available to catalyze further reaction after enough alkylate has been formed to hold all of the HF.

However, if the temperature

is raised, the apparent molecular weight becomes smaller, and some HF is liberated to catalyze more reaction.

Subsequent cooling does

not change the status of the reaction. The fact that the data do not correlate very well when this theory is assumed directly in the calculations does not mean that the theory is without validity.

Certainly the actual

occurrences in the reaction are more complex.

However, the data

give a very good correlation with the theory when they are applied more elastically. he found that if it was assumed that-all of the octene and all of the monoalkylate formed were dissolved in the acid phase, a limiting concentration of HF exists for each temperature above which the reaction is catalyzed and below which very little reaction takes place.

(See Figure 6)

when these limiting concentrations of HF

are plotted against the n representing the HF polymer size (see Figure 7, a. smooth curve results which shows that a higher con­ centration of HF is needed to catalyze alkylation when n is high than when n is low.

XXV*

60

YIELD

30°

40

PER CENT

OF OCTYLBENZENE

60

20

1

20

30 40 WEIGHT PER CENT HF IN ACID PHASE

Figure 6*

Limiting HF Conoentrfitioa lor Complete Reaction

30

20

WEIGHT

PER CENT

HF

IN ACID

PHASE

40

2.0

n

Figuare 7.

3.0 NUMBER OF FORMULAR WEIGHTS APPARENT MOLECULAR WEIGHT

4.0

Relation between Limiting HF Concentration and HF Polymer Size

CONCLUSIONS

Benzene can be alkylated in the liquid phase with 1-octene under the following general conditions: a.

Benzene-to-octene ratios of 1-to-l to 10-to-l;

b.

Hydrogen fluoride-to-octene ratios of 1-to-l to10-to-l

c.

Temperatures of 0° to 2I4O0 C.;

d.

In an open reactor or an autoclave, whichever one is necessary to maintain liquid phases;

e.

Vigorous agitation;

f•

Contact times of one minute or more.

The conversion of octene to monoalkylate is dependent upon temperature and quantity of hydrogen fluoride in the manner depicted in Figures 2 and 3.

Temperature is effective only

for intermediate concentrations of hydrogen fluoride; low conversions are obtained at low HF concentrations for all temperatures while high conversions {90%) are obtained at high HF concentrations at all of the temperatures studied. Time has very little effect on the extent of alkylation, the reaction being nearly instantaneous. Either low temperature or low catalyst concentration is necessary to prevent tar formation (olefin high-polymer). HF-octene ratios of 11-to-l at 220° C. and 78-to-l at room temperature do not cause the production of any appreciable quantity of tar.

xxviii.

Some polyalkylat ion takes place even with benzene-to-olefin ratios of 5-to-l.

Around 10 percent yield of dialkylate

(based on the olefin) have been found in some reaction products. The mixing of the reagents for the alkylation reaction is accompanied by a rapid release of heat and resulting evolution of vapors.

This heat has been proved to be caused by a rapid

reaction of the olefin with hydrogen fluoride.

No noticeable

heat is evolved upon adding benzene to mixtures of octene and HF. At extra-high temperatures (lj.200 G.) alkylation is accompanied by cracking of the octene or of octyl side chains, with the result that some cumene and similar products are formed. Approximate vapor pressure curves for octylbenzene and dioctylbenzene were determined.

(See Figure it)

The results of this investigation show that the HF is used up as the alkylation reaction progresses until no more is free to catalyze the reaction, unless the starting quantity was greater than the minimum required to complete the reaction.

There is

some evidence for the theory that the HF is entrapped as associated or solvating molecules (on tertiary hydrogens by hydrogen bonding) and that the quantity thus held is related to the number of molecules in the average HF polymer group at the temperature prevailing.

xxrx.

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1.

American Society for Testing Materials, Manual on Presentation of Data (19U6)

2.

Bauer, S. H., Beach, J. Y., Simons, J. H., J. Am. Ghem. Soc., 61, 19 (1939)

3.

Benesic, H. A., Snyth, C. P., J. Ghem. Phys., l£ , 337 (19U?)

k.

Brieglem, G., Z. Physik Ghem. B^l, 9 (19^1)

5.

Butler, E. B., Miles, G. B., Kuhn, C. S.,Jr., Ind. Eng. Ghem. 38, lit? U ? h 6 )

6.

Doss, LI. P., Physical Constants of Hydrocarbons (19l|3)

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Francis, A. If., Ghem. Rev., Ii3, 257 (19l|8)

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Friedel and Crafts, Compt. rend., 8lt, 1932 (1877)

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Gerhold, G. G., Iverson, J. 0., Nebeck, H. J., Newman, R. J., Trans. Am. Inst. Ghem. Engrs., 39, 793 (19U3)

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Grosse, A. V., & Thomas, November 5, 19ltl

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Huston, Guille, Sculati,

& Masson, J. Org. Ghem., 6, 252 (l9ltl)

lit-.

Ipatieff, V. N., Corson, 919 (1936)

1 Pines, H.,J. Am. Chen. Soc., 58,

15.

Jander, G., Haturwissenschaften, 32, 169 (19L5)

16.

Kilpatrick, J. S., Prosen, E. J., Pitzer, K. S., 1 Rossini, F.D. J. Research Natl. Bur. Standards, 36, 559 (19U6)

17.

KLatt, W., Z. anorg. allgem. Ghem., 232, 393 (1937)

C. L., U. S. Patent 2,220,713,

XXX.

18.

Long, R. Vf., Hildebrand, J. H., & Morrell, Vf. E. J. Am. Chem. Soc., 65, 182 (1943)

19.

Lottes, J. C., (unpublished Ph.D. thesis in chemical engineering Purdue University, June, 19^9)

20.

Phillips Petroleum Company, Hydrofluoric Acid Alkylation (19^6)

21.

Price, C. C., "The Alkylation of Aromatic Compounds by the Friedel-Crafts Method." in Organic Reactions by Adams, R., Bachznann, Vf. E., Fieser, L. F., Johnson, J. R. & Snyder, H.R., Vol. Ill, pp. 1-83 (19U6)

22.

Prosen, E. J,, Johnson, Vf. H., & Rossini, F. D., J. Research Natl. Bur. Standards, 36, 1*55 (191*6)

23.

Rossini, F . D. , & Knowlton, J. Vf., J. Research Natl. Bur. Standards, 339 (1937)

21*.

Simons, J. H., Chem. Revs., 8, 213 (1931)

25.

Simons, J. K., Ind. Eng. Chem., 32, 178 (191*0)

26.

Simons, J. H., & Archer, S., J. Am. Chem. Soc., 60, 2952 (1938)

27.

Simons, J. H., & Bassler, G. G., J. Am. Chem. Soc., 63, 880 (19*1)

28.

Simons, J. H., & Hildebrand, J. H., J. Am. Chem. Soc. 1*6, 2183 (192b)

29.

Socony Vacuum Corporation (Unpublished graph relating average molecular weight with temperature and pressure)

30.

Tananaev, I. V., A Deichman, E. VI., J. Applied Chem. (USSR), 19, 1018 (191*6)

31.

Taylor, Vf. J., VTagman, D. D., Williams, M. G., Pitzer, K. S. & Rossini, F. D., J. Research Natl. Bur. Standards, 37, 95 (191*6 ) —

32.

Toussaint, N. F., & Hennion, G. F., J. Am. Chem. Soc., 62,

nl*5 (i9l*o)

ACKHOWLEDGiTENTS

The author is indebted to Professor R. Norris Shreve for his sagacious and patient guidance in the pursuit of the many difficult problems encountered in this research, and for the personal interest taken in the writer’s over-all development during his stay at Purdue University. Special thanks go to Dr. J. C. Lottes for countless instances of unselfish help and beneficial advice in the laboratory. The writer wishes to acknowledge gratefully the valuable help of his wife, Margaret, in preparing the manu­ script of this thesis. The financial assistance given by the Purdue Engineer­ ing Experiment Station and by the American Cyanarnid Company, through the Purdue Research Foundation, is appreciatively acknowledged.

TABLE OF CONTENTS Page

INTRODUCTION

1

HISTORY OF ALKYLATION OF AROMATIC HYDROCARBONS LIT.. OLEFINS

k

Survey of the Literature The alkylation of 2-Lethylnaphthalene EXPERIMENTAL ALKYLATION STUDIES

4 13 18

Development of Laboratory Procedures and Apparatus

18

The Handling of Anhydrous Hydrogen Fluoride

18

High Temperature Alkylations

20

Low Temperature Alkylations

30

Distillation of Reaction Product mixtures

UO

Attempted Equilibrium and Kinetic Studies

fxL

Experimental Determination of Process Variables

6h

Alkylation Series at 0° C. and Atmospheric Pressure

6h

Alkylation Series at 30° G. and 120° C. in Autoclaves

71

Physical and Chemical Identification of Alkylates

75>

Discussion of Results

86

CONCLUSIONS

101

EEC0ÎAENDATI0NS FOR FURTHER LORK

103

BIBLIOGRAPHY

10^

LIST OF TABLES

Table

Page

1

Alkylations Reported in the Literature

11

2

Experimental Data on Tar Formation

22

3

Effect of Sequence of Reagent Addition

35»

k

Effect of Diluent

37

5

Compounds Separated by Distillation

1*0

6

Estimated Thermodynamic Properties of Reactants and Expected Products

3U

7

Free Energies and Equilibrium Constants for the Reactions Calculated from Generalized Correlations

8

Comparison of Equilibrium Constants

!?7

9

Experimental Alkylations for Equilibrium Measurements

60

10

Effect of Contact Time

62

11

Experimental Data for the Effect of Catalyst Concentration at 0° C.

68

Experimental Data for the Effect of Catalyst Concentration at 30° C.

7L

Experimental Data for the Effect of Catalyst Concentration at 120° C.

7h

ill.

Status of Identification of the TIonoalkylate

76

15

Status of Identification of the Dialkylate

77

16

List of Alkylates Obtained in Distillation Analyses

17

Material Balances

82

18

Molecular weights and Carbon-Hydrogen Analyses

86

19

Summary of Process Variables Data Showing Variability

12 13

80

88

LIST OF FIGURES

Figure

1

Page

Effect of Catalyst Concentration and. Temperature on Yields of Alkylated 2-Methylnaphthalene in U-Hour Runs

16

Effect of Catalyst Concentration and Temperature on Yields of Alkylated 2-Methylnaphthalene in 16-Hour Runs

16

Effect of Catalyst Concentration and Temperature on Yields of Alkylated 2-Methylnaphthalene in 2U-Hour Runs

17

Sketch of System for Handling Anhydrous Liquid Hydrogen Fluoride

19

6

Sketch of the Bomb Reactor

23

6

Flow Sheet of System for Arresting Equilibrium Reactions

26

7

Sketch of Low-Temperature Reactor

32

8

Temperature-Time Diagram for Course of LowTemperature Reactions

33

Volume Rate of Octene Addition in Low-Temperature Reactions

39

10

Sketch of M-Column Head

ill;

11

Sketch of M-Column and Accessories

12

Distillation Curve for Run #27, M-Column

lj.8

13

Sketch of Rapid Distillation Column

#0

iL

Calculated Equilibrium Compositions

56

15

Effect of Contact Time

63

16

Yield versus Temperature

69

2

3

Ij.

9

Page

Figure

1?

Yield versus Catalyst Concentration

70

18

Vapor Pressures of Alkylates

81

19

Interpolated Constant Catalyst-P.atio Curves

89

20

Slopes of Constant-Satio Curves

90

21

Apparent Molecular Weight of HF Polymers

96

22

Limiting HF Concentration for Complete Reaction

99

23

Relation between Limiting HF Concentration and HF Polymer Size

100

THE LIQUID PHASE ALKYLATION OF BENZENE LITE 1-OCTENE IN THE PRESENCE OF HYDROGEN FLUORIDE

INTRODUCTION

Anhydrous hydrogen fluoride as an alkylation catalyst was introduced in 1938 when Simons and Archer (U6) made known their discovery that hydrogen fluoride serves as a condensing agent for olefins or alkyl halides with benzene.

This publication was the

forerunner of much research which led ultimately to a tremendous increasein the importance of the compound

as an industrial chemical,

In a review article ihS), Simons discusses thesuitability of hydrogen fluoride as a catalyst for organic chemical processes. He describes certain advantages over other catalysts. 1.

They are:

Hydrogen fluoride is available in large quantities, and it is inexpensive.

2.

It catalyzes most of the reactions catalyzed by other alkylation catalysts and some reactions that others will not catalyze.

3.

High yields are obtained in many cases because fewer tarry residues are formed, and reagents are easily recoverable.

U.

Conventional equipment and materials can be used effectively.

5>.

Hydrofluoric acid is conveniently recoverable.

The alkylation of hydrocarbons catalyzed by anhydrous hydrogen fluoride has been developed in two general areas, the alkylation of isoparaffins and the alkylation of aromatic com­ pounds.

Generally speaking, most of the work with isoparaffins

has been directed toward its industrial use in the manufacture of aviation gasoline.

Some of the important problems studied were

the effects on yields and octane numbers made by changes in the process variables : isoalkane-alkene ratio, inert hydrocarbon in feed stock, acid-hydrocarbon ratio in the reactor, temperature, contact time, agitation, and acid strength (37).

These problems

were pursued so successfully that a large share of the alkylate gasoline (5,500,000 gal. per day) produced during the last years of the second World War was made by the hydrogen fluoride pro­ cess (15). The industrial development of the alkylation of aromatics catalyzed with hydrogen fluoride has been much less rapid, but con­ siderable academic research has been carried out.

This research

has consisted chiefly of the exploration of the many possible com­ pounds that might be made by this process and of the investigation of alkylating agents previously studied with other catalysts. The original purpose of our investigation was to determine experimental data concerning the equilibrium and kinetics of the alkylation of benzene with 1-octene in the presence of hydrogen fluoride.

This objective was not achieved, and a new problem

with the same process was studied with better results.

Although

the equilibrium and kinetics experiments gave no positive results,

many qualitative characteristics concerning the reaction were discovered and are described in this dissertation.

TiTe do not

believe that these are closed chapters, and we recommend that further study should be carried out as is suggested in the section on recommendations for further work. Most of the quantitative results reported in this paper concern the effect of variation of the process variables - tempera­ ture and hydrogen fluoride-octene ratio - on the yield of the monoalkylate formed from the alkylation of benzene with 1-octene.

HISTORY OF ALKYLATION OF AROMATIC HYDROCARBONS DTTH OLEFINS Survey of the Literature

The first direct alkylation of aromatic compounds was reported in 1877 by Friedel and Crafts (17).

They discovered that

alkyl or acyl halides will condense with aromatic compounds in the presence of aluminum chloride to give compounds in which one or more hydrogens of the aromatic compound are replaced by an alkyl or acyl group.

Two years later Balsohn (^) found that olefins could

be used in place of alkyl halides.

The use of sulfuric acid as

an alkylation catalyst was introduced in 1893 by Brochet (8_). Ipatieff is credited with finding that isoalkanes (27) can be alkylated, and with the introduction of phosphoric acid (25) as a catalyst.

Many other catalysts have been studied and employed,

but none have proved to be so universally acceptable for commercial alkylations as anhydrous hydrogen fluoride, introduced as a catalyst in 1938 by Simons and Archer (1+6). It would be well to orient this reaction, the condensation of benzene and 1-octene, within the general subject, alkylation. According to Shreve (l+l) alkylations can be divided into four general groups, depending upon the element to which the alkyl group is ultimately attached: (1) carbon, (2) oxygen, (3) nitrogen, and (1+) a metal.

Under carbon-bonded alkylations are the two divisions,

aromatic and alkane.

Aromatic alkylations (which are closely related

to isoalkane alkylations) involve hydrocarbon nuclei, some with other elements present as substituents or ring components.

Common

alkylating agents are alcohols, alkyl halides, alkyl sulfates, and olefins.

Catalysts commonly used in alkylations are acids like

HF, HgSO^, and H^POj^ and metallic halides of which AlClj and BF^ are the most important. Among the characteristics that make anhydrous hydrogen fluoride a good condensation catalyst are its high acidity, its great dehydrating tendency, and its good solvent properties (1+5)» It produces fewer undesirable products (mainly tars) than sulfuric acid (19) and aluminum chloride (1+5).

Unlike sulfuric acid, it

does not undergo oridation-reduction reactions (19) and it does not require low temperatures.

Thus cold water instead of refrigeration

may be used for process cooling.

Hydrogen fluoride as a catalyst

demonstrates characteristics of both the acidic and the metallic halide catalysts (1+9); it apparently forms complexes both with olefins and with alkyl halides. Simons and Bassler (5) found that the olefin was more reactive than the alkyl fluoride under the same conditions.

In

attempts to synthesize cyclohexylbenzene and octyltoluene in the presence of hydrogen fluoride, they found the olefin to be twice as reactive as the alcohol.

Cyclohexyl chloride did alkylate a

little, while the bromide and iodide did not.

Neither the octyl

chloride nor the bromide alkylated toluene under the conditions employed.

Best alkylation results were obtained when alkyl groups

being introduced contained three or more carbon atoms (10).

In

earlier work (1+6) Simons and Archer had reported that they believed that the amount of hydrogen fluoride was not critical ; however

they were using considerably more than molal quantities.

Calcott

and associates (10) found that some alkylation occurred even when the catalyst was diluted with water to a composition of 1+6 percent HF.

Simons and Archer (1+7) found that the moisture present in the

laboratory air had no adverse effect on the reaction.

Mention is

made in at least two places (6, 16) of the advantage of using high­ speed stirring with alkylations in which aluminum chloride is the catalyst. A brief summary of the reaction conditions described in the literature for the alkylation of benzene (and other aromatic hydrocarbons) by olefins in the presence of hydrogen fluoride includes the following: temperatures from 0° to 20° C., at least one mole of catalyst (usually more) for every mole of olefin, and a high benzene-olefin ratio to cut down polyalkylation and polymer formation.

This last can be accomplished either by a high ratio

in the original charge or by slow addition of the olefin to an agitated mixture of benzene and HF. In general, most investigators consider the alkylation reaction (olefin plus aromatic hydrocarbon) to be irreversible (16). Teitelbaum (55) speaks of thermodynamic irreversibility and kinetic reversibility.

He says that although the reaction goes to com­

pletion, different proportions of final products depend upon the length of contact time.

One example of the use of this mobility

of alkyl groups in the presence of catalysts is the dealkylation reaction in which more monoalkylate is produced from dialkylate and benzene.

Lee and Radford (31) have a patent for producing toluene

7

and trimethylbenzene from benzene and xylene; they use hydrogen fluoride as catalyst.

If a second alkyl group is mobile under

catalytic conditions, then surely the same is true for the first (or mono-) alkyl group.

Therefore, when a monoalkylbenzene is

subjected to the proper temperature, with a catalyst such as HF, it should decompose to an equilibrium mixture containing portions of the monoalkylate, the benzene, and the olefin.

As can be seen

in Table 7 in this report, such equilibrium mixtures should be expected at around 25>0° C. According to Ipatieff and associates (26), alkylations with benzene and olefins carried out under the general conditions described above, but using EgSO^ instead of HF, yield products indicating the presence of three reactions all competing for the olefins: (l) the alkylation of the aromatic hydrocarbon, (2) poly­ merization of the olefin, and (3) reaction of the olefin with the acid to form an ester.

Simons and Archer (1+7) observed that only

alkylation took place under the conditions they used. The rearrangement of alkyl groups during alkylation is a common occurrence.

Teitelbaum (5£) points out that such rearrange­

ments occur only under vigorous alkylatingconditions and that the trend is from primary to tertiary carbons.

Further evidence, then,

that hydrogen fluoride is a mild alkylating catalyst is the observation by Calcott (10) that no migrations or isomerization took place. Table 1).

This is true of most HF alkylations reported.

(See

The general rules of orientation of second substitutions on the benzene ring lead one to believe that the presence of one alkyl group would favor the replacement of ortho and para hydrogen atoms by another alkyl group.

And such is the case under mild

alkylation conditions; however, vigorous conditions produce a pre­ dominance of meta substitutions (38).

On the basis of experiments

with ethyl benzene using ALCl^ as catalyst, Francis (16) challenges the general belief that the substitution of second and subsequent alkyl groups proceeds at a faster rate than that of the first one. The reason that the apparent rate difference has been observed so frequently is that alkylated aromatic hydrocarbons are more soluble in the catalyst phase than are the unsubstituted aromatic compounds. The anomalous difference in rate of alkylation can be prevented by efficient agitation or by effecting the catalysis in the hydrocarbon phase only. The above theory depends on the belief that the reaction takes place in the catalyst phase.

However, early in his work with

hydrogen fluoride catalyzed alkylations, Simons (Vf) came to the conclusion that the reaction took place in the hydrocarbon phase, because enough HF had to be present to saturate the hydrocarbon phase, while very little change was effected by greater amounts. Gerhold (19) describes the alkylation of isoalkanes as taking place in the hydrofluoric acid phase and at the interface between the two phases.

The olefins dissolve in the acid phase and remain there

until they become transformed into elements of alkylated or poly­ merized products.

As in the ease of petroleum, alkylations (37), small but troublesome quantities of organic fluorides are formed in the alkyla­ tion of benzene (31;).

These are not completely removed by washing

with alkali, and they decompose during distillation, producing corrosive HF.

A number of successful methods of removal have been

developed however, A thorough study has been made of process variables in the petroleum industry’s hydrofluoric acid alkylation process and has been published by the Phillips Petroleum Company.

The dependent variables

studied were yield of alkylate having a desired boiling range and octane number of the alkylate.

Although their report does not make

any direct contributions to knowledge of the fundamental properties of the reaction, a brief description of the results of these tests is included here because of the value implicit in them. The ratio of isobutane to olefin was studied from two viewpoints.

The "external” ratio, a macro quantity, concerns the

overall charging and recycling rates to a continuous reactor.

Values

of 5-to-l or better are needed to make a good product and cut down on polymer formation.

The "internal” ratio has to do with the

condition of mixing at the points of charging.

Location of these

points and the use of jets are mentioned. Inert hydrocarbons in the feed stock do not affect the process greatly, but they should be kept as low as possible because their transportation, heating and cooling contributes to the cost without benefit.

Also, they must sooner or later be separated.

The general practice in petroleum alkylation is to use a 1—to—1 volume ratio of HF to hydrocarbons.

The Phillips investi­

gators found that a ratio as low as l-to-10 worked satisfactorily in a batch process but that l-to-25 gave incomplete conversion, "showing that the reaction is slow in the hydrocarbon phase, even though saturated with HF” (37). Temperatures of from I4.O0 to 1^0° F. gave satisfactory products.

This is a distinct advantage over the sulfuric acid

process, which requires refrigeration. At temperatures around H5>° F., contact times of from 5> to 25 minutes yielded the desired results.

Much shorter contact

times caused the production of excess organic fluorides. Agitation was not studied as a separate variable, but the Phillips 1 report states that vigorous agitation is necessary to maintain a low "internal” isobutane-olefin ratio. The remarks on acid strength are of particular interest to us, as will be seen in our discussion of results.

"Then alkyla­

tion proceeds, the hydrofluoric acid gradually becomes contaminated with organic impurities which stay in solution in the acid.

Then

the hydrofluoric acid content of the acid phase falls below 75 per­ cent by weight, under-reacting, made evident by high organic fluoride content of the hydrocarbon effluent, is encountered” (37). A very good review article on the alkylation of aromatic compounds, written by Price, is to be found in Organic Reactions (38). Tabulated at the end of the article are the descriptions of a great many alkylations reported in the literature. important to our topic are listed in Table 1.

Those considered most

11.

Table 1 Alkylations Reported in the Literature.from

Ref.

Alkylating Agent

1+8

Cyclopropane

1+7 1+7 1+7

Propylene Propylene Isobutylene

1+7 1+7

2-Pentene Trimethylethylene

8 52

52 52

1+7 52

1+9 1+9 1+9 52 26

56 21+ 22 21+ 21+ 22 22 21+ 21+ 21+

1+9 1+9 1+9 26

1-Hexene 3-Hexene 3-Hexene 3-Hexene Cyclohexene 3-Hexene Cyclohexene Cyclohexyl Fluoride Cyclohexyl Chloride 3-Hexene Octene n-Octyl Alcohol 2-Methyl-2-heptanol l+-Chloro-l+-Methylheptane 2,3-Dimethyl~2-hexanol 2,i+-Dimethyl-2-hexanol 2-Chloro-2,5-Dimethylhexane 3-Chloro-3-ethylhexane 3-Ethyl-2-methyl-2-pentane 2,2, l+-Trimethylpentanol 2,2,3-Trimethylpentanol 1-Octene 2-Fluorooctane 2-0ctanol Dodecene

Compound Alkylate