US3277196A - Alkylation process - Google Patents

Description

United States Patent 3,277,196 ALKYLATION PROCESS De Los E. Winkler, Orinda, Calif., assignor to Shell Oil Company, New York, N.Y., a corporation of Delaware No Drawing. Filed June 17, 1963, Ser. No. 288,537 11 Claims. (Cl. 260-671) This invention relates to a novel process for the alkylation of aromatic hydrocarbons. It further relates to a process whereby armomatic hydrocarbons are selectively alkylated with certain olefins.

Numerous methods are available in the art for the alkylation of aromatic hydrocarbons. Many of these are related -to the classical Friedel-Crafts alkylation procedure, wherein aromatic hydrocarbons are alkylated with alkyl halides, alcohols or olefins in the presence of What is now commonly referred to as a Friedel-Crafts catalyst, e.,g., aluminum chloride, boron tn'fluoride and the like. Such alkylation procedures, although widely employed, are not without disadvantage. When an aromatic hydrocarbon is mono-alkylated, the product that initially results is generally more reactive toward alkylation than the original reactant, and the product obtained by the alkylation process comprises a mixture of monoalkyl and poly-alkyl derivatives of the original hydrocarbon reactant. The subsequent separation of the components of the product mixture is a difficulty inherent in the alkylation procedure. An additional difficulty is frequently attendant to an alkylation process that is conducted as a large-scale process. Although small scale operations may efiiciently be conducted using halides or alcohols as alkylating agents, the success of large commercial operations is dependent upon the utilization of olefins. Such olefins are customarily obtained from refinery operations, particularly from thermal or catalytic cracking processes. The olefins obtained are frequently impure containing a mixture of olefins as well as saturated hydrocarbons, and not infrequently contain ethylene. This is particularly apparent when propylene is desired for the propylation of aromatic hydrocarbons, e.g., the production of cumene from benzene. Alkylation with a mixed olefin feed results in further problems of product recovery as conventional alkylation catalysts show little or no selectivity with regard to the olefin reactant, and the product mixture contains derivatives of all olefins present. For example, alkylation of benzene with a propylene-ethylene mixture normally produces both ethylated and propylated products, thereby further complicating product separation. Thus, some provision must be made for removal of the ethylene present before alkylation with propylene can be efliciently conducted. It would be of considerable advantage to employ a process for the alkylation of aromatic hydrocarbons with an olefin in the presence of ethylene in which the ethylene is non-reactive with regard to alkylation, thus obviating the necessity of ethylene removal prior to the alkylation process.

It is therefore an object of the present invention to provide a novel process for the alkylation of aromatic hydrocarbons. A further object is to provide a process for the alkylation of aromatic hydrocarbons with an olefin in the presence of ethylene, in which process alkylation with ethylene is not effected.

It has now been found that these objects are accomplished by the process of alkylating an aromatic hydrocarbon with an olefin other than ethylene in the presence of an alkyl aluminum dichloride catalyst. By the process of the invention, olefins containing three or more carbon atoms are effectively employed as alkylating agents, while ethylene is not reactive.

The material alkylated is an aromatic hydrocarbon,

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that is, contains only carbon and hydrogen atoms, and at least one six-member benzenoid ring. Suitable aromatic hydrocarbons have from 1 to 6 six-membered aromatic rings which are fused, non fused, or connected by nonaromatic hydrocarbyl linkages. The aromatic rings are suitably unsubstituted or are substituted with from 1 to 10 non-aromatic hydrocarbyl substituents, which preferably are saturated, i.e., alkyl or alkylene radicals, independently having from 1 to 8 carbon atoms. Best results are obtained when the aromatic hydrocarbon reactant has no non-aromatic unsaturation. Preferred aromatic hydrocarbon reactants have from 1 to 3 six-membered aromatic rings and from 0 to 4 saturated hydrocar-byl substituents independently having from 1 to 4 carbon atoms. It is further desired, for best results, that at least one aromatic ring have at least two hydrogen substituents. Such preferred aromatic ring systems are derived from benzene, naphthalene, anthracene, phenanthrene, biphenyl, bisphenyl alkanes and the like. In general however, best results are obtained when the aromatic hydrocarbon is mononuclear, i.e., benzene and alkyl and alkylene derivatives thereof.

Illustrative of mononuclear aromatic hydrocarbons suitable as reactants in the process of the invention are benzene, toluene, the Xylenes, ethylbenzene, rn-dihexylbenzene, Tetralin, o dibutylbenzene, p dioctylbenzene, 1 ethyl 2,4 dipropylbenzene, pseudocumene, durene, cumene, p -isopropyltoluene, and m -ethylbutylbenzene. Suitable dinnclear hydrocarbon reactants include naphthalene, l-methylnaphtha-lene, Z-butylnaphthalene, 1,8- diethylnaphthalene, 1 octylnaphthalene, l,2,4,6 tetramethylnaphthalene, biphenyl, 4-propylbiphenyl, 3,3'-di butyl-biphenyl, 2,4,6-tri-tert-butylbiphenyl, 2,3,3',5'-tetramethylbiphenyl and 4,4'-diisopropylbiphenyl, as well as diphenylalkanes wherein the aromatic nuclei are connected by an alkylene radical having from 1 to 4 carbon atoms, such as diphenylmethane, 1,3-diphenylbutane, 1,2-di(2,4 dimethylphenyDethane, 2,2-diphenylpropane, and 4- methylphenylphenylmethane. Aromatic hydrocarbon reactants that are trinuclear include anthracene, l-propylanthracene, l,3,5,7-tetrabutylanthracene, 1,4-diisopropylanthracene, phenanthrene, 2,9-dimethylphenanthrene, 9- butylphenanthrene, 3, fi-dioctylphenanthrene and 2,3,6,7- tetramethylphenanthrene. Also suitable are acenaphthene, fluorene, naphthacene, chrysene, pyrene, triphenylene and the like, and analogous alkyl derivatives thereof.

The olefin employed as a reactant in the alkylation process of the invention is a hydrocarbon monoolefin having more than 2 carbon atoms but preferably no more than 12 carbon atoms. The olefin is acyclic or cyclic, and has an internal or terminal olefinic linkage, i.e., a carboncarbon double bond. Illustrative of acyclic olefins are propylene, l-butene, Z-butene, isobutylene, l-pentene, isoamylene, Z-hexene, l-octene, 2,4,4-trimethyl-1-pentene and isomeric nonenes, decenes, and dodecenes; while cyclic olefins are exemplified by cyclohexene, cyclopentene, 2,3,5-trimethylcyclohexene and cyclooctene. Best results are obtained when the olefin is acyclic and has from 3 to 5 carbon atoms, and terminal olefins are generally preferred over internal olefins.

The alkylation process of the present invention may be conducted using an olefin having more than 2 carbon atoms as the sole olefinic material, or with a mixture of olefin and ethylene. When a mixture of olefin and ethylene is employed, the proportions of olefin and ethylene are not critical, as the process operates satisfactorily with mixtures predominantly olefin, or with substantial amounts of ethylene present.

The alkylation can be conducted efiiciently when the olefin feed contains inert materials as diluents, particularly saturated hydrocarbons such as methane, ethane,

propane and the like which are normally associated with impure refinery sources of olefin. The presence of such unreactivc diluents, although offering no apparent advantage, does not serve as a substantial detriment, and the separation of such materials from the olefin to be employed as the alkylating agent is not required.

The catalyst employed in the process of the invention is an alkyl aluminum dichloride. It has been found that such catalysts are effective for promoting alkylation with olefins other than ethylene, but are non-catalytic with regard to the ethyla'tion of aromatic hydrocarbons in the process of the invention. The ability to selectively catalyze alkylation with other olefins but not with ethylene appears to be limited to alkyl aluminum dichlorides, as aluminum trichloride is known to be an effective ethylation catalyst, and dialkyl aluminum chloride and trialkyl aluminum do not catalyze alkylation under the conditions of the process of the invention. The choice of any particular alkyl group in the alkyl aluminum dichloride catalyst is not critical, although largely for reasons of the availability thereof, alkyl aluminum dichlorides wherein the alkyl group has from 1 to 8 carbon atoms are preferred. Illustrative of the preferred catalysts are ethyl aluminum dichloride, methyl aluminum dichloride, propyl aluminum dichloride, n-butyl aluminum dichloride, isobutyl aluminum dichloride, n-hexyl aluminum dichloride, 2-ethylhexyl aluminum dichloride and octyl aluminum dichloride. Most preferred as catalysts for the process of the invention are alkyl aluminum dichlorides wherein the alkyl group has from 2 to 4 carbon atoms.

The alkyl aluminum dichloride is employed in catalytic amounts. Amounts of catalyst from about 0.0001 mole to about 0.1 mole per mole of aromatic hydrocarbon are satisfactory, while amounts of catalyst from about 0.01 mole to about 0.001 mole per mole of aromatic hydrocarbon are preferred.

Although the process of the invention can be conducted in the vapor phase, it is preferred to conduct the alkylation process in the liquid phase. When the aromatic hydrocarbon is liquid at the temperature of the reaction, best results are obtained when the aromatic hydrocarbon is also utilized as the reaction medium. Alternatively how? ever, when the aromatic hydrocarbon is not liquid at reaction temperature, the alkylation media may include an inert reaction solvent, e.g., a saturated hydrocarbon such as hexane, isooctane, cyclohexane, Decalin and the like, or mixtures thereof, which serves to dissolve the aroma-tic hydrocarbon and thus enable the alkylation to be conducted in the liquid phase. The temperature at which alkylation is effected is therefore somewhat dependent upon the aromatic hydrocarbon, as the alkylation is preferably conducted in the substantial absence of reaction solvent. An additional factor in determining the optimum reaction temperature is the boiling point of the olefin to be employed as the alkylating agent, for the process of the invention is most easily conducted and controlled when the olefin is utilized in the form of a gas, although it is also useful to employ an olefin that is liquid at the temperature of the reaction. Suitable reaction temperatures vary from about 10 C. to about 120 C. although higher temperatures may be employed. Preferred temperatures for the alkylation process are from about 20 C. to about 95 C., particularly when the aromatic 'hydrocarbon reactant is mononuclear, that is, contains only one six-membered aromatic ring.

The alkylation process of the invention is conducted at atmospheric, subatrnospheric or superatrnospheric pressure. Thus, pressures from about 0.1 atmosphere to about 50 atmospheres are satisfactory, although pressures from about 0.5 atmosphere to about 5 atmospheres are preferred. Frequently, best results are obtained when the pressure employed in the process of the invention is substantially atmospheric. When pressures greater than atmospheric are employed, it is advantageous to pressurize the reactor with the olefin reactant, although the presence of other inert gases such as nitrogen is'not detrimental.

It is preferred, however, to effect alkylation in the substantial absence of oxygen, as the presence of substantial amounts of oxygen results in loss of catalyst activity through oxidation of the catalyst.

The reactants and catalyst may be mixed in any convenient manner. One modification comprises mixing the aromatic hydrocarbon and catalyst and adding the olefin gradually to the mixture thus formed, as by bubbling a gaseous olefin into the hydrocarbon-catalyst solution. It is equivalently useful, however, to have the entire amount of olefin present at the outset of reaction. When alkylation is conducted using a mixture of ethylene and other olefin, a gradual addition of olefin is preferred, and some catalyst preparation is necessary. The effect of the presence of ethylene at the start of reaction is not clearly 11nderstood. When ethylene is initially present, the catalyst is in some manner deactivated, and is essentially non-catalytic with regard to alkylation. If'however, alkylation is initiated in the absence of'ethylene, as by initial alkylation using some other olefin, subsequent alkylation utilizing a mixture of ethylene and other olefin proceeds readily, al-' though the ethylene remains unreactive. No great amount of olefin is required to initiate alkylation, as all that is required is that alkylation be started. Subsequently, alkylation with an ethylene-olefin mixture is readily elfected.

Subsequent to reaction, the unreacted aromatic hydrocarbon and reaction solvent, if reaction solvent was employed, are separated from the product mixture by conventional means, e.g., flash distillation and may be recycled for further reaction. The product mixture may then be separated by fractional distillation or by other conventional methods.

The particular products obtained by the process of the invention are to a large degree determined by the man ner in which the alkylation is conducted, particularly the ratio of olefin to hydrocarbon employed. As previously stated, the alkylated products that are initially produced are more reactive toward further alkylation than the original aromatic hydrocarbon reactant. Thus, when high conversions of hydrocarbon reactant are obtained by employing comparably high ratios of olefin to hydrocarbon, substantial amounts of polyalky-lated products are observed. Alternatively, when a monoalkylated product is desired, it is best to utilize excesses of hydrocarbon and employ low hydrocarbon conversions, thereby obtaining a product mixture with a comparably high percentage of mono-alkylated product' Low conversion of hydrocar: bon does not serve as a substantial detriment, however, as unreacted starting material may be recycled to bring about further alkylation.

The alkylation process observes conventional considerations with regard to substituent orientation and the type of alkyl substituent introduced. When the olefin reactant has a tertiary carbon atom as one member of the carbon-carbon double bond, tertiary alkyl substituents are introduced, e.g., tertiary butyl derivatives of the aromatic hydrocarbon reactant are produced by alkylation with isobutylene. Alternatively, when the olefinic linkage connects secondary carbon atoms, or one secondary and one primary carbon atom, secondary alkyl groups are introduced upon the aromatic hydrocarbon, e.g., alkylation with l-butene or 2-butene produces secondary buty-l derivatives. Substituent orientation during alkylation normally occurs On the most electronegative ring carbon atom, for example, ortho or para to an alkyl substituent already present.

Illustrative of the alkylated products obtained by the process of the invention are cumene, di-, triand tetraisopropylbenzene obtained by alkylation of benzene with propylene; sec-butyltoluene and di-sec-butyltoluene observed when toluene is alkylated with l-butene; isomeric mono-, diand tri-tert-butyl derivatives of naphthalene obtained by the alkylation of naphthalene with isobutyl-.

' ene; monoand polycy'clohexylated biphenyls obtained when biphenyl is alkylated with cyclohexene; 2-octyland di-2-octylbenzene obtained from reaction of benzene and l-octene; tert-amyl derivatives of phenanthrene obtained from alkylation of phenanthrene with isoamylene; and analogous products derived from the reaction of other hydrocarbons and other olefins.

The alkylated products of the process of the invention find utility as solvents and as chemical intermediates. Exemplary uses of the latter type include the production of phenol from cumene, and the oxidation of p-dialkylbenzene to terephthalic acid.

An additional utility for the process of the invention, based upon the ability to alkylate with olefins other than ethylene, is in a process for the purification of ethylene. By the process of the invention, olefin contaminants can be efiectively removed from ethylene by passing the olefin mixture through an aromatic hydrocarbon in the presence of an alkyl aluminum dichloride.

To further illustrate the process of the invention, the following examples areprovided. It should be understood that they are not to be regarded as limitations, as the teachings thereof may be varied as will be understood by one skilled in this art.

Example I A reactor containing 4 gal. of benzene was pressurized with propylene to 10 p.s.i.g. at 25 C. An immediate re action occurred on the addition of 20 rm'llimoles of ethyl aluminum dichloride. The pressure dropped to p.s.i.g. and additional propylene which was introduced was consumed as fast as it could be added. Ethylene and propylene were then added at an equal rate until the pressure built up to 15 p.s.i.g. when the gas addition was stopped. No reaction occurred, as measured by the constant pressure within the reactor, despite the addition of an additional 4 millimoles of catalyst. The gas cap was removed and analysis thereof indicated only ethylene, the propylene apparently having been consumed. Upon the removal of the ethylene present, propylene addition was resumed and again the propylene was consumed as fast as it could be admitted. The addition of propylene was then halted and the product mixture was analyzed by gas-liquid chromatography to give the following composition:

Compound: Percent by weight Recovered benzene 48.9 Cumene 34.9 Diisopropy-lbenzene 12.2 Tn'isopropylbenzene 4.0 Tetraisopropylbenzene nil No indication of ethylbenzene was observed.

Example II A 300 ml. autoclave was charged with 150 ml. of

benzene and 4 millimoles of triethyl aluminum. The reactor was pressurized with propylene to 25 p.s.i.g. at room temperature and heated to 50 C. for one hour. The pressure remained constant at 35 p.s.i.g. The catalyst was washed from the product mixture and the mixture analyzed by gas-liquid chromatography. No trace of cumene was observed.

The above experiment was repeated using diethyl aluminum chloride as the catalyst. Again no trace of cumene was observed by gas-liquid .chromatography.

Example 111 diisopropylbenzene, 2.3% wt. triisopropylbenzene, and 1.6% wt. tetraisopropylbenzene.

Example IV A small reactor was charged with ml. of benzene and 1 millimole of ethyl aluminum dichloride. Butene-l was added rapidly over a 20 minute period while the reaction mixture was maintained, by cooling, below 30 C. The catalyst was removed by washing and the product mixture analyzed by gas-liquid chromatography and infra-red analysis. Found: 63.4% wt. benzene, 26.2% wt. sec-butylbenzene, 10.4% 'wt. di-sec-butylbenzene and a trace of higher boiling material.

Example V To a dry 2 liter glass flask was charged 1 liter of dried toluene. The flask was flushed with nitrogen and the toluene was saturated with propylene at 25 C. and atmospheric pressure. Upon addition of 2 millimoles of ethyl aluminum dichloride, the temperature of the reaction mixture rose rapidly to 50 C. Propylene, introduced at the rate of 900 ml. per minute was nearly 100% consumed. After two hours at a temperature of 3040 C. the reaction rate decreased somewhat, but the addition of 1 millimole of catalyst restored original reactivity. When the olefin feed was changed to 600 ml. per minute of propylene and 300 ml. per minute of ethylene, there was immediate evolution of gas. The ethylene introduction was stopped and the propylene cflow restored to 900 ml. per minute. Again, consumption of propylene was essentially complete. The catalyst was then removed by washing and the product mixture analyzed by gas-liquid chromatography. Found: 42.1% wt. toluene, 29.0% wt. isopropyltoluene, 20.6% wt. diisopropyltoluene and 8.3% wt. triisopropyltoluene. No ethyl-substituted product was observed.

Example VI When naphthalene is alkylated with 1-hexene in the presence of octyl aluminum dichloride, a mixture of monoand di-Z-hexylnaphthalene is obtained.

Example VII Isobutylene is passed into o-xylene in the presence of n-butyl aluminum dichloride until alkylation is initiated. When the olefin feed is then changed to a mixture of ethylene and isobutylene, the o-xylene reacts with the isobutylene, but not with the ethylene.

I claim as my invention:

1. The process of selectively alkylating an aromatic hydrocarbon with an olefin having more than 2 carbon atoms in the presence of ethylene by (1) bringing into initial intimate contact aromatic hydrocarbon having from 1 to 6 six-membered aromatic rings and from 0 to 10 non-aromatic hydrocarbyl substituents, said substituents independently having from 1 to 8 carbon atoms, and bydrocarbon monoolefin having more than 2 carbon atoms, but no more than 1-2 carbon atoms, in contact with a catalytic amount of alkyl aluminum dichloride wherein the alkyl is alkyl of 1 to 8 carbon atoms; and (2) bringing into subsequent continued intimate contact said aromatic hydrocarbon with a mixture of said olefin and ethylene in contact with said alkyl aluminum chloride at a temperature from about 10 C. to about C. and a pressure from about 0.1 atmosphere to about 50 atmospheres, in the liquid phase, to selectively alkylate said aromatic hydrocarbon with said olefin to the substantial exclusion of the alkylation of said aromatic hydrocarbon with ethylene.

2. The process of claim '11 wherein the hydrocarbon monoolefin is propylene.

3. The process of claim ;1 wherein the alkyl aluminum dichloride is ethyl aluminum dichloride.

4. The process of selectively alkylating an aromatic hydrocarbon by 1) bringing into initial intimate contact mononuclear aromatic hydrocarbon having at least 2 ring-carbon hydrogen substituents and from 0 to 4 saturated hydrocarbyl su'bstituents, said substituents independently having from 1 to 8 carbon atoms, and acyclic hydrocarbon 'monoolefin having from '3 to 5 carbon atoms, in contact with a catalytic amount of alkyl aluminum dichloride wherein the alkyl group has from 1 to 8 carbon atoms; and (2) bringing into subsequent continued intimate contact said aromatic hydrocarbon and a mixture of said monoolefin and ethylene in contact with said alkyl aluminum dichloride at a temperature from about 20 C. to about 95 C. and a pressure from about 0.5 atmosphere to about 5 atmospheres, in the liquid phase, whereby the aromatic hydrocarbon is selectively alkylated by said olefin to the substantial exclusion of the alkylation of said aromatic hydrocarbon with ethylene.

5. The process of claim 4 wherein the aromatic hydrocarbon is benzene.

6. The process of claim 4 wherein the aromatic hydrocarbon is toluene.

7. The'process of claim 4 wherein the olefin is propylene.

8. The process of claim 4 wherein the olefin is l-butene.

9. The process of claim 4 wherein the alkyl aluminum 11. The process of claim 4 wherein the aromatic hydro carbon is benzene, the monoolefin is propylene, and the alkyl aluminum dichloride is ethyl aluminum dichloride.

References Cited by the Examiner UNITED STATES PATENTS 2,271,956 2,388,428 11/1945 Mavity 260-671 X 'DELBERT E. GANTZ, Primary Examiner.

PAUL M. COUGHLAN, Examiner.

C. R. DAVIS, Assistant Examiner.

2/1942 Ruthrufi 260--67l X

Claims (1)

1. THE PROCESS OF SELECTIVELY ALKYLTING AN AROMATIC HYDROCARBON WITH AN OLEFIN HAVING MORE THAN 2 CARBON ATOMS IN THE PRESENCE OF ETHYLENE BY (1) BRINGING INTO INITIAL INTIMATE CONTACT AROMATIC HYDROCARBON HAVING INTO 1 TO 6 SIX-MEMBERED AROMATIC RINGS AND FROM 0 TO 10 NON-AROMATIC HYDROCARBYL SUBSTITUENTS, SAID SUBSTITUENTS INDEPENDENTLY HAVING FROM 1 TO 8 CARBON ATOMS, AND HYDROCARBON MONOOLEFIN HAVING MORE THAN 2 CARBON ATOMS, BUT NO MORE THAN 12 CARBON ATOMS, IN CONTACT WITH A CATALYTIC AMOUNT OF ALKYL ALUMINUM DICHLORIDE WHEREIN THE ALKYL IS ALKYL OF 1 TIO 8 CARBON ATOMS; AND (2) BRINGING INTO SUBSEQUENT CONTINUED INITIMATE CONTACT SAID AROMATIC HYDROCARBON WITH A MUXTURE OF SAID OLEFIN AND ETHYLENE IN CONTACT WITH SAID ALKYL ALYMINUM CHLORIDE AT A TEMPERATURE FROM ABOUT -10*C. TO ABOUT 120*C AND A PRESSURE FROM ABOUT 0.1 ATMOSPHERE TO ABOUT 50 ATMOSPHERES, IN THE LIQUID PHASE, TO SELECIVELY ALKYLATE SAID AROMATIC HYDROCARBON WITH SAID OLEFIN TO THE SUBSTANTIAL EXCLUSION OF THE ALKYLATION OF SAID AROMATIC HYDROCARBON WITH ETHYLENE.