US2436480A - Production of alkyl aromatic hydrocarbons - Google Patents

Description

Patented Feb. 24, 1948 UNITED s'rA'rEs PATENT OFFICE PRODUCTION OF ALKYL AROMATIC HYDROCARBONS Application March 22, 1946, Serial No. 656,471

9 Claims.

The invention relates to the conversion of hydrocarbon mixtures containing paraffinic and aromatic components into higher boiling compounds comprising alkyl aromatic hydrocarbons.

More specifically, it is concerned with a com-- bination of specific processes which individually involve the use of special catalysts and particular conditions of operation whereby hydrocarbon mixtures containing both parafhns and aromatics may be effectively converted into aromatic hydrocarbons containing one or more alkyl groups attached to the aromatic nucleus thereof.

It is one object of my invention to convert hydrocarbon mixtures containing parafiins and aromatics into mono or polynuclear and substituted alkyl aromatic hydrocarbons, the particular product obtained in the process depending upon the charging stock and the conditions f operation employed in said process.

Another object of this invention is to provide a highly efllcient and effective process, characterized by little or no decomposition of the charging stock and by the increased yield of desirable products, which comprises converting a mixture of paraflinic and aromatic hydrocarbons into alkyl aromatic hydrocarbons having `boiling points higher than said charging stock.

In one specific embodiment the present invention comprises a combination process wherein a parafiinic hydrocarbon is iir'st dehydrogenated in the presence of anv aromatic hydrocarbon and the product thereof is subjected to alkylating conditions to condense the olefins produced by said dehydrogenation with the aromatics to form an alkyl aromatic hydrocarbon in which the alkyl group contains the same number of carbon atoms as said paraffin hydrocarbon.

Other specific embodiments of the present invention relate to the utilization of particular charging stocks, methods of operation and to specio catalysts utilizable in said dehydrogenatlon and alkylation stagesy which variables will hereinafter be described in greater detail.

In the production of. alkyl aromatic hydrocarbons it is often desirable and in fact, in'some cases requisite, to produce said compounds under conditions such that the aromatic nucleus contains but one alkyl group of the type desired per molecule. A typical instance in which such compounds are preferred is in the manufacture of alkyl aromatic hydrocarbons for the production of the sulfonate type of detergents. In the latter instance the proper activity of the detergent product depends upon the introduction of but one alkyl group into the aromatic nucleus prior to sulfonation and neutralization of the resultant alkyl aromatic sulfonic acid. lIn order to obtain hydrocarbons of this type it is Anecessary to employ a. process whereby the desired mono-alkylation is obtained exclusive of any polyalkylated product or, alternatively. to separate the monoalkyl aromatic from a mixture'of the same with the polyalkylated product obtained by conventional alkylation processes. A simple expedient in 5 the economical production of mono-alkylates of the aromatic hydrocarbon is the utilization of a high molecular proportion of the latter compound in the alkylation reaction where such alkyl aromatic hydrocarbons are obtained, The effect, therefore, of the high molecular proportion of aromatic hydrocarbons to olenic hydrocarbons in the reaction zone is to provide for a dilution effect whereby the possibility of polyalkylation is substantially reduced because of the operation of the law of mass action.

A further advantage to the use of an excess of the aromatic hydrocarbons in the present combination process is that obtained by virtue of the heat carrying capacity of thearomatic hydrocarbonsin the dehydrogenation stage. In the dehydrogenation of parafilnic hydrocarbons to oleiins relatively large quantities of heat are consumed to effect said dehydrogenation. I have observed that it is highly desirable to introduce the necessary endothermic heat of reaction into the reaction zone by heating the hydrocarbon charging stocks prior to the introduction of the latter into the reaction zone rather than attempting to supply the required heat by externally heating the reaction zone. 'I'he presence of a large proportion oi' aromatic hydrocarbons, which are relatively stable at high temperatures and which have a high molar heat capacity in the charging stock to the dehydrogenation reaction, provides a means for supplying the required heat without resorting to the alternative of heating the parailins contained in the charging stock to an excessively high temperature and thereby subjecting'the latter to decomposition, particularly cracking thereof. The latter factor, that is the cracking of the parailins at high temperatures and in the presence of catalytic agents of the composition employed for dehydrogenation, is especially a factor of considerable importance when the parailin is a high molecular weight member of this class of compounds and is particularly true for parafns of 6 or more carbon atoms.

The high proportion of aromatic hydrocarbons I contained in the charging stock to the dehydrogenation reaction and also to the subsequent alkylation reaction enables the entire combination to be operated continuously on a highly eilicient basis. The excess aromatic hydrocarbons separated from the eiliuent product of said alkylation reaction are advantageously recycled in the dehydrogenatibn stage without any substantial L burden of separation since /the latter rionalkylated aromatics boil at reduced temperatures as compared to the alkyl aromatic hydrocarbons. so The charging stockin lthe present-process, as

previously noted. comprises a mixture of parailns and/or cycloparalns (naphthenes) and aromatics, said mixture being either a synthetically compounded solution of the desired components or a naturally occurring mixture such as a straightrun petroleum fraction boiling, for example, within the gasoline range. If the latter charging stock is selected. the aromatic content thereof may be and is preferably increased \by adding thereto the preferred aromatic hydrocarbon since straight-run petroleum fractions, depending upon the source thereof, do not usually contain the required content of aromatic hydrocarbons. Where the specific purpose of the process is the production of monoalkyl aromatic hydrocarbons containing a long chain al"yl group of 6 or more carbon atoms, the molecular proportion of aromatic hydrocarbons to long chain parans in the charging stock is maintained at a higher value than in the caselwhere the ultimate product contains a short chain alkyl group of from about 2 to about 6 carbon atoms. In the latter instance, that is, in the production of alkyl aromatics wherein the alkyl group contains from about 2 to about 6 carbon atoms, the molecular proportion of initial aromatic to parain is held at from about 1:1 to about 170:1. For the production of alkyl aromatics having alkyl groups of from about 6 carbon atoms and highern the proportion of aromatics to parafllns in the original feed is gen-` erally held at higher values. above about 3:1. but

preferably above about 10:1 up to about 30:1,A

although the upper limit is also determined by balancing of economical separation of large quantities of aromatic hydrocarbons from the ultimate alkylation product against the desirable.

production of mono-alkylated products.

Petroleum fractions containingy both paraffins and aromatic hydrocarbons, usually of varying structure and molecular weight, are obtained in the straight-run petroleum distillates boiling in the gasoline and/or gas-oil boiling range. Preferably. as indicated previously, additional quantities of aromatic hydrocarbons are added to said Y fractions in order to increase the aromatic content thereof above that normally present in the.

distillate. The resulting alkylate obtained by subjecting the product of dehydrogenation to al ylating .conditions contains a wide variety oi' alkyl aromatic hydrocarbons.

Aromatic hydrocarbons utilizable in the process of the present invention comprise, in general, the alkylatable aromatics or, in other Words, those members of the aromatic hydrocarbon series containing a substitutable position on the aromatic nucleus. Obviously, the process is inoperable as to aromatics having all the nuclear positions occupied by non-substitutable groups. Thus, benzene and naphthalene are utilizable, as well as their mono, diand tri-alkyl derivatives, such as toluene, Xylene or other polymethylbenzenes, such as trimethylbenzene. It is also obvious that aromatic hydrocarbons which undergo reactions foreign to the principal or desired reactions are not utilizable. Thus, vinyl aromatics which readily polymerize under the conditions employed herein or long chain a yl aromatic hydrocarbons which pyrolyze at relatively low temperatures are likewise not to be included in the above indicated group of utilizable aromatic hydrocarbons.

Catalysts which accelerate the dehydrogenation of parafiln-aromatic hydrocarbon mixtures to form a mixture of oleflns and aromatic hydrocarbons suitable for subsequent alkylation comprise refractory spacing agents or carriers selected from the group consisting of activated aluminamagnesia, silica and diatomaceous earth and minoramounts of the oxides of elements selected from'rnernbers of the left-hand columns of groups IV. V and VI of the periodic table 60nsisting of titanium, zirconium, cerium, hafnium \and thorium; vanadium, columbium and tantalum, chromium, molybdenum, tungsten and uranium.

The above dehydrogenation catalysts are normally utllizedvvat temperatures within the approximate range of from about 400 to about 650 C., at atmospheric or superatmospheric pressures up to approximately 10 atmospheres, and at an hourly liquid space velocity (dened, as employed in the speciiication and the hereinafter appended claims, as the volume of liquid parafilns contained in the feed to the reactor per hour, divided by the superficial volume of catalyst in said reactor) of from about 0.1.to about 10. Conversion of the parains to olens of approximately to 30% per pass are obtained by properly selecting conditions within the above designated ranges. The time of contact em- 25 ployed will vary greatly with the catalyst used, the temperature of operation employed and other factors, such as the time required for reactivation of the catalyst by removal of the carbonaceous deposits thereorn` formed during the dehydro- 80 genation reaction),l

The length of the operating cycle is ordinarily established by trial, since higher over-al1 results are obtained in continuous plants when operations are conducted for a relatively short interval followed by a corresponding short time of reactivation rather than when the catalyst particles are permitted to become contaminated excessively by carbonaceous deposits.

The eiiluentproduct of dehydrogenation containing the aromatic hydrocarbons charged into the latter reaction zone in substantially unaltered condition and the olelnic hydrocarbons formed by dehydrogenation of the paraiiins contained in the original feed is charged into an alkylation reactor containing a suitable alkylation catalyst and maintained at alkylating conditions which will cause the condensation or said aromatic and said olenic hydrocarbons. Alkylatlon catalysts useful for effecting the reactions between the oleiinlc and aromatic hydrocarbons according to the process of this invention comprise sulfuric -acid (of from about 80 to about 100% or higher concentrations, preferably an acid having a coneentration within the upper limit of said range),

phosphoric acid (usually the concentrated reagent containing a small percentage of the phos- .phoric acid anhydride), hydrogen fluoride (preferably of 95 to 100 per cent concentration), alumi- 5ynum chloride (anhydrous) with anhydrous hydrogen chloride, and a solid precalcined composite of an acid of phosphorus and a siliceous' adsorbent, generally referred to as a solid phosphoric acid" catalyst.

For production of high yields of alkylate with- 05 out substantial decomposition of the alkylation products through so-called destructive alkylation reactions when employing sulfuric acid, hydrogen uoride or aluminum chloride with hydrogen chloride as catalyst, the process is preferably operated at relatively low temperatures, usually below about 100 C. and under suiiicient pressure that substantial proportions of the hydrocarbons are present as liquids in the alkylation zone.

While the exact operating temperature for alkylation is dependent upon the composition of the mixture being treated, which alkylation proceeds at a practical rate are approximately 45 C. when utilizing substantially anhydrous aluminum chloride with hydrogen chloride as the catalyst mixture, at 50 C.

I others, the aromatic hydrocarbon such as benzene or toluene, for example, is alkylated by olenic hydrocarbons at a temperature within the approximate range of 150 to `375 C. under a pressure 'of the order of 50 to 200 atmospheres producing thereby the desired alkylate.

Following the alkylation treatment, the total product, consisting primarily of aromatic and alkyl aromatic hydrocarbons, together with the unconverted parains of the original charging stock is diverted to the alkylate separating zone in which the higher boiling alkyl aromatics are removed by fractional distillation from the other components. The fraction or fractions containing unconverted paraiilnsand excess aromatic hydrocarbons are recycled to the dehydrogenation stage and combined with fresh feed charged to said latter stage, thus providing for a continuous recycle of the unconverted portion of the feed,

For the purposes of illustrating the combination of steps characteristic of the present invention, the attached drawing shows diagrammatically a typical flow for producing alkylP aromatic hydrocarbons from a mixture containing 20 molecular proportions of benzene and one molecular proportion of normal butane to form monobutylbenzene.

Referring to the drawing, benzene is introduced through line l into dehydrogenation zone 2 containing a `catalyst selected from the above mentioned group of dehydrogenation catalysts supported on trays, if the reaction is of the xed bed type, or circulated in a finely powdered condition, if the reaction is of the fluid type of catalytic/process. A paraflinic hydrocarbon fraction containing butane separated as a natur1 fleasoline fraction boiling at about C. is iiitro ced into dehydrogenation reactor 2 through line 3. The paraln reactant may be mixed prior to its introduction into the latter zone 2 with recycle stock containing excess aromatic hydrocarbon and unused paraflins, the origin of which is hereinafter referred to in greater detail and which enters line 3 through line I5. The mixture of aromatic and paralnic hydrocarbons is contacted with a catalyst in dehydrogenation zone 2 under conditions hereinabove specified for `the dehydrogenation of butane to butylenes in the presence of benzene. The eilluent products of said dehydrogenation zone are removed through line 4 and are directed to separation zone 5 where the products are separated into a normally liquid hydrocarbon stream which is removed through line 6 into alkylation zone 1 and a light normallygaseous product removed through line 8 and discharged from the process. The light gases, consisting of hydrogen formed in the dehydrogenation cf the paraiilns and light gases comprising methane, ethane, ethylene and propylene formed by miscellaneous reactions such as pyrolysis in the the lower temperatures atv dehydrogenation zone, may be sent to storage or utilized as fuel for supplying the required heat of reaction in the dehydrogenation stage, or the hydrogen may be separated therefrom and recycled to the dehydrogenation zone through line 9 where it serves the purpose of suppressing carbon formation and cracking reactions.

The mixture of hydrocarbons containing benzene, unconverted butanes, and butylene formed by dehydrogenation of said butanes is introduced into alkylation zone I through line 6 where itis contacted with a catalyst selected from the above specified group of alkylation catalysts suitable for converting aromatic-olefin hydrocarbon mixtures into alkyl aromatic hydrocarbons. In the case of a liquid alkylation catalyst, such as anhydrous hydrogen fluoride, sulfuric acid or phosphoric acid, alkylation zone 'I is equipped'with a stirring device suitable for contacting the hydrocarbon components of the charge with the catalyst. Also, in the case of the above catalysts, as well as in the use of anhydrous aluminum chloride-hydrogen chloride catalyst, a sludge phase containing catalyst-hydrocarbon complexes is ordinarily produced during the, alkylation reaction ,and this is removed from the process through line Ill to a catalyst recovery process not illustrated in the accompanying diagramvor to an incidental apparatus for the production of by-products therefrom. The hydrocarbon product which ordinarily is an upper layer in the alkylation zone is removed therefrom through line II into separating zone ,I2 wherein' desired fractions of the alkylate product are separated from recycle fractions. Separation zone I2 is a fractionating apparatus for separating the higher boiling alkyl aromatic product from the lower boiling recycle fractions. Said alkylated product is removed through line I3 while the recycle fractions are removed from separation zone I2 through line I4 and may be either diverted to a secondary separating zone for further purification before recycling to the dehydrogenation zone or the fraction may be recycled directly through line I5 and admixed with the paraiiinic charging stock introduced throughV line 3 and connected therewith. The recycle stock consists of excess ben. zene not utilized in the alkylation zone to form the alkyl aromatic hydrocarbons and unconverted butanes which, when recycled to the dehydrogenation zone into paraffin feed line 3 are ordinarily roughly analyzed prior to their introduction into said zone 2 to adjust the aromatic to paramn ratio charged into said zone to the ,aforementioned optimum ratio of said reactants.

The following examples are included to indicate the nature of the operation and results obtainable by said operation of the present invention, however; the data indicated therein are not intended toidene in any manner the limits thereof and are therefore not to be interpreted' as restricting the broad 'scope of the invention in accordance therewith.

Example I A mixture containing 12 molecular proportions of benzene and 1 molecular proportion of normal butane is prepared and passed over a dehydrogenation catalyst comprising a synthetically Acom-v sure of approximately 5 atmospheres and a gase lMabuse ous space velocity of 500 are maintained through-,-

posite of kieselguhr and pyrophosphoric acid at a y temperature of 350 C., a pressure ol 100 atmospheres and at agaseous space velocity of 1000. The alkylation products are separated by fractional distillation into a hydrogen fraction containing minor quantities of methane, ethylene and propylene, a fraction containing benzene and butane, and a product fraction containing butyl benzene and minor quantities of dibutyl benzene, the total alkylate product comprising a nearly quantitative yield based upon the weight o! butane disappearing in the reactor.

Eample II y A hydrocarbon mixture containing -18 molecular proportions of toluene and 1 molecular proportion of a straight-run. petroleum distillate boiling within the range of 160 to 250 C. and containing paraflinic hydrocarbons ofapproxl'- mately Cin- C12 chain length is passed at a temperature of 500 C., at a pressure of 3 atmospheres and at a gaseous space velocity of 200 into a dehydrogenation reactor containing a catalyst similar in composition to the catalyst utilized in Example I above. The products of dehydrogenation are separated into a normally liquid fraction and anormally gaseous fraction, the latter containing hydrogen, methane, ethylene and propylene.

The normally liquid fraction separated from .the products o1 dehydrogenation is passed directly into liquid anhydrous hydrogen fluoride at 20 C. and at 1 atmosphere pressure to maintain the hydrocarbons in liquid phase. An upper hydrocarbon layer separatedI from the products thereof after a reaction period of one-half hour is passed over alumina at 200 C. to dehydrolluorinate the hydrocarbons contained therein. The resultant product is fractionated into toluene, a fraction containing the unconverted portion of the charged parafllns which is lcombined with the toluene fraction and recycled tothe dehydrogenation stage, and a fraction comprising the alkylated toluene (decyl-dodecyl toluene alkylate, boiling from about 300 to about 340 C.).

The latter alkylated toluene when sulfonated under suitable conditions with sulfuric acid yields an excellent hard .water detergent,

l claim as my'invention:

1. A process for the production of alkyl aromatic hydrocarbons which comprises contacting a mixture of an alkylatable aromatic hydrocarbon and a dehydrogenatable parafnhydrocarbon. said aromatic hydrocarbon being present in molecular excess over said parafn hydrocarbon, with a dehydrogenation catalyst at dehydrogenating conditions to forman olefin hydrocarbon having the saine number ol carbon atoms per molecule as said parailin hydrocarbon; contacting at least a portion oi the resultant dehydrogenation products, without further chemical treatment, with an alkylation catalyst at alkylating conditions to alkyiate said aromatic hydrocarbon with said olefin hydrocarbon; separating from the resultant alkylation `products the desired alkyl aromatic hydrocarbon and a recycle fraction comprising unconverted aromatic and paraffin hydrocarbons; and supplying said recycle fraction to the dehydrogenation step.

2. The process of claim 1 further characterized n hourly space velocity of from about 0.1 to about in that the molecular ratio of said aromatic hydrocarbon to said paraffin hydrocarbon in the feed to the dehydrogenation step is from aboutl 3:1 to about 30:14

3. The process of claim 1 further characterized in that undesired normally gaseous components are separated from said dehydrogenatlon products prior to the alkylation step.

4. The process of claim 1 further characterized in that said dehydrogenation catalyst comprises an oxide of an element selected from the lefthand columns of groups IV, V and VI of the periodic table and said dehydrogenating conditions comprise a temperature of from about 400 C. to about 650 C., a pressure of fom about atmospheric to about 10 atmospheres, and a liquid 5. The process of claim 1 furthercharacterlzed in that said alkylation catalyst comprises a'sold precalcined composite of an acid oi phosphorus andasiliceous adsorbent 6. The process of .claim 1 further characterized in that said alkylation catalyst comprises substantially anhydrous hydrogen iiuoride.

7. The process of claim 1 further characterized in that said alkylation catalyst comprises conceritrated sulfuric acid.

8. A process for the production of alkyl aromatic hydrocarbons suitable for conversion to detergents by sulfonatlon and neutralization, which comprises contacting a mixture of an alkylatable aromatic hydrocarbon and a dehydrogenatable paraffin hydrocarbon containing at least 6 carbon atoms per molecule, the molecular ratio of aromatic hydrocarbon to paraflin hydrocarbon in said mixture being from about 10:1 to about 30:1, with a dehydrogenation catalyst at dehydrogenating conditions to convert said parain hydrocarbon to a monoolefln hydrocarbon having the same number molecule as said parafn hydrocarbon; reacting at least a portion of the resultant dehydrogenation products, without further ychemical treatment, in the presence of an alkylation catalyst at' alkylating conditions to alkyiate said aromatic hydrocarbon with said monoolenn hydrocarbon; separating from the resultant alkylatlon products (l) an alkyl aromatic hydrocarbon contain- REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,143,493 Stanley et al Jan. 10, 1939 2,287,931 Corson et al. June 30. 1942 2,349,045 Layng et al May 16, 1944 OTHER. REFERENCES Ser. No. 390,534, Pier et al. (A. P. C.) published May 18, 1943.

of carbon atoms ,per`

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