US3484498A - Process for the preparation of aryl-substituted normal paraffin hydrocarbons - Google Patents

Description

Dec. 16, 1969 R. c. BERG 3,484,498

PROCESS FOR THE PREPARATION OF ARYL'SUBSTITUTED NORMAL PARAFFIN HYDROCARBONS Filed Deo. 11, 1967 ATTORNEYS United States Patent O U.S. Cl. 260--671 7 Claims ABSTRACT OF THE DISCLOSURE Concerns an improvement in a process for the preparation of aryl-substituted normal paraffin hydrocarbons. Process involves steps of: selective dehydrogenation of a normal parafiin having about 6 to about 20 carbon atoms to the corresponding normal mono-olefins, hydrogen separation, alkylation of an alkylatable aromatic hydrocarbon with resulting normal mono-olefins, separation by fractional distillation of alkylation products and recycle of unreacted normal paraffins to dehydrogenation step. Problem involves build-up of alkyl-aromatic hydrocarbons, formed from lighter hydrocarbons produced in the dehydrogenation step, in normal paraffin recycle stream causing dehydrogenation catalyst instability and deterioration in product quality. Solution embodied herein comprehends removing lighter hydrocarbons from the effluent from the dehydrogenation step.

DISCLOSURE The subject of the present invention is an improvement in a process for the preparation of aryl-substituted normal paraffin hydrocarbons. More particularly, the present invention relates to an improvement in one of the commercially feasible routes to this type of arylalkane which route uses a normal paraffin and an alkylatable aromatic hydrocarbon in conjunction with a selective catalyst dehydrogenation step, employing a nonacid platinum-alumina dehydrogenation catalyst, and an alkylation step. The improvement follows from my recognition of the detrimental effects caused by the presence of alkylaromatic hydrocarbons in the normal parafiin charged to the dehydrogenation step lof the combination process. Coupled with this recognition, was my observation that even Where substantially pure normal paraliins are charged to this combination process, economic and equilibrium factors dictate the recycle of unreacte-d normal paraffins to the dehydrogenation step. And such a process operated with this type of recycle will inevitably tend to build a concentration of alkylaromatic hydrocarbons in this recycle stream because of side-reactions such as cracking and hydrocracking which I have found are still induced by this platinum-alumina composite despite attempts to eliminate them by the incorporation of a non-acid component in the catalyst. These side reactions lead to a minor amount of lighter olefinic products in the dehydrogenation step, which in turn produce a distribution of alkylaromatic side products in the alkylation step. Some of these alkylaromatic side products inevitably boil within or close to the boiling range of the normal paraffin charge, leading to the contamination of the normal paraffin recycle stream. More to the point, these dehydrogenation catalysts can be designed to suppress undesired acid-catalyzed sidereactions that result in lighter hydrocarbon, but as of yet no practical method has been found to completely eliminate them. Drawing upon the above analysis of the problem, the present invention provides a continuous ICC procedure for the elimination of lighter hydrocarbons from the effluent from the dehydrogenation step, thereby substantially eliminating the concentration of alkylaromatic hydrocarbons in this paraffin recycle stream with corresponding increase in the stability characteristics of the dehydrogenation catalyst and in the quality of the arylalkane product.

One of the major problems prevalent in centers of population throughout the world is the disposal of sewage containing detergents in even small quantities. Such disposal problem is especially vexacious in the case of these detergents having an alkylaryl structure as the nuclear portion of the detergent molecule. These detergents produce stable foams in hard or soft waters in such large quantities that the foam clogs sewage treatment facilities and often appears in sufiicient concentration in such facilities to destroy the 4bacterial necessary for sufficient biological action for proper sewage treatment. One of the principal offenders of this type of detergent is the alkylaryl sulfonates, which, unlike the fatty acid soaps, do not precipitate when mixed with hard water containing calcium or magnesium ions. And since these compounds are only partly biodegradable, the detergent persists in solution and is carried through the sewage treatment plant in substantially unchanged form. Having a tendency to foam, especially when mixed with aerating devices and stirrers, large quantities of this detergent are discharged from sewage digestion plants into rivers and streams where the continuing presence of the detergent is marked by large billows of foam on the surface of these streams. Other offenders of this type of detergent are the polyoxyalkylated alkyl phenols and the alkylpheuyl-polyoxyalkylated amines. These same synthetic detergents also interfere with the anaerobic process of degradation of other materials, such as grease, and thus compound further the pollution caused by sewage plant effluents containing such detergents. These dilute detergent solutions often enter subsurface water currents which feed into underground water bodies from which many cities draw their water supply, and the alkylaryl-based detergents find their way into the water supplies drawn from water-taps in homes, factories, hospitals, and schools.

It has been established that the biodegradability of the ultimate detergent product is primarily determined by the arylalkane hydrocarbon that is used in the preparation of the detergent. And more particularly, it has been found that these detergents are more readily degradable by sewage bacteria if the long chain alkyl substituent on the aromatic nucleus is of a simple, straight-chain configuration. In fact, the preferred intermediate from the biodegrada-bility stand-point is an aryl-substituted normal paraflin hydrocarbon. Consequently, there has been established a substantial requirement for this type of hydrocarbon. In view of the fact that this type of hydrocarbon is customarily prepared by an alkylation operation, it commonly is referred to in the art as a species of detergent alkylate or linear detergent alkylate; for example, linear alkylbenzene.

The linear detergent alkylate can be converted into a wide variety of detergents and other products as is Wellknown to those skilled in the art. For example, the detergent alkylate may be sulfonated and thereafter neutralized with a suitable alkaline base, such as sodium hydroxide to form an alkylaryl sulfonate (anionic) type of detergent which is most widely used for household, commercial and industrial purposes. The detergent alkylate can also be converted to a non-ionic type of detergent by nitrating the alkylate to form a nuclearly mono-nitrated intermediate which on reduction yields the corresponding alkylarylamine. The amino radical is thereafter reacted with an alkylene oxide or an alkylene epichlorohydrin to form an alkylaryl-polyoxyalkylated amine (containing from 4 to about 30 oxyalkylene units) which is highly effective detergent. Still other products having an alkylaryl base are widely known in the art, although alkylaryl sulfonates constitute the largest single class of surfactant products which are typically synthesized from this detergent alkylate.

Responsive to the demand for this linear detergent alkylate, the art has come up with a number of ways to use normal parafns as a source for the straight chain alkyl substituent on the aryl nucleus. One such route to this linear detergent alkylate involves: selective catalytic dehydrogenation of the normal paraffins to the corresponding normal mono-olefin, followed by alkylation of an alkylatable aromatic hydrocarbon with the resultant normal mono-olefin using and acid-acting catalyst to yield an aryl-substituted normal paraffin hydrocarbon. The dehydrogenation step typically operates on normal paraffin hydrocarbons having about 6 to about 20 carbon atoms to produce a normal mono-olen having the same number of carbon atoms. The alkylation step has a dual function: the first being the preparation of the desired arylalkane, and the second being the separation of the product olefin from the unreacted normal parafiins. In this process a dehydrogenation catalyst is preferably employed which has a high selectivity for the production of a normal mono-olefin with the complementary capability to suppress undesired side reactions such as skeletal isomerization, secondary dehydrogenation, cyclization, dehydrocyclization, polymerization, cracking, etc. In view of the fact that equilibrium considerations necessarily limit conversion levels in the dehydrogenation step, the economics of the resulting process require that unreacted normal parafins be recovered and recycled to the dehydrogenation step. For example, typical conversion levels efficiently attained in this dehydrogenation step with preferred catalysts are in the range of about to about by weight of the normal paraffin charge depending on temperature pressure, catalyst life, etc. The preferred procedure is to allow the unreacted paraffins to pass through the alkylation zone (where they are substantially unchanged), and separate them from the products of the alkylation reactions by fractional distillation.

The problem of concern to the present invention stems for this necessity of recycling the unreacted parafiins to extinction. Despite the use of non-acid dehydrogenation catalysts having high selectivities for the desired monoolefin, I have now found that a small amount of lighter hydrocarbons are formed in the dehydrogenation step, the olefinic component of which can result in alkylaromatic hydrocarbons which can accumulate in this normal paraffin recycle stream. Furthermore, I have found that these alkylaromatic hydrocarbons adversely affect the stability of the dehydrogenation catalyst, and when the operating conditions in the dehydrogenation step are raised to compensate for their presence, product quality can be adversely affected because of the affect of higher severity levels on other side reactions taking place therein. Consequently, the broad concept of the present invention involves the removal of lighter hydrocarbons from the eluent from the dehydrogenation step of this process with resulting improvement in dehydrogenation catalyst stability and in the quality of the product alkylate.

It is, accordingly, one object of the present invention to provide an improvement in a process for the synthesis of aryl-substituted normal paraffin hydrocarbons utilizing normal paraln hydrocarbons and alkylatable aromatic hydrocarbons. Another object is to improve the quality of the linear detergent alkylate produced by such a process. Still another object relates to a selective catalytic dehydrogenation operation wherein unreacted normal parafiins having 6 to 20 carbon atoms are recovered and recycled to extinction, the object being to improve the stability of the dehydrogenation catalyst used in therein. A more particular object is to eliminate one source of catalyst instability in a hydrogenation process employing a non-acid catalyst wherein unreacted normal parafiins are recycled to extinction, the source of the instability being arylaromatic hydrocarbons that contaminate the recycle paraffin stream.

In one embodiment, the present invention relates to an improvement in a process for the preparation of an arylsubstituted normal paraffin hydrocarbon, which process utilizes a normal paraffin hydrocarbon having about 6 to about 20 carbon atoms and an alkylatable aromatic hydrocarbon. In this process the following steps are performed: (a) hydrogen and a hydrocarbon stream containing the normal paraflin hydrocarbon are contacted, in a dehydrogenation zone, with a dehydrogenation catalyst comprising a platinum metal component, an alkali component, and alumina, at conditions selected to form a normal mono-olefin having the same number of carbon atoms as said parain hydrocarbon with attendant formation of a minor amount of lighter hydrocarbons; (b) an effluent stream containing hydrogen, unreacted normal paraffin hydrocarbons, the normal monoolen, and the lighter hydrocarbons, is withdrawn from the dehydrogenation zone and separated into a hydrogen-rich vapor phase and a hydrocarbon-rich liquid phase; (c) the hydrocarbon-rich liquid phase and a molar excess of an alkylatable aromatic hydrocarbon, having a boiling point substantially different from said paraffin hydrocarbon, are contacted, in an alkylation zone, with an alkylation catalyst at conditions selected to form alkylarornatic hydrocarbons; (d) an effluent stream is withdrawn from the alkylation zone and separated, in a fractionation system, into a first fraction containing unreacted aromatic hydrocarbon, a second fraction containing unreacted normal parafn hydrocarbon and alkylaromatic hydrocarbons formed from a portion of the lighter hydrocarbons, and a third fraction containing an aryl-substituted normal paraffin formed from the normal mono-olefins; and (e) the third fraction is recovered as a product stream, the second fraction is recycled to the dehydrogenation zone, and the alkylaromatic hydrocarbons contained in the second fraction deactivates the dehydrogenation catalyst. The improvement in this process comprises removing the lighter hydrocarbon from said hydrocarbon-rich liquid phase, prior to introducing said phase into the alkylation zone, thereby eliminating one source of contaminants in the recycled second fraction with corresponding improvement in the stability of the dehydrogenation catalyst.

Other embodiments and objects of the present invention encompass further details about: the normal paraffin hydrocarbons and alkylatable aromatics that can be charged thereto, the types of catalysts used in the conversion zones thereof, the process conditions used in each step thereof, the mechanics of the conversion, separation, and product recovery steps employed therein, etc. These embodiments and objects will become evident from the following discussion of the elements of the present invention.

Before proceeding to a detailed discussion of the elements of the present invention, it is advantageous to define certain terms and phrases used in connection therewith. The phrase aryl-substituted normal parafiin hydrocarbon denotes a secondary aryl-substituted alkane having two straight-chain alkyl groups on the resulting trisubstituted carbon atoms attached to the aryl nucleus. For example:

where R1 and R2 are normal alkyl groups. The phrase normal or straight-chain hydrocarbon refers to a hydrocarbon having its carbon atoms linked in a continuous chain. The term alkali when it is employed in conjunction with a description of a catalyst component refers to a component selected from the group consisting of alkali metals, alkaline earth metals, and compounds thereof. The phrase lighter hydrocarbons as used herein denotes any hydrocarbons that boil outside of the range of the hydrocarbon stream charged to the present process; for example, when a C to C15 mixture of normal paraffins is charged to this process, lighter hydrocarbons would be C1 to C9 hydrocarbons. The phrase non-acid catalysts refers to the type of catalyst Which the art would consider to have little or no ability to catalyze reactions which are thought to proceed by carbonium ions mechanisms such as isomerization, cracking, hydrogen transfer, alkylation, etc.; in particular, as used herein, it refers to a platinum-alumina composite that has combined therewith an alkali component for the purpose of substantially eliminating the acid sites in the catalyst.

The hydrocarbon stream that can be charged to the process of the present invention contains a normal parain hydrocarbon having at least 6` carbon atoms and especially 9 to about 20 carbon atoms. Representative members of this class are: hexane, heptane, nonane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane, octadecane, eicosanes, and mixtures thereof. Of particular significance to the present invention are streams containing normal parafns of about 10 to about 15 carbon atoms since these produced mono-olefins which can be utilized to make detergents having superior biodegradability and detergency. For example, a mixture containing a 4 or 5 homologue spread such as C111 to C13, C11 to C14, or C11 to C15 provides an excellent charge stock. Moreover, it is preferred that the amount of non-normal hydrocarbons present in this normal paraffin stream be kept at low levels. Thus, it is preferred that this stream contain greater than 90 Wt. percent normal paraffin hydrocarbons, with best results achieved at purities in the range of 96 to 98 wt. percent or more. It is Within the scope of the present invention to pretreat the normal parain charge stock by any suitable means for removing aromatic compounds; for example, by contacting it with a solution of sulfuric acid. In a preferred embodiment, the hydrocarbon stream that is charged to the process of the present invention is obtained by subjecting a hydrocarbon distillate containing normal paraiin within the aforementioned range to a separation operation employing a bed of molecular sieves which, as is Well-known, have the capability to produce hydrocarbon streams having a very high concentration of normal paraffin hydrocarbons. A preferred separation system for accomplishing this is adequately described in D. B. Broughtons U.S. Patent No. 3,310,486, and reference may be `had thereto for details about such a separation system. For example, a preferred procedure would involve charging a kerosine fraction boiling Within the range of about 300 F. to about 500 F. to the separation system of the type described in U.S. Patent No. 3,310,486 and recovering therefrom a hydrocarbon stream containing a mixture of normal paraflins in the C10 to C15 range. Typically, this last procedure can be performed so that the hydrocarbon stream recovered contains 98 Wt. percent or more normal paraffins.

As is pointed out hereinbefore, the catalyst used 1n the dehydrogenation step of the present invention comprises: an alumina component, a platinum group metallic component, and an alkali component. In general, this catalytic composite preferably also contains an additional component selected from the group consisting of arsenic, bismuth, antmony, sulfur, selenium, telluriurn, and compounds thereof.

The alumina component of this dehydrogenation catalyst generally has an apparent bulk density less than about 0.50 gram per cc. with a lower limit of about 0.15 gram per cc. The surface area characteristics are such that the average pore diameter is about to about 300 angstroms; the pore volume is about 0.10 to about 1.0 milliliter per gram; and the surface area is about 100 to about 700 square meters per gram. It may be manufactured by any suitable method including a wellknown alumina sphere manufacturing procedure detailed in U.S. Patent No. 2,620,314.

The alkali component of this dehydrogenation catalyst is selected from both alkali metals-cesium, rubidium, potassium, sodium, and lithium-and the alkaline earth metals-calcium, magnesium, and strontium. The preferred component is lithium. Generally, the alkali component is present in an amount, based on the elemental metal, less than about 5% by weight of the total composite with a value in the range of about 0.1% to about 1.5% generally being preferred. In addition, the alkali component may be added to the alumina in any suitable manner, especially in an aqueous impregnation solution thereof; and thus suitable compounds are the chloride, sulfates, nitrates, acetates, car-bonates, etc.; for example, an aqueous solution of lithium nitrate.. It may be added either before or after the other components are added or during alumina formationfor example, to the alumina hydrosol before the alumina carrier material is formed.

The platinum group metallic component is generally selected from the group consisting of palladium, iridium, ruthenium, rhodium, osmium, and platinum-with platinum giving best results. It is used in a concentration calculated as an elemental of about 0.05 to about 5.0% by Weight of the catalytic composite. This component may be composited in any suitable manner with impregnation by Water soluble compounds such as chloroplatinic acid being especially preferred.

Preferably, the catalyst contains a fourth component selected from the group consisting of arsenic, antmony, bismuth, sulfur, selenium, tellu-rium, and compounds thereof. Arsenic is particularly preferred. This component is typically used in an amount of about 0.01% to about 1.0%A by weight of the nal composite. This component is typically present in an atomic ratio to the platinum metal component of from about 0.1 to about 0.8. Intermediate concentratiotns are preferably employed such that the atomic ratio is about 0.2 to about 0.5. This component can be composited in any suitable manner--a particularly preferred way being via a Water soluble impregnation solution such as arsenic pentoxide, etc.

This preferred catalytic composite is thereafter typically subjected to conventional drying and calcination treatments at temperatures in the range of 800 F. to about 1100 F. Additional details as to the preferred dehydrogenation catalyst for use in the present invention are given in the teachings of U.S. Patent No. 3,291,755 and 3,310,599 issued to Vladimir Haensel et al.

Any suitable alkylation catalyst may be utilized in the alkylation step of the present invention. Representative of these are: sulfuric acid of about concentration and preferably higher; substantially anhydrous hydrogen uoride, generally not containing more than 10% Water; anhydrous aluminum chloride or aluminum bromide, preferably in the presence of the corresponding hydrogen halide; boron trifluoride either with or Without the addition of hydrogen fluoride, and either as such or adsorbed on a solid support, such as :a boron triuoridemodified inorganic base; phosphoric acid which is generally deposited on a carrier material such as kieselguhr, hydrated silica, etc.; and the like. The preferred catalyst for the present invention is anhydrous hydrogen fluoride of from about 90% concentration or higher; another preferred catalyst is the previously mentioned boron trifluoride.

Details as to concentration, method of use, etc. of these preferred alkylation catalysts will be found in the teachings of U.S. Patent No. 3,249,650 insofar as the hydrogen uoride catalyst is concerned, and in the teachings 7 of U.S. Patent No. 3,200,163 for the boron trifluoride catalyst.

Having characterized the catalysts used in the dehydrogenation step and the alkylation stepof the process to which the present invention is applicable, reference is now had to the attached drawing for a detailed explanation of the flow scheme, process conditions, and operating parameters employed in the improved process of the present invention. The attached drawings is merely intended as a general representation of the flow scheme employed, with no intent to give details about heaters, condensers, pumps, compressors, valves, process control equipment, etc., except where a knowledge of these devices is essential to the understanding of the present invention or would not be self-evident to one skilled in the art. Moreover, in view of the fact that the present invention involves a combination process no attempt is made in this drawing to represent details about the specics of each of the process steps except where detailed information is essential for proper understanding of the invention.

Referring now to the drawing, a hydrocarbon stream containing a normal parain-of the type hereinabove characterizedenters the process via line 1, is cornmingled with a normal paraffin recycle stream at the junction of line 16 with line 1, and the resulting combined hydrocarbon stream is admixed with a hydrogen recycle stream at the point line 17 joins line 1. The hydrogen recycle stream comprises about 94 to about 98% hydrogen or more, with a minor amount of C1 to C4 hydrocarbons; it is used in an amount of about 1 to about 20 moles of hydrogen per mole of paraffin in the combined hydrocarbon stream and preferably about to about moles of hydrogen per mole of paraffin. The resulting mixture of hydrocarbons and hydrogen is passed into dehydrogenation zone 2.

In some cases, it is advantageous to use diluents such a steam, methane, carbon dioxide, benzene, etc. in one or more of the streams entering zone 2 in order to control heat of reactions therein, or to adjust the partial pressure of one or more of the reactants charged thereto or to activate the catalyst used therein. For example a preferred procedure with the hereinabove characterized dehydrogenation catalyst is to saturate at least a portion of the entering hydrogen stream with water prior to its introduction into zone 2.

Dehydrogenation zone 2 typically contains a fixed bed of the non-acid dehydrogenation catalyst which was characterized hereinabove. For example, excellent results are obtained with a fixed bed of 1/16 spheres of a catalyst containing about 0.75% by weight platinum, about 0.50% by weight lithium, about 0.3 atom of arsenic per atom of platinum, combined with an alumina carrier material.

Dehydrogenation zone 2 is operated at a conversion temperature of about 750 F. to about 1100 F. with a value of about 800 F. to about 1000 F. being especially preferred. This temperature level is conveniently attained by use of any suitable heating means on the inuence side of this zone. Similarly, the pressure within dehydrogenation zone 2 is maintained within the range of about 10 p.s.i.g. to about 100 p.s.i.g. with best results obtained in the range of 15.0 to about 40 p.s.i.g. Likewise, a liquid hourly space velocity based on the combined hydrocarbon stream charged thereto of from about 10.0 to about 40.0 is typically utilized.

The function of dehydrogenation zone 2 is to selectively convert the normal paraffin contained in the hydrocarbon stream charged thereto to normal mono-olens having the same number of carbon atoms. Despite the use of a non-acid dehydrogenation catalyst, there is still a minor amount of side products concurrently formed. For example, in the case where the hydrocarbon stream is substantially pure normal tetradecane, the principal product will be normal tetradecene and the side products are typically C11 conjugated dienes, C1., isomers, C14 naph- CII thenes and aromatics and lower molecular weight (i.e. C13-) paraflins and oletins, etc. As should be evident by now from the above discussion, it is these last lighter olelins which produce the problem of concern of the present invention insofar as they have the capability to contaminate the recycle paraffin stream. Accordingly, the eftiuent stream withdrawn from dehydrogcnation zone 2 contains unreacted normal parains, the normal monoolefins formed therein, hydrogen, some isomers of the normal parains charged thereto, a trace amount of aromatics and naphthenes, and lighter hydrocarbons comprising parains and olefins boiling below the range of the normal paraffin charge stock.

Accordingly, an effluent stream is withdrawn from dehydrogenation zone 2 via line 3 and passed through condensing means, not shown, in which the temperature of the mixture is lowered to a value of about F. The resulting cooled mixture is then introduced into separating zone 4. In separating zone 4, a hydrogen-rich gaseous phase separates from a hydrocarbon-rich liquid phase. The hydrogen-rich gaseous phase is withdrawn from zone 4 via line 1'7 and recycled through compressive means, not shown, to supply hydrogen to dehydrogenation zone 2. In addition, excess hydrogen is withdrawn through line 18 during the operation of the process in order to maintain pressure control within zone 2. Likewise, line 18 may be used during start-up operations to inject hydrogen into this hydrogen loop.

The hydrocarbon-rich liquid phase is withdrawn from separating zone 4 and passed via line 5 to stripping zone 6. As is pointed out hereinbefore, stripping Zone 6 is an essential feature of the prescrit invention and is designed to remove the lighter hydrocarbons formed in dehydrogenation zone 2. An additional function of stripping zone ei is to remove water from the hydrocarbon-rich liquid phase. if such has been added to the influent to dehydrogenatton zone 2. Typically, stripping zone 6 will comprise a multi-plate fractionation column wherein the hydroCarbon-rich liquid phase is introduced in the middle region 0f the column and a mixture of light hydrocarbons is taken over-head, condensed, and a portion recycled to the top of the column. A suitable stripping gas, such as steam, nitrogen, etc. may be used in some cases to and 1n the separation of the lighter hydrocarbons. In any event, a substantially lighter hydrocarbon-free mixture of normal paratiin hydrocarbons and normal monoolelins is withdrawn from the bottom of stripping zone 6 and passed via line 8 to alkylation zone 9.

Also charged to alkylation zone 9 is an aromatic stream which enters the process via line 15. Moreover, part of this aromatic stream may be a recycle stream, the origin of which will be hereinafter discussed. In general, any alkylatable aromatic may be used in the process of the present invention provided its boiling point diers substantially from the mixture of normal parat-tins and normal mono-olefins recovered from stripping zone 6; that is, the alkylatable aromatic hydrocarbon must be separable by fractional distillation from the unreacted normal paraftins which pass through alkylation zone 9 without undergoing any substantial change. Typical examples of suitable aromatics are: benzene, toluene, xylene, ethylbenzene, methylethylbenzene, diethylbcnzene, phenol, mono-nitrobenzene, naphthalene, alkyl naphhalene, etc. The preferred alkylatable aromatic hydrocarbons, from the view point of detergent alkylate production, are monocyclic aromatic hydrocarbons, with benzene giving excellent results.

In alkylation zone 9, the aromatic stream and the hydrocarbon stream from the bottom of stripping zone 6 are contacted with the alkylation catalysts which is preferably a solution of hydrogen uoride, as previously explained. It is understood that these streams may be introduced simultaneously, or in admixture with each other, or the aromatic stream may be contacted with the alkylation catalyst followed by the addition of the hydrocarbon stream thereto. The mole ratio of aromatic compound to the mono-olefin contained in the hydrocarbon stream is generally maintained above an equimolecular ratio, preferably from about '2:1 to about 30:1 in order to minimize polyalkylation of the aromatic compounds and/or polymerization of olefins.

-In alkylation zone 9, the reactants are maintained into contact with the alkylation catalyst for a reaction period of about to about 100 minutes, the exact contact time being dependent on the number of factors such as types of reactants, catalysts, temperatures, etc. The temperature maintained in the zone is within the range of about 0 F. to about 200 F. and preferably from about 70 F. to about 150 F. Likewise, a pressure sufficient t0 maintain the catalyst and reactants in liquid phase is generally employed. In the preferred mode of operation, where the alkylation catalyst is hydrogen fluoride, the effluent from the alkylation zone is passed to a separating drum wherein an acid phase settles out and it is returned to the alkylation zone. A small drag stream of the acid phase returning to the alkylation zone is typically charged to an HF regenerator column wherein HF is taken overhead and a drag stream consisting of tars and polymers is withdrawn as bottoms. Typically, the hydrocarbon layer recovered from this separating drum is heated and charged to an acid wash column and then to an HF stripper wherein HF vapor is taken overhead. The HF vapor is then condensed and returned to the alkylation zone and the hydrocarbon layer recovered as the product stream via line 10.

Accordingly, a mixture of hydrocarbons comprising the products of the alkylation reaction in combination with unreacted hydrocarbons which were charged thereto, is withdrawn from alkylation zone 9 via line 10 and passed to fractionation system 11. In general, fractionation sys tem 11 can comprise any suitable train of fractionation columns, designed to separate the hydrocarbons charged thereto into unreacted aromatic-rich fractions, a normal paraffin-rich fraction, and an aryl-substituted normal parafiin fraction, and a heavy alkylate fraction. Preferably, this system comprises three fractionation columns. The first column separates unreacted aromatics from the efent stream from zone 10. The unreacted aromatics are recovered as overhead from this first column and are recycled to the alkylation zone via line 14. The bottom stream from this first column is then typically passed through treating means wherein alkyl fluorides are substantially removed-for example, by contacting with alumina. The treated bottoms from the first column are then passed into a second column wherein a normal parafiin-rich stream is recovered as overhead and recycled via line 16 back to dehydrogenation zone 2. The bottom stream from the second column is then typically passed to a third column wherein the detergent alkylate product is recovered as overhead via line 12, with a minor amount of heavy alkylate typically comprising diphenyl alkanes, dialkyl benzene, etc., being recovered as bottoms. This heavy alkylate stream passes out of the system via line 13 and is produced primarily as a consequence of a minor amount of dienes produced as a side reaction in dehydrogenation zone 2.

Considering the normal paraffin recycle stream passing via line 16 'back to dehydrogenation zone 2, I have now found that if lighter hydrocarbons are not separated from the influent to alkylation zone 9 that a portion of these hydrocarbons will be alkylated therein and produce a -distribution of alkylaromatic hydrocarbons, some of which will overlap the boiling range of the normal parain recycle stream and consequently accumulate therein with resulting deactivation of the dehydrogenation catalyst in zone 2 as was hereinbefore explained. Accordingly, it is a key feature of the present invention that these lighter hydrocarbons are not allowed to pass into alkylation zone 9, thereby improving the stability of the catalyst employed in dehydrogenation zone 2.

The following example is introduced to illustrate fur ther the novelty, mode of operation, and utility of the present invention. It is not intended to limit unduly the present invention since the example is intended to be illustrative rather than restrictive.

EXAMPLE This example shows the benefits of using the present invention by contrasting the results obtained with and without it for substantially the same charge stocks, catalysts, and operating conditions. Case A represents the situation encountered when a process of the type pre viously described is operated without the improvement of the present invention, whereas Case B exhibits the benefits associated with the present invention. In terms of the attached drawing, Case A represents the situation encountered when the eiiiuent from separating zone 4 bypasses stripping zone 6 and is passed directly to alkylation zone 9, while Case B embodies the ow scheme given therein.

The hydrocarbon stream entering the process through line 1 is a mixture of normal paraflinic hydrocarbons containing: 0.3 wt. percent n-Clo, 26,6 wt. percent n-Cu, 31.3 wt. percent n-C12, 25.0 wt. percent n-C13, 13.2 wt. percent n-C14, 0.4 wt. percent n-Cl, 0.67 wt. percent mono-cyclic paraiiins, 0.66 wt. percent dicyclic parafiins, 0.17 wt. percent aromatics, with the remainder being nonnormal paraffin. In addition, a Type D-85 ASTM distillation shows this charge .stock to have an IBP of 392 F., a 50% point of 414 F., and an E? of 470 F.

The aromatic charge stock passing into the system via line 15 is substantially pure benzene.

In both of these cases, dehydrogenation zone 2 contains a fixed bed of 1/46 inch spheres which were manufactored according to the procedure given in U.S. Patent No. 3,291,755. Analysis of this catalyst shows it to contain 0.76 wt. percent platinum, 0.041 wt. percent arsenic, 0.55 wt. percent lithium, all on an elemental basis. These elements are composited with an alumina carrier material according to the teachings of the patent, and the resulting catalyst is found to possess an ABD of 0.46, a surface area of 145 m.2/g., and a pore volume of 0.40 ml./gr.

Also for both of these' cases, the catalyst used in alkyl ation zone 9 is a solution of' substantially anhydrous hydrogen fluoride.

In both cases, dehydrogenation zone 2 is operated with the objective of sustaining approximately a 10 wt. percent conversion of the combined hydrocarbon stream charged thereto to normal mono-olefins.. Conditions maintained therein throughout both tests are a LHSV of about 28.0 hrl, a hydrogen to hydrocarbon mole ratio of about 9.0 and a pressure at the outlet of zone 2 of about 30 p.s.i.g. Additionally, positive control over the temperature of the combined stream entering zone 2 is continuously maintained in order to achieve the desired conversion level; that is, a starting temperature of about 850 F. to about 890 F. is incrementally increased in order to compensate for the deactivation experienced during the course of the test.

Alkylation zone 9 is operated at: a mole ratio of benzene to total olefin in the influent thereto of Vabout 10, a liquid volume ratio of hydrogen fluoride solution to inuent hydrocarbon stream of about 2, a temperature of about F. to about 140 F., and a residence time of about 20 minutes.

With the exception of the bypass around zone 6 for Case A, the ow sequence through the various steps of the process for both cases is identical with that previously given in conjunction with the description of the attached drawing. After all process units are started up, lined out, and recycle is established through line 16, the test periods are begun. Each test period consists of 24 hours, and during each period an analysis of the hydrocarbon-rich liquid phase withdrawn from separating zone 4 via line 1 1 5 is performed. In line with the previous discussion, these analyses show that from about 0.20 to about 0.60 wt. percent of the combined hydrocarbon charged to zone 2 is converted into lighter hydrocarbons-that is, C- hydrocarbons. In addition, the results of these analyses are about carbon atoms are contacted, in a dehydrogenation zone, with a dehydrogenation `catalyst comprising a platinum metal component, an alkali component and alumina, at conditions selected to form a normal `mono-olefin having the same number of used to determine conversion levels in zone 2 and to moni- 5 carbon atoms as said parain hydrocarbon with tor the level of aromatics accumulating in the recycle attendant formation of a minor amount of lighter normal paratin stream. For Case A, these results for hydrocarbons; each period are given in Table I in terms of conversion (b) an etiiuent stream, containing hydrogen, unretemperature used in dehydrogenation zone 2, the correlo acted normal paratiin hydrocarbon, the normal sponding conversion level attained therein which is measmono-olefin and the lighter hydrocarbons is withured at Wt. percent of combined hydrocarbon feed condrawn from said dehydrogenation zone and separated verted to normal mono-olens, and the wt. percent arointo a hydrogen-rich vapor phase and a hydrocarmatics that are present in the effluent from dehydrogenabon-rich liquid phase; tion zone 2. 15 (c) the hydrocarbon-rich liquid phase and a molar TABLE L RESULTS oF CONTROL RUN [Case A] Period No 1 2 3 4 5 e 7 Temperature, F 887 890 892 894 895 897 000 n-Mono-olefi11s,wt. percent". 9.45 9.03 8.89 8.58 8. 29 8.07 8.03 Aromatics,wt. percent 0,60 1.025 1.100 1.125 1.250 1.275 1.225

As can be seen from this table, the aromatic level was excess of an alkylatable aromatic hydrocarbon, havsteadily increasing throughout this run. Since the fresh ing a boiling point substantially different from said feed only contained 0.17 Wt. percent aromatics, it is eviparaflin hydrocarbon, are contacted, in an alkylation dent that aromatics are being synthesized within the proczone, with an alkylation catalyst at conditions ess. My investigation shows that in this case about 70% selected to form alkylaromatic hydrocarbons; of the total aromatics being passed to dehydrogenation (d) an effluent stream is withdrawn from said alkylazone 2 are C10 through C15 alkylate produced by the alkyltion zone, and the alkylaromatic hydrocarbons conation of light ends contained in the zone 2 etiiuent. Fur- 3F into a rst fraction containing unreacted aromatic therrnore, the rate of temperature increase necessary to a hydrocarbons, a second traction containing unremaintain conversion for this case is greatly in excess of acted normal paratn hydrocarbons and alkylthat required for once-through operation, indicating that aromatic hydrocarbons formed from a portion of the catalyst in zone 2 is undergoing excessive deactivasaid lighter hydrocarbons, and a third fraction contion. taining an aryl-substituted normal parain hydro- In sharp contrast to these results are the results deposcarbon formed from said normal mono-olefin; and, ited in Table II for the improved process of the present (e) the third fraction is recovered as a product stream, invention wherein stripping zone 6 functions to remove said second fraction is recycled to said dehydrogena- C10 hydrocarbons from the eluent stream from the detion zone, and the alkylaromatic hydrocarbons conhydrogenation step prior to its passage into the alkylatained in said second fraction deactivates said detion step.

hydrogenation catalyst;

TABLE IL RESULTS WI'III TllE PRESENT INVENTION vi150 Period No 1 2 3 4 5 Here the level of aromatics is much lower with corresponding decrease in the rate of dehydrogenation catalyst deactivation as is evidenced by the generally higher level of conversion attained in Case B with comparatively less temperature increase per unit time.

Accordingly, this example demonstrates the deactivating atect of C10 to C15 alkylbenzenes that are produced by the lighter hydrocarbon formed in the dehydrogenation zone 2, and the corresponding improvement in activity stability (i.e., rate of temperature increase required to produce constant conversion) for the dehydrogenation catalyst that attends an operation conducted in accordance with the present invention.

I claim as my invention:

1. In a process for the preparation of an aryl-sub-V stituted normal paraffin hydrocarbon, wherein:

(a) hydrogen and a hydrocarbon stream containing a normal paraffin hydrocarbon having about 6 to the improvement which comprises removing the lighter hydrocarbons from said hydrocarbon-rich liquid phase prior to introducing said phase into the alkylation zone, thereby improving the stability of said dehydrogenation catalyst.

2. The improved process of claim 1 further characterized in that said alkylatable aromatic hydrocarbon is benzene.

3. The improved process of claim 1 further characterized in that said dehydrogenation catalyst comprises: an alumina component; a component selected from the group consisting of alkali metals, alkaline earth metals and compounds thereof; a component selected from the group consisting of arsenic, bismuth, antimony, sulfur, selenium, tellurium, and compounds thereof; and a platinum group metallic component.

4. The improved process of claim 1 further characterized in that alkylation catalyst is hydrogen fluoride.

5. The improved process of claim 1 further character ized in that said dehydrogenation catalyst comprises alumina, about 0.01% to about 1.5% by Weight of lithium, about 0.05% to about 5.0% by Weight of platinum, and about 0.01% to about 1% by Weight of arsenic.

6. The improved process of claim 1 further characterized in that said hydrocarbon stream is obtained from a kerosine distillate by selective separation using molecular sieves.

7. The improved process of claim 1 further characterized in that said hydrocarbon stream contains a mixture of C10 to C15 normal paran hydrocarbons.

References Cited UNITED STATES PATENTS Bloch 260--671 XR Johnstone 260-671 Bloch et al 260-671 Weaver 260-671 Jones 260--671 XR Alul et al. 260-671 10 DELBERT E. GANTZ, Primary Examiner CURTIS R. DAVIS, Assistant Examiner

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