US3322842A

US3322842A - Recycle of hydrodealkylation product for hydrogen enrichment

Info

Publication number: US3322842A
Application number: US463453A
Authority: US
Inventors: George J Czajkowski; Peter E Liakakos
Original assignee: Universal Oil Products Co
Current assignee: Universal Oil Products Co
Priority date: 1965-05-24
Filing date: 1965-05-24
Publication date: 1967-05-30
Anticipated expiration: 1984-05-30

Description

imy 30, 1967 G. J. CZAJKOWSKI ETAL RECYCLE OF HYDRODEALKYLATION PRODUCT FOR HYDROGEN ENRICHMLNT Filed May 24, 1965 Light Paraff/ns L l'ghf Paraff/ns Fracf/onafar 3 Sheets-Sheet 1 Compressar Stabilized Reformafe HV VE IV TORS.- George J. Czajkows/ri Peter E. L/a/ra/ros @WM 64 Z440? A T TOR/V5 Y5.

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- 3,322,842 RECYCLE @lF HYDRODEALKYLATION PRODUCT FQR HYDRQGEN ENRICHMENT This application is a continuation-in-part of our copending application Ser. No. 103,764, filed April 18, 1961, now abandoned and of our co-pending application Ser. No. 36,344, filed June 16, 1960, now Patent No. 3,296,118 issued Jan. 3, 1967.

The present invention relates to a process for the conversion of hydrocarbons and mixtures thereof. More particularly, the present invention is concerned with a process for converting hydrocarbons in contact with hydrogen to form useful products therefrom. Still more specifically, the present invention is directed toward a process for converting hydrocarbons by reacting said hydrocarbons in the presence of an excess of hydrogen and a catalytic composition of matter, said hydrogen being maintained in a relatively high degree of purity thereby permitting the process to proceed with a minimum of side reactions and in a more economical manner.

The hydrocarbon conversion processes which are contemplated within the scope of this invention are many and varied, the processes which may utilize the hydrogen enrichment step hereinafter more fully described include the reforming of gasoline boiling range hydrocarbons, the isomerization of relatively short chain paraflins such as butane and pentane to form isomers thereof which possess a higher octane number, the hydrodealkylation of alkylaromatic compounds such as toluene, the xylenes, methylnaphthalenes, dimethylnaphthalenes, etc., the hydrogenation of aromatic compounds to form cyclic paraffins, the contaminant removal process for removing sulfur and nitrogen and the hydrocracking of high boiling materials to form lower boiling materials which possess more useful properties.

While some of the processes which may be utilized in the present invention may be run in the absence of any catalytic material present in the reaction zone, the reaction being one which is thermal in nature, an example of which may be the hydrodealkylation of alkylaromatic compounds, the preferred method of elfectin-g the conversion of hydrocarbons is in the presence of a catalytic composition of matter. One of the predominant causes of catalyst deactivation is the deposition of coke and other heavy carbonaceous material upon the catalytically active centers and surfaces of the catalyst. The deposition of such carbonaceous material appears to be effected in two stages; that is, a major proportion of the coke is deposited during the initial, early stages of the conversion operation, while the catalyst employed therein exists in its most highly active state with regard to the entire period of operation. As the period of operation is extended, the deposition of coke continues at a comparatively constant, slower rate. The unusually high degree of coke deposition during the initial stage of operation is believed to be primarily due to the inherent ability of fresh, highly active catalyst to promote preferentially certain reactions which are detrimental to catalyst stability and activity. As more coke becomes deposited upon the catalyst, this preference diminishes until such time as it no longer exists effectively. However, at this time, the catalyst has become deactivated to the extent that it is incapable of performing its intended function to the necessary and desired degree. One particular reaction which is especially detrimental to 3,322,842 Patented May 30, 1967 the activity of catalytic composites comprising a platinumgroup metallic component and being utilized in processes for the conversion of hydrocarbons, and which reaction appears to be selectively promoted by fresh, highly active catalyst, is demethylation. Such demethylation is particularly pronounced when the platinum-group catalyst is utilized in catalytic reforming processes, isomerization processes, hydrodealkylation processes, and other hydrocarbon conversion reactions such as desulfurization, treating, hydrogenation, dehydrogenation, etc. The decomposition of methane to form carbon is strongly endothermic. At the normal operating pressures utilized in the process of this invention methane is stable, provided that the hydrogen purity of the system, which may be expressed as the mole ratio of hydrogen to hydrogen plus impurities such as methane, is maintained above a certain critical level. It is a desirable feature of the invention to operate the process at the highest possible purity rate of hydrogen in order to encourage the reaction rate. Although hydrogen purity in excess of about 50% will normally avoid massive carbon formation it is desirable to allow for some variation and therefore the minimum hydrogen purity should be above about 60%. By eliminating the decomposition of methane to form free carbon the elimination of massive carbon formation on the walls of the reactor and other pieces of apparatus, in the spaces surrounding the catalyst as well as on the catalyst particles themselves, thereby rendering the catalyst inoperative and necessitating frequent shutdowns for decoking of the catalyst or changing the catalyst entirely will be avoided.

Another primary cause of catalyst deactivation is the formation of a complex mixture of highly condensed, polycyclic aromatic compounds, of which the following have been identified as two of the constituents thereof:

1,2,3,4-dibenzpyrene Coronene As indicated by the following abbreviated chemical equations, one possible mechanism of carbon formation, as initiated by such polycyclic aromatics, is through cyclic olefin intermediates.

0 C I I Methyl- Methylcyclocyclopentane pentaue Substituted Decalin C- C C- C (j i J Substituted Naphthalene Similar successive steps result in the growth of the aromatic structure, whereby anthracene, phenanthrene, etc., and ultimately, the highly condensed aromatic structures previously identified as coronene and 1,2,3,4-dibenzpyre-ne, are produced. Another possible route to the highly condensed aromatic structures is through C C and C olefin intermediates which react with the polyacrylic aromatic nuclei to increase the polyring structure. This mechanism Further considerations indicate, in addition to the foregoing, that the methyl groups act to suppress further reaction and substitution. This has been evidenced by analyses of stabilized reformate product which indicate the presence of a large proportion of alpha and beta-methyl naphthalenes within the higher boiling portion of the product.

The object of the present invention is to effectively suppress those reactions which are especially detrimental to catalyst activity, increasing thereby the stability of the catalyst and, therefore, the effective period of time during which the catalyst performs its intended function to an acceptable degree. This method of the present invention reduces the quantity of these light paraffinic and olefinic hydrocarbons within the reaction zone, by which selective reactions occur with the various polycyclic aromatic compounds on the catalyst surface, whereby there is effected a decreased light hydrocarbon production, the removal of the coke precursor compounds from the catalyst surface, and the subsequent elution of these compounds from the reaction zone. The overall end result is a greatly decreased degree of carbon formation on the catalyst, whereby the effective life thereof is substantially increased.

It is not intended that the method of the present invention be unduly limited to the foregoing theoretical considerations. For example, when applied to the process of catalytically reforming gasoline boiling range hydrocarbons, the removal of C olefinic hydrocarbons, in addition to the light paraffinic and olefinic hydrocarbons will be effected. On the other hand, although the present invention is highly advantageous in the process of isomerizing pentanes, hexanes and cycloparaflinic hydrocarbons, it is equally well adaptable to the process of isomerizing butanes, in which case the removal of C hydrocarbons is obviously not effected to a substantial degree. The precise operation of the method of the present invention will, therefore, be dependent, to some extent, upon the process and reaction which is beingeffected. The necessary modifications to distinguish a catalytic reforming process from an isomerization and/or hydrodealkylation process, will be readily ascertained by one possessing skill within the art of petroleum refining and processing techniques, and it is not intended that such relatively minor modifications be removed from the generally broad scope of the present invention.

It is therefore an object of this invention to provide a process whereby the reactions which are especially detrimental to catalyst activity during the hydrocarbon conversion will be effectively suppressed, thereby increasing the stability of the catalyst and, therefore, the effective period of time during which the hydrocarbon conversion catalyst is capable of performing its intended function to the necessary desired degree.

A further object of this invention is to provide a process whereby the hydrogen which is necessary .in the hydrocarbon conversion process may be enriched or purified to the degree necessary to effectively convert the hydrocarbons to the desired products of the process.

-In one aspect, an embodiment of this invention resides in a conversion process which comprises (a) Catalytically converting hydrocarbons in the presence of hydrogen and a conversion catalyst in a reaction zone,

(b) Removing from the reaction zone the resultant reaction zone effluent comprising normally liquid hydrocarbons, normally gaseous hydrocarbons and hydrogen,

(c) Separating said efliuent into a hydrogen-rich gaseous phase and a liquid hydrocarbon phase,

(d) Recycling at least a portion of the gaseous phase to the reaction zone,

'(e) Separating light hydrocarbons from said liquid hydrocarbon phase,

(f) Commingling a portion of the remaining liquid hydrocarbon phase with the total reaction zone efiiuent in transit with the reaction zone to the separation zone and prior to the separation of said efiiuent into said phases, and

(g) Recovering another portion of the remaining liquid hydrocarbon phase as the product of the process.

A further embodiment of this invention is found in a process which comprises (a) reforming a hydrocarbon charge containing gasoline boiling hydrocarbons in a reaction zone in the presence of hydrogen and a platinum-containing catalyst,

-(b) removing from the reaction zone the resultant reaction product effiuent comprising reformed gasoline hydrocarbons, normally gaseous hydrocarbons and hydrogen,

(c) separating said efiiuent into a hydrogen-rich gas and a liquid reformed gasoline fraction containing normally gaseous hydrocarbons,

(d) recycling at least a portion of said gas to the reaction zone,

(e) stabilizing said liquid reformed gasoline fraction to separate normally gaseous hydrocarbons therefrom and from a stabilized gasoline product.

(f) commingling a portion of said stabilized gasoline product with the total reaction zone efiiuent prior to the aforesaid separation thereof in an amount to yield a recycle ratio of from about 0.5:1 to about 10.0:1, with respect to said charge-containing gasoline boiling hydrocarbons, and

(g) recovering the remainder of said stabilized gasoline product.

A specific embodiment of this invention is found in a process which comprises (a) hydrodealkylating an alkylaromatic hydrocarbon in a reaction zone in the presence of an excess of hydrogen and a catalyst at a temperature in the range of from about 1000 to about 1500 F., and at a pressure in the range of from about 500 to about 600 pounds per square inch,

(b) removing from the reaction zone the resultant reaction product effiuent comprising a liquid hydrocarbon phase, a normally gaseous hydrocarbon phase and hydro- (c) separting said effluent into a hydrogen-rich gas and a liquid hydrocarbon phase,

((1) recycling said hydrogen-rich gas to said reaction zone,

(e) separating the liquid hydrocarbon phase into a gaseous fraction containing light parafiinic hydrocarbons and a stabilized liquid fraction,

(f) commingling a portion of said stabilized liquid fraction with the total reaction zone effluent prior to separation of the latter into said gaseous phase and said liquid phase in an amount to yield a recycle ratio with respect to the alkylaromatic hydrocarbon charge in the range of from about 25:1 to about 50:1, and

(g) recovering another portion of said stabilized liquid fraction as a product of the process.

Other objects and embodiments will be found in the following further detailed description of this invention.

As hereinbefore set forth, the present invention is concerned with a process for the conversion of hydrocarbons in the presence of hydrogen and a hydrocarbon conversion catalyst wherein the hydrogen which is necessary for the process is enriched to such an extent that the hydrocarbon conversion catalyst will operate in a more efficient manner and with a concurrent increased efiiciency due to a lessening of the catalyst deactivation due to poisoning thereof.

Recent refining developments within the petroleum industry have produced a catalytic composite which is capable of converting low-quality hydrocarbons, and various mixtures of hydrocarbons, into a high-quality product possessing excellent anti-knock characteristics. This catalyst, comprising at least one metallic component selected from the platinum-group of the Periodic Table and halogen, promotes desirable reforming-type reactions including, as principal reactions, the dehydrogenation of naphthenes into aromatics, the dehydrocyclization of short-chain parafiins directly to aromatics and, to a particularly controlled degree, the hydrocracking of longchain parafiins into lower boiling normally liquid hydrocarbons. These reactions combine to effect a substantial increase in the octane rating of the hydrocarbons and hydrocarbon fractions being processed, and are especially suited to the processing of gasoline boiling range hydrocarbons including straight-run and natural gasolines, as well as thermally and catalytically cracked gasoline, and/ or mixtures thereof. Furthermore, this catalyst has been found to be of great advantage in selectively promoting, at specific conditions of operation, the isomerization of cycloparaffim'c hydrocarbons and low molecular weight, straight-chain hydrocarbons, such as pentanes and hexanes, and the hydrodealkylation of alkyl substituted aromatic hydrocarbons.

Through the appropriate selection of operating conditions, which are dependent to a great extent on the physical and/ or chemical characteristics of the material originally charged to the conversion process, whether reforming, isomerization, hydrodealkylation, or other specific conversion processes, the catalyst is capable of being employed for an extended period of time without regeneration when reforming saturated or substantially saturated gasoline fractions, or when effecting the isomerization of substantially pure straight-chain, or relatively straightchain, low molecular weight hydrocarbons. However, when effecting the conversion of hydrocarbons containing substantial amounts of sulfur and nitrogen, or complex compounds thereof, there is incurred the undesirable selective poisoning of the catalyst which inherently results in a decrease in the catalytic activity thereof. In addition to selective poisoning, catalyst deactivation may result from any one, or a combination of adverse effects, as for example from substances which are peculiar to a particular catalyst, and which either result in a change in the physical or chemical state of the components of the catalyst, or in a loss of said components. One of the more common forms of catalyst deactivation occurs upon the deposition of impurities which usually take the form of solids, or chemical complexes, and which shield the catalytically active centers and surfaces from the materials being processed. As hereinbefore set forth the deposition of coke and other heavy hydrocarbonaceous material is a direct cause of catalyst deactivation, and is generally experienced during the catalytic reforming of hydrocarbon fractions, the isomerization of substantially pure hydrocarbons, and the hydrodealkylation of aromatic nuclei. Although such hydrocarbons, or mixtures thereof, may comprise relatively small quantities of unsaturated hydrocarbons, nitrogenous compounds and sulfurous compounds, relatively rapid deactivation results from the deposition of coke which may be effected through uncontrolled hydrocracking, and other undesirable reactions, occurring simultaneously.

The present invention will be further illustrated with reference to the accompanying drawings in which FIG- URE 1 illustrates a simplified flow diagram of a catalytic reforming process, FIGURE 2 is a simplified flow diagram of a hydrodealkylation process, FIGURE 3 is a graph indicating the stability of the operation with respect to the volumetric yield of debutanized liquid product and FIG- URE 4 illustrates a comparison between two phases of a catalytic reforming process. Various valves, coolers, condensers, pumps, knockout pots, overhead refiux condensers, controllers, etc., have been reduced, or entirely eliminated, as not being essential to the complete understanding of the present invention. The utilization of these, as well as other similar appurtenances, will become obvious as the drawing is described.

Referring now to FIGURE 1, a full boiling range gasoline charge stock, such as a Midcontinent naphtha, enters the process via line 1 into fractionator 2, containing centerwell 3. Fractionator 2 serves to remove light paraffinic and olefinic hydrocarbons via line 4, and heavy bottoms material through line 5. There is produced a heartcut, withdrawn from a point above centerwell 3 via line 6 and pump 7, having an intermediate boiling range. The applicability of the catalytic reforming process to a multitude of charge stocks is well known, and it is not essential, therefore, that the heart-cut withdrawn through line 6 have a particular boiling range. In any event, the resultant intermediate naphtha charge stock is passed into line 8,

and is admixed with a desired quantity of a hydrogen-rich recycle gas stream in line 23, the production of which recycle gas is hereinafter described. The mixture is raised to the desired operating temperature in heater 9, and is passed through line 10 into reactor 11. Although indicated in the drawing as passing down flow through the reaction zone, it is understood that the reactants may pass in upward flow or radial flow, and may contact the catalyst as in a moving, or fluidized, catalyst-bed design. Whether effecting catalytic reforming, isomerization, or hydrodealkylation, reactor 11 will contain a catalyst comprising a platinumgroup metallic component, the precise composition of which will be dependent upon the reaction or reactions being effected. The total product efiiuent is removed from reactor 11 via line 12, and is passed into separating means 13. The total product effluent is separated to produce a gaseous phase rich in hydrogen, and containing some light parafiinic and olefinic hydrocarbons. The gaseous phase is indicated as leaving separator 13 via line 15, and entering compressor 22, the latter being employed to maintain the desired operating pressure upon reactor 11. The hydrogenrich recycle gas stream is then discharged from compressor 22 through line 23 to combine with the naphtha charge stock in line 8, prior to being raised to the desired operating temperature in heater 9. At least a portion of the gaseous phase is withdrawn through control valve 16, in line 17, employed for the purpose of pressure control. The normally liquid hydrocarbon phase, containing light parafiinic and olefinic hydrocarbons and butanes, is withdrawn from separator 13 through line 14 into stabilizer 18. In catalytic reforming processes, the stabilizer is employed primarily for the purpose of controlling the vapor pressure of the stabilized reformate product, through the removal of light paraffinic and olefinic hydrocarbons, and at least a portion of the butanes. The light paraffinic and olefinic hydrocarbons are withdrawn from stabilizer 18 through line 19, the stabilized reformate product being removed via line 20. At least a portion of the stabilized reformate product is recycled through line 20 to combine with the total reaction zone effluent in line 12, prior to the introduction of the latter into separator 13. The amount of stabilized reformate continuing as recycle through line 20, is sufficient to yield a recycle ratio, with respect to the naphtha charge stock entering reactor 11 through line 10, within the range of from about 0.5:1 to about 10:1. That quantity of stabilized reformate product, not required by the present invention as liquid recycle, is withdrawn to storage via line 21. Various modifications may be made to the simplified flow pattern illustrated in FIGURE 1. It is not intended that such modifications remove the resulting flow from the broad scope of the present invention. An essential feature is the recycle of stabilized reformate product to combine with the total reaction zone efliuent, whereby there is effected a significantly substantial decrease in the quantity of light paraffinic and olefinic hydrocarbons contained in the hydrogen-rich recycle gas phase leaving separator 13 via line 15. As previously described, the overall effect is to decrease the quantity of coke and other heavy hydrocarbonaceous material which becomes deposited upon the catalyst disposed in reactor 11.

Referring now to FIGURE 2 which illustrates a simplified flow diagram of a hydrodealkylation process. In this process a feed stock comprising alkylaromatic hydrocarbons is introduced into the system by means of line 31 and passes through line 32 into heater 33 whereby the feed is heatedto the desired operating temperature. The feed then passes through line 34 to reactor 35 which is maintained at the proper operating conditions of temperature and pressure and which in the preferred embodiment of the invention contains a hydrodealkylation catalyst of the type hereinafter set forth in greater detail and an excess of hydrogen. The reactor effluent is withdrawn from the bottom of reactor 35 through line 36 where it passes to a high pressure separator or flash drum 37. This high pressure separator or flash drum may be maintained at a pressure in the range of from about 500 to about 600 pounds per square inch. In this separator the effluent is separated into a hydrogen-rich gaseous phase and a liquid hydrocarbon phase which also contains normally gaseous hydrocarbons. The hydrogen-rich gaseous phase is withdrawn overhead from separator 37 through line 38 to compressor 39 wherein the gas is compressed and passed through line 40 where it is admixed with the alkylaromatic feed in line 32. In addition, it is also contemplated that make-up hydrogen may also be added to this system in line 40 through means not shown in the drawing. The liquid hydrocarbon phase is withdrawn as bottoms from high pressure separator 37 through line 41 and charged to low pressure separator 42. This low pressure separator may be maintained at atmospheric pressure if so desired. In low pressure separator 42 the light, normally gaseous, hydrocarbons are flashed off through line 43 to gas absorber 44, the lighter hydrocarbons being passed out through line 45 for utilization as fuel while the relatively heavier hydrocarbons are absorbed in a gas absorber oil entering gas absorber 44 through line 46 and thence out through line 47 to a stripper. The dealkylated aromatic hydrocarbons are withdrawn from low pressure separator 42 through line 48. A portion of these stabilized bottoms pass through line 49 and are recycled to line 36 in such a volume so that the recycle ratio of stabilized liquid hydrocarbon fraction from low pressure separator 42 to the alkylaromatic feed is in a ratio of from about 20:1 to about 50:1 or more. The other portion of the liquid hydrocarbon phase from low pressure separator 42 passes through line 50 to clay treating towers 51 and 52 through

lines

53 and 54 provided with valves 55 and 56, respectively. In the clay treating towers the aromatic compound is treated to remove impurities which may be present. From clay treating towers 51 and 52 the purified effiuent passes through

lines

57 and 58 provided with valves 59 and 60, respectively, to line 61. From line 61 the effluent passes to a benzene column or separator 62 where the unreacted alkylaromatics are separated from the desired aromatic compounds such as benzene. The overhead from benzene column or separator 62 is withdrawn through line 63 and passed back to low pressure separator 42, said overhead containing a small portion of light hydrocarbons. The desired aromatic compound such as benzene is withdrawn from the column through line 64 to storage while the bottoms from the column comprising unreacted alkylaromatic hydrocarbon and heavier boiling materials are withdrawn through line 65 and passed to a second separator or alkylaromatic column 66. In this column fractionation again occurs, the bottoms being withdrawn through line 67 while unreacted alkylaromatic compound is withdrawn through line 68 and recycled to line 31 where it is admixed with fresh alkylaromatic compound to form a portion of the feed.

While one modification of the process is illustrated by the drawing it is also contemplated within the scope of this invention that another separator or flash drum may be utilized. In the event that a third separator is used the system may be designated as containing a high pressure separator or flash drum in which the pressure is maintained in a range of from about 500 to about 600 p.s.i.g., an intermediate pressure separator in which the pressure is maintained in a range of from about to about p.s.i.g. and a low pressure separator in which atmospheric pressure is maintained. The gases or gaseous phases resulting from the flashing in the intermediate pressure separator and the low pressure separator are combined and passed to the gas absorber, said gases being compressed if necessary before entrance into the aforesaid absorber. The liquid hydrocarbon phase is withdrawn from the high pressure separator and passed to the intermediate pressure separator wherein the aforesaid light hydrocarbon gases are withdrawn as overhead while the liquid hydrocarbon phase passes to the low pressure separator. The remainder of the system is identical to that hereinbefore described, a portion of the liquid hydrocarbon phase being recycled while another portion of said liquid hydrocarbon phase is purified and the desired product recovered.

It is also contemplated that various modifications may be made to the simplified flow scheme which is illustrated in FIGURE 2. However, it is not intended that any such modifications remove the resulting flow from the broad scope of the present invention. As was hereinbefore set forth, an essential feature of the present invention is the recycle of a portion of the stabilized liquid fraction to combine with the total reaction zone eflluent, thereby effecting a significant and substantial decrease in the quantity of light paraffinic hydrocarbons which would ordinarily be contained in the hydrogen-rich recycle gas leaving separator 37 via line 38. The overall effect of this enrichment of the hydrogen recycle gas is to decrease the quantity of coke and other heavy hydrocarbonaceous material which would deposit on the catalyst in reactor 35.

Although one of the processes of the present invention, namely reforming, is specifically directed to those catalytic composites containing platinum, hydrocarbon conversion processes which utilize other platinum-group metals such as iridium, palladium, rhodium, ruthenium, osmium instead of or in addition to the platinum will be benefited. Still other metals can be utilized per se with a carrier material such as alumina, composited with the platinumgroup metallic component, and carrier material the latter being a suitable refractory inorganic oxide of the type hereinbefore set forth, and subsequently employed therewith as components of the catalyst. Such other metals include cesium, vanadium, chromium, tungsten, sodium and other alkali metals, silver, rhenium, other metals of Groups VI and VIII of the Periodic Table, and mixtures of two or more, etc. The utilization of such other metals, Whether existing in the elemental state composited on a carrier material, or in combination such as the halide, oxide, sulfide, nitrate, etc, is dependent upon the particular situation in which the catalyst is employed. It is understood that the benefits afforded a catalyst containing different metallic components are not equivalent, and that the effect of employing the method of the present invention to the benefit of those catalytic composites containing at least one metallic component from the platinum-group, are not necessarily the same effects observed in regard to some other metallic component, or mixtures of metallic components.

In the interest of simplicity, the following description of one of the catalytic composites will be limited to platinum-containing catalysts. It is understood that the various aspects discussed are equally Well adaptable to other metals of the platinum-group of the Periodic Table. Generally, the amount of the platinum component composited with the catalyst is small as compared to the quantities of the other components combined therewith. Calculated as the element, platinum will generally be present in an amount of from about 0.01% to about 10.0% by weight. Such conversion catalysts are often manufactured to contain halogen selected from the group of chlorine and/or fluorine which are thought to exist therein in some combined form and to provide an acidacting function therefor. The halogen, whether chlorine, fluorine or mixtures thereof, is composited with the catalyst in an amount of from about 0.1% to about 8.0% by weight thereof. The addition of these components to the catalytic composite may be effected in any suitable manner which serves to accomplish the desired result. Thus chlorine and/ or fluorine may be added in the form of an acid such as an aqueous solution of hydrogen chloride, hydrogen fluoride, or mixtures thereof. Volatile salts, such as ammonium chloride and/or ammonium fluoride, also afford convenient means of incorporating the chlorine and fluorine into the catalytic composite. The halogen is believed to be combined with one or more of the other components of the catalyst, and is therefore, generally referred to ascombined halogen; the concentrations thereof are, however, computed on the basis of the element.

Whatever the catalytically active components, they are generally composited with a highly refractory inorganic oxide such as alumina, silica, zirconia, magnesia, boria, thoria, titania, strontia, etc., and mixtures of two or more including silica-alumina, alumina-boria, silica-thoria, silica-zirconia-alumina, etc. It is understood that the refractory inorganic oxides hereinabove set forth are in tended to be illustrative rather than limiting upon the method of the present invention. It is further understood that these refractory inorganic oxides may be manufactured by any suitable method including separate, successive, or coprecipitation methods of manufacture, or they may be naturally-occurring substances such as ores, sands, clays or earths which may or may not be purified or activated with special treatment.

The particular method employed for the manufacture of the alumina and/or any of the other refractory inorganic oxides hereinabove set forth, is not considered an essential feature of the present invention. The alumina may be prepared by adding a suitable alkaline reagent such as ammonium hydroxide to a salt of aluminum, such 'as aluminum chloride, aluminum sulfate, aluminum nitrate, etc. Upon drying, and subsequent calcination at elevated temperatures, the resulting aluminum hydroxide is converted to alumina. The alumina may take the form of any desired shape such as spheres, pills, extrudetes, powder, granules, cakes, etc. The preferred form of alumina is the sphere and alumina spheres may be continuously manufactured by the well-known oil-drop method.

This method is described in detail in US. Patent No. 2,620,314, issued to James Hoekstra. Where utilized, an alumina-silica carrier material may be manufactured by commingling an aqueous solution of a water-soluble aluminum salt with an acidified solution of water glass. An alumina-silica hydrogel is precipitated from the resultant solution via the addition thereto of a suitable alkaline reagent such as ammonium hydroxide. Following a washing procedure, to remove sodium ions the precipitate is dried, calcined, and subsequently formed into any of the desired shapes hereinbefore described. Although the addition of halogen is generally accomplished through the utilization of an acid or volatile salt, such halogen may be incorporated into the carrier material during the preparation of the latter. Where the refractory inorganic oxide is prepared from a halide-containing hydrosol, the method of preparation affords a convenient manner of compositing halogen while at the same time manufacturmg the refractory inorganic oxide carrier material. In still another method of manufacture, the halogen may be composited with the refractory oxide during the impregnation thereof with the catalytically active metallic components.

Although the precise means by which the platinum component or other platinum-group metal is incorporated with the other components of the catalyst is not known it is believed that the platinum exists in some physical association or as a chemical complex therewith. Thus, the platinum-group metal may be present as such, or as a chemical compound or in physical association with the alumina or with the other catalytically active metallic components, or in some combination with both. Similarly, where other metallic components from the platinum-group are employed in combination with the platinum, they may be present as such or as a chemical compound or in physical association with either the refractory inorganic oxide or the platinum or both. The method of preparing the catalyst of the present invention is facilitated through the utilization of water-soluble compounds of the platinum-group metals and composited with the carrier material via impregnating techniques. Thus, where the platinum-group metal is platinum, it may be added to the carrier material by commingling the latter with an aqueous solution of chloroplatinic acid. Other water-soluble compounds of platinum may be utilized within the impregnating solution and include ammonium chloroplatinate, platinous chloride, platinic chloride, dinitrodiamino platinum, etc. Following the impregnating technique the carrier material is dried and subjected to a high-temperature calcination procedure.

Another particular catalyst composition which may be utilized in the process of this invention comprises a chromia-alumina composite in which an alumina such as gamma-alumina is impregnated with chromic acid, dried and oxidized at a relatively high temperature of about 1300 F. The finished catalyst will contain from about 15% to about 20% chromia and will be used as a hydrodealkylation catalyst.

Briefly, one embodiment of the present invention comprises passing a naphtha charge stock, following fractionation and other pretreatment to provide the desired boiling range into a reaction zone containing a catalyst comprising from about 0.01% to about 10.0% by weight of platinum, from about 011% to about 8.0% by weight of halogen and alumina in the presence of hydrogen being recycled at a rate of from about 2 to about 20 mols per mole of liquid hydrocarbon charge. The reaction zone is maintained at a temperature within the range of from about 800 F. to about 1050 F. and under an imposed pressure within the range of from about 300 pounds per square inch to about 900 pounds per square inch. The liquid hourly space velocity defined as volumes of liquid hydrocarbon charge per volume of catalyst disposed within the reaction zone will generally lie within the range of from about 0.5 to about 10.0. Lower space velocities are preferred, usually in excess of about 0.5 having an upper limit however, of about 6.0. The resulting oatalytically reformed product is passed in its entirety into a separating zone for the purpose of removing a hydrogen-rich gaseous phase which is recycled to combine with the liquid hydrocarbon charge. The normally liquid hydrocarbons, removed from the separating zone are subjected to stabilization for the purpose of removing light paraffinic and olefinic hydrocarbons. The stabilization of the liquid hydrocarbons may be effected by any means known in the art such as, for example, by passing the liquid to a fractionation zone or to a flash drum separator. The resultant stabilized reformate product is recycled at least in part to combine with the total reaction zone effluent passing into the separating means. The amount of stabilized reformate recycle is calculated on the basis of the total liquid hydrocarbon charge to the reaction zone and is within the range of from about 0.5:1 to about 1.

A similar procedure is employed when effecting the isomerization of substantially pure low molecular weight hydrocarbons or cycloparaffins. The catalytic composite for the isomerization reactions comprises a refractory inorganic oxide, platinum and combine halogen from the group of chlorine and fluorine. The combined halogen is preferred to be fluorine and is present in an amount of from about 2.0% to about 5.0% by weight. As hereinbefore set forth, alumina is utilized as the carrier material for the other catalytic components. The operating conditions to be employed within the isomerization zone will depend upon the particular compound being subjected thereto, and will generally be a temperature within the range of about 500 F. to about 900 F., although temperatures within the more limited range of from about 525 F. to about 800 F. are usually preferred. The pressure utilized will range from about 100 pounds per square inch to about 1000 pounds per square inch. The process of the present invention, utilizing the above described catalyst is particularly adapted for a so-called fixed bed type process. In such a process, the compound or compounds to be isomerized are passed in upward, downward or radial flow over the catalyst along with the requisite quantity of hydrogen. The reaction products are then separated from the hydrogen which is recycled, the normally liquid hydrocarbons being subjected to fractionation and separation from which at least a portion of the final product is recycled to combine with the total reaction zone effluent. In processes for the isomerization of paraffins and cycloparaffins the liquid hourly space velocity will be maintained within the range of 10.0, and preferably within the range of from about 2.0 to about 5.0.

In yet another embodiment of the invention the process is effected by passing a charge or feed stock comprising alkylaromatic hydrocarbons such as toluene, the xylenes, methyl naphthalene, etc., to a reaction zone wherein the aforesaid alkylaromatic compound is contacted with hydro gen and, if so desired, a hydrodealkylation catalyst such as a chromia-alumina mixture of the type hereinbefore set forth, said hydrogen being recycled at a rate of from about 2 to about moles per mole of liquid hydrocarbon charge. The reaction zone wherein the hydrodealkylation occurs is maintained at a temperature in the range of from about 1000 to about 1500 F. and at a pressure in the range of from about 500 to about 600 p.s.i.g. The feed stock is charged to the reaction zone at a liquid hourly space velocity (the volume of feed per volume of catalyst in the reaction zone per hour) in a range of from about 0.1 to about 20 and at a preferred range of from about 0.5 to about 5. The resultant reactor effluent is withdrawn from the reaction zone and passed to a high pressure separator or flash drum which is maintained at a pressure in the range of from about 500 to about 600 p.s.i.g. In this separator the effluent is separated into a hydrogen-rich gas phase and a liquid hydrocarbon phase,

from about 0.1 to about the former being then recycled back to the reaction zone at a rate hereinbefore set forth. The latter is Withdrawn as bottoms and passed to a second separator. This second separator may be maintained at an intermediate pressure such as a pressure within the range of from about 100 to about 150 p.s.i.g. or if so desired this second separator may be maintained at atmospheric pressure. In the second separator the light hydrocarbons are flashed off and passed in a gaseous state through a compressor if necessary to a gas absorber wherein they are finally separated from any aromatic compounds which may have been flashed off along with the light hydrocarbons and utilized for fuel. The bottoms comprising unreacted alkylaromatic compound and dealkylated aromatic compound are withdrawn from the separator. In the event that the second separator was maintained at an intermediate pressure within the range of from about 100 to about 150 p.s.i.g. the liquid hydrocarbons are then passed to a third separator which is maintained at atmospheric pressure. If this last named separator is required any light hydrocarbons such as methane and ethane which are still present in the liquid are flashed off and passed to an absorber while the liquid hydrocarbon portion is withdrawn. The liquid hydrocarbon after being withdrawn from the separator is divided into two portions, a major portion of which is recycled and admixed with the reactor efiluent prior to the separation of said etfluent to a gaseous phase and a liquid phase. By recycling a major portion of the liquid hydrocarbon phase at a rate so that the recycle ratio of liquid hydrocarbon to fresh feed is in a range of from about 20:1 to about :1 or more any light hydrocarbons which are present in the reactor efiluent will be preferentially absorbed by the aforesaid liquid hydrocarbon and the hydrogen-rich gaseous phase which separates in the high pressure flash drum will be of a relatively pure nature, that is, the hydrogen purity as hereinbefore defined will be above The other portion of the liquid hydrocarbon phase which has been withdrawn from the last separator or flash drum is purified and the desired product comprising the dealkylated aromatic hydrocarbon is recovered by conventional means such as, by fractional distillation from any unreacted alkylaromatic compounds and high boiling bottoms.

As is readily apparent from the above description many different types of hydrocarbons can be subjected to conversion processes when utilizing a hydrogen feed which possesses a relatively high degree of purity thereby allowing the catalyst, if one is utilized, to be used in a more effective manner with a minimum amount of catalyst deactivation due to coking, etc., of the catalyst. Feed stocks which may be used in the various processes hereinbefore described include paraffins such as the butanes, pentanes, etc., aromatic compounds such as benzene, toluene the xylenes, naphthalene, methyl naphthalene, etc., light oils, heavy oils, gasoline and naphtha fractions, high boiling materials which have a boiling range above the gasoline boiling range (those hydrocarbons having an end boiling point in a range of from about 400 to about 450 P.) such as middle distillate oil having a boiling point range of from about 450 to about 650 F. and high boiling materials having a boiling point range in excess of about 650 to about 700 F.

The following examples are given to further illustrate the process of the present invention, and to indicate the benefits afforded through the utilization thereof. It is not intended that the present invention be limited, beyond the scope and spirit of the appended claims to the conditions, reagents or concentrations employed within the examples.

EXAMPLE I A catalyst was prepared utilizing ;-inch alumina spheres manufactured in accordance with US Patent No. 2,620,314, issued to James Hoekstra and containing 0.35% by weight of chlorine. The spheres were intimately commingled with a suflicient quantity of an aqueous solution of hydrogen fluoride to composite therewith 0.35% by weight of fluorine. The halogen-containing spheres were then dried and subjected to a calcination procedure at a temperature of about 900 F. The calcined spheres were impregnated with an aqueous solution of chloroplatinic acid in an amount suflicient to yield a final catalyst containing 0.75% by weight of platinum calculated as the element thereof. The impregnated spheres were dried at a temperature of about 300 F., and thereafter calcined in an atmosphere of air at a temperature of about 900 F. This catalyst was placed as a fixed bed in a bench-scale reaction zone maintained under an imposed pressure of about 500 pounds per square inch. Kuwait heavy naphtha, having the properties indicated in Table I, was processed at a liquid hourly space velocity of about 2.0, a recycle gas ratio of 7.0 based upon the quantity of hydrogen within the recycle gas stream and at a temperature necessary to result in a final product, following debutanization having an F-l clear octane rating of 100.0. Following the determination of the temperature required to achieve a debutanized product of this quality, a second operation Was effected at the same conditions of operation except that the recycle gas ratio was increased to 12.0.

TABLE I.--CIIARGE STOCK AND PRODUCT INSPECTIONS Charge Product Gravity, API at 60 F 57. 9 44. 6 ASTM D-86 Distillation,

IBP a. 210 121 5% 229 141 236 152 255 200 275 250 295 281 320 314 328 330 353 398 Octane Ratings:

F-l Clear 34. 4 100. 3 F-l +3 cc. TEL 63.3 105.1 Hydrtocarbon Type Analysis, vol. percen Paraffins .c 70 Naphthenes 18 i Olofins 0.5 Aromatics 12 65.

Frequent samples of the debutanized liquid product were taken for the purpose of determining the F-1 clear octane rating, whereby the temperature of the operation was adjusted accordingly. The operation was ended at a catalyst life of about 3.5 barrels per pound, and the catalyst was removed and analyzed for the quantity of carbon deposition.

A third operation was elfected under the same conditions, with one exception. The debutanized reformate product was recycled to combine with the total effluent from the reaction zone in an amount to yield a reformate to liquid feed recycle ratio of 4.0. Frequent samples of the debutanized product were taken to determine the F-1 clear octane rating and the temperature again adjusted to maintain the octane rating at 100.0. This operation was terminated at about 5.0 barrels per pound of catalyst life with the catalyst being removed for the purpose of analyzing the same for the quantity of carbon deposited thereupon. The results of these analyses are given in the following ,Table II, along with various liquid recycle process considerations.

TABLE II.-RECYCLE PROCESS CONSIDERATIONS Reformate/Oharge Recycle Ratio Catalyst Life, bbl./1b Carbon Deposition, wt. percel Recycle Gas Ratio, Moles Hydrogen Concenctration Mole Percent. I-IQ/Light Paraffin Mole Ratio Temperature Increase, FJbbL/lb a temperature increase of 7 F. for each barrel per pound of catalyst life. During the catalyst life of 5.0 barrels per pound with liquid recycle operation there was no increase in reaction zone temperature in order to maintain the debutanized reformate product at 100.0 F-l clear octane rating. In addition, the catalyst from the operation without liquid recycle had deposited thereupon about 3.5% by weight of carbon whereas the catalyst from the liquid recycle operation was contaminated with only 0.6% by weight of carbon. A typical analysis of the debutanized reformate product resulting from the liquid recycle operation is given in Table I to facilitate a c0mparison with the original Kuwait heavy naphtha charge stock. These data indicate that the method of recycling at least a portion of the stabilized liquid product to combine with the total reaction zone efiluent, results in a longer catalyst life due to a decrease in carbon deposition and hence, a more economically favorable process.

EXAMPLE II This example is given for the purpose of illustrating the stability of the operation employing recycle of the stabilized reformate product as compared to the operation without such recycle. The catalyst employed in this example was identical to that utilized in Example I. The operating conditions were 300 pounds per square inch and 3.0 liquid hourly space velocity and the charge stock was Midcontinent heavy naphtha, 52.6 API, 23847 8 F. boiling range. As before, the temperature of the catalyst within the reaction zone was adjusted for the purpose of maintaining the octane rating of the debutanized liquid product at a level of 100.0 F-l clear. Referring now to FIGURE 3, which indicates the stability of the operation with respect to the volumetric yield of debutanized liquid product it is noted that the operation with liquid recycle as represented by line 102, drawn through points C, D, E and F, is significantly more stable than the operation effected without liquid recycle as represented by line 101 drawn through points A and B. It should be noted that these lines will intersect at a catalyst life of about 4.5 barrels per pound indicating that continued operation without liquid recycle will result in the economic loss of debutanized products thereafter. Similarly, with reference to accompanying FIGURE 4 illustrating a comparison between the reactor temperature differential of the operation without liquid recycle (line 10 3, drawn through points G, H, I, J, K, and L), and the operation with liquid recycle (represented by line 104 drawn through points M, N and P), it should be noted that at a catalyst life of approximately 4.5 barrels per pound, the operation being eiTected without liquid recycle will require a reaction zone temperature approximately 23 F. greater than that required while recycling a portion of the stabilized reformate product to combine with the total eflluent from the reaction zone. These figures clearly indicate the benefits to be afforded in regard to the stability of operation and particularly in regard to the severity thereof as indicated by the temperature differential required to maintain a steady-state operation at an octane rating of 100.0 F-l clear. Of greater significance, referring to FIGURES 3 and 4, is the fact that the operation Without liquid recycle was carried out with a recycle gas ratio of 11.0, whereas the operation with liquid recycle employed a recycle gas ratio of only 6.0. Such a significant decrease in hydrogen requirement is totally unexpected in catalytic reforming processes.

EXAMPLE III In this example, a feed of fresh toluene comprising 197.1 moles per hour is charged to a reactor containing a chromia-alumina catalyst and maintained at a pressure of 550 p.s.i.g. and an inlet temperature of 1200 F. The fresh feed is combined with 2 9.6 moles per hour of recycle toluene before entry into said reactor. A stream of hydrogen containing 1737.8 moles of hydrogen, 893.2

moles of methane, 54.5 moles of ethane, 17.6 moles of benzene and 1.1 moles of toluene per hour is admixed with the combined feed. In addition, a make-up hydrogen stream containing 315.7 moles of hydrogen, 19.3 moles of methane, 6.0 moles of ethane, and 1.0 moles of propane per hour is admixed with the recycle hydrogen. In addition a stream containing 0.9 moles of hydrogen, 3.0 moles of methane, 1.0 moles of ethane, 100.2 moles of benzene and 16.2 moles of toluene per hour is charged to the bottom of the reactor, said stream acting as a quench for the reaction mixture, thereby serving to control the temperature of the reaction. The reactor effluent is withdrawn from the reactor and passed to a high pressure separator maintained at a range of from about 500 to about 600 p.s.i.g., said reactor efliuent containing 1802.2 moles of hydrogen, 1110.5 moles of methane, 129.7 moles of ethane, 7175.7 moles of benzene, 1155.2 moles of toluene and 81.9 moles of bottoms per hour. The hydrogen is flashed ofl from this separator and the stream is recycled to the reactor, said stream having a hydrogen purity of about 64% and containing 1737.8 moles of hydrogen, 893.2 moles of methane, 54.5 moles of ethane, 17.6 moles of benzene and 1.1 moles of toluene per hour. The liquid bottoms from the high pressure separator are withdrawn and passed to an intermediate pressure separator which is maintained at a pressure in the range of from about 100 to about 150 p.s.i.g., said liquid bottoms containing 63.4 moles of hydrogen, 214.1 moles of methane, 74.1 moles of ethane, 7049.7 moles of benzene, 1136.6 moles of toluene, and 80.6 moles of high boiling material per hour. The reaction mixture is flashed in this separator and the gases are passed overhead to a flash gas absorber, said gas stream containing 55.5 moles of hydrogen, 106.5 moles of methane, 10.1 moles of ethane, 3.0 moles of benzene and 0.2 mole of toluene per hour. The liquid bottoms from this intermediate pressure separator containing 7.9 moles of hydrogen, 107 .6 moles of methane, 64.0 moles of ethane, 7046.7 moles of benzene, 1136.4 moles of toluene and 80.6 moles of high boiling materials per hour are with-drawn and passed to a low pressure separator which is maintained at atmospheric pressure. In this flash drum or separator the gases are also withdrawn as flash gases to a flash gas absorber, said gas stream containing 7.8 moles of hydrogen, 97.6 moles of methane, 39.5 moles of ethane, 32.5 moles of benzene and 1.8 moles of toluene per hour. The liquid bottoms are withdrawn from the atmospheric separator, said bottoms containing 0.1 mole of hydrogen, 10.5 moles of methane, 25.9 moles of ethane, 7050.6 moles of benzene, 1136.6 moles of toluene and 80.6 moles of high boiling bottoms per hour. This stream is split, a portion of the stream containing 0.3 mole of methane, 0.7 mole of ethane, 183.6 moles of benzene, 29.6 moles of toluene and 2.1 moles of high boiling bottoms per hour is passed to clay treating towers, the remainder of the stream containing 0.1 mole of hydrogen, 10.2 moles of methane, 25.2 moles of ethane, 6887.0 moles of benzene, 1107.0 moles of toluene and 78.5 moles of high boiling bottoms per hour being recycled to join the reactor effluent prior to entry into the high pressure separator. The flash gases from the intermediate pressure separator and the low pressure separator are combined and are passed to a flash gas absorber wherein the light hydrocarbons comprising 63.3 moles of hydrogen, 203.9 moles of methane and 48.9 moles of ethane are recovered and utilized as fuel. After passing through clay treating towers the liquid stream containing 0.3 mole of methane, 0.7 mole of ethane, 183.6 moles of benzene, 2916 moles of toluene and 2.1 moles of high boiling bottoms per hour are passed to a benzene column fractionator wherein fractional distillation takes place. The gaseous portion of the mixture along with a very small portion of benzene, said gaseous mixture containing 0.3 mole of methane, 0.7 mole of ethane and 0.9 mole of benzene per hour is recycled back to the low Pressuffi p rat r which is maintained at atmospheric pressure. A side cut containing 182.7 moles of benzene per hour is withdrawn and passed to storage. The bottoms containing 29.6 moles of toluene and 2.1 moles of high boiling bottoms per hour is passed to a toluene column fractionator wherein the unreacted toluene is fractionated and recycled to form a portion of the feed stock while the bottoms are withdrawn.

The foregoing examples and specification clearly indicate the process of the present invention and the benefits to be afforded through the utilization of the internal recycle of at least a portion of the stabilized liquid product to combine with the total reaction zone effiuent. The operation thus eflected results in a significantly extended catalyst life, during which the operation possesses a high degree of stability.

We claim as our invention:

1. A conversion process which comprises:

(a) catalytically converting hydrocarbons in a reaction zone in the presence of hydrogen and a conversion catalyst which undergoes loss of activity by carbon deposition thereon,

(c) separating said eflfluent into a hydrogen-rich gaseous phase and a liquid hydrocarbon phase,

(d) recycling at least a portion of the gaseous phase to the reaction zone,

(e) separating light hydrocarbons from said liquid hydrocarbon phase,

(f) com mingling a portion of the remaining liquid hydrocarbon phase with the total reaction zone efiiuent prior to the separation of said efiluent into said phases, in an amount to yield said hydrogen-rich gaseous phase enriched to at least 60 mol percent hydrogen, and

2. A conversion process which comprises (a) catalytically converting hydrocarbons in a reaction zone in the presence of hydrogen and a conversion catalyst which undergoes loss of activity by carbon deposition thereon,

(b) removing from the reaction zone the resultant reaction zone elliuent comprising normally liquid hydrocarbons, normally gaseous hydrocarbons and hydrogen,

(c) separating said efiluent into a hydrogen-rich gaseous phase and a liquid hydrocarbon phase,

(d) recycling at least a portion of the gaseous phase to the reaction zone,

(e) separating light hydrocarbons from said liquid hydrocarbon phase,

(f) commingling a portion of the remaining hydrocarbon phase with the total reaction zone efiluent prior to the separation of said efiiuent into said phases in an amount to yield a recycle ratio of from about 0.521 to about 50.0:1 with respect to said hydrocarbon charge, and separating into said phases at conditions of temperature and pressure to yield said hydrogenrich gaseous phase enriched to at least 60 mol percent hydrogen, and i (g) recovering another portion of the remaining liquid hydrocarbon phase as the product of the process.

3. A process which comprises (a) hydroealkylating an alkylaromatic hydrocarbon in a reaction zone in the presence of hydrogen and a dealkylation catalyst,

(b) removing from the reaction zone the resultant reaction product efiiuent comprising normally liquid hydrocarbons, normally gaseous hydrocarbons and hydrogen,

(c) separating said eflluent into a hydrogen-rich gas and a liquid hydrocarbon phase containing normally gaseous hydrocarbons,

(d) recycling at least a portion of said hydrogen-rich gas to the reaction zone,

(e) separating light hydrocarbons from said liquid hydrocarbon phase,

(f) commingling a portion of the remaining liquid phase with the total reaction zone efiluent prior to the aforesaid separation thereof in an amount to yield a recycle ratio With respect to the alkylaromatic hydrocarbon charge in the range of from about 25:1 to about 50:1, and

(g) recovering another portion of the remaining liquid phase as a product of the process.

4. A process which comprises (a) hydrodealkylating an alkylaromatic hydrocarbon in a reaction zone in the presence of an excess of hydrogen and a dealkylation catalyst at a temperature in the range of from about 1000 to about 1500 F., and at a pressure in the range of from about 500 to about 600 pounds per square inch,

(b) removing from the reaction zone the resultant reaction product efiiuent comprising a liquid hydrocarbon phase, a normally gaseous hydrocarbon phase and hydrogen,

() separating said efiiuent into a hydrogen-rich a liquid hydrocarbon phase,

(d) recycling said hydrogen-rich gas through said reaction zone,

(e) separating the liquid hydrocarbon phase into a gasegas and 18 ous fraction containing light paraffinic hydrocarbons and a stabilized liquid fraction,

(f) commingling a portion of said stabilized liquid fraction With the total reaction zone effiuent prior to separation of the latter into said gaseous phase and said liquid phase in an amount to yield a recycle ratio with respect to the alkylaromatic hydrocarbon charge in the range of from about 25:1 to about :1, and

5. The process of claim 4 further characterized in that said alkylaromatic hydrocarbon comprises toluene.

6. The process of claim 4 further characterized in that said alkylaromatic hydrocarbon comprises methyl-naphthalene.

7. The process of claim 4 further characterized in that said catalyst comprises chr-omia composited on alumina.

References Cited UNITED STATES PATENTS 2,358,912 9/1944 Dimmig 208-400 2,695,264 11/1954 Taft et al. 208100 2,703,308 3/1955 Oblad et al 208- 2,776,247 1/1957 Anhorn et al 208136 DELBERT E. GANTZ, Primary Examiner. H. LEVINE. G. E. SCHMITKONS, Assistant Examiners.

Claims

1. A CONVERSION PROCESS WHICH COMPRISES: (A) CATALYTICALLY CONVERTING HYDROCARBONS IN A REACTION ZONE IN THE PRESENCE OF HYDROGEN AND A CONVERSION CATALYST WHICH UNDERGOES LOSS OF ACTIVITY BY CARBON DEPOSITION THEREON, (B) REMOVING FROM THE REACTION ZONE THE RESULTANT REACTION ZONE EFFLUENT COMPRISING NORMALLY LIQUID HYDROCARBONS, NORMALLY GASEOUS HYDROCARBONS AND HYDROGEN. (C) SEPARATING SAID EFFLUENT INTO A HYDROGEN-RICH GASEOUS PHASE AND A LIQUID HYDROCARBON PHASE, (D) RECYCLING AT LEAST A PORTION OF THE GASEOUS PHASE TO THE REACTING ZONE, (E) SEPARATING LIGHT HYDROCARBONS FROM SAID LIQUID HYDROCARBON PHASE, (F) COMMINGLING A PORTION OF THE REMAINING LIQUID HYDROCARBON PHASE WITH THE TOTAL REACTION ZONE EFFLUENT PRIOR TO THE SEPARATION OF SAID EFFLUENT INTO SAID PHASES, IN AN AMOUNT TO YIELD SAID HYDROGEN-RICH GASEOUS PHASE ENRICHED TO AT LEAST 60 MOL PERCENT HYDROGEN, AND (G) RECOVERING ANOTHER PORTION OF THE REMAINING LIQUID HYDROCARBON PHASE AS THE PRODUCT OF THE PROCESS.

3. A PROCESS WHICH COMPRISES (A) HYDROEALKYLATING AN ALKYLAROMATIC HYDROCARBON IN A REACTION ZONE IN THE PRESENCE OF HYDROGEN AND A DEALKYLATION CATALYST, (B) REMOVING FROM THE REACTION ZONE THE RESULTANT REACTION PRODUCT EFFLUENT COMPRISING NORMALLY LIQUID BY DROCARBONS, NORMALLY GASEOUS HYDROCARBONS AND HYDROGEN, (C) SEPARATING SAID EFFLUENT INTO A HYDROGEN-RICH GAS AND A LIQUID HYDROCARBON PHASE CONTAINING NORMALLY GASEOUS HYDROCARBONS, (D) RECYCLING AT LEAST A PORTION OF SAID HYDROGEN-RICH GAS TO THE REACTION ZONE, (E) SEPARATING LIGHT HYDROCARBONS FROM SAID LIQUID HYDROCARBON PHASE, (F) COMMINGLING A PORTION OF THE REMAINING LIQUID PHASE WITH THE TOTAL REACTION ZONE EFFLUENT PRIOR TO THE AFORESAID SEPARATION THEREOF IN AN AMOUNT TO YIELD A RECYCLE RATIO WITH RESPECT TO THE ALKYLAROMATIC HYDROCARBON CHARGE IN THE RANGE OF FROM ABOUT 25:1 TO ABOUT 50:1, AND (G) RECOVERING ANOTHER PORTION OF THE REMAINING LIQUID PHASE AS A PRODUCT OF THE PROCESS.