US3853745A

US3853745A - Low temperature-low pressure naphtha reforming process

Info

Publication number: US3853745A
Application number: US00338992A
Authority: US
Inventors: A Welty
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1973-03-07
Filing date: 1973-03-07
Publication date: 1974-12-10
Anticipated expiration: 1991-12-10

Abstract

A hydrocarbon feedstock comprising naphthenes is catalytically reformed using a catalyst which promotes both dehydrogenation and isomerization. Cracking and other undesirable side reactions are substantially avoided by employing a reaction temperature in the range of 600* to 700*F and a hydrogen pressure not exceeding about 4 atmospheres. If the hydrogen partial pressure is about 1 atmosphere or less, satisfactory conversion of the naphthenes to aromatics is obtained without further steps. If the hydrogen partial pressure is between about 1 and about 4 atmospheres, the aromatics are adsorbed on a zeolite or other suitable substance as they are formed, thus shifting the equilibrium and promoting the dehydrogenation and isomerization reactions. The adsorbed aromatics are subsequently desorbed by, for example, heated hydrocarbon vapor. If the adsorption/desorption is used, a dual reactor set-up may be conveniently employed.

Description

[ LOW TEMPERATURE-LOW PRESSURE NAPHTHA REFORMING PROCESS Albert B. Welty, Jr., Westfield, NJ.

[73] Assignee: Exxon Research and Engineering Company, Linden, NJ.

Mar. 7, 1973 [75] Inventor:

[22] Filed:

[21] Appl. No.: 338,992

[52] US. Cl 208/139, 208/137, 208/138, 208/141, 208/310, 260/674 SA [51] Int. Cl Clog 35/06, ClOg 25/00 [58] Field of Search 208/137, 138, 139, 141, 208/310; 260/674 SA [56] References Cited UNITED STATES PATENTS 2,816,939 12/1957 Nozaki 208/138 2,870,083 1/1959 Elliot 208/138 2,967,823 l/l961 Langenbeck et a1. 208/137 2,972,643 2/1961 Kimberlin et a1. l 260/6735 3,125,503 3/1964 Kerr et al 208/15 3,364,137 1/1968 Bercendorf et al...... 208/139 3,372,108 3/1968 Epperly et a1. 208/141 3,562,147 2/1971 Pollitzer et al.... 208/139 3,574,091 4/1971 Hayes 208/138 [451 Dec. 10, 1974 Primary Examiner-Delbert E. Gantz Assistant Examiner-James W. Hellwege Attorney, Agent, or FirmL. A. Proctor [57] ABSTRACT A hydrocarbon feedstock comprising naphthenes is catalytically reformed using a catalyst which promotes both dehydrogenation and isomerization. Cracking and other undesirable side reactions are substantially avoided by employing a reaction temperature in the range of 600 to 700F and a hydrogen pressure not exceeding about 4 atmospheres. If the hydrogen partial pressure is about 1 atmosphere or less, satisfactory conversion of the naphthenes to aromatics is obtained without further steps. If the hydrogen partial pressure is between about 1 and about 4 atmospheres, the aromatics are adsorbed on a zeolite or other suitable substance as they are formed, thus shifting the equilibrium and promoting the dehydrogenation and isomerization reactions. The adsorbed aromatics are subsequently desorbed by, for example, heated hydrocarbon vapor. If the adsorption/desorption is used, a dual reactor set-up may be conveniently employed.

21 Claims, 3 Drawing Figures LOW TEMPERATURE-LOW PRESSURE NAPHTHA REFORMING PROCESS This invention relates to the catalytic conversion of hydrocarbon fractions boiling in the motor fuel range to obtain products of higher octane value. More specifically, this invention relates to an improved process for the catalytic reforming of naphthenes and particularly to a process which avoids undesirable side reactions such as cracking.

Hydroforming is a well known and widely used process for treating hydrocarbon fractions boiling within the motor fuel or naphtha range to upgrade them, primarily by increasing their aromaticity, thus improving their anti-knock characteristics. By hydroforming is ordinarily meant an operation conducted at elevated temperatures and pressures in the presence of solid catalyst particles and hydrogen, whereby the hydrocarbon fraction is increased in aromaticity. This increase in aromaticity arises from the conversion of the cyclohexanes and cyclopentanes, i.e., the naphthenes, as well as of paraffins, to aromatics. Aromatics concentrationalso occurs as a consequence of cracking nonaromatics to gas. The aromatics concentration required varies depending on feedstock, but typically 57 Vol.% aromatics will give about 90 clear Research Octane Number and 70 vol.% about 100. If the feed contains sufficient aromatics plus naphthenes, high octane number can be obtained without paraffin conversion. Hydroforming operations are ordinarily carried out in the presence of hydrogen-rich recycle gas and in the presence ofa suitable reforming catalyst at temperatures ranging from about 750to 1,050F with pressures of format least about 50 pounds per square inch to sometimes as high as 800 pounds per square inch.

A major problem encountered in catalytic hydroforming is the occurrence of cracking, which results in a reduction in the yield of liquid product. Hydrocarbon gaseous products, i.e., methane, ethane, propane and butane which are less valuable than liquid product, result from this cracking side reaction. lmportantly too, hydrogen is consumed when cracking occurs, thus reducing the yield of this valuable product. Therefore, it is desirable to minimize the cracking reaction, particularly where the feedstock to the hydroforming reactionv is especially valuable as in the case of hydrocrackate.

The desirable reactions which occur in the reforming process, listed in order to decreasing reaction rates are as follows:

(1) dehydrogenation of cyclohexanes to aromatics; (2) isomerization of cyclopentanes to cyclohexanes; (3) isomerization of straight chain paraffins to branched paraffins; and (4) dehydrocyclization of paraffins to aromatics. This invention is concerned primarily with reactions (1) and (2). Secondarily, the invention is also concerned with reaction (3). Maximum yield of high octane product will be obtained when these desired reactions are maximized and undesirable cracking is minimized or eliminated.

Accordingly, it is a principal object of the present invention to provide an improved catalytic reforming process which will increase the aromaticity of a hydrocarbon fraction boiling within the motor fuel boiling range but which will not result in any substantial amount of cracking. Other objects of this invention will be apparent from a consideration of the following descriptive material.

U.S. Pat. No. 3,577,474 to Robert L. Jacobson, dated May 4, 1971 discloses the use of a rhenium-platinumalumina catalyst for the production of benzene and toluene from C C, cycloalkanes at 50 to 750 psig. pressure and a temperature of 700 to 1,050F. From the example it can be seen that, although the addition of rhenium to the platinum-alumina catalyst represents an improvement, substantial cracking still occurs. In U.S. Pat. No. 3,669,875 dated June 13, 1972, Charles J. Plank, Pharez G. Waldo and Harry G. Doherty disclose a two stage reforming operation in which the first stage is primarily for effective naphthene dehydrogenation. pressure is to 600 psig. and temperature 800 to 1,050F. At these conditions cracking still occurs. Reference is made also to Catalyst, Volume Vl, Edited by Paul H. Emmett, published by Rheinhold Publishing Corporation, 1958 (Library of Congress Catalog No. 54-6801), pp 567-576, which shows the isomerization of naphthenes at 24.8 atmospheres total pressure over a temperature range of 547 to 734F. inthe presence of hydrogen.

It has been discovered that the desirable reforming reactions, i.e., isomerization of cyclopentanes of cyclohexanes, and dehydrogenation of cyclohexanes to aromatics, can be accomplished with a minimum amount of cracking by employing reaction temperatures of about 600 to 700F. and a hydrogen partial pressure no greater than about 4 atmospheres. The catalyst employed is a dual function catalyst, i.e., one that promotes both dehydrogenation and isomerization. This invention is useful in upgrading feedstocks such as petroleum naphthas, gasoline fractions, hydrocrackates, recycled reformates, and other refinery blends containing naphthenes, to produce high octane motor fuels.

The reforming catalysts useful for this process comprise a porous inorganic support containing catalytic amounts of platinum or other noble metals such as rhodium, palladium or iridium, or combinations of these; they may be promoted by rhenium. Nickel may also be used. When the catalyst is nickel, an acidicsupport is preferred, such as silica-alumina. Generally, the pre-' ferred supports are alumina and silica/alumina. However, other supports, such as kieselguhr, magnesium oxide, and titanium oxide may be employed. When noble metals are used, the metal components on the catalyst constitute from about 0.025 to 2.0 wt.% preferably from 0.1 to 1.0 wt.%, metal on the various supports. When nickel is used, from about 1.0 to 10%, preferably about 5% is used. These catalysts maybe promoted by 0.1 1.5 wt% fluorine or chlorine. Although a platinum-chlorine-alumina is a preferred catalyst, nickel-silica-alumina or similar types may also be used. These catalysts promote both the dehydrogenation and isomerization function.

In order to promote the dehydrogenation and isomerization reactions without substantial cracking, the catalytic reforming process must be carried out at a temperature in the range from about 600 to about 700F., temperatures at which the amount of cracking occurring is negligible or small. However, because of thermodynamic limitations, in order for substantial dehydrogenation to occur at this low temperature it is necessary that the hydrogen partial pressure be maintained at a low level, i.e., a level sufficiently high only to maintain adequate catalyst activity. Hydrogen partial pressure is the total absolute pressure multiplied by the mole fraction of hydrogen in the gas phase in the reactor. The difficulty in maintaining adequate activity will vary from one catalyst to another and particularly from one feedstock to another. It is much more difficult to maintain catalyst activity with high boiling feedstocks than with low boiling ones. In order to obtain the desired de gree of conversion of naphthenes, the hydrogen partial pressure should be no higher than about 4 atmospheres. If the cycle length obtained when the hydrogen partial pressure is maintained at a level of about 1 atmosphere or less is satisfactory with the feedstock employed, then the isomerization and dehydrogenation reactions can take place to a satisfactory extent. On the other hand, if the hydrogen partial pressure must be maintained at a level between about I and 4 atmospheres in order to obtain satisfactory cycle length, then the reaction is preferably promoted by the use of an adsorbent such as a zeolite to remove the aromatics as they are formed, thus shifting the equilibrium and promoting the dehydrogenation and isomerization reactions.

Therefore, in a first aspect, this invention comprises the reforming of a hydrocarbon feedstock comprising naphthenes at a temperature from about 600 to about 700F and a hydrogen pressure of about 1 atmosphere or less. A high degree of conversion of the naphthenes to aromatics is obtained, without formation of substantial amounts of cracked products. The following table shows the conversion which can be obtained at equilibrium for cyclopentane homologs.

Equilibrium Conversion of Cyclopentanes to Aromatics at 620F Hydrogen Pressure Atmospheres 0.1 l 3 Six-carbon cyclopentane 99.95 69 7.4

Seven-carbon cyclopentane 99.99 94 38 Eight-carbon cyclo- 99.99 991 79 pcntane While not shown intthis table, the equilibrium conversion for 9+ carbon cyclopentanes is more favorable than that for 8 carbon cyclopentanes. Thus, at a temperature of 620F. and a hydrogen pressure of one atmosphere, an extremely high aromatic conversion can be effected for those compounds having 7,8 or more carbon atoms. Conversion of the six-carbon cyclopentane, i.e. methyl-cyclopentane, would be limited to 69%. However, most practical feedstocks do not contain as much methyl cyclopentane as the higher molecular weight cyclopentanes; hence the conversion to aromatics over-all can be quite high. In general, the lower pressures should be used for lower molecular weight feeds, while higher pressures can be used for higher molecular weight feeds. it is apparent, of course, that if one can maintain the hydrogen partial pressure substantially below 1 atmosphere, one can obtain an even greater conversion. Conversely, raising the hydrogen partial pressure to 3 atmospheres does not give satisfactory results in the practice of this aspect of the invention at this temperature levei.

This first aspect of the invention is illustrated by the following example, which is included here by way of illustration only and not intended as a limitation.

EXAMPLE I A comparison of the results obtained at conventional catalytic reforming conditions and at the conditions practiced in this invention is given in this example. The hydrocrackate feed had the following composition:

Billings Hydrocrackate Composition Cyclopentanes Containing 6 carbon atoms Containing 7 carbon atoms Containing 8+ carbon atoms Cyclohexaries Containing 6 carbon atoms l.2 Containing 7 carbon atoms on Containing 8+ carbon atoms 12.6

Benzene Toluene l Aromatics containing 8+ carbon atoms 2 Paraffins 20.5 l Average carbon number 8.45 (2) Average carbon number 8.73 (3) Average carbon number 8.64

In reforming the Billings hydrocrackate to obtain a product having a clear Research Octane Number of 97, a conventional reforming process performed at 930F and 400 psig. using a catalyst consisting of platinum supported on alumina promoted by chloride gives a 90.5 vol.% yield of C liquid product. Using the process of this invention performed at 630F, 1.0 atmosphere hydrogen partial pressure, 0.25 V/V/hr using a 5.0 wt% nickel on silica-alumina catalyst having a surface area of 550 square meters per gram one obtains the C liquid product in a yield of 97.0%. This 6.5 vol. yield advantage means that less naphtha needs to be used to make a given amount of gasoline, which in turn means that less crude needs to be used. With a high quality reforming feedstock, such as Billings hydrocrackate, the feedstock need not be subjected to any additional reforming operations since the 97 clear Research octane number is sufficient for blending into modern motor gasolines. Of course, where the feedstock contains a greater amount of paraffins, an appro priate subsequent paraffin conversion step such as conventional reforming or dehydrocyclization is also generally conducted.

A second aspect of the instant invention employs somewhat higher hydrogen partial pressures. i.e., up to about 4 atmospheres. As in the first aspect of this invention, the catalyst used is one which has both dehydrogenation and isomerization functions and may be of the type previously described. in the second aspect, however, there is mixed with the catalyst a solid absorbent which adsorbs the aromatic hydrocarbons as they are formed. This shifts the equilibrium, thus promoting the formation of additional aromatics and thereby making it possible to achieve high conversion to aromatics in spite of the higher hydrogen partial pressures employed.

Conveniently, the practice of this invention involves a dual reactor system. After the reforming operation in the first reactor, the feed is switched to an identical second reactor while the aromatics are desorbed from the first reactor. Following desorption, the temperature of the reactor catalyst-adsorbent mixture is adjusted to that desired for the reaction and then the feed is switched back to the first reactor while the aromatics formed in the second reactor are desorbed. Depending upon the time sequence employed, it may also be advantageous to employ 3 or 4 reactors. It is also possible, of course, to employ a single reactor system. If this is done, it is necessary to interrupt the flow of feedstock whie the aromatics are being desorbed and the temperature of the catalyst-adsorbent mixture is adjusted.

Any solid adsorbent which has good capacity for and selectively absorbs aromatic hydrocarbons in preference to naphthenes and paraffins can be employed in the practice of this invention. Silica gel, activated alu mina and similar adsorbents can be used. However, it is preferred to employ as the adsorbent certain natural or synthetic zeolites or aluminosilicates. Those synthetic zeolites referred to as 13x molecular sieves and available from the Linde Division of Union Carbide Corporation which contain sodium as the cation or in which certain other cations have been partially or completely substituted for the sodium, are particularly suitable. These adsorbents are made up of porous matter or crystals in which the pores are of molecular dimension and are of uniform size. The zeolites used in the practice of this invention may be described as crystalline zeolites having a rigid three-dimensional anionic network and having interstitial dimensions of sufficient size to adsorb the aromatic compounds produced in the course of the reaction. These zeolites vary somewhat in composition but generally contain the elements silicon, aluminum and oxygen as well as an alkaline metal and- /or an alkaline earth metal element for example, sodium and/or calcium. Linde 13x molecular sieve, in which the cation is sodium and which has a B.E.T. surface area of about 760 square meters per gram and a pore volume of 0.32 cubic centimeters per gram, is suitable for this process. Even better adsorbents can be made by exchanging certain cations, particularly calcium, strontium or cadmium for all or most of the sodium. The means for preparing such cation exchanged zeolites is well known in the art; see, e.g., P.E. Eberly, Jr., Journal of Physical Chemistry, Volume 66, pp 812-816 (May, 1962).

This second aspect of the invention is illustrated by FIG. 1 of the accompanying drawing which shows schematically the reaction, desorption and reheating steps. The naphtha feed to the reactor in the reaction step comprises naphthenes as well as paraffins. Some hydrogen or hydrogen-containing gas is usually also fed to the reactor. In the reactor, there is present the dual function (dehydrogenation and isomerization) catalyst above described mixed with a solid such as a zeolite to selectively adsorb aromatics present in the feed and the other aromatics as they are formed. The cyclohexanes are regularly converted to aromatics by simply dehydrogenation; the cyclopentanes are converted first, by a ring isomerization, to cyclohexanes, and thence to aromatics. The aromatics remain in the reactor, adsorbed on the catalyst-adsorbent mixture. Coming out of the reactor are hydrogen gas and a major portion of the paraffins. The aromatics in the feed are adsorbed preferentially at the inlet end of the bed. In addition, the aromatics made from the naphthenes are made at a greater rate at the inlet end so these aromatics are also preferentially adsorbed at the inlet end of the bed. As the adsorbent becomes saturated with aromatics as the reaction period progresses, the adsorption front progresses from inlet to outlet of the bed. At first, during the reaction period a portion of the paraffins are adsorbed on the freshly regenerated catalyst-adsorbent mixture beyond the zone near the inlet where the aromatics are being adsorbed. Then, as more aromatics are adsorbed they desorb the paraffins in a progressive wave front passing'through the bed. The isoparaffins are more easily displaced and, as a consequence, the paraffins which are most branched in structure will tend to appear first in the effluent and the normal paraffins will tend to appear last. Thus, by the use of proper time valves, some separation of isoparaffins from n-paraffins can be achieved. This is useful because the isoparaffins have a higher octane number and may be used directly in motor gasoline if desired, more or less selectively leaving the lower octane number nparaffins for further processing.

In the desorption step, a hot hydrocarbon vapor, such as butane, pentane, hexane or higher molecular weight paraffin is introduced into the reactor. This may be supplemented by steam if desired. The aromatics are desorbed, condensed and removed from the system. Where the paraffin used has a substantially higher vapor pressure than the lowest boiling aromatic, the aromatics can be selectively condensed and the paraffin recycled if desired. In this desorption step, the aromatics do not desorb entirely homogeneously; rather, the low boiling aromatics tend to. be desorbed first, followed by the intermediate boiling aromatics and, f1- nally, by the higher boiling aromatics. By the use of appropriate time valves, a benzene concentrate (A a toluene concentrate (A and a xylene plus higher aromatics concentrate (A can be segregated. Some isomerization of the paraffins occurs during this step.

The third step is a temperature adjustment step in which additional hot-hydrocarbon vapor, which may or may not be the same paraffin as previously used, is introduced into the reactor. Normal butane'is particularly suitable for this step. In this temperature adjustment step, the catalyst in the reactor causes a partial isomerization of the paraffin. In the case of normal butane particularly, the extent of isomerization, as to isobutane, is favorable. At the temperatures contemplated, the equilibrium ratio of normal butane to isobutane is 1.5. Thus, in the temperature adjustment step, normal butane can be fed continuously into the reactor and a 60/40 mixture of normal and isobutane is withdrawn. Isobutane is valuable as a feed component to alkylation operations.

As a specific illustration of this invention, a system is set up to process 25,000 barrels per day of a certain Baton Rouge virgin naphtha having the following composition:

Baton Rouge Virgin Naphtha Composition Continued Baton Rouge Virgin Naphtha Composition Paraffins 40.5 (1) Average carbon number 8.58 (2) Average carbon number 8.58 (3) Average carbon number 8.28

Each of the three steps occurs in the reactor for a 1 minute period, thus giving a 3 minute overall cycle. Each reactor contains a mixture of l25,000 pounds of catalyst and 60,000 pounds of adsorbent. The catalyst consists of wt.% nickel on silica-alumina having a surface area of 480 square meters per gram. The adsorbent is Linde X" sieve in which 91% of the sodium has been exchanged for calcium.

In the reaction step, the feedstock is charged at a rate of 4,620 pounds per minute, along with 5,000 standard cubic feet (26.4 pounds) per minute of hydrogen, both at 670F. Total pressure is four atmospheres absolute. The hydrogen partial pressure at the reactor inlet is 14.4 psi (0.98 atmospheres) and at the reactor outlet it is 46.3 psi (3.15 atmospheres).

Coming out of the reactor are 2,006 pounds per minute of paraffins and 22,800 standard cubic feet (121 pounds) per minute of hydrogen. The product stream is cooled to 85F by heat exchange. For the first 35 secends the liquid product is collected in vessel A and the separated hydrogen released from the system. Then collection is switched to vessel B, where hydrogen is again separated and released from the system. The liquid product collected in vessel A is predominantly isoparaftins and that collected in vessel B is predominantly normal paraffins. In the desorption step, butane is introduced at a rate of 3,967 pounds per minute at a temperature of 800F. The aromatics come out of the reactor at an average rate of 2,520 pounds per minute and at a temperature of about 630F. Since the feedstock contains hardly any six-carbon hydrocarbons,

hardly any benzene is formed. The first aromatic to appear is toluene and this is collected in vessel E.-When xylenes begin to appear after l8 seconds, the values are switched and'the remaining aromatics are collected in vessel F. In the temperature adjustment step, butane is introduced into the reactor at a rate of 32,767 pounds per minute, at a temperature of 700F. The 60/40 mixture of n-butane and isobutane leaves the reactor at a temperature of 630 F.

The accompanying FIG. 2 illustrates the second aspect of the invention in a dual reactor system. Reactors l and 2 are identical and the drawing (solid line) illustrates dehydrogenation and isomerization taken place in reactor 1 and desorption and reheating taking place in reactor 2. These reactors alternate between dehydrogenation/isomerization and desorption/reheating. The dotted lines in the drawing show reactor 1 i being used for desorption and reheating and reactor 2 being used for dehydrogenation and isomerization.

The hydrocarbon feedstock comprising naphthenes and paraffins, together with hydrogen, is charged via line 10 to a preheating furnace II which raises the temperature of the feed to between about 600 and 650F. The heated feed and hydrogen are charged via line 12 into reactor 1, which contains a reforming catalyst and a zeolite adsorbent as above described. In this reactor, the temperature is maintained between 600 and 650F and the hydrogen pressure is maintained at between about I and 4 atmospheres.

The effluent from this reactor comprising principally paraffins and hydrogen is removed via line I4. Separate streams of isoparaffin concentrate, line 15, and nparaftin concentrate, line 16, are obtained by means of time valve 17. If desired, a portion of the effluent stream from reactor 1 can be recycled via line 18 to heater 11.

Reactor 2 is, in the Figure illustrated, employed in the desorption and reheating steps. A hot hydrocarbon gas, shown as n-butane, is fed via line 20 into reactor 2. The temperature of the gas should be between about 700 to about 820F, preferably around 780F. In this reactor, the aromatics are desorbed and the isomerization catalyst contained therein isomerizes a portion of the n-butane to isobutane. The effluent passes via line 21 to a time valve 25 which, when properly operated, permits the separation of a benzene concentrate via line 22, a toluene concentrate via line 23, and a xylenes and higher boiling aromatics concentrate via line 24. Along with the various aromatic fractions, butanes will be recovered in the approximate ratio of 60% n-butane to 40% isobutane.

FIG. 3 illustrates an alternate method of practicing this invention, i.e., with a fluid system. A feedstock comprising naphthenes and paraffins is charged along with hydrogen via line 30 into a furnace 31 and heated to a temperature of between about 600 and 650F. It is then fed via line 32 into reactor zone 33. In this reac tor zone, the heated feed is contacted with a reforming catalyst as above described and a zeolite adsorbent which adsorbs the aromatic hydrocarbons as they are formed.

Reactor zone 33 is preferably a fluidized bed reactor in which the catalyst particles are in the fluidizable size range, preferably from about to about 325 mesh. In this zone, the cyclopentanes are converted to cyclohexanes and the cyclohexanes are converted to aromatics which are adsorbed by the zeolite. Hydrogen pressure is maintained at between about I and 4 atmospheres. Because of the cold conditions obtaining in reactor 33, there is virtually no hydrocracking and, furthermore, catalyst deactivation is quite slow. The paraffins in the feedstock pass through the reactor with some isomerization, but otherwise virtually uneffected and are removed along with the hydrogen via line 35. Through proper use of time valve 36, an isoparaffin stream may be removed via line 37 by virtue of the fact that at the start of the reaction, some n-paraffins are adsorbed by the zeolite. The major portion of the nparaffins are obtained in line 38.

After the dehydrogenation and isomerization reactions in reactor 33 are complete, the catalyst and the zeolite are removed via control valve 39 and passed via line 40 into a desorbing zone 41. n-Butane at a temperature of about 780F is introduced into the desorbing zone via line 42. The aromatics adsorbed on the zeolite are removed via line 43 and passed through time valve 44. By proper adjustment of the time valve, a benzene concentrate is first removed via line 45, followed by a toluene concentrate via line 46 and a xylene and higher aromatic concentrate via line 47. Also removed at the same time is a mixture of isobutane and n-butane in a ratio of about 60 to 40.

After the desorption is complete, the catalyst and zeolite are removed via line 48. The catalyst is then regenerated in the ordinary manner by means not shown and returned to reactor 33. As will be recognized by those skilled in the art, continuous movement of the solids from one vessel to the other and back again, with or without intermediate regeneration in a third vessel with air can also be practiced.

The invention thus provides a means of catalytically reforming naphthenes to the virtual exclusion of undesirable side reactions such as cracking. Some isomerization of paraffms also occur. In addition, if the second aspect of this invention is used, i.e., the adsorption of aromatics formed in the course of the reaction, some separation of isoparaffins from n-paraffins and also the partial isomerization of the paraffin hydrocarbon vapor (e.g. n-butane) used in the desorption of zeolite on which the aromatics have been adsorbed can be achieved. A motor fuel of improved octane number is thus obtained through an economically attractive process.

Other modifications of the present invention will occur to those skilled in the art upon a reading of the present disclosure. These are intended to be included within the scope of this invention.

What is claimed is:

1. A process for reforming a hydrocarbon feedstock comprising naphthenes and paraffms in which the naphthenes are converted to aromatic hydrocarbons, which process comprises contacting said feedstock in a reforming zone with a dehydrogenation and isomerization catalyst at a temperature of between about 600 and 700F., maintaining a hydrogen pressure of4 atmospheres or less, and providing in the reforming zone a solid adsorbent mixed with the catalyst for adsorbing the aromatic hydrocarbons as they are produced.

2. A process according to claim 1 in which the hydrogen partial pressure ranges from about 1 atmosphere to about 4 atmospheres.

3. A process according to claim 2 in which the solid adsorbent is an aluminosilicate molecular sieve which selectively adsorbs aromatic hydrocarbons to the substantial exclusion of naphthenes.

4. A process according to claim 3 in which the aluminosilicate molecular sieve has a pore diameter of about 13 A.

5. A process according to'claim 3 in which the aluminosilicate molecular sieve having aromatic hydrocarbons adsorbed thereon is subjected to a desorbing step.

6. A process according to claim 5 in which the desorbing is accomplished by contacting the aluminosilicate molecular sieve with hot hydrocarbon vapor.

7. A process according to claim 6 in which the hydrocarbon is n-butane.

8. A process according to claim 6 in which the hydrocarbon is a mixture of n-butane and isobutane.

9. A process according to claim 6 in which the desorption step is performed at a temperature of between about 700 and 800F.

10. A process according to claim 6 which comprises, after the desorption step, the additional step of adjusting the temperature of the catalyst and aluminosilicate molecular sieve adsorbent to a temperature of between 600 and 700F.

11. A process according to claim 3 in which the hydrocarbon feedstock is a hydrocrackate comprising principally cyclopentanes and cyclohexanes.

12. A process according to claim 3 in which the catalyst comprises nickel on an acidic support.

13. A process according to claim 12 in which the catalyst comprises from about 1.0 to about 10% of nickel on a silica-alumina catalyst.

14. A process according to claim 13 in which the catalyst is a nickel-silica-alumina catalyst having about 5% nickel.

15. A process according to claim 3 in which the catalyst comprises from about 0.025 to 1.0 wt. of a noble metal on an acidic or non-acidic support.

16. A process according to claim 15 in which the catalyst comprises from about 0.1 to about 1.0% of a noble metal on a non-acidic support.

17. A process according to claim 16 in which the sup port is alumina promoted by chlorine or fluorine.

18. A process according to claim 16 in which the noble metal is platinum.

19. A process according to claim 17 in which the catalyst is a platinum-chlorine-alumina catalyst.

20. A process for reforming a hydrocrackate comprising principally cyclopentanes and cyclohexanes in which the cyclopentanes and cyclohexanes are converted to aromatic hydrocarbons, which process comprises contacting said hydrocrackate in a reforming zone, at a temperature between 600 and 700F., with a dehydrogenation and isomerization catalyst comprising from about 0.1 to about 1.0% platinum on a chlorided alumina support, maintaining a hydrogen partial pressure of 4 atmospheres or less, and providing in .the- I reforming zone an aluminosilicate molecular sieve adsorbent having a pore diameter of about 13 A, which selectively adsorbs the aromatic hydrocarbons as they are formed.

21. A process according to claim 20 in which the aluminosilicate molecular sieve having aromatic hydrocarbons adsorbed thereon is subjected to a desorbing step which comprises contacting said aluminosilicate molecular sieve with n-butane at a temperature of between about 700 and 800F.

Claims

1. A PROCESS FOR REFORMING A HYDROCARBON FEEDSTOCK COMPRISING NAPHTHENES AND PARAFFINS IN WHICH THE NAPHTHENES ARE CONVERTED TO AROMATIC HYDROCARBONS, WHICH PROCESS COMPRISES CONTACTING SAID FEEDSTOCK IN A REFORMING ZONE WITH A DEHYDROGENATION AND ISOMERIZATION CATALYST AT A TEMPERATURE OF BETWEEN ABOUT 600* AND 700*F., MAINTAINING A HYDROGEN PRESSURE OF 4 ATMOSPHERES OR LESS, AND PROVIDING IN THE REFORMING ZONE A SOLID ADSORBENT MIXED WITH THE CATALYST FOR ADSORBING THE AROMATIC HYDROCARBONS AS THEY ARE PRODUCED.

5. A process according to claim 3 in which the aluminosilicate molecular sieve having aromatic hydrocarbons adsorbed thereon is subjected to a desorbing step.

7. A procesS according to claim 6 in which the hydrocarbon is n-butane.

9. A process according to claim 6 in which the desorption step is performed at a temperature of between about 700* and 800*F.

10. A process according to claim 6 which comprises, after the desorption step, the additional step of adjusting the temperature of the catalyst and aluminosilicate molecular sieve adsorbent to a temperature of between 600* and 700*F.

15. A process according to claim 3 in which the catalyst comprises from about 0.025 to 1.0 wt. % of a noble metal on an acidic or non-acidic support.

17. A process according to claim 16 in which the support is alumina promoted by chlorine or fluorine.

18. A process according to claim 16 in which the noble metal is platinum.

20. A process for reforming a hydrocrackate comprising principally cyclopentanes and cyclohexanes in which the cyclopentanes and cyclohexanes are converted to aromatic hydrocarbons, which process comprises contacting said hydrocrackate in a reforming zone, at a temperature between 600* and 700*F., with a dehydrogenation and isomerization catalyst comprising from about 0.1 to about 1.0% platinum on a chlorided alumina support, maintaining a hydrogen partial pressure of 4 atmospheres or less, and providing in the reforming zone an aluminosilicate molecular sieve adsorbent having a pore diameter of about 13 A, which selectively adsorbs the aromatic hydrocarbons as they are formed.

21. A process according to claim 20 in which the aluminosilicate molecular sieve having aromatic hydrocarbons adsorbed thereon is subjected to a desorbing step which comprises contacting said aluminosilicate molecular sieve with n-butane at a temperature of between about 700* and 800*F.