US3849289A

US3849289A - Fluidized platinum reforming followed by fixed-bed platinum reforming

Info

Publication number: US3849289A
Application number: US00335028A
Authority: US
Inventors: A Voorhies
Original assignee: Individual
Current assignee: Individual
Priority date: 1973-02-23
Filing date: 1973-02-23
Publication date: 1974-11-19
Anticipated expiration: 1991-11-19

Abstract

A staged reforming process comprising charging a naphtha feedstock comprising naphthenes and paraffins to a first reforming zone, contacting said feedstock in the presence of hydrogen, in said zone with a fluidized bed of reforming catalyst at a temperature of from about 750*F. to about 850*F., at a pressure of from about 75 to about 250 psig., thereby substantially converting naphthenes to aromatics with minimum hydrocracking of said paraffins; charging at least a portion of the effluent stream from said first reforming zone to a second reforming zone, contacting said stream in the presence of hydrogen with a fixed bed of reforming catalyst within said zone at a temperature between about 850*F. and 1050*F. and at a pressure of from about 75 to about 250 psig., thereby selectively dehydrocyclizing said paraffins to aromatics with a minimum of hydrocracking of said paraffins and thereafter recovering the reformate.

Description

United States Patent [191 Voorhies, Jr.

[451 Nov. 19, 1974 [76] Inventor: Alexis Voorhies, Jr., 2569 E.

Lakeshore Dr., Baton Rouge, La. 70810 22 Filed: Feb. 23, 1973 [21 Appl. No.: 335,028

PrimaryExaminer-Delbert E, Gantz' Assistant ExaminerS. Berger Attorney, Agent, or Firm-Llewellyn A. Proctor [5 7] ABSTRACT A staged reforming process comprising charging a naphtha feedstock comprising naphthenes and paraffins to a first reforming zone, contacting said feedstock in the presence of hydrogen, in said zone with a fluidized bed of reforming catalyst at a temperature of from about 750F. to about 850F., at a pressure of from about 75 to about 250 psig., thereby substantially converting naphthenes to aromatics with minimum hydrocracking of said paraffins; charging at least a portion of the effluent stream from said first reforming zone to a second reforming zone, contacting said stream in the presence of hydrogen with a fixed bed of reforming catalyst within said zone at a temperature between about 850F. and [050F. and at a pressure of from about 75 to about 250 psig., thereby selectively dehydrocyclizing said paraffins to aromatics with a minimum of hydrocracking of said paraffins and thereafter recovering the reformate.

15 Claims, 2 Drawing Figures FLUIDIZED PLATINUM REFORMING FOLLOWED BY FIXED-BED PLATINUM REFORMING This invention relates to an improved process for the catalytic reforming of naphthenes and paraffins. More particularly, this invention relates to a staged catalytic reforming process wherein, in a first zone, comprising one or more stages, naphthenes are selectively and substantially completely converted to aromatics with minimum hydrocracking, thereby preserving the paraffins 10 of the feed for efficient dehydrocyclization in a second zone, comprising one or more stages.

Significant improvements in reforming yields at high octane levels can usually only be obtained by better selectivity for dehydrocyclization of paraffins, particularly with paraffinic feedstocks. In commercial practice, the obtainment of very high octane numbers is usually accompanied by considerable hydrocracking of paraffins, not only in the terminal or tail reactor of a reactor train, but also in the lead reactors concomitantly with the conversion of naphthenes to aromatics. This, of course, is wasteful of feedstock and it may also be accompanied by significant destruction of aromatics when the concentration of aromatics in the product approaches thermodynamic equilibrium.

Accordingly, it is an object of the present invention to provide an improved catalytic reforming process which overcomes the above and other deficiencies.

It is another object of this invention to provide a staged catalytic reforming process which provides maximum yields at high octane numbers.

It is still another object of the present invention to provide a staged reforming process wherein, in the first zone, highly. selective dehydrogenation of C naphthenes and isomerization and dehydrogenation of C naphthenes are effected with minimum hydrocracking of paraffins and naphthenes; whereas, in the second zone, highly selective dehydrocyclization of paraffins to aromatics is effected, also with minimum hydrocracking of paraffins.

These as well as other objects are accomplished by the present invention which provides a staged reforming process comprising:

charging a naphtha feedstock containing naphthenes and paraffins to a first reforming zone, contacting said feedstock in the presence of hydrogen, in said zone with a fluidized bed of reforming catalyst at a temperature of from about 750F. to about 850F., at a pressure of from about 75 to about 250 psig., thereby substantially converting said naphthenes to aromatics with minimum hydrocracking of said paraffins; charging at least a portion of the effluent stream from said first reforming zone to a second reforming zone, contacting said stream, in the presence of hydrogen, with a fixed bed of reforming catalyst contained within said second zone at a temperature of from about 850F. to about l050F. and at a pressure of from about 75 to about 250 psig., thereby selectively dehydrocyclizing said parafflns to aromatics with a minimum of hydrocracking of said paraffins; and thereafter recovering the reformate.

It is important to point out the significant discovery that is responsible for the superior performance in the fluidized bed, first reforming zone of the present invention as compared with a conventional fixed-bed or moving-bed first zone, necessarily employing catalyst of much larger particle size than used with the fluidized bed of the present invention. As already stated, this superior performance in the fluidized bed, first reforming stage manifests itself in an extremely high ratio of selective conversion of naphthenes to aromatics as com- 5 pared to hydrocracking of paraffins. This results from the discovery that with very small particle size reforming catalyst, such as used in the fluidized bed, the specific activity for converting naphthenes to aromatics is approximately times that of conventional fixed-bed catalyst particles; whereas, there is no appreciable effect of catalyst particle size on the specific activity for hydrocracking of paraffins.

Supporting data on the effect of catalyst particle size 5 on specific activity for converting naphthenes to paraffins are given in Table I below for a platinum-alumina catalyst:

TABLE I Test for Pore Diffusion Limitations at 775F. and 85 psia Cyclohexane Dehydrogenation and lsomerization over a Pt-AI O; Catalyst Og erating Conditions Feed Cyclohexane Catalyst Pt-Al,O Temperature. F. 775 Pressure, psia 84.7 Space Time, 6, gm cat-min/gm feed 0.55 Mole Ratio, H,/cyc|ohexanc -20 Experimental Results Rate Constant.

gm mols/gm cat-atm-min The data of Table I are plotted in FIG. 1 of the drawmgs.

From the data, and based on practical limitations regarding the nature of fluidized bed reaction, it can be concluded that a fluidized catalyst particle having an average of about 0.06 mm diameter is optimum, and has about ten times the specific activity for cyclohexane dehydrogenation as the smallest of conventional fixed-bed catalyst particles which average about 0.8 mm (1/32 inch) diameter. Thus, particles of average size less than about 0.06, inter alia, are lost from the bed, and may require operation at lower than desirable gas velocities. On the other hand, larger particle sizes can be employed, but as particle size is increased, the activity of the catalyst decreases proportionately. Hence, it is not generally desirable to employ particle sizes of average diameter ranging greater than about 0.1 mm.

While the preceding data show that dehydrogenation of naphthenes to aromatics is diffusion-limited with highly active reforming catalysts, such as Pt-Al O when using conventional-size fixed-bed catalyst particles, it is well known that there is no corresponding diffusion limitation in the case of hydrocracking of paraffins. This is illustrated by the following fixed-bed data on Pt-Al O catalyst of conventional particle size:

Mole & Conversion it is obvious from these data that the hydrocracking of paraffins is so much slower than the dehydrogenation of naphthenes that no diffusion limitation in paraffin hydrocracking would be expected when using larger particle size catalyst (e.g., one thirty-second inch) as in fixed-bed catalytic reforming.

The preceding data support the findings of this invention that with highly active reforming catalysts, such as Pt-Al O in fluidizable particles of about 0.06 mm diameter, the ratio of naphthenes conversion to aromatics as compared to hydrocracking of paraffins is about ten times the corresponding ratio for the same catalyst composition, using conventional fixed-bed catalyst particles of about 0.8 mm (l/32 inch) diameter.

There is another outstanding advantage in employing the fluidized-bed, first-stage reactor as compared to a conventional fixed-bed or moving-bed reactor with necessarily much larger particle size catalyst. This is the approximately ten-fold higher activity for converting naphthenes to aromatics. This means that the weight of the actual catalyst (e.g., 0.3 percent Pt on Al- O in the fluidized-bed reactor need be only about one tenth of that in a conventional fixed-bed or moving-bed reactor. This is of special significance, since the fluidizable catalyst particles can be diluted with nine times as much non-platinum-containing fluidizable particles (e.g., A1 without employing a greater weight of total fluidizable solids than in the case of a fixed-bed or moving-bed reactor. This dilution ofa 0.3 percent Pt catalyst to an average Pt content of 0.03 percent would have several advantages for fluidized-bed operation-such as much lower cost per pound and greater heat capacity due to the diluent.

The following conditions, which are simply illustrative and not restrictive, indicate the practicability of the fluidized-bed, first stage of this invention for a typical virgin heavy naphtha feed, using a Group VIII noble metal, especially a platinum-containing catalyst, e.g., a 0.3 percent Peon-M 0 catalyst, diluted with nine parts of Al O Temperature. F. 800 Total Pressure. Psig. l00 Recycle H /Oil 4/1 W/Hr./W Based on 0.03% Pt 3 7: Conversion of Cyclohcxancs 97 Catalyst Bed Height, Ft. l0

lnlct Superficial Velocity. FtJSec. 2 Density of Fluidized Bed. Lbs/Cu. Pt. 40

blends of naphthenes, paraffins and aromatics to produce high-octane motor fuels.

As shown in FIG. 2, the hydrocarbon feedstock con- I taining naphthenes and paraffins is charged via line 10 to a fixed preheat furnace 12 which raises the temperature of the feed to reforming conditions. The heated feed is charged to the first reforming zone 14 wherein it is contacted with a fluidized bed of reforming catalyst under mild temperature conditions ranging from about 750F. to about 850F., and at low pressures of from about to about 250 psig.

The reforming catalysts useful for the fluidized bed in the first reforming zone 14 may be platinum, platinum-rhenium, platinum-iridium, or other bi-metallics or multi-metallics on a refractory porous inorganic oxide support, e.g., alumina-gel or other suitable support. The metal components of the catalyst constitute from about 0.025 to about 5 weight percent, and preferably from about 0.l to about 1.0 weight percent metal on the various supports. A platinum-on-alumina catalyst is a preferred catalyst for the first reforming zone. If desired, a catalyst comprising platinum and/or other noble metals can be similarly employed. Most preferably, the catalyst will be admixed with 5 to 20 parts by weight of an inexpensive solids diluent, such as alumina gel.

The catalyst particles employed in the present invention are small particles in the fluidizable size range, preferably particles having an average diameter of about 0.06 mm (200-325 mesh, Tyler series).

Under the mild reforming conditions established in the first reforming zone and with the virtual absence of hydrocracking, catalyst deactivation is very slow; therefore, regeneration of the catalyst may be held to a minimum, permitting semi-regenerative operations. Another advantage obtained by minimizing hydrocracking is the high purity of the resulting make hydrogen. The e'ffluent from reactor 14 is at least partially condensed in condenser 15 and is then sent to separator 17 wherein hydrogen and light hydrocarbon gases are discharged from the separator 17 via line 21. A portion of the hydrogen and light hydrocarbon gases is withdrawn through line 22 for recycle to reactor 14. The net production of hydrogen and light hydrocarbon gas leaves the system through line 13 as tall gas. The recycle gas can be recycled at gas rates ranging from about 1000 to about 10,000 CF/B, preferably from about 3,000 to about 5,000 CF/B.

The liquid product from the first reforming zone 14, emerging from the separator 17, consisting primarily of aromatics and paraffins may, if desired, be subjected to a separation process (not shown) for separating the aromatics from the paraffins. In this case the paraffinic portion would be sent to the second reforming zone, as will now be described for the case shown in the drawing, wherein there is no intermediate separation of aromatics. The total liquid product from the first reforming zone 14, emerging from separator 17 can be fed via line 16 to a fired preheat furnace 18 which is adapted to bring said effluent to the reforming temperature conditions maintained with the second reforming zone shown generally as 20. The second reforming zone 20 comprises a plurality of fixed-bed

catalyst reaction zones

23 and 24 arranged in series. Each reaction zone is preceded by a heater l8 and 26, respectively, for heating the feed stream and recycle gas being processed. The temperature within the reactors forming the second reforming zone is maintained in the range of about 850l050F., and preferably ranges from about 875 to about 975F. The pressure within the reactors of the second reforming zone 20 is maintained above about 75 psig, and preferably ranges from about 75 to about 250 psig. The hydrogen gas rate ranges from about 1000-10,000 SCF/Bbl. and preferably ranges from about 3000-5000 SCF/Bbl. The space velocity, based on catalyst plus diluent, ranges from about 01-10 W/Hr./W, depending upon the particular catalyst employed. Thus, for platinum catalysts, the space velocity preferably ranges from 0.5-5 W/I-Ir./ W; whereas, for Pt-Ir catalysts, for example, the space velocity preferably ranges from 1l0 W/Hr./W. Under these conditions, selective dehydrocyclization of paraffins to aromatics is effected with a minimum of hydrocracking.

It is important to minimize temperature gradients in both the first and second reforming zones. Isothermal conditions are assured in the first reforming zone through use of a fluidized bed. Isothermal conditions can be approached in the second reforming zone by use of a series of fixed-bed reactors with intermediate reheating between beds as shown in FIG. 2. Alternatively, the second zone can employ a series of heat-exchange type of reactors.

Effective catalysts for the promotion of dehydrocyclization of paraffins in the second reforming zone include platinum and other noble metals, such as previously described for the first reforming zone. A platinum-alumina-chloride complex is an effective catalyst for the promotion of the dehydrocyclization of paraffins. Generally, the metal component of the catalyst comprises from about 0.1 to 1.5 weight percent of the final composition.

The effluent from reactor 24 is at least partially condensed in condenser 27 and is then sent to separator 28 wherein hydrogen and light hydrocarbon gases are discharged from the separator 28 via line 30. A high octane reformate product is recovered by line 32. A portion of the hydrogen and light hydrocarbon gases is withdrawn through line 34 for recycle to the second reforming zone. The recycle gas can be recycled at gas rates ranging from about 1000 to 10,000 SCF/B, preferably from about 3000 to 5000 SCF/B.

Thus, the present invention provides a two-zone catalytic reforming process wherein a first fluidized mild reforming zone (or stage, or stages) converts naphthenes selectively and almost completely to aromatics with minimum hydrocracking, thereby preserving the paraffins in the feed for an efficient dehydrocyclization operation in a fixed bed second zone (or stage, or stages) wherein the high partial pressure of aromatics formed in the first zone effectively minimizes hydrocracking in said second zone. A high quality, high octane motor fuel together with a high purity hydrogen by-product is thus provided.

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:

I. A staged reforming process comprising charging a naphtha feedstock comprising naphthenes and paraffins to a first reforming zone, contacting said feedstock in the presence of hydrogen in said zone with a fluidized bed of reforming catalyst comprising a noble metal or mixtures thereof composited with a support at a temperature of from about 750F. to about 850F., at a pressure of from about to about 250 psig., thereby substantially converting said naphthenes to aromatics with minimum hydrocracking of said paraffins; charging at least a portion of the effluent stream from said first reforming zone to a second reforming zone, contacting said stream in the presence of hydrogen, within said zone which contains a plurality of fixed-bed catalyst reaction stages arranged in series, with intermediate reheating heating between beds to provide near isothermal conditions, said beds of reforming catalyst comprising a noble metal or mixtures thereof composited with a support, said second reforming reaction being conducted at a temperature of from 850 to about 1,050F. and at a pressure of from about 75 to about 250 psig., thereby selectively dehydrocyclizing said paraffins to aromatics with a minimum of hydrocracking of said paraffins; and thereafter recovering the reformate.

2. Process as defined in claim 1 wherein the reforming catalyst in the fluidized reforming zone comprises from about 0.025 to about 5 weight percent of a Group VIII noble metal.

3. Process as defined in claim 1 wherein the reforming catalyst in the fluidized reforming zone comprises a platinum-on-alumina catalyst.

4. Process as defined in claim 1 wherein the catalyst particles in the fluidized reforming zone are about 0.06 mm average particle size diameter.

5. Process as defined in claim 1 wherein the catalyst particles in the fluidized zone are diluted with from about 5 to 20 parts by weight of a solids diluent material.

6. Process as defined in claim I wherein the temperature within the second reforming zone ranges from about 850 to about 1,050F.

7. Process as defined in claim 1 wherein the pressure within the reactors of the second reforming zone ranges from about 75 to about 250 psig.

8. Process as defined in claim 1 wherein the first reforming zone is operated under isothermal conditions.

9. Process as defined in claim 1 wherein the first reforming zone is operated at a space velocity of from about 01-10 W/I-Ir./W., based on catalyst plus diluent.

10. Process as defined in claim 1 wherein the first reforming zone is operated at a hydrogen gas rate ranging from about l,000-l0,'000 SCF/Bbl.

11. Process as defined in claim 1 wherein the second reforming zone is operated at a space velocity of from about 0.l-l0 W/Hr./W, based on catalyst plus diluent.

12. Process as defined in claim 1 wherein the second reforming zone is operated at hydrogen gas rate ranging from about 1000-10,000 SCF/Bbl.

13. Process as defined in claim 1 wherein the catalyst employed in the second reforming zone comprises a Group VIII noble metal or mixtures thereof on a support.

14. Process as defined in claim 1 wherein the catalyst in the second reforming zone is a platinum-aluminachloride complex.

15. Process as defined in claim 1 wherein the noble metal or mixture thereof of the catalyst employed in the second reforming zone comprises from about 0.1 to

1.5 weight percent of the catalyst. =i

Claims

1. A STAGED REFORMING PROCESS COMPRISING CHARGING A NAPHTHA FEEDSTOCK COMPRISING NAPHTHENES AND PARAFFINS TO A FIRST REFORMING ZONE, CONACTING SAID FEEDSTOCK IN THE PRESENCE OF HYDROGEN IN SAID ZONE WITH A FLUIDIZED BED OF REFORMING CATALYST COMPRISING A NOBLE METAL OR MIXTURES THEREOF COMPOSITED WITH A SUPPORT AT A TEMPERATURE OF FROM ABOUT 750*F. TO ABOUT 850*F., AT A PRESSURE OF FROM ABOUT 75 TO ABOUT 250 PSIG. THEREBY SUBSTANTIALLY CONVERTING SAID NAPHTHANENES TO AROMATIC WITH MINUMUM HYDROCRACMING OF SAID PARAFFINES; CHARGING AT LEAST A PORTION OF THE EFFLUENT STREAM FROM SAID FIRST REFORMING ZONE TO A SECOND REFOMING ZONE, CONTACTING SAID STREAM IN THE PRESENCE OF HYDROGEN, WITHIN SAID ZONE WHICH CONTAINS A PLURALITY OF FIXED-BED CATALYST REACTION STAGES ARRANGED IN SERIES WITH INTERMEDIATE REHEATING HEATING BETWEEN BEDS TO PROVIDE NEAR ISOTHERMAL CONDITIONS, SAID BEDS OF REFORMING CATALYST COMPRISING A NOBLE METAL OR MIXTURE THEREOF COMPOSITED WITH A SUPPORT, SAID SECOND REFORMING REACTION BEING CONDUCTED AT A TEMPERATURE OF FROM 850* TO ABOUT 1,050*F. AND AT A PRESSURE OF FROM ABOUT 75 TO ABOUT 250 PSIG. THEREBY SELECTIVELY DEHYDROCYCLIZING SAID PARAFFINS TO AROMATICS WITH A MINIMUM OF HYDROCRACKING OF SAID PARAFFINES; AND THEREAFTER RECOVERING THE REFORMATE.

6. Process as defined in claim 1 wherein the temperature within the second reforming zone ranges from about 850* to about 1, 050*F.

9. Process as defined in claim 1 wherein the first reforming zone is operated at a space velocity of from about 0.1-10 W/Hr./W., based on catalyst plus diluent.

10. Process as defined in claim 1 wherein the first reforming zone is operated at a hydrogen gas rate ranging from about 1,000-10,000 SCF/Bbl.

11. Process as defined in claim 1 wherein the second reforming zone is operated at a space velocity of from about 0.1-10 W/Hr./W, based on catalyst plus diluent.

12. Process as defined in claim 1 wherein the second reforming zone is operated at hydrogen gas rate ranging from about 1000-10, 000 SCF/Bbl.

14. Process as defined in claim 1 wherein the catalyst in the second reforming zone is a platinum-alumina-chloride complex.

15. Process as defined in claim 1 wherein the noble metal or mixture thereof of the catalyst employed in the second reforming zone comprises from about 0.1 to 1.5 weight percent of the catalyst.