WO1981000415A1

WO1981000415A1 - Catalytic reforming process

Info

Publication number: WO1981000415A1
Application number: PCT/US1980/000900
Authority: WO
Inventors: W Mayes
Original assignee: Cosden Technology
Priority date: 1979-07-12
Filing date: 1980-07-09
Publication date: 1981-02-19
Also published as: IT1131945B; NL8020292A; JPS56500890A; EP0031847A1; IT8023360A0; GB2070053B; JPH0147519B2; GB2070053A

Abstract

A multi-stage catalytic reforming process (11, 12, 13 and 14) wherein a hydrocarbon feedstock (15) and hydrogen-rich gas (17) are heated to reforming temperature by indirect heat exchange (18) and then introduced in admixture (19) directly into the first reforming reaction zone (11) thereby dispensing with the usual heater through which the feed material ordinarily is passed prior to entering the initial reaction zone.

Description

CATALYTIC REFORMING PROCESS

TECHNICAL FIELD

This invention relates to catalytic reforming. More particularly, this invention relates to multi-stage, adiabatic catalytic reforming of petroleum feedstocks. The present invention relates especially to catalytic reforming of petroleum naphtha.

BACKGROUND OF THE INVENTION

Catalytic reforming is a well known process for upgrading petroleum fractions to more valuable products. Catalytic reforming finds particular application in upgrading petroleum naphtha fractions, i.e., petroleum fractions boiling between 100 and 400°F, to increase the octane value thereof for incorporation in gasoline motor fuels. As increasing restrictions are applied for environmental reasons on the use of lead additives, such as tetraethyl lead, which have traditionally been utilized to increase the octane value of gasoline motor fuels, catalytic reforming assumes an ever increasing importance. In prior art catalytic reforming a feedstock material and hydrogen- containing gas are intimately mixed, before or after indirect heat exchange, and then passed through an alternating series of heaters and reaction zones. By a heater is meant a device or arrangement for adding heat energy to the mixture directly or indirectly frcm a primary energy service such as a gas or oil burner. In the prior art systems, the nuriber of heaters is the same as the number of reaction zones and the mixture of feed material and hydrogen passes through a heater before entering the first reaction zone. Each reforming zone contains either a fixed or moving bed of suitable refoiming catalyst. Alumina based catalysts containing platinum and halogen are frequently utilized. Promoters such as rhenium, iridium or germanium may be incorporated in the catalyst with the platinum. Refoiming catalysts are well known in the art and will not be described in further detail here.

The reforming reaction is strongly endothermic. Consequently, the temperature of the reaction mixture drops rapidly until it reaches a level where the reforming reaction proceeds very slowly, if at all. In most instances, the reduction in temperature and consequent ces¬ sation of the reforming reaction will occur before reforming is conplete. In order to counteract this problem, it has become standard procedure in the art to carry out reforming operations in successive stages in a series of reactors. Typically, three or four successive reaction zones are utilized.

In the prior art, feedstock material, either before or after admixture with a hydrogen-containing gas, is passed through a heater to raise the temperature of the material to reforming temperatures prior to introducing the feedstock and hydrogen mixture into the first reaction zone. Effluent from the first reaction zone is reheated by passing it through a second heater before being introduced into the second reaction zone in the second stage of the reforming operation. In similar fashion, effluent from the second reforming reaction zone is again reheated in a third heater before being introduced into the third reaction zone for the next stage of the reforming operation. Examples of such systems are disclosed in Webb, U.S. Patent No. 3,011,968; Greenwood et al. , U.S. Patent No. 3,725,248 and;Bonacci et al., U.S. Patent No. 3,899,411 (although Figure 2 of Bonacci does not show an initial heater, Bonacci's specification, col. 11, lines 9-14 notes "The naphtha feed may be brought to reforming temperatures in a suitable heater, not shown, ...").

In sane prior art installations, the several heaters have been combined into a single unit by mounting a separate coil for each reaction zone in a cαiroon firebox in heat exchange relation with the hot combustion gases from the fire and passing the feed-hydrogen mixture through the respective coil associated with each reaction zone, before it is admitted to that zone. The net result is the same.

In any event, it will be appreciated that construction and operation of such heaters contributes materially to the initial capital investment cost and the continuing operational cost of catalytic reforming installations. It would, of course, be highly desirable to eliminate or minimize such costs.

OΓ,PI . A,.. v.^""^:o OBJECTS OF TEE INVENTION

Accordingly, it is an object of the present invention to provide an improved multi-stage process for catalytic reforming of petroleum feedstocks. It is a further object of the present invention to provide a catalytic refoiming process which does not require that the feed¬ stock material be passed through a heater before being introduced into the refoiming reaction zone in each stage of the operation.

Another object of the present invention is to provide a process for catalytic reforming of petroleum naphtha wherein no heater is required to raise the temperature of the feedstock material and hydrogen prior to introducing then into the first stage refoiming reaction zone.

Yet a further object of the present invention is to provide a catalytic reforming process which reduces the investment and operating costs of a reformer installation.

SUMMARY OF THE INVENTION

These and other objects of the invention are achieved by providing a process for reforming a hydrocarbon feedstock comprising preheating said feedstock and a hydrogen-containing gas by indirect heat exchange to reforming conditions, passing said feedstock and hydrogen- containing gas in admixture successively through an alternating series of catalytic reaction zones maintained at reforming conditions and heaters; the number of heaters in said series being one fewer than the number of reaction zones in said series, and said admixture passing through the first reaction zone prior to entering the first heater. In a further aspect of the invention, the petroleum naphtha feedstock and hydrogen-containing gas are passed in indirect heat exchange relation with the effluent frαn the final reaction zone in the series of reaction zones in order to raise the initial temperature of the feedstock and hydrogen to reforming temperature. In another aspect of the invention, the reforming conditions in each subsequent reaction zone are more severe than the reforming conditions in the first reaction zone. The hydrocarbon feedstock and hydrogen-containing gas may be admixed prior to passage through the heat exchanger, or they may be preheated separately and then admixed. The reaction zones may each comprise an individual reactor or they may consist of separate zones in a single vessel.

It has now been discovered, surprisingly, that the initial heater in a conventional multi-stage reforming installation can be eliminated, and the feed-hydrogen admixture can be brought to refoiming temperature by passing it in heat exchange relation with the effluent from the final reaction zone of the refoiming installation. This is to be distinguished from prior art installations where the feed admixture has been passed in heat exchange relation with the effluent frαn one or more of the reactors, but has not been brought to refoiming teπperatures in the heat exchanger and has to be passed through a separate heater after leaving the heat exchanger and before intro¬ duction into the first reaction zone.

BRIEF DESCRIPTION OF IHE DRAWINGS

^• The invention will be explained in greater detail with reference to the appended drawing which is a schematic representation of a four-stage refoiming installation adapted for practicing the process of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Figure 1 is a schematic representation of a reforming installation 10 comprising a series of four reforming reaction zones represented by reactors 11, 12, 13 and 14. A petroleum feedstock such as petroleum naphtha is introduced into the refoiming installation through inlet line 15 by means of pump 16. A hydrogen-containing gas is supplied through line 17 and admixed with the feedstock. The mole ratio of hydrogen to feedstock may vary depending on the nature of the feedstock and the conditions of the reforming reaction. In most instances, the mole ratio of hydrogen to feedstock will lie between 1:1 and 10:1. For naphtha feedstocks processed according to the disclosed embodiment, it is preferred that the hydrogen/feedstock mole ratio lie between about 4:1 and about 6:1. The achiixed feed materials pass to a heat exchanger 18 in which the temperature of the feed materials is raised to at least 80CPF. Desirably, the temperature will be raised to between 825 and 85CPF. Frαn heat exchanger 18, the feed materials pass through inlet line 19 and are introduced into the top of reactor 11.

The feed materials pass through a bed of suitable reforming catalyst material, such as a platinum containing alumina based reforming catalyst in the reactor and react to produce an upgraded product. The catalyst bed may be either fixed or moving and the flow through the catalyst bed in this and the succeeding reactors may be either radial or non-radial, as desired. Due to the strong endotheimic nature of the reforming reaction, the temperature of the feed mixture decreases rapidly. Depending upon the exact nature of the feed material, teπperatures in the first reactor may decrease anywhere from about 140 to about 200°F. The effluent from the reactor 11 is.withdrawn through line 20 and passed to a first heater 21 where it is reheated to reforming temperatures. Desirably, the material will be heated to a temperature of at least 875°F. Preferably, heater 21 will raise the temperature of the effluent from reactor 11 to a temperature of about 900°F. to 930°F. Inlet line 22 carries the reheated partially reformed feed to the top of second reactor 12. The feed material then passes through the catalyst bed in reactor 12 and is further reformed therein. The temperature of the mixture again drops significantly in reactor 12 in consequence of the endotheimic nature of the refoiming reaction. Typically effluent frαn reactor 12 has a taπperature of not more than about 800°F.

Effluent frαn reactor 12 is conveyed through line 23, heater 24 and line 25 to reactor 13 where the same basic sequence of operations is repeated. The inlet temperature of the feed to reactor 13 is typically greater than 900PF, preferably, at least 935°F., and the outlet temperature is less than 90(PF. In similar fashion, the partially reformed feed passes through line 26, heater 27 and line 28 to reactor 14, the final reactor in the series. The inlet teπp- erature for reactor 14 is typically at least about 940°F, and the outlet temperature is normally within 10°F. of the inlet temperature.

Initially, as the feed mixture is introduced into the first reactor, the reforming reaction proceeds comparatively readily because of the comparatively high concentration of nonaromatic compounds in the feed mixture. As the reforming process proceeds through the successive stages, the concentration of nonaromatics becomes progres¬ sively more dilute, and more strenuous reaction conditions are required. Thus, the reaction conditions in each succeeding reactor ordinarily ■are made progressively more severe. As the reforming process approaches completion, the actual amount of reaction per unit of feed in each reactor becomes proportionately less, and concαnitantly, the temperature drop in each successive reactor is usually less. The progressive reduction in the temperature decrease in each successive reactor facilitates heating the feed material to progressively higher teπperatures before introduction into each succeeding reactor. Pressures throughout the reactor system may be ambient or elevated. Desirably the refoiming reaction is carried out at elevated pressures ranging between 100 and about 600 psi. In the disclosed embodiment, pressures ordinarily range between about 150 and about 400 psig.

Effluent from the fourth stage reactor 14 is passed directly to heat exchanger 18 via line 29 where it is used to raise the tetiperature of the initial feedstock/hydrogen-containing gas mixture. Heat exchanger 18 may be an efficient counterflow-type exchanger such as a one pass feed_-one pass shell and tube heat exchanger with either stream on the tube side. From heat exchanger 18, the reformed naphtha and hydrogen-rich gas pass through line 30 to condenser 31 and thence through line 32 to a conventional separator 33 where the condensed refoimate is separated from the reformer off-gases. The reformate is transmitted frαn the separator 33 via line 34 to such further processing units as may be desired, such as a stabilizer (not shown).

Hydrogen-containing reformer off-gases leave separator 33 via line 35. A portion of the hydrogen-containing gases is recycled via compressor 36 and line 37 to the hydrogen-containing gas supply line 17.

Hydrogen-containing reformer off-gases not required for recycle may be withdrawn via line 42 and collected or utilized as desired. • The catalyst material may be regenerated by known techniques.

If moving catalyst beds are utilized in the reaction zones, withdrawn catalyst may be regenerated externally. If stationary beds of catalyst are employed in the reforming reactors, the catalyst may be regenerated in situ by cyclic substitution of a spare reactor for a reactor in which the catalyst is being regenerated or by semi-cyclic shutdown of the entire regeneration systan while the catalyst in all the reactors is regenerated at one time. In the last mentioned case, it may be advantageous to first initiate regeneration in the final zone and preheat the oxygen-containing gas stream used to regenerate the first zone in the heat exchanger with the hot off gases from the final zone. Example I

A catalytic reformer comprising an alternating series of four reactors and three heaters, the heaters being disposed respectively between the first and second reactors, the second and third reactors and the third and fourth reactors, is charged with hydrocarbon naphtha feedstock at a rate of 17,000 barrels per stream day. Hydrogen-rich gas is also fed to the reformer at a rate sufficient to provide a hydrogen to hydrocarbon feed mole ratio of 5.0 to 1. The naphtha feedstock has a boiling range of 106°F to 39CPF and contains approxi¬ mately 52 percent paraffins and approximately 35 percent naphthenic compounds. The first three reactors each contain a 385 cubic foot

^"BU E4(7

OΛ'PI

, Afc Wii-0 ϊ bed of platinum containing alumina base refoiming catalyst; the fourth ■ reactor is larger and contains a 914 cubic foot bed of the catalyst. The naphtha feedstock and hydrogen-rich gas are intimately mixed and passed through a heat exchanger where the tetiperature of the admixture is raised to 825°F. The hot mixture is then passed through the first reactor wherein the temperature drops to 720 F. Effluent from the first reactor is heated to 938°F. in the first heater and then introduced into the second reactor wherein additional refoiming takes place and the temperature of the stream drops to 88CPF. The tempera- ture of the effluent from the second reactor is increased to 941°F. in the second heater and the reheated e fluent is passed to the third reactor. In the third reactor the temperature of the stream drops to 918°F. After leaving the third reactor the stream is heated to gSl^, in the third heater and introduced into the fourth reactor. The average reaction pressure in the system is 338 psig. Effluent leaving the fourth reactor at a temperature of 940°F. is passed directly to the heat exchanger to provide the necessary heat to preheat the initial feed mixture. After passing through the heat exchanger, the effluent is cooled and a C₅+ reformate product having a research octane number of 95 clear is separated frαn a stream of hydrogen-rich gases which are recycled. Nearly 14,000 barrels of C5+ reformate are produced per stream day for a yield of approximately 83 volume percent.

The foregoing embodiment and example have been described merely for purposes of illustration and are not intended to restrict the scope of the invention. It is recognized that numerous modifications of the disclosed embodiment are possible. For example, instead of employing an individual reactor for each stage of the refoiming process, separate reaction zones in a single cannon vessel might be utilized. Similarly, the heaters might be located in a single cannon firebox without departing from the spirit of this invention. Other modifica¬ tions of the disclosed embodiment also may occur to persons skilled in the art. Accordingly, the scope of the invention is to be limited solely by the scope of the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A process for reforming a hydrocarbon feedstock comprising preheating said feedstock and a hydrogen-containing gas by indirect heat exchange to refoiming conditions, passing said feedstock and hydrogen-containing gas in admixture successively through an alter¬ nating series of catalytic reaction zones at refoiming conditions and heaters; the number of heaters in said series being one less than the number of reaction zones and said admixture passing through the first reaction zone prior to entering the first heater.

2. A process according to claim 1 wherein the reforming conditions in each subsequent reaction zone are more severe than the reforming conditions in the first zone.

3. A process according to claim 1 wherein said admixture is passed in heat exchange relation with a source of process heat prior to being introduced into the first reaction zone.

4. A process according to claim 3 wherein said source of process heat is the effluent from the final reaction zone in the series of reaction zones.

5. A process according to claim 1 wherein the number of reaction zones is four and the number of heaters is three.

6. A process according to claim 1 wherein the inlet tenperature to each succeeding reaction zone in the series is progressively higher than the inlet taiperature to the iπmediately preceding reaction zone.

7. A process according to claim 1 wherein the inlet feedstock temperature of the first reaction zone lies between about 800 and 850°F and the inlet feedstock tenperature of each subsequent reaction zone is at least 9009F.

8. A process according to claim 7 wherein the number of reaction zones is four and the inlet teπperatures of the successive zones are at least 820°F, 930°F, 935°F, and 940°F, respectively.

9. A process according to claim 1 wherein the mole ratio of hydrogen to hydrocarbon feedstock is from about 4:1 to about 6:1.

10. A process according to claim 1 wherein the pressure in each reaction zone is at least 100 psig.

11. A process according to claim 10 wherein the pressure in each of the reaction zones is from about 150 psig to about 400 psig.

12. A process according to claim 1 wherein the feedstock and hydrogen-containing gas are mixed prior to passing through the heat exchanger.

13. A process according to claim 1 wherein said hydrocarbon feedstock is a petroleum naphtha fraction having a boiling range between 106 F and 390°F.

14. A process according to claim 1 wherein each reaction zone comprises a separate reactor.

15. A process according to claim 1 wherein each reaction zone is a separate zone in a common vessel.

16. A process according to claim 1 wherein the hydrocarbon feed¬ stock and hydrogen-containing gas are preheated separately and then admixed.