CA1098470A - Hydrogen-producing hydrocarbon conversion with gravity-flowing catalyst particles - Google Patents

Abstract

HYDROGEN-PRODUCING HYDROCARBON CONVERSION
WITH GRAVITY-FLOWING CATALYST PARTICLES

ABSTRACT
A multiple-stage catalytic conversion system in which a hydrocarbonaceous charge stock is reacted in a plurality of stacked catalytic reaction zones through which catalyst particles flow down-wardly via gravity-flow. The charge stock, in the absence of added, or recycle hydrogen, is reacted first in the lowermost reaction zone, from which deactivated catalyst particles are withdrawn from the system. Resulting reaction zone effluent is further reacted in the uppermost reaction zone, through which fresh, or regenerated catalyst particles are introduced into the system, and serially in one or more subsequent, lower reaction zones. Product effluent from the reaction zone immediately above the lowermost zone is separated to recover the desired normally liquid product.

Description

10"84~0 HYDROGEN-PRODUCING HYDROCARBON CONVERSION
~ITH GRAVITY-FLOWING CATALYST PARTICLES

SPECIFICATION

The present invention is directed toward an improved technique for effecting the catalytic conversion of a hydrocar-bonaceous reactant stream in a multiple-stage reaction system wherein (1) the reactant stream flows serially through the pl~r-ality of reaction zones and, (2) the catalyst particles are movable through each reaction zone via gravity-flow. More par-ticularly, the described process technique is adaptable for utilization in vapor-phase systems where the conversion reactions are principally hydrogen-producing, or endothermic, where the multiple reaction zones are vertically stacked, sharing a common vertical axis, and where the catalyst particles flow downwardly through and from one zone to the next lower zone via gravity-flow~
Various types of multiple-stage reaction systems have . found widespread utilization throughout the petroleum and petro-chemical industries for effecting multitudinous reactions, es-pecially hydrocarbon conversion reactions. Such reactions are either exothermic, or endothermic, and both hydrogen-producing and hydrogen-consuming. Multiple-stage reaction systems are :
~ generally of two types: (1) side-by-side configuration with -.
; 20 intermediate heating between the reaction zones, wherein the reactant stream or mixture flows serially from one zone to another zone; and, (2) a stacked design wherein a single reaction cham-ber, or more, contains the multiple catalytic contact stages.

~0~8470 Such systems, as applied to petroleum refining, have been employed to effect numerous hydrocarbon conversion reactions including those which are prevalent in catalytic reforming, alkylation, ethylbenzene dehydrogenation to produce styrene, other dehydro-genation processes, etc. My invention is specifically intendedfor utilization in endothermic, or hydrogen-producing, hydrocar-bon conversion processes, in the reaction zones of which the catalyst particles are movable via gravity-flow. Thus, it is contemplated that the technique encompassed by the present in-vention can be employed where the reaction zones (1) exist inside-by-side relationship, and catalyst particles are transported from the bottom of one zone to the top of the next succeeding zone, (2) where the reaction zones are stacked, sharing a common vertical axis, and the catalyst particles also flow from one zone to another via gravity and, (3) a combination thereof wherein one or more zones are disposed in side-by-side relationship with the stacked reaction zones. Therefore, since catalyst parti-cles which are movable through a system by way of gravity-flow are necessarily moving in a downwardly direction, the present process contemplates the withdrawal of catalyst particles from a bottom portion of one reaction zone and the introduction of fresh, or regenerated catalyst particles into the top portion of a second reaction zone. My invention is also intended to be applied to those reaction systems wherein the catalyst is dis-posed as an annular bed and the flow of the reaction stream, - serially from one zone to another reaction zone, is perpendicu-lar, or radial to the movement of catalyst particles. In the 10~84~0 interest of brevity, the following discussion will be directed toward those systems wherein a downwardly moving bed of catalyst particles is employed in the conversion of a hydrocarbonaceous reactant stream, with the catalyst particles being disposed in the form of an annular bed, through which the reactant stream flows laterally and radially.
A radial-flow reaction system generally consists of tubular-form sections, of varying nominal cross-sectional areas, vertically and coaxially disposed to form the reaction vessel.
Briefly, the system comprises a reaction chamber containing a coaxially disposad catalyst-retaining screen, having a nominal, internal cross-sectional area less than said chamber, and a perforated centerpipe having a nominal, internal cross-sectional area less than the catalyst-retaining screen. The reactant stream is introduced in vapor-phase, into the annular space created between the inside wall of the chamber and the outside surface of the catalyst-retaining screen. The latter forms an annular catalyst-holding zone with the outside surface of the perforated centerpipe; vaporous reactant flows laterally and , radially through the screen and catalyst zone into the center-pipe and out of the reaction ahamber. Although the tubular-form configuration of the various reactor components may take any suitable shape -- i.e., triangular, square, oblong, diamond, etc. -- many design, fabrication and technical considerations indicate the advantages of using components which are substan-tially circular in cross-section.

~'a847~) A multiple-stage stacked reactor system is shown in U.S. Patent No. 3,706,536.
The present invention encompasses a process wherein the fresh feed charge stock, in the absence of added, or re-cycled hydrogen, first contacts those catalyst particles which have advanced to the highest degree of deactivation, with re-spect to all the catalyst within the multiple-stage system.
A primary beneficial advantage stems from the accompanying elimination of the compressor otherwise required to recycle the hydrogen-rich vaporous.phase separated from the desired normally liquid product.
Thus, the invention eliminates compressive recycle of hydrogen, thereby achieving significant savings in utili-ties and energy.
Accordingly, the present invention is directed to a process for the catalytic reforming of a hydrocarbon charge stock in a multiple-stage system in which (1) catalyst parti-cles flow downwardly, via gravity, through each reaction zone in said system, (2) catalyst particles are transferred in series from reaction zone to reaction zone in said system, (3) deactivated catalyst particles are withdrawn irom said system through the lower end of the last reaction zone and, (4) fresh, or regenerated catalyst particles are introduced into the upper end of the first reaction zone, which process comprises the sequential steps of: (a) reacting said charge stock, in the absence of added hydrogen, in said last reaction zone, from which deactivated catalyst particles are withdrawn from said lQ~8~70 system, at catalytic reforming conditions; (b) further reacting the effluent from said last reaction zone in said first reaction zone, through which fresh or regenerated catalyst particles are introduced into said system, at catalytic reforming condi-tions; (c) further reacting the effluent from said first reac-tion zone in at least one intermediate reaction zone, at cata-lytic reforming conditions; and, (d) recovering a normally liquid, catalytically-reformed product from the effluent with-drawn from said intermediate reaction zone.
In a more specific embodiment, the present invention comprises the steps of: (a) introducing fresh, or regenerated catalyst particles into the upper end of a first reaction zone, through which said particles are movable via gravity-flow, and transferring catalyst particles from the lower end of said first zone into the upper end of a second reaction zone, through which said catalyst particles are movable via gravity-flow; tb) transferring catalyst particles from the lower end of said second zone and introducing them into the upper end of a third reaction zone, through which catalyst particles are movable via gravity-flow; (c) transferring catalyst particles from the lower end of said third zone and introducing them into the upper end of a fourth reaction zone, through which catalyst particles are movable via gravity-flow, and withdrawing deactivated catalyst particles from the lower end of said fourth zone; (d) reacting a hydrocarbon charge stock, in the absence of added hydrogen, in said fourth reaction zone at catalytic reforming conditions; (e) further reacting the resulting fourth zone effluent in said 1~9847~

first reaction zone at catalytic reforming conditions; (f) further reacting the resulting first zone effluent in said second reaction zone at catalytic reforming conditions; (g) further reacting the resulting second zone effluent in said third reaction zone at catalytic reforming conditions; and, (h) recovering a normally liquid, catalytically-reformed product from the resulting third reaction zone effluent.
In a preferred embodiment, the four catalytic reform-ing reaction zones are disposed as a vertical stack having a common vertical axis, and catalyst particles are movable from one reaction zone to the next succeeding reaction zone via gravity-flow. In another embodiment, the last reaction zone, into which the fresh feed charge stock is introduced and from which the deactivated catalyst particles are withdrawn from the system, contains the least amount of catalyst particles. Thus, for example, where the system comprises four reaction zones, the first zone desirably contains about 10.0% to about 20.0%
by volume of the total catalyst, the ~econd zone about 20.0%
to about 30.0%, the third zone about 40.0~ to about 60.0% and the last reaction zone, into which the charge stock is first introduced, about 5.0% to about 15.0%.
PRIOR ART
Various types of hydrocarbon conversion processes have utilized multiple-stage reaction systems, either in side-by-side configuration, as a vertically-disposed stack, or a combination of a stacked system in side-by-side relation with one or more separate reaction zones. In a conventional "stacked"

~(~'38470 system, the catalyst particles flow downwardly from one cata-lyst-containing zone to another and ultimately transfer to a suitable regeneration system also preferably functioning with a downwardly moving bed of catalyst particles. In effect, the catalyst particles are moved from one section to another in a manner such that the flow of catalyst is continuous, at frequent intervals, or at extended intervals, with the movement being controlled by the quantity of catalyst withdrawn from the last of the series of individual reaction zones.
U.S Patent No. 3,470,090 illustrates a multiple-stage, side-by-side reaction system with intermediate heating of the reactant stream which flows serially through the individ-ual reaction zones. A modified system is disclosed in U.S.
Patent No. 3,839,197 involving an inter-reactor catalyst trans-port method. Catalyst transfer from the last reaction zone to the top of the catalyst regeneration zone i8 possible through the technique illustrated in U.S. Patent No. 3,839,196.
A stacked reaction configuration is shown in V.S.
Patent No. 3,647,680 as a two-stage system having an integrated regeneration facility which receives that catalyst withdrawn from the bottom reaction zone. Similar stacked configurations are illustrated in U.S. Patent No. 3,692,496 and U.S. Patent No. 3,725,249.
General details of a three reaction zone, stacked system are present in U.S. Patent No. 3,706,536, wherein each succeeding reaction zone contains a greater volume of catalyst.
U.S. Patent No. 3,864,240 illustrates the integration of a ~C! '38470 reaction system having gravity-flowing catalyst particles with a fixed-bed system. The use of a ~econd compressor to permit the split-flow of hydrogen-rich recycle gas is described in U.S. Patent No. 3,516,924.
U.S. Patent No. 3,725,248 illustrates a multiple-stage system in side-by-side configuration with gravity-flowing cata-lyst particles being transported from the bottom of one reac-tion zone to the top of the next succeeding reaction zone, those catalyst particles being removed from the last reaction zone being transferred to suitable regeneration facilities.
The process of the present invention is suitable for use in hydrocarbon conversion systems characterized as multiple-stage and in which catalytic particles are movable, via gravity-flow, in each reaction zone. Furthermore, the present invention is principally intended for utilization in systems where the principal reactions are endothermic, or hydrogen-producing, and are effected in vapor-phase operation. Although the following discussion is specifically directed toward catalytic reforming of naphtha boiling range fractions, there i5 no intent to so limit the present invention. Typical reforming catalysts are spherical in form and have a nominal diameter ranging from ~ about 0.79 mm to about4.0 mm. When the reaction ~hambers are ;~ vertically stac~ed, a plurality (generally from 6 to 16) of relatively small diameter conduits are employed to transfer catalyst particles from one reaction zone to the next lower reaction zone. Following withdrawal of the catalyst particles from the last reaction zone, they are usually transported to the top of a catalyst regeneration facility, functioning with '8470 a descending column of catalyst particles; regenerated catalyst particles are transported to the top of the upper reaction zone of the stack. In a conversion system having the individual reaction zones in side-by-~ide relationship, catalyst transport vessels are employed in transferring the catalyst particles from the bottom of one zone to the top of the succeeding zone, and from the last reaction zone to the top of the regeneration facility.
Catalytic reforming of naphtha boiling range hydro-carbons, a vapor-phase operation, is usually effected at conver-sion conditions which include catalyst bed temperatures in the range of about 371C. to about 549C. Other conditions normally include a pressure from about 4.4 to about 69.0 atmospheres, a liquid hourly space velocity (defined as volumes of fresh charge stock per hour, per volume of total catalyst particles) of from 0.2 to about 10.0 and, prior to the present invention, a hydro-gen to hydrocarbon mole ratio from about 1.0:1.0 to about 10.0:
1.0, with respect to the lnitial reaction zone. Continuous re-generative reforming systems offer numerous advantages when ; 20 compared to the prior fixed-bed systems. Among these is the capability of efficient operation at lower pressures -- e.g.
4.4 to about 11.2 atmospheres -- and higher liquid hourly space velocities -- e.g. 3.0:1.0 to about 8.0:1Ø Further, as a result of a continuous catalyst regeneration, higher consistent inlet catalyst bed temperatures can be maintained -- e.g. 510C.
to about 543C. There can also exist a corresponding increase in both hydrogen production and hydrogen purity in the vaporous phase recovered from the product separator.

_g_ ~Q9847~

Catalytic reforming reactions in~lude the dehydro-genation of naphthenes to aromatics, the dehydrocyclization of paraffins to aromatics, the hydrocracking of long-chain paraf-fins into lower-boiling normally-liquid material and, to a cer-tain extent, the isomerization of paraffins. These reactions are commonly effected through the use of one or more Group VIII noble metals (e.g. platinum, iridium, rhodium) combined with a halogen (e.g. chlorine and/or fluorine) and a porous carrier material such as alumina. More advantageous results are attainable through the cojoint use of a catalytic modifier, such as cobalt, nickel, gallium, germanium, tin, rhenium, vana-dium and mixtures thereof. In any case, the ability to attain the advantages over the common fixed-bed systems is greatly de-pendent upon achieving substantially uniform catalyst flow downwardly through the system.
Catalytic reforming typically utilizes multiple stages, each of which contains a different quantity of catalyst, expressed generally as volume percent. The reactant stream, hydrogen and the hydrocarbon feed, flows serially through the reaction zones in order of increasing catalyst volume with interstage heating. In a three reaction zone system, typical catalyst loadings are: first, 10.0% to about 30.0%; second, from 20.0~ to about 40.0%; and, third, from ~bout 40.0% to about 60.0%. With respect to a four reaction zone system, suitable catalyst loading would be: first, 5.0% to about 15.0%;
second, 10.0% to about 20.0%; third, 20.0% to about 30.0%;
and, fourth, 40.0% to about 60.0%. Unequal catalyst distribution, increasing in the direction of reactant stream flow, facilitates and enhances the distribution of the reactions and the overall heat of reaction.
Current operating techniques involve separating the total effluent from the last reaction zone, in a so-called high-pressure separator, at a temperature of about 15.6C. to about 60C., to provide the normally liquid product stream and a hydrogen-rich vaporous phase. A portion of the latter is com-bined with the fresh charge stock as recycle hydrogen, while the remainder is vented from the process. It has now been found that, in view of the current improved catalytic composites and continuous catalyst regeneration, as illustrated in the prior art hereinbefore described, it is possible to effect catalytic reforming without a hydrogen-rich recycle gas stream. This permits a significant reduction in the initial capital cost of the unit by completely eliminating the recycle gas compressor.
When there is no recycled hydrogen-rich recycle gas, the hydro-gen/hydrocarbon mole ratio is obviously zero at the catalyst bed inlet of the first reactor. In catalytic reforming, most of the naphthenes are converted to aromatics in the first reactor;
this produces a large amount of hydrogen. In fact, as much as 50.0% of the overall hydrogen production from catalytic reform-ing stems from the reactions effected in the first reactor.
This hydrogen yield provides an increasing hydrogen/hydrocarbon ratio in the second reactor and subsequent reactors. ~his means that only reactor number one functions at zero hydrogen/
hydrocarbon ratic, and only at the inlet thereto. Therefore, . _ _ _ , .,, _ , ., , . . _ . _ ..................... . . _ . _ .
~, 1~9847(~

the formation of coke will b higher in this reactor than in any of the subsequent reactors. As hereinbefore stated, con-sidering a four-reactor system, the reactant flow is serially 1-2-3-4; in a stacked system, the number one reaction zone is considered to be at the top. Also, catalyst distribution is generally unequal and such that the catalyst volume increases from one reactor to the next succeeding reactor; that is, the number one zone contains the least amount of catalyst particles, while the last, or fourth reaction zone contains more catalyst than any of the others.
My invention, as directed to a multiple-stage system wherein catalyst particles flow downwardly via gravity through each reaction zone, involves initially contacting the fresh feed charge stock with those catalyst particles which have attained the greatest degree-of deactivation, and without recycle of hydrogen-rich gas. In accordance therewith, the flow of catalyst from one zone to another would be 2-3-4-1, with catalyst from number one being subjected to regeneration, and regenerated, or fresh catalyst particles being introduced into the number two reaction zone. Flow of the reactant str~am is 1-2-3-4, so that the fresh feed aharge stock initially contacts catalyst particles upon which about 5.0% by weight of coke has already been deposited. In the configuration wherein the reac-tion zones are stacked, the number one zone, containing the least amount of catalyst particles, is placed a~ the bottom of the stack. In addition to the advantages attendant the elimination of the recycle gas compressor, a principal benefit arises from an overall reduction in coke make.

10~8470 Coke deposition occurs at a considerably reduced rate on a catalyst that has already been partially deactivated by coke, than it does on the freshly regenerated catalyst particles entering the system via the top reaction zone. In view of the fact that there is an overall reduction in the amount of coke make, the size and operating costs of the attendant regeneration facilities i9 also reduced. Another advantage is that less catalyst circulation is required because the catalyst leaving the last reactor can have a coke content as high as about 20.0 by weight, instead of the usual 2.0% to about 5.0~. High ac-tivity is not required in this reactor since the main reaction is the conversion of naphthenes into aromatic hydrocarbons.

BRIEF DESCRIPTION OF DRAWING

The present invention can be further described with reference to the accompanying drawing which is presented solely for the purposes of illustration, and is not intended to limit the scope and spirit of the invention. Therefore, miscellane-OU8 appurtenances, not required for a complete understanding of the inventive concept, have been eliminated, or reduced in num-ber. Such items are well within the purview of one possessing skill in the art. The illustrated embodiment is a simplified schematic flow diagram showing a four reaction zone, stacked ; catalytic reforming system 1 having a charge heater 11 and reaction zone inter-heaters 14, 20 and 17.
The stacked, gravity-flowing catalyst system 1 is shown as having four individual reaction zones 2, 3, 4 and 5 which are sized both as to length and cross-sectional catalyst area such that the distribution of the total catalyst volume is 15.0%, 25.0%, 50.0~ and 10.0%, respectively. Fresh or regen-erated catalyst particles are introduced into the uppermost zone 2 by way of conduit 6 and inlet port 7, and flow via grav-ity therefrom into reaction zone 3, from zone 3 into zone 4, from zone 4 into zone 5, and are ultimately withdrawn from the system through a plurality of outlet ports 8 and conduits 9.
Catalyst particles so removed may be transported to a continu-ous regeneration zone (not illustrated), or may be stored until a sufficient quantity is available for batchwise regeneration.
The catalyst particles in reaction zone 5 contain about 10.0~-20.0~ by weight of coke; however, there is qufficient residual activity to effect substantial conversion of naphthenes to aro-matics and hydrogen. Therefore, the naphtha boiling range charge stock, without recycle hydrogen, is introduced via line 10, after suitable heat-exchange with a higher temperature stream, into charge heater Il, wherein the temperature is in-creased to the desired level. The heated feed emanates through conduit 12 and is introduced thereby into reaction zone 5.
Approximately 80.0% to about 90.0~ of the naphthenes are dehy-drogenated to aromatics, with the acaompanying production of hydrogen.
Since the dehydrogenation reactions effected in reac-- tion zone S are principally endothermic, the temperature of the effluent therefrom in line 13 will be increased through the use of reaction zone inter-heater 14. Heated effluent in line 15 is then introduced into uppermost reaction zone 2, into which .

regenerated, or fresh catalyst particles are introduced via conduit 6 and inlet port 7. Effluent from reaction zone 2 is introduced, via line 16, into reaction zone inter-heater 17 wherein the temperature is once again increased; heated efflu-ent is passed through conduit 18 into reaction zone 3. Efflu-ent from reaction zone 3 is passed via conduit 19 into inter-heater 20, and therefrom into reaction zone 4 via conduit 21.
Product effluent is withdrawn from reaction zone 4 through line 22 and, following its use as a heat-exchange medium, introduced thereby into condenser 23 wherein the temperature is further decreased to a level in the range of about 15.6C. to 60C. The condensed material is transferred into separator 25 by way of line 24, wherein separation into a normally liquid phase, line 26, and a hydrogen-rich vaporous phase, line 27, is effected.
By means of the present invention, the catalytic re-forming of a hydrocarbon charge stock is effected in a multi-ple-stage system, in which catalyst flows downwardly, via gravity, through each reaction zone in the system, and wherein particles from one reaction zone are introduced into the next succeeding reaction zone, and without recycling a portion of the hydrogen-rich vaporous phase separated $rom the desired normally liquid product effluent.

.

Claims (9)

I CLAIM AS MY INVENTION:

1. A process for the catalytic reforming of a hydro-carbon charge stock in a multiple-stage system in which (1) catalyst particles flow downwardly, via gravity, through each reaction zone in said system, (2) catalyst particles are transferred in series from reaction zone to reaction zone in said system, (3) deactivated catalyst particles are withdrawn from said system through the lower end of the last reaction zone, and, (4) fresh, or regenerated catalyst par-ticles are introduced into the upper end of the first reac-tion zone, which process comprises the sequential steps of:
(a) reacting said charge stock, in the absence of added hydrogen, in said last reaction zone, from which deac-tivated catalyst particles are withdrawn from said system, at catalytic reforming conditions;
(b) further reacting the effluent from said last reaction zone in said first reaction zone, through which fresh or regenerated catalyst particles are introduced into said system, at catalytic reforming conditions;
(c) further reacting the effluent from said first reaction zone in at least one intermediate reaction zone, at catalytic reforming conditions; and, (d) recovering a normally liquid, catalytically-reformed product from the effluent withdrawn from said in-termediate reaction zone.

2. The process of Claim 1 wherein said multiple-stage system comprises at least three reaction zones.

3. The process of Claim 1 wherein the reaction zones in said system are in side-by-side configuration, and the catalyst particles are transported from the lower end of one reaction zone to the upper end of the next succeeding reac-tion zone.

4. The process of Claim 1 wherein the reaction zones in said system are vertically-stacked, along a common verti-cal axis, and the catalyst particles flow via gravity from one reaction zone to the next succeeding reaction zone.

5. The process of Claim 1 wherein said last reaction zone contains the least amount of catalyst particles.

6. The process of Claim 1 wherein said multiple-stage system contains four reaction zones.

7. The process of Claim 6 wherein the four reaction zones are disposed in side-by-side relationship, and the catalyst particles are transported from the lower end of one reaction zone to the upper end of the next succeeding reaction zone.

8. The process of Claim 6 wherein the four reaction zones are stacked, having a common vertical axis, and the catalyst particles are movable from one reaction zone to the next succeeding reaction zone via gravity-flow.

9. The process of Claim 6 wherein the first reaction zone contains about 10.0% to about 20.0% by volume of the total catalyst, the second reaction zone from about 20.0%
to about 30.0%, the third reaction zone from about 40.0% to about 60.0% and the fourth reaction zone from about 5.0% to about 15.0%.