CA1098468A - Countercurrent hydrocarbon conversion with gravity- flowing catalyst particles - Google Patents

Abstract

COUNTERCURRENT HYDROCARBON CONVERSION
WITH GRAVITY-FLOWING CATALYST PARTICLES

ABSTRACT
A multiple-stage catalytic conversion system in which a hydro-carbon charge stock is countercurrently reacted in a plurality of catalytic reaction zones, in all of which the catalyst particles are downwardly movable via gravity-flow, The charge stock, in the absence of added, or recycled hydrogen, is reacted serially in the reaction zones in the order of increasing catalyst loading, the product ultimately being recovered from that reaction zone (1) into which fresh, or regenerated catalyst particles are introduced and, (2) which contains the greatest quantity of catalyst particles. Catalyst particles are transferred from one reaction zone to anotherin the order of decreasing catalyst loading, ultimately being withdrawn from the system through the reaction zone containing the least amount of catalyst particles.

Description

~Q~8468 WITH GRAVITY-FLOWING CATALYST PARTICLES
. _ , SPECIFICATION
The present invention is directed toward an im-proved technique for effecting the catalytic conversion of a hydrocarbonaceous reactant stream in a multiple-stage re-action cystem wherein (1) the reactant stream flows serially S through the plurality of reaction zones and, (2) the catalyst particles are movable through each reaction via gravity-flow.
More particularly, the described processing technique is adaptable for utilization in vapor-phase systems where (1) the conversion reactions are principally hydrogen-producing, or endothermic, (2) where fresh, or regenerated catalyst par-; ticles are introduced into one reaction zone, and are then ;l transferred therefrom into at least one intermediate reaction zone and, (3) deactivated catalyst particles are withdrawn from .
the last reaction zone in the system for subsequent regeneration.
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 are either exothermic, or endothermic, and both hydrogen-pro-ducing and hydrogen-consuming. Multiple-stage reaction systems are generally of two types: (1) existing in a side-by-side con-figuration with intermediate heating between the reaction zones, and wherein the reactant stream or mixture flows serially from ~-'` one zone to another zone; and, (2) a stacked design wherein a

2; single reaction chamber contains the multiple catalytic contact .

1~8468 stages, and wherein intermediate heating is ef~ected between stages. Such systems, as applied to petroleum refining, have been employed to effect numerous hydrocarbon conversion re-actions including those which are prevalent in catalytic re-forming, alkylation, ethylbenzene dehydrogenation to produce styrene, other dehydrogenation processes,etc. Our invention is specifically intended for utilization in endothermic, or hydrogen-producing hydxocarbon conversion processes, in the reaction zones of which the catalyst particles are downwardly movable via gravity-flow. It is contemplated, therefore, that the technique encompa~sed by our inventive concept is adapt-able where (1) the plurality of reaction zones tat least three) exists in a side-by-side configuration and, (2) where the re-action zones exist as a vertical stack having a common axis.
In the first configuration, the charge stock passes serially from one reaction zone into the next succeeding reaction zone.
Fresh, or regenerated catalyst particles are introduced into the top of the first reaction zone and are transferred from the bot-tom thereof into the top of the next zone. Deactivated catalyst particles, intended for regeneration, are withdrawn from the bottom of the last reaction zone in the series. In the second con-figuration, being the stacked system, fresh, or regenerated catalyst particles are introduced into the uppermost reaction zone, flow downwardly therethrough, into and through subsequent, intermediate reaction zones, and deactivated catalyst particles are withdrawn from the system through the lowermost reaction zone. Our invention is also intended to be applied to those ~g~3468 reaction systems wherein the catalyst is disposed as an annular bed, and the reactant stream flows serially from one zone to another reaction zone, but within each zone flows per-pendicularly to the movement of catalyst particles.
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 con-taining a coaxially-disposed catalyst retaining screen, having a nominal, internal cross sectional areas 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 annu-lar space created between the inside wall of the chamber and ~ 15 the outside surface of the catalyst retaining screen. The ,J latter forms an annular catalyst holding zone with the out-side surface of the perforated centerpipe; vaporous reactant flows laterally and radially through the screen and catalyst zone into the centerpipe and out of the reaction chamber. Al-though 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 com-ponents which are substantially circular in cross section.
A multiple-stage stacked reaction system is shown in United States Patent No. 3,706,536.
The present invention encompasses a process wherein the fresh feed charge stock, without added, or recycled hydro-~8468 gen, initially contacts gravity-flowing catalyst particles disposed as a stacked system, wherein catalyst flows through the zones in the order of decreasing catalyst volume. The reactant stream, however, flows completely countercurrently, in series, through the zones in the order of increasing cata-lyst volume. Thus, the reactant stream initially contacts the catalyst which has achieved the greatest level of coke depo-sition -- i.e. has attained the highest degree of catalyst deactivat1on. The primary advantage stems from the elimina-tion of the compressor otherwise required to recycle the hy-drogen-rich vaporous phase to combine with the fresh feed charge stock prior to the first reaction zone. Another major benefit, as hereinafter set forth, resides in the concomitant reduction ln the size of the catalyst regeneration facilities.
Thus the inventlon eliminates compressive recycle of hydrogen, *hereby achieving significant savings in utilities and energy.
The invention also achieves a reduction in the size ~ of the regeneration facilities integrated into the multiple-i 20 stage reaction system. Still another object of our invention is to coordinate riser-regeneration, similar to that practiced in the well-known Fluid Catalytic Cracking process, with the ~ gravity-flowing catalytic reaction system.
; ~ Accordingly, our invention is directed toward a pro-cess for the catalytic reforming of a hydrocarbon charge stock in a multiple-stage reactor system in which (1) catalyst par-ticles flow downwardly, via gravity, through each reaction zone in said system, (2) catalyst particle~ from one reaction zone 1~8468 are introduced into the next succeeding reaction zone, (3) deactivated catalyst particles are withdrawn from 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 in said system, 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 system, at catalytic reforming conditions; (b) further 10 reacting the effluent from said last reaction zone in at least one intermediate reaction zone, at catalytic reforming condi-tions; ~c) further reacting the effluent from said intermediate , reaction zone in said first reaction zone, through which fresh, or regenerated catalyst particles are introduced into said lS system, at catalytic reforming conditions; and, (d) recovering 1 a normally liquid, catalytically reformed product from the ef-`~ fluent withdrawn from said first reaction zone; said process .~; being further characterized in that said first reaction zone contains the greater amount of catalyst particles and said last reaction zone contains the least amount of catalyst particles.
In a more specific embodiment, the 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 trans-ferring catalyst particles from the lower end of said first zone into the upper end of a seoond reaction zone, through which said particles are movable via gravity-flow, said second zone containing a lesser quantity of catalyst particles than said first reaction zone; (b) transferring catalyst particles from the lower end of said second reaction zone into the upper end of a third reaction zone, through which said particles are movable via gravity-flow, said third zone containing a lesser quantity of catalyst particles than said second reaction zone;
(c) transferring catalyst particles from the lower end of said third reaction zone into the upper end of a fourth reaction zone, through which said particles are movable via gravity-flow, said fourth zone containing a lesser quantity of cata-lyst particles than said third reaction zone, and withdrawing -; deactivated catalyst particles from the lower end of said fourth reaction 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 re-- 15 sulting fourth reaction zone effluent in said third reaction zone, at catalytic reforming conditions; (f) further reacting the resulting third reaction zone effluent in said second re-action zone, at catalytic reforming conditions; (g) further reacting the resulting second reaction zone effluent in said first reaction zone, at catalytic reforming conditions; and, (h) recovering a normally liquid, catalytically reformed prod-uct from the resulting first reaction zone effluent.
In a preferred embodiment, where a stacked system consists of four reaction zones, the upper-most reaction zone : 25 contains about 35.0% to about 50.0% by volume of the total catalyst in the system, the first intermediate zone about 25.0%
to about 35.0%, the second intermediate zone about 15.0~ to about 25.0% and the lower-most reaction zone from about 5.0%
to about 15.0%.

1(~"8468 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"
system, the catalyst particles flow downwardly, via gravity, from one catalyst-containing zone to another, and ultimately transfer to a suitable regeneration system which can also func-tion with a downwardly moving bed of catalyst particles. We also contemplate employing regeneration facilities which are patterned after those utilized in the well known Fluid Cata-lytic Cracking process. The deactivated catalyst particles are transferred into an ebullient, constant-temperature bed.
Net upward combustion air flow ultimately reaches lift veloc-ity, and the flue gas lifts the catalyst into a disengaging vessel from which the regenerated catalyst particles are trans-ferred into the first reaction zone. With respect to the stacked reaction system, the catalyst particles are moved from one section to another in a mannex 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.
United States Patent No. 3,470,090 illustrates a multiple-stage side-by-side reaction system with intermediate heating of the reactant str,eam which flows serially through the individual reaction zones. A modified system is disclosed in U. S. Patent ~o. 3,839,197 involving an interreactor cata-l~Q84S8 lyst transport method. Catalyst transfer from the last re-action zone in the plurality to the top of the catalyst re-generation zone is possible through the technique illustrated in U. S. Patent No. 3,839,196.
A stacked reaction configuration is shown in U. 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 reaction system having gravity-flowing catalyst particles with a fixed-bed system. The use of a second 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-flow-ing catalyst particles being transported from the bottom af one reaction 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 fa-cilities.
~he 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-8~68 flow, in each reaction zone. Furthermore, the present inven-tion 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 fol-lowing discussion is specifically directed toward catalytic reforming of naphtha boiling range fractions, there is no in-tent 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 about 4.0 mm. When the reaction chambers are vertically stacked, 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 cata-lyst particles from the last reaction zone, they are usually transported to the top of a catalyst regeneration facility, functioning with 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-side relation-ship, 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 con-version conditions which include catalyst bed temperatures in the range of abou t 371C to about 549C. Other conditions normally include a pressure from about 4.4 to about 69.0 at-~8468 mospheres, a liquid hourly space velocity tdefined 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 hydrogen to hydrocarbon mole ratio from about 1.0:1.0 to about 10.0:1.0, with respect to the initial reaction zone. Continuous regenerative reforming systems offer numerous advantages when compared to the prior fixed-bed systems. Among these is the capability of efficient operation at lower pres-sures -- e.g. 4.4 to about 11.2 atmospheres -- and higher liquid hourly space velocities -- e.g. 3.0 to about 8Ø Further, as a result of continuous catalyst regeneration, higher consistent inlet catalyst bed temperatures can be maintained -- e.g. 510C
to about 543C. There also exists a corresponding increase in both hydrogen production and hydrogen purity in the vaporous phase recovered from the product separator.
Catalytic reforming reactions include the dehydro-genation of naphthenes to aromatics, the dehydrocyclization of of paraffins to aromatics, the hydrocracking of long-chain paraffin into lower-boiling normally-liquid material and, to a certain 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) com-bined with a halogen (e.g. chlorine and/ox fluorine) and a porous carrier material such as alumina. More advantageous results are sometimes attainable through the cojoint use of a catalytic modifier such as cobalt, nickel, gallium, germanium, tin, rhenium, vanadium and mixtures thereof. In any case, the ability to attain the advantages over the common fixed-bed sys-tems is greatly dependent upon achieving substantially uniform catalyst flow downwardly through the system.

1~"8468 Catalytic reforming typically utilizes multiple stages, each of which contains a different quantity of cata-lyst, 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 a-bout 30.0%; second, from 20.0% to about 40.0~; and, third, from about 40.0% to about 60.0%. With respect to a four re-action zone system, suitable catalyst loading would be: first, 5.0% to about 15.0%; second 15.0% to about 25.0~; third, 25.0%
to about 35.0%; and, fourth, 35.0% to about 50.0%. Unequal catalyst distribution, increasing in the direction of re-actant 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 hydrogan-rich vaporous phase. A portion of the latter is combined with the fresh charge stock as recycle hydrogen, while the remainder is vented from the process.
It has now been found that in a reaction zone system in which catalyst particles are movable via gravity-flow and using continuous catalyst regeneration, it is possible to ef-fect catalytic reforming without a hydrogen-rich recycle gas stream. This permits elimination of the recycle gas compressor.
When there is no recycled hydrogen, the hydrogen/hydrocarbon lQ~8468 mole ratio is "zero" at the inlet of the catalyst bed in the -first reaction zone which the charge stock "sees". ~ost of the naphthenes are converted to aromatics in this initial re-actor producing a large amount of hydrogen. In fact, as much as 50.0% of the overall hydrogen production in the entire pro-cess stems from the reactions effected in the first reactor.
This hydrogen yield provides an increasing hydrogen/hydro-carbon ratio in the second reactor and subsequent reactors.
This means that only reactor number one functions at zero hy-drogen/hydrocarbon ratio, and only at the inlet thereto. There-fore, the formation of coke will be higher in this reactor than in any of the subsequent reactors. As hereinbefore stated, considering 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 first zone contains the least amount of catalyst particles, ; while the last zone contains more catalyst than any of the others.
The most common method of operating a gravity-flow-ing catalytic reforming system, with integral continuous cata-lyst regeneration, is to stack the reaction zones such that catalyst particles also flow from one reaction zone into the next succeeding lower reaction zone. With this type of arrange-ment, catalyst circulation rate is the same through all the re-actors constituting the stack. Where no recycle gas compressor is provided, this becomes an unsatisfactory arrangement since ..

1~998468 the first (uppermost) reaction zone requires a higher catalyst circulation rate due to its high coke deposition. This reactor would then dictate the catalyst circulation rate for all the reactors in the stack. Furthermore, there is the additional disadvantage of highly coked, deactivated catalyst flowing into the second and subsequent reactors where maximum activity is required to effect paraffin isomerization, paraffin dehydro-cyclization and hydrocracking.
According to the present invention, as applied to a multiple-stage, stacked system wherein catalyst particles flow downwardly via gravity through each reaction zone, and from one zone into the next succeeding zone, is to reverse the re-action zonessuch that the uppermost zone contains the greater quantity of catalyst particles and the lowermost zone the least amount of catalyst particles. Thus, where the system consists of four individual reaction zones, the first zone, into which fresh, or regenerated catalyst particles are introduced, will contain from about 35.0% to about 50.0%, by volume of the to-tal catalyst. The first intermediate zone will contain from about 25.0% to about 35.0%, while the second intermediate zone about 15.0% to about 25.0%. The last reaction zone, rom which the deactivated catalyst particles are withdrawn from the sys-tem, will contain the least amount of catalyst, from about 5.0 to about 15.0%. The reactant stream flows countercurrentiy to ~ the descending column of catalyst particles, with the fresh charge stock initially contacting the catalyst in the last re-action zone. This means that the charge stock first contacts that catalyst having the highest degree of deactivation. Con-verseiy, the "last" catalyst which the reactant stream "sees"

. .

.
.

has experienced little, or no deactivation. In addition to the advantages attendant the elimination of the recycle gas compressor, a principal benefit from an overall reduction in coke make.
Coke deposition occurs at a considerably reduced rate on a catalyst thathas already been partially deactivated by coke, than it does on the freshly regenerated catalyst par-ticles 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 is also reduced. Another advantage is - that less catalyst circulation is required because the cata-lyst 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 activity is not required in this reactor since the main reaction is the conversion of naphthenes into aroma-tic hydrocarbons.
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, miscellaneous appurtenances, not required Por a complete understanding of the inventive concept, have been eliminated, or reduced in number.
Such items are well within the purview of one possessing skill in the art. The illustrated embodiment is a simplified schematic flow diagram of a four reaction zone process as stacked system 1. As shown, reaction zone 17 contains the greatest quantity of catalyst particles, while reaction zone 5 contains the least.

~98468 With respect to the volumetric distribution of cat-alyst particles, uppermost reaction zone 17 contains about 50.0~ by volume zone 13 about 25.0%, zone 9 about 15.0% and zone 5 about 10.0%. Fresh or regenerated catalyst particles are introduced into the system through conduit 22 and catalyst inlet port 23. These flow downwardly, via gravity, through reaction zone 17, and into zone 13. Likewise, the catalyst particles flow through reaction zone 13, and therefrom into reaction zone 9, from which they flow into lowermost reaction zone 5. The deactivated catalyst particles are withdrawn from the system through catalyst outlet port 24 and conduit 25.
These are then transported to sultable regeneration facilities.
Fresh charge stock is introduced into the process via line 2 and, after it has been heat-exchanged against another process stream of elevated temperature, passes into charge heater 3. The thus-heated feed, at the temperature desired -at the inlet to the catalyst bed in reaction zone 5, is intro-duced thereto via line 4. The effluent from the reaction zone 5, at a lower temperature due to the endothermicity of the re-actions, is introduced by way of line 6 into inter-heater 7.
Approximately 80.0% to about 90.0% of the naphthenes are de-hydrogenated to aromatics, with the accompanying production of sufficient hydrogen to effect efficiently the reactions in the subsequent reactions zones.
The heated effluent from zone 5 is passed through conduit 8 into the next intermediate zone 9; likewise, the ef-fluent therefrom, in line 10, is increased in temperature in heater 11, and introduced through line 12 into the second in-10~8468 termediate zone 13~ Effluent from zone 13 is introduced~
via line 14, into inter-heater 15, and the heated effluent passes through line 16 into the uppermost reaction zone 17.
The final, total product effluent passes through line 18 and, following its use as a heat-exchange medium, into a suitable condenser (not illustrated) wherein the temperature is lowered to a level in the range of about 15.6C to about 60C. The condensed material is then introduced into a sep-aration vessel 19, from which the normally liquid product is recovered in line 21. A hydrogen-rich vapor phase, contain-ing some light paraffinic hydrocarbons and a minor quantity of butane and pentane, is removed through line 20 and trans-ported thereby into suitable hydrogen concentration facilities.
The recovered hydrogen is extremely well-suited for use in vari-ous hydrogen-consuming processes.
By means of the present invention, the catalytic re-forming of a hydrocarbon charge stock is effected in a multiple-stage system, in which catalyst flows downwardly, vla gravlty, through each reaction zone in the system, and without recycling ; 20 a portion of the hydrogen-rich vaporous phase separated from the desired normally liquid product effluent, or without the addition of hydrogen from some external source.

Claims (9)

WE CLAIM AS OUR INVENTION:

1. A process for the catalytic reforming of a hydro-carbon charge stock in a multiple-stage reactor system in which (1) catalyst particles flow downwardly, via gravity, through each reaction zone in said system, (2) catalyst particles from one reaction zone are introduced into the next succeeding reac-tion zone, (3) deactivated catalyst particles are withdrawn from 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 in said system, 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 system, at catalytic reforming conditions;
(b) further reacting the effluent from said last reaction zone in at least one intermediate reaction zone, at catalytic reforming conditions;
(c) further reacting the effluent from said inter-mediate reaction zone in said first reaction zone, through which fresh, or regenerated catalyst particles are intro-duced into said system, at catalytic reforming conditions;
and, (d) recovering a normally liquid, catalytically-reformed product from the effluent withdrawn from said first reaction zone;
said process being further characterized in that said first reac-tion zone contains the greater amount of catalyst particles and said last reaction zone contains the least amount of catalyst particles.

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

3. The process of Claim 2 wherein said first reaction zone contains from about 40.0% to about 60.0%, by volume, of the total catalyst in said system; said intermediate reaction zone about 20.0% to about 40.0%; and, said last reaction zone from about 10.0% to about 30.0%.

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

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

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 vertically-stacked, along a common vertical axis, and the catalyst particles flow via gravity from one reaction zone to the next succeeding reaction zone.

8. The process of Claim 6 wherein the four reaction zones are in side-by-side configuration, and the catalyst par-ticles are transported from the lower end of one reaction zone to the upper end of the next succeeding reaction zone.

9. The process of Claim 6 wherein the first reaction zone contains about 35.0% to about 50.0% by volume of the total catalyst, the second reaction zone from about 25.0% to about 35.0%, the third reaction zone from about 15.0% to about 25.0%
and the fourth reaction zone from about 5.0% to about 15.0%