IE46297B1 - Countercurrent hydrocarbon conversion with gravity-flowing catalyst particles - Google Patents

Description

The present invention is directed toward an improved technique for effecting the catalytic conversion of a hydrocarbon charge stock in a multiple-stage reactor system in which (1) the reactant stream flows serially through the plurality of reaction zones and, (2) the catalyst particles move 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 particles are introduced into one reaction zone, and are then transferred therefrom into at least one intermediate reaction zone and, (3) deactivated catalyst particles are withdrawn from the last reaction zone in the system for subsequent regeneration Various types of multiple-stage reaction systems have found widespread utilization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 petrochemical industries for effecting multitudinous reactions, especially 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: il) existing in a side-by-side configuration 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 single reaction chamber contains the multiple catalytic contact -2stages, and wherein intermediate heating is effected between stages. Such systems, as applied to petroleum refining, have been employed to effect numerous hydrocarbon conversion reactions including those which are prevalent in catalytic re5 forming, alkylation, ethylbenzene dehydrogenation to produce styrene and other dehydrogenation processes. Our invention is specifically intended for utilization in endothermic, or hydrogen-producing hydrocarbon conversion processes, in the reaction zones of which the catalyst particles move downwardly via gravity-flow. It is contemplated, therefore, that the technique encompassed by our inventive concept is adaptable where (1) the plurality of reaction zones (at least three) exists in a side-by-side configuration and, (2) where the reaction 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 bottom 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 configuration, 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 -346297 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 perpendicularly to the movement of catalyst particles.

A radial-flow reaction system generally consists of tubular-form sections , of different nominal cross sectional areas, vertically and coaxially-disposed to form the reaction vessel. Briefly, the system comprises a reaction chamber containing a coaxially-disposed 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 centerpipe and out of the reaction chamber. Al20 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. Λ 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-446297 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 catalyst volume. Thus, the reactant stream initially contacts the catalyst which has achieved tho greatest level of coke deposition — i.e. has attained the highest degree of catalyst deactivation. The primary advantage stems from the elimination of the compressor otherwise required to recycle the hydrogen-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 in the size of the catalyst regeneration facilities.

Thus the invention eliminates compressive recycle of hydrogen, thereby achieving significant savings in utilities and energy.

The invention also achieves a reduction in the size of the regeneration facilities integrated into the multiplestage reaction system, in a further embodiment our invention seeks to coordinate riser-regeneration, similar to that practiced in the well-known FCC (Fluid Catalytic Cracking) process, with the gravity-flowing catalytic reaction system.

According to the invention there is provided a process for the catalytic reforming of a hydrocarbon charge stock in a multiple-stage reactor system in which (1) catalyst particles flow downwardly, under gravity, through each reaction zone in said system, (2) catalyst particles from each reaction zone -546297 except the last are Introduced into the next succeeding reaction zone, (3) deactivated catalyst particles are withdrawn from the 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 the system, which process comprises the sequential steps of: (a) reacting the charge stock, in the absence of added hydrogen, in the last reaction zone, the zone from which deactivated catalyst particles are withdrawn from the system, at catalytic reforming conditions; (b) further reacting the effluent from the last reaction zone successively in one or more intermediate reaction zones each at catalytic reforming conditions; (c) further reacting the effluent from the only or final intermediate reaction zone in the first reaction zone, the zone into which fresh or regenerated catalyst particles are introduced into the system, at catalytic reforming conditions; and, (d) recovering a normally liquid, catalytically reformed product from the effluent withdrawn from the first reaction zone; the process being further characterized in that the first reaction zone contains the greater amount of catalyst particles and the last reaction zone contains the least amount of catalyst particles.

Iii a more specific embodiment of the invention the process comprises the steps of (a) introducing fresh, or regenerated catalyst particles into the upper end of a first reaction zone, through which said particles move via gravity-flow, and transferring catalyst particles from the lower end of the first zone into the upper end of a second reaction zone, through which said particles move 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 the second reaction zone into the upper end of a third reaction zone, through which said particles move 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 the third reaction zone into the upper end of a fourth reaction zone, through which said particles move via gravity-flow, said fourth zone containing a lesser quantity of catalyst particles than said third reaction zone, and withdrawing deactivated catalyst particles from the lower end of the fourth reaction zone; (d) reacting a hydrocarbon charge stock, in the absence of added hydrogen, in the fourth reaction zone, at catalytic reforming conditions; (e) further reacting the resulting fourth reaction zone effluent in the third reaction zone, at catalytic reforming conditions; (f) further reacting the resulting third reaction zone effluent in the second reaction zone, at catalytic reforming conditions; (g) further reacting the resulting second reaction zone effluent in the first reaction zone, at catalytic reforming conditions; and, (h) recovering a normally liquid, Catalytically reformed product from the resulting first reaction zone effluent.

Preferably when the reactor system is a stacked system with four reaction zones, the upper-most reaction zone contains 35 to 50% by volume of the total catalyst in the system, the first intermediate zone 25 to 35%, the second intermidiate zone 15 to 25% and the lower-most reaction zone from 5 to 15%.

Various types of hydrocarbon conversion processes have utilized multiple-stage reaction systems, either in sideby-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 function with a downwardly moving bed of catalyst particles. We also contemplate employing regeneration facilities which are patterned after those utilized in the well known J?CC (Fluid Catalytic Cracking)process. The deactivated catalyst particles are transferred into an ebullient, constant-temperature bed.

Net upward combustion air flow ultimately reaches lift veloc15 ity, and the flue qas lifts the catalyst into a disengaging vessel from which the regenerated catalyst particles are transferred into the first reaction zone. With respect to the stacked reaction system, 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.

United States 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 individual reaction zones. Λ modified system is disclosed in U. S. Patent No. 3,839,197 involving an interreactor cata-II4 6 297 lyst transport method. Catalyst transfer from the last reaction zone in the plurality to the top of the catalyst regeneration 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 multiple20 stage system in side-by-side configuration with gravity-flowing catalyst particles being transported from the bottom of 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 fa25 cilities.

The process of the present invention is suitable for use in hydrocarbon conversion systems characterized as multiplestage and in which catalytic particles move, via gravity-946297 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 fol5 lowing discussion is specifically directed toward catalytic reforming of naphtha boiling range fractions, there is no intent to so limit the present invention. Typical reforming catalysts are spherical in form and have a nominal diameter ranging from 0.79 mm to 4,0 mm. When the reaction chambers are vertically stacked, a plurality (generally from 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 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 relation20 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 hydro25 carbons, a vapor-phase operation, is usually effected at conversion conditions which include catalyst bed temperatures in the range of 371°C to 549°C. Other conditions normally include a pressure from 4.4 to 69.0 at-1046297 mospheres, 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 10 and, prior to the present invention, a hydrogen to hydrocarbon mole ratio 1:1 to 10:1 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 pressures — e.g. 4.4 to 11.2 atmospheres — and higher liquid hourly space velocities — e.g. 3 to 8. Further, as a result of continuous catalyst regeneration, higher consistent inlet catalyst bed temperatures can be maintained — e.g. 510°C to 543°C. 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 dehydrogenation of naphthenes to aromatics, the dehydrocyclization paraffins to aromatics, the hydrocracking of long-chain paraffins 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) combined with a halogen (e.g. chlorine and/or 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 systems is greatly dependent upon achieving substantially uniform catalyst flow downwardly through the system. -1146297 Prior-art 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 prior art catalyst loadings are: first 10 to 30% second, from. 20 to 40%; and third, from 40 to 60%. With respect to a four reaction zone system, suitable prior art catalyst loading would be: first, 5 to 15%; second 15 to 25%. Unequal catalyst distribution, increasing in the direction of recatalyst 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 15.6°C to 60°C, to provide the normally liquid product stream and a hydrogen-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 move via gravity-flow and using continuous catalyst regeneration, it is possible to effect 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 -124629 mole ratio is zero at the inlet of the catalyst bed in the first reaction zone which the charge stock sees. Most of the naphthenes are converted to aromatics in this initial reactor producing a large amount of hydrogen. In fact, as much as 50% of the overall hydrogen production in the entire process stems from the reactions effected in this first reactor.

This hydrogen yield provides an increasing hydrogen/hydrocarbon ratio in the second reactor and subsequent reactors.

This means that only reactor number one functions at zero hy10 drogen/hydrocarbon ratio, and only at the inlet thereto. Therefore, the formation of coke will be higher in this reactor than in any of the subsequent reactors. As hereinbefore stated, considering a prior-art four-reactor system, the reactant flew 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-flowing catalytic reforming system, with integral continuous catalyst 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 arrangement, catalyst circulation rate is the same through all the reactors constituting the stack. Whore no recycle gas compressor is provided, this becomes an unsatisfactory arrangement since -1346297 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 dehydrocyclization 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, the reaction zones are reversed such 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 35 to 50%, by volume of the total catalyst. The first intermediate zone will contain from 25 to. 35%, while the second intermediate zone 15 to 25%. The last reaction zone, from which the deactivated catalyst particles are withdrawn from the system, will contain the least amount'of catalyst, from 5 to 15%. The reactant stream flows countercurrently to the descending column Of catalyst particles, with the fresh charge stock initially contacting the catalyst in the last reaction zone. This means that the charge stock first contacts that catalyst having the highest degree of deactivation. Conversely, the last catalyst which the reactant stream sees -144629·? has experienced little, or no deactivation. In addition to the advantages attendant the elimination of the recycle gas compressor, a principal benefit is an overall reduction in coke make.

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 made, the size and operating costs of the attendant regeneration facilities is also reduced. Another advantage is that less catalyst circulation is requirod because the catalyst leaving the last reactor can have a coke content as high as ZO%, by weight, instead of the usual to 5%. High activity is not required in this reactor since the main reaction is the conversion of naphthenes into aromatic hydrocarbons.

The present invention is 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 of the invention. Therefore, miscellaneous appurtenances, not required for 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 contciins the greatest quantity of catalyst particles, while reaction zone 5 contains the least.

With respect to the volumetric distribution of catalyst particles, uppermost reaction zone 17 contains about 50% by volume zone 13 about 25%, zone 9 about 15% and zone 5 about 10%. 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 suitable 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 introduced thereto via line 4. The effluent from the reaction zone 5, at a lower temperature due to the endothermicity of the re20 actions, is introduced by way of line 6 into inter-heater 7.

Approximately 80 to 90% of the naphthenes are dehydrogenated 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 effluent therefrom, in line 10, is increased in temperature in heater 11, and introduced through line 12 into the second in-164629·? 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 15.6°C to 60°C. The condensed material is then introduced into a separation vessel 19, from which the normally liquid product is recovered in line 21. A hydrogen-rich vapor phase, containing some light paraffinic hydrocarbons and a minor quantity of butane and pentane, is removed through line 20 and transported thereby into suitable hydrogen concentration facilities. The recovered hydrogen is extremely well-suited for use in vari15 ous hydrogen-consuming processes.

By means of the present invention, the catalytic reforming of a hydrocarbon charge stock is effected in a multiplestage system, in which catalyst flows downwardly, via gravity, through each reaction zone in the system, and without recycling 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 (14)

1. CLAIMS:1. A process for the catalytic reforming of a hydrocarbon charge stock in a multiple-stage reactor system in which (1) catalyst particles flow downwardly, under gravity, through each reaction zone in the system, (

2. ) catalyst particles from each reaction zone except the last are introduced into the next succeeding reaction zone, (3) deactivated catalyst particles are withdrawn from the 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 the system, which process comprises the sequential steps of: (a) reacting the charge stock, in the absence of added hydrogen, in the last reaction zone, the zone from which deactivated catalyst particles are withdrawn from the system, at catalytic reforming conditions; (fa) further reacting the effluent from the last reaction zone successively in one or more intermediate reaction zones, each at catalytic reforming conditions; (c) further reacting the effluent from the only or final intermediate reaction zone in the first reaction zone, the zone into which fresh or regenerated catalyst particles are introduced into the system, at catalytic reforming conditions; and (d) recovering a normally liquid, catalyticallyreformed product from the effluent withdrawn from the first reaction zone; the process being further characterized in that the first reaction zone contains the greatest amount of catalyst particles and the last reaction zone contains the least amount of catalyst particles. - 18 2. A process as claimed in claim 1 wherein the multiplestage system comprises three reaction zones.

3. A process as claimed in claim 2 wherein the first reaction zone contains from 40% to 60%, by volume, of the total catalyst in said system, the intermediate reaction zone 20% to 40% and the last reaction zone from 10% to 30%.

4. A process as claimed in .claim 1 wherein the multiplestage system contains four reaction zones.

5. A process as claimed in claim 4 wherein the first reaction zone contains 35% to 50% by volume of the total catalyst, the second reaction zone from 25% to 35%, the third reaction zone from 15% to 25% and the fourth reaction zone from 5% to 15%.

6. A process as claimed in any of claims 1 to 5 wherein the reaction zones in the system are verticallystacked along a common vertical axis and the catalyst particles flow via gravity from one reaction zone to the next succeeding reaction zone.

7. A process as claimed in any of claims 1 to 5 wherein the reaction zones in the system are in side-byside configuration 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. A process as claimed in any of claims 1 to 7 wherein the deactivated catalyst particles withdrawn are regenerated and reintroduced into the upper end of the first reaction zone.

9. A process as claimed in any of claims 1 to 8 wherein the charge stock is a napthta boiling range hydrocarbon material and the catalytic reforming conditions include a catalyst bed temperature of from 371 to 549°C, a pressure of from 4.4 to 69 atmospheres and a liquid hourly space velocity of from 0.2 to 10.

10. A process as claimed in any of claims 1 to 9 wherein the deactivated catalyst particles withdrawn have a coke content of more than 5% but not more than 20% by weight. 5

11. A process as claimed in any of claims 1 to 4 to 10 wherein when there is more than one intermediate reaction 'zone the effluent from the last reaction zone passes successively through each in the reverse order from the order of passage of the catalyst particles. 10

12. A process for the catalytic reforming of a hydrocarbon charge stock in a multiple-stage reactor system carried out substantially as hereinbefore described with reference to the accompanying drawing.

13. Reformate when obtained by a process as claimed in

14. 15 any of claims 1 to 12.