IE46296B1 - Hydrogen-producing hydrocarbon conversion with gravity-flowing catalyst particles - Google Patents

Description

The present invention is directed towards an improved technique for effecting the catalytic conversion of a hydrocarbon charge stock in a multiple-stage reactor system wherein (1) the reactant stream flows serially through the plurality of reaction zones, and (2) the catalyst particles move through each reaction zone via gravity flow. More particularly, the described process 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catalyst particles are introduced into at least two reaction zones, and (3) deactivated catalyst f particles are withdrawn from at least two reaction zones for subsequent regeneration.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 hydrogenconsuming. Multiple-stage reaction systems are generally of two types: (1) side-by-side configuration with 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 chamber, or more than one, contains the multiple catalytic contact stages. Such systems. - 3 as applied to petroleum refining, have been employed to effect numerous hydrocarbon conversidn reactions including those which are prevalent in catalytic reforming, alkylation, ethylbenzene dehydrogenation to produce styrene, and other dehydrogenation processes. Our invention is specifically intended for utilization in endothermic, hydrogen-producing, hydrocarbon conversion processes, in the reaction zones of which the catalyst particles move downwardly via gravity-flow. It is contemplated that the technique encompassed by our inventive concept is usable in particular where a first reaction zone exists in sideby-side relationship with a stacked system containing two or more reaction zones. In this configuration, the charge stock passes serially from the first reaction zone through the stacked reaction zones. Fresh or regenerated catalyst particles are introduced into the top of the first reaction zone and into the uppermost reaction zone in the stacked system, and deactivated catalyst particles, intended for regeneration, are withdrawn from the bottom of the single reaction zone and from the lowermost reaction zone in the stacked system. Our invention can also be applied to those 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. In the 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 hydrocarbon reactant stream, with the catalyst particles being disposed in the form of an annular bed, through which the reactant stream flows laterally and radially. - 4 46396 A radial-flow reaction system generally consists of tubular-form sections, of different nominal crosssectional 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 cehterpipe 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 eenterpipe and out of the reaction chamber. Although the tubularform configuration of the Various reactor components may take any suitable shape - i.e., triangular, square, oblong, etc. - many design, fabrication and technical considerations indicate the advantage of Using components which are substantially circular in cross-section.

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, without added or recycle hydrogen, initially contacts gravity-flowing catalyst particles in a first separate reactor whose small inventory of catalyst can be turned over very rapidly at a rate independent of that in the stacked reactors. The primary advantage stems from the elimination of the compressor otherwise required to recycle the hydrogen462ΰϋ - 5 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 multiple-stage reaction system.

According to the present invention there is provided a multiple-stage process for catalytically reforming a hydrocarbon charge stock which comprises the steps of: (a) at least periodically introducing fresh or regenerated catalyst particles into the upper end of a first reaction zone, through which catalyst particles move via gravity-flow, at least periodically withdrawing deactivated catalyst particles from the lower end of the first reaction zone, and reacting the charge stock, in the absence of added hydrogen, in the first zone at catalytic reforming conditions; (b) at least periodically introducing fresh or regenerated catalyst particles into the upper end of a stacked reactor system containing a plurality of reaction zones having a common vertical axis and through which catalyst particles move via gravityflow, at least periodically withdrawing deactivated catalyst particles from the lower end of the system and introducing the reaction product effluent from the first reaction zone into the uppermost reaction zone in said stacked reactor system, and reacting it there at catalytic reforming conditions; (c) further reacting the resulting uppermost reaction product effluent, at catalytic - 6 reforming conditions, in the next lower reaction zone in the stacked reactor system, and so on down the reactor system; and (d) recovering a normally liquid, catalytically-reformed product from the effluent withdrawn from the lowest reaction zone in the stacked reactor system.

Preferably, the stacked reactor system contains three reaction zones, through which catalyst particles move via gravity-flow, first through the uppermost reaction zone and then through each next succeeding lower reaction zone. In this case, the first reaction zone effluent is further reacted in the second reaction zone (which is uppermost in the stacked system), the resulting second reaction zone effluent is further reacted in the third reaction zone, and the resulting third reaction zone effluent is further reacted in the fourth reaction zone (which is the lowermost zone of the stacked system), all zones being at catalytic reforming conditions. The first reaction zone desirably contains the least amount of catalyst particles, preferably from 5 to 15% by volume of the total catalyst in the multiple-stage system. Further, where the stacked system consists of three additional reaation zones, the uppermost zone preferably contains 15 to 25%, the middle zone 25 to 35% and the lowermost zone 35 to 50% of the total catalyst.

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-byside relation with one or more separate reaction zones.

In a conventional stacked system, the catalyst particles flow downwardly from one catalyst-containing zone to another, and ultimately transfer to a suitable 46396 - 7 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 multiple10 stage, side-by-side reaction system with intermediate heating of the reactant stream which flows serially through the individual reaction zones. A modified system is disclosed in U.S. Patent No. 3,839,197 involving an inter-reactor catalyst 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 gravity30 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. - 8 U.S. Patent No. 3,725,248 illustrates a multiplestage system in side-by-side configuration with gravityflowing 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 facilities.

The process of the present invention is suitable for use in hydrocarbon conversion systems characterized as multiple-stage and in which the catalytic particles move 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 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 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 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-byside relationship, catalyst transport vessels are - 9 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 hydrocarbons, 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 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 10 and, prior to the present invention, a hydrogen to hydrocarbon mole ratio from 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 of 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 6 29« (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.

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 to 30%; second, from 20 to 40%; and third, from 40 to 60%. With respect to a four reaction zone system, suitable catalyst loadings would be: first, 5 to 15%; second, 15 to 25%; third, 25 to 35%; and fourth, 35 to 50%. 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 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 mole ratio is zero at the inlet of the catalyst bed in the first reaction zone which the charge stock sees. Most of the naph10 thenes 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 the 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 hydrogen/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 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 other s.

The most common method of operating a gravityflowing catalytic reforming system, with integral continuous catalyst regeneration, is to stack all the 4629 6 reaction zones such that catalyst particles 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. Where no recycle gas compressor is provided, this becomes an unsatisfactory arrangement since 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 , 10 for all the reactors in the stack. Furthermore, there ; is the additional disadvantage of highly coked, deactivi ated catalyst flowing into the second and subsequent 1 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 system wherein catalyst particles flow downwardly via gravity through each reaction zone, and from one zone into the next succeeding zone, the number one (uppermost) reactor is moved out of the stacked system, and disposed as a separate reactor in side-byside relationship with the stack. Fresh or regenerated catalyst is periodically introduced into the single side reactor and into the uppermost reaction zone in the stack? this can be accomplished by splitting the regen• erated catalyst into two separately controlled streams.

* Deactivated catalyst is withdrawn both from the single ' reactor and from the bottom of the lowermost reactor in the stack. Withdrawal of the two catalyst streams can ' 30 then be consistent with the required circulation rates, or coke deposition, for the side reactor and the stack.

| Another advantage resides in the fact that the regener. ation facility can be made much smaller since its size ! i 4639 β - 13 is dependent upon overall catalyst circulation rate.

The coke content of the catalyst withdrawn from the first reactor {single, side reactor) can be permitted to go as high as 20%, by weight, rather than the usual 2% to a maximum of 5%. This is possible because the principal function of the first reaction zone is to effect the dehydrogenation of naphthenes to aromatics.

The present invention is further described with reference to the accompanying drawing which is present 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 showing a four reaction zone process in which reactor 1 exists in side-by-side relationship with three reactors, 3, 4 and 5, disposed in a vertical stack 2. The charge heater which increases the fresh feed temperature in line 6 and the inter-heaters normally in lines 11, 16 and 17, are not shown. The use of such heaters is well-known.

With respect to the volumetric distribution of catalyst particles, the single side reaction zone 1 contains 10%, uppermost reaction zone 3, of stacked reactor 2, contains 15%, middle reaction zone 4 25% and lowermost reaction zone 5 50%. Fresh or regenerated catalyst particles are at least periodically introduced into reaction zone 1 through conduit 7 and inlet port 8. The catalyst circulation rate through zone 1 is primarily determined by the quantity of coke - 14 deposited thereon; in accordance with the present process ing technique, catalyst particles, withdrawn by way of a plurality of outlet ports 9 and conduits 10, can be permitted a coke deposition of about 20% by weight. Likewise, fresh or regenerated catalyst particles are at least periodically introduced into stacked reactor system by way of conduit 12 and inlet port 13. These flow downwardly via gravity through reaction zone 3 and therefrom into reaction zone 4. Catalyst particles also flow downwardly via gravity through reaction zone 4, into and through reaction, zone 5, and are withdrawn from stacked system 2 through a plurality of outlet ports 14 and conduits 15. These deactivated catalyst particles, and those withdrawn from reaction zone 1, are transported to suitable regeneration facilities, not illustrated. As above stated, the fact that the coke level of the catalyst withdrawn from reaction zone 1 can be as high as 20% by weight, results in a lower overall catalyst regeneration rate. The circulation rate through zone 1 is thus different from that through the stacked system containing zones 3, 4 and 5. Similarly, the rates of addition of fresh or regenerated catalyst via conduits 7 and 12 will not be the same.

The catalyst particles withdrawn from reaction zone 1 will contain up to about 20% by weight of coke deposit. However, sufficient activity remains to effect substantial conversion of naphthenes to aromatics and hydrogen. Therefore, the naphtha boiling range charge stock, without recycle hydrogen, after suitable heatexchange with a higher temperature stream and any necessary additional heating to raise its temperature to the level desired at the inlet to the catalyst bed, 46396 is Introduced via line 6 into reaction zone 1. Approximately 85 to 90% of the naphthenes are therein dehydrogenated to aromatics, with the concomitant production of hydrogen.

Since the dehydrogenation reactions effected in reaction zone 1 are principally endothermic, the temperature of the effluent therefrom in line 11 will be increased through the use of a reaction zone interheater . Heated effluent is then introduced into uppermost reaction zone 3, into which regenerated or fresh catalyst particles are introduced via conduit 12 and inlet port 13. Effluent from reaction 3 is introduced, via line 16, into another reaction zone inter-heater wherein the temperature is once again increased; heated effluent is then introduced thereby into reaction zone 4. The temperature of the effluent from reaction zone 4 is passed via conduit 17 into an inter-heater, and therefrom into reaction zone 5. Product effluent is withdrawn from reaction zone 5- through line 18 and (after use if desired, as a heat-exchange medium), introduced into condenser 19 wherein the temperature is further decreased to a level in the range of 15.6°C. to 60°C. The condensed material is transferred into separator 21 by way of line 20, wherein separation into a normally liquid phase, line 22, and a hydrogen-rich vaporous phase, line 23, is effected.

By means of the present invention, the catalytic reforming of a hydrocarbon charge stock is effected in a multiple-stage system, in which catalyst flows downwardly, via gravity, through each reaction zone in the system, and without recycling a portion of the hydrogenrich vaporous phase separated from the desired normally liquid product effluent.

Claims (5)

1. CLAIMS : 1. A multiple-stage process for catalytically reforming a hydrocarbon charge stock which comprises the steps of: 5 (a) at least periodically introducing fresh or regenerated catalyst particles into the upper end of a first reaction zone, through which catalyst particles move via gravity-flow, at least periodically withdrawing deactivated catalyst particles from the lower end of the 10 first reaction zone, and reacting the charge stock, in the absence of added hydrogen, in the first zone at catalytic reforming conditions; (b) at least periodically introducing fresh or regenerated catalyst particles into the upper end of a 15 stacked reactor system containing a plurality of reaction zones having a common vertical axis and through which catalyst particles move via gravity-flow, at least periodically withdrawing deactivated catalyst particles from the lower end of the system, introducing the 20 reaction product effluent from the first reaction zone into the uppermost reaction zone in the stacked reactor system, and reacting it there at catalytic reforming conditions; (c) further reacting the resulting uppermost 25 reaction product effluent, at catalytic reforming conditions, in the next lower reaction zone ih the stacked reactor system, and so on down the stacked reactor system; and (d) recovering a normally liquid, catalytically30 reformed product from the effluent withdrawn from the lowest reaction zone in the stacked reactor system. - 17

2. A process as claimed in Claim 1 wherein the stacked reactor system contains three reaction zones.

3. A process as claimed in Claim 1 or 2 wherein the first reaction zone contains the least amount of 5 catalyst particles.

4. A process as claimed in Claim 3 wherein the first reaction zone contains from 5% to 15% by volume of the total catalyst in the multiple-stage process. 5. A process as claimed in Claim 2 wherein the 10 first reaction zone contains from 5% to 15%, by volume, of the total catalyst particles in the multiple-stage process, the second reaction zone from 15% to 25%, the third reaction zone from 25% to 35% and the fourth reaction zone from 35% to 50%. 15 6. A process as claimed in any of Claims 1 to 5 wherein the charge stock is a naphtha 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 20 liquid hourly space velocity of from 0.2 to 10. 7. A process as claimed in any of Claims 1 to 6 wherein deactivated catalyst particles from the first reaction zone and from the lower end of the stacked reactor system are regenerated together and the regener25 ated particles are divided into two streams for separate return to the first reaction zone and stacked reactor system. 8. A process as claimed in any of Claims 1 to 7 wherein the deactivated catalyst particles withdrawn 30 from the first reaction zone have a coke content of more than 5% but not more than 20% by weight. 46 29 6 - 18 9. A multiple-stage process for catalytically reforming a hydrocarbon charge stock carried out substan tially as hereinbefore described with reference to the accompanying drawing.

5. 10. Reformate obtained by a process as claimed in any of Claims 1 to 9.