US3540996A

US3540996A - Split feed naphtha reforming

Info

Publication number: US3540996A
Application number: US749422A
Authority: US
Inventors: John Maziuk; Donald A Zanolini
Original assignee: Mobil Oil Corp
Current assignee: ExxonMobil Oil Corp
Priority date: 1968-08-01
Filing date: 1968-08-01
Publication date: 1970-11-17
Anticipated expiration: 1987-11-17

Description

Nov. 17, l97 J. MAzluK Erm.

SPLIT FEED NAPHTHA REFORMING Filed Aug. 1. 1968 e sheets-sheet 1 H .o l Eomtw :O Q60 mv Qu mm Gm mm om o.. m

8:28..; Bunooz :125m no e e BOB: SESZ 25m 2&0@ o E532 :125m 2000.0| Si mm3 al..

Omm

Nov.'17, 1970 J. MAzluK ETAL 3,540,996

' SPLIT FEED NAPHTH'A REFOIRIMINGv Filed Aug. 1, 1968 e sheets-sheet z FIGB AROMATICS PRODUCTION AT ZOOPSIG FROM (Z6-350? MESA Split Feed vs Conventional Reforming -C0nveniion0l Reforming -eSplif Feed Reforming 54 w C* 53 5 l o5 E 52 5| e@ /nVen/ors John Maz/'alf 0000/0' A Zan o/n/ y f/ Lynl/L? Agent Nov. 17, 1970 J. MAznuK ETAL 3,540,996

. SPLIT FEED NAPHTHA REFORMING I Filed Aug. 1, 1968 6 Sheets-Sheet 5 PRESSURE REFORMING CG- 400F KUWRIT FULL RANGE PARAFFINE NAPHTHA F l G.I[[ SPLIT FEED AGING BENEFITS IN LOW Days On Sream Split Feed Convenhonol o o suono 20110:; almmadwal 9| u| /m/en/Urs ./Ohn Maz/'uk Dona/d A. Zano//n/ Nov. 17, 1970 J. MAzluK ETAL 3,540,996

SPLIT FEED NAPHTHA REFORMING n Filed Aug. 1, lesa s sheets-Shadi EFF ECTOF SULFUR CONCENTRATION OF CATALYST PERFORMANCE Condition: ZOOPsig, I OLHSV, I4/I Total Gas/HC Recycle Ratio |02. (R+ 5) Raw Reormate Octane Number la.. Sulded 0.6% Pt Catalyst, Desiccafed Operation +|O 23 +5 "D 0 f a 2 G 5 o lo l O "oe |o E $5 +5 E m w qu u O IOO 200 300 400 500 600 700 800 Total Sulfur Entering Reformer,Weighr PPM of Naphfha /nl/enfO/,S

^ John Maz/'uk F G N A Dona] AZanQ//n/ Agent J. MAzluK ETAL 3,540,996

SPLIT FEED NAPHTHA REFORMING 6 Sheets-Sheet 5 V, l4/l Total Gas/ HC Recycle Ratio lO2.5( R+5) Raw Reformate Octane Number Sulfided 0.6

"/o Pt Catalyst, Desiccated Operation Nov. 17, 1970 Filed Aug. 1, 1968 EFFECTOF SULFUR CONCENTRATION OF CATALYST PERFORMANCE Condition: ZOO Psig, LOLHS 500 Total SulfurEntering ReformerWeight PPM of Nophtha N O\ om o lOO d lic 5 m o m. m. m w o w. m.. .w c o gmmoweoao 1Q E85@ O2 .NIQ coxe //7 V60/Org Jon/1 Maz/'uk Dona/0 A. Zano//n/ L 7J/'i Wm Agent FIGNB -Filed Aug. 1. 1968 FIGV J. MAzluK ErAL 3,540,996

SPLIT FEED NAPHTHA REFORMING' e sheets-sheet e U5. Cl. 20S-65 7 Claims ABSTRACT F THE DISCLOSURE A method for improving the octane rating of a pretreated full boiling range naphtha is defined to include reforming the light naphtha portion thereof in an initial reforming processing region and the heavy naphtha portion thereof in a final reforming processing region. The effluent from the initial reforming region is passed with the heavy naphtha through the final reforming region and the total efiiuent is pressure fiash separated to permit recovery of a hydrogen rich recycle gas from a liquid reformate fraction which is stabilized to remove residual hydrogen and light hydrocarbons therefrom. The described process provides a lower catalyst deactivation rate, increased aromatics production and an improved front end octane rating.

BACKGROUND OF THE INVENTION The method and combination of processing steps of the present invention is concerned with the catalytic reforming of a full boiling range naphtha fraction boiling in the range of from about C hydrocarbons up to about 400 F. so as to accomplish in the presence of suitable hydrogenation-dehydrogenation reforming catalyst a relatively more selective dehydrogenation of naphthenes to the corresponding aromatics, dehydrocyclization of paraflins to aromatics, isomerization and limited hydrocracking of some of the components of the naphtha charge to the exclusion of increased coke formation. During a naphtha reforming operation, all of the above reactions are desirable and those reactions leading to the production of high octane materials such as aromatics are usually more desirable than the other reactions of reforming.

It has been observed by those specializing in the catalytic reforming of naphthas that as the end boiling point of the naphtha is increased, there is a decided and significant tendency to increase coke formation rapidly when pushing to reach target octanes and such an increase effectively and undesirably limits the catalyst life of the process. As a result of this, the prior art has developed different approaches to reforming; one process effects regeneration of the catalyst after a short onstream period and the other adjusts the reforming process to maintain catalyst life as long as possible before shutting down the reforming operation to regenerate the catalyst. The conventional or current reforming practice involves the processing of naphtha through a series of reaction zones wherein all of the naphtha processed is passed in series through each of the reaction zones. If a three reactor system were used to process a full range naphtha, at a given set of conditions, all of the naphtha would be processed in turn through each of the three reactors. It has been proposed to separate a naphtha charge into a high boiling and a low boiling fraction and to reform the fractions separately so that the lower boiling fraction may be subjected to either more severe or less severe reforming conditions than the higher boiling fraction. When reforming the lower boiling fraction under more severe conditions than the higher boiling fraction, it is possible to upgrade the lower boiling hydrocarbons to a greater extent so that the blended 3,540,996 Patented Nov. 17, 19'70 reformates thereof combine to form a gasoline of higher octane number than would be obtained if the fractions were reformed together in the more conventional prior art manner. lHowever, reforming in this prior art spl1t feed manner has not been completely successful since the higher boiling fraction has most usually been incompletely reformed. To offset this deficiency, it has been proposed to subject the high boiling naphtha fraction to reforming under relatively high pressure conditions but such a method of operation is known to inhibit suitable conversion of paraffin constituents.

Another approach to the problem has been to separate the eiiiuents obtained from reforming operations and to recycle certain fractions of the reforming stage for upgrading with fresh feed. However, it has been observed that in any one of the proposed combinations of split feed reforming operations disclosed in the prior art that they all contain significant deficiencies which preclude obtaining a desired optimization of desired reforming reactions. Generally, the proposed split feed operations have been plagued with economic disadvantages which have precluded their commercial use to any significant extent.

An object of the present invention is to provide a processing combination for reforming a full boiling range naphtha such as a parafiinic naphtha boiling in the range of C5 hydrocarbons up to about 400 F under conditions which permit more selective optimization of the desired reforming reactions including dehydrogenation of naphthenes, dehydrocyclization of paraffins and isomerization reactions, and preferentially to modify those reactions contributing to the deposition of coke and formation of undesired gaseous constituents.

SUMMARY OF THE INVENTION The present invention is concerned with reforming a naphtha boiling in the range of from about C5 hydrocarbons up to about 400 F. which has been treated by hydrogenation to remove sulfur and nitrogen constituents from at least the lower boiling portions thereof to a desired low level. That is, desulfurization and denitrogenation of the naphtha charge is effected so that at least the lower boiling portion of the naphtha boiling below about 290 F. will contain less than about l p.p.m. 0f either sulfur or nitrogen therein. The full boiling range naphtha charge is separated such as by splitting or fractionation into a light naphtha fraction and a heavy naphtha fraction at a cut point selected from within the range of from about 250 F. to about 290 F. Desulfurization and denitrogenation of the low boiling naphtha fraction may be accomplished after splitting the naphtha as recited herein. The light naphtha fraction thus obtained or selected is mixed with a hydrogen rich recycle gas stream which is substantially free of innocuous concentrations of sulfur and nitrogen constituents so that when combined with the light naphtha the mixture will contain less than about l p.p.m. of sulfur or nitrogen. The light .naphtha-hydrogen gas mixture is also adjusted to provide a moisture level in the range of 5 to about 15 p.p.m. of water in the initial portion of the light naphtha processing region or section of the present invention. The light naphtha reforming section is formed by at least two sequentially arranged reaction zones provided with suitable heaters and heat exchange means in conjunction therewith for heating the light naphtha charge either alone or in combination with hydrogen to a desired elevated reforming temperature. The heated light naphthahydrogen mixture is then passed in contact with a platinum group metal reforming catalyst disposed in the sequentially arranged reaction zones comprising a first partial catalyst fill reaction zone followed by a full fill catalyst reaction zone. For example, the initial reforming zone first contacted by the light naphtha will contain only a portion of the reforming catalyst to be contacted by the naphtha and thus is referred to as a partial fill reaction Zone which may contain half or less than about half of the amount of catalyst employed in the second or full fill reaction Zone. In this combination of catalyst reaction zones, the low boiling naphtha fraction is initially selectively reformed in the partial catalyst fill reaction zone under conditions selected to optimize the dehydrogenation of naphthenes and thereafter the reforming conditions are adjusted for the full catalyst fill reaction Zone so as to effect primarily dehydrocyclization of paraffins and isomerization reactions therein. YAs described herein, heating means are provided upstream of the reaction zones for adjusting the temperature of the reactant streams as desired before being introduced to a reaction zone. Thus, the efliuent obtained from the first catalyst reaction zone is temperature adjusted prior to the effluent being passed in contact with the catalyst in the second or full fill reaction zone. The heavy or higher boiling portion of the naphtha charge boiling above about 250 or 290 F. is reformed in the presence of the reformate of the light naphtha reforming operation and a catalyst aging inhibitor such as, for example, a sulfur compound such as thiophene. The higher boiling portion of the naphtha charge containing a sulfur inhibitor in an amount of from about 150 p.p.m. to about 350 p.p.m. and combined with the total hydrogen rich effluent of the low boiling naphtha reforming operation is heated to a suitable reforming temperature and then reformed in a final reforming processing region. The final reforming processing region is formed of at least two sequentially arranged reaction zones, the first of which contains a smaller volume of catalyst than the latter. In these catalyst reforming zones, the reforming conditions are particularly selected for reforming the higher boiling hydrocarbon constituents found in the naphtha fraction boiling above about 250 F.290 F. In this final processing region, the high boiling naphtha fraction passes sequentially through the two reaction zones, the first of which contains less platinum reforming catalyst than the subsequent and first reforming zone. Thus, the naphtha charge comprising the high boiling naphtha sequentially contacts a partial fill of reforming catalyst followed by a second reactor containing a full fill of reforming catalyst. In this combination the amount of catalyst in the partial fill reaction zone may be about one half of the amount of catalyst employed in the full fill reaction zone. Suitable means are provided for adjusting the temperature of the hydrocarbon stream to a suitable reforming temperature before introduction to each reforming zone.

In the combination of processing steps above described comprising the initial and final reforming processing regions, hydrogen rich gas generated in the process is caused to move sequentially through a combination of reaction zones wherein the first and third reaction zones contain less than and only about one half of the catalyst employed in the second and fourth reaction Zones. By this arrangement of processing steps the reforming severity conditions for each of the low boiling and high boiling naphtha fractions can be more selective for reforming the hydrocarbon components found therein and when required the severity conditions for reforming the low boiling naphtha fraction can be more severe than required for the higher boiling naphtha. The hydrogen rich gas employed includes recycle hydrogen gas in combination with the hydrogen produced during reforming thel light naphtha fraction in the first and second reaction zones and provides the hydrogen requirements for the high boiling naphtha fraction reformed in the third and fourth reaction zones. 'I'he hydrogen concentration of the efiiuent obtained from the initial processing region comprising recycle and generated hydrogen may be adequate in one embodiment for furnishing the hydrogen requirements of the final processing region thereby contributing significantly to the overall economic advantage of the process. In yet another embodiment, a portion of the hydrogen rich recycle gas may be recycled directly to the high boiling naphtha reforming step. Thus hydrogen recycle gas may be passed in parallel flow arrangement to each reforming stage. The effluent recovered from the last reaction zone of the final processing region is then separated to recover a hydrogen-rich recycle gas drawn from a liquid reformate eiiuent stream, This separation may be accomplished by an initial pressure ash separation so as to recover a relatively high pressure recycle gas from a liquid reformate product. The liquid reformate product thus separated from hydrogen containing gaseous constituents is further separated in a suitable stabilizer tower maintained under conditions to effect the separation and recovery of any residual hydrogen and light hydrocarbons separated from a desired liquid reformate product.

The separated hydrogen containing gas is purified in a gas purifier for the removal of undesired sulfur and nitrogen compounds, combined halogen and Water, when found, from the recycle gas thereby providing a recycle gas enriched in hydrogen. The recycle gas purifier may be substantially any suitable gas purifier for accomplishing the above purpose. In the method of the present invention a molecular sieve gas purifier may be employed for this purpose. When using a molecular sieve gas purifier, it is preferred that at least two molecular sieve gas purifiers be employed in parallel arrangement so that while one is being regenerated, the other may be onstream removing undesired gaseous components from the hydrogen recycle gas employed in the process. Hydrogen rich gas thus purified is recycled in a desired quantity for admixture with the light naphtha fraction passed to the first reactor in the initial processing region. In cooperation with the processing steps above identified, selective reforming of the low boiling naphtha fraction is enhanced by controlling thc moisture content of the combined hydrogennaphtha charge passed in contact with the initial reforming catalyst. Thus, provisions are made for adding a desired and controlled amount of water to the recycle gas and/or naphtha charge prior to the mixture coming in contact with the catalyst in the first reactor of the initial reforming region.

The catalysts which may be employed in the reactors of the initial reforming region and the reactors of the final reforming region are known generally as platinum group metal reforming catalysts and may be a combination of several different ingredients which will be helpful to the selective operation herein discussed. Typical of the platinum group metal reforming catalysts which may be successfully used are catalysts comprising from about 0.l to about 2 percent by weight of platinum, preferably from about 0.35 to about 0.6 percent platinum alone or in combination with from about 0.1 to about 0.8 percent by weight of halogen dispersed in a suitable support material comprising an alumina support material. The alumina may be promoted with silica, glycerine, boron and combinations thereof and other activating ingredients contributing to provide a desired cracking activity to the catalyst.

The present invention contemplates and provides for reforming a full boiling range paraffinic naphtha at a reforming pressure below about 600 p.s.i.g. and preferably at a pressure in the range of from about to about 500 p.s.i.g. in the presence of a particle form platinum group metal reforming catalyst. Reforming of the low boiling naphtha fraction is generally effected in the presence of a controlled amount of water but in the substantial absence of any sulfur and nitrogen compounds which are preferably maintained at least below about 10 p.p.m. The higher boiling naphtha fraction on the other hand is reformed in the presence of a substantial amount of sulfur either added or present in the high boiling portion of the naphtha feed so that amounts greater than about 50 p.p.m. and preferably at least about 350 p.p.m. but not more than about 1000 p.p.m. of sulfur is provided. In the particular combination of this invention, the hydrogen to naphtha mole ratio is maintained in the range of from about 4 to about 20:1 and preferably from about 8 to about 14:1 While employing a space velocity in the range of from about 1 to about 20 and preferably from about 1 to about 3 volumes of naphtha per hour per volume of catalyst. The temperature employed in each of the reforming Zones is selected to optimize the reactions to be eifected therein and these temperatures will be dependent in part upon the activity of the catalyst employed and that required to produce a particular C5| octane product. Generally the temperatures employed will be in the range of from about 800 to about 1000 F. and preferably from about 850 to about 980 F.

The full boiling range naphthas employed in the development leading up to the present invention are identified in the following Tables 1 through 4. These tables are selfserving and elaboration thereon is not found necessary.

TABLE l Properties of light parainic naphtha (C6-290 F, Aramco) Distillation, ASTM F.:

IBP 152 5% vol. 180 10% vol. 185 vol. 190 vol. 198 vol. 207 vol. 215 vol. 225 70% vol. 236 80% vol. 247 90% vol. 260 EP. 283

Specific gravity .7128 Molecular weight 102 Octane rating (R4-3) 70 Composition, wt. percent:

Parans 73.9 Naphthenes 17.2 Aromatics 8.9

TABLE 2 Properties of heavy parat-linie naphtha (290-350" F. Aramco) Distillation, ASTM F.:

IBP 287 5% vol. 295 10% vol. 296 20% vol. 298 30% vol. 300 40% vol. 303 50% vol. 306 60% vol. 310 70% vol. 314 80% vol. 320 90% vol. 330

Specic gravity .7653 Molecular Weight 133 Octane rating (R4-3) 60.5

Composition, wt. percent:

Parains 58.6 Naphthenes 21.4 Aromatics 200 6 TABLE 3 Properties of wide range naphthenic naphtha (Cs-350 F. Mesa) Distillation, ASTM F.:

IBP 169 5% vol. 197 10% vol. 204 20% vol. 214 30% vol. 224 40% vol. 235 50% vol. 246 60% vol. 261 70% vol. 279 vol. 297 vol. 321

E.P. Y 352 Specific gravity .7632 Molecular weight 109 Composition, wt. percent:

Parains 41.2 Naphthenes 3 5 .1 Aromatics 23.7

TABLE 4 Properties of full range parainic naphtha (C6-400 F. Kuwait) Distillation, ASTM F.:

IBP 166 5% vol. 209 10% vol. 221 20% vol. 235 30% vol. 249 40% vol 268 50% vol. 289 60% vol. 309 70% vol. 332 80% vol. 351 90% vol. 371 E.P. 401 Specific gravity .7455 Molecular weight Octane rating (R-I-3) 64 Composition, wt. percent:

Parains 65.2 Naphthenes 20.7 Aromatics 14.1

DESCRIPTION OF SPECIFIC EXAMPLES Studies were made employing the split feed technique of this invention with a paraflinic as well as a moderately naphthenic wide boiling range naphtha. The initial investigation involved a series of yield-octane surveys processing C6350 F. Mesa naphtha split at about the 290 F. cut point employing a three reactor system maintained at an operating pressure of about 200 p.s.i.g. Light naphtha (C6-290 F.) was fed into the first reactor and the remaining heavy portion (29o-350 F.) was mixed with the processed light naphtha emerging from the secon-d reactor and the resulting mixture was then processed in th third reactor. In one yield-octane survey, a catalyst aging inhibitor was mixed with the heavy naphtha prior to processing as described above.

Results obtained with processing the Mesa naphtha leads to the following conclusions:

(1) The use of a sulfur compound such as thiophene as a catalyst aging inhibitor added to the heavy naphtha 7 has no significant detrimental effect on overall yields or product distribution.

(2) Split feed yields (C6-F, 05+, hydrogen purity and hydrogen production) were slightly lower than those obtained by conventional 200 p.s.i.g. operation.

(3) Split feed reforming produces a higher concentration of aromatics in the C6+ reformate which results in a higher aromatics production based on charge.

(4) Split feed reformates produced by present invention show significant improvement in front end octane number.

(5) No apparent catalyst aging was observed over the test period.

A second run was made using the split feed technique with the primary objective of determining the aging characteristics of a platinum group metal reforming catalyst when processing a Ces-400 F. Kuwait naphtha at 200 p.s.i.g. in a four reactor reforming system at a severity of 102 raw leaded octane. The full range naphtha was split at about the 290 F. boiling point and the heavy portion of the naphtha was dosed with a catalyst aging inhibitor thiophene to obtain 300 p.p.m. sulfur concentration therein. This heavy naphtha fraction was processed in only the last two reactors of the four reactor system. When compared with conventional 200 p.s.i.g. reforming without splitting the feed, the data obtained permit the following conclusions to be drawn.

(l) Split feed processing as dened by this invention has resulted in a drastic reduction in catalyst aging. Where conventional reforming shows about a one month catalyst life before reaching a 980 F. inlet temperature, split feed reforming practiced according to this invention will at least double the length of the catalyst life.

(2) A signicant improvement in the front end octane number has ybeen obtained.

(3) Overall product yields are lower than those obtained by conventional 200 p.s.i.g. operation (Table 5) but are considerably higher than estimated for a higher pressure operation which would be required to compensate for the aging normally observed at low pressure.

(4) When based on reformer charge, split feed reforming practiced according to this invention produces a higher yield of C6+ aromatics (Table 5).

(5 On a distribution octane number (DON) basis, the split feed reforming operation of this invention shows liquid yields comparable to those obtained with conventional reformer operation in conjunction with a significant improvement in C6+ aromatics production (Table 6).

TABLE 5.-A COMPARISON OF YIELDS OBTAINED ON FULL RANGE PARAFFINIC Cri-400 I". KUWAIT NAPHTHA AT 102.5 C-i- (Ri-3) O.N. SPLIT FEED VS. CONVENTIONAL REFORMING C-l- (R+3) O.N 102.9 102.5

A A Split S.F.- Split S.F. feed Conv. conv. feed Conv. conv.

C54-, Vol. of chg- 68. 9 7l. 4 -2. 5 68. 2 71.1 2. 9 05+, vol. of chg- 75. 7 78. 4 2. 7 75. 6 78. 2 3. 9 05's, Vol. of chg 6.8 7. 0 0. 2 7. 4 7.1 +0. 3 C4s, vol. oi chg 6. 7 6. 2 +0. 5 6. 9 6. 2 +0. 7 C3, wt. percent of chg 4. 6 4. 4 -l-O. 2 4. 7 4. 2 +0. 5 C2, wt. percent of chg 3. 6 3. 4 +0. 2 3. 7 3. 5 +0. 2 C1, wt. percent oi chg 2. 2 1. 9 +0. 3 2. 4 2. 0 +0. 4

Ce|-, (R+3) O.N 102.5

A Split Conv. S.F.. feed ref conv- Ce-I- yield, vol. percent chg 68. 4 71. 4 -3. 0 Cs-laromatics, vol. percent chg 43. 1 41. 6 +1. 5 Cia-{- Paraflns, vol. percent chg 19. 2 23. 8 -4. 6 C-laromatics, vol. percent of Ca-iref 63. 58. 2 +4. 8 Ca-I- Parans, vol. percent of ref- 28.1 33. 3 -5. 2 103. 6 Base +3. 6

Vol. percent of aromatics prod TABLE 6.-A COMPARISON OF YIELDS OBTAINED ON FULL RANGE PARAFFINIC (9e-400 F. KUWAIT NAPHTHA ON A DON (R4-3) BASIS SPLIT FEED VS. CONVENTIONAL REFORMING Raw reformate (DON+3) O.N 100.7

A Split Conv S.F. fee r conv C64-(R473) O.N 103. 5 Cel-liqu1d yield, vol. percent chg .2 68. 5 -0. 3 Cyl-liquid yield, vol. percent chg-- 75. 6 75. 9 0. 3 Ce-lproduct:

Aromatics, vol. percent oi Ciriref 63. 0 60. 5 +2. 5 Parailns, vol. percent of Ca-lref 28. 1 30. 5 -2. 4 Aromatics, vol. percent of chg 42. 8 41. 4 +1. 4 Parafns, vol. percent of chg 19. l 20. 9 -1. 8

In order to further identify the advantages accruing from the method and arrangement of processing steps of this invention, data developed and recorded during the investigation are graphically recorded for convenience of illustration.

FIG. I shows in graphical form the effect of continuous sulfur addition on the stability of a reforming catalyst of low platinum content when processing a heavy 290-350 F. Aramco naphtha at low pressure of about 200 p.s.i.g. The data are self serving and show that the stability of the catalyst (minimized rise in inlet temperature required for octane production over the operating period) was vastly improved when the amount of sulfur in the charge was increased from 3 to 150 ppm. and improved even further when the sulfur level was increased to 310 p.p.m.

FIG. II graphically shows the aromatics production at 200 p.s.i.g. when employing the split feed method of this invention as compared with that obtained by the conventional prior art method above described. These data clearly illustrate the significant improvement in C6+ aromatic yield obtained by the method of this invention.

FIG. III, on the other hand, graphically shows the catalyst aging benefits obtained by a split feed operation of the present invention over the conventional operation. In the conventional operation the catalyst ages much more rapidly and requires a much more frequent' regeneration cycle than the split feed operation of this invention.

FIG. IV provides graphically a group of curves which shows how sulfur addition affects product distribution when processing a light parainic naphtha (C6-290 F.) Aramco at 200 p.s.i.g. It is observed from these data that sulfur has an undersirable effect on the light naphtha fraction by causing a detrimental yield shift to lower C6+ liquid and H2 yields while increasing the amounts of C5 and light hydrocarbons.

FIG. V presents diagrammatically in elevation an arrangement of interconnected Vessels for practicing the method and concept of the present invention.

Referring now to FIG. V by way of example there is shown a pretreated naphtha charge substantially freed of undesired nitrogen and sulfur constituents and boiling in the range of from about C5 to about 400 F. being introduced to the split feed processing scheme of this invention by way of conduit 2 communicating with splitter tower 4. In splitter tower 4, the naphtha charge is separated into an overhead low boiling naphtha fraction or light naphtha boiling in the range of from about C5 hydrocarbons up to about 290 F. and a higher boiling bottoms or heavy naphtha fraction boiling from about 290 F. up to about 400 F. iIt is within the scope of this invention however to make the rough cut point between the low and high boiling naphtha fraction of some other boiling point and the cut point may be as low as about 250 F. depending upon the composition of the naphtha charge being processed. In the arrangement shown, the low boiling naphtha fraction is withdrawn from the upper portion of splitter 4 by conduit 6 com- 9 municating with heater 8. In heater 8 the light naphtha charge recovered from splitter 4 is combined with hydrogen rich recycle gas obtained as hereinafter described and heated to an elevated temperature suitable for introduction to the initial reforming region reactor 12 by conduit 10. Reactor 12, containing a suitable platinum reforming catalyst known in the art and described herein is diagrammatically shown as about half the size of the second downstream reactor 20. The reactors may -be of the same size and the first reactor only partially filled with reforming catalyst as hereinbefore discussed so that it contains only about one half of the amount of catalyst employed in the second reactor. In reactor 12, the light naphtha is subjected to reforming conditions selected to obtain desired naphthene dehydrogenation and thus partial reforming of light naphtha constituents most easily convertible to aromatics. The total effluent of reactor 12 is withdrawn and passed by conduit 14 to heater 16. In heater 16, the effluent of reactor 12 is reheated to a desired elevated reforming temperature and the reheated efliuent is then passed by conduit 18 to a second full fill platinum catalyst reactor 20. In reactor 20, the partially reformed light naphtha charge is further reformed under relatively more severe conditions selected to effect dehydrocyclization and isomerization reactions to desired product material without significant hydrocracking. The efliuent of reactor 20 is withdrawn by conduit 22 communicating with conduit 24. The heavy or high boiling portion of the naphtha charge obtained in splitter 4 is removed therefrom by conduit 24. In conduit 24 the heavy naphtha may be mixed with the total light naphtha efiiuent of reactor 20 and the mixture then passed to heater 26 or the light naphtha effluent which is at an elevated temperature may be mixed with heavy naphtha feed after heating the heavy naphtha either alone or in the presence of hydrogen rich recycle gas. In heater 26 the naphtha charge comprising the heavy naphtha either with or without the light naphtha effluent and recycle hydrogen is heated to a suitable elevated reforming temperature selected for reforming primarily the heavy components of the naphtha charge which are most easily convertible to aromatic constituents. The heated charge is then passed by conduit 28 to reactor 30 after the addition of the catalyst inhibitor as herein described. Reactor 30, similarly to reactor 12, contains only about one half of the volume of catalyst as employed in a second downstream reactor and thus is shown diagrammatically to be only about one half the size of the downstream reactor. Reactor 30, similarly to reactor 12, may be the same size as the other reactor but only half filled with active catalyst as discussed hereinbefore. A sulfur compound catalyst inhibitor such as thiophene and supplied by conduit 32 is added to the heated naphtha-hydrogen mixture in conduit 28 being passed to the reactor 30. In reactor 30 the reforming conditions are selected which are most suitable for converting naphthenes to aromatics. The effluent of reactor 30 is then passed by conduit 34 to heater 36 wherein the naphthahydrogen effluent is reheated to a suitable elevated reforming temperature to achieve further selective reforming in reactor 40 of the high boiling constituents of the naphtha charge to aromatics and isomerization products contributing to a desired high octane product. As noted above, reforming of the naphtha charge is completed in the full fill catalyst reactor such as represented by reactor 40. In reactor 40, the naphtha-hydrogen mixture is contacted with a suitable platinum reforming catalyst under those conditions most selective to complete dehydrocyclization and isomerization of the higher boiling components of the naphtha charge without experiencing undesired hydrocracking reactions therein. The total reformate product of the selective reforming steps above discussed is then passed by conduit 42 to a high pressure separator 44 for separating a hydrogen containing gas stream from a liquid reformate product stream. The

effluent in conduit 42 may be partially cooled before being passed to separator 44. A hydrogen containing gas stream is removed from the upper portion of separator 44 by conduit 46 and passed to recycle gas purifier 48.

In recycle gas purifier 48, the hydrogen containing recycle gas is treated with, for example, a solid adsorbent material such as a molecular sieve material under conditions to remove low boiling hydrocarbons, sulfur and nitrogen compounds as well as water and combined halogen compounds found in the recycle gas stream. It is to be understood that two recycle purifiers 48 may be employed in parallel flow arrangement with one anothenso that while one gas purifier is being regenerated, the other may be concurrently employed to treat hydrogen containing recycle gas as discussed above. The gas thus treated and thereby enriched in hydrogen is removed by conduit 50 and recycled for admixture with the light` naphtha fraction in conduit 6 before passage to heater.

8. Provision is made for withdrawing a portion of the enriched hydrogen recycle gas by conduit 52 and provisions are also made for adjusting the moisture content of the hydrogen rich recycle gas by conduit 54 provided for introducing water thereto or into the naphtha charge. The liquid reformate product separated in 44 is withdrawn from the bottom thereof by conduit 56 and passed to a stabilizer tower 5'8. In stabilizer tower S8, conditions are maintained to permit the recovery of LPG gaseous constituents from the upper portion thereof by conduit 60 and a stabilized liquid reformate product from the lower portion thereof by conduit 62. It is to be understood that the processing arrangement above discussed may be varied by the inclusion of pumps and valves, not shown, but is intended to be limited to the particular combination and sequence of steps generally described with respect thereto. It is also to be understood that the operating temperature conditions may be varied depending upon the type of naphtha being processed and the catalyst cycle life without departing from the processing combination intended to be covered by applicants invention.

We claim:

1. A method for reforming a naphtha charge comprising portions boiling above and below about 290 F. which comprises passing a portion of the naphtha charge boiling below about 290 F. which has been pretreated to obtain a low level of sulfur with hydrogen rich recycle gas sequentially through a plurality of reforming reaction zones arranged to have a volume of platinum containing catalyst in the first and third reaction zones substantially the same but the volume of catalyst in either zone being less than the volume of catalyst maintained in each of the second and fourth reaction zones, maintaining the reforming reaction conditions in the first and second reaction zones more severe than in the remaining reaction zones, reforming the naphtha portion boiling above about 290 F. in the presence of from about 150 to about 1000 p.p.m. of sulfur in the third and fourth reaction zones, separating an effluent recovered from the last of the reforming zones to recover a stabilized liquid reformate product and a hydrogen rich gas containing less than about 5 p.p.m. of sulfur and recycling the hydrogen rich gas to the first reaction zone under conditions to pro.- vide from about 5 to about 15 p.p.m. of moisture in the charge thereto.

2. The method of claim 1 wherein said low boiling portion is reformed under conditions of moisture control to inuence the dehydrogenation of naphthenes in a substantial amount prior to effecting substantial dehydrocyclization and isomerization of hydrocarbon constituents in the low boiling portion, reforming the high boiling naphtha portion in the presence of the total effluent obtained by the above recited low boiling naphtha reforming operation in the presence of a substantial amount of sulfur so as to inuence dehydrogenation, dehydrocyclization and isomerization of hydrocarbon components in the high boiling naphtha portion with a platinum reforming catalyst. v

3. The method of claim 1 wherein the catalyst employed to reform the low boiling naphtha portion contains about 0.35% by weight of platinum and the catalyst employed to reform the high boiling naphtha fraction contains about 0.6% by weight of platinum.

4. The method of claim 1 `wherein the sulfur content of the charge comprising the low boiling naphtha fraction is less than 10 p.p.m. of sulfur.

5. The method of claim 1 wherein the sulfur content of the low boiling naphtha is maintained below about 5 p.p.m. and at least about 350 p.p.m. in the high boiling naphtha. fraction.

6. The method of claim 1 wherein all of the hydrogen requirements of the high boiling naphtha reforming operation are provided by the efuent of the low boiling naphtha reforming operation.

7. The method of claim 1 wherein reforming of the References Cited UNITED STATES PATENTS 2,901,415 8/1959 Hemminger et al. 208-65 2,990,363 7/1961 Evans 208-65 2,946,737 7/ 1960 Potas 208-65 3,242,066 3/ 1966 Myers 208-138 3,347,777 10/ 1967 Davis 208-65 HERBERT LEVINE, Primary Examiner U.S. C1. X.R.