US3502573A - Continuous,low pressure catalytic reforming process with sulfur inclusion,water exclusion,and low space velocity - Google Patents

Description

United States Patent Ser. No 833,778 7 Int. Cl. C10g 35/08 US. Cl. 208-138 7 Claims ABSTRACT OF THE DISCLOSURE A hydrocarbon charge stock boiling in the gasoline range is continuously reformed by contacting, in a substantially water-free reforming zone, the hydrocarbon charge stock, hydrogen, and sulfur or a sulfur-containing compound with a reforming catalyst containing a platinum group component at reforming conditions, including a pressure of about 50 to about 250 p.s.i.g. and a liquid hourly space velocity of about 0.1 to about 0.9 hlf selected to produce a C reformate having an F-l clear octane number greater than 98. The sulfur or sulfurcontaining compound is continuously introduced into the reforming zone both during start-up and thereafter for the duration of the reforming operation in an amount, calculated on an elemental basis, equivalent to about 300 to about 3,000 wt. ppm. of the hydrocarbon charge stock. Key feature of the resulting process is the capability to achieve a temperature stability level substantially less than F./bbl./ lb. at the low pressure condition, thereby enabling a substantial increase in catalyst life before regeneration becomes necessary.

CROSS-REFERENCES TO RELATED APPLICATIONS This application is a continuation-in-part of our application entitled Catalytic Reforming of hydrocarbons, filed Aug. 9, 1967, and assigned Ser. No. 659,301 now abandoned.

DISCLOSURE The subject of the present invention is an improvement in the low pressure process for the continuous, catalytic reforming of hydrocarbon fractions boiling essentially within the gasoline range to produce singular yields of a C reformate having a P-l clear octane number greater than 98. More precisely, the present invention relates to an improved low pressure process for transforming, with minimum yield loss, hydrocarbon charge stocks having a low aromatic content and corresponding low octane number into a product stream having a substantially higher concentration of aromatics with corresponding higher octane number.

The conception of the present invention was a product of a number of recent developments associated with the art of continuous, low pressure reforming systems. The first development involves the finding that the inclusion of sulfur could be extremely beneficial in a low pressure reforming system using a catalyst containing a platinum group component. This finding was in sharp contrast to the traditional teaching in this art that the presence of sulfur is detrimental. Coupled with this development was the recognition of the detrimental effects of water in such a system. Now we have additionally determined, for a continuous reforming system operated at a high severity level effective to achieve a target octane of at least 98 F-l clear with sulfur inclusion and water exclusion, that the liquid 3,502,573 Patented Mar. 24-, 1970 hourly space velocity can be used to effect a further major improvement in stability of the process. More specifically, we have observed that a continuous low pressure catalytic reforming process, which is operated at a high severity level with sulfur inclusion and water exclusion, can be modified to achieve a temperature stability less than 10 F. per barrel of charge per pound of catalyst (abbreviated herein as F./bbl./lb.) if space velocity is restricted to a critical range of about 0.1 to about 0.9 hr.

It is well known in the art that the requirements for an optimum process for transforming low octane stocks into high octane stocks, at minimum loss to undesirable products, involves a specially tailored catalytic environment that is designed to promote upgrading reactions for paraffins and naphthenes, which are the components'of gasolines and naphthas that have the highest octaneimproving potential. For parafiins the upgrading reactions are: isomerization to more highly branched parafiins, dehydrogenation to olefins, dehydrocyclization to aromatics, and hydrocracking to lower molecular weight parafiins. Of these, the dehydrocyclization reaction is the one that shows the maximum gain in octane number and is, consequently, preferred. For naphthenes, the principal upgrading reactions involve dehydrogenation to aromatics and ring isomerization and dehydrogenation to aromatics; but (the change in octane number is not as dramatic here as in the case of dehydrocyclization of parafiins since the clear research octane number of most naphthenes is in the range of 65 to 80. Accordingly, catalytic reforming operations are designed to provide an optimum mix between the aforementioned reactions, generally employing for this purpose a multipurpose catalytic composite having at least a metallic dehydrogenation,component and an acidacting component.

It is not, however, to be assumed that the achievement and control of this optimum mix of upgrading reactions is without its problem areas. These, as is true with any complex set of reaction mechanisms, are injected into the picture by the uncontrollable side phenomena that are produced by a myriad of factors that color and complicate the actual operations of such a reforming process. Foremost among these complicating factors are those associated with undesired side reactions. Examples of these side reactions are: demethylation of hydrocarbons to produce methane, ring opening of naphthenes to give straight chain hydrocarbons, excessive hydrocracking of parafiins to yield light gases (i.e., C to C condensation of aromatics and other components to form carbonaceous deposits on the catalyst, acid-catalyzed polymerization of olefins and other highly reactive components to yield high molecular weight reactants that can undergo further dehydrogenation and thus contribute to the carbonaceous deposits on the catalyst, etc.

A successful reforming operation, therefore, minimizes the effects of these complicating factors by judicious selection of the catalytic environment and process variables for the particular charge stock of interest. But, adding an additional dimension of complexity to the solution of this problem is the interdependence of the set of desired reactions and the set of undesired reactions such that selection of the proper conditions to minimize undesired reactions has a marked effect on the set of desired reactions.

Nowhere is this interdependence more evident than in a continuous reforming process. By continuous reforming process, it is meant a reforming process that is operated for a catalyst life of at least 15 barrels of charge per pound of catalyst (BPP) without regeneration. As is well recognized in the art, continuous reforming processes are sharply distinguishable from regenerative reforming processes because in the latter type of process at least a portion of the catalyst is continuously being regenerated and the catalyst life before regeneration is always substantially less than 1 BPP. In regenerative reforming, stability is not a problem because of the continuous regeneration capability and the dominating objective in this type of reforming process is selectively at octane. Because regenerative reforming systems are not directly concerned with minimizing the side reactions that lead to catalyst instability, it is to be understood that the concept of the present invention has no relationship to regenerative reforming. Similarly, the art on regenerative reforming since it is directed at the solution of a different problem has little relevance to continuous reforming systems where the dominating problem is the stability problem. Indeed, it is but a truism to observe that if a regenerative reforming process could be operated in a stable fashion it would cease to require continuous regeneration capability. Hence, the concept of the present invention relates exclusively to continuous reforming systems because in this system it is necessary to suppress undesired side reactions that lead to catalyst deactivation in order to maintain catalyst activity at a high level for a catalyst life of at least 15 BPP.

Because regenerative reforming systems need not be concerned about stability, the universal practice has been to run them at low pressure because of well known short term yield advantages. The term low pressure as used herein means about 50 to about 250 p.s.i.g. For some time now, there has been a substantial need for a continuous reforming process that can operate at low pressure without sacrificing either stability or selectivity.

At this point, it is to be carefully noted that a low pressure, continuous reforming process is desired because the two main upgrading reactions mentioned previously dehydrocyclization of paraffins and dehydrogenation of naphthenesare net producers of hydrogen and as such they are favored by low system pressure.

The principal barrier to low pressure operation in the past has been the effect of low pressure on the previously mentioned catalyst-fouling reactions of condensation and polymerization which are believed to be the principal reactions involved in carbon or coke formation on the catalyst. It is thought that this carbon formation involves in part certain olefinic and aromatic hydrocarbons which appear to be adsorbed on the surface of the reforming catalyst, particularly at the dehydrogenation and aromatization sites, and that these catalytically active sites are thereby shielded from the materials being processed. Moreover, aromatics and olefinic materials in the presence of a reforming catalyst tend to undergo dehydrogenation, condensation and polymerization type reactions and to settle on the catalyst and undergo further dehydrogenation until carbonaceous deposits are formed. Low pressures tend to favor these catalyst fouling reactions because insufiicient hydrogen is available to suppress these catalystfouling reactions which are generally characterized as hydrogen-producers. In addition, a low partial pressure of hydrogen, since it suppresses hydrocracking and hydrogenation tends to allow carbonaceous deposit precursors to collect on the catalyst, whereas ordinarily the high cracking activity and hydrogenation activity of the catalyst would tend to keep the catalyst relatively free of these carbonaceous deposit precursors. In any event, this increase in catalyst-fouling at low pressures results in the decline in catalyst aromatization activity and, if a product of constant quality is desired, it is necessary to compensate for this deactivation. Usually the most direct and inexpensive method for compensating, in a continuous reforming system, involves increasing the reaction temperature. This in turn, however, leads to the promotion of hydrocracking to a greater extent than dehydrogenation and dehydrocyclization reactions. Hence, greater losses to light gases are encountered and hydrogen consumption goes up and C yield goes down. Furthermore, the rate of catalyst fouling increases dramatically as temperature is increased. Accordingly, prior attempts at operating a continuous reforming process at low pressure have been unsuccessful because of this severe stability problem.

Recently, a number of significant developments have occurred in the field of low pressure, continuous reforming systems. One major discovery involves the finding that, when a controlled quantity of sulfur is continuously introduced into a reforming catalyst environment which is maintained substantially free of water, a reforming process can be designed to take advantage of the favorable effects of low system pressure while avoiding some of the hereinbefore discussed adverse effects. Apparently, sulfur acts to inhibit the association reactions that tend to carbonize the catalyst at these low pressure conditions. This theory is supported by the fact that the catalysts used with sulfur under these conditions tend to contain much less carbonaceous material at the end of the reforming run than a similar catalyst run at the same conditions without the presence of sulfur. Despite this beneficial effect of sulfur, when this sulfur-modified reforming system is run at high severity levels effective to produce a reformate product having an octane number greater than 98, the effect of sulfur is not adequate to completely retard the association reactions and relatively rapid carbonation of the catalyst is typically observed with attendant decline in catalyst activity.

In order to express the rate of decline of activity for reforming systems, the art customarily employs a stability parameter computed as the increment in temperature per barrel of feed to the reforming zone per pound of catalyst employed therein. At a target octane of F-l clear with this sulfur-modified, low pressure reforming system, this stability parameter typically can attain a value substantially in excess of 10 F./ bbl./ lb. or more. For example, for a heavy Kuwait naphtha reformed in a sulfurmodified system to 100 F-l clear at 100 p.s.i.g. and a LHSV of 2.5, a temperature deactivation of 45 F./ bbl./ lb. is observed. In contrast, for a low severity operation with an ordinary high pressure system a value substantial- 1y less than 10 F./bbl./lb. is customarily observed.

One of the principal reasons for going to the sulfurmodified, low pressure, continuous reforming system was the advantages it offered over the complex, swing-bed, constantly regenerating systems that the prior art had found to be indispensable to successful operation under these conditions. An outstanding characteristic of this sulfur? modified system was the infrequency of regeneration re quired so that complex regeneration facilities were not necessary. However, the trend in the art towards higher octane levels in the product reformate (i.e., greater than 98 F-l clear) places this advantage in jeopardy because at stability levels above about 10 F./bbl./ lb. continuous reforming processes rapidly become infeasible, and the economics and technical considerations begin to point towards swing-bed systems. Therefore, moderate stability levels involving a temperature decline rate substantially less than 10 F./bbl./lb. are essential for the success of continuous reforming systems.

We have now discovered that in order to consistently achieve moderate stability levels in a low pressure, sulfur-modified continuous reforming process which is operated to make a C reformate having an octane num* ber greater than 98 F-l clear, a liquid hourly space velocity less than 1.0 is essential. The result is quite unexpected because of the subsetantial body of teachings in the art that a reforming system at low space velocities tends to favor the slow reactions such as hydrocracking of paraffins, condensation of aromatics, etc., which are productive of instability not only in yield but also in temperature. In fact, severe hydrocracking, resulting in rapid hydrogen consumption with a resultant fall in hydrogen partial pressure and a concomitant carbonization of the catalyst, were heretofore commonly experienced when a conventional continuous reforming process was run to produce 98 F1 clear reformate at low space velocity. In sharp contrast with this result, we have found for a low pressure, sulfur-modified, continuous reforming system run to produce at least a 98 F-1 clear reformate that a low space velocity is essential for theachievement of moderate stability levels.

It is, accordingly, an object of the present invention to provide an improvement in a continuous reforming process that operates with the continuous addition of sulfur thereto and the substantial exclusion of water therefrom. A related object is to increase the stability of such a process with corresponding increase in catalyst life before regeneration.

In a broad embodiment, the present invention is an improvement in a catalytic, low pressure process for continuously reforming a hydrocarbon charge stock boiling in the gasoline range for a catalyst life of at least 15 barrels of charge per pound of catalyst without catalyst regeneration. In this process, the hydrocarbon charge stock, hydrogen, and sulfur or a sulfur-containing compound are continuously contacted, in a substantially water-free reforming Zone, with a reforming catalyst containing a platinum group component at reforming conditions including a pressure of about 50 to about 250 p.s.i.g. selected to yield a C reformate having an F-l clear c tane number greater than 98. Moreover, the sulfur or sulfur-containing compound is continuously introduced into the reforming zone, both during the start-up of the process and thereafter for the duration of the reforming operation, in an amount calculated as elemental sulfur equivalent to about 300 to about 3,000 wt. p.p.m. of the charge stock. In this process, our improvement comprises selecting a liquid hourly space velocity from the range of about 0.1 to about 0.9 hr.- and adjusting the conversion temperature to a level suflicient to continue to produce a C reformate having an F-l clear octane number greater than 98, thereby achieving a temperature stability level substantially less than F./'bbl./lb. and enabling a substantial increase in catalyst life before regeneration becomes necessary.

Specific objects and embodiments of the present invention relate to details concerning process conditions used therein, particularly preferred catalysts for use therein, types of charge stocks that can be reformed thereby, and mechanics of the reforming step and product recovery steps associated therewith, etc. These specific objects and embodiments will become evident from the following detailed explanation of the essential elements of the present invention.

Before considering in detail the various ramifications of the present invention, it is convenient to define several of the terms and phrases used in the specification and the claims. The phrase gasoline boiling range as used herein refers to a temperature range having an upper limit of about 400 F. to about 425 F. The term naphtha refers to a selected fraction of a gasoline boiling range distillate and will generally have an initial boiling point of from about 150 F. to about 250 F. and an end boiling point within the range of about 350 F. to about 450 F. The phrase hydrocarbon charge stock is intended to refer to a portion of a petroleum crude oil, a mixture of hydrocarbons, of a coal tar distillate, of a shale oil, etc., that boils within a given temperature range. The expression sulfur entering the reforming zone means the total quantity of equivalent sulfur entering the reforming zone from any source as elemental sulfur or in sulfur-containing compounds. The amounts of sulfur given herein are calculated as weight parts of equivalent sulfur per million weight parts of charge stock (p.p.m.), and are reported on the basis of the elementalsulfur even though the sulfur is present as a compound. The pharse substantially water-free refers to the situation where the total water and water-producing compounds entering the reforming zone from any source is at least less than 20 ppm. by weight of equivalent water based on the hydrocarbon charge stock. The term selectivity when it is applied to a reforming process refers to the ability of the process to make hydrogen and C yield and to inhibit C -C yield. The term activity when it is applied to reforming processes refers to the ability of the process, at a specified severity level, to produce a C product of the required quality as measured by octane number. The term stability when it is applied to the reforming process refers to the rate of change with time of the operation parameters associated with the process; for instance, a common measure of stability is the rate of change of reactor temperature that is required to maintain a constant octane number in output C product the smaller slope implying the more stable process. The liquid hourly space velocity (LHSV) is defined to be the equivalent liquid volume of the charge stock flowing through the bed of catalyst per hour divided by the volume of the catalyst bed.

The hydrocarbon charge stock that is reformed in accordance with the process of the present invention is generally a hydrocarbon fraction containing naphthenes and paraffins. The preferred charge stocks are those consisting essentially of naphthenes and paraffins although in some cases aromatics may also be present. This preferred class includes straight run gasolines, natural gasolines, synthetic gasolines, and the like. On the other hand, it is frequently advantageous to charge thermally or catalytically cracked gasolines or higher boiling fractions thereof. Mixtures of straight run and cracked gasoline can also be used. The gasoline charge stock may be a full boiling range gasoline having an initial boiling point of from about 50 F. to about F. and an end boiling point within the range of from about 325 to 425 F., or may be a selected fraction thereof which usually Will be a higher boiling fraction commonly referred to as a heavy naphtha. It is also within the scope of the present invention to charge pure hydrocarbons or mix tures of hydrocarbons, usually paraffins or naphthenes, which it is desired to convert to aromatics.

The charge stock must be carefully controlled in the areas of concentration of sulfur-containing compounds and of concentration of oxygen-containing compounds. In general, it is preferred that the concentation of both of these constituents be reduced to very low levels by any suitable pretreating method such as a mild hydrogenation treatment with a suitable supported catalyst such as a cobalt and/or molybdenum catalyst. This is not to be construed to exclude the possibility that the concentration of sulfur-containing compounds in the charge stock could be carefully adjusted in order to furnish the required amount of sulfur to the reaction environment; but this latter method is difficult to control and is, consequently, not preferred. In any event, it is necessary that the total concentration of water and of wateryielding compounds be reduced to at least 20 p.p.m., calculated as equivalent water, and preferably substantially less than this.

In general, it is preferred to first reduce the sulfur and oxygen concentration of the feed to very low levels, and thereafter inject into the reforming zone a controlled amount of sulfur or sulfur-containing compound. Any reducible sulfur-containing compound, that does not contain oxygen, which is converted to hydrogen sulfide by reaction with hydrogen at conditions in the reforming zone may be used. This class includes: aliphatic mercaptans such as ethyl mercaptan, propyl mercaptans, tertiary butyl mercaptan, etc.; aromatic mercaptans such as thiophenol and derivatives; cycloalkane mercaptans such as cyclohexyl mercaptan; aliphatic sulfides such as ethyl sulfide; aromatic sulfides such as phenyl sulfide; aliphatic disulfides such as tertiary butyl disulfide; aromatic disulfides such as phenyl disulfide; dithioacids; thioaldehydes; thioketones; heterocyclic sulfur compounds such as the thiophenes and thiophanes; etc. In addition, free sulfur or hydrogen sulfide may be used if desired. Usually, a mercaptan such as tertiary butyl mercaptan is the preferredaadditive'for reasons of cost and convenience. 1:

Regardless of which sulfur additive is used, it is clear that it may the added directly to the reforming zone independently of any input stream, or that it :may be added to either the charge stock or the hydrogen stream or both of these. For example, one acceptable method would involve the addition of hydrogen sulfide to the hydrogen stream. However, the preferred procedure involves the admixture of the sulfuradditive with the charge stock prior to its passage into the reforming zone. The amount of sulfur entering the reforming zoneeat any given time is a function of residual sulfur in the charge stock, the amount of sulfur added to the charge stock, the amount 'of sulfur in the hydrogen stream, and the amount added directly 'to the zone. Regardless of the source of the sulfur entering the reforming zone, it is an essential feature of thepresent inventionthat the total from all sources must be continuously maintained in the range of about 300 p.p.m. to about 3,000 p.p.m.'bas2d on weight of charge stock entering the reforming zone, and preferably about 500 to 1,500 wt. p.p.m.

Furthermore, it is essential that the sulfur be present during start-up of the process and that the sulfur be continuously introduced in the amount given above for the duration of the reforming operation. More particularly, if the process is started-up and lined-out and then sulfur is added, the results will be negative. Likewise, if sulfur introduction is discontinued during the course of the run and then later reintroduced, the process wili not recover-that is, the sulfur effect is not reversible. In short, the continuous presence of sulfur in a low pressure, continuous reforming system is absolutely essential to prevent rapid and irreversible catalyst deactivation.

Another essential limitation associated with the use of sulfur is that the amount of sulfur entering the reforming Zone must not be increased during the course of the run because if this happens the catalyst will quickly deactivate and wiil not respond to a subsequent reduction in the amount of sulfur entering the reforming zone. Hence, the amount of sulfur entering the reforming zone is lined-out during start-up at a value within the range previously given and thereafter never increased above this level.

As hereinbefore indicated, the reforming catalyst utilized contains a platinum group component. Typically, this component is combined with a suitable refractory inorganic oxide carrier material such as alumina, silica, zirconia, magnesia, boria, thoria, titania, stronia, etc., and mixtures of two or more including silica-alumina, alumina-boria, silica-alumina-zirconia, etc. It is understood that these refractory inorganic oxides may be manufactured by any suitable method including separate, successive, or co-precipitation methods of manufacture, or they may be naturally-occurring substances such as clays, or earths which may or may not be purified or activated with special treatment. The preferred carrier material comprises a porous, adsorptive, high surface area alumina support having a surface area of about 25 to 500 or more m. gm. Suitable alumina materials are the crystalline aluminas known as gamma-, eta-, and theta-alumina, with gamma-alumina giving best results. In addition, in some embodiments the preferred alumina carrier material may contain minor proportions of other well known refractory inorganic oxides such as silica, zirconia, magnesia, etc. However, the preferred carrier material is substantially pure gamma-alumina. fact, an especially preferred carrier material has an apparent bulk density of about 0.30 to about 0.70 gm./cc. and has surface area characteristics such that the average pore diameter is about 20 to about 300 angstroms, the pore volume is about 0.10 to about 1.0 ml./ gm. and the surface area is about 100 to about 500 m. gm. A preferred method for manufacturing this alumina carrier material is given in US. Patent No. 2,620,314.

Another constituent of the reforming catalyst is a halogen component. Although the precise form of the chemistry of the association of the halogen component with the alumina carrier material is not entirely known, it is customary in the art to refer to the halogen component as being combined with'the alumina or with the other ingredients of the catalyst. This combined halogen may be either fluorine, chlorine, iodine, bromine, or mixtures thereof. Of these, fluorine and chlorine are preferred for the purposes of the present invention. The halogen may be added to the alumina support in any suitable manner, either before, during, or after the addition of the other components. For example, the halogen may be added as an aqueous solution of an acid such as hydrogen fluoride, hydrogen chloride, hydrogen broniide, etc. In addition,

the halogen or a portion thereof may be composited with the alumina during the impregnation of the latter with the platinum group component; for example, through the utilization of a mixture of chloroplatinic acid and hydrogen chloride. In another situation, the alumina hydrosol whichis typically utilized to form the alumina carrier material may contribute at least a portion of the halogen component to the final composite. In any event, the halogen will be typically composited in such a manner as to result in a final composite containing about 0.1 to about 1.5 wt. percent, and preferably about 0.4 to about 1.0 wt. percent of halogen calculated on an elemental basis.

As indicated above, the reforming catalyst must con tain a platinum group component. Although the preferred catalyst contains platinum or a compound of platinum, it is intended to include other platinum group metals such as palladium, rhodium, ruthenium, osmium, and iridium. The platinum group metallic component, such as platinum, may exist within the final catalytic composite as a compound such as an oxide, sulfide, halide, etc., or as an elemental metal. Generally, the amount of the platinum group metallic component present in the final catalyst is small compared to the quantities of the other components combined therewith. In fact, the platinum group metallic component generally comprises about 00.01 to about 3 wt. percent of the final catalyst, calculated on an elemental basis. Excellent results are obtained when the catalyst contains about 0.1 to about 2.0 wt. percent of the platinum group metal.

The platinum group component may be incorporated in the catalyst composite in any suitable manner such as coprecipitation or cogellation with the alumina support, ion-exchange with the alumina support and/or alumina hydrogel, or impregnation of the alumina support at any stage in its preparation either before, during, or after its caloination treatment. The preferred method of preparing the catalyst involves the utilization of a soluble, decomposable compound of a platinum group metal to impregnate the alumina support. Thus, the platinum. group metal may be added to the alumina support by commingling the latter with an aqueous solution of chloroplatinic acid or an equivalent compound.

Following the piatinum and halogen impregnation, the impregnated alumina carrier material is typically dried and subjected to a conventional high temperature calcination or oxidation technique to obtain an oxidized composite of a halogen component and a platinum group component with an alumina carrier ma erial. Similarly, additional treatments such as prereduction and/or presulfiding may be performed on the resulting oxidized composite if desired.

It is understood that the reforming catalyst may be manufactured in any suitable manner and that the precise method of manufacture is not considered to be a limiting feature of the present invention. Likewise, it is understood that the catalyst may be present in any desired shape, such as: spheres, pills, pellets, extrudates, powder, etc. Additional details on preferred catalysts for the process of the present invention are given in U.S. Patents Nos. 2,479,109, and 3,296,119.

attrition losses of the valuable catalyst and of well known operational advantages, it is preferred to use a fixed bed system. In this system, a hydrogen-rich stream and the charge stock are preheated, by any suitable heating means, tothe desired reaction temperature and then are passed in admixture with sulfur or a sulfur-containing compound, into a reforming zone containing a fixed bed of the catalyst. It is, of course, understood that the reforming zone may be one or more separate reactors with suitable heating means therebetween to insure that the desired conversion temperature is maintained at the entrance to each reactor. It is also to be noted that thereactants are typically in vapor phase and may be contacted with the catalyst bed in either upward, downward, or radial flow fashion with the latter being preferred.

It is an essential feature of the present invention that the reforming zone is maintained substantially Water-free. To achieve and maintain this condition, it is necessary to control the water initially present in the reforming zone and the water level present in the charge stock and the hydrogen stream which are charged to the reforming zone. It is essential that the equivalent water entering the reforming zone from all sources be held to a level less than that equal to 20 wt. p.p.m. In general, this can be accomplished by predrying the reforming zone with a suitable circulating dry gas such as dry hydrogen and by continuously drying the charge stock with any suitable drying means known to the art such as a conventional solid adsorbent having a high selectivity for Water, for instance, silica gel, activated alumina, calcium or sodium crystalline 'aluminosilicates, anhydrous calcium sulfate, high surface area sodium, and the like adsorbents. Similarly, the water content of the charge stock may be adjusted by suitable stripping operations. in a fractionation column or like device. Also in some cases a combination of adsorbent drying and distillation drying may be used advantageously to-effect almost total removal of water from the charge stock. Additionally, it is preferred to continuously dry the hydrogen stream entering the hydrocarbon conversion forming step, an effluent stream is continuously withdrawn from the reforming zone, cooled in a conventional cooling means and typically passed to a separating zone wherein a hydrogen-rich vapor phase separates from a hydrocarbon-rich liquid phase. A hydrogen-rich stream 7 is then withdrawn from the separating zone and a portion of it vented from the system in order to remove the net hydrogen production and to maintain pressure control. Typically another portion of this withdrawn hydrogen stream is recycled via compressing means to the reforming step. Similarly, the hydrocarbon-rich liquid phase is withdrawn and typically passed to a suitable fractionation zone wherein a C to C product is taken overhead and a C product recovered as bottoms.

It is within the scope of the present invention to operate with a once-through hydrogen stream, but the preferred procedure is to recycle a hydrogen stream recovered from the efliuent stream as indicated above. In this last mode, the recycle hydrogen stream can be selectively treated to remove H O without removing H 8 by using a suitable selective adsorbent (e.g., see U.S. Patent No. 3,201,343); however, this procedure requires the calculation of the equilibrium level of sulfur that will enter the reforming zone with the hydrogen stream for a given sulfur input in the charge stock so that the total quantity of sulfur entering the reforming zone, in both the charge stock and hydrogen stream, is lined-out at a value in the range previously given. An alternative approach which is simpler to control is to remove substantially all H 0 and H 5 from the recycle hydrogen stream and control the amount of sulfur entering the reforming zone exclusively by the amount admixed with the charge stock.

As indicated previously, a singular feature of the process of the present invention is the capability to operate in a stable fashion at low pressure. In the past, it has been the practice to operate at high pressure primarily to provide sufiicient hydrogen to saturate hydrocarbon fragments generated during the reforming process and to prevent excessive carbon deposition on the catalyst with the attendant decline in the catalysts activity for the upgrading reactions of interest. We have now found that a highly stable operation is achieved using the process of the present invention at pressures in the range of about 50 to about 250 p.s.i.g. and preferably about 75 to about 200 p.s.i.g. The exact selection of the operating pressure within these ranges is made primarily as a function of the characteristics of the particular charge stock and catalyst used in the process.

The temperature required in the reforming zone is generally lower than that required for a similar high pressure operation. This significant and desirable feature of the present invention is a consequence of the inherent selectivity of the low pressure operation for the octane-upgrading reactions as previously explained. In the past, when high octane was required, it was thepractice to run at higher temperatures in order to produce more hydrocracking of parafiins and thus concentrate the available aromatics in the product stream; however, this high cracking is not needed to make octane in the process of the present invention. Accordingly, the present process requires a temperature in the range of about 850 F. to about 1100" F. and preferably about 900 F. to about 1050 F As is well known to those skilled in the reforming art, the initial selection of the temperature within this broad range is made primarily as a function of the desired octane in the product reformate considering the characteristics of the charge stock and of the catalyst. Ordinarily, the temperature is increased during the run to compensate for deactivation that occurs and to provide for a constant octane product. For purposes of the present invention, the temperature is selected within the broad range previously given to provide a reformate having an F-l clear octane numbr of at least 98 and more typically about 100.

According to the present invention the process is conducted at a critical liquid hourly space velocity in order to achieve a temperature stability level substantially less than 10 F./bbl./lb. This critical value is about 0.1 to about 0.9 hr. with a value between about 0.3 to about 0.75 hr.- being preferred. This parameter is calculated on the basis of the volume occupied by the liquid at standard conditions of 0 C. and 1 atmosphere, and of the volume of the catalyst bed. As is well known, the contact time between the reactants and the catalyst is a complex function of the phase state of the reactants and products, of the available channel space in the catalyst bed, of the number of moles of product produced as compared with the number of moles of reactants, of the process conditions employed, and the like factors. Nevertheless, it is customary to consider that the inverse of the LHSV, times a constant factor approximates the contact time such that variation in the inverse of LHSV produces linear variations in contact time. Consequently, the limitation of space velocity to a value less than 1.0 is equivalent to specifying high contact times for the reactants with the catalyst. In the prior art, it had been established that for conventional reforming systems high contact times produced excessive hydrocracking with resultant deactivation of the catalyst and were to be avoided. In the present invention, results directly contrary to these teachings are obtained in that for the sulfur-modified, low pressure, continuous reforming system of the present invention, high contact times produce extraordinary stability.

The hydrogen necessary for the present invention is supplied to the reforming zone at about 2.0 to about 20 moles per mole of hydrocarbon in the feed. Excellent results are obtained when about to about moles of hydrogen are used for each mole of hydrocarbon in the feed stock.

An extraordinary feature of the process of the present invention is the infrequency with which the catalyst must be regenerated. Previously, low pressure operations have required extensive regenerating facilities if the associated catalyst is to be used for an economic period of time. The process of the present invention, since it achieves reasonable stability at low pressure with accompanying low catalyst fouling rate, can be built without extensive regenerating facilities, such as swing bed reactors, thereby efiecting great savings in initial investment. An additional incentive for avoiding frequent regeneration in the substantial danger of injecting small amounts of water into the system from the regeneration operation via ineffective or inefficient purging techniques once the oxidation step of the regeneration cycle is completed. As previously discussed, the presence of even small quantities of water in the system can jeopardize the stability of the process of the present invention; accordingly, stringent precautions must be taken to insure that the system is substantially free of water after the infrequent regeneration operations are performed.

The following examples are given to illustrate further the process of the present invention, and to indicate the benefits to be afforded through the utilization thereof. It is understood that the examples are given for the sole purpose of illustration and not considered to limit unduly the generally broad scope and spirit of the appended claims.

Example I Alumina spheres having a diameter of inch were prepared in accordance with the method given in U.S. Patent No. 2,620,314. The resultant spheres were commingled with an aqueous impregnation solution containing chloroplatinic acid and hydrochloric acid. The impregnated spheres were, thereafter, successively dried, calcined, reduced with pure hydrogen and sulfided with a mixture of hydrogen and hydrogen sulfide, essentially according to a procedure given in U.S. Patent No. 3,296,119. A portion of the resultant catalyst was analyzed and found to contain: 0.90% by weight chlorine, 0.75 by weight platinum, and 0.10% by weight sulfurcalculated on an elemental basis.

A 100 cc. portion of this'catalyst was then charged to a laboratory scale reforming plant having a single reforming zone, a separating zone, a debutanizer column, and associated equipment. In this plant a charge stock and recycle hydrogen were admixed and heated to the desired conversion temperature. The heated mixture was then passed to the reforming zone. The effluent from the reforming zone was cooled and passed to a separating zone wherein a hydrogen-rich gaseous phase separated from a liquid phase. A portion of the hydrogen-rich gaseous phase was passed over a high surface area sodium adsorbent and recycled through a compressor to the reforming zone. Another portion of this gaseous phase was recovered as excess recycle gas. The liquid phase from the separating zone was passed to the debutanizer column in which a light gas fraction was taken overhead and a debutanizer reformate recovered as bottoms.

The charge stock utilized in this example was a heavy Kuwait naphtha having an API gravity at 60 F. of 60.4, an initial boiling point of 184 F., a 50% point of 256 F., an end boiling point of 360 R, an F-l clear octane number of 40.0, 5.9 weight p.p.m. H 0, 71% by volume of parafi'ins, 8% by volume aromatics, and 21% by volume naphthenes. To this stock 1,200 ppm. of sulfur was added as tertiary butyl mercaptan. It is to be noted that this stock is considered to be relatively diflicult to reform and thus results here tend to reflect a worst case situation.

A series of tests Was then made with this stock wherein the effects of varying liquid hourly space velocity were determined. These tests were all conducted at a plant pressure of p.s.i.g., a hydrogen to hydrocarbon mole ratio of 10.0, and a reaction temperature sufficient to sustain throughout the test an octane level of 100 F-1 clear in the debutanized reformate product. A fresh batch of the aforementioned catalyst was used for each test.

The first test was run at an LHSV of 2.5 hr." and for 6 periods of 24 hours each. Results at the end of the first period indicated a reaction temperature of 985 F. and C reformate yield of 76.2% by volume of charge stock. Results at the end of the sixth period were, respectively, 1040 F. and 63.0% C yield. Placing these results on a barrel per pound of catalyst basis gives a catalyst stability parameter value of 45 F./ barrel of feed/ pound of catalyst (i.e., abbreviated F./bbl./lb.).

For the second test, the LHSV was reduced to 1.5 hr.- and an identical 6 day run was carried out. Results here were: for the first period, a reaction temperature of 950 F. and a C yield of 76.5; and for the sixth period, a reaction temperature of 97.6 F and a C yield of 75 .1. Catalyst stability here was 18 F./ bbl./ lb.

For the third test the LHSV was set at 0.75 hr? and such unexpected stability was encountered that the run was contained for 30 periods instead of 6 as heretobefore. Results here for the first period were 913 F. and 77.0% C yield. For the 30th period results were 941 F. and 74.2% C yield. Catalyst stability here was at a level of 9 F./bbl./lb.

In sum, these results evidence the sharp increase in stability which attends operation of a sulfur-modified, low pressure, continuous reforming system at low space velocities. Remembering that moderate stability levels are essential for the efficient use of continuous reforming systems, it can be seen that the presence of sulfur coupled with careful control of space velocity are essential constraints in the solution to this problem.

Example II Another series of tests were carried out using a reforming system that was similar to that described in Example I with the exception that a scrubber selective for H O was employed on the recycled hydrogen line instead of one that removed both H 0 and H S. Consequently, less sulfur was required in the feed because of sulfur circulation in the hydrogen stream. The catalyst employed in these tests was prepared in a manner identical to that delineated in Example I.

The charge stock used in this example was a high cyclic naphtha having a gravity API of 52.7 at 60 R, an initial boiling point of 213 F., a 50% point of 260 R, an end boiling point of 361 F., a paraffin content of 30.1% by volume, a naphthene content of 58.9% by volume, an aromatic content of 9.4% by volume, and an F1 clear octane number of 65.8.

These tests were run at 100 p.s.i.g., an H;;/ oil mole ratio of 9:1, and a reaction temperature sufficient to sustain throughout the test an octane level of 102 F-l clear in the reformate product.

The first test was run at an LHSV of 0.5 hr.- for a period of time corresponding to 2.0 barrels of feed per pound of catalyst utilized. During this time the C reformate yield varied between 84.7% and 83.0% (based on volume of feed stock) and the reactor temperature 13 between about 884 F. and about 882 F. Remarkably, the temperature stability of the catalyst over this period was incredibly low-Jess than 1.0 F./bbl./lb.

The second test was run at an LHSV of 0.75 for another period of time corresponding to 2 barrels of feed per pound of catalyst used. At the beginning of this period, an 83.1 volume percent C yield was recorded at a reaction temperature of 914 F. While at the end of the period an 82.1 volume percent C yield was recorded at a reaction temperature of 925 F. Stability here was computed at about 5.5 F./bbl./lb.

The final test was run at an LHSV of 1.0 for a period of about 1 barrel of feed per pound of catalyst at which point severe temperature instability made the continuation of the run undesirable; At the beginning of the test period an 83.5 volume percent C reformate yield was recorded at 940 F. However, by the end of the period, an 81.6 volume percent reformate yield was recorded at a block temperature of 958 F. Catalyst stability here was determined to be about 18 F./bbl./lb.

In short, the necessity of limiting the LHSV to a value less than 1.0 for this system is once again manifested by this data.

We claim as our invention:

1. In a catalytic, low pressure process for continuously reforming a hydrocarbon charge stock boiling in the gasoline range for a catalyst life of at least 15 barrels of charge per pound of catalyst without catalyst regeneration; wherein the charge stock, hydrogen, and sulfur or a sulfur-containing compound are continuously contacted in a substan tially water-free reforming zone with a reforming catalyst containing a platinum group component at reforming conditions, including a pressure of about 50 to about 250 p.s.i.g., selected to yield a C reformate having an F-l clear octane number greater than 98; wherein the sulfur or sulfur-containing compound is continuously introduced into the reforming zone, both during start-up of the process and thereafter for the duration of the reforming operation, in an amount, calculated as elemental sulfur, equivalent to about 300 to about 3,000 wt. ppm. of the charge stock, the improvement comprising selecting a liquid hourly space velocity from the range of about 0.1 to about 0.9 hr? and adjusting the conversion temperature to a level sufficient to continue to produce a C reformate having an F-l clear octane number greater than 98, thereby achieving a temperature stability level substantially less than 10 F bbl./ lb. and enablinga substantial increase in catalyst life before regeneration becomes necessary.

2. An improved process as defined in claim 1 wherein the sulfur level in the reforming zone is achieved by the continuous addition of a sulfur-containing compound to the hydrocarbon charge stock prior to contacting it with said reforming catalyst.

3. An improved process as defined in claim 1 wherein the sulfur level in the reforming zone is achieved by the continuous addition of H 8 to the hydrogen stream charged to the reforming zone.

4. An improved process as defined in claim 1 wherein said reformnig catalyst comprises a combination of catalytically effective amounts of a platinum group component and a halogen component with a refractory inorganic oxide carrier material.

5. An improved process as defined in claim 1 wherein said reforming catalyst comprises a combination of catalytically effective amounts of platinum and chlorine with an alumina carrier material.

6. An improved process as defined in claim 1 wherein said liquid hourly space velocity is selected from the range of about 0.3 to about 0.75 hrr 7. An improved process as defined in claim 1 wherein said reforming conditions include a hydrogen to hydrocarbon mole ratio of about 2:1 to 20: 1.

References Cited UNITED STATES PATENTS 2,952,611 9/1960 'Haxton et a1 208138 3,006,841 10/1961 Haensel 208138 3,067,130 12/1962 Baldwin et al. 208-138 3,201,343 8/19-65 Bicek 208138 3,234,120 2/1966 Capsuto 208-138 3,330,761 7/1967 Capsuto et al. 208138 HERBERT LEVINE, Primary Examiner US. Cl. X.-R. 208--139