US3502570A

US3502570A - Production of high octane gasolines

Info

Publication number: US3502570A
Application number: US672053A
Authority: US
Inventors: Ernest L Pollitzer
Original assignee: Universal Oil Products Co
Current assignee: Universal Oil Products Co
Priority date: 1967-10-02
Filing date: 1967-10-02
Publication date: 1970-03-24
Anticipated expiration: 1987-03-24

Description

E. L. POLLITZER Filed Oct. 2. 1967 PRODUCTION 0F HIGH OCTANE GASOLINES March 24, 1970 TTR/VEYS United States Patent O U.S. Cl. 208-65 6 Claims ABSTRACT OF THE DISCLOSURE Concerns a combination process for the production of a gasoline fraction rich in high octane aromatics and isoparaiiins. Input stream is a relatively low octane gasoline fraction containing substantial quantities of relatively straight chain paraffinic components. Output streams are: the desired high octane gasoline, a light gas stream, a C, parafnic cut, and hydrogen. Process comprises the steps of: low pressure reforming, separation of reforming products, isomerization of a C to C6 fraction, and final product blending. Principal features of the process are: (l) octane number of product gasoline of about 104 F-l clear, (2) relatively high volume yields of the product gasoline, (3) relatively uniform distribution of antiknock characteristics as a function of boiling point for the resulting gasoline product.

The subject of the present invention is a hydrocarbon conversion process wherein a hydrocarbon input stream rich in relatively straight-chain components is converted into a motor fuel rich in high octane aromatics and isoparaflins. More precisely, the present invention encompasses a combination process in which a hydrocarbon mixture boiling in the gasoline range is subjected to a sulfur-modified, low pressure reforming operation to produce a reformate having an F-l clear octane number of about 100; the resulting products from the reforming operation are separated in a C1 to C4 fraction, a C5 to C6 fraction, a C7 fraction, and a Ca-lfraction; the C5 to C6 is subjected to isomerization; and the products of the isomerization reaction are blended With the CS-- fraction to yield a gasoline fraction having an octane number of about 104 F-l clear.

Responsive primarily to the needs emanating from the designers of high compression internal combustion engines, the petroleum industry has since its inception devoted a considerable portion of its research efforts to the problem of discovering routes to high octane gasoline suitable for use as a motor fuel. Almost all of the routes currently used commercially depend to some extent upon the use of lead alkyls as additives to improve anti-knock characteristics of gasoline, However, despite the lack of scientific evidence to support the thesis, the recent clamor about lead as a pollutant of the atmosphere is tending to impose an additional constraint on solutions to this problem-namely, the amount of lead alkyls used to make octane must be greatly reduced or preferably eliminated. Accordingly, attention within the petroleum research industry is being specifically directed to methods of producing high octane gasolines that do not employ lead additives to meet required octane levels.

Today in the modern refinery many routes to high octane gasolines are available such as catalytic reforming, catalytic cracking, alkylation, isomerization, hydrocracking, and various combinations of these processes. Of these, three processes are particularly preferred to making high octane gasoline-namely, catalytic reforming, catalytic cracking, and alkylation. In fact, it has been estimated that 85% of the United States crude oil is processed in refineries which use all three of these processes and that 3,502,570 Patented Mar. 24, 1970 l'CC 95% is handled in refineries having at least catalytic reforming and cracking units. The first of these preferred methods, catalytic reforming, employs three principal octane-upgrading reactions to make an aromatic-rich gasoline; these are: dehydrogenation of naphthenes to aromatics, dehydrocyclization of parafns to aromatics, and isomerization of paraflinic components to isoparains. The second of these preferred methods, catalytic cracking, typically operates on a petroleum fraction boiling above the gasoline range to produce about 20% to about 50% by volume of a gasoline fraction having an F-l clear octane number of about 90 to about 95. The third method, alkylation, upgrades olefins and isobutane to gasoline having a clear research octane number of about 90 to 95. All of these methods of producing high octane clear gasoline share a common characteristic: as the requirement for octane is increased, yield levels of product gasoline tend to decrease dramatically, and this fact is particularly true when the octane requirement reaches octane levels of about 100 F-l clear. However, it has recently been determined that a catalytic reforming process can be designed to run at high octane levels with relatively high volumetric yield, and it is this process to which the present invention is applicable.

In the catalytic reforming art it has been found that if a controlled concentration of hydrogen sulfide is utilized in a reforming operation employing a platinum metalcontaining catalyst in combination with the exclusion of water therefrom, that conditions-primarily a low pressure of about 50 p.s.i.g. to about 250 p.s.i.g.-

resulting in the production of substantially increased quantities of high octane aromatic compounds, can be utilized without excessive deactivation of the catalyst. Accordingly, the continuous operation of a catalytic reforming process to produce high yields of a reformate having an F-l clear octane number of about is now commercially feasible. However, in view of the fact that the principal sources of octane improvement for this process are reactions that produce aromatics, it is evident that the gasoline produced is an aromatic-rich gasoline.

It is well known that aromatic hydrocarbons in admixture with air ignite under compression to provide an explosion Which has a relatively slow ame advance across the air-hydrocarbon vapor mixture, and such mixtures, therefore, provide fuel components for high compression engines having desired anti-knock properties. As the compression ratio of gasoline-burning engines has increased, however, it has been noted that aromatic hydrocarbons when utilized as a major component of motor fuels tend to deposit carbon in the combustion chamber of the engine at high temperatures and high pressure existing within high compression engines. This is generally assumed to be caused by the high ratio of carbon to hydrogen in the aromatic molecules. These carbon deposits tend to cause preignition of the fuel, and as a result, fuels which contain an unduly large proportion of aromatic components can produce an undesirable rumble response when ignited in high compression engines. It has been noted, however, that in admixture with parafiinic components having a relatively high hydrogen to carbon ratio in their molecular structure, this undesired response of aromatic compounds on ignition is typically reduced. Yet if the paraflinic component in admixture with normally high octane aromatic components are normal or relatively straight-chain hydrocarbons, the octane number of the mixture is unevenly distributed with respect to boiling point and is markedly reduced. On the other hand, if the parafnic components are isoparaffinic hydrocarbons, the octane number of the resultant mixture is relatively unevenly distributed with respect to boiling point and maintained at a high level,

while the undesired response of the aromatic-rich motor fuel is greatly reduced. Thus, a mixture of isoparaffins and aromatics makes a preferred motor fuel.

As might be expected the gasoline produced in this sulfur-modified, low pressure reforming process has this undesired rumble response when employed as a motor fuel since it is an aromatic-rich gasoline. For example, a heavy Kuwait naphtha having about 8% by volume of aromatic compounds when subjected to this sulfurmodified process, at a 100 p.s.i.g. and a temperature sufficient for 100 F-l clear, was found to produce a gasoline containing about 67.0% of aromatics by volume, and having this hereinbefore referred to undesired response when employed as a motor fuel. However, I have now found a method by which the gasoline product of this sulfur-modified, low-pressure process can be transformed into a high quality motor fuel having this preferred mixture of isoparafiins and aromatics as explained above.

The concept of the present invention resulted from my examination of the products of this sulfur-modified, low pressure process as a function of severity level employed in the process. From this examination, I determined that as the severity level is increased, and the process is forced to higher octane numbers, more and more paraffinic components are transformed into aromatics via the dehydrocyclization reaction. Furthermore, I have found that the higher molecular weight parafins are `converted at relatively low severity levels with the lower molecular weight parafiins contributing to octane at the higher severity levels. More specifically, l have found that the ease of dehydrocyclizing paraffinic components in this process is an inverse function of the molecular weight of these components. Moreover, I have found that at severity levels suicient to produce a reformate having an F-l clear octane number of about 100, that essentially no paraffinic components above Cr, exist in the product reformate, and in fact, the bulk of the parafiins are C5 and C6. Accordingly, I have found that the aromatic components of this 100 F-l clear reformate can be substantially separated from the paraffnic components by a simple fractionation involving recovery of a C84- fraction and a lower boiling fraction. For example, a reformate produced in this sulfur-modified, lower pressure process for a heavy Kuwait naphtha was fractionated into two fractions at a cut point of about 186 F. to yield,V C6| fractions having 97.9% by volume aromatics. This then effects a great simplification over some of the prior art procedures designed to effect this separation of aromatic components after ordinary catalytic reforming operations which procedures typically employ complex liquid-liquid solvent extraction methods.

Coupled with this observation about the distribution of aromatics in the product gasoline is my further finding that the C5 to C6 fraction of the lower boiling paranrich cut is an ideal feed stock to an isomerization process; and when the products of the isomerization process are blended with this aromatic-rich C6+ fraction, a preferred motor fuel is produced which does not have the undesired combustion response of an aromatic-rich fuel alluded to hereinbefore. Moreover, the blend of the isomerized C5 to C6 fraction with the Cg-lfraction yields a motor fuel having an F-l clear octane number of about 104, thus opening a new route to a high octane gasoline that does not depend on lead additives for its preferred characteristics.

It is, accordingly, an object of the present invention to provide a motor fuel having not only a high octane value but a good'response characteristic when employed in a high compression engine. Another object of this invention is to convert a paraflinic stock rich in normal parafiinic components which tend to knock upon ignition in a high compression engine into a preferred mixture of aromatics and isoparaiiinic hydrocarbons having high and relatively evenly distributed anti-knock properties. Another object of the present invention is to provide a procedure for manufacturing a motor fuel rich in isoparatiinic and aromatic compounds having an F-l clear octane number of about 104.

Broadly, my invention involves a process for producing a gasoline fraction having an F-l clear octane number of about 104 from a loW octane gasoline fraction. This process comprises the steps of: (a) contacting, in a substantially water-free reforming zone, the low octane gasoline fraction and hydrogen with a platinum metalcontaining reforming catalyst in the presence of sulfur entering the reforming zone in an amount of about 10 p.p.m. to 3000 p.p.m. of sulfur based on the weight of the low octane gasoline fraction, and at reforming conditions, including a pressure of about 50 p.s.i.g. to about 250 p.s.i.g., effective to produce a reformate having an F-l clear octane number of about (b) separating in a first separating zone, the effluent from the reforming zone into a first hydrogen-rich gaseous phase and a liquid reformate phase; (c) separating, in a fractionation system, the liquid reformate phase in the C1 to C4 fraction, a C5 to C6 fraction, a C, fraction, and a CS-lfraction; (d) contacting, the C5 to C6 fraction and hydrogen in an isomerization zone, with an isomerization catalyst at isomerization conditions; (e) separating in a second separating zone, the effiuent from the isomerization zone into a second hydrogen-rich gaseous phase and a liquid isomerized phase; and (f) blending the liquid isomerized product phase with the C8| fraction to form a gasoline fraction rich in aromatics and isoparains having an F-l clear octane number of about 104.

Other objects and embodiments of the present invention relate to details about the charge stock processed therein, the sulfur compounds used therein, the catalyst employed in each of the reaction zones, and the like particulars. These will be hereinafter discussed in the detailed explanation of each of these facets of the present invention.

Regarding the terms and phrases used herein, it is to be emphasized that the phrase effiuent from a zone is to be construed, unless otherwise qualified, to be the total output from the zone or the total amount of material withdrawn therefrom, and the withdrawal may be continuous or intermittent.

The low octane gasoline fractions that can be converted in accordance with the process of the present invention comprise hydrocarbon fractions containing naphthenes and paratins. The preferred stocks are those consisting essentially of naphthenes and paraflins although in some cases aromatics and/or `olens are also 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, Mixtures of straight run and cracked gasoline can also be used. The gasoline stock may be a full boiling range gasoline having an initial boiling point of from about 50 F. to about 100 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 -for example, a naphtha boiling in the range of C-lto 400 F.

The charge stock for the process of the present invention must be carefully controlled in the areas of concentrations of sulfur-containing compounds and of oxygencontaining compounds. In general, it is preferred that the concentration of both of these constituents be reduced to low levels by any suitable pretreatment means: that is, less than l0 p.p.m. calculated as water or sulfur respectively. 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 water-yielding compounds be reduced to at least p.psm. calculated as equivalent water. These restrictions are doubly significant in one preferred embodiment of the present invention, in which a portion of the hydrogen gas, contained in the efiiuent from the reforming zone, is separated from the other constituents in a separating zone and recycled to the reforming zone Without further treatment, because the available water and hydrogen sulfide will also be recycled with the hydrogen-rich gas. Accordingly, the concentration of these constituents will tend to build up to an equilibrium level in the recycle stream and small amounts of these materials in the input stream may, if the process is not carefully controlled, build up to substantial levels in the recycle stream.

In general, then, it is preferred to first reduce the sulfur and oxygen concentration of the charge stock to very low levels, and thereafter inject a controlled amount of a sulfur-containing compound into the reforming zone. Any reducible sulfur-containing compound, that does not contain oxygen, which is converted to hydrogen sulfide by reaction with hydrogen at the conditions in the reforming zone may be used in the process of the present invention. This class includes: aliphatic mercaptans such as ethyl mercaptan, propyl mercaptan, tertiary butyl mercaptan, etc.; aromatic mercaptans such as thiophenol and derivatives; naphthenic mercaptans such as cyclohexyl mercaptan; aliphatic sulfides such as ethyl sulfide; aro- |matic sulfides such as phenyl sulfide; aliphatic sulfides such as tertiary butyl disulfide; aromatic disulfides such as phenyl disulfide; dithioacid; thioaldehyde, thioketone, heterocyclic sulfide compounds such as the thiophenes and thiophanes; and the like compounds. In addition, free sulfur or hydrogen sulfide may be used if desired. Usually, a mercaptan such as tertiary butyl mercaptan is the preferred additive for reasons of cost and convenience.

Regardless of which type of sulfur is used to inject the sulfur into the reforming Zone, it is clear that it can be admixed with the charge stock as the hydrogen stream flowing thereto, or it may be independently introduced into the reforming zone. Usually, the preferred method is to commingle the desired sulfur additive with the charge stock.

In general, the amount of sulfur entering the reforming zone is a function of the amount added to the charge stock, the amount of residual sulfur in the charge stock, and the amount of hydrogen sulfide contained in the hydrogen stream. Considering all of these factors, it has been determined that the total amount of equivalent sulfur entering the reforming zone must be in the range of about 10 p.p.m. to about 3000 p.p.m. based on weight of the charge entering thereto, in order to achieve a stable reforming operation at low pressures. In one embodiment of the present invention `wherein a suitable adsorbent material is utilized to remove both H2O and H28 out of a recycle hydrogen stream before it is used to supply necessary hydrogen to the reforming zone, the above requirement necessitates the addition of about 100 p.p.m. to about 3000 p.p.m. of equivalent sulfur to the charge stock. In another embodiment in which H28 is not removed from the recycle hydrogen stream, it is clear that a substantial amount of sulfur will enter the reforming zone in this hydrogen stream depending on the exact recycle rate, etc.; consequently, proportionally less sulfur |must be added to the charge stock.

As hereinbefore set forth, the process of the present invention utilizes a catalyst containing a platinum metal in the reforming zone. Although the process of the present invention is specifically directed to the use of a catalytic composite containing platinum, it is intended to include other platinum-group metals such as palladium,

rhodium, ruthenium, etc. The platinum-group metallic to the quantities of the other components combined therewith. For example, a platinum and/ or palladium or `other metals from the platinum-group will generally comprise from about 0.01% to about 3.0% by weight of the total catalyst calculated on an elemental basis, and usually from about 0.1% to about 2.0% by weight.

Whatever the metallic component, it is generally cornposited with a highly refractory inorganic oxide such as alumina, silica, zirconia, magnesia, boria, thoria, titania, strontia, etc., and mixtures of two or more including silica-alumina, alumina boria, silica-alumina zirconia, etc. It is understood that the refractory inorganic oxides hereinabove set forth are intended to 4be illustrative rather than limiting unduly the process of the present invention. It is further understood that these refractory inorganic oxides may be manufactured by any suitable method including separate, succes-sive, or coprecipitation 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 refractory inorganic oxide for utilization in the process of the present invention comprises alumina, either in admixture with any of the a'forementioned refractory oxides, or as the Isole component of the refractory material selected to serve as the carrier for the catalytically active metallic components. In the present specification, the term alumina is employed to mean porous aluminum oxide in all states of oxidation and in all states of hydration, as well as aluminum hydroxide. Whatever type of alumina is employed, it lmay be activated prior to use by one or more treatments including drying, calcining, steaming, etc. It may be in a form known as activated alumina, activated alumina of commerce, porous alumina, alumina gel, etc.

A preferred catalyst for use in the reforming zone of the process of the present invention also contains cornbined halogen. This combined halogen may either be fluorine, chlorine, iodine, -bromine or mixtures thereof. Of these, fiuorine and chlorine are preferred because of their superior compositing characteristics and their ready availability. The halogen may be added to the calcined carrier material in any suitable manner, and either before, during, or after the addition of the catalytically active metallic component. For example, the halogen may be added as an aqueous solution of an acid, such as hydrogen fluoride, hydrogen chloride, hydrogen bromide, etc. At least a portion of the halogen 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 any event, the halogen will be composited in such a manner as to result in a final composite that contains about 0.1% to about 1.5%, and preferably about 0.4% to about 0.9% by weight of halogen calculated on an elemental basis.

The platinum group component may be incorporated in the catalytic composite in any suitable manner; for example, by impregnation or by coprecipitation with an appropriate platinum group compo-und, such as chloroplatinic acid, platinum cyanide, platinum hydroxide, platinum sulfate, palladium sulfide, palladium chloride, etc. Platinum is the preferred component; and it is generally added to the carrier material by commingling the latter with an aqueous solution of chloroplatinic acid. Following the impregnation technique the composite materials are dried and usually subjected to high temperature calcination, or oxidation procedures. Similarly, additional treatment such as reduction and/or sulfiding may be performed on the resultant composite if desired.

It is understood that the catalytic composite for utilization in the reforming zone of the process of the present invention, and may be manufactured in any suitable manner and that the precise method ofmanufacture is not considered to be a limiting feature of the present invention. Likewise, it is understood that the catalyst may be present any desired shape such as: spheres, pills, pellets, extrudates, powders, etc. Additional details on suitable catalysts for the process of the present invention are given in U.S. Patent No. 2,479,109 issued to Vladimir Haensel and U.S. Patent No. 3,296,119 issued to Edward J. Bicek.

While a catalyst of the above type comprising a cornposite of platinum, alumina, and combined halogen may be employed in the isomerization zone of the present invention, it is generally preferred to modify the composition of the catalyst in order to more readily effect acceleration of the isomerization reaction. 'i`his modification generally involves an increase in the acid-acting function of the catalyst. This, in turn, preferably involves increasing the amount of combined halogen to levels as high as about 8.0% by weight calculated as an element. Both uorine and chlorine may be used to supply the additional combined halogen, although the preferred halogen is chlorine in an amount of about 2.5% to about 5.0% by weight calculated as the element thereof. A particularly preferred catalyst lfor the isomerizatiori zone of the present invention may also be prepared by reacting the composites as hereinabove described with a metallic halide of the Friedel-Crafts type. For example, an excellent low temperature isomerization catalyst may be prepared by impregnating aluminum chloride on the hereinbefore described composite of platinum, alumina, and combined halogen. The isomerization step of the present invention may be effected in the presence of other isomerization catalysts but not necessarily with equivalent results. S'uch other isomerization catalysts include anhydrous aluminum chloride, aluminum bromide, aluminum chloride sludge, aluminum bromide sludge, boron trifluoride, ferrie chloride, etc. The preferred catalyst for use in the isomerization zone of the present invention comprises a calcined and reduced composite of alumina containing about 0.01% to about 2.0% by weight of platinum and being impregnated with about 10% to about 100% by weight of anhydrous aluminum chloride. Details as to the method of preparation for this preferred isomerization catalyst are given in U.S. Patent No. 2,999,074 issued to Herman S. Bloch.

The present invention is further described by reference to the accompanying diagram which illustrates a 110W diagram of a typical embodiment of the process of the present invention. In the drawing, numerous valves, coritrols, condensors, pumps, heaters, compressors, pressure control valves, etc., are eliminated as not being relevant to a complete understanding of the present invention. Moreover, for the sake of simplicity, the drawing is discussed With reference to a particular charge stock, reforming catalyst, isomerization catalyst, sulfur additive, etc., for the reason that permissible variations in the scope of these elements of the present invention have already been discussed.

Referring to the accompanying drawing, a naphtha fraction rich in relatively straight chain paraflins and containing about 12-00 wt. p.p.m. sulfur, as tertiary butyl mercaptan, is charged to the process of the present invention through line 1. A hydrogen-rich gaseous stream (the source of which is hereinafter explained) enters line 1, and is admixed with the naphtha fraction. The resulting mixture contains about 2 to about 20 moles of hydrogen per mole of hydrocarbon charge stock, and preferably about 6 to about 12 moles per mole. The mixture then passes through a heating zone (not shown in the accompanying drawing) wherein its temperature is raised to the desired reforming conversion temperature of about 850 F. to about 1050 F. The heated mixture then is passed into reforming zone 3. Although the reforming zone 3 is illustrated in the attached drawing as being a single zone, it may comprise one or more zones with suitable reheatng facilities in between, as is well-known to those skilled in the art.

Reforming zone 3 contains a solid bed of reforming catalysts of the type previously characterized herein-that is, preferably a composite of alumina, platinum and combined halogen. This reforming catalyst is preferably present in the reforming zone in the form of IAG diameter spheres, although any other similar shape may be utilized if desired. In accordance with the present invention reforming zone 3 is operated at a pressure of about 50 to 250 p.s.i.g., and preferably about 75 to about 200 p.s.i.g. In addition, a liquid hourly space velocity (LHSV) of about 0.1 to about 5.0 utilized in reforming zone 3, with a value in the range of about 0.5 to about 2.0 being preferred. The function of reforming Zone 3 is to increase the aromatic concentration in the naphtha charged thereto. According to the present invention, reforming zone 3 is operated at conditions selected from the Ipreviously mentioned ranges such that a reformate having an F-l clear octane number of about is continuously produced. In view of the fact that the exact conditions necessary to make 100 F31 clear octane reformate are a function of the characteristics of the charge stock of the particular catalyst used, etc., the exact selection for each individual case is typically made under the basis of engineering, judgement and experience well-known to those skilled in the art.

Regardless of the exact conditions employed in reforming zone 3, a hot elnent leaves this zone via line 4 and passes through a condensing zone (not shown in the attached drawing) wherein it is cooled to a temperature sucient to condense substantially all of the components thereof except normally gaseous components such as hydrogen, methane, ethane, and propane. Typically, this involves a cooling to a temperature of about 100 F. The resultant cooled eluent passes into separation zone 5 wherein the light, normally gaseous components (Le. primarily hydrogen) are separated from the condensed components of the reforming zone effluent. The light hydrogen-rich gaseous phase thus collects above the liquid reformate phase in separating zone 5 is withdrawn through line 20, and one portion of it passes via line 20 into line 2 where it is preferably recycled to reforming zone 3 through compressive means not shown. Another portion of this hydrogen-rich gas passes through line 20 into line 18 and then into line 17 to isomerization zone 16.

The liquid reformate phase that accumulates in the lower portion of separating zone 5 is withdrawn through line 6 and charged to fractionation system 7. The function of fractionation system 7 is to perform a separation of this liquid reformate phase efiiuent into a C1 to C4 fraction, a C5 to C6 fraction, a C7 fraction, and a CB-lfraction. As is well-known to those skilled in the art a separation along these lines typically requires a multi-column fractionation system, the exact details of which need not concern us here. For example, a three column system which I have found gives excellent results, involves charging the liquid reformate phase from zone 5 to a rst fractionation column wherein C4 and lighter components are removed overhead. The bottoms from this lirst column are then charged to a second fractionation column whereln a C5 to C7 fraction is taken overhead and a Cg-ifraction which is substantially rich in aromatic compounds is recovered as bottoms. The cut-point employed to effect this separation in the second fractionating column is generally in the range of about F. to about 225 F., depending somewhat on the exact composition of the charge stock. A third fractionating column can then be employed to effect a separation of the overhead from the second column into a C5 and Ca fraction and a C, fraction. Irrespective of the exact procedure that is employed to effect this desired separation, my invention involves recognition of the fact that CB-ffraction that is recovered will be substantially rich in aromatics-for example, a volume percent of aromatics in this stream of 95% or more is not unusual.

Returning now to the drawing, it can be seen that from fractionation system 7, a C, cut leaves the process via line 9 for use elsewhere in the refinery-typically as a low grade -blending stock, etc. Additionally, a C1 to C4 gaseous mixture leaves the process via line for typically, a gas recovery system. Also, a Ca-ifraction leaves fractionation system via line 8, and is charged to blending zone 11, and the last stream from fractionating system 7 is a C5 and C6 stream which is passed via line 17 to a point wherein a hydrogen-rich gaseous mixture from separating zone 5, via line 20 and line 18, is admixed therewith in an amount sufcient to result in a mixture having about 0.25 to about 10.0 moles of hydrogen per mole of hydrocarbon. The resulting mixture is charged to a heater (not shown in the accompanying drawing) wherein its temperature is raised to the desired isomerization conversion level of about 200 F. to about 800 F. before the mixture is passed into isomerization zone 16.

Zone 16 preferably contains a fixed bed of 1A; inch spheres of an isomerization catalyst containing about 0.4% by weight of platinum and about 4.7% by weight chlorine, composited with alumina. It is prepared according to the procedure given in U.S. Patent No. 2,999,074. This catalyst may be activated if desired by the utilization therewith of a hydrogen halide-typically, a hydrogen chloride or hydrogen bromide.

The mixture of hydrogen and C5 to C5 hydrocarbons is contacted with this catalyst at a pressure of about 100 to about 2000 p.s.i.g., and a liquid hourly space velocity (calculated on the basis of the liquid volume of the C5 to C5 stream charged to the zone per hour divided by the volume of the zone containing catalyst) of about 0.1

' to about 10.0. Excellent results are obtained at 300 p.s.i.g.

with a LHSV of about 1.0 and a temperature of about 400 F.

Regardless of the exact conditions utilized in isomerization zone 16, the total efiiuent therefrom is passed via line through cooling means (not illustrated in the attached drawing) into separating zone 14 wherein a gaseous phase rich in hydrogen is removed via line 2 and recycled to reforming zone 3 via compressing means not shown. In addition, excess hydrogen is vented from the system under positive pressure control via line 21. The liquid isomerized product phase that collects in the bottorn portion of separating zone 14 is withdrawn therefrom via line 13 and passed to blending zone 11. In blending zone 11 the isoparafiins from the isomerization zone are admixed with the aromatic-rich C-tfraction to produce a preferred high octane motor fuel having an F-l clear octane number of about 104.

It is to be noted that in some cases (e.g, where the charge stock contains undesired amounts of water) it may be necessary to pass the hydrogen-rich gas being recycled via line 2 to reforming zone 3 over an adsorbent material selective for water in order to maintain a substantially water-free condition in reforming zone 3. Suitable mechanisms for accomplishing this are: passing the recycle gas over high surface area sodium, aluminosilicates, alumina, silica gel, etc.; solvent extraction of the recycle gas with organic solvents such as diethylene glycol or diethanol amine, etc. It is to be noted also that in some cases the hydrogen sulfide and water present in the hydrogen-rich recycle gas are both removed therefrom in order to facilitate control of the amount of sulfur entering reforming zone 3 as was pointed out hereinbefore.

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

EXAMPLE A laboratory scale hydrocarbon conversion system is constructed according to the flow scheme given in the attached drawing. Into reforming zone 3, cc. of a reforming catalyst consisting of 1A; inch in diameter spheres is loaded and supported therein as a fixed bed, This reforming catalyst is prepared essentially by the method delineated in U.S. Patent No. 3,296,119 such that it contain's, on an elemental basis, 0.75% by weight platinum, 0.87% by weight chlorine, 0.15% by weight of sulfur, all composited with alumina.

Likewise, 100 cc. of an isomerization catalyst consisting by ls inch in diameter spheres is loaded into isomerization zone 16 and supported therein as a fixed bed. This catalyst is prepared according to the procedure given in U.S. Patent No. 2,999,074 in such a manner as to result in a final catalytic composite having, on an elemental basis, 0.4% by weight platinum, and 4.7% chlorine, both of which are composited with alumina.

The vcharge stock utilized herein is a heavy Kuwait naphtha having an API gravity of 60.4 at 60 F., an initial boiling point of 184 F., an end boiling point of 360 F., and an F-l by volume of aromatics, 71% by volume of paraf'ins, 21% by volume of naphthenes. To this feed 1200 weight p.p.m. of sulfur is added in the form of tertiary butyl mercaptan. In addition, an adsorption zone is added to recycle hydrogen line 2 for the purpose of removing H2S and H2O from the recycle hydrogen thereby facilitating the exclusion of H2O from reforming zone 3 and the positive control of the sulfur entering this zone. This adsorption zone contains an adsorbent consisting of high surface area sodium. Moreover, the water level in the charge stock is maintained at a value less than 5 p.p.m. thereby further facilitating the exclusion of water from reforming zone 3.

The charge stock is admixed with hydrogen in a mole ratio of about 10 moles of hydrogen per mole of hydrocarbon, and the resulting mixtures heated to conversion temperature by standard heating means not shown in the attached drawing. The heated mixture is then charged to reforming zone 3 wherein it contacts the reforming catalyst in a radial flow pattern. Reforming zone 3 is operated at a pressure of 100 p.s.i.g., and the charge stock is passed thereto at a rate resulting in a LHSV of 0.75. Throughout the run, the only operating parameter that is varied is reaction temperature, and it is continuously adjusted lby regulating the heat fiux into the mixture prior to its passage into the zone in such a fashion to continuously result in a reformate having an F-l clear octane number of 100.

The total eluent from reforming zone 3 is withdrawn and passed through cooling means to separating zone 5 maintained at 100 F. wherein a hydrogen-rich gaseous phase separates from a liquid reformate phase. A hydrogen-rich gas is withdrawn from separating zone 5 through line 20, and a portion of it is passed through lines 18 to isomerization zone 16; another portion is recycled via line 2, containing a high surface area sodium adsorbent, through compressing means (not illustrated) to reforming zone 3. The liquid reformate phase from zone 5 is withdrawn and passed to fractionation system 7.

In this case, fractionation system 7 consists of three columns connected in series flow. The feed to the first column is the liquid reformate from separating zone 5, and this column is operated as a stabilizer with a C1 to C4 fraction taken overhead and a C54- fraction recovered as bottoms. Because of the previously explained high yield characteristics of the sulfur-modified, low pressure re forming process, this C54- bottoms comprises about 78.3% by volume of the input naphtha. This bottoms fraction is then charged to a second column where it is separated into two fractions at a cut point of about F. An overhead fraction comprising essentially C5 to C7 hydrocarbons is recovered from this second column and passed to a third column wherein a C5 to C5 fraction is recovered as overhead with a C7 fraction as bottoms. The bottoms from this second column is approximately a C8+ fraction comprising about 51% by volume of the input naphtha, and, quite significantly, contains 97.9%

by volume of aromatics. Moreover, it has an F-l clear octane number of about 107.

The overhead from the third column comprises about 12% by volume of the input naphtha stream and has an F-l clear octane number of about 75. According to the present invention, it is then passed to isomerization zone 16 via line 17. A portion of the hydrogen-rich gas is withdrawn from separating zone and admixed with the C5 to C5 fraction in a mole ratio of about 2.0 moles of hydrogen per mole of hydrocarbon, and the resulting mixture heated, via heating means (not shown in the attached drawing), to a temperature of about 380 F. prior to passing into isomerization zone 16. The C5 to C5 fraction is charged at a rate corresponding to a LHSV of 1.0, and a pressure of about 300 p.s.i.g. is maintained in isomerization zone 16.

The total euent from isomerization zone 16 is then passed through cooling means to separating zone 14 maintained at a temperature of about 100 F. and a pressure of about 300 p.s.i.g. In this zone a hydrogen-rich gaseous phase separates from a liquid phase enriched in isomerized hydrocarbons. The gaseous phase is Withdrawn via line 2 and passed through suitable pressure control valves (not shown) back to the reforming zone. The liquid phase from separating Zone 14 is Withdrawn via line 13, and found to have an F-l clear octane number of about 92.

The resulting isomerized C5 to C6 fraction flows via line 13 to blending zone 11 where it is blended with the aromatic-rich C-ifraction from fractionation system 7 to form a gasoline motor fuel having an F-l clear octane number of about 104. This gasoline product can be admixed with a minor amount of C4 hydrocarbons (for front end volatility), and used as a premium grade motor fuel having high anti-knock properties and the capability to avoid the carbon deposit problem that is characteristic of aromatic-rich fuel. Alternatively, the gasoline product can be used as a high quality blending stock. In either case, the high octane gasoline is recovered at a yield level of about 62% by the volume of the input naphtha stream.

I claim as my invention:

1. A process for producing a gasoline fraction having an F-l clear octane number of about 104 from a low octane gasoline fraction, said process comprising the steps of:

(a) contacting, in a substantially Water-free reforming zone, the low octane gasoline fraction and hydrogen With a platinum metal-containing reforming catalyst in the presence of sulfur entering the reforming zone in an amount of about 10 p.p.m. to about 3000 p.p.m. based on weight of said low octane gasoline fraction, and at reforming conditions, including a pressure of about 50 p.s.i.g. to about 250 p.s.i.g., effective to produce a reformate having an F-l clear octane number of about and which is essentially free of parans above C7;

(b) separating, in a rst separating zone, the effluent from the reforming zone into a rst hydrogen-rich gaseous phase and a liquid reformate phase;

(c) separating, by fractional distillation, the liquid reformate phase into a C1 to C., fraction, a C5 to C5 fraction, a C7 fraction, and an essentially paraffinfree, aromatics-rich CB-lfraction;

(d) contacting, the C5 to C5 fraction and hydrogenin an isomerization zone, with an isomerization catalyst at isomerization conditions;

(e) separating, in a second separating zone, the effluent from the isomerization zone into a second hydrogenrich gaseous phase and a liquid isomerized product phase; and

(f) blending the liquid isomerized product phase with the C-I- fraction to form a gasoline fraction rich in aromatics and isoparaflins having an F-l clear octane number of about 104.

2. The process of claim 1 further characterized in that the reforming catalyst comprises a platinum metal component, a halogen component, and a refractory inorganic oxide component.

3. The process of claim 1 further characterized in that at least a portion of the first hydrogen-rich gaseous phase is recycled to the reforming zone.

4. The process of claim 1 further characterized in that at least a portion of the rst hydrogen-rich gaseous phase is passed to the isomerization zone.

5. The process of claim 1 further characterized in that at least a portion of the second hydrogen-rich gaseous phase is recycled to the reforming zone.

6. The process of claim 1 further characterized in that the isomerization catalyst comprises a platinum metal component, a metal halide component, and a refractory inorganic oxide component.

References Cited UNITED STATES PATENTS 5/1959 Christensen et al. 208-95 8/1965 Bicek 208-95 U.S. Cl. X.R. 208-95, 138