US3394073A - Catalytic reforming process to obtain naphthalenes - Google Patents

Description

J. C. STRICKLAND Filed Nov. 22, 1956 July 23, 1968 CATALYTIC HEFORMING PROCESS To OBTAIN NAPHTHALENES 3,394,073 Patented July 23, 1968 3,394,073 CATALYTHC REFGRMllNG PROCESS Tt) OBTAIN NAPHTHALENES .lohn C. Strickland, Houston, Tex., assigner' to Texaco Inc., New York, NY., a corporation of Delaware Filed Nov. 22, 1966, Ser. No. 596,323 5 Claims. (Cl. 20S- 65) ABSTRACT 0F THE DSCLUSURE This invention relates to a hydrocarbon conversion process and more particularly to a method of reforming gasoline boiling range hydrocarbons and enriching the aromatic content of kerosene boiling range hydrocarbons. In accordance with the process of the invention, gasoline boiling range hydrocarbons are contacted with a reforming catalyst at reforming conditions in an initial conversion zone, kerosene boiling range hydrocarbons are combined with the efliuent of said initial conversion zone and the resulting adrnixture contacted with a reforming catalyst at reforming conditions in a terminal conversion zone, and reformed gasoline boiling range hydrocarbon product and naphthalene and alkyl naphthalene product are separated from the efliuent of said terminal conversion zone.

Detailed description of the invention The expanding demand for naphthalene has outpaced the supply from usual sources and created a demand for increased production from petroleum sources. In order to produce the maximum amount of naphthalene, it is not only necessary to separate the naphthalene present in petroleum streams per se, but it has been found necessary to prepare naphthalene by the conversion of other hydrocarbons, for example, by the dehydroaromatization of decalin and tetralin and by the hydrodealkylation of alkyl naphthalenes. Catalytic reforming employing catalysts containing platinum group metals is widely used in the petroleum industry as a means of producing aromatics and to improve the anti-knock characteristics of gasoline fractions. In reforming gasoline, cycloparains are dehydrogenated to produce aromatics, straight chain hydrocarbons are isomerized to form more highly branched hydrocarbons and parafnic hydrocarbons are cyclicized to form aromatic compounds. Other reactions including hydrogen transfer and selective cracking contribute to the improved anti-knock characteristics of the reformed product. In conventional catalytic reforming for gasoline production the charge stock usually has an end point less than 400 F., for example, about 380 F., so that the reformate product may be included in gasoline without rerunning to gasoline end point specifications. However, charge stocks having components boiling above about 400 F. and up to about 425 F. end point may be included in the feed for conversion of these components to fractions boiling below about 400 F. for ultimate inclusion in gasoline but in this case it is usually necessary to employ rerunning to remove the resulting high end point tail which is undesirable in gasoline blends.

When catalytically reforming high end point gasoline feed stocks, the distillation bottoms from rerunning the catalytic reformate is rich in naphthalene and alkyl naphthalenes. However, the inclusion of large amount of high end point material in the feed to catalytic reforming is undesirable since the inclusion of such material correspondingly reduces the amount of gasoline produced, which gasoline is the primary product. Additionally, the higher end point material limits the severity which may be applied to the gasoline feed stock Without encountering accelerated deactivation of the catalyst..

In the catalytic reforming of gasoline fractions, a domihating reaction is the dehydrogenation of naphthenes to aromatics. This reaction is highly endothermic. In order to maintain high conversion, it is necessary to maintain the reaction temperature at a level of about 875 to 1000 F. It is customary therefore to divide the catalytic reaction zone into a plurality of individual reactors with reheat of the reaction mixture between reactors. The dehydrogenation reaction proceeds rapidly `and is largely completed in the rst two 0r three reactors. In a typical catalytic reforming system, the catalyst is divided into four reactors. Since most of the dehydrogenation occurs in the early stages, re-heat is required more frequently and the initial reactor vessels are smaller than the nal catalytic reforming reactor vessel. In the linal reactor, the principal reaction is hydrocracking yand hydroisomerization. Typically, about 40 percent of the catalyst in the system is placed in the last reactor.

It has been found that a 430 F. end point fraction of a straight-run kerosene, which is rich in materials which can be converted by dehydroaromatization to naphthalene and alkylnaphthalenes may be included in the feed of a catalytic reforming unit to produce naphthalene and alkylnaphthalenes. Alkylnaphthalenes are readily converted to naphthalene by hydrodealkylation and are frequently referred to as naphthalene precursors. The 430 F. end point fraction separated from kerosene typically has an initial boiling point within the range of about 275 to 375 F., a 50% point within the range of about 360 to 410 F. and `an end point of 420 to 440 F. and contains labout 35 to 85 volume percent of cycloparalns, dicycloparains and aromatics. However, when such a stock is included in the feed to the rst reactor of a catalytic reforming unit for conversion to naphthalene Aand naphthalene precursors, it is necessary to reduce the amount of gasoline charged to maintain the same elfective space velocity needed to maintain the quality of the reformed gasoline. Such operation results in an undesirable reduction in the production of reformed gasoline. I have found that this disadvantage may be avoided and an unexpectedly high yield of naphthalene and naphthalene precursors can be produced by introducing a 430 F. end point kerosene fraction into the feed to the last reactor of a series of catalytic reforming reactors. In this way the last reactor effects dehydrogenation of the naphthalene precursors of the kerosene cut Without interfering or diminishing the hydrocracking of the gasoline being treated therein. At the Isame time, a higher yield of naphthalene precursors is obtained than is obtained by inclusion of the same amount of high boiling material in the feed to the primary reaction zone.

In accordance with the process of this invention a gasoline boiling range hydrocarbon is contracted with a reforming catalyst comprising a platinum group metal on alumina. containing combined halogen in an initial reformassauts ing zone at a space velocity within the range of about l to 7 volumes of charge per hour per volume of catalyst. Reforming temperatures within the range of about 875 to 1000 F. and pressures within the range of about 200 to 800 pounds per square inch gauge are employed. Hydrogen is supplied to the reaction zone as recycle gas at a rate within the range of about 4 to 15 mols of hydrogen to each mol of hydrocarbon charged. Although the initial conversion zone may be a single reactor, it is usually made up of two or three reactors with associated preheater and reheaters in which case the reforming conditions stated apply to the reactors taken as a group. The partially reformed gasoline is then passed in admixture with a 430 F. end point kerosene fraction to a terminal reaction zone which again may be one or more reactors, but usually comprises a single reactor. The reforming conditions ernployed in the terminal reaction zone include a space velocity within the range of about 3 to 35, a temperature within the range of about 875 to 1000 F., a pressure within the range of about 200 to 800 pounds per square inch gauge and a hydrogen to hydrocarbon mol ratio of about 2 to 15. The amount of 430 F. kerosene fraction injected into the terminal reaction Zone is usually within the range of about 10 to 100 volume percent of the gasoline feed to the initial conversion zone. Conveniently, the amount of 430 F. end point kerosene employed is the normal ratio of production of the kerosene fraction to straight run gasoline feed which typically may be about 55% of the straight run gasoline feed.

The invention will be further described in conjunction with the following drawing, tests and examples. Although the drawing illustrates one form of apparatus in which the invention may be practiced, it is not intended to limit the invention to the particular apparatus or materials described. The drawing is a schematic liow diagram and for clarity omits auxiliary equipment such as pumps, compression controls, heat exchange means which are well known and form no part of the present invention.

Referring to the figure, catalytic reforming feed in line 1, typically having an initial boiling point of about 200 to 240 F. and an end point within the range of about 380 to 400 F. and recycle hydrogen from line 4 comprising about 80 to 95 percent hydrogen are admixed and passed through coil 2 in heater 3. In heating coil 2, the gasolinehydrogen mixture is heated to a temperature of about 950 F. and passed through line 6 to reactor 7. Reactor 7 contains a bed of solid reforming catalyst such as the well-known Platforming catalyst. As the reactants pass through reactor 7, the endothermic heat of reaction causes the temperature to drop so that the effluent is discharged at a temperature of about 840 F. Effluent in line 8 is passed through coil 9 in heater 10 to reheat the hydrocarbon-hydrogen mixture to a temperature of about 945 F. The reheated mixture from coil 9 is passed through line 12 to reactor 13. Again, the heat of reaction causes the temperature to drop so that the efiiuent of reactor 13 is discharged through line 14'- at a temperature of about 900 F. The hydrogen-hydrocarbon mixture is then passed through heating coil 15 in heater 17 where the temperature is raised to about 940 F. The heated mixture at a temperature of 940 F. is passed through line 18 to reactor 20. Again, the heat of reaction causes a temperature drop to about 930 F. Effluent from reactor 20 at 930 F. in line 21 is combined with a 430 F. end point cut of kerosene from line 22 and the mixture passed to heating coil 23 in heater 24. In heater 24, the reactants are heated to a temperature of about 940 F. and passed through line ZS to the terminal reactor 26. ln the terminal reactor 26 hydrocracking of the gasoline is effected and, at the same time, dehydroaromatization of the high boiling bicyclonaphthenes proceeds to form naphthalene and naphthalene precursors. The efliuent from reactor 26 is discharged through line 27, cooler 28 and line 29 to separator 30. Vapor and liquid phases separate in separator 30 and recycle gas is withdrawn and passed through line 4 to the feed line 1. Separated liquid is withdrawn through line 31 and passed to stabilizer 32. In stabilizer 32, low boiling hydrocarbons such as butanes and lighter are stripped from the liquid product and discharged through line 34. Stabilized liquid is withdrawn through line 33 and passed to rerun tower 35 where the liquid product is separated into reformed gasoline which is removed as distillate through line 36 and distillation bottoms comprising naphthalene and naphthalene precursors which are withdrawn through line 37.

EXAMPLE The effectiveness of the method of this invention of introducing a 430 F. end point kerosene cut into the terminal zone of a multi-reactor catalytic reforming system is shown in the following comparison with conventional catalytic reforming of straight run gasoline, and catalytic reforming of straight run gasoline with introduction of a 430 F. end point cut of gasoline into the initial zone of the same catalytic reforming system. In the tests, a conventional catalytic platinum-alumina-combined halogen reforming catalyst identified as UOP R-S catalyst is used in a four-reactor system. Each of the first three reactors contains 20 percent of the total catalyst and the terminal reactor contains 40 percent of the total catalyst. Feed stocks having the following tests are employed:

Four tests are made at; the conditions given below and with the results shown in Table I.

Test A shows the small amount of naphthalene and naphthalene precursor produced in conventional catalytic reforming operation employing a straight run gasoline feed. In comparison, Test B shows the amount of naphthalene and naphthalene precursor produced when operating with the same total amount of a mixed feed stock comprising 64.0 percent straight run gasoline and 36 percent of a 430 F. end point fraction of kerosene. Under these conditions, the space velocity and hydrogen to hydrocarbon mol ratio are maintained the same in Test B as in Test A whereby the gasoline component of the feed is subjected to the same severity. It will be recognized that although this method of operation substantially increases the yield of naphthalene and naphthalene precursors, it substantially reduces the amount of gasoline charged and hence the amount of catalytic reformate produced. Test C shows the effect of increasing the total feed rate of a mixed gasoline-kerosene feed to the extent that the feed contains the same amount of gasoline as employed in Test A. This increased throughput results in a higher space velocity and, accordingly, less severe gasoline reforming conditions, but produces an increased yield of naphthalene and naphthalene precursors. Test D illustrates the present invention wherein gasoline is charged t0 the initial reforming zone comprising three reactors at substantially the same rate as employed in Test A, a 430 F. EP kerosene cut is introduced with the effluent of the third reactor, and the mixture passed as feed to the fourth reactor. The yield of 40.55 cc. per hour 0f naphthalene and naphthalene precursors is higher in Test D than in any of the other tests and, surprisingly, is substantially higher than in Test C wherein the same amount of feed is employed but with all feed passed to the first reactor.

TABLE I Test A Test B All feed to first reaetor All iced to first reactor. Feed 680 cc.lhr. of SR gasoline 432 cc./hr. of SR gasoline plus 248 ce./hr. of 430 F. EP kerosene cut.

Conditions:

Reactor Temperature:

No, 1 970 97() N0. 2-- 970 970 No. 3- 970 970 No. 4.. 070 970 Pressure, p.s i.g 50u 500 H drogen Recycle Rate, Moles H2 per mol iced:

Basis 4 reactors 3 8.3 8. 3 Basis reactors 1-3 3 8. 3 8. 3 Basis reactor 4 4.. 8. 3 8. 3 Space Velocity, v./lir./v

Basis 4 reactors 1 3. 0 3. 0 Basis reactors 1-3 1 5i 0 5. 0 Basis reactor 4 2 7. 5 7. 5 NapthaleneNapthalene Precursor' Yield, cc./hr. 8. 9 23. 5

Test C Test D Flow All feed to first reactor Gasoline to first reactor,

430 F. El? kerosene added to feed to fourth reactor. Feed 675 cc./hr. of SR gasoline 675 ce./hr. of SR gasoline to plus 375 cc./hr. of 430 F.

EP kerosene cut.

first reactor, plus 375 cc.ll1r. of 430 I". El kerosehe cut to fourth reactor.

Conditions:

Reactor Temperature:

No. 1 97o No. 2 97o No. 3 97o No. 4-- 97o Pressure, p. 500 Hydrogen Recycle Basis 4 reactors L. 5 7

Basis reactors 1-3 3, Basis reactor 4 4. Space Velocity, v/hr./v.

Basis 4 reactors 1..... Basis reactors 1-3 1 Basis reactor 4 2 Napllithalene-Naphthalene Precursor Yield,

ce. hr

1 Calculated on the basis ofthe volume of liquid feed charged to the first reactor. 2 Calculated on the basis oi the volume of liquid feed charged to the first reactor plus, in Test D, the volume of additional liquie charged to the fourth reactor.

3 Calculated on the basis oi the mols of liquid charged to the first reactor.

4 Calculated on the basis of the mois of liquid charged to the first reactor plus the number of mois of additional liquid charged to the fourth reactor.

I claim:

1. In a process Iwherein a gasoline boiling range hydro carbon is contacted with a platinum group metal reforming catalyst at reforming conditions in a plurality of reforming zones in series, the method of concomitantly preparing a naphthalene precursor feed stock which comprises introducing a straight run kerosene fraction having an initial boiling point within the range of about 275 to 375 F., a 50% point within the range of about 360 to 410 F. and an end point of 420 to 440 F. and containing about to 85 volume percent of cycloparaflins, dicycloparains and aromatics intermediate to at least two of said plurality of reforming zones and separating reformed gasoline and naphthalene precusor feed stock from the effluent of the ylast of said plurality of reforming zones.

2. The method of reforming gasoline boiling range hydrocarbons and enriching the aromatic content of a straight run kerosene fraction vhaving an initial boiling point within the range of about 275 to 375 F., a 50% point within the range of about 360 to 410 F. and an end lpoint of 420 to 440 F. and containing about 35 to 85 volume percent of cycloparaffns, dicycloparaflins and aromatics which comprises,

passing said gasoline boiling range hydrocarbons to the first of atleast two separate catalytic reforming zones in series flow in contact with a platinum group metal reforming catalyst under catalytic reforming conditions,

passing said straight run kerosene fraction to one of said catalytic reforming zones subsequent to the catalytic reforming zone to which said gasoline boiling range hydrocarbons are passed whereby partially reformed gasoline and said kerosene fraction are subjected to catalytic reforming conditions in said subsequent reforming zone,

withdrawing effluent .from said subsequent reforming zone and separating therefrom a gasoline fraction and a fraction comprising naphthalene and alkyl na-phthalenes.

3. A method of reforming gasoline boiling range hydrocarbons and concomitantly forming a hydrocarbon stock rich in naphthalene and alkyl naphthalenes which comprises contacting said gasoline boiling range hydrocarbons and hydrogen with a platinum group metal reforming catalyst at reforming conditions in an initial conversion zone,

withdrawing effluent from said initial conversion zone,

admixing a straight run kerosene fraction having an initial boiling point within the range of about 275 to 375 F., a 50% point within the range of about 360 to 410 F. and an end point of 420 to 440 F. and containing about 35 to 85 volume percent of cycloparaiiins, dicycloparaiiins and aromatics with said eiuent from said initial conversion zone and contacting the resulting `mixture with a reforming catalyst at reforming conditions in a terminal conversion zone,

withdrawing effluent from said terminal conversion zone and separating therefrom a first product fraction comprising reformed gasoline boiling range hydrocarbons and a second product fraction comprising nephthalene and alkyl naphthalenes.

4. The method of claim 3 wherein said gasoline boiling range hydrocarbons are contacted with a catalyst comprising a platinum group metal reforming catalyst at a space velocity within the range of about 1 to 7 volumes of charge per hour per volume of catalyst, a temperature within the lrange of about 875 to 10UO F., a pressure Within the range of about 200 to 800 pounds per square inch gauge, and a hydrogen recycle rate within the range of about 4 to 15 mols of hydrogen per mol of hydrocarbon charged to said initial conversion zone and said partially reformed gasoline boiling range hydrocarbons and said kerosene boiling range hydrocarbons are contacted with a platinum group metal reforming catalyst at a space velocity within the range of about 3 to 35, a temperature within the range of about 875 to 1000 F., a pressure within the range of about 200 to 800 pounds per square inch gauge, and a hydrogen recycle rate within the range of about 2 to 15 mols hydrogen per mol of hydrocarbons.

References Cited UNITED STATES PATENTS 7/1957 Hengstebeck 20s-65 11/1960 Friedman 26o66s DELBERT E. GANTZ, Primary Examiner.

A. RIMENS, Assistant Examiner.

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