US2902427A - Hydroforming process - Google Patents

Description

Sept. 1, 1959 A. WELTY, JR

HYDROFORMING PROCESS Filed Dec. 28, 1955 Albert B. Wehy, Jr. I lnvetor Byj' Attorney United States Patent 2,902,427 HY DRQFORNDNG PROCESS Albert B. Welty, Jr., Westfield, NJ., assignor to Esso Research and Engineering Company, a corporation of Delaware Application December 28, 1955, Serial No. 555,885 l 7 Claims. (cl. 208;'65)

The present invention relates to improvements in hydroforming. More particularly, the present invention relates to the hydroforming of the naphtha in the presence of platinum in a fixed bed type of operation in which process the total naphtha is fractionated to obtain a low boiling fraction boiling up to 200 F. and a higher boiling fraction boiling above 200 F. and separately treating the said fractions under conditions which give improved results.

Hydroforming is a process in which a naphtha is treated in the presence of a solid catalytic material and hydrogen at `elevated temperatures and pressures with the result that the naphtha is improved in octane quality. The principal reaction during hydroforming is the dehydrogenation of naphthenes present in the feed to the corresponding aromatics. There is also some isomerization of normal paraihns to form isoparaiiins as well as isomerization of alkylated cyclopentanes to cyclohexanes and some hydrocracking of the higher boiling paraflins to lower boiling products. As ordinarily carried out, the process results in the net production of hydrogen but in any event there is no net consumption of hydrogen.

It is now a matter of record and commercial practice in this country to hydroform naphthas in order to produce high quality aviation gasoline and motor fuel. The catalyst employed in hydroforming may be in the form of fixed beds or the caalyst, in powdered form, may be employed utilizing the uidized solid technique. At the present time the catalysts principally in commercial use are platinum `carried on alumina, or molybdenum oxide carried on alumina, the former being used in the form of fixed beds in a multi-stage operation with reheating between stages, while the latter is being employed in the form of a uidized bed.

In hydroforming naphthas the optimum pressure is different for various boiling range naphthas. In general, high boiling naphthas are treated at moderately high pressures for best results. The lower boiling naphthas, on the other hand, and in particular, the naphtha fractions boiling below 200 F. are treated at fairly low pressures for best results.

These phenomena are due to the fact that the high hydrogen partial pressure characteristic of the high pressure operation tends to prevent formation of aromatics from parans and dimethylcyclopentanes, which are the principal constituents of all virgin napthas boiling below 200 F. These naphthas may contain some benzene and cyclohexane, but the quantity present is usually quite small. On the other hand, most naphthas, boiling above 200 F. and say up to 300 or 400 F., are relatively rich in cyclohexane homologues such as methyl cyclohexane, dimethylcyclohexane, etc. All cyclohexane homologues are very readily converted into aromatics by dehydrogenation at normal hydroforming temperatures even at very high pressures, like 400-600 p.s.1.

It is clear from this that higher operating pressure,

ceN

2 which results in higher hydrogen partial pressure, can be used on the high boiling feeds than on the low boiling feeds.

The rate of deactivating coke formation on the catalyst determines the length of time it may be used before regeneration is required and also the catalyst life or the length of time the catalyst may be employed before it is required to replace it and, therefore it is desirable to minimize this coke formation. It is common knowledge that the higher the hydrogen partial pressure, the lower the rate of coke formation will be. Therefore, higher pressure operations are required to produce aromatics in good yields with minimum coke formation and longer catalyst life. The optimum operating pressure for high boiling naphthas such as those boiling above 200 F. will be considerably higher than that for low boiling naphthas such as particularly those boiling below about 200 F;

The object of the present invention, therefore, is to hydroform light naphtha and heavy naphtha separately in the same equipment under optimum conditions for each. The present invention provides means whereby this can be accomplished.

In a hydroforming plant designed for hydroforming at say 400 p.s.i.g., if the pressure were to be reduced to say 200 p.s.i.g. during the treatment of the light naphtha, the recycled gas rate (the standard cubic feet of hydrogen containing gas feed to the reaction zone with each barrel of naphtha feed) would be greatly reduced because of the greater pressure drop through the system.

Since one is desirous of reducing hydrogen partial pressure anyway, this greatly reduced recycle gas rate would not be harmful from the standpoint of the reaction itself. However, from the practical standpoint, this is a very serious problem. The hydroforming reaction is highly endothermic, that is, a large amount of heat is consumed when the reaction occurs. The catalyst is disposed in one or more reactors in series and each reactor runs adiabatically, that is, no heat is put into or taken out of each reactor. Because of the large heat absorption by the reaction, there is a large temperature drop from the reactor inlet to outlet. This is undesirable because as the temperature drops, the rate of reaction decreases, and, in fact, this is the reason why it is necesessary to use more than one reactor in series and to reheat the hydrocarbon between reactors. The magnitude of this temperature drop is Very important in the hydroformer design. If the temperature drop is great, then a large number of reactors and reheat steps are required. This is expensive. If, on the other hand, the temperature drop is very small, only a few reactors with reheat are required.

The temperature drop for `a given amount of reaction depends solely on the heat capacity of the vapors flowing through the bed. The higher the heat capacity, the lower the temperature drop will be. For this reason, it is desirable to recirculate as much recycle gas as practical from the standpoint of pressure drop through the system, compresso-r horsepower required, size of heat exchangers required, etc. With a recycle gas rate, for example, of 6,000 s.c.f./bbl. of feed, the recycle gas actually has more heat-absorbing capacity than the feed itself. In this case, depending somewhat on the nature of the feed stock and severity of reaction, the 6,000 scf/bbl. of recycle gas might have a heat capacity of about 180 B.t.u.s per F. whereas the barrel of feed would have a heat capacity of about B.t.u.s/ F.

Modifying operating conditions, such as by reducing pressure, so that the recycle gas rate is sharply reduced, the .heat absorbing capacity of the vapors passing through the bed will be much reduced and, therefore, the temperature drop will be very much increased for a given amount of reaction. In practice, what would really happen is Vthat the temperature would-get so low that the same amount of reaction could no longerbe effected. ThisV means either that-the octane number and amount of conversion of the feed will be much reduced 'orthat the naphthafeed rate to 'the unit must be reduced.vr

vAsrpointed out previously," however, it is 'desirable to be'able to hydroform bo'th 'heavy and very light feed stocks in the same unit'at conditions approximating Vthe optimum for each. Optimum conditionsfor the relatively low boiling' feed 'require much lower hydrogen partial pressure than for the higher boiling feedstock. However, when the pressure is `reduced in a unit designed'fo'r Ahigh pressure operation on the high boiling feeds, "one can no longer maintain the vrecycle 'gas' rate necessary to provide the necessary heat-carrying capacity for the vapors as they pass through the bed. n

Theoretically, it would be possible to provide additional compressor capacity so as simply to overcome the higher pressure drop caused by the higher velocities when roperating at low pressures. Depending on conditions, this might require from two to five times as much compressor capacity and, furthermore, the pressure drop through the catalyst beds would beveryV high. The high pressure drop through the catalyst beds is undesirable becausethe catalyst is crushed and reduced in size.

The heat carrying capacity ofthe recycle gas depends -on'the gases of which it is composed. On a volumetric basis, hydrogen, which is the principal volumetric component, has a very low -heat capacity, `whereas a hydrocarbon, like butane, for example, Vhas a relatively high -heat capacity. The volumetric heat capacity of fbutane gas is approximately four times as high as that of hydrogen. The reason for this is the greaterweight of butane `per unit volume 'of gas as compared to hydrogen. Recycle gas is a mixture of many gases-its 'principal component is hydrogen but it also contains substantial quantities of saturated hydrocarbons. Generally, it contains, on a volumetric basis, more methane than ethane, more ethane than propane, more propane than butane, etc. Usually, relatively little C6 or C7 hydrocarbons are present. Y

One way to increase the heat carrying capacity of this recycle gas then is to reduce rits hydrogen content and at the same time increase the content of highermolecular weight hydrocarbons, particularly Cs, Cs, Css, etc. Usually, the hydroformed product is cooled toa `temperature of about 100 F. and thereafter the gas and liquid separated. This gas is the product gas and a portion of it is also the recycle gas. The composition of the recycle gas depends upon the quantities of gaseous materials being produced, to some extent on the nature of the liquid product, and very much upon the temperature and pressure of liquid-gas separation. To increase the recycle `gas heat carrying capacity, the product may be cooled not to the conventional 'temperature of about 100 E., but to some higher temperature, say .tofabout 300 F. The following table shows the eifect of separator temperature on the specic gravity of the recycle gas and its heat carrying capacity, lin `a particular case.

l Standard cubic feet.

Thus, by separating at a 300 F. separator temperature instead of 100 F., one Vcan use a recycle gas rate 0.028+0.065=42% as greatv and have the same temperaturedrop through the reactor system for the same total heat of reaction.

Since the main object ofthe present rinvention.is-.to

, `4 reduce the hydrogen partial pressure for light naphtha hydroforming by reducing pressure, this reduced hydrogen concentration in the recycle gas actually helps to attain the optimum condition for this light naphtha operation.

It will thus be seen that by means of varying the separator temperature, it ispossible to vary the hydrogen partial pressure substantially without any change in the total pressure whatsoever. In actual practice, however, it :is preferable not vonlyto .increasefthe separator itemperature `when lower hydrogen partial pressure is desired, but to reduce pressure at the same time. There are two reasons for this. The first is that thermal cracking reaction is encouraged by the use of Vhigher pressures. Since thermal cracking produces Aa greater proportion of gas and does not increase the octane number as much as the catalytic hydroforming reaction, the use of higher pressure results in slightly lower yields. Therefore, the combination of reducing pressure and raising separator temperature when running on light'feed stocks will give higher yields than the operationwhere pressure is not decreased but separator temperature is raised sufficiently to give the same hydrogen` partial pressure. Another practical reason for preferring the combination of decreasing, pressure and raising separator temperature has to do with the recycle gas compressor. Suppose, for example, that vone were operating at a pressure such that the suction pressure on the compressor is 350 p.s.i.g. when .hydroforming higher boiling 'feed stocks and using a'separator temperature of about F. `Now suppose one raises vthe separator temperature without changingthecompressor suction pressure. The lchange in gas composition'increases the horsepower requirement of the'compressor so that the compressor and the kmotor thatdrivesrit have to be capable `of handling this Vgreater energyrequirement. The reason this vhorsepower requirement'increases has todo with the increased density'of the recycle gas which it Ais compressing. While it is quite possible to design the compressor and its driver to handle this higher load, thisfdoes increase their cost very substantially. By reducingv the `suction pressure on the lcompressorby reducing the overall pressure on the system, one can maintain the horsepower requirement ofthe compressor essentially constant even whilel one raises thesseparator temperature to increasev its density.

The manner -of operating, outlined .above, would vresult in important economic advantages over a system in which-merely `the total pressure is decreased during fthe treatment of the low boiling naphtha constituentsbccausethe reheat furnaces 'and thecompressors would be utilized .at al1 times to the full extent vof their Arespective designed capacities. i

In the accompanying `drawing therefis lset forth diagrammatically van apparatus layout :in whicha preferred modification of the: present invention may .be carried into effect.

Referring yin `detail to thesdrawing, naphtha feed l"is introduced Ito the present system .through line '.1. '-'The naphtha is heated in furnace and thence withdrawn in vapor formvia line 4 and ycharged to a'separator or fractional distillation column V5, wherein a yfraction boiling from-Oto 200 P is 'withdrawn overhead throughline 6 and charged to a storage-drum 7, while va fraction boiling vfrom 200 F. 'to `say"400or F. is-withdrawn' as Ibottoms `from column 5, lineS andcharged tov a heavy naphtha storage ldrum 9. As will subsequently appear the hydroforrning of the naphtha is ina .blockedV type-ofV -operation, that yis vto say, the :heavy naphtha land the light naphtha are separately processed. Toward thisend, therefore, While the light naphtha remains Vin storage in 'tank 7 the heavy naphtha is withdrawnfrorn-tank through valvedline 10 and charged toa furnace 111. 'Simultaneyousl-y recycled gas obtained from Ythe'product recovery system, as will subsequently appear, is passed via linez12 into line 1Q and, therefore, heatediin furnace 1'51` withlthe heavy naphtha feed to hydroforming temperatures. This heated mixture is thence Withdrawn from furnace 11 through line 13 and charged to the first reactor 14 of a series of reactors. The mixture of heavy naphtha vapors and hydrogen-containing gas passes through reactor 14 in contact with a bed of catalyst C at conditions of temperature and pressure and residence time as hereinafter more fully specified with the result that the naphtha undergoes at least partial hydroforming. Due to the fact that the reaction is highly endothermic there is subsequently a temperature decrease from the inlet to the outlet of reactor 14 so that product withdrawn via line 15 is reheated in the second furnace 16, withdrawn from said furnace and thence passed via line 17 to a second reactor 18 Where again the naphtha contacts a bed of catalyst C and undergoes further hydroforming. The product is withdrawn from reactor 18 via line 19 and is reheated in a third furnace 20, withdrawn through line 21 and charged to a third reactor 22 also containing a bed of catalyst and wherein the hydroforming reaction is subsequently completed. The product is withdrawn from reactor 22 through line 23, cooled in 24 to a temperature of about 100 F thence withdrawn through line 25 and charged to a separation drum 26. From separation drum 26 recycled gas is recovered overhead via line 27, forced through a compressor 28 and charged via line 12 to line 10, as previously explained. Excess recycled gas may be ejected through line 33. The hydroformed product is withdrawn from separator 26 through line 30, passes through valve 37, line 32 and valve 42 to a conventional stabilizing and rerunning system.

In treating the light naphtha under a pressure substantially lower than that maintained during the treatment of the heavy naphtha, the ow of heavy naphtha from storage drum 9 is discontinued and light naphtha is withdrawn from storage drum 7 via valved line 34. It is mixed with recycled gas obtained via line 12 and line 12a and charged to furnace 11 wherein the mixture is heated to reaction temperatures and this mixture is then passed through the series of reactors in the same manner as that previously described in connection with the processing of the heavy naphtha with the exception that, as previously pointed out viz., that the system is now operated at a substantially lower pressure and the separator drum 26 is operated at a substantially higher ternperature by controlling the degree of cooling in cooler 24 so that the recycled gas recovered overhead from separator 26 via line 27 is at a substantially higher temperature than that at which the recycled gas exists when processing the heavy naphtha. Product gas for recovery leaves separator 26 through line 29, passes through valve 3S and line 39 to cooler 38. Liquid product passes from the bottom of separator 26 through line 30 through valve 36 and line 40 where it combines with the product gas and passes through cooler 38. Here gas and liquid are cooled to conventional temperatures suc'h as 100 F. and then separated again in vessel 31. Gas product leaves through line 33 and pressure control valve 31 and passes to a conventional gas recovery system. Liquid product leaves separator 31 through line 32 and valve 42, which controls the level in separator 31, and passes to a conventional liquid stabilizing and rerunning system.

The operation described above is completely self-contained. However, it is obvious that the desired increase in recycle gas density and decrease in hydrogen concentration can be augmented by the use of heavy gaseous hydrocarbons such as propane, butane, pentane, etc., from an extraneous source. When this is desired, these gases can be introduced to the recycle gas system through line 43 and valve 44. In the latter case the raw product may be cooled to about 100 F. in 24.

In order to more fully explain the present invention, the following specific example is set forth. A naphtha having the following inspection was processed in the manner set forth immediately below with the results shown.

Inspection:

Boiling range (total naphtha), F 152-387 Naphthenes, vol. percent 43 Parans, vol. percent i 49 Aromatics, vol. percent 8 Bromine number 0.2 Sulfur, wt. percent 0.005 Octane number, CFRR 55.7

Conditions in reactor 14 during processing of heavy naphtha:

Catalyst composition- 0.6 wt. percent Pt 0.6 Wt. percent Cl 98.8 wt. percent eta alumina Inlet temperature, F. 948 Pressure, p.s.i.g 420 Residence time, sec. 5.8

Recycle gas feed to reactor, s.c.f./bbl. oil 6000 Density of recycle gas relative to air 0.25 Concentration of H2 in recycled gas, mol

percent In reactor 18 and 22 the catalyst is the same, the pressures are substantially the same (except for the pressure drop involved), the amount of recycled gas in reactor 18 and 22 respectively will be increased somewhat due to the formation of hydrogen and the inlet temperatures of the feed to the reactors 18 and 22 respectively will be substantially the lsame as the inlet temperature to reactor 14.

Condi-tions in reactor 14 during processing of light naphtha:

Catalyst composition- 0.6Awt. percent Pt 0.6 wt. percent Cl 98.8 wt. percent eta alumina Temperature maintained in separator 26, F.

Inlet temperature, "F 965 Pressure, p.s.i.g 256 Residence time, sec. 12.1 Recycle gas feed to reactor, s.c.f./bbl. oil 2280 Density of recycle gas relative to air 0.96 Concentration of H2 in recycle gas 62 Temperature maintained in separator 26,

The light and heavy naphtha hydroformates were combined and inspected IWith the below results.

It will be understood that the foregoing example is illustrative of -the invention but does not impose any limitation thereof. `Good results are obtainable by operating within the following ranges.

Conditions during heavy naphtha hydroforming:

Catalyst-Platinum or palladium suitably supported. Inlet temperature, F. 900-1000 Pressure, p.s.i.g 350-600 Residence time, sec 4 20 vRecycle gas feed to reactor, s.c.f./bb1.

Density of recycle gas relative to air 0.l-().4 `Concentration f.H2-1'-nr.ecycled gas 70-95 Temperature ,maintained :in `separator i26,

Conditions duringligh-t naphtha hydroforming: YCatalyst-Plati'num or palladium suitably supported.

Inlet temperature, `F. 900-1000 Illressure, p-.s.i.g 50-300 Residence time, sec. 8-25 Recycle gas feed to reactor, .sl.c.f./bbl.

oil `150G-3000 Density of recycle gas relative .to air 0.401.0 Concentration of H2 in recycle ,gas 55-75 Temperature maintained in separator 26,

`In ordento recapitulatebrieily, the present invention contemplates hydroforming anaphtha in the presence of a platinum Vgroupmetal catalyst disposed in a plurality of reactors in which the naphtha is hydroformed by passage through the said reactorsin series vunder hydroforming conditions of temperature, pressure and contact time. -T he Ainvention is primarily characterized in that the Anaphtha is separated into a ylight boiling fraction and a high boiling fraction and the separated fractions are separately hy'droformed. 'The light naphtha is hydroformed under substantially -lower pressure than the heavy naphtha but in order to make full use of the heating and compres- `sor capacity the recycled gas fed to the reaction zone with the low boiling or light naphtha contains a higher percentage of hydrocarbons than does the recycled gas employed in the heavy naphtha. It is thus necessary to so operate the hydroforming of the .light naphtha that the recycled gas will contain at least 50% of the heat necessary to support the endothermic reaction of hydroforming. Thus additional .hydrocarbons over and above that normally obtained from the product separation drum lfor recycling is attained by operating the said separation drum at a higher temperature than .normally employed and also adding gaseous hydrocarbons leither from eX- traneous sources of from the finishing ofthe raw hydroformate itself.

Numerous modifications of the invention will be apparent to those who are familiar Iwith this artlwithout departing from the spirit thereof.

What is claimed is:

1. In an adiabatic blocked naphtha hydroforming proces-s carried out in the presence of a platinum group metal catalyst and added hydrogen under -hydroforming conditions of temperature, ,pressure and residence time in a system, the improvement which comprises separating the .feed naphtha into va fraction boiling below 200 F. and a second fraction boiling above about 200 F. alternately .treating the separated fractions in the same system under hydroforming conditions, characterized in that (l) the Ilower boiling fraction is treated under a relatively low hydrogen partial pressure, (2) under a Vlower total pressure land alower recycle -gas rate than said higher boiling fraction, and (3) in which the hydrogen-containing recycle, gas fed toV the .reaction zone during the hydroforming of the said lower boiling fraction possesses a heat capacity substantially greater than the said hydrogen-containing gas fed to the system during the hydroforming of said higher boiling fraction due to the inclusioin, in said hydrogen-containing recycle gas fed to the system during hydroforming of the lower boiling fraction of. a higher volumetric percentage of hydrocarbons than contained in the hydrogen-containing recycle gas fed to the hydroforming zone during lthe hydroforming of the said higher boiling naphtha caused by separating the said hydrogen-containing recycle gas from the product obtained by hydroforming the said lower boiling fraction ata temperature of from about '200 to 325 F., whereby increased quantities of aromatics are formed from paratlins-present 1in the said low boiling naphtha feed, furthercharacterized in that the energy requirements for circulating the said hydrogen-containing recycle :gas to the lhydroformingtreatment of the lower boilingfractionY is substantially the same as the energy requirements for circulating recycled gasto the hydroforming treatment of the higher lboiling fraction.

2. .The method set forth in claim 1 in which extraneous hydrocarbonsxare admixed with the hydrogen-containing lgas fed to the hydroforming .zone'during the hydroforming of said low boiling naphthas to reduce the hydrogen partial pressure `of the said hydrogen-containing gas and at the same time to increase the heat capacity of said hydrogenfcontaining gas.

3.V Animproved process for hydroforming a naphtha containing .both high and low boiling naphtha fractions in a'system comprising a plurality of reactors, each containing a platinum group metal catalyst characterized in that the naphtha is passed in series, together with a hydrogen-containing recycle gas, through the several reactors in contact with the said catalyst, the improvement resulting in .producing a hydroformed product Vof improved octane rating in increased yield due at least in part to an increased yield of aroma-tics formed from parafnic hydrocarbons in the said low boiling fractions which comprises separating the naphtha into a 10W boiling fraction and a ln'gh boiling fraction, separately hydroforming .the said .fractions in the said system at elevated temperatures and under -elevated pressures, the said fraction containing the low boiling naphtha fractions being hydroformed under a hydrogen partial pressure lower than that existing Aduring the hydroforming of the high boiling naphtha fractions, further characterized in that the rate at which the `hydro,gen-containing .gas is fed to the system during the low boiling naphtha treatment is substantially `less/than when the high boiling fractions are undergoing treatment, recovering raiw products from .the respective treatments, cooling the raw products to condense normally liquid constituents, recovering a hydrogen-containing gas from both treatments for recycle to the process and causing an increase in the heat carrying capacity of the hydrogen-containing recycled gas for use during the treatment of the low boiling hydrocarbon fractions by separating the said hydrogen-containing gas from tihe low boiling hydroformed liquid product at a temperature of from about 200-300 F., further characterized in that the energy requirements for circulating the said hydrogen-containing recycle gas to the hydroforming treatment of the lower boiling fraction is substantially the same as the energy requirements for circulating recycled gas to the hydroforming treatment of the higher boiling fraction.

4. The lmethod set foith in claim 1 in which the energy requirements for recycling `the hydrogen-containing gas is maintained substantially constant for both treatments by hydrofonning the light hydrocarbon fractions under a total pressure substantially lower than that existing in the reaction zones during the hydroforming of the higher boiling naphtha fractions.

5. The method set forth in claim 3 in which the hydroforming is carried out in the presence of a catalyst containing platinum.

6. The method set forth in claim 3 in which the said low boiling naphthas comprise a fraction boiling in the range of from about 0`200 F.

7. The method set forth in claim 4 in which the pressure maintained during the hydroforming of the lower boiling hydrocarbon fractions is from about 50 to 300

Claims (1)

1. IN AN ADIABATIC BLOCKED NAPTHA HYDROFORMING PROCESS CARRIED OUT IN THE PRESENCE OF APLATINUM GROUP METAL CATALYST AND ADDED HYDROGEN UNDER HYDROFORMING CONDITIONS OF TEMPERATURE, PRESSURE AND RESIDENCE TIME IN A SYSTEM, THE IMPROVEMENT WHICH COMPRISES SEPARATING THE FEED NAPHTHA INTO A FRACTION BOILING BELOW 200*F. AND A SECOND FRACTION BOILING ABOVE 200*F. ALTERNATELY TREATING THE SEPARATED FRACTIONS IN THE SAME SYSTEM UNDER HYDROFORMING CONDITIONS, CHARACTERIZED IN THAT (1) THE LOWER BOILING FRACTION IS TREATED UNDER A RELATIVELY LOW HYDROGEN PARTIAL PRESSURE, (2) UNDER A LOWER TOTAL PRESSURE AND A LOWER RECYCLE GAS RATE THAN SAID HIGHER BOILING FRACTION, AND (3) IN WHICH THE HYDROGEN-CONTAINING RECYCLE GAS FED TO THE REACTION ZONE DURING THE HYDROFORMING OF THE SAID LOWER BOILING FRACTION POSSESSES A HEAT CAPACITY SUBSTANTIALLY GREATER THAN THE SAID HYDROGEN-CONTAINING GAS FED TO THE SYSTEM DURING THE HYDROFORMING OF SAID HIGHER BOILING FRACTION DUE TO THE INCLUSION, IN SAID HYDROGEN-CONTAINING RECYCLE GAS FED TO THE SYSTEM DURING HYDROFORMING OF THE LOWER BOILING FRACTION OF A HIGHER VOLUMETRIC PERCENTAGE OF HYDROCARBONS THAN CONTAINED IN THE HYDROGEN-CONTAINING RECYCLE GAS FED TO THE HYDROFORMING ZONE DURING THE HYDROFORMING OF THE SAID HIGHER BOILING NAPHTHA CAUSED BY SEPARATING THE SAID HYDROGEN-CONTAINING RECYCLE GAS FROM THE PRODUCT OBTAINED BY HYDROFORMING THE SAID LOWER BOILING FRACTION AT A TEMPERATURE OF FROM ABOUT 200* TO 325*F., WHEREBY INCREASED QUANTITIES OF AROMATICS ARE FORMED FROM PARAFFINS PRESENT IN THE SAID LOW BOILING NAPHTHA FEED, FURTHER CHARACTERIZED IN THAT THE ENERGY REQUIREMENTS FOR CIRCULATING THE SAID HYDROGEN-CONTAINIG RECYCLE GAS TO THE HYDROFORMING TREATMENT OF THE LOWER BOILING FRACTION IS SUBSTANTIALLY THE SAME AS THE ENERGY REQUIREMENTS FOR CIRCULATING RECYCLED GAS TO THE HYDROFORMING TREATMENT OF THE HIGHER BOILING FRACTION.

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