US2886516A

US2886516A - Minimizing thermal reforming in catalytic reforming

Info

Publication number: US2886516A
Application number: US362847A
Authority: US
Inventors: Kenneth M Elliott
Original assignee: Socony Mobil Oil Co Inc
Current assignee: ExxonMobil Oil Corp
Priority date: 1953-06-19
Filing date: 1953-06-19
Publication date: 1959-05-12
Anticipated expiration: 1976-05-12

Description

May 12, 1959 M. ELLIOTT 2,886,516

MINIMIZING THERMAL REFORMING IN CATALYTIC REFORMING Filed June 19, 1953 4 Sheets-Sheet 1 IN VEN TOR. KENNETH M [LL/arr May 12, 1959 ELLIOTT 2,886,516

MINIMIZING THERMAL REFORMING IN CATALYTIC REFORMING 4 Sheets-Sheet 2 Filed June 19 1953 57m QQUM To 5754M 02041 INVENTOR. KEN/v5 TH M ELL/arr 18.51am firms/w K. M. ELLIOTT 2,886,516

MINIMIZING THERMAL REFORMING in CATALYTIC REFORMING May 12, 1959 4 Sheets-Sheet 3 Filed June 19 1953 3 wmtwwww r R V @mw www m. N @w m A w. RN A v A\ \VN\ vmm mm MMN KEN/wry M. 41 /0rr BY Z Z K. M. ELLIOTT May 12, 1959 MINIMIZING THERMAL REFORMING IN CATALYTIC REFORMING mm Q W t W m w NM M w 1 A M 4 w 3 5. 9 l w SQ SE Q m A w SQ 35km xsm m v m on MINIMIZENG THERMAL REFORMING 1N CATALYTIC REFORMING i Kenneth M. Elliott, Woodbury, N.J., assignor to Socony v Mobil Oil Company, Inc., a corporation of New York Application June 19, 1953, Serial No. 362,847-

Claims. (Cl. 208- 134) I Thev present invention relates to catalytic reforming in units designed to.provide a given soaking-time inthehydrocarbon reactant heating furnace for a given quan- 2,886,516 Patented May 12, 1959 greater. It is'recognized by those skilled in the art that designed to treat a given volume, say 10,000 barrels per tity of hydrocarbon reactant per unit of time when it is necessary or desirable toJintroduce a volume of hydrocarbon reactant per unit of time less than the designed volume and, more particularly, tominimizing thermal reforming in the naphtha heating furnace of a unit designed to treat a given volume of naphtha per unit of time when it is desirable or necessary to reduce the volume of naphtha treated per unit of time below the volume for which the naphtha heating furnace was designed. More specifically, the present invention relates to the catalytic reforming of hydrocarbon reactants in a unit designed to treat a given volume of hydrocarbon reactant under conditions of given severity when it is necessary or desirable to increase the severity of conditions by reducing the space velocity of the hydrocarbon in the reactor. And, more specifically minimizing thermal reforming by introducing into the hydrocarbon reactant feed upstream from the hydrocarbon reactant heating furnace an amount of inert fluid sufficient'to maintain the designed feed velocity in'the hydrocarbon reactant heating furnace.

As is well known to those skilled in the art, reforming is the designation applied to-those hydrocarbon conversions in which the molecular changes of isomerization, hydrogenation, dehydrogenation and dehydrocyclization occur. One of the foregoing molecular changes occurring as the sole conversion or two or more or all occurring as a series of reactions or as individual reactions are included in the term reforming. Those skilled in the art also know that reforming can take place in the presence or in the absence of a catalyst such as a dehydrogenating catalyst, an isomerization catalyst or a dehydrogenating-cyclicizing or aromatizing catalyst. Such catthermal reforming is incapable at commercially attractive yields to produce a naphtha having an octane rating of the order of 90, or greater. Consequently, when catalytically reforming naphtha any thermal reforming which may occur reduces the yield and octane rating of the product. As a matter of fact, it has been determined that yields of reformed gasoline are seriously lowered when the naptha is partially thermally reformed. Thus, for example, when operating a catalytic reforming unit on-stream day, of a naphtha having an octane rating of 84 (research clear) to produce a gasoline having an octane rating of 95 (research clear), the yield will be reduced from 2 to 6 percent by partial thermal reforming in the naphtha furnace when the severity of reactor conditions is increased by reducingthe liquid space velocity from 0.7 to 0.35. While 2 m6 percent loss due to thermal reforming may not appear to be a significant loss of product, it is to be noted that 2 percent loss on a unit treating. 10,00 0 barrels of naphtha per onstream day is about 65,000 barrels'of gasolineper year, and a loss of 6 percentin the same unitis a'loss of about 198,000 barr'els per year or a'monetary'loss of about $300,000 to abou t',i$900,000.' Consequently, it is manifest that for economic reasons alone, if not in the interests of conserving natural resources, it is desirable and, in fact, from a competitive standpoint, it is necessary to reduce this loss due to thermal reforming in the naphtha heatingfurnace and transfer line to a minimum. On the other hand, it is equally desirable from an economic view-' point to use 'the same'heating furnace to produce not only gasoline having an octane number of 84 (research clear), but also a gasolinehaving an octane rating of'95' (research clear) in the same unit. To achievesuch resultsgsince generally the major demand is'for gasoline having an octane rating of 84, i.e. motor gasoline, capital costs'require that the unit be designed to treat a given volume,,say' 10,000 barrels of hydrocarbon re-' actant, i.e., naphtha, per on-stream day under given conditions of severity. Such given conditions of severity involve certain feed inlet temperaturess, certain space velocities and similar conditions which provide the degree of severity necessary to produce a reformed naphtha having the desired octane rating. When, however, it

is necessary to use the unit for the production of gasoalysts are known generally as reforming catalysts, al-

though in some instances where a specific conversion, for example: isomerization, is the predominant conversion, the catalyst is designated by the particular conversion which predominates. Such conversions are known as catalytic reforming. the conversion can be carried. out at pressures from atmospheric to 1000 p.s.i.a with or without a net production of hydrogen. When the molecular conversions generally designated as reforming occur in the absence In catalytic reforming of any known catalyst, such conversions are known as I thermal reforming.

In general, the greatest industrial application of the reforming conversion is in the reforming of naphthas having a relatively low octane rating to naphthas having a higher octane rating such asof the order of 90, or

line having a higher octane rating, for example (research clear) the most easily and generally changed variable of those upon which severity of reaction conditions depend is the space velocity. To produce increased severity of reaction conditions, the space velocity is reduced. As a consequence of the reduced space velocity in the reactor, the velocity of flow in the naphtha heating furnace is decreased. As a result of the decrease in the velocity of flow in the naphtha heating furnace, the soaking time in the heating furnace and in .the transfer line is increased. As a result of this increasesd soaking time in the naphtha furnace and the transfer line,

thermal reforming with a loss in yield occurs. Thus, for example, the decreased yield resulting from'increased soaking time in the naphtha furnace and in the recycle gas furnace is about 4.1 percent when the octane rating of the reformed gasoline is raised from 84 (research clear) to 95 (research clear) when-treating a virginWest Texas naphtha having a boiling range of200" to 300 F. and an octane number of 55 (research clear). Comparative data are presented in Table I.

Table I Design Motor Usual Gasoline Aviation Operation Operation- Case A OaseB 5 st Counter-current):

lfl lgt eiiip F 1, 020 1, 055 Outlet Tempr, F 950 990 Average-Temp, p 964 1, 005 Space Velocity, V./Hr./V 0.7 0.35 Recycle Ratio; Mols Gas/M01 N aph r 6 12 Mols gig/M01 Naphtha 3.0 4. 8

Na htha urnace:

Outlet Temp, F... 930 930 Soaking Factor 0.07 0. 20

Recycle Furnace: Outlet Tem 1, 120 1, 1 20 Gasoline Yield, Volume percent Charge 92. 5 78. 6

Gasoline Octane Number:

Researc 84. 0 95 3 i311 94-5 102 Gasoline LossDue to Thermal Conversion 1n Naphtha Furnace, Volumepercent Charge. 0. 1 4. 2 Gasoline Loss Due to Thermal Conversion lIl Recycle Furnace, Volume percent Charge- 0.4 0.4 Total Gasoline Loss Due to Thermal Conversionin-Naphtha and Recycle Furnaces, Volume percent Charge 0.5 4. 6

It will be noted in the comparative runs, data for which are provided in Table I, that in Case A the recycle gas-to-naphtha mol ratio was 6, and that in Case B the corresponding value was 12. It will also be noted that in. Case Athe mols of hydrogen per mol of naphtha ratio was 3, while in Case B this ratio was 4.8. Study of the data provided in Table I establishes that, while the loss due to thermal conversion in the recycle gas heating furnaceis the same for both operations the loss in the naphtha heating furnace in Case B is 4.1 percent greater or 4200 percent of that of Case A. This entire loss was due to thermal conversion in the naphtha furnace and transfer line due to the increased soaking time therein. Aswill be established hereinafter, the; loss in yield can be. reduced about 80 to. about 95. percent by applying the'principles. of thepresent invention. That is to say, by introducing into the hydrocarbon reactant, feed upstream. ofv the hydrocarbon reactant. heating furnace. a volume,ofinertfiuidxsuflicient to maintain aflow velocity for the mixture of hydrocarbon reactant and inert fluid equivalent to the flow velocity in. the hydrocarbon, reactant heating furnace for which the hydrocarbon reactant heating furnace was designed, the. loss in yield at lower, reactor space velocities can' be reduced considerably if not practically completely eliminated.

The introduction of inert fluid into. the hydrocarbon reactant feed upstream from the hydrocarbon reactant heating furnace is not to be confused with the introduction of inert gas into the reaction zone for the purpose of supplying part of the heat of reaction as disclosed in:U.S. Patents Nos. 2,232,736; 2,273,224 and 2,364,453; for the reason that. introduction of inert gas into the reactionzone has. no effect or at best very slight effect, upon the, flow velocity of the hydrocarbon reactant in the hydrocarbon reactant heating furnace. In other words, when a part of the heat. of reaction is supplied by inert gases introduced into the reaction zone separately, or into the reactant line. downstream from the hydrocarbon reactantheating furnace, the flow velocity ofthe hydrocarbon reactant through. the. hydrocarbon. reactant heating furnace. is. substantially unchanged.-. On the other hand,.when inertfluid. is admixed. with the hydrocarbon reactant. upstream from. the hydrocarbonv reactantv heat,- ing furnace, the flow velocity of. the. mixture of. inert fluid and hydrocarbon reactant in the hydrocarbon reactant heating furnace is maintained at designed levels in accordance with the principles of the present invention.

The catalytic reforming processes most generally and presently in use industrially involve the use of a particleform solid catalytic material either in a bed-in-place operation, in a moving bed operation, or in What is industrially known as the fluidized state. For the purposes of illustrating the principles of the present invention, the application thereof of the moving-bed technique will be discussed. In this discussion reference will be made to a particle-form solid contact material comprising at least 70 mol percent alumina and 18 to 30 percent chromia, although any: particle-form solid reforming catalyst can be used. As noted hereinbefore, the reforming conversion can take place at pressures of 15 to 1000 p.s.i.a., and at reactor temperatures from about 800 F. to about 1100 F. However, for the purpose of illustrating the present invention, operating conditions such as given in Table II are exemplary of conditions under which naphthas such as straight run naphthas, cracked naphthas and mixtures of straight run and cracked naphthas can be reformed to yield gasolines having octane ratings of at least (research clear) in the presence of reforming Accordingly, it is the object of the present invention to prov de a method of catalytically reforming hydrocarbons wherein thermal cracking or reforming is. at least: mini.- mized or eliminated. It isv another object of the present invention to. provide a method of catalytically reform.-

ing hydrocarbons in which employing a hydrocarbon reactant heating furnace designed to minimize. or eliminate thermal cracking or reforming at a given charge stock velocity andv at a given reactor space velocity, said hydrocarbon reactant heating furnace is employed with reduced reactor space velocity but substantially constant designed hydrocarbon reactant heating furnace velocity. It is a further object of the present invention to provide a method of catalytically reforming hydrocarbons, wherein a hydrocarbon reactant heating furnace designed for a given charge stock velocity in conjunction with a given reactor space velocity is employed at a lower reactor space velocity, While the velocity of the material heated in the hydrocarbon reactant heating furnace is maintained at substantially constant designed capacity by diluting the. charge stock prior to introduction into the hydrocarbon reactant heating furnace with a fluid material substantially inert to thermal cracking and/or thermal reforming. The present invention also includes within its scope the provision of a method of catalytically reforming-hydrocarbons employing a hydrocarbon reactant heating furnace designed for a charge stock velocity, such as permits little or no thermal cracking and/or thermal reforming with a reactor designed for given space velocities, wherein the. reactor is operated, at. reduced space velocities but the velocity of the material being heated in the hydrocarbon reactant heating furnace is maintained substantially constant at designed velocities by admixing with the charge stock an amount of inert gas sufiicient to provide acombined volume of charge stock and inert gas of such magnitude that the velocity of the mixture of charge stock and inert gas through the hydrocarbon reactant heating furnace is substantially the designed velocity, whereas the reactor space velocity of the charge stock is reduced. Other objects and advantages of the present invention will become apparent to those skilled in the art from the following description of the present invention taken in conjunction with the drawings in which:

Figure 1 is a highly schematic flow sheet of a catalytic reforming process employing the moving bed technique wherein a portion of the recycle gas is admixed with the charge stock and that portion of the recycle gas not admixed with the charge stock is preheated to a temperature higher than that employed when operating at less severe reactor conditions;

Figure 2 is a highly schematic flow sheet of a catalytic reforming method employing the moving bed technique from which the reactor and kiln have been omitted and in which the recycle gas is contacted with the charge stock, under such conditions that the hydrocarbon constituents of the recycle gas having more than three carbon atoms in the molecule are substantially completely extracted from the recycle gas and the recycle gas substantially devoid of hydrocarbons having4' or more car-i bon atoms to the molecule is heated separately while the volume of the charge stock to be heated in the hydrocarbon reactant heating furnace is increased by the volume of constituents of the recycle gas to a total volume such that the velocity of the mixture of the hydrocarbon reactant heating furnace is sufiiciently high to minimize, if not completely eliminate, thermal cracking and/ or thermal reforming;

Figure 3 is a highly schematic flow sheet of a method of catalytic reforming of hydrocarbons wherein the reactor and kiln are not shown in the drawing and, wherein the recycle gas is contacted with the hydrocarbon reactant under such conditions that substantially all of the hydrocarbon constituents of the said recycle gas having 4 or more carbon atoms in the molecule are substantially completely extracted from said recycle gas, inwhi-ch a portion of the stripped recycle gas is admixed with the hydrocarbon reactant and constituents stripped from the recycle gas in amount suflicient that the total volume of stripped recycle gas, hydrocarbon reactant and recycle gas constituents stripped from the recycle gas by the hydrocarbon reactant is such that the velocity of the mixture in the hydrocarbon reactant heating furnace is suflicient to minimize if not eliminate thermal cracking and/ or thermal reforming; and

Figure 4 is a highly schematic flow sheet of a method of catalytically reforming hydrocarbons in which the reactor and kiln are not shown, in which the recycle gas is contacted with the hydrocarbon reactant under such conditions that substantially all of the constituents of said recycle gas having more than 3 carbon atoms in the molecule are extracted by the hydrocarbon reactant thereby increasing the volume thereof, wherein the stripped recycle gas substantially devoid of hydrocarbons having 4 or more carbon atoms in the molecule is .dried and a portion of the dried stripped recycle gas is admixed with the mixture of hydrocarbon reactant and extracted constituents of the recycle gas in such an amount that the velocity of the mixture of dried stripped recycle gas, hydrocarbon reactant and extracted constituents of the recycle gas is such that the velocity of the mixture in the hydrocarbon reactant heating furnace is substantially the designed velocity.

' In general, the present invention provides that method of catalyticallyreforming hydrocarbons in a reforming unit designed to heat a given volume of hydrocarbonreactant to a given temperature at a'given velocity in the hydrocarbon reactant heating furnace. The unit is capable of operation at various space velocities in the reactor. However, when it is necessary or desirable ,to increase the severity of reforming conditions, this is most readily achieved by reducing the space velocity of the hydrocarbon reactant in the reactor. Concomitant with such a reduced space velocity in the reactor is a reduced velocity in the hydrocarbon reactant heating furnace. In accordance with the principles of the present invention,

the hydrocarbon reactant prior to passage through the' hydrocarbon reactant heating furnace is diluted with an inert fluid in an amount sutficient to maintain the velocity words, recycle gas containing substantially only. constituents which are inert in the reaction, i.e., not sub-- ject to thermal cracking and/ or thermal reforming. The inert gas can also be derived from a source extraneous of the reforming unit and can be in addition to recycle gas, natural gas, nitrogen, etc. In other words, inert fluids are added to the hydrocarbon reactant in an 'amount such that the contact time of the hydrocarbon reactant in the hydrocarbon reactant heating furnace is suficient to raise the temperature of the hydrocarbon reactant to reforming temperatures, but insuflicient for thermal cracking or thermal reforming of the constituents of the mixture of inert fluid and hydrocarbon reactant.

Referring now to Figure 1. Active particle-form solid reforming catalyst in hopper 11 when using the moving bed technique flows into reactor 17. When reactor 17 is being operated at a pressure substantially in excess of atmospheric pressure, for example pressures in excess of 40 p.s.i.a., it is necessary to provide a reactor-sealing and particle-form transfer means by Which the particleform catalytic material can flow from hopper 11 at a pressure lower than the pressure in reactor 17 without substantial loss of hydrocarbon reactant vapors therethrough. Such a reactor-sealing and particle-form catalytic material transfer means is illustrated in Figure 1 and comprises gas-

tight valves

12 and 14 and intermediate pressuring chamber 13. The reactor-sealing and catalyst transfer means operated in a cyclic manner as follows: Recycle gas from liquid separator 18 flows through pipe 19 to pipe 20 and thence to pipe 21 under control of valve 22. The cycle is initiated by closing gas-tight valve 14, opening gas-tight valve 12 and allowing active catalyst in hopper 11 to flow through gas-tight valve 12 into pressuring chamber 13. When pressuring chamber 13 is filled with active catalyst to a predetermined level, gas-tight valve 12 closes. Inert gas from a source not shown flows through pipe 23 under control of valve 24 into pipe 21 through pressuring chamber 13 and is vented from pressuring chamber 13 through pipes 25 and 26, under control of valve 27. After chamber 13 has been purged with the inert gas which can be flue gas, valves 24, 27 and 28 are closed. Valve 22 is opened and recycle gas introduced into pressuring chamber 13 until the pressure therein is equal to or slightly higher, say about 0.5 to 5 psi. greater than the pressure in reactor 17. Thereafter gas-tight valve 14 opens and the catalyst in chamber 13 flows into surge chamber 15,'

This is- Inert gases can be recycle gas containing substantially no hydrocarbons hav-. ing 4 or more carbon atoms in the molecule. In other Gas-tight. valve: 14 thencloses and the pressure in chamv ber; 13-is reducedv to that of hopper 11. by venting the recycle gas through. pipes 25 and 29 under control of valve, 28. After the pressure has been reduced in chamber 13 to: that of the hopper 11 (usually atmospheric), chamber 13; is charged with an inert and/or non-flammable gas, such as flue gas, introduced from a source not.

shown. through pipes 23 and 21,, with valve 22 closed and valve; 24 open. The: purge charge is vented through pipes. 25: and 26 under the control of valve 27.

The. catalyst in surge tank 15- flows through conduit 16 into reactor 17 where it is contacted with hydrocarbon reactant introduced into reactor 17 as described hereinafter; The. catalyst, when passing through reactor 17, is inactivatedv by a deposit of carbon upon the particles thereof. Consequently, for economic reasons, the catalystmust be regenerated. Accordingly, the at least partially inactivated. catalyst flows from reactor 17 through catalyst flow control means 30. When the catalyst is regenerated at pressures less than the pressure existing in reactor 17, it is necessary to provide a reactorsealing. and particle-form transfer means constructed and arranged to transfer the particle-form solid catalytic material from reactor 17 to a catalyst transfer means, whereby the catalyst is transferred to the regenerator. The reactor-sealing and catalyst transfer means is constructed and arranged to minimize the escape of hydrocarbon vapors from reactor 17 therethrough. A suitable reactorsealing and catalyst transfer means comprises gas-tight valve 31, depressuring chamber 32 and gas-tight valve 33. This reactor-sealing and catalyst-transfer means operatesin. a cyclic manner as'follows: depressuring chamber32 is purged with aninertand/or non-flammable gas, such as flue gas, drawnfrom a source not shown through pipe 34, under control of valve 35 and flows through pipe 36 into chamber 32. The purge is vented through pipes 37 and 38 under control of valve 39. After chamber 32 has been purged, valves 35 and 39 are closed and valve 40 in'pipe 41' is open. Recycle gas. flows from pipe 79 through pipe 42 to pipe 41 and thence under control of valve 40 to chamber 32 with valves 39 and 43 closed. When the pressure in chamber 32 is substantially that of reactor 17, valve 40 is closed, gas-tight valve 31 is opened and catalyst flows through catalyst-flow control means 30 which can be a throttling valve, conduit 44 and gas-tight valve 31 into chamber 32. When chamber. 32 has been filled to a predetermined level with catalyst, gas-tight valve 31 is closed. Valve 43 is then.

opened and the pressure in chamber 32 reduced to that of the kiln or regenerator: by venting the gaseous contents thereof through pipes 37' and 45, under control of valve 43. When the pressure in chamber 32 has been reduced to that of the kiln or regenerator (usually atmospheric), valve 43 is closed and the contents of chamber 32 purged with an inert and/ or non-flammable gas drawn from a source not shown through pipes 34 and 36 under control of valve 35 and vented through pipes 37 and 38 under control of valve 39. After purging chamber 32, valves 35 and 39 are closed and gastight valve 33 is opened. The catalyst then flows from chamber 32 through gas-tight valve 33 into surge chamber 46. When chamber 32 has beenemptied of catalyst, gas-tight valve 33 is closed and chamber 32 purged with an inert and/or non-flammable gas as described hereinbefore, completing the cycle. The catalyst in surge chamber 46 flows through conduit 47 to chute 48 and thence to catalyst transfer means 49. Catalyst transfer means 49 can be of any suitable type, whereby catalyst can be. transferred from chute 48 to chuten50 and thence to kilnhopper. 51. Suitable catalyst transfer means are elevators, gas lifts, and the like.

The catalyst flows along chute 43 to catalyst transfer means 49 and thence to chute 50 and hopper 51. From hopper 51 the inactivated catalyst flows through conduit 52 into kiln or regenerator'53. Kilnorregenerator 53 is provided with. cooling coils 54 through which. a heat exchange medium such as steam,.low meltingpoint alloys, molten salt mixtures, etc., is circulated. As illustrated, steam is the. heat. exchange medium, condensate flows from. steam drum 55' through pipes 56 and 57 to: coils.

54- in regenerator 53 where it is. converted tov steamand as such flows back to steam drum 55 through pipe 58. Kiln or regenerator 53 can be of any suitable type, Wherein the carbon deposited upon the catalyst in reactor 17. is burned ofli. in a combustion-supporting stream of gas. such as air. During passage through kiln 53 the deposit of carbon is burned ofi the particles of catalyst andthereby the catalyst is regenerated. The regenerated. active catalyst flows from kiln 53 through conduit59'to chute 60- and thence to a catalyst transfer means 61 of any suitable type such as a gas lift and the like or an elevator. The catalyst. is transferred from chute 60 to chute. 62 by catalyst transfer means 61 and flows along chute 62 to catalyst feed hopper 11 ready to start av new cycle through the reactor.

Hydrocarbon reactant drawn from a source not shown is pumped. through line 63 under control valve 64 and thencethrough line 65 to heat exchanger 66 and line 67. Thehydrocarbon reactant flows through line 67 tohydrocarbon reactant heating furnace 68, wherein it. is heated to a temperature such that when mixed with recyclegas as described hereinafter, the temperature of the mixture of recycle gas and hydrocarbon reactant shall be about 800 F. to about 1080 F., and preferably about 960 F. to. about 1060 F.

Since the space velocity of the hydrocarbon reactant in reactor 17is'to besuch that the octane rating of the re-=' formate when treating a naphtha has to be in excess of about 90 to about 95, in'accordancewith the principles of the present invention, the volume of hydrocarbon reactant. passing through furnace 68 is increased by introducing into the stream of hydrocarbon reactant at a point such as 69 in line 65 a volume of recycle gas suflicient to'maintain the velocity of the mixture of hydrocarbon reactant and recycle gas in coil 78 of furnace 68- such' that thermal conversion therein is maintained at a minimum, or substantially eliminated.

Accordingly, recycle gas is diverted from pipe 20 through pipe 74 under control of valve 75 to line 65 at some point such as 69 upstream from naphtha heating furnace 68. When a fluid diluent extraneous to the unit such as natural gas is to be used, the fluid diluent is drawn from a source: not shown. by pump 76 through pipe under control of valve: 71 and discharged through pipe 77 into pipe 74.

The volume of recycle gas or other fluid diluent, admixed with the hydrocarbon reactant in line 65 at point 69, is sufficient that the total volume of hydrocarbon reactant and admixed inert recycle gas flowing through coil- 78 in hydrocarbon reactant heating furnace 68 issuch that the time ofcontact of the hydrocarbon reactant in coil 78 in furnace 68' is suificient to raise the temperature of the hydrocarbon reactant to the desired reforming tempera ture, but insutficient to cause substantial thermal cracking and/0r thermal reforming of the hydrocarbon reactant.- Thus, for example, when the hydrocarbon reactant heating furnace has been designed for a contact time such that the undiluted hydrocarbon reactant is not subjected to" thermal cracking and/or thermal reforming, when the spacevelocityof the hydrocarbon reactant in reactor. 17 is about 0.7, and the space velocity in reactor 17 is reduced toabout 0.35, i.e., 0.5 of the designed velocity in the hydrocarbon reactant heating furnace,.the hydrocarbon-reactant is diluted with about 800 cubic feet per bbl. of charge of an inert fluid such as recyclegas or inert fluid. from an extraneous source. That is to say, sufiicient of the inert. fluid is admixed with the. hydrocarbon reactant to maintain a soaking factor in hydrocarbon reactant.

heating furnace 68 and the transfer line to the reactor atleast-beloyy 0.15i-andipreferably. below 0.07.

9 It is general practice to introduce a portion of the heat of reaction into the reactor in a gaseous heat carrier. Such a gaseous heat carrier can be recycle gas. Accordingly, recycle gas flows under the pressure of pump 72 from liquid gas separator 18 through pipes 19 and 20 to pipe 79, thence through heat exchanger 80 to the pipe 81 and coil 82 of gas heater 83. The gaseous heat carrier is heated in coil 82 of furnace 83 to a temperature suchthat when mixed with the heated hydrocarbon reactant .in line 84 in the proportions set forth hereinafter, the mixture of gaseous heat carrier and hydrocarbon reactant has a temperature of about 900 to about 1060 F. The recycle gas is mixed with the hydrocarbon reactant in the ratio of about 2 to about 20 mols of reactant gas per mol of naphtha and preferably in the ratio of about 6 to about mols per mol of naphtha. When a hydrogen containing recycle gas containing at least 25 percent hydrogen and preferably in excess of 35 percent hydrogen is used as the gaseous heat carrier, the recycle gas and hydrocarbon reactant are mixed in the ratio of about 1 to about 10, preferably about 3 to about 8, mols of hydrogen per mol of naphtha. Generally, the gaseous heat carrier, i.e., recycle gas, is heated in the recycle furnace to a temperature of about 1000 F. to about 1400 F., preferably about 1100 F. to about 1200 F. The hydrocarbon reactant heating furnace is generally maintained at temperatures below about 1000 F. and preferably at a temperature below about 940 F. The heated mixture of hydrocarbon reactant and inert fluid flows from furnace 68 through line 85 to line 84. The heated gaseous heat carrier, i.e., recycle gas, flows through pipe 86 under control of valve 87 to line 84. The mixture of heated recycle gas, heated hydrocarbon reactant and heated inert fluid flows from line 84 to line 88 and thence to a distributor 89 in reactor 17. Reactor 17 is provided with two product lines, 90 and 91, each provided with a throttling means such as a throttle valve 91 and 93, respectively. The distribution of hydrocarbon reactant, recycle gas and inert fluid from distributor 89 flowing upward is controlled by the setting of throttling means 92. Throttling means 93 is then set to pass the balance of the mixture of the contents of reactor 17. The effluent from the upper portion of reactor 17 flows through line 90 under control of throttling means 92 to line 94. The balance of the reformate flows through line 91 under control of throttling means 93 to line 94. The combined efliuents from reactor 17 flow through line 94 to heat exchanger 80, thence through line 95 to heat exchanger 96 and flow through line 97 to heat exchanger 66. From heat exchanger 66, the combined efiluents from reactor 17 flow through line 98 to cooler 100. From cooler 100, the condensed constituents of the combined effluent from reactor 17 and the uncondensed constituents of the ef-. fluent in reactor 17 flow to liquid gas separator 102. In separator 102, the uncondensed constituents of the efiluent from reactor 17 are drawn upward through pipe 103 by compressor 72 and are discharged by compressor 72 into pipe 104. The condensed constituents of the effluent. from reactor 17 are transferred from liquid gas separator 102 through line 105 in which the uncondensed constituents of the eflluent from reactor 17 are introduced under the pressure of pump 72. The mixture of condensed and uncondensed constituents of the reactor effluent under the pressure created by pump 72 flow through line 105 to cooler 106, and thence through line 107 to liquid gas separator 18. Temperature and pressure conditions in liquid gas separator 18 are maintained such that effiuent constituents having more than 3 carbon atoms in the molecule are condensed and separated in liquid gas separator 18 and flow therefrom through line 73 to depropanizer 108. In depropanizer 108 an overhead is taken through pipe 109 to pipe 110 and thence to fuel gas system reservoir or sphere 111. The bottoms from depropanizer 108 flow through line 112 to primary rerun tower 113. Anoverheadisitaken from primary reruntower 113 through line 114 to reformate storage 115.

The bottoms from primary rerun tower 113 flow throughv line 115 to secondary rerun tower 116. An overhead is taken from secondary rerun tower 116 through line 117 to storage 115. When desirable, an aviation grade heart cut can be taken overhead from secondary rerun tower 116 and stored separately from the overhead taken from primary rerun tower 113. The contents of storage 115 is- Returning now to liquid gas separator 18, the uncondensed effluent constituents, i.e., uncondensible gas and a hydrocarbon having not more than 3 carbon atoms in the molecule flow upwardly through pipe 19 to pipe 20.

When desirable or necessary, a portion of the uncon.

densed constituents of the reactor effluent can be bled off through line 110 under control of valve 120. The uncondensed constituents of the reactor effluent flowing through pipe 19 to pipe 20, in whole or in part, flow therethrough to recycle heating furnace 83 and for use in pressuring and depressuring catalyst in

chambers

13 and 32. As stated hereinbefore, a portion of the uncondensed eflluents of the reactor 17, i.e., recycle gas, is drawn from pipe 20 through line 74 under control of valve to be admixed with the hydrocarbon reactant in line 65 at point 69. inert fluid so-mixed with the hydrocarbon reactant is suflicient to maintain the soaking factor in naphtha furnace 68 and transfer lines 84, and 88 below 0.15 and preferably below 0.07. (The soaking factor is defined as the product of the ratio of the thermal conversion velocity constant at the coil temperature to the thermal conversion velocity constant at 800 F., and the coil volume in cubic feet per barrel/per day, i.e.,

%X (coil volume in cubic feet per b./d.))

Since the present invention is not'concerned particularly with the method of operating the reactor, the reactor and kiln have not been shown inFigures 2, 3 and 4.

Referring now to Figure 2. Hydrocarbon reactant drawn from a source not shown flows through line to absorber 131. In absorber 131 the hydrocarbon reactant contacts intimately recycle gas flowing from liquid gas separator 132 through pipe 133. The recycle gas flowing from separator 132 comprises generally hydrogen and other uncondensible gases together with hydrocarbons having from 1 to 6 carbon atoms in the molecule.-

pipe 134 is substantially devoid of hydrocarbons having The stripped.

4 or more carbon atoms in the molecule. recycle gas flows through pipe 134 to pipe 135, thence through pipe 135 to exchanger 137 to pipe 138 and thence to coil 139 in recycle heating furnace 140. The hydrocarbon reactant after contact with the recycle gas having stripped hydrocarbons having 4 ormore carbon atoms in the molecule from the recycle gas flows throughline 141 to heat exchanger 142 and thence through line 143 to coil 144 of hydrocarbon reactant heating furnace 145. The volume of the constituents stripped from the recycle gas is suflicient to reduce the soaking factor in the hydrocarbon reactant heating furnace 145 and transfer line 146 to at least 0.15 and preferably below 0.07. The hydrocarbon reactant and constituents of the recycle gas stripped therefrom by the hydrocarbon reactant are heated in the naphtha furnace to a reforming temperature below 1000 F. and preferably below about 940 F. The heated hydrocarbon reactant and inert constituents of the recycle gas flow along transfer line 146 and are ad-- The amount of recycle gas, i.e.,.

hydrocarbon reactant.

mixed with stripped recycle gas, heated in furnace 140 and. flowing therefrom through pipe 147 under control of valve 148 in the ratio of about 2 to about 20, preferably about 6 to about 15, mols of recycle gas per mol of hydrocarbon reactant, or, in the ratio of about 1 to 10, preferably about 3 to 8, mols of hydrogen per 'mol of The mixture of recycle gas, hydrocarbon reactant and constituents of the recycle gas stripped therefrom by the hydrocarbon reactant flow through transfer line 146 to a distributor or distributors in a reactor not shown. The efliuent flows from the reactor not shown through line 149 to heat exchanger 137 and thence through line 150, heat exchanger 151, line 152, heat exchanger 142, line 153 and cooler 154 to liquid gas separator 155. Liquid gas separator 155 is operated under conditions of temperature and pressure such that substantially all of the C to C hydrocarbons together with uncondensible gases are not condensed and that heavier hydrocarbons are condensed. The uncondensed constituents of the effluent are drawn overhead through pipe 156 by compressor 157 and discharged into pipe 158. The condensed efliuent is transferred from liquid gas separator 155 through line 159. The uncondensed efliuent discharged by pump 157 into pipe 158 rejoins the condensed efiiuent in line 159 and flows therewith to cooler 160. The cooled condensed and uncondensed effluent flows from cooler 160 through line 161 to liquid gas separator 132 where the uncondensed effluent flows upwardly through line 133 to absorber 131. When desirable or necessary, a portion of the stripped recycle gas is bled from line 134 through line 162 under control of valve 163 to the refinery fuel system reservoir 164. The condensed efliuent flows from liquid gas separator 132 through line 165 to depropanizer 166. An overhead cut is taken from depropanizer 166 through line 167 to refinery fuel reservoir 164. The bottoms of depropanizer 166 flows through line 168 to primary rerun tower 169 wherein an overhead is taken to storage and/ or distribution through line 17 0 to storage 171. The bottoms from primary rerun tower 169 flows through line 172 to secondary rerun tower 173 from whence an overhead is taken through line 174 to storage 171. When desirable, an aviation grade heart out can be taken overhead frorn secondary rerun tower 173 and stored separately from the overhead taken from primary rerun tower 169. The bottoms from secondary rerun tower 173 flow through line 175 to polymer storage 176.

Referring now to Figure 3, it will be noted that the highly schematic flow sheet representing another embodiment of the present invention does not include a reactor and kiln or regenerator. The schematic flow sheet depicted in Figure 3 in a highly schematic manner differs from that of Figure 2 in that in the embodiment represented in Figure 3, a portion of the stripped recycle gas is admixed with the enriched hydrocarbon reactant flowing from the absorber. The amount of stripped recycle gas admixed with the enriched hydrocarbon reactant is sufiicient to maintain the soaking factor for the hydrocarbon reactant in the hydrocarbon reactant heating furnace at not greater than 0.15, and preferably at 0.07, when the space velocity in the reactor (not shown) is reduced to increase the severity of reforming conditions.

Reactor efliuent flows from reactor (not shown) through line 200 to heat exchanger 201, thence through line 202 to heat exchanger 203. From heat exchanger 203 the reactor efiiuent flows through line 204 to heat exchanger 205 and thence through line 206 to cooler 207. Cooler 207 and liquid gas separator 209 are operated under conditions of temperature and pressure such that C to C hydrocarbons are not condensed together with the uncondensible gases such as hydrogen. From cooler 207 the cooled reactor efliuent flows through line 208 to liquid gas separator 209. In liquid gas separator 209 the uncondensed effluent of the cooled reactor efiiuent flows upwardly through line 210 to pump 211 wherein the uncondensed constituents of the cooled efiiuent are pressured to a pressure somewhat greater than operating pressure and discharged through line 212. The condensed constituents of the cooled reactor effluent are transferred from liquid separator 209 through line 213 where the pressured uncondensed constituents of the cooled reactor effluent are remixed with the condensed constituents of the cooled reactor efliuent. The mixed condensed and uncondensed constituents of the reactor efliuent flow through line 214 to cooler 215 and thence through line 216 to liquid gas separator 217. The uncondensed constituents of the pressured cooled reactor efliuent flow upward through pipe 218 to absorber 219. The uncondensed constituents of the reactor etfluent flowing upward from liquid gas separator 217 are intimately contacted with hydrocarbon reactant to be treated in absorber 219.

Hydrocarbon reactant drawn from a source not shown by a pump not shown is discharged through line 225 into the top of absorber 219. In its passage downward through absorber 219 the hydrocarbon reactant absorbs substantially all of the hydrocarbon constit ents of the uncondensed effluent having 4 or more carbon atoms in the. molecule. Thereby the hydrocarbon reactant is enriched with hydrocarbons having 4 or more carbon atoms. The enriched hydrocarbon reactant flows from absorber 219 through line 226. The stripped uncondensed constituents of the reactor eflluent, now designated stripped recycle gas, flow upwardly from absorber 219 through pipe 220 to pipe 227. When desirable or necessary, a portion of the stripped recycle, usually about equivalent to the net gas make, is diverted from pipe 220 through pipe 223 under control of valve 221 to refinery fuel system reservoir 224. A portion of the stripped recycle gas in amount suflicient to maintain the soaking factor of the hydrocarbon reactant in coil 230 of hydrocarbon reactant heating furnace 231, below 0.15 and preferably below 0.07, flows from pipe 227 through pipe 232 under control of valve 233 to admix with the enriched hydrocarbon reactant in line 226.

The mixture of stripped recycle gas, i.e., inert fluid and enriched hydrocarbon reactant flows through pipe 226 to pipe 234, heat exchanger 205 and pipe 235 to coil 230 of hydrocarbon reactant heating furnace 231. In hydrocarbon reactant heating furnace the mixture of stripped recycle gas and enriched hydrocarbon reactant is heated to a reforming temperature below 1000 F. and preferably below about 940 F. The heated mixtures of stripped recycle gas, i.e., inert fluid, and enriched hydrocarbon reactant flow from hydrocarbon reactant heating furnace through line 236. The balance of the stripped recycle gas flows through pipe 227 to pipe 237. A portion of the stripped recycle gas can be used for pressurizing the catalyst as discussed in conjunction with Figure 1 by diverting the quantity necessary from pipe 227 through pipe 238 under control of valve 239. The balance flowing through pipe 237 passes through heat exchanger 201 to pipe 240 and thence to coil 241 in recycle gas heating furnace 242. In recycle gas heating furnace the recycle gas is heated to a temperature of about l000 to about 1400" F. and preferably to a temperature of about 1100 to about 1200 F. The heated recycle gas flows from furnace 242 through pipe 243 and is admixed with the inert fluid and enriched hydrocarbon reactant in line 236 in the ratio of about 2 to about 20, preferably about 6 to about 15, mols of recycle gas per mol of hydrocarbon reactant, or in the ratio of about 1 to about 10 mols of hydrogen, preferably about 3 to about 8 mols of hydrogen per mol of naphtha. The stripped recycle gas contains at least about 25 percent hydrogen and preferably about 35 to about 60 percent hydrogen, the balance C to C hydrocarbons. The mixture of heated inert fluid and heated enriched hydrocarbon reactant flows from line 236 to;

line 244 while heated recycle gas flows from heater hydrocarbon reactant, recycle gas and inert fluid which flows through line 244 to the reactor not shown.

Returning now to liquid gas separator 217 wherein the uncondensed constituents of the reactor effluent flow upward through pipe 218 to absorber 219, the condensed constituents of the reactor eflluent flow downward from liquid gas separator 217 through line 245 to depropanizer 246. In depropanizer 246 a cut is taken overhead through pipe 247 and

pipes

222 and 223 to refinery fuel system reservoir 224. The bottoms from depropanizer 246 flow through line 248 toprimary rerun tower 249. In primary rerun tower 249 a cut is taken overhead through line 250 to reformate storage 251. The bottoms of primary rerun tower 249 flow through line 252 to seconding rerun tower 253 wherein a cut is taken overhead through line 254 to reformate storage 251. When desirable, an aviation grade heart cut can be taken overhead from secondary rerun tower 253 and stored separately from the overhead taken from primary rerun tower 249. The bottoms from secondary rerun tower 253 flow through line 255 to polymer storage 256.

: Referring now to Figure 4. Figure 4 is a highly schematic flow sheet of an embodiment of the present invention wherein the reactor and kiln or regenerator are not shown. The embodiment of the present invention represented in the highly schematic manner in Figure 4 differs from those embodiments represented in Figures 1, 2 and 3 in that the stripped recycle gas drawn from the absorber is dried to remove any moisture remaining in the stripped recycle gas. Reactor eflluent flowing from a reactor not shown flows through line 300 to heat exchanger 301 thence through line 302 to heat exchanger 303 andline 304. From line 304 the reactor efliuent flows through heat exchanger 305, line 306, cooler 307 and line 308 to liquid gas separator 309. Cooler 307 and liquid gas separator 309 are maintained under conditions of temperature and pressure such that a large portion of the C to C hydrocarbons together with uncondensible gases such as hydrogen are not condensed. These uncondensed constituents of the reactor effluent are drawn upward from liquid gas separator 309 through pipe 310 by pump 311 and discharged therefrom through pipe 312. The condensed constituents of the reactor efliuent are transferred from liquid gas separator 309 through line 313, where the condensed reactor effluent is admixed with the uncondensed reactor efliuent flowing from pipe 312 under the pressure impressed thereon by compressor 311. The mixture of condensed and uncondensed reactor effiuent flows through line 313 to line 314 and cooler 315. The cooled mixture of pressurized uncondensed and condensed reactor eflluent flows from cooler 315 through line 316 to liquid gas separator 317.

v The uncondensed reactor effluent flows upward through pipe 318 to absorber 323 where it is intimately contacted with the hydrocarbon reactant to be treated, drawn from a, source not shown by a pump not shown, and discharged into line 324. The hydrocarbon reactant is introduced into absorber 323 in the region of the top thereof and flows downwardly in intimate contact with the uncondensed reactor efliuent now designated recycle gas. In its passage through absorber 323 the hydrocarbon reactant strips hydrocarbons having 4 or more carbon atoms in the molecule from the recycle gas. The hydrocarbon reactant thereby enriched flows from absorber 323 through line 325. The stripped recycle gas flows upwardly from absorber 323 through pipe 326. The stripped recycle gas passes through drier 328 wherein the moisture content of the stripped recycle gas is reduced to not more than about 0.13 mol percent. The dried recycle gas flows from drier 328 through pipe 329. A portion of the dried stripped recycle gas flows through pipe 331 under control of valve'332 to line 325 where the diverted dried stripped recycle gasis admixedwith the enriched hydrocarbon reactant in an amount sufiicient to maintain the soaking factor of the hydrocarbon reactant below about 0.15 and preferably below about 0.07 in the hydrocarbon reactant heating furnace 333 and transfer line 334. A portion of the dried stripped recycle gas can be bled off through line 335 under control of valve 336 for use in pressurizing the catalyst in the reactor as described in conjunction with Figure 1. When desirable or necessary, a portion of the stripped recycle gas usually about equal to the net gas make can be diverted from pipe 326 through pipe 319 under control of valve 320 to the refinery fuel gas system reservoir 322. Returning now to the mixture of driedstripped recycle gas and enriched hydrocarbon reactant in line 325, the mixture flows through line 325 to line 327 and thence through heat exchanger 305, line 338 and coil 339 in hydrocarbon reactant heating furnace 333. In hydrocarbon reactant heating furnace 333 the mixture of dried stripped recycle gas, i.e., inert fluid, and enriched hydrocarbon reactant is heated to a reforming temperature below about 1000 F. and preferably below about 940 F.

The dried stripped recycle gas in pipe 330 flows therefrom through pipe 340 to heat exchanger 301 and pipe 341. The dried stripped recycle gas flows through pipe 341 to coil 342 in recycle gas heating furnace 343. In recycle gas heating furnace 343 the recycle gas is heated to a temperature of about 1000 F. to about 1400 F. and preferably to a temperature of about 1100 F. to about 1200 F. The heated recycle gas flows from furnace 343 through line 344 and is admixed with the heated enriched hydrocarbon reactant and inert fluid in transfer line 334. The mixtures of heated recycle gas, heated inert fluid, and heated enriched hydrocarbon reactant flow along transfer line 334 to a reactor not shown.

The heated recycle gas is mixed with the heated enriched hydrocarbon reactant in the ratio of about 2 to about 20 mols, perferably about 6 to about 15 mols, of recycle gas per mol of hydrocarbon reactant. Or, in the ratio of about 1 to about 10, preferably about 3 to about 8, mols of hydrogen per mol of hydrocarbon reactant. The recycle gas contains at least 25 percent hydrogen and preferably about 35 to about 60 percent hydrogen, balance substantially C to C hydrocarbons. Returning now to liquid gas separator 317 wherein the uncondensed constituents of the reactor efliuent flow upwardly through pipe 318 to absorber 323 and the condensed constituents of the reactor effluent flow downwardly from liquid gas separator 317 through line 345 to depropanizer 346. In depropanizer 346 a cut is taken overhead through line 321 to pipe 319 and thence to refinery fuel reservoir 322. The bottoms of depropanizer 346 flow through line 347 to primary rerun tower 348, and thence to reformate storage 349. The bottoms of primary rerun tower 348 flow through line 350 to secondary rerun tower 351. In secondary rerun tower 351 a cut is taken overhead through line 352 to reformate storage 349. When desirable, an aviation grade heart cut can be taken overhead from secondary rerun tower 351 and stored separately from the overhead taken from primary rerun tower 348. The bottoms from secondary rerun tower 351 flow through line 353 to polymer storage.

For best utilization of the heat energy of the unit, a heat exchange medium is circulated through a recycle gas heating furnace 83 (Fig. 1), (Fig. 2), 242 (Fig. 3) and 343 (Fig. 4). Thus, in Figure 1 a heat exchange medium, for example, condensate, i.e., water, flows from steam drum 55 through pipe 56 to pipe 357 to coil 358 in recycle gas heating furnace 83. The steam produced.

in coil 358 in recycle gas heating furnace 83 flows therefrom through pipe 359 back to steam drum 55. A portion of the heat exchange medium in pipe 357 is diverted through pipe 360 under control of valve 361 through heat exchanger-'96 and thence through pipe362 back to storage s uch as steam drum 55. Similarly, in Figure 2, heat exchange medium flows from a reservoir (not shown) through pipe 357 to coil 358 in recycle gas heating furnace 140. The heat exchange medium flows from coil 358 in recycle gas heating furnace 140 through line 359 and thence back to the heat exchange medium reservoir (not shown). A portion of the heat exchange medium is diverted from pipe 357 through pipe 360 under control of valve 361 to heat exchanger 151 and thence through pipe 362 back to heat exchange medium reservoir (not shown). Similarly, in Figure 4, heat exchange medium flows through pipe 357 to heating coil 358 in recycle gas heating furnace 342. From coil 358 the heat exchange medium flows through pipe 359 to the heat exchange medium reservoir (not shown). A portion of the heat exchange medium is diverted from pipe 357 through pipe 360 under control of valve 361 to heat exchanger 303 and thence back through line 362 to the heat exchange medium reservoir not shown.

In general, the operating conditions for treating a naphtha in a unit designed to give a soaking time not greater than about 0.15 and preferably not greater than 0.07 in the hydrocarbon reactant heating furnace and transfer line, when operating at a reduced space velocity in the reactor, in order to produce more severe reforming conditions than necessary to obtain the degree of conversion necessary to produce gasoline having an octane rating of about 84, are as given in Table III.

Table III Operating Ranges Reactor Broad Preferred Average Reactor Temperature, F 800-1, 100 9001,025 Gas Recycle Ratio: Mols Gas/M01 Naphtha 2-20 6-15 Mols Hydrogen/M01 Naphtha 1-10 3-8 Space Velocity, Average in Reacto 0. 1-6. 0. 5-2. 0 Recycle Furnace Temp., F 1,0001,400 1,1001, 200 Naphtha Furnace Temp., F Below 1,000 Below 940 Soaking Factor in Naphtha Furnace and Transfer Linc Below 0.15 Below 0. 07 Pressure, p.s.1.a -600 100300 Inert Fluid Added to Naphtha Furnace, Kglilibic Ft./Bbl. Naphtha 1004,000 500-2, 000 Pressure, p.s.i.a 154500 15-35 Temperature, F 600-1, 400 700-1, 000

The volume of recycle gas necessary for admixture with the hydrocarbon reactant is readily determined in the usual manner from the A.S.T.M. boiling range curve. That is to say, the molecular weight of the hydrocarbon reactant, when said hydrocarbon reactant comprises a mixture of hydrocarbon capable of undergoing any one or all of the molecular conversions, enumerated hereinbefore as reforming conversions, is determined from an A.S.T.M. distillation and the boiling range curve derived from that data.

An advantage of the present invention over the prior art is readily discerned by a comparison of the yield of a gasoline of given octane rating produced in accordance with prior art practice wherein, due to the reduced velocity of the hydrocarbon reactant in the hydrocarbon reactant heating furnace and transfer line, the soaking time is increased above the maximum allowable with the result that thermal cracking and/ or thermal reforming occur, and the yield produced when reforming under more severe reforming conditions but in accordance with the principles of the present invention. Thus, a West Texas naphtha having a boiling range of about 200 to about 300 F. and an octane number (research clear 55: research plus 3 cc. TEL) of 75 when reformed over chromia-alumina beads under the conditions set forth in Table IV, was obtained at an increased yield of about 4' percent, representing an increased monetary return of about $600,000 per year (10,000 b.p.d. charge rate).-

Table IV Proposed Proposed Aviation Aviation Operation, Operation, Figure 1 Figure 2- Case C Case D Reactor (190 p.s.i.a., Counter-Current):

ulet Temp., F 1,055 1, 055 Outlet Temp., F 987 987 Average Temperature, F 1,004 1, 004 Space Velocity, V/Hr/V 0.35 0. 35 Recycle Ratio, Mols Gas/M01 Naph 12 12 Mols HflMol Naphtha 5.0 5.0 N aphtha Furnace:

Outlet Temp., F 930 930 Soaking Factor 0. 07 0. 07 Gas Added, Cubic Ft./Bbl. Naph 800 800 Recycle Furnace: Outlet Temp., F. 1,135 1, 137 Gasoline Yield, Vol. percent charge 82. 3 83.0 Gasoline Octane Number:

Research Clear 95 3 cc 102 102 Gasoline Loss Due to Thermal Conversion in Naphtha Furnace, Volume percent charge... 0. 1 0. 1 Gasoline Loss Due to Thermal Conversion in Recycle Furnace, Volume percent charge 0.8 0. 1 Total Gasoline Loss Due to Thermal Conversion in Naphtha and Recycle Furnaces, Volume percent charge 0. 9 0. 2

For convenience of comparison, the yields and source of loss when producing a gasoline having a 95. octane number (research clear) in a unit designed to produce a gasoline having an 84 number (research clear) are give in Table V.

Table V Aviation Opera- Design Prior tion according Motor Art to the-present Operating Conditions Gasoline Aviation invention Operation Operation Case 0 Case D Reactor (190 p.s.i.a.) (Countercurrent):

Inlet Temp., F 1,020 1, 055 1,055 1,055 Outlet Temp., F 950 987 987 Average Temp., F 964 1,005 1, 004 1, 004' Space Velocity, V./Hr./V 0. 7 0. 35 0. 35 0.35 Recycle Ratio:

Mols Recycle Gas/Mols Naphtha 6 12 12 12 Mols Hydrogen/Mols Naphtha 3. 0 4. 8 5. 0 5. 0 Naphtha Furnace:

Outlet Temp., F 930 930 930 930 Soaking Factor 0.07 0.20 0.07 0.07 Inert Fluid Added, Cubic Ft. Inert Gas/Bbls. Naphtha O 0 800 800 Recycle Furnace: Outlet Temp.,

F 1, 1, 120 1, 1, 137 Gasoline Yield:

Volume percent charge 92. 5 78.6 82. 3 83. 0 Octane Number:

(Research Clear) 84. 0 95 95 95 (Research, plus 3 cc.

TEL 94. 5 102 102 102 Loss Due to Thermal Conversion in Naphtha Furnace: Volume percent charge 0. 1 4. 2 0. 1 0. 1' Loss Due to Thermal Conversion in Recycle Furnace: Volume percent charge 0. 4 O. 4 0. 8' 0. 1' Total Loss Due to Thermal Conversion: Volume percent charge. 0. 5 4. 6 0. 9 0. 2 Decreased Loss of 95 O.N. Gas0- line, Minimizing Thermal Conversions in Naphtha and Recycle Furnace, Volume percent Char e 3. 7 4.4

It will be noted by those skilled in the art that in order to produce gasoline of higher octane rating than 84 when employing prior art principles of operation, that the inlet temperature, outlet temperature, and the average tem perature of the reactor were appreciably higher than the corresponding temperatures required to produce a gasoline of 84 octane number. It will be noted also that the space velocity when producing the gasoline of higher octane rating than 84 was reduced about 50 percent. Furthermore, it will be noted that when producing the gasoline at higher octane ratings than 84, the soaking factor in the naphtha heating furnace and transfer line was increased from about 0.07 to about 0.20, and that this increased soaking factor increased the loss in yield of gasoline of desired higher octane rating than 84, from 0.5 volume percent of the charge when producing motor gasoline under designed conditions to about 4.6 volume percent of the charge when producing an aviation gasoline of 95 octane number under prior art operating conditions. However, it will also be noted that when producing gasoline of the same octane rating, i.e., 95 O.N., in accordance with the principles of the present invention, the loss in yield suffered when operating in accordance with the prior art practice to produce 95 octane gasoline, is reduced from 4.6 to 0.9, a saving of 3.7 percent loss. This reduction in loss can be achieved by operating in accordance with the flow sheet, Figure 1 of the drawings of the present application. When operating in accordance with the flow sheet given in Figure 2, this loss in yield can be still further reduced to a loss of 0.2 volume percent of the charge or a reduction in loss of 4.4 percent. This is of considerable interest when operating in accordance with the flow sheet, Figure 2. The loss in yield is even less than the loss in yield when operating to produce motor gasoline under designed conditions. Thus, it is manifest that the present invention provides a method of reforming hydrocarbon reactants, and particularly naphthas, in a reforming unit designed to treat a maximum volume of charge stock under given conditions of reforming severity to yield a gasoline of given octane number to produce a gasoline of higher rating, for example aviation gasoline, wherein losses due to thermal conversions are minimized if not substantially eliminated.

I claim:

1. In the method of operating a hydrocarbon reactant heating zone and a hydrocarbon reactant transfer zone in conjunction with a reforming zone containing particleform solid reforming catalytic material, wherein a stream of hydrocarbon reactant is passed through and heated in a hydrocarbon reactant heating zone to a selected reforming temperature within a predetermined range of temperature, wherein the aforesaid heated stream of hydrocarbon reactant is passed through a transfer zone, and wherein the aforesaid heated stream of hydrocarbon reactant together with hydrogen-containing recycle gas is passed through a reforming zone at a predetermined space velocity in order to subject the aforesaid stream of heated hydrocarbon reactant to not more than a maximum predetermined soaking factor in the aforesaid hydrocarbon reactant heating zone and the aforesaid transfer zone, the improvement when the aforesaid maximum predetermined soaking factor is excessive by reason of at least one of (1) an increase in the aforesaid selected reforming temperature, (2) a decrease in the aforesaid space velocity, and (3) both an increase in the aforesaid selected reforming temperature and a decrease in the aforesaid space velocity which comprises introducing into the aforesaid stream of hydrocarbon reactant up-stream of the aforesaid hydrocarbon reactant heating zone inert fluid to reduce the aforesaid excessive soaking factor to at least the aforesaid maximum predetermined soaking factor.

2. The method of claim 1 wherein the hydrogen-containing recycle gas is heated to at least the selected reforming temperature but not higher than about 1200 F. in a second heating zone.

3. The method of claim 1 wherein a portion of the hydrogen-containing recycle gas is heated to at least the selected reforming temperature but not higher than about 1200 F. in a second heating zone, wherein the inert fluid is recycle gas substantially devoid of hydrocarbons having more than three carbon atoms, and wherein the total volume of recycle gas substantially devoid of hydrocarbons having more than three carbon atoms and the portion of recycle gas heated in the second heating zone is the amount of recycle gas required to provide the selected recycle gas to naphtha ratio.

4. The method of claim 1 wherein at least a portion of the inert fluid is hydrocarbons having more than three carbon atoms per molecule extracted from the recycle gas.

5. The method of claim 1 wherein the inert fluid is recycle gas substantially devoid of hydrocarbons having more than three carbon atoms in the molecule, wherein the hydrocarbon reactant is naphtha, and wherein the aforesaid inert fluid is mixed with the naphtha upstream of the naphtha heating zone in the proportion of about to about 4,000 cubic feet of said inert fluid per barrel of naphtha.

References Cited in the file of this patent UNITED STATES PATENTS 2,353,509 Schulze July 11, 1944 2,364,453 Layng et a1 Dec. 5, 1944 2,380,875 Schulze July 31, 1945 2,498,559 Layng et al Feb. 21, 1950 OTHER REFERENCES Intermittent and Fluid Catalytic Reforming of Naphthas, McGrath et al., pages 39 to 57, Progress in Petroleum Technology, published August 17, 1951, Amer. Chem. Soc., Washington, DC.

Claims

1. IN THE METHOD OF OPERATING A HYDROCARBON REACTANT HEATING ZONE AND A HYDROCARBON REACTANT TRANSFER ZONE IN CONJUCTION WITH A REFORMING ZONE CONTAINING PARTICLEFORM SOLID REFORMING CATALYTIC MATERIAL, WHEREIN A STREAM OF HYDROCARBON REACTANT IS PASSED THROUGH AND HEATED IN A HYDROCARBON REACTANT HEATING ZONE TO A SELECTED REFORMING TEMPERATURE WITHIN A PREDETERMINED RANGE OF TEMPERATURE, WHEREIN THE AFORESAID HEATED STREAM OF HYDROCARBON REACTANT IS PASSED THROUGH A TRANSFER ZONE, AND WHEREIN THE AFORESAID HEATED STREAM OF HYDROCARBON REACTANT TOGETHER WITH HYDROGEN-CONTAINING RECYCLE GAS IS PASSED THROUGH A REFORMING ZONE AT A PREDETERMINED SPACE VELOCITY IN ORDER TO SUBJECT THE AFORESAID STREAM OF HEATED HYDROCARBON REACTANT TO NOT MORE THAN A MAXIMUM PREDETERMINED SOAKING FACTOR IN THE AFORESAID HYDROCARBON REACTANT HEATING ZONE AND THE AFORESAID TRANSFER ZONE, THE IMPROVEMENT WHEN THE AFORESAID MAXIMUM PREDETERMINED SOAKING FACTOR IS EXCESSIVE BY REASON OF AT LEAST ONE OF (1) AN INCREASE IN THE AFORESAID SELECTED REFORMING TEMPERATURE, (2) A DECREASE IN THE AFORESAID SPACE VELOCITY, AND (3) BOTH AN INCREASE IN THE AFORESAID SELECTED REFORMING TEMPERATURE AND A DECREASE IN THE AFORESAID SPACE VELOCITY WHICH COMPRISES INTRODUCING INTO THE AFORESAID STREAM OF HYDROCARBON REACTANT UP-STREAM OF THE AFORESAID HYDROCARBON REACTANT HEATING ZONE INERT FLUID TO REDUCE THE AFORESAID EXCESSIVE SOAKING FACTOR TO AT LEAST THE AFORESAID MAXIMUM PREDETERMINED SOAKING FACTOR.