US2915455A

US2915455A - Combination catalytic reforming-catalytic dehydrogenation process

Info

Publication number: US2915455A
Application number: US511294A
Authority: US
Inventors: George R Donaldson
Original assignee: Universal Oil Products Co
Current assignee: Universal Oil Products Co
Priority date: 1955-05-26
Filing date: 1955-05-26
Publication date: 1959-12-01
Anticipated expiration: 1976-12-01

Description

United States Patent Office 2,915,455 Patented Dec. 1, 1959 COMBINATION CATALYTIC REFORMING-CATA- LYTIC DEHYDROGENATION PROCESS George R. Donaldson, North Riverside, Eli, assignor, by mesne assignments, to Universal Oil Products Company, Des Plaines, 111., a corporation of Delaware Application May 26, 1955, Serial No. 511,294 8 Claims. (Cl. 2&8-65) This invention relates to the catalytic conversion of hydrocarbons boiling within the gasoline range. It Is more specifically concerned with a novel combination of catalytic reforming, solvent extraction and catalytic dehydrogenation;

The recent developments in the automotive industry have increased the demand for high octane numbered gasolines and the petroleum industry has been striving to keep up with these demands. One process that has achieved great commercial acceptance is the catalytic reforming process. The term reforming is well known in the petroleum industry and refers to the treatment of gasoline fractions to improve the anti-knock characteristics thereof. A highly successful and economical reforming process is described in US. Patent No. 2,479,- 110, issued to Vladimir Haensel. However, the present reforming processes are all limited by decreasing yields at increasing octane numbers. There are also other limitations. For example, when a full boiling range straight-run gasoline or a relatively Wide boiling range naphtha is reformed in the presence of a catalyst that promotes dehydrogenation of naphthenes, dehydrocyclization of paraffins and hydrocracking of parafiins, relatively poor yields and considerable fouling of the catalyst are obtained when the operating conditions are selected to obtain large octane number appreciation. This apparently is due to the fact that the relatively severe operating conditions that must be maintained in order to satisfactorily upgrade some of the paraffinic constituents of the feed are too severe for some of the other constituents. The result is that an appreciable part of the feed stock is unnecessarily converted to gases and to catalyst carbon. I have invented a process which largely overcomes these objectionable features of the prior art reforming processes.

It is an object of the present invention to reform a full boiling range straight-run gasoline, or a relatively wide boiling fraction thereof, in such a manner that increased yields of reformate and longer catalyst life are obtained while producing a liquid product of the desired quality.

It is another object of the present invention to provide an improved combined operation which will effect an improvement in octane number from the straight chain or branched chain paraffins in the charge stock.

In one embodiment the present invention relates to a process which comprises subjecting hydrogen and a gasoline fraction to catalytic reforming in a reforming zone, introducing at least a portion of the efiluent from said reforming zone to a separation zone, separately withdrawing from said separation zone a predominantly aromatic fraction and a predominantly paraliinic fraction, introducing at least a portion of said predominantly paraffinic fraction to a fractionation zone, separately withdrawing from said fractionation zone at least a high boiling fraction and a low boiling fraction, subjecting at least a portion of said low boiling fraction to catalytic dehydrogenation in a dehydrogenation zone and recovering the effluent from said zone.

In another embodiment the present invention relates to a process which comprises subjecting hydrogen and a mixture of a gasoline fraction and a high boiling paraffinic recycle stock, prepared as hereinafter specified, to reforming in a catalytic reforming zone, fractionating the reformate in a stabilization zone to remove normally gaseous components therefrom, introducing the stabilized liquid fraction to a separation zone, separately Withdrawing from said separation zone a predominantly aromatic fraction and a predominantly paraflinic fraction, introducing said predominantly parafiinic fraction to a fractionation zone, separately Withdrawing from said fractionation zone at least a high boiling fraction and a low boiling fraction, recycling at least a portion of said high boiling fraction to said reforming'zone as said high boiling paraflinic recycle stock, passing at least a portion of said low boiling fraction to a catalytic dehydrogenation zone and therein subjecting said fraction to a dehydrogenation catalyst at dehydrogenating conditions and passing the efiluent from said dehydrogenation zone to said stabilization zone.

In a specific embodiment the present invention relates to a process which comprises subjecting hydrogen, a gasoline fraction and a high boiling paratfinic recycle stock, prepared as hereinafter set forth, to reforming in a reforming zone at a temperature of from about 600 F. to about 1000 F., in the presence of a catalyst comprising alumina, platinum, and combined halogen, fractionating the reformate in a stabilization zone to remove normally gaseous components therefrom, introducing the stabilized reformate to a selective solvent extraction zone wherein the aromatics are separated from the paraflins, separately withdrawing from said selective solvent extraction zone a predominantly aromatic extract and a predominantly paraifinic raffinate, introducing said raffinate to a fractionation zone, separately withdrawing from said fractionation zone at least a high boiling raffinate fraction and a low boiling rafiinate fraction, recycling at least a portion of said high boiling rafiinate fraction to said reforming zone, introducing said low boiling rafiinate fraction to a catalytic dehydrogenation zone and therein subjecting said low boiling raflinate fraction to a dehydrogenation catalyst at dehydrogenating conditions and passing the effluent from said dehydrogenation zone to said stabilization zone.

Briefly stated, my process comprises reforming a gasoline fraction in the presence of hydrogen and a reforming catalyst. It is a preferred feature of my invention that a high boiling parafiinic recycle stock, prepared from the effluent from the reforming zone as hereinafter set forth, be recycled to the catalytic reforming zone. Hydrogen is separated from the reforming zone eflluent and recycled to the reforming zone. The remaining liquid products are fractionated in a stabilization zone to stabilize them, that is to reject the normally gaseous hydrocarbons produced in the process, and the resultant stabilized liquid is separated in a separation zone to separate the aromatics therefrom. It is preferred that the separation be performed in a selective solvent extraction zone. The predominantly parafiinic fraction from the separation zone is preferably fractionated and at least a portion of the heavy fraction thereof is preferably recycled to the reforming zone. At least a portion of the low boiling portion of the predominantly paraffinic liquid fraction removed from the separation zone is subjected to a catalytic dehydrogenation conversion in the presence of a suitable dehydrogenation catalyst. The dehydrogenation conversion is at an elevated temperature and pressure to convert a substantial portion of the straight chain or slightly branched parafiins to 'olefins.

I have discovered, and my invention is based on this discovery, that the low boiling parafiins present in the efiluent from a catalytic reforming zone are not very much enhanced in octane number by subsequently treating these low boiling paraflins in a catalytic reforming zone. Therefore, it is not advantageous or economical to recycle the lower boiling paraffins to the catalytic reforming zone. Therefore, when the effluent from the catalytic reforming zone is separated in a separation zone into a predominantly paraffinic fraction and a predominantly aromatic fraction, it is preferred to fractionate the predominantly paraifinic fraction into at least a low boiling fraction and a high boiling fraction and to catalytically reform only the higher boiling fraction, preferably by recycling the same to the catalytic reforming zone. I have discovered that the low boiling fraction may be markedly increased in octane number by a catalytic dehydrogenation process performed on this lower boiling fraction. The efiluent from the catalytic dehydrogenation zone may be stabilized and combined with the aromatic-rich fraction from the separation zone to form a motor fuel of high octane number and excellent starting characteristics. In a preferred embodiment of my invention the effluent from the catalytic dehydrogenation zone is passed to a common stabilization-zone along with the effiuent from the catalytic reforming zone. In this manner of operation, the olefins produced in the process are removed along with the aromatics from the extractor and the light unconverted paraffins are recycled to the catalytic dehydrogenation zone while the heavy unconverted parafiins are recycled to the catalytic reforming zone.

An additional feature of my process is that mild processing conditions may be employed in the catalytic reforming step minimizing undesirable side reactions which otherwise reduce the yields of useful gasoline products. Reforming of the low octane number, high boiling paraffins in the reafiinate by recycling these parafi'ms to the catalytic reaction zone results in their being dehydrocyclicized to aromatics and/or their being converted to lower boiling paraflins without the excessive production of gaseous hydrocarbons that would result were these higher boiling parafiins substantially reacted in one pass in a reforming zone continued at conditions of high severity. High severity single pass operation is also not desirable from considerations of the chemical equilibria involved, as in such single pass operations the aromatics present in the product limit the extent to which such aromatics can be formed from naphthenes and paratfins. In contrast, however, the use of my process involves the removal of a substantial portion of the aromatics from the recycle charge to the reaction zone, which thus 'permits the formationof additional aromatics unrestricted by limitations of chemical equilibria.

The aromatics are separated from the parafiins and the naphthenes in the reformate for several reasons. One reason is that reforming in the presence of a high concentration of aromatics results in lower over-all yields of reformate presumably due to the conversion of aromatics to gaseous hydrocarbons and/or to hydrocarbons boiling above the gasoline range. Another reason is that high concentrations of aromatics in the reaction zone tend to result in a greater carbon deposition and consequently a shorter process period. Still another reason, which has hereinbefore been mentioned, is that high concentrations of aromatics in the reaction zone tend to suppress the dehydrogenation of naphthenes to aromatics and to suppress the dehydrocyclization of paraffins to aromatics, said dehydrogenation and said dehydrocyclization being equilibrium reactions. By lowering the amounts of low octane number paratfins from the final product, the end product is a reformate of high quality even though the charging stock has never been subjected to relatively severe operating conditions as previously were necessary to produce high quality reformate.

However, in the reforming process the aromatics in the charging stock, or the aromatics formed in the reaction zone tend to react with each other, probably in a condensation or polymerization reaction to form heavy polynuclear aromatics. These heavy polynuclear aromatics are undesirable in the reaction zone since it is these materials which are the hydrocarbonaceous materials or which form the heavy carbonaceous material on the catalyst which tends to deactivate the catalyst by coking the same. It is, therefore, preferred that these aromatics are removed from any recycle stock that is recycled to the reforming zone since otherwise these aromatics will readily react with each other in the reforming zone and deactivate and/or coke the catalyst.

As hereinbefore mentioned, I have discovered that the raffinate from a selective solvent extraction zone is not an entirely satisfactory material to recycle to the catalytic reforming zone since the lower parafiins in the raffinate are not substantially upgraded in octane number by subsequent catalytic reforming. I have also discovered that it is possible to catalytically dehydrogenate the lower boiling paraffins in the rafiinate thereby achieving sub stantial increases in octane number. The higher boiling paraftins in the rafi'inate may be recycled to the catalytic reforming zone. The effluent from the catalytic dehydrogenation zone may be recycled to the stabilization zone along with the effluent from the catalytic reforming zone.

The charge stocks that may be reformed in accordance With my process comprise hydrocarbon fractions that boil within the gasoline range and that contain naphthenes and paraffins. The preferred stocks are those consisting essentially of naphthenes and parafiins, although minor amounts of aromatics and even of'olefins also may be present. This preferred class includes straight-run gasoline, natural gasoline and the like. The gasoline fraction may be a full boiling range gasoline having an initial boiling point within the range of from about 50 F. to about F., and an end boiling point within the range of from about 350 F. to about 425 F., or it may be a selected fraction thereof which may be a higher boiling fraction commonly referred to as naphtha and having an initial boiling point within the range of from about F. to about 250 F., and an end boiling point within the range of from about 350 F. to about 425 F. Mixtures of the various gasolines and/or gasoline fractions may also be used, and thermally cracked and/ or catalytically cracked gasolines may also be used as charging stock, however, when these unsaturated gasoline fractions are used, it is preferred that they be used in admixture with a straight-run or natural gasoline fraction, or else hydrogenated prior to use as charging stock for my process.

The catalysts that may be used in the catalytic reforming step of my invention comprise those reforming catalysts that promote dehydrogenation of naphthenic hydrocarbons and hydrocracking of paraffinic hydrocarbons. Starting with a paraffinic hydrocarbon, from a yield-octane standpoint it is preferable to upgrade the parafiinic hydrocarbon by dehydrocyclicizing the same to an aromatic than by cracking the paraffinic hydrocarbon. Since the recycle rafiinate to the reforming zone consists predominantly of paraffinic constituents it is best 'to upgrade this recycle stream by dehydrocyclization. Therefore, it is preferred that the catalyst in the reforming zone be such that it has a substantial amount of dehydrocyclization activity. A satisfactory catalyst comprises a platinum-alumina-silica catalyst of the type described in U.S. Patent No. 2,478,916, issued August 16, 1949. A preferred catalyst comprises a platinum-alumina-combined halogen catalyst of the type described in U.S. Patent No. 2,479,109, issued August 16, 1949. Other catalysts such as molybdena-alumina, chromia-alumina,

and platinum on a cracking catalyst base may be used. As hereinbefore mentioned, it is preferred that the catalyst has substantial dehydrocyclicizing activity. I have found that catalysts of the platinum-alumina-combined halogen type, wherein the halogen content lies within the range of from about 0.1% to about 3% by weight of thefinal catalyst, especially those that contain about 0.01% to about 1% by weight of platinum and from about 0.1% to about 1% combined fluorine or those that contain about 0.1% to about 3.0% combined chlorine are especially effective and economical in my process because of the long life they exhibit, and also they promote isomen'zation reactionsof both paraflins and naphthenes and paratfin dehydrocyclization reactions as well as the naphthene dehydrogenation and paraffin hydrocracking reactions.

The operating conditions maintained in the catalytic reforming step of my process should be such that substantial conversion of naphthenes to aromatics and relatively mild hydrocracking of parafiins are induced. Further the operating conditions should be such that there is substantial conversion of paraffinic compounds to aromatics by dehydrocyclization. It is also preferred that process conditions be used which result in only minor amounts of olefins being present in the effluent from the catalytic reforming zone. -When employing platinumalnmina-combined halogen catalyst the reforming process will be effected at a temperature within the range of from about 600 F. to about 1000 F., pressure within the range of from about 50 to about 1000 pounds per square inch, and a weight hourly space velocity of from about 0.5 to about 20. The weight hourly space velocity is defined as the Weight of oil, per hour per weight of catalyst in the reaction zone. It is preferred that the reforming reaction be conducted in the presence of hydrogen. The hydrogen present in the reaction zone will be within the range of from about 0.5 to about 20 mols of hydrogen per mol of hydrocarbon.

The efiiuent from the catalytic reforming zone is usually passed to a stabilizer. In a preferred embodiment of this invention the effluent from the catalytic dehydrogenation zone is also passed to the same stabilizer. The stabilization effects the separation of the normally gaseous material which comprises hydrogen, hydrogen sulfide, ammonia, and hydrocarbons containing from one to four carbon atoms per molecule, from the normally liquid hydrocarbons. The effluent from the stabilization zone is then passed to a selective solvent extraction zone. An olefin-rich-aromatic-rich extract stream is removed from the solvent extraction zone and a predominantly paraffinic stream is separately removed from the solvent extraction zone.

The separation of an aromatic-rich-olefin-rich fraction may be accomplished in any conventional manner such as solvent extraction, solid absorption, fractional crystallization, mechanical separation, etc. However, the solvent extraction process is particularly preferred in the present invention since its use generally produces a rafiinate most suitable for catalytic reforming.

Solvent extraction processes are used to separate certain components in amixture from other components thereof by a separation process based upon a difference in solubility of the components in a particular solvent. It is frequently desirable to separate various substances by solvent extraction when the substances to be separated have similar boiling points, are unstable at temperatures at which fractionation is effected, form constant boiling mixtures, etc. It is particularly desirable to separate aromatc hydrocarbons by solvent extraction because a petroleum fraction is normally a continuous mixture of hydrocarbons whose boiling points are extremely close together and because the petroleum fraction contains numerous cyclic compounds which tend to form constant boiling or azeotropic mixtures. As hereinbefore stated, the basis of a solvent extraction separation is the difference in solubility in a given solvent of one of the substances to be separated from the other. It may, therefore, be seen that the more extreme this difference, the easier the separation will be, and an easier separation reflects itself process-wise, in less expensive equipment and greater yields per pass in the use of processing equipment as well as in higher purity of product.

A particularly preferred solvent for separating aromatic hydrocarbons from non-aromatic hydrocarbons is a mixture of water and a hydrophilic organic solvent. Such a solvent may have its solubility regulated by adding more or less water. Thus, by adding more water to the solvent, the solubility of all components in the hydrocarbon mixture are reduced, but the solubility difference between the components is increased. This effect is reflected process-Wise in less contacting stages required to obtain a' given purity of product, however,

' a greater throughput of solvent must be used in order to obtain the same-amount of material dissolved.

As hereinbefore stated, the solvent to be used in this invention is preferably a mixture of' a hydrophilic organic solvent and water, wherein the amount of Water contained in the mixture is selected to regulate the solubility in the solvent of the materials to be separated. Suitable hydrophilic organic solvents include alcohol, glycols, aldehydes, glycerine, phenol, etc. Particularly preferred solvents are diethylene glycol, triethylene glycol,

dipropylene glycol, tripropylene glycol, and mixtures thereof containing from about 1% to about 20% by Weight of Water. Other hydrophilic substances as sulfur dioxide, etc. may be used.

In classifying hydrocarbon and hydrocarbon type com pounds according to increasing solubility in such a solvent, it is found that the solubility of the various classes increases in the following manner: the least soluble are the paraffins followed in increasing order of solubility by naphthenes, olefins, diolefins, acetylenes, sulfur, nitrogen, and oxygen-containing compounds and aromatic hydro-carbons.

The solubility difference between parafiins and olefins is greater than the solubility difference between olefins and aromatic hydrocarbons, that is when comparing components of approximately equal boiling points. It, therefore, is possible to operate the solvent extraction process so that the olefins and aromatics are dissolved in the solvent while the parafiins remain in the raffinate phase. The extract phase from the separation process therefore will be olefin-rich and aromatic-rich.

The paraflinic compounds also differ in their relative solubility in the solvent. The solubility appears to be a function of the boiling point of the paraffin, with the lower boiling or lighter parafiins being more soluble than the higher boiling or heavier parafiins. Therefore, when heavy paraflins are dissolved in the solvent, they may be displaced from the solvent by adding lighter paraflins thereto. In an embodiment of this invention it is preferred to recycle the heavier paraffins to the catalytic reforming zone and, therefore, a light parafiin is charged to the extraction zone to displace the heavier paraflins from the solvent into the raflinate phase. In another embodiment a light olefinic fraction may be charged to the extraction column to displace the paraffins from the solvent into the raflinate.

The predominantly paraflinic fraction from the separation zone, preferably a rafiinate from a solvent extraction zone, is subjected to a fractionation to fractionate the raffinate into at least a high boiling fraction and a low boiling fraction. The raifinate may contain components which are high enough in octane number and low enough in boiling point so that they need not be chanced in octane number and it is, therefore, preferred that a light fraction be recovered from the raffinate and recovered as product or recycled to the solvent extraction zone as reflux on the extractor. Usually the isohexane and lighter fraction is not improved in octane number when catalytically dehydrogenated and, therefore, it is preferred that the isohexane and lighter fraction be removed from the raffinate before the light raffinate is dehydrogented in the catalytic dehydrogenation zone. It is to be understood, however, that the isohexane and lighter fraction may be passed to the catalytic dehydrogenation zone with the light fraction of the raflinate that is to be catalytically dehydrogenated.

The r'afiinate from the extraction zone may also-contain components which are heavier than are suitable for reforming and which may be removed by fractionation. For example, components boiling above about 425 F., and frequently above about 400 F. are generally not suitable for catalytically reforming since they tend to readily deactivate the catalyst. It is accordingly preferred to separate the 400 F. and higher fraction by fractionation. Therefore, it is the fraction boiling within the range of from about normal hexane or 156 F. to about 400 F. which is most suitable for reforming, and in accordance with the present invention the lower boiling fraction of this 156 F.400 P. fraction is most suitably treated by catalytic dehydrogenation while the higher boiling fraction of the 156 F.400 P. fraction is preferably recycled to the catalytic reforming zone. The exact point at which the raflinate is divided into the lower boiling fraction and the higher boiling fraction will vary with the particular raflinate, however, generally the end point of the low boiling fraction will be within the range of from about 225 F. to about 325 F. The initial boiling point of the heavy fraction should correspond to the end point of the light fraction, that is it will generally be the same and will be within the range of from about 225 F. to about 325 F.

As hereinbefore mentioned, the heavy portion of the raffinate is preferably recycled to the catalytic reforming zone. The light portion of the rafiinate, that is the fraction having an end point within the range of from about 225 F. to about 325 F. is subjected to a catalytic dehydrogenation treatment in the presence of a suitable dehydrogenation catalyst. The catalytic dehydrogenation is at dehydrogenating conditions, that is at a temperature, pressure and time sufiicient to convert a substantial portion of the paraifins in the light fraction of the rafiinate to olefins. The pressure is within the range of from about 50 to about 2000 pounds per square inch, the temperature is within the range of from about 200 F. to about 1000 F. The low boiling portion of the raftinate is subjected to these pressures and temperatures for a time suificient to convert a substantial portion of the paraffins to olefins. The weight hourly space velocity usually is within the range of from about 0.5 to about 20.

Any suitable dehydrogenation catalyst may be used. The preferred catalysts for this invention are characterized by the use of a particular group of composite catalytic materials which employ as their base certain refractory oxides and silicates which in themselves may have some slight specific catalytic ability in the dehydrogenating reactions, but which are greatly improved in this respect by the addition of certain promoters or secondary catalysts in minor proportions which comprise the elements and/or compounds and preferably the oxides of the elements in the left-hand columns of groups IV, V, and VI of the periodic table. Group VIII metals are also suitable components of the catalyst. These active compounds and promoters which are used in the catalyst composite of the present invention include generally compounds and/ or the metals and particularly platinum and palladium and the oxides of chromium, molybdenum, tungsten, uranium, vanadium, and cerium. The base supporting materials for these compounds are preferably of a rugged and refractory character, capable of withstanding the severe use to which the catalysts are put in regard to temperature during service and in regeneration by means of air or other oxidizing gas mixtures after Magnesium oxide Aluminum oxide Bauxite Bentonite clays Montmorillonite clays The effluent 'from'thecatalytic dehydrogenation zone is subjected to 'stabilization to separate the normally gaseous 'components'therefrom. In a preferred embodiment of this invention the effluent from the catalytic dehydrogenation zone is stabilized along with the efiiuent from the catalytic. reforming zone, that is a common stabilization zone is used. A portion of the stabilized material removed from the stabilization zone may be combinedwith one or'more of the product streams of the process. vHowever, at least a portion is passed to the selective solvent extraction zone. At least two streams are removed from the selective solvent extraction zone. One stream being the. predominantly paraffinic stream and the second stream containing the bulk of the aromatics and the bulk of the olefinic materials.

Additional features and advantages of my process will be apparent fromthe following description of the accompanying drawing which illustrates a particular method for conducting a gasoline upgrading operation in accordance with the present invention.

Referring now to'the drawing a straight-run gasoline fraction having an initial boiling point of 200 F. and an end point of 400 F. is passed through line 1, is picked up by pump 2, and discharged through line 3 containing valve 4 and then. through line 5. A'heavy raftinate recyclestrea'm in line 8, prepared as hereinafter specified, and a hydrogen-rich gas stream in line 7 mix with the charge in 'line 5 and the mixture in line 6 is passed into heater 9 wherein the combined stream is heated to a temperature of 910 F. The heated combined stream is withdrawn from heater 9 by way of line 10 and passes into reforming reactor 11.

Reforming reactor 11 contains a bed of cylindrical catalyst of approximately A; inch length and inch in diameter containing 0.4% platinum, 0.5% combined fluorine, and 0.2% by weight of combined chlorine. The pressure in the reactor is 650 pounds per square inch, the weight hourly space velocity is 2.5 and the hydrogen to hydrocarbon mol ratio is 8 to 1. During the passage of the charge stock through reactor 11 the bulk of the naphthenes containing six or more carbon atoms per molecule are dehydrogenated to the corresponding aromatics and a portion of the paraffins are hydrocracked to lower boiling paraffins. Some isomerization of the parafiins also takes place, this reaction being of particular importance in the isomerization of normal hexane as this hydrocarbon is of relatively low octane number and is not readily dehydrocyclicized. The important octane number increasing reaction of the dehydrocyclization also occurs in reactor 11 at these conditions. By this reaction a substantial portion of the parafiins are converted to aromatics. This reaction is extremely important in increasing the octane number of the paraffins which are recycled to the reforming reactor through line 8. The conditions in the reforming zone or reactor 11 are such that there are substantially no olefinic hydrocarbons produced. The effluent from reactor 11 passes through line 12, cooler 13, line 14, and into separator 15. Hydrogen is withdrawn from the top of receiver 15 through line 16. Excess hydrogen may be withdrawn through line 17 containing valve 18. At least a portion of the hydrogen in line 16 passes through line 19, is picked up by compressor 20 and discharged into line 7.

The liquid hydrocarbons, comprising the reformate and the bulk of the normally gaseous hydrocarbons pro- "duced in the process are withdrawn from rece ver 15 through line 21 and passed into fractionator or stabilizer 30. In a preferred embodiment of the invention, valve 86 on the efliuent line 85 from catalytic dehydrogenator 81 is maintained in a closed position and valve 88 on line 87 is maintained in an open position. Therefore, the etfiuent from the dehydrogenating reactor in line 87 combines with the reformatein line 21 and the combined stream in line 22 is passed into fractionator or stabilizer 30. Normally gaseous hydrocarbons are removed overhead through line 31. In stabilizer 30 the normally gaseous material, which includes hydrogen, ammonia, hydrogen sulfide, and hydrocarbon gases containing from one to four carbon atoms per molecule, is separated from the hydrocarbon liquid comprising aromatic hydrocarbons and parafiinic hydrocarbons.

The gaseous material passes overhead through line 31 into cooler 32 wherein a portion of the material is condensed and the entire stream passes through line 33 into receiver 34. In receiver 34 the liquid phase and the gas phase of the overhead material separate. The gases pass through line 41 from which they may be vented to the atmosphere or otherwise used. The stabilizer has heat provided thereto by reboiler 38 and connecting

lines

37 and 39. The conditions in the stabilizer 30 are usually such that 0.; and lighter components are removed as overhead, however, the gasoline therein may be cut deeper, that is C and/or C hydrocarbons may be removed overhead through line 31. It is contemplated that the stabilizer 30 and receiver 34 will operate at a sufficient pressure to liquefy at least a portion of the overhead material so that a liquid stream may be available to improve the separation in stabilizer 30. The liquid reflux passes from receiver 34 through line 35 into an upper portion of stabilizer 30. Liquid in receiver 34 may also be withdrawn through line 36.

The stabilizer bottoms, which comprise paraflinic, olefinic, and aromatic hydrocarbons, are withdrawn through line 40 and introduced into a lower portion of extractor 50. In extractor 50 the hydrocarbon material rises and is countercurrently contacted at an elevated temperature in the liquid phase with a descending stream of a selective solvent. In this embodiment 96% diethylene glycol and 4% water is used as the solvent. Water is introduced through line 42 containing valve 43. The diethylene glycol enters the upper portion of extractor 50 through line 65. As hereinbefore mentioned the water is added to increase the selectivity of the solvent in line 65. The

average temperature in the extractor is maintained at about 295 F. The pressure is maintained at 125 pounds per square inch.

As a result of the countercurrent contact of the selective solvent and hydrocarbon stock, the aromatic hydrocarbons and the olefinic hydrocarbons maintained in the charge stock introduced through line 40 are selectively dissolved in the solvent thereby forming an extract stream 52 containing the bulk of the aromatic hydrocarbons and the bulk of the olefinic hydrocarbons and a predominantly paraflinic raflinate stream 51 containing aflins passes overhead through line 61 and may be' recovered as product or subjected to a further rectification or purification step. Heat is provided for the stripping operation by reboiler 63 and connecting

line

62 and 64. The solvent stream is taken from the bottom of stripper 10 60 through line 65 and is passed into the ripper pardon of extractor 50.

The raffinate stream in line 51 is introduced into fractionator 70. A portion of the stream in line 51 may be withdrawn as product through line 55 containing valve 56. A light fraction is removed overhead through line 71, passes through cooler 72, line 73, and into receiver 74. A portion of the liquid material in receiver 74 is used as reflux and is passed through line 75 into an upper portion of fractionator 70. Another portion of the liquid material in receiver 74 is withdrawn through line 76 and introduced to dehydrogenation reactor 81. A portion of the stream in line 76 may be withdrawn through line 78 containing valve 79. In another embodiment of the present invention, not herein illustrated, a light overhead fraction, preferably an isohexane and lighter fraction is removed from the upper portion of fractionator 70, and the light fraction to be charged to catalytic dehydrogenator 81 is withdrawn from an intermediate portion of the upper-half of the fractionator 70. The isohexane and lighter fraction removed as overhead from fractionator 70 is preferably used as reflux to a lower section of extractor 50.

A heavy fraction, that is a fraction boiling above about 400 F. is withdrawn from the bottom of fractionator 70 through line 66. Heat is provided for the fractionation by reboiler 68 and connecting lines 67 and 69. A heavy rafi'inate fraction is withdrawn near the bottom of fractionator 76) through line 8 and this heavy rafiinate fraction is preferably recycled through line 8 and eventually-passes through reforming reactor 11.

The light raffinate fraction in line 76 is introduced to heater 77 wherein it is raised to the desired temperature of about 800 F. The heated stream is withdrawn from heater 77 by way of line 80 and passes into catalytic dehydrogenator 81. Catalytic dehydrogenator 81 contains a bed of granular catalyst of approximately inch average diameter containing alumina and 10% by weight of chromium oxide (Cr O The pressure in the reactor is 100 pounds per square inch, the Weight hourly space velocity is 5.0. During the passage of the charge stock through reactor 81 a substantial amount of the parafiins in the charge is converted to olefins.

The resulting catalytically dehydrogenated stream passes from reactor 81 through line 82, passes through cooler 83 and then through line 84. As hereinbefore mentioned, valve 86 in line is preferably maintained in the closed position While valve 88 in line 87 is maintained in an open position thereby introducing the efliuent from reactor 81 into stabilizer 30. In another embodiment of the invention, herein illustrated, valve 88 is maintained in a closed position and valve 86 is maintained in an open position. In this operation the catalytically dehydrogenated stream in line 84 passes through line 85 containing valve 86 and thence into stabilizer 90.

-Normally gaseous hydrocarbons are removed overhead through line 91, these hydrocarbons comprising hydrocarbon gases containing from one to four carbon atoms per molecule. The gaseous material passes overhead through line 91 into cooler 92 wherein a portion of the material is condensed and the entire stream passes through line 93 into receiver 94. In receiver 94 the liquid phase and the gas phase separate. The gases pass through line 95 from which they may be vented to the atmosphere or otherwise used. The gases in line 95 contain a substantial amount of butenes and therefore the stream, after a subsequent purification, may be charged to a polymerization or alkylation process. It is contemplated that the stabilizer will operate at a suflicient pressure to liquefy at least a portion of the overhead material so that a liquid stream may be available as reflux to improve the separation in stabilizer 90. The liquid reflux passes from re ceiver 94 through line 96 and into an upper portion of stabilizer 90. The stabilizer has heat provided thereto by reboiler 98 and connecting

lines

97 and 99. The

num, 0.5% fluorine, and 0.1% chlorine.

a manac stabilizer bottoms, which comprise substantial amounts of olefinic hydrocarbons are withdrawn throughline 100. Stream 100 and stream 61 may be combined to give a high octane number gasoline having excellent starting characteristics.

The following example is given to further illustrate my invention but is not given for the purpose of unduly limiting the generally broad scope of said invention.

Example A straight-run naptha having an initial boiling point of 190 F. and an end boiling point of 398 F. is reformed by passing the fraction through a catalytic reactor tube located in an electrically heated furnace. The tube is filled with a catalyst containing alumina, 0.3% plati- Hydrogen is also introduced into the reaction zone. A heavy rafiinate fraction, prepared as hereinafter set forth, having an initial boiling point of 250 F. and an end point of 400 'F. is also passed to the reaction zone along with the naphtha fraction and hydrogen. The reforming conditions maintained in the reactor are an average catalyst temperature of 880 F., a pressure of 500 pounds per square inch, a weight hourly space velocity of 2.5, and a hydrogen to hydrocarbon mol ratio of :1.

The effluent from the reactor as well as the effluent from the catalytic dehydrogenator, as hereinafter described, are stabilized in a fractionating column by removing C and lighter components. The stabilized product is passed to the lower portion of an extraction column. The hydrocarbon liquid is pumped into the extraction column, rises and is countercurrently contacted with a stream of 97% diethylene glycol and 3% water. The extractor is maintained at a temperature of 295 F., 100 pounds per square inch pressure, and a 4:1 solvent to feed ratio.

The extract phase containing the bulk of the aromatic and olefinic hydrocarbons is removed from the bottom of the extraction column and passed to a-stripper in which the aromatics and olefins are separated from the solvent by a steam stripping operation. The raffinate is removed from the top of the extractor and is passed to a fractionator. The rafiinate is fractionated into three fractions: (1) I.B.P.250 F., (2) 250 F.400 F., and (3) 400 F.E.P. The 250 F.-400 P. fraction is recycled direct to the reforming reactor. The I.B.P.-250 P. fraction is passed to catalytic dehydrogenator maintained at 100 pounds per square inch and 875 F. The weight hourly space velocity is 5.0. The effluent from the catalytic dehydrogenator is stabilized and analyzed. The catalytically dehydrogenated gasoline contains a substantial amount of olefins and is higher in octane number than the charge to the catalytic dehydrogenator. The catalytically dehydrogenated. gasoline may be stabilized andblended withthe400 F. E.P. fraction and the aromatics and olefins separated from the stripper. The blendis a motor fuel of high octane number and excellent starting characteristics. In this example the efliuent from the catalytic dehydrogenator is passed to the stabilizer along with the effluent from the catalytic reforming zone. In this manner the olefins are removed along with the aromatics from the extraction zone.

I claim as my invention:

1. A process which comprises subjecting hydrogen and a gasoline fractionto catalytic reforming in a reforming zone, introducing at least a portion of the efliuent from said reforming zone to a separation zone, separately withdrawing from said separation zone a predominantly aromatic fraction and a predominantly parafiinic fraction containing hydrocarbons boiling between about 156 and about 400 F., introducing at least a portion of said predominantly paraflinic fraction to a fractionation zone, separately withdrawing from said fractionation zone at least a high boiling fraction having an end boiling point of about 400 F. and a low boiling fraction having an end boiling point between about 225 and about 325 F., recycling at least a portion of said high boiling fraction to said reforming zone, and subjecting at least a portion of said low boiling fraction to catalytic dehydrogenation in a dehydrogenation zone and recovering the effluent from said dehydrogenation zone at a temperature of from about 200 F. to about 1000 F., a pressure of from about 50 to about 2000 pounds per square inch and a weight hourly space velocity of from about 0.5 to about 20 to convert paraffins to olefins.

2. A process which comprises subjecting hydrogen and a mixture of a gasoline fraction and a high boiling parafiinic recycle stock, prepared as hereinafter specified, to reforming in a catalytic reforming zone, fractionating the reformate in a stabilization'zone to remove normally gaseous components therefrom, introducing the stabilized liquid fraction to a separation zone, separately withdrawing from said separation zone a predominantly aromatic fraction and a predominantly parafiinic fraction containing hydrocarbons boiling between about 156 and about 400 F., introducing said predominantly paraffinic fraction to a fractionation zone, separately withdrawing from said fractionation zone at least a high boiling fraction having an end boiling point of about 400 F. and a low boiling fraction having an end boiling point between about 225 and about 325 F., recycling at least a portion of said high boiling fraction to said reforming zone as said high boiling parafiinic recycle stock, passing at least a portion of said low boiling fraction to a catalytic dehydrogenation zone and therein subjecting said fraction-to a dehydrogenation catalyst at a temperature of from about 200 F. to about 1000 F., a pressure of from about 50 to about 2000 pounds per square inch and a weight hourly space velocity of from about 0.5 to about 20 to convert paraffins to olefins, and recovering the efiluent from said dehydrogenation zone.

3. A process which comprises subjecting hydrogen and a mixture of a gasoline fraction and a high boiling paraffinic recycle stock, prepared as hereinafter specified, to reforming in a catalytic reforming zone, fractionating the reformate in a stabilization zone to remove normally gaseous components therefrom, introducing the stabilized liquid fraction to a separation zone, separately withdrawing from said separation zone a predominantly aromatic fraction and a predominantly parafiinic fraction containing hydrocarbons boiling between about 156 and about 400 F., introducing said predominantly paraffinic fraction to a fractionation zone, separately withdrawing from said fractionation zone at least a high boiling fraction having an end boiling point of about 400 F. and a low boiling fraction having an end boiling point between about 225 and about 325 F., recycling at least a portion of said high boiling fraction to said reforming zone as said high boiling parafiinic recycle stock, passing at least a portion of said low boiling fraction to a catalytic dehydrogenation zone and therein subjecting said fraction to a dehydrogenation catalyst at a temperature of from about 200 F. to about 1000 F., a pressure of from about 50 to about 2000 pounds per square inch and a weight hourly space velocity of from about 0.5 to about 20 to convert paraflins to olefins, and passing the effluent from said dehydrogenation zone to said stabilization zone.

4. A process which comprises subjecting hydrogen, a gasoline fraction and a high boiling paraffinic recycle stock, prepared as hereinafter set forth, to reforming in a reforming zone at a temperature of from about 600 F. to about 1000 F., in the presence of a catalyst comprising alumina, platinum, and combined halogen, fractionating the reformate in a stabilization zone to remove normally gaseous components therefrom, introducing the stabilized reformate to a selective solvent extraction zone wherein the aromatics are separated from the paraffins, separately withdrawing from said selective solvent extraction zone a predominantly aromatic extract and a predominantly parafiinc raffinate containing hydrocarbons boiling between about 156 and about 400 F., introducing said raffinate to a fractionation zone, separately withdrawing from said fractionation zone at least a high boiling raffinate fraction having an initial boiling point within the range of from about 225 F. to about 325 F. and a low boiling rafiinate fraction having an end point within the range of from about 225 F. to about 325 F., recycling at least a portion of said high boiling rafiinate fraction to said reforming zone, introducing said low boiling rafiinate fraction to a catalytic dehydrogenation zone and therein subjecting said low boiling raflinate fraction to a dehydrogenation catalyst at a temperature of from about 200 F. to about 1000 F., a pressure of from about 50 to about 2000 pounds per square inch and a weight hourly space velocity of from about 0.5 to about 20 to convert parafiins to olefins, and recovering the effluent from said dehydrogenation zone.

5. A process which comprises subjecting hydrogen, a gasoline fraction and a high boiling parafiinic recycle stock, prepared as hereinafter set forth, to reforming in a reforming zone at a temperature of from about 600 F. to about 1000 F., in the presence of a catalyst comprising alumina, platinum, and combined halogen, fractionating the reformate in a stabilization zone to remove normally gaseous components therefrom, introducing the stabilized reformate to a selective solvent extraction zone wherein the aromatics are separated from the paraffins, separately withdrawing from said selective solvent extraction zone a predominantly aromatic extract and a predominantly parafiinc rafiinate containing hydrocarbons boiling between about 156 and about 400 F., introducing said raffinate to a fractionation zone, separately withdrawing from said fractionation zone at least a high boiling rafiinate fraction having an end boiling fraction of about 400 F. and a low boiling raffinate fraction having an end boiling point between about 225 and about 325 F, recycling at least a portion of said high boiling raffinate fraction to said reforming zone, introducing said low boiling rafiinate fraction to a catalytic dehydrogenation zone and therein subjecting said low boiling raftinate fraction to a dehydrogenation catalyst at a temperature of from about 200 F. to about 1000 F., a pressure of from about 50 to about 2000 pounds per square inch and a weight hourly space velocity of from about 0.5 to about 20 to convert parafiins to olefins, and passing the effiuent from said dehydrogenation Zone to said stabilization zone.

6. A hydrocarbon conversion process which comprises catalytically reforming a gasoline fraction in a first con- 5 tionating said rafiinate to separate therefrom a heavy fraction having an end boiling point of about 400 F. and a light fraction having an end boiling point between about 225 F. and about 325 F., subjecting said light fraction to catalytic dehydrogenation in a second conversion zone at a temperature of from about 200 F. to about 1000 F., a pressure of from about 50 to about 2000 pounds per square inch and a weight hourly space velocity of from about 0.5 to about 20 to convert paraffins to olefins, and supplying said heavy fraction to said first conversion zone.

7. A hydrocarbon conversion process which comprises catalytically reforming a gasoline fraction in a first conversion zone, subjecting the resultant reformed gasoline products to solvent extraction to separate the same into 20 an aromatic extract and a parafiinic raflinate, fractionating said rafiinate to separate therefrom a heavy fraction boiling from about 250 F. to about 400 F. and a lighter fraction having an end boiling point around 250 F, supplying said heavy fraction to said first conversion zone, catalytically dehydrogenating said lighter fraction in a second conversion zone at a temperature of from about 200 F. to about 1000 F., a pressure of from about 50 to about 2000 pounds per square inch and a weight hourly space velocity of from about 0.5 to about 30 20 to convert paraifins to olefins, commingling resultant olefins with said aromatic extract and recovering the mixture.

8. The process of claim 7 further characterized in that said olefins are commingled with said aromatic extract by supplying normally liquid conversion products from said second zone to the solvent extraction step.

References Cited in the file of this patent UNITED STATES PATENTS 2,409,695 Laughlin Oct. 22, 1946 2,479,110 Haensel Aug. 16, 1949 2,697,684 Hemrninger et a1. Dec. 21, 1954 2,740,751 Haensel et a1. Apr. 3, 1956 2,767,124 Myers Oct. 16, 1956 OTHER REFERENCES Relation of Properties to Molecular Structure for Petroleum Hydrocarbons, by Cecil E. Boord, Progress in Petroleum Chemistry, pages 365 to 370, American Chem. Society Washington, D. C., Aug. 7, 1951.

Claims

1. A PROCESS WHICH COMPRISES SUBJECTING HYDROGEN AND A GASOLINE FRACTION TO CATALYTIC REFORMING IN A REFORMING ZONE, INTRODUCING AT LEAST A PORTION OF THE EFFLUENT FROM SAID REFORMING ZONE TO A SEPATRATION ZONE, SEPARATELY WITHDRAWING FROM SAID SEPARATION ZONE A PREDOMINANTLY AROMATIC FRACTION AND A PREDOMINANTLY PARAFFINIC FRACTION CONTAINING HYDROCARBONS BOILING BETWEEN ABOUT 156* AND ABOUT 400*F., INTRODUCING AT LEAST A PORTION OF SAID PREDOMINANTYLY PARAFFINIC FRACTION TO A FRACTIONATION ZONE, SEPARATELY WITHDRAWING FROM SAID FRACTIONATION ZONE, AT LEAST A HIGH BOILING FRACTION HAVING AN END BOILING POINT OF ABOUT 400*F. AND A LOW BOILING FRACTION HAVING AN END BOILING POINT BETWEEN ABOUT 225* AND ABOUT 325*F., RECYCLING AT LEAST A PORTION OF SAID HIGH BOILING FRACTION TO SAID REFORMING ZONE, AND SUBJECTING AT LEAST A PORTION OF SAID LOW BOILING FRACTION TO CATALYTIC DEHYDROGENATION IN A DEHYDROGENATION ZONE AND RECOVERING THE EFFLUENT FROM SAID DEHYDRATION ZONE AT A TEMPERATURE OF FROM ABOUT 200*F. TO ABOUT 1000*F., A PRESSURE OF FROM ABOUT 50 TO ABOUT 2000 POUNDS PER SQUARE INCH AND A WEIGHT HOURLY SPACE VELOCITY OF FROM ABOUT 0.5 TO ABOUT 20 TO CONVERT PARAFFINS TO OLEFINS.