US3001927A - Conversion of hydrocarbon distillates to motor fuel mixtures rich in aromatic and isoparaffins - Google Patents

Description

Sept. 26, 1961 c. G. GERHOLD ET AL 3,001,927

CONVERSION OF HYDROCARBON DISTILLATES TO MOTOR FUEL MIXTURES RICH IN AROMATIC AND ISOPARAFFINS Filed Nov. s, 1958 k k k 4 w (o Q a Q a s Q 5 5 Q g g 4 B o o A \A 3 1-5- i I\ E 4 ighf n-Paraff/n $23 as f v- V 0) m v (9 gym 3 o FQYQ J Stripping Zone T IKE Reforming Zone IV VE/V T095:

Clarence 6. Gama/d Donald B. Brough/on A TTORNE rs United State Patent F 3,001,927 CONVERSION OF HYDROCARBON DISTILLATES TO MOTOR FUEL MIXTURES RICH IN ARO- MATIC AND ISOPARAFFINS Clarence G. Gerhold, Palatine, and Donald B. Broughton,

Chicago, 111., assignors, by mesne assignments, to Universal Oil Products Company, Des Plaines, Ill., a corporation of Delaware Filed Nov. 3, 1958, Ser. No. 771,483 3 Claims. (Cl. 208-64) This invention relates to a hydrocarbon conversion process wherein a hydrocarbon feed stock rich in relati vely straight-chain components is converted in a combination of several reaction stages to a motor fuel rich in high octane aromatic and isoparaffinic hydrocarbons. More specifically, this invention concerns a process in which a hydrocarbon mixture boiling in the gasoline range is subjected to reforming conditions, the refonnate is extracted with the aid of a solvent selective for aromatic hydrocarbons to recover the aromatic component of the reformate and the parafiinic raflinate of the extraction stage is contacted with a solid sorbent of the molecular sieve type whereby the isoparaffinic components are separately recovered from the relatively straight-chain components of the raffinate and the latter are recycled to the reforming zone or subjected to isoinerization to increase either the proportion of aromatic product or isoparatfinic product, depending upon the type of motor fuel desired.

One object of the process of the present invention is to provide a motor fuel having not only a high octane value (that is, resistant to knocking in high compression engines) but also a quality characterized as high antirumble response when utilized as a motor fuel in high compression engines. Another object of this invention is to convert a paraflinic feed stock comprising a distillate fuel and containing normal paraflinic components which tend to knock upon ignition in a high compression engine into a mixture of aromatic and isoparaffinic hydrocarbons having high anti knock properties. Still another object of the present invention is to reform a parafiinic feed stock comprising normal paraffins in the presence of a dehydrocyclization catalyst to form thereby aromatic hydrocarbons as well as isoparaffinic hydrocarbons and by means of a separation stage in combination with said dehydrocyclization process, separating the residual normal paraflins from the product of the latter reaction for recycling purposes, to thereby convert the relatively straight-chain components of the feed stock to the desired aromatic and isoparafiinic products, substantially to the extinction of the straight-chain compounds contained in the feed stock. i

In one of its embodiments this invention relates to a process for producing a hydrocarbon mixture rich in aromatic and isoparaffinic hydrocarbons from a hydrocarbon feed stock boiling in the gasoline range and rich in straight-chain paraffinic hydrocarbons which comprises catalytically reforming said feed stock at reaction condition whereby at least a portion of said feed stock is converted to an aromatic hydrocarbon, extracting the resulting reformate with a solvent selective for aromatic hydrocarbons, separating a paraffinic raflinate from a rich solvent containing the aromatic components of said reformate, recovering an extract rich in aromatic hydrocarbon from the fat solvent produced by said extraction, contacting the raflinate with a solid molecular sieve sorbent capable of selectively retaining within the pores of the sorbent the relatively straight-chain paraflins within said raflinalte, withdrawing from the resulting spent sorbent a parafiinic efiluent rich in isoparaflins, contacting the spent sorbent at desorption conditions with a normal paraflinic hydrocarbon having a molecular weight Patented Sept. 26, 1961 different from the sorbed paraifin, recovering a desorbed stream rich in relatively straight-chain components and combining said parafiinic efiluent rich in isoparaffins with said extract rich in said aromatic hydrocarbon.

A more specific alternative embodiment of this invention relates to a combination process for producing a hydrocarbon mixture rich in aromatic and isoparaflinic hydrocarbons from a hydrocarbon fraction boiling in the gasoline range and rich in straight-chain hydrocarbons which comprises catalytically reforming said fraction at reaction conditions whereby at least a portion of said fraction is converted to an aromatic hydrocarbon, extracting the resulting reformate with a solvent selective for aromatic hydrocarbons, separating a parafiinic raffinate from a fat solvent containing the aromatic component extracted from said refonmate, recovering an extract rich in said aromatic hydrocarbon from said fat solvent, catalytically isomerizing at least the light n-paraflin components of said raffinate at isomerizing conditions whereby at least a portion of the relatively straight-chain paraffins of said rafiinate are converted to an isoparaflin in admixture with non-isomerized, relatively straight-chain parafiin, contacting the resulting isomate mixture with a solid molecular sieve sorbent capable of selectively retaining within the pores of the sorbent the relatively straightchain paraflin component in said rafiinate, withdrawing from the resulting spent sorbent a paraflinic efiiuent rich in. isoparaflins, contacting the resulting spent sorbent at desorption conditions with a normal paraffinic hydrocarbon having a molecular weight different from the sorbed isomate paraffin, recovering a secondary effluent comprising excess desorbent rich in the relatively straightchain component of said isomate, recycling said relatively straight-chain isomalte paraffin of said secondary eflluent to one of said reforming and isomerizing reactions and combining said parafiinic effluent rich in isoparafiin with said extract rich in aromatic hydrocarbon.

Another preferred alternative embodiment of the invention comprises contacting the raffinate stream in its entirety with said molecular sieve sorbent, recovering an effluent comprising branched chain and cyclic hydrocarbons from the sorbent, contacting at desorption conditions the spent sorbent with a light n-paratfin desorbent, recovering a secondary eflluent comprising excess desorbent in admixture with the sorbed, relatively straight chain parafiin component of said raffinate, fractionally distilling the secondary efliuen t, recovering a light fraction comprising C C and C components from a heavy fraction comprising relatively straight chain parafiins of higher molecular weight, separately isomenizing said light fraction, and recycling the heavy fraction to the reforming reaction, combining the podudt of the isomerization reaction with said rafiinate charged to the sorption zone and combining said effluent comprising isoparaffinic and cyclic hydrocarbons with said aromatic extract to form a blend of high octane motor fuel.

Other embodiments of the present invent-ion relating to specific reaction conditions and process flow arrangements will be referred to in greater detail in the following fur ther description of the invention.

It is well known that aromatic hydrocarbons in admixture with air ignite under compression to provide an explosion which has a relatively slow flame advance across the air-hydrocarbon vapor mixture and such mixtures therefore provide fuel components for high compression engines having the desired anti-knock properties. For motor fuels boiling in the gasoline range the arcmatic components are principally benzene and alkylbenzenes. On the basis of this relationship between anti-knock properties and the aromatic hydrocarbons has components of petroleum into motor fuels of high antiknock rating, the reforming reaction involving the dehydrogenation. of naphthencs to aromatics and/or the dehydrocyclization of aliphatic parafiins to aromatic hydrocarbons. As the compression ratio of gasoline-buming engines has increased, however, it has been noted that aromatic hydrocarbons when utilized as the major component of motor fuels tend to deposit carbon in the combustion chamber of the engine at the high temperatures and high pressures existing within high compression engines, presumably because of the high ratio of carbon to hydrogen in the aromatic molecule. These carbon deposits tend to cause pro-ignition of the fuel and as a result, fuels which contain an unduly large proportion of aromatic components. produce an undesirable socalled rumble when ignited in high compression engines. It has been found, however, that in admixture with parafiinic components having a relatively high hydrogen to carbon ratio in their molecular structures, the undesirable rumble characteristic of aromatic hydrocarbon upon ignition is reduced. If, however, the paraffinic components in admixture with the normally high octane aromatic components are normal or relatively straightchain aliphatic hydrocarbons, the octane number of the mixture is markedly reduced. On the other hand, in the presence of isoparaflinic hydrocarbons, the octane number of the resulting mixture is retained at a high level, while at the same time the ratio of hydrogen to carbon in the fuel mixture is maintained at a sufiiciently high level to obviate the rumble problem. It therefore becomes desirable in providing a tailor-made fuel composition of the highest quality for motor fuel use to provide a fuel mixture containing both a high proportion of aromatic hydrocarbons of the benzene series and a high proportion of isoparaffinic components, since both the aromatic and isoparafiins contribute to the enhancement of the desirable anti-knock properties and the isoparafiins provide components of high hydrogen to carbon ratio which eliminate the rumble characteristic of the aromatic components when utilized alone as motor fuels in high compression engines. The present process provides a means for producing blends of aromatic and isoparafiins by a highly efiicient and effectivemeans, enabling substantially complete conversion of a given hydrocarbon distillate to either one or both of these high quality components.

In the present process the feed stock rich in normal or substantially straight-chain paraflin hydrocarbons is contacted with a reforming catalyst capable of effecting isomerization and/or dehydrocyclization of the naphthenes and normal parafiinic components, followed by a separation process which removes the aromatic products, I

producing a parafiinic fraction which may be subjected to an isomerizing conversion process whereby the re-. maining normal parafiins are converted to isoparafiins or, alternatively, the parafiinic fraction recovered from the first stage of the aromatic separation process may be contacted with a molecular sieve type sorbent capable of separating normal from isoparaflins and the recovered normal parafiins thereafter subjected to isomerization for conversion to an enhanced yield of isoparafi'ins. By first removing the aromatics from the reforming reaction product (that is, reformate) both the isomerization and molecular sieve separation stages or either of them proceeds most smoothly, without the interference of aromatic hydrocarbons which would otherwise decrease the yield of isoparaflins in the isomerization stage and/or reduce the effectiveness of the molecular sieve sorbent. By means of the present process the paraflinic fraction recovered from the aromatic separation stage may also be recycled directly to the reforming step to enhance the yield of aromatic components by dehydrocyclization of the parafiinic components of the fraction in the absence of naphthenes and aromatics which would otherwise tend to displace the equilibrium in the direction opposing the production of aromatics from paraflins. In general, however, it is preferred to first separate the isoparafiins from the paraflinic raflinate stream recovered from the aromatic separation stage and thereafter separately subject the recovered normal parafiins to isomerization with a catalyst and at reaction conditions especially adapted to conversion of normal paraffins to isoparafiins, thereby realizing the maximum eflect of the equilibrium factor which enhances the total conversion of raffinate to isoparaflins when the latter are removed from the raflinate prior to isomerization.

Suitable primary charge stocks to the present process are herein characterized as hydrocarbon distillates generally boiling within the motor fuel range, that is, fractions having an initial boiling point of about 30 C. and an end boiling point of about 210 C., and more preferably, an end boiling point of about C. to 180 C. These hydrocarbon fractions may be derived from any suitable source, such as a straight run distillate, a natural gasoline, a naphtha cut of a thermally or catalytically cracked petroleum fraction or from any other source containing normal paraffins, naphthenes, olefins or aromatic components, including mixtures of, for example, straight run and thermally or catalytically cracked naphtha fractions as well as heart cuts thereof having generally narrower boiling ranges within the above distillate fractions.

The catalytic reforming stage of the present process is preferably effected in the presence of a catalyst which is not only capable of effecting dehydrogenation of the naphthenes present in the distillate fraction to form aromatic hydrocarbons thereby, but is also capable of effecting dehydrogenation and cyclization of the parafiinic and olefinic hydrocarbons to also form aromatic hydrocarbon compounds. Reforming catalysts having these properties are generally capable of effecting substantially simultaneous isomerization of the hydrocarbon components of the charge stock and because of such isomerizing properties, the catalyst may also be employed to upgrade the parafiinic fraction recovered, from the aromatic separation step by isomerizing the normal paraflins in such fraction to isoparafiins. Satisfactory reforming catalysts for this purpose generally contain a metal oxide or sulfide of a metal selected from the elements of group VIII of the periodic table supported on a refractory oxide, such as alumina. One of the preferred catalysts for this purpose is a mixture of platinum and an acidic component supported on alumina which is capable of effecting isomerization and cyclization reactions, the catalyst being described in US. Patent No. 2,478,916, issued August 16, 1949. A particularly preferred catalyst composition useful in the reforming stage of the process comprises alumina composited with platinum and a combined halogen, of the type described in U.S. Patent No. 2,479,109, issued August 16, 1949. The preferred platinum-alumina-combined halogen type of refroming catalyst contains from about 0.01% to about 1% by weight of a group VIII noble metal, such as platinum, palladium or rhodium and from 0.1% to about 5% by weight of combined halogen such as chlorine, or a portion of the chlorine may be replaced by fluorine in an amount of from about 0.1% to about 3% by weight of the total composite. Other reforming type catalysts may also beeffectively utilized in the present process, including such catalyst compositions as molybdena-alumina containmg. from about 1% to about 12% by weight of molybdena, chromia-alumina catalysts containing from 1% to about 10% by weight of chrornia, nickel and/or cobalt oxide or sulfide composited with alumina or combined molybdena and alumina and others recognized in the petroleum refining art.

The reforming reaction is preferably effected in the presence of hydrogen charged to the process in an amount proportions of hydrogen per mole of hydrocarbon feed stock, the excess hydrogen usually being recycled in the process until its concentration in the recycled gas stream falls below about 50 mol percent. The reformingprocess is an equilibrium reaction, the formation of aromatic hydrocarbons by dehydrocyclization and isomerization being favored by high temperatures and high pressures which may range from about 225 to about 500 C. and pressures of from atmospheric to 100 atmospheres, more or less, and more preferably at temperatures of from about 300 to about 510 C. and at pressures of from 10 to about 50 atmospheres, particularly with the aforementioned preferred catalyst comprising composites of alumina, platinum and combined halogen.

When a catalyst of the above preferred type comprising a composite of platinum-alumina-combined halogen is also employed in the isomerization stage to effect conversion of normal paraflins to isoparafiins, it is generally preferred that a separate reactor be employed for such isomerization stage wherein separately controlled reaction conditions may be provided for producing an enhanced yield of isomerization product, although the parafiinic fraction recovered from the aromatic separation stage may be recycled at least in part to the reforming zone, together with the incoming charge stock, to eifect the desired isomerization. When a separate isomerization reactor is provided employing the aforementioned combined platinum-alumina-halogen catalyst composition, the reaction conditions which favor isomerization of normal paraffins to isoparaffins are temperatures of from about 100 to about 300 C. and pressures of from atmospheric to about 20 to 30 atmospheres, the charge stream being made up in part of hydrogen, present in sufficient quantity to provide a molar ratio of hydrogen to hydrocarbons of from about 0.521 to about 10:1 moles of hydrogen per mole of hydrocarbon. Other isomerization catalysts also elfective in the isomerization reactor, include such catalysts as anhydrous aluminum chloride and aluminum bromide, boron-trifluoride, ferric chloride and ferric bromide, composites of various metallic halide salts, such as ferric chloride and boron trifluoride with an alumina support and others well-known in the refining art as isomerization catalysts. One of the preferred catalysts utilizable in the isomerization stage is anhydrous aluminum chloride which may be contacted with the paraffinic fraction at temperatures of from about -l to 100 C. and at pressures sufficient to maintain the paraffinic fraction in substantially liquid phase. In the presence of catalysts such as boron trifluoride and hydrogen fluoride individually or supported on a solid support such as pelleted aluminum oXide or if combined with a ferric hallide, such as ferric fluoride on such a support, the temperature in the isomerization zone may suitably be maintained at from 10 to about 100 C. and pressures may range from 1 to about 20 atmospheres.

The present invention is further described by reference to the accompanying diagram which illustrates a typical flow diagram of the various alternative process flow arrangements comprising this invention. Referring to the accompanying diagram, a naphtha fraction containing a relatively straight-chain parafiin having at least four carbon atoms per molecule, herein referred to as a distillate fraction or hydrocarbon feed stock, generally, and more preferably, boiling Within the gasoline range, is charged into the process flow through line 1 at a rate controlled by valve 2 and thereafter transferred at the pressure desired for the subsequent reforming conversion reaction by means of pump 3 through lines 4 and 6 containing heat exchanger wherein the charge stock is heated to the desired reforming conversion temperature into reforming zone 7 in which a fixed bed or moving bed (e.g., fluidized) of the reforming catalyst is maintained. Hydrogen initially charged into the process cycle through line 8 at a rate controlled by valve 9 to provide the desired hydrogen to hydrocarbon molar ratio in the reforming reactor is transferred through line 10 connecting with line 8 at the pressure provided for the reforming conversion by means of compressor 11 into' the charge stock feed line 4 connecting with line 10. After the initial period of operation, a major proportion of the hydrogen supplied at the feed inlet is derived from recycle sources, as hereinafter noted, line 8 thereafter supplying only SllffiClGIlt fresh hydrogen to the process for make-up purposes.

Reforming conversion zone 7 contains a solid reforming catalyst, preferably maintained in fixed bed relationship to the incoming feed stock, the preferred catalyst being the aforementionedcomposite of alumina, platinum and combined halogen which is capable of effecting dehydrogenation of any naphthenes which may be present in the distillate oil feed stock, hydrogenation of any olefins which may be present in the feed stock and dehydrocy-clization and/or isomerization of the relatively straight-chain parafiinic components of the feed stock, all of which reactions occur at the temperatures and pressures noted above and in the presence of a reforming conversion catalyst and hydrogen. The hot effluent of zone 7 is removed therefrom after the desired conversion period through line 12, cooled at the pressure existing in zone 7 to a temperature suflicient to condense substantially all except the light, normally gaseous components (such as hydrogen, methane, ethane and propane) present in the reactor effluent by heat exchange in cooler 13 and transferred under positive pressure flow through line 14 into receiver vessel 15 wherein the light, normally gaseous components (primarily hydrogen) are separated from the liquefied components of the reactor efiiuent. The light gaseous fraction thus collected above the liquid condensate in receiver 15 is predominantly hydrogen which may be recycled, either directly or after removal of light hydrocarbon gases (by means not illustrated on the accompanying diag m) to the reforming zone '7, thus providing a source of the aforementioned recycle hydrogen stream. For this purpose the gaseous recycle is removed from receiver vessel 15 through line 16 and valve 17 and recycled bymeans of pump 11 as heretofore indicated.

The normally liquid layer accumulating in receiver 15, containing a greater molar proportion of aromatic to paratfinic hydrocarbons, compared to the feed stock, by virtue of the conversion of the hydrogen components of the feed stock in reforming zone 7 to aromatics is withdrawn from receiver vessel 15 through line 18, at a rate controlled by valve 19 and charged to refer-mate stabilizer 20 wherein the light hydrocarbon components thereof, such as the butanes, are distilled overhead at a reduced pressure (e.g., atmospheric) from the reformate. Stabilizer 20 is generally in the form of a distillation column containing reboiler 21 for introductionof the necessary heat of vaporization required for stabilization of the liquid portion of the reformate, although the-necessary vaporization may also be obtained by reduction of the ambient pressure in column 20 without heating the liquid residue. The resulting light overhead vapor is removed from the top of column 20 through line 22, cooled in condenser 23, if desired, to liquefy the light components of the overhead and the resulting condensate discharged into receiver 24. Any remaining light normally gaseous, non-condensed components may be vented to the atmosphere from receiver 24 through line 25 and valve 26 or may be utilized as an internal source of .de sorbent in the subsequent stages of the process, depending upon the temperature and pressure at which stabilizer 20 operates, by discharge into line 27 from line 25 through connecting line 28 and valve 29. Thus, if normal butane (one of the preferred hydrocarbons for use in the subsequent desorption stage of the process) 'is desired as a .desorbent in the subsequent .sorption separation stage of the present process cycle, the temperature and pressure maintained in receiver vessel 24 may .be adjusted to provide for liquefaction of C and higher hy- 7 drocarbon components in the stabilizer overhead, the latter accumulating as receiver bottoms. In order to efiect more complete stabilization, the liquefied components of the stabilizer overhead are desirably refluxed to the top of stabilizer column 20, the latter liquefied overhead being returned to column 20 through line 30 at a rate controlled by valve 31. If desired, at least a. portion of the liquefied stabilizer overhead may be utilized as desorbent in the subsequent sorption stage of the process (for example, if the overhead condenser is operated at a temperature and pressure at which n-butane and/or n-pentane are condensed). The liquid condensate of the overhead if it is to be utilized as desorbent, is withdrawn from 'line 30 through line 32 by means of pump 33 and discharged into desorbent supply line 27. Alternatively, the temperature and pressure maintained in overhead receiver 24 may be adjusted to elfect liquefaction of only the components boiling at a higher temperature than the overhead component selected for use as desorbent in the subsequent sorption separation stage of the process. Thus if n-butane is to be separated from the overhead for use as desorbent, C and higher components may be condensed in overhead condenser 23 and refluxed to stabilizer 20 as 0.; is removed from receiver 24 in vapor form and discharged into line 27.

Stabilizer 20 bottoms containing the normally liquid components of the reformate product, including the aromatic products of the reforming conversion, accumulate in the reboiling section of column 20, thereafter being removed from stabilizer 20 through line 34 and valve 35 and transferred by means of pump 36 through line 37 and heat exchanger 38 into the feed inlet of countercurrent solvent extraction column 39.

The present process provides for the recovery of at least the aromatic components formed in reforming conversion zone 7 as a separate aromatic product for blending purposes with the isoparaflin product of the present process to produce a tailor-made fuel composition. For this purpose the reformate product is subjected to solvent extraction in the presence of a solvent selectively miscible with aromatic hydrocarbons in an aromatic separation zone 39, which in its prefer-red form is a countercurrent solvent extraction column.

The solvent employed in zone 39 to effect recovery of the aromatic components of the reformate product is generally an organic polar compound capable of selectively dissolving at the extraction conditions the aromatic hydrocarbon components present in the reformate and of selectively rejecting the aliphatic (e.g., p-araffinic) components of the reformate. Because of its generally greater density than the reformate hydrocarbon stream, the solvent composition is usually employed in a countercurrent liquid-liquid extraction system in which the liquid solvent of greater density is charged into the top of the extraction column and allowed to flow downwardly against a rising stream of hydrocarbon, charged into the column at a midpoint or in the lower portion of the separation zone. In order to replace feed stock paraflins which normally dissolve in the solvent at least to a slight degree, from the rich solvent prior to recovcry of the aromatic extract, a preferred method of removing the raflinate contaminants from the rich solvent comprises contacting the rich solvent stream containing dissolved aromatics and a small proportion of rafiinate parafiins just prior to the removal of the rich solvent from the extraction zone with a lighter paraflin boiling outside of the boiling range of the aromatic extract or the highest aromatic product to thereby countercurrently displace the raflinate paraflin contaminant into the rising hydrocarbon phase in the extraction zone, separately recovered as raflinate. The latter reflux stream employed for this purpose is introduced into extraction zone 39 through line 40 and is generally and more preferably a light paraffin having a boiling point below that of benzene, recovered from'recycle sources, as hereinafter noted.

Suitable solvents for effecting liquid-liquid extraction of the aromatic components of the reformate may be selected from a relatively large group of organic polar compounds, including the aliphatic alcohols containing up to about 10 carbon atoms, the aliphatic ketones, the glycols, particularly ethylene and propylene glycols and their polymers known as the polyalkylene glycols containing up to about 4 to 5 oxyalkylene groups, the methyl and ethyl ethers and the simple aliphatic acid monoand diesters of the glycols and polyalkylene glycols, as well as other classes of organic compounds which selectively dissolve aromatic hydrocarbons from admixture with paraflins. These solvents may also contain varying amounts of water in order to increase the selectivity for the aromatic component of the reformate. A particularly preferred class of solvents for use in the solvent extraction stage of the present process are the polyethylene and polypropylene glycols, as well as mixtures thereof containing from about 2% to about 25% by weight of water, especially diethylene and triethylene glycols containing from about 5 to about 15% by weight of water. The solubility of aromatic hydrocarbons of the benzene series in the solvent is enhanced by operating the extraction zone at an elevated temperature and pressure, a particularly preferred temperature range for the polyethylene glycols being from about to about 200 C. and at these temperatures, suitable pressures for maintaining the system in substantially liquid phase may range from slightly superatmospheric to 100 pounds per square inch or more. The selective solvent is initially introduced into the process flow from solvent supply through line 41 and valve 42, supply line 41 connecting with lean solvent recycle line 43 which transfers the solvent from the bottom of the stripping zone through valve 44, pump 45 and heat exchanger 46, into line 41. By means of heat exchanger 46 and pump 45, the temperature and pressure of the solvent stream is increased to the desired extraction conditions maintained in solvent extraction zone 39.

A fat solvent stream containing the aromatic components present in the reformate product is removed from the bottom of column 39 through line 47 and valve 48 while at the same time, a raflinate stream, substantially free of aromatics and comprising the non-extracted paratfinic components of the reformate as well as paraflinic Wash (if utilized as reflux herein) is removed from the top of zone 39 through line 49 and valve 50 for further treatment in accordance with the present process, as hereinafter described.

The aromatics dissolved in the rich solvent are ordinarily recovered therefrom by a type of distillation referred to as stripping, wherein the rich solvent at a superatmospheric pressure and at an elevated temperature is allowed to flash in a distillation column maintained at a lower pressure. For this purpose the fat solvent stream in line 47 is transferred by means of pump 51 into line 52 which may contain a heat exchanger (not shown on the accompanying diagram) to adjust the temperature of the fat solvent to a level suitable for stripping and thereafter discharged into fat solvent stripping zone 53. In a preferred method of operation, as indicated, the reduced pressure in zone 53 causes a portion of the hydrocarbon solute to flash overhead into line 54 containing condenser 55, liquefying the vapor overhead, which, thereafter flows through line 56 into receiver vessel 57. For most solvents selective for aromatic hydrocarbons, the aromatic component dissolved in the fat solvent boils at a temperature higher than its normal boiling point in the presence of the solvent, and the overhead, therefore, contains substantially all of the paraflinic reflux if utilized in the process and if not, the stripper overhead is made up predominantly of the lightest aromatic solution of the fat solvent stream, such as benzene. In any event, the temperature and pressure conditions in the stripper are adjusted to provide substantially complete vaporization of the paraflinic cornponents of the fat solvent into the stripper overhead and generally a substantial proportion of the lightest aromatic component of the solute, together with water vapor and solvent, also accompanies the last traces of paraflin removed by distillation. This mixture may be withdrawn from the process through line 58 and valve 59 to storage but in a preferred flow arrangement the mixture is removed from line '58 through line 60 and transferred by means of pump 61 into line 40 through valve 62 for recycle to the bottoms of the solvent extraction zone 39 wherein the aromatic components therein are recovered by extraction and the parafiin component serves its purpose as parafiinic reflux in zone 39', as aforesaid. V

Sttripping column 53 contains a reboiling coil 63 to complete the removal of the aromatic solute by distillations, the latter aromatic extract being removed from column 53 as a sidecut stream through line 64 containing condenser 65 which liquefies the aromatic sidecut, the condensed extract being drained through line 66 receiver vessel 67. The aromatic product consisting of benzene hydrocarbons when utilizing a feed stock to the process boiling in the light naphtha range and/or higher boiling alkylbenzenes when utilizing a higher boiling naphtha as feed stock is withdrawn from storage as required, through line 68 and valve 69 for transfer to blending equipment for the preparation of the present motor fuel blended product, as hereinafter more specifically described.

In accordance with the process of the present invention the paraflinic rafiinate recovered from the solvent extraction step is subjected to further conversion in order to increase the yield of aromatic and/or isoparaflinic hydrocarbons recoverable from the feed stock. In a preferred treatment of the raffinate stream, as hereinafter described, the entire raflinate stream is passed through a bed of solid sorbent which selectively recovers the straight-chain paraffins present in the rafiinate and after recovering these parafiins from the sorbent they are separated into a light fraction (for example, up to and including 0, paraffins) and a heavy fraction (containing the higher boiling straight-chain components), the light fraction thereafter being subjected to isomerization while the heavy fraction is recycled to the reforming zone.

The essentially paraifinic raftinate recovered from the reform-ate as a separate stream in extraction zone 39 and removed therefrom through line 49 by means of pump 70 is directed through line 71 into the various alternative processing stages hereinabove noted. In the particular flow in which at least a portion of the railinate stream is directed into a bed of molecular sieve sorbent to separately recover the isoparaifins present in the stream and the residue sorbed on the sieves is recovered and recycled directly to reforming zone 7, the portion of the Iafiinate reserved for the sorption stage is withdrawn from line 71 through valve 72 into line 73 containing valve 74 and heat exchanger 75 which adjusts the temperature of the stream to a level suitable for the sorption stage which provides a solid sorbent of the molecular sieve type capable of retaining relatively straight-chain aliphatic hydrocarbons in its porous structure while rejecting the isoparaffinic and/or cyclic hydrocarbon components present in the railinate stream. The resulting sorption thus provides a means for separating and recovering the relatively straight-chain aliphatic hydrocarbons of low quality characteristics as a motor fuel from the isoparafiinic and naphthenic raffinate components of more desirable characteristics as motor fuel. The operation of the sorption section of the process will hereafter be described in further detail.

The portion of the paraffinic raffinate stream recycled to the reforming zone (when. it becomes advantageous 10 blend to increase the conversion of feed stock to aromatic hydrocarbons via dehydrocyclization of the paraffinic components), is diverted from line 71 into line 76 by at least partially closing valve 72, thereby directing the portion reserved for recycle reforming through valve 124 and valve 77 into recycle line 78 containing valve 79 which controls the ilow of raflinate recycle to the feed inlet of reforming zone 7.

When the raifinate stream contains a relatively large proportion of normal paraffins, which occurs particularly when utilizing a straight run naphtha as feed stock to the process, the rafiinate may be preferably charged directly into an isomerization zone wherein the normal parafiins in the rafiinate are converted to their more desirable isoparafiin isomers. In such a flow arrangement valve 124 in line 76 is closed and valves 72 and 80 are opened, the hydrocarbon raflinate stream being thereafter directed into line 81 containing heat exchanger 82 which adjusts the temperature of the rafiinate to the desired isomerization temperature, into isomerization zone 83. In general, however, and for most feed stocks, the rai'finate contains an appreciable concentration of isoparaffins and it is therefore preferred to separate the isoparafiin components from the relatively straight-chain hydrocarbons in the total ralfinate and thereafter subject only these components of the entire raifinate to isomerization. Preference for this type of flow is based upon that fact that the isomerization process is an equilibrium reaction and any isoparaffins contained in the ratfinate tend to limit the conversion of normal paraifins to their isomeric components if the total raffinate is charged directly into the isomerization reaction. The present process provides a highly'eifective means for separating the normal paraffin components from the railinate as a relatively pure fraction by contacting the raffinate with a molecular sieve sorbent of the metallic aluminosilica-te class which sorbs the normal and relatively straight-chain components, but rejects isoparafiinic and cyclic hydrocarbons, separately recovered as a non-sorbed effluent from the sorption zone.

The molecular sieve sorbent utilized in the present process is a porous solid comprising particles of dehydrated metallic aluminosilicate crystals containing pores of from about 4 to about 5 Angstrom units in cross-sectional diameter, available commercially under the trade name: Linde 4A and SA molecular sieves. The particles of sorbent may be packed in a vertical column as a fixed bed, as illustrated in the accompanying diagram, or the particles may be maintained in a fluidized state, although generally fixed bed methods of contact between the liquid feed and sorbent are preferred. In order to provide a substantially continuous sorption process utilizing the solid particles in a fixed bed method of contact, the socalled swing reactor principle is employed wherein two individual contacting columns, each having separate inlet and outlet lines connected thereto, are provided, in one of which sorption is effected substantially at the same time that desorption and regeneration of the sieve particles are effected in the other contacting column, the flow of outlet streams being directed into separate channels for further processing in accordance with the present invention. Thus, the raffinate stream from solvent extraction zone 39 either in its entirety or a portion thereof, preferably treated, for example, by water-washing prior to the sorption stage by means not illustrated on the accompanying diagram, is transferred through line 73, valve 74 and heat exchwger 75 into distributor line 84 which directs the flow of raffinate into either sorbent bed 85 or sorbent bed 86, depending upon which of the alternate beds in onstream for liquid railinate and which bed is in the desorption stage. For purposes of description, bed 85 is initially assumed to be involved in the sorption cycle of operation in which the feed thereto is the aforementioned raflinate stream, while bed 86 is assumed to be undergoing desorption wherein the feed stream to the bed is a defrom the standpoint of preparing the present motor fuel 75 sorbent normal parafiin, hereinafter more fully charac- 'terized, which displaces rafiinate normal paraflins sorbed on the molecular sieve sorbent in a previous sorption cycle of the process from the sorbent. The raffinate stream transferred through line 73 to feed line 84 enters column 85 through valve 87 and 88 flowing downwardly through the fixed bed of sorbent, valves 89 in the desorbent supply line to bed 85 and valve 90 in the rafiinate feed line to bed 86 being closed in order to prevent desorbent from entering column 85 and raffinate feed from entering bed 86. As the raflinate stream flows downwardly through the fixed bed of molecular sieve sorbent, the relatively straight-chain components in the rainnate enter the porous structure of the molecular sieve particles and are thereby retained within the pores of the sorbent. The sorption phase of the cycle of operation is effected at atmospheric pressures or higher, up to about 30 atmospheres and at temperatures of from about 20 to about 100 C. or higher, depending upon the pressure and boiling point of the raflinate which is preferably suflicient to maintain substantially liquid phase in the sorbent chambers. Upon entering the sorbent bed, the desorbent n-paraffin hydrocarbon present on the sieve particles by 'virtue of the previous desorption cycle of operation are displaced from the pores of the sorbent and thus join with the non-sorbed components of the raflinate stream comprising isoparafiins and/or cyclic hydrocarbons flowing downwardly through the bed ahead of the raffinate feed front. Thus, the effluent leaving the bottom of column 85 through line 91 and valve 92 comprises a mixture of isoparafiins and desorbent as well as cyclic hydrocarbons,

if initially present in the rafiinate stream. The resulting mixture is drawn through valve 93 into line 94 by means of pump 95 and transferred through line 96 containing heat exchanger 97, which adjusts the temperature of the stream suitable for effecting distillation of the relatively volatile desorbent therefrom, into distillation column 98. Reboiler coil 99 which maintains the desorbent-isoparaflin mixture at its boiling point, vaporizing the relatively more volatile desorbent normal parafiin into overhead vapor outlet 100. The vapors thereby distilled are liquefied in condenser 101 and the resulting liquefied desorbent accumulated in receiver 102.

The desorbent utilized in the process is a normal parafiin of lower molecular weight than the relatively straightchain paraffin components of the raflinate, and contains at least four carbon atoms per molecule. Thus, if the raffinate stream is derived from a distillate oil boiling in the gasoline range, the hydrocarbon components generally contain an average of at least six to eight carbon atoms and a suitable desorbent for use in a process utilizing such a gasoline boiling range mixture as feed stock is a normal paraffin containing from four to five carbon atoms, such as normal butane or normal pentane. When recovered from the sorption efiiuent in desorbent stabilizer 98, the relatively pure desorbent overhead of column 98 is recycled directly to the desorbent inlet through line 103 and valve 104 into line 27 which feeds desorbent into the process flow from reformate stabilizer overhead, as previously described. Additional make-up desorbent, if required, may be withdrawn from storage connected to line 105 in amounts controlled by valve 106.

The residue accumulating in the reboiling section of column 98 comprising isoparafiins and/or cyclic hydrocarbons is withdrawn therefrom through line 107 and may be sent to storage through valve 108, but for purposes of preparing the present gasoline blend, it is withdrawn from line 107 through line 109 and valve 110 into line 68 wherein the highly knock-resistant isoparafiins are blended with the aromatic product of the present process.

At substantially the same time that the sorption stage of the process is being eifected in column 85, desorption of the straight-chain components sorbed on the molecular sieve by virtue of a previous cycle of operation in bed 86 is effected. The aforementioned desorbent stream, consisting of light normal paraifin is pumped from desorbent supply line 27 under positive pressure head by means of pump 111 through line 112 and heat exchanger 113 into line 114 connecting with line 84 which transfers the desorbent into the top of column 86 when valves 115 and 116 are open and valve 90 is closed. Although the molecular sieve sorbent preferentially accepts normal paraflins of higher molecular weight (that is, the selectivity for normal paratfins increases as the number of carbon atoms in the straight chain increases), a lighter, normal paraflin may be utilized as desorbent when a suflicient quantity of the light n-parafiin is supplied as desorbent to provide a molar ratio of light normal parafiin desorbent surrounding the molecular sieve particle to heavy normal paraffin sorbed on the particle of sorbent greater than 1:1, the resulting mass action effect efiecting displacement of the heavy normal parafiin from within the pores of the molec ular sieve by the light normal paraffin surrounding the spent" sieve particles. As desorbent enters the top of the sieve bed, preferably in liquid phase at a temperature of from about 20 to about 250 C. and at a pressure sufiicient to maintain the desorbent stream in substantially liquid phase, the displaced heavy normal paraffin previously sorbed on the molecular sieve sorbent flows downwardly through the bed of molecular sieve particles in column 86. A resulting efiiuent stream is simultaneously removed therefrom through line 91 and valve 117 into line 118 when valve 119 is open and valve 120 is closed, the desorbed normal parafiin being transferred by means of pump 121 from line 118 into line 78 which directs the flow of heavy normal paraffin into other stages of the present process as hereinafter described.

At the point at which desorbent normal paraffin begins to appear in the efiiuent from column 86 or heavy normal paraffin begins to appear in the efiiuent from column 85, whichever is sooner, the feed inlet to column and 86 are switched by manipulating the valves on the inlet and outlet lines to the respective columns. Thus, the raffinate feed in line 73 is directed into line 84 through valve by opening valves 90 and closing valve 87. Substantially simultaneously, valve is closed to discontinue the supply of desorbent into column 86 and valve 89 is opened to admit desorbent into column 85. After a sufficient volume of these inlet streams are supplied to columns 85 and 86 to replace the fluid surrounding the particles of sorbent from the previous cycle of operation with the new inlet composition (as determined by flow rates and/or analysis of the efiluent), the outlet valves from the columns are switched by closing valve 93 which controls the flow of effluent from column 85 into line 94 and opening valve which permits the eflluent of column 86 to flow into line 94 transferring the latter efiluent into the inlet of desorbent stabilizer 98. At this point the stream removed from column 85 through line 91 is composed of railinate normal paraffins and these are directed into normal paraffin recycle lines 118 and 78 by opening valve 123 in line 122 which connects with line 118 feeding into pump 122. Similarly the effluent from column 86 now consisting of displaced desorbent and non-sorbed raflinate components flows through line 91 and open valve 120 into line 94 which conveys the stream to desorbent stabilizer 98.

As heretofore indicated the normal and relatively straight-chain paraflins recovered from the efiiuent of the molecular sieve columns and present in the rafiinate stream recovered from solvent extraction zone 39 are hydrocarbons of relatively low value as motor fuel components because of their tendency to knock in internal combustion engines operated at high compression ratios. Accordingly, these relatively straight-chain hydrocarbons boiling in the gasoline range are desirably converted either into cyclic hydrocarbons (preferably aromatic) or into isoparaifins which have the highest anti-knock rating as motor fuels and reduce the rumble response of aromatic components blended therewith. Depending upon the ratio of aromatic to isoparafiinic components desired in the ultimate motor fuel blend recovered as product of the present process, the normal and relatively straight-chain hydrocarbons recovered from beds 85 and 86 may be either recycled to the reforming zone wherein the normal paraflins undergo dehydrocyclization to form aromatic hydrocarbons, thereby increasing the ratio of aromatic to isoparaflin components present in the ultimate motor fuel blend of this process or they may be diverted into isomerization zone 83 which effects rearrangement of the normal parafiins into branched-chain hydrocarbons (that is, isoparaffins) of higher octane rating, thereby increasing the ratio of isoparaffin to aromatic components in the ultimate motor fuel blend. In the former alternative flow arrangement, the normal paraflin effluent recovered from the molecular sieve sorbent beds is transferred by means of line 78 to the inlet side of the reforming zone 7 by a connection of line 78 with line 4 feeding into the inlet of the reforming reactor and thereby mixing with the feed stock initially charged into the process.

Since the preferred components of the ultimate motor fuel blend for use in internal combustion engines are i'soparaffins, it is generally more desirable to divert the normal parafiin effluent from the molecular sieve beds into an isomerization reaction zone operated at isomerizing conditions which convert the normal paraffins into their branched-chain isomers. For the latter purpose valve 79 in line 78 is closed, thereby directing the normal parafiins in line 78 into line 76 upwardly through valve 77. As heretofore indicated, the broad bofling range mixture of n-paraflins recovered as efliuent from the sorption stage of the process is preferably fractionated into a light paralfin cut (containing, for example, up to and including paraflins) and a heavy cut boiling above the light cut, the resulting fractions preferably being separately treated by isomerizing the light cut and recycling the heavy cut to the reforming zone. In effecting the latter preferred method of treating the n-parafiin eflluent of the sorption stage the total effluent in line 76 is directed into fractionating column 125 through line 126 containing heat exchanger 127 which heats the n-parafiin stream to the boiling point thereof at the pressure maintained on the feed. Column 125 contains reboiling coil 128 which distills the light out into the vapor overhead line 129 containing condenser 130 which liquefies the overhead collected in receiver 131. Pump 132 in line 133 leading from receiver 131 feeds the light n-paraffin cut in liquid phase into line 81 which transfers the latter fraction into isomerization zone 83. The isomerization reaction is generally effected in the presence of hydrogen in order to reduce side reactions of the normal paraflins with the isomerization catalyst normally employed in this stage of the process. Although most of the hydrogen is supplied from recycle sources, as hereinafter described, the initial charge and make-up hydrogen is charged into the process through line 134 at rates controlled by valve 135 and fed directly through line 1 36 by means of pump 137 into reactor feed inlet line 81. The temperature of the light parafiins charged into zone 83, as maintained by heat exchanger 82, depends upon the particular isomerization catalyst utilized in isomerization zone 83. Highly effective isomerization catalysts capable of converting straight-chain paraflinic hydrocarbons into their more branched-chain isomers may be selected from the general class of catalysts known as the Friedel-Crafts metal halides, such as anhydrous aluminum chloride and aluminum bromide, the halides of zinc, iron, tin, antimony, zirconium, etc. or boron trifiuoride, either alone or in admixture with hydrogen fluoride. These catalysts effectively isomerize normal paraffins to an equilibrium mixture of normal and isoparaflins at temperatures of from l0 to about 100 C. and at pressures of from atmospheric to 100 atmospheres or more. Other isomerization catalysts utilizable in isomerization zone 83 have been referred to in the foregoing specifications and reference is hereby made thereto for other species of isomerization catalysts which may be employed for catalyzing the isomerization reaction. The preferred catalysts of the platinum-aluminacombined halogen type, theretofore described, are effective isomerization catalysts at temperatures of from about 50 to about 300 C. and at pressures of from atmospheric to about atmospheres or more, sufiicient in any event to maintain the hydrocarbon stream in substantially liquid phase. The hydrogen-hydrocarbon mixture may be charged into isomerization zone 83 to flow downwardly through the bed of catalyst, the efiluent product stream being removed [from the bottom of the reactor through line 138 into receiver 139 wherein the normally gaseous components of the product stream such as hydrogen are separated from the normally liquid components. The gases, containing a substantial portion of hydrogen, may be recycled in the process through line 140 connecting with hydrogen supply line 134. The isomerization reaction occurring in zone 83 converts the essentially straightchain parafiinic feed stock charged thereto into an equilibrium mixture of normal and isoparafl'ins containing from 10 to generally not more than about 90% by weight of isoparaifins depending upon the composition of the feed stock subjected to isomerization. The resulting parafliinic mixture which may be treated to remove dissolved catalyst components, if present, by means not illustrated on the accompanying diagram, is separated into its normal and isoparafinic components by feeding the mixture through line 141 at a rate controlled by valve 142 into the feed outlet to the molecular sieve sorbent beds, line 73, the normal paraflins in the equilibrium mixture of isomate thereby being recovered and continuously recycled into the process, being ultimately converted to aromatic and/or isoparaflinic hydrocarbons by recycle to extinction.

Returning to distillation column 125 wherein the raffinate efiluent of the solvent extraction zone 39 or the nparafiin effluent of the molecular sieve sorption beds is separated into light and heavy fractions for subsequent treatment in separate conversion zones, as aforesaid, the liquid residue accumulating as bottoms in column 125 and from which the light fraction has been removed as overhead through line 129 is distilled by reboiler coil 128 to remove all of the light fraction components, leaving a residue consisting essentially of the so-called heavy fraction, or the tail ends of the raflinate. As previously indicated, the preferred treatment of these higher boiling n-paraflinic compounds is by recycle to the reforming zone wherein these higher molecular weight n-parafiins are subjected to a combination of dehydrocyclization and isomerization reactions which convert the n-parafiins into an additional yield of aromatics and/or isoparaifins. For this purpose, the bottoms of column 125 are withdrawn therefrom through line 143 and valve 144 and discharged into reforming recycle line 78 on the downstream side of valve 79 in line 78, pump 3 thereafter conveying the stream into line 1 on the inlet side of reforming zone 7 for further conversion, as aforesaid, in the latter reactor.

The present process and the advantages accompanying the particular process flow of this invention is further illustrated with respect to specific embodiments in the following example, which, however, is not intended to limit the scope of the invention necessarily in accordance therewith. I

A Mid-Continent, straight run gasoline fraction having an end boiling point of C. and comprising 20% by weight of normal parafiins containing from 4 to about 10 carbon atoms, 38% by weight of iso-paraffins (the majority of which are of the monornethyl-substituted nalkane types), about 34% by weight of naphthene hydrocarbons and 11% by weight of aromatics and having an F-l clear octane number of about 62 is utilized as feed stock in a combination process including platforming, solvent extraction, molecular sieve separation and isomfuel product of the process.

15 erization reaction stages. The foregoing fraction was heated to a temperature of 456 C. and at a pressure of 500 pounds per square inch it was combined with about 8 mols of hydrogen per mol of hydrocarbon and charged into a catalytic reforming zone comprising a fixed bed of platforming catalyst consisting of an alumina-platinumhalogen composite containing 0.4% by weight of platinum, 0.3% by weight of combined fluorine and 0.35% by weight of combined chlorine The platforming reactor efiluent is cooled to about 100 C. and the resulting liquid and gaseous product passed into a gas separator from which light, non-condensable gases consisting mostly of hydrogen and methane are removed and recycled to the platforming reactor inlet as the principal source of recycle hydrogen for the reforming reaction. The liquid products separating in the receiver were charged into a product stabilizer in which the pressure was reduced to 100 pounds per square inch and the resulting flashed vapors condensed and collected in a receiver vessel attached to the overhead vapor line. The non-condensed gases, consisting mostly of C and C hydrocarbons, were vented. The liquid accumulating in the receiver consisted of C -C hydrocarbons and contained about 43% by weight of n-butane. The recovered condensate was reserved for subsequent use in the process as a source of desorbent for the molecular sieve separation stage of the process. The liquid residue recovered as bottoms from the stabilizer, containing about 45% by weight of aromatic hydrocarbons of the benzene series, 14% by weight of normal parafiins, 36% by weight of isoparaflins and 5% by weight of naphthalene was charged at a temperature of about 145 C. and at a pressure of 100 pounds per square inch into a counter-current solvent extraction column at a point approximately midway between the raffinate and extract outlets. A recycle diethylene glycol solvent containing about 8% by weight of water, continuously recovered from a rich solvent stripping zone hereinafter described, was charged at a rate of 8 volumes of solvent per volume of feed stock into the top of a countercurrent liquid-liquid solvent extraction zone. A paraffinic raffinate stream was also continuously removed as a separate stream from the top of the extraction column. A light parafiin recycle reflux consisting of the light vapors recovered from the overhead of the rich solvent stripping zone and comprising pentane and hexane hydrocarbons, as well as a portion of the benzene recovered from the rich solvent, was charged into the bottom of the solvent extraction column and allowed to flow upwardly through the extraction column in countercurrent relationship to the rich solvent flowing downwardly through the extractor. The latter recycle reflux which countercurrently contacts the rich solvent in the lower portion of the extraction column effects displacement of the feed stock normal paraffins which tend to dissolve in the rich solvent and washes the same upwardly into the 'rafiinate outlet at the top of the extraction zone. A rich -lbs./in. and from which the light paraffin-light aromatic overhead utilized as recycle reflux is recovered and a distillation section operating at essentially atmospheric pressure below the flashing zone wherein the remaining rich solvent residue is isothermally contacted with a reboiling coil to effect vaporization of the aromatic solute at atmospheric pressure, the latter aromatic product being recovered as a side-stream from the column. The sidecut vapors are condensed and after water-washing to remove vaporized aqueous glycol, are removed to a motor fuel blending tank for preparation of the final blended The aromatic product recovered from the stripping column consists of benzene and short-chain alkyl benzenes and contains less than 0.3% by weight of paraffinic hydrocarbons. The recovered aromatic product contains about 5 by weight of benzene, about 15% by weight of toluene and about by weight of C aromatic components.

The raffinate stream recovered as non-extracted hydrocarbon eflluent from the solvent extraction zone was washed with water to remove glycol solvent vaporized into the overhead distillate of the stripping column, thereafter dried by atmospheric distillation and subjected to several alternative processes to arrive at a product of optimum quality, as hereinafter described.

The washed rafflnate stream in one method of treatment was divided into two equal portions, one portion being recycled to the inlet of the platforming reactor and mixed with the incoming feed stock for further conversion to aromatic components. The second portion was charged in liquid phase and at a temperature of 30 C. into the top of an n-paraflin separation column packed with a fixed bed of 5A molecular sieves (Linde Air Products Co.) comprising pelleted dehydrated calcium aluminosilicate crystals containing pores of about 5 Angstrom units in cross-sectional diameter. These crystals, imbedded in a clay binder are capable of sorbing normal paraflinic hydrocarbon containing at least 4 carbon atoms, rejecting isoparafiinic and aromatic hydrocarbons mixed with the normal components. An efiiuent stream recovered from the bottom of the molecular sieve bed in liquid phase was charged into a fractionating column from which an overhead consisting of light normal paraffin displaced from the sieve particles as the desorbent residue of a prior contacting cycle was recovered and reserved as recycle desorbent. A liquid bottom residue of the distillation column consisted of isoparafiinic hydrocarbons boiling in the gasoline range, having an F-1 clear octane number of 82. The liquid isomate was reserved for subsequent blending purposes to produce the present motor fuel blend product. The efifluent was continuously analyzed by chromatographic separation and at the point at which feed stock normal parafiins begin to appear in the etfiuent from the molecular sieve bed, the incoming rafiinate stream was switched into a second sorption column packed with molecular sieves from which the rafiinate n-paraflins have been displaced in a preceding desorption cycle of the process. A light normal paraffin desorbent stream consisting predominantly of normal butane recovered from the stabilizer column as previously described was charged in liquid phase into the top of the first-mentioned molecular sieve bed and passed through the bed of spent 5A molecular sieves for the purpose of desorbing the normal paraflins retained in the sorbent bed. An effluent stream consisting of normal paratfins derived from the raffinate feed stream to the molecular sieve bed and consisting mostly of C -C normal paraflins was recovered from the bottom of the sieve bed and charged into the paraffinic recycle line to the reforming zone for further conversion to aromatic and isoparafiinic hydrocarbons.

The ultimate product of the process comprising a blended mixture of the isoparafiinic product recovered from the molecular sieve beds and aromatic hydrocarbons extracted from the raffinate, containing 78% by weight of aromatic components is recovered from the blending tank. This blend has an F-l clear octane number of 100. With 3 cc. of tetraethyl lead per gallon of blend, the

octane number was 105.

1 7 sisting of -0 n-paraflins which is recycled to the platforming reactor.

The C -C overhead was charged in liquid phase at a temperature of 50 C. and in the presence of hydrogen at a pressure of 100 pounds per square inch into a vertical tubular reactor packed with pills of a platinum-aluminumhalogen isomerization catalyst containing about 0.3%

by weight of platinum, 0.3% by weight of combined fluorine and 0.5% by weight of combined chlorine. The liquid effluent of the isomerization zone contains 48% by weight of isoparaifin hydrocarbons, the majority of which are diand trimethyl-substituted normal alkanes, compared with the extraction rafiinate charged to the isomerization zone containing 89% normal paraffins and only by weight of isop-arafiins. The isomerization reaction product was combined with the liquid feed stock to the molecular sieve separation beds for recovery of a normal paraflin recycle stream to the isomerization zone. The ultimate conversion of feed stock to the motor fuel blend was over 95% and the blended product consisted of 49% aromatic hydrocarbons of the benzene series and 43% by weight of isoparaffins of C to C carbon atom content. The resulting motor fuel blend has an F-l clear octane number of 103 on the basis of an extension of the octane scale above 100. The resulting motor fuel blend produced in the latter process flow is a highly knock resistant motor fuel and ignites under compression (in an internal combustion engine, compression ratio 9:1) with a smokelms flame which deposits no carbon on the spark plugs of the engine.

In an operation in which none of the normal paraffins present in the rafiinate efiiuent of the solvent extraction zone are separated and separately recovered and in which the entire raflinate is recycled to the refiorming zone, the ultimate product is a motor fuel blend containing 80% by weight of aromatic hydrocarbons, 8% by weight of isoparaflins and 12% by weight of normal paraflins. The product has an octane number of 101 and because of the presence of the large proportion of aromatic components, it tends to ignite in an internal combustion engine with the formation of rumble and the deposition of carbon on the spark plugs. Furthermore, the net yield of motor fuel blend based on the straight run gasoline feed stock is about 88, a greater proportion of the feed being cracked to non-condensable gaseous hydrocarbons than in the preceding operation in which the normal components of the raffinate are separated and individually isomerized in a selective isomen'zation reactor.

We claim as our invention:

1. A process for producing a hydrocarbon mixture rich in aromatic and isoparaflinic hydrocarbons from a straight run gasoline fraction rich in straight-chain paraffinic hydrocarbons which comprises catalytically reforming said gasoline fraction at reaction conditions whereby at least a portion of said gasoline fraction is converted to an aromatic hydro-carbon, extracting the resulting reformate with a solvent selective for aromatic hydrocarbons, separating a paraflinic raflinatefrom a rich solvent containing the aromatic component of said reformate, recovering an extract rich in aromatic hydrocarbon from the fat solvent produced by said extraction, separating said raifinate into a light fraction consisting of relatively volatile components and a heavy fraction boiling above said light fraction, recycling said heavy fraction to the reforming step, subjecting said light fraction to isomerization in the presence of an isomerizing catalyst at isomerizing conditons, contacting the isomerized light fraction with a solid molecular sieve sorbent capable of selectively retaining within the pores of the sorbent the relatively straightchain paraflins contained in said rafii nate, withdrawing from the resulting spent sorbent a paraflinic efliuent rich in isoparafiins, contacting the spent sorbent at desorption conditions with a normal paraffinic hydrocarbon having a molecular weight difierent from the sorbed paraffin, recovering a desorbed sorbate stream rich in relatively straight-chain components and combining said par-aflinic efliuent rich in isoparaffins with said extract rich in said aromatic hydrocarbon.

2. The process of claim 1 further characterized in that said isomerization is eifected at a temperature of from about to about 300 C. and in the presence of a catalyst consisting of a noble metal of the elements of group VIII of the periodic table supported on a refractory metal oxide containing combined halogen.

3. The process of claim 2 further characterized in that said catalyst consists of from about 0.05 to about 0.3% by weight of platinum and from about 0.001 to about 1% by weight of combined halogen supported on an aluminum oxide support.

References Cited in the file of this patent UNITED STATES PATENTS 2,304,183 Layng et a1 Dec. 8, 1942 2,409,695 Laughlin Oct. 22, 1946 2,442,191 Black May 25, 1948 2,769,752 Evans Nov. 6, 1956 2,770,664 Horsley Nov. 13, 1956 2,818,449 Christensen et al Dec. 31, 1957 2,818,455 Ballard et al Dec. 31, 1957 2,859,173 Hess et al Nov. 4, 1958 2,888,394 Christensen et :al May 26, 1959

Claims (1)

1. A PROCESS FOR PRODUCING A HYDROCARBON MIXTURE RICH IN AROMATIC AND ISOPARAFFINIC HYDROCARBONS FROM A STRAIGHT RUN GASOLINE FRACTION RICH IN STRAIGHT-CHAIN PARAFFINIC HYDROCARBONS, WHICH COMPRISES CATALYTICALLY REFORMING SAID GASOLINE FRACTION AT REACTION CONDITIONS WHEREBY AT LEAST A PORTION OF SAID GASOLINE FRACTION IS CONVERTED TO AN AROMATIC HYDROCARBON, EXTRACTING THE RESULTING RFEFORMATE WITH A SOLVENT SELECTIVE FOR AROMATIC HYDROCARBONS, SEPARATING A PARAFFINIC RAFFINATE FROM A RICH SOLVENT CONTAINING THE AROMATIC COMPONENT OF SAID REFORMATE, RECOVERING AN EXTRACT RICH IN AROMATIC HYDROCARBON FROM THE FAT SOLVENT PRODUCED BY SAID EXTRACTION, SEPARATING SAID RAFFINATE INTO A LIGHT FRACTION CONSISTING OF RELATIVELY VOLATILE COMPONENTS AND A HEAVY FRACTION BOILING ABOVE SAID LIGHT FRACTION, RECYCLING SAID HEAVY FRACTION TO THE REFORMING STEP, SUBJECTING SAID LIGHT FRACTION TO ISOMERIZATION IN THE PRESENCE OF AN ISOMERIZING CATALYST AT ISOMERIZING CONDITIONS, CONTACTING THE ISOMERIZED LIGHT FRACTION WITH A SOLID MOLECULAR SIEVE SORBENT CAPABLE OF SELECTIVELY RETAINING WITHIN THE PORES OF THE SORBENT THE RELATIVELY STRAIGHT-CHAIN PARAFFINS CONTAINED IN SAID RAFFINATE, WITHDRAWING FROM THE RESULTING SPENT SORBENT A PARAFFINIC EFFLUENT RICH IN ISOPARAFFINS, CONTACTING THE SPENT SORBENT AT DESORPTION CONDITIONS WITH A NORMAL PARAFFINIC HYDROCARBON HAVING A MOLECULAR WEIGHT DIFFERENT FROM THE SORBED PARAFFIN, RECOVERING A DESORBED SORBATE STREAM RICH IN RELATIVELY STRAIGHT-CHAIN COMPONENTS AND COMBINING SAID PARAFFINIC EFFLUENT RICH IN ISOPARAFFINS WITH SAID EXTRACT RICH IN SAID AROMATIC HYDROCARBON.

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