US2938858A

US2938858A - Recycle reforming and solvent extraction

Info

Publication number: US2938858A
Application number: US639323A
Authority: US
Inventors: Kenneth M Brown
Original assignee: Universal Oil Products Co
Current assignee: Universal Oil Products Co
Priority date: 1957-02-11
Filing date: 1957-02-11
Publication date: 1960-05-31
Anticipated expiration: 1977-05-31

Description

May 31, 1960 K. M. BRowN RECYCLE REFORMING AND soLvENT EXTRACTION Filed Feb. l1, 1957 ESB@ . .a. mm n TB N MM. wm um VM Ne r um. lm MA 6 A MQ K m v X B WN m\ m bmmmuu /m i RECYCLE REFORMING AND SOLVENT- ;v EXTRACTION Kenneth M. Brown, Hinsdale, lll., assigner, by mesne assignments, to Universal Gil Products Company, Des Plaines, lll., a corporation of Delaware Filed Feb. 11, 19.57, Ser. No. 639,323

12 Claims. (Cl. 208-96) 'I'his invention relates to improvements in the process for producing motor fuels of high octane number involving a combination of catalytic reforming and solvent extraction wherein the highly knock-resistant aromatic components of the reformate product are extracted from unconverted non-aromatic hydrocarbons and the latter recycled to the reforming stage of the process, said improvements relating to the removal of undesirable hydro carbons retained by the solvent prior to recycling the non-aromatic raffinate to the reforming zone. More specically, this invention concerns the removal of polycyclic aromatic hydrocarbons from the lean solvent stream, following the extract stripping stage of the process, by a method which involves countercurrently Washing the lean solvent with a non-aromatic hydrocarbon stream under liquid-liquid contacting conditions.

It is widely recognized that certain aromatic hydrof carbons, particularly aromatics of the benzene series (that is, monocyclic aromatic and alkyl aromatic hydrocarbons) are highly' resistantto knocking when utilized as a component of a gasoline boiling range motor fuel for use in high compression engines. Benzene-type hydrocarbons, therefore, are desirable constituents of motor fuel blends in that they increase the octane number of paratiinic and naphthenic hydrocarbons with which they may be mixed in a typical petroleum-derived motor fuel. Processes have been developed for converting paranc gasoline boiling range fractions of petroleum, including fractions containing a large proportion of normal paraflins and/or naphthenes into hydrocarbon mixtures in which the proportion of aromatic constituents of the benzene series is increased, thereby increasing the octane number of the motor fuel fraction. These processes are generally referred to as reforming processes, one of the preferred methods of this type being the so-called catalytic reforming process whereby the gasoline boiling range feed stock, together with hydrogen, is passed over a reforming cata` lyst, as hereinafter described. In such reforming processes, the parainc and naphthenic components present in the feed stock undergo isomerization, hydrocracking, dehydrogenation and aromatization reactions, forming a 'relatively large yield of aromatic hydrocarbons of approximately the same average number of carbon atoms as the feed stock components.

In order to isolate and recover the aromatic components of high knock-resistant 'value (that is the monocyclic aromatic hydrocarbons) from the resulting reformate, the latter is contacted at -vsolvent' extraction conditions with a solvent which is particularly selective for the aromatic constituents of the 'for a'motor fuel of high octane number or utilized as a blending stock for motor fuels of lower octane number to thereby upgrade the latter.v The non-extracted portion v'of the vreformate etiiuent, generally referred to as the hydrocarbon rainate of the extraction process, contains parafinic and naphthenic components subject to further atout i f. ICC

conversion into aromatic hydrocarbons by the combined isomerization, dehydrogenation and cyclization reactions which occur during the reforming process and for this purpose the rainate eluent from the solvent extraction column is preferably recycled to the reforming stage for further conversion into aromatic extract. It has been noted, however, that the lean solvent recovered from the extract stripping operation (being the solvent residue after removal of the aromatic extract therefrom) geuerally contains a small proportion of bicyclic and even higher polycyclic aromatic hydrocarbons which are not stripped from the rich solvent under the conditions geuerally employed for 'stripping the desired monocyclic extract from the rich solvent stream because of their greater solubility in the solvent and their substantially greater boiling point which is further increased by the presence of the solvent. As a consequence of such retention by the lean solvent, the polycyclic aromatic hydrocarbons remain dissolved in the lean solvent and enter the top of the solvent extraction zone when the lean solvent is recycled to the extraction zone for reuse therein. It has been found, however, that although these polycyclic aromatic hydrocarbons are not readily removed from the solvent stream in the vstripping zone by vaporization therefrom, they are at least partially removed from the lean solvent in the top of the extraction zone by countercurrent contact of the lean solvent with the rat'nate, as the latter contacts the incoming lean solvent stream, the raflinate thus freed of Ithe polycyclic aromatics originally contained in the lean solvent being thereafter recycled to the reforming stage kof the process for further conversion into aromatics. Tlie polycyclic aromatic hydrocarbons in the raflinate when the latter stream is recycled to the reforming zione constitute undesirable constituents of a -suitable reforming zone feed stock inasmuch as they tend to undergo decomposition under the conditions maintained in the reforming zone, depositing catalyst deactivating residues such as coke and resinous materials on the surface of the reforming catalyst particles. Any polycyclic aromatic components of the recycle raffinate which are sufliciently refractory to resist decomposition and deposition on the reforming catalyst, re-enter the solvent extraction zone and thus are continuously recycled in the process until they overload the solvent and necessitate special treatment of the solvent to remove at least a portion -thereof from the recycle. By means of the present process, the lean solvent removed from the solvent stripping column and containing the polycyclic aromatic solute is washed with a liquid paranic hydrocarbon which extracts these polycyclic aromatics from the lean 'solvent and thereby permanentlly removes these polycylic aromatics from the lean solvent prior to recycling the latter to the solvent extraction zone. Substantial advantages are thereby realized in that the life 'of the catalyst in the reforming stage of the process and the efficiency of the reforming reaction are both considerably enhanced and the necessity for separate treatment of the solvent to prevent build-up of polycyclic aromatic solute therein is also obviated.

In one of its embodiments the present invention relates to an improvement in the process for producing an aromatic concentrate by the method which comprises catalytically reforming a gasoline boiling range fraction at reforming conditions whereby at least a portion of said fraction is converted into monocyclic aromatic hydrocarbons, and the resulting reformate product is thereafter contacted with -a solvent which selectively extracts the aromatic components therefrom to form a rich solvent containing said aromatic components in solution, said rich solvent is separated from a ratlinate comprising nonaromatic hydrocarbons invsaid reformate, said Yrich solvent is stripped to recover said aromatic extract from a lean cient quantity to .remove polycyclic aromatic hydrocarbons from said lean solvent and separately collecting wash efuent comprising excess wash hydrocarbon and said polycyclic hydrocarbon from lean solvent substantially free of polycyclicraromatics.

Specific embodiments of this invention relate to other aspects of the above process Ywherein particular boiling range hydrocarbon feed stocks,rand specific solvent compositions are employed in the extraction stage of the process and specific sources of wash hydrocarbon are utilized in the lean solvent washing stage of the process.

Typical hydrocarbonmixtures utilizable as feed stocks in the present 'process include hydrocarbon mixtures derived from any source in whicha substantial proportion (preferably, at least 20% by volume) of the hydrocarbon components have at least 6 carbon atoms per molecule Aand are hydrocarbons of the type which form monocyclic aromatic-hydrocarbons byrone or more of a combination of reactions, involving hydrocracking, isomerization, dehydrogenation and aromatization. Thus, for example, suitable feed stocks include straight-run petroleum frac- .'tions, catalytically and thermally cracked petroleum products, particularly fractions thereof boiling in the gasoline boiling range, hydrogenated alcohols, products of Fischer-Tropsch synthesis, and hydrocarbon fractions from other sources,the components of which yield aromatic hydrocarbons by means of the present reforming stage of the process. Particularly suitable feed stocks solvents. Still other types of compounds useful as solvents are the aliphatic alcohols, such as methanol, ethanol, propanol, and homologs thereof, up to and including octanol; various phenols, such as phenol, resorcinol, pyrocatechol, the ortho, meta, and paracresols, thymol; certain ketones, such as acetone, methylethyl ketone, dipropyl ketoneythe aldehydes, such as acetaldehyde, propionaldehyde, butyraldehyde, f urfural, etc.; the amines and alkanol amines, such as ethanol amine, diethanol amine, triethanol amine, phenylethanol amine, propanol amine, butanol amine, pentanol amine,

' phenylencdiamine, N,Ndimethyl phenylenediamine,.etc.;

contain an appreciable percentage of cyclopentane and cyclohexane derivatives which may be converted into benzene derivatives by dehydro-isomerizaticn reactions, such as methylcyclopentane, dimethylcyclopentane, cyclohexane, methylcyclohexane, dimethylcyclohexane, etc., as well as isopararins which undergo hydrocracking-dehydroisomerization reactions to form benzene and its derivatives, such as 2,2-dimethylbutane, Z-methylhexane, 2,2- dimethylhexane and other homologs and analogs.

The solvent utilizable in the extraction stage of the process isa normally liquid organic compound which preferentially dissolves aromatic hydrocarbons from hydrocarbon mixtures containing the same in admixture with aliphatic and naphthenic hydrocarbons. T he solvent may be a single component organic liquid, or a two-component mixture of normally Yliquid organic compounds, one component of which has a high solubility for aromatic hydrocarbons (termed the primary component) and a secondary component which increases the selectivity of the solvent for the aromatic components (termed the secondary solvent). Suitable organic compounds utilizable as the primary component of the solvent composition are preferably selected from the general groupy broadly characterized as oxygen-containing organic components and from certain nitriles and amines. Particularly suitable members of this group are the aliphatic and cyclic alcohols, the glycols, glycol ethexs (also referred to as the polyalkylene glycols), ythe glycol esters and the glycol ether-esters. Alkylene glycols and polyalkylene glycols which are selective solvents particularly preferred herein are ethylene and propylene g1ycols,.the di-, tri, and tetraethylene glycols, particularly diethylene and triethylene rglycols and the diand tri-propylene glycols, The above monoand Vpoly-glycol's which have their terminal hydroxyl groups etherified with short chain alkyl groups comprise another class of -compounds useful as solvents, including the methyl-, ethyl, propyl, and butyl-Cello- `solves and the corresponding methyl, ethyl-, and propylethers of diethylene glycols, referred to as the correspond.- ing alkyl Carbitols. The monoand poly-alkylene glycol esters of short chainaliphatic acids, such as the acetates and propionates, also v'constitute a Vdesirable class of the nitriles, such as acetonitrile, succinonitrile, adiponitrile, beta,betaoxydipropionitrile, alpha,alphaoxydi propionitrile, gamma,gammaoxydipropionitrile, benzonitrile, styryl nitrile etc.' and other classes of organic compounds as well as other individual specific organic compounds.

The above solvents are particularly satisfactory for the separation of hydrocarbon mixtures to recover a substantially pure extract when the compounds are mixed with an anti-solvent, selected from certain polar ymaterials which increase the selectivity of the solvent composition for the component to be extracted. One of the preferred anti-solvents for use in combination with a water-soluble organic primary solvent, such as the above, preferred polyalkylene lglycols, is water, which may be present in Vthe solvent composition in amounts of from about 0.5 to about 20%, and preferably from about 2% to about 15% by weight of the resulting composition. Other suitable highly polar anti-solvents which enhance the selectivity of the solvent composition for the extract are such mate- Irials as methanol, certain dicarboxylic acids, such as oxalic and malonic acids and other highly polar compounds.

The liquid hydrocarbon herein referred to as a "wash liquid is a hydrocarbon which would normally constitute a ranate-type component in the usual hydrocarbon feed stock mixture and is preferably a paranic or mixture of paraffinic hydrocarbons of relatively straightchain structure, such as a normal parain of only slight solubility in the solvent. It is also a hydrocarbon which dilfers in boiling point from the polycyclic aromatic hydrocarbonto be removed from the lean solvent stream by at least 10 C. and preferably by at least 40-50 C., boiling either above or below the boiling point of the polycyclic aromatic hydrocarbon present in the lean solvent. A particularly preferred liquid wash hydrocarbon is the volatile, parafrinic fraction separated from the .feed stock as an overhead distillate, boiling substantially below vthe initial boiling point of the extractor feed, normally comprising C5 and C6 normal and isoparafns. However, a paranic fraction boiling above the boiling point of the polycyclic aromatic contained in the lean solvent may also be utilized, such as a kerosene boiling Vrange fraction having. a boiling range above about 325 F., up to VV.about 500 F., preferably above about 415 F. l

Other embodiments of this invention will be further described with reference to the accompanying diagram which illustrates a particularvprocess ow in combination with a simple arrangement of apparatus for the separa-- tion and recovery of a mixture of benzene, toluene, xylenes and ethylbenzene, as well as higher monocyclic aromatic hydrocarbons, which mixture is useful as a blending agent for the production of a typical high octane gasoline blend. t

YReferring; to the accompanying diagram a crude, straight-run petroleum fraction, constituting one of the preferred sources of the initial charge stock in the present process, is charged intoV the process flow through line 1 and valve `2, being charged into a suitable Vfeed preparation Azone 3, such as a fractional distillation column, containing a reboiler 4 for heating the feed stock toits distillation temperature. A light fraction vcomprisngthe most volatile components present in the .feed stock and preferably having a sufficiently broad yboiling range zto 1inepesses clude C normal and isoparains, is taken overhead from column 3 through line 5 and transferred by means of pump 6 into subsequent stages of the process for use asa liquid wash hydrocarbon for the purpose -hereinafter described. An intermediate fraction boiling within the gasoline range, and containing the components which may be catalytically reformed into aromatic hydrocarbons by means of the reforming stage of the present process and having, for example, an end boiling point up to about 425 F. is separated as a side cut from said feed preparation column 3 through line 7 and diverted into the reforming stage of the process, as hereinafter described. A liquid bottoms residue, comprising components of the crude feed stock boiling above the end point of the gasoline fraction is removed from the bottom of column 3 through line 8 in amounts controlled by valve 9 and discharged from the process ow.

The gasoline boiling rangefraction of the crude feed stock, separated as an intermediate cut in column 3, removed therefrom through line 7 and valve 8 is transferred into catalytic reforming zone 9 by means of pump 10, being increased to the proper temperature and pressure conditions for the reforming conversion by means of said pump 10 which transfers the fraction at the desired pressure through line 11 into heater 12 and thereafter through line 13 into reforming reactor 9. In the preferred method of effecting catalytic reforming reactions, the conversion is accomplished in the presence of hydrogen, generally in the presence of suiiicient hydrogen to provide a molar ratio of hydrogen to'hydrocarbons of from about 0.5 to l to about 20 to 1, and preferably from about 2 to 1 to about 10 to 1. Hydrogen for this purpose is introduced into the process flow through line 14 in the extraction conditions. Since the solvent is generally the phase of Agreatest density in the extraction zone, it is preferably introduced into the top of the extraction column when a countercurrent extraction system is desired. Solvent for this purpose, such as an aqueous diethylene glycol solution, is initially introduced into the process iiow and make-up portions of the solvent are charged into the process through line 18 in amounts controlled by valve 19 at a pressure suitable for effecting the solvent hydrocarbons in the solvent generally increases with the required amount determined Vby valve 15, the hydrogen mixing with the gasoline fraction in line 11 by connecting line 14 therewith.

Depending upon the specific reforming catalyst employed in zone 9, the desired conversion of paraiiinic and naphthenic hydrocarbons into aromatic derivatives is obtained at generally superatmospheric pressures and at temperatures in the range of from about 500 to about 1200 F. and preferably at from about 750 to about 950 F. Suitable pressures may be within the range of from slightly superatmospheric to 100 atmospheres or more, preferably from about 10 to about 50 atmospheres. One of the preferred reforming catalysts known to the petroleum refining art is a catalyst comprising a composite of a metal selected from the group consisting of platinum, palladium and iridium, preferably platinum, and a halogen selected from uorine and chlorine combined with an alumina support, the latter catalyst being generally known in the refining art as a platforming catalyst. Particularly active catalysts of this type contain from 0.001 to about 1.0% by weight of platinum and from 0.01 to about 3% by weight of combined halogen. By virtue of the reforming conditions maintained in catalytic reforming zone 9, a substantial proportion of the aliphatic and cyclic parafns contained in the intermediate orgasoline boiling range feed stock is converted into monocyclic aromatic hydrocarbons, the remaining components being of saturated parafinic character. The efluent product of the reforming reaction may be separated into a normally gaseous fraction and a normally liquid material and the normally liquid material may be further fractionated into a select cut containing monocyclic aromatics by means of a fractional distillation column which, however, is not shown on the accompanying diagram.

The products of the reforming conversion are removed from reforming zone 9 through line 16 and the normally liquid portion thereof discharged in liquid phase into solvent extraction zone 17 wherein the hydrocarbon feed stock is contacted with a solvent which selectively dissolves thearomatic components from the charge stock under liquid-liquid, preferably countercurrent, solvent increase in temperature of the solvent and in the case of the preferred aqueous diethylene glycol solvent containing from about 2 to about 10% by weight of Water, the desired temperature is from about to about 200 C.,

the pressure required to maintain the feed stock and solvent in substantially liquid phase at the latter temperature being from about 1 to about 10 atmospheres, de-

pending upon the temperature. The hydrocarbon feed vstock introduced at a lower level in column 17, preferably at a point substantially in the mid-section ofthe column rises counter-currently to the more dense solvent stream introduced into the top of the column, the solvent preferentially dissolving the aromatic hydrocarbon components of the feed stock contacted therewith. At the point of entry of the solvent into the extraction zone, the hydrocarbon stream is substantially free of aromatic constituents, being removed as a rainate stream from the column through line 22 in amounts controlled by valve 23. This stream contains a large proportion of paraiiinic hydrocarbons which may be converted in the reforming zone into aromatic hydrocarbons of high octane number, and thus they constitute a suitable recycle stream to the reforming reaction zone. For this purpose, the raiiinate stream removed from extraction zone 17 through line 22 is returned to reforming zonefeed line 7 and mixed therein with fresh hydrocarbon feed comprising the intermediate gasoline boiling range fraction separated in column 3, as aforesaid.

The raiiinate stream removed from extraction zone 17 through line 22 may also contain unconsumed hydrogen, if the latter is not separated from the reforrnate eiuent prior to discharge of the reformate feed stock into extraction column 17. By thus recycling the raffinate directly into the hydrocarbon feed line, the hydrogen constituent present in the ramnate is also recovered for recycling purposes.

The rich solvent stream flowing downwardly through extraction zone 17 contains substantially all of the aromatic components present in the gasoline boiling range feed stock charged into column 17, but also contains a minor amount of feed stock raiiinate constituents because of the lack of complete selectivity of the solvents for aromatic hydrocarbons. These raffinate hydrocarbons, usually of paraflinic nature, are advantageously separately recovered and converted into additional yield of aromatic hydrocarbons of high octane rating. For the purpose of displacing these rafinate components from the rich solvent stream into the raiinate effluent from column 17 the rich solvent is contacted, preferably under countercurrent iiow conditions, with a suitable wash hydrocarbon stream comprising components preferentially soluble in the rich solvent. A material particularly suitable for this purpose (that is, for displacing feed stock raiinate components dissolved in the rich solvent) -is a lightV parafiin fraction (that is, a fraction made up of low molecular weight paraflins) which dissolve more readily in the solvent than the feed stock ratiinate parains or a portion of the aromatic extract recovered from the rich solvent stream in the subsequent stripping stage of the process, the portion thus recovered being herein referred to as a recycle reflux stream. The latter is introduced preferably into the lowermost portion of the column to provide maximum countercurrent contact with the rich solvent stream.V In the present process, the recycle reflux is' charged in controlled amounts into the bottom of solvent extraction zone 17 through line 24, being derived from the upper portion ofthe stripping column, as hereinafter described. The aromatic and light paran components present in the recycle reflux contact the rich solvent in the lower portion of the extraction zone, displacing therefrom the feed stock parains which combine withthe ratiinate removed from the top of the column.

The Vresulting washed'rich solvent containing light paraf tins and/or aromatics in place of the displaced raffinate paratiins iswithdrawn from( the bottom of column 17 through line 25, valve 26 and transferred by means of pump 27 into line 28 which discharges the rich solvent into solvent stripping zone 29. Zone 29 is generally operated at a lower pressure than that maintained in extraction zone 17, such that a major proportion of the dissolved hydrocarbonscontained inthe rich solvent vaporize therefrom by merely reducing the ambient pressure on the rich solvent streams; that is, at substantially isothermal conditions. The remaining monocyclic aromatic solute is stripped from the rich solvent by means of heat introduced into the solvent residue in the lower portion of zone 29 through reboiler 30. The light parafins and a substantial proportion of the most volatile aromatic constituent of the rich solvent stream (generally benzene) are flashed overhead from stripping zone 29 through line 31, valve 32 and constitutes the portion `of extract returned to the bottom of extractor 17 asl recycle reux for displacing feed stock parains from the rich solvent stream. For this purpose, the light vapor overhead is pumped from line 31 into recycle charge line 24 by means Vof pump 33 which increases the pressure on the recycle stream to the pressure maintained in extraction zone 17.

A higher boiling extract product is vaporized from the rich solvent as a side cut from stripping zone 29, being removed therefrom through line 34 and valve 35 into side cut condenser 36 wherein the predominantly aromatic extract vapors are liquefied and the liquid condensate drained through line 37 into receiver vessel 38. When utilizing a solvent composition in the process which contains water, such as the aforementioned aqueous diethylene glycol solution, at least a small portion of the water as well as a small portion of the solvent distills with the aromatic extract into receiver vessel 38 and collects as a lower liquid layer therein. rl`his portion of condensate may be drained from the receiver for recycle purposes through. line 39 and valve 40. For example, this aqueous stream may be charged into stripping zone 2'9 (preferably into the reboiling section) to provide a source of stripping steam in zone 29, not illustrated, however, on the accompanying diagram. The liqueed,

monocyclic aromatic hydrocarbon extract collects as an upper liquid. layer in receiver vessel 38 and may be drained from the vessel through line 41 and valve 42 into storage or transferred into suitable blending equipment for mixing with a gasoline fraction as a high octane blending stock.

As heretofore indicated, the rich. solvent stream even after substantially complete'removal of the monocyclicY extract product therefrom by distillation. in stripping Zone 29 still contains: a. small proportion. of dissolved polycyclic aromaticsv (mostly naphthalenes) which are not removed from the lean solvent by the aforementioned stripping, even at the relatively high temperatures to which the lean y'st'sl'vent isheated in the reboiling section of stripping the ranate into the Yreforming zone.

zone 29. Hence, .under the usualmethod of operating a combined solvent extraction-solvent stripping process, these polycyclicaro'matic hydrocarbonsV remain dissolved in the 'stripped solvent and are necessarily recycled in the lean solvent streamr tothe top of theextracton` column. As previously indicated, however, Ythe polycyclic aromatic soluteis removedwith easefrom the' lean solvent when'it iscont'actedin the upper sectionv of solvent extraction zone 17 with the raiinate stream, the raffinate washingthepolycyclics from the lean solvent andcarry` ing them in solutiontwith the parafrinic constituents of The presence .of the polycyclicaroma'tics inV the recycled ratiinate causes rapid deactivation of thereforming catalyst and if not removed from the hydrocarbon stream inthe reforming zone (for example, by conversion to coke or resins which form a deactivating deposit on. the reforming catalyst), the polycyclics are again extracted in thesolvent extraction zone, gradually buildingup in total quantity and over-burdening the solvent with a` constantly increasing load of polycyclicV aromatic solute. In accordance with the process of Vthis `invention the lean solvent stream removed from the bottom of stripping zone 29 and conf. taining dissolved polycyclic aromatics is withdrawn there-4 from through line 43, valve 44 and transferred bymeans of pump 451-through line 46 into the' top of a lean solvent washing zone, designated on the accompanying diagram as column 47 andcountercurrently contacted therein with a liquid, non-aromatic'hydrocarbon'wash stream which selectively removes the polycyclic' aromatic solute from the lean solvent. As heretofore indicated, the washhydrocarbon may comprise the light fore ends of the` crude feedstock (C4-C5 paratins) fractionally distilled in feed; preparation zone 3, being recovered as an overhead' from the latter column and transferred by means of pump 6 into wash hydrocarbon feed line 48 which introduces the light paraiiins at suiiicient pressure to maintain the same in liquid' phase into the lower portion of lean sol: vent wash zone 47 in controlled amounts determined by valve 49. A portion or substantially all of the wash hydrocarbon may be derived from recycle sources, as hereinafter described, and/or'further supplemented from external sources, for example, from extraneous sources through line 54 and valve 55. In order to operate the present combined process on an economical basis lthe solvent stream is desirably maintained at least at a' constant temperature throughout thefentire system in order to avoid substantial heating costs occasioned by changing the temperature of the solvent in various stages of the process. The wash hydrocarbon, therefore, is desirably charged into contact with the lean solvent in zone 47 at substantially the temperature of the nsolvent withdrawn from the solvent stripping zone 29 and at suiiicient pressure 'only to maintain the wash hydrocarbon in substantially liquid phase. The liquefied washy hydrocarbon rising countercurrently through the lean solvent descending downwardly through washV zone 47, removes the polycyclic aromatic hydrocarbon solute from the solvent the resulting stream of combined polycyclic aro'- matics and excess light paratnic wash hydrocarbon being withdrawn from the top of zone 47 through` line 50 and valve 571 into storage or into a suitable fractionating column for recoveryv of the wash hydrocarbon from the polycyclic aromatics dissolved therein. The volume ratio of liquid Wash hydrocarbon toV solvent required to effect the substantially complete removal of the polycyclic solute from the lean solvent is generally greater than 0.1 to 1 and may be as high as 1G to 1 depending upon the composition ofthe wash hydrocarbon. The preferred volume ratio of wash hydrocarbon to lean solvent charged into zoner47 is from about 0.5 to 1 to about 2 to l volumes per volume. The washed lean solvent, substantially free of polycyclic aromatic solute, containing dissolved wash hydrocarbon solute is desirably ashed before the washed lean solvent isV recycled back to the extraction zone 17 for reuse of the solvent composition therein. Removal of the dissolved wash hydrocarbon solute from the lean solvent prior to recycle of the latter, although not necessarily essential to the successful operation ofthe process, is nevertheless preferred in order to reduce the volume of hydrocarbon raiinate recycled to the reforming reactor, a portion of the raffinate being made up of wash hydrocarbon Adisplaced from the lean solvent when the latter contacts the aromatic-containing feed stock in solvent extraction zone 17. To accomplish such ash distillation the washed lean solvent is removed from the bottom of column 47 and charged into distillation zone 56 containing reboiling coil 57 which introduces sutlicient heat into the lean solvent to vaporize a substantial proportion of the paraffinic wash hydrocarbon solute therefrom. Alternatively, ambient the pressure on the lean solvent charged into zone 56 may be reduced in order to ash the hydrocarbons therefrom adiabatically. The wash hydrocarbons thus flashed from the lean solvent are taken overhead from column S6 through line 58, condensed in heat exchanger S9 and theV resulting liquefied wash hydrocarbons transferred from condenser 59 through line 60 by means of pump 61 into line 62 connecting with line 48 for recycle of the liquid wash hydrocarbon into the bo'ttom of the column 47. Lean solvent substantially free of wash hydrocarbon solute is removed from the bottom of column `S6 through line 63 and valve `63a by means of pump 64, the solvent thereafter being discharged into line 65 which connects with solvent return line 21 for recycle in the process.

It is to be emphasized that although removal of the wash hydrocarbon solute from the lean solvent by the aforementioned distillation prior to recycle of thelean solvent to the extraction column, to thereby relieve the hydrocarbon recycle duty on the reforming reactor, is the preferred mode of operation herein, such removal of the hydrocarbon solute from the'lean solvent stream is not necessarily an essential step in the process. The process of this invention is further described in the following illustrative example, which, however, is not intended to limit the scope of the invention necessarily in accordance therewith.

Example I In the following run an aromatic extract product useful for blending purposes for producing high octane motor fuel is prepared in accordance with the process of this invention, as f ollows. Mid-Continent petroleum crude is separated into three specific cuts by fractional distillation, (1) an overhead light .paratiinic cut containing C5 C8 parafl'ins having an end boiling point above about 110 F. is taken from the top tray of the distillation column at the rate of 35 'bbls./hn and diverted, together with an additional quantity of n-pentane from an external source, into a lean solvent wash tower for purposes hereinafter described to remove polycyclic aromatics from the lean solvent stream; (2) an intermediate cut having an initial boiling point of about 110 F. and an end boiling point of about 420 F. is separated from the feed preparation column at a rate of 108 bbls./hr. and charged, together with 64 bbls./hr. of a recycle fraction recovered as rafiinate from the solvent extraction stage of the present process into a catalytic reforming unit, hereinafter more fully described; (3) a bottoms residue from the feed preparation .column consisting of components boiling above the gasoline boiling range is removed from the column and discharged from the present process ow.

The 172 bbls./hr. of catalytic reforming reactor feed (made up of 108 bbls./hr. of straight-run distillate and 64 bbls./hr of recycle rafiinate) is charged, together with 189 s.c.f.m. of hydrogen (approximately 6 moles of hydrogen per mole of hydrocarbon feed) at a temperature of 752 F., at apressure of 200 p.s.i. and at a rate-sufcient to provide a space velocity of 1.0 into a catalytic reforming reactor packed with catalyst consisting of platinum supported on a combined alumina-halogen composite, the catalyst being of the type referred to in the petroleum refining art as a plat-forming catalyst, which is capable of converting the parafnic and naphthenic components of the feed stock into aromatic derivatives. The reformate efuent from the catalytic reforming zone, at a rate of 164 bbls./hr., containing 21% by volumeof aromatic hydrocarbons consisting predominantly of bcnzene, toluene and C8 aromatics, and some unconverted parains is charged into the mid-portion of a liquidliquid countercurrent solvent extraction column containing sieve-deck trays for effecting intimate contact between the hydrocarbon feed stock and solvent charged into the top ofthe column. The solvent, comprising recycledV diethylene glycol containing 7.5% by Weight of water isv charged at a rate of 16,000 bblsJhr. into the top of the extraction column at a temperature of 298 F. and at p.s.ig.4 vA light paraffin-aromatic hydrocarbon fraction-recovered from the overhead of the stripping column, hereinafter described and consisting predominantly of C5` parains and benzene is charged at a rate of 78 bbls./hr. into the bottom of the evtraction column at the aforesaid temperature and pressure conditions. A raffinate stream comprising'non-extracted parainic hydrocarbons is removed from the top of the extraction column at a rate of 64 bbls./hr. and after water-washing and drying, is fed into the platforming reactor in admixture with the straight-run distillate, as aforesaid.

, A rich solvent stream containing dissolved aromatic vhydrocarbons is removed from the bottom of the extraction column at a temperature of 290 F. and at a pressure of 100 p.s.i. and charged into the flashing section of a stepwise pressure reduced stripping column for recovery of the hydrocarbon solute from the rich solvent. The pressure is reduced in the flash section to 50 p.s.i., resulting in the vaporization of the aforementioned 78 bbls./hr. of light vapor overhead containing 88% by volume of benzene. The rich solvent residue from the flash section is allowed to flow into a secondary ash section wherein the pressure is reduced to atmospheric pressure and the rich solvent residue is heated in the reboiling section to a temperature of 304 F. Steam Ais injected into the reboiling section `at a rate of 4.5

bbls./hr. (equivalent) of water, the combined distillation effects removing 35 bblsJhr. of aromatic extract consisting of a 99.9% aromatic fraction containing 78% benzene, 14% toluene and the remainder C5 aromatics. This extract is reserved for blending with gasoline to form a high octane motor fuel.

The lean solvent stream removed from the bottom of the rich solvent stripping zone at a temperature of 304 F. and at atmospheric pressure contains approximately 0.016% by weight of polycyclic aromatics. In accord ance with the present process, this stream is -fed into the top of a countercurrent, liquid-liquid lean solvent wash column into which a combined stream comprising the light paraffin overhead from the feed preparation column (consisting of 35 bbls./hr. of C5 and C5 parafiins) and 2860 bbls./hr. of C5 hydrocarbon made up in part from recycle sources and the remainder from externally supplined n-pentane is fed into the bottom of the column. The overhead from the lean solvent wash column, at a rate of 940 bbls/hr. is fractionated lto recover 4.6 bbls./hr. of a mixture of naphthalene, monoand dimethylnaphthalenes and a small amount of higher naphthalene homologs. The light paratn overhead from this column is diverted into a gasoline blending tank for mixing with the monocyclic aromatic hydrocarbon extract hereinabove indicated. The washed, lean solvent substantially free of polycyclic aromatics removed from the bottom of the wash column at a rate of 17,000 bbls./hr.

and at 298 F. is passed into a packed distillationV column operated at atmospheric pressure. Heat is sup plied to the column through a reboiler in the bottom of the column. Approximately 11240 bbls./hr.. of light hydrocarbon overhead is removed Ytrom the top of the column and recycled to the wash hydrocarbonmake-up supply, as indicated above. The lean solvent residue from the bottom of the distillation column is pumped at 100 p.s.i. into 4the top of the solvent extraction column as recycled lean solvent at'a rate of 16,000 bbl'sJhi-j as previously described. Y

Utilizing the indicated combination of catalytically reforming, solvent extraction and lean solvent wash procedure,rthe catalyst in the reforming zone remains active for Vlong periods of time, having an average life of approximately 530 days. In a similar process, except that the lean solvent stream recovered from the stripping column is recycled directly to the solvent extraction zone without `washing with light paraln fraction, the reforming catalyst life `is1 of substantially shorter duration, averaging about 1-05 days. In the latter type of operation, furthermore, the quantity of polycyclic aromatics contained in ythe lean solventv stream gradually v.increases toa level at which the lean solvent must be'regenerated after 56 hours Yof recirculation in the process, effected by removing 2% by volume of the .solvent circulation per hour and redistilling the solvent' to recover the diethylene glycol. The polycyclic aromatics thus removed are separated in `an impure and unsatisfactory condition.

I claim as my invention:

l. A process for producing an aromatic concentrate whichY comprises catalytically reforming a gasoline boiling range fraction at reforming conditions whereby at least a portion of said fraction is converted into monocyclic aromatic hydrocarbons contacting the reformate product with a solvent which selectively extracts the aromatic componenets therefrom -to form a rich solvent containing said aromatic components in solution, separating said rich solvent from a raffinate comprising nonaromatic hydrocarbons in said reformate, stripping said rich solvent to recover an aromatic extract from a lean solvent residue, recycling said ratlnate toY said reforming step, washing said lean solvent with a liquid, non-aromatic wash hydrocarbon of suicient quantity tol extract polycyclic aromatic hydrocarbons from said lean solvent, separating wash hydrocarbon eluent comprising excess washz hydrocarbon and said polycyclic hydrocarbon from lean solvent substantially free of polycyclic aromatics, and recycling the thus washed lean solvent to said contacting step. Y

2. The process of claim l further characterized in that said wash hydrocarbon is substantially paratlnc.

3. Ihe process of claim 1 further characterized in 12 that said wash hydrocarbon comprises C5 paratiinic hydrocarbons.

4. The process ofv claim l further' characterized in'that said wash hydrocarbon is a paranic hydrocarbon fraction boilingata temperature above the end boiling point of said gasolineboiling range fraction.

5. Thev process of'claim 4 .further characterized in that said wash hydrocarbon is a fraction boiling in .the kerosene range. Y

6. The process of claim l further characterized in that said wash hydrocarbon is -a parainic hydrocarbon fraction boiling ata temperature below the initial boiling point of said pasoline boiling range -fraction.

7. The process of claim 1 further characterized in that said .wash hydrocarbon is mixedl with said lean solvent at substantiallyV the same temperature as said contacting step. v

8. The process of. claim 7 further characterized in that said wash hydrocarbon comprises C5k parafins and said washing step is eiected at a pressure sulicient Vto maintain the wash hydrocarbon in substantially liquid phase.

9. The process of claim 1 further characterizedin that said solvent is a polyethylene glycol.

10. TheY process of claim 1 further characterized in that the washed lean solvent separately recovered from the wash hydrocarbon effluent is subjected to distillation to thereby recoverwash hydrocbaron solute from washed lean solvent.

11. The process of claim further characterized in that the wash hydrocarbon overhead from said distillation is recycled to said washing step.

12. A process which comprisesfractionating agasoline distillate to separate therefrom a light fraction containving C5 parains anda Iheavier fraction, rcatalytically reforming said heavier fraction, subjecting ,resultant re-v formed products to solvent extractionwi-tha selective solvent for aromatica, separating the aromaticirich solvent from paranic ranate and supplying4 the latter to the forming step, stripping monocyclic aromatics from the solvent, washing the stripped solvent with a sucient quantity of said light fraction to extract polycyclic aromatic hydrocarbons from the solvent, and recycling the thus washed solvent to `the solvent extraction step.

References Cited in the tile of this patent Manley May l5, 1956

Claims

1. A PROCESS FOR PRODUCING AN AROMATIC CONCENTRATE WHICH COMPRISES CATALYTICALLY REFORMING A GASOLINE BOILING RANGE FRACTION AT REFORMING CONDITIONS WHEREBY AT LEAST A PORTION OF SAID FRACTION IS CONVERTED INTO MONOCYCLIC AROMATIC HYDROCARBONS CONTACTING THE REFORMATE PRODUCT WITH A SOLVENT WHICH SELECTIVELY EXTRACTS THE AROMATIC COMPONENTS THEREFROM TO FORM A RICH SOLVENT CONTAINING SAID AROMATIC COMPOUNDS IN SOLUTIONS, SEPARATING SAID RICH SOLVENT FROM A RAFFINATE COMPRISING NONAROMATIC HYDROCARBONS IN SAID REFORMATE, STRIPPING SAID RICH SOLVENT TO RECOVER AN AROMATIC EXTRACT FROM A LEAN SOLVENT RESIDUE, RECYCLING SAID RAFFINATE TO SAID REFORMING STEP, WASHING SAID LEAN SOLVENT WITH A LIQUID, NON-AROMATIC WASH HYDROCARBON OF SUFFICIENT QUANTITY TO EXTRACT POLY-