US2840620A - Segregation and recovery of naphthenic hydrocarbon concentrates - Google Patents

Description

I' I' Il' I* d n i 0 mw w m s 2 Mh. D@ Wh. .0.0 Nh. A h. S .M M. E 6 lv l# m .H e u N 0, 1v m G m R M e N M GB m 2, L1 E, mm/ mv v a A c Sv a om wm m d gf E nn a Lm m R. b Q w w S A' Mmmm m. L. m fr E V. E am mm R @A m Hm v. *mv dv S RE N .M J W 1| ER OJ. Ww ,1a Dv GD Wd S n D N 3 lo. M. ,WSW m/ U RF A D A| 6mm m, S W. 3 QN/ W /I M, w m ,Zn mm w w M/ mw w.. w w. m 1 w. 0 D a a .o m w, 3 w N, j w N w w E@ n w J w. Q j n S vm. w f, f u f u. w n. S /S w 9 l A .1 \.kv 1 m e 1| n lv l, m Rs n /mm mm HR. .J SQu .wv NN Q Ew Q United States Patent lO SEGREGATIN AND RECOVERY OFVNAPH- THENIC HYDROCARBON CONCENTRATES Clarence G. Gerhold, Riverside, and Donald B. Broughton, Chicago, Ill., assignors to Universal Oil Products Company, Des Plaines, Ill., a corporation of Delaware Application `luly 12, 19754, Serial No. 442,728

11 CIEIHS. (Cl. 26o-668) This invention relates to a process for segregating naphthenic hydrocarbons from a hydrocarbon charging stock in a solvent extraction process. More specifically, the present invention concerns a two-stage solvent extraction process wherein a select hydrocarbon stream from the primary stage is employed as the charging stock to the secondary extraction stage and a product consisting essentially of the most volatile naphthenic hydrocarbons from the feed stock is recovered from the secondary extraction stage.

It is thus one object of this invention to prepare a naphthenic hydrocarbon concentrate employing a hydrocarbon mixture comprising paraflinic, naphthenic and aromatic hydrocarbons as starting material, effecting such separation by simple and expeditious means. Another object of this invention is to increase the conversion of naphthenic to aromatic hydrocarbons in a reforming process.

' In one of its embodiments the present invention relates to a process for separating in acountercurrent solvent extraction zone a mixture of hydrocarbons comprising parainic, naphthenic, and aromatic components employing a solvent more dense than said mixture and in which the naphthenic and aromatic components are -at least partially soluble, removing from the lower portion of said zone a primary fat solvent stream, removing from the upper portion of said zone a ranate comprising the paranic components of said mixture, introducing said mixture into said zone at a point between the raflinate and fat solvent outlets of said zone, vaporizing from said primary fat solvent a light overhead comprising aromatic and naphthenic hydrocarbon components of said mixture, subjecting at least a portion of said overhead to solvent extraction in a secondary extraction zone, recovering a secondary raflinate from said secondary zone, comprising the relatively low molecular weight naphthenic components of said mixture, recycling a reux stream selected from l) a portion of said secondary ranate and (2) a portion of said light overhead to said primary extraction zone, and introducing said reuxsinto said primary extraction zone below the inlet of said mixture therein.

More specific embodiments of the invention relate to specific naphthenic hydrocarbons to be recovered as products, particular process flow arrangements to accomplish one or more of the aforementioned specific objectives, and particular operating conditions found to be most suitable for such objectives.

The process of this invention may be operated for the specicpurpose of recovering a naphthenic hydrocarbon individual or a naphthenic hydrocarbon concentrate consisting essentially of a single naphthenic hydrocarbon which is valuable per se as a raw material or as a starting material in the preparation of other derivatives, such as naphthenic acids or aliphatic acids by oxidation thereof. The process may also be operated to recover ice purpose of separating the unconverted naphthenes from the aromatic-containing product for further conversion in the reforming process to such aromatic product. In most naphthene-to-aromatic hydrocarbon reforming processes the conversion approaches an equilibrium state and the reformed product, by virtue of such equilibrium, contains a substantial proportion of unconverted naphthenes. Thus, in the conversion of cyclohexane and methylcyclopentane to benzene through the mechanism of dehydro-isomerization of such naphthenes in a reforming reaction, the product effluent from the reforming reactor generally contains a signicant proportion of unconverted cyclohexane and methylcyclopentane. In the operation of such typical reforming processes a fraction representing all of the unconverted naphthenes in the product is separated from the reforming reactor effluent and recycled as feed stock to the reforming reactor for further reprocessing. Since any fraction thus separated by simple or fractional distillation contains benzene as an azeotrope with the methylcyclopentane and cyclohexane components in the mixture, recycle of the fraction to the reforming zone without prior separation of the benzene therefrom tends to reduce the desired conversion of the naphthenes to benzene by virtue of the mass action effect of the benzene on the equilibrium in the reforming process. By applying the principles of the present invention, that is, by separating the benzene from the recycle fraction and discharging the benzene from the recycle fraction, thereby providing a naphthenerich recycle stream, the equilibrium is shifted in favor of the formation of benzene `from the recycled naphthenes when the latter is subsequently recycled to the reforming zone.

The present invention, therefore, may be operated for the alternative objective of either producing a naphthene concentrate which in the case of cyclohexane may be utilized to provide the source of raw material for Subsequent conversion to by-products such as adipic acid, for example, or the separation stage may be operated in combination with a reforming process for the ultimate production of benzene, toluene, xylene or a mixture-of two or three of these aromatics, in accordance with the aforementioned principles affecting the equilibrium conversion of naphthenes to aromatic hydrocarbons.

Suitable hydrocarbon mixtures utilizable as feed stocks in the present process may be selected from any sourceV a product comprising a mixture of naphthenes utilizable of hydrocarbon mixtures containing paraiinic, aromatic, and naphthenic hydrocarbon components, and most appropriately from such mixtures which normally form azeotropic or constant boiling mixtures with each other. Thus, straight run gasoline fractions which boil over a relatively narrow boiling range and which contain C5, Cs and/or C7 hydrocarbons of the paraffin, aromatic and naphthene series maybe utilized as a charging stock in the present solvent extraction process. Since such mixtures are inherently present in the product formed from thermal or catalytic reforming processes, distillate fractions separated from the products of such reforming processes provide one of the most suitable sources of feed stock in the present separation process. Thus, a fraction separated from a reformed gasoline stock and containing C6 hydrocarbons such as methylcyclopentane, cyclohexane, the normal and branched chain C6 paraflins, and benzene may provide a suitable charging stock in the present process. Such fractions generally boil up to about C. and are separated as adistillate fraction 2.84am. f

frnatths. liquid. predutotthe hydrpfsrmins@averses process. The naphthene orunaphthenes to be recovered from such a fraction may be cyclopentane, methylcyclo- Bestens.Qryslohexane.. Artes@ Stock having, a.V higher eadrroistfmay; also4 bei` massed.. t0l the Vprecie-Ss, forth@ 'www f.;CyC10hxane for an alkvlvclohexane for eX- amrlc 11s/.Charasse feed stokboilins up @about 140 C., such a fractioncontaining cyclohexane, the monoandrpolymethylcyclohexanes, tolueneA and thei normal and straightfuchainCe andC7 paranls. Broad and narrow boiling range fractions, including `higher end boiling point mixtures, may also be utilized, thenaphthene to be recovered generally. beingoneror morev of the lowest, molecular weight, naphthsnespressnt in` webV a mixture The method f Separating naphthnis hydrocarbons from `rnirwtttu'es of the same v,withother hydrocarbo-ns provided by the present invention involves a, two-stage'` solvent extraction process ,wherein the fat solvent stream` formed dwing the solvent extractionis subjected toI a stripping operation to separatea light overhead, comprising a mixturepof the desired naphthene product and its aromatic analogsLand thereafter subjecting-the resulting light overhead-to a secondary extraction to segregate the naphthenes from the aromatic hydrocarbons.- The v process for effecting such separation, comprising this invention, is further described in the accompanying diagram which illustrates the method in conjunction with a reforming process, the combination being one of the preferred embodirnents of the present invention.

Referring to the accompanying drawing, a suitable mixed `hydrocarbon feedstock containing naphthenic precursors of aromatic hydrocarbons is charged into a cornbined reforming-solvent extraction process comprising one of the embodiments of this invention through line 1 in amounts controlled by valvehZ and is thereafter transferred by means," of pumpk 3 and, line 4 Vat a suitable hydroforming-reaction temperature and pressure into reforminglreactor 5. The desired reaction pressure, usually fromwabout SOto about A2000 p. s. i. g. is determined by the pressure developed by pump 3 and the reaction ternperature, usually v from about 800 to about 1200i F., is determined by the temperature at which the feed stock is heated in furnace 6 which is placed in the feed line to the reforming reactor 5. The preferred operating temperatures and pressures are fixed by the process requirements for effecting the reforming reaction; that is, whether the reaction is effected by exclusively thermal means or with the aid1 of a suitable reforming catalyst. In order to suppress carbon formation during the'reforming reaction, hydrogen may be admitted with the charge stock, for example, through line 7 in controlled amounts determined by valve 8. Such mixed hydrogen-hydrocarbon feed stocks are particularly desirable when the reforming reaction is effected in the presence of a catalyst such as a metal selected from group VIII of the periodic table supported ou an inert or acidic support, such as platinum or palladium deposited on alumina containing a. small amount of combined halogen, or an iron, nickel and/ or cobalt metal or metal oxide, deposited on alumina or onwalumina-silica composite. Other suitable catalysts include the group VI metal or metal oxides composited with an inert support such as alumina, including, for example, chromia-alumina composites, molybdena-alumina composites, etc. Following the required period of residence of the feed stock in reforming reactor 5, during which time the naphthenic hydrocarbon components ofthe feed stock undergo dehydrogenation and isomerization reactions to form, `in part,` thc analogous aromatic hydrocarbons therefrom, the products are removed from reactor through line 9 and thereafter discharged into fractional distillation column 10.. Because of the vequilibrium relationships between the aromatic and naphthenic hydrocarbon components of the feed stockl and the resulting incomplete conversionof naphthenes to the yanalogous aromatichydrocarbons, the product of the reforming 4' @estiva contains @appreciable quantity 0f unconverted naphthenes, which in the case of benzene production, may. consist of methylcyclopentane, cyclohexane, and polyalkylated cyclopentanes which form benzene by dehydrogenation and isomerization, and which may be accompanied by cracking of one or more alkyl groups from the cyclopentyl nucleus. In the case of the ultimate production of toluene from the naphthenic hydrocarbon feed stock, the toluene precursors may consist of dimethylcyclopentane, methylcyclohexane and other polyalliylcyclopentanes and cyclohexancs. The naphthcnic precursors of xylene may consist of trialkylcyclopentanes and diand polyalkylcyclohexanes. These hydrocarbons may be present individually or in admixture 'in the hydrocarbon feed stock, depending upon the boiling point range of the latter; the product of the reforming reaction may therefore contain benzene, toluene, xyleneand polyalltyl-substituted jbenzencseither individually or 'in adm ixture,vas well as the unconverted naphthene precursors.

The reforming reaction product charged into fraction.- ator 10 is preferably segregated into select fractions whose boilingV ranges depend upon the product desired in the presentjprocess. Thus, when the aromatic primaryproduct to be recovered is benzene, a fraction boiling up to about 200 F. is separated from the reforming reaction product in fractionator 10 and thereafter utilized as feed stock in the subsequent stages of the present process. If the desired primary product is toluene, and only toluene, a fraction boiling from 200 to 270 F. is separated in fractionator10. A correspondingly higher end point boiling fraction for recovery of xylene or a broad boiling rangefraction, boiling up to about 300 F. for theV recovery of a mixture of aromatic hydrocarbons, including benzene, toluene and Xylene, may be selected as a sidecut from fractionator 10 for use as feed to the subsequent extraction stage of the process. One or more of these fractions may beseparated in fractionator 10 as side-cuts, removed from the column through side-cut draw-offs,` such as line 11. The light gaseous components of the reformed product, such as recycle hydrogen may be removed from fractionator 10 through line 12 and valve 13 while the bottoms comprising material boiling above the end point of therdesired side cut is removed from column 10 through lineA 14 and valve 15 to storageor other disposition.` Heat required for the fractionation may be supplied by means of reboiler 16.

The side-cut to be utilized as feed stock in the subsequent extraction stages of the process, removed from column`10-through line 11, is transferred by `means of pump 17 in. theliquid phase through line 18 in amounts controlled by valve 19 into primary solvent extraction zone 20 f or effecting thedesired separation of unconverted naphthenes from the aromatic primary product. A suitable selective solvent for the aromatic and naphthenic components of the feed stock, generally of higher density than the hydrocarbon feed, is introduced into the upper portion of extraction zone 20 through line 21, the solvent generally consisting of the lean, regenerated solvent recycled from subsequent stages ofthe process. Make-up portions of the solvent, designed to replace losses of solvent from the system, may be introduced into the processow from storage through line 22 in controlled amounts determined by'valve 23. The particular solvent composition for use in the present process is selected on the basis of its selective solvent action for the aromatic component of the feed stock, a more limited solvency for the 'naphthenic hydrocarbon components, -and the least solvency foraliphatic hydrocarbon components of the mixture. Solvents of this type may be selected from a widevariety of, organic compounds, including the alcohols, glycols, polygly'cols, .glycol,ethers, alcohol esters of Y organic acids, certain organicA nitriles. and others well 'y toward aromatichydrocarbons'.

recognized inL theA solvent extraction, art for their selectivityv The selectivity of the solvent for aromatic hydrocarbons may. be enhanced by the inclusion of an anti-solvent, suchv as water, in the composition, the latter further reducing the solubility of non-aromatic hydrocarbons inthe solvent. One of the preferred classes of such selective solvents are the glycols and the polyalkylene glycols containing from about 0.5 to about 25%, and preferably from 2 to about 10% by weight of water, such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, mixtures of one or more of the aforesaid glycols or the mixed ether-glycols, such as trimethyl ether of glycerol.

The mixed hydrocarbon feed stock is introduced into extraction zone 20 below the point of introduction of the solvent composition and ilows upwardly in countercurrent relationship to theV more dense solvent,v the aromatic hydrocarbon components of the feed stock being removed therefrom by the selective solvent action of the solvent in contact therewith. Under the counter-y current contacting conditions maintained in the column the solvent becomes progressively richer in aromatic components and leaner in paratlinic components of the feed stock, which may initially tend to dissolve in the solvent as a result of the initially low concentration of aromatic hydrocarbons therein. Although the solvent tends to dissolve aromatic hydrocarbons more readily than naphthenes, and naphthenic hydrocarbons more readily than aliphatic hydrocarbons, and although the aromatics and naphthenes tend to displace parafns from the solvent, a small proportion of the paratins contained in the mixed hydrocarbon feed stock remain dissolved in the fat solvent stream leaving the bottom of the extraction zone, unless such paranic components are completely displaced therefrom by a stream of such aromatic and/or naphthenic hydrocarbons contacted with the fat solvent just prior to removal of the latter from the extraction zone. In order to effect such displacement of aliphatic hydrocarbons from the fat solvent stream a reilux stream containing such aromatic and/or naphthenic hydrocarbons is introduced into the lower portion of the primary extraction zone 20 and countercurrently contacted with the fat solvent stream just prior to'its removal from the extraction zone, thereby displacing the dissolved parains into the railinate flowing from the top of the column. The reflux stream, derived from a recycley fraction as hereinafter indicated, is introduced into the extraction zone, preferably in the lowermost portion thereof, in order to provide the greatest countercurrent contact in the extractor with the fat solvent stream. By virtue of such selective displacement action of aromatic and naphthenic hydrocarbons on the parains normally dissolved in small amounts in the fat solvent, the parainic contaminants are displaced into the rising hydrocarbon rainate stream removed from the uppermost portion of the extraction zone through line 24 and valve 25. ,In order to provide the aforementioned countercurrent contacting action between the hydrocarbon feed and solvent and the displacement action in the lower portion of the extraction zone, the feed stock mixture is generally introduced into the column between the points of removal of the parallinate at the top of the column and the extract phase at the bottom of the extraction zone, the reliux stream being charged into the extraction zone at a point just above the outlet port of the fat solvent stream. The fat solvent or extract phase containing the aromatic and naphthenic hydrocarbon components dissolved in the solvent is removed from the extraction zoney through line 26 and is transferred by means of pump 27 and line 28 in controlled amounts determined by valve 29, into the upper portion of fat solvent stripping column30, wherein the hydrocarbon solute components ofthe fat solvent stream are vaporized therefrom by-distillation with heat supplied to the stripping column'by reboiler 31 or by a jet of steam, not illustrated, introduced into the column. The presence of the solvent inthe stripping zone tends to increase the boiling point of the aromatic component dissolved therein relative to the naphthenic components and in order to provide a fat solvent residue containing only dissolved aromatic hydrocarbons for subsequent vaporization from the residue in pure form, suticient heat is introduced into the fat solvent stream to strip the latter completely of non-aromatic hydrocarbons prior to vaporization of the aromatic solute therefrom. In thus stripping the non-aromatic solute from the fat solvent, however, a portion of the aromatic dissolved in the fat solvent necessarily distill over the light vapor overhead before the fat solvent residue is free of non-aromatic solute components because of the partial vapor pressure of these aromatics. The aromatic components, free of non-aromatic hydrocarbons, `are removed from zone 30 as a side-cut through line 32 and valve 33 into storage or for further treatment, not illustrated. In the case of a feed stream to the solvent extraction zone containing a mixture of homologous aromatic hydrocarbons, a greater proportion of the more volatile aromatic component, such as benzene, will be distilled out of the fat solvent in the light'overhead vapor, and a greater proportion of the homologous aromatic, such as toluene and xylene, will be stripped from the fat solvent as the side-cut product. The solvent residue from which the aromatic solute components have been more or less completely vaporized is removed as a bottoms stream from the lower portion of stripping zone 30 through line 34 and is transferred by meansV of pump 35 into regenerated solvent recycle line 21 for reuse as lean solvent in extraction zone 20.

The light vapor overhead stripped from the fat sol'- vent and containing all of the non-aromatic as Well as a` portion of the aromatic components of the `fat solvent stream is removed from zone 30 through line 36 containing valve 37 and introduced into fractionating column 38 for separation of the aromatic and non-aromatic components of this stream. In. the absence of the solvent which normally would otherwise increase the boiling point of the aromatic hydrocarbon component if distilled in its presence, the naphthenic and aromatic hydrocarbons present in the essentially hydrocarbon lightvapor overhead boil at their normal boiling points,ror at the boiling point of the azeotrope thereof, making a pre-r liminary partial separation between the aromatic and naphthenes feasible by fractional distillation. Because of the presence of naphthenes of the same number of carbon atoms as the aromatic present in the light vapor overhead, however, the lightest fraction distilled from the hydrocarbon mixture is an azeotropic mixture of the lightest aromatic, and the analogous naphthenic components present in the overhead. The overhead from fractional distillation column 38 is, however, richer in naphthenes thanrthe equilibrium mixture remaining in the column, the aromatics tending to concentrate through loss of overhead naphthenes in the higher boiling residue within column 38. The latter residue, heated by reboiler 39, and containing a major proportion of the aromatics charged into column 38, provides a desirable source of hydrocarbon reflux to extraction zone 20, the use of column 38 bottoms as the latter reflux stream -also providing a means of recovering the aromatic components inthe system. The aromatics ultimately recovered from the `fat solvent stream formed in zone 20 also recover the aromatics present in the aromatic bot-- aromaticsmwhich distill over from column 38, in thef' ofthe solventhasan azeotropic mixture, the overheadvapors being removed-from column 38through Enel and valve 45 and` transferred by means of pump A16am! line 47 into secondary `extraction zone 48. Selective solvent extraction of the jsecondary overhead in zolle.A in accordance with this invention eiects the separation of the naphthenic from the aromatic cornponents of this `fraction and thereby provides a means ofrecovering the naphthenic concentrate of this process. Solvent extraction asa method ofsegregating the aromatic from the naphthenic components of the secondary overhead provides the most Yconvenient and readily operable means for effecting such separation be-j causeof Ythe relative solubilities of the two classes of hydrocarbons Ain the solvent, the solubility of the aromatic componentsLcomprising the secondary overhead displacing ,heavier naphthenes, and parafns contained in the feedstock from thefat solvent inthe lower portion ofextraction Azonel20. The portion ofnaphthenic product reserved forV use as vreflux is `removed from product line l through line 53 in controlledjamounts determined by valye 54 and i`sk Vtransferred by means of pump 55 into line 56 VfromV which' the reflux portionis removed through line 57andvalve S8 for discharge into primary extractionV zone 20.l The reflux stream .is preferably charged into thelowermosttray of zone 20, immediately above the fat solvent outlet, in order to accomplish countercurrent Contact with the fat solvent stream just prior to removal of the latterfrom the extraction zone and transirf the solvent being substantially greater than the naph- `hydrocarbon components. Therefore, the mere contact of the secondary overhead with the selective solvent, preferably in a countercurrent ow arrangement, will form a fat solvent stream containing the aromatic components and a rainate stream consisting substantially ofpure naphthenic product. Any naphthenes dissolving fthe secondary fat solvent are returned to the process `tlow,"and,thereby ultimately recovered because of the provision herein for recycling the secondary fat solvent streamto `the primary fat solvent stripping column.V The solvent for the secondary extraction zone 48 may be the same, as or `different from the`solvent utilized in primary extraction Azone 20 and is preferably the same solventto enable a single fat solvent stripping column to( be `utilized for both the primary andsecondary fat solvent streams,` the product recovered from both streams being the aromatic component of'the feedstock.

`Apreferred arrangement for this purposeis to 4utilize the regenerated solvent recovered as the lean solvent stream from stripping column as the source of `lean solvent for secondary extractor 48, Yand forthis'purpose a side stream of solvent is removed frorn regenerated solvent return line 21 and'is thereafter transferred `by pnmpinto secondary solvent feed line 49 in controlled amounts `determined by valve 50. The solvent stream is conducted in to the upper portionof secondary extraction zone 48, and' permitted to flow downwardly` in countercurrent relation shop to the rising hydrocarbon stream introduced into zone 48 through line 47. The secondary overhead stream comprising the feed to extraction zone 48 is admitted into `column 48 at a point substantially below thesolvent inlet and preferably in thelowermost portion' of the column. The naphthenic hydrocarbon component or components, constituting the lightest naphthenes present in the initial `feed stock do not dissolve to any vsubstantial degree in the `presence of aromatic hydrocarbon in the solvent and therefore may be removed from the upper portion of zone 48` as a rainate stream through line 51 and valve 52 to product storage or for further fractionation to separate 4individual naphthenes therefrom. The aromatic hydrocarbons which selectively dissolve in the solvent stream charged into secondary extractor 48 may be recovered from the resulting fat solvent in a secondary stripper,rnot illustrated,

`but preferably are recovered with the aromatics present in the primary fat solvent stream in stripper 30; for this purpose thefat solvent from the secondary extractor 48 is! removed through line 51' and valve 52 and charged into line 26 leading to stripper 30. `The aromatic pro-V duct stream removedthrough line- 32 from stripper 30 thereby contains all the aromatics present inthe sys-l portion ofthe naphthenic product `asa reflux stream in primaryfextraction zone 20, thel light lnaphthenicwproduct The Vnaphthenic hydrocarbon recovered from secondary; extraction Vzone 48 through line 51 consists of substantially fer to the strippingrcolumn., Bythns contacting the fat solvent stream with the light naphthenes just prior to stripping the fat solvent, maximum effective displacement of heavy naphthenes and parains is thereby accomplished.

When the ultimate purpose of the present process is the conversion of naphthenes to aromatic hydrocarbons in the aforementioned Vreforming stage, rather than the recovery of a substantially pure naphthenic hydrocarbon product, the naphthenes removed from product line 51 throughline 53 may be transferred by means of pump 55 through line 56 and valve 59 into line 1 which feeds into reforming reactor 5, whereby the naphthene to aromatic molar ratio inthe reforming zone is increased, likewise increasing the conversion of naphthenes to aro-` matics.; By manipulation of valve 58 and 59, either a minor proportion or a major proportion of the naphthenic product may be either recycled to the reforming 'reactor or returned to the vprimary extraction zone as a reux stream therein. It is to be noted however that at least a portion of the light naphthenes recovered as product must be diverted into line 57 for use as reflux in order to obtain the aforementioned selective displacement of heavy naphthenes and parains from the primary fat solvent stream.r Since both the aromatics and light naphthenes are useful as a source of reflux in the primary ex-` traction zone to displace heavy parailins and naphthenes fromjthefat solvent prior to stripping, an alternate supply of the reflux stream which contains both of said aromatic and naphthenic components is the light overhead from the stripping zone,`the latter being` recycled to reflux line 53 .from overhead line 36 through conduit 60, the amount thereof being controlled by valve 61.

Other modifications of the process are obviously feasible and the preferred method of operation which is se. lected herein for illustrative purposes only in the following example isnot intended to limit the generally broad scope of the invention in strict accordance therewith.

Example A naphthene-base petroleum stock boiling from an initialboiling point of4 about 65 F., up to an end boiling pointfof about 400 F. and containing the following classes Aof hydrocarbons in their indicated proportions:

. Percent Paratfins, 63 Olens 1 Naphthenes Y 28 Aromatics L--- 8.3

` forming `reaction. f The conversion of f naphthenic` to aromatic hydrocarbons is anequilibrium conversion which-lis determined atleast in part by the concentration ofLla'ron'latiesl -intheefeed stock-to the Platformingreaetor:

9 The reformed product .contains the following classes of hydrocarbons in their indicated proportions:

The normally liquid portion of the product is subjected to solvent extraction under countercurrent ow conditions in a column into which the feedstock is introduced on approximately the center plate of the column, the solvent, consisting of a 7.5% aqueous solution of diethylene glycol, being charged onto the top tray of the column and allowed to percolate downwardly through the column against the rising stream of liquid hydrocarbon feed stock. A rainate stream composed almost exclusively of the paraflinic components of the feed stock is removed from the top tray of the column and discharged from the process ow. The naphthenes present in the rallnate, as shown by analysis of this stream were C7, Cs, and higher molecular weight alkylcyclohexanes and cycloheptanes, there being substantially no Cyclopentane, methylcyclopentane or cyclohexane present in -this stream.

A reflux fraction comprising Cyclopentane, methylcyclopentane and cyclohexane, recovered as a product stream in the subsequent stages of the process, as hereinafter indicated, was charged into the bottom of the extraction column at a rate of approximately 8% by volume of the charging stock feed rate.

A fat solvent stream removed from the bottom of the extraction column at a temperature of 280 F. and at a pressure of 90 p. s. i. g. was fed into a fat solvent stripper comprising a fractional distillation column containing a reboiler, and a steam inlet on the lowermost tray into which steam at 20 pounds pressure was admitted for the purpose of stripping the last traces of hydrocarbon solute from the fat solvent. The stripper operates at essentially atmospheric pressure, except-that the uppermost trays containing liquid seals between successive plates, were operated at successively reduced pressures from a maximum of 90 p. s. i. g. on the uppermost tray. An overhead vapor stream containing 35%- by Vvolume of aromatics (predominantlybenzene)and 65% by volume of light naphthenes (Cyclopentane, ,methylcyclopentane and cyclohexane) was removed from the top of the stripper and discharged in vapor state into a fractional distillation column. A side stream removed from a lower tray of the stripper consisted of water, benzene, toluene and xylene, the hydrocarbon content of which was 99.9% aromatic. A regenerated lean solvent stream, reconstituted to 7.5% water was pumped from the reboiler section of the stripper to the top of the primary extraction column, a small side-stream being separately removed for diversion to a secondary extractioncolumn, hereinafterdescribed. y v

The stripper overhead when fractionally distilled yielded a fractionator overheadv consisting predominantly of benzene and about 38% by volume of a mixture of cyclopentane, methylcyclopentane and cyclohexane. The bottoms from the column contained no naphthenes and was composed primarily of benzene, toluene and xylene which was recycled as a reflux stream to a lower plate of the primary extraction column, being introduced into the column into an inlet approximately two plates above the inlet for the light naphthene reilux which was introduced into the bottom of the primary extraction column and which was derived by further extraction of the fractionator overhead, as hereinafter described.

The napthenic-aromatic hydrocarbon fractionator overhead was charged into the bottom of a secondary extraction column of similar design but of substantially smaller size than the primary extractor. The rainate stream from the top of the column upon analysis contains no 'f1-0' aromatic components and contains none of the heavy naphthenes present in the initial feed stock. The small bleed stream of regenerated glycol solvent removed from the bottom of the stripper was charged into the top of the secondary extractor and allowed to dow downwardly therein, countercurrent to the liquid phase hydrocarbon mixturej(fractionator overhead). A fat solvent stream removed from the bottom of the secondary extractor contained the aromatic components present in the fractionator overhead, that is, all of the benzene distilled overhead with the light naphthenes from the fractionator. A small amount, (approximately 12% of the total hydrocarbon solute presentin the fat solvent stream) of light naphthenes was also dissolved in the secondary extractor fat solvent stream. The latter stream was pumped into the supply line leading into the primary fat solvent stripper.

The light naphthenes contained in tihe secondary extractor. rainate stream contained no aromatic or parafnic components and its analysis indicated that it is made up of approximately the following amounts of each of the indicated light naphthenes:

Percent Cyclopentane About 65 Methylcyclopentane About 22 Cyclohexane About 13 reactor for use therein as supplement for the feed stock to the process, which thereby increases the total conversion of naphthenes to aromatic product (benzene) by displacement of the naphthene-to-benzene equilibrium in the reforming reaction zone.

We claim as our invention:

l. In a process for separating in a counter-current primary solvent extraction zone a-mixture of hydrocarbons comprising paraifinic, naphthenic and aromatic components, employing a solvent more dense than said mixture and in which the naphthenic and aromatic components are atleast partially-soluble, removing from the lower portion of said Vzone a'primary fat solvent stream, and removing from the upper portion of said zone a raffinatepcomprising the'paratlinic components of said mixture,f the method which comprises introducing said mixture into said zone at a point between the raffinate and fat solvent outlets of said zone, vaporizing from said primary fat solvent a light overhead comprising aromatic and naphthenic hydrocarbon components of said mixture, subjecting at least a portion of said overhead to solvent extraction in a secondary extraction zone and therein separating naphthenic fromV aromatic cornponents, recovering a secondary rainate from said secondary zone comprising the relatively low molecular weight naphthenic components of said mixture, and recycling a rellux stream selected from the group consisting of (l) a portion of said secondary raiinate and (2) a portion of said light overhead to said primary extraction zone, and introducing said retlux into said primary extraction zone below the inlet of said mixture therein.

2. In a process for separating in a counter-current primary solvent extraction zone a mixture of hydrocarbons comprising paranic, naphthenic and aromatic cornponents, employing a solvent more dense than said mixture and in which the naphthenic and aromatic components are at least partially soluble, removing from the lower portion of said zone a primary fat solvent stream and removing from ,the upper portion of said avsaoge'ao zone a raffinate comprising the `pararinic components of said` mixture, the method whichJ comprises introducing said mixtureinto said zone'ata point between theraffnate and fat solvent outletsoffsaid zone, vaporizing from said primary fat solvent in a vaporizing zonealight overhead comprising aromatic "andnaphthenic hydrocarbon components vrof said mixture, segregating atleast a portion of saidoverhead and subjectingsaid portion t solvent extraction in a secondary extraction zone and therein separating naphthenic from aromatic components, recovering aV secondary raffinate stream from said secondary zonecomprising the relatively low molecular weight naphthenic hydrocarbon components `of saidmixmre, recovering a secondary fat solventasfbottoms from said secondaryextraction zone `and supplying vthe same to saidvaporizing zone, and` recycling a reflux stream selected from the group. consisting ofY (l) aportion of said secondary rallinate and V(2) a portion of said light overhead to said primary extraction zone, and introducing said reux into said 'primary extraction zone below the inlet of said mixture therein.`

3. The process of claim 1 further characterized in that said mixture of` hydrocarbons contains a C6 naphthenic hydrocarbon.

4; The process of claim l furthercharacterized in that said mixture of hydrocarbons contains C5 naphthenic and C5 aromatic hydrocarbons.

5. The process of claim'l further characterized by introducing said mixture at approximately the mid-point and said reux stream into approximately the` bottoni of: said primary extraction zone. t

6. The process of. claim l further characterized in that said light overhead isfractionated to segregate a relatively volatile fraction comprising a naphthenic hydrocarbonV component `of said mixture from va less: volatile fraction comprising an` aromatic hydrocarbon componentof said mixture, recycling `said less volatile fraction to said primary extraction zone as a` reux stream, and introducing said reflux into the lower portion of said primary zone. 1 t

7. The process of claim 1 further characterized by fractionating, said light overhead fraction to segregate a relatively volatile fraction comprising fa naphthenic hydrocarbon component of said mixturelfrom a less volatile fraction' comprising an aromatic hydrocarbon componentV of said mixture, recycling at least a portion of `said relatively yvolatile `fraction to said primary extraction `zone as a vreliu'x stream, andintroducing said retluxi into the lower portion of said primary zone.

8. A process for the conversion of naphthenic hydrocarbons to yaromatic hydrocarbons which comprises subjecting a hydrocarbon mixturecomprising a naphthenic hydrocarbon precursor of said aromatic hydrocarbon `to reforming conditions whereby said naphthenic hydrocarbon converted to an `equilibrium mixture of aromatic and naphthenic hydrocarbons, subjecting the product of said reforming stepto solvent extraction in a primary extraction zone with `a solvent more dense than said mixture and in which the naphthenicand aromatic components arel atleast partially. soluble, `removing from thelower portion of the extraction zone a primary fat solvent. stream, removing. a rainate comprising the parainic components of said` mixture from the upper portion ofsaid zone, introducing. said mixture into the extraction zone at apoint between..the raiinate and fat solvent outlets of said zone, vaporizing from said primary fat solvent a light overhead comprising aromatic and naphthenic hydrocarbon components of said mixture, segregating at least a portion` of said overheadand subjecting said portion to solvent extraction in a secondary extraction zone and therein separating naphthenic from aromatic components, recovering a secondary rafiinate stream fromsaid secondary zone comprising the relatively low molecular weight' naphthenic hydrocarbon components of said mixture, recycling a reflux stream selected fromV the group consisting of (1) a portionof said secondary rainate and (2) a portion of said light overhead to said primary extraction zone, introducing said reflux into said primary extraction zone below the inlet of said mixture' therein, and recycling a portion of said secondaryrafnate to said reforming step.

9. A process for recovering a naphthene concentrate from a mixture of parainic, naphthenic and aromatic hydrocarbons which comprisescountercurrently contacting said mixture in a primary extraction zone with a solvent more dense than said mixture and in which the naphthenic and aromatic hydrocarbons are at least partially soluble, removing `the resultant fat` solvent from the lower portion of said zone and 'vaporizing aromatic and naphthenic hydrocarbons therefrom in a stripping zone, fractionating the resultant vapors to separate the same into relatively llight and heavy fractions, introducing the heavier fraction to the lower portion of said primary zone as reflux therein, subjecting the lighter fraction to solvent extraction in a secondary extraction zone with a solvent for aromaticsto separate the naphthenic from the aromatic components of the lighter fraction, andV supplying the fat solvent from said'secondary zone tosaid stripping zone for vaporization of the dissolved aromatics therein.

10. The process of claim V9 further characterized in that there isV recoveredas aV iside-cut from said stripping zone an aromatic product ofhigher boiling point thansaid vaporsV from the stripping zone.

11.7The process of claim 9 further characterized in that separate streams of lean solvent from said stripping zone are introduced to the upper portions of said primary and secondary extraction zones.

References Cited-in the lc ofthis patent UNITED STATES PATENTS

Claims (1)

1. IN A PROCESS FOR SEPARATING IN A COUNTER-CURRENT PRIMARY SOLVENT EXTRACTION ZONE A MIXTURE OF HYDROCARBONS COMPRISING PARAFFINIC, NAPHTHENIC AND AROMATIC MIXPONENTS, EMPLOYING A SOLVENT MORE DENSE THAN SAID MIX TURE AND IN WHICH THE NAPHTHENIC AND AROMATIC COMPONENTS ARE AT LEAST PARTIALLY SOLUBLE, REMOVING FROM THE LOWER PORTION OF SAID ZONE A PRIMARY FAT SOLVENT STREAM, AND REMOVING FROM THE UPPER PORTION OF SAID ZONE A RAFFINATE COMPRISING THE PARAFFINIC COMPONENTS OF SAID MIXTURE, THE METHOD WHICH COMPRISES INTRODUCING SAID MIXTURE INTO SAID ZONE AT A POINT BETWEEN THE RAFFINATE AND FAT SOLVENT OUTLETS OF SAID ZONE, VAPORIZING FROM SAID PRIMARY FAT SOLVENT A LIGHT OVERHEAD COMPRISING AROMATIC AND NAPHTHENIC HYDROCARBON COMPONENTS OF SAID MIXTURE, SUBJECTING AT LEAST A PORTION OF SAID OVERHEAD TO SOLVENT EXTRACTION IN A SECONDARY EXTRACTION ZONE AND THEREIN SEPARATING NAPHTHENIC FROM AROMATIC COMPONENTS, RECOVERING A SECONDARY RAFFINATE FROM SAID SECONDARY ZONE COMPRISING THE RELATIVELY LOW MOLECULAR WEIGHT NAPHTHENIC COMPONENTS OF SAID MIXTURE, AND RECYCLING A REFLUX STREAM SELECT ED FROM THE GROUP CONSISTING OF (1) A PORTION OF SAID SECONDARY RAFFINATE AND (2) A PORTION OF SAID LIGHT OVERHEAD TO SAID PRIMARY EXTRACTION ZONE, AND INTRODUCING SAID REFLUX INTO SAID PRIMARY EXTRACTION ZONE BELOW THE INLET OF SAID MIXTURE THEREIN.

Images