US2375464A

US2375464A - Production of purified aromatic hydrocarbons from petroleum

Info

Publication number: US2375464A
Application number: US447788A
Authority: US
Inventors: Edmund G Borden
Original assignee: CITLES SERVICE OIL Co
Current assignee: CITLES SERVICE OIL Co
Priority date: 1942-06-20
Filing date: 1942-06-20
Publication date: 1945-05-08
Anticipated expiration: 1962-05-08

Description

E. G. BORDEN May 8, 1945.

' PRODUCTION GF PURIFIED AROMATIC HYDROCARBONS FROM PETROLEUM Filed June 20, 1942 2 .Sheets-Sheet l INVENTOR A fonwva avalent May 8, 1945. 2,375,464

PRODUCTION OF PURIFIED AROMATIC HYDROCARBONS FROM PETROLEUM E. G. BORDEN 2 sheets-smet 2 Filed June 20, 1942 Patented May 1945 UNITED STATE-s PATENT .OFFICE PaonUc'rioN or PURIFIED AnoMs'rlo mnocsanoNs rnoM PETROLEUM Edmund G. Borden, Lime Neck, N. Y., minor to Cities Service Oil Company, New York,` N. Y., a corporationvot Pennsylvania Application June zo, 1942, sen-m1 No. 447,788 1s claims. (ci. 26o-css) from paraiiln and naphthenic`base crude petroleum oils. -Most of the4 aromatic hydrocarbons produced from petroleum oils are now used as fuel and solvents. but the present invention contemplates, the production of aromatics, such as benzene, toluene and xylene which are s'uiliciently pure to be satisfactory as nitration grade products suitable for manufacture of explosives or other chemical derivatives therefrom.

It has been found that by means of proper temperature and pressure conditions and the use of catalysts for thermal cracking, condensing and polymerization reactions, that aromatic hydrocarbons can be produced from petroleum oils regardless of the source of the petroleum. That is, the cracking, condensing and polymerization reactions yproduce aromatic hydrocarbons from other types of hydrocarbons, such as paraflins, naphthenes and oleiins. Analyses oi products which have been produced by the above-mentioned cracking, condensing and polymerization reactions show that the desired hydrocarbons,

such as benzene, toluene and xylene, always` have associated with them, other unsaturated hydrocarbons, such as oleiins, diolefins and various other alkylatedbenzenes. The contaminating hydrocarbons are soluble in the desired hydrocarbons and have boiling points very close to the boiling points of the desired hydrocarbons. It

is not practicable to separate this hydrocarbon been found which will convert all of the con'- taminating hydrocarbons to productsl which may be easily and eectively separated' from the desired hydrocarbons.

Another object of the invention is to provide a process by which the contaminating hydrocarcons in a mixture containing the desired hydrocarbons maybe selectively separated in a plurality of separate treatments.

The contaminating hydrocarbons associated with the desired hydrocarbons, i. e., benzene, toluene, and xylene, usually are monooleflns, dioleiins, polyoleiins and low boiling polymers all of which are unsaturated hydrocarbons. l have round that the polyoleiins and low boiling poly- Y mers may be polymerized catalytically with clays lsuch as Iullers earth or with phosphoric acid to lorm tarry sludges that may be easily separated from the desired hydrocarbons by settling and distillation. I have also round that the monooleflns may. be catalytically polymerized or catalytically alkylated to produce products which may be easily separated from the desired hydrocarbons by fractionation.

Another object of the -invention is to provide a process of purifying aromatic hydrocarbon mixtures by separately removing the polyoleilns and the monooleflns prior to fractional distillation of the desired hydrocarbons.

80 A further object of the invention is to Provide a thereafter catalytically converting the monoolemixture even with the best type of fractionating apparatus to obtain commercially pure desired hydrocarbons.

The primary object of the present invention is to treat the hydrocarbon mixture to be puriiied to convert the undesired hydrocarbons, without Vsubstantially affecting the desired hydrocarbons,

fins, and separating the conversion products prior to the fractional distillation of *the` desired hydrocarbons.

Al further object of the invention is to provide a continuous process by which diierent types of unsaturated contaminating hydrocarbons may be separated from desired aromatic hydrocarbons.

In accordance with this object one feature of the invention contemplates a continuous process of catalytically promoting reactions in a hydrocarbon mixture inseparate zones at diierent 'temperatures and pressures andthe separate continuous removal of the contaminating reaction products.

With these and other objects and features in View the invention consists in the process of manufacturing'and refining a mixture oi' aromatic, olenic and polymerized hydrocarbons to produce commercially pure desired aromatic hydrocarbons as hereinafter described and particu.- larly donned in the claims.

v The various features of the invention are illustrated in the accompanying drawings in which- 1 Figure 1 is a diagrammatic view inthe form of a iiow sheet illustrating apparatus in which petroleum oil may be cracked to form an aromatic hydrocarbon mixture.

Figure 2 diagrammatically illustrates in/ the form of a flow sheet an apparatus by which an aromatic hydrocarbon mixture manufactured in the apparatus illustrated in Figure 1 may be rened to separate contaminating hydrocarbons from the desired aromatic hydrocarbons; and

Figure 3 isa diagrammatic view in the form of a iiow sheet illustrating one form of apparatus by which the polyolens which contaminate a desired hydrocarbon mixture may be converted into a product that may be readily separated from the desired aromatic hydrocarbon.

In accordance with the present invention it is desired to manufacture low boiling aromatic hydrocarbons, such as benzene, toluene, and xy- 1 lene from petroleum hydrocarbons by cracking whichmay be either thermal cracking, catalytic cracking, or a combination of thermal and cata- I lytic cracking. These cracking, operations when carried out under proper pressure and temperature conditions tend toform aromatic hydrocarbons from other types of hydrocarbons, such as drawn from one of the bubble trays through a paraiiins, olens, naphthenes and cyclic hydrotopped crude, or the entire crude, is introduced through a line Ill to a vaporizing coil l2 within a furnace .,I4. i 'I'he temperature and pressure are preferably controlled so that the heated oil which ows through a line I8 into the upper en'd of a separator |8'wi1l vaporize. and the higher boiling point constituents will condense and pass to the bottom of the separator to be withdrawn through a line 20 as a resid'uum. The vapors which constitute the lower boiling cracking stockl pass out'of the top of the separator` through a line 22 and then 'pass through a coil 24 in a furnace 28. The vpressure on the vapors passing through the coil `24 may varyfrom 200 to 600 lbs. and the furnacevtemperatures are controlled to heat the oil to a temperature of 950 to 1000 F. as it passes through the coils. The heated vapors are transferred through a line 28 to the upper end of a'reaction chamber 30.v In the reaction chamber the temperature and pressure is maintained for a sufficient time to complete the initial cracking reaction of the vapors. The length of the coil 24 and the size of the chamber 30 are such that with a 'temperature of about 980 F.

from to 65% of the-vapors will be converted into, a hydrocarbon mixture which Awill have a boiling point below 500 F. As the heatedv vapors leave the bottom of the reaction chamber 30 they l are suddenly cooled by means of a large body of oil which is introduced into a transfer line 32 through a.' line 34. The mixture of vapors and cooling woil which has a temperature of from 650 I to '100 F. `pisses mio-a quenching chamber as; wherein a separation takes. place between the vapors and the unvaporlzed oil. Furthermore Jthe quenching chamber 88 acts' partially as a dephlegm'ator for condensing high boiling' hydrocarbons. The high boiling hydrocarbon mixture- I is withdrawn from the quenching chamber through an outlet 38 as a residue oil substantially as fast as it collects so that an oil body does not accumulate in the chamber. This residue oil may be recharged again if desired through the line I0. The vapors pass out'of the top of the quenching tower 36 through a line 40 and enter the lower portion of a dephlegmatlng and fractionating column 42. In the column 42 three products are produced: rst-a light hydrocarbon mixture having an end boiling point of about 220 F. which passes'overhead through a. line 44 to a condenser 48 and is collected in an accumulator Y 48. This material may-be stabilized for gasoline or fractionated to produce solvents. 'Secondnear the top of thev column a distillate is withow through a line 58 back into the column 42..

Third-the higher boiling point hydrocarbons, which constitute a charging stock of the gasoil boiling point range and which accumulate in the bottom of the column 42, are withdrawn through a lin'e 58 by a pump 80 and forced by means of the pump through a line 82 back through the coil 24 in the furnace 26. This recycle stock constitutes the main body of oil being cracked thermally in the coil 24. If desired this recycle stock may be used as a quenching medium and introduced into the transfer line 32 through a valved line 84.

The cracking reaction carried out in the coil 241l and Ain reaction chamber 30 is preferably controlled so that the intermediate distillate which is separated in the stripper 52 will contain a comparatively small amount of paraiiin hydrocarbons. The distillate which accumulates at thebottom of the stripper 52 is composed principally of aromatics, monoand poly-olefinic and naphthenic hy,- drocarbons, and has a boiling point range of approximately '170 F. to 500 F. Any paraihnic hydrocarbons in this mixture will be converted to unsaturated hydrocarbons in the following cracking operations, but it is desired to have as small an amount of parafiins in this intermediate distillate as practicablebecause the cracking reaction which follows will produce a higher percentage conversion of unsaturated hydrocarbons to aromatic'hydrocarbons if it is not contaminated by tion chamber 18 are maintained at a pressure of 300 to 600 lbs. per square inch and are heated'to a temperature from 1025* to 1125 F. These heated vapors are held in the coil 10 and chamber 18 until from 75% to 93% ofthe hydrocarbons in thel mixture are converted to aromatic hydrocarbons.

The heater mixture leaves the bottom of the reac-v tion chamber 18 through a transfer line 18 wherer as keroseneor lgas oil, introduced through a line 82. The mixture of vapors and quench oil which has a temperature of from 650 to '100 F. nows into the bottom of a dephiegmator 84 wherein the vapors and oil are separated into three cuts. Light vapors pass up through the dephlegmating bubble tower and leave through a vapor line 86 bywhich they. are conducted into a condenser 88 and re` ceiver 80. Part of the distillate recovered in the receiver 80 may be passed by means of .a pump 92 through a line 84 back into the top of the deplegmator to assist the fractional distillation. This light cut may be stabilized and used as a A motor fuel or it may be fractionated to produce a solvent. It has a boiling point range of from 75 to 250 F. An intermediate fraction is withdrawn from the dephlegmator through a line 88 and passed into a stripping tower 88. -Superheated steam or preheated gas is introduced into the bot` tom of the stripper 80 through a coil |00 to assist in removing 4low boiling'point vapors. The low boiling vapors and gas pass up through the -top of the tower and out through a vapor line |02 to pass back into the.dephlegmator 84. V A condensed hydrocarbon mixture which is a distillate in the boiling range of kerosene and gas oil accumulates in the bottom of the dephlegmator 84. This product is desirable as a cracking st oclr and is passed vthrough a line by means of a pump |04 and forced through a line |08 back tothe transfer line 22 to be recracked.

The conversation of a cracked distillate into aromatic hydrocarbons may be advantageously carried out by catalytic cracking. To accomplish' this a catalyst is supported in the yreaction chamchromium that are preferably deposited in a por ous bed of alumina. The oxids of manganese also f may. be used. Zinc chlorid, phosphorus pentoxide and silica gel al1 havev catalytic properties which tend to produce aromatic hydrocarbons.

The liquid distillate collecting in the bottom of the stripper consists of a mixture of aromatic perature yin the tower is maintalned'at from 250 F. at thetop to 400' F. near the entrance of vapors in line 8 in order to condense the polymers and carry the-polymers along with the acid.

to the'bottom of the tower. The temperature at the top of the tower may vary from 175 to 250 F.

in accordance with the material being treated while the temperature at the entrance through the line ||8 is preferably 4held around 400 F.

'I'he temperature at thebottom of the tower ||8 is approximately 350 F. The mixture of acid and polymer is withdrawn from the bottom of the tower through a'valved line |22 into agseparator |24. bottom of the separator |24 and is -forced by means of a pump |28 through a line |28 back hydrocarbons with some unsaturated hydrocart bons. This distillate constitutes the main product from which the desired benzene, toluene and xylene hydrocarbons are manufactured. It is withdrawn from the bottom of the stripper 80 through valve line` |08.

'I'he refining of the cracked distillate to make vthe desired hydrocarbons is carried out more particularly in apparatus of the type illustrated in Figures 2 and 3. Referring to Figure 2, the aromatic hydrocarbon distillate is pumped through the line |08 into a heating coil |08 in a furnace ||0 and heated to a temperature of from 400 to 600 F'. to be vaporiaed. The vapors pass 4from the coil |08 through a line ||2 into a lime treatto the top of the tower ||8 to be recirculated. Fresh phosphoric acidmay be added from time to time to the line |28 through a valved line |30 and spent acid may bef removed through valved line |8|. The polymer overflows from the top of the separator |24 throughl a line |82 and passes into an accumulator |34.4 The accumulator may further act as a separator so that acid may be withdrawn from a line |08 and polymer through a line |30. The acid withdrawn from the line |08y may bereturned to the pump |20 to be recirculated back to the tower or may be discarded. v

The phosphoric acid catalytic polymerlzing treatment of the distillate isanvimportant feature of the invention in that the acid has a selective polymerizing reaction to polymerize 'the diolefins, polyolens, and low boiling unsaturated* polymers and place them in a condition whereby they may be effectively separated from the aromatic hydrocarbon distillate. The concentration of theacid is-not important, although it is preferred to use`100% phosphoric acid. If more dilute acid is used the water will be distilled out of the acid and it will soon reach 100% concentration. In the operationv a predetermined amount of the phosphoric acid will be withdrawn' from the apparatus through the line |80 as the through the top of the tower ||8 contains some ing tower ||4. A baille is located in the center u -pors pass from the tower |,|4 through a line H8 into the intermediate Portion of 'a catalyst tower ||8 wherein the vapors are treated catalyticaliy with phosphoric'V acid for the purpose of polymeriaing the dioleflns and polyoleiins polymer tendsto contaminate the acid. The acid withdrawn through the line |20 is replaced by the acid introduced into the system through the line |30.

The aromatic hydrocarbon distillate passing polymerized polyoletlns which are dissolved in I the aromatic hydrocarbons, but these are prei?-v erably separated from the aromatic hydrocarbons by distillation. To accomplish this the va.-

"hydrocarbons which also contain the oleiinie hydrocarbon. `The polymer withdrawn from 'I'he phosphoric acid settles to the them from the aromatics.

the bottom of the tower through a line |48 and the aromatic vapors pass through a line |48 into a condenser |50. YThe condensed vapors pass into an accumulator |52 and flow from the ac cumulator through a line |54 into a, pump |58 by which they are circulated through a cooler |58. As the distillate ilows through the line |54 'hydroiiuoric acid is introduced into the distillate through a line |80. The cooled mixture flows into a reaction and separating tower |82l where the hydroiluoric acid acts catalytically to polymerize the oleilns. A temperature oi'from 30 to '10 F. is maintained in the cooler |58 and tower ||i2 to provide the proper conditions for reacting on the olenic hydrocarbons to separate If the temperature is maintained around 30 F. an alkylation reaction will be carried on whereby the oleflns will react with part of the aromatic hydrocarbons to form higher boiling alkylates that can be separated by distillation. On the other hand if the temperature is held between 35 and 70 F. the hydroiluoric acid acts as a catalyst forpolymerizing the olens to produce a sludge polymer that can be separated partiallyby gravity and drawmfrom the system from time to time through valved line |81. Polymer may be withdrawn` from the bottom oi the tower |62 through a valved line |68. The aromatic distillate in liquid form passes out of the ltop of the tower v.|82 through a line from whichA it passes into a* coil |12 mounted in a furnace |14. In the furtaminated the aromatic hydrocarbon passing through the heating coil |12 accumulates in the bottom of the fractionating tower |90 and is withdrawn through a valved line 208.y

As described above phosphoric acid may be lused for the polymerizing of` the 4polyolerlns to separate them from the aromatic hydrocarbons. In place oi' phosphoric 'acid the catalytic polymerization of the polyoleflns may be effected by means of fuller's earth. An apparatus for accomplishing this is illustrated in Figure 3. The aromatic hydrocarbon passes through the line |06 nace |14 the oil is heated to a temperature of from approximately 300l to 450 F. to provide sufficient temperature to fractionate the product for the purpose of separating the benzene, toluene, and lxylene. Preheated vapors enter a midportion of a fractionating tower |16 wherein the temperatures are maintained at a suiiicient degree to cause the benzene vapors to iow overhead through a vapor line |18 into a condenser |80. The benzene condensed in the container |80 iiows into an accumulator |82. A portion of the benzene may be pumped through a line' |84 back into the tower to secure proper fractionation of the distillates. Thehydrocarbon mixture containing toluene and xylene accumulates vin the bottom of thetower r|16 and is pumped through a line |88 into the intermediate portion of a second fractionating tower |80. The temperatures maintained in the tower |80 are such that toluene vapors pass on from the top of the tower through a vapor line |92 and flow through a condenser |94 to be condensed. 'Ihe condensate collects in an accumulator |88. Toluene from the accumulator may be pumped through the line |98 back to the top of the tower for reuxing to secure the proper fractionation. An intermediate cut is withdrawn from the tower through a line 200 and passes to the bottom of a stripping tower 202. Steam introduced through a coil 204 in the-bottom of the stripping coil acts to force-lower boiling points vapors up through the tower and out through a line 208 back to the tower |80. I The steam introduced in the stripping tower 202 tends ,to fractionate the xylene and this product is withdrawn from the bottom of the stripper through a valved line 206. Anyhigh boiling point oil or polymer that contreatment with hydroiluoric acid.

into a heater |08 where the distillate is heated to a temperature o! 475 to 650 F. to be vaporized. The -heated vapors pass through a line 2|0 into the upper portion of a catalytic treating tower 2 v|2. In the main portion of the tower 2|2 is located a granular body of yfullers earth 2|4. As the vapors pass through the fullers earth the temperatures. vary from 475 at the top to 250 F. at the bottom. 'I'he vapors pass downwardly through the fullers earth and leave the bottom of the tower through a transfer line 2|5 from which they pass into the heating coil |40. The vapors are heated to a temperature of 300 to 500 F. in the heater and then'flow into the intermediate vportion of the column |44. From'the column |44 the aromatic vapors Aflow through a cooler into an accumulator |52 from which they pass into the catalytic apparatus for further noted in Figure 3 that the furnace |08 and the furnace |42. correspond to the same parts' of Figure 2, the distinction between the apparatus illustrated in Figures 2 and 3 being the use of a fullers earth catalytic treating tower 2|2 in Figure 3 in place of the phosphoric acid treating tower' ||8 ofv Figure 2. The fullers earth acts to selectively polymerize the dioleflns and the polyblens as well as some of the low boiling unsaturated polymers in the aromatic distillate and this material partially condenses in thebody of thefullers earth and drains to the bottom of the tower. 'I'his vpolymer may cbe withdrawnfrom the bottom of the tower through a valved line 2|6. Some polymer may be dissolved in the aromatic hydrocarbons and this polymer is sepailed in the bottom of 'the fractionating tower In the past it has been customary to reflne aromatic distillates to produce commercially pure aromatic hydrocarbons with strong sulfuric acid. The strong sulfuricacid has many disadvantages in that it yacts as an oxidizing agent and it acts as a sulfonating agent by reacting with the aromatic hydrocarbons.` This entails a loss of aromatic hydrocarbons as well as a loss of acid. On. the other hand the hydroiluoric acid treatment of thearomatic distillate givesV an accurate control by which the olefins contaminating the aromatic distillate may be selectively polymerized in order to separate them from the' distillate.'v Furthermore if some of the oleflns produce polymers which are difllcult to separate from the aromatic distillate these oleflns may be alkylated by carrying on an alkylating reaction between the oleflns and the aro- 'matics to convert the olens into products having It will be polymers.

asiatica4 actions may be carried on at temperatures of 30 to '10 F. while sulfuric acid reactions require very low temperatures, that is from 30 to 20 F. in

order to protectl the aromatis and preventI the sulfonating reactions.

Hydroiluoric acid may be used in concentrations of 80%' to 100% and still give effective results. Furthermore the'acid is heavy which assists'materially in eiecting a gravity separation It has been found furthermore that the selective separation of the diolefins and the mono-y oleiins from the aromatic hydrocarbons provides 'a process by which the contaminating hydrocarbons may be effectively separated without the use of excess acid'or entailing thev loss of aromatic hydrocarbons. The phosphoric acid and fullers earth treatments are very eifective in separating the oleilns and places the distillates in a condition so that the monooleflns may be easily poly merized to be separated fromthe aromatic distillates.

The preferred form of the invention having been thus described, what is claimed as new is:

1. The process oi' purifying a hydrocarbon distillate containing desirable aromatic hydrocarbons andcontaminating hydrocarbons such as monooleflns and polyoleflns', which comprises heating thesaid distillate and passing it into a reaction zone in contact with a catalyst adapted to selectively polymerize the polyolefins, separatel ing the resulting polymers from the distillate containing the aromatic hydrocarbons and monooleflns, passing thev puriiied distillate into a second reaction zone in contact with a hydrofluoric acid catalyst under conditions adapted to polymerize the monooleiins, and fractionally'distilling the resulting treated distillate to separate the oleiln polymers from the desired v aromatic hydrocarbons. Y

2. 'I'he process of producing commercially pure aromatic hydrocarbons from petroleum comprising, cracking petroleum at a high temperature to produce a product having a high unsaturated `content, fractionating the cracked product toV separate a distillate in the boiling point range of kerosene and light gas oil, cracking the distillate in thev vapor .phase vto obtain a high conversion to unsaturated hydrocarbons containing aromatics and oleilns while substantially eliminating paraiiins and naphthenes. fractionating the cracked distillate to obtain an aromatic distillate in the boiling point range of the desired aromatic kerosene and light oil-distillate is cracked by means of a catalyst to provide tillate.

4.' The process deiined in claim 2 inwhich the an aromatic diskerosene and light gas oil distillate is crackedbyf contactwitlr a heated catalyst comprising oxide of one of the metalszof the 5th group deposited on alumina.

5. The process of purifying a hydrocarbon distillate containing desired aromatic hydrocarbons and contaminating hydrocarbons, such as monof olefins, polyoleflns, and unsaturated polymers, comprising heating said distillate and passing it into contact with a catalyst to selectively polymerize polyolei'lns and unsaturated polymers, separating the polymers from the distillate, passing the purified distillate containing monooleiins into contact with a hydrofluoricacid catalyst to polymerize'monooleilns, and fractionally distilling the distillate to separate polymers from the desired aromatic hydrocarbons.

6. The process of purifying a hydrocarbon distillate containing desired aromatic' hydrocarbons` ing it into contact vwith a catalyst adapted to selectively polymerize the polyoleiins and the unsaturated polymers, separating the resulting polymersfrom the treated distillate, passing the resulting purified distillate containing monooleilns into contact with an alkylation catalyst at an alkylating temperature adapted to alkylate a part of the aromatic hydrocarbons with the monooleiins to form an alkylate having a boiling point different from the boiling points of the desired unalkylated aromatic hydrocarbons, and fractionating the treated distillate to separate the alkylate from the desired unalkylated aromatic hydrocarbons.

7. The process deiined by claim l in which the hydrogen sulfide content of the distillate to be treated is removed therefrom prior to passing the distillate into the mst-mentioned reaction zone. 8. The process definedf in claim 5 in whichV the polymerization of the pdlyoleiins is-promoted by the catalytic reaction of phosphoric acid. 9. The process defined in claim 5 in which the polymerization of monooleilns is promotedwith a temperature bepolymerization of the polyoleflns is promoted by the desired aromatic hydrovapor phasev by fullers earth at temperatures from 250 to 475 F.

13. The process defined in claim-5 in which the polyolefins are polymerized with 100% phosphoric acid and monooleilns are polymerized with 90% to 100% hydrouorlc acid.

14. The process dened in claim l. in which the y polyoleilns are polymerized inthe vapor phase with fullers earth and monooleflns are polymerized in the liquid phasewith 90% to 100% hydrolfluor-1c acid. e n

15. V'I'he process as deiined by claim 6 in' which -the polyoleiins are polymerized in thevapor phase ,with phosphoric acid and in which the'alkyla- Y' tion operation is carried out with hydrouoric acid asacatalyst at atemperature of 1from 30 m40? F. '16. The process deilned in claim 5in which the tillates containing desired aromatic hydrocarbons and contaminating hydrocarbons such as monooleiins, polyoleiins and unsaturated hydrocarbon polymers, which comprises heating said distillate and passing it into a reaction zone in contact with a phosphoric acid catalyst to selectively polymerize polyolens and unsaturated polymers, separating the resulting polymers from the treated distillate, passing the .purified distil-l late containing monooleiins into a second reaction zone in contact with a diierent catalyst .adapted topolymerize monoolenns. polyxnerlzingv the monooleiins in contact with said catalyst in said second reaction zone, and iractionally distilling theresulting treated distillate to separate monoolen polymers from the desired aromatic hydrocarbons.

18. The process deilned in claim 17 in which the distillate to be treated is passed in contact with an alkaline material to separate hydrogen suiiide from the distillate prior to passing it into said mst-mentioned reaction zone in contact with the phosphoric acid catalyst.

` EDMUND G. Bonomi.