3,256,356 United States Patent Office Patented June 14, 1966 2 3,256,356 naphthalene mainly multi-ring compounds with some un NAPHTHALENE PREPARATION AND RECOVERY reacted naphthalenes. The light aromatics fraction PROCESS can be processed to obtain a highly pure or used Frank E. James, Jr., Paris, France, assignor to Standard as such as a high octane blending component of gasoline. Oil Company, Chicago, Ill., a corporation of Indiana Hence a maximum recovery of the light aromatics frac No Drawing. Filed Dec. 26, 1961, Ser. No. 162,210 tion is highly desirable. The gasiform mixture from the 3 Claims. (CI. 260-672) hydrodealkylation reaction is cooled to condense the hy This invention relates to the conversion of alkyl drocarbons to a liquid product. To maximize the poten naphthalenes to naphthalene by the heating at elevated tial recovery of the light aromatics, the gasiform reactor temperatures and pressure of aromatic fractions contain effluent is cooled to as low a temperature as possible gen ing naphthalene boiling above 400 F. in the presence O erally without substantially decreasing the pressure more of hydrogen whereby there is produced a mixture of hy than to about 750 p.s.i.g. Thereafter a hydrogen stream drogen, alkanes, low boiling aromatics, naphthalene and containing the alkanes and is flashed off while aromatics boiling higher than naphthalene. More particu reducing the pressure on the condensed hydrocarbons larly this invention pertains to the recovery of naphthalene 15 about 15 p.s.i. Naphthalene freezes at 180° F. Cooling from said reaction mixture. the mixture of hydrogen and hydrocarbon in the reactor It has been long known that alkyl naphthalenes when effluent below 180° F. results in the solidification of heated with hydrogen at elevated temperatures in the naphthalene and other heavier aromatics and the plug presence or the absence of catalysts results in the removal ging of heat exchangers used for cooling as well as trans of the alkyl groups and the replacement thereof with 20 fer lines between the coolers and collecting vessels such hydrogen on the ring thus forming unsubstituted naphthal as those from which said hydrogen stream is removed as ene. The conversion of alkyl naphthalenes to naphthal well as depositing solid naphthalene and heavier aro ene by Such a reaction may involve hydrocracking or the matics in the flash vessels. A substantial amount of the substitution of hydrogen for the alkyl group substituent light aromatics are flashed off with the hydrogen stream on the ring. This hydrodealkylation of alkyl naphthalene 25 at temperatures above 180° F. To recover these flashed has been proposed for the manufacture of naphthalene off light aromatics from a hydrogen stream lean therein from aromatic fractions boiling above 400 F. contain required the use of large condensers, scrubbers, etc. to ing alkyl naphthalenes. Such aromatic fractions contain handle the large volumes of hydrogen stream. For ex alkyl , naphthalene benzenes such as tetralins, ample, when 32 barrels per hour of the alkyl naphthalene indanes, etc., dinaphthalene benzenes, a small amount of 30 fraction is fed with 5300 standard cubic feet per hour naphthalene generally less than 5% by volume, C1 of a hydrogen rich stream (85 mole percent hydrogen and naphthalenes (monomethyl naphthalenes), C12 naphthal 15 mole percent alkanes mainly methane) to a hydrode enes (ethylnaphthalenes and dimethylnaphthalenes) and process, about 5500 standard cubic feet per C13 naphthalenes (ethyl methyl naphthalenes and tri hour of hydrogen stream would have to be handled to methylnaphthalenes) and are generally derived from recover the light aromatics. A simple procedural step petroleum refining streams or fractions thereof high in or combination of steps to prevent carry over of light ethylnaphthalenes especially from the bottom fraction aromatics and permit cooling of reactor effluent below after gasoline-boiling range hydrocarbons have been re 180 F. even to as low as 80° F. would provide an ex moved from catalytically reformed naphtha or "catalytic tremely advantageous operating technique. reformate.” 40 Catalytic reforming is carried out with a naphtha The above problem of cooling the hydrodealkylation charge stock having a boiling range of from 100 to 400 reaction effluent below 180° F. can be readily solved by 500 F. in the presence of hydrogen and a dehydrocycliza adding to the reaction effluent as it is being cooled and tion catalyst at 880 to 1000 F. and 50 to 800 pounds prior to flashing off the hydrogen-alkane- stream, per square inch gauge (p.s.i.g.). After reforming, the re a portion of the light aromatics fraction removed from sulting mixture of hydrocarbons and recycle-hydrogen the hydrogen-free aromatics in the sequence of distilla containing gas is separated into a liquifiable hydrocarbon tion to recover naphthalene. The amount of light aro gross product and a hydrogen-containing gas for recycle, matics fraction recycled to the cooling step can be varied. generally after cooling the mixture from the reforming. To recycle an amount equal to that mole, that is to double operation. The hydrocarbon product contains volatile the amount in the reactor effluent and thereafter, during light ends hydrocarbons, hydrocarbons in the gasoline 50 the separation, split the light aromatics one half to prod boiling range (100 F. initial and 350 to 420 F. final luct and one half to recycle would amount, in general, to boiling points in the ASTM distillation) as well as higher adding about one part of light aromatics by weight per boiling materials. After removal and recovery of the 7 parts of reactor effluent on a weight basis. More of the gasoline-boiling range hydrocarbons by distillation, there light aromatics fraction could be collected for recycle 5 5 when lining out operations and gradually approaching the remains the bottoms which are almost entirely aromatics lower reaction effluent cooling temperature so that the with up to 2 to 5% non-aromatics mainly C4 to C6 alkanes light aromatics content of the reactor effluent would ulti and alkenes such as in a mixture having a gravity mately be trippled by adding about 1 part of light aro of 8.5 to 8.7 degrees API. Such a bottoms fraction can be used in a hydrodealkylation process, or the bottoms matics to about 3 parts of reactor effluent by weight. fraction can be stripped of light ends to provide an aro 60 Thus of the light aromatics recovered by distillation one matics concentrate which is then used in a hydrodealkyla third would go to product and two-thirds to recycle. As tion process. little as about 1 part of light aromatics per 10 parts of The use of the alkyl naphthalene fractions boiling reactor effluent will permit cooling of the mixture below above 400° F. in the hydrodealkylation processes whether 180° F. without naphthalene solidifying. The addition catalytic or non-catalytic produce a gasiform reaction 65 of 1 part of light aromatics fraction for 6 to 7 parts of re mixture containing unreacted hydrogen, since it is used actor effluent will permit cooling of the mixture to 90 in excess of the mole equivalents of alkyl groups to be 100 F. without solidifying naphthalene. Suitable for removed, alkanes mainly methane with Some ethylene, the purposes of this invention, therefore, is the addition ethane, and minor amounts of C3 to C5 alkanes and of 1 part of light aromatics fraction per 3 to 10 parts alkenes, light aromatics boiling below naphthalene and 70 of hydrodealkylation reactor effluent, and desirably, one mainly benzene, naphthalene, and aromatics boiling above for each 4 to 7 parts of reactor effluent when cooling 3,256,356 3 4 temperatures in the range of 80 to 100° F. are employed. The foregoing example of the process of this invention The preferred range is 1 part for each 6 to 7 parts where is illustrated by the following flow sheet type diagram: the resulting mixture is cooled to 90-100 F. When the above process is carried out without the re To illustrate the process of this invention there is ob cycle of the light aromatics fraction cooling of the re tained from a methyl naphthalene fraction (13.9 API) actor effluent to about 180° F. or below or a minimum containing about 4 mole percent paraffins and olefins, after flashing off the hydrogen stream results in solidifi 13 mole percent benzene and 80 mole percent other aro cation of naphthalene and plugging of heat eXchanger matics subjected to hydrodealkylation with hydrogen in the as well as solid deposits in the flash vessel. ratio of about 34 pounds hydrogen per 100 pounds of the What is claimed is: methyl naphthalene fraction, a reactor effluent contain 1. In a process for the preparation and recovery of ing about 60 mole percent hydrogen, 19 mole percent O naphthalene by heating together in a reaction zone (A) methane, 10 mole percent other paraffins and olefins, 2.4 an aromatic hydrocarbon fraction having 2 to 5% alkanes mole percent benzene, 6.7 mole percent naphthalene and and alkenes with the remaining 98 to 95% substantially 1.9 mole percent other aromatics. For each 65 parts aromatic hydrocarbons having alkyl naphthalenes of of the reactor effluent at 850 p.s.i.g. and 210 F., cooled 5 11 to 13 total carbon atoms in admixture with alkyl ben thereto by heat exchange with feed hydrogen and feed Zenes, naphthalene benzenes, dinaphthalene benzenes and stock methyl aromatics fraction and other cooling, there less than about 5% naphthalene with (B) excess hydro is added 10 parts of light aromatics fraction containing gen at hydrodealkylation conditions of elevated tempera about 55 mole percent benzene, about 10 mole percent ture and pressure with a net hydrogen consumption in a , 29 mole percent aromatics boiling above benzene 20 mole ratio equivalent to the alkyl groups replaced with and toluene and up to naphthalene and about 6 mole hydrogen and wherein said excess of hydrogen is an excess percent paraffins and olefins. The resulting mixture is above said net hydrogen consumption whereat from said cooled and a hydrogen stream (hydrogen and paraffins reaction zone a gasiform hydrodealkylation reaction efflu mainly methane) is flashed therefrom at a final tempera ent mixture at about said elevated temperature and pres ture of 90 to 100 F. The remaining liquid hydrocarbon 25 sure is obtained having as its components hydrogen, mixture is distilled to recover first a light aromatic frac methane and C to C5 alkane and alkene hydrocarbons, tion containing about 55 mole percent benzene and 10 aromatic hydrocarbons boiling at a temperature below mole percent toluene, then a naphthalene fraction of naphthalene down to and including benzene, naphthalene about 98% purity (79.4° C. freezing point) leaving a and aromatic hydrocarbons boiling at a temperature tar or heavy residue. 30 above naphthalene; flashing hydrogen and methane from said reaction effluent to leave a cooled and depressurized Hydrogen (A) liquid hydrocarbon residue consisting essentially of aro Methyl Naphthalene (B). HYDRODEMETHYLATION REACTOR Fraction: Reactor Effluent (c) : Paraffins and Olefins 2 mole % Hydrogen 6O mole Eezee 13 mole'? ethane 19 mote : Other Aromatics Other Paraffins Inciuding Methyl and Oleiras 1O mole Naphthalenes 80 mole Benzene 2. lg. mole Naphthalene 6.7 mole Weight ratio (A) to (B) is 34 to 100 Other Aromatics .9 mole i

HEAT EXCHANGE WITH (A) AND (B)

Flash Gas Hydrogen, (cooing and Methane Reactor Effluent (C) at 850 psig and 2OF FLASH AND COOL TO FINAL TEMPERATURE 90 TO OOF. Weight Ratio of 65 to 10 Recycle (F) Light

Aromatics Fraction, Liquid Hydrocarbons (D)

Remaining From Flashing Light Aromatics (E)-(F) Light Aromatics Fraction (E) Benzene 55 mole Touene 10 mole a Other Arotatics up to Naphtha ene 29 mole is Paraffins and Olefins 6 mole

Naphthalene Product 98; Purity-79 ...F. Freeze Point

ERACIONAL DISTILLiTION

| Tar or heavy Residue (G) 3,256,356 5 6 matic hydrocarbons and a small amount of C2 to C5 3. The process of claim 1 wherein the mixture result alkanes and alkenes and thereafter distilling said liquid ing from combining the hydrodealkylation reaction mix hydrocarbon residue to recover at least a light hydro ture and the portion of the light aromatic fraction is carbon fraction consisting of benzene and aromatic hydro cooled to 90 to 100 F. and the amount of the light aro carbons boiling below naphthalene and a naphthalene matic fraction admixed is one part for each 6.5 parts fraction; the improvement for said flashing step of adding of hydrodealkylation reaction mixture. to said hydrodealkylation reaction effluent mixture being flash cooled and depressurized said light aromatic hydro References Cited by the Examiner carbon fraction as recycle in an amount in the range UNITED STATES PATENTS of from one part by weight thereof for each 3 to 10 parts 10 by weight of said reaction effluent mixture and carrying 2,335,531 11/1943 Praeger ------208-101 out said flash cooling to a final temperature in the range 2,697,684 12/1954 Hemminger et al. -- 260-672 X of from below 180° F. down to about 80 F. whereat the hydrocarbon residue left is liquid. 2,700,638 1/1955 Friedman ------260-672 2. The process of claim 1 wherein the mixture result 15 2,952,616 9/1960 Hausch ------208-102 ing from combining the hydrodealkylation reaction mix 3,101,380 8/1963 Hariu ------260-672 ture and the portion of the light aromatic fraction is cooled to a temperature in the range of 80 to 100 F. DELBERT E. GANTZ, Primary Examiner. and the amount of the light aromatic fraction admixed A. D. SULLIVAN, Examiner. with the hydrodealkylation reaction mixture in the ratio 20 of one part of light aromatic fraction for each 4 to 7 J. E. DEMPSEY, C. R. DAVIS, Assistant Examiners. parts of reaction mixture on a weight basis.