US3384570A - Fractionation and conversion of a naphtha fraction - Google Patents

Description

May 21, 1968 c. s. KELLEY ET Al. 3,384,570

FRACTIONATION AND CONVERSION OF A NAPHTHA FRACTION Filed Feb. 6, 1967 zoCu/... wwzmls \J.

United States Patent O 3,384,570 FRAC'HNATIN AND CNVERSION 0F A NAPHTHA FRACTIN Carl S. Kelley, Eldred I. Cabauaw, and Vernon A. Cawi,

Bartlesville, Okla., assignors to Phillips Petroleum Company, a corporation of Delaware Filed Feb. 6, 1967, Ser. No. 614,097 3 Claims. (Cl. 208-79) ABSTRACT F THE DISCLOSURE Heart cut n-aphtha such as that produced by fractionating crude naphtha is reformed and the aromatic constituents are purified by extraction of parains and clay treated with subsequent recovery or hydrogenation of benzene and hydrodealkylation of heavier aromatics. The light and heavy naphthas produced in the original fractionation, yas well as reformed off gas and paratlinic material recovered from reformate extraction, are cracked to produce hydrogen, olens, gasoline hydrocarbon, and heavier gas oil, the gasoline range hydrocarbon being hydrotreated to convert a part thereof to aromatics which can be added to the feed to the extraction step, the heavy gas oils being employed as feedstock lfor carbon black production.

A considerable degree of interrelation between hydrocarbon refining process steps derives from `the usually complicated n-ature of feedstocks processed `and the variant kind and characteristics of products produced by such operations. It is, of course, desirable to utilize each feed component in a manner that will best contribute to the n-ature and quality of Ithe desired products. As a result, where more complex feedstocks are employed or where a broader spectrum of products is desired, the nature and interrelation of the process steps required -to effect the desired conversions becomes more complicated. `In an effort to improve the utilization of hydrocarbon feedstocks and the quality of products produced therefrom, we have discovered a new and useful combination of hydrocarbon processing operations uniquely integrated to effect this purpose.

It is therefore one object of this invention to provide a process for converting hydrocarbons more efiiciently. yIt is `another object of this invention to provide an integrated series of processing operations for more effectively utilizing hydrocarbon feedstocks. It is yet another object of this invention to provide an improved coordinated hydrocarbon refining process. It is yet another object of this invention to provide an improved integrated process for upgrading crude hydrocarbon naphtha.

'In accordance |with one embodiment of this invention, crude hydrocarbon naphtha is fraction-ated to produce a heart cut which is in turn subjected to reforming to increase the aromatic content thereof. The aromatics are then purified by solvent extraction, clay treated and fractionated after which benzene can be recovered as product or partially hydrogenated to produce cyclohexane, the heavier aromatics being hydrodealkylated and recycled.

Further in accordance with this invention, the light and heavy naphtha produced in Vthe initial crude naphtha fractionation can be subjected to a cracking operation along with the paraffinic rafiinate from the reformate extraction zone. Lighter hydrocarbons, e.g., C5s, and lower recovered from the reformate product can lalso be passed to the naphtha cracking zone wherein are produced oleiins, hydrogen, gasoline range hydrocarbons and heavier gas oils.

Further in accordance with this invention, these gasoline range hydrocarbons can be hydro-treated, e.g., hydro- 3,384,570 Patented May 2l, 1968 ICC genated, and fractionated to produce lighter hydrocarbons as recycled 4to the cracking operation, an intermediate boiling fraction enriched in aromatics, eg., bcnzene which can be extracted -along with the above-noted ref-ormate, and heavy gas oil fraction which can be combined with the gas oil recovered directly from the naphtha cracker as feedstock for carbon black production.

Further in accordance with this invention, hydrogen vproduced in the naphtha cracking operati-on can be passed to the hydrotreating, hydrodealkylating, and benzene hydrogen-ation steps as desired.

The invention can be better understood by reference to the drawing, which is intended only to be a schematic illustration of one embodiment of the concept of Ithis invention, The description includes examples, tiow rates, and Ioperating conditions |which can be employed.

Straight run naphtha comprising, for example, a mixture of hydrocarbons boiling from about to about 410 F. is passed at a rate of 17,580 b./d. by way of pipe l1 to fractionator 2 from which light naphtha, primarily C5 hydrocarbons, is removed by way of pipe 3 as overhead at 2,022 b./d.; 10,144 b./d. heavier naphtha boiling from 24U-410 F. is removed as bottoms product by Way of pipe `4 and 5,414 b./ d. of a heart fraction, boiling from 1Z0-240 F., being substantially enriched in C6 hydrocarbons, for example, methylcyclopentane, cyclohexane, and close boiling parafiinic materials is removed by way of pipe y5 and passed to reformer 6 wherein at Ileast a portion thereof is converted to additional aromatic material. The reformate .thus produced is passed by way of pipe 7 to a suitable separation Zone, for example, iiash vessel 8, from which hydrogen-rich gas is removed as overhead by way of pipe 9 at a rate of 9,142 M s.c.f./d. and passed to naphtha cracking zone 318. C6 and heavier materials comprising aromatic and paraffinic hydrocarbons are removed as bottoms product from separator l8 and are passed to fractionator 111 -by Way of pipe '10 wherein C5 'and lighter hydrocarbons are removed as overhead product by way of pipe 13 and accumulated in receiving vessel 14 from which C5 and lighter materials are removed at a rate of 286 b./d. as overhead `by Way of pipe 1-5, recycled hydrocarbon substantially reduced in C5 and lighter content being returned to fractionator 1\1 by way of pipe y16. As desired, a portion (1814 b./d.) of this more volatile hydrocarbon fraction being substantially reduced in C5 and lighter hydrocarbons can be passed to naphtha cracking zone 38 by way of pipe 17, as illustrated in the drawing. C5 and heavier hydrocarbons being substantially free of C5 and lighter materials are removed at a rate of 3062 b./d. as bottoms product from fractionator 11 and passed by Way of line 12 to extraction zone 18 from which parafiinic hydrocarbons (2475 b./d.) `are removed as raffinate by way of pipe 19 and passed to naphtha cracking zone 38. Aromatic materials (3504 b./d.) being substantially reduced in paraiinic content 'are removed as extract phase by way of pipe 20, passed lto clay treating zone -21 and are fed to fractionator 23 through pipe 2-2 from |which there are recovered an overhead product comprising primarily benzene (3002 b./d.) by Way of pipe 24 and a heavier aromatics bottoms product (2387 b./d.) by way of pipe y25. V

As desired, a portion (1360 b./ d.) of the benzene overhead from fractionator -23 may be passed by Way of pipe 26 to hydrogenation 27 wherein benzene is hydrogenated to cyclohexane. About 1608 b./d. of cyclohexane product is removed by way of pipe 30' while C5 and lighter hydrocarbons present in the benzene feed and produced in hydrogenation zone 27 are removed -as overhead by -way of pipe 28 at a rate of 80121 M s.c.f./d. and c-an be combined with the hydrocarbon gas exiting the system by way of pipe 415. Unconverted benzene can be separated from the hydrogenation product and recycled to clay `treating zone 21 by way of pipe 31. Product benzene (1642 b./d.) can be recovered by way of pipe 29.

The heavier aromatics bottoms products from fractionator 23 is passed -by way of pipe 25 to hydrodealkylation zone 33 wherein a portion thereof is converted to benzene. The hydrodealkylat-ion product (184-8 b./d.) containing the benzene thus produced is passed to fractionator 35 Iby way `of pipe 34 from which benzene is recovered as overhead product and passed by way of pipe 37 to clay treating Zone 21. Recycle feed to the clay treater by way of pipes 31 and 37 amounts to 1885 -b./d. Bottoms product (69 b./d.) containing C7 and higher aromatics, in particular, biphenyl, is recycled to hydrodealkylation `by way of pipe 36. Excess hydrogen recovered from hydrodealkylation can be passed by way of pipe 32 to benzene hydrogenation zone 27 as the hydrogen source for cyclohexane production.

The light and heavy naphthas recovered from fractionator 2 by way of pipes 3 and 4, respectively, along with lighter hydrocarbons introduced by way of pipes 9 and 17 and parafiinic material from extraction zone 18, are cracked in naphtha cracking zone 38ito produce lighter olefinic hydrocarbons, gasolinerange hydrocarbons, and heavy aromatic gas oil.

1n the presently preferred embodiment of this invention, hydrocarbons fed to cracking zone 38 are converted to, for example, ethylene, propylene, butenes and butadienes. The product can be fractionated to recover 1,096,000 lb./d. of ethylene by way of pipe 39, 3226 b./d. of propylene by way of pipe 40, and` 1627 b./d. of a C4 `fraction (butadiene and butylene) being recovered by way of pipe 41.

A heavy aromatics fraction (643 b./d.) is recovered by `way of pipe 49 as feed for carbon black production. A pyrolysis gasoline `fraction (4229 b./d.) is removed by way of pipe 42 and passed to hydrotreating zone 43. Hydrogen (3414 M scf/d.) produced in cracking zone 38 and purified in the hydrogen purification zone can be recovered and passed by way of pipe 60 to provide hydrogen to hydrotreating zone 43. A portion of this recovered hydrogen may also be passed by way of pipe 51 to hydrodealklation zone 33, the remainder being passed by way of pipe 32 to benzene hydrogenation zone 27.

Lighter hydrocarbons fed to hydrotreat-ing Zone with the gasoline range hydrocarbon by way of pipe 42 as well `as lighter hydrocarbons produced in the hydrotreating zone for example, hydrocarbons having 5 -or less carbon atoms, are recovered as off gas and passed at a rate of 1494 M s.c.f./d. by way of pipe St) to hydrogen purification unit located in the naphtha cracking zone 38. A portion (about 758 b./d.) of these lighter hydrocarbons, primarily amylenes, can also be recovered as product by way of pipe 44. The remainder of the hydrotreatin-g effluent is passed by way of pipe 45 to fractionation zone 46 from which about 2917 b./d. of an overhead product comprising primarily C6 hydrocarbons containing paranic and aromatic materials is passediby way of pipe 47 to extraction zone 18. About 333 b/d. of a heavy gasoline fraction is removed as bottoms product by way of pipe 48 and further processed. For example, it is presently preferred that this material be combined with the heavier gasoline fraction removed lfrom naphtha cracking zone 38 by way of pipe 49 and passed in combination therewith as feed for carbon black production.

The hydrogenation, hydrodealkylation, solvent extraction, clay treating, reforming, hydrotreating and cracking operations can be any of those known in the prior art which would be chosen by one skilled in the art. For example, the hydrogenation process can be a catalytic process employing a nickel on kieselguhr-type catalyst. The hydrodealkylation reaction can be thermal or catalytic (e.g., Hydeal), using a chrornia-alunrina type catalyst. The solvent extraction can be carried out using ,diethylene or triethylene glycol or sulfolane as solvent.

. Ethylene is a major product of naphtha cracking. Separated ethane can also be recycled and cracked to ethylene as desired. Other -olefins produced include propylene, butylene, butadiene, etc. @ther products include hydrogen, methane, pyrolysis gasoline, and heavy aromatic oil. Naphtha and ethane can be preheated by Iwaste heat, mixed with steam, and charged to reaction coils in the fire box.

' Reaction pressure is preferably siightly above atmospheric,

and the temperature is typically in the range of 1450- 1650 F. Exact conditions depend upon products desired, as is known in the art. This naphtha cracking zone has conventional separation facilities including fractionation towers, caustic washers for HZS and CO2 removal, and `water washing facilities to remove caustic from treated products. These separations are well known in the art and are not detailed herein.

The catalytic reforming can employ conventional catalysts such as platinum on alumina type reforming catalysis in one or more fixed beds in series. Suitable processes known in the art are, for example, Platformin-g, Houdriforming, and Powerforming. This operation converts part of the heart cut naphtha, e.fg., hexanes and heptanes to benzene and toluene, plus an excess of hydrogen which can be used in other processes as described. In addition, lighter hydrocarbons (C3 to C5, carbon hydrocarbons) are produced as well as fuel gas (C2 and C1 hydrocarbons).

The hydrotreating process 43 preferably comprises a two-step operation in which the pyrolysis gasoline 42 from naphtha cracking is treated to convert at least a portion of the diolefins therein to linear and cyclic olens; the` motor fuel constituents being fractionated from the product. In the first step Iraw pyrolysis gasoline 42 and hydrogen 60 are passed over a conventional catalyst known in the art, for example, cobalt-molybdenum type catalysts to convert diolens to monooleiins. The reaction products are fractionated to yield fuel gas 50, an amylenes concen trate 44, a heart cut comprising benzene, toluene, hexenes, and heptenes; a high octane gasoline and residual aromatics and polymers. in the second step, the heart cut is contacted over a conventional nickel on kieselguhr hydrogenation catalyst to convert hexanes and heptenes to paraiins and naphthenes. The hydrogenated heart-cut 47 is then passed to aromatic extraction zone 18 for recovery of benzene and toluene.

The thermal hydrodealkylation process 33 is well known in the art. Herein, -in one reactor, toluene and xylenes 25 are converted to 'benzene in the presence of hydrogen 51. Hydrogen is consumed, and the main by-products are methane and bipheuyl. The biphenyl is separated and recycled 36 preferably to a separate biphenyl reactor wherein it is converted into additional benzene in the presence of hydrogen. 14,560,000 standard cubic feet per day of hydrogen 51 can be charged to hydrodealkylation Zone 33.

TYPICAL CONDITIONS Tempera- Pressure, ture, F. p.s.l.g.

Naphtha cracking (38) 1550 10 Reforming (6) 1000 250 Hydrotreating (43):

age 350 400 (Stage II) 750 400 Solvent extraction (18) 150 50 Hydrodealkylation (33) 1400 500 Benzene hydrogenation (27) 400 400 (b) reforming said heart cut to convert at least a p0rtion thereof to aromatic hydrocarbons,

(c) fractionating said reformate to produce a fraction having a substantially reduced concentration of lighter hydrocarbons,

(d) solvent extracting said fraction to produce a parafiin rich raflinate and an aromatic rich extract, and clay treating said extract,

(e) fractionating the thus clay treated extract to produce a concentrated benzene overhead and a bottoms product being substantially reduced in benzene concentration,

(f) cracking said light hydrocarbons of step (c) to convert at least a portion thereof to olen hydrocarbons, hydrogen, gasoline range hydrocarbons and heavier gasoline hydrocarbons,

(g) hydrotreating said gasoline range hydrocarbons to hydrogenate at least a part thereof, and

(h) hydrodealkylating said bottoms product from step (e) to convert at least a portion thereof to additional benzene.

2. The method of claim 1 further comprising (I) passing at least ia portion of said light hydrocarbon removed from said reformate to said cracking step,

(II) passing said parain rich raftinite to said cracking step,

(III) hydrogenating at least a portion of said benzene loverhead from step (e) to produce cyclohexane,

(IV) fractionating the hydrodealkylated product of step (h) to produce a benezene rich overhead and a benzene lean bottoms product and recycling said bottoms product.

3. The method of claim 2 further comprising (A) passing unconverted benezene from said hydrogenatin g step to said clay treating step,

(B) passing said benzene rich overhead from said hydrodealkylatingV step to said clay treating step,

(C) passing hydrogen from said hydrodealkylation step to said benzene hydrogenating step (III), and

(D) fractionating dehydrogenated product of step (g) to remove heavy gasoline as bottoms product and passing the remainder of said overhead products to said extraction step.

References Cited UNITED STATES PATENTS 3,281,351 10/1966 Gilliland et al 208-93 25 HERBERT LEVINE, Primary Examiner.

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