US2963522A

US2963522A - Production of butadiene

Info

Publication number: US2963522A
Application number: US706050A
Authority: US
Inventors: Jr Joseph R Cobb
Original assignee: Phillips Petroleum Co
Current assignee: Phillips Petroleum Co
Priority date: 1957-12-30
Filing date: 1957-12-30
Publication date: 1960-12-06
Anticipated expiration: 1977-12-06

Description

PRODUCTION OF BUTADIENE Joseph R. Cobb, Jr., Bartlesville, Okla., assignor to Phillips Petroleum Company, a corporation of Delaware Filed Dec. 30, 1957, Ser. No. 706,050

3 Claims. (Cl. 26,0-4680) This invention relates to the production of 1,3-butadiene. In one aspect, it relates to an improved process for producing butadiene in increased yields. In another aspect it relates to a two-stage dehydrogenation of normal butane to butadiene and the recovery of the butadiene in substantially pure form.

A commercial process used in the production of 1,3- butadiene includes the following steps: (l) butane dehydrogenation into butenes, (2) butene recovery or purication, (3) butene dehydrogenation to butadiene, and (4) butadiene recovery or purification. In such a process, it is conventional to pass the eiuent from the step (1) dehydrogenation into a butene-1 fractionation column. The bottoms from this column containing principally normal butane and butene-2, after removal of any C5 and higher hydrocarbons, are then introduced into an absorber wherein they are contacted with a solvent which selectively dissolves the butene-2 (step (2) purification). The dissolved butene-2, which is stripped from the rich solvent, is then employed with the butene-1 recovered as overhead from the aforementioned butene-l column to form the feed for the step (3) dehydrogenation. The undissolved fraction from the extractive distillation is passed into a fractional distillation column from which a normal butane stream is taken overhead and then iiowed to the step (l) dehydrogenation. The effluent from the step (3) dehydrogenation containing principally C4 and heavier hydrocarbons is then subjected to fractional distillation in la butene-2 column so as to recover an overhead stream containing principally butadiene, isobutylene, butene-l and normal butane and a bottom stream containing principally normal butane, butene-2 and C5 hydrocarbons. The overhead stream from this latter fractional distillation is subjected to extractive distillation with a solvent selective for the butadiene which is subsequently recovered from the solvent as product of the process (step (4) puriication). A portion of the undissolved fraction from the extractive distillation containing principally isobutylene, butene-1, normal butaneand butene-2 is recycled -to the step (3) dehydrogenation while another portion is vented or otherwise removed from the system. After removal of C5 and heavier hydrocarbons, one portion of the bottoms lfrom the last-mentioned fractional distillation, i.e., the butene-2 column, `is recycled to the step (3) dehydrogenation while a second portion is recycled to the absorber used in the step (2) purification.

When operating in accordance with the above-described process the normal butane takes a free ride through the step (3) dehydrogenation, acting as a diluent therein. In order to prevent overloading of the system, it becomes necessary in normal operation to vent a portion of the undissolved fraction recovered from the absorber in the step (4) purication. It is also necessary to recycle a portion of the step (3) dehydrogenation lfeed recovered from the bottom of the butene-2 column to the butene-1 column in order to prevent buildup of n-butane in the step (3) dehydrogenation. V.It would be particularly desirable if a method could be provided whereby the amount nite States Patent O ice of free-riding normal butane could be reduced while also obtaining more effective utilization of normal butane in the step (l) dehydrogenation and butene-1 in the step (3) dehydrogenation. This invention is concerned with an improvement in the above-described process which produces this and other desirable results.

It is an object of this invention to provide an improved process for producing butadiene from normal butane.

Another object of this invention is to provide a process for producing butadiene wherein a large proportion of the normal butane which conventionally takes a free ride through the butene dehydrogenation is convertedV to butadiene.

A further object of the invention is to provide for a more eicient separation of the materials obtained during the dehydrogenation of n-butane to butene and during the dehydrogenation of butenes to butadiene.

A still further object of the invention is to reduce the amount of material which must be purged during a twostage dehydrogenation of n-butane.

Another object of the invention is to provide a process for the two-stage dehydrogenation of n-butane to butadiene in which a more efficient utilization is made of the n-butane and butenes available for the dehydrogenations.

Still another object of the invention is to provideV al process for the two-stage dehydrogenation of n-butane to butadiene in which it is unnecessary to recycle a portion of the step (3) dehydrogenation feed to the step (2) puriiication,

Other objects and advantages of the invention Will become apparent to those skilled in the art upon consideration of the accompanying disclosure and the drawing which shows schematically an arrangement of apparatus and flow diagram according to the invention.

This invention is concerned with a process for the twostage dehydrogenation of normal butane to 1,3-butadiene. In one embodiment, the process comprises the following steps: catalytically dehydrogenating normal butane to normal butenes in the rst stage dehydrogenation zone, subjecting the C., hydrocarbon content of the first stage dehydrogenation eiuent to a first extractive distillation with a solvent which is selective for butene-2, recovering an undissolved fraction containing butene-l and n-butane from the first extractive distillation, separating butene-1 from the undissolved fraction in a first fractional distillation zone and passing same to a second stage dehydrogenation zone, recovering a stream containing n-butane from the first fractional distillation zone and, after removal of C5 and heavier hydrocarbons, passing same into the first stage dehydrogenaton Zone, recovering a stream containing butene-1, butene-2, butadiene and n-butane from the selective solvent and passing same into a second fractional distillation Zone, catalytically dehydrogenating butenes supplied to the second dehydrogenation zone to butadiene, recovering a second stage dehydrogenation eflluent consisting essentially of C4 and heavier hydrocarbons and passing same into the aforementioned second fractional distillation zone, recovering a rst stream containing principally butene-2 from the second `fractional distillation zone and, after removal of C5 and heavier hydrocarbons, recycling same to the second stage dehydrogenation zone, subjecting another stream recovered from the second fractional distillation zone to a second extractive distillation with a solvent which is selective for butadiene, stripping the dissolved fraction from the selective solvent and recovering from this fraction an essentially pure butadiene product, and passing the undissolved fraction containing principally butene-1, n-butane and isobutylene from the second extractive distillation to the first fractional distillation zone. A comparison of the process of this invention with the commercial process described hereinbefore indicates that there are several important and distinct differences between the two processes. One of the most important differences between the two processes relates to the removal of butene-1 from the rst stage dehydrogenation euent. In the above-described commercial process,4 the butene-l is separated from the effluent prior to the introduction of this latter stream into the extractive distillation column. In accordance with the process of the instant invention, the feed to the butene-1 removal step consists of the, undissolved fractions from the extractiveA distillation steps. Operation in this manner makes it possible to effectively remove normal butane from the second stage dehydrogenation and eliminate the step of recycling a portion of the second stage dehydrogenation feed. Furthermore, the process of this invention provides for a more effective utilization of the normal butane and butenes in the dehydrogenation steps, thereby making it possible to increase the butadiene yield over that conventionally obtained.

A better understanding of the invention can beobtained by referring to the drawing which illustrate diagrammatically a preferred embodiment of the invention. In the apparatus as illustrated, various items of equipment, such as valves, compressors, accumulators, heaters, and the like, have been omitted in order to simplify the drawing; however the inclusion of such equipment can be readily accomplished by those skilled in the art.

Normal butane, obtained from natural gas or gasoline, or from any other suitable source, is passed by means of line 10 into dehydrogenation zone 11. Prior to introduction into zone 11, the normal butane is conventionally passed through a heater (not shown) wherein it is preheated to a desired temperature. In dehydrogenation zone 11, approximately one third to one half of the butane is catalytically converted to mixed butenes by dehydrogenation. A catalyst comprising alumina and chromia, together with small amounts of beryllia or magnesia, is prefer-red. However, any of the many parafn dehydrogenation catalysts known in the art may be used. The precise conditions used in the dehydrogenation depend upon the particular catalyst employed, its activity, and various other factors. However, a gas space velocity of 500 to 1500 volume of butane per volume of catalyst per hour, temperatures in the range of 1000 to l200 F., and approximately atmospheric pressure, in general, constitute suitable conditions for conducting the first stage dehydrogenation.

The dehydrogenation effluent recovered from zone 11 through line 12 is then passed into compressor system 13 where the reaction products are compressed and cooled between stages in a conventional manner. The dehydrogenation effluent contains principally hydrogen, butene-l, butene-2 (both low and high boiling) and normal butane. Small quantities of light gases other than hydrogen, e.g., methane, ethylene, ethane, propylene, and propane, are also produced in the reaction. Furthermore, small amounts of isobutane, isobutylene, and butadiene are present in the dehydrogenation effluent stream. The effluent may also contain hydrocarbons having or more carbon atoms, but the quantity of such hydrocarbons is usually very small.

After passage -through compressor system 13, the hydrocarbon vapors are then introduced via line 14 into a lean oil absorber and stripper unit. An overhead fraction containing C3 and lighter hydrocarbons is withdrawn from the lean oil absorber through line 16. The stripped hydrocarbons are recovered through line 17 and then passed into fractionator 18 which functions as a depropanizer to remove additional C3 and lighter hydrocarbons. The C3 and lighter hydrocarbons are withdrawn from depropanizer 18 as the overhead product through line 19. The kettle product from` depropanizer `18, which contains butene-.1, butene-,2, butadiene, n-butane and heavier hydrocarbons, is recovered through line 21 and then passed into fractionator 22. Fractionator 22 operates as a deoiler, C5 and Vheavier hydrocarbons being withdrawn through line 23. The stream containing principally C4 hydrocarbons recovered as the overhead product from deoiler 22 through line 24 is introduced into eXtractive distillation column or absorber 26. In extractive distillation column 26, the stream is contacted with a solvent which selectively dissolves the butene-Zs. Although it is not intended to limit the invention to any specific selective solvent, it is preferred to utilize furfural as the solvent. The solvent containing dissolved butene-2 is withdrawn from the bottom of absorber 26 through line 27 and then passed into stripper 28. The stripped solvent recovered from stripper 28 as the kettle product through line 29 is recycled to absorber 26. A stream containing butene-2 is recovered as the overhead product from stripper 28 through line 31. The unabsorbed hydrocarbons, consisting principally of butene-1 and normal butane, are removed from absorber 26 through line 32 and then introduced into fractional distillation column 35. Since column 25 operates as a butene-l column, a stream containing principally butene-l is recovered as the overhead product through line 34. The kettle product containing normal butane which is recovered from fractionator 35 through line I36 is passed into fractional distillation column 37. A stream containing principally normal butane is recovered as the overhead product from column 37 through line 38 while a stream containing heavier hydrocarbons and any solvent carried over from stripper 28 is recovered as the kettle product through line 39. The overhead product stream from column 37 is recycled to dehydrogenation zone 11 `wherein the normal butane is converted to butenes.

The overhead product streams recovered from stripper 28 and fractionator 35 through

lines

31 and 34, respectively, constitute the feed material utilized in the second stage dehydrogenation. As shown in the drawing, the overhead stream from column 35 is passed directly into butene dehydrogenation zone 41. However, the overhead stream from stripper 28 recovered through line 31 is further treated to remove normal butane and butadiene prior to being used as a feed in the second stage dehydrogenation. Accordingly, line 31 from stripper 28 is further connected to line 42 through which the feed to fractionator 43 is charged. Since fractionator 43 functions as a butene-2 column, the kettle product recovered through line 44 contains principally butene-2. In order to remove C5 and heavier hydrocarbons, the kettle product recovered from column 43 is passed into fractionator 46 which serves as a deoiler. rPhe C5 and heavier hydrocarbons are recovered from the deoiler as the bottom product through line 47. The overhead fraction from deoiler `46 containing principally butene-2 is recovered through line 48 and then passed into butene dehydrogenation zone 41.

In dehydrogenation zone 41, the butenes are catalytically dehydrogenated to butadiene. While the catalyst used in zone 41 is preferably one comprising about 93 percent Fe203, 5 percent Cr203 and 2 percent K2O, it is to be understood that other known olefin dehydrogenation catalysts can be used Without departing from the spirit or scope of the invention. Temperatures in the range of 1050 to 1350i F. are generally employed in the second stage dehydrogenation while the pressure maintained in zone 41 is preferably atmospheric or subatmospheric. The dehydrogenation effluent from zone 41 consisting principally of butadiene, isobutylene, butene-1, normal butane, and butene-2 is passed through line 49 into a compressor system1`51. After passage through the compressor system, the compressed effluent is introduced via line 52 into lean oil absorber and stripper unit 53. C3 and lighter hydrocarbons are withdrawn from the lean oil absorber through line 54 while C4 and heavier hydrocarbons are recovered from the stripper through line 56 and then passed into fractionator 57. Additional C3 and lighter hydrocarbons are recovered from fractionator 57, which functions as a depropanizer,

through line 58. The kettle product from; depropanizer 57 containing principally C4 and heavier hydrocarbons l tionator 43 through line 61 contains principally 1,3-butadiene, butene-l, normal butane and isobutylene. Thereafter, this stream is passed intoextractive distillation column or absorber 62 wherein it is contacted with a solvent which is selective for butadiene. While it is preferred to utilize furfural as a solvent, it is Vto be funderstood that other solvents suitable for making the desired separation can be utilized. The rich solvent containing absorbed b-utadiene which is recovered from absorber 62 through line 63 is then passed' into stripper 64. In stripper 64, the hydrocarbons are stripped from the solvent,` being removed as an overhead product through line A66 and then passed into fractionator 67. Lean furfural absorbent is recovered from the bottom of stripper 64 through line 68 and then recycled to absorber 62. Butadiene is recovered from fractionator 67 through line 69 as the product of the process while any heavier hydrocarbons and any solevnt or polymer carried over from the stripper are recovered las the kettle product from column 67 through line 71.

An undissolved fraction containing principally butenel, normal butane and isobutylene is recovered from absorber 62 through -line 72; A portion of this fraction is passed by means of line 73 into line 32 through which feed to fractionator 35 is charged. Butene-l, contained in line 73 and introduced into column 35 through line 32 is recovered as Ia portion of the overhead product from column 35 through 34. The butene-l so recovered is subsequently recycled to butene dehydrogenation zone 41 by means of line 34. Normal butane contained in line 73 is included in the kettle product recovered from column 35 and subsequentlyrecovered as a portion of the overhead product from column 37. As previously mentioned, the overhead product from column 37 is recycled to dehydrogenation zone 11. Line 74 provides means for venting a part of the undissolved fraction recovered from absorber 62. However, the

that vented in a conventional process.

portion of theu'nabsorbed fraction recovered from ahsorber 62 is generally recycled to butene dehydrogenation zone 41. However,v because such a conventional process provides no means for removing normal butane Yfrom the system, it is necessary to purge or vent a large i proportion of the stream recovered from the absorber in order to prevent the system from becoming overloaded.

Y According to the instant invention, it is seen that means are provided whereby the butene-l and normal butane contained in the overhead stream from absorber 62 ,are separated, the materials then being recycled to the appropriate dehydrogenation steps. As a result, a more efficient utilization is made of the normal butane and Y been included in the material balance.

In a conventional process for producing butadiene, a

butene-1, thereby making possible a greater yield of butadiene from that usually obtained.

A more comprehensive understanding of the invention can be obtained by referring to the following illustrative examples which are not intended, however, to be unduly limitative of the invention.

EXAMPLE I A feed material containing normal butane is dehydrogenated over an Al2O3-Or2O3-Mg0 catalyst at about 1100 F. and 24 p.s.i.g. The dehydrogenationr eiiluent is then treated, as described hereinabove with relation to the drawing, so as to separately recover normal butane and butenes. The normal butane is recycled to the aforementioned normal butane dehydrogenation step. The recovered butenes are dehydrogenated over an Fe2O3--Cr2O3-K2O catalyst at about 1150 F. and 20 p.s.i.'g. The eiuent from the butene dehydrogenation is then treated so as to recover a substantially pure butadiene product stream. As mentioned in the description of the drawing, an overhead fraction containing principally butene-1, n-butane, and isobutylene is recovered from the furfural absorber during the treatment of the butene dehydrogenation eluent. This .fraction is further treated so as to separately recover n-butane and butene-l which are then supplied to the butane and butene dehydrogenation steps as appropriate. The operating conditions for the various items of equipment are set forth hereinbelow in Table I while the amounts of materials in gallons per hour flowing in the various lines are shown in Table II'. Hydrocarbons other than those listed, such as acetylenes, may be present in the streams; however the amounts are so small that they have not The numerals used in the ltables correspond 15o-reference numerals used in the drawing to designate lines or pieces of equipment.

EXAMPLE II A control run is made in which the same feed material as that utilized in Example I is dehydrogenated in accordance with a conventional process. The catalysts and Table I Inlet Column Column Column Column Temp., Top Bottom Iop Bottom F. Temp., Temp., Pressure, Pressure,

F. F. p.s.l.g. p.s.i.g

Lean Oil:

Absorber (15) 95 Stripper (15) 341 Depropanzer (18)-.-. 100 Deoller (22) 196 Furfural:

Absorber (26)... 135 Stripper (28 298 Butene-l Column (35)-.. 110 n-Butane-Golumn (37) 185 Lean Oil:

98 pp 360 Depropanizer (57) 149 Butene-2 Column 140 Deoller (46).---;.'..`.-' 168 Furtural: t

133 pper 283 Butadiene Column (67 85 Table Il Streamy Isobuty- Butene-l Butan-Butane Butene-2 05's and Total lenes diene higher Feed to Deoller (17) 60 3, 040 590 26, 900 5, 900 375 36, 865 Deoiler Overhead (24) 60 3, 040 590 26, 860 5,890 235 36,675 Deoller Bottoms (23) 140 190 Furfural Absorber Overhead (32)... 60 2,215 5 26, 740 140 200 29,360 Furfural Stripper Overhead (31) 825 585 120 5, 750 35 7, 315 Butene-l C01.:

Recycle (73) 8, 195 85 380 160 10, 160

Feed (30) 10, 410 90 27, 120 300 200 29, 520

Overhead (34) 110 60 280 10 11, 860

Bittlzoms (36)--. 0 30 26, 840 290 200 27,660 11- 4 0 .I

Overhead (38) 300 30 26, 840 290 180 27, 640

Bottoms (39) 20 20 Butene Dehyd. Feed (48) plus (34). 1, 400 10, 180 130 1,080 19,050 325 32, 165 Butene Dehyd. Elueut (49) 1, 400 7,840 5,000 1,080 13,625 615 29, 560 Butene-2 Col.:

Feed (42) 1, 400 8, 665 5, 585 1, 200 19, 375 650 36, 875

Overhead (61) 1,400 8,595 5, 515 400 300 16,210

Bottoms (4 70 70 800 19,075 650 20,665 Deoiler Overhead (48) 70 70 800 19, 040 325 20, 305 Deoiler Bottoms (47).- 35 325 360 Furfural Absorber Overhead (72) l, 400 8, 565 400 170 10, 625 Purge (74) 60 370 5 20 10 465 Furfural Stripper Overhead (66) 30 5, 425 130 5, 585 Butadiene Col. Overhead (Product) (70) 5,415 60 5,475

Butadiene O01. Bottoms (71) 10 70 80 the dehydrogenation conditions are the same as those used in the run described in Example I. In the control run, the effluent from the n-butane dehydrogenation, after removal of C3 and lighter hydrocarbons in a depropanizer, is passed into a butene-l column prior to being treated in the furfural absorber. (It is noted that in the run of Example I the butene-l column is positioned after the furfural absorber and stripper.) The overhead from the butene-l column is passed to a butene-Z column, the bottoms of this latter column serving as a portion of the butene dehydrogenation feed after removal of C and heavier hydrocarbons in a deoiler. A part of this feed portion is recycled to the -furfural absorber used in the butene-2 separation. (This is eliminated in the instant process.) The bottoms from the butene-l column, after removal of C5 and heavier hydrocarbons in a deoiler, are passed into a furfural absorber. The unabsorbed overhead fraction from the furfural absorber is charged 25 to a n-butane column whose overhead is recycled to the butane dehydrogenation zone. The rich solvent recovered from the bottom of the furfural absorber is passed into a stripper, the overhead from which is used as a portion of the feed in the butene dehydrogenation. The overhead from the butene-2 column is charged to a furfural absorber for separation of the butadiene in this stream. A portion of the unabsorbed overhead Ifraction from the furfural absorber is recycled to the butene dehydrogenation step while another portion is vented. The bottoms of the furfural absorber is passed into a stripper, the overhead from which is treated in a butadiene column for the recovery of the butadiene product. 'Ihe various columns used in this run are operated at substantially the same conditions as the corresponding columns employed in the run of Example I. The amounts of material in gallons per hour ilowing in the various streams are shown in Table III hereinbelow.

Table III Stream Isobutyl- Butene-l Butan-Butane Butene-Z 05's and Total eues diene higher Feed to Butene-l Column 3, 040 590 26, 900 5,900 375 36, 865 Butene-l Col. Overhead (Part of feed to Butene-2 Col.) 60 2, 760 390 280 30 3, 520 Butene-l C01. Bottoms (Feed to Deoiler) 280 200 26, 620 6, 870 375 33, 345 Deoiler Bottoms 40 10 140 190 Deoiler Overhead (Part of feed to Furfural Absorber) 280 200 26, 580 5, 860 235 33, 155 Recycle from deoiled Butene-2 Col.

bottoms (To Furfural Absorber). 10 10 220 1, 330 20 1, 590 Furfural Absorber Feed (Deoiler Overhead plus Recycle) 290 210 26, 800 7, 190 255 34, 745 Furfural Stripper Overhead (Butene Dehyd. Feed) 240 205 120 7,050 40 7, 655 Furfur Absorber Overhead (Feed to n-Butane 001.)- 50 5 26, 680 140 215 27, 090 n-Butane Col. Overhead (To Butane Dehyd.) 50 5 26, 680 140 195 27,070 n-Butaue Col. Bottoms- 20 20 Butene Dehyd. Feed 540 8, 290 340 3, 320 19,015 350 31,855 Bntene Dehyd. Emuent 540 6,160 4, 970 3, 320 13, 500 640 29,130 Butene-2 Col. Feed (Butene-l Col.

Overhead plus Ediuent) 600 8, 920 5, 360 3, 600 13, 530 640 32, 650 Butene-2 Col. Overhead (Feed to Furfural Absorber) 600 8, 850 5, 290 1, 400 300 16, 440 Butene2 Col. Bottoms (Feed to Deoiler) 70 2,200 13, 230 640 16, 210 Deoiler Overhead- 70 70 2, 160 13, 195 330 15, 825 Deoiler Bottoms 40 35 310 385 Deoiler Overhead less Recycle (Butene Dehyd. Feed) 60 60 1, 940 11,865 310 14, 235 Furfural Absorber Overhead 600 8, 820 85 1, 400 170 11, 075 Purge 60 880 10 140 20 1, 110 Recycle to Butene Dehyd.

Abs. Overhead'less Purge) Y 540 7, 940 150 9, 965 Furural Stripper Overhead (B adiene Gol. Feed). Y 30 5,365 Butadiene Col. Overhead (Product) 30 5, 285 Butadiene Col. Bottoms A comparison of the data set forth in Tables II and III shows the advantages obtained by proceeding in accordance with the process of this invention. Thus, it is seen that only 465 gallons of material per hour are purged in the instant process as compared with 1110 gallons per hour in the control run. As a result, additional n-butane and butene-l are made available from which butadiene can be produced. In this regard, it is noted that in the run of Example I 5415 gallons of butadiene per hour are obtained as compared with a yield of 5195 gallons per hour in the control run of Example II. Operation in accordance with the instant process provides for the effective removal of n-butane, thereby greatly reducing the amount of this material recycling within the system. Furthermore, it is possible to eliminate the recycle of the deoiled bottoms from the butene-2 column to the furfural absorber used in the butene purification.

As Will be evident to those skilled in the art, many variations and modifications of the invention can be practiced in View of the foregoing disclosure. Such variations and modifications are believed to be clearly within the spirit and scope of the invention.

I claim:

1. A process for the production of 1,3-butadiene which comprises catalytically dehydrogenating normal butane to normal butenes in a rst stage dehydrogenation zone; subjecting the C4 hydrocarbon content of the eluent from said first stage dehydrogenation zone to a first extractive distillation with a solvent selective for butene-2; recovering an undissolved fraction containing butene-1 and nbutane from said first extractive distillation; separating butene-1 from said undissolved fraction in a first fractional distillation zone; passing said butene-1 to a second stage dehydrogenation zone; recovering a stream containing n-butane from said first fractional distillation zone; separating C5 and heavier hydrocarbons Ifrom said n-butane stream of said first fractional distillation zone; recycling the resulting n-butane-containing streams to said rst stage dehydrogenation zone; recovering solvent containing dissolved C4 hydrocarbons from said first extractive distillation; stripping a stream containing butene-l, butene-2, butadiene and n-butane from said solvent; passing said latter stream of butene-l, butene-2, butadiene and n-butane into a second fractional distillation zone; catalytically dehydrogenating butenes supplied to said second stage dehydrogenation zone; recovering an effluent containing C4 and heavier hydrocarbons from said second stage dehydrogenation zone; passing said eliiuent into said second lfractional distillation zone; recovering a stream containing butene-2 from said second fractional distillation zone; separating `C5 and heavier hydrocarbons from said butene-2 stream of said second fractional distillation zone; recycling the resulting butene-Z-containing stream to said second stage dehydrogenation zone, recovering a stream containing butadiene, butene-l, n-butane and isobutylene from said second fractional distillation zone; subjecting said butadiene, butene-1, n-butane and isobutylene stream to a second extractive distillation with a solvent selective for butadiene; recovering an undissolved fraction containing butene-1, n-butane and isobutylene from said second extractive distillation; passing said undissolved fraction into said first fractional distillation zone; recovering solvent containing dissolved butadiene from said second extractive distillation; and separating butadiene from said solvent as the product of the process.

2. The process according to claim 1 wherein said selec-i tive solvent is furfural.

3. A process for production of 1,3-butadiene which`= comprises catalytically dehydrogenating n-butane to n butene in a first stage dehydrogenation zone; compressing the efiiuent gases from said first stage dehydrogenation zone; separating C3 and lighter hydrocarbons from said compressed efliuent gases in a first absorption zone and a first depropanizing zone respectively; passing a product stream containing C4 and heavier hydrocarbons from said first depropanizing zone to a first deoiling zone; separating C5 and heavier hydrocarbons from said product stream in said first deoiling zone; subjecting said product stream containing C4 hydrocarbons to a first extractive disillation with a solvent selective for butene-2; recovering an undissolved fraction containing butene-l and n-butane from said second extractive distillation; separating butenel from said undissolved fraction in a first fractional distillation zone; passing said butene-1 to a second stage dehydrogenation zone; recovering a stream containing nbutane from said first fractional distillation zone; separating C5 and heavier hydrocarbon from said n-butane of said first fractional distillation zone; recycling the resulting n-butane containing stream to said first stage dehydrogenation zone; recovering solvent containing dissolved C4 hydrocarbons from said first extractive distillation; stripping a stream containing butene-1, butene-2, butadiene and n-butane from said solvent; passing said latter stream of butene-l, butene-2, butadiene and nbutane into a second fractional distillation zone; catalytically dehydrogenating butene supplied to second stage dehydrogenation Zone; recovering an efiiuent containing C4 and heavier hydrocarbons from said second stage dehydrogenation zone; compressing the effluent gases from said second stage dehydrogenation zone; separating C3 and lighter hydrocarbons from said compressed effluent gases in a second absorption Zone and a second depropanizing zone respectively; passing a C4 and heavier hydrocarbon stream from said seco-nd depropanizing zone into said second fractional distillation zone; recovering a stream containing butene-2 from said second fractional distillation Zone; separating C5 and heavier hydrocarbons from said butene-2 stream of said second fractional distillation zone in a second deoiling zone; recycling the resulting butene-2 containing stream to said second stage dehydrogenation Zone; recovering a stream containing butadiene, butene-1, n-butane and isobutylene from said second fractional distillation zone; subjecting said butadiene, butene-l, n-butane and isobutylene stream to a second extractive distillation With a solvent selective -for butadiene; recovering an undissolved fraction containing butene-l, n-butane and isobutylene from said second extractive distillation; passing said undissolved fraction into said first fractional distillation zone; recovering solvent containing dissolved butadiene from said second extractive distillation; and separating butadiene from said solvent as a product of the process.

References Cited in the file of this patent UNITED STATES PATENTS 2,209,215 Gaylor et al July 23, 1940 2,379,332 Arnold June 26, 1945 2,386,310 Hachmuth Oct. 9, 1945 2,395,016 Schulze et al Feb. 19, 1946 2,554,054 Owen May 22, 1951 2,750,435 Fetchin June 12, 1956

Claims

1. A PROCESS FOR THE PRODUCTION OF 1,3-BUTADIENE WHICH COMPRISES CATALYTICALLY DEHYDROGENATING NORMAL BUTANE TO NORMAL BUTENES IN A FIRST STAGE DEHYDROGENATION ZONE, SUBJECTING THE C4 HYDROCARBON CONTENT OF THE EFFLUENT FROM SAID FIRST STAGE DEHYDROGENATION ZONE TO A FIRST EXTRACTIVE DISTILLATION WITH A SOLVENT SELECTIVE FOR BUTENE-2, RECOVERING AN UNDISSOLVED FRACTION CONTAINING BUTENE-1 AND NBUTANE FROM SAID FIRST EXTRACTIVE DISTILLATION, SEPARATING BUTENE-1 FROM SAID UNDISSOLVED FRACTION IN A FIRST FRACTIONAL DISTILLATION ZONE, PASSING SAID BUTENE-1 TO A SECOND STAGE DEHYDROGENATION ZONE, RECOVERING A STREAM CONTAINING N-BUTANE FROM SAID FIRST FRACTIONAL DISTILLATION ZONE, SEPARATING C5 AND HEAVIER HYDROCARBONS FROM SAID N-BUTANE STREAM OF SAID FIRST FRACTIONAL DISTILLATION ZONE, RECYCLING THE RESULTING N-BUTANE-CONTAINING STREAMS TO SAID FIRST STAGE DEHYDROGENATION ZONE, RECOVERING SOLVENT CONTAINING DISSOLVED C4 HYDROCARBONS FROM SAID FIRST EXTRACTIVE DISTILLATION? STRIPPING A STREAM CONTAINING BUTENE-1, BUTENE-2, BUTADIENE AND N-BUTANE FROM SAID SOLVENT, PASSING SAID LATTER STREAM OF BUTENE-1, BUTENE-2, BUTADIENE AND N-BUTANE INTO A SECOND FRACTIONAL DISTILLATION ZONE, CATALYTICALLY DEHYDROGENATING BUTENES SUPPLIED TO SAID SECOND STAGE DEHYDROGENATION ZONE, RECOVERING AN EFFLUENT CONTAINING C4 AND HEAVIER HYDROCARBONS FROM SAID SECOND STAGE DEHYDROGENATION ZONE, PASSING SAID EFFLUENT INTO SAID SECOND FRACTIONAL DISTILLATION ZONE, RECOVERING A STREAM CONTAINING BUTENE-2 FROM SAID SECOND FRACTIONAL DISTILLATION ZONE, SEPARATING C5 AND HEAVIER HYDROCARBONS FROM SAID BUTENE-2 STREAM OF SAID SECOND FRACTIONAL DISTILLATION ZONE, RECYCLING THE RESULTING BUTENE-2-CONTAINING STREAM TO SAID SECOND STAGE DEHYDROGENATION ZONE, RECOVERING A STREAM CONTAINING BUTADIENE, BUTENE-1, N-BUTANE AND ISOBUTYLENE FROM SAID SECOND FRACTIONAL DISTILLATION ZONE, SUBJECTING SAID BUTADIENE, BUTENE-1, N-BUTANE AND ISOBUTYLENE STREAM TO A SECOND EXTRACTIVE DISTILLATION WITH A SOLVENT SELECTIVE FOR BUTADIENE, RECOVERING AN UNDISSOLVED FRACTION CONTAINING BUTENE-1, N-BUTANE AND ISOBUTYLENE FROM SAID SECOND EXTRACTIVE DISTILLATION, PASSING SAID UNDISSOLVED FRACTION INTO SAID FIRST FRACTIONAL DISTILLATION ZONE, RECOVERING SOLVENT CONTAINING DISSOLVED BUTADIENE FROM SAID SECOND EXTRACTIVE DISTILLATION, AND SEPARATING BUTADIENE FROM SAID SOLVENT AS THE PRODUCT OF THE PROCESS.