US2395016A - Process for the dehydrogenation of hydrocarbons - Google Patents

Description

Feb. 1 9, 1946. w. A. scHuLzE ET Al.

' PROCESS FOR THE DEHYDROGENATION 0F HYDROCARBONS 2 sheets-sheet 1 Filed May 6, 1943 l ATTORNEYS4 Feb. 19, 1946. w. A. scHULzE E'rAl.

PVROCESS FOR THE DEHYDROGENATION OF HYDROCARBONS 'Filed May 6,/1943 2 Sheets-Sheet 2 INVENToRs W A SCHULZE `1 c. HILLYEB ATTORNEYS Patentes Feb. 19,1946

' uNlrrzo STAT PROCESS FOR DEHYDROGEATION F HYDROCARBONS waiter A. Schulze and Johnc. muyer, Bartlesvllle, Okla., assignors to Phillips Petroleum ES PATENTl Company, a corporation of Delaware Application May 6, 1943, Serial No. 485,908

' V12 Claims. (Cl. Zim-680) butane to butenes in a first dehydrogenation step and dehydrogenation of a butene to butadiene in a second dehydrogenation step.

'I'his is a continuation-impart of the copending application Serial No. 358,008 iiled September 23, 1940, now Patent No. 2,362,218, issued November 7, 1944, disclosing a process in which butene-2 obtained from the catalytic dehydrogenation of normal butane is separated and subsequently dehydrogenated to produce butadiene. 'I'he present invention is directly concerned with the recovery of butene-Z from both stages of dehydrogenation and particularly with the catalytic isomerization of butene-l concurrently formed to promote the.

eiliciency oi' product segregation from both of said stages of dehydrogenation.

An object of this invention is to provide an improved process for the production of a diolefln from the corresponding paramn.

Another object of this invention is to' provide another arrangement of apparatus for carrying out the process of this invention.

It hasI been proposed to produce butadiene by the catalytic dehydrogenation of normal C4 parailins, oleiins, and mixtures thereof, with various methods being suggested to enable the provision vof suitable butylene concentrations in thedehydrogenation feed stocks. Such methods have included the dehydrogenation of normal butane to yield paraflin-oleiin mixtures, and the treatment Y of said mixtures im the same or diilerent dehydro- -genation steps to ".further econvert the oleilns to the dioleiins. Other methodshave indicated improved .eillciency and economy from the segregation of normal butylenes from unconverted paraflins prior to conversion to produce the dioleiin.

f The latter methods have been preferred generally such a process which is particularly applicable to the production of butadiene from butane.

Still another object of this invention is to prol vide an improved process for the production of butadiene from butane in which the butene-l, formed concurrently withl the formation of butene-2, is converted to butene-Z.

A further object of this invention is to provide an improved method for the separation of butene- 2 and butadiene from the products of the catalytic dehydrogenation of C4 hydrocarbons.

A particular advantage of the process of the present invention is that it provides for the extraction of butadiene and butene-2 from the emuents of .both dehydrogenation steps in a single operation.

Other objects and advantages of the invention will be apparent to those skilled in the art from a consideration of the following detailed disclosure and the accompanying drawings.

Figure 1 of the drawings is a diagrammatic ele-A vational view of an arrangement of apparatus suitable for carrying out the present invention.

Figure 2 is a diagrammatic elevational view 0f for the reason that the optimum' dehydrogenation conditions for the parafn-oleiin and the olefindiolen conversions are distinctly di'erent, and overall process yields and economics have favored the relatively complete segregation of butylenes as the feed stock to the olefln-diolen conversion step.

Heretofore, means for accomplishing butylene segregation or purificationv from n-butane have been handicappedv by the physical properties of the two isomers, butene-l and butene-2 produced in the dehydrogenation reactions. theseproperties, and particularly those oibutene- 1, have complicated the separation butadiene as the end product of the manufacturing process.

In our copending application, Serial No. 358,008,

referred to above, we have disclosed an improved method for producing butene-Zas the feed stock to a second dehydrogenation step by means of catalytic isomerlzation of butene-l to but'ene-Z. However, in said second step, theyre-establishment of the equilibrium between the normal butylene isomers at the temperature level of the dehydrogenation with formation of increased amounts of rbutene-l has resulted in increased difficulty-in butadiene separation and puriiication, and also in lthe presence of considerable amounts of butene-l in butylene mixtures recycled to the saidsecond dehydrogenation step.

We have now discovered a process whereby both butadiene puriiication and butylene segregation steps 'are accomplished more eillciently and the butylene feed to the second dehydrogenation stage 4 comprises essentially butene-2. This last-named improvement has been found to result in improved butadiene yields due .apparently to the more sat- Furthermore,v

and recovery of the olen-diolefln conversion step.

It is anfadditional feature of our new process that the basic operations are cooperative to an unusual degree, and may, if desired, be carried out in units of process-equipment serving both stages of dehydrogenation. 'This advantage may be utilized to reduce the equipment requirements and operating costs for butadiene production at the same that improved yields are obtained as a result of the present invention. Y

In one specific embodiment, our process comprises the following steps: (1) normal butane is catalytically dehydrogenated in a first dehydrogenation stage to produce normal butylenes; (2) the butane-butylene condensate from step 1 is catalytically isomerized to convert butene-l to butene2; .(3) the effluent from the isomerization treatment is treated by solvent extraction or frac.. tionation to separate butene2 from the-other C4 components which include unconverted n-butane tov be recycled to the first dehydrogenation stage: (4) the butene2 is catalytically dehydrogenated in a second stage to produce butadiene; (5) the C4 condensate from step 4 is treated with a selective solvent to separate butadiene and butene2 from butne-l and butane; (6) the butadienebutene2 mixture is fractionated to separate substantially pure butadiene from butene2; (7) the butane-butene-l stream is passed` to the isomerization unit and the butene2 produced is recovered with that derived from the first stage dehydrogenation. Y

In additionto these basic operations, several*l other auxiliary steps may be desirable in some circumstances. These may include a further fractionation oi. the n-bu'tane-butened mixture being recycled to the rst stage of dehydrogenation to yrecover and isomerizefurther quantities of butene-l, or the treatment of the recycle streams to either dehydrogenation stage to remove small amounts oi' higher boiling liquid and/or isobutylto butenes. The ei'lluent of the ilrst stage of the dehydrogenation comprises unconverted butane isfactory 'characteristics of butene-Zas feed t g maining in the n-butane recycle stream may be carried out in unit 5. This unit may be a simple fractionating column with the butylenes taken overhead and returned through line to either th'e isomerization unit 5 or the' isobutylene removal unit 29. The n-butane from fractionator l f is then recycled through line I0 to the first stage dehydrogenation.

'I'he butene2 is stripped from the solvent in 'stripper II and passes through line I2 to be A feed stream comprising fresh and recycle butene2 is catalytically dehydroganated in unit I3 under conditions selected to eilect partial conversion to butadiene, and the dehydrogenation products are cooled, compressed, and treated in units I4 and I5 to collect a`C4 condensate comprising butadiene and butylenes.

The second stage C4 condensate then vpasses to column IBin which a partial removal of butene2 along with traces of heavier liquid is carried out. The overhead product from this fractionation passes through line Il to absorber I8, while the bottoms fraction is taken through line I9 tov a subsequent depentanizing or stripping operation in column 25.

The absorberx I8 operates with a selective solvent for butene2 and butadiene, and these components are separated from the stream entering by line Il. The unabsorbed portion comprising butene-l and smaller quantities of isobutyle'ne and n-butane formed over the second stage catalyst passes out through line 20. Some butene2 may also pass throughand be recovered in subsequent processing. When isobutylene removal is practised, the stream may pass through removal unit 28 for selective polymerization treatment or 't ing through line 20.

and normlbutylenes, butene-l and the 2'bu l tenes, together with C3` and lighter hydrocarbons,

Cs and heavier hydrocarbons, and some isobutylene. Th'e reiiluent of the dehydrogenation is cooled, as, by the cooler 3, and passed to a separation step, designated by the numeral l, wherein the eiiiuent is subjected to compression and cooling to form condensate while at the same time the Cs and heavier vhydrocarbons and the, C: vand lighter hydrocarbons are separated from the C4 hydrocarbons. The 'C4 hydrocarbon stream, which may advantageously contain a part of the C: and/or lighter hydrocarbonsis passed to the isomerization step 5 where conversion of butene-'1` present in the stream to the butene-Zisomers is `effected in the presence of a suitable' catalyst. The egluent from ,unit 5 passes to absorber 'I where a selective solvent is utilized to absorb the butene2, while a stream oi' predominantly n-butane with a greatly reduced butene-l content passesv through line 8 to be recycled to the' first stage dehydrogenation. Optionally, treatment t0` separate relatively small amounts of butene-l reyso The butene2 and butadiene are stripped from the solvent in stripper 2| and pass through line 22 to butadiene column 23u. In this column substantially pure butadiene. is taken overhead through line 24 to storage, while butene2 is removed as the bottoms product through line I5 to column 25. 'This column 25 may be used to fractionate the total recycle butene2 from the botv toms of columns Il and 23, with recycle butene2 taken overhead throughlines '2l and `I2 to the second stage dehydrogenation unit. Alternately, the butene2 from the bottom of column 2l may be recycled directly through lines 21 and I2.

In Figure 2 a variation in the sequence of th'e same basic processsteps is shown whereby a singl solvent absorption unit is utilized to treat the C4 condensate from both stages of dehydrogenation. In this arrangement, the products' of n ormal butane dehydrogenation in unit 2 are treated to recover va predominantly C4 condensate com- The second dehydrogenation stage operating on a predominantly butene2 feed obtained' as de-v A'Ci scribed hereinafter is indicated by unit is. condensate comprising normalbutylenes and butadiene is collected in unit l5. This condensate -passes to fractionator I8 where partial removal of butene-Z along withtraces of higher boiling liquid is accomplished. 'I'he overhead product from column I8 passes through line 32 to absorber remaining butene-2. I .y

The unabsorbed hydrocarbons from absorber 1 comprise n-butane and butene-l from both the first and second stages of dehydrogenation. This mixture passes through line 8 to column 9 which is operated to produce a bottoms product of substantially olen-free n-butane removed through' line IU as recycle stock for the first stage dehydrogenation. The overhead fraction taken -1 for selective absorption of butadiene and the 1- hydrogenation stage.

through line 30 contains butene-l together with any isobutylene formed during dehydrogenation, and some n-butane may be included depending on the precision of the fractionation.

Said overhead fraction in line lsv-returned I to isomerization unit 5 for further conversion of butene-l to butene-2. 'I'he stream or a portion thereof may be passed intermittently or continuously to unit 29 for the removal of isobutylene by selective polymerization', or the like to prea vent the building-up of isobutylene in the system. The butene-2 produced by isomerization of recycled butene-l is thus combined with that rescribed feature the use of catalytic momerization to reduce fractionation requirements for butene- 1 separation and are particularly adapted to the utilization of solvents exhibiting relatively greater solubility for 2olens than for l-oleiln. In theV in the conversion of a substantial proportion of the butane to the corresponding 'oleiina Other sources loi' butylenes may of course be utilized if available, although preliminary purification steps.

e.l s. isobutylene separation, may be required.

The dehydrogenation catalysts and conditions for the paraiiin-oleiin'conversioxi are chosen 'to v yield adequate amounts of olens at reasonable covered from the two dehydrogenation operations, land the amount of butene-l separated in column 9 is controlled by the completeness of con version in unit 5.

'Ihe rich solvent from absorber I is stripped instripper Il to remove butene-Z and butadiene. This mixture then passes to butadiene column 23 which operates to separate substantially pure bu- ,diene as the overhead product.k The butadiene is removed through line 24 to storage, while the butene-2 bottoms fraction is taken through line I2 yand combined with the butene-2 from column y 25 as feed to the second dehydrogenation stage.-

This last-named column 25 -serves to strip butene-2 from higher boiling liquids in the bottoms fraction from column I 8. Ifnecessary, .the entire .butene-Z stream may be similarly treated in column 25.

Other possible .alternatives are illustrated in j Figure 2 for application in special circumstances.

l' lThus, in some cases depending on the butadiene concentration in the stream and the particular isomerization catalyst, it may be desirable to pass the butadiene-butylene mixture from fractionator I6 to the isomerization uniti. This flow enables the isomerization of butene-l in the second stage eiiluent prior to treatment with the selective solvent and may eliminate the use of column 0 for separating olefin from the n-butane recycle stream to the ilrst dehydrogenation stage.

Y However, in many instances, unless the isomerization catalyst is ,carefully chosen, th instability ofthe diolefln favors butadiene removal prior to isomerization. 1 v

Further, the ilrst stage condensate may," bepassed directly to the absorption unit'through lines 32 and 34 for absorption of butene-2 prior to isomerization. of butene-I. This arrangementfavors the isomerization reaction by-lowering .the butene-2 concentration in the feed to unit 5 and may be employed when suitable absorption and fractionation capacity are available to obtain clean: separation of the somewhat greater quantities of butene-l from butene2 and later from n-butane. l

selectivity in butylene production.

per pass conversion in order to maintain high While a great many dehydrogenation catalysts may be used, it is usually preferred'to employ solid contact catalysts comprising bauxite, synthetic aluminas or magnesia, 'often bearing or promoted wlth.,metai oxides including those of chromium. nickel, 'zirf conium, tungsten, zinc, iron, and copper.

I'he conditions of pressure, i'low rate, etc., used in the paramn-oleiin conversion will depend largely on the activity of the catalyst and its range of maximum eiilciency. The charge vapors may, for example, be treated at temperatures of about 900 to about 1200 F. and nearatmospheric pressures, to obtain adequate conversion to butylenes. The vapors may be subjected totwo ormore successive treatments in a series of catalyst chambers or sections containing catalyst of the same or gradually increasing activity, or any portion of the vapors may be recycled with fresh lfeed to the catalyst. These and other known operating devices may be utilized to attain the desired conversion of the normal butane feed.

The dehydrogenation products are handled in conventional equipment to segregate the components used in subsequent process steps. The customary methods of cooling.: compressing, and fractionally condensing or absorbing C4 hydrocarbons are suitable and may include one or more stages of compression followed by an oil absorption step or its equivalent to absorb C4 hydrocarbons from the Cs and lower boiling hydrocarbons and fixed gases. The condensate later stripped from the absorption oil may contain minor amounts of Ca hydrocarbons which may be removed at. any suitable point in the processing stepsy For the isomerlzation'of butene-l to butenc-Z.

catalysts are chosen on the basis of their activity in the temperature range favorableto maximum butene-Z formation, and should not promote polymerization or other undesirable' reactions which destroy or convert the butylenes to unusable form. Since the equilibrium vbetween butene- 1 and butene-2 favors maximum butene-2 concentration at low temperatures. catalysts ac.

s f 'rhs new diagrams ums ii'iusiratea and ae-v tive in the range of about 200 to about 600 F. are preferred.

Among the catalysts which have been found suitable for the isomerization are several of an acidic nature; These include mineral materials containing acidic substances such as certain clays and silicates, salts such as aluminum phosphate and the like, or strong mineral acids in suitable concentration and often supported on adsorbent carriers. In employing catalysts of this type, precautions are observed to avoid undesired polymerization, as by regulation of the water content of the catalyst and/or of the hydrocarbons.

Other types of catalysts which are active and often preferred are those comprising magnesia in natural or synthetic form. These catalysts have the peculiar property of being highly active in substantially anhydrous state, so that the feed, the catalyst mass, and the treating conditions are regulated to produce and maintain substantially anhydrous conditions Further catalysts such as brucite after activating treatment to remove water and adsorbed gases', as described in the copending application of Drennan, Serial No. 446,771, illed June 12, 1942,'are sufficiently active at temperatures in the range of about 100 to 'about 400 F. to enable substantially equilibrium isomerization at said temperatures. The

resulting butene-2 concentrations may amount to about 80-90 per cent or more of the total normal butylenes in the feed to the isomerization unit. Said catalysts are further characterized by low activity toward polymerization, and may be employed, if desired, to treat hydrocarbon mixtures containing relatively large concentrations of butadiene and/or isobutylene without losses of said components.

The operation of the isomerization unit involves conventional equipment, and may consist of passage of the hydrocarbon fluid at suitable flow rates over a bed or through a bodyjof catalyst. The feed is ordinarily preheated to operating temperature and may be substantially dehydrated when employing a catalyst most highly active in anhydrous state. Liquid phase contacting at relatively low flow rates is often preferred, and suitable pressures may be utilized t prevent vaporization. In other instances. vapor phase contacting may be utilized at lower pressures and/or higher temperatures. A

The eiiluent from the isomerization catalyst usually contains large prODOrtions of unconverted normal butane which must be separated from the unsaturated components for recycle to the first stage dehydrogenation. butylene production is the principal object, it will be desirable to limit the olefin content of this butane recycle stream'in order to prolong cata-- lyst life and improve the reaction eillciency.. In case of restrictions on the olefin content of the kbutane recycled, and in view of the benefits of "relatively complete butene-2 recovery. an absorpl ti'on operation utilizing a selective solvent is often preferred to separate butene-2 as charge to the second dehydrogenationstage.

However, when the rst stage condensate is treated over a highly efiicient isomerization catalyst, the unconverted butene-1 concentration may be reduced so low that the butane and lighter fraction separated from butene-2 by fractionation may be recycled satisfactorily to the nrst stage dehydrogenation..

'Theuse of certain selective solvents for thev present process is particularly advantageous because th'e solvents while exhibiting suitable pref- In many cases, whenv low one atmosphere.

`further treatment for olefin separation. In other cases, supplemental butene-1- separation and/or isobutylene removal may be desirable.

In the second dehydrogenation stage, the conversion of butene-2 to butadiene is usually carried 'out' at temperatures of about 1100 to about 1300 F., near-atmospheric pressures, and with butene partial pressures in the charge 'vapors be- A convenient method of operation with reduced butene partial pressures involves -the use lof an inert diluent, preferably steam, with the butene-2 charge to regulate the butene partial pressure and space velocity in the catalyst zone.

Catalysts for the -second stage dehydrogenation are in general less active than those employed in the first stage and may be pretreated and/or compounded with various materia to impart resistance to poisoning by water vapor and to suppress polymerization and cracking reactions at the high temperatures employed.

unconverted butene-2, butene-1, and isobutylene formed by isomerization of the butene-2 charge, and traces of butane produced over the catalyst may be first fractionated to separate some of the butene-2 and heavier material to facilitate the solvent absorption step.

The course of the absorption operation is sub- 'stantially the same as that described for'the first stage condensate, with butadiene absorbed along vwith butene-2. VComplete separation of butane is essential to the recovery of high purity butadiene. The butene-1 and n-butane when processed over the isomerization catalyst are handled in the same fashion as the components of the first stage condensate. Isobutylene removal may systemi be practised at any point subsequent to the solvent absorption step, and is preferably carried out at the stage where the isobutylene concentration reaches a maximum.

, The butadiene-butene-Z extract recovered from the solvent 'is separated into its components by precise fractionation, yielding substantially pure ybutadiene and butene-2 for recycling to the second stage catalyst after combination with the other butene-2 streams from other parts of the This inethod of supplying butene-2 as feed to the dehydrcgenation operation producing buta"` 'l diene Venables a more selective conversion' even under more severe conditions than when a mixed butylene feed 'or butene-l alone is` employed, This is apparently due to the greater stability;

of the carbon skeleton of butene-z as compared to butene-l and to the consequent-higher ultimate yields of butadiene and decreased losses of butylene feed in the form of light gases and car-` bon. Thus, the present process makes possible higher per pass conversions and/or higher b utadiene yields from equivalent amounts of butylene feed stocks by virtue of the isomerization of butene-l and the selective recovery of butene-2.

In view of the above-described operations and the advantages obtained, the benefits of the present process will be obvious. The sequencev of the various steps and the selection of operational schemes such as are illustrated in the lflow dia- Y grams lwill depend on process economics for each individual plant. Some further illustration of the principles and operations of the process may,

however, be provided in the following exemplary operation, substantially as shown in kFigure l.

Normal butane may be dehydrogenated` over Ca and lighter Butene-l 12413 Butene-2 23-24 n-Butane 61-62 After substantially complete dehydration, isomerization of this condensate over activated brucite catalyst at temperatures of Z50-300 F. produces a composition as follows:

Q, Mo'l per cent Ca-and lighter 2-3 Butene-l 2-3 Butene-Z 33-34 n-Butane 61-62 When the isomerized c ondensate is contacted inv a liquid-liquid absorption operation with furfural as the selective solvent, the following sepa- -ration of raffinate from extract is accomplished: v

, Raillnate, Extract, mol

mol per cent per cent Ca and lighter 8-4 1-2 Butane-1 3-4 Buteue-2 95-96 n-Butane 92-93 2-3 'I'he raiinate may be recycled directlyto the n-butane dehydrogenatlon step while the butene-2 is used as a portion of the feed to the second stage of dehydrogenation.

alumina-chromium oxide type catalyst to con- After a. preliminary fractionation to remove a portion of the butene-Z and heavier material, `the condensate is contacted with furfural in an absorption step, and the ramnate and extract show the following separation:

Rafllnate, Extract, mol

mol per cent peroen C; and lighter 16 Butadiene 68-70 Isobutylene-- 7 Butane-1...-. 50-60 Butane-2.. l-Z) Sil-32 Butane 5-6 Fractionation of the extract produces butadiene of 97-99 per cent purity. The butano-2 also produced is combined with that recovered `by stripping Cs and heavier from the preliminary con-r-y densate fractionation and that produced from the rst stage condensate togive a feed stock containing over 95 mol per cent of butene-2.

TheV raffinate is depropanized to continuously separate and vent a substantial portion of the C:

and lighter material, and treated over a selective.

polymerization catalyst to effect isobutyiene re,- moval. The adjunct of the polymerization step -is a fractionation operation which separates Cs and heavierliquid from the C4 raflnate.

When added to the first stage condensate ahead Aof the isomerization unit, the composition of the combined stream is approximately as follows:

Mol per cent C: and lighterv 2 Isobutylene 2 Butene-l 35-40 Butene-2 5;-10 n-Butane 51 arated to the isomerization unit, preferably byz addition ahead of the depropanizer of the isobutylene removal unit.

When the above described operation is altered to incorporate the flow oil-Figure 2, the composition of product streams is not greatly changed. The principal variation is the increased fractionation load for unit `9 separating butene-l from n-butane with greater precision.-

From the foregoing, it will beapparent that the isomerization of butene-l to butene-2 at the indil cated points in the two-stage dehydrogenation The butene-2 may be diluted with steam to produce a charge mixture with a steam-butene molar'ratio of three or somewhat higher and,

dehydrogenated over bauxite bearing barium hydroxide at '1200 F. to convert 30-40 per cent of the butene-2 per pass. The C4 condensate recovered from the 'dehydrogenation products will have the following approximate composition:

Mol per cent C3 and lighter '7.5 Butadiene 16-17 Butylenes '72-73 Butane v 3 05+ f 0.5

system enables the more efficient and economical operation of thebutylene segregation and butadiene 'purication steps. Of particular importance are the reduction in .the number and sizer of precise fractionating units which are otherwise required for butene-l separation, and the `added benefits of charging substantially only.

butene-Z to-the second stage dehydrogenation.

In case the butylenes for the olefln-diolefin conversion are available from a source other than n-butane dehydrogena'tiom the process of this invention is applicable to the treatment of anybutane-butylene mixture with, perhaps, suitable revisions for handling larger quantities of isobutylene and different disposal of the parailins discarded from the system. Such revisions may include the use of a single catalyst end/or reagent to eilect isobutylene removal and butene-l isomerization as described in our` copending applica- Aprocedure maylbe followed in the treatment of C hydrocarbons for-the production of pentadienes. Normal pentane may be dehydrogenated in a rst step'forming normal pentenes including pentene-l and 2-pentenes, the pentene-l isomerized to Z-pentenes, and the pentene2 separated for dehydrogenation in a second step to produce pentadiene. The pentene-l formed in the second dehydrogenation may be separated from the eiliuent and passed to the isomerization step. The various streams may be handled in the same manner as the C4 streams, hereinafter more fully discussed in detail, and this application of the invention will be evident to those skilledin the art.

These and other modifications and extensions of the present invention will be obvious in the light of the disclosure and speciiic descriptions provided. Therefore no limitations are implied except as defined in the following claims.

We claim:

l. The process for the production of a dioleiin of four to five carbon atoms per molecule from the Acorresponding normal parailin which coniprises catalytically dehydrogenating said paraffin under conditions effecting conversion of a substantial portion of the normal parailin to the corresponding oleiins including the 1-olenn -and 2- oleflns; catalytically isomerizing the olens in the effluent of the delrvdrogenation step under conditions effecting conversion of at least a portion of said 1-oleiln to 2olefins as the principal reaction; separating the 2-olens from the 1-olefin and unconverted parailln in the eiiluent of said isomerization; recycling the unconverted parailin to said dehydrogenation; catalytically dehydrogenating said Z-olenns under conditions effecting conversion 'of a substantial portion of said 2- olens to the corresponding diolefin with the simultaneous formation of some of the l-olefin;

` separatingA the dioleiin and unconverted 2 -olefln in admixture from the l-olefin in the eiliuent of said olen dehydrogenation step, treating the' r mixture of dioleiin -an`d unconverted 2oleiin to separate same into a fraction of substantially pure diolen and a fraction of the unconverted 2-olen, and recycling theunconverted Z-oleflns to the oleiin dehydrogenation step. Y

2. The process for the production of a 'diolen of 4 to 5 carbon atoms per molecule from the corresponding normal parain which comprises catalytically dehydrogenating said parailin in a first dehydrogenation step forming the corresponding oleilns comprising the l-olefln and 2- oleilns; catalytically isomerizing the olefins in the eilluent of the dehydrogenation step under condiy tions effecting conversion of at least a portion of said 1-olen to -2-olens as the principal reaction; separating the Z-olens in the eiliuent ofthe isomerization step from unconverted Dlf' and unconverted l-oleiin; separating the parafn from the l-olen; recycling the paratl'in to the first dehydrogenation step; recycling the uncon verted l-ole'iin to the isomerization step; catalytically dehydrogenating said 2-oleiins in a second y ldehydrogenation step formingthe corresponding dioleiin with the simultaneous formation of the 1'o lenn; separating 'the diolen and unconverted 2-olens from the l-oleiin in the effluent of the second dehydrogenation step; passing the l-oleiin to the isomerization step: separating the dioleiivn in substantially pure form from 'the unconverted 2-oleflns; and recycling the unconverted 2-o1efin to the second dehydrogenation step.

3. The process for the production of a dioleiin of four to five carbon atoms per molecule from the corresponding normal paraffin which comprises catalytically dehydrogenat-ing said paranin in a rst dehydrogenation step, forming the corresponding olens comprising the l-olen and 2-olefins with the simultaneous formation of the corresponding isooleiin and diolen; catalytically isomerizing the oleflns in the eliiuent of the dehydrogenation step under conditions effecting conversionv of at least a portion of said 1olefln to 2-o1eiins as the principal reaction; separating the 2-olens'and' the dioleiin in the eilluent of the isomerization step from the unconverted normal paraln, the isooleiin, and the unconverted l-oleiin; segregating the unconverted normal parailin, the l-olefln, and the isooleiin; recycling the unconverted normal parain to the'irst devhydrogenation step; recycling the unconverted .l-olen to the isomerization step; withdrawing the isooleiin from the system; separating the diolen from the 2olens in a -second separation step; catalytically dehydrogenating said .'Z-ole-V fins in a second `dehydrogenation step forming the corresponding diolen with the simultaneous formation of the l-oleiin and isooleiin; separating the diolen and unconverted 2-o1eiins from the l-olefin and isooleiin in the .eilluent of the second dehydrogenation' step; separating the 1- oleiin from the isooleiin;' withdrawing the isoolen from the system; passing ythe 1-o1en to the isomerization step; separating the dioleiin in substantially pure form from the unconverted 2- olens; and recycling the unconverted 2-oleiins to the second dehydiogenation step.

4. 'Ihe process for the production of pentadiene from normal pentane which comprises catalytically dehydrogenating normal pentane under conditions eiecting-conversion of a substantial portion of the normal pentane to the corresponding pentenes including pentene-l and the 2-pentenes; catalytically isomerizing the oleiins in the eiiluent of the dehydrogenation step uiider conditions effecting conversion of at least a portion of said pentene-l to pentene2 as the principal reaction, separating the pentene2 from the pentene-l' and unconverted normal -pentane in the eiiluent of said isomerization step, separating the pentene-l from the unconverted normal pentane, passing the pentene-l to the isomerization step, recycling the unconverted normal pentane to the dehydrogenation step, catalytically dehydrogenating the vsaid pentene2 under conditions effecting conversion of a substantial portion of said'pen tene-2 to pentadiene withthe simultaneous formation of some pentene-L separating pentadiene and unconverted pentene2 from the pen- Atene-l in the eilluent of said last-mentioned dehydrogenation step, separating substantially pure pentadiene from the Vunconverted pentene2, recycling the unconverted pentene2 to said lastmentioned dehydrogenation step, and passing the pentene-'l to the isomerization step.

5. 'I'he process for the production of butadiene from butane which comprises catalytically dehydrogenating normal butane under conditions etfecting conversion f a substantial portion of the normal butane to the corresponding butenes including butene-l and the Z-butenes, catalytically isomerizing the olenns in the eiuent of the y dehydrogenation step under conditions effecting conversion of at least a portion of said butene-l to butene-2 as the principal reaction, separating the butene-2 from the butene-1` and unconverted normal butane in the eiiluent 'of said isomerization step, separating the butene-l from the unconverted normal butane, passing the butene-l so separated to the isomerirati'on step, recycling the unconverted normal butane to the dehydrogenation step, catalytically dehydrogenating the bi1- tene-Z under conditions eiecting conversion of a substantial portion of said butene-2 to butadiene with the simultaneous formation of some butene- 1, separating butadiene and unconverted butene- 2 from the butene-l in theeiilue'nt of said lastmentioned dehydrogenation step, separating substantially pure butadiene from the unconverted the butadiene from the unconverted butane-2; and recycling the unconverted butane-2 to the second dehydrogenation step.

8. The process for the production of butadiene from normal butane which comprises catalytically dehydrogenating normal butane in a first dehydrogenation step, forming butene-l and 2-butenes with thev simultaneous formation of butadiene and isobutene; catalytically isomerizing the butenes in the eiiluent of the dehydrogenation step under conditions eecting conversion of at butene2,recyc1ing the unconverted butene-2 to said last-mentioned' dehydrogenation step andV passing the butenesl to the isomerization step.

6. The process for the production of butadiene from normal butane which comprisesJ catalytically dehydrogenating normalbutane in a rst dehydrogenation step forming butene-l and 2-butenes with the simultaneous formation of butadiene; catalytically isomerizing the butenes in the eiiluent of the dehydrogenation step under conditions effecting conversion of at least a portion of said butene-l to butene-2 as the principal c 'verted butene-2 from the butene-l in the eiiluent of the second Adehydrogenation step; passing the butene-l to the isomerization step; separating the butadiene from the unconverted butene-2; and

`least a portion of said butene-l to 2butenes as the principal reaction; separating butene-2 and the butadiene in the iiluent of the isomerizationstep from unconverted normal butane, isobutene, and unconverted butene-l; segregating the normal butane, isobutene, and the butene-l; recycling the uneonverted normal butane to the rst dehydrogenation step; recycling the unconverted butene-l to the isomerization step; withdrawing the isobutene from the system; separating the butadiene from the butene-2; catalytioally dehydrogenating the butane-2 in a second dehydrogenation step forming butadiene with the simultaneous formation of butene1;separating the butadiene and the unconverted butene-2 from the butene-l in the eilluent of the second dehydrogenation step; passing the butene-l to the isomerization step; separating the butadiene from theunconverted butene-2); and recycling the unconverted butene-2.to the second dehydrogenation step.

recycling the unconvert'ed butene-2 to the second f dehydrogenation step.

y7. The process for the production ,of butadiene from normal butane which comprises catalytically dehydrogenating normalbutane in a first dehydrogenation step forming butene-l and butene- 2 with the simultaneous formation .o f butadiene;

catalytically isomerizing the butenes in the ef` fluent of dehydrogenating step under conditions effecting conversion of at least a portion of said butee-l to 2-butenes as the principal reaction;v

separating the Z-butenes and. butadiene inthe v eilluent of the isomerization step from unconfverted normal butane and unconverted butane-1; separating the normal butane from the butene-l;

recycling the unconverted normal butane to the drawing the isobutene from the system; passing the butene-l to the isomerization step; separating 9. The process for the production of butadiene.

from normal butane. which comprises catalytically dehydrogenating normal butaneunder conditions eifecting conversion of a substantial portion of the normal butane to normal butenes including butene-l and Z-butenes; catalyticallyisomerlzing the butenes in the eiliuent of the dehydrogenation step undericonditionsA effecting conversion of at lea'st a portion of said butene-l to 2-butenes as the principal reaction; contacting the eiiiuent of said isomerization with a selective solvent effecting removal of lbutane-2 from the butene-l ,and unconverted normal butane; recycling the unconverted normal butane to the said dehydrogenation; catalytically dehydrogenating the butene-2 under conditions effecting conversion of a substantial portion of said butene-Z to buta- 1 diene with. the simultaneous formation of butene- 1'; contacting the eiiluent oi' said last-mentioned dehydrogenation with a selective solvent effecting removal of the butadiene and the butene-2 from the butene-l therein; passing the butene-I to the isomerization; separating butadiene from the unconverted butene-2; and recycling the unconverted butene-2 to said last-mentioned dehydrogenation.. A

10. The process for the production of butadiene from normal. butane which comprises catalytically dehydrogenating normal fbutane under conditions effecting conversion of a substantial portion of the normal butane to the butenes includingbutene-l and 2butenes with the simultaneous formation of butadiene; catalytically Qisomerizig the butenes in the euent of the de- \\hydrogenation step under conditions effecting conversion of at least a portion of said butene-l to 2-butenes as the principal reaction; contacting the eiiluent of said isomerizatlon step with a selective solvent in a separation step eiecting removal of the Z-butenes and the butadiene from the butene-l and unconverted normal butane therein; recycling the unconverted normal butane to said first debydrogenation step: separating the butadiene from the butene-2; catalyticaliy dehydrogenating the butene-2 under conditions effecting conversion of a substantial portion of said butene-2 to butadiene with the simultaneous formation of butene-1; separating at least a por--i tion'of the unconverted butene-2 from the butadiene and butene-1 in the eiliuent of the second dehydrogenation step; recycling the unconverted butene-2 to the second dehydrogenation step; and passing the butadiene and. butene-1 tothe firstmentioned vseparation step.

11. The process of producing butadiene from vnonxnal butane which comprises catalyticaily dehydrogenating noi-mal butane' to normal butenes including butene-1 and butene-2 in a rst dehydrogenation stage, segregating a predominantly C4 hydrocarbon fraction from the eiiiuent, said fraction containing the butane and butene content of said eiiiuent, passing said fraction through a catalytic isomerization step and thereby etlecting isomerization of said butene-l to,

the rich solvent. fractionally distilling the C4 hydrocarbon fraction from the eiliuent, said stripped butadiene and butene-2 to produce an overhead of substantially pure butadiene and a bottoms of butene-2, and recycling the butene-2 content of said bottoms to said second dehydrogenation step.

12. The process of producing butadiene from normal butane which comprises catalytically dehydrogenating normal butane to normal butenes including butene-1 and butene-2 in a first dehydrogenation stage, segregating a predominantly feed to the extraction step while allowing the butene-2 as substantially theV sole reaction, ex-

tracting the isomerization eilluent with a selective solvent having `preferential solubility. for butene-2 as compared to butene-1v and thereby eiecting solution of the butene-2 content while allowing the normal butane and butene-1 content to pass through undissolved, recycling the undissolved normal butane to said dehydrogenation step, stripping the dissolvedbutene-2 from therich solvent, catalytically dehydrosenating the stripped butene-2 to butadiene in a second dehydrogenation stage with the simultaneous for- `mation of some butene-1, segrgating-a C4 hydrocarbon fraction from the eiiiuent, said fraction containing the butadiene and butene-1 content and at least a portion of the butene-2 content of said eiiiuent, extracting said fraction with a selective solvent having preferential solubility for butene-2 as compared to butene-1 and thereby effecting solution of the butadiene and butene-2 content while allowing the butene-1 content to solved'butene-i to said isomerization step, stripping the dissolved butadiene and butene-2 from normalbutane and butene-1 content thereof to pass through undissolved, fractionally distilling the raffinate from said extraction step to segregate an overhead of butene-1 and a bottoms of normal butane and recycling said butene-l to said isomerization step and said normal` butane to said dehydrogenation step, stripping the dissolved butene-2 and butadiene from the rich solvent,

` fractionaliy distilling the stripped butadiene and ypass through. undissolved, recycling the undis-v 5 butene-2 to produce an. overhead of substantially pure butadiene and a bottoms of butene-2l catalytically dehydrogenating said butene-,2 to butadiene in a second hydrogenation stage with the simultaneous formation of some butene-1, seg? regating a C4' hydrocarbon fraction from the efuent, said fraction containing the butadiene, norinal butane and Abutene-1 content and at least a portion of the butene-:2 content of lsaid efv fluent, and commingling said fraction with said isomerization eilluent and, extracting it and otherwise treating it therewith as above.

WALTER A'. sCHULzE. JOHN c. mmm.

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