US2371817A - Production of diolefins - Google Patents

Description

March 20, 1945. F. E. FREY PRoDUcTIoN oF DIoLEFINs 2 Sheefs-Sheet 1 Filed Aug. 30, 1940 INVENTOR FREDERICK E. FREYV BY i MONEY March 20, 1945. F.- FREY 2,371,817

lPRODUCTFON OF DIQLEFINS Filed Aug. so, '1940 2 snets-sheet 2 DOLEFIN MMQW Patented Mar'. 2o, 1945 "unimo 4srii'rflis` vParamEor-.1=icla 'e Y l i I ritonuorrzo'limomrms I I' Frederick E. Frey.artlesyille, V)lxla.,l'assinor to Phillips -Petroleum Company, a corporationA of Delaware Application August 3o, i940, serial No. 354,890

6 Claims. (Cl.l 2GB-881.5)

This'invention relates to the production of diolenn hydrocarbons from paraflin hydrocarbons by 'dehydrogenation` larly t0 the production of such diolens by the f use of a single dehydrogenation step. The inventicn has particular reference to the production of diolenns such asbutadiene'l pentadiene,v andisoprene from the correspondingparain hydrocarbons.4

An appreciable number of diolens such as those just mentioned have been known to the art for a number of years. These have been produced in a number of ways which have included cracking ofheavier oils, the copolymerization of acetylene and ethylene to form butadiene,'cata lytic or thermal conversion of alcohols, both of the same number of carbon atoms per molecule as the desired diolefln and of a fewer number of carbon atoms per molecule, and other more or less involved chemical processes, aswell as the dehydrogenation of the corresponding olefins which in turn may have been produced bythe dehydrogenation ofthe corresponding parafllns.

1 This latter procedure, although it appears to be one of the more directmethods for the production of diolefins, has not as yet found very extensive commercial' application, andirlvolves4 a somewhat complicatedprocedure including de-` hydrogenation toform oleflns, separation of olefins in a more or less concentrated form, dehydrogenation of these olens to form diolens, and separation of a diolen so produced from unre- It relates more particutial quantities. However, in any clean cut dehydrogenation process the initial products, once formed, vtend to reunite by the reverse reaction of hydrogenation, so that equilibrium value, dependent on the various re'- action conditions present. For these'reasons, the

maximum value of the'dioleiin concentration, a1- though substantial, will be low.

My invention further comprises various pre- -feried methods of separating the dehydrogenation eilluent into the desired constituents.

4 ins disclosure and discussion.

acted olens. However, direct as this process apt pears to be, most of the commercial installations to date have been one of the former types rather than a process involving only direct treatment-ol hydrocarbons of the same number of carbon atoms per molecule.

. I havenow found that I can successfully produce substantial yields of diolens from -the'corresponding parans by a process which involves a single dehydrogenation step. In a simple modiiication my invention .comprises passinga parailln hydrocarbon` to a `dehydrogenation step which is adapted to effect a production of di olens, separating most or` all ofthe hydrogen and any light hydrocarbons, from the emuent,

paraiiins together with, the corresponding oleiins which have been produced in the dehydrogena- It is an object of my inventionto produce diolen hydrocarbons from parailln hydrocarbons hydrogenation wherein oiefins and diolefins, togetherf'with free hydrogen. are produced from parailin hydrocarbons.

It is another object of this invention to prov duce dilen hydrocarbons from the corresponding parafiin hydrocarbons ofthe lsame number of carbon atoms per molecule.

Further objects and advantages'of this invention will become apparent from the accompanylnfa preferred form of my invention I employ a dehydrogenation catalyst to eifect a production of dioleins. In order to obtain the best yields of dioletlns from my process, and to operate it mostv successfully, I find it necessary to employ onlyT the more eilicient dehydrogenation catalysts, and to employ'dehydrogenation-'conditions at which there is only a minimum of scission of carbon to carbon bonds. 4In this manner I am able toobtain high yields or dioienns `or the same number 'of carbon atoms per molecule as the original j paraillns, and also with the corresponding ar. rangement of carbon atoms. Furthermore, since Y my invention involvesth production and treat- 'separating and recovering the desired dioleilns so i produced, and returning to the dehydrogenation. a hydrocarbon material comprising uureacted tion. This dehydrogenation step'apparently does not form the major part of the d'ioleiln product by a dehydrogenaton of a parailln directly to a dlolefin with no intermediate reactions, but ap-4 parently cooperates with the rest of my process- 1 vto effect a dehydrogenation of paramns to oleflns and concomitantly a dehydrogenation of oleilns to diolenns, the latter being produced in substan- 55 the most desirable catalysts for my process are.

those that consist of or comprise chromiumoxide,

ment of olen'hydrocarbons corresponding' to the desired diolens, I am able to include in my |process relatively simple separation equipment for the recovery of the dioletlns, the` elimination of low.

boiling dehydrogenationv products, and the separation of a recyclefraction composed of paraillns and oleilns. Anydehydrogenation catalyst with the foregoine` characteristics is suitable for use in my process. However, I have found that and especially unglowed chromiumoxide or chromium o xide gel,` which 4is lgenerallydarkI or black, such as was nrst described byv Huppke. and Frey the concentration of dehydrogenation products approaches only an in U. S. Patent 1.905.383, or a modiiied form of this material as disclosed by Frey and Huppke in U. S. Patent 2,098,959, and is also disclosed in various copending applications which include Morey, Serial No. 113,091; Matuszak and Morey, Serial No. 173,708 (Patent No. 2,294,414); Morey and Frey, Serial No. 173,709 (Patent No. 2,312,572); Morey and Frey, Serial No.k 359,296, led October 1, 1940, and others. -The dehydrogenation pressure should not be very high, that is, generally it should not exceed 50 or 100 pounds per'square inch gauge, and in most instances should be only slightly above atmospheric. At times a subatmospheric pressure varray be used, but although a low pressure favorsthe dehydrogenation reaction subatmospheric pressures will generally not be used in plant operations. A low partial pressure of the hydrocarbon material present along with a total pressure above at mospheric may be realized by dehydrogenating the hydrocarbons in admixture with an inert gas such as nitrogen or the like, as is known to the t art. Although the presence of free hydrogen tends tohave an adverse mass action eiect, a small amount of free hydrogen in the charge stock often appears to have a benecial effect upon the catalyst, especially on the initial portions of the catalyst with which the charge stock comes into contact. Other modiiications of dehydrogenation operation known to the art may also be used. With a given dehydrogenation pressure and catalyst activity, the -dehydrogenation temperature and reaction time will be interdependent and will have'in general an inverse relationship. 'Ihe dehydrogenation temperature will be within the range known for catalytic dehydrogenation, but preferably will not be in the upper part of the range but will be between about 700 and 1150 F. Lower temperatures, even with long reaction times, willrgive uneconomically low yields, and higher temperatures, even with very short reaction times, willresult in excessive formation of low boiling hydrocarbon products. I prefer to operate under constant conversion conditions with gradually increasing temperatures as a particular body ofcatalyst becomes deactivated. With a satisfactory dehydrogenation at a relatively low temperature, a iiow rate adapted to give dehydrogenation not far short of equilibrium,'may be used. If this ow rate is maintained as the temperature is increased, to provide for a relatively constant extent of conversion as the catalyst becomes less active, the reaction conditions will generally be such atthe higher temperatures that excessive deleterious secondary or side reactions4 are not encountered.

The paraffin hydrocarbons charged to my process should be in a more or less pure state when it is desired to produce substantially pure diolens. My process is particularly adapted to the production of butadiene, normal pentadiene, and

isoprene irom'normal butane, normal pentane,

and isopentane respectively. yThese paraiilnhyl- -drocarbons may be considered as members of the group 0l Darailns of not more than five carbon atoms per molecule and of the type R-CHs-gH-Clr-CHI fresh body of'active catalyst, which will produce them, by simplefractional distillation and each adapted to eillcient nondestructive dehydrogenation under the conditions disclosed herein. While individual hydrocarbons of a purity greater than 99 per cent may be obtained by fractional distillation, .such purity is often quite expensive to obtain and is generally not necessary for the ordinary commercial application of my invention. The recycle feature of my process tends to build up undesirably high concentrations of isomers of the hydrocarbons whichV are being treated by my invention, and the charge stock should be sulciently pure that this eiect is not too predominant. This effect is also readily controlled by periodic or continuous removal and refractionation of a portion of the recycled hydrocarbon material, as will be discussed. For most uses of my invention the charge stock will preferably consist of a hydrocarbon material of a given carbon skeleton structure in a concentration of at least about per cent of the hydrocarbons present. Although the invention applies primarily to a paraiilnic charge'stock direct from some natural source, if a hydrocarbon fraction is availablewhich contains olens of the same carbon skeleton structure as the paraflins and substantially free lof isomerlc paraiins and/or olens, it will also be a material suitable for charging to my process, and a hydrocarbon material of a given carbon skeleton structure will be understood to include such olefins as well as the paraiilns.

My invention will now be more specifically described in connection with the accompanying drawings, which showv diagrammatically by way of iiow sheets two modifications of apparatus for practicing my invention,

Figure 1 illustrates an arrangement of appaat a relatively low pressure to dehydrogenation unit Il. The dehydrogenation unit Il is comprised of suitable heating units or furnaces, catalyst chambers, and the like known to the art for effecting and maintaining catalytic nondestructive dehydrogenation o! low boiling hydrocarbons.

The catalyst chambers may be so arranged that heat is supplied to the catalyst body, or bodies, and the reacting mixture. However, when a steady state of operation is reached only a limited amount of dehydrogenation actually takes place per pass, since the net amount kwill be the dehydrogenation of a small amount of butane to ,form butenes and of butenes to form a correspending amount of butadiene, when the process is operated to `produce butadiene, and a large substantially adiabatic catalyst chamber may be used with an adequate heating of the stream charged to such chamber. 'I'he hydrocarbons charged to the process are joined by recycled parailins, and olefins of a like number of carbon vatoms per molecule` previously produced in the dehydrogenation unit, passing through pipe 32.`

; ing hydrocarbons,v

' dehydrogenation step,

The dehydrogenation is conducted to eiecta dehydrogenation both of parafllns and oleiins to form olens and diolefins, respectively, along with free hydrogen. The resulting products pass through pipe I2 and valve I3 to the absorber I4, entering at a low point. Absorber I4 is-provided with suitable bubblev trays, or packing, or the like, not showrnknown to the art and suitable for eiectlng intimate contact between an ascending ilud and an immiscible descending liquid. The ascending fluid will be either liquid or gaseous, generally gaseous, comprising free hydrogen and paraflln and olefin hydrocarbons of the dehydrogenatlon eluent, and the descending liquid will comprise a suitable absorbent liquid introduced near the top of the absorber, together-with ab sorbed diolefln hydrocarbons. The dehydlogen` l ation eliluent will be suitably cooled before' entering labsorber I4, as by mea-ns of a coolerincorporated as a part of the dehydrogenation unit', or in pipe I2, not shown. The absorption liquid will be likewise suitably cooled, -by means not shown, such as a` cooler in pipe 51.

A trap-out tray I5 is provided near the bottom of the absorber, preferably below the inlet pipe I2. The rich absorbent liquid, which will contain some oleflns as well as the desired diolens, is removed .from the trap-out tray I5 through pipe I6, and Ais passed by suitable means through heating coil I1 and pipe I8 to a reboiler 20 which comprises the bottom of absorber I4; Vapors, released from the rich absorptlonliquid by this treatment, which will contaiha'higher ratio of olens to dioleflns than is present in the absorbed material containedin the liquid passing -through pipe I6, pass up through the trap-out tray I5 to meet the descending 'absorption liquid.

Unabsorbed material, which comprisesV essentially free hydrogen, unreacted paraflins, and oleflns of the same number of carbon atoms per molecule produce by the dehydrogenation, together with possible small amounts of lower bollpass from a .high point of absorber I4 through pipe 23 and valve24, ablycompressed by compressor or pump 25, and passed through pipe 26 to separatingI means 21. A-suitable cooling means, 'not shown, may be insertedl in pipe 28 or incorporated asa part of the separating means 21. The separating means is adapted to eiect a separation between a hydrocarbon material comprisingessentially paralns and oleflns'which are to be recycled to the rialcomprising essentially free hydrogen, which is removed from the .process through pipe 30 and valve 3|. The recycle'stock is withdrawn through pipe 32 and passed through valve 33 to pipe I0 to be mixed with a. paraiiin hydrocarbon material If desired, a part or lall charged to the process.' of the stream may be used to effect a part of the ycooling required in connection' with separating means I21, this being accomplished by passing the liquid stream through pipe 34. and valve 35 to and a lower boiling mateliquid in reboiler is suitf vaporizing or cooling coll 88, and then through y pipe 81 Vaud valve valve 83 being partly or completely closed, A1.. though it i's primarilyfintended to treat a'single paraffin hydrocarbon, it is generally not economical to isolate such a material' in acompletely pure state, though it is not toodiilicultor expensive to Produce terial which is 95'to 9'7 per centpure. I have found such a' charge to be of a satisfactory purity. However, impurities present in this charge. tend to build up inthe system, so that it is often de- 38 back `to pipe 32, with the sirable to remove a continuously or intermittently from pipe moved may be subjected to further separation, with the desired, recovered hydrocarbons being reintroducedto the system with fresh paraiiins through pipe Il).

The rich absorption diolens, is removed from the reboiler 20 through pipe 42 and .passes through valve 43 to -the top of a first stripperv 44. A portion only of the absorbed material is removed in this stripper, and will com prise a substantial portion of ldioleiin together with the major part 'of any remaining absorbed olen. The material so removed is returned, at least in part, through pipe 45 and valve 4B to the rated material may be removed from the system through pipe 41 and valve 4 8, if desired,for further treatment. The partially stripped rich absorbent passes from a low point of stripper 44 through pipe 50 and valve 5I 'to stripper 52, wherein itis completely freedofabsorbed hydrocarbons. The material so removed will comprise essentially the desired dioleiin'and is recovered as a product of the process through pipe 53 andivalve 54. As an'aid to the concentration of diolein in the original rich absorbent, and removal of undesired absorbed oleiins, a portion of this diolen material may be returned to the reboiler 2li `from pipe 53 through pipe 55 and valve 56. The denuded lean absorbent liquid is removed from 'a' low point of stripper 52 through pipe 51 andvalve 58 to a high point of absorber I4. Any heaviery hydrocarbons which may be formed in the dehydrogenatlon step in small amounts will 'collect in this absorption oil and build up in the system. Any such accumulation may be controlled andlmited by withdrawing' av portion ofthe lean absorption oil from the system through pipe 5I and valve 82, and removing such heavy hydrocarbons, and if desired returningthe purified oil-to the,V system by means not shown.

The procedure just described for the apparatus shown in Figure 1 is for the process'which has reached a steady state of operation. In initially starting the dehydrogenation step,- only a small amount of diolen will beformed, and it will gen` erally be desirable to recycle the entire hydroca bon material for a short period. This can be done by use of the by-pass -2I with valve 22' open and with valve I3 partially or completely closed.

.At this time aswell as during subsequent steadystate operation, it may be desirable to include a small amount 4of free hydrogen in therecycle stream passing through pipe 32, so that the initial part ofthe catalyst bed or beds used in the de:

hydrogenatlon unit II will operate in the presence of small amounts of free hydrogen. aswell as subsequent portions ofsaid'beds. After thefdiolefin concentration of the eilluent has risen to an lappreciable value, such as 3 or 4 to 6 or 8 per cent, the eilluent is passedto the absorber, as discussed.

The absorption liquid used in absorber I4 is one 4in which unsaturated hydrocarbons are preferentially dissolved and parailn hydrocarbons are only slightly soluble. It is desirable that this absorption medium have only a limited capacity for by fractional distillation a masolution even of theunsaturated hydrocarbons,

otherwise the resulting solution-will tend to' be completely" miscible with all hydrocarbons 4after taking up an appreciable quantity' of unsaturated hydrocarbons. uhiscan be somewhat limited and controlled byoperating at a suitably low tem- 4 3 portion of the recycle stock, i.

liquid, containing desired 20. A portion of this unsatu-l trays or packing or to ascending gases and vapors. Free hydrogen,

will tend to increase at ilrst upon the absorption of diolefins but which I have found can be counteract/ed and suitably controlled by proper control of temperature and pressure of the rich absorbent, together with judicious recycling of various streams as has just been described in connection with Figure l. 'Ihe rich absorbent, containing some mono-olens as well as the desired dioleflns, which collects on tray I5, is heated and returned to reboiler wherein it has added to it diolen concentrates introduced through pipe 'and/or pipe 55. 'Ihis treatment has the effect of vaporizing absorbed mono-olelns both as a result of the heating and of the increased concentration of diolen. Mono-oleflns which remain and are present in the material passed through pipe 42 are substantially completely removed in the preliminary stripper` 44.

Although some dioleiin is likewise vaporized at this point, it is recovered within the system, as will be readily appreciated, and after the absorption and recovery system has reached a steady state of operation the stream passing through pipe 23 will be substantially free of diolefn and contain mono-oleiin equivalent in amount to that .g

present in the stream entering the bottom of the absorber through valve I3. Likewise, the stream recovered as a product of the process through pipe 53 and valve 54 will comprise diolelns in high concentration and in an amount equivalent to that produced by the dehydrogenatin and entering the absorber through valve I3', an amount which will also be practically equivalent to the fresh hydrocarbon material of the samecarbon skeleton structure charged to the process through along with any light gases, is removed through pipe 30 and valve 3|. A rich absorption liquid passes from a low point of the absorber II4 through pipe I I5 and valve IIB to a high point of stripper II1. The absorbed hydrocarbons are removed from the absorption liquid, and thisr latter passes in a. lean state from a low point of stripper ||1 through pipe ||8 and valve ||9 to the top ofl absorber I I4.

Any heavier hydrocarbons which may be formed in the dehydrogenation step in small amounts will collect in this absorption oil and build up in the system. Any such accumulation may be conf trolled and limited by withdrawing a portion of the lean absorption oil from the system through pipe |2-6 and valve |21, and removing suchheavier hydrocarbons, and if desired returning the purifled oil to the system by means not shown.

The hydrocarbon material so removed, which comprises essentially paraiiins, olens, and diolefns of the same number of carbon atoms per molecule, passes through pipe |30 and valve I3I to a second separating means such as the absorber or fractionator I32. When vused as an absorber,

it is preferably used in conjunction with a material which reacts selectively with diolens to form a readily decomposable chemical compound. Such materials are known to the art and include aqueous solutions or compositions Iof a salt of a heavy metal of groups I and II of the periodic system, especially of suchl a metal in monovalent form; as a. cuprous halide, or a mercurous or silver salt, and especially an aqueous alkaliehalid'e-containing solution, or suspension, of cuprous chloride. Such a material is introduced near the top of absorber |32 and is intimately mixed, as it passes downwardly, with ascending hydrocarbon material. A hydrocarbon material comprising espipe I0. If the absorbent is suiciently selective in its action, the primary stripper y44 may be omitted, and the rich absorbent passed directly from pipe 42 through pipe 53 and valve 60 to pipe and stripper 52.

Referring now to Figure 2, this shows an alternative but not completely equivalent recovery process for recovering the desired diolefln product, the dehydrcgenation step being substantially the same as that .lust described in connection with Figure 1. A suitable hydrocarbon material enters the system through pipe I0 and is passed atl a relatively low pressure to dehydrogenation unit I I, as previously discussed. The paraflins charged to the process are joined by recycled paraiins, and oleflns of a like number of carbon atoms per molecule previously produced in the dehydrogenation unit, passing through pipe 32. The dehydrogenatlon products pass through pipe I2, compressor |25, and valve ||3 to separating means illustrated by absorber II.4, entering at a low point. Absorber ||4 is equipped with suitable bubble the like, and is operated primarily to effect a separation between free hydrogen and any light gases on the one hand, and dI- oleiins, olens, and unreacted paralns on the other. If a single absorber is used. as shown, this may be accomplished by passing a relatively nonselective absorption liquidto the top of the absorber, letting it pass downwardly countercurrent sentially parains and olens passesr from the top of absorber I32 through pipe 32, and is passed through valve 33 to pipe IU, to be mixed with the hydrocarbon material charged to the process. If desired a part or all of this material may be used to eiect a part of the cooling required in connection with separating means II4, especially if the material passing through pipe 32 is in the liquid state and is substantially above the pressure required in the dehydrogenation unit I This cool-r ing may' be carried'out by passing the material through pipe 34 and valve 35 to cooling coil 38, and then through pipe 31 and valve 38 back to pipe 32 with the valve 33 beingpartly or completely closed.' As previously mentioned in connection with Figure 1,l a portion of this stream may be continuously or intermittently removed through pipe 40 and valve 4I for further separation of its components.

A solution or slurry containing the resultant diolefin complex passes from absorber |32 through pipe I 33 and valve I 34 to stripperl |35, wherein the diolen is separated from the complex compound, as by heating, and is recovered as a product of the process through pipe |36 andvalve |31. The other component of the complex compound is recovered and returned to the absorber I3`. through pipe |38 and valve |39.

This procedure is adapted to the production and separation of all low boiling diolefins which are readily produced by the catalytic dehydrogenaltion of paraillns and olens. In the case of the means |32 may be operated as a fractonator, in

this case, andthe higher boiling pentadiene may be recovered by simple fractional `distillation from the lower boiling normal pentane andpentenes.' In such a case, the normal pentane and pentenes pass overheadthrough pipe 32, and pentadiene is `desirable at the start of a run to recycle a por-4 tion or all of the dehydrogenation ellluent, or of the hydrogen-freed hydrocarbon material, for a short period. Recycle of `Vthe entire vriiiuent can be effected by use of the bypass |2| with valve |22 open and valve l| |3 partially cr completely closed. Recycle of unseparated hydrocarbon material may be readily realized by 'removal of a part or all of the stream normally entering separating means |32, by means not shown, and returning it to thc processthrough pipe '|0. Y

`As an example of the operation of one mcdcation of my process, a butane stream compris- :ng about 97 per cent normal butane, with the remainder primarily isobutane, may be passed at a temperature of about 950 F. over a large mass of dehydrogenation catalyst comp'ising a dried and reduced mixed gel cf chromium oxide and aluinizia, prepared as described in U.. S. Patent 2,098,959 to Frey andHuppke. cn an inert granular support. The pressure .is only sufficiently above by volume, about 15 per cent each of hydrogen and normal bute'nes. the remainder being primarily unreacted butane with a practically negligible quantity of butadiene. Free hydrogen is removed from this initial eiiluent by simple cooling and liquefaction of the C4 hydrocarbons, with the C4 hydrocarbon material so recovered being returned directly to the inlet of the dehydrogenation step. As the products of th's first recycle portion of the continuous charge stream appear in the eiiluent the butadiene content of the eiiiuent, produced by dehydrogenation of butenes. rapidly approaches a value of about 4.5 per cent.'y with about 65 pei-'centr unreacted butaneV and about 18 per cent butenes, the remainder beiner essentially free hydrogen. Atthis stage of the operatiomin addition to the removal ofv free hysuiiicient to .maintain a substantiallyconstant amount of'conversion, and as the maximum temperature is reached afresh catalyst mass, at an initial temperature again of about 950o F. is

switched into operation. As the process reaches a steady state of operation the total charge, including added butane, and the efiiuent have approximately the following compositions, in per cent by volume of the gaseous mixture.,`

Component Elliuent Charge C4H|o 60 75- CHg 22 i 25 'C4H(Butadiene) 6 About 2 per cent ofthe recycle C4 hydrocarbon mixture is'continuously `discarded from the process, thereby maintain-'ng the normal C4 hydrocarbons in the total charge at a value greater than 95 per cent.

l As previously mentioned, the carried out in unit is conducted under a relatively'low pressure, which should not appreciably exceed about 50er l00pounds per square inch gauge, and which in most instances will be nearer atmospheric ypressure andmay even be subatmospheric. In many instances, therefore, the dehydrogenation pressure will be less than the pressureof the source of the material charged through pipe i0, and a pump or compressor will not be necessary for this stream. A compressor 25 has been shown in Figure 1, and a compressor |25I in Figure 2. For most adaptations of my invention such compression of part or all of the dehydrogenation 'efiluent will be the only compression and pumping used on the stream which contain or compriseolens and unreacted parafilns destined to be recycled to the dehydrogenation i unit a feature which is one of the advantages drogen from the eiiluent, the' eiiluent is also little over 20 ,per cent butenes, is recycled to the inlet of the dehydrogenation step, with additional normal butane being added in an amount sub'- stantially equivalent to the butadiene removed. so that thetotal quantity of C4 hydrocarbon` maconstant.- As the dehydrogenation catalyst mass loses activity,the temperature of the charge is raised to a maximum of about 1050 F. at a rate of my process. pressors for other streams have not been shown, the general` flow of the various streams is indicated and has been discussed, and suitable mechanical equipment oiA this nature can be readily supplied as required in any particular application of my invention by'one skilled inthe art. Similarly, other units of .eduipment have been shown only diagrammatically, but have beendescribed and the functions explained sofas to serve as suitable guides for adaptation of suitable specie )equipment for specific installations. It will be obvious t0 those skilled in the art that various modifications of my invention may be practiced as being included in the spirit of the disclosure and in the ,scope of the claims.y

I claim:

1. An improved processfor the separation-of butadiene produced by the. dehydrogenationmof normal C4 hydrocarbons from accompanying de-VU hydrogenation products, which comprises 'passing 1 theeiiiuent from such a dehydrogenation to a low-point of an'absorber, passing toa highpoint of said absorber a lean selective-absorption liquid to effect-a selective absorption of unsaturated!"` hydrocarbons, removing unabsorbed. gases from f the absorber, passing -a rich. absorbent .liquidM stream from saidabsorbent step to a rst stripper, effecting in said first stripper a partial stripterial subjected to dehydrogenation is `maintained i ping of said rich absorbent to remove therefrom a less unsaturated hydrocarbon material and re turning at leasta portion of the same to -a low' u `point or said absorber, passing the ,resultant pardehydrogenation Although other pumps or com-v a high point of said absorber a lean selective absorption liquid to euect a selective absorption of l unsaturated hydrocarbons, removing unabsorbed che' low-boiling diolen of four to uve carbon atoms" per molecule, produced by the dehydrogenation of a corresponding more saturated-hydrocarbon, from accompanying dehydrogenation products, which comprises passing the eilluentfrom such a dehydrogenation to a low point of an absorber. passing to a high point of said absorber a lean selective absorption liquid to effect a selectiye' absorption of unsaturated hydrocarbons, remov-V- ing unabsorbed gases from the system, passing a rich absorbent liquid stream from said absorbent step to a rst stripper, effecting in -said irst stripper a partial stripping of said rich absorbent to remove therefrom a less unsaturated hydrocarbon material and returning at least a portion oi' the same' to a low point of said absorber, passing the resultant partially stripped rich absorbent liquid to a second stripper. removing therefrom remaining absorbed material comprising predominantly doleiins, passing. a resultant lean absorption liquid to a high point oilsaid absorber, returning a portion of said separated absorbed diolen material to a low point of said absorber, andremoving from the process as a dioleiln product a further portion of said material.

3. An improved process for the separation of a low-boiling diolen of four to ve carbon atoms per molecule, produced by the dehydrogenation of a vcorresponding more saturated hydrocarbon, from accompanying dehydrogenation products, which comprises passing the ,eiiiuent -from such a dehydrogenation to a low point of an absorber, passing to a high point of said absorber a lean selective absorption liquid to eiect a selective absorption of unsaturated, hydrocarbons, removing unabsorbed gases from the system, heating the rich absorption liquid at the bottom of said absorber to vaporize a portion of the material absorbed therein, passing from the bottom of said absorber a rich absorption liquid stream to a first stripper, eiecting in said rst stripper-a partial stripping of said rich absorption liquid t'o remove therefrom lessv unsaturated hydrocarbon material and returning at least a portion of the same'to the heated liquid in the bottom of said absorber, passing the resultant partially stripped rich absorption liquid to a second stripper, removing therefrom remaining absorbed material comprising predominantly diolens, passing a resultant lean absorption liquid to a high point of said absorber, returning a portion of said separated diolefin material to the heated liquid in the bottom of said absorber, and removing from the process a further portion or said materialas a diolein product.

4. An improved process for the separation of pentadiene produced by the dehydrogenation of the corresponding Cs hydrocarbons from accompanying dehydrogenation products, which com l prises passing the eiiiuent from such a dehydrogenation to a low point of an absorber, passing to gases from the absorber, passing a rich absorbent liquid stream from said absorbent step to a ilrst stripper, effecting in said first stripper a partial stripping of said rich absorbent to remove there- `from a less unsaturated hydrocarbon material and returning at least a portion of the same to a low point of said absorber, passing the resultant partilally-stripped rich absorbent liquid to a sec-` ond stripper, removing therefrom remaining absorbed materials comprising predominantly pentadiene, passing a resultant lean absorption liquid to a high point o! said absorber, returning a portion of said separated absorbed pentadiene material to a low point oi said absorber, and removing from the process as a pentadiene product a further portion of said material.

5, An improved process for the separation of normal pentadienel produced by vthe dehydro sorbed gases from the absorber, passing a rich absorbent liquid stream from said absorbent step to a rst stripper, effecting in said iirst stripper av partial stripping of said rich absorbent to remove therefrom a less unsaturated hydrocarbon material and returning at least a portion of the same to a low point of said absorber, passing the resultant partially stripped rich absorbent liquid to a second stripper, removing therefrom remaining absorbed material comprising predominantly normal pentadiene, passing a resultant lean absorption liquid to a high point of said absorber, returning a portion of said separated absorbed normal pentadiene material to a low point of said absorber, and removing from the process as a normal pentadiene product a further portion of said material.`

6. An improved process for the separation of isoprene produced by the dehydrogenation of the corresponding more saturated Cs hydrocarbons from accompanying dehydrogenation products, which comprises passing the efiluent from such a dehydrogenation to a low point of an absorber, passing to a high point of said absorber a lean selective absorption liquid to eiiect a selective absorption of unsaturated hydrocarbons, removing unabsorbed gases from the absorber, passing a rich absorbent liquid stream from said absorbent step to a first stripper, effecting in said first stripper` a partial stripping of said rich absorbent to remove therefrom a less unsaturated hydrocarbon material and returning at least a portion of the same-to alow point of said absorber, passing the resultant partially stripped rich. absorbent liquid to a second stripper, removing therefrom remaining absorbed material comprising predominantly isoprene, passing a resultant lean absorption liquid to a high point of said absorber, returning a portion of said separated absorbed isoprene material to a low point of said absorber, and removing from the process as an isoprene product a further portion of said material.

FREDERICK E. FREY.

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