US2362218A

US2362218A - Process fob the dehydrogenation

Info

Publication number: US2362218A
Authority: US
Publication date: 1944-11-07
Anticipated expiration: 1961-11-07

Description

Nov.- 7, 1944.

W. A. SCHULZE ETAL 'PROCESS' FOR THE DEHYDROGENATION 0F HYDROCARBONS Filed Sept. 25,' 1940 Patented Nov. 7, 1944 UNiTE'D STATES PATENT OFFICE PROCESS FOR THE DEHYDROGENATION F HYDROCARBONS Walter A. Schulze and `lohn C. Hillyer, Bartlesville,- Okla., assignors to Phillips Petroleum Company, a corporation of Delaware V' Application September 23, 1940, Serial-No. 358,008

(c1. 26o-eso) 2 Claims.

This inventionrelates to the production of the valuable dioleiinic hydrocarbon butadiene from suitable four-carbon-atom hydrocarbons. It relates more particularly to the process of 'dehydrogenating normal butane in successive 'stages to produce successively butenes and butadiene. f In 1a more specific sense this invention is concerned with a new and improved process in which the mono-clelin butene-2 obtained as one of the products from the catalytic dehydrogenation of normal butane or;of the C4 fraction of thermally cracked gases is separated by fractional distillation and is subsequently dehydrogenated in al second catalytic step to produce a good yield of butadiene. It has already been proposed butadiene by the vcatalytic treatment of the total butene mixture resulting from the dehydrogenation of normal butane. However, it has been the practice of those attempting to carry lout asV a process 'to first dehydrogenate butane to produce mixed butenes and to recycle the treated va'pors until the desired concentration of butenes was reached o r the desired percentage of the butane charge had been converted. Because of the limitations -imposedby thermodynamic,equilibrium, it has Anot been possible to secure, satisfactorily pure mixed butenes by this Iprocedure without resorting to such severe conditions and excessive recycling* thatconsiderable .quantities of the butane and butenes were decomposed, and the reresulting yields of butenes were not commercially feasible. j

v Also attempts have been made to produce mixed butenes by dehydrogenating4 normal butane and separating the resulting butenes after each passage over the catalyst for further dehydrogena- `tion. Such attempts have involved various compleX solvent extraction and chemical separation methods which have proved expensive and generally unsatisfactory.

We have now discovered a novel process for the production of butadiene which eliminates the unsatisfactory practices of the art to date. Our invention not only provides for the economical production of butenes by catalytic dehydrogenation but also includes the segregation of butene-2 as charge to aseconddehydrogenation treatment [to produce butadiene. By the `practice of our infractionation, thus increasing the per pass recovery of substantially pure butene-2 by fractional distillation lwhile butene-1' Aand n-butane together with a portion of the butene-2 are recycled tothe dehydrogenation catalyst. It is therefore an object of this invention to convert normal butane to butadiene in two stages of dehydrogenation using a stream of substantially pure butene-2 separated after isomerization of the products of the iirst dehydrogenation step as a charge to the second dehydrogenation step.

In a mixture of C4 hydrocarbons such as is produced 'by dehydrogenating 4normal butane the boiling points of the components are as follows: (from- Physical Constants of Hydrocarbons, volurne I-EgloiT-Reinhold Publishing Company, 1939)'.

0 F. Bute'ne-1 2'0 Butadiene 23 n-Butane 31 Trans-butene-2 33 Cis-butene-2 39 It. has already been proposed in copending application Serial No. 352,787 led August 15, 1940, to separate butene-1 from thisl mixture by fractional distillation. However, the equilibrium concentrations established at dehydrogenation temperatures are such that of the total butenes produced, the predominant percentage is the 2- isomer. The following tabulation shows equili-brium concentrations of. butene-1, transbutene- 2, and cis butene-2 over a wide range or temperatures.

Concentrations in mol per cent of total butenes VTemperature, FF.' y Y Trans bu- Cs bu- Butene'l tene-2 tene-2 while the dehydrogenation of normal butane in the temperature rangefoflQOO to 1200" F. -yields high concentrations of. butene-1 this represents only aboutvone-third of the total butenes, the rel maining two-thirds being cis and trans isomers `of butene-2.

butane can be adjusted by isomerization to in- It may be seen also, in lthe above tabulation that at low temperatures the-equilibrium concentration ranges up to more than 97 percent of butane-2. We have now discovered that the rapid attainment of the low-temperature equilibrium concentrations of butene-2 is possible by passage of the partially cooled eluents from the first catalytic dehydrogenation step through active isomerization catalysts at temperatures in the range of 250-500 F. Even lower temperatures may sometimes-beused in this isomerzation. step. We have found it possible to convert nearly' all of the butene-l present in a C4 hydrocarbon mixture of the type described above into the higherboiling butene-2 isomers, thereby .concentrating the butenes on the higher-boiling side offnor'xnal butane.

We have found that after-the applicatignof this step of catalytic isomerization at the proper temperature levels to the partially cooled vapors from the dehydrogenation oflnormalgbutanefwe are able to secure a satisfactory separationhbetween normal butane and the butene-Z isomers .by :means of ordinary .,f-:roetioual distillation- .Although CleanseParetion .between-@nonna butanefiand trans floutene-.Z f een beA obtained only wwith;columns V:employing somewhat suore than A10o plates-:wade notfnormellyottepipt.toolean ,separationbut conduct the fractionation -insuoh manner .1 that :the bottoms product `is -oomposed Lpredoniinately-,of tutelle-2. By our-.iprocess,l the .overhead fraction comprising uneonverted vhu- Atene-,1. normal butane :and a. little trans butene-.z is: reoyeledftorthe; initial dehydrogenation gases instead of n-butane in our process the steps are not materially altered. In such a fraction comprising n-butane and butenes, the butene concentration is not usually great enough to Justify the segregation of butene-Z prior to dehydrogenation, and the entire stock may be dehydrogenated according to the first step of the process. Obviously, if such a C4 fraction contains normal `butenes in concentrations equal to or `greater A than those produced by the rst dehydrogenation voperation, the raw feed may be charged directlyl tothe, vsecond step of our process. Any isobutene sterazvvhile. tl;1eY bottomsfffreotion kco.inprising-fithe '-buteneez `rich `fraction isxthe ,oharsezfor .the .ond dehysirogenation step, to produce rbutadlV ne.

Operating-costano extremely ,lowfdue to (1), the 1,-.'

catalytic isomeriaationffstep fis performed .ont #the effluents from the dehydrogenation step `during ,the normal cooling operation in such manner that no.additional heat .inputis requiredaand '12)l .the fractionation step has been greatlysimf '.pliiied .by .concentrating .the ,butenes `on the highereboiling side. of l-norrnal butane.

Inour. processy .the recycled butane-1` doesnot build upi..i..n.the system. becausetheamount recycled .-is Ifor `below .the .equilibrium concentration at -dehydroeenation te.noperature..s4 and .further conversion of, ,.nonnai butane reesteblishes .the equilibrium.

. 11n .its broader.. aspects, our. invention comprises oonductinathe .conversion of n-butane .to butadienebyaserlesof ysteps llstedbelowin the order employed: 1) catalytic. dehydrogenation ofl `nhutane; A` 2). catalytic isomerization. .ofl .theehuents from (1) to increase the concentration 0f butene-2 therein; (3) separation of the efllllent` l from l(2) byfractional distillation into an overhead fraction `v,comprising butene-l, trans butene.2. and nebutane anda bottornsfractioncomprising cis and trans butene-Z with some n-butane;- (4) continuously recycling the overhead of (5) after separation of butadiene to the second dehydrogenation step'. In `the practiceot this inventionany butadiene formed 4in stepy 1) win distill overheadalong with the butane-1 andvk nbutane' fraction. If the lulldlltity 'thus'.formed ris. large enough to maken recovery step; Afs.ius..i.b le,

the butadiene may be absorbed-'fromthe recycle materalprior to re-introduction injaojthe iirstl dehydrogenation step.

-- -rf we use theCl' fraction from retlnery cracked present in the stocks mentioned above may be removed or utilized as desired prior to treatment by ourlprOceSs.

y'In order 4that the invention may be more clearly understood, reference will be made to the figure 'which is ai flow diagram of the steps of the process.

e In the gure the raw n-butane or suitable Cl -fhydrocarbon feed comprising butane and butenes entersyby line I into. heater 2 where the feed is raisedtothe desiredI temperature. The hot va- --pors thenpass by line 3ginto catalyst cases `4 `containing a suitable dehydrogenation catalyst.

Eromill the treated vapors pass throughl-ine 5 to cooler `6 where the vapor temperature is low.-

,through polymerseparator 8 wherein any heavy -material is .removed through line 9. The vapors .Ehen pass vthrough-line I0 into catalyst chambers II containing .an isomerization catalyst. The

V,efuer1-ts :from I Ipass throughline I2 and in turn .through cooler I3, compressor I4, cooler I5 and into accumulator I6. From I6 the .condensate passes .to .fraetionatoror depropanizer l'lafor .the

Sopliitililgf Propoli@ und. ,lghifdimaterial 0V??- head .whilevthe bottoms .comprisingy C3 and.C4 -rmaterialpasses ,through line I8 to vfractionator 1,8. .lh `flactionator laan overhead fraction pre- Jlduminantly lower boiling than trans butene-Z `and comprising butane-1, n-butane and some .trans 4buterjie- 2 istaken overhead whilel cis and trans buttano-2 .and some n-butane constitute thebolztoms .fraction predominantly higher boilring thantransbutene-Z. The overhead fraction is recycled `to the dehydrogenation step through linel. ,If `butadienererxioval is desirable the recyolematerial `passes .through line, 22 into labsorption unit,A 2.3, and by line 24 `back into the recycle line 2D. ,Refrigeration .(not shown) may .be required- .'.I'he butadiene addition product. is

removed by line 25. The conventional auxiliary 4.eauipnierit....for iracticnators l1 yand ls including heat exchangers, oondensers, reuX- accumulator and thelike is `familiar-to the art and Vthus ispot y showunthis fiowldiagram.

-.The ,butenef2 concentrate.. .namely the bottoms .fraoton from i9.. posses through line Z6 and together with `a diluent which may be .added through line 21 enters heaterI .ZB-Wherethe-A stream .is ,heated .todehydroaenation temperatures. The hot vapors ,then passthrough line. ,29 into ,catalyst ,ehambersll .contaminare dehydrogenotion-.oato- .1i/st. .The dehydroeenated, .vapors leave Vthrouah line .3l .andtheanass in .turn .through cooler 3,2,

.compressor 3.3.. .and .Cooler 34 .into accumulator ,35 .Where propane and. heavier material f. are l condensed and..lightermaterialis vented- .Theliduid from 35. may pass `thrcuieh line- 36 into .fractionator orA deproponizer 31. .In 3l.propane,=.and

liehtermaterlal is ,taken oyerheafsl.and-uoeyv enter line 2,6 through line 38 and serve..as..d.i,luent.aas or alternately.. may be vented through. line 33.

TheCi fraction'` from .the bottom :of fractionator The Ciiresiduum from the butadiene lAlternately, the Ca-C4 liquidffrom accumulator '35 may' pass with` suitable refrigeration (not shown) directly to the butadiene absorption unit 4| `through lines 44 and' 4I).y In this case, butadiene is absorbed from the totalcondensate without fractionation andthe C3-C4 residuum passes as` recycle to thejcatalyst .through line t2.` The vpropane thus included v.may serve` as diluent in .the dehydrogenation to I'replace all or a part of ithediluent indicated as added through lines 21 :and 38.. f x

,In the1 `operation of the first dehydrogenation step, the hydrocarbon vapors may be subjected `to two or more successive treatments ,with dehydrogenation catalyst in'a series of catalyst chambers,

or the vapors or any portion thereof may be recycled with thefresh feed r vapors through-the. .catalyst chambers. be applied to the recycled: vapors ifdesired.

Some additional heat may 'Other possible arrangements of the convention- Y. al equipment used in the practice of our invention willbe apparent to those skilled in the art, and thusare held within; the scope of our invention;

Also, the, conditions of temperature, pressure, flow rate and the ',like used in operating this requipment will, depend largely` on the selection ofccatalyst' to bewusedin each step`and on the desired degree of conversion, since each catalyst particularly difficult reducible oxides, but includingoxides,A rof metals in groups II toVIII inclus-5n ive of the periodic system, activated or lustrous carbon, clays. somegsilicates and many others. The great vvarietyjof oxide catalysts makes them of the most importance.

For the isomerization step, catalysts active in relatively low temperature ranges are preferred. These include catalysts of an acidic nature; either mineral materials containing acidic substances such as certain clays and natural silicates, acidic salts such as aluminum phosphate and the like or strong mineral acid catalysts are useful. Other types of catalysts may be used under substantially anhydrous conditions, including alkali and alkaline earth metal oxides, but the acidic catalysts are generally more uniform and more active.

In the practice of our invention the charging stock to the initial dehydrogenation operation is usually heated to temperatures in the range of 850 to 1200" F. and passed over the catalyst at such velocities that contact time is quite short of the order of 0.5 to seconds. Low superatmospheric pressures of about 5 to about 50 pounds gage are normally used, although higher pressures up to 200 or 300 pounds gage may be used if desired. Conditions of operation are selected with reference to economic and technical factors in any given installation.

In the isomerization step of our process the y eilluent vapors from the initial dehydrogenation are cooled and. any heavy polymerformed may beseparated prior to passage in vapor phase over the isomerizationcatalyst at temperatures within the range of 200 to 600 F. The temperature is maintained at the lowest level which will give rapid isomerization and a minimum of polymerization reactions since the equilibrium favors vbutene-2 at lower temperatures. Low superatmospheric pressures of 5 to 50 pounds gage are suitable in the isomerizationreaction, and flow rates equivalent to 0.5 to 51'liquid volumes of charge :per hour volume of catalyst are usually satisfactory. The eflluents from .the isomerization step are further cooled, compressed-and partially condensed prior` to the vfractionation for separation `of butene-2 for the second dehydrogenation operation.

In the second dehydrogenation step, the charge stock is heated sufficiently to maintain temperatures between about 1050 and 1350 F. in the catalyst chambers. The catalysts used may be those which give a suitable degree-of conversion of butene-2 to butadiene and which do not induce excessive polymerization and cracking reactions. Further, it is usually desirable to maintain low partial pressure of butene-2 in the charg to the second dehydrogenation step, for example by addition of an inert diluent, in order to suppress deleterious side reactions involving the unsaturated hydrocarbons.

Ordinarily two or more catalyst4 chambers would be provided for each catalytic step. Those chambers not in service would be under preparation for subsequent use, either by replacement or spent catalyst or by regeneration. Regeneration is contemplated for the dehydrogenation catalysts whenever the activity has declinedV t any predetermined level. i

The regeneration may be carried out by means such as controlled treatment with an oxygencontaining gas. l 1

'I'he following example will serve to further illustrate one method of practicing` our invention.

Example Normal butanewascharged to the system. diagrammed in the drawing, yoperated. ata pressure of 30 pounds per square inch gauge. The heated vapors emerged from the furnace and entered the catalyst cases at 1120 F. The multiple cases were filled with calcined 6-14r mesh bauxite to such depth that the total pressure drop was of the order of five pounds or less, and the temperature of the entire bed maintained within the range of about HOO-1120 F. The butane was processed at a space velocity of 1000 volumes (STP.) per hour, per volume of catalyst, equivalent to a contact time of approximately 1.7 seconds. About 15 per cent of the butane charged was converted to butenes, and the run was continued for 24 hours before catalyst activity had declined to a point at which regeneration was necessary.

'I'he efiluents were cooled quickly to about 450 F. and passed over an aluminum phosphate catalyst to isomerize butene-1 to butene-2. 'I'he vaporsemerging from this tower had approximately the equilibrium concentration, or about 14 per cent of the butene content as butene-1 and 86 per cent as butene-2. l

The eiiluents from this tower were depropanized and submitted to fractionation in the highly eflicient tower diagrammed. The cut was made in the trans butene-2 fraction, separating as `bottoms fcis butene"2 and party of the :trans `buten'eeZ lto- `ethenwith some .butane The light gases were separated-from the butane-butene-l overhead `Lanclthelatter was recycled. When the recycle fzstreamf ofbutane 1 andwbutene-l had been adm'itted and a steadystate of vdehydrogenationisomerization had beenestablished, hydrogen. and `light Lfgases separated accounted for f about rthree percent lay-weight of the-charge.' Butene-Zsepavratedfrom thezbottomof the tower accounted `rfor f.21per cent oi thev total vcharge tothe heater'with 4which additionalbuteneequivalent to 2. per cent `of the 'charge-was associated. The butene-l and trans f'butene-2`recycled` amounted to 24 per cent of the charge,y while vthevbutane'recycled was 50 per cent and fresh added butane was 26per cent of the charge. Thus an ultimate yield of about 81 per cent of the butane charged to the first dehy- "drogenation was' obtained as butene`2 in 5 the charge to the Vsecond dehydrogenation,

' The butene-Z-butane fraction was then charged vto the second dehydrogenaton step shown in the drawing, with sufcient volume of substantially inert, diluent'gas to yreduce `the partial pressureof -butenes to 25 per cent of the total pressure. vThis stock was vprocessedat a pressure of 5 pounds `gage and at a temperature of1125-1130" F. over A bauxite catalyst. A space velocity of 1400 volumes per hour was employed. About 28 per cent conversion per pass of the butene was obtained of which"'50 per -cent was butadiene and the vremainder light gases, polymer and coke. The C4 {fi-action `after removal of fixed gases and the :ex-

ltractionjo'fthe butadiene was recycled; A cycle l-oi six ylioursfoperation followed by regeneration .wagused in' 'this stage; `the streambeing changed "to-a; fresh set of catalyst gases at the end of'this period and the first catalyst regenerated by conytrolled combustion.

"The 'foregoing specification and example have disclosed and illustrated the invention,` but since it is oiV generallywide application and the num- .ber` o'f examples of results obtained by its-use with ka vdehydrogenating- :catalyst under suitable conditions to produce'a mixturecomprisingbutadiene, butene-l, bateria-2, and butane, passing said mixture over an isomerization catalyst under conditions Asuitable to promote the conversion of butene-l to butene-Z,v fractionating the eilluent from the isomerization stepto produce an overhead fraction 4predominantly lower-boiling lthan trans butene-Z and a bottoms fraction comprising essentially cis and transbutene-Z., recycling said overhead-fraction after absorption of' butadiene `therefrom fto the initial `dehydrogenationfstep alongwith fresh-'butane feed, treating vsaid bottoms fraction in asecond dehydrogenation step to convert a substantial proportion of the butene- 2 to butadiene, separating the lbutadiene -ilrom vthe products of the second dehydrogenation step prior to recycling the unconverted C4 material therefrom to the second dehydrogenation 'step along with `fresh added butene-2 stock'and'nally combining the butadiene sol recovered from' the two dehydrogenation steps.

.2. A process "for preparing butadiene from hydrocarbon mixtures containing major proportions of n-'butane which comprises catalytically dehydrogenating` said mixture under suitable conditions to convert a substantial portion'ofthenbutane to butenes-l and 2 with the simultaneous vproduction of some butadiene, catalytically isotion-step theunconverted butene stock along with freshadded butene-Z feed.

' WALTER A. SCHULZE.

JOHN C. HILLYER.