US2396854A - Manufacture of diolefins - Google Patents

Description

lPatented 19, 194s Jean Paul Jones, Bartlesville, Okla., assigner to Phillips Petroleum Company, a corporation of l Delaware Application January 1, 1944, Serial No. 516,617

(Cl. 26o-.680)

3 Claims.

This invention relates t the production of lcliolein hydrocarbons from paraln hydrocarbons by dehydrogenation. It relates more particularly to the production of such diolens by means of catalytic dehydrogenation wherein unreacted hydrocarbons comprising paraiins and olens are recycled' to a dehydrogenation step. The inventio-n has particular reference to the production-of diolei-ins such as butadiene and pentadiene from the corresponding parain hydrocarbons, preferablylby means of catalytic dehydrogenation. This application is a continuation-in-part of my copend.

ing application, Serial No. 404,420, led January 28, 1941.

It has been proposed to produce diolefns by dehydrogenation in a single step whereina paraffin hydrocarbon such as normal butane is charged to the'dehydrogenation step, a diolen such as butadiene is recovered from thedehydrogenation eiliuent, and a hydrocarbon fraction containing unreacted hydrocarbons, such as normal butane and butenes, are separated from the eiiluent and returned to the dehydrogenation step. It has also been proposed to produce diolens from parain hydrocarbons by the use ofy at least two dehydrogenation steps in the rst of which paraiiins are dehydrogenated to olens and in the second of which olens are dehydrogenated to dioleilns. In such a process there is generally a recycle of unreacted hydrocarbons to one or more of the dehydrogenation steps. In preparing the charge t such dehydrogenation processes it is impossible from a practical point of view to separate a hydrocarbon material such as normal butane in a state of high purity, and in most instances when the particular desired hydrocarbon ispresent in a concentration of about 95 per cent or more, it is considered to be in a suiciently high state of purity for practical operations. At times the concentration may even be somewhat lower than 95 per cent although generally it will not be appreciably lower than about 90 per cent. Also in such dehydrogenations there is a tendency for isoamount of such isomeric hydrocarbons which do not contribute directly to the production of the desired diolens which not only decrease capacity y of the dehydrogenation units but also tend to enter into undesired side reactions.

I have now found that this tendency for iso- 4 merio hydrocarbons to build up in such a. dehydromerio forms of the hydrocarbons being treated to be formed as by-products in the'dehydrogenation step. Thus, in the dehydrogehation of normal butane and/ or no-rmal -butenes to form butadiene, there is a tendency for small amounts of isobutene and isobutane to be formed. When a hydrocarbon fraction containing unreacted hydrocar bons is recycled to the dehydrogenation step, it

will contain such isomeric hydrocarbons in either case, and as a result after a steady state of operation has been reached, the total charge to a dehydrogenation step will contain a, substantial genation system may be effectively kept under control -md limited to any desired extent by removing a portion of the recycled' hydrocarbon fraction, separating such isomeric hydrocarbons from this removed portion of this hydrocarbon fraction, and returning uns-eparated hydrocarbons to the dehydrogenation system. In one specific form of my invention this is accomplished by subjecting a fraction containing branched chain aliphatic hydrocarbons separated from eiiluents of the dehydrogenation l system to non-destructive hydrogenation t0 form a fraction comprising isoparaiiins and subjecting such isoparafns to alkylation to form higher-boiling paraiiins. I have found that generally in producing butadiene and the like, suiiicient lower-'boiling olens are formed by side reactions to react with such isoparafiins so that the charge to the alkylation system can come entirely from eiuents of the dehydrogenation system for producing diolei'lns. 'I'his procedure may be followed either when the undesired isomeric hydrocarbons `are present as a result of formation within the dehydrogenation system or when they are present as a result of being included as impurities as a charge to the dehydrogenation system or for any other reason.

An object of my invention is to produce doleln hydrocarbons.

It is an object of my invention to produce lowboiling diolen hydrocarbons from paramn hydrocarbons of the same number of carbon atoms per molecule.

It is a further object of my invention to produce diolen hydrocarbons by means of catalytic dehydrogenation of more saturated hydrocarbons under conditions such that there is a minimum formation of undesired by-products.

Further objects and advantages of this inven- Referring now to the drawing, a suitable hydrocarbon material enters the system through a pipe I controlled by a valve I I and is passed to a separating means illustrated by the fractionating column I2. Preferably such a hydrocarbon mixture will comprise predominantly hydrocarbons of a single number of carbon atoms per molecule such as a butane fraction comprising both normal butane and sobutane, or a pentane fraction comprising both normal pentane and isopentane. For purposes of illustration it will be considered that the material charged through pipe Ill will be a butane fraction. The fractionating column I2 is so operated as to separate a normal butane fraction from other hydrocarbons contained in the material charged. Undesired low-boiling hydrov carbons are discharged from the system through a ably containing normal butane as at least 95 per cent of the mixture, is removed through a pipe I5 controlled by a valve I'B and may be passed through a valve I1 directly to a single dehydrogenation unit I8. The dehydrogenationunit I8 is comprised of suitable heating units or furnaces, catalyst chambers and the like known to the art for eiecting and maintaining catalytic nondestructive dehydrogenation of low-boiling hydrocarbons. The catalyst chambers may be so arranged that heat is supplied to the catalyst body or bodies and to the reacting mixture.v When a single dehydrogenation unit is used, the dehydrogenation is conducted to effect a dehydrogenation both of parai'lins and of oleiins to form olefins and dioleiins, respectively, along with free hydrogen. The resulting products pass through a pipe 20 controlled by a valve 2I to separating means 22. Separating means 22 will include suitable fractionating columns, condensing units, heat exchangers, solvent extraction units and the likev suitable for effecting a separation of the material charged into the desired fractions as will be discussed. A diolen fraction, in this case containing a high concentration of butadiene, is recovered as a product of the process from separating means 22 through a pipe 23 controlled by a valve- 24. A fraction containing light gases with a high concentration of free hydrogen formed by the dehydrogenation is removed from separating means 22 through a pipe 25 and may be discharged atleast in part from the system through a valve 2B. Any undesired heavy material may be discharged from the system through a pipe 21 controlled by a valve 28. A normally gaseous fraction comprising olefin hydrocarbons produced by side reactions in the dehydrogenation system and-having a fewer number of carbon atoms per molecule thanthe desired diolen may be separated from the system through pipe 13. Although such olens may be discharged through valve 14,

`I prefer to pass them from pipe 13 through valve 16 and pipes 15 and 10 to alkylation unit 12 as Will be more fully discussed hereinafter. A recycle fraction, which in this case will comprise predominantly normal butane and normal butenes, is removed from separating means 22 f through a pipe 30 and a substantial'portion thereisobutene. portion of the recycle material passing through pipe 30 is passed therefrom through a pipe 32 and is passed through valve 33 to a hydrogenation unit 34. Hydrogen in an amount suflicient to effect a substantially complete saturation of unsaturated material charged to hydrogenation unit 34 is added to the system through a pipe 31. This hydrogen may be added entirely or in part through a valve 38, but. generally there will be more than' sufficient hydrogen in the stream dis charged through pipe 25 to suice for this operation, and any desired portion of this' stream may be passed from pipe 25 through a pipe 40 controlled by a valve 4I to pipe 31 and hydrogenation unit 34.

In some instances it may be found more desirable to operate separating means 22 so as to separate a fraction containing isobutane and isobutene in higher concentration than would otherwise be present in the recycle stream passing through valve 3l back to the dehydrogenation system. Such a fraction can then be passed to hydrogenation unit 34, and a recycle stream with a depleted amount of isobutane and isobutene, or substantially free of these hydrocarbons, is lpassed to the dehydrogenation system as by being removed from separating means 22 through pipe 39 and valve 49.

The hydrogenation in unit 34 will be one of simple nondestructive substantially complete saturation of unsaturated 'hydrocarbons charged thereto and may be carried out in the presence of an active hydrogenation catalyst, such as finely divided nickel on an inert support such as pumice, silica gel, or the like, under a suitable pressure and temperature. Such temperature and pressure will generally not need to be greatly elevated and Y conditions for any particular stock being treated may be readily determined by trial by one skilled in the art. The efuent of the hydrogenation is passed from unit 34 through a pipe 42 controlled by a valve 43 to a separating means 44. Any undesired low-boiling material such as unreacted free hydrogen and hydrocarbons of a fewer number of carbon atoms than the material treated in the dehydrogenation unit I8 may be discharged from the system through a pipe 45 controlled by a valve 46, A paramn hydrocarbon fraction preferably predominately of a single number of carbon atoms per molecule, in this case a kbutane fraction, is recovered through a pipe 41 and may be passed through valve 48 directly to pipe I0 and fractionating unit I2. When the content of isoparaiiin is sufiiciently high in the stream passing through pipe 41, it may be passed directly to pipe 1I! and alkylation unit 12 through valve 69.

From fractionating unit I2 an isobutane fraction is removed through pipe 1B and is passed through valve 1I to alkylation unit 12. If such an isobutane fraction is present in excess, a portion of it may be discharged from the system through pipe 9| controlled by valve 92. In alkylation unit 12 isobutane is reacted with low-boiling olefins such as ethylene, propylene, and isobutylene to produce higher-boiling parailns which will generally be in the motor fuel boiling range, and which are suitable as blending Stocks for premium motor fuels. I prefer that such oleiins be those which have been formed as by-products in the dehydrogenation'system which is operated primarily to produce diolens and which may be passed from separating means through pipes 1.3, 1.5 and 1I! to alkylation unit 12. In case there is not a sufficient supply of olefins to react with all the isoparaffin In accordance with the invention a reactant hydrocarbons.

2,396,854 charged to alkylation unit 12, olefins from any drocarbons through pipe 30, a. portion f these may be passed to pipe 80 controlled by valve 8| to pipe 'I0 and alkylation unit I2 while a further portionv is passed through valve 33 to hydrogenation unit 34 as has been discussed.

The alkylation in unit 'I2 may be concluctetil` either in the presence or in the absence of a catalyst, but I prefer to conduct the operation Ain the presence of.a suitable alkylation catalyst. Such a catalyst may be -concentrated hydroiluoric acid promoted with a small amount of boron iluoride, particularly when ethylene is one 'of the olefin alkylating reactants, concentrated sulfuric acid, an active metal halide, preferably activated with a corresponding hydrogen halide, or one 1 n umerous others known to the art. A reaction temperature may be between about and 200 F. as may be found Suitable in any particular case with suflicient pressure to maintain at least a substantial part of hydrocarbon material in liquid phase. Preferably the olefin alkylating reactant is introduced to the 'alkylation step'in a manner such that its concentration in the reaction zone is maintained at a low value, as by successive addition at several points along the length of a reaction zone or at a single point with recycling of la substantial portion of the reaction mixture without non-destructive dehydrogenation of.l low-boiling hydrocarbons. The material charged to dehydrogenation unit 52 should be predominately parailinic, and the dehydrogenation conditions should rbe such that there is `an optimum formation of mono-oleflns of the same number of carbon atoms per molecule as the parans charged. The dehydrogenation effluent is passed through the pipev 53 controlled by Valve 54 to separatingl means 55.

4A fraction containing the desired olens produced by the dehydrogenation is removed `from separating means 55 through Va pipe 56 controlled by a valve 57 and is passed back to pipe I5 for introduction to dehydrogenation unit I8. 'With such an operation valve I1 in pipe vI5 will be closed. Undesired low-boiling materials, including free hydrogen produced by the dehydrogenation may be discharged from the system through pipe 58 controlled by a valve 59 passing from separating means 5 5. Free hydrogen contained in this stream4 may be used in the hydrogenation unit 34, and if such use is desired the hydrogen may be introduced through Valve 38 as will be readily appre-` ciated. In some instances the material passing through pipe 55 will contain substantially all of the unreacted paraiin charged to dehydrogenav fraction such as a butane-butene fraction from immediate fractionation, ,or the like as is well known in the art. Alkylation catalyst may be admitted to the alkylation unit 'I2 by means not shown or it may be admitted in admixture with Alkylation unit l2 will also comprise suitable equipment for separating alkylation catalyst from hydrocarbons effluent from lthe alkylation reaction zone and for discharging spent catalyst from the system together with necessary associated equipment, as will be understood by those skilled in the art. When it is found necessary to react individual oleiins under y individual reaction conditions, alkylation unit 72 may comprise several alkylati on reaction zones.

A hydrocarbon material eiiluent from alkylation unit l2 is passed through pipe 82 and valve 83 to separating means 8d. 'This hydrocarbon material will comprise primarily alkylate and unreacted normal butane.

through pipe 85 controlled by valve 81 and unrevalve 8B to pine I0 and fractionation unit I2. If this normal butane fraction has a suiciently high purityto be suitable for charging directly to the dehydrogenation system. it may be passed from pipe 86 through pipe 93 controlled by valve @It and introduced to the dehydrogenation system through pipe 60. In some instances it may be found desirable to employ' fractionation unit I2 to separate alkylate and unreacted normal butane, in which case. the hydrocarbon material .is passed from pipe S2 through pipe 89 and valve @Il to pipe I0 and fractionation unit I2.

In some instances it may be .desired to conduct the dehydrogenation operation in two or more steps; in such an event the stream passing through pipe i5 will be passed therefrom through pipe 50 controlled by a valve 5I toa dehydrogenation unit 52 which as in the case of dehydrogenation unit It is comprised of suitable heating units or furnaces, catalyst chambers and The alkylate may be recovered4 to dehydrogenation unit I8, and

y be` mad tion unit 52, in which case separating means.

can be operated simply to separate a hydrocarbon lower boiling material. However, Vin some instances it may be found desirable to have a high concentration of oleiins in the material charged to dehydrogenation unit I8. In such a case separating means 55 will also include suitable equipment for separating olens from parains, such as selective solvent extraction equipment as will be readily appreciated by those skilled in the art. Paraflin hydrocarbons -separated in such a manner.

may be-returned to dehydrogenation unit 52 as through pipe 6U controlled by'a Valve 6 I. Tn some instanceswith either modification of the dehydrogenation system, material charged through pipe may contain substantially only hydrocarbons of a single carbon atom skeleton structure and may in such a case constitute the sole charge to the process. When a fraction containing a high proportion of olens suitable for dehydrogenation into diolens is available from anyfoutside source such a material may be charged to the system through pipe 60 when dehydrogenation unit I S' is the only part of the dehydrogenation system.

When such a charge is available anda dehydrogenation system includes both units 52 and "I8, such an olefin-containing charge may be introduced to the process through pipe 62 controlled by a valve 53 passing into pipes in some instances material charged through pipe 62 may constitute the sole charge-tothe process. 1

It has previously been mentioned that the dehydrogenation carried out in units I8 and/or 52 will be conducted under conditions known to the art and will generally Ibe conducted under a relatively low pressure with or without the presence of diluent material such as hydrocarbons inert under the dehydrogenation conditions. nitrogen. steam, carbon dioxide and the like. Sometimes introduction of small amounts of free hydrogen along with the charge to a catalyst bed has a beneflcial eilect, especially upon the initial portion of a catalyst bed before hydrogen is produced by -dehydrogenation, and the presence of such added hydrogen'at ln reaction.

such introduction an gh pipe -BII and/or pipe 30 and I5 directly l genationcatalysts mayl be used, among which the more preferred are ,nection with dehydrogenation unit I8, is preferably carried out with a catalyst comprising chromium oxide. or chromium oxide and alumina, chromium oxide and zirconite, etc., at a temperature in the range of 950 to 110 F., while a twostage operation may be carried out with a similar catalyst under slightly less drastic time-temperature conditions in dehydrogenation unit 52, with subsequent dehydrogenation of resultant olens at a higher temperature, such-as Within the range of 1050 to 1250o F., using a catalyst such as bauxite treated with barium hydroxide, or temperaturestabilized chromium oxide, with or without the presence of steam, or the like, as diluent. In all s'uch deliydrogenation steps low pressures, which may ,be subatmospheric lbut which generallywill be slightly above atmospheric, are preferred. The

above conditions are particularly suitable for treating C4 hydrocarbons; the treatments of Cs hydrocarbons are substantially within the same ranges, with slightly lower temperatures in other- Wise comparable cases.

The amountv of the paraiiin-olcn mixture which, in any particular case, is removed and passed to the hydrogenation unit 34 will depend conditions to obtain more favorable operation than to operate so that more than about per cent is so treated. Suitable ratios in any particular case can be readily determined by oneV skilled in the art` Pumps or compressors for the various streams in connection with the drawing have not been shown; general lflow of the Various streams, howover, has been indicated and discussed, and suit-l able mechanical equipment for desired treatment of this material can be readily supplied, as required in any particular modification of my invention, by one skilled in the art. Similarly other units of equipment have been shown only diagrammatically but their functions have been described and explained so as to serve as suitable guides for adaption of suitable speclflc equipment for specific installations. It will be obvious to 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. In the present specification and claims when it is stated that a portion of a stream is removed therefrom, the term portion shall be understood to butenes and said iso-C4 hydrocarbon including l I claim:

1. A process for the production of butadiene which comprises catalytically dehydrogenating normal butane to form a dehydrogenation eilluent containing butadiene and a substantial amount of iso-C4 hydrocarbon including isobutylene, treating said eiiiuent to separately recover a fraction of butadiene, a normally gaseous fraction comprising olen hydrocarbons having less than four carbon atoms per molecule, and a. recycle fraction comprising normal butane and normal isobutylene, recycling a major portion of said recycle fraction to said dehydrogenatingr step, pass..

ing the balance of said recycle fraction to a hydrogenation step and there non-destructively hydrogenating same to eiect substantially complete saturation of the unsaturated hydrocarbons contained therein and thereby converting the isobutylene content thereof to isobutane, Passing the isobutane-containing C4 hydrocarbon content of the hydrogenation eiiluent directly to a catalytic alkylation step and there alkylating the isobutane content thereof with the oleiins contained in said normally gaseous fraction comprising olefin hydrocarbons having less than four carbon atoms I C4 hydrocarbon from building up to an objectionmean an unfractionated part which has the same separately recover an alkylate fraction and an unreacted normal butane fraction, and returning said normal butane fraction to the dehydrogenation step, the proportion of said recycle fraction passed to said hydrogenation step and thence to said alkylation step being such as to prevent isoable extent in the dehydrogenation step.

2. A process for the production of piperylene 'which comprises catalytically 4dehydrogenating normal pentane to form a dehydrogenation eilluent containing piperylene and a substantial amount of iso-Cs hydrocarbon including isopentylene, treating said eiuent to separately recover a fraction of piperylene, a normally gaseous fraction comprising olefin hydrocarbons having less than five carbon atoms per molecule, and a recycle fraction comprising normal pentane and normal pentenes and said iso-C5 hydrocarbon including iso-pentylene, recycling a major portion of said recycle fraction t0 said dehydrogenating step, passing thebalance of said recycle fraction to a hydrogenation step .and there non-destructively hydrogenating same to effect substantially complete saturation of the unsaturated hydrocarbons contained therein and thereby converting the iso-pentylene content thereof to iso-pentane, passing the iso-pentane-containing Cs hydrocarbon content ofthe hydrogenation eiiluent directly to a catalytic alkylation step and there alkylating the iso-pentane content thereof with the olefins contained in said `normally gaseous fraction comprising olefin hydrocarbons having less than live carbon atoms per molecule, treating the alkylation efliuent to separately recover an alkylate fraction and an unreacted` normal pentane fraction, and returning said normal pentane fraction to the dehydrogenation step, the propor.. tion of said recycle fraction passed to said hydrogenation step and thence to said alkylatlon step being such as to prevent iso-Cs hydrocarbon from building up to an objectionable extent in the dehydrogenation step.

3. A process for the production of a normal diolefin having from'4 to 5 carbon atoms per molecule which comprises catalytically dehydrogenating a normal paraflin hydrocarbon having from 4 to 5 carbon atoms per molecule to form a dehydrogenation eiuent containing the corresponding normal diolen and a substantial amount of the corresponding iso-hydrocarbons including the corresponding iso-oleiin, treating said eluent to separately recover a fraction of said normal di-I olen, a normally gaseous fraction comprising -oleiin hydrocarbons having fewer carbon atoms passing the iso-paraffln-containing hydrocarbon content of the hydrogenation eiliuent directly to a catalytic alkylation step and there alkylating the iso-paramn content thereof with the olefins contained in saidnormally gaseous fraction comprising olen hydrocarbons having fewer carbon atoms per molecule than said normal parailln, treating the alkylation eilluent to separately recover an alkylate fraction and an unreacted normal paramn fraction, and returning said normal paraln fraction to the dehydrogenation step, the

proportion of said recycle fraction passed to said hydrogenation step and thence to said alkylation step being such as to prevent iso-hydrocarbon corresponding to said normal paraffin from building up to an objectionable extent in the dehydrogenation step. A

- JEAN PAUL' JONES.

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