US2389230A - Process for treating hydrocarbons - Google Patents

Description

NOV- 1945- D. R. BLUMER 2,389,230

PROCESS FOR TREATING HYDROCARBONS Filed Nov. 25, 1941 2 Sheets-Sheet l HYDROCARBON MIXTURE CONTAINING SECONDARY AND TERTIARY BASE OLEFINS OF AT LEAST C l ISOMERIZATION g l HCL REACTION WITH HCL HYDROCARBON MIXTURE CONTAINING SECONDARY OLEFINS AND TERTIARY ALKYL. CHLORIDES DEACON 0.2 t PROCESS CHLORINATION MIXTURE CONTAINING SECONDARY ALKYL DICHLORIDES AND TERT'ARY ALKYL CHLORIDES FRACTIONATION SECONDARY ALKYL DICHLORIDES TERTIARY ALKYL CHLORIDES I F I DEHYDROHALOGENAT ION MONOCHLOROLEF l N HCL I II T- CONJUGATED DIOLEFINS INVENTOR DONALD R BLUMER II MIIWUW ATTORNEY 1945- D. R. BLUMER PROCESS FOR TREATING HYDRQCARBONS Filed Nov. 25, 1941 2 Sheets- Sheet 2 UOLVNOI LDVUJ BOLVNOI LDVBA HQLVNOUJVEH UOLVNOI .LDVUJ BOLVNIHO'WHD HOLDVBH 'DH H 32 I H BWOSI HOLVNC 'LDVUJ UOLVHVd 3S mubquIumm UOLVNOLLDVEH HOLVNOLLDVBJ Quum INVENTOR DONALD R BLUMER Patented Nov. 20, 1945 2,389,230 PROCESS FOR 'IREATING HYDDOCABBONS Donald R. Blumer, Bartlesv'llle,

Phillips Petroleum Company,

Delaware Okla, assignor to a corporation of Application November 25, 1941, Serial No. 420,431

6 Claims.

This invention relates to the treatment of a hydrocarbon mixture containing C4 or higher secondary and tertiary base oleflns to convert the olefin contentthereof into compounds which are readily separated in fairly pure form from the resulting conversion mixture and to recover therefrom coniugated dioleilns which are useful as a starting material for the preparation of synthetic rubber, and other chemicals which are useful as raw materials for organic synthesis. More particularly it relates to a process of recovering conjugateddioleflns such as butadiene, piperylene, etc. from the normal olefins of C4 and higher and recovering tertiary alkyl chlorides from the tertiary base olefins of C4 and higher.

The principal object of the present invention is to provide an improved process of recovering useful compounds from the C4 and higher olefin content of hydrocarbon mixtures.

Another object is to separately recover aliphatic conjugated diolefln from the secondary olefin content of a hydrocarbon mixture containing both secondary and tertiary olefins of C4 and higher.

Another object is to separately recover allphatic conjugated diolefin products from the secondary and the tertiary olefin content of a hydrocarbon mixture containing both secondary olefins of C4 and higher and tertiary olefins of Cs and higher.

Another object is to recover pure butadiene from the normal butene content of a mixture containing both normal butenes and tertiary butene (isobutene).

Another object is to so treat a hydrocarbon mixture containing Cs or higher normal and tertiary olefins as to convert the normal olefin content to straight chain aliphatic conjugated dioiefins and the tertiary olefin content to branched chain aliphatic conjugated diolefins, the straight chain and the branched chain diolefins being separately recovered in such manner as to avoid the necessity for separating the same from one another. I

Another object is to eliminate the necessity of fractionating or otherwise resolving at great expense a hydrocarbon stream containing oiefins in limited amount and having boiling points close to one another and/or close to paraflins present, to recover separate olefin fractions therefrom for conversion to diolefins.

Another object is to make possible more effective utilization of halogen in a process or treating a hydrocarbon mixture containing C4. or higher secondary and tertiary oleiins.

, any. other material and desirable Another object is to provide an improved proces of separately converting both the normal and the tertiary base olefins of at least 4 carbon atoms in a mixture containing the same.

Another object is to provide an improved process of preparing conjugated diolefins such as butadiene, piperylene, isoprene, etc.

Another object is to reduce the cost of preparation of aliphatic conjugated C4, Cs or Cs dioleflns and thereby the cost of synthetic rubber prepared therefrom.

Numerous other objects appear as this description proceeds.

This invention may be more fully understood by reference to the accompanyin drawings wherein Fig. 1 portrays a flow diagram or the process of the present invention in its preferred form; and Fig. 2 portrays diagrammatically one form of apparatus which has been found useful in carrying out the process or the present invention.

As used herein. the term "halogen" denotes chlorine, bromine or iodine. and the term hydrogen halide" ordinarily indicates hydrogen chloride or hydrogen bromide, although it may indicate hydrogen iodide or hydrogen fluoride where suitable reaction conditions are used. Likewise, unless the context requires otherwise. specific reference to a given halogen such as chlorine or compound thereof Or process involving the same is intended to include other halogens as alternative or equivalent. While chlorine and hydrogen chloride are generally employed because of their cheapness and availability. this does not necessarily means that chlorine is always preferred since occasions may arise where another halogen is preferred because of its superior reactivity or special properties for a particular use. Thus the use of bromine and hydrogen bromide is frequently more advantageous than the use of chlorine and hydrogen chloride.

As will be more fully brought out below, my invention seeks to separately convert the secondary and the tertiary C4 or highe olefins present in a mixture containing the same toclasses of compounds which may be readily separated from each other. thesecondary olefins being converted to dichlorolefins and the tertiary oleflns being converted to tertiary alkyl chlorides. These are readily separated from each other and are then-converted to materials, the dichlorolefins preferably being converted to diolellns by dehydrohalogenation and the tertiary alkyl chloride (where it of this invention will contains at least carbon atoms) preferably being converted to branched chain diolefins.

If a mixture comprising normal butene and isobutene be chlorinated and the resulting mixture dehydrochlorinated, the butadiene obtained by dehydrochlorination of the normal dichlorbutane will be contaminated with various decomposition products obtained by dehydrochlorination of the tertiary dichlorbutane. If a mixture comprising normal and tertiary pentenes is chlorinated and the mixture dehydrochlorinated, the aliphatic straight chain dioleiln (piperylene) derived from the normal pentene is contaminated with the branched chain diolefln (isoprene) derived from the tertiary pentene. The same is true of the hexenes.

Since synthetic rubber manufacture demands pure aliphatic conjugated diolefins, i. e., pure butadlene, pure piperylene, pure isoprene, etc, a process involving chlorination and dehydrochlorination of mixtures containing both normal and tertiary C4 or higher oleiins such as is outlined in the preceding paragraph is wholly unsuitable. It is the aim of the present invention to provide a process overcoming these diiiiculties.

The secondary oleflns are characterized by the grouping HH=CH- and consist of two types, namely, the normal oleilns (characterized by straight chain configuration) and the secondary iso olefins (having branched chain structure). The tertiary base oleflns are characterized by the grouping. V

In the case. of C4 olenns, there are only two possibilities, namely the normal butenes and isobutene which is tertiary. In the case of Ca and higher oleflns, if secondary iso oleflns are en: countered inthe refinery stream treated by my process they behave like the normal oleflns except thatthey form branched chain dioleflns which are recovered along with the straight chain dioleflns derived from the normal oleflns. For example, in the case of pentenes, if (as is unlikely) the secondary isopentene ii-methylbutene-l be present in the pentenestream treated by my process, it forms isoprene which is recovered along with the piperylene.

While my invention is particularly applicable to a hydrocarbon stream wherein the C4 or higher oletlns consist of normal and tertiary olefins, it is applicable to a stream wherein the olefins consist of secondary iso and tertiary oleflns, or normal, secondary iso and tertiary olcfins.

Briefly stated, my invention involves reacting a hydrocarbon mixture containing C4 or higher secondary and tertiary base oieflns with a hydrogen halide under conditions such that substantially all of the tertiary base olefins selectively react with the hydrogen halide to form tertiary alkyl halides. The reaction mixture thus obtained (in which the secondary oleiins are substantially unchanged) is then halogenated under such conditions that substantially all of the secondary oleflns are converted by additive halogenation to secondary dihalogen derivatives, while the other components of the reaction mixture, including the tertiary alkyl halides, are substantially unaflected. The resulting mixture is then fractionated to recover a fraction of the secondary dihalogenated derivatives and a second fraction of the tertiary alkyl halides. These materials may then be employed for the preparation of other compounds. Thus the secondary time 0- genated derivatives are preierablysubiected-to dehydrohalogenation to remove two molecules of hydrogen halide (a portion 0! which may be recycled for use in carrying out the initial step of the process and another portion of which may be converted to elemental halogen for use in the halogenation step) and thereby form a conjugated diolefin. Monochloroleiln recovered from the dehydrochlorination step may be recycled for dehydrohalogenation.

- A process suchas Just described, with chlorine as the halogen, is portrayed in the flow sheet of Fig. l of the drawings.

As applied to a predominantly C4 hydrocarbon raw material containing saturated and monoolefinic hydrocarbons, or the oleilns only, the oleflns present comprising normal butenes and isobutene, the, reaction mixture is first reacted with anhydrous hydrogen chloride to convert the isobutene to tertiary butyl chloride, which compound does not react further to any appreciable extent with chlorine under the conditions used in the subsequent chlorination. The mixture is then chlorinated to convert the n-butenes and particularly butane-2 to dichlorbutanes and particularly 2,3-dichlorbutane. The reaction mixture is then fractionated to separate the dichlorbutane and the tertiary butyl chloride, which have widely separated boiling points, from one another and from a y other material. The dichlorbutane fraction is then dehydrohalogenated to remove two molecules of HCl and form 1,8- butadiene.- The tertiary butyl chloride may be utilized in several ways,for example: for conversion by dehydrochlorination to pure isobutene: for the production of diisobutylene which can be hydrogenated to isooctane, as component of octane aviation gasoline: for production of high octane motor fuels by acid alkylation-of suitable aliphatic, olefinic. acetylenic or aromatic hydrocarbons: for production of valuable organic chemicals, such as tertiary butyl alcohol. Any trior higher chlorides of butane or polymers of these recovered as lay-products in the process may be utilized as intermediates, as solvents, etc. HCl recovered from the dehydrohalogenation of the dichlorbutanes or from the dehydrohalogenation of the tertiary butyl chloride may be recycled for reaction with isobutylene and also for regeneration of chlorine to be used in the chlorination of the normal butenes.

In a modification of the foregoing process, the butene stream may be reacted with hydrogen fluoride to convert the isobutene to tertiary butyl fluoride, followed by chlorination or bromination of the n-butenes to the corresponding dihalogen derivatives and fractionation to separate the tertiary butyl fluoride. Tertiary butyl fluoride iaa particularly valuable alkylating agent for film production of high octane fuels by alkylation' or hydrocarbons.

As applied to a predominantly Cs hydrocarbon stream, a corresponding'series of steps may be employed. The initial reaction with H01 produces tertiary amyl chloride from the tertiary base pentenes namely Z-methylbutene-i and Z-meth'yl butene-2. The subsequent additive chlorination converts the normal pentene content to mi ht chain dichlorpentanes, namely the 2,3 a 1,2 substituted products. After separation, the straight chain dichlorpentanes are converted to piperyle'ne by dehydrochlorination. As before. the separation of the dichlorpentane fraction and the tertiary amyl chloride fraction is readily effected because of the widely separated boiling assaaso points. The tertiary arnyi chloride may be dehydrohalogenated to form tertiary base Cs olefins, namely, 2-methylbutene-2 and Z-methylbutene-l, or may be utilized for the production of isoprene by conversion to 2,3-dichlor-2-methylbutane which upon dehydrohalogenation yields isoprene. The tertiary amyi chloride may be converted to 2,3-dichlor-2-methylbutane either by substitutive chlorination or by dehydrohalogenation followed by additive chlorination. Alternatively, the tertiary amylchioride may be hydrolyzed to form tertiary amyl alcohol, or may be used for polymerization or alkylation reactions, as an intermediate, etc.

If desired, in the case of a C4 hydrocarbon stream containing Cl olefins, the stream may be first subjected to catalytic isomerization in such manner as to convert any butane-1 to butene-Z ,so that upon chlorination an increased proportion of the preferred 2,3-dichlorobutane is formed. In the case of a Cl stream containlngCs olellns, the stream may be lsomerized in such manner as to convert Cs oleflns largely to 2-methylbutene-2 (the equilibrium isomerization reaction mixture containing approximately 50% of Z-methylbutone-2). The necessary lsomerization conditions for either type of isomerization are known to those skilled in the art. The resulting Cs mixture is reacted with HCl to convert the Z-methylbutene-2 and any 2-methylbutene-lpresent to tertiary amyl chloride and the reaction mixture is subjected to chlorination, followed by fractionation, as before, to separately recover the tertiary amyl chloride and the dichlorpentanes.

The invention is applicable to all possible mixtures of C4, Cs, Ca. 01, and higher oleflns, with or without Ci, Cs, Cs. C1 and higher paraflins, and containing both secondary and tertiary oieflns. The invention may beemployed to produce all possible straight or branched chain aliphatic conjugated diolenns, either in essentially pure forrh or in the form of all possible mixtures of the straight and/or branched chain dioleflns. Thus the invention may be employed to produce straight-chain dioleiins, as for example butadiene,

'plperylene, etc, or branched chain diolefins, as

for example: isoprene, 2.3-dimethylbutadiene, etc., either in pure form or as a concentrate thereof, or to produce mixtures of any of the straight chain dioleiins or mixtures of any of the branched chain dioleflns or, under certain circumstances, mixtures of straight chain dioleflns with branched chain dioleiins. It is particularly applicable to the production of pure or concentrated straight chain dioleflns on the one hand and branched chain dioleiins on the other hand.

Preferably the initial hydrocarbon stream treated in accordance with the present invention is free from hydrocarbons other than olefins or parafllns, such as dioleflns, cyclic hydrocarbons, aromatics, naphthenes. etc., having been previously treated to remove such hydrocarbons.

Care must be taken in the treatment of the initial stream with hydrogen chloride to use such conditions that it adds preferentially to the tertiary olefin content thereof. This reaction may be conducted in the liquid or vapor phase, preferably the former, using suflicient pressure to maintain the liquid phase. Temperatures may be from about -80 C. to about 100 C. The reaction proceeds in the absence of catalyst, though catalysts which speed up the reaction with the tertiary olefins without causing reaction of the hydrogen chloride with the secondary oleilns may be employed. It is preferred to use anhydrous H61 and to have the reaction mixture free from water. The tlmeof contact should be so limited that the HCl does not appreciably attack the secondary oleflncontent. The amount of HCl may vary from theoretical required to combine with the tertiary olefin content up to about a 10% excess thereoven. Too large an excess may induce additive reaction with the secondary olenns.

The conditions for the additive chlorination reaction should be such that chlorine adds preferentially to the secondary olefin content to form the dichloride without appreciably reacting with the tertiary monochloride, or any paraillns present, by substitutive chlorination. Liquid phase chlorination is preferred, although .in some cases vapor phase chlorination may be employed. The pressure should be such that the liquid phase is maintained. The temperature should be maintained at the lowest economically practicable level in order to avoid decomposition reactions and induced substitutive chlorination. Temperatures ranging from about ---20 C. to about 50 0., and preferably in the neighborhood of 0 0; are desirable. The heat of the chlorination is preferably continuously abstracted throughout the reaction preferably by circulating a liquid cooling medium through heat exchange surfaces or by refrigeration where compressed gases are available for expansion. The reaction is preferably conducted in the anhydrous state though in some cases small amounts of water or aqueous alkali may be presout to absorb any HCl evolved. Ordinarily no 1 catalyst is used, although mild catalysts which do not catalyze substitutive chlorination of the tertiary monochloride present may be used. Preferably the chlorination is conducted in the dark or in the absence of radiations which induce substitutive chlorination- Where the tertiary monochloride fraction is chlorinated in production of branched chain dioleilns therefrom, this substitutive chlorination is carried out under different conditions from the additive chlorination Just described. For this reaction a relatively active chlorine-substitution catalyst such as antimony chloride or iodine should be used. The conditions for carrying out such a chlorination in the liquid phase are wellknown to those skilled in the art. In order to avoid excessive formation of the triand higher chlorides, the chlorination is preferably terminated before all of the monochloride has been converted to the dichloride, whereupon the mixture is fractionated and the monochloride returned. Alternativel the substitutive chlorination may be conducted in the absence of a catalyst but in the presence of suitable light radiation, at such a temperature that the dihalide as formed condenses out and is removed from the reaction zone so that it is not further reacted upon to form triand higher chlorides.

The dehydrochlorination step to produce the diolefins may be carried out in accordance with conditions set forth below or in accordance with known conditions for catalyzed dehydrochlorination. As set forth below, I prefer to conduct this step in an open stainless steel tube without an! added catalyst and, in the case of C4, at temperatures of from about 500 to about C. As progressively heavier materials are treated the temperature should be progressively lowered in order to avoid excessive decomposition and side reactions. .When operating in the preferred temperature range the contact time should be so conthrilled that it is shorter at the higher temperatures [and longer at the lower temperatures. The

reaction may be expedited either by use of reduced pressure or by the reduction of partial pressure of the. material being decomposed by the introduction of an inert diluent.

The process outlined above efl'ects great economy. particularly in the case of C4 hydrocarbons, by preventing waste of expensive chlorine since it eliminates the chlorination oi the tertiary base oleflns by first reacting the tertiary base oleflns with dry HCl under such conditions that they are substantially completely converted to tertiary alwl chlorides while the secondary oleiins either do not or only slightly react with the HCl. In addition. the subsequent chlorination is carried out under such conditions that direct addition of chlorine-to the secondary oleilns takes place with a minimum of substitutive chlorination oi the saturated hydrocarbons or of the tertiary allryl chloride. The latter in particular is unaffected by chlorine at low temperatures in the liquid phase and in the absence of active catalysts or lisht.

Moreover the process further reduces the cost of producing the conjugated idioletins by permitting ready recovery and utilization of all other products such as the tertiary alkyl chlorides, triand higher halogenated paraiiins'and polymers thereof, etc., for production of useful materials such as high octane motor fuels, organic chemicals, etc. The recovery and recycling of the hydrogen chloride for use both as such and after partial conversion to chlorine effects a further reduction in the cost of operation.

The process is advantageous because it permits the easy separation oi the tertiary alkyi chlorides and the secondary dichlorides from each other and from other components so that each may be iurther individually processed.

The process is further advantageous because side reactions are kept to a minimum thereby making possible more economical production of products of high purity and because the process is capable 0! control in a convenient and economical manner to yield the desired products. The need (or expensive and difllcult fractionation or extraction methods to separate the tertiary base oleilns Irom the hydrocarbon stream is eliminated. Moreover less heat is generated during the chlorination step of the process than would be liberated were the hydrocarbon stream chlorinated directly with the tertiary base oleiins present; consequently, heat exchange requirements are less, there is less chance of side reactions occurring, and better control is possible using the process of the present invention.

In one embodiment, the invention comprises reacting dry hydrogen chloride under suitable conditions with vaporized C4 hydrocarbons consisting essentially of nand iso-butane, n-butenes (largely butene-Z), and isobutylene in such a way that the isobutylene reacts to form tertiary butyl chloride, whereas the n-butenes and butanes do not react to any appreciable extent. Prior to this treatment the C4 stream is preferably enriched in butene-2 and depleted in butene-l by means of a catalytic lsomerization process in known manner to such an extentthat the n-butenes present are largely butene-2. The reaction mixture containing the tertiary butyl chloride and any excess HCl in liquid phase is then chlorinated in such a way that chlorination takes place to form dichiorbutane practically completely by direct addition to the n-butenes, without any appreciable substitutive chlorination oi the nand is'o-butane.

tertiary butyl chloride or the desired dichlorbutane products. This may be accomplished by chlorinating in a iractionating tower which is packed with inert carbon or stoneware Raschig rings or other suitable packing in such a way that the inieed is introduced as a liquid, either under sumcient pressure to maintain liquid phase orat a low enough temperature to maintain liquid phase at atmospheric pressure, into the column packing at a point nearer the bottom than the top of the column. The chlorine is introduced, in molar quantity equal to that of the n-butenes present, into the column packing with provision for good dispersion at a point near that at which the C4 stream is introduced. The tertiary butyl chloride and the dichloro derivatives tend to pass down the column and collect in the kettle whereas the unreacted butanes and any excess of chicrine and HCl pass 0!! the top or the column, the chlorine and HCl being completely removed by scrubbing or further fractionation and the butanes being returned to the refinery for further processing. The reflux column should be long enough to permit complete reaction of the n-butenes with the chlorine before they reach the top oi. the column and thereby prevent unreacted n-butenes from passing out with the overhead butane stream. The chlorination may be conducted at temperatures ranging from about iii to about 50 C. depending upon the pressure and other factors.

The chlorination may be conducted in other ways, for example by passing the chlorine directly into the liquiiled C4 hydrocarbons with abstraction of the heat of reaction, being careful to stop the chlorination before or when the additiomreaction is substantially completed in order tqa'void substitutive reactions. However this in- ;voifies the use of staggered intermittent or batch operation or other special provisions for continuous operation which is not so convenient or eiilcient as the continuous process outlined above.

During chlorination, a catalyst. such as suliuryl chloride either addedas such or formed in situ by the introduction of sulfur dioxide which forms suliuryl chloride by reaction with the free chlorine: may be present in the chlorination zone. though use of a catalyst is unnecessary.

The chlorinated material is removed continuously from the chlorination apparatus and 'sent to a iractionating column where the mono-, di-, tri-, and higher chlorinated derivatives oi nand iso-butane are separated by distillation. The dichlorides, principally 2,3-dichlorobutane, are then sent to the dehydrohalogenation furnace where the crude butadiene is produced by liberation of two moles of HCl per mole of the 2,3-dichlorbutane. Also, one mole of HCl is liberated from 2,3-dichlorbutane to form 2-chlorbutene-3, which is subsequently removed by fractionation or scrubbing and recycled to the furnace to liberate another mole of R01 to form butadiene. The tertiary butyl chloride can be dehydrohalogenated to isobutylene or treated in any other desired manner.

The following example illustrates the foregoina process applied to a C4 hydrocarbon stream.

Example 1 A vaporized refinery C4 stream is catalytically isomerized to convert the butene-i substantially to butane-2. The isomerized material has the following composition, expressed in mole percentages: butane-2, 7.8; butene-l. 0.4; isobutylene, 0.5; n-butane, 64: isobutane, 21; propane, 6; and propylene 0.5. This material is then reacted with hydrogen chloride either in the liquid or in vapor phase, the hydrogen chloride being added in slight excess (not exceeding of the equimolar amount requird to react with the isobutylene. II this step is to be carried out in the liquid phase, as is preferred, the C4 stream is compressed to a pressure of from about 50 to about 150 lbs. per sq. in. (depending upon the external atmospheric temperature) and cooled to the surrounding atmospheric temperature to produce the liquid phase. This liquid phase is contacted with the dry hydrogen chloride which i pumped into a suitable reactor or absorber in countercurrent fashion, the liquid hydrocarbons flowing downward over suitable contact material and the hydrogen chloride flowing upward from the point of introduction at the bottom. Under these conditions, the hydrogen chloride reacts almost instantaneously with the isobutylene without the presence of a catalyst and very little oi the nbutenes react since the reaction or hydrogen halide with normal oleflns is very slow in the absence of a suitable catalyst.

The reaction just described may alternatively be carried out in the vapor phase by passing the isomerlzed C4 stream, to which dry HCl has been added in 10% excess over the molar concentration of isobutylene, over a suitable catalyst such as porous BaCl: or MgClz at 50-120" 0. in which case substantially all of the isobutylene but practically none of the butene-Z will be reacted. However. liquid phase addition reaction of HCl is preferable because it is desirable to carry out the subsequent additive chlorination oi butene-2 in the liquid phase in order to minimize substitutive chlorination reactions. Moreover, in order to avoid corrosion difflculties, it is desirable to compress the isomerized C4 stream before rather than after the addition of the HCl, for in the former case the reaction mixture containing slight excess HCl can be introduced directly into the chlorinator without removal of HCl, which would be necessary were it to be taken into an ordinary compressor for introduction as liquid phase into the chlorinator. Otherwise a compressor of expensive corrosion resistant construction would be required.

The reaction mixture irom the foregoing step is then chlorinated. This chlorination may be conducted continuously in a modified iractionator type reactor packed with inert carbon or stoneware Raschig rings or similar corrosion resistant material, the liquid C4 stream containing isobutyl chloride and hydrogen chloride being introduced into the column somewhat below the mid-point and the chlorine being introduced at several points nearby with provision for dlifuse introduction of the chlorine to prevent serious local overheating. The molar quantity of chlorine introduced. should equal or only very slightly exceed the molar quantity oi n-butenes present in the C4 stream in order to insure that the reactionproceeds principally by addition to n-butenes and to minimize substitutive chlorination. Since it is desirable to chlorlnate in the liquid phase rather than in the vapor phase in order to avoid substitutive chlorination, it is necessary to refrigerate the chlorinator ii the reaction is carried out at atmospheric pressure. Ordinarily, this is too expensive unless compressed gases are available which have to be expanded beiore using in other parts of the process, in which case they may be used for refrigerating the chlorinator. Thus the vaporization of the C4 stream before passage through the isomerization reactor can be used for this purpose.

Ordinarily it it is necessary to rely for cooling the chlorinator upon cooling water available at the refinery, the temperature of which may be as high as 46 C., it will be necessary to carry out the chlorination reaction under pressure to keep the C4 hydrocarbons in the liquid phase. Thus for a head temperature 0! the chlorinator ranging approximately from l0 to 46 0., the pressure required to maintain liquid phase will range approximately from atmospheric to about -120 lbs. sq. in. Use oi the lowest temperature and pressure economically possible is desirable in order to keep substitutive chlorination at a minimum. It is advantageous to remove the heat of chlorination as by circulation oi cooling liquid around or through the chlorinator column, or in other suitable manner to prevent development of excessive temperatures and pressures and any possibility of an explosion. The cooling medium is preferably introduced at the top section 0! the column first and subsequently in series to other cooling coils or Jackets arranged along the column from top to bottom so that the head of the column is the coolest point.

In the chlorination process, the introduced Ci stream tends to flow downward as reflux until it contacts the chlorine when the heat of reaction causes it to vaporize and pass upward through the column. The monoand dichlor derivatives, which have higher boiling points, pass downward through the column and collect in the kettle. thereby being removed from iurther contact with chlorine, eliminating the possibility of additional chlorination by substitution to form higher chlorides. The liquid phase absorbs the heat of chlorinatlon and aids in rapidly transmitting this heat to the external cooling means, thus avoiding local overheating which may result in flashing or explosions. The column is so designed and built that the mono. and dichlorbutane derivatives, substantially tree oi C4 hydrocarbons, collect in the kettle, the n-butenes are substantially completely chlorinated to the dichlor derivatives before they reach the head oi the column; and the C4 hydrocarbons that leave the head oi the column are tree of chlorinated products, the latter being higher boiling. This can be readily accomplished since .the boiling points oi the various possible compounds are as iollows:

Any higher chlorides have higher boiling points and hence concentrate in the kettle. Similarly, any C: or lighter hydrocarbons, hydrogen chloride, or unused chlorine pass ofl' at the top oi the chlorinator with the C4 hydrocarbons. Since the amount of hydrogen chloride and chlorine present in this C4 stream is very small, this fraction is given an alkali wash to remove these corrosive compounds before returning it to the refinery for further processing.

The product collected in the kettle is removed and distilled, preterably'under reduced pressure to prevent decomposition, to recover substantially pure separate fractions of monochlorbutanes, dichlorbutanes, and monochlorbutenes, and separate out the heavy ends. Because of the lowchlorination temperature, very little monochlo'rb'utene is formed. The monochlorbutane fraction is largely tertiary butyl chloride since there is very little substitutive chlorination to form other monochlor isomate. The tertiary butyl chloride can be readiLv decomposed by heating to 260 C. in the vapor phme which converts it practically completely to isobutyiene and hydrogen chloride.

The cut boiling in the range or 114424" C. and which consists essentially of 1,2- and 2,3-dichlorbutanes is decomposed thermally in a stainless steel or other suitable steel or metal tube to yield butadiene and hydrogen chloride.

Alternatively a cut boiling in the range or 64- 163 C. containing all the monochlorbutene and dichlorbutane isomers can be taken and similarly dehydrochlorinated to produce butadiene which is fairly pure since there is very little 2,2-dichlorbutane present to form non-conjugated dioleilns and very little other chlorinated compounds which would form other impurities in the butadiene.

The dehydrochlorination may be conducted thermally in a stainless steel tube at 600 C. For example. essentially pure 2,3-dichlorbutane may be thus decomposed with a contact time of 0.22 second with 33.4% and 3.8% of theoretical conversion of initial material per pass to 1,3-butadiene and 1,2-hutadiene, respectively, or 85.8% and 9.8% of theoretical conversion to 1.3-butadiene and 1,2-butadiene. respectively, based on the material completely decomposed per pass. Undecomposed dichlorbutane, and the monochlorbutene present, may be recycled for more complete conversion to 1.3-butadiene and hydrogen chloride. The 1,3-butadiene is separated from the conversion products as by fractionation or scrubbing and purified by suitable chemical or solvent extraction processes. The 1,2-butadiene isolated may be isomerized practically completely to 1,3-butadiene by known methods to improve the yield of 1,3-butadiene. The hydrogen chloride is recycled and partially converted to chlo- In another embodiment. the invention is applied to Ca oleflns or a Ca olefins-rich refinery stream. If the primary purpose is to produce piperylene, the initial catalytic isomerization is omitted. If isoprene principally is sought, the stock is first catalytically isomerized to produce trimethylethylene (2-methylbutene-2) in approximately a one to one ratio of n-pentenes to trimethylethylene.

Whether or not the initial catalytic isomerization step is employed, the Ca hydrocarbon stream is now reacted in the liquid phase with hydrogen chloride added in molar concentration equal to that of the tertiary base olefin, Z-methyl-butene-Z and Z-methylbutene-l, to produce tertiary amyl chloride, practically no secondary, normal or iso pentenes reacting.

The resulting mixture is now chlorinated in the liquid phase so that normal pentane dichlorides are produced by additive reaction with n-pentenes only. Secondary iso pentene (3-methylbutene-l) is normally absent from the Ca refinery stream. The mixture is then fractionated to recover separate fractions of the tertiaryemyl chloride, the normal pentane, dichlorides and of the unreacted pentanes. The normal pentane dichlorides are then dehydrochlorinated thermally or by means of organic or inorganic bases to form a mixture composed principally of piperylene, mon ochlorpentenes and uncracked dihalides, from which the piperylene is separated by fractionation or scrubbing and purified by chemical or selective solvent extraction methods. The tertiary amyl chloride is chlorinated in the liquid phase with a catalyst such as SbCls or iodine, or in the vapor phase in the presence of ultraviolet light or intense sunlight at a temperature low enough that the dichloride condenses out when it forms and is quickly drained or removed from the reaction chamber, thus avoiding substitutive chlorination to higher chlorine derivatives. Alternatively the tertiary amyl chloride may be dehydrohalogenated and the tertiary olefin material (trlmethylethylene) so formed subjected to liquid phase additive chlorination to form the dichloride. This additive chlorination should be conducted at a suiliclently low temperature, say about 0 C., to prevent dehydrochlorination of a portion of the dichloride initially formed to 3-chloro-3-methylbutene-l with liberation of 1101 which adds to trimethylethylene to form isoamyl chloride which does not dehydrochlorinate to isoprene. II desired, water or weak aqueous alkali may also be present, the mixture preferably being stirred to maintain an emulsion. to absorb any HCl liberated by any such dehydrochlorination and thereby prevent its addition to trimethylethylene. This addition prevents to that extent the desired formation of the dichloride by additive chlorination of the trimethylethylene. Similar precautions must be used in additively chlorinating any of the tertiary olefins. The dichlor derivative of trimethvlethylene formed by either of the foregoing procedures is largely 2,3-dichior-2-methylbutane, and is easily separated from the tertiary amyl chloride and from the hydrogen chloride by tractionation or scrubbing. The dichlor derivative is then dehydrochlorinated thermally or by means of organic or inorganic bases to form principally isoprene and uncraclred halides, from which the isoprene is separated by fractionation or scrubbing and purified by chemical or selective solvent extraction methods.

Instead of converting the tertiary amyl chloride produced in either of the foregoing ways to isoprene, it may be used as such or as a. starting material for other organic chemicals. It may be converted to a tertiary base olefin. Either the chloride or the olefin may be used for polymerization, alkylation or other syntheses.

The foregoing application of the invention is illustrated by the manufacture of piperylene and isoprene from a C5 hydrocarbon stream in accordance with the following example.

Example 2 The refinery C: olefin stream has the following composition, expressed in mole percentages: pentane-1, 39; pentane-2, 30.5; Z-methylbutene-Z. 30.5; 2-methylbutene-1, 0.0; 3-methylbutene-l, 0.0. This is treated with dry hydrogen chloride in such a way that the hydrocarbon stream in liquid phase passes downwardly through the upwardly passing dry gaseous hydrogen chloride, the absorber being filled with suitable contact material. The molar concentration of the dry hydrogen chloride should be equal to that of the 2-methylbutene-2, with which it reacts to form tertiary amyl chloride. This HCl addition reaction may be carried out at from 0 to 5 lbs. per sq. in. gauge for the temperature range of 0 to 46 C, in order to retain the Ca hydrocarbons in the liquid phase. The mixture of Cu olefins and tertiary amyl chloride is now chlorinated by additive chlorination in the dark and in the liquid phase either in a fractionator type chlorlnator 'aseaasti as in Example 1 with adequate cooling to remove the heat or chlorination or in a kettle, la'pe chlorinator with or without a mild catalyst such as suliuryl chloride but with adequate cooling. The pressure should be such as to maintain the Cs oleiins in the liquid phasedui'ing chlorination. Pressures of from to pounds per square inch gauge are necessary for temperatures ranging from 0 to'46" C. to maintain liquid phase during this additive chlorination. The reaction mixture may then be iractionated to separate the several components thereof. Since the amylenes boil in the range of 34-38 C., the tertiary amyl chloride at 85-88 C., and the dichlor derivatives of normal pentane at 139-1'l8 C. at atmospheric pressure, separation 01' these materials by fractionation is readily effected. The 'dichiorpentane fraction is then dehydrohaiogenated at 500 to 600 C. at contact times of the order of a few tenths of a second to producesubstantially pure piperylene. Reduced pressure'or the presence of an inert diluent favors the reaction. The piperylene. which boils at 43 C., is separated by fractionation andpurifled.

The tertiary amyl chloride is now chlorinated in liquid phase to 2,3-dichlor-2-methylbutane by substitutive reaction with chlorine gas, using a catalyst such as antimony chloride or iodine. Chlorination is allowed to proceed until the flnal weight is 1.22 times the initial weight, exclusive of catalyst, when the reaction is substantially completed. The 2,3- dichlor 2 methylbutane, whichhas a boiling point of 137 0., is separated from the other constituents by distillation and subjected to dehydrohalogenation to produce isoprene. Ordinarily the fraction boiling from 137 to 175 C. contains all of the dichlor isomers of pentane which produce lsoprene upon dehydrohalogenation, conditions for which are substantially the same as those indicated above for dehydrohalogenation of the dichlor derivatives or n-pentane.

Example 3 Example 2 is duplicated except that the stream of Cs oleiins is first subjected to catalytic isomerization to convert the Cu oleflns largely to trimethyiethylene by passing them in the vapor phase at 450 C. over calcined alumina, forming an equilibrium mixture containing approximately 50 percent trimethylethylene. The composition of the resulting Cs stream, expressed in mole percentages is: pentene-l, 28; pentene-2, 22; 2- methylbutene-2, 50; 2 methylbutene 1, none; and B-methylbutene-l, 0.0. This material is then treated in liquid phase with dry hydrogen chloride as 'in' Example 2, to produce tertiary amyl chloride from the 2-methylbutene-2. The resulting mixture is then subjected to treatment as in Example 2 to additively chlorinate the normal pentenes to the dichlorides and is then fractionated to recover separate fractions oi the dichlorides and oi the tertiary amyl chloride. The dichloride fraction is then dehydrohalogenaied as in Example 2 to form piperylene. The tertiary amyl chloride is chlorinated as before to 2,3- dichlor-z-methylbutane which may be dehydrochlorinated as before to form isoprene or used in any other desired manner.

Referring to Fig. 2 of the drawings, hydrocarbon i'eed stock containing both tertiary base and secondary olefins or at least C4, with or without saturated hydrocarbons, is charged to the system via line I. The feed may. for example, consist or refinery cracked gases or eflluent 1mm thermal polymerization processes; The hydrocarbon stream first passes in the vapor phase through lsomerization unit I, which may be bypassed by line 3 where iso'merization is not desired, and thence via line I through cooler 4, which cools the gases to a temperature suitable for compression, and via line 5 through pump 8 which compresses them, into heat exchanger or cooler I for condensation to liquid. The liquid hydrocarbons then are introduced into the absorber or contact tower 8 in'which they ilow downward over packing, dry gaseous hydrogen halide being introduced through line 0 by pump I0 into reactor 8 somewhat below the mid-point at sufllcient pressure to overcome that of the hydrocarbon.

The hydrocarbon stream containing the tertiary halide and the slight .excess of hydrogen halides passes via line i2 into fractionator-type halogenatlon reactorl3 below and near the midpoint. Halogen is introduced via line i4 and pump I 5 near the point at which the hydrocarbon stream is introduced. Additive chlorination of the normal olefins takes place in the column 13. The saturated hydrocarbons, excess hydrogen halide; and any unused halogen pass out the top of the column by line It into scrubber ll into which alkaline solution is introduced by way of line It through spray nozzle IS in order to scrub out hydrogen halide and tree halogen, the wash liquid collecting at the bottom of scrubber H from which it is recycled via line 20 and pump 22, spent alkali wash liquid being withdrawn through line 2|. The condensed distillate forms a layer above the aqueous alkali layer and is withdrawn via line 24 through drier 25 which may contain activated alumina for desiccant, after which part of it is returned to column [3 as reflux via line 26, the remainder being withdrawn through line 21 to be sent back to the refinery for further processing.

The mono-, diand higher halides pass downward through tower l3 and pass via line 28 into fractionator!!! in which the monohalides are fractionated oil and pass out through line 30 into the vaporizer and dehydrohalogenation or cracking coil ii in cracking furnace 32 where they are dehydrohalogenated. The cracked products pass into the separator 33 in which the hydrogen halide is fractionated from the teritary base olefin and leaves through line 84 to be eventually recycled back to the reactor 0 or to the Deacon equipment. The tertiary base olefin leaves through line 35.

The diand heavier halides leave fractionator 29 through line 36 and enter fractionator II where the halides heavier than the dihalides are separated and leave via line 38 and the dihalides pass via line 30 and pump 40 into vaporizer and cracking coil 4i in the cracking furnace 42 from which the cracked products consisting largely of conjugated diolefins and hydrogen halide pass into the low temperature iractionator 43 from which the hydrogen halide leaves via line 44 to be recycled or passed to the Deacon equipment. The diolefins and uncracked dichlor derivatives and monochlor monoolei'ins pass via line 45 to fractionator 40 where the dioleflns are separated from the unconverted halides and pass of! via line 41. The unconverted halides leave via line 49 and are recycled back to coil 4i for further dehydrohalogenation. Higher halides and polymerized materials, such as tars, for'med in the cracking operation are removed by any suitable means and not recycled. For example, a tar trap may be inserted in the line leading from coil ii to column 43, or these heavy materials may be separated out as a heavy fraction in column 46. If the low temperature fractionation carried out in 43 is too expensive because of lack of compressed refinery or other gases available for expansion to produce refrigeration, the emuent from coil I may be scrubbed with suitable organic or inorganic bases or water, which may be removed from the dioleflns and uncracked halides by fractionation or physical separation, respectively. The hydrogen halide may then be recovered from the water or organic hydrogen halide addition compound by concentration and dehydration or by suitable decomposition of the addition compound. respectively. The mixture of dioleflns and uncracked dihalides may then be dried, if water washed, and fractionated to separate the dioleflns from the uncracked material. Alternatively, the eifluent from the cracking coil I may be scrubbed with dihalide charge stock from line 88 in a countercurrent scrubber to separate the hydrogen halide from the dioleflns and organic halides present.

The solution of the dioleflns and monochloroleflns present is then sent to fractionator 46 from which the diolefins pass oil through line 41 and the dichlor and monochlor monoleflns derivatives leave through line 49 and are recycled to cracking coil 4|.

The line 50 serves to collect the hydrogen halide liberated from the various sources available, and may be connected to line 52 for recycling to reactor 8 and/or to line 55 whence it is introduced by pump 54 into Deacon reactor 6| for regeneration of halogen. Air or oxygen is taken through line 56 and pump 51 into preheated coil it inside furnace 59 and thence via line Bil into reactor 6| which may consist of a gas-tight enclosed checkerwork-type reaction chamber in which the hyddrogen halide is burned to halogen and water over a Deacon-type catalyst, using known operating conditions. The reaction products pass from the reactor GI via line 62 into condenser and separator 63 in which the water is removed via line 54 as an aqueous solution of hydrogen halide. halogen, and hypohalogenous acid. This solution may be treated for recovery of hydrogen halide and halogen.

The gases from separator 63 pass through line 65 into drier 66 wherein activated alumina, may be used as a desiccant, thence via line 61 into low temperature fractionator BB, whence the halogen passes via line Ill for recycling to chlorinator l3. The mixture of uncondensed gases consisting of 02, N2, hydrogen halide and a little free halogen leave 88 via line H and pass into lower temperature fractionator 12 in which the hydrogen halide and slight halogen residue are separated and removed via line 13 whence they may be passed through expansion coils to provide part of the refrigeration requirements of condenser 63 and fractionator 68 before being returned to line for recycling. The 02, N2 and any other other gases boiling at a lower temperature than the hydrogen halide leave vi line ll. These cold gases may be utilized for producing part of the refrigeration of the separation process. Compression of the dried gases in line 61 before introduction into fractionator 68 permits fractionation at higher temperatures in 68 and 12, thus reducing expensive refrigeration requirements.

Where H1 is the hydrogen halide used, the 1: formed in ii would condense largely in separator 83 and very little or no I: vapor would pass via line 61 to fractionator 6B. In such case fractionator it may be eliminated.

Instead of a distillation process for separating hydrogen halide and halogen from the Deacon reactor eilluent, suitable selective solvent or absorption extraction processes may be used. Other processes for regeneration of the halogen from the hydrogen halide such as, for example, the electrolytic process, etc., may be used instead of the Deacon process if desirable.

Ordinarily the Ca olefin-containing stream is free from the secondary isopentene, 3-methylbutane-1 (isopropylethylene) since this pentene is not commonly encountered in refinery Cu streams. This may be because of its thermodynamic instability, because of its ready lsomerization to other pentenes (chiefly trimethyletlwlene) in the reflneryprocesses to which the Cs stream has been subjected, or because of its low boiling point (20 C.) which causes it to weather ofi. Therefore the Ca oleflns usually encountered consist of normal pentenes (pentene-1 or pentene-2) and tertiary base pentenes (2- methylbutene-l or 2-methylbutene-2). If this secondary isopentene, 3-methylbutene-1, be pressent in the stream it is unaffected in the treatment with HCl but adds chlorine in the additive chlorination step to form 1,2-dichloro-3- methylbutane which evidently isomerizes in 2,3- dichloro-2-methylbutane, which upon subsequent dehydrochlorination yields isoprene which contaminates the piperylene. Ordinarily since 3- methylbutene-l content never exceeds more than a small percentage, the extent of contamination of piperylene with isoprene derived therefrom is negligible. If, however, it is desired to preclude such formation of isoprene, the initial stream may be readily freed from any 3-methylbutene-l by fractionation in view of its low boiling point, or the 3-methylbutene-l may be isomerized to other pentenes by initial isomerization of the stream. Since the initial concentration of 3-methylbutene-1 is normally very low or practically nil, a fractionation or other special treatment of the Cs olefins to remove it may not be economically justifiable, particularly since it is possible to purify the piperylene by a chemical or solvent extraction process if extremely pure piperylene is required.

This invention may also be applied to the production of aliphatic conjugated Co or higher diolefins, preferably of the butadiene series, from hydrocarbon mixtures comprising both secondary and tertiary base oleflns of Co or higher. However because of the relatively large number of isomers which are neither tertiary base nor normal secondary oleflns but branched chain or lso secondary oleiins, modifications may be required to produce relatively pure straight chain diolefins since the secondary iso oleflns do not add hydrogen halide rapidly as compared to the tertiary base olefins but rather are reserved for additive halogenation along with the normal oleflns. Therefore upon additive halogenation both normal and iso dihalogenated derivatives are produced. -Upon fractionation separate fractions of the teritary monochlorides and of the normal and secondary iso dihalides are obtained. Upon dehydrohalogenation of the dihalide mixture, a mixture of normal and lap dioleflns is formed in which the iso diolefin content may amount to as much as 27% in the case of Cu dioleiins. Upon conversion of the tertiary monochloride mixture to the dihalogenated derivatives and dehydrohalogenation there is obtained a mixture of branched chain conjugated 'dioleflns containing very little or no normal dioleflns. Small amounts of allwlaoetylene or non-conjugated dioleflns may be, formed and are preferably removed by chemical or solvent extraction procedures when required in order to produce pure conJugated dioleiln concentrates rich in only a few or one of the possible conj ted dioleiin isomers.

For example, a Ca olefin or olefln-paraflln mixture may contain as many as thirteen Cs olefin isomers several of which have cis and trans modiflcations having diflerent physical properties. All of these isomers have. boiling points lying within the range of 41-74 C. The only olefin or paraflin hydrocarbons having less than or more than six carbon atoms which lies within this range is 4.4-dimethylpentene-1 (boiling point 71.8 C.) Neither this heptene nor 3,3-dimethylbutene-l (boiling point41 0.) occurs in more than traces in rennerystreams, indications being that dimethyl substituted oleflns having two methyl substituents on a single carbon atom are thermodynamically less stable than other Co or higher oleflns and are therefore less likely to survive cracking or dehydrogenation reactions used in the refinery. It is desirable to eliminate 3.3- dimethylbutene-l completely since dihalides thereof upon dehydrohalogenation are not converted to dioleflns except possibly by molecular arrangement. i

I prefer to take first a Cs out starting at approximately 45' C. and ending at about 80 6., thereby eliminating the possibility of contamination by high boiling pentenes such as 2-methylbutene-2 (boiling point 38.6 C.), in this way the cut will contain in addition to any paraiilns in this range all of the secondary iso Ce oleflns and one of the tertiary Cs oleiins, as follows:

Secondary iso olenns: a 7 :IB. P. C. 4-methylpentene-1 54 4-methylpentene-2 (trans) 55 i-methylpentene-2 (els) 58 2.8-dimethylbu'ta1e-1 56 Such a fraction is then treated as .before in liquid phase atilo v temperature with HCl in such manner as to baustiereaction with the tertiary olefin to form z-chloro-zii-dimethylbutane without appreciably affecting the secondary iso oleflna, and is then additively chlorinated as before to convert the secondary iso olefin; to the corresponding dichloro derivatives. The mixture is then fractionated as before preferably under reduced pressure. The dichloro derivative fraction is then dehydrochlorinated to give a diolefin mixture consisting principally of il-methylpenta- (Ilene-2.4 (B. P, '16 C.) and containing smaller amounts of 3-methylpentadiene-l3 (B. P. 78 C.) as well as smaller amounts of alkylacetylenes and non-conlugated dioleilns which are preferably removed. 7 v

The 2-chloro-2.3-dimethylbutane is subjected to substitutive chlorination or otherwiu; converted largely to 2,8 dichlom 2.3 dimethylbutane which is dehydrochlorinated to produce largely ij-dimethylbutdiene 1,3 as well as small amounts of alkyl acetylenes, non conjugated dioleilns and other decomposition products which may be removed.

A second cut of the Ge hydrocarbons boiling in the range of from about 00 C. toabout 71- C. maybetahemwhichincludesallofthenormal secondary hexenes and all of the mtiary hexenes except 2,3-dlmethylbutene-2 whi may be more readily separately recovered and treated to produce pure 2,3-dimethylbutadiene. The hexenes in this second cut are:

This second fraction is then treated as before with HCl to convert the tertiary olefins substantially completely to the monohalogenated derivatives without appreciable conversion of the normal hexenes, followed by additive chlorination to convert the normal hexenes to their respective dichlorinated derivative. Upon fractionation as before the fraction of dihalogenated derivatives obtained is dehydrohalogenated to form normal hexadienes comprising largel hexadiene 1,8 (B. P. 73' C.) and hexadiene-2,4 (low-boiling, 76 C., high-boiling '19 C.) and small amounts of decomposition products. The product may be frac-. tionated and subjected to chemical or solvent extraction to recover-pure hexadiene-i,8 and hexadime-2,4. The monohalogenated derivative fraction is converted to the dihalogenated derivatives either by catalytic substitutive chlorination or by dehydrochlorination and additive chlorination. the dichlorinated derivatives being separated by fractionation and dehydroohlorinated to form conjugated dioleflns, consisting largely of 2- methylpentadiene-L8 (B. P. 18 C.) and B-methylpentadiene-1,3 (B. P. 78 C.) together with a smaller amount of 2 ethylbutadiene-1,3 (B. P. "72-'14 0.). Separation of these dioleflng from alkylacetylene, noneconlugated diolefins. and other contaminants is eiiected by fractionation and chemical or solvent extraction methods. Separation of the individual dioleflns. other than a 2-ethylbutadiene concentrate is dimcult because of the closeness of their boiling points.

A. third C's cutboiling in the range of from about 11' C. to about 76' C. will include 2,3-dimethylbutene-2 (B. P. 74' C.) and exclude heptanes and heptenes, the one having the closest boiling point being 3,3-dimethylpentene-1 (B. P. 77' C.) which is one of the least common heptene isomers. The 2,3-dimethylbutene-2 may be converteato the corresponding dihalogenated derivative by carefully controlled addition halogenation at low temperature in the liquid phase, or by addition of HCl to form 2-ehloro-2,3-dlmethylbutane followed by catalyzed substitutive chlorination to form dichlorinated derivatives. largely 2.3-dichloro-2,3-dimethylbutane, which are then dehydrochlorinated to give largely 2,3- dlmethylbutadiene-LS, which is then purified to remove contaminants.

Alternatively, though less preferably, the 2,3- dimethylbutene-2- may be included in the second cut by extending the boiling range therefor to an upper limit of about '16 C. Upon treatment with KCl, this tertiary hexen is converted to the mom ohalogenated derivative and after separation with the other monohalogenated tertiary derivatives and conversion to the dihalogen derivative followed by dehydrochlorination yields 2,3-dimethylbutadiene-i,3 in admixture with the other branched chain diolefins discussed above in connection with the second cut. I Because of its boiling point (70' C.) this dlolefin may be separated from the other dioleiins derived from the other tertiary hexenes, although production of pure 2,8- dimethylbutadiene-l,3 is diiilcult because the other possible isomers boil in the range 72-78 0.. making sharp separation diilicult.

Similarly. from C1 and higher streams, one akilledintheartcanbythepractice ofmyinvention produce 01 or higher aliphatic conjugated diolefins of high individual purity or at most containing only a few very similar diolefin isomers in the individual fraction.

From the foregoing it will be seen that my invention ofi'ers numerous advantages over prior processes oi making diolefins from olefin-containing streams. My process is markedly advantageous for example over a process wherein a C4 or higher stream containing both tertiary and secondary C4 or higher olefins, with or without 04 or higher paramns, is halogenated directly to form the dihalides which are then separated and dehydrohalogenated to yield a composite mixture containing aliphatic conjugated diolefins. since such a process in the case of C4 results in contamination of the butadiene with the decomposition products of the dichloride of isohutene, in the case of Ca yields a mixture of piperylene and isoprene and in the case of Co or higher produces a conglomerate mixture of straight and branched chain Co or higher dioleflns.

My invention is susceptible of numerous modifications in the illustrative disclosure above without departing from the inventive thought. For example, in some cases it may be desirable to subject the mixture after the halogenation step, without fractionation, to dehydrohalogenation, thereby converting the tertiary monohalides to olefin and the secondary dihalides to diolefin, and to then separate the olefin and diolefin from one another in any suitable way. In this way contamination of the diolefin derived from the secondary or normal olefin content with the diolefin derived from the tertiary olefin content is avoided.

I claim:

1. The process which comprises reacting in liquid phase a hydrocarbon mixture containin both tertiary base and secondary oleflns of at least four carbon atoms per molecule with anhydrous hydrogen chloride at a temperature within the reuse or -so to C. and thereby eifectins addition of the hydrogen chloride preferentially to substantially all of the tertiary base olefin content with the formation of tertiary alhl chloride without appreciable reaction with the secondary olefin content, and reacting in the absence of light the resulting mixture of tertiary allryl chloride and secondary olefin with substantially anhydrous chlorine at a temperature within the range of 20 to 50 C. and at a pressure sumclent to maintain a liquid phase of the secondary olefin. thereby efiecting the addition of the chlorine to substantially all of the secondary olefin with the formation of the secondary alkyl dichloride without appreciable reaction with the tertiary alkyl chloride, and separately recovering from the eiiluent of the chlorination by fractional distillation the tertiary alkyl chloride and the secondary alkyl dichloride.

2. The process as defined in claim 1 wherein the tertiary base olefin is isobutylene and the secondary olefin is butene-2.

3. The process which comprises reacting in the absence or light a mixture containing a tertiary alkyi chloride and a secondary olefin with substantially anhydrous chlorine at a temperature within the range 01 -20 to 50" C. and at a pressure sufiicient to maintain a liquid phase or the secondary olefin, thereby efiecting the addition of the chlorine to substantially all of the secondary olefin with the formation of the secondary allryl dichloride without appreciable reaction with the tertiary alkyl chloride.

i. The process as defined in claim 3 wherein the tertiary alkyl chloride is tertiary butyl chloride, and the secondary olefin is butene-2.

5. The process which comprises reacting in the absence 01 light a mixture containing isobutyl chloride and butene-2 withsubstantially anhydrous chlorine at a temperature of approximately 0 C. and at a pressure sufiicient to maintain a liquid phase or the secondary olefin. thereby eifecting the addition of chlorine to substantially all 01' the butene-Z with the formation of 2,3- dichlorobutane without appreciable reaction with the isobutyl chloride.

6. The process as defined in claim 3 wherein the chlorination is efiected with simultaneous fractional distillation of lower boiling constituents from the chlorides.

DONALD R. BLUMER.

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