US2334998A - Isomerization of alpha olefins - Google Patents

Description

Patented Nov. 23, 1943 ISOMERIZATION F ALPHA OLEFINS Arthur A. Draeger and Joseph J. Savelli, Baytown, Tex., assignors to Standard Oil Development Company, a corporation of Delaware -No Drawing. Application December 9, 1939,

Serial No. 308,390

13 Claims. (Cl. 260-6832) The present invention relates to the production of beta olefins from alpha, olefins, in particular, butene-2 from butene-l or mixtures containing substantial amounts of alpha olefins, in particular, butene-l.

It is already known to prepare substantially pure butene-2 from.butene-1 by subjecting butene-l to fairly high temperatures of the order of 400-600 C. with or without the use of catalysts, in particular, catalysts of a neutral or alkaline reaction, for example, the metal oxides, in particular, the difficulty reducible metal oxides, neutral salts of boric acid, phosphoric acid, or silicic acid and the like. It is likewise known to convert butene-l into butene-2 by treating bu-' tene-l with sulfuric acid of a fairly high concentration, such that the tertiary olefins present are polymerized and the normal butylenes are reacted simultaneously to form the acid extracts which are thought to be acid'sulfate esters. Any polymer or copolymer formed by reason of the reaction of the tertiary olefin, namely, isobutylene with itself or with normal butylenes, is removed as a liquid layer from the resulting sulfuric acid extract. The extract is then diluted with water and heated to regenerate the normal butylenes which are found to be chiefly butene-2.

Snow, U. S. Patent 2,128,971 of September 6, 1938, discloses the reaction of a paraihn-olefln mixture with sulfuric acid of a 75% to 85% concentration, the paraflin-olefin mixture being previously treated to remove the iso-olefins present therein. The normal olefins are thereby converted, presumably to the corresponding acid sulfate esters. This acid ester layer is then diluted with a quantity of water sufficient to reduce the acid concentration of the original 75% to 85% sulfuric acid to about 50% to 65% sulfuric acid and then heated preferably with reflux to a temperature between about 75 C. and 145 C. in order to regenerate the normal olefins chiefly as beta olefins. This disclosure contemplates the use of a distinctly two-step process in which strong sulfuric acid is employed to absorb the normal olefins rapidly, the resulting extract removed from the absorption zone, diluted with water and then heated to regenerate the normal olefins chiefly as beta olefins. From the standpoint of commercial operation, a considerable expense is incurred in operating according to this process by reason of the fact that the acid originally employed for converting the normal olefins to the corresponding acid sulfate esters must be diluted with water before itis possible to obtain the beta olefins. It is therefore necessary,

unless the sulfuric acid is discarded after each run, to reconcentrate the acid before it is reused in the process. Such aprocedure necessarily entails the construction and operation of further equipment with the incidental increase in operating costs. I

It is an object of the present invention to produce beta olefins from alpha olefins, in particular, butene-2 from butane-1, by contacting mixtures containing substantial amounts of alpha olefins or alpha olefins alone with sulfuric acid and correlating the acid strength and temperature so that beta olefins are obtained directly from the reaction mixture.

It is an object of the present invention to isomerize alpha olefins to form beta olefins in a simple one-step procedure readily adaptable to commercial operation employing a continuous process.

In order to accomplish the objects of the invention, as well as others which will be apparent from a full understanding of the invention to be hereinafter described, hydrocarbon mixtures containing substantial amounts of alpha olefins and which are substantially free of olefins containing tertiary carbon atoms, or alpha olefins alone, are contacted with sulfuric acid of a concentration between about 50 and about at a temperature between about F. and about 220 F. for a period of time between about 5 and about 60 minutes with vigorous agitation. Thus, it is possible to maintain a body of sulfuric acid of the desired concentration and at the desired temperature and to bubble into, or in some other convenient manner introduce, alpha olefins continuously. The effluent from the body of the sulfuric acid is found to contain chiefly beta olefins so far as the olefinic content thereof is concerned. The extra step of separating the .entire body of catalyst and corresponding acid sulfate esters of the catalyst followed by dilution and subsequent heating to liberate the beta olefins has'been obviated.

At the present time the desirability of perfecting processes for the production of large quantities of butene-2 becomes increasingly apparent. Large amounts of butene-2 are utilized in the efficient production of butadiene, for example, as obtained by the dehydrohalogenation of 2,3-butylene dichloride prepared by, halogenating butene-2. Furthermore, high yields of butadiene may be obtained by the thermal cracking of butane-2 in contrast to the yields obtained upon similarly treating butene-l. There are several other newly developed fields which require'the use of substantially pure butene-2, for example, in the production of isoprene, butadiene derivatives and the like, where fairly pure final products are required.

The process of the present invention may also be utilized for effecting the complete removal of any residual tertiary olefins which may be present in the feed stocks employed. Thus, for example, where a refinery C4 cut previously treated to remove the isobutylene is employed as the feed stock for the present invention, small quantities of isobubtylene are still present in the C4 cut. This isobutylene, under the present treatment, is largely copolymerized with the straight chain butylenes to give codimers which may be separated from the butene-2 and unreacted butene-l by any suitable means, for example, fractional distillation, or in any other convenient manner. It is desirable, however, to maintain the concentration of tertiary oleflns in the feed stock as low as possible where high yields of the beta olefins are desired. A specific feed stock for the process of the present invention as above mentioned is a refinery C4 out which has been previously treated to remove its isobutylene content. There are a number of ways of accomplishing this removal among which may be mentioned selective absorption of the isobutbylene followed by the heating of the extract to produce polymersthereof such as practiced according to the socalled cold acid polymerization process involving the use of sulfuric acid as the catalyst, selective extraction of isobutylene from refinery C4 cut with sulfuric acid of specified concentration and under specified temperature conditions to produce secondary butyl alcohol and various other types of selective treatment to remove the isobutylene content thereof. Tertiary olefins in similar manner may be removed from other olefin-containing mixtures, for example, isopentene may be removed from a mixture of C5 oleflns and the resulting pentene-l treated according to the process of the present invention in order to,

finery C5 cut from which the olefins containing tertiary carbon atoms in their molecules have been previously removed. Another particularly desirable source of feed stock for the present in-. vention is to be found in field butanes which have been subjected to at least partial dehydrogenation treatment to convert the parafilns into the corresponding olefins followed by selective removal of the isobutylene content thereof. The resulting partially dehydrogenated isobutylenefree field butanes may then be fed to the present process to convert the alpha butylene into the corresponding beta butylenes. r

The reaction may be carried out in either the liquid or the vapor phase. However, it is preferred to carry the same out in the liquid phase due to the greater economy eifected in commercial operations by operating in such a manner. The conditions of temperature, pressure, time of contact, and strength of acid required to convert alpha olefins to beta olefins vary somewhat with the molecular weight of the olefin hydrocarbon comprising the charge stock-the higher the molecular weight, the less severe are the conditions required. In general, the reaction temperature should range between about 100 F. and

about 220 1''. for butenes, pentenes and hexenes. The temperature of reaction preferred for butenes ranges between about F. and about 180 F., whereas that preferred for pentenes, hexenes or higher olefins is somewhat lower. Under these temperature conditions, it is necessary to employ super-atmospheric pressure in order to maintain liquid phase operation, particularly when employing a C4 fraction as the feed stock. It is preferable to employ only sufficient super-atmospheric pressure to maintain the reactants in the liquid phase under the conditions of operation. In general, super-atmospheric pressures of 350 lbs/sq. in. gauge or lower may be employed. The reaction is preferably carried out using a time of contact between about 20 and about 30 minutes when correlated with the other reaction conditions. However, when employing the lower temperatures or lower strengths of acid (50-70%), times ofcontact as high as 60 minutes may be employed and when employing the higher temperatures or higher strengths of acid (70-80%), times of contact as low as 5 or 10 minutes may be employed. In order to insure adequate conversion of the alpha olefins to the beta olefins, vigorous agitation of the acid and hydrocarbon reaction mixture is desirable. In the case of batch operations, mechanical stirrers or agitators are adequate. In continuous-operations turbo mixers, Jets of restricted internal diameter, porous thimbles and the like provide adaquate agitation and means for intermingling of the reaction mass with the catalyst. In a continuous process, in order to maintain the catalyst strength over long periods of time, fuming sulfuric acid or sulfur trioxide may be continuously or intermittently added to the reaction mixture. If the catalyst volume is to remain constant, a gradual or intermittent withdrawal of spent acid must be made at the time of the addition of fresh acid, fuming acid, or sulfur trioxide.

As heretofore indicated, it is not necessary to employ pure alpha olefins as the feed stock for the present invention. As the examples herein described show, a feed stock may contain material amounts of the product to be produced. It is only necessary that the feedstock does not contain equilibrium amounts of the beta olefins. The presence of isoparaflins and normal paraflns in the feed stock apparently causes no deterioration of the catalyst nor harmful effect upon the ultimate conversion of alpha olefins to beta olefins. If desired, however, the paraffinic constituents of the feed may be in whole or in part removed from the feed stock by any suitable means, for example, fractional distillation or the parafilnic constituents of the reaction mixture may be removed after the feed stock has passed through the catalyst zone at least once. In other words, the separation of the paraflinic constituents may be effected either before 'or after the feed stock has contacted the acid catalyst.

Any suitable apparatus which has heretofore been employed for the polymerization or alkylation of similar feed stocks employing sulfuric acid as the catalyst may be employed for carrying out the process of the present invention. Packed columns through which sulfuric acid fiows downwardly while the feed stock flows upwardly there thru, time-tank reactors in which an emulsion is maintained between the hydrocarbon and the sulfuric acid and continuously returned to the reactor by means of pumps and the like, and liquid bath type reactors in which the catalyst asaaoes is maintained as a liquid bath or pool are suitable units for operating the process. The reaction mixture may be maintained at the desired temperature in the reactor by employing autorefrigeration of the feed stock and reactants in the reaction vessel. In other words, the process is so correlated with the desired temperature as to effect a partial vaporization of the liquid reaction mixture when the reaction has a tendency to exceed the desired temperature for the reaction. The use of the autorefrigeration principles is particularly adapted for use with the jet type reactors.

The reacted mixture, upon completion of the reaction, may be subjected to any suitable process for the separation of the desired products. Where a relatively pure product is more particularly desired, fractional distillation may be employed. However, in order to secure a product from the reaction predominating in beta olefins, a more exact separation of the beta olefins from the other hydrocarbons present is necessary. There are a number of suitable methods for accomplishing this separation. For example, the reacted mixture may be subjected to a controlled halogenation reaction; the halogenated olefins may then be readily separated from the parafllnic constituents of the reacted mixture by fractional distillation; in particular, chlorine may be introduced into the olefin molecules for accomplishing this separation. The parafilnic eflluent from the reaction mixture may be subjected to at least a partial dehydrogenation reaction in order to provide additional feed stocks forthe present process. However, prior to the introduction of the dehydrogenated parafilnic mixture into the reaction zone, it is desirable to subject the same to the selective action of sulfuric acid, for example, of 60 to 65% strength, at a temperature of from about to C. in order to selectively remove any tertiary olefins, that is, oleflns containing at least one tertiary carbon atom per molecule, from the feed stock. The tertiary olefin extract may then be heated to produce polymers. The polymer is separated as the upper layer and the partially spent sulfuric acid is cooled and returned to the absorber for the extraction of further quantities of tertiary olefins from any of the feed stocks intended to be used in the present process.

The following examples are intended to be illustrative only and are not to be considered in any way as limiting the scope of the invention:

Example 1 A refinery C4 out which previously had been freed of isobutylene by treatment with dilute sulfuric acid and whose butene fraction consisted of 87 mol per cent butene-l, 9.5 mol per cent cis-2-butene and 3.5 mol per cent trans- 2-butene was placed in a bomb with fresh 70% sulfuric acid at a temperature of 170 1'. and agitated for 20 minutes. The resultant butene fraction had the following composition: 34% butene-l, 1.6% cis-Z-butene, 64.4% trans-2- butene.

Example 2 Sulfuric acid of 70% strength was saturated with normal butenes by contacting said acid at 140 to 158 F. with a sufllcient amount of a C4 naphtha out. This cut was discharged from a polymerization unit as a spent stock but still contained normal butenes, isoand n-butanes. 200 cc. of this saturated sulfuric acid extract were then admixed with 6'15 'cc. of spent 04 naphtha the composition of whichis given in the table below. This mixture was agitated at 1130 revolutions per minute for about one hour at 158 F. in a turbo mixer. The pressure in the reactor was maintained at about 93 lbsJsq. in. gauge. After the contact period, the contents of the reactor were permitted to flow into a cooling flask under a dry ice" condenser where the acid and the hydrocarbon phases were separated and drawn oil. Analyses of the spent C4 naphtha before and after the acid treatment are as follows:

Moi percentage composition of the GI fraction of the spent naphtha Before acid After acid Gain in contreatment treatment stituents 8. 4 l. 0 7. 4 l0. 0 22. 9 3. 9 l. 4 0. 2 l. 2 mutual-i: 11. 2 7s. a 4. 1 n-Butenea fraction 27. 4 23. 9 3. 6

Total nnsatumtion- B. 8 24. 1 4. 7

Mol percentage composition of n-butenes fraction from naphtha Before acid After acid Gain in contreatment treatment stituents Butane-1-.-; 30.7 4.2 -2e.5 Butane-2 69. 3 95. 8 so. 5

It is noted that there is a slight loss of unsaturates in the C4 fraction after treatment according to the above process. This is accounted for by reason of the fact that the total product contained a slight amount of higher boiling material amounting to about 6.3 mol per cent expressed as CeHs and to that extent represents a reduction in the C4 fraction. The major portion of the olefin loss is due to the formation of small amounts of dialkyl sulfates and polymers which distribute themselves between the acid and naphtha phases, but remain dissolved predominantly in the naphtha. In a commercial operation, these sulfates and polymers may be separated and utilized in various conventional ways, however, they may also be returned to the reaction zone of the present process to establish equilibrium conditions therein and to thereby suppress the ultimate formation of increased amounts of the same.

From Example 2 it will be seen that under the above described treatment the mol percentage of butene-l dropped from about 8.4 to about 1.0 while the butene-2 content of the feed stock increased from about 19 to about 22.9. The ratio of butene-2 to butene-i is about 2.26:1 in the feed stock whereas it is about 22.9:1 in the reactedCt cut. The actual increase in the amount of butane-2 in the product over the original butene-2 content of the feed stock was about 10% by weight.

Having now fully described and illustrated the process of the present invention and the nature and objects thereof, what is claimed as new and 1189111: and desired to be secured by Letters Patent 1. A process which comprises converting butene-1 into butenes-il which comprises contacting butene-1 substantially free of isobutylene with about 70% H2804 at a temperature of about 170 F., vigorously agitating for about 20 minutes, settling the reacted mixture to form an acid phase and a hydrocarbon phase, withdrawing the hydrocarbon phase therefrom and recovering cisbutene-z' and trans-butene-2 from the said hydrocarbon phase. w

2. A process as in claim 1 wherein the 11:80

has been previously substantially completely sat-' urated with at least one normal butene.

3. A process as in claim 1 wherein the H2504 has been previously substantially completely saturated with butane-1 and wherein the process is carried out continuously and under sufficient superatmospheric pressure to maintain the reactants in the liquid phase under the reaction conditions obtaining.

4. A process which comprises contacting in an isomerization unit a refinery C4 cut containing substantial amounts of butene-1 but substant tially free of isobutylene with a catalyst prepared by treating 70% H2804 at between about 140 and about 158 F. with said refinery C4 cut until the acid is substantially completely saturated with n-butylenes present in the said refinery C4 out, at a temperature of about 158 F. for about 60 minutes with vigorous agitation under superst-v mospheric pressure, thereby converting substantial quantities of butene-l to butenes-2, settling the reacted mixture to form an acid phase and a hydrocarbon phase, withdrawing the hydro-i carbon phase therefrom, distilling the said hydrocarbon phase into a fraction containing substantially all of the unconverted butene-1 and a fraction containing substantially all of the butenes-2 as products of the reaction.

5. A process as in claim 4 wherein the feed stock was prepared from a C4 cut containing nand isobutylenes, the isobutylene having been substantially completely removed by a selective absorption and polymerization process prior to introducing the feed into the isomerization unit.

6. A process which comprises converting pentene-i into pentenes-2 by subjecting pentene-l to the action of a preformed H:SO4-n-pentenes extract under isomerization conditions settling the reacted mixture to form an acid phase and a hydrocarbon phase, withdrawing the hydrocar bon phase therefrom and recovering pentenes-2 from the said hydrocarbon phase.

7. A process which comprises converting at least one normal alpha olefin into the corresponding normal beta olefin by subjecting said alpha olefin to the action of a preformed sulfuric acid-n-alpha olefin extract under isomerization reaction conditions. settling the reacted mixture to form an acid phase and a hydrocarbon phase, withdrawing the hydrocarbon phase therefrom and recovering the wrresponding normal beta olefin from the said hydrocarbon phase.

8. A process which comprises introducing a refinery C4 fraction containing a preponderating amount of butene-l with respect to the butenes present therein and substantially free of isobutene into a reformed n-butenes-sulfuric acid extract under isomerization reaction conditions, settling the reacted mixture to form an acid phase and a hydrocarbon phase, withdrawing the hydrocarbon phase therefrom and recovering butenes-2 from the said hydrocarbon phase.

9. A process as in claim 8 wherein the process is carried out continuously.

10. .A process which comprises converting at leastone normal alpha monoolefin substantially free... of tertiary olefin into the corresponding normal. beta monoolenn by subjecting said alpha olefin to the action of a preformed sulfuric acidn-alpha monoolefin extract, the acid having an original concentration of between about 50% and about the reaction being maintained at a. temperature between about F. and about 200? F. and with agitation for a sumcient length of time to efiect substantial conversion of the said alpha monoolefin into the corresponding beta monoolefin, settling the reacted mixture into an acid phase and a hydrocarbon phase, separating the hydrocarbon phase from the acid phase and recovering the beta monoolefin from the hydrocarbon phase.

11. A process as in claim 10 wherein the process is carried out continuously.

12. A process which comprises converting normal alpha monooiefins into the corresponding normal beta monooleflns by contacting said alpha oleflns substantially free of tertiary olefins with a preformed sulfuric acid extract of said alpha monoolefins and sulfuric acid under isomerization reaction conditions whereby thealpha olefins are converted into the corresponding beta oleflns, settling the reacted mixture into an acid phase and a hydrocarbon phase and recovering the beta monoolefins from the hydrocarbon phase by fractional distillation.

13. A process as in claim 12 wherein the feed stock is a refinery C4 fraction containing a predominating amount of butane-1 with respect to the total olefin content of the fraction and wherein the fraction is substantially free of isobutene.

ARTHUR A.- DRAEGER. JOSEPH J. SAVELLI.