US2379731A - Olefin isomerization process - Google Patents

Description

Patented July 3, 1945 NE'KE OLEFIN ISOMERIZATION PROCESS Sumner H. Mcilllistr, Lafayette, Calif., assignor to Shell Development Company, San Francisco, (Bahi a corporation or Delaware Noillrawing. Application February 24, 1942,

Serial No. 4132,111

Claims. (Cl. 2 60-6832) This invention relates to the isomerizatlon of olefins having at least four carbon atoms per molecule and deals more particularly with a method of cdnverting such olefins into isomeric olefins in which the double bond occupies a different position in the molecule. In one of its specflc embodiments, the invention is directed to the treatment of mixtures of isomeric olefins of at least four carbon atoms or hydrocarbin mixtures predominating in or containing such olefinic mixtures to obtain high yields of a, singlerolcfin or of less complex mixtures of olefins.

The cheapest and most readily available sources of olefins are the products of cracking, dehydroproved by the discovery that the more reactivetertiary olefins, i. e. iso-olefins h'avingan unsaturated tertiary carbon atom; could be selectively reacted or removed leaving the secondary olefins, i. e. olefins which form secondaryderivatives by normal addition at the double bond, in a more suitable. condition for subsequent separate reaction. This procedure is entirely satisfactory for the production of'many valuable products but it does not make available individual olefins of four or more carbon atoms per molecule but yieldsmixtures of olefins having double bonds at different positions in the molecule. Thus, for example, after'selective removal of isobutylene from the butane-butylene fraction of petroleum cracking gases, hydrocarbons containing-both normal, alpha and beta-butylenes are obtained and from higher fractions even'more complex olefinic mix- ,tures result. For many purposes these olefinic mixturesare much less desirable th'anhydrocarbons containing only one olefin as beta-butylene or alpha-butylene instead of mixtures thereof. In

.particular, it has been found that for the production of butadiene, whether by direct catalytic or non-catalytic dehydrogenation or by chlor-substitution followed by dehydrochlorination, betabutylene is referred as feed since it gives higher yields vunder-comparable reaction conditions and less undesirable by-products than when its isomers or mixturps containing substantial amounts of such isomers are used. Likewise, in the al lation of isoparamns and in interpolymerization wi h butadiene, beta olefins give better results than olefinic mixtures comprising the corresponding isomeric olefins. While the invention is not limited thereto, it has as an important object the provision of a process for making available more desirable olefins ironr olefinic mixtures. It is a further object to convert the less desirable olefins in such mixture into more desirable isomers Without substantial loss of olefins.

It has already been proposed to isomerize olefins in, various ways, particularly by converting them into a suitable derivative such, for example, as the corresponding alcoh'ol or ester, which may be decomposed to yield the desired isomeric olefin.

ever,the'cata1ytic methods heretofore suggested have not been entirely satisfactory. One of the drawbacks of previous catalytic methods: has been the-"high temperatures involved which have made rium between alpha and beta isomers favors the alpha olefin as the temperature rises. An object Y of the present invention is to overcome the disadvantages of the prior art methods and to provide a method of isomerizing olefins which is not only economical but also gives high yields ofmore desirable Products.

of the invention will be apparent from the followstood, however, that the same procedure may be Other objects and advantages ing description.

For the purpose of making the invention more clear it will be described with more particular reference to the production of-beta butylene from fractions. of cracking products predominating in olefins andparafilns having four carbon atoms per molecule. This application of the invention has been chosen as an'lllustration because it is not only of particular commercial importance but also involves fewer componen s than analogous higher boiling hydrocarbon mix ures. It will be underapplied to such higher boiling hydrocarbon mix- .tures, it being only necessary to modify the reacber' of carbon atoms per molecule, hydrocarbon giixtures of wider boiling range may be used and lxtures of homologous olefins thereby obtained.

Also, instead of oleflnic fractions ;of cracking products, pure or substantially pure olefins or olefins admixed with other compounds may be employed, the.invention being independent of the source or purity of the olefin or olefins isomerized. It has now been discovered that alpha butylene may be readily'converted to beta butylene by contact with an aqueous inorganic acid solution, preferably aqueous sulfuric acid, under carefully controlled conditions of operation at which the isomerization is effected catalytically and the cost of acid is very low. For the production of beta butylene from a C4 fraction of cracking gases containing isobutylene and butanes as well as alpha and beta butylenes, it is desirable that the isobutylene content be first removed or at least substantially reduced in brder that the loss of olefin through interpolymerization be kept low in the process. The removal of isobutylene may be effected by selectively absorbing the isobutylene in a suitable solvent, for example a dilute acid solution at low temperatures as described in United States Patents 2,007,159 and 2,133,732. Alternatively, selective polymerization of the isobutylene at higher temperatures as disclosed, for example, in United States Patents 2,007,160, 2,101,857 or'2,156,'718 may be used for its removal. Still other methods of selectively removing tertiary olefins from the corresponding secondary olefins may also be used. Thus, the isobutylene may-be selectively esterified or may be chlorinated, for example, as described in United States Patent 2,030,938, or other suitable removal methods may be used. It is not essential that the acid into which the olefin to be isomerized is fed at one point while taking off at another point in the circuit emulsion which is fed toa decantation tank or other means for separating product from catalyst acid. The latter may be returned to the circuit after suitable adjustment of its concentration, for'exainple, by replacing a part with fresh acid. The separated hydrocarbon phase,

after further settling or neutralization, if necessary, may be distilled or otherwise'treated for recovery of the isomerized olefin-containing hydroearbons. It is. also'feasible to carry out the isomerization step by bubbling the olefin or olefins through a columncontaining acid solution maintained under suitable conditions. The process may be carried out batchwise or intermittently instead of continuously. Reduced olefin concentration tends to reduce losses through polymerization and suitable diluents may be added for this purpose.

, When employing sulfuric acid as the catalyst it is preferred to maintain a concentration of acid between about'50% and about 85% on a hydrocarbon-free basis. The exact choice of acid concentration within this range depends upon the temperature of operation adopted. For the isomerization of alpha butylene to beta butylene it is preferred to employ sulfuric acid of about 65% to 75% concentration at about 170 F. to 180 F.

With acid. -of lower concentration higher tem-.

peratures up to about 250 F. are used, while with stronger acids lower temperatures, preferably above about 120 F., are employed. For the isomerization of otheroleflns somewhat different combinations of acid concentration and temperature so which substantial polymerizatiom' particularly conversion to derivatives such, for example, as polymers, etc., it is not necessary to separate the.

isobutylene derivative or derivatives from the unreacted secondary butylenes before treating the latter for conversion to beta butylene: however, 'such products are preferably removed, as by distillation or the like, as the capacity of the isomerization unit may thus be increased.

For the isomerization step of the process it is preferred to use sulfuric acid as the catalyst. The

- olefin or olefin-containing hydrocarbon may be used in either the liquid or gaseous phase. Any

suitable method of contacting the olefin with the.

like. Jet mixer or mechanically stirred contact vessels may also be used. For continuous operation with the olefin at least partly in the liquid phase it is advantageous to use mixing by means of a pump which is in communication with a separator wherein olefin-containing hydrocarbons may be separated at least in part from the catalyst acid and the latter returned to the reaction.-

A preferred method of operation which is more fully described and claimed in United States Patent 2,232,674 comprises circulation of anemulsion oi. olefin-containing hydrocarbon and sulfuric interpolymerization of isomeric secondary olefins, does not take place.

It is preferred, in liquid phase operations,' to maintain a substantial volume of acid in contact with the hydrocarbon undergoing treatment. About 0.3to about 1.5, preferably 0.7 to 1.3, volumes of acid per volume of hydrocarbon may be used. While frequently short times of contact of the olefin to be isomerized with the catalyst acid is suflicient and contact times of less than iive minutes may beused when employing strong acid at the higher temperatures, in liquid phase operations with sulfuric acid of'about 65% to concentration longer periods of contact of the order of about 5 to 60 minutes, preferably about 10 to 30 minutes, are advantageous. Under these conditions space velocities of about 0.1 to about 2.5 volumes of liquid olefin per volume of acid phase per hour may be advantageously used.

The following example illustrates one applica tionof the process of the invention to the production of beta butylene from'a butane-butylene fraction having a composition This hydrocarbon mixture was contacted with sulfuric acid of 65% concentration at about 1?. to selectively extract the isobutylene. Theex-..

traction was carried out in countercurrent using two cooled contact vessels, through each of which approximately as aerarer tinuously circulated. For the. extraction about 0.86 mols of sulfuric acid-per moi of isobutyiene were used.

After removal of isobutyiene the hydrocarbon This mixture was treated in a single stage continuous reactor with a mixture of sulfuric acid.

and disodium phosphate corresponding to 85.7%

.HzSOi and 1.2% HaPOi in an amount equivalent to about 0.6 moi of acid per mol of olefin. The reaction temperature was 153 F. and the contact time was 5.5 minutes. Under these conditions the alpha butylene was substantially completely convertedto beta butylene and th loss of olefin through polymerization was very low, therebeing only 8.8% polymer in the product.

In another run in which the hydrocarbon feed to the isomerization unit contained 50% of alpha butylene, the remainder being normalpentane, and 70% sulfuric acid was used as catalyst at 185 F., it was found that less than 3% of the olefin was unchanged after a contact time of minutes. By fractionation of the hydrocarbon product substantially pure beta butylenecould be recovered. Similar results were obtained with pur alpha butylene using 59.7% sulfuric acid at 220 F. and 30 minutes contact time, the butylene recovered in this case being over 95% beta butylene. I

Catalyst acid which has lost its effectiveness for isomerization of oieiins inpartor completely as a result of the accumulation of organic impurities, particularly absorbed olefin, in repeated use in the process, may advantageously e employed in the preliminary step of tertiary olefin removal. Such acid may also be regenerated, for example by vacuum distillation, and reused in the. isomerization step. Thus a portion of the acid phase separated from the isomerization products may be heated under vacuum to-effect removal of beta olefin therefrom and returned along with another portion of said separated acid phase to contact with alpha olefin containing hydrocarbon.

It will be apparent that the process of the invention offers. many advantages over prior methods of olefin isomerization, not only with respect to the .high yields of olefins which may be obtained but also in regard to the substantial savings in reagent and operating costs which may be effected thereby. While the rearrangement of alpha-unsaturated secondary mono-olefins such, for example, as'butene-1 and higher homologues has been emphasized in the foregoing discussion, it is to be understood that other nontertiary olefins may be analogously treated to produce oiefins' having the double bond further removed from the end of the chain. The invention is of wide scope, not only with regard to the olefinic compounds which maybe treated but instead of using acids for the preliminary separation of the tertiary olefin from the olefins to be isomerized, extraction with a mixture of cresols and a small amount of disecondary butyl sulfate or the like as described in United States- Patent 2,265,583 may be employed. Isobutylene may also be separated from mixtures of alpha and beta if butylenes by extractive distillation for example. Still other changes may be made and the invention is not limited to thevdetails of operation disclosed by way of illustration nor by any theory advanceddn explanation of the improved results obtained.

I claim as my invention:

1. A process of producingbeta butylene from a hydrocarbon mixture comprising isobutylene, alpha and beta butyienes and butaneswhich comprises extracting said mixture with sulfuric acid of less than 70% concentration to remove isobutylene therefrom without substantial polymerization, intimately mixing the remaining alpha and beta butylenes with about 0.3 to 1.5 volumes of sulfuric acid of about 70% to 75% concentration per volume of liquid hydrocarbon, at about 170 F. to 1-80" F. for about 5 to 30 minutes, separating the resulting mixture into a beta butylene-containing hydrocarbon phase and an acid phase without substantialiyweducing the concentration, on a hydrocarbon-free basis, of said acid, heating a portion of the separated acid phase under vacuum to efiect removal of beta butylene therefrom, returning at least a part of the thus heated acid and another portion of said Separated acid phase to contact with alpha and beta butylene-containing hydrocarbon, and distiliing the separated hydrocarbon phase to recover beta butylene in a more concentrated form. 2. A process of producing a normal beta olefin from the corresponding alpha olefin of at least to said beta olefin takes place, separating the resulting mixture into a beta olefin=containing hydrocarbon phase and an acid phase without substantially reducing the concentration, on a hydrocarbon-free basis, of said acid, heating a portion of the separated acid phase under vacuum to effect removal of beta olefin therefrom, returning at least a part of the thus heated acid and another portion of said separated acid phase to contact with said alpha olefin and recovering beta olefin from the separated hydrocarbon phase.

3. A process of producing a normal beta olefin V from a hydrocarbon mixture comprising the corresponding alpha olefin of at least four carbon atoms per molecule and a tertiary olefin, which comprises contacting said mixture with sulfuric also with respectto the methods of operation pure beta butylene it is generally preferable to' make such separation after isomerization. N50,

acid to selectively remove tertiary ole'fin'therefrom, intimatelymixing the remaining alpha- .olefin-containing hydrocarbon with sulfuric acid of about 50% to concentration at a ternperature between about F. and 250 F. at which isomerization of said alpha olefin to said beta olefin takes place, separating the resulting mixture into a beta-olefin-containing hydrocarbon phase and an acid phase without substantially reducing the concentration, on a hydrocarbonfree basis, of, said acid, heating a portion of the separated acid phase under vacuum to effect removal f beta olefin therefrom, returning at least a part of the thus heated acid to contact with said alpha-olefin-containing hydrocarbon and using another part of said separated acid in effecting said tertiary olefin removal.

4. A process of producing a normal beta olefin from a hydrocarbon mixture comprising the corresponding alpha olefin of at least four carbon atoms per molecule and a tertiary olefin, which comprises contacting said mixture with sulfuric acid .to selectively remoVe tertiary olefin therefrom, intimately mixing the remaining alphaolefin-containing hydrocarbon with sulfuric acid of about 50% to 85% concentration at a temperature between about 120? F. an which isomerization of said alpha efin to said beta olefin takes place, separating the resulting mixture into a beta-olefin-containing hydrocarhon phase and an acid phase containing absorbed olefin without substantially reducing the 250 F. at

spent ,acid in effecting said tertiary olefin removal.

5. A process of producing beta butylene from a hydrocarbon mixture comprising isobutylene, alpha and beta bfitylenes and butanes which comprises extracting'said mixture with sulfuric acid to remove sisobutylene therefrom without substantial polymerization, intimately mixing the remaining alpha and beta butylenes with about 0.3 to 1.5 volumes of sulfuric acid of about'70% to concentration per volume of liquid hydrocarbon. at about F. to F.- for about 5 to 30 minutes, separating the resulting mixture into a beta butylene-containing hydrocarbon phase and an acid phase without substantially reducing the concentration, on a hydrocarbon-free basis, of said acid, distilling the separated hydrocarbonv phase to recover beta butylene in a more concentrated iorm, continuously returning at least a part of said separated acid phase to contact with alpha and beta butylene-containing hydrocarbons until the acid is at least partly spent with respect to its effectiveness for isomerizing olefins as a result of the accumulation of organic impurities therein, and feeding at least a Part of said spent acid to said isobutylene extraction. SUMNER H. McALLIS'I'ER.