US3114785A - Process for shifting the double bond in an olefinic hydrocarbon - Google Patents

Description

United States Patent Ofilice 3,114,785 Patented Dec. 17, 1963 3,114,785 PROCESS FOR SHIFTING THE DOUBLE BOND IN AN OLEFINHJ HYDROCARBON George L. Hervert, Downers Grove, and Carl B. Linn, Riverside, I'1l., assignors to Universal Oil Products Company, Des Plaines, Ill., a corporation of Delaware No Drawing. Filed July 21, 1960, SE1. No. 44,249 Claims. (Cl. 260683.2)

This invention relates to a process for shifting the double bond of an olefinic hydrocarbon to a more centrally located position in the hydrocarbon chain. More specifically, this invention relates to the shifting of said double bond in the presence of a boron halide-modified metal oxide catalyst.

It is generally Well recognized that the high compression, ignition type automobile engines in present day use require fuels of a high anti-knock value to give the optimum performance for which they are designed. The industry has accorded further recognition to the fact that high anti-knock values are attributable to the molecular structure of the hydrocarbons which comprise the gasoline fraction; that highly branched chain hydrocarbons have better anti-knock characteristics than their corresponding isomers of straight chain or relatively unbranched structure.

Motor fuels containing highly branched chain hydrocarbon components may be produced by the condensation of an isoparaffin hydrocarbon with an olefinic hydrocarbon in the presence of an acidic condensation catalyst, the process being generally referred to as alkylation. The more desirable alkylates of this process result from the condensation of isoparaffins with olefinic hydrocarbons wherein the double bond of said olefin is in a centrally located position of the hydrocarbon chain rather than in a terminal position thereof. Thus, for example, the alkylation of isobutane with Z-butene yields trimethylpentanes with an exceptionally high octane number, whereas l-butene, reacted similarly, gives dimethylhexanes which possess a much lower octane rating. One may generalize and state that 1alkenes react with isobutane to yield dimethylalkanes of poor octane rating.

The olefinic feed stocks generally available for alkylation purposes, and normally utilized for the present reaction, are generally mixtures of olefinic hydrocarbons of approximately the same molecular weight, including both the l-isomer, 2-isomer, and other position isomers capable of undergoing isomerization to an olefin in which the double bond occupies a more centrally located position in the hydrocarbon chain. In order to provide an olefinic feed stock for alkylation purposes containing an optimum proportion of the more centrally located double bond isomers therein, it is desirable to convert the l-isomer, or other position isomer component of the mixed feed stock, into the corresponding 2-isomer or into olefins wherein the double bond is more centrally located in the carbon atom chain. When higher molecular weight olefinic feed stocks are utilized such as hexene, the land Z-position isomer components are desirably converted into isomers containing the double bond located in the 2- and 3- positions.

It is an object of this invention to present a process for shifting the double bond of an olefinic hydrocarbon to a more centrally located position in the hydrocarbon chain. It is a more specific object to effect said shifting of the double bond in the presence of a boron trifluoride-modified metal oxide catalyst.

Within its broad scope, this invention embodies a process for shifting a double bond of an olefinic hydrocarbon of more than three carbon atoms per molecule to a more centrally located position in the hydrocarbon molecule, which comprises contacting said olefinic hydrocarbon with a boron halide-modified, substantially anhydrous metal oxide under reaction conditions which are conducive to double bond isomerization reactions.

Another embodiment is in a process for shifting a terminal double bond of a normal olefin of more than three carbon atoms per molecule to a more centrally located position in the hydrocarbon molecule, which comprises contacting said olefin with a boron trifluoride-modified, substantially anhydrous alumina under reaction conditions which are conducive to double bond isomerization reactions.

A more specific embodiment is in a process for shifting the double bond of l-butene to produce Z-butene which comprises contacting said l-butene with a boron trifiuoride-modified, substantially anhydrous gamma-alumina at a temperature of from about 20 C. to about 250 C.

The olefinic hydrocarbons treated according to the process of this invention are hydrocarbons of more than three carbon atoms per molecule and may be derived from various sources. This process is particularly suited to the conversion of l-butene to Z-butene. The l-butene may be charged in a pure state or in admixture with other hydrocarbons. Thus, a mixture containing l-butene as Well as isobutylene, Z-butenes, n-butane, and isobutane may be recovered as the light vapor overhead from the products of a catalitically cracked gas oil fraction. By the proper regulation of the isobutane content of such a mixture it will be recognized as a typical alkylation charge stock. Thus the process of the present invention may be utilized for the conversion of the l-butene content in an alkylation charge stock to the more desirable Z-butene prior to utilization of the charge in the alkylation process.

The process of this invention can be further utilized to shift the double bond of higher molecular weight olefinic hydrocarbons to a more centrally located position. For example, 1-pentene, S-methyl-l-butene, l-hexene, Z-hexene, and 4-methyl-1-pentene, can be readily isomerized to Z-pentene, 3-methyl-2-butene, 2-hexene, 3-hexene, and 4-rnethyl-2-pentene respectively. However it is not intended to limit this invention to those enumerated olefins set out above as it is contemplated that shifting of the double bond to a more centrally located position may be effected in straight or branched chain olefinic hydrocarbons containing up to 20 carbon atoms per molecule according to the process of the present invention.

This process, whereby the double bond of an olefinic hydrocarbon is shifted to a more centrally located position, is eifected in the presence of a boron halidemodiiiecl, substantially anhydrous metal oxide. The preferred catalyst comprises boron trifluoride-mod-ified, substantially anhydrous alumina. ther boron halides with which the metal oxide can be modified include boron trichloride, boron tribromide, etc. However the results obtained through the use of other boron halides than boron trifiuoride are not necessarily equivalent therewith. Of the various types of alumina which may be successfully and satisfactorily modified with boron tril'luoride, three crystalline structures have been found to be particularly suitable. These crystalline structures are substantially anhydrous gamma-alumina, substantially anhydrous eta-alumina, and substantially anhydrous theta-alumina. The specific utility of gamma, eta, and theta-alumina is not fully understood. It is believed to be related to the number of residual hydroxyl groups occurring on the surface of these three particular crystalline modifications of alumina. It may be that the boron trifiuoride reacts with the residual hydroxyl groups on the alumina surface to yield the desired catalytic effect, although it may very well be that the catalytic effect results from the boron triiluoride complexiug with the alumina.

The above-mentioned aluminas can be modified with I cent fluorine.

boron trifluoride by various methods. Generally, the alumina is contacted with the boron trifluoride at a given temperature until a predetermined amount of boron trifluoride has been adsorbed or otherwise taken up by the alumina. selected temperature for the treatment of substantially anhydrous alumina, in particular gamma, eta and thetaalumina, the boron trifluoride content thereof attains a maximum which is not further increased by contact with additional quantities of boron trifluoride at that particular temperature. This maximum increases with temperature and varies with respect to the particular alumina being modified.

The process of the present invention is preferably effected in the presence of a boron trifluoride-modified, substantially anhydrous alumina wherein said alumina has been thus modified by contact with boron trifluoride at a temperature of from about 100 C. to about 250 C. The fluorine content of the resulting catalyst will vary somewhat depending upon the particular alumina which has been utilized. For example, gamma-alumina, treated with boron trifluoride within the temperature range set out above will yield a catalyst comprising from about 6 wt. percent to about 19 wt. percent fluorine, While theta-alumina so treated will yield a catalyst comprising from about 3 wt. percent to about 7 wt. per- The boron trifluoride-modified alumina can be prepared by placing substantially anhydrous alumina in a fixed bed within a suitable reactor and passing a stream of boron trifluoride through the alumina bed at a given temperature until boron trifluoride no longer combines with the alumina.

7 Other inorganic metal oxides, as well as combinations thereof, can be modified by boron trifluoride as hereinabove described. For example, substantially anhydrous 'zirconia, silica-alumina, silica-magnesia, silica-aluminamagnesia, silica-alumina-zirconia, alumina-boria, etc., are modified at least to some degree by boron trifluoride. It is necessary that the metal oxide utilized form a .fairly stable compound with boron trifluoride from which the latter is not readily driven off by heat or reduced pressure. The previously indicated substantially anhydrous alumina is preferred, and particularly, synthetically prepared alumina of a high degree of purity consisting of substantially anhydrous gamma-alumina or substantially anhydrous theta-alumina.

The process of the present invention is eifected at a temperature of from about 20 C. to about 250 C. and at a pressure ranging from about atmospheric to about 1000 p.s.i. or more. It does not appear that pressure is an important variable in the present process as the desired isomerization reaction is not benefited to any marked degree by any particular pressure range. Nor is it necessary that pressure be regulated to control the physical state of the reactants as they can be processed in either the liquid or the gaseous phase. Thus, the particular pressure utilized may be selected upon purely economical considerations and in regard to the stability of the particular olefinic hydrocarbon to be processed.

This process can be carried out in a continuous manner or by batch type method-s. In a continuous type of operation the olefinic hydrocarbon is continuously charged to a reactor containing therein a fixed catalyst bed comprising boron trifluoride-modified alumina, the reaction zone being maintained under the reaction conditions previously described. The isomerization reaction product is continuously Withdrawn from the opposite end of the reactor. The liquid or gaseous hourly space velocity, based on the quantity of olefinic hydrocarbon charged, may be varied over the relatively wide range. Olefinic hydrocarbon charge stocks in a gaseous state can be charged to the process at a gaseous hourly space velocity of from about 50 to about 8000 ormore, while liquid olefinic hydrocarbons can be charged at a liquid It has been found that at any particular pre-.

hourly space velocity of from about 0.1 to about 20 or more. However, equilibrium conversion conditions are attained within a more limited range of from about 50 to about 4000 space velocity in the case of gaseous olefinic hydrocarbons and from about 0.1 to about 10 space velocity in the case of liquid olefinic charge stocks. Another type of operation is the fluidized system wherein the charge and the catalyst are maintained in a state of turbulence under hindered settling conditions in the reaction zone. Still another type of operation is the moving catalyst operation in which the charge is passed either concurrent with or countercurrent to a moving bed of catalyst. Still another type of operation is the slurry or suspensoid type in which the'catalyst is carried as a slurry or suspension into a reaction zone.

In a batch type of operation the olefinic hydrocarbon and the boron trifluoride-modified alumina are charged to an autoclave maintained at the desired temperature and pressure, and the reaction continued until the desired degree of isomerization is attained, usually a period of one hour or less. The batch type of operation is particularly suitable when utilizing a liquid olefinic hydrocarbon charge sitock, such as an olefinic hydrocarbon of relatively high molecular weight, including, for example, such olefins as the octenes, nonenes, decenes, etc. In a batch process of the above type, the catalyst and the olefinic hydrocarbon are preferably mixed during the course of the reaction, for example, by utilizing a reactor con.- taining stirring paddles, or a rotating autoclave.

The utilization of the present process to shift the double bond in an olefinic hydrocarbon to a more centrally located position presents a number of advantages. With respect to the catalytic activity of the boron t-rifluoride-modified alumina, products are readily obtained under mild operating conditions wherein the 2-butene content, resulting from the isomerization of l-butene, approaches thermodynamic equilibrium composition. In addition, the migration of the double bond is not usually accompanied by skeletal rearrangement within the molecule.

The boron trifluoride-modified alumina, as utilized in the present process, is characterized by an exceptionally long catalyst life and obviates the necessity of promoters as generally practiced in the prior ant. It is contemplated that under extended periods of operation the catalyst will decline somewhat in activity. However, the nature of the catalyst is such that it may be readily regenerated simply by passing a stream of boron trifluoride through the catalyst bed, preferably in admixture with the hydrocarbon charge, thus obviating the necessity of shutting down the operation to charge a fresh catalyst.

A further advantage to be realized'from the utilization of the present process is in the comparative ease with which the catalyst can be prepared and subsequently handled. The transfer of the catalyst requires only ordinary precautions against undue exposure to the atmosphere. On the other hand the catalyst can be prepared in situ. For example, the alumina can be placed in a bed within the reactor subsequently to be used in the isomerization process. The boron trifluoride is then passed through the alumina bed until the desired catalyst composition is attained. The catalyst thus prepared stands ready for use in the double bond isomerization process.

The following examples are introduced herein for the purpose of illustration of the specific embodiments of this invention and it is not intended to thereby unduly limit the generally broad scope of this invention.

EXAMPLE 'I an ly is indicated the calcined spheres to be substantially theta-alumina. The calcined alumina spheres were placed in a fixed bed within a '78 ID. stainless steel tubular reactor. Boron trii'luoride, diluted with nitrogen, was charged to the reactor. The reactor temperature was brought to about 150 C. and maintained at this temperature until the boron trifiuoride no longer combined with the alumina spheres as evidenced by boron trifluoride in the gaseous reactor eflluent.

The boron trifiuoride-modified alumina was recovered and found by analysis to contain 3.5% fluorine. 31.7 grams thereof (60 cc.) was placed in a fixed bed within a As" I.D. stainless steel, vertical, tubular reactor. The reactor temperature was raised to about 150 C. The gaseous hydrocarbon feed stock, contained in a pressure cylinder, was charged down-now through the catalyst bed at the rate of about 54 grams per hour. The gaseous charge stock was a synthetic mixture made up as follows:

Wt. percent Ethane 1.0 Propane 0.4 Isobutane 68.6

n-Butane 2.8 l-butylene 25.3 Isobutylene 1 .4 Cis Z-butene 0.2 Trans Z-butene 0.3

The reactor efiluent was cooled and passed through a pressure control valve regulated to maintain a reactor pressure of about 525 p.s.i.g. The reactor efiluent was thereafter measured and collected for analysis by gasliquid chromatographic methods. The gaseous reactor eflluent analyzed as follows:

Wt. percent Ethane 0.7 Propane 0.4 Isobutane 67.2

n-Bwtane 4.2

l-butylene 4.3 Isobuty-lene 0.4 Cis 2-butene 11.1 Trans 2-butene 11.7

It will be observed that the recovery of 2-butene, based on the l-butene and the 2-butene present in the charge stock, shows an 84.1% conversion of l -butene to 2-butene.

EXAMPLE II This example is presented to illustrate the inability of boron trifluoride to catalyze the conversion of l-butene to Z-butene in the absence of alumina.

The equipment utilized in this example is essentially the same as in Example 1. e4 stainless steel helices were used as packing in the 60 cc. catalyst zone. The gaseous charge stock was charged at the rate of 80 grams per hour and had admixed therewith 365 ppm. (wt) boron trifluoride based on the total charge. The reactor was maintained at a temperature of about 120 C. and at a pressure of about 200 p.s.i.g. The charge stock composition as well as the product composition after approximately 56 hours of operation is set out in the table below.

It will be observed that only very limited isomerization of l-butene to Z-butene occurred when using boron trifluoride in the absence of alumina.

EXAMPLE III A l-pentene charge stock is continuously charged to a reaction zone at the rate of 50 grams per hour. The reaction zone, located within a tubular steel reactor, has disposed therein a fixed catalyst bed comprising 32 grams of boron triiluoridemodified gamma-alumina in the form of spheres. Said reaction zone is maintained at a pressure of about 500 p.s.i.g. and at a temperature of about 150 C. The reactor efiluent, consisting essentially of 2- and 3-pentenes is cooled, passed through a pressure reducing valve, and recovered in a Wet-ice condenser.

We claim as our invention:

1. A process for shifting a double bond of an olefinic hydrocarbon of more than three carbon atoms per molecule to a more centrally located position in the hydrocarbon molecule, which comprises isomerizing said olefinic hydrocarbon in contact with a preformed combined boron trifiuoride-alumina catalyst prepared by treating substantially anhydrous alumina With boron trifiuonide at a temperature of from about C. to about 250 C. until boron trifluoride no longer combines with the alumina.

2. A process for shifting a double bond of an olefinic hydrocarbon of more than three carbon atoms per molecule to a more centrally located position in the hydrocarbon molecule, which comprises isomerizing said olefinic hydrocarbon at an isomerizing temperature of from about 20 C. to about 250 C. and in con-tact with a preformed combined boron trifluoride-alurnina catalyst prepared by treating substantially anhydrous alumina with boron trifiuoride at a temperature of from about 100 C. to about 250 C. until boron trifluoride no longer combines with the alumina.

3. The process of claim 2 further characterized in that said olefinic hydrocarbon is l-butene.

4. The process of claim 2 further characterized in that said olefinic hydrocarbon is l-pentene.

5. The process of claim 2 further characterized in that said olefinic hydrocarbon is l-hexene.

References Cited in the file of this patent UNITED STATES PATENTS 2,404,788 Burk et al July 30, 1946 2,422,884 Burgin June 24, 1947 2,766,312 Serniuk Oct. 9, 1956

Claims (1)

1. A PROCESS FOR SHIFTING A DOUBLE BOND OF AN OLEFINIC HYDROCARBON OF MORE THAN THREE CARBON ATOMS PER MOLECULE TO A MORE CENTRALLY LOCATED POSITION IN THE HYDROCARBON MOLECULE, WHICH COMPRISES ISOMERIZING SAID OLEFINIC HYDROCARBON IN CONTACT WITH A PREFORMED COMBINED BORON TRIFLUORIDE-ALUMINA CATALYST PREPARED BY TREATING SUBSTANTIALLY ANNYDROUS ALUMINA WITH BORON TRIFLUORIDE AT A TEMPERATURE OF FROM ABOUT 100*C. TO ABOUT 250*C. UNTIL BORON TRIFLUORIDE NO LONGER COMBINES WITH THE ALUMINA.