US3217059A - Process for shifting the double bond in an olefinic hydrocarbon - Google Patents

Description

United States Patent 3,217,959 PROCESS FOR SEHFTTNG THE DOUBLE BOND IN AN GLEFINIC HYBRGCARBQN George L. Hervert, Downers Grove, and Carl E. Linn, Riverside, 111., assignors to Universal Oil Products Company, Des Piaines, 1th, a corporation of Delaware No Drawing. Filed Dec. 4, 1962, Ser. No. 242,089 Claims. (Cl. 260-6832) This application is a continuation-in-part of our copending application Serial No. 44,249, filed July 21, 1960, now Patent No. 3,114,785.

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 trifluoride-modified substantially anhydrous zirconium oxide.

It is generally well-recognized that the high compression, ignition type automobile engines in present day use require fuel of a high anti-knock value to give the optimum performance for which they are designed. The industry has accorded recognition to the fact that high anti-knock values are attributable to the molecular struc ture of the hydrocarbons which comprise the gasoline fractions; 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 isoparaffinic hydrocarbon with an olefinic hydrocarbon in the presence of an acidic acid condensation catalyst, the process being generally referred to an alkylation. The more desirable alkylates of this process result from the condensation of isoparaffins with olefinic hydrocarbons wherein the double bond of said olefinic hydrocarbon is in a centrally located position of the hydrocarbon chain rather than in a terminal position. 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 l-alkenes react with isobutane to yield dimethylalkanes of poor octane rating.

The olefinic feed stocks generally available for alkylation purposes, and subject to treatment in accordance with the present process, are generally a mixture of olefinic hydrocarbons of approximately the same molecular weight, including both the l-isorner, 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 amount of the more centrally located double bond isomers, it is desirable to con vert 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 1- and 2- 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 eifect such shifting of the double bond in the presence of an isomerization catalyst comprising boron trifluoride-modified substantially anhydrous zirconia.

In one of its broad aspects the present invention embodies a process for shifting a double bond of an olefinic hydrocarbon to a more centrally located position in the hydrocarbon molecule, which process comprises isomerizing said olefinic hydrocarbon at isomen'zation reaction conditions and in contact with an isomerization catalyst comprising a boron trifiuoride-modified substantially anhydrous zirconia.

Other objects and embodiments of the process of this invention will become apparent in the following detailed specification.

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 2-butene. The l-butene may be charged in pure state or in admixture with other hydrocarbons. Thus, a mixture containing l-butene as Well as isobutylene, 2-butenes, n-butane, and isobutane, recovered, for example, as the light vapor overhead product of a ctalytically cracked gas oil fraction, may be treated in accordance with the present process. By 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 2-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, l-pentene, 3-methyl-1-butene, l-heX- ene, Zahexene, and 4-methyl-l-pentene, can be readily isomerized to 2-pentene, 3-methy1-2-butene, 2-hexene, 3- hexene, and 4-methyl-2-pentene respectively. However, it is not intended to limit the process of 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 about 20 carbon atoms per molecule according to the process of the present invention.

The description substantially anhydrous, but not completely dry, zirconia, relates to zirconium dioxide which, on a dry basis, contains from about 0.1 wt. percent to about 10 wt. percent water in either physical or chemical combination with the zirconium dioxide. This water content is determined as volatile matter evolved from the crystalline zirconia upon heating of the same at 900 C. for an extended period, say from about 1 to about 50 hours or more. In contrast to the aluminas, the substantially anhydrous, but not completely dry, zirconias, appear to occur in only one crystalline modification when examined by X-ray diffraction techniques, although the amount of combined water varies therein. The exact reason for the specific utility of crystalline zirconia in the process of this invention is not apparent but is believed to be related to the number of residual hydroxyl groups occurring on the surface of the zirconia.

The above-described zirconias can be modified with boron trifiuoride by various methods. The so-called modification of zirconia with boron trifiuoride is an exothermic process resulting in, for example, an initial temperature rise to about C. or more when boron trifiuoride is passed over the zirconia at about room temperature. In general, the zirconia is contacted with boron trifiuoride at a predetermined temperature until boron trifiuoride is no longer adsorbed, or otherwise taken up, by the zirconia. It has been observed that in the treatment of substantially anhydrous zirconias with boron trifluoride, the capacity of the zirconia for boron trifluoride is determined by the particular temperature at which said treatment takes place, and at a given temperature, the boron trifiuoride content of the zirconia reaches a fixed maximum which is not further increased by contact with additional quantities of boron trifiuoride at the given temperature. The capacity of zirconia for boron trifiuoride increases with temperature. The exact manner in which the boron trifiuoride acts to modify the zirconia is not understood. It may be that the modification results from the complexing of the boron trifiuoride with the zirconia, or on the other hand, it may be that the boron trifiuoride reacts with the residual hydroxyl groups on the zirconia surface. In any case, the process of the present invention is preferably effected in contact with a catalyst comprising a boron trifiuoride-modified substantially anhydrous zirconia wherein said zirconia has been thus modified by contact with at least a slight excess of boron trifiuoride at a temperature of from about 50 C. to about 250 C.

One suitable method of preparing the boron trifiuoridemodified substantially anhydrous zirconia comprises placing the substantially anhydrous zirconia in a fixed bed located in a suitable reactor and passing a stream of boron trifiuoride therethro-u'gh. at a preselected temperature until such time as boron trifiuoride is no longer adsorbed or otherwise taken up, by the zirconia. When the zirconia is thus treated with boron trifiuoride it is noted that no boron trifiuoride passes through the zirconia until substantially all of the zirconia has been modified with boron trifiuoride in the manner herein contemplated. The boron trifiuoride stream may be diluted with an inert gas including nitrogen, hydrogen, helium, or the like, as desired.

The isomerization reaction of the present invention is efiected at a temperature of from about C. to about 250 C. and at a pressure ranging from about atmospheric to about 1000 p.s.i. or more. In general, the reactants can be processed in either the liquid or gaseous phase. In certain cases it may be desirable to maintain the reactants in a liquid phase downflow over the catalyst as a deterent to polymer formation thereon.

One preferred embodiment of the process of the present invention relates to a process for shifting the double bond of l-butene to produce 2-butene which comprises isomerizing said l-butene at an isomerization temperature from about 20 C. to about 250 C. and in contact with an isomerization catalyst comprising a boron trifiuoride-modified substantially anhydrous zirconia.

Another preferred embodiment is in a process for shifting the double bond of l-pentene to produce Z-pentene which comprises isomerizing said l-pentene at an isomerization temperature of from about 20 C. to about 250 C. and in contact with an isomerization catalyst comprising a boron trifluoride-modified substantially anhydrous zirconia.

Still another preferred embodiment of this invention is in a process for shifting the double bond of a 1-hexene to a more centrally located position, which process comprises isomerizin-g said 1hexene at an isomerization temperature of from about 20 C. to about 250 C. and in contact with an isomerization catalyst comprising a boron trifiuoride-modified substantially anhydrous zirconia.

The present process can be effected in any conventional or otherwise convenient manner and may comprise either a continuous or a batch type of operation. According to one method of operation, the olefinic hydrocarbon is continuously charged to a reactor containing therein a fixed catalyst bed comprising boron trifiuoride-modified zirconia, the reaction zone being maintained under the reaction conditions previously described. The reactor efiluent, comprising the isomerization reaction product, is continuously withdrawn from the opposite end of the reactor at a rate which will insure an adequate residence time therein. The hourly space velocity of the olefinic hydrocarbon starting material may be varied over a relatively Wide range. For example, a gaseous hourly space velocity of from about 50 to about 8000 or more is operable in the case of an olefinic hydrocarbon in the gaseous phase, while olefinic hydrocarbons in the liquid phase can be charged at a liquid 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.

Other suitable methods, including the moving bed type of operation in which the hydrocarbon charge is passed either concurrently or countercurrently to a moving catalyst bed, or a fluidized system in which the hydrocarbon is charged upflow through a dense catalyst phase in a reactor to maintain the catalyst in a state of turbulence under hindered settling conditions, may be utilized. 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 trifiuoride-modified zirconia 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. A batch type of operation is particularly suitable when processing a liquid hydrocarbon charge stock comprising olefinic hydrocarbons of a relatively high molecular weight, 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 containing stirring paddles, or a rotating autoclave.

Utilization of the present process to shift the double bond of an olefinic hydrocarbon to a more centrally located position results in a number of advantages. With respect to the catalyst activity of the boron trifiuoridemodified zirconia, optimum conversion of said olefinic hydrocarbon to the desired isomer or isomers thereof is readily obtained under mild operating conditions. For example, the Z-butene content of a charge stock, resulting from the conversion of l-butene in contact with said boron trifiuoride-modified zirconia at a temperature of about C., approaches thermodynamic equilibrium composition. In addition the migration of the double bond is not usually accompanied by skeletal rearrangement within the molecule.

The boron trifiuoride-modified zirconia, 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 art. 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 trifiuoride 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 zirconia can be placed in a bed within the reactor subsequently to be used in the isomerization process. The boron trifiuoride is then passed through the zirconia bed at a predetermined temperature whereby the desired catalyst composition is attained. The catalyst thus prepared stands ready for use in the double bond isomerization reaction process.

The following examples are presented in illustration of the specific embodiments of this invention and are not intended as an undue limitation of the generally broad scope of this invention.

Example I Zirconia was prepared by dissolving zirconium carbonate in nitric acid and precipitating zirconium hydroxide by the addition of ammonium hydroxide. The zirconium hydroxide precipitate was filtered from the solution, water washed, and dried. After drying, the zirconium hydroxide became powdery, and it was calcined at a temperature of about 650 C. for a period of about hours. X-ray diffraction analysis of the zirconia indicated that it consisted solely of the monoclinic crystalline zirconia containing about 3.20 wt. percent volatile matter (presumably water) which is the weight loss experienced upon heating the zirconia at 900 C.

A portion of the above zirconia was treated with boron trifluoride by passing the same over the zirconia at 150 C. until boron trifluoride was observed in the effiuent gas stream therefrom. After boron trifluoride-modification, the zirconia contained 1.0 wt. percent boron and 1.9 Wt. percent fluorine. It had an apparent bulk density of 1.925 g. per ml. and its color was a light grey.

About an 85% conversion of l-butene to the 2-butene isomer thereof is effected on passing a light vapor overhead from a catalytically cracked gas oil, containing about 25% l-butene, through a fixed bed comprising about 60 cc. of the above-described boron trifluoride-modified substantially anhydrous zirconia, at a gaseous hourly space velocity of about 361, an isomerization temperature of about 150 C., and at a pressure of about 525 p.s.i.g.

Example 11 This example serves to illustrate the relative inactivity of boron trifluoride per se with respect to the isomerization of l-butene as herein contemplated. A normally gaseous hydrocarbon charge stock comprising 60.7 wt. percent l-butene and admixed with about 365 p.p.m. boron trifluoride based on the total charge, continuously charged through a 60 cc. reaction zone packed with 31 stainless steel helices at a temperature of about 120 C., and at a rate of about 80 g. per hour, resulted in a reaction product substantially as charged and comprising 61,.4 wt. percent l-butene.

Example III A charge stock comprising l-pentene, continuously charged to a fixed bed of about 30 grams of the abovedescribed boron trifluoride-modified zirconia at an isomerization temperature of about 150 C., at a rate of about 50 g. per hour, and at a pressure of about 275 p.s.i.g., is converted to an efiluent stream comprising about of the desired Z-pentene isomer of said 1- pentene.

Example IV A charge stock comprising l-hexene, continuously charged to a fixed bed of about 30 grams of the above-described boron trifluoride-modified zirconia at an isomerization temperature of about C., at a rate of about 50 grams per hour, and at a pressure of about 200 p.s.i.g., is converted to an effluent stream comprising the 2-hexene isomer and the 3-hexene isomer of said l-hexene.

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 consists essentially of isomerizing said olefinic hydrocarbon in contact with a preformed combined boron trifluoride-zirconia catalyst prepared by treating substantially anhydrous zirconia with boron trifluoride at a temperature of from about 50 C. to about 250 C. until boron trifluoride no longer combines with the zirconia.

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 consists essentially of isomerizing said olefinic hydrocarbon at an isomerizing temperature of from about 20 C. to about 250 C. and in contact with a preformed combined boron trifluoride-zirconia catalyst prepared by treating substantially anhydrous zirconia with boron trifluoride at a temperature of from about 50 C. to about 250 C. until boron trifluoride no longer combines with the zirconia.

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 ig l-pentene.

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

References Cited by the Examiner UNITED STATES PATENTS 2,766,312 10/56 Serniuk 260683.15 2,924,629 2/ 60 Donaldson 260 683.2 2,939,890 6/60 Hervert et al. 260-671 3,054,834 9/62 Hervert et a1. 260-671 3,114,785 12/63 Hervert et al 260683.2

PAUL M. COUGHLAN, Primary Examiner. ALPHONSO D. SULLIVAN, Examiner.

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 CONSISTS ESSENTIALLY OF ISOMERIZING SAID OLEFINIC HYDROCARBON IN CONTACT WITH A PREFORMED COMBINED BORON TRIFLUORIDE-ZIRCONIA CATLYST PREPARED BY TREATING SUBSTANTIALLY ANHYDROUS ZIRCONIA WITH BORON TRIFLUORIDE AT A TEMPERATURE OF FROM ABOUT 50*C. TO ABOUT 250*C UNTIL BORON TRIFLUORIDE NO LONGER COMBINES WITH THE ZIRCONIA.