US2278934A - Process and catalyst for conversion of normal paraffins - Google Patents

Description

finic hydrocarbons.

Patented Apr. 7, 1942 PROCESS AND CATALYST CONVERSION I OF NORMAL PARAFFINS Milton W. Lee,

.Union Oil Company of Calif.,' a corporation of California Long Beach, Calif., assignor to California,

Los Angeles,

No Drawing. Application September 6, 1938, Serial No. 228,645

Claims. (Cl. 260-676) The invention relates to the treatment of hydrocarbons, and particularly pertainsto the conversion of normal or straight chain paraflinic hydrocarbons into isoor branched chain paraf- In one of its specific embodiments the invention consists of a process which involves the use of special catalyst mixtures and of specific conditions of operation for the realization of this isomerization of normal paraffinic hydrocarbons.

, Although the process of isomerization disclosed herein is described with-particular reference to the transformation of normal butane into isobutane, it is to be understood that the invention is applicable with equal tion of any normal paraffin with a molecular weight higher than that ess may therefore be applied to the isomerization of normal butane which is usually gaseous under normal or room temperatures and pressures-and to the open chain parafllnic hydrocarbons which are generally liquid or the normal pentanes, hexanes, heptanes and higher hydrocarbons of thisv series. Generally speaking, the isomerization reaction displaces one or more carbon atoms of the molecule towards the center thereof. The process, therefore, in-' cludes not only the isomerization of the'straight.

force to the isomerizaof propane. The proc-' solid, and which include fuels.

boiling isoparamnic hydrocarbons, such asisobutane and isopentane, these, together with the higher boiling normally liquid isoparafflns; find commercial use in the preparation or production of the higher branched chain hydrocarbons boiling within the gasoline range and .having high anti-detonating characteristics. As an example, isobutane is now employed as a starting material in the alkylation process for the manufacture of branched chain hydrocarbons suitable as motor These branchedchain saturated hydrocarbons are comparatively easily formed by reacting the isobutane or similar isoparafiins with certain olefins in the presence of an alkylating catalyst. In view of the outlined importance and commercial value of the isoparaflinic hydrocar-- bons, the main object of the present invention is to provide a process for realizing the isomerization of paraflinic hydrocarbons. It is a further object of the present inventionto provide a process and catalyst for effecting an economic isomerization of normal parafiins wherein high yields of isoparaflins are obtainable.

Recently it has been discovered that the isomerization of normal or straight chain paraflinic hydrocarbons can be realized by effecting the isomerization reaction at superatmospheric temchain or normal parafiinic hydrocarbons, but also I of the parafinic hydrocarbons, the structure of which, although already ramified to a certain degree, may be further modified by such isomerization to produce hydrocarbon molecules of a relatively more condensed or centralized struc-- ture. As an example, normal hexane may be isomerized. for example, to 2-methyl pentane. Also the partially isomerized hexane, such as 2- methyl pentane may be transformed according to the present process to produce 2,3-di-methyl butane, which is a compound relatively more condensed than 2-methyl pentane.

Insofar as the petroleum industry is concerned, the isoparaflinic and branched chain paraflinic hydrocarbons are considered to be of greater commercial value than the corresponding normal or straight chain paraflins. This is particularly true as far as the lower paraflinic hydrocarbons are concerned, particular reference being made to hydrocarbons boiling below and within the gasoline range. Thus, it is well known that the branched chain paraflinic hydrocarbons, such as iso-octane (which boils within the gasoline peratures and at pressures'sufficient to maintain the hydrocarbons substantially in the liquid state. Thus, it has been brought out that the rate of conversion and the yield of ramiiied or branched chain paraffins may be greatly increased by subjecting straight chain paraiiins in the presence of an aluminum bromide catalyst to superatmospheric temperatures and at least equilibrium pressures of the reacting mixture at range) possess anti-detonating characteristics corresponding As to the lower the temperature employed. The aluminum bro mide, at least at the temperatures and pressures described more fully hereinbelow, is substantially soluble in the normal paraflins of the type of normal butane and normal pentane. Thus, aluminum bromide is completely soluble in'normal pentane even at atmospheric temperature. As to the solubility of aluminum bromide in normal butane, most of the catalyst, in the quantities employed for the isomerization of normal butane, is soluble in the hydrocarbon under the preferred operating conditions. i

The optimum temperatures and pressures to be employed for theisomerization of a given paraflinic hydrocarbon will vary with the character and nature of the specific product treated. Also, the optimum operating conditions may change with the catalyst employed. When conducting the reaction in the presence of aluminum 2- I bromide, the lower temperature limit is in the neighborhood 0. 125 to 150 F. As to the upper limit, unless contemporaneous cracking is desired, the temperature must not exceed the dissociationor cracking temperature of the given paraflinc hydrocarbons. Since the pressures to be em-/ ployed must be such as to maintain the hydrocarbons substantially in the liquid state, these presmused, and

as to yields by conducting this reaction in the presence of a catalyst containing carbon and par-' ticularly, activated carbon. Thus; it has been discovered that the normal or straight chain parafiinsas well as the partially ramified or isomerized hydrocarbons can be converted into hydrocarbons having relatively more condensed molecules, by contacting the hydrocarbons at optimum temperatures and pressures for a period of time with a catalyst comprising aluminum bromide and carbon. It has been still further discovered that the presence of the "carbon increases the yield of isomers or branched chain hydrocarbons when compared with the results obtained from treatment of paraiflnic' hydrocarbons under identical conditions but for the absence of the carbon-in the catalyst mixture. The carbon mayeither be granulated or powdered and may be of any source. Thus, excellent yields were obtained irom the use of a catalyst containing aluminum bromide and activated carbons derived from wood, bone or vegetables.

'. tion also resides vated carbo As stated above, and as shown by the=examples presented hereinbelow, the presence of activated carbon greatly increases the yield of isomers. The exact reason for the catalytic action of the carbon, when used in connection with aluminum bromide, is not known at the present time. 1 However, it is not believed that the carbon acts merely as a distender or carrier agent. This is proved by the fact that experiments conducted under identical conditions but using certain natural and artificially treated clays instead of granulated or powdered charcoal, have produced yields of branched chain hydrocarbons which were not only lower than those obtained from the isomerization reactions employing aluminum bromide and activated carbon, but also from those reactions in which aluminum bromide was employed as the sole isomerizing catalyst. Since the clays employed in the comparative tests are known to be carriers or distending agents, the use of these substances in connection with aluminum bromide should have produced comparable results if the activated carbon acted simply as a carrier. The negative results and the greatly reduced yields prove that carbon does notmerely act as a carrier but that its use in connection with aluminum bromide catalyzes the reaction. Furthermore, as brought out hereinabove, aluminum bromide is substantially soluble in the normal paraiiins of the type of normal butane and normal pentane, at least at the operating temperatures and pressures. Under such conditions the activated carbon could not act as a carrier or distending agent since the complete solution of the aluminum bromide in the liquefied normal paraifins would cause intimate contact between the hydrocarbon molecules and the molecules of the catalyst, thus "fraction was then separated I agent.

The invention may therefore broadly reside in converting parafllnic isomers by conducting the isomerization reaction in the presence of a catalyst containing carbon, and particularly, activated carbon. The invenin realizing the above described isomerization reaction in the presence of a catalyst comprising aluminum bromide and acti- More specifically stated, the invention includes the conversion of normal or straight chain paraflins into branched chain paraflinic hydrocarbons by contacting the normal 'parafllns with a catalyst comprising aluminum bromide and activated carbon, and subjecting said mixture to superatmospheric temperatures and pressures sumcient to maintain the hydrocarbons substantially in the liquid state. In one of its specific embodiments the invention covers a process of isomerizing paraillnic hydrocarbons by contacting the hydrocarbons to be treated with aluminum bromide and activated carbon and subjecting the mixture to superatmospheric temperatures and pressures sumcient to maintain the hydrocarbons in a liquid state, thereby causing a substantial solution of the aluminum bromide in the hydrocarbon to be isomerized. The temperatures employed in the above process may vary from about F. to the dissociation temperature of the hydrocarbons treated. If simultaneous cracking of the hydrocarbons is not objectionable, higher temperatures may be employed. Since the reaction is to' be realized substantially in the liquid phase, the pressures should be at least equal to the equilibrium pressure of the mixture of the reaction temperature, thus maintaining a substantial solution between the hydrocarbons treated and the aluminum bromide portion of the catalyst.

The following examples are presented for the purpose oi showingthe beneficial results obtained by use of carbon in connection with aluminum bromide as the isomerizing catalyst. In all of the examples normal butane was subjected to isomerization. The aluminum bromide employed for the isomerization 01' this normal butane was used in a quantity equal to 25% by weight of the hydrocarbon treated.. In the examples in which the carbon was employed it comprised about 18% to 19% by weight or the butane treated. In each of the cases the reaction was conducted for a period of four hours at a temperature of 212 F. and at the hydrocarbon equilibrium pressure of approximately 220 pounds per square inch. The first two experiments presented herein were carried out in steel bombs which were washed with hydrochloric acid, and then with acetone and blown with air to remove any possible traces of acetone. In the next two experiments the inside walls of the steel bomb were glass lined, thereby tendingto prevent any reaction between the catalyst and the iron of the bomb. On the other hand, periments where carried out insteel bombs or vessels which had been heated to about 500 C. while being flushed with oxygen, and then cooled before the reactionswere conducted therein.

At the end of each experiment the bomb or vessel was first cooled prior to the withdrawal of the products of reaction. The hydrocarbon from the catalyst and analyzed for its normal tane content.

As stated, in a copending application, the preshydrocarbons into theirbutane and isobuence of excess or free bromine in the aluminum bromide catalyst is undesirable, at least when isomerization reactions ar conducted in steel or metal vessels. For this purpose and to prevent,-or at least, decrease to a possible minimum the free bromine content of the catalyst, the

aluminum bromide employed in the tests was manufactured by the inter-reaction of aluminum and bromine, the quantity of aluminum employed being about to greater than the quantity theoretically necessary the introduced bromine. Furthermore, the prodfor combining with ucts of reaction thus produced were then distilled j to remove most of the free bromine which has not reacted with the aluminum.

In the first experiment the normal butane was introduced into the steel bomb, treated as described above together with 25% of aluminum bromide, manufactured as described hereinabove, the two substances being soluble in each other. The solution was maintained under an equilibrium pressure of about 220 pounds for four hours at the temperature of 212 F. Thereafter,

the vessel was cooled and an analysis of the hy-' drocarbon fraction showed that 27% of the normal butane was converted into isobutane. 0n

the contrary, when 18% by weight of powdered action-in a glass lined vessel resulted in the con version of 41% of normal butane into its isomer. When, however, the same reaction was carried out by employing the aluminum bromide and about 19% by weight of granulated, activated carbon the yield of isomers recovered from the glass lined vessel was found to be about 74% of the starting material.

As stated in the third groupof examples, the steel bomb was first washed with water and then heated to about 500 C. while being flushed with oxygen. After cooling, two experiments were conducted under substantially the same conditions as those described hereinabove. Thus, the first experiment was carried out on a mixture of normal butane in the presence of about 25% by weight of aluminum bromide, while in the rate so that 68% by weight of the product was isobutane.

The above described examples clearly indicate the advantages of isomerizing normal parafiinic hydrocarbons, such as butane, pentane, etc., in the presence or an aluminum bromide catalyst containing carbon. Thus, the data presented herein shows that the addition of carbon increased the yield by as-much as 137%. It is obvious that the invention is not limited to the treatment of normal butane, but is equally applicable to the isomerization of other normal parafiins, as well as to a treatment or isoparafiinic hydrocarbons to produce hydrocarbon molecules of relatively more condensed type. It is also to be understood that there is no intention to be limited to any temperatures or pressures indicated herein.' Thus, it \is possible to operate-at different temperatures, preferably while employing equilibrium pressures, thus ensuring liquid phase treatment. Obviously, although higher temperatures causes a more rapid rate of reaction, it is highly desirable to operate at temperature which are below the dissociation or cracking temperature of the given hydrocarbon under treatment.

The above examples are to be considered as exemplary of the invention, which is limited only by the appended claims.

I claim:

1. A process for converting normal paraflinic hydrocarbons into branched chain hydrocarbons which comprises dissolving aluminum bromide in said hydrocarbons to be treated and conductsecond experiment bone charcoal wasadded in a quantity equal to about 18% of the treated butane. In both examples, the mixture was kept under the equilibrium pressure of about 220 pounds per square inch for fourhours at the temperature of. 212 F. After cooling, the hydrocarbon phases were analyzed, and it was found that whereas 53% of the butane was isomerized into iso-butane in the first experiment, the presence of carbon increased the conversion ing the isomerization reaction in the .presence of said aluminum bromide and activated carbon at temperatures in excess of F. but below' the temperature at which any substantial cracking takes place.

2. In a process according to claim 1, wherein the isomerization reaction is realized at superatmospheric temperatures, but below the dissociation temperature of the hydrocarbons, and at pressures sufllcient to maintain the hydrocarbons substantially in a liquid state.

3. A process for converting normal butane into isobutane which comprises commingling said normal butane with a catalyst containing aluminum bromide and activated carbon and conducting the isomerization reaction in a liquid state and at temperatures above about 125 F.

4. A process for converting normal butane into isobutane which comprises commingling said normal butane with aluminum bromide and activated carbon, heating said mixture to superatmcspheric temperatures for a period of time willient to cause conversion, while maintaining a pressure suiiicient to keep the butane substantially in the liquid phase, cooling-the mixture,

and separately recovering the isobutane.

5. A catalyst suitable for the conversion of normal paraflinic hydrocarbons into isoparafllnic hydrocarbons, said catalyst comprising a mixture of aluminum bromide and activated carbon.

MILTON W. LEE.