US2318226A - Production of isobutane - Google Patents

Description

Patented May 4, 1943 PRODUCTION OF ISOBUTANE Vladimir N. Ipatiefl' and Herman Pines, Chicago,

Ill., assignors to Universal Oil Products Company, Chicago, 111., a corporation Delaware N'o Drawing. Original application September 30, 1936, Serial No. 103,383.

Divided and this appllcation'March 16, 1942, Serial No. 434,904

3 Claims.

This is a division of our co-pending app c tion Serial No. 103,383, filed September 30, 1936.

This invention relates particularly to the treat- ;nentof butane of normal or straight-chain strucure.

In a more specific sense, the invention is com cerned with a process whereby normal butane is converted into isobutane, the process involving the use of special catalysts and particular conditions of operation which favor the isomerization reactions so that relatively high yields of the lso-compound are produced.

Since the invention is concerned principally with the two 4-carbon atom parafiin hydrocarbons and their transformation, one into the other,; the following table is introduced to indicate the structure and the principal physical characteristics of these two compounds:

Butanes are produced in considerable quantities in the oil refining industry. They occur in gasoline of desirable starting characteristics according to seasonal demands.

The butanes at the present tim bear a further important relationship to oil refining in that their excess production is being utilized as a source of gasoline either by ordinary thermal crackin or by special catalytic dehydrogenation processes followed by polymerization in which catalysts substantial amounts in natural gases (in which the normal compound usually predominates), in refinery gases which are evolved from crude petroleum storage tanks, and in the primary distillation of crudes, and they are also present in considerable percentages in the gases produced incidental to cracking heavy petroleum fractions for the production of gasoline. In the case of cracked gas mixtures the relative proportions of iso and normal butanes va y. but the ratio of the iso to the normal compound is as a rule considerably higher than in natural gas.

Butanes may be considered as more or less marginal compounds in respect to their desirability in ordinary gasoline, that is, a certain percentage of them is essential for sufliclent vapor pressure to insure ease in starting, while 'an excess tends to produce vapor lock. For these reasons the total percentage of 4-carbon atom hydrocarbons is commonly adjusted in conjunction with the boiling range and vapor pressure of the other gasoline component to produce a may or may not be used. Investigations have shown that iso-butane is considerably more amenable to cracking and dehydrogenation, both with and without catalysts, than the normal compound. Considering the corresponding monoolefins. the normal butenes are considerably more dlflicult to polymerize, either thermally or catalytically, than isO-butene, and it is found also that the octenes representing the dimers of the isobutene are of higher antiknock value than those from n-butenes which holds also for the octanes produced by hydrogenation. It is, therefore, of considerable importance at the present time to convert as much as possible of, the normal butane production into iso-butane, and he present invention is especially concerned with a process for accomplishing this object.

In one specific embodiment the present invention comprises the treatment of normal butane for the isomerization thereof into isobutane with catalysts comprising essentially metallic halides at elevated temperatures and superatmospheric pressures.

In a preferred embodiment the catalysts comprise essentially heavy metal chlorides and hydrogen halides.

We have determined that by the use of the class of catalysts mentioned, and particularly by the convenient use" of considerable superatmospheric pressure normal butane may be converted into iso-butane with a. yield of as high as to Evidently the use of superatmospheric pressures of the order of 10 to 50 atmospheres at temperatures of C. and higher, besides depressing the volatilization of granular catalysts tends also to, depres numerous undesirable side reactions which would result in the formation of. hydrogen and low molecular weight hydrocar- I bons, so that the reaction proceeds more or less in one direction until an equilibrium is established. 1

There are several alternative catalysts which may be employed in accomplishing the present isomerization reaction and, while they may be used more or less interchangeably, some are more effective than others and it is not intended to infer that they are equivalent. Among the compounds which may be employed may be mentioned aluminum chloride, zinc chloride, iron chloride, zirconium chloride, stannic chloride and boron fluoride. Experiments have indicated that best results are obtained when a minor percentage of a hydrogen halide is present in the reactions along with these compounds. Some of the compounds may be employed either in the dry state or in aqueous solution with suitable modifications of operating conditions. In the case of such compounds as aluminum chloride, which readily sublimes, stannic chloride, which boils at 114 0., and boron fluoride, which is normally gaseous, these are most conveniently employed in the anhydrous condition, the hydrogen halides, such as for example hydrogen chloride or bydrofluoric acid, being separately introduced in the gaseous state. There will be some variations in the relative amounts of metal salts and hydrogen halides used at optimum treating conditions, but the determination of the best ratios is somewhat a matter of experiment.

The process may be operated under batch or continuous conditions. Choosing aluminum chloride and hydrogen chloride as example of jointly used catalytic materials, batch operations may be conducted by separately adding aluminum chloride, hydrogen chloride and normal butane to a closed pressure container, after which the container is agitated or the contents stirred mechanically while the temperature and pressure are raised by the application of external heat to produce a temperature corresponding to maximum production of the iso-compound. This type of operation is better adapted to small scale production, and plants of considerable capacity are best operated in a continuous manner. In continuous operations the butane may be pumped through a tubular heating element at a given temperature and pressure within the approximate ranges previously specified and reaction brought about along the line of flow by the separate or joint injection of proportioned amounts of metal salts and hydrogen halides, the best example of this type or operation being the combination of aluminum chloride and hydrogen chloride or boron fluoride and hydrogen fluoride.

In the absence of moisture there will be substantially no corrosion when using these substances. After passage through the heating element the reactants may be passed to enlarged insulated chambers for the completion of the desired isomerization and the total products subsequently fractionated to recover catalysts and separate the normal and iso-butanes, after which the normal compound may be recycled for further treatment.

Continuous operations may also be conducted by passing normal butane mixed with a hydrogen halide through beds of heated, granular catalyst, which may comprise any of the solid salts mentioned, either alone or mixed with carrying or spacing materials of a relatively inert character. This type of operation is readily utilizable in the case of such compounds as zinc chloride, iron chloride and stannic chloride. Treatment of the products in these cases will involve merely the condensation of the hydrocarbon products and the recycling of the hydrogen halides for further use.

The following examples are introduced to indicate in a general way the nature of the results obtainable by theme of the process, though they are not introduced with the intention or correspondingly limiting the scope of the invention.

Example I 100 parts by weight of normal butane, parts by weight of aluminum chloride and 2 parts by weight of hydrogen chloride were introduced under a pressure of about five atmospheres into a pressure vessel, which was then rotated and heated for twelve hour-s at an average temperature of 150 C., the maximum pressure developed being about 30 atmospheres. After the bomb was cooled the hydrocarbons were released and fractionated and it was found. that they consisted of 66.5% of iso-butane and 31.9% of normal butane. This indicates that the equilibrium under these conditions is considerably in favor of iso-butane.

Example I[ In this operation normal butane was passed through a tubular heating element and then into an enlarged reaction chamber, into which sublimed aluminum chloride and hydrogen chloride gas were introduced. A pressure of about to atmospheres and a temperature of 160" C. were maintained on the reaction vessel, after which the reaction products were separated and it was found that the hydrocarbons consisted of about 63% iso-butane and 32% normal butane. This indicates a selective conversion of the normal butane into iso-butane under these conditions.

Example 11 I In this case the catalyst employed was a composite consisting of about parts by weight of ground pumice and 50 parts by weight of substantially anhydrous zinc chloride. This material was placed in a vertical cylindrical reaction chamber which was insulated to conserve heat and the normal butanelwas preheated to a temperature of approximately 200 C. and passed downwardly through the contact mass under a pressure of approximately 30 atmospheres. Approximately iso-butane and 30% normal butane were found in the reaction products, the remaining 10% comprising lighter fixed gases and other reaction products.

Example IV Normal butane was preheated to a temperature of approximately C. and passed into an insulated reaction chamber at the same time as boron fluoride and hydrogen fluoride were injected. The reaction chamber was nickel-lined, as this was found to further accelerate the isomerization reactions. An analysis of the hydrocarbon products showed that they consisted of approximately 62% by weight of iso-butane and 32% by weight of normal butane, the remaining products being lighter gases and some heavier polymerized products.

The character of the present invention and its value commercially have been shown respectively by the foregoing specification and examples introduced although the proper scope of the invention is not limited in exact correspondence with the descriptive o r numerical sections.

We claim as our invention:

l. A process for producing iso-butane which comprises subjecting normal butane to the action of boron fluoride in the presence of metallic nickel under conditions and in the presence of an amount of hydrogen halide such that isomeriza- 7 2,318,226 tion of normal butane constitutes the principal reaction of the process.

2. A process for producing iso-butane which comprises passing normal butane, hydrogen fluoride, and boron fluoride through a reaction zone containing metallic nickel therein maintained under isomerizing conditions. said conditions and the amount of hydrogen fluoride being such that