US2378208A - Production of synthetic benzene - Google Patents

Description

' hibitive.

Patented June 12, 1945 v 2,378,208 raonuo'rron or srn'rnnrrc BENZENE Donald L. Fuller and Bernard S. Greensfeider,

Oakland, Calif., assignors to Shell Development Company, San Francisco, Calif., a corporation of Delaware No Drawing. Application July 6,1942,

Serial No, 449,971

8' Claims. (01. 260-668 This invention relates to a process for the production of synthetic aromatic hydrocarbons and particularly synthetic benzene.

In view of the limited supply of benzene available from coal tar, various processes have been proposed whereby this exceedingly important chemical may be produced from other sources. The most important of these other sources is petroleum and its related products.

One method for the production of benzene from petroleum involves the separation and recovery of the naturally-occurring benzene found in certain low-boiling straight run and cracked gasoline fractions. This source is relatively unattractive. The available straight run naphthas usually contain only very small concentrations of benzene and the cost of recovery is usually pro- Cracked naphthas contain large amounts of olefins and some diolefins and, although the concentrations of benzene are appreciable, the problem of recovery of the benzene is again difficult and expensive.

Another method for the production of benzene from petroleum involves the synthesis of benzene from n-hexane. This synthesis is effected by contacting vapors of n-hexane under known cyclization conditions with a cyclizing catalystmore particularly chromium oxide. This method has the disadvantages that the process must be effected with short cycle operations, the equipment costs are high, and the yields are relatively poor. Consequently, although the process has been known for some time and has been. the subiect of much experimentation, it has never been practically applied.

A third often-'proposed method for the pro duction of benzene from petroleum involves the synthesis of benzene from the cyclohexane found to occur in small percentages in certain naphtha fractions. This is effected by first carefully fractionating the naphtha to separate a fraction containing the highest concentration of cyclohexane, subjecting the slaparated cyclohexane fraction to a catalytic dehydrogenation treatment, and finally recovering or concentrating the benzene so formed. In this method any one of a large number of dehydrogenation catalysts such as the oxides or sulfides of the heavy metals of roups IV to VIII of the periodic system of the elements can be used, the reaction may be effected under substantial hydrogen pressure, and.

the recovery of the benzene from the dehydrogenated products presents no special difficulties. This method therefore is believed to be the most promising of the hitherto known methods.

It is now found that aromatic hydrocarbons and particularly benzene may be produced directly by catalytic means from a totally different starting material, namely methyl cyclopentane. It is furthermore found that naphthenic petroleum fractions of suitable boiling range .contain appreciable quantities of this hydrocarbon, and that such fractions constitute a suitable starting material-for the production of very large quantities of synthetic benzene of any desired degree of purity.

According tothe process of the present invention aromatic hydrocarbons and particularly benzene are synthesized directly ,by catalytic means from methyl cyclopentane. As a starting material pure methyl cyclopentane or a methyl cyclopentane fraction consisting largely of methyl cyclopentane from any source may be employed. The most available and inexpensive source of methyl cyclopentane is in the so-called .naphthenic distillates such as straight run distillates from naphthenlc petroleums. Thus, for example, typical California petroleums contain between about 0.3% and 0.6% methyl cyclopentane. Straight run distillates, boiling, for example, between F. and 223 F., from such petroleums contain much higher concentrations,

for example, 5% to 12%. When the large amountsof these available distillates are considered, it is seen that-the potential supply of benzene producible by the process of the invention is indeed large. This potential supply of synthetic benzene, especially if added to the potential supply producibleby the above-described known methods, greatly enhances the available reserves.

According to the process of the invention such naphthenic' distillates are subjected to a fractional distillation to separate a relatively narrow boiling fraction containing substantially all of the methyl cyclopentane present and as little of higher and lower boiling constituents as the economy of the fractionation allows. By suitable fractionation a fraction boiling between 150 F. and 185 F. and containing about 30% to 40% methyl cyclopentane may be easily obtained. By fractionation to a narrower boiling range, for example 150 F. to F., fractions consisting predominantly of methyl cyclopentane can be obtained. Such a fraction contains only about 1% to 12% of cyclohexane.

The methyl cyclopentane fraction is treated under appropriate conditions with a specific catalyst, namely molybdenum oxide. Of the many common dehydrogenation catalysts such as chromium oxide, tungsten oxide, vanadium oxide,

titanium oxide, iron oxide, platinum, nickel, pai- V ladium, copper, and the metal sulfide dehydrogenation catalysts, the only one found to afford the desired result is molybdenum oxide. Chromium oxide is totally unsuitable. Certain ob- 1 active alumina, if this is employed, may suitably be stabilized against conversion into inactive alpha alumina by the admixture of a minimum amount of clay-or by the conversionof at least the surface into an alumina of the spinel type, for instance by reaction with calcium oxide, magnesium oxide or the like. Effective amounts of molybdenum oxide to be applied to such carrier or supporting substances are, for instance, from about 4% to about 80% (i. e. 3% to 22.5% molybdenum).

The treatment of the methyl cyclopentane with the above described catalyst may be effected under various conditions within the following approximate limits:

Temperature -C Pressure atm-- 2-25 Liquid hourly space velocity 0.1-1 Partial pressure of hydrogen .-atm 1-30 By liquid hourly space velocity is meant the volumes of liquid contacted (in the vapor form) per volume of catalyst per hour. Thus, a liquid hourly space velocity of 3 signifies that for every volume of reactor space filled with catalyst there is fed the vapors of three volumes of liquid.

Suitable preferred conditions are for example:

Temperature ..C About 490 Pressure About Liquid hourly space velocity About 0.5

Partial pressure of hydrogen..---atm About '7 Since these conditions are substantially equivalent to the conditions commonly employed in hydroforming higher boiling gasolines, they will be referred to hereinafter and in the appended claims as hydroforming conditions."

When treating the above-described methyl cyclopentane fractions under these conditions the following reaction predominates:

Side reactions, such as cracking and condensation to polynuclear hydrocarbons, etc., take place only to a minor extent. The conversion product therefore consists essentially of benzene with lesser amounts of polynuclear aromatic hydrocarbons.

The treatment of the methylcyclopentane or methylcyclopentane fraction may be effected in ,any one of the known suitable manners for effecting similar reactions, such as hydroforming,

with similar catalysts. Thus, the catalyst may be employed in a finely divided, granular, or pelleted form in converters of suitable design for such catalysts. A suitable method is, for example, to support the catalyst in granular or pelleted form in a reaction converter provided asvaaos with heating and temperature controlling means and to pass the vaporized methyl cyclopentane fraction in admixture with, for example, from 2 to 5 volumes of hydrogen therethrough. The catalyst is periodically regenerated by burning oif deposited carbonaceous matter with oxygen or an oxygen-containing gas in the known manner.

The product obtained from the catalytic treatment contains large amounts of benzene, for example, 40-70%. This product may be used per so, if desired, but it is most advantageously treated to recover the benzene in a pure or more concentrated form. For example, the product may be simply fractionally distilled to recover a relatively pure benzol or a crude benzol which may be further refined in the manner now used for the refining of coal tar benzol. Also, the benzene may be recovered either with or without a preliminary fractionation, by solvent extraction and/or azeotropic or extractive distillation in the known manner. The benzene produced by the present process is relatively free of sulfur compounds and in this respect is superior to the coal-tar product. However, a wash with dilute sulfuric acid is sometimes required as a final finishing step. In this way substantially pure benzene which can be made to meet the most rigid specifications may be efiiciently produced.- The process of the invention is illustrated by the following examples which it is to be understood are not intended to limit the invention in any way.

Example I Methyl cyclopentane was vaporized, the vapors mixed with 5 volumes of hydrogen and the mixture passed over a molybdenum oxide-alumina catalyst (14% M0) at a temperature of 490 C., a pressure of 20 atmospheres and a contact time of about 100 seconds. The yield of liquid product was 79% by volume (the theoretical volume yield based on 100.; conversion of the methyl cyclopentane to benzene is 79%) and the product contained about 2% by weight olefins. The

weight percentages of aromatics in theproduct after various periods of treatment without regeneration of the catalyst were as follows:

Methyl cyclopentane was converted as described in Example I except that the mole ratio of hydrogen to methyl cyclopentane was '3 and the total pressure was 10 atmospheres. The

7 weight percentages of aromatics in the product after various periods of treatment without re-- generation of the catalyst were as follows Per cent aromat- Hours its In later experiments with the same catalyst under the same conditions the corresponding yield of aromatics was:

Per cent Per cent Hours aromat- Hours aromatics ics Example II I Ier cent aromatics Eonrs 50 sec. 30 sec.

-We claim as our invention:

1. A process for the production of benzene which comprises treating a hydrocarbon fraction consisting essentially of methyl cyclopentan under hydroforming conditions with a molybdenum oxide catalyst and produce benzene as principal conversion product.

2. A process for the production of benzene which comprises treating a hydrocarbon. fraction consisting essentially Of methyl cyclopentane under hydroforming conditions with a molybdenum oxide-alumina catalyst and produce benzene as principal conversion product.

3. A process for the production of benzene which comprises treating a hydrocarbon fraction consisting essentially of methyl cyclopentane un der hydroforming conditions with a catalyst consisting essentially of an active alumina impregnated with molybdenum oxide and produce benzene as principal conversion product.

4. A process for the production of benzene from naphthenic petroleum distillates which comprises fractionally distilling a naphthenic petroleum distillate to separate a. methyl cyclopentane fraction boiling predominantly between 150 F. and 185 F. and treating said methyl cyclopentane fraction under hydroforming conditions with a molybdenum oxide catalyst so a to produce benzene as predominant conversion product.

5. A process for the production of benzene from naphthenic petroleum distillates which comprises fractionally distilling a naphthenic petroleum.

distillate to separate a methyl cyclopentane fraction boiling predominantly between 150 F. and 185 F. and treating said methyl cyciopentane fraction under hydroforming conditions with a molybdenum oxide-alumina catalyst so as to produce benzene as predominant conversion product.

6. A process for the production of benzene from naphthenic petroleum distillates which comprises fractionally distilling a naphthenic petroleum distillate to separate a methyl cyclop'entane fraction boiling predominantly between 150 F. and 185 F. and treating said methyl cyclopentane fraction under hydroforming conditions with a.

catalyst consisting essentially of an active alumina impregnated with molybdenum oxide so as to produce benzene a predominant conversion product. 1

7. A process for the production of benzene which comprises passing a. hydrocarbon fraction consisting essentially of methylcyclopentane over a catalyst comprising molybdenum oxide under hydroforming conditions so that benzene is produced as predominant conversion product.

8. A process for the production of benzene which comprises contacting a hydrocarbon fraction consisting essentially of methylcyclopentane with molybdenum oxide at 450 to 525 C. under a partial pressure of hydrogen of 1 to 30 atmospheres and at a liquid hourly space velocity for the fraction treated of 0.1 to 1.

DONALD L. FULLER. BERNARD S. GREENSFELDER.