US2426824A - Production of synthetic toluene - Google Patents

Description

Patented Sept. 2, 1947 PRODUCTI O N F SYNTHETIC TOLUENE FROM PETROLEUMx Donald Lal-uller and Bernard S. Greensfelder,

Oakland, Calif., assignors to Shell Development Company, San Francisco, Calif., a corporation of Delaware This invention relates to an improvement in uene from naphthenic petroleum fractions. The object of the inventionis to provide an improved process whereby commercial grades of toluene may be produced.from naphthenic petroleum fractions in a betteryield.

In view of the limited supply of toluene from coal tar distillates considerable attention has been given in the last few years to the develop-- ment of processes for the production of commercial grades of toluene from other sources. As a result of much research several methods for the production of toluene from petroleum products have been developed. One of the most promising of these methods now in large scale commercial use produces substantially pure toluene from straight run naplithenic distillates. In order that the present invention and its relation to the art may be readily understoodwe will first describe the hitherto employed method.

The starting material in the known method is a substantially saturated naphthenic petroleum distillate such, in particular, as naphthenio straight run gasoline. This distillate is first subjected to a series of careful and efficient fractionations to separate a fraction having an initial boiling point of 205 F. or very close thereto and a final boiling point in the range of from about 218 F. to 230 F. This narrow boiling fraction is then subjected to a catalytic dehydrogenation treatment. Although almost any of the many Q he method for. the production of synthetic tol- I well known dehydrogenation catalysts may be centration, etc. for both the reaction and regeneration for eachv catalyst, and to solve numerous engineering. problems encountered, the chemistry and basic principles of the process are very simple.

It is known that naphthenic petroleum fractions contain appreciable concentrations of methyl cyclohexane. It is also known that this hydrocarbon may be easily and eiliciently dehydrcgenated with a wide variety of known de- 55 ciency of the fractionation equipment. It is thus methods of extraction and distillation.

Application .luly 27, 1942, Serial No. 452,548

3 Claims. (Cl. 260- 668) hydrogenation catalysts directly to toluene. It is also known that toluene may be separated in a substantially pure state from mixtures of substantially saturated hydrocarbons by known The principle of the above-described process is based upon these known facts and consists of separating a narrow boiling methyl cyclohexane fraction from the naphthenic distillate by fractional distillation, subjecting this fraction to a dehydrogenation treatment to dehydrogenate the methyl cyclohexane to toluene, and extracting the toluene from the product.

In addition to the numerous improvements of the above-mentioned nature which have been combined to make the process practical, the

been carefully chosen at 205 F. as afiording the maximum economy. Since the boiling point of f methyl cyclohexane is 213.4 E, it would be possible to employ a fraction having an initial boiling point somewhat higher than 205 F. This. however, considerably increases the necessary fractionation efiiciency and, hence, expense of the fractionation step, and is also apt to result in the loss of a small portion of the methyl cyclohexane due to the .formation of certain azeotropes which boil slightly below 213.4 F; On the otherhand, if the initial boiling point of the cyclohexane fraction is taken below 205 F., the concentration of methyl cycle mane in the fraction is materially lowered due to the inclusion of large amounts of other hydrocarbons. This greatly increases the amount of material to be processed. Also, most dehydrogenation catalysts such, in particular, as those comprising chromium oxide are much less efl'ective when the initial boiling point is below about 205 F. due to the poisoning effect of included dimethyl cyclopentanes. separated fraction may be just high enough to include all of the methyl cyclohexane, for instance, 215? F.220 F., but is usually about 230 F. The choice of these final boiling points depends upon the concentration of toluene occurring naturally in the straight run naphthenic distillate. If the concentration of toluene is sufficient to warrant the inclusion of the relatively large amount of inert hydrocarbons, the higher end point is chosen; otherwise, the end point is out at a convenient margin above the boiling point of methyl cyclohexane, depending upon the em- The upper boiling point of the Pressure seen that in principle the fractionation step is designed and carried out to eflfect the most efficient concentration of the desired methyl cyclohexane that is possible without increasing the fractionation costs to such an extent as to decrease the economy of the process as a whole.

The process of the present invention which is an improved modification of the above-described process evolved from the discovery that molybdenum oxide has the unique ability when used under certain conditions to simultaneously isomerize and dehydrogenate dimethyl cyclopentanes directly to toluene. This reaction, has, as far as we are aware, never been recognized and has never been specifically utilized. In the process of the invention we utilize this reaction along with' the above-described dehydrogenation of methyl cyclohexane to produce substantially increased yields of commercial grade toluene from naphthenic distillates of the class described. We

accomplish this by changing the boiling range of the fraction treated to include substantially all of the dimethyl cyclopentanes and employing a molybdenum oxide catalyst under the conditions drocarbons which all boil below 198 F. are in-' cluded in the fraction to be treated:

1,1-dimethyl cyclopentane B. P. 189.5 F. 1,2-dimethyl cyclopentane B.P. 197.2" F. 1,3-dimethyl cyclopentane B. P. 195.3 F.

Careful investigation into the composition of typical naphthenic distillates reveals that these hydrocarbons are present in appreciable concentrations and that the sum of their concentration nearly always exceeds the: concentration of methyl cyclohexane. Thus, the concentration of dimethyl cyclopentanes in the separated fraction usually exceeds the concentration of methyl cyclohexane and the fraction may therefore be properly called a dimethyl cyclopentane fraction. The considerable yields of toluene obtainable by the treatment of these dimethyl cyclopentanes is illustrated by the following example:

- A 185 F.--19'7 F. fraction (i. e. a fraction, 95%

4 (The contact time is the apparent residence time of the total influent material in the volume occupied by the catalyst bed computed on the basis of the simple gas laws for the specified temperature and pressure.) The product from the first three hours of processing contained 70% by weight of aromatic hydrocarbons, and that from the tenth to the twelfth hours of processing contained 59% by weight of aromatic hydrocarbons.

When the treatment was effected at a pressure of 5 atmospheres, other conditions being the same, the product from ten hours of processing was found to contain 83% by weight aromatic hydrocarbons. The aromatic hydrocarbons con sisted of toluene with minor amounts of higher molecular weight aromatic hydrocarbons, probably of polynuclar structure.

The final boiling point of the fraction separated according to. the process of the invention is preferably chosen between about 215 F. and 232 F., depending upon the concentration of naturally-occurring toluene and the efilciency of the fractionation equipment. In separating the desired dimethyl cyclopentane fraction an efficient preferably continuou fractional distillation equivalent to at least 20 theoretical plates is preferably employed. The fraction so sep-.

arated, upon being subjected to an analytical distillation, will, in general, show at least 95% boiling within the specified range. Analytical distillation, as herein defined, is a laboratory batch distillation operation over 30 equilibrium plates and at a reflux ratio of at least 20:1.

It will be seen that the fraction separated differs fundamentally from the fraction separated according to the known process. Thus, in the process of the invention substantially all of the dimethyl cyclopentanes are separated in a dimethyl cyclopentane fraction whereas in the hitherto employed process a methyl cyclohexane fraction is separated and dimethyl cyclopentanes are excluded as far as possible.

The dimethyl cyclopentane fraction boiling between the above-specified limits is subjected to a catalytic treatment with a' molybdenum oxide catalyst under conditions chosen to simultaneously convert both the dimethyl cyclopentaneg and the methyl cyclohexane to toluene. Whereas in the known process any one of a number of known dehydrogenation catalysts may be suitably employed and chromium oxide catalysts are often preferred, in the process of the present invention the only suitable catalyst so far found is molybdenum oxide. All of the other common dehydrogenation catalysts tested were found to convert only the methyl cyclohexane and to have of which .boils within 185 F. and 197 F. in an analytical distillation) was separated from a California straight run gasoline by fractional distillation. This fraction had a gravity of 59.8-

A. P. I. and a refractive index of 1.4047 20/D; Careful investigation of the fraction showed that it contained about 67% by. volume of naphthenic hydrocarbons consisting almost exclusively of 1,1-dimethyl cyclopentane, 1,2-dimethyl cyclopentane, and 1,3-dimethyl cyclopentane. This fraction was contacted with a molybdenum oxide/alumina catalyst (containing about 14% molybdenum) under the following conditions:

F 914 Temperature mm 10 Contact time sec 100 M01 ratio of hydrogen to hydrocarbon"--- 3 no appreciable ability to effect the desired simultaneous isomerization and, dehydrogenation of dimethyl cyclopentane to toluene. Tungsten sulfide and molybdenum sulfide appeared to-be slightly active. With molybdenum oxide catalysts under proper conditions, on the other hand,"

mina. The alumina may be either in: the form of alumina. alpha monohydrate or gamma alumina, or in the form of one of the stabilized aluminas produced by reacting an adsorptive gamma alumina with a small amount of an oxide of an alkali metal or alkaline earth metal. The preferred concentration of molybdenum oxide in the supported type catalyst is between about 4% and 30% by weight. Qther known molybdenum oxide dehydrogenation catalysts may, however, also be employed.

' The treatment with the molybdenum oxide catalyst is effected under conditions conducive to the desired conversion of the dimethyl cyclopentanes to toluene. The desired reaction may be effected at temperatures of from about 800 F. to about 1000 F. A preferred range is between about 850 F. and 950 F. The pressure may be from about2 to about 50 atmospheres. .A preferred range of pressure is between about 4 and 12 atmospheres. The liquid hourly space velocity may vary between about 0.1 and 1.2 depending upon the conditions of temperature and pressure chosen.

The reaction is eflected in the presence of a substantial concentration of hydrogen. Thus, a mol ratio of hydrogen to hydrocarbon of at least 1:1 and preferably about 3:1 is maintained in the reaction zone. As pointed out above, it is generally found that dehydrogenation catalysts function poorly when the feed contains appreciable concentrations of dimethyl cyclopentane. This is particularly pronounced in the case of the chromium oxide usually preferred for such treatments. Molybdenum oxide catalysts, we have found, are comparatively little affected by these hydrocarbons and this adverse efiect is furthermore substantially eliminated by the use of suitable partial pressures of hydrogen. Most other dehydrogenation catalysts such as chromium oxide, on the other hand, lose a. substantial part of their activity when applied under substantial partial pressures of hydrogen. The partial pressure of hydrogen depends upon the operating pressure and the mol ratio of hydrogen to hydrocarbon in the feed. Suitable partial pressures of hydrogen range between about 0.5 to 25 atmospheres depending upon the severity of the reaction conditions but are in no case sufllciently high to cause substantial amounts of destructive hydrogenation. Under these conditions the reaction takes place in the vapor phase. The abovespecified operating conditions are hereinafter referred to as hydroforming conditions.

The treatment with themolybdenum oxide catalyst may be effected in any of the conventional manners commonly employed in effecting various vapor phasedehydrogenation reactions under approximately similar conditions with solid catalysts. Thus, for example, the process may be eitected by passing the hydrocarbon vapors with recycled hydrogen through a fixed bed oithe molybdenum catalyst, or concurrently or countercurrently with a moving bed or the catalyst. Also, it is possible to execute the reaction with the catalyst in a finely divided state either by a system wherein the catalyst is carried with the reactant vapors through the reaction zone or by a so-called hindered settling system. Inon'e suitable method, for example, the catalyst is maintained under suitable reaction conditions in a plurality oi catalyst cases and the vaporized hydrocarbon feedis admixed with the desired mol ratio of recycled hydrogen andpassed through theflxedcatalyst beds.

During use the catalyst gradually declines in activity due to the deposition thereon of carbonaceous matter. This deposited matter is periodi cally removed from the catalyst by a careful burning or regeneration treatment in the known manner. Y The product from the treatment with the molybdenum oxide catalyst contains substantial concentrations of toluene in admixture with appreciable amounts of paraflins, small amounts of unreacted naphthenes, small amounts of other aromatic hydrocarbons, and sometimes small amounts of olefins. This product is preferably subjected to a fractional distillation to remove small amounts of materials boilin above toluene and then treated in one of the known manners to recover the toluene in a substantially pure state. Any of the known methods may be employed. For instance, the product may be mixed with a higher boiling parafiinic naphtha such as smokeless kerosene and the mixture then extracted with a suitable solvent such as liquid sulfur dioxide to remove the toluol. The toluol is then recovered from the sulfur dioxide or other suit the hydroforming of a selected fraction thereof,

the improvement which comprises contacting a traction of the naphthenic petroleum having an initial boiling point between F. and 197 F. and including the major portion of the available dimethylcyclopentanes as well as the methylcyclohexane with a molybdenum oxidecatalyst at a temperature of 800 F. to 1000 F. and at a liquid hourly space velocity of about 0.1 to 1.2

under a total pressure of about 2. to 50 atmcwpheres with a partial pressure or hydrogen above about 0.5 atmospheres but below that at which substantial destructive hydrogenation occurs under the reaction conditions, thereby augmenting the production of toluene by the conversion of a substantial portion of the dlmethylcyclopentane as well as the-methylcyclohexane to toluene.

2. Process according to claim 1 in which the molybdenum oxide catalysts consist essentially of molybdenum oxide and an adsorptive alumina.

3. Process according to claim 1 in which the fraction treated has a final boiling point between about 218 F. and 232 F.

nomim'n. nouns. nnanenn soaEEN SFELDER.

ocs orrnn The foilowing'references are of record in the file of this patent:

UNITED STATES PATENTS u 110118.101 (1942). OopyinDivislcn 31.

2,279,198 Huppke Apr-.7. 1942 OTHER REFERENCES Eslol! et al.. Isomerlzation of Pure Hydrocar-