US 3483266 A
Abstract available in
Claims available in
Description (OCR text may contain errors)
United States Patent THERMAL DEALKYLATION 0F ALKYL ARO- MATIC COMPOUNDS EMPLOYING A HY- DROGEN DONOR AND MOLECULAR HY- DROGEN James C. Hill, Chesterfield, Mo., assignor to' Monsanto Company, St. Louis, Mo., a corporation of Delaware No Drawing. Filed Dec. 20, 1966, Ser. No. 603,089 Int. Cl. C07c 3/58, /00
US. Cl. 260672 9 Claims ABSTRACT OF THE DISCLOSURE Alkyl aromatic compounds are dealkylated in a thermal reaction zone in the presence of a hydrogen donor and molecular hydrogen. The hydrogen donor is an aromatic compound that has been at least partially hydrogenated. For example, a pure toluene feed is demethylated at about one-half the rate (68% versus 1l14% conversions to benzene) of a toluene feed containing 6% dihydrophenanthrene, in 13 seconds at 625 C., 48.6 atmospheres, and ratios of H ztoluene in the range of 37, whereas an equal concentration of phenanthrene increased the rate some 12% above the rate for pure toluene.
BACKGROUND OF THE INVENTION This application relates to assignees co-pending applications Ser. Nos. 527,049 and 604,614.
The present invention relates to a process for the dealkylation of alkyl substituted aromatic compounds. More particularly, the present invention relates to a process for the thermal hydrodealkylation of alkyl substituted aromatic hydrocarbons.
Within recent years, thermal hydrodealkylation of alkyl substituted aromatic compounds has become a relatively well known and commercially accepted route of upgrading the value of hydrocarbon streams. By such processes, the alkyl substituents of aromatic ring compounds are removed from the aromatic rings. These thermal processes involve subjecting the alkyl substituted aromatic compounds to elevated temperatures in the absence of catalysts. While a number of these processes have reached the point of present day commercial usage, still there is'a need and a desire for a significant increase in the efliciency of such hydrodealkylation processes.
It is an object of the present invention to provide a new and improved process for the dealkylation of alkyl substituted aromatic compounds. Another object of the present invention is to provide a new and improved process for the thermal hydrodealkylation of alkyl substituted aromatic compounds. An additional object of the present invention is to provide a new and improved process for the thermal hydrodealkylation of alkyl substituted aromatic compounds whereby substantially improved conversion rates of the alkyl substituted aromatic compounds to dealkylated aromatic compounds are obtained. A particular object of the present invention is to provide a new and improved process whereby alkyl substituted aromatic hydrocarbons may be dealkylated with increased conversion rates to-dealkylated aromatic hydrocarbon product. Additional objects will become apparent from the following description of the invention herein disclosed.
In fulfillment of these and other objects, it has been found that alkyl aromatic compounds may be successfully dealkylated at high conversions by thermal means according to the process of the present invention which process comprises subjecting a feed containing alkyl substituted aromatic compounds to a temperature of 400 to 850- C. and a pressure of 100 to 2,000 p.s.i.g. in a non-catalytic, thermal reaction zone, in the presence of molecular hydrogen in a mol ratio of hydrogen to alkyl substituted aromatic compounds Within the range of 0.1:1 to 20:1, and in the presence of a hydrogen donor, said hydrogen donor being a partially hydrogenated aromatic compound. The process of the present invention provides a method for the thermal dealkylation of alkyl aromatic compounds at somewhat lower temperatures than those conventional to other processes. Further, significantly higher conversion rates are obtained by the present process than are obtained through the use of similar but different dealkylation processes. Another advantage of the process of the present invention is that alkyl substituents generally are severed from the alkyl aromatic compound as one molecule rather than as several lower molecular weight molecules, thereby preserving the alkyl molecule and reducing the hydrogen consumption.
To further describe and to specifically illustrate the present invention, the following examples are presented. These examples are not to be'construed in any manner as limiting the conditions, application or objects of the present invention.
EXAMPLE I A series of nine runs were made using toluene as the alkyl substituted aromatic compound. Three of these runs were made in accordance with the present invention with both molecular hydrogen and 9, lO-dihydrophenanthrene, as a hydrogen donor, being added to the toluene feed. In three other of the runs, the hydrodealkylation reaction was carried out in the presence of molecular hydrogen only, no hydrogen donor being present. The remaining three runs were caried out in the presence of molecular hydrogen and phenanthrene, the purpose of these three runs being to illustrate that the advantages derived from adding a hydrogen donor such as the 9,10-dihydrophenanthrene are not merely diluent effects. In all nine runs, the toluene and hydrogen together with the 9,10-dihydrophenanthrene or phenanthrene, if any, were continuously and concurrently passed through a reaction chamber having an inside diameter varying from inch at the entrance to inch at the exit and having a length of 7% inches. Temperature within the recation chamber was 625 C., the residence time of the reactants therein 13 seconds, and the pressure was 700 p.s.i.g. The table below summarizes the flow rate of the various materials going into the reaction chamber, the molecular hydrogen to toluene ratio, and the conversion of toleuene to benzene for each of the nine runs.
Percent H2/ conver- Phenantoluene sion threue From the above table, the poorest of Runs 1, 2 and 3 carried out in accordance With the present invention, Run No. 1 represents a 30.6 percent increase in conversion over the best of Runs 4 through 9 which were not carried out in accordance wiht the process of the present invention. The best of the runs carried out in accordance with the present invention, Run 3, represents a 70.6 percent increase in conversion as compared to Run 9 which was not carried out in accordance with the process of the present invention. Comparison of Run 1 with Runs 4 and 7 which had hydrogen to toluene ratios similar to Run 1 further illustrates the advantages of the process of the present invention.
3 EXAMPLE II Runs 1 through 3 of Example I are substantially repeated with the .exeception that Tetralin is used as the hydrogen donor rather than 9, IO-dihydrophenanthrene. In each of the runs a good conversion of toluene to benzene is obtained.
EXAMPLE III Runs 1 through 3 of Example I above are again substantially repeated with the exception that the alkyl substituted aromatic compound is l-methylnaphthalene and the temperature within the reaction chamber is approximately 650 C. In each of the runs a good conversion of the l-methylnaphthalene to naphthalene is obtained.
EXAMPLE IV Run 1 of Example I is again substantially repeated with the exeception that the alkyl substituted aromatic compound is ethylbenzene. A gOOd conversion of the ethylbenzene to benzene and ethane is obtained.
Suitable feed stock The alkyl substituted aromatic compounds which may be dealkylated in accordance with the hydrodealkylation process of the present invention include practically any aromatic compound containing alkyl substituents of one or more carbon atoms per alkyl substituent. These aromatic compounds may be mono-nuclear or poly-nuclear and may contain one or more alkyl substituents. For example, the feeds to the process of the present invention may be mono-, di-, tri, or tetra-alkyl substituted aromatic hydrocarbons, such as dimethyl benzenes, trimethyl ben zenes, dimethyl naphthalenes, tirmethyl naphthalenes, tetramethyl naphthalenes, diethyl benzenes, toluene, ethyl benzene, methyl naphthalene, diethyl naphthalenes, methyl phenanthrene, dimethyl anthracenes, dimethyl pyrenes, tetraethyl phenanthrenes, dimethyl chrysenes, tetraethyl pyrenes, trimethyl anthracenes, diethyldimethyl phenanthrenes, methylethyl benzene, methylethyl naphthalene, and the like. The alkyl substituents of the aromatic compounds which may be dealkylated in accordance with the present process may be either straightchain or branched-chain alkyl substituents and may contan 1 to 20 carbon atoms and higher. The process of the present invention is equally applicable to the dealkylation of alkyl benzenes and/ or alkyl naphthalenes and/ or alkyl phenanthrenes and/ or alkyl anthracenes and/ or alkyl pyrenes and/or alkyl chrysenes and the like. In addition, such alkyl aromatic compounds as acenaphthenes, acenaphthenes, alkyl fiuorenes, alkyl indans, alkyl indenes, and the like may be dealkylated in accordance with the present process. In addition, the present invention finds application in the dealkylation of alkyl aromatic compound containing substituents other than alkyl groups. For example, the alkyl aromatic compounds may contain hydroxyl, alkoXy, alkoxycarbonyl, halogen, sulfide, sulfate, nitrate, amino, nitrile, nitro and other such radicals as substituents in addition to alkyl substituents. Also, the aromatic compound may contain elements other than carbon in the aromatic nucleus. For example, the present invention may be utilized in the dealkylation of alkyl pyridines, alkyl pyrans, alkyl furans, and alkyl substituted thiophenes. Also, the present invention is useful in the dealkylation of complex mixtures of the above alkyl aromatic compounds as well as the pure compounds. In the preferred practice of the process of the present invention, the alkyl aromatic compounds are alkyl aromatic hydrocarbons having no greater than two carbon atoms in the alkyl substituents.
The hydrogen donors which are used in the process of the present invention are aromatic hydrocarbons which have been at least partially hydrogenated. Generally, these hydrocarbons are di-nuclear or poly-nuclear aromatics having one or more of the nuclei partially or totally saturated. Several non-limiting examples of such compounds are Tetralin, dihydronaphthalenes, diand tetra-hydroalkylnaphthalenes, dihydrophenanthrenes, tetrahydrophenanthrenes, octahydrophenanthrenes, tetrahydrophenylnaphthalenes, dihydrochrysenes, tetrahydrochrysenes, octahydrochrysenes, tetrahydropyrenes, octahydropyrenes, tetrahydrofluorenthenes, octahydrofiuorenthenes, and the like. A particularly useful group of these hydrogen donor compounds are the hydrophenanthrenes and hydronaphthalenes. The source of the hydrogen donor used in carrying out the process of the present invention is immaterial. These hydrogen donors may be obtained by separating hydrocarbon fractions to obtain the aromatics which have been at least partially hydrogenated or may be obtained by hydrogenating specific aromatic hydrocarbons by conventional hydrogenation means. The present invention is not, however, to be limited to any particular source or method for obtaining the hydrogen donors.
The mol ratio of the hydrogen donor to the alkyl aromatic compounds in the thermal delakylation zone is most often within the range of from 0.01:1 to 10:1. However, in a preferred method of practicing the process of the present invention wherein the herein below defined preferred amounts of molecular hydrogen are used, the mol ratio of hydrogen donor to alkyl aromatic compounds in the dealkylation zone is usually within the range of from about 0.05:1 to 4:1. The molecular hydrogen which is used with the hydrogen donor is generally present in a molar ratio of the alkyl aromatic compounds within the range of 0.1:1 to 20:1. Preferably, however, the mol ratio of hydrogen to alkyl aromatic compound is within the range of 2:1 to 10:1.
The temperatures at which the present process is most often operated generally are within the range of from approximately 400 to 850 C. At temperatures below the lower temperature, the desired dealkylation reaction falls to a rate too low for practical utilization. At temperatures above 850 C., the aromatic nucleus of the various alkyl aromatic compounds as well as the hydrogen donors will begin to rupture excessively causing loss of aromatic product and severe carbon formation and coating of the reaction chamber. A particular preferred range of temperatures for operating the present invention are those within the range of from approximately 550 to 750 C.
Pressures at which the hydrodealkylation process of the present invention is usually operated are most often within the range of from approximately to 2,000 p.s.i.g. Preferably, however, the pressure at which the present thermal hydrodealkylation process is operated will be within the range of from about 500 to 1500 p.s.i.g.
The residence time of the reactants within the thermal hydrodealkylation zone most often is within the range of from about 1 second to about 60 minutes and longer. If longer residence times are used, there is a likelihood of destruction of a part of the feed material, products and hydrogen donor compounds resulting in poor efficiency and in the formation of undesirable carbon and coke. At lower residence times, the conversions and yields are far too low for practical application of the present invention. Residence time, of course, is dependent to a large extent upon the temperature and to a lesser extent upon the other variables of the process. If higher temperatures are used, lower residence times are required and vice versa. The present invention may be operated as either a batch operation or as a continuous flow system. Temperatures are usually somewhat lower in the former, thus requiring longer residence time. Conversely, in the continuous flow systems, higher temperatures with shorter residence times are used. In batch operations, the residence time is usually within the range of 10 seconds to 60 minutes while the preferred residence times for continuous flow operations are usually within the range of from about 1 second to 20 minutes, preferably 1 to 100 seconds. From a practical standpoint, it is generally preferred that the present process be operated as a continuous flow system.
The particular individual equipment used in carrying out the process of the present invention is not critical as long as it conforms to good engineering principles and will allow eflicient operation under the conditions set forth herein.
What is claimed is:
1. In a process for the hydrodealkylation of alkyl substituted aromatic hydrocarbons by subjecting alkyl substituted aromatic hydrocarbons to a temperature of 400- 850 C. and a pressure of 100-2000 p.s.i.g. in a non-catalytic, thermal reaction zone in the presence of molecular hydrogen in a mol ratio of molecular hydrogen to alkyl substituted aromatic hydrocarbons of 0.1:1 to 20:1, the improvement which comprises carrying out said subjecting in the presence of an aromatic hydrocarbon hydrogen donor which is a phenanthrene hydrocarbon that has been at least partially hydrogenated in a mol ratio of hydrogen donor to alkyl substituted aromatic hydrocarbons of 0.05:1 to 4:1.
2. The process of claim 1 wherein the residence time of the reactants within the non-catalytic, thermal reaction zone is within the range of 1 second to 60 minutes.
3. The process of claim 1 wherein the temperature is within the range of 550 to 750 C.
4. The process of claim 1 wherein the pressure is within the range of 500 to 1500 p.s.i.g.
5. In a process for the hydrodealkylation of alkyl substituted aromatic hydrocarbons by subjecting a feed stock consisting essentially of alkyl aromatic hydrocarbons to a temperature of 400-850" C. and a pressure of 100-2000 p.s.i.g. in a non-catalytic, thermal reaction zone in the presence of molecular hydrogen in a mol ratio of molecular hydrogen to alkyl substituted aromatic hydrocarbons of 2:1 to :1, the improvement which comprises carrying out said subjecting on a mixture of dihydrophenanthrene with the alkyl aromatic hydrocarbon in a mol ratio of dihydrophenanthrene to alkyl aromatic hydrocarbon in the range of 0.05:1 to 4:1.
6. The process of claim 1 wherein the alkyl substituted aromatic hydrocarbons are alkyl aromatic hydrocarbons selected from the group consisting of alkyl benzenes, alkyl References Cited UNITED STATES PATENTS 2,381,522 8/1945 Stewart 196-50 2,929,775 3/1960 Aristolf et a1 208-133 2,994,726 8/1961 Hodgson et al 260-668 3,102,151 8/1963 Haldeman et al. 260-672 3,145,238 8/1964 Kestner 260-672 3,193,595 7/1965 Kenton et al. 260-672 3,198,846 8/1965 Kelso 260-672 3,256,357 6/1966 Baumann et a1 260-672 3,284,527 11/1966 Gill et a1 260-672 3,288,873 11/1966 Moll 260-672 3,288,875 11/ 1966 Payne et al. 260-672 3,296,323 1/1967 Myers et a1 260-672 3,177,262 4/1965 Calkins 260-672 3,320,332 5/1967 Schneider 260-668 OTHER REFERENCES Curran et al.: Mechanism of Hydrogen Transfer,
US. Cl. X.R. 260-668, 675