WO2000043339A1

WO2000043339A1 - Hydroxylation of aromatic compounds at elevated pressures

Info

Publication number: WO2000043339A1
Application number: PCT/US2000/001154
Authority: WO
Inventors: Svetlana K. Rodkina; Mikhail A. Rodkin; Anthony K. Uriarte; Michael J. Gross; Steve T. Sautman
Original assignee: Solutia, Inc.
Priority date: 1999-01-20
Filing date: 2000-01-18
Publication date: 2000-07-27
Also published as: AU2509400A

Abstract

A method for partial oxidation of aromatic compounds with a molar deficiency of nitrous oxide over a zeolite catalyst at pressures above atmospheric pressure, while maintaining substantially equivalent phenol productivity compared to conducting the process at atmospheric pressure.

Description

HYDROXYLATION OF AROMATIC COMPOUNDS AT ELEVATED

PRESSURES

FIELD OF THE INVENTION

Disclosed herein is a method for the production of phenol and its derivatives by partial oxidation of benzene or a benzene derivative by nitrous oxide.

BACKGROUND

The production of phenol by partial oxidation of benzene using nitrous oxide over a variety of catalysts ranging from vanadium pentoxide on silica to zeolites, e.g., ZSM-5 and ZSM-11 zeolite catalysts, at elevated temperatures, e.g., 300 to 450°C, has been disclosed. In this reaction benzene is partially oxidized by an excess amount of nitrous oxide producing phenol and by-product nitrogen. See, for instance, Suzuki et al., 1988 chemistry Letters of the Chemistry Society of Japan at pages 953-956.

In United States Patent 5,001,280 Gubelmann et al. discloses the advantage of oxidizing benzene with nitrous oxide at 400°C using a zeolite catalyst having a silica to alumina ratio greater than 90. In United States Patent 5,110,995 Kharitonov et al. disclose that changes in the molar ratio of benzene to nitrous oxide does not substantially affect the yields of phenol but declare a preference for a reaction mixture of stoichiometric composition. Although benzene derivatives can also be oxidized by nitrous oxide to provide the corresponding phenol derivative, phenol is the most important commodity chemical in the class with uses in the manufacture of phenolic resins and the synthesis of chemicals such as caprolactam and adipic acid. Other processes for hydroxylating aromatics are set forth in U.S. Patents Nos. 5,110,995; 5,672,777; and 5,756,861, the subject matter of which is incorporated herein by reference. However, all of the above-mentioned processes perform the hydroxylation at atmospheric pressure, which results in significantly higher equipment costs (e.g., due to significantly larger equipment size), and ultimately, deleteriously affects the commercial viability of such processes.

Accordingly, there is a need for a process to product phenol on a large scale, economically, safely, and still maintain high yields and conversion rates. SUMMARY OF THE INVENTION

The present invention provides an improved process for the catalytic partial oxidation of benzene or substituted benzene to the corresponding phenol by employing a benzene and nitrous oxide feed stream that is rich in excess of the benzene reactant, with the oxidation reaction conducted in the gas phase at pressures above atmospheric pressure, while maintaining phenol productivity substantially equivalent to phenol productivity obtained at atmospheric pressure. Additionally, the process of this invention can allow for operation using a non-explosive gas mixture.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS In the catalytic oxidation process of this invention, aromatic compounds, e.g., benzene or substituted benzene, is partially oxidized to the corresponding phenol or substituted phenol by reaction with nitrous oxide over a catalyst at pressures above atmospheric pressure and still maintain about the same performance parameters (e.g., phenol productivity, half-life, nitrous oxide and benzene selectivity to phenol, catalyst performance, etc.) as when the reaction/process is conducted at atmospheric pressure. The process can be conducted at elevated temperature, e.g., 250 to 500°C or higher, e.g., up to at least 600°C using a molar excess of the aromatic compound to be oxidized. For example, a reactant feed mixture according to this invention would have a molar deficiency of nitrous oxide, i.e., a molar ratio of nitrous oxide to aromatic compound less than 2, e.g., in the range of 0.95 to 0.01 or lower. In preferred aspects of this invention, the molar ratio of nitrous oxide to aromatic compound is less than 0.5. In the case of oxidation of benzene to phenol, a preferred molar ratio of nitrous oxide to benzene is in the range of 0.9 to 0.01, often more preferably in the range of 0.1 to 0.01.

In an embodiment of the present invention, the oxidation process is conducted at pressures above atmospheric pressure. In accordance with the present invention, it has been unexpectedly discovered that higher pressures do not negatively affect the oxidation process. For numerous reasons, it was expected that the use of higher pressures would result in decreased yield. The yield of each nitrous oxide and benzene to phenol was expected to decrease at higher pressures because, (1) by-product formation would have been expected to be significantly higher due to increase in partial pressure of reactants leading to an enhancement in the reactions of phenol to form by-products and the products of deep oxidation; and (2) desorption of the product phenol from the solid catalyst after phenol formation would have been expected to be in inhibited at higher pressures and such high phenol concentration on the catalyst would have been expected to lead to coking. In addition, increased operating pressure creates additional safety concerns, as the peak pressure resulting from a deflagration is directly proportional to the absolute operating pressure.

In contrast to the expected problems associated with the use of high pressures in the oxidation of benzene to phenol, it has been discovered as a result of the present invention that high pressures utilized in oxidation of benzene to phenol do not provide a significant loss of performance parameters. For example, productivity, half-life, nitrous oxide and benzene selectivities to phenol are approximately equivalent when performing oxidation at atmospheric pressure compared to performing oxidation at elevated pressures.

Additionally, the oxidation process of the present invention may be conducted in such a fashion so as to reduce the increased risk of explosion as a result of operating at higher pressures. For example, an inert diluent can be added to the feed gas in such a manner that the feed mixture, the reaction mixture, and the product mixture at all points of the process (including separation equipment, recycle loops, etc.) is maintained in the non-flammable region.

The prior art identifies a variety of catalysts that are useful in the partial oxidation of benzene, e.g., vanadium pentoxide on silica and acidified zeolites. For many applications, ZSM-5 and ZSM-11 zeolite catalysts containing a catalytically effective amount of iron have significant advantages over other catalysts. Preferred catalysts are acidified ZSM-5 and ZSM-11 zeolites containing iron. The productivity of the process can be enhanced by using a zeolite that has been hydrothermally treated, e.g., exposed to up to 100% water vapor in air at about 500° to 900 °C for about 2 hours. In accordance with a process of this invention, the reaction is carried out with a molar deficiency of the nitrous oxide. In addition to vaporized aromatic compound and nitrous oxide the reactant gas feed to the catalyst can contain a variety of other gases as diluents or contaminants. Diluents typically will not adversely effect the desired reaction to produce the oxidized aromatic product, e.g., phenol, and typically comprise helium, argon, nitrogen, carbon dioxide or other such gases or mixtures thereof. Contaminants are characterized as species that adversely effect the desired reaction to produce the oxidized aromatic product whether by participating in a competing reaction or poisoning of the catalyst. The amount of contaminants is preferably very low, but in view of the practical difficulty of providing pure gases in industrial applications, certain low levels of contaminants can be tolerated. Contaminants typically found in industrial gas streams that can be tolerated at low levels include water vapor, ammonia, oxygen, carbon monoxide, nitric oxide, nitrogen dioxide and volatile organic species.

In addition to benzene, the aromatic compound may be any of a variety of substituted benzenes such as phenol, fluorobenzene, chlorobenzene, toluene, ethylbenzene and similar compounds having an aromatic ring with a substitutable hydrogen atom on the ring. The process can be used to produce polyols, e.g., hydroquinone, resorcinol and catechol, by oxidation of phenol. Thus, when phenol is produced from oxidation of benzene, the phenol product can be further oxidized by contact with the catalyst. Undesirable production of polyols can be avoided by employing a low ratio of nitrous oxide to aromatic compound, e.g., about 0.5 or lower, and by minimizing catalyst residence time. Similarly, a mixture of polyols can be prepared by extending catalyst residence time. Generally, it is preferred to keep catalyst contact time at a low level to preclude production of unwanted polyols. Such residence time can readily be determined by a person skilled in the art by routine experimentation in view of reaction conditions, catalyst activity, feed compositions, catalyst bed size and the like.

EXAMPLES

The benefits and advantages of the process of this invention are illustrated by reference to the following examples of various conditions in which benzene is oxidized to phenol in a plug flow reactor having an iron-containing ZSM-5 zeolite catalyst. In particular, commercially available ZSM-5 zeolite (Zeolyst CBV 8014 having a silica to alumnia ratio of 80, a sodium content of 0.05 wt.%, and a surface area of 425 sq. m/g) is subjected to hydrothermally treated as described in U. S. Patent No. 5,672,777, the entire subject matter of which is incorporated herein by reference. The reaction conditions and calculated reaction parameters are reported in the following tables. Example 1

The reactions are performed at 0 and 10 psig in a plug flow reactor containing 5 grams of catalyst at 460°C at space velocity of W/F = 4.52 with a feed containing 55 vol. % benzene and 3 vol. % nitrous oxide (N₂O) with balance helium. The duration of each experiment is 25 hrs. Table 1 contains a representative comparison of reaction performed at 0 and 10 psig.

TABLE 1

Example 2

The reactions are performed at 8 and 16 psig in a plug flow reactor containing 11.5 grams of catalyst at 430°C at contact time 0.8 seconds with a feed containing 95 vol. % benzene and 5 vol. % N₂O. The duration of each experiment is 4 hrs. Table 2 contains a representative comparison of reaction performed at 8 and 16 psig.

TABLE 2

Example 3

The reactions are performed at 8 and 16 psig in a plug flow reactor containing 11.5 grams of catalyst at 430°C at contact time 0.8 seconds with a feed containing 85 vol. % benzene and 15 vol. % N₂O. The duration of each experiment is 4 hrs. Table 3 contains a representative comparison of reaction performed at 8 and 16 psig. TABLE 3

Example 4

The reactions are performed at 8 and 16 psig in a plug flow reactor containing 11.5 grams of catalyst at 375°C at contact time 0.8 seconds with a feed containing 95 vol. % benzene and 5 vol. % N₂O. The duration of each experiment was 4 hrs. Table 4 contains a representative comparison of reaction performed at 8 and 16 psig.

TABLE 4

Example 5

The reactions are performed at 8 and 16 psig in a plug flow reactor containing 11.5 grams of catalyst at 375°C at contact time 1.8 seconds with a feed containing 95 vol. % benzene and 5 vol. % N₂O. The duration of each experiment was 4 hrs. Table 5 contains a representative comparison of reaction performed at 8 and 16 psig. TABLE 5

Example 6

The reactions are performed at 8 and 16 psig in a plug flow reactor containing 11.5 grams of catalyst at 375°C at contact time 1.8 seconds with a feed containing 85 vol. % benzene and 15 vol. % N₂O. The duration of each experiment was 4 hrs. Table 6 contains a representative comparison of reaction performed at 8 and 16 psig.

TABLE 6

Example 7

The reactions are performed at 8 and 16 psig in a plug flow reactor containing 11.5 grams of catalyst at 430°C at contact time 1.8 seconds with a feed containing 85 vol. % benzene and 15 vol. % N O. The duration of each experiment was 4 hrs. Table 8 contains a representative comparison of reaction performed at 8 and 16 psig. TABLE 7

Example 8

The reactions are performed at 8 and 30 psig in a plug flow reactor containing 14.6 grams of catalyst at 420°C at contact time 3.4 seconds with a feed containing 42 vol. % benzene and 5.35 vol. % N₂O, with balance being nitrogen. The duration of each experiment is 24 hrs. Five experiments are performed at each pressure. Table 9 contains a representative comparison of performance parameters averaged over 5 experiments in each set for reactions performed at 8 and 30 psig. The values in the following table are the average values observed for the 5 experiments at each pressure, with the +/- values encompassing the range of results for individual experiments.

TABLE 8

As is readily apparent from the data, the performance parameters, such as phenol productivity, are equivalent to those results obtained when conducting the process at atmospheric pressure with 95% confidence limit. While specific embodiments have been described herein, it should be apparent to those skilled in the art that various modifications thereof can be made without departing from the true spirit and scope of the invention. Accordingly, it is intended that the following claims cover all such modifications within the full inventive concept.

Claims

CLAIMS:

1. A method for oxidizing an aromatic compound using nitrous oxide by contacting a solid catalyst with a gaseous mixture of the aromatic compound and a molar deficiency of nitrous oxide at a pressure above atmospheric pressure, while maintaining substantially equivalent phenol productivity compared to conducting the process at atmospheric pressure.

2. A method according to claim 1 wherein the molar ratio of nitrous oxide to aromatic compound is in the range of 0.9 to 0.01.

3. A method according to claim 1 wherein said aromatic compound is benzene or substituted benzene.

4. A method according to claim 1 wherein said catalyst is a zeolite.

5. A method according to claim 4 wherein said catalyst is a ZSM-5 or ZSM-11 zeolite catalyst.

6. A method according to claim 5 wherein said aromatic compound is benzene.

7. A method according to claim 6 wherein the molar ratio of nitrous oxide to benzene is in the range of 0.1 to 0.01.

8. A method according to claim 7 wherein the gaseous mixture contacts said catalyst at a temperature in the range of 250 to 600 °C.

9. A method according to claim 8 wherein said gaseous mixture comprises benzene, nitrous oxide and one or more gases selected from the group consisting of helium, nitrogen, nitric oxide, nitrogen dioxide, carbon dioxide and argon.

10. A method according to claim 9 wherein said catalyst is an acidified ZSM-5 or ZSM-11 zeolite containing iron.

11. A method according to claim 1 , wherein said pressure is in the range of greater than 0 to 150 psig.

12. A method according to claim 1, wherein said pressure is in the range of 5 to 80 psig.

13. A method according to claim 1 , wherein said pressure is in the range of 10 to 50 psig.