RU2202532C2 - Method of production of phenol and its derivatives and method of oxidation of benzene and its derivatives - Google Patents

Abstract

FIELD: methods of selective oxidation of aromatic compounds (for example, benzene and its derivatives) into hydroxylated aromatic compounds (for example, respective phenols). SUBSTANCE: proposed method includes mixing of aromatic compound with nitrous oxide at reaction temperature of 225-500 C and acting on mixture of heterogeneous catalyst which contains high-silicon zeolite such as pentasil in acid form. Catalyst is subjected to preliminary activation performed at the following stages: heating zeolite at temperature of 350- 550 C in flow of inert gas or air continued for 4-6 hours; calcination of zeolite at 550-1100 C for 1-3 hours in continuous flow of inert gas or air and cooling of zeolite catalyst to reaction temperature, thus forming heterogeneous catalyst. It is preferable to use composition containing high-silicon zeolite, such as pentasil (for example zeolite, type HZSM- 5) at Si/Al ratio of 20 to 50 containing gallium at silicon-to-gallium ratio of 40 to 100. Impregnated zeolite is calcined in flow of air at 550-800 C. Molar ratio of N₂O-to-substrate is 1:7 to 5:1.Used as substrate is benzene or its derivatives, phenol, diphenols, chlorophenols, fluorophenols, difluorophenols, trialkylphenols with C₁-C₃. alkyl. EFFECT: increased productivity at high selectivity of oxidation reaction. 19 cl, 7 tbl, 21 ex

Description

 This application recognizes priority in accordance with section 35 of the U.S. Code of Laws, 119, based on Russian patent application 97112675, filed July 5, 1997.

Field of Invention
This invention relates to the field of organic synthesis and, in particular, relates to methods for producing hydroxylated aromatic compounds (e.g., phenol and its derivatives) by selective oxidation of aromatic compounds (e.g., benzene and its derivatives) by gas mixtures containing nitrous oxide (N ₂ O) in the presence of heterogeneous catalysts. As heterogeneous catalysts, industrial zeolites or zeolite-containing catalysts modified by the special treatment described herein are used.

BACKGROUND OF THE INVENTION
Various methods are known in the art for producing phenol and its derivatives, such as diphenols, chlorophenols, fluorophenols, alkyl phenols, and the like. Known methods include the direct oxidation of aromatic hydrocarbons or their derivatives with oxygen, N ₂ O, or other gaseous oxidizing agents in the presence of oxide catalysts, such as those described in US Pat. No. 5,110,995. However, most known oxide catalysts for the direct oxidation of benzene to phenol in the presence of molecular oxygen do not provide high selectivity and yield of the target product. The most successful example of such a catalyst is a catalyst obtained from phosphates of various metals. In particular, ZnPO _{4 was} used as a catalyst for the oxidation of benzene to phenol in the presence of alcohols. At temperatures of 550-600 ^o With the catalyst ZnPO ₄ gave a yield of phenol of about 25%. However, the selectivity of ZnPO ₄ was low (60%) [Japanese Patents 56-77234 and 56-87527, 1981]. In addition, phosphate catalysts are disadvantageous for the oxidation of benzene, since significant amounts of alcohols are consumed during their use.

Known oxide catalyst systems based on vanadium, molybdenum or tungsten for the direct oxidation of benzene with nitrous oxide (N ₂ O) at 500-600 ^o [Iwamoto et aL, J. Phys. Chem., 1983, v. 87, 6, p. 903]. The maximum phenol yield for such catalysts in the presence of excess water vapor is about 7-8% with a selectivity of 70-72%.

 The main disadvantages of these catalysts are the low selectivity and low yield of phenol, the high temperatures required for the reaction, and the need to add steam.

Zeolite catalysts are also used for the selective oxidation of benzene and its derivatives using N ₂ O as an oxidizing agent (E. Suzuki, K. Nakashiro, Y. Ono, Chem. Lett., 1988, 6, p. 953; M. Gubelmann et al ., European patent 341165, 1989; M. Gubelmann et al., US patent 5001280, 1990). In particular, high-silica zeolites ZSM-5 of the pentasil type were used as catalysts for the oxidation of benzene, chlorobenzene and fluorobenzene to the corresponding phenols. Oxidation of benzene with nitrous oxide on HZSM-5 zeolite at 400 ^{° C.} leads to the formation of phenol with a yield of up to 16% and selectivity close to 98-99%.

The disadvantage of these catalysts is that they give low degrees of conversion, low yields of phenol and low selectivity at high reaction temperatures. Pentasil type zeolites (e.g., ZSM-5, ZSM-11, ZSM-12, ZSM-23), mordenite, zeolite beta and EU-1, which are modified with small iron additives during their synthesis, are known systems for carrying out this catalytic reaction . For example, US Pat. Nos. 5,672,777 and 5,110,995 provide experimental results on the oxidation of benzene with nitrous oxide at 275-450 ^° C. The contact time was 2-4 s, the volumetric fluid rate for benzene was 0.4 h ^-1 , and the molar ratio benzene : N ₂ O was 1: 4. The phenol yield usually reached 20-30%, and the selectivity was 90-97%.

The disadvantages of these catalysts include the need to introduce iron ions into the zeolite and control the degree of oxidation of iron ions, the low volumetric velocity of the liquid for benzene, the significant contact time required to obtain acceptable, but not impressive yields of the final product, and low selectivity at elevated temperatures (~ 450 ^o C).

A catalyst of the HZSM-5 type, which is dehydroxylated at high temperatures, is also known in the art (VL Zholobenko, Mend. Commun., 1993, p. 28). It was found that such a treatment — dehydroxylation at high temperature — increases the yield of phenol from ~ 12 to ~ 20-25 wt.% With a N ₂ O: benzene ratio of 4: 1.

However, this catalyst also gives a low phenol yield. In the method described above, high temperature dehydroxylation was carried out in one step without controlling the nature of the active centers of the zeolite. Therefore, in this method, the formation of active centers both in the framework and outside the framework was quite possible. A significant drawback of all these methods is that they require a large excess of N ₂ O with respect to a hydrocarbon (for example, benzene) in order to provide a more complete conversion of the hydrocarbon to the desired oxidation products.

Another method for the oxidation of benzene was proposed in the patent of Panov G.I. et al. (PCT WO 95/2791). In this method, an excess of benzene with respect to N ₂ O (up to 9: 1) was used, and the selectivity of the conversion of N ₂ O to phenol was improved.

However, in this case, the catalyst contained iron as an active component. Problems arise with such catalysts since it is necessary to control the oxidation state of iron introduced into such a catalyst. In addition, the phenol yield barely exceeds 20 wt.%, Although the hourly space velocity of the liquid (hereinafter referred to as "LHSV") for benzene was increased compared to previous systems to about 2-2.5 h ^-1 .

In another known method, phenol is produced by the oxidative hydroxylation of benzene and its derivatives with nitrous oxide at 225-450 ^{° C.} in the presence of an iron-containing zeolite catalyst. This zeolite catalyst is preheated at 350-950 ^o C in an atmosphere of steam containing 0.1-100 mol. % H ₂ O (Kharitonov A.S. et al., US patent 5672777, 1977 - Russian patent 2074164, C 07 C 37/60, June 1997-1, application 94013071/04, C 07 C 37/60, 27.12. 1995).

 However, the processing of the zeolite catalyst by this method does not give a significant increase in activity. Another disadvantage of this method is the low stability of the resulting catalyst, which is deactivated during the oxidation process due to the formation of tar-like by-products. Another disadvantage of all the methods described above is the low partial pressure of benzene in the vapor mixture — the benzene content was 5 mol%, and the partial pressure of benzene was about 40 torr.

Thus, an object of the present invention is to provide a process for preparing hydroxylated aromatic compounds (e.g., phenol and its derivatives) by selectively oxidizing aromatic compounds (e.g., benzene and its derivatives). In particular, the aim of the invention is to use N ₂ O as a mild oxidizing agent in the presence of a suitable catalyst, which increases the productivity of the oxidation process by increasing the yield of hydroxylated aromatic compounds and the selectivity of the target product. Another objective of the invention is to simultaneously minimize the consumption of N ₂ O by reducing the ratio of oxidizing agent to hydrocarbon in the initial mixture and to increase the efficiency of the conversion of N ₂ O to the desired oxidation products. In addition, the purpose of this invention is to avoid obtaining by-products.

SUMMARY OF THE INVENTION
The objectives of this invention are carried out using a method for producing hydroxylated aromatic compounds (for example, phenol or its derivatives) by oxidizing aromatic compounds (for example, benzene and its derivatives) with nitrous oxide. The method of the present invention significantly increases the efficiency of the process by increasing the activity and selectivity of the catalyst and increasing the yield of the target products (i.e., hydroxylated aromatic compounds).

In order to achieve these results, aromatic compounds are oxidized using nitrous oxide at 225-500 ^{° C.} in the presence of a zeolite catalyst. The zeolite catalyst according to this invention is modified with acid-base centers of a specific nature containing strong Lewis acid and base. These centers can be introduced into the zeolite catalyst by carrying out a special high-temperature treatment. This preliminary thermal activation of the H-form of the zeolite is carried out in two stages. In the first stage, the catalyst is heated at 350-450 ^o C for 4-6 hours in a stream of inert gas (nitrogen or helium) or air. In the second stage, the catalyst is calcined at 450-1000 ^o C for 1-3 hours in a continuous stream of inert gas or air, followed by cooling of the zeolite catalyst to the reaction temperature (usually 300-450 ^o C). In a preferred embodiment of the invention, the hydroxylated aromatic compounds are phenol and its derivatives, and the aromatic compounds are benzene and its derivatives.

Applicants do not want to be bound by any particular theory explaining the effect of the invention. However, the applicants offer the following explanation of how heat treatment affects the catalyst. The purpose of the two-stage high-temperature treatment is to generate specific type centers containing a pair of Lewis acid-base, preferably Lewis acid-base centers located in the framework. This is achieved by separating the stage of removal of adsorbed water and / or ammonium ions (which are introduced by ion exchange at the stage of preparation of H- or NH ₄ -forms of zeolites) from the stage of removal of structural (bridging) OH groups included in the framework of H-zeolites. To this end, heat treatment is carried out in two stages. In the first stage, the zeolite is calcined at temperatures up to 350-450 ^o C (conventional pre-treatment). At this first stage, adsorbed water and ammonium ions introduced by exchange are intensively removed. In the second stage, the zeolite is calcined at temperatures in the range from 450 to 950 ^o C, depending on the composition of the zeolite. At this second stage, the structural (acidic) OH groups of zeolites are removed. This second stage solves two problems: (1) removal of acid OH groups, which are active centers for adverse reactions leading to the formation of gummy products; and (2) the creation of new (aprotic), rather strong Lewis acid-base pairs, preferably associated with the zeolite framework, which are able to activate N ₂ O molecules to cause their decomposition with the release of molecular nitrogen and the formation of atomic oxygen adsorbed on strong Lewis acid centers. Atomic oxygen acts as a mild oxidizing agent in the selective oxidation of aromatic compounds to the corresponding hydroxylated aromatic compounds. Strong Lewis acid-base centers that are precursors of active oxidative centers (atomic oxygen) can be determined using IR spectroscopy using adsorbed probe molecules such as CO, H ₂ , CH ₄ , etc.

DETAILED DESCRIPTION OF THE INVENTION
According to the present invention, the starting materials for the preparation of zeolite catalysts are industrial forms of zeolites, such as:
(1) high silica pentasil type zeolites like ZSM-5, ZSM-11, etc., obtained, for example, as described in US Pat. No. 3,702,886, which is incorporated herein by reference;
(2) zeolite H-mordenite; or
(3) isomorphically substituted pentasils, such as ferrisilicate, gallium silicate, etc.

 Preferably, the present invention uses industrial ZSM-type zeolites (ZSMe-5, ZSM-11, ZSM-12, ZSM-23, etc.) with Si / Al or Si / Me ratios (where Me = Ga, Fe) more than 20. In more preferred versions of the invention, the Si / Al or Si / Me ratio is in the range of 40 to 100.

 According to the present invention, a commercial zeolite is acidified by adding an inorganic or organic acid to it. In a preferred embodiment, the zeolite is acidified by impregnating it with 10-100 ml of acid per gram of zeolite, where the acid has a normality of 0.1 n. up to 2n. The acid impregnation may be carried out in a single step or, more preferably, in several steps.

 Acidic forms of zeolite can also be prepared by ion exchange of an industrial zeolite with an aqueous solution of an ammonium salt (e.g. nitrate or chloride). For example, the Na form of zeolite ZSM is treated with 0.1-2n. a solution of the corresponding ammonium salt. The degree of exchange of a sodium ion for an ammonium ion or for protons varies from 30 to 100%, and more preferably from 50 to 95%.

Zeolites can be used as catalysts in pure form or in admixture with a suitable binder. In a preferred embodiment, amorphous silica with a specific surface of 100 to 600 m ² / g, or alumina with a specific surface of 100 to 400 m ² / g, or a mixture thereof, is used as a binder. The content of the binder in the catalyst is in the range from 5 to 50 wt.% And more preferably from 20 to 30 wt.%.

 Nitrous oxide can be used in pure form or in a mixture with an inert gas such as nitrogen or helium, or in a mixture with air.

 Aromatic hydrocarbons such as benzene, toluene, ethylbenzene, cumene, xylenes and the like, halogenated aromatic compounds such as chlorobenzene, fluorobenzene, difluorobenzenes and the like, phenol, styrene or a mixture thereof are usually used as substrates for selective oxidation with nitrous oxide. It is also possible to further selectively oxidize an aromatic compound such as phenol using the method described herein. For the purposes of this description, these substrate substances will usually be referred to as "aromatic compounds."

In the method described herein, the substrate is mixed with nitrous oxide at a molar ratio of nitrous oxide to substrate of from 1: 7 to 5: 1, and more preferably from 1: 2 to 4: 1. LHSV substrate is in the range from 0.2 to 5 h ^-1 , more preferably from 0.5 to 2 h ^-1 . The reaction is preferably carried out at a temperature of from 300 to 500 ^o C and more preferably from 250 to 450 ^o C. the Contact time of the reaction mixture with the catalyst is in the range from 0.5 to 8 s and more preferably from 1 to 4 s.

 The gases leaving the reactor may contain a mixture of phenol and dihydroxybenzenes and are condensed and separated by any method known in the art (gas chromatography, liquid chromatography, mass spectrometry, or a combination thereof).

The catalyst can be easily and reversibly regenerated by calcination at 400-600 ^o C in a stream of air, oxygen and nitrous oxide or mixtures thereof with an inert gas. Regeneration is carried out within 1-3 hours

 In order to further illustrate the present invention and its advantages, the following specific examples are given, it being understood that they are for illustration only and in no way limit the invention.

 In the indicated examples below, the following parameters are used: C = percent conversion, S = percent selectivity; Y = yield per past product, Y = CxS. The characteristics given in the examples are average values for two hours of a continuous process.

Example 1
The synthesis of the starting zeolite HZSM-5 was carried out as described in US patent 3702886, which is incorporated into this description by reference.

Experimental oxidation conditions by nitrous oxide:
Vapor phase - Continuous
The catalyst is HZSM-5 (SiO ₂ / Al ₂ O ₃ = 42)
Standard pretreatment temperature - 350 ^o С
High temperature calcination at, ^o С - 450, 650, 750, 850, 920 or 1100
The reaction temperature, ^o C - 350
The molar ratio is Benzene / N ₂ / N ₂ O = 2/5/8
200 mg of HZSM-5 catalyst (Si / Al = 21) in the form of a powder (particle size 0.2-0.5 mm) dispersed in 400 mg of quartz sand with granules of the same size was placed in a tubular reactor made of quartz or stainless steel (with an inner diameter of 7 mm). Before the reaction, the catalyst was pretreated in two stages. In the first stage, the catalyst was conditioned for 5 hours at 350 ^° C in a stream of nitrogen or air (60 l / min) in a tube furnace. In the second stage, soft high-temperature annealing was carried out, including heating the catalyst for another two hours at a high temperature (450, 650, 750, 850, 920, or 1100 ^o C) in a continuous stream of nitrogen or air. After this treatment, the catalyst was cooled to a reaction temperature (i.e. 350 ^{° C.} ) in a stream of nitrogen. The reaction was carried out continuously by introducing a mixture of benzene with a space velocity (LHSV) of 0.5-2 h ^-1 nitrous oxide and helium (nitrogen). The contact time of the mixture was 1–4 s.

The data on the conversion, selectivity and yield of phenol depending on the final temperature of the high-temperature pre-treatment are presented in Table 1. In addition, table 1 shows the percent decontamination (i.e., the reduction in conversion over the next 60 minutes of the process). As can be seen from this table, high-temperature treatment in dry air, leading to the formation of a skeleton containing Lewis acid-base centers, significantly increases catalytic activity. At temperatures above 1000-1100 ^o With the destruction of the structure of the zeolite HZSM-5, resulting in a decrease in activity.

Example 2
The preparation of the catalyst and its tests were carried out as described in example 1, except that they used a higher reaction temperature, 450 ^o C. The obtained data are shown in table.2.

These data show that if a higher temperature is used (for example, about 450 ^{° C.} ), the activity and especially the selectivity of the catalyst increases with increasing temperature of high temperature calcination. So for the catalyst developed in the present invention, the reaction of direct oxidation of benzene to phenol proceeds with a selectivity close to 100%, even at high reaction temperatures.

Examples 3 and 4
The preparation of the catalyst and its testing was carried out as in examples 1 and 2, respectively, except that other types of catalysts were used. In order to determine the dependence of the catalyst parameters on the Si / Al ratio in the zeolite framework, HZSM-5 zeolite with a Si / Al ratio of 50 (Example 3) and HZSM-5 zeolite with a Si / Al ratio of 21 (Example 4) were compared. In these experiments, the partial pressure of benzene was 60-80 torr. The results are shown in table.3. An increase in the Si / Al ratio leads to an increase in phenol selectivity up to 100%. This 100% selectivity is maintained over a wide range of pretreatment temperatures.

Example 5
Zeolite HZSM-5 (Si / Al = 21), obtained by treatment with acid or ion exchange of NH ₄ ⁺ , as in example 1, was calcined at 450 ^o C for 5 h (cycle 1), then at 800 ^o C for 2 h in a stream of air. After this treatment, the catalyst was cooled to room temperature and kept in contact with water vapor for 24 hours (cycle 2). Then the sample was again calcined at 450, 650 or 800 ^o C for 2 h and the reaction of oxidation of benzene N ₂ O at 350 ^o C, as described in example 1. The results of catalytic experiments are presented in table 4.

These data show that the catalyst after pretreatment under conditions of high temperature calcination exhibits a higher activity than the initial catalyst treated under standard conditions (~ 450 ^o C). This remains true even if the pre-treated catalyst is then hydrated and calcined a second time at 450-500 ^o C. Thus, after the Lewis acid-base centers associated with the lattice are formed, they remain and when saturated with water vapor, provided that subsequent calcination is carried out at temperatures above 450 ^o C.

Example 6
2.3 g of the catalyst prepared according to example 3 and pretreated at 900 ^{° C.} were loaded into the reactor (particle size 1-2 mm). Benzene was supplied at a space velocity of 0.5 h ⁻¹ and the ratio of N ₂ O: C ₆ H ₆ was 2: 1. The partial pressure of benzene was 120 torr (the benzene content in the vapor phase was 16 mol%). At a reaction temperature of 370 ^{° C.,} the phenol yield was 25%, and the selectivity was 100%. At a reaction temperature of 420 ^{° C., the} yield was 32% and the selectivity was 99%.

Example 7
2.3 g of the catalyst prepared according to example 3 and pretreated at 900 ^{° C.} were loaded into the reactor (particle size 1-2 mm). Benzene was supplied at a space velocity (LHSV) of 0.3 h ⁻¹ , and the ratio of N ₂ O: C ₆ H ₆ was 1: 1. At a reaction temperature of 370 ^{° C.,} the phenol yield was 37%, and the selectivity was 100%. At 420 ^{° C., the} yield was 49%, and the selectivity was 99%. The efficiency of using N ₂ O for the selective oxidation of benzene to phenol was 98%.

Example 8
2.3 g of zeolite HZSM-5 (particle size 1-2 mm) with a Si / Al ratio of 40 was prepared according to Example 3, pre-heated at 850 ^{° C.} and loaded into the reactor. Benzene was supplied at a space velocity of 0.5 h ⁻¹ , and the ratio of N ₂ O: C ₆ H ₆ was 0.5: 1. At a reaction temperature of 400 ^{° C., the} yield of phenol calculated as N ₂ O was 28.3% and the selectivity was 99%. On the other hand, the yield per benzene was 14.2%. At 420 ^{° C.,} the phenol yield calculated as N ₂ O was 33.6%, and the selectivity was 98%. On the other hand, the yield per benzene was 16.8%. The efficiency of using N ₂ O for the selective oxidation of benzene to phenol was 96%.

Example 9
2.3 g of zeolite HZSM-5 (particle size 1-2 mm) with a Si / Al ratio of 40 was obtained according to Example 3, pre-heated at 850 ^° C and loaded into the reactor. Benzene was supplied at a space velocity of 0.3 h ⁻¹ , and the ratio of N ₂ O: C ₆ H ₆ was 0.5: 1. At a temperature of 420 ^{° C.,} the phenol yield calculated as N ₂ O was 28.2%, and the selectivity was 98%. The efficiency of using N ₂ O for the selective oxidation of benzene to phenol was 95%.

Example 10
2.3 g of zeolite HZSM-5 (particle size 1-2 mm) with a Si / Al ratio of 40 was obtained according to Example 3, pretreated at 850 ^{° C.} and loaded into the reactor. Benzene was supplied at a space velocity of 0.5 h ⁻¹ , and the ratio of N ₂ O: C ₆ H ₆ was 1: 1. A mixture of N ₂ O with air (1: 3) was used as an oxidizing agent. At a temperature of 370 ^{° C.,} the phenol yield was 26.8%, and the selectivity was 98%.

Example 11
Zeolite HZSM-5 (Si / Al = 40) was extruded with a SiO ₂ binder (20% SiO ₂ + 80% HZSM-5), and the extrudate (2x2 mm cylinders) was calcined in two stages according to the procedure described in Example 1. Final temperature high temperature processing was equal to 900 ^o C.

The catalyst was used in the oxidation of benzene N ₂ O. In this test, the space velocity (LHSV) of benzene was 1.7 h ^-1 , the molar ratio of benzene to N ₂ O was 7: 1 (a large excess of benzene relative to N ₂ O), and the temperature was 440-470 ^o C. The phenol yield (calculated on N ₂ O) was 20.6% at 440 ^o C and 30.2% at 470 ^o C. The efficiency of using N ₂ O for the selective oxidation of benzene was 95- 96%

Example 12
The gallium-modified zeolite HZSM-5 was prepared by impregnating zeolite HZSM-5 with an aqueous solution of gallium nitrate and subsequent calcining at 500 ^° C for 4 hours to remove nitrate ions (the content of Ga ₂ O ₃ was 3 wt.%). The zeolite was then pretreated at 850 ^{° C.} and loaded into the reactor. Thus, 2.3 g of zeolite (particle size 1-2 mm) were treated. Benzene was fed at a rate (LHSV) of 0.5 h ^-1 with a ratio of N ₂ O: C ₆ H _{6 of} 0.5: 1. At a reaction temperature of 420 ^{° C.,} the phenol yield was 20.8% based on N ₂ O or 10.4% based on benzene. Selectivity was 100%. The efficiency of using N ₂ O for the selective oxidation of benzene to phenol was 100%.

Examples 13 and 14
250 mg of a catalyst with a particle size of 0.5-1.0 mm was prepared according to example 3. This catalyst was diluted with silica sand (750 mg), and the mixture was loaded into the reactor. Benzene (Example 13) and phenol (Example 14) were used as substrates. The ratio of nitrous oxide: substrate was 4: 1, LHSV was 0.5 h ^-1 , and the reaction temperature was 430 ^o C. In the case of benzene, a product was obtained containing 75% phenol and 25% a mixture of o- and p-diphenols ( in a ratio of 1: 4). The total yield was 60% and the selectivity was 97%. In the case of phenol, a mixture of o-, m- and p-diphenols was obtained at a ratio of 1.0: 0.5: 4.0 with a total yield of 75%.

Examples 15-20
500 mg of the catalyst obtained according to examples 1 and 2 were placed in a flow unit. Fluorobenzene, o-, m- and p-difluorobenzenes, toluene, p-xylene, ethylbenzene and styrene were used as substrates (examples 15-20, respectively). The ratio of the components in the gas mixture was as follows: Not: air: N ₂ O = 1: 3: 5. LHSV substrate was 1-3 h ^-1 . The ratio of N ₂ O: substrate was 4: 1. Data on the oxidation of the substrates are given in table 5-7. Several conversion values in the tables correspond to different reaction times (10, 40 and 70 min). It was observed that the conversion of alkylbenzenes (Table 7) decreases with time. This observation can be explained by catalyst deactivation. In the case of the oxidation of fluorobenzene, a mixture is formed containing predominantly p-fluorophenol (up to 75% in the mixture) without the formation of the m-isomer.

Example 21
The HZSM zeolite containing Ga ³⁺ ions in the framework, which were introduced during the synthesis (Si / Ga = 40), was subjected to high temperature treatment by stepwise calcination at 450 ^° C for 2 hours. Fluorobenzene was oxidized using this catalyst, with LHSV benzene was equal to 2.3 h ^-1 , the reaction temperature was 400 ^o C, and the composition of the pelvic mixture was as follows: air: N ₂ O: Not = 3: 5: 2. The ratio of N ₂ About: the substrate was equal to 1: 4. Under these conditions, the fluorophenol yield was 20%, and the selectivity was 97%. Among the obtained fluorophenols, the para-isomer prevails (70%).

In conclusion, it can be said that the examples show that the catalysts proposed in the present invention, when used for the oxidation of benzene and its derivatives to the corresponding phenols in the presence of nitrous oxide as an oxidizing agent, have the following advantages over the known catalysts described in the mentioned patents :
(1) benzene conversion for the catalysts of this invention can increase from 10-20% to 50-75% without reducing selectivity (98-100%);
(2) the selectivity of conversion to phenol at a high reaction temperature (400-470 ^{° C.} ) can increase from 30-40% to 95-100%, and the phenol yield can increase to 70%;
(3) the efficiency of using N ₂ O for the selective oxidation of aromatic compounds can increase from 80-85% to 95-100%;
(4) if a zeolite catalyst is used that has been subjected to high temperature pretreatment, higher benzene partial pressures and lower N ₂ O: benzene ratios can be used. This gives a reduction in nitrous oxide consumption and an increase in phenol yield;
(5) the stability and service life of the catalyst can be significantly improved by modifying the zeolite catalysts by introducing strong Lewis acid-base centers. These centers have a specific nature and are formed as a result of high temperature calcination of zeolites before testing them as catalysts;
(6) a high yield and selectivity of phenol formation can be achieved without introducing special iron additives into the catalyst and steam treatment;
(7) in some cases, during the oxidation of benzene derivatives (e.g., halogenated benzenes, phenols), the process has high selectivity and regioselectivity with respect to the p-isomers of phenols.

 Although this invention has been described in the form of various preferred variants of its implementation, an experienced specialist will be able to determine that you can make various modifications, replacements, exceptions and other changes without deviating from the essence of the invention. Accordingly, it is intended that the scope of the present invention should not be limited by the preferred embodiments of the invention described herein.

Claims (19)

1. A method of producing a hydroxylated aromatic compound by oxidizing an aromatic compound in which said hydroxylated monocyclic aromatic compound has one hydroxyl group more than said monocyclic aromatic compound, the method comprising: mixing said aromatic compound with nitrous oxide at a reaction temperature in the range of 225 -500 ^o C, and exposing said nitrous oxide and said aromatic compound serving as a heterogeneous ka alizatora composition containing rich zeolite of pentasil type in acid form, subjected to preliminary activation, comprising the following steps: (a) heating the zeolite at 350-550 ^o C in a stream of inert gas or air for 4-6 hours; (b) calcining the zeolite at 550-1100 ^{° C.} for 1-3 hours in a continuous stream of inert gas or air; and (c) cooling the zeolite catalyst to a reaction temperature, as a result of which a heterogeneous catalyst composition is formed.  2. The method according to claim 1, characterized in that the hydroxylated aromatic compound is selected from the group consisting of phenol, diphenols, chlorophenols, fluorophenols and difluorophenols.  3. The method according to claim 2, characterized in that the molecule of the aromatic compound is selected from the group consisting of benzene, phenol, fluorobenzene, chlorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, styrene and mono -, di- and trialkylbenzenes having alkyl groups containing from 1 to 3 carbon atoms.  4. The method according to claim 3, characterized in that the zeolite in the first stage of pre-activation is heated in a stream of nitrogen.  5. The method according to claim 1, characterized in that the high-silica zeolite type pentasil is an H-form of zeolite ZSM-5 with a ratio of Si / Al in the range from 20 to 50.  6. The method according to claim 1, characterized in that the ratio Si / Al is in the range from 30 to 50. 7. The method according to claim 1, characterized in that the reaction temperature is from 300 to 450 ^o C. 8. The method according to claim 1, characterized in that the molar ratio of N ₂ O: substrate is in the range from 1: 7 to 5: 1. 9. The method according to claim 1, characterized in that the molar ratio of N ₂ O: substrate is in the range from 0.5: 1 to 1: 1. 10. The method according to claim 1, characterized in that the diluent is an inert gas, and the diluent is selected from the group consisting of N ₂ , He and Ar.  11. The method according to claim 1, characterized in that a diluent is added to the mixture of aromatic compounds and nitrous oxide, while the diluent is selected from the group consisting of air and mixtures of air with inert gases.  12. The method according to claim 11, characterized in that the diluent is air.  13. The method according to claim 1, characterized in that the zeolite contains gallium and the ratio of silicon to gallium is from 40 to 100.  14. The method according to item 13, wherein after the synthesis of the zeolite, the zeolite is impregnated with a gallium salt and then calcined in air. 15. The method according to 14, characterized in that said stage of calcination is carried out at a temperature in the range from 550 to 800 ^o C.  16. The method according to claim 1, characterized in that the composition of the heterogeneous catalyst further comprises a binder, while the weight content of the binder is in the range from 5.0 to 50.0 wt.%.  17. The method according to clause 16, wherein the weight content of the binder is in the range from 10 to 30 wt.%.  18. The method according to clause 16, wherein the binder is selected from the group consisting of silica, alumina and mixtures thereof. 19. A method of oxidizing an aromatic compound, comprising reacting said aromatic compound with nitrous oxide at a reaction temperature of 225-500 ^{° C.} , characterized in that it comprises contacting the aromatic compound with nitrous oxide in the presence of a composition containing a high-silicon zeolite of the type serving as a heterogeneous catalyst pentasil in acid form, subjected to preliminary activation, comprising the following stages: (a) heating the zeolite at 350-550 ^o C in a stream of inert gas or air in for 4-6 hours; (b) calcining the zeolite at 550-1100 ^{° C.} for 1-3 hours in a continuous stream of inert gas or air; and (c) cooling the zeolite catalyst to a reaction temperature, as a result of which a heterogeneous catalyst composition is formed. Priority on points and signs:
07/29/1997 according to claims 4-7, 10, 13 and 15 in the entire set of their attributes have priority;
05/13/1998 on PP.9, 12 and 16-18 in the entire set of their attributes have priority;
07.29.1997, each of paragraphs 1 and 19 has priority, with the exception of the following characteristics:
"reaction temperature in the range 225-500 ^o C" - has priority from 07.29.1997 in the range of 225-450 ^o C and priority from 05.13.1998 in the rest of the specified temperature range;
"heating of the zeolite at 350-550 ^o С" at the stage (a) of the pre-activation process - has priority from 07/29/1997 in the temperature range of 350-450 ^o С and priority from 05/13/1998 in the rest of the specified temperature range;
carrying out the same stage (a) "in an inert gas or air flow" - has priority from 07/29/1997 in terms of the use of air or nitrogen (as inert gas) and priority from 05/13/1998 in terms of the use of other gases used on the above definition stage (a);
p. 2 has priority from 07/29/1997 regarding the following compounds: phenol, diphenols, fluorophenols and difluorophenols, and priority from 05/13/1998 regarding chlorphenols;
p. 3 takes priority on 07/29/1997 in the following compounds: benzene, fluorobenzene, difluorobenzene, p-, o-xylene, toluene, ethylbenzene, styrene, halogenbenzenes, and priority from 05/13/1998 in other compounds. The sign of clause 8 "molar ratio N ₂ O: substrate in the range from 1: 7 to 5: 1" has priority from 07/29/1997 in terms of the interval of relations from 1: 1 to 5: 1 and priority from 05/13/1998 in the rest of specified relationship interval.  The sign of clause 11 "add a diluent, the diluent being selected from the group consisting of air and mixtures of air with inert gases" has priority from 07/29/1997 in terms of use as an inert gas diluent and priority from 05/13/1998 in terms of other possible diluents from the number indicated.  The sign of item 14, which consists in impregnating the zeolite after its synthesis with the gallium salt, has priority from 05/13/1998, and the sign of item 14, consisting in subsequent calcination in air, takes priority from 07/29/1997.

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