AU7393598A - Preparation of phenol and its derivatives - Google Patents

Description

YII_ Our Ref: 690783 P/00/011 Regulation 3:2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Applicant(s): Address for Service: Invention Title: Rhein Chemie Rheinau GmbH Dusseldorfer Strasse 23-27 D-68219 Mannheim

GERMANY

DAVIES COLLISON CAVE Patent Trade Mark Attorneys Level 10. 10 Barrack Street SYDNEY NSW 2000 Sulphurised unbranched compounds, a process for the production thereof and their use The following statement is a full description of this invention, including the best method of performing it known to me:- 5020 8CL-7174 UNITED STATES PATENT APPLICATION

OF

L.M. KUSTOV, V.I. BOGDAN AND V.B. KAZANSKY

SFOR

PREPARATION OF PHENOL AND ITS DERIVATIVES BACKGROUND OF THE INVENTION This application claims rights of priority under 35 U.S.C. 119 based on Russian Patent Application No. 97112675, filed July 5, 1997.

Field of the Invention This invention is related to the field of organic synthesis, and in particular, to the methods for preparing hvdroxylated aromatic compounds phenol and its derivatives), by selective oxidation of aromatic compounds benzene and its derivatives), with gaseous mixtures comprising nitrous S 5 oxide in the presence of heterogeneous catalysts. Commercial zeolites or zeolite-containing catalysts modified by special treatments described herein are used as heterogeneous catalysts.

Description of the Prior Art Various processes are known in the art for preparing phenol and its derivatives, such as diphenols, chlorophenols, fluorophenols, alkylphenols and the like. Known processes include direct oxidation of aromatic hydrocarbons or their derivatives with 02, N 2 0 or other gaseous oxidants in the presence of S oxide catalysts such as those referenced in U.S. Patent No. 5,110,995. However, the majority of the known oxide catalysts for the direct oxidation of benzene to S" phenol in the presence of molecular oxygen, do not provide high selectivity and 15 yield of the target product. The most successful example of such a catalyst is prepared from phosphates of various metals. In particular, ZnPO 4 has been used as a catalyst for benzene oxidation into phenol in the presence of alcohols.

8CL-7174 At temperatures of 550-600 OC, the ZnPO 4 catalyst produced a phenol yield of about 25%. However, the selectivity of ZnPO, was poor [Japan Patent No. 56-77234 and 56-87527, 19811. Furthermore, phosphate catalysts are disadvantageous for benzene oxidation because they consume substantial quantities of alcohols.

Vanadium-, molybdenum-, or tungsten-based oxide catalyst systems for direct benzene oxidation with nitrous oxide (N 2 0) at 500-600 °C are known [Iwamoto et al., J. Phys. Chem., 1983, v. 87, no. 6, p. 903]. The maximum phenol yield for such catalysts in the presence of an excess of steam is about with a selectivity of 70-72%. The main drawbacks of these catalysts are their low selectivity and yield of phenol, the required high temperatures for the reaction, and the requirement to add steam.

Zeolite catalysts are also available for the selective oxidation of benzene and its derivatives using N 2 0 as an oxidant Suzuki, K. Nakashiro, Y. Ono, Chem. Lett., 1988, no. 6, p. 953-1 M. Gubelmann et al., Eur. Pat., 341, 165, 1989- 1 M. Gubelmann et al., US Patent, No. 5,001,280, 1990). Specifically, high-silica ZSM-5 type pentasil zeolites are used as catalysts for oxidation of benzene, chlorobenzene, and fluorobenzene into corresponding phenols. The oxidation of benzene with nitrous oxide on HZSM-5 zeolite at 400 oC leads to the 20 formation of phenol with a yield up to 16%, and a selectivity close to 98-99%.

The disadvantage of these catalysts is that they have low conversion rates, low S"yields of phenol and low selectivity at high reaction temperatures.

S The zeolites of the pentasil type ZSM-5, ZSM-11, ZSM-12, ZSM-23), mordenite, zeolite Beta and EU-1, which are all modified with small iron S 25 additives during their synthesis, are known systems for performing this catalytic reaction. For example, in U.S. Patent Nos. 5,672,777 and 5,110,995, experimental results are presented for benzene oxidation with nitrous oxide at 275450 The contact time was 2-4 sec, the liquid space velocity of benzene was 0.4 h-i, and the molar benzene N20 ratio was 1:4. The phenol yield typically reached 20-30%, and the selectivity was 90-97%. The disadvantages of these catalysts include the necessity to introduce iron ions into the zeolite and to ~R-ay-~p-~rrrra~ 8CL-7174 control the oxidation state of iron ions, the low liquid space velocity value of benzene, the significant contact time necessary to obtain acceptable, but not impressive yields of the final product, and the low selectivity at elevated temperatures (-450 C).

An HZSM-5 type catalyst that is dehydroxylated at a high temperature is also known in the art Zholobenko, Mend. Commun., 1993, p. 28). This Shigh temperature dehydroxylation pretreatment was found to increase the phenol yield from -12 to -20-25 wt. at the N 2 0 benzene ratio of 4:1.

However, this catalyst also produced a low vield of phenol. In the process 1 C described above, the high-temperature dehydroxylation was performed in one stage with no control of the nature of the zeolite active sites. Therefore, in this process, the formation of both framework and extra framework active sites was quite possible. The significant disadvantage of all these methods is that they require a large excess of N 2 0 over the hydrocarbon benzene) to provide more complete conversion of the hydrocarbon to the desired oxidation products.

Another method of benzene oxidation was proposed in the patent by Panov G.I. et al. (PCT W095/27691). In this method, an excess of benzene over

N

2 0 was used (up to and the selectivity of N 2 0 conversion into phenol was improved. However, in this case, the catalyst contained iron as an active component. Such catalysts are problematic because the oxidation state of the iron introduced into such a catalyst must be controlled. Also, the yield of phenol barely exceeded 20 wt. although the benzene liquid hourly space velocity (hereinafter "LHSV") was increased as compared to the previous 25 systems to about 2-2.5 h- 1 In another known method, phenol is produced by 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 pretreated at 350-950 °C in steam containing 0.1-100 mol. H 2 0 (Kharitonov et al., U.S. Patent, 5,672,777, 1997- Russian Patent No. 2074164, C07C 37/60, June 1997-1 Application No. 94013071/04, C07C 37/60, 27.12.1995).

8CL-7174 4 However, treatment of the zeolite catalyst using this method does not cause a substantial increase in the activity. Another drawback of this method is the low stability of the resultant catalyst, which deactivates during the oxidation process due to the formation of tar-like side-products. Another disadvantage of all the methods described above is the low partial pressures 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 develop a method of preparing hydroxylated aromatic compounds phenol and derivatives) by selective oxidation of aromatic compounds benzene and its derivatives).

Specifically, it is an object of the invention to use N 2 0 as a mild oxidant in the presence of an appropriate catalyst that enhances productivity of the oxidation process by increasing the yield of hydroxylated aromatics and selectivity for the target product. It is a further object of the invention to simultaneously minimize the consumption of N 2 0 by decreasing the oxidant-to-hydrocarbon ratio in the feed, and increasing the efficiency of N 2 0 conversion to the desired Soxidation products. It is also an object of the invention to avoid producing side Sproducts.

SUMMARY OF THE INVENTION The objects of the invention are accomplished by a method of preparing hydroxylated aromatic compounds phenol or its derivatives) by oxidation of aromatic compounds benzene and derivatives) with nitrous oxide. The method of the present invention significantly increases the process efficiency due to the increase in the activity and selectivity of the catalyst, and the increase in the yield of the target products hydroxylated aromatic compounds).

25 In order to achieve these results, the aromatic compounds are oxidized using nitrous oxide at 225-500 °C in the presence of a zeolite catalyst. The zeolite catalyst according to the invention is modified with strong Lewis acidbase sites of a specific nature. These sites can be introduced into the zeolite catalyst by performing a special high-temperature pretreatment. This 8CL-7174 preliminary thermal activation of the H-form of zeolite is carried out in two steps. In the first step, the catalyst is heated at 350-450 OC for 4-6 h in an inert gas (nitrogen or helium) or air stream. In the second step, the catalyst is calcined at 450-1000 °C for 1-3 h in a continuous flow of an inert gas or air followed by cooling the zeolite catalyst to the reaction temperature (typically 300-450 OC). In a preferred version of the invention, the hydroxylated aromatic compounds are phenol and its derivatives, and the aromatic compounds are benzene and its derivatives.

Applicants do not wish to be bound by any particular theory of operation of the invention. However, Applicants offer the following explanation of how the temperature treatment affects the catalyst. The purpose of the two-step high-temperature treatment is related to the generation of a specific type of Lewis acid-base pair centers, preferably framework Lewis acidbase sites. This is achieved by separating the stage of removal of adsorbed water and/or ammonium ions (which are introduced via ion exchange at the stage of the preparation of an H- or NH4-forms of zeolites), from the stage of S; removing structural (bridging) OH groups intrinsic to the H-zeolite framework.

S For this purpose, the thermal treatment is carried out in two steps. In the first step, the zeolite is calcined at a temperature up to 350-450 °C (a conventional 20 pretreatment). In this first step, adsorbed water and exchanged ammonium ions are intensively removed. In the second step, the zeolite is calcined at temperatures ranging from 450 to 950 OC, depending on the zeolite composition. In this second step, structural (acidic) OH groups of zeolites are removed. This second step can solve two problems: removing acidic OH groups that are the active sites for side reactions leading to the formation of tarlike products; and creating new (aprotic) rather strong Lewis acid-base pairs, preferably related to the framework of the zeolite, that are capable of activating N0O molecules to cause evolution of molecular nitrogen and formation of atomic oxygen species adsorbed on strong Lewis acid sites. The atomic oxygen acts as a mild oxidizing agent in the reaction of selective oxidation of aromatic compounds to corresponding hvdroxylated aromatic compounds. The strong 8CL-7174 Lewis acid-base centers as precursors of the active oxidizing centers (atomic oxygen) can be detected by IR spectroscopy using adsorbed probe-molecules, such as CO, H 2

C-

4 etc.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE

INVENTION

According to the present invention, the starting materials for the preparation of the zeolite catalysts are the commercial forms of zeolites, such as: high-silica pentasil-type zeolites like ZSM-5, ZSM-11 etc., prepared, for instance, as described in U.S. Patent No. 3,702,886, which is hereby incorporated by reference; zeolite H-mordenite; or isomorphously substituted pentasils like ferrisilicate, gallosilicate etc.

Preferably, a commercial ZSM type zeolite (ZSMe-5, ZSM-11, ZSM-12, ZSM-23 etc.) with Si/Al or Si/Me ratios (where Me Ga, Fe) greater than 20 is Sused i the present invention. In more preferred versions of the invention, the Si/ Al or Si/Me ratio ranges from 40 to 100.

According to the present invention, the commercial zeolite is acidified by addition thereto of an inorganic or organic acid. In a preferred embodiment of the invention, the zeolite is acidified by soaking it with from 10 ml to 100 ml of acid per gram of a zeolite, wherein the acid has a normality of from 0.1 N to 2 N. The acid soaking may be done in a single step, or more preferably, in several steps.

25 Acid forms of zeolite may be also prepared by exchanging of a Scommercial zeolite with an aqueous solution of an ammonium salt a nitrate or chloride salt). For example, a Na-form of ZSM-,tpe zeolite is treated Swith a 0.1 2 N solution of an appropriate ammonium salt. The ion exchange degree of sodium for ammonium or protons is varied from 30 to 100%, and 3 more preferably from 50 to 8CL-7174 Zeolites can be used as catalysts in the pure form or in a combination with an appropriate binder. In a preferred embodiment of the invention, amorphous silica with a specific surface area ranging from 100 to 600 m 2 or alumina with a specific surface area ranging from 100 to 400 m 2 or a mixture thereof, are used as binders. The content of the binder in the catalyst ranged from 5 to 50 wt and more preferably from 20 to 30 wt Nitrous oxide may be employed alone, or in admixture with an inert gas such as nitrogen or helium, or in admixture with air.

Aromatic hydrocarbons, such as benzene, toluene, ethylbenzene, cumene, xylenes and the like, the halogenated aromatic compounds such as chlorobenzene, fluorobenzene, difluorobenzenes and the like, phenol, stvrene or a mixture thereof are typically used as substrates for selective oxidation with nitrous oxide. It is also possible to selectively further oxidize an aromatic compound such as phenol, using the process described herein. For purposes of this specification, these substrate materials will be generally referred to as "aromatic compounds." :'In the process described herein, the substrate is typically introduced in a mixture with nitrous oxide in a molar ratio of nitrous oxide to substrate ranging from 1:7 to 5:1, and more preferably, from 1:2 to 4:1. The LHSV of the substrate S 20 ranged 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 from 300 to 500 and more preferably from 350 to 450 The contact time of the reaction mixture with a catalyst ranges from 0.5 to 8 sec, and more preferably from 1 to 4 s.

The gases evolved from the reactor may comprise a mixture of phenol and dihydroxybenzenes and are condensed and separated by any technique known to this art (GC, LC, MS or a combination thereof).

The catalyst can be easily and reversibly regenerated by calcination at S. 400-600 °C in a flow of air, oxygen, and nitrous oxide, or mixtures thereof with an inert gas. The regeneration is carried out for 1-3 h.

In order to further illustrate the present invention and the advantages thereof, the following specific examples are given, it being understood that

C

8CL-7174 8 same are intended only as illustrative and in no way limitative.

In said examples below, the following parameters, are used: C percentage of conversion, S percentage selectivity, Y yield based on the product passed C x S. The characteristics reported in the Examples are averaged over a two hour time period on stream.

EXAMPLE 1 Synthesis of the starting HZSM-5 zeolite was carried out as described in U.S. Patent No. 3,702,886, which is hereby incorporated by reference.

Experimental conditions of benzene oxidation with nitrous oxide: Vapor phase continuous Catalyst HZSM-5 (SiO 2

A

2 0 3 42) Standard pretreatment 350 C temperature High-temperature calcination at 450, 650, 750, 850, 920 or 1100 °C 7 Reaction temperature 350 °C Molar ratio Benzene/N 2 /N20=2/5/8 Sa 200 mg of catalyst HZSM-5 (Si/AI 21) in powder form (particle size of 0.2 0.5 mm) dispersed in 400 mg of quartz grains of the same size were placed 2, into a tubular reactor constructed of quartz or stainless steel (with an internal diameter of 7 mm). Prior to the reaction, the catalyst was pretreated in two stages. The first stage was a conditioning of the catalyst for 5 h at 350 °C under nitrogen or air flow (60 ml/min) in a tubular oven. The second stage was a mild high-temperature calcination step comprising heating the catalyst for an additional two hours at a higher temperature (450, 650, 750, 850, 920 or 1100 OC) in a continuous nitrogen or air flow. After this treatment, the catalyst was cooled down to the reaction temperature 350 OC) in flowing nitrogen. The reaction was carried out continuously by introducing a mixture of: benzene with a LHSV of 0.5-2 h- 1 nitrous oxide and helium (nitrogen). The mixture's contact time was 1-4 sec.

The data on the conversion, selectivity and yield of phenol versus the II~;F=kim~iE3~iTTC=~n--c--P~ )l ~rr~ 8CL-7174 final temperature of the high-temperature pretreatment, are presented in Table 1. Also, the percent of deactivation a decrease of the conversion during the following 60 min of time on stream) is given in Table 1. As seen from this table, the high-temperature treatment in dry air leading to the formation of the framework coupled Lewis acid-base centers considerably enhances the catalytic activity. At a temperature above 1000 1100 oC, a collapse of the structure of the HZSM-5 zeolite takes place, thereby resulting in a drop of the activity.

Table 1. Benzene oxidation at 350 °C on HZSM-5 zeolite (Example 1) Conditions of high- Deactivation temperature treatment, C, S, Y, (during OC 60 min), 350 10 97 9.7 450 12 95 11.4 42 650 16 95 15.2 750 21 96 20.2 42 850 29 94 27.8 14 920 36 98 35.3 11 1100 0

*O

3 s 8CL-7174 EXAMPLE 2 The catalyst preparation and catalytic testing were done as described in Example 1, with the exception that a higher reaction temperature of 450 °C was employed. The data obtained are shown in Table 2.

These data show that if a higher reaction temperature about 450 OC) is employed, the activity, and especially the selectivity, of the catalyst increases with increasing temperature of the high-temperature calcination. Thus, for the catalyst developed in the present invention, the reaction of direct oxidation of benzene into phenol proceeds with a selectivity close to 100% even at high reaction temperatures.

Table 2. Benzene oxidation at 450 0 C on HZSM-5 zeolite (Example 2) Conditions of Deactivation high C, S, Y, (during temperature min), treatment, °C 350 47 38 17.8 24 450 51 35 17.9 18.5 650 55 37 20.4 18 750 52 41 21.3 17 850 54 68 36.7 920 58 95 55.1 11 S1100 0 0 EXAMPLES 3 AND 4 The catalyst preparation and catalytic testing were done as in Examples 1 and 2, respectively, except for the type of the catalyst used. In order to determine the dependence of the catalytic parameters on the Si/Al ratio in the framework, HZSM-5 zeolite with Si/Al 50 (Example 3) and HZSM-5 with Si/Al 21 (Example 4) were compared. In these tests, the benzene partial pressure was 60-80 torr. The results of the evaluation are summarized in Table C1~ 8CL-7174 11 3. The increase in the Si/Al ratio in the zeolite results in a 100% selectivity to phenol. This 100% selectivity is maintained over a wide range of preliminary high-temperature treatments.

Table 3. Comparison of the catalytic properties of zeolites with different Si/ Al ratio in benzene oxidation Conditions of Si/AI 50 Si/Al 21 high-temperature treatment, C (Example 3) (Example 4) S, Y, Reaction temperature 350 °C 550 2 100 2 14 95 13.3 650 13 100 13 16 95 15.2 750 21 100 21 21 96 20.2 Reaction temperature 450 °C 450 70 85 59.5 51 35 17.9 750 77 90 69.3 52 41 21.3 850 75 100 75 54 68 36.7 EXAMPLE The zeolite HZSM-5 (Si/AI 21) prepared via acid treatment or NHexchange as in Example 1, was calcined at 450 °C for 5 h (Cycle then at 800 °C for 2 h in flowing air. After this treatment, the catalyst was cooled down to room temperature, and was kept in contact with water vapor during 24 h (Cycle Next, the sample was again calcined at 450, 650 or 800 °C for 2 h, and S:the reaction of benzene oxidation with N 2 0 was carried out at 350 OC 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 better activity than the fresh catalyst treated under standard conditions (-450 OC). This holds true even if the pretreated catalyst is subsequently hydrated and calcined a second time at 450 500 OC. Thus, once the coupled framework Lewis acid-base centers are formed, C=~19ii~~ I*rL~L~LZ CI~ I 8CL-7174 they survive saturation with water vapor provided that further calcination is performed at temperatures above 450 "C.

Table 4. Influence of the pretreatment conditions on the activity and selectivity in direct benzene oxidation (Example Pretreatment conditions C, S, 1. Activation at 450 oC 12 (Cycle 1) 2. Cycle 1 activation at 800 24 96 'C Cycle 2 activation at 450 °C 3. Cycle 1 activation at 30 800 °C Cycle 2 activation at 650 °C 4. Cycle 1 activation at 34 97 800 °C Cycle 2 activation at 800 °C 5. Activation at 650 °C 16 EXAMPLE 6 2.3 g of the catalyst prepared according to Example 3, and pretreated at 900 was loaded (particle size, 1-2 mm). Benzene was supplied with a space velocity of 0.5 h- 1 and the N 2 0 C 6 1- 6 ratio is 2:1. The benzene partial pressure was 120 torr (the benzene content in the vapor phase was 16 mol. At the reaction temperature 370 the yield of phenol was 25%, and the selectivity was 100%. At the reaction temperature of 420 oC, the yield was 32%, the selectivity was 99%.

8CL-7174 13 EXAMPLE 7 2.3 g of the catalyst prepared according to Example 3, and pretreated at 900 OC, was loaded in the reactor (particle size, 1-2 mm). Benzene was supplied with a LHSV of 0.3 h-i and the N 2 0 C 6 H6 ratio was 1:1. At a 370 °C reaction temperature, the yield of phenol was 37% and the selectivity was 100%. At 420 OC, the yield was 49%, and the selectivity was 99%. The efficiency of utilization for selective oxidation of benzene to phenol was 98%.

EXAMPLE 8 2.3 g of the HZSM-5 zeolite (particle size, 1-2 mm) with Si/Al 40 was prepared according to Example 3, pretreated at 850 and was loaded in the reactor. Benzene was supplied with a LHSV of 0.5 h-I and the N 2 0: C 6

H

6 ratio was 0.5:1. At a 400 °C reaction temperature, the yield of phenol based on N 2 0 was 28.3%, and the selectivity was 99%. Alternatively, the yield on the basis of benzene was 14.2%. At 420 the phenol yield on the basis of N20 was 33.6%, and the selectivity was 98%. Alternatively, the yield on the basis of benzene was 16.8%. The efficiency of N 2 0 utilization for selective oxidation of benzene to phenol was 96%.

EXAMPLE 9 2.3 g of the HZSM-5 zeolite (particle size, 1-2 mm) with Si/ Al= 40 was P prepared according to Example 3, pretreated at 850 oC, and was loaded in the reactor. Benzene was supplied with a LHSV of 0.3 h- 1 and the N 2 0: C 6 -I ratio was 0.5:1. At a 420 "C reaction temperature, the yield of phenol based on N 2 0 was 28.2%, and the selectivity was 98%. The efficiency of N 2 0 utilization for selective oxidation of benzene to phenol was EXAMPLE 2.3 g of the HZSM-5 zeolite (particle size, 1 2 mm) with Si/Al =40 was prepared according to Example 3, pretreated at 850 and loaded in the reactor. Benzene was supplied with a LHSV of 0.5 h- 1 and the N 2 0: C 6 He, ratio 8CL-7174 14 was 1:1. A mixture of N 2 0 and air was used as an oxidant. At 370 OC, the yield of phenol was 26.8%, and the selectivity was 98%.

EXAMPLE 11 The HZSM-5 zeolite (Si/Al 40) was extruded with a SiO 2 binder SiO2 80% HZSM-5) and the extrudates (cylinders 2 x 2 mm) were calcined in two steps according to the procedure described in Example 1. The final temperature of the high temperature treatment was 900 The catalyst was tested in benzene oxidation with N 2 0. In this test, the benzene LHSV was 1.7 h- 1 the benzene-to-N20 molar ratio was 7:1 (a large excess of benzene over

N

2 and the temperature was 440-470 The yield of phenol (on the basis of

N

2 0) was 20.6% at 440 °C and 30.2% at 470 OC. The efficiency of N20 utilization for selective oxidation of benzene to phenol was 95-96%.

EXAMPLE 12 A gallium-modified HZSM-5 zeolite was prepared by impregnation of a HZSM-5 zeolite with an aqueous solution of gallium nitrate, followed by calcination at 500 °C for 4 h to remove the nitrate ions (the Ga2O 3 content was 3 i. wt The zeolite was subsequently pretreated at 850 °C and was loaded in the reactor. 2.3 g (particle size, 1-2 mm) of the zeolite was treated in this manner.

Benzene was supplied with a LHSV of 0.5 h- 1 at the N 2 0: C 6 He ratio of 0.5:1. At the 420 OC reaction temperature, the yield of phenol was 20.8% on the basis of

N

2 0, or 10.4% on the basis of benzene. The selectivity was 100%. The efficiency of N 2 0 utilization for selective oxidation of benzene to phenol was 100%.

EXAMPLES 13 and 14 250 mg of 0.5-1.0 mm particle size catalyst was prepared according to Example 3. This catalyst was diluted with quartz grains (750 mg), and the mixture was loaded into the reactor. Benzene (Example 13) and phenol (Example 14) were used as substrates. The nitrous oxide substrate ratio was 4:1, the LHSV was 0.5 h- 1 and the reaction temperature 430 In the case of 8CL-7174 benzene, a product comprising 75% phenol and 25% of a mixture of o- and pdiphenols (in a 1:4 ratio) was obtained. The overall yield was 60%, and the Sselectivity was 97%. In the case of phenol, a mixture of and p-diphenols I in the ratio 1.0: 0.5: 4.0 with the overall yield of 75% was produced.

j EXAMPLES 15-20 500 mg of the catalyst prepared according to Examples 1 and 2 was placed in a flow setup. The substrates used were fluorobenzene, pdifluorobenzene, toluene, p-xylene, ethylbenzene, and styrene (Examples 15-20, respectively). The ratio in the gas mixture was He: air: nitrous oxide 1:3:5.

The LSHV of the substrate was 1-3 The N 2 0: substrate ratio was 4:1. The data on the oxidation of the substrates are given in Tables 5-7. Several values for the conversion in the tables correspond to different reaction times of 10, 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 fluorobenzene oxidation, a mixture containing predominantly p-fluorophenol (up to 75% in the mixture) is produced without S formation of the m-isomer.

eme 8CL-7174

I

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Table 5. Oxidation of fluorobenzene on the zeolite catalyst (Example Liquid Space T, -C C, Selectivity to velocity, fluorophenol 2.3 400 52 92 400 60 92 39 27 450 74 58 56 Table 6. Oxidation of difluorobenzenes on the zeolite catalyst (Example 16) Substrate T, 0 C C, Selectivity to Selectivity to dilurorophenol. fluorophenol,% o-difluorobenzene 400 30 84 16 rn-difluorobenzene 40 28218 p-difluorobenizene 450 44 II~ DR~ 1~ 8CL-7174 Table 7. Oxidation of alkylbenzenes on the zeolite catalyst Examples 16 T, oC Alkvlbenzene 350 p-xylene C, Yield of alkylphenol, 2 8 T) 8 1

I

400 1 4 4 16 Other Products (yield, toluene pseudocumene toluene, pseudocumene stvrene (34) stvrene (37), benzofuran (14) 17 400 18 400 toluene ethvlbenzene 60 20 j1

P

,gi.

450 350 400 85 20 19 stvrene 10 37 0 benzofuran 0 benzofuran phenylacetic aldehyde, acid (13) EXAMPLE 21 zeolite containing Ga ions in the framework, which were introduced during the synthesis (Si/Ga 40), was subject to high-temperature treatment by stepwise calcination at 450 oC for 5 h and at 750 °C for 2 h.

Fluorobenzene oxidation was carried out using this catalyst wherein LHSV of benzene is 2.3 reaction temperature is 400 and the composition of the gas mixture is air: N 2 0: He 3:5:2. The N 2 0 substrate ratio was 1:4. Under these conditions, the fluorophenol yield was 20%, and the selectivity was 97%. The para-isomer predominates among the fluorophenols produced To summarize, the examples show that the presently invented catalysts, when applied to oxidize benzene and its derivatives into corresponding 8CL-7174 1 phenols in the presence of nitrous oxide as an oxidant, exhibit the following advantages over the known catalysts reported in the patents: The benzene conversion for the catalysts according to the invention may be increased from 10-20% to 50-75% without decreasing the selectivity (-98 100%,); The selectivity of phenol production at a high reaction temperature (-400-470 oC) may be increased from 30-40% to 95-100%, and the phenol yield may be increased up to The efficiency of N 2 0 utilization for the selective oxidation of the 1 0 aromatic compounds can be increased from 80-85% to 95-100%; When a zeolite catalyst which has been subjected to the preliminary high-temperature pretreatment is used, the use of a higher partial pressures of benzene, and lower N20z: benzene ratios may be employed. This produces a decrease in the consumption of nitrous oxide, and an increase in the phenol productivity; The stability and the life time of a catalyst may be considerably improved by modifying a zeolite catalysts to introduce strong Lewis acid-base sites. These sites have a specific nature, and are created by high-temperature calcination of the zeolites preceding the catalytic testing; The high yield and selectivity of phenol formation can be achieved without introduction of special iron additives into the catalyst and steam .treatment; In some cases of oxidation of benzene derivatives halogenated benzenes, phenols), the process has high selectivity and regioselectivity toward p-isomers of the phenols.

.While the invention has been described in terms of various preferred embodiments, the skilled artisan will appreciate that various modifications, substitutions, omissions and other changes may be made without departing from the spirit thereof. Accordingly, it is intended that the scope of the present invention shall not be limited to the preferred embodiments of the invention described herein.

I- P:\WPDOCSXPAnTCOMPIIRUS 29&'9 18a- Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

I* e s •e

Claims (18)

1. A process for preparing a hydroxylated aromatic compound by oxidation of an aromatic compound, wherein said hydroxylated monocyclic aromatic compound has one more hydroxyl group than said monocyclic aromatic compound, which process comprises: combining said aromatic compound with nitrous oxide at a reaction temperature between 225 500 oC, and exposing said nitrous oxide and said aromatic compound to a heterogeneous catalyst composition comprising a high silica pentasil-type zeolite modified with strong Lewis acid-base centers; wherein said Lewis acid- base centers are generated by a special preliminary activation procedure comprising the steps of: first, heating the zeolite at 350 550 oC in a first flowing gas for 4 6 h; second, calcining the zeolite at 550 1100 °C for 1 3 h in a S continuous flow of a second gas; and S(c) third, cooling the zeolite catalyst to the reaction temperature, thereby S forming the heterogeneous catalyst composition.

2. A process according to claim 1, wherein said hydroxylated aromatic compound is selected from the group consisting of phenol, diphenols, chlorophenols, fluorophenols, difluorophenols, alkyl phenols, and other phenol derivatives.

3. A process according to claim 2, wherein said aromatic compound molecule 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 Sgroups comprising 1 to 3 carbon atoms.

4. A process according to claim 3, wherein the first flowing gas is selected from the group consisting of nitrogen and air, and the second of gas is selected from the group consisting of an inert gas and air. 8CL-7174 A process according to claim 1, wherein the high-silica pentasil zeolite is an H-form of ZSM-5 zeolite with Si/Al in the range of from 20 to 100.

6. A process according to claim 1, wherein the Si/Al ratio ranges from 30 to

7. A process according to claim 1, wherein the reaction temperature is from 300 to 500 'C.

8. A process according to claim 1, wherein the molar ratio of N 2 0: substrate ranges from 1:7 to 10:1.

9. A process according to claim 1, wherein the molar N 2 0: substrate ratio is in the range of from 0.5:1 to 1:1. A process according to claim 1, wherein an inert gas diluent is added to the aromatic compound and nitrous oxide combination, wherein the diluent is selected from the group consisting of N, He, and Ar.

11. A process according to claim 1, wherein a diluent is added to the aromatic compound and nitrous oxide combination, wherein said diluent is selected from the group consisting of air and mixtures of air with inert gases.

12. A process according to claim 1, wherein a diluent is added to the aromatic compound and nitrous oxide combination, wherein said diluent is selected from the group consisting of oxygen and mixtures of oxygen with inert gas(es).

13. A process according to claim 1, wherein the zeolite comprises gallium, and the silica to gallium ratio is from 10 to 100.

14. A process according to claim 13, wherein the gallium is introduced into the zeolite during synthesis of the zeolite. A process according to claim 13, wherein after zeolite synthesis, the zeolite is impregnated with a gallium salt, and subsequently calcined in air.

16. A process according to claim 15, wherein said calcining step is performed at a temperature ranging from 550 to 800 *C. RI 8CL-7174 7

17. A process as claimed in Claim 1, wherein the heterogeneous catalyst composition further comprises a binder, wherein the weight content of the binder ranges from 1.0 to 99.0 wt

18. A process according to claim 17, wherein the weight content of the binder ranges from 10 to 30 wt

19. A process according to claim 17, wherein the binder is selected from the group consisting of silica, alumina, and mixtures thereof. An improved process for oxidizing an aromatic compound, which process comprises: reacting said aromatic compound with nitrous oxide at a reaction temperature of 225 500 wherein the improvement comprises contacting the aromatic compound with nitrous oxide in the presence of a heterogeneous catalyst composition comprising a high-silica pentasil-type zeolite modified with strong Lewis acid-base centers, wherein said Lewis acid-base centers are generated by a special preliminary activation S procedures comprising the steps of: first, heating the zeolite at 350 550 °C in a first flowing gas for 4 6 h; second, calcining the zeolite at 550 1100 °C for 1-3 h in a continuous flow of gas; and third, cooling the zeolite catalyst to the reaction temperature, thereby forming the heterogeneous catalyst composition.

21. A process for preparing a high-silica pentasil-type zeolite Smodified with strong Lewis acid-base centers which comprise the steps of: first, heating a high-silica pentasil-type zeolite at 350 550 'C in a first flowing gas for 4-6 h; second, calcining the zeolite at 550 1100 °C for 1 3 h in a continuous flow of gas; and third, cooling the zeolite catalyst to a temperature of from 225 500 °C.

22. A method and catalyst for the selective oxidation of aromatic coimpounds, substantially as hereinbefore described with reference to the Examples. DATED this 29th day of June 1998 GENERAL ELECTRIC COMPANY and ZELINKSY INSTITUT'E OF ORGANIC CHEMISTRY By Its Patent Attorneys DAVIIES COLLISON CAVE