Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
1998-05-13
2002-07-02
Geist, Gary (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S716000, C568S764000, C568S765000, C568S771000, C568S800000, C502S063000, C502S064000, C502S071000
Reexamination Certificate
active
06414197
ABSTRACT:
BACKGROUND OF THE INVENTION
This application claims rights of priority under 35 U.S.C. § 119 based on Russian Patent Application No. 97112675, filed Jul. 5, 1997.
1. Field of the Invention
This invention is related to the field of organic synthesis, and in particular, to the methods for preparing hydroxylated aromatic compounds (e.g., phenol and its derivatives), by selective oxidation of aromatic compounds (e.g., benzene and its derivatives), with gaseous mixtures comprising nitrous oxide in the presence of heterogeneous catalysts. Commercial zeolites or zeolite-containing catalysts modified by special treatments described herein are used as heterogeneous catalysts.
2. Description of the Prior Art
Various processes are known in the art for preparing phenol and its derivatives, such as diphenols, cheorophenols, fluorophenols, alkylphenols and the like. Known processes include direct oxidation of aromatic hydrocarbons or their derivatives with O
2
, N
2
O or other gaseous oxidants in the presence of oxide catalysts such as those referenced in U.S. Pat. No. 5,110,995. However, the majority of the 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 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.
At temperatures of 550-600° C., the ZnPO
4
catalyst produced a phenol yield of about 25%. However, the selectivity of ZnPO
4
was poor (60%) [Japan Patent No. 56-77234 and 56-87527, 1981]. 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
O) 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 7-8%, 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
O as an oxidant (E. 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., U.S. Pat. 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° C. leads to the 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 yields of phenol and low selectivity at high reaction temperatures.
The zeolites of the pentasil type (e.g., ZSM-5, ZSM-11, ZSM-12, ZSM-23), mordenite, zeolite Beta and EU-1, which are all modified with small iron additives during their synthesis, are known systems for performing this catalytic reaction. For example, in U.S. Pat. Nos. 5,672,777 and 5,110,995, experimental results are presented for benzene oxidation with nitrous oxide at 275-450° C. The contact time was 2-4 sec, the liquid space velocity of benzene was 0.4 h
−1
, and the molar benzene : N
2
O 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 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 (V.L. Zholobenko, Mend. Commun., 1993, p. 28). This high temperature dehydroxylation pretreatment was found to increase the phenol yield from ~12 to ~20-25 wt. % at the N
2
O:benzene ratio of 4:1. However, this catalyst also produced a low yield of phenol. In the process 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
O over the hydrocarbon (e.g., 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
O was used (up to 9:1), and the selectivity of N
2
O 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 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
O (Kharitonov A. S., et al., U.S. Pat. No. 5,672,777, 1997—Russian Patent No. 2074164, C07C 37/60, June 1997-1 Application No. 94013071/04, C07C 37/60, 27.12.1995). 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 (e.g., phenol and derivatives) by selective oxidation of aromatic compounds (e.g., benzene and its derivatives). Specifically, it is an object of the invention to use N
2
O 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
O by decreasing the oxidant-to-hydrocarbon ratio in the feed, and increasing the efficiency of N
2
O conversion to the desired oxidation products. It is also an object of the invention to avoid producing side products.
SUMMARY OF THE INVENTION
The objects of the invention are accomplished by a method of preparing hydroxylated aromatic compounds (e.g., phenol or its derivatives) by oxidation of aromatic compounds (e.g., 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 (i.e., hydroxylated aromatic compounds). 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 acid-base sites of a specific nature. These sites can be introduced into the zeolite catalyst by performing a special high-temperature
Bogdan Viktor Ignatyevich
Kazansky Vladimir Borisovich
Kustov Leonid Modestovich
Geist Gary
White Everett
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