Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
1997-10-02
2001-07-03
Shippen, Michael L. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
Reexamination Certificate
active
06255539
ABSTRACT:
BACKGROUND OF THE INVENTION
The production of phenol or phenol derivatives by catalytic partial oxidation of benzene or benzene derivatives is known. For example, the use of a variety of catalysts such as vanadium pentoxide on silica or zeolites (e.g. ZSM-5 and ZSM-11) at elevated temperatures has been disclosed in, for example, Iwamoto et al., J. Physical Chemistry (ACS), Vol. 87, No. 6, (1983) p. 903-905; Suzuki et al., 1988 Chemistry Letters of the Chemistry Society of Japan at pages 953-956; U.S. Pat. Nos. 5,001,280, 5,110,995, and 5,055,623, the disclosures of these publications being incorporated herein by reference.
Although useful for production of both phenol and phenol derivatives, the most significant potential utility of such processes is for the production of phenol in view of the commercial importance of that compound.
To date, practical commercial use of such processes has been hindered by low productivity, problems in controlling temperature rise of the highly exothermic reaction and resulting formation of undesired by-products, and the flammability of mixtures of nitrous oxide and benzene.
Recently processes of this type have been remarkably improved by the discovery that use of a molar deficiency of nitrous oxide (as opposed to the excess or at least stoichiometric quantities previously utilized) will increase selectivity to desired products, provide for higher conversion of nitrous oxide and higher catalyst production efficiency and can also allow for lower temperature rises resulting from the exothermic reaction and for operation with non-explosive mixtures. This discovery is described in detail in U.S. patent application Ser. No. 08/419371 filed Apr. 10, 1995 and copending herewith, the disclosure of said application being incorporated herein by reference.
However the use of large excesses of benzene beyond the amount required to optimize reaction selectivity requires the separation and recycle of large amounts of benzene. Even if benzene ratios are high enough to provide non-flammable mixtures in the reactor, the separation of benzene for recycle in downstream operations may leave flammable or explosive mixtures of benzene and nitrous oxide in downstream apparatus if nitrous oxide consumption in the reaction is less than 100%. Moreover, benzene is a flammable, toxic chemical and storage and handling of large excesses of that required for reaction increases the magnitude of potential leaks.
It is therefore recognized by those skilled in the art that techniques for limiting the excess of benzene to amounts dictated by productivity considerations and, simultaneously, achieving control of flammability and/or adiabatic temperature rise problems would represent a needed advance in the art.
SUMMARY OF THE INVENTION
The present invention provides mixtures for use in processes for production of phenol and phenol derivatives and processes utilizing mixtures of the type described. The mixtures are characterized by a nitrous oxide to benzene ratio less than 0.5 and sufficient inert gas to render the mixture non-flammable. The use of preferred proportions of nitrous oxide, benzene, and inert gas permits the reaction to be conducted adiabatically without excessive temperature rise.
The invention will be further understood from the description of the preferred embodiments.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention constitutes mixtures for use in processes and processes for catalytic partial oxidation of benzene or substituted benzene by reaction with nitrous oxide in the presence of a catalyst to form phenol or substituted phenol. The mixture and process will be described by reference to the reaction of benzene to form phenol. It will be understood that the use of substituted benzenes instead of benzene will result in production of the corresponding substituted phenols.
In accordance with the process of the present invention, a mixture of benzene and nitrous oxide is contacted with a catalyst in a reactor under conditions selected to oxidize the benzene to phenol. The molar ratio of nitrous oxide to benzene in the mixture will be less than 0.5. Preferably, the ratio of nitrous oxide to benzene will be sufficiently low to provide at least 50 mole percent, most preferably 75 to 85 percent, of the obtainable selectivity of the reaction of benzene to phenol. By “obtainable selectivity” is meant the maximum selectivity of benzene to phenol which can be obtained for given reaction conditions and catalyst by reducing the mole ratio of nitrous oxide to benzene. It is noted that selectivity approaching 100 percent can be obtained but usually at the cost of lower productivity. When preferred catalysts are utilized at normal reaction temperatures, obtainable selectivity is typically approached or attained at a nitrous oxide to benzene ratio of about 0.1. Down-stream from the reactor, the unreacted benzene is separated from the product by conventional separation techniques and recycled to the reactor.
A critical requirement of the invention is that an inert gas (that is, a gas which will not adversely affect or undesirably participate in the reaction, or adversely affect the catalyst) be present throughout the process in an amount sufficient to render the various benzene
itrous oxide mixes encountered throughout the process non-flammable. (Flammability
on-flammability is determined pursuant to ASTM Standard E918). For most catalysts and reaction conditions, nitrogen, carbon dioxide, helium, argon, or mixtures thereof will constitute a satisfactory inert gas. It will be understood that different proportions of inert gas may be required in different portions of the process to satisfy the minimum requirement. For example, the ratio of nitrous oxide to benzene in the reactor may be sufficiently low in the reactor to be non-flammable even in the absence of any inert gas. However downstream removal of benzene for recycle may leave residual flammable vapor mixes of nitrous oxide and benzene in separation apparatus or other portions of the system. Such a situation would require injection of inert gas prior to or in the separator. Preferably, from the standpoint of simplicity of process control, sufficient inert gas will be included in the reactor vessel mixture to assure that downstream mixes within expected nitrous oxide to benzene ranges will be non-flammable. The inert gas will remain admixed with nitrous oxide during separation of benzene and/or phenol and thus be available to make its anti-flame function available in any downstream nitrous oxide containing mixture.
Maximum protection against flammability can be provided by means of a mixture which has a sufficiently high ratio of inert gas to nitrous oxide that the mixture will be non-flammable regardless of the amount of benzene therein. This will be the case if the molar ratio of nitrous oxide to inert gas is 0.25 or less. Such a mixture may be safely stored as a premixed feed and its use will insure against problems resulting from unexpectedly low conversion of nitrous oxide or other reaction variation. Of course, preferred mixtures will also contain proportions of benzene and nitrous oxide optimized for selectivity of phenol product. Use of excess inert gas is, within practical limits, unobjectionable and provides added protection against leakage of oxidizer (air) into the system.
It is preferred that the mixture of nitrous oxide, benzene and inert gas used in the reactor contains at least 0.3 mole percent nitrous oxide but less than 5 mole percent, most preferably less than 3 mole percent. Lower amounts tend to restrict productivity and higher amounts make it more difficult to control flammability and adiabatic temperature rise.
By selecting the proportions of the mixture in the reactor adiabatic temperature rise from the exothermic reaction can be limited to 150 degrees C. or less. When this is done the reaction can be carried out adiabatically eliminating the use of costly heat exchange means without unduly increasing formation of undesired by-products. Increasing the inert gas or benzene content of the
Buechler Christopher R.
Ebner Jerry R.
Gross Michael J.
McGhee William D.
Morris Jayne E.
Arnold White & Durkee
Shippen Michael L.
Solutia Inc.
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