Organic compounds -- part of the class 532-570 series – Organic compounds – Amino nitrogen containing
Reexamination Certificate
2001-03-28
2002-07-23
Davis, Brian J. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Amino nitrogen containing
C564S423000
Reexamination Certificate
active
06423872
ABSTRACT:
CROSS-REFERENCE TO PRIORITY APPLICATION
This application claims priority under 35 U.S.C. § 119 of FR-00/03903, filed Mar. 28, 2000, hereby expressly incorporated by reference.
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to the continuous nickel catalyzed hydrogenation of nitrated aromatic compounds, the nickel catalysts of which optionally comprising low/trace amounts of aluminum values, namely, a content of up to at most 5.5% by weight of aluminum.
This invention more especially relates to such continuous nickel/low aluminum catalyzed hydrogenation of aromatic nitro compounds, which can be carried out for at least three days without any necessity or requirement for replenishing and/or reactivating the catalyst substrate.
2. Description of the Prior Art
Processes for catalytically hydrogenating aromatic nitrated compounds have long been known. In general, these prior art processes are carried out in apparatus usually comprising two zones and peripherals therefor. The first zone is that in which the actual hydrogenation reaction is carried out; the second zone is that in which the catalyst is separated from the reaction mixture and by “peripherals” are intended the pipes, conduits and other apparatus components (storage tanks, recycling tanks, pumps, etc.), by means of which the reaction mixture and/or the reactants are conveyed, and the zone or zones for preparing the reaction mixture. It should be appreciated that the nitrated compounds, fresh solvent, if indeed used, fresh catalyst and a catalyst suspension, emanating from the reaction zone and then the separation zone, are typically admixed in this preparation zone. It is not necessary for the reaction and separation zones to be separate; this because they may exist in the same apparatus, as for example when a reactor/settling tank is employed. The hydrogenation reaction is a very rapid reaction and highly exothermic. It is typically carried out in a stirred reactor, or in a loop reactor. The process of separating the catalyst from the hydrogenate may be carried out in various ways, such as tangential filtration, transverse filtration and settling.
Usually, the hydrogenation processes for aromatic nitrated compounds are carried out in the presence of catalysts comprising at least nickel and aluminum values. Very often the catalyst is of the Raney nickel type. This catalyst may optionally be doped with various metals, such as iron and/or chromium, for example. Such catalysts are obtained via a basic treatment on an alloy comprising the catalyst metal, in this instance nickel, aluminum and possibly dopant metal or metals.
Conventionally, the industrial processes that have been developed employ Raney catalysts whose residual aluminum content is relatively high, on the order of about 7% to 15% by weight of the catalyst.
The advantages of these catalysts are well recognized and deserved, but they present a few drawbacks when employed under conditions such that the reaction is carried out continuously, with long residence times of the catalyst. The same limitations apply if these catalysts are employed under high productivity conditions.
This is because, under such conditions, the parasitic oxidation of the nickel present in the catalyst becomes great. A very hard deposit is then formed over time on the walls of the reactor, of the settling tank and/or of the peripherals. This deposit, which has been identified as having a nickel aluminate structure, for example a lamellar double hydroxide of the takovite type, is due to this significant parasitic oxidation of nickel and to the concomitant presence of hydrated aluminum oxide.
Such deposit creates a screen on the walls of the reactor, the settling tank and the peripherals, thereby reducing the productivity of the process whereas the goal was to in fact increase same.
It is therefore necessary, at quite closely spaced regular intervals, to shut down the plant or the reaction zone in question, and to clean it. However, this operation is very burdensome as it requires the use of relatively powerful means to remove this deposit, such as, for example, high-pressure lances or scraping devices.
SUMMARY OF THE INVENTION
Accordingly, a major object of the present invention is the provision of an improved process for the continuous Ni/low Al catalyzed hydrogenation of aromatic nitro compounds, but which conspicuously avoids or markedly diminishes those disadvantages and drawbacks to date characterizing the state of this art.
Briefly, the present invention features a process for the catalytic hydrogenation of nitrated aromatic compounds, carried out in a reaction zone, a separation zone and peripherals therefor, in which process the hydrogenation is conducted continuously, in the presence of a catalyst which includes at least nickel and possibly/optionally aluminum; the total aluminum content, if aluminum is present, in the catalyst being at most 5.5% by weight of the catalyst. The residence time of the same unchanged catalyst in the reaction zone, separation zone and peripherals can be at least three days without adversely affecting the efficacy and/or productivity of the reaction.
DETAILED DESCRIPTION OF BEST MODE AND SPECIFIC/PREFERRED EMBODIMENTS OF THE INVENTION
More particularly according to the present invention, by the expression “total aluminum” is intended the sum of aluminum (0) values plus aluminum (+III) values.
Thus, it has now been found that by carrying out the hydrogenation under such conditions and by employing a catalyst having, immediately from the beginning of the hydrogenation reaction, a total aluminum content much lower than that present in the catalysts today employed on an industrial scale, or even containing no aluminum in certain cases, the formation of nickel aluminate is greatly diminished, or even eliminated.
The present invention therefore also features the use of a catalyst comprising at least nickel and optionally aluminum, the total aluminum content, if aluminum is indeed present, being at most 5.5% by weight, for the purpose of limiting the formation of nickel aluminates while carrying out the catalytic hydrogenation reaction of aromatic nitrated compounds continuously.
The reduction (or limitation) in the formation of nickel aluminate may especially be observed by the increase by a factor of at least 1.5, preferably at least 2, in the operating time of the process between two shutdowns. It should be appreciated that these shutdowns are necessary since the nickel aluminate deposit then prevents the plant from being operated properly (significant reduction in productivity, blockage of the pipes, especially). Though, when the amount of initial aluminum in the catalyst is low, or when there exists no aluminum whatsoever, it is possible that no shutdown is required between two predetermined stoppages or shutdowns.
In addition, surprisingly, the use of such a catalyst does not significantly degrade the performance of the reaction, especially the yield and the consumption of catalyst. It is even more remarkable to note that the use of this type of catalyst may even help to increase the performance of the reaction.
As one illustration, the process employed under the conditions of the invention makes it possible to achieve a yield of hydrogenated compound (and therefore of aromatic amine) of at least 99.5% by weight.
The catalyst employed in the subject process is particularly suitable for achieving productivities as high as 2 mol of hydrogen converted per hour and per gram of catalyst, or indeed up to 3 mol of hydrogen converted per hour and per gram of catalyst. More particularly, the productivities attained by the process according to the invention range from 0.1 to 3 mol of hydrogen converted per hour per gram of catalyst, preferably from 0.2 to 2 mol of hydrogen converted per hour per gram of catalyst.
Too, the process according to the invention makes it possible to employ, in this reaction, catalysts comprising nickel emanating from other hydrogenation processes such as, for example, those employed for
Burns Doane Swecker & Mathis L.L.P.
Davis Brian J.
Rhodia Chimie
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