Organic compounds -- part of the class 532-570 series – Organic compounds – Amino nitrogen containing
Reexamination Certificate
2001-06-11
2002-02-26
Siegel, Alan (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Amino nitrogen containing
C564S308000, C564S415000, C564S418000, C564S422000, C564S423000
Reexamination Certificate
active
06350911
ABSTRACT:
The present invention relates to a continuous process for the preparation of amines, in particular aromatic amines, by catalytic hydrogenation of the nitro compounds on which the amines are based.
The preparation of amines, in particular aromatic mono and/or polyamines, by catalytic hydrogenation of the corresponding mono and/or polynitro compounds has been known for some time and has been described many times in the literature.
In the preparation of aromatic mono and/or polyamines which is conventional in the art by reaction of nitro compounds with hydrogen, a considerable amount of heat is liberated. In industry, the hydrogenation is therefore usually carried out at very low temperatures in the liquid phase in the presence of hydrogenation catalysts. The compound to be reduced is mixed with the catalyst in a solvent and reduced batchwise in an autoclave or continuously in a loop reactor, a bubble column or a reactor cascade. These known processes have a number of disadvantages, for example the necessity to remove the deactivated catalyst fractions, in particular in continuous processes, which results in catalyst losses. Furthermore, the side reactions which frequently occur, result in the formation of interfering substances, for example tar-like constituents, and thus in reductions in yield, are a problem in many processes used hitherto.
In order to reduce these disadvantages, it is known to arrange the catalyst in a fixed bed. For example, DE-A 2 135 154 describes the hydrogenation of a nitro compound, alone or in the presence of a diluent, in the liquid state in a tubular reactor in the presence of a palladium catalyst on spinel in a fixed bed. Preparation of this palladium catalyst on spinel is very complex, and targeted immobilization on the support is only possible in some cases. Furthermore, this fixed-bed hydrogenation results in low hydrogenation yields and in the formation of high-boiling byproducts. Mention may be made by way of example in this connection of hydrogenolytic cleavage, ring hydrogenations or the formation of high-molecular-weight, tar-like substances. As a consequence of the highly exothermic force of the nitro group reaction and the high reaction rate at elevated temperatures, explosive side reactions can also occur.
In order to exclude these undesired side reactions as far as possible, industrial-scale hydrogenation of aromatic nitro compounds is therefore carried out at relatively low temperatures.
EP-A-124 010 describes a process for the preparation of aromatic diamines by catalytic hydrogenation of the corresponding dinitro compounds with simultaneous generation of steam at a pressure of >1 bar above atmospheric. The reactor used is a bubble column fitted with Field tubes. A reaction suspension essentially consisting of an aromatic dinitro compound, the corresponding diamine, a hydrogenation catalyst, a saturated, aliphatic alcohol having 1 to 6 carbon atoms as solvent and water is fed into the reactor with hydrogen. The amount of reaction suspension fed into the bubble column and the pressure, the temperature, and the amount of cooling water are set so that reaction temperature in the bubble column is from 140 to 250° C. The catalysts used are known hydrogenation catalysts, preferably metals from sub-group VIII of the Periodic Table, in particular Raney iron, cobalt and nickel.
The process described in EP-A-124 010 has the disadvantage that large amounts of solvent are used; although they do not produce the problems in the hydrogenation of polynitro compounds at elevated temperatures, they are not totally inert under the hydrogenation conditions, which results in undesired byproducts and reductions in yield.
EP-A-263 935 describes stirred-tank reactors for carrying out exothermic reactions which are distinguished by the fact that the reactors are cooled by means of water which is converted into steam in Field tubes. Field-tube heat exchangers are characterized by a high ratio between the heat-exchanger surface area and the volume of the reaction space and are thus particularly effective in dissipating heat of reaction that has been liberated. However, the process described in EP-A-263 935 is only of limited applicability for catalytic hydrogenations since there is no guarantee of optimum phase mixing. In particular, a high hydrogen concentration above the reaction mixture must always be ensured in order to guarantee continued dissolution of hydrogen in the reaction mixture. Nevertheless, zones with partial depletion of hydrogen form in the reactor. Owing to the inhomogeneities to be expected, uncontrollable side reactions take place to an increased extent, with losses of yield. In addition, the cooling surfaces become coated with high-molecular-weight compounds and/or catalyst components. In addition, the catalyst is subjected to high mechanical stresses in this process, which results in a reduced service life of the catalyst.
EP-A-634 391 describes a process for the hydrogenation of aromatic polynitro compounds to amines in which the abovementioned problems of hydrogenation of aromatic polynitro compounds are said to be minimized through technological optimization using a loop Venturi reactor with an ejector coupled with specific conditions, such as a precise circulation volume ratio, precise energy input and a precisely adjusted hydrogen volume flow rate. The catalysts used are the compounds described in EP-A-124 010.
In this process, the fact that a heat exchanger for dissipating the heat of reaction is arranged outside the loop reactor, local overheating can occur in the ejector and in the reactor, with immediate initiation of side reactions, such as ring hydrogenations, hydrogenolytic cleavage of the formation of high-molecular-weight, tar-like products which coat the catalyst surface. In addition, a pure bubble-column characteristic with respect to the flow and residence-time behavior, in which random small- and large-volume vortexes with comparatively low material transfer performance occur, becomes established in the reactor volume outside the ejector. There is therefore virtually no significant improvement in hydrogenation yield, hydrogenation selectivity and space-time yield in this process. In addition, the pumping of the entire reaction mixture again means that the catalyst here is subjected to high mechanical stresses, which again results in a reduced service life of the catalyst.
GB-A-1 452 466 describes a process for the hydrogenation of nitrobenzene in which an adiabatic reactor is installed downstream of an isothermal reactor. The majority of the nitrobenzene is reacted in a thermostatted tube-bundle reactor, with only the residual nitrobenzene being hydrogenated in an adiabatic reactor at a relatively low hydrogen excess of less than 30:1. However, this process is technically very complex.
DE-B-1 809 711 relates to the homogeneous introduction of liquid nitro compounds into a hot gas stream by atomization, preferably at narrowed points immediately before the reactor. However, the process reveals that, in spite of a considerable hydrogen excess, a large part of the reaction enthalpy does not leave the reactor with the product gas, resulting in cooling problems.
DE-A-36 36 984 describes a process for the coupled production of nitroaromatic and dinitroaromatic compounds from the corresponding aromatic hydrocarbons by nitration followed by hydrogenation. The hydrogenation is carried out in the gas phase at from 176 to 343.5° C. The hydrogen stream in this process also serves to dissipate the heat of reaction from the reactors. The gas-phase hydrogenation apparatus described essentially consists of two reactors connected in series with cooling and starting-material feed in between; however, their size is not discussed. The temperature profile of the reactors reveals, however, that a not inconsiderable part of the heat of reaction does not leave the reactor with the product gas stream owing to the low heat capacity of the hydrogen. A further disadvantage of this process is the energy-intensive evaporation of nitroaromatics.
It is
Böhling Ralf
Maurer Markus
Müller Jörn
Penzel Ulrich
Sander Michael
BASF - Aktiengesellschaft
Borrego Fernando A.
Cameron Mary K.
Siegel Alan
LandOfFree
Method for producing amines does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for producing amines, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for producing amines will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2979801