DE19857409A1 - Production of amine from nitro compound by catalytic hydrogenation, e.g. toluene diamine from dinitrotoluene, uses loop reactor with top spray for recycling part of reaction mixture from loop and reversed flow near bottom - Google Patents

Abstract

The production of amines (I) by hydrogenation of nitro compounds (II), carried out in a vertical reactor with length greater than its diameter. It has a spray at the top for introducing educts and reaction mixture and an outlet through which the reaction mixture is pumped into an external cycle. The circulation is reversed in the lower zone of the reactor.

Description

The invention relates to a continuous process for the manufacture provision of amines, especially aromatic amines, by Catalytic hydrogenation of the nitro on which the amines are based links.

The production of amines, especially aromatic ones Mono- and / or polyamines by catalytic hydrogenation of the corre sponding The appropriate mono- and / or polynitro compounds has been around for a long time known and widely described in the literature.

In the conventional production of aromatic Mono- and / or polyamines by reacting nitro compounds a considerable amount of heat is released with hydrogen. Mostly Therefore, the hydrogenation in technology is as low as possible Temperatures using hydrogenation catalysts in the Liquid phase carried out. The ver bond mixed in a solvent with the catalyst and discontinuously in an autoclave or continuously in a loop reactor, a bubble column, or a reactor cascade reduced. With these previously known methods there are a number of disadvantages, such as B. the need for Austra gene and especially the discharge of deactivated catalyst parts, which leads to catalyst losses. Furthermore, the frequently occurring side reactions that lead to the formation of disturbing Substances such as B. tar-like components, and thus too Reduce yields, a problem many have been using to date method.

To reduce these disadvantages, it is known to use the catalyst to be arranged in a fixed bed. So DE-OS 21 35 154 describes the Hydrogenation of a nitro compound alone or in the presence of a Diluent in liquid state in a tube reactor in Presence of a palladium catalyst on spinel in one Fixed bed. When using this palladium catalyst Spinel is very expensive to manufacture, and one targeted fixation on the carrier is only partially possible. Further this fixed bed hydrogenation leads to low hydrogenation yields and for the formation of high-boiling by-products. Exemplary Hydrogenolytic cleavage should be mentioned in this context gene, nuclear hydrogenation or the formation of high molecular, tar like substances. As a result of the strongly exothermic reac tion course of the nitro group conversion and the high reaction  speed at higher temperatures also explosive Side reactions occur.

To avoid these unwanted side reactions as much as possible close, therefore, was generally industrial hydrology tion of aromatic nitro compounds at relatively low Temperatures performed.

EP-A-124 010 describes a process for the preparation of aromati cal diamines by catalytic hydrogenation of the corresponding Dinitro compounds with simultaneous generation of steam with an overpressure of <1 bar. As a reactor bubble column equipped with Field tubes. A reaction suspension consisting essentially of an aromatic Dinitro compound, the corresponding diamine, a hydrogenation catalyst tor, a saturated, aliphatic alcohol with 1 to 6 carbons atoms of matter as solvent and water, is with What hydrogen fed into the reactor. The amount of in the bubbles column fed reaction suspension and the pressure that The temperature and the amount of cooling water are measured so that in the bubble column has a reaction temperature between 140 and 250 ° C is present. Known hydrogenation catalysts are used as catalysts used, preferably metals of subgroup VIII Periodic table and especially Raney iron, cobalt and nickel be used.

A disadvantage of the process described in EP-A-124 010 is the use of large amounts of solvent, which, although the Problems with the hydrogenation of polynitro compounds at higher ones Reduce temperatures, but under the hydrogenation conditions are not completely inert, leading to undesirable by-products and leads to reductions in yield.

EP-A-263 935 describes stirred tank reactors for carrying out described exothermic reactions, which are characterized by that the cooling of the reactors takes place by means of water which in Field pipes is converted into steam. Field tube heat exchangers are due to a high ratio of heat exchanger area to volume of the Reaction space marked and thus particularly effective in the Removal of heat of reaction released. The be in EP-A-263 935 However, the method described is only conditional for catalytic Hydrogenations can be used because of an optimal phase mixing is not ensured. In particular, always high Guaranteed hydrogen concentration above the reaction mixture to be a redissolving of hydrogen in the reaction mixture to ensure. Nevertheless, zones with par are formed in the reactor depletion of hydrogen. Because of the expected  Inhomogeneities are increasingly uncontrollable secondary reactions with loss of yield. The cooling surfaces are occupied also with high molecular weight compounds and / or catalytic converters share. In addition, in this process, the catalyst mechanically stressed, resulting in a reduced service life of the catalyst leads.

EP-A-634 391 describes a process for the hydrogenation of aromati described polynitro compounds to amines, in which by Technological optimization using a loop venturi reak tors with an ejector, coupled with special conditions such as exact circulation volume ratio, exact energy input, one precisely set hydrogen volume flow, the named pro problems of hydrogenation of aromatic polynitro compounds mini should be lubricated. The catalysts used in EP-A-124 010 described connections used.

In this method, it can be due to the arrangement of a Heat exchanger for removing the heat of reaction outside of Loop reactor, in the ejector and in the reactor to local over heating with immediate onset of side reactions such as core hydrogenation, hydrogenolytic cleavage or formation of high molecular, tar-like products, which are the catalyst upper occupy area, come. It also turns up in the reactor volume outside the ejector in terms of flow and Residence time behavior pure bubble column characteristic, in the random small and large-scale vortex with comparative low mass transfer performance occur. An essential ver improvement of the hydrogenation yield, the hydrogenation selectivity and Space-time yield is therefore hardly achieved with this method. In addition, by pumping the entire reacti onmixture the catalyst is mechanically stressed what in turn leads to a reduced service life of the catalyst.

GB-A-1 452 466 describes a process for nitrobenzene hydrolysis tion in which an adiabatic reactor is an isothermal reactor is connected downstream. Most of the nitrobenzene implemented in a thermostatted tube reactor, single Lich the hydrogenation of the residual nitrobenzene content takes place at relatively small excess of hydrogen of less than 30: 1 in one adiabatic reactor. However, this process is very technical complex.

DE-B-18 09 711 is concerned with the uniform introduction of liquid nitro compounds into a hot gas stream Spraying, preferably in narrowed areas immediately before Reactor. However, the process shows that despite one  considerable hydrogen surplus a large part of the reacti onsenthalpie has not left the reactor with the product gas, which leads to cooling problems.

DE-A-36 36 984 describes a process for coupled production of nitro and dinitroaromatics from the corresponding aromati hydrocarbons by nitration and their subsequent Described hydrogenation. The hydrogenation takes place in the gas phase at temperatures between 176 and 343.5 ° C. The hydrogen flow also serves to dissipate the heat of reaction in this process from the reactors. The described apparatus for gas phases hydrogenation, essentially consists of two in a row switched reactors with intermediate cooling and starting material between food, the size of which is not discussed. The Temperature profile of the reactors can be seen, however, that a not inconsiderable part of the heat of reaction due to the low heat capacity of the hydrogen not with the product gas stream leaves the reactor. This method is disadvantageous furthermore the energy-intensive vaporization of the nitroaromatics.

The object of the invention was to provide a continuous apparatus with simple equipment Lich process for the production of amines, especially aroma table amines, by hydrogenation of nitro compounds, especially aromatic nitro compounds in the presence of Hydrogenation catalysts, preferably supported metal catalyst sators, while improving the space-time yield and the Hydrogen selectivity while avoiding local overheating and thereby develop increasingly occurring side reactions.

The task could surprisingly be solved by a Process for the preparation of amines, especially aromatic ones Amines, by hydrogenation of the corresponding nitro compounds in a vertical, preferably cylindrical reactor, the Length is greater than its diameter, with one in the top Area of the reactor arranged, downward beam nozzle through which the starting materials and the reaction mixture are fed as well as a deduction at any point in the reak tors, preferably in the lower region over which the reaction gene mixing in an external circuit by means of a conveyor, preferably a pump to which the jet nozzle is fed again, and a flow reversal in the lower region of the reactor.

The invention accordingly relates to a method for the manufacture provision of amines, especially aromatic amines, by Hydrogenation of the corresponding nitroaromatics, characterized net that the implementation in a vertical, preferably zylin dynamic reactor, the length of which is greater than its diameter,  with one arranged in the upper area of the reactor, downwards directed jet nozzle through which the starting materials and the reaction mix can be fed and with a deduction at any towards the location of the reactor, preferably in the lower region the reaction mixture in an external circuit by means of a Conveyor, preferably a pump, the jet nozzle again is supplied, as well as a flow reversal in the lower area of the reactor is carried out. The reactor described is in hereinafter referred to as the loop reactor.

The flow reversal and thus the formation of an internal Loop flow can occur when withdrawing the reaction mixture in the upper Area of the reactor due to the impact of the injected reactors onmix on the reactor floor. With the preferred The reaction mixture is drawn off in the lower region of the reactor the flow reversal through internals, especially one for Vertical baffle plate, causes.

In a preferred embodiment of the method according to the invention The loop reactor points between the nozzle and the flow Conversion reversal a preferably concentric, para to the reactor wall All insert tube on. This insert tube can be as simple Pipe, as a tubular plate heat exchanger or as a spiral be designed cooling tube.

Through the concentric insertion tube in connection with the Baffle plate the loop flow inside the reactor, in fol referred to as internal loop flow, stabilized. In addition to the flow reversal, the baffle plate causes no gas blow into the external loop flow and damage the pump.

Because the diameter of the loop reactor is smaller than its height, a sufficient loop flow in the entire reactor and the formation of zones without stream prevented.

In a further preferred embodiment of the invention the reactor has integrated heat in the interior of the reactor exchanger. These heat exchangers should be designed so that they not obstruct the internal loop flow and no turbulence cause zen. As a heat exchanger, for example Pipes through which cooling medium flows, the direction of which is preferably parallel lel runs to the reactor wall, plate heat exchanger, the preferred run parallel to the reactor wall, or below closed boiler tubes as described in EP-A-263 935 so-called field tubes are used. In the  Using field tubes it is possible to steam the resulting to use as process steam.

In this embodiment, one can use the invention Describe the reactor as the reaction heat exchanger because the reacti heat is dissipated at the point of origin. It is also possible Lich, in addition to the heat exchangers integrated in the reactor to install a heat exchanger in the external loop flow gene.

The majority of the reaction mixture is in the internal Loop flow led, only a small proportion of the Reaction mixture is pumped externally and thus ensures that Drive the loop flow. The ratio of the volume flows from internal loop flow to external loop flow is 2 to 30, preferably 5 to 10.

Due to the small proportion of the external loop flow in the entire reaction mixture, significantly smaller amounts of Catalyst per unit time circulated via the circulation pump as in the case of cooling via an external heat exchanger. this leads to to reduce the mechanical stress on the catalyst and thus a longer life of the catalyst. Except this is ensured by this embodiment in conjunction with the integrated heat exchangers a high isothermal reaction, d. H. a very small temperature gradient across the reactor height, since the hydrogenation is practically completely internal Loop flow expires and the heat of reaction is already on The place where it was created. There are restrictions the reaction rate through mass and heat transport practically completely switched off. Side reactions caused by Temperature gradients in the reaction system are favored practically completely suppressed. The reaction speed is then only limited by the reaction kinetics. Moreover is the security of the process against cooling in the outside Improved the outer circuit because the reactor cooling still works works if the pump for the external circuit fails.

The jet nozzle can be designed as a one or two-substance nozzle. With the single-component nozzle, only the liquid reaction mixture is used injected and the hydrogen somewhere else, but preferably in the liquid phase, fed to the reactor. The simple structure is advantageous in this embodiment this nozzle, disadvantageous is the poorer dispersion of the Hydrogen in the reaction mixture. In the two-component nozzle, which in the Structure is more complex, the hydrogen is fed in the center of the nozzle leads and disperses. In this embodiment of the process  is the dispersion of hydrogen in the reaction mixture much better; significantly better. It can practically be excluded that partial depletion in individual zones of the reactor comes to hydrogen.

In the reactor, preferably regardless of the type of set nitro compounds, a pressure of 5 to 100 bar, preferred 10 to 50 bar, and an operating temperature of 80 to 200 ° C, preferably 100 to 150 ° C maintained. The service entry is preferably 15 to 30 kW / l at the nozzle, in the entire Re action system 3 to 10 W / l.

The product is continuously discharged from the system anywhere. The product is preferably discharged in the lower reactor area at the bottom of the reactor or in particular from the outer loop flow via a catalytic converter unit or without such. This separation unit can be a Gravity separator, e.g. B. a settler, a cross-flow filter or be a centrifuge. The catalyst can abge from the product separates and then returned to the reactor system the. The product is preferably discharged with the retention of Catalyst. The amine can then according to the usual and known processes, for example by distillation or extraction, getting cleaned.

Between the withdrawal of the reaction mixture and the separation unit a post-reactor can complete the implementation are located. This can be done like a reactor according to the invention be designed, it can also be at least one stirred tank and / or Flow tube can be used.

In the method according to the invention, the mono- and / or polynitro compound in pure form, as a mixture with the corresponding Mono- and / or polyamine, as a mixture with the corresponding Mono- and / or polyamine and water or as a mixture with the corresponding mono- and / or polyamine, water and one ins special alcoholic solvents used. The aromatic Mono and / or polynitro compound is finely divided into the Mixture entered. Preferably, the nitro compound is in the Jet nozzle entered, particularly preferably in the mixing room of the Jet.

Preferably, within the scope of the method according to the invention aromatic nitro compounds with one or more nitro groups pen and 6 to 18 carbon atoms, e.g. Nitrobenzenes such as e.g. B. o-, m-, p-nitrobenzene, 1,3-dinitrobenzene, nitrotoluenes, such as, for. B. 2,4-, 2,6-Di nitrotoluene, 2,4,6-trinitrotoluene, nitroxylenes such as e.g. B.  1,2-dimethyl-3-, 1,2-dimethyl-4-, 1,4-dimethyl-2-, 1,3-dimethyl-2-, 2,4-dimethyl-1- and 1,3-dimethyl-5-nitrobenzene, Nitronaphthalenes, e.g. B. 1-, 2-nitronaphthalene, 1,5 and 1,8-di nitronaphthalene, chloronitrobenzenes, such as. B. 2-chloro-1,3-, 1-chloro-2,4-dinitrobenzene, o-, m-, p-chloronitrobenzene, 1,2-dichloro-4, 1,4-dichloro-2, 2,4-dichloro-1 and 1,2-dichloro-3-nitrobenzene, chloronitrotoluenes, such as. B. 4-chloro-2, 4-chloro-3-, 2-chloro-4- and 2-chloro-6-nitrotoluene, nitroanilines, such as B. o-, m-, p-nitroaniline; Nitro alcohols, such as. B. Tris (hydroxymethyl) nitromethane, 2-nitro-2-methyl-, 2-nitro-2-ethyl-1,3-propanediol, 2-nitro-1-butanol and 2-nitro-2-methyl-1-propanol and any mixture of two or more of the nitro compounds mentioned.

Aromatic are preferred according to the inventive method Nitro compounds, preferably mononitrobenzene, methyl nitrobene zole or methyl nitrotoluene, and in particular 2,4-dinitrotoluene or its technical mixtures with 2,6-dinitrotoluene, where these mixtures are preferably up to 35 percent by weight on the total mixture of 2,6-dinitrotoluene in proportions of 1 up to 4 percent in vicinal DNT and 0.5 to 1.5% in 2.5 and Have 3,5-dinitrotoluene to the corresponding amines hydrated.

In particular in the hydrogenation of dinitrotoluene isomers to the Corresponding toluenediamine derivatives (TDA) can be the Invention appropriate methods are used advantageously. The formation of high-molecular, tar-like by-products, which in the process Ren of the prior art on losses in yield and Ver stick and thus to premature deactivation of the catalyst could be suppressed practically completely. In order to cleaning the TDA is also easier than with the State of the art methods.

The hydrogenation of the dinitrotouol can be carried out in solution become. The usual substances used as solvents are in particular lower alcohols, preferably ethanol, are used. Because of the optimal flow conditions and the immediate Removal of the heat of reaction in that used according to the invention Reactor it is possible to use hydrogenation without a solvent perform. This has the advantages that the volume of the reacti is less, which means a smaller dimensioning of the Reactor as well as the pumps and pipes allows that Side reactions between the solvent and the starting materials be closed as well as the effort for processing the End products is reduced.  

To carry out the method according to the invention known hydrogenation catalysts for aromatic nitro connections used. It can be homogeneous and / or in particular heterogeneous catalysts are used. The heterogeneous Catalysts are used in a finely divided state and are suspended in the reaction suspension in finely divided form. Suitable catalysts are metals of subgroup VIII Periodic table based on carrier materials such as activated carbon or Oxides of aluminum, silicon or other materials can be upset. Raney nickel and / or or supported catalysts based on nickel, palladium and / or platinum used.

By dispersing the individual reactants in Ver binding with the other reaction parameters an intensive through mixing of all components at low substrate concentrations, high mass transfer coefficient and high volume-specific Phase interfaces reached. The arrangement of the cooling pipes in the reak Gate parallel to the reactor walls has an almost complete Gradient-free reactor contents with regard to the reaction temperature temperature result. By avoiding local overheating who the side reactions clearly suppressed and catalyst activation largely avoided. It will never be so high space-time yields high selectivity achieved. Due to the presence of a external pumping circuit and the mixing ratios in the reactor has the loop reactor with regard to its residence time behavior the characteristics of a stirred tank.

As described above, the process according to the invention is particularly suitable for the hydrogenation of dinitrotouol to tolylene diamine. It is precisely this reaction that results in pronounced side reactions with the formation of tar-like constituents in the methods of the prior art. The production of toluenediamine by the process according to the invention takes place at the temperatures and pressures listed above which are customary for the production of aromatic amines. The ratio of fed dinitrotouol to the external loop flow is preferably in the range from 1 t dinitrotouol per 50 m ³ reaction mixture in the external circuit to 1 t dinitrotouol per 60 m ³ reaction mixture in the external circuit. This amount of dinitrotouol is added to the reaction mixture at any point. The dinitrotouol is preferably fed into the outer loop flow, particularly preferably in or shortly before the nozzle.

The removal of the Touylenediamine can also be at any Place. In particular, the removal takes place from the external a loop flow before feeding the dinitrotouol. There the hydrogenation of dinitrotoluene under the condition mentioned is practically quantitative in the internal loop flow, contains the external loop flow before feeding the Dinitrotouols essentially pure toluenediamine, water, optionally solvent and catalyst. The toluenediamine is separated from the withdrawn stream and fed to the cleaning leads, the catalyst and optionally water external loop flow fed again.

Due to the low concentration of dinitrotoluene in the Reaction mixture can not form explosive Gemi come.

The hydrogenation of dinitrotoluene is preferably carried out at tempera tures from 80 to 200 ° C and pressures in the range from 10 to 50 bar carried out.

The toluene produced by the process according to the invention diamine is very pure. The formation of tar-like components can be almost completely suppressed. Their share is mostly well below 1% by weight, based on the toluenediamine. The Space-time yield in the process according to the invention is included over 500 g / l / h.

The invention is illustrated in the following example become.

example

A cylindrical reactor with an external circuit, a baffle plate in the lower part of the reactor and a concentric insert tube, as shown in the figure, is used. The reaction volume of the reactor is around 0.05 m ³ . The reactor is equipped with 36 field tubes connected in parallel, which correspond to a total cooling area of approximately 2.5 m ² . The amount of cooling water fed into the field pipes was 1 m ³ / h, the temperature of the cooling water fed into the field pipes was 30 ° C.

40.3 kg / h of a dinitrotoluene, consisting of 80 parts by weight of 2,4-dinitrotoluene and 20 parts of 2,6-dinitrotoluene, were melted at 120 ° C. in a rapidly flowing mixture of about 62 parts by weight of a corresponding diaminotoluene mixture using a high-pressure pump , 36 parts by weight of water and 2 parts by weight of a finely divided Ni hydrogenation catalyst. A pressure of 25 bar was maintained in the reactor by simultaneously introducing 30 Nm ³ / h (where are standard cubic meters defined?). In order to maintain the loop flow, a volume flow of 2.6 m ³ / h was circulated in the external product circuit. A pressure of around 3 bar prevailed in the reaction nozzle and the power input was 5 kW / m ³ . The reaction proceeded under almost isothermal conditions, since the heat of reaction generated was already removed at the point at which it was generated. The maximum reaction temperature in the lower third of the reactor was 122 ° C. At the same time, 26.7 kg / h of a corresponding diaminotoluene mixture and 15.8 kg / h of water were continuously withdrawn from the reactor, with the catalyst being retained, which corresponded to a space-time yield of 580 kg of amine mixture / m ³ .h. The yield of diamine, based on the dinitro toluene used, was <99%. During the working up by distillation, 0.15% low-boiling by-products ("low boilers") and 0.75% tar-like products ("high boilers") were obtained. The content of nitro or amino nonitro compounds in the product discharge was below the detection limit of 10 ppm. A noticeable deactivation of the hydrogenation contact used could not be determined even after a reaction time of 100 h for the operating state described above.

Claims (11)

1. A process for the preparation of amines by hydrogenation of nitro compounds, characterized in that the hydrogenation in a vertical reactor, the length of which is greater than its diameter, with an ordered, downwardly directed jet nozzle in the upper region of the reactor, via which the starting materials and the reaction mixture are fed and with a fume hood at any point of the reactor, via which the reaction mixture is fed back in an external circuit by means of a conveyor to the jet nozzle, and a flow reversal in the lower region of the reactor. 2. The method according to claim 1, characterized in that the fume cupboard is located at the bottom of the reactor. 3. The method according to claim 1, characterized in that itself in the lower part of the reactor one perpendicular to the reactor wall arranged baffle plate is located. 4. The method according to claim 1, characterized in that in Reactor is a concentric insertion tube parallel to the reactor wall is attached. 5. The method according to claim 1, characterized in that in Reactor integrated heat exchangers are attached. 6. The method according to claim 1, characterized in that as Heat exchangers cooling pipes, plate heat exchangers and / or boilers tubes are used. 7. The method according to claim 1, characterized in that the Ratio of the pumped reaction mixture to that in the reak tor circulating reaction mixture is 2 to 30. 8. The method according to claim 1, characterized in that the ratio of the pumped reaction mixture to the reaction mixture circulating in the reactor is 5 to 10 . 9. The method according to claim 1, characterized in that the Implementation is carried out in the presence of catalysts. 10. The method according to claim 1, characterized in that the Hydrogenation of dinitroltouol at temperatures in the range of 80 to 180 ° C is carried out. 11. The method according to claim 1, characterized in that the Hydrogenation of dinitroltouol at pressures in the range of 10 up to 50 bar is carried out.