Method for operating hydrogenation reactor

Abstract

The invention relates to a method for operating a reactor for the continuous hydrogenation of aromatic nitro compounds, in particular for closed-loop control with respect to the completion of the conversion, during an increase in throughput, for example in a start-up phase after the start-up of the reactor until a steady-state operating state is reached. The method is characterised in particular in that, during a time period [Delta] t10 during which the throughput increase takes place, (1) the flow rate N (Ar (NO2) m) of the aromatic nitro compound supplied to the reactor and (2) the difference between the flow rate of hydrogen supplied to the reactor and the flow rate of hydrogen optionally discharged from the reactor [Delta] N (H2) = N (H2)-NAUS (H2) is determined n times, where n is a natural number from 10 to 3000, and (3) the difference between the flow rate of hydrogen supplied to the reactor and the flow rate of hydrogen optionally discharged from the reactor is determined n times. Wherein the supply of the aromatic nitro compounds to the reactor is interrupted when an imaginary value niFIK (Ar (NO2) m) of the (absolute) amount of the unhydrogenated aromatic nitro compounds in the liquid phase (F), calculated from summing (I) after each of the n assays described below, reaches or exceeds a predefined maximum allowable value NMAXFIK (Ar (NO2) m): # imgabs0 # wherein i is an operational number for numbering the n assays, ni (Ar (NO2) m) is shown as a molar flow rate # imgabs1 # (e.g., in mol * h <-1 >), S represents a stoichiometric factor, where S = 3 * m, [Delta] Ni (H2) is shown as a molar flow rate # imgabs2 # (e.g., in mol * h <-1 >), and [Delta] ti (Ar (NO2) m) and [Delta] ti (H2) each represent a time period between two successive measurements.

Description

[0001] The invention relates to a method for operating a reactor for the continuous hydrogenation of aromatic nitro compounds with increased throughput, in particular with closed-loop control with respect to the complete conversion, during the start-up phase after starting up the reactor until steady-state operation is reached.

[0002] A chemical reaction that is carried out continuously is characterized in that, in normal operation, a specific flow rate of reactants is continuously supplied to the reactor (the reactor is "loaded" with a specific flow rate of reactants; it is operated with a specific "load" of reactants), and a corresponding flow rate of products is continuously removed from the reactor. A continuously operated chemical reactor is designed and optimized to operate at a specific flow rate of reactants; this flow rate is usually referred to as the "nominal load". During the operation of such a reactor, there are usually different time periods in which, in order to increase the flow rate of the resulting product (hereinafter referred to as: production), the flow rate of reactants supplied to the reactor must be increased (i.e., an increase in "load" is carried out, i.e., an increase in throughput is carried out), for example when starting up the reactor after a downtime or when the reactor temporarily (e.g. due to lack of demand for the product) is operated at a load below the "nominal load" and the "load" should be increased to the "nominal load". The method of the present invention relates to such a time period of throughput increase for increasing the production. The method is characterized in particular in that, during the time period Δt during which the throughput increase is carried out 10 Inside,

[0003] (1) Flow rate of aromatic nitro compound supplied to the reactor N(Ar(NO2) m ),as well as

[0004] (2) The difference between the hydrogen flow rate supplied to the reactor and the hydrogen flow rate optionally discharged from the reactor is ΔN(H2) = N(H2) – N AUS (H2)

[0005] Determine n times, where n is a natural number from 10 to 3000,

[0006] where the fictitious value N for the (absolute) amount of unhydrogenated aromatic nitro compounds in the liquid phase (F) calculated according to the summation (I) after each of the n determinations explained below is: FIK (Ar(NO2) m ) reaches or exceeds the pre-specified maximum allowable value N MAX FIK (Ar(NO2) m ), interrupting the supply of the aromatic nitro compound to the reactor:

[0007]

[0008] in

[0009] i is the run number, which is used to number n measurements,

[0010] N i (Ar(NO2) m ) as the molar flow rate (For example, in mol·h -1 In units),

[0011] S represents the stoichiometric factor, where S = 3·m,

[0012] ΔN i (H2) as molar flow (For example, in mol·h -1 is shown in units), and

[0013] Δt i (Ar(NO2) m ) and Δt i (H2) respectively represents the time period between two consecutive measurements.

[0014] Aromatic nitro compounds are hydrogenated to the corresponding aromatic amines according to the following formula

[0015] Ar(NO2) m +3mH2→Ar(NH2) m +2mH2O

[0016] It is an important reaction in preparative organic chemistry and is also of great significance in industrial production. The most important aromatic amines in terms of annual production, namely aniline (ANL) and toluenediamine (TDA), are mainly or completely produced by hydrogenating the corresponding nitro compounds, namely mononitrobenzene (MNB; Ar=C6H5; m=1) and dinitrotoluene (DNT; Ar=CH3C6H3; m=2). For this purpose, the hydrogenation reactor must be operated continuously at high production capacity (and therefore high throughput), which poses a challenge to process control technology. Both safety aspects and quality aspects must be taken into account here. In particular, insufficient conversion of aromatic nitro compounds can cause problems in both aspects.

[0017] WO 2006 / 089906 A1 describes a process for preparing aromatic amines by hydrogenating nitroaromatic compounds or aliphatic amino alcohols by hydrogenating nitroalcohols in the presence of a catalyst, wherein a fluid reaction mixture containing the amine or amino alcohol is formed in a reactor, from which the catalyst is separated off. The process is characterized in particular in that, after separation of the catalyst, the absorption of UV / VIS radiation by the reaction mixture is measured in order to determine the concentration of nitro compounds and nitroso compounds in the reaction mixture. Monitoring the conversion by UV / VIS spectroscopy is naturally associated with a high expenditure on measurement technology. In addition, such an apparatus requires regular monitoring, since the accuracy of such optical measurement methods decreases over time, for example due to dirtiness of the measurement apparatus used, which can contaminate windows required for the measurement, etc.

[0018] EP 1077921 A1, published as WO 99 / 59956 A1, describes a process for preparing optionally substituted 4-aminodiphenylamine, comprising converting optionally substituted aniline and optionally substituted nitrobenzene in the presence of water and a base, wherein the water content is controlled so as to ensure that the molar ratio of water to the base used is not less than about 4:1 at the beginning of the coupling reaction and not less than about 0.6:1 at the end of the coupling reaction, to prepare 4-nitrodiphenylamine and / or 4-nitrosodiphenylamine and / or salts thereof. The coupling reaction is followed by a hydrogenation reaction, wherein the coupling reaction product is hydrogenated in the presence of a hydrogenation catalyst and added water so as to ensure that the molar ratio of total water to base is at least about 4:1 at the end of the hydrogenation. An aqueous phase and an organic phase are obtained, and the optionally substituted 4-aminodiphenylamine is obtained from the organic phase. Only discontinuous process operation is specifically described.

[0019] EP 2523933 A2, published as WO 2011 / 086050 A2, describes a method for preparing aromatic amines in a liquid phase by catalytically hydrogenating the corresponding nitroaromatic compounds in at least two reaction spaces connected in series, wherein at least one reaction space is operated isothermally, and at least the reaction space downstream thereof is operated adiabatically, and in a preferred embodiment, adiabatic temperature jumps are used to monitor the reaction, which is difficult to achieve or cannot be achieved at all when the production volume changes. It seems that the procedure cannot be used for a method in which only one reaction space is operated isothermally or only one reaction space is set. In addition, the method presupposes that the reaction mixture has a certain reactivity. If this is not the case, for example, due to the complete absence of a catalyst in the case of improper operation or technical defects, there is no adiabatic temperature jump, which makes the corresponding reaction monitoring impossible.

[0020] EP 2812308 A1, published as WO 2013 / 117622 A1, describes a continuous process for preparing at least one aromatic amine by hydrogenating at least one nitroaromatic compound with hydrogen at a temperature of 50 to 250° C. and a pressure of 5 to 50 bar in the presence of a catalyst suspended in a liquid phase, wherein there is at least a liquid phase containing the aromatic amine and at least a gas phase containing hydrogen. The reactor disclosed in WO 00 / 35852 A1 is described as being particularly suitable. In the process according to WO 2013 / 117622 A1, the pressure in the reactor is kept substantially constant by continuously adjusting the amount of hydrogen supplied to the reactor. The total amount of hydrogen supplied to the reactor is monitored, and if the amount of hydrogen absorbed in the reactor is not at least 50 mol%, preferably at least 70 mol%, more preferably at least 90 mol%, even more preferably at least 95 mol%, and especially at least 98 mol% of the amount of hydrogen required for the stoichiometric conversion of the at least one nitroaromatic compound to the at least one aromatic amine, the supply of the at least one nitroaromatic compound is interrupted. A disadvantage of this method is that it is not suitable for non-steady-state operating conditions, in particular in the case of increased throughput, such as during the start-up of a hydrogenation reactor from an operational shutdown.

[0021] This is because the hydrogenation reactor is usually put into operation when the flow rates of nitro compounds and hydrogen are significantly lower than the corresponding target flow rates. These initial flow rates are then gradually increased (e.g. continuously increased) until the desired target flow rates are reached. The hydrogenation reactor can then be in an operating state in the sense of a steady state, i.e., a specific continuous and (except for unexpected fluctuations) constant flow rate of aromatic nitro compounds and hydrogen is supplied, except for conceivable operating faults, and a specific constant flow rate of aromatic amines and water is discharged. However, in the intermediate state between the first supply of aromatic nitro compounds and hydrogen and the reaching of the target flow rate (start-up time), the flow rates vary continuously. Even in the time period when no changes are deliberately made (the "plateau period" when the flow rates are gradually increased), there will be fluctuations that are larger than the fluctuations in the steady-state operating state. In this sense, the start-up time is a non-steady-state operating state of the hydrogenation reactor. Monitoring hydrogenation in this state is related to the specific challenges solved by the present invention. In particular, it is very important to provide the plant operator with a criterion according to which a decision can be made, optionally in an automated manner, when the startup process deviates from the target sequence, so that the supply of aromatic nitro compounds must be interrupted in order to be able to comply with product quality requirements or even safety requirements. The above aspects are not only important when starting up a hydrogenation reactor from an operating shutdown, but also in the case of an increase in throughput during normal operation. For example, it is conceivable that the hydrogenation plant after startup is operated for a certain period of time, in which the throughput does not correspond to the maximum possible throughput of the plant in question (for example because the demand for hydrogenated product is not high enough). If the demand increases at a later point in time and the throughput increases accordingly, similar problems will arise as when starting up from a shutdown state.

[0022] Therefore, there is a need for further improvements in the field of hydrogenation of nitroaromatic compounds. In particular, it would be desirable to be able to operate the hydrogenation reactor in such a way that even in a non-steady state with increased throughput (e.g. at startup), reliable monitoring of the reaction is ensured, especially with regard to the presence of unconverted nitro compounds in the liquid phase. In this way, the reaction scheme would be improved in terms of quality and especially safety, and in particular could be operated without great expenditure on measurement technology.

[0023] In view of this need, the subject of the present invention is a process for operating a continuous hydrogenation of aromatic nitro compounds (Ar(NO2) m ), in particular a computer-implemented method,

[0024] The hydrogenation is carried out with hydrogen (H2) in the presence of a catalyst according to the following formula to obtain an aromatic amine (Ar(NH2) m )):

[0025] Ar(NO2) m +3mH2→Ar(NH2)m +2mH2O

[0026] wherein Ar is an aryl group and m is 1 or 2.

[0027] In the process of the present invention, during the hydrogenation process, a liquid phase (F) containing a catalyst suspension and a gas phase (G) containing hydrogen are present in the reactor. m ) and hydrogen at a flow rate N (H2), and a product stream (PS) comprising aromatic amine and optionally unhydrogenated aromatic nitro compound is withdrawn while retaining the catalyst. Optionally, a product stream (PS) is withdrawn from the reactor at a flow rate N AUS (H2) The hydrogen is discharged (so-called purge). A constant pressure is established in the gas phase (G).

[0028] The method comprises a time period Δt starting from time point t0 and ending at time point t1. 10 The throughput is increased (at least once) within a reactor. In the present invention, an increase in throughput is understood to mean an increase in the flow rate of the reactants (i.e. the aromatic nitro compound and hydrogen) supplied to the reactor. In the case of an increase in throughput in the sense of the present invention, the flow rate N(Ar(NO2)) is continuously or intermittently increased. m ) from the value N t＝t0 (Ar(NO2) m ) increases to the value N t＝t1 (Ar(NO2) m )>N t＝t0 (Ar(NO2) m ) and change the flow rate N(H2) from the value N t＝t0 (H2) increases to value N t＝t1 (H2)>N t＝t0 (H2) (i.e., t1 is reached when the flow rates of the aromatic nitro compound and hydrogen each reach the target value at the end of the throughput increase (wherein the two flow rates do not necessarily reach their respective values ​​at the same time). In the sense of the present invention, throughput increase refers in particular to N(Ar(NO2) m ) is increased by at least 0.5%, more preferably by at least 1%, of the starting value, so that in particular

[0029] N t＝t1 (Ar(NO2) m )≥1,005·N t＝t0 (Ar(NO2) m ),

[0030] Especially preferred

[0031] N t＝t1 (Ar(NO2) m )≥1,01·N t＝t0 (Ar(NO2)m ).

[0032] The flow rate N(H2) of hydrogen supplied to the reactor is increased so that - taking into account any hydrogen discharge (so-called purge) - there is always at least the stoichiometric amount of hydrogen required for the hydrogenation. The maximum value of the throughput increase is limited only by the maximum capacity of the reactor used.

[0033] The method of the present invention is characterized in that during the time period Δt 10 Inside,

[0034] (1) Flow rate of aromatic nitro compound supplied to the reactor N(Ar(NO2) m ),as well as

[0035] (2) The difference between the hydrogen flow rate supplied to the reactor and the hydrogen flow rate optionally discharged from the reactor is ΔN(H2) = N(H2) – N AUS (H2),

[0036] Determining n times, in particular by means of a sensor unit, wherein n is a natural number between 10 and 3000,

[0037] where the fictitious value N for the (absolute) amount of unhydrogenated aromatic nitro compounds in the liquid phase (F) calculated according to the sum after each of the n determinations explained below is: FIK (Ar(NO2) m ) reaches or exceeds the pre-specified maximum allowable value N MAX FIK (Ar(NO2) m ), the supply of aromatic nitro compound to the reactor is interrupted. It is appropriate here to use the molar amount (n) to establish the summation to convert N FIK (Ar(NO2) m ) is expressed as molar flow rate n FIK (Ar(NO2) m ), where the maximum permissible value should of course also be expressed in the same units, i.e., as molar quantity n MAX FIK (Ar(NO2) m ):

[0038]

[0039] in

[0040] i is the run number, which is used to number n measurements,

[0041] N i (Ar(NO2) m ) as the molar flow rate (For example, in mol·h-1 In units),

[0042] S represents the stoichiometric factor, where S = 3·m,

[0043] ΔN i (H2) as molar flow (For example, in mol·h -1 is shown in units), and

[0044] Δt i (Ar(NO2) m ) and Δt i (H2) respectively represents the time period between two consecutive measurements.

[0045] Another subject of the present invention is a method for the ring-closing control of an aromatic nitro compound (Ar(NO2) m ) of a computer system, a computer program product, and a method for continuously hydrogenating an aromatic nitro compound (Ar(NO2)) with hydrogen (H2) in the presence of a catalyst m ) production equipment, which includes the computer system of the present invention.

[0046] Completely surprisingly, it has been found that the determination of a hypothetical value for the amount of unhydrogenated aromatic nitro compounds, as described above, provides a suitable criterion for deciding when, during a throughput increase (e.g. during the start-up period), the supply of aromatic nitro compounds to the hydrogenation reactor must be interrupted for quality reasons and / or safety reasons. A person skilled in the art can easily determine a suitable maximum permissible value under given boundary conditions (reactor type, its operating conditions, in particular with regard to temperature and pressure, and the size of the desired target flow rates of aromatic nitro compounds and hydrogen). When, for the purpose of defining the criterion for interrupting the supply of aromatic nitro compounds, an absolute value is not used, but a value based on the mass of the liquid phase m is used. F The maximum permissible concentration of the unhydrogenated aromatic nitro compounds is calculated substantially or completely independent of the boundary conditions. This is the subject of a preferred embodiment, which will be explained in detail below.

[0047] The method of the present invention involves closed-loop control of the reactor in terms of completing the conversion during the throughput increase. Here, this throughput increase includes a time period Δt 10 During this period, starting from the time point t0, the flow rate of the aromatic nitro compound supplied to the reactor and the flow rate of the hydrogen supplied to the reactor increase (= throughput increase). The time point at which these two flow rates reach the respective required increase values ​​is called t1 (i.e., it applies: Δt 10= t1-t0). The flow rates of the nitroaromatic compound and hydrogen do not need to reach the respective desired increased values ​​simultaneously. If one of the two flows (particularly the hydrogen flow N(H2)) reaches the desired value at the end of the throughput increase later than the other flow, then this later time point corresponds to the time point t1.

[0048] According to the present invention, the reactor is operated continuously. This means that the reactants (i.e., aromatic nitro compounds and hydrogen) and optionally used additives such as solvents are continuously supplied to the reactor during the production cycle, and the formed products (i.e., aromatic amines and water) and additives (solvents) are continuously removed from the reactor. This does not necessarily apply to the catalyst used. The catalyst can be retained in the reactor, for example, by a filter, and only replaced after the end of the production cycle (or multiple production cycles), i.e., when the catalytic activity decreases very much. However, the method of the present invention also includes catalyst replacement during continuous operation (or just the supply of fresh catalyst). In the terms of the present invention, the production cycle refers to the time period from the start of continuous production until its end. The start of continuous production is understood here to refer to the time point (t B , t0 is a special case). The continuous production is terminated by stopping the supply of aromatic nitro compound (t2). (Generally speaking, after shutting off the supply of aromatic nitro compound, the hydrogen is allowed to continue to flow for a period of time before the reactor is completely shut down to ensure that any aromatic nitro compound still present in the reactor has reacted completely.)

[0049] The flow rate denoted by N in the terminology of the present invention can in principle be indicated as a mass flow rate, a volume flow rate or a molar flow rate. In industrial practice, the nitroaromatic compound flow rate N(Ar(NO2) m ) is usually used as mass flow Shown, for example, in kg·h –1 The hydrogen flow N(H2) (whether supplied or exhausted) is usually expressed as a volume flow Q(H2), for example in Nm 3 ·h -1 Unit (Nm 3 = standard cubic meter; volume converted based on standard conditions of 101325 Pa pressure and 273.15 K temperature). In the present invention, both can be used without difficulty. For simplicity, the above formula (I) is for molar flow is formulated so that the imaginary value of the amount of unhydrogenated aromatic nitro compound is taken as the molar flow rate n i FIK (Ar(NO2) m ) is given. In the embodiments already mentioned in which the maximum permissible (hypothetical) concentration of the unhydrogenated aromatic nitro compound is used, this concentration is then given as a ratio to the partial molar amount qMAX FIK (Ar(NO2) m ) is shown. For a person skilled in the art, it is simple in industrial practice to reformulate formula (I) for other flow units by adjusting the stoichiometric factor S accordingly and to show the preferred concentrations in terms of other parameters besides the molar amounts of the molar ratios. This does not constitute a departure from the scope of the present invention.

[0050] Attached photos show:

[0051] Figure 1 : A reactor including peripheral units operable by the process of the invention;

[0052] Figure 2 : Schematic diagram of the flow rate N of the hydrogenation reactant in one production cycle;

[0053] Figure 3 : A schematic diagram showing the relationship between a hypothetical value of the amount of the unreacted aromatic nitro compound and an interruption in the supply of the aromatic nitro compound;

[0054] Figure 4 : the relative flow rates of hydrogen and dinitrotoluene (DNT) (in % of nominal load) and the assumed concentration of unhydrogenated aromatic nitro compounds during normal start-up operation of a DNT hydrogenation plant; and

[0055] Figure 5 : Relative flows of hydrogen and dinitrotoluene (DNT) (in % of the nominal load) and the hypothetical concentration of unhydrogenated aromatic nitro compounds during conventional start-up operation of a DNT hydrogenation plant in which no catalyst is fed to the hydrogenation reactor.

[0056] First, various possible embodiments of the present invention are described. Brief Description :

[0057] In a first embodiment of the process according to the invention, which can be combined with all other embodiments, based on the mass m of the liquid phase M_MAX (F) The maximum allowable value of the meter n MAX FIK (Ar(NO2) m ) MAX FIK (Ar(NO2) m )

[0058] q MAX FIK (Ar(NO2) m )=n MAX FIK (Ar(NO2) m ) / mM_MAX (F),

[0059] 0.006 mol / kg to 0.550 mol / kg, preferably 0.010 mol / kg to 0.200 mol / kg, more preferably 0.013 mol / kg to 0.029 mol / kg,

[0060] in

[0061] m M_MAX (F) indicates that in n i FIK (Ar(NO2) m ) is equal to or greater than n for the first time MAX FIK (Ar(NO2) m ) is the mass of the liquid phase at the time point i (and wherein for the molar amount q MAX FIK (Ar(NO2) m ) Each range given is combinable with all other embodiments of the invention).

[0062] In a second embodiment of the process according to the invention, which can be combined with all other embodiments, n is from 80 to 3000 and the time period Δt 10 Preferably, n is from 100 to 2500, and Δt 10 More preferably, n is from 500 to 2200, and Δt 10 is 15 to 60 minutes. Most preferably, n is 1000 to 2000, and Δt 10 From 20 minutes to 40 minutes.

[0063] In a third embodiment of the process according to the invention, which can be combined with all the other embodiments, the nitroaromatic compound is mononitrobenzene (Ar═C 6 H 5 ; m=1) or dinitrotoluene (Ar═CH 3 C 6 H 3 ; m=2).

[0064] In a fourth embodiment of the process according to the invention, which can be combined with all other embodiments, the hydrogenation is carried out at a temperature of 80 to 200° C., preferably 110 to 180° C., and a pressure of 5.0 to 120 bar, preferably 10 to 100 bar.

[0065] In a fifth embodiment of the process according to the invention, which can be combined with all other embodiments, the catalyst comprises Pt, Pd, Rh, Ru, Ni, Co, Cu or mixtures thereof, wherein preference is given to catalysts comprising Pt, Pd, Ni or Cu.

[0066] In a sixth embodiment of the process according to the invention, which can be combined with all the other embodiments, the reactor is a stirred tank reactor, a trickle film reactor or a bubble column reactor.

[0067] In a seventh embodiment of the process according to the invention, which can be combined with all other embodiments, the suspension of the catalyst is an organic solvent and / or an aromatic amine (Ar(NH2) m )) (suspension from an earlier production cycle).

[0068] In an eighth embodiment of the process according to the invention, which can be combined with all other embodiments, the throughput increase comprises starting the hydrogenation from a state in which the reactor (R) is not in operation.

[0069] under Detailed explanation The embodiments briefly described above and other possible configurations of the present invention. Unless those skilled in the art clearly see the opposite from the context or clearly explain different contents, all the above embodiments and other configurations of the present invention described below can be combined with each other as needed.

[0070] Suitable aromatic nitro compounds are especially mononitrobenzene (Ar=C6H5; m=1) and dinitrotoluene (Ar=CH3C6H3; m=2). The aromatic nitro compounds are hydrogenated to the corresponding aromatic amines using hydrogen or a mixture of hydrogen and an inert gas as hydrogenating agent. The hydrogenation can be carried out at temperatures and pressures customary in the art. Preferred temperatures are 80° C. to 200° C., in particular 110° C. to 180° C. Preferred pressures are 5.0 bar to 120 bar, in particular 10 bar to 100 bar. (Here and hereinafter, all pressure data are to be regarded as absolute pressures.) The temperature measurement is carried out by means known to the person skilled in the art, for example thermocouples or resistance thermometers, semiconductor thermometers or infrared thermometers. The pressure measurement is preferably carried out by a mechanical pressure gauge or an electronic pressure sensor.

[0071] Catalysts that can be considered here are all catalysts that are usually used for catalytic hydrogenation. Preferably, catalysts containing precious metals such as Pt, Pd, Rh, Ru or non-ferrous metals such as Ni, Co or Cu or mixtures thereof are used. Particularly preferably, catalysts containing Pt, Pd, Ni or Cu are used, especially as aqueous suspensions. In the case of precious metal catalysts, these catalysts are applied to a support, such as activated carbon, SiO2 or Al2O3; in the case of Ni catalysts, both supported Ni and Ni skeleton catalysts can be used. The catalyst concentration in the liquid phase present in the reactor is preferably 0.01% to 20% by mass, preferably 0.50% to 10% by mass, based on the total mass of the liquid phase.

[0072] If a mixture of hydrogen and an inert gas is used, the preferred inert gas is ammonia, a noble gas and / or nitrogen. Hydrogen or a mixture of hydrogen and an inert gas is added so that a constant pressure is established in the reactor, i.e. the amount of hydrogen added corresponds to the sum of the hydrogen consumed chemically and the hydrogen optionally discharged as a purge stream. In the case of using a mixture of hydrogen and an inert gas as the hydrogenating agent, the ratio of hydrogen to inert gas in the supplied hydrogenating agent is gradually increased so that the reactor contents are not starved of hydrogen.

[0073] In the process of the invention, it is preferred to use an excess of hydrogen based on the amount required for hydrogenating the nitro groups to the amino groups. In particular, the excess of hydrogen is at least 0.01%, preferably at least 0.10%, and at most 10%, based on the molar amount required for hydrogenating the nitro groups to the amino groups. These values ​​apply to steady-state conditions except when the throughput is increased. Although these values ​​can generally also be used when the throughput is increased, there may also be differences, especially in the case of an increase in throughput to start up the reactor (put into operation).

[0074] Optionally, a solvent that is inert under the reaction conditions, such as an alcohol, for example methanol, propanol, isopropanol, or an ether, such as dioxane or tetrahydrofuran, can be used. In order to improve the economic feasibility of the process, a lower solvent concentration is generally advantageous. This is generally 1.0% to 50% by mass, preferably 20% to 35% by mass, based on the total mass of the liquid phase.

[0075] Furthermore, in the process of the present invention, 0.10% to 10%, preferably 0.20% to 5.0% of the hydrogen flow rate used may be discharged (to remove hydrogen N AUS (H2)). This purge prevents the accumulation of inert compounds or gaseous by-products. These values ​​apply to steady-state conditions outside of the throughput increase period. Although these values ​​can generally also be used during throughput increase, there may be differences, especially when the throughput is increased to start up the reactor (put into operation).

[0076] Figure 1 By way of example, a reactor which can be operated by the process according to the invention is shown. A stirred tank reactor is shown. Other suitable reactor types are in particular trickle film reactors and bubble column reactors.

[0077] To facilitate understanding of the present invention, the operation of such a reactor under steady-state conditions (i.e., in normal operation at a constant throughput, in particular at "nominal load") is described below:

[0078] The nitroaromatic compound is introduced into the reactor (R) through the nitroaromatic compound pipeline (1) at a flow rate N SOLL (Ar(NO2) m An aromatic nitro compound (e.g. molten dinitrotoluene) is supplied and hydrogen is supplied to the reactor (R) through a hydrogen pipeline (2) at a flow rate NSOLL (H2) hydrogen is supplied. A mixture of aromatic amine (i.e. toluenediamine in the selected embodiment) and hydrogen and a catalyst (e.g. nickel catalyst) is present in the liquid phase (F) of the reactor (R). The reactor (R) may be equipped with a device (not shown in the figure) for supplying fresh catalyst during operation. Aromatic nitro compounds (i.e. dinitrotoluene in the selected embodiment) are hydrogenated with hydrogen at a temperature of, for example, 130° C. and a pressure of, for example, 20 bar.

[0079] A portion of the liquid phase (F) containing the catalyst is circulated from the reactor (R) by means of a pump (P) via lines 3, 4, 5 and 6. Line 4 leads to a cooler (K) in which the reaction mixture is cooled. From there, the cooled reaction mixture is then fed via line 5 to a cross-flow filter (Q), from which a product stream (PS) containing the aromatic amine (i.e. toluenediamine in the selected example) is discharged in a catalyst-free form via product line (7). The remainder of the reaction mixture containing the catalyst is fed again to the reactor (R) via line 6, thus completing the cycle.

[0080] Adjust N SOLL (Ar(NO2) m ) so that the average residence time in the reactor (R) is, for example, 120 minutes. SOLL (H2) so that the pressure in the reactor (R) (measured in the gas space (G) above the liquid phase (F)) remains constant.

[0081] Through pipeline 8, the flow rate N SOLL AUS (H2) Continuous removal of hydrogen from the reactor (R) (so-called purge). AUS (H2) corresponds to N SOLL (H2)1%.

[0082] Figure 2 A schematic diagram showing the flow rate N of the hydrogenation reactant in a production cycle, wherein the flow rate N of the hydrogenation reactant in a production cycle is shown as follows: B The throughput increase is shown by way of example by increasing the flow rates of aromatic nitro compound and hydrogen from t = t0 until a (optionally first) steady-state operating state with a constant throughput is reached (from t = t1). This means that the throughput increase is shown when starting the hydrogenation from a state in which the reactor (R) is not in operation (reactor start-up), for which the process according to the invention is particularly suitable.

[0083] The hydrogenation should be carried out at time t B = t0, i.e., from this time point on, hydrogen and nitroaromatic compounds are fed to the reactor. In order to prepare for the actual startup (before time point t0; Figure 2The reactor is preferably charged with a suspension of the catalyst (i) in one of the above-mentioned organic solvents which are inert under the hydrogenation conditions, (ii) in water and / or (iii) in an aromatic amine (Ar(NH2)m)) (from an earlier production cycle) and heated to the desired reaction temperature. The hydrogen supply is preferably also started before t0, in particular in such a way that the operating pressure required for the steady state is established in the gas phase (G) from t1 onwards. If a purge flow N is provided AUS (H2) (which is preferred), then it has been established at this point in time.

[0084] From t0 onwards, the reactor is additionally fed with an aromatic nitro compound. The starting values ​​N for the two flow rates are t＝t0 (H2) and N t＝t0 (Ar(NO2) m ) in the time period Δt 10 Increase to the required value N t＝t1 (H2) and N t＝t1 (Ar(NO2) m ). In the figure, the flow rate of the aromatic nitro compound reaches the expected value set for the steady-state operating state earlier (optionally for the first time) than the hydrogen flow rate. However, the time point t1 is only considered to be reached when both flows have reached the set expected values. The time period Δt 10 Preferably, it is 5 minutes to 100 minutes, more preferably 10 minutes to 80 minutes, very particularly preferably 15 minutes to 60 minutes, and extremely very particularly preferably 20 minutes to 40 minutes. At time t1, the flow required for the (optionally first) steady-state operating state exists. At this time, the aromatic nitro compound is produced continuously in the reactor until the production cycle ends at time t2. The figure is not drawn to scale; usually, the time span t2-t1 is the time span t1-t0 (=Δt 10 ) times. The supply of aromatic nitro compounds is stopped at t2, for example because the demand for aromatic amines decreases or the catalyst is exhausted. As shown in the figure, this stop does not have to be carried out suddenly. Of course, a slow reduction is also possible. The time span from t0 to t2 is called the production cycle in the present invention.

[0085] The production cycle may include a plurality of different steady-state operating states with constant throughput. For example, the throughput of aromatic nitro compounds and hydrogen present at t1 may correspond to a first steady-state operating state, and after a certain period of time a second steady-state operating state with a further increased throughput may be established. In this case, the production cycle thus includes two time periods Δt 10 , that is, Δt 10 (1) and Δt 10 (2) In the case where there are multiple time periods with increased throughput, the method of the present invention is adopted in at least one time period, preferably in all of these time periods.

[0086] The operation mode of the present invention is at least one time period Δt 10 Included

[0087] (1) Flow rate of aromatic nitro compound supplied to the reactor N(Ar(NO2) m ),as well as

[0088] (2) The difference between the hydrogen flow rate supplied to the reactor and the hydrogen flow rate optionally discharged from the reactor is ΔN(H2) = N(H2) – N AUS (H2),

[0089] The measurement is performed n times, where n is a natural number between 10 and 3000. The measurement is performed in particular by means of a sensor unit, for example by means of a conventional flow meter.

[0090] Which value of n is most suitable depends on the time period Δt 10 Preferably, n is

[0091] 80 to 3000, when Δt 10 When the time is from 5 minutes to 100 minutes,

[0092] 100 to 2500, when Δt 10 When the time is 7.5 to 80 minutes,

[0093] 500 to 2200, when Δt 10 For 15 to 60 minutes,

[0094] 1000 to 2000, when Δt 10 From 20 minutes to 40 minutes.

[0095] The flow rate of aromatic nitro compound supplied to the reactor is N(Ar(NO2) m ) is essentially known at a specific point in time (because it is adjusted to a specific value) and can advantageously be monitored with a liquid flow meter and is usually read directly at the process control system. Hydrogen is supplied to the reactor under pressure control, i.e. the pressure drop caused by the consumption of hydrogen due to the continued hydrogenation can be offset by supplying a corresponding flow of hydrogen. The supplied hydrogen flow rate N(H2) is determined by a gas flow meter. In principle, it is therefore not absolutely necessary to remove hydrogen during the production cycle. However, as mentioned above, it has been found that discharging some hydrogen from the reactor as a purge flow is useful for discharging inert substances and gaseous secondary components. The amount of hydrogen discharged with the purge flow N AUS (H2)) is measured using a gas flow meter or regulated to a specific value using a perforated orifice or valve setting.

[0096] According to the invention, after each of the n determinations, a fictitious value for the amount of unhydrogenated aromatic nitro compound (=N FIK (Ar(NO2) m )). The values ​​N obtained here i FIK (Ar(NO2) m ) are summed, and once the sum reaches or exceeds the predetermined maximum permissible value of the amount of unhydrogenated aromatic nitro compounds (=N MAX FIK (Ar(NO2) m )), the supply of aromatic nitro compounds is interrupted. Figure 3 It is schematically shown in:

[0097] Hydrogenation starts at t0 (e.g. Figure 2 ). The time for the throughput increase, i.e. the start-up time in the selected example, is initially carried out without difficulty. Although low hypothetical amounts of unhydrogenated aromatic nitro compounds are determined, these amounts are initially still far below the predefined maximum values. However, at time t3 this maximum value is reached and the supply of aromatic nitro compounds is stopped. The time point for the stop is referred to here as t3 instead of t2 in order to distinguish it from the planned stop at the end of the production cycle.

[0098] As mentioned above, it is advantageous to express the maximum permissible value of unhydrogenated aromatic nitro compounds as a concentration, since the maximum value expressed in this way is essentially independent of plant-specific parameters, such as reactor size, etc. A useful reference parameter has been found to be the mass of the liquid phase (F). For this purpose, the volume of the liquid phase and, from this, its mass can be calculated from the filling level (which itself can be adjusted by a weir installed at an appropriate height or a liquid level closed-loop control system) and the known reactor dimensions.

[0099] In this case, the maximum permissible value of unhydrogenated aromatic nitro compounds is therefore expressed as the molar fraction q MAX FIK (Ar(NO2) m ). In particular, it has been found useful

[0100] q MAX FIK (Ar(NO2) m )=n MAX FIK (Ar(NO2) m ) / m M_MAX (F) (II)

[0101] is 0.006 mol / kg to 0.550 mol / kg, preferably 0.010 mol / kg to 0.200 mol / kg, more preferably 0.013 mol / kg to 0.029 mol / kg, wherein in formula (II),

[0102] m M_MAX (F) indicates that in n i FIK (Ar(NO2) m ) is equal to or greater than n for the first time MAX FIK (Ar(NO2) m ) is the mass of the liquid phase at the time point i (and wherein the molar mass q MAX FIK (Ar(NO2) m ) Each range shown can be combined with all other embodiments of the present invention).

[0103] Of course, for the molar ratio q MAX FIK (Ar(NO2) m ) The numerical ranges given in the following should not be regarded as limiting in the sense that the use of different concentration parameters (e.g. mass ratios) in industrial practice will lead to deviations from the scope of the present invention for this reason alone. On the contrary, the numerical ranges given should be regarded as essential in the sense that the concentrations (regardless of the units given in industrial practice) are included in the numerical ranges given after conversion into molar fractions.

[0104] Another subject of the present invention is a method for the closed-loop control of an aromatic nitro compound (Ar(NO2) m ), wherein the computer system comprises the following:

[0105] The interface unit is configured to 10 Read N(Ar(NO2) m ) and ΔN(H2), in particular read in by the sensor unit described above;

[0106] and

[0107] processor, which is configured to use the read N(Ar(NO2) m ) and ΔN(H2) values ​​to calculate the molar mass n i FIK (Ar(NO2) m ) and is compared to the maximum permissible value n which is recorded in a database connected to the processor and can be called up from it MAX FIK(Ar(NO2) m ) is compared, and when the maximum allowed value n is reached or exceeded MAX FIK (Ar(NO2) m ), the supply of the aromatic nitro compound to the reactor is interrupted.

[0108] The computer system of the invention is preferably integrated into a process control system of a production plant.

[0109] When the maximum permissible value n is reached or exceeded MAX FIK (Ar(NO2) m ) is interrupted by the following method: an interruption signal is sent and received by a receiving unit (such as a valve controller), and then the supply of the aromatic nitro compound is interrupted (for example, by closing the inlet valve).

[0110] Another subject of the invention is a computer program product comprising instructions which, when executed by a computer system according to the invention described above, cause the computer system to carry out the method according to the invention described above. In particular, this is a computer program product which, when loaded into a computer system according to the invention, is executed by a processor of the computer system and which, in the method according to the invention, periodically or continuously calls N(Ar(NO2) m ) and ΔN(H2) and the maximum permissible value n MAX FIK (Ar(NO2) m ) and when the maximum allowed value n is reached or exceeded MAX FIK (Ar(NO2) m ) when the feed of the aromatic nitro compound to the reactor is interrupted, in particular by sending an interruption signal received by a receiving unit (e.g. a valve controller) as described above, and then interrupting the feed of the aromatic nitro compound (e.g. by closing the inlet valve).

[0111] Finally, the subject of the present invention is a method for treating an aromatic nitro compound (Ar(NO2)) according to the formula m ) is continuously hydrogenated with hydrogen (H2) in the presence of a catalyst to produce aromatic amines (Ar(NH2) m ))Production equipment:

[0112] Ar(NO2) m +3mH2→Ar(NH2) m +2mH2O

[0113] wherein Ar is an aryl group and m is 1 or 2,

[0114] The production equipment includes:

[0115] (I) a reactor (R) for carrying out hydrogenation;

[0116] (II) a device for providing an aromatic nitro compound and introducing it into a reactor;

[0117] (III) means for providing hydrogen and introducing it into the reactor;

[0118] (IV) means for discharging a product stream (PS) comprising aromatic amines and optionally unhydrogenated aromatic nitro compounds;

[0119] (V) means for retaining the catalyst when discharging the product stream (PS);

[0120] and

[0121] (VI) Computer system of the present invention.

[0122] With regard to the devices mentioned in (I) to (V), reference may be made to the above description of the method of the present invention and the literature cited therein.

[0123] The present invention is further described in detail below by way of examples. Example:

[0124] Embodiment 1:

[0125] A plant for the preparation of toluenediamine (TDA) from dinitrotoluene (DNT) comprising a stirred tank and a device for separating and recovering the catalyst from the product stream is charged with a mixture of TDA and water formed during the hydrogenation (from an earlier production cycle). The plant is brought to the desired temperature and the catalyst is added in an average concentration of about 1% by mass, based on the total mass of the reaction mixture. Subsequently, hydrogen is added to the plant via a pressure-maintaining device until an absolute pressure of 25 bar is established in the gas phase. At time t=0, an increasing amount of DNT is added over time (see Figure 4 ), until after about 4.0 minutes it reaches a value of about 35% of the maximum possible DNT flow for the plant. After the initial fluctuations, the hydrogen flow also reaches an essentially stable value after about 7.5 minutes (= t1), which corresponds to about 37% of the maximum possible value for the plant. The calculated concentration of unreacted dinitrotoluene q FIK (Ar(NO2) m ) was significantly lower than 0.005 mol / kg at each time point.

[0126] Embodiment 2:

[0127] Figure 5The curve obtained when no catalyst is supplied to the reactor, for example due to operator error, is shown. The calculated concentration of unreacted dinitrotoluene increases with time and exceeds a value of 0.020 mol / kg after 4.0 minutes.

[0128] Example 1 shows that in this case, due to fluctuations in the pressure-maintaining closed-loop control circuit, pure ratio monitoring is only possible after about 7.5 minutes. In contrast, Example 2 shows that, by the present method, a maximum permissible concentration q of 0.020 mol / kg is selected. MAX FIK (Ar(NO2) m ), an impending dangerous accumulation of unreacted nitroaromatic compounds was already identified in almost half the time.

Claims

1. Operation of continuous hydrogenation of aromatic nitro compounds (Ar(NO2) during throughput increase m ) of the reactor (R), The hydrogenation is carried out with hydrogen (H2) in the presence of a catalyst according to the following formula to obtain an aromatic amine (Ar(NH2) m )): Ar(NO2) m +3mH2→Ar(NH2) m +2mH2O wherein Ar is an aryl group and m is 1 or 2, During the hydrogenation process, a liquid phase (F) containing a catalyst suspension and a gas phase (G) containing hydrogen are present in the reactor, and a flow rate of N(Ar(NO2) m ) and hydrogen at a flow rate N(H2), and a product stream (PS) comprising aromatic amine and optionally unhydrogenated aromatic nitro compound is withdrawn while retaining the catalyst, wherein optionally from the reactor at a flow rate N AUS (H2) discharges hydrogen, and wherein a constant pressure is established in the gas phase (G), The method comprises a time period Δt starting from time point t0 and ending at time point t1. 10 The throughput is increased within the range, and when the throughput is increased, the flow rate N(Ar(NO2) is continuously or intermittently increased. m ) from the value N t＝t0 (Ar(NO2) m ) increases to the value N t＝t1 (Ar(NO2) m )>N t＝t0 (Ar(NO2) m ) and change the flow rate N(H2) from value N t＝t0 (H2) increases to value N t＝t1 (H2)>N t＝t0 (Ar(NO2) m ), In the time period Δt 10 Inside, (1) Flow rate of aromatic nitro compound supplied to the reactor N(Ar(NO2) m ),as well as (2) The difference between the hydrogen flow rate supplied to the reactor and the hydrogen flow rate optionally discharged from the reactor is ΔN(H2) = N(H2) – N AUS (H2) Determine n times, where n is a natural number from 10 to 3000, and wherein the fictitious value n of the molar amount of the unhydrogenated aromatic nitro compound in the liquid phase (F) calculated after each of the n determinations according to the formula i FIK (Ar(NO2) m ) reaches or exceeds the pre-defined maximum allowable value n MAX FIK (Ar(NO2) m ), interrupting the supply of the aromatic nitro compound to the reactor: in i is the run number, which is used to number n measurements, N i (Ar(NO2) m ) as the molar flow rate Shown, S represents the stoichiometric factor, where S = 3·m, ΔN i (H2) as molar flow Shown, and Δt i (Ar(NO2) m ) and Δt i (H2) respectively represents the time period between two consecutive measurements.

2. The method according to claim 1, wherein the maximum allowed value n MAX FIK (Ar(NO2) m ) based on the mass m of the liquid phase M_MAX (F) is calculated as the molar amount of the part q MAX FIK (Ar(NO2) m ) q MAX FIK (Ar(NO2) m )=n MAX FIK (Sr(NO2) M ) / m M_MAX (F) is 0.006 mol / kg to 0.550 mol / kg, in m M_MAX (F) indicates that in n i FIK (Ar(NO2) m ) is equal to or greater than n for the first time MAX FIK (Ar(NO2) m ) is the mass of the liquid phase at time point i.

3. The method according to claim 1 or 2, wherein n is 80 to 3000, and the time period Δt 10 From 5 minutes to 100 minutes.

4. The method according to claim 1 or 2, wherein n is 100 to 2500, and Δt 10 7.5 minutes to 80 minutes.

5. The method according to claim 1 or 2, wherein n is 500 to 2200, and Δt 10 From 15 minutes to 60 minutes.

6. The method according to claim 1 or 2, wherein n is 1000 to 2000, and Δt 10 From 20 minutes to 40 minutes.

7. The process according to any one of claims 1 to 6, wherein the nitroaromatic compound is mononitrobenzene (Ar=C6H5; m=1) or dinitrotoluene (Ar=CH3C6H3; m=2).

8. The process according to any one of the preceding claims, wherein the hydrogenation is carried out at a temperature of 80°C to 200°C.

9. The process according to any one of the preceding claims, wherein the catalyst comprises Pt, Pd, Rh, Ru, Ni, Co, Cu or mixtures thereof.

10. The process according to any one of the preceding claims, wherein the reactor is a stirred tank reactor, a trickle film reactor or a bubble column reactor.

11. The process according to any one of the preceding claims, wherein the catalyst suspension is an organic solvent and / or an aromatic amine (Ar(NH2) m )) in a suspension.

12. The process according to any one of the preceding claims, wherein the throughput increase comprises starting the hydrogenation from a state in which the reactor (R) is not in operation.

13. A method for closed-loop control of an aromatic nitro compound (Ar(NO2)) in a method according to any one of claims 1 to 13. m ) of the invention, comprising: The interface unit is configured to 10 Read N(Ar(NO2) m ) and the results of n measurements of ΔN(H2); and processor, which is configured to use the read N(Ar(NO2) m ) and ΔN(H2) values ​​to calculate the molar mass n i FIK (Ar(NO2) m ) and is compared to the maximum permissible value n which is recorded in a database connected to the processor and can be called up from it MAX FIK (Ar(NO2) m ) is compared, and when the maximum allowed value n is reached or exceeded MAX FIK (Ar(NO2) m ), the supply of the aromatic nitro compound to the reactor is interrupted.

14. A computer program product comprising instructions which, when executed by a computer system according to claim 13, cause the computer system to perform the method according to any one of claims 1 to 12.

15. For the aromatic nitro compound (Ar(NO2) m ) is continuously hydrogenated with hydrogen (H2) in the presence of a catalyst to produce aromatic amines (Ar(NH2) m ))Production equipment: <h2 style=";text-align:left;direction:ltr">Ar(NO2)<h2 style=";text-align:left;direction:ltr"> m <h2 style=";text-align:left;direction:ltr"> +3m H2→Ar(NH2)<h2 style=";text-align:left;direction:ltr"> m <h2 style=";text-align:left;direction:ltr"> +2m H2O wherein Ar is an aryl group and m is 1 or 2, The production equipment includes: A reactor (R) for carrying out the hydrogenation; means for providing an aromatic nitro compound and introducing it into a reactor; means for providing hydrogen and introducing it into the reactor; a device for discharging a product stream (PS) comprising aromatic amines and optionally unhydrogenated aromatic nitro compounds; means for retaining the catalyst when discharging the product stream (PS); and The computer system of claim 13.

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