Uses of nitroaromatics in the adiabatic nitration of aromatics

Abstract

Use of nitrated aromatic organic compounds of claim 15 (nitroaromatics) for reducing the interfacial tension of the organ phase and acid phase and / or for improving the dispersibility of the organ phase and acid phase in adiabatic nitration reactions of the corresponding unnitrated aromatic organic compounds; wherein nitratable aromatic organic compounds (aromatics) are reacted in an adiabatic nitration reaction with a nitric acid / sulfuric acid-nitrating acid mixture to form the corresponding nitrated aromatic organic compounds (nitroaromatics); wherein the initial reaction mixture, which comprises the nitrateable aromatic organic compounds (aromatics) and the nitric / sulfuric acid-nitrous acid mixture, is supplemented with appropriate nitrated aromatic organic compounds (nitroaromatics), and the reaction and / or nitration reaction is initiated and / or carried out in the presence of the nitrated aromatic organic compounds (nitroaromatics); and / or . wherein the obtained nitrated aromatic organic compounds (nitroaromatics) are partially recycled back into the nitration reaction and the subsequent conversion and / or nitration reaction is started and / or carried out in the presence of the nitrated aromatic organic compounds (nitroaromatics); the conversion and / or nitration reaction is carried out under adiabatic reaction conditions; the process or conversion and / or nitration reaction is carried out in a tubular reactor.

Description

[0001] The present invention relates to the technical field of nitration, in particular the production of nitrated organic aromatic compounds (hereinafter also referred to as “nitroaromatics”, “nitrated products”, “aromatic nitro products”, “aromatic nitro compounds”, “nitrated products” or the like) by adiabatic nitration.

[0002] In particular, a process applicable according to the invention for the adiabatic nitration of nitridable aromatic organic compounds (aromatics) to the corresponding nitrated aromatic organic compounds (nitroaromatics) is described.

[0003] Furthermore, a production plant (nitration plant or plant) usable according to the invention for the adiabatic nitration of nitridable aromatic organic compounds (aromatics) to nitrated products in the form of the corresponding nitrated aromatic organic compounds (nitroaromatics) is described, in particular a production plant for carrying out the described process.

[0004] In particular, the present invention relates to the use according to the invention of nitrated aromatic organic compounds (nitroaromatics) to reduce the interfacial tension of the organ phase and acid phase and / or to improve the dispersibility of the organ phase and acid phase in adiabatic nitration reactions of the corresponding unnitrated aromatic organic compounds, or to increase the yields and / or to reduce the formation of by-products and / or to shorten the overall reaction times and / or to lower the reaction start temperatures in adiabatic nitration reactions of the corresponding unnitrated aromatic organic compounds.

[0005] Aromatic nitro compounds (such as nitrobenzene (MNB), mononitrotoluene (MNT), dinitrotoluene (DNT), trinitrotoluene (TNT), nitrochlorobenzene (MNCB), etc.) are usually produced by nitration of corresponding starting aromatics (such as benzene, toluene, xylene, chlorobenzene, dichlorobenzenes, etc.), in particular by reacting the corresponding starting aromatics with nitric acid in the presence of sulfuric acid as a catalyst and water-binding agent, i.e., by reacting the corresponding starting aromatics with a nitrating acid (i.e., a nitric acid / sulfuric acid-nitrating acid mixture, which is also referred to as a mixed acid at the beginning of the reaction and as a (nitrating) final acid at the end of the reaction).

[0006] In the prior art, the nitration of aromatics with the nitric acid / sulfuric acid nitrating acid mixture is preferably carried out as a heterogeneous liquid / liquid mixture of organ and acid phases, with the reaction of the aromatics to be nitrated with the nitric acid to form the corresponding nitroaromatic taking place in the acid phase. For this purpose, the aromatic to be nitrated must first be transferred from the organ phase to the acid phase in order to react with it. The nitroaromatic formed in the acid phase is then separated as the organ phase after the solubility limit has been exceeded. At the beginning of the nitration, this organ phase consists predominantly of the aromatic to be nitrated, and at the end of the reaction, when either all the nitric acid or all the aromatic to be nitrated has been converted, it consists mainly of the desired nitroaromatic.

[0007] A prerequisite for the rapid and effective conversion of the aromatic compound is that a sufficient amount of aromatic compound to be nitrated is constantly transferred from the organic phase to the acid phase. This is typically achieved by creating the largest possible exchange surface between the two phases, in particular either by dispersing the organic phase in the acid phase (oil-in-water or O / W emulsion) or vice versa, the acid phase in the organic phase (water-in-oil or W / O emulsion). The larger the exchange surface between the organic and acid phases (i.e., the smaller the droplet size of the dispersed phase), the greater the conversion during nitration, as in the nitration of benzene to nitrobenzene or of toluene to mononitrotoluene, etc. (as in all so-called mass-transfer-controlled reactions).

[0008] For example, if nitration is carried out continuously and isothermally in stirred tanks or in cascades of stirred tanks in co-current and / or counter-current flow, constant conditions prevail in each reactor, such as the composition of the organic and acid phases, and consequently, constant physicochemical conditions or parameters for the two-phase mixture of organic and acid phases. The nitration process thus proceeds under identical conditions in every reactor.

[0009] In contrast, nitration in a stirred tank reactor in batch operation with complete backmixing or in a tubular reactor with plug flow (so-called "plug flow") without backmixing proceeds quite differently. In both cases, as the nitration progresses, not only does the composition of the organic and acid phases constantly change, but also their physicochemical conditions and parameters, such as density, interfacial tension, etc. Under constantly changing conditions and parameters, it is much more difficult, if not nearly impossible, to maintain a consistently uniform exchange surface area for controlled reaction throughout the entire process.

[0010] It is also known that pure aromatics, such as benzene or toluene, are difficult to disperse in sulfuric acid or nitrating acid mixtures, and that dispersions of aromatics in sulfuric acid or nitrating acid mixtures decompose relatively quickly. As described, for example, in EP 0 373 966 A2, a single dispersion of the aromatic to be nitrated (benzene) in a mixed acid results in a conversion of only 55.3% of nitric acid and 52.5% of benzene due to the excessively rapid coalescence of the organic phase. Therefore, in nitration processes where two phases are present in the nitrating mixture (namely, on the one hand, an organic phase consisting of the aromatic to be nitrated and the nitroaromatic produced, and on the other hand, a nitrating acid mixture), it is necessary to continuously supply mixing energy to maintain the required exchange surface area between the two phases so that the desired conversion is achieved for a given residence time.

[0011] Especially at the beginning of a nitration reaction (e.g., in a tubular reactor), a particularly large amount of mixing energy must be supplied to create and maintain a sufficiently large exchange surface between the organic and acid phases so that the nitration process is initiated and continues. If this does not occur, the exchange surface is dramatically reduced due to more or less rapid coalescence of the dispersed phase, resulting in a drastic decrease in the conversion rate of the aromatic compound being nitrated per unit time.

[0012] If, for example, in a tubular reactor, it is not ensured that the onset of coalescence of the organ phase dispersed in the nitrating acid is prevented by the supply of additional mixing energy to a dispersion of the aromatic compound to be nitrated (e.g., benzene) in the nitrating acid mixture over the entire length of the reactor by repeatedly introducing mixing energy into a dispersion of the aromatic compound to be nitrated (e.g., benzene) in the nitrating acid mixture over the entire length of the reactor (as described, e.g., in EP 1 272 268 A2, EP 1 291 078 A2, or EP 0 708 076 A2), the nitration process collapses – which is recognizable by the fact that no more heat of nitration is released, even though nitric acid is still present in the nitrating acid and aromatic compound to be nitrated is still present in the organ phase.

[0013] The same applies to the start of the reaction: If the droplet size generated at the beginning of the reaction is not small enough, and thus the exchange surface area is too small, the mass-transfer-controlled conversion of benzene or toluene to nitrobenzene or mononitrotoluene, for example, proceeds only slowly – this is recognizable by the fact that no or only a slight temperature increase is observed in the reaction mixture, since the reaction does not start. Conversely, if the droplet size of the dispersed phase is sufficiently small and thus the exchange surface area is large, a rapid conversion of the aromatic compound to be nitrated occurs under otherwise identical conditions – this is recognizable by the rapid temperature increase in the reaction mixture and, associated with it, the desired high conversion of the aromatic compound to be nitrated to the corresponding nitroaromatic compound.

[0014] Especially in adiabatic reactions (e.g., in the adiabatic nitration of benzene to nitrobenzene), the conversion and the time required depend—in addition to the exchange surface area between the two phases and thus the droplet size of the dispersed phase—on other generally known parameters, such as the concentration of sulfuric acid and nitric acid in the nitrating acid (referred to as the mixed acid at the beginning of the reaction and as the final acid at the end), the starting temperature (see, e.g., EP 2 168 942 A1), the phase ratio between the organic and acid phases and thus the final temperature, etc.

[0015] The conversion rate in an adiabatic nitration (e.g., of benzene to nitrobenzene) in a tubular reactor is characterized—starting from a defined initial temperature—by the rise in temperature in the nitrating mixture due to the released heat of nitration (see, e.g., EP 2 168 942 A1 and EP 1 272 268 A2). The temperature difference determined for a specific nitrating mixture (also called Delta T or ΔT) can be directly, and in particular linearly, correlated with the conversion of nitric acid, as described, for example, in EP 2 168 942 A1.

[0016] To achieve the highest possible conversion rate (e.g., more than 98% of the nitric acid used) within a given residence time in a tubular reactor, in addition to optimal dispersion of the aromatic compound to be nitrated in the mixed acid, a suitable starting temperature is also necessary to initiate the reaction. This means that after mixing the reactants, the reaction proceeds in such a way that a steep, and in particular uniform, preferably exponential temperature increase is observed in the nitrating mixture, such that, for example, at least 60% of the nitric acid used is converted in the first 13 vol% of the reaction space in a tubular reactor (see, e.g., EP 2 168 942 A1). This is achieved, for example, by a specific arrangement of the dispersing elements for the necessary redispersion of the initially rapidly coalescing organ phase in the tubular reactor (see, e.g., EP 1 272 269 A1).

[0017] The starting temperature can be selected, for example, in the range of 50 to 120 °C. By mixing reactant streams at different temperatures (i.e., sulfuric acid, nitric acid, and the aromatic compound to be nitrated, such as benzene, see, for example, EP 0 436 443 A2 or EP 1 272 269 A1), a mixed temperature is formed, with the main contribution to the starting temperature coming from the sulfuric acid present in large excess.

[0018] The starting temperature, given a specific residence time, not only controls the conversion but also the formation of byproducts typical for adiabatic nitration, for example of benzene to nitrobenzene, such as the amount of di- and trinitrophenols (picric acid) and dinitrobenzene (DNB).

[0019] With starting temperatures of 80 to 120 °C (see, e.g., US 4 091 042 A), preferably greater than 97 °C and particularly preferably of 100 to 120 °C (see, e.g., EP 0 436 443 A2 or EP 2 168 942 A1), it is possible to achieve conversions of nitric acid of at least 99% with residence times in the reaction tube of less than 2 minutes (e.g., a maximum of 25 seconds, see, e.g., EP 0 436 443 A2).

[0020] Lower starting temperatures, however, require significantly longer residence times. For example, with a starting temperature of approximately 80 °C, a residence time of 300 seconds is described as necessary in state-of-the-art systems (tubular reactor) to achieve complete conversion of the nitric acid (see, e.g., US 8,692,035 B2 or WO 2010 / 051616 A1).

[0021] In comparison to state-of-the-art systems that operate at starting temperatures of around 97 to 110 °C, significantly larger nitriding reactors are required for lower starting temperatures, which are considerably more expensive as they are usually made of enamelled steel.

[0022] With a plant output of, for example, 20 tons of nitrobenzene (NB) per hour (i.e., 20 t NB / h), a tubular reactor with a diameter of 250 mm, a flow velocity of the nitrating mixture of 1.25 m / s, and a residence time of at least 300 s would be 2.5 times longer (i.e., approximately 375 m) than a standard state-of-the-art reactor of 150 m length with a residence time of 120 s and otherwise identical conditions (i.e., same mixed acid composition, same phase ratio, etc.).

[0023] Another objective of optimizing plants for the adiabatic nitration of aromatics, especially benzene, is to minimize the amount of byproducts in the nitrobenzene. As already described in EP 0 436 443 A2, the formation of di- and trinitrophenols increases rapidly with rising final temperature of the nitration mixture. For this reason as well, the final temperature of the nitration mixture should not exceed 135 to 145 °C. The nitrophenol content in the crude nitrobenzene (crude NB) then ranges from 2,000 to 3,000 ppm. The dinitrobenzene (DNB) content at these final temperatures ranges from 200 to 250 ppm. The removal of these nitrophenols from the crude nitrobenzene and their destruction in the wastewater, such as... B. by means of thermolysis (as described in EP 0 953 546 A2 and EP 0 005 203 A2), is complex and expensive.

[0024] Lowering the initial temperature, and consequently the final temperature, can significantly reduce the formation of byproducts. Each reduction of the initial temperature by 20 to 25 °C halves the nitrophenol content in the crude nitrobenzene. Lowering the initial temperature from approximately 110 °C to approximately 80 °C reduces the nitrophenol content by approximately 50%, i.e., to about 1,500 ppm or less (e.g., 1,000 ppm), compared to the levels described, for example, in EP 0 436 443 A2, particularly preferably to a value around 1,000 ppm. The dinitrobenzene (DNB) content decreases analogously to approximately 100 ppm (see, for example, US 8 692 035 B2 or WO 2010 / 051616 A1).

[0025] The temperature rise in the nitrating mixture between the starting and ending temperatures can be controlled by the phase ratio between the acid phase and the organic phase, given a specific nitric acid concentration in the mixed acid. With a constant phase ratio and a constant sulfuric acid concentration and starting temperature in the initial mixed acid, the ending temperature in the nitrating mixture increases with increasing nitric acid content in the mixed acid and a constant conversion rate, and vice versa.

[0026] As already described in EP 0 771 783 A1, achieving high selectivity at the start of the reaction in the tubular reactor through optimal mixing of the phases is advantageous. According to the prior art, various measures are described for achieving the most optimal possible dispersion of the aromatic compound to be nitrated in the starting mixed acid at the beginning of the reaction and for subsequent redispersion (see, e.g., EP 0 373 966 A2, EP 0 489 211 A1, EP 0 771 783 A1, EP 0 779 270 A1, EP 1 272 269 A1, EP 1 291 078 A2 and EP 2 168 942 A1).

[0027] Optimal dispersion of the aromatic compound to be nitrated (e.g., benzene) in the nitrating acid, especially at the beginning of the nitration process, is essential for initiating the reaction and thus a high conversion rate (see EP 1 272 269 A1 or EP 2 168 942 A1). As described in US 9 284 256 B2 and EP 2 877 442 A1, the addition of more than 4% aliphatic hydrocarbons to the benzene to be nitrated can prevent the nitration from starting. i.e. that no noticeable temperature increase is observed in the nitrating mixture after mixing the reactants and the first dispersion, whereas under otherwise identical conditions, with a benzene containing less than 0.1% aliphatic hydrocarbons, the nitration (as described in EP 1 272 269 A1 or EP 2 168 942 A1) starts with a steep temperature increase in the first 13 vol% of the tubular reactor and proceeds as intended.

[0028] The prior art has seen numerous attempts to achieve improved dispersion of the aromatic compound to be nitrated in the nitrating acid. One known prior art method for achieving this is, for example, a high ratio of acid phase to organ phase, which is intended to improve the dispersibility of the organ phase and reduce coalescence, as described, for example, in EP 0 436 443 A2 and US 8 692 035 B2. Another prior art method, as described in EP 1 272 268 A2 and EP 2 168 942 A1, involves carrying out the nitration in a tubular reactor with mixing or dispersing elements, using a non-uniform arrangement or distribution of these elements.The aim is to achieve a uniform, particularly exponential, preferably S-shaped temperature rise at the start of the reaction by means of dispersing elements along the entire length of the tubular reactor, thereby maximizing conversion in the front section of the reactor. However, the measures known from the prior art are insufficient to consistently achieve optimal dispersion of the aromatic compound to be nitrated in the nitrating acid and to compensate for the problems and disadvantages associated with insufficient dispersion, as previously described.

[0029] DE 1 468 575 A1 relates to a process for producing the mononitro compounds of benzene, toluene or chlorobenzene by isothermal nitration using nitrating acid (nitric acid / sulfuric acid mixture), and to a device for carrying out this process.

[0030] One object of the present invention is therefore to provide a method and a corresponding production plant (nitration plant or plant) suitable for carrying out this method for the adiabatic nitration of nitridable aromatic organic compounds (aromatics), wherein the disadvantages and shortcomings of the prior art described above are to be at least largely avoided or at least mitigated.

[0031] In particular, an object of the present invention is to provide a method and a corresponding production plant (nitration plant or plant) suitable for carrying out this method for the adiabatic nitration of nitridable aromatic organic compounds (aromatics), with which the nitridable aromatic organic compounds can be converted or reacted to the corresponding nitrated aromatic organic compounds (nitroaromatics) in a technically efficient, safe and simple manner.

[0032] Furthermore, an object of the present invention is to provide a method and a corresponding production plant (nitration plant or plant) suitable for carrying out this method for the adiabatic nitration of nitrateable aromatic organic compounds (aromatics), wherein, during the nitration process, the dispersion of the aromatics to be nitrated in the nitrating acid mixture is improved, particularly at the beginning of the reaction, preferably already after the reactants have been mixed. In particular, the dispersion of the organic phase and the acid phase should be improved even under unfavorable conditions (such as in the presence of impurities, e.g., an increased content of aliphatics in the aromatics to be nitrated, at a starting temperature that is too low, or with a low input of dispersion energy) to such an extent that the nitration can still be carried out efficiently, and in particular, the nitrating mixture should be dispersed in the predetermined reaction orThe residence time in the reactor can be implemented to at least 98%.

[0033] Finally, an object of the present invention is also to provide a method and a corresponding production plant (nitration plant or plant) suitable for carrying out this method for the adiabatic nitration of nitridable aromatic organic compounds (aromatics), wherein improved dispersion is achieved during the nitration process immediately after contact (e.g.(mixing) of the reactants, in particular of the nitrating acid phase containing nitric acid on the one hand and of the organ phase containing the aromatics to be nitrated on the other hand, preferably while avoiding rapid coalescence of the aromatics to be nitrated in the nitrating acid, preferably with the aim of starting the nitrating reaction even with lower starting temperatures compared to the prior art (without requiring longer reaction or residence times than in prior art processes with higher starting temperatures but otherwise identical conditions).

[0034] The problem described above is thus solved according to the present invention by the uses according to the relevant independent use claims.

[0035] The subject matter of the present invention according to the present invention is therefore the use according to the invention of nitrated aromatic organic compounds (nitroaromatics) to reduce the interfacial tension of the organ phase and acid phase and / or to improve the dispersibility of the organ phase and acid phase in adiabatic nitration reactions of the corresponding unnitrated aromatic organic compounds; wherein nitrifiable aromatic organic compounds (aromatics) are reacted in an adiabatic nitration reaction with a nitric acid / sulfuric acid-nitrating acid mixture to form the corresponding nitrated aromatic organic compounds (nitroaromatics); wherein the initial reaction mixture, which comprises the nitrateable aromatic organic compounds (aromatics) and the nitric / sulfuric acid-nitrating acid mixture, is supplemented with appropriate nitrated aromatic organic compounds (nitroaromatics) and the reaction and / or nitration reaction is initiated and / or carried out in the presence of the nitrated aromatic organic compounds (nitroaromatics); and / or wherein the obtained nitrated aromatic organic compounds (nitroaromatics) are partially recycled back into the nitration reaction and the subsequent conversion and / or nitration reaction is started and / or carried out in the presence of the nitrated aromatic organic compounds (nitroaromatics); the conversion and / or nitration reaction is carried out under adiabatic reaction conditions; the process or conversion and / or nitration reaction is carried out in a tubular reactor.

[0036] A further object of the present invention is therefore also the use according to the invention of nitrated aromatic organic compounds (nitroaromatics) to increase the yields and / or to reduce the formation of by-products and / or to shorten the overall reaction times and / or to lower the reaction start temperatures in adiabatic nitration reactions of the corresponding unnitrated aromatic organic compounds, wherein nitrifiable aromatic organic compounds (aromatics) are reacted in an adiabatic nitration reaction with a nitric acid / sulfuric acid-nitrating acid mixture to form the corresponding nitrated aromatic organic compounds (nitroaromatics); wherein the initial reaction mixture, which comprises the nitrateable aromatic organic compounds (aromatics) and the nitric / sulfuric acid-nitrating acid mixture, is supplemented with appropriate nitrated aromatic organic compounds (nitroaromatics) and the reaction and / or nitration reaction is initiated and / or carried out in the presence of the nitrated aromatic organic compounds (nitroaromatics); and / or wherein the obtained nitrated aromatic organic compounds (nitroaromatics) are partially recycled back into the nitration reaction and the subsequent conversion and / or nitration reaction is started and / or carried out in the presence of the nitrated aromatic organic compounds (nitroaromatics); the conversion and / or nitration reaction is carried out under adiabatic reaction conditions; the process or conversion and / or nitration reaction is carried out in a tubular reactor.

[0037] It goes without saying that any embodiments, designs, advantages or the like which are subsequently described – for the purpose of avoiding unnecessary repetition – only with regard to one aspect of the invention, naturally also apply accordingly to all other aspects of the invention.

[0038] Furthermore, it goes without saying that the following specifications of values, numbers and ranges are not to be understood as limiting; it is self-evident to the person skilled in the art that deviations from the specified ranges or specifications are possible in individual cases or depending on the application, without departing from the scope of the present invention.

[0039] Furthermore, it should be noted that all values ​​or parameters mentioned below, or the like, can generally be determined using standardized or explicitly specified determination methods, or using determination or analysis methods that are generally familiar to those skilled in the field.

[0040] Having said that, the present invention will now be described in more detail.

[0041] Within the scope of the uses according to the invention, a process for the adiabatic nitration of nitrifiable aromatic organic compounds (aromatics) to the corresponding nitrated aromatic organic compounds (nitroaromatics) is thus employed, wherein nitrifiable aromatic organic compounds (aromatics) are reacted in a nitration reaction under adiabatic reaction conditions with a nitric acid / sulfuric acid-nitrating acid mixture to form the corresponding nitrated aromatic organic compounds (nitroaromatics). wherein the initial reaction mixture, which comprises the nitrateable aromatic organic compounds (aromatics) and the nitric / sulfuric acid-nitrating acid mixture, is supplemented with appropriate nitrated aromatic organic compounds (nitroaromatics) and the reaction and / or nitration reaction is initiated and / or carried out in the presence of the nitrated aromatic organic compounds (nitroaromatics); and / or wherein the obtained nitrated aromatic organic compounds (nitroaromatics) are partially recycled back into the nitration reaction and the subsequent conversion and / or nitration reaction is started and / or carried out in the presence of the nitrated aromatic organic compounds (nitroaromatics); wherein the process or conversion and / or nitration reaction is carried out in a tubular reactor; wherein the reaction time and / or the residence time of the reaction mixture in the tubular reactor is 10 to 180 seconds; and wherein the reaction mixture flows through the tubular reactor by plug flow without backmixing, wherein the flow velocity of the reaction mixture in the tubular reactor is 0.01 to 10 m / s.

[0042] The term "corresponding nitrated aromatic organic compounds (nitroaromatics)," as used according to the invention, refers in particular, within the scope of the present invention, to those nitroaromatics which can be produced by nitration, preferably mononitration, of the starting aromatics used. For example, mononitrobenzene (MNB) is the corresponding nitrated aromatic organic compound (nitroaromatic) to benzene, mononitrotoluene (MNT) to toluene, mononitrochlorobenzene to chlorobenzene, etc.

[0043] The method used according to the invention – as well as the (production) plant used according to the invention, which is described in detail below, for carrying out the method used according to the invention – is associated with numerous special features and advantages, which will be discussed below:

[0044] In the context of the present invention, the applicant has surprisingly discovered that the addition of nitrated product to the initial reaction mixture leads to a reduction in the interfacial tension between the organic phase on the one hand and the acidic aqueous phase or acid phase on the other (where the organic phase comprises the starting aromatics to be nitrated and the added nitrated products as well as optionally nitrating by-products, and where the acidic aqueous phase or the acid phase in the initial reaction mixture comprises sulfuric acid at the beginning of the reaction and, after the addition of nitric acid, the nitrating acid or mixed acid, and at the end of the reaction the so-called aqueous nitrating acid or the so-called aqueous nitrating acid mixture and optionally dissolved proportions of added and / or formed nitroaromatics).

[0045] This results in significantly improved dispersibility and emulsification between the organic phase on the one hand and the aqueous acidic phase on the other; that is, the nitrated end product or the nitrated aromatic compound thus acts as a dispersant or emulsifier in the initial reaction mixture. It is, in effect, an inherent dispersant or emulsifier, as no foreign substances are used that could contaminate the reaction products.

[0046] Overall, the addition of the nitrated product to the initial reaction mixture results in improved, and in particular more intimate, mixing and dispersion of the two phases (i.e., the organic phase and the acid phase), leading to an improved and faster exchange between the two phases. This, in turn, results in a faster conversion or nitration reaction, particularly with improved yields, especially improved space-time yields.

[0047] Furthermore, significantly fewer byproducts are formed during the reaction process according to the invention. Overall, the addition of nitrated product to the initial reaction mixture allows for better control of the reaction or process, or the nitration reaction itself.

[0048] In addition to shortened reaction times and faster conversions with improved yields and reduced by-product formation, the inventive process also allows the starting temperature for the start-up or initiation of the reaction to be significantly lowered compared to conventional nitriding processes under otherwise identical conditions. This means that significantly lower (reaction) start temperatures can be used for the nitriding reaction, as will be explained below.

[0049] Overall, the present invention provides an improved process for adiabatic nitration processes for nitrifiable aromatic organic compounds, characterized by an overall improved efficiency, in particular improved technical efficiency and energy efficiency, and an overall improved process economy and also improved handling.

[0050] Within the scope of the present invention, in the adiabatic reaction procedure of nitration used according to the invention (e.g., adiabatic nitration of benzene to mononitrobenzene in a tubular reactor), the dispersion of the aromatic compound to be nitrated in the nitrating acid mixture can be improved, particularly at the beginning of the reaction, preferably already after contact (e.g., mixing) of the reactants, such that even under unfavorable conditions (such as in the presence of impurities, e.g., an increased content of aliphatics in the aromatic compound to be nitrated, or at a starting temperature that is too low, or with a low input of dispersion energy) the nitration can still be carried out efficiently, in particular the nitrating mixture in the predetermined reaction orResidence time in the reactor to at least 98%, in particular at least 99%, preferably at least 99.5%, in each case based on the nitric acid conversion in the nitrating acid mixture, can be achieved.

[0051] The method used according to the invention enables improved dispersion during nitration, particularly after contact (e.g., mixing) of the reactants, especially the nitrating acid phase containing nitric acid on the one hand and the organ phase containing the aromatics to be nitrated on the other, preferably while avoiding rapid coalescence of the aromatics to be nitrated in the nitrating acid, preferably with the aim of starting the nitration reaction at lower starting temperatures compared to the prior art (without requiring longer reaction or residence times than in prior art processes with higher starting temperatures but otherwise identical conditions).In particular, the process according to the invention makes it possible to initiate or start the nitration even at (reaction) start temperatures below 100 °C, preferably below 95 °C, and especially preferably below 90 °C, in such a way that no longer reaction or residence times are required than in prior art processes with higher start temperatures but otherwise identical conditions.

[0052] The present invention thus enables nitrifiable aromatic organic compounds (i.e. aromatics) to be converted or reacted to the corresponding nitrated aromatic organic compounds (nitroaromatics) in a technically efficient, safe and simple manner.

[0053] Within the scope of the present invention, it was thus found quite surprisingly that by adding nitrated product (e.g. nitrobenzene in the case of the nitration of benzene) to the initial reaction mixture, a significantly improved initial dispersion of the aromatic to be nitrated (in particular characterized by a steeper temperature rise in the nitrating mixture after the initial dispersion triggering the nitration) as well as a reduced tendency to coalesce this dispersion is observed.

[0054] In other words, the object of the invention is in particular an overall improved process for an adiabatic process for the production of nitroaromatics (such as nitrobenzene, nitrotoluene, nitrochlorobenzene, etc.) by an adiabatic reaction of the corresponding starting aromatics (such as benzene, toluene, chlorobenzene, etc.) with nitric acid in the presence of sulfuric acid as a water-binding agent and catalyst in a tubular reactor and preferably using a stoichiometric excess of aromatic to be nitrated, wherein a proportion of the corresponding nitroaromatic (e.g., nitrobenzene in the case of the nitration of benzene) is added or mixed into the reaction mixture or the starting reaction mixture.

[0055] As described in detail below, the process used according to the invention is completely flexible: The proportion of nitroaromatic to be added or mixed in (e.g., nitrobenzene in the case of the nitration of benzene) can be added, for example, to the recycled or fresh sulfuric acid required for the nitration and / or to the aromatic compound to be nitrated before the first joint dispersion of the other reactants (i.e., sulfuric acid and nitric acid), and / or only to a portion of the aromatic compound to be nitrated before the first joint dispersion of the other reactants (i.e., sulfuric acid and nitric acid as well as the remaining portion of the aromatic compound to be nitrated), etc., with combinations of these variants also being possible. Basically, it is only important that sufficient quantities of nitroaromatic are present in the initial reaction mixture at the beginning of the nitration reaction to ensure efficient dispersion of the organic and acid phases.

[0056] The following describes particular, advantageous or preferred embodiments of the method used according to the invention:

[0057] As previously described, in the process used according to the invention, the conversion and / or nitration reaction is carried out under adiabatic reaction conditions.

[0058] According to a particular embodiment of the present invention, the conversion and / or nitration reaction is further carried out, in particular, as mononitration.

[0059] According to a further particular embodiment of the present invention, the starting reaction mixture and the nitrated aromatic organic compounds (nitroaromatics) are typically present under the selected reaction conditions as a liquid / liquid mixture of an organic phase on the one hand and an acid phase, in particular an acidic aqueous phase, on the other. In particular, the organic phase can comprise nitratable aromatic organic compounds (aromatics) and nitrated aromatic organic compounds (nitroaromatics), and / or, in particular, the acid phase (i.e., in particular the acidic aqueous phase) can comprise nitric acid, sulfuric acid, and optionally water (as well as optionally dissolved portions of added and / or nitroaromatics formed during nitration).

[0060] In the process employed according to the invention, the nitridable aromatic organic compounds (aromatics) and the nitric acid / sulfuric acid-nitrating acid mixture, as well as the (added or recycled) nitrated aromatic organic compounds (nitroaromatics), constitute the (initial) nitrating mixture (i.e., the initial nitrating mixture or the nitrating mixture present at the beginning of the reaction and / or nitrating process); in other words, the nitrating mixture (i.e., the initial nitrating mixture or the nitrating mixture present at the beginning of the reaction and / or nitrating process) comprises the initial reaction mixture, which includes the nitridable aromatic organic compounds (aromatics) and the nitric acid / sulfuric acid-nitrating acid mixture, as well as the nitrated aromatic organic compounds (nitroaromatics). In contrast, the product obtained after the reaction and / or at the end of the nitrating process comprises...The resulting nitrating mixture consists primarily of nitrating acid and nitrated aromatic organic compounds (nitroaromatics), as well as, where applicable, small amounts of unreacted nitrifiable aromatic organic compounds (aromatics) (along with any impurities and by-products that may be present).

[0061] According to the present invention, virtually any nitrifiable aromatic organic compounds (aromatics) can be nitrated.

[0062] According to a particular embodiment of the present invention, the nitridable aromatic organic compounds (aromatics) can be liquid under the selected reaction conditions. In particular, the nitridable aromatic organic compounds (aromatics) can be in the liquid state under standard pressure (1.01325 bar) and at a temperature of 70 °C or higher, particularly 50 °C or higher, preferably 25 °C or higher, and most preferably 10 °C or higher. This enables efficient reaction control.

[0063] In particular, the nitridable aromatic organic compounds (aromatics) may be selected from optionally halogenated mono- or polynuclear organic aromatics.

[0064] According to a particular embodiment of the present invention, the nitridable aromatic organic compounds (aromatics) used for nitration can be selected in particular from the group consisting of benzene, mononitrobenzene (MNB), halogenated benzenes, in particular mono- and dichlorobenzenes, mononitrated halogenated benzenes, toluene, mononitrotoluene (MNT), dinitrotoluenes (DNT) and xylenes, as well as mixtures and combinations thereof. Benzene is particularly preferred.

[0065] According to the present invention, it is possible in principle to produce almost any nitrated aromatic organic compounds (nitroaromatics).

[0066] Regarding the produced nitrated aromatic organic compounds (nitroaromatics), these can be in a liquid state under the selected reaction conditions. Specifically, the nitrated aromatic organic compounds (nitroaromatics) can be in the liquid state under standard pressure (1.01325 bar) and at a temperature of 70 °C or higher, particularly 50 °C or higher, preferably 25 °C or higher, and most preferably 10 °C or higher. This ensures an efficient process.

[0067] In particular, the produced nitrated aromatic organic compounds (nitroaromatics) may be selected from optionally halogenated mono- or polynuclear mono-, di- or trinitrated organic aromatics.

[0068] According to a particular embodiment of the present invention, the prepared nitrated aromatic organic compounds (nitroaromatics) can be selected from the group consisting of mononitrobenzene (MNB), dinitrobenzenes (DNB), halogenated mono- and dinitrobenzenes, in particular mono- and dinitrated mono- and dichlorobenzenes, mononitrotoluenes (MNT), dinitrotoluenes (DNT), trinitrotoluene, and mono- and dinitrated xylenes, as well as mixtures and combinations thereof. Mononitrobenzene is particularly preferred.

[0069] According to a preferred embodiment of the present invention, benzene is used as the nitrifiable aromatic organic compound (aromatic) and mononitrobenzene (MNB) is obtained as the nitrated aromatic organic compound (nitroaromatic).

[0070] According to a conventional embodiment of the process used according to the invention, the reaction and / or nitration reaction can be followed by a separation of the acidic aqueous phase (acid phase) and / or a phase separation of the obtained nitrating mixture into nitrating acid and crude nitrated aromatic organic compounds (crude nitroaromatics), preferably followed by a washing of the crude nitrated aromatic organic compounds (crude nitroaromatics) with a washing medium, in particular in one or more washing steps, preferably with subsequent separation of the used washing medium to obtain the washed and thus impurity-free (i.e. purified) nitrated aromatic organic compounds (nitroaromatics).

[0071] According to a preferred embodiment of the present invention, the washing can be carried out in at least two washing steps, wherein at least one acidic washing step (“acidic wash”) and at least one neutral washing step (“neutral wash”) can be provided.

[0072] Preferably, the washing process may comprise (i) at least one first washing step carried out in an acidic environment (“acidic wash”), preferably with water or a mineral acid as the washing medium, (ii) at least one second washing step carried out in an alkaline (basic) environment (“basic wash”), preferably with a base as the washing medium, and (iii) at least one third washing step carried out in a neutral environment (“neutral wash”), preferably with water as the washing medium (in the aforementioned order or sequence of first to third washes).

[0073] According to a particular embodiment of the present invention, the used washing medium can be recycled and / or recirculated and / or returned to the laundry process, particularly after purification.

[0074] As previously explained, the washing of crude nitroaromatics to remove dissolved and suspended acids of the nitrating mixture, nitrophenols, and other acidic and otherwise extractable impurities typically comprises three washing steps (see, e.g., BF Meissner et al., Industrial and Engineering Chemistry, Vol. 46, pages 718 to 724 (1954); Ullmanns Enzyklopädie der Technischen Chemie, 4th edition, Vol. 17, pages 384 to 386; H. Hermann et al., “Industrial Nitration of Toluene to Dinitrotoluene”, ACS Symposium Series 623 (1996), pages 234 to 249, Editors: LF Albright, RVC Carr, RJ Schmitt; US 6 288 289 B1; EP 1 816 117 B1). Water can usually be used as the washing medium, with the washing usually being carried out as a liquid / liquid wash (i.e. at temperatures where the nitroaromatic to be washed is in liquid form).Furthermore, according to the present invention, the vapor condensate from the reconcentration of the nitrating acid can also be used as a washing medium in the acidic wash (washing step (i)) or in the alkaline wash (washing step (ii)).

[0075] As previously stated, the three-step wash process typically includes the following steps: (i) an acid wash with water to remove dissolved and suspended mineral acids, such as sulfuric acid, nitric acid and nitrose (“acid wash”); (ii) a basic or alkaline wash in the presence of a base (“alkali wash”), such as sodium carbonate (soda), sodium bicarbonate, sodium sulfite, sodium bisulfite, ammonia, caustic soda, potassium hydroxide, etc. (see, for example, US 4,482,769 A, US 4,597,875 A or US 6,288,289 B1), to remove the weakly acidic impurities dissolved in the crude nitroaromatics, such as nitrophenols, nitrocresols, nitrobenzoic acids, degradation products from the oxidative decomposition of phenols or of aliphatic or cyclic hydrocarbons, etc., such as oxalic acid, etc., or the asymmetric isomers in TNT (“basic wash”); (iii) a neutral wash to remove residual traces of alkali and to further reduce trace amounts of impurities remaining in the product (“neutral wash”).

[0076] The aim of these washing steps is, in particular, to obtain as little wastewater as possible per ton of product, in addition to a clean product, in which the washed-out impurities are present in such a way that their disposal can be carried out cost-effectively.

[0077] Advantageously, according to a particular embodiment of the present invention, the nitrating acid resulting from the reaction and / or nitration reaction is recycled and / or recirculated and / or returned to the nitration reaction after separation of the crude nitrated aromatic organic compounds (crude nitroaromatics), particularly after concentration and / or after the addition of fresh nitric and / or sulfuric acid. This further increases the process efficiency.

[0078] Furthermore, the amount of nitrated aromatic organic compounds (nitroaromatics) added and / or recycled for the conversion and / or nitration reaction can vary widely.

[0079] Advantageously, according to a particular embodiment of the present invention, the amount of nitrated aromatic organic compounds (nitroaromatics) added and / or recycled for the reaction and / or nitration reaction is selected such that the amount of added and / or recycled nitrated aromatic organic compounds (nitroaromatics) causes a reduction in the interfacial tension between the organ phase and the acid phase and / or the amount of added and / or recycled nitrated aromatic organic compounds (nitroaromatics) results in improved dispersibility, in particular emulsifiability, of the organ phase and the acid phase.

[0080] Similarly, according to a particular embodiment of the present invention, the amount of nitrated aromatic organic compounds (nitroaromatics) added and / or recycled for the reaction and / or nitration reaction is selected such that the weight-related amount of added and / or recycled nitrated aromatic organic compounds (nitroaromatics), based on the nitrateable aromatic organic compounds (aromatics) to be nitrated and / or reacted, is in the range of 0.01 to 60 wt.%, in particular in the range of 0.1 to 50 wt.%, preferably in the range of 5 to 45 wt.%, and particularly preferably in the range of 10 to 40 wt.%.

[0081] Furthermore, according to another particular embodiment of the present invention, the amount of nitrated aromatic organic compounds (nitroaromatics) added and / or recycled for the reaction and / or nitration reaction is selected such that the weight-based amount of added and / or recycled nitrated aromatic organic compounds (nitroaromatics), based on the sulfuric acid of the nitric acid / sulfuric acid-nitrating acid mixture, is in the range of 0.01 to 10 wt.%, in particular in the range of 0.2 to 5 wt.%, preferably in the range of 0.5 to 3 wt.%, and most preferably in the range of 1 to 2 wt.%.

[0082] With regard to other process management, the method used according to the invention is also flexible and can be adapted or adjusted almost arbitrarily to the respective conditions (e.g., equipment conditions).

[0083] The addition of nitrated aromatic organic compounds (nitroaromatics) can thus occur at various process stages and positions within the process employed according to the invention. In particular, it can be provided that the nitrated aromatic organic compounds (nitroaromatics) added and / or recycled for the reaction and / or nitration are added and / or supplied to at least one of the following positions (i) to (iv): (i) the initial reaction mixture of all other reactants; and / or (ii) the sulfuric acid of the nitric acid / sulfuric acid-nitrating acid mixture, especially before the preparation of the nitric acid / sulfuric acid-nitrating acid mixture; and / or (iii) the nitric acid / sulfuric acid-nitrating acid mixture; and / or (iv) the nitrateable aromatic organic compounds (aromatics) to be nitrated. Combinations of two or more of these variants are also possible.

[0084] Furthermore, the recovery of nitrated aromatic organic compounds (nitroaromatics) can also take place at various process stages and positions of the process used according to the invention. In particular, it can be provided that the nitrated aromatic organic compounds (nitroaromatics) added and / or recovered for the reaction and / or nitration reaction originate from at least one of the following positions (i) to (iv): (i) the crude nitrated aromatic organic compounds (crude nitroaromatics), preferably after separation of the acidic aqueous phase (acid phase) and / or after phase separation of the resulting nitrating mixture into nitrating acid and crude nitrated aromatic organic compounds (crude nitroaromatics); and / or (ii) the washed nitrated aromatic organic compounds (nitroaromatics), in particular after acidic or neutral washing;and / or (iii) the washed, in particular after acidic or neutral washing, as well as stripped, distilled or dried nitrated aromatic organic compounds (nitroaromatics); and / or (iv) the nitrated aromatic organic compounds (nitroaromatics) obtained after concentration of the nitrating acid in the vapor condensate. In principle, combinations of two or more of these variants are also possible.

[0085] Advantageously, according to a particular embodiment of the present invention, the nitrated aromatic organic compounds (nitroaromatics) added and / or recycled for the reaction and / or nitration are supplied and / or added to both the organic phase and the acid phase of the initial reaction mixture. This results in a particularly rapid and efficient distribution equilibrium of the added and / or recycled nitrated aromatic organic compounds (nitroaromatics) in the two aforementioned phases (organ phase on the one hand and acid phase on the other). In this embodiment, it is further particularly possible that 0.1 to 35 wt.%, in particular 10 to 25 wt.%, of nitrated aromatic organic compounds (nitroaromatics) are added to the organic phase, based on the organic phase, and / or that 0.01 to 3 wt.%, based on the acid phase, is added to the acid phase.-%, in particular 0.1 to 2 wt.%, preferably 0.5 to 1.5 wt.%, particularly preferably 1.1 to 1.5 wt.%, nitrated aromatic organic compounds (nitroaromatics) are added.

[0086] According to a particular embodiment of the process used according to the invention, it is particularly possible to proceed such that the nitrating acid resulting after the reaction and / or nitration reaction is recycled and / or recirculated and / or returned to the nitration reaction after separation of the crude nitrated aromatic organic compounds (crude nitroaromatics) and after subsequent concentration and optionally the addition of fresh nitric and / or sulfuric acid, wherein the nitrated aromatic organic compounds (nitroaromatics) added and / or returned for the reaction and / or nitration reaction are added and / or supplied to the concentrated nitrating acid and / or to the aromatic organic compounds (aromatics) to be nitrated, which may optionally be mixed with fresh nitric and / or sulfuric acid.In particular, in this special embodiment, the nitridable aromatic organic compounds (aromatics) can preferably be added and / or supplied immediately before the start of the reaction and / or as the last reaction component (reactant) in time, preferably immediately before the initial dispersion that triggers the conversion and / or nitration reaction.

[0087] According to a further particular embodiment of the process used according to the invention, it is particularly possible to proceed such that the nitrating acid resulting after the reaction and / or nitration reaction is recycled as circulating acid after separation of the crude nitrated aromatic organic compounds (crude nitroaromatics) and after subsequent concentration and / or is recycled and / or returned to the nitration reaction, wherein a dispersion of concentrated circulating acid and nitrateable aromatic organic compounds (aromatics) to be nitrated as well as nitrated aromatic organic compounds (nitroaromatics) is first produced, wherein nitric acid is then added to the dispersion, in particular dispersed into it, and the nitration reaction is initiated in this way.In this particular embodiment, the nitric acid can preferably be added and / or supplied immediately before the start of the reaction and / or as the last reaction component (reactant) in time, preferably immediately before the initial dispersion that triggers the conversion and / or nitration reaction.

[0088] As previously explained, the process used according to the invention is flexible and adaptable to almost any conditions (e.g., equipment conditions) with regard to its operation. In this context, the (reaction) starting temperature can also vary over a wide range.

[0089] Typically, the starting temperature for the conversion and / or nitration reaction can be selected in a temperature range of 70 °C to 120 °C, in particular 80 °C to 120 °C, preferably 80 °C to 110 °C, and most preferably 85 °C to 105 °C.

[0090] As previously explained in connection with the advantages and special features of the method used according to the invention, according to an advantageous embodiment of the method used according to the invention, it can be provided that the starting temperature for the reaction and / or nitration reaction is at most 120 °C, in particular at most 100 °C, preferably at most 95 °C, and particularly preferably at most 90 °C.

[0091] In particular, the process according to the invention makes it possible to start the nitration reaction even at lower starting temperatures compared to the prior art (without requiring longer reaction or residence times than in prior art processes with higher starting temperatures but otherwise identical conditions). Specifically, the process according to the invention makes it possible to initiate or start the nitration even at (reaction) starting temperatures below 100 °C, preferably below 95 °C, and particularly preferably below 90 °C, without requiring longer reaction or residence times than in prior art processes with higher starting temperatures but otherwise identical conditions.

[0092] As regards the nitric acid / sulfuric acid-nitrating acid mixture used as a nitrating reagent according to the invention, it can in particular be an aqueous nitric acid / sulfuric acid-nitrating acid mixture.

[0093] Typically, the nitric acid / sulfuric acid-nitrating acid mixture used contains, based on the nitric acid / sulfuric acid-nitrating acid mixture, sulfuric acid in amounts of 60 to 79 wt.%, in particular 62 to 75 wt.%, preferably 65 to 72 wt.%, and nitric acid in amounts of 1 to 8 wt.%, in particular 2 to 6 wt.%, preferably 3 to 5 wt.%. The remaining proportion to reach 100 wt.% is water.

[0094] According to a particular embodiment of the method used according to the invention, it is particularly possible to proceed such that the nitric acid / sulfuric acid-nitrating acid mixture is used in such quantities that the stoichiometric ratio of nitrifiable aromatic organic compounds (aromatics) to be nitrated to the nitric acid present in the nitric acid / sulfuric acid-nitrating acid mixture used is in the range of 1.0 to 1.5, in particular in the range of 1.05 to 1.15.

[0095] According to an advantageous embodiment of the method used according to the invention, it is particularly possible to proceed such that the nitric acid / sulfuric acid-nitrating acid mixture is used in such quantities that the volume-related phase ratio of nitrating acid to nitrated organic compounds (nitroaromatics) is in the range of 3 : 1 to 25 : 1, in particular in the range of 4 : 1 to 15 : 1, preferably in the range of 5 : 1 to 8 : 1.

[0096] According to the inventive procedure, the process used according to the invention or the conversion and / or nitriding reaction is carried out in a tubular reactor.

[0097] According to one embodiment of the method used according to the invention, it is particularly possible to proceed in such a way that the method or the conversion and / or nitration reaction is carried out in a tubular reactor, wherein the reaction duration and / or the residence time of the reaction mixture in the tubular reactor is selected such that the nitric acid of the nitric acid / sulfuric acid-nitrating acid mixture is converted to at least 98%, in particular to at least 99%, preferably to at least 99.5%.

[0098] According to the method employed in the invention, the process or the conversion and / or nitration reaction is carried out in a tubular reactor. The reaction time and / or the residence time of the reaction mixture in the tubular reactor is 10 to 180 seconds, in particular 30 to 180 seconds, preferably 40 to 120 seconds, and particularly preferably 60 to 90 seconds. Furthermore, in this embodiment, the reaction time and / or the residence time of the reaction mixture in the tubular reactor is ensured not to exceed 180 seconds, in particular 120 seconds. In addition, in this embodiment, the flow velocity of the reaction mixture in the tubular reactor is selected such that plug flow conditions without backmixing are present. In particular, in this embodiment, the reaction mixture flows through the tubular reactor with plug flow conditions without backmixing.The flow velocity of the reaction mixture in the tubular reactor is 0.01 to 10 m / s, in particular 0.1 to 5 m / s, preferably 0.2 to 3 m / s, particularly preferably 0.5 to 2 m / s, even more preferably 0.8 to 1.5 m / s.

[0099] According to a particular embodiment of the process used according to the invention, the process or the conversion and / or nitration reaction can be carried out in a tubular reactor, wherein the tubular reactor is equipped with one or more, preferably several, mixing elements (dispersing elements), particularly for the input of additional mixing energy. In this embodiment, the mixing elements can be designed, in particular, as plates, especially baffle or deflecting plates, as orifices, as static mixers, or as flow dividers. In particular, it can be provided that a mixing energy of 10 to 1000 joules / liter, preferably 10 to 500 joules / liter, and particularly preferably 20 to 200 joules / liter, is introduced by the mixing elements. Furthermore, it can be provided that the pressure drop per mixing element is 0.1 bar to 3.0 bar, preferably 0.3 to 1.5 bar, and particularly preferably 0.3 to 0.8 bar.Preferably, in this embodiment, the mixing elements are arranged in the tubular reactor such that the conversion of nitric acid in the nitric acid / sulfuric acid-nitrating acid mixture is at least 40%, particularly at least 50%, and preferably at least 60%, in the first 10 to 30% by volume of the reactor. It is also preferably in this embodiment that the mixing elements are arranged in the tubular reactor such that the conversion of nitric acid used at the end of the tubular reactor is at least 98%, preferably at least 99%, and particularly preferably at least 99.5%.

[0100] Finally, according to a further particular embodiment of the method used according to the invention, the process or the conversion and / or nitration reaction can be carried out in a tubular reactor, wherein a dispersing device, preferably a mixing element, is connected upstream of the tubular reactor, in particular for generating a dispersion or emulsion, especially the initial reaction mixture or the nitration mixture. In this embodiment, the dispersing device, in particular the mixing element, can be designed as a stirred tank, a jet mixer, or a pump, in particular a centrifugal pump. According to a particular variant of this embodiment, the dispersing device, in particular the mixing element, can be designed as a pump, in particular a centrifugal pump.According to another particular variant of this embodiment, the dispersing device, in particular the mixing element, can be designed as a jet mixer; in particular, the jet mixer can generate a preferably central propellant jet and a medium surrounding the propellant jet, in particular in the form of an annular jet. In this embodiment, it can be provided that the dispersing device, in particular the mixing element, is located upstream of the tubular reactor, preferably directly upstream, in particular wherein the dispersing device transitions into the reactor or, in particular, wherein the dispersing device is integrated into the reactor and / or is a component of the reactor.

[0101] In a particularly preferred manner, the process employed according to the invention is carried out as follows, wherein the process is described by way of example for the nitration of benzene to nitrobenzene. However, the process employed according to the invention can also be applied, in particular, to all other aromatics that are difficult to disperse in sulfuric acid or nitrating acid (such as toluene, xylenes, chlorobenzenes, etc.).

[0102] The process underlying an adiabatic nitration of benzene to nitrobenzene and the reactor used for this purpose are described by way of example in EP 1 272 268 A2, in EP 1 291 078 A2 and in EP 2 168 942 A1.

[0103] In general, in an adiabatic nitration, such as that used in the process according to the invention, a mixed acid (nitrating acid mixture or nitrating acid), typically with a weight-based sulfuric acid content of 60 to 79 wt.%, in particular 62 to 75 wt.%, preferably 65 to 72 wt.%, and with a weight-based nitric acid content of 1 to 8 wt.%, preferably 2 to 6 wt.%, particularly preferably 3 to 5 wt.%, can be mixed with the benzene to be nitrated, preferably with a stoichiometric ratio of benzene to nitric acid of 1.0 to 1.5, preferably 1.05 to 1.15, in a dispersing device. The phase ratio between the organic phase and the acid phase in the nitrating mixture is determined by the concentration of nitric acid in the mixed acid used: With a mixed acid with 4.5 wt.With a 10% excess of benzene by weight, a nitrating acid / benzene ratio of 16.3 is obtained. At the end of the reaction, a nitrating mixture, in which all the heat of reaction is stored, is obtained with a final acid / product ratio of approximately 10.3. The temperature rise in the nitrating mixture, i.e., the difference (ΔT) between the final and initial temperatures, is clearly determined by the phase ratio when the conversion of nitric acid to product exceeds 99%. If the phase ratio decreases, for example, due to a higher nitric acid content in the nitrating acid, the difference (ΔT) between the final and initial temperatures increases, and vice versa.

[0104] After mixing the reactants, the two-phase mixture of organic and acid phases is dispersed such that nitration begins, according to the invention in a tubular reactor, which is recognizable by a steep temperature rise in the nitrating mixture. The starting temperature is determined as the mixing temperature of the individual reactant streams and, for adiabatic nitration, particularly of benzene to nitrobenzene, typically ranges from 70 to 120 °C, particularly from 80 to 120 °C, preferably from 80 to 110 °C, and most preferably from 85 to 105 °C. In particular, the starting temperature for the reaction and / or nitration is at most 120 °C, particularly at most 100 °C, preferably at most 95 °C, and most preferably at most 90 °C.

[0105] Typically, the residence time of the nitrating mixture in the tubular reactor, during which at least 98%, preferably more than 99%, of the nitric acid used has reacted, can be 30 to 180 seconds, preferably no more than 120 seconds, and particularly preferably 60 to 90 seconds. The flow velocity of the nitrating mixture in the tube can be 0.1 to 5.0 m / s, preferably 0.2 to 3.0 m / s, particularly preferably 0.5 to 2.0 m / s, and most preferably 0.8 to 1.5 m / s, to ensure so-called plug flow conditions without backmixing in the tubular reactor. By specifying an hourly product output, a nitric acid content in the mixed acid, the residence time, and the flow velocity in the tubular reactor, the dimensions of the tubular reactor are unambiguously determined.

[0106] According to a particular embodiment, the mixed acid can preferably be produced initially by combining sulfuric acid and nitric acid. In a second step, the aromatic compound to be nitrated can then be dispersed into this mixed acid. The starting temperature then results as the mixing temperature of the individual reactant streams. The temperatures of the reactant streams are preferably adjusted precisely so that the desired starting temperature is present after mixing.

[0107] Besides selecting a suitable starting temperature, determining the temperature difference (ΔT) between the final and starting temperatures, and the final temperature of the nitrating mixture itself, a further prerequisite for a largely complete conversion of the nitric acid while adhering to the specified residence times is a dispersion of the aromatic compound to be nitrated in the mixed acid such that, immediately after the targeted initial dispersion, the nitration begins in such a way that the desired temperature rise in the nitrating mixture occurs (which is known and familiar to those skilled in the art). For this purpose, the aromatic compound to be nitrated can be, for example, B. dispersed in the mixed acid by appropriately shaped nozzles (see e.g. EP 0 373 966 A2, EP 0 436 443 A2 or EP 0 708 076 A2) or the nitriding mixture by static mixers (see e.g. EP 0 489 211 A1 or EP 0 779 270 A1) or by jet mixers (see e.g.EP 0 771 783 A1) or by using specially shaped apertures (see e.g. EP 1 272 268 A2 or EP 1 291 078 A2), which are also preferably used in redispersion.

[0108] Regardless of the dispersion technique used, the most unfavorable interfacial tensions between the phases occur during the initial dispersion of the phases, e.g., of benzene into the mixed acid present in large excess, thus hindering optimal dispersion. Additionally, the dispersions of the pure aromatics to be nitrated in the mixed acid, generated by energy input, tend to coalesce rapidly.

[0109] The interfacial tensions between the nitroaromatic compound and the aqueous phase (e.g., nitrobenzene and water) are significantly lower than the interfacial tensions between the aromatic compound to be nitrated (e.g., benzene) and water. By adding the nitrated product according to the invention before the initial dispersion that triggers the reaction, the interfacial tensions at the phase interfaces are efficiently and significantly reduced, thereby achieving improved dispersion at the start and reducing the tendency of the initially generated dispersion to coalesce.

[0110] For the additional addition of the nitrated product to the nitration mixture as a further component, alongside sulfuric acid, nitric acid, and the aromatic compound to be nitrated (e.g., benzene), as provided for in the invention, for an adiabatic nitration according to the invention in a tubular reactor, particularly shortly before the start of the reaction, i.e., before the first dispersion that triggers the nitration, various sequences of addition are possible. The product to be regenerated can, in particular, be... a) before adding the aromatic compound to be nitrated (e.g. benzene) and before mixing the nitric acid into the concentrated and recycled sulfuric acid (circulating acid) and / or b) before adding the aromatic compound to be nitrated (e.g. benzene) shortly after adding the nitric acid to the mixed acid and / or c) together with the aromatic compound to be nitrated and / or d) as a partial stream of the nitrating emulsion before phase separation into the circulating acid or mixed acid and / or e) also as a combination according to a) to c), in particular such that part of the added nitrated product (e.g. nitrobenzene) is added to the aqueous phase according to a) and / or b) and another part is added together with the aromatic compound to be nitrated according to c).

[0111] The addition of the aromatic compound to be nitrated as the second reactive component in the nitrating mixture alongside the nitric acid is advantageously carried out in cases a) to e) in particular always at the end, preferably shortly before the initial dispersion that triggers the reaction.

[0112] In addition to these variants, especially the addition of the aromatic compound to be nitrated to the nitration mixture as the last component before the initial dispersion, it is particularly advantageous to add the nitric acid as the second partner involved in the nitration as the last component before the initial dispersion to the nitration mixture.

[0113] It has proven advantageous that after each addition of a reactant to the concentrated circulating sulfuric acid, the main component in the nitrating mixture, suitable mixing devices (e.g., static mixers, aperture mixers, jet mixers, etc.) ensure homogeneous mixing with the circulating acid (in the case of nitric acid) or pre-dispersion in the circulating sulfuric acid (in the case of recycled nitrated product or aromatic compound to be nitrated) in such a way that only a small pressure drop occurs at these mixing devices.

[0114] The product (e.g., nitrobenzene) added to the concentrated circulating acid, mixed acid, or aromatic compound to be nitrated (e.g., benzene) can be taken from various stages of the process, i.e., A) as crude nitrobenzene, in particular after phase separation of the nitrating mixture of nitrating acid and nitrobenzene, before or after cooling, and preferably before treatment with a washing medium (this crude nitrobenzene contains, in addition to the product, 2 to 10% dissolved benzene, nitrophenols and traces of sulfuric acid, approximately 0.2 to 0.25%, and final acid as a microemulsion, but no water); and / or B) as partially purified nitrobenzene, free from acids, after acid washing (This nitrobenzene from acid washing contains, in addition to all the nitrophenols, all excess benzene and is saturated with water.); and / or C) as purified nitrobenzene after neutral washing (This nitrobenzene from the neutral washing contains only traces of nitrophenols, approximately 2 to 60 ppm, and all excess benzene, and is also saturated with water.); and / or D) as the nitrobenzene obtained in the vapor condensate during the concentration of the final acid to the circulating acid (This nitrobenzene, approximately 10-15% of the product, from the condensate of the concentration of the final acid is virtually free of nitrophenols, also contains small traces of benzene and is also saturated with water.) and / or E) as the final product, after removal of the excess benzene, anhydrous or saturated with water; and / or F) furthermore as a partial withdrawal of nitrating emulsion prior to phase separation with subsequent recycling into the nitrating process; and / or G) Combinations of A) to F).

[0115] It is advantageous to recycle a nitrobenzene still containing benzene according to the aforementioned positions A) to C) and particularly advantageous a nitrobenzene still containing benzene according to the aforementioned positions B) and C) in order to minimize the formation of by-products, especially dinitrobenzene from nitrobenzene, with traces of nitric acid in the circulating acid.

[0116] When the product is added to a concentrated circulating acid before the addition of nitric acid or to the mixed acid, in particular 0.1 to 5.0 wt.%, preferably 0.5 to 3.0 wt.%, especially preferably 1.1 to 2.0 wt.%, is added to the circulating acid.

[0117] By adding nitrobenzene to the benzene to be nitrated in such a way that a mixture of benzene / nitrobenzene of 0.1 to 50%, preferably 5.0 to 45%, particularly preferably 11 to 40% of nitrobenzene is added, an efficient reduction of the interfacial tension between the organic and acid phases is also achieved.

[0118] Both when adding the nitrated product (e.g., nitrobenzene) directly to the circulating acid and when adding the product (e.g., nitrobenzene) to the aromatic compound to be nitrated, it is advantageous to provide for pre-dispersion of the nitrated product or the mixture of nitrated product / aromatic compound to be nitrated and a certain residence time, the duration of which depends on the quality of the pre-dispersion of the added organic phases in the circulating acid, so that a distribution equilibrium of nitrated product can be established between the acid and the organic phase before the optimally altered interfacial tension between the two phases containing the nitrated product becomes effective.

[0119] To shorten this residence time before initial dispersion, it is particularly advantageous to add nitrated product (e.g., nitrobenzene) to the circulating acid or mixed acid in such a quantity that the solubility limit for the added product in the corresponding acid is exceeded. A two-phase mixture of nitrated product / acid is then formed.

[0120] Upon addition of the aromatic compound to be nitrated to this mixture, the portion of the added nitrated product not dissolved in the acid immediately mixes with the aromatic compound, resulting in a benzene / nitrobenzene mixture as the organic phase even before the first dispersion. Both phases, each containing nitrobenzene, thus contribute to the reduced interfacial tension desired for the initial dispersion.

[0121] Another way to shorten the residence time in the tubular reactor before the initial dispersion, and thus to accelerate the achievement of an approximate distribution equilibrium for the added product between the two phases, is to feed the product (e.g., nitrobenzene) into the nitration cycle via both the acid phase and the organic phase, in particular by adding, for example, 0.1 to 2.0 wt.%, preferably 0.5 to 1.5 wt.%, and especially preferably 1.1 to 1.5 wt.%, based on the amount of circulating acid to the acid phase, and / or by adding, for example, 0.1 to 32 wt.%, preferably 11.0 to 25 wt.%, of nitrobenzene to the organic phase consisting of benzene and nitrobenzene to be nitrated.

[0122] In addition to the variant of adding the aromatic compound to be nitrated as the last component before the initial dispersion of the complete nitration mixture, as described above, it can be equally advantageous to first predisperse the mixture of circulating acid, nitrated product, and aromatic compound to be nitrated, and subsequently add the nitric acid to the nitration mixture as the last component, in particular in such a way that not only is the nitric acid homogeneously and uniformly distributed in the aqueous phase within fractions of a second by suitable mixing devices, and the predispersed nitration mixture is not only preserved, but an additional further dispersion and, associated with this, an even larger exchange surface between the dispersed organic phase and the homogeneous acid phase is generated.

[0123] The foregoing invention or the method employed according to the invention is, in principle, applicable to any adiabatic nitration process known from the prior art, i.e., to adiabatic nitration processes in conjunction with a tubular reactor, in which the nitration with pure reactants, in particular the difficult-to-disperse aromatic compound (preferably benzene) and a pure mixed acid (aqueous nitric acid / sulfuric acid-nitrating acid mixture), is initiated by the input of mechanical mixing energy, as in the case of... B. in EP 0 373 966 A2, in EP 0 436 443 A2, in EP 0 489 211 A1, in EP 0 708 076 A2, in EP 0 771 783 A1, in EP 0 779 270 A1, in EP 1 272 268 A2, in EP 1 291 078 A2, in EP 2 168 942 A1, in EP 2 354 117 A1 and in EP 2 473 477 A1.

[0124] Within the scope of the uses according to the invention, a production plant (i.e., nitration plant or plant) for the adiabatic nitration of nitrifiable aromatic organic compounds (aromatics) to nitrated products in the form of the corresponding nitrated aromatic organic compounds (nitroaromatics) is also used. the production plant comprises the following units and equipment: (a) a nitration unit (N) for the adiabatic nitration of nitrifiable aromatic organic compounds (aromatics) to nitrated products in the form of the corresponding nitrated aromatic organic compounds (nitroaromatics) comprising one or more reactors for carrying out the nitration reaction, wherein the nitration unit (N) comprises at least one tubular reactor as reactor; (b) arranged downstream in the production line to the nitration unit (N), at least one separation device (S) for separating the nitrating acid from the nitrated crude products; (c) arranged downstream in the production line to the nitration unit (N) and to the separation device (S), at least one washing unit (W) for washing the nitrated raw products with a washing medium; (d) arranged in the production line downstream of the washing unit (W), a separating device for separating the washed nitrated products from the washing medium; wherein the production plant also includes at least one return device (R) for partially returning the nitrated products to the nitrating unit (N).

[0125] According to the invention, the nitriding unit comprises at least one tubular reactor as a reactor.

[0126] In particular, according to a preferred embodiment of the production plant used according to the invention, the tubular reactor of the nitriding unit may be equipped with one or more, preferably several, mixing elements (dispersing elements), especially for introducing additional mixing energy. In this embodiment, the mixing elements may be designed, in particular, as plates, especially baffle or deflecting plates, as orifices, as static mixers, or as flow dividers. Furthermore, in this embodiment, the mixing elements may be designed, in particular, such that, during operation, a mixing energy of 10 to 1000 joules / liter, preferably 10 to 500 joules / liter, and particularly preferably 20 to 200 joules / liter, is introduced by the mixing elements.Furthermore, in this embodiment, the pressure drop per mixing element during operation can be 0.1 bar to 3.0 bar, preferably 0.3 to 1.5 bar, and particularly preferably 0.3 to 0.8 bar. In a further particular variant of this embodiment, the mixing elements can be arranged in the tubular reactor such that, during operation, the conversion of nitric acid in the nitric / sulfuric acid-nitrating acid mixture in the first 10 to 30 vol% of the reactor is at least 40%, particularly at least 50%, and preferably at least 60%. Finally, in a further particular variant of this embodiment, the mixing elements can be arranged in the tubular reactor such that the conversion of nitric acid used at the end of the tubular reactor is at least 98%, preferably at least 99%, and particularly preferably at least 99.5%.

[0127] According to a particular embodiment of the production plant used according to the invention, it can further be provided that a dispersion device, preferably a mixing device, in particular for the production of a dispersion or emulsion, in particular the initial reaction mixture or the nitration mixture, is placed upstream of the tubular reactor(s) of the nitration unit.

[0128] In this embodiment, the dispersing device, in particular the mixing element, can be designed as a stirred tank, a jet mixer, or a pump, in particular a centrifugal pump. According to a particular variant of this embodiment, the dispersing device, in particular the mixing element, can be designed as a pump, in particular a centrifugal pump. According to another particular variant of this embodiment, the dispersing device, in particular the mixing element, can be designed as a jet mixer, in particular wherein the jet mixer generates a preferably central propellant jet and a medium surrounding the propellant jet, in particular in the form of an annular jet.In this embodiment, in particular, the dispersing device, especially the mixing element, can be positioned upstream of the tubular reactor, preferably directly upstream, in particular where the dispersing device transitions into the reactor or, in particular, where the dispersing device is integrated into the reactor and / or is a component of the reactor.

[0129] As regards the washing unit located downstream in the production line towards the nitriding unit and any separating device, this washing unit can typically - at least one dispersing device, in particular at least one mixing element, for bringing the nitrated raw products into contact with a washing medium on the one hand and emulsifying them on the other hand, and, - arranged downstream of the dispersion device, comprising a tubular reactor for feeding the emulsion of nitrated raw products on the one hand and washing medium on the other hand, produced in the dispersion device; in particular, wherein the tubular reactor is designed such that, during the passage of the emulsion through the tubular reactor, the removal of the impurities initially present in the nitrated raw products is made possible and / or that, during the passage of the emulsion through the tubular reactor, the impurities initially present in the nitrated raw products are transferred into the washing medium and / or neutralized therein.

[0130] It goes without saying that conventional washing equipment (e.g. mixers / settlers, extraction columns, etc.) may also be present.

[0131] Typically, the washing unit can be designed to carry out laundry in at least two washing steps, in particular at least one acidic wash and at least one neutral wash.

[0132] According to a preferred embodiment, the washing unit (W) may in particular be designed to perform a wash with at least three washing steps. In particular, the wash comprising at least three washing steps may include: (i) at least one first washing step carried out in an acidic environment (“acidic wash”), preferably with water or a mineral acid as the washing medium, (ii) at least one second washing step carried out in an alkaline (basic) environment (“basic wash”), preferably with a base as the washing medium, and (iii) at least one third washing step carried out in a neutral environment (“neutral wash”), preferably with water as the washing medium.

[0133] As previously explained in connection with the process used according to the invention, the process used according to the invention is flexible and can be adapted almost arbitrarily to the respective conditions (e.g., equipment conditions). Thus, as previously stated, the addition and removal of nitrated aromatic organic compounds (nitroaromatics) can take place at various process stages and positions within the process used according to the invention. This is also reflected in the production plant used according to the invention.

[0134] According to a particular embodiment of the present invention, the recycling device provided in the production plant used according to the invention for the partial recycling of the nitrated products into the nitration unit can be designed and / or arranged in such a way that the partially recycled nitrated products are taken from at least one of the following positions (i) to (iv) of the production stream: (i) the crude nitrated aromatic organic compounds (crude nitroaromatics), preferably after separation of the acidic aqueous phase (acid phase) and / or after phase separation of the resulting nitrating mixture into nitrating acid and crude nitrated aromatic organic compounds (crude nitroaromatics); and / or (ii) the washed nitrated aromatic organic compounds (nitroaromatics), in particular after acidic or neutral washing;and / or (iii) the washed, in particular after acidic or neutral washing, as well as stripped, distilled or dried nitrated aromatic organic compounds (nitroaromatics); and / or (iv) the nitrated aromatic organic compounds (nitroaromatics) obtained after concentration of the nitrating acid in the vapor condensate. In principle, combinations of two or more of these variants are also possible.

[0135] Furthermore, according to a further particular embodiment of the present invention, the recycling device provided in the production plant used according to the invention for the partial recycling of the nitrated products into the nitration unit can be designed and / or arranged in such a way that the partially recycled nitrated products are added to and / or fed into at least one of the following positions (i) to (iv) of the production stream: (i) the initial reaction mixture of all other reactants; and / or (ii) the sulfuric acid of the nitric acid / sulfuric acid-nitrating acid mixture, in particular before the production of the nitric acid / sulfuric acid-nitrating acid mixture; and / or (iii) the nitric acid / sulfuric acid-nitrating acid mixture; and / or (iv) the nitrateable aromatic organic compounds (aromatics) to be nitrated. In principle, combinations of two or more of these variants are also possible.

[0136] Finally, according to a further particular embodiment of the production plant used according to the invention, the production plant may also include at least one recycling device for recycling the nitrating acid. In this way, process economy and efficiency can be further increased. In particular, in this particular embodiment, the recycling device may include a device for concentrating the nitrating acid and, optionally, a device for adding fresh nitric and / or sulfuric acid.

[0137] Regarding further details concerning the production plant used according to the invention, reference can be made to the above statements concerning the method used according to the invention, which apply accordingly to the production plant used according to the invention, in order to avoid unnecessary repetition.

[0138] The subject of the present invention is - as previously stated - the use of nitrated aromatic organic compounds (nitroaromatics) to reduce the interfacial tension of the organ phase and acid phase and / or to improve the dispersibility of the organ phase and acid phase in adiabatic nitration reactions of the corresponding unnitrated aromatic organic compounds; wherein nitrifiable aromatic organic compounds (aromatics) are reacted in an adiabatic nitration reaction with a nitric acid / sulfuric acid-nitrating acid mixture to form the corresponding nitrated aromatic organic compounds (nitroaromatics); wherein the initial reaction mixture, which comprises the nitrateable aromatic organic compounds (aromatics) and the nitric / sulfuric acid-nitrating acid mixture, is supplemented with appropriate nitrated aromatic organic compounds (nitroaromatics) and the reaction and / or nitration reaction is initiated and / or carried out in the presence of the nitrated aromatic organic compounds (nitroaromatics); and / or wherein the obtained nitrated aromatic organic compounds (nitroaromatics) are partially recycled back into the nitration reaction and the subsequent conversion and / or nitration reaction is started and / or carried out in the presence of the nitrated aromatic organic compounds (nitroaromatics); the conversion and / or nitration reaction is carried out under adiabatic reaction conditions; the process or conversion and / or nitration reaction is carried out in a tubular reactor.

[0139] A further object of the present invention is the use of nitrated aromatic organic compounds (nitroaromatics) to increase yields and / or reduce by-product formation and / or shorten overall reaction times and / or lower reaction start temperatures in adiabatic nitration reactions of the corresponding unnitrated aromatic organic compounds. wherein nitrifiable aromatic organic compounds (aromatics) are reacted in an adiabatic nitration reaction with a nitric acid / sulfuric acid-nitrating acid mixture to form the corresponding nitrated aromatic organic compounds (nitroaromatics); wherein the initial reaction mixture, which comprises the nitrateable aromatic organic compounds (aromatics) and the nitric / sulfuric acid-nitrating acid mixture, is supplemented with appropriate nitrated aromatic organic compounds (nitroaromatics) and the reaction and / or nitration reaction is initiated and / or carried out in the presence of the nitrated aromatic organic compounds (nitroaromatics); and / or wherein the obtained nitrated aromatic organic compounds (nitroaromatics) are partially recycled back into the nitration reaction and the subsequent conversion and / or nitration reaction is started and / or carried out in the presence of the nitrated aromatic organic compounds (nitroaromatics); the conversion and / or nitration reaction is carried out under adiabatic reaction conditions; the process or conversion and / or nitration reaction is carried out in a tubular reactor.

[0140] Further advantages, properties, aspects and features of the present invention will become apparent from the following description of the figures shown in the illustrations. Fig. 1, Fig. 2a-d and Fig. 3 illustrated embodiments preferred according to the invention.

[0141] It shows: Fig. 1 a schematic representation of a method or production plant used according to the invention in a preferred embodiment of the present invention; Fig. 2a-d further schematic representations of various variants of the method or production plant used according to the invention according to further preferred embodiments of the present invention ( Fig. 2b-c) compared to the state of the art ( Fig. 2a); Fig. 3 a further schematic representation of a method or production plant used according to the invention according to a preferred embodiment of the present invention according to a further preferred embodiment of the present invention.

[0142] Fig. Figure 1 shows a schematic representation of an embodiment of a process used according to the invention for the various variants of the recycling of product into the nitrating mixture, using the nitration of benzene to nitrobenzene as an example, while in Fig. 2b-d schematically illustrates the most important of the various possible variants and sequences for the addition of the different reactants using the example of the nitration of benzene to nitrobenzene.

[0143] As in Fig. As shown in Figure 1, in a dosing / premixing unit PM of a tubular reactor TR, which is directly connected to this tubular reactor, the reactants nitric acid 1, benzene 2 and recycled nitrobenzene 9, 12, 13, 14 and 15 are added in a predetermined or defined order (as shown in Figure 1) to the concentrated circulating sulfuric acid 3, which is fed into the dosing / premixing unit PM by a suitable pump P (e.g. centrifugal pump) at a defined inlet pressure P1 (at least the sum of all pressure losses in the tubular reactor plus outlet pressure P2). Fig. (2b-d shown). The nitric acid dissolves completely and homogeneously in the recirculating acid. The benzene 2 and the recycled nitrobenzene 9, 12, 13, 14, or 15 react with the recirculating acid (sulfuric acid) / nitric acid (= mixed acid) to form a two-phase initial nitrating mixture 4 and are pre-dispersed. The temperature in this nitrating mixture 4 of mixed acid, benzene, and nitrobenzene is determined as the mixing temperature (i.e., the starting temperature) from the temperatures of the individual reactant streams (1, 2, 3, and / or 9, 12, 13, 14, 15) and is selected within a range of 80 to 120 °C such that nitration begins after the initial dispersion in the dispersion device FD. These reactants, premixed in the dosing / premixing unit PM, are subsequently dispersed in the dispersion device FD in such a way that a sufficiently large exchange surface (phase interface) is created between the organic and acid phases to initiate nitration.The process starts or begins, which is recognizable by a steep temperature increase in the nitrating mixture 4 after the dispersing device FD. This is further enhanced by additional dispersing elements RD1 to RD1 distributed throughout the tubular reactor TR. n The reduction of the phase interface between the organ and acid phases caused by coalescence during the passage of the nitrating mixture through the tubular reactor TR is counteracted. At the outlet of the tubular reactor, the nitrating mixture 5 (now a mixture of final acid and product) enters the phase separation apparatus S at a final temperature typically in the range of 120 to 145 °C and at a pressure P2. The pressure P2 is selected such that flash evaporation of the volatile components in the nitrating mixture 5, especially in the crude nitrobenzene (a mixture of aliphatics / benzene / nitrobenzene in the case of the nitration of benzene to nitrobenzene), is reliably prevented in the phase separation apparatus.

[0144] As in Fig. As further shown in Figure 1, after phase separation in the phase separation apparatus S, a partial stream 13 of the crude nitrobenzene 6, which, in addition to sulfuric acid, also contains all impurities (such as unreacted benzene, nitrophenols, etc.) as a microemulsion and in solution, can be recycled to the nitration before or after cooling via the metering / premixing unit PM. The main quantity of the crude nitrobenzene 6 is cleaned of all acidic compounds (e.g., mineral acids, nitrophenols, etc.) in the washing unit W with water (with and without the addition of bases) in one to three washing steps. A partial stream 14 of this nitrobenzene / benzene mixture 7, diverted from one or more of the washing units consisting of several washing steps, is preferably recycled to the nitration. The main quantity of the nitrobenzene / benzene mixture 7, which is free of all mineral acids and nitrophenols except to traces, can then be, for example,The unreacted benzene 10 and volatile aliphatic impurities are removed by distillation or steam stripping in the purification unit DS. The recovered benzene 10 is recycled to the nitration process after removal of excess aliphatics. A partial stream 9 of the completely purified nitrobenzene 8 can also be recycled to the nitration process.

[0145] As finally in Fig. As shown in Figure 1, the water originating from the nitration and the nitric acid, as well as the nitrobenzene dissolved in the final acid up to its solubility limit and traces of other volatile components (such as benzene, nitric acid, aliphatics, etc.), can be completely removed from the final acid 11 separated in the phase separation unit S at a temperature of 120 to 145 °C (e.g., by flash evaporation in the evaporator AR). The vapor condensate obtained during the flash evaporation of the final acid, which is a mixture of water and pure nitrobenzene 12 (consisting of approximately 10% to 15% of the total nitrobenzene produced), is usually combined with the crude nitrobenzene 6 from the phase separation apparatus S in the washing unit and further processed. According to the process employed in the invention, this pure nitrobenzene 12 from the vapor condensate can also be completely recycled back into the nitration after phase separation.

[0146] Additionally, nitrobenzene from the nitration can be recycled into the nitration cycle in such a way that a partial stream 15 of the nitrating mixture 5 is recycled before phase separation.

[0147] Another variant of the method used according to the invention, which is not shown, consists of recovering nitrobenzene from wastewater treatment, e.g. from wastewater stripping.

[0148] Regarding the figure depictions according to Fig. In particular, the following must be done in sections 2a-d:

[0149] In Fig. Figure 2a shows, for comparison, the state of the art for the usual sequence of adding the reactants to the circulating sulfuric acid, nitric acid, and benzene: Nitric acid 1 is first added to the circulating acid 3 and mixed homogeneously. Benzene 2, to be nitrated, is then added to the resulting mixed acid (stream 3 + 1), and the resulting initial nitrating mixture 4 or the initial reaction mixture (mixed acid / benzene) is dispersed in the dispersion unit FD in such a way that a sufficiently large exchange surface (phase interface) is created for the nitration to begin, recognizable by the steepest possible temperature rise in the initial nitrating mixture 4 after the dispersion device FD.

[0150] In Fig. 2b According to the invention, the reactants nitric acid 1, benzene 2, and nitrobenzene from the various sources 9, 12, 13, 14, or 15 are added to the circulating sulfuric acid in the following order: nitrobenzene from source 9, 12, 13, 14, or 15, then nitric acid 1, and finally benzene 2. The nitrobenzene can be pre-dispersed in the circulating sulfuric acid 3 before the nitric acid is added. The nitric acid is mixed in homogeneously as quickly as possible, and after the benzene is added to the mixed acid / nitrobenzene mixture, the initial nitrating mixture 4 is dispersed in the dispersion device FD in such a way that a sufficiently large exchange surface (phase interface) is created for the nitration to begin, which is recognizable by the steepest possible temperature rise in the initial nitrating mixture 4 after the dispersion device FD.

[0151] In Fig. 2c The reactants, nitric acid 1, benzene 2, and nitrobenzene from the various sources 9, 12, 13, 14, or 15, are added to the circulating sulfuric acid 3 in the following order: nitrobenzene from source 9, 12, 13, 14, or 15; nitric acid 1; and finally benzene 2, which is present as a mixture of benzene and nitrobenzene from source 9, 12, 13, 14, or 15. The nitrobenzene can be predispersed in the circulating acid 3 before the nitric acid is added. The nitric acid is mixed in homogeneously as quickly as possible, and after adding the benzene / nitrobenzene mixture to the mixture of mixed acid (nitrating acid) / nitrobenzene, the initial nitrating mixture 4 is dispersed in the dispersion device FD in such a way that a sufficiently large exchange surface (phase interface) is created so that the nitration starts, which is recognizable by the steepest possible temperature increase in the initial nitrating mixture 4 after the dispersion device FD.

[0152] In Fig. 2d Finally, the reactants, i.e., nitric acid 1, benzene 2, and nitrobenzene from the various sources 9, 12, 13, 14, or 15, are added to the circulating sulfuric acid in the following order: nitrobenzene is added from source 9, 12, 13, 14, or 15, then benzene 2 alone and / or as a mixture with nitrobenzene from source 9, 12, 13, 14, or 15, or in separate streams, to the circulating acid. The nitrobenzene / benzene mixture is pre-dispersed in the circulating acid before the nitric acid is added. The nitric acid is added last and mixed in homogeneously as quickly as possible. This initial nitriding mixture is dispersed in the dispersing device FD in such a way that a sufficiently large exchange surface (phase interface) is created so that the nitriding starts, which can be recognized by a steep temperature increase in the initial nitriding mixture 4 after the dispersing device FD.

[0153] Fig. Figure 3 shows a further schematic representation of the method or production plant used according to the invention according to a particular embodiment of the present invention: According to Fig. 3. In a nitration unit N, the nitration of the nitratable aromatic organic starting compounds (aromatics) to the corresponding nitrated aromatic organic compounds (nitroaromatics) first takes place under adiabatic conditions according to the reaction formula described above (i.e., initial reaction mixture of aromatics to be nitrated and nitric acid / sulfuric acid-nitrating acid mixture, as well as the addition of the corresponding nitrated product). A separation device S, in particular a separator, is located downstream of the nitration unit N in the production line for separating the nitrating acid or the nitrating acid mixture from the nitrated crude products.In the production line downstream of the nitration unit N and the separation device S, a washing device W is located for carrying out a washing of the nitrated raw products, as described above, so that subsequently (after separation of the washing medium and, if necessary, drying of the washed nitrated products) the washed and purified nitrated products NP are produced.

[0154] The system and process according to the invention are used in accordance with Fig. As previously described, the 3 is characterized by the fact that a return device R is additionally provided for the partial return of nitrated product to the initial reaction mixture, which enables the previously described process according to the invention. The return device used according to the invention is designed such that the nitrated product can be removed and returned at various levels of the production plant used according to the invention or at various levels of the process used according to the invention, as previously described in detail (e.g.,as a two-phase nitrating mixture immediately after nitration and / or as a nitrated crude product after separation of the nitrating acid and / or before, from or after washing, in particular after acidic or neutral washing, and / or as pure nitrobenzene from the concentration of the nitrating acid in the recycling unit RA or as a purified and optionally dried nitrated end product, combinations of these possibilities may also be provided).

[0155] The partial recycling of the nitrated product to the initial reaction mixture is associated with the advantages previously described in detail, in particular with the improvement of the dispersibility of the organ phase and acid phase and thus with an overall improved reaction control (i.e. improved yields, reduction of by-product formation, lower starting temperatures, improved energy efficiency, improved handling, etc.).

[0156] As in Fig. As shown in Figure 3 and previously explained, according to a further particular embodiment of the production plant used according to the invention, the production plant may also include at least one recycling device RA for recycling the nitrating acid. In particular, as explained above, in this particular embodiment the recycling device RA may include a device for concentrating the nitrating acid and optionally a device for adding fresh nitric and / or sulfuric acid.

[0157] Overall, the present invention provides an improved process for a nitration process for nitrifiable aromatic organic compounds and a corresponding (production) plant for carrying out this process, which are characterized by an overall improved efficiency, in particular an improved technical efficiency and an improved energy efficiency, and an overall improved process economy and also an improved handling.

[0158] Further embodiments, modifications, variations, or the like of the present invention are readily apparent to the person skilled in the art upon reading the description and are feasible without departing from the scope of the present invention.

[0159] The present invention is illustrated by the following exemplary embodiments, without, however, limiting the present invention to these. IMPLEMENTATION EXAMPLES: Example 1 (Comparative Example)

[0160] Into a tubular reactor with an internal volume of 231 ml, equipped with 17 mixing elements (a combination of static mixing elements and orifices) at irregular intervals, 762 g / h of benzene (10% excess) and 15.4 kg / h of mixed acid with a sulfuric acid content of 65.73% and a nitric acid content of 4.99% are dosed for a starting temperature of 80 °C. The benzene is introduced into the reactor via a nozzle at an internal pressure of approximately 9 bar for initial dispersion. With a residence time of 80 s in the reactor of the nitrating mixture (with a final acid / product phase ratio of 11.7 by weight or 9.6 by volume), the flow velocity of the nitrating mixture is 0.42 m / s. The temperature in the reactor after the fifth mixing element following the initial dispersion is 98 °C and at the end of the reactor is 121 °C. The residual content of nitric acid in the nitrating acid is 1,200 ppm (corresponding to a nitric acid conversion of 97%).The temperature rise in the nitrating mixture is 41 °C. The crude nitrobenzene contains – besides the excess of dosed benzene – less than 120 ppm of dinitrobenzene (DNB) and less than 1,200 ppm of nitrophenols with a very small proportion of picric acid. Example 2 (according to the invention)

[0161] In a tubular reactor, as described in Example 1, a mixture of 762 g / h benzene (10% excess), 190.5 g / h nitrobenzene recycled from nitration (corresponding to 25% of the dosed benzene), and 15.4 kg / h mixed acid with a sulfuric acid content of 65.73% and a nitric acid content of 4.99% is dosed for a starting temperature of 80 °C. The benzene / nitrobenzene mixture is introduced into the reactor at an internal pressure of approximately 9 bar via a nozzle for initial dispersion. With a residence time of 78 s in the reactor (with a final acid / product phase ratio of 10.2 by weight or 8.0 by volume), the flow velocity of the nitrating mixture is 0.43 m / s. The temperature in the reactor is 102 °C after the fifth mixing element following the first dispersion and 122.1 °C at the end of the reactor. The residual nitric acid content in the nitrating acid is less than 200 ppm (corresponding to a nitric acid conversion of 99.5%).The temperature rise in the nitrating mixture is 42.1 °C. The crude nitrobenzene contains – in addition to the excess of dosed benzene – approximately 80 ppm of dinitrobenzene (DNB) and less than 900 ppm of nitrophenols with a very small proportion of picric acid. Example 3 (according to the invention)

[0162] In a tubular reactor, as described in Example 1, a mixture of 15.4 kg / h of mixed acid with a sulfuric acid content of 65.73% and a nitric acid content of 4.99%, 190.5 g / h of nitrobenzene recycled from nitration (corresponding to 1.31% of the mixed acid), and 762 g / h of benzene (10% excess) is fed to a starting temperature of approximately 80 °C. The nitrobenzene is pre-dispersed before being added to the mixed acid. For initial dispersion, the benzene is introduced into the reactor mixture of mixed acid and nitrobenzene via a nozzle at an internal pressure of approximately 9 bar. With a residence time of 78 s in the reactor of the nitrating mixture, which has a final acid / product phase ratio of 10.2 by weight or 8.0 by volume, the flow velocity of the nitrating mixture is 0.43 m / s. The temperature in the reactor after the fifth mixing element following the first pre-dispersion is 102 °C and at the end of the reactor is 122.1 °C.The residual nitric acid content in the nitrating acid is less than 200 ppm (corresponding to a nitric acid conversion of 99.5%). The temperature rise in the nitrating mixture is 42.1 °C. Besides the excess of dosed benzene, the crude nitrobenzene contains approximately 80 to 90 ppm of dinitrobenzene (DNB) and less than 900 ppm of nitrophenols with a very small proportion of picric acid. Example 4 (according to the invention)

[0163] In a tubular reactor, as described in Example 1, a mixture of 15.4 kg / h of mixed acid with a sulfuric acid content of 65.73% and a nitric acid content of 4.99%, 160 g / h of nitrobenzene (corresponding to 1.1% of the circulating acid), and a mixture of 762 g / h of benzene (10% excess) and 76 g / h of nitrobenzene (corresponding to 10% of the metered benzene) is metered for a starting temperature of approximately 80 °C. The nitrobenzene is pre-dispersed in the mixed acid before the benzene is added. For initial dispersion, the benzene / nitrobenzene mixture is introduced into the reactor via a nozzle into the mixture of mixed acid and nitrobenzene at an internal pressure of approximately 9 bar. With a residence time of 78 s for the nitrating mixture with a final acid / product phase ratio of 10.2 weight-based or 8.0 volume-based in the reactor, the flow velocity of the nitrating mixture is approximately 0.43 m / s.The temperature in the reactor after the fifth mixing element following the first pre-dispersion is 102 °C and 122.1 °C at the end of the reactor. The residual nitric acid content in the nitrating acid is less than 200 ppm (corresponding to a nitric acid conversion of 99.5%). The temperature rise in the nitrating mixture is 42.1 °C. Besides the excess of dosed benzene, the crude nitrobenzene contains approximately 80 ppm of dinitrobenzene (DNB) and less than 900 ppm of nitrophenols with a very small proportion of picric acid.

Claims

[1] Use of nitrated aromatic organic compounds of claim 15 (nitroaromatics) for reducing the interfacial tension of the organ phase and acid phase and / or for improving the dispersibility of the organ phase and acid phase in adiabatic nitration reactions of the corresponding unnitrated aromatic organic compounds; wherein nitratable aromatic organic compounds (aromatics) are reacted in an adiabatic nitration reaction with a nitric acid / sulfuric acid-nitrating acid mixture to form the corresponding nitrated aromatic organic compounds (nitroaromatics); wherein the initial reaction mixture, which comprises the nitrateable aromatic organic compounds (aromatics) and the nitric / sulfuric acid-nitrous acid mixture, is supplemented with appropriate nitrated aromatic organic compounds (nitroaromatics), and the reaction and / or nitration reaction is initiated and / or carried out in the presence of the nitrated aromatic organic compounds (nitroaromatics); and / or . wherein the obtained nitrated aromatic organic compounds (nitroaromatics) are partially recycled back into the nitration reaction and the subsequent conversion and / or nitration reaction is started and / or carried out in the presence of the nitrated aromatic organic compounds (nitroaromatics); the conversion and / or nitration reaction is carried out under adiabatic reaction conditions; the process or conversion and / or nitration reaction is carried out in a tubular reactor. [2] Use of nitrated aromatic organic compounds of claim 16 (nitroaromatics) to increase yields and / or to reduce by-product formation and / or to shorten overall reaction times and / or to lower reaction start temperatures in adiabatic nitration reactions of the corresponding unnitrated aromatic organic compounds, wherein nitratable aromatic organic compounds (aromatics) are reacted in an adiabatic nitration reaction with a nitric acid / sulfuric acid-nitrating acid mixture to form the corresponding nitrated aromatic organic compounds (nitroaromatics); wherein the initial reaction mixture, which comprises the nitrateable aromatic organic compounds (aromatics) and the nitric / sulfuric acid-nitrating acid mixture, is supplemented with appropriate nitrated aromatic organic compounds (nitroaromatics) and the reaction and / or nitration reaction is initiated and / or carried out in the presence of the nitrated aromatic organic compounds (nitroaromatics); and / or wherein the obtained nitrated aromatic organic compounds (nitroaromatics) are partially recycled back into the nitration reaction and the subsequent conversion and / or nitration reaction is started and / or carried out in the presence of the nitrated aromatic organic compounds (nitroaromatics); the conversion and / or nitration reaction is carried out under adiabatic reaction conditions; the process or conversion and / or nitration reaction is carried out in a tubular reactor.

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