EP2188248A1

EP2188248A1 - Method for producing isocyanates

Info

Publication number: EP2188248A1
Application number: EP08787187A
Authority: EP
Inventors: Gerhard Olbert; Torsten Mattke; Carsten KNÖSCHE; Andreas Daiss; Jens Denecke
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2007-08-30
Filing date: 2008-08-13
Publication date: 2010-05-26
Also published as: KR20100075863A; CN101848890A; US20100305356A1; WO2009027234A1; CN101848890B; JP2010536912A

Abstract

The invention relates to a method for producing isocyanates.

Description

Process for the preparation of isocyanates

description

The present invention relates to a process for the preparation of isocyanates.

For the preparation of isocyanates by phosgenation of the corresponding amines, there is in principle the possibility of a liquid-phase or a gas-phase phosgenation. The gas phase phosgenation is characterized in that the reaction conditions are chosen so that at least the reaction components diamine, diisocyanate and phosgene, but preferably all starting materials, products and reaction intermediates, at these conditions, particularly preferably until the completion of the reaction are gaseous. The present invention particularly relates to gas phase phosgenation.

EP 1 275 639 A1 describes the gas-phase phosgenation of (cyclo) aliphatic diamines in a reaction zone with constrictions of the walls.

In the mixing device, the amine and phosgene-containing educt streams are fed coaxially to a mixing zone, wherein the phosgene-containing educt stream is guided on the inside and the amine-containing educt stream on the outside. In the area of the merging of the educt streams, ie the reaction zone, there is a further reduction or slight enlargement of the flow cross section, so that the flow rate increases due to the volume increase in the course of the reaction. A disadvantage of this arrangement is that the amine stream is guided coaxially outside. This can lead to the formation of solids on the walls of the mixing device, since the amine is present in excess of the phosgene on the walls, which promotes by-product formation. Another disadvantage of the method is that too much acceleration of the flow through the cross-sectional constriction results in attenuation of the turbulent flow velocity fluctuations that are critical to rapid mixing in a turbulent flow.

It is also described in EP 1275639A1 that in the mixing device before the merging of the reactant streams, the educt streams should be twisted, so that the turbulent fluctuation rates in the educt streams are increased and mixing during the merging of the two educt streams then takes place more rapidly.

EP 1526129 A1 describes the increase of the turbulence in a mixing nozzle by means of spin-producing internals. This creates a tangential turbulence of the entire stream, which, however, does not significantly affect the mixing of the different streams with one another. EP 1 275 640 A1 describes the gas phase phosgenation of (cyclo) aliphatic di- and triamines in a mixing tube with reactor, in which the gas flow in the mixing region is accelerated.

A disadvantage of this method is that not immediately at the beginning of the mixing, the maximum speed difference between the reactant streams is achieved and thus not the minimum possible mixing time is achieved.

DE 10359627 A1 discloses a gas-phase phosgenation in which amine is mixed in through a concentric annular gap between two phosgene streams, wherein the areas through which the phosgene streams flow are in a ratio of 1: 0.5 to 1: 4.

International patent application WO 2007/028715 discloses a process in which amine and phosgene are metered in via annular gaps, that is to say in an annularly closed column.

In all these documents only smooth nozzles are disclosed, which may optionally contain spin-generating internals.

The inflow of educts into the mixing chamber is usually turbulent in the disclosed mixing organs. The airfoil has a turbulent core flow and a wall boundary layer. The wall boundary layer consists of a near-wall, laminar lower layer and a laminar-turbulent transition area. In the boundary layer, in particular the laminar lower layer, flow velocities are lower than in the core. At the contact point of Eduktzuführungen thus creates a low speed area and consequently a high residence time. This can lead to the formation and deposition of solids.

The slower boundary layer also reduces the shear rate between the jet and the environment when entering the mixing chamber and thus the mixture-effective edge turbulence (start of the free jet). As a result, the mixing time is increased. A reduction of the boundary layer thus leads to a reduced tendency to deposit and a shorter mixing time.

The object of the present invention was to develop a reaction regime for a gas phase phosgenation, with which a large-scale implementation is possible and which causes a reduction of the boundary layer thickness at the mouth point of the educt streams in the mixing chamber. In addition, it is an object of the invention to develop a mixing nozzle, which has the highest possible turbulence intensity in the core of the educt streams at the outlet point, so that the fastest possible mixing is possible. should be carried out over the entire nozzle cross-section of the educt streams.

The object is achieved by processes for preparing isocyanates by reacting the corresponding amines with phosgene, optionally in the presence of at least one, preferably exactly one inert medium, in the gas phase, by contacting fluid streams of amine and phosgene and their subsequent reaction with each other, in the reducing the turbulent flow boundary layer of at least one stream immediately before contacting with the other stream through at least one flow-mechanical baffle.

By this measure, the turbulence level in the core of the educt streams is simultaneously increased.

Another object of the present invention is a device for mixing at least two different fluid substances, comprising at least one flow channel per fluid, in which at least one of the flow channels upstream of the point at which the different substances come into contact with each other at least has a baffle.

Another object of the present invention is the use of such devices in chemical reactions in which fluid chemical compounds are mixed together.

It is known, for example, from EP 289840 B1 or from EP 1275639 A1 the mixing of amine and phosgene in the gas phase phosgenation with the aid of a combination of nozzle and annular gap. This mixing principle is shown by way of example in FIG. 1.

According to the invention, the disturbance of the flow is preferably generated by such flow-mechanical baffles 4 or 5, which in the relevant flow channel, ie even before the mixing of the components, detach the flow through an extension which is limited in length (FIGS. 2 and 3) or Create constriction (Figure 4 and 5).

The effect of the baffles 4 and 5 in the flow channel is such that a detachment of the flow is enforced by them. On the other side of the baffle and a forming recirculation area, the flow again rests against the wall and the turbulent boundary layer forms again. In this start-up phase, the boundary layer thickness is reduced compared to the flow conditions upstream of the baffle. The mouth point should be as close as possible to the application point in order to realize a minimum boundary layer thickness. The muzzle point is allowed However, do not lie before the application point of the flow to the wall, otherwise there will be recirculations of the mixing chamber in the Eduktzuführung.

For the description of the invention, the following quantities are used (see FIGS. 2a and 4a):

The diameter D is the diameter or the gap width of the respective flow channels, in each case measured at the location of the merging of the streams to be mixed, ie the location at which the streams to be mixed can have the first possible contact.

In the case of a narrowing of the flow channel, the height of the baffle 5 is described by the size d1, in the case of an expansion by means of a baffle 4 by the size d2.

The length of the baffle is described by the size l, the distance of the baffle upstream of the location of the merger of the streams to be mixed by the size L (see figures).

The height d1 or depth d2 of the baffles 5 and 4 and their length έ according to the invention must be sufficient to fluidically create a separation and the formation of a Rezirkulationsgebietes.

The distance L must be greater than the length of the forming recirculation area. However, it should be significantly smaller than the run-up path to complete formation of a turbulent flow.

This depends on the type and speed of the flowing fluid and can be determined experimentally or by simulations by the person skilled in the art.

The mechanical design of such baffles must generate a flow-mechanical separation of the flow and the formation of a Rezirkulationsgebietes, wherein it is not essential according to the invention, in which way the baffles are executed.

Cross sections of exemplary embodiments of baffles are shown in FIG. 6: a: rectangles b: trapezoids c: diamonds in the flow direction (arrow) d: diamonds against flow direction (arrow) e: half or partial circles f: saw teeth in the flow direction (arrow) g: saw teeth against flow direction (arrow) h: polygon or polygon i: triangles.

Preferably, a, b, e, h and i. Particularly preferred are a, b, e and i, very particularly preferably a and e and in particular a.

The ratio d1: D is preferably from 0.002 to 0.2: 1, particularly preferably from 0.05 to 0.18: 1, very particularly preferably from 0.07 to 0.15: 1 and in particular from 0.1 to 0.12: 1.

The distance L is preferably greater than twice the height d1, more preferably greater than four times, and most preferably eight times the size d1. The length L is preferably less than fifty times the diameter D, more preferably less than twenty times and most preferably less than ten times the diameter D.

In the case of an extension, the distance L is preferably greater than the simple of the depression d2, particularly preferably greater than twice, and very particularly preferably six times the depression d2. The length L is preferably less than fifty times the diameter D, more preferably less than twenty times and most preferably less than ten times the diameter D.

In the case of a depression, d 2: D is from 0.001 to 0.5: 1, more preferably from 0.01 to 0.3: 1, and most preferably from 0.1 to 0.2: 1.

Of subordinate influence, in the case of a constriction, the ratio d1: i, which as a rule is 10: 1 to 1:10, is preferably 5: 1 to 1: 5 and particularly preferably 2: 1 to 1: 2.

In the case of an extension, the ratio d2: i should generally be 2: 1 to 1:20, preferably 1: 1 to 1:15, and particularly preferably 1: 2 to 1:10.

Whether a narrowing or an enlargement of the flow cross-section is to be preferred depends on whether an increased turbulence level is desired in the core of the educt streams. A noticeable increase in the turbulence level results only from a narrowing of the cross section. On the other hand, an expansion, compared to a narrowing of the cross section, causes a more efficient reduction in the thickness of the laminar boundary layer.

In contrast to EP 1526129 A1, the baffles are according to the invention on the

Walls of the flow channels applied, ie a narrowing of the diameter D takes place by d1 from "outside to inside", while those disclosed in EP 1526129 A1 Inclined plates and helical elements are mounted as turbulence generators in the interior of the flow channel and thus narrow the diameter D "from inside to outside".

The only embodiment explicitly disclosed in EP 1526129 A1 in the example completely fills the flow channel.

The mixing device disclosed in EP 1 275 639 A1 discloses a constriction only in the region in which mixing has already taken place or taken place. This promotes the risk of the formation of deposits or blockages. In contrast, the object of the present invention is to produce a separation and recirculation prior to mixing.

Furthermore, the baffles can include an angle φ (phi) with the flow direction (Figure 7, top view).

An angle φ = 0 ° means that the baffle is transverse to the flow direction (arrow), φ = 90 ° means that the baffle is longitudinal to the flow direction (in the flow direction). Preferably, φ is from 0 to 80 °, particularly preferably from 0 to 60 °, very particularly preferably from 0 to 45 °, in particular from 0 to 30 ° and in particular φ = 0 °.

Angle φ ≠ 0 produces a tangential velocity vector (spin) in the respective flow, in addition to the axial turbulence according to the invention.

It has been found that material flows in which the baffles according to the invention produce a separation and a recirculation zone upstream of the orifice are better mixed with one another. This results in a mixture of phosgene and amine as streams to the fact that form less deposits in the area in which the streams are brought into contact with each other, as if the mixing takes place without fluidic baffles.

The thickness of the laminar boundary layer in fully developed turbulent flow Prandtl (62.7 ^χ D) / (Re ⁰ ^'875) wherein Re is the Reynolds number of the fluid under the prevailing conditions. According to W. Bohl, "Technical Fluid Mechanics", 12th Edition, Vogel-Buchverlag, 2001, for the area fraction a of the laminar lower layer at the mouth cross-section a = 1 - (1-2x62, 7 / (Re ⁰⁸⁷⁵ ) ² ). For a Reynolds number of 5000, the laminar boundary layer then absorbs about 14% of the mouth cross-section. Accordingly, laminar flow at low velocities prevails in these 14% of the cross-sectional area. If the described improvement principle implemented in an optimal manner, this laminar area can be almost completely avoided. Accordingly, the zones of slow flow velocity near the wall can be avoided, and thus the formation of Abla wrestled. Furthermore, the jet now enters the mixing zone with a higher edge velocity, so that increased edge turbulence and therefore better mixing are achieved.

The mixing device may preferably be static mixing elements, for example a nozzle mixing device, for example coaxial mixing nozzles, Y or T mixers, jet mixers or mixing tubes.

In a coaxial jet mixer, one component (preferably the amine) is passed in a mixing tube through a concentric tube with a small diameter (nozzle) at high speed into the other component (then preferably phosgene).

The reactors can be, for example, cylindrical reaction spaces without internals and without moving parts.

An embodiment of a mixing / reaction unit is described in EP

1275639 A1, there especially in paragraphs [0013] to [0021] and the example together with Figure 1, which is hereby incorporated by reference into the present disclosure. However, in contrast to the disclosure there, the metering of the amine through the inner tube and of phosgene as external stream is preferred.

An embodiment of a mixing / reaction unit is described in EP

No. 1275640 A1, there in particular in paragraphs [0010] to [0018] and the example together with FIG. 1, which is hereby incorporated by reference into the present disclosure. However, in contrast to the disclosure there, the metering of the amine through the inner tube and of phosgene as external stream is preferred.

A further embodiment of a mixing / reaction unit is described in EP 1319655 A2, there in particular in paragraphs [0015] to [0018] and the example together with FIG. 1, which is hereby incorporated by reference into the present disclosure.

It may be expedient to incorporate flow comparator as described in EP 1362847 A2, there especially in paragraphs [0008] to [0026] and the example together with FIG. 1, which is hereby incorporated by reference into the present disclosure.

Also conceivable is the use of several parallel aligned nozzles, as described in EP 1449826 A1, there especially in paragraphs [0011] to [0027] and Example 2 together with Figures 1 to 3, which is hereby incorporated by reference into the present disclosure , Another embodiment of a mixing / reaction unit is described in DE 10359627 A1, there especially in paragraphs [0007] to [0025] and Example 1 together with the figure, which is hereby incorporated by reference into the present disclosure.

A preferred embodiment for a mixing nozzle is a slot mixing nozzle, as described in WO 2008/55898, there particularly from page 3, line 26 to page 15, line 31 and a reaction chamber as described there from page 15, line 35 to Page 31, line 38 together with the figures, which is hereby incorporated by reference into the present disclosure.

A particularly preferred embodiment for a mixing nozzle is an annular gap mixing nozzle, as described in International Patent Application WO 2007/028715, there especially from page 2, line 23 to page 11, line 22 and a reaction chamber as described there from page 1 1, line 26 to page 21, line 15 together with Figure 2, which is hereby incorporated by reference into the present disclosure.

It is essential according to the invention that a baffle is set up in the course of at least one of the streams to be mixed in the nozzle.

In order to prevent solid deposition and blockages, the phosgene-containing educt stream is preferably conducted in the mixing device according to the invention so that all the apparatus walls are filled with the phosgene-containing feed streams after the feedstreams have been combined and the aminous feed streams are completely enveloped by the phosgene-containing feed streams until complete mixing of the streams or substantially complete conversion of the amine has occurred.

Therefore, preferably, the amine is metered in, so that the stream is completely surrounded on all sides by a phosgene stream.

The amines that can be used in a gas phase phosgenation must meet certain requirements (see below).

These may be monoamines, diamines, triamines or higher amines, preferably diamines. Accordingly, the corresponding monoisocyanates, diisocyanates, triisocyanates or higher isocyanates, preferably diisocyanates, are obtained.

The amines and isocyanates may be aliphatic, cycloaliphatic or aromatic, preferably aliphatic or cycloaliphatic and more preferably aliphatic. Cycloaliphatic isocyanates are those which contain at least one cycloaliphatic ring system.

Aliphatic isocyanates are those which have exclusively isocyanate groups attached to straight or branched chains.

Aromatic isocyanates are those which have at least one isocyanate group bonded to at least one aromatic ring system.

(Cyclo) aliphatic isocyanates are in the context of this application briefly for cycloaliphatic and / or aliphatic isocyanates.

Examples of aromatic diisocyanates are preferably those having 6 to 20 carbon atoms, for example monomeric 2,4'- or 4,4'-methylene-di (phenyl isocyanate (MDI), 2,4- and / or 2,6-toluene diisocyanate ( TDI) and 1, 5 or 1, 8-naphthyl diisocyanate (NDI).

Diisocyanates are preferably (cyclo) aliphatic diisocyanates, particularly preferably (cyclo) aliphatic diisocyanates having 4 to 20 C atoms.

Examples of common diisocyanates are aliphatic diisocyanates such as 1, 4-tetramethylene diisocyanate, 1, 5-pentamethylene diisocyanate, hexamethylene diisocyanate (1, 6-diisocyanatohexane), 1, 8-octamethylene diisocyanate, 1, 10-decamethylene diisocyanate, 1, 12-dodecamethylene diisocyanate, 1 , 14-Tetradecamethylene diisocyanate, derivatives of lysine diisocyanate, tetramethylxylylene diisocyanate (TMXDI), trimethylhexane diisocyanate or tetra-methylhexane diisocyanate, and 3 (or 4), 8 (or 9) -bis (isocyanatomethyl) -tricyclo [5.2.1.0 ²⁶ ] decane Isomer mixtures, and also cycloaliphatic diisocyanates such as 1, 4, 1, 3 or 1, 2-diisocyanatocyclohexane, 4,4'- or 2,4'-di (isocyanatocyclohexyl) methane, 1-isocyanato-3,3, 5-trimethyl-5- (isocyanatomethyl) cyclohexane (isophorone diisocyanate), 1, 3 or 1, 4-bis (isocyanatomethyl) cyclohexane, 2,4- or 2,6-diisocyanato-1-methylcyclohexane.

Preference is given to 1, 5-pentamethylene diisocyanate, 1, 6-diisocyanatohexane, 1-isocyanato-3,3,5-trimethyl-5- (isocyanato-methyl) cyclohexane, 4,4'-di (isocyanatocyclohexyl) methane and tolylene diisocyanate isomer mixtures. Particularly preferred are 1,6-diisocyanatohexane, 1-isocyanato-3,3,5-trimethyl-5- (isocyanatomethyl) cyclohexane and 4,4'-di (isocyanato-ocyclohexyl) methane.

For the process according to the invention, it is possible to use those amines for the reaction to give the corresponding isocyanates, in which the amine, its corresponding intermediates and the corresponding isocyanates are present in the selected reaction conditions in gaseous form. Preference is given to amines which decompose under the reaction conditions to at most 2 mol%, more preferably at most 1 mol% and most preferably at most 0.5 mol% during the duration of the reaction. Particularly suitable here are amines, in particular diamines, based on aliphatic or cycloaliphatic hydrocarbons having 2 to 18 carbon atoms. Examples of these are 1,5-diaminopentane, 1,6-diaminohexane, 1-amino-3,3,5-trimethyl-5-aminomethylcyclohexane (IPDA) and 4,4'-diaminodicyclohexylmethane. Preference is given to using 1,6-diaminohexane (HDA).

Likewise, aromatic amines can be used for the process according to the invention, which can be converted into the gas phase without significant decomposition. Examples of preferred aromatic amines are toluenediamine (TDA), as a 2,4- or 2,6-isomer or as a mixture thereof, for example as 80:20 to 65:35 (mol / mol) mixture, diaminobenzene, 2,6-xylidine Naphthyldiamine (NDA) and 2,4'- or 4,4'-methylene (diphenylamine) (MDA) or isomer mixtures thereof. Preferred among these are the diamines, more preferably 2,4- and / or 2,6-TDA.

In the gas phase phosgenation, by definition, it is desirable that the compounds occurring in the course of the reaction, ie starting materials (diamine and phosgene), intermediates (in particular the intermediately formed mono- and dicarbamyl chlorides), end products (diisocyanate), and optionally metered inert compounds, remain under the reaction conditions in the gas phase. Should these or other components be from the gas phase, e.g. deposited on the reactor wall or other apparatus components, it can be changed by these deposits, the heat transfer or the flow through the affected components undesirable. This is especially true for occurring amine hydrochlorides, which are formed from free amino groups and hydrogen chloride (HCl), since the resulting amine hydrochlorides are easily precipitated and are difficult to re-evaporate.

The educts, or just one of them, can be metered into the mixing chamber together with at least one inert medium.

The inert medium is a medium which is gaseous in the reaction space at the reaction temperature and does not react with the compounds which occur in the course of the reaction. The inert medium is generally mixed with amine and / or phosgene before the reaction, but can also be metered in separately from the educt streams. For example, nitrogen, noble gases such as helium or argon, or aromatics such as chlorobenzene, chlorotoluene, o-dichlorobenzene, toluene, xylene, chloronaphthalene, decahydronaphthalene, carbon dioxide or carbon monoxide can be used. Preferably, nitrogen and / or chlorobenzene is used as the inert medium. In general, the inert medium is used in an amount such that the ratio of the gas volumes of inert medium to amine or to phosgene is more than 0.0001 to 30, preferably more than 0.01 to 15, particularly preferably more than 0.1 to 5 is.

The starting amines are evaporated before carrying out the process according to the invention and heated to 200 ⁰ C to 600 ⁰ C, preferably 300 ° C to 500 ⁰ C and optionally diluted with an inert gas or with the vapors of an inert solvent supplied by the mixer to the reactor.

The phosgene used in the phosgenation is also heated to a temperature within the range of 200 ° C to 600 ° C, preferably 300 ⁰ C to 500 ° C before carrying out the inventive method optionally diluted with an inert gas or with the vapors of an inert solvent.

In a preferred embodiment, the amine streams are heated to higher temperature than the phosgene up to 50 ⁰ C, preferably up to 30 ⁰ C, more preferably up to 24 and most preferably up to 20 ° C higher. Preferably, the temperature of the amine streams at least 5 ⁰ C, particularly preferably at least 10 ⁰ C above the phosgene.

According to the invention, phosgene is used in excess with respect to amino groups. Usually, a molar ratio of phosgene to amino groups of 1, 1: 1 to 20: 1, preferably from 1, 2: 1 to 5: 1 before.

The mixing and reaction of the two gaseous educts takes place according to the inventive method after the introduction of the educt streams diamine and phosgene via the slots as entry surfaces in the mixing chamber as a reaction space.

The reaction usually starts with contact of the reactants immediately after mixing.

Thus, in the front part of the reaction space, the mixing of the educts, optionally mixed with inert medium, takes place (mixing space).

To carry out the reaction according to the invention, the preheated stream containing amine or mixtures of amines and the preheated stream containing phosgene are passed continuously into the reactor, preferably a tubular reactor.

The reactors are generally made of steel, glass, alloyed or enameled steel and have a length sufficient to allow complete reaction of the diamine with the phosgene under the process conditions. It may be useful to incorporate in the reactant supply lines Strömungsvergleichmäßiger, as they are known for example from EP 1362847 A. However, to equalize the speed of the educt streams, a long feed length in the educt feed line, which is 2 to 40 times the feed diameter, more preferably 4 to 30 times, very particularly preferably 5 to 20 times, is preferred in relation to the diameter of the feed line.

A narrowing of the flow cross-section as described in patent EP 1275640A1 after the merging of the educt streams to avoid backflows is possible, but preference can be given to this.

In order for an amine stream according to the idea of the invention not to be in contact with the walls of the apparatus after the mixing has begun, but is enveloped by phosgene-containing product streams, the amine stream 1_ is metered in between phosgene streams 2.

This requires, according to the invention, that the topmost, the lowermost or the outermost stream are each a phosgene stream which prevents the amine stream (s) from the walls of the reactor.

The flow cross sections of the phosgene-containing educt streams or streams are designed in such a way that the characteristic mixture length dimension is again as small as possible. Since the starting material phosgene is supplied in stoichiometric excess and, moreover, the phosgene velocity is preferably less than the amine velocity, a larger cross-sectional area must be chosen than for the amine-containing stream, which also results in larger characteristic dimensions. The mixing path length is less than 200 mm, preferably less than 100 mm, more preferably less than 50 mm, very particularly preferably less than 25 mm and in particular less than 10 mm. The mixing path length is defined as the distance that the fluid elements of two or more reactant streams perpendicular to the direction of flow of the product streams must travel maximally until a molecular mixing of the product streams has taken place.

The ratio of the total area of the amine streams to the total area of the phosgene streams is greater than 0.00002, preferably greater than 0.0002, more preferably greater than 0.002, and most preferably greater than 0.02.

The ratio of the total area of the amine streams to the total area of the phosgene streams is less than 5, preferably less than 1, more preferably less than 0.5 and most preferably less than 0.2. The area ratio of two phosgene-bearing surfaces which are separated by an amine-introducing slot is 0.1 to 10, preferably 0.2 to 5, particularly preferably 0.4 to 2.5, very particularly 0.8 to 1.25 in particular 0.9 to 1, and especially 1.

Since the intensity and rapidity of the mixing of the amine and phosgene-containing educt streams depend essentially on the shear gradient that occurs in the mixing zone, the mixing zone must be designed so that the shear gradient is particularly high.

For this purpose, on the one hand, the differential speed between the amine- and phosgene-containing educt streams should be selected to be particularly high and, on the other hand, the characteristic length dimensions should be as small as possible, since the shear gradient is proportional to the quotient of the velocity difference and the characteristic length measure.

Since the difference in velocity between the amine- and phosgene-containing product streams should be high, either the phosgene-containing or the amine-containing feed streams must have a higher velocity. Since the amine feeds to the mixing zone are more sensitive to the formation of deposits and blockages and reflux in the amine feed is in any case to be avoided, the flow rate of the amine-containing feed stream is preferably chosen to be greater than the rate of the phosgene-containing feed stream. The higher the velocity of the amine-containing educt streams, the higher the rate of phosgene-containing feed streams can be selected with the same shear rate. A higher phosgene velocity causes smaller flow cross sections of the phosgene feed and thus smaller mixing path lengths and thus faster mixing.

In order to achieve the highest possible amine velocity, it is therefore desirable to set a local Mach number of greater than 0.6 in the amine stream at the point of combination with the phosgene stream.

The Mach number means the ratio between local flow velocity and local sound velocity. In a particular embodiment of the method, the feed of the amine-containing educt streams is selected such that there is just a Mach number of 1 at the exit of the amine streams into the mixing zone.

In the case of a so-called adapted amine feed, the pressure of the amine stream at this point corresponds precisely to the pressure of the phosgene-containing feed stream at the point of the merger. In the case of an unmatched amine feed, the pressure of the amine stream at the exit from the amine feed is greater than the pressure of the phosgene-containing stream during the merge. In this case it comes then to a further expansion of the amine-containing stream, which is associated with a pressure drop to the pressure of the phosgene-containing stream. Whether a nozzle is adjusted or not adapted depends on the pre-pressure of the amine-containing and the phosgene-containing stream in front of the mixing nozzle. In a further particular embodiment, the amine feed is designed such that Mach numbers of greater than 1 are already reached in the feeds. This can be achieved, for example, by designing the supply of the amine-containing streams in the form of one or more Laval nozzles, which are characterized in that the flow cross-section initially narrows until a Mach number of one is reached and then expanded again, resulting in a further expansion and acceleration of the flow leads. In order to achieve a supersonic flow (Mach number greater than 1), the ratio of the Aminkesseldruckes to the mixing zone pressure must be greater than the so-called critical pressure ratio. The higher the pressure ratio and the higher the boiler temperature of the amine stream, the higher the maximum achievable speed.

Since the educt amine is often thermally damaged at too high temperatures, however, temperatures that are too high must not be set. Also, the Aminvor- pressure can not be increased arbitrarily due to the amine vapor pressure. Preferably, the amine feed is therefore designed so that in the amine-containing E- stream directly to the merger with the phosgene-containing stream or in the

If there is an unmatched nozzle shortly behind it, set Mach numbers of 0.6 to 4, particularly preferably 0.7 to 3, very particularly preferably 0.8 to 2.5 and in particular 0.9 to 2.0. The specified Mach numbers, the expert can easily convert at known boiler temperature and known material data in flow rates. Likewise, the skilled person can calculate the required form depending on the specified Mach number and the substance data.

The high rate of entry of the amine stream into the mixing zone serves, as shown above, to achieve the greatest possible difference in velocity between amine- and phosgene-containing reactant streams. Furthermore, due to the high flow rate, the system pressure and thus also the educt concentrations and the temperature are locally reduced, which leads to a reduction of the reaction rates and thus to a simplification of the mixing task. In order to achieve the shortest possible mixing path lengths, it is desirable to also choose the flow velocity of the phosgene-containing educt stream as high as possible, without, however, excessively reducing the differential velocity between amine-containing and phosgene-containing educt stream. For this purpose, the cross-sectional area of the phosgene stream is selected so that a Mach number of 0.2 to 2.0, preferably 0.3 to 1, 5, particularly preferably 0.4 to 1, 0, most preferably from 0.5 to 1 , 0 and in particular 0.7 to 1, 0 results.

The flow cross sections of the amine-containing educt streams are designed in the mixing unit according to the invention in such a way that, on the one hand, a high operational stability is ensured. is performed and are kept as small as possible Mischungsweglängen otherwise. Therefore, characteristic length dimensions of 0.5 to 50 mm, preferably 0.75 to 25 mm, particularly preferably 1 mm to 10 mm and very particularly preferably 1 mm to 5 mm are selected for the supply of the amine-containing Eduktsstromes. The term "characteristic length dimension" here means the smallest linear scale of the flow cross-section, ie, for example, in the case of a gap, the gap width or, in the case of a circular opening, the aperture diameter.

Preferably, the individual educts are fed into the mixing device at a flow rate of 20 to 400 meters / second into the reactor, preferably from 25 to 300 meters / second, more preferably 30 to 250, most preferably 50 to 200, in particular more than 150 to 200 and especially 160 to 180 meters / second.

In one possible embodiment of the invention, it may be useful to introduce the phosgene streams, in particular the outer phosgene stream with a higher flow rate into the mixing chamber, as the amine stream they envelop, more preferably at least 10 m / s more, most preferably at least 20 m / s more and in particular at least 50 m / s more.

But it may also be possible and useful to introduce the outer phosgene stream at a higher flow rate into the mixing chamber, as the amine stream, and the inner phosgene stream with a lower flow velocity. This represents another possible embodiment of the present invention.

In a preferred embodiment of the invention, it is useful to introduce the phosgene streams, in particular the outer phosgene stream with a lower flow rate into the mixing chamber, as the amine stream they envelop, more preferably at least 50 m / s less, most preferably at least least 60 m / s less, more preferably 80 m / s less and in particular at least 100 m / s less.

In a preferred embodiment of the present invention, with a plurality of phosgene streams, these are connected to exactly one phosgene feed line with low pressure loss, without additional control devices, so that the rate at which the phosgene flows is approximately the same.

Likewise, with a plurality of amine streams, these are preferably connected to precisely one amine feed line with little pressure loss, without additional control devices, so that the rate at which the amine flows is approximately the same. However, it is also possible to connect the phosgene and / or amine streams of the slots, each with a separately regulated supply line, so that the speeds per supply line are individually and independently adjustable.

The educts enter the mixing chamber with a velocity vector. In this case, the velocity vector can be subdivided into an axial, radial and tangential directional component. In the axial direction, the directional component of the velocity vector is understood to be parallel to the longitudinal axis of the mixing chamber. The radial direction is understood to mean the directional component of the velocity vector from the outside to the longitudinal axis, that is to say enclosing a right angle with the longitudinal axis. Under tangential direction, the directional component of the velocity vector is understood to be parallel to the boundary of the mixing space, that is to say an annular circulation movement.

To mix the reactant streams, an improvement of the mixing which results from the incorporation of elements producing a tangential velocity can be achieved, for example in the feed line of the partial streams of the excess components into the mixing chamber. A suitable tangential-speed generating element would be, for example, a spirally twisted band (spiral) embedded in the supply line, round or angular guide plates (guide vanes) or the like. The

The effect of the tangential velocity-generating internals is to increase the shear between flow layers of different composition in the flow of the nozzle.

To generate a tangential velocity, tangential entry of the feed line of one or more reactant streams is also possible or, in the case of a radial inflow of one or more reactant streams, a blade ring.

Furthermore, it may be useful to introduce the phosgene and amine streams into the mixing chamber with opposite tanential velocity, for example by observing the phosgene streams at a tangential velocity along the longitudinal axis of the reactor in a clockwise direction, and the intervening amine stream with a counterclockwise tangential velocity into the mixing space be metered.

The angle which the sum vector includes from the vectors of the tangential velocity and from the vector of the axial velocity of the streams metered in this way with the longitudinal axis of the reactor can be from 5 to 85 °, preferably 17 to 73 °, particularly preferably 30 to 60 ° for the one Streams, for example, the phosgene streams, and from -5 to -85 °, preferably -17 to -73 °, more preferably -30 to -60 ° for the other streams, for example, the amine stream. Furthermore, it makes sense to meter in the flows with different radial velocities in the mixing chamber. In this case, an angle between the sum vector from the radial velocity vector and from the axial velocity vector with the longitudinal axis is established. This angle usually corresponds to the angle of the associated metering channel with the longitudinal axis of the mixing chamber. In this case, a negative angle means a metering from the inside out, a positive angle metering from outside to inside, an angle of 0 ° means a parallel to the longitudinal axis of the mixing chamber flow and an angle of 90 ° to the longitudinal axis of the mixing chamber vertical flow.

The outer phosgene stream can be metered through the mixing device at a radial angle of 0 to 85 °, preferably 5 to 85 °, particularly preferably 7 to 65 °, very particularly preferably 15 to 35 ° and in particular 18 to 30 ° into the mixing space.

The amine stream can be metered into the mixing chamber through the mixing device at a radial angle of -50 ° to + 50 °, preferably -25 to 25 °, more preferably -10 to 10 ° and most preferably -3 to + 3 °.

The inner phosgene stream can be passed through the mixing device at a radial angle of 0 to -85 °, preferably -5 to -85 °, particularly preferably -7 to -65 °, very particularly preferably -15 to -35 ° and in particular -18 to - 30 ° are metered into the mixing chamber.

It is advantageous if outer phosgene stream and amine stream relative to each other include a radial angle of 1 to 60 °, preferably 7 to 50, more preferably 15 to 45 ° and particularly preferably 18 to 35 °.

It is further advantageous if the amine stream and the internal phosgene stream relative to one another include a radial angle of 1 to 60 °, preferably 10 to 50 °, particularly preferably 15 to 45 ° and particularly preferably 18 to 35 °.

In order to achieve as complete a conversion of the amine to the respective desired product, a mixing time of the phosgene-containing with the amine-containing Eduktstromes of less than 10 ms, preferably less than 5 ms, more preferably less than 2 ms, most preferably less than 1 ms and in particular less than 0.5 ms. In this case, the mixing time is defined as the time it takes for the fluid elements which emerge from the amine feed to maximize until they have a phosgene / amine ratio of greater than or equal to 4. The time counts in each case from the exit of a fluid element from the amine feed.

reaction chamber The reaction space in the front region comprises the mixing space, in which predominantly the mixing of the gaseous mixture of phosgene, amine, optionally mixed with inert medium takes place, which is usually accompanied by the onset of the reaction. In the rear part of the reaction space then essentially only the reaction takes place and at most subordinate the mixing.

For the purposes of distinction, the mixing space can be defined as the area of the reaction space in which the mixing of the educts takes place to a degree of 99%. In a preferred embodiment of the present invention, the conversion in the mixing space, i. the consumption of the amine used, less than 15%. The degree of mixing is given as the ratio of the difference between the locally averaged mixture fraction and the initial mixture fraction before mixing to the difference between the mean final mixture fraction after mixing and the initial mixture fraction before mixing. For the concept of mixture break see, e.g. J. Warnatz, U. Maas, R.W. Dibble: Combustion, Springer Verlag, Berlin Heidelberg New York, 1997, 2nd edition, p. 134.

By reactor is meant the technical device containing the reaction space. These may be all customary reaction spaces known from the prior art, which are suitable for the non-catalytic, single-phase gas reaction, preferably for the continuous, non-catalytic, single-phase gas reaction, and which withstand the required moderate pressures. Suitable materials for contact with the reaction mixture are e.g. Metals, such as steel, tantalum, nickel, nickel alloys, silver or copper, glass, ceramics, enamels or homogeneous or heterogeneous mixtures thereof. Preference is given to using steel reactors. The walls of the reactor can be hydraulically smooth or profiled. As profiles are, for example, scratches or waves.

It may be advantageous if the material used, preferably the material used for the mixing device and / or the reactor and more preferably the reactor used for the reactor has a low roughness, as described in unpublished International Patent Application with the file reference PCT / EP2007 / 063070 and the filing date 30.1 1.2007, to which reference is hereby incorporated by reference in the present disclosure.

Generally, the reactor types known in the art may be used. Examples of reactors are known from EP-B1 289840, Sp. 3, Z. 49 - Sp. 4, Z. 25, EP-B1 593334, WO 2004/026813, S. 3, Z. 24 - P. 6, Z 10, WO 03/045900, page 3, Z. 34 - page 6, line 15, EP-A1 1275639, page 4, line 17 - page 5, line 17 and EP-B1 570799, Sp. 2, Z. 1 - Sp. 3, Z. 42, which are expressly referred to within the scope of this disclosure. Preference is given to tubular reactors.

It is likewise possible to use essentially cuboid reaction spaces, preferably plate reactors or plate reaction spaces. A particularly preferred plate reactor has a width to height ratio of at least 2: 1, preferably at least 3: 1, more preferably at least 5: 1 and especially at least 10: 1. The upper limit of the ratio of width to height depends on the desired capacity of the reaction space and is in principle not limited. Reaction spaces with a ratio of width to height up to 5000: 1, preferably up to 1000: 1, have proven to be technically feasible.

The reaction of phosgene with amine in the reaction space takes place at absolute pressures of more than 0.1 bar to less than 20 bar, preferably between 0.5 bar and 15 bar and particularly preferably between 0.7 and 10 bar. In the case of the reaction of (cyclo) aliphatic amines, the absolute pressure is very particularly preferably between 0.7 bar and 5 bar, in particular from 0.8 to 3 bar and especially 1 to 2 bar.

In general, the pressure in the feed lines to the mixing device is higher than the above-mentioned pressure in the reactor. Depending on the choice of mixing device drops at this pressure. The pressure in the supply lines is preferably 20 to 2000 mbar, particularly preferably 30 to 1000 mbar, higher than in the reaction space.

In one possible embodiment, the reactor consists of a bundle of reactors. In one possible embodiment, the mixing unit need not be an independent apparatus, but rather it may be advantageous to integrate the mixing unit into the reactor. An example of an integrated unit of mixing unit and reactor is a tubular reactor with flanged nozzles.

According to the process of the invention, the reaction of phosgene with amine takes place in the gas phase. Reaction in the gas phase is understood to mean that the conversion of the educt streams and intermediates to the products in the gaseous state react with each other and in the course of the reaction during the passage through the reaction space to at least 95%, preferably at least 98%, more preferably at least 99%, very particularly preferably at least 99.5%, in particular at least 99.8 and especially at least 99.9% remain in the gas phase.

Intermediates are, for example, the monomino-monocarbamoyl chlorides, dicarbamoyl chlorides, monoamino monoisocyanates and monoisocyanato monocarbamoyl chlorides formed from the diamines, and the hydrochlorides of the amino compounds. In the method according to the invention, the temperature in the reaction space is chosen so that it is above the boiling point of the diamine used, based on the pressure conditions prevailing in the reaction space. Depending on the amine used and set pressure usually results in an advantageous temperature in the reaction chamber of more than 200 ⁰ C, preferably more than 260 ⁰ C and more preferably more than 300 ⁰ C. In general, the temperature is up to 600 ⁰ C, preferably up to 570 ⁰ C.

The average contact time of the reaction mixture in the process according to the invention is generally between 0.001 seconds and less than 5 seconds, preferably more than 0.01 seconds to less than 3 seconds, more preferably more than 0.015 seconds to less than 2 seconds. In the case of the reaction of (cyclo) aliphatic amines, the average contact time can be very particularly preferably from 0.015 to 1.5 seconds, in particular from 0.015 to 0.5 seconds, especially from 0.020 to 0.1 seconds and often from 0.025 to 0 , 05 seconds.

The term "average contact time" is understood to mean the period of time from the start of the mixing of the educts until they leave the reaction space in the workup stage. In a preferred embodiment, the flow in the reactor of the process according to the invention is characterized by a Bodenstein number of more than 10, preferably more than 100, and more preferably more than 500.

In a preferred embodiment, the dimensions of the reaction space and the flow rates are chosen such that a turbulent flow, i. a flow having a Reynolds number of at least 2300, preferably at least 2700, is present for the reaction mixture, the Reynolds number being formed with the hydraulic diameter of the reaction space.

Preferably, the gaseous reaction mixture passes through the reaction space at a flow rate of 10 to 300 meters / second, preferably from 25 to 250 meters / second, more preferably 40 to 230, most preferably 50 to 200, in particular more than 150 to 190 and especially 160 to 180 meters / second.

As a result of the turbulent flow, narrow residence time distributions with a low standard deviation of usually not more than 6% as described in EP 570799 are achieved and good mixing is achieved. Measures such as the constriction described in EP-A-593 334, which is also prone to blockage, are not necessary.

It may be useful to incorporate into the reactor Strömungsvergleichmäßiger, as they are known for example from EP 1362847 A. The reaction volume can be tempered over its outer surface. To build production plants with high plant capacity, several reactor tubes can be connected in parallel. The reaction can also be carried out preferably adiabatically. This means that heating or cooling energy flows do not flow via the outer surface of the reaction volume with technical measures.

In a preferred embodiment, the reaction conditions are selected such that the reaction gas at the outlet from the reaction space has a phosgene concentration of more than 25 mol / m ³ , preferably from 30 to 50 mol / m ³ . Furthermore, an inert medium concentration of more than 25 mol / m ³ , preferably from 30 to 100 mol / m ^3, is generally present at the outlet from the reaction space.

The reaction space may have a constant diameter or in the course of the flow through a series of constrictions or extensions. This is described, for example, in WO 2007/028715, page 14, line 29 to page 20, line 42, which is hereby expressly part of the present disclosure.

However, according to the invention, the execution of the reaction space plays no role in the mixing of the components.

The flow-through volume of the reactor can be filled with static mixers, for example, packings, moldings, fabrics, perforated or slotted sheets, but the volume is preferably as free of internals as possible.

Also conceivable is the installation of baffles in the reaction space. A suitable turbulence generating element would be, for example, a recessed spirally twisted band, round or square slant plates or the like.

In order to comply even with large amounts of amine and phosgene, as is customary in isocyanate production on a large scale, small Mischungsweglängen and thus short mixing times, offers a parallel circuit of many small mixing nozzles with subsequent mixing and reaction zone, wherein the parallel-connected units Walls are separated from each other. The advantage of this process variant lies in a more favorable length to diameter ratio of the mixing and reaction zones. The larger this ratio is, the more favorable (narrower) is the residence time distribution of the flow. Thus, with the same residence time and flow rate through many units connected in parallel, the length-to-diameter ratio can be increased and thus also the residence time distribution can be narrowed. In order to minimize the expenditure on equipment, the individual reaction zones open into a common post-reaction zone in which the residual conversion of the amine then takes place. quench

After the reaction, the gaseous reaction mixture is preferably washed at temperatures greater than 130 ⁰ C with a solvent (quench). Suitable solvents are preferably hydrocarbons which are optionally substituted by halogen atoms, such as, for example, hexane, benzene, nitrobenzene, anisole, chlorobenzene, chlorotoluene, o-dichlorobenzene, trichlorobenzene, diethyl isophthalate (DEIP), tetrahydrofuran (THF), dimethylformamide (DMF), Xylene, chloronaphthalene, decahydronaphthalene and toluene. The solvent used is particularly preferably monochlorobenzene. The solvent used may also be the isocyanate. In the wash, the isocyanate is selectively transferred to the wash solution. Subsequently, the remaining gas and the resulting wash solution are preferably separated by rectification in isocyanate, solvent, phosgene and hydrogen chloride.

After the reaction mixture has been reacted in the reaction space, it is passed into the workup device with quench. This is preferably a so-called scrubbing tower, the isocyanate formed being separated off from the gaseous mixture by condensation in an inert solvent, while excess phosgene, hydrogen chloride and optionally the inert medium pass through the work-up device in gaseous form. The temperature of the inert solvent above the solution temperature of the carbamoyl chloride belonging to the amine is preferably maintained in the selected quench medium. In this case, the temperature of the inert solvent is particularly preferably kept above the melting temperature of the carbamyl chloride belonging to the amine

In general, the pressure in the workup device is lower than in the reaction space. The pressure is preferably 50 to 500 mbar, more preferably 80 to 150 mbar, lower than in the reaction space.

For example, the laundry may be placed in a stirred tank or other conventional equipment, e.g. in a column or mixer-settler apparatus.

Technically, all known extraction and washing processes and apparatus can be used for a wash in the process according to the invention, for example those described in Ullmann's Encyclopedia of Industrial Chemistry, 6th ed, 1999 Electronic Release, Chapter: Liquid - Liquid Extraction - Apparatus are. For example, these may be one-stage or multistage, preferably single-stage extractions, as well as those in cocurrent or countercurrent mode, preferably countercurrent mode. The quench can be embodied, for example, as described in EP 1403248 A1, there in particular in paragraphs [0006] to [0019] and the example together with FIGS. 1 to 2, which is hereby incorporated by reference into the present disclosure.

The quench can be embodied, for example, as described in WO2008 / 055904, there especially from page 3, line 30 to page 11, line 37 together with example 1 and the figures, which is hereby incorporated by reference into the present disclosure.

The quench can be embodied, for example, as described in WO2008 / 055904, there especially from page 3, line 26 to page 16, line 36 together with example 1 and the figures, which is hereby incorporated by reference into the present disclosure.

The quench may be preferably carried out as described in WO 2005/123665, there especially from page 3, line 10 to page 8, line 2 and the example, which is hereby incorporated by reference into the present disclosure.

In this quench zone, the reaction mixture, which consists essentially of the isocyanates, phosgene and hydrogen chloride, is mixed intensively with the injected liquid. The mixing is effected such that the temperature of the reaction mixture ⁰ C C, preferably at 140 to 180 ⁰ C to 100 to 200 ⁰ lowered starting from 200 to 570 and the isocyanate present in the reaction mixture by con- densation fully or partially in the liquid droplets sprayed while the phosgene and hydrogen chloride remain substantially completely in the gas phase.

The proportion of the isocyanate contained in the gaseous reaction mixture, which passes into the liquid phase in the quench zone, is preferably from 20 to 100% by weight, more preferably from 50 to 99.5% by weight and in particular from 70 to 99% by weight, based on the isocyanate contained in the reaction mixture.

The reaction mixture preferably flows through the quench zone from top to bottom. Below the quench zone a collection container is arranged, in which the

Separated liquid phase, collected and removed via an outlet from the reaction space and then worked up. The remaining gas phase is removed via a second outlet from the reaction space and also worked up.

The quench can be carried out, for example, as described in EP 1403248 A1, or as described in international application WO 2005/123665. The liquid droplets are for this purpose by means of single- or Zweistoffzerstäuberdüsen, preferably Einstoffzerstäuberdüsen generated and produce depending on the embodiment, a spray cone angle of 10 to 140 °, preferably from 10 to 120 °, particularly preferably from 10 ° to 100 °.

The liquid that is injected via the atomizer nozzles must have a good solubility for isocyanates. Preferably, organic solvents are used. In particular, use is made of aromatic solvents which may be substituted by halogen atoms.

In a particular embodiment of the process, the immersed liquid is a mixture of isocyanates, a mixture of isocyanates and solvent or isocyanate, it being possible for the particular quench liquid used to comprise proportions of low-boiling components, such as HCl and phosgene. Preferably, the isocyanate is used, which is prepared in the respective process. Since the reaction comes to a standstill due to the lowering of the temperature in the quench zone, side reactions with the injected isocyanates can be ruled out. The advantage of this embodiment is in particular that can be dispensed with a separation of the solvent.

In an alternative preferred embodiment, the inert medium used together with at least one of the educts and the solvent used in the quench are the same compound, very particularly preferably monochlorobenzene is used in this case.

Small amounts of by-products which remain in the isocyanate can be separated from the desired isocyanate by means of additional rectification, by stripping with an inert gas or else by crystallization, preferably by rectification.

In the subsequent optional purification stage, the isocyanate is separated off from the solvent, preferably by distillation. Likewise, the separation of residual impurities, including hydrogen chloride, inert medium and / or phosgene, can also take place here, as described, for example, in DE-A1 10260092.

Another object of the present invention is a mixing device comprising at least one flow channel 1 are arranged on both sides of at least two flow channels 2 so that the openings of the flow channels λ_ and 2 open in a mixing space, wherein at least one of the flow channels λ_ and 2 at a diameter D has at least one baffle of the height di and / or at least one baffle of the depth 62 at a distance L from the mouth into the mixing space, the ratio di: D being from 0.002 to 0.2: 1, especially preferably 0.05 to 0.18: 1, very particularly preferably 0.07 to 0.15: 1 and in particular 0.1 to 0.12: 1 or the ratio d2: D of 0.001 to 0.5: 1 , particularly preferably 0.01 to 0.3: 1 and most preferably 0.1 to 0.2: 1 and the distance L in the case of an increase greater than 2 times the height d1, particularly preferably greater than that 4 times and most preferably 8 times the size d1. The length L is preferably less than 50 times the diameter D, more preferably less than 20 times, and most preferably less than 10 times the diameter D. In the case of a recess, the distance L is preferably larger than the simple one of the recess d2, particularly preferably greater than twice and very particularly preferably six times the depth d2. The length L is preferably less than fifty times the diameter D, more preferably less than twenty times and most preferably less than ten times the diameter D.

The information given above in the text applies to this device according to the invention.

The effect of this device according to the invention is based on the generation of a separation of the flow or the formation of a recirculation area with subsequent rebuilding of the turbulent boundary layer. The resulting smaller boundary layer in the building phase causes beyond the mouth higher shear rates between the beam and the environment and thus smaller mixing times.

This inventive principle can generally be applied to processes in which a rapid mixing of fluid, that is gaseous or liquid, substances is desired, especially in chemical reactions.

Such chemical reactions are preferably those in which solid substances are formed as end products or intermediates under the reaction conditions. The cause of the solids formation is a local supersaturation of the solid-forming component with respect to the equilibrium solubility. The faster the mixture, the higher the supersaturation. Higher supersaturation leads to the formation of more solid germs and generally to smaller primary particles. If this is an intermediate product, small primary particles react faster than large ones because they have more surface area. The speed of the subsequent reaction thus largely depends on the size of the particles formed. For high space-time Aubeuten therefore the smallest possible particles must be generated in the mixing device. Furthermore, the formation of larger particles leads to the risk of the formation of deposits in the mixing element. In order to avoid solid deposits and to achieve short mixing times, therefore, small boundary layers are to be striven for. This principle is applicable to both single-phase and multi-phase, miscible or immiscible media.

Advantageously, the device according to the invention can be used in the preparation of isocyanates by reacting the corresponding amines with phosgene as a mixing device for the mixing of amine and phosgene. Initially, it does not matter whether the reaction takes place in the gas phase or in the liquid phase, it can be used particularly advantageously in the gas phase phosgenation as a mixing device.

Another advantageous reaction in which the device according to the invention is used as a mixing device is the preparation of diaminodiarylmethanes by condensation of the corresponding amines with formaldehyde or its storage compounds. These storage compounds are, for example, commercially available aqueous formalin solutions, paraformaldehyde, trioxane or highly concentrated formalin solutions. In place of or in a mixture with formaldehyde, it is also possible to use at least one formaldehyde-releasing compound. In particular, the formaldehyde is used as aqueous formalin solution, alcoholic formalin solution, hemiacetal, methylene-imine of a primary amine or N, N'-methylenediamine of a primary or secondary amine and paraformaldehyde.

Particularly noteworthy is the preparation of 2,4'- and 4,4'-methylenediphenylamine (MDA) isomeric mixtures of formaldehyde and aniline. As a rule, this reaction is acid catalyzed.

Such methods are generally known and are described, for example, in Kunststoffhandbuch, Volume 7, Polyurethanes, Carl Hanser Verlag Munich Vienna, 3rd edition, 1993, pages 76 to 86, and in a large number of patent applications, for example DE 100 31 540 or WO 99/40059 , described. By varying the ratio of acid to aniline and formaldehyde to aniline, the proportion of the 2-core product in the crude MDA can be adjusted as desired.

For its preparation, the reactants in the desired ratio are metered continuously into a reactor and this reactor is taken from the same amount of reaction product to the feed. As reactors, for example tubular reactors are used. In the continuous or semi-continuous procedure, the reactants are metered into a preferably provided with a stirrer and / or Umpumpkreis batch reactor, from which the reacted reaction product is removed and fed to the workup.

Preferably, the preparation is preferably carried out at a molar ratio of aniline to formaldehyde greater than 2. The molar ratio of acid (as catalyst) sator) to aniline is preferably greater than 0.05. At these ratios, there is an increased formation of the respective binuclear products in the reaction mixture.

The continuous reaction is preferably see be- at a temperature in the range 0 to 200 ⁰ C, preferably carried out between 20 and 150 ⁰ C and in particular between 40 and 120 ° C. It has been found that with increasing the temperature, the proportion of 2,2'- and 2,4'-isomers in the reaction product increases.

The pressure in the reaction is 0.1 to 50, preferably 1 to 10 bar absolute.

In the batchwise and semi-continuous implementation of the reaction, the reaction mixture can be subjected to a so-called aging after complete dosing of the starting materials. For this purpose, the reaction mixture is left in the reactor or transferred to another, preferably stirred reactor. The temperature of the reaction mixture is preferably above 75 ° C, in particular in a range between 1 10 and 150 ⁰ C.

The preparation of the condensation product is followed by a work-up which is not relevant to the use of the mixing nozzles according to the invention in the process.

The advantage of using the mixing nozzles according to the invention in the production of diaminodiarylmethanes is that a faster mixing and finer dispersion of droplets in the multiphase reaction mixture is realized. In this way, formaldehyde can react quickly to the desired intermediate. Regions of high formaldehyde concentration which results in the formation of N-methylated by-products (N-methyl-MDA) can be reduced to produce less by-product.

characters

FIG. 1: Mixing of amine and phosgene in the gas-phase phosgenation with the aid of a combination of nozzle and annular gap

Figure 2: embodiment of the present invention with extension of the channel

Figure 2a: Definition of the sizes D, L, d2

Figure 3: embodiment of the present invention with extension of the channel

Figure 4: embodiment of the present invention with narrowing of the channel

Figure 4a: Definition of the sizes D, L, d1

Figure 5: embodiment of the present invention with narrowing of the channel

FIG. 6: Exemplary embodiments of baffles

FIG. 7: Definition of the angle φ (phi) of baffles

List of reference numbers in the figures:

1_ amine stream 2 phosgene stream

3 reaction mixture

4 baffles

5 baffles

Claims

claims

1. A process for the preparation of isocyanates by reacting the corresponding amines with phosgene, optionally in the presence of at least one, preferably exactly one inert medium, in the gas phase, by incontacting fluid streams of amine and phosgene and their subsequent reaction with each other, characterized in that the turbulent flow boundary layer of at least one stream is reduced by at least one flow-mechanical baffle immediately before it is brought into contact with the other stream.

2. The method according to claim 1, characterized in that the flow-mechanical baffle consists in a limited in length extension of a flow channel through which the respective fluid flow is performed.

3. The method according to claim 2, characterized in that the ratio of the depth d2 of the extension to the diameter D of the flow channel is 0.001 to 0.5: 1.

4. The method according to claim 1, characterized in that the fluidic baffle consists in a limited in length constriction of a flow channel through which the respective fluid flow is performed.

5. The method according to claim 4, characterized in that the ratio of the height d1 of the constriction to the diameter D of the flow channel is 0.002 to 0.2: 1.

6. The method according to any one of the preceding claims, characterized marked, that the baffles have a shape selected from the group consisting of rectangles, trapezoids, diamonds, semicircles, pitch circles, saw teeth, multi-corner, polygons and triangles.

7. The method according to any one of the preceding claims, characterized marked, that the baffles include an angle φ (phi) with the flow direction, where φ can be from 0 to 80 °.

8. The method according to any one of the preceding claims, characterized in that the mixture takes place in a mixing device selected from the group consisting of Koaxialmischdüsen, Y-mixer, T-mixer, jet mixer and mixing tubes.

9. The method according to any one of the preceding claims, characterized in that the mixture via annular gap mixing nozzles or slot nozzles.

10. mixing device comprising at least two flow channels λ_ and 2 which are arranged so that the openings of the flow channels λ_ and 2 open into a mixing space, wherein at least one of the flow channels λ_ and 2 at a diameter D at least one baffle height di and / or has at least one baffle of depth 62 at a distance L before the mouth in the mixing space, wherein the ratio di: D is 0.002 to 0.2: 1 or the ratio d ₂ : D 0.001 to 0.5: 1, and the distance L is at least twice the diameter D.

1 1. Use of a device according to claim 10 for mixing fluids.

12. Use of a device according to claim 10 for mixing fluid substances in chemical reactions in which solid substances are formed as end products or intermediates under the reaction conditions.

13. Use of a device according to claim 10 in the preparation of isocyanates by reacting the corresponding amines with phosgene as a mixing device for the mixing of amine and phosgene.

14. Use of a device according to claim 10 in the preparation of Diaminodiarylmethanen by condensation of the corresponding amines with

Formaldehyde or its storage compounds.