Method and mixing unit for manufacturing isocyanates by phosgenesis of primary amines

(54) Title: MIXING PROCESS AND AGGREGATE FOR THE PREPARATION OF ISOCIANATES BY PRIMARY AMINES PHOSGENATION (30) Unionist Priority: 12/19/2007 of 102007061 688.2 (73) Holder (s): Bayer Materialscience Ag (72) Inventor (es) ): Andreas Rausch, Christian Steffens, Dietmar Wastian, Joachim Ritter, Manfred Keller-Killewald, Marcus Grünewald, Matthias Bõhm (57) Summary: mixing process and aggregate FOR PREPARATION OF ISOCIANATES BY PRIMARY AMINES PHOSGENATION. The present invention relates to a rotor-stator reactor mixer essentially comprising a symmetrically rotating housing, which is bounded at the front by a front plate and which contains a mixing chamber with independent inlets for at least two substances and one output, the inlet for the first substance being provided on the axis of rotation of the mixing chamber and the inlet for the at least second substance being configured in the form of a plurality of openings arranged in the form of symmetrical rotation with respect to the axis of rotation on the front plate, for which one pin is displaced in axial direction at a time, characterized by the fact that on the front plate channels are provided for the first substance to enter the rotation axis in an outward direction.

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Descriptive Report of the Invention Patent for MIXING PROCESS AND AGGREGATE FOR PREPARATION OF ISOCIANATES BY PRIMARY AMINES PHOSGENATION.

The present invention relates to a process for preparing isocyanates by phosgenation of primary amines and a rotor-stator-type mixing aggregate suitable for the mixture of the phosgene and primary amine educts. The rotor-stator mixing unit is a mixing reactor and is suitable for mixing, introducing and executing a reaction of at least two substances capable of flowing, which can present considerable differences in viscosity, particularly for the preparation of mono- or polyisocyanates by the reaction of mono- or polyamines with phosgene dissolved in organic solvent.

Rotor-stator mixers generally consist of at least one rotor provided with mixing elements and a stator surrounding the rotor, which is provided with current switching elements. Rotor-stator mixers of this type are generally known. The rotor rotates at high speed while the stator remains stationary. By the movement of the rotor, the liquid that is in the interstice of the ring between the rotor and the stator is turbulently mixed. In the case of non-miscible liquids, one of the two liquids is finely dispersed in the other liquid due to the high energy input. With this, the resulting dispersion is all the finer the greater the number of revolutions and, consequently, the energy introduced. During mixing, due to the high number of rotations of the rotor, a lot of energy is introduced into the liquid and transformed into heat. During the mixing process this leads to an increase in the temperature of the liquid mixture.

It is known to perform quick-start reactions, such as the preparation of mono- or polyisocyanates by reaction of mono- or polyamines with phosgene in a rotor-stator-type reactor-mixer (and possibly additional reaction devices connected downstream) which consists essentially of a symmetrically rotating housing, the housing essentially having a symmetric rotating mixing chamber with separate entrances for at least two substances and an outlet, the entry for the first substance being provided on the axis of the mixing chamber and the entry for at least the second substance is developed in the form of a plurality of openings arranged in a symmetrical rotation with respect to the axis of the mixing chamber (EP 291 819 B1, EP291 820 B1).

Preferably, according to the state of the art, mixing aggregates are used in which each entrance, which is developed in the form of a plurality of openings arranged in a symmetrical rotation in relation to the axis of the mixing chamber, is provided with a displaceable pin. in axial direction with which the opening can be pierced in the event of pressure increase in the supply line, or periodically, thus being able to release any deposits that may exist (EP 830 894 B1).

It is also known to carry out rapid reactions such as the reaction of mono- or polyamines with phosgene in mixing aggregates that essentially consist of a symmetrically rotating housing, the housing having an essentially symmetrically rotating mixing chamber with independent inputs for at least two substances and an outlet, the entry for the first substance is provided on the axis of the mixing chamber and the entry for at least the second substance is radial or lateral to the axis of the mixing chamber and the mixing chamber has no moving part (EP 322 647 B1, WO 2002/002217 A1).

In addition, it is known to carry out quick-start reactions such as the reaction of mono- or polyamines with phosgene in mixing aggregates, which essentially consist of a symmetrical rotation housing, with the housing essentially having a symmetric rotation mixing chamber with inlets independent for at least two substances and one outlet, with at least both inlets arranged radially with respect to the axis of the mixing chamber (DE 10 034 621 A1, US-A 488 6368, DE 42 20 239 C2).

The quality of the mono- or polyisocyanates prepared in

Children of this type decisively depend on the quality and speed of the mixing of at least two substances capable of flowing. It is particularly important here to maintain a uniform mass flow through the reactor mixer, since with this it is possible to avoid a reverse mixing of substances already reacted with each other in the substance flows of the substances to be used, not yet reacted.

As a general criterion for the quality factor of a mixing device, it is worth the mixing time that can be achieved with it. The mixing time of a mixing plant used to obtain a quick reaction such as the preparation of mono- or polyisocyanates by reaction of mono- or polyamines with phosgene dissolved in organic solvent is, as a rule, 0.0001 s up to 5 s , preferably 0.0005 to 4 s, particularly preferred 0.001 s to 3 s (DE 10 2005 014846 A1). The mixing time must be understood as the time that elapses from the beginning of the mixing process until 97.5% of the fluid elements of the mixture obtained have reached the interruption of the mixing which, in relation to the value of the final theoretical value of the interruption of the mixing of the mixture obtained when reaching the perfect mixing state presents less than 2.5% of this final value of the interruption of mixing. The concept of interruption of mixing is clarified, for example, in J. Warnatz, U. Maas, RW Dibbla: Verbrennung, Springer Verlag, Berlin Heidelberg New York, 1997, 2^The edition, page 134.

The quality of the mixing and the complementation to avoid reverse mixing can be recognized in a concrete way by several criteria:

Due to insufficient mixing, adherences to clogging occur in the opening openings of at least two substances, so that the supply of uniform mass flows through all openings will be impaired. This influences the flow behavior through the reactor-mixer, which leads, in a reinforced way, to reverse mixing.

Another criterion for the good quality of the mixture is the size and size distribution of the amine hydrochloride particles and carbamoyl chloride particles that are formed during the reaction and whose size should be in the nanometer to micrometer range. The formation of larger amounts of these solids should be avoided, as this leads to the formation of larger particles and agglomerates of amine hydrochloride, whose phosgenation is very slow, as described in the literature (WO 2004/056756 A1).

As another criterion for the good performance of the mixture, the color or viscosity of the mono- or polyisocyanate obtained is also valid, since in the complete suppression of all secondary reactions, a colorless and low viscosity product can be obtained.

Another criterion for the good quality of the mixture is the content of free isocyanate groups (NCO-value) in the product obtained, since the content, in case of insufficient mixing, remains low and with reverse mixing it decreases even more. The content of free isocyanate groups can be easily determined as the so-called NCO value. The determination of the NCO value is made by the reaction of the isocyanate with excess dibutylamine in relation to the corresponding urea and reverse titration of the unused amine with standard hydrochloric acid solution. A high NCO value is preferred for the industrial use of mono- and polyisocyanates.

In known mixing units of the rotor-stator type, mixing is done so that the first substance metered in an axial manner flows out due to the centrifugal force of the first rotor disk, thus triggering the second substance introduced, causing the components of the rotation of both substance flows are mixed together.

When preparing mono- or polyisocyanates by reacting mono- or polyamines with phosgene dissolved in organic solvent with a rotor-stator type mixing aggregate, the phosgene solution is preferably dosed axially in relation to the axis of the mixing chamber and the amine solution through the inlet openings arranged in a symmetrical rotation. This is due to the fact that the inlet of the amine solution is more susceptible to clogging and, therefore, the amine solution is preferably dosed through the inlet openings, for which a pin is adapted with which they can be removed. adhesions. The disadvantage of known rotor-stator mixer reactors is that two solutions with viscosities whose proportion is less than 0.5 or greater than 2, can no longer be mixed sufficiently when the substance with the lowest viscosity is dosed axially to the axis of the mixing chamber, since the centrifugal force transmitted through the first rotor disk is no longer sufficient to push the second higher viscosity substance out of the openings arranged in symmetrical rotation towards the outlet of the mixing chamber. This leads to reverse mixing, which in the mixing chamber - this is particularly in the front plate and in the housing walls between the stators - causes adherence of solids and in the obtained mono- or polyisocyanates leads to a low content of free isocyanate groups.

Disadvantageous in rotor-stator mixer reactors, it is furthermore that the concentrations of dissolved substances cannot be chosen at will, however the concentration of the higher viscosity solution is limited by the fact that its viscosity cannot exceed twice viscosity of the at least second solution. This is particularly disadvantageous in the preparation of mono- or polyisocyanates, by the reaction of mono- or polyamines with phosgene in organic solvents, since the viscosity of the mono- or polyamine solution changes strongly with the concentration of the mono- or polyamine in the solution, while The viscosity of the phosgene solution with different concentrations of phosgene only increases insignificantly. Thus, the viscosity of phosgene solutions in monochlorobenzene (MCB) in the concentration range from 0 to 80% by weight at 0 ° C is between 0.5 and 1.0 mPa s (viscosity 0.765 mPas and density 1.27 g / L at 0 ° C and 50 or 56% by weight), while the viscosity of a solution of methylenediphenyldiamine (MDA) in monochlorobenzene in the concentration range of 15 to 65% by weight at 25 ° C is between 1 and 200 mPas (table 1). The difference in density of the solutions is, on the contrary, only small and does not aggravate the mixing task.

<td>MDA concentration in MCB in%</td><td>Temperature in ° C</td><td>Density in g / ml</td><td>Viscosity in mPa · s</td>

<td> 15</td><td> 25</td><td> 1,10</td><td> 0,99</td>

<td> 30</td><td> 25</td><td> 1,10</td><td> 1,89</td>

<td> 45</td><td> 25</td><td> 1,10</td><td> 4,29</td>

<td> 50</td><td> 25</td><td> 1,10</td><td> 5,40</td>

<td> 65</td><td> 25</td><td> 1,14</td><td> 20,98</td>

<td> 95</td><td> 25</td><td> 1,20</td><td> &gt;200</td>

Table 1: Densities and viscosities of different MDA in MCB solutions at 25 ° C, determined with a strokes viscometer according to Höppler by Haake according to DIN 53015.

The task therefore consists of providing a reactor-mixer that avoids the mentioned disadvantages and that also allows the mixing of two substances capable of flowing, with viscosities strongly different in quality and speed that allow a process for the preparation of mono- or polyisocyanates with high content of free isocyanate groups and, thus, allow the use of highly concentrated solutions of amine and phosgene.

The invention relates to a rotor-stator type reactor-mixer essentially comprising a symmetrically rotating housing which is bounded at the front by a front plate and which contains a mixing chamber with independent inlets for at least two substances and an outlet , the inlet for the first substance being preferably provided on the axis of rotation of the mixing chamber and the inlet for at least the second substance being configured in the form of a plurality of openings arranged in the form of symmetrical rotation with respect to the axis of rotation on the front plate, for which one pin is displaced in axial direction each time, characterized by the fact that on the front plate, entry channels are provided for the first substance on the axis of rotation in the outward direction.

The reactor-mixer according to the invention is suitable for mixing and executing or initiating a reaction of at least two substances capable of flowing. It is preferably used to mix at least two substances, suspensions or solutions capable of flowing, in which the viscosity ratio of the first substance and at least the second substance at the inlet of the reactor-mixer is less than 0.5 or greater 2 (determination of viscosity with a strokes viscometer according to Höppler from Haake according to DIN 53015). The reactor-mixer is particularly suitable for mixing and executing or initiating a phosgenation reaction, when phosgene dissolved in a solvent is used as the first substance and a solution of a primary amine as the second substance.

The channels preferably lead from the entrance to the first substance in the mixing chamber (axis of rotation) to the front plate, radially outwards. The channels preferably end in the space of the axis of rotation in which the inlet openings, further out, for at least the second substance are also housed. The channels are executed as recesses in the front plate or as overlapping guides and can have any desired shapes, such as triangular, square, rectangular, semicircle or oval cross-section. The channels are open, at least at the beginning, therefore at the entrance site for the first flow and at least at the end, that is, at the most external location located in the axial direction of the entrance openings for the second substance. The intermediate space of the channels can be opened or closed, that is, in the direction of the mixing chamber closed by covers (for example, by plates) and opened only in the direction of the flow parallel to the plane of the front plate. Preferably, the channels in the intermediate space are closed or covered, as this makes mixing faster and better. The channels are preferably closed or covered in 5 to 95% of their length, particularly preferred in 20 to 90% of their length, most particularly preferred in 40 to 85% of their length. In a preferred embodiment, the covers cover the channels already at the entrance to the first substance, so that the first substance must necessarily go through the channels and then leave the channels again through the channel openings for the first flow that arrives to the mixing chamber where it is mixed with the second substance.

The reactor-mixer preferably has between 2 and 48 channels. In addition, the reactor-mixer preferably has between 2 and 48 openings (inlet openings) for the second flow. Preferably the openings (inlet openings) of the second flow are arranged in one, two or three concentric circles around the axis of rotation. Inlet openings can also be arranged in even more concentric circles around the axis of rotation.

The reactor-mixer according to the invention is particularly suitable as a phosgenation reactor for the preparation of mono- or polyisocyanates. For this, as the first substance, phosgene dissolved in an organic solvent is used and as at least the second substance a primary mono- or polyamine eventually dissolved in a solvent.

The invention also relates to a process for the preparation of isocyanates by the phosgenation of primary amines, in which the primary amines and phosgene are mixed and reacted in the reactor-mixer according to the invention. Here, phosgene dissolved in a solvent as the first substance and a solution of a primary amine as the second substance are preferably used. Preferably, the proportion of viscosities of the first and second substances at the entrance to the reactor-mixer is less than 0.5. The viscosity determination is preferably made with a ball viscometer according to Höppler from Haake, according to DIN 53015.

Suitable substances of use and reaction conditions are disclosed in EP 291 819 B1, EP 322 647 B1 and EP 1616 857 A1.

The reactor-mixer according to the invention is suitable for the phosgenation of any primary mono- and polyamines, particularly for the preparation of organic polyisocyanates usual in polyurethane chemistry such as di- and polyisocyanates of the diphenylmethane series (MDI, MDI and / or MDI polymers), toluylene diisocyanate (TDI), xylene diisocyanate (XDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), or naphthaline diisocyanate. Preferred starting materials for the process of the present invention are solutions with 3 to 95% by weight, preferably 20 to 75% by weight of phosgene in suitable solvents as well as solutions from 5 to 95% by weight, preferably 20 to 70% 70% by weight of mono- or polyamines in appropriate solvents.

Suitable solvents for the preparation of phosgene and amine solution are any inert solvents under reaction conditions such as, for example, chlorobenzene, ortho-dichlorobenzene, dioxane, toluene, xylene, methylene chloride, perchlorethylene, trichlorofluoromethane or butyl acetate.

Preferably chlorobenzene or orthodichlorobenzene is used. The solvents can be used neat or as random mixtures of the solvents mentioned as an example. Advantageously, the same solvent or mixture of solvents is used for the amine and phosgene components, although this is not necessarily necessary.

The phosgene and amine solutions are used in the reactor mixer, preferably in quantities such that a molecular proportion of phosgene: primary amine groups of 1.1: 1 to 30: 1 is present, particularly preferred of 1.25 : 1 to 3:

1.

The phosgene and amine solutions used can be quenched before being introduced into the reactor-mixer. In general, the phosgene solution has a preferred temperature of -50 ° C to + 80 ° C, particularly preferred of -20 ° C to + 70 ° C. The amine solution can be quenched to a preferred temperature of + 25 ° C to + 160 ° C, particularly preferred + 40 ° C to + 140 ° C. Most preferably, the temperature of the amine solution is between +50 and + 120 ° C. Preferably the solutions of the educts are quenched and dosed in a pressure stage that is above the vapor pressure of the respective solutions. Phosgene and amine solutions are preferably used at temperatures from 0 ° C to + 70 ° C or + 80 ° C and + 120 ° C. Here, absolute pressures of 100 to 7000 kPa, preferably 300 to 4500 kPa, can be used.

For mixing phosgene and amine solutions in the reactor-mixer, it can be heated, isolated or cooled, preferably it is only isolated. The insulation can be done according to the different methods known in the art and can include the mixing aggregate.

The invention is better clarified in view of the attached figures:

Figure 1 shows a reactor-mixer according to the invention of the rotor-stator type, containing a front plate with channels.

Figure 2 shows a front plate, which is an integral part of the reactor-mixer according to the invention.

The reactor-mixer represented as axial section according to figure 1, consists of a housing 1, which has a mixing chamber 2 and a distribution chamber 3. The at least first stream of substance 4 is introduced axially into the mixing chamber 2 through a bent tube 5 disposed on the side wall of the distribution chamber (and forms the entrance to the axis of rotation 22 of the mixing chamber 2, for the first substance ) and through channels (not shown in figure 1) on the front plate 23 to the channel openings for the first substance (not shown in figure 1). The second stream of substance 6 is introduced into the distribution chamber 3 and reaches the mixing chamber 2 through a plurality of parallel inlet openings 7 arranged concentrically with respect to the axis of the reactor-mixer. The mixing chamber 2, through an axis 10 which is arranged on the axis of rotation 22, has rotor elements 8 and stator elements 9 connected to the housing. In addition, a movable wheel 11 is provided which transports the mixture via circular channel 12 into the outlet tube 13. For each inlet opening 7, pins 15 are provided fixed on a support ring 17. The support ring 17 is connected through spacer pieces 18 to a plate 19 which can be displaced in axial direction by a flywheel shaft 21. The passage of this axis through the wall of the distribution chamber is made with a gas-tight bellows 20.

Figure 2 shows a front plate 23 that is an integral part of the rotor-mixer according to the invention, shown in figure 1. Front plate 23 has an entrance 26 for the first flow of substance, as well as channels 24 that carry this substance radially to the space of the inlet openings 7 of the axis of rotation 22 for the at least second flow. The channels 24 can be applied as recesses or be superimposed on the front plate 23. They can be completely opened, but preferably in the range of 5 to 95% of their length towards the mixing chamber, they are provided totally or partially with covers 25. The first flow of substance is then conducted through inlet 26 to the first flow, travels through channels 24 covered with covers 25 and then leaves the channels through channel openings 27 for the first flow. In a preferred embodiment (not shown in figure 2) the covers 25 cover the channels 24 already from the height at the entrance 26 for the first substance, so that the first substance must go through the channels and then leave the channels again through the channel openings 27 for the first flow and force input into the mixing chamber.