EP3199230A1 - Device for continuously mixing at least two substances - Google Patents

Abstract

Device (1) for continuously mixing at least two substances (X, Y), in particular diaminodiphenylmethane (MDA) with carbon dioxide dichloride (phosgene) a mixing space (4) in which a mixing element (6), in particular a rotor-stator mixer (6), is arranged, - At least two inlets (3) through which the substances to be mixed separately and continuously inserted into the mixing chamber (4), at least one outlet (5) for continuously discharging the product (Z) produced in the mixing chamber (4) out of the mixing chamber (4), a drive arrangement (9, 16, 17) for driving the mixing element (6), wherein the mixing chamber (4) is hermetically enclosed by a housing (2), wherein parts (17) of the drive assembly which are non-rotatably connected to the mixing element (6) are arranged completely inside the hermetically enclosing housing (2), the drive arrangement (9, 16, 17) comprising an arrangement (9, 16) for generating a rotating magnetic field which is arranged completely outside the hermetically enclosing housing (2), and the drive arrangement (9, 16, 17) comprises a second magnet element (17) which is arranged completely inside the hermetically enclosing housing (2) and is in magnetic drive connection with the arrangement, in particular the first magnet element (16), and with the magnet Mixing element (6) is rotatably connected.

Description

The invention relates to a device for continuously mixing at least two substances. In particular, this device is used for mixing di- and polyamines of the diphenylmethane series (hereafter MDA total) with carbon monoxide (phosgene) for the preparation of di- and polyisocyanates of the diphenylmethane series (henceforth MDI).

For the production of numerous polyurethanes (PUR) MDI is required. MDI is produced industrially by a phosgenation of MDA. Due to the extremely high reactivity of the carbon dioxide dichloride (phosgene), the reaction between MDA and phosgene takes place immediately after mixing the two substances together.

In the large-scale implementation of this phosgenation some framework conditions are taken into account. First, all the substances involved are toxic. An escape of the substances is therefore to be avoided. In particular, the phosgene should be used in hermetically closed circuits. The mixing devices used must be hermetically sealed; Sealing rings on rotating components can not adequately provide this hermetic seal according to the required safety.

Phosgene is added to the reaction in proportion to MDA in excess of the stoichiometrically exact amount. The supplied MDA should be fully implemented, while a certain amount of phosgene remains unreacted in the starting material. The excess should be adjusted as low as possible for economic reasons, so that the amount of recirculated phosgene is minimized.

The input materials MDA and phosgene are dissolved in the preparation of MDI in a solvent such as monochlorobenzene (MCB) or ortho-dichlorobenzene, which promotes viscosity and miscibility. However, the solvent in the purchase and disposal is quite expensive; therefore it is processed by distillation and used several times. This distillation is associated with an energy input and is therefore costly. For economic reasons, therefore, efforts are always made to keep the proportion of solvent as low as possible.

The reaction of MDA and phosgene is an exothermic reaction. Due to the reactivity, local temperature peaks arise, which have to be reduced; the local temperatures in the mixing room should not exceed about 145 ° C, in order to produce no unwanted by-products. The cooling is usually provided by the solvent. However, if you reduce the proportion of the solvent, so the cooling agent is also saved to cool the reaction.

Furthermore, the by-product hydrogen chloride tends to react with MDA to form solid MDA hydrochloride (MDA * HCl). This reaction is undesirable in itself, but can not be completely avoided. The more critical the formation of MDA * HCl, the finer the MDA * HCl. The MDA * HCl can in turn be converted to the MDI with phosgene, so it is not lost for the target reaction. This reaction proceeds the better, the finer the MDA * HCl. Another factor that influences this reaction is the solubility of MDA * HCl in the solvent, which increases with increasing temperature. On the other hand, phosgene tends to outgas at too high a temperature. This can be counteracted by increasing the pressure in the mixing chamber to at least 20 bar, preferably more than 30 bar.

Increasing the pressure in the reaction space to at least 20 bar, however, requires massively higher safety requirements for the mixing device, since, as already stated, the starting materials are toxic substances. A leakage of substances even in small quantities must be excluded.

So far, for example, for the mixing of MDA and phosgene aggregates are used, which are based on rotors and stators. Such a mixer comprises a rotor with a plurality of radially aligned bolts. The mixing takes place here on an outer circumference of the mixer (see also EP 2 077 150 A1 ). In order to achieve the required high peripheral speeds, so far rotational speeds of more than 1000 U / min are set.

In order to still provide a good mixing at high pressure and elevated temperature and also to mix the starting materials quickly, and in particular to avoid the local temperature peaks, rotational speeds of the rotor-stator mixer of at least 3000 U / min are desired.

Hitherto hermetically sealed drive systems, however, have not been able to provide this so far, since in the hermetically sealed drive unit it is not possible to realize sufficient cooling on the basis of a coolant flow. The mechanical storage at speeds of 3000 rev / min reaches its limits. The maximum permissible operating pressure is usually well below 20 bar. Known mixers can therefore not be used. Special designs allow a speed of max. 3000 rpm.

In the example of phosgenation, the only flow of interest for cooling is by inert components, e.g. Solvents such as orthodichlorobenzene (ODB) or MCB provided. This flow is then unavailable to the reaction as a cooling inert component for the reaction. However, since the mass flows are in the range of ml / s on a small scale, but the gaps in the gap pockets of the magnetic couplings are in the mm range, like on a large scale, the entire solvent flow would have to be used for purging the gap.

Despite all these adversities, the phosgenation of MDA to MDI at high pressure and low solvent use theoretically seems to promise a considerable potential for savings, but it has failed so far due to the lack of availability of the apparatus for laboratory and technical center as well as the safety concerns and has therefore not been implemented.

In this respect, it is an object of the present invention to provide a technical implementation, with which the phosgenation of MDA to MDI under improved conditions, in particular higher pressure and lower solvent content, is made possible.

The object underlying the invention is achieved by a device according to claim 1 and a use of such a device according to claim 6; preferred embodiments will be apparent from the dependent claims.

The device according to the invention for continuously mixing at least two substances comprises a mixing space in which a mixing element, in particular a rotor-stator mixer is arranged, at least two inlets through which the substances to be mixed are introduced separately and continuously into the mixing space, at least one drain for the continuous filling of the mixing chamber produced product from the mixing chamber and also a drive arrangement for driving the mixing element. The device is suitable and is especially used for mixing MDA with carbon monoxide (phosgene) to produce MDI. The solvent used is in particular MCB (chlorobenzene). The mixing chamber is hermetically enclosed by a housing. Rotating members rotatably connected to the mixing element are disposed entirely within the hermetic enclosure. This means in particular that no rotating parts penetrate the hermetically enclosing housing, which is a prerequisite for a high level of safety against undesired escape of highly toxic substances.

The invention is characterized in that the drive arrangement comprises an arrangement for generating a rotating magnetic field, which is arranged completely outside the hermetically enclosing housing. This arrangement may comprise a motor and a first magnet element rotatably driven therewith, and is disposed entirely outside the hermetically enclosing housing. The drive arrangement comprises a second magnetic element, which is arranged completely within the hermetically enclosing housing and is in magnetic drive connection with the arrangement, in particular the first magnetic element. The second magnetic element is rotatably connected to the mixing element.

In essence, the principle of a magnetic stirrer is used here. The second magnetic element in this case represents a kind of stirring fish, which is arranged in the mixing chamber, and causes by its rotation a mixing of the introduced substances. In this case, the second magnetic element may be formed integrally with the mixing element. In particular, it is suitable that the second magnetic element is a spiked ring, which is associated with a rotor-stator mixer. The second magnetic element is mounted in contrast to known magnetic stirrers in the mixing chamber, in particular based on magnetic bearings.

Preferably, the device comprises a rotor-stator mixer arrangement with a spiked ring. Such a spiked ring is rotatably supported in the mixing space about an axis of rotation. A plurality of circular and coaxial arranged around the axis of rotation of the spiked inflows is provided for the separate introduction of the substances into the mixing chamber.

Continuous mixing is understood in particular to mean that the substances undergo a largely constant flow during the mixing process, and that in the mixing chamber produced product is constantly discharged. In contrast, static mixing operations are understood as those in which first all the substances to be mixed are introduced in a mixing chamber in a chord, then the inflow is stopped and mixing takes place and after complete mixing the end product is removed from the mixing chamber; only then refilling with substances to be mixed. Such static mixing operations are not encompassed by the term continuous introduction.

The spiked ring is arranged directly axially adjacent to the tributaries. Axially adjacent means that in the axial direction (ie in a direction parallel to the axis of rotation) a maximum of a narrow gap, in particular less than 2 mm, is provided between the outlet of the inflows and the spiked ring.

Preferably, the mixing element is supported by magnetic bearings. Such magnetic bearings may be formed without contact; that is, there is no contact between relative moving parts at these bearings. As a result, high rotational speeds can be realized without friction and thus heat exposure between the elements involved occurs.

Preferably, the device described above is used for the continuous mixing of at least two substances, in particular diaminodiphenylmethane MDA and carbon dioxide dichloride (phosgene). The pressure in the mixing chamber is preferably at least 19 bar, preferably at least 20 bar, more preferably at least 30 bar.

The mixing element is operated at a rotational speed of at least 3000 revolutions per minute. The temperature in the mixing chamber is in particular a maximum of 135 ° C, preferably 85 ° C.

By means of the invention, a possibility for mixing the substances is created, which can be used without hesitation at pressures well above 20 bar; In this case, a magnetic coupling is essentially designed such that the interior of the magnetic coupling becomes the mixing and reaction space. The second magnetic element can be embodied as an anchor stirrer or stirring fish with, for example, Teflon-coated permanent magnets, which are driven by the first magnetic element arranged outside the housing. So can be very high Torques in the range of a few Nm achieve in small gap cans, which allows the required mechanical power inputs in the range of several kW. Similarly, very high speeds are possible, so that the peripheral speeds (20-30 m / s) of the production mixers are achieved, which is an important parameter for scale-up investigations. The required high speeds (10,000 1 / min) can be made possible with magnetic and / or hydraulic storage of the inner rotor. Since the question of the need for purge and cooling flows also applies to larger magnetically driven intensive mixers (eg rotor-stator mixers in the production of MDI), an application of the invention on a larger scale, in particular in the production of MDI, advantageous because so inert side streams can be avoided in particular by solvent, which is beneficial to a reduction of cycle streams.

In the phosgenation of MDA, the excess of phosgene at given target NCO levels can be reduced if free MDA is no longer available for side reactions to ureas. In this case, the excess can be reduced to almost zero, so that a use of phosgene is possible quite close to or exactly at the stoichiometric ratio. In addition to the great economic advantages (phosgene destruction, plant size), the phosgene holdup in the plant part can significantly reduce, which is seen as increasingly critical safety aspect.

Due to the high pressure, the inevitably formed HCI remains in the liquid phase and is available for masking the MDA to the hydrochloride available.

FIG. 1

eine Vorrichtung umfassend eine Stachelmischanordnung in herkömmlicher Bauweise;

FIG. 2

die Rotor-Stator-Mischervorrichtung nach FIG. 1 Schnittdarstellung gemäß der Schnittlinie I-I aus FIG. 1;

FIG. 3

eine Schnittdarstellung aus der Rotor-Stator-Mischeranordnung nach FIG. 2 entlang der Schnittlinie III-III aus FIG. 2;

FIG. 4

eine erfindungsgemäße Abwandlung der Vorrichtung nach FIG. 1 in einer ersten Ausgestaltung;

FIG. 5

eine erfindungsgemäße Abwandlung der Vorrichtung nach FIG. 1 in einer zweiten Ausgestaltung.

The invention will be explained in more detail with reference to the drawings; herein shows:

FIG. 1

a device comprising a spiked mixing assembly of conventional construction;

FIG. 2

the rotor-stator mixer device after FIG. 1 Sectional view according to the section line II FIG. 1 ;

FIG. 3

a sectional view of the rotor-stator mixer assembly according to FIG. 2 along the section line III-III FIG. 2 ;

FIG. 4

a modification of the invention according to the invention FIG. 1 in a first embodiment;

FIG. 5

a modification of the invention according to the invention FIG. 1 in a second embodiment.

The pictures FIG. 1 to FIG. 3 are described together. Shown is a mixing device 1 with a rotor-stator mixer assembly of the conventional type. In a mixing chamber 4, two substances X, Y are supplied separately and continuously via inlets 3. The substances X, Y are dissolved in a solvent L. Within the mixing chamber 4, a mixing device 6 is provided in the form of a rotor-stator mixer. This rotor-stator mixer 6 comprises a plurality of spiked rings 7. At each spiked ring 7 protrude radially single spikes 8. The spiked rings 7 are held on a common rotary shaft 14 and rotatably connected to each other. About a motor 9, the rotor-stator mixer 6 is driven. The motor 9 includes a stator 10 and a rotor 11. An electrical lead 12 is connected to the stator. The rotor 11 is rotatably connected to the shaft 14.

The mixing device 1 comprises a hermetically sealed housing 2, in which all rotating parts of the mixing device 1 are located, in particular the spiked ring 7, the rotor 11 and the shaft 14. Also bearings 13 for supporting the shaft 14 are held within the hermetically sealed housing 2 , The stators 10 of the motor are held outside the housing 2. A partition 22 separates the interior of the housing 2 in two different spaces, to one the mixing chamber 4, on the other hand, the rotor chamber 21. In the last is the rotor 12 is received. Essentially, it is prevented by the partition 22 that fluid can flow from the mixing chamber 4 into the rotor chamber 21, only individual slots 23 in the region of the partition or the bearings are provided to allow a solvent flow L from the rotor chamber 21 into the mixing chamber 4. This solvent flow serves for a cooling of the rotor 11; On the other hand, this solvent flow L should ensure that none of the substances X, Y or the final product Z reaches the rotor space 21.

In the mixing chamber 4, the two substances X and Y are mixed to the final product Z. The substances X and Y are dissolved in the solvent L before. Similarly, the final product Z is dissolved in the solvent L. Via an outflow 5, the end product Z flows in dissolved form completely from the mixing chamber 4 and enters a solvent separator 18, in which the solvent L is separated from the end product X. The separated solvent L passes into a solvent treatment 19, and from there the solvent passes again into the Rotor space 21 for cooling and purging the rotor; Further, the solvent L is used again for dissolving the substances X, Y (not shown).

In FIG. 2 and FIG. 3 Details of the rotor-stator mixer are shown. The spiked ring 7 rotates in the direction of rotation D about the axis of rotation A. In this case wipes a radial outer portion of a spigot 8 each over an inlet 3 away and so takes the inflowing substance in the circumferential direction or in the direction of rotation D and leads them to the other inflow, the is arranged adjacent in the circumferential direction, whereby the mixing of the two substances is effected. To recognize a total of twelve feeds 3, wherein the feeds of the first substance X and the inlets of the second substance Y are arranged alternately in the circumferential direction. The spiked ring 7 also has twelve spikes, the inlets are arranged adjacent to each other in the circumferential direction. In principle, in such rotor-stator mixers, the number of spikes 8 on a spiked ring 7 coincides with the number of circumferentially distributed inlets 3.

In FIG. 3 the spikes 8 are shown in cross-section. It can be seen that the spikes 8 are only spaced from the tributaries 3 by an axial gap of a few millimeters. In the radially outer region, which is in overlap with the tributaries 3, the spike 8 has a bevel 15. This chamfer 15 serves to entrain the flow S of the inflowing substances from the axial direction, as it first flows out of the inflows 3, in the direction of rotation D. First, an acceleration of the substances in the circumferential direction is thus effected by the rotor-stator mixer.

The arrangement after FIG. 1 requires a large amount of solvent L, which is used for cooling and purging the rotor. In this respect, the structure of the mixing device is quite complex. In FIG. 4 is now a modification of the mixing device according to FIG. 1 shown, wherein the described details of the mixing device according to the figures FIG. 1 to FIG. 3 largely on the mixing devices according to the invention according to the figures FIG. 4 and FIG. 5 are applicable.

FIG. 4 shows a mixing device 1 with a rotor-stator mixer 6, comprising a significantly smaller hermetically sealed housing 2 as the mixing device according to FIG. 1 , The motor 9 is a commercial motor, which is supplied via a power line 12 with electrical energy. A magnetic disk 16 (first magnetic element) is driven via a shaft 14 "The motor 9, the shaft 14 and the magnetic disk 16 are arranged outside the housing 2. Within of the housing 16 is a magnetic stirring fish 17 (second magnetic element) is arranged, which is integrally formed with a spiked ring 7. By the movement of the magnetic disk 16 of the stirring fish 17 is likewise set in rotation. As a result, the spiked ring 7 rotates and causes a mixture, as it already has FIG. 1 was shown. The separate solvent flow for cooling and purging parts of the engine can be omitted.

FIG. 5 shows a modification of the device according to FIG. 4 , In addition to the rotor-stator mixer 17, which is integrally formed with a spiked ring 7 more spiked rings 7 are provided, which are arranged axially adjacent to the stirring fish 17 and are connected to each other via a shaft 14 '. About magnetic bearing 20, the shaft 14 'is mounted in the housing 2.

LIST OF REFERENCE NUMBERS

1

mixing device

2

hermetically sealed housing

3

inflows

4

mixing room

5

outflow

6

Rotor-stator mixer

7

thorn crown

8th

sting

9

engine

10

stator

11

rotor

12

Electrical supply

13

camp

14

wave

15

bevel

16

magnetic disk

17

stir bar

18

solvent separator

19

Solvent applicator maker

20

magnetic bearings

21

rotor chamber

22

partition wall

23

slots

S

flow

D

direction of rotation

X

first substance

Y

second substance

Z

end product

L

Solvent stream

Claims (9)

Device (1) for continuously mixing at least two substances (X, Y), in particular diaminodiphenylmethane (MDA) with carbon dioxide dichloride (phosgene) a mixing space (4) in which a mixing element (6), in particular a rotor-stator mixer (6), is arranged, - At least two inlets (3) through which the substances to be mixed separately and continuously inserted into the mixing chamber (4), at least one outlet (5) for continuously discharging the product (Z) produced in the mixing chamber (4) out of the mixing chamber (4), a drive arrangement (9, 16, 17) for driving the mixing element (6), wherein the mixing chamber (4) is hermetically enclosed by a housing (2),
wherein parts (17) of the drive assembly which are non-rotatably connected to the mixing element (6) are arranged completely inside the hermetically enclosing housing (2),
characterized,
that the drive arrangement (9, 16, 17) comprises an arrangement (9, 16) for generating a rotating magnetic field, in particular comprising a motor (9), and a thus rotatably driven first magnetic element (16) which is entirely outside of the hermetic housing enclosing (2) is arranged, and
that the drive arrangement (9, 16, 17) comprises a second magnetic element (17) which is arranged completely inside the hermetically enclosing housing (2) and with the arrangement, in particular the first magnetic element (16) is in magnetic drive connection and to the Mixing element (6) is rotatably connected. Device (1) according to the previous claim,
characterized,
that the second magnetic element (17) is formed integrally with the mixing element (6). Device (1) according to the previous claim,
characterized,
in that the second magnet element (17) is designed as a spiked ring (7) of a rotor-stator mixer (6). Device (1) according to one of the preceding claims,
characterized,
in that the device comprises a rotor-stator mixer arrangement with a spiked rim (7),
wherein the spiked rim (7) is held rotatably about an axis of rotation (A) within the mixing space (4),
wherein a plurality of circular and coaxial about the axis of rotation of the spiked ring (7) arranged inflows (3) for separate and continuous introduction of the substances are provided in the mixing chamber (4),
wherein the spiked ring (7) is arranged directly axially adjacent to the tributaries (3). Device (1) according to one of the preceding claims,
characterized,
that the mixing element (6) is mounted by magnetic bearings (20). Use of a device according to one of the preceding claims for continuously mixing at least two substances, in particular diaminodiphenylmethane (MDA) and carbon dioxide dichloride (phosgene). Use according to the preceding claim, wherein in the mixing chamber (4) a pressure of at least 19 bar, preferably at least 20 bar, preferably at least 30 bar prevails. Use according to one of claims 6 or 7, wherein the mixing element (6) has a rotational speed of at least 3000 U / min. Use according to one of claims 6 to 8, wherein the mixing chamber (4) has a maximum temperature of 135 ° C, preferably of not more than 85 ° C.

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