METHOD AND DEVICE FOR THE HYDROLYSIS OF A COMPOUND

Abstract

The subject matter of the invention is a device for the hydrolysis of at least one compound. The device comprises a first cylindrical section having a diameter D.sub.max, a central duct, an outer duct which surrounds the central duct coaxially, an outlet having a diameter D.sub.A, and a second section which tapers towards the outlet and into which the ducts issue. The second section has, in cross-section along a longitudinal axis A.sub.L of the device, a profile which is described by two radii R1 and R2 which merge tangentially into each other, where 0.2<R1/D.sub.A<4.0 and 0.3<R2/D.sub.A<5.0. The invention also relates to a method for the hydrolysis of at least one compound. In the method, the device is used to conduct water at least through the outer duct and to conduct the compound to be hydrolysed through the central duct and/or through at least one intermediate duct and to mix them with each other at least partially in the second section. The compound and the water are in liquid form.

Claims

1. A device (10) for hydrolyzing at least one compound, comprising: a first cylindrical section (12) having a diameter D.sub.max, a central channel (18), and an outer channel (20) coaxially surrounding the central channel (18); an outlet (24) having a diameter D.sub.A; and a second section (14) tapering in the direction of the outlet (24) and comprises a hollow volume (15) into which the channels (18, 20, 22) open, wherein the second section (14) has, in a cross section along a longitudinal axis A.sub.L of the device (10), a profile (28) of an outer wall delimiting the hollow volume (15), which is described by two radii R1 and R2 which go tangentially over into one another, where a profile subsection described by R1 adjoins the outlet (24) and a profile subsection described by R2 adjoins a wall (21) of the outer channel (20) which runs straight in its profile and where 0.2<R1/D.sub.A<4.0 and 0.3<R2/D.sub.A<5.0.

2. The device of claim 1, wherein 0.8<R1/D.sub.A<2.0 and 1.0<R2/D.sub.A<3.0.

3. The device of claim 1, wherein eight, preferably four, particularly preferably two, in particular one, intermediate channel(s) (22) which coaxially surround(s) the central channel (18) is/are arranged between the central channel (18) and the outer channel (20).

4. The device of claim 1, wherein the channels (18, 20, 22) open into the second section (14) at least partially at the height of a point of inflection P of the radii R1 and R2 going tangentially over into one another.

5. The device of claim 1, wherein the channels (18, 20, 22) have a constant or decreasing flow cross section up to the entry into the second section (14).

6. The device of claim 1, wherein there is a ratio between a flow cross section A.sub.outer of the outer channel (20) and a flow cross section A.sub.A of the outlet (24) of 0.3<A.sub.outer/A.sub.A<20.0, preferably 1.0<A.sub.outer/A.sub.A<10.0, particularly preferably 2.0<A.sub.outer/A.sub.A<8.0.

7. The device of claim 1, wherein 1<D.sub.max/D.sub.A<8, preferably 1.5<D.sub.max/D.sub.A<6, particularly preferably 2<D.sub.max/D.sub.A<5.

8. The device of claim 1, wherein a third cylindrical section (16) having a length l of 0<l/D.sub.A<100, preferably 3<l/D.sub.A<40, particularly preferably 5<l/D.sub.A<20, is arranged downstream of the outlet (24).

9. The device of claim 1, wherein a punching device (19) which can be moved along the axis A.sub.L for removing deposits is arranged in the central channel (18).

10. A method for hydrolyzing at least one compound, comprising: conveying water at least through an outer channel (20); conveying the at least one compound to be hydrolyzed through a central channel (18) and/or through at least one intermediate channel (22) by a device (10) as claimed in claim 1; and mixing water and at least one compound, at least partially, with one another in a second section (14), where the at least one compound and water are present as liquid.

11. The method of claim 10, wherein a channel conveying the at least one compound is flanked at least by a channel conveying water.

12. The method of claim 10, wherein channels conveying the at least one compound and channels conveying water are arranged in an alternating order.

13. The method of claim 10, wherein the absolute value of a difference between V.sub.V and V.sub.H2O for two adjacent channels of which one conveys the at least one compound at an average exit velocity V.sub.V and one conveys water at an average exit velocity V.sub.H2O is 0 m/s<|V.sub.VV.sub.H2O|<200 m/s, preferably 2 m/s<|V.sub.VV.sub.H2O|<100 m/s, particularly preferably 5 m/s<|V.sub.VV.sub.H2O|<50 m/s.

14. The method of claim 10, wherein water leaves the outer channel (20) at an average exit velocity V.sub.outer of more than 0.5 m/s, preferably more than 2 m/s, particularly preferably more than 4 m/s.

15. The method of claim 10, wherein the channel conveying the at least one compound has a mass flow {dot over (m)}.sub.V and the channel conveying water has a mass flow {dot over (m)}.sub.H2O, where a ratio of the sum of the mass flows {dot over (m)}.sub.Vi of all channels conveying the at least one compound and the sum of the mass flows {dot over (m)}.sub.H2Oj of all channels conveying water is 0<{dot over (m)}.sub.Vi/{dot over (m)}.sub.H2Oj<1.0, preferably 0<{dot over (m)}.sub.Vi/{dot over (m)}.sub.H2Oj<0.5, particularly preferably 0<{dot over (m)}.sub.Vi/{dot over (m)}.sub.H2Oj<0.2.

Description

[0054] FIG. 1 shows the cross section of a device for carrying out the method of the invention.

[0055] FIG. 2 and rig. 3 in each case show a velocity profile of average exit velocities of liquids during the method of the invention.

[0056] FIG. 1 shows a schematic cross-sectional depiction of the device 10 of the invention along a longitudinal axis A.sub.L. The device 10 comprises a first cylindrical section 12 having a diameter D.sub.max, a second tapering section 14 and a third cylindrical section 16 having a length I. The device 10 further comprises a central channel 18, an outer channel 20 which coaxially surrounds the central channel 18 and an intermediate channel 22 which coaxially surrounds the central channel. The first section 12 and the second section 14 are constituents of a nozzle which has an outlet 24 having a diameter D.sub.A. The third section 16, which is not depicted in its entirety, is a reaction tube, for example a tube made of stainless steel, which adjoins and is flush with the outlet 24 and the internal volume 17 of which has the same diameter D.sub.A. The ratio l/D.sub.A is 10. The ratio D.sub.max/D.sub.A is 3.

[0057] The second section 14 into which the channels 18, 20, 22 open comprises a hollow volume 15 which extends from the outlet 24 to a preferably circular opening plane 26 of the channels 18, 20, 22. The second section 14 is defined by a profile 28 which extends between the points A and B and can be described by two radii R1 and R2 which go tangentially over into one another. P defines the point of inflection at which the two radii R1, R2 go over into one another. The profile 28 is in sections a wall 27 delimiting the hollow volume 15. The wall 27 is described by a profile section between the points B and P, where P is the point of intersection of the opening plane 26 with the profile 28. A part of a wall 21 of the outer channel 20 between the points P and A forms a further section of the profile 28. The ratio R1/D.sub.A is 1 and the ratio R2/D.sub.A is 2.

[0058] A punching device 19 which is preferably pointed at its front end is arranged in the central channel 18. This can be moved along the axis A.sub.L at least as far as the outlet 24 and serves to remove deposits which can occur during operation of the device 10, especially in the region of the hollow volume 15 and of the outlet 24. The dimensioning of the punching device 19 is such that a liquid can flow through the central channel 18.

Example 1

[0059] The chlorosilanes formed in the production of polysilicon (typically a mixture of tetrachlorosilane, disilanes and disiloxanes) were subjected to hydrolysis by means of water using a device 10 as depicted schematically in FIG. 1. Both the chlorosilanes and the water were fed as liquid into the device in a temperature range from 20 to 30 C. under a pressure of from about 1 to 3 bar absolute. Here, water was conveyed through the outer channel 20 and the intermediate channel 22, while the chlorosilanes were conveyed through the central channel 18.

[0060] FIG. 2 shows a velocity profile of the exit velocities of the liquids at the position of the opening plane 26 where the liquids enter the hollow volume 15 (cf. FIG. 1). The radius r of the circular opening plane 26 on the basis of FIG. 1 is plotted on the ordinate. The exit velocity v is plotted on the abscissa. The zone III (chlorosilane stream) shows the flow velocities of the central channel 18, while the zones II and I (water stream) correspond to the exit velocities of the intermediate channel 22 and the outer channel 20, respectively.

[0061] The chlorosilane stream in zone III has the highest average velocity (40 m/s), the water stream in zone II flanking this has the lowest average velocity (2 m/s). Owing to this difference, intensive shear forces arise at the interface of the two streams, as a result of which thorough mixing takes place immediately after leaving the channels. The particularly good mixing results in the hydrolysis being concluded in the region of the output 24. In this way the reaction tube serving for cooling can be kept short, which leads to a saving of materials.

[0062] The water stream from the outer channel 20 (zone I), which has a higher velocity (4 m/s) than the water stream from zone II, firstly encloses the mixing zone formed, in which, in particular, water from zone II and the chlorosilanes from zone III mix. This prevents hydrolysis products from being able to come into contact with the wall 27. The formation of deposits is thus largely avoided. Secondly, in conjunction with the specially configured profile 28, fast flow of water along the wall 27 is produced, by which means any deposits formed on the wall 27 are flushed away. The time on stream of the device is significantly increased. Compared to the hydrocyclones used hitherto, the time on stream could be increased by a factor of 7 to about 200 hours. The throughput of chlorosilanes could be increased by a factor 3 to 600 l/h.

Example 2

[0063] The chlorosilanes typically formed in the production of polysilicon were subjected to hydrolysis by means of water using the device shown in FIG. 1. The reaction conditions were identical to those in example 1.

[0064] However, according to FIG. 3, the chlorosilanes were, in contrast to example 1, conveyed through the intermediate channel 22 (zone II) at a maximum average exit velocity of 10 m/s. The chlorosilane stream was flanked by two water streams (zones I and III), with the water stream of the central channel 18 having the lowest exit velocity of 2 m/s. Here too, the large velocity difference brought about intensive mixing of the chlorosilanes with the water stream (zone III). Since the high boiler stream (zone II) is flanked on both sides by water, larger amounts of chlorosilanes could be reacted. Compared to the hydrocyclones previously used, the time on stream could be increased by a factor of 5 to 143 hours. The throughput of chlorosilanes could be increased by a factor of 6 to 1200 l/h.

[0065] The embodiment shown in FIG. 3 is particularly suitable for hydrolyzing compounds which are less problematical with regard to formation of deposits. As a result of the particularly large mixing zone formed in this embodiment, it is possible to achieve a very rapid hydrolysis reaction, so that a third section 16 in the form of a reaction tube may be able to be dispensed with.

Example 3

[0066] The chlorosilanes typically formed in the production of polysilicon were subjected to hydrolysis by means of water using the device shown in FIG. 1. The reaction conditions were identical to those in example 1.

[0067] The chlorosilanes were conveyed at an average exit velocity of 8 m/s through the central channel 18 (zone III). Water was conveyed at an exit velocity of 35 m/s through the intermediate channel 22 (zone II) and at an exit velocity of 3 m/s through the outer channel 20 (zone I). The velocity profile corresponded essentially to that shown in FIG. 3. Due to the large velocity difference between the zones III and II, intensive mixing occurs in the region of the hollow volume 15, with reaction products formed being kept away from the wall 27 by the water stream in the outer channel 20. Compared to the hydrocyclones previously used, the time on stream could be increased by a factor of 10 to about 290 hours. The throughput of chlorosilanes was 200 l/h and thus at the value in the hydrocyclone previously used.

[0068] This embodiment is particularly suitable for hydrolyzing high boiler mixtures whose hydrolysis products have an increased tendency to form deposits. Here, mention may be made of, in particular, media which have relatively high concentrations of metal chlorides, e.g. Al.sub.2Cl.sub.3 or TiCl.sub.4.

Example 4

[0069] The chlorosilanes typically formed in the production of polysilicon were subjected to hydrolysis by means of water using the device shown in FIG. 1. The reaction conditions were identical to those in example 1.

[0070] The chlorosilanes were conveyed through the intermediate channel 22 (zone II) at an average exit velocity of 2 m/s. The chlorosilane stream was flanked by two water streams (zones I and III), with the water stream in the central channel 18 having the highest exit velocity of 50 m/s. The velocity profile here corresponds essentially to that shown in FIG. 2. As regards mixing, reference may be made to what has been said for example 2. Compared to the hydrocyclones previously used, the time on stream could be increased by a factor of 8 to about 220 hours. The throughput of chlorosilanes could be increased by a factor of 3 to 600 l/h.

[0071] This embodiment is particularly suitable for hydrolyzing high boiler mixtures whose hydrolysis products have a very great tendency to form deposits. Here too, mention may be made of, in particular, media which have relatively high concentrations of metal chlorides, e.g. Al.sub.2Cl.sub.3 or TiCl.sub.4. Furthermore, this embodiment is particularly suitable for strongly exothermic hydrolysis reactions, since the heat evolved can be removed quickly by the excess of water.

Comparative Example

[0072] The chlorosilanes typically formed in the production of polysilicon were subjected to hydrolysis by means of water using a hydrocyclone. The mode of operation and construction of the cyclone are known from DE 28 20 617 A1.

[0073] The halosilanes are sprayed into a cyclone through a free-hanging two-fluid nozzle with the aid of an inert gas, for example nitrogen. Due to a tangential addition of water at an upper end of the cyclone, the halosilane mixture comes into contact with water. Since the reaction between high boilers and water is an exothermic reaction, the water introduced is partially vaporized. The ascending water vapor moistens the two-fluid nozzle, as a result of which blockages which can lead to blocking of the two-fluid nozzle regularly occur. Owing to the large ratio between the wetted surface area of the cyclone and the volume stream of water, the reactants are not completely washed off (low flow velocities). This likewise leads to regular occurrence of blockages. The time on stream of the cyclone is therefore only about 28 hours. The throughput of chlorosilanes is 200 [l/h].

[0074] A further advantage of the device of the invention is the small cleaning requirement compared to the hydrocyclone, which is reflected in a shorter time on stream. While a maximum of only 2 hours are required for cleaning the device of the invention, a time of about 48 hours is required for cleaning the hydrocyclone. If the device of the invention is provided with a punching device for removing deposits, the time required for cleaning purposes can be reduced further since the punching device can remove blockages even during ongoing operation.