CONTACTING FINE PARTICLES WITH A GAS PHASE IN A STIRRED BED REACTOR

Abstract

A process for producing products by contacting particles that are stirred in a fixed bed with a gas phase. Where the particles are treated in a process zone of a gas-traversed reactor where the process zone is the region in a reactor in which the stirred particle bed is brought into contact with the gas phase. The particles are circulated in the process zone by use of a close-clearance stirrer during the contacting with the gas phase and the stirrer mechanism is close-clearance when in equation 1

[00001]$\begin{array}{cc}W\left(h\right)=\frac{u_R\left(h\right)}{u_B\left(h\right)}.& \left(1\right)\end{array}$

Claims

1-7. (canceled)

8. A process for producing products, comprising: contacting particles of Geldart class C having a particle size d.sub.90<20 m in a stirred fixed bed with a gas phase; treating the particles in a process zone of a gas-traversed reactor, wherein the process zone is the region in a reactor in which the stirred particle bed is brought into contact with the gas phase; and circulating the particles in the process zone by use of a close-clearance stirrer during the contacting with the gas phase, wherein the stirrer mechanism is close-clearance when in equation 1 $\begin{array}{cc}W\left(h\right)=\frac{u_R\left(h\right)}{u_B\left(h\right)}& \left(1\right)\end{array}$ wherein for half of all values of h the close clearance W(h) in the process zone W(h) is >0.9, wherein u.sub.R(h) is equal to the outer circumference of the stirrer mechanism in the sectional face at the height coordinate h, and wherein u.sub.B(h) is equal to the inner circumference of the reactor in the sectional face at the height coordinate h.

9. The process of claim 8, wherein the process zone of the reactor is rotationally symmetrical; wherein the stirrer mechanism is close-clearance when in equation 1 $\begin{array}{cc}W\left(h\right)=\frac{u_R\left(h\right)}{u_B\left(h\right)};& \left(1\right)\end{array}$ wherein W(h) is equal to the close clearance of a stirrer mechanism in a rotationally symmetrical reactor, defined as the quotient of the circumferences of two planar sectional faces perpendicular to the axis of rotation of two surfaces of rotation, with h representing the height coordinate; wherein u.sub.R(h) is equal to the circumference of the inner sectional face of the circular inner sectional face calculated according to equation 2 $\begin{array}{cc}{u}_R\left(h\right)=2r_R\left(h\right);& \left(2\right)\end{array}$ wherein at a plurality of arbitrary points h of the surface of rotation perpendicular to the axis of rotation through a planar section; wherein r.sub.R(h) is equal to the distance from the axis of rotation to the outer contour of the stirrer mechanism, wherein the stirrer mechanism includes all components attached thereto; wherein u.sub.B(h) is equal to the circumference of the outer surface of rotation of the circular outer surface of rotation calculated according to equation 3 $\begin{array}{cc}{u}_B\left(h\right)=2r_B\left(h\right);& \left(3\right)\end{array}$ wherein at each arbitrary point h of the surface of rotation perpendicular to the axis of rotation through a planar section, said circular outer surface of rotation being formed by rotation of the inner contour of the reactor about the axis of rotation; wherein r.sub.B(h) is equal to the distance of the inner contour of the reactor to the axis of rotation; and wherein for half of all values of h the close clearance W(h) in the process zone W(h) must be >0.9.

10. The process of claim 8, wherein the contacting of the particles with the gas phase takes place at 0.08 to 5 MPa.

11. The process of claim 8, wherein the bed temperature in the process zone of the reactor equipped with the close-clearance stirrer is in the range from 30 to 1500 C.

12. The process of claim 8, wherein the process is conducted in two or more interconnected reactors.

13. The process of claim 8, wherein chemical or physical processes take place in the process zone of the reactor.

14. The process of claim 13, wherein the chemical processes are selected from covering of particle surfaces with a new functionalization, a reaction of the gas phase with the particles and a reaction of the gas phase at the particles.

Description

EXAMPLES

[0143] The SiH.sub.4 used, of quality 4.0, was obtained from Linde GmbH.

[0144] In all of the examples, the amorphous porous carbon was used as porous particles: [0145] spec. surface area=1907 m.sup.2/g [0146] pore volume=0.96 cm.sup.2/g [0147] median volume-weighted particle size D50=2.95 m [0148] particle density=0.7 g/cm.sup.2 [0149] cohesive, classified as Geldart class: C

Conversion Calculation for the Examples

[0150] The conversion is calculated as the quotient of the amount of substance in mol of the converted starting material relative to the amount of substance in mol of the employed starting material (reactant). In these examples it indicates how much of the SiH.sub.4 molecules used are converted to Si.

[00013]$\mathrm{Conversion}\mathrm{of}{\mathrm{SiH}}_4\mathrm{in}\%=\frac{\mathrm{amount}\mathrm{of}\mathrm{substance}\mathrm{of}\mathrm{obtained}\mathrm{Si}}{\mathrm{amount}\mathrm{of}\mathrm{substance}\mathrm{of}\mathrm{employed}{\mathrm{SiH}}_4}*100\%$

Yield Calculation for the Examples

[0151] The yield is the quotient of the mass of product actually obtained and the theoretical maximum possible product mass. The yield is expressed as a mass ratio quantity in percent:

[00014]$\mathrm{Yield}\mathrm{in}\%=\frac{\mathrm{Actual}\mathrm{mass}\mathrm{of}\mathrm{product}}{\mathrm{Maximum}\mathrm{possible}\mathrm{mass}\mathrm{of}\mathrm{product}}*100\%$

[0152] It is a measure of the losses of particles entrained by the gas stream.

[0153] The following reactors were used when conducting the experimental examples:

[0154] The reactor used for all examples 1 to 5 according to the invention consisted of a cylindrical lower part (beaker) having an internal radius r.sub.B=121.5 mm and a height h=512 mm and of a lid having multiple connections (for example, for gas supply, gas discharge, temperature measurement and pressure measurement) and of a flat base. Internals on the wall were not present. The volume of the reactor was V.sub.B=24I. The circumference of an arbitrary sectional face of the surface of rotation produced by rotation of the inner reactor contour about the axis of rotation is calculated as 763.4 mm. The stirrer used was a multi-flight helical stirrer having a radius of r.sub.R=119.5 mm. Complete revolution of the helical stirrer produces a surface of rotation. The circumference of an arbitrary sectional face perpendicular to the axis of rotation of this surface of rotation is 750.8 mm. From the two circumferences, a close clearance of W=0.98 is obtained. The height of the helix corresponded to around 75% of the clear height of the reactor interior. The reactor was filled such that the height of the stirred particle bed is lower than the height of the helix. Accordingly, more than 50% of the process zone is in the region of the stirrer having the close clearance W=0.98. The beaker was heated electrically with a jacket heater. The temperature was measured in principle between the heater and the reactor. The gas was supplied in the lower half (125 mm above the reactor base) of the bed, via two submerged tubes having an outer diameter of d=6 mm, which introduced the gas directly into the moving bed.

[0155] The fluidized bed reactor used in comparative example 1 (not in accordance with the invention) consisted of a cylindrical part having an outer diameter of 160 mm and a height of 1200 mm. The cylindrical part was composed of a bottom chamber and the fluidized bed reactor itself. The two parts were separated from one another by the gas-permeable base. The cylindrical reactor part was followed at the top by a reactor part with cross-sectional widening to twice the cross-sectional area by comparison with the cylindrical reactor part. At the top end of the reactor there was a lid with filter elements for the exit of gas. The reaction temperature was adjusted via heating of the reactor wall, with the height of the heated region being 80% of the cylindrical length beginning at the gas-permeable base. The measure used for the process temperature was the temperature between heating jacket and reactor outer wall. Heating was effected electrically. The fluidizing gas was accordingly preheated with a gas heater prior to flowing into the fluidized bed reactor. The fluidizing gas stream was pulsed using a directly controlled solenoid valve. As a measure of the quality of the fluidized bed, the fluidization index was employed.

[0156] In preliminary tests, the minimum fluidization velocity was determined by measuring the pressure drop of the fluidized bed.

[0157] Definition of fluidization index: The fluidization index F/is defined as the ratio of the pressure drop measured over the fluidized bed p.sub.WS,measurement to the theoretical maximum attainable pressure drop p.sub.WS,th and is calculated by the following equation 1:

[00015]$\mathrm{FI}=\frac{p_{\mathrm{WS},\mathrm{measurement}}}{p_{\mathrm{WS},\mathrm{th}}}$

[0158] The theoretical maximum attainable pressure drop is calculated, disregarding the gas density, from the mass of the bed m.sub.S, the acceleration due to gravity g and the reactor cross-sectional area A.sub.WS, as p.sub.WS,th=m.sub.s.Math.g/A.sub.WS.

[0159] In the case of a completely fluidized bed, the fluidization index adopts values of not more than 1.

[0160] Determination of the fluidization index: The fluidization index is the ratio of measured pressure drop to theoretical maximum possible pressure drop. For determining the fluidization index, it is necessary to detect the pressure drop of the fluid bed by technical measurement. The pressure drop is measured as a differential pressure measurement between bottom and top ends of the fluidized bed. The differential pressure measurement instrument converts the pressures detected on membranes into digital values and displays the pressure difference. The pressure measurement lines must be configured such that they are arranged directly above the gas-permeable base and directly above the fluidized bed. For the determination of the fluidization index, the precise detection of the weight of the particle bed introduced is additionally necessary. See also [VDI-Warmeatlas [VDI Heat Atlas], 11th edition, section L3.2 Strmungsformen und Druckverlust in Wirbelschichten [Types of Flow and Pressure Drop in Fluidized Beds], pp. 1371-1382, Springer Verlag, Berlin Heidelberg, 2013].

[0161] Determination of the minimum fluidization velocity: The minimum fluidization velocity is the fluidizing gas velocitybased on the empty reactor cross-sectional areaat which the particle bed transitions from the flow-traversed fixed bed into a fluidized bed. The minimum fluidization velocity can be determined through simultaneous measurement of the regulated fluidizing gas stream, using a mass flow meter, and of the pressure drop of the fluidized bed, using a digital differential pressure meter. Given knowledge of the cross-sectional area of the reactor, the fluidizing gas velocity can be calculated from the fluidizing gas stream measured. The plotted profile of the pressure drop against the fluidizing gas velocity is referred to as the fluidized bed characteristic curve. It should be noted that the fluidized bed characteristic curve is recorded, starting from a high fluidizing gas velocity, by gradual reduction of this velocity. In the case of a pure fixed bed traversing flow, the pressure drop increases linearly. The associated fluidization index FI is less than one. For a fully developed fluidized bed, the pressure drop measured is constant. The associated fluidization index FI is equal to one. The state of minimum fluidization is situated at the transition between the two regions. The associated fluidizing gas velocity, based on the empty reactor cross-sectional area, is equal to the minimum fluidization velocity. If the transition from the fixed bed to the fluidized bed is characterized by a range, the point of intersection of the extrapolated fixed bed characteristic curve and the extrapolated fluidized bed characteristic curve is defined as the point of minimum fluidization. See also [VDI-Warmeatlas [VDI Heat Atlas], 11th edition, section L3.2 Strmungsformen und Druckverlust in Wirbelschichten [Types of Flow and Pressure Drop in Fluidized Beds], pp. 1371-1382, Springer Verlag, Berlin Heidelberg, 2013]. In comparative example 2 (not in accordance with the invention), an indirectly heated rotary kiln was used. This rotary kiln possessed a rotary tube made of quartz glass, rotatable about its longitudinal axis, having a diameter of 20 cm and a heatable volume of 30 L. The outer wall temperature of the quartz tube was used as a measure of the process temperature. Heating was effected electrically and could be regulated through 3 zones. For the implementation of the silicon infiltration reactions, the rotary tube ought to be sealed gastight.

Comparative Example 1 (not in Accordance with the Invention): Production of a Silicon-Containing Material in a Fluidized Bed Reactor with Pulsed Fluidizing Gas Stream

[0162] 500 g of an amorphous carbon as porous starting material (specific surface area=1907 m.sup.2/g, pore volume=0.96 cm.sup.3/g, median volume-weighted particle size D.sub.50=2.95 m, particle density=0.7 g/cm.sup.3, particles of Geldart class C) were introduced into the reactor.

[0163] The particle bed was fluidized with a fluidizing gas consisting of nitrogen, the quantity of gas being such that the minimum fluidization velocity was at least 3 times that ascertained in the preliminary tests. At the same time, using the solenoid valve, the gas stream was induced to oscillate, with the frequency between the open and closed positions of the valve being 3 Hz. The temperature in the reactor was then raised to the setpoint temperature of 430 C. On account of the rise in temperature, the fluidizing gas stream was adapted such that the fluidization index adopted a value >0.95.

[0164] On attainment of the setpoint temperature of 430 C., the fluidizing gas was replaced by reactive gas containing 10% by volume of SiH.sub.4. The pulsation of the gas stream with the frequency between the open and closed positions of the valve of 3 Hz was maintained during and after the switch of the fluidizing gases, and, in addition, not only the values for the fluidization index of FI=0.98 but also, owing to the change in density of the porous starting materials during the deposition of the silicon, the gas quantity of the fluidizing gas were adjusted in such a way that the fluidization index values were always greater than 0.95.

[0165] After a reaction time of 2.6 hours, the fluidizing gas was switched back to a pulsed stream of nitrogen. The heating power was reduced. When a temperature of 50 C. was reached, the fluidizing gas stream was changed over to a fluidizing gas consisting of 5% by volume of oxygen in nitrogen and was maintained for 60 min in order to allow for controlled reaction of any reactive groups present on the surface of the product obtained. The reactor was subsequently cooled down to room temperature.

[0166] After the ending of the operation, 990 g of a black solid were discharged from the reactor. The silicon-containing material obtained was introduced into a cylindrical vessel and homogenized in a drum hoop mixer. The agglomerates formed as a result of the fluidized bed process could be eliminated by sieving. The reaction conditions for the production and also the material properties of the silicon-carbon composite particles are summarized in table 2.

Comparative Example 2 (not in Accordance with the Invention): Production of a Silicon-Containing Material by a Process not in Accordance with the Invention in the Rotary Tubular Reactor

[0167] A rotary tubular reactor (internal volume 30 L) was charged with 0.9 kg of the same porous carbon as in comparative example 1 (specific surface area=1907 m.sup.2/g, pore volume=0.96 cm.sup.3/g, median volume-weighted particle size D.sub.50=2.95 m, particle density=0.7 g/cm.sup.3, particles of Geldart class C). After inertization with nitrogen, the reactor was heated to 430 C. When the reaction temperature was reached, the reactive gas (10% SiH.sub.4 in N.sub.2, metering rate 2.3 m.sup.3/h) was passed through the reactor for 8.5 h, during which the reactor was rotated at a speed of around 7 revolutions per minute. The reactor was subsequently purged with inert gas. Before the product was withdrawn from the reactor, it was cooled to room temperature under inert gas. The reaction conditions for the production and also the material properties of the silicon-carbon composite particles are summarized in table 2.

Examples 1-5 (According to the Invention): Production of Silicon-Containing Materials by the Process According to the Invention Using Monosilane SiH.SUB.4 .as Silicon Precursor Under Standard Pressure (0.1 MPa) (the Respective Values for the Parameters A-D and Also the Example Number are Summarized in Table 1)

[0168] 2.4 kg of the same porous carbon as in comparative examples 1 and 2 (specific surface area=1907 m.sup.2/g, pore volume=0.96 cm.sup.3/g, median volume-weighted particle size D.sub.50=2.95 m, particle density=0.7 g/cm.sup.3, particles of Geldart class C) were introduced into the reactor according to the invention with the stirrer mechanism (volume 24 L, diameter 25 cm). The temperature of the reactor was subsequently adjusted to 350 C. for 240 minutes and the reactor was inertized with nitrogen.

[0169] The reactor was subsequently heated to 430 C. When the reaction temperature was reached, the reactive gas was passed through the reactor with concentration A and metering rate B for C hours. The gas phase was supplied to the reactor, while the particle bed was circulated by a close-clearance stirrer mechanism according to the invention, a helical stirrer, such that the ratio of circulation time to the average residence time of reactive component was D and the state of motion of the bed could be described by Froude number 3.

[0170] Subsequently, the silicon-containing material was cooled within 120 minutes to a temperature of 70 C. The reactor was subsequently purged for one hour with nitrogen, for one hour with lean air having an oxygen content of 5% by volume, for one hour with lean air having an oxygen content of 10% by volume, for one hour with lean air having an oxygen content of 15% by volume, and subsequently for one hour with air. Lastly, the product was withdrawn from the reactor.

TABLE-US-00001 TABLE 1 Experimental parameters for Examples 1 to 5 according to the invention Experimental Example number parameters Designation Ex 1 Ex 2 Ex 3 Ex 4 Ex 5 SiH.sub.4 conc., mol % A 10 50 50 100 100 Metering rate, m.sup.3/h B 6.1 1.2 4.6 0.6 0.3 Duration of SiH.sub.4 C 9.7 6.9 2.5 5.3 8.5 addition, h Ratio of t D 0.075 0.015 0.015 0.007 0.007 circulation time/t residence time

[0171] The reaction conditions for production and the material properties of the silicon-carbon composite particles are summarized in the following table 2.

TABLE-US-00002 TABLE 2 Comp ex 1* Comp ex 2* Ex 1 Ex 2 Ex 3 Ex 4 Ex 5 Reactor type Fluidized bed Rotary kiln SBR SBR SBR SBR SBR pulsed Amount of reactant, kg 0.5 0.9 2.4 2.4 2.4 2.4 2.4 SiH.sub.4 conc., mol % 10 10 10 50 50 100 100 Jacket temperature 430 430 430 430 430 430 430 during SiH.sub.4 addition, C. Duration of the SiH.sub.4 2.6 9.9 9.7 6.9 2.5 5.3 8.5 addition, h Reactor volume, L 20 30 24 24 24 24 24 Reactor diameter, m 0.15 0.20 0.25 0.25 0.25 0.25 0.25 Fr number n.a. 0.005 3 3 3 3 3 Ratio of t circulation n.a. n.a. 0.075 0.015 0.015 0.007 0.007 time/t residence time Conversion of SiH.sub.4, % 20 40 41 60 40 75 98 Amount of product, kg 0.99 1.84 5.67 5.74 5.51 5.66 5.80 Product yield, % 80 82 95 96 92 95 97 Particle discharge yes yes no no no no no Si, % by weight 56 56.5 56 57 55 56 57 O, % by weight 3.8 3.04 2.1 2.64 3.62 2.64 2.84 BET m.sup.2/g 11 10 23 26.6 43.6 26.8 23.8 *not in accordance with the invention

[0172] Regardless of the reactors used, the same characteristic material properties can be obtained. However, SiH.sub.4 conversion, product yield and reaction time in the reactor system according to the invention were improved compared to fluidized beds and rotary kilns.