DE2167070B1 - Continuous process in a bubble column cascade reactor - Google Patents

Description

35

The object of the invention is to provide a method for the continuous contacting of liquids with Gases or liquids with liquids in the presence of gases or liquids with To create solids in the presence of gases or liquids with gases and solids using a bubble column reactor with spaced apart perforated plates a ratio of the total free hole area of a perforated plate to the free reactor cross-section of a maximum 15%, in particular a maximum of 5%, with the perforated plates arranged horizontally and against the reactor wall are sealed, and wherein the individual holes are preferably the same size and evenly across the respective perforated plate are distributed and the perforated plates are preferably equidistant from one another, which is larger than three times the reactor diameter, due to the corresponding liquid and gas throughput a residence time behavior is achieved that comes close to or corresponds to that of an ideal stirred tank cascade.

From DE-PS 10 28 096 egg is already known by Installation of sieve trays, the holes of which must be smaller than 1 mm in diameter, in flow reactors Generate gas cushions below the sieve bottom. It was found, however, that in this DE-PS none Measures are described how the reproducible formation of the desired gas cushion takes place.

The object of the invention is achieved by a method for the continuous contacting of liquids with gases or of liquids with liquids in the presence of gases or of liquids with solids in the presence of gases or of liquids with gases and finely divided solids using a bubble column reactor with perforated plates arranged at a distance from one another with a ratio of the total free perforated area of a perforated plate to the free reactor cross-section of a maximum of 15%, in particular a maximum of 5%, the perforated plates being arranged horizontally and sealed against the reactor wall, and wherein the individual holes are preferably of the same size and evenly across the respective perforated plate are distributed and the perforated plates are preferably equidistant from one another, which is greater than three times the reactor diameter, the process being carried out in cocurrent and with the upwardly flowing gas below each perforated plate forms a gas cushion, whereby a liquid backflow is prevented, which is characterized in that the ratio ReLd to reed is a maximum of 0.1.

A particular embodiment of the method according to the invention is characterized in that the finely divided solid on contacting the liquid with solids up to 15% of the current i Flüssigkeitsmassen- by weight.

The influence of reactor diameter, hole plate spacing, number of holes, hole diameter, Hole division and plate sealing on the one hand as well as the liquid and gas volume flow and the Material properties of gas and liquid such as density, viscosity on the other hand on the gas cushion formation or examined for the liquid backmixing.

Surprisingly, it was found that with every geometry of perforated plate and reactor with the Above features for each liquid flow rate is a characteristic gas flow rate, in which according to the invention it is achieved that no backmixing occurs through the perforated plate and that a gas cushion forms under the perforated plates. This flow condition is referred to below as "Special flow condition" referred to.

At constant hole diameter and constant hole total required to reach the "special state of flow" gas flow rate with increasing liquid flow rate decreases, increases while at the same λ time of the liquid content in the individual Abschnit- * th and decreases the gas cushion thickness.

With the following definitions

^e Ld

'IL

'/G

The following applies to the formation of gas cushions:
ReJRe _Gd < 0.1.

In the case of gases with a very low density, there may be a significant deviation from the above relationship demonstrate.

The gas pressure loss of the bubble column cascade reactor is for all pairs of substances examined and Geometries for all possible flow conditions by the following empirical relationship with a Errors of ± 5% reproduced:

With the definition

^w g

gd

applies in the range 3 ■ ΙΟ " ⁷ < Fr _GD <ΙΟ

" ³

AP _tot =

The pressure loss coefficient ε can be given by the following Determine dimensionless relationship: ι ο

_ 0.31

r _GD

- 0.0.

r _GD

The symbols used in the equations have the following meanings:

d Hole diameter based on the hole diameter D. Reactor diameter based on the reactor diameter G Acceleration due to gravity Gas phase H Perforated plate spacing liquid π Number of reactor sections Ap Pressure drop W. speed ε Pressure loss coefficient η dynamic toughness Q density Ψ relative free hole area Fr. Froude number re Reynolds number Indices: d D. G L.

When designing the geometric dimensions of the reactor and the perforated plates within the framework of the device features mentioned, while maintaining the relationship ReiJ'Recd = ma \ 0.1 for the volume flows of gas and liquid or suspension to be enforced, stable gas cushions form under each perforated plate, in the following » special flow condition «called.

Due to the high gas throughput and the constant redispersion of the gas on the perforated plates the liquid and gas contents are mixed and turbulent in the individual reactor sections thus a high mass transfer is achieved. It was found that when the gas flow rate is reduced up to 50% of the value required for cushion formation, the back-mixing between the sections is still sufficiently prevented. However, the mass transfer intensity is reduced.

In the procedure according to the invention, each reactor section contains an effervescent layer, its Gas holdup with increasing height of the reactor section gets bigger. The so-called gas cushion is located above the bubble layer, which extends the space up to the fills the next floor and thus completely prevents liquid mixing.

This achieves the same residence time behavior as in an ideal stirred tank cascade, since the gas at the same time causes a good mixing of the liquid in the individual reactor sections.

As is well known, the ideal stirred tank cascade is characterized by the fact that there is an ideal one in each stirred tank Mixing of the liquid is present and a

15th

20th

25th

30th

35

40

45

50

55

60

65 back-mixing between the individual stirred tanks is not possible.

Since the bubble column cascade reactor is like a stirred tank cascade in terms of residence time behavior behaves, can be used to determine the average residence time and thus the dependency of the reactor content the known calculation equations are used for the required product throughput (See, for example, J. Kardos, Chemische Technik, Volume 21 [1969], No. 4, pages 216-220; No. 5, pages 275-280). With the method according to the invention, the same residence time distribution can be achieved with considerably less technical effort can be achieved than with a stirred tank cascade. It is also possible for as long as you like To generate residence times of the liquid or the suspension.

The process according to the invention is particularly advantageously suitable for the production of organometallic Compounds, especially for the production of organoaluminum compounds according to the Ziegler process. It is finely divided aluminum in the presence of aluminum trialkyls with hydrogen and optionally implemented olefins. Other implementations involve the production of aluminum trialkyls from dialkyl aluminum hydrides with olefins.

To design a reactor with the required geometry and a method therein according to the invention to operate with the formation of the desired gas cushions, one goes using the in the Invention given teaching, for example, as follows:

Calculation example

1. The substances to be converted are known, thus also the physical properties (ρ, η) and the desired throughputs Va and Vl.

2. From the usual point of view (e.g. risk of contamination) a hole diameter d is assumed.

3. If Wu is specified, the relation ReulRecd ^ 0.1 results in a value for WGd ·

4. The required number of holes z results from the relationship from WGd and the gas throughput Vb

■ - iP- 7

5. It is to be checked whether the determined value for hole diameter and number of holes also enforces Vl

(after V _L =

Ld

If necessary, the previous steps must be repeated iteratively with new default values.
6. A value must be selected for the relative free hole area φ (preferably up to 5% of the reactor diameter).

7. This results in the reactor diameter D after

d ¹ D ²

8. Depending on the desired residence time distribution, it can now be done in analogy to an ideal stirred tank cascade the number of stages can be calculated.

9. From the number of stages and the distance between the perforated plates (= three times the reactor diameter) results in the height of the reactor.

10. Apparatus costs and the expected operating costs are calculated. For the latter, the determination of the pressure loss Δ Ρ and the pressure loss coefficient ε is important. The calculation is based on the specified relationships.

11. If the values are unsatisfactory, the calculations to repeat iteratively with other default values until favorable expenditure values are reached.

The method according to the invention was initially applied to one for the observation of the cushion formation and the Backmixing was carried out using a suitable transparent model of a bubble column cascade reactor.

Fig. 1 shows the reactor in the state of cushion formation.

A b b. 2 shows a suitable hole division.

The gas flows into the reactor at (a) below the first perforated plate. Above the first perforated plate, the liquid or the suspension enters the reactor at (b).

Gas and

Table 1

Model experiments on bubble column cascade reactors. Liquid or suspension is drawn off from the reactor and fed to a separation vessel (h). The gas is fed back into the reactor via a cycle compressor (k). The amount of gas required for the reaction is continuously added to the gas cycle in (1). The liquid or suspension is removed from the separation vessel at (m).

The height of the bubble layer (n) and thus the gas cushion (o) can be changed by changing the gas resp.

ι ο liquid volume flow (p, q) can be set.

The method according to the invention was investigated with model substances (see Table I) and then chemical reactions are used (see table H). As an example of such reactions, namely the Implementation of liquids with gases according to the method according to the invention, is the production of Triethylaluminum from diethylaluminum hydride and ethylene called. As an example of the reaction between Liquid, solids and gas allow aluminum to react with triethylaluminum and hydrogen Diethyl aluminum hydride.

liquid Fluid- gas gas Pressure/ Hole 0 Suitor Medium Fluid- gas gas DEAH = diethyl aluminum hydride. Pressure/ Hole 0 Suitor Medium Columns Fluid gas ability by Tempe Colon- Cross Stay ability by TEA = triethylaluminum. Tempe Colon- Cross Stay height/ ability pad by- sentence rature nen-0 cut Time by- sentence Al = aluminum powder. rature nen-0 cut Time floor contents height sentence sentence number kg / h kg / h ata / ° C mm % H kg / h kg / h ata / ^: C mm % H m / - % mm 1) dibutyl 21.8 Stick 38.5 1/20 4/140 2.49 0.9 19.8 Ethylene 13.1 7.5 / 100 3 / 70.3 3.4 0.51 3/4 50 100 ether material 15.0 water 9.65 150/100 4.5 / 100 2.4 2 2) octene 13.8 Stick 17.2 1/20 2/140 1.6 1.5 material 3/4 57 55 material 406 Ethylene 355 10/100 3/300 3 0.75 3) water 46.4 air 35.5 1/20 4/140 2.5 0.55 236 water 122 150/140 5/300 4th 2 3/4 50 30th 4) water 45.8 air 14.8 1/20 2/140 1.6 0.65 material 3/4 59 40 5) water 29.2 air 12.0 1/20 4/140 1.25 1.1 3/4 66 35 6) water a) 46.9 air 4.0 1/20 4/140 2.5 0.93 3/4 87 0.0 Water b) 46.9 air 11.9 1/20 4/140 2.5 0.7 3/4 65 15th Water c) 46.9 air 19.0 1/20 4/140 2.5 0.62 3/4 53 40 Water d) 46.9 air 33.4 1/20 4/140 2.5 0.51 1 sheet of drawings 3/4 48 70 Table 2 Examples with chemical reactions in bubble column cascade reactors Liquid, Columns Fluid gas possibly solid height/ ability pad floor contents height number m / - % mm 1) DEAH 5.5 / 12 60 20th 2) TEA and 6.55 / 12 60 20th Al 3) DEAH 10/10 60 20th 4) TEA and 12/14 60 20th Al Legend:

Claims (2)

Patent claims: 1. Process for the continuous contact of liquids with gases or of liquids with liquids in the presence of gases or of liquids with solids in the presence of gases or of liquids with gases and finely divided solids in cocurrent using a bubble column reactor with spaced perforated plates with a ratio of the total free perforated area of a perforated plate to the free reactor cross-section of a maximum of 15%, the perforated plates being arranged horizontally and sealed against the reactor wall, and the individual holes being equally large and evenly distributed over the respective perforated plate and the perforated plates being the same distance from one another have, which is larger than three times the reactor diameter, the upward flowing gas below each perforated plate forms a gas cushion preventing the liquid backflow, characterized in that the ratio of Reu to Reed, ie the Reyno The id number of the liquid in relation to the hole diameter to the Reynolds number of the gas in relation to the hole diameter is a maximum of 0.1. 2. The method according to claim I _1, characterized in that when the liquid comes into contact with solids, the finely divided solid makes up up to 15% of the liquid mass flow.