DE3709219C2 - Process for desublimation of gaseous aluminum chloride contained in a gas mixture in a fluidized bed - Google Patents

Description

The present invention relates to a method for desublimation of in a gaseous mixture containing vaporous aluminum chloride Introducing the gas mixture into a bed through a fluidizing gas aluminum chloride particles kept in swirling condition and condensation of the vaporous aluminum chloride on the swirling particles subtracting the heat of desublimation from the Fluidized bed.

In the production of aluminum chloride by chlorination of aluminum or aluminum-containing raw materials, reaction gas mixtures are formed which the desublimatable reaction product by cooling in the solid Condition must be transferred and separated. By cooling one such reaction gas mixture in a fluidized bed Aluminum chloride particles can be the aluminum chloride win advantageously in free-flowing granular form.

It is known that vaporous aluminum chloride is part of a Gas mixture in one consisting of this aluminum chloride Fluid bed by growing on the solid particles and by forming new particles in the fluidized bed in the solid state can be transferred. In DE-A 28 04 744 it is stated that one for the production of solid aluminum chloride by condensing vaporous aluminum chloride in a fluidized bed of aluminum chloride Particles the gas containing aluminum chloride into the bed with one Entry speed of 18-90 m / sec must introduce. Through this Measure is to be achieved so that sufficient mixing of the hot gases containing aluminum chloride with the cold Fluid bed particles takes place. The temperature in bed is 60 up to 80 ° C, while the feed temperature of the aluminum chloride vapor Gases above the condensation temperature of the Aluminum chlorides can be varied up to 350 ° C. In one example is the method claimed in said DE-A 28 04 744 an entry speed of 90 m / sec explained.

The work that led to the present invention has been accomplished observed that at feed temperatures of more than 200 ° C and entry speeds within that claimed in DE-A 28 04 744 Aluminum chloride area at the outlet of the inlet pipe into the Fluid bed, which is designed as a nozzle because of the high gas velocities  is growing up. This increases the pressure loss. The growing up of Aluminum chloride can clog the nozzle completely only with the help of mechanical cleaning devices can be prevented.

At the risk of clogging of nozzles is also in DE-B 29 10 830th pointed out, but these are nozzles through which the Fluidizing gas is introduced into a fluidized bed desublimator, however this fluidizing gas as a result of the special reaction procedure contains vaporous aluminum chloride.

If one now on the other hand according to DE-A 28 04 744 cited above works in the upper range of the claimed entry speed, so the pressure loss in the inlet nozzle increases sharply, d. H. to values of well over 500 mm W. S., so the total pressure drop of such a operated fluidized bed desublimator with the addition of Pressure loss of the fluidized bed increases to over 1000 mm W. S. This On the other hand, high pressure can be for example in a reactor in which the aluminum chloride Reaction of aluminum with chlorine is generated, not applied so that additional technical effort to overcome the Pressure loss is required.

The present invention is therefore based on the object Process for desublimation of vaporous gas contained in a gas mixture Aluminum chloride by introducing the gas mixture into a bed aluminum chloride particles kept in a swirling state by a fluidizing gas and condensation of the vaporous aluminum chloride on the swirling particles subtracting the heat of desublimation from the Provide fluidized bed, which has the disadvantages of the known methods do not occur d. H. where on the one hand a high pressure loss and on the other hand, at the same time there is a risk of the discharge point becoming blocked is avoided by growing aluminum chloride.

It has been found that this object can be achieved by: the gas mixture containing vaporous aluminum chloride at an angle from 20 to 70 °, in particular 40 to 50 °, measured against the Direction of flow of the fluidizing gas, introduces into the bed, wherein the feed temperature of the gas mixture below the triple point temperature of the aluminum chloride is.

Surprisingly, it succeeds in compliance with the invention Measures, even at low introduction speeds of less than 30 m / sec to avoid an overgrowth of the discharge point, taking it above  It is even possible to increase these speeds significantly fall below speeds of 1 m / sec. However, in order to Not having to choose too large a diameter of the inlet point, on the other hand the advantages of minimizing the pressure loss in the delivery system to exploit as much as possible, one works preferably at entry speeds from 2 to 15 m / sec. The energy consuming pressure loss at the The method according to the present invention is practically exclusive limited by the height of the bed swirling above the inlet pipes, which are minimized in a manner known per se according to DE-A 31 38 861 can by placing the heat exchanger below the inlet pipe.

The triple point temperature of the aluminum chloride is at a pressure of 2.2 bar at 192.6 ° C. According to the feed temperature are below this temperature, because at higher temperatures like them can not be excluded in the known methods, even with Introducing the gas stream containing aluminum vapor in a peak Angle to the fluidizing gas an increase in the inlet point is not certain can be prevented. On the other hand, the gas should be in the Inlet system have a temperature that is above the Sublimation temperature of the aluminum chloride at the respective pressure lies.

The aluminum chloride-containing gas mixture is preferably at an angle from 40 to 50 °, measured against the flow direction of the fluidizing gas, introduced.

With the method according to the invention it is possible not only one Overgrowth of the introduction point of the vapors containing aluminum chloride into the To prevent fluidized bed, but also because of the possibility of low Inlet speeds to choose, the pressure loss in the inlet system too minimize.

Another advantage of the present invention is that in Contrary to the known methods for the introduction of desublimatable Gas mixtures containing substances in fluidized beds from particles of desubliming substance with the help of nozzles in the event of failure of the to desublimating substance containing gas stream, for example in a technical system due to an emergency shutdown, the swirling particles of the fluidized bed do not run back into the inlet pipe as far as desired and when restarting the sublimator the particles with no difficulty the low inlet speeds from the inlet pipe into the Fluid bed can be blown back.  

There is a fluidized bed ( 3 ) made of aluminum chloride particles in the column ( 1 ), nominal width 100 mm, with a re-blowable top filter ( 2 ) of the figure below. The aluminum chloride particles are kept in a good vortex state with the fluidizing gas ( 4 ) with the aid of the gas distributor tube ( 5 ). The gas mixture ( 6 ) containing aluminum chloride vapor is introduced into the fluidized bed ( 3 ) at an angle of 45 °, measured against the direction of the fluidizing gas, arranged inlet tube ( 7 ). The inlet pipe ( 7 ) protrudes far enough into the fluidized bed ( 3 ) and, with the aid of a suitable temperature control device ( 8 ), receives a constant wall temperature of less than 192 ° C. With the cooling system ( 9 ), the heat of desublimation is removed from the fluidized bed ( 3 ) via the heat exchanger ( 10 ) and the fluidized bed ( 3 ) is kept at a constant temperature. The level control ( 11 ) ensures constant bed height ( 12 ) of the fluidized bed ( 3 ) above the inlet pipe ( 7 ). If the bed height ( 12 ) rises slightly above the target height by desublimating aluminum chloride vapor from the gas mixture ( 6 ) in the fluidized bed ( 3 ), the level control ( 11 ) switches on the screw ( 13 ) for the product discharge ( 14 ) until the bed height ( 12 ) has dropped to the target height. The exhaust gas ( 15 ) of the gas mixture ( 6 ) and fluidizing gas ( 4 ), which still contains traces of aluminum chloride and, for example, residual chlorine from a chlorination reactor, is cleaned in a subsequent wash.

Examples 1 and 2

In a desublimator described above, an aluminum chloride-containing Gas mixture containing 8.7 or 12.3 vol .-% aluminum chloride introduced. The fluidized bed made of aluminum chloride particles with 2.5 Nm³ / h fluidizing gas kept in swirling condition.

The other test parameters can be found in the following table.  

table

In both experiments, there was no pressure loss at the inlet pipe. The pressure loss of the pressure-effective bed height ( 12 ) above the end of the inlet pipe ( 7 ) changes in proportion to the set effective bed height ( 12 ) of 310 or 280 mm by 4 mbar and only reaches 44 (example 1) or 40 mbar (example 2 ).

The aluminum chloride vapor from the gas mixture ( 6 ) desublimates trouble-free in the fluidized bed ( 3 ) under the operating conditions used.

With a throughput of 1.55 (example 1) or 1.48 kg (example 2) Aluminum chloride per hour were in 5.3 and 5.1 hours of operation 7.84 and 7.91 kg aluminum chloride produced. The generated Aluminum chloride consisted of spherical good in both examples free-flowing particles with bulk density approx. 1.6 kg / l and diameters in Range about 0.1-0.9 mm.

Claims (1)

Process for the desublimation of vaporous aluminum chloride contained in a gas mixture by introducing the gas mixture into a bed of aluminum chloride particles kept in a swirling state by a fluidizing gas and condensation of the vaporous aluminum chloride on the fluidizing particles with deduction of the heat of desublimation from the fluidized bed, characterized in that that the gas mixture containing vaporous aluminum chloride is introduced into the bed at an angle of 20 to 70 °, in particular 40 to 50 °, measured against the direction of flow of the fluidizing gas, the feed temperature of the gas mixture being below the triple point temperature of the aluminum chloride.