IE63079B1 - Process for condensing aluminium chloride - Google Patents

Abstract

A process in which the cold wall is the outer surface of vertical pipes closed at their lower end and attached to a tube plate at their upper end.

Description

PROCESS FOR CONDENSING ALUMINIUM CHLORIDE The present invention relates to a process for condensing anhydrous aluminium chloride.

Aluminium chloride is frequently employed as a catalyst in organic chemistry and also in the cosmetics industry. When being manufactured, aluminium chloride is obtained in the gaseous phase, possibly mixed with other products, and it is isolated by being condensed on a cold wall at ambient temperature. A crust of aluminium chloride is thus obtained, and it is detached from the wall by mechanical means such as vibrations or impacting the wall. The cold wall is simply the inner wall of a steel tank exposed to ambient air.

The crusts of aluminium chloride are ground to produce a product in the form of lumps which are of various shapes, the largest dimension of which lumps being less than 5 cm. The grinding operation produces dust, and it is necessary to screen the aluminium chloride and to recycle the fines. Japanese Patent Applications 34,988/70 and 3,989/70 and Japanese Application 42,243/70 describe a process for isolating aluminium chloride in the gaseous phase consisting in passing the gas over a wall maintained at 80 or 85’C, and then when the aluminium chloride has formed crystals, this wall is heated to 220°C in order to detach the aluminium chloride, which is recovered, in the course of their formation and their growth, these crystals frequently tend to stick together and to form a crust which has to be ground and screened.

These applications describe the condensation of aluminium chloride on planar walls under specific temperature conditions; or on the inner wall of a cylinder fitted with a scraper blade at the base in order to collect the aluminium chloride and to discharge it. In all these processes aluminium chloride is recovered in the form of agglomerates or plates which it is difficult to remove from the place where they have been produced. If no mechanical device is employed in order to reduce these agglomerates, there is a risk that removal will be obstructed.

Furthermore, in all these processes, the apparatus is subjected to thermal cycles which cause fatigue resulting in breaks.

A process has now been found, according to the present invention, which makes it possible to produce aluminium chloride which cannot form plates and which employs an apparatus which is much less sensitive to thermal stresses than the equipment previously employed.

According to the process of the present invention 1 aluminium chloride by itself or contained in a gaseous stream is condensed as a solid phase on the outside of substantially vertical tubes, which are closed at their lower end and which are fastened to one another by a tube plate at their upper end, the tubes being maintained at a temperature of 40° to 60°C while the aluminium chloride is being condensed and the said tubes being then heated in order that the aluminium chloride may part from the tubes.

This process applies to any gases containing aluminium chloride, and more particularly to those obtained during its manufacture.

In one of the stages of the manufacture of aluminium chloride, aluminium chloride is obtained in the form of a gas which is either pure or mixed with other gases which may be inert substances such as nitrogen or air or reaction residues such as carbon dioxide, carbon monoxide, chlorine or chlorinated products. It may be a stage in the manufacture of aluminium chloride as such, or a stage of a process during which aluminium chloride is prepared during the manufacture of aluminium.

The present invention will now be illustrated, merely by way of example, with reference to the accompanying Figure which illustrates, diagrammatically, a typical device which can be used to carry out the process. Vertical tubes (2) closed in their bottom part, are welded to a tube plate (4) in the top part and are arranged in a container (1) which is closed by a valve (3) in its bottom part. Gas containing aluminium chloride is introduced at (10) and the noncondensable materials are vented via pipe (11). A heat-transfer fluid is introduced at (12) and distributed by tubes (5) into each tube (2) and is then discharged via pipe (13). The gas containing aluminium chloride is brought into contact with the outer wall of substantially vertical tubes. These tubes are maintained at 40° to 60°C in order that the aluminium chloride may crystallize, and these tubes are then heated, for example by circulating a heat-transfer fluid in order to sublime the aluminium chloride in contact with the tube, the aluminium chloride becomes detached and is collected using gravity.

The substantially vertical tubes may be of any size, but it is preferable for the ratio of their height to their external diameter to be from 1:1 to 100:1 and advantageously from 2:1 to 50:1. These tubes may be made of any material provided that it can withstand aluminium chloride; common steel, stainless steel or a nickel-based alloy are preferably employed. It is also preferable that the outer surface of these tubes should be smooth. It is preferable for these tubes to be arranged in a container.

The inner walls of this container are preferably maintained at a sufficiently high temperature to prevent the deposition of aluminium chloride thereon. This container may be provided with a closure such as a valve in its bottom part. It will be appreciated that tubes of conical shape with their widest cross-section situated at the top part, on the tube plate side, for example, can also be employed.

When the gas containing aluminium chloride is introduced into this container, aluminium chloride deposits on the tubes and the noncondensable gases are preferably vented through an orifice other than that for the entry for the gases containing aluminium chloride.

The tube wall is maintained at a temperature of 40 to 60°C by means of a heat-transfer fluid. Any heattransfer fluid may be employed, such as a gas, an organic product, hot water or low-pressure steam.

When a metal wall is employed, the temperature of the fluid is very close to the wall temperature. In order * to adjust the wall temperature it then suffices to adjust the temperature of the heat-transfer fluid. The wall t temperature is maintained at 40° to 60°C. It is also preferable for the wall temperature to be kept constant during the condensation of aluminium chloride.

In these conditions, aluminium chloride condenses in the form of granules which are substantially conical in shape. The height of the cone is generally 0.5 to 5 cm and the ratio of the height to the base diameter is from 1:1 to 10:1. The apex of the cone is against the cold wall, the bases of the cones generally touch each other and the cones generally neither adhere nor agglomerate together.

The pressure of the gas containing aluminium chloride is of no importance, nor is the pressure in the container. This gas is almost always at atmospheric pressure or very close to it, and the condensation of aluminium chloride takes place at this pressure. As soon as aluminium chloride is in contact with the cold wall, it condenses. To recover the solid aluminium chloride, the wall temperature, previously cold, is raised in order that the aluminium chloride may liquefy or sublime, and this causes the solid to become detached owing to gravity.

Liquefaction or sublimation takes place, depending on * whether the pressure is above or below that of the triple point (2.3 atm abs). It is preferable that the solid be detached under the effect of sublimation. Heating of the wall for only a short instant is sufficient to detach the solid. In most cases, heating to 200° to 250° is applied.

In order to heat the wall, a heat-transfer fluid may be employed, which is heated to a sufficient temperature for the wall to be hot enough to liquefy or sublime the aluminium chloride. The heat-transfer fluid employed may be the same as that which heats the wall to 40 to 60°C but whose temperature can be changed by any known means; it is also possible to have a storage vessel of hot fluid and a storage vessel of cold fluid, it being possible for these two fluids to be identical or different, and caused to circulate alternatively against the wall.

While the wall is being heated in order to detach the aluminium chloride, the introduction of the gas containing aluminium chloride into the container may be interrupted in order to prevent loss of the product. It is preferable to heat the wall quickly in order not to heat all the solid.

During the heating which produces the separation of the aluminium chloride from the wall a little aluminium chloride may sublime; it is therefore advantageous to permit this aluminium chloride to deposit on a cold wall, for example in another container which is connected to the first. If a continuous gaseous stream containing aluminium chloride is to be processed, it is convenient to provide at least two containers, one having a cold wall, while the other is being heated in order to detach the aluminium chloride; and the functions of the containers are subsequently alternated. It is also possible to have any number of containers. Instead of a container in which the inner cold wall is employed to collect aluminium chloride, it is possible to have cold walls arranged in any manner in such containers or other volumes, or which are arranged in the passage of the gases containing aluminium chloride. It is also possible to have, in the same container, cold walls on which aluminium chloride crystallizes and hot walls with aluminium chloride which is being detached. An advantage of employing tubes or elongate members according to the present invention, which are fastened to a tube plate at only one of their ends, is that they are not subjected to differential expansions during the heat cycles.

The following Example further illustrates the present invention.

EXAMPLE; An apparatus as described in the Figure, having the following dimensions, is employed: - tube plate (4) diameter: 750 mm - 8 tubes (2) arranged uniformly spaced in a 210-mm square grid, and such that there are: . 2 tubes with an outer d i ameter of 88.9 and thick- ness of 3.2 mm, made of steel . 2 tubes with an outer d i ameter of 88.9 and thick- ness of 3.05 mm, made of Inconel 600 . 2 tubes with an outer d i ameter of 88.9 and th i ck- ness of 3.05 mm , made of Monel 400 . 2 tubes with an outer d i ameter of 88.9 and thick- ness of 4 mm , made of Uranus B6 - the working length of the tubes is 700 mm - the remaining parts of the device are made of steel - the cylindrical part and the conical part of the container (1) are maintained at 200°C the valve (3) is a straight-through valve, 0 200 mm.

Aluminium chloride is introduced through the pipe (10) at a rate of 30 kg/h for 6 hours. The wall temperature of the tubes (2) is maintained at 55°C by circulating heat-transfer fluid. The temperature of the heattransfer fluid is 50°C, measured at the pipe (13).

After 6 hours, the circuit is modified to heat the heat-transfer fluid to 260°C and to bring the wall to 190°C as rapidly as possible, in approximately 1 minute.

After approximately 1 minute, AICI3 falls off and is recovered below the tubes and isolated by a straightthrough valve of 0 = 200. 180 kg of AICI3 are obtained in the form of cones 30 to 35 mm in length, with an end Zi of 8 to 12 mm.

The detachment is complete after approximately 2 minutes, the heat-transfer fluid is readjusted to 50°C and is ready for the following cycle.

Claims (6)

1. Process for condensing aluminium chloride, which comprises condensing gaseous aluminium chloride as a solid phase on the outside of two or more substantially 5 vertical tubes which are closed at their lower end and which 5 are secured to one another by a tube plate at their upper end, the temperature of the tubes being maintained at 40° to 60°C while aluminium chloride is being condensed; and the said tubes are then heated so that the aluminium chloride detaches 10 therefrom. 10

2. Process according to claim 1 in which the ratio of height to external diameter of the tubes is from 2:1 to 50:1.

3. Process according to claim 1 or 2 in which 15 the aluminium chloride is detached from the tubes by 15 sublimation.

4. Process according to any one of the preceding claims in which the aluminium chloride to be condensed is in the form of a gas containing it. 20

5. Process according to claim 1 substantially 20 as described in the Example.

6. Aluminium chloride whenever condensed by a process as claimed in any one of the preceding claims.