DE1215662B - Device for the production of sodium dithionite from sodium amalgam and sulfur dioxide - Google Patents

Description

Apparatus for the production of sodium dithionite from sodium amalgam and sulfur dioxide It is known to produce sodium dithionite (trade name "hydrosulfite") from sodium in the form of amalgam and sulfur dioxide in aqueous solution according to the gross equation 2 Na + 2 S02 = Naß204 (1) to create.

It is also known that the reaction mechanism in aqueous solution in the sense of the equation 2 Na + 4 HSOJ = 2 Na- + S204 " + 2 SO," + 2 H20 (2) and that this reaction occurs within the range between the amalgam and the aqueous phase located boundary layer, the "diffusion layer" takes place.

It is also known that 1. for a sufficiently large amalgam-water interface, 2. for sufficient dilution of the amalgam and 3. for the presence of a sufficiently large amount of HSOJ in the interface, so that the reaction is possible completely within the meaning of the above equation (2) takes place and as little sodium as possible reacts with water to form NaOH and H2.

To achieve these operating conditions, several are already available Devices have been used, for example, a shallow stirring vessel is used with a paraboloidal arched bottom, in which one is buffered with sulphite Bisulfite solution using stirring paddles quickly over a slower rotating amalgam layer is set in rotation, the paddles a little into the amalgam layer immerse and so, by stripping off the diffusion layer, an intensive exchange of substances effect within the latter.

In another known device, a vertical spreading funnel is used or preferably a horizontally arranged cylinder is used within it the amalgam under the centrifugal effect of a rapidly rotating, centrally located Impeller forms a coherent liquid rotary cylinder, whose Inner surface the boundary or diffusion layer against the likewise circulating aqueous Phase represents.

Furthermore, through the German patent specification 941481 a device become known, in which the bisulfite solution buffered with sulfite in continuous Circulation by means of a pump through an approximately meter high, but narrow cross-section Amalgam layer is pushed through.

In another device again a beforehand is made to the required Measure of diluted amalgam in the form of the finest droplets continuously through a high, The tower filled with the buffered bisulfite solution was dropped as "mercury rain".

A method is also known according to which - with the exclusion of water or aqueous solution - amalgams of various metals with gases, including SO2, are brought into direct contact reactions within a tube made of mercury-wettable material, the amalgam-wetted inner surface of the tube by means of brushes or Scratches is kept open and free of reaction products, namely in that the aforementioned cleaning elements rotate at high speeds of, for example, 750 to 1000 revolutions per minute.

The invention now relates to a device for the production of sodium dithionite from sodium amalgain and sulfur dioxide in the presence of aqueous solutions containing sulfite and bisulfite, this device being characterized by a simplified structure; In addition, however, this device brings further advantages over the known, which can mainly be summarized in the following points: 1. The relative movement between the mercury and the aqueous phase is increased to a maximum in the immediate vicinity of the diffusion layer and so the mass transfer within the Diffusion layer intensified to such an extent that by far the best reaction yields are obtained with the same reaction load per unit area; 2. While the thickness of the mercury layer lying below the diffusion surface is 8 to 25 mm in the known devices, in the disk reactor forming the subject of the invention, two diffusion layers are formed from a mercury lamella of only 2 to 4 mm thick - one on each side of the lamella . educated; the amount of mercury required to generate a reaction surface of a certain size is therefore only a fraction of that of the other devices; 3. The aids required for the formation of the reaction layer and for the dilution of the amalgam are very simple and the required power requirement is very low compared to the known devices, namely the plate reactor and the droplet reactor.

4. The space and space requirements of the disk reactor are very small in relation to the other devices, and its simple construction - in contrast to the devices based on the action of centrifugal forces - does not set any limits to any increase in the generation capacity. Compared to the direct contact reaction between amalgam and gaseous SO in the absence of water, according to German patent specification 958 736 , the present invention has the main advantage that, according to the invention, ten times the amount of sodium per amalgam area unit can be achieved with the highest yield values.

The new device consists in principle of a horizontal one Reaction tube made of lined iron or plastic, in which one with washers occupied and provided with a drive rotor rotates slowly, such that the discs alternate the three stacked one on top of the other inside the tube Phases, namely the mercury, water and gas phase, happen.

The rotating discs consist of an electrically non-conductive, well water-wettable material, preferably made of absorbent ceramic material or such plastic, so that the disc surface when passing through the aqueous phase covers itself with a well-adhering lamella of liquid; with further rotary movement This aqueous, sulphite and bisulate gets into the circular disc The skin protrudes into the mercury phase, which contains the sodium, and thus forms a widespread one Diffusion layer, within which the reactants (HS03 'from the aqueous and Na from the amalgam phase) in the sense of equation (2) above Formation of S204 "respond.

The disk can additionally be provided with grooves, depressions, bores and the like in order to enlarge the surface.

As in-depth research has shown, it is beneficial to have the Providing discs with open pores, honeycombs or cavities, whose function it is is, more liquid per rotor revolution from the aqueous phase in the mercury sump to transport where the chemical conversion takes place.

According to the invention, the disc surface can be used, for example cover with a highly absorbent material, i.e. with an open-cell foam, Felt, deerskin or any other porous material. You can also use discs, which have larger cavities on the inside, which are created by drilling with the pane surface are connected.

By using numerous such disks, for example 4 to 10 mm thick, a large amalgam-water boundary layer is thus created within a relatively small space.

The discs are spaced apart from one another by means of rubber or plastic rings or plates, so that there are gaps 1 to 4 mm wide between them, and they are combined in packs of 5 to 10 pieces.

These disk packs connected to the rotor shaft in a suitable manner are separated from each other by wide gaps, the clear width of which is a multiple of the above-described spacing between disks.

Inside these wider gaps are strips of rubber or plastic, which contains the mercury located within this space during rotation in the sense of the rotational movement of the rotor from one side of the tubular Transport the housing to the other, then this same, to a higher level The amount of mercury that has built up through the gaps in the disk packets is transferred to the Side of the lower level flows back.

In such a way, therefore, is located within the reaction tube Mercury level caused a back and forth circulation in itself. In the course of this circulation of the mercury content, this is what happens in the electrolysis cell concentrated amalgam fed to the reactor by means of a distribution pipe diluted the required amount (about fifty times), whereby this diluted Amalgam the absorbed sodium then on its way back within the gaps of the package to the one brought into the mercury sump by the rotating disks gives off aqueous diffusion layer.

The invention is illustrated more clearly with the aid of the figures. It shows A b b. 1 shows an embodiment of the device according to the invention in a lateral section, A b b. 2 shows a plan view and a section along line II 'of A b b. 1, A b b. 3 shows a section through the rotor of A b b. 1 along the line II-II ', A b b. 4 shows a section through the rotor of A b b. 1 along the line III-III ', A b b. 5 a felt disk, top view on the left, cross section on the right, A b b. 6 a cavity disk, left center section parallel to the disk surface, right in cross section along section line 4-B.

The reaction tube 1 , lined with rubber or plastic or made of such a material, is provided with a rotor 2, which is set in slow rotary motion by a drive not shown in the figure.

This rotor carries on a shaft coated with rubber or plastic 3 disks 4, which are combined in individual packages of , for example, 5 to 10 pieces. Between the individual round disks of such a package there are spacer plates, for example 1 to 4 mm thick 5, and in the gaps between the individual packages there are transport members 6, the latter preferably being designed as three-ribbed stars. The disks of the rotor and the transport elements are threaded together with the spacer plates on guide rods7 and clamped to the shaft by means of a fixed disk.

A b b. 5 shows a felt disk made of plastic. The approximately 2 to 4 mm thick, suitably also made of plastic, felt or foam covering 14 soaks up with solution as it passes through the aqueous zone; If the disk then dips into the mercury sump below the aqueous phase during further rotation, part of the solution is pressed out of the felt under the increased pressure and thus the reaction-promoting liquid volume within the amalgam sump is increased.

In A b b. 6 shows a cavity disk. This plastic plate, which is expediently made of two parts, has a large number of cavities 15 on the inside, the side walls of which are pierced by a large number of small bores 16. Furthermore, gaps 17 are recessed in the plate edge, which also lead into the interior of the mutually separate cavities.

When passing through the aqueous zone, the cavities of the disc fill with liquid; if the cavity sector then reaches the area of the mercury sump as the disk continues to rotate, the mercury flows through the frontal gap 17 from below into the cavity and displaces the aqueous solution therefrom; reaction layers are thus already formed within the cavity when the two phases meet; the solution escaping from the numerous lateral bores then forms further diffusion layers on the disk surface within the mercury sump.

The concentrated amalgam formed in an electrolytic cell is fed to the mercury sump through a bored distribution pipe 8.

The sulfur dioxide required according to the gross equation (1) taking into account the partial reactions 2Na + 4NaHSO, = Na, S, 0, + 2Na, SO, + 21-1.0 (3) 2Na2S01 + 2S0, + 2H, 0 = 4NaHSO3 (4) becomes the gas space occupying the upper third of the reaction tube by means of a pipeline 9 provided with bores, according to A b b. 2, supplied.

The heat of reaction formed in the chemical process is expediently dissipated outside the reactor; for this purpose, the reaction solution is continuously circulated through a cooling device by means of a pump. In this case, the cooled solution emerging from the latter according to A b b. 1 and 2 fed to the apparatus via the spray tube 10 , while the excess liquid below the immersion weir 11, which determines the liquid level in the reaction tube, passes into a batch container and is returned from the same via an overflow 12 to the - not shown - pump and cooling device. The mercury excess corresponding to the continuous amalgam inflow drains from the device via the weir 13 , which determines the mercury content in the reactor, in order to start the cycle again after passing through the cell, loaded with sodium.

The question that can be asked is why disk packs and transport bags are to be provided alternately and why, for example, the disks are not simply distributed evenly over the entire length of the rotor, with approximately every second gap being equipped with narrow transport ribs. In the latter case, however, there would be no relative movement between the mercury lamella and the wetted disc wall in the gaps provided with ribs during the passage through the amalgam sump; However, it is precisely this relative movement that first brings about the intensive exchange of substances within the diffusion layer, which, according to point 3 of the introduction, must be achieved in the interest of a good reaction yield.

Claims (2)

Claims: 1. Device for the production of sodium dithionite from sodium amalgam and SO, in the presence of an aqueous solution containing bisulfite and sulfite in a rubber or plastic lined or made of plastic, closed on both sides, horizontally lying, with inlets and outlets provided for the amalgam for sulfur dioxide and for the aqueous solution tube, d a d u rch g e k s nz eichnet that within the same a slowly rotating rotor is arranged, one behind the other fixed in parallel with narrow gaps on a common shaft, circular discs made of electrically non-conductive, easily wettable material is composed. 2. Apparatus according to claim 1, characterized in that the rotor axis is arranged below the axis of the pipe jacket. 3. Apparatus according to claim 1 and 2, characterized in that the disks with grooves, depressions, holes or the like. Are provided for the purpose of enlarging the surface. 4. Apparatus according to claim 1 and 2, characterized in that the disc surface is covered with an absorbent felt or foam covering. 5. Apparatus according to claim 1 and 2, characterized in that a plurality of separate cavities are provided inside the discs, which are in communication with the outer environment of the disc through numerous small holes, bores or channels. 6. Apparatus according to claim 1 to 5, characterized in that the disks of the rotor are assembled into packages, the individual disks within a package are only about 1 to 5 mm apart, while in the many times wider gaps between the packages are radial Bars are built in which, when the rotor rotates, transport the mercury located within these gaps.