US2392235A - Process for the manufacture of alkali hydroxides and apparatus for carrying out reactions - Google Patents

Description

Jan. 1, 1946. G. E. EDWARDS 2,392,235

PROCESS FOR THE MANUFACTURE OF ALKALI HYDROXIDES AND APPARATUS FOR CARRYING OUT REACTIONS Filed July 9, 1941 INVENTOR. GEORGE ERNEST EDWARDS,

BY'K y Patented Jan. 1,

PROCESS FOR THE MANUFACTURE OF AL- KALI HYDROXIDES AND APPARATUS FOR I CARRYING OUT REACTIONS George Ernest Edwards, Runcorn, England, as-,

signer to Imperial Chemical Industries limited, a corporation of Great 1 Application July 9, 1941, sci-a1 No. 401,686

In Great Britain August 28, 1940 11 Claims. I (CI. 23-48!) v This invention relates to improvements in processes and apparatus for carrying out reactions involving liquid amalgams, that is to say, solutions or liquid alloys of metals in mercury; 1 and especially for carrying out reactions between liquid alkali metal amalgams and aqueous solutions.

Various processes are known in which alkali metal amalgams are treated with aqueous solutions so as to cause the alkali metal in the amalgam to react with the solution. Thus amalgams may be used in this way for reducing aqueous solution of organic compounds, for reducing sulphites to'hydrosulphites, and for reducing alkali metal polysulphides to sulphides. One type of apparatus used for contacting a liquid amalgam with a solution comprises a trough having a slightly sloping bottom over which the amalgam flows either co-current or counter-current to the aqueous solution. Such an apparatus enables the reaction to be carried ing from the said upper edge at least down to the level of the amalgam in the trough on the one hand, and on the other hand .downwards along out efficiently but has the disadvantage that it occupies a large floor space in comparison with its output, and for .this reason many attempts have been made to devise an apparatus in which the flow of amalgam is s bstantially vertical; thus it has been proposed (so flow the amalgamdown vertical sheets or hands of a. metal such.

as iron, immersed inthe'aqueous-solution. 1 with such arrangements, however, difllculties have been experienced in maintaining an even flow l of amalgam to the supporting surfaces; slight irregularities in the supply. from point to point,

the supporting surface each to the same level below that of the amalgam in the trough.

By this means, the rate at which amalgam travels along the several passages is determined by the difference in hydrostatichead between the level at which these passagesterminate on the supporting surface, and the level of the amalgem in the trough. Once the formerlevel has been fixed, as will be done when the apparatus for carrying out the process is setup, the head for tageously created by making use of the capillary attraction between the amalgam and adjacent surfaces of metal members of a small cross-section. e. g., of metal wires or strips. ber of amalgamated wires or strips may be arranged over the edge of the supporting surface and of the trough and the amalgam level in the trough adjusted to be high enoughfor the amal gam to rise between the wires as the result of surface tension to the edge of the trough and to flow thence down between the adjacent wires to output vi and efliciency.- Such diiilculties have I been largely responsible for the fact that no vertical apparatus of this yp has achieved commercial success in spite of the advantages which it would possess in'respect of saving of mercury, economy of floor space and compactness of si n. I

1 According to the present invention in carrying out reactions involving liquid amalgams in which amalgam is caused to flow downwards over a vertical or steeply sloping supporting surface wetted by the amalgam, irregularities in thesupply of amalgam thereto are largely obviated by siphon- .18- the liquid amalgam over the upper edge of the supporting surface. Capillary attraction will then maintain acoating of amalgam between adiacent wires or strips and enable amalgam to travel under the influence of the hydrostatic head.

to the supporting surface. Advantageously, a plurality of amalgamated wires are provided in close proximity to each other and to an amalgamated metal surface, whereby capillary attraction 1 way.

will cause amalgam tobe held between adjacent wires-and between the wires and the metal sur- I face and provide the necessary passage in that es-., water) a supporting surface the liquid With'such an arrangement a greater voladjacent surfaces.

gain extending downwards in the said tank, -a trough having one edge substantially coincident with the upper edge ofthe said surface,- means for supplying liquid amalgam to the trough, means for regulating the level of amalgam in the trough, means for maintaining a reactive fluid in contact with the said surface, capillary channels for transferring amalgam from the trough to the said surface formed by a plurality of amalgamated metal members of small cross section, disposed at intervals along the said edge of the trough and extending on the one hand down into the trough and on the other hand down each to substantially the same level on the supporting surface below the level at which the amalgam in the trough is maintained. Suitably the members are wires or tapes. They may be placed sufliciently close together for the spaces between adjacent members to form the capillary channels; advan- 2o formed between the members and the said sur-f convex curve over the edge of the trough. The 5' height of the top of this curve above the level of the amalgam in the trough should not exceed the distance up which the amalgam can be drawn by capillary attraction between two adjacent surfaces of the metal used to make the feeding device and this will depend on the distance between With very small separation the distance will be large, but then because of frictional forces the rate of flow of the amalgam tends to become too small for practical purposes. Using amalgamated iron, the height of the curve above the level of the amalgam should not be more than about one-fourth inch. Thus-in one form of the invention the apparatus comprises a deep tank having near the top maintained in the trough. By adjusting this weir the level can be altered to any. suitableposition.

part of the surface of theiron sheet. Suitably wires are used which are, e. g., 0.1 to 0.05 inch in diameter and are spaced apart by a distance I of the same order. The narrow spaces formed 5 between the plane surfaces of the trough or iron sheet and the cylindrical surfaces of the wires then act as capillaries up which the amalgam will be drawn when it is supplied to the trough up to a suitable level. The sheet is suitably supported with the amalgam. An outlet for the reacted solution is also provided in the upper part of the tank, preferably above the level of the amalgam tro'ugh.. a

If desired, a number of troughs can be arranged in parallel close to .each other in the same apparatus, each trough having a corresponding metal sheet and set of wires and being provided with means for supplying amalgam. In

this way a compact apparatus with a comparatively large capacity is obtained.

Priorto putting the apparatus into operation the surfaces of the iron sheet and wires are thoroughly cleaned and amalgamated by any suitable means.

In usuing the apparatus the circulation of aqueous solution through the tank is set up and amalgam is delivered to the trough until the level of the amalgam is not more than one-fourth inch below the lower edge ofthe trough. It is then drawn by capillary attraction between the wires and the amalgamated iron surfaces and thus is delivered to the downwardly extending.

surface of the iron sheet where it has ample opportunity to react with the aqueous solution during its passage to the bottom of the, sheet.- The supply of amalgam is maintained at such-a rate that denudation of the mercury is substantially complete by the time it has travelled to the bottom of the tank. In practice it is found that a considerable variation in the .rate of flow of the amalgam is possible while still maintaining a suitable level in the trough, and thusno difficulties. are encountered in settingup a flow which enables denudation to be substantially complete when the denuded amalgam reaches the bottomof the tank and at the same timemain- One side of the trough is'preferably higher than the other to prevent amalgam seeping up over it,

and from the outside of the lower edge or lip an iron sheet of width approximately equal to the length of the trough extends downwards to the lower part of the tank to form the, surface onthe other side they lie closely along the upper 75 A. number of iron wires tains a suitablelevel of amalgam.

. In the accompanying drawing there is shown be more readily seen; for the sake of simplicity only a few or the wires have been shown in position and .the weir and means for supplying liquid amalgam to the trough and for regulating its level have been omitted. The tank and the lower part of the iron. sheet have also been omitted for the sake of simplicity.

In this diagram,- the trough has a'forward side 2 which is sloped inwards to form a' sloping face 3, the thickness 'of' this'sloping side of the trough forming a second sloping face 4 at right angles to it. The rear side 5 of the trough extends ver tically upwards higher than the edge formed by.

.- the join or faces-3 and 4. From thelower edge of face v3 a steeply inclined iron sheet 8 extends downwards into the reaction tank (not shown).

1 (a feworly are shown) i escapes equal to their diameter, parallel to the lines of greatest slope of sheet 8, and faces 3 and l touching these surfaces, they are kept in position by a retaining member 8. The ends of the wires within the trough are approximately at the lower edge of face I, and the second endof each wire is at the same level on sheet I, which level is below that of the lower edge of face I. i

In operation the faces 3 and l and sheet- 8 are' amalgamated, and liquid amalgam is supplied to trough I so as to maintain th surface 8 at such a distance below the loin-of faces 3 and! that having a maintained level and then to flow downwardly in open closely adjacent paths longer than the rising paths onto a continuous receiving surface arranged for gravity flow.

' 3. An apparatus for feeding a liquid to a reaction zone comprising a trough adapted to contain a liquid at a maintained level therein, .a surthe amalgam can rise by capillary attraction in the narrow passages between the wires I and face 4 to the join. Having reached this level, the amalgam will flow down the narrow passages between wires .1 and face 3, the wires I and sheet 8, and the diflerence in hydrostatic head between the ends of wires 1 on sheet 6 and the i'ree surface 9 of the amalgam in the trough will ensure the continuous flow of amalgam along these passages. The hydrostatic head is the same for all the wires and thus an equal supply of amalgam is delivered to the sheet 6 from each of them,

, and thus an equal supply along the whole of the width of the sheet. 1

Although in the above description the manufacture of a particular product has not been mentioned it will be realised that the methods may be applied to-any suitable-reaction. Thus the method and apparatus may very conveniently :be applied to the manufactured alkali metalhydroxides by reacting a liquid alkali metal amalgam-with water, or to the manufacture of alkali metal sulphides by reacting an alkali metal amalgam with a solution of the corresponding alkali metal polysulphide; similarly aqueous solutions of organic compounds may be reduced, or sulphites may be reduced to the. corresponding hydrosulphites.

In my copending applicationSerial No. 401,687, filed July 9, 1941, there is described a process and apparatus for carrying out reactions involving a liquid alkali metal amalgam with an aqueous liquid, by allowing the amalgam to flow down the surfaces of a plurality of spaced downwardly extending metal members of small cross-section;

'. advantageously the amalgam is fed to the members from a vessel, e.. g., a trough, over one edge of which the members pass into the amalgam so that capillary channels for the amalgam are formed between adjacent members and between adjacent members and the sides of the trough, along which amalgam can be fed from the vesselto the downwardly extending members. The present application is primarily concerned with the method of feeding the amalgam from the 'capillary ch'annels disposed side by' side and closely spaced laterally from each other, and dellvering' the amalgam from said channels to a receiving surface arranged for gravity flow.

, 2. The process of submitting a liquid amalgam to reaction conditions, which comprises causing it to rise by capillary action in a plurality of closely adjacent openpaths from a body thereof face wettable by the liquid having an upper edge near said trough and extending downwardly into the reaction zone, and a plurality of independent capillary passages uniformly spaced across said edge and leading from below said level upwardly over said edge and downwardly onto said surface.

4. An apparatus as defined in claim 3 wherein said capillary passages are formed by a plurality of amalgamated metal members of relatively small cross section disposed in substantially closely lat erally spaced relationship throughout their effective length. v I r 5. An apparatus for feeding a liquid to a re-, action zone comprising a trough having a side terminating upwardly in a horizontal edge, a plurality of membersextending upwardly from said trough over said edge and downwardly outside the trough,'and a continuous surface' in con tact with the said downwardly extending portions of said members and itself extending downwards into the reaction zone, said members being of such length, small cross-sectional area and relationship that liquid will be caused to flow between adiacent members from a maintained level in said trough onto said surface. for continued flow thereon.

as 6. An apparatus for feeding a liquid to a reaction zone comprising 'a trough, a portion thereof which defines an upper horizontal edge of said trough forming part of a continuous surface structure extending upwardly from within said trough 40 over said horizontal upper edge and downwardly therefrom, said surface being prolonged downwardly within said reaction zone, a plurality of members lying on said surface extending parallel to each other from within said trough over said edge'and terminating on the downward extension thereof, said members and said surface being wettable by the'liquid and said members being of such length, small cross-seetiona1 area, and relationship that liquid will flow from a maintained level in said trough onto said surface for continued gravity flow thereon.

7. An apparatus for feeding a liquid from an open vessel adapted to contain the same at a maintained level comprising a plurality of sideby-side elongated members of small cross-sectional area extending upwardly from below the said level in said vessel to a point above that level and then downwardly outside the vessel to below said level, said members being disposed closely together so as to" define capillary passages between them, a surface underlying said members and in contact therewith and extending downwardly to a reactionzone, said members and said surface being wettable by the liquid and the extent of said members above said level being such that capillary attraction will cause liquid to rise over the highest point thereof to flow by gravity along the downwardly extending portion thereof.

8. An apparatus for feeding a liquid-to a reaction zone comprising 'a trough adapted to containthe liquid at a maintainedlevel, said trough .having a portion'which defines an upper horizontal edge and forms part of a continuou surface extending upwardly from within'said trough over said edge and downwardly therefrom, said and terminatingon the downward portion of said -members above said level being such that capilsurface being prolonged downwardly into said reaction zone, a plurality of members lying on said surface extending parallel to each other from be-v i low the said level in said trough over said edge surface below the said level, said members being of such small cross-sectional area and in such adjacent relationship, and the extent of said lary action will cause liquid to rise between adia-' cent members over the highest point thereof to flow by gravity down said surface to the reaction zone.

9. An apparatus for feeding a liquid to a reaction zone comprising a trough having a portion which defines an upper horizontal edge of said trough and forms part of a continuous surface structure extending upwardly from within said trough over said horizontal edge and downwardly therefrom, said surface being prolonged downwardly within said reaction zone, means for maintaining the liquid in the trough at a predetermined levelbelow said edge, a plurality of members lying reactive fluid which comprises in combination a tank, the lower part of which constitutes a reaction zone, a trough in the upper part of the tank having a side terminatingupwardly in a horizontal edge, a plurality of members extendingupwardly from said trough over said edge and downwardly outside the trough, and a continuous surface in contact with the said downwardly extending portions of said members and itself extending v downwardly into the reaction zone, said members and said surface being wettable by the liquid and said members being ofsuch length, small cross-sectional area and relationship that'liquid r will flow between adjacent members from-a maintained level in said trough onto said surface for continued flow thereon. v

11. An apparatus for reacting a liquid with a reactive fluid comprising in combination a tank, the lower part of which constitutes the reaction zone, a trough in the upper part of the tank, a continuous surface extending upwardly from within said trough, across an edge of the trough and downwardly outside of the trough into said reaction zone, a plurality of members lying on said surface extending parallel to each other from within said trough and terminating on the downward extension of said surface, means for supplying liquid to the said trough, and means for maintaining the liquid therein at such a level that liquid will rise by capillary action along and be- GEORGE ERNEST EpwARns.

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