US2392236A - Process for the manufacture of alkali hydroxides and apparatus for carrying out reactions - Google Patents

Description

1946- G. E. EDWARDS 2,392,236

PROCESS FOR THE MANUFACTURE OF ALKALI HYDROXIDES AND APPARATUS FOR CARRYING OUT REACTIONS Filed July 9, 1941 VINVENTOR. I ES T EDWARDS,

ATTOJE/V B R BY Patented Jan.- 1, 1946,

UNITED STATES? PATENT OFFICE PROCESS FOR rim MANUFACTURE or AL- KALI nrnaoxmas AND srrsna'rus F csnarmocu'r anac'rions George Ernest Edwards, Runcorn, England, as-

aignor to Imperial Chemical Industries Limited, a corporation of Great Britain Application July 9,1941, sci-n1 No. 401,681 In Great Britain August 28, 1940 13 Claims. (Cl. 23-184) This invention relates to an improved process j and apparatus for carrying out reactions involving liquid amalgams, that is, solutions or liquid alloys of metals (e. g. sodium) with mercury; and

more especially for the manufacture of alkali metal hydroxides.

It is well-known that the amalgams of alkali metals can be reacted with water or with aqueous solutions. An important process for the manufacture of caustic soda is based on the reaction of electrically produced sodium amalgam with water. Various types of apparatus have been proposed to carry out this reaction; thus it has been proposed to flow the amalgam down vertical sheets, bands or gauzes of a metal such as iron immersed in the water. with such arrangements, however,- diiliculties-have hitherto been experienced in avoiding irregularities in. the feed to the different parts of the band or sheet and in setting the upper edge of the supporting surface accurately level. Even if uniform initial distribution of amalgam on the surface is achieved, it I frequently happens'that dueto surface tension effects, the distribution may become unequal lower down the surface, leaving partsof the surface unwetted by the amalgam. As a result, the output and efilciency have been seriously affected. Hence no'vertical denuder of this' type has yet achieved commercial success in spite of the advantages which such denuders possess in respect of saving-of mercury, economy of floor space and maintaining the level of amalgam in the vessel such that the amalgam can rise in the said channels to the edge of the vessel, and thus pass to I the downwardly-extending surfaces of the amalgamated members. Alternatively, or, in addition, the members may pass into the vessel in close proximity to its sides, which latter are capable of being wetted bythe amalgam so thatcapillary.

v spaced members of small cross-section of a metal so ing at least to the level inside the trough at which 25 with the amalgam, means for withdrawing the capable of being wetted by the amalgam-extendthe amalgam is maintained, over the edge of the trough, and thence downwards into the lower part of the vessel, means for suppl in to the reaction vessel the aqueous medium to .be contacted treated aqueous medium, and means for withtrough over the edge ofwhich they pass and that side is capable of being wetted by the amalcompactness of design in comparison with those types employing an almost horizontal trough for contactingthe amalgam with the aqueous liquid.

drawing denuded amalgam. Preferably the members are in close proximity to the side of the gam.

In accordance with the present invention a number ofseparatepaths are provided by the narrow spaces between the amalgamated sur- The'vertical typewould also possess the advan faces of adjacent metal members in which the tage as regards conservation of heat when work- 1 ing at an elevated temperature.

According to the present invention, the above mentioned difllcuities are largely avoided or even entirely obviated by providing a process for reacting a liquid alkali metal amalgam with an aqueous liquid, e. g., water, or a dilute aqueous soluamalgam is retained by capillary attraction,

. which also ensures that the amalgam will not be diverted from one channel to the other, leaving part of the surfaces incompletely wetted as may 40 be, the case when vertical sheets or games of tlon .of an alkali metal hydroxide, in which the metal are usedfor the purpose. Moreover, irregularities in the feed, or inaccurate levelling of the trough will not seriously aflect the distribution amalgam is contacted with the aqueous'medium i of amalgam to 'thesupporting surfaces. In the by allowing it to flow down the surfaces of a plu-H preferred form of the invention capillary chan-c rallty of spaced vertical or steeply inclined amal- *nels a lsoeformed betweenlthe wires and the sides of the trough, thus increasing-the capacity "of the apparatus.-'

vganiated metal members of small cross-section,

e. g., iron wires or narrow strips, immersed'in the aqueous medium. Advantageously, the amal-- gum is fed to the amalgamated, metal members from a vessel, e. 8., a trough;

by arranging the members to pass over the edge-of the vessel into the amalgamltherein in close proximity to each other so as to-form channels in which theamalin parallel close to each other inthe sameapparstuaea n, r shbeins fitted with'a set of close; Sp ced wires dippin intoit; eachtrough may havea separate feed for amalgam, or all the troughs may befsupplied with amalgam fro m m can be y "P 17 mfl n, and .so common distributing device. In this way a If desired,a number-of troughs can be arranged pact apparatus with a comparatively large catrough is arranged parallel to the long sideof the rectangle, and within which trough is a horizonv tal bar adjustable in a vertical direction. In the lower part of the tank and in substantially :the

same vertical plane, as the trough is a second fixed horizontal bar. Amalgamated vertical iron wires pass beneath the upper bar, over the edges of the trough and round the lower bar, bein spaced apart from .each other by approximately their diameter, which suitably may be 01' the order of 0.1 or 0.05 inch. 'li'he spaces between successive wires thus formcapillary channels 'along which amalgam will be drawn. The wires may be separate, or one length of wire may be wound over 1 the trough and lower bar many times to form a plurality of members, the ends of the wire or wires being in either case fixed, e. 8., to the lower ing out the invention.

encountered in setting up a flow which both enables denudation to be, substantially complete when the-amalgam reaches the bottom of the tank and maintains a suitable level of amalgam in the trough.

The accompanying drawing illustrates a vertical transverse section of an apparatus for carry- In. this'drawing, the reactionvessel I, which is deep in comparison withits cross-section, has in its upper part a horizontal trough 2 maintained in position by supports 3. The trough has one side 4 with a lip 5 extending the length of the trough and projecting inwardly. and upwardly, the thickness of the lip forming a surface 6 over which wires pass, as will be explained hereinafter.

The rear side I of the trough is higher than lip 5, and thusamalgam in the trough cannot. seep over it. Inside the trough is a vertical bar It having its'lower edge belowthe level of lip 5. In the lower part of vessel I vertically below the trough are two rods 9 acting as spacer bars for the wire 8, and bar I0 vertically adjustable by bar. By means of the vertical adjustment of the upper bar the wires can be made sufficiently taut to steady them in position, and they can be bent downwards within the trough below the level of the amalgam therein. Between the sides of,v the tank and the vertical wires arecarbon blockseither in direct contact with the wires or separated from them by a short distance, and in electrical contact with them by means of internal or external connections.

Means are provided for feeding a liquid alkali metal amalgam to the trough through a regulating device from a stock tank or direct from the electrolytic cell in which it is made, and for withdrawing denuded amalgam from the bottom of the tank for return to the cell. A weir and overfiow may be provided for regulating the level of amalgam in the trough or alternatively this re gmeansof the screw thread and lock nuts II. Wire 8 which provides the downwardly extending paths for the amalgam has one end (not shown) fixed to one end of bar I II and is wound helix-wise around bar III and trough 2 so thateach turn passes under bar I0, over the edge of side I, under bar I5, over and in contact with surfaces 8, 5 and l, and then vertically downwards to pass again under bar I0 and so on. The

second end of the wire is fixed to the second end of bar II). The turns are spaced apart by ap-- proximately the diameter of the wire, so that extending downwards from face 4 are a large number of lengths of wire, the various spaces between adjacent ones constituting 1 separate paths for amalgam extending from. inside the trough, over 40 the lip 5, and thence downwards through the reulation may be achieved by a valve, a niveau'Tor equivalent means in the amalgam supply pipe. In the lower part of the tank an inlet pipe for water or caustic liquor is provided and slightlyabove the level of the trough .an outlet for the caustic liquor produced. Alternatively, when higher strength caustic liquor is required a circuit ineluding a pumping mechanism may be set up,

whereby the eflluent caustic liquor is returned to the-lower part of the tank, means being alsoprovided for bleeding off part of the caustic liquor leaving the tank, and for introducing to the lower part of the latter a corresponding amount of water. '-In many cases, howeventhe re-circulation system will not be necessary, for-a strong of reaction vessel I.

liquor can be obtained by one passage through the apparatus. For example, in the manufacture I of caustic soda a liquor containing 45% to 50% NaOH canbe obtained without recirculating.

In using this apparatus the tank is filled with water'or dilute caustic liquor and amalgam is delivered to the trough until the lowest part ofthe wires in it are covered, and the level or the amalgam is such that it is able to travel along the spaces between the amalgamated wires bent over the trough up to the edge of the latter and thence down the descending portions of the wires;-the

action vessel I 1 Reaction vessel I has an inlet I6 for water or dilute caustic alkali and an outlet I8 for denuded amalgam and the side of reaction vessel I is disposed a block of graphite I2 to promote the decomposition of the amalgam by the aqueous liquor; the block is fixed to the vessel I by bolts I3 and metal strips II, are provided in 800d electrical contact with bolts I3 and the. outside indirectly in electrical communication with the amalgam through bolts I3, strips I4, reaction vessel I, support 3 and-trough 2. Means; not shown, arealso provided for delivering amalgam to the trough 2 and for regulating the supply so as to maintain a suitable level in the trough.

In carrying out the process with the aid of I this apparatus, the surfaces 4', 5, 8 and the surfaces of wire 8 are amalgamated, water or dilute causticalkali is supplied to the vessel I so as to fill it up to the level ofoutlet I1, and amalgam is supplied to'the' trough up to somewhatabove supply of amalgam is then maintained at such a rate that denudation o! the amalgam is substantially completeby the time it has travelled to the bottom of the tank. In practice it is found that ,is possible while still-maintaining an operative, I

level in the trough, and thus no difliculties are to in eflect it is siphoned over the edge-of the trough.

a. considerable variation in the flow of amalgam the lower edge of face 6 of the lip 5. As the result of capillary attraction the amalgam is drawn up in the narrow channels between the flat surface 8 and the. rounded surfaces of the adjacent turns of the wire 8,'and thus reaches the join of faces 6 and 5. The amalgam then flows downwards still held by capillary attraction between adjacent turns of the wire, so that The graphite block is thusneath the trough 2.

In travelling down between the wires the amab gam is denuded by reaction with the aqueous caustic alkali in the vessel I, and on reaching the part of the wire curtain between the spacer bar l and the bottom bar In the denuded amalgam will fall from the wires to the bottom or the tank and can be drawn oil through exit II. The flow ct amalgam and of caustic alkali are regulated relative to one another so that optimum denudation of the amalgam is obtained while a concentrated liquor can be drawn oil at the caustic liquor outlet il.

It will be appreciated that various alterations may be made in the apparatus and in its mode of operation without departing from the spirit of the invention. Thus instead of having one wire 8 passing many times into trough 2 and un- 'der bar ill, a number of separate wires may be used,.one end of each being fixed to bar It,

and the other to bar It. On-the other hand,

both sides of trough 2 may be arranged to delive'r amalgam to wires passing over themdown into the tank.

Again, instead or in addition to graphite block it, a similar graphite block may be inserted on the other side of the wires to which amalgam is supplied, i. e., in the space immediately be- Although the invention has been described with reference to the production of caustic alkalies the apparatus may be used to carry out other processes for reacting liquid amalgams with aqueous liquids, e. g., for reducing aqueous solutions of organic compounds, for reducing -sul-. phites to hydrosulphites, or for reducing alkali metal polysulphide solutions to sulphide lutions. In such cases,,however, the carbon b ocks acting as depolarizing devices described in connection with that form of the invention illustrated in the accompanying drawing will not, in

general, be required. v In my related copending application SerlalNo.

401,686 of even date with this application there is described a process and apparatus for car-- rying out reactions involving liquid amalgams, in which the amalgam is fed to a downwardly extending supporting surface by siphoning the liquid amalgam over the upper edge of the sur' face from an adjacent trough containing a supply of the amalgam along a plurality of independent passages reaching from the amalgam supply to a'lower level on the supporting surfaces. The independent passages are advantageously capillary channels formed between ad jacent amalgamated surfaces or metal members of small cross section, or between such members and an adjacent amalgamated surface.

I claim:

1. The process action between a liquid amalgam and a reactive fluid, comprising the operation of causing liquid amalgam to now down continuous exposed capillary channels disposed side by side and close- -ly spaced laterally from each other, and bringing said reactive fluid into contact with the amalgam while flowing in said channels. 1

2. The process of reacting a liquid alkali metal amalgam and a reactive fluid selected from the group consistin or water andga dilute aqueous alkali metal hydroxide solution, which comprises submitting the amalgam to reaction conditions by causing it to flow down the surface of a pinor amalgamated metal members oi small cross section arranged side. by side and spaced 'meachotherlaterallywithsubstantiallyclear' messa es for carrying out continuous rein a body of the reactive fluid, whereby a large total surface of amalgam is exposed to the re-'- active fluid.

3. The process oi reacting a liquid alkali metal group consisting of water and 'a-dilute aqueous alkali metal hydroxide solution, which comprises submitting the amalgam to reaction conditions by in open closely adjacent paths longer than the rising paths and in continuation of the latter.

-5. The process of reacting a liquid amalgam with a reactive fluid, which comprises causin the amalgam to rise from a supply thereof by capillary action in a plurality of closely adjacent open paths and then to flow downwardly in open closely adjacent paths longer than the rising paths and in continuationo the latter, and contacting the amalgam with t e reactive iluid during its downward flow.

6. The process of reacting a liquid amalgam with a reactive fluid which comprises causing the amalgam to rise from a supply thereof by open paths and then to flow downwardly in open a closely adjacent paths in continuation of and longer than the rising paths in contact with the reactive fluid until the amalgam is substantially denuded. g

7. An apparatus 'ior carrying out a reaction between a liquid and a reaction fluid in a continuous manner, comprising a tank, an inlet at one level for supplying reactive fluid to the tank,

an outlet at a different level for removing reacted fluid from the tank, a curtain of members of small cross-section wettable by the liquid exoov tending downwardly in the tank between the two said levels, said members being disposed side by side and closely spaced laterally from each other to define therebetween capillary channels in which the liquid can be retained by surface 5 tension, and means for supplying the liquid to the top portionv of said curtain.

8; An apparatus for feeding a liquid to a reaction zone, comprising a trough having one side terminating upwardly in a horizontal edge, and 5 being adapted to contain the, liquid at a maintained level below the said edge, anda plurality of members of small cross-section wettable by the liquid disposed side by side in laterally spaced I relation to define capillary channels therebetween, which members extend from the .trough below the said level over the said edge and downwardly outside the trough to below the said'level. the extent of said members above said level being such that the liquid can rise by capillary action 7 between them and flow over said edge.

9. apparatus for reacting a liquid with a reactiv fluid, comprising a tank. an inlet at one level for supplying reactive fluid to the mm, an

passages therebetween and extending downwardsamalgam with a reactive fluid selected from the capillary action in a plurality of closely adjacent thereof. 7

' 11. An apparatus for feeding a liquid to a retion of said tank having one side terminating upwardly in-a horizontal edge and being adapted to contain the liquid at a maintained level below said edge, and a plurality of members of small cross-section wettable by the. liquid disposed sideby side in laterally spaced relation to define capillary channelstherebetween, which members extendirom the trough below the saidmembers being in such laterally spaced relation that capillary action will cause the liquid to rise over said horizontalqedge for gravity flow down and between the partsof the said members, within the tank.

- 12. An apparatus for feeding a liquid to, at

- reactive fluid comprising a tank adapted'to con maintained level, over the said edge, and 'downwardly to the lower part of the tank, the extentof said membersiabove the said maintained level being such that the liquid can rise byv capillary action between them and-flow'bvensaidedge;

- a ing from within said trough over the horizontal edge-anddownwardlyintothelower part oLthe 10. An apparatus for feedings. liquid from an a open vessel/adapted to contain the same at a maintained level, comprising a plurality of side by side elongated members. of small cross-sectional area wettable by the liquid and extending edge for gravity flow down and between the said members into the lower part of the tank.

upwardly from the vessel below the maintained level to a point above it and then downwardly outside the vessel to below said level, said mem-- bers being'disposed closely. together-so as to define capillary passages between them, and the extent of said members above said level being such that capillaryaction will cause the liquid to rise between said members to the highest point active fluid comprising a trough for the liquid having a horizontal edge, a tank below said trough adapted to contain the reactive fluid, a' plurality of separatemembers of small cross-- sectional area wettable by 'the' liquid leading from within said trough over the horizontal edge and downwardly into the tank, said plurality of said fluid; a troughior the liquid in theunper part of the tank having a horizontal edge. and a' plurality of separate. members of small cross-sectional area wettable by the liquid leadtank, said plurality of members, being in such laterally spaced: relation that, capillary action will cause the liquid to rise over said horizontal l3. apparatusior reading a liquid to a. reactive fluid'comprising a tank adapted to contain said fluid, a trough for the liquid in the upper part of the tank having a side portion wettable by the liquid terminating'upwardly in a horizontal edge, and aj'plurality of separate members of small cross-sectional area wettable by the liquid leading from within said trough over said horizontal edge, downwardly and in contact with said side portion, and thence into the lower part of the tank, said'members being GEORGE Emms'r nnwanns

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