Improvements in and relating to the production of highly-concentrated solutions of alkali hydroxide

摘要

PICT:0627767/III/1 In making concentrated solutions of alkali-metal hydroxides by decomposing alkali metal amalgams, the caustic alkali solution to be concentrated is passed through the compartments of a horizontal soda cell, the liquor following the upper wall of each compartment for the greater part of its length, the passage between the top of the cell or compartment and the top of the end partition of the compartment being so arranged that in addition to the caustic alkali solution, the water vapour produced and the hydrogen evolved are allowed to pass, and the hydrogen and water vapour entering the following compartment at its base and there bubbling through the solution, so that the heat produced or recovered in one compartment passes into the next. In one form of apparatus, the amalgam from brine cells enters a soda cell, at a high temperature, at head E by a tube 8 dipping into a hydraulic seal 9, overflows on to the base of the cell in contact with graphite grids 5 and, passing from one compartment to the next by hydraulic seals 3, arrives free from alkali metal in the last compartment A which is provided with heat exchange blades 4 and from which mercury is returned to the brine cells. The water necessary for the decomposition enters compartment A, absorbs heat from the mercury by means of the blades 4, and the steam thus formed, together with hydrogen evolved and water, pass into the next compartment B1 by partitions 1 and 2, this process being repeated in each succeeding compartment, in the last of p which hydrogen accumulates in a collecting dome 6 and is separated from alkali solution in a separator 11 of known type. Where the temperature in the brine cell is lower than that of the soda cell, the amalgam may be introduced not into the final compartment of the soda cell, but into another compartment at lower temperature; two cells can then be put in series, the mercury and liquor circulating co-currently and counter-currently in the first and second cells respectively, Fig. 2 (not shown), being a combination of two such cells. Specification 612,322 is referred to.