| 摘要 |
<p>Caustic soda is obtained by the electrolysis of the black liquor produced in the manufacture of paper pulp by the alkaline processes. The liquor is introduced into the primary compartment of a mercury cell, Fig. 1, and is decomposed, the sodium produced amalgamating with the mercury cathode, and the organic materials, such as lignin, being deposited at the anode. The electrolyte, after having had about 60-70 per cent of its soda content removed, passes through a separator to remove more of the lignin. The presence of the remaining soda keeps the cell resistance down and consequently increases the cell efficiency, Fig. 6 (not shown). The liquid from the separator is passed to the secondary compartment of the cell, wherein the regenerated caustic soda dissolves in it. Losses of soda may be made up by adding sodium hydroxide to the resulting digester liquor, but preferably by adding sodium carbonate to the black liquor immediately prior to electrolysis. Fig. 2 shows how the excess organic material may be removed from the electrolyte by hydrolysis and fermentation after it has been electrolysed until the liquor becomes acid. Black liquor may be supplied direct to the secondary compartment to regenerate the caustic soda. In <PICT:0580123/IV/1> <PICT:0580123/IV/2> a modification, Fig. 3 (not shown), about two-thirds of the soda is removed in a normal cycle and periodically the electrolysis is continued to obtain the optimum yield of soda, the effluent liquor being treated by hydrolysis and fermentation. These methods, described as applied to the "soda" process, may also be used with the "sulphate" process. The Specification as open to inspection under Sect. 91 also states that the electrolytic process may be carried out in diaphragm type cells and that some of the black liquor may be removed before electrolysis to be concentrated and incinerated to produce sodium carbonate which is fed back into the system. This subject-matter does not appear in the Specification as accepted.</p> |
