| 摘要 |
<p>1,218,821. Alkali metal carbonates. DYNAMIT NOBEL A.G. 26 Jan., 1968 [28 Jan., 1967], No. 4337/68. Heading C1A. Alkali metal carbonate is produced from alkali metal liquors containing alkali metal hydroxide, where the desired concentration of carbonate is greater than that of the hydroxide, by introducing the following to a cation exchange material in an ion exchanger: (i) the alkali metal liquor, whereby at least some of the alkali metal ions are adsorbed on the exchange material; (ii) successive fractions, of increasing concentration, of a first alkali metal carbonate solution; (iii) successive fractions of a second solution comprising alkali metal carbonate (in decreasing concentration) and bicarbonate (increasing concentration), the total concentration of carbonate and bicarbonate in each fraction being not less than that of the desired carbonate; (iv) fraction(s) of a third alkali metal bicarbonate, of total concentration below that of the product but of greater (at least double) bicarbonate ion concentration than the alkali metal ions in the product solution; (v) fraction(s) of a fourth solution of alkali metal bicarbonate, in decreasing concentrations; (vi) eluting the respective above solutions from the exchanger and collecting the desired fractions; and (vii) treating the effluent fractions of the third and fourth solutions with CO 2 to convert carbonate therein to bicarbonate, which bicarbonate may be used in subsequent cycles. The treatment with CO 2 is preferably at a pressure up to 2 atmospheres above that of the liquid in the exchanger. The ion exchanger preferably comprises a " very weakly acid cation exchanger " (pK of 7-11) and a " weakly acid cation exchanger " (pK of 4-7) downstream thereof, alkali metal ions being removed from the latter with aqueous CO 2 solution, the bicarbonate produced being added to the fractions of the third and fourth solutions. Various ion exchangers are referred to. The alkali metal liquor may comprise alkali metal hydroxide and an alkali metal salt; in examples the alkali metals are sodium and potassium respectively.</p> |
