M. Paleologou et al., ENHANCEMENT OF THE CURRENT EFFICIENCY FOR SODIUM-HYDROXIDE PRODUCTIONFROM SODIUM-SULFATE IN A 2-COMPARTMENT BIPOLAR MEMBRANE ELECTRODIALYSIS SYSTEM, Separation and purification technology, 11(3), 1997, pp. 159-171
Sodium sulphate, a by-product of chlorine dioxide generators and proba
bly of most totally chlorine free (TCF) pulp bleaching sequences, was
split into sodium hydroxide and sulphuric acid by using a two-compartm
ent bipolar membrane electrodialysis (BME) system employing WSI4010/10
30 bipolar membranes and Nafion417 cation-selective membranes. The cur
rent efficiency was enhanced by using the buffering effect of divalent
anions such as sulphate to reduce the free hydrogen ion concentration
in the feed compartment. In the optimized experiment, sodium hydroxid
e (1.08 M at 46 ml min(-1)) and sodium sesquisulphate (0.74 M at 68 ml
min(-1)) were produced at a current efficiency of 78% for the product
ion of both acid and base. The power requirement was 1986 k Wh t(-1) o
f sodium hydroxide at a current density of 142.9 mA cm(-2) and with an
effective membrane area of 728 cm(2). Under the conditions of this ex
periment, it was possible to extract 25% of the sodium content of sodi
um sulphate in the form of sodium hydroxide. (C) 1997 Elsevier Science
B.V.