Purification of caustic soda

Details Purification of caustic soda Purification of caustic soda

1998-03-13

2000-09-05

Nguyen, Ngoc-Yen

Chemistry: physical processes

Physical processes

Crystallization

23301, 423641, 423184, C01D 130

Patent

active

061136573

ABSTRACT:
In a process for preparing crystalline NaOH.3.5H.sub.2 O, NaOH.3.5H.sub.2 O is allowed to crystallize from an aqueous sodium hydroxide solution which contains sodium chloride and is saturated in respect of NaOH.3.5H.sub.2 O and the crystals formed are separated from the solution using a mechanical solid/liquid separation apparatus, wherein the solid/liquid separation is carried out under conditions under which the crystalline NaOH.3.5H.sub.2 O is freed sufficiently of residual solution adhering to the surface for the sodium chloride content of the crystalline NaOH.3.5H.sub.2 O obtained to be less than 100 mg per kg. The crystalline NaOH.3.5H.sub.2 O is subjected to an additional purification step, which may include the at least superficial melting or the at least superficial dissolution of the crystals, in combination with a solid/liquid separation step. The additional purification step. The additional purification step comprises washing the crystalline NaOH.3.5H.sub.2 O separated off.

REFERENCES:
patent: Re30411 (1980-10-01), Nakaya et al.
patent: 3922154 (1975-11-01), Kawasaki et al.
patent: 3983215 (1976-09-01), Hirata et al.
patent: 4676971 (1987-06-01), Cooper et al.

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