Abstract:
This is an experimental investigation to find out yield of caustic soda in causticization
reaction for industrial application. Commercial and analytical grades of sodium carbonate
and lime were used to carry out the reaction. Industrially single stage causticization is
used to produce caustic soda and theoretical yield cannot be achieved by single stage
causticization. To increase conversion, thc reactions were carried out in two and three
stages. Two stage causticization was found to be good enough to achieve the maximum
conversion for the concentration of sodium carbonate used in this work.
The reaction was carried out under established conditions; at 90°C and at atmospheric
pressure. The optimum time to carry out the reaction was 2.5 hours. In the selected two
stage causticization process, first stage was carried out keeping lime as limiting reactant
while the second stage was performed with excess lime. The first stage inlet composition
of the reactants was 10.22% Na2COJ, 1.15% NaOH, 6.42% Ca(OHh while that for the
second stage was 1.62% Na2COJ, 8.6% NaOH, 1.7% Ca(OHh. The filtrates from the
washing of calcium carbonate were used to prepare all solutions for reactions.
The conversion of sodium carbonate from first stage was 85.64-86.72% and 87.6-88.1 for
analytical grade and commercial grade reactants respectively. The overall conversions of
sodium carbonate for both grades were 93 to 94% in two stage causticization. Calcium
oxide conversion from first stage was about 94.8-95.2% and 97-97.5% for analytical
grade and commercial grade reactants respectively.
The byproduct calcium carbonate obtained from the process was very pure and it was
comparable with the commercially available precipitated calcium carbonate produced
from carbonation method. The byproduct calcium carbonate contained 98.3% and 96.67%
calcium carbonate by weight for analytical and commercial grades respectively. It's
crystal structure was calcite.
