(319f) Evaporative Crystallization of Sodium Sulfate Dicarbonate

Crystallization of sodium sulfate dicarbonate (~2Na₂CO₃•Na₂SO₄) is known to be a primary contributor to fouling heat-transfer equipment in spent-liquor evaporators used in the pulp and paper industry [1]. Therefore, understanding the conditions leading to formation and the in-process stability of this double salt and the related burkeite salt is crucial to the elimination or reduction of industrial problems. This poster summarizes a recently-completed project [2, 3], in which double salts were generated in a batch crystallizer at near-industrial process conditions. X-ray diffraction, calorimetry, and microscopic observation were used to investigate the stability of the salts to in-process aging, isolation and storage, and exposure to high temperature. The results verify that sodium sulfate dicarbonate exists as a unique phase in this system and remains stable at process conditions. The existence of sodium sulfate dicarbonate in industrial equipment deposits has recently been verified [4]. Microscopic observation of crystals under polarized light revealed two apparent growth habits of sodium sulfate dicarbonate crystals, monoaxial rods that tend to form 10-100µm agglomerates and 20-50µm hexagonal-dipyramidal structures [2, 3]. Investigation of the interaction of the two crystal shapes with heat-transfer surfaces may provide an important key to resolving sodium salt fouling problems in spent-liquor evaporators.

References

1. Frederick, W. J., Jr.; Shi, B.; Euhus, D. D.; Rousseau, R. W. Crystallization and control of sodium salt scales in black liquor concentrators. TAPPI J. 2004, 3(6), 7-13.

2. Bayuadri, C., Stability of Sodium Sulfate Dicarbonate (~2Na₂CO₃•Na₂SO₄) Crystals. M.S. Thesis, Georgia Institute of Technology, 2006.

3. Bayuadri, C.; Verrill, C. L.; Rousseau, R. W. Stability of sodium sulfate dicarbonate(~2Na₂CO₃•Na₂SO₄) crystals obtained from evaporation of aqueous solutions of Na₂CO₃ and Na₂SO₄, Ind. Eng. Chem. Res. 2006, accepted for publication August 15, 2006.

4. Bayuadri, C.; Verrill, C. L.; Rousseau, R. W. Stability of sodium sulfate dicarbonate in black liquor concentrators. Paper 37-2 at TAPPI Engineering, Pulping, and Environmental Conference, Atlanta, GA (November 6-8, 2006).