Effect of calcium based additives on the sodium bicarbonate crystallization in a MSMPR reactor

The objective of this work was to study the impact of calcium ions addition on the crystallization of sodium bicarbonate during the reaction of sodium carbonate with carbon dioxide in aqueous solutions. A continuous MSMPR (Mixed Suspension Mixed Product Removal) reactor for the production of sodium bicarbonate was developed, built and tested at pilot scale. This experimental set-up was used to study the impact of process parameters and the effect of calcium based additives on the quality of the NaHCO3 crystals obtained. The nucleation and crystal growth rates were determined from the experimental population density distribution when the steady state was reached. Experiments have firstly shown that the addition of calcium ions greatly reduced the nucleation rate. In contrast, the addition of calcium ions had little impact on crystal growth rate in the temperature range between 70 °C and 80 °C.

Experiments in a continuous MSMPR reactor show that the use of calcium based additives greatly influences the morphology: NaHCO3 crystals are almost spheroidal compared to thin elongated needles without calcium ions. Also, nucleation rate without additive is sensibly higher while the crystal growth rate remains almost the same.Figure optionsDownload as PowerPoint slide