Influence of Gassing Crystallization Parameters on Induction Time and Crystal Size Distribution

Gassing in combination with linear cooling profiles is an innovative technology to induce nucleation and control product properties. Previous work found that among gassing parameters like gassing supersaturation, gassing duration, and gas volume flow, gassing supersaturation has an effect on product properties only. This paper investigates why gassing duration and volume flow cannot be used to control product properties. Therefore, the influence of gassing parameters on induction time and final crystal size distributions were evaluated. Experiments were performed using succinic acid/water as model system in a 1 L crystallizer. Compared to normal cooling crystallization, induction time could be reduced by about 60 min by gassing. The difference in the specific bubble surface areas during gassing with the gas volume flows applied was too low to create an effect on the amount of nuclei induced and thus on induction time. Only gassing at different supersaturations resulted in different amounts of nuclei induced and thus affected induction time and crystal size distributions. Varying gassing duration did not change induction time, indicating that nuclei were induced at the beginning of the gassing period only.