Crystal growth rates and secondary nucleation threshold for γ-dl-methionine in aqueous solution

The Secondary Nucleation Threshold (SNT) of γ-dl-methionine (dl-met) in aqueous solution was measured for the temperature range 10-61 °C. The width of the SNT is weakly temperature dependent with slightly smaller induction times at higher temperatures. Seeded batch crystallizations of γ-dl-met were performed isothermally at 10, 25, and 40 °C in an agitated batch crystallizer, and within the SNT region to avoid nucleation. The effect of the initial supersaturation and seed mass on crystal growth were also studied at 25 °C. The initial growth rate (during the first 20 min of the batch) is significantly higher than subsequent crystal growth, a phenomenon previously seen with other species. The measured growth rates are independent of seed mass, as expected, for the usable portion of the growth rate data. The growth rates were found to linearly depend on the relative supersaturation of the total dl-met in the system. The growth rate constants increase with increasing temperature and follow an Arrhenius relationship. The growth kinetics of the γ-dl-met will be used to study in order to begin characterization of the polymorphic transformations and the overall crystallization rate of dl-met.