Analysis of Nucleation Rate Measurements in Precipitation Processes

Abstract

For precipitation processes, measurement of the nucleation rate as a function of supersaturation is not so easy because the formation of the precipitate is fast and often hard to control due to the high supersaturation. For a number of studies on both ionic and molecular precipitating compounds, the experimental methods are discussed. From the experimentally determined nucleation rates, the probable nucleation mechanism, homogeneous or heterogeneous, is derived and compared to the theoretically expected mechanism. For all ionic compounds and for one molecular compound considered in this work, theoretically homogeneous nucleation is achievable. However, only for two ionic compounds, barium sulfate and boehmite, the measurements possibly indicated a homogeneous nucleation mechanism. For the other studies, including all molecular compounds, a heterogeneous mechanism was more likely. The difference between a theoretically expected and experimentally observed mechanism may be explained by not only the use of less suitable experimental methods and measurement techniques but also by secondary processes, such as agglomeration and transformation, taking place in the precipitated suspension. On the basis of these findings, an experimental procedure is suggested to standardize and to improve nucleation rate measurements in precipitation.

In situ WAXS synchrotron radiation study on particle formation of precipitated barium sulfate

“…A similar comparison of measured nucleation rates, not only for barium sulfate, was made by Roelands et al 26 Furthermore, Roelands discusses the fact that the use of concentration-based (S c ) instead of activity-based (S a ) supersaturations will lead to different slopes in the nucleation data fits, resulting in different values for the interfacial energy. With the activity-based supersaturation model used in this study, Roelands's thesis can not be supported by the authors.…”

Modelling and Simulation of Particle Size Distribution of Precipitates in Continuous Tubular Crystallizers

“…Applying the standard method of moments for Eq. (14), we obtain the system of moment equations However, the system of ordinary differential equations (13) and (18), because of the size-dependent agglomeration kernel is not closed so that it has to be closed by means of some closure method [7][8][9][10][11][12][13][14][15][16][17]. Here, we apply the quadrature method of moments as presented in [15][16][17].…”

“…Micromixers of different types, such as impinging jet mixers [5,6], vortex-type mixers [7,8] and Y-mixers [9,10] are often used in controlled reaction and anti-solvent precipitation which ensure fast and good mixing of reactant solutions and may produce precipitates with desired particle size distributions [2,11]. Micromixers, not depending on geometries, usually are combined with tubular reactors ensuring the subsequent plug flow transport of the crystalline suspension.…”

Formates for green catalytic reductions via CO2 hydrogenation, mediated by magnetically recoverable catalysts

“…As a matter of fact, both Ru and Pd appears to be homogeneously distributed on the granules surface. This is likely due to the faster precipitation rate on the granules respect to the solution, because of the nucleation effect of the support [26].…”