Byeongho Ahn

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Ahn

First Name

Byeongho

ORCID

0000-0002-4405-5041

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Publications1 - 6 of 6

Secondary Nucleation by Interparticle Energies. I. Thermodynamics
Bosetti, Luca; Ahn, Byeongho; Mazzotti, Marco (2022)
Crystal Growth & Design
Secondary nucleation, in the absence of attrition, is known to be dependent on external fields, such as contact forces, shear, or interparticle forces. In this contribution, the thermodynamic effect of the presence of the seed crystal surface on secondary nucleation is derived in the context of the classical nucleation theory. The Gibbs free energy for the formation of a cluster close to a seed crystal is calculated with the addition of interparticle energies, namely, van der Waals attractive forces and Born repulsive forces. This results in the stabilization of a subcritical cluster close to the seed surface that can become a secondary nucleus more easily than under homogeneous nucleation conditions. Far from the seed surface, the developed model is reduced to the homogeneous nucleation described by the classical nucleation theory. The crystallization of paracetamol from an ethanol solution is taken as a case study, and the stabilization effect, given by the presence of interparticle energies, can be observed at different values of supersaturation. Three key indicators have been defined and calculated to describe the intensity of the stabilization effect, two of which, namely, the distance from the seed surface where the stabilization is active and the enhancement factor for supersaturation, are used in Part II of this series to describe the kinetics of secondary nucleation by interparticle energies.
Secondary Nucleation by Interparticle Energies. II. Kinetics
Ahn, Byeongho; Bosetti, Luca; Mazzotti, Marco (2022)
Crystal Growth & Design
This work presents a mathematical model that describes growth, homogeneous nucleation, and secondary nucleation that is caused by interparticle interactions between seed crystals and molecular clusters in suspension. The model is developed by incorporating the role of interparticle energies into a kinetic rate equation model, which yields the time evolution of nucleus and seed crystal populations, as in a population balance equation model, and additionally that of subcritical molecular clusters, thus revealing an important role of each population in crystallization. Seeded batch crystallization at a constant temperature has been simulated to demonstrate that the interparticle interactions increase the concentration of the critical clusters by several orders of magnitude, thus causing secondary nucleation. This explains how secondary nucleation can occur at a low supersaturation that is insufficient to trigger primary nucleation. Moreover, a sensitivity analysis has shown that the intensity of the interparticle energies has a major effect on secondary nucleation, while its effective distance has a minor effect. Finally, the simulation results are qualitatively compared with experimental observations in the literature, thus showing that the model can identify operating conditions at which primary or secondary nucleation is more prone to occur, which can be used as a useful tool for process design.
Influence of Liquid Binder Dispersion on the Size of Spherical Agglomerates of Organic Compound
Ahn, Byeongho (2018)
The effect of the liquid binder dispersity on the size of spherical agglomerates is explored. Small primary crystals, exhibiting a needle-like habit, were prepared in a reproducible manner. The spherical agglomerates were produced by feeding the liquid binder through a capillary in various ways that affected the liquid binder dispersity. The size of the resultant agglomerates were measured by conducting the image analysis of their microscopic pictures. The results of the agglomeration experiments were further supported by the size measurement of the liquid binder droplets. The binder droplets were generated in the in-house flow channel that reproduced the flow conditions at the tip of the feeding capillary in the stirred reactor. By utilizing a high-speed camera, the droplet formation was monitored and the size of the droplets were also characterized. We demonstrate the correlation between the size of the spherical agglomerates and the size of the binder droplets by combining the understanding of the underlying agglomeration process and the examination of the droplet formation process.
Characterizing Mesoscopic Species Present in Solution and Modeling Their Roles in Crystallization Processes
Ahn, Byeongho (2022)
Crystallization usually occurs in two steps: nucleation (appearance of a crystalline phase) and growth (increase in the size of crystals). In both steps, solute molecules arrange into a highly ordered crystal lattice, thus enabling the separation and purification of solute molecules from the rest. Solute molecules in solution compose a mixture of monomers and molecular clusters. These clusters are typically mesoscopic (i.e., 10 nm to 1000 nm) species (mesospecies), and amorphous mesospecies often play a critical role in multistage crystallization pathways acting as nucleation precursors, heterogeneous nucleation sites, or even nucleation inhibitors. Despite the continuous advancement in knowledge of multistage crystallization pathways, the associated kinetics have been much less understood, because of a lack of suitable methodologies for modeling crystallization while accounting for the role of molecular clusters as well as due to the absence of a suitable technique to obtain the time-resolved concentration of amorphous and crystalline mesospecies. The purpose of this thesis is twofold. The first is to conceive and validate methods to account for the role of molecular clusters in modeling crystallization phenomena, focusing on the nucleation process. The second is to develop a technique for monitoring the concentration of amorphous and crystalline mesospecies in solution. The key accomplishments of this thesis are as follows: - A methodology that considers the effect of molecular cluster formation on the thermodynamic driving force for crystallization and, consequently, on crystallization kinetics has been developed and validated using both in silico and experimental data. - A kinetic rate equation model for describing the kinetics of growth, primary nucleation, and secondary nucleation caused by interparticle energies (SNIPE) has been developed. Here, SNIPE is a novel surface-induced secondary nucleation mechanism, which has been originally conceived and mathematically modeled in this thesis. - A nucleation rate model for describing the kinetics of SNIPE has been derived theoretically, verified numerically, and validated experimentally. Furthermore, the model's capability to describe time-resolved experimental data has been proven, while its goodness of fit and theoretical consistency has been assessed in comparison with those of two other, well-known secondary nucleation rate models. - A depolarized light sheet microscopy device to monitor the concentration of amorphous and crystalline mesospecies present in solution has been conceived and materialized. Using the device, the direct measurement of the crystal nucleation rate in a lab-scale stirred crystallizer has been achieved. In summary, the results presented in this thesis represent an essential step toward a better understanding and characterization of crystallization processes, particularly nucleation phenomena, where mesospecies play a crucial role.
Online Monitoring of the Concentrations of Amorphous and Crystalline Mesoscopic Species Present in Solution
Ahn, Byeongho; Chen, Michele; Mazzotti, Marco (2022)
Crystal Growth & Design
Despite the growing evidence for the existence of amorphous mesoscopic species in a solution and their crucial roles in crystallization, there has been the lack of a suitable method to measure the time-resolved concentrations of amorphous and crystalline mesospecies in a lab-scale stirred reactor. This has limited experimental investigations to understand the kinetics of amorphous and crystalline mesospecies formation in stirred solutions and made it challenging to measure the crystal nucleation rate directly. Here, we used depolarized light sheet microscopy to achieve time-resolved measurements of amorphous and crystalline mesospecies concentrations in solutions at varying temperatures. After demonstrating that the concentration measurement method is reasonably accurate, precise, and sensitive, we utilized this method to examine mesospecies formation both in a mixture of two miscible liquids and in an undersaturated solution of DL-valine, thus revealing the importance of a temperature change in the formation of metastable and amorphous mesospecies as well as the reproducibility of the measurements. Moreover, we used the presented method to monitor both mesospecies formation and crystal nucleation in DL-valine solutions at four different levels of supersaturation, while achieving the direct measurement of the crystal nucleation rates in stirred solutions. Our results show that, as expected, the inherent variability in nucleation originating from its stochastic nature reduces with increasing supersaturation, and the dependence of the measured nucleation rate on supersaturation is in reasonable agreement with that predicted by the classical nucleation theory.
Secondary Nucleation by Interparticle Energies. III. Nucleation Rate Model
Ahn, Byeongho; Bosetti, Luca; Mazzotti, Marco (2022)
Crystal Growth & Design
A nucleation rate model for describing the kinetics of secondary nucleation caused by interparticle energies (SNIPEs) is derived theoretically, verified numerically, and validated experimentally. The theoretical derivation reveals that the SNIPE mechanism can be viewed as enhanced primary nucleation, i.e., primary nucleation with a lower thermodynamic energy barrier (for nucleation) and a smaller critical nucleus size, both caused by the interparticle interactions and the associated energy between the surface of a seed crystal and a molecular cluster in solution, as shown in part I of this series. In the case of a sufficiently agitated suspension, the model depends on four parameters: two reflecting primary nucleation kinetics and the other two accounting for the intensity and effective spatial range of the interparticle interactions. As a numerical verification of the model, we show that the nucleation kinetics described by the SNIPE rate model is in quantitative agreement with those given by the kinetic rate equation model developed in part II of this series. A sensitivity analysis of the SNIPE rate model is conducted to present the effect of key model parameters on the nucleation kinetics. Moreover, the SNIPE rate model is validated by fitting the model to the time-resolved data of secondary nucleation experiments as well as to two other, well-known secondary nucleation rate models. Importantly, all of the estimated parameter values for the SNIPE model were consistent with the theoretical estimates, while some of the estimated parameter values for one of the well-known secondary nucleation models deviated from the corresponding theoretical values significantly.

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Byeongho Ahn

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