Modeling and measurement of abraded particles

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Nowadays, it is common to analyze crystallization processes and crystalline products using two-dimensional image analysis. Various techniques exist but they are not fundamentally capable of capturing the full morphology of particles due to their limitation in two dimensions. This is particularly true when complex shapes, e.g., through agglomeration or broken crystals, occur. Here, an approach is presented in which potash alum crystals are sampled from a laboratory-scale reactor at six time points over the course of a crystallization process. Three-dimensional (3D) images of all crystals in the samples were obtained by microcomputed tomography and used for morphological characterization. The method directly yields volume and surface area distributions without the need for any assumption regarding particle morphology. Applying geometric crystal models allowed for a more detailed analysis of the crystals. In the example considered, it was shown that most crystals assumed nonideal shapes over the course of the process. The supporting model provides indication that the shapes approach ideality through face-independent crystal growth. Overall, more than 11 000 crystals were analyzed. In general, this work aims at demonstrating the potential of crystal analysis by means of microcomputed tomography and 3D image analysis.

Section: Introductionmentioning

confidence: 99%

Analysis of Nonideal Shape Evolution during Potash Alum Crystallization Using Microcomputed Tomography and Three-Dimensional Image Analysis

Schiele

Antoni

Meinhardt

et al. 2021

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“…In the literature, the effect of abrasion on crystal shape is studied. 6 Here, the effect of crystal growth on the shape of abraded crystals is studied, to advance the understanding of the interaction of crystal growth and abrasion.…”

Section: T H I S C O N T E N T Imentioning

confidence: 99%

“…More recently, the shape of crystals has attracted increasing attention. The shape of crystals is not only important to yield certain product features, , but it is also an important process parameter. − Crystal shape engineering ,− has emerged from the need to control the shape of crystals. Crystal shape is often described using a geometric characteristic, which is often a shape factor, such as aspect ratio. − There are also approaches in which another geometric measure, such as surface area, is used as a proxy for shape .…”

Section: Introductionmentioning

confidence: 99%

“…Crystallizers are often agitated to suspend crystals and to equalize concentration and temperature gradients. Agitation imposes mechanical stress on crystals, leading to attrition, abrasion, and breakage, which can result in nonideal crystal shapes. ,, We use the term attrition for damage events that are caused by the impact of crystals with reactor components, such as the stirrer. In contrast to breakage, the size of a crystal is largely preserved during attrition.…”

Section: Introductionmentioning

confidence: 99%

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Growth of Abraded Crystals Tracked in Three Dimensions

Schiele

Hupfer

Luxenburger

et al. 2021

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The interaction between crystal growth and abrasion is essential during crystallization. Although each of these phenomena has been independently studied in the literature in detail, their interaction is not well understood. Here, we present a method to track the growth of abraded potash alum crystals in three dimensions. The method is based on micro-computed tomography. This technique distinguishes between different growth domains in three dimensions and is used to track the growth of crystal faces and abraded regions. We observed how abraded regions grew faster than crystal faces. Therefore, growth leads to ideally facetted crystals. Further, growth rates in all directions were derived and used to parametrize a growth model. The model is able to describe the size and shape evolution of abraded potash alum crystals in three dimensions.

“…1,5 In the literature, methods to study attrition are under vacuum, 1 in aqueous solutions, 8 and in the presence of antisolvent. 9 This study was performed with potassium alum, which is a substance extensively used in the past to study secondary nucleation, 10 growth, 11,12 agglomeration, 13,14 and attrition as well as in the context of continuous crystallization processes. 15 Synowiec et al 16 studied attrition of potassium alum in the presence of antisolvent, namely, ethanol, and developed a model that takes into account the formation of fines due to the turbulent nature of the flow field.…”

Section: ■ Introductionmentioning

confidence: 99%

Study of Secondary Nucleation by Attrition of Potassium Alum Crystals Suspended in Different Solvents

Bosetti

Mazzotti

2020

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Secondary nucleation by attrition was studied in a milliliter-scale reactor, where the effects of different stirring rates and of different solvents were investigated. The experiments in suspension were performed in a Crystal16 system, and the evolution of the attrition process was monitored through transmissivity measurements, which can be qualitatively correlated to the number of attrition fragments produced, thus giving information about the extent of secondary nucleation by attrition, if other crystallization phenomena are not present. Higher stirring intensities correspond to faster and more intense production of attrition fragments, as expected. In order to explain the transmissivity measurements in the case of different solvents, an interpretation involving the difference between fluid and crystal densities, and polarity was developed, which is consistent with the experimental evidence. The difference in density between the crystals and the solvent influences the amount and the rate of production of fines (buoyancy and breakage), while polarity affects agglomeration. The determination of a secondary nucleation rate from the attrition experiments is not straightforward, and it has not been performed in this work, since the final result is a superposition of different effects, i.e., production of fines and agglomeration, depending on the fluid dynamics and the operating conditions of the system.