Suspension Crystallization Research Articles

Crystallization Behavior of Palm Kernel Oil Monitored by <i>In-Situ</i> Focused Beam Reflectance Measurement (FBRM) and Particles Video Microscope (PVM) during Suspension Crystallization

Crystallization behavior and kinetics study of palm kernel oil (PKO) were investigated using differential scanning calorimetry (DSC) by controlling cooling and reheating rate within a certain range of temperature. The evolution of morphology and particle counts was analyzed by focused beam reflectance measurement (FBRM) and particles video microscope (PVM) at the nucleation stage during suspension crystallization. The particle counts and morphological evolution from needle-like aggregations to amorphous form from PVM were observed during the initial crystallization stage, which meant that a phase transition was likely to occur. This work can give a better understanding of complicated fat system crystallization behavior and provide some critical instructions to control fractionation process.

Nematic and lamellar liquid-crystalline phases in suspensions of charged silica-coated gibbsite platelets

Computer simulations, theoretical investigations and experiments carried out over the last 20 years have demonstrated that suspensions of hard plate-like colloids display a rich liquid-crystal phase behaviour including nematic and columnar phases. Recently, it has become clear that charged colloidal platelets display an even richer phase behaviour including smectic A and smectic B phases. Here, we report on the formation of liquid crystals in suspensions of charged silica-coated gibbsite platelets in dimethylformamide in the presence of 1 mM salt and without added salt. A nematic phase is observed in the system with added salt, while in the system without added salt a lamellar (smectic A) liquid-crystalline phase is formed as demonstrated by optical observations and synchrotron small angle X-ray scattering measurements. The observed phases are in contrast with the columnar phase that would be expected if the platelets were interacting through hard-core repulsions. A bifurcation analysis suggests that, on decreasing ionic strength, first the columnar phase is destabilised in favour of nematic order, which in turn is destabilised in favour of lamellar order. Our experimental and theoretical results support the suggestion that the appearance of nematic and lamellar phases is related to the strength and range of the double-layer repulsion.

Aggregation of growing crystals in suspension: II. Poiseuille flow crystalliser

We describe the design and operation of a Poiseuille Flow Crystalliser (PFC) that allows direct exploration of the effect of hydrodynamic and physico-chemical conditions on the aggregation of crystals growing in suspension. The PFC operates as a differential reactor where changes between inlet and outlet are small enough not to change the rate, but large enough to be measureable. Automatically measured changes in size distribution yield very clear quantitative evidence of aggregation. We use these data to explore the three open questions of Hounslow et al. (2013) and show how to average underlying point aggregation kinetics over a whole vessel and how to extract point data from average data. We introduce the critical aggregate size, D, as the particle size that at the average shear rate has a Mumtaz number, M=1, and so disruptive forces are in balance with the strength of growing bridges.In a study of rounded calcium oxalate monohydrate particles we show that values of D can readily be determined by fitting the change in size distribution in the PFC. We are able to discriminate among candidate models relating aggregation efficiency to M by means of an empirical fitting investigation and by directly determining the aggregation efficiency – both averaged and un-averaged for the vessel. We conclude that aggregate rupture happens under simple tension and that the effective average size of two colliding particles is their geometric mean.D2 is predicted and observed to be directly proportional to the ratio of crystal growth rate to flow rate squared. We demonstrate that no attractive or repulsive inter-particle forces are active in aiding or retarding aggregation in this system. The constant of proportionality from these results allows the material property controlling aggregation – the product of yield strength and a geometric factor with dimensions of length – to be determined as L⁎σY=1.35±0.01Nm−1.

Potential foliar fertilizers with copper and zinc dual micronutrients in nanocrystal suspension

Control preparation, aqueous stability, and ion release of several Cu–Zn-containing crystals in suspensions have been investigated as potential dual micronutrient foliar fertilizers. These crystals were prepared by quick co-precipitation through simultaneously adding potassium hydroxide and copper salt solutions into zinc salt solution, and characterized in structure and composition with XRD, FTIR, SEM, TEM, and ICP in detail. As-prepared Cu–Zn mixed hydroxide nitrate was identified as a two-phase mixture while Cu–Zn mixed hydroxide sulfate as a single-phase compound. These crystals are all sheet-like in morphology and stable in aqueous solutions with pH 5–9. No phase change was detected after the samples were kept in shelf for >3 months, suggesting that these crystals have long shelf lives. In terms of ion release, Cu–Zn mixed hydroxide nitrate and Cu–Zn mixed hydroxide sulfate can afford ~4 and ~1 mg L−1 of Cu2+, respectively, which could be suitable for different levels of copper deficiency in plants. Moreover, both compounds can provide 38–39 mg L−1 of Zn2+ in aqueous suspensions. Thus, our findings suggest that as-prepared compounds can be potentially applied as long-term foliar fertilizers to simultaneously correct deficiencies of copper and zinc in various crops. Cu–Zn dual micronutrient foliar fertilizer crystals provide a certain concentration of Zn2+ and Cu2+ for foliar uptake by the plant to correct the element deficiency.

Heterogeneous cryogenic crystallization of suspensions containing carbon nanotubes

The mechanism of structure formation is proposed in heterogeneous crystallization of droplets of binary eutectic solutions containing carbon nanotube particles in cryogenic liquids. Theoretical relationships are derived for calculating the rate of crystallite growth and the size of salt nanocrystals that form. Calculated values of the size of produced nanocrystals are compared with experimental data.

Liquid Crystals in Spheroid Macroions and Spherocylindrical Biomacroions Suspended into Water using Sogami-Ise potential

Structure factor S(Q) and its Fourier transform pair correlation function g(r) have been calculated for the stabilized spheroid bovine serum albumin BSA protein molecules and spherocylindrical biomacroions of tobacco mosaic virus TMV and fd viruses suspended into water using SogamiIse SI potential by reducing the spherocylindricity into spherical macroions of volume equal to the volume of spherocylindrical biomacroions. The nature of the first peaks in S(Q)-Q and g(r)-r curves corroborates presence of liquid crystals in the aqueous suspension of BSA macroions and fd biomacroions. The results obtained compare well with that obtained using screened coulomb repulsive Derjaguin, Landau, Verwey and Overbeek DLVO potential and the experimental results. Liquid crystals of the body centered cubic BCC type with coordination number nearly eight have been found amongst the present system of study of aqueous suspension of spheroid BSA macroions and spherocylindrical fd biomacroions.

Erratum: “On the influence of a patterned substrate on crystallization in suspensions of hard spheres” [J. Chem. Phys. 136, 044702 (2012)

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Capturing the Formation of Sub-nanometer Sized CdS Clusters in LTL Zeolite

The radiolytic preparation of sub-nanometer sized CdS clusters in LTL-type zeolite crystals in suspension is reported. The growing process of CdS in the zeolite crystals using a γ-ray irradiator (low dose rate) and a pulse electron accelerator (high dose rate) is followed by UV–vis spectroscopy. The pulse electron accelerator equipped with a transient absorption setup allowed the real-time capturing of CdS formed in the zeolite suspension. Two distinct stages during the formation of sub-nanometer sized CdS clusters in the LTL-type zeolite are identified: (i) fast formation of dispersed small oligomers exhibiting a well-defined sharp absorption peak, which is shifted from 292 to 350 nm in the course of the growth process, and (ii) formation of interconnected CdS clusters along the zeolite channels by diffusion-assisted process. Additionally, the presence of sub-nanometer sized CdS clusters in the zeolite channels is confirmed by transmission electron microscopy (TEM). The sub-nanometer sized CdS clusters formed in the LTL-type zeolite suspension exhibit good stability under hydrous conditions, and no coalesce in the presence of water is observed.

906 懸濁結晶法を用いた凍結濃縮システムにおける製氷部の撹拌混合に関する基礎研究

906 懸濁結晶法を用いた凍結濃縮システムにおける製氷部の撹拌混合に関する基礎研究

High accuracy online measurement of multidimensional particle size distributions during crystallization

A novel stereoscopic image acquisition setup and a procedure for measuring multidimensional particle size distributions (nD PSDs) during crystallization based on image analysis are presented. Images of crystals in suspension passing a flow through cell are generated by two cameras which are arranged in an orthogonal manner. Particles are conveyed to the flow through cell using a sampling loop, thus allowing for online monitoring. Automated image analysis provides contour data which can be used to classify crystals into different generic particle model classes. For each type of particle size data is calculated and stored. Finally, time resolved nD PSD data can be calculated. The accuracy of this novel size measurement was confirmed by comparison to measurements obtained with a Coulter Multisizer. The non-invasive nature and repeatability of experiments are shown by monitoring populations of sodium chloride and of the β polymorph of l-glutamic acid under different conditions. Finally, crystal growth of acetaminophen during cooling crystallization is shown. In addition, a virtual test bench is used to study the measurement method in silico.

Crystallization in glassy suspensions of hard ellipsoids

We have carried out computer simulations of overcompressed suspensions of hard monodisperse ellipsoids and observed their crystallization dynamics. The system was compressed very rapidly in order to reach the regime of slow, glass-like dynamics. We find that, although particle dynamics become sub-diffusive and the intermediate scattering function clearly develops a shoulder, crystallization proceeds via the usual scenario: nucleation and growth for small supersaturations, spinodal decomposition for large supersaturations. In particular, we compared the mobility of the particles in the regions where crystallization set in with the mobility in the rest of the system. We did not find any signature in the dynamics of the melt that pointed towards the imminent crystallization events.

Aggregation of growing crystals in suspension: I. Mumtaz revisited

When growing crystals aggregate, they do so at a rate that depends on the frequency of collisions and the efficiency of those collisions. In this paper we revisit the work of Mumtaz to show from first principles that the efficiency depends on Mumtaz's dimensionless strength, M. Mumtaz's original work was restricted to collisions between particles of the same size, to failure under simple tension and to collisions originating with a point of contact. The current work extends that approach to include polydisperse systems, shear stress and linear contacts. In all cases studied the location of the efficiency curve is at M of O(1), while the spread of efficiency depends on the mechanism of failure and the contact geometry. To a first approximation the efficiency of collision of two colliding particles depends on the geometric mean of their sizes.The work presented here provides aggregation kinetics at a point in a crystallizer. Further experimental work is required to determine which failure mechanism is appropriate, the relevant materials properties and an appropriate method for averaging over a vessel.

Crystallization in a sheared colloidal suspension

We study numerically the crystallization process in a supersaturated suspension of repulsive colloidal particles driven by simple shear flow. The effect of the shear flow on crystallization is two-fold: while it suppresses the initial nucleation, once a large enough critical nucleus has formed its growth is enhanced by the shear flow. Combining both effects implies an optimal strain rate at which the overall crystallization rate has a maximum. To gain insight into the underlying mechanisms, we employ a discrete state model describing the transitions between the local structural configurations around single particles. We observe a time-scale separation between these transitions and the overall progress of the crystallization allowing for an effective Markovian description. By using this model, we demonstrate that the suppression of nucleation is due to the inhibition of a pre-structured liquid.

Protein crystallization in stirred systems—scale‐up via the maximum local energy dissipation

Macromolecular bioproducts like therapeutic proteins have usually been crystallized with µL-scale vapor diffusion experiments for structure determination by X-ray diffraction. Little systematic know-how exists for technical-scale protein crystallization in stirred vessels. In this study, the Fab-fragment of the therapeutic antibody Canakinumab was successfully crystallized in a stirred-tank reactor on a 6 mL-scale. A four times faster onset of crystallization of the Fab-fragment was observed compared to the non-agitated 10 µL-scale. Further studies on a liter-scale with lysozyme confirmed this effect. A 10 times faster onset of crystallization was observed in this case at an optimum stirrer speed. Commonly suggested scale-up criteria (i.e., minimum stirrer speed to keep the protein crystals in suspension or constant impeller tip speed) were shown not to be successful. Therefore, the criterion of constant maximum local energy dissipation was applied for scale-up of the stirred crystallization process for the first time. The maximum local energy dissipation was estimated by measuring the drop size distribution of an oil/surfactant/water emulsion in stirred-tank reactors on a 6 mL-, 100 mL-, and 1 L-scale. A comparable crystallization behavior was achieved in all stirred-tank reactors when the maximum local energy dissipation was kept constant for scale-up. A maximum local energy dissipation of 2.2 W kg(-1) was identified to be the optimum for lysozyme crystallization at all scales under study.

The Effect of Morphology of Crystals in Suspension on Scale Formation Dynamics in Cooling Crystallization for Organic Compound

In cooling melt suspension crystallization, scale formation becomes a problem which seriously reduces the heat transfer coefficient of cooling surfaces, and the scale formation results in low productivity and low energy effectiveness. Scale formation still remains an issue to be discussed in cooling melt suspension crystallization, although some previous studies have been reported. The mechanisms of scale formation have been investigated based on surface interaction between crystal and cooling surface. However, studies on the operation method to prevent the scale formation have been insufficient. In the present study, the effect of the morphology of suspended crystals on scale formation dynamics (especially the transition speed of scale formation process) during start-up operation is investigated experimentally in melt crystallization for organic compounds. Scale formation dynamics are investigated using two kinds of seed crystals of different morphologies. As a result, the scale formation dynamics at the initial stage changed with morphology of seed crystals. Therefore, it is clear that crystal morphology is an important factor to consider scale formation dynamics. Moreover, this result suggests that modification of morphology in suspended crystals can be applied to prevent scale formation.

Rheological behavior and stability of ciprofloxacin suspension: Impact of structural vehicles and flocculating agent

Ciprofloxacin is a fluoroquinolone and is used against a broad spectrum of gram-negative and gram-positive bacteria. The aim of the study is to investigate the effect of structural vehicles and other formulating factors on physical stability and rheological behavior of ciprofloxacin suspension. To formulate the suspensions, the effect of glycerin and polysorbate 80 as wetting agents was evaluated. Then to achieve controlled flocculation, different concentrations of sodium chloride and calcium chloride were added. After choosing suitable wetting and flocculating agents, structural vehicles such as sodium carboxyl methyl cellulose (NaCMC), hydroxypropylmethylcellulose (HPMC) and Veegum were evaluated. Physical stability parameters such as sedimentation volume, the degree of flocculation and the ease of redispersion of the suspensions and growth of crystals were evaluated. After incorporation of structural vehicles, the rheological properties of formulations containing were also studied to find out their rheological behavior. According to the results, suspension containing glycerin (0.2% w/v) and sodium chloride (0.05% w/v) as wetting agent and flocculating agent, respectively, were the most stable formulations regarding their F and N. Microscopic observations showed the growth of crystals in ciprofloxacin suspension in formulation without excipients and the minimum amount of crystal growth was seen in suspension containing NaCMC (0.25% w/v), Veegum (0.1% w/v) and NaCl (0.05% w/v). Rheological studies showed that almost all of the formulations had psuedoplastic behavior with different degree of thixotropy. The formulation containing NaCMC (0.25% w/v), Veegum (0.1% w/v) and NaCl (0.05% w/v) was the most stable formulation. It may be concluded that by altering the amount ratios of formulation factors, the best rheological behavior and the most proper thixotropy may be achieved.

The interplay of sedimentation and crystallization in hard-sphere suspensions

We study crystal nucleation under the influence of sedimentation in a model of colloidal hard spheres via Brownian Dynamics simulations. We introduce two external fields acting on the colloidal fluid: a uniform gravitational field (body force), and a surface field imposed by pinning a layer of equilibrium particles (rough wall). We show that crystal nucleation is suppressed in proximity of the wall due to the slowing down of the dynamics, and that the spatial range of this effect is governed by the static length scale of bond orientational order. For distances from the wall larger than this length scale, the nucleation rate is greatly enhanced by the process of sedimentation, since it leads to a higher volume fraction, or a higher degree of supercooling, near the bottom. The nucleation stage is similar to the homogeneous case, with nuclei being on average spherical and having crystalline planes randomly oriented in space. The growth stage is instead greatly affected by the symmetry breaking introduced by the gravitation field, with a slowing down of the attachment rate due to density gradients, which in turn cause nuclei to grow faster laterally. Our findings suggest that the increase of crystal nucleation in higher density regions might be the cause of the large discrepancy in the crystal nucleation rate of hard spheres between experiments and simulations, on noting that the gravitational effects in previous experiments are not negligible.

Purification of phosphoric acid in a gravity wash column

AbstractA gravity wash column is a common type of continuous solid–liquid separator, which can be applied in the final step in the suspension crystallisation process of purifying phosphoric acid. In this work, a mathematical model based on material balance was presented for the purification process in a gravity wash column, and the experimental data of suspension crystallisation of phosphoric acid hemi‐hydrate were correlated. The developed purification model can be used to calculate concentration profiles of impurities along the column axis and to predict the effect of operating conditions on the purity of the product stream of phosphoric acid. The model parameters were also estimated by fitting the model with experimental data. © 2012 Canadian Society for Chemical Engineering

Phosphoric acid purification by suspension melt crystallization: Parametric study of the crystallization and sweating steps

AbstractIn order to purify phosphoric acid, the suspension melt crystallization process was studied. The suspension crystallization experiments were carried out with 80, 84 and 88 wt% phosphoric acid melt at the cooling rates of 0.05, 0.1 and 0.2 K/min, respectively. Sweating experiments were executed for various crystals obtained in suspension crystallization step. The purification effects of the sweating parameters including sweating time, initial inclusion amount and initial impurity content were studied. The inclusion fraction increases with the increase in cooling rate. The inclusion fraction of the crystals which were formed with feed concentration of 84 wt% phosphoric acid melt is lowest among the three feed concentrations. Different impurities have different purification performances during sweating. High inclusion amount and low impurity concentration favor the purification of H3PO4·0.5H2O crystals during sweating.

Numerical simulations of convection in crystal‐bearing magmas: A case study of the magmatic system at Erebus, Antarctica

The sustained heat and gas output from Erebus volcano reflects a regime of magma convection that we investigate here using a bi‐phase (melt and crystals), fluid dynamical model. Following validity and verification tests of the model, we carried out four single‐phase and three bi‐phase numerical 30‐year‐ simulations, in an idealized 2D geometry representing a lava lake cooled from above and a reservoir heated from below that are linked by a 4‐to‐10–m‐diameter conduit. We tested the effects of crystals on convection while changing conduit size and the system boundaries from closed to open. Neglecting crystal settling yields only a limited number of features, i.e., (i) the formation of a central instability, (ii) the average temperature evolution, and (iii) the average velocity range of the surface flow motion. Bi‐phase simulations show that while crystals are quite efficiently transported by the liquid phase a small decoupling reflecting their large size (5 cm) results in settling. This leads to more complex circulation patterns and enhances the vigor of fluid motion. A sufficiently large conduit sustains convection and retains 6 and 20% of crystals in suspension, for a closed and open system, respectively. Model outputs do not yet correspond well with field observations of Erebus lava lake (e.g., real surface velocities are much faster than those modeled), suggesting that exsolved volatiles are an important source of buoyancy.