Suspension Crystallization Research Articles

Rheological study of [formula omitted] hydrate slurry in a dynamic loop applied to secondary refrigeration

An original rheological characterisation of CO 2 hydrate slurries in flow is proposed in the present paper. Hydrate slurries are two-phase fluids composed of hydrate crystals in suspension in a liquid phase. One of the applications of CO 2 hydrate slurries relates to secondary refrigeration, principally due to the high latent heat of melting of CO 2 hydrates used as phase change materials and the expected lower cost of gas hydrate production compared to scrapped and brushed surface exchangers (classically used in the field of refrigeration and air-conditioning). In order to be considered as suitable for refrigeration applications, CO 2 hydrate slurries must, however, fulfil other criteria such as satisfying flowing conditions. An experimental loop was used in this work to produce CO 2 hydrate slurries by gaseous CO 2 injection in pre-cooled water and to measure pressure drops as a function of volumetric flow rates for various fractions in solid particles. As most of multiphase solid–liquid fluids, CO 2 hydrate slurry can be rheologically characterised by its pseudo-homogeneous apparent viscosity, strongly depending on the mass fraction, the type and the organisation of the solid particles in the liquid phase related to following parameters: nucleation, growth, shape, size distribution, agglomeration, etc. In order to improve the description of the rheological behaviour of the studied slurry, an empirical model based on the method of the capillary (Ostwald) viscosimeter was applied from our experimental data and provided a Herschel–Bulkley (HB) type equation integrating the solid fraction of the slurry. The results of the empirical HB model were compared to a classical pseudo-homogeneous pressure drop model.

Raman spectroscopy of particles in suspension concentrated by an ultrasonic standing wave

An ultrasonic standing wave field of 2MHz was used to manipulate yeast cells and theophylline crystals in suspension to control the local concentration of solid material in the focus of a Raman spectroscope to improve the signal quality of such measurements for suspensions. In case of agglomerated yeast cells the signal-to-noise ratio was significantly increased in comparison to Raman spectra of the suspension. The spectra corresponded well with yeast dried on glass used as reference. Measurements of theophylline suspensions confirmed these results. Furthermore, it was possible to show the absence of theophylline crystals between the pressure nodal planes of the ultrasonic standing wave. This opens the possibility to specifically measure the solid fraction and the pure liquid of a suspension almost simultaneously by only changing the optical focus of the Raman microscope in respect to the location of the ultrasonic standing wave's nodes.

A nidus, crystalluria and aggregation: key ingredients for stone enlargement

The in vitro study of calcium oxalate (CaOx) stone formation is usually based on crystallisation models but it is recognised that both healthy individuals and stone formers have crystalluria. We have established a robust in vitro stone growth model based on the principle of mixed suspension, mixed product removal system (MSMPR). Utilising this technique we studied the influence of CaOx crystallisation kinetics and the variation of calcium and oxalate concentrations on CaOx stone growth in vitro. Six stones received standard concentration of Ca (6 mM) and Ox (1.2 mM) in the medium while another six received variable concentrations of both Ca and Ox at various intervals. Stone mass was plotted against the experiment duration (typically 5-7 weeks). The stone growth was dependent on sufficient input calcium and oxalate concentrations and once triggered, stone growth could not be maintained at reduced calcium and oxalate inputs. The stone growth rate was positively correlated to the number of crystals in suspension around the stone and to the crystal nucleation rate and negatively correlated to the crystal growth rates. This leads to the conclusion that aggregation of crystals from the surrounding suspension was the dominant mechanism for stone enlargement.

Suspensions of Silica Particles Grafted with Concentrated Polymer Brush: Effects of Graft Chain Length on Brush Layer Thickness and Colloidal Crystallization

We previously reported that monodisperse silica particles (SiPs) afforded with a high-density brush of poly(methyl methacrylate) (PMMA) and suspended in a good solvent for PMMA formed a colloidal crystal in a certain concentration range (Macromolecules 2006, 39, 1245). Here we investigated similar hybrid particles with respect to the influence of graft chain length Lc on their hydrodynamic diameter Dh in dilute suspension and on colloidal crystallization in more concentrated suspension. The average radius r0 of SiPs was 65 nm, and the surface density σ0 of PMMA grafts at the SiP surface was about 0.7 chains/nm2 (about 36 000 chains per particle). The hydrodynamic thickness of the swollen brush layer h (=Dh/2 − r0) was qualitatively interpretable by a modified Daoud−Cotton-type scaling model. Namely, for short graft chains, h obeyed the universal relation, h[1 + (h/2r0)] ∼ Lcσ01/2, applicable to concentrated polymer brushes on flat as well as spherical surfaces, and for chains longer than a critical length...

Critical nuclei and crystallization in colloidal suspensions

The aim of this paper is to review and to preview some selected topics of crystal nucleation in colloidal suspensions. First we discuss how the structure of critical nuclei can be calculated by computer simulations, in particular how linear shear flow affects the size and shape of the critical nuclei. Second, we preview the possibilities to access heterogeneous crystal nucleation and dynamics of a crystal by using the recently developed formalism of dynamical density functional theory. In particular, data for global crystal heating are presented.

A new parallel plate shear cell for in situ real-space measurements of complex fluids under shear flow

We developed and tested a parallel plate shear cell that can be mounted on top of an inverted microscope to perform confocal real-space measurements on complex fluids under shear. To follow structural changes in time, a plane of zero velocity is created by letting the plates move in opposite directions. The location of this plane is varied by changing the relative velocities of the plates. The gap width is variable between 20 and 200 microm with parallelism better than 1 microm. Such a small gap width enables us to examine the total sample thickness using high numerical aperture objective lenses. The achieved shear rates cover the range of 0.02-10(3) s(-1). This shear cell can apply an oscillatory shear with adjustable amplitude and frequency. The maximum travel of each plate equals 1 cm, so that strains up to 500 can be applied. For most complex fluids, an oscillatory shear with such a large amplitude can be regarded as a continuous shear. We measured the flow profile of a suspension of silica colloids in this shear cell. It was linear except for a small deviation caused by sedimentation. To demonstrate the excellent performance and capabilities of this new setup we examined shear induced crystallization and melting of concentrated suspensions of 1 microm diameter silica colloids.

Formation of submicron of periodic structure in high-clean suspensions

Experimental studies have revealed a dependence of the dimension and texture of supramolecular crystals in clean suspensions (the concentration of inorganic admixtures in dry conglomerates less than 0.4 × 10−4 wt.%) on the width of the counter-ion layer around the submicron spherical silica particles. At pH = 7–10, the pinching-out upward of the 0.5 mm narrow crystals is determined by the interaction of the crystal structural units, which present elongated dipoles due to a great width of the counter-ion layers (χr = 2.5). At pH < 7, the enlargement of the crystals to 3 mm and the absence of the crystals pinching-out upward is reached by the narrowing of the counter-ion layer (χr = 17.6) and, as a result, a decrease of the dipole elongation of the crystal structural units.

Fragmentation behavior of aggregated crystal in suspension crystallization processes

In chemical engineering processes in which crystal is produced, the strength of the substances plays a key role. In this study, micro-level measurements of the fracture strength of aggregated crystal were performed under various operating conditions of an MSMPR crystallizer. The attrition and the fragmentation mechanisms were considered from the fracture strength, the fracture energy and impact velocity calculated from micro-hardness properties. The results showed that these properties had different values between aggregated and non-aggregated crystals. Inclusion of mother liquor caused by aggregation was accounted for the decline of the crystal strength. According to these parameters based on microhardness, there was a possibility that the collision between aggregated crystal and impeller caused not only attrition but also fragmentation.

57Fe Mössbauer, FT-IR and FE SEM investigation of the formation of hematite and goethite at high pH values

The ferrihydrite suspensions were precipitated at high pH values, and crystallizations of α-Fe 2O 3 and α-FeOOH were monitored by Mössbauer and FT-IR spectroscopies and thermal field emission electron microscopy. α-Fe 2O 3 crystallization in dense ferrihydrite suspension at 160 °C was a fast process governed by the dissolution/reprecipitation mechanism. Between 40 and 60 min of crystallization traces/small amounts of α-FeOOH precipitated and dissolved, so that between 6 and 24 h only platelet-like α-Fe 2O 3 particles were present. On the other hand, the kinetics of crystallization in a dense ferrihydrite suspension at RT was slow and upon 90 days of ageing α-FeOOH as an end-product was detected. These α-FeOOH particles were strongly elongated along the crystallographic c-axis. α-FeOOH particles were also obtained as a single phase at 160 °C, but with decreased Fe 3+ concentrations (0.1 or 0.05 M FeCl 3). These particles also showed a strong lateral aggregation and the formation of a dendritic microstructure. The crystallization process in a dense ferrihydrite suspension was strongly influenced by ultrasound energy. The application of ultrasound energy of 141 W cm −2 for 2 h induced a coalescence-like effect in the ferrihydrite suspension, as observed by FE SEM. With ultrasound energy increased up to 424 W cm −2 the crystallization of α-Fe 2O 3 particles was observed. The geometrical shape of these α-Fe 2O 3 particles was poor compared with those crystallized in the absence of ultrasound.

Methods for the Preparation of Micro‐ and Nanocrystals of Urethane‐Substituted Polydiacetylenes

Urethane‐substituted polydiacetylene (PDA) crystals of bis(ethyl)‐urethane of 5,7‐dodecadiyne‐1,12‐diol (poly(ETCD)) with micronscale and nanoscale dimension were fabricated by either ultrasonication, surfactant addition or vapor phase processing approaches. Scanning electron microscope (SEM) and transmission electron microscope (TEM) were used to evaluate the sizes and the shapes of the obtained poly(ETCD) microcrystals. Dynamic light scattering (DLS) was performed to investigate in situ size distributions of these crystals in aqueous suspension. A UV/Visible/NIR Spectrometer (UV/Vis/NIR) was used to study the electronic absorption of the poly(ETCD) microcrystals. Thermochromic phenomena for poly(ETCD) crystals still exist after their dimension was decreased to the nanoscale.

Generalization and numerical investigation of QMOM

AbstractA generalized framework is developed for the quadrature method of moments (QMOM), which is a solution method for population balance models. It further evaluates the applicability of this method to industrial suspension crystallization processes. The framework is based on the concepts of generalized moments and coordinate transformations, which have been used already in earlier solution approaches. It is shown how existing approaches to QMOM are derived from the suggested unified framework. Thus, similarities and differences between the various QMOM methods are uncovered. Further, potential error sources involved in the different approaches to QMOM are discussed and assessed by means of a series of test cases. The test cases are selected to be challenging. The error in the QMOM solution is evaluated by comparison to an adaptive, error controlled solution of the population balance. The behavior of a range of different QMOM formulations is analyzed by means of numerical quadrature, dynamic simulation, as well as numerical continuation and bifurcation analysis. As a result of this detailed analysis, some general limitations of the method are detected and guidelines for its application are developed. This article is limited to lumped population balance models with one internal coordinate. © 2006 American Institute of Chemical Engineers AIChE J, 2007

Crystal Shape Control by Manipulating Supersaturation in Batch Cooling Crystallization

This paper describes a study on the shape control of potassium dihydrogen phosphate (KDP) in batch cooling suspension crystallization by selecting the supersaturation as a media control variable. The effects of different cooling modes on the supersaturation level and hence on the crystal shape were investigated. The results clearly show that different shapes of crystals were obtained at the various supersaturation courses. When a specific shape of crystal is desired from suspension batch cooling crystallization, a suitable cooling mode should be selected and furthermore the optimal one can be found.

Attrition behavior by micro-hardness parameters in suspension-crystallization processes

We measured the elastic modulus and fracture strength at the micro-level for various types of crystal generated by an MSMPR crystallizer. The attrition behavior was determined from the fracture energy and attrition coefficient, which were calculated from micro-hardness properties. The different values observed for each tested crystal size revealed that crystal size was an important factor in attrition behavior. Therefore, we could predict the amount of attrition through the fracture energy. Future work will involve applying the estimation method in a scaled-up suspension crystallizer.

Investigation and mathematical modeling of attrition

A mathematical model is developed to describe attrition, which is the main source of nuclei in suspension crystallization. The model allows one to calculate the mass median size of the crystals obtained and the particle size distribution function. The effect of the suspension volumetric flow rate, the geometric sizes of a impingement device, and the initial size of a seed on the size of the crystals obtained is revealed. The model is applicable to describing the contact mechanism of nucleation in impact of crystals with a stirrer, pump blades, etc. To study attrition on a laboratory scale, a set of experiments was carried out with the ammonium sulfate crystal system under various conditions.

Immobilization of colloidal crystals, formed by polymer-grafted silica in organic solvent, in physical gels

Immobilization of colloidal crystals by gelation of polymer-grafted silica suspension in acetonitrile with alkyl amides derived from amino acids was investigated. Addition of N-benzyloxycarbonyl-l-isoleucylaminooctadecane (Z-Ile-C18) and 1,12-bis(N-benzyloxycarbonyl-l-valylamino)dodecane [Bis(Z-Val)-C12] to poly(maleic anhydride-co-styrene)-grafted silica suspension in acetonitrile resulted in formation of physical gels preserved colloidal crystal structure. From the reflection spectra, intersphere distance and size of crystallite in the gel formed with Bis(Z-Val)-C12 were confirmed to be mostly same as those of colloidal crystals in suspension.

Temperature-induced crystallization in concentrated suspensions of multiarm star polymers: A molecular dynamics study

In this work, we study temperature-induced crystallization in dense suspensions of multiarm star polymers. This is a continuation of a previous study, which identified and studied the emergence of "glassy" amorphous states, in accordance with experimental observations. We performed molecular dynamics simulations on two types of star polymers: 128-arm stars and 64-arm stars dissolved in n-decane in the temperature range of 20-60 degrees C. These supramolecules are modeled as "soft spheres" interacting via a theoretically developed potential of mean field. Both systems attain a crystalline structure with the characteristics of a face-centered-cubic (fcc) crystal beyond a certain temperature. Kinetics is sensitive on initial configuration. Interestingly, kinetic trapping in "temporary" energy wells leads to highly crystalline structures, yet less ordered than their genuine equilibrium fcc structure. This complication illustrates the difficulty in reaching the equilibrium state, which is crystalline at high temperatures. A structural analysis of the final conformations is presented. The effect of size dispersity and star functionality of soft spheres on microstructure is also examined. Both factors influence crystallization and their effect is quantified by our study.

Physical changes of β-sitosterol crystals in oily suspensions during heating

The aim of this research was to describe the thermal behavior of beta-sitosterol crystals in oil-suspensions with a focus on the role of water during heating. The suspensions were prepared by recrystallization in order to achieve a microcrystalline particle size. The structural changes together with the mechanical properties of the suspensions during heating were studied by using variable temperature X-ray powder diffractometry (VT-XRPD), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). Hydrated beta-sitosterol crystals in an oil-suspension dehydrated, despite the composition of the suspensions, at low temperatures. At high beta-sitosterol concentration, the monohydrate crystal form changed partially to a hemihydrated form, and when only a small amount of water was initially incorporated, the hemihydrate crystal form dehydrated to a mostly anhydrate crystal form. The released water, which was immiscible in the surrounding oil, caused the recrystallization of hydrated beta-sitosterol during cooling. This procedure indicated a reversible dehydration process. Structural and thermal analysis of beta-sitosterol crystals in suspensions, together with mechanical analysis made it possible to understand various physical changes during heating.

The liquidlike ordering of lipid A-diphosphate colloidal crystals: The influence of Ca2+, Mg2+, Na+, and K+ on the ordering of colloidal suspensions of lipid A-diphosphate in aqueous solutions

A comprehensive study was performed on electrostatically stabilized aqueous dispersion of lipid A-diphosphate in the presence of bound Ca2+, Mg2+, K+, and Na+ ions at low ionic strength (0.10-10.0-mM NaCl, 25 degrees C) over a range of volume fraction of 1.0 x 10(-4)< or =phi< or =4.95 x 10(-4). These suspensions were characterized by light scattering (LS), quasielastic light scattering, small-angle x-ray scattering, transmission electron microscopy, scanning electron microscopy, conductivity measurements, and acid-base titrations. LS and electron microscopy yielded similar values for particle sizes, particle size distributions, and polydispersity. The measured static structure factor, S(Q), of lipid A-diphosphate was seen to be heavily dependent on the nature and concentration of the counterions, e.g., Ca2+ at 5.0 nM, Mg2+ at 15.0 microM, and K+ at 100.0 microM (25 degrees C). The magnitude and position of the S(Q) peaks depend not only on the divalent ion concentration (Ca2+ and Mg2+) but also on the order of addition of the counterions to the lipid A-diphosphate suspension in the presence of 0.1-microM NaCl. Significant changes in the rms radii of gyration (R2G) 1/2 of the lipid A-diphosphate particles were observed in the presence of Ca2+ (24.8+/-0.8 nm), Mg2+ (28.5+/-0.7 nm), and K+ (25.2+/-0.6 nm), whereas the Na+ salt (29.1+/-0.8 nm) has a value similar to the one found for the de-ionized lipid A-diphosphate suspensions (29.2+/-0.8 nm). Effective particle charges were determined by fits of the integral equation calculations of the polydisperse static structure factor, S(Q), to the light-scattering data and they were found to be in the range of Z*=700-750 for the lipid A-diphosphate salts under investigation. The light-scattering data indicated that only a small fraction of the ionizable surface sites (phosphate) of the lipid A-diphosphate was partly dissociated (approximately 30%). It was also discovered that a given amount of Ca2+ (1.0-5.0 nM) or K+ (100 microM) influenced the structure much more than Na+ (0.1-10.0-mM NaCl) or Mg2+ (50 microM). By comparing the heights and positions of the structure factor peaks S(Q) for lipid A-diphosphate-Na+ and lipid A-diphosphate-Ca2+, it was concluded that the structure factor does not depend simply on ionic strength but more importantly on the internal structural arrangements of the lipid A-diphosphate assembly in the presence of the bound cations. The liquidlike interactions revealed a considerable degree of ordering in solution accounting for the primary S(Q) peak and also the secondary minimum at large particle separation. The ordering of lipid A-diphosphate-Ca2+ colloidal crystals in suspension showed six to seven discrete diffraction peaks and revealed a face-centered-cubic (fcc) lattice type (a=56.3 nm) at a volume fraction of 3.2 x 10(-4)< or =phi< or =3.9 x 10(-4). The K+ salt also exhibited a fcc lattice (a=55.92 nm) at the same volume fractions, but reveals a different peak intensity distribution, as seen for the lipid A-diphosphate-Ca2+ salt. However, the Mg2+ and the Na+ salts of lipid A-diphosphate showed body-centered-cubic (bcc) lattices with a=45.50 nm and a=41.50 nm, respectively (3.2 x 10(-4)< or =phi< or =3.9 x 10(-4)), displaying the same intensity distribution with the exception of the (220) diffraction peaks, which differ in intensity for both salts of lipid A-diphosphate.

Crystallization in charged two-component suspensions

We report on the crystallization of colloidal crystals comprising of charged particles with different size ratio dispersed in thoroughly deionized water. Single components were characterized carefully and their nucleation behavior was investigated before the preparation of mixtures. Mixtures investigated at constant particle number densities showed body centred cubic structure, conductivity, and shear moduli comply with the assumption of a randomly substituted crystal. Most importantly, for the first time we obtain the dependence of the nucleation rate densities in dependence on the composition and (for one fixed composition) the particle number density. The process of nucleation in random substitutional crystals is found to be similar to the one-component case.

３３ゲージのテーパー型注射針を懸濁インスリン製剤が通過したときのＮＰＨ結晶の形状とインスリンの血糖降下作用への影響について

The Nanopass®33 micro-tapered needle (MT 33 G, Terumo Corp., Tokyo, Japan) is tapered in form : 33 G at the tip end and 28 G at the cartridge end. We examined the structure of insulin crystals in insulin suspensions before and after passing through the MT 33 G needle to determine if there were any changes in it that might adversely affect the pharmacodynamics and action of insulin. We also examined the hypoglycemic effect of insulin in dogs after it had passed through a MT 33 G needle to see if it had been modified by it.No changes were observed in the insulin crystal structure when the insulin preparation in a syringe was discharged at a rate of 10 units/sec through the MT 33 G needle connected to it. Also, when insulin was administered to dogs, there was no significant difference between the MT 33 G and the Micro-FineTM Plus, 31G, Thin Wall needle (Nippon Becton Dickinson Co., Ld., Tokyo, Japan) as regards the blood insulin and blood glucose levels measured.