Final Crystal Size Research Articles

Modelling and experimental validation of ultrasound assisted unseeded batch cooling crystallization ofl-asparagine monohydrate

A population balance model for ultrasound-assisted unseeded batch cooling crystallization of L-asparagine monohydrate (LAM) from its aqueous solution is developed and validated. The model considers nucleation, growth, and breakage phenomena and is solved by high resolution finite volume discretization with a flux limiter. An additional kinetic expression is introduced for induced nucleation due to ultrasound irradiation. The kinetics are extracted using a nonlinear optimization technique that uses solute concentration data measured by high performance liquid chromatography and mean crystal size measured by laser diffraction. The developed model shows good quantitative agreement with experimental observations on solute concentration and final crystal size distribution (CSD). Experimental data and model simulations show that ultrasound significantly reduces the metastable zone width for LAM, enhances the nucleation rate, and induces early nucleation.

An Improved Multi-Objective Evolutionary Optimization Algorithm For Sugar Cane Crystallization

Abstract The nature of optimization for intermittent sugar cane crystallization process is to obtain ideal crystals. One typical difficulty in crystallization optimization refers to the simultaneous effects of both seeding characters and process variables on the final crystal size distribution (CSD) parameters, including mean size (MA) and coefficient of variation (CV). And the application of traditional multiobjective evolutionary algorithm in crystallization process could not optimize all of them. Therefore, this paper puts forward a different multi-objective framework, and correspondingly, an improved optimization algorithm is applied to intermittent sugar cane crystallization. This method combines the elitist non-dominated sorting genetic algorithm (NSGA-II) with technique for order preference which is similar to an ideal solution (TOPSIS), and it provides a quantitative way to analyze the effect of both seed characteristics and process variables on the trade-off between MA and CV. Furthermore, the proposed algorithm has been adapted here to be compared with the NSGA-II, and the comparing results demonstrate better Pareto-optimal solutions of the novel approach

A mathematical model based parametric sensitivity analysis of an evaporative crystallizer for lactose monohydrate

Lactose is produced from whey by crystallization after a series of concentration steps. Evaporative crystallization is the process where both concentration and crystallization occur simultaneously. There is no current literature on an industrial scale evaporative crystallizer producing lactose monohydrate. Crystal size is the most important output parameter for the lactose crystallization process. In order to understand the effect of various operational and kinetic parameters on the final crystal size coming out of the crystallizer, a mathematical model was developed to mimic the operation of the industrial unit. The model includes mass and crystal population balances along with mutarotation and nucleation kinetics for lactose. A sensitivity analysis was conducted by simulating the developed model for a range of values for parameters like residence time, evaporation rate, crystallizer temperature and growth and nucleation kinetics. It was found that the secondary nucleation rate was the factor most affecting the crystal size. The crystal size and dissolved lactose data from the industrial unit were collected and fitted to the model predictions to estimate the crystallization kinetics of lactose in the industrial unit. Based on the simulation results, operational and design guidelines for an evaporative crystallizer were laid down.

Initial Reaction Mechanism of Platinum Nanoparticle in Methanol-Water System and the Anomalous Catalytic Effect of Water.

Understanding the detailed reaction mechanism in the early stage of noble metal nanoparticles is very critical for controlling the final crystal's size, morphology, and properties. Here, we report a systematic study on the initial reaction mechanism of Pt nanoparticles in methanol-water system and demonstrate an anomalous catalytic effect of H2O on the reduction of H2PtCl6 to Pt nanoparticles using a combination of UV-vis, X-ray absorption spectroscopy (XAS), liquid chromatography mass spectrometry (LCMS), and first-principles calculation methods. The observations reveal the transformation route [PtCl6](2-) → [PtCl5(CH3O)](2-) → [PtCl4](2-) → [PtCl3(CH3O)](2-) → [PtCl2](2-) and finally to form Pt nanoparticles in a pure CH3OH solution. With 10 vol % water adding in the CH3OH solution, a new and distinct chemical reduction pathway is found in which the precursors change from [PtCl6](2-) to [PtCl5(CH3O)(H2O)](2-) to [PtCl4](2-) to [PtCl3(CH3O)(H2O)](2-) to [PtCl2](2-) and to Pt nanoparticles. Notably, the supernumerary water molecular can significantly accelerate the rate of chemical reduction and greatly shorten the reaction time. This work not only elucidates the initial reaction mechanism of Pt nanoparticles but also highlights the pronounced influence of H2O on the reaction pathway, which will provide useful insights for understanding the formation mechanism of noble metal nanoparticles and open up a high efficient way to synthesize new functional nanomaterial.

Enhanced Nucleation of Lysozyme Using Inorganic Silica Seed Particles of Different Sizes

In this work we investigate the impact of differently sized plain silica nanoparticles (NPs) between 10 and 200 nm on the crystallization of lysozyme (LSZ). In the first part of our work we investigate the electrostatic interactions between LSZ and NPs by zeta potential measurements and place special emphasis on the adsorption behavior of LSZ@SiO2. The determined adsorption isotherms—derived from UV–vis spectroscopy—indicate that with increasing particle size more LSZ is adsorbed per NP surface area probably due to a size-dependent surface chemistry and the variation of surface curvature. Second, seeded crystallization experiments both at the microliter and milliliter scale and thus close to a technically relevant scale were performed. A clearly extended crystallization window upon the addition of seed particles toward lower protein and salt concentrations was found. Moreover, induction times of crystal formation and crystallization times were considerably reduced. These effects were intensified with the addition of larger seed particles. In general, with the addition of silica seed particles, a shift of the final crystal size distribution to larger structures is observed.

Analysis of the crystallization process of a biopharmaceutical compound in the presence of impurities using process analytical technology (PAT) tools

BACKGROUND. The crystallization of biopharmaceuticals can be problematic since, because the biosynthesis of these compounds is very difficult to control, they can contain a significant amount of impurities that have to be eliminated. In fact, impurities can lead to changes in the properties of the drug that can significantly reduce its effectiveness or even put the user in danger. The aim of this work is to exploit process analytical technology (PAT) tools to study the crystallization step of vitamin B12 crude product extracted via fermentation. RESULTS. Linear cooling crystallization experiments were performed using different conditions. The effects of solvent, cooling rate, seeding and purity of the initial material on the final size distribution and purity of the crystals were investigated through the use of UV/Vis spectroscopy, focused beam reflectance measurement (FBRM) and the CryPRINS software (Crystallization Process Informatics System). It was found that impurities strongly inhibit the growth of vitamin B12 crystals, promoting nucleation and leading to poor final crystal size distribution. CONCLUSION. Slow cooling can help to increase the purity of the final product but also generates a broad crystal size distribution because of secondary nucleation. Preparing the solution with material already crystallized once and using purified seeds helped to obtain a narrower crystal size distribution and also to reduce breakage.

Role of Nanoscale Confinement on Calcium Phosphate Formation at High Supersaturation

An important factor controlling bone mineralization is spatial restriction within collagen fibrils and matrix vesicles. Such nanoscale confinements in addition to chemical control restrict the growth and final size of calcium phosphate crystals (CaP). To study the role of spatial control on CaP mineralization exclusively, we investigated formation of CaPs under high supersaturations (0.84 M Ca2+ and 2.1 M Ca2+) within ordered aqueous domains (8–27 nm) of polymerized liquid crystals (PLCs). The mineralization of CaPs was achieved by a pressurized gas induced pH rise. CaPs mineralized within varying degrees of confinements showed contrasting results. Confinements ≤10 nm mediated the formation of CaPs to phase pure calcium apatite (CaAp), while confinements between 11 and 27 nm resulted in a mixture of phases such as CaAp, amorphous calcium phosphates (ACP), and acidic polymorphs such as brushite and monetite. Results indicated that smaller confinements offer a low particle/solution interface effectively forming small nucleation clusters leading to a metastable ACP phase. We suggest that CaP formation from high supersaturations strongly depends on the degree of confinement around the nucleation site to efficiently control the mineral phase purity. Moreover, a possible insight from this study is that synthetic and biological confinements, in addition to spatial restriction, also rely on chemical control to obtain phase pure CaPs such as bone apatite.

Design of co-crystallization processes with regard to particle size distribution

Many active pharmaceutical ingredients (APIs) are poorly soluble and therefore poorly bioavailable. Advances in crystal engineering have motivated research into the design of pharmaceutical co-crystals. This study examines the formation of agomelatine–citric acid co-crystal in a batch cooling crystallization. Three linear cooling profiles (10°C, 20°C and 30°C/h) were applied for both unseeded and seeded crystallization and the effect of the seeding temperature on the final crystal size distribution was systematically investigated. A mathematical model of the crystallization process, consisting of the population and mass balance, was formulated and solved using the finite difference method. The growth and nucleation rate constants were evaluated iteratively by the comparison of measured and simulated crystal size distributions. The similarities and differences between classical single-component crystallization and co-crystallization were discussed.

Controllable synthesis of hierarchical beta nanozeolites from tailorable seeds

Hierarchical beta nanozeolites were controllably synthesized by tailoring seeds (or protozeolitic units, nanocrystals) grafted with phenylaminopropyltrimethoxysilane (PHAPTMS). The investigation of beta zeolite crystallization reveals that it proceeds through condensed-step mechanism, gradually growing in size along two populations of particles and evolving in internal structure. Based on the zeolitic seeds formation process, there were two roles of organosilane: the more-like mesoporogen agent in short precrystallization time and the growth inhibitor after the formation of secondary particles with significant amounts of terminal silanol groups. It was also found that both the mesopore properties and the crystal size of the prepared hierarchical beta nanozeolites were also strongly dependent on the properties of seeds. Moreover, the mechanisms for the formation of hierarchical beta nanozeolites, including size of the nanoseeds as well as its nature on the final crystal size, pore characteristics, crystallinity, and morphology were proposed and discussed in detail.

Developing in Biodegradable Stents Technology

Biodegradable stents have been used for the treatment of cardiovascular diseases and are often placed inside coronary arteries. The manufacture of Biodegradable stents is an challenging issue because of the features, like geometry design, machine processing way and the material select of stents. An improved manufacturing process of biodegradable stents is presented. The proposed processes consist of the following steps: tube drawing (is use tube sinking manufacture), laser cutting and surface modification (annealing and ultrasonic cleaning). The precision injection and drawing operation is used to obtain the required wall thickness for seamless tube. The laser cutting is performed to change the shape of the stent, and the finishing operations are selected to modify the surface features, like smoothness and texture of stents. The smoothness of surface finish is one of the properties that determine the performance of a stent. Therefore, the surface modification process (vacuum annealing and ultrasonic cleaning) is important in the production of stents and in clinical treatments involving stents. Annealing is the key technology that affects the material’s final crystal grain size. Ultrasonic clean was of the stents to remove the slag (oxides) and burrs formed in laser production. Poly Lactic Acid material sample with an outside-diameter of 1.5 mm, a wall thickness of 0.08 mm, and a length of 10 mm, had been manufactured and demonstrated the proposed manufacture technology. The surface roughness of a stent manufactured is the value of Ra 13.7 nm which basically meets the design requirement for further performance evaluation. It is hoped that the above finding can be used for future study of stents.

Development of Nano-Structure Cu-Ti Alloys by Mechanical Alloying Process

Cu-Ti system with a terminal solution in the Cu-rich portion of equilibrium Cu-Ti phase diagram with a decreasing trend with temperature shows a potential to develop age hardenable alloys with suitable strength and thermal and electrical conductivities. In the present study, the mechanical alloy process has been employed to increase solubility of Ti in Cu matrix to make age hardenable Cu alloys. Cu-Ti powder mixtures with different rations of 1 and 6 wt% of Ti were milled in planetary ball mill for different milling times of 4, 12, 48, 96 and 192 hours. The milled powder mixtures were investigated and characterised by X-ray diffraction (XRD) technique. The results show increasing in lattice parameter of Cu, which indicates that Ti atoms are dissolved in the Cu matrix. Cu crystal sizes showed decreasing trend which were more obvious in the mixture with higher Ti contents. The final crystal sizes were in the range of 17-23 nm after 192 hours of milling.

Crystal Structure of a Voltage-gated K+ Channel Pore Module in a Closed State in Lipid Membranes

Voltage-gated K(+) channels underlie the electrical excitability of cells. Each subunit of the functional tetramer consists of the tandem fusion of two modules, an N-terminal voltage-sensor and a C-terminal pore. To investigate how sensor coupling to the pore generates voltage-dependent channel opening, we solved the crystal structure and characterized the function of a voltage-gated K(+) channel pore in a lipid membrane. The structure of a functional channel in a membrane environment at 3.1 Å resolution establishes an unprecedented connection between channel structure and function. The structure is unique in delineating an ion-occupied ready to conduct selectivity filter, a confined aqueous cavity, and a closed activation gate, embodying a dynamic entity trapped in an unstable closed state.

Ultrasound Assisted Cooling Crystallization of Sodium Acetate

The present work deals with improvement in the cooling crystallization of sodium acetate using ultrasonic irradiations. Initially the effect of different operating parameters in the conventional approach such as seeding temperature, seed amount, and initial amount of dissolved sodium acetate has been investigated. It has been found that seeding is essential for the onset of crystallization, and the amount of the seed had a significant effect on the final crystal size distribution and average particle size. Also the seeding temperature affects the type of crystals generated with formation of trihydrate crystals at a temperature higher than 10 °C, whereas a seeding temperature of 10 °C results in formation of only anhydrous crystals. Experiments under ultrasonic irradiation revealed that the intentional seeding can be avoided using ultrasound provided the irradiation was applied as soon as the cooling is started. The average particle size was found to be dependent on the power dissipation and it decreased w...

Determination of struvite crystallization mechanisms in urine using turbidity measurement

Sanitation improvement in developing countries could be achieved through wastewater treatment processes. Nowadays alternative concepts such as urine separate collection are being developed. These processes would be an efficient way to reduce pollution of wastewater while recovering nutrients, especially phosphorus, which are lost in current wastewater treatment methods. The precipitation of struvite (MgNH4PO4∙6H2O) from urine is an efficient process yielding more than 98% phosphorus recovery with very high reaction rates. The work presented here aims to determine the kinetics and mechanisms of struvite precipitation in order to supply data for the design of efficient urine treatment processes. A methodology coupling the resolution of the population balance equation to turbidity measurement was developed, and batch experiments with synthetic and real urine were performed. The main mechanisms of struvite crystallization were identified as crystal growth and nucleation. A satisfactory approximation of the volumetric crystal size distribution was obtained. The study has shown the low influence on the crystallization process of natural organic matter contained in real urine. It has also highlighted the impact of operational parameters. Mixing conditions can create segregation and attrition which influence the nucleation rate, resulting in a change in crystals number, size, and thus final crystal size distribution (CSD). Moreover urine storage conditions can impact urea hydrolysis and lead to spontaneous struvite precipitation in the stock solution also influencing the final CSD. A few limits of the applied methodology and of the proposed modelling, due to these phenomena and to the turbidity measurement, are also discussed.

Minimization of Attrition and Breakage in an Airlift Crystallizer

Minimization of secondary nucleation by attrition in industrial crystallizers is a major challenge. In this work, a novel airlift crystallizer has been designed, constructed, and experimentally tested aiming at the reduction of attrition by using air for mixing instead of a stirrer or a circulation pump. It is experimentally demonstrated that in this crystallizer ideal growth, i.e., growth of crystals without any nucleation, can be approached up to a seeding load of 0.5% and crystal size of up to 600 μm. Attrition is considerably decreased in an airlift crystallizer compared to conventional impeller-mixed crystallizers. This air-mixed crystallizer enables the production of crystals of high quality and offers a large flexibility of the final crystal size by manipulating the air flow rate and the sparger design. Comparison of different designs showed a large effect of a gas disengagement zone on the performance of the crystallizer, especially when large crystals were desired. The disengagement zone allows high circulation velocities and thus good mixing without entrainment of the gas bubbles in the downcomer, approaching a uniform suspension of the crystals.

Preparation and characterization of ITQ-29/polysulfone mixed-matrix membranes for gas separation: Effect of zeolite composition and crystal size

This work concerns the preparation and characterization of ITQ-29 zeolite crystals with high Si/Ge ratio (100–∞) and different particle size for obtaining mixed matrix membranes. The Si/Ge molar ratio and seeding content of the synthesis gel appeared to have an effect on the final crystal size, and particles of 2.5μm were obtained for pure silica composition with good crystallinity. These were introduced, at 4, 8 and 12wt% loadings, into a commercial polysulfone matrix to prepare mixed matrix membranes that showed promising results in the separation of H2/CH4 mixtures (highest H2 permeability 21.9 Barrer and a separation factor of 118 for the 4wt% ITQ-29/polysulfone membrane). The thermal treatment of the membranes and the type of solvent were also optimized to provide good interaction between the zeolite and the polymer, limiting aggregation of the particles in the matrix, and removing all residual solvent that hinders gas permeation performance.

Direct formation of organic semiconducting single crystals by solvent vapor annealing on a polymer base film

We report single crystal formation of organic semiconducting small molecules via solvent vapor annealing (SVA) on a polymer base film (PBF). The soluble PBF strongly assists the self-assembly of small molecules to form single crystals; this sharply contrasts typical SVA where the inorganic base film such as SiO2 plays little or no role. We use a matrix of organic solvents and polymers to systematically investigate the re-crystallization of dioctylbenzothienobenzothiophene (C8-BTBT) by SVA on polymer surfaces. Crystallization by SVA clearly correlates with the miscibility of solvents and PBFs. The PBF dramatically increases the amount of condensed solvent on the surface. The additional solvent enhances the molecular mobility of small molecules to allow self-assembly in a distance over hundreds of microns, and stimulates crystal growth via Ostwald ripening. Based on this mechanism, the final crystal size of small molecules can be controlled to vary from tens of microns to millimetres simply by modifying the thickness of the base film. The approach was successfully applied to several semiconducting small molecules to form single crystals that exhibited field-effect response. Hence SVA on PBF is presented as a general and promising method for the direct fabrication of organic single crystals on polymer dielectrics.

Effect of initial dextrose concentration, seeding and cooling profile on the crystallization of dextrose monohydrate

A batch seeded cooling crystallizer was used to study dextrose monohydrate crystallization. Experiments were conducted to investigate how a 2% increase in the initial dextrose concentration (from 65.5 to 67.5%) would influence final crystal yield and size. The crystallizations were performed for three different seed masses and cooling profiles, consequently the influence of these parameters was also investigated. The parameters were varied in accordance with an industrial scale process. An in-line focused beam reflectance measurement probe and an in-line process refractometer were used to continuously monitor the crystallizations. The experimental results showed that the 2% increase in initial dextrose concentration had a major influence on the rate of crystallization and yield over a 24h crystallization period, and only a minor influence on the median crystal size.

Pentaerythritol crystallization – Influence of the process conditions on the granulometric properties of crystals

The quality of crystals depends on many factors that determine their granulometric properties. In order to obtain crystals of desired size distribution, proper selection of the operating conditions is of a great importance. Commonly, the unseeded cooling crystallization is controlled by selecting the appropriate cooling profile. The crystallization process can also be controlled by adding a certain number of seed crystals of a uniform size in the crystallizer at the saturation temperature. This paper investigates the influence of the process conditions (mixing intensity, cooling profile, batch time, saturation temperature and seeding) on the granulometric properties of pentaerythritol obtained by batch cooling crystallization. All investigated process conditions influence the crystal size distribution (seeded and unseeded experiments). On the other hand, the shape of crystals was the same for all experimental conditions. Optimal cooling profile, lower retention time, higher mixing rate, and smaller initial seed surface area improves the final crystal size distribution.

Role of ethanol in sodalite crystallization in an ethanol–Na2O–Al2O3–SiO2–H2O system

Crystallization of sodalite was studied in an ethanol–Na2O–Al2O3–SiO2–H2O system. The addition of ethanol was observed to significantly affect the crystallization process and final crystal sizes and morphologies. Micron-sized sodalite particles with disc and thread-ball-like shapes were produced at low ethanol contents whereas sodalite particles with core-shell nanostructures were dominant at high ethanol contents. Prolongation of the reaction time led to hollow architectures with polycrystalline shells. This study showed that the formation of core-shell and hollow sodalite structures followed a surface crystallization process, including the following steps: the formation of amorphous spherical aggregates, multiple nucleation on the surface, growth of shell nanocrystals, and amorphous core digestion. The present work provides new insights into a better understanding of the role of ethanol in zeolite crystallization, and controllable synthesis of sodalite crystals with different morphologies.