This work aims at developing a dynamic layer crystallizer operated batchwise, for freezing desalination of sea water. The experiments were performed with water/NaCl solutions and with samples of sea ...water from Nice, Rabat and Marseille. The pilot crystallizer consists of a cooled tube immersed in a cylindrical double jacketed tank. The solution is poured into the tank and the crystallization takes place on the external surface of the tube, by applying a cooling ramp in the tube. The solution is agitated by air bubbling. The whole process involves the freezing step, leading to the crystallization of the ice layer and the sweating step, which consists of purifying in depth the ice layer by melting the impure zones. A parametric study on the effect of the operating parameters has allowed quantifying the role of the different key parameters of the freezing and sweating steps. Three experiments allowed reaching salinities lower than 0.5g/kg, satisfying the standards of drinking water. The duration of the whole process dropped to only 8h (5h for freezing and 3h for sweating), with a yield of sweating equal to about 50%, provided severe conditions were applied for sweating. Higher yields required longer times. Overall, the results show the feasibility of the technique.
► Initial temperature, ice growth rate and solution salinity are the parameters affecting ice purity. ► The sweating step is able to efficiently complete the purification. ► The duration of the whole process dropped to only 8h (5h for freezing and 3h for sweating).
Seeded batch crystallizations of monohydrate citric acid were performed under isothermal conditions (15 °C). Continuous monitoring of the overall solid concentration during the crystallization ...process was developed using in situ Raman spectroscopy. Quantitative estimation of the crystal size distribution (CSD) was made possible thanks to in situ image acquisition: off-line CSD measurements were further computed from the recorded pictures. The growth rate of monohydrate citric acid was estimated from solid concentration. Through in situ particle size visualization and quantitative analysis of the pictures, activated surface secondary nucleation was also shown to significantly impact the final CSD. It is underlined that, in addition to continuous Raman in situ spectroscopic concentration measurements, image acquisition yields highly valuable data on the dispersed phase. Advantages and drawbacks of the technique for the monitoring of solution crystallization are discussed.
Co-crystallisation is a recent method of great interest for the pharmaceutical industry, since pharmaceutical co-crystals represent useful materials for drug products. In this study, an active ...pharmaceutical ingredient (carbamazepine (CBZ)) co-crystallized with a vitamin (nicotinamide (NCT)) was chosen as a model substance. This work was focused on the construction of a phase diagram for the system CBZ/NCT, split in six domains for kinetic reasons (the different solid phases which might appear during the crystallisation) and in four domains according to thermodynamic aspects (the stable final phase obtained). Although co-crystals are not ionic compounds, the supersaturation of co-crystals can be evaluated by considering the solubility product. Batch crystallisation operations were carried out in a stirred vessel equipped with an in situ video probe. This latter device was a powerful analysis tool to monitor the CBZ/NCT co-crystals and single CBZ crystals since these two crystalline phases grown in ethanol exhibited needle and platelet habits. As concerns kinetics, the different solid phases which might appear during the experiments were observed and competed against each others. In accordance with thermodynamics, the stable solid form was obtained at the end of the operation. Finally some preliminary results indicate that the nucleation of co-crystals may be favoured by the presence of CBZ crystals. Epitaxial relationships between CBZ/NCT co-crystals and CBZ crystals were suspected.
Understanding the evolution of liquid–liquid dispersion is a key factor in operation and control of emulsification process. A dynamic tracking of an evolving droplet size distribution (DSD) in a ...dilute oil-in water (O/W) emulsion has been developed with the implementation of an
in situ video probe dipped in a stirred vessel and coupled with an image analysis treatment. The optical probe allows real time recording of 2D images of the droplets. Recent image analysis software developed originally for an application in micromechanics was adapted and applied in delayed time on the video sequences regularly recorded. It automatically provided a measurement of the diameter of several thousands of droplets in the range of 10–100
μm. The relative accuracy on the droplet number average diameter was 10%. This measurement technique was then used to investigate at lab scale in a stirred vessel and in warm conditions the influence of several process parameters on the evolution with time of a dispersed melted cosmetic ingredient in a water solution containing a surfactant. The specific power input of stirring was the main parameter acting on the reduction of the mean droplet diameter and of the width of the DSD owing to its action on the droplet break-up mechanism. The surfactant concentration was a parameter of secondary relevance on the DSD probably due to the reduction of the coalescence rate and to a faster stabilization of the O/W interface. The use of a flat blade propeller instead of a Rushton turbine was preferable for the production of a narrower DSD. Finally the time required to reach equilibrium was found higher by a factor of 3–4 than predicted in the literature.
The process of encapsulation by complex coacervation includes several steps that have been investigated in order to reach a better control over the whole process. This has been carried out for the ...encapsulation of linseed oil by the classical gelatin/acacia gum pair of coacervating polymers. Fabrication of an oil‐in‐water emulsion is the first step that has been studied so as to reach a definite picture of the emulsification process under intermediate flow regime in a stirred unbaffled vessel. The classical scheme of oil droplet break‐up by turbulent eddies in the turbulent inertial regime gave a fair agreement with the experiments and can be used as a possible framework for a process scale‐up. Polynuclear microcapsules containing several oil droplets have been obtained during the deposition of the coacervate onto the surface of oil droplets. According to the emulsification conditions and microparticles growth caused by multiple droplets encapsulation, microcapsules of ∼130 µm were produced. A video probe immersed in the stirred vessel allowed an in situ monitoring of the successive events taking place as acid was added into the medium. This technique allows dynamic observations of microcapsules formation. These observations confirmed the deposition of coacervate droplets around oil drops and clearly showed that the formation of coacervate particles and their deposition onto oil droplets were successive events.
The crystallization-in-emulsion process allows the production of solid particles exhibiting specific features. Here, the batch crystallization process carried out by cooling a melted oil dispersed as ...an oil-in-water emulsion was studied. Two experimental set-ups allowing the in situ visualization of the nucleation and growth phenomena occurring in the dispersed liquid phase were developed. Observations in quiescent medium of motionless droplets having a diameter of few tens of micrometers showed that primary nucleation started on the inner surface of the droplets. The fast growth of the crystals consumed all the liquid contained within each droplet and was confined within each droplet by the oil–water interface. Solid polycrystalline particles similar in size to the parent droplets were produced. Dynamic tracking of the transient evolution of the size distributions of the two populations of droplets and solid particles during the cooling process in a stirred vessel was carried out using an in situ optical probe. It was shown that the droplets crystallized very progressively during cooling, starting with the largest droplets and ending with the smaller size droplets since the induction time of primary nucleation was dependent on droplet volume. In dilute conditions (1%wt% of dispersed phase) each droplet was converted into a single solid particle. Secondary nucleation based on inter-droplet collisions was not observed in these conditions.
►Crystallization-in emulsion process of a cosmetic melted compound. ► Development of two experimental set-ups (thermostated well and in situ video probe). ► Nucleation and growth events inside droplet under stagnant and agitated conditions. ► Real time video tracking of the transition from droplet to particle populations. ► Simultaneous measurement of size distributions of droplets and particles.
Two in situ process analytical technologies were used to investigate a cocrystallization process: a focused beam reflectance measurement probe and a video probe. The cocrystallizations were conducted ...batch‐wise in a stirred thermostatted vessel with carbamazepine and nicotinamide. The experiments were started in three domains of the phase solubility diagram. When carbamazepine crystals were also formed, a solution mediated phase transition from carbamazepine crystals towards cocrystals was initiated by the addition of the cocrystallizing agent (nicotinamide crystals). As the carbamazepine crystals and the carbamazepine/nicotinamide cocrystals exhibit prism‐like and needle‐like habits, respectively, it was possible to discriminate between them with the two sensors. The mechanisms involved in the solution mediated phase transition were investigated.
Two in situ process analytical technologies were used to investigate a carbamazepine (CBZ)/nicotinamide cocrystallization process: a focused beam reflectance measurement probe and a video probe. As the CBZ crystals and the cocrystals exhibit different habits, it was possible to discriminate between them with the two sensors.
The main objective of this study was to develop and to set up a new optical direct microscopy method, based on the reflected light flux differences, with episcopic axial lighting to characterize the ...different phases structure of commercial overrun ice creams. Firstly, the results obtained have been validated by two others methods, a destructive method by dispersion and observation by light microscopy and, an indirect method, by scanning electron microscopy after freeze-drying sample. It was observed that the three methods were in agreement and led to the same conclusions concerning the main freezing parameters influence.
So, this technique has been principally used to investigate the effects of the freezing conditions on the ice crystal structure. One of the most important parameters is the freezing rate that governs not only the size, but also the ice crystals texture of the ice cream. The air introduction (overrun) tends to limit the ice crystal growth. Besides, by this method, it was also possible to observe and to quantify the air bubbles size distribution. This direct microscopy method could be extended to other frozen food structure analysis.
