Hydrodynamics and Mass Transfer in a Concentric Internal Jet-Loop Airlift Bioreactor Equipped with a Deflector

The gas–liquid hydrodynamics and mass transfer were studied in a concentric tube internal jet-loop airlift reactor with a conical bottom. Comparing with a standard design, the gas separator was equipped with an adjustable deflector placed above the riser. The effect of riser superficial gas velocity uSGR on the total gas holdup εGT, homogenization time tH, and overall volumetric liquid-phase mass transfer coefficient kLa was investigated in a laboratory bioreactor, of 300 mm in inner diameter, in a two-phase air–water system and three-phase air–water–PVC–particle system with the volumetric solid fraction of 1% for various deflector clearances. The airlift was operated in the range of riser superficial gas velocity from 0.011 to 0.045 m/s. For the gas–liquid system, when reducing the deflector clearance, the total gas holdup decreased, the homogenization time increased twice compared to the highest deflector clearance tested, and the overall volumetric mass transfer coefficient slightly increased by 10–17%. The presence of a solid phase shortened the homogenization time, especially for lower uSGR and deflector clearance, and reduced the mass transfer coefficient by 15–35%. Compared to the gas–liquid system, the noticeable effect of deflector clearance was found for the kLa coefficient, which was found approx. 20–29% higher for the lowest tested deflector clearance.

SUBSOLIDUS STRUCTURE OF THE MgO – FeO – Al2O3 SYSTEM

Three-component systems constitute the physicochemical basis of most refractory materials and the analysis of their subsolidus structure makes it possible to accurately predict the areas of compositions with optimal properties, as well as give recommendations on the technological parameters of production, sintering, and operation of the materials obtained. As a result of the carried out thermodynamic analysis of the MgO – FeO – Al2O3 system, it was found that the partition of the system into elementary triangles undergoes changes in two temperature ranges: I – up to a temperature of 1141 K and II – above a temperature of 1141 K. By calculation methods, the geometrical-topological characteristics of the subsolidus structure of the system are determined MgO – FeO – Al2O3: areas of elementary triangles, degree of their asymmetry, area of regions in which phases exist, probability of phase existence in the system. It has been established that, over the entire temperature range, there is a fairly extended concentration region of spinel phases: hercynite (FeAl2O4) – noble spinel (MgAl2O4). Moreover, periclase (MgO) coexists simultaneously with both spinels only in the low-temperature region. This indicates that when obtaining periclase-spinel refractories with increased heat resistance, an important technological parameter is a cooling rate below 1141 K. To obtain periclase-spinel refractories with branched microcracking of the structure due to differences in the thermal expansion coefficients of periclase, hercynite and noble spinel, the most rational concentration region of the system under study is which is common for two elementary triangles (MgO – FeAl2O4 – MgAl2O4 and MgO – FeO – MgAl2O4) existing in different temperature ranges. At high firing temperatures, the elementary triangle MgO – FeO – MgAl2O4 has a maximum area and a minimum degree of asymmetry, and upon cooling, MgO – FeAl2O4 – MgAl2O4 is formed, which is quite large in area, but has a high degree of asymmetry. Therefore, the composition of the charge for periclase-spinel refractories should be predicted with a high dosage accuracy and with a significant homogenization time of the components during mixing, since the concentration region common for both of the above elementary triangles is significantly reduced. Thus, the division of the MgO – FeO – Al2O3 system into elementary triangles and the analysis of the geometrical-topological characteristics of the phases of the system made it possible to select in the system under study the range of compositions with optimal properties for obtaining spinel-containing materials.

Stabilization and Release of Palm Tocotrienol Emulsion Fabricated Using pH-Sensitive Calcium Carbonate

Calcium carbonate (CaCO3) has been utilized as a pH-responsive component in various products. In this present work, palm tocotrienols-rich fraction (TRF) was successfully entrapped in a self-assembled oil-in-water (O/W) emulsion system by using CaCO3 as the stabilizer. The emulsion droplet size, viscosity and tocotrienols entrapment efficiency (EE) were strongly affected by varying the processing (homogenization speed and time) and formulation (CaCO3 and TRF concentrations) parameters. Our findings indicated that the combination of 5000 rpm homogenization speed, 15 min homogenization time, 0.75% CaCO3 concentration and 2% TRF concentration resulted in a high EE of tocotrienols (92.59–99.16%) and small droplet size (18.83 ± 1.36 µm). The resulting emulsion system readily released the entrapped tocotrienols across the pH range tested (pH 1–9); with relatively the highest release observed at pH 3. The current study presents a potential pH-sensitive emulsion system for the entrapment and delivery of palm tocotrienols.

Structure and Size Distribution of Powders Produced from Melt-Spun Fe-Si-B Ribbons

This work studies the production of melt spun Fe78Si9B13 ribbons with amorphous or nanocrystalline structure. The main objective is the preservation of the amorphous structure after obtaining powders by mechanical milling of the ribbons, as well as the study of the influence of the milling conditions on the size distribution and structure of the obtained powders. In order to obtain high quality amorphous ribbons, the wheel rotation speed, crucible-wheel distance, melt homogenization time, ejection pressure and the ejection temperature were optimized in the melt spinning process. Different mills were used for powder production, studying the size distribution, efficiency, and preservation of the amorphous character as a function of the milling time. Ribbons and powders were characterized by X-ray diffraction (XRD) and electron microscopy (SEM and TEM); laser diffraction was used for powder granulometry.

Microstructural Evolution of Al–Zn–Mg–Cu Alloys in Accordance with Homogenization Time

The microstructural evolution of Al–Zn–Mg–Cu alloys has been investigated for the homogenization time effect on the texture, grain orientation and dislocation density. The Al–Zn–Mg–Cu alloys were casted and homogenized for 4, 8, 16 and 24 hours. Electron backscatter diffraction (EBSD) analysis was conducted to characterize the microstructural behavior. Micropillars were fabricated using focused ion beam (FIB) milling in grains of specific crystallographic orientations. Coarse precipitations in the grain boundaries are S (Al2CuMg) and T (Al2Mg3Zn3) phases verified by scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) observation. With increasing homogenization time, equiaxed cell sizes increased. The volume fraction of S and T phases decreased with the diffusion of atomic elements into matrix. The Vickers hardness and tensile strength values decreased with homogenization temperature. The micropillar compression analysis was compared to macro tensile test results to understand the size effect and strain burst phenomenon on the mechanical properties of Al–Zn–Mg–Cu alloys.

Effect of Processing/Formulation Parameters on Particle Size of Nanoemulsions Containing Ibuprofen - An Artificial Neural Networks Study

Background: Nanoemulsions are colloidal transparent systems for the delivery of hydrophobic drugs. This study aimed to determine the effect of parameters affecting particle size of a nanoemulsion containing ibuprofen using artificial neural networks (ANNs). Methods: Nanoemulsion samples with different values of independent variables, namely, concentration of ethanol, ibuprofen and Tween 80 as well as exposure (homogenization) time were prepared and their particle size was measured using dynamic light scattering (DLS). The data were then modelled by ANNs. Results: From the results, increasing the exposure time had a positive effect on reducing droplet size. The effect of concentration of ethanol and Tween 80 on droplet size depended on the amount of ibuprofen. Our results demonstrate that ibuprofen concentration also had a reverse relation with the size of the nanoemulsions. Conclusion: It was concluded that to obtain minimum particle size, exposure (homogenization)time should be maximized.

Preparation of Curcumin Nanosuspension with Gum Arabic as a Natural Stabilizer: Process Optimization and Product Characterization

Low aqueous solubility and poor bioavailability of curcumin have limited its application in various fields. One approach to address this issue is to formulate a nanosuspension that incorporates curcumin, which has been previously shown to exhibit remarkably improved solubility in comparison with that of a bare compound. In this study, the preparation process of curcumin nanosuspension was optimized with a median particle size as the outcome. Gum arabic was used as a natural polymeric surfactant and the suspension was formulated using high speed homogenization. Optimization results, realized via a response surface methodology, showed that a minimum median particle size (8.524 µm) could be attained under the following conditions: curcumin:gum arabic ratio of 1:6 g/g; homogenization speed of 8300 rpm and homogenization time of 40 min. Under these conditions, the particle size of obtained suspension was shown to be consistent for around seven days without major aggregation. The homogenization process could be scaled up to five times in terms of suspension volume. TEM also showed that curcumin nanoparticles had a nearly spherical shape and homogeneous structure with a size range of 40–80 nm.

THE ROLE OF COMBINED MOLTEN SALTS IN SODIUM-CERIUM (III) ORTHOPHOSPHATE CRYSTALLIZATION

The efficient crystallization conditions for high temperature synthesis of sodium-cerium(III) orthophosphate from binary molten salts have been investigated in a light of influence of the inert reaction media addition. Taking into consideration NaF and Na2MoO4 as an addictives to a convention phosphate melt the crystallization regions of CePO4 and Na3Ce(PO4)2 have been identified by means of IR spectroscopy and powder X-Ray diffraction methods. The initial Na/P ratio in the melt has been shown to play the key role in pure Na3Ce(PO4)2 phase formation. The concentration of NaF has been chosen as 20–60 mol. % and MoO3 in a range of 30–60 mol. %, while the cerium(III) content has been maintained equal to 10 mol. %. Additional application of NaF or Na2MoO4 lowers the temperature from 1400 in comparison to Na4P2O7 flux to 1000°C and homogenization time from 12 to 1h., respectively. Thus, the optimal conditions for the high-temperature growth has been found to be Na/P = 1.67 and NaF content equal to 30–45% mol. in case of fluoride-containing systems, and Na/P> 4,00 with MoO3 content of 25–36% mol for a molybdate one. In case of both fluoride and molybdate addition the crystallization region of the target compound has been bordered by a wide area of CePO4 phase. Three crystallization regions has been estimated during crystallization process: CePO4, Na3Ce(PO4)2 and a wide field of their co-crystallization. With Na/P ratio in the binary melt there is a simultaneous change in the solids structure prepared. Thus, when CePO4 possesses highly condensed CeO8 polyhadra in the framework and crystallizes at lower Na/P ratio, Na3Ce(PO4)2 corresponds to isolated CeO8 moieties that are stabilized under higher Na/P values. Within the synthetic conditions investigated, the melts have shown to play a depolymerizing role for the phosphate chains found in the melt, leading to crystallization temperature lowering in initial melt. The approach proposed for the of Na3Ce(PO4)2 synthesis allows to expand the temperature range of its formation and to carry out its uniform doping with fluorescent activators to modify its characteristic spectrum for the needs of modern inorganic LEDs.