Low Stirring Speed Research Articles

Ultrasound-assisted preparation of emulsion and its application in 1-naphthol wastewater treatment

A stable emulsion with NaOH as the inner phase, sorbitan monooleate (span80) as the surfactant, and kerosene, cyclohexane, n-heptane, methylbenzene or p-xylene as the organic membrane phase, was prepared successfully by a magnetic stirring apparatus at low stirring speed (720rev min−1) to make the pre-emulsion and then using the ultra-sonication devices. The separation efficiency in emulsion liquid membrane system to remove 1-naphthol was investigated. The parameters that affect the removal efficiency of 1-naphthol were studied systematically. At the optimal conditions, cyclohexane as the solvent phase, 2% NaOH as the inner phase, ultrasound time 5 minutes, the ratio of oil to inner phase 1:2, pH of feed phase without adjusted (pH = 6·4), contact time 15 minutes, ratio of emulsion to water 1:5, 1-naphthol removal can nearly reach 98% with a low level of 1·14% of emulsion leakage at 20 minutes.

Thermodynamic and kinetic study of CaCO3 precipitation threshold

Calcium carbonate is one of the most sparingly soluble salts among those forming the scale. As its solubility is dependent on CO2 and then pH, natural water exploitation equipment such as process, drinking or irrigation systems are often faced with a serious scaling problem. Having as an objective to control the scale formation, this present work aims at studying the CaCO3 precipitation threshold using the classic fast controlled precipitation method. Studied solutions to be used are calco-carbonic waters ([Ca(HCO3)2] = 0.4g L −1). Obvious results show that CaCO3 precipitation threshold occurs at higher nucleation time and lower supersaturation coefficient with lower temperature, stirring speed and dissolved CO2 degasification rate. The probability of CaCO3 heterogeneous precipitation has increased with low stirring speed, low dissolved CO2 degasification rate and low temperature.

Morphology transformation of micrometre-sized giant vesicles based on physical conditions for photopolymerisation-induced self-assembly

The physical conditions to vary the morphology of vesicles formed by amphiphilic poly(methacrylic acid)-block-poly(methyl methacrylate-random-methacrylic acid) were determined for the self-assembly induced by the nitroxide-mediated photocontrolled/living radical polymerisation performed in an aqueous methanol solution. The copolymer produced micrometre-sized spherical vesicles in the solution with a 30 wt% water content. The vesicles were transformed into a film-like morphology by decreasing the water content, whereas they were changed into nanometre-sized spherical vesicles by increasing it. The concentration of the growing polymer chain also varied the morphology. Large spherical vesicles formed at a low concentration were transformed into much smaller vesicles, followed by rod-like vesicles as a result of increasing the concentration. Furthermore, the stirring speed during the polymerisation-induced self-assembly dominated the morphology. Large elliptical vesicles produced at a low stirring speed changed into spherical vesicles, but decreased the size as the speed increased.

Assessment of air entrainment in stirred tanks using capacitive sensors

Air entrainment is among the key issues in solid–liquid mixing operations. In this paper, both analytical and finite element methods are employed to study the relationship between the volume of entrained air and the changes of capacitance. With a capacitance sensor installed at the bottom of the stirred tank, an experimental platform is established, which integrates a stirring system and a capacitive detection system. The pitched-blade turbines with four blades (PBT-4) are employed as the impellers in the experimental system and made of Plexiglas. Afterwards, the experiments are conducted with an empty tank to study the influences of propellers on capacitance. The capacitance values are measured at different stirring speeds in the single-phase (deionized water) and two-phase (deionized water and glass beads) stirring systems and applied in the assessment of air entrainment. The results are as follows. In the single-phase system, there is scarcely any air entrained in stirred tanks at low stirring speeds, and air entrainment occurs after the stirring speed (N) reaches a certain value. In the two-phase system, air entrainment is not observed obviously when the solid particles are at rest, but can be found after solid particles are mixed uniformly. Nevertheless, in the transition period between the two regions above, the capacitance becomes increasingly larger along with the growth of N due to the decrease of volume fraction of solid particles in the sensing area, which hinders the assessment of air entrainment. The discussions in this paper may serve as guidelines for solid–liquid mixing processes and can be further generalized for the assessment of air entrainment in solid–liquid mixing operations under other different parameters.

Separation of Nickel in Manganese Sulfate Solution Soaked out from Low-Grade Pyrolusite with Pyrite and H<sub>2</sub>SO<sub>4</sub>

The study on separation of nickel ions with S.D.D from six kinds of solutions or systems was conducted. One of six kinds of systems was prepared with the solution (called as original solution here) leached from pyrolusite with pyrite and H2SO4, and the other five kinds of systems were prepared with analytical reagents, they are respectively: a monophyletic system of NiSO4, two binary systems of MnSO4NiSO4 and (NH4)2SO4NiSO4, a ternary system of MnSO4(NH4)2SO4NiSO4, a pentanary system of MnSO4(NH4)2SO4NiSO4CoSO4ZnSO4. The experiments about reaction time and S.D.D dosage were conducted. Results showed that the equilibrium time of reactions for the prepared five systems were equally 10min at most, while 3h was needed at least for original solution under the conditions of low temperature and low stirring speed. The residual nickel ion concentrations of the six systems were different when the same multiples of S.D.D theory dosage of each system was used for separation of nickel ions, and the S.D.D dosages for the six systems needed to meet the requirement of electrolysis were also different.

Study on Energy Consumption Distribution of High Ferric-Based Silicon Coagulant Using Fractal Dimension

High ferric-based silicon coagulant is a kind of new self-made coagulant. The high ferric content was introduced in the preparation process of the coagulant, and the effect was good in dealing with simulated industrial wastewater with lead. The beaker test indicated that the lead removal rate reached the highest 96.48% when the rapid stirring speed was 300r/min and stirring time was 1min, low stirring speed was 80r/min and stirring time was 15min, the dosage of the coagulant was 3.5ml/L. And the fractal dimension of flocs was 1.67674 under that optimum conditions. The low stirring stage was divided into three different stages in the orthogonal experiment of energy consumption, and the result showed that the optimum combination of flocculation was: velocity gradient G1=67.7s-1, stirring time T1=4min; G2=57.8 s-1, T2=5min; G3=23.9s-1, T3=6min. The removal rate of lead ion improved and the energy consumption decreased when the flocculation was divided into different stages. The relations between fractal dimension and energy consumption distribution can be obtained by calculated the fractal dimension of different stages. The stirring speed can be controlled and the flocs can be prevented from being broken by observing the flocs.

Control strategy of pH, dissolved oxygen concentration and stirring speed for enhancing β‐poly (malic acid) production by Aureobasidium pullulans ipe‐1

AbstractBACKGROUND: β‐poly(malic acid) (PMLA) can be used as a pro‐drug or for a drug‐delivery system. Effects of pH, dissolved oxygen concentration (DO) and stirring speed were investigated to improve PMLA production by A. pullulans ipe‐1.RESULTS: The strain produced a high PMLA concentration when pH and DO remained at about 6.0 and above 70%, respectively, and the yeast‐like cells were the main PMLA producers. To further promote PMLA production, the cultivation could be divided into three phases. In phase I, cell growth was accelerated by maintaining high DO (>70%) with a constant stirring speed of 800 rpm. In phase II, PMLA production was increased by controlling DO at 70% using the automatically controlled stirring speed. In phase III, PMLA production on per gram of glucose (Yp/s) was enhanced by keeping DO at 70%, and using a low stirring speed to decrease cell growth. Compared with batch cultures, a higher PMLA yield was obtained with this strategy, i.e. PMLA production and Yp/s increased by 15% and 18%, respectively.CONCLUSION: Control strategies for pH, DO and stirring speed provide a good reference for process development and optimization of PMLA production. © 2012 Society of Chemical Industry

Emulsification/internal gelation as a method for preparation of diclofenac sodium–sodium alginate microparticles

Emulsification/internal gelation has been suggested as an alternative to extrusion/external gelation in the encapsulation of several compounds including non-steroidal anti-inflammatory drugs such as diclofenac sodium. The objective of the present study was a trial to formulate diclofenac sodium as controlled release microparticles that might be administered once or twice daily. This could be achieved via emulsification/internal gelation technique applying Box-Behnken design to choose these formulae. Box-Behnken design determined fifteen formulae containing specified amounts of the independent variables, which included stirring speed in rpm (X1), drug:polymer ratio (X2) and the surfactant span 80% (X3). The dependent variables studied were cumulative percent release after two hours (Y1), four hours (Y2) and eight hours (Y3). The prepared microparticles were characterized for their production yield, sizes, shapes and morphology, entrapment efficiency and Diclofenac sodium in vitro release as well. The results showed that the production yield of the prepared diclofenac sodium microparticles was found to be between 79.55% and 97.41%. The formulated microparticles exhibited acceptable drug content values that lie in the range 66.20–96.36%. Also, the data obtained revealed that increasing the mixing speed (X1) generally resulted in decreased microparticle size. In addition, scanning electron microscope images of the microparticles illustrated that the formula contains lower span concentration (1%) in combination with lower stirring speed (200rpm) which showed wrinkled, but smooth surfaces. However, by increasing surfactant concentration, microspheres’ surfaces become smoother and slightly porous. Kinetic treatment of the in vitro release from drug-loaded microparticles indicated that the zero order is the drug release mechanism for the most formulae.

Controlled Delivery of Gentamicin Using Poly(3-hydroxybutyrate) Microspheres

Poly(3-hydroxybutyrate), P(3HB), produced from Bacillus cereus SPV using a simple glucose feeding strategy was used to fabricate P(3HB) microspheres using a solid-in-oil-water (s/o/w) technique. For this study, several parameters such as polymer concentration, surfactant and stirring rates were varied in order to determine their effect on microsphere characteristics. The average size of the microspheres was in the range of 2 μm to 1.54 μm with specific surface areas varying between 9.60 m2/g and 6.05 m2/g. Low stirring speed of 300 rpm produced slightly larger microspheres when compared to the smaller microspheres produced when the stirring velocity was increased to 800 rpm. The surface morphology of the microspheres after solvent evaporation appeared smooth when observed under SEM. Gentamicin was encapsulated within these P(3HB) microspheres and the release kinetics from the microspheres exhibiting the highest encapsulation efficiency, which was 48%, was investigated. The in vitro release of gentamicin was bimodal, an initial burst release was observed followed by a diffusion mediated sustained release. Biodegradable P(3HB) microspheres developed in this research has shown high potential to be used in various biomedical applications.

Mass transfer of chlorobenzene in concentrated sulfuric acid

Mass transfer of chlorobenzene in sulfuric acid is very important in the nitration of chlorobenzene by mixed acid. This article presents the determination of mass transfer coefficient at high-concentrations of sulfuric acid at 298 K and 313 K at 2 π rad/s and 4 π rad/s impeller speeds. The experiments were carried out under flat-interface conditions in an unbaffled glass reactor of 10 cm diameter and 1 dm 3 capacity. A glass stirrer with two paddle-type impellers was employed for stirring. The upper paddle stirred the organic phase and the lower paddle stirred the aqueous phase. High mass transfer coefficients were obtained at high-concentrations of sulfuric acid. Dynamic light scattering of the aqueous phase revealed that a dispersion of chlorobenzene spontaneously formed in sulfuric acid, which is believed to be the main factor behind the high mass transfer coefficient. NMR analysis of the aqueous phase showed that no chemical reaction occurred at 298 K and 313 K, but some amount of 4-chlorobenzenesulfonic acid formed at 323 K. The high mass transfer coefficient is expected to result in high yield of chloronitrobenzenes at moderate temperatures and low stirring speeds.

In the presence of strong P2Y12 receptor blockade, aspirin provides little additional inhibition of platelet aggregation

Aspirin and antagonists of platelet ADP P2Y(12) receptors are often coprescribed for protection against thrombotic events. However, blockade of platelet P2Y(12) receptors can inhibit thromboxane A(2) (TXA(2))-dependent pathways of platelet activation independently of aspirin. To assess in vitro whether aspirin adds additional antiaggregatory effects to strong P2Y(12) receptor blockade. With the use of platelet-rich plasma from healthy volunteers, determinations were made in 96-well plates of platelet aggregation, TXA(2) production and ADP/ATP release caused by ADP, arachidonic acid, collagen, epinephrine, TRAP-6 amide and U46619 (six concentrations of each) in the presence of prasugrel active metabolite (PAM; 0.1-10 μmol L(-1)), aspirin (30 μmol L(-1)), PAM + aspirin or vehicle. results: PAM concentration-dependently inhibited aggregation; for example, aggregation in response to all concentrations of ADP and U46619 was inhibited by ≥ 95% by PAM at > 3 μmol L(-1) . In further tests of PAM (3 μmol L(-1)), aspirin (30 μmol L(-1)) and PAM + aspirin, aspirin generally failed to produce more inhibition than PAM or additional inhibition to that caused by PAM. The antiaggregatory effects of PAM were associated with reductions in the platelet release of both TXA(2) and ATP + ADP. Similar effects were found when either citrate or lepirudin were used as anticoagulants, and when traditional light transmission aggregometry was conducted at low stirring speeds. P2Y(12) receptors are critical to the generation of irreversible aggregation through the TXA(2) -dependent pathway. As a result, strong P2Y(12) receptor blockade alone causes inhibition of platelet aggregation that is little enhanced by aspirin. The clinical relevance of these observations remains to be determined.

The effect of stirring speed and induction time on flotation

A computational fluid dynamic model has been developed for a modified Denver flotation cell used in laboratory batch tests. The model incorporates fundamental aspects of bubble–particle interactions including bubble–particle collision, attachment and detachment. Model predictions are compared against carefully planned laboratory experiments with narrowly-sized spherical ballotini. Flotation results for different impeller speeds have been obtained for a constant air flow into the cell. The particles have been made hydrophobic by methylation with trimethylchlorosilane. For a given particle size, the results from the model and experimental work indicate that there is an optimum stirring speed that produces a good compromise between attachment and detachment rates in the cell for flotation. For less hydrophobic particles, a lower stirring speed is beneficial in having a longer contact time because of the longer induction time required for attachment.

Copper Extraction Kinetics by Beta-Diketone Derivatives (Acylpyrazolones and Acylisoxazolones) in Water/Chloroform Biphasic System

Copper(II) extraction and back-extraction rates were determined in a water/chloroform system using a bell-shaped transport cell. Various 1-phenyl-3-methyl-4-acyl-pyrazol-5-ones (with acyl = benzoyl, 2-thenoyl, octadecanoyl, p-tert-butylbenzoyl, 3-phenyl-propanoyl, and iso-nonanoyl) and 3-phenyl-4-acylisoxazol-5-ones (with acyl = benzoyl and p-tert-butylbenzoyl) were considered. The back-extraction rate is shown to be limited by the diffusion of the complex in the organic unstirred layer, whatever the stirring speed and whatever the ligand considered. At low stirring speed, the extraction rate appears to be limited by the diffusion of either a complex or a ligand species in the unstirred layers, depending on the pH. At high stirring speed, the extraction rate is limited by the interfacial complexation. The extraction rate dependence on side-group variation cannot be correlated with hydrophobicity or acidity of the extractants and may be explained by structural differences of the CO vicinal group of the acyl.

Study on Semi-Solid Magnesium Alloy Produced by Mechanical Stirring

Semi-solid magnesium alloy slurry was produced by a newly self-developed mechanical stirring machine in order to prepare continuous semi-solid slurry. The changing principle of semi-solid microstructure was studied under different conditions—the changing of temperature, stirring rate, cooling rate and stirring time. It was showed that the lower the temperature of slurry, the higher the stirring rate, the longer the stirring time and the faster the cooling rate, the grain will be smaller and more evenly rounded. When the stirring speed and temperature are the same, better semi-solid spherical grains can be gained by increasing the stirring time. At the same stirring temperature and higher stirring speed, semi-solid spherical particles are smaller, rounder and more evenly; at a low stirring speed, we can't get ideal semi-solid spherical grains even if we increase the stirring time. The ideal technological parameters of semi-solid AZ61 alloy produced with no-dendritic structure were recommended to be 600°C～605°C (stirring end temperature) 、3min～ 5min(stirring time) and 500r/min(stirring rate). Compared with conventional casting alloy, semi-solid alloy mechanical properties were greatly improved. The non-dendrite semi-solid forming mechanism was studied; mechanical stirring semi-solid non-dendritic formation was the result of a variety of factors, the key cause is mechanical shear stress.

Start-up and stabilization of an Anammox process from a non-acclimatized sludge in CSTR

Development of an Anammox (anaerobic ammonium oxidation) process using non-acclimatized sludge requires a long start-up period owing to the very slow growth rate of Anammox bacteria. This article addresses the issue of achieving a shorter start-up period for Anammox activity in a well-mixed continuously stirred tank reactor (CSTR) using non-acclimatized anaerobic sludge. Proper selection of enrichment conditions and low stirring speed of 30 +/- 5 rpm resulted in a shorter start-up period (82 days). Activity tests revealed the microbial community structure of Anammox micro-granules. Ammonia-oxidizing bacteria (AOB) were found on the surface and on the outer most layers of granules while nitrite-oxidizing bacteria (NOB) and Anammox bacteria were present inside. Fine-tuning of influent NO2(-)/NH4+ ratio allowed Anammox activity to be maintained when mixed microbial populations were present. The maximum nitrogen removal rate achieved in the system was 0.216 kg N/(m(3) day) with a maximum specific nitrogen removal rate of 0.434 g N/(g VSS day). During the study period, Anammox activity was not inhibited by pH changes and free ammonia toxicity.

Open porous emulsion‐templated monoliths: Effect of the emulsion preparation conditions on the foam microstructure and properties

AbstractHighly open porous polymer foams were prepared via the polymerization of 10 : 1 styrene/divinylbenzene high‐internal‐phase emulsions (HIPEs) prepared under various emulsifying conditions. The effects of the emulsification stirring speed (SS) and rate of aqueous droplet‐phase addition on the HIPE equilibrium torque value, an approximate characterization of HIPE viscosity, and the microstructure and properties of the resulting HIPE polymer solid foams were investigated. SS was varied over the range 400–1200 rpm for aqueous‐droplet‐phase addition rates (AARs) of 0.53 and 1.3 mL/min. The microscopic results showed that at lower AARs, increasing SS decreased the weighted‐average cell diameter from 24.31 to 13.55 μm, whereas the cell size distribution was broadened, and the intercellular pore size varied irregularly in the range 0.76–1.42 μm. The average cell diameter and intercellular pore size for the solid foams prepared at higher AARs were greater than that of those prepared at lower AARs. The density of the foam materials ranged from 0.057 to 0.072 g/cm3, whereas their thermal conductivity varied from 0.649 to 0.705 W m−1 °C−1. The highest compressive stress–strain properties were found for the foam sample prepared with highest SS and a lower AAR. Adding electrolyte CaCl2 to HIPE produced remarkable increases in the void diameter and intercellular pore size, especially at lower SS values. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Preparation and Evaluation of Gelatin/Sodium Carboxymethyl Cellulose Polyelectrolyte Complex Microparticles for Controlled Delivery of Isoniazid

The ratio of gelatin to sodium carboxymethyl cellulose (SCMC) at which maximum yield was obtained was optimized. This optimized ratio of gelatin to SCMC along with other parameters was used to prepare microparticles of different sizes. Vegetable oil was used as emulsion medium. Effect of various factors like amount of surfactant, concentration of polymer on the formation, and size of the microparticles was investigated. These microparticles were used as carrier for isoniazid. Among different cross-linkers, glutaraldehyde was found to be the most effective cross-linker at the temperature and pH at which the reaction was carried out. The loading efficiency and release behavior of loaded microparticles were found to be dependent on the amount of cross-linker used, concentration of drug, and time of immersion. Maximum drug loading efficiency was observed at higher immersion time. The release rate of isoniazid was more at higher pH compared to that of at lower pH. The sizes of the microparticles were investigated by scanning electron microscope. In all the cases, the microparticles formed were found spherical in shape except to those at low stirring speed where they were agglomerated. Fourier transform infrared study indicated the successful incorporation of isoniazid into the microparticles. Differential scanning calorimetry study showed a molecular level dispersion of isoniazid in the microparticles. X-ray diffraction study revealed the development of some crystallinity due to the encapsulation of isoniazid.

Microcalorimetric Studies on Chemical Oscillation of Microgels

By use of isothermal titration calorimetry (ITC) and ultrasensitive differential scanning calorimetry (US-DSC), we have investigated the energy change in the periodic swelling-to-deswelling of thermally sensitive poly(N-isopropylacrylamide) (PNIPAM) microgels containing ruthenium(II) tris(2,2'-bipyridine) (Ru(bpy)3) which is a catalyst for Belousov-Zhabotinsky (BZ) reaction. As temperature increases, the induction period and oscillation period of BZ reaction decrease because the reaction rate increases. However, the oscillation disappears at a temperature above the lower critical solution temperature (LCST) of the microgels since Ru(bpy)3 is trapped in the microgels and cannot react with BZ substrates. As microgel size increases or the cross-linking density decreases, the restriction of polymer networks on Ru(bpy)3 decreases, so that Ru(bpy)3 can readily contact with BZ substrates, leading the oscillation amplitude to increase. In addition, the so-called transient chaos occurs at a low stirring speed, and it wanes with the increasing stirring speed. All the facts indicate that the contact between Ru(bpy)3 and BZ substrates determines the oscillation of the microgels.

Preparation and characterization of cross‐linked polymeric nanoparticles for enhanced oil recovery applications

AbstractChemically cross‐linked nanoparticles from dilute aqueous alkali solutions of hydroxyethylcellulose (HEC) in the presence of a cross‐linker agent (divinyl sulfone, DVS) were prepared from a reaction mixture, which was exposed to different stirring speeds during the cross‐linking process. At various stages during the cross‐linking procedure, the reaction was terminated and the species were characterized by means of turbidimetry, asymmetric flow field‐flow fractionation (AFFFF), dynamic light scattering (DLS), and rheo‐small‐angle light scattering (rheo‐SALS) methods. During the cross‐linking of a dilute polymer solution, the competition between intrapolymer and interpolymer is a prominent feature. The DLS results show that at early times in the cross‐linking process, intrachain cross‐linking with contraction of the complexes is promoted by high stirring speeds; at later times the growth of aggregates is inhibited by high stirring speeds. The results from the rheo‐SALS measurements disclosed that at early times during the cross‐linker reaction, the complexes are fragile against shear forces if the reaction mixture had been subjected to low stirring speeds. At a later state of cross‐linking, more cross‐links lead to better stability of the species, even for solutions that have been exposed to low stirring speeds during the cross‐linking process. This study shows that the sizes of the particles can be tuned by exposing the solutions to different stirring speeds during the cross‐linker reaction and to terminate the reaction at desired reaction times. The strategy discussed in this work for the preparation of particles of various sizes is of special interest in connection with enhanced oil recovery applications. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Response surface analysis to evaluate the influence of deposition parameters on the electrodeposition of Cu–Co alloys in citrate medium

Copper–cobalt alloy coatings were deposited on mild steel substrates using sodium citrate electrolytes at room temperature and under direct current. A set of cathodic polarization curves was plotted by varying the mechanical stirring speed of the solution (0–400 rpm), using a range of current densities during the electrodeposition experiments. Factorial design was used to verify the influence of these deposition parameters on the cathodic efficiency, the copper and cobalt content in the coating, the corrosion current density of the coating/substrate system, and the efficiency of the coating in protecting the substrate. The electroplating experiments showed that, with the studied bath composition, high stirring speed and low current density lead to greater cathodic current efficiency and copper-rich coatings. On the other hand, high current density and low stirring speed yields coatings with high cobalt content and a lower cathodic efficiency. Our results show that the studied parameters affect the corrosion current density and the coating efficiency of the coating/substrate system in opposite ways. The best results were obtained increasing the current density and decreasing the mechanical stirring speed. Additionally, three samples were produced in selected deposition conditions. The coatings morphologies were compact, and their grain sizes seemed to enlarge with increasing stirring speed and decreasing current density.