Efficient Agitation Research Articles

Dispersion Polymerization versus Emulsifier-Free Emulsion Polymerization for Nano-Object Fabrication: A Comprehensive Comparison.

Although the preparation of nano-objects by emulsifier-free controlled/living radical emulsion polymerization has drawn much attention, the morphologies of these formed objects are difficult to predict and to reproduce because of the much more complex nucleation mechanisms of emulsion polymerization compared to only one self-assembling nucleation mechanism of controlled radical dispersion polymerization. The present study compares dispersion polymerization with emulsifier-free emulsion polymerization in terms of nucleation mechanism, polymerization kinetics, and disappearance behavior of the macrochain transfer agent, gel permeation chromatograms curves of the obtained block copolymer as well as the structural and morphological differences between the produced nano-objects on the basis of published data. Moreover, the effects of the inherently heterogeneous nature of emulsion polymerization on the mechanism of reversible addition-fragmentation transfer polymerization and the nano-object morphology are examined, and efficient agitation and adequate solubility of the core-forming monomer in water are identified as the most crucial factors for the fabrication of nonspherical nano-objects.

ALLODUST augmented activated sludge single batch anaerobic reactor (AS-SBAnR) for high concentration nitrate removal from agricultural wastewater

Nitrate is among the most widespread contaminants that threaten water bodies and waterways. Under favourable environmental conditions, high nitrate concentrations in water can contribute to eutrophication, thus presenting a high potential for risk to ecosystems and human health. Low-cost allophanic soil material and carbon-based bio-wastes have great potential to reduce nutrient concentrations from contaminated waters. This study investigated the mechanisms that underpin the reduction of nitrate concentrations and nitrous oxide (N2O) emission in the presence of novel developed media in an activated sludge process. A new operating approach, employing a newly developed media (ALLODUST), was evaluated for enhanced NO−3-N removal from agricultural wastewater. Two anaerobic-aerobic batch reactors were developed, where the coupled bottom aeration method was used for efficient agitation and aeration in the aerobic reactor. The reactor was run at high NO−3-N concentrations (110 mg L−1), under anoxic conditions at low- to long-term contact times (2, 12, and 22 h), while the aerobic period (clarification) was constant for all the experimental designs (2 h). ALLODUST retained its integrity and stability over the long-term operation. Low ALLODUST concentrations (5.95 g L−1) removed 87% of the NO−3-N from the wastewater within 12 h. Further exploration revealed that the same amount of the media was optimal for decreasing N2O emissions from the anaerobic activated sludge reactor by 80%.

Research on Mechanism of Fluid Flow Characteristics in a Stirred Tank with Stirrer Composed of Perturbed Six-Bent-Bladed Turbine

The power consumption and pressure distribution of Newtonian fluid and pseudoplastic fluid in a stirred tank with stirrer composed of perturbed six-bent-bladed turbine (6PBT) were calculated by CFD combined with laminar viscosity model. The test liquid used were glycerine and 1.25% (wt) xanthan gum solution, a pseudoplastic fluid with a yield stress. Compared with the stirrer composed of six-bent-bladed turbine (6BT), the effects of the 6PBT impeller on fluid pressure distribution were extensively analyzed, and the Coriolis force role of strengthening swirling motion and efficient agitation mechanism of 6PBT impeller were made a thorough inquiry, respectively. Results show that 6PBT impeller can lead to an energy saving effect as the increasing speed, and generate a larger low pressure region in flow field at the same time, so this is more beneficial to the whole circulation. Moreover, the stronger swirling motion may emerge in stirred tank with 6PBT impeller under the action of Coriolis force, which is exceedingly advantageous to promotion of mixing efficiency. As a result, 6PBT impeller is found to have a obvious superiority on mixing process of pseudoplastic fluid. The research results provide valuable references and instructions for the development of new type impeller.

A New Entry to Sonochemical/Efficient Agitation Switching: Alkene Formation through Epoxide Deoxygenation

‘Sonochemical switching’ whereby the pathway of a reaction is changed under sonication conditions was first reported by Ando, and in fact could just be the consequence of efficient agitation. We herein report a new addition to this switching phenomenon in which epoxides are converted to cyclic carbonates by addition of CO2 under standard heating/electrolysis conditions but are ‘switched’ to alkenes under deoxygenating sonochemical conditions.

ChemInform Abstract: Design and Evaluation of Improved Magnetic Stir Bars for Single‐Mode Microwave Reactors.

AbstractA new vertical blade stir bar that improves the stirring performance in flow‐constricting microwave vessels is designed and evaluated for several transformations where stirring and efficient agitation are known to be of importance.

Design and evaluation of improved magnetic stir bars for single-mode microwave reactors

Magnetic stirring in sealed cylindrical vessels designed for use in single-mode microwave instruments is typically less than optimal, and is not comparable to the efficient agitation that can be generally obtained in a round-bottomed flask fitted with a suitable magnetic stir bar or using overhead mechanical stirring systems. A new "vertical blade" stir bar design that improves the stirring performance in the very narrow, flow-constricting microwave vessels has been developed and evaluated for several different transformations where stirring and efficient agitation are known to be of importance. The better performance of these novel stirrers compared to the traditional cylindrical stir bar design is not only due to the geometry of the stirrer but also to the utilization of a magnetic material with a stronger magnetic transmission force (Sm2Co17) compared to standard ferrite or AlNiCo alloys. For all three tested cases involving solid/liquid, liquid/liquid and highly viscous reaction systems, the new vertical blade stirrers showed a distinctively improved performance resulting in higher conversions and/or product yields.

ChemInform Abstract: Harnessing Mechanochemical Effects with Ultrasound‐Induced Reactions

AbstractReview: 90 refs.

Harnessing mechanochemical effects with ultrasound-induced reactions

Chemical reactions may experience numerous and varied effects under the influence of ultrasound. This soft radiation, often viewed as a lab trick, induces and improves both physical and chemical transformations by means of efficient agitation, dissolution, mass and heat transfers, and reagents sonolysis, which all arise from the cavitational collapse. An empirical rationale that distinguishes between true chemical effects and mechanical ones, especially in heterogeneous reactions, was introduced more than two decades ago and has been a useful guidance on reporting sonochemical mechanisms. Recent studies have witnessed a truly remarkable data set that boosts sonochemistry over the wall of applied science. This perspective highlights the importance of the so-called false sonochemistry-closely related to mechanochemistry-in modern synthesis, thus illustrating the advantages of using pressure waves in chemistry. Emphasis is put on green transformations, mild polymerization reactions and the selective cleavage of functionalized polymers, which may have an effective impact in process chemistry and represent a realistic option in industry.

Influence of ultrasound and cathode rotation on formation of intrinsic stress in Ni films during electrodeposition

The influence of 25 kHz ultrasound and cathode rotation during electroplating of Ni films on Si wafers has been studied with respect to intrinsic stress formation. Current densities from 1·6 up to 28·3 A dm−2 were used in an additive free Ni sulphamate electrolyte. In general, more efficient agitation by either ultrasound or cathode rotation was found to reduce intrinsic stress towards compressive levels compared with conventional agitation with an electrolyte circulation pump. Furthermore, intrinsic stresses become less dependent on changes in current density. The latter effect is most pronounced for ultrasonic agitation. Structure analysis of samples deposited by ultrasonic agitation shows dense deposits with initially smaller grains at high ultrasonic effect. Locally increased temperature at the substrate surface could be an important effect of ultrasound agitation.

Nanoprecipitation of cellulose acetate using solvent/nonsolvent mixtures as dispersive media

An efficient nanoprecipitation technique using good cellulose acetate (CA) solvents as modifier for the dispersive media (nonsolvent) was developed for the generation of CA nanoparticles. Addition of tetrahydrofuran (THF) to the nonsolvent leads to smaller particles than obtained with pure water or standard stabilizing agents like surfactants and block copolymers. Sonication, efficient agitation, and optimization of process parameters like temperature, THF content, pH value and stirrer velocity reduces nanoparticle sizes and improves substrate recoveries. With the optimized process, spherical nanoparticles of 60 nm with 87% yield can be generated reproducibly. This is obtained by addition of good polymer solvents (tetrahydrofuran (THF)) to a nonsolvent (water) and applying those mixtures as nonsolvents for nanoprecipitation. Main theoretical models in discussion are not able to explain sufficiently the particle size reduction by the addition of a good polymer solvent to the nonsolvent. CA nanoparticles can be used to produce ultrathin layers deposited onto positively charged surfaces. Possible applications are seen in surface science (e.g. surface modifications and surface functionalization of CA foils and membranes).

Cu(II)−Azabis(oxazoline) Complexes Immobilized on Magnetic Co/C Nanoparticles: Kinetic Resolution of 1,2-Diphenylethane-1,2-diol under Batch and Continuous-Flow Conditions

Carbon coated cobalt nanoparticles were tagged with azabis(oxazoline)−copper(II) complexes utilizing a copper(I)-catalyzed azide/alkyne cycloaddition (CuAAC) reaction, and the efficacy of the resulting nanomagnetic catalyst was tested in the kinetic resolution of racemic 1,2-diphenylethane-1,2-diol via asymmetric monobenzoylation. The novel semiheterogeneous catalyst was examined under batch conditions and in a continuous flow-type reactor. The extremely high ferromagnetism of the cobalt cores not only facilitates the recycling of the nanobeads via magnetic decantation in the batch reactions but also enables a novel continuous flow-reactor design: This further allowed efficient agitation and containment of the particles to occur without the need for sophisticated separation strategies such as nanofiltration.

Nonthermal Microwave Effects Revisited: On the Importance of Internal Temperature Monitoring and Agitation in Microwave Chemistry

The concept of nonthermal microwave effects has received considerable attention in recent years and is the subject of intense debate in the scientific community. Nonthermal microwave effects have been postulated to result from a direct stabilizing interaction of the electric field with specific (polar) molecules in the reaction medium that is not related to a macroscopic temperature effect. In order to probe the existence of nonthermal microwave effects, four synthetic transformations (Diels-Alder cycloaddition, alkylation of triphenylphosphine and 1,2,4-triazole, direct amide bond formation) were reevaluated under both microwave dielectric heating and conventional thermal heating. In all four cases, previous studies have claimed the existence of nonthermal microwave effects in these reactions. Experimentally, significant differences in conversion and/or product distribution comparing the conventionally and microwave-heated experiments performed at the same measured reaction temperature were found. The current reevaluation of these reactions was performed in a dedicated reactor setup that allowed accurate internal reaction temperature measurements using a multiple fiber-optic probe system. Using this technology, the importance of efficient stirring and internal temperature measurement in microwave-heated reactions was made evident. Inefficient agitation leads to temperature gradients within the reaction mixture due to field inhomogeneities in the microwave cavity. Using external infrared temperature sensors in some cases results in significant inaccuracies in the temperature measurement. Applying the fiber-optic probe temperature monitoring device, a critical reevaluation of all four reactions has provided no evidence for the existence of nonthermal microwave effects. Ensuring efficient agitation of the reaction mixture via magnetic stirring, no significant differences in terms of conversion and selectivity between experiments performed under microwave or oil bath conditions at the same internally measured reaction temperatures were experienced. The observed effects were purely thermal and not related to the microwave field.

Influence of agitator design and catalyst concentration on partial hydrogenation of sunflower oil

AbstractIn this study, lab‐scale hydrogenation of sunflower oil was conducted at 190 °C and 2 bar using two different catalyst types at varying concentrations and two different agitator designs (surface gassing and hollow shaft) at varying power inputs. At identical power input and reaction conditions, the reaction rate with the hollow‐shaft agitator was 1.68 times higher than with surface gassing agitation. The catalyst concentration had to exceed a certain feedstock‐dependent threshold value of 25 ppm Ni in order to start the reaction. At low catalyst concentration, the reaction rate increased proportionally with increasing catalyst concentration. When hydrogen consumption became higher than the available mass transfer provided by the agitation system, the reaction time became less dependent on the catalyst concentration. For the hollow‐shaft agitator, this situation was observed at a reaction rate of 3.7 ΔIV/min, where trans formation was at its maximum with more than 40% trans fatty acids in partially hydrogenated sunflower oil with IV 65. The region in which hydrogen mass transfer did not limit the reaction rate could be extended by more efficient agitation design or increased agitation power. In this way, productivity can be increased and trans formation can be controlled in a better way when compared to hydrogenation with a less efficient agitator.

On the Quantitative Measure of a Sonochemical Effect in Heterogeneous Sonochemistry

The measurement of a sonochemical effect (SE) requires the definition of the reference conditions for the so-called “silent reaction”. It is shown that it is impossible to define SE correctly in the case of heterogeneous reactions, due to the dramatic effect of the agitation on reaction rates. This is true not only from the quantitative point of view (effect of ultrasound on reaction rates) but also from the qualitative perspective (change of reaction pathway when ultrasound is applied). The first, and most dramatic, example of chemical switching described in the literature, and claimed to be due to ultrasound, is proven also to be observable under efficient agitation conditions.

Sonochemistry: Scope, Limitations… and Artifacts

Heterogeneous sonochemistry, generally described as the most useful aspect of sonochemistry, suffers from the difficulty of defining the experimental conditions for the reference (silent) reaction. Clearly the use of an efficient agitation system for the silent reaction strongly reduces the value of the so-called sonochemical effect, which becomes in some cases, less than 1 (anti-sonochemical effect!).The 'cleaning' effect of ultrasound is extremely efficient to expel micro-crystals from the surface of an electrode which is simultaneously an immersion ultrasonic horn. By sending out-of-phase electric pulses and acoustic pulses, new nano materials (metals, alloys, semiconductors, oxides) are easily prepared in high purity.

CRITERIA AND PROCEDURES FOR EVALUATION OF SOLIDS MIXING IN AGRICULTURAL SPRAYER TANKS

An agitation effectiveness index (AGEF) was defined to help evaluate the effectiveness of hydraulic agitation systems in agricultural sprayer tanks regardless of tank size and shape. AGEF was calculated based on three measured mixing criteria: particle deposits remaining on the bottom of the tank following the application, the coefficient of variation of the mixture concentration in the line to the boom, and the ratio of maximum deviation of the mixture concentration at the tank outlet to the mean concentration measured during the application. The ratio of AGEF to required hydraulic power of the agitation system, named Power Ratio, was also used as another parameter to evaluate sprayer tank agitation systems. The method suggested in this article was applied to evaluate a large number of agitation experiments conducted as well as a previous researcher’s unevaluated agitation data in order to show its applicability. Use of this method is limited to solid-liquid type mixtures in order to determine the suspension uniformity achieved with hydraulic agitators. Kaolin clay was used as solid particles since this is a common carrier for wettable powder and granular pesticides. The results showed that AGEF was sensitive enough to enable reasonable comparisons and that this method can be used to standardize minimum requirements of a hydraulic jet agitation system. AGEF and Power Ratio provided a novel approach to identify efficient agitation systems with low energy requirements.

Applying mass transfer models for controlling organic compounds in ozonation process

Mass transfer plays a significant role in the ozonation process. The prediction models associated with the volumetric overall mass transfer coefficient (K La) and initial fractional ozone absorption (FOA 0) during the ozonation process were developed through the use of dimensional analysis. It was found that the volumetric overall mass transfer coefficient is the function of diffusivity, agitation speed, and gas flow rate, and the parameters in the K La equation are determined. Application of the prediction models for K La and FOA 0 would yield information to choose the most practically feasible operating parameters. The removability of total organic carbon (TOC) can be estimated based on the mass balance relationship and kinetic expression of TOC oxidation, during continuous laboratory ozonation of humic acid solution. The reaction rate constant averaged 0.0291 L/mg·min. The developed model in combination with the mass transfer and reaction kinetics can be used successfully in forecasting the most efficient agitation speed to control the formation of organic compounds. Also, the critical value of ozone partial pressure to achieve the highest TOC removability can be determined through the use of the above developed model.

Kinetic Model of Membrane Extraction with a Sorbent Interface

Membrane extraction with a sorbent interface (MESI) is an unique sample preparation alternative for trace organic analysis. The main features of MESI include its solvent-free nature, the rugged and simple design with no moving parts for long-term reliable performance, the fact that it is a single-step process which ensures good precision, its easy automation, and its feasibility for on-site operation. Among the available membrane extraction modules designed for the MESI system, the headspace configuration has continued to show its superior durability and versatility in membrane applications. The headspace membrane extraction configuration effectively eliminates the need for a sampling pump and flow metering and hence prevents the extraction system from plugging and greatly simplifies the extraction process. The module can be used for extraction of VOCs from gaseous, aqueous, or solid samples. A mathematical model has been developed for headspace membrane extraction of an aqueous sample, based on the assumption that the aqueous phase is perfectly stirred. The model is in good agreement with the experimental benzene extraction results obtained with an efficient agitation method such as high-speed magnetic stirring or sonication. The model has also been used to study the effects of various extraction parameters with respect to the sensitivity and response time of the MESI system. Sample agitation facilities analyte mass transport and hence improves both the system sensitivity and the response time. The sensitivity of the extraction method also increases with an increase of the extraction temperature.

On-line monitoring of flowing samples using solid phase microextraction-gas chromatography

The rapid sampling and concentration response of solid phase microextraction (SPME) facilitate the monitoring of organic analytes present in a flowing stream. It was determined that in addition to convection introduced by flow in the system, an efficient means of agitation is required to achieve rapid extractions. Three agitation techniques; magnetic mixing, intrusive mixing and sonication were tested. While magnetic stirring is inexpensive and easy to automate, it exhibited low mixing efficiency. Intrusive mixing allows efficient agitation but caused sample heating and is not easily amenable to on-line analysis. Sonication proved to be the most efficient and the most convenient means of agitation for sampling from flowing streams. For example, toluene, equilibrates in less then 1 min, which is very close to theoretical predictions assuming perfect agitation conditions. The on-line SPME-GC technique allows gas chromatography to be incorporated into a flow-injection analysis system.

Dyeing of Polyacrylonitrile Fibers

A new method for the study of dyeing rates and equilibria combines the accuracy and ease of various other methods used previously. The dyehaths are closed systems in Erlenmeyer flasks modified to provide very efficient agitation during horizontal motion of a holding tray in a shaking bath of good temperature constancy. When a stopcock is opened, pressure inside the flasks pumps the solution directly into modified spectro photometer cells. Dilution is avoided by the use of spacers and various parts of the dye spectrum, so that the measured solution can be returned to the system. Illustrative ex amples include the effect of steam annealing temperature, orienting stretch sequence, and shaking speed on the dyeing rate of polyacrylonitrile fibers with Malachite Green, dyeing rate with Orange II on various fibers, its concentration dependence on poly acrylonitrile fibers and desorption with temperature increase. Many of the methods can be used for other than dyeing studies.