Collection of submicron particles by H2 bubbles

A theoretical analysis is presented to describe the deposition of Brownian particles onto H₂ bubbles (flotation) by analogy with classical filtration theory.Experimentally, it is shown that submicron and smaller particles of MnO₂ are collected by H₂ bubbles without using the special collector or chemicals usually employed in flotation. The experimental technique for determining the total collection efficiency is described.A comparison between the theory and our experiment makes it clear that there are cases in which the simpler filtration theory is adaptable to a complicated flotation analysis. In addition, we find that the collection mechanisms of submicron particles of MnO₂ is predominantly characterized by interception and Brownian diffusion.     

Collection of hydrophilic and hydrophobic charged submicron particles by charged water droplets

An experimental system capable of measuring the collection efficiency of charged submicron particles by charged water droplets is described. Collection efficiencies are measured for both hydrophilic and hydrophobic particles to clarify the effect of wettability on collection. Excellent agreement with the theory is obtained for hydrophilic submicron particles when the Coulombic force is dominant. No significant difference in collection efficiencies between hydrophilic and hydrophobic particles is observed. It is concluded that the wettability of submicron particles has no effect on its collection by water drops when Coulombic attraction is the dominant mechanism.     

超细颗粒物增湿团聚技术研究进展

流化床内喷雾增湿可以使颗粒在不断的碰撞中发生强烈的传热传质而团聚长大。综述了颗粒物化特性、操作参数及加入团聚促进剂对颗粒团聚的影响,分析了循环流化床烟气脱硫工艺的工艺过程、床内增湿团聚机理以及综合脱除SO2以及超细颗粒物的可行性,指出增湿团聚技术可以有效提高燃煤烟气中超细颗粒物的脱除效率,有很好的应用前景。     

Vapor-phase surface modification of submicron particles

Submicron iron oxide red, TiO₂ and talc particles were chemically modified twice in the same double-cone reactor with vapor of 2,4,6,8-tetramethylcyclotetrasiloxane(TMCTS) and then 1-dodecene, 1-tetradecene or vinyl terminated poly(dimethylsiloxane). For the second modification alumina balls coated with hexachloroplatinic(IV) acid by simple impregnation of the catalyst-containing solution were used as a catalyst, reducing aggregation of the particles as well. The conversion of the second modification was even higher than that obtained in conventional liquid-phase hydrosilylation under comparable process conditions. Segregation of the particles from the ball was important for large volume modification. Under the given particle loading, the optimal ball size and catalyst concentration existed for the efficient use of catalyst. The ball catalysts were effective in four consecutive batches without any appreciable decrease in the conversion. Intermittent tumbling and the use of baffle enhanced the conversion of any gas-solid reaction such as both the first and the second modifications, minimizing simple tumbling (no mixing) and lump formation of particles.     

Swelling behavior of submicron gel particles

We prepared submicron Poly(N-isopropylacrylamide) gel particles. Their swelling behavior was investigated by a photon correlation spectroscopy (PCS) technique. The swelling behavior of submicron gel particles showed a continuous volume phase transition for various temperatures. We combined the extended Flory-Huggins model for mixing solvent and network with a modified Flory-Rehner theory for the elastic contribution. The proposed model agreed very well with swelling behaviors of both submicron gel particles and bulk gels. A continuous volume phase transition behavior of submicron gel particles was predicted successfully by the proposed model. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 109–114, 1998     

Classification of submicron Ni particles by heterocoagulation

In this work, the size classification of a mixture of submicron and micron size Ni particles dispersed in aqueous solution was investigated. The suspension of Ni particles was allowed to flow, under laminar condition, through a burette filled with an adhesion medium (i.e. substrate). The difference between zeta potentials of larger particles and adhesion medium created a base for the heterocoagulation. Thus, the larger particles move towards the medium assisted by the Saffman lift force and are attracted to its surface. The finer particles, on the other hand, flow off the burette and were collected as a separate fraction. This phenomenon was then explained by numerical simulating the particle's motion and showing that a stronger Saffman lift force will act in the direction of the substrate only for large particles, leaving the smaller ones unaffected as they sediment out.     

Finite size effects in submicron barium titanate particles

An experimental and theoretical analysis of finite size effects in submicron barium titanate particles is presented. The dielectric data show that the dielectric constant (ε = 734) of small particles (d = 20 nm) remains very similar to that of single crystals provided that the particles are grown from an amorphous phase and not mechanically crushed into powder. This shows that what has in the past been mistaken for true size effects (i.e., depolarization fields) is due to lattice strain. The X-ray data show that the Curie temperature (cubic-tetragonal transition temperature) decreases monotonically to zero degree Kelvin as particle size is reduced. However this is shown to be a simple function of lattice constant: The lattice constant expands as the particle diameter d contracts. This is similar to surface relaxation in thin films.     

荷电水雾脱除超细颗粒物的研究进展

综述了荷电水雾脱除超细颗粒物的作用机理和影响因素,分析了荷电水雾脱除燃煤电厂烟气中超细颗粒物及综合脱除其它燃煤污染物的可行性,指出利用荷电水雾对燃煤电厂烟气进行处理能够有效提高传统静电除尘器对超细颗粒物的脱除效率,并能实现燃煤污染物的联合脱除,应用前景广阔。     

Development of apparatus for electro-flotation

A new apparatus for electro-flotation has been developed by using the impeller of stirred tank as electrode(s). The principle of this apparatus reported is that the gas bubbles generated by electrolysis float the flocs while flocculation is promoted by the rotation of electrode(s). The collection efficiency of this apparatus for tap water containing blue ink of 10^?3m³/M³ in concentration has been discuss by using various electrode(s) and changing the rotation speed of the electrode(s).     

Collection efficiency of sintered ceramic filters made of submicron spheres

The performance of filters made of sintered submicron alumina particles was evaluated. The filter has a high collection efficiency and high pressure drop, requiring the development of a special measuring system for its evaluation. The system consists of a polydisperse NaCl particle generator, a differential mobility analyzer (DMA), an ejector to supply aerosols for testing filters with high pressure drop, and a mixing-type condensation nucleus counter (CNC) capable of obtaining a stable reading of very low concentration particles. Penetrations as low as 10⁻⁹ can be measured in the particle diameter range of 0.02-0.14 μm. Two filters made by sintering 0.60 and 0.84 μm alumina particles were evaluated. The experimental data collected served as the basis of theoretical development. Following the single fibre theory, the filter penetration is calculated by using a single sphere as the element. Both the diffusion and interception collection mechanisms were taken into account. The resulting equation gives a general trend of efficiency curves as a function of the parameters involved, e.g. the test aerosol size, packed particle size and filtration velocity. However, it is not sufficiently accurate for providing quantitative performance results.     

Mechanical production and stabilization of submicron particles in stirred media mills

A joint research project between the Technical University of Braunschweig and the Technical University of München investigates the possibilities for the production of stable product suspensions in a particle size range smaller than 100 nm. This paper shows the experimental setup which allows the measurement of the most important electrochemical properties and the analysis of the particle size distribution of the product suspension as well as an adjustment of the pH value for stabilization during the comminution process. Results for comminution of fused corundum with different grinding media materials and grinding media sizes are shown. In addition, results showing the influence of the electrostatic stabilization on the grinding progress are presented. Further, the rheology of the product suspension is examined depending on grinding progress and suspension stability.     

Brownian dynamics simulation of the aggregation of submicron particles in static gas

A Brownian dynamics simulation was conducted to investigate the formation of aggregates that are composed of submicron particles such as soot. Three models were considered for aggregation: a diffusion-limited aggregation model, in which an aggregate grows around a fixed particle; a particle–cluster aggregation model, in which a single aggregate grows by collisions between particles and the aggregate; and a cluster–cluster aggregation (CCA) model, in which many particles and aggregates form multiple aggregates. A comparison of the three aggregation models showed that the CCA model resulted in a soot-like branching shape. The aggregation was investigated by employing the CCA model; it was determined that increase in gas temperature affected the shielding effect of the aggregate branch by changing the displacement and velocity of Brownian particles. Furthermore, these simulations demonstrated that the size and aspect ratio of the field and the particle density also affected aggregation shape.     

Formation and stabilization of submicron particles via rapid expansion processes

Submicron particles were produced by rapid expansion of supercritical solution into air (RESS) or an aqueous surfactant solution (RESSAS) to minimize particle growth and to prevent particle agglomeration. Thereby the effect of process conditions on the size of the particles precipitated was investigated. The obtained product was evaluated by measuring particle size by 3-wavelength extinction measurements, dynamic light scattering, specific surface areas by nitrogen gas adsorption, melting behaviour by differential scanning calorimetry, particle morphology by X-ray diffraction, scanning electron micrographs (SEM), and drug loading by high performance liquid chromatography.Prior to the particle formation experiments, the melting temperature of Salicylic acid under CO₂ pressure and the solubility of Salicylic acid in CO₂ were measured. The size of Salicylic acid particles produced via RESS decreased from 230 to 130 nm as the pre-expansion temperature decreased from 388 to 328 K and the specific surface area of the micronized particles was found to be up to 60 times higher than that of the unprocessed material. RESSAS experiments demonstrate that in 1 wt.% Tween 80 solutions Salicylic acid concentrations of 4.6 g/dm³ could be stabilized with particle diameters in the range of 180 nm. Additional experiments show that Ibuprofen nanoparticles with an average size of 80 nm and a drug concentration of 2.4 g/dm³ could be stabilized in 1 wt.% Tween^® 80 solutions. The use of a SDS solution instead of Tween^® 80 results in a stable aqueous suspension of phytosterol nanoparticles, where the average particle size is 50 nm at a drug concentration of 5.6 g/dm³.     

Polymerization of MMA at the surface of inorganic submicron particles

Inorganic submicron particles, such as TiO₂, were modified with titanate coupling agents. The structure and stability of some titanates, both in solution and at the particle surface, were investigated by various methods. The modified titanium dioxide was dispersed in a solution of sodium dodecylsulphate (SDS) in water. The surfactant adsorbs at the now hydrophobic particle surface, thus creating a micellelike structure with an inorganic particle in the centre. In this system an emulsion polymerization of methyl methacrylate was carried out. Product formed at the particle surface is either physically bound by entanglement or chemically bound by covalent bonding to the titanates. In this way a core-shell morphology is obtained with an inorganic core and a polymer shell. The effects of several reaction parameters on the kinetics of the polymerization were studied. The encapsulated TiO₂ particles may offer interesting prospects in those applications where good coupling between polymer matrix and inorganic particles is necessary, such as latex paints and polymer composite materials.     

Investigating the chemical species in submicron particles emitted by city buses

Detailed chemical characterization of exhaust particles from 23 individual city buses was performed in Helsinki, Finland. Investigated buses represented different technologies in terms of engines, exhaust after-treatment systems (e.g., diesel particulate filter, selective catalytic reduction, and three-way catalyst) and fuels (diesel, diesel-electric (hybrid), ethanol, and compressed natural gas). Regarding emission standards, the buses operated at EURO III, EURO IV, and EEV (enhanced environmentally friendly vehicle) emission levels. The chemical composition of exhaust particles was determined by using a soot particle aerosol mass spectrometer (SP-AMS). Based on the SP-AMS results, the bus emission particles were dominated by organics and refractory black carbon (rBC). The mass spectra of organics consisted mostly of hydrocarbon fragments (54–86% of total organics), the pattern of hydrocarbon fragments being rather similar regardless of the bus type. Regarding oxygenated organic fragments, ethanol-fueled buses had unique mass-to-charge ratios (m/z) of 45, 73, 87, and 89 (mass fragments of C₂H₅O⁺, C₃H₅O₂⁺, C₄H₇O₂⁺, and C₄H₉O₂⁺, respectively) that were not detected for the other bus types at the same level. For rBC, there was a small difference in the ratio of C₄⁺ and C₅⁺ to C₃⁺ for different bus types but also for the individual buses of the same type. In addition to organics and rBC, the presence of trace metals in the bus emission particles was investigated.

Copyright © 2017 American Association for Aerosol Research     

燃煤超细颗粒物团聚促进机制的实验研究

煤粉燃烧排放大量超细颗粒物对大气环境和人类健康造成了严重的危害。提出一种燃后区烟尘团聚促进新方法，通过在燃后区烟道喷射团聚促进剂，利用絮凝理论，增加超细颗粒之间的液桥力和固桥力，促使超细颗粒物团聚长大，进而被现有除尘装置捕获，减少超细颗粒的排放。在自行设计搭建的团聚实验台上进行了系统的实验研究，分析了团聚促进剂溶液的pH值、流量、浓度，团聚室的温度以及模拟烟气中粉尘浓度等因素对超细颗粒物团聚效率的影响。结果表明，化学团聚对于超细颗粒物的脱除具有显著的作用，喷入团聚促进剂后的烟尘排放浓度远比无团聚和喷水的情况要低；团聚促进剂的高分子链对超细颗粒的吸附絮凝作用促进超细颗粒团聚，显著降低烟尘排放浓度，实现超细颗粒物经济高效脱除，达到国家新的烟尘排放标准。     

Deposition of submicron particles in deep bed filtration under unfavorable surface conditions

Deterioration in the filter removal efficiency of submicron particles (λ/λ_o) under unfavorable surface conditions is affected by the number of deposited particles per filter grain. In the case of above micron particles, the deterioration of filter removal efficiency has been mainly due to the blocking effect of deposited particles and not by the number of deposited particles. Deposition of large number of submicron particles changed the surface characteristics of collectors (filter grain associated with deposited particles) and enhanced unfavorable surface conditions. Filtration experiments were conducted with monodispersed suspensions of known sizes of submicron latex particles at different ionic strengths, using glass beads as filter grains. The filtration performance was predicted by using a mathematical model, assuming a linear relationship between λ/ λ_o and Σ (i.e. λ/λ_o=1 − kΣ). For both particles, k was found to decrease andλ _o was found to increase with the increase in the ionic strength. A comparison was made of the importance of blocking effect for the filtration of submicron particles.     

High‐density polyethylene reinforced with submicron titania particles

Submicron titania particles were prepared by means of two different synthetic procedures in order to obtain different particle size (diameter ranging from 20 to 350 nm), shapes, and morphologies (amorphous or crystalline). Titania particles were surface modified with octadecylsilane in order to improve their compatibility with respect to polymeric matrices. High‐density polyethylene (HDPE)–titania composites were prepared by melt blending by using an internal mixer. The obtained composites were mechanically characterized in quasi static and creep tensile conditions. The presence of submicron titania particles (1 %vol) led to a significant increase of elastic modulus (20–25%) with respect to the unreinforced HDPE together with a slight increase of yield stress and a decrease of ultimate elongation. An interesting reduction for both elastic and viscoelastic creep compliance components was also evidenced. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers