China Particuology最新文献

A magnetically stabilized bed (MSB) reactor for selective hydrogenation of olefins in reformate was developed by combining the advantages of MSB and amorphous nickel alloy catalyst. The effects of operating conditions, such as temperature, pressure, liquid space velocity, hydrogen-to-oil ratio, and magnetic field intensity on the reaction were studied. A mathematical model of MSB reactor for hydrogenation of olefins in reformate was established. A reforming flow scheme with a post-hydrogenation MSB reactor was proposed. Finally, MSB hydrogenation was compared with clay treatment and conventional post-hydrogenation.

Sedimentation based processes are widely used in industry to separate particles from a liquid phase. Since the advent of the “Nanoworld” the demand for effective separation technologies has rapidly risen, calling for the development of new separation concepts, one of which lies in hybrid separation using the superposition of a magnetic field for magnetic particles. Possible product portfolio of such separation consists of pigment production, nanomagnetics production for electronics and bio separation. A promising step in that direction is magnetic field enhanced cake filtration, which has by now progressed from batch to continuous operation.

In sedimentation processes in a mass force field the settling behaviour of particles strongly depends on physico-chemical properties, concentration and size distribution of the particles. By adjusting the pH, the interparticle forces, in particular the electrostatic repulsion, can be manipulated. For remanent magnetic particles such as magnetite, pre-treatment in a magnetic field could lead to a change of interparticle interactions. By magnetizing the particles apart from van der Waals attraction and electrostatic repulsion, an additional potential is induced, the magnetic attraction, which could easily dominate the other potentials and result in agglomeration in the primary minimum. By sedimentation analysis, a wide spectrum of parameters like pH, magnetic field strength and concentration have been investigated. The results show a strong increase of sedimentation velocity by magnetic flocculation of the raw suspension. This leads to a rise in throughput due to the acceleration of sedimentation kinetics by imparting a non-chemical interaction to the physico-chemical properties in the feed stream of the separation apparatus.

This paper originates a discussion on dimensional analysis and scaling in magnetically assisted fluidized beds. Basic examination of process variables, merging mechanical and magnetic units, allows the conversion of mixed sets of variables into unified terms representing surface forces as effects of the fields contributing to the assisted fluidization behaviour. This transformation is termed “pressure transform” since the new variables are all characteristic pressures generated by three basic fields: gravity, magnetic and fluid flow. This approach addresses the physical basis in terms of dimensionless groups rather than formal algebraic manipulations pertinent to classical dimensional analysis.

Basic dimensionless group termed granular magnetic Bond number is introduced as the ratio of characteristic pressures of gravity and of magnetic field. This analysis also provides a set of named dimensionless numbers characterizing magnetic field assisted fluidization such as Filippov number, Rosensweig number, Kwauk number and Siegell number, derived as ratios of characteristic pressures.

Liquid–solid (L–S) mass transfer coefficients (K_s) were characterized in a gas–liquid–solid (G–L–S) three-phase countercurrent magnetically stabilized bed (MSB) using amorphous alloy SRNA-4 as the solid phase. Effects of superficial liquid velocity, superficial gas velocity, magnetic field strength, liquid viscosity and surface tension were investigated. Experimental results indicated that the external magnetic field increased K_s in three-phase MSB, as compared to those in conventional G–L–S fluidized beds; that K_s increased with magnetic field strength, superficial gas and liquid velocities and decreased with liquid viscosity and surface tension; and that K_s showed uniform axial and radial distributions except for small increases close to the wall. Dimensionless correlations were established to estimate K_s of the G–L–S countercurrent MSB using SRNA-4 catalyst, with an average error of 3.6%.

Fingerprints and source profiles of fine and coarse sands that originate from Central Inner Mongolia during Asian continental sandstorms (ACS) can be used to identify the origin of Asian sands and to trace them as they travel downwind. Soil samples collected at various land surfaces in Central Inner Mongolia were resuspended using a dry powder atomizer in an enclosure chamber. The resuspended sands were then sampled by two dichotomous samplers situated at the bottom of the enclosure chamber for fine (PM_2.5) and coarse (PM_2.5-10) sands, respectively. The chemical composition of sands, including water-soluble ionic species, metallic contents, and carbonaceous contents, were further analyzed. Results from resuspension tests indicated that the soils contained considerably more coarse particles than fine. Moreover, Mg, K, Al, and Fe in coarse sand had strong correlations with each other. The ratio of Mg, K, Fe (or Al) to Al (or Fe) and OC/EC in the coarse sands can be used as the fingerprints of Asian sands originating from Central Inner Mongolia.

Two common surface-dust emission schemes using critical wind speed and friction velocity were compared with the regional climate model RegCM3 in East Asia. In the comparison, transport of mineral dust and its distribution were simulated from March to April, 2001. Simulation results were also compared with TOMS aerosol index, showing that obvious differences exist in dust emission quantity and its column burden simulated by the dust emission schemes of friction velocity and wind speed criteria. The results obtained by the wind speed criterion are higher than that by friction velocity, bringing forth the problem whether or not the dust emission scheme matches the model. The obvious difference in the two schemes also explains the uncertainty of simulating mineral dust aerosol by modeling.

PM_1.0 (fine particles, with diameter < 1 μm), PM_2.5 (fine particles, with diameter < 2.5 μm) and PM₁₀ (coarse particles, with diameter < 10 μm) were measured at 24-hour intervals near a high-traffic road in Hong Kong, from October 2004 to September 2005. Mass concentrations were determined for the three particle fractions, averaging for PM_1.0, PM_2.5 and PM₁₀, respectively, 44.5±18.4, 55.4±25.5 and 81.3±37.7 μg·m⁻³. PM_2.5 was 3.7 times the U.S. EPA's annual NAAQS of 15 μg·m⁻³. Overall, PM_1.0 accounted for 44 to 69% (average 57%) of PM₁₀, while PM_2.5 accounted for 58 to 82% (average 71%) in this study. The particulate masses showed obvious seasonal patterns with high concentrations in cold seasons and low in warm seasons, especially high concentrations of PM_2.5-10 during the cold seasons. Diurnal variations of mass concentrations of PM_2.5 were determined during July, showing two major peaks in the morning and afternoon rush hours.

Indoor dustfall samples were collected in Pit 1 and Pit 2 of Emperor Qin's Terra-cotta Warriors and Horses Museum in Xi'an, Shaanxi Province, China. The morphological and elemental analysis for long-term (>10 years) and short-term (∼0.5 year) dustfall particles and lacquer pieces on the faces of partly assembled warriors were performed with scanning electron microscopy with energy dispersive X-ray spectrometer (SEM/EDX). The results showed that the majority of dustfall samples appeared to be composed of mineral dust particles, fly ash, and biological particles with different elemental compositions. Most of the mineral particles had irregular shapes with smooth edges. Small floccules of calcium sulfate were more frequently observed in long-term dustfall samples than in short-term samples, implying a progressive chemical reaction between continuous dustfall particles and atmospheric sulfur dioxide. Crystals of calcium sulfate were also found near pits on both inner and outer surfaces of lacquer pieces, revealing an acid chemical reaction between sulfur dioxide and lacquer material as the cause of the formation of erosion pits and cracks on surface of lacquer pieces.