Solid size reduction

Chemical manufacture Fluid transport Handling of bulk solids Size reduction and enlargement Heat generation and transport Distillation Gas absorption Bioreactions... 

Although rotor-stator devices are not considered highly energy intensive relative to some types of solids size-reduction devices, they are sometimes employed when more controlled size reduction is desired, especially when it is desirable to minimize the production of fines. One example of such use is the conditioning of seed particles for crystallization operations when the seed is a portion of the previous batch ( heel crystallization). 

Solid size reduction increases the sinterability of a zeolite crystal at the ambient temperature. On heating nanocrystallites of 40-80 nm at 80 °C, solution-mediated mass transport results in additional substantial crystal growth that occurs at... 

Surface spins are weakly coupled and more disordered at the ambient temperatures compared to the bulk spins. Spins in the bulk interior dominates the magnetization. Solid size reduction lowers the number of bulk spins [50]. 

Phase stability of nanostructures has been one of the central issues in nanoscience and technology. For a given specimen of a fixed size, phase transition takes place when the temperature is raised to a certain degree. The value of the critical temperature (Tc) varies with the actual process of phase transition. The Tq values are different for the magnetic-paramagnetic, ferroelectric-non-ferroelectric, solid-solid, solid-liquid, and liquid-vapor phase transitions of the same specimen. Generally, solid-size reduction depresses the Tc of a nanosolid because atomic undercoordination lowers cohesive energy of atomics in the skin. 

Fig. 3. Stressing mechanisms (a) single particles or (b) a bed of particles cmshed between two solid surfaces impact of a particle against (c) a solid surface or (d) another particle (e) cutting (f) shearing forces or pressure waves and (g) plasma reaction, an example of size reduction by nonmechanical energy.

Your company receives a nickel compound (nickel compound is a listed toxic chemical category) as a bulk solid and performs various size-reduction operations (e.g., grinding) before packaging the compound in 50 pound bags. Your company processes the nickel compound. 

Institution of Chemical Engineers, 1975. In Comminution, Institution of Chemical Engineers Working Party concerned with the theory and practice of the size reduction of solid materials. Ed. V.C. Marshall, Institution of Chemical Engineers, Rugby, 83pp. 

Before MPW is fed into the process, a basic separation of the non-plastic fraction and size reduction is needed. This prepared feedstock is then introduced in the heated fluidised bed reactor which forms the core of the process. The reactor operates at approximately 500 °C in the absence of air. At this temperature, thermal cracking of the plastics occurs. The resulting hydrocarbons vapourise and leave the bed with the fluidising gas. Solid particles, mainly impurities formed from, e.g., stabilisers in plastics, as well as some coke formed in the process mainly accumulate in the bed. Another fraction is blown out with the hot gas and captured in a cyclone. 

In practice, the process regime will often be less transparent than suggested by Table 1.4. As an example, a process may neither be diffusion nor reaction-rate limited, rather some intermediate regime may prevail. In addition, solid heat transfer, entrance flow or axial dispersion effects, which were neglected in the present study, may be superposed. In the analysis presented here only the leading-order effects were taken into account. As a result, the dependence of the characteristic quantities listed in Table 1.5 on the channel diameter will be more complex. For a detailed study of such more complex scenarios, computational fluid dynamics, to be discussed in Section 2.3, offers powerful tools and methods. However, the present analysis serves the purpose to differentiate the potential inherent in decreasing the characteristic dimensions of process equipment and to identify some cornerstones to be considered when attempting process intensification via size reduction. 

Alternative terms for size reduction to describe the operations that subdivide solids mechanically are crushing and grinding. An ideal crusher or grinder should (i) have a large capacity (ii) require a small power input per unit of the product and (iii) yield a product of the size and/or the size distribution desired. 

To obtain representative samples from nonhomoge-neous sample materials, such as polymer compounds, particle-size reduction techniques need often to be applied (not for film) [50]. Also, for destructive inpolymer additive analysis it is advantageous to change the physical state of solid samples to provide a larger surface area per unit mass. Complete extraction is sometimes achieved only after grinding the sample. Typically, Perlstein [51] has reported recoveries of only 59 % for extraction of Tinuvin 320 from unground PVC after 16 h of Soxhlet extraction with diethyl ether while recoveries rise to 97 % for ground polymer. 

Miniaturisation of scientific instruments, following on from size reduction of electronic devices, has recently been hyped up in analytical chemistry (Tables 10.19 and 10.20). Typical examples of miniaturisation in sample preparation techniques are micro liquid-liquid extraction (in-vial extraction), ambient static headspace and disc cartridge SPE, solid-phase microextraction (SPME) and stir bar sorptive extraction (SBSE). A main driving force for miniaturisation is the possibility to use MS detection. Also, standard laboratory instrumentation such as GC, HPLC [88] and MS is being miniaturised. Miniaturisation of the LC system is compulsory, because the pressure to decrease solvent usage continues. Quite obviously, compact detectors, such as ECD, LIF, UV (and preferably also MS), are welcome. 

RESS [Rapid Expansion of Supercritical Solutions] A process for depositing a film of solid material on a surface. The substance is dissolved in supercritical carbon dioxide. When the pressure is suddenly reduced, the fluid reverts to the gaseous state and the solute is deposited on the walls of the vessel. Used for size-reduction, coating, and microencapsulation. First described in 1879. Developed in 1983 by R. D. Smith at the Battelle Pacific Northwest Laboratory. 

Obviously, the technology exists for obtaining analytical results without special preparation and analysis in a laboratory. However, at the present time there is no acceptable substitute for direct laboratory examination of samples if we want the kind of accuracy and confidence we have come to expect. All conventional methods for analysis of solid materials require one or more of the following preparation activities before an analytical method can be properly executed 1) particle size reduction, 2) homogenization and division, 3) partial dissolution, and 4) total dissolution. Let us briefly discuss each of these individually. 

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