Suspensions Containing Small Solid Particles

In the case of small insoluble primary particles with a diameter of, typically, dv.so 2 [xm within the droplet, the drying process takes place from the outer shell. 

At a high speed of shrinkage, the diffusion rate of sohds accumulated with a high concentration in the outer regions of the suspension droplet is not fast enough to equalize the particle concentration difference within the drop. The diffusion coefficient Dsp of suspension particles with diameter dp is usually about 1 to 4 orders of magnitude smaller than, for example, low molecular solutes. It can be estimated from the relationship 

For suspensions, Minoshima et al. (2001, 2002) proposed a model based on the buckling behavior of the crust. According to this model, a particle is allowed to shrink as long as the buckling pressure is larger than the permeation pressure of the evaporating fluid. The buckling pressure depends on the shell thickness as 

E is the Young s modulus of the primary particles, v is the Poisson number of the material, is the drop diameter and dgheii is the inner shell diameter. 

Smaller primary partides lead to a higher strength of the agglomerate spray particle (Rumpf, 1975). However, the strength may still be insufficient for the subsequent treatment of the product. It is, therefore, often necessary to add some binder, which helps to provide the necessary adhesion between the primary partides, even in the dry state. Different binders are known such as carbon hydrates 

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Ideal for sprays containing small solid particles mixed inside liquid (a suspension spray)... 

Fluidized beds have also been used for generating suspensions of solid particles with diameters in the range of 0.5-40 gm. Air flows through the fluidized bed, which contains beads kept suspended by the motion of the air dust injected into the bed is broken up into small particles and carried out with the air flow (Raabe, 1976). 

Many industrial processes are affected by the influence of particulate materials on the flow properties of material. Flow properties of materials can be adjusted by fillers to meet the requirements. Flow properties can also be adversely affected by numerous phenomena related to the presence of filler in formulations.One common example is related to the flow of industrial slurries which contain concentrated suspensions of small particles. Such suspensions are usually non-Newtonian fluids with a yield stress which is formed through strong interactions between particles. During flow, these interactions are continuously broken and rebuilt. A solid deposit formed on the slopes and walls is an adverse effect of this property. 

High level solid waste (HLSW) originates at the dissolver. The hulls from the dissolution contain activation products and small amounts of imdissolved fuel ( 0.1%). The dissolver solution contains finely divided particles of undissolved seminoble metal alloys (Ru, Rh, Mo, Pd, etc.). This suspension is treated by filtering or centrifugation prior to the solvent extraction. Past practice in the USA and the USSR has been to put the HLSW in shielded containers which are transported to and stored at a dry disposal site. In the future the same disposal is expected to be used for the HLSW as for the solidified HLLW ( 21.12). 

Suspension polymerization can be considered as a form of mass polymerization. It is carried out in small droplets of liquid monomer dispersed in water and caused to polymerize to solid spherical particles. The process generally involves dispersing the monomer in a nonsolvent liquid into small droplets. The agitated stabilized medium usually consists of water containing small amounts of some suspending or dispersing agent. The initiator is dissolved in the monomer if it is a liquid. It is included in the reaction medium if the monomer is a gas. 

Evidently, liquid-phase viscosity has a marginal effect on Fr, . This is expected since both Equations 9.20 and 9.21 from which Fr is derived do not contain liquid-phase viscosity. The small effect observed nonetheless is likely to be due to finite nonidealities and viscosity effects such as the blade slip factor introduced by RieUy et al. (1992). A major application of gas-inducing systems is in solid-catalyzed gas-liquid reactions. Aldrich and Deventer (1994) studied the effect of presence of solid particles on It was found that was unaffected up to solid loading of 15wt%. Above this loading, there was an increase in presumably due to increase in the effective viscosity of the suspension. This study, however, used a relatively very small-size system (T=0.2m and D=0.065m), and therefore, it is difficult to derive quantitative conclusions. 

To avoid agglomerated colloids in the aerosol, one additional issue is to use suspensions sufficiently dilute to lead to no more than one particle per droplet As a result, many of the electrosprayed droplets will contain no colloidal particles, and will give rise to a solid residue even in the purest solvent However, at sufficiently small values of (QW /dp, the diameter drof the residues will be considerably smaller than the diameter dp of tne dissolved particle. Furthermore, dr depends on Q according to equation 4, while dp does not, providing a reliable criterion to discriminate between particles originally m solution, and residues from solution droplets. 

When a water-miscible polymer is to be made via a suspension process, the continuous phase is a water-immiscible fluid, often a hydrocarbon. In such circumstances the adjective inverse is often used to identify the process [118]. The drop phase is often an aqueous monomer solution which contains a water-soluble initiator. Inverse processes that produce very small polymer particles are sometimes referred to as inverse emulsion polymerization but that is often a misnomer because the polymerization mechanism is not always analogous to conventional emulsion polymerization. A more accurate expression is either inverse microsuspension or inverse dispersion polymerization. Here, as with conventional suspension polymerization, the polymerization reaction occurs inside the monomer-containing drops. The drop stabilizers are initially dispersed in the continuous (nonaqueous phase). If particulate solids are used for drop stabilization, the surfaces of the small particles must be rendered hydrophobic. Inverse dispersion polymerization is used to make water-soluble polymers and copolymers from monomers such as acrylic acid, acylamide, and methacrylic acid. These polymers are used in water treatment and as thickening agents for textile applications. Beads of polysaccharides can also be made in inverse suspensions but, in those cases, the polymers are usually preformed before the suspension is created. Physical changes, rather than polymerization reactions, occur in the drops. Conventional stirred reactors are usually used for inverse suspension polymerization and the drop size distribution can be fairly wide. However, Ni et al. [119] found that good control of DSD and PSD could be achieved in the inverse-phase suspension polymerization of acrylamide by using an oscillatory baffled reactor. 

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