Solid-liquid mixing wetting solids

Precipitation is usually understood as obtaining a solid from a liquid solution. In the production of precipitated catalysts, the first step is the mixing of two or more solutions or suspensions of materials, causing the precipitation of an amorphous or crystalline precipitate or gel. The wet solid is converted to the finished catalyst by filtration, washing, drying, forming, calcination and activation. Adjusting production conditions can vary cristallinity, particle size, porosity, and composition of the precipitate or gel. 

Mixer granulators contain an agitator to mix particles and liquid cause granulation. In fact, mixing any wet solid will cause some g... 

Binder liquid should wet the solid particles and not the interior walls or the mixing tools of the equipment. If parts of the mixer are wetted, build-up occurs which is difficult to remove. Different spray patterns are available with commercially available single or two phase nozzles (Fig. 7.22c and 7.23) and a suitable pattern should be selected to assure that liquid impinges only on the moving powder. Since the spray pattern depends critically on the cleanliness of the orifice area, as mentioned before, nozzles must be drip free and installed such that they remain clean or are blown free by the action of atomizing gas. This is particularly important for low capacity nozzles which are often preferred because the binder liquid should be always completely ab-... 

D6. We are removing barium sulfide BaS from insoluble solids (see Problem 14.D14 for data) in a batch washing process. We initially have 10.0 kg of wet solids (each kg dry insoluble solids carries with it 1.5 kg underflow liquid). The initial underflow liquid is an aqueous solution with 0.05 mass fraction BaS. The wet solids are mixed with 10 kg of pure water, the solids are allowed to settle (each kg dry insoluble solids carries with it 1.5 kg underflow liquid), and the overflow liquid is removed. This process is then repeated twice using 10 kg of pure wash water each time. Assume that liquid density is constant and that the underflow liquid held by the solids has the same concentration of BaS as the overflow liquid. 

Surfactants are essential for the preparation of solid/liquid dispersions (suspensions). The latter are generally prepared using two main procedures (7) Bmlding up of particles from molecular units. (2) Dispersion of bulk performed powder in a liquid followed by dispersion and wet milling (comminution) to produce smaller particles. An example of the first system is the production of polymer latex dispersions by emulsion or dispersion polymerization. The monomer is emulsified in an aqueous solution containing a surfactant to produce an emulsion of the monomer. An initiator is added to initiate the polymerization process. In some cases, initiation occurs in the micelles that are swollen by the monomer. The number of particles produced and hence their size is determined by the number of micelles in solution. In dispersion polymerization, the monomer is mixed with a solvent in which the resulting polymer is insoluble. A surfactant (protective colloid) and initiator is added. The surfactant prevents flocculation of the polymer particles once formed. Again the size of the particles produced depends on the nature and concentration of the surfactant used. 

What are the physical properties of the solid and liquid phases present The degree of difficulty in solid suspension depends on several properties of the fluid and solid particles discussed in Section 10-2. The properties of interest include the relative density of the solid and liquid phases, the viscosity of the liquid, the wetting characteristics of the solid, the shape of the solid particles, and the mass or volume ratio of solids to liquid. Large and dense solids are more difficult to suspend than small light ones spherical particles are also more difficult to suspend than thin flat disks. The impact of these properties on solid-liquid mixing mnst be studied and understood early in process research and development. 

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