Solid-liquid mixing dissolution

Leaching (mixing and solid/liquid separation)—dissolution with acid, alkali, or bacteria, using redox, pressure (autoclave), etc. 

Solid-liquid mixing is used extensively throughout the chemical process industries. Examples include the suspension of solid catalysts in a reactor, the dissolution of solids to form a solution, the suspension of solids in crystallization, suspension polymerization, and fermentation. Crystallizers are usually designed to maximize flow, hence solids suspension, and to minimize shear to avoid crystal attrition. A common application is to provide solids-liquid mixing to feed a solids separator such as a centrifuge. Here the task is to provide a uniform solids feed as levels recede in the feed vessel. 

Among the various mechanisms that have been proposed for the dissolution of solids [101,102], two of the simplest are depicted in Fig. 15. The common features of these are that an infinitesimally thin film of saturated solution of concentration cs (the solubility) is formed at the solid-liquid interface and that in the well-mixed bulk of solution, the concentration of the dissolving solid at any given time is cb. 

Sodium hydroxide (concentrated). To 5 g solid sodium hydroxide, NaOH, add 5 ml water and mix. Dissolution is slow first but becomes rapid as the mixture gets hotter. Use the cold liquid for the tests. 

In Figure 1 a simplified process scheme of the antisolvent crystallization of sodium chloride is displayed. The process is divided into three steps the crystallization, the solid-liquid separation and the antisolvent recovery or liquid-liquid separation. In the first step sodium chloride is crystallized by mixing the feed brine with an antisolvent. The crystallization is carried out at temperatures below the liquid-liquid equilibrium line in the single liquid phase area (see Figure 2). In the second step the crystals are separated from their mother liquor, e.g. by filtration or in a centrifuge. In the third and final step the antisolvent is separated from the water phase at a temperature above the liquid-liquid equilibrium line in the two liquid phase area, in which the ternary amine-water-salt system splits up into an amine and an aqueous phase. The recovered antisolvent is recycled within the process and most ideally the water phase is reused for the dissolution of crude sodium chloride. In this paper the crystallization and the liquid-liquid separation steps will be treated. 

Basket USP 1 EP basket JP method 1 BP 1 Rotating stirrer Dosage form confined leads to consistent solid/liquid interface Floating products kept immersed Limited sink conditions Trapped bubbles in basket can slow dissolution rate Inadequate mixing at slow speed Floating dosage forms Dosage forms that tend to adhere to the vessel surfaces... 

Solutions are homogeneous mixtures of two or more substances, which may be solids, liquids, or gases. The ease of dissolution of a solute in a solvent is governed by intermolecular forces. Energy and the increase in disorder that result when molecules of the solute and solvent mix to form a solution are the forces driving the solution process. 

Is there a chemical reaction of the solid with the liquid Sohd-liquid mixing operations involving chemical reactions often require a high relative velocity between the solid particle and the liquid—high local shear rate or agitation intensity—to minimize the thickness of the boundary layer for mass transfer. This is also due for the dissolution of a sparingly soluble solid, as discussed further in Chapter 13. 

Figure 10-4 Degrees of suspension, (a) Partial suspension some solids rest on the bottom of the tank for short periods useful condition only for dissolution of vray soluble solids, (b) Complete suspension all solids are off the bottom of the vessel minimum desired condition for most solid-liquid systems, (c) Uniform suspension solids suspended uniformly throughout the vessel required condition for crystallization, solid catalyzed reaction. See Visual Mixing CD affixed to the back cover of the book for sevraal illustrative videos.

The analytical solution of the transient diffusion problem of selective anodic dissolution of a binary alloy in the potentiodynamic polarization mode allowed us to obtain the equations for the concentration profiles of an electronegative metal in an alloy, voltammograms as well as modified Randles-Sevcik expressions, taking into accoimt the mixed solid-liquid phase diffusion nature of the kinetic limitations of the process, equilibrium solid phase adsorption of the components, and surface roughness of an electrode. 

Leaching is the removal of a soluble fraction, in the form of a solution, from an insoluble, permeable sohd phase with which it is associated. The separation usually involves selective dissolution, with or without diffusion, but in the extreme case of simple washing it consists merely of the displacement (with some mixing) of one interstitial liquid by another with which it is miscible. The soluble constituent may be solid or liquid and it may be incorporated within, chemically combined with, adsorbed upon, or held mechanically in the pore structure of the insoluble material. The insoluble sohd may be massive and porous more often it is particulate, and the particles may be openly porous, cellular with selectively permeable cell walls, or surface-activated. 

The bone cement used in these studies was a two-component system. The liquid component [9.75 mL methyl methacrylate (MMA) 0.25 mL A,A-dimethyl-p-toluidine (DMPT) 75 mg/kg hydroquinone] was mixed with a solid component [3.0 g poly(methyl methacrylate) (PMMA) 15.0 g MMA-styrene copolymer benzoyl peroxide, mass fraction 2% 2.0 g BaSOJ to form the cement. Dissolution of the solid component proceeded simultaneously with polymerization once the cement was mixed. 

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