REACTORS FOR PROCESSES WITH REACTIVE SOLIDS

Chemical processes in which the solid phase changes during the reaction are of considerable industrial importance. Three types of reactions take place in these kinds of processes reactions between a gas and a solid component reactions between a liquid and a solid component and reactions between a gas, a liquid, and a solid component. The majority of the processes with a solid phase are two-phase reactions, but three-phase processes also exist. For three-phase systems, the liquid phase is often used as a solvent, and a suspension is facilitated for the reactive gas and solid phases. 

In reactions between a solid and a fluid phase, it is important to note the amount of solid-phase changes during the reaction. If all reaction products are gases, the solid phase shrinks during the reaction. The reacting solid particle decreases in size, even when the differences in densities between the solid reactant and the solid product are large tensions in the product layer around the solid particle are developed, and the product layer is continuously peeled away from the surface of the reactant. 

A few processes with reactive solids are listed in Table 8.1. Oxidation of zinc ore, that is, zinc sulfide, is a process in which the size of the reactive solid particle remains approximately the same zinc sulfide is oxidated to zinc oxide. Similar reactions occur, for example, in the oxidation process of pyrite to hematite. Reduction processes of metallic oxides with hydrogen in the production of pure metals are also processes in which the size of the solid phase remains unchanged. Another example of a reduction process is the reduction of magnetite to metallic iron. 

In organo-chemical processes, there are also reactions involving a solid phase the cellulose derivative, carboxymethyl cellulose (CMC), is formed from Na-cellulose suspended in a liquid phase and monochloroacetic acid is dissolved in the liquid phase, usually 

TABLE 8.1 Processes Involving a Solid Reactive Phase 

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